1,447 research outputs found
The 2nd order renormalization group flow for non-linear sigma models in 2 dimensions
We show that for two dimensional manifolds M with negative Euler
characteristic there exists subsets of the space of smooth Riemannian metrics
which are invariant and either parabolic or backwards-parabolic for the 2nd
order RG flow. We also show that solutions exists globally on these sets.
Finally, we establish the existence of an eternal solution that has both a UV
and IR limit, and passes through regions where the flow is parabolic and
backwards-parabolic
To the modification of methods of nuclear chronometry in astrophysics and geophysics
In practically all known till now methods of nuclear chronometry there were
usually taken into account the life-times of only fundamental states of
-radioactive nuclei. But in the processes of nuclear synthesis in stars
and under the influence of the constant cosmic radiation on surfaces of planets
the excitations of the -radioactive nuclei are going on. Between them
there are the states with the excited -particles inside the parent
nuclei and so with much smaller life-times. And inside the large masses of
stellar, terrestrial and meteoric substances the transitions between different
internal conditions of radioactive nuclei are accompanied by infinite chains of
the -radiations with the subsequent -absorptions, the further
-radiations etc. For the description of the -decay evolution
with considering of such excited states and multiple -radiations and
-absorptions inside stars and under the influence of the cosmic
radiation on the earth surface we present the quantum-mechanical approach,
which is based on the generalized Krylov-Fock theorem.
Some simple estimations are also presented. They bring to the conclusion that
the usual (non-corrected) "nuclear clocks" do really indicate not to realistic
values but to the \emph{upper limits} of the durations of the -decay
stellar and planet processes.Comment: 6 pages, Standard LaTeX v.2
Wave-like aquatic propulsion of mono-hull marine vessels
The present paper describes the results of the experimental investigation of a small-scale mono-hull model boat propelled by a localised flexural wave propagating along the plate of finite width forming the boat’s keel. Forward propulsion of the boat was achieved through flexural wave propagation in the opposite direction, which is similar to the aquatic propulsion used in nature by stingrays. The model boat under consideration underwent a series of tests both in a Perspex water tank and in the
experimental pool. In particular, the forward velocity of the boat has been measured for
different frequencies and amplitudes of the flexural wave. The highest velocity achieved
was 32 cm/s. The thrust and propulsive efficiency have been measured as well. The
obtained value of the propulsive efficiency in the optimum regime was 51%. This
indicates that efficiency of this type of aquatic propulsion is comparable to that of
dolphins and sharks (around 75%) and to that of a traditional propeller (around 70%). In
contrast to a propeller though, the wave-like aquatic propulsion has the following
advantages: it does not generate underwater noise and it is safe for people and marine
animals
Experimental investigation of a mono-hull model boat with wave-like aquatic propulsion
Experimental investigation of a mono-hull model boat with wave-like aquatic propulsio
Towards a feasible implementation of quantum neural networks using quantum dots
We propose an implementation of quantum neural networks using an array of
quantum dots with dipole-dipole interactions. We demonstrate that this
implementation is both feasible and versatile by studying it within the
framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic
phonons. Using numerically exact Feynman integral calculations, we have found
that the quantum coherence in our neural networks survive for over a hundred ps
even at liquid nitrogen temperatures (77 K), which is three orders of magnitude
higher than current implementations which are based on SQUID-based systems
operating at temperatures in the mK range.Comment: revtex, 5 pages, 2 eps figure
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