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Thursday, January 28, 2021

What does "Entropy" mean?

What does "Entropy" mean?


What does "Entropy" mean?

Posted: 27 Jan 2021 02:20 PM PST

so i know it has to do with the second law of thermodynamics, which as far as i know means that different kinds of energy will always try to "spread themselves out", unless hindered. but what exactly does 'entropy' mean. what does it like define or where does it fit in.

submitted by /u/bert_the_destroyer
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AskScience AMA Series: I am Avi Loeb and I'm here to explain how I noticed the first tentative sign for Intelligent life beyond earth. AMA!

Posted: 28 Jan 2021 06:12 AM PST

I am the Frank B. Baird, Jr., Professor of Science at Harvard University. I received a PhD in Physics from the Hebrew University of Jerusalem in Israel at age 24, while leading the first international project supported by the Strategic Defense Initiative (1983-1988). Subsequently I was a long-term member of the Institute for Advanced Study at Princeton (1988-1993). Throughout my career, I have written 8 books, including most recently, Extraterrestrial (Houghton Mifflin Harcourt, 2021), and about 800 papers (with an h-index of 112) on a wide range of topics, including black holes, the first stars, the search for extraterrestrial life and the future of the Universe. I had been the longest serving Chair of Harvard's Department of Astronomy (2011- 2020), Founding Director of Harvard's Black Hole Initiative (2016-present) and Director of the Institute for Theory and Computation (2007-present) within the Harvard-Smithsonian Center for Astrophysics. I also chair the Board on Physics and Astronomy of the National Academies (2018-present) which oversees all Decadal Surveys in Physics and Astronomy. I am an elected fellow of the American Academy of Arts & Sciences, the American Physical Society, and the International Academy of Astronautics. In addition, I am a member of the President's Council of Advisors on Science and Technology (PCAST) at the White House and a member of the Advisory Board for "Einstein: Visualize the Impossible" of the Hebrew University. I also chairs the Advisory Committee for the Breakthrough Starshot Initiative (2016-present) and serve as the Science Theory Director for all Initiatives of the Breakthrough Prize Foundation. In 2012, TIME magazine [pdf] selected me as one of the 25 most influential people in space and in 2020 I was selected among the 14 most inspiring Israelis of the last decade. Click here for my commentaries on innovation and diversity.

I will be on at 11a.m. EST (16 UT), AMA!

Username: /u/Avi-Loeb

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When astronomers refer to distances between galaxies, do they mean the distance as we observe them or as they are now?

Posted: 27 Jan 2021 11:20 PM PST

For example, if astronomers describe the distance between two galaxies in a supervoid that is a billion light-years away to be 150 million light-years. Is that distance representative of what we have observed (essentially an image from a billion years ago) or as it is now (accounting for the expansion of the universe)?

submitted by /u/stuffdude99
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Do older people vaccinated for Covid have a “good” immune response from it?

Posted: 28 Jan 2021 05:18 AM PST

My otherwise very healthy and independent 94yo grandmother received her first Covid vaccine 5 days ago. I asked her if her arm was as sore as mine and she said it doesn't hurt at all. I was wondering if the immune response in the older population has been studied much. I'm just curious if her complete lack of side effects is an indication that her body did not get a strong immune response.

submitted by /u/BRCRN
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If all electrons are identical, then how can they have different energy levels?

Posted: 28 Jan 2021 06:33 AM PST

I've heard that the farther an electron is from the nucleus, the more energetic it is. But how can this be if all electrons are identical?

submitted by /u/imgoingdef
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Do gravitional waves effect time?

Posted: 27 Jan 2021 09:47 PM PST

Since gravitional waves are ripples in space-time, how do they effect the time component? Is there any kind of time dilation?

submitted by /u/RigbyAtNight
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How does an increase in humidity assist plant growth?

Posted: 27 Jan 2021 11:14 PM PST

For many indoor plants that have evolved to live in more humid environments, it appears that reducing humidity levels can impair their growth. Why is this? Given that an increase in humidity decreases the rate of transpiration and thus slows nutrient uptake from the soil, why would they grow faster?

submitted by /u/Fartfenoogin
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How laser measuring tools work?

Posted: 27 Jan 2021 07:23 PM PST

Ultrasound space measuring works by measuring the time it takes to a sound wave go, reflect and return to the tool. But we cant really measure the speed of light cuz it is too fast to be detected, so laser measuring tools can't work like ultrasound tools. So how does it work?

submitted by /u/MCarooney
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Do all vaccines get tested for sterilising immunity?

Posted: 27 Jan 2021 03:11 PM PST

People are saying that we don't know if the new COVID vaccines will affect transmission of COVID. Every other vaccine I heard of stops transmission of whatever they're vaccinating against, so I don't understand why this would be different. However, if they all need to be tested for this I would understand, as it would then just be a routine question. Do all vaccines need to be specifically evaluated for sterilising immunity, or is this something we're only worried about with the new vaccines?

submitted by /u/namedbymybrother
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With sunglasses on, one of my computer monitors is almost unaffected, only slightly darker, and the other one turns entirely black. What about monitors or sunglasses makes them react differently?

Posted: 27 Jan 2021 02:30 PM PST

Optics/Eye anatomy: How *exactly* does the eye perceive the color green from a mixture of yellow and cyan pigments on a white sheet of paper?

Posted: 27 Jan 2021 02:18 PM PST

Thanks in advance for entertaining my very basic question. Here's what I think I know so far:

White light shines from a light source and hits the cyan and yellow pigments. The pigments reflect the wavelengths that correspond to cyan (ca 475nm) and yellow (ca 580nm) respectively, and absorb the rest. The "cyan" and "yellow" wavelengths then enter the eye.

If the above is correct, does that mean that the tristimulus values of spectral green and cyan+yellow are the same, like in the case of yellow and green+red?

Apologies if this is a dumb question. I think my confusion comes in part from trying to figure how additive and subtractive color models fit in the real world. Would it be accurate to say that subtractive color is a part of physical reality, while additive color exists only as a part of human perception?

Bonus question: I understand that in reality a blue object does reflect other wavelengths besides "blue" ones, albeit at a lower intensity. But are there chemicals or chemical structures that manage to exclusively reflect an incredibly narrow range of wavelengths (say, 500-505nm), without reflecting any other wavelengths at any degree of intensity?

Thank you for your time!

submitted by /u/Grain_in_a_Jar
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Why do infected cases grow in waves during a pandemic?

Posted: 27 Jan 2021 11:04 AM PST

At the beginning of the coronavirus pandemic they kept telling us on the news about how it would come in waves, and from looking at regional charts, it really has happened in waves.

Is that because of human behavior or something to do with the virus itself or what?

Edit: to clarify my question, if we didn't do lockdowns, didn't have holidays, or other human type of social behavior changes, would we still see the disease spread in waves?

submitted by /u/mntgoat
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What causes the steams different behaviour?

Posted: 27 Jan 2021 11:02 PM PST

Why is it that the steam coming from outside into my bathroom, through my window, is falling to the floor, whilst the steam coming from inside the shower cubicle rises to the ceiling?

PS: I'm not sure which category this is, but I believe it's physics

submitted by /u/Kasper_II
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Are the current COVID-19 vaccines not as effective for certain races?

Posted: 27 Jan 2021 04:45 PM PST

I just read an article from MIT that said the immune response was not as strong in people with certain genetic backgrounds (they specifically mentioned Asians).

I don't understand the science behind the research. Is this a concern? If so, can the drug manufacturers improve the vaccines?

submitted by /u/bob_ross_happy_tree
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Is it possible to store video data as a photo?

Posted: 27 Jan 2021 09:45 PM PST

This probably sounds like a dumb pointless question and I'm sorry if this isn't the right sub to be asking this sort of thing. I know there are ways of making sounds into images and vice versa, like using SSTV image generators and decoders for example. I was wondering if there is a way you can take the digital video data from a video and save it or transform it into a single picture? Hopefully this makes sense.

submitted by /u/Awkwarddruid
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I'm watching Fritz Lang's 1931 silent film "Woman in the Moon" and they got surprisingly accurate with some of the science of orbital mechanics. When (and who) calculated the physics of spaceflight to the moon?

Posted: 27 Jan 2021 01:28 AM PST

Outside the whole "we can breathe on the moon" aspect, the 1931 silent film surprised me with the accuracy of the spaceflight facts a decade or two before the big rocket programs:

  • "we will land 36 hours later on the far side of the moon"
  • "necessary speed of 11,200 meters per second" (escape velocity)
  • The need to cut the rocket motors or speed past the moon.
  • 8 minutes of acceleration, then at 227,00km above Earth, coasting, and weightlessness.

Kepler and Newton advanced planetary mechanics and Halley famously applied that to his comet, but I can't seem to find info on the first to figure out spaceflight parameters for a flight to the moon. (Probably just flubbing search terms late at night.)

submitted by /u/westtxfun
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Wednesday, January 27, 2021

I keep reading about how Covid has had a worse effect on minorities in the US particularly blacks. Is this all because of environmental/societal reasons, or do people of African decent actually have a harder time with the virus physically?

I keep reading about how Covid has had a worse effect on minorities in the US particularly blacks. Is this all because of environmental/societal reasons, or do people of African decent actually have a harder time with the virus physically?


I keep reading about how Covid has had a worse effect on minorities in the US particularly blacks. Is this all because of environmental/societal reasons, or do people of African decent actually have a harder time with the virus physically?

Posted: 27 Jan 2021 05:33 AM PST

do your teeth move at night?

Posted: 27 Jan 2021 03:09 AM PST

ik this sounds weird lol but i think i remember someone saying/reading somewhere that your body swells a little bit while you sleep. but when i stay up way extra too late it feels like when i bite down my teeth aren't in the right place.. if that makes sense, just slightly shifted. so are your teeth included in this? or your skeleton i guess

submitted by /u/lakendra758
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How do they make COVID-19 mRNA?

Posted: 27 Jan 2021 07:10 AM PST

I've learned that mRNA is essentially a direct order for your cells to make COVID-19 antigens, so instead of your cells taking mRNA from the nucleus, the COVID-19 vaccine mRNA hijacks the mechanism to make COVID-19 antigens.

Now I'm curious how do they actually make such mRNA? Do they snip the genetic material from the virus itself? Or do they have to actually create one?

Sorry if this has been asked before, a link to the thread would be appreciated. Thank you!

submitted by /u/paulaldo
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What causes the boundary layer to separate?

Posted: 27 Jan 2021 02:37 AM PST

I was looking at a example of a fluid flowing past a sphere, it was mentioned that at low velocities the air hugs the ball evenly everywhere, low speed means that less impulse is given to the fluid, therefore the effects of pressure will be much stronger and the back of the ball will suck in the airflow and even out the pressure on the back and front, is this correct?

Then I looked at examples of flow around a ball but a much faster one, then the thing with the boundary layer separating confuses me a lot, i think the cause is the side inertia (can i even call it that, i know its some kind of side force gained from moving in a not straight direction around the ball, it looks like inertia to me) can fight the ow pressure on the back for a time, is this correct it makes sense to me but i cant find any way to confirm it.

submitted by /u/nekoi_si_tam
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Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology

Posted: 27 Jan 2021 07:00 AM PST

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Economics, Political Science, Linguistics, Anthropology

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

Answering Questions:

Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience.

If you would like to become a member of the AskScience panel, please refer to the information provided here.

Past AskAnythingWednesday posts can be found here. Ask away!

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What’s the reasoning for different needle lengths with vaccines?

Posted: 26 Jan 2021 11:24 PM PST

While I do have a background in clinical laboratory science, I'm more versed in the "how it works" from an immunological standpoint and not the "how to deliver it." I understand gauge (we were taught this as it applies to hemolysis, lol), but I'm curious about lengths.

I noticed that my Covid vaccine (Pfizer) needle was quite long today, longer than my flu vaccine. I didn't realize the first time, but for some reason I really wanted to take a look today!

Is this to do with viscosity? I did "feel" the first dose, and my second dose today really did feel like syrup in my arm.

Either way, I'm glad to be vaccinated, I'd love to learn more about this.

submitted by /u/hyphaeheroine
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Does the percentage of vaccinated per capita include children and others that medically or legally can't vaccinate?

Posted: 27 Jan 2021 06:20 AM PST

And if so, why? It's very confusing.

submitted by /u/Yuval8356
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Is there any particular reason that Pangea broke apart parallel to the Appalachian Mountains? If and when Asia and India separate again, are they more likely to do so along the original convergent boundary?

Posted: 26 Jan 2021 06:24 PM PST

How do antibodies fight viruses and bacteria, and what are the differences in dealing with the two? How do they 'know' what to attack? And for a local infection (like from a cut), does the body know to send extra antibodies there, or are they always equally dispersed through the body?

Posted: 27 Jan 2021 07:43 AM PST

Why are there so many Coronavirus variants all of a sudden?

Posted: 27 Jan 2021 06:22 AM PST

I understand that the virus can evolve and mutate, but why is it that after a year of pandemic with no significant mutations, suddenly there are 3 new variants in a few weeks?

Thanks a lot and sorry for English mistakes.

submitted by /u/ChenTasker
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Why are some masks effective against the "normal" covid but not good enough for some of the variants?

Posted: 27 Jan 2021 06:19 AM PST

A lot of people are buying different masks because of the new variants, why don't the masks work if the virus structure/size is basically the same?

submitted by /u/Chora123
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Why are people with Down syndrome more susceptible to covid?

Posted: 26 Jan 2021 02:27 PM PST

I was scrolling Twitter and saw this tweet and became curious. The tweet essentially claims that people with Down syndrome face "risks 10x greater with covid" I did a quick google and found this site that states people with Down syndrome are more likely to have sleep apnea which can add to the risks with covid. Apologies if I haven't thoroughly checked my own source but I can't readily find any more info.

My main question is why are people with Down syndrome so much more at-risk than others, and if it really is all about sleep apnea then why isn't that being discussed more considering many more people suffer from sleep apnea (I believe that is very common with overweight folks, shout-out USA) than Down syndrome to the best of my knowledge.

submitted by /u/JoshRichardson4MVP
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Why do we say electrons in a metal move around with velocities determined by kT instead of the Fermi level?

Posted: 26 Jan 2021 09:42 AM PST

It's all over solid state text books that the velocity of electrons in a metal (assume no applied field) is something like root(kT/m) (I don't care about the 2's and/or 3's that I'm missing). This perspective makes sense because it's sort of the amount of energy an electron might get from the thermal bath it's sitting in.

But also, from QM, if we keep adding fermions (electrons in this case) to the metal, they'll occupy higher and higher energy states. Even at T = 0, the electrons will have nonzero energy, in particular, electrons at the top will be at the Fermi energy. In this case, the thermal velocity would be zero, but the Fermi velocity can get up near a percent of the speed of light (graphene for example). Clearly this is a huge discrepancy.

So, why do we say electron speed is governed by kT instead of the Fermi level?

It's a quantum vs classical issue as pointed out. Dense systems of electrons should go by Fermi energy, sparse systems can use kT.

submitted by /u/rice_jabroni
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In terms of the vaccines, what’s the difference between JNJ-78436735 and Ad26.COV2.S? How many types of vaccines is Johnson & Johnson developing, and which one is planned to roll out soon?

Posted: 26 Jan 2021 06:58 PM PST

Maybe I'm misunderstanding this, but can someone clearly delineate the differences between these two vaccines? Which one is currently being tested and considered for authorization in the coming weeks? What makes the two different, is that significant?

I did not previously realize that Johnson & Johnson is developing and testing two or three separate vaccines: JNJ-78436735, Ad26COVS1, and Ad26.COV2.S. Basically, my question is about which one is planned for use, and what are the differences between them?

submitted by /u/ano1067
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Does widespread immunity decrease virus mutation rates?

Posted: 26 Jan 2021 02:52 PM PST

With ongoing news about mutations to the covid-19 virus (and potential impacts to vaccine programs) I'm curious what the relationship between the level of population immunity and mutation rate is. It would stand to reason that lower infection rates -> fewer opportunities for mutation -> greater long term vaccine efficacy; but of course what's intuitive isn't always right.

Are we in a race to get ahead of mutations, or does it not really matter?

submitted by /u/fishsticks40
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How and why did they detonate the little boy 580 meters above Hiroshima?

Posted: 26 Jan 2021 09:59 AM PST

Multiple vaccinations for same disease?

Posted: 26 Jan 2021 08:02 PM PST

What would happen if someone was administered multiple vaccines for the same disease?

For example, for Covid-19, we have the moderna/Pfizer, astrazeneca-oxford, j&j vaccines which differ from each other (I think). What will happen if someone received each of them?

submitted by /u/anantj
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Why are some people unable to speak after a stroke?

Posted: 26 Jan 2021 10:45 AM PST

How fast did the Chicxulub Impactor appear as it collided with Earth?

Posted: 26 Jan 2021 05:54 AM PST

To an observer, did it travel like a bullet hitting a wall? Or like a cruise ship hitting a pier (slow velocity but huge momentum)?

The film Melancholia, for example, shows a relatively slow impact in the final scene. Definitely not "blink and you miss it"

submitted by /u/blishbog
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How do debris/people move back into the ocean during tsunami?

Posted: 26 Jan 2021 07:35 AM PST

I understand that it is a wave phenomenon and water currents but I can't seem to grasp why like in events or tsunami the debris flows back into the ocean?

submitted by /u/hus1999
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Tuesday, January 26, 2021

AskScience Panel of Scientists XXIV

AskScience Panel of Scientists XXIV


AskScience Panel of Scientists XXIV

Posted: 25 Jan 2021 01:49 PM PST

Please read this entire post carefully and format your application appropriately.

This post is for new panelist recruitment! The previous one is here.

The panel is an informal group of Redditors who are either professional scientists or those in training to become so. All panelists have at least a graduate-level familiarity within their declared field of expertise and answer questions from related areas of study. A panelist's expertise is summarized in a color-coded AskScience flair.

Membership in the panel comes with access to a panelist subreddit. It is a place for panelists to interact with each other, voice concerns to the moderators, and where the moderators make announcements to the whole panel. It's a good place to network with people who share your interests!

-------------------

You are eligible to join the panel if you:

  • Are studying for at least an MSc. or equivalent degree in the sciences, AND,
  • Are able to communicate your knowledge of your field at a level accessible to various audiences.

-------------------

Instructions for formatting your panelist application:

  • Choose exactly one general field from the side-bar (Physics, Engineering, Social Sciences, etc.).
  • State your specific field in one word or phrase (Neuropathology, Quantum Chemistry, etc.)
  • Succinctly describe your particular area of research in a few words (carbon nanotube dielectric properties, myelin sheath degradation in Parkinsons patients, etc.)
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  • Provide links to comments you've made in AskScience which you feel are indicative of your scholarship. Applications will not be approved without several comments made in /r/AskScience itself.

-------------------

Ideally, these comments should clearly indicate your fluency in the fundamentals of your discipline as well as your expertise. We favor comments that contain citations so we can assess its correctness without specific domain knowledge.

Here's an example application:

Username: /u/foretopsail

General field: Anthropology

Specific field: Maritime Archaeology

Particular areas of research include historical archaeology, archaeometry, and ship construction.

Education: MA in archaeology, researcher for several years.

Comments: 1, 2, 3, 4.

Please do not give us personally identifiable information and please follow the template. We're not going to do real-life background checks - we're just asking for reddit's best behavior. However, several moderators are tasked with monitoring panelist activity, and your credentials will be checked against the academic content of your posts on a continuing basis.

You can submit your application by replying to this post.

submitted by /u/AskScienceModerator
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Israel has now given approximately 42% of its population one or more doses of Covid-19 vaccine. Has the vaccination program had a noticeable impact on covid-19 cases, hospitalizations and deaths so far in Israel?

Posted: 26 Jan 2021 07:12 AM PST

Moderna has announced that their vaccine is effective against the new variants but said "pseudovirus neutralizing antibody titers were approximately 6-fold lower relative to prior variants" in regards to the SA Variant. What are the implications of this?

Posted: 25 Jan 2021 09:40 AM PST

Here is the full quote from Moderna's article here...

"For the B.1.351 variant, vaccination with the Moderna COVID-19 Vaccine produces neutralizing antibody titers that remain above the neutralizing titers that were shown to protect NHPs against wildtype viral challenge. While the Company expects these levels of neutralizing antibodies to be protective, pseudovirus neutralizing antibody titers were approximately 6-fold lower relative to prior variants. These lower titers may suggest a potential risk of earlier waning of immunity to the new B.1.351 strains."

Does "6 fold lower" mean 6 times less effective? If the vaccine was shown to be over 90% effective for the older variants, is this any cause for concern?

I know Moderna is looking into the possibility of a third booster shot.

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What part, or mechanism within the brain is responsible for monitoring the perception of time? This mechanism is clearly at work when someone is asked to keep a rythm, for example the maintaining of 100 beats per minute in CPR. What mechanism is responsible for that?

Posted: 26 Jan 2021 01:41 AM PST

How do messaging apps ensure that private keys are not stolen in end to end encryption?

Posted: 26 Jan 2021 01:53 AM PST

Surely they have to store private keys in a central datastore. Technically couldn't an engineer just grab the private key and use it to decrypt any message?

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What is the most up to date assumption of number of unconfirmed cases of COVID in a given population?

Posted: 25 Jan 2021 08:52 AM PST

I remember reading after early antibody testing, assumptions were that the number of unconfirmed COVID cases was significantly high. According to worldometers the US has had over 25 million confirmed covid cases, how many cases is it assumed we have missed? Are we looking at 50 million total cases? 75?

submitted by /u/Fahamu
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Other than making profits, what is stopping vaccine makers such as Pfizer and Oxford from simply sharing their vaccine patents?

Posted: 25 Jan 2021 10:54 AM PST

Would there be a way for government to require them to share their patents with less successful biotech companies?

submitted by /u/Kingfin
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Is it possible to use MRI to diagnose mental illnesses?

Posted: 25 Jan 2021 07:51 PM PST

Explanation for USA's fairly dramatic and sustained drop in daily lab confirmed cases of Covid-19?

Posted: 25 Jan 2021 08:10 AM PST

The US, the UK and Israel have all had very dramatic reductions in the number of lab confirmed cases recently. The US and the UK in particular have seen their numbers decline very steadily since about January 10, and that would suggest that the number of infections started to drop for both of them by about January 1 (given the typical lag between infections and when they turn up in lab confirmed results).

Israel's drop in numbers has been shorter, only about a week, but it has been very dramatic. Such sharp drops are usually due to results being reported late, but in this case the sharp decline has been apparent for over a week now - it's real. Israel has reportedly given the first does of the Pfizer vaccine to at least 37% of their population and their high vaccination rate is probably what is causing this sharp reduction for them.

The UK has been in a fairly strict lockdown for weeks now, and that is the most likely explanation for their rapid and steady drop in lab confirmed numbers.

But the US has seen a drop in daily lab confirmed numbers very similar to the UK's. For when the drop started, it's steepness and for how long it's been going on.

I can't find any reason for why the US's numbers are dropping so quickly. They're vaccination rate isn't that high. They haven't implemented any new strict lockdowns (a football game I listened to for a few minutes last night mentioned that there were only 17,000 fans there but that it was still nearly as loud as when it's at it's 70,000 capacity - that is not a lockdown).

What happened around January 1 that could explain the USA's rapid and sustained decline in daily lab confirmed cases?

TL;DR: The US, UK and Israel all have had very sharp drops in cases. Israel has very high vaccination rate. The UK has strict lockdown. What explains the USA's drop? Timeline suggests January 1 as when the number of infections peaked and started to come down.

submitted by /u/Pointede8Pouces
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Why does COVID-19 location-tracking apps (e.g. CA Notify) only track positive test results, and not both positive and negative test results?

Posted: 25 Jan 2021 12:37 PM PST

When I say "COVID-19 location-tracking apps," I am referring to any app that tracks the location history of your phone alongside other phones with that app installed (e.g. CA Notify). These apps then allow you to submit positive test results, so that everyone who you interacted with prior can be notified that they might have COVID-19 and should quarantine. This is my general understanding of what the purpose of these apps are.

I just tested negative for COVID-19, but CA Notify will only allow me to submit data if the results are positive. This seems inefficient... Why not gather more data? Why gratuitously decide to not collect info?

I understand why CA Notify might not want negative test results - they don't really mean anything to the people who previously interacted with, considering the people who you previously interacted with also interacted with dozens of other people during that time and could still test positive even though you tested negative...

But then again, many people have these apps, and many people carry their phones. Knowing that 50% of the people you interacted with tested negative is much better than knowing that 24% of the people you interacted with tested negative. The more you know how much you are NOT interacting with the virus, the more you can understand about who is infection, right? I just feel like more data makes data easier to look at, but maybe I'm wrong.

A negative result is more information than nothing. I don't understand why we are not tracking this and using some AI and machine learning or something. I'm sure we could find ways to give weight to who is MORE likely to have COVID-19 than others. This doesn't seem hard to add to an app (imo)...

What do you all think?

submitted by /u/kodyamour
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Is COVID’s loss of taste/smell symptom more sever depending on age?

Posted: 25 Jan 2021 09:10 AM PST

Since it's known that senses of taste and smell diminish naturally with age, I've been curious to know if younger people are generally more likely to fully regain their sense of taste/smell faster than elderly. I read a bunch about people's sense of taste/smell being diminishing with COVID infections—some say that they recover it fully, partially, or barely at all even after months. Usually people don't post their age when they explain their recovery, but I feel it could be useful information in gauging if older people are less to regain their senses faster or at all. If you have or anyone you know has experienced loss of taste/smell due to COVID, how old were you/they and how long did you/they take to recover? Thanks so much for any insight! Edit: dangit, I misspelled "severe" :(

submitted by /u/advilqt
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So I know that wet winters+dry summers= worse fire seasons. Anybody know what the impact of snow pack on that equation is? I would think that greater snowpack would mitigate fire risk by providing moisture for longer. Potential feedback I haven’t heard discussed.

Posted: 25 Jan 2021 02:47 PM PST

Do all vector quantities obey superposition?

Posted: 25 Jan 2021 11:55 AM PST

In my recent physics courses, we've studied electrical and magnetic fields. Both of these quantities obey superposition (fields created by independent sources can be summed using vector addition). Are there any similar quantities that DON'T follow this simple pattern?

submitted by /u/Magnetd
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What is the biological reason some trees require a "chill period" below a certain temperature to set fruit?

Posted: 25 Jan 2021 04:43 PM PST

Several fruit tree species require a certain period of "chill" in order to set fruit.

What causes this biologically or what is the mechanism?

Does the entire tree need to be exposed, or can only a certain portion of the tree be exposed to chill in order to simulate the chill period?

Is the mechanism that occurs for the fruit tree the same for seeds that require chill periods?

Thank you!

submitted by /u/NotSoPsychic
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How do breastfed babies absorb mom’s antibodies through their digestive tract?

Posted: 25 Jan 2021 07:24 AM PST

Bonus question - does this work for all kinds of diseases? Or just some?

submitted by /u/dlo221
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Can cross pollination occur between different plant species?

Posted: 25 Jan 2021 10:18 AM PST

In my Agricultural Science class today we were discussing how "superweeds", weeds that are resistant to total pesticides, can be formed when a GMO crop (pesticide resistant) cross pollinates with a weed. I was wondering whether or not it is actually possible for this to occur? Isn't it like trying to cross a dog and a cat? Same kingdom, two completely different organisms?

If not, how do weeds actually develop resistance to pesticides?

submitted by /u/Low_Celery_5978
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Why are all archeological finds buried so deep?

Posted: 25 Jan 2021 10:59 AM PST

Why are all archeological finds buried so deep? Old villages and fossils are found many 10+ meters below our present surfaces. How is that?

Does this mean our Earth was smaller in dimension for millions of years ago?

submitted by /u/Regndroppe
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How do ants “smell” the location of a food accurately and how far are they able to detect it?

Posted: 25 Jan 2021 05:37 AM PST

Can someone explain, on a mechanical level, how acetic acid kills bacteria?

Posted: 25 Jan 2021 05:57 AM PST

As the title, thanks :)

submitted by /u/Equivalent_Focus3644
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A very hot iron bar will lose its ferromagnetic properties. How is it that the earth's core can be hotter even than molten iron, and still exert such an enormous magnetic field?

Posted: 24 Jan 2021 07:57 PM PST

What is the purpose of the resistors in a Marx generator?

Posted: 25 Jan 2021 01:26 PM PST

Every Marx generator i've seen on the internet has high-value resistors between the capacitors. Diagram of Marx generator (Wikipedia)
What is the resistor's use in this circuit? Would the generator still work without them? (direct electrical connection in place of resistor)

submitted by /u/aolivier747
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