Why should the nuclear physicists have all the fun? Let the chemists play too.
I assume the huge density difference between plutonium allotropes contributes to making a density wave (explosion) an effective way to trigger criticality?
Lower initial density isn't really an advantage. If I recall correctly, alpha phase plutonium was used in early nuclear weapons cores because it was easier to shape. The brittle, harder, denser delta phase (with mechanical properties comparable to cast iron) was used in later weapons once the difficulties of machining it were overcome.
The decisions made during the Manhattan Project were not aimed at high efficiency nuclear weapons; the project needed to ensure that reliable weapons could be constructed quickly with the limited information available at the time. Even before fusion weapons were invented, atomic bombs became significantly more powerful, efficient, and lightweight due to realizing design optimizations that couldn't be tested before the war ended.
> Lower initial density isn't really an advantage.
Wouldn’t larger change in density for a given force be an advantage, though? It allows you to have a larger subcritical mass (at the lower density) that becomes critical as force is applied, without having to play geometric games; but maybe those games are trivial?
The chemistry and solid state physics of the actinides is pretty interesting because of all the electrons whizzing around: consider the infrared spectrum of thoria which makes it the choice for gas light mantles or the glow in the dark behavior of uranium glass which has nothing to do with radioactivity.
Not forgetting the Lanthanides, their cousins in the f-block, which have various interesting optical / catalytic / magnetic properties (e.g. Europium, Cerium, Neodymium).
Titan is outside the frost line. There’s no question that there’s a huge amount of water in solar systems, the question is if there’s a consistent transport system (comets, in this case) that moves it inside the frost line to where liquid water can, given an atmosphere and gravity, exist in conditions that match our familiar conditions for life.
FYI - the inclusion of UWB (specifically the FiRa consortium secure ranging standard) was not part of the CCC Digital Key specification until v4.0.0, which only left its draft state very recently, at least in terms of automotive security standards.
I’m sure that that one line manager who reported the fraud to the CEO was well rewarded. How he learned what he did? We’ll never know. Too bad his team had to be let go.
I use my M1 Max MacBook Pro for pretty serious CFD with OpenFoam. It’s astonishing how good it is… but a newer machine would be nearly 2x faster, which matters when single runs can take 1-3 hours.
> Isn't that something that's more the responsibility of the airlines, who decide how many seats are put in a plane, following the limits of the aircraft?
For pitch, yes. For width, no —- you run into quantization pretty quickly. The difference between sardines and standard economy is less than the difference between 3+3 and 3+2 — it’s not really feasible for most traditional airlines to choose a different number of seats across than the design point. And for a 3+3 setup, adding 6” to fuselage diameter makes a noticeable difference to (wider) passengers, which the airlines can’t really take away.
Seat and aisle widths are customer selectable options. Hence, a customer may order a 787 with 3-3-3 seating or 2-4-2 seating. The vast majority of airlines chose sardines instead of comfort. In a 737, customers only can get 3-3 seating, but they can choose wide (17.8”) seats and skinny aisles, like Southwest does, or they can choose skinny (17.1”) seats and wider aisles, like Alaska does.
Sort of timely because I was on an Alaska Max 9 yesterday I couldn't believe how narrow the aisle was. I actually looked up whether a Max 9 fuselage was narrower than a traditional 737, it was that bad. Now, it's possible this plane had the wider seat option (possible ex-Hawaiian, if they used a different config?), but even so, I've been on a lot of planes, and this is the first where I felt like I had to walk down the aisle sideways.
... with wider seats and skinny aisles bringing more weight (-> more fuel consumption), and slower boarding/deboarding times (-> more time on the ground), both of which are cost drivers.
Boeing is in constant communication with the airlines on new airplane designs, as they want to build the most profitable airplane for their customers that they can. This means the airline has a lot of input on fuselage diameter.
There's no incentive. Passengers rarely know what type they'll be flying on when they book, and prioritize it over price even less. For airlines, a bigger airplane is a distinct disadvantage though, as it's operationally more expensive (increased cross section equals increased drag equals increased fuel burn).
The real issue with the 747 is people will take a point to point route if at all possible. Worse, flying a small plane point to point is cheaper for the passenger than flying 2 747s. If you live in Lincoln NE - sorry your city is too small to get direct flights to anything but close major hubs (even then odds are you drive to nearby Omaha thus further reducing demand options). However if you live in a Larger non-hub city airlines can undercut each other by just doing direct flights to other large non-hub cities.
The 747 was at its most efficient when flying long haul routes, like overseas. The 747 was immensely profitable for Boeing for several decades. Every sale was a giant chunk of cash dumped on the company. But none of that would have happened if the 747 wasn't also immensely profitable for the airlines.
True but small planes are profitable too even for long flights. They have to compete against the more profitable large ones but they do that by emptying the large ones. I want to get to a destination and if a small plane isn't much more money it is cheaper to not transfer at a hub and pay for the 2nd plane to where I want to be. More smaller planes can also fit my schedule which can save money.
there is a reason nobody flies the 747 anymore. It isn't profitable enough agaisnt the 777 and small planes which are cheaper to run.
Mostly it's about engine tech. A 777/787 or whatever can fit almost as many passengers as a 747, but has only two engines, burning less fuel and requiring less maintenance.
Back when 747 was designed engine tech wasn't there yet to build really big two engine airplanes. There was also the issue of ETOPS limits. The regulations on how far away from nearest airport you can fly with two-engine aircraft were stricter than today, so for many routes flying over oceans you needed more than two engines.
There's also the issue of cargo space. The 777-300 actually has a larger hold, about 11% more. Cargo is pretty lucrative so even passenger airlines like being able to devote some of their hold space to it.
Modern wings could be retrofitted to the 747. Maybe not completely, but the more important features. However there are a lot of other parts of the 747 that don't make sense, and so not enough buyers (if any!) would exist if they did.
It was an old airplane too and not as optimized as newer airplanes in terms of engines, aerodynamic design, weight and so forth.
The A380 was a step up in size and had additional problems such as there not being that many airports which had upgraded their gates and other facilities to support an airplane that big.
As aviation technology improved, the 747 could not improve its aerodynamics and so became relatively costlier to fly. It's longevity, however, was due to it's cost effectiveness for several decades.
That only works if you make the airplane enough bigger so that you can fit more seats and thus paying passengers. The parent comment was arguing to make the plane only a little bigger so that each passenger has more space, but not enough so that extra seats can be fitted.
> Passengers rarely know what type they'll be flying on when they book, and prioritize it over price even less.
Virtually every booking page gives you that information during booking, and I (and several of my friends) actively avoid any flight that has a MAX operating it, to the point that we'd rather fly longer and/or more expensive alternative routes operated with other models.
> SRAM has virtually stopped scaling in new nodes.
But there are several 1T memories that are still scaling, more or less — eDRAM, MRAM, etc. Is there anything preventing their general architecture from moving to a 1T technology once the density advantages outweigh the need for pipelining to hide access time?
I’m pretty sure that HBM4 can be 20-30x faster in terms of bandwidth than eDRAM. That makes eDRAM not an option for AI workloads since bandwidth is the main bottleneck.
Really? I haven’t used it, but I’ve mostly heard good things. It really has ads everywhere and needs regular reinstalls and malware scrubbing?
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