Will the speed camera trigger on M1 UK if driving below 70?

Question: If I'm driving on the M1 motorway in the UK, and the caution speed (smart motorway) is lowered because of some congestion ahead perhaps, say 60 mph, will the camera trigger if I'm going at 68mph? Or will it only trigger if I'm going above the national speed limit, i.e. 70mph?
Comment: @Mahmood smart motorways can and do have average speed enforcement, as can other motorways
Comment: @Harper-ReinstateMonica all of our speed limits are in miles per hour, and British people would typically always talk about driving distance in miles too. In general conversation, km would typically not be understood very clearly while people have an intrinsic "feel" for how far a mile is. Would it surprise you to learn that we also drink in pint measures too, not litres?
Comment: This question would have been easier to answer if the reduced speed limit was 50 rather than 60. With 60 you might just get away with 68 [depending on local authority]. If it had changed to 50, you'd be in for a fine, no doubt. I doubt the OP is referring to averaging systems, they are advertised separately. Also, your average gets a whole lot more leeway in changing conditions. Most authorities operate 'benefit of the doubt' except notable ones like Northamptonshire.
Comment: Why are people using miles on a British road?  I thought the whole world except USA and Liberia used kilometers. And Myanmar but they switched.
Comment: @Harper-ReinstateMonica -  *Why are people using miles on a British road?* Simply because road distances, and speeds, are still measured in miles. Google could have answered that. Everything but roads & beer is in metric  - though we buy fuel in litres, we still use miles per gallon. Beer in pubs, but not in pre-packaged bottles/cans, comes in pints. We never adopted the €uro as currecy either - we can be stubborn that way [for good or bad].
Comment: I think you're referring to average speed limit zone here. On smart motorways, the speed changes as per events taking place ahead on the road, e.g. accident, congestion, etc, and changes back to National limit when all is clear.
Answer: It's probably safe to assume that on a smart motorway the cameras are as smart as the variable speed limit. Note that many of the cameras don't measure your speed, but record the time that you passed, which will be networked to the next camera to check your average speed.
But anyway, the true speed is usually less than what your speedometer says. The UK Construction & Use Regulations require that a speedometer may not under-read at all, but may over-read by up to 10% (See Hansard). So manufacturers typically calibrate the speedometer so that it over-reads by 5% to give them the greatest flexibility of being within the law.
So if the speedometer reads 68 mph, your true speed might be 64-65 mph. But perhaps your satnav was telling you the 68.
And then there is the leeway that the speed cameras allow. Advanced Driving UK says:

Even though you must adhere to all speed limits at all times, many Police forces have some tolerance for their speed cameras. For those that do, the tolerance is usually 10% over plus 2 mph.

This means that in a 60 mph restriction some police forces may allow you to travel at (60 + 6 + 2) = 68 mph. They say some forces and I am told that in Scotland there is no leeway allowed.
If they do allow the leeway, and your true speed was 65 mph, you may "get away with it".
Comment: **Comments have been [moved to chat](https://chat.stackexchange.com/rooms/149553/discussion-on-answer-by-weather-vane-will-the-speed-camera-trigger-on-m1-uk-if-d); please do not continue the discussion here.** Before posting a comment below this one, please review the [purposes of comments](/help/privileges/comment). Comments that do not request clarification or suggest improvements usually belong as an [answer](/help/how-to-answer), on [meta], or in [chat]. Comments continuing discussion may be removed.
Answer: There are two types of display you can find:

The ones that look like a proper speed limit signs, just digital:

These are mandatory speed limit signs and are considered the same as a "real" speed limit sign, so you need to take them into consideration, see the other answers on how they are measured and what leeway you might get away with.

The ones that are only yellow numbers:

These are only advisory, e.g. you should reduce your speed if it's above this value, but they are not measured and going over it will not get you a speeding ticket.
Comment: @jcaron - this covers compulsory vs advisory limits - https://www.drivingtesttips.biz/advisory-mandatory-speed-limit-signs.html - the 'old' advisory limits on motorways were if not because of, then a direct result of the cameras being 'dumb'. They were set to 70 [-ish, the ones on the M25 wouldn't go off at 85] & couldn't be changed without climbing up the gantry. Modern ones are switched with the same data network the signals use.
Comment: The first image is from a smart motorway where there limits are not only for safety but for congestion management. These are always camera-enforced. You can see the speed camera symbol to the right of the gantry. The second is from a "traditional" motorway - these are for safety only (though since congestion causes a safety issue they are usually applied in the case of congestion anyway). I can't corroborate that they are only advisory but they are frequently ignored (people generally slow down but not by that much) and I've never heard of anyone being prosecuted for that.
Comment: It's just as well the advisory limits are only advisory — at least around Glasgow it's quite common to see wildly different limits on successive gantries!
Comment: Indeed, the absence of a red ring on the speeds in the second photograph indicate the speed given there is advisory. These gantries are normally controlled by highway control centres in response to incidents or congestion detected ahead. The Traffic Signs Regulations and General Directions 2016, section 10, part 2. The advisories are given in section 11, part 2. https://www.legislation.gov.uk/uksi/2016/362/contents/made ... the advisories, given they can be activated manually, can sometimes be erroneously left active some time after they are no longer required!
Comment: Do you have a source for that? Is the difference in presentation not just a matter of generation of the displays?
Comment: Yes and the appearance has been changed to make it very clear to drivers that it's something new and enforceable. You don't see many drivers speeding on a smart motorway.
Comment: +1 and I think the answer would be improved by including the comment by @CosmicOssifrage
Answer: You should assume it will trigger at the displayed speed limit.
From RAC What are the rules on a smart motorway?

The same laws and sentencing applies for speeding on a smart motorway, but with more cameras on smart motorways and variable speed limits, motorists typically have a much higher chance of getting caught and fined for speeding.

This is further fuelled by the fact that many drivers do not realise cameras on smart motorways that enforce variable speed limits can still catch you travelling over the national speed limit, when a variable limit isn't in place.

Highways England has stated that: "If no special speed limit is displayed then the national speed limit applies. Speed cameras are in operation on smart motorways. If you don't keep to the speed limit, you may receive a fine."
Comment: @PeterM British English usage :-)
Comment: @PeterM There's no national minimum speed, however there are certain roads that will display the slowest speed that you can drive.  https://www.moneyexpert.com/car-insurance/uk-speed-limits-explained/ I interpret 'to' in the Highways England advice in my answer as  'within'.
Comment: I would interpret 'keep to' the speed limit to mean 'obey' the speed limit.
Comment: @SteveMelnikoff why shouldn't they? The systems know who the registered keeper is (who gets the ticket), and the class of vehicle.
Comment: Thanks, @traveller. Really helpful.
Comment: That last sentence seems weird. "If you don't keep to the speed limit, you may receive a fine."   (To me) This implies that that if you are also under the speed limit then you may also receive a fine.  But I have no idea if the UK has minimum limits on any roads.
Comment: @Traveller IMHO the use of "to" is ambiguous
Comment: "...the national speed limit applies. Speed cameras are in operation...": how can they enforce that, given that the speed limit on motorways is different for different types of vehicle? Do the camera systems look up the vehicle type when checking licence plates?
Comment: @SteveMelnikoff If the camera detects speeding, it takes a digital image. The image will catch the vehicle's colour, type, make and registration plate. It may also capture the face of the driver, depending on the type of camera and which way it's facing. The camera will also record the:
Time and date of the offence
Speed you were travelling
Speed limit on the road [How do speed cameras work](https://www.theaa.com/driving-advice/legal/speed-cameras)
Comment: @SteveMelnikoff There are radar detectors available that can determine the probable vehicle type from the target range and size.  The photograph that is taken by the camera can then be used as proof of the vehicle type.
Comment: Anyone not familiar with the capabilities of the latest UK camera network should look up "ANPR" automatic number plate recognition. Cameras can track where and for how long you park [retail parks etc], whether you travel within specified zones [ULEZ, Congestion Zone], whether your MOT, tax & insurance are up to date; average speed along road segments… Smile, you're on camera wherever you go. The motorway cameras are actually primitive by comparison.
Answer: If the motorway is 'smart' - indicated by compulsory speed limits above each lane [ie there is a red circle around the number] then the cameras are also equally likely to be 'smart' & will change their trigger speed based on the posted speed limit.
From Advisory And Mandatory Speed Limit Signs

These small cameras are 'smart'. You should be able to see the cameras as you approach. They must be painted bright yellow…

… though sometimes even if the letter of the law is obeyed, they get a bit sneaky. This one is very hard to spot on approach, as it sits a couple of meters the far [driving] side of the gantry, rather than directly alongside.

Based on observation over many years, if the speed limit changes, then you are allowed approximately 5 seconds to comply. Many a time I've seen the first few past the camera get flashed just after a change. I have no idea whether those few actually got tickets, or whether a human decided against it afterwards.
One thing to point out is that not all gantries have cameras & not all cameras are on gantries, some are stand-alone at the side of the road. They can capture traffic on all 3 or 4 lanes from that vantage point.
The older 'dumb' cameras do not change when the speed limit chnges. These are usually on motorway sections that haven't yet been updated to 'smart' status, and are usually accompanied by the advisory speed limit signs [because they can't be practically enforced]. Some of them used to flash once not twice as a warning, if you were over but not by enough for a ticket. This seems to no longer be the case.
You can just spot these on approach [though Google Streets seems to not be able to catch them from their viewing angle], as large grey boxes on brackets, hanging on the far side of a gantry. You cannot rely on absence of cameras on the opposite carriageway meaning corresponding absence on your side.
Picture looking back…

Picture showing gantry & brackets. You can usually see these as you get close - some still have the brackets but no cameras.

Some of them wouldn't even trigger at 85mph [whatever the speed limit said]. Few of them seem to be active at all any more. Many of the early ones were loaded with actual film which required changing periodically. Highly impractical in this day & age, but it's easier to leave them up as a visible deterrent than take them all down.
Vehicle speedometers are allowed to read high, but not low - so in all possibility, you were not going quite as fast as you thought.
Practically, at 68 in a 60 zone, you are borderline. Some authorities allow you to do speed limit + 10% + 2mph. Some do not. Few authorities actually publish their limit allowance, so much of this is hearsay. Scotland & Northamptonshire are notoriously tight on their limits. There may be others.
If you triggered the camera, you should have noticed the double camera flash, one second apart. Just because you triggered it does not necessarily mean you will get a ticket. It may have been someone else who triggered it, so you get away with it. They may decide you were so close to their allowance that it's not worth a ticket. The only way to know for certain is keep watching your post box.
From comments…
Anyone not familiar with the capabilities of the latest UK camera network should look up "ANPR" (automatic number plate recognition). Different types of camera can track where and for how long you park [retail parks etc], whether you travel within specified zones [ULEZ, Congestion Zone], traffic light, bus lane & yellow box violations; whether your MOT, tax & insurance are up to date; average speed along road segments…
Smile, you're on camera wherever you go.
The motorway cameras are actually primitive by comparison.
Comment: Thanks, @Tetsujin , your last para is exactly describing my situation :D.
Fingers crossed.
Comment: If you ever drive abroad you will not be warned as much for speed cameras. Most are not announced at all.
Comment: Sure - but when I don't know the roads, I stick to the limit anyway. I've driven in much of Europe & the US… carefully, and used to do 1,000 miles a week in the UK. When I know where all the cameras are, then it's a fun game to play ;) [I already knew where to look for each of these camera types on Google Streets, because I've passed them all a thousand times.]


Import/merge with socialsounddesign.com?

Question: http://socialsounddesign.com is another audio recording and production SO-engine-driven site, and it's been around much longer.  It already has a large user base and a lot of questions and answers.  Is there any way the two efforts could be merged?  I don't know who runs social sound design, if it's a commercial endeavor, etc, but it would be nice to get all the Qs and As in one place.
Comment: I like snippets like **Don't forget to up-vote the question or answer if you find...** and **Please note: When commenting on someone's question or answer, you will not receive...**. Useful (and unobtrusive).
Answer: I think this is similar to this discussion on DJ questions.  SocialSoundDesign has some hardware, software, and engineering questions that would be on topic here, but their focus seems to be more on the artistic and creative aspects of sound design.
Another thing I noticed is that their community seems a little looser than most StackExchange sites.  Questions that would be closed here are answered and upvoted on SocialSoundDesign.  Some examples (just from the first page of questions):

Assembling my first recording package. What to buy?
Your most interesting recording of 2010
A good read for Xmas holidays!

So my opinion is that there may be opportunities for referrals between the two sites but I don't think they're similar enough for a merge to work.  Regardless, I emailed Andrew Spitz who runs the site and linked him to this discussion so we'll see if he has any input.
Answer: Andrew Spitz from SocialSoundDesign.com emailed me his response to this thread since he didn't have the 5 rep required to post on meta.

On one hand I would love to merge and
  attempt to be part of the SE 2.0, on
  the other they made it very
  unappealing for me to let go what we
  have built and go towards something
  that is not a guaranty that we'll even
  make it though the beta phase. I'm
  pretty annoyed with SE, as at the
  beginning they kept changing their
  ethos and criteria so often that it
  reached a point where I couldn't keep
  up anymore and just gave up. Even
  though SSD has got a really nice
  community and a relatively big one for
  this kind of topic, they said I
  wouldn't be able to do the jump
  without starting again. Their standard
  is a general one, not one based on the
  topic, we don't qualify.
In terms of content I think both our
  SE sites would fit. Although somewhere
  down the line, users on SSD mentioned
  they would prefer not to merge. As you
  mention, I like that we can keep it
  looser and do our own thing. As I
  mentioned before, it's really
  frustrating when you're with a company
  that changes their ways everyday. I
  don't know how fair it is on the users
  of SSD to move everyone and have them
  loose their reputation points.
Basically, moving to 2.0 is a gamble -
  even merging with you guys, which
  would be a good option. If we decide
  to move, and don't fit their quota,
  then we loose everything, and I don't
  think it's worth the risk. They
  explicitly said that once we decide to
  go to 2.0 we can't go back :-( sad.
It's a pity, cause it would be great
  to be part of the bigger picture.
  Would love to have the iPhone/iPad
  app, and the rep points that go from
  one to the next SE site.
Please understand that it's not your
  SE site the problem, but the jump to
  2.0. I hope you guys make it past the beta, but if you don't, you have a
  home with SSD!
Answer: It looks like a SE 1.0 site. If they're open to migrating to SE 2.0 and being merged with this site, I have no problem with it. But this audio.se has very little in the way of questions yet.
They've been around since February. Just a guess, but I think it more likely they'd want to be migrated to 2.0 and questions here would be merged with their content; that's what I'd want if I were a member of a community that had been around for a while.


Salesforce Marketing Cloud RetrieveSalesforceOgject

Question: I am planning to use Marketing Cloud Journey Builder to send emails based on case status changes in sales cloud. We are connected with MCconnect.  Apparently I need to use RetrieveSalesforceObject formula in the email to surface different fields on the case/order/orderItem objects. We are using the contactid as our subscriber id. Can someone point me toward resources or share additional information on examples, syntax, gotchas and how to use this formula? I've tried a few times and keep getting stuck.  Thanks for any help!
Comment: Here's the RetrieveSalesforceObject function: https://ampscript.guide/retrievesalesforceobjects/, but I wouldn't use it in an email as it could affect performance. I suggest synching the case data and using lookups to Synchronized Data Extensions instead
Answer: Thanks. I am still struggling with this. I do have Synchronized Data Extensions, but i need data from 3 different objects/extensions.  I want to send an email to each Order in a specific status. That email will have the order detail and will need to pull all of the product line items associated with that order.  The subscriber key is our contact. A contact may have multiple orders at one time.
I have created a SQL query for the contact and order, and another one to join contact, order, and order product.
I thought i could use a lookup into the contact and order data extension and then a lookuprows into the contact/order/orderproduct to get the rest of the info, but its not working.
Do i need all of the fields in the same data extension? How can i get the right starting order? I am clearly very new to this. Any help would be appreciated!
Thanks!


The tensor product in the Hamiltonian of graphene

Question: I have the Hamiltonian of pristine graphene
\begin{equation}
H=v_{F}.\boldsymbol{\gamma}.\boldsymbol{p}
\end{equation}
with $\boldsymbol{p}=(p_{x},p_{y})$ is the momentum operator, $v_{F}$ is the Fermi velocity and  $\boldsymbol{\gamma}=(\gamma_{x},\gamma_{y})$ given by
\begin{equation}
\gamma_{x}=\sigma_{z}\otimes\tau_{x}\otimes s_{0}, \qquad  \gamma_{y}=\sigma_{z}\otimes\tau_{y}\otimes s_{0}
\end{equation}
The unit $2\times2$ matrices $\sigma_{0}$, $\tau_{0}$ and $s_{0}$ together with the pauli matrices $\boldsymbol{\sigma}$, $\boldsymbol{\tau}$ and $\boldsymbol{s}$ act  on the valley-$1/2$, sublattice-$1/2$ and spin-$1/2$ two-dimensional subspaces of graphene, respectively.  We can be written $H$ in the matrix form
\begin{align}
&H=
\begin{pmatrix}
0 & v_{F}\left(p_{x}-ip_{y}\right)  &0   &0  \\
v_{F}\left(p_{x}+ip_{y}\right)   & 0 &0 &0  \\
0 &0&0&-v_{F}\left(p_{x}-ip_{y}\right)  \\
0 &0 &-v_{F}\left(p_{x}+ip_{y}\right)  &0
\end{pmatrix}
\end{align}
My question is that: why we have a  $4\times4$ matrix ? Normally the tensor product of the three matrix given matrix $8\times8$.
Answer: $s_0$ is just the unit matrix. It is not explicitly written in the Hamiltonian  - every entry in the $4\times4$ matrix is a $2\times2$ unit matrix itself, but since it's just a unit matrix, a simplified notation is used.
Comment: is there the possibility of giving some explanations concerning that because I understood well and thank you so much for your answer


Rehosting Windows Workflow Foundation Usage

Question: I need to create an application to auto generate C code. ie. User can design the logic from the G-UI using basic blocks from C. This is similar to Matlab Code Generation. I need to do this using .net framework. When I search for the samples, I've seen about rehosting workflow foundation. I don't have any idea about WF4. Can you please anybody tell me is it possible to do the designer(Design is like flowchart) using WF4? And also I have seen some samples using MFC? I'm not sure which one can be applicable for my situation..
Answer: I think you are confusing the Flowchart and Rehosted Workflow designer in WF  as some kind of UI to draw  the flowcharts.
Workflows are meant for executing business process and the different blocks like If-Else
While etc help to implement a business logic.
Workflow Designer just provides a visual way of representing those if else / whiles etc so that developers and possible super users of the application can modify the business logic in a more visual manner instead of writing them using code.


A bijective function $f$ is continuous iff it is open(?)

Question: I'm reading Matsuzaka Topology and it says a bijective function $f$ is continuous iff it is open. Then how can I prove this? The book also says it is obvious but it's not obvious to me. I'm so confused, how can I prove this?
Comment: This is false. $f$ is continuous if and only if $f^{-1}$ is open. Can you see why now? It should be much easier, it's just the condition $$\mbox{ for all open $U$, $f^{-1}(U)$ is open}$$
Comment: In general, this claim cannot be correct, since a bijective, continuous and open function is a homeomorphism, which is (much) stronger than bijective+continuous. In which context does Matsuaka make this claim?
Comment: not $f$ but $f^{-1}$
Comment: Oh, I'm so sorry...I misread my textbook. Thank you very much Crostul and Haemi!
Comment: What *did* it say then?
Answer: The author probably means that a bijective function $f:X \to Y$ is open iff its inverse is continuous. And $f$ is continuous iff its inverse is open. This is just the observation that if $g: Y \to X$ is the inverse of $f$: for any (open) subset of $Y$: $f^{-1}[O] = g[O]$.
Also true for bijections: $f$ is open iff $f$ is closed, because
$f[X\setminus A] = Y \setminus f[A]$ for all $A$ (so if $f$ is open, the image of a closed set, which is of the form $f[X\setminus O]$ is again the complement of an open set $f[O]$, hence closed, and vice versa).
Answer: This isn't true: consider the function $f:[0,1) \rightarrow S^1$ given by $f(x) = e^{2\pi ix},$ where the notation $S^1$ refers to the $1$-sphere, defined by: $$S^1 = \{z \in \mathbb{C} : |z|=1\}.$$
Then:

$f$ is a bijection
$f$ is continuous
$f$ isn't open; for instance, the set $f([0,1/2))$ isn't open in $S^1$.


Accuracy on the test set do not change. Why?

Question: I train a SVM classifier using 36 features. If I use all the features, the train accuracy is about 0.96, the test accuracy is about 0.77. Then I change the number of features. The train accuracy drops while the test accuracy remains the same. Even if I just use one feature, the test accuracy is still about 0.77. I use cross validation, but the result does not change. I can not figure it out. So how does it come about?
Comment: What's the ratio of positives in your dataset? (Is it 0.77, or 0.23?)
Comment: http://pages.cs.wisc.edu/~shavlik/roc.pdf
Comment: @Dougal About 0.77. Is it because that I have an unbalanced training set? Meanwhile, the features are often sparse, it means that maybe many entries of the feature vector are just zero due to the unavailability of data.
Answer: It seems a bit suspicious that your constant accuracy number and the ratio of positives in your dataset are about the same, doesn't it?
It seems that your model is always predicting a positive label on the test set, though in some cases it's predicting negative on the train set.
Some possible remedies:

Try other hyperparameters. This sounds in particular like maybe your RBF kernel bandwidth is too small, if you're using that. Maybe try different kernels altogether.
Weight your training instances, so that the model cares more about getting the negatives right than it does about positives. Do this only if that's what you actually care about....
Maybe your features just aren't any good. Try getting better ones if you can, or perhaps weighting them differently or otherwise transforming them.


$f^+\mathscr{G}$ not a sheaf even if $\mathscr{G}$ is

Question: I have read that there are continuous maps $f:X\to Y$ and sheaves $\mathscr{G}$ on $Y$ such that $f^+\mathscr{G}$ is not a sheaf. Do you have an easy example for me?
Comment: What is $f^{+}\mathscr G$?
Comment: $(f^+ G)(U) := \varinjlim_{V \subseteq Y \text{ open}, f(U) \subseteq V} G(V)$.
Answer: Let $X$ be a topological space containing two closed points $x,y$ and let $i : \{x,y\} \to X$ denote the inclusion map. Notice that $\{x,y\}$ carries the discrete topology. Let $F$ be a sheaf on $X$. Then $i^+ F$ is a presheaf on $\{x,y\}$ which is given by $(i^+ F)(\emptyset)=1$ (the terminal set), $(i^+ F)(\{x\}) = F_x$ (the stalk at $x$), $(i^+ F)(\{y\})=F_y$ (the stalk at $y$)
and
$$(i^+ F)(\{x,y\}) = \varinjlim_{ U \subseteq X \text{ open}, ~ x,y \in U } F(U).$$
Hence, $i^+ F$ is a sheaf if and only if the canonical map
$$\varinjlim_{ U \subseteq X \text{ open}, ~ x,y \in U } F(U) \to F_x \times F_y.$$
is an isomorphism. But this doesn't have to the case, even if $F$ is a sheaf. At least, the map is injective. When $x,y$ can be separated by disjoint open neighborhoods, then the map is surjective.
If $F$ is a sheaf of rings, then surjectivity of the map would imply that $(1,0)$ lies in the image, which means that there is a section $s \in F(U)$ with $x,y \in U$ such that $s_x = 1$ and $s_y = 0$. Now consider for example an integral scheme $X$ and its structure sheaf $F = \mathcal{O}_X$. Then $F(U) \to F_x$ is injective. Then $s_x=1$ implies $s=1$, but $s_y=0$ implies $s=0$, a contradiction. Hence, any integral scheme with two closed points (for example $\mathrm{Spec}(\mathbb{Z})$) provides a counterexample. This is just what came into my mind, I am sure that there are many other (possibly more natural) counterexamples.
Comment: Thanks for your answer. To understand the last part it's probably the best when I first go on reading in the book for a few pages. But it's nice that you mentioned that $(i^+F)(\{x\})=F_x$. When I read page 54 in the book I wondered if we already have $i^{-1}F=i^+F$ so that we don't need a sheafification in this case ($i:\{x\}\to X$ is the inclusion map here again). By the way: Is it correct that the author means $i^{-1}F(\{x\})$ when he writes $i^{-1}F$?
Answer: The following counterexample should work, if I am not missing anything.
Let $X$ be an infinite set equipped with the cofinite topology (the one where closed subsets are given by the finite subsets and the whole $X$). Since $X$ is infinite, it is connected (if $U\subsetneq X$ is a proper, non-empty subset, it cannot be both open and closed, because it cannot be both infinite and finite). Furthermore, it is immediate to see that any subspace of a cofinite topological space is a cofinite topological space and, if this subspace is finite (as a set), then it is also discrete. In particular, our $X$ is a topological space such that every (non-empty) open subset is connected: this is the key point we need.
Indeed, let $Y$ be a finite subset of $X$ (having at least two distinct elements), endowed with the subspace topology and  denote with $i\colon Y\to X$ the inclusion map. Let us consider a set $A$ which is not empty nor a singleton and the constant sheaf $\mathscr{F}$ over $X$ with fiber $A$ (so, up to isomorphisms, $\mathscr{F}$ is the sheaf of locally constant functions on open subsets of $X$, with values in $A$). Now, for each open subset $U\neq \emptyset$ of $X$, connectedness of $U$ means that $\mathscr{F}(U)\simeq A$.  This implies that, given any non-empty subset $V$ of $Y$,
$$
(i^{+}\mathscr{F})(V)=\varinjlim_{V\subseteq U\subseteq X} \mathscr{F}(U)\simeq A.
$$
So, for an open subset $V$ of $Y$, if $\mathscr{G}:=i^{+}\mathscr{F}$, $\mathscr{G}(V)\simeq \{0\}$, if $V=\emptyset$, whereas $\mathscr{G}(V)\simeq A$, if $V\neq\emptyset$. This is not a sheaf, because $Y$ admits disjoint open subsets $V,\ W$, with $\emptyset\neq V\neq W\neq\emptyset$ ($Y$ is a discrete space, so it is totally disconnected). Indeed, if $a\neq b$ are elements of $A$, $(a, b)$ is a compatible family for $\mathscr{G}$ with respect to $\{V,\ W\}$ (which is an open covering of $V\cup W$) and it clearly does not admit any amalgamation in $\mathscr{G}(V\cup W)\simeq A$.

EDIT: As required by the OP, I try to explain better why $\mathscr{G}(\emptyset)\simeq \{0\}$ above. Firstly, let us take a look at the definition of $(i^{+}\mathscr{F})(V)=\mathscr{G}(V)$; it might be worth saying that writing
$$\varinjlim_{V\subseteq U\subseteq X} \mathscr{F}(U)$$
is a sloppy (but quite acceptable, I would say) notation to mean the following. For $V\subseteq Y$ open, let $I_{V}$ be the full subcategory of $(\text{Open}(X))^{op}$ given by those $U\in\text{Open}(X)$ such that $V\subseteq U$ (here $\text{Open}(X)$ is the poset of open subsets of $X$, ordered by inclusion and seen as a category in the canonical way). If $\mathscr{F}_{\vert I_{V}}$ denotes the restriction of $\mathscr{F}$ to $I_{V}$, then
$$\varinjlim_{V\subseteq U\subseteq X} \mathscr{F}(U):=\varinjlim \mathscr{F}_{\vert I_{V}}.$$
Now, if $V$ is open also in $X$ (and of course this is the case when $V=\emptyset$), then $I_{V}$ has a terminal object, given by $V$. This implies that $\varinjlim \mathscr{F}_{\vert I_{V}}\simeq \mathscr{F}(V)$ thanks to an easy exercise in general category theory: given a functor $\mathscr{T}\colon\mathcal{J}\to\mathcal{C}$ between arbitrary categories, if $\mathcal{J}$ has a terminal object $1$, then $\varinjlim\mathscr{T}\simeq\mathscr{T}(1)$.
Comment: I don't know the term fiber. But is the sheaf you define on $X$ just the sheaf of Example 2.25 in the book (the sheafification of the presheaf where every open set $U$ gets assigned the set $A$ as set of sections)? However, I don't understand why $\mathscr{G}(\emptyset)=\emptyset$. Can you explain that to me?
Comment: @principal-ideal-domain Yes, I mean that sheaf (here, the term "fiber" is referred to the fact that each fiber of the etale space associated to the constant sheaf with stalk $A$ is precisely $A$). As for the second part, I suspect you want to understand why $\mathscr{G}(\emptyset)\simeq\{0\}$, as I stated in my original post. If this is the case, I've just edited the post above to try and answer your question ;)
Comment: Thanks. So for each subset $V$ of $Y$ we have that $(i^{+}\mathscr{F})(V)$ is the set of all constant functions $V\to A$ (in particular if $V=\emptyset$ there is only one such function, hence $|(i^{+}\mathscr{F})(\emptyset)|=1$) and $(i^{-}\mathscr{F})(V)$ is the set of all functions $V\to A$. If $|V|>1$ and $|A|>1$ that's obviously not the same, therefore $i^{+}\mathscr{F}\ne i^{-}\mathscr{F}$.


animation character not working

Question: I made a character in makehuman and imported it in blender and then I downloaded the animation of dancing from cmuconvert and loaded it and played the animation and it shows like this
Answer: I don't know cmuconvert, but I know for sure that animations are not compatible with any rig. Basically, an animation can be used on your rig only if your rig is quite close to the rig used for creating the animation. Including bone names.
That being said, I did some research and found this thread about importing animations from cmu.
You might find the needed plugins here.

animation character not working


Source for North American public boat and kayak launch sites?

Question: Does anyone know of a good source for North American public boat and kayak launch sites for mapping in a GIS. I would prefer a web service.
Comment: Worldwide? Or for a specific country?
Comment: Sorry, I should have put that in. North America only..
Comment: Did you do it by state? Would you consider sharing?
Answer: I am not aware of a National Dataset with this information in it.  There are several regional web pages that have this information for the state/county level.  Is there a specific state you are interested in?
For Example:
See this topic as it seems to be exactly what you are looking for:  http://freegeographytools.com/2009/marine-navigation-gis-data
Great Lakes Boat Launches - http://www.great-lakes.net/gis/metadata/acp/
Boat Launch Ramps in Many States - http://www.launchingramps.com/
State Files:
LA - https://catalog.data.gov/dataset/louisiana-marinas-and-boat-launches-geographic-nad83-losco-2004-marinas-losco-2004
NY - https://catalog.data.gov/dataset/boat-launch-sites-by-waterbody
CA - http://www.dbw.ca.gov/maps/facilityindex.asp?searchfield=FACILITY_TYPE&searchterm=Launch
MA - http://www.mass.gov/anf/research-and-tech/it-serv-and-support/application-serv/office-of-geographic-information-massgis/datalayers/ofba.html
WI - http://dnr.wi.gov/topic/lands/boataccess/
MD - http://dnr2.maryland.gov/Boating/Pages/water-access/boatramps.aspx
PA - http://fishandboat.com/access.htm - fill out the form to send to Commission office for this information
CT - http://www.depdata.ct.gov/maps/boating/boatingmap.htm
CO - https://www.arcgis.com/home/item.html?id=6b17044b2d2a4ef69b7b30c503bf8828
WA - http://wdfw.wa.gov/lands/water_access/
And finally a third party proprietary application that holds this data:
https://activecaptain.com/
Comment: Thx, that's great. Yeah I was coming to the to the same conclusion that there is no central source but will do state by state. Thx!
Comment: Did you do it by state? Would you consider sharing?


Which article should be used in this sentence: "J'aime (les or des) livres qui contiennent des dessins."?

Question: If we consider this a generic reference to books and use les it does not seem like we are referring to all books in general since I only like some books, that is, the ones which have drawings in them.  On the other hand if we use des are we then not saying that we only like some of the books which contain drawings and not all of the books which contain drawings and it is this second interpretation which is intended.
Thanks
Comment: Your question needs some editing.
Comment: Perhaps it was the relative pronoun which caused my problem, but it is now obvious as Thomas and LPH pointed out that les applies to the whole phrase.  Similarly, J'aime les femmes avec les cheveaux roux, means a generic reference that I like all red haired women, and J'aime des femmes avec les cheveaux roux means I like some red heads.  Thanks Again.
Answer: Your interpretation of using "des" seems correct; it would seem a shortened way of saying "J'aime quelques-uns des livres qui contiennent des dessins." But with "les", the whole phrase becomes the object of "aime". So to say that you like all the books which contain drawings, "J'aime les livres qui contiennent des dessins." is the way to go.
Comment: C'est J'aime et Tu aime**s**. Quelques-unes ne convient pas ici. Le livre est un nom masculin.
Answer: I

J'aime les livres qui contiennent des dessins.

This specifies all books that have drawings in them; it is a generic reference to "book that has drawings in it". The article "les" (as in English "the" (singular noun), although "zero article + plural noun" is used much more often) is used to speak about species, kinds of things, etc. When you say that then you are saying that you are sure to like any book containing drawings and you could say it that way too;

J'aime n'importe quel livre qui contient des dessins. ("n'importe quel" is "any") or
  J'aime tout livre qui contient des dessins. or
  J'aime tous les livres qui contiennent des dessins. (same thing for the three sentences, but you insist on the fact you like them all)

II Yes, in this grammatical context "des" is "some".

J'aimes des livres qui contiennent des dessins. translation: "I like some books that contain drawings." ("des" is "some")

In this sentence you use the indefinite article "des"; it's the plural of "un". So in the singular you'd have to say this;

J'aime un livre qui contient des dessins. translation: "I like a book that contains drawings."

It means that you know a book, may be you don't own it (it's in the library or it's your friend's book) but whatever the book, you like it. If you use the plural, it's the same thing: there is a group of books and you know all of them and you like all of them. You didn't use a generic reference in this case and that means that you don't necessarily like all the books that exist which have drawings in them.


How do disable background downloads?

Question: App Store just ate all my mobile data trying to download Xcode. Is there a way to tell OS X that WiFi I'm currently using is expensive and it should not download its stuff without asking me first?
Comment: https://www.tripmode.ch might help.
Comment: This is what I was looking for!
Answer: Xcode will not download automatically until you actually press the download button in the App Store.
The only way I can think of minimising the chance of using the WiFi extensively is to disable the installing available updates in the background.
Go to App Store->Preferences->uncheck Download newly available updates in the background

You could uncheck the automatic check for updates all together, but this increases the risk of not getting latest security updates - what is not really recommended.
All these modifications mean that you would need manually download updates.
Comment: It would be awesome if there was a tool that pauses these settings. For when you are on limited data wifi or cellular...
Comment: @pjctech I don't see a way for macOS to recognise limited data as it doesn't have the internal cellular module (where you insert the SIM card). Meaning if you connect for example your iPhone's wireless hotspot running on a limited data to macOS then macOS will recognise it as a WiFi network.
Comment: Is there a way to change those settings programmatically?
Comment: @alljamin Win10 has metered connections for this purpose.
Comment: @Bowen how is this relevant for Apple software/hardware forum? Are you suggesting spinning a VM just for this purpose?
Comment: @pjctech May be there is one, but I'm not aware of it.

How do disable background downloads?


I got an error that says curl: (7) Failed to connect to localhost port 18332: Connection refused

Question: I could succeed to work the testnet at once.However after I restarted my Mac,bitcoind came not to work.
Answer: bitcoind doesn't restart after your computer restarts. Start bitcoind after you start your computer.


If the tuber of a chinese artichoke (Stachys affinis) is damaged, will it still grow?

Question: I wanted to harvest the tubers, and transplant some of them, but then I saw that they already started growing due to warmer weather than usual. I still transplanted them but many are broken or damaged where the "new growth tip" came out. Will they still grow?
Answer: Although called tubers, they are not like potato tubers that have many eyes.  From the photos on the internet, it would appear that they grow from one spot only. I have not found any article that suggests that you can chop them up to make many plants.
So, I think they will not sprout again.
I can only find statements such as this

Growing Chinese Artichokes
These vegetables may only be propagated from tubers which are planted to a depth of about 75-100 mm (3-4 inches) and 225-300 mm (9-12 inches) apart. Rows should be well spaced - 450 mm (6 inches) - which means they do take up quite a lot of room.

Article Source: http://EzineArticles.com/6513730
Answer: It appears from an illustrations in this article that there are in fact two growth tips to each tuber, one at either end. One tip connects to the root that formed it, and from which other roots may grow (similar to a Lily of the Valley plant) and the other tip forms new roots and plants. I assume you mean that your plants are damaged at this end. If they were not damaged at the other end (especially if some of the root were still attached there), then it's possible your artichoke will sprout from that spot, as is seen in many other rhizomatous perennials. I suspect that any tubers planted with both growing points missing will not sprout, however.


Uniqueness of checksums using DES-MAC encryption?

Question: I'm in an Intro to Computer Security class, and one concept I'm having trouble understanding is how two different files could produce the same checksum. How would you produce the same checksum given two different files? So far, through reading the book, I found mention of something called the "pidgeonhole principle" that seems to indicate this is possible, but I'm not sure how.
Answer: Think of it this way:

How many possible files are there?
How many possible checksums are there?

If the number of possible files is larger than the number of possible checksums, then there must be at least two files with the same checksum.
This is one of the things known as the "pigeon-hole principle"; the idea is that if you are placing pigeons in pigeon holes, and there are more pigeons than holes, then some hole somewhere will have two pigeons.
Now, if you go on further, you'll find that, if you know the MAC key, it's actually quite easy, with DES-MAC, to produce two files with the same checksum (or, for that matter, a file with a specific checksum).  However, you're not quite ready for that.


what can I do to measure the system load on my Linux box?

Question: I want to measure the system load on my Ubuntu media center computer. What commands and utilities are available? I've explored the w, top, iostat, and uptime commands. Anything else I could use?
Answer: htop is a bit more interactive way for viewing your processes. It is almost like an improved version of top.
Answer: try "sar" from the sysstat package. It'll record every 10 mins and give you a historical view.
Comment: +1 for sar, it has a multitude of options and, as well as showing regular snapshots throughout the day you can use it interactively to show a specified number of snapshots at specified intervals (e.g 5 at 10 sec intervals). There are also 3rd party tools that (I think) make recommendations based on sar. E.g. [sarcheck](http://www.sarcheck.com/)
Answer: Use top.
Comment: Yep, because it's the right tool for measuring system load, which was your question. Now that you've edited your question to be more specific about what you've already tried, you could explain why something like top isn't sufficient for your needs.
Comment: Thats it ? Just one option?
Answer: uptime is maybe the simplest way to get the CPU load. This information is mirrored in the special file /proc/loadavg.
iostat tells you the load on the IO subsystem.
Load can mean many different things, however. Depending on what you need, it could be the amount of thrashing in the virtual memory system, the load on the network interface, etc. But if all you want is an aggregate, the above two utilities are a good start.
Answer: The vmstat program can get you a time-series record of system performance.


How to make your own Tempeh?

Question: I'm looking for information on Tempeh, especially how one make it themselves. Any info would be appreciated.
Answer: Do you mean tempeh?
Tempeh is a fermented soybean product, grainier and denser than tofu. Making it requires a starter to help it ferment.
Recipes can be found here.
Otherwise, you'll have to move to Arizona.
Answer: Tempe is a fermented with the fungus Rhizopus oligosporus, you will need to find a strain or starter to make it in your home.  Once you have that, some boiling and some vinegar and a day and a half later you have tempeh.
Comment: Sorry for my misspelling. Any recipes on using it?
Comment: Sorry @abe, i'll be happy to help you fix any recipes that you find but we don't really do recipes exchanges here.  It is a javanese product so I would start looking for recipes there.

How to make your own Tempeh?


Why are Excel macro dangerous?

Question: Can someone explain me why Microsoft Excel 2012 is telling me that accepting automatically every macros is dangerous, I mean how can they be dangerous, for my worksheets, for my entire computer ?
Answer: Excel macros are written VBA (Visual Basic for Applications). Those scripts can (potentially) gain access to your operating system, and file system: deleting files, uploading data, downloading spyware etc. That's why you have to be sure you trust the script source before allowing it to run.
Answer: Macros written with malicious intent could harm your computer, the same way any malware could.
Here's an article from Boston College on the subject.
From the article:

ABOUT MACROS AND MACRO VIRUSES
A macro is a series of program commands
or instructions designed to simplify repetitive tasks within a program
in the Microsoft Office suite (such as Microsoft Word, Excel,
PowerPoint, etc.). Any operating system can receive a macro virus,
even Macs, as long as you have Microsoft Office installed on it. A
macro virus is a virus that is created by using the built-in macro
programming language, designed to execute as soon as the file is
opened. It attaches itself to a document file and waits until an
application like Microsoft Word opens it.

Why are Excel macro dangerous?


what kind of custom header add to encrypted file to identify my encryption,consider safe and reliable.like pseudo format extension or file size

Question: I want to  add some  custom header to encrypted file to identify my encryption,consider safe and reliable.like pseudo format extension or file size.Is there any algorithm or tool to make it?
Comment: I don't agree, the header format can actually have a strong influence on security, including those of crypographic protocols.
Comment: I'm not sure how this is a cryptography question. Once you've encrypted it, the ciphertext is just binary data. Of course you can add any kind of header you want to it.
Comment: I'm voting to close this question as off-topic because it's about non-cryptographic encoding and asks for tools which are themselves off topic.
Answer: As indicated, the header format of your proprietary encryption is entirely up to you. Still, as I see this forgotten or done imperfectly a lot of times, I'll give some general hints in the right direction.
First of all, complexity is the enemy of security. If you make your header overly complex you may get into trouble. It could be possible to generate invalid packets, buffer overruns because of incorrect length fields or simply combination that do not make sense.
Furthermore you must be aware that attackers may be able to mess with your header format. This is mainly a problem for encryption formats that are or can be used for transport security. For transport security you should take care of man-in-the-middle attacks. So if an attacker can downgrade your security level through the header format then that's obviously a bad thing. You don't want to end up with all the configuration options for, e.g. IPSec. It makes no sense to allow (and code, and test!) AES-256 with MD5 configured together.
If you have lots of configuration options then those are likely to have a big influence on security if they haven't been established beforehand. So you must make sure you check your header format in advance. It's highly recommended to let your header format be included in any authentication tag calculation (MAC), and to make sure that that MAC verification itself isn't an issue. The simplest attack is simply to remove the MAC authentication tag entirely if your protocol supports it. This sort of attack actually happened on protocols like WS-Security (web services) due to broken implementations of both Glasfish and Apache/Tomcat where the signature was simply stripped off and the server accepted those messages without issue.
Probably the simplest header is a single identifier defining the version of the protocol. That version then defines a well defined suite of algorithms with parameters that make sense. So for instance byte version 01 would indicate that AES-GCM is used with a security level of 128 bits. The security level of 128 bits is then maintained for all other algorithms as well (e.g. key derivation with 256 bit hashes and RSA with 4K bit keys.
It may be useful to define an additional 8 byte constant value so you can identify the file type by looking at the content instead of the file extension (if applicable, e.g. for in place file encryption).
So there you are:

apply the KISS principle, don't allow overly flexible configuration;
make sure you are protected against attacks on the header and that buffer overruns are not possible (or at least warned against);
verify the validity of the header upon receival, checking as much as possible, and at least an authentication tag;
include a constant value for file identification when applicable.
Comment: Note that I'm a bit at odds with many people on how flexible a security protocol should be. Unfortunately I could not stop the idiotic amount of configuration options for some protocols (each option multiplies the number of configurations you have to test, e.g. running up to over 4 billion options for some protocols I've reviewed). I view just defining logical *sets of* configuration options a better idea.
Comment: So you recommend against a header that says something like "AES-GCM256-HMAC-SHA256", and favor one that says "\x01" with the implication that "\x01" encodes for AES-GCM-HMAC-SHA256?
Comment: @EllaRose Yes, I do precisely that. Especially for proprietary protocols.


How to change nofollow links to dofollow links in WordPress

Question: I am running a self hosted WordPress site and almost all settings run on default. One of my guest author asked me to change the nofollow links to dofollow links. I don't know how to do that for my web site.
Answer: This plugin should do the job: it allows to add dofollow / nofollow on author basis.


What is relationship between "significant correlation" and "significant difference"

Question: What is relationship between "significant correlation" and "significant difference" between two variables?
Answer: If you have two different variables, you can calculate how they are correlated. Does height correlate with blood pressure? Does age correlate with income? You can also compute a 95% confidence interval for the correlation coefficient.
If you have one variable measured in two groups, you compute the difference between the two means. You can also compute a 95% confidence interval for the difference.
The concept of "significance" is so often misunderstood, I think it is best to just stop with the confidence intervals. But you can ask if the correlation coefficient is far enough away from zero (considering the sample size) to be statistically significant, and if the difference between the two means is far enough from zero (considering the sizes of the two samples, and the variability within the two samples) to be statistically significant.
The key distinction is whether you have two variables, or one variable in two groups.
Comment: My question is that what is relationship between "correlation" and "difference" between two variables?
X and Y are correlated. Do they must have difference?
X and Y are different. Do they must have correlation?
Answer: Your comment is clearer than your original question – enough so that I may be able to clear things up for you.

My question is that what is relationship between "correlation" and "difference" between two variables? X and Y are correlated. Do they must have difference? X and Y are different. Do they must have correlation?

The short answer to both is no.
If $X$ and $Y$ correlate, any less-than-perfect correlation $(|\rho|<0)$ implies differences in individual values, but not necessarily in summary statistics like means, medians, variances, etc.
For example, with $X=\{0,0,1\},Y=\{0,1,0\},\mu_x=\mu_y,\rho=-.5$. With $X=Y,\rho=1$. However, with with $X=-Y,\mu_x=-\mu_y,\rho=-1$.
Thus only in the case of a perfect correlation can two variables exhibit no differences whatsoever, but the possibility remains that they are exact opposites. Correlation implies nothing about differences in means, medians, or variances.
If $X$ and $Y$ differ, they may or may not correlate; there is no "must" here.  For example, with $X=\{0,0,0\},Y=\{0,1,0\},\mu_x<\mu_y$, but since $X$ has $\sigma=0$, $\rho$ is undefined. Conversely, with $X=\{0,0,1\},Y=\{1,1,0\},\mu_x<\mu_y,\rho=-1$. These examples are the simplest I can think of.
Comment: Dear Nick, What is your interpretation about undefined ρ?
Comment: There is no information to interpret about correlations involving one variable with completely invariant data.
Answer:
Testing the statistical significance of correlation coefficients involves the same logic as testing the statistical significance of differences between group means or proportions.  Whereas the null hypothesis in the latter tests states that there is no real difference between groups in the population and that any observed differece in our sample is due to sampling error, the null hypothesis with correlation coefficients states that there is no real correlation in the population (i.e., $r= 0.00$) and that any observed correlation in our sample is due to sampling error.  Just as in other tests of significance, sampling error when testing the statistical significance of correlation coefficients involves the use of theoretical sampling distributions with an assumed mean correlation of $0$.

From :Statistics for Evidence-Based Practice and Evaluation
By Allen Rubin

Comment: I'm sorry I can't even read that. You're welcome to type in a short quote if you want your answer to be legible, but it would also be a good idea to add some of your own thoughts, e.g. interpreting the material in the light of the question.


How many troops did the Confederate and Union army have in each year of the Civil War?

Question: How many troops did each army of the civil war have in each year of the war from 1861-1864 and how many casualties did they have each year?
Comment: Welcome to History:SE. Could you edit your question to clarify what you've looked into already, complete with links and references, and context if applicable? In particular, please let us know what you find missing or unclear about the Wikipedia entry on the topic, if one exists. This allows those who might want to answer to do so without needing to redo the work you've already done. You might find it helpful to review the site tour and Help Centre and, in particular, How to Ask.
Answer: As I remember, at the beginning of 1861 there were about 16,000 soldiers in the United States Army, the regular army, and the United States Volunteers were not yet formed.
And at the beginning of 1861 the Confederate States of American was not yet formed and didn't have any armed forces.
By January 1865 the Confederate army had already some time earlier reached its maximum size and had been declining rapidly in numbers for some time, probably having about 200,000 to 300,000 total men available for duty in January 1865.
The total number of Union soldiers reached about 1,000,000  in May 1865, when enlistment stopped and men started to be discharged.  At that time there were about 600,000 men available for duty out of the 1,000,000 enlisted.
I remember seeing a table  somewhere like you asked about, with the numbers of Union and Rebel soldiers for each year of the war, but I have not found it yet.
Added 03-09-2020:
Here is something:

In July 1861, the two armies were nearly equal in strength with less than 200,000 soldiers on each side; however at the peak of troop strength in 1863, Union soldiers outnumbered Confederate soldiers by a ratio of 2 to 1. The size of Union forces in January 1863 totaled over 600,000. Two years later, that number had not changed dramatically for the Union Army but had dropped to about 200,000 for the Confederate Army.

https://www.nps.gov/civilwar/facts.htm2
Here is a link to a chart with the size of the United States armed forces by branch each year from 1789 to 1997:
https://www.alternatewars.com/BBOW/Stats/US_Mil_Manpower_1789-1997.htm1
Comment: @Pieter Geerkens  I have rewritten my sentence to make my meaning clearer. "By January 1865 the Confederate army had already some time earlier reached its maximum size and had been declining rapidly in numbers for some time, probably having about 200,000 to 300,000 total men available for duty in January 1865."  I think that makes my meaning clearer.
Comment: Upon reconsideration, I suspect your original claim may be correct.  Although broken into pieces, the area of the C.S.A. isn't really beginning to lose population centres (except New Orleans) until early 1865.
Comment: That works for me.


Acceleration in free fall

Question: A body in free fall "feels" no gravitational force (equivalence). Why does it continue to accelerate.
Why is your program refusing my question?
Comment: Possible duplicate of [Why does a free-falling body experience no force despite accelerating?](https://physics.stackexchange.com/q/196136/)
Comment: @Maxim The OP is specifically talking about feeling gravitational force which no freely falling (small enough) observer can feel. Yes, sure, you can feel the drag, anxiety, excitement, and many other irrelevant things--but that is not the point here.
Comment: It can also be seen as conservation of mechanical energy(neglecting the losses). The body at a height has potential which goes on decreasing as it falls so the Kinetic energy must increase ie velocity must increase.
Answer:
A body in freefall "feels" no gravitational force

Sure it does! It does on the space station too. You just don't feel it. "Wait!", you say, "you just said I feel it and don't feel it!" Yes, that's because there's two definitions of "feel".
One is "feels a force", that is, "there is a force". In that case all bodies "feel" gravity, even on the space station.
But then there's the other "feel", which is "a sensation on your body". By that definition you never feel gravity. No, really, think about it...
You're sitting in a chair reading this right? Do you feel your butt on the chair? Maybe your elbows on the arms of the chair? Yes?
But think about what you're actually feeling - you're feeling the chair pushing up on you. Just stop and experience it for a second.
Do you actually feel gravity? No! Not directly anyway (your inner ear gets a little finicky).
Free fall is literally the state when nothing is pushing back. You still don't feel gravity in either case. But in free fall, you don't feel any of those things you would normally ascribe to gravity but aren't actually gravity, because you remove those objects.
So the confusion is the question is mixing two very different definitions of "feel". Objects continue to accelerate because "there is a force", but you do not "experience the sensation" because you never do.
Comment: Forces between the fluid in your inner ear and the walls of the chamber that contains it are no different in principle from the forces between your butt and your chair.  They "feel" different only because of how the nerves are arranged (sensing motion of the fluid in your ear, vs. sensing pressure on your skin.)
Comment: -1: This answer is misleading. There is a force of gravity on a person in the space-station with respect to the Earth's frame of reference. But there isn't one with respect to the local inertial frame in the vicinity of the space station that the space station itself is.
Answer: Whether you're standing on Earth or falling towards it, a gravitational force is acting upon you. It's because both you and the Earth have mass. The reason you "feel" gravity when standing is because you're being pushed or squished onto the surface of the Earth. It's a solid thing and it's giving resistance so your body, bones etc are being "compressed". That's what you feel. When you're falling there's nothing except for some small air resistance so all parts of the body are equally accelerating towards the Earth and they're not in any strain in relation to each other. So you feel "relaxed" as if nothing is acting upon you.
Answer: When you stand still on the ground / on a chair etc you "feel" something.
That something is the upward force due to the ground / chair on you.
The magnitude of that upward force on you is equal to the magnitude of the gravitational attraction of the Earth on you a force which you do not directly "feel".
If you are in free fall with no air resistance then there is no upward force on you and so you "feel" weightless although there is still the force of gravitational attraction on you due to the Earth which you do not directly "feel".
That force of gravitational attraction on you due to the Earth is the force which gives you a downward acceleration.
Answer: we feel things trough our five senses. Any thing outside the domain of those senses we never feel, see or hear.
We do not have a sensory system to feel forces in a gravity, magnetic or electrical field, but we do have sense of touch, pressure...on our skin, distributed with uneven intensity, like our fingers are more wired with nerve endings.
So when we are not falling free, there is something stopping us, a floor, an elevator or earth. these are pushing against our feet, and we feel their pressure and relate it to a consequence of gravity.
When we are falling free in a gravity field there is nothing resisting it other than very small air friction, so we don't feel a force field. But its there and pulling us down. Say hold a chain letting it hang down, it will hang straight and true vertical, because you and every up hand link is fighting the gravity keeping the one below from falling. Now let it fall it will twist and dance freely while gravity is pulling it down. Why because the restrain of upward force is gone.
just as an example when we watch free parachute jumpers do things in suspension like holding hands and spiraling into flower patterns as if they are weightless, its not because gravity is not working to pull them down, its because they are free from the responsibility of having to fight the upward reaction of their weight on the floor.They are falling non the less. You can mimic that by just jumping up into a pirouette turn, albeit the period of weightlessness is short.
Comment: Yes, sorry, chain.
Answer: The only thing that changes is that you no longer feel the ground. You still experience acceleration, but you are not subject to the normal force opposing your weight. You still have a weight, just that you no longer feel its magnitude acting on you.
Answer: Imagine an infinite series of nested spheres (like skins on an onion). There is a radial (gravitational) force on each sphere directed towards a mass point located at the center of the sphere.  The magnitude of the mass determines the force on the sphere. (the sphere represents the curvature of space around the mass point. if the mass was distributed along a line instead then the sphere would be replaced by a cylinder with a force gradient between the mass line and the wall of the cylinder. however, due to the principal of least action, the mass is concentrated at a point.)  Now as we work our way out from the center of the earth we encounter a certain sphere representing the surface of the earth.  This is the limit of the earth's mass density.  Continuing outward the spheres are just mathematical.  When you are standing on the earth the force you feel is not the force pushing down on the sphere but rather the reaction force pushing up. (for every force there is an equal and opposite reaction force).  When you are a mile high and in free fall you are passing through a series of spheres (mathematical) who's surface area is ever decreasing and who's gravitational force is becoming less dispersed and more concentrated.  You must accelerate to maintain your momentum.

Acceleration in free fall


How i put some erc721 token on markelace in a game?

Question: Hi I'm building a game and wanted to implement a marketplace. The user puts the token on the marketplace and then someone buys it. I've already managed to implement something to create the market place, the problem is how to transfer the token to whoever buys it. Because when I click on buy, it gives an error saying that you don't own the token and that you can't transfer it.
Comment: Can you include the contract in your question? It hard to say what needs to be fixed without it.
Answer: First, the seller has to Approve() the marketplace contract manually or automatically, it depends on your design characteristics, for that token. Then marketplace could take care of transferring the ERC721 token from seller to buyer whenever the asked amount from the seller is completely paid.
This is the solution if your error is like this: "Caller is not approved nor the owner "
Go check out Approve() section of the ERC721 contract. I think it may help you. If your problem is something else, please provide more information.
Comment: And How i make the seller Approve() the marketplace contract automatically when the buyer press the buy button?
Comment: You have to design a button that whenever it is clicked, it should ask the seller for permission, like e Metamask pop up, to Approve the marketplace smart contract. It is more related to Web3 stuff and you should search the net for more precise information.
Comment: If you are using Remix, you have to do it by selecting the seller account and doing it manually. But if you are trying to make a user interface you should use Web3 and ask for permission by a pop-up from the seller.


The effect of gravitational lensing during the lunar eclipse

Question: During the lunar eclipse, the Moon turns into bloody colour while the shadow of the Earth is casting over the lunar surface. The red hue can be explained by means of the refraction of light and Thomson scattering. Besides these two, will the gravitational lensing effect take a role in the eclipse? That is, the Sun light is bent due to the Earth and shone onto the lunar surface, and then the light is reflected towards the Earth. If so, how significant will this effect be?
Comment: The moon's red hue can be explained by scattering, but not by refraction.  Shorter wavelengths are bent more than long, so any color shift from refraction will be towards blue, not red. This is apparent in the "green flash" sometimes seen seconds after sunset. If you observed the eclipse from the Moon (it would be a Solar eclipse, not a Lunar eclipse) the Earth's disk would be rimmed in red since you would be observing every sunset and sunrise at the same time.
Answer: Yes, the Earth will act as a (very, very weak) gravitational lens bending light from the Sun on its way to the Moon. No, this won't have any noticeable effect, unless you are looking at the Sun with an array of radio detectors spanning the surface of the Moon (maybe).
We can use the following equation to calculate the angle of deflection for light that passes within a distance $b$ of some mass $M$ (source)
\begin{equation}
\alpha = \frac{4 G M}{c^2 b}
\end{equation}
Taking $M$ to be the mass of the Earth and $b$ to be the radius of the Earth, we find
\begin{equation}
\alpha = \frac{4 G M_\oplus}{c^2 R_\oplus} = 3\times 10^{-9}\ {\rm rad}  = 0.6\ {\rm milliarcseconds\ (mas)}
\end{equation}
Remarkably, apparently this level of lensing is around the order of magnitude that modern technology can resolve (https://arxiv.org/abs/1902.07046) which is able to detect gravitational lenses at the milliarcsecond level. However to see the effect of Earth's lensing, I imagine you would need a very long baseline radio telescope array on the Moon (although, I am not an expert on the technology, so take what I'm saying with a grain of salt). In this context, "very long baseline" means an array spanning thousands of miles. Regardless, this nanoradian level of deflection is not something that would have a noticeable effect on a photograph of the eclipse you would take with an ordinary camera.
Comment: Would the variation in the refraction due to Earth's atmosphere swamp this effect? Would it be possible to filter that out?
Comment: @Barmar Let me put it this way. I found it interesting that VLBI has the angular resolution to be able to see milliarcsecond deflections. If for some reason one actually wanted to measure this effect, there is a lot more work to do to control for factors beyond angular resolution that would affect the observation, and there likely are many (including the atmosphere) that could ruin the experiment before it even starts. But, experimentalists are also very clever at figuring out what these things are and controlling them. Take this as more "not obviously impossible" than "definitely possible."
Answer: Earth's gravity is far to weak to make much difference. But the Sun's gravity makes a solar lens that could be used as a telescope, if we devoted enough resources and ingenuity to it. We could literally map the surface of an exoplanet $100$ light years away at $25$ km/pixel. See The Solar Gravitational Lens will Map Exoplanets. Seriously.


What can I do with super salty cream cheese mixture?

Question: I whipped up a cream cheese filling for sweet bread. By accident, I added salt instead of sugar... an entire cup. Now I have disgustingly salty mixture of 16 oz cream cheese (2 packages), two eggs, six tablespoons of AP flour, and a cup of salt. I'd prefer not to waste it. Any ideas? Maybe lots of spinach and more eggs and bake it quiche style? Or do you think it's beyond salvaging? Worried it might take an absurd amount of salt-free added ingredients to adjust for the entire cup of salt.
Answer: This is too salty to be worth salvaging. You could use small quantities of the mixture in place of salt in recipes where the cheese would be complementary. But since it is so salty you cannot use very much; it would take weeks to get through it all. Salt is pretty cheap, so instead, I would just discard the mixture.
To go with your quiche idea, take a look at a few recipes. They use between 1 and 2 teaspons of salt for a single large quiche. Since you have a cup of salt to deal with, this is 48 teaspoons, or at least 24 quiches! I assume you do not want to bake this many.
Comment: Agree with this answer, but if you come up with a baked quiche or dip recipe you legitimately like... Make however many, freeze it, and you just got a whole lot of Christmas presents taken care of. You could probably make some nice cheese bread with it too. Or add a lot of flour, maybe some cheddar, and roll it out for crackers.
Answer: I think your idea with the spinach and eggs is probably workable, so long as you only use a little.
You could mix some of it into soups, chowders, white sauces for pasta, biscuit batters, and many other savory dishes. Maybe even gravy. I'd probably even add it to spaghetti sauce and chili, but that would be unconventional. Just don't use all of it at once (as Benjamin already indicated; use as much as you need until there's enough salt in the dish—then don't add more). With all that salt, it shouldn't go bad any time soon. So, you shouldn't need to hurry.


Code structure to handle multiple markets? (different business rules for every state in the USA)

Question: We're developing an app that has slightly different requirements for each business market (countries and states) that it's available from.  It seems like a common situation but I can't seem to find a good article about structuring code/modules for this scenario.
It's a C# app and we're debating between Strategy vs Template patterns but there's also the consideration of folder structure and naming conventions.
It seems like a separate project for each state would get unmanageable quickly (e.g. 5 core services X 50 state-custom projects) = 250 projects!!)
Perhaps 1 custom project per service handling specializations organized in sub-folders per state?
Comment: Can you add more specifics about what exactly is different between states?
Answer: Have a single app and design the appropriate configuration solution.
JacquesB hints at this, but I want to state it more strongly.  You must do this by configuration rather than developing 50+ versions of the codebase.  Anything else will be insanely unmanageable.
If there are complex requirements which can't be handled by simple configuration parameters, design a more complex configuration solution.
Your configuration might even have a simple scripting language that defines logic requirements.  That is ok.  The key is that the "configuration" must be cleanly separated from the codebase of the app.
Otherwise, things like identifying and fixing bugs will be a mess.  With normal versioning in addition to locale-specific versions, you will have hundreds of versions in the field.  And you won't be able to easily tell whether a bug is related to the locale-specific code or the base code.
Start thinking about edge cases now.
This is a situation where there is a high risk of making bad assumptions that will be incredibly costly.  Such as "Each app user will only ever need to operate within one locale."  Is that true?  Make sure you think really hard about such issues as early as possible.
Comment: We're setting up a configuration solution using AutoFac Multitenancy.  Any advice on organizing and naming the components (classes/projects)?
Comment: Yes.  I was going to comment that this is a great example for Dependency injection.  You can define the common interface and create specific components that are then passed in per some configuration.  this should allow for much better testability and maintainence than custom scripting as mentioned in another answer.
Answer: It really depends on what is different. Is it something which can be expressed purely by configuration (eg. tax rates), or do you really need separate code logic for each state? The more you can handle purely by configuration the better!
You most likely does not need separate code by state. For example you mention that some markets issue refunds while other issue replacements. This is still only two code paths you need to test. Then you can have a configuration indicate which path should be used for which state. This is much better that having separate code for each state. You still only need to test two code paths rater than 50.
If you ever feel the need to write individual code for each of 50 states, you are probably doing it wrong. You should definitely not have separate projects per state, or even having "50 different" of anything except configurations sections.
Comment: it's more than just taxation but the extent of differences is unknown at the moment.  We're also dealing with multiple countries.  There's workflows can also be slightly different such as some markets refund purchases while others issue replacements.  And certainly different pricing per market.
Comment: What JacquesB is getting at is abstractions. IOW, how might things that look different actually be the same? "All states charge tax" Now I have a general concept I can encode universally: "CalcTax()". And then all you need is the specific tax rates (tax table) -  that is configuration. Hear me now and believe me later, "configuration data" - the abstract concept! - will greatly simplify code.
Comment: If there's a lot of overlap in functionality between the states (beyond an effective "default" option), this is sound advice. If states are prone to nuance that makes it difficult/dangerous to lump them together as a kind of "Option B", it isn't. The OP will need to figure that out. There's also a danger of headache should one state pass new laws forcing code updates, but that's going to be true of any conditions where multiple states are using the same code.
Answer: I've had some practical experience with such projects, and can at least offer some general guidelines.

JacquesB is absolutely right that configuration is your bestest friend. Whether you put that configuration in files or in database tables is a stylistic choice (though I'd be leaning towards config files, since once you get a service set up, I'm willing to bet it won't change much).
Expect code that looks a lot more indirect than what you're probably accustomed to. There will be many places where instead of saying "Do this next," you'll be saying "Ask the config for what we're supposed to do next, then go do that". Which can be a development headache, but you'll get used to it.
I'd recommend a structure of "These are the common elements that everybody probably wants, and these are the bespoke elements hand-designed for individual states." To that end, correctly identifying that default functionality will be a big part of how easy/awful the code is to work with in the future. Be prepared to do some refactoring when you learn that more stuff than you thought needs to be configurable.
Always make sure that any error messages coming from the custom elements identify exactly where they came from. The huge number of different execution paths mean that debugging will suck no matter what; anything you can do to reduce the amount of easter-egg hunting will be more than worthwhile.
Invest the time to make a good automated test suite. A REALLY good automated test suite. This is always good practice, but for you, it could literally mean the difference between success and failure. Again, it's the huge variety of execution paths; any modifications to the common code will leave you vulnerable to butterfly-effect bugs in branches you weren't expecting. You need to catch those bugs before they hit production.
Comment: Thanks.  Any suggestions for naming classes, grouping projects? Should the implementations be suffixed with the market name or try to describe the different functionality?
Comment: I'm not a c# guy, so I can't speak to specifics of how you name classes. But honestly, I'd think you'd want a package name that incorporates both market AND functionality, so you can tell at a glance what it's supposed to do. Something like `ourproject.calculations.tax` for the default and `ourproject.florida.calculations.tax` for whatever custom mods Florida law forced upon you (if any). Where you put that market name is a point of discussion, but I'd be inclined to make it easy to see what customizations a particular market is forcing upon you.
Answer: Although config can help its not going to solve all your problems an it may create new ones.
By far the best way in my experience is to create a multi tenancy solution which can handle all or any of the states(tenants)
This will require configuration. ie sales tax percentage by state but also conditional code LegalMethodOfCalculatingWorkingHoursA vs B
If your app is hosted/online you could take microservices approach to the conditional code but an off line solution will have to bundle all the optional modules and select between them
You will find some modules reused across all states, such as sales tax and some crazy law ones only used in a single state. You will also find that laws change over time. so the modules used will vary by time within a single state
So I would go with naming by functionality rather than state.
Comment: I like this - code branches based on functionality, e.g. "must ask address" "delivery is tax free". Then configuration to that maps each state to a set of functionality.


Does grass-fed beef have lower carbon footprint than feedlot-finished beef?

Question: I have read this article of 2019 and still don't understand which one is better (climate-wise). Grass-fed beef involves more belches and produces less meat but seqesters carbon in grass. But what's the bottom line? Does grass-fed beef have lower carbon footprint than feedlot-finished beef or not? It's been a while since 2019. Do they have any recent life-cycle analyses published in peer-reviewed journals?
Answer: It is complicated, on the one hand you have longer growing times and lower food conversion efficiency of pasture raised cattle, on the other pastures are a way of carbon sequestration.
There is a report prepared for Whole Foods Market, Inc. which may not be considered impartial, that concluded that pasture raised cattle were marginally (~10%) better than feedlot.

Emission Sources
Feedlot
Pasture

Time (days)
303
450

Final Live Weight (kg)
637
505

Feed Production (kg CO2 eq/kg live weight)
1.47
3.14

Transportation (kg CO2 eq/kg live weight)
-
-

Enteric Fermentation (kg CO2 eq/kg live weight)
2.20
3.56

Manure Management (kg CO2 eq/kg live weight)
1.67
2.11

Total (kg CO2 eq/kg live weight)
5.48
8.58

Carbon Sequestration  (kg CO2 eq/kg live weight);
-
-3.55

Total with Carbon Sequestration Factor (kg CO2 eq/kg live weight)
5.48
5.03

The the difference in enteric fermentation methane emissions are discussed by this paper:

When the cattle were grazed on pasture, they produced .23 kg CH4·animal−1·d−1, which corresponded to the conversion of 7.7 to 8.4% of gross energy into CH4. When the same cattle were fed a highly digestible, high-grain diet, they produced .07 kg CH4·animal−1·d−1, corresponding to a conversion of only 1.9 to 2.2% of the feed energy to CH4. These measurements clearly document higher CH4 production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets.

It is worth noting the difference in magnitude between these two sources.  I read this as significant uncertainty about the values.  What is certain is that beef of one of the most environmentally damaging foods and we should be doing all we can to reduce its production.
Comment: I think it's disingenuous for those raising cattle to claim credit for the carbon sequestration of the grass - especially as pastures have often replaced woodland, which sequesters vastly more carbon than pasture does.
Comment: Great answer! But haven't cows evolved to eat grass, not corn? It's as if they don't stomach grass as well as grain, given how much they belch after eating it
Answer: You seem to think that the majority of footprint of beef (and similarly, milk) is caused by the carbon footprint of the stuff we feed to cows.
Not so!
The carbon footprint of beef is almost completely caused by methane emitted by cows. This obviously depends on the timescale, if you consider for example a 10000 year timescale then that would be different but the timescales of interest for climate change are 100 years (used to be the most important timescale) but today more like 20 years (because climate change is happening way too fast).
In the long term, one methane molecule converts to one carbon dioxide molecule. Its weight increases from 16.042 grams/mole to 44.01 grams/mole. Thus, 16.042 grams of methane has the same 10000 year carbon footprint as 44.01 grams of carbon dioxide, or stated in another way: global warming potential is 44.01/16.042 = 2.7434.
But in short term, methane is a terrible greenhouse gas. In 100 years, GWP is 25-30 and in 20 years, it's 86.
An in those timescales, the problem with beef is the methane. It isn't what you feed to cows.
Any small increase of that methane more than offsets differences caused by the stuff you feed to cows. A cow produces ~100 kg of methane per year and gives ~200 kg of beef. Beef cattle lives for 2-3 years so it's 200-300 kg of methane per 200 kg of beef, or 1-1.5 kg of methane per 1 kg of beef. In 20 year time scale, that would be 86-129 kg of CO2 equivalent per 1 kg of beef. For pork it's about 5-10 kg of CO2 per 1 kg of pork, and that's almost entirely CO2 and not methane. So beef is more than 10x as bad as pork in 20-year timescale, the most important for preventing climate change from becoming dangerous.
About the only positive features of beef and milk are that their production is independent of production of cereal. If we have multiple poor years in cereal farming, we don't have much opportunities for feeding the world population since so large percentage of our foodchains is dependent on cereal. Beef and milk produced from grass offers another way to produce food from stuff humans can't eat. Pigs and chickens eat what humans could eat, but cows eat stuff humans can never eat (or you can eat grass but don't expect to get any nutrients out of it).
But I personally think that it would be far better to just start gradually increasing stored amounts of cereal (only gradually to not cause a global famine) to prepare for multiple consecutive bad years in farming cereal, and entirely phase out beef and milk. That would do wonders to slow down climate change, and at the same time removing the usefulness of main benefit of cows: food security.
Lab-grown beef is an entirely different matter, though. We will have lab-grown beef, and it will phase out using cows to produce beef. But how quickly lab-grown beef becomes cheaper than real cows, we can't be sure. It could be too slowly to prevent dangerous climate change.
Comment: But what about pasture v. feedlot?


Looking for research data for amount of hearing loss resulting from otitis media with effusion (OME)

Question: I'm looking for some research data for the amount of hearing loss resulting from otitis media with effusion (OME), or glue ear, or fluid in the middle ear. The typical answer I read is "20-30dB" but this result is never referenced. Median/average, 90 percentile, kind of data would be very useful.
Comment: Are you referring to hearing loss while the effusion is present, or to permanent hearing loss resulting from scarred due to (usually recurrent) infection?
Answer: Otitis media with effusion (OME) is most common in young children (under 2) making studying the effects on hearing difficult. While newborn hearing screening is common, it does not provide a full audiogram. Collecting an audiogram a a child who does not speak or understand direction and has limited attention is hard. Collecting an audiogram on a sick child is even harder. With a some serious caveat regarding sample size, Werner and Ward (1997) provide the best study on this that I am aware of. They conclude that the effect of OME is 15-30 dB (while the child is sick).


What is "braid Scotch"?

Question: A family history mentions that a set of my ancestors in New Brunswick, CANADA, spoke "braid Scotch", but I cannot figure out what that is. There are only a few mentions of the phrase online, but they provide no clear definition.
Comment: Where I live if someone speaks "broad Oldham" (or Lancashire)" it simply means they have a very strong **local** accent
Answer: There is technically no such thing as the Scotch language, although that term was used historically. It is more commonly referred to as the Scots language.
Braid Scots (English broad Scots) is simply the vernacular (native dialect). This phrase alone does not localise the dialect within Scotland further.
What the author probably meant was: they could hardly understand a word of what they were saying when they spoke in "braid Scotch".
Comment: ...so this is _not_ Scottish Gaelic.
Comment: I had to look up the meaning of "vernacular"; it's domestic or of the people.
Comment: I don't think that he was saying that he couldn't understand them. I think that he was giving a piece of information to describe them more fully. They were from the lowlands/boarders.
Comment: Sorry, I meant that last part a bit tongue-in-cheek – obviously no way to know from this whether he could understand braid Scots
Answer: Braid Scots was mostly a mix of old, old English and Scottish Gaelic. The most famed use of braid Scots is written by
John Barbour, a poet from early Britain

What is "braid Scotch"?


What do you call the holes in a flute?

Question: I am wondering if the holes in flutes have a particular name. I am assuming that all wind instruments share the same name for their holes, but I am not sure what it might be.
Answer: StoneyB has given you the basics and I mainly agree with him (except I've always spelled tone hole as two words), but here's a bit of illumination.
I am a flutist (you can call me a flautist if you pay me more) and here is a picture of my concert flute, with which I used to play in orchestras when I was younger:

You may be surprised to learn that there are two kinds of holes for that instrument: the tone holes, which are covered by the padded keys, and on certain keys there are holes in the keys themselves. (This is true for clarinets and a few other woodwinds as well, though not saxophones and not the bass versions of woodwind family).
The holes in the keys are there to ensure correct finger posture, and a flute with these "perforated" keys is called an "open-hole" or French model flute.
I have never heard the holes in the perforated keys called "finger holes," but it's possible they are called that in languages other than English. That designation is reserved for a flute that has no (or few) keys, like a Baroque flute, the unkeyed holes of which are called "finger holes" because the fingers directly cover the tone holes.
Comment: "The holes in the keys are there to ensure correct finger posture" - that is really a side effect. They also allow alternative fingerings, better intonation for quarter tones, easier multiphonics, etc. In fact many beginners start with *closed* hole flutes for simplicity (not for laziness), but professionals use open hole flutes for the extra functionality.
Comment: And the hole that you blow across is called the *embouchure hole*, right?
Comment: and just to clarify, the "finger holes" are optional on a flute and a flute with them is referred to as an open hole'd flute, they were often used as practice for people who had issue with finger positioning, however, when you think about it, the normal flutes with closed holes allow for lazyiness..
Comment: @Mixolydian: Yes, the hole on the lip plate is the *embouchure hole*.
Comment: @alephzero: That's what Wikipedia would have you believe. I've never found any of those things to be very useful or practical.
Answer: Holes in wind instruments which control pitch are generally called toneholes or tone holes, but this term is often reserved for holes covered by pads operated by "keys". Holes covered by the fingers are fingerholes or finger holes.
Comment: I learned them both as tone holes, but the ones on keyed instruments being also called keys (confusingly, given the key is also the key), and those on non-keyed instruments being also called finger holes.
Comment: My axe during the brief time I left percussion was the bassoon, which has both fingerholes and keyed toneholes AND 'ring' keys activated by covering the fingerholes they surround. But my instructor almost never referred to the holes themselves, just the fingers (or 'heel') used to cover them.

What do you call the holes in a flute?


"netsh wlan start hostednetwork" - The hosted network couldn't be started

Question: I have Realtek RTL8187SE version 6.9071.822.2008 on Windows 8.1 and I'm trying to start a network but when I try to start the network it gives me "The hosted network could not be started". I set the mode to allow before I tried it. I went to enable ICS I installed the program Connectify to see if that would work but it tells me that my card isn't supported. I updated my driver from the website but I got a Code 31 so I uninstalled it and went back to the older version. I had the same driver when I was on Windows Vista/7 and it worked then. How do I fix this?
Comment: Did you try the command from an elevated command prompt? Right click on cmd.exe -> open as Administrator -> run the command
Comment: @doenoe Yes I tried it that way but it didn't work.
Answer:
In Device Manager :View -> Show Hidden Devices
In Network adapters enable "Microsoft Hosted Network Virtual Adapter"
Comment: That driver is missing.
Comment: Does "netsh wlan show drivers" say "hosted network supported : yes" ?
Comment: I remember it saying no but I remember being able to start networks on Vista/7 with the same driver (but it may have been a different version).
Answer:
Try to uninstall your physical WiFi adapter
In device manager, click on Actions - Find hardware changes - Wifi adapter should automatically appear again and so the Microsoft Hosted Network Adapter.
If the Hosted Network Adapter is still greyed out, right click on your Physical Wifi adapter, Properties, Drivers, Revert driver changes


How to delete files when the node that displayed them is deleted?

Question: Is there a way to delete files/images from the server automatically when the main node is deleted?
How do I implement this?
Answer: It's a revisions thing. I guess it makes sense. If you have revisions enabled for that content type, it keeps all your old files on the server (associated with old revisions), so replacing a file definitely is harder. If you try to remove it and add it again to the node, the name/link is updated, as I mentioned in my question. Since a file with that name is kept on the server and there is a name duplication, it adds those "_0", "_1" etc suffixes to future uploaded versions of that file's name.
I understand why this is happening though, since the whole point of revisioning is being able to revert to any past version of the page.
The work-around is that you can actually delete the old revision from the 'Revision' or 'Moderate' tab (if using Workbench Moderation) that contained the file you're trying to replace. Then upload it again, and the name should then match without you having to go back and edit any links pointing to that file.
Hope that makes sense and that it helps somebody else too!
Comment: If a node is deleted, as the OP is saying, also the revisions are deleted. It's not a matter of old revisions.
Answer: When a node is deleted. the images and other files uploaded in the node edit form are automatically deleted during cron tasks; the files are deleted if they have been uploaded more than 6 hours ago.
If, for any reason, you need to delete them faster, and before 6 hours are passed, you could use the following code. Put it in a file (e.g. delete-files.php) in the directory where Drupal is installed (which is the same directory where you find the cron.php file).
<code>  /**
   * Root directory of Drupal installation.
   */
  define('DRUPAL_ROOT', getcwd());

  include_once DRUPAL_ROOT . '/includes/bootstrap.inc';
  drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

  // Delete 100 files at time.
  $result = db_query_range('SELECT fid FROM {file_managed} WHERE status <> :permanent AND timestamp < :timestamp', array(
    ':permanent' => FILE_STATUS_PERMANENT,
    ':timestamp' => REQUEST_TIME - 60 * 60
  ));
  foreach ($result as $row) {
    if ($file = file_load($row->fid)) {
      $references = file_usage_list($file);
      if (empty($references)) {
        file_delete($file);
      }
    }
  }
</code>


Caching proxy server with just a router?

Question: Trying to set up a caching proxy server using a router running tomato firmware.  I'm not sure if this is even possible, but figured i'd give it a try.
Answer: It is theoretically possible, but with one major caveat - storage. Not sure why anyone would want to try it though. Good luck!
You will need to solve the storage problem as Chris suggested. You have several options depending on your router's capabilities:

USB drive - only if your router has a USB port or if one can be soldered directly onto the board.
SD card - some routers have the ability to interface to SD/MMC card devices. Again, you may need to solder the connector if interface is available on the board.
NFS/SMB - your last resort is to mount a network share on your router. Most of these WRT firmware allow you to do that.

Your next problem would be with RAM. Unless you got one with 64Mb or more RAM, you will truly be pushing the limits. However, you can possibly do with less RAM if you configure the caching software to reduce the RAM cache and use only the disk cache.
If all you want is to have a caching proxy on your network, why not consider setting a proper one up as a transparent proxy and the configuring your router to force HTTP connections through the external proxy.
Comment: I will just add that I run a "real" linux box as a cache at home, and along with a well set up bind the result is just wonderful.


Built-In methods to backup app.config

Question: Are there any built in methods in System.Configuration that would allow one to backup the currently running apps XXX.exe.config file.  Or if not, how would one retrieve the current applications config file name for backup.
Comment: This would be double handy if it was available during the install process too.
Answer: You should be able to do this using the System.Configuration.ConfigurationManager class.
The OpenMappedConfiguration method can be used to open a instance of the System.Configuration.Configuration type based on your app/web config (or any other file in the right format, so someone else's app/web config). Then the Configuration type has a Save method and a SaveAs method.
Can't say that I've used them to do exactly what you want but (to speak to @StingyJack's comment) I have used them in a Installer subtype (a ProjectInstaller for a service).

Built-In methods to backup app.config