Danijel Gorupec

To perfectly match gears their 'pitch' value must match. When you have a rack, it is easy to measure its pitch distance because it equals to the distance between two teeth (like between the center of one teeth and the center of the next teeth). With gears (pinions) that have small numbers of teeth it is not so easy to measure their pitch distance... [As you noticed, gears pitch do not have to match perfectly, and gears will still mesh. However in this case you might have problems with wear, noise, lash, vibration...] In practice, instead of 'pitch' more often the value called 'module' is used. The module is equal to pitch/pi... To very roughly calculate gear diameter you can multiply its module by number of teeth (the actual diameter is somewhat larger than that). Generally, the minimum number of teeth a gear can have is about 17, most people say. To have smaller number of teeth, some additional precautions are needed (come with price of increased wear or decreased strength...) There are standard modules for imperial and metric gears, and it is likely that your rack is made using some standard module.

Hmm... yes, the similar happened to priests and monks that were once above-average educated. I don't know what do you mean by 'clearly', but I don't think it is easy for a person without science education to understand who talks rubbish and who talks real deal. There are only two ways out, imo: a) to increase general population science education level, and b) to create infallible group of science people that others can ultimately trust... I have seen politicians asking experts for advice, only to be asking wrong experts. (Regarding Trump in particular, I am starting to think that his 'dumbness' is not genuine. He makes too few mistakes. A scary thought.)

Absolutely. Another example if imprecise wording in my post that I see now is when I say that instantaneous power in an AC system "changes at 60 Hz rate". The more precise wording would be 'continuously changes within one period'.

A funny post, Sorcerer While I didn't check details from the paragraph you quote, to me it seems more or less right at first reading. Harmonics: While we consider AC currents/voltages to be pure sine waves, this is practically never true. There is always some sort of distortion from the pure-sine form. A very important form of distortions are so called 'harmonics' - we call it that way because these are periodical distortions whose frequency is an integer multiple of the base frequency of the AC current. For example, a 60Hz AC current might have harmonics of 120Hz, 180Hz, 240Hz etc... Harmonics are unwanted and are often created as a result of non-linear loads, transmission systems and generation systems.... If you know something about Fourier analysis, you should be able to understand what harmonics are. Power factor: The instantaneous power consumed by some load, is always equal to instantaneous current multiplied by instantaneous voltage. However in AC systems we rarely talk about instantaneous power (because it changes at 60Hz rate) but we are talking about average power (within one period). As a result we will calulcate the power cunsumed by a load as "average" current multiplied by "average" voltage multiplied by the power factor (I put the word average into quotation marks because it is actually RMS, root-mean-square, average)... Many times the power factor is not equal to one but is smaller - this means that power was delivered to the load during one part of one period, but is then taken back during the other part of that period. In an extreme case of power factor equal to zero you have a system that transfers lots of energy through wires, but no net power is actually delivered. The energy only goes back and forth. Cu depletion: Now this is a word game - copper is not actually depleted. It just means that because existing wires only have so much current capacity, all this energy that goes back and forth (because the power factor is less than one) is just spending this capacity (and if we don't take care about power factor we are not using our expensive wires very efficiently).

I suppose if you want to make an 'air core' winding and you make it with iron wire instead of copper wire, you might see some difference (but then, I suppose, this should not be classified as an air core winding because iron is ferromagnetic - however this would be a bad design of a winding).

These are good possible explanations, Swansont, thank you. I particularly like "two reactions to occur near each other in a short period of time" because I was not thinking in this direction. I can also confirm that the fourth-power law is most likely an empirical approximation, at least according to wording used in documents where it was mentioned.

UV curable dyes/paints are, for example, used in high-speed offset printing. UV light 'dries' the dye in a fraction of a second... My understanding is that UV light polymerizes certain component of the dye turning it from liquid to solid. But for years one thing I cannot understand... In this particular offset printing example, there is a claim that UV curing speed is proportional to about fourth power of the UV light intensity. As a result, parabolic reflectors are made to concentrate UV light from lamps into a few-millimeters thin line across the web (instead of the light being spread over a larger surface). How can UV curing speed depend on fourth power of light density? For me, it is only intuitive that UV curing speed is directly proportional to the light density (not to the fourth power). Can anyone here explain (provide hints on microscopic level) how this fourth-power dependence came to be? (Please be gentle with your wording because I dedicated my life to learn about women, not chemistry.)

I made mistake... Can I have my +1 back? I gave you +1 and only then I read this is only you, swansont.

Ordinarily I would flame to death!... But because Maitreya is here I don't see the point any more.

Fred, I like Swansont's solution. But if you must have an electromagnet... 1. For magnetic core you should use 'soft' magnetic material (soft iron, permalloy, mu-metal...). You will not find anything better than iron and its alloys. The material must be 'soft' because I understand you want to be able to switch your magnet off. 2. As I understand, your core does not have to be laminated. It would need to be laminated if you employ fast magnet switching (few tens of Hz or more). 3. The magnetic core will face the object you handle. Magnetic field lines will close through the handled object. Make sure the handled object is made from sufficiently thick ferromagnetic material so that it allows for strong magnetic flux... The surface area between your magnetic core and the object should be large. The overall length of magnetic field lines should be as short as possible. You magnetic core (as well as the object you handle) must have iron cross-section as large as possible. All this will reduce magnetic resistance... Take a look at so-called "lifting electromagnets" and notice their shape. 4. More iron you have in your magnetic core more powerful magnet you can make. Iron is limited to about 1.5T (Tesla) and everything above it is just a dream for a hand-held device generating permanent magnetic field. In practice, you might have trouble to achieve more than about 1T of flux density. 5. Iron is heavy. This limits the 'power' of your hand-held magnet. 6. Gap (you mentioned 1 cm) is crucial for your success. I suggest to get rid of the gap! At least keep it in sub-millimetre range... You will not be able to generate strong magnetic field over 1cm gap - this would require large number of ampere-turns and you cannot afford it with your battery power supply. 7. The energy needed to permanently keep the strong electromagnetic field is theoretically zero. In practice you need to spend at least some energy because your winding will have non-zero resistance. Use wire gauge and number of wire-turns to match your battery voltage and preferred discharge rate. 8. I suggest an easily-exchangeable battery - like in some battery supplied power tools. You might share the battery with some power tools. 9. If an exchangeable battery is not an option you might make an induction charger that will charge your magnet battery wirelessly. Far above the Moon Planet Earth is blue And there's nothing (more) I can do (for you). ***D. Bowie (spoiled by me)***

Ok, I see that you are not very crazy about using multi-letter variables inside math formulas. This is understandable, some people say that using single-letter variables makes it easier to see the equation structure. I agree. Also, copying line after line of math is easier if variables are shorter. I tried to write the Pythagorean theorem using names BC, AB and AC for triangle sides (instead of a, b and c): AC^2=BC^2+AB^2... This looked very weird at first, but after I was looking at it for some longer time it settled down. The important thing imo is that if you ever decide to use multi-letter variables in your math formulas, then you should always use cdot (and keep this consistent through the whole paper). Multi-letter function names are often cast in some different font to reduce ambiguity. Also, function names are often standard and well known. (Ajb, I noticed that you used capital first letter in your function names - Is this Mathematica influence or your suggestion?) ... Regarding programming, I would generally allow single-letter variables only for a very short scope (several lines). Very few exceptions from that. (Unless, of course, the intention is to make sw unreadable).... Interesting is this difference between multi-letter variable usage in pen-written math and keyboard-written software.

What is your opinion on using multi-letter variables in math formulas? Should they be used more often or avoided? If I use a quantity called 'Gross Domestic Product' in a formula, I might want to use 'GDP' as the variable name representing it. But this actually seems as a rare example - I cannot think of many such examples, can you? Should I better come up with a single letter representing some money quantity (like 'M') and then use the 'GDP' description in its index? That is what I usually do when I have several quantities of the same type in the same formula (for example, to represent a current through resistor R1 and a current through resistor R2 I might use indexed variables i_R1 and i_R2). If I still use multi-letter variables, should I always explicitly use the multiplying dot (cdot) between any two variables or is the 'invisible times' still appropriate? We already use multi-letter function names often. There are also some multi-letter measurement units (mol, cd). In my opinion, there are some examples where typing whole words might be beneficial. Like when you state a definition or a law... In the following three examples, I find example #2 to be the clearest: Example1: a distance equals to the product of speed and time Example2: distance = speed x time Example3: s = v t When using computers, multi-letter variables might be easier to type than indexed variables. On the other hand, computer monitors are of limited width so one might prefer single-letter variables. I am posting this into the lounge because I am mostly interested in your personal opinions and aesthetics.

CasualKilla, the circuit you found makes sense, but it is a step-up converter. For what you are asking, I think the best would be to combine two transistors. Like on the first picture below. If you insist on NPN-only solution you might try the second picture, but I don't think it will be as good.

If you didn't do much stabilization in your past projects, I would suggest you to try to stabilize some inherently unstable process (maglev, segway...). When I am doing something for fun and when I feel that it might be too easy, then I limit myself to lowest possible budget or only to components that can be found everywhere. BTW, are you more hardware-interested or software-interested person?

In the NPN transistor case, the base voltage cannot be much higher than the emitter voltage. Higher the voltage difference, larger current will pass through the base-emitter junction. This dependance is exponential, and so once the voltage difference becomes higher than cca 0.7V the current might become so large that it might destroy the transistor. On the other hand, if the voltage difference is lower than cca 0.5V the current will be very small, too small for most practical purposes. That is why we say that transistor base-emitter voltage drop is about 0.6V-0.7V - it is because for all practical base currents, the base-emitter voltage drop is somewhere in this range. As Studiot said, the leakage current from collector-base junction is only about 15nA - this is a seriously small current. That is why I am pretty sure that the base-emitter voltage drop that passes such small current is (much) below 0.5V. I said "who cares" because the question - what is the base voltage when the base is non-connected - has no practical value. Once you connect anything (including a voltmeter) to the base, the voltage level will probably change significantly (that is why i said the voltage is 'quite floating'). Yes. If, for example, the base voltage is at 0.7V, and you put a voltmeter between collector and ground, a small current will start to flow from base to collector to voltmeter and finally to the ground. This current will generate maybe 0.5V (just a guess) voltage drop in the base-collector junction and the voltmeter might show some 0.2V... However, making an experiment would be a better way to get the exact answer (as it always is).

Sure. That is why I was careful to use 'human civilization' instead of 'humans' in my post. I would consider 'human civilization' anything that follows the continuity, even if there will be no human beings.

But I don't think that the base resistance is the main component that generates the base voltage... In addition to base resistance, the 15nA current must also pass through p-n junction (base-emitter junction). The U/I curve of this p-n junction is exponential, and some "considerable" voltage difference is needed for the p-n junction to pass 15nA. Now, I didn't find any base-emiter voltage/current diagram for any real transistor. But for a real diode a very rough calculation says that it will take about 25mV of forward voltage to pass such currents. Okay, I admit that this can still be called 'a few millivolts'. (Edit: this was my answer to Studiot's post #6)

I suppose it depends on the doping levels in the transistor... The collector-base junction is reverse biased, but it still leeks some tiny current (in a diode case that would be called 'reverse saturation current'). This current then goes through the base-emiter junction toward GND... The base-emiter junction voltage rises up slightly so that the system reaches equilibrium (reverse saturation current of the collector-base junction equals to the forward current of the base-emiter junction). The voltage needed is small, but I suspect that in some cases (transistor doping levels) it might be above few millivolts.

We could debate this. It might actually be higher than with the connected voltmeter (but certainly below some 0.5V). In any case it is quite floating and so who cares... ... Regarding the picture 4-44 in the OP, I think the book might be partially in error. Depending on the voltage supplied at the transistor base, the voltage at the collector lead might be higher than few mV. It is actually similar to the 4-39f case.

Ha ha, you must believe that Strange is some kind of Superman able to compress steel with his fingers. Okay, I need help with this... there is an 'infinite'-length steel rod. 1. I push its one end by some centimeters. I suppose the rod resists. But after a looong time does the back-force drops to zero? 2. I start pushing its one end by some subsonic speed. Is back-force constant now? Does it depend on the speed? Can Strange really push it long way with his fingers if he does it very slowly?

Interesting, I am thinking in a similar way although for me this is a scary thought. I always remember the saying "no atheists in foxholes" and I am afraid this could happen to me... So dearest people, remember me as man that was strong and rational, not as a human shadow that was weak and delusional. Every man should be remembered as when strongest in his/hers life.

My mother is a medium-devoted Christian, and my father is a low-profile atheist. For sure I was not under any pressure.

Hey DrP, are you being honest? I ask because your post can also be read as a pamphlet. But I suppose you are honest and you are actually telling us about your personal feelings and decisions. I applaud you (not that much because what you decided, but becuse you made one brave decision). At the same time I am puzzled with some statements in your post. First you say that you cannot call yourself a scientist and a Christian at the same time. Is this something that just cannot work for you, or you believe that nobody can call himself a scientist and a Christian? In my opinion, while I am not sure about calling oneself a Christian, I think a scientist can still easily believe in a deity (a very spritual deity, perhaps). Second, your words "...look at all the evidence and I have come to the conclusion that there is no god" sound iteresting to me. For sure you can reject many Chrisitan teachings by looking at evidence, but I don't know how to do the same with the very idea of god. God is usually understood as something that can evade any probing. Rational approach should give no answer... Basically, in my opinion, a person may need/want god, or a person may not need/want god. I differ from you because I am a 'native atheist' meaning that I never believed in any god. I just did not need it/him. For me, god never fit anywhere. Maybe that is why I always find posts like yours fascinating... Anyway, I suggest you to rethink: did you really come to the conclusion that there is no god, or did you just conclude that you don't need any idea of god in your further (confortable) life. The difference is in how you will approach other people. (Edited a stupid spelling error: wrote 'good' instead of 'god')

I suppose, with an offset handle you can reach the ground level with (effectively) shorter handle and still maintain nice body and blade positions. To do the same with a straight handle, the handle would have to be longer -> thus more difficult to lift.... But, I would choose the straight handle anyway (as I like long handles on snow shovels). With an offset handle, I suppose it should be harder to push the shovel into a compact snow. I have less experience with swords, sorry.

I can agree with this particular part... This should be true in general - whenever a group is nourishing symbols, behavioral patterns or ideas in order to bind group members together, the group becomes responsible for their usage. If these symbols ever become 'hijacked' by another (parasitic) group, it is expected that the original group confronts it first and strongest. Bystanding is not a moral option in this case. While I can clearly hear Muslim community (majority) condemns any terrorism in the name of Islam, I am not sure I could classify this reaction as 'first and strongest' (and I am quite disappointed because of this). If this is because there is actually a silent sympathy among large body of Muslims toward anti-western terrorism, then this world is in deeper shit than it seems. (Don't get me wrong, when I look at the overall picture I am not sure we are victims here. But still, terrorism will not make this world any more righteous place.) .... Unrelated to above, F. Hollande and its government failed to protect people. I see this as a fact. Not that they were not warned (I would not be surprised if security spendings were also increased since the Charlie Hebdo attack)... I am not sure what is the best thing for France to do now... to keep the unable government or choose extreme nationalism. I hope there is also a third way.