Why is water evaporated from the ocean not salty?

Question: I am wondering about this. When salty water in the ocean evaporates we are getting the clean distilled water. Why is that?
I was trying to think on this and maybe the comparative size/mass of water molecules to the size of different salts molecules plays a role here, but it is not likely. The size/mass of e.g. alcohol molecules is much higher but they still evaporate quite well.
Could you explain intuitively?
Comment: I think that it's better to think in terms of energy than in terms of size/mass in this case. Salt dissolves into water as charged Na+ and Cl- ions. When water  molecules evaporate it's difficult for individual Na+ or Cl- ions to latch onto them for a ride up into the atmosphere because that would greatly increase the electrostatic energy associated with the water molecule by a lot. So the water evaporates while the Na+ and Cl- ions tend to be left behind.
Comment: Actually the sea is salty *because* the vapor is not.
Comment: Alex, water evaporates as whole molecules. It would take extremely high temperatures to start breaking down water molecules to their constituent atoms. As for the energy considerations involved here with water and dissolved NaCl, there's a nice, easy-to-understand explanation here: https://van.physics.illinois.edu/qa/listing.php?id=1490
Comment: Samuel, could you elaborate? This is a very interesting aspect of evaporation. I mean that I do understand that the more water is evaporated the more ions of Na and Cl are binding together again and form crystals. But I still do not see how is it `difficult for individual Na or Cl ions to latch onto them for a ride`... Probably this is because I do not really understand how the `clean` water evaporates. Is it evaporating as a whole molecules or it also breaks into some ions/atoms?
Comment: @RomanReiner not really; it is salty because minerals have dissolved in it. If the vapor would be salty (whatever that might mean...), then the rain would be salty, and the rivers would be salty, bringing back the salt to the sea, with slightly more dissolved in it, building up the salt level over time. It would possibly reach an equilibrium after a long time, but not at the current salt levels.
Answer: Water molecules are polar; this basically means that they have a "positive side" and a "negative side"
Salt is composed by Na$^+$ and Cl$^-$ ions held together by electrostatic forces (is a ionic compound). When salt is put into water, it dissociates, i.e. the Na$^+$ ions are separated from the Cl$^-$ ions.
When in the water, such ions are surrounded by water molecules facing them with the side which has charge opposite to that of the ion; this is because this way they can reach a lower energy state, being their electrostatic field screened by that of the water molecules (picture below [source]).

Water evaporates when the thermal energy of the molecules is high enough to break about half the hydrogen bonds between them [source]. For the ions, it is much more difficult to evaporate, because their thermal energy would have to be enough to compensate the effect of the water molecules which surround them.
Basically, both the water molecules and the ions are in what is called a potential energy well: to "kick them out" of the well, we have to provide them with an energy as high as the depth of the energy well $\Delta E$ (picture below).

The depth of the well in which the water molecules are (due to hydrogen bonding) is much lower than the depth of the well where the ions are. So, a far higher thermal energy is needed to take an ion out of the water. Since thermal energy is proportional to $k_B T$, where $k_B$ is Boltzmann's constant, this means that a far higher temperature is needed.

Update: Some numbers
To get an idea of the order of magnitudes of the energies involved, we should consider the following:

At room temperature ($T_r\simeq298$K), $k_B T_r = 0.026$ eV (however, we should keep in mind that this is just an order of magnitude...)
The energy of an hydrogen bond (hydrogen bond enthalpy) in water is around $23.3$ kJ/mol = $0.24$ eV = $9.3 \ k_B T_r$, and in order a volume for water to evaporate, about half of all the hydrogen bonds in the volume must be broken:

There is no standard
  definition for the hydrogen bond energy. In liquid water, the energy of attraction between water
  molecules (hydrogen bond enthalpy) is optimally about $23.3$ kJ/mol (Suresh and Naik, 2000)  and
  almost five times the average thermal collision fluctuation at $25$°C. This is the energy required for
  breaking and completely separating the bond, and equals about half the enthalpy of vaporization ($44$ kJ/mol
   at $25$°C), as an average of just under two hydrogen bonds per molecule are broken when water
  evaporates. [source]

The energy gained by putting an ion in water (technical term "hydrating" the ion) is known as the hydration energy or hydration enthalpy ($\Delta H_{hyd}$). Since we are interested in the opposite process (the remotion or de-hydration of the ion), we have to take $-\Delta H_{hyd}$. Here we can find some numbers. We can see that

$$\Delta H_{hyd}(\text{Na}^+) = -406 \ \text{kJ/mol} = -4.2 \ \text{eV} =  -162\ k_B T_r$$
$$\Delta H_{hyd}(\text{Cl}^-) = -363 \ \text{kJ/mol} = -3.8 \ \text{eV} =  -145 \ k_B T_r$$
Comment: I'd love if some ballpark figure could be offered in this answer (or as a comment) in eV, just so there is an order of magnitude to which we can compare the relevant energies. I take that kT is about 0.025 eV, while the hydrogen bond has an energy close to some 0.21 eV (from wikipedia). What would be the energy in eV for the ions? About their hydration energy (~38,5 eV, if my math and understanding is right)? I am curious if those numbers are close to what your answer suggests. To me, those seem to be important complements to the answer...
Comment: @pentane Added reference for the first one. The second one is my work.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/46908/discussion-on-answer-by-valerio92-why-is-water-evaporated-from-the-ocean-not-sal).
Comment: @Vendetta You are right. Some numbers would be good! I will try to add them. And by the way, you are correct, it is exactly the hydration energy, only I'm not sure about the order of magnitude, I shall see what I can find online.
Comment: Unless the very nice images here are your work would you cite their source?
Comment: @GFG Who talked about the breaking of the O-H bond? I only talked about [hydrogen bonds](https://en.wikipedia.org/wiki/Hydrogen_bond), which are fundamental in the phase transitions of water.
Comment: Wikipedia isn't the actual source; that image is from an online textbook produced by Rice University. Cite "OpenStax, Inorganic Compounds Essential to Human Functioning (online textbook)" and link here http://cnx.org/contents/e4e45509-bfc0-4aee-b73e-17b7582bf7e1@4
Comment: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/47022/discussion-between-valerio92-and-gfg).
Comment: @valerio I can accept it in this form
Answer: At any given temperature and pressure, liquids (like water) and solids (like salt) are in equilibrium with their respective gaseous form.  The vapour pressure describes this phenomenon. Often, solids have a lower vapour pressure as liquids. The higher the vapour pressure, the more volatile a compound is.  And in the instance of pure sodium chloride / NaCl, this vapour pressure is much lower than the one of water.  This alone contributes why heating sea water, and condensing the vapour, will first yield water.
In addition, to perform such a distillation, the Raoult's law applies, too.  Basically, there is a total pressure $p$ in the system observed that is the sum of the individual partial pressures of the two components (water and salt).  The partial pressure takes into account the vapour pressure the pure component possess (at this temperature and pressure) times the concentration of this component in the mixture (expressed as molar fraction):
$p (\mbox{total}) = p(\mbox{water}) * x(\mbox{water}) + p(\mbox{NaCl}) * x(\mbox{NaCl})$
where the molar fractions will add up to one.  So if we simplify "seawater" as a solution of NaCl in water:
$x(\mbox{water}) + x({\mbox{NaCl}}) = 1$
The contribution of the total pressure $p$ by NaCl is lowered further as at ambient conditions, water may dissolve only 359 g NaCl per litre of water (reference), hence excluding a solution of higher concentration of NaCl than about 36 mass%.
This is a simplified view, leaving out any idea of "molecules" or "ions". Raoult's law is an idealization, too (hence, for example, azeotropes like ethanol/water).  Of course, sea water contains more than NaCl; and to remove the later from the former, reverse osmosis is an energetically more favourable technique.  Eventually, to distill NaCl, you need conditions of very high temperature and very low pressure, far distant from the ones to distill water.
Comment: @Paparazzi : The scenario of the Question is *not* that of salt poured into clean water.  It is that of seawater.  Separating the NaCl from the other non-water components of seawater does not happen if all one does is drive off the water.  Put seawater at its boiling point (which moves as the non-water concentration changes) and what you get is not pure salt.
Comment: To distill NaCl you just let the water boil off. Put a quart of water on your stove add a cup of salt and let the water boil off.  What did you get for vapor pressure of NaCl at 100 °C?
Comment: I think this answer would benefit from a comparison of some vapor pursues of typical salts vs. water. The difference is, of course, tremendous even without the Raoult's law effect
Answer: Alcohol will boil off first
The boiling point is 78.37 °C
There will be some water but the ratio of alcohol in the vapor phase will be higher than the liquid.  Water and alcohol are azeotropes so things flop at about 70% alcohol.
The size is not that much of a factor - hexane is volatile.
wiki
Table salt (NA CL) is not much more volatile than a rock
melting point 801 °C (1,474 °F)
boiling point 1,413 °C (2,575 °F)
wiki
The lowest vapor pressure I could find is at 759.88 °K = 486.73 °C
1.88322997019E-006 kPa
Vapor Pressure of Sodium chloride
The vapor pressure of water is 101.32 kPa at 100 °C
Water is 53,801,182 times more volatile at 100 °C than salt at 486.73 °C
Salt is dissolved in water but that does not make the salt more volatile.
Basically no salt evaporates.  With very rapid boiling you might get some entrainment.   The vapor phase is going to have essentially not salts or minerals as they are solids are at 100 °C.
Take a quart of water and add a cup of salt.  Put it on the stove and let all the water boil off.  You will have a cup of salt.
Comment: Comparing the melting point/vapor pressure of *solid crystalline* NaCl to the one of dissolved ions seems a bad idea to me.
Comment: @Paparazzi Wikipedia disagrees with your definition of solution. As above: https://en.wikipedia.org/wiki/Solution#Liquid_solutions
Comment: @Sanya OK seems like a bad to you.  That is the vapor pressure of salt.   With heat applied to pure salt it does not disassociate before melting and/or evaporating.  Those ions don't see the don't see the light of day (touch air).  The ions only exists surrounded by water molecules.
Comment: Although I kind of agree with @Sanya, this answer _does_ illustrate intuitively why alcohol dissolved in water _does_ evaporate (which was also mentioned in the question). It's a liquid at the relevant temperatures.
Comment: @oerkelens Alcohol is not dissolved.  It is mixed.  It is the same molecule.
Comment: Alcoholic beverages are solutions of ethanol in water:  https://en.wikipedia.org/wiki/Solution#Liquid_solutions
Comment: @HardScale Solution and dissolved are not the same thing.  The alcohol is still the same molecule.
Comment: @HardScale Semantics that has no effect on my answer.  The alcohol molecule is whole.
Comment: @Paparazzi -- Sugar, like alcohol, dissolves in water without any molecular change.
Comment: @DavidHammen True.  Still does not change may answer.
Answer: There need to be clear distinctions between forces holding atoms (charged or neutral ) together and molecules (e.g., water, H$_2$O; Salt, NaCl) together. It is ionic or covalent bond that holds atoms together.
Covalent bond:
Two processes for the formation of water molecule.
1) Two hydrogen atoms form H2 molecule, i.e,
H + H = H$_2$;
2) 2 hydrogen molecule and 1 Oxygen molecule form 2 molecules of water,i.e.,
2H$_{2}$ + O2 = 2H$_{2}$O)
Ionic bond:
Salt, NaCl if formed from 1 sodium ,Na$^+$ ion and 1 chlorine ion, Cl$^-$, i.e,
Na$^+$ + Cl$^-$ = NaCl
An attractive or repulsive force binds the molecules together (e.g., more than one H$_{2}$O molecules). This force is different from ionic or covalent bonds because it binds neutral molecules or atoms together and is called van der Waals force (wiki). This force ceases to exist when the molecules are further apart.  During neutral and equilibrium condition, the water molecules and the dissolved salt get bound by van der Waals force. Additional thermal energy hence would create vibration and weakens this force between the molecules. Once this force weakens,  H$_{2}$O (molar mass, ~ 18g) is much lighter than NaCl (molar mass, ~ 59g). Compare it with the molar mass of dry air (Nitrogen, and Oxygen and other trace gases), ~29g. So, water is lighter than air hence buoyed up into the air leaving behind the heavier NaCl.
In conclusion, it is not covalent or ionic bonding that brings about phase change. It is rather van Der Waals force (the force binding molecules together) that weakens when the molecules are not close enough by applying additional thermal energy (e.g., water starts to vaporize at 100 $^o$C and hence the H2O molecules fly into the air so easily because of their lighter weight than air).


What functions & features should I look for when buying a multimeter?

Question: Going to be used for car maintenance/restoration work and around the house repairs.
Comment: I'm asking what multimeter features are relevant to auto maintenance... how is that offtopic at all?
Comment: Very offtopic - suggest migration to electronics.se
Comment: Hmmm - I guess I see your point, however the whole point of a multimeter is it does everything the hobbyist should need. Will add an answer with some specifics.
Comment: Ummm... Don't most multimeters do the same things? (Volts AC/DC, Amp, Ohm, Conductance, and sometimes Continuity).
Comment: Digital automotive multimeter LCD automotive scanner EM133A.    Not all multimeters are the same.  I have three meters the one listed I use on my cars/engines.
Answer: Core functionality of a multimeter:
Measures Voltage - the majority will cope here, as you typically are only dealing with 0 - 12 volts across most areas. You aren't going to need it to measure high tension things such as spark plugs, as you can check them using far simpler methods (such as a spark from engine block to removed spark plug)
Measures Current - currents in automotive circuits and audio circuits can be very high (4 or 5 Amps in a headlight circuit, 100s of Amps to the starter), look for a multimeter with high current capability (2 to 10 Amps isn't too hard to find).
Measures Resistance - you'll probably find the most useful part of this is an audible continuity checker for checking cables deep in the bowels of your car
Frequency - less common on multimeters, but can be useful when working out speed/timing issues
Also make sure it is water resistant, and ideally comes in a rubber housing (as per @CodeBlend - Fluke are generally a robust and accurate brand to go for)
Anything more, and you're likely to need a computer with adapter and software to look at your ECU.
Comment: I like to have a digital and an analog on hand.  Digital is more precise, but analog lets you see trends/changes better.
Answer: While I've got quite a bit of electronics and mains test gear, I just got what I missed for automotive use - a multimeter with a clip on DC amp function.  On vehicles currents are often quite high and it's nearly always very difficult to insert a meter into wires.  Fluke would be nice but are expensive, so I got a small Uni-T model.  Seems to do the job.
Comment: Many clamp on amp probes output either a scaled current or a voltage, and so can be used with any meter. I've gotten some very good deals on used Fluke meters on e-bay.
Answer: Ohm per volt rating the higher the better, Digital are minimum 1 M ohm per volt -Maximum 10 M ohm per volt.  Analogs are in range of  k ohm per volt- more loading of the circuit resulting in a lower than actual value. The frequency function probably would be worth not much as tach signal are pulses and would be read better with a scan tool. The frequency function might be good for audio or steady sine wave. AC and DC function for current and voltage. An Ampclamp (essentially a current transformer) would be on my wish list.
Comment: Hmm, a current transformer type ampclamp will work with AC only. Since there's not much AC in a car, put a more expensive/complex DC ampclamp on your list ;-)
Answer: I know a couple of bits and pieces but not enough to recomend, here is a forum with some people that sound like they know thier stuf;

I hear Fluke meters are the business. But for 90% of people just go and drop $50 or something at a decent
  tool store.
Comment: Given the choice between a 5 year old fluke off eBay and a new cheap unbranded DMM with the same features, I would take the fluke every time. They stay in calibration for decades and can take some serious abuse. Few other DMMs will survive being thrown around a workshop as well as your average fluke.
Answer: A couple of other features worth having are duty cycle measurement and a diode test function. The Fluke 87/88 meters have this and have been around long enough that you can often find good deals on them used.


What is the name for this round metal drain cover?

Question: Rainwater drains from an acre uphill from us into an underground system that has been in place for 50 years.  It works fine, except that the 16-inch round metal cover for the drain has rusted through.  What is the name of this round piece, almost like a city sewer cover, but smaller and thinner?  Without the right name, it's hard to find a replacement.  Any suggestions on what it might be called?
Comment: I would say "I need a 16" round outdoor iron drain cover."
Comment: A picture is always helpful.
Answer: Sump cover. Technically what you have is a Rainwater Collection Cistern, so Cistern cover, Cistern access cover or Cistern hatch cover all would apply.


What is the difference between meaning and denotation?

Question: In programming language semantics, it is often heard that people talking about meaning and denotation.  They seem not to be the same.  What is the difference?  Is the former associated with operational semantics while the latter with denotational semantics?  Thanks.
Comment: Can you cite a source that does this, please?  In my experience, meaning and denotation are used to refer to the same concept in programming language semantics literature (though, in Philosophy, they are used in different ways, as Neel explains below).
Comment: @UdayReddy: The question happened to come to my mind.  I can not recall where I got it, probably from philosophical texts.
Answer: "Meaning" is used in a broader way than denotation is.
The original dichotomy, inherited from logic and philosophy, is between "sense" and "denotation" (which philosophers call "reference").
This distinction can be illustrated by Frege's original example. He noted that phrases "the morning star" and "the evening star" referred to the same object --- the planet Venus --- but that the sentence "the morning star and the evening star are the same planet" actually conveys some information to a reader. He suggested that the meaning of a noun phrase can go beyond the actual object it denotes, including something about how it presents the object it denotes.
Similarly, in a programming language, the expression $8 \times 7$ is not the same as the expression $56$, even though they may be (ought to be!) completely indistinguishable by any client program. But even though they are indistinguishable, they are not the same -- when evaluating the two programs, your machine does a multiplication in the first case, and doesn't in the second.
When building a denotational semantics, we try to build a model of a language in which indistinguishable programs denote --- refer to --- the same mathematical object.  The goal is to simplify reasoning about the behavior of programs, since we can reason about the denotations, the mathematical objects, without having to worry about the details of how the program is presented. This lets us avoid having to deal with aspects of the meaning of programs that are not of interest to us.
The way sense and denotation relate to operational semantics is more complicated, and different. I may extend my answer later to cover this, but I have to run now. :)
EDIT: Okay, I'm extending this answer now.
The connection between "denotation" and "reference" is pretty much exact, and it's exact because the people who invented denotational semantics (e.g., Scott and Strachey) were quite consciously appropriating ideas from philosophical logic as part of their project.
To understand how meaning and operational semantics relate, it's helpful to recall the philosopher Michael Dummett's notion of a "meaning theory" and how it differs from a "semantic theory".
In Dummett's terminology, a semantic theory is a compositional way of relating  sentences to determinate mathematical objects. In logic, the meaning of a sentence is its truth-value, and it is determined from the truth-values of its constituents. Denotational semantics of programming languages uses a much wider variety of mathematical objects, but it works the same way -- we give the meaning of a program term in terms of the meaning of its subterms. So in Dummett's terminology, denotational semantics offer semantic theories of programming languages.
A meaning-theory is also a compositional way of relating sentences to mathematical objects, but in addition it contains an account of what justifies the relationship between the sentence and the mathematical object. He developed this idea in order to understand how intuitionistic mathematicians understood the notion of truth. In particular, they had a compositional account of the meaning of logical connectives, but did not give them semantic values in the same way that classical logicians do. For example, in the Brouwer-Heyting-Kolmogorov account of intuitionistic logic, truth is defined in the following way:

A canonical proof of $A \land B$ is a pair $(p_1, p_2)$, where $p_1$ is a canonical proof of $A$ and $p_2$ is a canonical proof of $B$.
A canonical proof of $A \vee B$ is a pair $(i, p)$, where $i$ is either $0$ or $1$, and if $i$ is $0$, then $p$ is a canonical proof of $A$, and if $i$ is $1$, then $p$ is a canonical proof of $B$.
A canonical proof of $A \to B$ is an effective procedure, that takes any canonical proof of $A$ and computes a canonical proof of $B$.
A canonical proof of $\forall x.\;A(x)$ is an effective procedure which takes a numeral $n$, and computes a canonical proof of $A(n)$.
A canonical proof of $\exists x.\;A(x)$ is a pair $(n, p)$, where $n$ is a numeral and $p$ is a proof of $A(n)$.

A proposition $A$ is said to be true when it is possible to give a canonical proof of $A$.
Now, note that this definition connects propositions and truth values, but the connection must be justified by the possibility of giving a canonical proofs.
Operational semantics enters the picture via this notion of justification. An operational semantics is just a description of what an abstract machine does. After we give a denotational semantics, we generally want to show that the denotational semantics is faithful to the operational semantics. This property is called adequacy (along with its big brother full abstraction), and it exactly amounts to giving a meaning-theory that connects abstract machine states with denotational objects, which is closed under the reduction of the abstract machine.
This is actually not the whole story, since what I've laid out here is how to connect operational and denotational approaches via a realizability model. Type theories can also have proof-theoretic semantics (indeed, this prospect was what Dummett was most interested in), but I have not explained that connection in this post.
Comment: Thanks for the nice explanation.  Looking forward to the expansion covering their relations to operational semantics.
Comment: Great explanation, Neel.  Thank you very much.  So if I understand correctly, the so-called meaning theory is more formal.  In the case of intuitionistic logic, truth is defined proof-theoratically.
Comment: Meaning-theories aren't necessarily more formal; a denotational semantics is completely formal mathematics! A semantic theory says an "$X$ equals a $Y$", and a meaning theory says "$X$ is related to $Y$, because of $Z$". If you say $X$ is $Y$, you don't supply a justification because it's an equation. Anyway, *The Logical Basis of Metaphysics* is a really fantastic book, and it's well worth persevering through Dummett's ponderous philosopher-English to read it.


Is a Rubik's cube an appropriate gift for a 15-month-old child?

Question: I am planning to buy some meaningful toys (puzzles, learning toys) to my friend's daughter. She has completed 15 months. Would it be appropriate to buy Rubik's cube. I would appreciate other toy suggestions as well
Comment: If you want a gift that works for a baby, and is also a puzzle for adults, consider the Towers of Hanoi.
Comment: From personal experience, I'm unsure if it's appropriate for a 42 year old *adult*...
Comment: My 18-month-old *loved* to play with my Rubik's Cube. She can't use it as a puzzle, but it comes to pieces quite entertainingly and FWIW that's as good a reason as any to have it. The only reason I'd say it's not appropriate at this age is a) if you expect them to actually understand it or b) they might choke.
Comment: A 15 months old child? I don't know, but never underestimate! Here is a video of a 35 months old child solving a Rubik's cube in an extremely short time. https://www.youtube.com/watch?v=Slzg2zIPVG8
Comment: @200_success Have to agree. This was a fairly standard toy for kids when I was young. They were typically made of soft plastic rings instead of anything hard, but the idea was the same. I'm sure I could find some of the rings if I looked hard enough.
Answer: At 15 months old, a rubik's cube would not be appropriate.
First, it's kind of a complex puzzle.  Most adults can't solve it.  A 15 month old is going to see it as a brightly colored cube and nothing more.  She will get entertainment value out of it by probably trying throw it or eat it (the stickers aren't good to eat and the individual block pieces are choking hazards).  She won't even understand the goal of a rubik's cube, much less be interested in accomplishing it.
Second, most rubik's cubes I've seen are small enough the fit comfortably in an adult's hand.  Being so small, she won't have the muscle control to really handle it properly.  She won't be able to precisely turn the sides of the cube, much less line it up to be able to turn another side.
Kids at that age generally need bigger toys that require less fine motor skills.  Go google toddler toys.  That should give you a better idea what to look for.
Comment: Just @Becuzz they can't solve the puzzle doesn't necessarily mean it is inappropriate.  At 15 months, the color squares are good for helping their eyes develop, and the fact that they can change it helps also.
Comment: @SDsolar: I  agree with you on saying "If they  can't solve the puzzle doesn't necessarily mean it is inappropriate", However considering the motor skills (Muscle control) and Choking hazards, I also feel it may not be appropriate.
Comment: I'd disagree that they're complex puzzles. They're fairly simple; it just takes a lot of time to learn how to solve one. However, yes, it is too difficult for a 15 month old to hold, but can be suitable for young children with good motor control.
Answer: I would not recommend this as a toy, but for a different reason.
As a brightly colored geometric shape a Rubik's cube would probably be appealing to small children, and at that age they will likely try to put it in their mouths.

Many cubes can be dismantled into separate pieces, which could be small enough to be swallowed. Also, some cubes use colored stickers for the faces which can come off and also be swallowed. That is a strong reason to avoid these as toys in my opinion.
Comment: @apnorton never underestimate the ability of a toddler to find the weakness of anything with moving parts. :D
Comment: With majority of qubes I'd expect them to be dismantled pretty soon. Twisty behaviour looks interesting, but if one side is halfway turned it provides handhold to tear the corner away, and then you can tear the qube into pieces. Definitely not something a small child (small enough that choking hasard is an issue) should play alone with. I've added a pic to show size of separate pieces.
Comment: @barbecue sometimes not even moving parts are needed. One of our family's toddler dismantled a wooden kitchen chair in 3 minutes when no-one was looking at her.
Comment: @Daerdemandt The standard Rubik's construction makes it *very* difficult to tear off a corner in my experience.  Instead, you twist the side halfway and must then pinch (somewhat hard) on the "edge" piece and pop that out.  That said, I still think there's too much of a risk for a young child who'd put such things in their mouth.
Comment: I was in my mid 20s before I discovered how to take them apart.
Comment: My now 8 year old took my oldest son's completed Rubik's cube apart in an instant (for the 1st time of many) when he was about 2. He probably would have eaten it if his brother hadn't forcefully evicted him out of the room. It is definitely a choking hazard, but would be fine with *supervision*. BTW- I now have 2 kids who can complete the cubes: one by solving it "properly" and another who does it by taking it apart and putting it back together w/colors aligned, if the pieces don't get lost.
Answer: There are huge soft 2x2 rubik's cubes for toddlers.
Like this one: Jumbo 12157 - Rubik's Baby - My first Cube, Kleinkindspielzeug
They are soft and not easily breakable.
There is a youtuber called "redkb" who gave one these as a present to his nephew if I remember correctly for his 2nd birthday. So maybe that could be an alternative for you?
Comment: It can't hurt. I think of toys, food, everything we do with children as an introduction to other experiences. It's a buffet of experiences. Your child may or may not like something, but without an opportunity, they can't choose anything they don't know about. If your kid likes trains -- it is because somehow s/he was introduced to that experience. Introduction doesn't mean they will love trains, it means that they are able to.
Comment: Looking at [the video](https://www.youtube.com/watch?v=IKR1GPfaMHQ) you mentioned, apparently there are two kinds of soft Rubik's cubes for small kids: the one you linked to, which is basically a plush toy made up of 8 cubes connected by elastic, and [this one](https://www.amazon.com/Rubiks-Soft-Cube-Plush-Activity/dp/B00H1LB0Q4), which is an actual working 2x2 Rubik's cube, just with soft padding over the mechanism, and is recommended for age 3+. Confusingly, both seem to be sometimes marketed as "My First Rubik's Cube", even though the latter one actually says "Rubik's Soft Cube" on the box.
Comment: Welcome! I think even at 2, these cubes are not puzzles, but just blocks that are coloured brightly. Nothing wrong with blocks.
Comment: You are probably right, but maybe they really like it, like a stuffed animal and become more open for these cubes later? I remember my niece playing with stuffed horse toys all the time and she started horse back riding by the age of 3. Now with 7 years old it is her favorite hobby.
Comment: @Ilmari Karonen You are right! I didn't look at the link for too long and just searched for "My first Rubik's Cube" Thank you for clarifying!
Comment: Whether the child perceives it as a puzzle is immaterial. If it is attractive and safe to play with, it is appropriate.
Answer: No, at 15 months this doesn't make sense.
I'd recommend a book with little flaps that show pictures underneath. These are fun for kids that age. Pick a book that shows colors, numbers, animals, etc.
Activity books that ask the kid to find objects in the picture are also appropriate. That way parents can say "where is the horse?" and kids learn the words and going from language to picture.
Answer: I agree with Becuzz. The child at 15 months will simply ignore the toy. If you think it encourages intelligence, you'd be incorrect. It seems counter-intuitive perhaps, but truly it makes sense.
Accomplishment makes learning fun and is encouraging. There are hundreds of great learning toys available. Bright colours, safe-size pieces and basic lessons are the way to go. Manipulation, colour/shape matching,  shapes into holes, patterning, sorting... all these activities are appropriate.
Answer: I would recommend a Rubik's Cube for a 15 month old if, and only if, the parent (or nanny or other constant companion) is able to easily solve the cube already.
This is a slightly odd answer, but I do have some experience: I can solve a Rubik's cube in under two minutes every time (under a minute if I hurry) and my three-year-old son has enjoyed playing with my Rubik's cube for the last year and a half.  He doesn't play with it very often, as he has other toys that are of greater interest to him personally—but he enjoys scrambling it (and has for many many months).
Also, if I do one or two quarter turns away from the solved state and hand the cube to him, he can (if he feels like it) reverse the turns to solve the cube.
So for most 15-month-old kids, no, this would not be an appropriate gift.  However, there are exceptions to that.

As for other toys, personally, I would go with almost anything from Melissa and Doug, but probably the wooden block set to start with.  The set is marked ages 3+, but younger kids (yes, even down to 15 months) will enjoy picking up the smaller blocks and learning to grip (developing dexterity), and these blocks are durable and will last for years and years and years.  (Actually I expect they'll last for generations, if you keep them in the family that long.)
Comment: I quite like this answer. Makes a lot of sense.
Answer: My two boys, 8 and 10, just received Rubiks Cubes for Christmas. They're both above average IQ ("Gifted"), but they've also quickly become frustrated with the puzzles and given up on them.
These really are not age-appropriate for young children, certainly not for a toddler of 15 months. There are plenty of meaningful puzzle toys available for younger ones, like shape and colour matching puzzles, which would be much more developmentally appropriate for a young one.
Comment: Hi and welcome to Parenting SE!
Answer: From my personal experience I started to be interested about puzzle and game like Rubik's Cube around 8 years old.
I found an interesting article that may help you in your research and explain what kind of games a Children Between 12 to 18 month can be interested in :
http://www.babycenter.com/0_toys-for-children-12-to-18-months-old_5688.bc
Answer: Consider the stickers that are on them, or the paint. Maybe they don't have these stickers anymore (my old one has them) but if swallowed that wouldn't be good.
Just because something seems safe doesn't necessarily mean it is.
Answer: No, a Rubik's cube is not appropriate for such a young child.
Obviously, they wouldn't understand what the puzzle is and what the goal is, but that wouldn't matter if they could treat it as just a brightly coloured moving cube. However, they can't treat it as just a brightly coloured moving cube.  Rubik's cubes actually have a pretty limited range of movement. The only thing you can do to one is to rotate one of the faces 90°, to make it look like a cube again. If you've partially rotated a face, the only thing you can do is either fix that face or rotate the opposite one. At fifteen months, a child can't even figure out that the square block doesn't fit through the round hole; they're not gonna figure out that the brightly coloured moving cube requires you to rotate faces by 90° at a time.
Add to that the fact that new cubes are quite stiff and are a good deal larger than a toddler's hands and I'd question whether a toddler would be able to manipulate the cube at all.  Net result: it's not a brightly coloured moving cube; it's just a brightly coloured cube.
And then we get the safety problems that have been covered in plenty of other answers: peeling stickers and the cube coming apart. If all you wanted to give the child was a brightly coloured cube, you could give them one made of a single piece of plastic that isn't going to come apart. The manufacturer says that the cube is suitable for children of age 8 years and up. Partly, that's because they think that younger children won't be interested in or understand the toy but, partly, it's because it's not built in a way that's safe for much younger children.
Answer: Rubik 3x3 failed my 5 year-old miserably; he is simply not interested. But 2x2 is more appropriate for him. I bet some other kids can do 3x3 at this age. A 15-month old will most probably have difficulty twisting/rotating the cube pieces. My kids can barely tear candy wrappers at 3 year old.
Answer: I don't think a Rubik's cube is an appropriate gift for a 15-month old child. However, I think you could give it to the child's parents, and tell them, "Let her play with it when you think she is old enough."
That might be age 3, that might be age 6, that might be age 9. It really depends on when the child will take an interest in that sort of thing, and the parents are the best ones to make that judgement call.
You don't want to give the child too many things that will be tucked away for months or years (that becomes a storage hassle), but, unless the family lives in a small apartment, I don't think there's anything wrong with a few things being tucked away in a closet for later use.
Insofar as other meaningful learning tools go, a globe might be a good suggestion. It's not a toy per se, but I've seen several young children take an interest in geography at an early age.
However, if you're looking for an age-appropriate toy that the child will enjoy now, consider something more along the lines of a shape ball:
Answer: No, 15 months too young. I'll say above 3 years for the 2x2.
My son start playing the 2x2, and he is 4 years old. He was able to solve it in two days.
There also a easier versions that are only two sided. The rest of the sides are same colors. I think that it is a good gift for a little child but not that young.
Answer: My toddler is 15 months and loves to hold his brothers rubix cube. He enjoys twisting the sides back and forth in between his hands. It's quite cute how he will walk around doing this, and is thoroughly entertained by it.
Answer: This is completely age appropriate.  Toddlers love blocks, toddlers love colors, and toddlers love moving things.  Bing bing bing.
Even better toddler's parents hardly ever get a toy that they may play with.
What all of the answers on here are missing is that a toddler isn't going to understand what should be done with a Rubik's cube.  They don't understand that they need to solve it.  It is just a group of blocks that don't fall apart...  Until the toddler figure out how to tear the thing apart and figures out the easiest way to solve a Rubik's cube.
(My opinion is biased as I got one for my second birthday and have pictures from 80s of me tugging it around from ages 2-6 and solving it at 4.)
Comment: @DavidRicherby, It doesn't matter that the child doesn't understand how to move the parts at 15 months. At some point it will move it just right by accident and then become curious, move it this way and that and see what works. Or the child will simply figure it out (not the puzzle, but how to move the sections). At 15 months my first son was even more entertained by the packaging of the toy than the toy itself (even the age-appropriate one), so there is no doubt it would receive just as much entertainment from a colorful cube (and its packaging) - or virtually anything that's new for him.
Comment: I'd agree, except that I think a 15 month old would probably find the sections of a brand new Rubik's Cube difficult and frustrating to manipulate.  Granted, I haven't played with one in decades, but I remember them taking a bit of pressure to move.
Comment: I agree that the child doesn't need to understand that the cube is a puzzle and that it can be treated as just a brightly coloured moving toy. But I don't think it's an appropriate brightly coloured moving toy for a 15-month-old. The cube actually only has a limited range of movement: until you return it to a cube shape, you can't move it in any other way. 15-month-olds can't even understand that the square block doesn't fit in the round hole; they're not going to understand how to manipulate a cube. And cubes _do_ come apart, into pieces that a frustrated 15-month-old might try to swallow.
Answer: I don't belive in "age-appropriateness" as a parent. I believe what I see and if I see my child can handle something then I let him. A Rubik's cube is a colorful cube. At 15 months old the child might not be able to solve a Rubik's cube, but that doesn't mean it won't be a fun toy. I would definitely go with it and not mind what others think about it being appropriate.
My thinking is that the child will gradually discover how the cube works, how to rotate sides, how to take it apart and put it back together, etc. In time it will discover all on its own how to solve it. It's amazing what children learn when you give them free, unstructured play time.
Comment: @NikolaNovak: it's not just choking hazard, if you give a stickered cube, that's colored paper and glue with who knows what it is made from. If you give stickerless cube, each corner and edge pieces can be deconstructed further into three and two pieces that's very small and also somewhat sharp.
Comment: @NikolaNovak: Also, a 3x3 Rubix cube isn't a toy where you can discover the solution through unstructured playtime. The inventor of the Rubik's cube took a month of intentional study to figure out how the pieces move together before he can do his first solve. That's not to say that you can't **teach** a 2 years old how to solve a Rubik's cube, because it's been done before. But if you just leave someone with a Rubik's cube to solve a cube on its own, giving just the minimal instruction so they know the goal of the game, chances are they'll just lose interest quickly.
Comment: @LieRyan, you absolutely can find the solution through unstructured play.  Probably not at that age—but that's irrelevant.  As this answer states, it is still a fun toy.  (If you as a parent can solve it, it works much better as a fun toy, though.)
Comment: If the downvoter could explain the reason for the downvote, I'd be happy to add clarifications/explanations if needed.
Comment: I didn't downvote, but according to other responses, if you want votes I'd suggest you to explain why a Rubik's cube doesn't mean a choking hazard to toddlers.
Comment: Uhh, because it's too big? Even when taken apart the pieces are too big to be a choking hazard.
Comment: @LieRyan, I'll admit I may be wrong on the suffocation hazard matter as I have ever only had the low-quality cubes in my hands and they had no small parts. Still, "hazard" in "suffocation hazard" means unavoidable danger for the manufacturer, not the parent. The manufacturer could not have avoided using these small parts, but that doesn't mean the parent is powerless to prevent it while still letting their child play with the toy. As for solving the cube, I disagree. I might be biased towards self-motivated learning such as in Montessori and Sudbury models, but with my kids it's worked so far.


How I warm my feet in the winter season?

Question: My feet can't warm in socks, shoes, or even under a quilt. I am not feeling well in the winter season because of this problem. How can I warm my feet in winter?
Comment: You will find your answer here:
https://outdoors.stackexchange.com/questions/56/how-can-i-stay-warm-in-subzero-0f-18c-weather?noredirect=1&lq=1
Answer: Jogging is a one good way, hot tea, warm sweater.
Answer: Move your feet around, even if it's just wriggling your toes. Keep your surroundings warm (don't stay outside too long or keep the thermostat too low). Essentially, you need to keep your blood circulating through your feet normally.
Answer: First of all start with warm feet. Rub them with your hands throughly to get blood flowing to your feet. If that is ineffective➖put them in a basin of warm water while wiggling your toes.
Continue in warm water until they feel warm. Dry them off immediately upon removing them from water.
Once dry put on really good wool socks. Merlino wool are the best. They're expensive but nothing will keep feet as warm.

My favorite sock are a brand called Darn Tough Socks. They are pricey but come with a lifetime warranty. If they wear out➖return them for a brand new pair. They are available from the company online or many other retailers.
Finally➖if you have circulation problems you should mention it to your doctor. It could be a sign of an underlying health issue.
Answer: I am answering with science. naturally the cold feet means the blood is not enough for the warming process or the measure is too down. so if you had wear sucks, its not from measure!I think its better to check it with a doctor or do a Doppler Ultrasonography.
*if your feet is cold after you eat food or something in winter, its just safe and normal.
Answer: The best solution I've found is to use bags of wheat kernels heated in the microwave.  Get about 4-6 cups of raw, whole wheat kernels from a bulk grocery store, then sew them up into a flannel bag so they are loose inside.  Microwave them on high for about 2 minutes for each bag (I use 2 bags so 4 minutes for me).  They come out of the microwave toasty warm with moist heat that will last for 20-30 minutes.
They can warm up your feet, or the bottom part of your bed where your feet go, or sit them on your lap while you work at the computer.  They are magical!  They also last many, many re-heatings so they are a permanent solution!
Answer: When my feet are impossibly cold, I put them in warm water (or take a warm shower) in order to bring them up to a "normal" temperature. From there, I can use more conventional solutions like warm socks or slippers. Additionally, I recommend a heated blanket for nighttime.
Answer: When I was a boy, we used a bit of powdered cayenne pepper in our socks and shoes. It did work to warm our feet; just start off with a little until you get a feel for how much to use.
Answer: Here are some things you could do:

get some warm fuzzy socks as i call them, the ones that are just soo soft and fluffy
sit in front of a fireplace or other source of heat that is coming torwards you
put some socks and slippers into your dryer and when they come out they will be super warm
fill up a bathtub (with hot water of course) and put your feet in there or put them in a hot tub or jacuzzi


Install agp driver on my Fujitsu v6555 laptop using Ubuntu 11.10

Question: My laptop came with Windows7 home basic operating system but I am interested for on Ubuntu.
I downloaded Ubuntu 11.10 and tried to install it using dual boot. I faced a problem with installing it, I solved it using f6 key.
After the installation it rebooted. While booting, I see that my screen is froze. Any ways, I hit my power button and started again using recovery mode. Whenever I use normal mode, I face this problem.
After a week I have learned that my laptop has two AGP card, one is a 12 MB and other 512 MB. 12 MB is installed normally but 512 MB AGP requires a driver. I downloaded this driver to my hard disk in .run format. So, please tell me how to install it?
AGP card model is: NVIDIA GeForce 8200M G
Anyone please help me.
Answer: In Ubuntu the Nvidia card drivers are installed via the system.
In a terminal, type:
<code>sudo jocket-gtk
</code>
enter your password and follow the instructions


about ethereum swarm download speed

Question: Torrents also increase in speed as the number of peers increases. swarm Is the same? This is because dividing the data into chunks is the same.
Answer: In swarm there are at least two factors to consider in this case. Rather simplified:
In a torrent, a "saturated" peer (seeder) would mean a peer that has all the chunks of that particular torrent.
In swarm, nodes are responsible of certain subsets of chunks of all the data chunks that exist in the whole network. A "saturated" peer would here rather mean a peer that has all the chunks it's responsible.
In the simplest mode, swarm nodes takes an opportunistic approach to storing data; they store the data that is most profitable to them. This is the content they currently get the most requests for, because their earnings come from the number of chunks they deliver.
Because of this, nodes will tend to keep chunks which are also outside their responsibility, if they notice those chunks are in high demand.
That means that popular chunks will tend to propagate more, which ultimately means that any path to those chunks will tend to be shorter. And shorter path means more speed.
That said, there are other factors that might influence the speed of delivery, of course, like geographical distribution and node bandwidths. There considerations aren't currently part of the consideration in the swarm architecture. These may just as well be a factor with torrents, but with torrents, since you connect directly to all peers that have the particular chunks you know you want, it's trivial to detect which ones who suck.

about ethereum swarm download speed


What Vim features do you use?

Question: I spend almost all day programming in Vim and I am sure that a lot of you do too.  What features do you use that make your day to day coding that much better?  One that I use
is gv, which will let you reselect the previously selected text. It is great for reindenting!
Comment: For historical purposes, here's a link to the original SO question:

http://stackoverflow.com/questions/95072/what-are-your-favorite-vim-tricks
Comment: Note my comment below, and you won't even have to type `gv`. :)
Answer: :%s/x/y/g
This command replaces all instances of x in the current file with y. This is basically just a find and replace, but I use it so often since I've learned it at work that it has become invaluable.
Also, /search string
then n to navigate through all instances of the search string within the file. Great for doing manual tweaks a lot more easily, especially if you can't apply a rule to the entire file.
Comment: Note that the `%` is where to do the substitution - `%` means "the current file." If you visually highlight some lines and type `:s`, you can do a substitution just in that selection.
Comment: I'm actually working on converting a largish section of our codebase at work and I'm doing it entirely with vim regular expressions (so far).  It works really well!
Comment: Add 'c' to the end of that to make the command interactive. e.g. :%s/x/y/gc
Answer: == does nice auto-indenting on the current line.
Normally, though, I use = with a motion, like =G to indent to the end of the file, or =i} to indent inside the current set of curly braces.
Comment: Also keep in mind >> and << which can manually do (un)indenting.
Comment: @Frew - yep. Also, if you add `vmap  >gv` and `vmap  <gv` to your `.vimrc`, you can indent and unindent with Tab and Shift-Tab, respectively, **AND** it will go right back into visual selection mode so you can indent or unindent further.
Answer: =% for auto-indenting everything within a block of code.
Comment: Oooh!  That's new to me!
Comment: That works if your cursor is on the beginning `{`. If you're inside the block, you can do `=i{`, for "indent inside the curly braces."
Answer: The :! command - invaluable for lsing, and the "sudo tee" trick.
I've been asked to explain the tee trick. Basically, it allows you to save a text file with admin priveleges, even if you didn't start VIM as root:
:w !sudo tee %

Comment: You might want to explain the "sudo tee" trick in here :-)  Also I like to do :!sort after highlighting variable definitions and whatnot.
Comment: You can really turn Vim into a great "scriptable" editor using :! and some shell/Python/Perl/other scripts.
Comment: I actually have an alternative to `!ls`, which runs a `vnew`, outputs `r!ls` into the new buffer, and shrinks it horizontally. I can't be bothered to remember all of the files in a directory with over three in it ;)
Answer: Use * in command mode to search for the word under the cursor.
Comment: And don't forget it's sister command, #, which does the same thing but goes backwards instead of forwards!
Answer: .

Hitting the . key repeats the previous command. Lovely for, say, editing an .ini, or so.
Comment: this is surprisingly powerful, but it takes a bit of vim-ing before you can really get good with it.
Answer: syntax color highlighting
Answer: I am always using gq to re-do line breaks on email, text files, etc.  Really useful when replying to email (I use pine) and editing multiple previous replies.
Comment: Oooh, I'd totally forgotten about this!
Comment: Why, oh why, can't the more popular email clients support similar functionality?
Comment: Recently I am using gw instead of gq because it keeps the cursor position
Answer: Where to start... Here's the things I can recall I've used in the last 5 minutes or so.

NERD Tree - File exploring.  Makes VIM more like an IDE.

One huge thing for me is the ability to cd to a directory and then drop to a shell prompt through my shell mappings (below).

ci for emptying whatever you're stuck between.
:! for launching standard apps.

I have mappings for launching a shell prompt, mysql client, apache log files, etc.
Subversion integration is always nice.  Quick diffs, stats, etc.

:abbr for making repetitive typing of large blocks go away.
Tabs.  Need I say more?
Splitting out files, always good.  :Sex is always nice.
:set paste! to keep from having auto-indent run amok.
Comment: I use all of these except for abbr.  I tend to make a lot more macros than abbreviations.
Answer: ZZ save and exit (instead of :wq!)
Comment: Huh? What about **x**?
Answer: I heavily use following commands while writing or traversing C/Tcl/Perl code:
copy-paste code
CTRL-f and CTRL-b for page forward and backward traversal
% for block-by-block traversal
^  goto start of line
$  goto last end of line
start selecting code using command v (visual mode) and any of the traversal key above
y for copy
p for paste
s to delete a character and goto insert mode to type new text.
Code level traversals  (requires coding style discipline)
]] for start of next function
[[ for start of prev function
CTRL-] to jump to definition of a variable/function/macro if tags are available.
Search
*  => search word (or text selected using v) in forward direction
#  => search word (or text selected using v) in backward direction
n  => execute previous search command in forward direction
N  => execute previous search command in backward direction
All the above commands can be prepend with a number to signify how many times to execute it. The realization of the power of this additional dimension comes slowly as one uses vim more and more and challenges oneself to improve.
Comment: Ah, ]] and [[ are new to me. That's cool!
Answer: I'm a former user of TextPad, and had memorized many of that program's accelerator keys. One of the first things I did in Vim was learning the map function to keep consistency (F5 search, F8 replace, etc.). I created my personal colorscheme, and borrowed alot from others' vimrc files. Viva Vim! Configurable to any degree.
Answer: I just enter Text. Everything else is just ... Sugar.

What Vim features do you use?


Is it possible to both move and stabilize a two wheeled robot with no gyroscopes?

Question: With two wheeled robot like this one, I have managed to stabilize it while keeping it stationary. This was done using a digital feedback control system by reading the position of the wheels to determine position, and the natural back electromotive force from the wheel motors was used in the feedback loop to determine velocity. It was kept stable with a PID controller, which was designed using a root locus algorithm to keep it stable and modulate the performance parameters (such as percent overshoot, settling time, etc.). I wanted to attempt to keep it stable while simultaneously propelling it forward, but I couldn't figure out how to go about designing a linear controller that could do that. Is it possible to both propel the robot forward and keep it stable using a feedback controller on the wheels, or is a gyroscope necessary?
Comment: Is there any particular reason why you can't use a gyroscope? Just out of interest.
Comment: This is about an assignment I did my last term. We were assigned the robot and could only use what was given to us. The assignment was only to keep it stationary, but I have simply been curious as to whether or not (and if so, how) it could moved forward and still kept stable.
Answer: You could use other ways of measuring orientation, such as an accelerometer, optical tracking of markers, or a depth sensor pointed at the floor.
Comment: AN optical distance sensor pointing at the floor is a pretty good way to measure the tilt of the robot. Just remember that it will measure the actual tilt, whereas a gyro measures the *rate of change* of tilt
Answer: If you managed to get it stable in a stationary configuration, I don't really see how it would be much more difficult to get it stable for a constant velocity. From a system model point of view it would effectively be the same thing bar some velocity offsets. If the transitions between velocities are not very large it should fall within the range of the natural system perturbations.
Answer: You need some sensors to detect the state of the system.
First linearize the system into a state space form, then consider what sensors you do have. Then check if it is observable. If it is observable, then you can feed the estimated states into your controller.
Currently, it sounds like you are using the wheel position and back EMF (for velocity) as direct measurements. Without checking the observability matrix, I am unsure if the system is observable.
Answer: Mathematically, the fact that you now have rotation (mostly) eliminates that parameter as a possible control parameter.  Basically you'd have to redesign your algorithm to accept a large and variable angular velocity component while still using angular velocity in your feedback.  The less noisy this is, the better the probable outcome simply because you're likely going to apply a differential of position to derive another control parameter.  Or rather that is one way.  So it does look like you need another control input, but it need not be an accelerometer.  You could do a horizon, fixed marker location or even tilt sensors.


Is center tank fuel required to start the 737-800 engines?

Question: I have been doing some simulation flights with the 737-800 and when there is no fuel in the center tank, the engines won't start. Is it like that in real life?
Comment: So you did them in a simulator? In which simulator?
Comment: In X-Plane 11, Zibo's 737-800 mod, I can fly with no fuel in the center tank. :-)
Answer: No, it is perfectly normal to operate without any fuel in the center tank. Until your fuel load is over about 17,000 lbs, the center tank should be empty. That's enough for about 2 hours of flying, plus reserves.
If your simulator requires fuel in the center tank in order to start the engines, it isn't accurately replicating the real aircraft.
Answer: (airliners.net)
Be sure to turn on the appropriate pumps on the lower-left of the overhead panel. The APU can start without them via suction.
Otherwise, it's a simulator problem.
Also see: Why are fuel tanks in the wings filled first, and why are they used last?
Comment: Thanks!Seemed to be a bug and thank you for the extra article!
Answer: If you let the center tank go completely dry you'll get an EMDP malfunction along with an overheat warning.  (See ELEC 2 & ELEC 1 hydraulic pump switches on the overhead panel).
The EMDPs are cooled using what are best described as fuel cooled heat exchangers. The temperature sensor for the EMDPs is monitoring the temperature of the case drain fluid, which reflects the source of greatest heat output on a normal pump. There are a number of events that will cause the EMDP to overheat:

Every time you cycle the pump from OFF to ON, it increases the pump temperature briefly. Cycling the pump off/on repeatedly without allowing adequate time to cool will cause the overheat indication.
Operating the EMDP without sufficient fuel in the main tanks (from memory: 1,675lbs) will also cause overheating because the fuel quantity is insufficient to provide an adequate cooling mass to the heat exchanger.
An internal failure of the pump might also cause the overheat light.
Comment: In the 1st paragraph, you say "center" tank & that's incorrect - fuel in the center tank doesn't cool the electric hydraulic pumps. Later in the answer you discuss the role of the main tanks cooling those pumps, and that's correct. You may want to edit that first paragraph.


broadcom bcm4318 [airforce one 54g] losing connection

Question: I've done everything in the ubuntu forums and in ask ubuntu and I got it working the wifi. the wifi card is an broadcom bcm4318 [airforce one 54g] on a acer aspire 3630. But the wireless connection doesn't stay connected. It loses connection repeatedly. I'm forced to my wired connection. What can I do to get the laptop to stay connected and not lose connection the whole time?
Answer: This helped:
How can I prevent iwconfig power management from being turned on?
It minimized my issue along with uninstalling network-manager And installing wicd instead.  I did this first to install wicd: in terminal, sudo apt-get -yd wicd-gtk wicd-kde, this puts the packages in your apt cache because you will loose connectivity with the next step, apt-get remove -y network-manager, then finally, apt-get install -y wicd-gtk or apt-get install wicd-kde.  I still get disconnects even after doing some things in the link above but WICD seems to reconnect more easily.
Edit: I just saw this as well: will try later: http://ubuntuforums.org/showthread.php?t=1390174


Can taking photo of the moon and/or stars at night cause damage to the camera sensor?

Question: We know that taking photo of the sun can cause some degree of damage to the camera and our eyes. So, are there any damage to the camera (point and shoot / DSLR) when taking photo of the moon and/or stars at night? (Because the moon gets the light from the sun.)
Comment: With regards to the moon getting light from the sun, so does every daytime outdoor (non artificially lit) shot and they're far brighter than the moon
Comment: @Dreamager Well, no, they're not.  The Moon is in direct, unfiltered sunlight (on the bright side).  The atmosphere costs at least one stop, even at a tropical noon, for scenes on Earth.  The only way Earthly scenes can be brighter is if they have a significantly higher albedo than the Moon, which is the color of worn asphalt pavement, similar to an 18% gray card.  Beaches, snowscapes, and light colored walls or fences in direct sun will be brighter, but general scenes aren't.
Comment: @Zeiss Ikon - But the Moon light reflection passes through the same filtering atmosphere to reach the Earth.
Comment: @user10216038 That's why it's Sunny f/16 rather than Sunny f/22.
Answer: The light from such objects is nowhere near bright enough to cause damage to the sensor, however using really long exposures to capture dim distant stars could damage the sensor by overheating.
Most modern DSLRs have heat sensors and cutoffs to prevent this, but if you're using an older camera and keeping the shutter open for hours with an external power source I imagine you could do some damage!
I'm not trying to be alarmist, but I would recommend a series of short exposures (less than one minute) with cooloff time in between for the best results. Multiple exposures can then be stacked in software to reduce noise. Unless you have a tracking mount you'll get star trails with longer exposures so that's another bonus of short exposures.
Answer: The moon is not anywhere close as bright as the sun (it's basically a giant diffuse, grey reflector), and so there is little risk. According to Wikipedia, the full moon at its brightest is about 400,000 times dimmer than the sun. That's 18 1/2 stops!
However, the moon does tend to get overexposed in photographs, since it's hard to fill the frame without a really long lens and space is really dark. As such it's best to shoot in manual mode or bring exposure compensation way down.
Comment: The Moon is in direct sunlight, and is pretty close to an 18% gray card, so Sunny 16 rule works for photos of the Moon.  If you're using a telescope, don't forget to adjust your f ratio for any added magnficiation (from, say, a Barlow lens or eyepiece projection).
Comment: ...or use spot metering on the moon.  That's how I do it.
Answer: This is a repeat of
https://physics.stackexchange.com/questions/25825/can-you-damage-your-eyes-viewing-venus
No, there cannot be any damage, not to the camera and not to your eyes either.
In the case of the moon and/or planets, there is not enough brightness to cause any damage, and the lens cannot increase the surface brightness. In the case of the stars, they are never more than a single point of light, so even with the largest telelens the brightness is too low to damage anything.
Answer: I assume that your question is based on the idea that a lens concentrates light. That way, any light source could be concentrated into an area small enough to make that area exceed combustion temperatures. The good news is, according to XKCD: lenses do not concentrate light.

Except lenses don't concentrate light down onto a point—not unless the light source is also a point. They concentrate light down onto an area—a tiny image of the Sun.

https://what-if.xkcd.com/145/


What is Depth Of Field bracketing?

Question: I understand the concept of (auto-)bracketing, in general. And I understand that exposure bracketing is used for HDR and focus bracketing is used for focus stacking. But I am unable to imagine what DOF bracketing is or what its use could be. Any pointers?
Answer: DoF bracketing is essentially the same as focus bracketing, but rather than change the focus point/plane for each shot, you change the aperture to vary the depth of field.
Imagine you are taking a shot of, say, a cluster of cherry blossoms. You want the background blurred so you open the aperture right up. But this means only part of the cluster is in focus. So you stop down the aperture a little, which gives you deeper DoF, so more of the flowers are in focus, and so on.
Once you've got the shots you need to get the entire cluster in focus, you can put them all together in post - sharp flower cluster and blurred background. Bracketing in small increments means you can get a nice transition between the fore and backgrounds. If you just took one at f/2.8 and another at f/16 it would be tricky to get a natural looking result.
Comment: Yup. Though focus stacking usually refers to photos where the plane of focus has been varied rather than the aperture.
Comment: This is also known as focus stacking. Used often with macro photos
Comment: Can you give examples? I know in practise, you are changing the aperture rather than the focus points, then stacking them. But are the results actually different?
Comment: Yes, the results will look different.
Answer: Depth Of Field bracketing is performed by taking several shots of same scene with different aperture (compensating change in exposure by adjusting ISO, shutter speed or lighting power).
Bracketed images are then used to have a wider selection of images to select the one with most appropriate depth of field in post. Or you could use masking and combine background from wide aperture shot with subject from tight aperture shot.
Answer: In general "bracketing" means taking a series of shots near the settings you or your camera has chosen.
There are two kinds. Exposure bracketing attempts to achieve the perfect exposure (sort of a shotgun approach) while the goal of Depth of Field (DoF) bracketing is to achieve the perfect composition.

Exposure bracketing involves the photographer or camera takeing an exposure at the suggested speed, aperture and ISO, then one or more exposures while varying either the speed, aperture or ISO setting. Usually, there is one or two over and one or two under the suggested by a full, half or third stop.
DoF bracketing can be considered part of the composition and artistic interpretation, something better left to the photographer rather than the camera. First, one exposure is taken at the suggested speed, aperture and ISO settings, and then one or more exposures are taken while varying the aperture and a complimentary change in speed or ISO setting that compensates for the change in aperture. So, two settings are changed not just one.

Canon cameras once had a function also called DoF bracketing that allowed the photographer to focus to select the nearest and furthest points they wanted in focus. This locked in that focus range by setting the aperture even while modifying the other two settings. I haven't owned a Canon or worked at a camera shop since Moses' time so I'm not sure if Canon still uses that terminology.
Comment: The Canon system was called A-DEP mode and is not found on current models.
Comment: "something better left to the photographer rather than the camera" - actually FujiF550EXR is quite good at it.
Answer: I do depth of field bracketing a lot.  I shoot at different apertures to see what background I like best.
On the K-5, it's not that hard to use exposure bracketing as depth of field bracketing when using RAW.  It's close to an ISOless sensor due to it's dark read noise— it's digital gain performance performance is near equivalent to it's analog amplifier gain.  On other sensors, you will get somewhat higher noise at the smaller apertures than manually doing it.  Here are the steps:

Set the camera to take the overexposed shot first
Go to shutter priority and turn auto ISO off
Set exposure bracketing.  Calculate what X.X EV stepsize and number of shots you want to get the apertures you want (too much and you'll hit f/22, which is a bit worthless)
Use -EV compensation so the overexposed shot is at 0 EV, to not clip highlights
Set your shutter to what you're comfortable with regards to motion blur and camera shake, if applicable
Set your ISO such that your aperture is the widest that you want
Shoot your images
In post, set each shot +X.X EV (or use auto tone in lightroom)
Comment: Your answer could be a little clearer that the first shot is taken at 0 EV EC, and that subsequent shots are taken at -1, -2, -3, etc.

What is Depth Of Field bracketing?


How can large data handling be a special requirement for job?

Question: I chanced to see some job requirements of Oracle SQL programmer or C# developer jobs, who want a person who can handle terabytes of data in ETL or data migration.
I have worked on data migration to move data from one system to the other. As a C# developer or Oracle SQL programmer, I am not able to understand how things will be different if large data is involved. (Oracle documentation says that it can easily handle even 8000 terabytes, why do I have to worry about volume then?)
Can someone please advice what is special about handling data migration of large volumes?
Answer: Simply put inefficient algorithms on small amounts of data is trivial.  It take maybe a second longer.  No one will miss that amount of time.  As the amount of data you work with increases, efficiency really comes into to play.  That O(N)^2 loop that took say 5 seconds on a gig of data, now can take hours on 100 gigabytes.  You have to know what to look for before you are done writing the code, because in a large data scenario, there is rarely a "Hey let's try it out and see how it works," possibility.  In scenarios like this it is not uncommon to take an entire day to load the data into memory on the server to handle processing.  You don't get many shots to get it right.
Comment: +1 "Hey let's try it out and see how it works" you can, but you have to unplug your fon :)
Comment: Hours? Try days! ANd locking up the whole system as well so nobody else can use it while it goes on. That's what you can get if you don't know what you aredoing.
Answer: Sadly even writing an algorithm that is O(10n) and writing an algorithm that is O(2,5N) matters in such conditions.
Such jobs require VERY careful planning, excellent understanding of pipelining, parallelization (how the ETL engine will parallize it), Task-Based paradigm and other things. Sometimes even You have to be aware of hardware limitation (how the data is split among disk, how are the partitions and logs organized, do YOu need transactions etc.)
You need to know that an UPDATE is more expensive than insert for example... Lot's of things. You need to think DATA, memory. This is really NOT that easy as it looks like.
luke


How do I know if condiments in refrigarator are good?

Question: no not about cooking my refrige broke  getting a new one tomorrow at what point does all the condiments start to go bad its at 60 degrees and has been for several hours just wondering if I have to start from scratch and throw away everything
Answer: A really accurate answer would require analyzing each individual condiment, but there are some general principals you can apply.
Some condiments would be shelf stable outside of the refrigerator because they inhibit pathogen growth by being:

acidic, like ketchup or vinegar
salty, like soy sauce or Worcestershire sauce
sweet, like jam or jelly, or chocolate syrup
sufficiently dry, like peanut butter

These are not going to be bothered by a day or two outside of refrigeration.   We keep them in the fridge because it extends their shelf life to be much, much longer, on the order of months instead of weeks.
Of course, you should still discard them if you see any signs of mold, unusual wateriness, or strange smells.
Other condiments in the refrigerator such as mayonnaise and salad dressings should be considered subject to the normal rule for how long foods can be outside the refrigerator.   This would normally be a cumulative period of about 2 hours maximum, to be on the safe side.
While normally I would not mention any... more liberal... interpretation of the best recommended safety standards, I will point out that 60 F, while technically in the danger zone, is still moderately cool, and the danger increases exponentially with temperature.   You can assess your own risk, but you may decide a few more hours is still a risk you are willing to accept.
As always, check for off smells, colors, or appearance of mold or other spoilage, and apply common sense.
See also:  How do I know if food left at room temperature is still safe to eat?


When would one use UDP over TCP?

Question: It seems TCP is quite a reliable service with error checking, end-to-end delivery assurance etc/, while UDP is a connectionless unreliable service.
In what occasion would application engineers use UDP over TCP?
Comment: Network engineers don't chose protocols. Application developers do.
Comment: A similar question was asked and answered [here](http://networkengineering.stackexchange.com/a/24313/3675).
Answer: This is a frequently asked question. The answer below is one of the best answers from another site.
https://stackoverflow.com/questions/1099672/when-is-it-appropriate-to-use-udp-instead-of-tcp

In situations where you really want to get a simple answer to another
  server quickly, UDP works best. In general, you want the answer to be
  in one response packet, and you are prepared to implement your own
  protocol for reliability or to resend. DNS is the perfect description
  of this use case. The costs of connection setups are way too high
  (yet, DNS does support a TCP mode as well).
Another case is when you are delivering data that can be lost because
  newer data coming in will replace that previous data/state. Weather
  data, video streaming, a stock quotation service (not used for actual
  trading), or gaming data comes to mind.
Another case is when you are managing a tremendous amount of state and
  you want to avoid using TCP because the OS cannot handle that many
  sessions. This is a rare case today. In fact, there are now user-land
  TCP stacks that can be used so that the application writer may have
  finer grained control over the resources needed for that TCP state.
  Prior to 2003, UDP was really the only game in town.
One other case is for multicast traffic. UDP can be multicasted to
  multiple hosts whereas TCP cannot do this at all.
Comment: "... is one of the best answers from another site." - in which case it would be just fair to at least link to this answer instead of just copying it without giving the source. Here is the source and this answer is a  plain copy and paste: [Stackoverflow: When is it appropriate to use UDP instead of TCP?](http://stackoverflow.com/questions/1099672/when-is-it-appropriate-to-use-udp-instead-of-tcp)
Answer: The answer is as simple as it can get:
speed
TCP, due to its connection establishing and error checking mechanism is considered a slow protocol (although reliable).
While UDP does not have all those time consuming mechanisms and so it is much faster, not reliable but fast. He just streams out the data and does not really care about the receiver getting the whole message or not.
It is actually a trade off, speed over reliability, sometimes you need quick data transmission and you don't care about loosing some packets in the process, like live chat and video streaming.
But sometimes (of course) you need a reliable data transmission for your purpose, something that makes sure the receiver gets the whole message, however a little bit later. Like sending email or chatting in chat-rooms.
Answer: TCPs reliability comes at a price in several areas.

Compexity: a UDP only stack is simpler than a TCP one.
Startup time: A UDP protocol can send a request and get a response in one round trip. A TCP protocol needs to go through the TCP connection setup process first which means a second round trip.
Head of line blocking: If a TCP packet is lost all subsequent packets will be held in the network stack and unavailable to the application until the lost packet is resent.
Server resource use, all that buffering and connection state tracking takes memory and CPU.
Extra network chatter, UDP can deliver a small request and response in two packets. TCP is likely to send substantially more.

Taking some practical examples:
TFTP uses UDP because of point 1, it was designed to be implemented in very limited environments.
DNS uses UDP because of points 2,4 and 5. The small request and response doesn't justify the resource use of TCP.
Low latency realtime stuff like games, VOIP etc uses UDP because of point 3. Having the whole stream be delayed by a retransmission can be worse than having a packet not arrive at all (though this is somewhat mitigated by TCP fast retransmission).
Answer: one increasingly common reason is to use udp to wrap a new transport that can be distributed without operating system permission. QUIC is an example of this, as is SCTP over UDP ala webrtc. Tunnels/VPN also work this way, because you don't want to tunnel TCP in TCP as two layers of flow and congestion control interact poorly.
Native application use of UDP might make sense, in addition to the reasons cited above, when you desire out of order delivery (i.e. avoiding head of line blocking that TCP imposes because it delivers in order).
Comment: In addition to operating system permission issues wrapping your new protocol in UDP also helps it go through NATs and similar.
Answer: A property of UDP which is frequently overlooked is that fact that it can work with entirely one-way traffic.
Consider two systems T and R.  T wants to transmit something, R receives it.  Under normal behaviour (with a few preconditions eg no ARP, no ICMP unreachables) T will not receive a single packet from R.  Appropriate filtering can then prevent all traffic from R to T, which means that faults/intrusions on R can never affect T in any way.  This is an extremely important property in complex systems, which can be used to overcome unforeseen boot-order dependencies, for example.  I've seen this used in various vision systems.
I've also seen UDP "syslog sinks", where log data is sent to multiple inward-only systems to create multiple cross-referable logs.  In some sites you can't even ssh to them, you have to go to the machine room and use the console.
It is frequently stated that UDP is unreliable, which makes it sound as though it has inherent non-delivery.  This is false: what it lacks is an inbuilt retry mechanism, leaving it to the upstairs protocols (compare DNS and streaming for approaches).  Further, under many real-world conditions (decent switches, non-saturated network), you will find 100% UDP delivery.
Under some very nasty real-world conditions with very high packet loss, you also find that UDP gets through where TCP often doesn't.  For example when packet loss is say 90%, it's basically certain to break a TCP connection, whereas at least some of the UDP packets would get through.  Protocols such as NTP and DNS will still work, syslog and SNMP are likely to work well enough to find the cause.
Answer: In fact, both TCP and UDP are necessary to design of good network comms. They each do one job well. Because of the separation of comms into discrete tasks, testing and debugging is much easier

When would one use UDP over TCP?


Windows 7 computer not showing up on Apple TV

Question: Both iTunes on Windows 7 and the Apple TV 3 are updated to the latest versions.  My PC is connected to the router via Cat 5 and the Apple TV is connected on wireless.  I can AirPlay with my iPad or iPhone. I've had this work just fine before with other computers. Home sharing is enabled on both devices and connected to the same account with the correct password. I can't figure out what's going on.
Comment: Is iTunes running and are both the computer and AppleTV using the same networking subnet?
Comment: Yep, everything is set up as it SHOULD be for it to work.  Like I said, it has worked before.
Answer: The problem could be with your firewall. You should check the firewall software you use and open relevant ports. Some firewalls actually have predefined rules for the services, but for most you'll have to define them manually.
Most commonly the services used are named mDNS or Bonjour sharing. If these aren't found, you can find a list of relevant ports here and add them manually.
Answer: I had a similar issue with my Mac and Apple TV
I was able to exchange it at a Apple store after creating a case with Apple support.  Info on the exchange program here.
For me, everything worked on the network except for Home Sharing on the Apple TV.  It passed all tests and otherwise worked fine.  In my case, restarting iTunes would 'enable' Home Sharing access from the Apple TV for a little while, then it would drop again.
Good luck.
Answer: In Apple TV, Go To Settings > General and hit restart - beyond that I think Apple Support would be a good way to go


What are the document grid settings in inkscape for making an isometric tilemap for tiled?

Question: I am using inkscape to create a isometric tilemap.  What settings do I need on the grid in document properties in inkscape to make it match up to a 64 x 32 grid in tiled?
Comment: http://www.mbeckler.org/inkscape/isometric_projection/ Maybe this will help.
Answer: As the link that Sidar comment alluded to, in the document properties you have the set both of the angles on the grid to 26.56 degrees. This will give you a size ratio where the height is half the size of the width.
From there, as long as all the other numbers are in pixel units and set to a value that is in the base 2 set (2, 4, 8, 16, 32, 64, etc...) you should be able to get set up a grid that matches you're requirements.


Is it possible to feel pain in some part of a body, but the pain "feeling" is introduced somewhere else?

Question: Is it possible to feel pain in some part of a body, but that the cause of the pain is situated elsewhere in the body? For example, somebody feels pain in his toe, but it turns out that this pain is not signaled by nerves in his toe, but caused by a damaged nerve in the spinal cord, or somewhere in the brain.
Answer: Yes, this is pretty common.  Examples include

sciatica, pain felt down the back of a leg to the foot, from irritation to components of the sciatic nerve but commonly at the level of the sciatic nerve roots
angina pectoris, pain from myocardial ischaemia felt in the throat (Latin angina "infection of the throat"), arms, chest etc
shoulder tip pain from a subphrenic abscess

The clearest possible example of this is phantom limb pain, where pain is perceived to be arising from an amputated limb indicating that the pain is arising from central mechanisms.
Comment: As a side note, transferred pain is actually pretty critical to know about as a ski patroller. To use your example of myocardial ischemia (and, for that matter, infarction) one of the big symptoms in males is pain radiating down the left arm and up into the throat, in some cases reaching as far as the hand, which is pretty far from the heart.
Comment: Referred pain* whoops. I haven't had to use the generic term… ever, that I remember.
Answer: An example of pain evoked by distant sites in the body is referred pain.  It's defined as pain perceived at a location other than the site of the painful stimulus. An example is the case of angina pectoris (chest pain), caused  by myocardial ischemia (decreased oxygen supply to the heart due to a narrowing or complete blockage of the coronary arteries). Angina often results in pain felt in the neck, shoulders, and back rather than in the thorax (chest), which is the actual the site of the injury.
A massage-related field of therapy has evolved around this - trigger point therapy, where trigger points are defined as the cause of pain elsewhere in the body. From personal experience I can add my gratitude to this field of therapy; it's been good to me.

Trigger points. source: Trigger Point Therapy
Answer: Another common medical condition that causes pain elsewhere is the spinal disc herniation. The disc pushes against the nerves in the spinal and causes pain, usually in the leg, foot or arm. https://en.m.wikipedia.org/wiki/Spinal_disc_herniation
Sometimes the pain disappears with rest, sometimes surgery is necessary and sometimes the pain partly remains even after surgery.
Comment: When I went to a doctor years ago because of pain in my arm that had lasted months, he diagnosed it as tendonitis. It wasn't until a chiropractor recommended I see a sports medicine specialist, who recommended an MRI, that I learned I had herniated a disc in my back that was the cause of the pain in my arm, which didn't go away until over a year later.
Comment: @moonpoint It is not uncommon that disc herniation is not immediatly diagnosed. The pain may go away, or it may not, not even after surgery :-(
Answer: Just as an FYI, the answer is emphatically yes.  I have two separate areas of my body which exhibit those symptoms.  But my answer does not "track" those of others here.  They talk about (I would guess) some relatively standard off-site pain actions.  In my case, it appears to be more simply the action of (for want of a better term) CrossedNerves.  As one example, there is an area of about two square inches, just right of center, on my chest which, when poked with a sharp object, will cause a stabbing  pain to appear on the back of my right shoulder just below the shoulder blade. This is repeatable and has been that way since as long as I can remember.
Glad to see I'm not the only one with these strange biological oddities.
Comment: interesting answer - is there any cited literature on this phenomena that you describe? could you cite that in your answer - it would improve your answer significantly
Comment: @VanceLAlbaugh to me this sounds like a specific form of [synesthesia](https://en.wikipedia.org/wiki/Synesthesia).


GIMP - Dithered brush tools

Question: Is there a way to paint dithered in GIMP? Indexed mode will make existing gradients dithered, but using the brush tool or airbrush tool after dithering will just make a solid color, instead of just dithering what should be gradients around the brush.
Comment: Have you tried searching google for dithered brushes? There are some [here](https://itch.io/t/72233/dither-brushes-for-photoshop)
Answer: Two-color dithering, mostly usable if you have a tablet:

Add layer, put in "dissolve" mode
adjust brush opacity (with tablet, use Pressure Opacity dynamics)
paint on "dissolve" layer

(brush spacing has an influence)
Using 25, 50, and 75% brush opacity:
Answer: Paint with a cloning tool. Have a dithered texture as the source. The dithered texture can be as well random grain as some algorihmic looking repeating pattern.
You can also have a full layer of dithered texture. Paint to its layer mask.
Reverse it. Have a dithered pattern in the layer mask and paint normally. That allows fast color changing, but the colors in the same layer have the same dithering pattern. The following sample is made this way. There are different layers and patterns for green and red.

As the 4th way I suggest to paint as normally. Then insert just over it a layer of dithered texture that simulates mid grey with 2 different greys (not full black and white). Give to that layer blending mode = hard light.
None of these methods unfortunately can directly dither R, G and B by using a recognizable sized pattern to produce the wanted dithered RGB color.

GIMP - Dithered brush tools


Being yotzee a bracha while only having intention from the middle?

Question: Someone was making havdallah and another person was there who decided to not have kavana (intention) to fufill their obligation of the aish (fire) part of havdallah with that person. In the middle of the bracha (for example after they said "Baruch Atah HaShem Elokeinu Melech Ha'Olam...") the person decided they yes wanted to be "yotzee" with that bracha. Does there kavana help now in the middle of the bracha (since in reality they did hear the whole bracha) or in order for the kavana to work must they have kavana from the beginning of the bracha? Would there be difference of lichatchila and b'dieved?
Answer: This is discussed in Shulchan Aruch 213:3 it seems one has to,hear every word and the motzei has to have the yotzei in mind.The Mishna Brurah seems to say the same,but the Shar Hatziyon 20 brings that missing some word one can still yotzei bdeieved,but not miss the ikar of the bracha ,like Baruch atah... It is best to see the halachas inside and see how your case fits because the halacha is there just applying it to your case is not so simple because of maybe Stam daas to be yotzei .what was the persons intention?


Why doesn't Ubuntu make a DVD iso?

Question: I mean, I think it might be kind of cool if they made a bigger installation media with more applications, maybe include various other environment( okay, probably not going to do that but as it seems you are downsizing your based off of distros).  You might also have like option bundles like say a security bundle with nmap or something like that or perhaps a artsy one with gimp and other multimedia creation apps.  Just wondering?
Answer: DVD releases can be found in cdimage.ubuntu.com:
http://cdimage.ubuntu.com/releases/oneiric/release/
This question outlines the differences between what is on the CD and DVD:

What is on the DVD Edition of Ubuntu?

The "bundles" you mention could be fulfilled by the "variants", such as kubuntu, Ubuntu Studio (artsy one as you mention)! and others.
Answer: If you want a distro that bases itself on security then there are many.  Backtrack being one of the more famous and used by many sys admins to check the overall security of their networks.  Your options bundles are all over the internet to download rather then trying to pick out which ones might be best to fit on a dvd for distribution.  This is the basis of the overall Open Source concept, being able to start with a good working distribution and building on that to fit an individuals needs.
Answer: I'm not sure this is the sort of question anyone here can answer.  It'd fit much better in Ubuntu Forums, where speculative questions and answers are welcome and fun, and can even run into dozens or even hundreds of posts.
Having said that, though, I'll add that I don't see a real advantage to Ubuntu producing special option bundles, at least not yet.  I've been using Linux and Ubuntu less than a year, but even I know how to download and install the special apps I need in order to make Ubuntu be what I want it to be.  (And how to find very specialized distros, too, if I really want such.)

Why doesn't Ubuntu make a DVD iso?


Can astromech droids control and fly the ships they're mounted in?

Question: I was wondering if astromech droids (like R2-D2) could fully control any unmanned ship they're mounted in.
Answer: Yes
We see R2 pilot Mace Windu's Jedi Starfighter in "R2 Come Home", an episode of The Clone Wars

Not only does he do some pretty fancy flying (surviving a dogfight with Slave I), he docks with a hyperspace ring and flies all the way to Coruscant.
He also flies a Y-Wing bomber in "Nomad Droids", a later episode, and even blows up some vulture droids:
Answer: Yes
In Revenge of the Sith we see Obi-Wan's R7 unit take his Starfighter back to the Republic ship  with a message for Commander Cody, tricking General Grievous into thinking he has left Utapau so he can surprise the Separatist forces.
Answer: Yes

In Revenge of the Sith Obi-Wan has his droid take control of the flying for a bit.

OBI-WAN: All right, R4. No, no. Nothing too fancy.

and later he even says

OBI-WAN: Flying is for droids!

He has his droid fly the ship again on Utapau.

OBI-WAN: Take the Fighter back to the ship

In Empire Strikes Back R2 also makes a suggestion about taking control of the ship.

LUKE: (into comlink) Yes, R2?
R2 utters a soft, carefully phrased steam of whistles.
LUKE: (into comlink, chuckling)   That's all right. I'd like to keep it on manual control for a while.
The little droid lets out a defeated whimper.  Luke smiles, and
  continues on his course.
- Ep. V script

So yes, droids can fly the ships they're mounted in, even without a pilot inside the cockpit.
Answer: Also answered by this scifi exchange post.
Does R2D2 Try to Trick Luke in Episode V - Empire Strikes Back?
R2D2 could control Luke's X-Wing in Episode V.
Comment: +1 And props for an answer based on the original trilogy.
Comment: This answer would be better if it pulled in the relevant quotes instead of just linking, especially since the entire (and long) passages there aren't completely relevant to this question; only a small section is.
Answer: The answer is yes. There are a few examples for this. One is an episode in The Clone Wars where R2-D2 even outmanoeuvred the slave one. Another is in the films in The Empire Strikes Back. There R2-D2 during the evacuation scene flies the X-Wing towards the landing zone and Luke.
Comment: is there a source for your claim that R2 did this: "R2-D2 during the evacuation scene flies the X-Wing towards the landing zone and Luke."?
Comment: https://www.youtube.com/watch?v=HgY3rOOascY 11:08 - 11:20 would be the time there. it is just a small movement though as he hovers the ship more towards luke
Comment: @JakeGould the evacuation scene was not mentioned so far in any answer else I wouldn't have bothered making this an answer and instead had at max commented.
Answer: During Empire Strikes Back, after leaving Hoth:

R2, set a course for the Dagobah system

Also, a droid can handle more G-Forces than a human,
so outmaneuvering a bounty hunter was no big deal for him.
Comment: hmmm, 1) setting a course like a navigation computer *isn't* the same as flying the ship, and 2) I don't remember when that quote happens, do you have a source for that quote?
Comment: 36m:20s. I stand corrected. As luke was setting the course, R2 questioned him (Being able to see the nav controls from his vantage point was all but impossible, so I'm guessing he could see changes to the flight computer WHILE they were still being made. We all know R2 likes to hack into EVERY computer he comes in contact with...
Comment: I thought BRIEFLY that I had confused a line from the Star Wars Gangsta Rap, at 2m:02s, but once again, Luke answers R2's question and says "Yeah, that's right Artoo, I just set a new course"    https://www.youtube.com/watch?v=Ij4w7ChpuaM       But yes, setting a course in the nav computer to let the ship fly itself IS different you are right... But we all know if R2 can hack a Deathstar , he could hack an X-Wing and control it. We see him PHYSICALLY rerouting ship systems from the outside on the Nubian ship  in EP1.
Comment: Also in EP1, when Anikin was told to "Stay in the cockpit" R2 did NOT have control of the gun, Anikin told R2 he was trying, instead of R2 taking over. BUT when the ship took off ON AUTOPILOT, Anikin asked R2 to try and override it. So, it was probably locked, but WAS hackable. When they got to the control ship Anikin was still asking him to turn it off, and after a few seconds said "Yeah! You did it!".
Answer: Yes.
In the new (canon) novelisation of Star Wars: The Empire Strikes back, we have the following passage, just after the Battle at Hoth.

A short distance farther sits your X-wing, a spaceship outfitted for one   pilot and one droid. R2 is in his place. He's the one who piloted it out here to the muster site, to wait for you.
The Empire Strikes Back: So You Want to Be a Jedi?
Answer: In addition to the above examples of droids piloting starfighters, droids are also capable of piloting capital ships. There are many examples of Separatist capital ships being piloted by droids in The Clone Wars, not to mention the scene at the beginning of Revenge of the Sith.
Further, some droids are starfighters, again, at the beginning of Revenge of the Sith. Obviously, a droid that functions as a starfighter is capable of piloting itself, and is therefore capable of piloting a starfighter.
Comment: The droid starfighters we see in Revenge of the Sith are largely not piloted by ***astromech*** droids.