neuroscience - What are the main mechanisms of interaction between the nervous and immune systems?

We know from pop science that our psychological states have an effect on our immune systems ("worrying ourselves sick", etc.), but what are the actual mechanisms through which our nervous systems pass information to the immune system?

Cell mediators come to mind, but where in the body would a nerve cell release an interleukin or other factor? (Put another way, are neurons releasing these factors as a part of their normal cell metabolism and the side effect is a communicative effect with the immune system?)

How do I prevent or reduce shake when observing with binoculars?

For binoculars, your best option isn't just a simple tripod, but a parallelogram mount (link for representation only, not a product recommendation) on a tripod. While many standard to slightly larger than standard binoculars will have an adapter to attach them to a standard tripod; except for looking at things near the horizon it won't be comfortable to use. The problem is that because they're short the binocular eye pieces will often be too close to the tripod legs themselves for comfortable head positioning. If you're showing things to other people a parallelogram mount has the added bonus of being adjustable in height without changing what its pointed at.

If you're hand holding the most important thing you can do is to use both hands and brace your arms in some way. The top rail of a tall fence or a table (if you're seated) often work well. If you don't have anything else you can use your body itself by resting your upper arms against your chest to form a cantilever brace.

A last option, although not one I particularly recommend for other reasons (RSI injuries in particular) would be to get a job filling jars in an artisan scale canning/bottling plant. A friend of mine does that and after several years has bulked up his arms to the point he was able to use my 15x70 binoculars with 1 hand the way an average person could do with a light weight 5x35 pair.

evolution - What evolutionary explanations are there for death?

From a systemic point of view, if we wish to evolutionarily induce our descendants (descendants of the current human race on the whole) to live longer lives, we would need to pro-create later.

If the whole of human race enforced a statute that prohibits pro-creation before the age of 40, then two pronged dynamics would happen

• only adults fit enough to pro-create after 40 would produce off-springs.


• only off-springs born to parents older than 40 who are fit enough would survive.

Since, there is a high tendency of abnormality and low survival of off-springs born to parents of older ages, absence of resource contention and genetic dynamics would encourage the initial propagation of the rare few fit off-springs.

Hence, unnatural "natural selection" would encourage the propagation of humans of longer life-spans. Perhaps, a natural disaster or viral outbreak could discourage humans from pro-creating before age 40. Perhaps, high rates of abortion. So long as the human race does not die out due to such restrictions. Perhaps, to the satisfaction of conspiracy lovers, a secretive organisation carries out a plan every 100K years to raise the bar for child-bearing age.

Therefore, it might be less of a question of advantage and more of the effects of motivation. That current status where

• high motivation for humans to pro-create early in life.


• low motivation for humans to have more children as they wise-up by being tired of raising kids too early.

Therefore, since no such secret organisation exists, there is infinitesimally little motivation for the existence of a "super-virus" type of humans to exist.

There is no motivation for super-humans to exist, because the distribution of life-spans have crowded out the food and survival resources of any possible primeval super-human.

genomes - Examples of intracellular parasites of medical or economic importance?

As Armatus pointed out above, all viruses are obligately intracellular, and their medical and economic importance cannot be overstated.

Many bacterial species live intracellularly. The arthropod specific Wolbachia has a wide variety of consequences for its host, including alteration of reproduction and sex ratios, induction of reproductive isolation possibly driving speciation, and conferring protection from some viral infections.

Eukaryotes can be intracellular parasites as well: Malaria is a well-known example. Toxoplasma gondii is another intracellular parasite that uses cats as a primary host, but can use other warm-blooded animals (such as humans, rats, and birds) as intermediate hosts. T. gondii infection has been shown to induce behavioral changes in rats, causing an attraction to cats (thereby increasing the chance that the parasite will infect the cat and sexually reproduce). There is also some evidence that T. gondii infection in humans causes behavioral and psychological changes such as decreased reaction times, and links to depression and suicide.

Is there Kuiper belt/Oort cloud like structure in gas giants?

The gravitational region around the planets isn't hard to calculate, sometimes called the Sphere of Influence, sometimes called the Hill Sphere. They're calculated differently but they define pretty much the same idea.

The actual long term stable region is somewhere around 50% of the Hill Sphere. A gas giant like Jupiter simply doesn't have a large enough stable region that it has gravitational control of to have it's own Kuiper Belt or Oort Cloud equivalent. Also, proximity to the sun and the gravitational stability of the trojan points is a factor. What actually happens with a Sun-Jupiter system is that the stable regions are the trojan points and (because of Saturn) the Cis-Resonance orbits but not trans-resonance (Saturn is too big and too close to Jupiter, so it disrupts trans-resonance). Jupiter's crowded Trojan points and Hildas (mostly Cis-resonance) are a little bit like it's kuiper-belt equivalent and that's a result of the sun-jupiter system, the sun being dominant and jupiter, a thousandth the mass of the sun, but large enough to be dominant among the planets.

It's worth pointing out that at Jupiter distance from the sun, the solar system is quite a bit more crowded and has largely flattened out into a plane, unlike the Kuiper belt, so it's not a real comparison to the kuiper belt, but that's where orbiting objects tend to collect, cause those are the most stable regions. The Kuiper belt and Oort cloud aren't really regions as they encompass the entire sphere around the sun at certain distances.

It might be possible, I would think, for a gas giant in the right situation to have something like it's own Kuiper belt and Oort Cloud, but it would need to be hugely distant from it's star and far from other large planets and preferably quite massive. The limitations would still be no more than 1/2 of that planet's hill sphere, but it's theoretically possible, I would think, under the right circumstances. Even so, such a situation, the Trojan points and trans and cis orbitals might still be more common than any possible kuiper belt or oort cloud equivalent, so I'm just speculating that it might be possible. I'm not 100% sure.

spectroscopy - Can stars be observed from space by x-rays, near infrared and radio wavelengths?

Yes, and not only from space but from the Earth surface too. Stars emit in almost all wavelengths depending on their surface temperatures. The hotter the star is the shorter (higher energy) wavelengths it'll emit.

You can try this simulator to check this:

http://astro.unl.edu/naap/blackbody/animations/blackbody.html

homework - Is Aspergillus clavatus an unicellular organism?

You're right in saying that yeast is single celled.

However, moulds are described to be filamentous fungi that are multicellular. The filaments of the mould give colonies "a woolly, fluffy, or velvety appearance, sometimes punctuated with a granular or powdery aspect that is produced by the formation of asexual reproductive structures"(1).

Aspergillus is such a species. The filaments are called hyphae. In Aspergillus, hyphae have divisions or walls which separate it into multiple cells. This is called septate hyphae.

1. McPherson, et al. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. 2011. Saunders.

the moon - How unusual is the solar system?

In Isaac Asimov's Foundation series, the main characters are looking for the long-lost Earth. There are two major features of the solar system that seem to make it unusual among the millions of inhabited systems: the rings of Saturn and the size of the Moon.

The conversations below are mostly between Golan Trevize, ex-military, well-versed in astronomy, and Janov Pelorat, a naïve and recluse history teacher.

The rings of Saturn

"That's what the poem was speaking of. Three wide rings, concentric, wider than the planet itself."

Trevize said, "I never heard of such a thing. I don't think rings can be that wide. Compared to the planet they circle, they are always very narrow."

---

"Is that sort of thing common?" asked Bliss, awed.

"No," said Trevize. "Almost every gas giant has rings of debris, but they tend to be faint and narrow. I once saw one in which the rings were narrow, but quite bright. But I never saw anything like this; or heard of it, either."

Pelorat said, "That's clearly the ringed giant the legends speak of. If this is really unique-"

"Really unique, as far as I know, or as far as the computer knows," said Trevize.

The Moon

"A giant satellite is more difficult to accept. No other inhabited world in the Galaxy has such a satellite. Large satellites are invariably associated with the uninhabited and uninhabitable gas-giants. As a Skeptic, then, I prefer not to accept the existence of the moon."

---

"Yes. It's rather farther from the planet than one might expect but it's definitely revolving about it. It's only the size of a small planet; in fact, it's smaller than any of the four inner planets circling the sun. Still, it's large for a satellite. It's at least two thousand kilometers in diameter, which makes it in the size range of the large satellites that revolve about gas giants."

"No larger?" Pelorat seemed disappointed. "Then it's not a giant satellite?"

"Yes, it is. A satellite with a diameter of two to three thousand kilometers that is circling an enormous gas giant is one thing. That same satellite circling a small, rocky habitable planet is quite another. That satellite has a diameter over a quarter that of Earth. Where have you heard of such near-parity involving a habitable planet?"

Pelorat said timidly, "I know very little of such things."

Trevize said, "Then take my word for it, Janov. It's unique. We're looking at something that is practically a double planet, and there are few habitable planets that have anything more than pebbles orbiting them. Janov, if you consider that gas giant with its enormous ring system in sixth place, and this planet with its enormous satellite in third—both of which your legends told you about, against all credibility, before you ever saw them-then that world you're looking at must be Earth. It cannot conceivably be anything else. We've found it, Janov; we've found it."

^{Quotes are from Foundation's Edge (1982) and Foundation and Earth (1986).}

My question is in two parts:

1. Are the various descriptions and facts given above generally correct?


2. How unusual are Saturn's rings and the Moon compared to other systems we've observed?

Sequencing from PCR - Biology

All sequencing methods, be it classical Sanger sequencing or next-generation sequencing (or even third generation) need a certain amount of DNA to work with.

You either need to extract DNA from a large-ish tissue sample or you need to amplify DNA content from a smaller sample. The first approach is often impractical, or downright impossible (when you want to work with single cells or very small organisms).

So PCR is used routinely to amplify DNA before sequencing. The sequencing itself isn’t influenced by this – you use whatever technique is appropriate. However, the PCR may introduce biases into the data because not all DNA fragments amplify equally efficiently. This needs to be taken care of in the downstream analysis of the sequence data if quantitative information is required (as in RNA-seq or ChIP-seq).

Coming back to your question, PCR isn’t a sequencing method in itself. It just helps getting the necessary amount of raw material in order for sequencing to work. Furthermore, most sequencing methods actually include PCR steps as well, since they rely on the generation of of overlapping DNA fragments to be stitched together.

units - Astrophysical "unitised" version of the Gravitational constant

Useful formulations which have taken some time to dig out:

$Gsim{4.3times{10^{-6}}},mathrm{kpc},mathrm{M}_{odot}^{-1},mathrm{km}^{2},mathrm{s}^{-2}$

or

$Gsim{4.3times{10^{-3}}},mathrm{pc},mathrm{M}_{odot}^{-1},mathrm{km}^{2},mathrm{s}^{-2}$

fundamental astronomy - How can we be 13.2 billion light years from another galaxy?

Don't think of inflation as super luminal movement of our galaxy from others. Think about the 'stuff' that makes space-time between the galaxies simply increasing (this is inflation). This causes the light to travel through more and more 'stuff' as time is passing by.

Imagine a clump of space-time A, and another B, next to each other at the start of the Big Bang. Then add some more clumps of space-time between them. You wouldn't think that the objects within space-time A and B have actually moved. A really basic analogy would be two pool balls next to each other with an ant on each. The ants can only travel to the next ball by walking on the the balls (ignore the ground). Then imagine the same scenario, but you add another ball between them. The ants haven't moved on the balls, but they would have to travel further now to get to the ball the other ant is on. The balls in the example would represent space-time, and the ants any galaxy/star.

solar system - Brown Dwarf transcending past the sun with the naked eye

Although the picture is too low rez to be certain, it looks like the object is very nearly circular. Pixels along the edge vary from pink to dark blue, while pixels in the center seem to be gray to black.

Without seeing the original image, I don't think one can draw any conclusion from the image, but the fact that it's so circular and seems to be exactly centered on the sun makes me suspect that this is a photoshopped hoax.

FWIW, the bright feature towards the left side of the picture is a sun dog, a refraction of sunlight through ice crystals, and shows no indication of the black spot, which means that if it was a real object, it was below that cloud layer, rather than above it.

zoology - Why animals can move and plants cannot in general?

Animals and plants are both classified as Eukaryotes, and as such can form large, complex, multi-cellular organisms. There are several major differences at the cellular level that distinguish the 2 Kingdoms (Animalia and Plantae). Without getting technical, the most crucial difference in relation to your question is that plants contain chlorophyll, and as such can generate their own food using sunlight.

This is very important when you consider that plants (by definition, those Eukaryotes that contain chlorophyll) have therefore evolved to be very efficient at converting sunlight to 'energy', whereas animals have evolved without this option and have to eat what food they need. So they have instead evolved mechanisms that allow them to forage, or even to hunt, for their food.

At some point, a unicellular organism incorporated chlorophyll, leading to multicellular plants in the course of evolution. The ancestor of animals evolved independently from the last common ancestor of plants and animals. Therefore, plants and animals are quite diverged, e.g. in mating 'rituals' (in plants this involves flowers and seeds - whereas in animals there are mating and gestation periods), and systemic changes, such as the immune system and the circulatory system (these are generally much more complex in animals than plants). All of which has stemmed from the difference in evolutionary pressures applied by the choice of food-source.

As you have pointed out, there are exceptions to all rules, so not all plants have chlorophyll, but as a rule it is the case! (Wikipedia: "Some plants are parasitic and may not produce normal amounts of chlorophyll or photosynthesize.").

Why won't the Milky Way colliding with Andromeda affect the Solar System?

I've always found that somewhat strange when they say no stars will hit out of billions, but I also trust the scientists that they know their stuff.

Lets look closer at your numbers. If the Oort Cloud has a diameter of 2 light years (I think it's a bit less than that, but numbers vary), that's a radius of 1 light year, and the Solar System to the Oort Cloud has a volume of $frac{4}{3} pi R^3$, or $frac{4}{3} pi$ cubic light-years.

With 5 light-years average distance from stars, that's an area 125 times larger. So our Sun fills up (to its Oort Cloud) 1/125th of its region of space, and 5 light-years might be low too. The average closest star might be a bit more than that.

But not all stars are as big as our Sun; many are smaller and if two Oort Clouds pass through each other, not much happens. A star has to pass within our Oort Cloud for the gravitational changes to be interesting, and that doesn't happen very often.

Another thing to consider is that the Earth is in a spiral arm of our galaxy, and both the Milky Way and Andromeda are flat disk-shaped galaxies. Are we crashing head on or at an angle where our spiral arms won't be directly hit?

I don't think we'll care much 4 billion years from now. I like to think we'll have traveled beyond the Solar System by then, but the danger to the Sun from Andromeda probably isn't huge. That said, I'd guess that some stars will pass near other stars, even if the experts say direct hits are unlikely (from the article)

If the Sun were a ping-pong ball, Proxima Centauri would be a pea about 1,100 km (680 mi) away, and the Milky Way would be about 30 million km (19 million mi) wide. Although stars are more common near the centres of each galaxy, the average distance between stars is still 160 billion (1.6×1011) km (100 billion mi). That is analogous to one ping-pong ball every 3.2 km (2.0 mi). Thus, it is extremely unlikely that any two stars from the merging galaxies would collide

If stars are ping pong balls every two miles and we use our Solar System as an example (it's really not, because the ping-pong-ball-every-two-miles example is in the center of the Solar System), but if the Sun is a ping pong ball, the Earth orbits at a radius of 4.3 meters and Neptune at a bit over 120 meters and the outer edge of the Kuiper Belt about 200 meters. That's still small compared to the average distance between stars, even in the galactic center, but not so small that interaction would never happen.

The ping pong balls might miss each other but I think it's a safe bet that there will be the occasional star-to-outer planet close encounter. From a local perspective these will be rare, but from an entire galaxy perspective, I'd think there would be quite a few of what could be called, planetary fly-bys/near misses.

temperature - What is the minimum size of a ball of gas to become a star?

There is no equation, you need a detailed model of the interior physics of very low mass stars. Very roughly, you can say that
hydrogen fusion occurs when the central temperature exceeds about $10^{7} K$ (the density dependence is secondary) and that from the virial theorem, the central temperature is given approximately by $T simeq 1.6times 10^{7} M/R$, where the mass and radius are in solar units. $M/R$ decreases slowly down the main sequence towards lower mass stars, but then what happens is that electron degeneracy pressure becomes important and less massive objects do not become much smaller than Jupiter-sized and thus $M/R$ decreases and fusion stops - or rather it never starts.

In detail the minimum mass for hydrogen fusion in a manner that is capable of sustaining a star in equilibrium against gravitational contraction is about $0.075M_{odot}$. With an uncertainty of about $0.002M_{odot}$.

It is slightly more complicated than this, since at lower internal temperatures the deuterium in a star can fuse. This will happen during the early life of any ball of gas more massive than about 13 Jupiter masses.

Your assumptions about the relative H and He abundances are completely wrong. Even in the early universe the gas is $sim 25$% He by mass.

planet - BIG CRUNCH Theory

To answer your question: yes it can happen.

Three major theories exist: big crunch, big freeze (or heat death), big rip.

Big crunch means everything is eventually crushed into a single point. Big freeze is that things get so far appart that "nothing" can happen anymore (except quantum stuff but that's another story), the universe becomes the most boring place in the ...hmm universe... Big rip means that eventually the fabric of time and space stretches so much that everything is torn appart (absolutely everything) in a rather short instant.

To simplify, they really depends on a ratio being smaller than 1, equal to 1 or greater than 1. Right now, the measurement of this ratio is that it's very close to 1... + or - a small quantity. But this small quantity makes all the difference. So until we can refine this measurement, we don't know. It's like keeping a pencil on its end: whether it falls left or right can depend on a very subtle initial imbalance. Right now, we say "it's sort of in the middle" which is not very useful!

astrometry - Open access table of visible stars with magnitude, coordinates, and possibly color?

I'm looking for a link to a table of visible stars that is open and available to everyone. It should have magnitude, RA, dec, and possibly some indication of color. This will be used to produce somewhat realistic night skies as a backdrop for showing the motion of the planets in the sky.

I'm not so interested in names, constellations, etc. These are of course useful to know and possibly to plot, but what I'm primarily after is the information necessary to illustrate star position, brightness, and some color information.

edit: to reiterate, "...table of visible stars that is open and available to eveyone." I'm assuming that in 2016 the visible stars are not behind a paywall, am I wrong? Approx RA, dec, mag - are these available for open access and usage?

What constellations touch the 9-degree wide Zodiac?

Say Barry, could you abuse the answer-your-own-question feature of
this site, and answer the following question:

As noted in How many constellations in the Zodiac? the
ecliptic itself touches 13 constellations, but the Encylopedia
Brittanica defines the Zodiac as "a belt around the heavens extending
9 [degrees] on either side of the ecliptic":

http://www.britannica.com/topic/zodiac

The Old Farmer's Almanac for 2014 (and previous years) notes (page
114) that Moon occasionally crosses into 5 "non-Zodiac" constellations
at times:

So, exactly which constellations are "in the Zodiac" if the Zodiac
extends 9 degrees on either side of the ecliptic?

And why 9 degrees? I know Venus can be as much as 8.25 degrees from
the ecliptic,

What makes the Moon and Venus shine?

The sun is an excellent source of light for all the planets and moons, although it gets a little dodgy way out near Pluto. The moon reflects about 10% of the sunlight that hits it, that's why we see it. Venus' albedo is about 0.75, what with its clouds and all. That means 75% of the sunlight that hits it is reflected back into space for us to see.

cell biology - What is the difference between "dikaryotic" and "heterokaryotic" states in the sexual lifecyles of fungi?

dikaryotic does - by definition - mean that there are exactly two nuclei in the cells, it does not say that the two nuclei are genetically distinct!
heterokaryotic does also mean only one thing: the nuclei (the number is not important) are genetically distinct.

that's the reason why, for example webster, writes "heterokaryotic dikaryon".

in fact the nuclei are distinct in almost all cases, that's why some only write "dikaryon"

human biology - Why would diffusion be faster across a non-specialised tissue?

There are several issues here:

1) Any mucous membrane is a specialized tissue for absorption.

Mucous membranes are indeed not so good for passive diffusion, that makes them absolutely perfect tools for active absorption of certain substances, almost independently from the membrane type. To provide some examples: many drugs like cocaine are inhaled and absorbed in nasal cavities, whereas the rectum is also known and favorite delivery way for medicines.

Generally the absorption force of the mucous membrane is dependent upon how well it is vasculated, for after going through the basal membrane the substance directly enters the blood flow and quickly travels away, thus the concentration gradient on both sides of the basal membrane -- the main barrier in mucosa -- remains relatively high.

See Bhat P. 1995. The limiting role of mucus in drug absorption: Drug permeation through mucus solution for an experimental model for this statement.

2) Mouth mucosa can absorb many substances.

There is a special term called "oral absorption" to describe the rapid drug absorption into blood flow from the mouth cavity. The mucous membrane is not specialized here, but small molecules are able to permeate here through all barriers.

3) Advantages of oral absorption.

There are some:

• The mucous membrane in the mouth cavity is very highly vascularized. The whole mouth can be seen as a bundle of skeletal muscles and every muscle requires a lot of energy and oxygen, therefore they have one of the highest vascularity rates, having much less distance between single capillaries.




• Blood flow is higher in the mouth cavity walls than in other inner organs. This is mostly because muscle contractions (during chewing) lead to increased propulsion of blood through capillaries and small vessels here.




• Any substance that enters blood flow here bypasses the hepatic-portal system. This means that the substance does not have to wait until it is filtered by our liver, it is immediately distributed through the whole body.




• There are special reflexes from oral mucosa to inner organs. Even not so important in case of aspirin, this is very important for some placebo drugs like methyl valerate (known as "Validol" in many countries) used a lot for treating angina pectoris whose only action is to activate the cold receptors in mouth and thereby leading to reflectory dilating of cardiac vessels.

---

This is why many drugs, like for example loperamid, are administered only as sub-lingual tablets. And this also explains why in emergency medicine many remedies are injected directly into the tongue.

Examples of Equal Mass, Unequal Mass and Double Binary Star Systems

Alpha Centauri, the nearest star system to us, is composed of a binary star and Proxima Centauri (making it a triple star system). Alpha Centauri A has a mass of 1.1 M$_{odot}$, while Alpha Centauri B has a mass of 0.9 M$_{odot}$.

If you count brown dwarfs, Luhman 16 are a good target, with each being about 0.04 M$_{odot}$.

Eta Carinae contains a Luminous Blue Variable (LBV) with a mass of 120-160 M$_{odot}$ and a smaller (but still very massive) star with a mass of 30-60 M$_{odot}$.

Sirius is okay, though with two stars of much smaller masses, 2 M$_{odot}$ and 1 M$_{odot}$.

Mizar, in reality part of a six-star system (Mizar/Alcor), has four stars separated into two pairs. This ensemble then interacts with the binary star Alcor.

---

You can find plenty of stars here.

cosmology - Does the radius of the Universe correspond to its total entropy?

Holographic entropy bounds are upper bounds for the maximum amount of entropy a given region can have, rather than its current entropy--for example, the spherical region of space just large enough to enclose the Earth and its atmosphere would currently contain a much lower entropy than a spherical black hole of the same radius, whose entropy is given by the Bekenstein bound. The scholarpedia article on the Bekenstein bound mentions the issue of cosmological entropy bounds:

Problems with bound (1) or the holographic bound are known to occur in extreme situations. Both fail when the gravitational potential is large (strong self-gravity), e.g. system already collapsed inside a black hole. In an infinite universe the holographic bound fails when applied to a sufficiently large region. In a closed (finite) universe the specification of R or bounding area becomes ambiguous (Bousso 1999, 2002). The covariant entropy bound corrects these and other shortcomings.

So apparently the "covariant entropy bound" (also known as Bousso's holographic bound) is the thing to look into when considering the maximum entropy of the universe (and I assume you just mean the observable universe here rather than whatever may lie beyond it). This set of lecture slides by Raphael Bousso, the physicist who originally proposed the covariant entropy bound, says that this bound is "conjectured to hold in arbitrary spacetimes, including cosmology." But it also says "If correct, origin must lie in quantum gravity", probably meaning one can't derive this fact in a non-conjectural way from basic laws of physics without having a complete theory of quantum gravity.

For an introduction to this stuff, I recommend this Scientific American article that discusses various holographic bonds, including the Bekenstein bound along with Bousso's conjectured more general bound (the article was written by Bekenstein himself). Though it is from 2003 so I'm not sure what kind of theoretical progress has been made since then. Anyway, here's what it says about Buosso's entropy bound:

In 1999 Raphael Bousso, then at Stanford, proposed a modified holographic bound, which has since been found to work even in situations where the bounds we discussed earlier cannot be applied. Bousso’s formulation starts with any suitable 2-D surface; it may be closed like a sphere or open like a sheet of paper. One then imagines a brief burst of light issuing simultaneously and perpendicularly from all over one side of the surface. The only demand is that the imaginary light rays are converging to start with. Light emitted from the inner surface of a spherical shell, for instance, satisfies that requirement. One then considers the entropy of the matter and radiation that these imaginary rays traverse, up to the points where they start crossing. Bousso conjectured that this entropy cannot exceed the entropy represented by the initial surface—one quarter of its area, measured in Planck areas. This is a different way of tallying up the entropy than that used in the original holographic bound.

Bousso’s bound refers not to the entropy of a region at one time but rather to the sum of entropies of locales at a variety of times: those that are “illuminated” by the light burst from the surface. Bousso’s bound subsumes other entropy bounds while avoiding their limitations. Both the universal entropy bound and the ’t Hooft-Susskind form of the holographic bound can be deduced from Bousso’s for any isolated system that is not evolving rapidly and whose gravitational field is not strong. When these conditions are overstepped—as for a collapsing sphere of matter already inside a black hole—these bounds eventually fail, whereas Bousso’s bound continues to hold. Bousso has also shown that his strategy can be used to locate the 2-D surfaces on which holograms of the world can be set up.

But again, this bound should be the upper limit on the entropy of a given region, not necessarily the actual entropy in that region, so this type of holographic bound shouldn't imply that when we increase the entropy of the universe, the universe needs to grow. This paper specifically discusses how most matter-containing regions in cosmology apart from black holes would fail to "saturate" the covariant entropy bound, meaning that the actual entropy in the region is smaller than the maximum possible according to the bound.

universe - Is there any proof of space being created?

As is always the case in physics, there is no proof.

But if your scenario were true, it would have to be rather fine-tuned in order to create the observed expansion of the Universe.

First of all, the expansion is observed to be highly isotropic, i.e. the expansion rate is the same in all directions. Hence, your lumps couldn't really look like your drawing, but would have to lie in a shell around our Universe.

Second, the matter farthest from us would achieve a larger acceleration since it were closer your surrounding matter. In fact the opposite is observed; in the "local" Universe, the expansion accelerates, whereas in the distant Universe (which due to the finite speed of light also means the early Universe), the expansion actually decelerated.

Third, we would have to be located near the center of the Universe which, while not impossible, would be regarded as a highly improbable coincidence.

Fourth, preferably you would have to come up with some mechanism that could result in such a configuration of matter.

Dark energy, at least in the form of the cosmological constant which is usually assumed, is so far (!) the simplest explanation for the observed fact that the expansion of the Universe is accelerating, and that the geometry of space seems to be flat. But several other models that fit the observations exist, and although I personally think dark energy makes the most sense — partly because this is so far from my field that I'll have to rely on what I read — I think most cosmologists are rather open to the possibility that we may one day have to severely reshape or even reject this model.

star - Calculating AZ and ALT from RA and DEC: values are slightly different from Stellarium

I'm developing my own planetarium software and I using Stellarium to check if the values a get from my software are correct or not.

All values are roughly equal, being different only in the seconds.

These are Stellarium coordiantes followed by my coordinates.

Note, this is a CSV txt file. I don't know if I can attached to this question so I have pasted here:

Star;RA J2000;DEC J2000;RA J2016;DEC J2016;Hour Angle;AZ;Alt.
Betelgeuse (Stellarium);5h55m10.34s;7d24m25.6s;5h56m2.38s;7d24m22.0s;23h52m25.55s;+176d38m27.3s;+55d59m52.0s
Betelgeuse (My software);5h55m10.34s;7d24m25.596s;5h56m2.32s;7d24m31.74s;23h52m25.6662s;+176d38m29.643s;+56d00m01.836s
Rigel (Stellarium);5h14m32.28s;-8d12m05.9s;5h15m18.50s;-8d11m12.8s;00h33m09.44s;+190d42m52.5s;+39d51m52.8s
Rigel (My software);5h14m32.279s;-8d12m05.9s;5h15m18.46s;-8d11m03.24s;00h33m09.5262s;+190d42m55.996s;+39d52m02.033s
Bellatrix (Stellarium);5h25m7.86s;+6d20m58.7s;5h25m59.49s;+6d21m37.1s;00h22m28.45s;+189d40m43.7s;+54d38m14.4s
Bellatrix (MySoftware);5h25m7.9s;+6d20m59s;5h25m59.42s;+6d21m46.71s;00h22m28.5662s;+189d40m48.830s;+54d38m23.685s
Mintaka (Stellarium);5h32m00.41s;-0d17m56.7s;5h32m49.55s;-0d17m27.8s;0h15m38.38s;+185d52m14.8s;+48d11m30.9s
Mintaka (MySoftware);5h32m00.42s;-0d17m56.6988s;05h32m49.51s;-0d17m18.1958s;00h15m38.4762s;+185d52m18.043s;+48d11m40.40s
Alnilam (Stellariumm);5h36m12.82s;-1d12m06.9s;5h37m01.63s;-1d11m44.00s;00h11m26.31s;+184d13m21.1s;+47d21m31.3s
Alnilam (My software);5h36m12.82s;-1d12m06.912s;5h37m01.57s;-1d11m34.2547s;00h11m26.4162s;+184d13m24.435s;+47d21m40.929s
Alnitak (Stellarium);5h40m45.54s;-1d56m33.2s;5h41m34.07s;-1d56m16.6s;00h06m53.87s;+182d30m42,7s;+46d40m01.3s
Alnitak (My software);5h40m45.55s;-1d56m33.2160s;5h41m34.03s;-1d56m06.8887;00h06m53.9562s;+182d30m45.212s;+46d40m10.931s
Saiph (Stellarium);5h47m45.40s;-9d40m10.6s;5h48m31.01s;-9d40m03.7s;23h59m56.93s;+179d59m01.5s;+38d57m56.3s
Saiph (My software);5h47m45.38s;-9d40m10.5960s;5h48m30.9500s;-9d39m54.0031s;23h59m57.0362s;+179d59m03.631s;+38d58m05.992s

Is that different a problem?

I don't know which value is the correct one (the one from Stellarium or the one from my software). The maximum difference is about 10 seconds.

And the difference between declinations (Stellarium and mine) is always greater that the difference between right ascensions.

genetics - Effect of single-gene overexpression in the cell's response

Which are the factors that modify the overall gene differential expression by introducing a vector for single-gene overexpression?

If you overexpress a gene for a protein involved in signal transduction (e.g., a kinase, scaffold, or receptor) by vector cell transfection, then you overdrive the cell using this signaling pathway, it's useful to isolate the pathway and study them.

Is there any way to modify the overall gene expression or cell differential expression pattern by gene transfection? I think this would work if you delivered a gene for overexpression in proteins involved for RNA processing (e.g., splicing, ribosomal proteins, etc.), RNA transcription (e.g., TFs) or protein translation.

neptune - Why do some planets have rings?

Rings are made up of tiny (and not so tiny) pieces of rock and ice that are in some way the bits "left over" from the formation of the planet. The theory involves the Roche limit - and is that particles that are already within this limit can't accrete into a larger body because of the tidal forces involved.

Another theory is that they are formed when a moon comes closer to a planet than the Roche limit, the tidal forces cause it to break up and form a ring. Though the presence of "shepherd" moons in the rings of Saturn does hint that this may not be major source of material.

Both explanations, to me, imply that you'd only get major ring systems around larger (gas giant) planets, though it doesn't preclude rings around smaller (rocky) planets. This seems to be borne out by our solar system where the gas giants have rings whereas the rocky planets don't.

Source

As to being able to see them, you should be able to see the rings of Saturn with an amateur telescope which has a 50 - 100 powers of magnification. With binoculars you'll probably see a misshapen blob.

Source

Does the Moon have any oxygen in its atmosphere?

Just to add to GreenMatt's answer, according to the article "The Lunar Atmosphere: History, Status, Current Problems and Context" (Stern, 1999), the lunar atmosphere is in fact a tenuous exosphere, which the authors describe as being composed of

"independent atmospheres" occupying the same space.

This is further elaborated in "The Lunar Dusty Exosphere: The Extreme Case of an Inner Planetary Atmosphere" (NASA), that

in direct response to these intense and variable environmental drivers, the Moon releases a low density neutral gas forming a collisionless atmosphere. This ~100 tons of gas about the Moon is commonly called the lunar surface-bounded exosphere

There is also an ionosphere, due to (from the ANSA article):

Ions are also created directly either by surface sputtering or subsequent neutral photoionization, forming a tenuous exo-ionosphere about the Moon.

The authors also suggest that ionic oxygen may be present due to surface sputtering.

Due to solar radiation and the solar wind, dust particles become charged as well, and can be subsequently listed from the lunar surface.

amateur observing - Which of Jupiter's moons did I most likely see?

I was gazing through my binoculars at Jupiter last night and noticed 3 (maybe 4) tiny dots in line with it. A first I thought they might have been background stars but quickly realised their colour was similar to that of Jupiter and their brightness was larger than expected considering their size. As a result, I'm pretty certain I was looking at Jupiter's moons.

Presumably, I was seeing the largest of its moons (Io, Europa, Ganymede, Callisto). They were far too tiny to see any details, obviously, but would it have been only those moons I could see? I assume the rest are too small. And is seeing those 4 moons as tiny bright dots through my 7x50s feasible?

What lies at the center of a neutron star if any?

Certainly not a black hole! That would not be stable situation at all.

The content of the core of a neutron star is the subject of much speculation. The possibilities fall into a number of categories. (i) An increasingly hard neutron equation of state, such that neutrons retain their identities as they are squeezed closer, but an increasingly repulsive many-body strong nuclear force provides support. (ii) Additional hadronic degrees of freedom, such that the neutrons (and protons) transform into other heavy hadrons such as lambda or sigma particles. (iii) Some sort of quark plasma. (iv) Boson condensations involving the neutrons decaying into pions or kaons with zero momentum.

There are a number of diagnostics of these possibilities: primarily, the maximum possible mass of a neutron star should decrease from about 3 solar masses for (i) down to about 1.5 solar masses for (iv). Secure measurements of a 2 solar mass neutron star would seem to rule out (iv), but even that seems not completely agreed. Another diagnostic is how quickly neutron stars can cool. The presence of quark matter or boson condensations should lead to much more rapid cooling by neutrino emission. Again, nothing conclusive has emerged yet.

For how many bodies can there be a stable orbit with no very heavy central body?

The question is a bit vague, but let me explain:

Take for example 2 bodies of the same mass. They can orbit around their centre of mass/gravity. Is something like this possible with multiple bodies of varying mass and distance from the centre of gravity without a relatively extremely massive body there?
i.e. would it be possible to have a planetary system that orbited around the centre of mass without there being a massive star (roughly) in the middle?

I know that the Sun also has an orbit around the centre of gravity of the solar system, but that orbit is very small compared to its size, which puts it roughly in the centre.