647 research outputs found
The one-dimensional Hubbard model with open ends: Universal divergent contributions to the magnetic susceptibility
The magnetic susceptibility of the one-dimensional Hubbard model with open
boundary conditions at arbitrary filling is obtained from field theory at low
temperatures and small magnetic fields, including leading and next-leading
orders. Logarithmic contributions to the bulk part are identified as well as
algebraic-logarithmic divergences in the boundary contribution. As a
manifestation of spin-charge separation, the result for the boundary part at
low energies turns out to be independent of filling and interaction strength
and identical to the result for the Heisenberg model. For the bulk part at zero
temperature, the scale in the logarithms is determined exactly from the Bethe
ansatz. At finite temperature, the susceptibility profile as well as the
Friedel oscillations in the magnetisation are obtained numerically from the
density-matrix renormalisation group applied to transfer matrices. Agreement is
found with an exact asymptotic expansion of the relevant correlation function.Comment: 30 pages, 8 figures, reference adde
Lattice vs. continuum theory of the periodic Heisenberg chain
We consider the detailed structure of low energy excitations in the periodic
spin-1/2 XXZ Heisenberg chain. By performing a perturbative calculation of the
non-linear corrections to the Gaussian model, we determine the exact
coefficients of asymptotic expansions in inverse powers of the system length N
for a large number of low-lying excited energy levels. This allows us to
calculate eigenenergies of the lattice model up to order order N^-4, without
having to solve the Bethe Ansatz equations. At the same time, it is possible to
express the exact eigenstates of the lattice model in terms of bosonic modes.Comment: 17 pages, 8 Figures. The latest version can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Bethe Ansatz study of one-dimensional Bose and Fermi gases with periodic and hard wall boundary conditions
We extend the exact periodic Bethe Ansatz solution for one-dimensional bosons
and fermions with delta-interaction and arbitrary internal degrees of freedom
to the case of hard wall boundary conditions. We give an analysis of the ground
state properties of fermionic systems with two internal degrees of freedom,
including expansions of the ground state energy in the weak and strong coupling
limits in the repulsive and attractive regimes.Comment: 27 pages, 6 figures, key reference added, typos correcte
Study of the island morphology at the early stages of Fe/Mo(110) MBE growth
We present theoretical study of morphology of Fe islands grown at Mo(110)
surface in sub-monolayer MBE mode. We utilize atomistic SOS model with bond
counting, and interactions of Fe adatom up to third nearest neighbors. We
performed KMC simulations for different values of adatom interactions and
varying temperatures. We have found that, while for the low temperature islands
are fat fractals, for the temperature 500K islands have faceted rhombic-like
shape. For the higher temperature, islands acquire a rounded shape. In order to
evaluated qualitatively morphological changes, we measured averaged aspect
ration of islands. We calculated dependence of the average aspect ratio on the
temperature, and on the strength of interactions of an adatom with neighbors.Comment: 6 pages, 6 figures. Proceedings of 11-th Symposium on Surface
Physics, Prague 200
Biological age estimation using circulating blood biomarkers
Biological age captures physiological deterioration better than chronological age and is amenable to interventions. Blood-based biomarkers have been identified as suitable candidates for biological age estimation. This study aims to improve biological age estimation using machine learning models and a feature-set of 60 circulating biomarkers available from the UK Biobank (n = 306,116). We implement an Elastic-Net derived Cox model with 25 selected biomarkers to predict mortality risk (C-Index = 0.778; 95% CI [0.767–0.788]), which outperforms the well-known blood-biomarker based PhenoAge model (C-Index = 0.750; 95% CI [0.739–0.761]), providing a C-Index lift of 0.028 representing an 11% relative increase in predictive value. Importantly, we then show that using common clinical assay panels, with few biomarkers, alongside imputation and the model derived on the full set of biomarkers, does not substantially degrade predictive accuracy from the theoretical maximum achievable for the available biomarkers. Biological age is estimated as the equivalent age within the same-sex population which corresponds to an individual’s mortality risk. Values ranged between 20-years younger and 20-years older than individuals’ chronological age, exposing the magnitude of ageing signals contained in blood markers. Thus, we demonstrate a practical and cost-efficient method of estimating an improved measure of Biological Age, available to the general population
Soft versus Hard Dynamics for Field-driven Solid-on-Solid Interfaces
Analytical arguments and dynamic Monte Carlo simulations show that the
microstructure of field-driven Solid-on-Solid interfaces depends strongly on
the dynamics. For nonconservative dynamics with transition rates that factorize
into parts dependent only on the changes in interaction energy and field
energy, respectively (soft dynamics), the intrinsic interface width is
field-independent. For non-factorizing rates, such as the standard Glauber and
Metropolis algorithms (hard dynamics), it increases with the field.
Consequences for the interface velocity and its anisotropy are discussed.Comment: 9 pages LaTex with imbedded .eps figs. Minor revision
Ground-state properties of the attractive one-dimensional Bose-Hubbard model
We study the ground state of the attractive one-dimensional Bose-Hubbard
model, and in particular the nature of the crossover between the weak
interaction and strong interaction regimes for finite system sizes. Indicator
properties like the gap between the ground and first excited energy levels, and
the incremental ground-state wavefunction overlaps are used to locate different
regimes. Using mean-field theory we predict that there are two distinct
crossovers connected to spontaneous symmetry breaking of the ground state. The
first crossover arises in an analysis valid for large L with finite N, where L
is the number of lattice sites and N is the total particle number. An
alternative approach valid for large N with finite L yields a second crossover.
For small system sizes we numerically investigate the model and observe that
there are signatures of both crossovers. We compare with exact results from
Bethe ansatz methods in several limiting cases to explore the validity for
these numerical and mean-field schemes. The results indicate that for finite
attractive systems there are generically three ground-state phases of the
model.Comment: 17 pages, 12 figures, Phys.Rev.B(accepted), minor changes and updated
reference
Effects of Lateral Diffusion on the Dynamics of Desorption
The adsorbate dynamics during simultaneous action of desorption and lateral
adsorbate diffusion is studied in a simple lattice-gas model by kinetic Monte
Carlo simulations. It is found that the action of the coverage-conserving
diffusion process during the course of the desorption has two distinct,
competing effects: a general acceleration of the desorption process, and a
coarsening of the adsorbate configuration through Ostwald ripening. The balance
between these two effects is governed by the structure of the adsorbate layer
at the beginning of the desorption process
Local Inhomogeneity in Asymmetric Simple Exclusion Processes with Extended Objects
Totally asymmetric simple exclusion processes (TASEP) with particles which
occupy more than one lattice site and with a local inhomogeneity far away from
the boundaries are investigated. These non-equilibrium processes are relevant
for the understanding of many biological and chemical phenomena. The
steady-state phase diagrams, currents, and bulk densities are calculated using
a simple approximate theory and extensive Monte Carlo computer simulations. It
is found that the phase diagram for TASEP with a local inhomogeneity is
qualitatively similar to homogeneous models, although the phase boundaries are
significantly shifted. The complex dynamics is discussed in terms of
domain-wall theory for driven lattice systems.Comment: 11 pages, 5 figure
Excitation lines and the breakdown of Stokes-Einstein relations in supercooled liquids
By applying the concept of dynamical facilitation and analyzing the
excitation lines that result from this facilitation, we investigate the origin
of decoupling of transport coefficients in supercooled liquids. We illustrate
our approach with two classes of models. One depicts diffusion in a strong
glass former, and the other in a fragile glass former. At low temperatures,
both models exhibit violation of the Stokes-Einstein relation,
, where is the self diffusion constant and is the
structural relaxation time. In the strong case, the violation is sensitive to
dimensionality , going as for , and as for . In the fragile case, however, we argue that
dimensionality dependence is weak, and show that for , . This scaling for the fragile case compares favorably with the
results of a recent experimental study for a three-dimensional fragile glass
former.Comment: 7 pages, 7 figures, submitted to Phys. Rev.
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