Thermal Expansion and Conductivity

• Related Questions

What exactly happens would absolutely 100% depend on the RF Amplifier (and VCO).In many cases though, an amplifier designed for a 900MHz centre band will have transistors that are fast enough for, let's say 1200MHz, maybe 1.5GHz. Which means at the least trying to get them to work at their designed set points at nearly three times the design frequency will have them heat up and possibly get damaged. It's not generally a great idea to try it without knowing any specifics.What's sure, though, is that putting in a 2.4GHz signal will almost certainly not get you a clean 900MHz output. There may be some 900MHz induced oscillation per chance, but it will most certainly not be clean and probably not very strong either

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When two wires touch, electrons can flow from one to the other. Is that a metallic bond?

This becomes clear with the band theory of solids:It is a collective quantum mechanical model for the solid stateIn this model it is the collective lattice of the solid to which all electrons are bound. In the conduction band of metals the electrons can move over the whole system because very little energy is needed for a bound to the atoms electron to belong to the whole lattice, just the ambient heat is enough. So for two touching cold metals the conduction band becomes easily one topology if there is no air between the surfaces. So it is not a metallic bond in the sense of a chemical bond, just a topological one .In hot wires melting the atoms at the valence level bond where the melt happened and the two wires become one

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What causes reverse leakage current in an LED?

As Horta answered, there are a few pathways for current leakage in a classical pn junction. Both phonon and photon generated carriers contribute to leakage current. Look up the derivation of the ideal diode equation. Forward bias current is due to diffusion, the exponential term. Reverse bias current , the constant term, is due to drift of generated carriers by the built in field of the junction. At equilibrium, they balance.The key here is the word "ideal". If that equation held everywhere, you could bias to negative infinity with no additional current. Other processes occur at high reverse field. These include Zener tunneling, defect assisted tunnelling, Avalanche breakdown, and dielectric breakdown. They all contribute at some point, and will cause "leakage" current. These processes aren't included in the ideal diode equation!

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2003 automaitic 2.4l dodge stratus transmission concern?

It is definitely not good for an automatic tranny to be pulled in neutral, but it doesn't mean it's automatically fried. The reason it's not good for the transmission is, the pump which distributes the tranny fluid is just behind the torque converter (in most automatic transmissions) which is attached to the engine. When the engine isn't running, there is nothing lubricating the final drive. Since the final drive is spinning while being towed, it can build up heat, which can cause damage. This shouldn't affect any of the bands or clutches, as these are not engaged at all during the tow.At this point, I wouldn't worry about it until the car is running again, but I will bet you will find there won't be an issue.

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Specific Heat of Nano Particles

The specific heat of the bulk is the integral of the specific of all the applicable energy carriers. Let us consider electrons and phonons for simplicity$$ C_v-total C_v-electrons C_v-phonons (fracpartial Upartial T_v-electrons) (fracpartial Upartial T_v-phonons)$$.Taking into account that energy distributions, we can calculate the specific heat as

$$ C_v-total fracddTint E f_FD(E)D(E)dE fracddTint E f_BE(E)D(E)dE $$Where the distributions are the fermi-dirac and the Bose-Einstein distribution. Obvioulsy, when you have a bulk material, like a solid, the density of states is modified to accommodate the overalap of the electronic states resulting in band formation. This does not happen in free particls (nano-particles e.g).

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At what temperature does water become a liquid on Mars? On the asteroids? And in a vacuum?

Water does not form a liquid at very low pressure. Here is the this phase diagram:

(image from and appears to be under the creative commons non-commercial no-derivatives)The lowest pressure at which water is liquid is that of the triple point: 273.15 K and 611.73 Pa. That pressure is about 0.006 atmospheres.Wikipedia puts the surface pressure on Mars at around 636 Pa, from which we conclude that there is just barely room for water to be a liquid in a very narrow temperature band above the Earthly freezing temperature (and even this relies on getting the full pressure quoted above which won't be true except at the lowest elevations). No asteroid has sufficient atmosphere to maintain liquid water. If you have ice and heat it, it will sublime (convert directly to vapor).

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Filament in a lightbulb, thermal radiation

The answer can be calculated by referring to band emission tables of any introductory heat transfer book. I use the heat transfer book by Incropera and DeWitt where are concept is explained and the tables given in chapter 12.Here is how its done. The fraction of total energy emitted as wavelengths from 0 to a certain wavelength $lambda$ can be obtained from the band emission table ($F_(0-lambda)$). This way the emissions from 0 to 400 nm ($F_(0-0.4mu m)$) and between 0 to 800 nm ($F_(0-0.8mu m)$) can be obtained. The difference in these two quantities gives the emission from 400 nm to 800 nm and is the required answer. The energy fractions $F_(0-lambda)$ as a function of $lambda$ and $T$ are given in the table Here $T$ 2,573 K, while $lambda$ is the upper limit of wavelength

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band / cylinder style heating element wattage calculations

The wattage is easy. First convert to SI units to make life simpler, then it's simply heat capacity (J/k/kg) * temperature increase (K) * mass flow rate (kg/s) - giving J/s, namely, Watts.The heat transfer, however, is not so simple. You have a very small contact area (the wall of a 10" cylinder) and poor contact between the gas and the wall - some texts would use the tube diameter, 4", as the characteristic length. I suspect you're going to have to massively rethink the heat exchanger to increase the contact area and reduce the characteristic length (distance the gas is away from the wall). For example, many small diameter tubes (shell and tube HX) or given it's electric, directly heated wire matrix inside the tube.Which is a much bigger topic, and not EE

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Should I be worried about my iPhone overheating?

Since you used the word "slightly", I'd say no, you don't need to be worried. Generally if your device gets heated when you doing some heavy duty stuff (for example like you said, playing infinity blade), I don't think it's a problem because in this case, most heat comes from the CPU, which has a fixed maximum power. The device is designed to withstand that power and should be able properly transfer that heat to the environment (that's one purpose of the steal band around iPhone 4).

However if you device is just doing nothing, and you feel it's hotter than usual, you may need to check and close some background programs. If it's still hot, turn off the device and see if it cools down. If not, there probably is something wrong with the battery.

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How does infrared radiation increase temperature?

Many people have the misconception that only infrared radiation creates heat. Actually electromagnetic radiation over all frequencies carries energy. The shorter the wavelength, the higher the energy.

Different elements and compounds (or molecules and atoms) have different resonant frequencies and so electromagnetic radiation of the same frequency tends to excite those particular materials, leading to heating - the absorption of the energy.It just so happens that the everyday materials we are in contact with (water in your skin for example) is resonant with infrared frequencies, and so absorbs the infrared.Why does the black pavement tend to be hotter than the white concrete on a sunny day? Because black tends to absorb a wider band of wavelengths and thus more energy.

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Using LC filter instead of RC filter in mains powered circuits

A dimmer typically works by using a triac to take only a portion of each 60Hz input power cycle. When the cycle gets chopped off abruptly by the triac this creates a pulsed power draw at the input.

The pulsed power draw will have harmonics of the 60Hz waveform in it. In order to comply with FCC regulations regarding conducted emissions a filter must be added isolate the mains power from those pulses.

So why use RC vs LC?

LC FILTER:

PRO: Dissipates less power than RC filter (so less heat)

PRO: Second order filter, which means better noise rejection

CON: May resonate if not properly damped

CON: More expensive than RC due to higher inductor cost.RC FILTER:

CON: Dissipates more power than LC filter

CON: First order, worse noise rejection

PRO: Inherently free of resonance

PRO: Cheaper than LC due to low cost resistor

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Large scale reverse transcription?

The best way for scaling up these kinds of reactions is to set up many reactions. Prepare a mastermix for lets say 20 reactions. You can pool them together, precipitate the RNA and dissolve to appropriate concentration in nuclease free water. Also, use gene specific primer instead of oligo-dT and don't add poly-A tails (poly-A does not affect the in-vitro stability of RNA).As Mad Scientist already indicated, you would not need to make DNA again from RNA. Simply take 1:2 molar ratio of your IVT template dsDNA (restriction digested) and the RNA (post IVT). Heat and anneal slowly. DNA-RNA hybrids are stronger then DNA-DNA hybrids and the former is more likely to form after annealing. You can digest the unpaired strands using enzymes like mung bean nuclease

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Why walls are blocking infrared waves? If bricks absorbs only certain infrared frequency as shown in the infrared absorption spectroscopy graph below

A clarification, as the answer by BowlofRed covers the specifics. my argument is,how can they reflect a photon if they don't absorb it.as you know infrared is absorbed by molecule which has same vibrational frequency as the incoming infrared photonThis is only part of the story of how photons interact. Absorption by certain frequencies or frequency bands is one way, but also photons can scatter elastically from the collective field of the electrons at the outer layer of the material, this is called reflection. And also compton scatter , i.e. lose some energy by kicking an electron out.So it depends on the material. Aluminum foil is very good in reflecting infrared, I use it behind a wood stove in order to keep the wall cool and reflect the heat to the room, for example.

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Why do you need to change gears in car?

Get on a mountain bike and change between gears. The same reasons apply to changing your car's gears and changing your bike's gears: you can't pedal faster than x, and you can't get away when the gears are too extreme.The point is that humans and engines operate best at a certain cadence or RPM. If the engine spins too slowly, it can't put enough power down. If it spins too fast, components will endure too much stress, overheat and break quickly. A formula 1 car can rev up to 18000 RPM, but the engine needs to be rebuilt after every race. A large truck only revs to about 2000 to 3000 RPM, and while it's pretty strong, it can't go very fast