neuroscience - Are cerebellar basket and stellate neurons actually different cell types?

You are completely right with your guess that is was Ramón y Cajal who first described these cells in his famous monograph "Histologie de systeme nerveux de l'homme et des vertebres." published in Paris Maloine in 1911.

Since the only method he had at his disposal was Golgi's staining which is a pure anatomical staining (there is no living cell left in the tissue after the treatment with potassium dichromate and silver nitrate) with silver chromate filling completely single cells at random.

Using only this staining and his eyes Cajal did classify the neurons according to their size, location in the brain and their shape. This is why we have such names like basket, stellate, moss, pyramide etc. in neuron description. This classification is purely anatomical and does not reflect any intrinsic properties of these cell, as for example being motor neurons or interneurons.

When I was studying histology at my medical school I was always told that there is new "mollecular biology"-based classification of neurons is about to come and to replace the existing classification by Cajal, many cell types were supposed to be merged there, among others also different anatatomical groups of interneurons. (This was one of the major research topic of the research facility where I studied neurohistology).

As far as I can see, this classification is still not here...

general relativity - How far should the source be, for the gravitation waves to be visible on Earth?

The waves pass by at the speed of light. So you you would'nt see ripples, they would pass too fast, and remember the waves would be passing through you too. The wavelength was (relativly) long about 3000km. The wave doesn't pass you, you are inside the wave.

The amplitude of the waves detected by LIGO was small, one part in $10^{21}$, Now while the intensity of the waves follows an inverse square law, because intensity is proportional to amplitude squared, the amplitude is inversely proportional to distance from source.

We are familiar with strains that are one part in 1000, that is a variation of one millimetre for every metre. To get that we would have to be a lot closer to the source, $10^{18}$ times closer. Since the black holes were about 1 billion light years distant, to get a strain of 1 part in 1000, the black hole merger would have to be about 10000km away

Now if you are 10000km from a merging pair of 30 solar mass black holes, the strain of gravitational radiation is the last of problems. If it is any consolation, your problems won't lost long.

amateur observing - Can you see pleiades and sirius at the same time on the sky?

Stellarium is a free planetarium software, and it allows you view the position of stars in the sky at any date.

Sirius and the Pleiades are actually rather close in the sky. On the line of Orion's belt, on opposite sides. So for much of the the winter months, both are visible in the sky. For example in mid-December, they will be visible at midnight, in south-western skies. At the time of writing (8th October) they will be visible in the early morning.

It is a well known starscape, with Orion central, the Pleiades and the V of the Hyades on one side, and Sirus, scorching on the other.

Of course, the Pleiades and Sirius are "fixed stars", so the separation between them doesn't change. There is no time when they approach each other.

star - Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?

The test to see whether degeneracy pressure is going to be significant is to compare $kT$ with the Fermi energy $E_F$

The Fermi energy is the energy level up to which all energy states would be occupied in a completely degenerate fermion gas. It is given by (for non-relativistic conditions)
$$ E_F = frac{h^2}{2m}left(frac{3}{8pi}right)^{2/3} n^{2/3},$$
where $m$ and $n$ are the mass and number density of the fermions (in this case, electrons).

If $E_F gg kT$, then the gas can be considered completely degenerate and the electrons exert a non-relativistic degeneracy pressure. If $E_F sim 10 kT$ the electrons are partially degenerate.
In both these circumstances, the pressure exerted by the electrons is much higher than they would have in a perfect gas, because a large fraction of electrons occupy high energy (and momentum) states.

Degeneracy can be achieved either by having a low temperature or a high number density of fermions. In a white dwarf, electrons are completely degenerate because the number density of electrons is extremely high. In a gas giant, the electron density is nowhere near as high, but then the temperature is a lot lower and so they reach a state of partial degeneracy.

The pressure of a partially degenerate gas is higher than that of a perfect gas at the same density and temperature. More importantly, the pressure is only very weakly dependent on temperature. As a gas giant radiates away its potential energy, it is able to do so whilst only contracting very slightly and the core does not become hot enough to initiate nuclear fusion.

Note that degeneracy pressure and thermal pressure are not two different things. Both arise merely as a consequence of particles having a distribution of momenta and obeying (in this case) Fermi-Dirac statistics to determine how they occupy the possible energy states. The expression $P = nkT$ is simply a convenient approximation for fermions that holds only when $E_F ll kT$ and the quantum nature of the particles is not apparent.

amateur observing - Was that actually a shooting star during the supermoon eclipse on September 27th 2015?

During the super-moon total lunar eclipse on September 27th a meteor-like streak passed very close within view of the event. It appeared to happen at the very middle, the maximum eclipse.

[CafferyPhoto][1]

At the time, I thought it must have been some organization shedding an unused satellite. This would be a pretty epic time to do so as so many eyes around the world are looking at the same thing. Maybe even NASA marking the halftime of the event. Can anyone confirm or shed any amount of light on what this was?

[1][https://www.facebook.com/cafferyphoto/photos/a.279223605465113.81307.120967987957343/915070541880413/?type=3&theater]
note - photo for proof only - shutter cut off leading edge

QUESTIONS:

People on the Caffery's Facebook page seem to have seen in in California and other locations as well, I happened to be in St Thomas, Virgin Island at the time of the event. CafferyPhoto quotes. "I was only exposing for half a second so the shutter cut off the latter half of the trail, darn it!" - Seems in was taken in the NorthWestern US sometime around 7:30pm.

planet - Where might a semi proficient amateur analyst participate in meaningful astronomical efforts

I haven't managed to formulate a coherent single answer, but here are several suggestions for where to find some hints of current topical research where you might be able to contribute.

Open source projects

Astronomy is increasingly using large open source projects, many written in Python, which itself free. For example, the Astropy project is trying to create an extensive Python library for astronomical data manipulation, so you could try to contribute some of the desired features in a project like that. (There are other, more substantial, projects, especially in various kinds of modelling, but they require an understanding of the physics and are often big chunks of code, written in Fortran.)

Review articles

If possible, I'd suggest looking at review articles (e.g. in Annual Reviews in Astronomy & Astrophysics). Though many of the articles are probably behind paywalls, most of the recent ones should also be available on the arXiv. Similarly, you can also try searching arXiv for lecture notes from summer/winter schools.

Departmental PhD project listings

In a similar vein to contacting people, you might find that potential projects are listed online, in which case you'll see what kinds of things people would like to do. For example, so quick Googling netted me information at Manchester, St Andrews, QMUL, and UCL. (Clearly Google thinks I'm in the UK...) While it probably doesn't make sense to actually try to carry out these projects, they might give you a better idea of the sorts of things that need doing.

Observation projects with public data

I'd particularly watch out for anything that involves data-mining, since that mostly involves spending time crunching some of the huge datasets available. I'm mostly aware of projects in the time domain (e.g. OGLE and WASP) but there are also larger projects like SDSS that I think have more data than people to sift (intelligently!) through it all.

I'd note here the special cases of Kepler and it's continuation K2. In these cases the actual analysis of the cameras' pixel data is still an open question, especially for K2. Any clever progress on automatically reducing the data better would be a boon in that field, although several active research groups are also working on it full time.

orbit - Is the size and heat of a star important in the development of a solar system?

I think the quick answer to this is no, at least, any solar-system around a Wolf-Rayet or similarly large star wouldn't have time to develop. I would think that large stars have solar-systems cause I see no reason why they wouldn't, but the stars don't last long enough for their solar-systems to develop much. The formation period, including bombardment period(s) and time for the planets to cool down from the heat of formation takes a significant amount of time, perhaps a couple hundred million years minimum.

Our solar system's late heavy bombardment occurred between about 4.1 and 3.8 billion years ago, ending some 700 million years after our solar-system formed and Earth didn't cool down enough to have a magnetic field until about 3.5 billion years ago, roughly 1 billion years after formation. Granted, that's a sample size of one, so numbers could vary quite a bit, but I have a hard time imagining that planet's could cool down and complete most of their early bombardment in the lifespan of a very large star.

For developed solar-systems where the planets had time to cool and the solar-systems had time to mostly coalesce and get past early-bombardment, I don't think there's much of a window beyond maybe 2 solar masses (a 2 solar mass star would have roughly 1/16th the lifespan of our sun, or a bit less than a billion years in main sequence), based on an exponential ratio to the 4th power of the star's mass. Source.

Now, as to whether a solar-system could survive a Wolf-Rayet star's enormous ejections, that's another question. I'm not 100% sure but large planets are pretty resilient, so my guess is yes, but it's just a guess.

Another interesting question is gravity vs luminosity. Our solar-system the furthest planet Neptune, about 30 astronomical units from the Sun, and, presumably a planet could orbit a fair bit further out than that and be in a stable orbit, but lets go with 30 AU.

A star with 10 times the mass of our sun during it's main sequence has roughly 3,000 times the luminosity (using the exponential relationship of 3.5 Mass to Luminosity - see here)

The gravity for 10 solar masses, gravity reduces by the square of the distance, so square root of 10, a Neptune equivalent orbital velocity would be about 95 Astronomical Units, so, at 95 astronomical units from a star with 3,000 times the luminosity of our sun, the energy received from that star at that distance would be roughly 1/3rd the energy the Earth gets from the sun.

Too much larger than that, somewhere around 20 solar masses or, not much more than that, the star gets too hot to have much of a solar-system within it's theoretical Goldilocks zone. Not that that matters much, cause the short lifespan of the star kind of answers the question anyway, but my guess would be, if planets survive around a Wolf-Rayet star, even the outer parts of such a solar-system should be hot unless they were enormously distant, like a couple hundred AUs. There might be no ice or water planets around a star of that size.

atmosphere - How do solar winds affect the atmospheric composition and density of planets?

Do these particles contribute to the planets' atmospheres? Or do they
do more harm than good? (define: good = contribute).

That depends on the size (mass/escape velocity) of the planet. See atmospheric escape and pretty picture

For the 4 inner planets, the solar wind strips gas from the planets. This process if fairly straight forward. It has more to do with heat than traditional "blowing", and when the when the outer atmosphere gas molecules reach a certain temperature they can achieve escape velocity. Earth mostly just loses hydrogen and helium and very little of it's heavier gases. Venus over time has lost most of it's Methane and Water Vapor, the key difference between Earth and Venus is that Earth has a magnetic field.

Mars has lost most of it's atmosphere and what atmosphere Mars retains may be related to the thawing and re-freezing of it's icy poles, and Mercury's atmosphere is so thin that it's atmosphere actually is little more than a loosely retained collection of solar wind particles.

The 4 outer planets don't lose much to the solar wind and the Solar wind (I would think) adds to rather than takes away from their total mass, but this addition is very small compared to the mass of a planet.

Do solar winds contain any larger atoms than helium. For instance,
Oxygen?

Yes, but only trace amounts. The Solar wind is 92% hydrogen and 8% helium. Source. Very close to the universal average ratio. Solar particles are so hot that when they're ejected from the sun the electrons and atomic nuclei are largely separated so you get a stream of charged particles, electrons and protons being the most common and Alpha Particles (Helium Nuclei) 3rd. This means that any planets with a magnetic field, those particles get caught in planet's magnetic field. That's why a magnetic field is considered very important in preserving a planet's atmosphere.

Some of the captured solar wind particles would probably get deposited into the Planet's atmosphere over time but I'm not clear on that process and I don't know the percentages.

Getting back to the Sun, it has about 2% "heavy" elements in it, see article, and by "heavy" I mean, Oxygen, Carbon, Neon, others, but gravity draws the heavier elements towards the center of the sun. Also, the helium the sun creates is largely formed near the center of the sun, so the outer parts where the solar wind gets ejected has a more standard/universal balance of about 92% hydrogen by element.

My intuition on this issue is mixed since we have Mars with a very
thin atmosphere, but Venus with a very thick atmosphere, neither
having a very strong magnetosphere to protect them from solar winds

Venus mass is sufficient to make a difference. Atmospheric escape has to do with escape velocity from the planets and Venus' escape velocity is over twice Mars'. Source. Venus' atmosphere is also sufficiently thick that it generates it's own magnetic protection of sorts, (I've read that, didn't see a good article to reference just now).

Jupiter has an enormous magnetic field, which casts a pretty big net, much larger than the planet itself and that captures solar wind particles, but compared to the mass of Jupiter, the captured solar particles, even with the large magnetic net, is teeny-tiny and makes no real difference in the mass of the planet.

Interestingly, when the sun approaches it's red giant stage, it's ejections will significantly increase, so it's possible that, 5 billion or so years from now the sun will feed Jupiter a stream of particles in a measurable way and Jupiter will grow larger and perhaps, visibly glow due to the particles it receives. Jupiter might be a fun planet to watch when our sun goes red giant, perhaps from the safe distance of a colony on Saturn's moon titan. But that's just speculation. :-)

It will never turn into a star, it's far far far too light for that, but Jupiter could still be fun to watch (from a safe distance) 5 billion years from now. (My answers always tend to be too long). . .

Corrections welcome.

nucleosynthesis - Is a star powered by fission possible?

I think it's an interesting question. The trick would be a sustained fission reaction, faster than half life, but slower than a chain reaction. A chain reaction could hardly be considered "star like" - it would just explode.

Lets say you had a planet sized object, maybe 100 parts Iron, basically inert, to 1 part Uranium , which would generate heat through half life decay and some neutrons would spread from uranium to uranium - many wouldn't. And as the object got hotter, more and more uranium would drift towards the center. You'd have gradual heating, and the object, in time, would probobly begin to glow. I'm guessing it's not possible using anything close to pure uranium, as the neutrons released in a uranium rich ball of matter would do 1 of 2 things - either blow the thing apart, or increase the rate of reaction and cause a chain reaction. But i think, with the proper mix of uranium and inert elements, and the uranium spread out, not all in the center, you probobly could get something sort of star-like. It would have much less available energy so it wouldn't burn nearly as long as a star. At least, that's my thought experiment answer to this question.

The problem with nothing but heavy, neutron rich elements is that, I don't see any way that wouldn't cascade and burn or blow up quickly. The nuclear reaction is driven by neutrons hitting the nucleus with potential energy and as the reaction happens, more free Neutrons are produced which speeds up the reaction significantly. A ball of of Uranium many miles across would undergo fission and explode. A ball heavy enough to not explode - say, jupiter sized, it would heat up and burn quickly and then settle down and cool off slowly. - perhaps similarish to a star going Nova then settling into a white dwarf.

If you have a material inside that slows the reaction, absorbs and re-admits Neutrons you could probobly generate a sustained burn - similar to what happens inside a nuclear plant while maintaining enough gravity to keep the object in one piece and over time, That would heat up and glow like a star in time and last for a while. Planet sized, even moon sized would probobly be more than sufficient, but you'd need the material to slow the reaction and keep the Uranium spread out. That's my take at least.

biochemistry - What triggers meiosis in gonadal cells?

Ultimately, it seems that follicle-stimulating hormone (FSH), released from the pituitary gland, may be the direct signal for spermatocytes to enter meiosis [1]. It's worth noting, though, that these results come from in vitro studies, where spermatocytes were co-cultured with all cell types of seminiferous tubules in an artificial medium, which makes it a rather crude approximation of in vivo conditions: mimicking the complete spermatogenic cycle in vitro remains to be done [2].

It's a little bit more complicated with oocytes. They start meiosis during prenatal development, are arrested in diplotene stage of the first meiotic division, and then a surge of luteinizing hormone (LH), just before ovulation, makes them resume. But they are arrested again in the last phase, and only after conception do they finish meiosis. The pause occuring in prenatal development is thought to be induced by some kind of an "arrester" secreted by cells in the oocyte environment (specifically, mural granulosa cells) and sustained by high cAMP levels, that are produced in response to both intrinsic and extrinsic stimuli. [3]

Another matter, and quite interesting, is the issue of timing: meiosis starts in a distinct moment of a male mammal develompent, and then goes on continuously, but mammal oogenesis is a series of starts and stops. More on this can be found in [3] and [4].

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[1] Tesarik, J., Guido, M., Mendoza, C. & Greco, E. Human spermatogenesis in vitro: respective effects of follicle-stimulating hormone and testosterone on meiosis, spermiogenesis, and Sertoli cell apoptosis. J. Clin. Endocrinol. Metab. 83, 4467–4473 (1998). PMID: 9851795. Free access.

[2] Sousa, M., Cremades, N., Alves, C., Silva, J. & Barros, A. Developmental potential of human spermatogenic cells co-cultured with Sertoli cells. Hum. Reprod. 17, 161–172 (2002). PMID: 11756382. Free access.

[3] Zhang, M. & Xia, G. Hormonal control of mammalian oocyte meiosis at diplotene stage. Cell. Mol. Life Sci. Epub ahead of print. (2011). PMID: 22045555.

[4] Albertini, D.F. & Carabatsos, M.J. Comparative aspects of meiotic cell cycle control in mammals. J. Mol. Med. 76, 795–799 (1998). PMID: 9846949.

stellar evolution - death of a red dwarf star / minimum mass needed for a white dwarf?

Stars that have a mass lower than about $0.5 M_{odot}$ will not ignite helium in their cores, in an analogous fashion to the way that stars with $M<8M_{odot}$ have insufficiently massive cores that never reach high enough temperatures to ignite carbon.

The cause in both cases is the onset of electron degeneracy pressure, which is independent of temperature and allows the core to cool at constant pressure and radius. [A normal gas would contract and become hotter as it loses energy!]

The end result for a $0.5M_{odot}$ star will be a helium white dwarf with a mass (depending on uncertain details of the mass-loss process) of around $0.2M_{odot}$. Such things do exist in nature now, but only because they have undergone some kind of mass transfer event in a binary system that has accelerated their evolution. The collapse to a degenerate state would be inevitable even for the lowest mass stars (which would of course then be very low-mass white dwarfs). As an inert core contracts it loses heat and cools - a higher density and lower temperate eventually lead to degenerate conditions that allow the core to cool without losing pressure.

The lowest mass stars ($<0.3 M_{odot}$) do get there via a slightly different route - they are fully convective, so the "core" doesn't exist really, it is always mixed with the envelope. They do not develop into red giants and thus I guess will suffer much less mass loss.

The remnant would be a white dwarf in either case and is fundamentally different from a brown dwarf both in terms of size and structure, because it would be made of helium rather than (mostly) hydrogen. This should have an effect in two ways. For the same mass, the brown dwarf should end up bigger because the number of mass units per electron is smaller (1 vs 2) and also because the effects of a finite temperature are larger in material with fewer mass units per particle - i.e. its outer, non-degenerate layer would be more "puffed up". NB: The brown dwarfs we see today are Jupiter-sized, but are still cooling. They will get a bit smaller and more degenerate.

A simple size calculation could use the approximation of an ideal, cold, degenerate gas. A bit of simple physics using the virial theorem gives you
$$ left(frac{R}{R_{odot}}right) simeq 0.013left(frac{mu_e}{2}right)^{-5/3} left(frac{M}{M_{odot}}right)^{-1/3},$$
where $mu_e$ is the number of atomic mass units per electron.
Putting in appropriate numbers I get $0.32 R_{Jup}$ for a $0.07M_{odot}$ Helium white dwarf versus $1.01 R_{Jup}$ for a $0.07M_{odot}$ completely degenerate Hydrogen brown dwarf (in practice it would be a bit smaller because it isn't all hydrogen).

However, it would be interesting to see some realistic calculations of what happens to a $0.07M_{odot}$ brown dwarf versus a $0.08M_{odot}$ star in a trillion years or so. I will update the answer if I come across such a study.

EDIT: I knew I'd seen something on this. Check out Laughlin et al. (1997), which studies the long-term evolution of very low-mass stars. Low-mass stars do not pass through a red giant phase, remain fully convective and can thus convert almost all their hydrogen into helium over the course of $10^{13}$ years and end up cooling as degenerate He white dwarfs.

light - In what manner is the spectrum of a black body really a continuum?

A blackbody spectrum is continuous.

As Dean comments, there are no true blackbodies. But this is not really the issue here:

It's true that most emitted photons from, say, a star, which is quite close to a blackbody, is the result of some discrete process. E.g. an electron is brought to an excited state by a collision, the atom de-excites, and a photon with the wavelength corresponding to the given transition is emitted.

But two mechanisms make the total spectrum of the star truly continuous:

1. Firstly, ionized atoms recombine with free electrons. The electron will go to any state, ground or excited, and with various probabilities. The energy of the photon emitted is equal to the energy it would take to remove the electron from the atom (i.e. ionize it again), plus the kinetic energy it had before recombination. And this kinetic energy can have any value (although if it's too large, the probability of recombination decrease).




2. Secondly, even without recombinations, you will not observe only the discrete lines. The reason is that the atoms of the blackbody are not stationary, but move with a ("thermal") velocity $v=sqrt{k_mathrm{B}T/m}$, where $k_mathrm{B}$ is Boltzmann's constant, $T$ is the temperature, and $m$ is the mass of the atom. This motion causes a Doppler broadening of the emitted lines, resulting in a continuous, and Gaussian$^dagger$, probability distribution.

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$^dagger$_{Actually the probability distribution is a convolution of the Gaussian random motion, and the Lorentzian natural line profile, resulting in a so-called Voigt profile. This profile is dominated by the Gaussian in the line center, and only becomes Lorentzian in the wings.}

cellular respiration - Where is the line between Anaerobic and Aerobic?

Anaerobic respiration is a respiration where the final electron acceptor is different than oxygen. The final acceptor can be a less oxidizing than oxygen, like sulfate (SO₄^2-), nitrate (NO^3-), or sulfur (S). For example bacteria that use sulfate are obligate anaerobs.

The Krebs cycle cannot take place in the absence of oxygen, although oxygen is not directly involved in the cycle. The oxygen is required for the electron transport chain, which oxidized NADH and FADH₂ back to NAD⁺ and FAD⁺, which are involved in the four reduction reactions of the cycle.

Thus, aerobic respiration includes both Krebs cycle and final electron acceptor of oxygen, whereas anaerobic respiration does not.

neuroscience - How does cerebrospinal fluid circulate in the central nervous system?

It is something of a misnomer to speak of CSF “circulation,” particularly in the spinal canal, as there is no continuous loop circulation of CSF as there is in the cardiovascular system.

For quite some time, it has been known that CSF movement results from the formation of new CSF and motion of cilia on the surface of the choroid plexus and ependyma lining the ventricles. - Fluids and Barriers of the CNS

The "circulation" of the CSF, as already mentioned, is something of a misnomer. CSF is not known to "circulate" in the manner of blood. It does get agitated by pressure differentials, and it is 'circulated' in terms of being reabsorbed and replaced every 6-7 hours. Other than that, no circulation occurs.

Blood circulation is not generated only by the heart. Pressure differentials throughout the body affect the circulation of blood as well. One that is easily demonstrated (first documented in 1733) is the effect of intrathoracic (chest) pressure on circulation. The blood pressure of healthy people falls during spontaneous inspiration. When someone takes a deep breath, the blood return to the heart via the vena cava decreases, and pressure is exerted on the right atrium. Both cause decreased filling, which will drop blood pressure. Although this is best demonstrated with a blood pressure cuff, it can be demonstrated without. An unrecommended method is exemplified in a childhood game of passing out. A Valsalva maneuver (deep breath and glottal closure) decreases blood flow to the heart. Squeezing the chest further decreases return, resulting in fainting.

The same pressure differentials agitate the CSF. Additionally, smaller movements were seen with pressure differentials caused by the beating of the heart.

By employing this respiration-induced spin labeling bSSFP cine method, we were able to visualize CSF movement induced by respiratory excursions. CSF moved cephalad (16.4 ± 7.7 mm) during deep inhalation and caudad (11.6 ± 3.0 mm) during deep exhalation in the prepontine cisternal area. Small but rapid cephalad (3.0 ± 0.4 mm) and caudad (3.0 ± 0.5 mm) movement was observed in the same region during breath holding and is thought to reflect cardiac pulsations.

This image from Wikipedia shows "circulation" that normally occurs with heartbeat.

There are other factors that cause movement of CSF, but they are intermittent and variable.

^{Influence of respiration on cerebrospinal fluid movement using magnetic resonance spin labeling, Yamada et. al., Fluids and Barriers of the CNS 2013, 10:36
MRI showing pulsation of CSF}

dna sequencing - Why do restriction enzymes tend to have an even number of bases in their recognition site?

I think this is due to the over-representation of recognition sites with length 6:

data<-c(16, 16, 12, 12, 6, 6, 6, 6, 4, 16, 6, 6, 6, 6, 15, 15, 6, 6, 6, 6, 11, 11, 6, 6, 4, 4, 6, 6, 11, 12, 6, 6, 23, 23, 6, 6, 6, 6, 9, 12, 4, 4, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 10, 10, 6, 4, 6, 6, 11, 11, 9, 9, 6, 6, 6, 6, 5, 5, 8, 8, 6, 6, 8, 8, 6, 9, 10, 10, 6, 6, 6, 5, 5, 6, 4, 6, 6, 5, 5, 14, 14, 6, 6, 6, 16, 6, 6, 6, 6, 15, 15, 6, 6, 6, 6, 6, 18, 18, 7, 7, 11, 11, 20, 20, 6, 13, 4, 4, 6, 6, 6, 6, 6, 6, 6, 11, 6, 6, 7, 7, 6, 6, 6, 6, 6, 12, 6, 6, 10, 10, 23, 23, 7, 7, 23, 23, 12, 12, 6, 6, 6, 6, 10, 10, 6, 6, 8, 8, 6, 6, 35, 35, 11, 11, 7, 7, 6, 6, 9, 9, 8, 8, 16, 16, 6, 6, 17, 17, 6, 6, 6, 6, 23, 23, 6, 6, 4, 4, 21, 21, 12, 12, 20, 20, 6, 6, 6, 6, 6, 7, 7, 6, 6, 6, 6, 5, 5, 11, 11, 6, 11, 11, 6, 6, 5, 5, 7, 7, 11, 11, 11, 11, 6, 6, 12, 12, 6, 6, 6, 21, 21, 9, 9, 8, 8, 7, 7, 16, 16, 4, 4, 6, 6, 6, 6, 7, 7, 18, 18, 6, 6, 6, 6, 6, 23, 23, 7, 34, 34, 39, 39, 6, 6, 12, 12, 5, 5, 19, 19, 8, 8, 8, 8, 4, 6, 6, 6, 6, 6, 5, 5, 6, 6, 6, 6, 7, 7, 4, 4, 15, 15, 7, 7, 7, 7, 14, 14, 11, 11, 27, 27, 12, 12, 4, 4, 10, 10, 6, 6, 8, 8, 7, 7, 8, 8, 7, 7, 5, 5, 7, 7, 6, 7, 7, 6, 6, 8, 8, 39, 39, 6, 6, 12, 12, 8, 8, 7, 13, 13, 8, 8, 8, 8, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 5, 5, 7, 17, 17, 17, 17, 11, 11, 15, 15, 6, 6, 6, 5, 5, 5, 6, 6, 5, 7, 7, 12, 6, 12, 6, 6, 6, 5, 6, 6, 7, 2, 5, 11, 5, 6, 4, 5, 7, 5, 4, 4, 6, 4, 5, 6, 7, 12, 6, 7, 7, 7, 6, 4, 4, 7, 5, 6, 6, 6, 7, 5, 12, 13, 5, 6, 6, 6, 5, 11, 11, 5, 6, 10, 5, 5, 11, 6, 5, 5, 6, 5, 6, 5, 6, 6, 7, 7, 6, 5, 5, 7, 6, 5, 6, 5, 6, 5, 5, 7, 6, 6, 6, 3, 5)
h<-hist(data, breaks=0.5:40.5)
df<-data.frame(counts=h$counts, mids=h$mids)
df$even <- (df$mids%%2 == 0)
ggplot(df, aes(x=mids, y=counts, fill=even))+geom_bar(stat="identity")

If you look at the histogram of lengths, there is no bias towards even recognition site lengths except for length 6.

amateur observing - Affordable night sky photography

As an amateur with limited budget, I'd be interested in taking photos of the night sky, trying to capture more detail than human eye armed with a lens of comparable parameters to what I have in my camera normally could see. I doubt I'd ever get down to details as fine as Jupiter's moons, but I'd hope to see detail of some nebulae I have a hard time seeing through my inexpensive telescope, stars too dim to notice in less-than-perfect conditions etc. I'm interested in taking full-sky images just as well as zooms on specific objects too.

Currently, I have a lower-end SLC camera, with two lenses - good sharpness though lower aperture with 50-120mm focal length, and a wide-angle, high-brightness one (about 12-50mm) currently. Firmware hacks allow me to take photos of arbitrarily long time, and I have the remote to start and stop it without touching the camera, and generally software-wise the camera is quite powerful. One of the lenses (the longer focal length) is of "standard professional" quality level too.

Is this sufficient to get started? If so, what kind of settings should I use? If not, what other kind of entry-level equipment would I need to obtain/build on budget to get started with night sky photography?

zoology - What are the frequency ranges of most marine mammal vocalizations?

I am trying to determine a list of frequency ranges into which marine mammal vocalizations fall.
Ideally, I would like a list showing where the most popular marine mammal vocalizations fall, followed by the species name. That being said, I only really care about frequencies above 20 kHz, should they exist.

Example: (Numbers fabricated)

• Orcas : 30-40 kHz


• Dolphins : 100 kHz


• Blue Whales : 60-88 kHz

etc.

Even if the list is 'quick and dirty', thats ok. The list will essentially point me to which species' songs/sounds I need to study.

Some additional context, this wikipedia link as well as this one have some nice sound files of many marine mammals' songs/sounds. I am trying to avoid having to download each one and analyze their spectral content. (I could, but would rather not).

universe - Is there any practical use for astronomy?

This question begs the question, does everything need a practical use? The answer is a resounding no. What's the practical use of the Louvre, or of your local neighborhood public park where you enjoy weekend barbecues?

There are some things that are very worthwhile that have little or no economical gain. Your local neighborhood public park in fact has negative economic gain. Admission is free, but maintenance is not. Think of how much money your city would make if they sold it to a condominium developer, and how much money it would save by not having to pay to have the park maintained.

Despite having no obvious economic gain, some things are nonetheless worth quite a bit. Many of the sciences fall in this category. For example, what is the practical use of archeology? (There are some, but that's not the point.)

Astronomy, like archeology, the Louvre, and your local public park, doesn't need a practical economical purpose. The purpose of the science is good enough.

That said, there are practical applications of astronomy. The key application has been and still is navigation. Knowing the location of a ship at sea or the orientation of a vehicle in space requires astronomy.

A less direct but still very important application of astronomy is in how it informs physics. Kepler was an astronomer, not a physicist. (Those two disciplines were very, very distinct in Kepler's day). Yet Kepler's work informed Newton on how to describe gravitation. More recently, astronomy has informed physics that its standard model was not quite correct. The observed neutrino flux from the Sun (see http://en.wikipedia.org/wiki/Solar_neutrino_problem) was a third of what physics at the time said it should be. This resulted in a change to the standard model. Neutrinos have a small but non-zero mass, and they oscillate from one form to another.

Astronomy continues to inform physics to this day. Physicists (and astronomers) remain clueless with regard to what constitutes dark matter and dark energy. But whatever they are, they certainly do exist.

biochemistry - What are the olfactory chemicals in whiteboard/permanent markers and what do they bind to in the nose, lungs, and brain?

The smell of dry erase markers come from the chemicals ethanol, butanol and isopropyl alcohol. Like all chemicals inhaled through the nose, they bind to the Receptor neurons in the located in the back of the nose. The neurons interpret the chemicals using a 'lock-and-key' model but the specific way its coded and perceived in humans is still being researched and the process is not completely understood.

biotechnology - Electricity generated by the body and its applications?

You'd think if such devices were used in humans, they wouldn't require a change of lifestyle.

They don't say the power always decreases over time:

Katz’s snails, for example, produced up to 7.45 microwatts, but after
45 minutes, that power had decreased by 80%. To draw continuous power,
Katz’s team had to ramp down the power they extracted to 0.16
microwatts.

This is really a chemistry question. The glucose has to be brought to the fuel cell some way. In this case, the glucose is oxydized directly in the hemolymph. As oxygen PP in the hemolymph is always greater than glucose concentration(1), your limiting rate (which is related to the power you can get from the device) is that of glucose intake at the fuel cell. Therefore, the more you oxidize glucose per unit time, the greater intake you need to keep the output from dropping.

The glucose intake at the fuel cell is a function of biological parameters such as quantity eaten, metabolic efficiency, metabolic speed, blood flow, but also diffusion. The kinetics of glucose intake at the fuel cell are such that you can't ask for too much power for too long.

I suggest you read the article to get a more detailed answer. Nature news is good, but there's nothing like reading the real paper.

1 http://pubs.acs.org/doi/full/10.1021/ja211714w