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[
"Do all brains throughout the animal kingdom work in similar ways?"
] |
[
false
] |
Do all brains work with the same nuero-transmitters e.g. serotonin, dopamine etc. Or are there many different ways for a brain to fuction?
|
[
"In a way, you're asking the wrong question. If you want to know how similar our brains are to those of other animals, neurotransmitters are not what's important. What's important is whether other have the same brain structures as we do, serving similar functions, and containing similar circuits. ",
"Within the realm of mammals, at least, the answer is certainly yes. Take Parkinson's disease as an example. It's caused by the death of a specific group of neurons in the substantia nigra, pars compacta. Rats have this structure too, and it's possible to cause the same damage in rats, resulting in rats with Parkinson's symptoms. ",
"Most mammals have brains a lot like ours. They've got a cerebellum, sensory systems that work more or less the same way, hypothalamus, thalamus, and so on."
] |
[
"Within the realm of mammals, at least, the answer is certainly yes",
"To add on that, some neurotransmitters are found in nearly all animals. Glutamate receptors, for example, are found in mammals, amphipians, insects, and even sea cucumbers. And Proteins very similar to glutamate receptors are even found in plants."
] |
[
"Well I guess the obvious follow up question is, what makes us different then?"
] |
[
"Is the universe’s rate of acceleration increasing, decreasing, or steady?"
] |
[
false
] |
So I know the current scientific consensus is that the universe is expanding at a rate that is accelerating. My questions are: Is this rate of acceleration steady? Would a decreasing rate of acceleration suggest that some day the universe may start condensing? Do we have this information, or do we even have a way to calculate it?
|
[
"Per current evidence, the universe's rate of acceleration is increasing. Large scale stuff is expanding away from each other at ever increasing rates. Of course science hasn't really answered the why and how of the mechanism behind this. This has lead creation to the construct of dark energy. Again, what exactly this dark energy is still a huge matter of scientific research at this point. From what we can tell, the universe expanded ",
" quickly after the big bang, then the rate slowed. Then again around 5 billion years ago this rate started expanding at ever increasing rates to what we see today. ",
"There are ",
"over 50 references",
" on the Wikipedia article on this subject. One can delve in there for days reading articles. Because accelerated expansion is a more recent discovery, there are lots of unanswered questions. It is one of those subjects for me that is unsatisfying because we have massive holes in our knowledge on the subject, yet excited because there is so much more to learn. "
] |
[
"Per current evidence, the universe's rate of acceleration is increasing.",
"It depends on how you measure it. Our observations point to a future where distances increase exponentially. If you calculate r(t) - the distance as function of time - then all derivatives of it are increasing. If you calculate the derivatives and divide them by r then they are not increasing: Our universe approaches a state where the distance to things at a given distance increases at a fixed rate."
] |
[
"In short, yes.",
"https://en.wikipedia.org/wiki/Scale_factor_(cosmology)#Dark_energy-dominated_era",
"https://en.wikipedia.org/wiki/Vacuum_energy",
"Sorry for mostly posting links to other sources, this quickly gets beyond my ability to explain it. "
] |
[
"If particles cant traven faster than the speed of light, shouldn't there be a absolute max temprature?"
] |
[
false
] |
Since the hotter a particle is the more it vibrates, and that vibration should only be able to vibrate as fast as the speed of light? Im thinking of a absolute max temprature as there is a absolute minimum.
|
[
"You also have to consider the Lorentz factor when calculating the kinetic energy at velocities near c. The faster a massive object moves, the higher its momentum and its kinetic energy.",
"http://en.wikipedia.org/wiki/Lorentz_factor",
"http://en.wikipedia.org/wiki/Tests_of_relativistic_energy_and_momentum"
] |
[
"Temperature depends on the average kinetic energy (not the speed) of the particles, and kinetic energy goes to infinity as speed approaches c. ",
"Links that may be of interest:",
"http://en.wikipedia.org/wiki/Absolute_hot",
"http://en.wikipedia.org/wiki/Negative_temperature"
] |
[
"Oh cool, ill try to understand this!\nThanks"
] |
[
"Is it a coincidence that countries closer to the equator are generally poorer?"
] |
[
false
] | null |
[
"if you look at ",
"The Equator",
" you see it pass through, Rainforest\n, Desert\n, Archipelago\n, and Ocean.\nNow if you're talking about North Africa, East Indies, and Central/South America in general that's a different story. Europeans developed shipbuilding/navigation techniques and began to explore the world. When coming into contact with these regions they colonized them, this happened around the world largely by the Spanish, French, British, Dutch, Portuguese, and other like-minded European powers who saw an opportunity to expand their influence to these militarily inadequate lands."
] |
[
"Let me point out that Brazil has one of the fastest growing economies on earth, and with-in 20' of the equator sits Saudi Arabia, India, and Mexico's fast growing or strong economies. But The R. of Congo, or Indonesia make good examples. ",
"I could offer up my thoughts, but I don't really have the back-ground (unless you include N. Africa/Mid-east) and would rather let someone with a little more substance in the discipline answer this. "
] |
[
"Its perhaps something to do with the fact they they were all conquered. ",
"Missing out on the Industrial Revolution.",
"Equatorial weather, lots of vegetation, better climate made it easy to survive & multiply. There was never a need to explore or venture out into the oceans in like the European nations did. "
] |
[
"are sound waves affected by gravity?"
] |
[
false
] | null |
[
"Yes.",
"Sound waves need a medium to travel through (air or water as an example) and the density of those materials will be affected by gravity. ",
"The density of a medium absolutely affects how sound travels in that medium."
] |
[
"This isn't entirely accurate. Although we commonly teach that gravity is a force, the study of general relativity tells us that objects with some mass actually ",
" spacetime itself. So, while sound waves do not have any mass, they are still affected by the curving of spacetime around such objects.",
"For example, a ",
" electromagnetic wave can bend around a star - this is a huge part of modern astronomy.",
" Sorry, I misspoke - certain waves ",
" bend around massive objects, but not sound waves in space, since they require a medium to travel through."
] |
[
"Related question: Do phonons have mass, and are they affected by gravity?"
] |
[
"If there's a lottery with a 50% chance of winning, and you buy one ticket per week for an infinite number of weeks, are you guaranteed a winning ticket."
] |
[
false
] |
note - spinoff from thread.
|
[
"The question is not well-formed because there's no such thing as \"after an infinite number of weeks\". "
] |
[
"The probability approaches 1.",
"You can pick any number less than 1 and find a week where your chances are better than your given number, but the probability is never 100%."
] |
[
"And yet you're still not guaranteed to win."
] |
[
"Wouldn't it be greener to produce green power for homes and manufactures and still be on gas-powered cars instead of electric cars?"
] |
[
false
] |
Hello there, I have always had this question on my mind that if electric cars are mostly using power that is produced by fossil fuels, what is their purpose? I mean, electric cars make more pollution in manufacturing process than traditional cars, their batteries are bad for the environment and are produced out of rare resources. For electric cars to be green, there should be green manufacturing process and green power not fossil fuel power, to actually make a difference. And here is another thing, wouldn't it be better, to produce green power and use that in homes, and still rely on gas cars until most homes are using green energy and then start thinking about electric cars? I mean we want to use green power in electric cars to reduce carbon footprint. But using that green energy in homes which are using fossil power would have the same effect as using them in electric cars, BUT without the difficulty of producing electric cars or its bad environment impact. So this is the picture on my mind, what do you think? And I didn't know which flag to add, but chemistry seemed more relating than others, so sorry to select it randomly 😅
|
[
"You're making a lot of faulty assumptions here.",
"if electric cars are mostly using power that is produced by fossil fuels, what is their purpose?",
"EVs can use power from either fossil fuels and renewable sources, while ICEVs are stuck with only fossil fuels. But even when they're using electricity generated by \"dirty\" coal or natural gas plants, EVs use that energy more efficiently than an ICE, which is about ",
"30% efficient.",
"I mean, electric cars make more pollution in manufacturing process than traditional cars, their batteries are bad for the environment and are produced out of rare resources.",
"And production of ICEVs is just squeaky-clean, yeah?"
] |
[
"I would like to challenge OP to read ",
"this",
" it’s only one case of how EVs vs ICE cars are produced. Sure EVs use may pollute more being made but over the lifetime of the car it is better for the environment"
] |
[
"That would take fossil fuels off the table - I think Norway is getting there",
"The Norway Paradox.",
"On one hand the 15th biggest exporter of oil and 8th largest global exporter of natural gas. It is growing it's oil & gas sector and created new laws to facilitate drilling in the Arctic.",
"On the other hand, a world leader in electric vehicle uptake because of cheap domestic hydro electricity (and subsidies from the oil & gas revenue)."
] |
[
"What kinds of negative effects does farming have on the environment and the planet as a whole?"
] |
[
false
] | null |
[
"We can address this in parts:",
"1) Farming requires lots of clear land. This has led to enormous amounts of clear cutting and burning of other vibrant and old ecosystems to install a man made one. See the Amazon.",
"2) Monoculture. To maximize automation, we plant large swathes of identical crops. While this helps us to tailor our efforts toward a specific crop, it maximizes the environment for some animals and minimizes it for others. This can lead to specialized pests that become difficult to get rid of. See Monsanto.",
"3) Demand for high yields and large crops lead to extensive use of toxic herbicides and pesticides that washed into the environment and wreak havoc. See DDT, Clean Water Act.",
"4) Soil depletion and destruction of deep rooted plants can cause widespread problems when combined with adverse weather, such as extreme soil erosion. See the Dust Bowl.",
"These are just some of the direct environmental repercussions that spring to mind. There are many others that are based in more complex interactions (how do food prices effect economics and the environment?) "
] |
[
"The question was what affect does it have on the environment. Whether it's banning led to starvation in Africa or not is irrelevant to the fact that it had a negative environmental impact.",
"As I said later, there are long tail, complicated issues to discuss arising from farming and consumption, I just didn't want to address them, as doing so would take writing a doctoral thesis."
] |
[
"DDT",
"You should do some research before putting that statement out there. The fertilizers they used caused thousands of times more damage than DDT did. Also, the ban on it is directly responsible for hundreds of millions of dead children in Africa."
] |
[
"How do Astronomers 'Know' that Gas Giants are Different than 'Normal' Planets? What if Gas Giants are just Planets like Earth but with Thick Atmospheres?"
] |
[
false
] |
I hope my question makes any sense. I know that no one knows what really is inside of a gas giant, but there is a difference. I remember in grammar school we learned that there were gas giants and 'normal' planets like Earth with solid cores. How do we know this difference?
|
[
"For starters, current theories on planet formation are very difficult to reconcile with very massive Earth like rocky planets. Past a certain point, a rocky protoplanet in a protostellar disk will begin accumulating Hydrogen and Helium, which will always represent the majority of the disk. When that starts happening, the planet will always progress to be largely gaseous with a small rocky core (unless there is some catastrophic process which might prevent gas accumulation, which seems unlikely).",
"But, if you don't care to rely on our incomplete understanding of planet formation, you can study the size and gravity of a gas giant to get a sense for it's mass, composition, and density. With the planets massive sizes, they would need to be much more massive than they actually are if they were mostly rock. It's very easy to observe the composition, pressures, total mass, and size, and we can model the interiors of the planets and see that the only way to have planets that large and that (relatively) light is if they are almost exclusively gas. Keep in mind that Saturn, for example, is less dense than water. There's no room inside for a very large rocky body. ",
"We don't have the whole story in complete detail, but it's easy to establish upper limits on core sizes, and none of them are larger than a few dozen Earth masses at the largest; for comparison, Jupiter weighs about 300 Earth masses total. The cores account for no more than ~10-15% of each planet's total mass, and since rock is so dense, they make up an even smaller portion of each planet's volume."
] |
[
"In a way, gas planets are the result of an Earth-like object gaining too much of an atmosphere, if we assume the core-accretion model of planetary formation (i.e. that the gas planets started out as solid cores, and that these gained enough mass to trap significant amounts of hydrogen with their gravity) is correct.",
"But, to answer your question... the main give-away is that, thanks to Kepler's laws of planetary motion and Newton's later work on them, we can calculate the mass of a planet if we know its orbital parameters (orbital distance, speed, eccentricity, etc. - which we know very well for the Solar System planets). Since a planet's orbital velocity is influenced by the mass of both the planet and its host object, you can use that to accurately derive the planet's mass.",
"When we finally calculated the masses of the Solar System's planets and compared them with the planets' radii, we found that the gas planets had much lower densities than that of Earth. This meant that they couldn't be dominated by iron and silicate rock like Earth - they had to mainly be composed of lighter, less dense materials. In Jupiter and Saturn's cases, the best fit is an almost entirely hydrogen composition, while the two ice giant planets have only moderate hydrogen in comparison, and are instead dominated by \"ices\" (a catch-all term for a variety of ",
"volatile compounds",
" - in Uranus and Neptune's case, it's mostly water, along with some ammonia and methane).",
"Keep in mind that the four gas planets are thought to have rocky cores though - Jupiter and Saturn's should be about 10x Earth's mass, and Uranus and Neptune's should be around an Earth mass each. I don't think Jupiter has been confirmed to have a solid core, but IIRC, Saturn seems to have one, and there are still a lot of uncertainties surrounding the exact composition of the ice giants (although we can already infer a lot just by knowing their densities - like how Uranus has more hydrogen than Neptune because it has a higher radius and lower mass, and therefore isn't as dense).",
"TL;DR: At their masses, the radii of the gas planets aren't dense enough to be composed mainly of rock and metal. This means they must be dominated by lighter materials."
] |
[
"The wording of your last sentence is confusing. Reading it seems like you're saying Uranus has a larger mass and smaller radius, not Neptune. You change subjects within the sentence, so it took me a second to parse what you were referring to. ",
"Something like \"because Neptune has higher mass and is a smaller radius, and therefore Uranus is less dense.\" The pronouns aren't ideal. "
] |
[
"Is it possible that human couples share each other's internal electricity?"
] |
[
false
] | null |
[
"What is internal electricity?"
] |
[
"http://health.howstuffworks.com/human-body/systems/nervous-system/human-body-make-electricity.htm",
"It was quite vague. I got thinking about what people can share other than any physical connection. I landed on electricity. I own a restaurant and have seen a lot of people pass over the years and, in elderly couples, when one goes, the other seems to follow shortly. Almost as if they are now missing something. Most of the time I hear he/she died of heartache, but maybe there's another reason. "
] |
[
"Yes, neurons communicate via electrical impulses, but that has nothing to do with colloquial notions of \"electricity between people\"."
] |
[
"How is colour change and movement emulated in case of video games?"
] |
[
false
] | null |
[
"So electron guns existed in CRTs. The electron beam from the electron gun is magnetically (usually) deflected to scan the phosphor screen in a sawtooth (Z) pattern. See ",
"https://en.wikipedia.org/wiki/Raster_scan",
" and the page on CRTs. For a 60 Hz refresh rate, it really does do this scan 60 times in one second. Nothing is physically moving; the beam is just being deflected."
] |
[
"ok, one focused beam is launched from one point, yes? I saw that, but how, without movement, is it possible to have this beam deflected so it flls the entire screen with proper colours>",
"",
"Also with modern Liquid Crystals, what exactly makes the color change if nothing is moving? This is exactly what fascinates me. How, in simple language it is possible for a single focused beam to form such variety of colors in any given time?",
"Edit: Yes I am familiar with this topic, and with the general info about how lcd screen work (all I could google and youtube on this subject), but my question is a specific one. How is any of this possible without movement?",
"the exact same thing I cannot wrap my head areound is how computer performs all calculation without any movement inside it? Abbacus needed movement, clocks need movement, hourglass needed movement. so what the f... hell? :D",
"I would also appreciate checking another one of my computing question ",
"https://www.reddit.com/r/askscience/comments/cijcep/how_are_correlations_between_hardware_matter_and/",
" this stuff looks like magic from the outsider's point of view and I am quite curious about it :)"
] |
[
"This",
" site has an excellent explanation and demo of how magnetic fields (in the demo, depicted as little magnets, but actually the result of passing electricity through two, unmoving electromagnetic coils) can affect the direction of the beam. Changing the magnetic field is as easy as changing the amount of electricity passing through the coil. This can be done extremely quickly. ",
"Think of a hose shooting out water -- as you press on the hose, the direction of the stream changes. You didn't have to actually move the hose itself to change the direction of the water. That's not quite what's happening here, but it's just another example of you can change the direction of something without big moving parts.",
"In (typical) color CRTs, there are actually three guns, not one, and they use a \"shadow mask\" to get each beam to hit a green, red, or blue phosphor. ",
"Here",
" is a good illustration and description. Different intensities of the beams activate the phosphors by more or less, so we can get different combinations of red, green, and blue light (not really using precise terminology here). The phosphors are placed very closely next to each other and we experience their combined emitted light as one color. Any color can be created from the combination of red, green, and blue at different intensities. You can think about this sort of like a pointilist picture: when you are really close up, you can see the individual dots and they are of all sorts of weird colors, but when you are far away and the dots are small, to our eye, they get combined into other colors.",
"LCDs work differently. There is no gun and no phosphors. Electrical current is still used, which is what allows each pixel to change color so quickly. ",
"The wiki page",
" is actually pretty good at describing how they work, and I recommend reading that."
] |
[
"How can brains (human or otherwise) accurately keep time? What do we use as a \"clock signal\"?"
] |
[
false
] |
I'm referring to a person's ability to keep a rhythm over time, which can be highly accurate with practice. Edit: for clarity, I mean really short term timekeeping, like less than 10 second intervals.
|
[
"There's a constant cycle of protein breakdown within your brain that gives your body an internal \"sense\" of time; it appears that it is regulated/kept \"tuned up\" by factors such as light exposure: ",
"http://en.wikipedia.org/wiki/Circadian_clock",
" (and see also ",
"http://en.wikipedia.org/wiki/Circadian_rhythm",
" )"
] |
[
"KingSloth's explanation works for seconds or hours",
"KingSloth is specifically referencing circadian systems which refer to those of \"about a day\", by definition.",
"Furthermore, while it's conceivable that there are purely protein-protein interactions that could potentially keep time on fast time scales, these would probably be somewhat more temperature dependent and more subject to various perturbations than the larger, fairly stable, core circadian system. The core timekeeper elements for most circadian rhythms are transcription factors and the protein expression for most of these elements lags behind mRNA expression (peak to peak) on the order of hours. As ctcrk notes, most of these short timekeeping mechanisms that have been studied are electrical/neural in nature.",
"Interesting aside: There ",
" some instances of protein-protein interactions which keep time of about a day, though, and one of the more interesting implications of this was that even red blood cells, lacking a nucleus, have a method of timekeeping."
] |
[
"We have a three phase clock running into our hippocampus. The three waves are heterodyned to give a unique \"address\" for each moment since you woke up. (Adrenaline increases the frequency, leading to more addresses per time interval). ",
"The rest is entrainment using the thalamus as a delay line and the phonological loop to acts as a kind of phase locked loop. Once entrained, anything that misses fires dopaminergic neurons in the auditory system. Some time keeping also occurs in the cerebellum and motor cortex, for gross sequencing. All of these systems work together."
] |
[
"My father and I want to conduct an experiment to determine if our cat can count. How can I go about this?"
] |
[
false
] |
I found a paper that seems to be just what I need for this (Quantity discrimination in felines: a preliminary investigation of the domestic cat), but couldn't find a free version on Google Scholar. Neither of us are scientists, so I have no idea how to go about setting up an experiment like this.
|
[
"Apparently children have to rewire their brains to think about numbers linearly (instead of logarithmically). Before they do, kids can easily distinguish one from a few and/or many, but not, say, 7 from 8. I would guess cats would be similar -- very interesting question!"
] |
[
"Wow, thanks dude! I only regret that I have but one up-vote to give."
] |
[
"Wow, thanks dude! I only regret that I have but one up-vote to give."
] |
[
"Does it require more, or less energy to climb stairs two steps at a time as opposed to one?"
] |
[
false
] | null |
[
"From a physics standpoint as long as you are going up to the same height you are always doing the exact same amount of work. ",
"If you lift one pound ten feet in 10 seconds or in 10 minutes you still do the same work. ",
"From a physiological standpoint it might be different. "
] |
[
"but there are so many things to consider! its not an easy question to answer.",
"i would assume it would require more energy. if you think of each step being 20 centimeters tall, your leg has to lift you 20 centimeters twice. if you do two steps at once, your leg has to lift you 40 centimeters once. still following?.. but when your doing two steps at once, your leg has to do a lot more work for the first 20 centimeters of increase in height because the angle is more difficult. Then for the second 20 centimeters increase it should be the same as doing one step.... so its really like doing one hard step for the first 20 centimeters, and then one normal step for the other 20 centimeters"
] |
[
"The muscles that flex the leg (quads, sartorius, etc.) generally stretch along the front of the thigh from the pelvis down to attach at the bottom of the femur or the top of the tibia/fibula. That is, they run vertically when you are standing straight up. Right when you raise your foot off the ground, the thigh is still mostly vertical, with the lower leg dangling at the end. As the thigh flexors continue to contract, though, the thigh changes continually rotates to become more and more horizontally stretched out in front of you, with the weight of your lower leg still dangling at the end. ",
"When your leg is close to vertical, the torque (length of thigh x weight of lower leg x sin(angle)) exerted by the weight of the lower leg itself is minimal, and doesn't need to be countered by the hip flexors, because the sine of a small angle is small. However, the higher the leg goes toward 90 degrees, the more torque the leg has to work against.",
"I can't speak to how big a deal this is in the long run, but no one seems to have mentioned yet that the sheer vertical distance isn't all that bears on the work done. Bending the hip to raise the knee at a distance from the body exerts an increasing torque for the muscle to work against until it is at 90 degrees, too."
] |
[
"Hey AskScience, Will you help educate me?"
] |
[
false
] |
[deleted]
|
[
"Check out MIT's ",
"OpenCourseWare",
"."
] |
[
"There's a ",
" website here, which I think you'll find as awesome as I do: ",
"http://khanacademy.org/",
" "
] |
[
"I doubt you'll get someone to personally mentor you, but good luck anyway. However, you might want to check out ",
"Academic Earth",
" for some free university level education."
] |
[
"If I am traveling through space at the speed of light then how fast is the light from my spaceships headlights moving?"
] |
[
false
] | null |
[
"The light from your headlights will propagate at exactly the speed of light, as for you and for any outside observer. The Problem with your argumentation is the same with which any relativity discussion starts, that time is a fixed thing. According to Einsteins theory however, this is not true. The only thing that stays fixed in any frame of reference is the speed of light. Time does change according to the lorentz factor, which tends to zero when approaching the speed of light. This means that the time in your spaceship is significantly larger for an outside observer. \nJust to clarify: 1. We cant even think about the concept, since your mass grows with that same lorentz factor and goes to infinity approaching the speed of light. That would mean infinite energy which simply is not there. Therefore thinking about that concept is physically very wrong!\n2. Newtons laws of motion are only valid for \"slow\" speeds. Anything faster than about 0.3c will have significant differences. "
] |
[
"The speed of light. See: Theory of Relativity. "
] |
[
"My hypothesis is this: If Light moves at a constant speed then I believe that if the source of light is moving than the photons emitted from it move at the speed of light relative to how fast the source is moving.",
"The way it works is that the measured speed of light in a vacuum will be the same, for all observers, in all inertial frames of reference.",
"So if you (observer A) are in your spaceship travelling at close to light speed, then you will measure the light from your headlights moving away from you at light speed.",
"Somebody on Earth (observer B) will also measure that light beam moving away from you at light speed.",
"What changes is that your speed will be measured differently by observer B than by yourself, as will the physical dimensions of your ship. Observer B will also see time moving more slowly for you than it does for him/her."
] |
[
"How did astronomers determine the mass of the rogue planet SIMP J01365663+0933473 if it’s not orbiting a star and has no known natural satellites?"
] |
[
false
] |
I heard about this planet yesterday from this post over at and haven’t got an answer yet According to the post / article, the free-range planet is said to be 13 times the mass of Jupiter but does not orbit a star and no moons have been found yet. If this is the case, how could have astronomers determined its mass without looking at its gravitational effects on other bodies?
|
[
"It sounds like a statistical correlation. Kind of like how if you know how long a blue whale is, you can guess it’s weight because you’ve measured the length and weight of thousands of other blue whales and have noticed a correlation."
] |
[
"I don't think we've ever used a laser \"ping\" to measure any distance in space for extrasolar objects."
] |
[
"Yes, but we know the new species is an aquatic mammal with fairly similar habits, but an intermediate size between other known whales. Which, in real life, would work well - there's only so much the density of an animal like that can vary and still be made up of warm-blooded meat.",
"To pull back from the metaphor, we know basically *what* SIMP J01 is - a gas giant that didn't quite reach brown dwarf status. And so the models aren't just \"other things this size weigh this much\" but \"other things which are formed by this process cannot have properties outside a certain range\". We understand how dust clouds form planets and stars pretty well, which puts some very helpful boundaries on what properties the resulting objects can have."
] |
[
"A person falling into a body of water from a high altitude can get seriously injured or even die due to the impact against water's surface tension. What happens if they fall into a liquid that has less surface tension, like rubbing alcohol?"
] |
[
false
] |
Can they survive the impact from a further distance than they would if they fell into water? Bonus: Is there a way to calculate the furthest distance a person could fall into a liquid without hurting themselves for different types of liquids? I was just curious because I don't think I've ever seen someone dive into a pool of alcohol from a high distance... Would they sink in a lot deeper too?
|
[
"It's actually not due to the surface tension of the water, it's due to the fact that water really isn't compressible. Basically, if you jump into the water from a small height, you aren't moving as fast and the water has time to \"move out of the way,\" and therefore you can jump into the water. If you jump from a larger height, you will be moving much faster when you hit the water, and the water won't have time to move out of the way when you hit it. Surface tension really doesn't have much to do with the impact when you hit the water, so a liquid with a different surface tension will not change the end result much. You would need to find a more compressible fluid for the end result to change."
] |
[
"Good answer. ",
"One way to get a more compressible liquid is to put air bubbles into the water. This is what they do for some high divers. They pump compressed air to the bottom of the pool and release it."
] |
[
"Cool! Wow I had always thought it was because of surface tension. So what are some examples of fluids that are more compressible? "
] |
[
"Is there any validity to this article regarding the Fukushima radiation spread? If so, what can be done to truly prevent radiation absorption in our food supplies/daily life?"
] |
[
false
] |
Samples of milk taken across the United States have shown radiation at levels 2000 percent higher than EPA maximums. The reason that milk is so significant is that it is representative of the entire food supply. According to an article published on Natural News, “Cows consume grass and are exposed to the same elements as food crops and water supplies. In other words, when cows’ milk starts testing positive for high levels of radioactive elements, this is indicative of radioactive contamination of the entire food supply.” The Food and Drug Administration and the Environmental Deception Protection Agency, instead of refusing to prohibit the sale of tainted foods and mandatory testing of foods produced and harvested from the Pacific Coast, have simply raised the “acceptable levels” of radioactive material in foods. Infant mortality rates across the United States have increased by more than 35% since the nuclear disaster, according to a court statement by Dr. Sherman with independent scientist Leuren Moret, MA, PhD. A study published in The International Journal of Medicine indicates that more than 20,000 deaths right here in North America can be directly attributed to the release of radioactive material from Fukushima. Radioactive isotopes of the type released from Fukushima have a half-life of 30,000 years. This means that we must permanently change the way we prepare our food.
|
[
"Ok, first off this link is not science at all. ",
"secondly, now that I'm home and have had more time to look at the article, allow me to start debunking stuff directly from it.",
"babies born with thyroid issues linked to radiation are rising quickly ",
"A rooftop water monitoring program managed by UC Berkeley’s Department of Nuclear Engineering detected substantial spikes in rain-borne iodine-131 during torrential downpours …",
"The Iodine-131 and 133, which would actually cause thyroid issues, is already completely decayed away after Fukushima. I-131 has an 8 day half life, and was gone in a few months, and 133 is gone in a few hours. Iodine is primarily responsible for thyroid cancer from a nuclear accident, so to say that the levels of iodine from Fukushima are causing thyroid issues to increase this far after the accident is a statement which is not founded in science of physics. ALL of the iodine from that reactor is gone, and has been gone for over a year. Additionally, and while this is anecdotal evidence, it is evidence, when I was working at Columbia Generating Station when Fukushima occurred, we had to do samples of our HVAC filters which concentrated particulate collection just to even detect ANY iodine, and it was only detectable for a few days following the accident. The dispersal of iodine kept it so low that it was virtually negligible in the US.",
"Samples of milk taken across the United States have shown radiation at levels 2000 percent higher than EPA maximums.",
"The low levels of radioactive material in air, precipitation, drinking water and milk that EPA has seen since the Japan nuclear incident were expected. To date, all of EPA's sampling and monitoring results have been below levels of public health concern.",
". Taken from the EPA website about how Fukushima was going to effect the US. The whole page is a good read.",
"Also from the EPA site",
"\"EPAs drinking water MCL for the radionuclide iodine-131 is 3 picocuries per liter. It is important to note that this drinking water MCL was calculated based on long-term chronic exposures over the course of a lifetime 70 years.\"",
"\"FDA's DIL for iodine-131 in milk is 4,770 picocuries per liter. FDA's DIL for total cesium in milk is 33,000 picocuries per liter.\"",
"Notice, the EPA does not have a milk standard. they directly reference the FDA's standard. So the article claiming it was 2000 times over an EPA limit is false. ",
"this is indicative of radioactive contamination of the entire food supply.”",
"Again no reference as to how much contamination. There IS radioactive material in all of us from nuclear weapons testing. It is in all our food. There is stuff there from Chernobyl. But the important thing is HOW MUCH. No sources on the web page to check against.",
"The Food and Drug Administration and the Environmental Deception Protection Agency, instead of refusing to prohibit the sale of tainted foods and mandatory testing of foods produced and harvested from the Pacific Coast, have simply raised the “acceptable levels” of radioactive material in foods.",
"The \"acceptable levels\" part links to ",
"this article",
". This article does not say the government actually changed any limits. I'm surprised they didnt link ",
"things related to the EPA PAGs",
". While the EPA revised its PAGs, it did so only for nuclear accidents, and used available studies to do so. The PAGs are used to determine when to allow people to return to an area. A person could simply not return to that area ever, and the changes to the PAGs won't affect them.",
"1.) SEAFOOD: Question the origin of ALL seafood. Fish and crustaceans from the Pacific Ocean should all be considered to be poisoned with radiation.",
"Outside of the areas directly near the accident, this statement is not consistent with testing done at other harbors in Japan. Additionally it is inconsistent with ocean dispersion models.",
"2.) WATER: The rainfall and snowfall are all radiated. Do not drink any water that has not been filtered. The tap water that flows from your faucet has NOT been treated to rid it of radioactive particles. A recent report from the NY Times stated, “A rooftop water monitoring program managed by UC Berkeley’s Department of Nuclear Engineering detected substantial spikes in rain-borne iodine-131 during torrential downpours …",
"This is just silly. First the I-131 thing, from before, its gone now. Secondly, all water has some level of radiation. Third, i doubt anyone has the filtering equipment in their home to remove radioactive material. A brita filter does NOT do this. You need ion exchange to get most of it out. We use resin beds and anion/cation exchange in nuclear plants and we still cant get it all out of our reactor water or spent fuel pools. So the statement to just use a water filter is false. Water from the tap is probably treated much better than someone could treat their own water.",
"3.) DAIRY PRODUCTS: Milk and milk products from the West Coast states currently have the highest levels of radiation in North America.",
"I'm going to refer back to the EPA responses.",
"4.) PRODUCE: Leafy Vegetables, Wines, Tomatoes, Strawberries….all produce from California or any other West Coast State are also likely to be tainted.",
"no evidence. \"likely\" does not mean anything. If all these vegetables are tainted, then we need to assume the entire planet is tainted, including ourselves.",
"If you eat the above foods from areas with high radiation levels, you are eating radiation and feeding it to your children. Slowly the radiation levels within your body will build up. This is PERMANENT.",
"This is false. Most radioactive material has a biological half life, until it leaves your body. This is entirely scare tactic.",
"Infant mortality rates across the United States have increased by more than 35% since the nuclear disaster, according to a court statement by Dr. Sherman with independent scientist Leuren Moret, MA, PhD. A study published in The International Journal of Medicine indicates that more than 20,000 deaths right here in North America can be directly attributed to the release of radioactive material from Fukushima.",
"Their link goes to an in the middle page that eventually goes to radiation.org. There are a number of studies linked directly on their page that either have never been peer reviewed, or are known to use faulty methods or people who are known to be anti-nuclear.",
"Radioactive isotopes of the type released from Fukushima have a half-life of 30,000 years. This means that we must permanently change the way we prepare our food.",
"This statement is just ridiculous. The most concerning isotopes are <300 years. And to say we must change how we prepare our food....I question....if its already EVERYWHERE, then how can you simply prepare food differently to get rid of it? No science here.",
"Wash your food with soap and rinse it in filtered water. ",
"This doesn't get rid of material that is IN the food.",
"Be aware of the origins of your vegetables, fish, game and seafood.",
"This is legitimate if you are getting food from certain parts of the fukushima exclusion zone.",
"Use only filtered water for drinking, cooking and ice.",
"how are we filtering it? again brita doesn't help",
"The bottom line is there is a lot of not-science here. The closest it comes to fact is the statement that the EPA adjusted their PAGs. Believe at your own risk."
] |
[
"Nope. There are a number of red flags, but probably the best one is common sense.",
"When the FDA suspects beef to be tainted with e. coli they recall all the beef.\nWhen the FDA finds listeria in food, the perform a recall and again all food that might be tainted is removed.\nIf the FDA found dangers levels of radiation, why wouldn't they do likewise?",
"The EPA has no authority to bar the sale of milk. Yet the article implies that they do.",
"The truth is that this story combines a number of unrelated scientific facts to paint a sensationalized picture of terror. "
] |
[
"at levels 2000 percent",
"Smells like fearmonging. The author should have written \"20 times\", but of course, \"2000\" is better from a journalistic perspective.",
"Also, that's just a comparison to some other value. What's the absolute number?",
"If all those figures come from a random number generator, disregard them. If they come from an actual scientific paper, read that paper. Even if you don't understand all of it, you'll probably understand more than the journalist did.",
"Not to mention, this article actually cites a \"World Truth TV\", whose name tells me it's very probably just uninformed fearmonging crap."
] |
[
"Do ice breaking ships speed up the rate that the arctic ice melts?"
] |
[
false
] |
It is clear that if I put in one large lump of ice in my cola, it will take longer to melt than if I put several lumps whose combined volume equals the single lump. More and more ships are now crossing the arctic ocean, breaking through "thin" ice as they do so. They are effectively chopping up the ice into smaller lumps. Does this have an effect on the melt rate on the arctic ice, have any studies looked at it?
|
[
"When you crush an ice cube you increase the surface area which allows the room temp/outdoor air/cola (which is usually above 0C and cola always is) to exchange heat more effectively with the ice thereby melting it faster.",
"With ice in the arctic while if you do break it up the temperatures are below freezing which would heal back the breaks relatively quick. If anything I'd think that breaking the ice and displacing chunks onto other ice sheets would increase the overall amount of ice in the area. As the place that is now open water freezes back and the ice that was displaced is still frozen.",
"So no it would not increase the amount of ice lost every year, and it's effect on a global scale is negligible.",
"Edit: added that ice exchanges heat with cola"
] |
[
"Probably not, that thin of ice should have no problem freezing over again. Luckily melting ice that's afloat in the ocean doesn't effect sea levels much anyway."
] |
[
"As others pretty much note, yes, it does make the ice melt faster ",
" it also makes the ocean itself colder faster (you increase the rate of heat transfer, but not the amount), so it'll freeze faster.",
".",
"When water at 0C loses heat, it turns into ice when enough heat (the heat of fusion) is lost. By increasing the ice's surface area, you're changing water at 0C to ice at 0C faster."
] |
[
"If everyone had to go to the doctor once a year, would this result in more or less work for the health service?"
] |
[
false
] | null |
[
"Preventative medicine is well known to reduce health care costs and improve health and quality of life.",
"An annual trip to the GP might not be the best way to achieve this but measures such as regular screening for certain condtions and vaccinations help."
] |
[
"Or, to add to the question: if not a year, what would the ideal frequency be on average?"
] |
[
"\"Due to\"?"
] |
[
"Can a person test negative for COVID, but still be contagious? (Assuming that person is in the process of being COVID positive)"
] |
[
false
] | null |
[
"Yes, if you test too early and your viral load is too low you may not test positive. In addition too this, there is also always the chance of a false negative or false positive with any test. No test is 100% accurate and incorrect results could come from things as simple as mislabeling of a specimen or some other human error."
] |
[
"That is true, but I'm not sure that answers the question fully. If you test negative because your viral load is too low, are you contagious (assuming you are already infected)?"
] |
[
"Depending on the timing, yes.",
"https://www.hackensackmeridianhealth.org/HealthU/2020/12/03/exposed-to-covid-heres-when-to-get-tested/"
] |
[
"How would a nuclear reactor setup fare in space?"
] |
[
false
] |
My main question is about the heat dissipation in space. Since space is generally very cold, would it be more efficient for a nuclear reactor to be cooled in space or would it be less efficient to rely on heat radiation without any air vs an air or water-cooled system as they're designed to work in an atmosphere?
|
[
"They work. There are several satellites that actually use nuclear reactors to generate electrical power. Wikipedia has a list: ",
"https://en.wikipedia.org/wiki/List_of_nuclear_power_systems_in_space",
" (which also includes RTGs, they are a different thing, but still nuclear).",
"My main question is about the heat dissipation in space. Since space is generally very cold, would it be more efficient for a nuclear reactor to be cooled in space or would it be less efficient to rely on heat radiation without any air vs an air or water-cooled system as they're designed to work in an atmosphere?",
"Okay, the issue of dissipating heat in space is actually a bit more complicated. The thermal environment in Low Earth Orbit (LEO) has mainly 4 heat sources:",
"- Sunlight. Around 1360 W/m2 mostly in visible and near-infrared wavelengths.",
"- Planetary albedo (i.e. reflected sunlight). 39% of the above figure in the same wavelength, only on the day side.",
"- Planetary infrared. Around 200 W/m2 on every side (even on the poles).",
"- Internal heat sources (equipment consuming electricity, and the nuclear reactor in your case).",
"I omitted the CMB in this list because 2.7K is really negligible.",
"I mentioned wavelength because it's important indeed. Materials that reflect visible light (white paints, beta cloth) are usually not good at reflecting infrared, and those that reflect infrared (shiny polished metals) cannot be exposed to direct sunlight because they can get very hot.",
"The last part about metals may sound counterintuitive since they are so reflective, but they absorb like 3% of visible and 2% of infrared, reflecting the rest. This small difference means that after a long time of exposure to sunlight they will have accumulated a lot of energy that they cannot get rid of because of their low infrared emissivity (equal to absorption by Kirchoff's law). In practice this means they get very hot and it can be an issue. Fortunately in LEO infrared isn't that much (it is a more serious issue for lunar satellites though).",
"So, saying that \"space is cold\" isn't really true. You have to choose your external surfaces carefully and make sure you point them in the right direction. If you design poorly then space can actually be very hot!",
"In some cases the satellite's external surfaces are enough to emit all the power you need to get rid of, but this is not always the case. Then you need a radiator. You don't want your radiator to point to heat sources, or it will start absorbing. At most, you can paint it white and expose it to visible light, relying on the fact that infrared emission is still good, and make sure they are at a very oblique angle, almost parallel, so that little sunlight is absorbed. But it's definitely much better if it points into deep space. This also influences the design of your satellite's attitude: will it always have a side pointing at the Earth, like the ISS? Communications and Earth observation satellites reasonably would. Or will it point always at the Sun? This makes more sense for satellites that rely on solar power and don't have moving solar arrays. You may also have space telescopes that may be pointed in whatever direction the scientist operating them needs to observe. All of this has implications for choosing the direction where your radiators will be pointed. So sometimes you have to paint them white, make them oblique and expose them to the Sun though it's not optimal. Consider also that due to solar UV, after a few years the paint will turn yellowish, affecting its ability to reflect visible light.",
"Finally, you have to conduct heat from the internal sources into the radiator. Small satellites with just solar power sometimes have just a metal rod to conduct heat into external surfaces, sometimes even with no radiators. If more power is generated you may think of ",
"passive heat pipes",
". But if we're talking about high power, like a nuclear reactor, then most likely you're going to need an active thermal control system with pipes carrying some fluid and pumps forcing it to circulate. Consider also that the pumps consume electricity, which in turn causes them to generate heat. Your radiator and thermal control system must be sized for that.",
"Anyway, doable. As I said above, there are real ones in orbit."
] |
[
"Okay, I didn't have any hint that OP was asking about megawatts but it's still answerable. There aren't any MW-scale reactors in space as of today, but there are some designs that have been proposed for nuclear-electric propulsion, which would have power requirements of this order of magnitude.",
"The spacecraft would look like this: ",
"https://www.nasa.gov/images/content/112905main_prom_1.jpg",
"In the tip you have the nuclear reactor and a radiation shield. Most likely there would be two cycles of cooling fluids, a hot one operating in the reactor, and a cooler one operating on the radiators side, that exchange heat by contact in the middle. The radiators have this triangular shape resembling wings because they are located in the shadow of the radiation shield. They could be hundreds of m2 (exact figures vary for each design depending on the reactor's power and the radiators' operating temperature).",
"Finally in the back you have another radiation shield to lower the dose further, the payload, and the ion thrusters.",
"So the spacecraft looks like a big array of radiators with a small payload and a small reactor. Well, that's the price of dumping heat without an atmosphere! Worth also noting that on Earth radiators can have several parallel plates, ",
"like this",
", it works fine as long as air can flow between them and it lets you save a lot of space. But for radiative cooling this wouldn't work because each plate would absorb the heat of its neighbors, so only the external ones would be actually dumping heat. So you need that flat and big spacecraft design."
] |
[
"The mass budget for that concept certainly seems to make the accountants sweat blood.",
"Still better than using huge fuel tanks for chemical propulsion"
] |
[
"As fish, like Koi, grow larger do the rods and cones in their eyes become larger or increase in number?"
] |
[
false
] |
...or both? I am curious to learn if an older and larger Koi would have greater ability to see fine details and/or better light sensitivity compared to its younger and smaller self.
|
[
"What does this have to do with fish?",
"And you are wrong. Adult humans have larger eyes than babies."
] |
[
"What does this have to do with fish?",
"And you are wrong. Adult humans have larger eyes than babies."
] |
[
"They increase in number.",
"The growth occurs in the ciliary margin, which is the bit of the retina closest to the iris."
] |
[
"If different races aren't like different dog breeds, what are they and is \"race\" even real?"
] |
[
false
] | null |
[
"but outside of that the difference is just skin color",
"Not true.",
" There are DNA differences between the races. The DNA from neanderthals can effect ",
"blood cholesterol levels, schizophrenia, eating disorders, and rheumatoid arthritis."
] |
[
"The caveat \"other examples\" meant that there are other conditions I do not know about."
] |
[
"There is no genetic difference that all \"black\" people have vs all \"white people\" for example.\nThere is NO such scientific thing as race. It is a social construct. Yes, there are genetic mutations that are common in different societies, I am not positive why, but a guess would be due to breeding and passing it down continuously. ",
"http://annals.org/aim/article-abstract/710064/medicalization-race-scientific-legitimization-flawed-social-construct",
"To add, human physical variations are MORE Drastic WITHIN a \"race\" than outside of it. That is to say, people from the same country of origin are likely to share physical features with someone from another country than their own. ",
"[I would have sourced ",
"http://faceresearch.org/",
" but these photos look more stereotypical than I have seen before, where the average really looks different from what I would have expected to come from a particular country.]"
] |
[
"Does the human body heal injuries / repair itself faster while sleeping?"
] |
[
false
] | null |
[
"In terms of say, tissue repair, lack of sleep does not seem to matter, at least in rats (",
"study",
", ",
"study",
"). However sleep is implicated in the functioning of your immune system (",
"review",
"), so your ability to fight of an infection for example, could be compromised by lack of sleep, but that doesn't necessarily imply that it happens \"faster\" during sleep.",
"Edit: I found this ",
"human study",
" which found no association with total sleep hours and healing speed following a punch biopsy. "
] |
[
"Unfortunately, there doesn't seem to be too much current literature on the topic. Most of the papers I found discuss sleep in the context of ICU care, so it's more an issue of chronic sleep deprivation rather than the difference between sleep/wake cycles.",
"This",
" paper says ",
"Sleep is an essential restorative process, with important circadian variations in protein synthesis and cellular division being present with peak activity during sleep. It can be postulated that this ultimately will impact the healing process. [...] Sleep deprivation in humans has been associated with disruptions in the normal restorative processes. In study with healthy volunteers, immunization with hepatitis A vaccine and influenza vaccine was associated with approximately 50% lower antibody response in those volunteers who were sleep deprived.",
"This older paper",
" says",
"The exact physiologic importance that sleep has in healthy individuals, let alone critically ill ICU patients, is still uncertain. It has been suggested that sleep is an essential restorative process, with important circadian variations in protein synthesis and cellular division being present, with peak activity occurring during sleep. ",
" ",
"So we know that sleep is important and that there is increased cellular division (and thus, cellular repair/healing, possibly) during sleep, but I'm not sure that that definitively says that there's a real difference in healing rates during sleep. Labeling processes as purely 'catabolic' or 'anabolic' and linking them to sleep vs wake seems like dangerously oversimplifying the complex biological mechanisms at play."
] |
[
"Related, I imagine some wounds would heal faster simply because you'd stop picking at them."
] |
[
"FTL Signalling with Entangled Photons - Why Doesn't it Work?"
] |
[
false
] |
Hello wonderful people of AskScience. I've been thinking through a notion for faster than light signalling. It's based on a fairly simple demonstration. Set up two polarizing filters, one rotated 90˚ relative to the other, and notice that light is not transmitted through them. [ GENERIC LIGHT SOURCE ] ---> [ FILTER at 0˚ ] ---> GAP ---> [ FILTER at 90˚ ] ---> [ NO LIGHT TRANSMITTED ] Now add a third polarizing filter between the first two, rotated 45˚ relative to both, and notice that light is transmitted through all three. [ GENERIC LIGHT SOURCE ] ---> [ FILTER at 0˚ ] ---> [ FILTER at 45˚ ] ---> [ FILTER at 90˚ ] ---> [ 25% OF LIGHT TRANSMITTED (according to the Law of Malus) ] See: Now, for the main event. Replace the generic light source with a source of pairs of entangled photons. Direct half of each pair left and half right. Set up the same filters symmetrically on both sides. (For our purposes, the 90˚ filter on the left is just a distance marker, but bear with me.) [ FILTER at 90˚ ] <--- GAP <--- [ FILTER at 0˚ ] <--- [ ENTANGLED PHOTON SOURCE ] ---> [ FILTER at 0˚ ] ---> GAP ---> [ FILTER at 90˚ ] ---> [ NO LIGHT TRANSMITTED ] Now, wave a filter rotated 45˚ relative to the others into the gap on the left. [ FILTER at 90˚ ] <--- [ FILTER at 45˚ ] <--- [ FILTER at 0˚ ] <--- [ ENTANGLED PHOTON SOURCE ] ---> [ FILTER at 0˚ ] ---> GAP ---> [ FILTER at 90˚ ] ---> [ 25% OF LIGHT TRANSMITTED ] Now, you can signal by waving the 45˚ filter in and out of the gap. When the filter is present on the left, light is transmitted on the right. The time between signal and transmission is the time taken by light to travel over the distance between the 45˚ and 90˚ filter on the left. This is shorter than the time taken by light to travel between the 45˚ filter on the left and the 90˚ filter on the right. I'd like to know what's stopping this working. Thanks for any insight you can share!
|
[
"The photons that are transmitted are not transmitted unscathed; they are forced (so to speak) into a vertically polarized state. so its polarization state has been measured, and so it is no longer entangled with the other photon.",
"If you had N mutually entangled photons and measured the polarization of one of them, that photon would no longer be entangled with its partners, even though the remaining N-1 photons would still be mutually entangled with each other."
] |
[
"There are several errors here.",
"First, in your initial set-up, only 1/8 of the light is transmitted; it gets cut in half when the natural light hits the 0",
" polarizer as well as when it crosses the other two polarizers.",
"Second, in your second set-up, whether you wave the 45",
" polarizer in or out on the left, there will be no photons emerging on the right. You will be sending a vertically polarized photon through a horizontal polarizer; nothing will emerge.",
"Finally, I think your fundamental misunderstanding is that entanglement is like a marker on the photons, so no matter what, these two photons will always do the same thing. That is not the case. Entanglement means that you have a quantum state that cannot be viewed as the product of separate one-particle states. If I start with two photons in an entangled state, as soon as one of them encounters a linear polarizer, the state is no longer entangled, and subsequent measurements on each photon will not influence the state of the other photon.",
"Using the mathematics of bras and kets, this is easy to see. Your initial state is (|00>+|11> )/2",
", whereas after the first photon encounters the vertical polarizer, the state becomes |00> or |11>."
] |
[
"This is one of the features of quantum measurement. If you have a system in a mixed state, a measurement will force that state to shift into a state in which the observable measured has a definite value; this is what is meant, in fact, by a measurement. (As to what happens at the time of measurement: this is a subject about which there is no consensus, and about which various interpretations of quantum mechanics disagree, but the fact that a measurement will take an observable from a mixed to a pure state is clear.)"
] |
[
"Can a vaccinated adult get pertussis?"
] |
[
false
] |
[deleted]
|
[
"The answer is absolutely. The probability is going to be hard to determine. Remember that we vaccinate of course to protect ourselves, but also to protect one another. ",
"Herd immunity",
" works best such that if a vaccine happens to fail in me, it's not a big deal because it worked in you and you won't get me sick.",
"Peak antibody levels against pertussis are reached by day 14. So you're protected to the best of our ability pretty quick.",
"Here's an article on it if you're interested"
] |
[
"Vaccine efficacy for pertussis vaccines is around 70-90%, so a significant minority of vaccinated people are potentially at least partially susceptible. (Most of the susceptible people do have some degree of immunity, reducing severity and/or transmissibility of the disease.)",
"Two other points: Immunity for just about anything wanes over time, and immunity to pertussis is no exception; in fact it seems to fall off relatively quickly, so that about 5 years after vaccination the efficacy is somewhat lower. Again, even though people may be susceptible, they're likely at least partially protected. ",
"The other point is that it's possible that there are antigenic variants of pertussis that are relatively resistant to the vaccine-induced immunity. This has been proposed in several countries, and there are some hints that the potentially-resistant strains are increasing due to widespread vaccination, but as far as I know there's no real smoking gun actually linking all the pieces together."
] |
[
"Except herd immunity doesn't work with the acellular pertussis vaccine. The old whole-cell vaccine (TDP) did protect against transmission, but all the new-fangled ones (the -aP ones) unfortunately don't. "
] |
[
"How do you weigh something in space?"
] |
[
false
] |
[deleted]
|
[
"For starters, landing the rocket is done with computers using sensors to measure the rocket's position and acceleration (search for IMU for a better idea of the type of measurements). It's a less error-prone method to just measure the position of the spacecraft and adjust than try to work out the kinematics using the weight. Also, for most payloads, the exact weight would already be known - everything on the ISS was once on Earth.",
"Measuring the weights of things in space is done by applying a force and measuring the acceleration. See ",
"SLAMMD",
" for an example.",
"And I think it's just called a vertical rocket landing."
] |
[
"The simplest method I can think of (which may not be how they do it!) is to see how quickly something accelerates when you apply a force. Quite simply, if you apply the same force to a heavy object and a light one, the lighter one will accelerate more quickly, as described by ",
"Newton's second law",
" (F=ma)."
] |
[
"Space travel is generally a closed system. You pack out what you pack in, to borrow terminology from hiking. Even biowaste will have the same initial and final mass unless you jettison it, in which case, you probably won't really care since it is going to be ejected at a low velocity and already low mass. Plus if you are using waste recycling systems it is even less waste. Ergo an inventory is really all you need."
] |
[
"How do yeasts contribute to flavour in beer, wine and bread making?"
] |
[
false
] |
As a keen homebrewer I am very aware that the yeasts you use can have a huge impact on the flavour profile of anything you make. However, my crappy school-level biochemistry and some cursory searching and wiki trawling only seems to discuss the fermentation of sugars into alcohols. Clearly that can't be all that's going on if esters and various other flavinoids are getting produced. So where in the process do these other chemicals get formed? What else is the yeast doing other than C6H12O6 → 2 C2H5OH + 2 CO2 ? My guess is that other sugars result in other break down products, but I've really not found any specifics, and that would also imply that the type of yeast is less important than the type of sugars available. I'd really like to understand the process better from the biochemical perspective.
|
[
"Well yeasts (all cells really) take up all sorts from their environment and release all sorts of chemicals and proteins too. As well as sugars they take up any micronutrients they need. These are appropriately metabolised and some of the metabolic products will be released to the environment, some will be excretory products that they don't need (CO2) some may be toxic (ethanol). But many other things are released as well small molecules, signalling molecule, proteins, etc...",
"It's not really possible to enumerate all the possible things that yeasts can emit here but the Yeast Metabolome Database is a database of all the small (and large) molecules which yeast metabolise.",
"http://www.ymdb.ca/",
"If you go to the search function and search for \"extracellular -membrane\" you'll get a vast list of all the things that yeast can excrete, which will mostly not be embedded in the cell membrane. This is a bit of a start and obviously not all of those will contribute to the flavour profile of beers but you can refine that by adding \"esters\" or other chemicals. It's kind of fascinating quite how many chemicals can be produced by yeast cells and gives you an idea of the scale of the problem of characterising exactly which chemicals add flavour notes to beers and wines.",
"Not sure if you'll be able to read it but this paper gives a fairly full review of the state of contemporary brewing research.",
"http://mmbr.asm.org/content/77/2/157.long",
"\n(I'm sure I could get you a copy if you want to read it)",
"Diagram 2 gives a good overview of the main products which influence flavour:",
"Ethanol\nDiacetyl\nAcetoin\n2,3-Butanediol\nVolatile Aglycon\nGlycerol\nH2S\nSO2\nThiols\nThiolesters\nDimethyl sulfide (DMS)\nAldehyde\nEsters\nVinylphenols\nFatty Acids\nAcetic Acid\nHigher order alcohols)\n",
"Some of those are obviously individual chemicals (ethanol) some are classes of chemicals (Fatty Acids). The authors go on to point out that: ",
"All brewing strains produce glycerol, vicinal diketones (VDKs), alcohols, esters, short-chain fatty acids, organic acids, and diverse sulfur-containing substances. The levels of each category that are found in beer are dependent in part upon the yeast strain, but at least as important are the precise fermentation conditions that exist, including pitching rate, temperature, extent of oxygen addition, C:N ratio, and duration of fermentation and maturation ",
"Flavour chemicals they specifically discuss are"
] |
[
"Awesome, thank you so much. That metabolome database is a phenomenal resource."
] |
[
"Also, several of these compounds are actively avoided in brewing. Some by allowing the yeast to continue metabolizing (they'll resorb and digest some of the things they secrete as the sugar is used up), and some by adding finings to bind and precipitate certain components.",
"Don't remember all the details exactly, but I just finished reading ",
"this book",
" which was quite good."
] |
[
"I just mixed some Acetone and Water and the beaker warmed up. Why?"
] |
[
false
] |
[deleted]
|
[
"No thats not corret. You're right there is no reaction, but it has to do with the delta G of mixing."
] |
[
"I think the answer to this question is going to be complicated, depend on the ratio of water and acetone, and ultimately have to do with the thermodynamics of how the acetone and water molecules arrange themselves. But to be overly simplified, I think you could just state that the acetone/H2O molecules fit together better and exist at a lower energy state together than they do by themselves."
] |
[
"You can have heat release even with mixing. For most mixtures it is just so small that it isn't noticeable. "
] |
[
"What determines the radius of curvature of a rainbow?"
] |
[
false
] | null |
[
"See ",
"this",
" thread for a pretty good description, with diagrams, of what causes rainbows.",
"However, I think it's clearer to think of a rainbow not as a \"circle,\" or a curve at a fixed ",
" position in space, but rather as an entire ",
", with the vertex at your eye. It makes sense to talk about the half-angle of that cone (about 42 degrees), but its \"radius of curvature,\" ",
"strictly speaking",
", would depend on ",
" circular cross section of the cone (i.e., how far away) we're talking about."
] |
[
"But there is also the fact that the rainbow is formed due to reflection, refraction, and dispersion caused by water droplets. These droplets have to be in the atmosphere at some distance away from the observer. Not one exact distance, for sure, but some range of distances - the droplets aren't at all distances along the cone. Since 42 degrees is pretty close to 45 degrees, this means the radius of the rainbow is approximately equal to the distance of the observer from the water droplets causing it. "
] |
[
"Here is a simple fact that helps explain the shape: It is a ring at 42º centered around the antisolar point. Guess what the antisolar point is? The shadow of your head. ",
"It illustrates the fact that not everyone in a group of people is seeing the same rainbow, and helps you realize that light is being scattered every which way. Its one easy to grasp fact that explains a great deal about how rainbows work."
] |
[
"\"Perhaps most mind-boggling of all is the math that shows that at any given moment, each of us has at least a million atoms in our body that were once in the body of every person who has ever lived, from Moses to Lady Gaga, from Marcel Proust to Newt Gingrich.\""
] |
[
false
] |
I've heard this, or some variation, quite a few times. Is this possible and, if so, how? EDIT: Words. Can't brain today; I got the dumb.
|
[
"So, not \"Every single atom.\" as you said above."
] |
[
"I think it's mostly a statistics trick to make this kind of a claim, based on people having ~7e27 atoms in their body (according to wolfram alpha) and less than 7 billion people alive at a time (7 billion times 1 million is only 7e15, so our bodies would at least consist of 99.99999...% unrecycled material, since we need only to have 7e15 atoms that were once in someone else). I don't think there is any kind of physical principle or even adequate modeling for the \"drift\" of atoms throughout the Earth to support or properly refute the claim."
] |
[
"What about hydrogen? Isn't all, or a vast majority, of hydrogen primordial?"
] |
[
"Why can you rename, or change the path of, an open file in OS X but not Windows?"
] |
[
false
] | null |
[
"The Windows filesystem identifies files by their paths (including the file names)—if you change a file’s path, applications and the operating system will perceive it as a new file with no connection to the original.",
"The OS X filesystem identifies files by an independent file ID, which remains fixed if the file is moved or renamed."
] |
[
"I've taken a class in Operating Systems. The simplest answer is probably this:",
"In this case specifically, there may not be many repercussions. However, let's consider an extrapolation of these two mindsets. Windows is keeping things simple, but disallows some operations like the one that OP asked about. OS X is keeping things easy for the user to use, at the price of more file metadata per file. This can add up over time, particularly if a user has many small files (then the ratio of file metadata to actual data will be small, and you want it to be large so that disk space is not wasted on metadata)."
] |
[
"Follow up question,..what's the pro/cons of both method ?"
] |
[
"As a ball's velocity approaches the speed of light, does the Higgs field effect on the ball increase because the mass of the ball increases?"
] |
[
false
] |
.
|
[
"(1) We no longer talk about mass increasing as speed does, because it is a misleading concept. We instead just talk about momentum no longer being a linear function of momentum.",
"(2) The Higgs is not responsible for most mass. It is responsible for the mass of individual particles like quarks, but in fact that rest mass is very little compared to most of the actual mass of objects. Most mass actually comes from the binding energy of the strong nuclear force."
] |
[
"As i understand it, the faster it goes, relative to some other inertial reference frame, the more it will interact with the higgs field, relative to that inertial frame, thus making one in the other frame measure it as heavier. But i dont think it actually aquires particles."
] |
[
"Thanks, that's certainly a better, and accurate, way of putting it."
] |
[
"Can a parasite get parasites?"
] |
[
false
] | null |
[
"Yes; there's even a word for it, ",
"hyperparasitism",
". Depending on the definition of parasite you choose to work with, some examples of hyperparasitism may or may not apply, but an example that I think would fit most definitions is ",
", a parasite genus that lives in insects, particularly parasitic fleas."
] |
[
"Yes!",
"The Chestnutblight fungus, ",
" is susceptable to a mycovirus which lessens the damage that is done to the tree."
] |
[
"Yes, there is an example in the disease Diphtheria. It is caused by a bacterium, a parasite that is itself the victim of a bacteriophage virus, a parasite. ",
"The gene for the toxin in Diphtheria is not in the bacterium's genome, it is encoded by the virus."
] |
[
"Angular momentum question."
] |
[
false
] |
I'm not sure if his is a dumb question or not but why does angular momentum follow the right hand rule? You know the rule that says if you point the fingers of your right hand in the direction of rotation your thumb points in the directon of angular momentum. Was 'God" right handed? Is it the same in the Southern Hemisphere? It just seems very arbitrary an unscientific. Again please inform me if I'm dumb, you wouldn't be he first.
|
[
"It's just convention. There are only two options. I suppose more generally it follows from the right hand rule for cross products."
] |
[
"It doesn't matter which hand you use, as long as you're consistent. If you change all of our right hand rules to left hand rules everything works out the same."
] |
[
"You could use a left hand rule for ",
" without changing physics. Whether it is the right or left is arbitrary. ",
"What is true of angular momentum, and must be addressed in our rules is that angular momentum appears to be opposite in a mirror. ",
"Take a bottle cap, or a frisbee...or anything disklike. Look in a mirror while you spin it. Find the angular momentum vector in reality, and look at the mirror and notice that the mirror image shows it pointing the opposite way.",
"This is true whether you define ",
" as ",
" x ",
" or \n",
" x ",
"."
] |
[
"Evolution: Do all current \"versions\" of a species derive from one single individual?"
] |
[
false
] |
[deleted]
|
[
"Well, for this question:",
"Does this mean that, since all sharks now have this ability, that they are all ancestors of one particular shark?",
"Yes, assuming you mean descendants rather than ancestors.",
"But for this question:",
"Do all current \"versions\" of a species derive from one single individual?",
"No. ",
"Or rather, all current versions derive from multiple single individuals, as it were. So, to use the shark example, one particular shark gained the multiple teeth thingamobob, and then it went and had babies with ",
" The multi-tooth invention was quite useful, so its descendants had an advantage, and grew in numbers, until all sharks had it. But, as mentioned above, all this involved mating with other sharks. So, though eventually all sharks would be descendants of this one shark, that doesn't mean that they didn't have other ancestors as well. ",
"Over time, this scenario would be played out for every trait: each is derived (generally speaking) from a single individual, and so, for that ",
" everybody is descended from a single individual. For each allele that has reached fixation (i.e., everybody has the same DNA at that region of our genome), that is true, but the individual ancestors are different for each bit of DNA. In each generation, bits of DNA from each parent get mixed together (genetic recombination), this is how different parts of our genome can be derived from different ancestors.",
"This is why 'Y chromosomal Adam' and 'mitochondrial Eve' could have existed at different times and/or different places; just because all known mitochondrial DNA derived from one ancestor doesn't mean all our other DNA had to have come from her or her mate -in fact, that would be absurdly unlikely. The only reason we can talk of a Y chromosomal Adam and a mitochondrial Eve at all is because those two chunks of DNA are not subject to genetic recombination- the mixing I mentioned above.",
"This is for sexually reproducing organisms only, btw. Ancestry in asexual organisms is simultaneously much simpler and much more complex."
] |
[
"I'm not familiar enough with this to speak for all animals, but there are two relevant common human ancestors (because of sexual reproduction): ",
"Mitochondrial Eve",
" and ",
"Y-chromosomal Adam",
"."
] |
[
"But it didn't happen in one stage, so your \"one shark\" example isn't that realistic. ",
"It would also probably be a mistake to call the creatures that started the process as \"sharks\". They were ancestors of sharks, but not sharks.",
"And we needn't feel sorry for those who didn't contribute to the shark teeth evolution. They didn't necessarily loose out, they probably became the ancestors of some other animal."
] |
[
"What percentage of a person's mass is made up of up quarks, of down quarks, and of electrons?"
] |
[
false
] |
Wiki has an article on , but it got me wondering, what is the composition of the body in terms of elementary particles? Also, is the mass of photons, gluons, Higgs', and other particles statistically insignificant when calculating this?
|
[
"I want to make note to anybody playing at home with their calculator, the measured masses of the quarks are ",
" lower that what you'd expect when considering the mass of the protons and neutrons—this is because the majority of the mass results from binding energy in what's oddly enough a special relativity effect."
] |
[
"Assuming we have roughly even numbers of protons and neutrons (which is pretty close to true, although we'll have an excess of protons due to the large amounts of water in the human body, since hydrogen atoms mostly consist of a single proton and no neutrons), we're 50% up quarks, 50% down quarks, and a fraction of a percent electrons. Other particles aren't stable on their own."
] |
[
"I think that would really depend on what you consider a characteristic. The binding energy will pretty much always be present anytime you find a quark. However, the binding energy being there is based on conditions that aren't necessarily mandatory given or current knowledge of physics. But then again, the same thing could be said about the mass of an elementary particle, and most people would certainly consider that a characteristic."
] |
[
"Why do atoms need to fill up their orbitals?"
] |
[
false
] |
I am an undergrad doing first year chem and I was wondering why atoms need to fill up their electron orbitals, even if it means creating an unbalanced charge? Do we know why particles do this or were theories created based on observations made from experiments?
|
[
"Good question! Because they actually ",
" create an unbalanced charge. What I mean is that if you were to (somehow) take a single NaCl molecule and pull the two atoms apart in a vacuum, you would ",
" end up with Na",
" and Cl",
" but with two electrically neutral atoms; Na",
" and Cl",
" (asterisks here mark that they're radicals with an unpaired electron, on paper I'd write a dot instead). ",
"The same goes for KCl or HF and so on, and also if you have, say, H2 you'll end up with 2H",
" and not H",
" + H",
". In short, separating charges does indeed 'cost' too much energy for that to happen. ",
"However, when you put ions in a polar solvent (e.g. water), the solvent molecules arrange themselves around the ions, stabilizing the charge. So in water, the energy required to pull apart two oppositely-charged things is much smaller, and that's why NaCl will then split into Na",
" and Cl",
" instead. Once the issue of separating the charge is taken out of the picture, ",
" the 'need' to have filled shells overweighs. And if you have an 'ionic bond', then of course the charges aren't really separated much, so there too you can view that way.",
"So it's important to remember you're not dealing with absolutes here. It ",
" requires energy to ",
" remove an electron from a neutral atom making it positive, and you ",
" gain energy by adding a free electron to a neutral atom making it negative. ",
"So when you say that the atom 'wants' to have a filled shell, this is ",
". You gain relatively more energy by adding the last electron needed to fill a shell, and it requires relatively less energy to remove an electron from a shell that only has one.",
"Explaining ",
" this is the case is more difficult and technical. (Among other reasons a filled shell has spherical symmetry and no net angular momentum) The order in which orbitals are filled in the periodic table is given by the ",
"Madelung rule",
". The basic theories (e.g. orbitals) were known at the time but the rule was actually found experimentally, and only justified theoretically much later. (It's not an absolute rule, and it's hard to rigorously prove what is not rigorously true!) "
] |
[
"Thanks for your answer!",
"If I understand correctly, you're saying atoms never ",
" get an unbalanced charge, and if they do, there is a way to balance the charges? (e.g. NaCl in water)",
"And are you referring to electronegativity in your second last paragraph?",
"Can you explain, even if briefly, why atoms/particles have a need to fill orbitals, please? I may not understand it, but I'd like to try. "
] |
[
"No, I'm saying that two atoms in a molecule won't break apart into charged fragments in a vacuum, because separating two charged particles like that costs too much energy. If there's a way to ",
" the charges (lower the energy of having a situation with separated charges) ",
" you can get two atoms to separate into a positive and negative ion.",
"Orbitals are states of electrons. Atoms don't 'need' to fill them. Again, the point is that a filled shell is relatively stable, meaning the electron affinity (energy gained by adding an electron to a neutral atom) is lower if it has a filled shell, while the ionization potential (energy required to remove an electron) is higher. If the energy required to remove an electron from atom A is lower than the energy gained from adding an electron to atom B, then an electron will move over from A to B. ",
"If you have a filled shell on an atom (e.g. a noble gas) then the electron affinity is low relative other atoms and the ionization potential is high; in short it requires more energy to change the number of electrons there, or equivalently the electrons are most stable in that configuration. ",
"See ",
"the electron affinities here",
" (numbers are relative Helium), the scale is negative upwards, so the higher the peak, the more energy is gained by that atom grabbing an electron. As you can see there, the halogens which are one electron short of noble-gas structure have the highest affinity. ",
"Here's the ionization potential",
" (this happens to be the absolute number) positive energy upwards, so the higher up an atom is on the chart, more energy is required to remove an electron from it. As you see, the noble gases aren't big on losing electrons either. The lowest atoms, from which an electron can most easily be lost, are the alkali metals, since they've got a filled shell plus one. ",
"Together those two graphs describe why atoms tend towards a noble gas configuration of electrons. They don't 'need to fill orbitals'. Shells and sub-shells ",
" of orbitals, and orbitals are the states which electrons can occupy. A bound electron is ",
" in an orbital."
] |
[
"Why is there (at least) three space-like dimensions and only one time-like dimension?"
] |
[
false
] | null |
[
"What do you mean \"why\"?"
] |
[
"Wow, this is surprisingly difficult to answer. I guess I mean why is it presumed or why do we only work with one time-like dimension? ",
"I am sort of thinking aloud here and I hope that is ok. Is it a result of our experience in a way similar to how it was presumed that there are three space-like dimensions ",
"obligatory classic Sagan clip",
"? Is it possible that there are more than one time-like dimensions? "
] |
[
"Why do we work that way and why is it that way, if that's even the case, are two diffrent questions. That is unless you belive in a strong anthropic principle, and therefore think that the universe not only is the way to is because we are here and require it to be this way, but ",
" because we are here and observed it, which collapsed the wave of all possible universes down to the particular one that can support life as we know it. That, BTW, presumes that only consious observation collapses wave states, and we are the only consious observers in the multiverse, and that nothing really is when it acts as a wave, which is silliness."
] |
[
"What does a 1kW solar panel realistically produce in average?"
] |
[
false
] |
What is a solar panel rated at 1kW realistically going to produce in average? Not when only the sun shines, but all year round, night and day. So if we took all the power it produced through a year, and calculated the average, what would it realistically be?
|
[
"The rating for the panel is produced through testing by a company in Florida (there are others but the one in Florida does most of the testing) where the average insolation is about 5.25 kWh per square meter per day which is high, but not the highest on Earth. In these conditions, a solar panel will produce electricity exactly at its rated capacity (since the rating was made in those conditions). If you increase the insolation by moving to a sunnier place, it will outperform its rating. Move to a less sunny place, like Minnesota, and it will almost never perform at its rating.",
"EDIT: Actually, I think the Florida company only tests panels for solar heating applications - heating water etc. However, the point stands: exceed test conditions and you will exceed rated performance. CertifiedEvil made a comment elsewhere in the thread about the test conditions for electric solar panels."
] |
[
"It really depends on where the panel is located and many other factors. ",
"This",
" is a great tool to find out. I just checked my area in Portland, Oregon, and a 1kW system would produce 1018 kWh in one year."
] |
[
"It generates more than 1 kWh per hour in the day, due to the stronger than normal sunlight."
] |
[
"Why do most earthquakes have a magnitude between 4.0-4.9?"
] |
[
false
] |
When I looked at the amount of earthquakes each year it was very weird to realise that atleast 90% of all earthquakes have a magnitude between 4.0-4.9. What is even more weird is that magnitudes could increase because the spin of earth is slowing down. So I was wondering if that 4.0-4.9 could also change in 5.0-5.9 or worse.
|
[
"Luckily for everyone, it is ",
"not true",
" that most earthquakes are magnitude 4.0-4.9. It just ",
" that a majority of quakes are in that range because lists of earthquakes normally don't include smaller quakes, even though there are ",
"vastly more of them",
" (play with the \"all magnitudes\" setting vs. the \"only 2.5 or greater\" and \"only 4.5 and greater\" settings to see the differences). On reason for this is that there are so many of them, and hardly anyone can feel them. And a very large number of earthquakes occur in places where no one would notice them anyway, such as in underpopulated areas or in the middle of the ocean. This idea that earthquakes are related to the slowing spin of the earth seems to be entirely based on one single paper (",
"this one",
") predicting an increase in major shakes in 2018. I know that Wikipedia isn't a peer-reviewed source, but based on their list of ",
"earthquake numbers worldwide for 2008-2018",
", there does not seem to have been any significant uptick in earthquakes in 2018. It seems to have been a pretty average year."
] |
[
"That's not exactly true. The number of earthquakes increases with lowering the magnitude. So the most earthquakes have a very little magnitude. Maybe the list of earthquakes that you've been seen just have the minimal magnitude of 4.0 so it is the most widespread magnitude because it is the lowest."
] |
[
"The ISC is usually good, ",
"ANSS catalog",
" is one of the other big global datasets. Most global catalogs, especially ones that are populated with a lot of teleseismic data (i.e. info on earthquakes relatively far away from contributing stations) will have magnitude of completeness well above Mw 1. Local networks in the area of interest will usually have more complete records, but not all of these (1) share all their data with global catalogs like ISC or ANSS and/or (2) make all their data publicly available. E.g. for Iceland, the ",
"meteorological office",
" operates a local network of seismometers, but doesn't seem to make the catalog available, other than being able to see the last 48 hours.",
"EDIT: ",
"IRIS",
" also has a lot of data, including contributions from local networks in different places."
] |
[
"How do other animals see television? As a series of still images, a blur, or like we do (as motion)?"
] |
[
false
] |
I realise this may depend a lot on the animal - so lets says a a cat, a dog & a bird of prey. **Lets assume it's it's either a movie or a tv show, so 24 frames per second or above.
|
[
"ultraviolet"
] |
[
"Related: The red, green and blue displayed by TVs correspond to the cones in our eyes. Turtles have four types of cones, so the color on a TV doesn't look like real life to them."
] |
[
"AskScience discussion about how dogs see television"
] |
[
"What is the mechanism for antimicrobial behavior of silver or copper?"
] |
[
false
] |
How does putting these materials in the fabric of my shirt so anything to kill microbes?
|
[
"Copper and silver ions disrupt bacterial membranes and viral protein coats which can lead to them spilling their contents out into the world, killing them. One of the ways they do this is by reacting with thiol (sulphur containing) groups on membrane proteins. ",
"If this disruption isn't enough to kill the microbe, silver ions inside can then bind to thiol groups in key respiratory enzymes which inhibits their ability to utilise food for energy (in the case of bacteria or fungi, viruses don't respire). Silver also binds to the bases of the bacterial or fungal DNA, inhibiting cell division and growth of the bacterial colony. ",
"Putting silver or copper in fabrics can help to prevent bacterial or fungal growth in problem spots such as armpits or groins, where sweat collects. The silver used for this purpose are normally silver nanoparticles suspended in some kind of polymer matrix. This has some issues itself as these nanoparticles can be washed out of the fabrics. These end up in wastewater in lower concentrations which can lead to some degree of adaption by bacteria to counteract it. ",
"some refs:",
"\n",
"https://www.sciencedirect.com/science/article/abs/pii/S1748013215000493",
"https://pubs.rsc.org/en/content/articlelanding/2018/ra/c7ra13597a#!divAbstract",
"https://www.nature.com/articles/s41565-017-0013-y"
] |
[
"Silver also has the ability to denature key enzyme systems within bacteria."
] |
[
"Silver also has the ability to denature key enzyme systems within bacteria."
] |
[
"Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical 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...". 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 , 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. Please only answer a posted question if you are an expert in the field. . 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 . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Is there any substantive evidence to suggest ranked choice voting significantly changes electoral outcomes vs. winner-take-all?"
] |
[
"Somewhat to the contrary, fairvote.org lists ",
"some data",
" that seems to suggest the impact is minimal:",
"A FairVote report on incumbency in the Bay Area of California shows that incumbents are re-elected at the same rate both with and without RCV.",
"There have been 15 RCV races in the U.S. which were won by a candidate other than the first-round leader. That’s 3.8% of all single-winner RCV races in the U.S. since 2004",
"I've also seen it cited in a couple of places that in 2013 in Australia, 90% of the RCV elections were won by the person with the most first-choice votes (i.e. the first-round leader). Although I haven't been able to find the original source to link it.",
"On the other hand, for the second point in particular, I will note that the first-round leader in an RCV system is not ",
" the person who would have received the most votes in a winner-takes-all election. You still have to account for potential differences in voter behavior, where voters may change who they list as first choice compared to who they vote for when it's winner-takes-all. But I have not really seen any data that attempts to analyze that, unfortunately."
] |
[
"Interesting! Thank you"
] |
[
"Why do insects trapped in amber look the same as insects today? Is there anything in particular about modern insects that distinguishes them from insects that lived 250 million years ago?"
] |
[
false
] |
From an evolutionary perspective, it seems on the surface that bugs looked the same today as they did back when dinosaurs roamed the earth. Amber of frozen insects don't immediately make apparent that millions of years of evolution separate that trapped insect with insects in 2019. Is there anything, perhaps internally or otherwise, that we know has changed about insects over the course of all these years? What do their evolution, or ostensible lack thereof, tell us about the Earth?
|
[
"I'd argue they aren't really any more similar to modern insects than ancient vertebrates are similar to modern vertebrates, it's just that you do not see the differences as readily because your eye is trained to look at vertebrates and notice details it just misses when looking at insects. Many modern insect groups don't really get going until the mid-Cretaceous, long after mammals and birds first evolved. ",
"Sure, mammals look different from dinosaurs (although they both follow the same general body plan of four limbs, head at the front with similar arrangement of eyes and mouth and nose, etc), but does a modern shark or lizard or turtle look that different to the untrained eye? Or for that matter a small mammal? On the flip side, while various insect groups look broadly similar to modern groups, some don't. Butterflies and the widespread eusocial wasps, bees, and ants are pretty recent."
] |
[
"it's just that you do not see the differences ",
"This. I imagine that entomologists are screaming as they read the original question. Insect species today might be visually differentiated by a pattern of hairs or the veins in their wings, things that a lay person (like myself) don't register. I was recently on a ship with a naturalist who got excited that what she'd thought might be a pygmy sperm whale was in fact a dwarf sperm whale, a species she hadn't seen in person before. All I saw was a dark blob out towards the horizon. Training helps you see differently and notice more.",
"Evolutionary change is mostly driven by a shift in the environment that presents new challenges; there's not much of relevance to a fruit fly or a mosquito that has changed since the Jurassic and today, so we shouldn't ",
" to see gross morphological change."
] |
[
"Aside from perhaps size I can’t think of much, I’m no expert in insect biology and evolution but usually when an animal does not further change in physiology it is because they’ve no need to adapt, they are already evolved to fit their purpose and survival needs. That would suggest that in earths state for the last however many years certain insects have been able to continue to prosper without changes being necessary. Their developments for finding food have continued to be successful, their method of transport has continued to be successful, their method of breeding has continued to be successful. "
] |
[
"How do mathematicians discover more digits to pi?"
] |
[
false
] |
[deleted]
|
[
"No. Mathematicians aren't particularly interested in the digits of Pi. I know 3.14159, and that's it. Digits are not an important property of a number, we try to ignore them as much as possible. ",
"But most formulas for Pi are in terms of infinite sums, which means you can add up a finite number of them to get an approximation of pi. If someone found an expression that got better approximations of pi earlier on in the sum, then that would probably be interesting. But it would be interesting how they got that formula, rather than the fact that we could approximate Pi better. One of the fastest formulas for Pi is a product of very involved, interesting and difficult math. We don't care that we can get more digits (they're useless), we care that new math was made!"
] |
[
"usually a fairly ",
"convoluted formula",
" derived from an identiy by Ramanujan is used, because it converges ",
" quickly"
] |
[
"Actually, supercomputers discover the digits of pi using polygons. Think of an hexagon. It tends to be a circle. Now add more sides. Think of a polygon with 1,000 sides. Think it with even 1 million or billion sides. It certainly is very close to a circle. From these, supercomputers calculate the perimeter and the radious of the circle, so they get pi."
] |
[
"Does relativity imply that gravity is a pseudo-force?"
] |
[
false
] | null |
[
"\"Force\" is not the best-defined term in physics. We tend to call it a force more often than not, but you're right that it's different than all the other forces because it's not an effect particles have on each other, but rather an effect of particles moving on natural paths through spacetime itself."
] |
[
"That's correct, the appearance of the downwards force of gravity is just an artifact of the fact we are working in an accelerated reference frame with respect to spacetime geodesics. So in that sense, it's a fictitious force, in exactly the same way as centrifugal force, with which people are familiar. ",
"(Of course, the coupling of the curvature of spacetime to the stress-energy-momentum tensor is very non-fictitious.)"
] |
[
"Depending on what the correct quantum theory of gravity looks like, that may well end up being a reasonable interpretation."
] |
[
"If electric is transferred via electromagnetic waves and the speed of these waves are near the speed of light, why does the type of conductor matter?"
] |
[
false
] | null |
[
"Conductors matter for how efficiently the wave is transmitted (how much energy is lost in the wires), but they don't matter for speed as you say."
] |
[
"Fiber optics lets you send more data at once with higher frequency without it getting attenuated or scrambled as much over distance. It has nothing to do with how fast the signal travels.",
"Think about it as the difference between ping and bandwidth if you are familiar with networks. The ping stays the same, the bandwidth increases."
] |
[
"Ahh I get it now. But when we are using ways of communication such as internet, why are we using fiber optic cables? They transmit it at the speed of light but, isn’t a normal cable doing the same too? How is it faster?"
] |
[
"Is there a critical time window for puberty? If you gave a eunuch, who was castrated pre-puberty, hormone supplements late in development would he undergo puberty or gain a sex drive?"
] |
[
false
] | null |
[
"Would a male with only one testicle mature more slowly than regular?"
] |
[
"It wouldn't affect height, but it would certainly affect penis enlargement. A trans man, a person transitioning from female to male, will take testosterone. One of the things this causes is a large amount of clitoris growth. The clitoris will elongate, become more penis-like. A length of 1-2 inches is common. This can then further be extended with surgery.",
"So if testosterone can basically induce penis growth in someone who is genetically female, it will certainly trigger penis enlargement in someone who is genetically male and already has a pre-pubescent penis."
] |
[
"It wouldn't affect height, but it would certainly affect penis enlargement. A trans man, a person transitioning from female to male, will take testosterone. One of the things this causes is a large amount of clitoris growth. The clitoris will elongate, become more penis-like. A length of 1-2 inches is common. This can then further be extended with surgery.",
"So if testosterone can basically induce penis growth in someone who is genetically female, it will certainly trigger penis enlargement in someone who is genetically male and already has a pre-pubescent penis."
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical 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...". 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 , 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. Please only answer a posted question if you are an expert in the field. . 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 . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Why are most fruits spherical or oval? And what about bananas? "
] |
[
"The rotation of the earth doesn't change the gravitational acceleration itself, but rather introduces a second force that counteracts part of it. It results in an apparent outward force that varies from 0 at the poles to a maximum at the equator. This force reduces the apparent gravity at the equator by ",
"~0.034 m/s",
". That's about 0.35%. "
] |
[
"It is. It's just rotating at the same speed as it is going round the earth - once every 28 or so days. So from the earth, it looks like it's not rotating."
] |
[
"What is the logic behind a retailer pricing its sole two items $1 apart? Why would the consumer buy the cheaper item when it seems like a bad deal?"
] |
[
false
] |
[deleted]
|
[
"This is known as \"decoy pricing\" [1] [2] [3].",
"[1] ",
"http://en.wikipedia.org/wiki/Pricing_strategies#Decoy_pricing",
"[2] ",
"http://en.wikipedia.org/wiki/Decoy_effect",
"[3] ",
"http://conversionxl.com/pricing-experiments-you-might-not-know-but-can-learn-from"
] |
[
"The retailer wants you to purchase the $9 juice and not the $8 juice. The pricing is done so that the consumer will think the $9 is a better deal. It's the same logic as 1.99 vs 2.00 people see 1.99 and think, oh it's only a dollar when it's really two dollars but it feels cheaper. "
] |
[
"To use your juice as an example.... The juice guy makes an extra dollar, however the time taken to make a small compared to a large is the same, his overheads are the same. The increase in ingredients would cost very little as would the increase in cup size. ",
"Most people would look at those prices and feel that the bigger one is the better deal, which I guess it is. It it were $3 difference, most people wouldn't 'upsize'."
] |
[
"Are elements organized in periods by energy level? Period 1 has two elements, and the first energy level also has 2 elements. But Period 3 has eight elements, while the third energy level can hold 18 electrons. Are period and energy level related at all?"
] |
[
false
] |
Edit: Assuming this is a stable atom of course...
|
[
"Yes, the period corresponds to the principle quantum number for the s and p blocks. The d block is in the n+1 period due to the way the orbitals are filled, ie the 3d is in period 4.",
"The principle quantum number is directly related to energy levels."
] |
[
"They are correlated, but things get a bit tricky when you hit the fourth energy level. I'll give the simpler explanation first.",
"Once the third energy level hits eight electrons, the fourth energy level starts filling up. Then we hit the part of the periodic table where the third and fourth energy levels get a bit flip-floppy, called the Transitional Metals. In the transitional metals, valence electrons are less strict about their adherence to a single atom, and instead more or less resemble a \"sea of electrons\" that are easily influenced by electromagnetic force. This is the reason for both the famous magnetic properties of transitional metals, and the common use of transitional metals as conductors. ",
"The more complicated explanation is, energy level is separated into four orbital blocks - S, D, P and F. ",
"Here's a simple diagram of what I mean.",
" These blocks are the actual structural configurations of the orbitals. Even though two electrons may be in the same energy level, they can be in two completely different orbital blocks that may cause the atom to exert completely different chemical properties. These orbitals are configured such that the 3d block starts filling up ",
" the 4s block (the S-block, by the way, is what gives alkali and alkaline metals their highly reactive properties. As for the D-block, those are the electrons that I mentioned in the first explanation, the ones that give transitional metals their electromagnetic advantage)."
] |
[
"Periods are related to ",
"orbitals",
" and orbitals are related to ",
"spherical harmonics",
". Electrons are actually waves, and when electrons \"orbit\" an atomic nucleus they actually form standing waves (which take the form of spherical harmonics) centered on the nucleus. This is a minimum energy configuration. Different kinds and orders of spherical harmonics have different energy levels. In general, if the difference between the corresponding spherical harmonics for two orbitals is ",
" a difference in degree or order then the higher degree/order orbital will have a higher energy level. But if both are different, then it's more complex which one has a higher energy level. This is how you end up with the 3d orbital having a higher energy level than the 4s orbital, for example. This is because as you go up in degree (shell) you're only really guaranteed that the lower bound of the energy levels in that set of orbitals will be higher than the lower bound from the previous shell, you're not guaranteed that there won't be an overlap, which indeed there is.",
"This is probably the most helpful graphic that shows what's going on: ",
"http://chemwiki.ucdavis.edu/@api/deki/files/27833/ac662f17f8c173fdb82c3bd7d35b81f2.jpg",
"This is the reason why the 3rd/4th period is weird on the periodic table, because it includes elements that are filling out the 4th as well as 3rd energy levels (4s, 3d, 3p).",
"Hopefully that makes sense."
] |
[
"How does lactose (milk sugar) metabolize compared to sucrose (table sugar), and do they affect health differently?"
] |
[
false
] |
I know that sucrose is glucose+fructose and lactose is glucose+galactose, and I know fructose is primarily metabolized in the liver, but I don't know anything about what happens to galactose when it enters the body. There have been lots of studies and reports on the harmful combination of glucose and fructose consumed in large quantities over many years, but what about the combination of glucose and galactose found in dairy products? Is it the lesser of two evils due to its lack of fructose, or does galactose pose problems of its own?
|
[
"To my knowledge, there is little evidence that galactose is any more dangerous than glucose to normal, healthy people. Galactose is metabolized to glucose efficiently, so lactose ultimately becomes two glucose molecules anyway. Glucose tends to trigger the insulin response better than fructose. This inhibits appetite, but can be worse for diabetics, natch.",
"However, lactose is substantially less sweet in taste than sucrose... so it wouldn't work as some sort of alternative to table sugar."
] |
[
"one thing about glucose that makes it special is that it makes you feel much more full than other sugars. this is one of the dangers of high-fructose corn syrup—while its calorie content per mass is the same as glucose, it makes you feel much less full, causing you to consume much larger quantities of it"
] |
[
"Ah okay, that's what I was looking to find out. I wasn't wondering about lactose as an alternative sweetener, more like wondering if drinking lots of milk is \"as bad\" or \"worse\" as eating food with the equivalent amount of regular sugar."
] |
[
"How can tube/cones make sounds \"louder\" without any input energy?"
] |
[
false
] |
see: how does this not break the laws of thermodynamics? i understand the answer must be loudness=/=energy but its still confusing
|
[
"The total energy is still the same, but it comes out more concentrated in a certain direction. "
] |
[
"Your ear does the same thing, in order to overcome the density change from the tectum (ear drum) to the cochlea sound is 'focused' (by way of some cool level action too) by lowering the surface area from one side to the next"
] |
[
"hm, i guess i just never observed this. thanks :D"
] |
[
"How do quarks interact inside a proton?"
] |
[
false
] | null |
[
"The force that binds quarks together to form a proton is called the strong force, and perhaps the most distinctive feature of this force is something called ",
".",
"The strong force acts on a property of quarks that is rather fancifully called ",
" (although it has nothing to do with actual color). There are three colors that play the role that electric charge plays for electromagnetic forces.",
"But here is the key point: The strong force becomes weaker and weaker as quarks get closer and closer together; this is called asymptotic freedom. Or phrased in reverse, the force grows stronger as the quarks separate. When the separation between the quarks gets as ",
" as 10",
" meters, the force is so strong that the quarks cannot separate further; to do so would require the input of so much energy that a new quark-antiquark pair would form, and so we'd not wind up with a free quark, but instead with, say, a bound state of three quarks plus another particle made of a quark-antiquark.",
"Thus, a crude model of a proton is given by a ",
". The simplest form of such a model is that the quarks are stuck inside a bag of size ~10",
" meters; inside that bag, they move freely, while the boundary of the bag acts as a barrier that quarks cannot pass.",
"You can read more ",
"here",
"."
] |
[
"Up would only annihilate anti-up.",
"A particle/antiparticle pair can form a particle that decays after a short amount of time. An electron and positron, for example, can form positronium (sort of like a hydrogen atom, except with a positron replacing the proton), though it will quickly decay, typically into photons.",
"Likewise, a meson can form that pairs like-type quarks and antiquarks. Examples of such mesons are the neutral pion, the eta, and the J/Psi. These particles are all unstable, and decay (e.g., neutral pion typically into photons, the J/Psi can decay into an electron/positron pair among other things, etc.).",
"Edit: typos fixed."
] |
[
"Here is a good picture of the model",
"."
] |
[
"Can high amount of concentrated electromagnetic waves warp space like gravity does?"
] |
[
false
] | null |
[
" Yes.",
" Mass warps spacetime. That's Einstein's theory of general relativity. But that's not all. ",
" energy warps spacetime. Remember, E=mc",
" - mass and energy are basically the same thing, packaged different ways. ",
"This means something weird. For example, suppose you had two identical planets - each with the exact same numbers of atoms arranged the same way. If one was hotter, that means it has a greater total energy, so it would warp spacetime more strongly, effectively giving it stronger gravity than it's colder twin.",
"But this also means that electromagnetic waves, because they carry energy, warp spacetime. Light carries a very tiny amount of energy compared to any massive object so the effect is basically negligible, but it's still very real. In fact, if you put enough light in one spot, you can warp space enough to make a black hole! This black hole will be completely indistinguishable from one formed from matter, because black holes don't present any 'memory' of what they were made from. ",
"This black-hole-made-of-light actually has a fun name. It's called a ",
"kugelblitz",
" (that's German for Ball Lightning)!"
] |
[
"So suppose the sun was 1 million Kelvin all throughout. Not a bad assumption, it's about 15 million in the core, and about 5,000 K at the surface.",
"The kinetic energy of a proton in a 1 million Kelvin gas is found from 3/2 k T (k is the Boltzmann constant). That's 0.0001 MeV. Compare that to the mass-energy of a proton, 939 MeV/c",
". That thermal energy is less than a millionth of the energy per particle. ",
"For all practical purposes, you never really need to consider this. "
] |
[
"So suppose the sun was 1 million Kelvin all throughout. Not a bad assumption, it's about 15 million in the core, and about 5,000 K at the surface.",
"The kinetic energy of a proton in a 1 million Kelvin gas is found from 3/2 k T (k is the Boltzmann constant). That's 0.0001 MeV. Compare that to the mass-energy of a proton, 939 MeV/c",
". That thermal energy is less than a millionth of the energy per particle. ",
"For all practical purposes, you never really need to consider this. "
] |
[
"Why don't stem cells manage to replace cells lost to cell death as the body ages?"
] |
[
false
] |
Cell death is a good thing. Getting rid of broken cells is necessary, and stem cells react by replenishing the the tissue, at least until adulthood. What makes the stem cells less effective with age, so that tissue deterioration and plaque buildup occurs?
|
[
"... wat...."
] |
[
"... wat...."
] |
[
"Cell death is a good thing. Getting rid of broken cells is necessary, and stem cells react by replenishing the the tissue, at least until adulthood. What makes the stem cells less effective with age, so that tissue deterioration and plaque buildup occurs?",
"Hm, there's a couple of things I'll try to elaborate on in regards to this. My research focus is on stem cell-based heart tissue engineering, but not senescence, so I'd also refer you to this ",
"excellent Nature review",
" article on stem cell aging if you want to know more.",
"Tissue deterioration is related to two things - the damage/trauma to the tissue, and the regenerative potential of that tissue. What I mean by this is that every organ in your body (although this is controversial regarding some organs) has an intrinsic ability to repair itself - as you've noted, getting rid of broken cells is necessary. However, that intrinsic repair potential varies from tissue to tissue. Your heart, for instance, will regenerate maybe 1% of the cells lost per year for maintenance, but certainly cannot repair itself fully after a heart attack. So for certain types of degeneration, such as heart disease, the age of the stem cells matters far less than the type and extent of the injury.",
"However, you're right, stem cell effectiveness also does decrease with age. In fact, the article in which elaborated that about 1% of the heart is regenerated per year (really cool article ",
"here",
") actually notes that after 25, the turnover decreases until about 0.45% at the age of 75. Again, even a 25 year old heart with \"full regenerative potential\" won't be able to repair itself after an injury (you'd have to go back to the fetus...speculative, although neonatal mice can regenerate their heart after injury within the first 24 hours of birth), so being 25 versus 75 doesn't matter much. I'd say this is also the case with one of your specific examples such as plaque buildup, in which endothelial dysfunction is largely the mediator of plaque build up, and in fact, the existence of a so called endothelial stem cell (or endothelial progenitor cell in this field) is really ",
"controversial",
".",
"However, in other tissues, it seems that the overall stem cell population does in fact age, and this aging does decrease the regenerative potential. The aging process is fairly mysterious with resident tissue-stem cells because it's so hard to get at them and see what happens. These stem cells are generally quiescent and can self-renew themselves fairly well, although they don't divide and are less metabolically active to prevent possible DNA damage due to mitosis. Starvind elaborates on this, but to be a bit more specific, one theory suggests that the DNA damage of the resident tissue stem cells can cause tumor surpressing genes to activate, and this activation leads to loss of regenerative function and aging. Here is a ",
"nifty picture",
" which expands upon other hypothesis regarding stem cells, cancer, and organ dysfunction.",
"So, a tl;dr summary - DNA damage accumulated by the stem cells can lead to senescence/the stem cells losing their regenerative ability as a defense mechanism against cancer. However, in a lot of other organs that \"deteriorate\" over time, it's not the aging of the stem cells that may affect the organ's ability to function normally but possibly other mechanisms, such as how the injury was caused."
] |
[
"Why do chimps have nearly twice as many genes as humans, while having nearly the same genome size?"
] |
[
false
] |
[deleted]
|
[
"They don't. Where are you getting your numbers from? All placental mammals that I know of have around 20-25 thousand genes, and the difference between humans and chimps is around a hundred."
] |
[
"It's a misprint."
] |
[
"I got the number from a ",
"biochemistry textbook."
] |
[
"Question about relativity, a long pole, and black holes."
] |
[
false
] |
I hope I can word this in a way that makes sense. So as I understand it, relativity dictates that the laws of physics work the same in any inertial reference frame. So if we take out our telescopes and look at an object, we should be able to measure its mass and size. The results should vary between reference frames, but the effects should match the measurements, right? So we should not, for example, be able to measure an object that is smaller than its schwartzchild radius, because if it was actually smaller it would have collapsed into a black hole. I guess my question is, let's say you have a very dense bar/pole in space. This object is 2 kilometers in radius, and has the total mass of the sun (it is very long). The sun has a schwartzchild radius of ~ 3 km. Now length contraction is something that occurs at relativistic speeds. If you get in a spaceship and travel fast, objects are measured as being squished along the axis of your travel. So if you travel at a significant fraction of the speed of light toward the end of this pole, parallel to its long axis, it should appear to shrink along that axis. If you go fast enough, it should appear 4 km in length. It now is a pole 2 km in radius and 4 km in length. It has the mass of the sun. This mass in completely contained within a radius of 3 km, so it should collapse into a black hole, right? Obviously that doesn't happen, so what am I missing? If different reference frames are all just as "true" as any other, why isn't the reference frame in which the bar is squished a valid reference frame for the formation of a black hole? Thanks.
|
[
"This is really tough to solve, but I'm going to go out on a limb here and guess that you're neglecting the momentum term in the stress energy tensor; ie, mass doesn't inform General Relativity alone, but so too does momentum. The Schwarzschild metric is for a spherical mass at rest. I'm not sure what the solution would be for the situation you describe."
] |
[
"This is an outdated way of teaching relativity. An object in relative motion may act ",
" it had an increase in mass, but its mass has not actually increased.",
"Consider that Newton defined momentum ",
" = m",
". Well, he was right for sufficiently small speeds. But relativistically, we find that ",
"= (1-(v/c)",
" )",
" m",
" . At some point, someone smushed that first term with the mass and said that it was a \"relativistic mass.\" But that leads to a lot of confusion. It's better to just say that mass is mass and that momentum is only ",
" m"
] |
[
"The answer is given here:\n",
"http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html",
"In short, shavera is correct that you're neglecting the fact that you no longer have a static spacetime; things like momentum and angular momentum become important. "
] |
[
"When two photons are emitted in two exact opposite directions, what is their speed relatively to each other?"
] |
[
false
] |
[deleted]
|
[
"There is no such thing as \"speed relative to a photon\". When we say \"speed relative to something\" we mean the speed as measured in that something's rest frame of reference. Photons do not have a rest frame of reference. This is a foundational pillar of relativity. Therefore you can never measure a speed relative to a photon. It simply makes no sense. To try to force it to make sense is to throw out all of Special Relativity. "
] |
[
"There cannot be a reference frame for a photon because the fundamental postulate of special relativity is that light/photons travel at c in all reference frames. If there were rest frame for a photon, its speed in that frame would be 0, not c by definition. So no such frame exists. "
] |
[
"At rest is a relative term to describe in relation to something. When you are at rest with the earth, the net velocity between you and the earth is zero. "
] |
[
"There's no such thing as a perfect vacuum. But what's the closest to a perfect vacuum in nature? In the least dense part of space, how far apart are two atoms?"
] |
[
false
] |
[deleted]
|
[
"Does a defect inside a metal, i.e. a missing atoms, count as perfect vacuum? If so, would there be any special properties?"
] |
[
"Does a defect inside a metal, i.e. a missing atoms, count as perfect vacuum? If so, would there be any special properties?"
] |
[
"Does a defect inside a metal, i.e. a missing atoms, count as perfect vacuum? ",
"It shouldn't. ",
"The mean free path for a molecule in air at STP is about 70 nm",
". If you have a single-atom defect in, say, a block of iron, the gap between two adjacent atoms is at most on the order of 2*the lattice parameter. The lattice parameter for α - iron is about 3 Å at room temperature, so the gap is on the order of at most 1 nanometer. ",
"So the gap between two atoms of iron associated with a single-atom defect is ~ 1 / 100 as large as the gap between two particles of air at STP. Do you propose that the space between two particles of air at STP counts as a perfect vacuum?",
"All this goes to show that it's not really meaningful to talk about \"degree of vacuum\"; it's like talking about \"degree of darkness\" -- you can't measure an absence, only a presence."
] |
[
"How does circular polarization work?"
] |
[
false
] |
I understand how linear polarization can give two orthogonal signals completely independent of each other, but I don't see how this could be the case for circular polarization.
|
[
"You can think of circular polarization as the sum of two linear polarizations that are 1/4 of a wave out of phase. That is to say, take two in phase waves that are linearly polarized (one vertically and one horizontally) and then shift the phase of the vertically polarized wave by 1/4 wave. The horizontal wave will have zero amplitude when the vertical wave has maximum amplitude, and a short time later the horizontal polarization has maximum amplitude and the vertical polarization component has zero amplitude. If you look at the sum of the two electric fields, it traces out a circle over a few optical cycles.",
" you can convert circular polarization to linear polarization by using a 1/4 wave plate. This device advances or lags one component (horiz or vert) of the polarization by 1/4 wave causing the light to become linearly polarized. Once the light is linearly polarized you can use linear polarizers to filter out the signal of interest. The reason they use circularly polarized light is probably so the contrast between the two images is good when you tilt your head a bit."
] |
[
"It's a bit more complicated to explain how a ",
"circular polarisation filter",
" works than a linear filter, but basically the key is that it's possible to change the components of polarisation in different directions with a crystal called a ",
"wave plate",
", and the thickness affects how the components are altered.",
"A quarter-wave plate allows you to transfer half of the polarisation vector in linearly polarised light to an orthogonal direction 1/4 out of phase, which gives you circularly polarised light. Combined with a linear polariser, you can circularly polarise unpolarised light by passing it through the linear polariser first, or you can split circularly polarised light by passing it through the quarter-wave plate (which turns left and right circularly polarised light into linearly polarised light which are orthogonal to each other) and then a linear polariser (which cuts out one of the two linear components).",
"I realise this is quite complicated, but there's more detail in the articles I linked, with handy diagrams."
] |
[
"The reason they use circularly polarized light is probably so the contrast between the two images is good when you tilt your head a bit.",
"This is correct, but it isn't a complete solution because your eyes need to be pretty level for the optical illusion to work. ",
"It might also be done so the lenses don't need to be aligned perfectly in the glasses and the glasses don't need to be worn perfectly level."
] |
[
"How similar are other mammals taste buds to ours?"
] |
[
false
] |
Also, if other mammals only eat to survive, why do my dogs drool over steak and things like that when they've already been fed that night?
|
[
"I'm not versed in all the tastes across species, but the T1R family is key for sensing sweet and umami flavors. Combining T1R2 and T1R3 proteins allows transmission of sweet flavors, while T1R1 and T1R3 together transmits umami. The T1R2 receptor is ",
"structured differently in mice",
" and ",
"missing in domestic and large cats",
", suggesting that these species do not have a sense for sweet tastes."
] |
[
"The taste ",
" is the \"tasting\" part of the taste bud. Taste receptors are proteins, and are therefore coded by specific genes. This means that we can compare the genetic sequences of taste receptor genes across many species. For bitter taste receptors, for example, it is possible to identify similarities across distantly related species, e.g., humans and zebra fish, which diverged about 450 million years ago. Nevertheless, bitter taste receptors are genetically diverse, almost certainly because different species have different diets. ",
"The ",
" of bitter taste receptors changes quite a bit across species too. For example, it appears the dolphin does not have intact bitter taste receptor genes, whereas the mouse has 35 different bitter taste receptor genes. Most taste receptor genes are ",
" taste receptors. There is an enormous variety of plant compounds, many of which are toxic and must be avoided, selecting for a similarly diverse repertoire of receptors to detect them.",
"There are also sweet and umami taste receptors. But, sugar is sugar and protein is protein -- no need for a diverse array of receptors to detect those compounds.",
"In general, carnivorous mammals, such as dogs and cats, which don't eat too many plants, have fewer taste receptor genes compared to other mammals. Cats are indifferent to sweet, for instance.",
"As for your dog drooling over your steaks, I guess you cook good steaks (and also, for most animals, including us humans, it was probably adaptive to eat whenever food was available, because often it wasn't)."
] |
[
"Pointless to put it that way. All it means is they sense certain chemicals. It just so happens when our tongue senses those chemicals, it sends specific signals to the brain that we experience as flavors. ",
"You could theoretically make an infinite variety \"flavor receptors\" that send \"flavor signals\" to the brain for any given chemical -- there's nothing sweet about sugar, our tongue interprets the shape of sugar as sweet. Calling any chemical that binds to a cell receptor a \"flavor\" is illogical, even if that receptor happens to be involved in taste when used on the tongue. ",
"Again, things don't have flavors, our tongue reads the shape of things, sends that reading to the brain, the brain interprets the reading, and we call that interpretation \"flavor.\" "
] |
[
"On a bicycle, do fatter tires = more friction?"
] |
[
false
] |
Assuming same tread patterns. Bonus question: How much of an aerodynamic penalty is there with fatter tires?
|
[
"Rolling friction does generally go up with increased surface area in contact with the road. So yeah, if a fatter tire has a larger cross section radius it will result in slightly more rolling friction. But it probably depends on a lot of different things, like tire pressure, your weight, road properties etc.",
"",
"I know there exists hybrid tires with wider and rougher threads but a \"road\" line down the middle, as I have used some in the past. If pumped hard enough they will roll primarily on this line, reducing roll friction greatly. So they have quite good performance on road while not being terrible off-road either.",
"",
"Aerodynamically there wont be much difference. Unless you are specifically doing road racing(in which case you would never go with a fat tire), you wont reach speeds where aerodynamic forces really become an issue."
] |
[
"This is a fairly complex area of dynamics, but I think I can get it distilled down for you.",
"Rolling resistance is related to the length of the contact patch. The area of the contact patch is controlled by tyre pressure. So at the same pressure, a 26x1.75 will have the same contact area as a 26x2.35.",
"Because the wider tyre will have a wider contact patch, it will have one which is not as long in the direction of travel: It will have less rolling resistance. It will have greater air resistance, however. For the lower speeds a MTB is normally used at, the lower rolling resistance is normally preferred."
] |
[
"What you're after isn't friction, but rolling resistance.",
"23 mm tryes were standard in bicycle racing for a long time. Smaller contact patch, less rolling resistance, right!",
"Actually it gets more complicated. If you fix the carcass construction, and pressure, different sizes have the same size contact patch. A fatter tyre can result in less rolling resistance though. It relates to the shape of the contact patch. A skinny 23 has a skinny oval patch, but a 25 or 28 mm has a more circular contact patch that actually has less rolling resistance.",
"This has deminnishing returns though, and wider than 28 mm and you do hit a point where the increase in air resistance due to the increase in cross sectional area robs any further rolling resistance gains.",
"Having said all of that, these are marginal gains for serious cyclists. They're only really going to pay off in long races. For most riders the majority of wind resistance is caused by the rider themselves. Up to 80 % of the forces that you have to overcome as a rider, can be wind resistance caused by yourself.",
"Get a good bike fit and nail your aero position before worrying about the cross sectional area of your tyres.",
"Pros used to all ride on 23 mm at 120 psi. Many ride 25 or 28 mm at something like 90 psi. It's just more comfortable if you're going to be in that saddle for hours on roads that are nothing like a velodrome."
] |
[
"How far are we to companies growing organs in labs for transplant (kidneys, livers, hearts, etc.) and what is standing in the way?"
] |
[
false
] |
for what is standing in the way, I mean technical, and medical terms. Also, what fields would make this possible? Stem Cell researchers? Any citations would be awesome
|
[
"Simple organs, like a trachea, have already been ",
"made and transplanted",
" into people. ",
"A ",
"beating rat heart",
" was made from a rat stem cells seeded into the leftover extracellular matrix from a dead rat's heart -- a similar process to what was done in my first example, except not quite as advanced and cool.",
"I would say that as 3D printing gets better, these sorts of things will become more common. The heart is not nearly as complicated, structurally (and based on the number of different cell types) as, say, a kidney, so I think each organ will be its own battle."
] |
[
"Depends on what type of organ you are talking about and what methodology is used.",
"The presently most advanced method is decellularization: take a donor organ, strip its cells, repopulate with the patient's cells. That doesn't really count as growing a new organ, and you still need the donor. It is still a massive leap ahead, and, interestingly, makes xenotransplantation a plausible intermediary technology for the time between now and the advent of completely lab-grown organs.",
"In addition to the tracheas noted elsewhere in the thread, some children have received decellularized donor heart valves. Pseudo-blood-vessels are also fairly well advanced.",
"Different organs are very different in terms of how far advanced researchers are in making everything work. Simpler is easier; the heart will be solved before lungs and kidneys. Lungs in particular are years behind -- it was only very recently that researchers managed to isolate stem cells sufficiently well to be able to grow small amounts of lung tissue.",
"In terms of printing or culturing or growing in a bioreactor a whole organ from scratch, I can say that the people who run the ",
"New Organ prize",
" are looking at a 20 year timeline for pushing through from where we are now to organs on demand in the same way as heart surgery is on demand today.",
"I think that there is a very good chance that the whole idea of building organs for transplant will be overtaken by advances in the ability to reprogram stem cell populations in the body. After all, surgery is a great thing to avoid if you can, and cells in the body already have much of the necessary programming to rebuild organs buried in there somewhere - they already did it once. The trick is waking them or transforming them, sending them to do the job, and avoiding cancers of enthusiasm along the way. "
] |
[
"I'm commenting on your post since I'm not really answering the question but rather adding more info on your answer.",
"In relation to the 'obstacles' part, one of them might be that there are potentially other more efficient (perhaps easier to commercially manufacture) alternatives: machines.",
"I happened to pass by this article, where a man got his heart replaced by a machine that 'pumps' the blood instead of his heart (more like pushes the blood), hence the man has no pulse.\n",
"http://news.discovery.com/tech/hearts-with-no-beat-pulse-could-save-lives-110614.html"
] |
[
"Can you someone please debunk this silly 'hollow earth theory' for me?"
] |
[
false
] |
It just seems entirely ridiculous to me. This doesn't seem to be how gravity or planet formation works. I would just like some examples of how unlikely it might be. That, or if it can be disproven - would also be nice. Thanks!
|
[
"As someone in geology, the hollow earth theory is a painful theory to discuss. Just the shear volume of complete lies and mis-interpreted facts shoved into those arguments is awful. I'll try to work through some of the points on that web-page, but discussing the theory is an unpleasant experience for me so I may not delve too much into this.",
"1) Newtons Theory of Gravity has been outdated for a long time now. The actual formula for gravitational pull is a stronger more robust approach which explains many observed interstellar phenomena to extreme accuracy. Of course, Newton's Theory of Gravity is good enough by itself when it comes to the structure of planets, so I don't even know what they mean by \"untested\" outside the solar system. Now in that site they discuss the possibility for the force of gravity to change depending on where in the universe you are. This goes against all measurements we have ever made of the universe ",
", for gravitational pull ",
" many other things, which show that the physics in the universe appear to be identical no matter where you are.",
"2) The section on seismology is especially painful. We have a fantastic, extremely robust collection of data which shows directly the structure of the interior of the planet. He mentions that there are cases where the tested seismology is different than predictions, which is of course what would occur since we don't know the interior of the Earth to 100% perfectly everywhere. For example, maybe seismic waves showed that the lithosphere extends down to 101 km in some location rather than the predicted 100 km. If that's the sort of discrepancies the person is referring to, then those discrepancies would seem to support the validity of seismology. So just pointing out that there are discrepancies is completely meaningless and tells us nothing. But the important take home message here is that seismology is an extremely well understood and robust field that returns results that are undeniable representations of the interior of the planet.",
"3) The section on geology is even worse. It's not only filled with lies, but even assuming its premises are correct it reaches an absurd conclusion. We know we have evidence for magmas that originate deep in the planet. We also have magmas that originate in the crust, and they are very different types of magmas and our predictive power for the types of magmas we get in different locations in phenomenal and complete in line with a solid Earth. Furthermore, there are more than the two proposed mechanisms mentioned for magma melting (radioactive elements and shear stress). There are a whole suite of mechanisms that the author seems completely oblivious too, and these mechanisms come into play differently depending on your location on the planet. The author also just says \"Lava cannot possibly be rising from the centre of the Earth as some may be tempted to think\", which is of course true because the center of the Earth is solid and iron/nickle. But there is strong evidence that magmas that form hotspot volcanoes do originate from the core-mantle boundary or close to it. If not, they certainly originate from deep in the mantle.",
"4) As for the author's mentioned 'shadow zone', the author just completely mis-interprets what the shadow zone is. There is no portion of the Earth that seismic waves ",
"can not penetrate",
". He completely mis-interprets the shell theorem, which would not diffuse hydrogen toward a core, but diffuse it evenly throughout then entire hollow interior of a structure.",
"I only briefly touched on each of these points. I didn't point out every problem in the post you linked to. The body of evidence out there to support the current model of the planet is so overwhelming I could spend my life writing many books just on how solid and varied that evidence is. Furthermore, I could also write books just debunking how completely absurd the hollow earth theory is and how it would contradict (even if you are generous) a vast quantity of data of a vast variety.",
"All I can say is that the people writing these books are either deluded or actively lying to you and making it sound scientific. Just because something sounds scientific doesn't make it true, so be extremely wary of sites like this that provide literally zero evidence of any sort to back up their claims.",
"EDIT: just to expand on why talking about this is painful - it's because someone can quickly come up with an \"alternate\" theory for how the world works, lazily throw in some words like atoms and pressure and electromagnetic force, and all of a sudden you are forced to recount the entire body of science on each of those things in order to convince anyone they are wrong - and even they it often doesn't pan out."
] |
[
"There's a load of response you could have, starting with something like Occam's razor: there is no real reason to suppose that the earth could be hollow, so why try and create a massive implausible system to justify the hypothesis.",
"Secondly, it's not supported by evidence:",
"We can work out the relative masses of the Earth and other bodies in the Solar system (masses, not weights), and from this we can safely say that the earth would require a very dense core in order to maintain its weight.",
"The author's suggestion is that the void between the shell and the core is filled with hydrogen. Hydrogen would easily escape from such a gap, causing it to collapse if it ever formed, so the outer crust would need to be airtight, but seismology, even if it is considered entirely crustal, would not allow for a situation like that to be maintained for billions of years",
"He mentions the existence of anomalies in the transmission of p and s waves, which is very true and interesting, but then doesn't add that it is due to p and s waves that we know of the existence of a dense core to our planet, and that if there were a void completely around the core these waves would not transmit, and we would get a very different picture",
"These are just a few objections, there are plenty more which I'm sure others will point out, but rest at ease, the ground beneath your feet is definitely solid"
] |
[
"The varying density of the inside of the earth causes differential diffraction of mechanical waves produced by seismic events. We can use this to map the inside of the earth, and we have done so.",
"http://en.wikipedia.org/wiki/File:Earthquake_wave_paths.svg",
"Also, a hollow planet would collapse in on itself."
] |
[
"Is there a way in which a person can increase their mental ability / IQ?"
] |
[
false
] |
[deleted]
|
[
"100 IQ is calibrated to average human intelligence. Theoretically you could kill or mentally impair people of above average intelligence and readjust the average thereby improving your own IQ."
] |
[
"According to ",
"some research",
", cognitive training with ",
"dual n-back",
" can potentially increase working memory and IQ scores. Here is a ",
"Wired article",
" on the topic. "
] |
[
"This is a big question. First of: There are multiple ways to improve cognitive functions once you lose them. Old people can increase their cognitive functions through a number of means, such as ",
"Physical activity",
". But that's not really what's you're asking.",
"What you're asking is if a normal, healthy person in his 30s could improve. And that is not easy to answer. Mental ability and IQ is a little to vague.",
"You can train yourself to be better at quickly calculate things, or remember faces or numbers or other mental feats. And while that is certainly an increase in mental ability, it's still not really what you're after, or so I believe.",
"As for IQ. IQ is simply a measure of how well you score on an IQ-test. And training for any test will improve your results. But getting better at a test, doesn't really make you smarter, now does it?",
"That said, there are studies that shows that ",
"meditation",
" will make you \"smarter\", at least short term. Stimulants like coffee will also make you more alert, which makes you better able to solve cognitive tasks. More effective stimulants are things like Ritalin and Provigil, which some studies suggest improve memory (short term).",
"Also: ",
"this article discuss the scientific finding around some of the things I mentioned a little more indept"
] |
[
"CRT displays show weird colors in presence of a magnet due to deflection of electrons. Why does the effect last even when the external magnet is removed?"
] |
[
false
] | null |
[
"Colour CRTs have three electron guns which are directed using magnets. There is also a metal plate with holes just in front of the phosphor screen that prevents electrons from hitting the wrong colours. When you place a magnet near a CRT, you are redirecting the electrons, producing weird images. If you use a strong enough magnet, you can magnetize the metal plate, which will continue to deflect the electrons even after removing the magnet.",
"This is why CRTs will usually have a degaussing circuit which is designed to demagnetize the plate by producing a rapidly oscillating magnetic field that decreases in amplitude leaving the metal plate with a small, randomized field."
] |
[
"My dad was a TV/AV engineer up until he retired about 5 years ago. When I was about 12 (waaay back in the 80's) we learned about this affect on CRT's at school. I had a nice big magnet - a CB radio antenna mount, and tried it on our TV at home. Got into a lot of trouble, as the magnet was powerful enough to WARP the shadow mask, causing permanent damage even though my dad tried for hours to fix it with a degaussing wand (a big electro-magnet).",
"Never lived that down. Fortunately, LCD's and other flatscreen technologies don't have that problem, though I believe magnets affect Plasma screens to some extent."
] |
[
"The shadow mask (or aperture grille, depending on design) in color CRTs is often made of steel-- the magnet you're holding is turning the shadow mask itself into a permanent magnet."
] |
[
"What happens to the fishing/game population if there was/is no fishing/hunting?"
] |
[
false
] |
I often read and hear about how hunting is allowed in some areas to control the population and fishing is regulated to make sure we don't over fish. What happens to the population of these animals if fishing/hunting were to stop or never existed. I also have kept in mind that some of the reason why hunting is needed is to keep groups of humans living close to these animals safe. I have no knowledge whatsoever of this field so please do enlighten me with whatever knowledge or correction you have for me.
|
[
"Well if you include the natural predators in this question then our backyards would be quite a bit wilder. But if we were killing the natural predators out of fear and necessity for farms and ranches then we would have an overpopulation of deer and other prey type animals. "
] |
[
"Then that overpopulation would cause the animals to starve to death when the environment can no longer support their increasing numbers."
] |
[
"Without hunting or fishing, populations would be much higher. Fish populations in particular are vastly smaller (both in number and individual body size) than they were before extinsive commercial fishing. There used to be schools of fish so thick boats could hardly sail through them. On land, flocks of birds that darkened the sky for miles and immense herds of animals roamed every continent."
] |
[
"From seeing the supermoon tonight it made me curious, is there ever a night with no moon?"
] |
[
false
] |
To clarify I don't mean a new moon, but it more like on the other side of the planet.
|
[
"Yes, roughly half the month, every month there is no moon in the night sky. And in the same token, for about half of the month the moon is visible during the day, something which apparently routinely surprises people who have presumably lived on this planet their entire lives. ",
"This can all be made pretty clear by just looking at a diagram of why we see the moon as having different phases at all:",
"https://en.wikipedia.org/wiki/File:Moon_Phase_Diagram_for_Simple_English_Wikipedia.GIF",
"From roughly the whole right half the moon is up during the day and not in the night sky."
] |
[
"When the Moon is on the far side of the planet at night also happens to be during a New Moon!",
"The closer the Moon is to the Sun in the sky, the more the Moon is up during the day and the less the Moon is up at night. But the closer the Moon is to the Sun in the sky, the more we're seeing the shadowy side of the Moon.",
"So when the Moon is very close to the Sun, it's basically up all day and down all night. But it's also basically invisible, because we have the shadowed side of the Moon facing us."
] |
[
"If you are far enough north or south, then there will be at least one day a month when the moon never rises, and another when it never sets. It's for the same reasons that the midnight sun happens.",
"The tilt of the moon's orbit compared to Earth's equator varies on an 18.6 year cycle, so how far north is \"far enough\" likewise varies. When the angle between the moon's orbit and the equator is at its maximum, places north of 62°N (or equivalent in the south) can have 24-hour periods when the moon never rises. For example Reykjavik is far enough north to experience this."
] |
[
"What is “personality” and how does it differ from a “personality disorder”?"
] |
[
false
] | null |
[
"The definition of when a personality becomes 'disordered' is a social construct. There is no accurate yardstick, and often the diagnosis is highly subjective with psychiatrists disagreeing about cases.",
"Generally disorders are diagnosed when behaviour is seen as dangerous, outlandish, or eccentric from the point of view of the local culture."
] |
[
"From an animal behavior perspective, personality is any set of behaviors which an organism consistently exhibits."
] |
[
"This is a biiiig question. But I'll try to simplify it for you.\nPersonality is basically how a person interacts with their environment. For better or for worse. It is how somebody prefers their environment to be structured, and how they view their environment. I'll take two big personality characteristics and give a simple explanation about what I mean.\nSo take Extroversion and Introversion. Somebody who is extroverted prefers to be in the company of others. They enjoy communicating and interacting with others, and many times feel strengthened by it and that it \"recharges\" them when they are around others. Being alone can sometimes feel uncomfortable. Somebody who is introverted tends to want to be left to their own thoughts. They prefer working in more solitary environments. They usually are adverse to big groups and feel drained of energy when hanging out with a lot of people for extended periods of time, but they \"recharge\" when they are alone.\nSo you can see how these two facets, with neither being necessarily better than another, changes how the person interacts with their environment (an extroverted person will probably seek others to be around because that is more comfortable to them, and introverted person would probably seek more alone time), as well as how they perceive their environment (an extroverted person will perceive being alone as uncomfortable, while an introverted would enjoy that).\nSo what a personality disorder is then, is basically when your personality characteristics line up in a certain way that causes problems in your social, work, or personal life. For example, you can have borderline personality disorder which is characterized by a person who is constantly fearful of being abandoned, but also highly dependent upon others, which gets to the point that they can be abusive, manipulative, cause self injury/attempt suicide, and a bunch of other things that might be very detrimental to their lives."
] |
[
"Are there any health risks to saving plastic take-out containers to use as tupperware (and microwaving them)?"
] |
[
false
] |
Title says it all.
|
[
"Yes. Those containers are designed to hold hot food once. The most immediate health risk is burning yourself because the plastic breaks or melts and you spill hot food on yourself.",
"But dioxin or bpa in those containers? Not likely. That doesn't mean ther are no carcinogens or that it is a good idea; they aren't microwave safe. Heat breaks down plastic, some of that will get in your food. ",
"Read this",
"."
] |
[
"There is no such thing as \"Cl\". There is Cl",
" and there is Cl₂, but not plain Cl."
] |
[
"There is a difference between plastic that has not been broken down to plastic that has been broken down. Same reason why NaCl in moderate quantities is harmless, but Cl by itself is toxic."
] |
[
"Due to the conservation of energy, if you had a pendulum in a vacuum would it continue on forever reaching the same height each side every time?"
] |
[
false
] | null |
[
"There would still be friction at the pivot point. The friction dissipates energy as heat, even in a vacuum. The pendulum would slow down and eventually stop."
] |
[
"You can do a lot of things to reduce friction, but you'll never get rid of it completely. You could get the pendulum to swing ",
" all the way back to where it started, but not quite all the way. You could get the pendulum to swing for a ",
" time, but not forever.",
"The friction might be negligible (in the sense that it's not noticeably effecting the pendulum's motion) over a day, but over a century the friction would not be negligible. "
] |
[
"Friction could be very small, but as long as it is non-zero, it will stop the pendulum. Second, I haven't seen it mentioned here, but materials that you make the pendulum with aren't rigid. Everything is vibrating and wiggling and that will sap energy from the pendulum."
] |
[
"What makes the timbre of an oboe different from that of a violin?"
] |
[
false
] |
I'm a musician and composer in school and I'm wrangling together a music theory class for the University of Reddit. I fully expect this question to come up - and it's a really good one, I think. If I understand correctly, it has to do with the harmonic series. Certain instruments emphasize certain partials, and what we refer to as 'that oboe sound' is the result of those partials heard together. 'Brightness' is an emphasis on upper partials, and a 'dull' sound lacks partials altogether. At least, that's what I understand. Is that correct? Am I missing anything? And is there a more effective way of communicating this? Thanks!
|
[
"You've got it right. The characteristics of a certain instrument or sound is defined by what harmonics that instrument produces and emphasizes, and when you can identify different instruments, this is how you do it. ",
"A sound without harmonics, such as a clean sine wave, does sound dull.",
"If you want to actually demonstrate it, you could do this: On a piano, hold down the keys for one or more of the notes in the ",
"harmonic series",
" without sounding them – preferably not those who are too far from being tempered, though. ",
"Then, play the base note on either that piano or a nearby instrument. After the base note is muted, you will still hear the overtones resonating in those non-muted strings. If you can make it work, it's fun with notes over the seventh partial, as you can't distinguish them by ear if they don't have anything to resonate with."
] |
[
"The answer lies largely in the acoustics.",
"It is a combination of harmonic series and resonances.",
"A string excited with a bow will generate a particular harmonic series, typically plus a nice chunk of noise, particularly at the start of the note. The excited reeds of the oboe generate a different harmonic series.",
"A \"harmonic series\" is a description of which partials are present in a note; in reality, you'll find plenty of inharmonics too, which pertain to the mechanics of how the note is played; an oboists tongued transient to lip the note will also generate a little thump at the start of the note. The harmonic series (with the relevant phase information) also tells us something about the shape of the excitation signal. Two vibrating reeds cause a certain waveshape, and it's the shape of that which leads to the harmonics we hear.",
"Also, quite crucially, resonances play a massive part. The shapes of the instruments aren't that way by accident, and an oboe-shaped violin would sound a lot more like an oboe! Every part of the instrument resonates, around a certain frequency range. This acts to dampen certain tones (note that in a piano the damper is placed to mute the 7th harmonic of the string), and to enhance others. The delicate craft of violin-making (or making any instrument for that matter) is one of shaping the tone by careful selection of woods and carving of shapes to produce an instrument with pleasing resonances."
] |
[
"A reed instrument produces ",
"sine waves",
", while bowed instruments produce waves that are more ",
"saw tooth",
" -like in character.",
"Furthermore (as you suggested), the conical shape of the oboe's cavity lends to the tone, as it allows for complex (both odd and even) overtones. Cylindrical cavities (flutes, clarinets) suppress even numbered harmonics, yielding a purer sound. This is why oboes / saxophones / etc. can be heard over ensembles."
] |
[
"What happens to detergents and soaps after they go down the drain?"
] |
[
false
] |
I recently bought a bottle of Costco environmentally friendly dish detergent that claims it biodegrades 70 percent in 28 days after cleaning. I think this is a plant based detergent (or soap) and I understand that many detergents are made from petroleum based chemicals. For a few years now, I have only used Dr Bronner's castile soap because the stuff I found in supermarkets and Target, etc, were making me itch be it bar or liquid. Dr Bronner's claims their castile soap is : Water, Saponified Organic Coconut and Organic Olive* Oils (w/Retained Glycerin), Organic Hemp Oil, Organic Jojoba Oil, Essential Oils**, Citric Acid, Vitamin E So what happens to the soaps like Zest or Dove, or anything else I find in most stores? What happens to plant, animal, and petroleum based soaps detergents after I use them and they go down the drain? Does petroleum based detergents break down or do they remain the same and go into the ocean and stay there like the Pacific garbage patch? Do plant and animal based soaps decompose like how my kitchen scraps turn into compost except that it occurs in the sewage plant or ocean? I have sanitary sewers where I live and they go to a sewage plant a couple miles away. The effluent then goes into the Pacific Ocean.
|
[
"Everything that goes down your drain goes to a waste water treatment plant. They have ",
"ways to treat water with detergents",
", but biodegradable makes it a lot easier. What's bad is soaps with antibacterial agents like triclosan. Triclosan degrades into dioxins in sunlight, and there are limits to how successfully these can be removed or detoxified. Still ",
"up to 98% can be removed",
"."
] |
[
"Now antibacterial soap is fine, just not antiMICRO-bacterial soap.",
"Wat? There is no such thing as \"anti-micro-bacterial\" soap (or \"micro-bacteria\" for that matter). Do you mean \"anti-microbial\" soap? That's the same thing as anti-bacterial soap; all bacteria are ",
"microbes",
". Are you really an EnvE grad student? Sounds like you need to brush up on your undergrad biology. "
] |
[
"Some soaps and detergents are petroleum based, does bacteria still chew on those? Or is other stuff added at the waste water facility to remove it?"
] |
[
"How unhealthy is smoking 1-2 packs of cigarettes a month?"
] |
[
false
] |
[deleted]
|
[
"According to ",
"this study",
", \"Light and intermittent smoking carry nearly the same risk for cardiovascular disease as daily smoking\" \nand \n\"the risk of ischemic heart disease in light-smoking men and women aged 35 to 39 years who smoke 1 to 4 cigarettes per day is ",
"\""
] |
[
"Reading further on... ",
"in that study",
" you can say that your risk of cancer is a lot less than 20+ cigarettes per day smokers. Normally, the risk of lung cancer is very low for most people: it's one of the rarer cancers, but very often fatal. Many cancers can be cured now, but ",
"lung cancer still has a poor prognosis",
" at around a 50% death rate 5 years after diagnosis.",
"Quoting from another site:\n\"According to the American Cancer Society, lung cancer continues to be the biggest cancer killer of both men and women in the United States, with over 80% of cases attributable to cigarette smoking. Lung cancer causes 1 out of every 3 cancer deaths in men (31%), and about 1 in 4 cancer deaths among women (27%).\"",
" Some of those cancers are from asbestos, black lung, industrial chemicals, etc. The regular daily risk only accounts for about 5% of lung cancer. That study, quoted from youexpecttoomuch states that mild smoking carries 3x the risk of causing lung cancer. Since the risk is low, 3x that is still pretty low. It's heavy smoking that will get you.",
"\"Lung and Other Cancers\nIn the United States, lung cancer causes 1 of every 3 cancer deaths in men (31%) and {approx}1 in 4 cancer deaths among women (27%).44 There is a dose-response relationship for cigarette smoking and lung cancer, with no evidence of a threshold.27 For daily smokers (>20 cigarettes per day), the risk of dying of lung cancer is >23 times higher in men and {approx}13 times higher in women than in nonsmokers.1 ",
" (relative risk, 2.8; 95% CI, 0.9 to 8.3) as nonsmokers.28",
"The risk of low-level smoking is greater among certain ethnic and racial populations. Blacks and Native Hawaiians who smoke ≤10 and between 11 and 20 cigarettes per day are more susceptible to lung cancer than whites, Japanese Americans, and Latinos who smoke the same amount of tobacco.45 When adjusted for sex and duration of smoking, the relative risk of developing lung cancer among blacks and Native Hawaiians is nearly twice that of whites despite consuming the same number of cigarettes.45 Consistent with these data, the incidence of lung cancer has been found to be substantially higher among blacks, Native Hawaiians, and other Pacific Islanders compared with whites in the United States.46",
"Light smoking also results in an increased risk of gastrointestinal (esophagus, stomach, pancreas) cancers \""
] |
[
"I don't think this particular anecdote should be considered due to the large biological differences between individuals, as well as damage that may not be evident and ex-smokers who live healthily possibly doing better than non-smokers who live unhealthily."
] |
[
"Of we were to send mirrors into space in all directions, would we be able to look back in time once the mirrors have travelled far enough?"
] |
[
false
] | null |
[
"Yes and no. ",
"If you send the mirrors away at 70% of the speed of light, then after 10 years they will be 7 light-years away. Light reflected at that moment will have been travelling for 7 years... and will have to travel another 7 years to get back. In other words 17 years after you sent the mirrors away you get images from 3 years after you sent the mirrors away. ",
"So yes: In 17 years you will be able to see 14 years into the past...",
"But no: You won't be able to see back further than the point when you launched the mirrors. ",
"This is not the case if you somehow can move the mirrors faster than the speed of light. In that case you really would be able to see into the past."
] |
[
"If you can go faster than the speed of light you don't need mirrors to see the past. You can visit it. Which is one of the many reasons why faster than light travel is silly."
] |
[
"Travel to the future is easy. Travel to the past is not."
] |
[
"8 glasses of water per day?"
] |
[
false
] |
[deleted]
|
[
"If you feel that way you should see a doctor rather than assume its just dehydration.",
"Those symptoms can fall under a long list of ailments which can have different causes. Dehydration is just one of many."
] |
[
"If you feel that way you should see a doctor rather than assume its just dehydration.",
"Those symptoms can fall under a long list of ailments which can have different causes. Dehydration is just one of many."
] |
[
"That entirely depends on the person. A lethargic person in a high humidity environment who eats high moisture food might actually not need any water per day. ",
"A marathon runner might consume 1L/hr during training (~4 glasses). That doesn't even include what the person consumes the rest of the day. "
] |
[
"What makes a phobia a phobia?"
] |
[
false
] |
[deleted]
|
[
"That is ostensibly irrational by virtue of the inanimate, abstract nature of a number. In direct opposition to this, I have acrophobia, or, a fear of heights. To me, this is not a real phobia as a significant fall may result in loss of life or serious injury and is therefore perfectly rational.",
"Part of the criteria is a fear in excess of the actual danger poised. For instance, being afraid of heights while on top of a tight rope would be quite reasonable. On the other hand, being unable to go to the 20th floor of the Chrysler Building because of how high it is could be irrational. "
] |
[
"One of the central ideas in diagnosing a mental disorder is the level of impairment it causes. Nearly every diagnostic criteria seen in the DSM-IV or 5 is something also seen in most people, but often to a lesser degree. (I guess I would compare this to regular medical symptoms and how everybody always jokes about how sites like WebMD always point to cancer as the cause of mild, common symptoms like having a sore throat.)",
"Even the sorts of things you might consider to be very severe in and of themselves are actually quite normal. For example, ",
"most people experience hallucinations",
". ",
"A large percentage of people report experience dissociative phenomena.",
" Obviously, everybody is sad -- to an unbearable degree, sometimes -- at some point in their lives. People lose family members, or get divorced. The difference between these normal experiences and something that can be called a \"symptom\" is the degree of severity, or the degree of impairment is has on everyday life. It's normal if you hallucinate while falling asleep -- it's not if you hallucinate all day.",
"I have a good friend who is absolutely terrified of clowns, but not to the degree that he will refuse to leave his house for fear of encountering one. Is his fear irrational? Yes. Does it cause significant impairment or distress? No, because he very rarely runs into clowns, and he never orders his life around the avoidance of them. You can make a similar example out of \"heights\". Being afraid of them might be normal, but it would be debilitating and limiting if you refused to ever go above the first floor of a building because you were so afraid of falling. ",
"It should also be noted that phobia has more than one meaning. There's \"fear\", which most people might use the word for. But it also means something beyond that -- something of a clinical nature. Just like you might feel \"depressed\" after a bad day at work, but not in the way that means you actually meet the criteria for depression. "
] |
[
"Also, phobias significantly interferes with normal functioning. It is a sub-type of anxiety disorder. Specifically, it is known as an \"",
"Axis I",
"\" disorder. That is, it is not a pervasive personality disorder that generally affects all thoughts.",
"The initial diagnosis of anxiety disorder are pretty diverse, but they all involve ",
" (as stuthulhu already mentioned) and ",
". Driving 2000 miles just to avoid flying, or not leaving the house on the 13th of any month would be considered as such.",
"All this being said, there's healthy debate whether the DSM diagnostic system is representative of the pathogenesis of disorders. Are phobias really developed the same way as some anxiety? Can they really be diagnosed the same way? This is why a trained psychiatrist/psychologist is needed to really make the diagnosis, and why these questions are still being asked."
] |
[
"Can we change our ways? For an example, could someone who's lazy become a super motivated person, or are we just genetically wired to be certain ways?"
] |
[
false
] | null |
[
"We can change our actions, yes. Whether or not we can change our inclination towards certain thoughts is less likely. For example, you can't prevent being a homosexual, but you can definitely refrain from homosexual acts. (A whole different topic is the damage to yourself vs damage to others these decisions cause). "
] |
[
"Whether or not we can change our inclination towards certain thoughts is less likely.",
"Actually I have found that if you make a consistent conscious effort changes, even in inclination can change. Personally I have found it usually takes a minimum of 30 days.",
"For example",
"I have radically changed my diet and eating habits, it took time, it is still evolving, but foods I used to crave never enter my mind anymore and some even disgust me. Foods (like sweet potato) I never used to like, I thoroughly enjoy now."
] |
[
"But you still crave food, right?"
] |
[
"How does obesity affect the procedure of surgery? If the patient carries excessive body fat, how much does it hinder the surgeon?"
] |
[
false
] |
This is mainly referring to surgeries done in places with typically more body fat, such as stomach or chest area.
|
[
"Yes we do.",
"A lot",
"Bigger incisions, more complications, poorer visualization, more complications (did I say that 2x?), longer surgery times, takes longer to close wound, harder to position implants, and they're a work out.",
"Obesity can be a code 22 modifier, but it's a pain to justify. (code 22 is a billling code that allows you to charge 20% more for a surgery if it is harder. Of course it has to be justified, and takes longer to process, gets rejected, you have to argue......sigh)"
] |
[
"Great answers!",
"Also, I would like to add that post-operative complication is relatively high in the obese and morbidly obese.",
"First of all, the anesthesiologist has to use more medication to maintain sedation during surgery. Due to the weight-based dosing of these drugs but the variable nature of individual metabolism, the odds of using too little or too much increases drastically. Either is bad, but too much is very bad, and is associated with post-surgical issues like delayed bowel and bladder return of function, aspiration, and so on.",
"Also, bariatric patients are harder to mobilize (get walking and performing ADLs, or activities of daily living) leading to needs for longer hospitalization after surgery. This is associated with nosocomial infection and need for PT/OT to regain strength due to the muscle tissue loss from being bedridden. This is further associated with an overall decrease in function post-surgery, due to the patient not being able to regain full strength and ADL performance.",
"Finally, they are more prone to wound dehiscence and infection, due to surgical wounds taking longer to heal, both due to direct healing delays (poorer circulation, etc) and secondary factors (weight of the fat causing a mechanical separation of the wound bed)."
] |
[
"Great answers!",
"Also, I would like to add that post-operative complication is relatively high in the obese and morbidly obese.",
"First of all, the anesthesiologist has to use more medication to maintain sedation during surgery. Due to the weight-based dosing of these drugs but the variable nature of individual metabolism, the odds of using too little or too much increases drastically. Either is bad, but too much is very bad, and is associated with post-surgical issues like delayed bowel and bladder return of function, aspiration, and so on.",
"Also, bariatric patients are harder to mobilize (get walking and performing ADLs, or activities of daily living) leading to needs for longer hospitalization after surgery. This is associated with nosocomial infection and need for PT/OT to regain strength due to the muscle tissue loss from being bedridden. This is further associated with an overall decrease in function post-surgery, due to the patient not being able to regain full strength and ADL performance.",
"Finally, they are more prone to wound dehiscence and infection, due to surgical wounds taking longer to heal, both due to direct healing delays (poorer circulation, etc) and secondary factors (weight of the fat causing a mechanical separation of the wound bed)."
] |
[
"How is it possible to generate light from mechanical energy?"
] |
[
false
] |
There are these juggling balls which at the moment of impact with the ground or your hand thy emit light. These balls have no batteries. How is this possible?
|
[
"Most likely a piezoelectric effect, but I can't really say I've never seen those balls you speak of. ",
"http://en.wikipedia.org/wiki/Piezoelectricity"
] |
[
"I'll let a physicist give you the indepth explanation but the simple one is: ",
"Band gaps",
".",
"Most balls, when compressed from the force of falling and impacting the ground, generate energy in the form of heat. But your juggling balls most likely have florescent material in them, that absorbs some of the energy that would otherwise go to heat. The absorption increases the energy level of the valence electrons in the fluorescent material, as these electrons \"fall\" back down to their normal energy level they emit light."
] |
[
"Piezoelectric crystals maybe?"
] |
[
"What was the environmental impact of the opening of the Suez Canal? Did the connection of two biomes (Mediterranean and Red Sea) result in the mutual introduction of exotic species and a disruption in the food chains?"
] |
[
false
] | null |
[
"As you predict, there was substantial biological interchange as a result of the Suez canal. The two seas are slightly different: the Red Sea is saltier, has fewer nutrients, and is generally considered a \"tougher\" environment to live in. It's also at a higher altitude, so water naturally flows from the Red to the Med. As a result, life from the Red Sea was better at invading the Med than the inverse, as the life indigenous to the Med couldn't compete with the native life that was adapted to the difficult conditions in the Red Sea",
"[1]",
". ",
"Generally speaking, any biotic interchange will decrease biodiversity. Many species will be adapted to the same evolutionary niches, and will end up competing for them. This happened when North and South America first connected a few million years ago, and it happened when the Panama Canal was opened as well. So, it shouldn't be a surprise that lots of native fish species in the Eastern Med were outcompeted by their Red Sea equivalents. A lot of Red Sea species have also become invasive in the Med, such as soldierfish, lionfish, moon crabs, ",
" (jellyfish), etc",
"[2]",
".",
"As a side note, because the Suez canal led to ships from the East coming to the Med more frequently, it can probably be blamed for the introduction of invasives from other parts of the world as well."
] |
[
"There was talk of digging a sea level canal between the Atlantic and Pacific in Nicaragua, although last I heard it had sort of dissolved due to financial issues. The current canal involves a freshwater section which reduces passage of life between the oceans, a sea level one would have a much bigger impact, but that isn't likely to be the thing that stops it from being constructed...neither Nicaragua or China (the two major players) seemed overly concerned with environmental impacts (that's pretty par for the course as canal builders go). So it's not like the modern world necessarily cares a whole lot more about such things."
] |
[
"Thanks for the detailed answer. That sounds pretty devastating. I suppose nowadays, a project like that wouldn't pass the Environmental Impact Analysis part of development without some major alterations."
] |
[
"Are there bicellular organisms?"
] |
[
false
] |
[deleted]
|
[
"I’m not aware of any organism that is limited to two cells. Some bacteria, the ",
"Cocci",
", come in relatively small packets but without strict size limit. Among the eucaryotes, the ",
"Placozoa",
" are the simplest and smallest muticellular organism.",
"\nThe ‘idea’ behind multicellularity is that of better chances of survival in a group (safety in numbers), and task specialization. Both advantages are not really evident at low numbers. To get that advantage, a few thousand cells minimum need to start working together to get a palpable advantage. Placozoa are borderline as their cells specialize, but there are so few different types."
] |
[
"There was a ",
"recent question",
" that is somewhat related to yours which I took a shot at answering. The smallest organisms which I think can be truly considered multicellular had four cells; to quote the relevant part:",
"You may have seen the relatively famous ",
", which contains a few hundred or thousand cells, but this group actually contains ",
"a continuum from single-celled to larger colonial species",
" (figure from ",
"Arakaki et al. 2013",
"). As you can see, there are at least two species in this group (",
" and ",
") which consist of only ",
" cells, which is quite impressively small. However, this does start to get into the argument of whether such an arrangement should be considered a true organism or simply a colony of single cells (though the paper I cited above does seem to argue the former). ",
"I did actually specifically check for anything that could be considered bicellular before posting that, but couldn't find any truly definitive examples. One which sort of maybe comes close is the pollen grains of most flowering plants, which can consist of just ",
"one reproductive and one non-reproductive cell",
". And pollen grains are technically a distinct organism from the parent plant which produced them, since they are just a very reduced version of the gametophytes that are part of the ",
"alternation of generations",
" in plants. But pollen of course just represents a single short-lived portion of the full life cycle of a (male) flowering plant, and you certainly wouldn't consider the whole plant to be bicellular because of this. ",
"Also, various kinds of bacteria (including ",
" and some types of ",
") are classified as diplococci based on the fact that they are usually found as pairs, but personally I wouldn't really consider this a separate organism from the individual bacteria."
] |
[
"However, this does start to get into the argument of whether such an arrangement should be considered a true organism or simply a colony of single cells (though the paper I cited above does seem to argue the former). ",
"In my opinion, that question is just as problematic as asking for an exact species definition. It's trying to impose an artificial classification on what really is a continuum."
] |
[
"If a bowl of fresh strawberries is sprinkled with sugar, and a few minutes later the berries are covered with juice, how does that happened?"
] |
[
false
] |
[deleted]
|
[
"It's called ",
", and it works through osmosis.",
"A solvent \"wants\" to move from a region of lower solute concentration to a region of higher solute concentration. In this case the solvent is the water in the strawberry, and the solute is the sugar. ",
"When you sprinkle a strawberry with sugar, there's a higher concentration of sugar on the outside of the strawberry. The water migrates out through the cell membranes, dissolving the sugar, and bringing some of the other chemicals inside of the strawberry cells with it.",
"The juice is a mix of water, sugar, and strawberry cell innards.",
"This is also how sugar curing and salt curing work to kill bacteria. They suck the water out of bacteria cells before they get a chance to colonize the cured food."
] |
[
"Diffusion. Water (which makes up the majority of strawberry juice) always moves to even out a diffusion gradient. More sugar on one side than the other of the cells in the strawberry draws out the juice to even the gradient."
] |
[
"Technically yes, since all osmosis is diffusion, but not all diffusion is osmosis."
] |
[
"Is 3 spatial dimensions optimal for life? I know 2D life would be hard, but would life be possible in a 4 spatial dimensional universe?"
] |
[
false
] | null |
[
"Obviously any answer to this would be theoretical because we can't do experiments in higher or lower dimensions, but in greater than three spatial dimensions you have an issue where gravitational fields no longer lead to stable orbits, which makes it hard for planetary life as we know it to form. You can read about it here: ",
"http://space.mit.edu/home/tegmark/dimensions.pdf"
] |
[
"Something to note: In three dimensions, there's a property of any system that the angular momentum can always be resolved into one direction, with an axis and the whole thing rotating closckwise or anti-clockwise. ",
"This ends up meaning that the momenta along that axis cancel out for everything in the densely populated region of a proto-star-system and you end up with everything spinning in a plane. ",
"This is also why most planets will spin in the same direction as they orbit - barring huge, rare events like what may have happened to Venus, or less densely populated areas like Pluto, it all balances out and most large objects have angular momentum going the same way.",
"Now, in 4 dimensions, this just isn't true. There's not always a single axis about which the up/down momentum is 0. This is why it is unlikely to form decent star systems - not everything will be on a plane, severely decreasing clumping and reducing the chance for real planets to form."
] |
[
"It can't be explained visually because you can't see 4 dimensional things."
] |
[
"Why do some genes skip a generation? Is this True?"
] |
[
false
] |
Do genes usually skip generation's? You often here people saying that you pick up trait's, diseases, and tendencies from grandparents such as Alcoholism. Why is this?' Edit. Oh by the way thanks people. Answered my question's.
|
[
"Genes cannot skip generations (they would be lost) but traits can if that trait is caused by a recessive allele. A recessive allele is a version of a gene is not expressed if the other allele in the individual is dominant. A recessive trait might skip a generation if:\ngrandparent's genotype is a/a (both recessive) Expresses Trait\nparent: a/A (recessive/dominant) - not- expressed\nchild is a/a expressed",
"The traits you list however are much more complex and probably influenced by dozens of genes and hence would not follow this pattern but are more likely influence by environmental effects also"
] |
[
"Most addicitions, while they exhibit strong genetic influences, also exhibit strong environmental biases as well.",
"See here.",
"I can't find the study I can remember at the moment, but the general gist was this:",
"Foster Children with alcoholic parents who grow up in a home free of alcohol have less risk than those who grow up in an alcoholic home, but more risk than those foster children whose parents were not alcoholic, when in a non-alcoholic home. Children with non-alcoholic parents in an alcoholic home have a greater risk than foster children with alcoholic parents growing up in a non-alcoholic home.",
"It was an interesting proof that both nature/nurture are responsible for addiction."
] |
[
"Yes that was the point I was trying to make sorry if it was not clear"
] |
[
"How are radio stations able to broadcast silence and have it not sound like static?"
] |
[
false
] |
For example, in MC Hammer's , what is going on between the radio station and my car stereo that makes it so that there is a pause between "Stop" and ". . . Hammertime" rather than the random noise I'd hear if I tuned to an empty station? Thanks.
|
[
"Let's back up a little bit and talk about how the radio station sends ",
" over the air. If it's an AM radio station, the transmitter broadcasts a constant radio-frequency tone at (say) 1.000,000 MHz, but ",
" that tone: it makes the broadcast slightly stronger or slightly weaker depending on where the speaker cone in your car radio should be. Slightly stronger - the cone in your car radio pushes out a little. Slightly weaker - the cone pulls in a little. Do that a lot, really fast, and you hear stuff. ",
"That style of modulation is called ",
" and it's what AM stands for (my dad used to say AM stood for \"awful music\"). It's really easy to decode - you just run the radio signal through a diode, and then smooth it out a little - once you've done that you can just amplify it and send it to the speakers. The problem is that, when you're close to the station, the signal is REALLY STRONG AND THE MUSIC IS NATURALLY VERY LOUD, but when you're far from the station ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" Your car radio gets over that with a special circuit called an \"Automatic Gain Control\" (AGC). The AGC senses just how strong the incoming radio signal is, and adjusts a radio-frequency amplifier to higher or lower gain to keep the signal at constant strength. The AGC circuit is constructed to adjust the gain slowly compared to the modulation -- it might take 1/10 of a second to go from quiet to loud -- so that it doesn't mess with the sound itself.",
"AGC works really, really well when you're tuned to a radio station. But when you tune between stations there isn't any RF signal and it turns the gain all the way up! It amplifies the incoming (non-)signal so much that thermal fluctuations in the receiver circuit components make a loud hissing noise come out of the speakers.",
"So - when the station is broadcasting silence, it is broadcasting a constant radiofrequency wave with no modulation. That maintains the AGC circuit at whatever level it normally holds, and no sound comes out of the speakers. When you tune between stations, there is no signal coming in the RF stage, and the AGC \"turns up the volume\" so high that the thermal excitation of individual electrons in the receiver circuit makes the familiar static.",
"FM has a different modulation scheme but the principle is the same: a radio carrier wave with zero modulation is different from no signal at all."
] |
[
"Sorry to take so long to get back to you... No, there's no AGC for modern FM units. There was in the early days. FM is, of course, ",
" modulation - the station tunes itself to a slightly higher frequency when the speaker cone is supposed to move outward a little bit, and lower to move it in. In the old days, you would demodulate that by tuning a filter circuit so that the base carrier frequency was on one edge of the passband of the filter - that would convert the frequency modulation to amplitude modulation, and you could decode as above. That required an AGC circuit.",
"But nowadays FM demodulators use phase-locked loops: you have a thing called a \"voltage-controlled oscillator\" that is continuously adjusted (by feedback) to oscillate in synch with the incoming RF signal, and the oscillator control voltage is the sound. The frequency and amplitude are independent, so no AGC is required (except maybe to condition the incoming signal for the phase detector in the phase-locked loop [Edit: as ",
"huyvanbin pointed out, below",
"]). ",
"That's why FM static sounds different from AM static: as the signal degrades, you get little bits of static as the phase detector jitters around a little, but it's much less sensitive to interference than an AM radio is. But when you ",
" lose phase-lock you lose it in a big way. When two AM stations interfere, the signals get superimposed and you hear one on top of the other. When two FM stations interfere (with a modern receiver) the signal chops back and forth between them."
] |
[
"The Cosmic Microwave Background is only a small percentage of the total radio background (around 1%).\n99% of it comes from the thermal noise in the atmosphere (which is hotter than the CMB and thus noisier)."
] |
[
"Vehicle Tech of the Near Future: What are the (dis)advantages of hydrogen fuel cells versus Lithium-ion batteries, when used on a large (e.g., nationwide) scale?"
] |
[
false
] |
Five or so days ago various media that Japan intends to focus on using hydrogen as the energy storage medium of choice for its nation's vehicles. On a purely technological and pragmatic level, what are the advantages and disadvantages of doing so? Aspects worth mentioning might include: The efficiency of the hydrogen producing reaction The J/Kg energy density after factoring in its heavy-duty housing The efficiency of oxidization into kinetic energy The cost of building and maintaining a massive state-wide hydrogen supplying infrastructure The scalability (economies of scale) of the processes involved I would find it especially informative if you could juxtapose these considerations against an all-electric solution of the kind Tesla seems to be aiming for, and backed up your comparisons with hard science!
|
[
"Hydrogen tends to leak through containers. Storing it as a gas limits the density. Storing it as a liquid is prohibitively expensive and not all that much of an improvement anyway. Storing it as a metal hydride tends to require exotic metals. However, it's fast and usually easy to refuel, and there's no shortage of hydrogen on this planet.",
"Batteries in general have tended to not be particularly energy-dense, though they are nowadays getting into the same ballpark as H2 (by volume at least) and even gasoline. That's why it's such a big deal these days when laptop or cell phone batteries cut loose all at once. They seem to be improving at a much faster rate than any H2 storage systems. Electric motors are incredibly efficient, so losses are minimized within the car. Generally the battery will know how to charge itself, so all it needs is a ready supply of electricity. No worries about purity and quality of the fuel. Some types of batteries require rare-ish materials, but the trend of late has been to use components that are, in one case ",
", dirt common. They take much longer to refuel, but again there are trends towards faster and faster recharge rates.",
"Hydrogen could conceivably be manufactured on-site at fuel stations, but it would require an electricity source, so batteries would just skip the middleman. On the other hand, H2 could be \"stockpiled\", while electricity generation would always have to meet peak demand. Somewhat analogous to tank vs tankless water heaters here, and the pros and cons for each are very similar.",
"On the whole, batteries look to me like the best bet. They will only ever get better, while the energy capacity of hydrogen is fairly well set in stone."
] |
[
"The proper and thorough answer to your question would be several pages long, I will mention a few things only:",
"Hydrogen production: Currently the most economic source of hydrogen is natural gas, but it makes little sense to convert natural gas to hydrogen rather than using the gas itself. For renewable energy, you can make hydrogen via hydrolysis at about 70% efficiency. Combined with ~60% fuel cell efficiency, the overall system efficiency would be around 40%, this compares with ~80% for battery storage of electricity.",
"Energy density: Compressed hydrogen, including container weight, has 5-10 times higher energy density (depending on how expensive, safe and proven the technology is)than Li-ion batteries... but that is not ",
" energy. To get the electrical energy for say powering a car ('cos burning the hydrogen would be terribly inefficient), you need a fuel cell. These have efficiency of up to 60%, and power-to-weight ratio of up to 1kW/kg. So to get the Tesla-equivalent power and range, the energy storage weight would come down, from ~500 kg to say 150 kg, but the fuel cell would add 310 kg. I do not know how responsive fuel cells are to sudden changes in power, perhaps a better solution would be to have a low power fuel cell plus a low capacity battery.",
"Overall feasibility: AFAICT, battery-electric vehicles are by far the better option (this is my opinion, based on a fair bit of background knowledge and research)."
] |
[
"Also note that electricity would be used to generate the hydrogen, which would still come from the same power plants used to charge an electric car."
] |
[
"What is this? Neither Space or Geology could tell what it is. Maybe you can?"
] |
[
false
] |
[deleted]
|
[
"Looks to me like a lot of broken glass cast in some resin. Perhaps part of an old sculpture or other piece of art, abandoned years ago?"
] |
[
"What area did you find it in?"
] |
[
"The only thing I can think of is bauxite, an aluminum ore: ",
"http://product-image.tradeindia.com/00179034/b/0/bauxite.jpg",
"but the red inclusions (crystals?) in your sample are much more rectangular as opposed to rounded. It would help if you could break it open with a hammer."
] |
[
"In terms of evolution, why are glasses a thing?"
] |
[
false
] | null |
[
"There is currently a myopia epidemic going on. This article discusses incidence rates and current thoughts about causes: ",
"https://www.nature.com/news/the-myopia-boom-1.17120"
] |
[
"This is actually an interesting read and answers my question fairly well. I was under the impression it was related to genetics (article states this was believed in the past). I always scoffed at my mother when she said staring at the TV all day would ruin my eyesight but it turns out while she wasn't exactly right, she more or less was. Crazy to think simply being indoors can cause this."
] |
[
"I should clarify that this is not settled science. There is evidence in favor of the sunlight exposure theory, but this is an active area of research."
] |
[
"How old is the ISS REALLY?"
] |
[
false
] |
GPS satellites have to regularly reset their clocks to stay accurate to earth surface time due to the relativistic time difference between the satellite and the earth surface. How much younger than its Earth surface age is the ISS due to the fact it’s been spinning around since 1998? Do they have to reset their clocks too? Yes I know different parts went up at different times some as late as 2011. 1998 was when the first part went up.
|
[
"Orbital velocity: ~8km/sec",
"\nSeconds since original launch date: ~765,849,600",
"\n",
"Seconds at observer",
": ~765,849,600.27268 ",
"So to answer your question, the original section of the ISS is about a quarter of a second younger than it would be if the parts had stayed on Earth."
] |
[
"GPS clocks are not reset. They run at adjusted frequency. In general in a satellite mission you want to avoid resets and be prepared to do adjustments not only for time dilation. In a satellite mission I worked we had an onboard clock that was the source of mission time in \"milliseconds\" since the satellite was powered on soon before the launch. The clock was never adjusted or reset. Time dilation and other errors accumulated. The satellite periodically transmitted a GPS time stamp along with the mission time to the mission control. Based on that the mission control uploaded a schedule of actions in mission time."
] |
[
"Thank you for answering the question."
] |
[
"Would it be possible to change somebody's blood type by draining their body completely of blood, and then replacing it with a different blood type?"
] |
[
false
] |
This is assuming you have all the necessary equipment to keep someone alive during such a process. We know a person with type A blood can only receive blood from people with types A or O. Their body will reject types B and AB. But if you completely removed the type A blood from their body, could you replace it with type B without it being rejected?
|
[
"No. In short, blood is created in the bone marrow, and if you just replaced someone's blood, eventually it would die out (erythrocytes live only around 120 days on average) and be replaced by the original blood. However the immune system of the recipient will act much faster and destroy the donated blood much faster, most likely killing the recipient.",
"The only way to change the blood type is to destroy the bone marrow ",
" using drugs or radiation, and then replace the bone marrow (bone marrow transplant). Of course this is highly dangerous, the body could still mount an attack on the donated marrow or vice versa (graft-versus-host disease) which is something you ",
" want to have."
] |
[
"It should be noted that this is exactly what happens in stem cell transplants used to treat leukemia and other blood diseases. The bone marrow is completely destroyed as described. The donor stem cells are introduced into the blood stream and find their way to the bone marrow where they begin producing blood cells of the same type as the stem cell donor. Some graft-vs-host disease is expected and welcome as it will likely finish off any surviving cancerous blood cells."
] |
[
"That's \"host-vs-graft\", wherein the recipient's body rejects the transplanted organ. In \"graft-vs-host,\" it's the opposite. The new blood cells reject some parts of the host. Like 7-sidedDice said in another comment, nothing is 100%. When used to treat blood cancer, the patient can experience both host-vs-graft and graft-vs-host. The process is extremely hard on the body. People that go through this hell are vulnerable to infections and diseases. They live in the hospital for weeks or months until their immune system reaches some bare minimum ability.",
"Here is a link to the American Cancer Society's information on stem cell transplants as used in treatment of acute myeloid leukemia: ",
"http://www.cancer.org/cancer/leukemia-acutemyeloidaml/detailedguide/leukemia-acute-myeloid-myelogenous-treating-bone-marrow-stem-cell-transplant"
] |
[
"Does cloud cover affect the power output of solar panels?"
] |
[
false
] |
If cloud block the sun light, would electrical output fall to 0? would it stay the same because the UV radiation still goes through the clouds?
|
[
"Solar panels get most of their energy from the visible part of the spectrum, not UV, so the output drops a lot. Not to zero though, because there's still some diffuse light getting through the clouds (it's not pitch black out).",
"Here's one set of graphs of how much power some panels produced over days with different weather"
] |
[
"thanks those graphs are helpfull"
] |
[
"For maximal efficiency solar panels should try and use the whole spectrum of sunlight. Most of the energy in sunlight is in the visible range, it would not be that useful to design panels that would work best on wavelengths other than what the sun provides."
] |
[
"If the theory of parallel universes is real, in the infinite possibilities of universes would exist one where the theory of parallel universes is not real?"
] |
[
false
] | null |
[
"To see this easily, consider the set of odd numbers. Clearly, there are infinitely many odd numbers. However, this is not all numbers. The same can be seen with the set of all numbers except for 7, or the set of negative numbers, or the set of prime numbers.",
"Even if there are infinitely many universes, that does not mean that all possible universes exist. (And it certainly doesn't mean that impossible universe would exist i.e. those that fundamentally break logic.)"
] |
[
"No.",
"I think you might have a wrong idea how \"parallel universe\" is used in this context.",
"In Quantum Mechanics, particles may be described by a mathematical tool called the \"Wave Function\".",
"In QM, the sum of two solutions to a given problem is also a solution. This is sum is called \"a superposition of two solutions\".",
"\n Thus there is an infinite number of solutions to a problem.",
"The many worlds interpretation states, that the reality we are in is merely one of all those possible superpositions of wave functions. Thus there is an infinite amount of other Universes, which simply represent a different superposition of two states.",
"The essential thing here is, though, that all those Universes follow the same laws. ",
"Thus it is not true to say that",
"there is infinite numbers of parallel universes where any kind of possibility is real",
"but rather, that any kind of possibility within the laws of nature are possible.",
"Since a universe in which no parallel universes exist violates this principle (assuming the many worlds interpretation is correct), it cannot exist.\nIf the many worlds interpretation is not correct, on the other hand, parallel universes (in this sense) do not exist in the first place and the parallel universe in which all other parallel universes are not real cannot exist either."
] |
[
"What you're describing is the issue of defining a ",
"Level 4 multiverse",
", as outlined by Tegmark, in a manner consistent with ",
"Godel's incompleteness theorems.",
" It's still entirely speculative, so there's not yet a way treat it scientifically."
] |
[
"From an engineering standpoint, how plausible is this \"Phonebloks\" concept from a video that keeps floating around my Facebook?"
] |
[
false
] |
I keep seeing YouTube video in my Facebook feed. It is a three minute video suggesting that we should start using interchangeable parts on our cell phones. It seems all well and good in theory, but is it really plausible for phones to be this flexible? Edit: Also, is this a computing or engineering question?
|
[
"It was discussed",
" pretty thoroughly a couple days ago on ",
"/r/askengineers",
". ",
"The overwhelming consensus is \"not at all\""
] |
[
"It's a very plausible way of getting gullible people to give you free money through kickstarter, however."
] |
[
"It's not easily possible at all. It's probably possible (with some design concessions) but there are ",
" engineering hurdles to be overcome. Off of the top of my head, some of the problems are:"
] |
[
"Since the earth orbits in an ellipse, and sometimes the distance between it and the sun can differ by thousands of miles, why does a slight tilt affect climate and seasons so much?"
] |
[
false
] |
[deleted]
|
[
"Axial tilt affects the season because it affects the duration of a day and the \"altitude\" of the sun in the sky. It's not simply because some parts of the earth are closer to the sun.",
"Longer day means more exposure to the sun. When the sun is \"higher\" in the sky, its heat and radiation have less atmosphere to travel through, thus more heat and radiation reaches the surface of the earth."
] |
[
"I think it's also due to the same amount of sunlight being spread over more surface of the earth due to the tilt. This site explains it better than me:",
"http://www.loc.gov/rr/scitech/mysteries/seasons.html"
] |
[
"Because the length of time an area is exposed to sunlight on a given day can be drastically different depending on time of the year and latitude.",
" There is far more seasonal variation near the poles than at the equator. "
] |
[
"Why are there so many acidic fruits, but few if any alkaline ones?"
] |
[
false
] | null |
[
"Fruits are \"designed\" by natural selection to lure animals to help spread their seeds in exchange for a nutritious snack. Therefore fruits must be apetising to the target animals. Most animals use acids as a part of their digestion and therefore alkaline substances, which react with acids can, at least make digestion less efficient, and at worst create toxic or dangerous by products when consumed. This is why acidic foods taste sour, which is a pleasant taste as long as it isn't too strong. But alkaline foods taste bitter, which leads to them initially being unpleasant (you can acquire a taste for bitter foods like coffee, if they end up being safe and bring other pleasant sensations like a caffeine buzz). Because of the predisposition of animals to avoid bitter foods on first tasting them, it is not to a plant's advantage to produce an alkaline fruit. It will scare off potential seed vectors."
] |
[
"Ascorbate (anion of ascorbic acid/\"vitamin C\") is used in a lot of metabolic reactions in plants.",
"Citrate (citric acid) helps oxidize macromolecules like fats, proteins and carbs.",
"Acetic acid comes from the bacterial breakdown of sugars.",
"Tartrates (tartaric acid) comes from the breakdown of ascorbic acid I believe, I don't know what it's purpose is though."
] |
[
"Isn't coffee very acidic though?"
] |
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