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[
"Why can't diabetes type 2 be interpreted as a mechanism of action, instead of a malfunction?"
] |
[
false
] |
Good morning, and please forgive my poor understanding of metabolism. Why can't diabetes type 2 be interpreted as a defense condition, instead of a malfunction? Some chemical threshold has been reached and the immune system decides glucose is a threat and not a primary food, maybe the immune system is just wise. So it wants to prevent sugars from entering the cells. But if new environmental conditions ensue, and the person is starving, the insulin resistance drops, allowing again sugars to feed the cells. This doesn't look like a malfunction, maybe a questionable decision of the immune system, a defense condition. So the solution can't be administering more insulin since the body has enabled measures exactly to prevent insulin from delivering sugar. The solution would be just to stop eating sugars. What am I missing? Thanks in advance.
|
[
"There are multiple theories about type II diabetes. One says that fat is gumming up the works and preventing insulin from having the proper effect on glucose absorption. Another says that is about energy storage; the problem is that glycogen stores are full and that there is no good and quick energy sink for the excess glucose.",
"Intend more towards the latter; if your glycogen stores are full, the only place to put the excess energy is fat. Some people seem to do that well and while they may gain weight, they don't get type II diabetes. Others do it poorly, and may get type II diabetes even while looking thin.",
"I agree that the best solution is to reduce carb intake."
] |
[
"What you're proposing would require a mechanism of gene regulation by second messengers responding to receptors or growth factors stimulated by the presence of carbohydrates, as far as I can imagine. This is much more complex than the concept of diabetes as a product of desensitising insulin receptors, or as an autoimmune disease.",
"Further to that, I have never heard of nor can I find any evidence that such interaction exists. Carbs stimulate a blood sugar spike and insulin spike, but I can't find anything anywhere mentioning other direct damage caused by carbs. Particularly with refined carbs, they're quick to digest and cause turbulence of insulin levels, seemingly. More complex carbs are slower to digest and coexist with fibre and proteins so they have a gentler effect on the system.",
"Yes, the problems are only caused by eating carbs. But you could again say that about a ton of diseases. Anaphylaxis only happens if a peanut allergy sufferer eats nuts. But we know that nuts don't cause damage implicitly, in fact they're quite nutrient rich for non-allergic people. But going by your theory, we should assume that peanuts are intrinsically dangerous and the body is making a wise protective decision rather than just crossing its wires a little bit.",
"I think you need to realise that our bodies ",
" mess up. The immune system included. Unless you can point me to significant evidence that carbs directly cause harm to our bodies, or something giving major evidence to support your idea, this is simply over complicated conjecture. I don't claim to fully understand diabetes type 2, and nobody really completely does, but there are simpler and better hypotheses than this."
] |
[
"We consider it a malfunction because it's harmful. A questionable decision of the immune system that causes harm is considered a malfunction or disorder of the immune system in cases of allergies and autoimmune diseases, why would we not consider it as such for diabetes? Resistance or insensitivity to any other hormone or growth factor is a malfunction of the body, when they are present at correct levels, why would it not be considered as such here?",
"Alternatively, what actual benefit does it provide?",
"You could apply your reasoning to any other condition which alters dietary requirements, as far as I can see."
] |
[
"Are there environmental triggers that can \"turn on genes\" or is evolution purely survival of the fittest and random beneficial mutations?"
] |
[
false
] | null |
[
"Gene expression and evolution are different but related things. There are plenty of triggers, environmental and otherwise, that can turn on genes. Some of these changes can even affect future generations. For example, children of people who have experienced famine and low caloric intakes during childhood generally pass on a trait to their offspring that increases fat production. This does not require mutations. The study of this is called epigenetics. ",
"Evolution is a combination of a lot of factors, including mutations, random selection, epigenetics, and survival of the fittest. Note, not all evolution is a result of \"beneficial\" mutations. Success is often situational."
] |
[
"There are various epigenetic mechanisms that can activate or deactivate genes based on environmental triggers, and these gene states can be inherited. But these genes have to evolve in the first place, and the epigenetic mechanisms that control them are themselves controlled by other genes."
] |
[
"Yes, many things can change how much of a gene is being produced. For example if you get an infection, genes that produce antimicrobial proteins could be switched on. ",
"This is not in contradiction with evolution via survival of the fittest. For an example an animal that has a superior antimicrobial protein OR an animal whose antimicrobial proteins are correctly triggered to be switched on by infections that protein can kill will survive. Those with non-functional antimicrobial proteins OR antimicrobial proteins that fail to be switched on during infection OR those that have antimicrobial peptides that are switched on all the time, will not survive to pass on their genes.",
"How/when genes are switched on and off is controlled and encoded in our genome also, mostly in non-coding or untranslated regions. So differences in how genes can be switched on and off are still encoded in our genome, and still inherited."
] |
[
"Does cork absorb any liquid?"
] |
[
false
] |
I know corks don't absorb water but I purchased a bottle of Crystal Head vodka with the intention of using it as a decanter for my scotch later. My question is if I put my scotch in there will the cork have residual flavor or even residual vodka that could potentially change the taste of my scotch? ( by the way this is a deal breaker because I'm a pretty serious scotch drinker and I don't want my high end stuff to change!)
|
[
"Corks can have surface cracks and open joints especially when left to expand or dry out and can allow leakage through the small gaps in its structure which leaves behind residue from drinks such as wine, which is why cork is generally put in a bottle under pressure.",
"You possibly will get some residual flavour although one would expect the scotch to over power any vodka taste. get a fresh cork."
] |
[
"Bartender here. Never store corked spirits on their side--prolonged direct contact with the cork will impart a musty, \"corky\" taste to your liquor. (Much) Wine is stored cork-down in riddling racks prior to sale, and aficionados don't seem to mind the contact--but wine is much higher in sugar content and viscosity and much lower in alcohol. This probably changes things. Note that the cork comes out of a wine bottle stained with wine, indicating a degree of permeability.",
"tl;dr corks get soaked with liquids a little bit."
] |
[
"Thankfully, more and more bottles are going to screw tops or artificial corks, but some things are sticking to tradition."
] |
[
"Why do some people snap better/louder with their non-dominant hand?"
] |
[
false
] |
Me and a few of my friends all noticed that we snap louder with our non-dominant hand. Why does that happen? Is it normal?
|
[
"The snapping sound is caused by your middle finger hitting your ring finger. If you haven't practiced this with your hand your middle finger will hit your palm and make a much quiter noise. However I don't know why you would only be able to do this with one hand and not the other."
] |
[
"Is the reason for me not being able to snap with my non-dominant hand the difference in muscle strength?"
] |
[
"Well you can snap without using a lot of muscle strength the trick is positioning your ring finger so your middle finger hits it on the way down. So it's definately not your muscle strength. "
] |
[
"Strange behavior in squirrels [X-post from r/biology]"
] |
[
false
] |
My office and I recently noticed some odd behavior from the squirrels outside our window. They started picking the leaves off the trees and dropping to the ground. We noticed it on a Thursday afternoon, and this morning on Monday, they are still at it. Leaves are getting all over the landscaping and the . Can someone please explain what they are doing?
|
[
"Depending on where you are and what species are endemic, I assume this is nesting behavior. Squirrels generally give birth one-two times a year - usually once in spring and maybe once again in late fall. They might be gathering leaves for a nest.",
"Edit: ",
"Actually, no, I think it really is leaf nest building.",
" Keep on the lookout for the nests in a few weeks."
] |
[
"Possibly these squirrels are young and don't have the hang of it yet, explaining the leaves on the ground instead of in the tree. Practice makes perfect, even in many animal behaviors."
] |
[
"Correct me if I am wrong, but it looks like the squirrels are eating the Juniper berries; they do the same thing at my apartment complex in Missouri. They munch off a little branch and then scavange for the berries and ditch the leaves. ",
"Here",
" are a couple ",
"pictures",
" I took a while back.",
"On a fun note, since Juniper contains caffeine, I've often wondered if the berries get them all hyper, like \"Over the Hedge\" Hammie style."
] |
[
"Why binary logic in computers?"
] |
[
false
] |
I am currently perusing a degree in computer engineering and I have yet to hear a solid explanation of why binary logic is used inside computers. After making several integrated circuits, I can see why it would be considered easier to work with binary, and how it is more cost efficient since the reduction that can be done with Boolean algebra, but what exactly is preventing us from having more than 2 stable forms of logic? I am not looking for the answer, "because it can either be on or off, 0v or 5v" since it is not true as far as my knowledge. In communication, a signal element can be assigned by voltage, such as 0v is 00, 2v is 01, 4v is 10 and 5v is 11. So in communication, we can have more than 2 states by using something as simple as a potentiometer.
|
[
"You can indeed work in bases that are not binary - ethernet seems to have 5 voltage levels and various buses easily work on logic that is ternary/tristate (pulled-up, pulled-down and floating) or quaternary if you want to make an obscure joke (pulled-up, pulled-down, floating, on fire). The fundamental issue is so:",
"Consider any system for encoding numbers that is based on summing over a something that looks like a geometric series but with various coefficients:\na0 b",
" + a1 b",
" + a2 b",
" ...",
"Now, b = 1 is a bit of a special case. It is a unary representation system. It has some severe shortcomings in that the size of the representation of a number grows linearly with the actual size of a number. Writing out 1 million in unary is a thousand times longer than writing out 1000. As you can imagine, it quickly become unfeasible to perform any practical computation using this number system although it is still used extensively in the field of logic and theoretical computer science. For example, see the ",
"http://en.wikipedia.org/wiki/Church_encoding",
" of numbers of a rather deep understanding of what \"counting\" or \"numbers\" means within the context of computing and why using unary representations is really the only way to go in that context.",
"Now for all the other numbers where b > 1. b = 2 is binary. b = 10 is decimal etc. etc. If you work the math a bit, you can show that for all b > 1, your encoding grows logarithmically with respect to the size of the actual number you are encoding. Now, you can see that the size of the encoding of 1000000 is only as much longer with respect to the size of the encoding of 1000 as the size of 1000 is with respect to the size of 1. For increasing a number by a factor of b, you increase it's encoded length by one unit. You can also see that for any 2 bases b1 and b2, their respective encoded lengths are only off by a factor of b1/b2 i.e. all bases b > 1 are equivalent in terms of representation except for a constant.",
"You may have realized by now that all I was doing was giving you a round about explanation for why log_b x = (log_a x) * (log_b a). It may have given you a more intuitive understanding for this identity. As since computer science tends to deal with the more theoretic and basic aspects of computing in general, we tend to use the simplest structures that get the job done. If base 2 is equivalent to base 10, then why waste time defining complex operations that have to deal with 10 different symbols. We can define it for 2 and then generalize it for 10. It's the same reason why you're taught binary trees first and not ternary trees (they exist) or n-ary trees (they're called tries). Any operation you learn on binary trees (push-down, percolate-up, zig, zag, rebalance etc.) can be generalized to some sensible operation of an n-ary tree. It just makes it superfluous to start with a more complicated structure when a simple one works just as well. Computer science is all about teaching you how to use a certain set of tools and getting you comfortable with combining and repeatedly applying those tools to various problems your encounter. In the interest of making those tools easy to use, we always tend to use the simplest possible representation of a given tool that still conveys all the core ideas without hurting understanding.",
"Edit: Oh and a PS: If you take more upper level theoretical CS courses (as opposed to CE - they are different; I hold degrees in both of them), you may have the opportunity to take a course on the foundations of logic. This very question will be handled quite thoroughly in such a course. You may encounter various different logics and encodings with various different rules that you may consider as \"mere intellectual wankery\" but that produce surprisingly different results within their various frameworks. You'll encounter ",
"http://en.wikipedia.org/wiki/Intuitionistic_logic",
", ",
"http://en.wikipedia.org/wiki/Classical_logic",
", ",
"http://en.wikipedia.org/wiki/Substructural_logic",
" (such as linear logic), various encodings of computation itself in terms of lambda calculus, simply typed lambda calculus, ",
"http://en.wikipedia.org/wiki/System_F",
", Turing machines, regular expressions, ",
"http://en.wikipedia.org/wiki/Pushdown_automaton",
" etc. You'll also encounter the wonderful theorems from Church and Godel that put various rather inconvenient inequalities over the capabilities of these various systems. It was at the end of such a course that I truly appreciated how amazingly complex the simple act of being able to add two numbers was and why we use the various common encoding schemes that we do."
] |
[
"There are a lot of reasons but a big one is fault tolerance (which leads to a lot of the other advantages, such as simplicity of design, low cost, etc.)",
"The core component of digital logic is a transistor, which is basically an amplifier. Why would you use an amplifier as a switch? Well, for one it makes a very compact switch, which is handy. But also it erases input fluctuations. Let's say you have a simple ordinary switch (input on -> output on, off -> off). What happens when the input is at, say, 10% of the \"on\" level? In a transistor based gate the result will be that the output is driven to one or another of the extremes, either the fully off or fully on voltages (in this case, fully off). This is amplification. What this means is that if there is ever any noise in the signals along the way it gets squashed each time it hits a transistor and doesn't carry through.",
"Now, compare this to even a 3-level system. In order to achieve the same level of noise dampening you would need to not only drive low values low and high values high you'd also have to drive middle values to the same middle value. Achieving that with a simple chunk of electronics that can be duplicated literally a billion times over on a tiny spec of silicon is not so easy."
] |
[
"It's entirely possible to make computers which use ternary logic (see ",
"ternary computers",
"). "
] |
[
"Does stainless steel rust?"
] |
[
false
] |
[deleted]
|
[
"No it doesn't rust or corrode because although it is a ferrite it does not contain enough iron to be able to rust."
] |
[
"nope"
] |
[
"it will eventually corrode, but it takes a lot longer."
] |
[
"Are parasites microflora, microfauna, flora, or fauna? Does it vary for each species?"
] |
[
false
] |
I think I covered it? I will elaborate if necessary.
|
[
"\"Parasite\" is a role that one organism plays in relation to another. Organisms of all the kingdoms can play a parasitic role toward an organism of any kingdom as well. For example, ",
"a plant may be a parasite to other plants",
"; an animal may be parasitic toward a plant (sap-sucking insects for example) or toward animals (blood-sucking insects). It can pretty much go in any direction; but, normally the parasite is much smaller than the host -- otherwise, it's just predation. In parasitism, the host organism continues to live.",
": TIL: ",
" isn't parasitic toward the ",
", but toward the fungi that are mutualistic to the plant."
] |
[
"Well, first of all, \"flora\" and \"fauna\" are informal terms, roughly meaning \"plants\" and \"animals\". We talk about \"intestinal flora\", which are bacteria, but if we want to be precise, we'll call them by the ",
"kingdom",
" they're actually a part of, not \"flora\" or \"microflora\". ",
"I hadn't heard of ",
" until you mentioned it, but reading the wikipedia page, it sounds like this little guy feeds off sediment and dissolved / suspended nutrients ... so he's not a parasite nor a predator ... a ",
"detritavore",
" perhaps, or an autotroph.",
"As for our \"intestinal flora\", they're not parasites because both they and us benefit from the interaction. This is a case of mutualism, or symbiosis. ",
"Our gut bacteria",
" help us break down the food we eat, and even excrete waste (for them) that is nutritious for us."
] |
[
"So in a sense our intestinal flora are tiny parasites? ",
"What about larger bacteria like say Thiomargarita namibiensis is that still considered flora?"
] |
[
"When it is quoted that we share '96% of our DNA' with chimpanzees or '99%' of our DNA with other humans, what exactly do they mean?"
] |
[
false
] |
I have a pretty good background in genetics, so feel free to be relatively complex. My question, more specifically, is are they talking about gene loci, individual nucleic acids or alleles. For example: If we have the same Gene, but my Allele is ATAT T and your allele is ATAT T do we share 5/6 (83%) same genetic material, 0% (because our alleles are different), or 100% because we have the same gene. Thanks!
|
[
"The percentage refers to the amount of nucleotide sequence divergence since a shared common ancestor. For the human and chimp genomes, the divergence is in Single Nucleotide Polymorphisms (one base substituted for another base, as in your example) is 1.23 % ",
"Source",
"When two ore more genomes are aligned, the algorithms are making assumptions about homology between the two sequences: ",
"http://en.wikipedia.org/wiki/Homology_(biology)#Sequence_homology",
"Typically, when nucleotide homology cannot be unambigously determined, it is removed from the analysis. Confusion can arise from mutations that are not substitutions, but are insertions or deletions of genetic material. This brings the total amount of divergence between humans and chimps to about 4% (30 million nucleotide differences and 90 million bases worth of insertions/deletions) ",
"Source",
".",
"Similarity can also be measured a different way-- in genome organization. We have 23 pairs of chromosomes and chimps have 24 pairs. By matching up long stretches of chromosome, we can ",
"see how the genomes have been shuffled around",
" in the last 3-4 million years. "
] |
[
"That image is a little different since it's a protein alignment, so it's looking at substitutions in the 20 amino acids, rather than the 4 bases of DNA. You were right in your original post that you simply take the number of columns where there is a difference and divide by the total length. However, this only accounts for substitutions. ",
"Here's a better figure to illustrate insertions and deletions: ",
"http://www.nature.com/ng/journal/v41/n3/images/ng.304-F1.jpg",
"There, we can see that relative to the Wild Type (WT), the mutant (MUT) has had five bases removed, and three bases added. Those are represented by dashes. In the lower part of the figure you can see a protein alignment for many species, with several insertion-deletion mutations.",
"Both types of mutations should definitely be included when comparing the genomes of two organisms. Insertions and deletions can account for changing the amount of gene expression-- even silencing the genes. ",
"The initial 1% estimate between humans and chimps was made from the substitution count back when the chimp genome was first published. It was indeed an underestimate, as three times as much divergence comes from insertions and deletions.",
"Let me know if I can clear anything else up! "
] |
[
"Ok. I think I overestimated my genetics background. However, I do have a few followup questions.",
"It seems that insertions and deletions would be where the most differences would happen. By removing those from the analysis, doesn't that severely overestimate the percentage overlap? ",
"Secondly, could you break it down with respect to this image:",
"http://en.wikipedia.org/wiki/File:Zinc-finger-seq-alignment2.png",
".",
"How would one calculate the percentage shared there? ",
"EDIT: Also, thank you for the reply!"
] |
[
"How come when I take a shower/bathe in plus-100 degree water it is enjoyable, but not plus-100 weather?"
] |
[
false
] | null |
[
"Top comment is actually atrocious and does not explain anything at all.",
"Showers heat you up more than they cool you down, and the reason they feel good is because your personal body temperature is low enough that you enjoy the sensation. I assure you that if you spend enough time in a hot shower, you will stop enjoying it, or the shower simply isn't hot enough.",
"The same is true of a hot day, if you are cold, because you've been say, locked in a freezer, and you go outside into 105 degree heat, you'll be loving it until your body doesn't want to heat up anymore.",
"Now it becomes complicated because your body's sense of hot and cold is subjective, and is based on personal experience of hot and cold extremes and average experienced temperatures, so what seems hot or cold will shift as you change climates, of if you go through a spell of locking yourself in freezers or spend lots of time in a sauna.",
"Ultimately though, your body is looking out for itself, and if you absorb heat in a way where there is a net gain, it will feel good if your body is a bit low on heat, and will feel bad when your body becomes heat saturated. This can happen outside, in a shower or in a sauna. When you are outside in 100 degree heat, you are often already heat saturated, and your body is looking for ways to drop heat, but sweating is not very effective at that temperature, so your body transmits displeasure in an attempt to encourage you to find a different condition which is less hot."
] |
[
"There are different ways heat can be transferred - conduction, convection, thermal radiation, and phase changing. Conduction heat transfer comes from coming into physical contact with a substance: here, that substance is water. Convection occurs when air blowing across the body results in heat transfer. One example of thermal radiation is the heat we feel from the sun. And phase change we experience in this situation is the evaporation of water, which takes heat away from the body.",
"Water conducts heat really well, which is why 70 degree water seems a lot colder than 70 degree weather. Now you're probably thinking that this would make hot showers seem even more unbearable than hot days. Here's why it isn't.",
"When you're in the shower, not only are you feeling the heat transferred to your body from the warm water, but that warm water is also evaporating, and taking heat away from your body, and simultaneously cooling you. So you are getting heat transferred to your body through conduction by the water, and transferred away from your body when it evaporates. So you are being simultaneously cooled and warmed while in the shower.",
"\nOn a hot summer day, these things are going on, but at a much slower rate. Heat is being transferred to our body at a pretty high rate via radiation from the sun (and other warm objects surrounding us) while our body is also generating heat. The only way to cool down is through evaporative heat exchange, and convection. We sweat which draws heat away from the body through evaporation. Remember how I said water conducts heat better than gasses? Well when you are sweating, the liquid on your skin will cool you down faster if you add convection into the mix by standing in front of a fan, or catching a breeze. That's why those misting fans at theme parks feel so damn good. But usually on a hot summer day you will not catch many breezes, and you end up getting more heat transferred to your body by the sun (on top of the heat your body is already generating) than you are losing via evaporative heat loss or convection. Where as in the shower, you are losing and gaining heat via conduction and evaporative heat loss at a fast rate. If you were to add a source of heat radiation to the mix, then your shower would get uncomfortable. Ever take a hot shower in a hot house? It doesn't feel nearly as good. ",
" Showers simultaneously cool and heat you at a fast rate, due to water's ability to conduct heat better than gases. On a hot day, you are gaining more heat from the sun than you are losing to the environment - leading you to feel uncomfortable. ",
"I hope this makes sense. I got this all from my animal physiology textbook. "
] |
[
"There are different ways heat can be transferred - conduction, convection, thermal radiation, and phase changing. Conduction heat transfer comes from coming into physical contact with a substance: here, that substance is water. Convection occurs when air blowing across the body results in heat transfer. One example of thermal radiation is the heat we feel from the sun. And phase change we experience in this situation is the evaporation of water, which takes heat away from the body.",
"Water conducts heat really well, which is why 70 degree water seems a lot colder than 70 degree weather. Now you're probably thinking that this would make hot showers seem even more unbearable than hot days. Here's why it isn't.",
"When you're in the shower, not only are you feeling the heat transferred to your body from the warm water, but that warm water is also evaporating, and taking heat away from your body, and simultaneously cooling you. So you are getting heat transferred to your body through conduction by the water, and transferred away from your body when it evaporates. So you are being simultaneously cooled and warmed while in the shower.",
"\nOn a hot summer day, these things are going on, but at a much slower rate. Heat is being transferred to our body at a pretty high rate via radiation from the sun (and other warm objects surrounding us) while our body is also generating heat. The only way to cool down is through evaporative heat exchange, and convection. We sweat which draws heat away from the body through evaporation. Remember how I said water conducts heat better than gasses? Well when you are sweating, the liquid on your skin will cool you down faster if you add convection into the mix by standing in front of a fan, or catching a breeze. That's why those misting fans at theme parks feel so damn good. But usually on a hot summer day you will not catch many breezes, and you end up getting more heat transferred to your body by the sun (on top of the heat your body is already generating) than you are losing via evaporative heat loss or convection. Where as in the shower, you are losing and gaining heat via conduction and evaporative heat loss at a fast rate. If you were to add a source of heat radiation to the mix, then your shower would get uncomfortable. Ever take a hot shower in a hot house? It doesn't feel nearly as good. ",
" Showers simultaneously cool and heat you at a fast rate, due to water's ability to conduct heat better than gases. On a hot day, you are gaining more heat from the sun than you are losing to the environment - leading you to feel uncomfortable. ",
"I hope this makes sense. I got this all from my animal physiology textbook. "
] |
[
"Is this BBC video (concerning CO2 and the Greenhouse effect) slightly misguided?"
] |
[
false
] |
Firstly, I accept the theory of AGW and understand the basic mechanisms behind the Greenhouse effect. Here's the video that prompted my question: (Summary for those unable to view, the demonstrator has two lamps, two thermometers and two jars. One jar contains "Earth's Air" the other contains "Air + more CO2". She shines the light on each of them and the jar with CO2 is hotter after a certain period of time.) Now, obviously the greenhouse effect is playing a role. , CO2 has a lower specific heat capacity than air. As there is no mention of how much CO2 is in Jar 2 (and I'd be willing to bet it is a few orders of magnitude higher than 350 ppm) is there any way to attribute the warmer temperature solely to the Greenhouse effect and not just to CO2's lower specific heat capacity? Additionally, would a better experiment be heating the two jars to the same temperature and seeing which one cooled quicker? (Would the CO2 (despite its lower heat capacity) still cool slower...) (My hypothesis is that the slightly lower heat capacity does have an effect but not enough to change the outcome by it's lonesome. But I guess my point in writing all this is that I would like someone to reassure me?) Thank you for reading. :)
|
[
"I have my doubts about this demonstration, but instead of talking about those I'll try to address your questions about it.",
"First, what's being tested is the absorptivity of CO2. If you want to think in terms of specific heat, you have to compare Cv, not Cp. CO2 has a higher specific heat per mol than air. That's why CO2 causes a greenhouse effect in the atmosphere. I'm pretty sure this is your main point of confusion.",
"As for your thought experiment, the CO2 container will cool faster. Objects emissivities are equal to their absorptivities, by Kirchhoff's Law. Since CO2 is more absorptive it is also more emissive."
] |
[
"Watching the the demo again, I'm actually more impressed by it. I had four objections, three of which were not actually problems in the video: First, that the temperature increase was from the increase in pressure from the addition of CO2. But the canister was filled and then capped, so not a problem. Second, I thought the reaction producing the CO2 might be exothermic, it is, but not very, and really that doesn't matter because...Third, heating by radiation should take a good long while, which it did, hence the cuts. Fourth, the bottles should be equally distant from identical radiation sources, perhaps the experiment was good enough.",
"Performing the experiment oneself shouldn't be too hard. Mercury thermometers might actually be better than temperature probes–more of an ambient measurement–be sure they aren't touching the walls. Glass absorbs a lot of infrared, use clear plastic containers: you won't have to wait as long for the gases to heat up.",
"Calculating an expected change isn't really reasonable. Not because we don't know the concentration of CO2, probably very high, we could just guess 100%. But because we don't know the spectrum of the incoming radiation, you could measure the temperature of the light-bulb, but I've melted thermometers that way. As for the math, you can't really use specific heats, you need to use Stephan-Boltzmann with the absorptivity/emissivity curves for CO2 and air and the incoming Plank spectrum. Not a a back of the envelope calculation, more like grad-school homework. "
] |
[
"Alright, thanks for taking the time to reply. My confusion was due in part to reading the comments on the video haha. Thank you for clearing this up for me.",
"The validity of the demonstration itself is partially why I ask though. Are your doubts because of the editting cuts made, not knowing the concentrations of the gases, etc. or do you believe that there is a more fundamental flaw in it?"
] |
[
"What is the most imminent event that would be fatal to the human race or Earth itself?"
] |
[
false
] |
[deleted]
|
[
"It would have to be a new viral disease."
] |
[
"In my mind, a global nuclear war is number one, and a comet or astroid strike would be number two. "
] |
[
"Be concerned about the environment. We are definitely going to run out of oil fairly soon, but there is also a big shortage of fresh water. And don't forget food. Global warming isn't helping any of these situations, of course. But what will happen when these things start to run out? War will determine who gets the resources. It could be biological, nuclear, traditional... who knows. There are a multitude of things we have to worry about, but the sun exploding is not currently one of them."
] |
[
"How will my donated platelets be used?"
] |
[
false
] |
Just a few questions about my platelet donation. Most of the materials I could find referred only to whole blood donation. I had a scheduled donation of platelets at my local Red Cross donor center today. I am a 24 year-old male, 173cm, 70kg, type A+. I was told that I needed a platelet measurement of over 100 to donate at all, and the test on my blood had shown 355. I was hooked up to an apheresis machine for a hour and a half, and they took "three units" of platelets out, which more or less filled a large IV bag (maybe 500mL) and was approximately 1 trillion platelets total. I was told I would "save three lives" with my donation. What are the likely units on that platelet count? My count apparently isn't pathologically high, so how high would it have to be before it's be troublesome? What proportion of my platelets did I just donate, and how much more freely would I bleed if injured now? What sort of patients will receive my platelets (other than hemophiliacs, I guess)? Are they usually given via IV, like I conceive of whole blood transfusions? Is it likely to actually go to three different patients, or possibly to just one who really needs them?
|
[
"You actually wouldn't use platelets for hemophiliacs, since their defect is in Factor VIII of the clotting cascade. Platelet transfusions are important for people with thrombocytopenia (literally, platelet deficiency), which can be the result of pathologies like immune thrombopenic purpura, thrombotic thrombopenic purpura, or disseminated intravascular coagulation. All of these processes use up the patient's platelets, leaving them deficient. Thrombocytopenia can also occur with defects in production (such as from myelodysplastic disorders where the bone marrow fails to produce platelets). For hemophiliacs, you would actually give them desmopressin to increase endogenous Factor VIII levels or concentrated Factor VIII precipitates to directly add to their coagulation factor levels.",
"The range on normal platelet levels is rather large - ~140k-390k/uL. You also don't really get any problems until your levels drop below ~50k/uL. Each 'dose' of platelets generally increases the patient's count by 30k/uL. Platelets can be given as single-donor infusions by IV, or be mixed with a couple of random donors. ",
"I hope this answered your questions, and good for you for donating!"
] |
[
"To elaborate on the range a little bit...it's my understanding that ~50k is an approximate threshold for immediate concern. 50-140k is a range where you should still be relatively careful, but you won't have major spontaneous issues.",
"Source: a few different doctors I've had for my fluctuating platelets over the last 10 years or so. I'm actually currently hovering at ~30k and I have been fine, but have noticed occasional small bruises, and petechiae around my feet, but when I go for a bike, I stay on flat paths because there is a good change that a seemingly minor collision or fall could case major bleeding."
] |
[
"I used to work in a blood centre, issuing blood to hospitals (who then have their own internal blood banks).",
"The great thing about your donation is that someone who needs a lot of platelets could get them all from one donor. When they take platelets from whole blood there are less of them, so to make a single unit requires platelets from several donors. ",
"As you can imagine, this increases the risk of exposure to infection and the foreign antigens. A lot of precautions are taken to ensure blood products are safe, but minimising donor exposure where possible helps too.",
"In terms of usage, I never really saw that side. Sometimes you'd see several platelet units from one donor and you'd send them all for the same patient. Sometimes they would go to different people. From our end we would see a name for the patient but we were rarely told what was wrong. Except for liver transplants, you knew when one of those was going down because the hospital would order stacks of red cells and fresh frozen plasma, as well as some platelets iirc.",
"In terms of haemophilia, they don't tend to use platelets to treat them as far as I am aware, but they do use clotting factors which they can get from donated plasma."
] |
[
"How much meaningful data (words) can the average person memorize and be able to perfectly recall at will indefinitely?"
] |
[
false
] |
Say I wanted to memorize a random book, or 5 books, or 20 books, but then I wanted to be able to perfectly recall, or orally recite, the information I have memorized at will. Is there an upper bounds to the amount of information the average person can memorize in this manner and keep it all straight within the context of each source? From my own experience with memorizing various long passages of text, I have to periodically "refresh" myself to maintain the integrity of what I have memorized. This is usually accomplished through simple recitation to myself from memory. I am just curious how much I can realistically memorize.
|
[
"It's limited by number of words to be memorized and number of words need to be recited in a day.",
"Let say you can memorize X words each day. But you also need to recite it at different time interval. Assume you need to recite a word in 1 day after, then 2 days after, then 4, 8, 16 up to 1024 days after (everyone may have different patterns). With this pattern, you will need to recite a word 11 times in order to recall it indefinitely. ",
"Turning it around, in average, every day you will need to recite (1+1/2+1/4+1/8+...1/1024)* X words or 2X words.",
"Overall, you have X words to memorize and 2X words to recite in a day. It's up to the person how large the X is and reserve more time to recite if needed."
] |
[
"The phrasing of my question is probably not the best way to get the point across. For instance, I currently have approximately 15,000 words worth of information that I have memorized on a particular subject, from various sources and of varying lengths, that I can recall at will and recite with very little error. I did not learn it all at one time, rather over the course of several months or years. It's not something I would necessarily need to recite all at once, but I could if I wanted to. ",
"The information I have memorized could be equated to paragraphs from various books on similar topics. All 15,000 words do not go together in a sequence. For instance, there may be some parts that are only a few words to recite at once, but there are other parts that are up to 2,500 words to recite at once. ",
"Not taking into account the learning process or how long it takes to memorize a particular passage, my question is more of how much information in this manner can the average person memorize? ",
"If there is a better sub suited for this, I would gladly cross-post there. I just know there are a lot of smart people here. "
] |
[
"Hi, thx for clarify. maybe I try to estimate it using the formula above. Instead of using \"word\", maybe I called it item. An item can be a group of words / information/ a meaningful data point that one can handle at one time. Assume an average person can memorize 1 item in 6 minutes and recite each previously memorized item in 2 minutes. Since there are 2X items to recite in average, it take 6 X + 2 (2X) = 10X minutes.\nIf X is 6, it will take an hour to handle for each day. If a person can spend, say 2 hours/day, there will be 12 items/day.",
"Let the average person can do it continuously for 40 years, it become 40 * 365.25 *12 = 175,320 items ",
"what a large number...!",
"ps.: I have no idea what an average person can perform, so just makeup the assumptions..."
] |
[
"What is the root cause of certain language speakers not being able to use certain sounds of other languages?"
] |
[
false
] |
The example that made me think of this: Asian language speakers often have problems with the 'R' sound from English. I understand that this can be overcome, but my question relates to the root cause of this inability to vocalize the sound in language without practice. Does this stem from those speakers not having trained their muscles or brain to create this sound (in essence, just needing practice to make them), or is it that they need to teach themselves how to about this sound being part of language. To simplify, can a Chinese language speaker make the 'R' sound while imitating a low dog growl but not in language because of how they think about language, or is the 'R' sound itself mechanically difficult to do?
|
[
"Not sure if this helps... But basically language acquisition works in young children by acquiring different phenomes. A child who grows up speaking Korean will learn different phenomes than a child who grows up speaking English. So I guess in a way it can have to do with practise -- you're just not exposed to the phenomes or sounds throughout your life (specifically childhood which is when language acquisition occurs the most rapidly -- children can pick up new languages much easier than adults). It's kind of like when someone is trying to get you to say something in a different/foreign language. You ",
" you're saying it right, and they insist you are still saying it wrong. This is because you can't discriminate between the different phenomes in the foreign language, since you never learned them. ",
"Going back to your example -- Chinese people may lot have been exposed to the R sound which is what makes it difficult for them to pronounce that particular sound; they lack the skill since they never learned it. It is definitely possible to learn that sound, it will just take time and practise, especially in adults. Similarly, English speakers can have difficulty pronouncing certain words or sounds in other languages simply because they were not exposed to those phenomes as a child, when the brain is very plastic (which is why children can acquire language and vocabulary at such a fast pace -- the brain is still wiring itself at this time and has higher plasticity than a developed adult, or even adolescent, brain) "
] |
[
"This.",
"My father was a linguist and he used to say you get the majority of an accent by trying to read other languages using your own memorized pronunciations - whether that's through symbols or repeating things you thought you heard."
] |
[
"The answer has to do with what a phoneme is.",
"A phoneme is NOT a sound. A phoneme is actually a sort of \"potential\" sound, that can come out several different ways. The sounds in a language get grouped into phonemes. Errors often occur when someone's native language groups sounds into phonemes differently than the language they are speaking.",
"For example, in English, the 't' sound that you make in the word \"tap\" and the 't' sound you make in the word 'pat' are regarded as similar, even though they have some important differences. For example, the 't' sound you make at the beginning of 'tap' has a sort of puff of air behind it, called 'aspiration.' The 't' at the end of 'pat' does not. They are different manifestations of the same phoneme.",
"In some languages, those sounds are actually two different phonemes (you could say this is equivalent to being two different letters). So 'tap' (the way an English speaker says it) and 'tap' (without that puff of air on the end of the T) are two different words. ",
"When two sounds are grouped together in the same phoneme, the language has rules to tell you which way the phoneme manifests. So in English, the /t/ phoneme manifests with a puff of air if it's at the beginning of a word.",
"In some Asian languages, the 'r' sound and 'l' sound are grouped into the same phoneme. This is why speakers of those languages may produce an 'r' sound where an 'l' sound is called for, e.g. because their language has a rule like \"if it's before a vowel, it comes out as an ",
", but otherwise it comes out as an ",
"\". These rules are deeply ingrained and hard to overcome. If you don't believe me, see if you can stop yourself from aspirating T's (putting a puff of air behind the T) at the beginning of words.",
"So even if two languages use most of the same sounds, it can still be very hard to go from one to the other if those sounds are grouped into phonemes differently. Many languages, for example, put 't' and 'd' together as the same phoneme, because the only difference between them is that one is 'voiced' (try putting your finger on your throat when you say 't' and 'd') and the other is not. Those languages would also likely group 'k' and 'g' into the same phoneme, or 'p' and 'b', since those pairs also are only different because one is voiced and the other is not."
] |
[
"Why does it seem like cancer always attacks specific places, i.e. prostate, breast, colon, etc? Can you ever just have a random tumor like on your arm or something?"
] |
[
false
] | null |
[
"Cancer is the uncontrolled and unlimited division of cells which is why we cant stop aging because we would just be cancer balls",
"Actually, all of us have been cancer-free for 4 billion years of glorious cell division! And through our germ cells, most of us will continue forward for thousands or millions more to come. :)",
"(I understand your point, I just like this optimistic perspective.)"
] |
[
"I believe it has to do with cell division rates. Cancer is the uncontrolled and unlimited division of cells which is why we cant stop aging because we would just be cancer balls. Many cancer types are in places where the cells of that part of the body divide relativly quickly. More division means higher rates of mutations and after enough mutations compound cancer forms."
] |
[
"You can have cancer in \"random places.\" Moles (those dark freckles you see on people's skin) are benign tumors. This is why you should get them checked if they are discolored, large, or unsymmetrical. Additionally, you can have a tumor, for example, a lipoma in adipose tissue. These are typically painless, but can impinge on nerves if they are intramuscular or abnormally large. These, too, are generally benign and not serious (key word = generally).",
"Cancer, itself, is uncontrolled cellular division. Usually when it is on organs, it grows due to something (e.g. breast cancer typically feeds on estrogen, so they give their patients medication that inhibits estrogen production). They're also painful and damaging to the actual organ or whatever surrounds it (nerves, blood vessels). This can cause referred pain in random places (e.g. liver cancer can cause right shoulder pain).",
"TL;DR: Yes, you can have random tumors on your arm or something."
] |
[
"How large could a rocky planet get?"
] |
[
false
] |
I know gas giants have a maximum size before they turn into a star, but do rocky planets have a maximum size before they destroy themselves or otherwise no longer act as a planet?
|
[
"It all really depends on your definition of a rocky planet. Or a rock for that matter. ",
"Athleticon93",
" is right for normally formed planets. Any planet getting really big as just a rocky planet is going to accrete lots of gas too and become a gas giant. But if we want to ",
" a really big rocky planet, physics won't stop us for a while",
"Start with a chunk of rock floating around in space. Let's say we borrowed mars for a bit. Don't worry, the solar system won't ask for it back. Now toss a rock down onto it. You have a bigger rocky planet. Keep doing that for a bit. The planet gets bigger and bigger. Surface gravity increases, and for now, the density of material at the core stays the same (ish). Things start to fork at this point though, depending on the thought experiment. ",
"First off, just dropping the rocks is going to be a problem. Dumping planetfulls of rocks onto an ever larger planet makes heat. A ",
" of heat, which will liquefy, and eventually boil our rocks. This will also drive out any volatiles in the rock; gasses, bound water, sulfur, etc. Pretty much anything that isn't iron or nickel or another high boiling element or very stable compound. For example, limestone, a common rock, will happily decompose to CO2 and CaO. Now our ball of rocks is surrounded by an ever thickening atmosphere of gasses. Whoops, we made a gas giant. ",
"So lets start again, but instead we'll teleport our rocks down to the surface. Compaction will produce some heat, but not enough to boil our rocks. ",
" ",
"The planet could get quite big (somewhere around 3-4 times the radius of the earth), but eventually the compressive forces of gravity will be enough to start severely compressing even solid material. The density of the core will go way up. You'll notice you're adding hundreds of cubic kilometres of stuff and your planet is only growing by tens of cubic kilometers. This is going to make a lot of heat. If our rocks have a fair bit of lighter elements in them (pretty much anything higher on the periodic table than iron), eventually somewhere around 60 times the mass of Jupiter the heat and pressure will be too much and our \"rocky planet\" will ignite into a very weird star ",
"Let's start again, again. We can't use rocks anymore, but we can use iron. Iron is at least a solid, and we can imagine running around on it pretty similarly to a regular planet. Get a big ball of iron and start the teleportation machine again with chunks of iron instead of rocks. Again, you'll see the planet grow, but after a certain point, roughly 2.5 times the radius of the earth, and several hundred times the mass, adding more mass will actually cause the radius to shrink. The iron planet will also be getting very very hot (tens of thousands of kelvin). What's happening is that the additional matter is causing increased gravity, and your planet is no longer being supported by the everyday pressure of electrostatics, like what keeps your feet from compressing a concrete floor. Instead the core is now dominated by electron degeneracy pressure. It's acting like a very hot, ultra dense gas. As you add more iron, you create more gravity. More gravity makes more pressure, more degenerate matter, and a smaller radius. Your \"planet\" is now a white dwarf. If you let it cool off for a few trillion years you'd be left with a ball of iron that, if you could walk around in about a hundred thousand g's of gravity, you could walk on and would be (sorta, kinda) like a planet. And that's as big as you can make a planet."
] |
[
"First, I think you should distinguish between size and mass. There are some planets that are more massive without being much larger than Earth. For example the largest known planet is Kepler-10c, with a mass similar to Neptune, but it only has a radius 2.35x bigger than Earth.",
"You also must think about the difference between a gas giant and a terrestrial planet. Most people think of it as either gaseous or rocky, but large planets gravity will suck in gases, so they will have large atmospheres. Maybe even gaseous enough to be called a gas giant? Also, most people don't know that gas giants DO have a rocky core! It's even theorized that a gas giant's atmosphere could be destroyed by their star, leaving a terrestrial planet behind.",
"So instead of just terrestrial, or just gaseous, it's actually much more of a gradient. If you really want an answer, around 2.5 Earth Radii, or about 20x Earth's Mass is about the limit for terrestrial size planets."
] |
[
"What do you mean \"tear its atmosphere up?\""
] |
[
"What happens to oxygen (gasses in general) that get lost into the vacuum of space? Could (theoretically) we pump oxygen in space to create breathable pockets?"
] |
[
false
] | null |
[
"Gravity.",
"You need something to \"anchor\" that gas locally, and only gravity can do that. To have enough gravity, you need a big enough lump of something. That's basically a planet.",
"TLDR: You need a planet to keep the gas from wandering off into space. EDIT: Otherwise the gas cloud just keeps expanding."
] |
[
"The Shuttle, back when it was operational, was never too far from Earth. Gases from the vehicle would have remained bound to Earth by gravity, for the most part - doing orbits around Earth, most of those orbits would have decayed the usual way and bumped into atmosphere eventually.",
"(It's a bit tricky with gases, because there's always the odd lone molecule with lots of kinetic energy that can go off into the distance on its own. But on average, the above is true.)",
"Further away from Earth, again, gases would remain bound by gravity to the Sun and spend millions or billions of years orbiting though the solar system.",
"Further away, well, it's always a matter of speed versus gravity. If local gravity is strong enough, thing remain bound locally - except for very fast things which can escape.",
"If you were out there in the intergalactic medium, if you let some oxygen escape, you'll make a puff of gas that would just keep expanding nearly forever.",
"So I guess this is the answer to the question you're really asking: puffs of gas \"out there in space\" tend to expand forever. The \"puff\" as a whole would orbit whatever is nearby, until it would become too bloated to be recognized as such. Some gas would fall onto the nearest large body (planet, star, cluster, galaxy, etc), the rest would keep shooting away into space. What proportion falls down (or remains trapped in a long-term-stable orbit), versus how much expands into space, depends on many factors - between 0% and 100% for either of them."
] |
[
"I'm fairly sure he is saying without a body of mass to attract the gas, the molecules go in their own directions. Imagine putting a few drops of red dye in the ocean. The molecules spread out, becoming more diffuse, and eventually are not detectable. The molecules are still in there, but your chances of finding one after an hour or so are nearly nonexistent."
] |
[
"Why are the physical electromagnetic fields only the real part of E and B?"
] |
[
false
] |
says that the physical fields are only the real part of E and B, but this is not obvious to me. Since e = cos(x) + i sin(x) We get an imaginary part of the fields in the picture, but somehow these aren't actually a part of the fields, or how should i interpret i?
|
[
"Maxwell's equations are linear. So if ",
" and ",
" are solutions, so are their real and imaginary parts separately. Writing ",
" and ",
" in complex exponential form just makes the math easier since exponential are easier to deal with than sine and cosine individually."
] |
[
"ok, the basic idea is this: you want to solve some ",
" linear differential equations (example: Maxwell's equations). By real, I mean the coefficients and differential operators in the equations are all real (they send real functions to real functions). In fact, let's be explicit, the system of eqts is something like this",
"D E = 0",
"where D is some real R-linear operator and E is the field you're solving for. You want to get real solutions for E, because say E is meant to be a physical observable. You do this:",
"D E = D Re E",
" = Re D E",
" = Re 0 = 0",
"why could I swap D and Re? Well, that's the definition of D being real. Think of D as a sophisticated version of multiplication by a real scalar. Surely if r is real then r * Re(z) = Re(r*z).",
"PS: I wanna stress how important for this to work that the equation itself is real. For example, Schroedinger's equation is not real (there's an i there) and thus even if ψ is a solution, Re ψ and Im ψ are not."
] |
[
"Often you will see that electromagnetic equations contain some complex exponentials and then a \"+ c.c.\" for ",
" at the end of each line to make the whole expression real. Quite frequently people will just omit the \"+ c.c.\"."
] |
[
"Is hydraulic fracturing and shale gas really harmful to the environment? How would it compare to other energy sources including all steps from extraction to consumption?"
] |
[
false
] | null |
[
"I would link the EPA article but I'm on my phone. Extensive studies have tested the process and find it safe when the proper protocols are followed. "
] |
[
"I would link the EPA article but I'm on my phone. Extensive studies have tested the process and find it safe when the proper protocols are followed. "
] |
[
"It depends on a lot of factors. Fracing itself isn't dangerous, but if placed near a valuable groundwater source it is. Even then it depends very highly on the nature of the natural gas itself.",
"Its best to think of the problem from an environmental engineer's perspective - source, pathway, receptor. These three elements make up the foundation of contaminant transfer and environmental susceptibility. In the case with fracing, the source is the natural gas itself (full of lovely chemicals, especially those related to the BTEX combo... benzene, toluene, ethylene, xyrene... and many other potential carcinogens), the short term receptor is groundwater and the long term receptor is users of that ground water. Before fracing there is no pathway for transfer. The act of fracing, in some cases, opens the gas formation to connect with the water formation. This allows the gas to bubble through the water and release some of its nastier chemicals to the water supply.",
"Before you start thinking that, \"yes, fracing is harmful to the environment,\" we have to address the transfer triangle described above. If any components of that triangle are removed, either consciously or not, contaminant transfer is inconsequential. In this case, we can never remove the source - natural gas is pretty much everywhere in north america - but the constituents of transfer and receptor greatly vary. Ex 1/ If you have a fractured gas well whose zone doesn't protrude into a ground water table, there is no short term receptor. Ex 2/ If you have a fractured gas well whose zone protrudes into a ground water source, but its too deep for same consumption, then there is no long term receptor. ",
"Hydraulic fracturing is used ubiquitously in the oil and gas industry, but these problems aren't everywhere. I used to be a gas operator in eastern Alberta, and to the best of my knowledge, it has never been addressed as a problem. I imagine that this was because our target horizon was 500 m plus below surface, and most water wells for drinking water don't extend past 10 m. Canadian drinking water standard also require that water wells for human consumption (even in rural areas) are spot checked for quality standards. Wells around industrial sites are required to be tested on a more frequent basis.",
"Something to think about - almost all natural gas zones are naturally fractured and full of water. Why isn't this a problem before they are drilled...",
"TLDR: It depends on the depth of the natural gas horizon, and the depth of potential receptor aquifers. If the two are close together, there is a potential for environmental impact due to fracing."
] |
[
"Say there was a pot of water that was heated to 150 degrees fahrenheit, and another pot's water temperature measured 50 degrees fahrenheit, if both were placed in an environment that held a steady 100 degree fahrenheit temperature, which would reach the 100 degrees faster?"
] |
[
false
] |
The pots are the same size, and the water amount is the same. The numbers are essentially arbitrary, and the unit of temperature isn't relevant. The question I'm trying to get across is - if two items were placed in an environment, and one item were just as much hotter than the other was cold, which one reach the base temperature of the environment first? Feel free to correct me on, inquire about, or even dismantle my inquiry; all I ask for is closure. Thank you,
|
[
"This is true if the only heat transfer is sensible heat (proportional to the temperature difference). However, if the pots were open to the air there is also the factor of latent heat of evaporation. The heat loss due to evaporation would be in addition to the heat loss due to temperature difference (delta-T) so the hot water would reach 100° more quickly."
] |
[
"Th mpemba effect has more to do with freezing temperatures as the molecules can align more easily into crystals at higher temperatures. For this situation, the simple model you use is what I'd consider. It's important to remember that the specific heat of a material is temperature dependant, and for water, like many is higher at higher temperatures (by a small amount). Ignoring any changes in conduction through the pot or convection to the air, the warmer pit would require more energy, and take a small bit longer."
] |
[
"The formula for change in temperature is (delta)T = Q / mc where Q is the amount of heat energy, m is mass, and c is specific heat. Judging by this equation, the pots should reach 100 degrees equally fast. But there is also the ",
"Mpemba effect",
" which could make the hotter water reach 100 quicker.",
"For the record I have no qualifications, I'm just posting what I've learned so far. I'm just a college freshman, so you should wait until an actual chemistry major comes in"
] |
[
"Is there a better measure than expected value for bets that you can only make once?"
] |
[
false
] |
My girlfriend was badgering me to buy a bingo card in a $1000 bingo game once. The cards were $10. I told her we could do it if it looked like less than 100 people showed, because I figured the expected value of the card would be more than the cost under that condition. I realized that we only got to make this bet once, and I think that expected value is the average value the cards approach as you play the game an infinite number of times (right? it's been a while since I took stat). Assuming 98 other people showed up, despite expecting a profit, there was still a 98/99 chance that I'd simply be out $10. Is there another measure that's more appropriate for that situation? It would account for (1) you can only play the game once and (2) the potential profit?
|
[
"So, the distinction here is that expected value is the only statistic that matters if you're allowed to play the game an infinite number of times (i.e., you have an infinite bankroll or can go arbitrarily deep into debt). A related concept (for dealing with a finite bankroll, and either limited or unlimited plays) is a ",
"random walk",
".",
"Assuming 98 other people showed up, despite expecting a profit, there was still a 98/99 chance that I'd simply be out $10.",
"This is almost the definition of a ",
"risk-return tradeoff",
", and is a central problem in investing. Essentially, there are often investment opportunities (potentially including bingo tickets) that have a high expected return, but also a high chance of failure (i.e., losing everything). What level of risk you're willing to tolerate in an investment for a given return depends on a number of factors. If you're interested in understanding these trade-offs, you should read some books on investing.",
"In this particular situation though, there's a major factor you haven't accounted for- that many people at bingo play multiple cards simultaneously. Even if only 50 people showed up, there could easily be several hundred bingo cards in play, making the risk-vs-return question a moot point."
] |
[
"Ah, I see. Thanks.",
"Even if only 50 people showed up, there could easily be several hundred bingo cards in play, making the risk-vs-return question a moot point.",
"We didn't end up getting a card. Bingo's boring as hell."
] |
[
"This doesn't directly address your questions, but expected value isn't the end all for decision making.",
"It is better to be concerned with expected utility rather than expected value. Money often has a diminishing return on utility. Thus, it is often the case that a loss of a dollar hurts you more than a gain of a dollar helps you. An even bet could end up having a negative expected utility even if it has a neutral expected value.",
"On the other hand, the act of the bet could carry a positive utility. People often derive enjoyment from the excitement associated with risk taking. Thus the bet could carry some benefit beyond the potential monetary gain.",
"However, the issue is that both of these factors are hard to quantify. The first is highly situational, depending on many factors including your current financial status, and somewhat subjective. The second is very subjective. The potential gain or loss of money, by comparison, is much simpler to evaluate, and is often a good estimate."
] |
[
"What type of radiation is produced by the annihilation of interacting matter and antimatter particles?"
] |
[
false
] |
It is said that when an particle of matter and antimatter interact they annihilate releasing all of their energy. What is the frequency of the radiation energy that results? What determines this?
|
[
"Typically high energy photons aka gamma rays. If the collision is relatively low-energy then they photons will have the same energy as the mass of the particles, so for electron-positron collisions that's 511 keV or about 10",
" Hz."
] |
[
"Not necessarily only two; larger numbers are possible (of course, they still have to obey conservation laws) but less common because the probabilities for such processes quickly decrease with the number of photons emitted.",
"There's even a case where the minimum amount of photons produced is actually 3, not 2: if the electron and positron form a ",
"short-lived system",
" where they \"orbit\" each other for a short while and their spins are parallel, the so-called ortho-positronium can only decay into an odd number of photons - but not into 1, as that would violate conservation of momentum. So the minimum is 3."
] |
[
"Specifically two, emitted at 180 degrees to each other if I'm not mistaken? "
] |
[
"Does the Sun have poles?"
] |
[
false
] |
Similar to either the two geographical or magnetic poles that Earth has? Do stars in general have poles? If the Sun does have poles, are the orbits of most planets roughly perpendicular to the Sun's polar axis?
|
[
"The sun rotates. So yeah the North and South pole are the points where the rotational axis coincides with the surface. Furthermore the sun has a magnetic field that has a significant dipole component. This dipole is aligned with the rotational axis, so the dipole poles are at the North and Southpole as well.",
"\nThe planets orbit roughly on the solar equatorial plane. The orbits are slightly inclined but only a few degrees. (Pluto has a much stronger inclination with ~17°, another factor that makes it different from the other planets.)"
] |
[
"You are probably thinking about permanent magnets, like neodymium magnets. However this does not apply to electromagnets. Remember that any moving charge, i.e. any electric current, creates a magnetic field.\nStellar magnetic fields of solar mass stars (of any star with a convective envelope really) are created in a process not unlike planetary magnetic fields. It is called ",
"dynamo effect",
". "
] |
[
"What allows the sun to have a magnetic pole? I thought that materials lose their magnetic properties as they get hot? "
] |
[
"Vasoactive drugs like Norepinephrine, Epinephrine, Vasopressin work differently on the heart. What are their actions on the heart and how is it determined which order these drugs are given?"
] |
[
false
] | null |
[
"Another thing to consider is the sensitivity of these compounds for specific receptors. The heart contains predominantly beta-1 adrenergic receptors, while the vasculature contains both beta-2 and alpha-1 receptors, that vasodilate and vasoconstrict when activated, respectively. Norepinephrine is much more selective for alpha-1 receptors than beta-1 receptors, while epinephrine has a more equal selectivity for all receptors. This is why epinephrine is given for anaphylaxis instead of norepinephrine. If NE was given, the sudden increase in blood pressure would trigger your body's baroreceptor reflex, resulting in a reflex lowering of your heart rate (which can be very dangerous, especially in the context of anaphylaxis). Epinephrine avoids this by also stimulating your heart to increase its rate and contractility, which masks the effects of the baroreceptor reflex. ",
"Also, an important thing to note is that while vasopressin (also known as anti-diuretic hormone, ADH) does have an effect on blood pressure, this is only at higher concentrations of the hormone, as its primary function is to cause water retention in the collecting ducts of the kidneys. This water retention also helps with the maintaining of blood pressure."
] |
[
"Sorry if this is late: Your question is very vague, so i'll try to answer best as I can. ",
"Norepinephrine is a neurotransmitter, such that it is only released by neurons and is not a hormone (unlike epinephrine and vasopressin, meaning it is not released into the blood stream). On the heart, NE acts to chronotropically (increases heart rate), dromotropically (increases conduction action potential conduction velocity), lusitropically (reduces the duration of diastole and systole), and inotropically (elevated contractility). In layman's terms, it increases the cardiac output (increases blood pumped out of the heart and increases heart rate). ",
"Epinephrine (adrenaline) is a hormone, as the name suggests, adrenaline will act inotropically to increase stroke volume (blood pumped out of the heart)",
"Vasopressin is a hormone released by the posterior pituitary gland that acts to increase blood pressure, and therefore, does not have any direct effect on the heart (that i know of?). ",
"Of the three chemicals you listed, NE has the most drastic effects on the heart because the NE would be released locally and directly targets target the heart, unlike epinephrine which has many other target organs. "
] |
[
"NE is released into the bloodstream by the adrenal medulla, in addition to being a neurotransmitter."
] |
[
"Does learning a language continuously get harder as one ages, or is there an age where the difficulty plateaus?"
] |
[
false
] | null |
[
"Finally an opportunity to give something back to the mighty jorgfeldkt!",
"Here's",
" an article (containing two reports) that pretty much supports my personal experience as a trilingual+ person, but I am certainly a layman here. (If you're curious, the languages are Norwegian, English, French, I speak some Serbocroatian, Greek and Japanese. Arabic coming soon, but the reading is a bitch.)",
"Basically, you're not impaired in language learning as you get older unless you count degrading mental faculties or senses. Bad eyesight or hearing obviously gives you some trouble in learning a new language. What makes it harder is your own impression that it is, and the fact that you are less patient -- you were probably not a very good English speaker (and certainly not writer) before you were well into your teens, so expecting instant results, which many people seem to do, is not realistic.",
"So, go ahead and learn a new language, but be patient and use a method that works for you -- I recommend the Pimsleur and Michel Thomas methods for something geared towards adults using a language mainly for conversation, I could go from zero to simple conversation in a matter of weeks with these. If you have other goals, there are other methods. ",
"Immersion is a thing that is talked about often, and while it is a good way to learn a language, it can impair your progress especially if you try to cut your mother tongue cold turkey in a work setting. One of the papers linked talk about it a bit, especially how children should not be overexposed too quickly to a new language while learning other things. Immersion, understood as \"using the language as much as possible\", can also be done in other ways -- print flash cards for plane rides, try to read news or even children's literature, and so on.",
"To my experience too, the \"learn like a child\" mumbo jumbo marketed by the likes of Rosetta Stone deserves being labeled scientifically proven bullshit -- however, it's very nice to have a somewhat inefficient method that can be reproduced in tons of languages with little work, at least for those who sell it. ",
"Adults learn differently, most importantly more understanding and focus on what you're actually learning the language for, and less repetition. Michel Thomas starts his French lessons with an overview of how English and French are linked and what words can be easily translated for this very reason. But they learn more efficiently, probably because you have the rest of your vastly improved knowledge to build on.",
"I couldn't find it in a quick search, but I can't remember ever seeing any neurological reasons why you would learn slower either. I'll look into it some more.",
"(The website seems flaky, I know, but it's the full text of two DOE-commissioned reports. I can dig up some more if you want.)",
"TL;DR: There's plenty of proof of the fact that you do ",
" learn slower as you age. You learn differently, but it's not harder.",
"Edit: Corrections."
] |
[
"It's not that it doesn't work, it will eventually. The US government uses Rosetta Stone a lot, for reasons passing understanding, and while I don't expect them to get the best, they wouldn't use it if it did nothing. So it will teach you a new language, just not in a way that makes good use of your time.",
"It's because, as I mentioned, learning a language as a child is different from learning as an adult. When you learned your first language, you learned it by connecting it to the world around you. You need to learn everything there is to learn, while when you learn a new language, knowing ~500 (active vocabulary is ~500-1500) words gets you a very long way. There are things that adults can do that children cannot. ",
"Basing everything on the world around you, as Rosetta does (there's ",
" English involved) works, but it's ineffective. Adults can do it differently. Free French lesson ahead: A lot of words suffixed with -ible (possible, compatible, combustible, audible) and -able (acceptable, comfortable, pliable) can be directly translated to French with a difference in pronunciation, and the suffixes mean the same. A lot of words suffixed -~ly can be switched with -~ment in the same way, at least orally (practically -> practiquement, chemically -> chimiquement, complacently -> complaisamment.) Congratulations, you now know several hundred words in French.",
"Now tell me how to do that with pictures."
] |
[
"In addition to the poop ctolsen said, there are fundamental things different from how adults learn and how babies learn that put us apart in language. For a real simple example, take trying to teach someone the first consonant sound in \"this.\" Turns out not a lot of languages have this sound so a lot of people have trouble with it. But a baby is going to eventually learn this sound if it's in his environment by experimenting with mouth shapes and shit like that until he comes up with something sufficiently close to \"th\" that he can communicate the noise (actually probably not a baby at that point but anyway), and this differs from an adult who can't really learn noises like that any more. So the way you try to teach an adult is to tell him using language \"put your tongue between your teeth and make the z sound\" or something like that.",
"So basically we lose some faculties of learning that babies have (babies are way way better at distinguishing certain noises than adults are, babies are better are experimenting with mouth shapes, etc etc), and we gain some faculties that mean trying to replicate the baby process isn't even as efficient any more, for instance the ability for ideas to be communicated in words (I can tell you that 이 is used to mark the subject of a sentence in Korean, and you don't need to listen to a million sentences and pictures of boys kicking balls to pick it up), and maybe some things like more ability for abstract thought and just the general mental improvements adults have over babies. "
] |
[
"What happend to the Enigma Machine?"
] |
[
false
] |
In school we are currently doing a short unit on Turing and how he decrypted the Enigma machine. I was wondering if there was anything which improved upon the designs of the Enigma machine? Or something that became the "spiritual" child of the enigma machine during the korean/Vietnam time period in order for the super powers to protect their secret messages/orders? I've tried to do some searching myselfand have found nothing. My history teacher is drawing a blank as well. So I was wondering if any of you knew anything?
|
[
"It's interesting to note that the Enigma was technically obsolete by the start of WWII and should not have been used by the German military. A big problem with the Engima and other devices like it is that it does a piss poor job of increasing entropy (i.e. randomness) of the cipher text. What this means is that the message you send over the air (and which the enemy can intercept) is packed full of meaning and can be attacked relatively easily. This is laborious by hand, which is what the Enigma relied upon. However, once computers arrived on the scene at Bletchley park, Enigma was done.",
"The current gold standard for encryption was invented just after WWI. The Vernam cipher, or \"one time pad\" is a deceptively simple way of encrypting messages. You take your message and convert it to binary, then you take a random sequence of 1's and 0's (i.e. the \"key\") and XOR the message with it. This can be done by hand and the outcome is indistinguishable from random noise ",
" you have the key. This method of encryption is impossible to attack, and provably so. If the key is random, so will the cipher text be. The big problem with using a vernam cipher is that keys can only be used once, so it is necessary to get those random keys to the person who will need them to decode the message. The Germans could have sent key-books out with U-boats, etc. and used Vernam ciphers instead of the Enigma. If they had done this, their messages would have been impossible to decrypt unless the allies managed to capture one of the key-books. Fortunately for the allies, the Germans did not do this.",
"It's important to note that the Germans really ",
" have used the Vernam cipher instead of Enigma, because they were ",
" using it for high level diplomatic communications from the interwar Weimar republic era onwards. The allies also made extensive use of the vernam cipher in a variety of forms during WWII, and ever since. It's bizarre that the grossly inferior Enigma system is so much more famous, but understandable. Enigma machines are intrinsically linked with the development of the computer, and it's difficult to say how and when computer would have evolved were it not for Enigma. ",
"Today, using a Vernam cipher remains difficult in a lot of circumstances. If you aren't in regular physical contact with the person you are sending coded messages to, you have to rely on an intermediary to transfer key material. How much trust can you place in your intermediary? Also, how can you communicate with someone you've never met, but be assured it's not somebody pretending to be them? The vernam cipher does nothing for authentication. Public key encryption solves many of these problems, although at the cost of being technically possible (but currently very difficult) to crack.",
"If you're curious about the state of the art, that would probably be quantum key distribution in combination with the venerable vernam cipher. Google BB84 for the earliest, simplest form if you're curious. QKD allows two widely separated people to obtain a random key that they both know, but which is impossible for other people to intercept (in theory). Once they have that key, the rest is relatively easy. "
] |
[
"The algorithms that are used nowadays are so sophisticated they couldn't run on a electromechanical machine like that, they use super computers. ",
"The last part of that isn't true. Encryption algorithms run on your smart phone. Breaking encryption is a much, much, much harder problem than performing the encryption and decryption. That's why encryption works. You don't want to have to run your encryption on an NSA supercomputer in order to protect yourself from having the NSA snoop on you"
] |
[
"Are you asking about the Enigma machines (of which there were 100's or 1000's used by the Germans) themselves? Wikipedia says this:",
"An estimated 100,000 Enigma machines were constructed. After the end of World War II, the Allies sold captured Enigma machines, still widely considered secure, to developing countries...The effort to break the Enigma was not disclosed until the 1970s. Since then, interest in the Enigma machine has grown. Enigmas are on public display in museums around the world, and several are in the hands of private collectors and computer history enthusiasts",
"Or are you asking about Colossus, the computer developed to break the Enigma code? Because that is the one with the tragic history:",
"Colossus documentation and hardware were classified from the moment of their creation and remained so after the War. Tommy Flowers was ordered to destroy all documentation and burnt them in a furnace at Dollis Hill...Most of the Colossus computers were dismantled and parts returned to the Post Office. Two, along with two replica Tunny machines, were retained, moving to GCHQ's new headquarters at Eastcote in April 1946, and moving again with GCHQ to Cheltenham between 1952 and 1954. One of the Colossi, known as Colossus Blue, was dismantled in 1959; the other in 1960.",
": added to first quote."
] |
[
"How do rocks naturally get knto the position of balancing on another rock?"
] |
[
false
] |
Like in finladn there's a 500 tonne rock balancing on top of another one for ages, its so heavy that there is no way someone moved it there, smaller one's are also in Poland and all over europe, just how do they get there?
|
[
"Depending on the examples in question, there's going to be a few different options, I'll discuss two common/possible ones here.",
"(1) For ",
", or as their often referred to in a paleoseismic context ",
" or just PBRs, these often form ",
". As described in a variety of publications (e.g., ",
"Bell et al., 1998",
", ",
"Balco et al., 2011",
" with most referencing the Twidale, 1982 book - ",
" with respect to formation mechanisms for PBRs), one common way they can form is basically having a series of vaguely spheroidal shaped boulders in the subsurface defined by sets of intersecting fractures (which form via exhumation jointing, spherodial weathering, etc) surrounded by looser regolith (i.e., much more broken up rocks). As weathering and erosion continues, the looser bits get eroded away, but the boulders (i.e., the ",
") get left behind, and if they're stable, they'll end up staying in their stacked position as the surrounding regolith is evacuated. The Balco et al PDF has a schematic diagram to help visualize this process in their figure 2. ",
"(2) Another possible option are ",
"glacial erratics",
". These are large rocks that are dropped by large ice sheets and glaciers. These were rocks that were picked up (or fell into) a large ice sheet/glacier and transported, usually significant distances, until they were dropped by the ice sheet/glacier, usually as a result of melting. Most erratics don't appear as balanced rocks (more just kind of large, random boulders, often in areas that otherwise do not have many exposed rocks), but theoretically it's possible for a glacial erratic to end up as a balanced rock.",
"In terms of distinguishing between the two, classic PBRs usually will all be the same rock, i.e., the individual boulders balanced on each other will be largely derived from the same original bedrock and have the same composition, etc. Also, in a given area, there will probably be several PBRs as their formation reflect the right sets of conditions and processes that allow for their formation (and thus you would likely expect it to have happened in more than one spot in that area, though not always). In contrast glacial erratics, by definition, are very different rock than the surrounding bedrock. Similarly, a stacked erratic is probably going to be just one rock high, i.e., a single glacial erratic sitting on top of the local bedrock, as the ability to form actual columns of corestones (like with in-situ formed PBRs) is not really present. Also, while you might expect to see groups of erratics in a particular area, you wouldn't necessarily expect groups of balanced erratics as an erratic ending up as a balanced rock is going to be a bit more \"by chance\" as opposed to by process like with traditional PBRs."
] |
[
"Wow, thank you, this was educational"
] |
[
"If you want to see a lot of big rocks balanced on small rocks, in the most amazing setting you can imagine, head to Palm Springs CA and the nearby Joshua Tree National Park."
] |
[
"Why do we have earlobes? What purpose do they serve?"
] |
[
false
] |
[deleted]
|
[
"Here is an excerpt on Pinna from ",
"a lecture on Perception",
":",
"With the ears, there are at least two aspects of the sound that are different between the two ears as the function of sound sources' position.",
"inter-aural amplitude and timing differences - Differences in when the sound arrives and how loud it is when it gets to the two ears; ",
"we can use this information to figure out how far to the left or right some sound source is. If you think this through however, it's just not enough information. We perceive more about the source of the sound than its approximate direction. ",
"consider the idea that maybe some sound source is right in front of your face directly ahead. If that's the case then there will be no timing differences as the sound will reach both the ears simultaneously. Also, there will be no loudness difference. These timing and loudness differences or lack of differences are present if the sound source is right in front of me. It should be able to tell me if the sound source is right in front of me. On the other hand, \nthey are exactly the same directly overhead or even behind me. If I close my eyes and listen however, I don't have any trouble knowing when something is in front of me or whether it is overhead or behind me.",
"There must be something else that our auditory system is doing to figure out where sound sources are.",
"Enter Pinna.",
"Why does this rubbery Pinna matter so much? How does it create a compelling soundscape?",
"It is related to something called the \"Head Related Transfer Function\".",
"For low frequencies, head doesn't cast a good auditory shadow. This relationship between frequency and the amount of interference created as it passes through and around solid surfaces, is the information we are talking about with the Pinna. ",
"If a sound source is directly in front of us, then the Pinna will selectively attenuate the different frequencies to particular extents. As the sound source moves up or down, this amount of attenuation changes in specific predictable ways. And your brain seems to know what they are. By looking at the relative proportion of different frequency information in the sound input, your auditory cortex can figure out just how high or low or left or right, some sound source is. ",
"Some interesting studies have been done on this. As with the tonotopic maps, it seems that this Head Related Transfer processing is dynamic and flexible as the body and environment change over time."
] |
[
"I've just done some quick googling, and got to this ",
"http://en.wikipedia.org/wiki/Pinna_(anatomy)",
"The whole outside of your ear is used to increase the amount of sound you can pick up, and that would include the lobe too. I have no idea whether or not the Lobe would really be detrimental to \"catching\" sound, but it certainly gives the whole Auricle its shape, so it does have a purpose, along with the entire ear shape itself. "
] |
[
"So if I held my Pinna and closed my eyes, I would have problems determining wheter a sound source is in front or behind me?"
] |
[
"How does a wireless signal get converted into binary?"
] |
[
false
] |
When you send a wireless signal from, for instance, a remote control to a tv, how does the tv interpret these signals and convert them into binary? Does the remote control just turn off to represent a 0 and on to represent a 1 or is the process more complex?
|
[
"The whole process a signal takes is a little different for analog and digital, so this will be primarily from the digital perspective.",
"The process begins by taking any source (sound file, video file, Web page, etc.) and representing it as a binary string. From there we usually first compress the string. How we compress the information, and how we transmit the information are completely separate. Which is generally justified by ",
"source-channel separation (PDF, read intro for background)",
", which states that we suffer no loss in rate by doing so.",
"From there we apply the error correction code. This is where most of the magic happens. Here we take a k string binary sequence, and transform it into a n symbol output sequence where each sequence is spaced far apart. Think 0 as 000 and 1 as 111. There would have be two errors before I could no longer correct as 010 is most likely 000 and 110 is most likely 111.",
"So now that our code can be easily corrected, the process of actually modulating the signal begins. There are many many different ways of doing this, and a lot of misinformation. Hence I will stick with the abstract. For each symbol we are going to send, we associate a certain waveform. Think sine wave for 0 and cosine wave for 1, or square wave for 1, no signal for 0. By signal processing techniques we can ",
"arbitrarily shape",
" this waveform so that it fits in a particular frequency range. If we want each symbol on a different frequency, that is ",
" (FSK)",
". If we want the symbols to look the same but have different amplitudes, that is ",
" (ASK)",
". So on and so on. The type of modulation used depends on the circumstances. FSK is best used for low power communications, since it allows for me to increase the distance between any two symbols simply by spacing them at frequencies that are further apart. ",
"In general, the most important concepts to be aware of here are ",
" (QAM)",
". And ",
" (OFDM)",
". A QAM signal sends bits concurrently on two channels, using both sine and cosine. That is 4-QAM may look like",
"QAM is very commonly used because it allows a pretty easy to separate out signals. Indeed think of the power difference from going from a 4 by 4 grid to a 5 by 5 grid, you just need a little bit more power but gain 25-16 = 9 extra symbols you can send. The other, OFDM, encodes the information in the frequency domain, and then converts the signal into the time domain for transmission.",
"Recapping modulation, each symbol (such as 0 or 1) has an associated signal (such as sin or cos) which is sent out. Regardless of modulation, the important part is how well the symbols can be distinguished. Obviously right? If I send a 1 I want to receive a 1 with high probability. Choosing modulation simply amounts to what the required parameters are that allow for maximum maximum separation at the demodulator.",
"The demodulator's job is to take the signal and supply a probability vector that denotes which symbol was transmitted. This is typically implemented with ",
"matched filters",
" which look for the waveforn transmitted. You can think of them like a card board cut out. Does the picture fit in this cutout? Yes? Well it must be this symbol. No? Let me grab another cut out. ",
"Matched filter banks supply us with the probability a certain transmitted symbol was sent. We then pass this to the error correction decoder, which uses the distance between valid input sequences to find the correct message and out put it to the end user.",
"The ratio of bits k to the n symbols transmitted, is known as the code rate. Since we sent k bits in n symbols, we have k/n bits/symbol. The maximum value possible is determined by the capacity of the channel. And trying to go above this rate, sends the probability of error to 1, even for small values above the maximum rate. While the terminology varies, this is one thing people may mean when they say strong converse. Not all channels have a strong converse, but the ",
"point to point does.",
"Once again, the major magic part is the error correction code. Usually wireless communication has some nasty symbol error rates, think 1/4 or 1/3 symbols are received in error. As much as you try and change modulation scheme you only get very minimal gains. On the other hand, the error correction code usually drops the errors to infinitesimal probabilities as long as you are below the channel capacity."
] |
[
"Remote controls for a TV are a bit more complex than the process you've mentioned (0 = off, 1 = on), but not much.",
"A common IR remote protocol is the so-called RC5 protocol. This protocol always sends a pair of signals to encode a single bit. A \"0\" is represented by the signal \"on-off\", whereas a \"1\" is represented as \"off-on\".",
"Simply turning off to send a 0 wouldn't be very practical, because then the receiver has no way to determine whether the remote stopped broadcasting (perhaps because something moved in the way of the signal) or whether it's broadcasting a stream of zeroes."
] |
[
"Thanks for the explanation! Especially on QAM. I'll look into that."
] |
[
"Is there a such thing as a perfect laser? Do all lasers eventually lose their focus over a long distance? Does the strength of a laser affect its accuracy?"
] |
[
false
] | null |
[
"People think of lasers as a perfectly cylindrical beam of light. That's only an approximation which does not exist in reality.",
"A laser beam, like any other light beam, is an electromagnetic wave. What makes it approximately cylindrical near the source is the fact that it's emitted as a coherent wave from a circular surface that's much larger than a wavelength. ",
"Being a wave, it will start to ",
"diffract",
" at the edges. It will spread out. Close to the source, this diffraction will be negligible, but the spreading out will increase over distance. Far away from the source, the beam will behave like a spherical wave that has been emitted from a point source. It will spread out in a spherical wavefront, whose intensity falls with the square of the distance from the source.",
"In electromagnetism studies, this is known as ",
"near field and far field",
"."
] |
[
"Diffraction limited angular resolution",
"A red laser which starts at 3 mm has a minimum beam width of 100 arcseconds or 0.00048, meaning that at 1 km it has already spread to 48 cm. And this is assuming that the laser manufacturers did an absolutely perfect job with everything (they didn't)."
] |
[
"Yes, but the divergence angle can be reduced by increasing the width of the beam, e.g., by shining it through a wide aperture telescope. A wider beam from the transmitter gives a narrower beam at the receiver and vice versa, provided that we have a collimated beam at the transmitter."
] |
[
"Is there a way for humans to gather information faster than reading?"
] |
[
false
] |
With the advent of the internet and smartphones, we have access to an enormous amount of information. But with our fast-paced fun-filled lives, we don't seem to have the time to research everything we'd like to learn about. Has anyone heard of a device or technology that uses a different sense, outside of sight and sounds, that allows a faster 'download' of information?
|
[
"Interesting question.. But I guess it depends on what you define \"learning\" as. Reading is simply using our sense of vision to recognize symbols and lines on a page, and our brain applies meaning to them.",
"You could say that we \"learn\" not to touch a hot stove because after touching it once, our sense of touch tells our brain to pull back and we feel pain, and therefore have learned (hopefully) not to do it again. And that all happens much faster than reading does.",
"But yeah, I totally wish I could learn kung fu by plugging in a cable into the back of my head too man."
] |
[
"Sight allows for amazingly fast transfer of information if it's formatted correctly. Two-dimensional data is particularly easy to transfer in the form of graphs and charts. However, procedural knowledge is limited in transfer rate (actually limited to a speed much slower than typical reading speed) due to the increased amount of processing required. "
] |
[
"You might be interested in \"Decoded Neurofeedback\". Straight upfront; I don't know much about this field, nor I don't know how much headway has been being made in it recently.",
"That said, the basic premise is to upload skills directly into an individual's visual cortex using FRMI. As I understand it, if this works it would essentially provide the ability to copy skills from one individual to another.",
"There has apparently been at least one experiment showing promising results by Boston University.",
"Here is a wikipedia link:\n",
"http://en.wikipedia.org/wiki/Decoded_Neurofeedback",
"Also, no, the irony that this uses the visual cortex is not lost on me."
] |
[
"Why don't humans, unlike other animals, produce Vitamin C even though it is necessary for our health?"
] |
[
false
] |
Currently sick and drinking Emergen-C. It got me thinking that if Vitamin C is integral to our well being why are we one of the only animals, besides guinea pigs and other apes, that don't produce it internally?
|
[
"Because we ate so much fruit historically that losing the ability to create vitamin C didn't cause us any harm. If you go through the human genome, you can still see the mutated remnants of the same vitamin C producing gene that still works in our relatives.",
"Of course, it's probably a disadvantage nowadays with the advent of agriculture, since fruits with vitamin C tend to be less calorie dense than most of what else we cultivate, but evolution is short sighted like that."
] |
[
"it's an acid and it's essential but it's not an amine which is where \"vitamin\" comes from.",
"It's a fun and totally useless fact."
] |
[
"Modern humans don't manufacture vitamin C because we lost that ability much earlier in our evolutionary line, and have not regained that mutation since.",
"Humans, apes, and monkeys all share this deficiency as a heirloom from a common ancestor that developed a mutation that had fundamentally no effect on their survival because vitamin C was likely present in their diet."
] |
[
"Why is it hard to pull a magnet off a metal surface but so effortless to slide it across the surface?"
] |
[
false
] |
Playing with my name tag and it got stuck to my pen holder. I wasn’t able to pull it off but it easily slid off. I don’t get why a magnet doesn’t pull back to the original position when sliding.
|
[
"It's the same reason why a couch is difficult to lift but easy to slide across the floor: trying to lift the object means opposing its full mass, but sliding it only requires opposing its \"mass x coefficient of friction\", which depending on the materials involved can be tiny, which will result in far less force necessary than directly lifting. I'm treating magnetism the same way here because it's an attractive force like downward gravity."
] |
[
"The magnetic field creates forces that oppose the forces from your hand lifting the magnet up. But there's nothing opposing motion side-to-side besides friction. Friction along smooth surfaces can be modeled by taking the normal force of the object (in this case, the weight of the magnet plus magnetic forces pulling it towards the surface) and multiplying it by a number. That number is a friction coefficient.",
"For a lot of materials, including many smooth metal objects, the static friction coefficient is around 0.5 to 0.7. This is less than one, meaning it's easier to get your magnet moving sideways than it is to pull it off of the surface.",
"If there was a very high friction material wedged between your magnet and the metal surface (such as rubber), it would be much harder to move the magnet sideways than it would be to just lift it off."
] |
[
"Striction is not deliberately factored in since it behaves differently (ex: a piece of tape can pick an object up, but friction between two things cannot do that), but there is a bit of handwaving with the standard friction formula since it is partially determined by experiment so there is probably a bit of it factored into the coefficient of friction."
] |
[
"Why is the aurora borealis phenomenon typically only visible at higher latitudes?"
] |
[
false
] |
With recent solar activity I had read an article that showed this phenomenon visible farther south than normally seen and it got me wondering.
|
[
"That is where Earth's magnetic field is the ",
". The auroras are caused by solar winds being deflected strongly and ionizing parts of the upper atmosphere."
] |
[
"There are actually two auroras- the aurora borealis is in the northern hemisphere and aurora australis is in the southern hemisphere.",
"In general, the lights can only be seen within around 10 degrees of earth's magnetic poles. This is because the auroras are caused by charged particles that originate from solar wind. The vast majority of these particles are deflected by earth's magnetic field. Because of the shape of magnetic field lines, the charged particles are directed towards earth's poles, where they enter the atmosphere and collide with other particles, causing the lights."
] |
[
"Thanks!"
] |
[
"Why is the salinity of the worlds oceans not constant?"
] |
[
false
] | null |
[
"simple answer is saline water is denser than fresh water, and the cycle of evaporation to precipitation generates fresh water, which eventually ends up back into the ocean and due to density, it floats on top.",
"another cycle happens near the poles where cold saline water freezes and also differentiates freshwater from hyper saline."
] |
[
"Surface waters in ocean regions for which evaporation exceeds precipitation tend to increase salinity (the middle of the subtropical gyres, for example). Regions for which average precipitation exceeds evaporation become fresher (North Pacific ocean). Ocean currents slowly mix the salty and fresh regions so that a quasi-steady balance is reached."
] |
[
"You already have an answer to your specific question, so I’ll just add that even though salinity does vary in the oceans, causing water masses to have different densities (salinity and temperature control seawater density) so that they do not easily mix, there is still something about salinity which remains remarkably constant throughout the oceans. This is the relative proportion of the dissolved salts in the water relative to eachother. ",
"There are definitely departures from the relative proportions due to local conditions in certain areas, eg. at a river mouth where input of fresh water with a different ionic composition is added, or in a restricted basin where seawater cannot so easily mix with the oceans as a whole. But in open waters you will almost always have the same ratio of one dissolved salt to another (say the ratio of sodium to potassium for example) ",
". ",
"This is a result of the major ions which are dissolved in seawater all being well mixed in the oceans. That is to say, they persist as dissolved constituents in seawater longer than the overall mixing time of the ocean (which is about 500-1000 years) before they are passed on to the seafloor sediments or the oceanic crust. "
] |
[
"Most sites say cats become malnutritioned if fed only meat and never any \"cat food\". Is this a marketing scam, or how would wild cats have been able to survive in nature?"
] |
[
false
] |
Been reading about how one would provide a full nutritious plate to a cat without using super processed "cat food"s, and this always strikes me as weird (seeing as cats are obligate carnivores).
|
[
"Wild cats survive by eating animals. Not just what we call \"meat\" (muscle tissue), but organs, bones, entrails, and the contents of the digestive systems of those animals (mostly plant matter.) That gets them a lot more varied nutrition than just muscle tissue (which they do need to be healthy.)"
] |
[
"First, wild and feral animals don’t necessarily get the best nutrition. Feral cats sometimes only live a few years and succumb to diet/related disease. ",
"Second, it’s a misconception that they only eat meat. Obligate carnivore meant it must eat meat, not that it excludes other nutrient sources. The stomach contents of their prey are actually very important to their diet. They don’t necessarily need a lot of plant matter, but they DO get it in the wild. A lot of raw food proponents will still add supplements to account for other vitamins found in plants. ",
"Third, we’re kind of conditioned as a society to think mass produced = bad. But it’s really important to dig deeper. There’s a website (which I am struggling to find again) that actually surveyed the qualifications of nutrition experts at various cat food companies. Those boutique “grain free” or raw brands that look good on paper might consult someone with a masters degree in animal nutrition. The big commercial firms like Science Diet and Royal Canin have departments run by PhDs with a large staff of animal nutritionists. They have a much better grounding in science. ",
"Finally, there is an emerging problem with grain free pet food (disclaimer - it’s been a while since I read up on this). There is a firm link between grain free diets and heart problems in dogs (cats to a lesser extent, but there is still concern). Last I read, it’s not known if the cause is a damaging component of commercial grain free foods, or if it’s a nutrient deficiency in a grain free diet."
] |
[
"Cats in nature don't eat only meat, if by 'meat' you mean muscle. Cats eat almost all of whatever they catch, which includes bone, marrow, liver, brains, lungs, and other organs. Eating muscle alone would lead to malnutrition."
] |
[
"Are quantum dot solar cells all hype?"
] |
[
false
] |
There seems to be a lot of hype regarding nanocrystals/ quantum dots for solar cells. Could someone explain something to me? A lot of the cool effects like tunable bandgap and strong absorption come from the quantum confinement. Quantum confinement implies that the electrons and holes are confined to a very small space. This seems completely opposite of what you'd want to do for a solar cell, which is to move the generated electrons and hole out to contacts. If you enable movement of electrons and holes, you destroy the quantum confinement. If there's all of this hype out there for making super efficient and cheap solar cells using quantum dots, I'm obviously missing something. What am I missing? TLDR: Quantum dots confine holes and electrons to a very small space. Solar cells move electrons and holes. How do quantum dot solar cells make sense? Cross posted from :
|
[
"In the ground state, they are confined. In the electronic excited state (if they work), the electrons and holes should be mobile. This relies on there being a suitable donor or acceptor nearby to keep the process going."
] |
[
"\"In the ground state, they are confined. In the electronic excited state (if they work), the electrons and holes should be mobile.\" ",
"I completely agree. How would you excite those states? Thermalization (relaxation to the ground state by phonons) happens very quickly. I would think you'd have to apply a huge voltage to cause the carriers to tunnel out of the ground states, which is not what you want for a solar cell.",
"On the other hand, it has been recently demonstrated that it is possible to collect \"hot carriers\", carriers that haven't yet relaxed to the ground state, using TiO2 and PbS (maybe it was PbSe) QDs. With hot carrier collection, the question then becomes, \"Why wouldn't you just use a higher bandgap absorber instead of trying to collect hot carriers?\" The only advantage that I see is if you collect BOTH the hot carriers and colder carriers (carriers that have already lost some energy or carriers that were created by less energetic photons), but an energy selective contact like TiO2 won't be able to do that."
] |
[
"I'd think that you would have your quantum dots on a substrate that would allow for electron transfer. If they're really worth using, a monolayer of dots should be all that you need. ",
"I'm not sure what you mean by \"exciting\" the excited states. The challenge in all photovoltaics has been harnessing the energy of the excited state before it finds its way back down to the ground state. It's all a probability game there, and it's not always predictable what will work for a particular electron donor or acceptor. ",
"There are lots of examples of these types of solar cells, called ",
"dye-sensitized solar cells",
". The dye is generally only concerned with harvesting light, and that's the role that the quantum dot is filling. Where the electrons go from there is up to the cell design (its usually TiO2). What I can tell you about these is that the best dyes we have today are made using ruthenium compounds, and they're hella expensive. If the quantum dots can be made cheaper and still work, that's great (actually, for a broadband absorption, you wouldn't need to worry about making the dots monodisperse, which would save a lot of money in production)."
] |
[
"Can being crushed by magnetic field?"
] |
[
false
] |
Saw this youtube and I'd really like to know the physics behind it.
|
[
"This effect can be replicated at home (less impressively but more safely) with a fridge magnet and a sheet of aluminum. Just set the aluminum at an angle and let the magnet slide down it. You will notice that the magnet slides more slowly than if you replaced the aluminum with wood. ",
"Here's what is happening. The changing magnetic flux through the aluminum induces eddy currents in the metal, which in turn induce a magnetic field that interacts with that of the permanent magnet.",
"Same principle in the video, only here the changes in flux density (resulting from the large current spike through the coil associated with the discharge of the capacitor) are big enough for the forces to distort the aluminum."
] |
[
"You can also drop a cylindrical magnet through a copper pipe. It will fall very slowly."
] |
[
"Cf quartershrinkers. "
] |
[
"Are there any studies on the long term health effects of very light smoking (1 or 2 cigarettes per day)?"
] |
[
false
] |
I've been a light smoker for about 10 years. I keep it around 1 or 2 per day and usually stop completely during the winter since I don't smoke indoors and it gets too cold outside where I live! I was looking at studies on light smokers but it's usually defined as way more than 1-2 per day. Sometimes it's less than 20, or less than 10. That's not my definition of light smoking.
|
[
"Cancer is believed to be a ",
"stochastic",
" effect. This means that the probability of getting a disease is proportional to your exposure to cigarette smoke. So a light smoker would have a lower chance of getting cancer but not a zero chance, ie there is no safe amount of tobacco smoke that won't give you cancer. It's like driving a car, someone who drives for hours every day is more likely to be in a car crash than somebody who drives for 10 minutes once a week. However, a car crash isn't certain or impossible for either group.",
"Other long term health effects of smoking such as high blood pressure, emphysema, chronic bronchitis etc are deterministic. For these, there is a minimum amount of smoke needed to cause damage and the damage increases with exposure to tobacco smoke. You can smoke lightly and be fairly confident you won't get these problems."
] |
[
"I found a Norwegian study with n>40,000:",
"\"Results: Adjusted relative risk (95% confidence interval) in smokers of 1–4 cigarettes per day, with never smokers as reference, of dying from ischaemic heart disease was 2.74 (2.07 to 3.61) in men and 2.94 (1.75 to 4.95) in women. The corresponding figures for all cancer were 1.08 (0.78 to 1.49) and 1.14 (0.84 to 1.55), for lung cancer 2.79 (0.94 to 8.28) and 5.03 (1.81 to 13.98), and for any cause 1.57 (1.33 to 1.85) and 1.47 (1.19 to 1.82).",
"Conclusions: In both sexes, smoking 1–4 cigarettes per day was associated with a significantly higher risk of dying from ischaemic heart disease and from all causes, and from lung cancer in women. Smoking control policymakers and health educators should emphasise more strongly that light smokers also endanger their health.\"",
"So, among male light smokers, we see a 2.74x and 2.79x increase in heart disease and lung cancer deaths, respectively."
] |
[
"You always have a non-zero chance of getting cancer. But what I think you meant was a lower but non zero increase in your chance to get cancer."
] |
[
"Why (in technical terms) the video cards are the best for Parallel Computing?"
] |
[
false
] |
What the GPU's and memorys from Video cards have, that make them good for that?
|
[
"Modern GPUs are best described as vector processors with specialized instructions for graphics rendering. A vector processor is very much like a CPU (actually, it ",
" a type of CPU in some architectures), but it is designed to perform the same instructions (or sets of instructions) on multiple pieces of data.",
"Think of it like this: Imagine a simple problem where you wish to multiplay a number (let's say 5) by a set of numbers (say, 50000 numbers) and produce a list of the results. What would be faster? Get one guy who's ",
" good at math to do them in sequence, or 500 4th graders who maybe aren't so hot at math, but are absolutely capable of doing ",
" task in a reasonable amount of time, dividing the work among them.",
"Obviously, the latter. Even though our math wizard will perform these multiplications ten to a hundred times faster than the average fourth grader, he won't be able to keep up with the fact that there are 500 of them doing it.",
"However, there are situations in which this technique does not grant you performance benefits. In fact, the technique may even slow you down.",
"Imagine you have a list of 100 numbers, and you want to perform a complex operation on them, with the caveat that the next number in the sequence relies on the results of the last number in the sequence:",
"There are clever ways that this can be parallelized, but for the sake of argument, lets say we can only use a naive implementation.",
"The math wizard will get through this problem way faster than your pool of 4th graders (and may even know a trick or two to optimize the process). In this case, your faster, more complex, single core would do a better job."
] |
[
"Games use the GPU for more than graphics, but not much more. There are GPU implementations of integration engines for physics engines, for instance.",
"A good rule of thumb for determining if a vector processor is a good choice for an operation is, does this operation need to wait for any other operation? If so, then you should do it on the CPU. The CPU is really good at waiting for things (with context switching, hyperthreading, and interrupts). You GPU is ",
" good at this. When you have software that spends lots of time waiting for things (as most software does), then expect the software to run ",
" as fast as a single core in your GPU, that is to say, very, very slow.",
"Your English is OK. It's better than many \"native\" English speakers on the internet anyway :-P"
] |
[
"Thank you for you backup!",
"But, may i ask one more thing =p? You said that the GPUs good for operations that are repeated many times, but they arent good for complex operations, and i can presume that CPU'S are good for that.",
"May question is? In a game for example, the GPUS only process grafhics, because graphics aren't complex operation, but only a \"hard-working\" operation? And the IA and I/O tasks, who process this, the CPU or both? ",
"Sorry for the English, just a Brazilian student of Computing area.",
"Thank You!!! =D"
] |
[
"Why do men tend to only go bald on the top of their head and not on the back or sides?"
] |
[
false
] | null |
[
"Citation? This is all insanity. ",
"Male baldness is thought to be predominantly caused by hormones called androgens. The hair follicles on the top of the head have more androgen receptors.",
"The hormonal cause of male pattern baldness is demonstrated through the fact that people with hormonal deficiencies or disease, especially those which prevent or inhibit a person from going through puberty, do not ever suffer any hair thinning or baldness in the typical pattern as is seen in those who do.",
"Cite"
] |
[
"Citation? This is all insanity. ",
"Male baldness is thought to be predominantly caused by hormones called androgens. The hair follicles on the top of the head have more androgen receptors.",
"The hormonal cause of male pattern baldness is demonstrated through the fact that people with hormonal deficiencies or disease, especially those which prevent or inhibit a person from going through puberty, do not ever suffer any hair thinning or baldness in the typical pattern as is seen in those who do.",
"Cite"
] |
[
"What in the fuck did I just read? I actually can't stop laughing this is hilarious. "
] |
[
"Does the use of LSD cause anxiety, OCD, or other neurotic tendencies latter in life? What about other \"entertainment\" drugs kids use - are there any studies that tie them to psychological problems later in life?"
] |
[
false
] |
After seeing the question about Marijuana being linked to schizophrenia, I wanted to ask if there is any scientific research linking LSD to neurotic tendencies when people get older. What about other recreational drugs like speed, etc? Anecdotally, most of my childhood friends who were acid-freaks have now have major OCD or anxiety issues. Most have to take Ambian or something like that to calm them down enough to function.
|
[
"There is very little formal research into the long term effects of LSD.",
"The work that was done while it was legal suggests that it has significant potential as a tool in psycho-therapy. That it can be a significant aid in overcoming addictions. And that it is pretty useless at creating drug fuelled super-soldiers.",
"Anecdotal evidence suggests that it may unbalance some people (as with cannabis - degree of prior conditions may be relevant). \"Flash-backs\" might be a form of PTSD.",
"Anecdotal evidence can be heavily biased. e.g. it might be that mentally unbalanced people are more likely to seek out drug experiences through existing dis-satisfaction with life.",
"There are a vast number of 'entertainment' drugs (to the point where it may be easier to list drugs that aren't used for entertainment). Some are also prescription drugs and have (reasonably) well understood short and long term effects. Knowledge on illegal drugs varies.",
"As such, you will need to narrow your parameters somewhat.",
"wiki on recreational drugs."
] |
[
"My understanding is that there are no physical effects from LSD that can cause any type of permanent brain damage. From a chemical point of view LSD is extremely safe.",
"The hallucinogenic LSD experience can be profound. Intense.",
"In the same way that any profound, intense experience can be life changing - so can the experience while under the influence of LSD.",
"For some, it is a Road to Damascus experience. For others it unbalances them from the tightrope they've been walking. For most it is merely interesting."
] |
[
"My understanding is that there are no physical effects from LSD that can cause any type of permanent brain damage. From a chemical point of view LSD is extremely safe.",
"The hallucinogenic LSD experience can be profound. Intense.",
"In the same way that any profound, intense experience can be life changing - so can the experience while under the influence of LSD.",
"For some, it is a Road to Damascus experience. For others it unbalances them from the tightrope they've been walking. For most it is merely interesting."
] |
[
"I Can't Figure Out Climate Change"
] |
[
false
] |
Ok, first of all, no, I am not some right wing lunatic that thinks global warming/climate change is a plot by the filthy liberals to take my guns or something. I just have a few questions that I'd be too embarrassed to ask to real life friends. 1.) I 100% agree that both the world is getting warmer and that the carbon dioxide level in the air is going up. Humans obviously have caused this increase in carbon dioxide. My question is: How do we know this increase in carbon dioxide is the cause of the rise in temperature? Is the answer just "greenhouse effect" and that's it? Do we know that holds on a huge scale, like, well, the earth? 2.) From the statistics I have taken in both high school and college, it has been repeatedly slammed into my head that extrapolating data/models into the future is an very inexact science, at best. How do we know the current trends in temperature will continue? Carbon dioxide will continue to increase, for obvious reasons, but if it is causing the warming, how do we know it won't hit diminishing returns? 3.) I keep hearing that the line of no return for doomsday temperature increase is six degrees Celsius. Could someone explain why that would be so damaging to the health of the planet/humanity? Any answers would be appreciated. Sorry if they're dumb questions, I know this is an old-ish topic.
|
[
"RealClimate.org",
" and ",
"SkepticalScience.com",
" have well researched answers to most climate questions so I would mostly just point to places at those sites.",
"The planet is not warming up uniformly. For me, the most compelling evidence is the many detailed signatures of global warming predicted by models have now been observed: ",
"empirically observed fingerprints of anthropogenic global warming",
". If the warming was caused by something other than greenhouse gases (such as changes in solar activity, volcanoes, El Nino), it would be characterized by a different set of fingerprints.\nThe detailed changes that have been observed in the structure of the atmosphere and ocean are consistent with greenhouse gas induced warming and inconsistent with all other postulated mechanisms. ",
"Future predictions are not based on extrapolating current trends. Rather, future predictions of temperature are based on running climate models with concentrations of greenhouse gases expected in the future. So the your question really reduces to ",
"How reliable are climate models?",
". See also the ",
"page at the IPCC.",
"In summary, confidence in models comes from their physical basis, and their skill in representing observed climate and past climate changes.",
"I'm not sure why some people talk about 6° as opposed to 5° or 7°. There are several concerns. One is that we reach some ",
"tipping point",
" which shifts the climate into a different regime. Once we pass a tipping point, even if we stopped burning all fossil fuels, the climate would not return to its present state for thousands of years. Another concern is agriculture. It would be very challenging to match today's agricultural output on a a planet 6° warmer. Finally there is the ice. It is probably already the case that Greenland is going to melt over the next few hundred years which will create 6 meters (20 feet) of sea level rise. If the temperature increase is enough to also melt Antarctica that will add another 60 meters (200 feet) to the oceans. I'm not sure what temperature increase will result in melting the Antarctic ice cap but I hope we never exceed it. ",
"edit: formatting and wordsmithing."
] |
[
"We can measure absorption of infrared radiation by carbon dioxide. We can put it in a tube, shine an IR light in one end, and measure the intensity of the light making it to the other end. Some will have been absorbed and re-emitted back towards the light source. I can't think of a reason why these properties wouldn't hold on the scale of the Earth. The warming we expect from CO2 alone is rather modest. However, we expect positive feedbacks from water vapour and clouds to amplify this, which means that for a doubling of CO2 we expect about 3-4 K of warming (this is climate sensitivity and it could be rather higher or lower than this - this is just a central estimate).",
"I agree that extrapolation is pretty suspect. However, if we establish that CO2 causes warming and expect CO2 to increase in the future, we expect more warming in the long term. Of course, the Earth is perfectly capable of warming up and cooling down without our CO2 emissions, so we expect 'wiggles' on top of this warming trend. We can establish this without looking at climate models. Climate models solve real physical equations - so it's not statistical extrapolation. On the diminishing returns point - we in fact will hit diminishing returns. We can work out from lab measurements that absorption by CO2 increases as the logarithm of the concentration change. This means that doubling CO2 concentrations should have the same warming effect. That is, 300-600 ppmv (a 300 ppmv increase) provides the same warming as 100-300 ppmv. There is a point at which the effect saturates, and CO2 doesn't cause more warming, but that's at CO2 concentrations ",
" higher than we have today. Again, we can calculate all this from lab measurements.",
"Any temperature threshold is pretty arbitrary. For example, the '2 degree' limit often talked about isn't based on any science of topping points. It's just a useful number to target. We expect to have trouble dealing with a climate rather different to the one we are currently adapted to. This is the initial impact of global warming, a kind of 'inconvenience'. No disasters, but lots of costly low-level damage and having to modify our societies. In a 6-degree warmer world the Greenland ice sheet would probably melt over a few centuries, giving us several metres of sea level rise. The shifts in precipitation zones would leave much of what is now densely populated (e.g. Mediterranean) essentially desertified. There are genuine tipping points in the climate system, but they all have quite different thresholds, so any single number target is one of convenience rather than scientific fact. There's some good discussion of tipping points (including my summary of the main ones) ",
"here",
".",
"Hope that helps! Let me know if something doesn't make sense."
] |
[
"My question is: How do we know this increase in carbon dioxide is the cause of the rise in temperature?",
"Carbon dioxide gas absorbs infrared radiation. So do other gases- water vapor, for example. But anthropogenic production of carbon dioxide has demonstrably increased ",
"the concentration of atmospheric carbon dioxide.",
"Now, ",
"carbon dioxide absorbs energy based on how the bonds react with incoming energy.",
" The absorption is very specific. Aaaaand I'm not finding one just right now, but absorption of infrared radiation depends upon concentration so- more carbon dioxide = more energy absorption."
] |
[
"How can we be sure of the precision and accuracy of modern measurement tools?"
] |
[
false
] |
Suppose I have defined a 'redditmeter' [rm] in some acceptable way (that is - I can always know that this 'thing' that I measure is indeed rm units in size). After a few months, a new way was invented to measure 0.5rm, so on so forth - we get to the smallest scales. I logically conclude that this process is a very crude way of what happened in the way we humans measure things like length, weight etc. But how can we be sure that the scales we measure today are actually accurate? if we can measure 0.5rm with 99% accuracy, then measuring 0.25rm might have even less accuracy, going all the way to 1*10 rm. How can we know that our measurement tools are actually acceptably precise? Or to put it in another words - How do we check our most modern and precise measurement tools? Thank you for your current attempts of answering, but my question wasn't how can we be sure that a kilogram is a kilogram. To clarify furthermore - How can we be sure that the most modern measurement device actually measures with a good enough precision and not with it's measurement fault being 50% of accuracy (50% of times or 50% of given value).
|
[
"Currently, most units of measurements are derived from fundamental physical properties. For example, the meter is defined as the distance that light travels in a vacuum in 1/299792458 seconds. There is no ambiguity or inaccuracy in this definition, because it's defined relative to an unchanging constant of the universe. ",
"If you look up various other units, you'll see that they are defined in this same sort of way. This was done to avoid any confusion as to the accuracy or measurement issues with picking a set of units. "
] |
[
"The second is the duration of 9,192 631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom",
"So, you have an exact definition there. This allows derived units to be exact as well. "
] |
[
"National time standards like NIST and the Naval Observatory use dozens of clocks and statistical methods to arrive at the best \"average\". The difference between the standards is quite small and their stability meets our current needs. "
] |
[
"How does a CPU decide which instructions use which RAM addresses? (In terms of digital logic)"
] |
[
false
] |
I've spent a small amount learning about digital logic to further my understanding of computers but 1 thing I can't really understand is how the computer decides that RAM address X will be allocated for program Y and then after processing other instructions can come back to address X and can still associate it with program Y.
|
[
"It doesn't.",
"When the CPU powers on it's hardcoded to run some code from somewhere. x86 for instance, will start executing whatever happens to be at address FFFF:0000, which is where the BIOS code is located. The BIOS initializes some hardware and tries to find a disk to boot from, loads the boot sector from there and executes it. Then the OS starts up.",
"Processes are all up to the OS. While the CPU certainly has functionality to help with multitasking, and the architecture places some constraints on things (eg, on x86 VGA video memory is at segment A000, so you can't go loading programs there), it's really up to the OS to decide how to handle multitasking (if at all), and how to allocate memory to different programs and how to keep track of all that."
] |
[
"This question touches on many aspects of modern computing systems. I'll try to address a few:",
"The addresses used by each instruction are either fixed at a constant value, or drawn from another location that has the desired value. For example, one instruction might say \"write contents of register A to the address contained in register B\". (",
" are the small memory locations used to store intermediate results by the processor.) So in these cases, the CPU doesn't decide where to place the data --- the program tells it instead.",
"Physically, addresses map to locations in a DRAM chip inside your computer. You have multiple DRAM chips, and each contains a fixed subset of addresses. Every time you access address, say, 1039249, the CPU goes to the same physical location. There is no ambiguity here.",
"...Except that modern processors have \"virtual memory\" and \"physical memory\". Virtual memory is the address space seen by the program, whereas physical memory is the addresses actually used to access the DRAM chips. They are kept separate so that each program can run without worrying about what other programs in the system are doing. However, again the CPU isn't deciding this. The operating system is responsible for deciding which parts of virtual memory go to which parts of physical memory. The CPU simply takes what the OS decides and uses it to translate the virtual address into the physical address. There are possible issues that arise from this --- what if two virtual addresses point to the same physical address? --- but they have been solved in modern processors.",
"Most pertinent to your question, the processor also keeps a ",
" of memory. This is because main memory is very far away: accessing a DRAM chip means going off the processor, through the bus, and reading from slow DRAM cells. It's much faster to keep that data, once its been read, on the processor itself. However, once this is done, the processor is indeed responsible for tracking where each address is and making sure that it keeps the data consistent with memory and between other processors. (This is called ",
".) The processor does so by keeping ",
" along with the data. The tags tell the processor which memory address each piece of data corresponds to. Essentially, the cache is just a familiar key-value store, where the address is the key (stored in the tags) and the memory contents are the data.",
"If you'd like more information about any part of this, please ask. This is a big of a rough-shod summary of a lot of different ideas."
] |
[
"TLDR: What instruction goes where, and how it gets there, is a concern of software, not hardware.",
"Memory allocation and separate programs is more of an OS-level thing than a hardware-level thing.",
"The CPU pretty much has exactly one instruction address hard coded inside it, called the ",
". This address is the initial value of the instruction pointer / program counter register when the external hardware activates the CPU's reset pin [1]. As ",
"/u/dale_glass",
" notes, on x86 the reset vector is FFFF:0000.",
"The system board designer is also responsible for including external hardware (usually a ROM chip) that will respond to a bus request for the reset vector address and contain a useful program.",
"The \"meaning\" of RAM addresses depends on what the ROM program does. For PC's the ROM initializes the hardware and loads the first sector (boot sector) of the hard disk into a standard location in RAM, then jumps to the beginning of the code area of the boot sector. The boot sector typically contains a program that instructs the BIOS to load more sectors (boot loader) into some hard-coded location in RAM, then jump to the boot loader. The boot loader typically contains a program that loads an OS kernel from disk and jumps to it. Then after initialization the OS kernel (on UNIX-like systems such as Linux or Mac) runs the first user program, init. Then init launches other user programs according to the system's startup scripts. So deciding which program goes where is decided in software: the memory allocation routines in the boot sector, boot loader, and kernel. Hardware just obeys instructions from the software (\"load 4096 bytes from the disk starting at sector 073A62 to address 79410000, then jump to address 79410000\"). ",
"I've sort of glossed over certain CPU functionality that makes writing multitasking OS's easier and more secure (in particular ",
" and ",
" functionality).",
"[1] The system / motherboard designer is responsible for including external electronics to cause the reset pin to be activated on power-up or reboot."
] |
[
"Does scratching a (non-contagious) rash, such as poison oak, help or hinder healing?"
] |
[
false
] |
I recently came in contact with poison oak and it itches to high heaven and scratching it is almost the greatest feeling ever before it starts itching again. I understand that itching helps bring more blood to the area. Aside from itching so much that you break the skin and cause more damage, does scratching speed up the recovery?
|
[
"The rash caused by poison oak is due to a T cell mediated reaction to the toxin urushiol. If you were recently exposed, scratching would make it worse because you are more likely to spread the toxin to other parts of your body. Once the toxin is removed and you're left with the rash, scratching wouldn't do anything to speed up recovery because the problem isn't lack of immune response, but in fact an undesired effect of your immune system. Scratching could also make things worse by introducing bacteria into the wound possibly leading to a secondary infection."
] |
[
"More blood to the area is bad. The poison oak sap soaks into your skin and shreds your blood vessels causing them to leak plasma. Scratching won't spread the rash but will cause more/bigger pustules. ",
"It take 7-14 days to go away. Cold-packs have been shown to speed recovery in some individuals. ",
"Your body is not repairing the damage, it is waiting for it to grown out. Nothing will heal it but time."
] |
[
"I'm mostly guessing, but maybe it helps against something like a bee sting. If the stinger is still stuck, it will pump more and more poison into you, Scratching might dislodge it."
] |
[
"Do bugs have muscle tissue?"
] |
[
false
] |
How do insects or arachnids move their legs?
|
[
"Yes, they do have muscle tissues. However, their muscles are slightly different from mammals. Insect muscles do not need to be constantly oxygenated to function. They mostly just need sugar that comes from the hemolymph (insect blood), and can get away with less oxygen. In the laboratory, we can perfuse insect muscles in hemolymph-like saline for hours, and they can still move when stimulated. ",
"Insect and arachnids move their muscles similar to how we move ours. Both arises from the firing of motorneurons that leads to muscle depolarization and contraction. There is a fine difference though, in that insect neuromuscular junctions are mostly glutamatergic while mammalian ones are mostly cholinergic (i.e. they use different neurotransmitter for signals)."
] |
[
"You're on the right track about \"much bigger scale\". There are good reasons why our muscles need to be constantly oxygenated. Our muscle size is gigantic comparing with insects. The strength we can muster from our muscles is much larger, so our muscles need to obtain much more energy than insects muscles to function. So practically, we can't really employ anything from insect DNA. If our muscles behave like insect muscles, we'll probably only have the strength of a grasshopper. ",
"Yet, we do have a \"buffering system\" in our muscles. When our blood is incapable of delivering sufficient oxygen during exercise, our muscle cells turn to \"anaerobic respiration\". This is an inefficient method of obtaining energy. It can only provide about 5% of energy per sugar molecule released by aerobic respiration. So a ton of sugar molecule is wasted. But it lets us get that extra power very quickly while we are still lacking that oxygen. The downside is that anaerobic respiration leaves lactic acid as a byproduct instead of just water and CO2 from aerobic respiration. When lactic acid builds up, we feel pain/fatigue, and our muscles cannot function efficiently. This is why we get muscle pain after intense exercise, and we feel the lack of strength during that period. Yet, moving the painful muscle actually helps its recovery, because it stimulates blood flow to carry that lactic acid away. "
] |
[
"It's kind of a dumb question, but what do you think would happen if we did some DNA engineering and placed insects' genes for muscle tissues in our DNA? It seems advantageous that our new muscle would need much less oxygen. But then again, I suppose insect muscles wouldn't work in a much bigger scale."
] |
[
"Can a bee or ant colony survive without a queen?"
] |
[
true
] |
[deleted]
|
[
"Only queens reproduce. However, the death of a queen is not the death of a colony, necessarily: ",
"National Geographic",
"If the queen dies, workers will create a new queen by feeding one of the worker females a special diet of a food called \"royal jelly.\" This elixir enables the worker to develop into a fertile queen."
] |
[
"How do they choose the worker? Is it random? Do they chose only one or do they feed them all jelly till one is ready and then she executes the others, like african bees or Queen Elizabeth I?"
] |
[
"It really depends on the which specific ant or bee species you are asking about. Many species are monogynous, meaning they only have one queen. For some of these species, if the queen dies, thats it. They will not produce or acquire a new queen. The colony will eventually die out. For some species, they can actually make a new queen, as Wrathchilde stated. Other species though can be polygynous, meaning they have more than one queen to begin with. The species I work on are monogynous, so I don't know much about polygynous species other than that they exist.",
"EDIT: Oh, and to really get at your question. All a queen really does in colonies like these is lay eggs. So the colony can certainly survive without her. But no new workers will be produced. So as the older workers die off, the colony will start to decline until it eventually dies."
] |
[
"If you could survive the molten hot lava of a valcano, if you went in it and went down would you reach the centre of the earth."
] |
[
false
] |
[deleted]
|
[
"The simple answer is a big no.",
"The detailed answer is that volcanoes erupt when a batch of magma within a chamber int eh crust overpressurizes. That can be due to a number of factors, but at best the continuous fluid magma will not penetrate more than a few kilometers into the crust. Once you're below the high-level magma chambers the magma supply comes up in batches through an often very complex feeder system. A batch comes up, and magma resolidifies int eh channel through which it travelled, leaving nothing but solid rock. A new batch can only come up when it has enough internal pressure to crack the overlying rock to grnerate a new (or re-open an old) transport fissure.",
"Magma itself is either generated in the lower crust, or at the very base of the crust from partial melting. The mantle itself is a solid - even where melting is occurring, the melt fraction will only be a few percent. Everything from the base of the crust down to the base of the mantle is solid rock. The outer core is again fluid, but we're talking molten high pressure iron at several thousand degrees C.",
"As far as building somethign to travel down the throat of a volcano there's a number of massive problems. The first and most significant is building anything that can survive and do anything useful in 1000 degree C temperatures. Then it has to be denser than lava in order to sink. Assuming we're trying to go down into a nice low energy eruption like Erta Ale you need it to be 5 times denser than water. At least. And a method of getting said massive and incredibly heavy object to the crater of a remote volcano. And a method of controlling and communicating. And a way of travelling down to depth when the magma you're travelling through is moving upward.",
"So no, we've not done it, and there's no feasible way to construct such a machine with any tech we have or are likely to have in the forseeable future."
] |
[
"Have we found anyway to stop a volcano or even make one dormant? Whether it be earily stages that we catch it or days before it erupts?"
] |
[
"The enrgy involved in an eruption is orders of magnitude greater than we can do anything about with present technology. The energy ofa volcano is due to the great depth at which the magma is generated, and physical buoyancy, coupled with expansion and depressurisation effects. I't simply not something we have the tech to even think about attempting."
] |
[
"Is it possible for 2 total strangers be more genetically similar than 2 siblings?"
] |
[
false
] |
I recently came across a photo collection of strangers who look almost identical, which left me with 2 questions: When 2 people look alike does that mean they are genetically similar, or is it just an anomaly that they ended up looking the same? Is it possible for 2 total strangers (regardless of looks) to be more genetically similar than 2 siblings or relatives? If so, how often does this occur in nature? If not, why not? Thanks! :) EDIT: I was in no way implying any specific definition of "sibling" versus "stranger", nor referring to separated twins (still genetic siblings and social strangers), nor implying that adopted siblings aren't truly siblings. Sorry for any unintentional offense.
|
[
"Possible? Certainly. Probable? Highly unlikely. They ",
" have to be in the same family lineage, though the odds would still be astronomical even then. ",
"Basically, imagine a parent has two kids. With a crazy toss of the dice, one parent (say, dad) passes one half of his genes to one child, and the ",
" alleles to the other child. Bear in mind that ",
"all humans share 99.9% of their DNA",
" so the only part of the passed DNA that would have to match is that remaining 0.1%. This helps the odds, though they're still pretty slim.",
"They both separately have kids, and those kids, through another crazy toss of the dice, also get ONLY the genes directly passed by the original father (their grandfather). ",
"Do this for a few generations and you could have a male and female that are so far separated that they don't even realize that they're related. They meet, make beh-behs. Now, same crazy toss of the dice and their offspring now gets both halves of the alleles that were initially passed by the original ancestor. ",
"In this one in a bagazillion situation, you would have a genetic \"clone\" of the original. So depending on how \"closely\" you'd want them to be similar for the purposes of your question, people vaguely in the same lineage ",
" be able to match up better than their direct family members. (This is why DNA testing always says it's \"99% accurate\". They have to leave themselves an \"out\" for the near impossible \"what-if\" scenarios.)",
"Edit: changed the word \"trillion\" coz too many nerds were getting hung up on it."
] |
[
"They ",
" have to be in the same family lineage, though the odds would still be astronomical even then. ",
"Wait... this kinda deflates the original proposition by narrowly redefining things, but also muddies it by undefining things.",
"Every living thing is to some extent or another in the same family lineage, so far as we can tell.",
"I disagree that it is ",
" that 2 \"total strangers\" (I will define as having equal or greater than average ",
" than the general population) would be \"more genetically similar than 2 siblings or relatives.\" IE, I suggest it is ",
" that 2 total strangers* would have more closely matching DNA than 2 siblings.",
"2.a. For one thing \"Total Strangers\" are actually somewhat related. The ",
" is pretty high compared to the possibility of genetic isolation in general animal populations. ",
"See Also",
"2.b. For a second thing, even if humans were more dispersed in genetically interacting population (more highly isolated reproductive populations) there would still have to be enough commonality of genome for 2 individuals to produce viable offspring. Otherwise they would be considered separate species. So, no matter what there will be at least some portion of the DNA between \"Total Strangers\" that must be similar enough to count both as a single species. (Caveat that it is possible that genetically unlike species could swap genetic material successfully, but that is beyond this discussion probably).",
"2.c. Even if 2.a and 2.b weren't true, one could consider that the genomes of humans are of finite length and composition. There will always be ",
" chance of accidental similarity out of chaos, not ",
" chance as your words \"would have to be\" describe.",
"As to the OP's first question:",
"When 2 people look alike does that mean they are genetically similar, or is it just an anomaly that they ended up looking the same?",
"It generally means there is a high likelihood that the observable similarities (phenotypes) reflect genetic similarities (genotypes), but there isn't usually anything absolute about this on general principle as genotype =/= phenotype. Genes are code that may or may not get expressed depending on myriad factors of the organism's development (embryology), environment, etc.. Some genes require other genes to be turned on in order to be expressed, for example.",
"On the other hand, some identical or similar appearances could be arrived at through different sets of genetics running through alternate expressive pathways. Like how you could have 2 Chess strategies that under certain conditions would actually end up using the same moves. The observable effect would be indistinguishable in that particular game, but change the circumstances and the underlying strategies would be revealed as actually different.",
"Also, some of the observed similarities could be highly genetically dependent while others could be less so, meaning that the factors that would account for you saying \"They look similar\" could contain both genetically-rooted similarities and more genetically amorphous morphology. For example, perhaps cheek bone angle is highly genetically dependent, but skin tone can be arrived at through tanning or melanin, etc.. While it's easy to understand that skin tone is maleable some morphology you may assume is genetically determined may be as discussed above: Existing somewhere in the relationship between genetics and gene expression, environment, and the potential for convergent phenotypes to arise from various genetic determinants.",
"Hope that helped."
] |
[
"Good answer, but FYI, 3 billion is the haploid genome number, so the estimate should actually be 4"
] |
[
"How do most antidepressant drugs cause weight gain?"
] |
[
false
] |
Do they make us eat more? Does it change the metabolism? Can they be used in anorexia?
|
[
"The mechanism of weight gain by antidepressants is still under study, but can be explained by the antagonism effect on the histamine-1 (H1) and serotonin 5-HT2C receptors, and the disruption of leptin signaling. The evidence is strongest with histamine-1 antagonism. ",
"Histamine-1 Receptor:\nBlockage of this receptor is shown to increase carbohydrate craving and intake. Tricyclics, antipsychotics, monoamine oxidase inhibitors (old-school antidepressants), and mirtazapine (Ki=0.14-1.6, very high affinity) have a large degree of H-1 antagonism. ",
"Serotonin 5-HT2C Receptor:\nAntagonism of this receptor leads to increased appetite, though may result in acute, transient weight loss. Fluoxetine is observed to have this effect.",
"Leptin Hormone:\nValproate and lithium are observed to block the effects of leptin, a hormone that helps suppress appetite. ",
"References:\nAbosi O, Lopes S, Schmitz S, Fiedorowicz JG. Cardiometabolic effects of psychotropic medications. Horm Mol Biol Clin Investig. 2018",
"Ricken R, Bopp S, Schlattmann P, et al. Leptin serum concentrations are associated with weight gain during lithium augmentation. Psychoneuroendocrinology. 2016;71:31-5."
] |
[
"Kinetics, transport, and metabolism of macromolecules are altered. If the drug or toxicant changes the pathway so that more “stuff” goes into the fat cell rather than going into the liver or muscle to be broken down and used, it will promote weight gain over the long run.",
"As an additional example, say we transiently knocked down your expression of the CYP1A2 gene, a metabolic enzyme. Now when you drink coffee, you’ll feel stronger/longer effects from the caffeine because you can’t get rid of it it as quickly.",
"It’s the same thing with weight gain but more complicated in the mechanisms involved.",
"And by the way, I didn’t get a PhD just to have random people on the internet tell me I’m wrong about the field I’m an expert in."
] |
[
"Kinetics, transport, and metabolism of macromolecules are altered. If the drug or toxicant changes the pathway so that more “stuff” goes into the fat cell rather than going into the liver or muscle to be broken down and used, it will promote weight gain over the long run.",
"As an additional example, say we transiently knocked down your expression of the CYP1A2 gene, a metabolic enzyme. Now when you drink coffee, you’ll feel stronger/longer effects from the caffeine because you can’t get rid of it it as quickly.",
"It’s the same thing with weight gain but more complicated in the mechanisms involved.",
"And by the way, I didn’t get a PhD just to have random people on the internet tell me I’m wrong about the field I’m an expert in."
] |
[
"If Planck length is the smallest length possible, then isn't the smallest volume possible 1 cubic Planck length? Does this mean that the universe is made of tiny cubes?"
] |
[
false
] | null |
[
"Contrary to what you often read or hear, the Planck length is not the smallest length possible.",
"The Planck length is part of a system of units called Planck units or natural units. In this system, a number of commonly used constants of nature are set to 1, for ease of calculations (the constants drop out of equations when they're rescaled to Planck units, making equations easier to read and manipulate).",
"In the system of Planck units, the base unit for length is the Planck length, just like the meter is the base unit for length in the SI (Système International, the default set of units we all know and love (except Americans)).",
"The Planck length is, in some theories in physics, close in value (within a factor 10) to notions such as the shortest measurable length, but there is no indication that space is discretized in Planck-length-sized blocks."
] |
[
"There was actually an experiment recently that, amongst other goals, showed whether the universe was broken into Planck sized \"pixels\" or if it was continuous. Here's the wiki page: ",
"https://en.wikipedia.org/wiki/Holometer",
"And the relevant text:",
"\"A new result of the experiment released on December 3, 2015, after a year of data collection, has ruled out Hogan's theory of a pixelated universe to a high degree of statistical significance (4.6 sigma). The study found that space-time is notquantized at the Planck scale.[10]\""
] |
[
"Just to add a little, even if there were some fundamental discretization of spacetime it ",
"wouldn't have to be cubic",
"."
] |
[
"Your input on a cosmological thought experiment..."
] |
[
false
] |
Sitting here wondering about how fast something travels as it enters the event horizon of a black hole. Let's say I am falling towards a black hole and I have a flashlight. I shine this flash light in the complete opposite direction in which I am falling. In other words, I shine the flashlight away from the blackhole. By definition light cannot escape the gravity of a black hole. So what would happen to the light being emitted from my flashlight? If light cant escape and the event horizon is thus the line where the escape velocity balances with the speed of light (Schwarzschild radius), and therefore beyond that point the speed at which something falls towards the singularity should be faster than the speed of light. A particle traveling faster than the speed of light would have infinite mass. If so, this would no doubt be like a puncture in space time. Well redditors, what do you guys think? I have not though this out very thoroughly as it is something I just recently pondered. Please fell free to correct me, challenge me, or maybe even expand on my thoughts. Thanks
|
[
"Inside a black hole, moving towards the centre is mathematically equivalent of moving forward in time, and moving away is equivalent to moving back in time."
] |
[
"As you fall in photons have to climb out and get redder.",
"See also ",
"http://en.wikipedia.org/wiki/Black_hole",
" and especially ",
"http://en.wikipedia.org/wiki/Photon_sphere"
] |
[
"Just to tease you, i say again that photons don't have a frequency, their wavefunctions do. The frequency observed is determined by the length of the waves you see from your frame of reference."
] |
[
"What exactly is taking place to allow a substance to exist at the triple point?"
] |
[
false
] |
[deleted]
|
[
"The three phases exist in thermodynamic equilibrium. None of the three is preferred over the other two.",
"The chemical potentials of all three phases (or equivalently, Gibbs free energies per particle) are the same."
] |
[
"Do we understand how this is possible? Maybe it's jut me but I can't wrap my head around how something can be frozen yet boiling at the same temperature and pressure."
] |
[
"Does each combination of two of those make sense to you? ",
"Ice melting. Water boiling. Ice in vacuum. "
] |
[
"Would a solid state-refrigerator work?"
] |
[
false
] | null |
[
"Thanks for that. Will post over there instead",
"Should I go ahead and delete this post then?"
] |
[
"A good home for this question would be ",
"/r/AskScienceDiscussion",
"."
] |
[
"You can leave the post here, no problem."
] |
[
"What prevents the \"polishing\" of any white surface to make it a mirror?"
] |
[
false
] |
To my (limited) understanding, the only difference between a mirror and a piece of paper is the way light is reflected off the surface, with a mirror being perfectly predictable and paper creating a bunch of "noise." They both reflect all wavelengths of visible light, but one is opaque. Is that because of the surface texture of the paper, and if so, why can't all white objects become perfectly reflective with enough polishing? If it's down to a molecular scale, is there a chemical treatment that can have that effect?
|
[
"I think if you take the idea out of it having to be white, it will make more sense. Copper, bronze, brass, etc. can all be polished to a mirror finish and reflect an image well, it will just be that color. You can even see yourself reflected in a screen when it goes black! So it is the surface/construction/density of the material. With the given example of paper, the material is quite fibrous, and not dense. No matter how smooth you got the surface, by any reasonable means, it wouldn't ever be even enough to clearly reflect. Now compare to a metal, or obsidian. The material is dense enough and truly solid enough that an even smooth layer capable of reflecting light can be achieved via polishing. ",
"TL-DR little bumps on the surface of paper scatter light, and paper (there is glossy paper but I think that is more the coating reflecting light, not truly the paper itself) can't really be polished due to it's construction. An even, more dense material that can form a smooth, reflective layer, could be. You may also want to just look into mineral luster. Wow, that looks awful typed out in the modern Era, but it's a science term."
] |
[
"s there a chemical treatment that can have that effect?",
"Saturate it with acrylic or coat it with a liquid that hardens to a polishable surface. Paper is too rough and never will be smooth enough on its own. In a microscope it's just a mat of cellulose and lignin fibers.",
"Glossy paper isn't polished glossy, it's finished with enamel or shellac that is pressed against a smooth surface to harden."
] |
[
"if you get one of those sheets that's been stuck in the printer a while getting tumbled in there somehow, they come out a bit shinier. Don't think you can see yourself but it does take a polish with the right printer jam"
] |
[
"Are space-based solar panels different than Earth-based solar panels (and if so, in what ways)?"
] |
[
false
] | null |
[
"Yes! They are ",
" more expensive!",
"So, for a ground based solar panel what you care about it $ per watt.",
"\nSo to setup a solar panel for my house I would want the cheapest solution that gets me to 5kW. So I might pay between 2-8$ per watt installed. These panels will be as cheap as possible, with cells under 1$ per watt. This means generally means a polycrystalline solar panel. It is a single layer assembled from many crystals of silicon. Because of the ",
"Shockley–Queisser limit",
" their theoretical maximum efficeny is 32%. ",
"In reality their effiency is between 12-20%",
".",
"Why is this? Because the solar diode needs to be setup to absob Photons, and kick out an electron at a specific voltage. Any Photon that doesn't have enough energy to get to this voltage is lost to heat. Any Photon that has ",
" than this voltage loses all extra energy to heat. You only get 1 voltage per layer.",
"Now for a space based solar panel? Suddenly cost is not relevant. Even if we lauch the absolute cheapest solar panel, the ",
" price is 10,000$/kg. This so dwarfs the cost of basic solar panels that any weight and efficacy savings is critically important.",
"So, how do we get around the SQ Limit? By stacking Layers! Now we can have our high energy photons in 1 layer, then medium energy in 1 layer, and low energy in another layer. This allows us to maximize the efficiency of the solar cell, while exploding the cost! However we can now get efficiency around double that of a basic solar cell, with >30% efficiency possible.",
"So a nearly 2x power per gram, what about cost? ",
"Try over 900$ per watt!",
" for a 3 junction solar panel. Compare this to new single junction solar cells that are ",
"less than 1$ per watt."
] |
[
"What about micro-meteors etc? Is structural integrity taken more into account?"
] |
[
"Add a layer of shielding against smaller particles, make it modular enough to handle the loss of an element from a larger impact if needed. Most damage is just minor degradation of the optical properties of the surface."
] |
[
"If our solar system is moving through space at hundreds of Km/s, does that mean Astronauts 'at rest' are as well?"
] |
[
false
] |
I know it's all about references frames and I assume the answer to be yes but I've never heard this really mentioned before and I wanted insight from someone who really knows. Also what does this mean for space travel? From what I can find, our solar system is orbiting in the milky way (or something along those lines) so does this movement of or solar system need to be accounted for for just about anything in space the same way you travel faster going against the earth's rotation in a plane?
|
[
"I know it's all about references frames",
"but from the rest of your text, I get the feeling as if you think that there is some true zero velocity. If that is so: You're mistaken. Spacetime itself doesn't care about speed, and there is no true zero speed.",
"The only kinda-quasi-objective zero speed one could make up is that in which there is no red/blue shift in regards to the CosmicMicrowaveBackground. But that has nothing to do with how spacetime functions. It is indifferent.",
"In an otherwise empty universe, a lone spaceship would literally have no speed, no matter how much it accelerates. Yes, it would technically become faster. But it could do that for eternity (and indeed keep going faster) without experiencing ",
" change in relationship to spacetime. It just. Doesn't. Matter.",
"So, what do we have to account for? Depends on what we want to achieve. But for all our local intents and purposes, it doesn't matter that we're orbiting the center of the galaxy, because the time spans (estimated 225 to 250 million years) are too great and our activities are too locally confined."
] |
[
"My understanding is extremely limited so this may make no sense related to the question above but what about at absolute zero? I thought at 0K there was no molecular motion (or at least there wasn't supposed to be though I think current research has found 0K wasn't actually low enough). Wouldn't speed be 0 at absolute zero and if not, how would that work?"
] |
[
"What you refer to is about relative movement. A particle by itself can not have a temperature. You can achieve an understanding by picturing the following:",
"Imagine a 3D isometric arrangement of balls with some space in between. Like math paper, only in 3D, and every cross section has a ball. In reality, they are not really balls, and they are not really arranged like this, but this model is good to achieve an understanding of temperature.",
"The image you have in your head now shows what's going on at 0K: Nothing. And this 3D matrix can move through space relative to other stuff like any other object. 0K doesn't mean: \"It's at speed zero relative to ...\" Yeah, relative to what? I mean, if you assume that 0K means some magical objective standstill, does this mean that Voyager, which is moving relative to Earth, has a different reality in regards to the workings of temperature? No, it works exactly the same there.",
"The movement-statement about temperature is about relative moment. So, back to the imagining:",
"Now, one of the little balls moves a bit to the left. Another moves slightly diagonally up/backwards. Another moves sideways, but a bit stronger. And so forth: Every ball moves a little. Since they interact via forces, this affects the surrounding balls, so they \"bounce\" back, but not in the exact same angle. And that one, over there, was bounced to the side even though it was previously going upwards. It's like you're shaking a box full of these, only more chaotic.",
"That is thermal energy in a material. Temperature is a statement about the average chaotic motion of the particles of a chosen portion of matter.",
"Now imagine that the matrix would consist of only ",
" ball. What does it do? It moves to e.g. the left - and it keeps moving. It's just an object that drifts through space. No temperature."
] |
[
"Why is the orbit of manned spacecraft usually so steeply inclined?"
] |
[
false
] |
[deleted]
|
[
"Let's say that the space race wasn't between the US and the USSR, and instead it was Brazil that pioneered spaceflight.",
"That country can launch directly to equator orbits. When you do this, you end up with an orbit that doesn't change the latitude that it is over. So those wavy graphs showing where a satellite is would be flat.",
"The equator is the ",
" place where you can do this. The latitude of an orbit is like a sin wave. It will spend half of its time in the north hemisphere, and half of its time in the southern. That's just the way the physics work. The only alternative is to remain flat over the equator.",
"So because of that, US launches actually do minimize the inclination of their orbits. The launch location is around the highest latitude the satellite rises to.",
"The plane of the ecliptic is a solar system concept and isn't really relevant here, except for figuring out where sunlight falls. It would be relevant for other interplanetary probes and moon missions."
] |
[
"Yes, I looked it up and found that same fact. A simple approach would be that a launch from there would have a 5 degree inclination.",
"Plane changes are normally very costly in terms of propellant. However, if you're launching to a higher orbit (like geosynchronous satellite), you combine the plane change with the increase in altitude, and this makes it much less costly. So US companies will still launch these satellites, and they're not at ",
" much of a disadvantage to the French Guiana spaceport.",
"If you needed to get an equatorial orbit, and did this from the French Guiana spaceport, the plane change would cost a delta_v of about sin(5 degrees)*7.8=0.68 km/s. That's still a good deal. But I don't know if equatorial LEO has much of any use anyway."
] |
[
"How do launches work on the equatorial orbits? I'm thinking of French Guiana's spaceport being a meager 5 degrees north of the Equator."
] |
[
"What happens if one breathes pure oxygen?"
] |
[
false
] |
I've always found it particularly fascinating that the atmosphere and the air we breathe is composed of mostly nitrogen (roughly 78%), followed by oxygen (21%). How is it that we can breathe this air with oxygen being, comparatively, at such a low percentage? How would we be affected if the air we breathed was pure oxygen? (I remember vaguely reading that it is actually detrimental to breathe pure oxygen, but I can't remember how accurate that was, nor the reasons why it would be) Thank you for any input. EDIT: Thank you for all the responses! Learned quite a lot.
|
[
"Pretty much every bad thing you can think of",
"."
] |
[
"It's actually not about either the mixture or the pressure directly. It's literally how many oxygen molecules you inhale per second. So you can say it depends both on total pressure and partial pressure together; less oxygen is less oxygen, even if there's inert gas \"padding\" it out."
] |
[
"I used to work on a boat with divers, they will go absolutely ",
" if you refer to their ",
" as oxygen. Oxygen is deadly poisonous."
] |
[
"When it's said that areas of the brain \"light up\" via electrical signals, are there actual photons in the brain that get emitted?"
] |
[
false
] | null |
[
"I assume you're referring to fMRI (functional magnetic resonance imaging) or PET (positron emission tomography), the results of which are often talked about in terms of the brain 'lighting up'. Both don't measure electrical activity but other markers of brain activity. ",
"In the case of PET, a radioactive tracer molecule is injected, that way, you can infer where brain activity has taken place by looking at where the signal coming from its radioactive decay is the most active. The tracer molecule will typically be chemically very similar to either glucose (used to provide energy) or some other molecule used in the brain. For example, you might find that the radioactive signal is greater in brain region a than b on a given task, so you'd conclude that it's involved in task performance, but b might not be.",
"fMRI makes use of the fact that the magnetic properties of oxygenated and deoxygenated blood are different - this means you can distinguish between the two using magnetic resonance imaging, although the signal is quite faint. The maker of activity measured is called the blood oxygenation level dependent (BOLD) response - this is based on the assumption that brain activity will use up oxygen, so areas that were particularly active will change over time in terms of the oxygenation levels of the blood. ",
"The statistics are pretty complex, but when you see colourful images of both PET and fMRI results, the bright spots where the brain 'lights up' really are just statical maps of your signal, with the signal being the markers of brain activity described above. So in this sense, nothing in your brain literally lights up, but the measured signal shines some light on where and how brain activity might occur under specific conditions "
] |
[
"It's possible to encounter all sorts of problems when trying to measure brain activity using BOLD, in part because the signal to noise ratio is often very low and the statistical methods ",
"aren't perfect",
". Some more detail about the BOLD response is summarised in ",
"this article",
", including some factors that can mess with your measurements."
] |
[
"fMRI makes use of the fact that the magnetic properties of oxygenated and deoxygenated blood are different...The maker of activity measured is called the blood oxygenation level dependent (BOLD) response - this is based on the assumption that brain activity will use up oxygen",
"Has there ever been a situation where that assumption has been wrong and the BOLD response hasn't occurred?"
] |
[
"Would it be possible to build invincible / very resistant car brakes that would need little or no maintenance?"
] |
[
false
] |
I was thinking about it the other day as I was going to the garage to fix my brakes, again !
|
[
"As long as we're still using disk/drum brakes, probably not. The stopping power comes from friction between your brake pads and the disk/drum on your wheel. In order to generate that friction, there have to be surface interactions between the two. The pads have been designed specifically to wear slightly more than the brake itself, so that maintenance costs are lower. (Imagine if you had to replace the wheel every 50,000 miles). ",
"That said, there are other paradigms for braking. The Prius and other electric vehicles use regenerative braking - the motion of the wheel turns a generator which harnesses that energy as electricity, charging the battery and slowing the car. But this system isn't good for quick stops - it relies on the braking being slow and smooth. ",
"Essentially, the braking system takes the kinetic energy of your car moving and moves that energy somewhere else. Traditional brakes turn it into heat via friction. Regenerative braking turns it into electricity via magnetic fields. To this day, we haven't really come up with a better way to quickly and on-demand remove energy from the system - the current way it's done is better than other ways we ",
" do it. "
] |
[
"Thank you for your answer! So that means even if we took harder materials for either the pads or the disks we'd still have one of them using more than the other ?"
] |
[
"Partially that, and there are other considerations. The abrasion of your existing disc brakes turns a lot of energy into heat. If you take two very hard materials and press them together, you get quite a bit more noise (read: screaming, screeching brakes). The abradable ones are much quieter. This is apparent even in existing braking materials. If you put racing brakes on a street car, you'll find stopping at a stop sign to be a loud and obnoxious experience."
] |
[
"What determines the ideal cruising altitude for an airplane?"
] |
[
false
] |
I assume various factors such as the shape, size, weight, thrust, the density of air at various heights, etc. play a role. How do these (and any others I missed) factor into calculating the ideal cruising altitude?
|
[
"\"Ideal\" can mean different things. Primarily, the first major factor will be the overall weight of the aircraft, and that will vary from flight to flight depending on fuel and passenger loads (the added weight of them). That will initially limit the height the aircraft can climb to (which will normally be below it's maximum service ceiling, the maximum altitude it is certified for), and it won't be economical for it to climb any higher (if it is still below it's service ceiling) until some fuel has been \"burned off\" during cruise flight. Then it could do a \"step climb\" to a higher cruising altitude (if the flight was going to be long enough) to possibly be more economical. This usually happens on larger aircraft (like a B777 or B747, etc) on long overseas flights taking numerous hours. But...",
"Another factor would also be the wind directions and speeds at the altitudes the aircraft fly (referred to as \"winds aloft\"). At commercial flight altitudes it is not uncommon to find headwinds and tailwinds exceeding 100+ knots, so it may be more economical to fly at a certain altitude instead of the aircraft's best \"no wind\" performance altitude for a given situation.",
"\"Dispatchers\" for the airlines figure all of it out before the pilot gets to the aircraft. The pilot is given a \"flight plan profile\" based on the projected aircraft weight and winds aloft for the flight (there are other factors, but these will be the main two that will determine the cruising altitude).",
"Source: I've been a licensed pilot for over 40 years.",
"EDIT: If you want to look at a more detailed example containing the math of some of it (but still good narrative explanations too), click here. ",
"https://aviation.stackexchange.com/questions/3272/how-do-pilots-decide-what-their-cruising-altitude-will-be"
] |
[
"Moving air is expensive, and you need to move air out of the way to get the plane where it needs to go.",
"Turns out there is less air the higher you go, so that is a plus. It also happens to be less turbulent on average up there. Win win. Turns out you also need to keep air under the wings to stay in the sky. Then you can just go faster, but your engines have an optimum speed for efficiency. ",
"So it's a trade-off between having enough air around to not crash, running your engines efficiently, and not wasting energy moving dense humid air. "
] |
[
"ATC's job is to accommodate pilots when possible while maintaining safety. ",
"/u/falconAF",
" is correct in saying that a dispatcher will create a flight plan profile. When the pilot files the flight plan, he gets pre-cleared by ATC, meaning they will let him fly at his desired altitude assuming nothing weird is going on. "
] |
[
"Can an object be in orbit while still being in the atmosphere of a planet?"
] |
[
false
] |
[deleted]
|
[
"Not stably, its orbit will degrade due to air resistance. In fact, the ISS is in the very upper reaches of our atmosphere, such that it has to periodically correct its orbit with rockets."
] |
[
"Yes. It decays at about 2 km/month according to Wikipedia, so it would take about 17 years at that rate, but it would actually be faster because as it gets lower the atmosphere gets thicker and gravity gets stronger."
] |
[
"just a fact we have to deal with if we want a low orbit space station",
"The cost for the fuel to periodically push it up again is lower than the savings you get from only having to launch all the crew and resource exchange missions to a lower orbit."
] |
[
"What are certain parts of animals called when you are not describing a specific animal?"
] |
[
false
] |
[deleted]
|
[
"You'd use terms like those already posted, and also directional terms. For example, if it had three things coming out the back, bottom end, you'd say something along the lines of \"the organism has three appendages posterio-ventrally.\" You'd probably also give reference to other appendages, and be more specific."
] |
[
"try to get your hands on a comparative vertebrate anatomy textbook if you want very precise terms. "
] |
[
"Thorax and abdomen are pretty universal for dealing with the torso."
] |
[
"can someone please explain how light from a flame is electromagnetic in nature?"
] |
[
false
] |
My physics textbook says light shows wave and particle nature but I'm having a tough time relating this to real life. It defines EMW are caused by charges oscillating periodically to give perpendicular electric and magnetic waves. In the case of a lit candle, how do I relate this?
|
[
"In classical electrodynamics, the mathematics produces a wave equation which has solutions that self propagate at some speed called \"c\". These waves can impart energy and momentum onto electric charges and be produced themselves by charges. These waves are the things we call light and they travel at the speed of light, known as \"c\" in vacuum.",
"Light is produced classically when a charge accelerates. Consider an electron, it will have electric field lines which look like this,",
"https://upload.wikimedia.org/wikipedia/commons/thumb/9/95/VFPt_plus_thumb.svg/480px-VFPt_plus_thumb.svg.png",
"If flick the electron with my finger, those field lines will respond to the changing position of the electron, but this will not happen instantaneously. The field at some distance X away won't know the electron moved until at least some time T = X/c.",
"The flick will cause a \"shockwave\" that radiates away from the center at the speed of light. This shockwave is light. The produced light looks like this, ",
"http://www.tapir.caltech.edu/~teviet/Waves/empulse.html",
"If I very precisely wiggle the electron at a constant rate, like rocking a baby in a cradle, I will continuously produce radiation at a single frequency or color. Doing this I can produce any color I want. Taking this concept further, I can absorb or emit radio waves (which are also forms of light) using an antenna. The Wikipedia page on dipole antenna has some really cool animations showing this process, ",
"https://en.wikipedia.org/wiki/Dipole_antenna",
"Now we can introduce quantum theory which requires light to come in packets called photons, which you've probably heard about. Photons have an energy which is proportional to their frequency, the shorter the wavelength (more blue) the more energy each photon has. It is still correct to call light \"oscillating magnetic and electric fields,\" but we can't use purely either the wave or particle picture. Photons are quantum objects and thus has aspects of both, but are truly neither. ",
"This quantum behavior is important as it turns out all objects emit light in a very specific way called blackbody radiation, but the wavelength spectrum given off at room temperature cannot be seen with the human eye. You can picture all the trillions of atoms in your body as wiggling some amount depending on their temperature. Wiggling atoms produce radiation as outlined above.",
"Now: Let's get to candle flames. When a candle burns it primarily produces light through two mechanisms, ",
"Incandescent soot particles are little hot chunks of carbon. They are hot enough that the radiation they produce is noticeably in the visible spectrum of light.",
"Atomic and molecular transitions of broken up molecules. Because of quantum mechanics, these only occur at specific wavelengths, like this butane spectrum, ",
"https://upload.wikimedia.org/wikipedia/en/2/26/Spectrum_of_blue_flame_-_intensity_corrected.png",
"A regular fire is usually a mixture of these two."
] |
[
"I've been meaning to ask this question for a while. How do classical EM waves as the product of an accelerated charge relate to photons? Is a photon considered a quantum 'unit' of the classical wave? "
] |
[
"In a way, photons are the 'units' of light. Just remember that photons come at different energies/wavelenghts/momentums. So they are not units like 1 is a unit.",
"Photons represent the invidual packets that as a whole are light. When the accelerating charge produces EM waves, it produces it in discrete packages or quanta, that we call photons. As a whole the radiation can be very smooth (like blackbody radiation) or not so much (like light from LEDs). "
] |
[
"On this cloning a wooly mammoth thing...I'm not a scientist, but based on the technique wouldn't the resulting mammoth have elephant RNA? And does it matter?"
] |
[
false
] |
Sorry if this is a dumb question.
|
[
"I am concerned that donaldjohnston has been unclear, so let me clarify: the egg into which the mammoth DNA is placed would contain RNA from the egg donor, meaning that they would be elephant maternal RNA and elephant proteins, including transcription factors. ",
"If the elephant RNA, proteins, and proteins translated from maternal RNA are similar enough to the mammoth equivalents to activate the normal developmental pathways of the very early embryo (and this is a ",
" \"if\", the mammoth embryo will start to produce its own RNA and proteins, and take over its own development (as all embryos do at some point). ",
"The maternal molecules will soon be degraded completely, and will disappear. They are not, in any way \"passed on\". After a short time, none of the molecules within the mammoth embryo will be any different from those in a mammoth growing within another mammoth. There would be no lasting inheritance of elephant RNA."
] |
[
"Thank you!"
] |
[
"In this case the genome would be mammoth but the mitochondria and any extra-chromosomal DNA would be elephant."
] |
[
"Can we be sure there is nothing smaller than an elementary particle?"
] |
[
false
] |
[deleted]
|
[
"\"Elementary particles\" are such until we prove the contrary: with the current tools (e.g. LHC) we continuously look for evidence of their \"compositeness\", but no luck so far!"
] |
[
"There's no proof of the existence of such things in the physical world yet: it's just specilative models at this point."
] |
[
"At the moment, we don't even know what the 'size' of an electron is, if such a concept can even be applied to an elementary particle so I think it's probably a little premature to worry about anything smaller than it. :c)"
] |
[
"Would I be able to feel the difference between moving my hand through air and moving my hand through a vacuum?"
] |
[
false
] | null |
[
"You would feel quite a difference. If we assume that your hand wouldn't undergo any nasty side effects from being in a vacuum, more on that later, you wouldn't feel any wind resistance. In the atmosphere when you move your hand it is pushing the molecules in the air out of the way as it moves. This causes your hand to feel a force acting against the direction you are moving. In a vacuum there are no molecules to push out of the way so no force is felt.",
"The problem with being in a vacuum for humans is that we have a pulse and blood pressure that is acting out against our skin. This is countered by the atmospheric pressure. So if there is no atmosphere, like in a vacuum, our blood pushes on our skin and it can cause us pain and physical damage. Additionally, in a vacuum the water in our blood would begin to evaporate. This would seem to us as if our blood is boiling. This evaporation would put pressure on our tissues and cause physical damage."
] |
[
"The moon feather/hammer experiment was not performed by Neil Armstrong, it was done during the Apollo 15 mission by David Scott."
] |
[
"Some astronaut on the moon once showed that a feather and hammer drop at the same rate on the moon which has practically no atmosphere (vacuum). The feather didn't feel anything whereas on earth it feels the air and swoops around, dropping slower than the hammer. Your hand is the feather, Daniel-son."
] |
[
"Why is Chickenpox more dangerous to adults than it is to children?"
] |
[
false
] | null |
[
"Chicken pox and shingles are caused by the same virus, herpes zoster. When a person first gets the disease (usually as children) it manifests as chickenpox. Once recovered, the virus still stays in body's nerve cells in a dormant state and can reemerge as shingles. So anyone who gets shingles had chickenpox at some point in the past."
] |
[
"This is a very good question - and one that it appears has yet to be answered. ",
"The only scientifically-based information that I could find",
" is that the antiviral cytokines interferon-alpha and interferon-gamma are upregulated after varicella virus (VZV) infection. However, adults with primary VZV infection had lower amounts of interferon-gamma compared to the levels found in infected children. The theory is that the lower interferon-gamma production might be the key to why adults have more severe infections. The ",
" why adults produce lower levels than children is not currently known.",
"Edit: The book chapter link I provided is now no longer working, but the information came from a great Herpesvirus book that you can find ",
"here",
"."
] |
[
"Well actually I confess, I know of congenital varicella from personal experience. I have it. I'm one of the rare few who survive past the first few days and even rarer still that I am not too severely disabled. For me it stunted my growth as a fetus, cause my lungs, kidneys, bowl bladder and Esophagus to be deformed to varying degrees. Without going into huge detail I can say that my kidneys are slowly failing as my bladder is both.. Sort of locked in an ever expanded position because the bladder tissue is somewhat.. Callus, not literally but it is so covered in inconsistent thickness of the bladder wall and scar tissue that it can hardly expand. This being that it both pressed against my kidneys as well as flashing urine into my kidneys and damaging them. I am also Incontinent, more so in the bladder, so I can neither hold it in or push it out. I had a colostomy bag until I was 5 before learning and strengthening my bowl muscles to be able to go to the bathroom at least twice a day so's not to.. Leak. And I keep my bladder empty by self catheterizing 7 times a day, also stopping me from leaking and reducing the amount of urine going into my kidneys. My esophagus is somewhat paralyzed, I am diagnosed with vocal cord paralysis and have a very noticeable speech impairment. As well as my esophagus not being able to push my food down into my stomach and keeping it there, it used to reflux into my lungs which caused significant damage which affects my breathing somewhat. And in the case of becoming immune to the zoster virus it is debated amongst doctors whether I am immune because I have technically already had my one off Bach of chicken pox or if I gained immunity through some sort other genetic means.. I'm not very clear on that part. I also have a sort of epilepsy condition thought it is quite different to the conventional definition. In my case rather then convulsions my brain sends the wrong messages to the wrong parts or just damn right thinks the wrong think, I often feel a sort of tingling or sometimes even pain throughout my limbs cause but my \"epileptic\" fits. In more extreme cases I have what my family have seemed to coin an \"episode\" I get sever head aches, loss of appetite, my saliva glands seem to go into over load rather then vomiting I am constantly 'vomiting' large quantities of spit, and just overalls feelings of nausea.\nI expressed strong interest in doing an AMA about my story, I asked the mods of what proof I have, I mean it was a complicated question did you want photos of official documents saying that I have congenital varicella cause I have not a single document rather many documentations of my times spent hospitalized. Ik I went a little of track but perhaps if you could direct as many people to this post and to my comment it would be extremely appreciated. "
] |
[
"How does a metal detector work?"
] |
[
false
] | null |
[
"The ",
"Wikipedia entry",
" describes it quite well: ",
"\"The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a magnetometer), the change in the magnetic field due to the metallic object can be detected.\""
] |
[
"Well, I wouldn't say it that way, but that's kind of the general drift. Usually the term \"electromagnet\" is reserved for something that we are using in a different way, and is constructed with a ferrous core to concentrate the magnetic field. If you use an electromagnet as part of your metal detector, be prepared for stuff to get stuck to it. ",
"The key principle at work is that changing electric fields induce magnetic fields, and vice versa. So you can use an inductor (a coil) to produce a magnetic field by passing a current through it, and you can also use inductors to detect changing magnetic fields, by monitoring the current going through it. "
] |
[
"Electromagnets make object turn into electromagnet, causing coil in detector to be an electromagnet, which is detectable. Got it.... :) "
] |
[
"What is the maximum size a tornado can be?"
] |
[
false
] |
edit- on Earth
|
[
"By \"maximum size\" I'll assume you mean the \"Largest tornado path width\". ",
"The ",
" recorded occurred on May 31, 2013 in El Reno, Oklahoma; with a peak length of 16.2miles and width of 2.6 miles with 296mph winds; however this tornado was predicted as a F5 it was downgraded to a F3 [Sources ",
"1",
",",
"2",
"].",
"When calculating the strength of tornados, on Enhanced Fujita Scale (EF-Scale) the highest possible is a F5s (261-318mph) level tornado; with F6s (319-379mph) being highly unlikely. "
] |
[
"Just wanted to add some info about the EF scale. The ",
"EF scale",
" is what is used now, as it takes a number of factors into account and isn't based solely on wind speed. (EF is Enhanced Fujita, F is just Fujita.) The original scale also wasn't based solely on wind speed either, but many people view it that way. The wind speeds are in place to allow for initial estimates of tornado strength; a team of meteorologists will typically analyze each tornado's path the day after the storm passes to determine the official rating based on the damage found. This is why many tornadoes are originally reported as having one rating but it is later changed.",
"Further reading:",
"List of damage indicators used",
"Full paper on the development of the EF scale"
] |
[
"Not a biologist but according to ",
"this article",
" new plants can grow fruit up to 10 inches in diameter (about the size of an average pumpkin). I'd imagine that through crossbreeding with other plants that produce extremely large fruit that diameter could be pushed about 40-50% higher. (As is the case in ",
"this article",
" about a related species, seabuckthorn). The first article speaks of tomatoes growing to 3 lbs with a diameter of 10 inches, so if we assume the biggest tomato ever will grow to a diameter of 15 inches, the mass will increase with the cube of the radius (mass = density * volume and the volume of a sphere is 4/3* pi * r²). The mass will therefore increase to (7.5³ / 5³) * 3 lbs = 10 lbs. So, the maximum size will be about 15 inches in diameter with a mass of 10 lbs. "
] |
[
"Are Organelles randomly shuffled in animal cell?"
] |
[
false
] |
Are they placed in a specified pattern? Or just randomly shuffled around? Are they uniform?
|
[
"Of course there is structure! Eukaryotic cells are filled with cytoskeleton elements such as actin filaments or microtubules. Motor proteins such as dyneins and myosin can latch on to these filaments and carry cargo. For example, this is how many marine organisms change color: by moving pigment-filled vesicles towards the inside/periphery of the cell. As for organelles, the Golgi apparatus is positioned using microtubules as a guide and sends vesicles outwards or inwards on them. They act as a 'map' for the cell. ",
"Edit: here's a link to a video that helps explain color change. ",
"https://youtu.be/foqEeOWVdd0"
] |
[
"What about mitochondria, then?"
] |
[
"I can't think of any specific examples of the placement of mitochondria, but something else to keep in mind is that cells are incredibly, incredibly dense. Certain structures require specific places, and everything else sort of fills in accordingly. A good example is a skeletal muscle cell. Practically the entire cell is an array of actin and myosin. There are few mitochondria because they don't really have time to go through oxidative phosphorylation of glucose for energy. So, by the time you line up the myofibrils and sarcomeres, there is very little room for \"randomness\" of organelles."
] |
[
"what is the history behind using deciliters as a denomination for blood tests?"
] |
[
false
] |
how and why did this occur? it would seem to liters or milliliters would be more ”standard” than a tenth of a base unit. was μg/dl and the like simply more convenient?
|
[
"I don't think the units have anything to do with the amount of blood drawn for examination.",
"Think about it: a deciliter are a tenth of a liter, or 100 milliliter. That's still a ridiculously huge amount of blood for a test.",
"The normally used blood collection tubes only hold a couple of milliliters up to 10 ml in the largest ones, if I recall correctly.",
"Even so, you aren't limited in the choice of the unit used by the amount of substance analysed. You could simply convert any unit into another. The difference between mg/dl and mg/l is a factor of ten.",
"Long story short, there doesn't seem to be any ",
" reason for the choice of the unit, except maybe tradition and/or convenience of having more manageable numbers."
] |
[
"We test a ",
" of different things. Some we do use mL for, some we even use L for. In the US, it's common to adjust the denominator to make the numerator easily readable (i.e. 14 mg/mL vs 0.014 mg/dL). Over time, dL just becomes a common denominator to use for lots of things, and winds up the de facto default.",
"But we do actually use mL and L plenty too."
] |
[
"fair enough!",
"i thought maybe there might be an interesting story behind it, as i really only encounter deciliters when reading medical papers or looking at the associated lab work on blood.",
"thanks :)"
] |
[
"What decides whether something burns up (like paper) or melts (like steel) when exposed to high temperatures?"
] |
[
false
] | null |
[
"Burning is a chemical reaction; the molecules in the paper react with the molecules in the air, and the role of heat is to provide the activation energy for that reaction.",
"Melting is a physical reaction; the molecules in steel are vibrating fast enough that the bonds between them cannot hold them in a rigid structure any longer so they begin to flow, and the role of heat is to provide kinetic energy to each of the molecules to increase their vibration.",
"To answer your question directly, what \"decides\" between burning or melting is whether the object can perform an exothermic reaction with the surrounding atmosphere that has an activation energy below its melting point."
] |
[
"This is entirely the case. For example you'd have a hard time getting anything to burn in an argon atmosphere, and similarly hard a time stopping it in a fluorine-rich atmosphere."
] |
[
"steel wool will burn in air, but melt in argon",
"im using steel wool here because of its high surface area allowing a reaction like burning to occur",
"edit: paper, on the other hand will decompose/gassify in an inert atmosphere because the bonds between molecules like cellulose, lignin and other components of paper are stronger than the intramolecular bonds. On the hand, you can melt sugar at a lower temperature, and burn it at a higher temperature."
] |
[
"When did animals start defecating?"
] |
[
false
] |
When did multi celled organisms begin to "Package" fecal matter and send it out in one lump?
|
[
"I'm sure there will be better answers later, since I'm not a biologist, but I'll pitch in with a bit of info to get things started. It doesn't really address your question, but it's somewhat related, anyway.",
"Excretion has always been around, since biological processes can create compounds that would be toxic if left unchecked. The easiest way to solve this problem is clearly to throw it somewhere else instead of having to develop a complicated metabolic pathway to neutralize the toxin, or having to isolate the toxins somehow while still carrying them around.",
"Defecation, however, is ",
" excretion in the biological sense, which goes against most people's intuition. Rather, urination is excretion, and it serves mostly to filter out ammonia from living cells, either by eliminating it directly or after having converted the ammonia into other compounds such as uric acid or urea. Defecation is merely getting rid of matter that couldn't be digested. Why couldn't it? Well, most likely the organism in question was not selected during its evolution to make use of part of the matter ingested. There are lots of different types of compounds that make living things, and developing biochemical strategies to process all of them is an inefficient use of limited energy, in most cases. "
] |
[
"Sooo... it's been a while since I took biology, and someone please correct me if I'm wrong, but Cnidarians were the first Phylum to have \"mouths\". They took care of all of their eating/respiration/excretion through their multi-use body cavity/mouth/anus. Those we have fossil records of I think as far back as 500 million years.",
"The scientific name for it escapes me, but a complete digestive tract (with a mouth and anus, 2 openings) didn't appear until the Molluscs/Annelids/Flatworms came about. Can't remember any dates on those critters for you, sorry."
] |
[
"would this mean that a perfectly digestible food would not get defecated? P.S. sorry for the late comment"
] |
[
"Why is Tritium radioactive?"
] |
[
false
] |
So like charges repel. Protons naturally repel each other because they both have a positive charge. Am I correct in saying that neutrons are sort of like the buffer of atoms? Why then is Tritium radioactive with 1 proton and 2 neutrons? Do neutrons also repel each other even though they have no charge?
|
[
"It's not due to electromagnetic repulsion; the decay is due to the weak interaction.",
"Decays occur if they can. Because the mass of the helium-3 nucleus is less than that of tritium, and the mass difference is greater than the mass of an electron, tritium can turn into an electron and a helium-3 nucleus without violating conservation of energy. Because it can happen, it does."
] |
[
"The thing I didn't mention is that in order to not violate conservation of electron number, an electron antineutrino must also be emitted.",
"Also, the difference between the mass of a proton and the mass of a neutron is about three times the mass of an electron."
] |
[
"The thing I didn't mention is that in order to not violate conservation of electron number, an electron antineutrino must also be emitted.",
"Also, the difference between the mass of a proton and the mass of a neutron is about three times the mass of an electron."
] |
[
"What about the world would be different if the earth’s axis was tilted 90° instead?"
] |
[
false
] | null |
[
"Here's a recent discussion: ",
"https://www.reddit.com/r/askscience/comments/7ahcfl/uranus_axis_is_rotated_onto_its_side_meaning_it/"
] |
[
"This would be extremely interesting to see. \nIn the very middle of North Pole summer, the sun would be directly over head 24 hours a day. Any ice would surely melt. However during this time, the south pole would be facing directly away from the sun, it would spend 6 months of the year facing away from the sun. ",
"The big issue however is that during this season, the entire Southern hemisphere would be in darkness and the northern hemisphere not experiencing any nightfall at all. Those on the equator would be trapped in twilight.",
"\nAutumn and spring would be the only seasons with actual sunrise and sunset."
] |
[
"Ignoring climate differences and focusing just on the movement of the Sun in the sky...",
"From about 3 weeks before the March Equinox until about 3 weeks after, nothing would seem all that different. The sun would pass overhead somewhere in the tropics, moving north from the Tropic of Capricorn to the Tropic of Cancer in those 6 weeks. (This is currently its complete range of travel and requires 6 months.) ",
"Now things get weird. The Sun would continue to travel northward a little each day, and 24 hr daylight would progress south from the Arctic circle all the way to the Equator by the June Solstice.",
"As the Sun moves northward in the sky, it is actually tracing a spiral toward the N celestial pole. On the Solstice, it reaches the pole, and will appear to stop moving in the sky. It will appear to just spin in one place before spiralling back to the south. This awesome sight would be visible from the entire N. Hemisphere, not just the pole.",
"The Sun would move South in the sky, reaching the tropics by September. After that, the mirror image of the spectacle I just described will repeat for the Southern Hemisphere at the December Solstice. ",
"Too cool."
] |
[
"How do you visualize a photon of radio frequency?"
] |
[
false
] |
I can visualize photons that fall in visible spectrum. Like right now photons from my screen being emitted by the backlight and hitting the molecules of my retina. Because their wavelength is of the order of nanometers, QM stops me from knowing where each single photon is at any given moment, but what about a photon of wavelength 1 meter? Does it travel like being anywhere in an area of 1 meter? I'm sorry if I'm unable to convey what I'm trying to know because if I already knew I wouldn't be asking in the first place :) In case my question doesn't make any sense, please tell me what I need to know before asking this kind of question again.
|
[
"They describe oscillations in an electric field, over all space.",
"ok, so a photon with wavelength 1m is nothing but oscillation of electric (and magnetic?) fields with a wavelength of 1 meter. And since no atom has electron with such low energy, they pass right through most matter, and you need large antennas that resonate at that frequency to \"capture\" those photons. Is this all makes sense?"
] |
[
"Photons are not localized objects. They describe oscillations in an electric field, over all space. They have fixed momenta and hence, infinite uncertainty in position. X-ray photons have positions just as uncertain as infrared ones.",
"One photon of frequency 700 nm = Oscillations in the electric field over all space, with a wavelength of 700 nm, having an amplitude of 1 unit.",
"N photons = same thing, oscillations with amplitude of N units."
] |
[
"Yea, you got it ",
"To be pedantic : Rather than an atom having electrons with such low energy, there needs to be a process that takes such an energy as its input. Like moving an electron far away from the nucleus to a closer orbit. These energies are of the order of the frequency of visible light and range a few orders of magnitude on either side."
] |
[
"What is the inner monologue for a deaf person like?"
] |
[
false
] | null |
[
"Considering that they can't imagine \"hearing\" any more than you can imagine \"sensing magnetic fields\", yes. Though from various AskReddit threads, it seems to be more a combination of visualization of kinesthetics. Kind of like if you were to imagine yourself performing the \"YMCA\" dance or something, where you kind of imagine body position combined with the visual."
] |
[
"The voice in your head, your inner monologue, is something we all experience all day everyday, and we \"hear\" it in whatever language it is we speak.",
"Exactly. Deaf people experience their inner monologue in the language that they \"speak\", just like hearing people do. For someone born deaf and taught sign language, their inner monologue will be in sign language."
] |
[
"So they visualize their inner monologue more than they \"hear\" it? "
] |
[
"How does the immune system know it's allergic to something that touches the skin?"
] |
[
false
] |
[deleted]
|
[
"Here",
" is an excellent article on contact dermatitis. It is important to keep in mind that the skin is not a perfect barrier but a semi-permeable one. After prolonged exposure to non-protein antigens called haptens, CD8 T cells become sensitized and are recruited from lymphoid organs upon subsequent exposure to the hapten. There are skin specific macrophages and dendritic cells that process these antigens and aid in the priming of antigen specific T cells that then cause the inflammatory damage in the skin known as contact dermatitis. "
] |
[
"This is perfect for type IV hypersensitivity, just bear in mind that acute urticating reactions (as in when someone swells up ",
" quickly after touching an allergen) is a different mechanism."
] |
[
"Yup, type I is a very different beast. "
] |
[
"If the ozone layer was obliterated by a gamma radiation burst, how long would it take to return to normal levels?"
] |
[
false
] |
Would any plant or animal species be capable of adapting to something like that?
|
[
"Answering your followup question first - underwater species and cave species would survive without adaptation.",
"I'm not able to comprehensively answer the main question, except to state that the ozone hole (caused by human use of chlorofluorocarbons, and to a lesser extent other things) is repairing over a timeframe of decades. I can't generalize that to answer it for a complete destruction of the ozone layer worldwide."
] |
[
"It's worth noting that part of the cause for this timeframe in response to eliminating CFCs is that they take a couple decades to reach the ozone layer before pholyzing and reacting with the office."
] |
[
"One should also keep in mind, that repairing of the ozone hole is hindered by remaining CFCs in the atmosphere. So ozone will be constantly created via sun radiation, but the CFCs are breaking down the ozone. So the actual rate of ozone layer recreationg should be higher than what me see nowadays with the repairing of the ozone hole."
] |
[
"Second Universe?"
] |
[
false
] |
[deleted]
|
[
"Currently evidence does not support a \"big crunch\" scenario, which is what you're envisioning. Because the observed density of the universe seems to be below the critical density for it to overcome its observed expansion, current models predict the universe will continue to expand without end."
] |
[
"While TheZaporozhianReply is correct, evidence suggests we'll continuously expand to a 'Big Chill', IF we consider your idea, which has been theorized already in the past as I'm sure you're aware, then yes, what you are describing is called the ",
"Big Bounce",
" Theory."
] |
[
"While TheZaporozhianReply is correct, evidence suggests we'll continuously expand to a 'Big Chill', IF we consider your idea, which has been theorized already in the past as I'm sure you're aware, then yes, what you are describing is called the ",
"Big Bounce",
" Theory."
] |
[
"Could anyone explain the renormalizable concept of the standard model to me?"
] |
[
false
] |
In the book "LEP The Lord of the Collider Rings at CERN 1980-2000" by Herwig Schopper he summaries some of the results of the LEP Collider. One sentence I can't get a grip on/understand is "The proof that the standard model is a renormalizable quantum field theory, a result worth the award of the Nobel Prize to the theorists." - page 141 Help appreciated (I'm writing a paper on the failed SSC-project in the US and the successful LEP/LHC-projects at CERN)
|
[
"Glad to help. The key thing to remember is that if a theory is not renormalizable, it is not sensible. "
] |
[
"For a quantum field theory to make sense, it must be renormalizable. If you just write down an arbitrary quantum field theory and calculate, you'll find that it generates infinite terms for essentially any process, and even if you impose a rule to make one or two or five processes finite, the others remain infinite.",
"Renormalizable field theories have an important feature: once you put in a rule to ensure that you get a finite value for a few basic processes, then everything else you calculate will be finite.",
"So, for example, if you take classical electromagnetism and make it quantum, you get quantum electrodynamics, which superficially looks like it predicts infinite results for things from the mass of the electron to the scattering of light. But Feynman, Schwinger, and Tomonaga in the 1940s figured out how to make sense of this theory via a process called renormalization. 't Hooft and Veltman figured out how to show that you could do this for the standard model as well, which incorporates forces based on what are called ",
" and, in the case of the weak force, also incorporates the Higgs mechanism, and for this, they won the Nobel Prize.",
"To give you a crude idea, it is if when calculating, your theory predicted",
"(1+1/2)+(1+1/4)+(1+1/8)+...",
"but you realized if you add the rule \"after you calculate each term, subtract 1,\" your prediction becomes the much better behaved",
"1/2 + 1/4 + 1/8 + ...",
"The first version is infinite, but the second (\"renormalized\") version is finite."
] |
[
"Thank you for the explanation. It didn't make a whole lot of sense the first time I read it, but now I believe I have a grasp on the concept",
"Cheers mate!"
] |
[
"What is the next, most basic scientific breakthrough we would need for a complete global impact?"
] |
[
false
] | null |
[
"A technique to rapidly (re)generate soil and humus that doesn't require a shitton of water. This would allow to reclaim deserts as arable land. Increasing food production and water retention",
"Currently, you can take waste organic material such as cellulose (grass, paper, ...) and use fungi (such as mushrooms) to turn into humus quickly, but it takes huge amounts of water which is generally unavailable in a desert environment."
] |
[
"Although now I believe you probably know where to hit your head to get superpowers or something and you're keeping it secret.",
"It's actually about how to insert the Q-tip up your nose really far and get superpowers, but close!",
"Maybe try ",
"/r/PhilosophyofScience",
" ??"
] |
[
"We don't allow broad general questions like this, sorry. All the best!"
] |
[
"Will Voyager 1 eventually slow down/stop due to drag caused by gas and dust in interstellar space?"
] |
[
false
] |
I was reading about Voyager 1 today, and found out that it is quite close to leaving the heliosphere, after which it will come into contact with interstellar gasses. Is this likely to slow it down? Or even stop it?
|
[
"interstellar gas is almost non existent (a few atoms per meter) so there is very little matter to actually interact with. Think of the mass of these few atoms vs the entire mass of voyager - many orders of magnitude different. ",
"If you mean slow it down relative to its current direction of travel something would have to act on it fairly significantly for this to happen (eg run into a planet/stars gravity) it wouldn't stop, its velocity would be changed in either direction or magnitude by this. "
] |
[
"The interstellar gas within the galaxy is actually of density ~1 atom per cubic centimeter. It's the intergalactic space that averages more like 1 per cubic meter."
] |
[
"voyager is travelling at 17 km/s it weighs 733 kg so ",
"ke = 1/2mv",
" = 10",
"ke",
" = 1/2*(733000)*(1700)",
" = 10",
"assuming perfectly elastic collisions and all dust is hydrogen atoms",
"ke",
" = 1/2*1.6*10",
" *17000",
" =2.3*10",
" ",
"to slow down by 1 order of magnitude it would take",
"100/(2.3*10",
" = 4.3 *10",
" collisions ",
"edit: I misread that and made a false assumption it's 10",
" meters since it's 4.3 collisions per meter not per year. A light year is 10",
" meters so 10",
" lightyears is how far it'll take to slow down. Since I don't really want to do the math with the exponetially decreasing function assume it will always go 17000 m/s until you accumlate enough KE to stop it.",
"10",
" / 1.7*10",
" = 5.9*10",
" years"
] |
[
"What is it exactly that energy boosting substances like caffeine and ginseng do to our body in order to provide an alert/energized state?"
] |
[
false
] | null |
[
"Well, for caffeine, it doesn't actually give you energy. Caffeine is an adenosine receptor antagonist. It prevents adenosine from binding to sites in the CNS. Over time as you are awake, adenosine builds up and begins binding to these receptors which induces drowsiness, but with caffeine in your system, this is blocked and you feel less tired and more alert."
] |
[
"Wow that's really interesting! In that case I wonder how it manages to \"perk up\" someone who is already tired if, mechanically, it more staves off drowsiness more so than providing energy.",
"Placebo effect perhaps? "
] |
[
"Being tired means adenosin is docked at the receptor and activates it and that makes you feel tired. If caffeine as an antagonist docks there, too, it \"pushes away\" the adenosin and blocks he receptor without activating it. Think of it like a bouncer at a club. He comes and prevents people from entering but doesn't enter himself."
] |
[
"Put a cup of water in front of speaker, doesn't vibrate?"
] |
[
false
] |
[deleted]
|
[
"Sound is basically a medium vibrating back and forth. First the air vibrates back and forth, and that's transferred to the glass, and then the water."
] |
[
"It could also just be that you're not seeing the vibrations. What frequency is the speaker playing at? Try deep bass with high volume. Also, try turning the speaker so it's facing up and putting the glass on top. And maybe mix some corn starch in with the water."
] |
[
"There are many pictures and videos around if you're worried about breaking things. (which you should be)"
] |
[
"What were cows like and how were they able to survive before being domesticated by humans?"
] |
[
false
] |
Slow, docile, seemingly defenseless. I know all these traits were preferred and actively chosen thru thousands of generations of selective breeding by humans, but what were the progenitors like?
|
[
"Many large herbivorous animals are able to survive through sheer size (the larger you are, the less likely you are to become prey) and ",
"numbers",
". Also, ",
"aurochs",
" (ancestor to the modern cow), modern cows, and many other ungulates have horns. ",
"Docility and tameness can happen within a ",
"few generations",
", and with it may come physical changes."
] |
[
"Aurochs were serious beasts, well-respected by contemporary hunters. They were swift and fast, and could get very aggressive if provoked. There were probably no non-human predators that could normally take down a healthy adult individual. "
] |
[
"The aurochs was the progenitor of the domestic cow - and for that matter, I wouldn't entirely count out the defenses of cattle. They're big, and strong, and many of them have horns. Bulls remain famously dangerous, and rodeos are largely about how dangerous even domestic cattle can be.",
"That's after all the domestication and breeding and training. ",
"For an aurochs, though, maybe imagine something like a wild bison in terms of survival."
] |
[
"Are Thymine, Adenine, Guanine, and Cytosine present/used in DNA of all living organisms on earth?"
] |
[
false
] |
Are there any organisms anywhere that dont use ATCG DNA or a variation of it?
|
[
"As far as I’m aware, all DNA for living things is made from ATCG on Earth. There are viruses and such that use single and double stranded RNA which contains uracil instead of thymine, but those are generally not considered to be living things. "
] |
[
"The cell is considered to be the smallest unit of life in the world of science, yes. Viruses are not made of cells though or are a cell themself. Viruses are made of proteins and form capsules that carry genetic information. Why are they not considered living if they have some form of genetic code? Because they can not reproduce on their own is a huge reason. Viruses rely on infiltrating and taking over cells and using their reproductive machinery to create more viruses. Another reason they wouldn’t be considered living is that they do not have organelles to perform all the functions that life requires. They gather most of the molecules they need from their environment or from host cells. ",
"The way they are able to infect things and reproduce is what makes them hard to classify. I would have to get one of my textbooks out from a couple years ago to tell you exactly how they are able to take over cells, but basically they have receptors that are used to attach to a cell’s membrane and then are able to penetrate through it. They then inject proteins and their genetic material into the cell to start creating new virus RNA and proteins. And then most viruses will cause a cell to lyse (burst) and release all the new viruses held inside. "
] |
[
"Thank you for your answer, it is quite thought provoking.",
"What does it mean in this context when a virus is not considered living? I was under the impression that all cellular-based things on Earth were living - dogs, birds, grass, spiders, trees, algae, iguanas, etc.",
"How can a nonliving entity reproduce and infect like viruses do if they are not living?"
] |
[
"Does light have mass?"
] |
[
false
] | null |
[
"No it does not. It doesn't need to do the things you're describing. It still has momentum. Light consists of electric and magnetic fields. Electric fields move things, magnetic fields move things, and neither of those has mass."
] |
[
"Why do you ",
"keep",
" ",
"asking",
" this question?"
] |
[
"My Alien Blue app must be bugged. It says it never posted. I apologize for multiple posts!"
] |
[
"Is all \"sense\" DNA on the same strand of a double helix (i.e. is one particular strand always the one that gets copied)?"
] |
[
false
] |
Transcription is the process of copying a section of "sense" DNA into a strand of "anti-sense" RNA. When transcription bubbles are created, what prevents the anti-sense DNA from being transcribed? Furthermore, is all "sense" DNA on the same strand of a double helix (i.e. is one particular strand always the one that gets copied)?
|
[
"No. The coding sequence for a gene can reside on either strand of the DNA and hence, there is no fixed strand of DNA that RNA is always transcribed from. As for what's preventing antisense RNA from being transcribed, that would be the gene regulatory elements that are found upstream of a gene. For gene transcription to be initiated, transcription factors have to be recruited to these regions and they are only found on the strand that carries the gene sequence to be transcribed.",
"Edit: Reworded to avoid confusion."
] |
[
"You are indeed correct. Sense should refer to the sequence you can read directly for the protein sequence. Hence, the sequence of the DNA that will be transcribed into RNA is actually referred to as antisense. I have corrected and reworded my answer."
] |
[
"You are indeed correct. Sense should refer to the sequence you can read directly for the protein sequence. Hence, the sequence of the DNA that will be transcribed into RNA is actually referred to as antisense. I have corrected and reworded my answer."
] |
[
"Absolute zero and gas laws"
] |
[
false
] |
According to Gay-Lussac, Boyle, and Charles' laws wouldn't absolute zero bring us to a point where we can make something with no pressure and a negligible amount of mass? If that is the case couldn't we eventually (if we do reach absolute zero) compress liquids for long space travel? Or is there some quantum physics stuff that I am missing that makes this impossible?
|
[
"An ideal gas has zero volume at zero temperature. However, gasses aren't ideal under all conditions. Ignoring the fact that gasses turn liquid or solid at low temperatures, eventually they behave more like van der Waals gasses and you have to take into account their interactions and finite volume."
] |
[
"We can't reach absolute zero."
] |
[
"The third law of thermodynamics."
] |
[
"Is the need for sleep still not understood? If so, what are the current leading theories for why animals/humans need sleep?"
] |
[
false
] | null |
[
"Not sure if this has been answered, but I'll give a quick summary(it says 4 comments on the post but nothing is visibly deleted).",
"There's a lot of thought that some of the \"brainwaves\" we see during sleep (non-dreaming sleep, specifically) are linked to learning/memory during the day. A couple interesting studies ",
"1",
" and ",
"2",
" found that when subjects had to learn tasks closely associated with a given brain area, that specific area had a higher density of \"brainwaves\" (sleep spindles and slow waves, respectively) during the following night's sleep.",
"A prevalent theory ",
"\"Synaptic Homeostasis\"",
" suggests that our brains tend to increase in the overall strength of their connections during the day. To restore things to baseline, the authors suggest that the waves observed during sleep may act to lower the overall strength of connections back to baseline, leaving the connections strengthened during the day intact. Worthy of note is that seizures are the result of overactive neuronal firing (hence the need to keep things at a stable baseline).",
"Separately, there's also strong evidence that both non-dreaming and dreaming (you may have seen these as non-REM and REM sleep, respectively) sleep are involved in \"replaying\" the activities of the day. ",
"This",
" is a good place to start with that line of work.",
"tl;dr: Sleep helps us consolidate memories and re-establish healthy baseline firing rates."
] |
[
"There is also recent evidence that the brain waits until sleep to activate some of its waste-clearing mechanisms, this providing a vital period in which the brain prepares for its high metabolic rate during wakefulness."
] |
[
"Yeah it's something of a tradeoff. Though I'd baselessly speculate that social living helps."
] |
[
"Can we engineer \"evolution\" in small organisms (e.g. bacteria) in short periods of time?"
] |
[
false
] |
For example, if we have heat up bacteria in a petri dish to 45 degrees celsius, are we genetically selecting for bacteria that can survive in that temperature? Or if we expose it to chemicals (like soap), are we creating super-bacteria? How long would it take to see meaningful changes in the genetic structure of this bacteria, as compared to larger organisms such as plants and animals.
|
[
"Just adding on to point out that this is abundantly, extremely commonplace in microbiology research, and has been for various purposes for decades. A common teaching lab demonstration of this in undergrad and even high school courses is to generate antibiotic resistant bacteria by creating gradient media and inoculating the side with the lower concentration of antibiotic with a bacteria. Here is a ",
"description of exactly this type of experiment",
"."
] |
[
"Well thats No science fiction but reality. ",
"You describe mutant screenings. \nIf you want to analyse new pathways but don't have a starting point you create Mutants by radiating them with radioactive substances. (Or other mutagenic substances)\nThen you look what is different and analyse the genome. After this you know which gene may result in the defect (or benefit). After this you do much more research to identify involved proteins and so on.\nThis a mainly done in research for plants an mice.\nBut it is also done in the agraculture. You Pick plants that suit your plan",
"There are some data for mean Mutation per Generation depending in the organism. You can calculate by yourself \nE. Coli (gut bacteria) divides every 20 Minute. They have a mutation rate of 3 Base pairs per 10",
" divisions. And their Genome ist around 4 million bp with roughly 3000 genes. \nIf you want something specific IT IS easier to modify the genome If you know what you want."
] |
[
"Yes we can! The 2018 Nobel prize in chemistry went to Frances Arnold, George Smith and Gregory Winter for this exact type of work.",
"There’s also a great video out there, not sure made it (maybe Harvard), that shows the growth of bacteria on a huge petri dish with differing amounts of antibiotic, and certain strains can reach the next layer because they have evolved resistance."
] |
[
"How does an Archimedes Screw work?"
] |
[
false
] |
An was used historically for raising water for various purposes. It consists of a helical "screw" inside of a pipe, and as the screw is turned, the water level within the pipe rises. Some descriptions detail a series of wells along the screw that scoop up water and transport the water to the top of the pipe. However, I do not understand how the water actually rises. If the wells are stationary along the screw, how would the well rise as the screw is turned?
|
[
"The animation in the article isn't the best.",
"Think about a stationary screw inside of a closely fitting column, and the whole thing nearly parallel to the ground but at a slight angle. Now consider the area around just one bit of the screw's thread. If you think about it it should be obvious that you can hold water in the bottom part of such an arrangement, only the water above the shaft of the screw could possibly flow out down the screw, everything else is contained within that particular area. Now what happens when the screw turns? Within our sub-section the screw turning is identical to the screw being pushed upward. A rotation of the screw by a small amount leads to the same arrangement as before except with the parts of the screw threads higher. That's where ",
"this animation",
" really helps explain what's going on. To the water within one section of the screw the motion of the screw seems to be exactly identical to being pushed up the column.",
"And there's nowhere for the water to go except up as the screw turns. It can't fall out of the \"bowl\" formed by the wall of the column and the screw threads, so instead it is carried upwards.",
"The wells move because the sides of the screw's thread continuously increase in height along the screw's length. And rotating the screw effectively replaces each part of the screw's thread with another part that is just a tiny bit higher than the one before. It's like climbing a spiral staircase, except the staircase is moving instead of the climber, and it's at an angle which prevent falling down the staircase.",
"Another way to think about it is to imagine the water temporarily frozen in place relative to the screw. The screw turns a little bit, the water stays in the exact same well it was in before, then the water is unfrozen. But now the surface of the water is no longer level, which isn't going to last. The water then flows to make itself level again, and in so doing it falls into a new well that is exactly identical to the old one only just a little bit higher along the column."
] |
[
"I just had an A-Ha moment. The cavity is not a divot in the thread of the screw. But the bottom of the cavity is the side of the pipe, and the sides of the cavity are the threads of the screws. Thanks for the explanation!"
] |
[
"The screw itself moves the water. Look at the animation in the wiki article. The balls are being carried along by the screw itself as it turns. Each ball rests in the lowest area it can roll to, the bottom of the screw area it is in. As the screw twists, these areas are raised higher and higher and the ball sort of rolls along to keep up. Replace the ball with water and you've got a water pump. ",
"You can also make an Archimedes screw with a bit of tubing wrapped around a pole. The way it works is exactly the same, both give you a spinning spiral shape. Maybe this video will help you see what's going on. Notice how the water always runs \"downward\" in the turn, but still winds up going upward.",
"http://www.sciencechannel.com/tv-shows/what-the-ancients-knew/videos/what-the-ancients-knew-the-archimedes-screw.htm",
"EDIT:",
"Fun fact about this kind of pump--it moves water without disturbing the animals ",
" the water very much. Turbine pumps just blend everything up, but these scoop them up nice and easy. So you can pump plankton or even fish around without damaging them. I've always wanted to set up an aquarium with an Archimedes pump and keep a healthy population of plankton growing in it."
] |
[
"Is there a metal that heats up slowly, yet disperses heat quickly?"
] |
[
false
] |
Metals such as aluminum are excellent conductors of heat, but they distribute changes in temperature, whether that be an increase or decrease, quite quickly. Is there such a metal that would heat up slowly (say several hundred degrees above ambient temperature), yet disperse that heat much faster than it was gained? Is such a material even possible?
|
[
"My understanding is that heat capacity depends on temperature, so if the metal heated up slowly at a certain temperature (that is, required a lot of energy to increase the temperature) it would also lose heat at that same rate at the specific temperature. There may be something that would, let's say, heat up slowly and then quicken as the temperature gets higher (decreasing heat capacity with temperature), but this results in something that disperses heat quickly and then as the temperature lowers disperses heat slowly. I don't think it's possible to have what you stated unless the heat capacity depends on more than just temperature. "
] |
[
"This is correct and it's called the \"specific heat\". It's the amount of heat per unit mass required to raise that mass by one degree C. ",
"If you're thinking of making a better heat sink, you should know that those work by increasing surface area. Aluminum works well because it has a low specific heat. The goal is to maximize the amount of area that's touching the heat source so that it can \"suck up\" as much of the heat as possible, and also to maximize the surface area of the vents so that it can dissipate as much as possible. ",
"For this application, even if you had a substance that would dissipate it faster than absorb it, it wouldn't be very functional because it wouldn't be able to draw the heat from the source very well.",
"But maybe you're thinking of a different application where it would be useful?"
] |
[
"I was indeed thinking about such a material's application in a heat sink."
] |
[
"Is the belief that a comet triggered the Cretaceous–Paleogene extinction still the most widely held belief?"
] |
[
false
] |
If so, can someone explain to me how a comet could have triggered such a mass extinction?
|
[
"In general, the idea that the object that made the ",
"Chicxulub crater",
" is at least partially responsible for the K-Pg mass extinction is not really controversial. However, there has been some suggestion that the late Cretaceous was already a somewhat difficult time for many large vertebrates, and so this impact may have been the giant asteroid that broke the camel's back, so to speak.",
"Arens and West 2008",
" suggest what they call a \"press-pulse\" model of extinction, wherein several of the worst extinction events throughout Earth's history are associated with the co-occurrence of both impact events ",
" changing climates on Earth (mostly due to periods of volcanic activity). There is at least some appeal to this idea, since we know of a few other large asteroid impacts that took place in the past but which don't seem to be responsible for extinction events of anywhere close to the same magnitude as the K-Pg (e.g., the ",
"Manicougan crater",
" in Québec, which at best is loosely associated with a minor extinction in the middle of the Triassic; ",
"source",
").",
"One finding that appears to support this idea somewhat is that many groups of dinosaurs were already experiencing ",
"negative net diversification rates",
" (i.e., species were going extinct faster than new species evolved) by the late Cretaceous (",
"source",
"). But of course, dinosaurs are just one group of animals that suffered the effects of the K-Pg extinction, and the cause of this decline is not clear, so it doesn't necessarily imply any kind of strong extrinsic pressure. It might be the case that the asteroid impact was pretty much the sole culprit after all. On the other extreme, there is also still a minority of researchers who maintain that the K-Pg extinction was mostly or even entirely caused by volcanic effects, most notably Gerta Keller (see her ",
"2008 paper",
" for example)."
] |
[
"Oh, and as for the second part of your question which I didn't see before, the details of how this mass extinction would have unfolded after the impact are somewhat variable depending on who you ask, but the overall picture is pretty consistent. Obviously, anything living in the immediate vicinity of the impact would have instantaneously been vaporized. Organisms living a bit further out would have been killed over the subsequent minutes and hours by massive tsunamis and other direct effects of the impact. Something like 500-1000 million tons of material were thrown into the air by the impact (",
"source",
"), and many of these pieces would have fallen back to Earth, heating up the atmosphere in the process which would have started huge fires as well as killing some animals just from the debris itself. And there probably would have been various earthquakes and tsunamis at further distances triggered by the impact; this is suggested to be the fate of the animals found in a ",
"recently described fossil deposit",
" you may have read about in the news.",
"All of this would have taken place within the first day after the impact, but until this point deaths and extinctions would have mostly been localized to the Americas. The expansion from this to a global mass extinction would have taken a bit longer, though still very little time by geological standards. It is generally accepted that the main long-term effect was a sort of unnatural winter due to dust and other particles filling the atmosphere and blocking out light. This probably would have lasted somewhere in the range of 6 months to a year or two (",
"source",
"), which is long enough to pose problems for any photosynthesizing organisms. Most likely, ocean plants would have suffered more than land plants due to their smaller average size (a lot of marine primary production comes from single-celled algae) and therefore energy reserves, and so some marine ecosystems may have pretty much collapsed. There are some variations on this theme; for example ",
"this paper",
" suggests that the long term effects of the mass extinction were more likely caused by climate change rather than direct blocking of photosynthesis, but the results would be pretty similar regardless.",
"While the actual direct effects of the impact would have only lasted a decade or so at most, Earth's biodiversity took quite a bit longer to recover. Though perhaps not as long as you might expect; ",
"one recent study",
" suggests that the impact site itself may have been recolonized by some organisms quite quickly, though fully functional ecosystems took somewhere on the order of tens of thousands of years to reappear."
] |
[
"Thank you! That was very detailed and well referenced. I appreciate the effort you put into that response"
] |
[
"What would it take for a fungi virus, such as cordyceps, to mutate and become a threat to humans?"
] |
[
false
] | null |
[
"Earth Sciences"
] |
[
"Earth Sciences"
] |
[
"Earth Sciences"
] |
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