21,116 research outputs found
Dynamic stability of space vehicles. Volume 8 - Atmospheric disturbances that affect flight control analysis
Space vehicle and control system dynamic response to atmospheric disturbance
Perturbation Theory of Schr\"odinger Operators in Infinitely Many Coupling Parameters
In this paper we study the behavior of Hamilton operators and their spectra
which depend on infinitely many coupling parameters or, more generally,
parameters taking values in some Banach space. One of the physical models which
motivate this framework is a quantum particle moving in a more or less
disordered medium. One may however also envisage other scenarios where
operators are allowed to depend on interaction terms in a manner we are going
to discuss below. The central idea is to vary the occurring infinitely many
perturbing potentials independently. As a side aspect this then leads naturally
to the analysis of a couple of interesting questions of a more or less purely
mathematical flavor which belong to the field of infinite dimensional
holomorphy or holomorphy in Banach spaces. In this general setting we study in
particular the stability of selfadjointness of the operators under discussion
and the analyticity of eigenvalues under the condition that the perturbing
potentials belong to certain classes.Comment: 25 pages, Late
Ergodic property of Markovian semigroups on standard forms of von Neumann algebras
We give sufficient conditions for ergodicity of the Markovian semigroups
associated to Dirichlet forms on standard forms of von Neumann algebras
constructed by the method proposed in Refs. [Par1,Par2]. We apply our result to
show that the diffusion type Markovian semigroups for quantum spin systems are
ergodic in the region of high temperatures where the uniqueness of the
KMS-state holds.Comment: 25 page
Major shifts at the range edge of marine forests: the combined effects of climate changes and limited dispersal
Global climate change is likely to constrain low latitude range edges across many taxa and habitats. Such is the case for NE Atlantic marine macroalgal forests, important ecosystems whose main structuring species is the annual kelp Saccorhiza polyschides. We coupled ecological niche modelling with simulations of potential dispersal and delayed development stages to infer the major forces shaping range edges and to predict their dynamics. Models indicated that the southern limit is set by high winter temperatures above the physiological tolerance of overwintering microscopic stages and reduced upwelling during recruitment. The best range predictions were achieved assuming low spatial dispersal (5 km) and delayed stages up to two years (temporal dispersal). Reconstructing distributions through time indicated losses of similar to 30% from 1986 to 2014, restricting S. polyschides to upwelling regions at the southern edge. Future predictions further restrict populations to a unique refugium in northwestern Iberia. Losses were dependent on the emissions scenario, with the most drastic one shifting similar to 38% of the current distribution by 2100. Such distributional changes might not be rescued by dispersal in space or time (as shown for the recent past) and are expected to drive major biodiversity loss and changes in ecosystem functioning.Electricity of Portugal (Fundo EDP para a Biodiversidade); FCT - Portuguese Science Foundation [PTDC/MAR-EST/6053/2014, EXTANT-EXCL/AAG-GLO/0661/2012, SFRH/BPD/111003/2015
Local bulk S-matrix elements and CFT singularities
We give a procedure for deriving certain bulk S-matrix elements from
corresponding boundary correlators. These are computed in the plane wave limit,
via an explicit construction of certain boundary sources that give bulk
wavepackets. A critical role is played by a specific singular behavior of the
lorentzian boundary correlators. It is shown in examples how correlators
derived from the bulk supergravity exhibit the appropriate singular structure,
and reproduce the corresponding S-matrix elements. This construction thus
provides a nontrivial test for whether a given boundary conformal field theory
can reproduce bulk physics, and where it does, supplies a prescription to
extract bulk S-matrix elements in the plane wave limit.Comment: 24 pages, 3 fig
Steady state existence of passive vector fields under the Kraichnan model
The steady state existence problem for Kraichnan advected passive vector
models is considered for isotropic and anisotropic initial values in arbitrary
dimension. The model includes the magnetohydrodynamic (MHD) equations, linear
pressure model (LPM) and linearized Navier-Stokes (LNS) equations. In addition
to reproducing the previously known results for the MHD and linear pressure
model, we obtain the values of the Kraichnan model roughness parameter
for which the LNS steady state exists.Comment: Improved text & figures, added references & other correction
The Hartree limit of Born's ensemble for the ground state of a bosonic atom or ion
The non-relativistic bosonic ground state is studied for quantum N-body
systems with Coulomb interactions, modeling atoms or ions made of N "bosonic
point electrons" bound to an atomic point nucleus of Z "electron" charges,
treated in Born--Oppenheimer approximation. It is shown that the (negative)
ground state energy E(Z,N) yields the monotonically growing function (E(l N,N)
over N cubed). By adapting an argument of Hogreve, it is shown that its limit
as N to infinity for l > l* is governed by Hartree theory, with the rescaled
bosonic ground state wave function factoring into an infinite product of
identical one-body wave functions determined by the Hartree equation. The proof
resembles the construction of the thermodynamic mean-field limit of the
classical ensembles with thermodynamically unstable interactions, except that
here the ensemble is Born's, with the absolute square of the ground state wave
function as ensemble probability density function, with the Fisher information
functional in the variational principle for Born's ensemble playing the role of
the negative of the Gibbs entropy functional in the free-energy variational
principle for the classical petit-canonical configurational ensemble.Comment: Corrected version. Accepted for publication in Journal of
Mathematical Physic
Toward an accurate mass function for precision cosmology
Cosmological surveys aim to use the evolution of the abundance of galaxy
clusters to accurately constrain the cosmological model. In the context of
LCDM, we show that it is possible to achieve the required percent level
accuracy in the halo mass function with gravity-only cosmological simulations,
and we provide simulation start and run parameter guidelines for doing so. Some
previous works have had sufficient statistical precision, but lacked robust
verification of absolute accuracy. Convergence tests of the mass function with,
for example, simulation start redshift can exhibit false convergence of the
mass function due to counteracting errors, potentially misleading one to infer
overly optimistic estimations of simulation accuracy. Percent level accuracy is
possible if initial condition particle mapping uses second order Lagrangian
Perturbation Theory, and if the start epoch is between 10 and 50 expansion
factors before the epoch of halo formation of interest. The mass function for
halos with fewer than ~1000 particles is highly sensitive to simulation
parameters and start redshift, implying a practical minimum mass resolution
limit due to mass discreteness. The narrow range in converged start redshift
suggests that it is not presently possible for a single simulation to capture
accurately the cluster mass function while also starting early enough to model
accurately the numbers of reionisation era galaxies, whose baryon feedback
processes may affect later cluster properties. Ultimately, to fully exploit
current and future cosmological surveys will require accurate modeling of
baryon physics and observable properties, a formidable challenge for which
accurate gravity-only simulations are just an initial step.Comment: revised in response to referee suggestions, MNRAS accepte
On a certain class of semigroups of operators
We define an interesting class of semigroups of operators in Banach spaces,
namely, the randomly generated semigroups. This class contains as a remarkable
subclass a special type of quantum dynamical semigroups introduced by
Kossakowski in the early 1970s. Each randomly generated semigroup is
associated, in a natural way, with a pair formed by a representation or an
antirepresentation of a locally compact group in a Banach space and by a
convolution semigroup of probability measures on this group. Examples of
randomly generated semigroups having important applications in physics are
briefly illustrated.Comment: 11 page
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