17,182 research outputs found
Fourier mode dynamics for the nonlinear Schroedinger equation in one-dimensional bounded domains
We analyze the 1D focusing nonlinear Schr\"{o}dinger equation in a finite
interval with homogeneous Dirichlet or Neumann boundary conditions. There are
two main dynamics, the collapse which is very fast and a slow cascade of
Fourier modes. For the cubic nonlinearity the calculations show no long term
energy exchange between Fourier modes as opposed to higher nonlinearities. This
slow dynamics is explained by fairly simple amplitude equations for the
resonant Fourier modes. Their solutions are well behaved so filtering high
frequencies prevents collapse. Finally these equations elucidate the unique
role of the zero mode for the Neumann boundary conditions
A Green's function decoupling scheme for the Edwards fermion-boson model
Holes in a Mott insulator are represented by spinless fermions in the
fermion-boson model introduced by Edwards. Although the physically interesting
regime is for low to moderate fermion density the model has interesting
properties over the whole density range. It has previously been studied at
half-filling in the one-dimensional (1D) case by numerical methods, in
particular exact diagonalization and density matrix renormalization group
(DMRG). In the present study the one-particle Green's function is calculated
analytically by means of a decoupling scheme for the equations of motion, valid
for arbitrary density in 1D, 2D and 3D with fairly large boson energy and zero
boson relaxation parameter. The Green's function is used to compute some ground
state properties, and the one-fermion spectral function, for fermion densities
n=0.1, 0.5 and 0.9 in the 1D case. The results are generally in good agreement
with numerical results obtained by DMRG and dynamical DMRG and new light is
shed on the nature of the ground state at different fillings. The Green's
function approximation is sufficiently successful in 1D to justify future
application to the 2D and 3D cases.Comment: 19 pages, 7 figures, final version with updated reference
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Exchange Bias Effect in Au-Fe3O4 Nanocomposites
We report exchange bias (EB) effect in the Au-Fe3O4 composite nanoparticle
system, where one or more Fe3O4 nanoparticles are attached to an Au seed
particle forming dimer and cluster morphologies, with the clusters showing much
stronger EB in comparison with the dimers. The EB effect develops due to the
presence of stress in the Au-Fe3O4 interface which leads to the generation of
highly disordered, anisotropic surface spins in the Fe3O4 particle. The EB
effect is lost with the removal of the interfacial stress. Our atomistic
Monte-Carlo studies are in excellent agreement with the experimental results.
These results show a new path towards tuning EB in nanostructures, namely
controllably creating interfacial stress, and open up the possibility of tuning
the anisotropic properties of biocompatible nanoparticles via a controllable
exchange coupling mechanism.Comment: 28 pages, 6 figures, submitted to Nanotechnolog
Mechanisms for electron transport in atomic-scale one-dimensional wires: soliton and polaron effects
We study one-electron tunneling through atomic-scale one-dimensional wires in
the presence of coherent electron-phonon (e-ph) coupling. We use a full quantum
model for the e-ph interaction within the wire with open boundary conditions.
We illustrate the mechanisms of transport in the context of molecular wires
subject to boundary conditions imposing the presence of a soliton defect in the
molecule. Competition between polarons and solitons in the coherent transport
is examined. The transport mechanisms proposed are generally applicable to
other one-dimensional nanoscale systems with strong e-ph coupling.Comment: 7 pages, 4 figures, accepted for publication in Europhys. Let
Quantifying regional biodiversity in the tropics : a case study of freshwater fish in Trinidad and Tobago
Funding: European Research Council (AdG BioTIME 250189 and PoC BioCHANGE 727440) (AEM).Extinction rates are predicted to accelerate during the Anthropocene. Quantifying and mitigating these extinctions demands robust data on distributions of species and the diversity of taxa in regional biotas. However, many assemblages, particularly those in the tropics, are poorly characterized. Targeted surveys and historical museum collections are increasingly being used to meet the urgent need for accurate information, but the extent to which these contrasting data sources support meaningful inferences about biodiversity change in regional assemblages remains unclear. Here, we seek to elucidate uncertainty surrounding regional biodiversity estimates by evaluating the performance of these alternative methods in estimating the species richness and assemblage composition of the freshwater fish of Trinidad & Tobago. We compared estimates of regional species richness derived from two freshwater fish datasets: a targeted two year survey of Trinidad & Tobago rivers and historical museum collection records submitted to The University of the West Indies Zoology Museum. Richness was estimated using rarefaction and extrapolation, and assemblage composition was benchmarked against a recent literature review. Both datasets provided similar estimates of regional freshwater fish species richness (50 and 46 species, respectively), with a large overlap (85%) in species identities. Regional species richness estimates based on survey and museum data are thus comparable, and consistent in the species they include. Our results suggest that museum collection data are a viable option for setting reliable baselines in many tropical systems, thereby widening options for meaningful monitoring and evaluation of temporal trends.PostprintPeer reviewe
Slip Behavior and Hardness Indentations in MnSe and MnSe-MnS Solid Solutions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65510/1/j.1151-2916.1969.tb11957.x.pd
Tracking system analytic calibration activities for the Mariner Mars 1971 mission
Data covering various planning aspects of Mariner Mars 1971 mission are summarized. Data cover calibrating procedures for tracking stations, radio signal propagation in the troposphere, effects of charged particles on radio transmission, orbit calculation, and data smoothing
Highlights from Five Years at the B Factories
The highlights and conflicts at the B Factories are briefly reviewed.
violation was established in 2001 in and related modes,
which has now become a precision measurement of CP violation in - mixing. However, the situation for the and charmless
modes, which probe also CP violation in the {\it decay} amplitude, are
not quite settled yet. They could be hinting at presence of both strong (CP
conserving) and new physics (CP violating) phases. We critically assess the
developments and discuss some related discrepancies and highlights, such as
observation of direct CP violation, and make a projection towards the next few
years.Comment: 16 pages, 5 figures, to appear as Brief Review in Mod. Phys. Lett.
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