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Physics, Astronomy & Cosmology / Re: Would a Mylar sheet with holes to allow some heat to pass prevent over-heating?

« on: 21/10/2016 08:53:22 »

Do you mean the emergency space blankets?
They also have a reflective surface which keeps heat in so it's not just conducted and convection loss that is being prevented. Also, the ones I've used tend to crackle when you move, not good for getting to sleep unless you are exhausted.

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Physics, Astronomy & Cosmology / Would a Mylar thermal blanket with holes to allow some heat through be feasible?

« on: 21/10/2016 08:06:46 »

I have heard mylar blankets can trap some 90% of your body heat. The issue being, they're so good at it, they can also cause overheating, and I understand this as the reason we don't see the material used more widely than it already is. This made me wonder, however.

Could you poke minuscule holes in the mylar, so that it only traps 85%, or 70%, or 50% of the heat? Then, perhaps, you could have overlapping layers of mylar, and a simple adjustment could let you control this?

I expect this is a stupid question, and I apologize. I don't know much about how heat radiates. The issue I see with this idea is that, say the air was at -30C, traces of that could get through the tiny holes so that it's not a matter of 50% of the heat escaping, but of 50% of your heat escaping and cold air absorbing heat as well.


If someone could please help me to understand this, I would appreciate it. Thank you.

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Chemistry / Re: Could Mussel Byssus be Processed into a Rubber-Like Material?

« on: 20/10/2016 08:47:15 »

Mussel "glue" is certainly an active area of research; scientists are looking for resilient underwater adhesives that are also non-toxic:]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3801061/

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Chemistry / Re: Could Vulcanized Rubber be Invented with Primitive Technology?

« on: 18/10/2016 11:01:24 »

I think you could use acetic acid (from vinegar) instead of formic.

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Technology / Re: How Powerful a Microwave would you need for an Effective Weapon?

« on: 18/08/2016 04:59:25 »

Some of these advanced prototype microwave weapons were tested on dry land, causing the ground water to boil and explode with almost unbelievable destruction.


Sincerely,

William McCormick

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Technology / Re: How Powerful a Microwave would you need for an Effective Weapon and Radiation-?

« on: 09/08/2016 03:12:58 »

10 KW would no doubt take out any human intruder quickly. Electronic disruption may require quite a bit less. Ionization of missiles may require quite a bit more.

I was told by someone that built microwave prototype weapons that helium was used, basically put through a flow valve in a quantity, to just maintain its presence in the aluminum horn, as it expanded and heated, in the microwave horn. To achieve much greater results from the same input power. That might be the weapon you are looking for.

Some of this fellows prototypes were capable of boiling the water off of a submarine. Which is usually the end for the submarine.

Sincerely,

William McCormick

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Technology / Re: How do you Calculate the Effectiveness of a Faraday Cage?

« on: 24/07/2016 22:58:25 »

The effectiveness of a Faraday Cage doesn't just depend on power, but also on frequency and time.
At low frequencies, the mesh can be fairly coarse, while maintaining protection.
However, higher frequencies will find their way inside through the mesh, or through seams between sections of mesh.

Joints between sections of mesh will have a maximum current carrying capacity, and will burn out if the current is maintained for too long; fortunately, lightning only continues for tens of microseconds. So duration is also important.

Note: Do not mess with aircraft - authorities jump on people who shine laser pointers at aircraft; microwave weapons will be viewed even more dimly - especially by their operators or nearby bystanders, who are likely to fry their eyeballs. High intensity microwaves are best kept inside a sealed oven.

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Technology / Re: Can an Electro-Laser use AC (Alternating Current)?

« on: 24/07/2016 22:44:22 »

What makes it difficult is that the magnetic fields associated with a changing electric current tend to push the current to a thin ring with high impedance, through the skin effect.

The skin effect is more pronounced with AC than with DC; but even rapid ramp-up of DC current is associated with very high frequency components.

According to the link below, AC has often been used as it is easier to produce the high voltages necessary to maintain a discharge path.

Another major problem with such weapons is that as soon as you ionize air with a laser, the plasma then becomes opaque to the laser, and ionization fades beyond the first point with a plasma. So you first have to generate the plasma close to the target, then focus in to extend the plasma closer to the laser before the electric current can flow. Having an electrical return path for the current would also be problematic.

See: https://en.wikipedia.org/wiki/Electrolaser#Examples_of_electrolasers

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Physics, Astronomy & Cosmology / Re: Which Electromagnetic Wave Builds Electric Charge (in Metal) the Fastest?

« on: 20/07/2016 12:32:02 »

Forks in microwave ovens are known to spark.

The breakdown voltage of dry air is about 1 million volts per meter.
Voltage differences as low as 100-200V can produce visible sparks, if the objects are almost touching.

The following website suggests that a domestic microwave over (850W) can generate electric fields inside the oven of 2000V per meter. So its not surprising that close conductors in a microwave oven can cause sparks.
http://www.astrosurf.com/luxorion/qsl-em-radiation2.htm

which electromagnetic wave builds charge the fastest/most efficiently?

I suggest any wave at over 1000V peak will produce visible sparks.
The frequency most available in homes and labs is 50Hz or 60Hz (depending on the country).
A step-up transformer will produce dramatic sparks.
Note: Do not try this at home!

Van De Graaf generators (DC) or Tesla Coils (kHz) also produce dramatic sparks, and are available in laboratories and science museums.

laser in the infrared and visible light spectrum don't build much or any charge on metal

I assume here that you are trying to emulate the photoelectric effect? (Einstein got his 1915 Nobel prize for explaining this.)

It requires several eV of energy to eject an electron from metal, so this works best with violet, ultraviolet and higher frequencies (not infra-red: not enough energy).

As soon as you eject an electron, the metal becomes charged, and then it takes even more energy to eject another electron.
So measuring the photoelectric effect is usually done in a vacuum (which also avoids buildup of insulating oxides on the surface). A circuit is used to return the emitted electrons to the metal, so a charge does not build up and halt the electron emission.

See: https://en.wikipedia.org/wiki/Photoelectric_effect

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Technology / Re: How Powerful a Microwave would you need for an Effective Weapon and Radiation-?

« on: 19/07/2016 12:44:54 »

You can get arcing inside a domestic microwave oven, with a power of around 1kW.

But to create that same electric field in a missile which is perhaps 1km away would require considerably more power, and a very large antenna.

There was a story about a phased-array radar with a peak power output in the Megawatt range (short pulses).
It was built in a pyramid-style building near a military airport, and they had to turn it off whenever planes came into land, because there was a chance that if a plane flew through the radar beam, it might trigger the explosives that fire the ejector seat.

Phased-array radars can quickly scan the entire sky to search for missiles without physically moving. Then they could focus more power in one direction to target one object.

Missiles are hard to disrupt, because they are often sealed inside a metal case - although sensors like optical, infra-red and radar sensors must be exposed to the outside world.
See: https://en.wikipedia.org/wiki/Active_Phased_Array_Radar

Another possibility is a ElectroMagnetic Pulse device (EMP). This disrupts electronics - so you don't want to set it off too close to your electronics! And military equipment is designed to withstand EMP.
See: https://en.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator

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Technology / Re: How Powerful a Microwave would you need for an Effective Weapon and Radiation-?

« on: 19/07/2016 07:15:08 »

10 KW would no doubt take out any human intruder quickly. Electronic disruption may require quite a bit less. Ionization of missiles may require quite a bit more.