zoology - If I put a cup over a spider, and leave it there for a day, will the spider survive?

To answer the first part of your question: it is extremely unlikely that the spider will die or be weakened after just one day.

Wolf spiders (Lycosids) are all predators. Due to variations in prey populations, and low efficiency of consumption at higher trophic levels, they are subject to inconsistent and unpredictable food supply (Greenstone and Bennett, 1980). They are very well adapted to this lifestyle and consequently, long periods of starvation often yield no behavioural changes (Persons, 1999). It is highly unlikely that the spider will die after just one day: Anderson, (1974) observed no changes in activity after starving Lycosa lenta (a species of wolf spider) for 30 days; and Tanaka and Ito, (1982) observed Pardosa astrigera (another species of wolf spider) living for up to 54 days of starvation. Age and sex of the spider are more likely to affect its behaviour and performance than food or oxygen availability (Persons, 1999).

As for oxygen consumption, Greenstone and Bennett, (1980) measure an oxygen consumption of 100µL/hr for wolf spiders. Assuming that your cup is of the size of the unit of volume of the same name, the cup (~0.237L), a small calculation (see figure) shows that there will be enough oxygen for the spider to survive for over 98 days. The oxygen concentration within the cup may decrease as it is used by the spider, however this is likely to have a minimal effect as a cup placed on a surface is unlikely to be hermetically sealed.

In short, oxygen availability is unlikely to have an effect on the spider before other limitations (such as food) are reached. However neither of these effects are likely to cause behavioural changes during the first month.

References

• Anderson, J.F., 1974. Responses to Starvation in the Spiders Lycosa Lenta Hentz and Filistata Hibernalis (Hentz). Ecology, 55(3), pp.576-585.


• Greenstone, M.H. & Bennett, A.F., 1980. Foraging Strategy and Metabolic Rate in Spiders. Ecology, 61(5), pp.1255-1259.


• Persons, M.H., 1999. Hunger effects on foraging responses to perceptual cues in immature and adult wolf spiders (Lycosidae). Animal Behaviour, 57(1), pp.81-88.


• Tanaka, K. & Itô, Y., 1982. Decrease in respiratory rate in a wolf spider,Pardosa astrigera (L. Koch), under starvation. Researches on Population Ecology, 24(2), pp.360-374.

What is Curved DNA? - Biology

I'm hardly an authority on this topic, but I distinctly recall an amazing report the mid-1990s of the co-crystal structure the yeast TATA binding protein in complex with DNA. The structure shows that TBP bends the DNA axis by approximately 80 degrees, presumably in order to expose bases and improve recognition. The structure is available at RCSB: http://www.rcsb.org/pdb/explore.do?structureId=1ytb . (Make sure you check out the Jmol view.)

Thermodynamically speaking, bending DNA would require energy. Therefore, DNA that was pre-bent (e.g., due to auxiliary binding proteins or composition bias) would improve binding.

So, I suspect that in the context DNA binding proteins, "curved" refers to the static curvature of unbound DNA or to the bending of DNA upon binding in order to facilitate recognition.

Tidal lock of earth and moon

The Earth and the Moon do interact, but because they have different sizes and masses the effect on each is different.

The Moon rotates once in its orbit around the Earth, causing it to constantly show the same face. This was the Earth's effect on the Moon due to tidal dragging by gravity.

It's pretty stable, the Moon will continue to show the same face to the Earth even as the tidal forces cause it to orbit farther and farther away.

We actually see slightly more than 50% of the Moon. The Moon's orbit causes its aspect to nod because its orbit is slightly elliptical and shimmy because it's not orbiting directly over the equator. Over time we actually see almost 60 percent of the surface of the Moon (an effect called libration).

The Moon's effect on the Earth has been to slow its daily rotation to 24 hours. In the past, the Moon was much closer to the Earth, and the day was much shorter. As time passes and the Moon moves into a wider orbit, the length of the Earth's day will increase (see e.g. this Scientific american post).

I've read that the Moon would recede to a certain point, then begin approaching the Earth again, but unfortunately the Sun will swell into a red giant before then and swallow the Earth and the Moon.

distances - Where can I look up the 3D positions of the closest stars?

You can determine the 3D position for a star, $p$, by using the distance from Earth, $R$, as well as the right ascension, $Omega$, and declination, $delta$, within the following formula.

$p = R begin{bmatrix} cos Omega cos delta \ sin Omega cos delta \ sin delta \ end{bmatrix}$

Note this will yield positions within the Earth-centered inertial reference frame.

molecular biology - In C. elegans, why does knock-down of cco-1 in some tissues increase lifespan, and knock-down of cco-1 in other tissues decrease lifespan?

Let us first answer the question: what is the effect of cco-1 knock-down in C. elegans. Durieux J., Wolff S. and Dillin A. in their paper "The cell-non-autonomous nature of electron transport chain-mediated longevity". Cell 144:79-91 (2011) provide the following explanation:

The life span of C. elegans can be increased via reduced function of
the mitochondria; however, the extent to which mitochondrial
alteration in a single, distinct tissue may influence aging in the
whole organism remains unknown.

So, by slowing-down the mitochondria function you manage to slow-down the normal wear-and-tear of the mitochondrial enzymes, which are normally responsible for the so-called respiratory chain -- one of the fundamental biological process for storing energy in cells (despite the common belief, ATP is rarely to store energy, but mostly to transfer it to the target!).

If we group the tissues where the knock-down leads to similar effects we will get muscle cells opposed by neurons and intenstine cells.

This is just my suggestion, but if we approach those groups with the idea of energy storage and re-use in mind, we'll see that muscle cells have much higher turnover of energy (for contraction and even more for dilation), whereas nerve and intestine cells are not that dependent upon energy and have much lower baseline of energy consumption and turnover.

Now we can suggest that cco-1 knock-down decreases the functions of mitochondria in muscle cells below the acceptable level and the decreased life span is due to depletion of mitochondrial energy storage under light stress conditions which would have been easily coped with under normal conditions. And vice versa, nervous/intenstine cells requiring a constant energy source at a much lower level just help the animal to cope with stress more effectively even during old age, leading to increased life span.

observation - Is stacking welder's glasses a safe way to watch at the eclipse?

You can find in many place on the Internet that welder's glass #14 is good for looking at an eclipse. Tomorrow (March, 20th 2015 at 10:45 CET) there's a solar eclipse and yesterday I could only find glasses #11 and #9. I tried briefly this morning, and combining a #11 and a #9 was giving me a good view of the sun. Using 2 #11 gave a too dark image. Now, I read different opinions on the internet.

Against (Perkins Observatory):
http://perkins.owu.edu/solar_viewing_safety.htm

Be careful that you use the right kind of glass! Welder's glass is
numbered from 1 to 14 with 14 being the darkest. It is only number 14
glass that is dark enough for solar viewing! And NO STACKING! A pair
of number 7's or a 10 and a 4 together DO NOT have the same protection
as a single piece of number 14 (see unsafe methods for more details).

Favorable (Royal Astronomical Society of Canada):
https://www.rasc.ca/tov/safety

If SN14 filter is not available, it is possible to combine lower shade
numbers to get roughly the same level of eye protection from solar
radiation, e.g. combining SN 6 and SN 8 filters. However the image
quality may be considerably poorer than that seen through the single
SN14 filter

I could not find a table or something explaining which kind of protection gives each number; according to the Canadian website, the only concern is about how much infrared light goes through, ultraviolet does not seem to be a problem in almost any case (I was surprised to read that).

Note: It's not my intention to open here the discussion on what could be other safe methods to watch the eclipse, this is well explained everywhere around. I read too late about the eclipse to order specific glasses.

Edit:
One of the answers here report the following formula: (more insight at this link)

13 or darker is safe enough. Also, you CAN add up welding glass, using
the formula S(sum) = S1 + S2 -1. S(sum) should be greater than or
equal to 13

fundamental astronomy - Finding Mass of Star with only Luminosity

Sounds like homework (correct me if that assumption is wrong, as you may want a somewhat different answer then.), so here is a hint:

Clean up the equation first, to something that looks more like an equation for mass:

$$frac{L}{L_{sun}} = left(frac{M}{M_{sun}}right)^{3.5}$$

$$left(frac{L}{L_{sun}}right)^{frac{1}{3.5}} = frac{M}{M_{sun}}$$

botany - How will rising carbon dioxide levels in the troposphere affect photosynthetic producers?

There are several key ways in which rising atmospheric CO₂ concentrations will affect photosynthesis, and these are related to the different types of photosynthesis. In order to properly answer your question, I'll provide some background about photosynthesis itself.

Photosynthesis evolved in a high-CO₂ atmosphere, before the oxygen-enrichment of the atmosphere (which actually happened as a result of photosynthesis). Most plant species operate C3 photosynthesis. In these plants, carbon dioxide diffuses into the cell where it is fixed by Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) into a 3-carbon molecule (hence C3), which is then polymerised to make sugars. A crucial fact about RuBisCO is that it has both carboxylase (carbon-fixing) activity and oxygenase (oxygen-fixing) activity. This means that oxygen and carbon dioxide compete for the active site on the enzyme complex, leading to RuBisCO being quite inefficient and slow at fixing carbon in higher oxygen concentrations. That didn't matter in the high-CO₂ atmosphere of the early Earth, but in todays atmosphere O₂ concentrations are high enough that they severely limit the productivity of C3 plants.

However, plants haven't just been growing slowly all that time - several mechanisms for increasing photosynthetic efficiency have evolved. The most influential systems involve concentrating carbon dioxide in a particular area, excluding oxygen, and concentrating RuBisCO in that same area. This avoids the oxygen competition for the active site and allows RuBisCO to operate more efficiently. The key adaptation here is C4 photosynthesis - the system which is present in most grasses and many of the most productive plants on Earth (e.g. maize, sugarcane, Miscanthus). It has evolved at least 62 times independently. It works by having RuBisCO concentrated within 'bundle sheath' cells which are surrounded by a layer of suberin wax. This layer prevents CO₂ escaping and O₂ from getting in. CO₂ from the atmosphere is then fixed in different cells - 'mesophyll cells' - by another enzyme - Phosphoenolpyruvate carboxylase (PEPC), resulting in a four-carbon molecule (hence C4). This 4-carbon acid, (malate or oxaloacetate depending on the system) is then shuttled into the bundle sheath cells. There, the CO₂ is released again by a variety of enzymes depending on the system, creating a high CO₂ concentration in the cell where RuBisCO can then work efficiently.

In general, C4 plants are much (about 50%) more efficient than their C3 counterparts, and they are particularly well adapted to high temperatures and moist environments. So, to answer your first question: as atmospheric CO2 levels continue to rise, C3 plants will gradually be able to photosynthesise more efficiently. Interestingly though, C4 plants are predicted to also benefit from increased atmospheric CO₂. If global temperatures rise as predicted, both C3 and C4 plants will be able to operate more efficiently than they currently do, up to a maximum temperature beyond which enzymes will begin to denature faster and efficiency will drop. One consideration is that the difference in efficiency between C3 and C4 systems will decrease, which may significantly alter the makeup of plant communities around the world.

This is a vast oversimplification, but it is accurate for the predicted overall effects. Localised effects (i.e. productivity changes in a particular region or for a particular crop) will depend on habitat, physiology, etc.

Some key papers to launch you into the literature:

• Leakey, A.D.B., Bernacchi, C.J., Dohleman, F.G., Ort, D.R. & Long, S.P. (2004) Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres? An analysis of diurnal courses of CO2 uptake under free‐air concentration enrichment (FACE). Global Change Biology. [Online] 10 (6), 951–962. Available from: doi:10.1111/j.1529-8817.2003.00767.x [Accessed: 31 January 2012].


• Morgan, J.A., LeCain, D.R., Pendall, E., Blumenthal, D.M., Kimball, B.A., Carrillo, Y., Williams, D.G., Heisler-White, J., Dijkstra, F.A. & West, M. (2011) C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland. Nature. [Online] 476 (7359), 202–205. Available from: doi:10.1038/nature10274 [Accessed: 31 January 2012].

Are cells really the basic unit of all life?

According to Gerry Joyce: "Life is a self-sustained chemical system capable of undergoing Darwinian evolution."

From a meta-analysis of 123 definitions of life: "Life is metabolizing material informational system with ability of self-reproduction with changes (evolution), which requires energy and suitable environment."

According to Alexander Oparin: “Any system capable of replication and mutation is alive”.

At hand are some key elements in order to match these criteria. Maintaining a Darwinian cycle requires replication, mutation, and selection. Thus, we can break down the above into 5 criteria (personal communication with Gerry Joyce).

• Life stores information


• Life reproduces its information


• Life alters that information


• Life does something with that information (uses energy)


• Life does all of this in a self-sustained manner

I would point out that the above criteria is quite different from what is currently on wikipedia described by metabolism and homeostasis. There are certainly additional criteria that certainly raise the threshold for what may be considered life. The common discussion revolves around viruses which do many of these things but not in a self-sustained way.

The question at hand then asks if cells are the minimum unit of life? What makes a cell a cell is that there is compartmentalization. The underlying reason behind this compartment is due to the necessity of tying the phenotype to the genotype. Paraphrasing using our definition of life, it links the information with the function that the information carries out. In the modern biological scheme, it keeps the proteins (phenotype) with the DNA (genotype).

The necessity of compartmentalization is negated when the phenotype is already linked with the genotype. The most frequent example is RNA where the material that carries the information is also the material that carries out its function. It tend, is reasonable to hypothesize that life can be made entirely with RNA without the need for compartmentalization (although compartmentalization certainly helps see Paegal and Joyce and Chen and Szostak).

Recent experiments by Gerry Joyce and others have been able to satisfy several of the requirements of life. The have self-replicating RNAs, that store information, that reproduce their information, that introduce alterations to their information, and do it in a self-sustained manner. What Gerry and his colleagues agree on is that their current self-replication Ribozyme system doesn't do anything particularly novel. However, by introducing a larger variety of functional elements to their ribozymes perhaps they will.

stellar evolution - If a star were to suddenly lose nearly all of its stored heat, would it be able to return to its normal state?

If you suddenly sucked all the heat out of a normal star like the Sun, nuclear reactions would cease, the gas pressure would fall to zero. The star would collapse, initially on a freefall timescale (about 1 hour for the Sun).

The released gravitational potential energy would half be radiated away and half would go into re-heating the interior. The temperature would rapidly rise, the collapse would be halted, nuclear reactions would restart, the star would slowly expand again and a thermal and hydrostatic equilibrium should be restored on a Kelvin-Helmholtz timescale (about 10 million years for the Sun).

One way to see this, is to compare the current thermal content of a star with its capacity for generating new heat by nuclear reactions. e.g. approximate the Sun as a uniform ball of ideal gas at an average temperature of a few million degrees. The thermal content is roughly $10^{41}$ J. The Sun generates this much energy in nuclear reactions in only 8 million years - coinciding with the timescale to reestablish an equilibrium. Or you could compare it with the gravitational potential energy of around $2times 10^{41}$ J. i.e. There is enough gravitational potential energy to reheat the Sun.

However, not everything would be a continuation. The collapse and reheating would be similar to the star repeating its pre main sequence phase. During this phase the star becomes fully convective and so the core material would get completely mixed with the rest of the star again. This would have the effect of rejuvenating the star as a new zero age main sequence star, but with a slightly higher helium abundance.

gravity - Is there any way a meteor can hit at less than escape velocity?

Edited.
No if you talk about the escape velocity form Earth. This follows simply from the fact that energy $E$ is conserved. An object that is not gravitationally bound to Earth has $E>0$ and hence $v>v_{mathrm{esc}}$ when hitting ground.

---

Yes, if you meant the escape velocity from the Solar system, because the Earth moves with $v_{rm Earth}=v_{rm escape}/sqrt{2}$ relative to (but not towards) the Sun. Here $v_{rm escape}=sqrt{2GM_{odot}/1{rm AU}}$ is the local escape speed from the Sun, while $v_{rm Earth}=sqrt{GM_{odot}/1{rm AU}}$ is the speed of the local circular orbit. An object at 1AU form the Sun and bound to the Sun cannot have speed greater than $v_{rm escape}$.

Now, the impact speed of an object that moves at $v_{rm escape}$ can be as low $v_{rm escape}-v_{rm Earth}=v_{rm escape}(1-1/sqrt{2})$ if it hits Earth "from behind", i.e. moving in the same direction as Earth at the time of impact.

Note also that meterors typically move not faster than $v_{rm escape}$, for they don't come from outer space, but from the Solar system.

solar system - Were there any images of a transitary event of Jupiter or Saturn as imaged by a deep probe mission

I'm quite certain that there isn't any actual images of a transitory event of Jupiter or Saturn across the solar disk from say e.g.,s the Voyager probe, Pioneer 10/11 or even recent New Horizons mission?

Another related question I have, what would the approximate transit of Jupiter look like as seen from Saturn. The distance between Saturn and Jupiter is approximately 4-5AU, and the diameter of Jupiter is one tenth that of the Sun's. Are we looking at perhaps a transit which covers 10-15% of the solar disk?

N.B. Please note I understand that to observe a transit of Jupiter we have to be superior to it in the Solar System, hence I am asking for images taken by deep Solar System probes only.

immunology - How does the immune system "learn" from a vaccine?

Vaccines work by introducing an attenuated strain of the pathogen (or alternatively the antigens that are normally present on the pathogens surface) into the body, whereupon the body mounts an immune response. As this will (hopefully) be the first time that the body has encountered the antigens on the pseudo-pathogen's surface, the response is called the primary response.

This consists of two main divisions: the cell mediated pathway and the humoral pathway. In vaccination it is the humoral pathway that is important. This is where a division of white blood cells (B-Cells) produce antibodies that are complementary to the antigens on the pathogen surface, causing a negative effect to the pathogen (death, inability to reproduce, de-activation of toxins, etc.). However as each B-Cell produces a different antibody, there needs to be a mechanism to select the correct one:

1. Antigen Presentation (technically part of the cell-mediated-response) - a phagocyte engulfs the pathogen and displays the pathogenic antigens on its own surface.


2. Clonal Selection - B-Cells that are attracted to the invasion site attempt to bind their antibodies onto the pathogen's antigens. It takes time for this to occur successfully as you are essentially waiting for the correct mutation to happen.


3. Clonal Expansion - Once a complementary antibody producing B-Cell has been found it is then activated with the help of a T-Helper cell. This causes it to divide rapidly whereupon these cloned specific B cells can secrete their antibodies which will cause detriment to the pathogen.

---

It's at this point that I can start to answer your specific question. The large clone of B cells will then sub-divide into two types. Plasma Cells remain in the blood and produce antibodies to fight the infection. The other type, much smaller in proportion, are called Memory Cells. These cells have a very long lifetime and move to lymph nodes across the body (including the spleen), where they remain dormant until the same pathogen is found again.

When this is the case, the memory cells are activated by T-helpers so that they can divide into massive numbers of plasma cells to fight the infection the second time. This secondary response is a much faster as the clonal selection stage does not have to wait for the right mutation - they are already waiting in the lymph nodes. The response is also much stronger as each memory cell can produce large numbers of plasma cells - i.e. you can start with multiple activated B-cells (as many as you have memory cells) rather than just the one that has mutated into a complementary shape in the primary immune response.

The aim of the vaccine is for the secondary response to be so quick that potentially life threatening symptoms do not occur; the body has time to find and store the correct antigen in a safe environment as the pathogen has been deactivated.

orbit - Longitude of the Ecliptic

I originally went to math.stackexchange.com and they suggested I try here as well.

I'm trying to figure out how to calculate times of moonrise and moonset for a given position on the earth on a particular date. I'm using Vallado's Fundamentals of Astrodynamics and Applications because there is an example in the book that lays out a simplified process. I'm stuck at the point where I'm trying to calculate Longitude of the ecliptic for the Moon. The formula is below where T = -0.013634497.

λEcliptic = 218.32° + 481,267.8813T + 6.29Sin(134.9 + 477,198.85T) - 1.27Sin(259.2 - 413,335.38T) + 0.66Sin(235.7 + 890,534.23T) + 0.21Sin(269.9 + 954,397.70T) - 0.19Sin(357.5 + 35,999.05T) - 0.11Sin(186.6 + 966,404.05T)

The expected answer is -0.8412457°. However, I'm unable to figure out how to get this answer. My calculations are below:

1) 218.32° + 481,267.8813T = -6343.525

2) 6.29Sin(134.9 + 477,198.85T) = 5.963779

3) -1.27Sin(259.2 - 413,335.38T) = -0.900843

4) 0.66Sin(235.7 + 890,534.23T) = -0.292285

5) 0.21Sin(269.9 + 954,397.70T) = -0.126871

6) -0.19Sin(357.5 + 35,999.05T) = 0.138211

7) -0.11Sin(186.6 + 966,404.05T) = 0.054722

Simply adding or subtracting gets me -6338.688731. How can I get the value -0.8412457° from this. My trigonometry is rusty and I'm not sure how to get the right answer. Any help would be greatly appreciated. Thanks.

zoology - intravenous (IV) in the tail vein of an anaesthetized mouse

Cleaning the tail with ethanol is of some help and also, as you said, warming the tail. We sometimes put one of those flexible lamps (such as this) to heat up only the tail.

When anesthesized (ketamine/xylazine or isoflurane) we keep our mice on a heated pad anyways.

Cannulation in the tail does not sound like a good idea to me, especially if you are going to have the animal wake up afterwards. If you're going to cannulate then go for the jugular, but be aware that doing it on a mouse requires quite a bit of experience and it's definitely way longer than a tail injection.

It really depends on your experiment

Is there any difference between rotation axis 90 degrees and 270 degrees?

No, I don't believe there's any meaningful distinction.

A planet's axial tilt can be thought of as a 2-dimensional quantity: its angle relative to the ecliptic (or to whatever baseline you're using), and the direction in which it's tilted. When we talk about a planet's axial tilt as a number of degrees, we're only talking about the first component.

A planet whose rotation axis is perpendicular to the ecliptic would have a tilt of 0°. If its rotation axis is parallel to the ecliptic (rotating "on its side"), its tilt is 90°. If its axis is "vertical" but it's spinning backwards, its tilt is 180°. The range from 0° to 180° is enough to express all possible tilts, both prograde and retrograde.

Consider taking a planet with a 0° tilt and tilting its axis by 270°. The result is exactly the same as tilting it 90° in the opposite direction. Since the axial tilt is usually expressed as just the magnitude of the tilt, and not its direction, the distinction between 90° and 270° can be ignored.

And if we want to express the direction as well, we'll just say that it's tilted 90° in some specified direction.

We could have had a convention where the tilt ranges from 0° to just under 360°, with the direction specified more narrowly, but that would be less useful; the particular direction of a planet's axial tilt is less interesting than its magnitude. Also, the direction varies over time due to precession.

We could also have had a convention where the tilt ranges from 0° to 90°, and we also specify whether it's retrograde or not; then Venus would have a tilt of 3° rather than 177°.

Which are the best American universities/colleges for observational astronomy?

Out of curiosity: where does this limit of 70 lightyears come from? Exoplanets can be detected to way beyond that. This strikes me as a strangely restrictive limit.

Be that as it may. There are several great astronomy departments in the US, and it really depends on what you want to do exactly. For exoplanets, Harvard would be a great choice. Professor David Charbonneau is a heavy weight in the field.

Similarly, many of the other renowned Universities have good astronomy departments. Yale, for instance, or Berkeley (although since the Geoff Marcy incident I imagine the exoplanet department has taken a hit).

So at this point it is not really a matter of choosing 'the best' University. I suggest you have a look at some papers by the professors at different Universities, to get a sense of what you'd like to work on.

And don't forget: for your research to be fruitful the environment is also very relevant. Just have a look and see what city you'd like to live in.

atmosphere - Why do most meteors vanish just before hitting the ground?

Only very few meteors actually make it anywhere near the surface of Earth; most burn up 75–100 km above the surface. From your point of view, however, the curvature of Earth's surface may make it look as if they get much closer, and even fall below the horison. But depending on where you live, the horison often has quite a lot more background light (e.g. from cities far away). That means that when they get near the horison, which you may interpret as "several feet above the ground", the seemingly disappear.

general relativity - Can we measure/detect GR light bending during solar eclipse using ordinary equipment?

The deflection you are looking for is $sim 1.7$ arc seconds, which should be within the seeing limits at a good site. It should also be within the resolution limits of a telescope with $ge200$mm diameter primary.

Having said that you will not be able to see it with the naked eye, you will need to be able to photography the star field during the eclipse and again when it is visible at night and then do some arduous plate measuring and data reduction to detect the shifts of stars in the field.

So amateur equipment is up to detecting the bending of light around the Sun in a total eclipse, but if by witness you mean see the stars move with the naked eye the answer is almost certainly no.

biochemistry - What limits the maximum spacing of Nodes of Ranvier and which organisms tend to have the widest gaps?

This is best answered via something called cable theory. Basically, as the action potential (AP) propagates along the membrane of the axon, it's tripping voltage gated channels that "renew" the flux of ions into the stream at the nodes. There are no ion channels under the sheathing (or they are there anatomically and inactive, but I don't remember), so the current is able to zip through that area. There's no renewal of AP, but there's no loss due to leak of ions either. Since there's no influx of ions from outside of the membrane until the next node, the capacitance and resistance of the membrane is exponentially decaying the voltage. So, if the distance between the nodes was too long, the voltage would just die off and the AP wouldn't propagate.

I don't have any anatomical data about individual species, but know that only the smaller diameter axons require sheathing to compensate for the slower ion flow due to higher resistance (e.g., the squid giant axon(not to be confused with the "giant squid" axon) has no myelination due to its large diameter).

Are there collected data about the direction of rotation of black holes and the direction of the magnetic field?

Is there a relation between the direction of rotation of black holes or neutron stars and the magnetic dipole moment of BH or neutron stars? BTW, are there different directions of this two parameters for suns?

Edit

I want to be sure there are or there are not the direction of rotation (which one can expressed by an arrow on the rotation axis) and the direction of the magnetic field (expressed by an arrow from the south to the north pole (both arrows are simple conventions)) parallel only. I'm not sure that the direction of the magnetic field is observable at all. And the comment from Zibadawa Timmy about pulsars perhaps a good extension to my question about BH, neutron stars and Suns.

mars - What is the next planned mission that can discover life on another planet?

The Exomars rover of ESA and Roscosmos would be the obvious answer. To be launched in 2018. It will drill 2 meters deep and as far I know is the only mission since the Vikings in the 1970's, to explicitly be equipped to find biosignatures, signs of life. But the Russians, who will land the rover, have had a very poor Mars mission success rate, ESA cooperates with them since NASA abandoned the project a few years ago, and ESA's only own landing attempt on Mars failed too, Beagle 2. And some biologists think it is more challenging to detect sparse exotic microbial life than what that rover is capable of. It weights about 1/3 of MSL Curiosity, and underground life can maybe be very local.

I want to recommend the blogger Robert Walker who writes at great length and well informed, still interestingly speculative, about possibilities for life on Mars, what one maybe should be looking for.

I should add that since 1960 SETI uses telescopes to pick up evidence of interstellar life which is powerful enough to somehow change its environment to make itself astronomically detectable. That's the other main potential except for probes in the Solar system. But not even SETI people sit up waiting for it any more.