128,822 research outputs found
Selection-mutation balance models with epistatic selection
We present an application of birth-and-death processes on configuration spaces to a generalized mutation4 selection balance model. The model describes the aging of population as a process of accumulation of mu5 tations in a genotype. A rigorous treatment demands that mutations correspond to points in abstract spaces. 6 Our model describes an infinite-population, infinite-sites model in continuum. The dynamical equation which 7 describes the system, is of Kimura-Maruyama type. The problem can be posed in terms of evolution of states 8 (differential equation) or, equivalently, represented in terms of Feynman-Kac formula. The questions of interest 9 are the existence of a solution, its asymptotic behavior, and properties of the limiting state. In the non-epistatic 10 case the problem was posed and solved in [Steinsaltz D., Evans S.N., Wachter K.W., Adv. Appl. Math., 2005, 11 35(1)]. In our model we consider a topological space X as the space of positions of mutations and the influence of epistatic potential
Created-by-current states in long Josephson junctions
Critical curves "critical current - external magnetic field" of long
Josephson junctions with inhomogeneity and variable width are studied. We
demonstrate the existence of the regions of magnetic field where some fluxon
states are stable only, if the external current through the junction is
different from zero. Position and size of such regions depend on length of the
junction, its geometry, parameters of inhomogeneity and form of the junction.
The noncentral (left and right) pure fluxon states are appeared in the
inhomogeneous Josephson junction with increase in the junction length. We
demonstrate new bifurcation points with change in width of the inhomogeneity
and amplitude of the Josephson current through the inhomogeneity.Comment: 7 pages, 8 figure
Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap
We present a rigorous theoretical study of low-temperature collisions of
polyatomic molecular radicals with ^1S_0 atoms in the presence of an external
magnetic field. Accurate quantum scattering calculations based on ab initio and
scaled interaction potentials show that collision-induced spin relaxation of
the prototypical organic molecule CH_2(X^3B_1) (methylene) and nine other
triatomic radicals in cold 3He gas occurs at a slow rate, demonstrating that
cryogenic buffer-gas cooling and magnetic trapping of these molecules is
feasible with current technology. Our calculations further suggest that it may
be possible to create ultracold gases of polyatomic molecules by sympathetic
cooling with alkaline-earth atoms in a magnetic trap.Comment: 5 pages, 3 figures, 1 tabl
Evidence for a new light spin-zero boson from cosmological gamma-ray propagation?
Recent findings by Imaging Atmospheric Cherenkov Telescopes indicate a large
transparency of the Universe to gamma rays, which can be hardly explained
within the current models of extragalactic background light. We show that the
observed transparency is naturally produced by an oscillation mechanism --
which can occur inside intergalactic magnetic fields -- whereby a photon can
become a new spin-zero boson with mass m << 10^(-10) eV. Because the latter
particle travels unimpeded throughout the Universe, photons can reach the
observer even if the distance from the source considerably exceeds their mean
free path. We compute the expected flux of gamma rays from blazar 3C279 at
different energies. Our predictions can be tested in the near future by the
gamma-ray telescopes H.E.S.S., MAGIC, CANGAROO and VERITAS. Moreover, our
result provides an important observational test for models of dark energy
wherein quintessence is coupled to the photon through an effective
dimension-five operator.Comment: 4 pages, 1 figur
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