Free bitcoins are real?

Question: That's confusing the bitcoins used for marketing are real or not.. like some posted a code in facebook or in social media for free bitcoin so those bitcoin are real or a just marketing, hacking strategies  etc.
Comment: Hard to say without seeing what is actually claimed. Anytime someone offers free money you should be extremely cautious, though.
Answer: I rather wanted to comment this but since I lack the required reputation I'm answering it.
If it's through faucets then it's real. If not, it's probably fake.
Moreover, faucets give out reasonable amount bitcoins for free such that the income generated from displaying adverts is more than the payout you'd get per hour or so..
Answer: There ain't no such a thing as a free lunch.
If something sounds to be unbelievable it probably is.
Also, Internet is full of scams.

Free bitcoins are real?


German Visa application

Question: I am planning to visit my boyfriend in June for three months, however my biggest problem is proving that I have a reason to come back. I recently completed my studies in Hotel Reception and was employed at the same company I did my internship, but my contract is only until 31 May 2013,and thereafter I'll be leaving for Germany. My question is ... how do I prove that I have a reason to come back to South Africa besides family ?
Comment: Is it correct to assume you are a holder of South African passport, and your boyfriend lives in Germany?
Comment: Do you actually have any reason to go back? Only as you've described it, you sound like quite a high risk case for just staying... So you're likely going to need to work hard to prove otherwise!
Comment: If you are single, do not have a lot of savings or dont have a high income, do not have sufficient family ties (and only God knows how various embassies judge that), and if you are not going with the sole purpose of tourism, I can *almost* bet, you ain't getting that visa.
Comment: You can not . Options :  1-  Do you have any listed assets ? ( car, house, monetary ? )  2 . Get another contract for the period when you are back. 3. Or a letter from some company saying that you have a secure job when returning. ( ask a friend that runs a company .. ). And Don't mention the boyfriend , it will put you in High risk.  Just say a colleague or a friend .
Answer: Here's the full rules:

The mission must ensure that the following requirements have been met
  in each individual case:

The purpose of the trip to Germany must be plausible and comprehensible.
The applicant must be in a position to finance his/her living and travel costs from his/her own funds or income.
The visa holder must be prepared to leave the Schengen area before the visa expires.
Documentary evidence must be provided of travel health insurance with a minimum coverage of 30,000 euro valid for the entire Schengen
  area.

Should an applicant be unable to prove that he/she can finance the
  journey and stay from his/her own funds, a third person may undertake
  to cover all costs associated with the trip in accordance with
  sections 66 and 68 of the Residence Act.

For 1, a written invitation from your boyfriend and proof of his residency status should be sufficient. I'll assume that 2 and 4 are straightforward as well. That leaves 3 as the main hurdle. According to this website, embassies will typically require proof of family ties and sufficient income.
The best option I can think of would be to already secure a job (i.e. employment contract) for the time after your return from Germany.

German Visa application


Can I substitute bread flour with all purpose for hot water crusts?

Question: Many recipe for a hot water crust I have seen calls for something like 15%-20% of the flour to be bread flour? Is going AP flour fine, or do I need to do more/something else to make the substitute?
Comment: I've seen tons of recipes with only all-purpose flour. To confirm just now, I searched for "hot water crust recipe" on Google and in the top ten results, there were seven unique recipes (two pages were article/recipe versions of the same thing, two were general articles), of which six used only all-purpose flour, and only one used a combination like you describe. I think you still have a really good question - what does the bread flour do, what happens if you replace it? - but the assertion about "basically every recipe" is an awkward starting place.
Comment: Adjusted, so far I've seen about 5 different recipes, all were using bread flour in varying amounts
Answer: The hot water method is all about making gluten (flour strength) ineffective, so using bread flour has very doubtful merit. A recipe insisting on its use might have other problems (baking too hot or too long, having too high or too uneven thickness (use a rolling pin, period), or using too little fat) that it tries to compensate by using strong flour. Note that fat content is essential - medieval style hot water crusts that used little or no fat were intended as a food preserving shell, not as an edible part of the dish.


Mercedes 2003 unpredictably shudders and acts like it's going to stall at a stop light, then hesitant to accelerate

Question: My 2003 Mercedes has acted like it's going to stall at stop lights occasionally for the last few months-shudders at stop signs, then recovers.  Today I rev'd it in neutral out of fear it would stall.  Immediately following, for the first time, it shuddered...then stopped shuddering, but then it wouldn't accelerate for a few seconds.  Just sat there.  It then accelerated.  Also there was an odd burning smell briefly (that has come up in the past).  The smell almost smelled electrical, but unsure.
Husband thought it bad gas that's caused the shuttering, but we've used premium or unleaded with occasional STP fuel engine cleaner.  Also 25 percent ethanol regularly in the past.  (Car ran great for 10 years)
Comment: Welcome to Motor Vehicle Maintenance & Repair! Have you followed the maintenance schedule for the vehicle? And when was the last time it was serviced? There are a great number of things that can cause similar symptoms, and electrical shorting *is* on the list - *although other causes are more probable*. Any additional info that you can provide (maintenance actions done, last work, other symptoms, exact model, etc.) will all help us to help you. Cheers!
Comment: Is the check engine light on? If so, what are the codes?
Answer: I can not post comments as I am too new to this site. I offer this as a suggestion to help in diagnosing the issue.
Have you performed a Battery Reset and Idle Relearn Procedure?
This is where I would start, as it's the most basic possible solution.
Answer: Have you ever cleaned the throttle body (or had it cleaned)? First thing, check if your vehicle requires any throttle position relearning procedure after throttle body cleaning and, if so, learn that procedure. Then, identify the gaskets that mate the throttle body to the intake manifold and to the pipe coming from the airbox and buy them, buy a throttle cleaner (carb cleaner isn't good for that, it has to be throttle cleaner and nothing else), remove the throttle body from the car and clean it, being careful not to scratch the plate in any way, then replace the gaskets and reinstall the TB and do the relearning procedure if required. Or have all of this done by someone competent, if you don't feel like doing it.
Reduced airflow around the plate at idle position, due to an excessive carbon soiling of the throttle plate edges, causes what you experience. The smell might be a completely different issue.
Another possibility might be a dirty or faulty MAF.


What would one experience travelling through an invisible Krasnikov tube, and how much could they be used to cut travel times?

Question: Effectively what the title says;
What would different observers experience while travelling through / seeing one travel through the tube,
and how could they be used to cut travel times? (Just answering one of these questions is ok)
Within my world, I have no "proper" (causality violating) FTL travel; only Wormholes, subluminal warp drives and Krasnikov Tubes. I had the idea that a very large line-layer ship with 2 wormhole mouths could travel to a system, lets say 10 light years away. The ship could then break in twine and send one of the wormhole mouths back through the tube while expanding the other on site. The wormhole mouth sent back would appear after I had originally left, as far as I'm aware, the ship-time it took me to get there. So assuming I was moving at highly relativistic speeds so that the 10ly journey was 1 year, the wormhole mouth would arrive at Earth 1 year after I had left, effectively acting as if my linelayer ship could travel at 10c, and massively increasing the amount of systems I can colonise within a certain timespan. I just wanted to know if this could really work without causing causality issues? (CTC's destroy causality violating space-times in my universe)
Comment: You asked this questions earlier, and also back then you were asked to focus your question more. "just answer one of these" is not giving more focus.
Comment: This is significantly more focused. I am simply asking more than one question. If I cannot ask more than a single specific question per post then I would prefer not to post at all.
Comment: you are asking two questions: What would different observers experience and how could they be used to cut travel times? Then you add (Just answering one of these questions is ok).
Comment: I know. I said that.
Comment: Can you comment on the times involved, i don't get the concept you are proposing. A star 10ly away can be reached after 10y at he earliest (without FTL). You'd then send back some thing that can act as the mouth of a KT (why? could you not leave one aperture at earth and only travel with the other aperture?), but you also seem to send this aperture back through a KT? are there now two KT? And how does this cut your expansion time? You still go to your destination at sub-light first, then establish a Kt, do you not?
Comment: @bukwyrm KTs are wormholes through both time and space.  I think he is asking if you can use a KT to go back to a time that would allow you to reclaim your lost travel time basically making your travel time almost instantaneous but without actually going far enough back to proceed the cause in your local frame.
Comment: Hi Mr.Kred, Welcome to World Builder SE.  I removed the Hard Science tag for you since wormholes, FTL, and Krasnikov Tubes are only theoretical at best and there is no scientific consensus on how or if these could exist.  Theoretic sciences and science fiction generally just fall under the Science Based tag.
Answer: Okay, even if these are in fact three highly connected questions I'll try to answer them as good as possible.
What would observers experience while seeing one travel through the tube?
A Krasnikov tube is in the end nothing else then a wormhole with some special settings and abilities, so traveling trough or into one is not different for the observer. In theory a wormhole is not that much different from a black hole regarding effects of gravity and matter with the special difference that where we can see nothing in the center area of a black hole we see the area of the universe where the tube Ends in a wormhole . So watching someone enter a Krasnikov tube is like watching him  entering a black hole. As even light is bend by the gravitational forces, in the view of the observer the object entering the hole gets elongated and deformed until it seems to vanish in the circular border of the hole.
What would observers experience while traveling through the tube?
According to Luke Butcher, theoretical physicist at the university of Edinburgh (in an interview concerning the movie 'Interstellar'), their presentation of wormhole-travel is highly realistic.

"Things will look a bit like you're traveling down the center of a wide tunnel. Directly in front of you you'll see the region of space you're heading to, and behind you is the region you've left behind. These views would be surrounded by concentric circularly-distorted repeats of the same view, a bit like an Einstein ring, with the whole sky (of one end of the wormhole) wrapped into a series of rings that get more and more closely packed together as you move your line-of-sight from the longitudinal direction, to a perpendicular direction." (L. Butcher)

Like this.
Credit: Public domain via Les Bossinas (Cortez III Service Corp.) and NASA.
How can it be used to cut travel-times?
I'm not realy sure what you want to do here. As stated above, Krasnikov-tubes are already special cases of wormholes so 'bringing a wormhole through it' will not change anything as you had to implement the Krasnikov tube in the first place. The cut in travel time will depend on the structure of the wormhole/Krasnikov tube and can not be answered in general.
Answer: What would different observers experience while travelling through / seeing one travel through the tube
A Krasnikov tube differs from a wormhole in that the "throat" of a Krasnikov tube actually occupies normal space, and the mouths are effectively two dimensional.
The wall of a Krasnikov tube is formed from extremely distorted space which compresses a huge distance along the outside surface into a very small distance along the inside surface. Unless the spacetime of the tube is additionally specially engineered to bend external radiation around it, an observer traversing the interior of the tube would see pretty much the same thing they'd see traversing normal space... but with the side view longitudinally compressed, thus increasing the radiation intensity. This might end up putting a practical limit on the amount of travel-time reduction you can get with such a tube, since you wouldn't want your travelers to get fried by amplified star light.
An external observer would see right through it, possibly with some radial distortion from light being bent by its passage through the tube walls. A vehicle passing through the tube would appear externally to accordion out as it enters, with its image stretching by the spatial compression ratio of the tube, and then collapse again as it exist the other end.
Unlike a wormhole, the space inside a Krasnikov tube is not cyclic, so you would not be able to see yourself, or ring echoes of the surrounding environment, looking off to the side, nor can you move an arbitrary distance off to the side while inside the tube. Rather, the walls of the tube would feel much like regular solid walls; any matter that tried to force its way through from the inside would be violently torn apart, while matter impacting the tube from the outside would be compressed.
and how could they be used to cut travel times?
By reducing the distance you have to travel. That's the whole point.
I just wanted to know if this could really work without causing causality issues? (CTC's destroy causality violating space-times in my universe)
If you build your network carefully, yes. You will be restricted in the order in which you build a cyclic network of tubes to ensure that no lightlike paths through the network end up being closed, but that is certainly doable. If you end up running into the borders of some alien civilization's independently-constructed tube network, however, you may run into problems.
Answer: Krasnikov Tubes & Wormholes are Areas of 3-Dimensional Finite Space
So 4 Dimensional space is super hard to express in a 2 dimensional diagram, but here is the best way I can think to show it:

We are used to thinking in terms of infinite space where you look in a direction and there is something to see/somewhere to go as far as the eye can see, but this is not the case with finite space.  Now how finite space expresses itself can happen in a few ways:
Option A - Reality has a vector terminating edge:  In this scenario, the edge of reality  resolves itself by looping perpendicular movement into parallel movement.  Much like your mouse cursor being stuck inside of the workable area of your monitor, there is a point where there is literally nowhere left to go. When the light from your ship hits the edge of the tube it will simply not have anywhere to continue going along that vector so it will bend to follow along the edge of reality.  When you look around inside of this version of finite space, you will see only darkness with the exception of the points of light entering at either end of the tunnel.
Option B - Reality has a vector reflective edge: In this scenario, the edge of reality resolves itself by looping perpendicular movement back into itself essentially reflecting any light or matter that touches it.  In this model you could see the edge of reality by the light it reflects back at you.  Traveling in a wormhole that does this would look like flying through a cylindrical mirror.
Option C - Reality is wrap-around:  In my opinion, this is the most likely scenario for a wormhole.  In this situation, you could never actually hit the edge of reality, but you could see yourself and the light that you are radiating.  Here you would see infinite versions of yourself spreading out into space to every side.  You could fly left right up or down as far as you want, but you will always end up just circling back to your original location in that dimension, but forward and backwards do not loop because they let off into regular space when you hit thier boundary.
A few things that will be true of all three versions of finite space:

The tunnel does not traverse "normal space" so you would not see any stars or galaxies passing by as you would with an Alcubierre Drive.
A person who is is the middle will not see the ship fly by.
If you are moving at relativistic speeds, any reflections will be red-shifted and trail behind you.
If you go through any wormhole at faster than 1C, it will be black.
Outside observers would be able to see someone traveling in a wormhole, only by looking into its mouth.
The mouth would appear black which is not quite the same as invisible when the wormhole is empty, but any light emitted inside of a wormhole will eventually work its way out; so, the mouths will glow when light emitting ships pass through it.

Krasnikov Tubes violate causality
While a few solutions have been suggested to say that they don't "necessarily" violate causality, their basic concept is almost impossible to justify in a world where causality violation is actually impossible without hand-waving in a bunch or rules of physics just to control for such exploits.  Since you don't want to challenge causality, I would just stick to normal wormholes if I were you.
Using normal wormholes, the expansion of you empire would be limited to the speed of light, but once you have a network of wormholes, you could quickly move new line layers to the edge of your expanding empire from inner worlds to start laying new lines from the outside of your sphere of influence.  It is also possible that your civilization will occasionally hook up with alien civilizations (living or dead) that have already built thier own networks of wormholes.  When this happens you could very quickly expose large new areas of space for exploration, colonization, and conquest.


How will they mitigate the effect microgravity has in the BFR on manned trip to mars?

Question: Very curious to know this, since it doesn't look like the BFR will utilize centrifugal force to emulate gravity as far as I know.
Comment: I think, in general, the strategy for mitigating the effects of the trip is to keep it as short as possible, around three months. If you keep yourself in decent shape with resistance machines aboard the ship, I would think that you'd be able to handle .38g.
Answer:
Make trips that carry humans as short as possible.
Frequent physical resistance exercise, as on the ISS.
Build extra muscle mass and strength before departure, to help counter losses during the trip.

Perhaps mission planners will also look into the idea of putting a slight spin on the BFS while in transit. I haven't seen any reports of that yet, though.
IMO, it's likely that the low-gravity environment on Mars will also have an adverse effect on human health in the long term, without focused efforts to counter it.
Comment: Spin on a compact spacecraft like BFS won't give significant gravity without severely nauseating inner-ear effects.
Comment: For rotation around the long axis of the BFS, yes. However, rotation around the short axis (end-over-end) may also be an option. Whether that would help enough at low enough speeds to avoid inner-ear problems to be worth the engineering headaches involved, I don't know.
Comment: The BFR is large enough for a Skylab-style ring track to work: running in circles against the inner hull is enough to create some personal spin gravity - enough to actually run against the wall without restraints, and maybe enough to help mitigate some of the effects of microgravity.


How to compute momentum from equity time series?

Question: Let's say I have time series of stock prices for many stocks.  What's the best way to sort the stocks based on which have been going up/stayed the same relative to others?  Can this be done with a weighted average, putting more weight on the most recent numbers, to account for trends?
Comment: A question for the quant.SE probably. The whole problem is defining what is valuable. The result will depend on this definition.
Comment: Well, I'm *trying* to define the problem.  I started with a plain average, but I want to weigh more recent data higher.  So thus weighted average.
Comment: Since this user has long since left stack exchange, we are left wondering whether he really was looking to measure value, or merely momentum (as his explanation of value implies).  I have edited the question assuming the user intended to ask how to compute momentum.
Answer: This entire approach hinges on how you define "value."  Once you've defined value, you can define a metric for "stability" or "risk."  A working hypothesis would be that stock that have been stably valuable in the past would continue to be valuable in the future.  Of course, this is a hypothesis.
Let's say (for sake of an example, this is not financial advice) you define value as "mean of log returns" and stability as "standard deviation of log returns."  You could then sort your stocks by these metrics and pick ones with a high value and a low risk.
If you want to get fancy, you can use another metric of risk, such as drawdown.  You can also do a rolling analysis or use bootstrap re-sampling to distributions around your "value" and "stability" metrics.
Here's some code in R that illustrates my example:
<code>#Load Data
rm(list = ls(all = TRUE)) #CLEAR WORKSPACE
set.seed(1)
library(quantmod)
myStocks <- c('AAPL','MSFT','GOOG','F')
getSymbols(myStocks,from='01-01-2004')
Data <- na.omit(cbind(Cl(AAPL),Cl(MSFT),Cl(GOOG),Cl(F)))
names(Data) <- myStocks

#Define value and risk
returns <- function(x) {diff(log(x))}
value <- function(x) {mean(returns(x))}
risk <- function(x) {sd(returns(x))}

#Estimate value and risk
StockScreen <- data.frame(  risk=apply(as.matrix(Data),2,risk),
                            value=apply(as.matrix(Data),2,value))
round(StockScreen,6)
plot(StockScreen)
text(StockScreen$risk+.001,StockScreen$value,labels=row.names(StockScreen))

#Estimate value and risk, different risk measure
library(PerformanceAnalytics)
risk <- function(x) {maxDrawdown(returns(x))}
StockScreen <- data.frame(  risk=apply(as.matrix(Data),2,risk),
                            value=apply(as.matrix(Data),2,value))
round(StockScreen,6)

#Boostrap value and risk measure
library(meboot)
library(plyr)

bootstrap <- function(x) {
    reps <- as.data.frame(meboot(as.ts(x), reps=100)$ensemble)
    valueDistribution <- apply(reps,2,value)
    riskDistribution <- apply(reps,2,risk)

    valueMean <- mean(valueDistribution)
    valueSD <- sd(valueDistribution)
    riskMean <- mean(riskDistribution)
    riskSD <- sd(riskDistribution)

    data.frame(valueMean=valueMean,valueSD=valueSD,riskMean=riskMean,riskSD=riskSD)
}

bootstrapScreen <- ldply(as.list(Data),bootstrap,.progress = "text")
row.names(bootstrapScreen) <- bootstrapScreen$.id
bootstrapScreen$.id <- NULL
round(bootstrapScreen,4)
</code>
Answer: you might want to rank stocks on the basis of standard dev of a forecast divided by the forecast. In this way the "tighter" the value the more predictable the stock.
Comment: what do you mean by forecast?  can you please elaborate via an example, thanks.
Comment: Doesn't "predictable" have to do with the relationship between a forecast and *reality* rather than with the coefficient of variation?  In the context of the question, a highly variable stock (high beta) that nevertheless trends upward rapidly (high alpha) would be considered "valuable" but a low-beta ("predictable") stock that trends downwards consistently would be considered the opposite of "valuable".
Comment: @whuber, yes that's something that I'm trying to create a model for...
Answer: It sounds as if you would be interested in computing Relative Strength
http://www.investopedia.com/terms/r/relativestrength.asp
You could either measure it against a benchmark index such as the Dow 30,  or compute your own index from your 50 stocks and measure each individual stock against the index.
-Ralph Winters
Answer: What you are describing is momentum investing.  It is typically done in two steps:

Compute a momentum statistic from past prices/returns.
Compare momentum statistics across all equities in your universe.

Step 1 is typically done using a moving average of past returns (it is wrong to use prices because splits and dividends will skew the results).  This can be done using a simple moving average, or using exponentially weighted moving averages.  In either case, your results will depend strongly on the window/half-life of the moving average.  For equity momentum, most studies use momentum in the last 6-12 months excluding the most recent month or so.
Step 2 may be done either using an ad hoc sorting rule (Jegadeesh and Titman (1993) use top/bottom deciles) or with the aid of a risk model.


Schengen rule apply to non-EU spouse with Croatian residency card?

Question: For the next couple years, my family and I are planning on traveling all through Europe with our camper. I am a Croatian (and US) citizen, as well as my kids. My husband is a US citizen with Croatian residency. Will the 90/180 Schengen rule apply to us? We will travel to each country in the Europe but will never stay longer than 3 months in each one. Thanks.
Answer: The 90/180 rule does not apply because your husband is a beneficiary of the free movement directive (2004/38/EC) under its article 3 when he travels with you (or to join you).  He therefore enjoys the right of entry and the right of residence of up to three months outlined in articles 5 and 6.  The only documentary requirement is to have a valid passport.
This means, among other things, that your husband is (perhaps surprisingly) not a "third-country national" for the purpose of border control when he is traveling with you.  See the Schengen Borders Code at paragraphs 5(a) and 6 of Article 2:

'persons enjoying the right of free movement under Union law' means:
(a) Union citizens within the meaning of Article 20(1) TFEU, and third-country nationals who are members of the family of a Union citizen exercising his or her right to free movement to whom Directive 2004/38/EC of the European Parliament and of the Council ( 1 ) applies;
(b) ...
'third-country national' means any person who is not a Union citizen within the meaning of Article 20(1) TFEU and who is not covered by point 5 of this Article;

(Another consequence of the Schengen Borders Code is that you can use the "EU passports" lane together at Schengen border crossings; see Article 10(2), where those lanes are designated for "persons enjoying the right of free movement under Union law" rather than actual EU passport holders.)
Comment: Thank you for your response. I am having a hard time getting a clear answer from Europa.eu. The last time I asked this question they responded with the statement below. I find it strange they used the word "seems". Here is their response to me:

"Based on the information in your message, it seems that your husband would still have to adhere to the 90 days in any 180 days rule even if he may not need a visa as he is from a visa waiver country. You can find general information here: https://europa.eu/youreurope/citizens/travel/entry-exit/non-eu-family/index_en.htm"
Comment: @Umarlene yes.  We've had someone else (perhaps on [Travel.SE]) post similar communication from Your Europe Advice, and I have got a thorough message from them that says as much, too.  But it is clearly wrong as a matter of law, and I have been looking for some time to write to them again with a thorough debunking of their assertion.  I'll try to get to it this week.
Comment: @Umarlene among other things, they advised the US spouse to get a national visa from the country where she would be when the 90 days expire, regardless of the fact that this country has no national visa for which she would qualify.


How do I REALLY setup a ETH mining on Ubuntu Linux together with Jaxx? Polo: ethereumpool.co

Question: I tried to setup a ETH miner on Linux Ubuntu 16.04.2 together with Jaxx. But it was too messy. Can someone go through step by step together with me?
Comment: Hi there. What instructions were you following when you ran into a messy dead end? Asking a specific question about a particular part of the process you were following is more likely to get responses.
Comment: i tried following this tutorial.
https://www.meebey.net/posts/ethereum_gpu_mining_on_linux_howto/
Comment: Is Ethereumpool.co still up? I thought they stopped in Januari 2017...
Answer: I myself am on the Ethereumpool.co pool. Also, I am on Linux 16.04, the problem you said is that you can't get it together with Jaxx?
So first off you need to install the Prerequisites.
Open a terminal and type the following one at a time.
sudo apt-get clean
sudo add-apt-repository -y ppa:ethereum/ethereum-qt
sudo add-apt-repository -y ppa:ethereum/ethereum
sudo apt-get update
sudo apt-get install cpp-ethereum

After you do that, I suggest making a note file to keep your starting command. To connect to the pool, you want to use the command
ethminer -G -F http://ethereumpool.co/?miner=[HASHRATE IN MHASH]@[ADDRESS]@[OPTIONAL RIG NAME]

Where the hash rate is the speed, the address is your Jaxx address and your rig name. So for me it looks like this:
ethminer -G -F http://ethereumpool.co/?miner=19@0x516976cE81751eBe077Ca01C57B97c9665b0e10b@LLG

Notice, no brackets. Also the -G means GPU. Remember, the address is your Jaxx address that you get from in-app. the ETH, not ETC
If you have any issues comment at me.
Comment: What about for Yakkety onwards? There's no `cpp-ethereum` package since.
Comment: What binary tarball download on their GitHub download page has the miner?
Comment: @Antinous You need to download the repo now that it's different from the original. github --> ethereum cpp
Comment: The `sudo apt-get install cpp-ethereum` does not work - `cpp-ethereum` does not seem to exist... what's wrong?
Answer: @liam W: The repository 'http://ppa.launchpad.net/ethereum/ethereum-qt/ubuntu zesty Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/ethereum/ethereum-qt/ubuntu/dists/zesty/main/binary-amd64/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.


Is the immune system suppressed during sleep?

Question: Of course we have heard that during stress our immune system is suppressed. This leads me to wonder, does the immune system get suppressed when we are sleeping and why? During both these conditions the body might need to save energy for other biochemical processes, so I wouldn't be surprised that the immune system is suppressed while a person is asleep.
Comment: I don't have the time for a full answer, so I may come back, but generally 'no'. There is a difference between hibernation (a reduction in metabolic rate to survive prolonged periods of fasting) and sleeping. Humans do not hibernate, and when we are asleep the body doesn't try to save energy. Our brains go through REM sleep, which is just as active as waking hours, our organs -- especially dermal and muscle tissues -- amp-up their repair mechanisms while sleeping. Given that prolonged poor and/or lack of sleep significantly lengthens illnesses, the immune system should be very active.
Comment: Nope. 'I' and 'my' should be removed. Importantly, questions should be generalizable and interesting to the community at large. No one can possibly know why *your* immune system is, or is not suppressed. Again, it is an interesting question, but it needs re-wording.
Comment: @AliceD what about this question?: http://biology.stackexchange.com/questions/24555/what-causes-feeling-of-feet-falling-asleep-to-be-delayed/25875#25875
Comment: It is a gray area, but that linked question is not a medical issue, it is an observation of a physiological process that is generalizable to something everyone has experienced in their life. Your question is not readily generalizable as you start of with an unsupported personal anecdote that likely not many folks agree upon.
Comment: @AliceD is this better?
Comment: @AliceD I have significantly edited it, now what do you think?
Answer: During stress glucocorticoids, which are steroid hormones produced by adrenal glands (such as cortisol and corticosterone), are released into the blood-stream. These hormones have anti-inflammatory effects. You may say that they suppress the immune system.
The circadian rhythm, which controls the sleep-wake cycle, also controls glucocorticoid secretion, thereby reinforcing the sleep-wake responses [1]. Sleep deprivation is a form of stress and it causes an elevation in the levels of glucocorticoids. The effect of sleep deprivation could be replicated by adrenectomy (surgical removal of adrenal glands); there is a transcriptional downregulation of several neuroprotective genes [2]. Via glucocorticoid mediated signalling, sleep deprivation also results in inhibition of adult neurogenesis in the hippocampus [3].
Another study says that cytokine (TNFα and IL6) secretion by immune-system cells, are inherently affected by circadian rhythm via a glucocorticoid independent mechanism [4].
Overall, sleep is inversely correlated with reduced inflammation because both the processes are under the control of the circadian clock. Sleep deprivation, as a form of stress, is also correlated with glucocorticoid secretion. It should be understood that sleep doesn't necessarily inhibit glucocorticoid secretion and it would be incorrect to say that reduced inflammatory effects are because of sleep.
Comment: So this means that sleep does NOT cause immunosupression?
Comment: @TanMath Yes it is the opposite actually- immune system may be activated during sleep. But I wanted to refrain from saying that. Because such a strong statement cannot be made.


What are the advantages of the Riblett airfoil over the Original Pietenpol Airfoil?

Question: Some builders have opted to build a Riblett airfoil based wing for the Aircamper rather than using the original Pietenpol wing.  What are the basic characteristics of the Riblett wing which differentiate it from the original wing, and what are the pros and cons in construction and performance?
Answer: Assuming that the same wing chord is used for both, one technical difference between the Pietenpol and the Riblett is the depth of the airfoil.  The Riblett that has been used on the Air Camper is the 612 (or sometimes the 613.5), which makes it 12% (or 13.5%) deep.  With a 60" chord, that's a depth of 7 to 8".  The deepest section of the stock Pietenpol airfoil is only 6-9/32", which makes it roughly a 10.5%.  The offshoot is that a taller spar can be used with the Riblett, and in spar strength the height makes a great deal of difference because the section modulus goes as the square of the height and the section modulus is what determines bending strength.  A taller spar can be made lighter with proper design.  Another useful consequence of using the Riblett is that a deeper wing section allows a larger fuel tank to fit in the space between the spars.  The stock Pietenpol wing centersection can accommodate maybe 10 gallons, but the Riblett should be able to fit more up there.
I've attached a graphic overlay comparison of the Pietenpol airfoil with the Riblett GA30U-612; Piet in red, Riblett in white.  The 613.5 is similar but the differences are a bit more accentuated.
For performance differences, I will defer to both a technical treatise by Mike Shuck (on the airfoil list) and the flight comparison between two very similar Piets conducted several years ago and documented in the BPA Newsletter.  Very similar performance in all flight regimes.


Why does the X Window System use a server?

Question: I never really understood why a window system must have a server. Why do desktop environments, display managers and window managers need xorg-server? Is it only to have a layer of abstraction on top of the graphics card? Why do window systems employ a client-server model? Wouldn't inter-process communication via named pipes be simpler?
Comment: Unix and X evolved before PCs became so powerfull and cheap, in an eviroment where you typically had lots of rather simple terminals connected to one or a few more powerfull computers.  This division was carried on with X: You had "terminals" - simple cheap computers with graphics-card - running just the X-server, and gathering input from mouse/keyboard and drawing the screen... The actual programs (the X-clients) on the other hand, ran on one or a few more powerfull computers - shared by all the users using the terminals.  So splitting X in two parts (which could run seperate), made sense.
Comment: Named pipes would not be simpler because pipes are for one way communication only. If you want two way communication you use sockets rather than pipes. And actually certain newer systems use named (unix domain) sockets by default rather than TCP sockets. For example on Ubuntu 14.04, X is configured to not listen on a TCP socket by default.
Comment: @BaardKopperud X Terminals came years after the X Window started to be popular so they cannot be the reason why X Window was architectured that way. X started with Unix workstations that were running more than the X server.
Answer: I think you've already noticed that some sort of "server" is needed.  Each client (desktop environment, window manager, or windowed program) needs to share the display with all of the others, and they need to be able to display things without knowing the details of the hardware, or knowing who else is using the display.  So the X11 server provides the layer of abstraction and sharing that you mentioned, by providing an IPC interface.
X11 could probably be made to run over named pipes, but there are a two big things that named pipes can't do.

Named pipes only communicate in one direction.
If two processes start putting data into the "sending" end of a named pipe, the data will get intermingled.

In fact, most X clients talk to the server using a "new and improved" named pipe called a UNIX-domain socket.  It's a lot like a named pipe except that it lets processes talk in both directions, and it keeps track of who said what.  These are the same sorts of things that the network has to do, and so UNIX-domain sockets use the same programming interface as the TCP/IP sockets that provide network communications.
But from there, it's really easy to say "What if I ran the server on a different host than the client?"  Just use a TCP socket instead of the UNIX socket, and voila: a remote-desktop protocol that predates Windows RDP by decades.  I can ssh to four different remote hosts and run synaptic (graphical package manager) on each of them, and all four windows appear on my local computer's display.
Comment: X used named pipe on SysV systems where named pipes were bi-directional, including Solaris & SCO Unixes.
Answer: A window system does not have to have a server, but you can decide to implement window system based on a client-server model. Doing so has several advantages as you clearly separate the activities in the client and the server, they don't need to run on the same machine and it is more easy to service multiple clients. That is currently still very handy (e.g. when you ssh into another machine), but you have to realise that at the time X was developed, that was seen as a necessity: your local machine might not be powerful enough to run the client.
Named pipes  would not give you the automatic advantage of being able to run over the network as a TCP implementation would do. But named pipes were e.g. not available on DOS, with DosExtender running Desqview/X (1992), and AFAIK also not on VMS. For those implementations a Unix specific communication would be a problem.
TCP is not Unix specific and it is possible to have a client run under VAX/VMS (X development started in 1984) and serving the output to your local UNIX based graphics workstation. From the "X Window System:
The Complete Reference to
Xlib, X Protocol, ICCCM, XLFD"¹:

During the fall of 1986, Digital decided to base its entire desktop workstation strategy
  for ULTRIX, VMS, and MS-DOS on X. Although this was gratifying to us, it also
  meant we had even more people to talk to. This resulted in some delay, but, in the end,
  it also resulted in a better design. Ralph Swick of Digital joined Project Athena during
  this period and played a vital role thoughout version 11's development. The last ver-
  sion 10 release was made available in December 1986.

From the "X Protocol Reference Manual"²:

Division of responsibilities
In the process of designing the X protocol, much thought went into the division of capability between the server and the client, sind this determines what information has to be passed back and forth through requests, replies and events. An excellent source of information about the rationale behind certain choices made in designing the protocol is the article The X Window System, by Robert W. Scheifler and Jim Gettys, published in the Association of Computing Machinery journal Transaction on Graphics, Vol 5, No. 2, April 1986 The decisions ultimately reached were based on portability of client programs, ease of client programming, and performance.
First, the server is designed, as much as possible, to hide differences in the underlying hardware from client applications. ...

I remember the article in TOG being an interesting read. It certainly triggered my interest in X and (this was before the WorldWideWeb) the difficulty we had laying my hands on more information until O'Reilly starting publishing their series X books.
¹ X Version 11, Release 4, page 2-X, PDF available online here
² This is from page 9 in the 2nd edition, published by O'Reilly, that I bought in 1990. There are newer editions but I never bothered to buy these and they are AFAIK only available in paper as well. I don't think they changed the rationale of the division of responsibilities.
Comment: We also used dedicated X terminals that were diskless, passively cooled and immediately replaceable, all of which are great if you need 100 seats.
Answer: A windowing system means that several independent programs share a common resource, the screen and input devices. Shared resources can only safely be implemented in two ways:

The resource may be controlled by the kernel, and applications make kernel calls to access it.
The resource may be controlled by a dedicated process (server), and applications contact the server to access it.

Of course, access to the actual display hardware is controlled by the kernel, but that's not sufficient for a windowing system: There must be a way for a process to get assigned a certain part of the display (the window) where it can be reasonably sure that no other process will interfere, and there must be a certain level of protection of what application can access which part of the ressource at which time.
Now the whole thing could have gone into the kernel, which is AFAIK what Windows does. This has the advantage of being faster (usually calling the kernel is much faster than contacting another process), however it has the disadvantage of possibly opening up security holes (any exploit of the system is an exploit at kernel level), and at the same time restricts portability (a system implemented in the kernel is strongly coupled to the kernel; you'll not be able to easily port it to another operating system, and completely unable to do if you have no access to the kernel code).
If you don't want to implement it in the kernel, the only other way to implement it is as a dedicated process, that is, a server. Note that a server that is contacted through named pipes still is a server. Also, when running on the same machine, a lot of the communication between X server and clients happens through shared memory these days; that still doesn't change the fact that the display server is a server.
Now, why is the server contacted using sockets, and not using named pipes? Well, if you do it using sockets, you just need to have one socket for the whole server, which can do all of the communication. If you communicate with pipes, you need two pipes per client. Apart from the fact that managing all those pipes would be quite cumbersome, you might also hit some operating system limits on the number of open pipes if sufficiently many programs try to talk to the server at the same time.
And of course another advantage of sockets over pipes is that with sockets you can have connections across machines, which was especially important at a time where the actual computer was shared by many people sitting on dedicated terminals, so the programs on the computer had to communicate to the different terminals, but it is still very useful even today in networked environments.
Comment: While I indeed didn't know about that specific design, looking at the image in the linked article, I see a box *in the kernel space* which contains the term "window manager". Since the actual window decorations are drawn by the individual programs (so there's nothing like the X11 window manager), I can only conclude that this is the component that does basically the same thing that the X11 display server does. The Win32 parts are likely a combination of the functionalities of the X11 window managers (which are *not* part of the X11 server!) and X11 toolkits (in client context also in X).
Comment: Your MS Windows assumption is *partly* true - *some* of the structure needed for the windowing system is *sort-of* in-kernel - but it's complicated. What may surprise you about Windows is that much of what we associate with it is really specific to a single user-mode *subsystem* - the Win32 subsystem - something like a vm. The kernel itself - and its constituent *Executive* modules - sit apart from all of that. It's that separation that allowed for a separate POSIX subsystem to operate atop the NT kernel. [Check it out](http://en.wikipedia.org/wiki/Architecture_of_Windows_NT)
Comment: Yeah - that's what I meant by *sort/some of* - that's the *executive service* layer - it's like a hodgepodge of services that run in kernel mode but are separate modules in and of themselves. I guess that's kernel - in the same way linux kernel drivers needn't be compiled in but can be loaded/unloaded modularly. It's just weirder with Windows because it's all under wraps. Anyway, I've always thought it was interesting - but I'm *no expert*. Your answer just reminded me of it.
Answer: X was originally, developed and maintained by M.I.T.  And, it was with an open source M.I.T license, not that, that really, matters.
While seen as uncoventional, consider for a moment; how you would explain a choice to use a client-server paradigm in a piece of software? And, perhaps I should say to a C.E.O...
Here's how I learned to appreciate the choice in college.  In client-server, the server manages the resources, and especially, any resources that must be shared. So, the X server is the process that serves out, to the client apps,
the keyboard, mouse, and framebuffer (or, however you write to the screen on your system).
While not really correct, the window manager is often explained away like this: It's simply, that thing, that put handles, and other decorations on an app's frame, and windows, dialogs, etc.
Answer: Client-server models are a popular design for all sorts of applications, even when there's only one server and only one client. They allow a clean, well-defined interface between domains of responsibility.
While there are many ways a server and client could communicate, the choice made by X (regardless of the advantages mentioned by others) is not superfluous: You can connect to an X server on a different machine and open windows on your desktop (or on another cooperating desktop). This used to be very common in the days when X was developed, when many Universities and businesses would have a Unix server and many "X terminals" that talked to it. By using an internet-ready communications protocol, X can be seamlessly used within or across hosts.
X was the first GUI environment that could transparently display windows from another machine, consistent with the history of UNIX as a multi-user environment rather than an OS for a single user on a single computer. A lot of UNIX features seem like overkill if you're the only person who ever gets to interact (physically or remotely) with your computer.
Answer: I believe the x-server was designed as a client-server architecture because initially computing resources were scarce and mainframes did most of the heavy lifting.  X-terminals were just thin clients that connected to x-servers and displayed whatever needed to be displayed to the user.
It does have a lot of benefits (albeit the communication protocol for X is very heavy nowadays), notably you can display the same display on multiple clients, sharing a screen with multiple users is easy in X.
Comment: X Terminals came many years after the X Window started to be popular so they cannot be the reason why X Window was architectured that way. Another point: X Terminals did not connect to X servers, they were running X servers.


Using an AirPort Express to extend an AirPort Extreme's signal in 2.4 GHz from 5 GHz

Question: I have an older AirPort Extreme and a new AirPort Express. Now because the 2.4 GHz bandwidth is very crowded I want to switch the signal towards 5 GHz. However I have a number of devices that only operate in the 2.4 GHz range. These devices are however clustered together so that if I can place my AirPort Express in the middle of them I should be able to service them all. So my question is how do I make my AirPort Express extend a 5 GHz signal in 2.4 GHz range?
Answer: It should be as simple as just setting up each band individually. Remember to setup WDS for 5GHz on both access points to "extend" a network.
Answer: It should "just work". Just configure your Express to extend the network of the Extreme. The mid-2012 AirPort Express will automatically connect to the Extreme on whichever band the Extreme is on (or, if it's a simultaneous dual-band Extreme; it'll pick whichever band is better for the conditions) and will automatically make that network available over both 2.4GHz and 5GHz.
Note that Apple uses the "Extend the network" terminology to refer to using a wireless backhaul. If you have the ability to use a wired Ethernet backhaul between the APs, that would be best, because it saves wireless bandwidth for mobile devices that really need it. In that case you would just set up the Express to have the same wireless network name, wireless security type, and wireless network password as the Extreme has, and make the Express be just a bridge (both NAT and DHCP server OFF). See How can I get the same SSID for multiple access points? for more details of this setup.


What are the current known weaknesses/attacks on quantum key distribution?

Question: I am writing a paper on the implementation of QKD in the future. I want to know if there are any viable attacks on the BB84 protocol or QKD in general? I know of the Photon Number Splitting attack or spectroscopy in the case of diode manufacturing but I have heard that there are already solutions for those. Are there any other attacks that I have missed out?
Comment: I can vaguely remember something about side channel attacks on implementations of QKD. And I think it was performed using power analysis.
Answer: The Attack you mentioned (PNS) is a "hardware attack" it depends on how you physically distribute the qubits.
The only "protocol attack" (known for the BB84) is the "intercept & resend" that can be applied on every hardware you use and can be performed very easily(but Eve is easy to detect if the key is, at least, 72 bit long).
Another attack that can be performed is the man-in-the-middle, but this is not related to the protocol but to the total absence of authentication in the BB84.
This answer is focused on the BB84 protocol because of every protocol have different points of strength and weakness so "QKD in general" is a bit vague... i hope this can help you.
Comment: The [BB84 article](https://doi.org/10.1016/j.tcs.2014.05.025) mentions the need for authentication, and explains how to solve that: "Alice and Bob have agreed beforehand on a small secret key, which they use to create [Wegman–Carter](https://doi.org/10.1016/0022-0000(81)90033-7) authentication tags".
Answer: The attacks mentioned in that other answer are theoretical, and relatively easily dealt with. There is report of another, the Phase Remapping attack (which flies high over my head).
But practical adversaries think outside of the box and actively modify the quantum experiment so that the model is no longer a close fit. Like they blinds the photon detector! Quoting Lars Lydersen, Carlos Wiechers, Christoffer Wittmann, Dominique Elser, Johannes Skaar and Vadim Makarov: Hacking commercial quantum cryptography systems by tailored bright illumination, in Nature Photonics Letter 2010:

we demonstrate how two commercial QKD systems id3110 Clavis2 and QPN 5505, from the commercial vendors ID Quantique and MagiQ Technologies, can be fully cracked. We show experimentally that Eve can blind the gated detectors in the QKD systems using bright illumination, thereby converting them into classical, linear detectors. The detectors are then fully controlled by classical laser pulses superimposed over the bright continuous-wave (c.w.) illumination. Remarkably, the detectors exactly measure what is dictated by Eve.

More generally, the full spectrum of classical side-channel attacks and hacks appears applicable to QKD decices, or the classical cryptography devices they seed.
[This is extracted from my overly long answer on what makes QKD secure - or not]