1,371 research outputs found
Kinetic Path Summation, Multi--Sheeted Extension of Master Equation, and Evaluation of Ergodicity Coefficient
We study the Master equation with time--dependent coefficients, a linear
kinetic equation for the Markov chains or for the monomolecular chemical
kinetics. For the solution of this equation a path summation formula is proved.
This formula represents the solution as a sum of solutions for simple kinetic
schemes (kinetic paths), which are available in explicit analytical form. The
relaxation rate is studied and a family of estimates for the relaxation time
and the ergodicity coefficient is developed. To calculate the estimates we
introduce the multi--sheeted extensions of the initial kinetics. This approach
allows us to exploit the internal ("micro")structure of the extended kinetics
without perturbation of the base kinetics.Comment: The final journal versio
Invasive Allele Spread under Preemptive Competition
We study a discrete spatial model for invasive allele spread in which two
alleles compete preemptively, initially only the "residents" (weaker
competitors) being present. We find that the spread of the advantageous
mutation is well described by homogeneous nucleation; in particular, in large
systems the time-dependent global density of the resident allele is well
approximated by Avrami's law.Comment: Computer Simulation Studies in Condensed Matter Physics XVIII, edited
by D.P. Landau, S.P. Lewis, and H.-B. Schuttler, (Springer, Heidelberg,
Berlin, in press
Changes in epidemiological patterns of sea lice infestation on farmed Atlantic salmon, Salmo salar L., in Scotland between 1996 and 2006
Analyses of a unique database containing sea lice records over an 11 year period provide evidence of changing infestation patterns in Scotland. The data, collected from more than 50 commercial Atlantic salmon farms, indicate that both species of sea lice commonly found in Scotland, Lepeophtheirus salmonis and Caligus elongatus, have declined on farms over the past decade. Reductions for both species have been particularly marked since 2001 when more effective veterinary medicines became available. Treatment data were also available in the database and these show a growing trend towards the use of the in feed medication emamectin benzoate (Slice), particularly in the first year of the salmon production cycle. However, this trend to wards single product use has not been sustained in 2006, the latest year for which data are available. There is some evidence of region to region variation within Scotland with the Western Isles experiencing higher levels of infestation. However, compared to the levels observed between 1996 and 2000, all regions have benefited from reduced lice infestation, with the overall pattern showing a particular reduction in the second and third quarters of the second year of production
Gate-controlled spin polarized current in ferromagnetic single electron transistors
We theoretically investigate spin dependent transport in ferromagnetic/normal
metal/ferromagnetic single electron transistors by applying master equation
calculations using a two dimensional space of states involving spin and charge
degrees of freedom. When the magnetizations of ferromagnetic leads are in
anti-parallel alignment, the spins accumulate in the island and a difference of
chemical potentials of the two spins is built up. This shift in chemical
potential acts as charge offset in the island and alternates the gate
dependence of spin current. Taking advantage of this effect, one can control
the polarization of current up to the polarization of lead by tuning gate
voltages.Comment: 5 pages, 4 figure
Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers
In antiferromagnetically coupled superlattices grown on (001) faces of cubic
substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or
Fe/Cr, the magnetic states evolve under competing influence of bilinear and
biquadratic exchange interactions, surface-enhanced four-fold in-plane
anisotropy, and specific finite-size effects. Using phenomenological
(micromagnetic) theory, a comprehensive survey of the magnetic states and
reorientation transitions has been carried out for multilayer systems with even
number of ferromagnetic sub-layers and magnetizations in the plane. In
two-layer systems (N=2) the phase diagrams in dependence on components of the
applied field in the plane include ``swallow-tail'' type regions of
(metastable) multistate co-existence and a number of continuous and
discontinuous reorientation transitions induced by radial and transversal
components of the applied field. In multilayers (N \ge 4) noncollinear states
are spatially inhomogeneous with magnetization varying across the multilayer
stack. For weak four-fold anisotropy the magnetic states under influence of an
applied field evolve by a complex continuous reorientation into the saturated
state. At higher anisotropy they transform into various inhomogeneous and
asymmetric structures. The discontinuous transitions between the magnetic
states in these two-layers and multilayers are characterized by broad ranges of
multi-phase coexistence of the (metastable) states and give rise to specific
transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio
Recoil correction to the ground state energy of hydrogenlike atoms
The recoil correction to the ground state energy of hydrogenlike atoms is
calculated to all orders in \alpha Z in the range Z = 1-110. The nuclear size
corrections to the recoil effect are partially taken into account. In the case
of hydrogen, the relativistic recoil correction beyond the Salpeter
contribution and the nonrelativistic nuclear size correction to the recoil
effect, amounts to -7.2(2) kHz. The total recoil correction to the ground state
energy in hydrogenlike uranium (^{238}U^{91+}) constitutes 0.46 eV.Comment: 16 pages, 1 figure (eps), Latex, submitted to Phys.Rev.
Evaluation of the low-lying energy levels of two- and three-electron configurations for multi-charged ions
Accurate QED evaluations of the one- and two-photon interelectron interaction
for low lying two- and three-electron configurations for ions with nuclear
charge numbers are performed. The three-photon interaction is
also partly taken into account. The Coulomb gauge is employed. The results are
compared with available experimental data and with different calculations. A
detailed investigation of the behaviour of the energy levels of the
configurations , near
the crossing points Z=64 and Z=92 is carried out. The crossing points are
important for the future experimental search for parity nonconserving (PNC)
effects in highly charged ions
The experimental program for high pressure gas filled radio frequency cavities for muon cooling channels
An intense beam of muons is needed to provide a luminosity on the order of 10(34) cm(-2)s(-1) for a multi-TeV collider. Because muons produced by colliding a multi-MW proton beam with a target made of carbon or mercury have a large phase space, significant six dimensional cooling is required. Through ionization cooling - the only cooling method that works within the lifetime of the muon - and emittance exchange, the desired emittances for a Higgs Factory or higher energy collider are attainable. A cooling channel utilizing gas filled radio frequency cavities has been designed to deliver the requisite cool muon beam. Technology development of these RF cavities has progressed from breakdown studies, through beam tests, to dielectric loaded and reentrant cavity designs. The results of these experiments are summarized
A review of size and geometrical factors influencing resonant frequencies in metamaterials
Although metamaterials and so-called left-handed media have originated from theoretical considerations, it is only by their practical fabrication and the measurement of their properties that they have gained credibility and can fulfil the potential of their predicted properties. In this review we consider some of the more generally applicable fabrication methods and changes in geometry as they have progressed, exhibiting resonant frequencies ranging from radio waves to the visible optical region
Two-electron self-energy contribution to the ground state energy of heliumlike ions
The two-electron self-energy contribution to the ground state energy of
heliumlike ions is calculated both for a point nucleus and an extended nucleus
in a wide interval of Z. All the two-electron contributions are compiled to
obtain most accurate values for the two-electron part of the ground state
energy of heliumlike ions in the range Z=20-100. The theoretical value of the
ground state energy of heliumlike uranium, based on currently available theory,
is evaluated to be -261382.9(8) eV, without higher order one-electron QED
corrections.Comment: 12 pages, 1 figure, LATE
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