How To Adjust The Fees On A Running Substrate Chain?

Question: Fees for transactions in our test net are too high and we would like to adjust them to be some factor lower across the board. Is there a simple way to do that using a call from the Polkadot.js apps interface? Or would that need to be set within the JSON or constants.rs file prior to chain start?
Answer: In general a runtime upgrade is the way to go, as @Purple_Turtle pointed out.
(You could also try to hack around it with System::set_storage to overwrite the fee multiplier with PolkadotJS, but that can go quite wrong.)
The exact change depends on what you want to adjust;

The cost of the Weight that an extrinsic consumes:
Weight is converted into a deducible amount of balance that the user pays for (aka fees).
This is defined in the pallet_transaction_payment::Config::WeightToFee and LengthToFee configs. Polkadot uses Polynomials in the form of WeightToFeePolynomial for both, which then automatically implements the WeightToFee trait.
The way the fee multiplier is adjusted in accord to block fullness:
Substrate supports the adjusting of block fees depending on the utilization of your chain. This is also part of pallet_transaction_payment, namely FeeMultiplierUpdate. In Polkadot this is defined here, according to all the constants a few lines above. The fee multiplier for the next block is updated in the current block and adjusts to the target block fullness over time. The mechanisms is rather involved and implemented here. Fuller blocks will increase the multiplier over time and lower blocks will decrease it. Both withing limits.
Comment: Thank you, Oliver!
Answer: Fees defined as part of the runtime. A substrate chain allows you to upgrade your runtime, so you would be required to perform a runtime upgrade with the changes.
Comment: Runtimes are unique for each chain, but see my answer below for a general answer. Please include some source links into future questions for easier answering.
Comment: Got it! Do you know where in the runtime code one would adjust the fees?


What is the purpose of the inlet doors of the Pratt & Whitney JT3D?

Question: I have a question about the 707 Engine Inlet Doors, according to Wikipedia the Pratt & Whitney JT3D inlet doors purpose is to provide additional air. Is the thrust higher on more air intake? And why modern engines don't have it anymore?
Answer: The intake speed at the compressor is between Mach 0.4 and Mach 0.5 and changes little with airspeed. That means that at low speed the intake has to suck in air from a wide capture area, (even from behind the inlet lip at low speed) while at high speed only the part that flows into the center of the intake is digested, while surrounding air will spill over the intake lip and flow around the nacelle.
The surface that separates the flow going into the engine and that which does not is called the stagnation stream line or surface. This surface is way aft of the inlet lip at low speed, and the pressure near it is the highest (stagnation pressure). The challenge for the inlet designer is to design the lip with a rounded shape so that the flow going into the engine is uniform. It won't be if the lip is as shaped in the sketch. The high pressure on the outside and the low pressure inside the lip open the doors to admit a small percentage of the air to the engine inlet at low speed. As airplane speed increases, the stagnation point (or line) shifts to the lip itself and the pressure equalizes on the doors, closing them.

The fairly sharp intake lip of the JT3D will capture air rather inefficiently at low speeds (the topmost case in the sketch above), which could even lead to flow separation right after the intake lip, reducing mass flow and compressor efficiency. By adding the suction-activated doors, the intake can capture more air and keep the flow attached.
More recent intake designs have thicker intake lips, so the flow stays attached even at very low airspeed.
Comment: How sensitive to either design (with and without doors) are the engines at high angles of attack where the relative direction of the ambient airflow is not fully aligned with the engine?
Comment: @SkipMiller: This question is worthy to be asked officially and not hidden in a comment. The biggest angle changes you see with supersonic combat aircraft, and the short answer is: It needs a lot of optimization to make intakes work well. Low speed with high angle of attack is one sensitive point, and the other is supersonic flight with sideslip or unusual angle of attack. Airliners have less angle of attack variation, so their intakes are fairly easy to design.
Comment: I presume this is then similar to the series of radial suck-in auxiliary doors on that AV-8B harrier as well?
Comment: @CarloFelicione: Absolutely! In case of the Harrier, it needs a lot of air while standing still - the intake is already much bigger than that of comparable conventional jets, but the blow-in doors are still needed so the Harrier can hover.


12 volt led powered by 0-10v

Question: I am running 12 x led strips controlled by a 0-10v dimmable controller however the led strips are 12v dc and are not operating at their full output at 10v.  How can I amplify the 0-10v output to produce a 0-12v output to get the full brightness out of the leds?  When I connect the strips to a 12v dc source they operate perfectly but I need to use the programmable 0-10v dimmer to control them.
Comment: Can't you simply use Opamps to do this?  Make it rail to 12V
Comment: It is not a matter of "amplifying" the 0~10V control voltage.  It is a matter of CONTROLLING the LED supply (typically by Pulse Width Modulation PWM) as directed by the 10V control signal.
Answer: You need an LED dimming supply which can be controlled by a 10V control signal. 0~10V control signals are a very common way of controlling lamp brightness regardless of whether they operate on low DC voltage (like 12V) or mains-voltages (like 115V or 230V).
Google returned about 721,000 results (in 0.66 seconds) when I searched for: LED dimmer 10V controller
Comment: This is the rigth answer. Unless OP is on a very tight money budget and on a very large time budget, and already has some components around.

12 volt led powered by 0-10v


Etymology of Portuguese numbers 10, 20, 30...?

Question: I myself am a native Finnish speaker and the whole numbers 10, 20 and so on translate word for word as ten, two tens etc. Why in Portuguese are these said dez and vinte. The rest make sense to me as they are some form of the numbers three, four, five...
Comment: Portuguese is a romance language, so it's just because 10 in Latin is *decem* and 20 is *viginti*. Now you have to ask about the Latin etymology...
Comment: I really do not understand  this. In **English and Portuguese** no number such as 20 is said two tens. Also, do you mean etymology?
Comment: If the answer addressed your question sufficiently please don't forget to upvote and [accept it by clicking the green check mark](https://i.stack.imgur.com/LkiIZ.png) on the left side of the answer.
Comment: Severi, because Latin did it and, as Portuguese comes from Latin, we do as the Romans do. Though, you could say *dezena*, which is *ten* as a noun; for example, «três dezenas de queijo» (= «three tens of cheese»), but its use is stricter and less common than the cardinal numerals, and saying *X dezenas* is used usually only with things that are somehow separated in tens, as with the number system. Do you want a list for the etymology of *ten*, *twenty*, ..., and *ninety*, or do you want an explanation?
Comment: I asked the same question regarding the [variations of the *"three"* morpheme](https://portuguese.stackexchange.com/q/6400) as we know them today.
Comment: If you look at German languages, "vinte" makes more sense, the inicial "t" being elided in Latin, and consequently in Portuguese.
Answer: Well, if you go far, far, far, back, according to Wiktionary, vinte ultimately comes from Proto-Indo-European (PIE) dwi(h₁)dḱm̥ti, meaning 'two tens, two decades'; dwóh₁ was 'two' (Wiktionary), and déḱm̥ 'ten' (Wiktionary;  these were reconstructed by linguists, not attested words). These eventually became viginti, duo and decem in Latin, which became vinte,  dois and dez in Portuguese.
Of the similarity between PIE dwi(h₁)dḱm̥ti and dwóh₁ + déḱm̥ very little survived into Classical Latin: only the vi in viginti, pronounced as uí (listen in Wiktionary), was related to uo in duo; and viginti and decem (listen) were pronounce with hard [g] and [k], two very similar sounds (as in frango and franco), and were both heirs to the k in déḱm̥. But even that was lost in Portuguese vinte and dez.


Is using isTouched or justTouched multiple times bad?

Question: Suppose you have justTouched or isTouched method multiple times in your game screen, is that bad? Is it better to create booleans and as few input listeners as possible? or it doesn't matter?
Answer: You can reference justTouched or isTouched as much as you like. I'd be surprised if they reevaluated on every call during a single frame. However, even if they were reevaluated each time you called them, it's likely to be one of the least of your performance concerns.
Make your game, then worry about these little optimizations later, when you're profiling the game to improve performance.
Comment: You're right: https://github.com/libgdx/libgdx/blob/master/backends/gdx-backend-android/src/com/badlogic/gdx/backends/android/AndroidInput.java#L619
At line 619 you can see it returns a boolean. While this boolean is calculated once every time a touch happens.


not allow tap gesture on UIImageView when other finger already on other UIImageView

Question: I have one UIView. in that there are more than one UIImageViews. and i added tapgesture in all that UIImageView individually. so i have to not allow tap gesture function called when tap on UIImageView when other finger is already on other UIImageView. any help appreciate.
Answer: You have to implement the UIGestureRecognizerDelegate method gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: and return NO.
Answer: Have you tried to set the UIView multipleTouchesEnabled to NO? You can also try to subclass the UIImageView and override the following methods, so you can control the state and forbid additional touches to be executed.
– touchesBegan:withEvent:
– touchesMoved:withEvent:
– touchesEnded:withEvent:
– touchesCancelled:withEvent:
Answer: add a unique tag to all images you have
when your tapgesture selector is called, check for the tag, if it matches the tag of the image you are interested in, then go ahead with what you want to do, else do nothing


Disadvantages of operating system on external drive

Question: I am constantly traveling between two countries and I am constantly forced to bring my laptop with me. I was wondering if it is possible to install an operating system such as Linux or Windows on my external 1TB HDD. I would be very thankful if someone who is more knowledgeable share his or her thoughts on this subject. Also are there any disadvantages in having your operating system stored on external drive? Thank you in advance!
Comment: for Windows you need [Win8/10, here you can create a WindowsToGo on the 1TB HDD](https://superuser.com/a/1149759/174557). This works ok, if you have USB 3.0, USb 2.0 is a bit too slow.
Comment: For Linux, you've to use live bootable media, for Windows, you need [Windows-To-Go](https://en.wikipedia.org/wiki/Windows_To_Go). See more [Live CD](https://en.wikipedia.org/wiki/Live_CD). You can make a pluggable SSD with portable apps.
Comment: Why does it have to be live bootable?
Comment: The OS is more likely to become corrupted due the nature of things being easily disconnected, susceptible to phyiscal impact and bumping, etc.  Imagine if you HDD inside your computer got unplugged while running and bumped 100x more (compared to not at all); things just are not as reliable in such a case even with special care.
Answer:
Are there any disadvantages in having your operating system stored on external drive?

Generally there are no disadvantages.
Practically: An external drive conneted via ESATA works just as well. An external SAS or an external SCSI drive will work just as well. A drive connected over USB will be slower. Partially due to needless packet overhead. If you use USB 2 expect it to be much slower, while USB 3.1 with UASP might be almost as fast as a regular laptop drive.
If you use windows (and you tagged it windows) its get tricky. For most versions you want to succesfully boot windows so it can start recognising USB devices. Catch 22...
There are at least two ways around that:

Windows to go.
Put windows in a VM. The vm disk image itself is just a data file. This will work extremely well for some things (like office stuff, reading mail etc) and poorly for others (mainly high FPS gaming).
Answer: It would be perfectly functional to do. (I recommend persistent Linux [Arch, Ubuntu/Debian {which do you prefer}, or RHEL are best] on the external drive. So much easier to set up, and properly configured to be minimal will make it nicer) Here is the rub: Imagine your internal hard drive can do RW @ 300MB/s (just for argument's sake). Now image that streaming from an external drive at, say, 50MB/s. Then add delays from the USB interface, and the massive latency change, and life sucks. If your SSD boot takes 10seconds, then a HDD boot will take 5(ish)minutes, and your external HDD boot will take 10-20 years. (Yes, I'm estimating those first values, and yes, I'm exaggerating the external, but you should get the point). I recommend upgrading your internal drive (I use a 2TB Segate SSHD that I got for $99.99 USD), and doing a dual boot. Yes, a dual boot has its own pains, but it generally will work better and not be painful to use.
Answer: The only real disadvantage is possible bottlenecks due to using USB instead of SATA or PCIe, and the fact that you may accidentally unplug the drive during usage.


Using Empty Object Coords for shading (Multiply Vector by Matrix)

Question: I'm making a setup that reduces the complexity of shading by replacing the Normals with coordinates from an object. If you take Object Coords of an empty and plug them into the normal socket of a shader, you end up with the object being shaded as if it were a sphere. If you make some edits to each axis, then you can change the shape more. In this setup, the sphere is distorted quite a bit to give the shading I want for the face:

So this all works quite nicely. The problem is when the head moves:

What we see here is that the altered normals are masked only to the face, with the real normals still in use further up the forehead. As the head rotates, you can see the shading desync. It rotates with the head, instead of the light moving over it. This is because the Empty is parented to the head bone. I'm not sure exactly what's going on, but its something to do with the coords of the object being in the wrong space (world or object). I've tried Vector Transform node, but it doesn't help.
If the Empty only copies the location of the head and not the rotation, then there's no problem. But that only works if the head only rotates on Z, and never tilts or rolls. So it's not a proper solution.
I'm looking to understand why the coords from the empty are behaving wrong in the first place, and what can be done to make things stay properly synced up as the head moves. Someone has suggested that they might need to be multiplied by the Matrix of the object. I could get the Matrix info via drivers, but I'm not sure what to do with it after that.
Answer: The solution was to multiply the Vector by the empty object's Matrix. I built this group with some help and a lot of trial and error. The values are driven by the Matrix World of the Empty from the Data API. I'm not sure I have the component nodes of the matrix laid out properly or not, but this is working.


Azure Site Recovery - Disk Size Unusable message after shrinking disks

Question: I have a customer with a Hyper-V VM (running under a Windows 2012 R2 Hyper-V Cluster) that had drives larger than 1023GB.  When I went to replicate the VM to Azure using Azure Site Recovery I got an error message that said "Disk Size Unusable".  I then shrank all of the disks in the VM to under 1023GB (actually 1000GB or less) expecting that I could then select the VM for Site Replication.  But I still get the message "Disk Size Unusable" even after making the change two days ago.  How can I get the Azure Portal to re-query the VM and see that the drives are now all under the 1023GB limitation?
Any ideas would certainly be appreciated!
dave
Answer: It turns out that if you go into the Azure portal and go into the "Recovery Services Vault - Site Recovery Infrastructure - Hyper-V Hosts - select host - Refresh Server" this will re-read the existing VM's and now I can replicate this VM with resized disks.


Do relativistically measured rotation speeds (Special Relativity) change planetary mass slightly through Lorentz transformation?

Question: Thanks @ConnorGarcia for your Answer. Avoiding 'Tidal Locking' for now - the rotational angular momentum Lrot is 10,000,000 times smaller, so negligible, but could it still be a factor in eccentricity? I realise this is a controversial question, but, does the angular momentum between two rotating planets 'literally' take Relativity into account? i.e. if Planet-Earth with 'clockwise' rotation: Se, is measured relative to 'clockwise' rotation of Planet Mars: Sm, then their nearest equatorial 'purely-relative' rotation speed will be: (Se + Sm) (for Mars and Earth, this is approximately twice their individual rotation speed relative to a 'Rest' frame). If two fictitious planets had the same rotation speed S and anti-parallel rotation (one clockwise and one anticlockwise), they would - by similar logic - have 'relatively' Zero rotation speed (along the shortest distance between them). General Relativity influences the precession of the perihelion of Mercury, but I'm wondering about Special Relativity) My question is: if these 'Relative' speeds were used in the Lorentz transformation, then the masses would change - by a tiny amount.  Could this deflect the orbits by a minute amount over a long period?
Comment: The recent edit makes the question look like nonsense. Editing questions is not intended for thanking for answers (no matter how polite) or asking new questions: it will only make everything unclear.
Answer: No. The idea of relativistic mass is an outdated concept. There are many questions over on the Physics Stack Exchange about this.  Mass is an invariant quantity in GR and SR. It does not change due to the motion of a particle.  The energy of the particle may change, but the mass doesn't.
But things like the spin angular momentum of a body do effect its gravitational field.  So it can matter for orbits.
Special relativity (SR) is a subset of general relativity (GR).  It describes a special case of the full theory.  If you complete a calculation using full GR, SR is included without you doing anything else.
Any actual calculation will use an approximate model.  If you say the Earth follows a geodesic of the Sun's spacetime, that geodesic includes SR, but you are neglecting the effects of the Earth's mass on the common spacetime of the system.  For the Earth--Sun system, this probably doesn't matter.  The sun is rotating, but for most calculations we still model its gravitational field using the Schwarzschild metric, for a non-rotating point mass.
If the Earth or Sun were rotating fast enough, then we would need to include their spin angular momenta in calculations.  For instance, we could model the background spacetime the Earth moves through with the Kerr metric instead of the Schwarzschild metric.
There are all sorts of effects that technically matter, but we ignore.  When modeling a system, we always have a target precision goal in mind.  Based on that goal, we will ignore effects that don't matter to the precision we care about.
When building a GR orbital model, the tool to use is the perturbative post-Newtonian expansion.  This approximates the motion of the bodies as a power series in $\frac{GM}{c^2 r} \sim \frac{v^2}{c^2}$.  Successively higher powers in the expansion are less important since $\frac{GM}{c^2 r}<1$.  You can simply truncate the series when the required precision is reached.
In this formalism it's easy to sort effects by what post-Newtonian order they first appear.  The spin-orbit and spin-spin coupling effects come in at "second post-Newtonian" order, $\mathcal{O}\left(\frac{GM}{c^2 r}\right)^2$, or higher.
We can measure the position of the moon incredibly precisely ($\sim 1$ cm) thanks to laser ranging.  To model the Earth--Moon system to the required precision, several usually ignored effects matter. For instance, the fact that they are both extended bodies of non-uniform density matters.  General relativity also matters.  The state of the art orbital model used in lunar laser ranging only needs to extend to the first post-Newtonian order (see Müller et al, 2019).  So even in this highly precise use case, the spins of the Earth and Moon don't matter to the precision needed to compare to measurements.


Obout controls in C# .Net

Question: Is anyone using the Obout controls in C# .Net?  How would you rate these controls, especially the Grid Control?
Answer: I was thoroughly impressed with them.  Of all the other control sets out there (infragistics, telerik) this is the only (more than) respectable one I've worked with that was 1) free! and 2) lightweight!.  The only caveat to Obout is I had trouble with merging some of these controls and some of the stock AJAX components.
Infragistics is by far my favorite (my comment about Obout being "lightweight" is in comparison with the heavy use of viewstate in some of the Infragistics controls) but it's around 1000-1500 a seat, so it can get expensive if you have a larger team.
Comment: Infragistics is a mess. I like Telerik a LOT bnetter. And they're customer service/bug fixing is very good and timely.
Comment: I used Infragistics before, its controls are so complex.
Answer: I like obout for their lightweight'ness. Their licensing policy is very fair (pay once free updates for life) and they also give (free) educational licenses.
However, I had to use Developer Express on one of my projects and never looked back since. Very powerful and not as bloated as Infragistics.
Basically, if you decide to go obout way, you probably will not regret it.
Answer: I like obout for their simplicity and functionality. They have pretty good documentation and samples of almost everything. And they cost a fraction of price than others (Componentart/Telerik). I am currently testing their Grid control ( after I gave up on Componentart grid for client side functionality) and find it pretty straightforward.
Answer: I purchased the license a few years ago and have been using it ever since.  The support is pretty good and the controls are great.  I have looked at some of the other vendors (telerik, etc) but haven't moved any where because of cost transition.  The nice thing with obout is that I bought it a few years ago and they still give me free updates.  That may change inthe future, but for now, its great.  The products work as expected and they are always making updates to the software.
Answer: This is the first time I was working with obout controls.Previously,I was working with telerik controls and so,I had a good chance of comparing these two set of controls.I would prefer Obout for its light weight and functionality.
Answer: I used their tree for a project.  Not bad for free controls.
Answer: I have been using their Calendar control for nearly 2 years. All of a sudden it stops working on Google Chrome (Vr: 17.0.963.56 m). Even their live demos don't work, try scrolling through the months a few times and it will just hang with the error 'Uncaught TypeError: this is not a Date object.'.
I've emailed the company on two occasions regarding this issue as it has brought my site down and I'm getting customers contacting me incessantly. I'm afraid as of yet no reply!! Very frustrating!!
It's really a shame because the tool is otherwise excellent...If they could at least acknowledge the fault and assure me they are working on a solution that would be something, but to be left in the dark shows a complete lack of basic customer service etiquette.

Obout controls in C# .Net


how do I access the SPDIF signal from my phone

Question: my galaxy s has the option to have 5.1 surround enabled. what plug on my phone produces the digital audio signal to carry the 5.1 surround?
is this option only available through bluetooth or can it be used through the headphone port or USB port?
Answer: The Samsing Galaxy S series has a virtual surround, not a true surround. Therefore there is no way to get multichannel audio out of the device, only analog stereo.
Source: Phandroid, Unleashthephones, Intomobile


Could magnetics circuits be invented before electric circuits?

Question: Magnetic fields behave in many of the same ways as electric fields. Could a society develop a magnetic based system of computation before they invent an electric method like modern integrated circuits? If so, what might cause this to happen?
Comment: No. Magnetism and electricity are essentially the same phenomenon. Magnetic systems simply have more lag, both in the mechanical and the figurative term
Comment: Thanks, @Raditz_35, I meant whether or not it could replace their role in modern society. I've clarified the title.
Comment: It is a bit unclear as modern integrated circuits do not actually work on either electric or magnetic fields, they work on currents and voltages instead. Older computers did work on both on electric fields (in the vacuum tubes) and magnetic fields (in magnetic coil memory) but ultimately it all went down to current and voltages.
Comment: What's a magnetic circuit?
Comment: Your title asks if they could replace them, your actual question asks if they could be there first and you kind of imply that they actually could be replaced by the "electric method" eventually. Please sort that out
Comment: @GretchenV - Currents and voltages, are properties not of the underlying physics but are useful numbers that we define over the underlying physics, it does not seem impossible that similar ideas could be formed relating to magnetic fields.
Comment: "Magnetic fields behave in many of the same ways as electric fields" -- This first sentence is the key of the misunderstanding.  They are not just similar in many ways, but are aspects of the same thing. Semiconductors in your computer rely on magnetic fields to allow electricity to flow, and the flow of electricity induces these magnetic fields.  It's like asking for water, but asking if you can leave either hydrogen or oxygen out of it.
Answer: Technically yes, but it would look more like a mechanical clock than a computer.
Electricity and magnetism behave similarly because they are really the same force. The main difference is that magnetism is related to a separation in charge, whereas electricity is just a buildup somewhere.
If you have a block of iron that is magnetic, it will have a magnetic field around it, with north and south poles. However, it won't have an electric charge (unless it's hooked up to a battery or something), because it has the same number of electrons and protons: the movements of the electrons are just aligned in the same direction.
An electrically charged block of iron isn't necessarily magnetic. It just means that it has a certain surplus or deficiency in electrons floating around inside it. Notice that there is no direction- just an amount of charge.
Electricity is great for circuits, because this charge is easy to move around - it's just a buildup of electrons, which are a) very light and b) respond to electric fields, which are easy to create. Moving electrons around is a very easy and fast task, and movements of electrons can be used to control other movements of electrons.
Magnetism, however, doesn't move electrons unless the magnetic item itself is moving. In fact, since magnetism operates on the direction of the field, the components of the circuit would have to be changing direction, ie. rotating. A complex machine with tons of tiny rotating components? Sounds like clockwork. Basically you have a bunch of tiny magnetic switches that rotate around and flip each other, moving small magnetic fields which can be used to influence the movements of more fields.
The problem with this is that magnetic fields, like electric fields, get less strong over a large distance. Electric circuits get around this by moving the source of the field (the electron) until it's close enough to have an effect, which works because electrons don't experience a lot of friction (when they do, it's called resistance and it's pretty minimal on a small scale) and can make it pretty far in a circuit without losing energy. Magnetic switches, though, would be rotating on an axle, and would lose energy to heat and friction.
One way that magnetic fields have been used in computing (a long time ago) is relays, which are just that: tiny magnetic switches. They are activated by an electric current, moving a magnet and flipping a switch closed. That's more of a hybrid magnetic/electric system though.
Basically- electromagnetic fields, when used in the way you're suggesting (complex circuitry) behave as electric fields. To force them to be magnetism would require emphasizing the parameters involved magnetism: orientation and movement, which would make an interesting mechanical/magnetic computer.
Comment: _The movement of_ the electrons is aligned in the same direction, not the electrons themselves. Magnetism is a property of _moving_ charge. The rest is fine
Comment: You're not describing a magnetic computer, you're still pushing electrons and still have an electronic (not magnetic) computer.
Comment: @nzaman thanks, you're right, I'll change it
Answer: No
It's true that the movement of electrons causes a magnetic field.  However, magnetic fields are caused by all kinds of things, many having nothing to do with electrticity.  Ferrous magnets, for example, won't shock you with electricity when you pick them up.
The problem is that modern computers run on the flow of electrons, NOT the presence of an electric field
A magnetic field is not the flow of electrons.  A very applicable analogy is, "can I turn a water wheel with humidity in the air?"  Obviously the answer is no.  A magnetic field is analogous to humidity in the air, not the flow of water in a stream.  Electricity is analogous to the flow of water in a stream, and therefore you can use it to do work.
Magnetism is not a particle, nor can it be broken down into particles.  A "magnetic field" cannot be channeled, amplified, reduced, gated, or any of the other things we do with electrons to compute.
But I can push things with a magnetic field, why can't I push gears?
OK, you could do that, it's the waterwheel effect.  But you're not computing with magnetism.  You're just hooking a Babbage Engine up to a magnetic waterwheel.  You could also hook it up to an actual water wheel and get the same computations.  In otherwords, what you have is a mechanical computer, not an electronic computer, a magnetic computer, nor an optronic computer.
Wait... you just said "optronic"
Indeed I did.  Photons, like electrons, are particles — kinda.  They're voodoo juju, but they have an aspect that acts entirely like charged particles.  Consequently I can make reducers, amplifiers, gates, and all the other neato stuff I need for computing.  The "wires" (optic channels) are still a bit of a problem, and doing things on the nanometer scales we really want is a bigger problem, but it can be done.
Because I'm not working with a field of energy, I'm working with a particle.
So, I regret, the answer is no.  You can't build a "magnetic computer."  A mechanical Babbage engine is the best you can do.
Answer: Yes
but only if the inventing civilization is completely made of Magnetic Monopoles.
Magnetic Monopoles (MM's) are isolated carriers of magnetic charges, much like protons and electrons are carriers of electric charges. In a way, your north carriers can  behave like protons or positrons, depending on their charge which is directly proportional to their mass. South carriers can then be antiprotons or electrons.
Something called Magnetricity also exists, but as a less appreciated technology.
Comment: Except they don't exist


My toilet runs when the kitchen sink is running

Question: My toilet runs when the kitchen sink is running. I have replaced the fill valve and the flapper and have set everything to the correct heights/levels etc. Also, the toilet doesn't completely run a full flush without using a plunger, which is  making me think clog somewhere. I should note a few things, one, the toilet is upstairs, while the sink is downstairs. Two, the toilet is almost 40 years old from the stamp in the tank (flush problem could be jets) and last but not least, we are renters and the house is over 200 years old. We have no idea how old the plumbing actually is. We will be replacing the actual toilet soon, but, I am wondering if the two problems could be due to the same issue and also if there's anything I can do before I give up and call a plumber.
Comment: "We're renters", yet the landlord isn't fixing the issue for you?
Comment: What do you mean by the 'Toilet runs'?  Do you mean that you can hear it filling, or that water is running into the bowl?
Comment: I've seen a similar post on this site before but cannot find it at the moment. The issue occurs due to a pressure drop in the cold water line. Does your home have a proper 3/4" or 1" main supply line and then just a 1/2" leading to the bathroom? You can buy  a hose bib water pressure gauge and see what kind of pressure drops you're experiencing.
Answer: You should call the plumber in. It sounds like you have a failed or failing Pressure Regulator on the plumbing system that needs replacement, this will likely need to be soldered in. Though, you can try tightening/loosening the screw on top of the regulator to see if you can get it fixed temporarily or even permanently...as street pressure may have changed over the years.
As far as the toilet not flushing, a new toilet would be very good. A lot of the time there's a cast iron drain pipe that has rusted itself to a much smaller diameter, which needs to be chiseled and vacuumed out to restore any old or new toilet's proper operation connected to it.
Answer: One thing I can think of is the water pressure change.
That could make the toilet fill valve to open.
Adjust the floater to bit lover position so there is more pressure on it in closed position.
Comment: @HandyHowie The point is that the valve isn't fully closing (or rather, might not be - I'm not convinced).  That means a lack of pressure on it.  The level in the tank is also limited by the overflow, so if adjusted too high the float will sit on this maximum water level without applying much pressure to the actual valve, and running water will be heard.  Adjust it lower, more force for the same water depth.  But I'd expect running the kitchen tap to reduce. not increase the pressure, so this probably isn't the fix
Comment: Why would adjusting the float add more pressure to the valve?  Wouldn't it just close the valve at a lower water level?
Comment: @HandyHowie if more of the float is submerged, it will push harder (displacing more water).  It will try to close lower, but might succeed around the current water depth.  But I've never had much luck trying this
Comment: @ChrisH That is the point, how can more of the float be submerged?  The float will always rise until the point the valve is fully closed.  Adjusting the float only adjusts the water level.
Comment: @ChrisH I agree, if water is flowing down the overflow, but this is more likely a sign of a faulty valve which needs repairing rather than the float adjusting.


Distance of a point from a fixed line

Question: If the distance of a point from a fixed line is fixed , why do we say that the locus of the point is a line parallel to the given line ? The point also lies on a line which is perpendicular to the given line right ?
Please ask me to elaborate with an example if the statement is not clear. Thank you.
Comment: The word *locus* here has the significance of *all points* that satisfy the condition.  The problem statement may have been slightly jumbled, but the "given" condition probably involved a line $L$ and a distance $d\gt 0$ from that line.  Then one asks about where to find all points $p$ which are that distance from that line.
Comment: Actually the locus is a pair of lines, on either sides.
Comment: Are you clear what "locus" means?  Yes, a point a given distance from a given line lies on many different lines, including the perpendicular to the given line.  But the "locus" is the set of **all** points that distance from the given line.  In two dimensions, that locus is a *pair* of lines. parallel to the given line on either side of it.  In three dimensions it is a cylinder.
Comment: @user247327 I'm sorry ! I get it now ! All points on the parallel lines would be the same distance from the given line ! Thank you !
Comment: @hardmath thank you ! I understood the concept !
Answer: Ok, so excuse the bad drawing. But imagine we tie a rope to a broomstick of length $d$ (for distance). Then the end of this rope (assuming it remain taut) has a few degrees of freedom. It can move along the length of the broomstick (the black line), it can also move around the broomstick. This process, if you were to consider the collection of all places where the green point can go, creates a cylinder around the broom.
If we were to cut right through the middle of this broom we lose one degree of freedom: going "around" the broom. So we're left with two lines whose distance - at every point - from the broom is $d$. This is the definition of a parallel line.
The key understanding here, is that the "locus" is the collection of all points for which a certain condition holds (a distance $d$ from the line)
Comment: Thank you ! That was a fun way of visualizing it. :)

Distance of a point from a fixed line


Ubuntu 18.04 freezes on shutdown/restart on Dell XPS 15' 9560 & won't boot after hard shutdown

Question: I use a Dell XPS 15' 9560. It has 16GB RAM, i7 processor, Nvidia GTX1050 graphic card, 512 SSD. I ran Windows10 home until now.
I've finally tweaked some settings in BIOS config and installed Ubuntu.
But, when I click restart to complete installation, it freezes my computer. I then have to do a force shutdown. Still, when I boot the computer it freezes on boot as well.
I'm currently running ubuntu from a bootable pen drive. I've tried a new config and I'm reinstalling ubuntu alongside right now.
Need help please.
Answer: This most likely needs the nouveau.modeset=0 fix...
ie: add GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nouveau.modeset=0" to /etc/default/grub file.
But you can only do that if you can boot..
So, you would need to press e when you see the grub load screen.
and then manually edit the grub settings
so that the GRUB_CMDLINE_LINUX_DEFAULT line looks like this:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nouveau.modeset=0"
assuming that allows you to boot, add the setting permanently
by running:
sudo gedit /etc/default/grup
and making the change there.
also How do I set 'nomodeset' after I've already installed Ubuntu?


Possesive pronomen + eins..?

Question: Could someone explain the grammar of the amalgation of possesive pronouns with eins? For example consider the word 'euereins' source: example.
Comment: Hiding the topic in a link is not recommended practice and unlikely to increase number of answers.
Comment: oops, I didn't mean to 'hide' it. I've put in post body now. I read the word when I was reading a story book.
Comment: Good point @CarstenS
Answer: I seldom encounter another combination than unsereiner, which is defined in DWDS as indefinite pronoun and as colloquial with the meaning sombody like us. The singular form meinereiner (somebody like me) is even more colloquial but sometimes used in conversation, likely due to its internal repetition.
I can't address the historic part, but the used einen is already the indefinite pronoun. DWDS just mentions that the first part is no genitive form.
Comment: I think DWDS doesn't mean "unser" is not genitive, but that "unsereiner" has no genitive. E.g. *"Autos unsereiner" is wrong. Also note that "unsereins" ist much more frequent than "unsereiner" according to DWDS.

Possesive pronomen + eins..?


Are there References on Whistling Technique?

Question: Are there any known references on professional whistling out there? I love to whistle, but I feel like it's not very pretty the way I do it and would like to learn from a professional the best way to do vibrato, increase my range, change registers quickly, etc.
Comment: To my knowledge, no one has ever defined a "school of whistling." There are certainly different ways of generating a pitched whistle, but is there anyone out there who you would call a "professional whistler?"
Comment: @NReilingh: There are [whistling championships](http://www.youtube.com/watch?v=FK1DCWrW02s).
Comment: Here's [another one for your enjoyment](http://www.youtube.com/watch?v=ntksmFXynbs&feature=grec_index). But I'm also curious to know if there is some training for it.
Comment: I like jazz- http://www.youtube.com/watch?v=4n3QJ3k7OZg
Answer: I'll make this a community wiki to encourage the addition of more resources in the future.
Thanks to NReilingh♦ for the reference to the "Pucker Up" documentary. The documentary contained some references to important resources, which helped me find more.
Whistling was popular basically until the end of the swing era, so most of the whistling related materials shown in the documentary were pre-1945. Agnes Woodward's book, however, is still around:

"Whistling as an Art: a method for the development of tone, technic and style", by Agnes Woodward (1923, 1925 and 1938). There are details on this, Woodward and the style used in the Dictionary of Whistling. I just scanned and uploaded the 1938 edition here.
"How to Whistle Like a Pro (Without Driving Anyone Else Crazy)", by David Harp (1993). This is not a thorough treatment of whistling but might get someone started with useful exercises.
"Dictionary of Whistling", by J.M. Schlitz (2013). This is an online resource containing names of techniques, famous figures, and interesting history. It is apparently only one appendix in the author's PhD dissertation, below:
"Guide to Artwhistling", by J.M. Schlitz (2006 with recent updates). Only some samples are available online (along with the dictionary), and the full text is not available to the general public, though it may be for official artwhistling instructors.
"Kunstpfeifen: an Overview", by same author (2002). This was apparently the first study of whistling to appear online, though it is outdated now (probably only in comparison to the author's own works, though).
I think I should also link to the International Artwhistling Philharmonic Society.
Comment: The dictionary of whistling is now offline and the Wayback Machine didn't archive it! T_T
Answer: I have a feeling that, while there may be professionals that would give you advice, you'd be as well off simply practicing different techniques and mimicking. For example I whistle on an inhale in the mid-high register for more volume. I'm sure that there are as many techniques as people whistling.
I have a hunch, however, that if you practice isolating harmonics (such as in harmonic singing) it may improve your ability to ascend/descend quickly/cleanly through the registers.
Just two cents (okay, maybe just one) from a strictly nonprofessional whistler.
Answer: If you want to see a good example for real "palatal" or "roof" whistling with open mouth , search for "palatal whistling " on YouTube and see videos of Thomas Molnar (my own performance).
Many think , it is something miraculous. IT IS really NOT.
The key is the completely different way of creating whistling tune. Instead of rounding lips and press the airflow between them (causing resonance outside  the mouth) the airflow  passes the bent-- up tongue left and right and crosses before the front teeth  within the mouth , creating a smooth- sounding whistle tune . Moving the lips (narrowing and widening it ) regulates the pitch of the tune.
Of course I use the "traditional"  technique too for lower  and higher pitches ,too - I can even breathe in during whistling so there is no need to make pauses or interruptions during the performance(see. Marcia Alla Turca)
How it works? See my above mentioned videos. If you have any questions, write me.
Comment: So after reading the Dictionary of Whistling, I realized that palatal whistling is actually apico-alveolar (unless what you're talking about is different). I might ask a separate question on getting a good tone (mine is very breathy).
Comment: I've been trying to learn this style of whistling. It's really difficult to find any explanation of it. Thank you for writing this. I would be really glad for any further tips on how you do it. Could you please describe the tongue position more? Thank you
Answer: From one of the videos you referenced:

Wow, Geert Chatrou is really something. After some research, it appears he collaborated with the makers of this documentary:
http://www.amazon.com/Pucker-Up-Fine-Art-Whistling/dp/B000IOM0UG
... which might be a good resource, and seems to contain some information about how to do palatal whistling.


What is the significance of the name John Doe in the 1940's?

Question: What is the significance of the name John Doe in the 1940's?
Comment: Why do you believe the name had a different significance in the 40s than it does now? (In other words, more details can help us pin down the correct answer.)
Comment: as opposed to what? Can you clarify what you mean - are you referring to the name's origin in general?
Answer: The name "John Doe" is used in several English-speaking countries to refer to a person whose actual identity is unknown. You may hear this in police reports, hospital admissions, forensic examinations, or any other context in which officials need to refer to a person whose actual name they don't know. John Doe (and its feminine equivalent Jane Doe) are effectively "placeholder names" used when a name is required and nothing else is available.
This is not unique to the 1940's, and as far as I know the usage has not changed since that time.
Answer: Looking for a John Doe in the Corpus of Historical American I notice that the phrase was used before the 1940s in sentences like the following ones.

Mr. Craig could be spared from his office as readily as Mayor Hylan has been, nor would his family be left in want as in the case of many a poor devil of a John Doe.
  The proceedings before the grand jury will be in the nature of a John Doe action involving a possible indictment for felony under the law forbidding the granting or obtaining of public office in exchange for a gift, promise or other compensation.

The CoHA didn't report any sentences containing a John Doe dated 1940s, but it reports sentences like this:

Filipino health was about, the best in the Orient: in 35 years, cholera, smallpox and bubonic plague had been wiped out; the population had increased from seven to 16 million, and the average height of the "tao" (John Doe) from 4 ft. 11 in. to 5 ft. 4 in.
Answer: If anything, its usage to mean "anonymous man" started during or before the 1940s. This is largely used in English speaking North America, as I believe that the UK has a different term.


Prove that $\lim_{x \to 0} \frac{x}{|x|}$ doesn't exist using epsilon delta definition

Question: I'm trying to prove that $\displaystyle\lim_{x \to 0} \dfrac{x}{|x|}$ doesn't exist using epsilon-delta definition. I know i'm supposed to assign a value to epsilon and assume $\displaystyle\lim_{x \to 0} \dfrac{x}{|x|} = L$ and work backwards to get delta. But I'm now stuck on finding delta.
Comment: You don't have to choose a delta. Instead, for each real number – each candidate for the limit – you have to choose an epsilon and show for every positive delta that the delta-neighbourhood of $0$ isn't taken to that epsilon-environment of that candidate. This means, no matter how close you come to $0$, you won't come as close as the chosen $\varepsilon$ to the limit candidate.
Answer: First note that the function you are considering is:
$$
f(x) = \frac{x}{\lvert x \rvert} = \begin{cases}1 & \text{for }x>0 \\ -1 & \text{for } x<0\end{cases}.
$$
(So the function is not defined at $0$.)
Now let $\epsilon= \frac{1}{2}$ be given. You want to prove that there does not exist an $L\in\mathbb{R}$ and a $\delta > 0$ such that if $\lvert x \rvert < \delta$ then $\lvert f(x) - L\rvert < \epsilon = \frac{1}{2}$. Assume that such did exist. So then for $x\in (-\delta , \delta)$, you would have
$$
\lvert f(x) - L\rvert < \epsilon = \frac{1}{2}.
$$
That is, you have for all $x\in (-\delta, \delta)$ that
$$
-\frac{1}{2} < f(x) - L < \frac{1}{2}.
$$
In particular for $x= \pm\frac{\delta}{2}$ you get the two equations
$$
-\frac{1}{2} < -1 - L < \frac{1}{2} \\
-\frac{1}{2} < 1 - L < \frac{1}{2}.
$$
So you get
$$
\frac{1}{2} < - L < \frac{3}{2} \\
-\frac{3}{2} <  -L < -\frac{1}{2}.
$$
But that obviously doesn't work.
Here is my challenge to you: redo this with $\epsilon = 1$.
Answer: Hint: $|x|=-x$ when $x<0$ and $|x|=x$ when $x>0$. Now calculate the limit from the left and from the right. Do they match? What does this imply?
Comment: @Yunhui Shi Another hint: Draw the function $x \mapsto \tfrac{x}{\lvert x \rvert}$, have a look at it, and then choose your $\varepsilon$ wisely. Clayton, he wants to do this by epsilon-delta.
Comment: @K.Stm.: This argument shows him exactly what $\varepsilon$'s he can pick. From there, this argument validates the $\varepsilon$-$\delta$ proof he wants.
Comment: Ah, right. That's the hint.


Rotational diffusion - why isn't $\hat n(t)=\hat n(0) \; \forall t$?

Question: Consider the rotational Langevin equation in the absence of an external force:
$$\frac{d \hat n(t)}{dt} =\vec{\xi}(t) \times \hat n(t)$$
where $\vec \xi(t)$ is a Gaussian white noise and $\hat n(t) \cdot \hat n(t)=1$. Take the dot product of this equation with $\hat n(0)$ to get:
$$\frac{d\hat n(0)\cdot \hat n(t)}{dt}=\hat n(0)\cdot\left(\vec{\xi}(t) \times \hat n(t)\right)$$
$$=\vec{\xi}(t)\cdot\left( \hat n(t)\times \hat n(0)\right)$$
Now take the average $\langle \ldots \rangle$ over the noise:
$$\frac{d\langle \hat n(0)\cdot \hat n(t) \rangle}{dt}=\langle\vec{\xi}(t)\cdot\left( \hat n(t)\times \hat n(0)\right)\rangle$$
But since $t\gt 0$ we have that $\vec{\xi}(t)$ is independent from $\hat n(0)$ as the present value of the noise cannot effect a past orientation. And also $\vec{\xi}(t)$ is independent of $\hat n(t)$ as the current orientation does not depend on the current value of the noise. Hence:
$$\frac{d\langle \hat n(0)\cdot \hat n(t) \rangle}{dt}=\langle\vec{\xi}(t)\rangle \cdot \langle\left( \hat n(t)\times \hat n(0)\right)\rangle$$
but $\langle \vec \xi(t)\rangle=0$ Thus:
$$\frac{d\langle \hat n(0)\cdot \hat n(t) \rangle}{dt}=0$$
$$\langle \hat n(0)\cdot \hat n(t) \rangle=\langle \hat n(0)\cdot \hat n(0) \rangle=1$$
Which actually implies that $\hat n(t)=\hat n(0)\; \forall t$ - an answer this is clearly wrong and contradicts with other calculations.  That said I cannot see a floor in my reasoning. Thus my question is: What is conceptually wrong with the above calculation?
Answer: Sorry, I just remembered I saw an explanation of something similar in "Quantum Field Theory and Critical Phenomena" by Zinn-Justin 4th ed pg63. The reason is that in general averages over the noise $\langle\ldots \rangle$ and time derivatives $\frac{d}{dt}$ do not commute i.e. in this case the equality that fails (I did it implicitly in the question) is:
$$\langle \frac{d}{dt} (\hat n(t) \cdot \hat n(0))\rangle\ne\frac{d}{dt} \langle \hat n(t) \cdot \hat n(0)\rangle$$


Prerequisites to start the study of non-commutative geometry in physics

Question: What are prerequisites (in mathematics and physics), that one should know about for getting into use of ideas from non-commutative geometry in physics?
Answer: I am not a fan of Alain Connes's ideas of non-commutative geometry, I prefer Michael Artin.  Nor do I think he was Dixmier's best student, although Dixmier thought so.  Nevertheless, to be fair, you should understand the physics of General Relativity and Quantum Field Theory first. I recommend Einstein's original papers still, and Yvonne Choquet-Bruhat's two books, Géométrie Différentielle et Systèmes Extérieurs, short and to the point and mathematically clear...obviously it is still commutative geometry, and her much longer, too long, Analysis, Manifolds, and Physics with two excellent co-authors.  I also recommend Dirac's own short physics book on the subject.  Then for QFT, Pierre Ramond is accessible and standard but very far from the point of view of Connes, which is why it would be good for you to read so you do not stay way too isolated.  Also for QFT read the work of Irving Segal (sometimes with Roe Goodman) on relativistic quantum fields from the operator algebra point of view, but he is not a physicist so you should also look at Streater and Wightman PCT, Spin and Statistics, And All That...  to see how physicists do operator algebra approaches to QFT.
If you do not yet even know Quantum Mechanics, I can recommend Sudbery's Quantum Mechanics and the Particles of Nature.
I assume from the way you phrase your question that you already are familiar with Connes's work itself.  If not, you would need to prepare by studying Dixmier's book on von  Neumann algebras or Guichardet or Dixmier, Les $C^*$-algebres et leurs représentations.  Hope this helps.
Comment: Dixmier only had [eight students](http://www.genealogy.math.ndsu.nodak.edu/id.php?id=34272), and although some of them are quite distinguished, it looks to me like none of the others even came close to winning a Fields medal (which I believe Connes won for work done before he started investigating noncommutative geometry).
Comment: During Hilbert's lifetime, Hecke (his student) was way under-appreciated.  The big man was Landau.  Nowadays, where is Landau? But Hecke's work is seen as more and more important every day....  I predict the same for Vergne.
Answer: Physical applications of noncommutative geometry rely mainly on the spectral triple formalism. This being a noncommuative version of Riemannian (spin) geometry, it would be advisable to know then first the commuative case (spin geometry itself)-Friedrich's book on Dirac operators is a good reference. This generalization uses lots of operation algebraic concepts. Varilly's books on NCG are recommended. The recent survey arXiv:1204.0328 is adressed to physicists.
The next level would be the book of Connes and Marcolli: "NCG, QFT and Motives  " http://alainconnes.org/docs/bookwebfinal.pdf


Is there a way to increase the contrast of a PDF that was created by scanning a photocopy in B-W

Question: I've tried opening the Accessibility menu and choosing black background with green font, but it seems this does not work if the document was originally scanned in Black/White mode.  Is there any other way to enhance the PDF's contrast?
Comment: Extract images (scanned pages) from PDF, use some image manipulation to enhance contrast, put images back. I don't know of any PDF viewers that allow you to manipulate image contrast directly.
Comment: Unless you ran OCR on the scan, there is no text, just a picture of text, so no text-related settings will affect anything.
Answer: If it has tons of pages, the easier tool is a command line one: http://www.imagemagick.org/script/download.php
(ImageMagick is a very popular image manipulation library.)
You will have to do three steps.

Convert PDF pages to individual image files. See: Convert PDF to image with high resolution or Convert PDF to JPG images with ImageMagick - how to 0-pad file names?
convert -density 600 your_pdf_filename.pdf  output-%02d.jpg

Adjust image quality. If you have only a few pages, Photoshop or GIMP (free and open-source alternative to Photoshop) will simply import each page as an image. Update the contrast as you'd like and save. For more info see Gimp: how to remove background noise/artifacts and enhance handwritten text or continue to use ImageMagick: Batch-processing images of documents to look like a fax
convert output*.jpg -normalize -threshold 80% final-%02d.jpg

If you want a pdf back:
convert final*.jpg my_new_highcontrast.pdf

Comment: Problem with this is, if you have lots of bookmarks in the pdf, they are all lost.
Comment: On windows the command is `magick convert` instead of `convert`. Additionally, Ghostscript must be installed otherwise you will get a `FailedToExecuteCommand gswin32c.exe The system cannot find the file specified`.
Comment: @bgmCoder good point. Moving from pdf to images and back to pdf will essentially kill every single PDF feature besides the content itself. Even pure text will become an image. But the question was about a PDF created from a scan, so I assumed it would only have images anyway.
Comment: Tip: if your book has more than 99 pages, use %03d instead of %02d, otherwise the pages will be in the wrong order, because page 100 will be after 10.
Comment: Very good solution. Not sure what happened on my side I have to output each intermediate step into `.png` not `.jpg` so that my final `.pdf` won't be broken with purple color whole page.
Answer: I have a PDF with a lot of gray images (manga). So I used the answer of gcb, changing the 2nd command to:
convert output.jpg -level 25% output_contrast.jpg

Just change the level value percentage to what serves you.

Observation.
With the arg -threshold you get a "black and white" (only) image. But I want to keep the gray scale, which is possible with the arg -level: you keep the gray, letting the image with a darker or lighter gray scale.

The commands order will be:
convert your_pdf_filename.pdf output-%02d.jpg
convert output*.jpg -level 25% final-%02d.jpg
convert final*.jpg very_readable.pdf

Comment: The -level parameter accepts one, two, or three numbers separated by a comma. For instance -level 30%,100%,0.3. The first is "black level" , next is "white level", and finally "gamma". Anything pixel darker than 30% becomes black, and pixel brighter than 100% becomes white, and then a nonlinear power law transformation with gamma=0.3 is applied for the in-between values (gamma=1.0 means linear, no transformation). Use a single image to quickly play around with the parameters to get desired result.
Comment: With "threshold" you get a "black and white" (only) image. With "level" you keep the gray, letting it "darker" or "lighter"
Comment: So what is the advantage of this variation compared the answer by gcb?
Comment: That would be good information to edit into your answer.
Answer: In case you want a solution in python: github gist.
The script converts the pdf to images, modifies their contrast and writes it back to pdf.
Usage example
$ python pdf_contrast.py 2.3 -i in.pdf -o out.pdf
Loading pdf in.pdf
Pages: 48
Contrast x2.3: 100%|███████████████████████| 48/48 [00:02<00:00, 18.42pages/s]
Saving pdf to out.pdf

Comment: Very helpful script!. Since I already had a pipeline manipulating each page, just added `enhancer = ImageEnhance.Contrast(pil_img); enhanced_img = enhancer.enhance(contrast)` and  voila!, images & the end pdf now have more contrast!
Comment: `cannot find the file specified` >> `Unable to get page count. Is poppler installed and in PATH?` :/
Answer: Nuance Paperport has the ability to increase contrast on scanned pdf pages.
The free software NAPS2 is also able to do this, either in combination with scanning or after importing a scanned page. NAPS2 also has other features, e. g. to crop and to automatically deskew a scanned page. On my machine (Core i5, 8 GB) import is a bit slow, but the page editing seems to work fine.
Comment: NAPS2 works great - it is easy enough and intuitive, but if you have any bookmarks already in the pdf, they will all be lost.
Comment: NAPS2 was a great answer.
Answer: For Windows, I wrote a batch file .bat to automatically generate the PDF upon drag-and-drop onto the batch file. (linux/OSX would require translating this to a shell script)
You first need to have ImageMagick (allow installer to add to PATH so magick convert works from the command line) and GhostScript installed. Don't worry, they are easy to install.
Here is the batch file. Make a file pdf_darkener.bat with the following contents:
@echo off
echo Darkening the pdf at %1
echo Converting PDF to JPGs...
magick convert -density 500 %1 darken_pdf_preprocess_%%02d.jpg
echo Darkening JPGs...
magick convert darken_pdf_preprocess*.jpg -level 50%%,100%%,0.3 darken_pdf_postprocess_%%02d.jpg
echo Converting JPGs to PDF...
magick convert darken_pdf_postprocess*.jpg darkened.pdf
echo Deleting JPGs...
del darken_pdf_*.jpg
echo Done!
pause

Drag any PDF file onto the batch file. Wait for operations to complete (slowness / level of detail is controlled by density 500, higher = more pixels, bigger file size, slower). The output pdf will be in the same directory as the original pdf. The batch file cleans up after itself, deleting the intermediate jpgs created during processing.

Note that this contrast-increasing operation is controlled by three numbers: 50%%,100%%,0.3 which means 50%, 90%, and 0.3. These are black_level, white_level, and gamma, according to the ImageMagick documentation. black_level is the percentage of brightness below which everything gets mapped to pure black, visa-versa for white. Gamma controls a non-linear mapping for the in-between values (1.0 is linear).
Please share any improvements or useful modifications in the comments section.
Answer: You can convert pdf to jpg online . Adjust pictures on a photo editor. I used Adobe Lightroom to adjust contrast on multiple photos at once with synchronized settings to save time. Then convert JPG to PDF online
Answer: If you are not comfortable with Image Magick and command line and want more control over the process, I suggest using Foxit PdfPhantom (Business Version) along with adobe Photoshop. You can simply convert your pdf to any image format that you want with Foxit under the Convert tab. Then you can use Photoshop to apply a specific sequence of operations to a series of photos. For this purpose, see this tutorial. Finally, you can turn back to pdf using Foxit.
Comment: tried Foxit to export to JPG, TIFF, JP2 on max settings - it degrades the quality of picture. Not working solution
Answer: I do not think that any of the PDF viewers have built in filters or adjustments for pictures, only for fonts backgrounds and colors.
You could adjust your monitor, and/or if your video card software supports it adjust the video cards, video settings. Save the video settings in a profile to use again, for this purpose, it would not be too bad.
You could print it and adjust your printer (most printer preferances allow adjusting).
  You could Screen grab it , then paste it into a picture/photo editor and adjust.
 If your "allowed" and have PDF creation program you could fix each picture used, and remake it.
If you have Adobees photoshop program, some versions of it would open a PDF, I do not know what it could do.
See also Adjust PDF Contrast with Adobe Reader/Acrobat?
It has some very good and easy answers if the PDF is not locked down.
You did not indicate if it is one picture, or many, which would help the question. You did not indicate the operating system (even a tag for it works). adding that information to the question will improve being able to answer.


Why is mean normalization useful in gradient descent?

Question: I understand that feature scaling speeds up gradient descent by making the geometry of the cost function more hospitable (i.e. more circular), but why is mean normalization useful? Doesn't it just "move" the cost function closer to the origin?
Answer: Normalization of data is a tricky process. You have your terminology a little bit mixed up, but your intuition seems correct. What you refer to as normalization is in fact the centering of data. This is beneficial for certain algorithms (PCA for instance), or as @Alex R. pointed out for activation functions for neural networks. It does not have any bearing on gradient descent itself.
The process of normalization is in fact what you refer to as scaling. As you correctly point out, normalizing the data matrix will ensure that the problem is well conditioned so that you do not have a massive variance in the scale of your dimensions. This makes optimization using first order methods (i.e. gradient descent) feasible.
Your confusion may stem from the fact that the process of normalizing and centering your data is sometimes referred to as standardizing the data.
Comment: Ok, that makes sense, and clears up my confusion. (I now realize I was confused because in the video by Andrew Ng I was watching on feature scaling and its usefulness in gradient descent, he sort of tacks on centering of data (or what he calls "mean normalization") without giving it context. Video is at https://www.youtube.com/watch?v=cOrx5-9-YjQ )
Answer: Your wording is bizarre. Normalization makes your input commensurate in size with the initializations you pick for your weights/parameters. The mean shift balances your input to have both negatives and positives, which is important when your model has asymmetric functions, such as ReLU neurons or the sigmoid of a logistic regression. It also prevents your functions from being saturated, I.e. have vanishing gradient


how to disable vertical auto-centering of cursor

Question: I recently had my Ubuntu Linux upgraded to 14.04, and my emacs got upgraded to 24.3.1 in the process. I noticed that it scrolls by itself. I finally realized that it automatically centers the cursor vertically after a few seconds. This is extremely annoying to me. I decided to give it a try for an hour or so to see if I can get used to it, but it still annoys me. I went to the options menu, but I see nothing about that feature. Can anyone tell me how to disable it? Thanks.
Comment: That's definitely something in your init file. I remember trying this feature too. If memory serves, it was implemented as a minor mode, so to identify it, press `C-h m` and look at the description of minor modes you have enabled, most likely it will be there somewhere.
Answer: Try to start with emacs -Q first and see if the problem still exists (it should not).  Then bisect your init file to figure out what causes it.
I'm using centered-cursor-mode as a global minor mode to keep the cursor vertically centered, but it behaves somewhat differently than what you describe.  Your best bet is to bisect your init file (comment half of it and concentrate on the half that appears to be responsible, then repeat on that half until you are at the line that causes the undesired behaviour).
Answer: Please check this answer to a similar question.
Try killing any buffer-list buffer.
Comment: This answer is a link to an answer that is also a link. Could you either expand the answer here so that it stands alone, or, if this is a duplicate, mark it as such?
Comment: I finally tracked it down to this line: (setq global-auto-revert-non-file-buffers 0)
Comment: Yes, when I kill my buffer list the problem ceases. That's progress. But how am I supposed to work without a buffer list? I use that constantly. Also, I see that the problem is not fixed in the next version. Is it finally fixed now, or do I need to go back to an earlier version (if so, which)? What a clusterf**k!
Comment: I took the liberty of marking this a duplicate. Answering your question, @RussP., this was indeed fixed in 24.4 (which was released last year). Ubuntu takes a long while to update its official packages, but I'm sure there's a way to install 24.4 from the ubuntu package manager (try googling a bit).
Comment: I installed 24.4.1 and that solved the problem. Thanks.
Comment: Well, my assessment was premature. I am still having this problem even in 24.4.1. This is rapidly becoming a huge waste of time for me. Moreover, I don't understand how such a major bug could have persisted for this long. Doesn't everyone use the buffer list? If not, how do you select buffers and directories?


Diversity Bronze Badge Idea

Question: I was thinking maybe it would be good to offer a badge for those that have a minimum score of 1 across 50 tags.  Perhaps this would help get user's to read/answer questions on other tags more often, instead of just camping in the high-traffic ones trying to get upvotes...
Comment: That's an interesting idea, but it is just too tempting to throw hit or miss answers at tags I am barely competent in until I get a single upvote. The segregation of answerers into tags relevant to their area of expertise isn't necessarily a bad thing.
Comment: 50 tags is way too low of a threshold. You don't need to be _active_ in many tags just to have activity in different tags, you just need to be active period. Most questions will have other tags tacked onto them, not just the one you're interested in.   I primarily hang around the [c#] and [knockout.js] tags and have gotten "votes" for many other tags as well just because the questions I've been active in had those tags added as well.
Comment: 50 tags and one bronze. I dont have much reps still i have 1+ upvotes in 350 tags.
Answer: A large number of questions have one or two relatively irrelevant tags in addition to the more popular ones. This makes it fairly easy for a user to rack up scores on these tags, even if they never branch out from the high-traffic tags. So just requiring 1 upvote on any 50 tags is pretty bad, IMO.
Instead of just upping the number of tags or upping the upvote requirement, I think you should restrict the tags to a more relevant subset. This might make for a decent bronze-level version of the Generalist badge, if it were changed to something like:

Provided non-wiki answers of 1 total score in 50 of top 200 tags

This would make it a far more interesting badge, as well. Users would be forced to target a specific set of tags. It would drive many of them to visit the Tags page to see what tags count toward their goal—and hopefully find areas where they can provide more quality answers in the process.
I also think diversity is not quite the right name. If it's a bronze-level version of Generalist, perhaps Versatilist might be a better term, but who knows…

I took the liberty of running some very crude simulations, just for comparison:

Using OP's original spec, typical users who would earn the badge would do so at around 1.8K rep.
Using my modified spec, typical users who would earn the badge would do so at around 8.0K rep.

Of course, this looks at current behavior patterns. One would expect if either spec is implemented, many users would try to get the badge earlier, bringing the average rep down. Similar analysis suggested the typical user who earns the Generalist badge does so at around 25K.
Comment: Your points about a score of 1 are completely valid; I don't quite understand why you went on to suggest exactly the same thing... I have a score of more than 1 in almost 300 tags; it's guaranteed that I fulfil the conditions of this. I only have a score of 5 (for e.g.) in 86 tags though... seems more reasonable.
Comment: @benisuǝqbackwards My point was not that it's too easy to get 1 score, but that it's too easy to get it *many* irrelevant tags. If the goal is to encourage users to explore other areas of the site, then making it just any 50 tags doesn't accomplish that. Sure you could bump the limit up, but still I don't feel that properly encourages, users to look for areas they can contribute--they're likely just to search for questions in tags where they have a score of 4, whether or not that tag is actually useful to future users. I think this is the same rationale underlying the **Generalist** badge.

Diversity Bronze Badge Idea


How to normalize filters in convolutional neural networks?

Question: Usually, when convolving images, the elements in the filter sum to one.
Is this criterion enforced in convolutional neural networks? If yes, how?
Answer: No, in convolutional neural networks, there's no criteria that enforces the learned filters to sum to $1$. In fact, there is nothing in the definition of a convolution $f * g$, continuous or discrete, that says the filter $g$ needs to sum to one. You may be thinking of a discrete gaussian kernel for blur operations that often (but not necessarily) sum to one.
Convolving two continuous 2-D functions $f$ and $g$ is defined as [1]:
$$
\int_{\tau_x=-\infty}^\infty \int_{\tau_y=-\infty}^{\infty} f(\tau_x, \tau_y)\, g(x - \tau_x, y - \tau_y)\, d\tau_y\, d\tau_x
$$
In machine vision and image processing, we're dealing with discrete images and thus discrete convolutions. Not only are we dealing with discrete images, but the filters that we use are finite filters; for computational efficiency we won't convolve an infinitely large discrete filter over the original image $f$.
A discrete 2-D convolution of a discrete function $f$ and a finite filter $g$ of size $(w, h)$ is defined as [2][3]:
$$
(f * g) [x, y] = \sum_{x_f=0}^{w - 1} \sum_{y_f=0}^{h-  1} f[x - x_f, y - y_f]\,g[x_f,\, y_f]
$$
These types of discrete 2-D convolutions are central to the feed forward pass of a convolutional neural network. They're typically implemented with either FFTs and multiplication or matrix multiplication with Toeplitz matricies.[4][5]
As you can see, there's no constraint or rule in the definitions that says that the double improper integral of $g$ from $(-\infty, -\infty)$ to $(\infty, \infty)$ (in the continuous case) or the sum from $(0,0)$ to $(w - 1, h - 1)$ (in the discrete case) needs to equal $1$.
I want to add that there are a variety of normalization steps that can happen before you input images into a convolutional neural network, such as PCA whitening or homomorphic filtering. You can even normalize your network output so that the feature vector sums to one. Some papers ([6]) do this. However, the point is that these normalization steps are not inherent to the convolution operation or CNNs.

http://en.wikipedia.org/wiki/Convolution#Definition
http://en.wikipedia.org/wiki/Convolution#Discrete_convolution
http://www.cim.mcgill.ca/~langer/558/10-edgecorner.pdf
http://en.wikipedia.org/wiki/Convolution_theorem
http://en.wikipedia.org/wiki/Toeplitz_matrix#Discrete_convolution
http://www.cv-foundation.org/openaccess/content_cvpr_2014/papers/Taigman_DeepFace_Closing_the_2014_CVPR_paper.pdf
Answer: As sabalaba points out in his answer, this is not enforced in convolutional neural networks.
Nevertheless, in some applications you may want to enforce unit norm. When training with standard SGD backpropagation, the simplest way to obtain unit-energy filters is to perform a normalization operation after each SGD update.


Book of drug interactions

Question: Where can I find full list of drug _ drug interaction & adverse reaction, apart from pdr.net, I mean to say in a book form. What books of medical science contain these information? Please name a few. I have read Lippincott's Pharmacology but I did not find any list.
Answer: Definitive manuals, or textbooks for drug interactions tend not to be published on their own any longer, due to their need to be constantly updated, and having been superseded by better ways to search for the information required, in a digital format. OR - they are tremendously expensive, like this. Otherwise, drug interactions and adverse reactions are integrated into clinical pharmacology textbooks such as Rang and Dale.
Other study books, such as this, do have commonly prescribed drugs with major interactions listed per each drugs.
In the United Kingdom, we tend to use the British National Formulary (BNF) which is given to all doctors in a paper-copy, but is also online - here which has a fully searchable interactions section. It can be bought in paper copy here - but it's not a good study book, it's a reference for working prescribers.
https://www.drugs.com/ is reliable, an USA-based, with an interactions - but is again a website.
If you want to let us know what specifically you are revising for, or what you need it for - perhaps we'll be able to point you to a more specific book. :)
Answer: One of the most well-known books dedicated to drug interactions and serving as a comprehensive reference for this topic specifically is Stockley's Drug Interactions. You can find a sample chapter here.
Highly recommended!

Book of drug interactions


Copy other cells if EITHER column has specific text

Question: In a single sheet wanting to copy D3:N if either B3:B or C3:C = S2.  I'm sure there is a simple formula to do this I am just unable to find it!
Answer:
you can solve this easily with QUERY formula:
=QUERY(D3:N; "where B='"&S2&"' or C='"&S2&"'"; 0)

if S2 cell is a number then it would be:
=QUERY(D3:N; "where B="&S2&" or C="&S2; 0)
Answer: Try a formula like the following:
=FILTER(D3:N,(B3:B=S$2)+(C3:C=S$2))

Since FILTER conditions are treated as ANDs, using in your two conditions directly would only let rows through if B3:B AND C3:C matched S2. Instead I use a plus sign to add TRUEs and FALSEs since that works as the Boolean OR we need.
Here's the above formula showing matching rows starting in V3:


As a Terran, how can I punish a Protoss if I know he's going 4 gate?

Question: I'm in Gold League and all day I play against 4 Gate Protoss. How can I take advantage of this as soon as I scout it? Obviously, it's hard to take advantage with an expansion against this kind of early aggression, even with bunkers.
Comment: With Terran? or any race?
Comment: @Wipqozn I edited the headline to clarify. Thanks.
Answer: Wall in, tech up to siege tanks w/ siege, build a few, and plant them at your base entrance. Assuming you scout early enough, this method requires the least micro and will allow you a solid transition into an expansion.
You can also try to build up a few bunkers & stock them with marine/marauder. This can be effective as well as long as you keep the ranged Protoss units out of range of your repairing SCVs (a.k.a. walling in).
For either of the above, you'll want to watch out for void rays. That's usually how your 4-gate counter will be countered.
Banshees with cloak can be somewhat effective but the siege tanks have more longevity in terms of utilization for the rest of the match.
Marauders with concussive shells can also be effective if you have the micro for it.
Comment: +1 Siege Tanks are really effective at stopping ground rushes. In fact a wall-in with a few siege tanks can make an early game aggression  pointless
Comment: How are you going to get a helpful amount of siege tanks before 7 minutes? That's even besides the point that you have to target fire stalkers, because if you hit the zealots, you will be killing your own bunkers. You cannot punish a 4 gate. The correct way to win is to bunker up, 3-4, pull scvs to the front of the bunkers and keep pumping marines & scv's (along with a few marauders). Once it ends, you win. This is all asumming you do 1rax FE, which is the standard for Terran if not rushing themselves.
Comment: @jsn We're basically saying the same thing. I'm not saying you should have tons of tanks out by the 7-minute mark, but you want to wall-in to hold it off. If they keep pushing the 4-gate, pumping out M&Ms isn't going to change the situation. You have to tech into a counter so you're not just throwing units against one-another.
Comment: @Shaun siege tech takes way precious gas (and minerals) from medivacs and upgrades that early in the game. Seige tanks are useless in TvP. You are going to have 1 tank out with siege tech only finishing (not finished) by the time 4gate hits. It is not going to help you.
Answer: I've been trying to wrack my brain about how to punish the protoss player, but unless you can stay alive through the push, it would be very difficult to punish them before they come up with an army knocking on your front door.
So assuming you survive with bunkers and marines/marauders/scvs set on repair the ideal tech path would be to go cloaked banshee.
If they are 4gating they cut probe production which means you're already ahead economically. It also means they won't have a robotics bay to build an observer, you are free to pick off as many probes as you have energy, which will give you even more of an economic advantage and you will get the win assuming you continue to macro effectively.


Prove that $x^4-2x^2-11$ is irreducible over $\Bbb Q$

Question: To find the minimal polynomial of $i\sqrt{-1+2\sqrt{3}}$, I need to prove that
   $x^4-2x^2-11$ is irreducible over $\Bbb Q$. And I am stuck. Could someone please help? Thanks so much!
Comment: @DHMO  I think it can only gives us the result that it has no root. But it does not necessarily imply it is not reducible.
Comment: Rational root theorem.
Comment: You're right. I'm sorry.
Comment: If it has a factor ovet Q then the lowest coefficient of the factor is a product of roots and rational. Find all four roots and check that no products of a subset s rational.  You only need check products of one or two roots.
Answer: The rational root theorem (or the quadratic formula, solving for $x^2$), shows that there are no linear factors over $\Bbb Q$. That means that if the polynomial is reducible, then it reduces to two irreducible quadratic polynomials.
However, if that were true, then your number would be a root of one of them. The quadratic formula then says it can be written in the form $a\pm\sqrt b$ with $a,b$ rational. The number is pure imaginary, so $a=0$, which means that $b=1-2\sqrt3$, which clearly isn't rational. This is a contradiction.
Answer: As there are no rational roots the only possible factorisation is into two quadratics whose coefficients we may assume to be integral by Gauss. As 11 is prime and as there is no $X^3$ term we must have
$$
(X^2 +\alpha X +\epsilon)(X^2 -\alpha X -11\epsilon)
$$
where $\epsilon=\pm1$.
Now look at the $X$ term and get $\alpha=0$, and a contradiction.
Answer: If you have a candidate $f$ for the minimal polynomial of an algebraic element $\alpha$ over $\mathbf Q$ but you don't know if $f$ is really irreducible and want to avoid trying possible factorizations, you might want to compute the degree $$[\mathbf Q(\alpha): \mathbf Q]$$ and check if it agrees with the degree of $f$.
For instance, in your question, let $$\alpha = i\sqrt{-1 + 2\sqrt 3}$$.

Exercise: show that $[\mathbf Q(\alpha): \mathbf Q] = 4$ using the inclusions $$\mathbf Q \subset \mathbf Q(\sqrt{3}) \subset \mathbf Q(\alpha).$$

See also this answer for a similar application of this philosophy.
Answer: As noted already, the rational root theorem excludes rational roots, which only leaves a product of rational quadratics as a potential factorization.
By the way the polynomial was constructed, it is known that its roots are $\,\pm i \sqrt{2 \sqrt{3}-1}\,$ and $\,\pm \sqrt{2 \sqrt{3}+1}\,$. Any quadratic factor of the quartic would need to have two of those as roots, and among quadratics with rational (non-complex) coefficients the only possible pairings would be between the two real roots, or between the two complex roots, respectively. However, both cases result in quadratics that have irrational coefficients $\,(x^2 - 2 \sqrt{3} - 1)\cdot(x^2 + 2 \sqrt{3} - 1)\,$, thus no factorization over $\mathbb{Q}$ exists.


Does increased water vapour in atmosphere increase the risk of hypoxia?

Question: I recently found that each degree of warming increases water vapour by 7% and I've also learned that the atmosphere contains (on average) between 1-5% water vapour when saturated, this confused me a bit, and I wondered if this could affect the oxygen concentrations in big cities or maybe the effect is too small.
Answer: The atmospheric concentration of oxygen is 20.8 percent, which is a significantly large proportion of the atmosphere.
Oxygen is being depleted because of the burning of fossil fuels, but the rate of depletion is very small compared to the amount of oxygen present in the atmosphere.
The burning of fossil fuels is more of problem for oxygen depletion than the amount of water vapor in the atmosphere. There is no risk of hypoxia due to increases in atmospheric water vapor. What risk there is is of increased humidity and temperature discomfort resulting from that.


Phantom TFS workspace will not let me map to another workspace?

Question: I type this command:  tf workspaces into a command line and it tells me there are no workspaces on the machine. I then try the same command on the server, nothing. So I go into Visual Studio 2010 and create a new workspace and try to map the TFS path to my local path. I then get an error that the mapping already exists in another workspace. But I cannot find that workspace on my local or on the tfs server. Any ideas?
Answer: You can run tf workspaces /remove:* to clear out your local cache of workspaces. See this link for more details.
Comment: I found this after I wrote it, but I give you the props! I also used this: http://www.attrice.info/cm/tfs/
Answer: I know this is an old question, but I just came across this issue on a Linux machine running TEE (Team Explorer Everywhere).  Running "tf workspaces -remove:*" didn't work, because it said there were no workspaces in the cache.
The user was trying to create a new workspace, which worked, but when he tried to map folders, it told him it didn't exist.
When he ran "tf workspaces" on the machine and when I looked in TFS Sidekicks on the server itself, it didn't show any workspaces for him on the Linux box.
If he tried to create the workspace again, it told him that it already existed, but every time he tried to map, he was told it didn't.
We could see the workspace from the tf command line if I did "tf workspaces /owner:", and it required me to run "tf workspace /delete ;" from the command line to get rid of it.
Once we did that, he was able to create it again and everything worked properly.
No idea why that happened, but figured I'd post my answer here just in case someone else comes across a similar issue in the future.


What's the verb for "color commentator"?

Question: What's the verb for "color commentator"? What verb do you use to say that a color commentator is commenting on a sports game? Sometimes, I want to avoid using the word "color commentator" and I want to use the verb variant of the term "color commenting" or "color commentator".
Comment: Can you give us an example sentence in which you'd use this?
Answer: There isn't a dictionary defined verb for this, but "provide colour" is commonly used.
Answer: I'd never heard the term "color commentator" but it seems to be typically an ex-player who gives expert analysis on the game. So you could call them an analyst, or a pundit
So you would say that the color commentator is analysing the game.

Today I'll be joined by former Penguins player, Rick Martindale, who'll be analysing the game and offering insights based on his 20 years as a player and a coach.

At any given time the color commentator could also be summarising the play, reflecting on the performances or just cracking a joke.
Answer: In the U.S., we often say that someone "provides" color commentary. There is no verb form. (I.e., you can't say that someone "color comments".)
You could also say that someone "analyzes" or "comments on" a game, but those terms are not as specific.
Answer: The color commentator provides commentary on the game as opposed to analysis.  The CC will tell you the quarterback's wife, Melinda, just gave birth to their second set of twins.   The analyst will tell you the last time his wife gave birth he was 22 for 22 in passing.
In practice, most sports announcers provide both color commentary and analysis.


NMAP SSMTP Service Detection

Question: When I examined a NMAP -sV scan on a host running Exim on port 465, it uses the standard SYN scan to determine if the port is open, and then issues a Client Hello to which the server responds with a Server Hello. There is a Encryted Handshake from NMAP and Application Data from the server but nothing seems to suggest how NMAP determines what is running on the port, which is quite different than how it identifies other services like IMAP or POP3. So, how does it do it?
Answer: Nmap is "smart enough" to recognize SSL encapsulation. In this case, it marks the port as having an SSL tunnel, then on subsequent rounds of version detection it establishes the tunnel, then sends the same probes that would be sent to the plaintext service.
You could see this in action by using stunnel to convert some other service to SSL-tunneled, then scan it with Nmap while running a packet sniffer on the loopback adapter of the target machine. You would see that the traffic looks the same as Nmap probing an unencrypted service.
Answer: It's the same as any other service just over SSL I suspect. So you might just see the encrypted part it's still the same protocol beneath the SSL layer.
Comment: SSL is an encryption layer, so you just use normal SMTP , but the connection is secured by SSL or TLS. There for you are unable to see the communication.
Comment: But with almost every service I've seen (except DNS) NMAP just grabs the server version from the response it receives fter its establsihed a connection which is very visible and obvious when viewed in wireshark. But in the case of SSMTP I can't seem to find any information related to service version. Does SSL service detection work diffrently?

NMAP SSMTP Service Detection


Chrome back/forward gestures no longer working after Mavericks update

Question: Has anyone else noticed their 1 finger back/forward gestures no longer working in Chrome?
I have tried the gestures on other applications such as Safari and Mission Control, they are all still intact.
Answer: Make sure you enable: System preferences > Mouse > Swipe between pages
AND OPEN A NEW TAB in Chrome
If you had it working before but then it stopped working suddenly (usually after an OS / Application update) you might just have to uncheck / recheck the "Swipe between pages" option. That should solve it.
Comment: I didn't even need to open a new tab.
Comment: works for me too!
Comment: i upgraded to el capitan to use magic trackpad 2, and it seems like the gesture changed from 'swipe with two fingers' to 'scroll with two fingers'. Make sure the gesture matches your expectations even after the Swipe between pages gesture is enabled.
Answer: In System preferences > Trackpad > Swipe between pages (under more gestures tab)
Uncheck it and recheck it.
Should work in Chrome now. You may need to do it when first installing Chrome or updating Chrome.
Comment: UNCHECK / RECHECK. Perfect ✅
Answer: Make sure you enable: System preferences > Mouse > Swipe between pages
Comment: It worked for me by doing: System preferences > Mouse > Swipe between pages Thanks, couldn't live without it! :)
Answer: I disabled my chrome extension (crxMouse), and the problem is gone.
Answer: Yes, I've noticed that too. I already reported that error to Google via the Chrome's Options panel -> tools -> report errors.
Hopefully they'll fix it soon!
Answer: Do you have Better Touch Tool installed?  If so, uninstall it as it doesn't play nice with Mavericks atm.  Also if you dont have it installed, I changed the tracking speed, as I had previously set it with Better Touch Tool.
I'm pretty sure it's not an issue with Chrome.
Answer: There is a bug report already on the Chrome forums. Check it out here and add your info too.
It seems to be a sporadic problem; I have the issue every hour or so, but my colleague doesn't get it at all.
Answer: Mine stopped working too, but realised I had installed a chrome plugin called 'SmoothScroll' (or something similar).  Uninstalling this gave me my gestures back, Happy times!
Comment: Thanks Jac, SmothScroll is the culprit!! I disabled it on mine and got my swipe between pages back!
Answer: This is a Chrome bug which is fixed in the 64-bit Beta which I use. It's a beta but works fairly well, I haven't noticed any problems except the headbar occasionally not retracting in presentation mode.
Answer: I ran into this issue a while back as well.  When I looked at my Chrome extensions, I had one enabled called Smooth Scroll.  When I disabled that extension, my gesture swipe returned to normal.  Hope that helps.
Answer: I can confirm this annoying bug.
The magic mouse right swipe for "back" doesn't work most of the time, but does after swiping with the trackpad once.
Chrome 60
macOs 10.13 public beta 5
Answer: I too faced the same issue before chrome update, after the update Version 69.0.3497.100 (Official Build) (64-bit) issue is resolved.


24 hour yogurt calcium content

Question: How much calcium in 24 hour yogurt? I use a half gallon of Organic whole milk & starter. I have heard yogurt has more calcium than milk after fermentation, but can find no measurements (or %DV)for calcium on homemade 24 hour yogurt.
Answer: Calcium is an element, so the biological-chemical processes of fermentation can neither create nor destroy it (and it does not become a gas which could float away). Therefore, the calcium content of your end product will be exactly the calcium content of your ingredients, so you if you know how much calcium is in your milk and starter then you have your answer.
Note that:

This is true of the absolute quantity of calcium, not the proportional quantity (to take an exaggerated example, if 1 litre of ingredients produced 0.75 litres of yoghurt then even if the quantity of calcium was the same the proportion would be much higher).
It may be that the calcium after fermentation is in a different form which the body is more or less able to use (this is called bioavailability); you would need to research that question separately (my instinct, though, is that this is not the case).
As rumtscho's comment points out, if your recipe involves discarding whey or some other part of the mixture then this reasoning no longer applies, and you would have to investigate whether the whey/discard contains proportionately more or less calcium than the remainder of the ingredients. However, the recipes I have seen for 24-hour yoghurt don't involve discarding whey or any other part of the mixture.
Comment: @rumtcho I was just hedging against the possibility that the process involves some step with a change of volume (by evaporation, gas given off in fermentation, growth of culture or whatever) – the numbers were deliberately exaggerated to make the point about proportion. The recipes I saw when googling '24 hour yogurt' didn't involve discarding whey.
Comment: I am not completely with you on the first note. If 1 litre of ingredients produces 0.75 l of yogurt, this means the OP threw away 0.25 l whey (unless you are implying that 0.25 l evaporated during the scalding? That would be really unusual). I wouldn't make any guesses about whether the calcium is all in the yogurt, all in the whey, or distributed in some unknown proportion between the two.
Comment: @rumtscho I think the answer is close to right. The main calcium compound in milk ([dicalcium phosptae](https://en.wikipedia.org/wiki/Dicalcium_phosphate)) isn't very soluble in water (0.02g CaHPO4 per 100ml H2O) and [binds to casein](https://chem.libretexts.org/Ancillary_Materials/Exemplars_and_Case_Studies/Exemplars/Foods/Low_Solubility_Salts_in_Dairy_Products%3A_Calcium_Phosphate_and_Lactate) which will keep it in the yoghurt.  However it's more soluble at low pH so the figure at my first (wikipedia link will be a slight underestimate of the solubility)
Comment: ... but it would take more research than I'm prepared to put in now to be absolutely sure.  Approaching it from the other end we could consider the calcium in commercial yoghurts, but of course then we don't know how much whey is lost
Comment: I had a quick look at recipes, and some of the comments under them do imply discarding; others suggest whisking the final product so it may be that a little whey separates but not enough to worry about.  My own yoghurt making is a more typical 8 hours

24 hour yogurt calcium content


Objects not in Viewport appearing in Render (Armatures/Rigging)

Question: As you can see in the image below, I have a scene with three characters, which are all animated, either
doing a dance or just sitting idle. I downloaded a minecraft rig and uploaded it to Mixamo to get
them animated. Everything looks good until you hit render and see geometry that you do not see in the viewport. I'm trying to figure out what it is, and what I can do to get rid of it to have a normal render. Currently using EEVEE. Issue also persists in Cycles. I am pretty new to rigging so I assume the issue comes from somewhere in the armature that should not be rendered, but I just cannot figure this one out.

Below are source files on Google Drive.
This is the .blend for the scene >>> https://drive.google.com/file/d/1Jr0czbMXa2m8NSEZZBQlSQq14pE1q_9E/view?usp=sharing
This is the .blend for the rig I uploaded to Mixamo.com >>>
https://drive.google.com/file/d/1XWKYnwbYEhUykrwM2hDitCmJzSD921mb/view?usp=sharing
Thank you for your time.
Answer: These 3 objects were hidden in Viewport but not in Render as you can see in the Outliner: