Why can't the light from a candle light the whole of a dark room?

Question: If you light a candle it starts emitting photons, right? And photons travel at the speed of light. But how come they can't light the whole of a dark room? It means that the photons are not reaching the dark corners of the room, but that is impossible if they travel at 300 thousand kilometres per second?
Comment: Put a mirror in a dark corner. Can you see the candle in the mirror? What does this tell you about the supposition of your question?
Comment: Clearly you haven't heard of the theory of dark suckers: http://www.travel-watch.com/mario/dark_suckers.htm  ;)
Answer: It might well be that the photons reach the corners of the room but that doesn't mean that you can see the corners. Why?
For you to see something, photons have to be emitted or reflected by the object and afterwards reach your eye. Also, it is not enough that one photon reaches your eye, but several photons are necessary for you to see the object (e.g. here).
So why does a single candle not suffice to light the whole room?
While the candle emits photons in (nearly) all directions, the number of photons it emits is too small. There are simply not enough photons being reflected back into your eye to see the whole room.
The reason that you can see objects close to the candle but not far away is the inverse square law.
  (source: http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/imgfor/isq.gif)
The candle emits (approximately) an equal number of photons in each direction. If an object is very close to the candle nearly all photons emitted in the direction of this object will hit it and be reflected. However, if the candle is far away, the number of photons per unit area gets smaller and smaller because the number of photons emitted in this direction is constant but the area becomes larger. Thus, an object far away is hit by much less photons. Then, the photons are either absorbed or reflected in all directions and while some travel into the direction of your eye, the inverse square law becomes important again. Hence, in the end, only very few photons are reflected by the corner and reach your eye and you can't see it.
Comment: The final piece you're missing is the sensitivity range of the eye.  You can see a single photon.  You can see a sunlit snowfield.  But you can't see both at the same time.  The eye adjusts its sensitivity range for the environment; the sensitivity for seeing the bright candle flame can't also see the dim reflections from the corners of the room.
Comment: Thanks for adding this! This fact is (implicitly) mentioned in the article of Baez I linked to (cf. photopic and scotopic vision), but it probably would have been better to include it in the answer.
Answer: The light does reach every corner of the room, because from every corner you can actually see the candle light.
To light the surface of the walls, the light needs to be reflected and then hit your eye again with enough energy so that your receptors register it. Reflection however drains energy from the beam, and irregular surfaces require many reflections (on average) till the beam ejects at an angle that aims towards your eye.
If you cover the walls of that room with a flat, non-absorbing surface like a mirror, you would see the reflection of the candle clearly. So the light obviously traveled to the corner of the room and back to your eye.
If you use an irregular, absorbing surface like black cloth, the beam will bounce back and forth inside that surface till all its energy is consumed/transformed. As in this case the remaining energy of the beam that is able to reach back to your eyes is very low to none, the corners appear dark even though they are hit by the same intensity as in the case with the mirrors.
Comment: Note that the answer has been edited to address the issues raised by @OrangeDog.  However, it should be pointed out that reflection and intensity loss can be described in the photon picture as well as the wave picture.
Comment: @garyp yes, just not in the way they tried to. It's still a bit iffy, as they apparently just replaced "photon" with "beam", so now we have a beam bouncing around inside a black surface, which also makes no sense.
Comment: @OrangeDog Yes, I agree.  The ideas in this answer are ok, but they are not expressed clearly.
Comment: I am open for suggestions, but as said: I am trying to keep the answer simple, and simple doesn't necessarily mean correct in every detail.
Comment: Simplicity must *not* include incorrect claims, unless specifically noted so. You can easily talk about photons and intensity loss in same sentence, but you should not claim that 'photons lose energy' (which doesn't happen in linear optics, although can be said for nonlinear effects, where photon can be absorbed and re-emitted with different energy - simplification of course). You could say that 'some photons can be lost', which is simplified again, but not incorrect.
Answer: Every source of light emits certain amount of photons of certain wavelength. Every photon travels at the same speed in the medium.
But to light the whole area, what actually matters is the luminous intensity of the light source and not the speed of light.
If the light source has high luminous intensity, it emits more photons in a solid angle at a given time than a light source with low luminous intensity.
As candles don't have enough luminous intensity to light the whole room, still some parts of the room remain dark.
Answer: In order to "light the dark corners of the room" several things need to happen:
The candle needs to emit photons. This it certainly does and at a fairly large rate, something like 10^18 (!?) photons per second or so. A large part of these photons are however not in the visible spectrum, but infrared, so you cannot see them.
As you move away from the candle, the number of photons that hit a certain area diminishes proportional to one over the distance squared (surface area of a sphere). So only a small fraction of these photons will end up in the corner of the room that is several meters away as most photons will end up lighting other parts of the room.
Now, at the wall/corner some of the photons will get absorbed (lost), some will get reflected/re-emitted, but for typical walls this would be diffuse reflection in all kind of directions. In order for you to see the corners, only part of the reflected light (only that part which gets reflected into your direction) can be used for observation. And as with the candle lighting the corner, also for the reflected light your eye's distance from the corner will matter with the same proportionality ($\propto 1/r^2$). So ideally you'd be close to the corner, but then you run into the risk of throwing a shadow on the corner.
Lastly the light hits your eyes and needs to be detected which seems to be possible with a threshold of only around 10 photons.
In the discussion above I neglected (at least) light absorption in the air and the eyes (before hitting the receptors). Also I neglected second order processes (multiple reflections), but I believe both of these are minor compared to the factors mentioned.
Answer: They are reaching the corners but are then absorbed by the material. The material must re-emit light to hit your eyes, before you see it and think of it as lit. If there simply arrives too few photons to a specific point, then not enough light is re-emitted from that point to your eye and your eye won't register this as lit.


Unban recalculation of reputation

Question: When a user is unbanned from a site, how is their reputation recalculated? Is it just the reputation before they were banned or is it lower?
Comment: It is the reputation they would have had without the suspension. Of course, if they were suspended for voting fraud then there could have been account deletions and vote invalidations involved as well.
Comment: When suspended there is no calculation done. It is simply displayed as **1**. Once unsuspended, reputation is again displayed to be its actual value. During suspension, as Martijn notes, the value may have changed as a result of removed votes, and also as ChrisF notes it may have changed from upvotes or normal interactions as well.
Answer: It will be their real reputation including any votes received during the suspension period. This means it could be higher than their pre-suspension reputation. It could be lower than their previous reputation, but that would depend on other actions taken on their account, not the suspension itself.
For example, if the user had been using sock-puppet accounts to inflate their reputation then these accounts (and votes) would have been removed and their reputation will be lower. Note that, however, this removal is independent of the suspension and could have happened without the suspension.
If the user had been suspended for some other reason, then it's less likely to be lower.

Unban recalculation of reputation


Which is correct "The house is (being sold | selling)"?

Question: Will it be correct if I would say "This house is selling" meaning that someone is selling the house? Or I should only say "The house is being sold" to be understood right?
Answer:
The house is being sold.

means the owners have put a single house up for sale.

The house is selling.

can be said to meaning there is keen interest by several buyers in the house.
It can also be used in the plural to mean houses in general

(The) houses are selling.
Comment: That said, to say "The house is selling" in isolation sounds rather odd to this US English speaker, and I wouldn't ever use it to mean "Someone is selling the house."  I would expect to hear it in a context like "The house is selling *for two million dollars.*"
Comment: It might be used by a realtor in answer to the question by the seller "How's it going?" that there is interest in the house "The house is selling." meaning people have been coming by for the open house, asking questions and showing interest. Maybe it's more a New Yorker way of expressing it.


Why do different drivers change the noise of steppers?

Question: I've upgraded my stepper drivers.
I'm looking to understand why my stepper motors made noise in the first place.
Answer: Stepper motors contain two distinct sets of coils. The current in these coils is governed by your stepper motor driver.

To move the motor in either direction, the coils are being driven one after another, and in different directions.
Imagine this being a normal 3-phase AC motor, but instead of three phases, only two are used.
A "full steps" (1/1 "microstepping") would mean switching one coil off and the other on - resulting in a jerky motion to the next position. Real stepper motors have multiple sets of those coils (rather than two like in the diagram) - usually 200 or 400, giving 1.8° or 0.9° of rotation per "full step".
Such motion is usually not desired, since the immediate movement of the motor creates noise and vibration.
If both coils are driven with less current (71% of the full current, the reciprocal of the square root of 2, so that the total force on the motor remains the same) during the switch from one current to the other, another position can be achieved - a "half step" between two full steps.
This can be repeated for higher number of "microsteps", with 16 being the usual compromise.
Optimal smoothness - and next to no noise - would be achieved by driving the stepper motor with pure sine waves. The closer a stepper driver can get to that pure sine wave, the lower the noise made by the stepper motor will be:

Some stepper motor drivers, most notably the TMC family of chips, can generate 256 microsteps internally, approximating a sine wave quite well.
Other stepper motor drivers (like the LV8729) can also handle 128 microsteps, but they require the printer control board to send an individual step signal for each of those steps - which may limit speed because of the additional load on the board's MCU.
Answer: To make a stepper perform a step, block signals are send to energize the coils to position the rotor. Such a block signal causes abrupt motion and triggers harmonic frequencies. This is audible as stepper noise. If the block signal is smoothed, the motion is more fluent and less noise will be observed. A similar effect is achieved using micro-stepping.
It could be that the new stepper drivers use more/less microsteps1) or a smoothed/block1) signal opposed to the previous drivers, hence less/more1) noise.

1) The question does not state if the noise is reduced or increased, but noise reduction is most probable
Answer: The coils in the stepper act like speakers. Its not that the stepper is making less noise, it's just making it in frequencies that are above the average person's hearing.


Reverse Current Protection using two PMOS in back to back configuration

Question:
I am working on a circuit that needs reverse current protection. Back to back mosfet configuration has been suggested by many people, and it seems to make sense at the beginning. But after I built my PCB, after fully charged my capacitor, and then turned off the power supply, the current flowed right back to the power supply.
Let me explain my circuit a little bit. I need to charge C1 and use it to run a pulsed (D=10%) circuit that requires every large current. I have a separate circuit that controls the max current to charge the capacitor, so that I do not need to worry about charging current for this circuit. During charging, my intention is to using R4 and R10 to keep Q1 and Q2 on when power supply is turned on; R2 and R8 sets up a node voltage that is always less than the gate voltage at Q1 and Q2 unless Q6 is turned off. When the power supply is on, R7 and R11 keep Q6 on. D2 blocks the current flowing to C1. Everything works on charging my capacitor. During discharging, when Power supply is turned off, R7 and R11 has no current flowing through and Q6 is off, and the gate voltage on Q1 and Q2 is pulled up to something like +49.5V, and Q1 and Q2 shuts off. Here is the problem, Q1 and Q2 were never turned off. My theory is that any parasitic capacitance or slow power supply turn off action that can keep Q6 on for a very small mount of time, Q1 and Q2 will stay on, and current starts to flow back, and then most of the voltage on C1 appears at Vin and keeps Q6 for longer period of time. It creates a positive feedback loop and keep Q1 and Q2 on.
I have done simulation and confirmed that the Q1 and Q2 are on during discharging(Discharging circuit not shown here).
I would love to have some feedback from someone who has gotten this circuit working before or someone who knows what's keeping Q1 and Q2 on when the power supply is turned off.
If you have different ideas on how to block the reverse current, I would love to hear them too. Using diode is not an option because forward current is too high, diode gets too big and consumes a lot of power.

Thanks!
Comment: Have you tried giving Q6's gate some other path to discharge? Or just reducing the magnitude of the resistors in that voltage divider might be enough.
Comment: Tried to simulate R7=390 and R11 = 100. Still cannot keep Q6 off. Even if it did at this resistance, it's impractical because +50V/(R7+R11) allows too large of a current to be wasted during normal operation. I did manually pulled Q6 gate low in the simulation, Q1 and Q2 remained off after I let go Q6 gate manual control. But I would like this control signal to be derived from Vin. When Vin is not present, control signal turns off Q6. The only way I got it to work was to put a resistor in the path and detect the reverse current.
Comment: Rather than troubleshoot your circuit, I would go with you opening the door to "using other ideas to block the reverse current." Towards that end, Texas Instruments has a 10 page Application Report on how to use back-to-back connected devices to achieve bidirecitonal control and proection: https://www.ti.com/lit/an/slva948/slva948.pdf
Answer: You cannot expect Q1 & Q2 to turn off when all of the bias paths to their gates pull them towards ground (I.e., |Vgs|>0 always).
You have to explicitly pull up the gates to their source voltage to turn them off. Although it is a useful approximation, it is a misconception that |Vgs|<|Vt| turns a FET completely off, its current will be relatively small, but it actually enters what is known as the subthreshold regime. You are applying around 0.6V, depending on the diodes you are using.
The "leakage" current in this regime might be more than enough to justify what you are seeing.
Comment: I did a simulation where I replaced D2 with a wire. Q1 and Q2 still got turned on. I did another simulation where I pulled Q6 gate low "manually". It turned off Q1 and Q2 and no more reverse current flowed as soon as I turned off Q6. Even after let go of the Q6 gate control, Q1 and Q2 remained off. I do not think D2 is the problem here. But thanks for your idea.
Answer: You are absolutely correct - the circuit will remain on until Q6-gate goes below its gate threshold voltage of one volt.  Q2 will conduct through it body diode, so Q1-source has to make it down to a voltage below its gate threshold voltage before it turns off and the voltage on C1 will appear on at Vin until this occurs.  In addition to lowering the impedance to speed up switching times as @Hearth suggests, you will have to actively drive "off" circuit  after comparing Vin and Vout.
You might look into an ideal diode controller such as the LT4320/4321.
Comment: It seemed very obvious that my control signal to Q6 is flawed after I built and tested the circuit. And I did a lot more research on the internet afterwards. No one seems to use PMOS for reverse current protection on the high side. It is always NMOS with driver IC. NMOS might have lower Rds,on, but I think the reason is because PMOS is too easy to turn on and stay on on the high side, whereas NMOS needs gate voltage is higher than input voltage to turn on.
Answer:
Here is the problem, Q1 and Q2 were never turned off.

Correct. Back-to-back FETs can be used to isolate two supplies, but only if the control signal is separate. You are trying to control them with the same voltage that they are switching, which won't work because when the FETs are on Vin is shorted to C1 so when you turn off the power supply Vin still has the voltage of C1 on it - therefore preventing Q6 from turning off.
To block reverse current using only the input and output nodes you need a diode, or a circuit that simulates a diode (ie. measures the voltage drop or current flow from one side to the other, and derives a control signal from its polarity).

Using diode is not an option because forward current is too high,
  diode gets too big and consumes a lot of power.

Your proposed circuit uses two IRF5210 MOSFETs which have on-resistance of ~0.06Ω and drop ~0.6V each at 10A, for a total voltage drop of 1.2V and power loss of ~12W. A Schottky diode like the VB40100G (40A, 100V) would have lower voltage drop and power loss, and since no other components are required it would take up less board space. Also, unlike a FET the diode's voltage drop reduces as it gets hotter, making it more efficient. The only downside is increased leakage current (~5mA at 125°C and 50V).
Comment: You're exactly right about that the way my control signal to Q6 is flawed. But I really wanted to a  control signal to turn off Q1 and Q2 coming from detecting the presence of Vin.   There is a separate current limiting circuit using one of the PMOS that is not shown because I did not want to add confusion. At a slow ramping duration of 200ms, the IRF5210 was barely staying in the safe operating area because initial voltage drop is so high when current limit is at 3A. I am really only using one PMOS as reverse current block. If you do that calculate, using Mosfet has more advantage.
Comment: @hongpan can you explain that circuit which is controlling your maximum inrush current initially and charging the capacitor C1.


How to choose right inductors for a matching circuit

Question: I would like to chose an inductor to make a matching circuit. Operating frequency is 6.1 GHz. I am more concerned with self resonance frequency and Q of an inductor.
Would an inductor with SRF > 7 GHz and Q > 10 be okay at above frequency?
Comment: At 6 GHz it would be better to do your matching with transmission lines.  A length of higher impedance line will act similar to a series inductor, and a short circuited stub similar to a parallel inductor. You can transform impedance with a line in series, and also add capacitance. All for free on the PCB.
Comment: Can anyone look at this post and share your thoughts. http://electronics.stackexchange.com/questions/190998/rectifier-input-impedance-does-not-change-when-load-changes?noredirect=1#comment395271_190998
Answer: As others have pointed out, the discrete components, suchs as capacitors and inductors, start to be quite challenging in higher frequencies. In general, transmission lines tend to have lower losses and higher repeatability around your frequency.
Long story:
While the transmission lines might be better for practical applications, I wanted to share the simulations I did for this problem to help to understand the challenges. Consider a $75 \Omega$ load that you want to match to $50 \Omega$ source. Most practical loads would have also a imaginary component and vary as function off the frequency, but constant resistance will do nicely in this example. One solution, at 6 GHz, would be a 0.25 pF parallel capacitor and a 1 nH series inductor. The left hand side of the figure shows a maximum in the power transmitted to the 75 $\Omega$ load resistance R_load (blue curve) and that the feed impedance is $50 \Omega$ at 6 GHz (green curve). This means that the load got matched at that frequency.
In reality, the 1 nH inductor has also some capacitance between the legs and windings (C1) and some resistive losses (R1). See the right hand side of the figure. Parallel inductor and capacitor in series with your load create a band stop filter: low frequencies cannot pass the capacitor and the circuit seems like inductance. At high frequencies the circuit behaves like a capacitor. In the middle, at the resonance frequency, the impedance is very high and no current can flow through the circuit.
The self resonance frequency found on the datasheet of the inductor corresponds the frequency at which the inductor starts to behave like a capacitor, that is, above the resonance frequency the parasitic capacitance of the inductor is the easier path for the current flowing through the component.
The component values for the better model of inductor can be calculated from the equations. Parallel capacitor from the self resonance frequency:
$C =  1/((2\pi f_{res})^2L)$. And equivalent series resistance from the Q value: $R = 2\pi f_{res}L/Q$. The simulations show that with all non-idealities taken into account, the matching circuit is quite horrible and also the power delivered to the resistor has dropped significantly.

The situation can be improved by optimizing the matching network while taking into account the non-idealities of the inductor. The figure below shows one solution: it turned out to be impossible to get the circuit tuned with 0.25 pF parallel capacitor: if the inductor value decreases and SRF is constant, the value of parasitic capacitor gets up and the circuit is newer matched to $50 \Omega$. For practical inductors, this probably would not be the case: by removing turns from otherwise identical inductor the capacitance would actually drop. A few sample inductors from Farnell had tolerances of e.g. 0.5nH $\pm$ 0.2 nH.
Answer:
Would an inductor with SRF > 7 GHz and Q > 10 be okay at above frequency?

Could it be made to work? I suppose. But any discrete inductor at 6 GHz is going to have significant non-ideal behaviors that you will need to model (or empirically measure) to get an accurate match. At the SRF the inductive reactance and capacitive reactance are equal, but this does not mean below the SRF the capacitive reactance is zero, so you'll need to include that in your model.
Moreover, you'll need to consider how repeatable and stable these parameters are. The answer is usually "not very".
For these reasons (and also cost), transmission line stub matching is usually used at these frequencies. I suggest starting with the Smith chart tutorial at fourier-series.com to get an intuitive understanding of the technique. Then you can research some of the practical considerations and fabrication techniques.


Global ethical implications of a US patent

Question: I would like to understand the ethics of Patents. There is a product that is currently sold worldwide, with a patent in the US only. If I was to sell the same product (diff. logo) in the UK/EU, what are the ethical implications pls?
Answer: Patents are territorial. A U.S. patent only gives its owner rights to try to exclude others from making, selling, offering for sale, importing and using the invention in the U.S.
If there is no patent in some other jurisdiction then anyone else might be able to make. sell, etc. in that location. I say might becasue there may be some other reason that the product could not be sold (regulations, a completely different patent possibly held by a different party, etc.).
Patents are about law, not morality. However, an important part of the theory of patent systems is that the inventor must disclose how to make and use the invention to the public. This promotes progress. In your case it promotes progress immediately everywhere the inventor does not get a patent. I would not worry about any ethical issue. You can worry about the inventor having an application pending in the UK or some other patent that you would also infringe.
Comment: In my opinion there isn't an ethical issue at all.
Comment: Thanks so much George, that's much appreciated.


When does identical twinning happen?

Question: What is the window during which division into twins is possible (for instance can it still happen after implantation in the uterus)?
Is one twin the "original" and the other its clone?
Answer: In the case of two healthy, viable identical twins, the separation generally occurs at the first division from one zygote to two cells. So they are equal partners in the split, not an original and a clone. During the first several cell divisions in the morula and blastula, there is no significant growth. So these divisions produce smaller and smaller cells. If one of these smaller cells is separated, it is very unlikely to be substantial enough to survive and implant in the uterus.
Comment: That answer is partly wrong so I gave another one. Twinning isn't about a single cell breaking off from the rest but about the whole structure (or relevant parts of it) splitting in two, so it isn't limited to the first division.
Answer: This page describes what happens pretty well:
http://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-30-multiple-pregnancies
Division into twins can apparently happen at several stages up to and including implantation, but not much after that. The later the division the worse the prognosis because the more the twins share. The article mentions three stages in particular: division at the 2-blastomere stage (i.e. when the original zygote is cleaving), which leads to two completely separate embryos that implant separately, division at the embryoblast stage which leads to the embryos sharing a chorionic cavity (i.e. placenta), and division at the embryonic disk stage, which happens after implantation and involves the fetuses sharing everything - apparently to the point that they rarely survive until birth because they get tangled in each other's umbilical cords. Later divisions, after the primitive streak starts forming (i.e. about two weeks after fertilization), can lead to conjoined twins, because the division happened when the cells have already started to differentiate into which part of the body they'll be.
In no case can one twin be considered "the original" and the other not. Twinning involves whatever stage we're at dividing into two; we can't talk about one being an offshoot of the other, anymore than if you pour cake batter into two molds instead of one you don't end up with an original cake and a copy, you just end up with two cakes. Whose batter happened to be in the same bowl until some point in the baking process.
Moreover the twinning events usually involve a symmetrical division, meaning we can't even talk of one twin having a claim to a higher percentage of the original embryonic material or whatever. An exception may be parasitic twins and other examples of asymmetrical twins, but I haven't been able to find a good source on what causes those - it's unclear whether it involves twins resulting from an unequal division, or whether later development made them unequal.

When does identical twinning happen?


How long do refrigerator pickles keep?

Question: I pickled zucchini slices last summer with plenty of vinegar, sugar and spices and still have some jars in my refrigerator.  They look fine but I wonder about bacteria etc. Thanks
Answer: It is impossible to answer this. Normally, food is quite clearly divided into the categories of "perishable" and "shelf stable", with perishable food being safe for 3-5 days in the refrigerator and shelf stable food being safe indefinitely prior to opening.
Refrigerator pickles are one of the very rare cases in the middle. They are not shelf stable (else they would be suitable for canning), but they are still not very pathogen friendly. Just how much slower is bacterial growth in them? It will differ from recipe to recipe. And just saying "plenty of vinegar" is not at all sufficient to predict a real use-by date. Not even the exact recipe in gram of each ingredient would be sufficient for this, since bacterial growth is a complex system, which makes it practically impossible to calculate such a prediction.
Your only information source is your original recipe. If it gives you a time period, you should use that (and hope it is trustworthy). If it doesn't, then there is no way for somebody to just say how long it is safe.

How long do refrigerator pickles keep?


Why has my inner tube enlarged after moving from bicycle to repair

Question: I got two punctures in my front inner tuner of my bike and when I have gone to reassemble, the inner tube appears to have stretched a significant amount and no longer fits along the rim of the bike, not sure why this has happened and is there anything to be done to fix this?
Comment: How deflated is the tube when you're putting it back?  If it has any significant pressure at all it will expand in circumference as well as diameter.  You don't want it *completely* flat but it should barely hold its shape.
Comment: After I patch a tube, I leave it inflated overnight with ~5 psi in it.  This significantly stretches the butyl rubber, to the point reinstalling it immediately is a challenge.  Perhaps 25% larger diameter. So I roll up the tested tube and put it in my on-bike toolbag.  By the time I need it, the rubber has reverted to a normal size and its easier to re-fit.
Answer: You can just stuff it into the tire. It will be fine.

Get one of the tire's beads on the rim.
Put a little air in the tube so it holds its shape.
Put the tube's valve through the valve hole and work the rest of the tube inside the tire.
Work the other bead onto the rim. As you get close to the end, you may need to deflate the tube. Make sure none of the tube is pinched between the tire and rim.
Comment: "stuffing it in" works to a point, but too much tube is asking for a zig-zag fold or a tube pinched in the bead.


How do I get a clean path inset/offset in Adobe Fireworks CS5?

Question: I've tried a number of different settings in the GUI, and have tried manual path tools from the path panel, but no matter what the inset path function completely mutilates the path into a blob.  Distance of the inset or offset doesn't make a difference, and these are very simple paths like a square, or a circle.  I'm on Mac, OS 10.6.
Comment: I have the exact same problem, I can't believe no one else has come across this issue. Being an avid Illustrator and Photoshop user, I've switched to using fireworks to create icons. (For the simple fact of being able to add effects/filters to a vector shape without having to rasterize it.) So far so good but the stupid inset path issue is driving me crazy.
Answer: I'm not on a Mac, but I did try to re-create the blob that Inset Paths generates. Unfortunately, I didn't get the blob with simple paths, but I did learn that rounded corners do not always play nice with concave vector nodes.
Just to be clear, here's what I did:
(1) add a Star Autoshape to the canvas - 1 px black stroke, no fill, centered path
(2) ungroup the autoshape to make it a regular path
(3) Open the Path panel and select the Inset / Expand Path option in the Alter Path section
(4) Entered these settings:
inside, 10, miter, 10
(move the path inside the original by 10 px, mitered corner, miter limit = 10)
(5) The resulting path was a smaller version of the original star.
If the corners are "round" or "bevel" (instead of miter), then some of the vector nodes will be modified. "Round" appears to convert concave nodes into Bezier curves. "Bevel" appears to convert concave nodes into flattened angles rather than points.
I also found that I needed to use CTRL+K to "snap to pixel" to get rid of the non-integer pixel coordinate blurriness, but this is a common effect of numeric transforms or scaling.
I did not extensively test different shapes and settings, but when I used "miter" as the corner setting and kept the miter limit low, the results were pretty accurate.
Hope this helps,
Dave
Comment: Hougue "CTRL+K to "snap to pixel"" , where is that option in the menus? [in Fireworks, in Commands? in Modify ?]
Answer: That sounds quite bizarre. I can't reproduce this, but I'm running on a Win7 system and my Mac isn't handy. Try, in sequence, the "usual suspects": quitting and relaunching Fireworks, logging out and back in, restarting the OS, deleting the Fireworks preferences file (it's Fireworks CS5 Preferences and it's in Library/Preferences in your user folder), resetting permissions, and, if all else fails, uninstalling and reinstalling the application.


Is there a self-timer mode on the GoPro Hero 3+?

Question: I might have missed the option in the plethora of settings, but it seems that there's no self-timer mode on the GoPro 3+. If there isn't, how do you take a "selfie" group shot with monopod?
Comment: "selfie" group shot with *monopod* sound like quite a feat. but since you later talk about scuba diving I guess you'll be holding it at the other end of the pod.
Comment: @MichaelNielsen That is correct. The GoPro3+ loses quite a bit of its wide angle range under water so a longer monopod is needed for a good underwater group selfie.
Answer: No, the GoPro Hero 3+ does not have a self-timer mode.
But there are several ways of taking 'selfie' photos:

You could set the Hero to timelapse mode, ie taking a photo every
0.5, 1 or 2 seconds. Press the shutter, and it will start taking a series of photos. So you can then get in position for the selfie, and it will get a number of photos of you.
You can do a similar thing in video mode. ie just record a video clip. Then you can get a still photo by taking a snapshot from the video (VLC media player is useful for this). This image won't be as high quality as the photo mode, videos are a bit lower resolution. But probably still good enough for sharing online.
You could use the camera in standard single photo or burst mode, using a remote control to press the shutter. Either the GoPro Wifi Remote, or the GoPro app on a phone or tablet. Though this means you need to have a suitable remote control, and be holding it while you take the selfie.
Comment: This is sad. A self timer is pretty useful. But yeah, there's the remote. However, the remote isn't very useful when scuba diving.
Comment: +1 for the scuba. still looking for a dive pole with a dive casing for the remote.
Answer: Yes there is:

Changing Modes: Once camera is on, quickly pressing the POWER/MODE button will
  change modes from video mode to self-timer, to photo mode, etc.

Source
Comment: That source is the manual for the original HD Hero. The Hero 3+ is a much newer model, and is quite different. It seems the Hero 3+ does not have a self-timer mode.
Comment: Yeah, I saw this, too. It is for an older model.


What to do with the Naughty and Nice Winter Crates?

Question: Last year in Team Fortress 2, there was a random occurrence that you would get a Naughty or Nice Winter crate, which you could unlock with a specific key for that. This year, I have almost a full page of mixed naughty and nice crates, and I did get all of them this year, but noticed that in the shop there was no key for those crates. Are the keys available later or is it just an ordinary key that you buy?
Answer: The keys probably are not on sale yet.
You will have to wait a little bit until they are on the Team Fortress 2 item store. It will probably appear as "New items" in the store tab when you Launch Team Fortress and then you can buy them for $2.50 each.
Comment: This applies to all crate-events. They release the crates early, and the keys afterwards. I guess they must expect people to buy more keys when they have more crates (as opposed to buying a key for one, and then forgetting about the rest of the crates they earn)
Answer: Nothing.  You cannot unbox those crates anymore, as the 2013 Winter Event has already expired.
Answer: Honestly, I would trade them. Seeing as many people would want them before the keys come out, so they can get unusual hats/strange weapons, I would sell them for about a reclaimed metal each on http://www.tf2outpost.com or http://www.trade.tf. Many people love festive items, and this is time to sell your unwanted crates.


Players in snooker, now having to use separate rests

Question: Why are the players in snooker now using separate rests?  They are both touching the wood all around the sides of the table, where they rest their hand to play a shot, so what difference does touching the same wooden rest make?
Comment: Hi! Welcome to the site.  It sounds like you're asking about a particular accommodation being made for the current COVID-19 situation.  Is that correct?  If so, are you asking about a particular league (such as the World Snooker Tour) you've seen on TV, or are you asking about your local Snooker hall?
Answer: I imagine the justification is based on practicality. It would be virtual impossible to have players avoid touching the table and/or to sanitise the table after each shot.
The issue is that having separate rests for players to use is a low-cost and low-effort solution to reducing risk in an environment that is already fairly safe, at least in relation to grocery stores, schools and work places.
With the Championship League all players, referees, commentators and
staff are required to take tests for COVID-19.

There will be social distancing measures throughout the venue and
players seated at least two metres apart during matches, which is not
a problem for snooker.
Players must use anti-bacterial hand sanitiser before matches and
avoid handshakes, while first aid personnel will be on site at all
times.
While the tests are being analysed, players will be required to wait
in isolation in a private area and unable to move until given the
all-clear.
If a player wins a match and leaves the building, he will be tested
again on his return before being allowed to re-enter the venue, though
no guests will be allowed to attend.
A catering service will be provided at the hotel, though no-one is
allowed to share food or have dinner together.

https://www.bbc.co.uk/sport/snooker/52848049

They are both touching the wood all around the sides of the table,
where they rest their hand to play a shot, so what difference does
touching the same wooden rest make?

In reality most players would avoid making any poor positional shots that require them to place their bridge hand on the rail. In some cases this isn't possible, especially if the opponent leaves the ball in an undesirable position. The area where players will be resting their bridge hand (either on the cloth or rails) is a much larger surface area than the handle of a rest.


And of number and its Two's complement

Question: Is there any semantic meaning when doing an and operation of a number and its two's complement?
for example:
int x = 31;
int result = x & (-x)

Does result hold any semantic meaning?
Answer: The result will have one bit set, which is the least-significant set bit in x. Put another way, the result indicates how "round" x is in terms of powers of 2: 1 for odd numbers, 2 for multiples of 2, 4 for multiples of 4, etc.
This is because -x is equal to ~x + 1. x & ~x is 0, of course, but by adding 1 to ~x all of the lowest-order 1s in ~x will become 0s, and the lowest-order 0 in ~x will become a 1, and this will be the only bit that x and ~x + 1 have in common.

And of number and its Two's complement


Separation of Duties - Can a DBA patch or Upgrade a SQL Server 2008 R2 DB without TDE Encryption keys?

Question: Are there any considerations I should have in mind when I patch or upgrade a TDE encrypted database? In the context of separation of duties, does the person executing the patch or upgrade process need access to the Keys or certificates of a TDE encrypted database or can the database be patched without the keys. The answer is important because we are a legal shop and would like an application administrator to encrypt the database and outsource the db maintenance functions to a dba to patch and upgrade the database without having access to the "application data". Could you throw some light on this please?
Comment: I'm not sure what you're referring to when you say patch a database. You mean patching on the instance, for example applying CU4 or patching as in the end user application has a new version or patch? In either case, the encryption keys should at a minimum be backed up (whether you're patching or not) for recoverability and also be encrypted with limited high level employees that can allow access to them.
Answer: TDE only encrypts the data at rest.  If they have the access to connect to the server and query the database then they can get to the data.
But I don't think the person running the patch (CU or Service Pack) needs permissions to the database proper, just permissions on the server.
The only way to separate the job functions as you seem to want would be to use the application to encrypt the data, that way it's actually encrypted in the database.  Then even if someone has select rights to the database they can't read the data without the key.  But that adds a lot of overhead and makes a lot of things harder.
Answer: I've used TDE in production many times and it in no way affects Windows/SQL Server patching unless there's some horrific bug or something of the sort; which has not yet happened.
TDE simply uses the Windows DPAPIs to generate a cert in Master that then is used to make other certs which can encrypt/decrypt the remaining DB data at rest.
Heads up though, if your DBA has SA rights, your DBA has all the keys and can back them up, then restore your backups or copy mdf/ndf/ldf files anywhere.  What is the purpose of separation of duties in this scenario?  Is it to give another team a 'backup operator' role and only let them deal with backups?


Installing XP guest on virtualbox OSX snow leopard host - no function keys

Question: I'm trying to install XP as a guest VM and cannot get past the liscense agreement because it requires you press f8 to continue. This key press is not recognised by Virtualbox, rather it is interpreted by OSX as the itunes hotkey. Can this be fixed, am I mising something simple?
Thanks
Answer: Right Ctrl + F8


Copy Exchange Database from Passive to Active

Question: I have a CCR running with a total of 6 servers 2 MB, 2HT, 2 CAS.
I had a failure on active node this morning and everything failed to my passive server, i had some issues with the logs, as the werent replicating to the passive, which made sense since the active server failed because of a backup that was running on the exchange system, so the logs didnt trunk and passive and active didnt have the same logs, so no problem right? just reseed.... so i got everything working and i was about to start reseeding, then something happen, the cluster failover to his primary server making the passive a passive node again!! my problem now, is that i deleted the transaction logs and Database from the active node ( which was the passive after the failover) so i have a good database on the passive node, how do i re-seed from passive to active? i know that you re-seed onlye to passive from active... what options do i have here?
I was thinking on check the status of the database, if i have a clean shutdown, can i copy the edb to the active and try to mount the db?
Thanks!
Answer: It does work, just make sure to run eseutil, and verify that you DB is on clean state, also make a copy before you do anything to the DB, including eseutil.


Connecting RSS news reader with Facebook?

Question: How can I get the things which I like on Facebook on my RSS news reader?
Answer: Facebook pages are not per se news feeds. Although there are probably some workarounds, they are very non mainstream, and in short, you're probably best off with following facebook pages, just as that, facebook pages.
If you're however interested in following your own wall, as in getting notifications, there is a plethora of browser extensions for that.
Answer: Your can use Facebook News Feed Reader to read you news feed, if that's what you meant. It can read the pages you like (and friends) and notifications also.


Nano Ledger and baking

Question: I'm looking to delegate my Tezos for some baking. Considering hardware options, can I use a Nano Ledger X or only a Nano Ledger S.
Answer: Ledger has indicated that applications for the Ledger Nano S will also work on the Ledger Nano X, although by default they will not take advantage of the device's difference from the Nano S such as the larger screen and bluetooth capabilities.
We (Obsidian Systems) are awaiting delivery of a few Ledger Nano X devices so we can confirm that and begin development specific to the device :)
Answer: You can delegate with the Ledger. I know of three (soon four) good guides.

Using a command line approach (the tezos-client). This requires that you run a node. Yet, if you do so, then why not to bake yourself? The link contains information on baking with the Ledger. There is now an easy to use GUI available too, with Kiln (see here or here).
Using Tezbox.
Using Magnum Wallet.
(soon) Using Bakechain

Nano Ledger and baking


Why couldn't the UN lift the siege of Sarajevo?

Question: The Siege of Sarajevo lasted for more than three years, and the people inside were very much trapped. This was in 1992, at which time the UN had ~40,000 troops, which it had mobilized for the specific purpose of stabilizing the situation. My question is then: what were the main reasons for the UN not being able to intervene and lift the siege for such a long time, despite having the means to do at least something?
Comment: A few corrections on the details in the question: [UNPROFOR](https://en.wikipedia.org/wiki/United_Nations_Protection_Force) wasn't created until early 1992, and it had about 40,000 troops. The Siege of Sarajevo began in the spring of 1992.
Comment: Since your question makes a false citation, how many troops the UN  had (when in fact the UN had no troops, but member nations had contributed less than half the number you assert, I suggest that (1) you edit your question to remove the inherent error, and (2) you do a bit of basic research before asking a question.
Comment: Here is some basic research material. http://publications.gc.ca/Collection-R/LoPBdP/BP/bp374-e.htm
Answer: When looking at why the UN does (or usually does not) do things, it's important to know two things: only resolutions by the UN Security Council are binding, and all of the permanent members have veto power. The permanent members at the time were the People's Republic of China, France, Russia, UK, and the US. With the Cold War just having ended, this was a period of unusually strong international cooperation. Even so, resolutions have to be watered down so as not to go against the wishes of those five.
That's the best I've got for why the UN did what it did. What I can cover is what they resolved to do and how that turned out.
The UN was looking to negotiate a cease fire and bring the warring parties back to the negotiating table. While this was happening, they tried to reduce civilian casualties and war crimes. To carry this out, in Feb 1992 the UN Security Council Resolution 743 created the United Nations Protection Force (UNPROFOR) with about 40,000 personnel. In particular they make it clear that:

...in accordance with paragraph 1 of the United Nations peace-keeping plan, the Force should be an interim arrangement to create conditions of peace and security required for the negotiation of an overall settlement of the Yugoslav crisis;

They were not looking to get themselves involved in the fighting, nor to impose a new peace by force; that would go from peace keeping to war making. They weren't looking to be an occupying force nor enforce a Pax Romana.
Resolution 770 upped the ante by declaring the war in Bosnia a violation of Chapter VII of the UN Charter which prohibits UN members from attacking each other. A violation of Chapter VII allows the UN to use military force.
UNPROFOR's mission expanded over the coming years. It began by protecting Sarajevo airport to allow humanitarian shipments (Resolution 758). A few months later it added protecting and escorting humanitarian aid convoys. In April 1993 Resolution 819 added safe areas, eventually including Sarajevo, which UNPROFOR had to protect. Finally, they had to monitor cease fire agreements.
All sides, especially the Bosnian Serbs, interfered with this mission. Yet Sarajevo airport remained open and relief supplies got through.
However, the safe zones were not adequately protected. Bosnian Serbs continually tested the UN's resolve by taking UN hostages, seizing weapons caches, and brazenly ignoring UN demands. The most obvious violation was Sarajevo, still under siege. It all culminated in the Srebrenica massacre when thousands of Muslim men and boys were massacred while the UN troops on the ground were too few to stop them, bound by rules of engagement from calling in support, and overrun.
After this UN failure, NATO intervened. They had previously been enforcing no-fly zones and making limited, reactionary air strikes. Now they began Operation Deliberate Force to provide air support for UNPROFOR. In September 1995 NATO aircraft struck hundreds of Bosnian Serb targets including air defenses, armored vehicles, and artillery pieces.
After the peace agreement, UNPROFOR was relieved by IFOR, NATO's [Peace] Implementation Force sent to enforce the treaty consisting of 60,000 NATO soldiers. This was later replaced by a NATO-led Stabilization Force (SFOR) until 2004 when it was replaced (mostly in name) by EUFOR Althea.
My conclusion is the UN bureaucracy was not ready to conduct a military campaign against an adversary that was not playing by UN rules. In their attempts to avoid escalating the conflict they failed to give their troops the means to conduct their basic missions. The Bosnian Serbs prodded UNPROFOR in a series of escalating incidents, learned their limits, what lies they would believe, and how to tie them up diplomatically.
The safe zone massacres finally cut through international hand wringing and allowed NATO and the UN to provide their peace keeping forces with the clear ability to retaliate and enforce the UN's demands. It's a shame it took three years and tens of thousands of lives to work that out.
Additional Reading

For exhaustive detail on the UN mission, read Study of the battle and siege of Sarajevo which is Annex VI of the Final report of the United Nations Commission of Experts
established pursuant to security council resolution 780 (1992).
UNPROFOR and UNTAC: Lessons Learned as to Requirements for Planning, Training, and Equipment by John O. B. Sewall, M. Gen., USA (Ret.) Vice Director of the Institute for National Strategic Studies, National Defense University
Comment: His book "Peacekeeper: the Road to Sarajevo" covers some of it, but I am trying to find something web friendly.
Comment: Another valuable source for understanding the whole pol/mil mess is Major-General Lewis MacKenzie (Canada); his critique of the "dual key" RoE is spot on.
Comment: @KorvinStarmast Got a link or reference to that?
Comment: heh, I heard it from the horse's mouth about 20 years ago, but I think I can find you a summary.  https://openparliament.ca/committees/national-defence/40-3/22/mgen-lewis-mackenzie-1/only/  is a brief statement. I'd need to check some archives for a fuller treatment.
Comment: @KorvinStarmast - IIRC there was an hour-long interview about the conflict with one of the UN commanders several years back on NPR, perhaps on FreshAire. I believe they keep those archived online.


How are composite aircraft canopies constructed that sit flush with the fuselage?

Question:
More specifically, how is the composite frame of the canopy manufactured? Attached picture as an example.
Comment: Yes! How to make the joggle on the fuselage that receives the canopy and the canopy frame that sits in it.
Comment: It's done with a mold, I'm not sure what you're asking though, do you want to know the molding process?
Answer: That is a complicated process. You need:

A positive mold (mandrel) for the canopy.
A negative mold for the canopy frame. For a single prototype you can also use the unfinished fuselage itself.
A fuselage mold with a molded window sill.

First the fuselage positive mold core is built. From that the negative mold is taken, but also a negative mold only for the canopy area. From that negative mold the mandrel for canopy manufacture is built. If you have enough money, you can of course CNC mill the mandrel directly from a large block of aluminium.
The plexiglass canopy is deep-drawn over this mandrel by the canopy manufacturer, e.g. Mecaplex. There aren't many who get this process right!
Meanwhile, the window sill has been added to the fuselage mold and can be used for manufacturing the canopy frame mold. Once that is finished, the canopy frame is built by first lining the mold with diagonal weave fabric (glass or carbon, as you like) and filling the core of the frame with unidirectional rovings. Then another couple of diagonal weave layers is added on top. After removal from the mold the frame is trimmed and now the transparent part is added. The frame has a recess where the plexiglass fits in and the plexiglass is fixed to the frame with a special polyurethane adhesive. A couple of screws make sure it stays in the correct location.
To finish the canopy, the fittings are added and the frame is painted.
Comment: The canopy frame on my PL-2 is f-glass built over steel tubing, with the f-glass joggled around the perimeter to accept the moulded plexi flush, but the builder attached it with screws through the plexi into drilled and tapped holes right in the epoxy matrix.They were leading to hole cracks and bits of the edge of the plexi breaking off and after I repaired the plexi I thot of replacing the screws with that polyur glue like the RV guys do,but instead just enlarged the plexi holes and installed the screws with large c-sunk washers so there are no lateral forces on the holes. No problems so far.
Comment: Peter Kämpf, the last paragraph is where I'm having difficulties. How exactly did we move from a  solid mold to a mold with window sills? I know that a tool is attached to the fuselage molds to get that joggle, but I can't think of a way to manufacture of the pattern for the tool other than CNC.
Comment: @Mridul It's a long time since I did it, so I'm no longer exactly sure. One way would be to cut the profile of the frame in high density styrofoam with a hot wire and bend that strip into shape and fix it to the fuselage mold, then cover it with packaging tape. But that was for a prototype, so serial production would use a layer of glassfiber and filler for a smooth surface instead.
Comment: @JohnK The cracks emanating from the screws is a known problem. The trick is to not tighten the screws all the way so the plexiglass is not compressed by the screw head. And countersink liberally, so the screw head does not stick out a bit.


What should I do if caught in a sand storm?

Question: If I find myself caught in a sand storm, what should I do? Should I sit it out, or try to keep moving somehow? Can this depend on the severity of the sand storm?
Answer: Sandstorms (or, here in the southwestern part of the US, dust storms) impair the ability to see and breath. The winds also carry heavier debris. Because the storms often occur when it is hot, the wind can contribute to dehydration. The reverse is also true--cold, winter dust storms occur in some places, and hypothermia can become an issue.
Fortunately, most of the time, there is advance warning. Even if you don't hear the alert, you can see the wall of sand or dust moving your way.

You don't want to be moving around during the storm, the potential for reduced visibility is great. Even if you are wearing goggles, there's a chance you won't be able to see where you are going.
Bring your water canister and seek shelter--something sturdy. Even something that leaves you partially exposed will provide a degree of protection from sand/dust and debris.
If shelter is not available, then a higher spot is often better than a lower simply because there is usually less particle density at the top of the storm.
Move away from roads and freeways. In storms like this, drivers are advised to pull off the road, turn off their lights and keep their foot off the break. (Visibility can be so low that other drivers can't see the roadway. Terrible accidents occur because a driver mistook a car parked off the road with a car they thought was travelling on the road.)
Cover yourself--arms, legs, neck, eyes, ears, nose, mouth, etc.
Once you have yourself situated, then try to stay low to the ground and protect your head.

There are related conditions of which you'll want to be aware. These storms are often accompanied by lightening and rain. Particularly in desert regions, the rain can cause flash flooding.
You asked if the precautions can depend on the severity of the storm. Yes, the size and intensity of these storms vary greatly. When they are gathering steam, it's often not possible to distinguish the storm that has the potential to be more dangerous. Don't be misled, though--these storms are changeable and have the potential to become both fast moving and destructive.
Comment: In #4 I would also note that plenty of people have also been hit as another car decided to pull off the road and couldn't see them because their lights were off, so pull off as far as you safely can or make it to an exit.
Comment: Felix I believe since you've pulled over off the road keeping your lights off the driver should just keep going on the road as is. If the driver sees your break lights, they might think they're the one off the road or react in another weird way.
Comment: Unsure (sorry) if my inquiry about my own answer is or is not acceptable. Suggestions about how I could improve this answer are welcome.
Comment: You should keep wet cloths or bandanas on your face try to keep the sand out and wait it out
Comment: About #4: Why turn your lights off? I understand visibility is very poor in a sandstorm, but wouldn't you risk being rammed by a driver who can't see you at all?


What is the meaning of 2:102?

Question: Some translators translate 2:102 as: "(Allah sent these two angels to teach black magic so that people could save themselves from its harms", is this correct? if not than what is the meaning?
Answer: Here is a better translation:

And they followed [instead] what the devils had recited during the
reign of Solomon. It was not Solomon who disbelieved, but the devils
disbelieved, teaching people magic and that which was revealed to the
two angels at Babylon, Harut and Marut. But the two angels do not
teach anyone unless they say, "We are a trial, so do not disbelieve
[by practicing magic]." And [yet] they learn from them that by which
they cause separation between a man and his wife. But they do not harm
anyone through it except by permission of Allah . And the people learn
what harms them and does not benefit them. But the Children of Israel
certainly knew that whoever purchased the magic would not have in the
Hereafter any share. And wretched is that for which they sold
themselves, if they only knew.
Surat Al-Baqarah 2:102

Harut and Marut were angels who were sent to Babylon to test people by performing magic. It was the devils who taught people to use that magic, and not the angels.
Answer: In fact they taught people magic to avoid them and to recognize magic and they told people do not use this magic for bad intentions but they learned and misused it and then they saidthat soleman was also a magician and he disbelieved but Allah gives us promise that :{ Assuredly Allah defends those who have believed} hajj 38
And he sais in this verse that solemon wasn't among the disbelievers.

What is the meaning of 2:102?


if one site blocks the entrance with tor browser, what can I do?

Question: I want to visit to a site anonymously, but I can not login with Tor.
How to make sure that this site did not know that I use Tor?
They are forbidden clones, but I need them.
Comment: Tor exit relays are published information, aside from a small fraction of some relays some of the time providing false negatives. If a site wants to block Tor, it can block Tor. You should ask the site operators to allow Tor users and encourage them to allow anonymous use through, perhaps an alternative means to prevent abuse.
Comment: this is not possible. as stated, the tor exits are public domain. your best bet would be to configure TOR > SSH server as a SOCKS5 proxy.
Answer: It's not possible to hide this from websites. Unless the website operators unblock Tor, there is nothing you can do.
You said right in your question "they are forbidden clones," which means you are using Tor to do something you shouldn't be doing anyway.


Is filtered water healthy for dogs?

Question: Is filtered water (Brita filters, etc.) healthy for dogs? If so, what are the risks? I know that some owners give their dogs unfiltered water, e.g. from the sink. I was also going to give my dog some filtered water but wasn't sure if it was safe.
Comment: Filtering -- assuming a clean filter -- is certainly not going to make the water less safe. If you feel you need to filter the water before humans drink it, you should probably consider doing so for pets. If you don't have reason to distrust the water than -- despite Flint -- I wouldn't worry.
Comment: Interesting related question [Is tap water safe for reptiles?](http://pets.stackexchange.com/questions/5523)
Answer: Depending on where you live, I don't know that I would consider it necessary to filter water for pets, however people have expressed concerns with respect to many municipal water supplies and their chemical treatment. The reason I mention this is that there have been concerns expressed about normal tap water for pets.
Now, with respect to filtering, there's no reason for this to pose any risk to your dog (or cat for that matter) and there's some opinion that it's better. We use Drinkwell Fountains for our cats (we're on a well system) and these are designed for both cats and dogs, by a Veterinarian, and would see no reason that they would need to be different in this respect. They use a charcoal based filter system very similar to what you'd find in a Brita system and there's no evidence I've seen that this poses a risk to either animal.
Answer: Now, this question can be answered logically, without knowing anything about pets, or if the water is for dogs, horses or rabbits.
Think about it! If the filtering is just this: filtering, i.e. removing stuff, chemicals or particles from water so as to make it more pure, how could this possibly pose a risk? This would mean that pure water poses a risk (which one?) and additives, like calcium compounds, chlorine compunds, dirt or bacteria reduce that risk.
Comment: Depending on the technique of water preparation the water coming out of the treatment may have things in that it did not have going in.  [Example 1](http://www.livestrong.com/article/167906-problems-with-drinking-water-filtered-through-charcoal/), [example 2](https://en.wikipedia.org/wiki/Water_softening#Health_effects).  There are actually very few commercial home treatments that deliver pure water.
Answer: I'm not sure about filtered water, but Smartwater and its derivatives should be a great viable alternative. The electrolytes in it will help to hydrate your pet.
Check out http://www.petmd.com/blogs/fullyvetted/2009/july/magic-waters-why-i-love-smart%C2%9D-water-therapy-pets-6860 for some awesome advice.
Comment: Maya welcome to Pets.se.  Can you improve your answer by including in your answer some of the points from the link you provided?  That way if the link dies your answer will still have value to others.

Is filtered water healthy for dogs?


css responsive not working and overwriting my inline style

Question: I have a wordpress site and i am using bootstrap css for a popup. Please check the page here: http://aboutpubliseek.staging.wpengine.com/test-page/
When I reduce the width of the browser less then 770px the text box for email reduces in height. I found no way to solve it. I used inline css for input element, I used media query with !important tag, I also tried with removing all other css but bootstratp.css. But same result. So I think issue with bootstrap.css. Some thing is overwriting my css when I reduce the width less then 770px.
Please check the following code i used for test:
<code>@media screen and (min-width:481px) and (max-width:770px){
    #gform_fields_2 {
        input[type='email'] {
            background-color:#EEE;
            padding:5px 10px !important;
            min-height: 30px !important;
        }
    }
}
</code>
Here background color works but padding.
Can you please help me to sort out this.
Thanks.
Answer: Add this
<code>min-height: 42px !important;
</code>
to this
<code>#gform_fields_2 input[type='email'] {

}
</code>
so it becomes
<code>#gform_fields_2 input[type='email'] {
/*..css defs that are already there */
min-height: 42px !important;
}
</code>
this is in your commander_less.css file
Comment: Thanks for you ans. But I already tried with this style. The height will be 30px actually. But problem is when resize the browser by reducing width with less the 770px then input[type=email] filed is changed in height. Please check yourself.


A real world example for the divide and conquer method

Question: Can someone give a real world example for the divide and conquer method? For example, I've heard the boomerang used to explain the idea of a loop back address. What is a real world example we can use to teach students about the divide and conquer method before going to more complex algorithms?
Comment: You will have to enlighten us on "boomerang".
Comment: Divide and Conquer was originally a military term. You can look for example at the British conquest of India.
Comment: My teacher used the way we look for a word in a dictionary.
Comment: My mother taught me binary search for finding words in a dictionary in the 1950's.
Comment: @ctrl-alt-delor if I had to guess, OP is referring to the 'throw and it returns to you' boomerang, since OP is talking about a *loop back* address.
Comment: Related: https://stackoverflow.com/questions/14415881/how-to-pair-socks-from-a-pile-efficiently
Comment: @heather. I don't see how that relates to divided and conquer. And it seems like a very bad analogy to loopback. With network loopback the packet does not leave (so has no need to come back). A better analogy to a loopback address is "home".
Comment: @ctrl-alt-delor it doesn't relate to divide and conquer, I don't think - seems like OP is saying 'just like we use this real world example for this thing, what real world example can we use for divide and conquer?' I also can't really comment on the quality of the boomerang analogy; I was just trying to guess as to what the OP meant =)
Comment: @PatriciaShanahan and Jimbot: You should expand your comment into an answer. To me, this seems to be the most obvious application of divide and conquer in real life, and everybody immediately understands the process. Another one might be guessing a number where you're just told whether your guess is too high or too low.
Comment: A boomerang would be a good analogy for a ping, not for loopback!
Answer: Back around 1985, Susan Merritt created an Inverted Taxonomy of Sorting Algorithms. The idea is that to sort an array you have two phases, the split phase and the join phase. She divided the various algorithms into two types easy split/hard join and hard split/easy join varieties. Merge sort is of the former type. Quick sort is the latter.
But all sorts, envisioned in this way are divide and conquer. Her original paper (part of her doctoral work) is a wonder and worth exploring by any CS teacher.
Answer: The simplest example that still bears enough complexity to show what's going on is probably merge sort. It's no coincidence that this algorithm is the classical example to begin explaining the divide and conquer technique.
I am not sure at what level you teach, but your students should be comfortable with both recursion and inductive proofs before venturing far into this territory.
Coincidentally, there is a list of divide and conquer algorithms found here.  It's a pretty long list, and might have cast too wide a net.  I'm not convinced that I agree that all of the algorithms are genuinely divide and conquer.  However, it could be that upon closer inspection, they are.
In any case, it's a great starting point to find algorithms to present to your students. Just be sure that you can clearly explain the central divide/conquer/combine throughline for any algorithms you choose to bring to your students.  This area of algorithms is full of traps for unwary beginners, so your students will benefit greatly from thought and care put into your presentation.
Answer: These sorts of patterns are a bit tricky in real life.  In nice easy computer-science land, every step is the same, just smaller.  Merge sort is clearly the ultimate easy example of this.
In real life, we tend to break things up along useful lines.  If we're sorting change, we first divide the coins up by denominations, then total up each denomination before adding them together.  When we put together a puzzle, we divide out the edge pieces first, put them together, then build the rest of the puzzle on that.  In war, we divide an opponent into pieces which cannot work as a cohesive unit, then crush them.
We see this in real life more often than blind divisions because we, as humans, know we can divide along useful lines.  The closest I know of that is quicksort's attempt to find a middle index to partition with.
One thing I find tricky about these divide and conquer algorithms is that they look like an infinite regression.  You keep proving you can sort lists as long as you can sort smaller lists.... which you know you can do because you can sort smaller lists... so on and so forth.  Infinite regression is a serious faux pas in modern logic, so I think people may get confused by that.  Showing that "if I can sort a list of length n, I can sort a list of length 2n" would be the more traditional mathematical induction approach.
Then again, all may be for naught, for it is quite clear the best use for divide an conquer in real life is to put together a thrilling Hungarian dance.
Comment: +1 for the Hungarian dance example :)
Answer: If you want to divide a long loaf of bread in 8 or 16 equal pieces, generally people cut it into two equal halves first and then cut each half into two equal halves again, repeating the process until you get as many pieces as you want - 8, 16, 32, or whatever. Almost nobody tries to divide the loaf into 8 pieces all at once - people can guess halves much better than eighths.
Comment: Hello, and welcome to Computer Science Educators SE! While your example is good, you may want to add some explanation of why your example appropriately addresses the question. Thanks!
Answer: MergeSort is fairly easy to implement in Python and it's a straightforward divide-and-conquer algorithm.  You keep splitting the collection in half until it is in trivial-to-sort pieces.  This splitting reduces sorting from O(n^2) to O(nlog(n)).
Second example:  computing integer powers.  if the power is even, square base and integer divide exponent by 2.  If it's odd, do the same and multiply by a factor of the base.  This algorithm is O(log(n)) instead of O(n), which would come from computing an integer power with a simple loop.
Comment: Would you mind providing a bit more explanation for why you think merge sort is a good example to use for teaching divide and conquer? Not every divide and conquer algorithm will be useful for teaching the concept of divide and conquer, so why do you think merge sort is?
Answer: The typical examples for introducing divide and conquer are binary search and merge sort because they are relatively simple examples of how divide and conquer is superior (in terms of runtime complexity) to naive iterative implementations. FFT can also be used in that respect.
Among these, merge sort is the best example. Binary search is a degenerate case for explaining divide and conquer because you divide the problem into two subproblems, but you discard one of them almost trivially, so you are not actually combining the solution of several subproblems but just solving one of them.
But on my experience (I have lectured that several years), merge sort makes it also very hard for many novice students to grasp the idea of divide and conquer because it combines too many different conceptual problems at the same time. In order to implement merge sort efficiently, they will need to understand the technique of divide and conquer, the execution tree that occurs under the hood, the implementation of the division phase (thus working with indices if you want efficiency) and the implementation of the conquer phase (linearly).
You can start with an easier example such as computing the average of an array:
<code>def average(arr):
    assert arr, 'Expected non-empty array'
    if len(arr)==1:
        avg = arr[0]
        n = 1
    else:
        mid = len(arr)//2 # or any value with 0 < mid < len(arr)
        avgL, nL = average(arr[:mid])
        avgR, nR = average(arr[mid:])
        n = nL + nR
        avg = (avgL*nL + avgR*nR) / n
    return (avg, n)
</code>
This example introduces the idea (instead of the advantages) of divide and conquer in a way that all students can intuitively understand. The key point is to highlight that the recursive calls solve exactly the same problem but for small instances, and that you can use those solutions of smaller instances to solve the problem for the large instance.
The example may appear trivial for many professors, but it is already shocking for many students and it will let them focus on understanding the technique itself and its execution, rather than details and optimizations. The example can also serve as guinea pig for analyzing the complexity of several different scenarios, such as when the array is copied on each call instead of being passed as a slice reference, or when mid is chosen as one third or as a constant.
Moreover, this example will naturally raise questions among students about its complexity and the possibility of parallelizing the computation, which may make some of them enthusiastic and creative.
Afterwards you must of course explain and analyze merge sort and binary search, emphasizing on how important they are because they beat naive iterative implementations.
Comment: This is the first time I've ever encountered multiple multiple assignments in a single statement like that.  Weird!
Comment: That's rather typical in python. It's called iterator unpacking.


Double slit detector

Question: Everybody has an animated cartoon of the double slit experiment and how amazing it is. Does anyone have an actual video of it actually being done? In particular, I want to see how they detect which slit the photon goes through without destroying the waves. NO CARTOONS PLEASE.
Comment: This is this Veritasium video about it in which he claims to detect single photons with a "photomultiplier tube". I cannot vouch for it one way or another: https://youtu.be/GzbKb59my3U?t=145
Answer: Here's Brian Greene demonstrating an interferometer to Stephen Colbert after the LIGO's discovery of gravitational waves.  There the question is "which arm of the interferometer did each photon travel down," rather than "which slit did the photon go through," but the idea is the same, as is much of the mathematical treatment.  You can see the interference pattern disappear when Greene blocks one arm of the interferometer, removing the "which-arm" ambiguity.
(You can also see the interference pattern changing throughout the piece as the floor of the performance stage flexes under the interferometer, well before Colbert shouts "SCIENCE!")
The answers to this question suggest a way you could perform the experiment yourself and take your own video. You should be able to pick up an appropriate laser pointer next time you're at an office supply store, for about $10.
A manifestly quantum-mechanical double-slit experiment requires turning down the intensity of your light source until the most probably number of photons in your experiment is zero. You'd need a position-sensitive photon detector and data acquisition hardware to determine whether the interference pattern still emerges after you've accumulated enough statistics. It does, because each photon interferes with itself:

I snatched that image, published in 1989 by Tonomura et al., from this answer to a similar question, which includes a link to this Veritaseum video which seems to be exactly what you're after.  (Note that a double-slit experiment operating in the single-photon brightness regime would, all on its own, make for pretty unsatisfying video, because "one photon at a time," to most video cameras, is not distinguishable from "complete darkness."
What you see in the video is pretty much what you'd see if you came to my lab with a shopping list and we built such an experiment together.)
The tail end of your question ("I want to see how they detect which slit the photon goes through without destroying the waves") implies a misunderstanding: determining which slit the light travels through destroys the interference pattern. A Scientific American article from ten years ago describes a home experiment to that effect, but doing it looks just like in the first link where Brian Greene blocks one interferometer arm and the interference pattern goes away.
Answer: There's an excellent video of double-slit interference for electrons here. Your statement "how they detect which slit the photon goes through without destroying the waves" doesn't make sense, though.
Comment: That shows a result and not the experiment set up. Many double slit experiment animations claim that the act of observing which slit it goes through causes the partical to know and magicly pick a slit thus destroying the interference pattern. I think they are just doing bad science or missing a critical concept. I see lots of post of "lots of people have done it" but none of them seem to have cameras.
Comment: The act of observing does nothing to the experiment. It's the act of detecting that interferes. If you place the detector somewhere in the middle of the experiment it will block the photon from making it to the detection screen where it can add to the derivation creating a fringe pattern on the wall. The pattern you see on the detection screen is live and happening in front of you. You can record it if you want to.
Answer: There's an actual video of the electron double-slit experiment included in this article:  http://physicsworld.com/cws/article/news/2013/mar/14/feynmans-double-slit-experiment-gets-a-makeover

Double slit detector


Wordlists on Kali Linux?

Question: I notice that in /usr/share/wordlists in Kali Linux (former Backtrack) there are some lists. Are they used to bruteforce something? Is there specific list for specific kind of attacks?
Comment: Fire up John the Ripper and see if you can crack some passwords with the provided list
Answer: Kali linux is a distribution designed for penetration testing and computer forensics, both which involve password cracking. So you are right in thinking that word lists are involved in password cracking, however it's not brute force.
Brute force attacks try every combination of characters in order to find a password, while word lists are used in dictionary based attacks. Many people base their password on dictionary words, and word lists are used to supply the material for dictionary attacks. The reason you want to use dictionary attacks is that they are much faster than brute force attacks. If you have many passwords and you only want to crack one or two then this method can yield quick results, especially if the password hashes are from places where strong passwords are not enforced.
Typical tools for password cracking (John the Ripper, ophtcrack, hashcat, etc) can do several types of attacks including:

Standard brute force: all combinations are tried until something matches. You tpyically use a character set common on the keyboards of the language used to type the passwords, or you can used a reduced set like alphanumneric plus a few symbols. the size of the character set makes a big difference in how long it takes to brute force a password. Password length also makes a big difference. This can take a very long time depending on many factors
Standard dictionary: straight dictionary words are used. It's mostly used to find really poor passwords, like password, password123, system, welcome, 123456, etc.
Dictionary attack with rules: in this type dictionary words are used as the basis for cracks, rules are used to modify these, for instance capitalizing the first letter, adding a number to the end, or replacing letters with numbers or symbols

Rules attacks are likely the best bang for the buck if all you have are standard computing resources, although if you have GPUs available brute-force attacks can be made viable as long as the passwords aren't too long. It depends on the password length, hashing/salting used, and how much computing power you have at your disposal.
Comment: Very nice answer @GdD, can't vote up im sorry .... Thanks for clarifying for me the diferrence between brute force and standard dictonary ... i thought they was the same .... And how the Rules on dic works ?
Comment: @Stephenloky, the rules are applied by the cracking engines, each one is different in implementation. Some tools have more flexibility than others.
Answer: One of the better basic wordlists in Kali is /usr/share/wordlists/rockyou.txt.gz.  To unzip simply run gzip -d /usr/share/wordlists/rockyou.txt.gz.
Be sure to add "known weak" passwords that are used by the organization you are testing.  I like to add these "additional" custom passwords to the top so they are tested first.
Comment: Welcome to the site. While your answer has useful information in it, it doesn't really answer the question. The OP is asking what the lists are used for, not which list is best.
Answer: Those lists can be used to feed into several programs. So for instance aircrack-ng has an option -w where it takes a wordlist as argument. The password testing program John the Ripper also takes wordlists to accelerate the guessing.
Answer: In addition to what's already mentioned here, the wordlists are used in conjunction with some of the web app tools and things such as sqlmap. If you're looking for places to use them, download some of the "boot to root" VMs like Kioptrix and De-ICE and have a go at brute-ing some passwords.
As for specific lists for specific types of hacks - not really. Unless you're doing something targeted against a person you know some facts about (in which case you'll use something like CUPP - Common User Passwords Profiler - to generate a custom wordlist for that particular target).

Wordlists on Kali Linux?


How do chess websites relay the moves for tournaments?

Question: I know the DGT boards are used for this. But, do they all do so? Does every chess website connect their server to the DGT board and relay the moves? Or do they simply "steal" the moves from another site?
Answer: That depends on the tournament organisation. If the tournament organiser is happy, they provide an online PGN file which is updated everytime the player makes a move. A good digital board software can easily do that. Broadcast websites such as chess24.com simply has to poll that PGN file. Easily scaled to any number of chess boards.
Obviously, the last strategy requires cooperation. The 2018 world chess championship has no such facility. The broadcast websites has to hire someone constantly monitor the offical website (they have to pay for subscription), and relay the moves manually.
Generally, organisers especially open competition are more than happy to assist. It's a nice way for promoting their events. Chess moves don't make money.
Answer: They "steal" the moves. The organizers of the last world championship didn't like that and sued, but lost. See some discussion at What are the laws concerning copyright of chess games?. In short, the judge said that "it is well-established that sports scores and events, like players' moves in the Championship, are facts not protectable by copyright".
I can't speak for every site, but in my experience you can tell that they are doing it this way based on comments like "I just heard there was a move" and by the fact that the clocks are generally wrong. Also, why would the organizer make it easy for sites which they see as freeloaders?
(Of course, this depends on the event. I wrote the above thinking of high-profile events such as the world championship which is taking place as of this writing, and which I thought might have been on the questioner's mind.)


Charcoal grill not getting hot enough

Question: I purchased a cheap kettle charcoal grill a few weeks ago, and I feel like it's not getting hot enough. I'm using a charcoal chimney which takes about 40 minutes to get the coals ashy. I've read it should only takes 15 minutes to light. Once I dump the charcoal into the grill it gets cold fast. When I first put my hand over it the grill is hot, and I can barely keep my hand over it for a few seconds. After closing the lid and letting the grill warm up for 5-10 minutes I can typically keep my hand over the coals much longer. I also never see any smoke coming from my grill after I initially light the chimney.
I'm currently using briquettes as lump charcoal was even colder. The bottom and side vents are fully open, so there should be plenty of air flow in my grill.
Comment: Hello, and welcome to Stack Exchange. A picture of the grill and briquettes might be helpful here.
Answer: It really sounds as if you're just getting the tail-end of the fuel left in the charcoal.. that you've let it burn too far in the chimney .. 40 minutes does sound like a long time .. the right time to start cooking on charcoal is when any self-sustained flames have gone down, and the surface appears grey-white in daylight.. if you fan it, there should be a clearly perceptible glow.
If you want to use your chimney, give the charcoal just enough time in there to propagate its own burn.. don't spread it too thin in the grill after transfer, and let it settle to a glow in the grill, not the chimney. That will also help the metalof the grill heat up.
Or, light the charcoal in the grill by fanning it gently, and later, not so gently, with whatever comes to hand, or an electric fan.
Comment: OK, that's not an even light, is it? I think I would transfer it  to the grill then. Or before then. Mix it up,and pile it up, to begin with, and fan it until you think  there's no completely raw charcoal, spread it, and let it settle down. If you need the grill to be hot for longer, there's nothing to stop you introducing more raw fuel on the leeward side (not attempting to cook over that part) and mixing it into the rest when it's got going.
Comment: BTW, there's nothing wrong with your grill being 'cheap'. Mine's made of a (now blackened) bent-up old oil can, and discarded oven racks. I light my charcoal in the grill, using a blowtorch to get one or two pieces going, and then spread the burn, gradually putting other pieces on top, and fanning with a square of woven bamboo, made for that purpose, as used by street-vendors all over Asia.
Comment: After about 10-20 minutes there is a red hot glow through maybe 1/2-1/3 of the chimney, but the top briquettes are barely ashy and still mostly black
Comment: There's definitely an airflow issue. I got my coals red hot yesterday (about 35 minutes in the chimney) and dumped them in the grill. I closed the lid with both the side and bottom vent fully open to let the grill heat up. After 5 minutes the coals looked dead, but with the lid off for a few minutes there was enough oxygen to get them red hot again on their own. Should I not preheat the grill and/or cook more with the lid off for better airflow?
Comment: I don't use a lid at all. I do all my firing up in the grill itself. Maybe your two vents,(one above and one below the fuel) create a sufficient chimney effect from the lid to obviate fanning... but I prefer a little gentle bowing followed by fanning. It takes maybe 10 minutes to get the charcoal going, (putting some work in), followed by another 10-15 minutes of intermittent judicious stirring and fanning while I'm basically doing other things, for the embers to settle down to even cooking temperature, with the faintest trace of  active, transparent flame.. certainly not floppy yellow flame.
Comment: I still have not improved the chimney time, but cooking without the lid is night and day. The coals now get hot enough that a two zone setup is necessary.

Charcoal grill not getting hot enough


Nearest Neighbor Focal Statistics and Map Algebra

Question: I would like to use a nearest-neighbor type analysis to iterate over a raster. The nearest neighbor analysis will give a cell value of 1 IF AND ONLY IF the cell being analyzed has a cell value larger than all adjacent cells, and 0 otherwise. Is this type of analysis possible with Arcobjects or with the raster calculator tool using map algebra?
Comment: I am testing this statistical methodology as part of a raster extraction process for an automated ArcObjects implementation. I wanted to see if the statistical methodology provides the desired results without ArcObjects if possible first (it didn't unfortunately), so in this case Luke's ArcGIS Spatial Analyst implementation worked best for me. Thank you for your input.
Comment: What software would you prefer to use?  ArcGIS Spatial Analyst or ArcObjects?  I would expect this to be easy with the Raster Calculator of Spatial Analyst so am wondering whether you have tried that without success.
Answer: Use the Con and FocalStatistics tools.  Something like:
Con(inraster > FocalStatistics(inraster, NbrIrregular(kernel_file), "MAX", ""), 1, 0)

Where: kernel_file is a path to a text file that defines a neighbourhood that excludes the currently processed cell, something like:
3 3
1 1 1
1 0 1
1 1 1

You might also be able to do this with an annulus neighbourhood, but I can't test as I'm not at work.
Comment: You are the hero that this forum needs.


2002 Ford Windstar only blowing hot

Question: Helping a neighbor with her 2002 Windstar and it is having an issue with the climate control.  At the moment, it only blows hot air (on and any setting for temp or vent direction) or no air at all (off.)  Already checked the vacuum hoses, checked to see if the compressor engaged and those checked out and the freon was good.  The issue I'm having is that I know there is a blend door under the dash, but a failure on that wouldn't explain both the front and back vents only blowing hot air to my knowledge.  Before I end up on my back to get the door out, is there other items I should check>
Comment: I guess it's an automatic AC? Cabin temperature sensor and blend doors would be the usual suspects. The back vents probably use the same blend doors, unless your neigbor's vehicle is a truly high-end vehicle, as usually the system is two-zone, one zone for left of the car and one zone for right of the car.
Comment: And it's usually the actuator which is at fault, not the blend door itself.
Answer: I guess the only question is. Do the rear HVAC controls work to control the blend door in the rear?
If they do it's probably a fuse or the Function Selector Switch Assembly. This isn't 100% though as IIRC the FSSA overrides rear HVAC controls until the REM receives a signal from the FSSA to allow rear HVAC control. There may also be multiple problems, such as a stuck blend door or failed actuator. You can rule out a vacuum problem as the blend door actuators are all electric and the vacuum controls only operate the recirc and airflow doors.
The two systems are independent with only some module signalling between them. The front and rear auxiliary HVAC are controlled by the FSSA, Instrument Cluster and the Rear Electronic Module, plus it's switches. When selecting a rear temperature or fan speed, the FSSA sends a voltage to the IC. Which then talks to the REM via a serial data line, to operate the blend door actuator.
The front blend door actuator is controlled by the FSSA and is a 3 wire setup with power, ground and control signal.
The rear blend door actuator is a little more complicated. It obtains power and ground from the REM. Has a position signal and two command signals for opening and closing the door.
The First thing I'd check is the fuse for the temperature select control. Fuse 10 in the Central Junction Box. If that fuse is OK you need to check the  output at the temperature control connector on the back of the FSSA.
Honestly anything more other than doing some basic wiring checks or checking blend door actuators for power, ground and a control signal. You're probably going to need a scantool to communicate with both the IC and the REM. To verify module operation.

2002 Ford Windstar only blowing hot


compute a vector which is perpendicular to another given vector (all are in 3D)

Question: I have a vector $v_1$ (suppose $v_1= \langle a_1, b_1,c_1\rangle$) and this $v_1$ passes through the point $(x_1,y_1,z_1)$. Now I need a second vector, $v_2$ which is perpendicular to $v_1$. Suppose that $v_2$ is passing through the second point $(x_2,y_2,z_2)$. However, my final goal is to find the intersection point of above two lines. So, could you help me to find the vector which is perpendicular to another given vector?  Please anyone help me.
Comment: The question, as stated, is unclear. Since you are in 3-dimensional space, the answer is by no means unique. Given a vector $v=(a,b,c)$ the vectors perpendicular to $v$ are those whose components $(l,m,n)$ satisfy the relation $al+bm+cn=0$. They form a plane (2-dimensional linear subspace).
Comment: ok, if i explain my question in another way;I have a point (x1,y1,z1) and a vector (a,b,c). This vector goes through that point. So, I am able to get the parametric equation of respective line. Now I have another point (x2,y2,z2) which locates closer to that line. If I draw another line, passing through (x2,y2,z2) and perpendicular to the above line, then what would be the coordinates of intersection point. That is what I am expecting at the end.
Answer: Ok, so your line $\ell$ has parametric equations
$$
x=x_1+at,\qquad
y=y_1+bt,\qquad
z=z_1+ct.
$$
If $Q=(x_2,y_2,z_2)$ is a point, the equation of the plane $\pi$ perpendicular to $\ell$ and passing through $Q$ has equation
$$
a(x-x_2)+b(y-y_2)+c(z-z_2)=0.
$$
Now just plug the former equations into the latter and solve for $t$.
Comment: for my understanding, i would like to ask you; the values in the equation a(x−x2)+b(y−y2)+c(z−z2)=0 i.e. a,b,c values are the same values which belongs to the first vector which passes first point? that mean, i don not want to find the perpendicular vector and equation of the line which is perpendicular to the first line? (sorry, i am so poor in vector and plane geometry). please comment me.
Comment: @ Andrea Mori=> i got the value for t={a(x2-x1)+b(y2-y1)+c(z2-z1)}/(a^2+b^2+c^2). then, for this t, i belive i can get the intersection point directly from the equation l. is that?
Comment: Yes, the point is that a plane described by an equation $ax+by+cy+d=0$ is perpendicular to the vector $(a,b,c)$. Then you need to fix the coefficient $d$ so that the given point belongs to the plane, but that is automatic writing the equation as in my answer. And finally, once you solved for $t$ the equation obtained plugging the parametric equation in that of the plane, the value of $t$ corresponds to the point of intersection $\ell\cap\pi$.
Comment: ok, thank you soo much. its clear now.
Answer: Make a plane which is perpendicular to a given vector, then all vectors which lies on that plane will be perpendicular to that vector.