For Questions That Don't Merit Their Own Thread

[AHHans]

On 5/22/2021 at 4:58 PM, JoeSchmuckatelli said:

.... It is a distinction that does not matter. 

Exactly.
In the end it may be that our idea that electromagnetic radiation consists of "photons" is deeply flawed. But for the time being it lets us predict how it behaves with remarkable precision. And that latter is the essential test for a good theory.

Edited May 25, 2021 by AHHans
grammer

[kerbiloid]

When a wave reflects from the coast, is it the same wave, or another one?

[Silavite]

Today I discovered the wonderous program which is CEA (Chemical Equilibrium with Applications), and I'm unsure as to what some of the outputs are. Here's an example of what I mean using CH₄ and O₂

Spoiler

THEORETICAL ROCKET PERFORMANCE ASSUMING EQUILIBRIUM

           COMPOSITION DURING EXPANSION FROM INFINITE AREA COMBUSTOR

 Pin =   300.0 PSIA
 CASE = _______________

             REACTANT                    WT FRACTION      ENERGY      TEMP
                                          (SEE NOTE)     KJ/KG-MOL      K  
 FUEL        CH4                          1.0000000    -74354.628    305.000
 OXIDANT     O2                           1.0000000       201.360    305.000

 O/F=    2.84947  %FUEL= 25.977576  R,EQ.RATIO= 1.400000  PHI,EQ.RATIO= 1.400000

                 CHAMBER   THROAT     EXIT
 Pinf/P            1.0000   1.7317   20.414
 P, BAR            20.684   11.945   1.0132
 T, K             3366.30  3193.75  2425.94
 RHO, KG/CU M    1.4359 0 8.8515-1 1.0277-1
 H, KJ/KG        -1199.37 -1965.02 -4837.60
 U, KJ/KG        -2639.84 -3314.49 -5823.58
 G, KJ/KG        -46470.2 -44915.3 -37462.3
 S, KJ/(KG)(K)    13.4482  13.4482  13.4482

 M, (1/n)          19.431   19.678   20.458
 (dLV/dLP)t      -1.03147 -1.02498 -1.00323
 (dLV/dLT)p        1.5813   1.4868   1.0808
 Cp, KJ/(KG)(K)    7.1015   6.4980   3.2060
 GAMMAs            1.1353   1.1348   1.1694
 SON VEL,M/SEC     1278.8   1237.5   1073.8
 MACH NUMBER        0.000    1.000    2.512

 PERFORMANCE PARAMETERS

 Ae/At                      1.0000   3.9513
 CSTAR, M/SEC               1888.4   1888.4
 CF                         0.6553   1.4285
 Ivac, M/SEC                2328.0   3063.0
 Isp, M/SEC                 1237.5   2697.5


 MASS FRACTIONS

 *CO              0.33556  0.32808  0.29846
 *CO2             0.18537  0.19715  0.24370
 COOH             0.00001  0.00001  0.00000
 *H               0.00192  0.00160  0.00035
 HCO              0.00001  0.00001  0.00000
 HO2              0.00005  0.00002  0.00000
 *H2              0.01586  0.01553  0.01575
 H2O              0.40217  0.41286  0.43751
 H2O2             0.00001  0.00000  0.00000
 *O               0.00527  0.00353  0.00010
 *OH              0.04219  0.03299  0.00388
 *O2              0.01157  0.00821  0.00025

  * THERMODYNAMIC PROPERTIES FITTED TO 20000.K

 NOTE. WEIGHT FRACTION OF FUEL IN TOTAL FUELS AND OF OXIDANT IN TOTAL OXIDANTS

What are:

• (dLV/dLP)t
• (dLV/dLP)p
• M, (1/n)
• SON VEL,M/SEC

I suspect M is related to molecular weight and SON VEL is the velocity of... something, but that's as much as I can figure.

Edited May 23, 2021 by Silavite

[JoeSchmuckatelli]

Speed of sound through the substance as a sole media?  e.g. https://www.google.com/search?q=speed+of+sound+through+steel&oq=speed+of+sound+through+&aqs=chrome.2.69i57j0l4.8164j1j9&client=ms-android-samsung-ss&sourceid=chrome-mobile&ie=UTF-8

[K^2]

36 minutes ago, Silavite said:

• (dLV/dLP)t
• (dLV/dLT)p

These are partial derivatives. I'm not entirely sure what L is meant to stand for, but first one is how volume changes with pressure at constant temperature, second how it changes with temperature at constant pressure. These are related to compressibility and thermal expansion. I suspect that L might be "limiting" as in "limiting flow," which would make sense for a rocket exhaust, but I'm kind of guessing on it.

40 minutes ago, Silavite said:

• M, (1/n)

Mass per mol.

39 minutes ago, Silavite said:

• SON VEL,M/SEC

Critical velocity of the fluid. Abbreviation for "sonic velocity".

[Spica]

15 hours ago, Silavite said:

Today I discovered the wonderous program which is CEA (Chemical Equilibrium with Applications),

If your goal is to try out all kinds of propellant combinations, you should also give RPA a look: https://www.rocket-propulsion.com/RPA/download.htm.

The 1.2.9 lite edition is free to download and use.

I've also found it a good bit easier to use than CEA for rocket engine analysis.

[DDE]

On 5/15/2021 at 2:53 PM, K^2 said:

You'd be moving a smaller mass but a larger volume. I also expect hydrogen gas to have more viscosity at the same temperature, since lighter molecules are going to diffuse faster. So you are going to have a significantly higher pressure differential at higher flow velocity, and that means a lot more energy consumed pushing the gas through the pipe, but more importantly, it will require the pumping stations to be able to handle the higher pressure and power requirements.

This might also put a limit on how far you can push gas along a given pipe, since they are rated to a specific pressure. So if the pressure differential has to be higher, some pipelines that are close to the limit might become overpressurized with hydrogen unless you subdivide the length and put additional pumping stations in the middle.

This is definitely not a case of, "We'll just swap out the gas and everything will work." Some amount of retrofitting will have to be done.

Hydrogen also leaks and ignites a lot easier, so there will be more accidents, further increasing costs. Whether that's significant, I don't know, but something to consider for sure.

Coming back to the topic, remembring @MatterBeam's blogpost, and completely disregarding the bottomless puns, how would ethanol compare as a 'drop-in' (in relative terms) pipeline-based energy transport mechanism?

Same flammability issues and, IIRC, annoyingly hygroscopic, but density should be quite sane. One problem I forsee is that the current pipeline is ultimately designed for gas and not liquid, and water hammers are... fun.

Edited May 24, 2021 by DDE

[JoeSchmuckatelli]

Is there a limit to the distance from the central star that objects in orbit should be self organized into a planetary disk? 

(numerous Kuiper Belt and presumably Oort Cloud objects are off axis.) 

Do we have enough info on exoplanets to confirm that they typically organize into a disk? 

[kerbiloid]

Having infinite time and no other stars - no.

[K^2]

6 hours ago, DDE said:

how would ethanol compare as a 'drop-in'

I think, there are a lot of issues at the terminal end. You can inexpensively retrofit just about any infrastructure running on natural gas to hydrogen, from kitchen stoves to power plants. Ethanol? Not so much. Obviously, you need completely different way of generating fuel-air mixture. You can't just squirt ethanol out of a pipe and light it. You need to create fine spray, mix it with air... That's considerably more hardware than burning gas. But there are less obvious problems too. Ethanol will contain up to about 10% water. It will literally pull it out of air, so avoiding it is exceptionally difficult. That's enough water content to start causing problems. And if your pipes were not built to withstand corrosion and now they suddenly have to, well, that's a problem. I don't think it's going to do any appreciable damage to the pipeline itself, but various control valves and thinner pipes at the terminal end are another matter entirely.

So I don't think ethanol is a viable alternative even before we get into questions of pipeline physics.

But yeah, moving something that dense will require adjustments. There might be portions of pipelines that simply aren't designed to withstand the weight of the pipe filled with ethanol. Nearly a ton to a cubic meter is no joke and adds up really fast.

5 hours ago, JoeSchmuckatelli said:

Do we have enough info on exoplanets to confirm that they typically organize into a disk? 

I don't think we have seen anything in exoplanet observation that contradicts the notion. That said, some detection methods rely on the assumption that planets mostly move in the same plane, which means you can't rely on this information too strongly. But I think most of the data comes from observations of young stars with detectable protoplanetary disk and computer modeling. The Wikipedia article on protoplanetary disk actually has quite a few pictures of the ones we've been able to image directly. And we're mostly seeing things consistent with computer models.

[tater]

 

[Admiral Fluffy]

2 hours ago, tater said:

 

That is a great quote

[ARS]

Does humans actually have an ability to 'sense' other human's attention in close proximity? (aka the sensation of being watched) Like in a lot of sci-fi movies, we can see the character said 'I think we're being watched', 'someone's watching us' and other similar remarks. I've run an experiment with some of my relatives to sit with me in a room with me facing a wall and I can consistently tell who's watching me from behind and who doesn't, even without me looking over my shoulder (this also happen without the experiment, like when I'm walking on the roadside I can tell who sets their eyes on me in close proximity). Does this kind of behavior has some explanation or it's just a myth?

[kerbiloid]

Try to suddenly cross with glance someone's wrist on the street to make let him drop a bag. (No strong intention, just lazily).

Try to breath in tact with somebody sleeping, then do it more often and then stop, to let him awake from coughing.

(obsolete) Probably no more tram tickets at your place.

The universal "Of course, this happens, what can go wrong."

Edited May 26, 2021 by kerbiloid

[SOXBLOX]

5 hours ago, ARS said:

Does humans actually have an ability to 'sense' other human's attention in close proximity? (aka the sensation of being watched) Like in a lot of sci-fi movies, we can see the character said 'I think we're being watched', 'someone's watching us' and other similar remarks. I've run an experiment with some of my relatives to sit with me in a room with me facing a wall and I can consistently tell who's watching me from behind and who doesn't, even without me looking over my shoulder (this also happen without the experiment, like when I'm walking on the roadside I can tell who sets their eyes on me in close proximity). Does this kind of behavior has some explanation or it's just a myth?

I've always wondered that. If we do, I would guess that it's a combination of sight and hearing. You see who's in what position, and then you turn away. After that, you can hear any changes in their position by changes to acoustics in the room. IDK. That's just my guess.

To test for it, I suppose we'd get a couple of groups of people and sit them down, as in your own experiment. One would be stared at, and the other wouldn't. Finding out exactly what is going on might be harder. Testing on another group, we should not let them know they're being watched, and not permit them to see the watchers, and again, compare them to a control group. If they still have the sensation, then something besides sight is involved. To test the auditory hypothesis, maybe we'd use an anechoic chamber or something?

[ARS]

43 minutes ago, SOXBLOX said:

I've always wondered that. If we do, I would guess that it's a combination of sight and hearing. You see who's in what position, and then you turn away. After that, you can hear any changes in their position by changes to acoustics in the room. IDK. That's just my guess.

To test for it, I suppose we'd get a couple of groups of people and sit them down, as in your own experiment. One would be stared at, and the other wouldn't. Finding out exactly what is going on might be harder. Testing on another group, we should not let them know they're being watched, and not permit them to see the watchers, and again, compare them to a control group. If they still have the sensation, then something besides sight is involved. To test the auditory hypothesis, maybe we'd use an anechoic chamber or something?

I found out that Wikipedia has an article about it, it's called psychic staring effect

It's mostly relied upon recognizing the specific pattern of human eyes (iris, sclera, etc.) when angled directly on you. If the target's eyes are directly set on you, the brain automatically registers the human eye pattern to alert you that you're being watched, and if the target shifts his/her field of view, even if it's just a few degrees to break the line of sight staring effect (still looking at your direction, but not directly on you) the brain stops registering the specific eye pattern and you feel not being stared at. However, the way human can still recognizing that someone's watching outside the field of view is still unclear

[kerbiloid]

1 hour ago, SOXBLOX said:

I've always wondered that. If we do, I would guess that it's a combination of sight and hearing. You see who's in what position, and then you turn away. After that, you can hear any changes in their position by changes to acoustics in the room. IDK. That's just my guess.

To test for it, I suppose we'd get a couple of groups of people and sit them down, as in your own experiment. One would be stared at, and the other wouldn't. Finding out exactly what is going on might be harder. Testing on another group, we should not let them know they're being watched, and not permit them to see the watchers, and again, compare them to a control group. If they still have the sensation, then something besides sight is involved. To test the auditory hypothesis, maybe we'd use an anechoic chamber or something?

The described test conditions are dirty, as all of you know about each other's presence.

Following a walking person is more pure.
Following somebody step-by-step, don't look at him, and don't think about him, that's well-known.

21 minutes ago, ARS said:

It's mostly relied upon recognizing the specific pattern of human eyes (iris, sclera, etc.) when angled directly on you.

If you can see by back.

[StrandedonEarth]

7 hours ago, ARS said:

Does humans actually have an ability to 'sense' other human's attention in close proximity?

Interesting question. Try this: while driving (ideally stopped, of course), watch a pedestrian.  Or another person in another car. Not one that’s going to or did cross your path, but one that will otherwise have no interaction with you or your vehicle at all. Ideally one not even looking in your direction. 

The number of people Ive observed that soon make eye contact with me is unnerving. With no motion or noise to draw their attention. It may be the psychic staring effect mentioned above, and the subconscious is good at picking important stuff out of the peripheral vision, but still...

[Terwin]

7 minutes ago, StrandedonEarth said:

Interesting question. Try this: while driving (ideally stopped, of course), watch a pedestrian.  Or another person in another car. Not one that’s going to or did cross your path, but one that will otherwise have no interaction with you or your vehicle at all. Ideally one not even looking in your direction. 

The number of people Ive observed that soon make eye contact with me is unnerving. With no motion or noise to draw their attention. It may be the psychic staring effect mentioned above, and the subconscious is good at picking important stuff out of the peripheral vision, but still...

Sounds like a combination of the subconscious recognition of eyes looking at you and drivers trying to be aware of their surroundings.(or pedestrians trying to be aware of the large metal murder machines near them)

I try to look around on a regular basis when driving so as to A) be better aware of my surroundings and B) prevent 'roadway hypnosis'.  I also tend to look around when walking if I hear vehicles near-by.

 

[JoeSchmuckatelli]

8 hours ago, ARS said:

Does humans actually have an ability to 'sense' other human's attention in close proximity? (aka the sensation of being watched) Like in a lot of sci-fi movies, we can see the character said 'I think we're being watched', 'someone's watching us' and other similar remarks. I've run an experiment with some of my relatives to sit with me in a room with me facing a wall and I can consistently tell who's watching me from behind and who doesn't, even without me looking over my shoulder (this also happen without the experiment, like when I'm walking on the roadside I can tell who sets their eyes on me in close proximity). Does this kind of behavior has some explanation or it's just a myth?

Short answer is 'yes'. 

 

Give me a bit for references

- basics, before I continue: it is actually part of your visual sense - you can spot the one person in a crowd that is looking at you, even if they are far away.  Your brain is working on a variety of levels and has evolved for survival - so if a pair of eyes are focused on you within your field of view - you will sense that. (1 person in a crowd of 100... You will identify that person) even if you are not immediately cognitively aware that you saw a potential threat (or mate) you will be subconsciously cued to look again for the individual and will most likely correctly identify the 'starer'. 

 

You will not - despite what some may say - 'feel a tingle' if someone outside of your field of view is looking at you (psychic gaze sense).  The brain does not work that way. 

On the other hand, if you have a crowd in front of you, and someone behind you is oddly focused on you - you can pick up clues from the crowd's behavior that will direct you to look behind you for a threat 

 

If you can find the full episode (and correct episode) Brain Games did a piece on this several years ago - same episode talks about proprioception, vestibular sense and others 

 

Edit - having spent a minute googling, there is a lot of utter horse pucky out there on this and other 'psychic' subjects (people so want to believe).  The subconscious 'sense' that I describe is actually supported by scientific research - but good luck finding it casually.  I hope the info I gave you is helpful if you want to keep digging. I don't have the patience to debunk the 'faith' of the internet psychic crowd and the pseudoscience that clouds actually true things 

Edited May 26, 2021 by JoeSchmuckatelli

[DDE]

2 hours ago, kerbiloid said:

The described test conditions are dirty, as all of you know about each other's presence.

Following a walking person is more pure.
Following somebody step-by-step, don't look at him, and don't think about him, that's well-known.

Off-topic

Spoiler

 

 

[TheSaint]

1 hour ago, JoeSchmuckatelli said:

Short answer is 'yes'. 

 

Give me a bit for references

- basics, before I continue: it is actually part of your visual sense - you can spot the one person in a crowd that is looking at you, even if they are far away.  Your brain is working on a variety of levels and has evolved for survival - so if a pair of eyes are focused on you within your field of view - you will sense that. (1 person in a crowd of 100... You will identify that person) even if you are not immediately cognitively aware that you saw a potential threat (or mate) you will be subconsciously cued to look again for the individual and will most likely correctly identify the 'starer'. 

 

You will not - despite what some may say - 'feel a tingle' if someone outside of your field of view is looking at you (psychic gaze sense).  The brain does not work that way. 

On the other hand, if you have a crowd in front of you, and someone behind you is oddly focused on you - you can pick up clues from the crowd's behavior that will direct you to look behind you for a threat 

 

If you can find the full episode (and correct episode) Brain Games did a piece on this several years ago - same episode talks about proprioception, vestibular sense and others 

 

Edit - having spent a minute googling, there is a lot of utter horse pucky out there on this and other 'psychic' subjects (people so want to believe).  The subconscious 'sense' that I describe is actually supported by scientific research - but good luck finding it casually.  I hope the info I gave you is helpful if you want to keep digging. I don't have the patience to debunk the 'faith' of the internet psychic crowd and the pseudoscience that clouds actually true things 

All of which is useless if you are walking around looking at your phone! (Personal pet peeve of mine.) Gotta keep your head on a swivel.

[kerbiloid]

2 hours ago, JoeSchmuckatelli said:

Edit - having spent a minute googling, there is a lot of utter horse pucky out there on this and other 'psychic' subjects (people so want to believe).  The subconscious 'sense' that I describe is actually supported by scientific research - but good luck finding it casually.  I hope the info I gave you is helpful if you want to keep digging. I don't have the patience to debunk the 'faith' of the internet psychic crowd and the pseudoscience that clouds actually true things 

A typical Psi Corps explanation.

[JoeSchmuckatelli]

32 minutes ago, kerbiloid said:

A typical Psi Corps explanation.

Shhhhh.  I'm trying to stare at the goats. 

 

[kerbiloid]

1 minute ago, JoeSchmuckatelli said:

Shhhhh.  I'm trying to stare at the goats. 

 

People on the bus stop are better.  You can stare at them for an hour, they can see you, but they will stay still because they don't want to skip the bus.