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Everything posted by sevenperforce

  1. That's true. I knew a man whose memory and sense of smell were affected by it. But a close relative got it and only had mild cold-like symptoms. It's weird how it hits some folks hard and barely touches others. It's a lot like polio. Most cases are asymptomatic. A small amount of cases see moderate symptoms. A fraction of cases end up dead or crippled for life. Only it is VASTLY more contagious than polio and the percentage of dead or crippled is MUCH higher than polio.
  2. Oh, I'm not suggesting the media balances viewpoints properly. A while back, media companies realized that the appearance of controversy is even better at generating clicks/views than traditionally "raw" clickbait or scare headlines, especially because a plethora of scare headlines ends up injuring the company's reputation in the long run. If you lean into scare headlines, then you end up narrowing your audience more and more, which can be useful for an audience of one (cough) but is otherwise bad for profits. It's much more lucrative to create the appearance of controversy even where there is none. If you have an obvious and straightforward story ("economic expansion in industrialized city disproportionately impacting low-income minority communities") then there's only so much attention you draw from it, even if you cover it well. But if you can drum up some nutter who will say "No, it's not the fault of industry, it's the fault of these poor people" then you will have attention from people outraged on both sides, and you get to hide behind the disingenuous veneer of "we're just showing both sides" while raking in profits.
  3. It's a wild card, but cannot be played by just anyone, usually requires being in the good graces of press-academia-capital, kind of like the church in the middle ages and accusations of heresy. I'm afraid that "press-academia-capital" is not a cognizable entity. Academia does generally recognize the reality that past decades of racial and ethnic discrimination have ongoing and pervasive effects on minority communities today, particularly in the the way that the burdens of pollution, climate change, and adverse economic pressure (as @Rakaydos pointed out) fall disproportionately on POC, but academics are generally ignored. As for the press, the media seems utterly incapable of presenting anything on racial or social injustice (no matter how explicit and obvious) without the need to "balance" coverage with an opposing view. Media coverage of racism is generally designed to increase a sense of controversy but not to actually draw conclusions, identify real issues, or propose solutions. Eh. As @Beccab points out, few if any of these complaints are going to be taken seriously. There is no need for the accused to rebut if the fact-finder simply dismisses it out of hand, along with the "I want better beach access" and "Starship is a WMD" complaints. It's a shame, because there are legitimate issues here. Cameron County is one of the poorest counties in the state, and while Starbase definitely represents economic benefits for the region, those benefits are going to fall mostly to a small number of wealthy people who control much of the property in the region. The bottom line is that when you already have a region or community marked by racial and economic segregation and injustice, any changes to that region represent an opportunity to either better or worsen those issues. It's something that SpaceX should consider and account for, but going to the FAA to force this consideration is not a useful strategy.
  4. The CDC never said that vaccines prevent infection and never said that vaccines prevent poor outcomes. The CDC's page says that the vaccines remain effective at reducing the risk of infection and remain highly effective at reducing the risk of poor outcomes. Excerpts from the current CDC page (last update 9/15/2021): Early data suggest infections in fully vaccinated persons are more commonly observed with the Delta variant than with other SARS-CoV-2 variants. However, data show fully vaccinated persons are less likely than unvaccinated persons to acquire SARS-CoV-2, and infections with the Delta variant in fully vaccinated persons are associated with less severe clinical outcomes. In the Moderna trial, among people who had received a first dose, the number of asymptomatic people who tested positive for SARS-CoV-2 at their second-dose appointment was approximately 67% lower among vaccines than among placebo recipients (0.1% [n=15] and 0.3% [n=39], respectively). Efficacy of Janssen COVID-19 vaccine against asymptomatic infection was 74% in a subset of trial participants. [M]eta-analyses indicate an average effectiveness of full vaccination against SARS-CoV-2 infection of 85%–95% shortly after completion of vaccination. Studies [of the Delta variant] from the United Kingdom have noted effectiveness of the Pfizer-BioNTech vaccine against confirmed infection (79%) and symptomatic infection (88%), compared with the Alpha variant (92% and 93%, respectively). Even with waning antibody counts and more contagious variants, the vaccines continue to significantly reduce the risk of primary infection. No pox or polio around. It took 184 years for vaccines to fully eradicate smallpox. These vaccines have had about 13 months at most.
  5. Getting a booster prematurely won't hurt you, but it may reduce the immune response you would receive if you waited and got a booster later. So for many younger people the added protection conferred by a booster is not very significant. We can think about immunity as two lines of defense. Your antibodies are like riot police; they stop intruders before they even get in. Your T cells and B cells, on the other hand, are like club bouncers; they throw out any intruders who are able to make it past the riot police. The vaccines (particularly the mRNA ones) are effective at preventing infection because they cause your antibody counts to go through the roof. At the same time, the T cell and B cell activation gives you long-lasting protection against serious illness. The trouble is that we haven't been tracking everyone's antibody titers. It has been just over 8 months since I was fully vaccinated, but I don't know what my antibody titers were like at that point. If my antibodies have fallen by 50% in the past 8 months, that's fine; I'm not worried. If they've fallen by 95%, on the other hand, I would want to get a booster right away to bring the "riot police" defense back up (even if I know my T cells and B cells are still just as active). The antibodies provide the most protection against transmission, which is my biggest concern (since I'm otherwise fairly healthy). Are you sure the age-adjusted rates of infection are higher in the vaccinated population? That's not what I've seen. The numbers of infections are higher in the vaccinated population, yes, but that's because the UK has almost everyone over 18 vaccinated. The mRNA vaccines are 85-90% protective against infection immediately after vaccination. Protection against infection wanes over time (though it doesn't drop below 55-60%), but protection against serious illness remains high.
  6. That's not the correct take-away. The vaccine isn't 100%. It does seem to provide some (most) people with the ability to not get sick at all, some people who do get sick have mild symptoms and less fatality, and then there are a very few who (likely because their immune systems are already compromised) have serious cases. The problem is that there are too many variables: such as the blood type thing. Well, my take-away was certainly not that the vaccine is 100%; it definitely isn't. If people have a breakthrough infection, then it is more likely that they have some latent vulnerability (either due to blood type or due to weak immune response) and so they are more likely to benefit from a booster. That's all I'm saying. What do you mean, "no effective vaccine"? All the vaccines authorized for use are extraordinarily effective. When all this started, we were hoping to get lucky with vaccines that were 40-50% effective at preventing serious illness. Instead we got vaccines that were 85-90% effective at completely preventing infection/transmission and 90-95% effective at preventing serious illness. They're also not comparable in terms of disease duration and prognosis (AIDS is lifelong and incurable while most COVID-19 cases are asymptomatic and all cases resolve) or prevention (AIDS is 99% preventable by a combination of abstinence, monogamy, and barriers while masking and distancing only lowers COVID-19 transmission risk by 50-70%). That's probably because full booster authorization only happened yesterday, and even now you're probably not in a booster-eligible group. Doctor's aren't going to push you to take something they're not yet able to give you. Masking as a way of protecting yourself was never believed to be particularly effective. Cheap cloth masks do not offer significant protection to the wearer. Masking is effective, however, for source control: reducing transmission. If I'm in a room with someone who has presymptomatic COVID and I am wearing a mask, my odds are not great; if they're wearing a mask, my odds are much better. This is one of the first respiratory viruses in human history with a significant presymptomatic contagious period. With most communicable respiratory diseases, you begin to be contagious when your symptoms first emerge, and you remain at the same level of contagiousness until your primary symptoms start to wane. But with COVID-19, you are extraordinarily contagious 2-3 days before you show any symptoms, and by the time you realize you are infected, you are less than half as contagious as when you started. The primary mode of transmission for COVID-19 is superspreader events by presymptomatic carriers who find out later that they are infected (or whose symptoms are mild enough that they never even realize it was more than a head cold). The goal of masking is not to protect the wearer, but to protect everyone else in case the wearer is presymptomatic and doesn't know it yet.
  7. Your maths are off. According to the CDC’s most recently-updated data, the primary mechanism of action for the vaccine is infection prevention. Your antibodies are high enough that you are 85-90% less likely to become infected at all. And that risk reduction is consistent across the range of age and pre-existing conditions. So if you have a million unvaccinated people and a million vaccinated people who all have an otherwise-similar range of ages, lifestyles, heath issues, and exposure risk, any given adverse outcome will be 5.7-9 times more common in the unvaccinated group. Remember, COVID-19 is much more deadly than polio. The vaccines are effective at preventing illness because they stimulate antibody production. High antibody counts keep you from becoming infected in the first place, and they reduce the severity and transmissibility of breakthrough infections. If you are in an age group or other risk group that has a weaker immune response, your antibody counts will drop more quickly, and so you need a booster. If it has been more than 8 months since you were vaccinated, your antibody counts have dropped, and so you need a booster. Not everyone needs a booster. Spacing out shots produces higher immunity response. But keeping antibody counts high across the population is the best way to keep infections, hospitalizations, transmissions, and deaths low. If people were fully-vaccinated and caught COVID anyway then their immune systems aren’t working particularly well and so they absolutely need a booster. If they got vaccinated after recovering from COVID, then they probably don’t need a booster.
  8. It seems settled that the mRNA vaccines produce a stronger antibody response. It is possible that the viral vector vaccines produce more persistent, broad-spectrum immune system activity at the expense of lower antibody response. We also have good evidence that if you’ve had a viral vector vaccine, getting a subsequent mRNA booster raises your antibody titers just as high as if you started with mRNA from the beginning. Arguably, then, if the viral vector vaccine provides enough antibody priming to reap the benefits of the the mRNA booster, the viral vector booster would have enough effect to reactivate the antibody response of the mRNA vaccine, and so getting Moderna+Moderna+J&J might just be the best possible approach. The Moderna booster is still larger than the Pfizer booster, so I suppose that going Moderna^3 would result in the highest possible antibody count. However, antibody count drops asymptotically so the value of an overwhelming antibody count might be less important.
  9. I don’t *think* this gets political. There are a few differences between the Pfizer and the Moderna. Moderna uses 100 micrograms of active ingredient while Pfizer only uses 30 micrograms. The Moderna booster is a half-dose but it will still be more of a dose than Pfizer. There is some evidence that Pfizer’s immunity waned more quickly even though it was a higher initial immunity. However, that could be due to confounding variables (Pfizer was released first and so more Pfizer recipients are elderly, whose immune systems are weaker) or due to administration mode (Moderna shots were given 28 days apart while Pfizer shots were given 21 days apart, and the delay may mean better long-term immunity). Evidently the J&J vaccine tends to stimulate more cellular immunity because part of the vector DNA ends up being transcribed and expressed in addition to the spike protein code. So I am wondering whether it is worthwhile to get the J&J booster on top of my Moderna course.
  10. The FDA has now officially expanded the EUA for the three COVID-19 vaccines currently available in the United States to allow boosters regardless of what initial vaccine a person formerly received. In addition, the FDA has approved individuals to "mix and match" boosters, so that a person who received the J&J vaccine could get a Moderna booster or someone who received the Pfizer vaccine could get a J&J booster. This raises the question -- what's the best booster to get? There's a recent study out of the NIH which suggests that if you got the J&J single-shot vaccine, you will do better with an mRNA booster than with another J&J shot. However, it didn't address what happens if you take the J&J booster after the mRNA vaccine, and it also used only a single-date antibody test so it's hard to know for sure that the J&J booster didn't catch up with or exceed the mRNA booster levels. Any ideas? I got Moderna...would I be better off with J&J?
  11. Whenever I think about next-generation nuclear reactor designs, I’m reminded of the Cecil Kelley criticality incident. There was an unfortunate excursion in a plutonium reprocessing lab that claimed the life of one of the technicians when an extraordinarily high level of dissolved plutonium was introduced to a vat in the lab. The operator turned on the vat to mix it, not realizing how high the plutonium levels were, and the plutonium-enriched layer of fluid at the top was pulled down into a vortex, creating a critical mass: One way to make an “inherently safe” reactor would be to use a liquid fuel solution that could have its criticality controlled by geometry through rotation, thus requiring a constant source of energy to maintain operation. Lose power, and the fluid spins down quickly and can no longer maintain critical geometry.
  12. Efficiency loss due to physical separation hasn’t stopped molten salt reactors before; there are lead-cooled salt reactors, for example. And I would have to imagine that there would be a geometry solution to salt deposition, right? Helium is not known for being particularly dense….
  13. Yep. This proposal quickly reduces to a pulsejet engine, which of course works very well for backyard projects or 1940s-era cruise missiles but is incapable of accelerating to spacecraft-useful speeds.
  14. Is there anything you can use in place of graphite with the same design? That's one of the things we all love about molten salt reactors -- they are SUPPOSED to be melty, and if they get too hot they simply melt through the freeze plug and are dumped. It's also fairly low-pressure. One of the challenges in a molten salt reactor is that the salt is the coolant and so the salt has to be pumped around in a loop, which is very challenging to get right. Would it be possible to have a helium-cooled molten core reactor?
  15. To start with, keep in mind that you want to conceptualize everything in terms of field interactions, not interaction between the object and the field. The electrically charged particle in a magnetic field experiences the Lorentz force because its electrostatic field is moving through a magnetic field and the motion of one field through the other produces a field interaction. a So, what does the magnetic field of a monopole look like? Unlike dipole electrostatic fields, magnetic dipoles do not arise from the aggregate of negative charges on one side and positive charges on the other, but rather arise from the intrinsic dipole magnetic moment of elementary particles. The field of a magnetic monopole would be a monopole magnetic moment, which is NOT merely the bisection of a dipole moment, but something else entirely which we haven't ever observed. But our best guess would be to analogize to the Coulomb and Lorentz interactions. This is the Lorentz equation: and this is the Lorentz equation with the monopole extension: So just as a moving electrical charge in a magnetic field experiences a force which is the cross product of its charge*velocity and the vector strength of the field, a moving magnetic monopole in an electric field experiences a force which is the cross product of its magnetic charge*velocity and the vector strength of the field. And so, by analogy, a monopole in a magnetic dipole field would act the same as an electrical charge in an electric dipole field. In other words, yes, your intuition is right.
  16. It’s worse than that. As I pointed out upthread, the maximum detonation speed in a fuel-air mixture is 1,800 m/s, which means the greatest speed you can obtain using fuel-air detonations is 1,800 m/s. I completely reverse my prior stance. This is an excellent idea. Except you will want to use many small fuel-air bombs instead of large ones. By making the bombs smaller, you will be able to wrap the pressure plate around the explosion in a cone shape and thus make it more efficient. You will also want to have an extra hole in the center so that air can flow through to participate in the fuel-air bomb. You will need some sort of reverse-pressure-plate at the front to compress that air so that it comes in and mixes well with the fuel. Instead of dropping the bombs in one by one, you should make them into a liquid that can be sprayed continuously into the flow of compressed air so that it detonates continuously. Congratulations, you have invented the ramjet.
  17. Is it like thermonuclear, where efficiency continues to go up no matter how big you get, or is there a power level where you basically max out your benefits? Modular-distributed makes a lot of sense for a lot of reasons, but I find myself wondering whether we could ever see the entire eastern seaboard running on one offshore megareactor.
  18. I would like to get a better idea of the scaleability characteristics of nuclear. Is bigger better/more efficient? Is there a lower limit?
  19. On suggestion by @CastleKSide, I decided to start a thread on nuclear reactor design, particularly with a focus on near-term next-generation reactors, but generally open. This will split the discussion on the SpaceX thread about startups working in modular reactors. Tagging possibly-interested parties @mikegarrison @KSK @JoeSchmuckatelli @RCgothic @CatastrophicFailure @Rakaydos @AHHans
  20. No, it will not work. The maximum detonation wave speed in an ideal thermobaric explosive is around 1.8 km/s. This means that once you are moving at 1.8 km/s, blowing up more fuel-air bombs behind you won’t do anything, because you’re moving away faster than the shockwave can reach you. A thermobaric Orion will not get you anywhere. There will NEVER be an occasion or situation where a "non-nuclear Orion" makes ANY sense. Never. Thermobaric explosives are effective because they are able to use atmospheric oxygen to support detonation, rather than depending on an oxidizer chemical premixed with the reducer chemical to create the explosive. Since oxidizer makes up over half the weight of an explosive, you can get more kaboom per kilogram (pow per pound in freedom units) if you can use atmospheric oxygen instead. But if you're trying to propel a vehicle and you want to use atmospheric oxygen, you use a jet engine. A pusher-plate system is WILDLY inefficient. The ONLY reason for a pusher-plate is if you cannot control the release of energy from your engine, which is ONLY applicable when using nukes. If you want to use atmospheric oxygen to help you get to orbit, try Skylon.
  21. I suppose that would be necessary, yes. “The company began to create a budget microreactor that could fit in a regular shipping container. The megawatt model will be capable of powering up to 1,000 homes and is expected to use helium for cooling instead of water. The main places of use are remote settlements, zones of natural or other disasters, and military bases.” So presumably it would be limited to a locale with water access…not scaleable or suitable for residential solutions, for example. At least that’s what I would imagine. At 1 MW and a Braxton efficiency of ~65% (enabled by a high-temperature coolant), that’s 1.53 MW of thermal power that needs to be rejected. I ran the numbers (after typing that) and it’s not as bad as I thought. If your water heat sink loop raises water temperature by 20 degrees Celsius, you only need a flow of 1100 liters per minute.
  22. Here's the typical schematic for a helium-cooled reactor. Cool, pressurized helium is pumped around the reactor and through the reactor core, gaining thermal energy. It is then expanded through a turbine, which operates a series of compressors. The helium is cooled via heat sink and passed through the compressors in cycles to return it to its compressed, cool state. The turbine also operates the generator. I wonder what kind of heat sink is used for cooling the helium. I'm also curious to know how cool the helium is supposed to be when it enters the reactor. Helium obviously can remain gaseous at very low temperatures; is there an advantage to getting the largest temperature swing possible? Would the system efficiency be improved by a secondary refrigerant loop?
  23. Aye. There are radioactive isotopes of helium, but the only one that could be created in a reactor by neutron capture would be 5He, which decays back into 4He by neutron emission in about 6e-22 seconds.
  24. It was not initiated by a helium leak; it was initiated by LOX crystals freezing in the composite overwrap layers, resulting in COPV failure. Of course once the COPV failed then the helium certainly "leaked" in a very sudden and dramatic sense. The first Falcon 9 failure was also a helium "leak" in the sense that a failed strut caused the COPV to break free and fall through the LOX and then fail on impact with the common bulkhead; the rupture of the COPV released the pressurized helium. AFAIK the latter. But that's mostly "I haven't heard anyone complaining about helium diffusing everywhere" and not "I know that helium is well behaved." Helium diffuses through solids just like hydrogen does -- in fact, I believe it may diffuse a little better. However, diffusion is not what makes hydrogen so nasty. Hydrogen embrittlement happens because individually-migrating hydrogen atoms meet up inside the tank/pipe wall and decide to bond with each other, essentially producing nanoscale bubbles inside the metal, rapidly degrading its material strength. It's like when Vision phases his hand into someone's chest and then unphases his hand while it's still inside.
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