title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"Does dissolution affect volume differently than just addition?"
] |
[
false
] |
Say I have two glasses of x amount of water. If I add y amount of salt to one and y amount rocks to the other, will both volumes be x+y
|
[
"Yes. Well, sometimes. Take alcohol, and add water. The total volume won't be x+y as the tiny water molecules \"nest\" themselves in the spaces in between the way bigger alcohol molecules, taking up less space in the end. This isn't always true though"
] |
[
"For dilute aqueous solutions one can assume that the solute does not take up any volume. As it gets more concentrated, however, this is not true and the volume will change with more solute added.",
"So for you, a little salt will not change the volume. 10% salt probably will."
] |
[
"Not necessarily. In case of salt (NaCl) the volume will be less than x + y. The term you're looking for is \"apparent molar volume\", see: \n",
"https://en.wikipedia.org/wiki/Apparent_molar_property",
"and also\n",
"https://en.wikipedia.org/wiki/Partial_molar_property"
] |
[
"Are people with high reward dependence more affected by low expectancy?"
] |
[
false
] |
Since people high in reward dependence ( ) are finely tuned to rewards, I would think that low expectancy ( ) would cause them to procrastinate more than people with low reward dependence, all other things being equal. Do you agree?
|
[
"Perhaps I don't understand your question, but I don't really see them as related. \"Expectancy\" is the level of perceived behavior control or self-efficacy in relation to a particular behavior (see Theory of Planned Behavior, Icek Ajzen 1985). We approach each behavior with a certain subjective belief that we will or will not be able to do that certain thing, both accounting for our own perceived abilities as well as any environmental factors which may hinder or assist us.",
"Are you saying that if people expect to fail, then they are consistently rewarded for their expectation?",
"Or that with low expectancy, any small success is a reward?"
] |
[
"I interpret OP to mean that people who seek reward are unlikely to begin a task which they perceive as having little to no potential for reward. I think OP wonders if that form if procrastination outweighs the \"more traditional\" form."
] |
[
"Thanks. I think, then, that not taking on tasks with low reward is not the same as procrastination. It is the wrong label. No one can do everything. Maximizing reward involves careful task selection. Reward seekers are likely to be active on tasks that provide rewards and likely not to be active on unrewarding tasks. Procrastinators are likely to be inactive on tasks that do provide reward.",
"Note that the definition of reward can be warped by external forces. The reward for filing taxes is being allowed to spend the rest of the year working on rewarding tasks. Filing taxes removes a barrier to further reward seeking. It is a form of groundwork. Procrastination contains the concept not only of avoiding high reward tasks but also of avoiding tasks for which there is a, possibly significant, penalty for lack of completion. Procrastination contains elements not only of failure to advance as far as possible but also of self harm. I imagine reward seekers who are not procrastinators choose not to do tasks with low reward but also choose to do tasks that, undone, would cause self harm."
] |
[
"How did astronomers discover the expansion of the universe was accelerating, given the huge uncertainty the Hubble constant?"
] |
[
false
] |
According to my physics teacher, depending on who you ask, they would say the Hubble constant is anywhere from 60-80km s MPc . But if that's the rate of expansion of the universe, how could they prove it's increasing if they don't know what the actual value of it is?
|
[
"Having some uncertainty doesn't mean we have no idea what's going on. If we say it's from 60-80 km/s/Mpc, then we really do mean it. If we said the Hubble constant is somewhere from -50 to 200 km/s/Mpc, then it would be okay to say that there is quite possibly no trend. But if we're saying it's 60-80 km/s/Mpc it means there's some scatter in the trend, but there is ",
" a trend.",
"This",
" is Hubble's original data. You can see there's clearly an upwards trend, there's just some scatter in it. The ",
"top plot here",
" is a more modern one. There's still a little bit of wiggle room, but you can't look at that data and say it doesn't look like a straight line."
] |
[
"Astronomers use a type of supernova called type 1a supernovas to measure redshift. Since type 1a supernovas always have the same absolute magnitude (brightness) and can be seen from very far away, it is possible to measure redshift extremely accurately. The Hubble constant is proportional to the redshift divided by the distance. It is the distance which we are not sure about in this equation, and which gives the hubble constant its uncertainty. Redshift is known well.",
"The redshift tells us how fast an object is moving away from us, then we compare the known absolute magnitudes (of type 1a supernovae) with the observed brightness, which gives us an idea of how far away it is. The results of such studies show that the further away objects are moving away from us FASTER than the closer ones, which implies acceleration.",
"this might help ",
"http://hyperphysics.phy-astr.gsu.edu/hbase/astro/univacc.html",
" "
] |
[
"The Hubble parameter (not a constant) is just a scale factor. If we are wrong by 10% that simply means that our distance scale is off by that amount. It's like using a meter stick that is only 90 cm long. It is still useful for comparing the distances to objects. For example, we can compare the speeds of objects whose distances differ by a factor of two, even though we don't know precisely how big the distances are."
] |
[
"How can energy be quantized if both speed and wave length are both continuous quantities? How discrete is energy?"
] |
[
false
] |
We all know that energy of electromagnetic radiation is equal to Planck's constant times the frequency. But both wave length and speed are continuous quantities that can take on any value, so how can it still be discrete? Thanks!
|
[
"The range of energy of electromagnetic radiation is not discrete.",
"EM radiation does come in discrete packets, though (photons).",
"Maybe you were confusing these two things?"
] |
[
"Energy is not quantized. What is quantized is the energy ",
". A more palpable way of saying it is that a wave of a given frequency or wavelength has a ",
".",
" This was not meant to be a reply to dukwon above, who has a fine answer."
] |
[
"Second quantisation is when you describe a system in QFT using a basis composed of the number of particles occupying each state.",
"First quantisation is just using states as a basis.",
"The advantage of (or need for) second quantisation is that it facilitates being able to describe interactions where particles are 'created' and 'destroyed'."
] |
[
"How does stress actually make you ill?"
] |
[
false
] |
I've been told, and read many times that stress makes you ill, and I don't doubt it; but how does it happen, biologically? It's always puzzled me as to how what is essentially an emotion or a feeling can make you physically ill.
|
[
"The answer here is a hormone called cortisol, as other posters have pointed out.",
"Whenever you have stress, you will get a hormone from your adrenal gland (your adrenal gland looks like a beanie hat that sits atop each of your kidneys) called cortisol. This hormone was designed with real stress (fight-or-flight, being chased by a lion) in mind; it raises your blood sugar and increases delivery to the brain, increases the breakdown of fat, protein, and carbohydrates to provide fuel to your muscles, and also suppresses the immune system as an anti-inflammatory. In fact, when you have an infection your immune system uses cortisol to ensure that it keeps itself in check too.",
"The problem is if you have a lot of cortisol around all the time, you'll continue to suppress your immune system and with your immune system dampened you will be less able to fight off pathogens and more likely to get sick. Cortisol was designed to be a short-term hormone-- in people with chronic elevations, it can be really bad (i.e. people with pathologic high levels of cortisol all the time from certain tumors, etc, known as Cushing syndrome)."
] |
[
"Actually the mechanisms are pretty well understood, go grab a physiology textbook if you have any questions about the stress response.",
"Yes, the hypothalamus and pituitary gland are involved, but cortisol is released from the adrenal glands which sit on the anterior of the kindeys (closest to the head).",
"The actions of cortisol are wide ranging and can be read here:\n",
"http://en.wikipedia.org/wiki/Cortisol",
"I browsed the wiki article and it seems good to me.\nEDIT: Mechanism for DNA damage by cortisol.\n",
"http://www.dukehealth.org/health_library/news/at-last-a-reason-why-stress-causes-dna-damage"
] |
[
"sort of. cortisol suppresses your immune system, which weakens your ability to fight off infections. the reason for the suppression is that maintaining the immune system takes a ton of extra energy that cortisol redirects into being used against external threats."
] |
[
"How do I stop crystalization in a non-hygroscopic sweetner?"
] |
[
false
] |
How do I prevent Erythritol from recrystalizing in drinks, candies, baked goods, etc? I've asked this in askcullinary and nobody could help me. It dawned on me it may be more of a science question. My diabetic father is eating himself to death. I am desperate to make some low carb deserts that will fool him and hopefully convince him to switch to some of my recipes i'm trying to work on. (Wikipedia) is the best candidate so far, there is absolutely no aftertaste. I'll spare you all a description, you can click the link for more info. Please correct me if I'm asking the wrong questions. Unlike sugar the erythritol does not readily absorb water, it repels it. That seems to cause it to easily crystalize. For example, when adding them to a cheesecake it will be fantastic at first. Twenty-four hours later and the sugar has recrystalized and the treat now feels as though it has sand inside it. Gummy-Bears were awesome for about 10 minutes, then opaque speckles apeared which started growing till the whole candy became crunchy. I've heard of mixing sugar with corn syrup and the long molecular chains disrupt the sugar recrystalizing. This (even if it worked) isn't an option because of the carbs. I've heard cream of tartar can help prevent sugar from crystalizing. Is this because of the acidity? I'm willing to do tests, but I was hoping I could get some direction instead of baking $20-$30 failures every day.
|
[
"Amateur candy-maker/chemist here. ",
"The usual MO is to add glucose/corn syrup/inverted sugar to a sucrose mixture to stop crystalization. Corn syrup is glucose, mostly. The similar-but-not-quite-the-same structure of sucrose to glucose or other sugars means the crystals can't form efficiently. Even with sucrose being hygroscopic there will still be sugar crystals if you don't have the correct recipe and technique (which is tricky to do at home).",
"Cream of tartar is an acid, as you noted, and the hydrolysis of sucrose to glucose and fructose is acid-catalyzed. So basically by adding cream of tartar you make your own invert sugar out of sucrose instead of adding it. It will do nothing useful to erythritol.",
"Swapping out one chemical for another is always going to cause problems, as you're finding out. But you could try to mix a few sugar alcohols together to keep any single one from crystallizing out. Or stick to confections like hard candy or fudge where you want crystals. "
] |
[
"The hygroscopic properties have nothing to do with it. A sweetener that doesn't affect blood glucose levels, as is the case with erythritol, is what is sought after. However, conventional sugars (sucrose, glucose, fructose) are much easier to bake and cook with, as this is what we are used to."
] |
[
"The mixing is a good idea. I'll have to read up on the digestive stability of all the other ones. Thanks!"
] |
[
"When a ventilator is removed from a patient in order to allow them to die, is it possible for that patient to feel as though they are suffocating? And if so, can any steps be taken to prevent or mitigate this?"
] |
[
false
] |
[deleted]
|
[
"Patients are generally taken off ventilators when they are ",
"bread dead",
", and since there is no brain activity, the patient should, in theory, feel nothing.",
"Brain death is not the same as ",
"persistent vegetative state",
" or being terminally ill. I do not believe patients are taken off respirators under those conditions unless the decision has been taken to euthanize, in which case other drugs will be used - the ventilator will not just be switched off, as it were.",
"Edit: grammar."
] |
[
"Very unlikely. Even if the person isn't unconscious from their illness or injury the pain killers and sedatives used should prevent any awareness of the situation and prevent any suffering. ",
"In the uncommon situation where you believe that there is a possibility of consciousness or awareness then you'd administer either more pain killers or more sedatives or both. ",
"The caveat is that the approach to end of life care varies significantly between areas and counties. Timing of withdrawal of care, who makes the decision, and how is it done, are all managed differently in different countries. Not unsurprisingly there is considerable controversy surrounding the issue."
] |
[
"Thank you for this response. This puts my mind at ease."
] |
[
"A gardener I know had an argument against GMO crops that to my layman mind seems \"sciency\" and makes sense. Is there any truth in this?"
] |
[
false
] |
[deleted]
|
[
"His argument has nothing to do with GMO and is an argument against monoculture, which we already practice quite extensively. \nMonoculture is the practice of using a single variety of plant across wide areas. It is done to control exact features of the crop so they are all identical and require identical management and are harvested at the same time. Most Western world farmers plant monoculture fields already and are susceptible to the issues he listed above already whether those crops are GMO or not. We have even seen the worst case happen pre-GMO when ",
"Gros Michel",
" bananas were virtually wiped out by a fungus. ",
"GMO crops have little to no diversity, sudden and unexpected changes can be catastrophic, whereas an organic crop will be relatively ok.",
"GMO is not the opposite of organic. You can grow a GMO seed to harvestable crop organically. GMO describes how the genes arrived in the seed, by manipulation in a lab rather than by natural crossings. Organic is a method of growing crops using no artificial fertilizers or pesticides. Neither protect from the ravages he is worried about, only not planting monoculture crops would. "
] |
[
"He said that in a normal organic crop there is a lot of genetic diversity and in normal conditions won't produce as big a yeild as a GMO crop. ",
"Unless you are growing heirloom; all organic, conventional and GM crops come from the same hybrid stock. GM crops are not clones and are exactly the same as the others with 1 -2 genes changed.",
"He said that if a new disease emerges, or an unexpect plague, or unseasonable and/or extreme weather happens, a GMO crop could be effectively completely destroyed.",
"GM crops are not clones. They have the same genetic diversity as organic and hybrid crops."
] |
[
"So they have to change the genes in every plant individually?",
"No, they just cross a hybrid crop with GM plants. The resulting plants have a group of GM \"Fathers\" but different \"mothers\". They only need enough GM plants to have broad enough genetic diversity. And additional genetic diversity comes from the crossing. ",
"It is the same method used in hybridization"
] |
[
"Why is the \"Great Attractor\" further from the site of the Big Bang than the rest of the universe? How did it get out there first?"
] |
[
false
] |
[deleted]
|
[
"This is not the case, and that's not what the term Great Attractor means.You've got several misconceptions here.",
"There is no \"site of the Big Bang\" or center of the universe. The universe appears to be infinite in size. The bang happened everywhere in the whole universe, all at the same time.",
"There's nothing \"pulling\" things \"outward.\" Galaxies move apart because the space between them continually expands. ",
"The \"Great Attractor\" is just the name for a particular object, observed in one specific spot in intergalactic space. We don't have a good name for it, because we can't see well in that direction, and therefore don't know what the object is. The name we use was invented because we infer it to be very massive and therefore to have very powerful gravity.",
"In short: we can't answer the question because you have based it on many incorrect assumptions."
] |
[
"To be fair, the Great Attractor is somewhat separate from the dark flow (and predates its discovery by a couple of decades).",
"You have a perturbation theory tag. Maybe I should get you to do my current project for me...",
"...",
"..."
] |
[
"We know that all visible bodies are moving \"outward\" at an ever accelerating pace, and that some giant mass is probably \"pulling\" them.",
"We only know that galaxies are moving outward at an accelerating pace -- there is nothing to suggest that something is \"pulling\" them, and in fact none of our best models actually predict this. The best models we have of this effect involve what is known as the ",
"metric expansion of space",
", which is an ",
" expansion that is ",
" caused by any pushing or pulling due to forces. This type of expansion is caused by the definition of distance (known as the \"metric\") getting larger over time. No external mass is required for this -- no forces are exerted.",
"Also as other people have noted, there was no \"site of the Big Bang.\" The Big Bang also involved a very rapid metric expansion (known today as ",
"cosmic inflation",
". So in other words, nothing \"exploded\" -- it just \"inflated,\" similar in some ways to how a balloon is inflated. Nothing on the surface of the balloon is acting on anything else on the surface, but because the balloon is expanding the things on the surface still get further away from eachother."
] |
[
"After reading of a redditor that is collecting his earwax, I ask science: What kind of stuff and how much is coming out of the human body during an average life?"
] |
[
false
] |
[deleted]
|
[
"Excretion is any process which gets rid of unwanted metabolic products. This includes carbon dioxide, in the air we breathe out; nitrogen and salts in sweat; urine; bile pigments in faeces; hair and nails can also be considered excretion.",
"Copypasta'd from an overview of the excretory system.",
"Here's more",
"Talk about the excretory system won't include phlegm or ear wax, I don't think. This would be because those two specifically are necessary biological processes to protect your health, not just waste to be expelled."
] |
[
"It'd be interesting to know how much 'dust' (skin flakes, dandruff) we create (and subsequently wipe off our house) each month?"
] |
[
"Of those billions of skin cells, between 30,000 and 40,000 of them fall off every hour. Over a 24-hour period, you lose almost a million skin cells."
] |
[
"Interresting Physic-experiments with light bulbs?"
] |
[
false
] |
Hi there, . Some of my buddies, and I are doing some experiments with light bulbs, for a physic-assignment. Do you guys know any interesting/radical/fun experiments, involving light bulbs? Preferably experiments where you can calculate a specific result based upon the experiement, and/or its result(s). I want to thank you all in advance, for taking the time to read this.
|
[
"If you have something to measure light intensity and some filters:\nApply some voltage over the bulb and measure the light intensity at different wavelengths (using filters). Plot the intensity as a function of wavelength and compare to a blackbody radiation (and estimate the temperature). ",
"Repeat with different voltages and plot the bulb temperature as a function of voltage and compare to something like P = V",
" *R (you have to convert temperature to power before doing so). "
] |
[
"Thanks for the suggestion! We'll ask our teacher next class. Hopefully, its releated to the assignment, but to us, it sounds like it is."
] |
[
"When I was taking a computational physics course, the prof mentioned that before we had supercomputers to do many body simulations (e.g. a bunch of point particles with gravity between them), a team used light bulbs to represent masses. Because, like gravity, light intensity goes as 1/r",
" they were able to come up with a force on each particle and advance the simulation in time. Obviously for a lot of particles this is a huge amount of work - you have to record the position and velocity of each particle at each timestep - but for just 2 light bulbs this might be feasible. You could see if you could achieve a stable orbit/verify Kepler's laws."
] |
[
"Are there any substances the Liver or Kidneys can't remove? Therefore in our blood forever."
] |
[
false
] | null |
[
"The liver can’t directly remove substances. It can, however, chemically break down many substances, rendering them harmless.",
"\nThe kidneys work like inverse filters, wih the ",
"Nephron",
" being the functional subunit.",
"\nAt the first step, everything under a certain size (approx. 60000 dalton) gets thrown out of the blood, including water, salts, smaller proteins etc.",
"\nThis happens at the basal membrane inside the glomerulus. This ‘primary urine’ then enters the decending limb followed by the loop of Henle, then the ascending limb. Cells making up these structures then reclaim everything the body still needs. Unknown substances are neither necessary nor recognizable so they just get thrown out.",
"\nMolecules larger than 60000d can’t be handled in this fashion but then it is hard to see how such large molecules would enter the body other than trauma. In those cases the Glomeruli can get ‘clogged’ and the kidneys can fail. "
] |
[
"60000 dalton",
"The unified atomic mass unit or \"dalton\"",
"A dalton is a standard unit of mass that quantifies mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit (dalton) is approximately the mass of one nucleon (either a single proton or neutron)."
] |
[
"Re: The Kidney.",
"If it gets into the blood stream then it needs to go through the filter (the glomerulus) then it would need to be reabsorbed by the loop of Henle otherwise it would just go out through the collecting duct and urine.",
"If it can’t get through the filter (in cases where substances crystallize and get caught in the filter), the kidneys stop working and the patient would need to go onto dialysis in order to live."
] |
[
"Why does the parsec exist?"
] |
[
false
] |
Why does the parsec exist next to the lightyear? The difference between the two (a parsec is just over 3 lightyears) means that using one or the other doesn't make much of a difference, does it? Most of the time I see distances to other planets expressed, it's in lightyears, too.
|
[
"The parsec is named for the ",
"allax of one arc",
"ond. Now parallax deals with perspectives, and how things closer to you seem to move more quickly than things that are further away, so the observed, or apparant shift with regards to more distant objects,and arcseconds are a measure of angle.",
"\n Now the parsec is used to measure large distances, and if you imagine a right angled triangle, if the angle is 1 arcsecond, and the opposite is 1 astronomical unit (distance between the Earth and the Sun) then the adjacent will be 1 parsec. This gives us a unit for long distance that can be related to known values.\n Now we use the parallax as we determine distances in space by the change in apparent angles to bodies in space. Once we have determined the angle, we can then use trigonometric small angle approximations to calculate the distance between the body in space, and the Sun, as that us the reciprocal of the angle in arcseconds. ",
"Wikipedia's diagram"
] |
[
"The Parsec is handy because it allows one to determine distance from earth by just measuring the parallax angle as the earth moves around the sun (which is why the Parsec is fundamentally related to the AU). That convenience aside, it is just another distance unit. If it is used to specify something like the length of an astrophysical jet in a particular article, that's probably because the author thinks that the audience for that article will find that the most natural unit to use. It's likely just a matter of convention."
] |
[
"And it is easier to measure an angle in the sky than to directly measure a distance. Indeed you don't even need a good distance estimate to start tabulating parallax angles. Only if you want to convert them to the distance we now know it represents"
] |
[
"Does the ringing in the ear emit an audible sound?"
] |
[
false
] | null |
[
"The \"ringing\" sound you hear is purely your perception, there isn't actually any sound or vibration being produced in your ear."
] |
[
"Audiologist here - no, the ringing you refer to is called tinnitus and research at this stage is showing that it is central in nature (i.e. it is happening in the auditory centre /pathways in the brain, and is not coming from activity of the hair cells in the cochlea).",
"People often try to relate spontaneous onto acoustic emissions to tinnitus, Which is not accurate. While otoacoustic emissions do emit a measurable sound (very very small though), this sound is not strongly associated with, nor is it the cause, of tinnitus. :)"
] |
[
"There are some sounds people report hearing that can be heard or recorded from the outside. These are collectively called \"objective tinnitus.\" Someone already mentioned otoacoustic emissions. Many people have spontaneous otoacoustic emissions, meaning that their ear just starts emitting sound without any stimulation. Some people can hear their own spontaneous otoacoustic emissions, and they usually report that as hearing ringing. Some people also notice that their baby's ears make a ringing sound, and even other animals like dogs. This is not the typical reason people hear ringing, but these cases are a definite yes to your question.",
"The other sounds that come out of the ear (objective tinnitus) don't necessarily sound like ringing. If your Eustachian tubes don't close you can hear your breathing like a whooshing noise (patulous Eustachian tubes). That wooshing can be recorded from outside of the ear. Some people can hear their pulse, and I stuck a microphone in a friend's ear and recorded this once. That's usually just because of a vein or artery that grew close to the surface of the middle ear, but it can be a sign of a middle ear pathology. Another thing that people sometimes hear is their TMJ clicking, because it's right next to the ear canal. I can't think of any more types of objective tinnitus off hand. Good question."
] |
[
"Does light affect our organs?"
] |
[
false
] |
Since our organs are always in the dark, presumably one of the only circumstances they get exposed to light is during some sort of surgery. Does this sudden exposure to light have any effect on our insides?
|
[
"evolved (or were created with depending upon your theory of the origin of life)",
"Please refrain from making the implication that evolutionary theory and creationism are on the same footing here. Evolution is well substantiated and supported by thorough evidence, while creationism is an unsupported religious teaching.",
"There's no need for you to try to play safe by including that line. I trust we are in a place where science denial is uncommon."
] |
[
"Tl;dr: UV light affects hematopoiesis so it occurs in the bones cuz it’s dark.",
"Idk about visible light but UV certainly does! We all know that it can cause DNA damage, thus leading to cancer. But I want to talk about blood, which is also susceptible to UV damage. In fish hematopoiesis (the process of making blood cells) occurs in the kidneys, which are covered in a layer of melanocytes (“melanin cells”). Terrestrial animals, however, don’t have a water column to protect them from the bulk of the UV radiation, so hematopoiesis happens in the bones! Because it’s the darkest part of the body. Google “Kapp et al 2018 Nature” if you’re interested in further reading."
] |
[
"I do recognize your comment as being one regarding some fairly interesting concepts about blood production and it's sensitivity to light.",
"That being said, statements that are based strictly on belief don't belong in science (even if its just cursory). All data points to humans having evolved over millions of years. The only open question where the creationist belief may be valid is in biogenesis. But since your comment only pertains to the trait of bone marrow based blood production it simply does not fit.",
"Science is not and should never be based on beliefs. Science is naturalistic and relies on empirical data collection. Any theory which may contradict experiment must be thrown away regardless of how appealing it may be."
] |
[
"Why doesn't the Alcubierre drive violate causality?"
] |
[
false
] |
With the understanding that don't exist yet, but are theoretically possible if we ever discover the requisite type of exotic matter. However, I was under the that any faster than light communication could result in a causality violation. So why are Alcubierre drives theoretically OK?
|
[
"It does. Anything moving faster than light can be used to communicate with the past, regardless of how it functions. There are other reasons why such a thing can't exist, see ",
"here",
"."
] |
[
"No.",
"General relativity states that no two objects in the ",
" reference frame can go faster that the speed of light relative to each other - which would otherwise cause violations of causality and time travel.",
"How Alcubierre drives[1] move is different: they move in a ",
" reference frame of space, while the space is contracting and expanding around it - the drive is actually ",
" ",
".",
"What basically happens is that the alcubierre drive allows an object to seperate it's frame of reference from any object around it aka a \"warp bubble\". Which does not violate GR."
] |
[
"Although it is worth noting that historically, nonsense which is mathematically consistent has, on occasion, not been nonsense.",
": I'm not saying I expect negative mass to be a real thing. I'm saying we should not so eagerly dismiss it. ",
": I gave a brief summary of the physicality of Alcubierre drives ",
"here",
"."
] |
[
"Pick a (uniformly) random integer 0 <= a1 < 1000, then pick another 0 <= a2 < a1, and so on. What is the expected number of steps to reach 0?"
] |
[
false
] | null |
[
"Hmm I should be packing but you caught my attention.",
"With problems like these it's often helpful to start smaller to build the intuition. Perhaps we can generalize the problem to E_x(Y), where x is the starting number and Y is the number of steps to reduce it to 0. We can find out that E_0(Y) = 0 and E_1(Y) = 1 fairly easily. From here on I'm going to drop the (Y) from the notation because I'm lazy. ",
"Now we can look at this as a recursion problem. E_2 = 1 + (1/2)E_0 + (1/2)E_1. This is true because you will use one step to reduce the problem to E_0 or E_1, each with equal probability. Since we already know both these smaller values, we can compute that E_2 = 3/2.",
"We can generalize this formula:",
"E_n = 1 + (1/n)SUM(E_i) over 0 <= i < n\n",
"But since each E_i can be rewritten as previous E_i's, why don't we try to get this strictly in terms of the previous one?",
"Recall that E_2 = 1 + (1/2)(E_0 + E_1). This means that E_0 + E_1 = 2(E_2 - 1). We can substitute this into the formula for E_3 to get E_3 = 1 + (1/3)[2(E_2-1) + E_2] = 1 + (1/3)[3E_2 - 3] = E_2 + 1/3.",
"Now, in general terms, E_n = 1 + (1/n)[E_(n-1) + SUM(E_i)], where our sum is from 0 to n-2. Also, E_(n-1) = 1 + [1/(n-1)]SUM(E_i) where the sum is also from 0 to n-2. We can combine these by solving the second for the sum, SUM(E_i) = (n-1)(E_(n-1) - 1).",
"Putting this back into our expression for E_n, we get E_n = 1 + (1/n)[E_(n-1)+(n-1)(E_(n-1) - 1)] = 1 + (1/n)[nE_(n-1)-(n-1) = E_(n-1) + 1 - (n-1)/n = E_(n-1) + 1/n.",
"Long story short, E_n = E_(n-1) + 1/n and E_0 = 0. This recursion is solved with the ",
"harmonic sequence",
", or E_n = SUM(1/i) where i ranges from 1 to n. ",
"This means that your question has no closed form answer, but it does act like ln(n). Your experimental value of 2.66 is fairly close to e, so this makes sense. ",
"Now if only I were writing this in LaTeX so you could actually follow it... But thank you for the interesting question! I thoroughly enjoyed solving it this morning. "
] |
[
"Haven't done any programming for a few months and it would be nice to start doing it again. This seemed like an easy and fun enough thing to do. Wrote a short code that did what you described a 1,000,000 times and got an average of 7.486 random integers to get to 0 each time."
] |
[
"For more info on the sum, these are ",
"harmonic numbers",
" H",
". What you found numerically was that for large N, H",
" is approximately log(N). This is actually the beginning of a series in large N for the harmonic numbers: ",
"H",
" = γ + log(N) + 1/(2N) - 1/(12N",
") + ...",
"where γ ~ .577 is the Euler-Mascheroni constant, and you can see the rest on the wiki link above. But the above terms already give you great accuracy all the way down to N = 1.",
"EDIT: And I should mention the answer to your OP! Plugging in N = 1000, you get 7.48547, consistent with ",
"/u/geckon",
"'s numerics."
] |
[
"The Pacific Northwest had a particularly wet and gloomy summer recently. As a consequence many trees that were not covered in moss are now blanketed. What effect does this blanket of moss have on the tree's health?"
] |
[
false
] |
[deleted]
|
[
"In terms of an exact relationship between the two, the moss wouldn't really have a negative effect on the tree. Mosses are not ",
"parasitic",
", and therefor would be simply using the trees as a ",
"substrate",
")(a medium to grow on).",
"Mosses are ",
"epilithic",
", therefor they will gather all of the water and nutrients they need from their surroundings and not from the tree itself. ",
"Mosses won't necessarily 'steal' water or nutrients from the tree. The tree has a vascular system that will gather these in the soil. The mosses on the other hand, as mentioned above, will collect water and nutrients from the atmosphere and their surroundings. ",
"I hope this answers your question, if you have any further inquires please do ask. If this isn't suffice, I will try my best to look through some literature and peer reviewed sources to find more appropriate answers. "
] |
[
"Actually, a number of mosses (Sphagnum for instance) are known for their production of antifungal/antifeedant compounds. I'm not sure of the exact literature for their relationship with trees, but I'd assume that they may confer a certain degree of protection.",
"I'm not an ecologist though, so take what I say with a pinch of salt."
] |
[
"Actually, a number of mosses (Sphagnum for instance) are known for their production of antifungal/antifeedant compounds. I'm not sure of the exact literature for their relationship with trees, but I'd assume that they may confer a certain degree of protection.",
"I'm not an ecologist though, so take what I say with a pinch of salt."
] |
[
"How do we have accurate records of hurricanes before satellites?"
] |
[
false
] |
For example, the 1899 San Ciriaco hurricane. We have a track for it, and even a time frame for intensification and weakening.
|
[
"Reports from different places at the same time and different times in the same place, from ships at sea as well as land-based observers. Put the data together like pieces in a puzzle. Fill in the holes with educated inference."
] |
[
"Historical investigation can tell a lot. ",
"We know that a major super quake occurred in a Cascadia in 684AD because of very specific descriptions of a massive tsunami wiping out coastal settlements in Japan on November 29, 684, then they could estimate the actual date of the quake by how long it should take for a tsunami to cross the Pacific Ocean, then look for geological evidence that lines up with the dates in the western US.",
"They even found oral histories in First Nations tribes in B.C. and Washington that seem to describe the event as well.",
"Like was said, it’s all about finding different pieces of the puzzle and fitting them together"
] |
[
"Going back even further -- paleoclimatology! Using lake cores, geologists can discover hurricanes hundreds of years in the past. Here's an article about it: ",
"https://insideclimatenews.org/news/01102019/hurricane-warm-water-climate-change-history-science-study-sediment-core-donnelly-muller"
] |
[
"It is a better strategy to attempt to appeal to the logical or emotional nature of a jury (or equivalent person(s)), given similar/equal strengths of each argument?"
] |
[
false
] |
My intention is to ignore any counterargument by an outside party in this case (i.e. considering only the target party's reaction to your argument). Stated more generally, is a person (or group of people) more likely to be susceptible to holes in an argument of logical vs. emotional nature? Also, are they more likely to be swayed by equivalently compelling arguments of one type vs. another?
|
[
"This is a difficult question to answer because the line between the emotional and the logical is not clear cut. I am going to try and answer you by separating out affect and cognition based on their deliberative components. ",
"Think of affect and cognition as two separate sources of input driving us towards an attitude or decision. Consider affect as the sum of the jury's intuitions, automatic associations, and general feelings toward the question they are considering. Consider cognition as the mental processes that the members of the jury actively and deliberately engage when trying to sort out the information that they have been given. ",
"The way these two processes are going to interact and the ultimate answer to your question is going to come down to the decision making strategy employed by the members of the jury. I suggest that individuals in the situation that you have described are likely to be engaging in deliberate cognitive processes and that these processes have a tendency to bias people against affective information even when that information is useful and relevant to the judgment that they are being asked to make. The reason for this bias is debated but generally it is attributed to the difficulty associated with verbalizing many types of affective information and the general consensus among many western thinkers regarding the usefulness/accuracy (or lack thereof) of affective information. Worded another way: when individuals are motivated to consciously consider their reasons for an attitude or decision there is strong evidence that they are particularly biased towards immediately salient and easily verbalizable information, often at the expense of other types of useful information.",
"My short answer to your question would be that your best bet is to rely on logical holes because people in this situation may be biased against using emotional information in their decision making even if that emotional information is relevant or important. ",
"Here are a few references if you are interested, also I research the interplay between affect and cognition and the specific way that the generation of reasons can alter attitude formation and maintenance. Reasons generation has been shown to decrease accuracy in some situations. Also, people who make decisions based on reasons that they have generated have been shown to be less happy with those choices at a later date. I think the key is realizing that both sources of information have a place in our decision making and attitude formation.",
"The last reference is a fairly long paper and its from 1977, but its still worth a read if you have the time and interest. Feel free to send me a message if you want to talk more about these effects.",
"References: ",
"1) Dijksterhuis, A., & Nordgren, L. F. (2006). A theory of unconscious thought. Perspectives on Psychological Science,\n1(2), 95–109.",
"2) Halberstadt, J., & Hooton, K. (2008). The affect disruption hypothesis: The effect of analytic thought on the flu-\nency and appeal of art. Cognition and Emotion, 22, 964–976.",
"3) Halberstadt, J. B., & Levine, G. L. (1999). Effects of reasons analysis on the accuracy of predicting basketball games.\nJournal of Applied Social Psychology, 29, 517–530. ",
"4) Wilson, T. D., Kraft, D., & Dunn, D. S. (1989b). The disruptive effects of explaining attitudes: The moderating effect of knowledge about the attitude object. Journal of Experimental Social Psychology, 25, 379–400.",
"5) Wilson, T. D., Lisle, D. J., Schooler, J. W., Hodges, S. D., Klaaren, K. J., & LaFleur, S. J. (1993). Introspecting about reasons can reduce post-choice satisfaction. Personality & Social Psychology Bulletin, 19(3), 331–339.",
"6) Nisbett, R. E., & Wilson, T. D. (1977). Telling more than we can know: Verbal reports on mental processes. Psy-\nchological Review, 84, 231–259.",
"Edit: changed 'out' to 'our' in the last line of my second to last paragraph before references."
] |
[
"Interesting read. Thanks for posting it. I'm curious about something relating to your reply and the OP's question.",
"Do you think that the different sides in a trial would prefer more logical vs more emotional jurors?",
"The reason I ask is that several criminal case attorneys in the past I have spoken with have said that the Defense would prefer more emotional jurors. The supposed reason being that the defense attorney has to get a juror \"emotionally involved\" with the defendant in order to negate the effects of evidence against the defendant. I actually had one defense attorney tell me how to use this to not get selected as a jury member (I'm NOT advocating this as a way to avoid jury duty, but was told in many cases it would work. But you COULD be found in Contempt of Court by the Judge if they thought you were doing it). I was told that during the jury selection process, one or the other of the attorneys (prosecutor or defense) must ask a potential juror if they believed they could objectively evaluate the evidence to arrive at a verdict. If the potential juror answered something like, \"Yes, I will not allow my emotions to prevent me from an objective analysis of the evidence...\", the defense attorney is going to probably eliminate that potential juror in the first round of \"without cause\" exclusion, simply because they don't want a totally objective juror who would weigh the evidence alone sitting on the jury.",
"Your thoughts? "
] |
[
"Hey, sorry for the delayed response. I think the answer to your question is related to the decision making strategy part of my original response. If you can determine that certain individuals are unlikely to engage in a deliberative, analytic process, even when instructed to do so, then you may be able to lessen the impact that concrete evidence has on those individuals' reasoning. One element that I neglected to mention in my first post is the willingness to engage in extra cognitive effort beyond simply going with your first reaction to the evidence/question. I would speculate that most individuals would take the extra step when instructed to do so directly but there will inevitably be a subset of individuals who will not or cannot apply any extra cognitive effort and who will be chained to their intuitive responses. Some people even operate with the belief that intuition is superior to cognition across the board. Check out this article for a quick overview of the 'smarter' intuition issue."
] |
[
"Helicase - how does it work?"
] |
[
false
] |
How does this enzyme decide to move its arms around to cut bits of dna up to make two copies of dna? This is what happens in your cells - but what motivates huge molecules to move around and do the things they do?
|
[
"I can't speak to ",
" they do it, but ",
"helicase",
" hydrolyzes ",
"ATP",
" to create the energy needed to do it's task.",
"Contrary to what you said, Helicase only unwinds the two annealed strands of DNA. If you think of DNA as two pieces of string twisted together, Helicase moves along the two strands, and separates them into two separate strands. You may also want to think of it as the zip on a zipper (except it only unzips). ",
"The energy needed for this task is provided by ATP. ATP, Adenosine Tri-Phosphate, is essentially the base unit of energy used in our bodies. It's a long task to explain how it's created ",
"(read more here)",
", but in short, all the food we eat gets catabolized into ATP for use in energy-requiring tasks.",
"The thing that actually does the duplicating is ",
"DNA Polymerase",
". After the two halves are separated, DNA polymerase comes along, and starts adding on the DNA base pairs. ",
"The actual biochemical mechanism behind base-pair attaching and detaching, and the kinetics behind the motion of helicase I am unsure."
] |
[
"http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Projects04/HELICASE/FUNCTION.html",
"Best I could find!"
] |
[
"Here's an article about how DNA helicase is recruited and loaded"
] |
[
"Why do cymbals/hi-hats still sound so horrible in high bit-rate mp3's?"
] |
[
false
] |
They sound like they're vibrating against a bunch of sand, or something. Are the standard codecs not suited to something unique about cymbals' spectrum of tones? If so, what?
|
[
"Cymbals are a \"",
"canary in the mine",
"\" indicator of low-bitrate mp3's. A crash cymbal's decay, for example, sounds quite different as you drop the bitrate while they generally sound fine at 320kbps and up. And yes, the standard codecs require a higher bitrate to encode such sharp, wideband sounds.",
"What bitrate are you using?"
] |
[
"Mp3s are smaller than their wav counterparts because the encoder uses an algorithm to literally truncate the higher frequencies (where cymbal crashes occur). A frequency needs to be sampled at least two times to get an accurate \"idea\" of its shape and amplitude, so in order to sample 18,000Hz it needs to be sampled at 36,000Hz. But those bits of information take up a TON more space than the bass frequencies, so the algorithm starts looking for ways to remove ones that are deemed to be removed. I know there is more to it, but I think this is the gist of it."
] |
[
"Sound about right. Just a side note, there's not a 1:1 correlation between file size and quality, even though as a general rule of thumb it does hold somewhat true. "
] |
[
"Could nuclear power plants on the moon transmit wireless energy to an earth based receiver?"
] |
[
false
] | null |
[
"It could, but there would be a few problems:"
] |
[
"I disagree about that second part being a problem."
] |
[
"Why? It would seem that a microwave beam or something carrying gigawatts would fry just about anything. Or, if it is not concentrated enough to do damage, the receiver on the Earth must be huge.",
"Furthermore, it would seem to me that the expected damage (chance of failure times damage caused in event of failure) from such a wireless power beam would be comparable, if not significantly more, than that of a nuclear power plant on Earth."
] |
[
"Why do batteries have internal resistance?"
] |
[
false
] |
College student here with some questions after my basic EMF physics lecture. The prof brought up a lot of things but can't go over them due to time constraints so I'd ask here. 1) Why do batteries have internal resistance? 2) How does a defibrillator return the heart to a normal beating rate when such a current through the body would stop it in the first place? 3) Why has the conventional "positive charges flow" not been changed now we know it is electrons that move through the circuit? Thank you everyone for your time, I'm sure to be back with more questions in the future.
|
[
"1) Why do batteries have internal resistance?",
"Well, imagine you're an ion heading through the electrolyte to be oxidized/reduced at the anode/cathode. You're going to be bumping into other molecules, giving off heat. ",
"2) It wouldn't necessarily kill someone, but anyway, the mechanism is that it depolarizes the heart muscle, resetting the action potential ion gradient.",
"3) The ",
" is that charge flows from positive to negative in an electrical circuit. There is no reason to change that because A) It's an established convention and the underlying physics of the charge carriers is irrelevant at the circuit design level. B) It's simply not the case that electrons are the only charge carriers. Batteries have positive ions moving in one direction and negative ones moving in the opposite direction. Even in a metal you have virtual positive particles (",
"holes",
") moving in the opposite direction. C) Because of A and B, the concept of the direction of an electrical current is and always will be a separate thing from the direction of the charge carriers anyway. All you'd be doing is changing so that the direction of current matched the direction of ",
" charge carriers ",
"."
] |
[
"then they'd immediately short out rather than powering a circuit",
"No, they would work fine. The reason a battery does not short itself out, (there are some leakage currents), is that when no load is applied, the ",
"ions build up a barrier",
") that counters the electrostatic potential. The system just sits there in equilibrium. Thereby stopping current flow.",
"Leakage current is what runs down a battery during shelf life. At room temperature some ions will have enough energy, through ",
"thermal distribution of energies",
" to jump this barrier. Leading to the battery running down. There is a very wide range of self discharge rates depending on the battery chemistry. When you apply the load, you disturb this equilibrium and the electrons have a way to get to the positive electrode through the circuit. One interesting battery type was the magnesium battery. When you initially applied the load there is no current. Then gradually over a few seconds it \"comes to life\"."
] |
[
"then they'd immediately short out rather than powering a circuit",
"No, they would work fine. The reason a battery does not short itself out, (there are some leakage currents), is that when no load is applied, the ",
"ions build up a barrier",
") that counters the electrostatic potential. The system just sits there in equilibrium. Thereby stopping current flow.",
"Leakage current is what runs down a battery during shelf life. At room temperature some ions will have enough energy, through ",
"thermal distribution of energies",
" to jump this barrier. Leading to the battery running down. There is a very wide range of self discharge rates depending on the battery chemistry. When you apply the load, you disturb this equilibrium and the electrons have a way to get to the positive electrode through the circuit. One interesting battery type was the magnesium battery. When you initially applied the load there is no current. Then gradually over a few seconds it \"comes to life\"."
] |
[
"Why aren't viruses considered alive?"
] |
[
false
] |
I get that we have a list of criteria for something being alive (i.e. it has to grow, reproduce, evolve, respond to stimuli, etc.) and that viruses fail several of these criteria. Here is my issue though, isn't this list arbitrary? Like, why draw the line at a place that excludes viruses. They sure alive by many standards. They even have genetic material, reproduce, and evolve. It has been proposed before that our definitions of life could exclude life on other planets that evolved differently from Earth. Doesn't that mean we are just arbitrarily choosing to exclude some from Earth itself too? Is there a reason or a benefit to exclude viruses from the tree of life?
|
[
"It's semantics, someone drew a line in the sand and here we are. ",
"Definitions get fuzzy in biology sometimes. There isn't a great way to determine how different two organisms need to be to be two different species, and biologist will often fall into two different camps on how to do it (called ",
"lumpers and splitters",
").",
"Your genome is filled with sequences that are basically retroviruses that have lost the ability to escape the cell (called ",
"LTR Retrotransposons",
") but still replicate and move around your genome. It's even possible that some viruses evolved from transposons. If you look hard enough you can even find LTR Retrotransposons that still have parts of the genes they needed to burst out of a cell (called ",
"Endogenous Retroviruses",
"). Where are you going to draw the line here? Is your genome filled with living organisms? Or has it been part of the genome so long (all eukaryotes have transposons to some extent) that it is just part of who you are?",
"Dichotomies are useful for discussing biology, but the reality is that things are rarely black and white."
] |
[
"As a virologist, this question comes up quite a bit. To be 'alive' a few things have to be true: (1) it must maintain homeostasis, (2) it must make its energy, ie ATP, (3) it must be able to grow/divide by its own machinery. Now by their very definition viruses do not meet any of these points and as such are not considered alive."
] |
[
"Parasites need the conditions of a host to reproduce, they still have all the proteins and organelles needed to do so. Viruses utilize the infrastructure of the host cell (enzymes and organelles) to reproduce."
] |
[
"Has anyone in the international community confirmed the findings at CERN showing faster than light neutrinos?"
] |
[
false
] |
[deleted]
|
[
"No, it's pretty much unanimously agreed that the results are wrong, but even the people who know the experiment best can't figure out where."
] |
[
"You have inherently assumed that FTL neutrinos are the same speed for all energies. The 1987 supernovae were MeV neutrinos, these are GeV neutrinos.",
"That being said much of the attention now is on the other beam-experiments to improve their timing game so they can refute this."
] |
[
"Wonderfully put, iorgfeflkd. ",
"To the OP:\nWith almost every physics article you will find a discussion of the physical effect that you or your team measured and contested. In the case of the OPERA neutrino 'experiment' the paper explicitly only stated the factual findings and refused to speculate any physical theory that could be behind the measured effect. The published paper was basically an invitation to everyone to find the 'flaw'. This is what the idea of 'peer review' is about. ",
"It's weeks now and even with adding thousands of more good brains stabbing into it, we still cannot put a finger on it. Sometimes nature baffles the best of us and incites minds to ask further. It makes science so unique and special."
] |
[
"Why does light differ from everything else?"
] |
[
false
] |
What caught me dumbfounded is that why is light/photons (including the visible and not visible spectrum and microwaves, radio waves etc.) the only thing that can pass through objects transparent or not(light specifically for transparent and the other waves for both transparent and opaque). I know they are like waves but a light can pass through a window while water cannot so to speak. ELI5 if you can EDIT: I know there are other things that can pass through objects aside from light BUT what I want to know is why can they while others cannot.
|
[
"First of all, light is not the only thing that can pass through matter. For example, neutrinos are constantly passing through even the most solid objects.",
"To understand why water can't pass through glass but light can, you have to understand electromagnetism. Matter that interacts with electromagnetism can interact with other matter that interacts with electromagnetism. So when the two objects get really close, they get repelled from each other and can't pass through each other. ",
"Photons are electromagnetic excitations, and objects that allow them to pass through like glass allows the light to be absorbed remitted in the same direction as it came in. There is no repulsive effect like with matter.",
"So that was a very simple explanation but I hoped it help. It comes down to the fact that photons are like waves on the ocean (excitations) while other matter is more like boats (can interact with photons, but not excitations)."
] |
[
"On an atomic scale atoms are actually pretty far apart from eachother. The majority of matter is actually \"empty\" space. I say \"empty\" space because space is never actually empty; it is filled with particles from photons; gluons; neutrinos and other types of matter in a sea of particles.",
"However with that being said particles even with the great distance they are apart only interact with other particles depending on the force. All interactions of Earth almost rely on electromagnetism, and is why one object can't just pass through another object. They are repelled, however a gas is to dispearse and it's electromagnetic interactions to weak to stop a solid object, water can be stopped by solid object as well, but it really depends on the material and it's electromagnetic interaction.",
"However neutrinos don't interact with electromagnetism at all, so it's easy to see why neutrinos will fly through the entire earth undisturbed without hitting anything.",
"Photons are actually what carry the electromagnetic force, they are emited from particles such as electrons and protons to mediate the force accross a distance.",
"However photons don't really pass through a material; most times they do collide with matter such as atoms; but when they do they are re-emited and eventually make it's way through the matter by being absorbed and re-emited until they leave."
] |
[
"there are many things that can go through a window, take for example neutrinos, they can even go through the earth without interacting with anything. "
] |
[
"How does a strong acid or base burn your skin?"
] |
[
false
] |
So I've tried to google this, and my bio/micro teacher doesn't have an answer for me. My money is on rapid denaturation of proteins in human cells, but all I can find from searching is "it causes a chemical burn." Thanks for any information you can provide!
|
[
"A strong acid is a strong dehydrating agent and what it does is take up all water from skin cells in an exothermic reaction, effectively \"burning\" them."
] |
[
"And a strong base causes your fat to undergo a ",
"saponification",
" reaction changing a bit of you into soap. Very painful soap."
] |
[
"this is why bases (even weaker ones) feel soapy. they free the fats that make up your cell membranes and use them, as stated above, to make soap"
] |
[
"How do meteorologists determine the chance of rain?"
] |
[
false
] |
[deleted]
|
[
"Very very very large simulations of the Earth climate integrated over millions if not billions of weather station readings. ",
"basically if you know that one point has a high barometric pressure and a nearby Point has a low barometric pressure wind will move in that direction. ",
"And then you have to predict how the clouds will change the increase in temperature at one point because hotter air is less dense and colder air is more dense.",
"This system by definition is chaotic and has to be done with supercomputers"
] |
[
"This is basically correct, however it's worth expanding on the importance of the fact that we're dealing with a chaotic system. Chaotic systems are, by definition, very sensitive to initial conditions. No matter how good our weather station readings (and in fact they're not that great over and within the oceans), we are never going to know the exact initial conditions of our weather models that we're running. To deal with this, we run sets of models with slightly varying initial conditions to represent our uncertainty of the system now, and then analyse the outputs and generate probability density functions to estimate the likelihood of measurable weather phenomena, like temperature and rain. This is called ",
". ",
"One last thing...",
"basically if you know that one point has a high barometric pressure and a nearby Point has a low barometric pressure wind will move in that direction.",
"This isn't really true. The earth is a rotating sphere which means that for large scale phenomena like the motion of the atmosphere and the oceans, you have to take into account the Coriolis force. For much of the atmosphere, the Coriolis force and Pressure force are actually almost exactly balanced, which means the wind actually blows at right-angles to the pressure gradient (i.e. along pressure contours). There are plenty of exceptions to this like eddies and boundary effects but for the bulk of the atmosphere, the statement \"wind blows from high pressure to low pressure\" is wrong."
] |
[
"Thank you. I tried to stress and chaotic point but you hit the nail on the head. As for the quoted portion I was pulling what little knowledge I have of weather physics but you are absolutely correct."
] |
[
"How is genetic information arranged across chromosomes?"
] |
[
false
] |
We all learn in school that (nearly) all animal cells contain DNA. We also learn that humans have 46 chromosomes, arranged in pairs. But that's where the details seem to end unless we go study this stuff on our own. Therefore, my questions: Basically I'm trying to understand why we have two kinds of DNA and how our genetic instructions are arranged. I've been studying neurology and neuroscience (you know, for fun); and it's making me start thinking about also studying gene expression.
|
[
"These are all great questions to be asking about DNA so I'll try to give you good answers to them.",
"In non-meiotic cells that are not actively going through the cell cycle there are exactly 46 mostly contiguous DNA molecules. Our cells are, of course, always in flux whether it be transcription, repair or new replication but outside of replication there are statically 2 copies of each Gene. The copies are not identical as one is from each parent and these will have sequences that are slightly variant, which is good because some mutations only cause disease if you have 2 bad copies. ",
"There are examples of single chromosome eukaryotes but as far as humans are concerned our genome is spread across distinct molecules which is why the distinction between the 23 chromosomes is important. Again, this is evolutionarily advantageous because sometimes terrible things can happen to genetic material and the impact of serious mishaps is somewhat reigned in by spreading the information around. ",
"Mitochondrial DNA has been sequenced, although it is not typically considered when discussing the human genome from a broader perspective - it is not one of the 23 chromosomes. Unlike the rest of our DNA, mtDNA exists in a circular chromosome just like most prokaryotes and it codes for not just the machinery used for cellular respiration but also it's own large and small subunit of the ribosome and 22 different tRNAs. ",
"Ok this part is incredibly complex and we truthfully don't understand the whole picture still but I'll give it a shot. There are many factors that go into Gene expression but a few include promoters and repressors. These are sequences that recruit different proteins that interact with the replisome machinery differently, either encouraging or discouraging expression. There are also transcription factors that get involved with these players and even deeper there is the actual structure of DNA and epigenetics. ",
"DNA is involved, as you may know, in binding to histone protein complexes - textbooks like calling it \"beads on a string.\" Well, depending on how tightly bound the DNA is, it may be inaccessible to the replication machinery. This is modulated by different chemical modifications on the tails of the histone protein, loosening or tightening the DNA on the protein. This is known as epigenetics and helps explain how a Gene can be turned on or off on a larger scale. ",
"Finally, another important concept that factors into expression is the domainization of the nucleus. This is a newer idea, but it has been shown that certain parts of chromosomes occupy specific territories of the nucleus and they don't really move around. How this plays into expression is largely unknown still but it is thought to be relevant to the bigger picture. ",
"Overall, having 2 copies of everything is very beneficial as it allows us to be more resistant to mutations which could be injurious. There are repair mechanisms that depend on that other \"good\" copy to fix a bad one, not to mention the benefits of genetic diversity. I hope I've answered your questions but if you have any more I'm happy to try to answer them!"
] |
[
" The mitochondrial genome exists because mitochondria were once free living microbes with their own unique genome. Over billions of years, pretty much every gene that's not ",
" necessary to perform cellular respiration (ie creating ATP from sugars) has actually ",
"migrated into our chromosomes",
". So while many people ignore what remains of the mitochondrial genome inside the mitochondria itself, when we look at the genome contained in our nuclear chromosomes, a non-insignificant amount of that material originated from mitochondrial sequences millions or billions of years ago."
] |
[
"How the DNA from mitochondria physically gets into the nucleus isn’t very well understood, as the two genomes are stored in separate membrane-bound compartments inside the cell. What we think happens is that when the cell degrades messed up/unhealthy/etc mitochondria to recycle their components, ",
"stray bits of DNA can occasionally randomly find their way into the nucleus",
". Once the DNA is near the chromosomes in the nucleus though, we have a pretty good idea if what happens. Sometimes DNA will randomly break in half, what’s called a double strand break (both of the strands in the double helix are severed). This is really problematic, because if the DNA is completely severed the whole chromosome is essentially cut in half and SEPARATED. The cell will basically do anything to reconnect the severed DNA, including forcing the DNA back together with a super error prone process called “non-homologous end joining.” For a parallel: imagine if you have a wood 2x4 that snaps in half. Its super fragmented and little wood pieces have gone everywhere. While you could collect all the little bits and glue the wood back together perfectly as it looked before it broke, it would be much quicker and easier to cut the jagged bits off so the break is blunt and flat so you can glue the 2x4 back together in 1 step. You discard some wood this way, but its quick. This is what the cell does with nonhomologous end joining — when the dna breaks, little bits of the dna from both end break off so they don’t fit back together perfectly. So the cells just chops the broken ends and “glues” then back together. During the “glueing back together” step, mitochondrial dna can get caught and randomly inserted into the genome."
] |
[
"Will we ever be able to view exoplanets with a telescope?"
] |
[
false
] |
I know we currently detect exoplanets based on the wobble effect on the parent star or whether they block some of their star's light from reaching our telescopes. However, I am curious as to whether we would ever be able to "see" exoplanets with a powerful telescope. Are there any technological developments that would ever help us achieve this amazing feat? Or on a more realistic not, could we at least be able to detect the atmospheric composition of the exoplanet someday? I have high hopes for this considering that we would almost certainly never be able to see distant exoplanets within our lifetimes if we were to send a probe.
|
[
"It's been done"
] |
[
"Aloha... I work for an observatory where we do (among other things) exoplanet hunting (naoj.org).",
"As lorgfefikd mentioned, it has been done. We routinely find new exoplanets.",
"However, our method for finding them currently revolves around watching for periodic disturbances in a stars brightness that indicate orbiting planets.",
"That given, new instruments already in the design stage will allow us to get closer images - and more importantly, spectroscopic analaysis of the planets. While not as interesting, for most people, as a visual picture of trees and galloping alien beings - a spectroscopic analysis of a exoplanet will tell us things like does it have oxygen and water, does it support life. Does it support intelligent (industrialized) life, etc."
] |
[
"So could we theoretically view a high resolution image of an exoplanet one day that shows surface features or is this outside the realm of possibility?"
] |
[
"With regards to the \"black hole ripping apart a red dwarf\", is the red dwarf exerting any attraction/gravity thats noticeable towards the BH?"
] |
[
false
] |
This:
|
[
"It's there in the article:",
" Because the star is the lighter object, it lies further from this point and has to travel around its larger orbit at a breakneck speed of two million kilometres per hour – it is the fastest moving star ever seen in an X-ray binary system. On the other hand, the black hole orbits at ‘only’ 150 000 km/h.",
"Elsewhere in the article we find that the black hole is 15 times the mass of the red dwarf, and the red dwarf is 1/5. By contrast, the Earth is 82 times the mass of the Moon, and they co-orbit a point about 1,000 miles below the surface of the Earth. Without knowing the separation between the black hole and the red dwarf, it's hard to say where the c of g is exactly, except that it's 1/15th of the distance between them.",
"edit: Hang on, it's not that hard. The red dwarf is going 2 million km/h and the system has a period of 2.4 hours. So that means it's going 2*pi*r km in 2.4 hours, which works out to a radius of 7.5 million km from the c of g, with the black hole orbiting at 570,000 km from the c of g."
] |
[
"The force the black hole exerts on the red dwarf is exactly the same as the force the red dwarf exerts on the black hole.",
"Namely, Newton's law of universal gravitation is",
" = G m_1 m_2 / r",
"for the attraction force between two bodies."
] |
[
"Yes the red dwarf is held together by its own gravity, but that is pretty minor compared with the gravitational field of the black hole."
] |
[
"How do we know that mass extinctions happened in the past ?"
] |
[
false
] |
How can we know that ? or even know how many extinctions happened ?
|
[
"Its easy to see in the fossil record. You can find many fossil species in one strate (lets say end of Permian) while the next one (Begining of Triasic) is very empty of species and most of the groups that you could find before have disappeared. In the case of the Permian extinction it affected 96% of marine species and like 70% of vertebrates, so it is a very big difference between both fossil records."
] |
[
"In some cases you can find the reason for the extinction too. The mass examination that killed the dinosaurs 60 million years ago was caused by a meteor. We know this for sure because some meteors contain a big amount of iridium an element that is rare in the crust of the earth. We found a thin layer of iridium in the geological formations that marks the end of dinosaur bones. There was another mass extinction, where we didn’t find the reason for, so scientists assume that a gamma ray storm from a super nova killed the life in that event."
] |
[
"There was another mass extinction, where we didn’t find the reason for, so scientists assume that a gamma ray storm from a super nova killed the life in that event.",
"What is the name of this theorised event?"
] |
[
"Why is it so hard to wake up from an induced coma? Example of F1 pilot Michael Schumacher"
] |
[
false
] |
*For those who don't know, Schumacher was skiing off-piste, he fell and hit his head on a rock, sustaining a head injury despite wearing a ski helmet. Towards the end of January, doctors at Grenoble University Hospital began trying to gradually bring Schumacher out of his induced coma but he just won't wake up.* What exactly goes on in the brain or rest of the body that prohibits one from waking up? Why is it harder to wake up the more time you continue in that coma?
|
[
"When someone is put into an induced coma, it's generally because they are in very dire straits. They may have severe brain swelling (likely the case with Schumacher), or they may have intractable seizures. The purpose of the coma is to make the brain calm and slow down its metabolism, so that it uses less blood, lowering intracranial pressure (to prevent the brain crushing itself against the skull or even herniating) and hopefully preventing the brain from harming itself with dysfunctional overactivity as in a seizure.",
"Because of how bad-off all patients who are put into an induced coma are to begin with, it's really tough to tell whether the difficulty in waking up, or even the long-term neurological sequelae (assuming they do successfully wake up), are related to the drugs used to maintain the coma, or simply the inevitable result of the brain injury that prompted the induction in the first place.",
"Obviously, putting a healthy person into a coma for a few weeks to a few months to verify what the long term effects of the drugs are at these dosage levels is not ethically defensible, and I doubt many people would volunteer. All the studies done on this are either aiming to verify that an induced coma does at least as good or better than the conventional therapy, or trying to understand the mechanism by which it helps.",
"Damage to the reticular activating system (brainstem), the thalamus, or widespread injury to the cerebral cortex (or some combination of the three) generally underlie permanent unconsciousness/inability to wake.",
"As for why it seems like people that stay in an induced coma longer have a harder time coming out of it, that's probably sampling bias. Doctors are constantly checking to see if they can begin the weaning process while someone is in an induced coma, similar to how they really don't want people staying on a ventilator any longer than they absolutely have to. So, the people who are required to be in an induced coma for a long time (due to not showing encouraging signs of recovery), are also the people who are most likely to have had a ",
" severe injury capable impairing consciousness all on it's own.",
"TL;DR If you're in an induced coma, you're not the sort of patient that is expected to come out of it at the drop of a hat, no worse for the wear."
] |
[
"That was very well explained, thank you.",
"Are there any drugs that can be used to aid or \"force-wake up\" the brain just like another kind of drugs are used to induce a coma?"
] |
[
"Are there drugs that could be tried? Yes. Modafinil (used for narcolepsy) and amphetamine derivatives come to mind. I don't think they're ever used in this context, since it's usually the case that if someone won't wake up naturally after weaning off of the sedatives, then there's likely severe brain damage that would prevent the patient from waking up even with \"help.\" If your thalamus is trashed, for example, even Meth isn't going to make you wake up.",
"Also consider: you have a patient who's just been in a pharmaceutically enforced low brain activity state, intended to protect the brain from excessive swelling/overactivity. While painstakingly weaning the patient off of the drugs maintaining this state, you're going to be worried that their intracranial pressure might rise again. The last thing you probably want to do in that situation is to suddenly force the brain to go into overdrive and draw a bunch of blood in there."
] |
[
"Since a focal point can theoratically be infinitely small and photons have an impulse, does this mean that we could theoratically create an \"impulse-singularity\"?"
] |
[
false
] |
In physics class my prof told me that a focal point can theoratically be 1-dimensional. I don't know too much about photon-impulse, but shouldn't that mean that we can focus a certain impulse on an infinitely small "area", meaning 1 point? Would this have any interesting consequences?
|
[
"In theory, photons have energy and they curve spacetime just like mass so a high enough density of photons can produce a black hole. Such a thing is called a kugelblitz. And again, in theory, we often assume lenses are perfect geometric objects whose focal points are 1 dimensional, so on paper your idea isn't crazy.",
"In reality, any lens will have imperfections that will cause the focal point to not be an exact point. Additionally, diffraction will cause your waves to spread a tiny bit so I doubt you'll find it easy to focus any light to an ",
" point. ",
"To give you an example of just ",
" impractical this is, suppose we want to make a black hole using a lens and a really powerful laser. How many photons do we need? We can approximate the focal point as a sphere with a radius of 1 mm, which all the photons leaving the lens pass through. Taking the equation for the Schwarzchild radius: ",
"R = 2 G M / c^2\n",
"We can solve for an equivalent mass for the photons in this volume, nE = mc",
" implies that m = nE/c",
" where n is the number of photons. If we use green photons (~500 nm) then ",
"we'd need approximately 10",
" photons.",
" ",
"For perspective, our sun puts out approximately ",
"10",
" photons per second.",
" That means you'd have to focus several hundred million years worth of sunlight into a box the size of a grain of sand in order to produce a black hole. "
] |
[
"Wow, thanks for the explicit answer, that's really cool. Follow up question: Would it be possibly for \"gravitational lense\" to exist that is optimal enough to create a kugelblitz?"
] |
[
"The photon density is simply too high - I don't know anywhere that this sort of thing would happen by accident. ",
"Additionally, gravitational lenses don't work in exactly the same way as a normal converging lens. If you had a spherically symmetric mass (i.e. a black hole) acting as a gravitational lens, ",
"parallel rays are most strongly deflected near the center",
" while converging lens is most ",
"strongly deflecting at the edges.",
"Since he made that first figure I linked to, perhaps ",
"/u/rantonels",
" would like to offer his thoughts."
] |
[
"What is the effect of numerous atmospheric nuclear tests on global warming?"
] |
[
false
] |
After watching a video on youtube about all the nuclear blasts from 1944-1998 i am curious what effect that radiation would have on global warming and/or any other short/long term effects on the planet?
|
[
"An nuclear explosion is impressive-looking, but ultimately the energy-content is pitiful, compared to that of the global circulation. ",
"The thermal energy from a single mature hurricane equates to a 10 megaton nuclear explosion every 20 minutes",
". The impact of a single hurricane on the global climate is incredibly small, so you can imagine how small the impact is from nuclear tests."
] |
[
"Yes, but...the energy of a 10-megaton blast is so localized that it allows some serious convective overshoot, far more than any mesoscale weather phenomenon would allow. I was under the impression that even large hurricanes are still vertically confined by the tropopause, while large mushroom clouds can pierce deep into the stratosphere.",
"I'd be curious to see a side-by-side analysis of how much mass is injected into the stratosphere by a 10-megaton blast vs. a typical hurricane, because once it gets there, it takes a very long time to get out. (Side note: I suspect large volcanoes like Pinatubo vastly overpower either in this respect.)"
] |
[
"Not much, if any. The general thought is that nuclear tests actually provided a cooling effect as the dust kicked up from the explosion reflected a lot of sunlight. ",
"This",
"\npaper actually claims is the reason for the global warming stagnation in the middle of the century.",
"Here",
" is some related discussion"
] |
[
"What inductance and resistance do I need for 500v system with 30a and power factor of 90%."
] |
[
false
] | null |
[
"The final inductor value will be frequency-dependent, but the system impedance can be calculated without knowing frequency.",
"PF of .9 means the phase angle is ~25.78deg. 500v@30a at the input means the system has to have an equivalent real impedance of 16.66ohm. ",
"This is all speculative as I'm working from memory and haven't had to do AC power stuff in a long while. As always one should verify all calculations via phasors / whatever method wasn't used to make sure it works.",
"e: I'm assuming sinusoidal waveforms. Not entirely sure if the power factor stuff is waveform-dependent, but as this is very likely homework related I can't imagine they would use anything else.",
"e2: Nope I borked this calculation up good. The total system impedance has to have magnitude 16.66ohm, not the resistor you'd use to make it.",
"\n ",
"Sin[25.78 deg] = (reactive component) / 16.66 => reactive component = 7.24 ohm",
"\n ",
"Cos[25.78 deg] = (real component) / 16.66 => real component = 15.00 ohm"
] |
[
"What are you doing? And isn't it frequency dependent as well?"
] |
[
"Answering a random math question my brother asked on Facebook. i.e. nothing important"
] |
[
"What does it mean for a discovery to be \"7 sigma\"?"
] |
[
false
] |
According to just posted on , the Higgs boson is close to the "7 sigma" level. I know it's some sort of measure of certainty that the finding is accurate, but can someone give me a more exact definition?
|
[
"You are correct in that it is a measure of certainty. I'll refer you to ",
"this article",
" that gives a more detailed explanation. Essentially the \"sigma\" for an event like the discovery of a particle can be converted into the probability that the evidence for the particle arose due to random chance. Higher sigma values mean that the discovery is less and less likely to be accidentally a mistake."
] |
[
"Higher sigma values mean that the discovery is less and less likely to be accidentally a mistake.",
"Just want to make a clarification on that. Mistake can only mean \"random chance\". A high sigma value can not discount systematic errors, such as faulty equipment or computation that might shift a result in one direction. The faster-than-light neutrino result reached 6.2 sigma. But it was really due to delayed signal in a loose cable. ",
"I'm sure you knew all that but I wanted to make it clear for anyone else."
] |
[
"The sigma level is the chance that the trend in the data occurs if we assume the thing we're looking for didn't exist.",
"For example, if we assume that the Higgs doesn't exist, then there's a 1 in 390 billion chance that the data we see as evidence for the Higgs occurred due to some statistical fluctuation. "
] |
[
"Why do arctic climates often have days where night is warmer than day?"
] |
[
false
] |
I just looked at the weather for McMurdo Station in Antarctica and Longyearbyen in Svalbard, and this upcoming week has many consecutive days where it is 3C warmer at night. How is this possible? My guess is that the sun loses much of its influence on the daily weather cycles, and that wind and sea currents become more influential.
|
[
"As close to the poles as these places are, “day” and “night” are rather meaningless - at McMurdo Sound it’s currently perpetual daylight and at Svalbard the sun doesn’t rise for a few months. Basically it’s weather and local topography which matter."
] |
[
"Thank you!"
] |
[
"Further poleward the diurnal solar cycle is less important. There are a couple of linked effects.",
"There is less solar energy overall overall so less absolute day/night difference. The sun is at lower angles so there is less incident energy per unit of surface and more attenuation due to a longer path through the atmosphere.",
"There is proportionally less difference in insolation between day and night. The extreme case is where the sun is above/below the horizon most or all the day in summer/winter. Obviously if don't see the Sun all day it is out of the temperature equation.",
"In polar conditions other meteorological effects (winds, air mass temperature, vertical mixing, etc) will have more impact on temperature. "
] |
[
"Why is a frozen and thawed banana so much sweeter, and how does this change its nutritional value?"
] |
[
false
] | null |
[
"Putting together the information here",
"One of the main processes in bananas (and all fruit) ripening is the amylase dependent conversion of savoury or flavourless starches in to sugar (specifically glucose). Amylase is a common enzyme (also present in your saliva) which converts starch to sugar and is an important part of your digestion.",
"There are essentially 2 ways something will taste sweeter.",
"1) There is more sugar present ",
"or",
"2) Your tastebuds can access the sugar more rapidly",
"Freezing and then defrosting fruit essentially lets both of these things happen. Freezing causes water in the fruit cells to crystallise and expand. This destroys the cell walls and is the principal reason defrosted fruit is soggy and limp. However it also means that the cell contents (all those sugars) are now in the juices that are running off the fruit and if you taste the juice you'll find it is very sweet. You can experience this at the most extreme if compare the difference in sensation between holding a mouthful of orange juice in your mouth or holding a slice of orange (without chewing). In the case of a banana there isn't much excess of liquid to run off so those exposed cell contents will largely stay within the fruit pulp/body rather than running off.",
"The other thing that happens while the fruit is defrosting is that all the amylase and starches in the cells are now able to diffuse (a little) through the defrosting fruit pulp. The amylase is no longer confined to the cell it started in, where it may have completed its starch converting job, and is free to find any remaining starch that may have come out of other nearby cells. This means that some of the remain starches will be converted to some extra sugars."
] |
[
"Because the cell walls are destroyed by ice crystals forming inside the cell and rupturing them. A single amylase enzyme is far smaller than a cell so it doesn't get pierced. For the same reason why you can drill a hole in a giant block of sandstone but if you try to drill loose sand the sand will get pushed out of the way."
] |
[
"Fruits like banana contain water. When you freeze them, the resulting ice crystals breaking the cellular structure of the fruit. The result is that thawed fruit is mushy. Subsequently as they warm up again, a lot of the juice leaks out and you're left with less flavor. ",
"Harold McGee pointed out in his book “On Food & Cooking” that in some cases frozen fruit is better in taste. Many fruits and vegetables never reach their optimal point for taste once they are harvested. If picked too early, fruits like pineapple, melon, most citrus, and most berries will not continue to ripen or reach an optimal quality and sweetness.",
"\"In many instances, the food you take off the shelf in a grocery store has been harvested under ripe to avoid damage during travel time. This means that it hasn't yet reached its peak nutrition. Furthermore, the minute it was picked, its nutritional content began to deteriorate. The food is then loaded on a truck, boat or plane, travels for days and waits on a shelf for you to choose it. After, which it may sit in your fridge for a few more days before being eaten. Over this period of potentially weeks, the food may lose up to 50% of its nutritional value.",
"Frozen foods on the other hand are picked when they're ripe and frozen immediately. And while the quick freeze process does affect some vitamin content, it essentially freezes, or locks most of the nutrients in place. Next to the fresh produce that has been sitting around for weeks, there's no doubt that frozen foods can contain more nutrition, particularly during the month that local produce is not in season and travelling far distances.\" (",
"Source",
")",
"It depends on the water content of the fruit. When water freezes, it expands, so when the water in the cells of the fruit freezes, it breaks through the cell membranes. This can be seen when you freeze and then thaw a high water content food such as strawberries; you'll be left with a squishy mess when you defrost them.",
"So the amount of damage depends on the water content. Melons will be affected more than strawberries which will be affected more than bananas, which are affected the least because they are only 75% water. As an example, nuts would hardly be affected at all.",
"So you do diminish the nutrient content of the bananas used in banana ice cream, but not anywhere near as much as the bananas used in banana bread (cooking does far more damage than freezing, including the causation of autoimmune reactions).",
"A way to get around this nutrient damage issue is to chill the bananas but not let them freeze, and then mash them into ice cream. Or just eat them cold as is! This would result in a cold fruity treat (but make sure they are ripe before chilling them). In practical terms, most people just throw frozen bananas through a Champion juicer (the best machine) or a Vitamix (which takes some muscle but it can be done, just be sure to run the Vitamix only as much as needed to turn the bananas into ice cream or you'll warm up the ice cream too much).",
"Bananas are known for their high potassium. In fact, a large bananas has over 450 mg of potassium. Fresh bananas are a bit different than buying bananas frozen in the store. Because commercially frozen bananas are usually blanched before they are frozen, you lose a little bit of the potassium. Blanching is a process that takes the fruit and boils it for about a half of minute and then immediately cools it in ice. It is not the freezing of the banana, but rather the blanching process that is thought to reduce the potassium content. Interestingly enough, potassium is a mineral that is not affected by the freezing process. So if you are taking your own fresh bananas and freezing them to throw in a shake or smoothie you are all good. However, you may pull a brown banana out of your freezer, but the potassium will remain intact.",
"If the only way you eat bananas is as ice cream, then you're obviously missing out on some nutrition. But if you eat most of your yearly banana intake unfrozen, and you're not cooking the other foods you eat, then you can probably afford to trade some nutrition for a tasty dessert if it helps you stay on your raw food diet.",
"Source 1",
"Source 2",
"Source 3"
] |
[
"How do cows and other large grazing mammals stay so heavily muscled when all they eat is grass?"
] |
[
false
] | null |
[
"Hi Hillano thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Biology"
] |
[
"when an organism consumes another organism, it only gains 10% of it's energy. since we normally eat meat, we gain less energy. the organism only gained 10% energy from their food, so we only gain 1%. cows gain 10x more energy than us."
] |
[
"What determines the rate of action potential propagation?"
] |
[
false
] |
I'm going to ask what I think is the same question three times in three different ways because I can't quite pin down what I'm trying to say. Hopefully it makes sense... Assuming no myelination, what is actually responsible for mediating the change in charge along an axon during an AP? It's not the diffusion of Na+, is it? My understanding is that Na+ flows into the axon, creates a localized positive relative potential, which then activates nearby channels and repeats this process. If that's the case, then this should be slower than diffusion alone, yes? Since it's local diffusion plus the time it takes to open the next set of sodium channels? Myelination speeds signal conduction, but what is actually being conducted if there are no sodium channels to open under the sheath? None of this is instantaneous, but then what factors influence the time it takes for one node to activate the next (aside from distance?)? Na+ isn't diffusing down the covered regions of axons is it? Assuming myelination, does the influx of sodium across the membrane produce a local electric field which is then felt at the next node of Ranvier faster than diffusion alone could explain? If so, what mediates this? What is the ultimate determinant of signal propagation velocity? Thanks!
|
[
"The Na+ is diffusing down the covered regions of the axon. Time is saved by not having to open successive ion channels. The signal propagation velocity is limited by the diffusion rate of Na+."
] |
[
"So the equation for AP propagation velocity is proportional to 1/Cm * sqrt(d/4RmRi), where Cm and Rm are capacitance and resistance of the membrane, and Ri is the resistance along the internal aspect of the axon. ",
"How is Ri calculated? Is the information regarding diffusive properties of the cytoplasm of the axon contained within this term? If so, how?",
"Thanks."
] |
[
"Action potentials are propagated by voltage gated Na channels, and are typically triggered at the axon hillock, where there is the spatial proximity to the axon, and density of vg Na channels to start an action potential. This is slower than diffusion, since you need to open channels, but without those channels you have no way to regulate when you depolarize (fire an action potential).\nAs to why mylenation speeds up action potentials: It's important to remember that membrane potential is mediated by more than just sodium, and the net interaction of these ions triggers vg Na channels. For example, leaky potassium channels dissipate the positive charge let in by vg Na channels, this weakens the signal that might otherwise go on to open more vg Na channels if it were stronger (there are also leaky Na channels, but in much lower numbers ~40:1). Fatty mylenation insulates the axon and prevents the passive diffusion of positive ions/charge out of the cell. This means that your ion influx can now move farther and faster, until you need to repropagate it to regain strength, at the next node of Ranvier. "
] |
[
"How can you figure out the age of water? Thermohaline circulation related."
] |
[
false
] |
I was talking to a gentlemen from the UK a few months back, and we were talking about the age of water. He was telling me that you cannot date water unless it's pre-WWII water/post WWII water because of tritium found in water. I was trying to do some searching on how long it takes for a cycle in thermohaline circulation to take place, but can't find anything on it. I keep reading that it takes 2,000 years, but how do they know that? How do they know that the water they are drinking started as glacier melt 2,000 years ago? Thanks in advance!
|
[
"Ocean water incorporates atmospheric carbon, some of which has been converted to the radioactive species (C-14) through reaction of cosmic rays with nitrogen atoms in the upper atmosphere. We can thus date oceanic waters using carbon 14. Here are two summaries of the results from such work, ",
"this one",
" and ",
"this other one",
"."
] |
[
"Yep, radiocarbon is the main way to get ages for the entire ocean. Of course radiocarbon has its issues, too (e.g. mixing and dispersion, incomplete equilibration with the atmosphere, etc). There are other tracers, like ",
"chlorofluorocarbons",
" (CFCs), sulfur hexafluoride, and ",
" H/",
" He dating, which all take advantage of known (but not constant through time) atmospheric input rates to the surface ocean, and can be used to date younger surface water and calculate mixing rates in the ocean.",
"For some background on the other methods, this ",
"USGS website",
" (click background underneath SF6, CFC, or H/He tabs) for groundwater dating (principles are similar as to the ocean) is an excellent way to learn the basic physics and chemistry behind using tracers to date water masses. "
] |
[
"Thank you for these responses guys. It's time to dive in and do some more reading! "
] |
[
"What's the earliest animal that plays games?"
] |
[
false
] |
Anyone with a cat or a dog knows animals like to play games. How about evolutionarily simpler animals? Do turtles or frogs play? What is the earliest animal that plays? Is playing an emergent trait that evolved separately in different places and times?
|
[
"Playing might have evolved as a way for young animals to develop motor function as well as to hone stalking/hunting skills. At least this is true for dogs and cats and other carnivorous animals. There is no way to know for sure, but it could be that it simply came about that the cubs/pups/whatever who played ended up more successful hunters than their lazy counterparts. Of course, this is speculation. I don't know if simpler animals play as youngsters. Piranhas hunt, but don't exactly play as spawnlings. "
] |
[
"Komodo dragons and octopuses are probably the \"earliest animals\", although we can't totally conclude that they play in the way that \"higher vertebrates\" do",
"I would suspect that some shark species also play, as well as (possibly) manta rays"
] |
[
"Until more expert opinion arrives, I will continue your speculation with the fact that in order to have viable \"play\" mechanisms you need a \"play\" environment and some other bits:\n- A safe environment for the children (nest, pen, den, whatever)\n- Caring parent(s) that would help \"guarantee\" the safety\n- Socially learned behaviour (and the required mental ability)",
"A possible problem with this proposition is that I don't know whether birds' chicks do play (while they certainly fulfill all requirements). Non-nesting, non-caring and non-socially-able species like fish and amphibians do seem to \"comply\"."
] |
[
"Would a flower maintain its color in a room totally void of light?"
] |
[
false
] | null |
[
"Color is a psychological, not a physical property. Objects have surface reflectance properties which do not depend on whether there is or isn't light any more than their mass does."
] |
[
"I thought the physical properties determined which color from the light spectrum is reflected. So a total absence of light would mean no color is being reflected from the object, but the object is still there. I could be misunderstanding. "
] |
[
"Physical properties of the object determine which ",
" of light get reflected. The visual system is what determines how those wavelengths are experienced. Different combinations if wavelengths can produce the same color experiences. Some wavelengths produce no color experiences whatsoever (e.g. infrared). It is true that in a lightless room, no light is being reflected by the object, but that does not mean that its physical nature has changed."
] |
[
"Why is blood group O+ so common?"
] |
[
false
] |
Would it not be a rare blood type as the allele for blood group O (I is recessive to the other alleles?
|
[
"Whether an allele (type of gene) is dominant or recessive, doesn't really determine if it is common or not. Just think of an island of mostly red-heads and a couple brunettes. If mating isn't biased by hair color, the number of red hair alleles and the number of brunette alleles wont change. In fact if a number of assumptions are made, the number of red-heads and brunettes will reach an equilibrium known as ",
"Hardy-Weinberg",
" equilibrium.",
"Basically, allele frequency wont change between generations unless some force acts upon them (nonrandom mating, mutation, natural selection, gene flow, genetic drift). Without something driving change, the alleles are simply \"reshuffled\" every generation. ",
"I can't say ",
" O is a common allele. Perhaps it was advantageous in our past/right now. Perhaps it became more common by chance. However, the fact that is is recessive, doesn't impact its frequency.",
"EDIT: I feel I should add that the O allele is present in some type-A and type-B people, as it is recessive. A person with type-A blood can be AA (two \"A\" alleles\") or AO (an \"A\" and \"O\" allele). A person with type-B blood can be BB (two \"B\" alleles\") or BO (an \"B\" and \"O\" allele). If an \"AO\" and a \"BO\" have children, there is a 25% change of having an blood type-O (\"OO\") child. If an \"AO\" or a \"BO\" have a child with an \"OO\", there is a 50% chance of having an \"OO\" child. No other combination of parents will result in an \"OO\" child expect for two type-O parents, but sometimes the \"O\" allele will still be passed on to the next generation.",
"EDIT EDIT: The Rh factor (the + or - of the blood type) is inherited rather simply with Rh+ being dominant to Rh-. For whatever reason, the Rh+ allele is more common than the Rh- allele. So Rh+ blood-types are more common than Rh- blood types. ",
"This link explains Rh in inheritance.",
" ",
"This link explains ABO inheritance and has a nice table of blood-type frequencies.",
" Notice that for any given ABO bloody type there are more Rh+ than Rh-. This is not because Rh+ is dominant but simply because it is a more common allele."
] |
[
"Just because it's recessive doesn't mean it is less common. Given enough time it can become an overwhelming majority. The gene for 5 fingers and toes is recessive but just about everyone I know has five of each "
] |
[
"Genetic testing, assuming we know where the relevant genes are.",
"Look back further: Are any of your grandparents or other relatives type O? This doesn't guarantee anything (eg. one grandparent could be OO, your parent AO, and you AA), but it might give some idea. ",
"Have a bunch of kids with someone with type O (either + or -), see if any of them are O."
] |
[
"Why does left handedness only make up approximately 10% of the population? Is there a reason for such an unequal distribution?"
] |
[
false
] |
[deleted]
|
[
"Although there appears to be a hereditary component to determining handedness, like most traits it does ",
" follow simple Mendelian inheritance. There is no \"left handed gene\"."
] |
[
"I had to read this a few times but ",
"2 right-handed parents usually have RH kids because of the dominant gene, but because of that square(you know with genes on different sides) you can sometimes have a lefty.",
"Why does that mean two left handed parents have no chance of a righty?"
] |
[
"If the left handed gene is recessive, you would need two left handed genes to be left handed. For two left handed parents, where would the child get a right hand gene?",
"Edit: It seems that ",
"handedness",
" is not completely genetic. ",
"Also here",
"."
] |
[
"Is it possible for animals to have mental disorders?"
] |
[
false
] |
If so, are human mental disorders common in animals (A dog with schizophrenia)? Are there unique disorders specific to animals?
|
[
"Although there are certainly objective physical changes in some disorders, much of what we deem psychiatric disorders are based on subjective states--the person ",
" depressed, the person is hearing voices, etc. Since we can't ask animals how they feel, we can't know much about the subjective internal states of animals.",
"We can, however, note behavioural changes that seem to match up with the behaviours noticed in humans with mental problems. For example, this classic experiment (don't read if you're a huge animal lover! ",
"http://people.whitman.edu/~herbrawt/classes/390/Seligman.pdf",
") established a paradigm known as \"learned helplessness\"--you basically put an animal in a situation where bad things keep happening to them and they have no control over them. Soon enough, they start acting a bit like people do when they're depressed. This paradigm was applied to humans for a long time: depression happens when people feel like they're losing control over their environment and nothing they do will change it. They actually have used this to test anti-depressant treatments and whatnot--basically, if you do this to a rat then give it prozac, it gets better.",
"(This view is now viewed as overly simplistic, btw. It's still used as the \"closest we've got\" in animals, but they realize there's a lot more complexity in human depression. Here's a good wiki summary: ",
"http://en.wikipedia.org/wiki/Learned_helplessness#Attributional_reformulation",
")",
"Another way to look at it is that many mental disorders can be considered extreme versions of normal behaviour that causes problems with the person's functioning in society. In almost all DSM-IV diagnoses, it mentions that the disorder must actually be causing problems for the person in their personal/professional life. If somebody is a bit ADD but they're happy, successful, and it's never really affected them negatively, a good psychiatrist would never diagnose them with having a problem. If we think about it that way, we certainly see maladaptive patterns of normal behaviour in animals."
] |
[
"Most animals probably can. We are animals, so what's to say other animals can't get them? Although, the types of disorders would probably differ."
] |
[
"I'm sure they do, nature isn't perfect, there's lots of room for error and error does happen. The thing is though, in the wild, say in a heard of bison. The animals with a mental disorder (depending on severity) would probably die off a lot quicker and humans wouldn't have as good of a chance to find and test these animals. Reasons for this would be, they would be the slow weak ones that the predators would pick off, or they wouldn't be able to function properly enough ( again based on severity ) even to perform basic survival tasks. Or possibly they would be pushed aside by the herd because of that disorder. Maybe this thread will help answer your question ",
"http://scienceforums.com/topic/9731-animals-with-mental-illness/"
] |
[
"Morals and ethics aside, could a developed nation feasibly develop and grow their own army of cloned humans/soldiers with our current technology?"
] |
[
false
] | null |
[
"We don't have artificial wombs so there will always be a birth mother and biological father. They're still going to be little kids who have to grow up and get an education. Either way, you're going to have to sequester a bunch of women as brood mares and steal their infants; whetehr or not those infants are all genetically identical doesn't seem to make much of a difference to me."
] |
[
"Doesn't africa already have this? When roving militias invade a village, kill all the men, rape and disfigure all the women, and steal all the children for military training? (then make it a point to come back 10 years later to see what the women of the past have grown / produced) You then have an army of young boys, 8-15 when you find them, that you train in war over the next few years after convince them their family is all dead. ",
"Also Cambodia did something similar, no? "
] |
[
"http://www.youtube.com/watch?v=kcUvSeEm7fc",
"This could potentially answer your question. "
] |
[
"What exactly does it mean that a vaccine/booster etc is X% effective?"
] |
[
false
] | null |
[
"Typically they are referring to “Relative risk reduction”. Take 100 people and give them vaccine, 100 people who don’t get it (or better, get a placebo). After some period of time, see how many in each group got the virus.",
"Let’s say 2 in the treatment group got the ‘vid and 20 in the placebo group.",
"2/100=0.02",
"20/100=0.2",
"So the relative risk reduction is= (0.2-0.02)/0.2 = 0.9",
"So the relative risk reduction is 90%. You can think of it as having a 90% less chance of catching the virus if you get the vaccine compared to if you don’t."
] |
[
"This obviously gets a lot more complicated if you want - anyone who has ever taken an epidemiology class knows exactly what I’m talking about. Just a few questions to show how complicated this can get:",
"How are we defining who got disease? Are we looking at symptomatic people who got tested? Are we looking at people who got sick enough to go to the doctor? Are we just testing everyone every day?",
"How do you pick a time period? Do you start immediately after the second shot? Do you wait some time for the vaccine to work? When do you stop measuring? 1 month? 6 months? 10 years? ",
"What if you happen to start testing the vaccine during an outbreak vs when there aren’t that many cases? (note- the “relative risk reduction” should not change based on disease prevalence, but your estimates can - imagine if you had 2 cases in the placebo group vs 0 in the treatment group. ). What if an outbreak happens during your study and the prevalence of the virus changes dramatically? What if you have a different strain that changes everything?",
"What if people who know they got vaccinated start acting differently and increase their chance of getting infected?",
"Having major flashbacks to getting my masters in public health now…. The simple answer is simple, but the details definitely matter"
] |
[
"Gotcha. All this makes perfect sense to me. I guess a lot of what that number means depends on the parameters/definitions employed by the particular study. Sometimes I feel like certain study designs should be formalized if they're useful enough, but that also would lead to limitations/controversies over what the criteria of those designs should be. But this clarifies a lot!"
] |
[
"Do insects sleep? Do they dream?"
] |
[
false
] |
[deleted]
|
[
"Wikipedia",
" suggests that insects exhibit sleep-like behavior.",
"Unfortunately, since their behavior is so simple, it is difficult to tell exactly what is sleeping. The studies Wikipedia describes base their conclusions on the fact that sleep-deprivation causes the insects to lose cognitive ability.",
"I can't find any material that suggests insects dream, and I consider it unlikely due to the simplicity of their nervous systems and limited cognitive abilities. It would also be difficult to determine if and when they do dream, if they did."
] |
[
"Insects have a state called tropor. So yes they do 'sleep'.",
"\nAs for dreaming, i guess you could set up a test an see if conditioning goes faster if the insect is put in tropor after it.",
"Hard to test actual b rain activty on that sdale"
] |
[
"Can you explain what tropor is?"
] |
[
"What's the difference between two experiments using laser emitters and slits, one of which demonstrates \"quantum physics\" behavior and the one showing diffraction? Is diffraction involved in the quantum one or is it unrelated?"
] |
[
false
] |
I have a big question and a minor question about experiment(s?) involving shining light through narrow slits. I've seen descriptions and videos of the double slit and how it's "quantum mechanics". I also did an experiments in high school physics to demonstrate diffraction using a laser emitter and a slit that was similar. It was a while ago so I don't remember all the details. But you achieve the "venetian blind" pattern because the waves cancel each other out in dark spots and amplify in the bright spots. My first question is: What are the differences between the diffraction experiment and the quantum physics one? From what I can remember they seem to be the same experiment, but I doubt that's the case. Second question: In the quantum experiment, I remember reading about "when the light was being observed it converges into two slits", and something about how when the data collected was set to automatically be erased (so it was still collected, but then discarded), it... did something, but I can't remember how it affected the results. Anyone know?
|
[
"There aren't any, that's the point! One involves light and the other involves a stream electrons (or any other particles) aimed at the slits. The fact that they both result in a diffraction pattern demonstrates that it's not just light that has wave-like properties, but matter too! i.e. the wave-particle duality"
] |
[
"Yes, this is exactly it. The quantum physics version uses electrons instead of light, and it demonstrates quantum mechanical properties because ",
" In other words, the diffraction thing is part of the quantum mechanics thing."
] |
[
"The way I learned on how to imagine how this happens is by doing a thought experiment for a second and picture this. ",
"You are in a bath tub and you have a piece of plastic that has 2 lines in it. You drop one drop of water creating one wave with the drop. The wave expands in all directions evenly and when the wave hits the slits they cause 2 new waves, one coming out of the left slit and one coming out of the right slit. These 2 waves interact with one another and where the 2 waves meet it will either increase the size of the wave or it will cancel each other out. Which makes that look of \"venetian blinds.\" The photons work that same way because they are waves just like the water waves. Also, to detect which slit the photon goes through you have to measure it which leads to you forcing the photon to take up a particle like state because in observing the photon going through one or the other slit causes the photon you are using to measure the photon going through the slit to interact and causing it to give definite position in space at the time of observation. "
] |
[
"Why can animals like honey badgers eat snakes that are extremely venomous, whole, and not die/get sick?"
] |
[
false
] |
[deleted]
|
[
"Venemous =/= poisonous. ",
"Venom is injected, whereas poison can be ingested/absorbed etc. So by eating the animal, the honey badger swallows the venom sacs or whatever the venom is in and it is processed, diluted, broken down or excreted like all other food. ",
"The venom of a snake would be dangerous to it if it injected it into the honey badger's blood stream (this actually happens, but the honey badgers are also really tough and usually pass out, sleep and then wake up to eat the snake afterwards!)."
] |
[
"Yes, as far as I know, ",
"most venoms can be ingested by humans without harm",
". The human digestive system does an excellent job of breaking down the proteins that compose venom into relatively harmless amino acids. ",
"Venom is most harmful if it is injected into the bloodstream or comes into contact with sensitive tissues (such as eyes, lungs, etc.) Most venom proteins are fairly large molecules and cannot penetrate the skin on their own."
] |
[
"So by eating the animal, the honey badger swallows the venom sacs or whatever the venom is in and it is processed, diluted, broken down or excreted like all other food.",
"Are there snakes for which this is also true in humans?"
] |
[
"Does the orbit of an artificial satellite at the equator tilt with the earth's seasonal tilting?"
] |
[
false
] |
[deleted]
|
[
"The Earth's tilt axis doesn't actually change throughout the seasons. Instead, the direction of the tilt ",
" changes.",
"Imagine you're walking around a table, but you always face north - so at one point, you face towards the table, but halfway round you're then facing away from the table. It's a similar idea - no matter where the Earth is, the direction of the tilt always faces the same way."
] |
[
"Yup. If you're having trouble picturing that, ",
"see this picture",
"."
] |
[
"Typical, the one time I don't bother to look for an image, there's one which shows ",
" the point I'm trying to make."
] |
[
"How do electromagnets work?"
] |
[
false
] | null |
[
"Electric currents produce magnetic fields. If you have an electric current traveling through a resistive medium, there are energy losses to heat. If the resistance of the medium is zero, like in a superconductor, there are no losses to heating."
] |
[
"Any electric current produces a magnetic field."
] |
[
"Any electric current produces a magnetic field."
] |
[
"Why are surgical leg amputations done either above the knee or below the knee but not right through the joint itself?"
] |
[
false
] |
Why not just separate the joint and take the tib-fib portion?
|
[
"I think the question relates to why not leave the end of the bone as the termination point - that is to say why not simply remove the tibia, fibula and patella, leaving the smooth articulating surface of the femur as the termination point."
] |
[
"The kneecap is a bone, the patella, specifically. Are you suggesting we leave a portion of that bone behind?",
"This would be incredibly complicated and dangerous to a patient as well as making a smooth fitting and operating prosthesis replacement near impossible.",
"Check out a good anatomical image of the ",
"knee",
" and let me know what you mean."
] |
[
"We do this, it's a transfemoral prosthesis.",
"I'm not sure what he means, because he said above/below the knee.",
"Above is transfemoral, below the knees is transtibial."
] |
[
"Age of the Galaxy"
] |
[
false
] |
So, the recent article about the discovery of the oldest spiral galaxy got me wondering how old our own Milky Way is. A quick google and I find that the internet gives an answer of around 13 billion years - almost as old as the universe itself and more than 2 billion years older than the newly discovered ancient spiral galaxy. Seeing as our own galaxy is spiral, what is going on here?
|
[
"The discovery isn't of the oldest spiral galaxy thought to exist, it's the oldest spiral galaxy we've ever taken a picture of.",
"Because light takes time to go through space, the light we're receiving from the galaxy is that old. All galaxy are effectively the same age.",
"The discovery is of a galaxy that is both old and spiral, and is the oldest spiral that we have seen to date. "
] |
[
"I suppose it comes down to your definition of galaxy - I think what I was really driving at with this question is: what is the nature of a galactic life cycle? \nAll other galaxies that we observe from as long ago as the one the article, at least that we know of, are crude, shapeless lumps. So, if the crude shapeless lump that became the milky way formed very soon after the beginning of the universe, at what point did it become the magnificent barred spiral we know today? When it formed, did it contain all the matter it does today, or will the forthcoming (if not imminent) collision with the Andromeda galaxy be simply one in a long line of amalgamations with other vast accumulations of stuff? \nDo galaxies collide and split and change all the time, and if so what do we mean by the age of a galaxy, or are these events relatively rare? I'm very interested in how the universe works on large scales, so any knowledge you could share along these lines would be very welcome. "
] |
[
"I suppose it comes down to your definition of galaxy - I think what I was really driving at with this question is: what is the nature of a galactic life cycle? ",
"Loooooooooong, of course, but other than that, a lot of this question can be best answered ",
"here",
".",
"So, if the crude shapeless lump that became the milky way formed very soon after the beginning of the universe, at what point did it become the magnificent barred spiral we know today? ",
"That I don't know the answer to, but the process would look similar to that of a solar system forming, with the laws of the conservation of angular momentum holding true, and \"averaging\" out the spin of the stars within the galaxy.",
"When it formed, did it contain all the matter it does today, or will the forthcoming (if not imminent) collision with the Andromeda galaxy be simply one in a long line of amalgamations with other vast accumulations of stuff? ",
"Our galaxy has likely eaten many companion galaxies, and is in the process of devouring ",
"at least one right now",
". ",
"Do galaxies collide and split and change all the time, and if so what do we mean by the age of a galaxy, or are these events relatively rare? ",
"They don't split, at least not within the criteria of any known phenomena. Galaxies are bound by gravity, so while individual stars can be ejected under specific circumstances (like interactions with the supermassive blackhole at the center of our galaxy, 3 body problem), the galaxy as a whole isn't likely to spontaneously split apart. ",
"But yes, they do collide regularly, if infrequently (especially on the scale of humans!). "
] |
[
"Why aren't all mammals omnivores? Is there a benefit on being able to eat nothing but plant/meat compared to being able to eat both like humans are?"
] |
[
false
] |
While herbivores have a more easier access to food than carnivores, they are more susceptible to droughts and changes in the environment than carnivores are. While carnivores do not need to eat as often, they have to use more energy to catch and kill their prey which can be a more riskier lifestyle than grazing in a field. Is there any evolutionary benefit on being a carnivore like a cat, a herbivore like a cow than an omnivore like a human or a goat? Are omnivores in general any better at surviving times of famine than carnivores or herbivores?
|
[
"why aren't all mammals omnivores?",
"So, let's start here. Mammalian diets are more flexible than the boxes \"omnivore\", \"carnivore\" would indicate. ",
"Here",
" is a great example of an herbivore engaging in predation. Certainly not common, and animals will be a very small minority of their diet, but not that strange either. ",
"We also can see examples of obligate carnivores eating plants; you might be able to observe ",
"that behavior",
" in your own home!",
"So, don't think of strict categories like \"carnivore\" and \"herbivore\", think of a range. And think of another scale that ranges from \"specialist\" to \"generalist\".",
"While carnivores do not need to eat as often",
"This is a false generalization. I have done some small mammal field work, and often if you leave traps out overnight any ",
" shrews that wandered into your trap will be dead in the morning of starvation. These little opportunistic predators eat insects, worms, salamanders, baby mice, nuts, etc, constantly in order to stay alive. This overnight death of starvation doesn't happen to any other of the small mammals you'll commonly catch, which are generally more herbiverous in nature. ",
"So, our shrew would be a mostly carniverous generalist. ",
"Next I would recommend thinking about the different biological tools that organisms might need to eat various items. ",
"What teeth do you need? What digestive track? What behaviors and metabolism?",
"And who else are you competing with?",
"Let's imagine a source of food that is easy to get a hold of: A fruit. Fruits are made by plants largely in order to spread the seeds around; they are a payment to the organisms that eats them, in energy, that hopefully allows the spread of those seeds far away. Do we need special teeth to eat the fruit? No. Special digestion? No. However, we do need to outcompete all the other organisms that are trying to eat that same fruit! You can think of lots of ways we can compete. ",
"Compare to a resource that is very difficult to eat: let's say, grass. Very tough for you and I to get much nutrition our of it; you need specialized tools to do so. So, cows and other ungulates have special teeth and digestive tracks to help break the grass into something that is nutritious. There is a cost and a benefit: the cost is that they have to grow lots of extra disgestion, have specialized teeth that aren't good for other things, as well as constraints on their size. The payoff is access to a foodsource that a lot of other critters can't eat. An example of extreme end member specialists are pandas (eat bamboo) and koalas (eat eucaltyptus). Bamboo and eucalyltus are barely even food, but these extreme specialists make a fine living. On the other hand... if the food you specialize on dies, you are in big trouble. ",
"Hyper-predators are also specialists in a similar way. A lion has very specialized teeth, but their bodies and behavior are also very specialized towards active hunting. The payoff is that they are getting a food resource that other animals don't get access to: Healthy antelopes. But the lions have to pay for that, as well. They need to be able to deal with uneven times between meals; they need to be able to run incredibly fast and attack an often larger animal ",
", they need to defend that dead meal from everything else out in the world (a dead antelope is much more like a fruit; you don't need to specialize to eat it, you just need to compete with everyone else that is trying ot eat it!)",
"Every kind of animal is a solution to the problem of staying alive. Every single one has a evolved into a niche that is benefitical, and there are a million tradeoffs along the way that come into play. Making generalizing statements about \"herbivores\", \"carnivores\", or \"omnivores\" probably isn't very useful because those aren't biologically real categories, they are labels that we have put on organisms that generally describe what they happen to eat. If you want to start generalizing, also think about whether an organism is a specialist or a generalist. Think about the environment they live in: it is stable, or does it vary a lot? "
] |
[
"So how do humans fit in? Are we specialized in a trait, or generalized? In any event, we've been successful."
] |
[
"I would categorize humans as very generalized and flexible in digestive tract/teeth, with a very specialized nervous system and limb arrangement that allows for a very broad range of behavior and interaction with the world. ",
"Overall, I would say that our digestive and hunting capabilities match our intellect; flexible. ",
"Humans are such a weird species that we often just break most conventions open. It's even a bit of a running joke for scientists to make their go at completing the sentence \"humans are the only species that....\""
] |
[
"Can other animals get allergies as well?"
] |
[
false
] |
[deleted]
|
[
"There are cases of dogs testing positive for allergies to cats. Many domestic dogs are tested and treated for allergies. Dogs can get allergy shots just like humans or can be treated with Benadryl (and I believe other allergy meds as well). ",
"Dogs can also have anaphylactic allergic reactions to things like bees that require immediate medical intervention."
] |
[
"Absolutely. An allergy is just a particular type of immune response. Humans do have an unusually high rate of allergic response but its because a) we're one of the only species that regularly eats foods processed with other foods, thus contaminating them with other allergens and b) many people are raised in relatively sterilized environments where their immune systems never get exposed to potential allergens to learn that these things aren't supposed to be bad for them. Then when they do encounter them the first time the immune system overreacts and voila, allergy."
] |
[
"Dogs are frequently allergic to grass (it gives them contact dermatitis, just like in people). It's not uncommon for dogs to become allergic to pollen. They're get itchy watery noses/eyes and it's treated with Benadryl if it's short term, and Claratin long term, just like in humans. ",
"Cats and dogs are frequently allergic to grains in feed (wheat, soy, and corn are the most common offenders). Usually it comes out in hives or raised red itchy spots, or hairloss. Same commonly happens with flea bites, then there are bee/hornet stings which can make the stung area swell up badly. "
] |
[
"Do plants need \"rest\"?"
] |
[
false
] |
Can plants go through photosynthesis nonstop without a break? Or do they need some time to slow down? EDIT: Let me rephrase, if a plant is given light 24/7, watered when needed, and new/changed soil when required, would it work itself to death?
|
[
"In general, most plants have increased photosynthesis rates during the day and decreased or no photosynthesis during the nights. This is simply because there is light during the day which is necessary for the light dependent reactions of photosynthesis (the light independent reactions of photosynthesis do not require light but occur alongside the light dependent reactions). Stoma pores also open during the day and close during the night for gas exchange (photosynthesis needs carbon dioxide and releases oxygen).",
"One interesting exception to this is CAM plants. CAM is a specialized type of photosynthesis that exists in plants from extremely hot, dry, or windy climates. CAM photosynthesis has adapted to these particular conditions. Adaptations include the stomata opening during the night instead of the day for gas exchange. This is because hot, dry, or windy conditions cause evaporation of water from leaves or other plant material to occur faster. So for example, cacti and other CAM plants store carbon dioxide in the form of an organic acid during the night, and release the carbon dioxide for use in photosynthesis during the day when there is light."
] |
[
"Lots of growers give their cannabis plants 24hours of light during the vegetative period. No ill effects."
] |
[
"This isn't 100% related, but: chloroplasts (the light capturing organelles that contain chlorophyll) relocate themselves according to light intensity. During the peak sunlight hours, a plant may need to protect its chloroplasts from damage, so the organelles will line up behind one another and \"hide\" from the sun. The opposite response is also true for low-light conditions. So when there is very little light, plants will optimize their chloroplast arrangement for maximum light capture... meaning that they will flock to the surface and increase their light capturing area.",
"Check out ",
"this",
" link for a diagram."
] |
[
"Help me figure out a weird sky phenomenon I saw this morning."
] |
[
false
] |
I'm an early riser, so even on my days off I'm up at 6. I was outside just before 7 am - the sun wasn't up yet. I hopped in my car to drive to the store for some coffee, donuts, and (you guessed it) bacon. I pulled out of my driveway and drove west. I live in a valley and so I was looking at mountains; beyond those mountains is the Pacific Ocean. The Sun was not quite up yet, still tucked behind the mountains to the east. The sky was quite clear, one or two high fluffies here and there and a little mistiness along the horizon to the north and west. Here is what I saw: in the western sky extending from the tops of the mountains to about a third of the way through the sky was a column of shadow. That's the best way to explain it - the sky was bright (the sun was almost up) except for this one column which was considerably darker. It was like a reverse searchlight was mounted behind the mountains to the west. The "sides" of the column, then, were not parallel to each other, but instead spread out slightly. The sides, though, did seem to be true - they weren't wavy and did not bend (except to follow the arc of the sky). I drove to the store, looked at it from the parking lot, went inside to shop. When I came back out, the column was still there. It was not as dark and not as focused. I'm not sure about this, but it also seemed to have changed its angle in the sky - where before it was coming roughly straight up from behind the mountains, it now seemed to be tilted slightly to the south. This may have been an illusion based on the fact that it's really hard to judge angles across a spotlessly clear sky in the daytime. It was gone by the time I got home - maybe 15 minutes total from the time I noticed it. Here's what it wasn't - the shadow of a jet contrail. That was my first guess, but jets do not travel that direction in my neck of the woods. There is nothing to the west except for the ocean, and it's kinda big. Jets travel north/south or variations thereof (northwest/southeast, etc.) I also should mention that one of the clouds in the sky looked a bit like the FSM. Perhaps the shadow column was one of His Noodly Appendages? I forgot to buy bacon.
|
[
"I couldn't exactly paint a mental picture of what you are describing here (maybe I need an ms paint pic to help sort it out), but one possibility may be ",
"Anticrepuscular rays",
", shadows of clouds beyond the horizon being cast upwards instead of the normal case, downwards. A good site with an overview of various atmospheric phenomena is ",
"http://www.atoptics.co.uk/",
". The site can be a bit obnoxious to navigate."
] |
[
"It looked like anti-crepuscular rays except there was only one of them, and instead of emanating from the area near the sun, they came from the opposite side - the sun was rising (in the east, of course) and the \"pillar of shadow\" was in the west. "
] |
[
"This is an anticrepuscular ray. Where crepuscular rays merge at the point that the sun is, anticrepuscular rays merge opposite the sun. ",
"From what you say here, this suggests that the sun was shining in the upper atmosphere, and not on the ground, thus how you were able to see the shadow. If there was just one, this is no real problem; often anti-crepuscular rays can be caused by the shadow of thick clouds, thunderstorms, etc.",
"Check out the ",
"Wikipedia article",
" too."
] |
[
"What would happen if Antarctica melted instantaneously?"
] |
[
false
] |
This question came up because I was experimenting with and put a nuke on Antarctica because I was bored. Would the water displace equally in all directions? Or would currents,etc have anything affect on this displacement. Would the entire world flood water world style? How quickly would it happen(if it happened)?
|
[
"Global average sea level rise would be 60-70 meters. I don't remember the exact number, but that's okay because the exact number isn't known anyway. Large parts of Antarctica remain unexplored, without ice thickness measurements.",
"However, the sea level rise would not be uniform worldwide. The biggest effect would come not from ocean currents but from the loss of the gravitational pull of the ice itself (or, strictly speaking, from the loss of concentrated gravitational pull near the pole). Near Antarctica the sea level would actually fall, as the ocean would no longer be attracted by the ice sheet. To compensate for this, sea level would rise more than the average in the far field.",
"To complicate matters further, this pattern of sea level rise would be temporary. The Antarctic continent is presently depressed by hundreds of meters by the weight of the overlaying ice, and when that weight is removed it will slowly rise up to a new equilibrium position over the course of thousands of years. This rise will lower local relative sea level as the land will rise relative to the ocean. However, because the mechanism of the rebound is slow creep of mantle rock to fill in the space underneath the continent, the mass deficit that caused the change in the Earth's gravitational field will eventually be erased. Eventually absolute sea level will be raised by a constant amount worldwide, but relative sea level on the Antarctic continent will still be lower because the whole continent will move upwards.",
"This is all posted from my phone while I'm waiting for my clothes to finish at the laundromat. I can provide a source when I get home.",
" ",
"Mitrovica et al., 2001"
] |
[
"Here's an interactive map of the effects",
". Set for +60 m."
] |
[
"Small? ",
"http://www.neatorama.com/2009/11/09/how-big-is-antarctica/"
] |
[
"Does charging your phone slower, by connecting it to a pc by usb-a, makes the battery last longer than connecting directly into a outlet?"
] |
[
false
] | null |
[
"This is no longer correct with the new charging methods, like \"Quick Charge\" that boost the current and the voltage substantially. Normally USB 2 would be at 5V at 2.5 Watts, Quick Charge is up to 18 Watts.",
"This will boost the charging Voltage to up to 20V. This allows you to very rapidly charge your phone, but will cause the battery to heat up much more. This extra heat will cause the battery to degrade more quickly than if charging by 5V at 500 mA (usb2) or 2000mA"
] |
[
"This is no longer correct with the new charging methods, like \"Quick Charge\" that boost the current and the voltage substantially. Normally USB 2 would be at 5V at 2.5 Watts, Quick Charge is up to 18 Watts.",
"This will boost the charging Voltage to up to 20V. This allows you to very rapidly charge your phone, but will cause the battery to heat up much more. This extra heat will cause the battery to degrade more quickly than if charging by 5V at 500 mA (usb2) or 2000mA"
] |
[
"The low and slow methods are less stressful on the battery because the heating is related to the square of the power (P=I",
"*R) and some will overheat until you don't really want to hold it in your hand or shutdown entirely. Thermal expansion and contraction flex a battery that doesn't want to be flexed, but most batteries compensate and slowly degrade instead of catching on fire. Quick chargers are best when you can swap batteries at the end of life"
] |
[
"Are there chemical elements that no longer exist? Could we continue to create man-made elements past what we've already made?"
] |
[
false
] | null |
[
"The big bang created almost nothing besides Hydrogen and Helium. The reasons for this are complicated, but basically boil down to all the fusion pathways from Helium to heavier elements take a long time, and Big Bang Nucleosynthesis was only occurring for a few ",
".",
"Every element found in nature that is heavier than iron is made in supernovae, via several different processes. The theoretical upper limit for the elements that can be created by supernovae is for the number of ",
" (total neutrons and protons), and the upper limit is ",
"thought to be around 270",
". Thus the heaviest element produced in nature is probably just past the actinides, possibly Meitnerium or Darmstadtium (elements 109 and 110), and of course they will only exist for a few seconds before decaying. ",
"Heavier elements created in labs are created by bombarding heavy elements with other heavy elements, a process which does not occur in nature, therefore these higher elements (like the recently created Ununseptium) can not occur in nature, even the most extreme types of nature like supernovae."
] |
[
"I can say that, because the formative methods are different. ",
"Superheavy elements made in supernovae are created by extremely rapid sequences of neutron capture/beta decay, and the upper limit to elements that can be created by this method is listed in the source I linked above.",
"Superheavy elements beyond this limit are made in labs by purposefully striking already heavy elements with other heavy ions. For instance, Ununoctium was first produced by bombarding Californium with Calcium ions; an interaction that would happen only very rarely even in supernovae. But considering it took ",
"2 x 10",
" interactions to produce just three atoms of Ununoctium",
", the odds of this happening spontaneously in nature ",
" are inconceivably low."
] |
[
"I can say that, because the formative methods are different. ",
"Superheavy elements made in supernovae are created by extremely rapid sequences of neutron capture/beta decay, and the upper limit to elements that can be created by this method is listed in the source I linked above.",
"Superheavy elements beyond this limit are made in labs by purposefully striking already heavy elements with other heavy ions. For instance, Ununoctium was first produced by bombarding Californium with Calcium ions; an interaction that would happen only very rarely even in supernovae. But considering it took ",
"2 x 10",
" interactions to produce just three atoms of Ununoctium",
", the odds of this happening spontaneously in nature ",
" are inconceivably low."
] |
[
"Why would our sense of smell become selected to be worse than what we had before? (Evolution)"
] |
[
false
] | null |
[
"It's not that it was a disadvantage to have a strong sense of smell, but that this was no longer an important trait. Individuals were just as likely to survive long enough to reproduce regardless of how well they smelled."
] |
[
"Very good question. You're thinking about the root of the issue so that is an excellent start. Evolution in simple terms is about keeping some things and getting rid of others based on what you need now. Consider evolution as learning to ride a bike. When you start out, you're riding in the day time and you need training wheels. You need them because you might fall over, and if you fall over you die. So if a windy day comes or you're going over some rough terrain, and you've got training wheels, but you buddy doesn't, he's going to die but you will die, and you're kids will hopefully have training wheels too. This is just like say, a wolf who relies heavily on a good sense of smell for survival. It needs to pick up scents of pray to be able to survive, so when theres an ice age, and there's hardly any elk around, the wolf, or wolf pack with the better sense of smell will be able to find the little elk there is and survive. ",
"Now, consider you a billion years have gone by and you're a new species, you've got your training wheels still on ,but something about the world changes. Now its dark all the time but its flat and there's no wind. So you're training wheels really don't do you any good, you really wish you had a light to see. Your friend doesn't have training wheels, but he's got a light, and luckily he's got a couple of kids that are the same way. You and the rest of your species all ride off cliffs in the dark and remove yourself from the gene-pool. You're friend however, can see the cliff so he avoids it, and lives on. ",
"The same thing happened with sense of smell. We share a common species ancestor with wolves and we both needed the training wheels to survive at that time. Could have been a stronger sense of smell than both humans and wolves now, or could have been worse, or different and more tuned for other smells. But at some point, having a strong sense of smell wasn't really important for our ancestors survival, but it was for the wolves. Things that aren't important for survival stick can stick around but they don't have to unless our survival is dependent on it. One of our ancestors had a mutation that made his/her sense of smell worse that the wolves ancestors, but it didn't kill them and would have killed the wolves, so we lost it and the wolves still have it. ",
"So, basically it's not a disadvantage form humans to have a good sense of smell. But it wasn't a life/death ADVANTAGE after we diverged from wolves so as a result it has steadily decayed. Evolutionary changes are driven by traits that make organisms \"more fit\", or able to survive and have offspring better than the guy next to them. What we are now is largely remnants of what our distant and recent ancestors needed to survive. Some of those traits are essential to our survival now, but some aren't and if it continues that way they will be eroded no matter how important they were before. Pretty cool that we've got a bit of everyone of our ancestors in us, and that they all found a way to survive long enough to have sex with others or themselves, through natural gifts and dumb luck or shear will power. "
] |
[
"Everything becomes worse if it's ",
" selected for. There's no need to select for non-function to lose function, random mutation can take care of that very easily. More than half of our potential olfactory receptors simply aren't expressed or have frame shift mutations rendering them useless, but this doesn't mean that lost smell capabilities gave our ancestors better reproductive success, it just suggests that mutations occurred and losing those functions didn't cause a problem, so the mutant alleles stayed in the population. "
] |
[
"If the cyclin/cyclin-dependent kinase inhibitor p21/WAF1/CIP1 were to be silenced in humans, could its absence help reduce the chance of breast cancer?"
] |
[
false
] |
So basically, we have what's called the BAF180 ( a subunit of the PBAF chromatin complex) which, when mutated, binds to the p21 gene and arrests the G1 phase of the cell cycle. The p21 gene apoptosis and does not under any circumstances induce cell death. In breast cancer, the PB1, which encodes BAF180, is found to be mutated. While I know that cancer is caused by multiple mutations, there is still a chance to significantly reduce the risk if a method to silence the p21 gene were to be implemented. What does Reddit think?
|
[
"This Google Scholar search",
" may be a good place to look for relevant journal articles.",
"A few look promising, such as this one ",
"\"Linkage of Curcumin-Induced Cell Cycle Arrest and Apoptosis by Cyclin-Dependent Kinase Inhibitor p21/WAF1/CIP1\"",
"And this one ",
"\"Cyclin-Dependent Kinase Pathways As Targets for Cancer Treatment\""
] |
[
"We have to be very careful with p21. Remember, even though it is reported to have oncogenic activity, it is classically thought of as a tumor suppressor (though arguably an atypical one). p21 is in the middle of a very delicate axis of cell control and feeds not only into apoptosis and senescence but also DNA repair and genomic stability in general -- that's a lot of potential for varied effects. ",
"It's true some tumors show high levels of p21 expression correlated with malignancy -- breast cancer among them (also multiple myeloma, gliomas and AML if I remember correctly). Other types show reduced p21 expression correlated to malignancy and, importantly, many show a positive contribution to prognosis with higher p21 expression (cervical and some breast cancer comes to mind). So, messing with p21 levels is typically considered a delicate matter in the cancer therapy community.",
"The approach some are taking is to specifically target the oncogenic activities of p21 (directly or things up/down stream) while trying to preserve its importance for tumor suppression, a more nuanced approached than silencing the p21 expression entirely. This may be possible because p21 apparently has oncogenic potential separated from its role as a suppressor of apoptosis, perhaps due to a role as some kind of ",
"adaptor protein controlling CDK-cyclin complex functions",
" (as first described in this paper) among other things. Also, from a more clinical perspective, a lot of cancer therapeutics function as DNA damaging agents and can lead to upregulation of p21, so it could be very useful to selectively stop its anti-apoptotic actions while preserving tumor suppressor activity. ",
"TL;DR - targeting p21 is probably going to be more nuanced than silencing the gene because it has desirable tumor suppressor properties as well. "
] |
[
"Thanks for the response. I've been working on my abstract for a while now, just thinking.",
"Edit: Spelling"
] |
[
"While earthquakes are considered a natural disaster now, were they a big deal back when we were just hunters and gatherers?"
] |
[
false
] |
Thinking about it, the only reason earthquakes are destructive to us now is because of the sheer amount of buildings we have built everywhere. There's also the tsunami afterwards but ancient people away from the coastline shouldn't have problems even with the strongest of earthquakes. Am I missing something here, or are they just not as big of a deal before than it is now?
|
[
"Our built environment along with population density in earthquake prone places certainly does increase the hazard posed by earthquakes, and in detail the majority of damage and death in earthquakes are at least in part related to buildings (e.g., ",
"Doocy et al, 2013",
"). In the absence of buildings, the earthquake shaking itself is unlikely to be deadly. There are however associated hazards that come with either the shaking or the displacement from the earthquake that can be deadly. You mentioned tsunamis, and these can indeed be devastating to coastal communities regardless of the level of infrastructure (and critically could happen without warning in the time before a global seismic network or telecommunication because they can travel very far from their original source, i.e., much further away than where you would feel the earthquake shaking, and still be incredibly damaging).",
"Another earthquake hazard that wouldn't require a building to kill you are seismically induced landslides, which can be destructive to anything living in steep terrain or at the bottom of the slope where a landslide happens. These can also produced delayed hazards that can effect lowland areas, e.g., a seismically induced landslide blocks a river in the mountains effectively producing a dam that can start to impound water, but eventually this dam will fail which can lead to extremely large and rapid flooding downstream (e.g., ",
"Huang & Fan, 2013",
" as an example of a discussion of the broad risk from earthquake induced landslides along with floods from landslide dam breaches).",
"Even in lowland areas, far away from coastlines or mountains terrain, surface deformation from earthquakes can have potentially deadly results, though very localized. Take for example the ",
"New Madrid earthquakes",
", which produced abundant small scale landslides and local flooding of the Mississippi river and tributaries (e.g., ",
"Johnston & Schweig, 1996",
" or ",
"Guccione et al, 2002",
"). As with many of the other hazards, these are relatively localized and to some extent, you as a hunter gather would need to be a bit unlucky (i.e., wrong place - wrong time), but these are still potentially deadly. ",
"You might also be interested in the response to this somewhat related question ",
"from a few months back",
".",
" a lot of death and destruction associated with earthquakes are in part a product of our modern (or past) built environment, i.e., buildings collapsing on us, fires from ruptured gas lines, etc. However, there are certainly hazards associated with earthquakes (tsunamis, landslides, landslide dam breach induced floods, etc) that could still kill you even if you were not living in a building, but the effects would be more localized than what we see today for the most part.",
" Another way to look at this would be the prevalence of discussions of earthquakes (or other natural hazards) in folklore and oral tradition. These events, or descriptions thereof, are pretty pervasive (e.g. ",
"Ludwin et al, 2007",
"), giving us a sense that while these may have not been as deadly in our early history, they were still potentially damaging (and terrifying) enough for them to persist in these stories/histories."
] |
[
"They were a very big deal. For one thing, they were not understood so a great deal of effort was expending creating stories about their god and why their gods destroyed everything, trying to make the incomprehensible comprehensible.",
"Especially in coastal areas, where hunter gatherers congregated, earthquake associated tsunamis often devastated entire tribes.",
"If you are really interested;",
"https://youtu.be/UJ7Qc3bsxjI",
"Nick Zentner spends time talking about decoding First Nations oral histories of an extreme earthquake in 1700, prior to written history in the Pacific Northwest in the USA. A tsunami from that earthquake did impact Japan where they did have written histories."
] |
[
"Thanks for the link to the video.Very interesting."
] |
[
"How can a \"point\" particle exist if we, as macroscopic beings, have volume?"
] |
[
false
] |
We cannot be simply composed of INFINITE point particles, can we? There has to be a limit.
|
[
"Yes, we are composed of finitely many point particles. Roughly 10",
" or so."
] |
[
"When we experience something in the macroscopic world as being solid and taking up space, what we're really experiencing is something that light and/or objects can't pass through. As an example, a chain link fence appears like a solid sheet to a soccer ball, even though there's lots of room between the links. To a fly, a chain link fence can be passed through easily."
] |
[
"If you accept the idea of being composed of finitely many point particles, then you have to admit that we are unconnected and thus have no volume.",
"Topologically, since we are the set of finitely many points this means we closed (we have no limit points, thus the set of points we are made up of contains all our limit points). Granted, topological \"closed-ness\" has nothing to do with layman \"closed-ness\"."
] |
[
"Why do digital cameras have real shutters? Can't they turn on and off the sensor electronically?"
] |
[
false
] |
I'd imagine that it'd be quicker to do things electronically, avoiding the hassles of a physical object opening and closing.
|
[
"A lot of point and shoot cameras ",
" have an electronic shutter. There are pros and cons to both devices. A mechanical shutter lets the manufacturer use a simpler and more efficient sensor (lacking the electronics needed to turn it of and on) with a higher fill factor.",
"From ",
"http://www.steves-digicams.com/knowledge-center/why-digital-cameras-have-mechanical-shutters.html"
] |
[
"To understand the answer to this fully, it would be helpful to understand how digital sensors work. Most cameras these days use CMOS sensors, but the somewhat outdated CCD sensor is a bit easier to understand. \nFrom a report I did on CCD sensors: \n\"CCD sensors are a type of charge transfer devices. The actual device consists of densely packed metal-oxide-semiconductor (MOS) capacitors. Charge is stored in the potential well of each capacitor, and is then moved by applying a varying voltage over the device. The voltage waveform is timed to apply voltages on each pixel's gate at just the right time. The applied voltage increases the size of the potential well and causes charge to move from one capacitor to another. Care must be taken to allow time for the charge to move properly. The voltages should be applied very fast and taken away relatively slowly over time. This process of analyzing the captured charge is called “integrating” the sensor.",
"The sensors utilize the photoelectric effect to capture images through charge transfer. When photons strike the sensor carriers are freed from their atoms. Therefore, the photon must have at least as much energy as the band gap of the material. Assuming a silicon substrate at room temperature, this puts an upper limit of mid-range infrared radiation. Each capacitor acts as a pixel in the device. The incident photons generate free carriers that then get stored in the built in potential well of the capacitor. This charge is then maintained until the sensor is integrated.\"",
"Basically,\nCCD sensors are a series of very small capacitors-- each pixel is a capacitor. Capacitors store charge, like batteries, so when light hits the pixel it will generate an electron, AND store it. Then all of the electrons from each pixel are made into a digital signal, representing the image. Because the sensor is measuring charge, and not light, the amount of noise in the image will be dependent on the temperature of the sensor (less noise at lower temperatures) and the light hitting the sensor.",
"Light always hitting the sensor can also damage it. In the mid-1960s Canon tried to make an SLR with a mirror that stayed in place. The idea was that the mirror would split the image from the lens and show part to the viewfinder and part to the film. More on that here: ",
"http://en.wikipedia.org/wiki/Canon_Pellix"
] |
[
"One aspect is that image quality is higher if the sensor is kept cool and dark. Noise levels increase if the sensor gets warm."
] |
[
"Why isnt Planck length a base unit?"
] |
[
false
] |
[deleted]
|
[
"G is a very poorly known constant, being very hard to measure. This makes it, and all derived constants, very unpractical units.",
"By contrast, before using the speed of light to define the metre, we had independent definitions based on more... down to Earth phenomena and the value of c in old meters per second was measured, and very well too. This measured value has no fundamental physical significance but it's inestimable for the value of the resulting new metre, because the more accurately we knew c in old units, the more accurately we know the ratio old metre/vs new metre (which is 1 +- 10",
"). We know very well how many new metres is, idk, the Eiffel tower tall.",
"G instead is not very well measured in our units. It doesn't tell you anything about fundamental physics but a lot about how our current units relate to Planck units. Since this relationship is not known to a satisfying accuracy, Planck units are not particularly useful as a system of units, in the sense that the number of Planck lengths in the height of the Eiffel tower has an unsatisfying uncertainty.",
"More precisely, G is known to about 5 decimal places. This propagates to l_P which has 5-6 digits. That's not good enough. "
] |
[
"TL-DR: the Plank length is actually derived from the gravitational constant (G), speed of light, and Planck constant. It does not have an exact (known) value. "
] |
[
"all dimensionful fundamental constants are no different. The difference between c and l_P is just the accuracy to which the ratio with the corresponding SI unit is known."
] |
[
"We've had an magnum opus of a thread about the speed of light, but I feel like I could use one about evolution and abiogenesis. Can anyone help explain to us how it all happened?"
] |
[
false
] |
I know that the two are separate things, but they get confused a lot, and I think it would be nifty If we had a thread like one to help clear everything up. Also, how did life come into existence and what were the mechanics behind primitive nucleotides turning into humans and flowers?
|
[
"Abiogenesis is incredibly difficult to study for several reasons. First, all of the evidence was sub-microscopic, on the scale of chemicals less complex than ordinary proteins. Even if any remnants from pre-cellular life still existed from then (keeping in mind that such stuff would serve as food for many living organisms) it would be nearly impossible to find and study today. Second, the earliest pre-cellular life or proto-life would have been far less capable at living compared to later life that there is no hope that any ancient examples could still be around exploiting some niche. Third, the time-scales involved (tens to hundreds of millions of years) make it impractical to study in the laboratory. Nevertheless, there has been a fair amount of research on the subject which provides interesting insights into the likely origin of life on Earth from non-living environments.",
"Various experiments have established that certain fairly complex chemicals (including sugars, primitive amino-acids such as glycine, and nucleotide bases such as adenine) can be produced from simple chemical precursors in environmental conditions similar to the conditions on an early Earth (e.g. lightning, high UV radiation, etc.) The best example of this is the ",
"Miller-Urey experiment",
". The hypothesis of abiogensis is that some example of self-replicating molecule arose naturally from these primitive chemical ingredients, likely some variant of RNA. Such a chemical would catalyze the duplication of itself within an environment enriched in such pre-biotic chemical ingredients. However, duplication of that sort could take a very long time at such a stage (perhaps even years), waiting for the right chemicals to be formed and to interact in the right way. Over time the self-replicating chemical would change. Multiple copies of it would exist, but some would have errors (in the case of a short RNA snippet, additions, deletions, differences of single bases, etc.) These mutations would influence the properties of the chemical, perhaps facilitating self-replication in one way or another. In the case of RNA snippets they could form \"ribozymes\" which are similar to enzymes. One likely early property would be facilitating the formation of nucleotide bases. Over geological time (millions of years) such self-replicating proto-life-forms would gradually acquire various traits until they started to look like proper organisms, and then from there would evolve the various characteristics we associate with all organisms (the DNA->RNA->protein process, use of ATP, etc.) The existence of the ribosome (which is composed mostly of RNA) at the core of the genetic machinery of all life is perhaps evidence of the earliest days of life on Earth.",
"As far as evolution, that is a remarkably simple process to describe. If you have a population of self-replicating creatures such that the characteristics of the creatures are encoded in heritable material (such as genes) that is not always copied 100% perfectly then evolution is a natural consequence. Even if the population begins as entirely identical clones over time slight variations (mutations) will lead to some individuals in the population having slightly different characteristics. If this leads to an improved chance of survival in the given environment then those genes will tend to predominate relative to the genes of the rest of the population, and the species will have changed very slightly. Note that the changes do not have to be extreme, because the advantages will express themselves over generations, much like compound interest. How much would 1% compound interest add up to over a hundred, a thousand, or a million generations? In this way small changes transform the gene pool, and then further small changes stack on those, etc, etc, until eventually you end up with big changes. This can cause populations to change completely or it can cause sub-populations to become significantly different from main populations (creating a new species). Over time populations die off, new populations form, and life becomes ever more diverse and complex.",
"These processes are extremely simple, but over geological time (millions and then billions of years) they can lead to enormous changes."
] |
[
"Look up the Miller-Urey experiment. Basically, the researchers proposed one explanation of how life arose by recreating the primordial environment.",
"They put inorganic compounds common at the time (water, methane, ammonia, and hydrogen) in a flask and fired a quick spark into it to simulate lightning hitting it. They found that it had produced amino acids, sugars, and lipids that are the building blocks of life.",
"Since no one was there, the researchers couldn't say that's definitely how it happened, but with this they're proposing a possible scenario. "
] |
[
"i believe the point of the miller urey experiment's findings and their significance was not that life could arise from those specific conditions, but that life could arise from ",
" condition that was at least somewhat similar to the one in the experiment. it was more of a proof of concept than a perfect model."
] |
[
"Would rum cake show up positive on an alcohol test?"
] |
[
false
] |
[deleted]
|
[
"Except in most rum cakes, you put the rum on the cake after it's baked."
] |
[
"It is certainly possible. A rum cake is basically a sponge cake soaked in rum, so it still has alcohol in it (i.e. none of it has baked out). Therefore, if you eat enough of the cake it can conceivably get you drunk. You would have to eat a lot of the cake to actually feel anything, and I'm not sure about what the sensitivity of the typical breath test is. ",
"Basically, you're probably fine, but if it's critical wait a few hours before taking the test. "
] |
[
"Actually this doesn't happen as much as people think! In fact, to completely get rid of the alcohol you would have to cook the food item for over 3 hours.",
"Cooking for 15 minutes leaves 40% of the alcohol, one hour leaves 25% of the alcohol. A very significant number.",
"Source: Augustin, Alcohol Retention in Food Preparation, Journal of the American Dietetic Association, April 1992, Volume 92, Number 4.",
"Also",
"http://en.wikipedia.org/wiki/Cooking_with_alcohol"
] |
[
"Conceptually, how does the speed of light relate to the permeability/permittivity of free space?"
] |
[
false
] |
I know the equation that relates the three constants: c=(ε0*µ0) However, I never understood why this worked or if there was a conceptual reasoning behind it, so any explanation would be greatly appreciated.
|
[
"Light can be described as an electromagnetic wave. Electromagnetism is described by Maxwell equations. When you work out those, you end up with the equation of wave motion for light, with speed value equal to c as you described.",
"This by the way prompted a crisis: that speed value is the same regardless of the reference frame. So the speed of light is the same even if you chase it at 99% its speed.",
"Einstein eventually explained this with special relativity. "
] |
[
"The idea behind the permittivity and the permeability of free space is to represent empty space as a material. In gaussian units, for example, they don't appear. They only enter the picture when one describes electromagnetic fields in matter.",
"Once the analogy is done, and one treats empty space as if it were a material with a given permittivity and permeability, an electromagnetic wave propagating in it can be thought of as a stretching and compressing of an abstract medium, whose properties are given precisely by those parameters. Oscillations in an elastic medium always have a characteristic speed, given by the medium properties, and in this case it is the speed of light. If you do the same for, say, a solid, where the thing that stretches and compresses are the distances between neighboring atoms, the waves that appear in there are sound waves, and their characteristic speed is the speed of sound in that medium.",
"I hope this helped!"
] |
[
"https://newt.phys.unsw.edu.au/einsteinlight/jw/module3_Maxwell.htm",
"There's the derivation of how c is calculated and what it comes from, hope that helps!"
] |
[
"If two small moons or planets collide together in space, over time they can essentially create one big moon or planet. My question is, by that logic, shouldn't our own moon be getting closer and closer to us, instead of further away each year?"
] |
[
false
] |
I'm not sure if I worded my question good enough in the title for others to understand so I'll try to go more in depth here. Just tonight, I saw a simulation on what it would be like if two planets collided together. The result was chaotic. Over time the debris from the two masses, through gravity, were able to come together and create a larger mass. I've also seen this being talked about by the likes of Neil deGrasse Tyson and other big name astronomers on the science channel. But going by that logic, shouldn't our moon be getting closer to us instead of further away? As in one day our moon should collide into the earth effectively making the two masses into one mass that is slightly larger than Earth? I appreciate any feedback. Thank you.
|
[
"I don't see the logic that because some things that crash melt together, nothing can move away from eachother..... Why would our moon have to be moving inwards?"
] |
[
"If two small moons or planets collide together in space",
"You said it: \"if\". The answer is that they don't always collide.",
"In the simulation that is currently in the front page of ",
"/r/space",
" (",
"gif",
" - ",
"comments section of the thread",
") most of the debris ejected gets into very elliptical orbits, which are unstable and eventually collide with the central attracting body. But stable orbits are possible; if the debris from the collision starts coalescing into a small body then the conservation of angular momentum may lead to an almost circular, stable orbit.",
"When there are no collisions and no gravitational perturbations (i.e. in the pure two-body problem), orbits can be stable over billions of years or more.",
"In the specific case of the Moon, it's actually getting away from us due to tidal effects. ",
"Xkcd",
" has a very simplified diagram, but you can take a look at ",
"wikipedia",
" for more info:",
"Gravitational coupling between the Moon and the bulge nearest the Moon acts as a torque on Earth's rotation, draining angular momentum and rotational kinetic energy from Earth's spin.[132][134] In turn, angular momentum is added to the Moon's orbit, accelerating it, which lifts the Moon into a higher orbit with a longer period. As a result, the distance between Earth and Moon is increasing, and Earth's spin is slowing down.[134]"
] |
[
"going by that logic, shouldn't our moon be getting closer to us instead of further away?",
"No. Just because something can happen does not mean that the circumstances that lead to it are currently happening. That's like saying that because eating a bunch of Snickers makes me fat, I should be getting fatter. "
] |
[
"Is it possible for a person to be colorblind in only one eye?"
] |
[
false
] |
Something like the heterochromia mutation?
|
[
"Heterochromia is the result of more or less pigment in the iris of one eye. While there is usually a genetic component, there are a whole collection of genes that interact with each other and the environment to regulate melanin production. So it's a lot easier for a mistake to happen.",
"Color blindness is more of an on/off thing though. It's caused by a single faulty gene and either a cell has that gene or it doesn't.",
"So to be color blind in only one eye, a person would need two types of cells. Some of them with a normal working copy of the gene for color vision, and some cells with the defective version that causes color blindness.",
"This is actually possible. It's called chimerism and is the result of two embryos fusing in the womb to develop into one organism. There's even documented cases of it happening in humans. ",
"https://en.wikipedia.org/wiki/Chimera_(genetics)#Humans",
"The only problem is that which particular cell becomes which particular tissues in a chimera seems to be largely random. And the odds of getting a pair of color blind and not color blind twins fusing in exactly the right way is extremely tiny."
] |
[
"Could we argue that a random mutation during embryo/fetal develop could allow for colorblindness in just one of the eyes? At the stage where a single cell mutating would affect the entire eye, but only one. Admittedly, this is also very low, but probably lower than your example. Maybe. "
] |
[
"That's also a plausible way it could happen and one I didn't consider.",
"But the odds of either scenario are so minuscule that it's really hard for me to make a guess at which one is less likely."
] |
[
"Can you become resilient to 3D?"
] |
[
false
] |
[deleted]
|
[
"It is after all, only an optical illusion.",
"It actually functions in the same way that gives us 3-D vision, it displays a separate image for each eye. "
] |
[
"depth perception operates through the brain processing two images that are slightly apart from each other, with 3d movies and games the two images are created artificially either by alternating images or using polarised light, both of which require special glasses. ",
"However I have noticed that with 3d heavy movies there tends to be a sweet spot\" that they put everything into focus for, i.e. where the director wants you or assumes you will be looking, looking elsewhere can cause confusion and headaches."
] |
[
"It's an optical illusion as much as your regular vision is. The only difference is that it has a finite resolution.",
"You're probably just more used to it. It's not that you've \"become resilient,\" the quality is the same, there's just less awe involved."
] |
[
"Is the Mars curiosity rover waterproof?"
] |
[
false
] | null |
[
"The sealant to keep out environmental dust is as good as the sealant to keep out water. Electronic components are also in a sealed environment to facilitate temperature control. ",
"The rover probably isn't balanced with respect to buoyancy, so wouldn't function as intended underwater (let alone the instrumentation), but if you suddenly plopped it in water, barring physical damage like flipping over or whatever, it wouldn't suffer any electrical or motor issues."
] |
[
"The sealant to keep out environmental dust is as good as the sealant to keep out water. Electronic components are also in a sealed environment to facilitate temperature control. ",
"The rover probably isn't balanced with respect to buoyancy, so wouldn't function as intended underwater (let alone the instrumentation), but if you suddenly plopped it in water, barring physical damage like flipping over or whatever, it wouldn't suffer any electrical or motor issues."
] |
[
"This is sort of besides the point; it's like me saying 'This is heat resistant!' and you saying 'Yes, but can it survive being submerged IN LAVA?!'",
"The sealants the Rover has are for an environment that is approximately 70-150 millibars. There's probably a good deal of redundancy in place, and remember, the thing survived a very traumatic landing. But the Marianas Trench are not the conditions the Rover was designed to survive in. Which isn't to say that it would explode catastrophically in a couple dozen feet of water. "
] |
[
"What are the differences between a cold dead star and a planet?"
] |
[
false
] |
[deleted]
|
[
"A black dwarf is a stellar remnant of any star not massive enough to become a neutron star. Actually, a white dwarf is what I just described, but as a white dwarf cools over time, it will become a black dwarf. It's thought that no black dwarfs exist yet, as it takes longer than the age of the universe to cool from a white to black dwarf (estimates are on the order of 10",
" years).",
"Dwarf stars are composed of electron-degenerate matter: ",
"Under high densities the matter becomes a degenerate gas when the electrons are all stripped from their parent atoms. In the core of a star, once hydrogen burning in nuclear fusion reactions stops, it becomes a collection of positively charged ions, largely helium and carbon nuclei, floating in a sea of electrons, which have been stripped from the nuclei.",
"The density of this matter can vary, but most dwarf stars have roughly the mass of the sun in the volume of the Earth.",
"Note that \"cold\" is relative - the coolest dwarf stars observed are around 4000 K ( 6700°F )."
] |
[
"It's not just the limit of detectability - that's the temperature of the oldest white dwarfs as well. 10",
" is the time it takes for a white dwarf to cool based on estimates that ignore the possible existence of WIMPs. If that assumption of particle physics is wrong, the length of time can increase by a factor of 10",
" ."
] |
[
"So, here it really depends what you call a 'cold dead star'.",
"There are things called ",
" that are small stars with about 0.08 solar masses (about 80 jupiter masses) that can only really liberate energy by gravitational collase. Incidentally, this mechanism is the reason that Jupiter is so 'hot' - the energy from the sun it recieves is not enough to be the temeperature it is. ",
"So these are just basically a 'big planet'.",
"These will eventually become ",
", which I will explain later.",
"There is another class of star, called a ",
". These are 'stellar remenants' - hot balls of carbon and oxygen that have insufficient pressure and temperature to continue the fusion process up to iron, so the star simply stops and falls apart.",
"These are what are left from stars that are about the mass of our sun, and are held up by something called ",
", which is a consequence of the Pauli exclusion principle, if you are familiar with that. They used to be stars, but got old and died in the way I mentioned above.",
"These stars aren't actually fusing anything - so eventually they will cool down and become a black dwarf.",
"These are what is left when the above 'stars' eventually cool down enough to stop glowing white/red hot. They are balls of atoms held up by the aforementioned electron degeneracy pressure.",
"You may have noticed that above I said that the white dwarves were made up of carbon and oxygen - these black dwarves eventually become giant, planet-ish-sized diamonds! They are much smaller than the stars that they were created by because they are extremely dense.",
"Neutron stars are what's left when a medium mass (larger than the sun, not a huge hulk though) star ends it's life. They are usually what's left after a supernova, and are held up by neutron degeneracy pressure. They're essentially (we think) giant atoms.",
"These guys are nothing like planets. They are far too dense.",
"The final stellar remnant. This is what's left when a huge star goes supernova. Again, nothing like a planet.",
"So, you can see that it's a scale. Planets, like Jupiter, are simply to low mass to become a star. Compared with the black dwarf (the closest 'cold, dead star' to a planet), they are considerably lower density, and have completely different make-ups - Jupiter is made up of hydrogen and helium, whereas the black dwarf is made up of carbon and oxygen - even if they are about the same size."
] |
[
"How does LIGO relate to relativity?"
] |
[
false
] | null |
[
"Gravitational waves are a prediction of general relativity."
] |
[
"So this form of information transfer is very interesting. Does the acceleration of any matter result in gravitational waves as the curvature of surrounding space is modified"
] |
[
"Gravitational waves are only produced if the matter distribution has a changing mass quadrupole moment (it needs to have a nonzero third time derivative). So something like two black holes orbiting around their common center of mass will emit gravitational waves."
] |
[
"If a salmon's birth stream/river was filled in, what would they do?"
] |
[
false
] |
Salmon go back to their birth stream to reproduce, right? What would they do if a dam or natural formation blocked off their access to the stream? Would they go somewhere else, reproduce at the closest point, do nothing and die, or what?
|
[
"They would most likely hand around the base of said obstruction until either they die from starvation, spawn at the point they were stopped or leave.",
"I am guessing a mixture of the first two. However being semelparous (die after one large spawning event), even if they were to spawn the adult population would die and then depending where in the river they spawned the juvenile population could die also from a lack of food etc. "
] |
[
"IIRC they die trying to go back. "
] |
[
"How? do they beach themselves where the former mouth of the river was? or something else?"
] |
[
"The soil triangle: Is there a name for charts of this type?"
] |
[
false
] | null |
[
"I am not going to release this question, but I will tell you that it is called a \"ternary diagram\" or \"ternary plot\"",
"It is commonly used in many fields, such as geology, materials science, chemistry, and more",
"https://en.wikipedia.org/wiki/Ternary_plot"
] |
[
"Great, thank you very much for answering my question! I had trouble googling it because every query inevitably returned a myriad of geology-related results and no results about charts proper."
] |
[
"haha! I understand. The only reason why I know the answer is because of my degree in materials science."
] |
[
"What happens when lightning hits a beach of sand?"
] |
[
false
] |
[deleted]
|
[
"They're called ",
"fulgurites",
".",
"Cool, huh?"
] |
[
"You get a piece of fulgurite if you're lucky.",
"http://en.wikipedia.org/wiki/Fulgurite"
] |
[
"On a related note, a saw a beautiful 20 foot high fulgurite on display at the local science museum a while ago. If you are interested in this sort of thing, drop by a science museum or natural history museum and take a look around."
] |
[
"Massive black holes can spew out huge amounts of energetic material. Would this process convert heavy elements back into hydrogen and helium?"
] |
[
false
] | null |
[
"For example, if a nickle-iron planetary core is ripped apart, is it converted into protons and other light nuclei?",
"For example, if a nickle-iron planetary core is ripped apart, is it converted into protons and other light nuclei?"
] |
[
"For example, if a nickle-iron planetary core is ripped apart, is it converted into protons and other light nuclei?",
"The core would get ripped apart long before it got close due to the Roche Limit dynamics.",
"The required tidal forces to rip an atom apart are likely only encountered inside the event horizon of small black holes.",
"As such, no heavy nuclei are going to get smaller."
] |
[
"The material itself doesn't enter the black hole at any time it is merely accelerated and ejected in massive jets at Hugh energies. The forces at work in this are likely not enough to overcome nuclear bonds (although perhaps it could effect some very heavy, unstable elements) and so the actually element would not change "
] |
[
"How can a car battery be rechargeable if the voltage is produced by a chemical process?"
] |
[
false
] |
As far as I understand, lead and lead oxide are suspended and diluted in sulfuric acid. If this is the case, how can a battery 'die' if left charging something overnight, and how can a jump bring it back to life? I'd think that if the battery died, it'd be dead forever as there is no more chemical reaction taking place?
|
[
"Charging a battery undoes the chemical reaction. You put in energy to put it back to the high-energy state.",
"The full chemical equations are spelled out on the ",
"wikipedia page",
".",
"This is also true in lithium-ion batteries. When you discharge the battery, the lithium ions move from negative electrode to positive. When you charge it, they go back from positive to negative."
] |
[
"Discharging a battery requires the motion of ions inside of it. The motion of ions creates an electron current from one battery terminal to another. So, if the terminals are not connected at all then there is zero current and thus no ions are moving.",
"This process is reversible. So pushing a current through the battery from an external source will move ions in the opposite direction they moved when they were in the discharging phase. This situation is quite analogous to pushing a mass up a hill so that it can roll down again."
] |
[
"Thanks for your response, that makes sense. "
] |
[
"Is Magma the Same?"
] |
[
false
] |
Is all magma the same? for example if you have a piece of shale and it melts into molten rock (magma), would the magma be the same magma as molten marble? Or would the magma be made of a different combination of materials.
|
[
"No. The chemical compositions of your two hypothetical melts would be different and thus the physical properties would be different.",
"This is more easily discussed in terms of more realistic magma/lava types that we see regularly. In considering types of magma, we usually think of them in terms of what types of rocks they will form when they solidify and crystallize. For lava (and rock types) we commonly see at the surface, we can think of a continuum between basalt (mafic) to rhyolite (felsic). The principle difference, or at least what we use to classify them, is the percentage of SiO2 (silica) but this accompanied with various differences in composition and thus resulting mineralogy. These differences in composition importantly cause differences in other properties like temperature of solidification, density, and viscosity. The ultimate cause for the differences in composition can be tied back to formation mechanism and location. This ",
"page",
" from a course at Penn State goes through the basics of some of the physical differences in different types of magma/lava."
] |
[
"Living in Hawaii, I am amazed at how different \"lava\" can be in different places, even though it is the result of the \"same\" hotspot. How well mixed is the magma beneath the earth's crust? I would have expected it to be well mixed, but it seems that it is not."
] |
[
"Can you explain a little more about what you mean about different lavas? do you mean surface structural expression? or chemical composition?"
] |
[
"Can other sources of light be concentrated through a magnifying glass to start a fire? Like the light from a flashlight, or from a full moon?"
] |
[
false
] | null |
[
"You can only focus light to reach the temperature of the light source.",
"That is only true for thermal emission, not for light sources like LEDs (e.g. in a flashlight)."
] |
[
"In the 1960's there was a company called Aerometerics. They made a line of products that were basically quartz/halogen lamps in reflectors. The focused light intensity was high enough that these were used to braze metal, heat treat steel, and could even melt through a steel sheet if left long enough on a spot. They made some 12kw modules that could be arranged in a matrix for large area heat treating. I took a 750 watt one, focused it on a copper penny, and in four minutes the penny was molten."
] |
[
"Yes you can do this, most laser used for cutting work like this. Something emits light then it is highly focused to heat the material to very high temperatures. An object in general can only get as hot as the thing that is heating up if both are acting like perfect black bodies. This is because when something is heating up it emits light waves back out. If the temperature of the light is increasing the amount of energy in the waves increases as well. This goes till the 2 are balanced out so when the energy of the incoming light is equal to the energy of the outgoing light then you reach a steady state temp."
] |
[
"What effects did the weight and size of a dinosaur have on the type of environment it needed to support it?"
] |
[
false
] |
I am not 100% sure I used the right flair, if another would be more appropriate, please change it! I used to drive semi trucks, and one of our major rules was never leave a loaded trailer on anything but concrete, because it's supports would sink into the ground on anything else. In addition to that, I play and watch a number of scifi mecha type games, movies, and anime, and the discussion always comes up how mecha are unfeasible especially when they get big, because the ground wouldn't support their weight focused on where their feet were. That had me wondering if the huge multi-ton dinosaurs had similar problems. I am interested in hearing anything about how their mass/size/weight effected them.
|
[
"Wow - this is a very cool question. I'm a geotechnical engineer, so I'm going to come at this from that perspective. A quick apology to most of the world, I'm going to do this in US Engineering units. I'll provide a couple conversions as I go. ",
"From a quick look at ",
"Wikipedia",
", it appears one of the heaviest known dinosaurs was Argentinosaurus huinculensis, clocking in at an estimated 212,500 lbs (96.4 metric tons). ",
"Spinosaurus",
" seems to take the cake for bipedal dinos at 46,100 lbs (20.9 metric tons). So we have our upper-bound static loads. 212,500lbs/(4 legs) we get about 53.1 kips/leg (1 kip is 1000 lb), and 46,100lbs/(2 legs) we get 23 kips per leg.",
"With these quick calculations, I can give a general answer to your questions. YES! Especially when you account for the dynamic effect of Dino movement, these are big loads. I can say I don't even need to consider foot-size and load distribution here. Your standard light-weight, single-story, pre-engineered steel building has maximum column loads of around 30 kips. Often I've had to recommend expensive ground improvement to support a building like that in delta deposits. A Titanosaur walking around with 50-something kip legs, applying dynamic loads to soil would settle a bit and would need to avoid some environmental settings entirely due to how much they would sink. ",
"That is my only conclusion from this quick look; that some environments (think river deltas, marshland, peat bogs, etc) would be incabable of supporting the weight of some of the very largest land dinosaurs. To try and determine just how limited they would be in terms of environment (what about loess plains, etc?) would require a lot more time, thought, and information. Like, do we have good information on what the gait of Titanosaurs looked like? ",
"Edit: Adding an edit to emphasize that the anecdote about a small building is not intended to compare the effect of prolonged static loading to a dinosaur walking around, but to give a sense of the magnitude of weight these guys were throwing around."
] |
[
"Before maybe 50 years ago it was believed that sauropods would have to live in water to support their weight, but the idea has been rejected, because they show no adaptations to such a lifestyle and the upright stance is best suited to moving overland. Spinosaurus, on the other hand, is one of the few dinosaurs believed to have had a semi-aquatic lifestyle, but this appears to be an ecological adaptation rather than a structural necessity. ",
"I wouldn't compare dinosaurs too closely to a truck; Legs do a much better job than wheels in dealing with soft terrain. I'm also a bit skeptical of comparing them to buildings for similar reasons, and because dinosaurs have muscles and joints to help deal with irregular loads. A sauropod can let its feet sink into mud and then pick them back out.",
"This isn't to say supporting that weight is easy. Analysis of trackways indicates they moved with a stable walking gait. They probably had to eat pretty much constantly to support themselves, which would have been the main constraint on their environment. A sauropod herd may have been something of a moving ecological disaster zone, stripping and knocking down trees as they went, but they'd probably have trouble moving into a thick forest. Swampland may similarly have slowed them down too much to be worth entering."
] |
[
"In addition to the follow-up questions you mentioned, I'll add my own: ",
"Would that mean such large creatures would be more inclined to spend time in the water where they wouldn't have to worry about that nearly as much, kind of like hippos and elephants can, despite having legs like typical land creatures, or would that mean they would spend their time in areas with harder packed ground or rock that might support their weight better? ",
"Presumably the herbivores of that size would need to be in terrain that could support their weight that could also provide the vegetation they needed, what kinds of terrain would qualify? I would think swampy terrain would be right out due to soft ground that isn't quite deep enough for massive creatures like that, but maybe places like the Amazon River?",
"I would ask the above question about the massive predators as well, but I assume they would go to where their prey was, and if massive herbivores were in terrain that can support them, then massive predators would probably be int he same places? Correct me if I'm wrong please!"
] |
[
"Similar to the Chladni Figures, are there 1-dimentional nodes on the surface of the Earth during the earthquake, i.e. the lines (curves) of points that act like wave's nodes, with locally smallest amplitude?"
] |
[
false
] | null |
[
"Interesting question. My suspicion is probably not. Chladni patterns are standing waves because they are resonances on a plate, like a 2D analog of a vibrating string. Seismic waves, in contrast, radiate outward from the source and dissipate with distance, more like the ripples on a pond."
] |
[
"If you have problem imagining what I mean, try to see these videos:",
"Chladni Sound Figures (U2-05-02)\n",
"https://www.youtube.com/watch?v=nqx_joZFLDI",
"Chladni Figures - random couscous snaps into beautiful patterns\n",
"https://www.youtube.com/watch?v=CR_XL192wXw"
] |
[
"I think the intuition here is correct that with earthquakes there can be local differences in wave amplitude due to interference in regions subjected to reflected/refracted energy or from multiple sources. But, the likelihood of source dynamics and governing spatial geometry resulting in stationary nodes seems very low."
] |
[
"If we were to construct a tube going from the surface of the earth to outer space, would the vaccum of space create a sucking action that could be used as some sort of garbage shoot?"
] |
[
false
] | null |
[
"Not likely as the vacuum would be immediately replaced by incoming air."
] |
[
"No.\nThe vacuum of space is there now, and it isn't sucking much out into it. Believe it or not, gravity is what holds our atmosphere in place, so if you were to build a big tube going into the vacuum of space, gravity would keep the air in the bottom of the tube from escaping; the same way it does now without a tube.",
"Certain light gasses (Helium, Hydrogen) will escape into space because gravity of the earth isn't enough to hold them in, and the buoyant force of the other gasses in the atmosphere will push them out. Balloons are actually a good way to get stuff high into the atmosphere; higher than any airplane even, but not all the way out.",
"Look up the space elevator as an easy way to get stuff into space: ",
"http://en.wikipedia.org/wiki/Space_elevator",
"The only technological problem to solve is that we would need a very long, very strong rope. There is no solution at the moment, but there are ideas (some of them involving carbon nanotubes)"
] |
[
"The only technological problem to solve is that we would need a very long, very strong rope. There is no solution at the moment, but there are ideas (some of them involving carbon nanotubes)",
"This is not the only problem with a space elevator. The lower part of the cable will be subject to high winds while the upper part will be subject to space debris. The space elevator will also need to go through the Van Allen belt and naive designs have the elevator itself go through slowly. That's not good for living cargo (generally when astronauts have gone through the belt they've done so quickly). Even if one were able to make carbon nanotubes of the requisite quality and consistency, the total amount of material needed to put up a space elevator by an optimstic estimate is more than the total amount of mass that has been put up into space in total by every launch, which means that launch costs need to go down a fair bit before you have a space elevator. That's a lot. That said, these are still engineering issues and may be beatable with enough technology. There's a NIAC report(",
"phase 1",
", ",
"phase 2",
")which discusses the technical issues and how they might be overcome that is worth reading. "
] |
[
"Can bubbling result from cooling as opposed to heating of a liquid?"
] |
[
false
] |
[deleted]
|
[
"You are talking about a dissolved gas. This is not what happens in an autoclaved liquid; the phase transition is a not dissolved aqueous species to gas but rather liquid water to water vapor."
] |
[
"You are talking about a dissolved gas. This is not what happens in an autoclaved liquid; the phase transition is a not dissolved aqueous species to gas but rather liquid water to water vapor."
] |
[
"Boiling is actually a cooling process. That is to say, when a liquid boils, energy from the liquid is being removed into the vapor phase.",
"It is possible to achieve \"boiling\" by cooling things rapidly due to phase separation. I learned this first experimentally by putting an opened beer in liquid nitrogen and witnessing a pretty awesome beer fountain as a result. I doubt this is the case in an autoclaved medium because the most common vapor species is the same as the most common liquid species... both water.",
"The reason you see it in the autoclave is two-fold, at least in my experience. Standard autoclaving is done at a pressure that corresponds to the saturation vapor pressure of water at 121 C. That means when you remove the medium and steam is allowed to escape from the headspace, the pressure at the interface of the liquid decreases and the boiling point drops. Steam can escape quickly, but the thermal energy in the liquid is a big reservoir so it is still there when the steam is equilibrated to the room pressure. For a short period the water is super-critical and so it boils. ",
"Importantly, You will ",
" observe this boiling upon cooling if you close the lid the moment you remove the medium from the autoclave. I know because I've done it. This should be enough to convince you that it is pressure driving the boiling, not a temperature change in the strict sense.",
"There's also a change in the dielectric constant of water at increased pressure. In short, water acts more like a non-polar solvent at higher pressures. Polarity does impact boiling point but that's likely a trivial effect in this scenario."
] |
[
"If you were sitting in an open field when an earthquake happened, how bad would it have to be to be deadly?"
] |
[
false
] | null |
[
"what would you expect to kill you then? "
] |
[
"Just the shaking? I was wondering if it the shaking itself could get bad enough to kill someone"
] |
[
"You would have an acceleration equivalent to about 9 ish G's in order to have internal damage, and that's just not going to happen in an earthquake."
] |
[
"Why does air become hot or cold when you blow/suck through material (e.g. your clothes)"
] |
[
false
] |
[deleted]
|
[
"Because comparatively, you are blowing out considerably warmer air after it was heated up from your internal body heat. The deal with the cloth, is that it slows down the air a bit after exiting your mouth, and therefore feels even hotter because it sticks around longer, compared to just blowing on your skin normally."
] |
[
"Going off on a bit of a tangent: its important to realize that there is a difference between actual measured (with a thermometer) and perceived (through physical touch and brain signal interpretation) temperature. Take three bowls, one with room temperature water, one with hot water, and one with cold water. Put one hand in the hot water and the other in the cold water. Let it sit for a minute or so and the quickly dive both hands into the room temperature water. You will receive signals from your brain telling you that the hand which moved from hot water to room temperature water is cold and that the hand which moved from cold water to room temperature water is warm even though both hands are sensing water of the same temperature.",
"The air coming from your mouth is already warmed from your body upon exhalation, which is warmer than the temperature of your lips, so your brain tells you that the fabric is warmer. The air entering your mouth is cooler than your lips and the interior of your mouth so your brain registers it as cool.",
"The air did not become hot or cold, it was already hot or cold when you sensed it with your mouth and lips. Its the change in temperature that your brain registers."
] |
[
"ty all makes sense now :)"
] |
[
"How much does nutrition actually affect a person's height?"
] |
[
false
] | null |
[
"20% - 40% of human height.",
"20% - 40% of human height variation, not 20-40 percent of human height. These aren't the same. "
] |
[
"The question is not being answered. Yes, a significant portion of height is determined by environmental factors, obviously if malnourished, height will be affected.",
"What I think the OP is wondering is, in a 1st world society where calories and a wide variety of foods are abundant, what significance is specific nutrition to height?",
"For example, if you give your kid certain macro nutrient proportions, supplements, specific diets, etc... will that change their height?",
"OR is height almost completely genetic, assuming a person is sufficiently(but not ideally) fed.",
"Can my kid grow significantly taller than what he inherits from me and his mother by making sure he gets certain nutrients? Or is he fixed to be about the height that wold be predicted from his parents."
] |
[
"http://www.scientificamerican.com/article.cfm?id=how-much-of-human-height",
"This article claims that nutrition is quite significant. It suggests that nutrition and environmental factors accounts for 20% - 40% of human height.",
"Edit: 20% - 40% of human height variation, not human height."
] |
[
"When a doctor says to a patient that they have 6 months to live, how do they know?"
] |
[
false
] | null |
[
"Ultimately, what you are inquiring about is the ",
"prognosis.",
" Once you have been diagnosed with a particular disease and it's severity, it is not too difficult to predict the outcome for you based on the statistical experiences of previous patients in your condition. Sure sometimes a patient that should die survives and vice versa, however these people are statistical exceptions and not the rule. "
] |
[
"A good doctor will also give you some statistical numbers. ",
"I.e. 95% of patients with similar condition do not live past 6 months. "
] |
[
"Do they also undershoot the life expectancy so the family won't be mad if the guy dies earlier?"
] |
[
"My grandpa died of Alzheimer's years ago, but exhibited some strange behavior/symptoms. How are these possible?"
] |
[
false
] | null |
[
"We cannot speculate on individual cases like this. "
] |
[
"Why not?"
] |
[
"Because we don't offer medical advice and we don't want to comment on individual medical cases. We don't want the personal medical information posted here. We've also found that anecdotal questions lead to anecdotal answers, which are not allowed. We also don't allow speculation, and speculation is almost always necessary with questions like this. "
] |
[
"At what point in time do we stop seeing wolf fossils near humans and start seeing \"dog\" fossils associated with humans?"
] |
[
false
] |
Did dogs also go through intermediaries to transition between wolf and dog? Ie, we have H. erectus before H. sapien. Or are modern dog and modern wolves too similar ro be classified differently?
|
[
"There's almost no chance wolves weren't a food source, especially from hunting. Realistically speaking they're less dangerous than a lot of large herbivores and if you've hunters capable of safely taking down deer, boar etc, you can handle wolves. And if you're following a herd of deer, you'll find wolves. "
] |
[
"It's not clear-cut, but not because wolves and dogs are skeletally identical (they're not). Dog and wolf fossils are found at the same site as late as the ",
"Mesolithic",
", probably because they played different roles: dogs for pets, wolves for butchering."
] |
[
"dogs for pets, wolves for butchering.",
"That's interesting. Is there fossil evidence that wolves were hunted for food then?"
] |
[
"What does it mean to be double jointed?"
] |
[
false
] |
I've heard people being double jointed in wrists, thumbs and shoulders. Some people claim to be double jointed and are extra flexible in said region. I can twist my shoulders all the way around like in this video (that's not me). Is that double jointed-ness or something else? What is a double joint? Is it actually just a misnomer for something else?
|
[
"'Double jointedness' refers to joint hypermobility. It can affect one, or multiple joints in the body and is characterised by an ability to extend or flex a joint beyond the typical range.",
"Most commonly, hypermobility is caused by misaligned joints, abnormally shaped bones or some sort of connective tissue defect which results in weakened ligaments, muscles and/or tendons. ",
"It can also result from certain musculoskeletal injuries where healing does not restore perfect function (dislocations are a good example).",
"Edit: Spelling"
] |
[
"Double-jointedness is a lay-term for hyper-laxity of constraining elements in the joint. All joints have degrees of freedom for motion but are constrained by bony and soft-tissue anatomy. In a person with hyper-laxity, either the bony constraints are inadequate, or the ligamentous constraints are more elastic than normal (or absent). Certain connective tissue disorders (such as Marfan's syndrome etc) can cause this, but most times it's just individual variation."
] |
[
"It's a misnomer, there's no such thing as being double jointed. Rather, the proper term would be hypermobility. A number of things can contribute to this including weak/loosened ligaments, shape of the bone, and tone of the muscles surrounding/supporting a particular joint. ",
"See: ",
"Hypermobility",
"Edit: \"shaped\" to \"shape\""
] |
[
"On average, how far back do we need to trace an individual's family tree in order to find their most recent common ancestor with any other random person from the population?"
] |
[
false
] | null |
[
"I'm not sure why you think that statistics won't work in this case. Statistics never gives \"the answer.\" It gives ",
" together with a range of confidence or probability. In this case a simple demographic model could be devised that provided an answer quite easily, but with a very broad confidence interval. On the other hand, demographic factors like overlapping adult generations, fluctuating rates of migration, and assortative mating can be included in much more complex models that will give better estimates.",
"This paper",
" develops population models that include several of these factors and finds the most recent common ancestor of all living humans was probably alive sometime between 3000 and 4000 years ago. This is not the question OP asked and I don't know of anyone who's attempted to answer that question, but it would involve essentially the same type of model.",
"Taking the estimate from that paper (or even an estimate two or three times as old) and a basic understanding of the relatedness distribution of humans would yield an \"average time to pairwise common ancestor\" most likely less 1000 years."
] |
[
"That would only be true if the distribution of relatedness among humans was flat or normal. In fact the distribution is highly skewed. The vast majority of people around the world are very closely related and only a few isolated populations are more distantly related to the rest. So if you pick two random people from the global population, their relatedness is much more likely to be high than low, which pushes the whole average down considerably."
] |
[
"That would only be true if the distribution of relatedness among humans was flat or normal. In fact the distribution is highly skewed. The vast majority of people around the world are very closely related and only a few isolated populations are more distantly related to the rest. So if you pick two random people from the global population, their relatedness is much more likely to be high than low, which pushes the whole average down considerably."
] |
[
"After a bone marrow transplant do you produce blood with a different set of DNA?"
] |
[
false
] | null |
[
"Yes definitely - and with this comes cells that may also react to \"self\" antigens in the new host so careful matching is required. Otherwise graft vs host disease may occur. On the other hand, in cases of cancer a tiny bit of this is OK as there may also be a graft vs cancer effect.",
"http://www.ncbi.nlm.nih.gov/m/pubmed/19735262/"
] |
[
"Not only blood - your immune system will be of an entirely different genetic code as well. \nIt depends on exactly how the process is done - in some cases your bone marrow can be entirely depleted, and a transplant will give you an entirely new system. On the other hand, with a partial transplant, you will have both your own DNA and DNA of the other person until one or the other eventually takes over.\nThis new DNA and the immunity that comes with it essentially means that you are transplanting immune systems as well. Therefore, the donor has to be very similar, otherwise the new immune system will attack your own organs and lead to death."
] |
[
"Your body is constantly making both lymphocytes (T cells, B cells and NK cells) and leukocytes (granulocytes) - they aren't produced once and then never again like ovarian follicle cells.\nThese immune cell types come from the stem cells present in the bone marrow - if it weren't for this, adaptive immunity would not be able to tackle any new invaders after the initial cells were made."
] |
[
"Why does air moved through a fan feel cooler?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/askscience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"You can find the answer by searching for something like \"fan cool air\". Unfortunately, because of the high volume, a lot of great questions and answers can get buried quite quickly. The searchbar can be a great way of exploring ",
"/r/askscience",
" and we encourage everyone to use it before posting.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Did some searching and all and it answers the more basic end of why our bodies feel cooler, but in a closed system (imagining somehow that the fan didn't need electricity from an outside source) ",
"Wouldn't a fan just eventually make things hotter? What I read was it was the particles random movement that determined tempature, but like in a Datacenter aren't all the fans just adding to the overall tempature eventually not reducing it? "
] |
[
"I think all of your questions can be answered by these posts:",
"https://www.reddit.com/r/askscience/comments/1hv26j/why_does_air_seem_to_cool_as_it_moves_like_from_a/",
"https://www.reddit.com/r/askscience/comments/u2qpd/why_does_air_blowing_from_a_fan_feel_cooler_than/",
"https://www.reddit.com/r/askscience/comments/3aa3lm/how_can_fans_cool_the_air_if_theyre_only_moving/"
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.