821 research outputs found
Stability and Dynamics of Crystals and Glasses of Motorized Particles
Many of the large structures of the cell, such as the cytoskeleton, are
assembled and maintained far from equilibrium. We study the stabilities of
various structures for a simple model of such a far-from-equilibrium organized
assembly in which spherical particles move under the influence of attached
motors. From the variational solutions of the manybody master equation for
Brownian motion with motorized kicking we obtain a closed equation for the
order parameter of localization. Thus we obtain the transition criterion for
localization and stability limits for the crystalline phase and frozen
amorphous structures of motorized particles. The theory also allows an estimate
of nonequilibrium effective temperatures characterizing the response and
fluctuations of motorized crystals and glasses.Comment: 5 pages, 3 figure
Metastable states of hydrogen: their geometric phases and flux densities
We discuss the geometric phases and flux densities for the metastable states
of hydrogen with principal quantum number n=2 being subjected to adiabatically
varying external electric and magnetic fields. Convenient representations of
the flux densities as complex integrals are derived. Both, parity conserving
(PC) and parity violating (PV) flux densities and phases are identified.
General expressions for the flux densities following from rotational invariance
are derived. Specific cases of external fields are discussed. In a pure
magnetic field the phases are given by the geometry of the path in magnetic
field space. But for electric fields in presence of a constant magnetic field
and for electric plus magnetic fields the geometric phases carry information on
the atomic parameters, in particular, on the PV atomic interaction. We show
that for our metastable states also the decay rates can be influenced by the
geometric phases and we give a concrete example for this effect. Finally we
emphasise that the general relations derived here for geometric phases and flux
densities are also valid for other atomic systems having stable or metastable
states, for instance, for He with n=2. Thus, a measurement of geometric phases
may give important experimental information on the mass matrix and the electric
and magnetic dipole matrices for such systems. This could be used as a check of
corresponding theoretical calculations of wave functions and matrix elements.Comment: 29 pages, 12 figure
Method of filling databases of electronic components based on the uniform tables of document parameters
Рассматриваются вопросы разработки методики автоматизированного наполнения баз данных электрорадиоизделий, основанной на объединении таблиц параметров нормативного документа. Показаны её основные этапы и особенности. Предложено оформлять связи между параметрами и правило формирования наименования элементов в текстовом файле-шаблоне. Приводится предварительная оценка времени оформления файлов-шаблонов различных нормативных документов. Показано применениеметодики для автоматического наполнения технологических справочников.The problems of the development of the methodology for the automated filling of databases of electronic products based on the integration of the parameters tables of the normative document are considered. Its main stages and features are shown. It is proposed to formalize the relationship between the parameters and the rule for the formation of the names of elements in a text file-template. A preliminary estimate of the time for creating template files for various normative documents is given. The application of the technique for automatic filling oftechnological databases is shown
Phase separation of a repulsive two-component Fermi gas at the two- to three-dimensional crossover
We present a theoretical analysis of phase separations between two
repulsively interacting components in an ultracold fermionic gas, occurring at
the dimensional crossover in a harmonic trap with varying aspect ratios. A
tailored kinetic energy functional is derived and combined with a
density-potential functional approach to develop a framework that is
benchmarked with the orbital-based method. We investigate the changes in the
density profile of the phase-separated gas under different interaction
strengths and geometries. The analysis reveals the existence of small,
partially polarized domains in certain parameter regimes, which is similar to
the purely two-dimensional limit. However, the density profile is further
enriched by a shell structure found in anisotropic traps. We also track the
transitions that can be driven by either a change in interaction strength or
trap geometry. The developed framework is noted to have applications for other
systems with repulsive interactions that combine continuous and discrete
degrees of freedom.Comment: 14 pages, 4 figure
Longitudinal Atomic Beam Spin Echo Experiments: A possible way to study Parity Violation in Hydrogen
We discuss the propagation of hydrogen atoms in static electric and magnetic
fields in a longitudinal atomic beam spin echo (lABSE) apparatus. Depending on
the choice of the external fields the atoms may acquire both dynamical and
geometrical quantum mechanical phases. As an example of the former, we show
first in-beam spin rotation measurements on atomic hydrogen, which are in
excellent agreement with theory. Additional calculations of the behaviour of
the metastable 2S states of hydrogen reveal that the geometrical phases may
exhibit the signature of parity-(P-)violation. This invites for possible future
lABSE experiments, focusing on P-violating geometrical phases in the lightest
of all atoms.Comment: 6 pages, 4 figure
A preliminary census of the macrofungi of Mt Wellington, Tasmania- the sequestrate species
This is the fourth and final contribution in a series of papers providing a preliminary documentation of the macrofungi of Mt Wellington, Tasmania. The earlier papers dealt with the gilled Basidiomycota, the non-gilled Basidiomycota and the Ascomycota, respectively, excluding the sequestrate species. The present paper completes the series by dealing with the sequestrate species, of which seven Ascomycota, 76 Basidiomycota, three Glomeromycota and one Zygomycota were found. Seven new genera and 25 new species to be formally described elsewhere, are recorded
Phase Transitions of Repulsive Two-Component Fermi Gases in Two Dimensions
We predict the phase separations of two-dimensional Fermi gases with
repulsive contact-type interactions between two spin components. Using
density-potential functional theory with systematic semiclassical
approximations, we address the long-standing problem of itinerant
ferromagnetism in realistic settings. We reveal a universal transition from the
paramagnetic state at small repulsive interactions towards ferromagnetic
density profiles at large interaction strengths, with intricate particle-number
dependent phases in between. Building on quantum Monte Carlo results for
uniform systems, we benchmark our simulations against Hartree-Fock calculations
for a small number of trapped fermions. We thereby demonstrate that our
employed corrections to the mean-field interaction energy and especially to the
Thomas-Fermi kinetic energy functional are necessary for reliably predicting
properties of trapped mesoscopic Fermi gases. The density patterns of the
ground state survive at low finite temperatures and confirm the Stoner-type
polarization behavior across a universal interaction parameter, albeit with
substantial quantitative differences that originate in the trapping potential
and the quantum-corrected kinetic energy. We also uncover a zoo of metastable
configurations that are energetically comparable to the ground-state density
profiles and are thus likely to be observed in experiments. We argue that our
density-functional approach can be easily applied to interacting
multi-component Fermi gases in general.Comment: 23 pages, 8 figure
Time Resolved Correlation measurements of temporally heterogeneous dynamics
Time Resolved Correlation (TRC) is a recently introduced light scattering
technique that allows to detect and quantify dynamic heterogeneities. The
technique is based on the analysis of the temporal evolution of the speckle
pattern generated by the light scattered by a sample, which is quantified by
, the degree of correlation between speckle images recorded at
time and . Heterogeneous dynamics results in significant
fluctuations of with time . We describe how to optimize TRC
measurements and how to detect and avoid possible artifacts. The statistical
properties of the fluctuations of are analyzed by studying their
variance, probability distribution function, and time autocorrelation function.
We show that these quantities are affected by a noise contribution due to the
finite number of detected speckles. We propose and demonstrate a method to
correct for the noise contribution, based on a extrapolation
scheme. Examples from both homogeneous and heterogeneous dynamics are provided.
Connections with recent numerical and analytical works on heterogeneous glassy
dynamics are briefly discussed.Comment: 19 pages, 15 figures. Submitted to PR
Modeling mycorrhizal fungi dispersal by the mycophagous swamp wallaby (Wallabia bicolor)
Despite the importance of mammal-fungal interactions, tools to estimate the mammal-assisted dispersal distances of fungi are lacking. Many mammals actively consume fungal fruiting bodies, the spores of which remain viable after passage through their digestive tract. Many of these fungi form symbiotic relationships with trees and provide an array of other key ecosystem functions. We present a flexible, general model to predict the distance a mycophagous mammal would disperse fungal spores. We modelled the probability of spore dispersal by combining animal movement data from GPS-telemetry with data on spore gut-retention time. We test this model using an exemplar generalist mycophagist, the swamp wallaby (Wallabia bicolor). We show that swamp wallabies disperse fungal spores hundreds of metres—and occasionally up to 1265 m—from the point of consumption, distances that are ecologically significant for many mycorrhizal fungi. In addition to highlighting the ecological importance of swamp wallabies as dispersers of mycorrhizal fungi in eastern Australia, our simple modelling approach provides a novel and effective way of empirically describing spore dispersal by a mycophagous animal. This approach is applicable to the study of other animal-fungi interactions in other ecosystems.Funding provided by: Hermon Slade FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001109Award Number: HSF08-6Funding provided by: Australian Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000923Award Number: DP0557022Methods are described in the published article
Experimental Verification of Electromagnetic Simulations of a HIFI Mixer Sub-Assembly
Phase II of the study "Far-Infrared Optics Design &
Verification", commissioned by the European Space Agency (ESA), we
investigate the ability of several commercial software packages (GRASP,
CODEV, GLAD and ASAP) to predict the performance of a representative
example of a submillimeter-wave optical system. In this paper, we use the
software packages to predict the behaviour of a Mixer Sub-Assembly (MSA) of
HIFI, and we compare the simulations with near-field measurements at 480 GHz.
In order to be able to distinguish between the predictions of the packages, we
move the corrugated horn of the MSA through its nominal focus position. A
unique feature of the experimental arrangement is that the measured position of
every field point is known absolutely to within fractions of a wavelength. In this
paper we present the results of this through-focus experiment, which give a good
first-order indication of the agreement between measured and simulated
behaviour of a typical submillimeter-wave optical system
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