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Comment Re: Batteries just don't store enough energy... (Score 1) 143

Also, there's a lot of diversity in terms of aircraft electrification that one can take, it's not an all-or-nothing thing. There's lots of different proposals for varying degrees - for example, high bypass with electric turbofans, using onboard electricity to spin the compressor so that you don't have to have a turbine, and so forth.

Comment Re: Batteries just don't store enough energy... (Score 1) 143

Yes. Also, you can't ignore comparative efficiencies of engines. Or engine mass to weight ratios. Or the length of time to market, and the expected level of battery change during that time period. Or side benefits (for example, the ability to have small, very light engines was made use of in one NASA experiment that placed numerous small engines along a wing, causing an effect that created drastically more lift at low speeds and allowing for a much shorter takeoff distance).

And beyond that, you can't ignore economics. Having reduced range but getting your fuel at a fraction of a cost may ultimately prove to be more desirable. It's a very complex issue that one can't just make all-encompassing statements based on a single figure like "energy density of batteries vs. energy density of fuel".

Anyway, this is hardly Elon's first time to mention it. Years ago he mentioned that he wants to be the first person to have an electric plane break the sound barrier. If there's anything one can say about Elon, it's that he sure doesn't set the bar low...

Comment Re: What's the viable alternative? (Score 1) 118

Then parents insisted that every school offer typing classes, now what was once a career option is now a basic job requirement for any white collar job.

How many white collar professionals know how to touch type without looking a keyboard. That's a skill many schools don't teach anymore. Always embarrassing to run into programmers and engineers who have to hunt-and-peck every key on the keyboard (not just the special symbols). I've learned touch typing as a kid because I thought typewriters were the coolest mechanical devices in the 1970's. A useful skill to have in the early 1990's when I submitted typewritten college papers because instructors didn't accept printouts from dot matrix printers (not even in Near Letter Quality mode), and laser printers weren't in widespread use until 1995.

Comment Re:Visual vs wall of code (Score 1) 118

In reality, they didn't solve the problem - the computer did.

I saw this quite a bit during the early days of the web. Many so called "web designers" knew how to create web pages in Dreamweaver, Frontpage or Word. But occasionally something broke, they couldn't fix it and asked me to take a look. Because I learned HTML coding with a text editor (still my preferred tool 20+ years later), I was able to plow through the bloated spaghetti code that these programs produced and fix the offending line of code.

Comment Re:If it was easy (Score 1) 118

Like engineering, like medicine, like pro football, like many other things.

My nephew wanted to be a pro baseball player. He played through grade school, high school and college. A scout sent him off to a summer baseball camp in Texas. After six weeks and 500 games later, he made the top 50 before being cut from the competition. Now he's doing PR work because he took an easy major in college. Meanwhile, a half-dozen of his friends are playing pro baseball.

Comment Re:Icebergs float on glaciers (Score 5, Informative) 35

No, it does not form "one huge crystal". Nitrogen ices at these temperatures have little structural integrity. It was well known before we got to Pluto that if we saw any sort of relevant topography, we'd know immediately that it was from water ice, as nitrogen ices are so weak that they'd just flow slack over time.

Comment Re:Icebergs float on glaciers (Score 5, Informative) 35

Nitrogen ices at these temperatures, while crystalline, have rather low viscosity. If you put weight on them, they slowly diffuse around it until the object either sinks or is buoyantly balanced out. The latter happens in the case of water ice.

Also, it's worth noting that it's not pure nitrogen ices, it's a nitrogen-carbon monoxide-methane eutectic. Nitrogen is the most common component, however. Also, there are multiple crystal phases that can be taken, depending on the conditions. Nitrogen ices are most famous for having some rather "explosive" phase transitions between different states.

Comment Re:Surprised? (Score 1) 515

Nooo the surprising thing is even corporate users cannot disable the spying as this was Windows 10 ENTERPISE, the version that they sell to huge megacorps, and even turning everything to OFF it still called thousands of times!

So this should be more than enough to convince any corp that has to abide by S/OX or HIPPA that Windows 10 has to be verbotten, its as big a risk for data breaches as allowing USB sticks...who would have thought that Windows would go from being a spyware risk to being actual spyware?

Comment Re:sunfire / in my stellerator / makes me... happy (Score 1) 98

Fast neutron cross scattering sections in the couple MeV range barely vary over more than the range of 1-10 barns

1-10 barns is, of course, by definition, an order of magnitude. There is a massive difference between 10 barns and 1 barn. Tenfold, to be precise. ;)

More to the point, you can't just combine all cross sections like that. The energy imparted from an elastic collision isn't the same as from an inelastic collsiion, which isn't the same as an (n, gamma), and so forth. Elastic collisions are particularly low energy, particularly the higher Z the target. Taking them out of the equation yields much greater differences between materials in the range of a couple MeV. The upper end of the neutron energies are "somewhat" similar (up to about one order of magnitude), but down below 6 or 7 MeV or so there's quite a few orders of magnitude difference.

Likewise, total cross sections have no bearing on the accumulation of impurities in the material. The particular cross sections are relevant not only in terms of reaction rate, but also what sort of impurities you tend to accumulate and what effect they have on the properties of the material. Which of course varies greatly depending on what exactly they are.

Integration of annealing cycles into blanket design is not brought up enough in some design studies, but is a consideration to help

It's not a side issue, it's a fundamental issue to the design of a material designed for high temperature operation under a high neutron flux.

Blanket design is extremely constrained by tritium breeder ratio to ensure more tritium is produced than used, which squeezes volume allowed to be used by coolant, ... but they have much lower neutron flux to worry about. Gen 4 reactor designs are in the 500-1000 C temperature range, exceeding in some cases what is thought reasonable for fusion blanket design. ... Blanket replacement is considerably more complex than fuel replacement in a fission reactor

Perhaps they've been heading in a different direction since I was last reading on the topic, but I was under the impression that a prime blanket material under consideration was FLiBe. Which operates in a temperature range of 459-1430C, and is its own coolant. That doesn't change what the first wall has to tolerate, but as for the blanket itself, you have no "structural properties" to maintain, and cooling is only limited by the speed that you can cycle it.

The last paper I read on the subject also suggested that for breeding purposes one needs not only beryllium (they were reporting really poor results with high-Z multipliers), but the optimum ratio (to my surprise) worked out to be significantly more beryllium than lithium. So building structural elements out of beryllium serves double purpose, you don't have the excuse of "I need to use steel because it's cheaper" - you need the beryllium either way. It's strong, low density, similar melting point to steel, but retains strength better with heat, and highly thermally conductive. Beryllium swelling from helium accumulation stops at 750C+ as helium release occurs. So pairing a beryllium first wall with a FLiBe-based blanket seems like a very appropriate option.

Please don't get me wrong, I'm not at all disputing the great amount of engineering work left to do. I'm just more optimistic that appropriate solutions will be found. Perhaps I'm just naive in that regard ;)

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