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Cake day: August 11th, 2023

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  • Ligo provides great science summaries for most publications, here is the one for this.

    By comparing the data to these models, we found that these black holes weighed approximately 137 and 103 times the mass of the Sun, respectively. Taking all uncertainties into account, their total mass was likely between 190 and 265 solar masses, dethroning GW190521 as the most massive black hole binary observed so far.
    […]
    The merger produced a black hole with a mass likely between 182 and 251 solar masses.

    So it seems 137 and 103 solar masses are the best estimates for each single black hole before merger. Due to uncertainty however, their total mass is in the range of 190-265 solar masses, of which 182-251 remain after merger. The rest of mass is emitted as gravitational waves.


  • What you describe is more like black start, providing power to the grind when it is down. This has to be controlled well, and only a few plants need to be capable of it.

    Grid following means something like whatever the grid does, the inverter injects power supporting it. A grid forming generator or inverter also follows the grid somewhat, but tries to get it to an optimal condition. This entails things like voltage control by reactive power, frequency control by operating reserve, fault ride trough capability and so on. Many of those are naturally provided by large conventional power plants using synchronous generators like gas, nuclear or hydro. For inverter based systems, they have to be considered explicitly. For battery storage most are relatively easy to implement, some also in solar inverters. The tech exists, but yes, in some countries the regulations have not kept up with rapid expanse of inverter based power generation in the last years.



  • Out of interest I did some estimates and it seems that an asymmetry of three billionth of the total thermal radiation would be enough to rotate the probe once over a timescale of 10 years. So if the radioisotope generator has even just a tiny bit of a different infrared brightness on one side, it would turn voyager in a few years.

    notes on calculation

    Voyager weight: 815 kg
    Approximate Diameter: 1 m
    Assume mass and thermal radiation emitted with a center distance of this diameter. Then we can calculate as it would need to move 2π 2 m. It should be enough as coarse estimate and underestimate the acceleration. Distance to move: d = 6.3 m

    Assume constant acceleration due to thermal radiation
    RTG power at start: 3 * 2.4 kW = 7.2kW
    RTG power now: 7.2kW * 10^(48/88) = 4.9 kW
    Total of thermal radiation: 4.9kW / c = 16 uN
    distance moved: d = a t^2 / 2
    assuming 10 years accelerated movement movement:
    a = 63 mm/yr^2
    F = 52 fN
    3 * 10^-9 of thermal force



  • The thing is, now we have one 1-2 3.7 meter sized antenna on the voyager probes and a 100 meter sized antenna on earth with high transmission power. Signal decays with distance squared. To get the same signal power to the voyager probe assuming an relay in the middle, it would need an 25 meter antenna with the large transmitter/receiver currently on earth on space.

    In short it’s easier to build a 4 times better transmission system on earth than in an relay in space.

    One point where relays are used are mars rovers. There the orbiter has an large antenna and is close to the rover, so you don’t need to land the large antenna at the surface.

    Edit: fixed antenna diameter



  • lurker2718@lemmings.worldto196@lemmy.blahaj.zonerule
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    1 year ago

    The more self-sufficient you can be, the fewer societal resources you will take up, which could then go to someone else in greater need. That’s my perspective at least.

    But the more self-sufficient you are, the more resources of yourself you need to supply yourself. So you can provide less societal resources. If you do not need to provide clothes for yourself, you have more time caring for elderly, etc.

    As another view, the total resources need does not directly change by changing who does what. The advantages of helping each other are in the OP. At some point however, I would think, the overhead of organization grows so large that it may not be worth it anymore. Just think of the amount of work put into “useless” administration in many countries. But in a 30 person village, this is probably negligible.

    Edit: Thanks for helping other people on the feet!


  • lurker2718@lemmings.worldtomemes@lemmy.worldnuanceposting
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    1 year ago

    I think your post is exactly what is criticized by OP. In the first part of the post it is explicitly stated men should not talk over the fear of women. A message like yours seems to blame people just because they criticize the way of discussion in some places. I think it is obvious that men are influenced in a possible negative way, when they are always seen as danger. At least for me it probably contributed to my low self esteem, especially in all sex/gender related topics. I think, we as men do so much harm, I don’t want to take part in this. But i took it to the extreme, so I was ashamed of everything sexual about me. But as OP said, all of this doesn’t invalidate the feeling of any woman. But for example this situation here is not governed by fear, still it seems you can’t discuss the social effects of this sentiment “against” man, without discrediting the other side. Sure, violence done mainly to women is the most important topic. But if men always get portrayed as danger, I can understand some are open to other, more misogynist worldviews.



  • Yes. One place in space has different temperatures. I would assume even individual particles are not distributed by a Maxwell distribution, so the concept of temperature is hard to apply. The background radiation has one temperature. If you add the sun, however, you already have a problem as the sun radiation is not in thermal equilibrium. So depending on how you look at it, you get different temperatures. The particles have a high energy, so also a high temperature. But they are so rare, that radiation is the dominant mode of heat transfer and determines the temperature of a thermometer placed in space.


  • I think it is actually the other way around. You can consider the air inside the balloon to have internal energy from the heat. And additionally you have to make room for the balloon in the atmosphere, so you have removed the atmosphere from the volume the balloon takes, which also needs energy. If you consider both you arrive at the concept of enthalpy (H = U + pV), which is very useful for reactions in the atmosphere as pressure is constant. For this example it is not that useful as outside pressure changes when the balloon rises.

    Another way to see it, the pressure has no “real” energy. In a ideal gas, the only energy comes from the kinetic or movement energy of the atoms. Each time a gas molecule is hits the balloon envelope it transfers some momentum. The cumulative effect of the constant collisions is the pressure of the gas. If the balloon is now expanding slowly, each collisions also tranfers some energy, in sum building the work the system has to do to the atmosphere. Leading to a decrease in internal, so “real” energy in the balloon. This corresponds to a decrease in temperature.



  • While I agree in general, one point is a bit to simplified in my opinion

    In other words, there are fewer air molecules per cubic foot (volume of air). The molecules are farther apart and can hold less heat energy. Because “heat” is what we say when we mean molecules are moving around.

    Less molecules mean less heat, it has nothing to do with the temperature, if you just decrease the density by removing half the molecules, you have the same temperature.

    It cools down because it expands adiabatically. Consider a very thin balloon filled with air which is warmer than the surrounding. This now rises up, but as it does, the pressure decreases, causing the balloon to expand. During this expansion, the balloon transfers energy away from itself, because it has to push away air, to make room for expanding in the surrounding. This work cools the air inside the balloon. Assuming the air inside is dry, it would cool around 10 °C per km it rises. Now if you think about it, the balloon just stopped the inside from mixing with the outside. If you look at a large “piece” of air, it does not mix very fast, so you can remove the balloon and just consider what happens with warm air heated from the ground.

    Now this does not mean, it has to be cooler when higher up. The same points hold, inside a house, but there it is often warmer when higher.

    The best explaination is when looking where the heat comes from and goes too from the air. The atmosphere is mostly heated from the surface of earth, so the bottom and cooled from the upper layers. So naturally it gets hotter where it is heated. The question is now by how much? There are three modes of heat transfer in the atmosphere: radiation, conduction and convection. The first two are very slow. Connection is fast but has limits. Consider the piece of air, if it rises, it cools. So at some place it may be the same temperature as the surrounding air, so it stops rising. This means the convection works only when the air gets cooler by 10 °C/km going up (~6.5°C when the air is moist and precipation happens). So this temperature gradient is observable very often.


  • I just want to say, i loved Dragon’s Egg for this level of detail to the physics. I even did some quick calculations why you want 6 compensator masses not less to reduce the effect of tidal forces. Or the black holes inside the sun, at first i thougt, this is impossible. Then i read some more on it an noticed its well researched.


  • lurker2718@lemmings.worldtomemes@lemmy.worldIt's cheaper is what it is
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    2 years ago

    I think I understand you. I also think there are needs for extreme emotional response. However, I would be interested how often they helped you in, and how often the only effect of these was making you feeling worse?

    I did some therapy in this direction. And I am generally more content. I can enjoy way more time of my life than a year ago, even in similar situations.
    But if we talk about the status of the world, I am at least as angry and sad as before. And I also do at least as much to change it as before. Which, to be honest, is not as much as I would like.

    Edit: I think I can actually experience emotions more intense now, while not being overwhelmed by them.


  • I want to thank you for your messages here. I agree with promethil that you need to consoder yourself, i think texts like yours can do quite something good. Sure you won’t heal someone with a few messages. However, I was brought to a mindfulness training* mostly by a reddit chain of comments and this helped me, along other things, a lot, getting out of difficult times.

    *An app called “Mindfulness Coach” by the US Department of Veterans Affairs