"Attenuated S4" means you get less S4 sleep (the kind you need).
Please read it again. It was the high 6700K color temperature (i.e. not f.lux) that reduced good sleep, while the 3000K color temperature (e.g. f.lux) increased good sleep. This means f.lux is good for sleep.
"not statistically significant" -- removing the blue did nothing useful -- "exposure to the computer monitor only was reduced slightly relative to the dark control condition" -- the computer monitor putting out the blue light was the same as not having the thing on at all: blocking the blue did nothing useful.
Granted that it wasn't statistically significant, perhaps due to a small sample size, but the measured effect was in the direction of f.lux (blocking blue light) being good for sleep. They emphatically did not find that f.lux was bad for sleep.
" lower color temperature bright light exposure during a night rest break led to a reduction of subjects' arousal level during the subsequent work." -- you have to intentionally get up in the *middle* of a sleep cycle for there to be any effect; prior to a sleep cycle, there was no effect. This is basically "If you wake up in the middle of the night, you are less alert the next day". That's a big "duh".
You are misunderstanding the experiment. The subjects worked from 11pm to midnight, then took a break from midnight to 1am, then worked again from 1am to 2am. Being exposed to f.lux-like light during the hour break made them sleepier. So yes, obviously, f.lux is bad for staying awake if you're trying to stay awake. But the direct implication is that f.lux is good for going to sleep if you're trying to go to sleep. So again, f.lux is good (for its intended purpose, which is to use it before sleep).
In the early phase of the sleep period, the amount of stage-4 sleep (S4-sleep) was significantly attenuated under the higher color temperature of 6700 K compared with the lower color temperature of 3000 K." https://www.ncbi.nlm.nih.gov/p... == color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. "Attenuated" means reduced. High color temperatures (i.e. not f.lux) reduced good sleep, compared to lower color temperatures (e.g. f.lux).
"Melatonin concentrations after exposure to the blue-light goggle experimental condition were significantly reduced compared to the dark control and to the computer monitor only conditions. Although not statistically significant, the mean melatonin concentration after exposure to the computer monitor only was reduced slightly relative to the dark control condition." https://www.ncbi.nlm.nih.gov/p... == color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. The "dark control condition" was the orange-tinted glasses, creating f.lux-like conditions. The "blue-light goggle" condition was a goggle that _added_ blue light, the opposite of f.lux. Read the abstract again.
"After exposure to bright light of 3000 K but not at other color temperatures, the EEG alpha1 band ratio and the beta band ratio at 02:00 h were higher and lower, respectively, than that at 01:00 h. These findings indicated that lower color temperature bright light exposure during a night rest break led to a reduction of subjects' arousal level during the subsequent work." https://www.ncbi.nlm.nih.gov/p... == color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. Lower color temperature (e.g. f.lux) made people more sleepy.
...many of the other articles were self-published by companies and associates selling products like fl.ux and "Blue Blockers".
No one sells f.lux. f.lux is free software. I am happy to link to it here: www.justgetflux.com
20%, not 30%. Wind resistance increases with the cube of speed, but energy-per-mile efficiency (assuming all energy is spent fighting wind resistance) is only squared. That's because you spend less time driving a given distance at higher speed.
The Tesla P100D's dual motors combine for 760 horsepower, which would be more than enough to sustain 200mph+ with proper gearing and tires. By comparison, a Lamborghini Gallardo achieves a top speed of 202mph with just 562 horsepower. The Tesla's motors redline at about 16000rpm, which at the 9.7:1 fixed gearing ratio corresponds to about 155mph. If the gearing ratio were halved, the low-speed acceleration would reduce but the top speed would go up dramatically.
True, at 200mph the P100D battery pack would only be good for about 40 miles. But gas supercars don't do much better. At top speed, a Bugatti Veyron can burn through an entire 26-gallon tank of gas in just 12 minutes (51 miles).
So if we're hypothesizing replacing all ICE vehicles with EVs, we need 30x as many Supercharger plug-in spaces as there currently are gas pumps along major highways.
Taking into account both home-charging and destination-charging, I think you're right back down to 1x. On top of that, charging speeds will only ever get faster over the next 5-10 years. So there will likely never need to be as many EV supercharging spots as there are gas pumps now.
Sigh. One of the crashes resulted in one fatality. The other two crashes, no fatalities. (And it is not yet known whether Autopilot was engaged at the time of those two incidents.)
Getting distracted with Autopilot engaged is like removing your seatbelt because you have airbags. You may be able to occasionally get away with it, but it's still an incredibly dumb thing to do. (And the former endangers other drivers, not just yourself.) The silver lining of these incidents is that maybe more drivers will start paying more attention while using AP, though it should have been up to Tesla to properly instill this sense of caution to begin with.
And side skirts/guards should really be mandated for trailers nationwide. (They're already mandated in California.) It may not physically prevent an underride at high speed, but it doesn't have to; the radar is much more likely to detect them and trigger collision-avoidance braking. It's only a small patch for a small part of the problem, but better than not patching it at all.
As a Tesla owner myself (albeit a pre-Autopilot version), I am as shocked and saddened as anyone else by this incident. Obviously we don't know for sure that he was watching a movie, or even that he wasn't paying attention. For all we know he might have been paying full attention, but fully assumed the autopilot would brake, "froze" when it didn't, and failed to brake himself. Possible but unlikely. (Especially for a Navy Seal.) I'm sure we'll learn more as the investigation continues.
In the more likely scenario that the driver was distracted, my line above was just a way of emphasizing that even with autopilot, it's critically important to watch the road at all times. (Just as it's important to wear a seatbelt at all times, even though removing it usually has no consequences.) I meant the line in a somber, wry way, not in a fozzie-bear laugh-out-loud way. (if that helps.)
Boy, those 40-tonne tanker trucks must stir up a crap-ton of particulate pollution. If only there existed a car that didn't require all the gasoline those trucks are toting around.
Third reason: Wind. In the post-launch press conference, Elon mentioned that the wind was significant during landing. (And may reach up to 50mph tomorrow on the way back to port.) So the rocket had to tilt somewhat into the wind to avoid being blown sideways relative to the landing pad, and only went vertical at the last moment. It also explains why the droneship maintains a slight tilt in some of the post-landing footage; this is to cancel out the considerable force of the prevailing wind.
And after these five years, I'd expect the range of the car to have dropped 20% or so.
Um, no. I own a vintage 2008 Tesla Roadster, and its range has dropped only about 10% over nearly 8 years. The battery chemistry and durability used by Tesla has only increased since then, so I the Model 3 will do substantially better even than that. Over five years, it might drop 5%. Possibly 10% at the outside, but not anywhere close to 20%.
Now here's a huge issue I haven't seen anyone talking about that gets progressively worse as the track/tube length increases, subsidence and ground movement.
The subsidence / ground movement effect is dwarfed by the simple thermal expansion of the tube over the day/night cycle, which can grow/shrink up to hundreds of meters over the length of the tube. This effect can be compensated for by allowing the tube to slide smoothly across the pylons to achieve tensile equilibrium. (Perhaps with motorized assist to overcome friction.) The "slack" is taken up at the endpoint stations, through a telescoping system. Each pylon can allow for perhaps a meter of lateral flex to account for local ground shifting, and the pylons themselves can be easily repositioned if they start to get close to their tolerances in a local area.
By the way, how much material would such a full sized tube use up, and whats the current national production of said materials?
The complete Alpha-design hyperloop from LA to SF would use about 1 million tons of steel, or about 0.02% of the world's current annual steelmaking output. For scale, this is about 10x more steel than the Birds Nest stadium in Beijing, or about 100 Eiffel Towers' worth.
Presumably every Hyperloop capsule would be instrumented to gather data along its journey to immediately reveal any imperfections or problems. Since the travel surface is a completely controlled environment (no birds pooping on the tracks, etc.), it ought to be far easier to maintain than open highways or exposed railroad tracks. The Hyperloop system will directly generate revenue for its own maintenance and upkeep, whereas bridges really don't. (Toll bridges, maybe.)
Much less than would be if there weren't so much CO2 in the atmosphere trapping the heat. As we inject more CO2 into the atmosphere, less heat escapes to space, and the equilibrium surface temperature rises quickly. This is why the human-caused rise to its current value of >400ppm is so alarming, and where the ultimate 350ppm "safe" limit calculation (to avoid catastrophic temperature increases) comes from.
You are wildly off. A Cat-5 hurricane sustains about 1 petawatt of power output, or ~50x the rate of humanity's fossil fuel consumption. A year's worth of human output could power this hurricane at full strength for about a week. These storms typically last at peak intensity for a couple days. In other words, humans are adding about two or three Cat-5 hurricanes' worth of energy per year to the global environment.
The MacBook product page, in the Graphics and Video Support section, states: "Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on an external display, both at millions of colors". However, it looks like this will require either 4k displays with USB-C inputs (passing DisplayPort 1.2), or else USB-C to DisplayPort adapters, neither of which seem to be currently available. The USB-C to HDMI adapters sold by Apple seem to be limited to 1080p.
A person needs at least 20kPa *from the mask to breathe*. Not 20kPa *ambient pressure*. Please learn to read.
The mask pressure must match the ambient pressure, or else the wearer's lungs will rupture (unless they're wearing an enclosed pressure suit). Please learn physics. Again, this is the reason for the 40,000ft flight ceiling for commercial aircraft; oxygen masks rapidly lose their effectiveness with an ambient pressure below 0.2atm, which is why pressure suits are required for pilots flying at higher altitudes. The absolute physical limit for unpressurized flight is known as the Armstrong Limit, which occurs at about 62,000 ft; even wearing an oxygen mask, your bodily fluids will start to boil above that altitude.
The "problematic loading on the capsules" is from the high speed aerodynamics, not the ambient pressure
Aerodynamic loading = pressure. If you have high loadings, you have high pressures. Period.
The high loadings are from high _variations_ in pressure. The average pressure around the capsule is still equal to the ambient pressure. Leaks in the passenger compartment are almost certainly side-facing, so the capsule will equalize to the pressure of the air on the sides of the capsule (which will be close to ambient or likely below, due to the Bernoulli principle), not the higher pressure in front. And note that the variations in pressure don't have to be very high to cause serious buffeting. The Hyperloop capsule masses 15000kg, with a frontal cross-section of about 2 m^2. Applying an extra 1atm to the front of the capsule will decelerate it faster than 1g. If the air beneath the capsule transiently becomes about 0.03atm higher density than the air above (due to turbulence or ground effect), it will lift the entire capsule off the track. This is the worrisome high-speed aerodynamics I was talking about.
Wait, meaning that while it's technically possible, but it'd be really tricky to accomplish? Gee, I wish I had written something like "Branching would be really tricky, but there's no physical barriers" at the top of my post;)
Well, there are physical barriers to a static design that allows branching. Actively moving an entire section of tube to reconnect it to a new one is sort of a brute-force approach, and highly unlikely that it would be worth the complexity and risk, in my opinion at least.
Drag is reduced in the first place by using hydrogen even at a given pressure. And you can use 1/4th the pressure and still maintain lift because you're moving four times as fast. And given how few reboosts are needed from LA to SF in the base case, a few more per unit distance hardly seems limiting.
1/4th the pressure is still problematic, because what do you do while you're accelerating up to speed? You'd have to use pressurized onboard gas to levitate with, which would then require more vacuum pumping with every run. The Alpha design uses wheels for "taxiing" at low speeds; it's unclear at what speed the compressor is able to provide all of the needed lift.
If you consider that the steel Hyperloop pipe draped across 30m-spaced pylons will approximate a vertical sine wave, then at 700mph the allowable sag is only about 5cm
Irrelevant because earthquakes impose far more deflection that you have to be able to counter (and that the proposal calls for countering) than a craft moving past.
Relevant because the problem is the frequency, not the amplitude. Large earthquakes tend to cause much lower-frequency deflections, which are far easier to deal with, even if the amplitude is higher. The problem I described has to do with the static height profile of the tube, not the effect of the passing capsule distorting it (which is negligible). Even if the skis (on springs) can accelerate at 10g's to maintain contact with the tube surface, then a 5cm oscillation with 30m wavelength is sufficient to cause the skis to completely lift off the surface of the tube after each pylon, causing a very jarring ride. A low-frequency earthquake deflection on the other hand, say with 200m wavelength, could not realistically have high enough amplitude to cause the skis to skip like this. Of course, if you have the bad luck to be riding the hyperloop straight over the epicenter when the earthquake lets loose, then there will be high-amplitude earthquake waves of all frequencies and all bets are off.
Mechanical braking from 1500mph in the event of an emergency is also a non-starter
What, you're picturing drum brakes or something? You're moving at high speeds in a giant steel tube. Magnetic braking couldn't possibly be easier.
The Alpha proposal calls for a "mechanical braking system"; I agree that magnetic brakes would be preferable in principle, though at Hyperloop speeds there's enough kinetic energy involved that the capsule component of the brakes would likely melt from the induced current. Permanent magnets on the capsule would probably be too heavy. And magnets/electromagnets on 350 linear miles of tube would likely be too costly/complicated. So unless there's a way to have the electromagnet component on the capsule, but make sure that nearly all the heat is dissipated in the steel tube and not the capsule, I'm not sure it would be workable. I have similar concerns about the aluminum capsule rotor, and whether it might become problematically hot during the linear acceleration/deceleration phase. A solid aluminum rotor could absorb the electromagnetically induced waste heat from 0-700mph acceleration without melting (by a factor of about 2), but the Alpha design calls for it to be hollow. And accelerating to 1500mph involves >4x the energy of 700mph
Clever, but probably unworkable given the large cross-section of the capsule relative to the tube. Even on a perfectly straight track (no banking), taking the upper branch would require the skis to "split" wide enough that the entire capsule width would fit between them. Given the Alpha design numbers (ski width 0.9m, tube diameter 2.23m, capsule width 1.34m), the skis would have to split nearly horizontal to avoid the lower-branch "gap", and it's unlikely they could function at such a steep angle. Maintaining the precise shape of a non-circular tube against vacuum pressure is also a very difficult problem.
Slashdot Mirror
"In the case of autism, the risk associated with parental age is DWARFED by the impact of inheritance."
What about the risk of Dwarfism?
Well no, it could have scored a near direct hit on Jupiter (or another planet), thereby becoming gravitationally captured by the Sun.
I think you are failing to understand:
"Attenuated S4" means you get less S4 sleep (the kind you need).
Please read it again. It was the high 6700K color temperature (i.e. not f.lux) that reduced good sleep, while the 3000K color temperature (e.g. f.lux) increased good sleep. This means f.lux is good for sleep.
"not statistically significant" -- removing the blue did nothing useful -- "exposure to the computer monitor only was reduced slightly relative to the dark control condition" -- the computer monitor putting out the blue light was the same as not having the thing on at all: blocking the blue did nothing useful.
Granted that it wasn't statistically significant, perhaps due to a small sample size, but the measured effect was in the direction of f.lux (blocking blue light) being good for sleep. They emphatically did not find that f.lux was bad for sleep.
" lower color temperature bright light exposure during a night rest break led to a reduction of subjects' arousal level during the subsequent work." -- you have to intentionally get up in the *middle* of a sleep cycle for there to be any effect; prior to a sleep cycle, there was no effect. This is basically "If you wake up in the middle of the night, you are less alert the next day". That's a big "duh".
You are misunderstanding the experiment. The subjects worked from 11pm to midnight, then took a break from midnight to 1am, then worked again from 1am to 2am. Being exposed to f.lux-like light during the hour break made them sleepier. So yes, obviously, f.lux is bad for staying awake if you're trying to stay awake. But the direct implication is that f.lux is good for going to sleep if you're trying to go to sleep. So again, f.lux is good (for its intended purpose, which is to use it before sleep).
In the early phase of the sleep period, the amount of stage-4 sleep (S4-sleep) was significantly attenuated under the higher color temperature of 6700 K compared with the lower color temperature of 3000 K."
https://www.ncbi.nlm.nih.gov/p...
== color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. "Attenuated" means reduced. High color temperatures (i.e. not f.lux) reduced good sleep, compared to lower color temperatures (e.g. f.lux).
"Melatonin concentrations after exposure to the blue-light goggle experimental condition were significantly reduced compared to the dark control and to the computer monitor only conditions. Although not statistically significant, the mean melatonin concentration after exposure to the computer monitor only was reduced slightly relative to the dark control condition."
https://www.ncbi.nlm.nih.gov/p...
== color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. The "dark control condition" was the orange-tinted glasses, creating f.lux-like conditions. The "blue-light goggle" condition was a goggle that _added_ blue light, the opposite of f.lux. Read the abstract again.
"After exposure to bright light of 3000 K but not at other color temperatures, the EEG alpha1 band ratio and the beta band ratio at 02:00 h were higher and lower, respectively, than that at 01:00 h. These findings indicated that lower color temperature bright light exposure during a night rest break led to a reduction of subjects' arousal level during the subsequent work."
https://www.ncbi.nlm.nih.gov/p...
== color shift by fl.ux and others: bad for sleep
No, this means f.lux is good for sleep. Lower color temperature (e.g. f.lux) made people more sleepy.
No one sells f.lux. f.lux is free software. I am happy to link to it here: www.justgetflux.com
20%, not 30%. Wind resistance increases with the cube of speed, but energy-per-mile efficiency (assuming all energy is spent fighting wind resistance) is only squared. That's because you spend less time driving a given distance at higher speed.
The Tesla P100D's dual motors combine for 760 horsepower, which would be more than enough to sustain 200mph+ with proper gearing and tires. By comparison, a Lamborghini Gallardo achieves a top speed of 202mph with just 562 horsepower. The Tesla's motors redline at about 16000rpm, which at the 9.7:1 fixed gearing ratio corresponds to about 155mph. If the gearing ratio were halved, the low-speed acceleration would reduce but the top speed would go up dramatically.
True, at 200mph the P100D battery pack would only be good for about 40 miles. But gas supercars don't do much better. At top speed, a Bugatti Veyron can burn through an entire 26-gallon tank of gas in just 12 minutes (51 miles).
He should have said the fees would be donated to a charity as part of the announcement.
Or to Exxon Mobil for oil exploration. That'd get people to move their cars!
Taking into account both home-charging and destination-charging, I think you're right back down to 1x. On top of that, charging speeds will only ever get faster over the next 5-10 years. So there will likely never need to be as many EV supercharging spots as there are gas pumps now.
I interviewed for a high-level engineering position at Google last year at age 42, and was hired. Just saying.
Sigh. One of the crashes resulted in one fatality. The other two crashes, no fatalities. (And it is not yet known whether Autopilot was engaged at the time of those two incidents.)
Getting distracted with Autopilot engaged is like removing your seatbelt because you have airbags. You may be able to occasionally get away with it, but it's still an incredibly dumb thing to do. (And the former endangers other drivers, not just yourself.) The silver lining of these incidents is that maybe more drivers will start paying more attention while using AP, though it should have been up to Tesla to properly instill this sense of caution to begin with.
And side skirts/guards should really be mandated for trailers nationwide. (They're already mandated in California.) It may not physically prevent an underride at high speed, but it doesn't have to; the radar is much more likely to detect them and trigger collision-avoidance braking. It's only a small patch for a small part of the problem, but better than not patching it at all.
As a Tesla owner myself (albeit a pre-Autopilot version), I am as shocked and saddened as anyone else by this incident. Obviously we don't know for sure that he was watching a movie, or even that he wasn't paying attention. For all we know he might have been paying full attention, but fully assumed the autopilot would brake, "froze" when it didn't, and failed to brake himself. Possible but unlikely. (Especially for a Navy Seal.) I'm sure we'll learn more as the investigation continues.
Why People Freeze
In the more likely scenario that the driver was distracted, my line above was just a way of emphasizing that even with autopilot, it's critically important to watch the road at all times. (Just as it's important to wear a seatbelt at all times, even though removing it usually has no consequences.) I meant the line in a somber, wry way, not in a fozzie-bear laugh-out-loud way. (if that helps.)
That driver shouldn't have been watching the movie. He should have been watching the trailer.
Boy, those 40-tonne tanker trucks must stir up a crap-ton of particulate pollution. If only there existed a car that didn't require all the gasoline those trucks are toting around.
There are no stupid questions. But there are a LOT of inquisitive idiots.
There are two reasons that I've seen.
Third reason: Wind. In the post-launch press conference, Elon mentioned that the wind was significant during landing. (And may reach up to 50mph tomorrow on the way back to port.) So the rocket had to tilt somewhat into the wind to avoid being blown sideways relative to the landing pad, and only went vertical at the last moment. It also explains why the droneship maintains a slight tilt in some of the post-landing footage; this is to cancel out the considerable force of the prevailing wind.
And after these five years, I'd expect the range of the car to have dropped 20% or so.
Um, no. I own a vintage 2008 Tesla Roadster, and its range has dropped only about 10% over nearly 8 years. The battery chemistry and durability used by Tesla has only increased since then, so I the Model 3 will do substantially better even than that. Over five years, it might drop 5%. Possibly 10% at the outside, but not anywhere close to 20%.
AlphaGo 'Speechless' after 2nd Win vs Human Go Champion
Now here's a huge issue I haven't seen anyone talking about that gets progressively worse as the track/tube length increases, subsidence and ground movement.
The subsidence / ground movement effect is dwarfed by the simple thermal expansion of the tube over the day/night cycle, which can grow/shrink up to hundreds of meters over the length of the tube. This effect can be compensated for by allowing the tube to slide smoothly across the pylons to achieve tensile equilibrium. (Perhaps with motorized assist to overcome friction.) The "slack" is taken up at the endpoint stations, through a telescoping system. Each pylon can allow for perhaps a meter of lateral flex to account for local ground shifting, and the pylons themselves can be easily repositioned if they start to get close to their tolerances in a local area.
By the way, how much material would such a full sized tube use up, and whats the current national production of said materials?
The complete Alpha-design hyperloop from LA to SF would use about 1 million tons of steel, or about 0.02% of the world's current annual steelmaking output. For scale, this is about 10x more steel than the Birds Nest stadium in Beijing, or about 100 Eiffel Towers' worth.
Presumably every Hyperloop capsule would be instrumented to gather data along its journey to immediately reveal any imperfections or problems. Since the travel surface is a completely controlled environment (no birds pooping on the tracks, etc.), it ought to be far easier to maintain than open highways or exposed railroad tracks. The Hyperloop system will directly generate revenue for its own maintenance and upkeep, whereas bridges really don't. (Toll bridges, maybe.)
And how much gets bled off into space?
Much less than would be if there weren't so much CO2 in the atmosphere trapping the heat. As we inject more CO2 into the atmosphere, less heat escapes to space, and the equilibrium surface temperature rises quickly. This is why the human-caused rise to its current value of >400ppm is so alarming, and where the ultimate 350ppm "safe" limit calculation (to avoid catastrophic temperature increases) comes from.
You are wildly off. A Cat-5 hurricane sustains about 1 petawatt of power output, or ~50x the rate of humanity's fossil fuel consumption. A year's worth of human output could power this hurricane at full strength for about a week. These storms typically last at peak intensity for a couple days. In other words, humans are adding about two or three Cat-5 hurricanes' worth of energy per year to the global environment.
The MacBook product page, in the Graphics and Video Support section, states: "Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on an external display, both at millions of colors". However, it looks like this will require either 4k displays with USB-C inputs (passing DisplayPort 1.2), or else USB-C to DisplayPort adapters, neither of which seem to be currently available. The USB-C to HDMI adapters sold by Apple seem to be limited to 1080p.
The mask pressure must match the ambient pressure, or else the wearer's lungs will rupture (unless they're wearing an enclosed pressure suit). Please learn physics. Again, this is the reason for the 40,000ft flight ceiling for commercial aircraft; oxygen masks rapidly lose their effectiveness with an ambient pressure below 0.2atm, which is why pressure suits are required for pilots flying at higher altitudes. The absolute physical limit for unpressurized flight is known as the Armstrong Limit, which occurs at about 62,000 ft; even wearing an oxygen mask, your bodily fluids will start to boil above that altitude.
The high loadings are from high _variations_ in pressure. The average pressure around the capsule is still equal to the ambient pressure. Leaks in the passenger compartment are almost certainly side-facing, so the capsule will equalize to the pressure of the air on the sides of the capsule (which will be close to ambient or likely below, due to the Bernoulli principle), not the higher pressure in front. And note that the variations in pressure don't have to be very high to cause serious buffeting. The Hyperloop capsule masses 15000kg, with a frontal cross-section of about 2 m^2. Applying an extra 1atm to the front of the capsule will decelerate it faster than 1g. If the air beneath the capsule transiently becomes about 0.03atm higher density than the air above (due to turbulence or ground effect), it will lift the entire capsule off the track. This is the worrisome high-speed aerodynamics I was talking about.
Fortunately, a vacuum spill is much easier to clean up than an oil spill.
Well, there are physical barriers to a static design that allows branching. Actively moving an entire section of tube to reconnect it to a new one is sort of a brute-force approach, and highly unlikely that it would be worth the complexity and risk, in my opinion at least.
1/4th the pressure is still problematic, because what do you do while you're accelerating up to speed? You'd have to use pressurized onboard gas to levitate with, which would then require more vacuum pumping with every run. The Alpha design uses wheels for "taxiing" at low speeds; it's unclear at what speed the compressor is able to provide all of the needed lift.
Relevant because the problem is the frequency, not the amplitude. Large earthquakes tend to cause much lower-frequency deflections, which are far easier to deal with, even if the amplitude is higher. The problem I described has to do with the static height profile of the tube, not the effect of the passing capsule distorting it (which is negligible). Even if the skis (on springs) can accelerate at 10g's to maintain contact with the tube surface, then a 5cm oscillation with 30m wavelength is sufficient to cause the skis to completely lift off the surface of the tube after each pylon, causing a very jarring ride. A low-frequency earthquake deflection on the other hand, say with 200m wavelength, could not realistically have high enough amplitude to cause the skis to skip like this. Of course, if you have the bad luck to be riding the hyperloop straight over the epicenter when the earthquake lets loose, then there will be high-amplitude earthquake waves of all frequencies and all bets are off.
The Alpha proposal calls for a "mechanical braking system"; I agree that magnetic brakes would be preferable in principle, though at Hyperloop speeds there's enough kinetic energy involved that the capsule component of the brakes would likely melt from the induced current. Permanent magnets on the capsule would probably be too heavy. And magnets/electromagnets on 350 linear miles of tube would likely be too costly/complicated. So unless there's a way to have the electromagnet component on the capsule, but make sure that nearly all the heat is dissipated in the steel tube and not the capsule, I'm not sure it would be workable. I have similar concerns about the aluminum capsule rotor, and whether it might become problematically hot during the linear acceleration/deceleration phase. A solid aluminum rotor could absorb the electromagnetically induced waste heat from 0-700mph acceleration without melting (by a factor of about 2), but the Alpha design calls for it to be hollow. And accelerating to 1500mph involves >4x the energy of 700mph
Clever, but probably unworkable given the large cross-section of the capsule relative to the tube. Even on a perfectly straight track (no banking), taking the upper branch would require the skis to "split" wide enough that the entire capsule width would fit between them. Given the Alpha design numbers (ski width 0.9m, tube diameter 2.23m, capsule width 1.34m), the skis would have to split nearly horizontal to avoid the lower-branch "gap", and it's unlikely they could function at such a steep angle. Maintaining the precise shape of a non-circular tube against vacuum pressure is also a very difficult problem.