For Questions That Don't Merit Their Own Thread

[p1t1o]

34 minutes ago, peadar1987 said:

At the moment, it's filling a vehicle with portable storage and delivering it directly: https://what-if.xkcd.com/31/

As Randall says, great bandwidth, lousy ping.

If you don't want to rely on information storage, it will probably be fibre optics.

I feel that that would be limited by the time it would take to select and upload the content to the drives themselves, before you even load the car. But heh, cool. XKCD is smart.

[RainDreamer]

Hmm, then let's say you only have merely fraction of a second to transmit your message, what method of information transmission would you use? Only information density is important here.

I am thinking of a scifi story where FTL communication is made using enormous amount of energy to make microscopic wormhole with exceptionally short life span, and so the transmission process can only have a very small window to send the message. They can initiate it any time, but the energy cost makes it unpractical to send rapidly. So the most efficient way of communicating is packing as much information as possible per transmission. What method of communication would be best?

Edited July 27, 2016 by RainDreamer

[peadar1987]

1 minute ago, RainDreamer said:

Hmm, then let's say you only have merely fraction of a second to transmit your message, what method of information transmission would you use? Only information density is important here.

I am thinking of a scifi story where FTL communication is made using enormous amount of energy to make microscopic wormhole with exceptionally short life span, and so the transmission process can only have a very small window to send the message. They can initiate it any time, but the energy cost makes it unpractical to send rapidly. So the most efficient way of communicating is packing as much information as possible per transmission. What method of communication would they likely use?

Well if you know when you're going to be sending, opening the wormhole and firing a pre-loaded high-density storage device through is definitely the best way to get information density.

If you can't make the wormhole big enough to transmit matter, you're completely limited to using electromagnetic radiation of some form. For packing the most information into the smallest amount of time, you'd probably be best off using a short-wavelength laser, most likely a hard X-ray laser, as I doubt gamma ray lasers are every going to be possible.

[magnemoe]

53 minutes ago, peadar1987 said:

Well if you know when you're going to be sending, opening the wormhole and firing a pre-loaded high-density storage device through is definitely the best way to get information density.

If you can't make the wormhole big enough to transmit matter, you're completely limited to using electromagnetic radiation of some form. For packing the most information into the smallest amount of time, you'd probably be best off using a short-wavelength laser, most likely a hard X-ray laser, as I doubt gamma ray lasers are every going to be possible.

Probably better to use the setup you use in high speed fiber optic with multiple wavelengths of light point at wormhole and have receiver on the other side, possible to get up to 100 TB/s then receive on the other side, this give the benefit of using very short duration wormholes if you just wanted to send some megabyte. 

For normal uses freight is good if you want to send many TB however that is more limited by cost and end point bandwidth, in this setting you just want to transmit stuff an very short distance over minimum time shooting an chip would would not give 100 GB in an millisecond for lower cost.

[Guest]

Do gases expand when ionized?

Let's say you have a 1 cubic meter balloon filled with Helium at 273K. We then run a high voltage current through it, turning the Helium into a plasma. Should the balloon expand?

[p1t1o]

6 hours ago, Aperture Science said:

Do gases expand when ionized?

Let's say you have a 1 cubic meter balloon filled with Helium at 273K. We then run a high voltage current through it, turning the Helium into a plasma. Should the balloon expand?

No matter which way you cut it, you wont be able to do that without dumping some heat into it, it will expand.

[RainDreamer]

Going to ask a possibly sensitive question: currently, the NATO base in Turkey contains 50 B-61 hydrogen bombs. If all 50 of them detonated, how big would the explosion be? 

I just want to know the effect, not how or why or whatever make it happen. No politics or anything.

[peadar1987]

4 hours ago, RainDreamer said:

Going to ask a possibly sensitive question: currently, the NATO base in Turkey contains 50 B-61 hydrogen bombs. If all 50 of them detonated, how big would the explosion be? 

I just want to know the effect, not how or why or whatever make it happen. No politics or anything.

Well its maximum yield is about 340kt, so the total yield would be 17Mt. A bit of digging about the B-61, and it appears as though the unboosted primary has a yield of about 300 tonnes, so the yield of the device is primarily due to fusion.

The excellent website NUKEMAP can do the rest: http://nuclearsecrecy.com/nukemap/?&airburst=0&casualties=1&humanitarian=1&fallout=1&ff=1&fallout_angle=47&fallout_rad_doses=1,10,100,500,1000&linked=1&kt=17000&lat=36.9952584&lng=35.422839&hob_ft=0&zm=10

Estimated 800,000 fatalities due to the explosion, and a further 460,000 injuries. 

As for fallout, the central part of the plume (the darkest orange) corresponds to a dose of 10Sv/hour (if you are unprotected). a dose of 5Sv is usually lethal. Fallout usually decays fairly quickly. After 48 hours it is about 1/100th of the initial dose rate. About 700,000 people live in a zone with a fallout dose rate of 0.1Sv/hour. These people are going to have a real risk of developing problems from the fallout before it decays.

Of course, it's incredibly unlikely all of the bombs will detonate at once. Nuclear weapons just don't do that. They're very precise pieces of kit, it one goes off, it will most likely blow the other ones to pieces without causing a nuclear explosion.

If just one of the bombs was to explode, you would have a situation more like this:http://nuclearsecrecy.com/nukemap/?&kt=340&lat=36.9952584&lng=35.422839&airburst=0&hob_ft=0&casualties=1&humanitarian=1&fallout=1&ff=1&fallout_angle=47&fallout_rad_doses=1,10,100,500,1000&zm=12

Fatalities of around 50,000, with about 167,000 injuries. About 20,000 people live in the dangerous fallout zone.

With a higher proportion of fission yield, fallout is higher, but initial fatalities are far lower, due to a smaller radius of third degree burns.

[DDE]

On ‎20‎.‎07‎.‎2016 at 1:18 AM, Duski said:

Oh, I thought the F9 second stage did all the rendezvous burns and Dragon is deployed then grappled on board basically. But gee, using those tiny draco engines? Well looks like i'm going to have a lot of patience for the Dragon i'm using

FYI the four prograde RCS motors on the Soyuz have higher Isp than the central engine, so on one occasion when the Progress needed to keep enough dV round because it was going to take Mir for a swim, they went for those over the main engine, the whole way.

On ‎24‎.‎07‎.‎2016 at 4:10 PM, PB666 said:

Problem is not thevdrive system, its the survival systems for manned flight. 

With a torchship like Orion you can really cut down on travel time using more energetic trajectories. Say, less than a year roundtrip, then you're in the realm of the long-term missions on Mir. Add the possibility of full-on armour, and you're off!

[RainDreamer]

A question that would be fitting for xkcd "What if?":

What would happen if we have a radio transmitter with enough power to send radio waves with enough energy to reach the whole world without any relay (meaning enough juice to penetrate the  whole earth)?

[p1t1o]

1 hour ago, RainDreamer said:

A question that would be fitting for xkcd "What if?":

What would happen if we have a radio transmitter with enough power to send radio waves with enough energy to reach the whole world without any relay (meaning enough juice to penetrate the  whole earth)?

This is actually already possible, it can be used to communicate with submarines, for example, although the data rate is staggeringly low. Essentially, the wavelength is so long that a substantial portion of the globe can be used as part of the antenna, if I understand correctly.

https://en.wikipedia.org/wiki/Very_low_frequency

https://en.wikipedia.org/wiki/Extremely_low_frequency

https://en.wikipedia.org/wiki/Super_low_frequency

 

Sorry if you were expecting the standard XKCD answer of "effects resemble a nuclear explosion"!

Edited August 3, 2016 by p1t1o

[RainDreamer]

Indeed I was expecting it to be powered by a small sun and would essentially microwaved the planet.

Well, the more you know~

[p1t1o]

I suspect it might be impossible at shorter wavelengths, regardless of power. If the depth of rock/iron doesn't effectively block 100%, the cloud of plasma now surrounding you will...

Of course, once most of the planet is an expanding cloud of plasma, it will rapidly move out of the way allowing you to send your signal...

[RainDreamer]

How does these things work?

 

A co-worker of mine is thinking of buying it, and I feel like these kinds of things are scams. How are nitrates in food usually tested, and does it matter?

Edit: for some reason the video is not what it is supposed to be.

The thing I want to verify are the nitrate tester from Soek.

Edited August 6, 2016 by RainDreamer

[p1t1o]

On 8/6/2016 at 10:35 AM, RainDreamer said:

How does these things work?

 

A co-worker of mine is thinking of buying it, and I feel like these kinds of things are scams. How are nitrates in food usually tested, and does it matter?

Edit: for some reason the video is not what it is supposed to be.

The thing I want to verify are the nitrate tester from Soek.

It uses a probes that you have to stick into the food. The sensor will use some kind of ion-specific material (an ion-exchange resin, a special type of glass etc.) in the electrode to select for the ion of interest - nitrate in this case. The material chosen will have specific permeability for your ion, different materials having different properties and trade-offs. Different materials will have different specificities for different ranges of ions, and accuracy can be heavily affected by the environment in which it is being used. After the ion-specific electrode is your common-or-garden voltmeter which will be calibrated to give you an ion concentration. I am unable to tell the quality or reliability of the sensor, it may be a high-quality sensor or it may be a glorified "E-meter".

Nitrates in food do have health effects, and can be of interest, it can be a contaminant in drinking water supplies, but is usually of interest when considering so-called "organic" foods. Nitrates are a factor when it comes to nutritional health, but as with all topics of food/diet, beware of misinformation and hype, especially around the advertisement of various "organic" foods/diets. For example there exist similar sensors advertised as being able to "detect if your food is organic", however nitrate content can be elevated/reduced by many factors other than fertiliser use.

[TheDestroyer111]

Emm... Why do airbreathing jet engines "compress" air at all? According to @Brotoro,

Spoiler

A turbojet burning a monopropellant or bipropellants in a vacuum (without air for the compressor to push into the combustion area) will end up expelling exhaust out of both the rear and FRONT of the engine. The wall of compressed air from the compressor serves as the front of the combustion chamber, which would be missing in a vacuum.

But why? Why don't airbreathing jet engines use a typical rocket engine combustion chamber, instead of having to make one's life harder and the engine itself less efficient with a compressor (because running the compressor sacrifices some of the thrust that goes into the turbine)? Although a compressor can pull more air into the engine, you don't need that much air anyway, and you can just make a bigger intake, or push the plane with your hands electricity powered wheels before starting up the engine.

[shynung]

@TheDestroyer111 Because compressing the air enables the engine to burn more fuel for a given size of combustion chamber.

Rocket engines typically burn their fuel with pure oxygen, in liquid form, often referred to as LOX. This liquid is quite dense, so we don't need much of it, in terms of volume, to burn a given quantity of fuel. In stark contrast, atmospheric air not only contains 1/5th oxygen rather than the pure version used in rockets, it's also in the gaseous form, which is at a much lower density. This means less oxygen is available for combustion at its current state, which is why a compressor is used to compress the atmospheric air to gather enough oxygen to support combustion.

As a comparison, this is an acetylene welding torch before the oxygen line is opened (burning with atmospheric oxygen):

And this is the same torch, after the oxygen line has been opened (burning with compressed pure oxygen gas):

The blue flame indicates higher temperatures, therefore more energetic combustion. The same principle applies in gas turbine engines.

[StrandedonEarth]

The more air you pull into an engine (any engine, even a car engine), the more fuel you can add to burn. With a jet engine more air equals more reaction mass to push out the back. Also, more compression means greater efficiency, as the combustion products will expand more. Finally, in the thin air at high altitudes, compression is needed even more just to get enough oxygen into the engine.

Also, what shynung ninja'd me with.

[TheDestroyer111]

@shynung @StrandedonEarth But why? Aside from sucking in air (which becomes irrelevant at higher speeds, even below mach 1), the compressor cannot increase the amount of air that enters the engine. With your example for acetylene torches, you can just mount five times bigger/more effective air intakes. Also, a typical turbojet's combustion chamber has a bigger diameter and more volume than the compressor. And one more thing. If the compressor was actually used for sucking in air as its main purpose, it would not have stator blades.

[shynung]

1 hour ago, TheDestroyer111 said:

@shynung @StrandedonEarth But why? Aside from sucking in air (which becomes irrelevant at higher speeds, even below mach 1), the compressor cannot increase the amount of air that enters the engine. With your example for acetylene torches, you can just mount five times bigger/more effective air intakes. Also, a typical turbojet's combustion chamber has a bigger diameter and more volume than the compressor. And one more thing. If the compressor was actually used for sucking in air as its main purpose, it would not have stator blades.

A compressor does increase the amount of air entering the engine. This it does by compressing the incoming air. Compressed air holds more masses of air than air at atmospheric pressure, hence more amounts of air.

A turbojet combustion chamber is larger than the compressor because the chamber is meant to hold an expanding cloud of hot combustion gases. A compressor does not need that volume because it runs counter to the compressor's purpose: compressing intake air.

Also, stator blades in compressors are meant to improve compression efficiency. A compressor without stators would simply increase the velocity of the fluid, without increasing much pressure. Stator blades convert the fluid velocity into pressure, while also redirecting the fluid to prepare for the next compressor stages. Without stators, compressors would act as ducted fans.

Edited August 14, 2016 by shynung

[TheDestroyer111]

10 hours ago, shynung said:

A compressor does increase the amount of air entering the engine. This it does by compressing the incoming air. Compressed air holds more masses of air than air at atmospheric pressure, hence more amounts of air.

A turbojet combustion chamber is larger than the compressor because the chamber is meant to hold an expanding cloud of hot combustion gases. A compressor does not need that volume because it runs counter to the compressor's purpose: compressing intake air.

Also, stator blades in compressors are meant to improve compression efficiency. A compressor without stators would simply increase the velocity of the fluid, without increasing much pressure. Stator blades convert the fluid velocity into pressure, while also redirecting the fluid to prepare for the next compressor stages. Without stators, compressors would act as ducted fans.

Don't get me wrong, I don't try to be annoying. I just don't understand this and I want to understand, not just know it.

If the compressor didn't have suction, I don't think it would give more air than an intake without one. In my mind, I split the job of a compressor into 2 things: suction, and actual compression. If you cast a magical spell on a compressor that would make it compress air without creating any additional suction (suction with little to no compression can be created with a single ducted fan, but I can't come up with a way to disable suction while keeping compression other than a magical spell  ) do you think it would bring in more air than without the compressor itself? The compressor blades decrease true area of the intake (because they cover a part of it. so if they didnt rotate, they wouldn't help at all, but that's not what I mean).

[DoctorDavinci]

44 minutes ago, TheDestroyer111 said:

Don't get me wrong, I don't try to be annoying. I just don't understand this and I want to understand, not just know it.

If the compressor didn't have suction, I don't think it would give more air than an intake without one. In my mind, I split the job of a compressor into 2 things: suction, and actual compression. If you cast a magical spell on a compressor that would make it compress air without creating any additional suction (suction with little to no compression can be created with a single ducted fan, but I can't come up with a way to disable suction while keeping compression other than a magical spell  ) do you think it would bring in more air than without the compressor itself? The compressor blades decrease true area of the intake (because they cover a part of it. so if they didnt rotate, they wouldn't help at all, but that's not what I mean).

I refer you to this: https://en.wikipedia.org/wiki/Gas_turbine_engine_compressors

Should help you understand how it works

[TheDestroyer111]

I think I'll have to ask the physics teacher - discussing it IRL is much more effective if you want to understand, not just know. (the article you provided me with is a little crappy  ) For now you can assume the question is answered (if you want, you can ask another question in this thread).

[K^2]

On 8/14/2016 at 0:51 PM, TheDestroyer111 said:

If the compressor didn't have suction, I don't think it would give more air than an intake without one.

Compressor actually does several things. The way in which it improves air flow is by reducing ram pressure in front of the engine. Even if you simply have a pipe that narrows a bit near the back, and start carrying it through fluid/air, because of the restriction in the back, it will start building up pressure in the pipe which will reduce the flow. (Technically, so will completely straight pipe, due to viscosity.) This is similar to problem encountered by Hyperloop train and the reason why Hyperloop is designed with a huge compressor fan in the front. Without compressor, this ram pressure reduces amount of air that can flow through.

But the second part is the fact that you actually need a significant pressure increase inside the combustion chamber. That has to do with thermodynamic cycle of the engine. (Lenoir Cycle for jet engines) The higher the pressure change, the more efficient the engine. Of course, at some point, losses in the compressor exceed gains due to pressure increase. This threshold also depends on the air speed and the bypass ratio. Hence the difference between compressors on different jet engine types, starting with turbofans with giant compressors taking up most of the engine, and to the ram/scram jets that forego compressor entirely and use the ram pressure for the heat engine cycle.

Feel free to talk to your physics teacher about this, but keep in mind that they aren't necessarily versed in heat engine thermodynamics beyond the very basics of Carnot Cycle. This is the sort of thing that's only very briefly covered in undergraduate courses at university, so they aren't always expected to have learned anything about it to teach physics. If you can track down a university professor, preferably one that deals with thermodynamics, they will be able to explain it much better. Alternatively, a savvy engineer should do just fine.

Edited August 15, 2016 by K^2

[wizzlebippi]

I might be a savvy engineer, so I'll take a crack at this.  Engines work by using a heat source to cause a working fluid to expand as a means of transferring energy from fuel into mechanical energy.  The problem is most working fluids don't hold much thermal energy at useful temperatures, limiting the energy output and efficiency of the engine.  The solutions are either increasing the operating temperature or increasing the mass of the working fluid.  Increasing operating temperature usually isn't an option, at least not by enough to make a difference, due to material properties and cooling.  Increasing the size of the engine can dramatically increase energy output by increasing the volume of working fluid, but at the expense of efficiency due to difficulty heating all the working fluid.  Compressing the working fluid increases the mass being heated while keeping the volume being heated reasonable, allowing more chemical energy to be captured as heat, resulting in increased energy output and efficiency of the engine.