Can the Raspberry Pi Zero be powered by a real usb port?

Question: I have a powered USB hub. Can I use it to power the Raspberry Pi Zero using up just one Micro USB port?
Or does the power have to come from one particular port that is only used to provide power?
Edit (2021-10): What i'm trying to ask is, can i use the micro USB port for both power and data simultaneously? This is still unclear.
Answer: The Pi zero has only one USB port.  It has two microUSB sockets.
The socket closer to the edge of the long side of the board is the power socket.  The socket closer to the middle of the long side of the board is a USB port.
You seem to be able to back power via the USB port.  You will have to judge the reliability of back powering the Pi zero by personal experience.
Comment: Raspberry Pi newbie here - does supplying power via the Pi zero's USB port instead of the intended power socket have any chance of damaging it?
Comment: I don't know.  My guess would be no as it is the sort of thing everyone (like me) will do by mistake and that would be an awful lot of returned Pis.
Answer: Assuming the micro-USB socket "power" of the Pi Zero is used to power the Pi, I take it that the question refers to the USB ports or sockets of the used hub as a source. Further assuming that we're talking about a self-powered hub here, as a bus-powered hub cannot supply more than 500 mA in total to its downstream ports. So according to USB spec a USB port should provide 100 mA per default and 500 mA after annoucement of the device to the hub/host (USB 1.x and 2.0), and 900 mA (USB 3.x).
In real life most hubs out there don't care much about those limits. Typically their ports supply more than 500 mA. We can now call that non-compliant devices or embrace the fact to power the Pi.
I've used both a Pi B+ and a Pi 2 with a USB 2.0 hub and a simple wiring: USB downstream port to the Pi's micro-USB power socket. Works just fine. Given the available technical data on the Pi Zero, it's safe to assume it would not consume more power than a Pi 2.
Bottom line: assuming a "reasonably non-compliant" USB hub it will probably just work.
Comment: @neuhaus - no.  the power port is for power only, the data lines in the micro usb connector are not connected to anything on the board.
Comment: What I meant is: Can I use the power port for **both** powering the Pi Zero and doing data transfer?
Comment: Yes, I think you are right, I misunderstood what the questioner wanted to know.


What hood fits a Canon 70-300mm telephoto USM IS lens?

Question: I have a Canon 70-300mm lens on my 1200D. I am at college and have been told we need to get a hood for my camera. I do wildlife photography, and I have no idea what type of hood would be best. Can someone advise please?
Answer: If your lens is the Canon EF 70-300mm f/4-5.6 IS USM, the official lens hood is specified as ET-65B on the Canon website.
If you search "ET-65B hood" on Google or eBay et al, you'll get lots of options to purchase an official Canon one or a third-party imitation.
Answer: If you are on a really tight budget, you can download and print a pattern to make a hood for your lens out of stiff paper or cardboard.
This site has patterns for many popular lenses.
Answer: Just check Canon's website for the appropriate hood for that lens.  Then you can check any camera store or ebay for the genuine article or a cheaper third party knock off.


When and why was the notation changed from descriptive to algebraic?

Question: When I was young I used to play chess with the the old form of notation KB<number> (King Bishop square number), even books used to have the same notation, then later found that everyone was using algebraic, is descriptive notation dead? Why?
Comment: Related (on BCG): [Does anyone use the P-K4 type of chess notation anymore?](http://boardgames.stackexchange.com/q/3977/1444)
Answer: Though the previous answers have made some solid points, I think they have not yet given the main reason why algebraic notation has generally come to be preferred over descriptive notation: it is more absolute, less relative, than descriptive notation. What I mean is just this: in algebraic notation each square on the chessboard receives only one name, while in descriptive notation each square receives a different name depending on whether a move by white is being notated or a move by black. This alone makes algebraic notation more transparent, because things aren't relative to which side is on the move.
Consider, say, the g4 square (in algebraic notation). When white moves a piece there, descriptive notation says it is headed to KN4. But if black is moving a piece there, it is headed to KN5. There is just no need to have two names for this square, and it serves only to sow possible confusion in a way that algebraic notation does not.
Answer: The two forms of notation you are referring to are called Descriptive Notation and Algebraic Notation respectively. Descriptive notation was the most used form from recent antiquity up until about 1970 in English speaking countries. Algebraic notation has been around since the 19th century, but didn't rise to its current prominence until the 20th century. These days, descriptive notation is considered obsolete, though it is still permitted in tournament play in the FIDE. There are a minority of players that exercise this choice, though. Primarily, descriptive notation is learned and used for reading older chess books which were authored that way.
There are also some other interesting notations in use around the world. Hope that helps clear things up.
Answer: To answer your question if descriptive notation is dead, I would say YES.  Even though it maybe more descriptive, it can be more confusing for newer players and the algebraic notation is so much more intuitive and simpler to understand.  I have read books with the descriptive notation and sometimes I scratch my head.
Answer: I used to read chess books in the 1960's. Then DN was the only commonly understood system.  I didn't go looking for chess books again until this year 2018.  Now everything is in AN.  I have a book published in the 1970's bought recently second hand it actually uses both.  I recently found some chess magazines in Spanish from the 1990's they all use AN.
For me DN is much more intuitive...not really intuitive ...just common sense.  There are two people sitting at the board, so there really ARE two perspectives.
WW


How does a non-segwit full node ensure validation of the blockchain?

Question: Let's say a block been created with most tx are segwit , now the block is more then 1MB and will be near to 4MB, I understand that a non-SegWit node ( let's say bitcoin-core 0.15 ) cannot get a block with that size, so How does it see this block as valid ? and if it's because the transactions omit the part of segwit in the inputs then how can the legacy nodes validate the block ?
Answer: Non-segwit nodes validate blocks in the exact same way they did before. The still check the Proof of Work, they still check the inputs and outputs of a transaction, they still verify scripts, etc. Everything is validated the same way as was validated before segwit.
The only difference is that with segwit inputs, the non-segwit node does not validate the signature because it does not have access to that data nor does it know how to interpret it. The scriptSig and scriptPubKeys for segwit inputs are still validated as normal scripts and still validate to true (they were designed to always validate to true).
Segwit does not redefine anything that was already in Bitcoin. Instead it defined a new  standard output script, with that output script already being valid without segwit. So blocks and transactions that contain spends of such outputs will always see those as valid, even if the new data required for such outputs (i.e. the signatures) is invalid.
Comment: No, non-segwit nodes do participate in the validation of a segwit transaction, they just are not able to fully validate it.
Comment: So a non-segwit nodes don't participate in the tx validation of a segwit tx ?


Ubuntu in Windows 8

Question: Do I need to install a specific version of Ubuntu to run it alongside my Windows 8? I've downloaded the typical version.
Answer: Install Ubuntu 12.10. Since Ubuntu 12.10, there's support for Secure Boot as the ISO is firmed and you'll be allowed to boot from it by default. The installer also supports UEFI, as far as I know.
Of course you can also install Ubuntu 12.04.2, but you'll have to disable Secure Boot from your BIOS configuration (if you're able to) and perhaps installing it will be a bit trickier as you may have to deal with UEFI partitions.
Note that those Secure Boot/UEFI things are only important if your machine came with Windows 8 by default; if you upgraded Windows 7 to Windows 8 you shouldn't have any problem related to that. Then I'd recommend 12.04 over 12.10 because it has Long Time Support and (for me) it's more stable and fast - but you don't get some of the amazing 12.10 features like previews in the Dash or the online accounts integration.
See also

See this question for the differences between Quantal (12.10) and Precise (12.04).
Answer: It all depends on what you want. I would recommend the 12.04 seeing as it has Long Term Support. 12.10 has a few extra bells and whistles. Also, if you're using a 64-bit machine be sure to get the 64-bit version. It will allow you to use your RAM more effectively.
Also be careful during the install as it is possible to overwrite your Windows 8 install. Just read all of the options and select wisely.
Answer: The best thing you can use is the wubi installer
Assuming you have the iso image, download from ubuntu website wubi installer for the corresponding distribution.
Next, since it is windows 8, one of the best things you could do is right click -> Mount Iso the particular iso file (iso image), as if it were some CD Drive.
Next run the wubi.exe and follow the steps, specify the user name and password, and give  the partition, and its size, and you are done.

Ubuntu in Windows 8


Some queries not logging using RDS's SQL Server with C2 Auditing enabled

Question: Similar to a past issue I had with audited queries not showing when using Extended Events, I'm having an issue with queries not logging when using C2 Auditing on an RDS SQL Server instance.  (I would prefer to use Extended Events for my auditing, but this apparently cannot be enabled on RDS SQL Server instances currently.)
In this case, I enabled C2 Auditing via an RDS Parameter Group.  I verified that C2 auditing is enabled by going to my server instance's Properties (via SSMS).  I created a database, mytestdb, and then created a table within it, mytesttable.  I ran a few queries (e.g., INSERT INTO mytesttable ...; SELECT * FROM mytesttable).
I then determined the path to my trace log file (SELECT id, path, is_default FROM sys.traces;) and then retrieved the SELECT queries that have been run: SELECT starttime, textdata FROM fn_trace_gettable('D:\RDSDBDATA\Log\log_2.trc', DEFAULT) WHERE textdata LIKE N'select%' ORDER BY starttime;.
The result is my queries on mytesttable did not show up. My queries on the trace table do show up though, so some queries are being logged.
I also tried a query on one of the master database tables, but that didn't show up as well.  I also tried disconnecting from the database server and reconnecting (in SSMS), hoping that ending the session might clear some buffering going on, but that didn't help with getting the queries to show in the audit results.
I connected to the RDS instance with my "Admin" user account (created during RDS setup) and there is no associated Active Directory. This is an "SQL Server Standard Edition" RDS instance.
Any ideas on why these queries would not be logged?  Any other debugging ideas? Thanks!
Answer: You have to query file located on D:\RDSDBDATA\DATA\audittraceXXX.trc, It is the first query you ran to get trace path


translation of vayikra

Question: I believe the vav of vayikra is a vav hamehapeich, meaning it switches yikra from asid to avar. To that extent I heard that the correct translation would be He called, rather than "and He called" (unlike [chabad translation])1.
If so, why does targum translate ukra? which would indicate vav hamoseif?
Comment: Related: https://judaism.stackexchange.com/q/2720/8775.
Answer: The וַ (plus the dagesh in the yodh) is called "waw consecutive".  At one time it was thought that this converted the verb from future to past, and the waw was called "waw conversive".  We now know that the yiqtol form of a verb does not always indicate future and the qatal form does not always indicate past.
In prose, the wayyiqtol form is usually used to continue a narrative that was begun with a regular qatal form.  In this case, the qatal and the following wayyiqtol generally do refer to the past.  (Probably, the wayyiqtol form is a fossilized form that was originally a preterite form, as in Akkadian.  The difference between the preterite and imperfect yiqtol was lost when short final vowels were lost in Hebrew.)
Since waw consecutive is not the same as waw conjunctive, it does not necessarily mean "and".  (None of this was known to author of the Targum.)  However, it's not possible to use both a waw conjunctive and a waw consecutive on one word, so whether the writer intends "and" or not, the form will still be wayyiqtol. In a narrative, a conjunctive often makes sense ("this happened and then this happened and then...) so translators have to make choices. Most (but not all) modern translators avoid using "and" so often that it sounds annoyingly repetitive. Robert Alter, however, believes that the writers intentionally used the repetition of waw to put a rhythm into the text, and therefore he does translate "... and ... and ... and ...".  In the particular case of Wayyiqra, however, there may be a literary issue to be considered.  Since, as I mentioned, the wayyiqtol form is the continuation of a narrative, it may be that it was intentionally used at the start of the book to emphasize its close connection to what came before (i.e., Exodus). Thus, some translators might use "And He called" to reflect this possible original intent.
Comment: Very good answer! It would be even better if you included sources for "We now know...", "it's not possible to use both...", and "the particular case of Wayyiqra...". The one indicating a shift in understanding of this pattern, which was borne by the _m'targem_ among others is crucial to the question at hand.

translation of vayikra


combining "no results" second query with first query in MySQL

Question: This is probably very easy, but I'm wanting to know the "best" or "standard" way of writing this query.
I have two tables. One is a work schedule with a task name and start timestamp and end timestamp. This table is populated by a schedule manager ahead of time.
UserId |   task |        startTime |          endTime
   joe | dishes | 2010-05-15 10:00 | 2010-05-15 14:00
   joe | papers | 2010-05-15 14:00 | 2010-05-15 15:00
   joe |  trash | 2010-05-16 09:00 | 2010-05-16 10:00
   joe |cooking | 2010-05-16 11:30 | 2010-05-16 13:30

The second table is a work log with the number of minutes worked per day and a datestamp. This table is populated by the employee.
UserId |       date | timeLogged
   joe | 2010-05-15 |        300
   joe | 2010-05-16 |        180

The way my app works currently is it queries the workLog table first to see if the user has already logged hours for a given date range. If the query returns 0 rows, a second courtesy query is done against the schedule table, so that the form is pre-filled, making it easier for the user to make adjustments, etc.
What I would like is a query that does both in one go. The problem is that it should only do the "second" query if the "first" is null, so doing any joins or if nulls seems incorrect to me, since it would combine results of both queries when the workLog table needs to prevail. For instance, if the user was sick on Tuesday and Wednesday, but logged hours for Monday and Thursday, I don't want results that use the logged hours from Monday and Thursday and the scheduled hours from Tuesday and Wednesday. But if he was sick every day that week, it's okay to populate the form with the schedule table data, as the user would not (or at least should not) be submitting a form.
I can think of one or two approaches, mainly using a third aggregate query and a UNION statement, but that seems sloppy.
Update
Here are the queries I'm wanting to combine:
SELECT date, timeLogged
FROM workLog
WHERE userID = '$userid'
AND date BETWEEN $startDate AND $endDate

If that returns no results:
SELECT DATE(startTime) AS date,
SUM(TIME_TO_SEC(TIMEDIFF(startTime,endTime)))/60 AS timeLogged
FROM schedule
WHERE userID = '$userid'
AND date BETWEEN $startDate AND $endDate
GROUP BY DATE(startTime)

So any functions that follow after both queries don't need to know which table the results came from.
Answer: Those queries return different stuff. You can only combine them into one sentence if you join them by user and date and then getting duplicate rows for worklog:
SELECT ws.UserId, ws.task, ws.startTime, ws.endTime, wl.timeLogged
FROM workSchedule ws
LEFT JOIN workLog wl ON ws.UserId=wl.UserId
    AND DATE(ws.startTime)=wl.date
WHERE UserId='joe'

would return:
UserId |   task |        startTime |          endTime | timeLogged
   joe | dishes | 2010-05-15 10:00 | 2010-05-15 14:00 |        300
   joe | papers | 2010-05-15 14:00 | 2010-05-15 15:00 |        300
   joe |  trash | 2010-05-16 09:00 | 2010-05-16 10:00 |        180
   joe |cooking | 2010-05-16 11:30 | 2010-05-16 13:30 |        180
   joe | dishes | 2010-05-17 09:00 | 2010-05-17 13:30 |       NULL
   joe | papers | 2010-05-17 13:30 | 2010-05-17 15:00 |       NULL

... and only considering the startTime. (Can you ahve a range like 2010-05-17 23:30 — 2010-05-18 00:30?)
Honestly, I don't think it makes sense. I'd keep them separate.
Comment: Currently,the second query creates columns that match the worklog table. I'll add examples so it makes more sense.
Comment: Also, the join in your code would cause the problem I mentioned before, I think, where it would fill in dates that are supposed to be blank.


Target Groups based Content

Question: Its mentioned in one of the Post that Target groups are used while sending out the mailings.
Unable to personalize content using tracking key in Target Group?
Is it possible to use Target groups for showing content on Website pages too?
Comment: It depends. Are you looking to create a web version of an e-mail? Or do you just want to show/hide some content on a Page in general? You've tagged this question with SmartTarget - is your question actually related to that?
Comment: If I want to show/hide some content on a Page in general.
Answer: Absolutely. That is the original use case for Target Groups.
To read more about this, have a look at the documentation for "Target Groups", as well as its parent topic "Profiling and personalization" (login required for both links)
Comment: Ok I have already read the docs but got confused with the post which I mentioned above. So this means that if I need to target my content based on some User Group I can go with Target groups instead going with Smart Target. And do I need some coding for implementing Target Groups based Content delivery. Or just allowing Targetgroups on Component Presentation will work out?
Comment: You'll need to provide the data that P&P will use to determine whether to show a given Component Presentation. That part _may_ require coding, depending on your use case and where the data comes from.
Comment: Nuno - you mentioned about P&P API.From where I can get this API as I am not able to find it out. Can you tell me the name of this API
Comment: SmartTarget is certainly also an option (particularly if you want your business users to decide what to show to who, as opposed to writing code to do that). But SmartTarget doesn't involve Target Groups.
Comment: P&P is "Profiling and Personalization". The API is all under the com.tridion.personalization package and is a standard part of Tridion Content Delivery
Answer: Just to add and summarize the post:-
Minimal feature of customizing which can be achieved from Profiling and Personalization  provided within SDL Tridion Tool itself and no extra licencing fee required.
I tried implementation of personalization through Target Groups using Custom Characteristics.
Create Target Group.
Add Target group with a component presentation on the page.
Note: Condition will only come after page is published and will not be visible at the time page is previewed.
Using Target group will lay Tridion conditions tags on the page which is published.
These conditions will be use to Show/Hide component presentation added on the page.
condition will be used by java code through Tridion CD APIs which will use input parameter.
Sample  page will be like :-<code><tridion:Conditions negate="false" operator="AND">
<tridion:Conditions negate="false" operator="OR">
<tridion:Conditions negate="false" operator="AND">
<tridion:Condition type="CustomerCharacteristic" operator="=" negate="false" name="customerType" value="1"/>
<tridion:Condition type="CustomerCharacteristic" operator="=" negate="false" name="customerType" value="0"/>
</tridion:Conditions>
</tridion:Conditions>
</tridion:Conditions>
</code>
Answer: Here is a good link explaining about PnP
http://blog.building-blocks.com/technical-tips/how-to-setup-sdl-tridion-profiling-personalisation
Comment: Hi Aman, Can you please comment if above BB link you mentioned for PnP can be used for below scenario or not: 1)Pages have CP Embedded in page, sdl web8 cms 2)on Presentation Server we are using DXA 1.6 to render web pages

Target Groups based Content


Where in the world can you tour a live nuclear reactor?

Question: Are there nuclear plants that allow you to tour the facility and learn more about nuclear power while the plant is running?
Comment: I don't have enough rep to answer, but you can tour the Advanced Test Reactor, operatored by INL at Idaho Falls, Idaho in the U.S.A.

https://inlportal.inl.gov/portal/server.pt/community/community_outreach/265/inl_tours/1447

When I went we could even see spent fuel rods in the holding tanks that were still glowing with Cherenkov radiation!
Comment: If you want to learn about physics in a reactor it might be even more interesting to visit a scientific reactor (neutron source). These reactors are a lot smaller, but work similar. They do not generate electricity, but neutrons for scientific experiments. You can visit one in Germany (Munich) http://www.frm2.tum.de/en/aktuelles/info-documents/contact/visitorsinformation/index.html
Comment: Related: http://travel.stackexchange.com/questions/11694/are-there-any-tours-or-opportunities-available-to-the-public-where-one-can-see-c
Comment: This really should be a community wiki.
Comment: I also cannot comment, but we recently visited a nuclear reactor being disassembled in [Vandellos I](https://es.wikipedia.org/wiki/Central_nuclear_de_Vandell%C3%B3s) (not to be confused with Vandellos II). While not live, it's still active (takes many years to put it down) and it was a nice visit.
Comment: Not a live reactor, but the culham centre for fusion energy in the UK runs tours of it's fusion reactor research facility. It's quite an interesting tour.
http://www.ccfe.ac.uk/Visits.aspx
Comment: A little known fact is almost all Nuclear Power Plants (in the 'free world' anyway) will allow tours.. generally they want to promote safety and invite the public in order to do so.
Answer: You can do that in Switzerland:

Beznau. This is the oldest still running nuclear reactor in the world. According to their brochure you can contact the visitor center for guided tours.
Mühleberg. They have regular guided tours in French or German.
Gösgen. They have daily tours as well as a visitor centre.
Leibstadt. They also have tours and a visitor centre.

Something else along the same lines is the ZWILAG, the temporary storage for radioactive waste. I visited that one and it was quite interesting.
Answer: In the UK. EDF Energy is opening new visitor centres at their nuclear power plants across the country, specifically:

Hunterston B in West Kilbride and Torness in Dunbar, Scotland,
  Sizewell B in Suffolk, Hinkley Point B in Bridgwater, Dungeness B in
  Kent and Heysham in Morecambe.
The visitor centres are where you can find out more about our nuclear
  power station operations, how we generate electricity and more about
  EDF Energy.

It also says that pre arranged site tours are available.

The visitor centres are open for you to visit between 09.00 and 16.00
  Monday to Friday. All station tours require advanced booking.  Tours
  will be available at the weekend, subject to availability and demand.
Comment: What do you expect to see anyway, glowing rods?  This isn't the simpsons, the interesting mechanisms arn't visible
Comment: The tours should be good if you can get onto one. I went on a tour of Hinkley Point B about 20 years ago when my dad worked there.  I don't think we were given any special access or anything but we got to see a lot of the site including the working systems, and I found it fascinating as a teenage geek.  I remember we stood directly on top of the reactor core, where there was a little sign explaining that the radiation dose you receive up there is a fraction of what you would get outside Bridgewater town hall (which is made of [granite](http://en.wikipedia.org/wiki/Granite#Natural_radiation)).
Comment: The tours of UK Magnox stations used to be really good, but since 2001 they wont let you into anything interesting anymore, and in any case I don't think there are any of those stations running anymore.
Comment: When I went to the  visitor center at sellafield, it was aimed at children and you could not see any of the side, a total waist of time.
Comment: @IanRingrose Visitors centres and site tours are very different.
Comment: @IanRingrose I quite enjoyed my visit to the Sellafield visitor centre but I agree that it was aimed at children and I learned nothing.  Worth visiting if you are in the area but not worth travelling from afar.  I am not sure whether it is operating any more.  I drove past the plant recently and I saw no signs for it.
Answer: In addition to commercial nuclear power plants, the world has many small university reactors used for research and education. For example, in the Los Angeles area a quick google search showed that UC Irvine has a reactor that allows group tours by appointment.
Comment: Another such one is at Faculty of Nuclear Science in Prague, Czech Republic. However, I wouldn't say it "gives tours", it does, but moreorless only for local high schools.
Comment: The University of Texas at Austin also has a teaching reactor with opportunities for group tours: http://nuclear.engr.utexas.edu/index.php/netl/netl-access-a-procedures
Answer: In France, you can visit EDF's energy plants. You just need a valid ID (passport, ID card, etc.)
The tours are great! You can talk with technicians, engineers, plays with interactive setups to understand the processes, etc.
Comment: http://www.businessweek.com/news/2011-09-15/france-opens-doors-to-nuclear-sites-to-woo-public-post-fukushima.html
I remembered seeing press about touring French nuclear plants
Comment: Do you need to be French?  EU?  Anyone?
Comment: No, you can have any nationality. But you need a valid ID and to book the visit in advance because there is a light investigation on your person.
Answer: You can also visit Kozloduy NPP in Bulgaria.

When Kozloduy NPP can be visited?
The Information Centre is open for visitors every workday from 8 am to
  4 pm. Visits to plant facilities are organised in workdays on a
  year-round basis with closing time at 3.30 pm. Visits to the Main
  Control Rooms and Turbine Halls of Units 5 and 6 are not organised
  during annual outages (advanced information is available at Tel.: +359
  973 7 21 00 and +359 973 7 27 68).
Open Door Day
Anyone who is interested in visiting Kozloduy NPP may use the
  opportunity on Open Door Days organised biannually. The date of the
  Open Door Day (usually Saturday) is announced in advance in the mass
  media and on the website of the plant in Section Current Information,
  News.
Answer: In Australia you can tour the Lucas Heights nuclear reactor, the only one in the nation.  Note that while it is indeed a nuclear reactor it is not a nuclear power plant, as it is dedicated to producing radioisotopes as a research facility.
Answer: Poland doesn't have any nuclear power plants (yet), but it has a research reactor Maria in Świerk, near Warsaw, which provides tours for organized groups, targeted mostly for students.
Key information from the web site (Polish only):

all participants must be over 15
you should announce the group at least 2 weeks in advance
foreign citizens need to fill special application forms, which needs to be approved by the Director of the Institute for Atomic Energy POLATOM
entry costs 10 PLN for each person (about 3.3$)
Answer: Just east of Toronto is the Darlington Nuclear Generating Station. The operators claim:

Located in the Municipality of Clarington in Durham Region, 70 km east of Toronto, Darlington Nuclear provides about 20 per cent of Ontario's electricity needs, enough to serve a city of two million people.

That site offers a link to a video tour of the site. Reporters and teachers have clearly been on a physical tour, since pictures and reports of the inside are easy to find, but I can't find a page online with the details. You could call or email the information centre to ask:
<code>Information Centre
Darlington Nuclear Ontario Power Generation
Box 4000, Bowmanville, Ontario L1C 3Z8

Telephone: (905) 623-7122 Toll Free: (800) 461-0034

Email: email@example.com
</code>
Time sensitive update: I just received an email that reads in part:

Darlington Refurbishment - Doors Open
We would like to invite you and your family and friends to learn more about the Darlington Refurbishment Project, take a behind-the-scene tour of the reactor mock-up and check out the new Darlington Public Visitor Centre. Project staff will be on hand to answer any questions you may have. Pre-registration is not required.
The key to project success in Refurbishment is the front-end planning. Replacing the core reactor components inside each Darlington reactor is a critical part of the refurbishment exercise. High-quality training, with the right tools, in the right environment, will help maximize efficiency and minimize costs. This is your chance to get a first-hand look at this upfront work.
Please join us at the Darlington Energy Complex: 1855 Energy Drive, Courtice, ON
Dates:

Tuesday Nov. 4, between 5:30 - 8 p.m. or
Wednesday, Nov. 5, between 5:30 - 8 p.m. or
Saturday, Nov. 8, between 10 a.m. - 2 p.m.

Refurbishment is a significant investment and a major construction project for our company one which involves a great deal of, planning, hard work and dedication. It is a tremendous opportunity for us all to be a part of this vitally important project. A refurbished Darlington Nuclear Station will provide 30 more years of safe, clean, reliable electricity.
Answer: There are two in Texas that I know of.
Quoting http://www.texasoutside.com/glenrose/sites.htm, "About a mile inside the front gate of the Comanche Peak Nuclear Power Plant is the Visitors Center, open from 9 am to 4 pm Monday through Saturday. Group tours can be arranged by reservation only. The Visitors Center offers several interactive displays and a 10-minute video explaining how nuclear power is made. The tour includes a view of a control room simulator in which reactor operators are trained, as well as a driving tour for an up-close view of Comanche Peak Power Plant. Travel north on FM 56, to the Comanche Peak Nuclear Power Plant — (254) 897-5554."
There's also one at the University of Texas at Austin / Pickle Research Campus:
https://nuclear.engr.utexas.edu/netl/netl-access-a-procedures


Sharepoint tagging like serverfault?

Question: Does a Sharepoint plug-in / add-in exist that will support serverfault-style tagging for documents?
Key features:

Users can add their own tags just by typing them
Autocompletion whilst typing shows the user what tags already exist
Answer: One thing to take into consideration is how these things will upgrade to the next version of SharePoint. Is the data stored in a list or a custom database?
The Office server team bought a company a couple years ago that specialized in metadata and taxonomy management that was to be integrated into future products. Hopefully we'll know more at the SharePoint Conference coming in November.
In the meantime, you might want to check out the Podcasting Kit for SharePoint. They have some tagging features that they built out and there is a good chance that team will have some migration to SharePoint 2010. Would love to see someone on the team confirm or deny what their plans around 2010 is.
Answer: Yes.  A search on Codeplex.com for "tag cloud sharepoint" reveals a variety of choices.  I have never used any but the site has rankings, reviews, and comments that can help you narrow down your options.
Comment: http://nuage.codeplex.com/
Answer: You can download the SharePoint Community Kit from CodePlex.  That improves the OOB tagging functionality (which is very basic).
There are some non MS companies that provide extensions for SharePoint.  I do not have a lot of experiance with these so I cannot say much.  One example would be Telligent.

Sharepoint tagging like serverfault?


Why does our body regulate metabolic processes using the thyroid hormone?

Question: People with hypothyroidism do fine when taking medication containing their daily dose of thyroid hormone. This means that the signaling function of the thyroid hormones is, in principle, unnecessary. If a constant signal would do, then there is no need for that signal in the first place, as you could just by default switch on whatever process is now switched on by the thyroid hormone. So, what's the whole point of regulating metabolism via the thyroid hormone, especially considering that it predisposes us to thyroid disease?
Comment: @Count I disagree slightly with "...the signaling function of the thyroid hormones is, in principle, unnecessary..." Thyroid hormone (T4 - aka "Thyroxine") has a half-life of 4-5 DAYS. It is essentially a constant level in the circulating plasma that is important - this is why patients with hypothyroidism that take exogenous T4 do fine. It doesn't have anything to do with T4 not being important biologically. If you take exogenous thyroid hormone away from someone with hypothyroidism or who has had their thyroid removed surgically, once their plasma T4/T3 is gone they do horribly.
Comment: Because it evolved that way, and there was not a significant evolutionary pressure to change it?  And possibly not a mechanism to allow the change, once humans' distant ancestor had evolved a proto-thyroid.
Answer: The answer is in special situations, where a trade-off has to be done between thermogenesis and energy saving. This applies to hibernation of animals as well as to critical illness in humans.
This kind of adaptation is referred to as TACITUS syndrome (thyroid allostasis in critical illness, tumours, uraemia and starvation), NTIS (non-thyroidal illness syndrome) or ESS (euthyroid sick syndrome). In this situation, total and free T3 are downregulated, and, in special cases, TSH and T4, too. See an open review article by Wajner and Maja, which is available from http://dx.doi.org/10.3389/fendo.2012.00008 , for details.


What are the advantages of getting an expensive server?

Question: Server CPUs cost multiple times more than Desktop CPUs; so do Motherboards and PSUs.
What are the advantages of getting a server system rather than a desktop system?
Stability can be one, but what are others?
Comment: Please read our FAQ, this isn't a forum, we're a Q&A site, we don't do discussions.
Answer: Usually there are extra features for either remote administration (such as "Integrated Lights-Out Management") or reliability (dual power supplies, use of higher quality components, better heat management). If you're not putting the machine in a datacentre and it doesn't cost you money if it goes down, then it's seldom worth the cost.
Answer: The choices for fitting desktop mainboards into 1U cases are limited, and usually leave you with a system that cannot take extension cards (especially systems that can take 2 or 3 PCI cards in a 1U case use very specialized form factor mainboards (look at the Supermicro X7DCU or X8DTU for an example...).
A server mainboard usually comes with at least 2 network ports, and uses network chipsets with good performance and low host cpu usage (Intel 8257x are very common on server boards, whereas Realtek is typical for desktop boards).
The power supplies usually come with redundant options and are designed suitable for 24/7 operations (and a server mfg likely cannot afford to build power supplies that can ever short out the mains!, which occasionally happens with Desktop PSUs).
HCLs for server operating systems often only list server grade hardware.
You want ECC memory capability, which is usually only found on server systems.
Server designs tend to avoid small and unreliable fans (passive heatsinks and either very big or very fast fans (one common 40mm counterrotating type is quite capable of blowing papers across the shop, these make far too much of a din though to ever find use in desktops) that cater to ALL these heatsinks in a redundant manner are common).
Managed harddrive backplanes (with hotswap, status LEDs....) also tend to be rare in desktops.
With the CPUs it is probably less a matter of reliability than of workload... many mid end and high end servers are used for virtualization, where you want systems with many cores (multi socket!) and a lot of memory.
Server grade harddrives are optimized for 24/7 operations, withstanding typical vibration stress in a mechanically close array of disks, and error handling that works together well with RAID controllers. They also come in some very low latency variants.


Free service for scheduled cross-posting to major social networks

Question: I'm looking for a free and simple web-service for posting to multiple social networks (at least it should support Facebook, Google+ and Twitter) with ability to schedule messages for a specific time.
Answer: I think Buffer would best solve your purpose.
Buffer is an auto-posting service that's widely used to schedule posts to Twitter, Facebook, LinkedIn, and even App.net. In addition to these services, Buffer has recently added support for Google+ Pages. This support uses Google's official API, so Buffer should work very well for people who need to schedule updates to Google+ Pages.

Just create a Buffer account — or log into one, if you already have one — and connect your Google+ Page to Buffer as you'd connect any other type of social media account. You'll then be able to schedule posts from the Buffer website, with the Buffer browser extension, or anywhere else you can schedule Buffer posts from. Google+ support is available to everyone, even users of Buffer's free accounts.
My experience with the app: None. My friend recommended it a while ago (and he's quite happy with it. He schedules statuses at the time when the number of his online friends is at it's peak and manages to get infinite likes). I found the description to be pretty compelling and it serves the OP's purpose.
Source: MakeUseOf
Answer: My recommendation would be Hootsuite. Hootsuite is social media management dashboard where you can  manage multiple social networks directly from Hootsuite (Facebook, Twitter, LinkedIn, Wordpress, Google+, Foursqare) or by adding available apps (Flickr, Youtebe, Gmail, Instagram, Reddit, Pinterest and others). Hootsuite permits scheduling tweets and messages, it analyzes traffic and offer other options. Basic account is free but paid options are available too

I personally never used it for Google + but I do manage Facebook, Twitter Flickr, Reddit and LinkedIn accounts through it. The thing I like about this web app is that you can add different streams to every social media, for example in Facebook I have contemporaneously open 4 streams:

My Wall posts,
News feeds - most recents,
Status updates of my friends
Events

Scheduling of messages or  tweets is quite easy, you can chose which social media to post too and  then and arrange scheduling

Among other features Hootsuite offers mobile apps for Android, Ipod and Iphone and extensions for Chrome and Firefox, RSS feed, Analytics. Only thing I miss is some kind of app connecting it to Stack Exchange.
Answer: I haven't used it for almost a year, so I'm not sure how much, if at all, it has changed. However, when I used it, Buffer was a great service. They do have a free plan, which, unless you're running an organisation or business of some sort, should probably be enough. And if you really need to have some major s**t going down, then see here.
But, anyway...

The Good
Website & Account

Clean UI (not sure about the UX)
Pretty awesome support (at least they did back when I used them; also, they have email AND chat!!!)
They don't muck around when you want to delete your account
2-Factor Authentication (text or mobile app)
Ability to transfer account ownership to someone else
Robust time zone setting (per connected profile or globally!)

Browser Addons

Chrome App
Chrome Extension
Firefox Extension
Safari
Opera

Mobile Apps

iOS
Android

Social Media Integration

Facebook
Twitter
Tumblr
Pinterest (7-day trial, then Paid only)
RSS (Paid only)

Social Media Usage

Tag users on Twitter
Schedule images in posts
Drag-and-drop copy/paste across social media profiles
Drag-and-drop to change schedule order of posts
Shortened buff.ly URLs
Optional custom domain for shortened URLs
Schedule by email
Adjust Facebook visibility settings just for the Buffer Facebook app
Exact date-and-time scheduling
Ability to pause and resume buffer schedules
25-posts-per-day limit for Facebook

Analytics

Notification of top tweets
Optional weekly report
Click tracking for Facebook pages
Campaign link tracking
Reach potential

If you have 100 followers on Twitter, when you tweet out the update, your reach potential is 100. Now if someone retweeted your update, and they have 150 followers on their Twitter account, your potential becomes 250. The same applies to Facebook friends and LinkedIn connections.

The Bad
Social Media Integration

No Google+ support (no API access)
Feeds are Paid-only
No website support for auto-repost (though the browser extension has support for this; you can also manually "re-buffer" it)
As mentioned above, Pinterest is a 7-day free trial for Free users and then you have to upgrade to a Paid account to continue.
No Instagram support (no API access)

Social Media Usage

Requires being an admin to post to Facebook groups
Profile limits

On the Individual Plan you can connect one account from each of these platforms whereas with the Awesome Plan you can add a combination of up to 10 accounts.

Scheduling rate limits (At any given time, Free: 10 posts, Paid: 100 posts)
Scheduling Time limits

With the Individual Plan you can choose days and times but not different times for different days. So, I can have my posts go out at 3 PM and 5 PM, Monday and Wednesday. On the paid plan, you can have 3 go out every Monday, 2 on Tuesday, 6 on Friday, etc. All at whatever times you set.

Tagging is only supported on Twitter

If you post to other networks at the same time it will convert the @ mention on all social profiles (other than Twitter) to a full account name. Unfortunately tagging isn't possible just yet on other social media platforms, but we know that it's something that many folks have asked for, so it's on the short list! It's an improvement we hope to make down the road.

Only 1 image can be attached per post
No video upload
No posting to secret boards on Pinterest
25-posts-per-day limit for Facebook

Analytics

LinkedIn has link-tracking issues

When LinkedIn displays a link, they un-shorten the link before they display it in the link box below the update text. Unfortunately, we are unable to gather analytics for the un-shortened links in the link box. We are, however, are able to gather click counts for clicks on the shortened link in the update text. This can sometimes result in a discrepancy in the analytics data, depending on where the update is receiving clicks.

No link tracking on Facebook profiles

We can no longer show clicks for Facebook profiles. We were getting inaccurate clicks from Facebook because they un-shorten the link before they display it, so people were just clicking the long link instead of the short link, which causes the click not to be counted. So, because the stats were being under-reported, we removed the link reporting for Facebook Profiles. (Because Pages provide analytics, we can provide accurate clicks for Pages, just in case that was a concern.)

No follower-count tracking for Facebook profiles

We are a little bit limited in the statistics we can show by what Facebook makes available to us. We used to be able to get this information, although in April 2015 Facebook changed what was available so that the only follower count we could retrieve would be the number of followers you had that used Buffer (and, more specifically, had connected the Buffer app to Facebook). This didn't seem like particularly useful or insightful information to have and so we made the decision to remove follower counts completely to remove any confusion that might arise. Full follower counts are still available for Facebook Pages and Groups as before.

The Meh
Paid Plans (All Values in USD)

Awesome Plan: $10/mo or $102/y
Small Business Plan: $50/mo or $510/y
Medium Business Plan: $100/mo or $1 020/y
Large Business Plan: $250/mo or $2 550/y

None of these charge any tax.
They also offer a 50% discount for non-profits; in any case, I don't know whether these prices would be cheap, although I suppose this would depend on what you plan to do with it.

Learn More: You can find out more here, which just so happens to be where I got most of this info.


How to post deleted question

Question: I posted this question and soon after deleted it. Now some days later I think it is a good question and want to repost it. When I try to post the system refuses it saying it is a duplicate and showing the link to the deleted question which if followed returns a 404 page. Is it possible to undelete a question? If not is there any other solution than rewriting it?
Answer: It is possible but not for you, it would have to be for a mod to undelete. The best way to do that is to post on meta and ask for our help.
But be aware that this being a hardware question, it might not be so well answered here. If you want to focus on the semantics of the hardware, you might also consider asking on https://electronics.stackexchange.com/ altho it might also be offtopic for them. Just a thought.

How to post deleted question


Late May or early September for a beach holiday in Kusadasi, Turkey?

Question: I want to go for a beach holiday in Kusadasi, Turkey this summer with a family but can't decide -- should we go late May or better early September?
What are pros/cons going late May/early September?
Answer: The answer will depend of course on what you're looking for in a vacation.  But September looks better since the water and air would be warmer and there will be less rain.
Source: Weather averages from Holiday Weather
Answer: The weather is decent in May and September, with September being a bit warmer. May is really off-season in that region. In September the place is less crowded than during July and August, but you may still feel the spurs of the high-season.
To conclude, both are fine. Check the prices and pick the period which suits you best.


Force Linear Phase for a FIR Filter Synthesized Using Berchin's FDLS?

Question: As a follow-on to this post, how would you force linear phase for a FIR filter you synthesized using Berchin's FDLS?
Answer: Remember that, as its name suggests, Berchin's frequency-domain least squares method (FDLS) is really just a least-squares fit of a desired frequency-domain response. Recall that for an arbitrary transfer function of the form:
$$
H(z) = \frac{\sum_{k=0}^{M} b_k z^{-k}}{\sum_{k=1}^{N} a_k z^{-k}}
$$
you can write the system's frequency response by simply letting $z=e^{j\omega}$:
$$
H(\omega) = \frac{\sum_{k=0}^{M} b_k e^{-j\omega k}}{\sum_{k=1}^{N} a_k e^{-j\omega k}}
$$
This sort of system can be implemented as an IIR filter with $b_k$ as the feedforward (numerator) coefficients and $a_k$ as the feedback (denominator) coefficients. The FDLS method simply requires you to define the desired (complex-valued) frequency response at a collection of frequencies $\{\omega_k\}$. Evaluating the above expression for each frequency $\omega_k$ yields a system of linear equations in the $b_k$ and $a_k$ variables. You can then solve this using least-squares methods to yield the best coefficients for the desired frequency response and filter order (in the LS sense, of course).
If you have the requirement for exact linear phase (i.e. better linear phase response than you might get by just applying the method itself and specifying a desired linear phase response), then you could reformulate the above a bit, if you're willing to accept an FIR-only filter structure.

Recall that linear phase in the frequency domain corresponds to symmetry in the filter's time-domain impulse response. For FIR filters, this impulse response is the same as the filter's coefficients $b_k$.
Let $a_k=0\ \forall\ k$ in the above expression, yielding:
$$
H(\omega) = \sum_{k=0}^{M} b_k e^{-j\omega k}
$$
The symmetry constraint corresponds to a loss in the number of degrees of freedom in the linear system; instead of each of the coefficients being independent variables, the linear-phase constraint requires that coefficients that are symmetric about the impulse response's midpoint to be equal.
Rewrite the above equation taking these constraints into account. For example, for a type I FIR filter (odd length, even symmetry), then you would have something like:
$$
H(\omega) = \sum_{k=0}^{\frac{M}{2}-1} b_k e^{-j\omega k} + \sum_{k=\frac{M}{2}+1}^{M} b_{M-k} e^{-j\omega k} + b_{\frac{M}{2}} e^{-j\omega \frac{M}{2}}
$$
where the filter has $M+1$ taps. You would then solve the system for the reduced set of coefficients, then reconstruct the overall filter impulse response using the symmetry constraint:
$$
h[k] =
\begin{cases}
b_k, && 0 \le k \le \frac{M}{2} \\
b_{M-k}, && \frac{M}{2}+1 \le k \le M
\end{cases}
$$
The result is an FIR filter that will have linear phase.
Answer: Jason R's answer is correct, but a little more information is needed in order to know how to apply it specifically to FDLS. That information may be found here:
https://groups.google.com/forum/?hl=en#!original/comp.dsp/qgYsnf5aIXs/NSg6VSXhkqoJ
If you are using my MATLAB code for FDLS, then you will have to modify it as indicated in that link.
Greg Berchin
Comment: this is more of a comment than an answer, should be edited into Jason's answer
Answer: Given an FDLS solution as a transfer function with a closest fit to your desired magnitude response, all possible stable phase responses can be derived by trying all permutations of flipping the zeros of that transfer function inside and outside the unit circle.  This set can be evaluated for the closest fit to your desired phase response, linear or otherwise.  The closest fit in phase for that constellation of poles and zeros may not be an exact fit.
Comment: By flipping, you mean taking the conjugate of the zeros?
Comment: By flipping inside/outside, I meant reflecting a zero to the same angle but reciprocal distance with respect to the unit circle:  z => (1/z)*


How to access to VPS without SSH

Question: The provider de-activate and re-activate my VPS account. Now everything seems to be OK on control panel (SolusVM), but my IP is not responding, and I cannot access to my server via SSH. He says this is a misconfiguration or firewall settings within the VE blocking external access, and a re-install is needed. How can I access to my server to at least take a backup of my data?
Comment: I'm pretty sure the admin of the physical server can login via chroot to your VPS and fix the firewall problem (if it's that). Ask him to do it.
Comment: I have to ask the obvious question: Why don't you already have a backup?
Comment: No excuse for my fault; but I made backup with SolusVM central backup which is now on the same machine.
Answer: If your firewall is not allowing any connections, and you can not get into your server. I'm afraid physical is the only solution.
Ask your provider for a dump of your virtual machine or ask them to shut down your firewall.
Answer: You could ask your provider to boot your VM with a livedisk and set up SSH. This way you can still access your data, make a backup, and even change the configuration if you think you have found the culprit.

How to access to VPS without SSH


How do we track the exact location of the spacecraft which is millions or billions of miles away from us?

Question: How do we track the exact location of the spacecraft which is millions or billions of miles away from us? What things do we study for tracking purpose? How exactly do we predict?
Comment: [This answer](https://space.stackexchange.com/a/14683/12102) is a good start but it is not a complete answer to *your* question. Tracking precise locations of spacecraft in deep space in 3D is much more than sending and receiving radio signals to get distances, and you may want a location at a certain point in the present or future when a spacecraft passes near a planet while the data you receive might be 12 or 18 hours old! A good answer will address how this is done.
Comment: I think someone will leave a good answer. I just wanted to make sure nobody closed this question as a duplicate, so I left a comment to point out why your question is particularly interesting, and different.
Comment: Really appreciate that. Hope, somebody would answer.
Comment: Re *How do we track the exact location of the spacecraft?* We don't. There are always errors in measurements, in the behaviors of the spacecraft when it makes maneuvers, and in our models of the solar system. Perfection is unattainable.
Comment: Thank you, can you please share how it is done? Really appreciate your time here.
Comment: I ague that the answer to point 1 is "we do not". I am sure that the measurements are approximate, not EXACT. Which really is all that is needed. And to your third question - predict WHAT? Please learn formulating coherent questions.
Comment: Possible duplicate of [How are precision trajectory measurements made of trans-Neptunian spacecraft?](https://space.stackexchange.com/questions/14681/how-are-precision-trajectory-measurements-made-of-trans-neptunian-spacecraft)
Comment: The distance may be measured very precisely using a measurement of the time for a signal needed to go to the spacecraft and back. The error of the direction measurement is much larger. The speed may be measured precisely using the doppler shift.
Comment: @RussellBorogove I don't think so and I've described why in [this comment](https://space.stackexchange.com/questions/21256/#comment59047_21256). Look at how the answer below is shaping up. No. Not possibly a duplicate. My question is about precision measurements. This question is about the trajectory itself. The trajectory includes *all of the points in between ones that can be established by measurements (if you are lucky)* as well as points in the future. This is a broader question and needs a broader answer, and it will be a very interesting answer, if we are lucky!
Answer:
How do we track the exact location of the spacecraft which is millions or billions of miles away from us?

We don't track the exact location of spacecraft. There are always errors in measurements, errors in the behaviors of the spacecraft when it makes maneuvers, and errors in our models of the solar system. Exactness (perfection) is unattainable. It is far better to model those errors than it is to pretend they don't exist.

What things do we study for tracking purpose?

This depends very much on the object of interest. A key distinction is whether the object of interest is a cooperative or uncooperative target. A cooperative target somehow actively cooperates in determining the object's trajectory. The Moon, the Sun, the planets, asteroids, etc., are obviously uncooperative. All objects of interest in space were uncooperative until the middle of the 20th century, and the only available measurements were the object's angular position (azimuth and elevation) as seen by an observer on the surface of the Earth.
This changed drastically in the latter half of the 20th century when humanity developed radar and when humanity started sending cooperative targets into space. Radar enables the measurement of the range to somewhat nearby objects in space, where "somewhat nearby" means a few astronomical units or so. These range measurements alone are quite precise, enough so that direction measurements (azimuth and elevation) are of lesser importance.
Cooperative targets that relay a signal sent from the Earth back to the Earth drastically improve the range of this already very precise range measurement and enable an even more precise measurement, range rate (the rate at which the distance to the target changes with respect to time).
With one exception, measurements of where a cooperative target is in the sky are so imprecise compared to range and range rate that those measurements are essentially useless. That one exception is Delta-Differential One Way Ranging, or ΔDOR, for short. This involves simultaneous observations of a deep space probe by two or more ground stations separated by thousands of kilometers. Interferometric techniques yields nanoradian level precision on the angular position of the observed object.

How exactly do we predict?

Even with range, range rate, and ΔDOR measurements, a single set of measurements provides information on only four measurements of an object's state. Moreover, because ΔDOR requires using two ground stations simultaneously, it is rather expensive. In many cases, there are only one (range) or two observations (range and range rate) at any point in time. Whether it's one, two, or four measurements, that's does not suffice because an object in space has six translational degrees of freedom. Inferring orbital state from a single set of measurements is an underdetermined problem.
What's done is combine multiple sets of measurements gathered over time. This is an overdetermined problem. Each of those measurements has an error associated with it, the propagation from one measurement to another induces additional errors (process noise), and imprecise behaviors of a probe when it performs a correction burn or adjusts its attitude induce yet other errors (plant noise).
Describing the techniques needed to combine those multiple measurements and to account for measurement noise, process noise, and plant noise would require multiple books. If you want to study this on your own, you'll need to understand statistical filtering techniques. One set of keywords of interest is "precision orbit determination", or POD for short.
Comment: @Uwe - Position and velocity. Attitude maintenance is the spacecraft's job. With regard to your previous question, triangulation is pretty much useless. The Deep Space Network antennae with the smallest beamwidth are the 34 meter dishes when used in the Ka band. These have a half power beamwidth of 0.016 degrees. As an example, for a spacecraft 5 astronomical units away, that corresponds to a circular patch of sky 200000 km in diameter (50% larger than Jupiter). All other antenna/receiver combinations involve significantly larger beamwidths, making that already huge patch even larger.
Comment: Is triangulation used too by simultaneous distance measurements from several ground stations? Unfortunately the diameter of the earth is very small when compared with the enormous distance of these spacecrafts. Even the diameter of the earth orbit around sun is small in comparison.
Comment: @Uwe you can consider ΔDOR to be fancy triangulation. It's even got a triangle in the name. But seriously, it's a time-difference-of-arrival thing, which is basically the same concept.
Comment: "an object in space has six translational degrees of freedom"? I think of three degrees of freedom for location and another three for the attitude. But is attitude translational, I would call it rotational?
Answer: While this site does not give a very detailed answer, it gives a relatively good idea on how this is achieved:
The JPL has five groups, that handle the navigation together.

Ephemerides Group
Calculates the positions of astronomical objects at predicted times.
Orbit Determination Analysts
Study radio transmissions and images from cameras to determine the spacecraft's current location.
Maneuver Designers
Plan propulsive maneuvers to keep the spacecraft on the correct flight path.
Radiometric Tracking Team
Assesses techniques for acquiring and improving the accuracy of radio-based measurements of the spacecraft's velocity, location, and angle relative to Earth.
Trajectory Designers
Plot the most efficient path for the spacecraft.

So it really is a team effort involving large groups of experts employing several different methods to locate a satellite.
Comment: This is an interesting breakdown. In which group or category would the actual computation reside? For example, the Ephemeris group might supply the state vectors and masses of all gravitational bodies that could affect a spacecraft, but who combines those gravity fields with the radio-based measurements and actually does the mathematical integration and iterative fitting to compute the complete trajectory solution? When I look up a spacecraft's trajectory in the JPL Horizons database [as I did here](https://space.stackexchange.com/q/21261/12102) who does that final calculation?
Comment: Also, note that the question is how, not who. While your first sentence contains the word "how", the rest of the answer is really just a list of groups, not an explanation of a process


Why should I use JMS and not RMI+Queue?

Question: At the moment I am using RMI or hessian library to communicate between my server and clients (via a LinkedBlockingQueue). Now I read about JMS which could be used in this area too. Is this correct? If yes, would you mind to give me a simple list of advantages/disadvantages, because it seems to be a pretty complicated and 'fullblown-enterprise' area.
What are the benefits? And what about the performance compared to RMI+Queue? Could JMS beat RMI+Queue?
PS: I know there are similar questions, but I would like to have JMS compared to RMI+Queue.
Comment: It would be great if at least one of the answers gave even a single positive aspect of RMI+Queue...
Comment: pro of RMI+Queue is: its very simple! No additional packages or knowledge required etc ...
Answer: A simplified comparison would be (not particular to JMS, more like comparison against MQ in general)...

Automatic retry
If you are a client doing a RMI to a server and for some reason RMI fails, you have to try again yourself. If you'd use JMS and you are the client, you'd just send the JMS message. When the server can not be reached, your message will be stored and then delivered when the server is up again.
Persistent queue
Since you are using a LinkedBlockingQueue, you can either have a bounded queue or an unbounded queue in-memory. The former will start to trap threads once the queue is full and will eventually fail under high load. The later would eventually throw OutOfMemoryError instead. If you'd use JMS though, it can automatically start to "persist" messages to "persistent storage". Normally "persistent storage" is DB, which has usually much more capacity than in-memory queue. Of course, content of in-memory queue is lost when the server goes down etc., whereas in JMS you can choose durable message/persistent message that survives such event. This also allows you to have clustering, which is also very important for enterprise programs...
Abstraction
You'll be using a standardized API (ok, you have protocols in RMI too, but if what you want is  passing around messages, MQ provides much more high level abstraction than RMI+in-memory queue). Which means, you get to use future implementations of JMS.. Perhaps something that doesn't need a DB to provide durability and persistence, more scalable than today's implementation etc. Or maybe you can send the same message to completely different service, because of the standerization. Basically, the higher abstraction could give you flexibility, that RMI+in-memory queue doesn't.

Some time ago, I worked with a big company that wanted to use their in-house framework to integrate our stuff. At that time we weren't using a MQ. We asked them to use our own asynchronous protocol based on RMI. Trust me, we regretted that decision very, very much...
Comment: `Trust me, we regretted that decision very, very much`...a testament to the fact that there's no such thing as a bad technology, only bad choices. +1
Answer: The other answers cover many aspect of JMS, but I feel a very important one needs more emphasis, namely the fact that JMS supports multiple concurrent consumers in a transacted way. This is to me the killer feature.

You can easily build a system with a single consumer and producer that is non-transacted.
You can also make it (more or less) transactional with a bit more work.
Similarly, you can add support for multiple producer and single consumer relatively easily, e.g., if you use a transactional database to store the message.
But it becomes very hard to have multiple concurrent consumer and have message consumption be transactional. This basically require a non-trivial locking scheme, and even with the usage of a transactional database the task is not easy.

When we speak of JMS scalability, we however speak of this: the ability of the app. server to add/remove consumer/producer to manage the load.
Other advantages of JMS are quality of service and management, e.g. redelivery attempt, dead message queue, monitoring, etc.
If you don't really need that, a somewhat simpler solution might work. You can also see an other answer of mine where I cover a similar question: Why choosing JMS for asynchronous solution ?
Answer: What are you using for the "Queue" part of your solution? Your own code?
JMS is just an API above some vendor's queuing system, but one that incorporates the remoting aspects. So from client perspective you just put a message on a queue (or topic if you are doing pub sub), and forget about it. The infrastructure delivers it to the listener(s).
I see much of the power of JMS coming from the quality of implementation of the queuing infrastructure rather than the API itself, that's pretty simple.
Simple RMI doesn't scale well or deal with reliability concerns, a good queuing system can be both scalable and resilience.
I think it's fair to say that JMS and the rest of Java EE is intended to allow your application to be enterprise quality. Initially I think Java EE overal was complex, though I thought JMS was one of the simpler corners. Today, I'm not sure that writing RMI + your own queuing is any easier than just using JMS.
Possibly a significant difference is that using JMS pretty much assumes that you have some infrastructure such as an App Server in place.
Answer: JMS is transactional, can be coordinated with database transactions.
JMS Decouples the producers and consumers, meaning they do not need to be running at the same time.
JMS Is guaranteed delivery, meaning that the messages are guaranteed to get there, in case of a failure (Depending on failure type might require clustering).
JMS Can do Synchronous, Asynchronous point to point as well as Publish/Subscribe.
Most JMS implementations use a Queueing System that can work with other languages, OSes.
Answer: 'Automatic retry
If you are a client doing a RMI to a server and for some reason RMI fails, you have to try again yourself. If you'd use JMS and you are the client, you'd just send the JMS message. When the server can not be reached, your message will be stored and then delivered when the server is up again. '
I think answer is misleading. It's resilient in the sense messages sent to a destination for which they are no consumers will be stored until there is a consumer for that message or that message expires. This assumes that the JMS broker is viable.
If you try to send a message to a broker which is unreachable then you should get a JMSException and in that sense you're client messages may be lost unless your application makes some proviso to store them itself and retry. In this sense a client to a JMS server behaves the same as the client to a RMI server. You'll still lose the message if that server is down.

Why should I use JMS and not RMI+Queue?


Using Public Nodes in IOTA Tangle for testing purpose

Question: I want to send some string data using MAM over IOTA Tangle. Right now, I am using devnet. I want to know how can we test our transactions using public nodes on Mainnet? What is the process for it? I could not seem to find any instructions on how to set up public node to pass transaction using MAM. Any leads would be highly appreciated.
Comment: Hey, are you able to send your MAM transactions to the Devnet at the moment? If so, can you share the code that you're using to connect to the Devnet?
Comment: Hey, I have used [this](https://docs.iota.org/docs/client-libraries/0.1/mam/js/create-public-channel) code to send MAM transactions to the Devnet
Answer: You can change the URL in the provider field to a node that's on the Mainnet.
You can use this URL as an example: https://nodes.thetangle.org/
Or, you can run your own node.
Be sure to use a minimum weight magnitude of at least 14 for the Mainnet.
For example, for the code you linked to, you need to use something like the following:
const provider = 'https://nodes.thetangle.org/';
await Mam.attach(message.payload, message.address, 3, 14 /*this is the minimum weight magntiude*/)


Why is the centre of the board considered important in chess?

Question: Yes, we have all heard phrases like 'control the centre'. I would like to know the concrete reason why the centre of the board - in particular the 4 squares - e4, e5, d4, d5, are considered important in chess. What makes them different from any other square? What is the reason that these squares supposedly enjoy such a privileged status compared to other squares? Are they important only in the opening and not so important in the middle and end game? Why? Or is it all just a myth?
Comment: I have an old cloth-on-fiberboard chessboard where the center of the board clearly shows more wear.
Comment: possible duplicate of [What is the theory behind center control?](http://chess.stackexchange.com/questions/251/what-is-the-theory-behind-center-control)
Comment: Simple answer: every piece except the rook becomes more powerful as it approaches the center. Do you want to hide in a corner or come out and fight where your influence is greatest?
Answer: While (e4, d4, e5, d5) are generally regarded as the central squares, the same principle can sometimes be extended to the adjacent squares like (c4, c5, d3, d6, e3, e6, f4, f5). So we have a kind of central polygon -

Controlling the center is not an end in itself but a means to an end. The end results could be any combination of the following-
1. Greater influence over the board.
Normally, if you control the center, then your pieces have more control over the whole board in general. Thus, a knight centralized on e5 generally controls more important squares than a knight passively placed, say, on a4.
Recommended Game:
Karpov vs Kasparov World Championship Match (1985), Game 16 - Kasparov anchors a Black knight on d3 which was famously described as the "octupus", controlling several key squares in White's position and greatly influencing the entire board. White's knights on the other hand are pushed to passive squares like a4 and b1, exerting almost no control over the board.
<code>  [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
  [White "Karpov"]
  [Black "Kasparov"]

  1. e4 c5 2. Nf3 e6 3. d4 cxd4 4. Nxd4 Nc6 5. Nb5 d6 6. c4 Nf6 7. N1c3 a6
  8. Na3 d5 9. cxd5 exd5 10. exd5 Nb4 11. Be2 Bc5 12. O-O O-O 13. Bf3 Bf5
  14. Bg5 Re8 15. Qd2 b5 16. Rad1 Nd3 17. Nab1 h6 18. Bh4 b4 19. Na4 Bd6
  20. Bg3 Rc8 21. b3 g5 22. Bxd6 Qxd6 23. g3 Nd7 24. Bg2 Qf6 25. a3 a5
  26. axb4 axb4 27. Qa2 Bg6 28. d6 g4 29. Qd2 Kg7 30. f3 Qxd6 31. fxg4 Qd4
  32. Kh1 Nf6 33. Rf4 Ne4 34. Qxd3 Nf2 35. Rxf2 Bxd3 36. Rfd2 Qe3 37. Rxd3 Rc1
  38. Nb2 Qf2 39. Nd2 Rxd1 40. Nxd1 Re1 0-1
</code>
2. Greater mobility of pieces.
Often, if the central pawns are not advanced two squares, they can hinder the bishops from development. They provide less space for the pieces to move. If these pawns are advanced to the central squares, then the mobility of the pieces is greatly enhanced. Thus, e2-e4 frees the bishop on f1 and d2-d4 does the same for the bishop on c1. Besides, these moves also make room for the queen on d1 and later for the rooks to come into the game on the d or e files if they have been opened.
Recommended Game:
Paul Morphy vs James McConnell, 1849 - Morphy follows basic opening principles; develops pieces towards the center, advances pawns to e4 and d4, his bishops come to life and the Black queen is at the mercy of his centralized pieces.
<code>  [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
  [White "Morphy"]
  [Black "McConnell"]

  1. e4 e5 2. Nf3 Qf6 3. Nc3 c6 4. d4 exd4 5. e5 Qg6 6. Bd3 Qxg2 7. Rg1 Qh3
  8. Rg3 Qh5 9. Rg5 Qh3 10. Bf1 Qe6 11. Nxd4 Qe7 12. Ne4 h6 13. Nf5 Qe6 14. Nfd6 Bxd6
  15. Nxd6 Kd8 16. Bc4 Qe7 17. Nxf7 Kc7 18. Qd6 Qxd6 19. exd6 Kb6 20. Be3 c5
  21. Bxc5 Ka5 22. Rg3 b5 23. Ra3 1-0
</code>
3. Restricted mobility of enemy pieces.
Suppose white manages to place both pawns on d4 and e4. This makes it difficult for the Black bishops to find good squares like c5 or f5. They thus have to remain passive or try a fianchetto, which might not always be convenient. Also, the pawns on d4 and e4 restrict and also have the ability to attack the Black knights which might normally be developed on c6 or f6. This constant potential to threaten the Black knights can make it difficult for Black to develop pieces comfortably.
Recommended Game:
Karpov vs Kasparov World Championship 1986, Game 5. - Karpov demonstrates how pawns in the center can restrict a fianchettoed Bishop.
<code>  [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
  [White "Karpov"]
  [Black "Kasparov"]

  1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. Bf4 Bg7 5. e3 c5 6. dxc5 Qa5 7. Rc1 Ne4 8. cxd5 Nxc3
  9. Qd2 Qxa2 10. bxc3 Qxd2 11. Kxd2 Nd7 12. Bb5 O-O 13. Bxd7 Bxd7 14. e4 f5 15. e5 e6
  16. c4 Rfc8 17. c6 bxc6 18. d6 c5 19. h4 h6 20. Nh3 a5 21. f3 a4 22. Rhe1 a3
  23. Nf2 a2 24. Nd3 Ra3 25. Ra1 g5 26. hxg5 hxg5 27. Bxg5 Kf7 28. Bf4 Rb8 29. Rec1 Bc6
  30. Rc3 Ra5 31. Rc2 Rba8 32. Nc1 1-0
</code>
4. Pawns move closer to the enemy king.
Generally, in an attack on the enemy king, it is important to have a few pawns near the enemy king to make it difficult for the opposing pieces to defend the position. If the Black king (for example) castles to the kingside, then it usually helps White to have a pawn on e5, because then Black cannot place a knight on f6, which is the most natural defensive position for the knight on the kingside.
Recommended Game:
Fischer vs Myagmarsuren, 1967 - Bobby Fischer fixes a pawn on e5 to drive the Black knight from f6 and then proceeds to win with a kingside attack in instructive fashion.
<code>  [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
  [White "Fischer"]
  [Black "Myagmarsuren"]

  1. e4 e6 2. d3 d5 3. Nd2 Nf6 4. g3 c5 5. Bg2 Nc6 6. Ngf3 Be7 7. O-O O-O
  8. e5 Nd7 9. Re1 b5 10. Nf1 b4 11. h4 a5 12. Bf4 a4 13. a3 bxa3 14. bxa3 Na5
  15. Ne3 Ba6 16. Bh3 d4 17. Nf1 Nb6 18. Ng5 Nd5 19. Bd2 Bxg5 20. Bxg5 Qd7
  21. Qh5 Rfc8 22. Nd2 Nc3 23. Bf6 Qe8 24. Ne4 g6 25. Qg5 Nxe4 26. Rxe4 c4
  27. h5 cxd3 28. Rh4 Ra7 29. Bg2 dxc2 30. Qh6 Qf8 31. Qxh7 1-0
</code>
5. A favorable exchange of pawns in the center leaving the enemy camp with weaknesses.
Normally, when pawns are placed in the center, the opponent has to challenge them at some point in the future. This can often lead to favorable pawn exchanges and may lead to isolated pawns or backward pawns in the enemy camp, which can be vulnerable in some positions.
Recommended Game:
Rubinstein vs Salwe, 1908 - Here, Rubinstein creates a backward pawn on c6 and then masterfully exploits it.
<code>   [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
   [White "Rubinstein, Akiba"]
   [Black "Salwe, Georg"]

   1. d4 d5 2. Nf3 c5 3. c4 e6 4. cxd5 exd5 5. Nc3 Nf6 6. g3 Nc6 7. Bg2 cxd4
   8. Nxd4 Qb6 9. Nxc6 bxc6 10. O-O Be7 11. Na4 Qb5 12. Be3 O-O 13. Rc1 Bg4
   14. f3 Be6 15. Bc5 Rfe8 16. Rf2 Nd7 17. Bxe7 Rxe7 18. Qd4 Ree8 19. Bf1 Rec8
   20. e3 Qb7 21. Nc5 Nxc5 22. Rxc5 Rc7 23. Rfc2 Qb6 24. b4 a6 25. Ra5 Rb8
   26. a3 Ra7 27. Rxc6 Qxc6 28. Qxa7 Ra8 29. Qc5 Qb7 30. Kf2 h5 31. Be2 g6
   32. Qd6 Qc8 33. Rc5 Qb7 34. h4 a5 35. Rc7 Qb8 36. b5 a4 37. b6 Ra5 38. b7 1-0
</code>
As I mentioned, these are the end results that a side tries to achieve by controlling the center. If the end result is already achieved, or if it can be obtained in a better way, then there is no need to control the center.
Answer: In addition to things already said, notice that pieces have more moves if they're in the center of the board.  E.g., a knight on one of the squares in the 4x4 space in the center has 8 moves; as the knight moves towards the edge, he has fewer moves that he can make.  It is the same with the other pieces.
Books with precise speech will say that what's important is to control the center, not necessarily be in the center -- an important difference.  Just having pawns in the center, for instance, would not get you any advantage.  They need to be controlling one or more squares that pieces can use.
Answer: It is certainly not a myth! As pointed out control of the centre squares either by direct occupation with pieces or pawns or indirectly via major and minor pieces gives more control over the chess board. Pawns and pieces in the centre of the board affect the most squares compared to being on the outer flank squares and those on the board edge squares exert the least control of the board.
If you don't control these centre squares and let your opponent control them, they will have an easier game than if they have to fight for their control (so don't concede the centre without some other form of good compensation or you will regret it against any good player whose pieces and pawns in the centre will in effect be stronger!).
Some games are classed as open/semi-open or closed. Central openings often give rise to open or semi open games where centre files may become fully open or semi-open (ie with only one pawn on the file or no pawns). In open games pieces can be used more to control the centre. In closed games the pawns are supported and make it harder for the pieces to find good squares.
Some openings are designed to take central control. In the aggressive Sicilian defence black tries to exchange his c pawn for a centre pawn of white and try and control the centre that way. The Scandinavian opening immediately challenges the centre.
This central control concept does hold true more in the opening and midgame than the end game. In the endgame with only Kings and pawns left, other factors are more important (eg pawn structure, numbers and king position).
Still like many principals in chess there is more to chess than controlling the centre, but if you can control the centre you will have an advantage! This though does not mean you should neglect the flank/outer squares. If you let your opponent attack at will on the flanks with pieces and/or pawns you will be at a disadvantage too. So you need to be alert ("on the ball") in chess over the whole board and if you do concede the centre then beware!


Is the Nikon 55-300mm a good choice for indoor and outdoor portraits?

Question: I have the most basic model of Nikon DSLR, the Nikon D3200, with the 18-55 kit lens. I'm thinking of buying the Nikon 55-300mm lens, mainly for its zoom purpose. Is it a good lens? Can I take portrait shots using this? Like indoor and outdoor? How's the bokeh effect while taking portrait photos?
Comment: Knowing the camera you plan to use will be helpful. The sensor size affects the answer. I assume it is a DX sensor because you said most basic.
Answer: It should be OK but not great for portraits. Its a decent lens for its price but still entry level. So, I don't think you will like it much better than your kit lens for portraits.
Many shooters look for a portrait lens that:

Has a focal length around 80-110mm on a full-frame sensor*
A wide aperture
A nice look to out-of-focus background (the bokeh you mentioned)

(*) Assuming your basic Nikon DSLR has a DX sensor, the crop factor is 1.5, so this lens is equivalent to 83-450mm on full frame.
I am also assuming you want to be able to shoot with available light.
This lens is mostly designed for a long zoom range. This is helpful when subject (such as wildlife) are not cooperating with regards to their distance.
The maximum aperture is f/4.5 which doesn't get you much light. The Bokeh is good but not beautiful like some lenses.
On the budget of the 55-300 (around $250) I don't think you're going to get much improvement over your kit lens for portraits, so I would stick with your kit lens.
If you can afford the one-time investment (I don't know if this is a business for you or a hobby) good portrait lenses include NIkon 85mm f/1.4D and 135mm f/2 which you should be able to pick up used for less than $1000.
You may have other reasons you want a long zoom, but I'm not sure that portraits would be a justification for this upgrade.
Lens selection is highly personal. My recommendation is that you attempt to try out (even rent) a lens before buying. Also check out the store's return policy, especially for used lenses.
Comment: @"Assuming your basic Nikon DSLR has a DX sensor, the crop factor is 1.5, so this lens is equivalent to 83-450mm on full frame." - Not sure but you should rather divide instead of multiplying...?
Comment: @user681768917 nope.
Comment: Also worth noting Nikon's 85mm f/1.8 for portraits as a budget portrait lens option — or even the 50mm f/1.8, both for much less than $1000.
Comment: I have a DX format Nikon and my 35mm prime lens gives me the range of view of a 52.5mm lens on a full frame camera ~ 35*1.5 crop factor. To get a range of 80-110mm equivalent for DX, look for something between ~50, maybe 55-75mm
Answer: I own this lens. The lens is really nice, but I have only used it twice. It is an entry level, but the image quality is really nice. The 300 mm zoom creates a really dramatic DOF. The limitation of course is the ƒ/5.6 aperture – significantly less than the ƒ/2.8 (2 stops less light). If you would like to use it for indoors portrait this would not be so easy with available light; however, for wildlife is really good.
I can say that it is good value for the money.
Answer: I would suggest to stick with the kit lens for portraits. The maximum aperture of 18-55 is f 3.5 which is good for the bokeh effect. Also the kit lens has VR II.
On the other hand if you purchase 55-300 without a VR (assuming as not specified in the question) it will be difficult to get sharp images as you will experience camera shake if you don't have steady hands.
I would suggest nikkor 55-200 VR II. The bokeh effect will be a little less compared to prime lens, but will serve both the purposes of portrait as well as zoom lens.
Comment: But the kit lens is f/3.5 only at 18mm, which is most definitely not the focal length you want to be using for portraits.
Comment: I agree to the above comment. But still I believe that good portraits  can be taken by physically moving close to the subject(If possible).


sum of Perron-Frobenius operators

Question: My operator is the transfer operator $P$ on $L^1$ functions defined on compact $X$. It is the pre-dual of the operator $U:L^∞ \rightarrow L^∞$ defined by $U(ϕ)=ϕ\circ f$, for a fixed map f on X. I have PU=Id and UP is the projection. Now my specific question is, if $P_1$(h)=h and $P_2$(g)=g for g,h ∈ L1, and if 1 is the leading simple isolated eigenvalue for both $P_1$ and $P_2$, then does $(P_1+P_2)/2$ have 1 as a leading eigenvalue and what about the corresponding eigenfunction?
Answer: Not clear what you mean by this. If $P$ has a non-trivial kernel, (say $Pf=0$) then isn't $f+aUf+a^2U^2f+\ldots$ an $L^1$ function and an eigenfunction of $P$ with eigenvalue $a$?
I think that to have isolated eigenvalues you need to be working in a smaller Banach space.

sum of Perron-Frobenius operators


How can I get dictionaries for more input languages?

Question: Ok, so I figured out I can enable other input languages through settings, which at least makes it easier to enter some special characters, but only the biggest languages have "Dictionary available". Is it possible to somehow add dictionaries for the other selectable input languages?
Answer: It looks like that all dictionaries are embedded into keyboards, but you can try to find the dictionary by searching in Android market with query:

Your_desired_language language pack

For example for "Finnish language pack" there are packs for 3 different keyboards: SlideIT, AnySoftKeyboard and Gingerbread keyboard (unfortunately not the original one, you should install Gingerbread keyboard app from market even if you already have original Gingerbread keyboard).


Build My Own Sound Effects Library to Meet SMPTE Specifications

Question: I'd like to start build my own sound effects library from the ground up for the use in motion pictures and gaming. When building this library, is there a standard from SMPTE to meet? Are there better digital signal sampling rates that are easier to integrate into the films, especially going from HD to UHD? If anyone has experience in signal analysis and process, is it better to use analog microphones to get a raw signal and post-process it through signal conditioning with A-to-D converters for optimal sample rates, and low, high and/or band pass filters for cleaning up the sounds? Is there any other information to be captured and included into the library infrastructure? Thanks!
Comment: Since I see many questions on naming conventions, those posts answer that question. So specifically, is there a SMPTE sound library or sound effect standard that a file, a library or both must strive to meet for use in film making?
Answer: There are no standards as such for Sound Effects libraries. There are related standards around file data formats maintained by the AES but generally there is nothing required that is related to Sound Effects libraries specifically.
There are industry conventions that you might consider, such as:

Recording at a minimum of 48kHz sampling rate (preferably more)
Recording at a minimum of 24-bit resolution

Audio resolution has no relevance whatsoever to video resolution (i.e. HD/UHD).
The reason you would record sound effects at a higher sampling rate is due to the needs of sound designers and sound mixers to potentially pitch-change the material.


When you export from Adobe Illustrator cs4, is it done as png-24?

Question: In Adobe Illustrator CS4, when I do Save for Web & Devices I get to choose explicitly that I want png-24. But when I export I do not get asked it, is this because it is the default? I need it to make android phone icon buttons. They ask for png-24. I use the export because it will save each artboard automatically and in the Save for... option I have to go through each artboard manually which is time consuming.
Answer: Yes, Export saves as PNG24 with 8bit alpha. So it's actually a 32-bit RGBA PNG, with 8bits for red, green, blue and transparency.
I use the export because it will save each artboard automatically and in the Save for... option I have to go through each artboard manually which is time consuming.
Maybe using one artboard with slices would be a better option? That way everything can be exported all at once.
An Illustrator document with multiple slices selected and PNG output:

File size
Using Export usually produces bigger files than Save for Web. I just tested here and the example document I used ended up with 1,320 bytes for Export vs 531 bytes for Save for Web. Using Export created a file that was almost 2.5× bigger.
If you're exporting for use in an app or on the web, you really want to use Save for Web.
Quality
I'd be a little careful when using Illustrator for icon or user interface design. There's some significant drawbacks in its rendering quality. Illustrator doesn't dither gradients, has antialiasing issues including stray pixels and a few other problems.
Comment: Both Photoshop and Fireworks are better choices, in terms of rendering quality. If you duplicate the icon, scale to the correct final size and build a slice for it, you'll be able to export for mdpi, hdpi and xhdpi all at once (or any other scale you might need). It'd also let you tweak the icon for each size, which is important if you want things to look sharp.
Comment: great answer, what would be an alternative to AdobeIllustrator? If I use slices for the artboard, I don't get separate files coming out which is needed. They always ask for hd md and ldensity.
Answer: Im pretty sure when you export and save and get the resolution screen and you will pick med resolution it already saves it in png-24 and png-32 and it shouldn't really matter for your app.
You can also write your own script for illustrator to do exactly what you want and save the image in the format you need. It will take some effort though (you can ask on stack overflow for help)
Update
Here is a script that will do it for you, just add it to your mainIllustratorDir\Presets\en_US\Scripts and then run it and it will give you an option to pick 24 or 8 png file. (the script is designed to do something else but it should still do the trick) I hope it works like regular export though... it might not crop the images which could make it not useful to you (you need to change your layer names from default ones or they wont get exported)
Did you try saving the images you export in the med resolution and then with the Save for Web & Devices way and see if it makes any difference?
Comment: thanks for the answer. I have always wanted to make Adobe Illustrator scripts to make the workflow efficient, but never got up to speed with it. I have tried both save methods;  export will automatically produce different files for each artboard, but Save for web doesn't so I don't use  that option. Best would be to script the save for web option to save each artboard in a separate file.
Answer: If using export, you do get asked. There's a "formats" menu at the bottom of the dialog box just above the line of buttons saying "save/cancel".
You can select other useful file formats such as DXF from this menu.
Yes, it's exported as PNG-24. The alpha channel would be visibly horrible – no antialiasing – if it was PNG-8.


Stereo to mono Jack!

Question: My mixing desk only supports stereo outputs. To connect a mono grotbox i need a mono signal. Is there an Adapter or cable that feeds the two stereo signals in one mono Jack or xlr?
Comment: I found an Adapter on a local Shop by incident! 7 bucks seemed fine. Thx
Answer: Simple answer is if you are feeding a stereo signal to a single input you need the signal to be summed so you do not lose any elements.
To do this you need 3 resistors in the XLR end, diagrams are available online however its not a simple solder job. If you shop around you can get stereo to mono cables but make sure they have resistors and are summed to one pin. The 3rd pin in the XlR mono should not be used. Otherwise you'll get a weird effect.
Comment: I'm not sure this is correct. By not using Pin 3 of an XLR plug you're basically creating an unbalanced line. Even if you don't actually merge "cold" lines from the output, it's relatively simple to create an impedance-balanced combiner. In fact, I'd bet that's what some of the resistors in the design are for (at least one will be to reduce the voltage on the "hot" lead by 3dB).
Answer: You don't say what size you require, but looking at somewhere like StudioSpares you'll see what is available.  Failing that, buy the jacks you want, get a soldering iron and ideally a test meter and then you can make your own leads.  There are plenty of video tutorials online to guide you through……it's a good skill to have and only takes a bit of practice.

Stereo to mono Jack!


What is the difference between RTK GPS and GBAS?

Question: My understanding is that real-time kinematic (RTK) is also a differential GPS technology to enhance accuracy by using a ground-based station to provide the correction data to the onboard GPS receiver. Is it similar to GBAS? Then what is the difference between RTK and GBAS?
Answer: There are two primary differences between RTK GPS and GBAS, function and implementing technology.
Functionally, RTK is a differential GPS (DGPS) positioning system. It allows for very precise position measurements (~1 cm). Its primary application is for survey and related measurements.
GBAS also provides a DGPS function but it adds specialized support for aircraft approach guidance. To that end it provides via data broadcast to the using receiver reference path data for a number of runway approaches. It also provides signal integrity data (e.g. fault detection and alerts) to the user.
The difference in implementing technology is that the RTK reference station and using receiver determine position by carrier-phase tracking and the GBAS reference station and using receivers use code tracking.
Answer: My understanding is that RTK is a specific implementation of the more general GBAS  (Ground Based Augmentation System) principle. RTK uses measurements of the phase of the signal's carrier wave in addition to the information content of the signal:
https://en.wikipedia.org/wiki/Real-time_kinematic
A summary of different augmentation technologies is here:
https://en.wikipedia.org/wiki/GNSS_augmentation


LAPACK equivalent on c++ , which is the best one?

Question: I am following a course of computational material physics. The professor uses fortran to code and uses lapack to solve eigenvalue problems.
So far I just know c++. There is an equivalent library that make the same as LAPACK but in c++? Which is the best one ?
Should I prefer to use fortran rather than c++ for my scope?
Thank you
Comment: You should prefer C++ of you ever intend to code outside of a legacy academic context. It's much more widely used in other domains and most new scientific software is written in it. However, Fortran does linear algebra style calculations well and is still used in style scientific applications, especially if there's a large legacy code base.
Comment: Fortran has 9.5k questions on StackOverflow versus 608k questions for C++. SO Jobs shows 1 offering for Fortran and 534 for C++. It wouldn't hurt to know both, if knowing was free. But the benefit of Fortran has to be balanced against the cost (and difficulty) of learning a specialized tool with limited career prospects versus developing a deeper knowledge of a more general tool with similar performance characteristics. Unless OP already knows C++ well or explicitly plans on a career working with Fortran, I couldn't advise them to invest time on it.
Comment: @Richard To be fair, there *is* a reason, apart from legacy code, why Fortran is still used. It's performance is great due to the absence of pointer aliasing. It won't hurt to know Fortran and C++.
Answer: Definitely use C++ and Eigen. Reasons:

Sounds like it fits best for your case.
Eigen beats LAPACK using optimization flags (-O3) and a good compiler (GCC, Clang). At least for most tests I recently performed (dense linear algebra)
Once you debug your application use the -ffast-math compiler flag for a huge speedup, but test your output to see if it remains correct. I've noticed this is specially useful with Eigen.
C++ is an actively evolving high-performance language. Eigen takes advantage of its advanced features to optimize your code and make most things compile-time and SIMD/vectorized.
Virtually the only disadvantage of Eigen over LAPACK is that LAPACK has a standardized API. You can switch to another LAPACK library for higher performance in some cases.
Still, keep an eye on LAPACK for any routines from Eigen that are not serving you well.
Many production code in my field (computer vision, augmented reality, etc) that I've seen is using Eigen, and previously used LAPACK.
You can always use LAPACK as well with your C++ code when you want to follow your professor more closely, and compare with Eigen to be a good student. But if you just wanted to follow the professor, without regard to the best alternative, you might as well just learn Fortran.
See this: How does Eigen compare to BLAS/LAPACK

That said, Fortran can be simpler and faster than C++ in common usage. See the beginning of this video and the first answer to this stackoverflow post.