What will happen if a black hole appears near our solar system?

When you say "destroy anything in it's path", that's true, but it's also true for a star, even a red-dwarf or white-dwarf star would effectively eat or destroy almost anything in their path.

It's also worth mentioning that your scenario is very unlikely. According to this source, stars outnumber black holes 1,000 to 1 in the Milky way and most of those likely near the center of the Milky way. There are probably a few stellar black holes within 75 or maybe 100 light years, based on probability and since they would be hard to detect (see Rob jeffries' comment). But even so, one passing near enough to affect the Earth is very rare. Story about a star passing within 1 light year of earth here.

So, onto your question:

If such a black hole appears near our solar system, are we going to
survive? Is there any way not to fall in a black hole?

It depends how near and how big. A stellar mass black hole, with a mass range of about 3.8 solar masses to maybe 16 solar masses would need to get quite close to cause real problems.

Our Solar system has a very sparse Oort Cloud, extending perhaps almost 2 light-years and a much more densely packed, but still quite diffuse, Kuiper-belt, mostly about 30-50 AU (less than a thousandth of a light year). If we assume that a black hole, as much as 16 times the mass of our sun has similar orbital debris at larger orbits, an oort cloud around a 16 stellar mass black hole it could extend several light-years though still likely very diffuse, as well as perhaps a more densely packed asteroid belt and maybe even a few planets in the I dunno, 5-300 AU range or something.

The effect of a close pass gets pretty speculative and depends on the amount of objects in distant orbit around the black hole, but a pass as close as 1 or 2 light-years could increase the chance of a good sized comet or other objects striking Earth. Not a guarantee at that distance, but an increased chance.

Now if you get a pass-by of a few hundred AU to maybe 1,000 AU (about 1/50th to 1/100th of a light-year), you begin to get measurable Kuiper belt stirring up. If the black hole has it's own Kuiper belt equivalent, this could create a significant increase in asteroids and meteors flying around the solar system. A significant meteor strike on earth at this point becomes a distinct possibility, perhaps even likely and it could be a life killer and ocean evaporator.

With proper technology, it might be possible to deflect any asteroids on an impact trajectory. We'd probably observe multiple impacts on other planets too and at this distance, our solar system might even pick up a planet from the black hole if there was one in distant orbit.

At about 100-200 AU, the black hole has a chance of pulling some of the outer planets out of our solar system. It could also visibly alter Saturn's or maybe Jupiter's orbits and stir things up in our solar-system pretty good.

That's the most likely effect of a very near pass of either a star or black hole is a stirring up of more distant orbiting objects and a significant increase in the chance of planet killing or at least, dinosaur killing impact, but it needs to be very close. The article I linked above says that the star that passed within 0.8 light years (about 50,000 AU), some 70,000 years ago didn't measurably increase comet impacts.

To measurably change the Earth's orbit, maybe 30-50 AU. About the distance of Uranus or Pluto. This wouldn't pull the Earth away from the Sun, but it could change the Earth's orbit enough to alter the seasons and change climate on Earth. An elongation of our orbit could make the seasonal changes bigger and change the length of a year. The gas giants would all be moved. If the Earth survives any bombardment from a pass that close, it might quickly enter a new ice age, as one possible outcome, but we might be able to fix that by burning lots of fossil fuels. :-)

At somewhere around Maybe 12-20 AU, the Earth might get moved too much for us to adapt, perhaps outside of the Goldilocks Zone.

At somewhere around 5-10 AU (estimates are pretty rough), but this is where things get really interesting. We begin to see a measurable increase in tides and at this point and we could lose the moon. The earth could also get pulled outside the solar system, thrown into the sun or captured by and end up in an orbit around the black hole. We might begin to see a small tidal bulge on the sun from the black hole and a corresponding small increase in solar output, but that might require the black hole to be closer. Not sure. If the black hole gets close enough to the sun it could stretch the sun somewhat oblong and start to draw some solar gases towards it, but that might be pretty close, maybe 1 or 2 AU.

At maybe 3-6 AU, depending on the relative velocities, the sun might get captured into an fairly close orbit around the black hole, turning our solar-system into a binary and the planets could end up pretty much anywhere in that scenario.

At 1 or maybe 2 AU from Earth, we could see some cracking of the Earth's crust and a big increase in volcanoes and earthquakes.

Even at 1 AU, the black hole still wouldn't be visible unless it's acquired enough matter to form a bright accretion disk, in which case it might be very bright, but still visibly very small like a super bright star in the sky. Without an accretion disk the gravitational lensing should be visible by telescope but not to the naked eye.

Much closer than that and it hardly matters. The Earth's would be largely be re-surfaced with magma and the oceans would probably boil. All that said, the Earth still isn't being eaten. To eat the Earth a black hole would need to pass somewhere around maybe 5 or 10 million miles. Super-close for another stellar object.

I welcome correction if any of my math is broken, but that's my roughly calculated estimate.

article with some of the same conclusions.

Edit - due to comment above

I mean a supermassive black hole, like the one we have in the center
of Milkyway

My long answer above is basically gravitational effects when the black hole is in the general vicinity of the solar system. That kind of very close pass happens very rarely, but the odds of a black hole hitting earth is very slim. The odds of a black hole passing close enough to our solar-system and stirring things up in an undesirable way, also unlikely but more likely than a black hole actually hitting earth.

The most likely effect is some gravitational swirling (if you will) due to the massive object passing kinda close to the solar system, and as a result, possible impacts, possible orbital changes - stuff that wouldn't be fun, even if it passes outside the orbit of Pluto.

With a super-massive black hole, it's basically the same answers but the distance can be much further out. Sagittarius A is about 4 million solar masses, compared to a stellar mass black hole which is about 4 to 16 solar masses. That's 250,000 to a million times bigger, so equivalent gravitational occurs at the square root of that, about 500 to 1,000 times further.

The tidal effects are actually much smaller. A 4 to 16 stellar mass black hole could fly by at roughly Pluto's orbital distance (30-50 AU) and as it passes, it could pull Jupiter into a very different orbit, perhaps even away from the sun, but a super-massive black hole fling past some 500 times the distance of pluto (about 1/3 to 1/2 light year) would exert the same gravitational tug, but that tug would be much the same across the entire solar system, so the entire solar system could be pulled effectively into orbit around the super-massive black hole without changing shape too much. It still be visibly very tiny though the gravitational lensing might be visible to the naked eye at that point, but not much bigger than a star.

The real danger with a super-massive black hole passing within a few light-years of our solar system is the stuff it carries with it. Super-massive black holes are orbited by stars and presumably all the stuff that generally orbits stars, like planets, moons, asteroids, comets. All that stuff would approach our solar-system long before the black hole came close and that's the mostly likely answer. Our solar-system would likely be pelted by orbital debris when the super-massive black hole was still a few light-years away. I don't think I should try to guess how many but a super-massive black hole would carry with it orbiting debris for several light years.

My quick and dirty answer to the super-massive question. You mgiht think a black hole of that size would strip the atmosphere off the earth and stuff like that, but with a super-massive black hole, the tidal forces are much smaller at the event horizon. The atmospheric striping and earthquakes and other effects don't happen until it's enormously close, at which point the earth would be orbiting around it quite fast, perhaps fast enough that the night sky might visibly appear to spin to the naked eye. We could get pretty close to it before life on earth became unlivable, provided we're not bombarded by orbiting debris first.

There could be other effects. Gamma rays from any matter falling into the black hole or perhaps strong magnetic effects. More precise predictions gets a bit difficult for me.

That's my layman's attempt at an answer anyway.

human biology - What is the mechanism behind "acquired" alcohol tolerance?

So, judging by your answer to my comment you are most likely talking about so-called consumption-induced alcohol tolerance, that one might develop by regular drinking of alcoholic beverages.

We can group the reasons for increased tolerance to the following groups: better adaptation for the elevated concentrations (functional) or increased break-down (metabolic).

Functional tolerance.

This means that your body and its organs, especially your CNS, adapt to compensate for the increased alcohol concentration and manage to sustain its functioning despite the elevated blood alcohol concentrations (BAC). So, the dose of alcohol which previously led to trembling and disorientation now evokes only some coordinatory disturbances.

The physiological mechanisms involved here are:
1. Desensitization of the alcohol-sensitive (primarily GABA-ergic) receptors in CNS.
2. Changes in the neuron firing rates (to compensate for the deterioration of the GABA-ergic inhibition).

Metabolic tolerance.

This condition is characterized by the increased alcohol break-down by the liver, that slows down the increase of blood alcohol concentration (BAC) upon its consumption leading to the attenuation or complete disguise of alcohol intoxication (inebriation).

The main enzyme that is responsible for alcohol transformation is the so-called alcohol dehydrogenase (ADH), that represents a group of substances catalyzing the alcohol oxidation to aldehydes. This enzymes are located in the liver cells (hepatocytes) and the increase in their activity (and most likely also the absolute amount) is not well understood. It happens, by the way, not only on alcohol consumption: the intake of barbiturates also leads to the increase of ADH and tolerance.

Here you can find much more information about acquired alcohol tolerance, but mostly from the behavioural viewpoint.

human biology - How does the brain's energy consumption depend on mental activity?

I answered on the facts of this question already on skeptics.SE, here and here. You should read both papers very carefully, I highlighted the most important facts but this is a very tricky question, esp. when it comes to defining what mental activitiy is. The papers also give an explanation of how fMRI signal is linked to NEURONAL activity, as far as I remember there is no strong direct link.

You assume in your question that a mathematician solving a differential equation needs higher mental activity than a child reading a book. Is this legitimate? It seems intuitive but also very subjective. In the paper they mention that for the highest and lowest energy consumption we lose consciousness. I will not draw conclusions from this. However, you are talking about conscious mental activities so this may answer your question. To me it means more that the understanding of the human brain in neurobiololgy is on the level of the Rutherford Atomic Model in Physics at the beginning of the 20th century. We have not really got a clue how information is processed and how it's constrained by physical laws and principles of entropy and energy. By reading the 2 papers it looks more like the human brain is not raising energy consumption as a computer would (the computer analogy pretty much fails when compared to the human brain). Most of the energy is used for unconscious processes in "standby mode".

As in physics, extreme cases such as savants and the mentally disabled are probably the best starting point to exclude possible models of human brain and physical boundary conditions as we cannot approach the questions of human brain in a reductionistic way. How can savants like Kim Peek process such huge amounts of information AND save it. He is able to scan books pages just once and know them by heart thereafter. His brain does not, however, consume more energy than an average human brain. So mental activity is probably not a very good term, quantity, or even really suited to be scientifically used. Does neuronal activity mean mental activity (in the sense of your definition?) Reading the papers, the problem is the separation of mental and neuronal activities. At first you have to know what are the basic brain functions and processes that are consuming most of the energy. However the brain is not built in modular way like a computer (most energy is used here for constantly refreshing RAM). So there is not really a objective way to analyse and separate this modular energy consumption, if it even is modular.

In my opinion, most models about information processing in human brain are intuitive guessing (again Rutherford). We need much more detailed experiments and data (Blue Brain Project). fMRi is like analysing a atom with a magnifying glass. Also, the more prosperous approach from a biophysical perspective is probably not the level of "mental activity" but the hard-based amount of information processed by human brains and linked energy consumption (Kim Peek). But therefore we need a model of how this information is saved in human brain. Do normal humans save the same information as Kim Peek scanning a page or are we just unable to recall it consciouscly? When solving a differential equation, how much energy do you consume when recalling facts and is that experience not similar to reading a book? How much is mental logical tasks and is there really a difference at all?

I will stop here, hope you gained some insight that the question is of course important but too early to be definitively answered. I think we will learn a lot more from projects like Blue Brain as we have from fMRI experiments.

exoplanet - 3D array in FITS data

It appears to me that the full Spizter frame should normally be 256x256 but, if observing a very bright source or when requiring high temporal resolution, a different observing mode is performed wherein only 32x32 pixels are read from the CCD. However, what happens is that the exposure times are short and a total of 64 frames are observed in total, creating a data cube of 64x32x32. If you want, you can treat each individial 32x32 frame as its own image, or else stack them all together for the full image.

Full details can be found here.

star - How do astronomers determine the texture of an exoplanet?

This is known as spectroscopy. Every molecule and atom in the universe emits and absorbs light at specific frequencies. This is a result of the quantization of the energy levels (for electrons) in an atom. Although there are lots of complicating factors, such as redshift, to account for, the patterns are usually so distinctive that the complications can be accounted for, and do not prevent scientists from figuring out chemical compositions (and even, to some extent, how abundant each chemical is).

For example, here are the emission spectra of several common atoms at rest (with respect to the observer):

Absorption spectra, on the other hand, appear as darker regions in the band. Here's an example of an absorption spectra, which identities several elements by knowing that it is distinguished by absorbing light at specific wavelengths that others do not:

For exoplanets with significant atmospheres, we can only expect to see the spectra for its upper atmosphere. All other signals will be muted out by the rest of the atmosphere. We will not be able to tell what the surface looks like, or what it is made of.

the sun - How do star densities work?

The mean density of the star is really only defined by the formula $barrho=M/V=3M/4pi R^3$. The radius of a star is a generally a very complicated function of a star's other properties. When we determine the radius in stellar models, it's only because we've solved equations that describe the structure of the whole star, and read off the value at what we define as the surface. So no simple formula in general.

That said, one can derive the approximate functional dependence for stars of various evolutionary states through the principle of homology. i.e. assuming that stars of a certain type are just rescaled versions of each other. Glancing at my old course notes, on the upper main sequence, where stars burn hydrogen principally through the CNO cycle and have radiative envelopes dominated by electron-scattering opacity, we derived $Rpropto M^{15/19}$. The same principle (but with different assumptions about the star) is used to determine the location of the Hayashi track for pre-main-sequence stars, along which $Rpropto M^{-7}T^{49}$. Particular formulae can be found for different types of star but the relationships between $M$ and $R$ vary wildly.

Neither the two stars you mentioned are typical main-sequence stars. R136a1 is a Wolf-Rayet star, which is basically a star that has blasted away most of its hydrogen envelope. Mass-radius relations are usually strongly dependent on mean molecular weight, which is higher without hydrogen, so the relations break down (or, rather, would have to be derived separately). But usually higher mean molecular weight gives a more compact star. UY Scuti has probably finished burning hydrogen in its core and has moved off the main sequence. So again, it'll follow a different relation.

terminology - Are meteors and meteorites considered "Small Solar System Bodies"?

The difference between meteorites, meteors, and meteoroids is one of altitude relative to a celestial surface: in space, it's a meteoroid; in the atmosphere, it's a meteor; and on the surface, it's a meteorite. (See here and here for more information.)

The International Astronomical Union (IAU) defined the term Small Solar System Body (SSSB) in 2006 with Resolution B5 as

(3) All other objects³,except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

[Footnote 3] "These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs),comets, and other small bodies."

And, although this official definition clearly states, "All other objects ... orbiting the Sun", I'm not sure how verbatim this definition is meant to be treated.

What I mean by this is, well, for example, in Law, all definitions are, by default, unless previously stated, treated in an context of exactness. But although science is oftentimes based on specificity, it is not always, and the degree thereof in this context is thus not wholly clear to me.

galaxy - What are the 10 most abundant elements in the universe by number of atomic nuclei?

All right, so I took the first list on wikipedia listing the 10 most common elements by mass in parts per million, and did what Rob recommended and here's what I got.

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe

Hydrogen - 739000amu(H)/1amu(H)=739000 H atoms

Helium - 240000amu(He)/4amu(He)=60000 He atoms

Oxygen - 10400amu(O)/16amu(O)=650 O atoms

Carbon - 4600amu(C)/12amu(C)=383 C atoms

Neon - 1340amu(Ne)/20.1amu(Ne)=66 Ne atoms

Iron - 1090amu(Fe)/55.845amu(Fe)=19.5 Fe atoms

Nitrogen - 960amu(N)/14amu(N)=68.5 N atoms

Silicon - 650amu(Si)/28.1amu(Si)=23 Si atoms

Magnesium, - 580amu(Mg)/24.3amu(Mg)=24 Mg atoms

Sulfur - 440amu(S)/32.1amu(S)=13.7 S atoms

So therefore, the 10 most common elements in the universe by atom, with the relative ratios between them, is;

1.Hydrogen (739000)
2.Helium (60000)
3.Oxygen (650)
4.Carbon (383)
5.Nitrogen (68.5)
6.Neon (66)
7.Magnesium (24)
8.Silicon (23)
9.Iron (19.5)
10.Sulfur (13.7)

If anyone sees a mistake that I made with my reasoning or calculations then please point it out.

orbit - How (un)stable are the Lagrangian points 1, 2 and 3?

All five Lagrange points are unstable

L1, 2, and 3 are "saddle points" in the effective potential formed from the combination of gravity and the centrifugal force of a rotating frame of reference. An object which is in front or behind in the orbit would tend to approach the Lagrange point, and then move away, either towards or away from the sun, following the lines in the picture.

However note that in the picture, the lines around the Lagrange points are not close together, this means that the motion towards, or away from the point is very slow (in the rotating frame) An object near the Lagrangian point would not be "ejected" at high speed. Any cosmic dust that was near the Lagrangian point would drift slowly away.

However although the L4 and L5 points are unstable, there are quite stable orbits that (in the rotating frame) orbit around the L4 and L5 point, allowing for Trojan satellites.

Is sundial time entirely dependent on solar azimuth?

Any sundial that gives the same result as this is correct and any other is wrong (but sometimes close enough):
_ /############
/| /#############
skewer / /############## (central) v / /###############
| north /################
| (S in S. /#################
| hmsphre) /##################
________|________ /###################
hoop | /##### LEVEL #######
(from the | side) /###### GROUND #######
| /####### (SOIL) #######
latitude--|- /#######################
(use || /########################
protractor)| /#########################
|V /##########################
| /###########################
|/############################
j#############################
,|#############################
/#|#############################
/##|#############################
/###|#############################
/####|#############################
/#####|#############################
/######|#############################
/#######|#############################
/########V#############################
/#######################################

#

write noon on hoop's inside closest to ground, midnight opposite, 6 pm on the east side, 9 pm midway between the last two, and so on (hours only occurring in darkness optional).

If your sundial reads 6 pm at due west all the time then you're doing it wrong. Let's say I put a vertical stick in the ground, draw a 24 hour clock face around it, put noon poleward and think it's a sundial. In New York City, it could literally be saying 6 am when a genuine sundial says 9 am. That's just middle latitudes. At the equator on the equinox, it would read 6 am all morning and 6pm all afternoon at the equator. If you go 1 mile south of where the next noon, summer solstice and Tropic of Cancer coincide, it would say about 4:30am at sunrise, go forwards at first, then backwards, finally showing the middle 6 hours of the night passing in 7 seconds. Backwards. At noon. Then it will run forwards again until it reaches 7:30pm at sunset. If you place the stick right, you can even make it stay between 4:30a and 6a all morning, stop at 6 am at the instant of noon then instantly become midnight, run infinity years per second backwards for an infinitely short amount of time, go almost 6 hours backwards in seconds, then later forwards again very slowly until it shows about 7:30pm at sunset. This is why sundials cannot be made that way.

(of course, this is theoretical, there are no infinitely thin, vertical, and straight sticks, shadows are fuzzy, they can be too short to see, the Earth wobbles a bit, the speed of light is not infinite, this would only be true if only the Sun and Earth existed, even a flea jumping in Russia moves the Earth etc.)

And yes, the sundial time can be up to 16 minutes away from mean solar time (the equation of time), easily noticeable, but if you wanted correct local clock time instead of correct sundial time then you could put as many dates as needed on another dial and rotate the hour scale until the arrows point at the current time of year. The shadow then shows mean solar time.

That should be close enough to mean solar time that you wouldn't care for a number of centuries, certainly a century if you're real picky. As for clock time, what sundial disagreements are possible is limited only by the whims of man. The sundial is several hours wrong in West China. Cause they use the zone that's good for Shanghai (or Tokyo when daylight savings).

And all sundials without moving parts are latitude specific. Some are adjustible, though. Some designs are more suited for some latitudes or even become impossible in some places, like the kind with a wedge or rod on a level face. They will also not work on days with polar night. Though you could use a moondial if it's also not polar moon's below the horizon for days or weeks. Yes, moondials exist! You need to correct for moon phase and time of year or they're useless.

Click edit to see the drawing. Don't click save of course.

zoology - Species with reproduction barriers that can both reproduce with a third species

To start with, I do not have a sound knowledge in biology or any formal education in the area.

I was told that one of the definition of a species is a reproductive barrier, which means that if two animals can't reproduce, they are of different species. The barrier can be either the inability of the sperm to fertilize an egg, or a physical trait that inhibits reproduction, e.g. a cricket species that has a different mating song than another species or two species of flies, one that mates on yellow flowers, and the other on red flowers.

But what happens when, while two species can't reproduce, but there is a "chain" of "intermediate" sexual partners that can produce reproductive connection step by step. Like 6 degrees to Kavin Bacon, but with animal sex.

I'll try to explain with an example:

A Great Dane and a Miniature Pinscher dogs can't mate due to obvious size differences. But The Pincher can mate with a German Pincher (a slightly bigger breed of Pincher), which can mate with a Doberman Pincher. And the Doberman can mate with a German Shepard which can mate with a Great Dane.

I've also heard that such things happen with birds and crickets, where there is an original species, from which evolved several other, and while the original species (which still exists) can mate with all the new species. Some new species can't mate with some, or all of the other new species.

How are such species are defined, and at what point dogs stop being dogs anymore?

Is there Dark Matter inside the Earth?

Yes, there should be dark matter within the Earth, but at very low densities - a few $10^{-22}$ kg/m$^3$ (Bovy & Tremaine 2012), something like one hundredth of the density of the interplanetary medium. The whole of the Earth would contain few hundred grammes!

Of course, this density averaged over a sphere a lot larger than the Galaxy adds up to a lot of mass, but unlike luminous matter, dark matter should not be particularly concentrated in the plane of the Galaxy (and observations of the dynamics of local stars confirm this).

Neither do we expect dark matter to be especially concentrated within the Earth. Although it does interact gravitationally, the kinetic energy it receives from falling in to the Earth's gravitational potential will be exactly sufficient for it to escape again, unless it suffers some inelastic interaction inside the Earth. Some researchers do think that it may be possible that weak interactions may trap dark matter in the core of the Sun (e.g. Vincent et al. 2015) or even more likely, in neutron stars (Guver et al. 2012). But the Earth is not large or dense enough for this to be a likely scenario.

molecular biology - Why is SOC medium recommended for transformations?

To summarize from Hanahan's paper (see below for reference), he carried out a systematic review of conditions necessary to improve transfection efficiency. Among the conditions tested were the presence of various cations (Ca²⁺, Cs⁺, Mn²⁺, K⁺, Mg²⁺), DMSO, and growth temperatures (and a few other conditions not so commonly used these days). He worked with a strain that he subsequently isolated a derivative of, called DH1, which is now available commercially as DH1-alpha and other strain derivatives.

He defined transformation efficiency to be the number of transformed colonies on a plate, a measurement still used today. He found when the transforming media contained: certain cations, specifcally Mn²⁺, Ca²⁺, Rb⁺; as well as DTT, hexamine cobalt (III) and DMSO; greatly improved the transfection efficiency compared to the standard Ca²⁺ treatment. He also found that sucrose and K⁺ were useful, though not strictly necessary for his experimental strain. It was stated in this paper, though not explained, that sucrose acted as a stabilizer, possibly to guard against his initial use of 0°C incubation and/or freeze/thaw cycling. For the rest of his work, he did not use sucrose.

Among his conclusions, he states that DTT is necessary, as well as di-valent and mono-valent cations, but that they seem to be nonspecific. In other words, there is no strict requirement for having Ca²⁺, since Mg²⁺ and Mn²⁺ perform equally well, nor is there a requirement for K⁺, though it's admittedly easier to use than Rb+.

There are today a number of "rich" media broths that are available: SOB, SOC (SOB + MgCl₂ and sucrose), 2xYT, NZY+, TB, etc. All of these are superior to LB for transformation purposes because of the refined salt balance and in particular the inclusion of these di-valent and mono-valent cations. Sucrose seems to be included for the ease of metabolism and stability of the heat shock process (though I can't find a paper explicitly explaining why it is used, other than tradition).

The two most common ways to transform bacteria are to have them chemically compentent (E. coli already in a rich media broth) or to electrically transform them (electroporation). The purpose of both of these is to induce holes into to cell membrane of the E. coli (chemical transformation relies on the heat shock process for this). Once these holes are made, DNA is free to enter into the bacteria. Naturally, this process is very traumatizing to the E. coli, especially since chemical transformation has the added insult of temperature shock (0°C to 42°C then back down to 0°C).

Substituting LB for any rich broth, such as SOC, will greatly improve transformation yield. If a protocol calls for SOC media, and you don't have any, you may substitute for another rich media. I have used 2xYT for SOC many times quite successfully, and as I stated earlier, only the valence number for the various ions seems to matter, so just make sure they are present.

It was my understanding that sucrose/glucose was added as an additional nutrient source for E. coli to expedite their recovery from the transformation protocol. I speculate that this is the case. Hanahan refers to sucrose as a stabilizer but does not define what it is stabilizing. I speculate that it acts as a cryopreservation aid and prevents ice crystal formation when undergoing cooling on ice in the heat shock method. Given the earlier bio.SE question about shifting E. coli feedstocks, it seems unlikely that sucrose will be used as a nutrient source in the one hour growth period immediately after transformation because that article quotes 4-12 hours as the common time range to shift metabolism from amino acids to carbohydrates.

Sources:

Is a black hole heavier than the star from which it was created?

The mass of a black hole is always much less than the star from which it formed.

A very large star such as Eta Carinae (which is expected to form a black-hole some day) is about 100 times that of the sun, Having already lost as much as 50 solar masses, blown off the star by powerful outbursts in the past.

The future of the star is not fully understood. It is possible that it will collapse in a supernova, in which most of the rest of the star will be blasted into space, forming a supernova remnant, and the core of the star will collapse. The black hole formed may have a mass of more than 3 times the sun, but much less than the mass of the original star.

So while the black hole is not heavier, it is much denser. A 3 solar mass black hole would have a diameter of about 20km.

evolution - Did human hairs actually evolve from scales?

As to the early evolution of mammalian hair, Rowe et al. (2011) hypothesized that the primitive function for hair was not thermoregulatory, but rather for tactile sensation (contra the hypotheses of Spearman and Maderson). Rowe et al. say:

Body hair develops as migrating neural crest cells induce patterns of
tiny placodes that mature into hair follicles equipped with
mechanoreceptors. These include lanceolate endings (velocity detectors
excited by hair deflection), Ruffini receptors (tension receptors
activated as hair is bent), and Merkel cells (slowly adapting
sensors). In ontogeny, hair is first sensory, and only later does it
insulate, as underfur thickens and thermoregulation matures.

So the developmental argument is in favor of tactile sensation.

neuroscience - Are Schwann cells the sole source of myelination in PNS?

Schwann cells seem to be the most common type of glial cells outside of CNS, and the myelinating Schwann cells are the only known source of myelin in PNS. Other types of neuroglia in PNS, for example non-myelinating Schwann cells and astrocytes-like cells do not seem to take part in myelination, neither in CNS nor in PNS.

cell biology - How do nuclear receptors locate each other to form a DNA loop?

This probably isn't the complete answer as I don't know so much about eukaryotic transcription, but maybe I can start the answer.

First of all DNA bending can be sequence dependent - the double helix is not intrinsically straight. DNA is also pretty easy to bend - it spends most of its time coiled pretty easily around histones, and eukaryotes, supercoiled into chromatin.

In transcription though, there are proteins that come along and effect bends in the DNA or even tight loops, so that the transcription initiation complex (TIC) can be activated by transcription factors (TFs) upstream as the DNA flops over.

see this happening in this video at about :40:
http://www.youtube.com/watch?v=5MfSYnItYvg&feature=related

I think in some cases there might be other proteins bound upstream of the TIC to make the influence of various TFs greater. I know in highly regulated genes (such as developmental genes in animals) transcription regulation can be impossibly complicated with lots if internal logic. The classic example is ENDO16 from sea urchin (see second image) which has scores of protein binding sites in front of it.

I was told that DNA binding proteins find their binding sites at a rate faster than diffusion. The prof told me that she thought that there might be a tendency to diffuse along the length of the DNA because of its charge. I have no reference for this, but it might help answer your question as to how the NRs pair up so quickly.

data analysis - Fortran Fits writer/reader

It looks like CFITSIO has an interface for F77.

I'm always thinking about programmer time vs. computation time in research settings. If your data is reasonably small and simple in structure, I'd be very tempted to have Fortran write to a text file, and then use something like astropy to turn the text file into a FITS file. It's slow and icky, but it takes fifteen minutes of thinking if you've used astropy before.

What are the best candidates for solar lensing of exoplanets, and what would the results be?

I've seen this question for the past few days and have shied away from it because it seemed too difficult, but here goes:

550AU is the focal point of the sun, so theoretically anything on the opposite side would be focused into a perfectly coherent image right? Unfortunately due the density of the sun (Mass to radius ratio specifically) only radio waves that just miss the sun would be focused to that point, all other shorter wavelengths don't diffract enough and simply 'collide' with the sun or form a lense ring at a greater distance. So radio-observation only. Explained at this article http://physics.stackexchange.com/a/25501

A star such as a neutron star however would make an excellent candidate for stellar lensing because it has a high density and low radius, meaning much shorter wavelength radiation is able to go around the star.

This wouldn't be particularly effective at discovering new exoplanets, only observing them in more detail.

A good book for history of biology/biotechnology for lay people

I have many friends who are interested in Biology and want to know more about the subject in general (like a history of biology, from Darwin's theory, to DNA structure discovery, to the human genome project). Of course, I cannot suggest to them to read Alberts or Lenninger. Do you know whether such a book exist? I guess that a book that covers most fields of biology cannot be compiled, but even more focused book would do.

Let me try to narrow it down: something like the greatest discoveries in the field of biology (like this article) would be an interesting book to read.

I am not sure how appropriate this question is for SE, but I am sure that I will get the best answer here. Besides, it would be great if lay people can be more excited about biology and contribute to the site growth.

mass - What are the masses of the two stars (given the information provided)?

We can assume that the stars are equal in mass, and their orbits are circular

The orbital speed is 80000 m/s and at an orbital period of 10 months (or $2.628times 10^7$s) the length of the orbit is $2.1024times 10^{12}$ m or 14.05 AU The radius of the orbit therefore is $14.05/tau$ = 2.237AU.

The version of Keplers law given is $$T^2 =frac{a^3}{m_1+m_2}$$

substituting $T^2 =(10/12)^2 = 0.6944$ (divide by 12 to convert to years) and $a^3= 11.19$ gives $$m_1+m_2 = frac{11.19}{0.6944} = 16.12 mathrm{solar mass}.$$

Since $m_1=m_2$, the mass of each star is 8.06 solar masses, or $1.6times 10^{31}$kg

solar system - Why are planets round?

Gravity makes objects compress to their centers of mass, since gravity extends in all directions.

For planets, gravity continues compressing the object until the rocks cannot be compressed anymore, since the pressure will fight against gravity. At this point (called hydrostatic equilibrium), the object has become a spheroid. One of the requirements for an object to be called a "planet" is that it has reached hydrostatic equilibrium.

For black holes, the shape of their event horizons really depend on whether the black hole is spinning or not. For non-spinning black holes, gravity extends in all directions, so the event horizon will become spherical in shape. For spinning black holes, it will likely be an oblate spheroid.

Most galaxies are only spherical when they are forming. Their angular momentum usually causes them to flatten out over time. However, one part of galaxies, called the "halo", is spherical.

Wormholes are purely hypothetical, so I won't really entertain that.

plant physiology - Compare and contrast "Rubisco activity" and "assimilation rate" (is there a difference, and if so, what is it)?

Both are measures of carbon fixation rate.

RuBisCO activity specifically refers to the rate at which the enzyme RuBisCO fixes carbon to RuBP, and is measured by isolating the enzyme from tissue samples and, usually, using radiolabelled CO2 to measure how much carbon is fixed in a set amount of time in controlled conditions and with controlled supply of substrate.

Carbon assimilation rate is generally a whole-plant or whole-leaf variable, measured on a larger scale. It is usually measured by measuring leaf sugar carbon before and after a set period, again using radiolabelling. Conditions may or may not be controlled, and it can be measured in the field (unlike RuBisCO activity).

RuBisCO activity might differ from net fixation in the short term in plants which have an intermediate carbon fixation step, such as in CAM or C4 plants, if the net fixation measurement includes the intermediates - the pool of intermediate carbon-containing molecules have technically been fixed but not by RuBisCO. However, over longer time periods this effect will disappear, as ultimately all CO2 is fixed or re-fixed through RuBisCO.

space telescope - Could the Earth be used to cast an arago/poisson spot on something

One constraint is the recommendation $F=frac{d^2}{blambda}geq 1$, in this case with $d=12700 mbox{ km}$ about the diameter of Earth, $lambda=600 mbox{ nm}$ some wavelength of visible light, and $b$ the distance between circular obstacle and observer.
The distance between Earth and the observer should hence be

$bleq frac{d^2}{lambda}=frac{(12700cdot10^3mbox{ m})^2}{600cdot 10^{-9}mbox{ m}}=481.67cdot 10^{18}mbox{ m}$

Another constraint is the surface roughness of the circular object:
$Delta r < sqrt{r^2 + lambdafrac{gb}{g+b}}-r$, with $r=6350mbox{ km}$ the radius of the circular obstacle (here Earth), $g$ the distance between the point light source and the circular obstacle, and $b$ the distance between the circular obstacle and the screen.

To simplify calculations, say $ggg b$. Then approximately
$Delta r < sqrt{r^2 + lambdafrac{gb}{g}}-r = sqrt{r^2 + lambda b}-r$.

After adding $r$ and squaring you get
$(Delta r +r)^2<r^2+lambda b$.
This simplifies to
$(Delta r)^2+2rDelta r<lambda b$.
Assume $Delta rll r$, and neglect the second order $(Delta r)^2$ to get
$2rDelta r<lambda b$. Divide by $lambda$ to get an approximate constraint for $b$ as

$b>frac{2rDelta r}{lambda}$.
With $2r=12700 mbox{ km}$ about the diameter of Earth, $lambda=600 mbox{ nm}$ some wavelength of visible light, we get

$b>frac{12700cdot 10^3mbox{ m}cdotDelta r}{600cdot 10^{-9}mbox{ m}}
= 21.1667cdot 10^{12}Delta r$.

The two constraints allow for reasonable values of $Delta r$.
Assume a surface roughness of Earth of e.g. $Delta r = 1mbox{ km}$.
Then a valid range of distances of observers would be between
$0.00224$ and $50912$ lightyears of $9.4607cdot 10^{15}mbox{ m}$ from Earth.

In astronomcal units of $149597870700mbox{ m}$ the closest distance of an observer would be $141.49 mbox{ au}$ from Earth.

Due to Earth's oblateness, however, you would get a point spread function significantly different from a dot for this "short" distance from Earth. It might be possible to correct this by an appropriate telescope optics.

The effect of gravitational lensing is
$theta=frac{4GM}{rc^2}=2.969cdot 10^{-27}frac{mbox{m}}{mbox{kg}}frac{M}{r}$, after applying the constant of gravitation $G$ and the speed of light $c$. With the mass $M=5.97237cdot 10^{24}mbox{ kg}$ and a radius of $r=6350000mbox{ m}$ of Earth, we get an angle of
$theta=2.793cdot 10^{-9}$ by gravitational lensing at the surface of Earth.

This would focus parallel rays of light to a point near a distance of
$b=frac{r}{tan theta}=130.27cdot 10^{15}mbox{ m}$, or $13.77$ lightyears, hence well beyond the minimum distance where an Arago spot could form. But, of course, the innermost peak of the point spread function would be closer to a circular disc at this larger distance with relevant gravitational lensing.

observational astronomy - SDSS Image FITS files have negative values. What do these negative values mean?

Without further details I would guess your fits file is using 16 bit signed integers between -32768 and +32767.

In which case you should find that the fits header item called bzero has been set to 32768.

The true integer values are given by your pixel value*bscale + bzero.

This is a very common format for raw data from CCD cameras.

On the other hand if you are talking about processed sky subtracted SDSS images, then of course some pixels are negative - the average pixel in a "sky" region will be zero, so a substantial fraction must be negative.

human anatomy - Why can hair grow without limit while eyebrow cannot?

Hair actually does have a limit to its growth. All hair cycles between periods where it grows, and when a new stand appears, which pushes the older, long hair out. Hairs that are generally shorter, like eyebrows or arm hairs, have a shorter growth period before a new hair pushes the old one out. The hair on your head actually grows much faster than many other hairs as well, so with the longer cycle and the faster growth, it can grow to be much longer before being replaced.

I remember hearing that for many women (the cycle does vary from individual to individual, which explains why some men can't grow beards while others look like ZZ Top) the growth cycle ends between the waist and butt.

My speculation would be that hair on the head could grow for longer because there are more capillaries in the scalp, which might lead to more nutrients, higher cell turnover (like you see in dandruff), and hence more hair. That's just a guess, mind you.

zoology - Is there any reason the common housefly continues to return to an area?

I don't think it's a silly question, but it is a common error to anthropomorphise animals.

Insects respond to cues which they have evolved to respond to, and this is how they 'make decisions'. They do not have free will or any more complex decision-making process like common sense. This is evident is lots of insect behaviour: flying repeatedly at a closed window; landing on brightly coloured clothes instead of flowers; and returning to a food source when they are in real danger of being swatted!

When a fly senses the food (often by olfactory receptors), they are 'programmed' to fly towards it in response to some chemical they sense depending on the species and food. They may not have adapted a response to swatting, or perhaps the food cue overrides others. In nature swatting is not so much of a threat to a fly. Some animals may brush them away, but since they are not really doing any harm in feeding from another animal's food, they are mostly ignored.

CO2 traps are used to entice and kill mosquitoes. The mosquitoes are attracted to CO2 (as it is dispelled from the animals from which they blood feed), they will only evolve to avoid the traps if there is another cue which they could eventually associate with a negative effect.

Another thing to remember when thinking about insect behaviour is that their life strategy is very different to ours. Insects are more r-selected than humans, meaning that each individual life has not had so much energy put into it as a more K-selected animal (such as humans), and to compensate for this, many more young are produced. This often results in more risks being taken by individuals since there will still be a viable population even after many deaths.

Chapter 4 of 'The Insects' by Gullan & Cranston gives a good introduction to the sensory responses of insect behaviour. There are other books on the subject, 'Introduction to insect behaviour' by Atkins looks like a good starting point, but I have not read it yet.

distances - How do we know galaxy GN-z11 is as far away as it is?

So GN z-11 is the latest "furthest away" galaxy. It has a claimed redshift measurement of $z=11.1$, meaning that we are seeing the light it emitted about 400 Myr after the big bang (dependent on an assumed set of cosmological parameters).

To get the redshift measurement, the discoverers used grism (relatively low resolution) spectroscopy in the near infrared. What they were looking for is the rest-frame Lyman alpha continuum break, which would be redshifted into this wavelength range.

The Lyman alpha continuum break is caused by the absorption of nearly all ultraviolet photons with wavelengths smaller than 121 nm. These high energy photons are capable of photoionising the neutral hydrogen present in the intergalactic medium at a range of lower redshifts. This neutral hydrogen is present in abundance at redshifts greater than 6, as it had not yet been re-ionised by quasars and starlight. The consequence is that no light is expected to reach us from rest-frame wavelengths shortwards of 121 nm, but a galaxy's light can reach us from rest-frame wavelengths that are longer than this. When one observes the spectrum, we see flux at long wavelengths which suddenly cuts off at shorter wavelengths. The wavelength of the break is $lambda = 121 times (1+z)$ nm, where $z$ is the redshift.

It is this Lyman alpha continuum break that has been identified at an observed wavelength of 1470 nm. This leads to the redshift estimate of $z= (1470/121)-1 = 11.1$.

The details are presented in Oesch et al. (2016). The continuum break is the only thing visible in the spectrum. The authors are confident that this is what it is because their previous broadband photometry had given them an estimated redshift of $>10$ (which is why they observed this candidate in the first place).

homework - Difference between biological control and introducing species for conservation?

Biological control does not have to be with an introduced species. It can also be accomplished by either artificially inflating the number of existing predators.

E.g. Spruce bud worm has a natural predator in the form of a tiny wasp. But budworm can spread through a stand faster than the wasp can. By moving popluatins of the wasp to the forefront of the budworm advance, you get most of the 2nd generation budworms. The trees have a bad needle year but aren't killed.

It can also be done with habitat modification. If you create conditions that favour the existing predator, then there are more predators in place. E.g. create places for ladybug overwintering to reduce aphid populations. (I have no idea if this would work.)

Anohter example -- although ecological controll may be better than biological -- I had a significant mosquito problem. Lots of small puddles in spring. I created a permanent pond. This has resulted in much smaller mosquito population.

• The pond is a local year round water supply for insectivorous birds.


• The pond is by far the largest water body around, so tends to get most of the mosquito eggs.


• The pond now has a permanent population of boreal and chorus frogs. Tadpoles of these make it tough to be a mosquito larvae.

Is this species introduction? Only if you consider immigrant species from neighborin populations to be introduction.