Bacteria Replication

Question: I learned this at a lecture, but somehow I have trouble in understanding this. It is said that the bacteria such as E.coli need 20 minutes to divide, but its chromosome require 40 minutes to multiply. It is explained that the E. coli will have copied half of it, which will spend 20 minutes and after divided, it will continue another 20 minutes to complete the chromosome copy. However, it is said that each daughter cell will have one complete and half copy after they divide. I am confused that if the bacteria only spend 20 minutes to copy half of it, how  can each daughter cell could have one and a half?
Answer: Referring to the six stages in your diagram as Stage 1 through Stage 6, let's look at Stage 3: At that point, there is one bidirectional replication in progress, having made it about halfway around the chromosome. So it has 2 copies of the first half of the chromosome, and 1 copy of the rest, which is yet to be copied.  To get to this state of replication took 20 minutes.
Now the cell starts two new replications, one at "origin of replication" on each of the two copies of the first halves of partially replicated chromosome.  This is the state shown in Stage 4.  There are now three replications going on: the original, which is working on the last half of the chromosome, and two replications, which are working on (their own copy of) the first half of the chromosome.  All three replications will continue working for about 20 minutes.
We then get to Stage 5: the original replication has finished and the septum forms to separate the daughter cells.  The two replications started in stage 4 are continuing, and are about halfway down the chromosome.
The cells separate, and we are at Stage 6.  But stage 6 is the same state for each daughter cell as we had in Stage 3: a chromosomal replication that is halfway through (thus having one and a half copies).  It took 20 minutes to get from Stage 3 to Stage 6, where we are ready to double again.  During that 20 minutes, only one half of a chromosome had time to be copied, so it takes twice that (40 minutes) for replication of the whole chromosome.  This works out because the cell is doing three replications at once.
Answer: Your question has already answered reasoning behind it. Just remember this happens only in rich media. Now I tried to build simple model of this to illustrate how DNA levels are changing over the period of time in given scenario. I will assume very simple (but reasonable) numbers for model. Rules are very simple,

Cell division in 20 min ( Cell will lose half DNA )
DNA replication in 40 min ( Cell will double DNA copy )
Firing of origin of replication in 10 min ( Cell will have one more origin of replication )
At each time point, cell will have DNA replication depending on number of origin of replications

I wrote simple code in python and simulated,
<code>import math
import numpy as np
import matplotlib.pyplot as plt
import matplotlib
cell_division_time = 20 #min
full_DNA_replication_time = 40 #min
firing_of_new_Ori = 10 #min
origin_of_replications = 1
total_DNA = 1 #initial condition
time_for_simulation = 400 #min
time_coordinates = range(time_for_simulation)
DNA_number_coordinates = [] #This will be updated at each time step
for t in time_coordinates:
    if (t%firing_of_new_Ori) == 0:
        origin_of_replications = origin_of_replications + 1  #Add more origin of replications
    total_DNA = total_DNA + (1.0/full_DNA_replication_time)*origin_of_replications #Add total DNA accordingly
    if (t%cell_division_time) == 0:
        total_DNA = total_DNA/2.0  #At cell division, total DNA will be half
        origin_of_replications = 1  #We will reset origin of replication to 1
    if (t%full_DNA_replication_time) == 0:
        total_DNA = total_DNA + 1 #DNA will be double when you complete one full replication
        origin_of_replications = origin_of_replications -1  #Remove that origin of replication
    DNA_number_coordinates.append(total_DNA)  #record amount of total DNA in cell
plt.plot(time_coordinates, DNA_number_coordinates,linewidth=2, label='DNA copies')
plt.axvline(x=40,linestyle='--', color='red',label='Cell Division')
plt.legend(loc=0)
plt.axvline(x=20,linestyle='--', color='red')
plt.axhline(y=1,linestyle='--', color='red')
plt.axhline(y=1.5,linestyle='--', color='red')
plt.xlabel('time (min)')
plt.ylabel('Total DNA copies in single Cell')
plt.show()
</code>
This simple game can give you intuition, check how DNA levels are changing in following image

At steady state, these will be sustained oscillations,

Bacteria Replication


Why aren't linear aerospike engines in common use?

Question: Linear aerospike engines are an old idea that seem so full of promise.  Why are they not widely used today by the likes of Boeing, SpaceX, etc.?
Comment: I know this is an old post but check this: http://www.arcaspace.com/en/haas2c.htm
Comment: Everyday Astronaut does a serious deep dive on this very topic here: https://www.youtube.com/watch?v=D4SaofKCYwo
Comment: I would also add that there's only so much impulse one can "extract" from chemical fuel, so supporting multiple engine topologies is hardly worth the trouble. The similar situation exists with Wankel and Stirling engines for automotive use - those are being in research stage for ages, but hardly justify the effort of switching.
Comment: oakad: I would add that engine topology can improve atmospheric specific impulse, which is expressly what aerospikes are supposed to do. Engines with high atmospheric Isp are a Holy Grail of sorts to the development of high-payload-fraction launch vehicles, such as SSTO craft.
Answer: Money. Most engine designs we're now using are an evolution of the space race era in one form or another, from the times when financing research in rocket engine / nozzle design wasn't such an issue. Linear spike fundamentally changes rocket design, for one engine support structure, and would as such require a revolution in engineering if someone expects it on the cheap. Steady evolution simply isn't good enough, the changes required are too big.
So either rocket engine research & development would get a huge injection of money from somewhere, or we reach some engineering breakthrough that doesn't require so much of it, like maybe more reliable engineering simulators (one fine example, but not enough). Short of that, designing, building and testing cycles are simply too expensive. Engineering side of it is challenging, but no engineer will ever tell you it's impossible.
Answer: Aerospikes are notoriously difficult to cool efficiently.
With a bell nozzle, you have a minor part of rapidly expanding(+cooling)  exhaust touching the broad, actively cooled nozzle - that means little conductive heat transfer, lower temperature gradient, lots of area for coolant plumbing on the outside (or within) the bell, and outer area radiating a lot of heat out (or passing it to air while in atmosphere) besides coolant drawing it away.
In aerospike the pressure (and temperature) of the gas remains very high all along the spike surface, and the sharp tip leaves very little room for cooling systems. You have a lot of extra-hot, very dense gas in contact with the narrow spike that must pass all the coolant and dissipate the heat somehow, not to melt.
That means short test runs of aerospike engines, proving all the benefits, are perfectly viable - but the experimental rigs are shut down before they could overheat and suffer critical damage. They just couldn't run continuously for as long as a typical rocket needs to lift payload to orbit. Work on efficient, fault-proof cooling of the engines is ongoing, but it's not nearly as easy as in case of bell nozzles - a major challenge that seriously throws a wrench into broad adoption of this engine type.
Comment: This reads rather interesting, and I fully believe it. But do you have some sources or references for further reading?
Comment: @Polygnome: sorry, just word-on-mouth and general understanding. This is especially true for circular aerospikes where the tip nearly tapers off to a point; you'll often see it glowing nearly white-hot in test videos. Linear aerospikes should be less vulnerable to that problem, but definitely not immune to it.
Comment: Of course TildalWave is right, this all boils down to money to research and proof the solution, but the most difficult and expensive to research part is cooling. Science and engineering of the flame/combustion part is quite mature; cooling is still behind on Technology Readiness Level.
Answer: The Everyday Astronaut just released an hour long video investigating this question.
Some of the main points are:

Aerospikes are especially advantageous to single stage to orbit vehicles, and current space companies are not building those. There isn't really an advantage in SSTOs compared to multi stage rockets.
The efficiency advantage of aerospikes isn't actually that big, if it exists at all. Aerospikes have a higher specific impulse compared to bell nozzles, i.e. converting heat and pressure into exhaust velocity, but the many small combustion chambers that aerospikes require reduce the reaction efficiency (converting chemical energy to heat and pressure) compared to a single large combustion chamber. This was mentioned by Elon Musk as part of the reason why they didn't pursue aerospikes
Aerospikes may have some physics advantages to bell nozzles, but have a whole lot of engineering drawbacks. A whole lot of small combustion chambers requires an order of magnitude more cooling than a single large one. While not insurmountable, why would you invest in it when the advantage over bell nozzles is small or nonexistant.
The NASA funded aerospike research was cancelled for reasons that didn't have much to do with the aerospikes itself, but that boil down to political choices and technical issues with other parts of the projects they were part of. One aerospike engine would have been an upgrade to the Saturn V, another one was for the Venture Star. Why these projects got cancelled is a different question but in the end the choice was up to the US Government. One of the engineers on the Venture Star aerospike engine says that he expects that the engine would have done fine and been able to hit its design targets if the project was completed.
Elon Musk of SpaceX says they looked into it, and their conclusion was that investing in aerospikes wasn't worth it, due to the above reasons. But they'd love to be proven wrong.
Comment: @EverydayAstronaut your video, for one. I didn't specify at what altitude, which I guess you're hinting at: they have a higher average specific impulse over the trajectory of a rocket through the atmosphere.
So I guess with this answer I stole your reputation score >:).
Comment: I like this answer. Just one question: what's the source of the statement "Aerospikes have a higher specific impulse compared to bell nozzles"? Would love to know more about this.
Answer: Having worked at Rocketdyne for many years my understanding was that although they wanted to put it on the Space Shuttle, the politics of a single source caused NASA to write a proposal that required usual rocket nozzles.
At that point there was no funding to finish full scale development and flight testing.
Answer: The answer is simple

lack of proven reliability
lack of proven flight experience
lack of performance validation..

more surface area exposed to hot gas . So it must be cooled which is difficult ..
Answer: Firefly Aerospace will use an (annular) aerospike engine with their Alpha rocket.  They have a planned launch in 2018.
Comment: "The plans for engine development were significantly altered by the new management, and the revised Alpha vehicle features a pump-fed engine and removes the aerospike configuration"
Answer: Arcaspace have been bulding a hydrogen peroxide test engine they hope to fire later in 2018, with the stated aim of flying a RP1/H2O2 eSSTO. https://newatlas.com/arc-aerospike-linear-engine-complete/51431/
Comment: I admire Arcaspace's enthusiasm, but it is Dunning-Kruger in action. It would be like SpaceX if Musk didn't have the money to hire people that know what they're doing. the first design was a victim of the pendulum fallacy - the latest one confuses characteristic length with physical length.
Comment: Welcome to Stack Exchange! Answering questions here is a little different than on other sites. Can you add more and explain the key points in the link that are relevant? In SE, answers should be able to stand on their own after links break, so link-only answers are not considered helpful. Also, "We should see this in use this year." sounds intriguing; why do you think so? Can you add some specific information here why you believe it will happen so soon? Thanks!
Answer: This answer is supplemental to the other excellent answers here.
This Curious Droid video also confirms it's just a question of time and money. The first few words "History is full of decisions..." Due to the details of development history, bell shaped nozzles made it first, and people stuck with it.
This may be slightly reminiscent to the current non-use of Thorium based nuclear power, though that is also related to the need for nuclear weapons development.
Comment: Nice.  Agree.  Great link!


Do professional event photographers commonly require payment in full before a shoot?

Question: I am trying to hire an event photographer for my company to shoot a series of public open houses.
I photographer that was recommended to me has contacted me with pricing information and she is requesting payment in full either before the event or at the end of the event.  This means that we would have to pay in full before we even see any of the photos.  Is this common?  I am in Ontario, Canada.
Comment: The other problem event photographers run into is that if they take a job on 'spec', then they show up to shoot only to discover there are 20 other people (employees, relatives, other for-hire photographers) taking photos at the event. If the images the 'customer' gets from their own people meet their satisfaction, then they find every reason in the world why the hired photographer's images are 'unacceptable' and they refuse to pay for them.
Comment: It has nothing to do with your company or its reputation. It has to do with too many potential customers seeing nothing wrong with buying one copy of an image (or even just taking the digital proofs without paying anything for them) and then redistributing those images to everyone else who may be interested. In the past event photographers made most of their income from the sale of prints after the fact and only a small appearance fee was charged up front. Now most event specialists figure the cost of editing and delivery of the digital images into the base fee.
Comment: Thanks for your input. I am a little surprised because nobody else does this - services are provided, an invoice is issued, expense is approved and the bill is payed. We are an international gold mining and exploration company and very well known in that region. There is practically no chance that an invoice would not be payed.
Comment: Pretty much. With digital technology it is the only way you can get paid.
Answer: Yes, this is very common.  Often, much of the fee is actually to cover the cost of shooting the event and it is unfortunately relatively common for people to decide after an event that they don't care to get photos after all.  You can find photographers who will charge a smaller sitting fee (the cost of actually shooting the event) and then more for each photo you want a copy of, but it's generally easier and cheaper (for both) to offer a bundle that includes everything and the cost of that is typically due at the time of the event.
The reason a photographer can offer the bundle is that it is guaranteed money for their time.  Sitting fees are generally not enough for a photographer to get by on alone, so they have to sell images as well.  Doing a bundle means the customer takes a risk that the images might not be as good as they would like, but it also means the photographer sells the images much more cheaply because the customer chooses to trust them.
When doing sitting fee only, the photographer may not sell a single photo, so they have to charge more for each photo that they do sell to make sure they still make enough money from the job.  This almost always ends up being more expensive for the customer (at least if the photographer is any good) since the photographer is taking all the risk.
If you are uncomfortable paying for everything up front, you could ask if they offer an option to separate the sitting fee and the image fees, but that is generally (much) more expensive as there is no guaranteed income beyond the sitting fee.  The image fees would be paid on delivery of the images under that kind of a setup though.  (The sitting fee would still be due at the time of the event.)
As to making exceptions for a company that is going to be reliable, you really don't know who is and isn't reliable and you run in to problems if you vary your policies from one customer to another.  I've been ripped off by national companies with TV deals that decided not to pay for service (they actually canceled the check they had already given) because of mistakes made because they didn't fully disclose details that I had asked for.  Bad experiences dictate caution and it's just too messy to make exceptions for people you trust since then people get upset that you don't trust them enough to give them the same exception.
Answer: I would write a proper contract with him if you are afraid of paying up-front.
If I contracted someone for shooting, I would define target goals, cancellation terms, no-show penalties, etc. I would give a partial payment if needed. I would want to see initial results at the end of the event, and I would pay on delivery.
If I was shooting for you, I would ask for a partial payment beforehand, I would require you to hold your end in the contract or pay some penalty. I would show you pre-selected shots at the end of the event, so you could select those you would like me to post-process, and deliver when you pay.
You should not contract for any kind of perceived "beauty". That just leads to open-ended battles. You can contract for objective, measurable qualities. You should not ask for pictures before paying. Some people give out pictures before payment but with an agreement that the business deal is done and he will be paid within X days. Yet, you need a good relation with a photographer for delayed payment.
The customer and the photographer has both to lose (e.g. lost opportunity to receive photos, lost opportunity to create photos and income elsewhere ) and both to win (great photos, great income). So if you feel unbalanced with a photographer, he has to be FREAKIN' good world-star, otherwise handle photographers fairly, and they will handle you fairly as well and you can start building on that. :-)
Good luck with your event and photos!


Slider with 3 handlers vs Input fields

Question: I am working on a feature were you need to distribute the total of the feature value (100%) between 4 factors, I think the best option is the input fields, but I like the visual feedback from the slider, any suggestion?
Comment: Will you need to support mobile (phone) users? If so, the slider may be less than optimum. OTOH, how about supporting both, so you can drag slider points, or enter numbers in the boxes, then you get best of both, assuming you have sufficient space.
Comment: Can you clarify whether each vector is limited to 25%? For example, could a user select 0% for three vectors and 100% for one, or 10% for two vectors, 30% for one and 50% for the other?
Comment: Hi Steve, no I think this is just for desktop right now, well yeah on the slider option you can actually enter values manually on the boxes.
Comment: Hey Monomeeth, there are no limits you can give 100% to one option and 0% to the other 3
Answer: The slider design as shown above could be incredibly confusing from an accessibility standpoint. What if someone could not properly see the colours?
I see 3 slider "handles" but 4 fields. That seems odd, too.
What happens when vector 1 needs to be 25% and vector 2 needs to be 26%? That seems like some very tedious mouse dragging.
Using form fields, you can quickly tab to each one or after a value is filled in, automatically move to next form field.
This is precise work, I think direct number entry is the best choice.
However, if you want something more visual, show a graph or something of how the 4 values are distributed across the 100%; for example, in vector 1, they enter 25%. Draw a graph then that shows the progress left or something.
Answer: I think your slider could certainly work, but a) I fully agree with the color accessibility issues, b) make sure that the slider track clearly represents 100% regardless of the position of the handles, and c) you might change a few things around a bit to make the associations clearer:

Keep the fields and vector names centered (as much as possible) over/under their related segments (they could both be over or both under, whatever), and don't let color confuse the issue. I also wouldn't use any light grays: low-contrast controls are NOT cool, they are just harder for a segment of your customers to use.
Just $0.02.
Comment: I completely agree with you! A slider implementation is an easy way to make sure that the end user is unable to submit any total value beside 100% and is also a great way to save space! It is both space efficient and more robust against invalid inputs! Which should result in much happier clients who didn't have to do math themselves. (The less they have to do, the happier they are) ;)
Comment: I consider this option but the issue is that you can give to one vector 100% and 0% to the other 3, that reduce the space and could be hard to arrange, thats why I added the static boxes below the handler, but yeah depend on colors is not the best.
Comment: @VADO is that a likely circumstance? You could certainly just have the other labels/fields "cluster" at the other end, not appearing in literally the 0% spot, but in the rough position, and with the numbers doing the work. If this IS likely to be common, the slider might not be the best control for you; fields with validation may be easier for users.
Answer: Using bar-chart that auto-completes to 100 can work better. Connecting them on a linear scale is more complex action than deciding on each variables. when you increase one, automatically decrease the neighborhood variable.
You can add unassigned percentage bar, to make things a bit clearer...
Answer: I think that you're spot on with the form fields being the best way to get user entered data, it's not as difficult as trying to move around handles on a bar; I'm thinking Fitts' law. No reason you couldn't have both though.
As for displaying the information, a bar graph works well, or a 'donut' graph might also work. I like this idea as it shows a complete circle so you can easily see it total up to 100%.
Out of interest, do you have a default factor that always fills up the rest of the percentage? Like if I put 20%, 20%, and 15% - will say factor 4 automatically fill in to 45%? I ask because a linear slider might not represent that there is a percentage missing. If I put 20%, 20%, 20% and 20%, I might not realise that the bar is only 80% long, as I don't know what 100% looks like. If you used a donut graph you would have an incomplete circle indicating the totals don't add to 100.
If you wanted to stick to a linear slider/bar, I would just recommend using and 'end point' indicator, so you could see if the 100% total wasn't reached, and obviously use something other than just color to distiguish between the factors.
Example 'donut' or pie chart:
Comment: I would expect that the linear slider would always represent 100%... that would solve the issue.

Slider with 3 handlers vs Input fields


Are these grocery store oyster mushrooms OK to eat?

Question: I bought these at the grocery two days ago. They have been in the fridge. They are firm. The white fungus in the gills is firm too. No bad smell. Can I cook and eat?
Comment: My first thought is, given the ways mushrooms are cultivated, the most likely fungus to be in the gills of your oyster mushrooms is other oyster mushrooms, since direct access to the spores is pretty likely.  I have no proof, though, and while I probably would risk it (given the lack of soft spots or bad smells), I'm not sure I can recommend someone else take that risk without more information than I have.  Maybe if you go back to the store and see if these are common on other oyster mushrooms and/or check with an employee that they're good (or at least salable)?
Comment: they're store bought mushrooms, they have no immune systems. expect that stuff to happen to them.
Answer: They're likely mycelium rather than other moulds, its not uncommon for certain varieties of stored mushrooms to start producing mycelia (the root system of mushrooms generally). According to this link, mould on mushrooms is more likely to be green,black or brown
http://www.gourmetmushroomsinc.com/fresh-restaurants-faq.htm


How do I balance the double bass against my body?

Question: A lot of times when I play double bass, I find myself trying to keep the double bass steady. After some research I did, I found out that I need to balance it against my body. How do I do that? Every time I try, the bass slides to side.
Comment: No, because that will limit my left hand's movement
Comment: You shouldn't need to be taking much weight, if you are you must be doing something wrong (like angling it too much towards yourself). They should take most of their weight from being almost completely upright, and the remainder of the weight should be absorbed by your left hand (the palm of it, leaving your fingers open to work the magic).
Comment: Isn't the idea that you keep it steady with your left hand (if you're right handed)? I have never had any trouble with a double bass sliding side to side while I play it...
Comment: How heavy is this thing? Are you sitting or standing?
Comment: It is pretty heavy (don't know the exact weight). I am standing
Answer: It is much easier to balance the bass sitting on a stool than it is standing.  When on a stool, you can take your left hand entirely off the bass without it sliding; but when standing, I have found that a small amount of the bass's weight will always be on the thumb of your left hand.  For this reason I always prefer sitting to standing, but it's possible to have most of the weight on your body when standing also.
Standing
The main thing is to let the upper bout of the bass rest on the left side of your crotch area, between your left leg and your stomach.
The bass should be standing mostly straight up, tilted slightly towards you.  If it is tilted to much in any direction, it will not stand still without left hand support.  Also, you may have to raise or lower your endpin to get the bass to rest correctly.
You can play around with different angles and positions of the bass to see what works for you.

Sitting
Sitting is much easier because you can prop your left leg up on the stool, so that your left knee sticks out and the bass rests against it.

I have also found that when I play sitting down, my bass usually rests closer to the right side of my crotch rather than the left side.
Answer: Sitting is much easier than standing, as has already been pointed out.
One tip if you must stand is to raise the toe of your left foot so that the bottom of the bass to the left of the spike rests against the tip of your shoe. (The spike will have to be fairly short for your foot to be able to reach.) I find that if I do this then the bass remains steady even when I take both hands off it. Make sure there is no chance of the spike slipping on the floor if you are going to try this.
Try experimenting with different positions, and find what works best for you.


Java Twitter Bot tweets to another account but using my accessToken?

Question: I wrote this simple code that works just fine :
<code>        //access the twitter API using your twitter4j.properties file
    Twitter twitter = TwitterFactory.getSingleton();

    //create a new search
    Query query = new Query("\"your welcome\"");

    //get the results from that search
    QueryResult result = twitter.search(query);

    //get the first tweet from those results
    Status tweetResult = result.getTweets().get(0);

    //reply to that tweet
    StatusUpdate statusUpdate = new StatusUpdate(".@" + tweetResult.getUser().getScreenName() +" I believe you meant \"you're\" here?");
    statusUpdate.inReplyToStatusId(tweetResult.getId());
    Status status = twitter.updateStatus(statusUpdate);
</code>
The problem is, even using my own parametres (Acessstoken, Consumerkey,,) that I generated manually from app.twitter.com, the code still sends the tweet to this account : Twit4j . it seems that too many had tweeted through it too!
twitter4j.proprieties is set up correctly
libs are correctly integrated
anyone knows what could be wrong ?
Answer: The Problem were (I guess) in the class name! the package name+ my class name are "Twitter" and the Object name from the Twitter4j is "Twitter" too!  think the IDE got confused maybe ?
anyway now it works just fine !


Rights if we possess Carta di Soggiorno?

Question: I have searched the internet but could not find specific information so if we have got the following document "Carta di Soggiorno di Familiare di Un Cittadino Dell'Unione" (Residence Card of a family member of a Union Citizen, Italy) issued by the Italian authority, what rights do we possess of working inside Italy and EU? What about travelling? Will we be requiring visas for the states which are are not in Schengen?
Answer: Work
Work inside Italy is permitted.  The card gives no right to work outside Italy.  However, the holder enjoys freedom of movement when traveling with the EU family member, which implies a right to work.  Other countries can ask for independent proof of this right before allowing work, but individual countries may be more permissive.  Independent of the card, the holder may also be permitted to work in other countries under the freedom of movement of services.
Independent travel
The holder can travel independently within the Schengen area for 90 days out of 180.  I'm not sure about the Schengen-candidate countries like Romania and Bulgaria, but the UK and Ireland will require a visa for the holder of this card unless the holder is exempt from that requirement by virtue of holding a passport from a country whose citizens are visa exempt.
Travel with (or to join) the EU-citizen family member
The 90/180 rule does not apply within the Schengen area, though countries may require registration for stays longer than three months.  For countries outside the Schengen area, it is not permitted to require a visa.  The UK requires proof of relationship, however, and it may also be prudent to carry such proof when traveling elsewhere.
Comment: "I'm not sure about the Schengen-candidate countries like Romania and Bulgaria" OP can enter those independently using a residence permit, **except** a family member's residence card, in which case they must be travelling with or to join the family member
Comment: @Crazydre So they don't recognize a residence permit from a Schengen country even though they recognize a visa from this countries?
Comment: You miunderstood me. They do accept residence Permits; however if it's in the shape of a Family member residence Card, the holder cannot travel independently
Comment: @Crazydre a Schengen residence permit is a Schengen residence permit.  Do you have a reference to support your assertion?  If what you say is true then the restriction on the family member's movements are greater than those on a third-country national with no ties to the EU beyond a residence permit in some Schengen country. That is difficult to believe, and it's certainly counter to the intention of the directive.
Comment: Timatic states this exactly
Comment: @Crazydre Timatic appears to be wrong.  See https://www.mae.ro/en/node/2040.  If you want to discuss further, Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/61133/discussion-between-phoog-and-crazydre).
Comment: Right, OK, writing to the sourcing manager about this hands down (I have contact with him). So we can conclude, I suppose, that residence permit holders can visit Croatia, Romania, Bulgaria and Cyprus, which, as stated in Timatic, residence permit holders can


What is the difference between a Bible College and a Seminary?

Question: I see some Christian education institutions refer to themselves as "Bible College" and some as "Seminary" and some as "Bible College and Seminary". What is the difference between those, if any?
Comment: This question needs more geographical scoping. From my experience there is no real difference. Perhaps because they don't call themselves seminaries here. You've left out theological colleges and schools of theology, divinity schools etc.
Comment: Reading this from my Bible College dorm ;) But yeah, seminary is like grad school basically.
Answer: In the US, a Bible college is typically a 2 year or 4 year school that specializes in Christian undergraduate education. (typically with programs like Biblical Studies, youth ministry, things like that, rather than traditional math/science/teaching programs you'd find at say a Christian liberal arts school)
A seminary is typically a graduate school that specializes in training people for the ministry (pastorate, counseling etc).
A school that advertised as both may offer a double degree or cater to people seeking either a four year degree in something bible related, or people heading into the ministry. Doing both is good synergy and they may be able to save a pastor some time (get under grad and seminary done in 5 years instead of 6 or something).
Comment: @GregMcNulty Lots of Bible Colleges are accredited. They just don't usually offer graduate level programs.
Comment: adding to this - I usually don't see accreditation's when I see "Bible College".
Comment: @curiousdannii it's pretty typical for how this verbiage is used in the US.
Comment: Yup. I took some graduate level classes in counseling at Capital Bible Seminary, which shared facilities with the undergraduate Washington Bible College
Comment: Is this answer for any particular country or state? Because it is completely inaccurate for where I live.
Comment: There are lots that aren't, but there are some that are. I attend Lincoln Christian University and it is accredited.
Answer: I've recently figured this out for myself. Bible Colleges typically offer Bachelor degrees, which some are accredited and some are not. Then, seminary is usually always referring to a graduate program in Biblical-focused areas. I've still heard of people who have gone straight into "seminary" from high school, to which I cannot explain but most likely not accredited. I'd assume some places might take advantage of the loose term "seminary" just like "bible colleges" not always being accredited.
To provide some context, I attend North Central University in Minneapolis. NCU is accredited for a ton of Bible and liberal art bachelor degrees and they also offer an accredited graduate/masters degree in strategic leadership. While NCU offers an accredited grad program, I'd assume we're not a "seminary" due to the fact we don't offer grad programs within the biblical studies-ralm, but general leadership.
Comment: Thank you for the edit, this now does answer the question  Welcome to the site.  Please do take some time to read the links in Lee's comment.  This really would be better if it were well-referenced, rather than your personal observation, but not bad for a first post.  I hope you decide to stick around.
Comment: Welcome to Christianity.SE. For a quick overview, please take the [Site Tour](http://christianity.stackexchange.com/tour). Thanks for offering an answer here. However, it really doesn't address the question, which is about the difference between a Bible college and a seminary. See: [What makes a good supported answer?](http://meta.christianity.stackexchange.com/questions/692/what-makes-a-good-supported-answer) Though your answer will likely be deleted, I hope you'll stick around and read some of the other questions and answers here.
Answer: A "bible college" is like a community college or small liberal arts college, offering a bachelors degree or certificate.
Seminaries are for professional formation of clergy or ministers, and might also be called a "divinity school" especially if attached to a university.
Answer: The dictionary states that seminary is "a college that prepares students to be priests, ministers, or rabbis." In addition to this, Wikipedia gives some of the same definitions regarding seminary... I wondered about this some years ago before going to a university, that had a bible college that I attended. I received my four year degree in Practical Theology and will be going back for my MDiv. I also asked some of my religion professors this question as well. All in all, if a person is attending a bible college for a ministry degree that prepares them for ministry (pastors, ministers, priests, etc.) they are in seminary. Doesn't matter if its a bachelor's, master's, or doctorate's degree.
Hopefully this response helps. Please excuse typos...
Comment: Welcome to Christianity.SE. For a quick overview, please take the [Site Tour](http://christianity.stackexchange.com/tour). For more on what this site is all about, see: [How we are different than other sites](http://meta.christianity.stackexchange.com/q/1808/20394). And for some tips on writing good answers here, see: [What makes a good supported answer?](http://meta.christianity.stackexchange.com/q/692/20394) Meanwhile, I hope you'll browse some of the other questions and answers on this site.


Warm ups for swimming?

Question: A few weeks back I managed to pull a muscle while swimming.  I'm fairly certain it's because I didn't warm up before I got in the pool and did some higher intensity swimming than I normally do.  What warm ups are there for swimming so that I can prevent this from happening again?
Comment: While not a full answer, [this article](http://www.activbodypt.com/article.php?aid=2292) gives some warm up ideas, some dynamic stretches and some after workout passive stretches.
Answer: Your best warmup is going to be swimming. What I usually do for a warmup is a 500m swim of SKIPS. Swim 100m, Kick 100m, 100m IM, 100m Pull, 100m Swim. If you can't do all the strokes, do 400m SKPS.
I might also not make my most intense set the first one after the warmup, I might put in a threshold set of 10x100 on 1:45 (or whatever suits your swimming speed), before I did any kind of high intensity interval type work.
I'm not a fan of leaping around a pool deck waving your arms and legs for a swimming warmup. One, the deck is often wet/slippery, two you get funny looks. Swimming is non impact enough that you can just get in and swim at a low level, so as long as you don't jump in and start banging out 50m on a :25 sendoff you should be fine just swimming as a warmup.
Comment: For a longer warm up I've done 1000 yd SKIPS before. Swim 200 yds, Kick 200 yds, 200 yds IM, 200 yds Pull, and Swim 200 yds.
Answer: Warm ups are important for all sports, both physical and also a mental warm up. Here are some warm ups for swimming:

Physical, structure your work out so that you go from low intensity
-> techniques -> high intensity -> cool down. E.g. swim 2x50m slow freestyle and 2x50m slow breaststroke, then work on various
techniques for 200m-300m, and then (as an example) swim various sets
of 200m, 400m for a total of 1000m - 1200m, last, cool down through
swimming 2x100m backstroke. The pattern of "low intensity ->
techniques -> high intensity -> cooldown" is not unique for swimming,
you will find it in all sports where you involve the whole body in a
complex way.
Mental, before the workout, think through the goals for the workout
and picture yourself doing the work out (in this context, going
through the swim drills, how intense the 200m and 400m sets should
feel). On a personal level, when I do this, I can feel my pulse
quickening, hands getting warmer, and that I want to start moving.

Various warm up drills for swimming that are integrated in a swim workout can be found at - for example - Swim work out generator
Answer: I feel your pain!
Thinking that I should be ready to swim under any circumstances I hopped in the water last summer completely cold, sprinted a 50m freestyle and tore an intercostal muscle in my rib cage.
Not fun.
Warming up properly before you go swimming has a heap of benefits, not the least of which is injury-prevention. Increased oxygen delivery to muscles, increases respiratory system ability, and more.
Here is what I usually do:
1. 5-8 minutes of arm and leg swings. Forward and backward, make figure 8's, lateral arm swings, leg swings to open up your hips and hamstrings.
2. 400-600m of easy swimming. Nothing crazy here (unlike my example above). Alternate strokes to open up your shoulders. I like to alternate freestyle and backstroke by 25 or 50 depending on whether it is a short course or long course pool.
3. Add in some moderate/high intensity stuff at the end. Build up to about 70-80% effort over the last 100m to get your heart rate up and "prime" your body for the work to come.
Source: National level swimmer, Olympic trials qualifier.

Warm ups for swimming?


When and why was the samurai class abolished?

Question: I am aware the Emperor Meiji abolished the Samurai class during the reformation.  Why did he do so?  How was it enforced?
Comment: Many samurai found it difficult to exist and took the drastic move to emigrate to the US and Latin America as exploited labor force. Bushido went with them. Bushido did not really exist in the Japanese modern military, which was influenced by going to the US and observing wars against Indigenous Nations by the US military Custer was the Japanese military in WW2. The samurai soldiers were the Nisei boys in the segregated 442nd combat unit of the 101st Battalion for the US Army, which suffered 300% casyakty rate. I learned this point of view from an indigenous elder who is a WW2 military buff.
Answer: The Charter Oath  promulgated at the enthronement of Emperor Meiji of Japan on 7 April 1868 includes several parts that identify the reasons for the radical social restructure that followed the Meiji restoration and an indication of the motivations for the dissolution of the warrior class that had been a defining characteristic of Japanese society.

Deliberative assemblies shall be widely convoked and all matters of state shall be decided by public discussion;
All classes, high and low, shall unite in vigorously promoting the economy and welfare of the nation;
All civil and military officials, and the common people as well, shall be allowed to fulfill their aspirations, so that there may be no discontent among them;
Base customs of the past shall be abandoned, and all actions shall conform to the principles of international justice;
Knowledge shall be sought throughout the world, and thus shall be strengthened the foundation of the Imperial polity.

The determination to remove the "base customs" of the past drove the new government to dismantle the old Confucian based social order. This included the removal of the restrictions and privileges that had defined the samurai, peasant, artisan and merchant classes.
During the summer of 1869 Tokyo formally reclassified the population as nobles, former samurai and commoners.
In 1871 the Tokyo government assumed the responsibility for paying stipends to the former samurai. This immediately accounted for almost one-third of the government's expenditure. This massive financial obligation created pressure to abolish the subsidies entirely.
Despite less than universal support amongst the new leaders, in 1873 the Daijō-kan (department of state) offered interest-bearing goverment bonds to former samurai who surrendered their stipends. Three years later it made that exchange obligatory.
In 1876 ex-warriors were deprived the right to carry swords.
These steps to dissolve the military estate coincided with the establishment of a conscript army based on the Prussian and French models. Vice minister of military affairs Yamagata had seen the efficacy of these armies first hand in Europe and in 1873 enacted a Conscription Ordinance:

By this innovation the rulers and the ruled will be put on the same basis, the rights of the people will be equal, and the way will be cleared for the unity of soldier and peasant

This landmark measure was a major step in the disfranchising of the samurai estate and vastly strengthened the regime's authority by creating a force capable of dealing with countercoups and providing internal security.
Quotes and references from:
James L. McClain. Japan, a modern history W.W. Norton & Co, 2002
Answer: ... and as Steven I think implies, the power of the samurai continued in the Japanese Army.  This was one reason why the army had no problem doing all their evil in the name of the 'Emperor', while actually doing everything they could to ensure his opinion was never allowed to interfere.  This reflected previous Japanese history when Emperors were puppets of the shogun.
Comment: Actually, the samurai influence was stronger in the Russo-Japanese war of 1904-5.  In that war, the Japanese were often praised for their very correct fighting and treatment of prisoners.  I've seen arguments that the WWII behavior is more typical in Japanese history when arming the non-samurai classes.
Answer: This appears to have happened roughly around 1873, when Emperor Meiji decided to change his military structure to use a conscripted army. He was attempting to modernize Japan by following the examples he had seen from England and Germany. Most of the Samurai volunteered to become soldiers and many eventually became officers in the new modernized Japanese army. By eliminating the Samurai, the emperor was also attempting to eliminate the feudal domains that had separated the country into different political domains, thereby reinforcing support for his centralized government.


How do I cross-compile the kernel on a Ubuntu host?

Question: I would like to understand more about how the kernel works. Part of this is to compile it myself. How do I cross-compile the Kernel on a Ubuntu host?
Answer: Preparation
First, we need to install the required prerequisites. I assume you have sudo access.
sudo apt-get install git ncurses-dev make gcc-arm-linux-gnueabi

git is the version control system used by the Linux kernel team.
ncurses is a library for build console menus. It is necessary for menuconfig.
make runs the compilation for us.
gcc-arm-linux-gnueabi is the cross-compiler.

Next, we need to retrieve the source, run:
git clone https://github.com/raspberrypi/linux raspberrypi-linux
cd raspberrypi-linux

This will clone the source code to a directory called raspberrypi-linux and change to it.
Compilation
We first need to move the config file by running
cp arch/arm/configs/bcmrpi_cutdown_defconfig .config

Then configure the kernel build
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- oldconfig

Optional: Customise the build using menuconfig
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- menuconfig

Then run the compilation
make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- -k

References

http://elinux.org/RPi_Kernel_Compilation
https://github.com/raspberrypi/linux
http://packages.ubuntu.com/precise/gcc-arm-linux-gnueabi
http://mitchtech.net/raspberry-pi-kernel-compile/
Comment: Thank you very much for providing an alternative to using **crosstool-ng**.
Comment: In my case CROSS_COMPILE is just a prefix, so the follow should be enough (without gcc at the end):

```make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- -k```
Answer: I think Alex is right but the gcc-arm-linux-gnueabi is compiled for arm cpus without hardware floating point unit. You can find a cross-compiler with armhf support on: https://github.com/raspberrypi/tools
and a good tutorial to start with here: http://hertaville.com/2012/09/28/development-environment-raspberry-pi-cross-compiler/
Answer: Official documentation
https://www.raspberrypi.org/documentation/linux/kernel/building.md (GitHub)
I would recommend that you just follow the steps there, or send a pull request if something becomes outdated or is not clear enough: those instructions are the most likely ones to be correct and up to date since they are part of the official documentation of the project.


PC has a mind of it's own

Question: When I put my PC into standby, sometimes it randomly awakes, scaring me and waking me up. What could be causing this. No it is not my mouse moving, it can only be powered back on by the power button. It's really strange.
Comment: It could be haunted.
Answer: It could be network activity. A lot of "default" standby configurations are set to resume on network activity.
Answer: Does it then proceed to turn off again? If the computer is set to hibernate after a given amount of time, it will wake itself from standby, then put itself into hibernation. This is normal. Another possibility is that a scheduled task is waking it up on a timer - does it wake up at the same time every time, or seemingly randomly?
Comment: It's completely random, I don't use hibernate. It might do it tonight it might not, it happens 1 - 2 times per month.
Comment: The strange thing is that it is a new pc, and my old pc was doing the exact same thing. I might have some ghosts or stuff haha.

PC has a mind of it's own


What do people mean when they ask me what the chord progression of a song is?

Question: I an amateur pianist and I have theory knowledge. I know what a chord progression is. Although I mostly read from score I can easily listen a music and reproduce it on the piano. People often ask me for the chords, but recently I was asked the chord progression for the music. What do they expect?
Answer: A chord progression is a series of chords that are played in a song (or a part of the song).
If a song has the chords C, Em, F, G, It means that all these chords together form the chord progression of the song. Many people abbreviate 'chord progression' to 'chords'. It's the same thing. You might also hear harmonic progression and/or chord changes (or simply 'the changes').
Someone might ask you for the chords or the chord progression, but basically he's asking for the chord progression.
Answer: Actually, "chord progression" connotes a different level of abstraction than simply "chords".   For each chord in a particular key, let's say the key of C:  C major would be the "I" chord.  D major would be the "II" chord, etc., up to B major which would be the "VII" chord. Of course, major chords are composed of minor thirds on top of major thirds. Minor chords are composed of major thirds on top of minor third intervals and hence, minor chords are noted as lower case roman numerals:  i, ii, iii, etc.   The PURPOSE of such a notation is to allow you to transpose this relationship among chords from one particular key to any of the eleven others.   Now, "chord progression" is then the RELATIONSHIP among the chords that then define the harmonic construction of the song.  So, "I, IV, V, I"  would be an example of a chord progression.  Read any decent music theory book and all this should be covered.    cheers, Paul.
Comment: I've never personally come across this distinction between 'chords' and 'chord progression' - I wouldn't assume that either term specifies either chord names in a specific key (C, Am etc) or Roman numerals.
Comment: I think you're over-thinking this!  He's being asked for the chord sheet.
Comment: I agree; if I were asked for the chords of, say, "Stand By Me", then I'd say C, A minor, F, G7. Were I asked for the chord progression I'd say one-six-four-five and assume that the person who asked would be familiar enough with this standard pop music chord progression to know where the minors and sevenths go.
Comment: While you could use Roman numerals to describe the progression, you don't need to describe a chord progression with them especially since most people get the analysis wrong like you would never see a II chord, but instead it would be a V/V.
Comment: Conventionally you'd assume D minor (not major) in the C of C major, and B diminished.
Answer: All the answers so far are correct but I would like to see if I can explain it in a different way that might make it easier for some folks to understand.
Every song has a basic harmonic structure to go with the melody of the song.  The chords provide the harmony and appear in a predictable predetermined order.  So the chord progression of a song is not only a list of all the chords, but the order they are played.
The chord progression of the verses of a song are often different from the chord progression for the chorus or bridge. But the chord progression for the verses will repeat for each verse - same with chorus.
There are common progressions that appear in many songs because the follow a logical order of ascending harmony and returning back to home base.
A chord progression can be identified by naming the exact chords such as "G - D - Em -  C" or you can identify a chord progression by the chord degree based on the root key.  So that in the key of G major -  G D Em C becomes "I - V - vi - IV" (capital Roman Numerals indicate Major and lower case indicate minor).  By translating the chord progression into the numeric representation, an accomplished musician should be able to play the song in any key.
Answer: They just want to know how the harmony of a song progresses though the chords of a song. The chord progression can just be viewed as the precises order of the chords in a song. The chords used and the order appear in offer a lot of information about the song and how they can play it.
For example off the top of my head I know the chord progression for Let It Be by the Beatles which is C G Am F C G F C. The song itself only uses four chord which are C, G, Am, and F, but the order of the chords and how they progress is important to the song and how it feels. Especially since this song is unique by using a IV-I cadence instead of the typical V-I cadence.
Using the progression, I can voice the chords in a way that makes sense for the progression, figure out the key which is C major in this case, figure out what scales and modes make most sense to use at this part of the progression, and even reduce the progression to its Roman Numeral analysis using the chord progression to not only analyse the harmonic movement of the progression, but easily be able to transpose it to any key.
Answer: Chord progressions are written with a sequence of letters representing the chord along with its attributes such as minor, suspended, or diminished. (Note: All chords are assumed to be major unless otherwise indicated.) An example would be C,G7, Am, F with the assumption that it would be repeated. Typically the bass line defines what your progression will be. This is particularly true for piano. So they basically want to know what "progression" is guiding the music. Also keep in mind that the measure count is also important. It may be 1 measure of each chord that repeats or it may be 2, or even a half a measure here and there. But basically the notation they'll expect is simply a sequence of letters with minor as a lowercase "m", suspended as "sus" and so on.
Answer: In the key of C Major using 7th chords as in jazz, the chords are C Major 7, D minor 7, E minor 7, F Major 7, G7, A minor 7, and B minor 7 flat 5.
Count starting with C Major, 1,2,3,4,5,6,7.
So in answer to your question, What would a ii, V, I be?  Answer is
D minor 7 (the ii), G7 (the V) and C Major 7 (the one).  Other common chord progressions in jazz are I, vi, ii, V ; iii, vi, ii, V.
If you look at your music, you will see the ii, V,I or other progressions in the song.  A progression such as ii, V, I, is always a ii, V, I, no matter what key you play in, so musicians communicate in the language of chord progressions.


How can I get back my dead mother's ring, which I gave to a family friend?

Question: My mother has been dead for a couple of years now and upon her death I received her butterfly ring and her ashes. I had given her ring to a family friend who was like a mother to mine, but unfortunately I may have to cut contact with her. Is there a way for me to get my mothers ring back? I was unaware she had several things from my mom and I had foolishly given it too her, while all I have to remember my mom is three photos and a name tag from her last job.
Comment: Have you tried a solution outside of the legal system? Either directly approaching the friend, or if that is not practical, then getting a mutual friend to talk to them? It's likely to be cheaper, and as soon as you get the law involved you are likely to destroy any change of a reconciliation.
Answer: Sarah, thanks for your question. You have asked this on the Legal forum; and whilst there might be many moral or ethical considerations surrounding your situation - I'll try to deal with the legal principles here - which are distinct from what people consider 'fair' in the common sense of the word - simply discussing the legal basis of what you are asking.
The relevant law here is 'Gifting' under the Law of Property - here

A gift, in the law of property, is the voluntary transfer of property
from one person (the donor or grantor) to another (the donee or
grantee) without full valuable consideration. In order for a gift to
be legally effective, three requirements must be met:

Intention of donor to give the gift to the donee (donative intent)
Delivery of gift to donee.
Acceptance of gift by donee.

Gifts are generally considered by the court to be either 'outright, remunerative or onerous' - so there can be conditions placed on the acceptance/receipt of a gift. However, it doesn't sound like these apply and that you have given this gift, free of conditions to the donee.
There are special legal considerations with respect to engagement rings between would-be spouses where the donee actually typically keeps an engagement ring even if they fail to get married. This is under revocation.
Unfortunately, from a strict legal point of view - a gift, is a gift - which broadly speaking means that if the person is not willing to return the gift, they are under no strict duty to do so.
One can sue for return of the gift if undue influence was exerted over the donor by the donee:

There are two main forms of conduct that are unacceptable:

Acts of improper pressure or coercion such as unlawful threats. In the
case of Etridge the judge made it clear that the court will intervene
to set aside a transaction which is the product of "excessive
pressure, emotional blackmail or bullying".
Failure to perform an
equitable duty; g. where A trusts B and B takes unfair advantage of A.

see here
It would ultimately be for first, your solicitor and secondarily a court (or similar) to decide whether you had a legal case based on any undue influence you may have been under, based on the situation which you did not know that she had other items of your mother, leading you to gift her the ring. This is very context dependent. This legal process would be under a civil action against the donee. Of interest, the supreme court have limited the scope of 'undue influence'; the technical details can be seen here.
I hope this is helpful.
Comment: Yes this could be considered an onerous gift. The reality is something as complex as this arrangement it would need to be documented somewhere, or have substantial witnesses to this effect. Another instrument to formally recognise such an arrangement is literally a contract. Many of the components you mention would need defined such as "reasonable length of time".
Comment: Is there any formal means of recognizing an "indefinite loan" of an item with the understanding that X would allow Y to possess the item and use while exercising normal reasonable care, unless or until either X wanted it back or Y no longer wished to maintain possession, but with the recognition that Y would not dispose of the item without offering to return it to X, and that if X asked for the item back Y would return it within a reasonable length of time?
Comment: basically there's not really a 'divorce' (can change mind) for a gift, but there is an 'annulment' (can say that the gift giving was invalid) ?
Comment: @DrDee: Such an arrangement may be "complicated", but it's essentially how many people share things.  If someone asks a friend "Do you mind if I take [item]", the normal intended meaning would, depending upon the item, be either "Do you mind if I borrow this item for awhile?" or "Do you mind if I take and consume this item, and later allow you to take and consume something similar?"  Not "would you like to gift of this item to me, without consideration?"
Comment: @supercat When I imply complicated, I mean legally complicated. All of what you have just said is, of course, very standard in life - but litigation/lawyers would argue/contend each and every point there and the intent, meaning behind all of it and the ultimate remifications in law etc - so it can get very contentious and complicated, very quickly!
Comment: ["Not "would you like to gift of this item to me, without consideration?"] - "prove this is what happened" - therefore = complicated/frustrating territory.
Answer: One could imagine a woman giving a ring to a girl going off to college. Then later, the woman asks for it back saying that it was her mother's ring and obviously it was just given to use temporarily so that the girl would make a good impression with her classmates (maybe the girl didn't have good jewelry of her own) and not to keep.
But it sounds like you (1) knew that you gave her the ring, and (2) its significance, and that (3) you intended her to actually own it and keep it. And even without you telling us this, her having it for years makes it seem that way.
Tough situation.


Is there a setting to tell Deja dup when to make full backup?

Question: Is there some settings to tell Deja dup when to make full backup? I using this just two weeks and today hit full backup again. I do backup at least once per day, but usaly 2-5 times per day. And Want full backup for every two month. I wish to prefer when. Is tah possible?
Answer: It's difficult to control that precisely.  Two main things affect it.  How frequently your automatic backups happen and how long you told DD to keep backups.
By default, with weekly backups and keeping them forever, DD will make a fresh backup every three months.
If you change it to daily backups, I believe it switches to monthly fresh backups.
It sounds like you already make regular manual backups.  I'd say change the automatic backup setting to weekly and continue with your manual backups.  DD should use three month intervals.
In Ubuntu 12.10, DD will always use three months no matter what.  Though you can fiddle with a secret config key to change it if you really want to.


Is there a way that I can rank NBA teams in each season?

Question: I would like to rank NBA teams in each season by some sort of metric, and I'm not sure if something like this exists already or not. It would be better if it was a metric that can tell me how good an NBA team is before the start of the season.
Comment: "It would be better if it was a metric that can tell me how good an NBA team is before the start of the season." As in akin to preseason NCAA basketball rankings?
Comment: How are the preseason basketball rankings determined?
Comment: For NCAA men's basketball, by a series of polls: http://espn.go.com/mens-college-basketball/rankings/_/year/2014/week/1/seasontype/2
Answer: A very easy, and direct way to rank the NBA teams, is by their record. So a team that has won for example 50 games in the season, and lost 32 (a total of 82 games in the season), would have a 50-32 record, as they call it. This team, even if in a difference conference, would be better than a team with let's say, a 40-42 record.
Firstly, however, the above method only takes into account the regular season, and doesn't mention anything about the post season (i.e, the playoffs). Therefore, if for example both the 50-32 and the 40-42 teams do make it to the playoffs, and the latter beats the former, then obviously the 40-42 should be ranked higher than the 50-32, even if they had a lower winning percentage than them during the regular season.
Another thing to keep in mind is that there is a difference, albeit slight, between the two conferences (the East and West), especially this year. The West, based on winning percentages of the teams, was considerably stronger than the East for this season's NBA. Therefore, it might be something to take into account because Eastern conference teams play each other more often than they play Western division teams for example. Some might say then that the Indiana Pacers or Miami Heat for example, who ranked 1 and 2 respectively in the regular season, might have had an "easier schedule" than the San Antonio Spurs who finished first in the Western conference, even as they had a better winning percentage.
All in all, winning percentages (i.e a teams' record) usually is what determines a teams rank overall in the NBA, but something that might be taken account, as mentioned, is how far a team advances into the playoffs, or which conference it stands in.
Answer: Basketball, like many other sports (e.g. Baseball) is starting to lean toward statistical analysis to judge efficiency and overall success from not just an individual players standpoint but also from a lineup and team performance basis.
Former ESPN analyst and current front office personnel man for the Memphis Grizzlies Greg Hollinger created a power ranking system (which can still be seen via espn.com, although you might need an paid insider pass to gain access) in which scoring margin (or average margin of victory) plays a heavy role in determining which team is better than the other.
While this is not an official science, Mr. Hollinger's rankings are commonly accepted by a lot of his former analyst counterparts.
Answer: The www.nba.com website is very useful for this. It gives you stats and standings and allows you to play around with figures, efficiency ratings and sortable player statistics.
Answer: FiveThirtyEight uses Elo and CARMELO metrics to rank NBA teams before the start of each season and during the season. Elo is "a simple measure of strength based on game-by-game results." CARMELO is FiveThirtyEight's "Career-Arc Regression Model Estimator with Local Optimization".
Here are their rankings prior to the start of the 2018-2019 NBA Season (choosing the forecast from Oct. 15, the earliest available projections).
Elo:

Warriors (1685)
Rockets (1654)
Jazz (1623)

CARMELO:

Warriors (1751)
Rockets (1662)
Raptors (1655)

Elo is most likely more accessible than CARMELO, so that is one way you can rank NBA teams beyond a given team's record.


``What is life?'' by a physicist definition

Question: The question is about defining ``What is life?'' in the field of Physics.
Whether there is any (insightful) way of defining ``What is life?'' from physicists.
There are pioneer works, including Erwin Schrödinger's nice book What is life?, cf. Wikipedia.
But it will be helpful to hear from someone here if there are alternate new viewpoints. Starting from as basic concept as possible.
Probably involving concepts of entropy, thermodynamics, randomness, order-ness, emergence, aging/time-evolution, etc. But not necessary.
Since this question has been criticized being opinion based as [on hold] (I doubt there is a way to save this issue to be non-opinion-based for a less-developed frontier land like this). Let me focus on this sharp question. The sharp question, I would like to know, is that, suppose only (quantum) mechanical/physical robotic/computer measurement is available,
how can one detect whether an object is being defined as life or lifeless by some physical measurement or computer algorithm?
I imagine, if answered by a quantum physicist, perhaps it will involve with the measurement on a (ground) state wavefunction of the living/lifeless object? Detect certain electronic/magnetic/response signal, etc?
Comment: I'd say that this question will not generate opinion based answers only. It's because we can all observe living beings and after elimination of non-common properties say what is common among them and define it as life. I'd say it's local enthropy reduction and tendence to multiplication. It's even on wikipedia.
http://en.wikipedia.org/wiki/Entropy_and_life
Comment: @ user46147, thanks for the link and the comment.
Answer: Perhaps let me try to address this question based on a discussion with Prof. Frank Wilczek. This post is not going to be complete or anything.
The punch line question I discussed with him: is there a set of mathematical equations from physical principles to distinguish life and lifeless beings? (say, hand in a system as an input, one can check its live or dead, by running algorithms/numerics/experiments in computer, which outputs the answer.)
Take virus for example may be hard to tell the "phase" difference between life or lifeless, as Brandon suggested. However, I believe, there is certainly a distinction between life and lifeless beings. An extreme example is simply the moment when life beings becoming dead (due to natural process, illness or external factors). Live or dead all concerns the same "organic" system. However, some properties changes between it is live or it is dead. So the virus example is confusing because it is about the complexity of its composition - whether it is organic enough. It is not exactly what Idear is pushing after, I thought.
There may be this distinction between life and lifeless, because the former(life) has "too many degree of freedoms" than the later(lifeless), especially in a time dependent dynamical process. The former (life one) is difficult to reconcile with Determinism.
So let me share with you, Prof. Frank Wilczek's mail response after a conversation, (I wished his generous understanding on sharing his thought to the community here, every copyright on his thought goes to his):
``Hi,
I enjoyed talking with you about this.   It's an interesting question.   As we discussed, I think the common notion of "life" is a vague around the edges, but of course that was (and still is) true of concepts like "symmetry", "energy", "force", "temperature" -- the scientific notions don't necessarily completely coincide with the everyday notions that inspired them, but capture what can be captured consistent with precision.    Also as we touched on, I think that life may probably can only be viewed usefully in terms of how a system responds to an appropriate environment.   Thus a living system, roughly, is one that grows and at some level reproduces in an appropriate class of environments.   (If we want to exclude crystals, the last phrase is important.)    One could attempt to make that definition more "physical" with some notion that life is connected with creating, maintaining, and amplifying entropy gradients.
All the best,
Frank W.''


Quantcast reporting

Question: Looking at a Quantcast report I see that they have metrics like women, male, children and different age groups, etc. How do they determine which visitor to the site is woman, male, child, old man, etc?
Answer: TL;DR
Simple, it's mostly estimates and guesswork based on studies and demographics bundled with some math.
A (very simplified) example for male/female:
500 website visitors prior surfed on Elle.com (tracked by Quantcast)
500 website visitors prior surfed on Vogue.com (tracked by Quantcast)
500 website visitors prior surfed on Style.com (tracked by Quantcast)
+
500 website visitors prior surfed on Engadget.com (tracked by Quantcast)
+
1.000 website visitors prior surfed on multiple untracked sites (by Quantcast)
So mostly we have 1.500 female website visitors, 500 male visitors and 1.000 visitors (asumed 500 male and 500 female; if the demographics of their origin country is 50/50 with male/female).
This leads to the assumption, we have 2.000 females and 1.000 males in total.
Now, you just got to throw in some studies on demographics of internet usage, split it up with the traffic you know, calculate the traffic you don't know anything about and combine the numbers.
It's of course much more complicated than that, but basically that's how it's done ...
Comment: Pretty much how it's done. And according to some website owners who've gotten their analytics module, website statistics drop to real levels showing the guestimates to be 4-10x over reality. WAG, WAG, WAG!
Answer: The approach Quantcast uses is called an "inference model". Quantcast uses an inference model to characterize audiences of nearly any size. Quantcast has NOT built its model on PII (personal identifiable information), but instead uses a large-scale mathematical model to infer demographics of visitors.
How inference modeling works is fairly well documented in literature on statistics. An example of an inference modeling technique would be Bayesian Inference.
DISCLAIMER: I work at Quantcast

Quantcast reporting


How to I cut glass and marble tiles when they are on a mesh backing?

Question: How do you cut combination marble and glass tiles when they are both on the same mesh backing?  When I tried this, the tiles move and the glass shatters.
Comment: you can remove from the backing the set of tiles that need to be cut, then cut them individually and set them individually.
Answer: Ahhhhh no wet saw for small glass mosaics.  First it will bounce all over when cutting and second you might get a nice chunk of glass in you.
You will be cutting everything one mosaic tile at a time.  Take it off of the mesh.
#1 Make sure when laying out your tile that your cuts are in the corners or in less seen areas.
#2 If you need to cut the corner of a tile or odd shapes use glass nippers.

The nippers are not a precision tool.  With a little practice you can get close to what you want.  Luckily doing mosaics breaking a couple of squares is relatively cheap.   If you have a weird corner cut on a tile or a circular cut and you can get it done in 2-3 tries the great job.
#3 For straight cuts you use a wheel scorer.  The picture I have below is a double sided.  Often you will just see a single wheel.  Just like cutting drywall it is most important to get a good score on the glass side.  With a little muscle you should only have to roll an area 2-3 times.

#4 Once you have a line on the top of your tile we are going to move it over to the tile cutter.  You are going to place this faced up with the edge right on the cut line.  This takes practice and is a little different with each cutter.  You will gently (do it to hard and cut may not be clean) bounce the lever to put pressure on the tile.  If it is lined up right eventually it will break clean on your scored line.  If your cut isn't clean then you may need to score a little deeper or line it up better on your cutter.  Also do one tile at a time.  I know it seems a PITA but you can do 2-3 tiles in a minute once you get it down.  Also do your cuts before you start applying thinset or have a helper.
Answer: I just finished my kitchen backsplash using a Dremel with a diamond blade($18). It helped for me to have tape next to the cut. Advise using respirator and safety glasses.
Answer: Are you using a wet saw? I leave it on the cardboard it because it helps prevent stuff from moving around.
Answer: My trick for cutting with a wet saw is similar to using a narrow throatplate (zero clearance) on a tablesaw:
Get a smooth 12x12 tile and use it under the mosaics.  Just cut it no more than 3/4 of its length, such that you keep the narrow kerf for support.
Having a smooth, continuous rim glass blade helps, also.
I used this technique to do 4ft by 4 ft by 8 ft shower enclosure of 1x1 glass mosaics.  I was able to keep the sheets of mosaics intact, for the most part.
Comment: I tried my first few mosaic jobs this way.  Then I just found it easier to not have to get out a saw, make a mess, and all of that stuff plus the fact that I found glass shards in my arm.  It can be done but I am not sure it is faster.
Answer: To add to DMoore's answer, cut off any full tiles you won't be using by cutting the backing with a utility knife.

Then, use the tile nippers to cut individual tiles. You'll be able to nip the tiles in half, or maybe 1/4 off if you're careful.

Then the important part comes down to planning your cuts and taking advantage of the mesh backing. Plan your cuts so they fall into an inside corner that will be covered by the adjacent tile, behind some trim, or under the faceplate for an outlet. Use the mesh backing to your advantage, shifting tiles a little further apart or closer together with a little push. By using those techniques, I avoided the need for any precision cuts on my last tile job.
Answer: I clamp a speed square to mosiac and cut with a angle grinder with 4" diamond blade
Comment: http://diy.stackexchange.com/help/be-nice
Answer: I had a Glass and Aluminum interlocking mosaic that needed to be cut around part of a window on the back wall of shower and the shower valve! I cut each piece individually using a diamond encrusted jig saw blade (8 Fed. Notes + the tax of course) and my 32 pt. hacksaw blade for the Aluminum. Using the low adhesive blue painters tape, I wrapped each glass piece where it was to be marked and cut to help from chipping. the Aluminum I had to deburr with a fine file. the circular cuts were not that difficult due to the 6 inch diameter. The whole process took WAY too long, but it looks like a professional tile layer did it, and I didn't have to spend the 2000 fed. notes to have the guy do it.
Answer: I have seen the sheets of glass herringbone tile back buttered with something, let dry so they stiffen up and then run through a wet saw with a glass tile blade....seemed to work pretty slick.


Why am I getting a segmentation fault? Valgrind?

Question: I have written a program to determine the longest common subsequence between two strings. I have tested my function LCSLength() with a small hard coded test case and it returns the correct value.
Now, I am reading strings from a file to compare, and my program gives me a segmentation fault. Here is the code:
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;

int LCSLength(string X,string Y);

int main()
{
    ifstream inData("sequences.dat");
    vector<string> lines(1);
    string line;
    int LCS;

    while (getline(inData,line))
    {
        if (line.empty())
            lines.push_back("");
        else
            lines.back() += line;
    }

    LCS = LCSLength(lines[0],lines[1]);
    cout << "The LCS is: " << LCS << endl;
    return 0;
}

int LCSLength(string X,string Y)
{
    int m = X.size();
    int n = Y.size();
    int L[m+1][n+1];
    for(int i=0; i<=m; i++)
    {
        for(int j=0; j<=n; j++)
        {
            if(i==0 || j==0)
                L[i][j] = 0;
            else if(X[i-1]==Y[j-1])
                L[i][j] = L[i-1][j-1]+1;
            else
                L[i][j] = max(L[i-1][j],L[i][j-1]);
        }
    }
    return L[m][n];
}

When I compile using -pedantic -ansi, I get the following error: In function LCSLength(std::string, std::string): ISO C++ forbids variable size array 'L'.
I compiled using Valgrind, and here are the errors it produced:
==15183== LEAK SUMMARY:
==15183==    definitely lost: 8,624 bytes in 14 blocks
==15183==    indirectly lost: 1,168 bytes in 5 blocks
==15183==      possibly lost: 5,518 bytes in 58 blocks
==15183==    still reachable: 44,925 bytes in 278 blocks
==15183==         suppressed: 0 bytes in 0 blocks
==15183== Reachable blocks (those to which a pointer was found) are not shown.
==15183== To see them, rerun with: --leak-check=full --show-reachable=yes
==15183==
==15183== ERROR SUMMARY: 23 errors from 23 contexts (suppressed: 0 from 0)
==15183==
==15183== 1 errors in context 1 of 23:
==15183== Invalid read of size 4
==15183==    at 0x38326: std::string::_Rep::_M_grab(std::allocator<char> const&, std::allocator<char> const&) (in /usr/lib/libstdc++.6.0.9.dylib)
==15183==    by 0x388EF: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) (in /usr/lib/libstdc++.6.0.9.dylib)
==15183==    by 0x100001AAE: main (firstt.cpp:23)
==15183==  Address 0xfffffffffffffff8 is not stack'd, malloc'd or (recently) free'd
==15183==
==15183==
==15183== 1 errors in context 2 of 23:
==15183== Invalid read of size 8
==15183==    at 0x388DC: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) (in /usr/lib/libstdc++.6.0.9.dylib)
==15183==    by 0x100001AAE: main (firstt.cpp:23)
==15183==  Address 0x100023d28 is 0 bytes after a block of size 8 alloc'd
==15183==    at 0x5237: malloc (in /usr/local/Cellar/valgrind/3.8.1/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==15183==    by 0x4B346: operator new(unsigned long) (in /usr/lib/libstdc++.6.0.9.dylib)
==15183==    by 0x100002DFE: __gnu_cxx::new_allocator<std::string>::allocate(unsigned long, void const*) (new_allocator.h:91)
==15183==    by 0x100002E42: std::_Vector_base<std::string, std::allocator<std::string> >::_M_allocate(unsigned long) (stl_vector.h:131)
==15183==    by 0x100002E9D: std::_Vector_base<std::string, std::allocator<std::string> >::_Vector_base(unsigned long, std::allocator<std::string> const&) (stl_vector.h:116)
==15183==    by 0x1000030E4: std::vector<std::string, std::allocator<std::string> >::vector(unsigned long, std::string const&, std::allocator<std::string> const&) (stl_vector.h:215)
==15183==    by 0x1000017D9: main (firstt.cpp:11)
==15183==
==15183== ERROR SUMMARY: 23 errors from 23 contexts (suppressed: 0 from 0)
Segmentation fault: 11

My test file has two lines of sequences. I check lines.size() and it returns 2. I also cout << lines[0] and cout << lines[1] and the correct strings are printed.
Can anyone help me figure this out? Thanks.
Comment: I think it is because you cannot do this: int L[m+1][n+1];
The compiler doesn't know the size of X and Y when compiled, and the L array won't be initialized correctly. Try initialize with values
Answer: your lines vector always contains one element, therefore accesing it by index 1 causes UB
LCS = LCSLength(lines[0],lines[1]);
                          here ^

Answer: Did you confirm that after exiting the while loop, both lines[0] and lines[1] exist? This will happen only if you have at least one empty line in your input file (and recognized as such).
According to Valgrind (do read its output!) - you are doing something wrong from within main (lines 11 or 23) and not from LCSLength.


How can I tether a camera to a laptop, to show its menus and functions for teaching purposes?

Question: I understand the tethering process and have connected my Nikon D90 to my laptop.  I am able to see images that are on the memory card just fine.  My question is this:  I am teaching a class on camera functions, and I want to be able to show on my laptop the menu and various functions of my camera. I will be connecting the laptop to a projector, so it will be available to all students at once. It would be so much easier to show everyone where to find settings, how to use manual exposure, etc.  Is that even possible this way, or is there another way to connect these devices I have not considered?  I also have a Nikon D500 with more sophisticated connection capability.  Thanks for the help.
Answer: I think your best bet would be to use the HDMI output of the camera to connect it directly to the projector. If you have multiple inputs on the projector, you should even be able to switch between showing the camera's screen and the laptop while still having the camera connected to the laptop through USB for tethering. The best case scenario would be if the projector can show picture from the two inputs side by side or overlaid in some way.
This way you can show the information display and menus to explain settings and take pictures which the people will see on the projection screen as if they're looking at the camera's screen. You can always switch to the laptop to show the pictures in more detail or to show slides for your presentation (if you have any).
Comment: Does the D90, first introduced in 2008, even have an HDMI port?
Comment: @MichaelClark Yes, it does, but even if it didn't, a D500 is available as the author said.
Comment: That is a very helpful response.  Thanks so much.  My projector has a USB connector, too, so I may be able to use the three together in a creative way.  I will check it out.
Comment: I doubt that the USB on the projector would be useful with the camera - I bet it's meant for simple tasks like showing pictures from a flash drive. What model is the projector anyway?


Is "doing everything in your head" a good proxy for intelligence?

Question: Suppose Bob never takes notes in class and just mentally "gets" a subject. Is this ability of mentally learning a subject without actively recording the information a good proxy for intelligence?
Answer: Subject performance is not intelligence: Doing well in a single subject is a weak measure of intelligence. While the correlation between IQ and GPA is fairly high. The correlation for a given subject will typically be much lower. So another way of framing this subject is whether doing a subject in your head is a good proxy for subject understanding.
More broadly, your question implies a few other questions:

Does note taking improve learning?
Are students who are either more generally intelligent or more capable in the subject less likely to take notes?
Is there an interaction such that the benefits of note taking is less for more skilled students?

1. Is note taking effective?
I assume that note taking is generally effective and helping students to retain the information presented in a lecture. It encourages students to focus on the material. Deeper information processing increases depth of learning and retention. It also provides a means of revision, which in turn should increase retention.
That said, there are a lot of different types of note taking. In particular, part of the skill of note taking is working out what is important and what is not important.
There are also many different pedagogical contexts. For example, in some settings note taking is required for keeping a record whereas in other settings slides or recordings of the lecture may be provided. Logic says that if note taking is the only record, then it would be more important. Similarly, lectures vary in the degree to which the specific material needs to be mastered as opposed to providing an overview and relying on textbooks or other activities to hone skills. I would assume that where a subject requires students to repeat or apply information presented in the lecture, then taking notes will be more effective.
2. Are students who are either more generally intelligent or more capable in the subject less likely to take notes? I don't know of specific research into this, but I think there would be two key factors operating. First, less capable students are more likely to use poor study skills. So this might involve either no note-taking or poor note taking (e.g., taking down too much information). Second, more capable students are likely to know more material and also be able to absorb the material better. So in some cases, they may have less need to take notes, which in turn may lead them not to take notes.
It might also be related to self-efficacy beliefs which are only partially grounded in reality. So for example, the student might think that they are understanding more of the subject than they are, and fail to see the benefit that they would derive from taking notes.
3. Is there an interaction such that the benefits of note taking is less for more skilled students? Certainly at a certain extreme level of prior understanding where the student already knows all the material, then there may be little benefit from note taking. Likewise, as mentioned previously many features of the context may influence the need for note taking.  However, in contexts where the material is somewhat new to all students, and the test is on the material presented in the lecture, and there are no slides or other material I imagine that note taking would be fairly valuable for all students.
Some research:
It seems there is quite a lot of research on note-taking. Check out "note taking" on google scholar.
Hartley and Davies (1978) review note taking looking at why students take notes and the research on note taking.
Kiewra (1989) provides another review of the learning benefits of note-taking:

This review article investigates the encoding and storage functions of
  note-  taking. The encoding function suggests that the process of
  taking notes, which  are not reviewed, is facilitative. Research
  specifying optimal note-taking behaviors is discussed as are
  several means for facilitating note-taking, such  as viewing a lecture
  multiple times, note-taking on a provided framework,  or generative
  note-taking activities. The storage function suggests that the  review
  of notes also is facilitative. Research addressing particular review
  behaviors, such as organization and elaboration, is discussed as
  are the advan-  tages of reviewing provided notes, borrowed notes, or
  notes organized in  a matrix form. In addition, cognitive factors
  related to note-taking and review  are discussed. The article
  concludes with an alternative means for defining  and investigating
  the functions of note-taking, and with implications for edu-  cation
  and for research.

References

Hartley, J., & Davies, I. K. (1978). Note‐taking: A critical review. Programmed Learning and Educational Technology, 15(3), 207-224.
Kiewra, K. A. (1989). A review of note-taking: The encoding-storage paradigm and beyond. Educational Psychology Review, 1(2), 147-172.


Quaternions: Difference(s) between $\mathbb{H}$ and $Q_8$

Question: What is the difference between $\mathbb{H}$ and $Q_8$? Both are called quaternions.
Answer: A good analogy here is the difference between the complex numbers $\mathbb{C}$ and the cyclic group with 4 elements, which can be realized as the group $\{1, i, -1, -i\}\subset\mathbb{C}$ with complex multiplication.
$\mathbb{C}$ is a 2-dimensional vector space over $\mathbb{R}$, and there is a group inside it denoted $\mathbb{Z}/4\mathbb{Z}=\{\pm 1, \pm i\}$ with complex multiplication. This is the cyclic group with four elements.
Analogously, $\mathbb{H}$ is a 4-dimensional vector space over $\mathbb{R}$, and there is a group called $Q_8$ inside of it, namely the standard basis (with negatives) $\{\pm 1, \pm i, \pm j, \pm k\}\subset\mathbb{H}$ where the operation is quaternion multiplication.
tl;dr -- $Q_8$ sits inside $\mathbb{H}$. The first is known as the quaternion group, and the second thing is the quaternions.
Comment: The symmetry group of the square has $8$ elements, and whether you take $D_4$ to mean the dihedral group with $4$ or $8$ elements (both conventions exist, the latter is the symmetry group of the square) _neither_ of them is a cyclic group, while $\{1, i, -1, -i\}$ _is_ cyclic.
Comment: @MarcvanLeeuwen Oops, that's what happens when you write answers at 2am. Thanks for the correction.
Answer: One is the Hamiltonian Quaternions and has many descriptions, perhaps the most important (for things that immediately interest me) is that it is the )up to equivalence) only non-trivial central simple algebra over $\mathbb{R}$--it is also an object of fundamental importance in geometry.
$Q_8$ is the quaternion group. It is of great importance for the many weird properties it has that cause it to be a counterexample to many simple group theoretic questions--it is a non-abelian group all of whose subgroups are normal.
Answer: The first is a division ring (also called skew field, which is obviously infinite, and necessarily so by Wedderburn's theorem) and the second is a finite non-abelian group (in fact a subgroup of the multiplicative group of the first). So they are not even the same kind of algebraic structure. Indeed $Q_8$ has only $8$ elements, those unit quaternions that have only one nonzero component. The reason it is called quaternion group is probably that it captures the essence of the definition of multiplication in $\Bbb H$ (the general case follows by $\Bbb R$-bilinearity), and that the quaternions are in fact the most easily descibed context in which one comes across $Q_8$ (but may of course find $Q_8$ in some settings totally unrelated to the quaternions).
Incidentally $Q_8$ shows that the theorem saying that finite subgroups of multiplicative groups of fields (and more generally of integral domains) are cyclic fails for skew fields.


Can we buy a car in the EU as American citizens?

Question: We want to travel Europe for a year or so in a car we buy over there. Can we do that and what about insurance?
Comment: I suspect that registering the car will be more difficult than insuring it.  What sort of visa or visas are you planning to get?  If you won't have a residence in Europe, leasing a car is probably a better option.
Answer: In France, it is possible for tourists to lease a "transit temporaire" vehicle. This is a scheme whereby a new car for use by non-residents can be registered tax free, and is then rented to for a temporary period, deferring the taxes. At the end of the period, the manufacturer gets the car back, and pays the taxes on the (now depreciated) vehicle. Due to the tax advantages, you're unlikely to find a cheaper way to rent a car, and this is much easier to organise than buying a car. The car receives an attractive pair of red registration plates.

This is beneficial for the tourist and for the car manufacturer, so several French car manufacturers offer this service, including Renault, Peugeot, and Citroen.
The length of lease possible seems to vary based on your situation. Insurance is included. The car can be delivered to locations outside France if required. Since the service is explicitly targeted at non-residents, you must prove that you aren't resident in the EU in order to qualify.
In order to compare the different schemes available you should search for "europe tax free lease".
Comment: Isn't there a six months limit to this ? http://www.douane.gouv.fr/articles/a10758-achat-d-un-vehicule-lors-d-un-sejour-temporaire-en-france ?
Answer: Europe is still 27/28 different countries with as many different legislations. So it will be hard to answer your question in general. For each single country you may get answers here.
So let me start with Germany:
Of course, you can buy a car, but obviously you will have to insure and register it. In Germany, this is going to be the sequence of things, i.e. you first have to buy insurance, then you go and get the car registered. In order to register a car in Germany, you will have to be a resident, which I guess you will no be able to produce.
That means either you have any nice person (relatives?) living in Germany which will register the car on your behalf or you will be out of luck.
Please note that AFAIK the UK (part of the EU until March 2019) does not have that concept of registered address, so it may be easier there. Also of course as you can do everything in English there.
Just be aware that the UK is one of the very few countries in Europe which drives on the left. It may turn out very inconvenient if you buy a right hand steering car in the UK and then spend most of your time in continental Europe where we drive on the "right" side of the street.
Comment: As a UK citizen living in Germany, driving on the "wrong" side of the road really isn't that big a deal.  More to the point, the OP needs to be aware that most UK (and German) cars are manuals (stick-shift); automatics are not unknown, but they are definitely less common than in the US.
Comment: The European Union contains "27/28 different countries," but Europe includes several more, including Norway, Serbia, Ukraine, Andorra, and parts of Turkey and Russia.
Comment: We do have good friends in the UK so I will ask them about the possibilities.
Comment: Note that France, just like the UK, has no concept of registered address (and no mandatory ID law). That's not to say that things like registering a car do not require you to be a resident or produce some form of ID, cf. https://www.gov.uk/vehicle-registration/new-registrations or https://www.service-public.fr/particuliers/vosdroits/F10293.


How can I dispose of cement pavers in Delaware County, Pennsylvania?

Question: I have roughly 110 (8 by 16) cement pavers that I need to dispose of in Delaware County, PA. How can they be disposed of?
Comment: I also live in Delaware County PA.  I would love to have them
Comment: As others have said, definitely give them away! Find @Mark S, (the chat room can help), and give them to him! Donating to a charity, like Ecnerwal suggested, is awesome! Many will come get them. We have a church email chain where we offer things to each other. Lots of people are doing projects, or know people who are, and can't afford things like these. You're a kind person. Don't underestimate the power of your gift. "One man's trash is another man's treasure!"
Comment: I'd take em, neighbor.. :p
Answer:
A: Craigslist, curb alert, free pavers.
B: By the side of the road, with a sign "free pavers".
To really make them move,  C: by the side of the road, a sign,
"pavers, $2 each" (don't expect the $2, but you could get lucky, and
the folks that think they are stealing them might be more eager than
the ones that are taking them for free.)
Contact your local community garden or Habitat for Humanity and donate them.
Comment: *Love* option three!
Answer: Sell them on Craig's list or Ebay!!  Those things are valuable.  Do you have any neighbors with drainage issues, land slides in their back yards?  Find a RESTORE type outfit nearby.  They'll come and do all the work (as they should)and take them away.  Put an ad up in your neighborhood hardware/lumber yard.  Don't forget to go TALK to the manager(s) of the store, they'll know someone who would love to get paver CMU's cheaply.
I am sure that there is a concrete/asphalt recycling place nearby.  You just have to load, haul, unload all of this GOLD with no help.
Another option is to use them as a garden wall, similar to ledger stone.  15 to 18 inches high, slightly battered, drainage and soil behind, a thick concrete cap and you've increased the value of your home more than a remodeled kitchen or an extra bathroom.  This enables a new dimension to your yard versus 2 dimensional flat.
Look up debris hauling, recycling, concrete removal...if you want to get rid of those pavers you shouldn't have to lift a finger other than making a few calls.
Answer: Do you have a local "freecycle" e-mail group? Always works for me, where I live. Just join (free), post your offer, sit back and wait for e-mails from people who want them.