How long is DNA stable in a freezer?

If the DNA is pure, it should last quite a long time. If there are enzymes and other biological molecules in there, -80C will work much better.

I think you could keep pure DNA at -20C practically indefinitely.

Purity is the main issue there, also pH stabilized, sealed properly, etc. That makes all the difference.

Cosmological deflation? - Astronomy

There are a number of flaws with your idea (despite the relativity breaking transatlantic journey times that would be possible).

Inflation is a popular theoretical model put forward to solve three main issues with the Big Bang cosmology: the horizon problem, the flatness problem & the magnetic monopole problem (see the wiki for details). It consists of a scalar field called the inflaton, a physical field that pervades all space. During inflation it undergoes a phase transition to a lower energy state, releasing huge amounts of energy that drive the expansion. To force the field back to a higher energy state would require inconceivable amounts of energy, and have to be applied across the entire universe. Not only is this impossible, but also annoyingly prevents its use for local galactic travel.

Or maybe a technically very advanced civilization could keep its solar system inflated by the time of a deflation of the whole universe

I assume you mean contraction, as opposed to the current expansion that we see today due to dark energy. Again this would be unfeasible due to the reasons outlined above, and if contraction was to proceed to it's conclusion, i.e. a singularity like the Big Bang, then no information from this universe could be carried through that singularity, even if there was another universe on the other side.

visualisation of the universe's expansion

You were correct, you teacher was incorrect.

It is the space that expands - much as a surface of a balloon does.

An explosion is a poor analogy in contrast because - as you suggest - it implies something to expand into.

For another way, not as accurate as the balloon analogy but maybe helpful - imagine being trapped inside an expanding loaf of bread in an oven. You have no knowledge of the world outside the loaf - and you may assume the loaf is infinite in extent. But as the dough rises the gaps inside the loaf get larger without the mass of the loaf itself increasing. You could compare our position in the universe to being inside such an infinite loaf.

distances - Can we tell how fast bodies are moving away by measuring their frequency?

Your understanding is correct. The doppler shift observed from a galaxy is the sum of its peculiar velocity with respect to the "Hubble flow" and the redshift due to the Hubble flow, which is caused by the expansion of the universe.

There is no direct way from a spectrum to separate these two components - they have the same qualitative result.

In principle, the expansion of the universe (or a change in the peculiar velocity) could be directly measured by looking for a change in redshift with time, which would depend on the cosmological parameters.

This is an extremely small effect and is confused by the peculiar motions of individual galaxies. Nevertheless, measuring this redshift drift is one of the prime goals of the Codex Instrument on the E-ELT (see Pasquini et al. 2010, http://esoads.eso.org/abs/2010Msngr.140...20P )
using Lyman alpha absorption systems towards distant quasars. This experiment is also planned for the Square Kilometre Array, using the 21cm line (Kloeckner et al. 2015 http://arxiv.org/abs/1501.03822 ).

In both cases, to overcome the experimental uncertainties (eg at 21 cm, it amounts to line drifts of 0.1 Hz over a decade), then observations of millions of galaxies must be combined.

There is no prospect of measuring this effect in an individual galaxy, furthermore I fear your understanding of cosmological redshift is flawed. The dependence on distance is a statistical average, not an absolute dependence. Individual galaxies are moving in individual gravitational potentials from objects around them. This gives them their peculiar velocities with respect to the flow. This velocity could increase or decrease as a galaxy got further away, but is never expected to be large enough to be detectable on human timescales for any individual galaxy. In addition, any change in peculiar velocity should average to zero when looking at millions of galaxies, leaving the redshift drift due to the expansion.

How can a supernova affect black hole in a binary system?

The likely result would either be a black hole-black hole binary system; a neutron star-black hole binary system, or the black hole and the compact remnant from the second supernova explosion would go their separate ways at reasonably high speeds.

You cannot disrupt a black hole in this way. In fact all that will happen to the original black hole is that it will likely get a bit more massive from accreting some of the supernova ejecta.

newtonian gravity - Can the centripetal force be inverted?

The simple answer is no.
The centripetal force is what we call an 'inertial force', as contrary to 'fundamental force'. This means there are no charges attached to it, and no field (-analogue) that propagates this force - unlike e.e. for electromagnetism and gravity.

A inertial forces originate purely in changes of your frame of reference (or 'viewpoint') and how this frame moves relative to your originating frame.
The name fictious force for this concept is also very common. To this the corresponding wikipedia-page discusses an example with a deccelerated bus, which I can only very strongly recommend to study in order to understand the concept of inertial forces.

The direction of the centripetal force is tied to the acceleration at any given moment. Any path that a massive object has through space has a curvature at every point of this path. This local curvature defines a so-called osculating circle (see below) towards which the centripetal force points. Thus, there is no way to reverse this.

(c) Wikipedia, Wiki commons license

Sorry, if this answer seems a bit vague, but I think this is the best I can do without going deeper into the math of classical mechanics that covers those topics.

biochemistry - Why insects are so energy-efficient while flying?

Insect flight muscle is capable of achieving the highest metabolic rate of all animal tissues, and this tissue may be considered an exquisite example of biochemical adaptation.

Locusts, for example, may (almost instantaneously) increase their oxygen consumption up to 70-fold when starting to fly. In humans, excercise can increase O₂ consumption a maximum of 20-fold, and for birds in flight the figure is about 10-fold (Wegener, 1996; Sacktor, 1976).

As Wegener (1996) has put it (in his definitive paper):

The aerobic scope (the ratio of maximal to basal rate of respiration) of insects is unrivalled in the animal kingdom

Flight is powered by ATP hydrolysis, and these impressive metabolic rates are achieved by very effective control of ATP hydrolysis and regeneration.

• Metabolism is aerobic, thus allowing for much more efficient ATP production from hexoses (as compared with, say, anaerobic metabolism).




• Flight muscle may account for up to 20% of body mass.



• In insects, haemoglobin and myoglobin are absent. Instead, gaseous O₂ is transported to the tissues by a system of tubules and deposited so close to the site of consumption that (seemingly) it may reach mitochondria by diffusion.



• Locusts fuel flight by burning sugars in the early stages, gradually changing to use lipids as fuel. (In bees, flight is totally fuelled by hexose consumption).
  
  This is achieved by effective control of glycogen breakdown and glycolysis, by modifying the activity glycogen phosphorylase (glycogen breakdown) and phosphofructokinase (PFK), a key control enzyme of glycolysis.



• There is an enormous literature on these topics, but suffice it to say, in the case of glycolysis, control is very efficiently achieved by allosteric regulation of PKF, where fructose 1,6-bisphosphate and fructose 2,6-bisphosphate play key roles (see Sacktor, 1976).



• This allosteric control very effectively allows glycolysis to be (almost instantaneously) turned on and operate at a maximum value, and to be (almost instantaneously) turned off.

References

Wegener, G. (1996) Flying insects: model systems exercise physiology
Experientia May 15;52(5):404-12. (See here)

Sacktor B. (1976) Biochemical adaptations for flight in the insect.
Biochem Soc Symp. 1976;(41):111-31. (See here)