Search results for query: *

  1. D

    Limits on exposure to high power RF

    Are there limits to exposure to microwave frequency power within a certain range, for example with workers on a transmission tower? What would be the applicable standards? I understand that RF is non ionizing radiation, but I have read that high power RF radiation can cause burns if too...
  2. D

    Everything can be represented by ones and zero

    Are there any counter arguments to the conclusions made in these papers? Edit: by counter arguments, I mean papers written by authors who address the conclusions made in these papers or similar ideas. While the papers are not entirely rigorous, they make good points. Some things said raise my...
  3. D

    Calculating Transfer Function off Bode Plot? they have examples, and there is also a controls wiki website with examples, I believe: Given a bode plot, you look for changes in slope. At any frequency that the slope changes, first look to see...
  4. D

    News Trip to Istanbul this November

    You've probably heard this already, and it applies to anywhere on the European/Asian continents, but guard your valuables from pick pockets at all times, especially in busy places like shopping areas and especially if you have bags, backpacks, or purses. Even unsuspecting well dressed men in...
  5. D

    Are unstable system really possible?

    Well, I think you are using a definition outside of OP's context. That's why I tried to clarify because it would be confusing to someone learning LTI theory. You cannot write down a non-linear transfer function that self limits in terms of a single function: O = F(I). To describe a non-linear...
  6. D

    Are unstable system really possible?

    I'm thinking in terms of systems and controls theory with the laplace operator. I always have been under the impression that this is the definition of the transfer function. This fact is the inherent limitation to transfer functions in nonlinear systems and is at the heart of the OP's...
  7. D

    Are unstable system really possible?

    In what context are you using the word "transfer function"? Transfer functions can never be nonlinear, but you can limit their outputs after the fact that their outputs have reached the physical system's linear region limits (and no longer are modeled accurately by the transfer function). In...
  8. D

    Separating Acoustic Waves from Background Reflections

    I'll pass along something I picked up here a while ago. Try researching the cepstrum technique and comb filters. In the time domain, reflections are ideally just time delayed copies of the original signal with some distortion or attenuation, and they translate into the frequency domain as a...
  9. D

    Distance Measuring Sensor Advice

    what about acoustic ranging?
  10. D

    Electrical schematic troubleshooting program?

    LTSpice is a good free option.
  11. D

    Electrical schematic troubleshooting program?

    Have you looked at using pspice?
  12. D

    Nobel Prize 2012 Physics

    Well, probably, but then again, at 83, he isn't getting any younger..
  13. D

    Thesis Writing: Is Crying Typical for Advisors?

    Much better to have a strict thesis advisor with high expectations and well thought out goals than one who doesn't set any specific goals for you, expecting you to basically guide yourself with guesses down the road.. The example quotes you listed would only make a sensitive baby cry. However...
  14. D

    Snagging incoming Math Students

    I think glorifying some of the encryption techniques used in internet and security as well in communication would be really cool. A poster about what people did with stuxnet and flame on the cryptography end explaining how it works and how it enabled access to computers would be really cool...
  15. D

    Temperature generated from crushing metal into powder

    Say I have a brittle metal that I start smashing up with a hammer to crush it into a powder. How do I know how much the material's temperature will rise from this if I assume an average repetitive force crushing onto 5 grams of the material?
  16. D

    LaTeX A light, readily available glue, that can adhere metal to latex.

    Actually, I implied the opposite when I expressed my lack of materials knowledge.
  17. D

    LaTeX A light, readily available glue, that can adhere metal to latex.

    Hello, I have next to no materials specific knowledge, so I was hoping someone here could guide me in the right direction. I'm looking for a spreadable adhesive that has the following properties listed by priority: 1. Can adhere metal to latex or other rubber-like materials. 2...
  18. D

    MATLAB Matlab: Butterworth Filter Bode Plot

    I've had to do this without the tf toolbox before. Why can't you just plot the magnitude and phase of the function with a frequency variable f = 0:1:100000 or whatever range you're interested in, where s = f*i*2*pi?
  19. D

    I'm 28 and wanting to make a start in physics studies.

    It depends on where you live to find an available first course in physics, but many of them are offered in such a way as to omit calculus and differential equations. You basically should be good at algebra and trigonometry to make it through introductory physics courses easily. That's like 2...
  20. D

    I'm young and my hair is thinning

    My roommate was already on his way to being bald when we entered college at 18. He ALWAYS wore this baseball cap, no matter what the situation. It was so out of place that it became obvious to anyone that he was hiding his baldness. I don't blame him for being insecure about it, but he didn't...
  21. D

    What's Smart and What's Dorky?

    Its ok. You will probably not even still know most of the people in your class in 5 years, so don't feel too bad about it. That's really cool that your teacher has discussions with you; you should keep that up and see if there's other people like him in interest groups/clubs. Also, don't be...
  22. D

    What's Smart and What's Dorky?

    Honestly, I have no ill feelings towards people who innocently speak out or try to assert their knowledge for the rest of the audience (who did not ask or expect to hear from them), but I always do feel a bit embarrassed for them. Its often one of those eye roll moments where the person comes...
  23. D

    Is there a delay of 1 or 2 seconds in generation of back emf in a dc motor

    Back EMF is directly dependent on the angular velocity of your motor's rotor. Whatever rate your rotor is rotating at in any instant of time will directly relate to the back EMF generated at that instant of time. The time for your motor to reach a given angular velocity depends on the...
  24. D

    Liquid being pushed out of a nozzle - how to calculate it?

    I don't think it does matter either. This would be a different story if the liquid were compressible, which is usually assumed not to be. You can see that no matter the shape of the inside of the plunger, the dV/dx of the mass inside the tube will be the same, because the other side of the...
  25. D

    Calculating coefficient of friction

    Yes see here: he explains why friction is independent of surface area (and hence independent of pressure).
  26. D

    Calculating coefficient of friction

    μ has no units. The pressure and weight are related to the normal force. μ is related to the materials, and it tells the relation of friction force to normal force, depending on the material.
  27. D

    Calculating coefficient of friction

    Hmm, I don't know how to model friction as a function of surface material/microscopic geometry. That is a bit more advanced I think.
  28. D

    The Classic Physics Problems.

    Another one that I have encountered in multiple intro physics courses is the escape velocity problem. Also the velocity needed to acquire orbit (variation was shooting a cannon ball fast enough that it would travel around the Earth and hit you in the back before falling enough to hit the...
  29. D

    The Classic Physics Problems.

    Another good one with capacitors is shorting 2 capacitors in parallel and determining their steady state voltages that shows an apparent violation of the conservation of energy/charge. It is referred to at least in my intro...
  30. D

    The Classic Physics Problems.

    The plate capacitor derivation, including the small gap to plate area approximation.
  31. D

    Calculating coefficient of friction

    You should measure the friction at several constant velocities (no acceleration) so that you can can extract the coulomb and viscous friction components. The offset will be your coulomb friction (constant for all velocities), and the increase in friction that is proportional to speed will be...
  32. D

    Inrush current limiting for inductive load

    Couldn't you put capacitance on the primary input to supply the inrush current?
  33. D

    Turning FETs off in presence of AC signal at Drain or Source

    I'm not sure if a resonant switch would help or not, as they are designed to use resonance to turn on. But it sounds like you need some kind of dummy reactive load or a resistance in series with your switch to impede the AC signal. I'm just trying to offer shotgun approach to your problem...
  34. D

    Turning FETs off in presence of AC signal at Drain or Source

    Are you really using 2 NMOS in series just so that their body diodes oppose each other or did I read your description wrong? When you say high load and light load, do you mean in terms of current draw or current resistance? The bottom FET should never turn on as its Vgs (-5V) is always less...
  35. D

    What's Your Philosophy of Mathematics?

    Well, I only use human computation as the example. I am talking purely computational in the generic sense, like a Turing machine. A computer has no mind or existence, it is an object, and yet it can compute math based on what the laws of the universe allow it do. It might take infinitely long...
  36. D

    What's Your Philosophy of Mathematics?

    I never thought about the symmetry and that is something I don't know much about, as it goes deeply into theoretical physics. It definitely does sound compelling to my layman ears tho :P In another thread I thought of the negative roots problem as a type of computational efficiency. You have...
  37. D

    Duty Cycle and Frequency of PWM: Explained

    I think you will get different results, but 50Hz and 100Hz might not be a significant change. That was my experience when I played with frequency on my motor controller. When I increased frequency to a certain point, my motor became less efficient. The thing is that if you have a closed loop...
  38. D

    PF Photo Contest - Too cute (9/8-9/14)

    Scout is so small that her arm fits in the space between tiles.
  39. D

    New species of monkey discovered with creepy face

    "And adult males have a huge bare patch of skin in the buttocks, testicles and perianal area" I think the authors spared the monkey some embarrassment by only showing his face.
  40. D

    Duty Cycle and Frequency of PWM: Explained

    The motor's inductance and its mechanical friction and inertia acts like a low pass filter, and so if your frequency is too high, the majority of the energy will be dissipated as heat. You still want it high enough that only the DC component of your PWM signal gets through. If you PWM a low...
  41. D

    What's Your Philosophy of Mathematics?

    What about mathematical equations that possesses both solutions that are grounded in the physical world and solutions that would seem impossible physically? There are solutions to equations that give positive and negative energies for example, and we simply ignore/throwaway the negative roots...
  42. D

    Physics is now becoming metaphysical

    I don't think you should say physics is becoming metaphysical. Physics is very specific in what it is used for and what it can explain. It should be completely objective. Any interpretation we make of it could be metaphysical, but that doesn't mean physics is becoming metaphysical.
  43. D

    Consciousness and the Perception of Time

    With reference to the above 2 posts: couldn't the way our brains perceive time be related to how fast we can process information? Similar to the sentiment that a millisecond is a lifetime to a computer. Could adrenaline increase the number/performance of neurons used to process what you're...
  44. D

    Consciousness and the Perception of Time

    That is what I was getting at too. I think OP was going in the wrong direction to make such bold and general claims about the relationship between time and the concept of change, to where it sounded like more of a philosophical viewpoint than a scientific one. Time is only one specific piece...
  45. D

    Consciousness and the Perception of Time

    Did he ever measure a beating of 40 hz in some way?
  46. D

    Consciousness and the Perception of Time

    Not trying to attack your premise, and I don't know enough about this subject to say its right or wrong. I just thought I'd point out some examples that came up as I read these sentences: You can have change without using time to quantify it. The colors across my screen change as I vary...
  47. D

    Refreshing stuff - transfer function

    That transfer function result is the same that I got :)
  48. D

    Refreshing stuff - transfer function

    You are already there when you define s as s = jw. There is actually a real part too (s = jω + σ), but the sigma is ignored.
  49. D

    Refreshing stuff - transfer function

    Hello, Assuming your Y and U functions are voltages, then your Y function is incorrect for starters. You have equated your Y and U voltages to resistances, which is an incorrect approach (it doesn't make sense to have volts on the left side and ohms on the right side). You got steps 1 and 2...
  50. D

    Looking for Analog to PWM signal -

    Oh I see, then you'd definitely want to buy something already made or refine your own design a lot. I'd say just use a modern signal generator, but that is not cheap itself. If miss-operation would result in disaster, I think this forum is not the right place to find your answers since someone...