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That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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General Science Thread
#817989 - 08/10/16 05:49 PM (8 years, 4 months ago) |
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For general science discussion, questions, or thoughts that you guys have but don't want to devote an entire thread to...just throw it in here and we can talk about it a little.
Please keep the dicussion polite, we can joke around without turning into a shit show.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: Magash]
#817999 - 08/10/16 09:04 PM (8 years, 4 months ago) |
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Haha he's a trip, that's for sure.
But it did get the brain juices flowing, and reminded me just how much I love science-related discussion. I'm fine with a little poking fun at each other, but I posted it in the smoke lounge in the hopes that we can get something going without worry about the feeble-minded insults that some threads quickly deteriorate into.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: Stoneth]
#818016 - 08/11/16 09:08 AM (8 years, 4 months ago) |
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Yea, the main limiting factor to desalination is energy costs.
Chemical, they actually do use reverse osmosis (membrane desalination) in many new plants through out the world, as it s currently the most efficent desalination process.
A other succesfully implemented method is to vaporize the water under a vacuum, using rhe waste heat from a local power plant. While the efficiency of the distillation process is terrible, the fact that you are using waste heat from a power plant (that was going to be generat ed and wasted anyway) kinda makes up for it.
With membrane desalination (reverse osmosis), a membrane acts as a molecular filter, and dirty water is pumped across the membrane. This requires that some part of the "dirty water" be diverted away from the membrane, in order to keep the dirty side from acculumating too many salts (the higher the difference in salt concentration across the membrane, the harder it is to pump the dirty water across it). So any places where water is very scarce would have some difficulties sacrificing the water needed to keep the membranes clean.
Even the most efficient membrane designs bottom out at about 2kWh/m3 of water, with most operating plants in the 6 - 17 kWh/m3. This is, at best, 10 times the maximum energy requirements for freshwater capture, treatment, and pumping.
Additionally, any solid salts obtained from the process are water soluble, and placing them in the ground would result in poisoning of clean groundwater supplies. Although, the salts could possibly be uses for seasoning (sea salt), road salts, and certain uncommon metals such as manganese, magnesium, and uranium could be further refined from the waste minerals. There is definitely some potential for reclaiming billions of years of natural mining (erosion).
I've always thought that the extremely dry desert regions near certain coat lines of Africa and South America could be utilized for slow but steady solar distillation, as the lack of rain in the atacama desert would prevent too much spread of waste salts and there is little to no interupption in the supply of solar energy. But the cost of construction, and the potential piping system needed to pump the water inland would vastly outweigh the savings in energy costs.
It's definitely an interesting topic, and one that's quickly becoming much more important now that water scarcity is becoming a bigger problem.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: Magash]
#818019 - 08/11/16 10:42 AM (8 years, 4 months ago) |
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Is that colloidal silver in your sprays?
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Oh I gotcha, and yea that's a great way to constantly generate drinking water and store it for future use without risking significant losses from evaporation.
I can't see any problems with doing that besides the risk of accidental release of contaminates or microbes into a large aquifer...but then again that risk is already present when you start poking wells into an aquifer.
That would also work extremely well in high elevation, desert location for solar distillation. Once the seawater is pumped into surface ponds covered by a clear material (glass or plastic). The clear panes or sheets act to trap the water vapor that forms, and are tilted towards a collector system, such that water condensing on the inner surface drips down into the collection system. The collection system could act like a sewer, directing condensate (clean water) by gravity to a single well. This would allow the clean water to just feed the aquifer below via gravity, as it is created, and the depth of the well pipe would provide the pressure needed to drive fresh water into all of the aquifer volume.
Then, anyone living above the aquifer could just tap into it, rather than running crazy long piping systems from the desalination plant.
That's a pretty solid idea man! Sounds like a feasibility study might be the next step.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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That's actually where I've seen it before too, a way to reclaim water from say a disgusting mud-puddle, cactus (or really any plant material), or even your own urine.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: drawde]
#818036 - 08/11/16 06:36 PM (8 years, 4 months ago) |
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Oh yea, you definitely need to make sure that the land for the solar desalination plant would have to be a barren wasteland in order to justify the magnitude of that kind of construction project.
For any other ecosystem, you would have to try and optimize the maximum water production while minimizing impacts to local marine and terrestrial ecosystems (in which case, a combined power/distillation plant or membrane plant would be the best choice). We need water, but not to the point that we set the world any further off balance, it kinda defeats the point.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
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Re: General Science Thread [Re: poor boy]
#818043 - 08/11/16 08:18 PM (8 years, 4 months ago) |
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Adenosine and Melatonin
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
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Re: General Science Thread [Re: Data] 1
#818046 - 08/11/16 08:36 PM (8 years, 4 months ago) |
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But really, adenosine builds up as a natural byproduct of brain activity, which binds to adenosing receptors, causing vasodilation (lower blood pressure), and fatigue. Caffeine blocks these receptors, and thus fights fatigue (and causes vasoconstriction).
As the light levels go down at night, melatonin is produced in the brain, which is part of the circadian rythym that sigals the onset of sleep.
Production of melatonin is halted in the presence of blue light, which is why it's a good idea to put away cell phones and tablets before bed. For those people that have trouble sleeping or are suffering from jet lag, melatonin supplements are available to help reset the circadian rythym and as a sleep aid.
As to why we require sleep, there are tons of theories, and to be honest there are probably a ton of different things going on during sleep.
For instance, it's thought that larger, more active brains (such as our own) use sleep as a time to increase brain permeability, such that waste products that build up during the day can be washed away more completely, in order to get the brain chemistry to a very reliable baseline prior to starting back up with heavy activity during waking periods. Another theory is that sleep allows the brain to process through the days experiences, categorize, and burn high-priority stuff into longterm memory. Maybe it's all of the above, combined with the fact that most animals are evolved to survive better when active either during the day or during the night, because it's very difficult to do both without becoming incredibly inefficent...so by crawling into a safe place and staying quiet and still for the part of the day when we are most likely to die helps to increase our chance of passing on our genetics, and thus sleep evolved as a natural advantage for most animals.
That's all I've got
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: poor boy]
#818048 - 08/11/16 08:37 PM (8 years, 4 months ago) |
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Quote:
poor boy said: I stopped taking mel. I dont like the dreams.
Same here, shit gets crazy if I take it before bed.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: poor boy] 1
#818063 - 08/12/16 06:50 AM (8 years, 4 months ago) |
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Quote:
poor boy said: Hows about this one...
A mirror reflects all color and light, correct? Then why is the color of the mirror silver?
Silver isn't really a color, since you can't make it with any of the primary colors. Silver or "metallic" describes the way that the light is reflected.
Reflection happens when materials absorb incoming photons, and immediately re-emit photons back out into the surroundings. The structure and general optical properties of the material determine how this is done. For instance, in a material that is a certain color, only certain wavelengths are efficiently re-emitted, while the rest of the incoming photons are converted to heat in the material.
In silvery/metallic or white materials, almost all incoming photon energy is re-emitted. The difference between white and metallic is the depth of interaction.
Most uniformly white substances are partially transluscent, i.e. they allow light to penetrate many hundreds of atoms (or more) down below the surface. This allows the photons to be absorbed and re-emitted many different times on its way into and then back out of the material, much like a pinball bounding around a pinball machine. This ultimately randomizes the paths of the exiting photons, and causes a loss (or random dispersion) of any information that the photons were carrying when they first arrived. This results in a uniform white light, without an semblance of reflected images. Optical properties of certain materials (ie not maintaining the original velocity (direction) of the photon during absorption/emission) amd surface properties (very rough surfaces) will enhance this dispersion effect.
Metallic surfaces, on the other hand, only allow penetration into the first few atomic layers of the surface, greatly reducing the randomization of information in the photons. This results in a clear image of the source of the photons in the surface, which if given a color based purely on the wavelengths of light reflected, would classify as white...but because it doesn't look like what we all normally consider to be the color white, we call it silver or metallic.
As a final note, mirrors dont reflect all light, just a large majority of visible light. This is why if you place two mirrors so that they are facing each other, the infinite series of images created seems to fade off into a green haze. The glass and metallic backing are absorbing a small portion of the photons each time they bounce off the mirror, and the glass absorbs less green light than other wavelengths, so the last few reflections are the last bit of green light that hasn't been absorbed yet.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
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Quote:
Chemical Addiction said: Hey agmotes, what do you think it will take for us to reach other planets in the "goldilocks zone" and possibly find other life, or just to explore beyond our front door.
I believe it will take the death of this planet before we allocate the time/resources to figure out how traverse space. This idea first came to me when I saw a bumper sticker about strip mining. I thought "maybe strip mining can be a good thing" For the human race anyways not the millions of other lifeforms here.
We spend time/resources and brain power researching thimgs that don't really progress the race of man just distract them or makes them feel pretty. Once this planet is irredeemable we won't be studying new cosmetics, or how to use advertisement to sell product, we would focus on the survival of the species.
I hear ya, and you're right, it may take something crazy like a mass die-off of a significant portion of the world population, the discovery of life elsewhere (especially intelligent life), or a partial collapse of a major portion of the world biome in order to shake people's heads out of their asses.
We also have to remember that, with the exception of solar energy (which is still not a viable solution), we only have access to finite energy sources (fossil, nuclear, and geothermal being the larest and easiest to harness in large quantities. If we piddle around wasting the large energy stores, and run out of them prior to development of solid space travel technology, then we will be stuck wasting time trying to develop a technology that is power hungry, has unique chemical and physical requirements, all on the scraps that are left over after we use up all of the rare metals and semiconductors on entertainment purposes.
And that doesn't even take into account the increasing problem of space garbage building up in orbit. If a major collision were to take place in orbit, it could spawn a runaway series of collisions that spread into other orbits, and forms a shell of small, high speed debris that would make launches into space impossible for at least a few hundred years. This is called Kessler Syndrome, and the more garbage that we leave in orbit, the greater the chances are of this occuring, setting us back centuries or even imprisoning us on a dying planet.
As far as getting to an exoplanet in a nearby solar system, there are two options; multi-generational/longterm (stasis) space travel at subluminal (slower than light) speed, or superluminal (faster than light) speed travel. Both are currently out of our reach.
In my opinion, you have a much better chance of preserving humans, building robots that can raise humans once the ship arrives, or building a ship (or ships) that can house many generations of humans for centuries than we have of breaking the current laws of physics or producing exotic matter that would be required for superluminal travel.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
Posts: 4,038
Loc: Southwestern US
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Yea we could do that for part of the debris, but a lot of it is diamagnetic material, meaning that it doesn't react strongly to magnetic fields. It would also be very tricky to control and coordinate orbital maneuvers between either extremely distant magnets, or magnets on board another object in orbit. Even the slightest force between two objects can throw both of the object's orbits off.
I think current protocol for aging satellites is to initiate a controlled re-entry so that the satellite burns up in the atmosphere rather than float out there in orbit, loses contact with the control team, drifts out of orbit, and crashes into something else. That being said, there are several large satellites that have broken in orbit and are now adrift, some weighing as much as 18,000 lbs (Envisat)...which could generate some serious debris if they were to impact something else in orbit.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
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Posts: 4,038
Loc: Southwestern US
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Re: General Science Thread [Re: poor boy]
#818094 - 08/13/16 04:46 PM (8 years, 4 months ago) |
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I didn't know that such a thing existed.
Preeze, tell me more
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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That Guy
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Yea, anything in orbit around the earth is constantly being pulled toward the earth, and thus must be moving pretty fast in order to maintain orbit.
Even in geosynchronous orbit, where the satellite is floating stationary with respect to the earth's surface, it must be moving at roughly 6900 mph relative to the earth's center.
Most of the space junk is in low earth orbit (LEO), where the gravitational pull is strongest, and 17,000+ mph is a pretty standard velocity for anything in a mostly circular, stable LEO.
The best way to move stuff like that around is to slightly change its direction and use its momentum to carry it where you want it. This requires precise knowledge of its mass, mass distribution, materials, etc.
And despite the fact that these things are travelling incredibly fast in LEO, they still require crap loads of energy to push put beyond the earth's gravitational influence.
Space is a bitch
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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That Guy
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There are several ways an orbit can lose energy. The most significant mode is through air drag, as the atmosphere does extend over 1000 miles above the surface of the earth (although it gets crazy thin up here). We'll focus on air drag since all other loss modes are negligible compared to this one.
Air pressure varies in low earth orbit from 700 nanopascals at 160km to about 10 nanopascals at 2000km. Since air pressure with respect to altitude is generally a linear relationship above the mesopause, we can easily come up with a y=ax+b style equation for air pressure P(h) through low earth orbit. If we apply the ideal gas law and plug in our pressure function, then a function for air density as a function of height rho(h) can be derived.
P(h) = (-3.75 e-13)h + 7e-7
rho(h) = (-1.64 e-18)h + 3.06e-12
If we look at the definition of drag force:
Fd = (1/2)rho(u2)CdA
where:
rho = rho(h) u = velocity (m/s) Cd = Drag coefficient A = projected area of object (m2)
and consider the example of a standard 1U frame cubesat with the following characteristics:
m = 1.33 kg Cd = 0.925 (average from tables) A = .1 m * .1135 m = .01135 m2
and place it at the initial height and velocity of:
uinitial = 17500 mph = 7823.2 m/s hinitial = about 141,430 meters above earth
then our drag function becomes
Fd = 0.00525u2rho(h)
our acceleration (slowing down) due to drag becomes
a = Fd/m = 0.00395u2rho(h)
and our velocity equation with respect to time (t) becomes:
u(t) = uinitial - a*t = 7823.2 - a*t
Now, because this drag force is so small, and the drop in orbit will occur very slowly, it is safe to assume that the difference in centrifugal force (the imaginary force that flings the object up) and gravitational force (the force pulling the object down) are in balance. This will allow us to define the height above the ground as a function of velocity:
Fc = centrifugal force = (m2u2)/r Fg = gravitational force = (Gm1m2)/r2
Where:
m1 = mass of earth (5.972 e 24 kg) m2 = mass of object (1.33 kg) G = Gravitational constant r = distance from center of earth to center of object = 6.371 e 6 meters + h
At this point, we can plug these definitions into a rough iterative spreadsheet, just to get a rough estimate of orbital decay time (this would take differential equations to actually solve the true path of the object, but the excel sheet will give us a pretty accurate result in this case).
I stepped the iteration time by 100 seconds per iteration, and calculated out 58 days in orbit (not 58 days until impact, its just that my calculation took up 50,000+ rows, and I got tired of running the simulation)...and only got a 380 meter loss of height (about 0.27% of the orbit height). Since our starting height was technically re-entered from the get-go (87 miles above the surface), a decay rate of 22 feet per day will be the absolute maximum decay rate a standard object will see up there.
The farther up you go, the slower you will need to go to maintain orbit (remember, geosynchronous sats are only moving at about 6900 mph, through much less dense air, and have a lot farther to decay (22,240 miles instead of 87 miles). Since the drag force depends on the density of the air, and strongly depends on velocity of the object, any objects in this area would be orbiting for a lonnnng time.
We won't even get into orbits higher than that...or the satellites that sit stationary with respect to earth in Lagrangian points.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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That Guy
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I called it a simulation, but it's really just a big excel table lol.
And yea man, I love this stuff and love discussing it with other people. Ideas and questions are how people learn and grow, and maybe even come up wits "the solution" for a particular problem. For insrance, after our discussions, you might ponder and research and figure out the space debris solution, and that would be badass!
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
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Re: General Science Thread [Re: Data] 1
#819578 - 09/24/16 11:51 AM (8 years, 3 months ago) |
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Anybody excited for the Europa announcement from NASA on Monday? It's not aliens, but I'm sure it'll be exciting nonetheless.
-------------------- “The Universe is under no obligation to make sense to you” -NDT
Edited by Data (09/24/16 11:51 AM)
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Data
That Guy
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Re: General Science Thread [Re: poor boy]
#819596 - 09/25/16 08:04 AM (8 years, 3 months ago) |
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-------------------- “The Universe is under no obligation to make sense to you” -NDT
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Data
That Guy
Registered: 08/12/08
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That was pretty neat, we studied standing waves on steel beams under cyclic motion in school. If you take a rope or a slinky, let it hang vertically, and shake the top back and forth, at particular shaking frequencies the rope/slinky will take on this shape.
This is called a vibrational mode, or a standing wave. In reality, the waves aren't stationary, but rather the initial wave travels down the rope/slinky, is reflected in a particular manner determined by the configuration of the end of the beam (as in, whether its attached to a stationary wall/floor, or free swinging, etc.), and overlays back over the original waves on its way back to you're hand. At certain frequencies (natural frequencies), this overlay ensures that certain points on the rope/slinky never move back and forth. The points that aren't moving are called nodes, and the points that have the maximum movement are called antinodes. There are (theoretically) an infinite number of vibrational modes, and each mode comes with an increasing number of nodes/antinodes, spaced closer together along the lenght of the rope/slinky.
When you set up a flat, horizontal steel beam in this manner (you have to mount it to a giant speaker core and use a much higher frequency than you're hand can achieve), then you can sprinkle a little salt or sand over the beam and the sand will line up across the beam at the nodes when one of the natural frequencies is dialed in.
In two dimensions (a horizontal flat plate either supported at the edges or in free space with the same speaker core for vibration input), the different vibrational modes (when sprinkled with sand to highlight the node lines) form interesting patterns. In the video below, the plate is supported in the center, which is also the point at which the vibrational input is transmitted into the plate (aka a Chladni plate).
In the case of the tractor beam, it gets a little complicated. The vibrating medium is the air, the source wave does not move in a straight line but rather radiates out from the speaker in a 3D ripple pattern (much like the 2D ripple pattern radiating out from the Chladni Plate), and the source wave shape doesn't necessarily reflect back over itself to create the 3D standing wave. This is why you have multiple source speakers, so that each source wave overlays over each other to create a 3D field of quasi nodes and antinodes. You can manipulate the relative timing of the source waves to change the spatial locations of the nodes, and thus a small object trapped in a 3D node can move with the node's changing location.
Notice that the objects tend to vibrate or spin while they are levitating, this is because the standing waves are actually constantly changing in the space around node, but the changes happen so fast that the object (which has a very small resistance to acceleration due to its mass) can't get up enough speed to escape the node before the pressure differences across the object flip in the opposite direction, thus keeping the object forever vibrating around the node point indefinitely. In one of the videos you posted, you'll notice that when he puts his hand above the dish to demonstrate how high the ball could levitate, the little ball falls out of the node. This is because by placing his hand into the acoustic field radiating out from the dish, he temporarily reflects some of the sound back down towards the dish, and changes the vibrational mode (I think that he actually destroyed the node field temporarily).
Standing waves can also occur with light. In fact, a standing light wave along a single axis is the heart and soul of all lasers. The optical material and length of the "resonating chamber" must be tailored to the frequency of light that you are trying to produce in order to work correctly. Additionally, complex 2D and 3D electron vibrational modes can be set up on metallic cylinders with various insulator materials to act as bandpass filters for microwave radio transmissions (used heavily in microwave ovens, cell phones, radioastronomy, radar, and high-bandwidth line-of-sight communications relays).
Basically, standing waves in any media are cool as shit
-------------------- “The Universe is under no obligation to make sense to you” -NDT
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