You could do a mixture of air with other gases, and gain many of the advantages while still avoiding a hard air vacuum. For instance, 50Pa air + 50Pa water vapor, or even 50Pa air + 50Pa H2. A promising approach would be for the capsules to store on board some of the air they're compressing anyway, to help maintain the tube pressure. The alternate gases could even be added as part of the cooling system; if liquid nitrogen or liquid hydrogen were injected directly into the compressed air stream to cool it, it would greatly reduce the need for water intercoolers and onboard steam storage, increase the available pressure to the skis, and be balanced by onboard storage of some of the compressed air stream. And the pressures are low enough that combustion shouldn't be a problem, even with H2. Vacuum leaks are most likely to come from two sources: the end station airlocks, and the capsules themselves. Most of the tube is just Big Dumb Pipe (tm), which really shouldn't leak. And 100Pa is really not too difficult to maintain; the volume of the entire LA-SF Hyperloop tube is equivalent to a cube about 130 meters on a side.

Branching at full speed is probably not possible with the Hyperloop as designed; the skis are curved to match the diameter of the tube, with a ~1mm clearance with the tube surface, so there is no passive tube design that could accommodate a "switch". In order to continue from Section A to either Section B or Section C, you'd have to make an intermediate length of tube several hundred meters long that could be physically moved at one end from B to C, with sub-millimeter precision, with the entire thing enclosed in vacuum. By the time demand is great enough to warrant branches, it's probably more cost-effective to make a dedicated parallel tube than to re-purpose a single tube with a ridiculously complicated switch. Hydrogen (or water vapor) would be most helpful in reducing Kantrowitz effects near the sound barrier, but not necessarily in enabling higher absolute speeds. The reason is threefold: drag continues to increase at higher speeds regardless of the speed of sound, lateral acceleration increases with the square of velocity, and the vertical precision of the pipe also improves with the square of the velocity. 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 between pylons before the capsule's vertical suspension is overwhelmed and it starts "bouncing". (Assuming the mass of the skis/suspension is 10% of the capsule mass, so it can accelerate vertically at 10g to keep contact with the track.) At 1500mph, the tube requires a vertical precision of 1cm between 30m-spaced pylons, and its trajectory would have to be ridiculously straight to avoid problematic lateral g-forces. Mechanical braking from 1500mph in the event of an emergency is also a non-starter; 700mph is right at the edge of what can be feasibly done without melting brakes or destroying the tube. And in the event of a rapid tube repressurization, a 700mph capsule will incur about 2g's of aerobraking deceleration; at 1500mph it would experience about 10g's, likely enough to destroy the capsule and/or kill the passengers.

Air travel between LA and SF metro areas is the busiest air route in the US (and third-busiest in the world), with about 7.7 million passengers annually, or 21,000 per day. Assuming a 12-hour day, the Hyperloop could accommodate this with one 30-passenger capsule every two minutes each way, and the system is designed to quadruple this capacity at rush hour. (one capsule every 30 seconds.) Of course, if the Hyperloop is built, it will generate plenty of its own demand. And of course, it can be modified to carry cargo too (and possibly vehicles), not just passengers. The cost as outlined in the Hyperloop Alpha document is about 1/10th that of the proposed HSR.

"Existing elevated rail" is not a valid comparison. The Hyperloop infrastructure needs to support about 1/10th the weight per meter as traditional rail, therefore it can be done with 1/10th the materials. The proposed Keystone XL pipeline is 36 inches in diameter; the Hyperloop would be about 100 inches, but hollow and empty most of the time. Oil pipelines are full of oil, therefore quite heavy relative to diameter. In practice the total weight per linear meter of oil pipeline vs Hyperloop is about the same; 1 metric ton per meter. Traditional elevated rail is about 10 metric tons per meter.

Does the Touch ID imply that it also has an NFC chip for ApplePay? (Apparently it does, and the iPad Mini 2 doesn't.) That's an odd thing to leave off the comparison chart.

16:x sucks for work.

Unless x = 12.

Any '07 Roadster owners out there care to share how well the batteries are holding up?

My '08 Roadster (there are no '07 roadsters) has 33k miles on it, and after 4 1/2 years, its battery capacity has been reduced about 8%. I now get 225 miles on a full charge, down from 244 on day 1. That's even better than Tesla's initial projections, actually.

Evolution? If his is so, why do we not see a continuum of life over the spectra of species?

We do; they just aren't all alive at the same time. As you go backward into the past, the genotypes of humans and other apes (e.g. chimpanzees) gradually converge, until several million years ago, they are the same. Taken as a whole, there HAS been a continuous spectrum of creatures from humans to apes. (And traced far back enough, between all living things.) It staggers me that people find this difficult to understand.

And also: 1,354,320 grams is 2,986 pounds, not 25,031 pounds. (Correcting for this, as well as the number of connectors, makes the actual failure rate cutoff 1 in 30,180.) You didn't work on the Mars Climate Orbiter, did you? ;-)

It has 171 miles of wiring. Let's assume that we want to add connectors every 100 feet; That gives us 902,880 connectors.

Um, you're off by two orders of magnitude. 171 miles / 100 feet = 9,029 connectors, not 902,880. So the failure rate cutoff (assuming the rest of your calculations are correct) works out to 1 in 3600. Care to re-analyze?

Well obvious answer then, move it closer for an even stronger effect!

Close enough that it blocks out the sun? Problem solved!

Several years ago, a friend of mine was issued the CA sequential plate: 2GRT269. She immediately swapped it out for a custom plate, which, ironically, was much less memorable.

In a similar vein, once in a while I check the availability of the "sequential" plate 3XIV159. (I'd call it my Pi Plate: 3 14 159. Get it?) But it still seems to be in use. I wonder if its owner realizes what it means?

You will never get rid of the imperial system in the US for automobiles..

But are you aware that the US Environmental Protection Agency uses Grams per Mile as the unit for vehicle emission standards?

I always thought R was Reverse and D was Drive. (and L was Low Gear.) Fitting, actually.