742 research outputs found
Testing weighted splitting schemes on a one-column transport-chemistry model
In many transport-chemistry models, a huge system of ODE’s of the advection-diffusion-reaction type has to be integrated in time. Typically, this is done with the help of operator splitting. Rosenbrock schemes combined with approximate matrix factorization (ROS-AMF) are an alternative to operator splitting which does not suffer from splitting errors. However, implementation of ROS-AMF schemes often requires serious changes in the code. In this paper we test another classical second order splitting introduced by Strang in 1963, which, unlike the popular Strang splitting, seemed to be forgotten and rediscovered recently (partially due to its intrinsic parallellism). This splitting, called symmetrically weighted sequential (SWS) splitting, is simple and straightforward to apply, independent of the order of the operators and has an operator-level parallelism. In the experiments, the SWS scheme compares favorably to the Strang splitting, but is less accurate than ROS-AMF
Injected Power Fluctuations in 1D Dissipative Systems
Using fermionic techniques, we compute exactly the large deviation function
(ldf) of the time-integrated injected power in several one-dimensional
dissipative systems of classical spins. The dynamics are T=0 Glauber dynamics
supplemented by an injection mechanism, which is taken as a Poissonian flipping
of one particular spin. We discuss the physical content of the results,
specifically the influence of the rate of the Poisson process on the properties
of the ldf.Comment: 18 pages, 8 figure
Magnetic Fluctuations and Correlations in MnSi - Evidence for a Skyrmion Spin Liquid Phase
We present a comprehensive analysis of high resolution neutron scattering
data involving Neutron Spin Echo spectroscopy and Spherical Polarimetry which
confirm the first order nature of the helical transition and reveal the
existence of a new spin liquid skyrmion phase. Similar to the blue phases of
liquid crystals this phase appears in a very narrow temperature range between
the low temperature helical and the high temperature paramagnetic phases.Comment: 11 pages, 16 figure
Membrane fluctuations near a plane rigid surface
We use analytical calculations and Monte Carlo simulations to determine the
thermal fluctuation spectrum of a membrane patch of a few tens of nanometer in
size, whose corners are located at a fixed distance above a plane rigid
surface. Our analysis shows that the surface influence on the bilayer
fluctuations can be effectively described in terms of a uniform confining
potential that grows quadratically with the height of the membrane relative
to the surface: . The strength of the harmonic
confining potential vanishes when the corners of the membrane patch are placed
directly on the surface (), and achieves its maximum value when is of
the order of a few nanometers. However, even at maximum strength the
confinement effect is quite small and has noticeable impact only on the
amplitude of the largest bending mode.Comment: Accepted for publication in Phys. Rev.
Goal pursuit during the three stages of the migration process
Migration poses a strong contextual change for individuals and it necessitates the adjustment of goals and aspirations. Although goal-related processes seem highly relevant to migration success (e.g., migrant well-being and adjustment), existing research in the area is scattered and lacks an overarching theoretical framework. By systematically analyzing the current literature on goal pursuit in the migration context, we aim to give an overview of the current state of the field, identify areas that need further research attention, and recommend alternative methodological approaches for future studies. This systematic literature review uses the different stages of the migration process (pre-migration, during migration, and potential repatriation or onward migration) and the three different goal facets (goal structure, goal process, and goal content) as an organizing framework. Our discussion focuses on the theoretical and methodological implications of our findings. The article demonstrates the need for further research in the field of goal pursuit in the migration context
Pseudo-boundaries in discontinuous 2-dimensional maps
It is known that Kolmogorov-Arnold-Moser boundaries appear in sufficiently
smooth 2-dimensional area-preserving maps. When such boundaries are destroyed,
they become pseudo-boundaries. We show that pseudo-boundaries can also be found
in discontinuous maps. The origin of these pseudo-boundaries are groups of
chains of islands which separate parts of the phase space and need to be
crossed in order to move between the different sub-spaces. Trajectories,
however, do not easily cross these chains, but tend to propagate along them.
This type of behavior is demonstrated using a ``generalized'' Fermi map.Comment: 4 pages, 4 figures, Revtex, epsf, submitted to Physical Review E (as
a brief report
ΛCDM Cosmology + Chaotic Inflation
ΛCDM cosmology is described in terms of general relativity and the Robertson-Walker metric. The evolution of the observable universe, currently dominated by dark energy (Λ) and cold dark matter (CDM), is presented in terms of its thermal history. CDM is extended to include an inflation epoch that accelerates the early expansion rate to near exponential levels. It is shown that inflation solves several problems in CDM and produces perturbations in the metric that lead to the observed anisotropies in the Cosmic Microwave Background and the formation of large scale cosmological structures. Various theories of inflation are explored. Predictions of inflation theories are compared to observations published by the Planck Collaboration. The paper concludes with an examination of “��-attractor” theories of inflation based on a modified form of gravity
Globular Structures of a Helix-Coil Copolymer: Self-Consistent Treatment
A self-consistent field theory was developed in the grand-canonical ensemble
formulation to study transitions in a helix-coil multiblock globule. Helical
and coil parts are treated as stiff rods and self-avoiding walks of variable
lengths correspondingly. The resulting field-theory takes, in addition to the
conventional Zimm-Bragg (B.H. Zimm, I.K. Bragg, J. Chem. Phys. 31, 526 (1959))
parameters, also three-dimensional interaction terms into account. The
appropriate differential equations which determine the self-consistent fields
were solved numerically with finite element method. Three different phase
states are found: open chain, amorphous globule and nematic liquid-crystalline
(LC) globule. The LC-globule formation is driven by the interplay between the
hydrophobic helical segments attraction and the anisotropic globule surface
energy of an entropic nature. The full phase diagram of the helix-coil
copolymer was calculated and thoroughly discussed. The suggested theory shows a
clear interplay between secondary and tertiary structures in globular
homopolypeptides.Comment: 26 pages, 30 figures, corrected some typo
Microscopic formulation of the Zimm-Bragg model for the helix-coil transition
A microscopic spin model is proposed for the phenomenological Zimm-Bragg
model for the helix-coil transition in biopolymers. This model is shown to
provide the same thermophysical properties of the original Zimm-Bragg model and
it allows a very convenient framework to compute statistical quantities.
Physical origins of this spin model are made transparent by an exact mapping
into a one-dimensional Ising model with an external field. However, the
dependence on temperature of the reduced external field turns out to differ
from the standard one-dimensional Ising model and hence it gives rise to
different thermophysical properties, despite the exact mapping connecting them.
We discuss how this point has been frequently overlooked in the recent
literature.Comment: 11 pages, 2 figure
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