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Sunday, July 28, 2019

Can electricity arc in a vacuum?

Can electricity arc in a vacuum?


Can electricity arc in a vacuum?

Posted: 27 Jul 2019 01:09 PM PDT

How is dirt/debris/inorganic material handled or processed when a caterpillar passes through the pupal stage (and digests itself)?

Posted: 27 Jul 2019 12:36 PM PDT

Where I live (rural area) there are always lots of caterpillars seen near the fields and crossing roads this time of year. It is hot and the roads are oily and lots of tar/rock chip, etc. There have to be oil / tar / debris that sticks to the hairs of the caterpillars, and I was wondering how this stuff is accounted for when the caterpillar turns itself into soup inside the chrysalis. Do they shed an outer layer or dispatch of the hairs/fur before going through this process, to avoid complications? Could certain debris or chemicals cause issues during this transitional phase?

submitted by /u/vonKemper
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Can a person with high blood pressure donates blood?

Posted: 28 Jul 2019 08:02 AM PDT

Let's say his/her blood pressure was high but still donates blood anyway. What would happen to him/her?

submitted by /u/bernamadanial
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Why do conventional spin echo MRI do not seems to have problem of signal saturation like gradient echo with large flip angle?

Posted: 27 Jul 2019 09:00 PM PDT

Hello, I am a radiographer and was taking a course in MRI medical imaging.

According to the lecturer, the gradient echo sequence was designed to have a short repetition time (TR) to reduce scan time. However, with short TR, there will be signal saturation for each scan cycle due to the low recovery of longitudinal magnetization after each scan cycle. The solution is to use a small flip angle to compensate for the signal saturation.

Then, there is a problem that confused me. If what he said was true, then when we do a conventional spin-echo sequence (use 180 degrees RF pulse for echo). Why the signal saturation is not a problem? I asked this question to my lecturer. He answered that "that's why we should not use too short TR even in conventional spin-echo sequence"

I thought of an example.

By definition, T1 relaxation time is the time required for the z-component of M to reach (1 − 1/e) or about 63% of its maximum value (Mo).

Let's say I want to do a T1 weighted scan for a muscle with a typical TR time of 800msec. The T1 relaxation time of a muscle is around 900msec.

According to the T1 relaxation equation. after each cycle, the longitudinal magnetization will be recovered to 58.9% of its original value. According to this calculation, then, after 10cycle, there will be only 0.5% of magnetization remains? If using 256 phase encoding level. There should be no signal left at the end of the scan?

I know there must be a mistake in my thinking. Because it contradicts the real life situation. What mistake did I make here?

submitted by /u/CXR_AXR
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How many years ago did insects emerge?

Posted: 27 Jul 2019 12:26 PM PDT

Since insects has no bones and fossils, does anybody know which age probably did insects emerge?

submitted by /u/crapheap
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How does the collapse of a magnetic field cause a voltage spike?

Posted: 27 Jul 2019 12:47 PM PDT

In ignition coils in the automotive world, a large surge of voltage is needed to jump the air gap of a spark plug. the primary coil receives 12 vols and generates a magnetic field, that field directly effects the secondary coil in this case to step up the voltage, and i feel like i understand that much. My question is what is special about the collapse that allows for a surge large enough to jump the air gap, or is it simply because the stored voltage in the secondary coil is finding the quickest path to ground. i am also not sure which flair is best here...

submitted by /u/Mccreesuschrist
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If cells are often dying and being replaced (I often here you have an “entirely new body” every seven years) then why does damage from youth (alcohol, drugs, sun exposure) lead to health problems later in life?

Posted: 27 Jul 2019 06:06 AM PDT

How widespread (or not) are songbird languages?

Posted: 27 Jul 2019 05:33 AM PDT

Can different species understand each other? If so, can introduced species communicate with native ones?

I've asked this before, but that category didn't work out. Google only gets me stuff about birds speaking English. Is this something no one knows?

submitted by /u/tracishea
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Why did/do video and computer games need save points?

Posted: 27 Jul 2019 11:57 AM PDT

Playing a rerelease of an old game, and it struck me how strange it is to have to go to a specific save point to save my game data. Some modern games also have this feature, though most (in my experience) autosave or let you save whenever, so I assume this is just for nostalgia/familiarity in these games rather than by necessity.

Could anyone explain why save points like that were necessary? What's going on behind the scenes that makes that location be the only one saving data can occur?

submitted by /u/arh1387
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Why do Acids Melt Stuff?

Posted: 27 Jul 2019 02:14 AM PDT

Obviously, they don't annihilate the very atoms of a substance they come into contact with, but why do acids actually melt stuff?

submitted by /u/LjSpike
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How did humans of the past deal with wisdom teeth? Did they remove them without anaesthetics or did some people just suffer in pain?

Posted: 26 Jul 2019 10:14 PM PDT

How do our brains conceptualize math at the neurological level? Do our neurons seem to act like little Turing machines? Or do they operate on some other model?

Posted: 26 Jul 2019 07:46 PM PDT

Is acne as common on lesser primates as it is on humans?

Posted: 27 Jul 2019 12:53 AM PDT

Where is the asteroid that creates extinction for dinosaurs?

Posted: 27 Jul 2019 03:18 AM PDT

What changes the color of electricity?

Posted: 27 Jul 2019 02:11 AM PDT

I've seen footage of lightning striking ground, and the flashes are often a pale orange.

As an industrial battery technician, I've seen plenty of arcs and they are almost always blue.

Lightning in the clouds looks white.

I've seen high voltage line arcs that are bright turquoise. Which is the same color as the corrosion produced by sulfuric acid on copper.

Arc flashes are often yellow.

submitted by /u/Halorym
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What is happening within my body/pores when I pop a pimple and it returns later? *resubmitted

Posted: 26 Jul 2019 11:32 PM PDT

I'm curious about what exactly goes on in this situation; especially since the time gap between the initial pop and the return of the whitehead can range (anecdotally) from an hour to a day, and sometimes returns more than once in the same day.

submitted by /u/nina_qj
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When they say that epithelium/parenchyma is the functional part of cells, what precisely do they mean by functional?

Posted: 27 Jul 2019 02:50 AM PDT

The epithelium covers outer organ and inner part of cavities, but what about that is functional?

submitted by /u/Firm_Salamander
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When in tense or scary situations, why does the heart beat faster? Does increased blood flow make you more alert or capable?

Posted: 26 Jul 2019 08:21 PM PDT

The hormone adrenaline causes the increase in heart rate, but why?

submitted by /u/Professor155
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Saturday, July 27, 2019

How does seedless produce get planted and reproduced?

How does seedless produce get planted and reproduced?


How does seedless produce get planted and reproduced?

Posted: 27 Jul 2019 01:06 AM PDT

Does a star visibly change when it begins using a new fuel? And is the timescale observable?

Posted: 26 Jul 2019 05:54 PM PDT

For example, if a star fusing hydrogen has enough mass to fuse helium when the hydrogen is depleted, will it visibly change? And if so, will it happen quick enough for us to see the change?

submitted by /u/WippitGuud
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As we age, do our organs lose transplant value? If they do, are there any with more longevity? Like, a 70 year old heart might not be desirable, but maybe kidneys or something else retain some value despite age?

Posted: 27 Jul 2019 07:42 AM PDT

What is created when white phosphorous burns on aluminum metal?

Posted: 27 Jul 2019 07:19 AM PDT

I was asked recently by a friend who works for the US military about what would happen if burning white phosphorous were to make contact with aluminum metal. Of course I didn't have an answer so I started researching and couldn't really find much on the subject. Do any of you have any reading material on this or something similar? Or can you explain what would happen and if it would form something toxic? The only thing I can find is aluminum phosphate and aluminum phosphide, but I have no clue if these would form with white phosphorous burning on aluminum metal. He works with munitions for the US national guard and seemed to be fairly concerned. Any and all info would be greatly appreciated. Thank you in advance.

submitted by /u/backyardscience2000
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Why don't autogyros roll?

Posted: 27 Jul 2019 06:25 AM PDT

Why don't autogyros roll? As I understand it, the advancing rotor blade has a higher relative airspeed (and therefore higher lift) than the retreating rotor blade.

Thanks!

submitted by /u/baffledexpert
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Have we already observed a moon with a submoon? Is this even theoretically possible?

Posted: 26 Jul 2019 04:23 PM PDT

Why does the decibel scale use powers of 10 instead of some other number?

Posted: 27 Jul 2019 03:16 AM PDT

I'm confused about why the decibel specifically scale uses powers of 10 instead of some other number , for example 9 or 11 or even some other number that isn't really round. Is it used conventionally because powers of 10 is easier to use? Or is it a coincidence? Or is it something else altogether? Help me out

submitted by /u/zerostarzero
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Does digital data have mass as it's transferred from one device to another?

Posted: 26 Jul 2019 11:17 AM PDT

I have been curious if there is a physical limitation to the transference of data as its volume continues to grow at an incredible rate year after year.

Does digital data have mass as it's transferred over both fiber optic and/or through the airwaves? Is there any relevance to the type and size of data that can be quantified in terms of a tangible measurement?

Could we hypothetically run out of "space" to transfer data?

submitted by /u/CommodoreSixty4
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Why do we still use bike and car tires that can lose air?

Posted: 26 Jul 2019 10:22 AM PDT

It seems like by now we would have come up with a solution that doesn't allow for car and bike tires to deflate and have to be refilled - is there a practical reason that something completely air tight and factor inflated isn't a good idea? Is it simply easier, or to make it possible to repair a flat?

submitted by /u/filmhamster
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How do you make sure that there is always enough oxygen in the ISS?

Posted: 26 Jul 2019 11:00 AM PDT

Do we have pictures of Mars' moons from Mars?

Posted: 26 Jul 2019 02:16 AM PDT

‪The lining of our stomachs are completely replaced every week without us noticing. Why can’t uterine lining do the same thing without bleeding and causing pain for days?

Posted: 26 Jul 2019 10:01 AM PDT

Separate volatile solvent from solution with two solvents?

Posted: 25 Jul 2019 11:05 PM PDT

I have a solution of polycaprolactone in a mix of dichloromethane (DCM) and dimethylformamide (DMF). I first dissolved it in DCM and then added DMF because it took too long to dissolve in DMF even with heating. As per this resource, DCM and DMF mixture is zeotropic. So, I think it should be possible to get rid of all the DMF by heating. I left the solution stirring overnight at 60°C, but there was only a small drop in the liquid height that indicated that all the DCM was not removed. Since DCM boils at around 39.6°C, all of it should have evaporated. The ambient temperature may have been around 28°C or more. The heat transfer from the hot plate would not have been the most efficient considering that the solution was in an uncapped ~10cm x ~3 cm dia. vial, being stirred on a 60°C hot plate. But the vial felt warm enough. I cannot figure out what I may be missing here.

submitted by /u/pfung
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Why are the largest craters on the moon facing us? Is there a reason or is it just a coincidence?

Posted: 25 Jul 2019 08:04 PM PDT

Have planet sized objects fallen into the sun?

Posted: 25 Jul 2019 08:38 PM PDT

The sun has a lot of mass. Was that all from dust and gas? Or could it be that planet sized objects have fallen into the sun?

submitted by /u/federal_employee
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How do astronauts enter the space from their space station? Doesn't the air in the station move out into the vacuum?

Posted: 26 Jul 2019 09:34 AM PDT

Friday, July 26, 2019

Do space stations lose air from using air locks?

Do space stations lose air from using air locks?


Do space stations lose air from using air locks?

Posted: 26 Jul 2019 05:15 AM PDT

If an astronaut needs to repair something outside, doesn't the air in the air lock room come out with them? Wouldn't that limit the amount of times it can be used?

submitted by /u/bullerick
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Is there any theoretical reason why the sun/moon relative sizes and distances are nearly the exact same?

Posted: 26 Jul 2019 05:57 AM PDT

It seems insanely unlikely that the sun and the moon apparent sizes are nearly identical in the sky. Is there any even theoretical reason that this happens, or is it truly pure chance?

submitted by /u/joe40001
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How is the instantaneous efficiency of nuclear reactors measured by nuclear power plant operators?

Posted: 26 Jul 2019 05:29 AM PDT

When a black hole is said to be spinning, does that refer to the accretion disk or can we actually make observations about the behavior of matter below the event horizon?

Posted: 26 Jul 2019 06:45 AM PDT

How does Mars look from the Moon, assuming that the Moon is at the point in it’s revolution where it’s closest to Mars?

Posted: 25 Jul 2019 02:50 PM PDT

If light slows down in water, then does causality also slow down?

Posted: 25 Jul 2019 06:24 PM PDT

Nothing can travel faster than light, and my elementary understanding of the speed of light is that it's also the maximum speed at which two particles can have a causal impact on one another. With that in mind, since light slows down in water, does causality also slow down? If so, it is possible to make a solution that further slows causality?

submitted by /u/cincycusefan
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How do those arm band blood pressure machines work?

Posted: 25 Jul 2019 12:14 PM PDT

I got a check-up today and realized I have been wondering this for basically my entire life up till this point.

submitted by /u/ramenayy
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How did paleontologists come to the theory that dinosaurs are more closely related to modern birds than reptiles? Does this hold true for all dinosaurs, or does this only apply to certain species?

Posted: 25 Jul 2019 03:47 PM PDT

If I = V/R, and we want to use the smallest amount of current in power transmission lines, then why do we use high voltage? Using the equation wouldn’t that result in high current?

Posted: 25 Jul 2019 08:15 PM PDT

What does it mean for an electromagnetic wave to be linearly polarized?

Posted: 25 Jul 2019 06:57 PM PDT

I was going through one of my textbooks from last year and found this from my waves and optics class: https://imgur.com/a/w8YbBn3

It says that when an EM wave is linearly polarized in a certain orientation, that corresponds to the plane of the electric field. Why is it the plane of the electric field in particular rather than the magnetic field or any other direction? Is that just a convention or is EM in general more "relevant" to things with electric charge? I assume that the latter could be the case because magnetism arrises from the spin of electrons, but I don't know for sure as I haven't yet taken electrodynamics.

submitted by /u/_Sunny--
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What kinds of geological processes could result in a desert with blue sand (lapis lazuli or azurite) over a strike slip fault?

Posted: 25 Jul 2019 04:55 PM PDT

How do we get digits for pi in the hundreds of thousands place and actually know if they are accurate?

Posted: 25 Jul 2019 05:25 AM PDT

I just can not understand how it is even possible to measure anything to that sort of accuracy. furthermore the digits have virtually zero impact on the value of pi once you get that far out into the decimals so how can you even validate your findings?

submitted by /u/Metroidman
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How are Martian dust storms able to occur?

Posted: 25 Jul 2019 08:20 AM PDT

Winds are caused due to uneven heating of the ocean and the earth. In Mars this phenomenon obviously does not exist. So, how are massive dust storms able to take place.

submitted by /u/sastachappati
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How is the Hubble Telescope still finding things after 30 years?

Posted: 25 Jul 2019 05:29 AM PDT

I saw in the news today that Hubble found a huge spiraling galaxy zillions of miles away. What I don't understand is why it takes nearly 30 years to point the telescope in that direction. It's just 360 degrees to turn it slowly around and then doing that same turn on its axis to cover its 3D space. Doesn't that take like a week or two? Maybe a month? But 30 years? So no one ever pointed it in that direction for all this time?

submitted by /u/parquet7
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Why do men have nipples?

Posted: 25 Jul 2019 12:57 PM PDT

How many X-rays are emitted and absorbed in a standard medical X-ray radiograph?

Posted: 25 Jul 2019 01:35 AM PDT

This seems like it should be easy to find out, but most of the data talks about dose, rather than number of photons, so I hoped someone here would be familiar with doing that conversion!

submitted by /u/nick_hedp
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