5,743 research outputs found
Spin-Peierls transition in TiOCl
Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2
quantum magnet TiOCl shows that the phase transition at T_{c2} = 90 K
corresponds to a lowering of the lattice symmetry. Below T_{c1} = 66 K a
twofold superstructure develops, that indicates the formation of spin-singlet
pairs via direct exchange between neighboring Ti atoms, while the role of
superexchange is found to be negligible. TiOCl thus is identified as a
spin-Peierls system of pure 1D chains of atoms. The first-order character of
the transition at T_{c1} is explained by the competition between the
structurally deformed state below T_{c2} and the spin-Peierls state below
T_{c1}.Comment: Phys. Rev. B (Rapid Communications) in pres
Refraction in a pulsar magnetoshpere - the effect of a variable emission height on pulse morphology
Equivalence of particle-particle random phase approximation correlation energy and ladder-coupled-cluster doubles
We present an analytical proof and numerical demonstrations of the
equivalence of the correlation energy from particle-particle random phase
approximation (pp-RPA) and ladder-couple-cluster-doubles (ladder-CCD). These
two theories reduce to the identical algebraic matrix equation and correlation
energy expressions, under the assumption that the pp-RPA equation is stable.
The numerical examples illustrate that the correlation energy missed by pp-RPA
in comparison with couple-cluster single and double is largely canceled out
when considering reaction energies. This theoretical connection will be
beneficial to future pp-RPA studies based on the well established couple
cluster theory
Boundary Zonal Flow in Rotating Turbulent Rayleigh-Bénard Convection
For rapidly rotating turbulent Rayleigh–Bénard convection in a slender cylindrical cell, experiments and direct numerical simulations reveal a boundary zonal flow (BZF) that replaces the classical large-scale circulation. The BZF is located near the vertical side wall and enables enhanced heat transport there. Although the azimuthal velocity of the BZF is cyclonic (in the rotating frame), the temperature is an anticyclonic traveling wave of mode one, whose signature is a bimodal temperature distribution near the radial boundary. The BZF width is found to scale like Ra1/4Ek2/3 where the Ekman number Ek decreases with increasing rotation rate
Collecting standardised oral health data via mobile application: A proof of concept study in the Netherlands
Collective fluctuations in networks of noisy components
Collective dynamics result from interactions among noisy dynamical
components. Examples include heartbeats, circadian rhythms, and various pattern
formations. Because of noise in each component, collective dynamics inevitably
involve fluctuations, which may crucially affect functioning of the system.
However, the relation between the fluctuations in isolated individual
components and those in collective dynamics is unclear. Here we study a linear
dynamical system of networked components subjected to independent Gaussian
noise and analytically show that the connectivity of networks determines the
intensity of fluctuations in the collective dynamics. Remarkably, in general
directed networks including scale-free networks, the fluctuations decrease more
slowly with the system size than the standard law stated by the central limit
theorem. They even remain finite for a large system size when global
directionality of the network exists. Moreover, such nontrivial behavior
appears even in undirected networks when nonlinear dynamical systems are
considered. We demonstrate it with a coupled oscillator system.Comment: 5 figure
ESTIMATION OF AND ADJUSTMENT FOR RESIDUAL EFFECTS IN DAIRY FEEDING EXPERIMENTS UTILIZING CHANGEOVER DESIGNS
A procedure is presented which demonstrates estimation of and adjustment for residual effects in changeover designs. The method utilizes all data collected in an experiment by including treatments imposed on animals prior to initiation of data collection. Estimation is achieved via general linear models. An example is given of a nutrition experiment conducted with dairy cattle. Such analyses should increase efficacy of changeover designs and reduce concern by researchers about biased estimates of direct effects which could result from residual effects. Methods from popular computer programs for estimating direct effect treatment means are compared. Practical problems encountered in computing standard errors of mean estimates in mixed linear models
Photoemission investigation of the electronic structure of Fe-Pd and Fe-Pt alloys
A photoemission investigation of Fe-Pd and Fe-Pt transition-metal alloys, using ∼50–150-eV synchrotron radiation, is presented. We consider in particular the spectral distribution of Fe states when approaching the dilute limit. By means of the Cooper minimum in the 4d and 5d photoionization cross section, we identify structures that have mainly Fe minority- or Fe majority-spin character. The relative position of these peaks is discussed in terms of the covalent interaction between Fe 3d and Pd or Pt d states. Also, the strong resemblance between the distribution of Fe states in the Pd-based and in the Pt-based alloys is demonstrated. We find a consistent behavior of interacting d states towards the dilute limit. It is concluded that the Fe states that are observed in the photoemission spectra of the dilute alloys have mainly majority-spin character and are, because of the covalent interaction with host states, widely distributed over the energy range of the host d band. The Fe minority-spin band, which is centered near the Fermi level, gradually empties with increasing Fe dilution
First detailed analysis of multiple system V2083 Cyg
Main aim of this paper is the first detailed analysis of multiple system
V2083 Cyg and to reveal its basic physical properties. The system was studied
by method of the light and radial velocity curves analysis, together with the
interferometric data of the visual pair obtained during a last century. There
was found that the close subsystem contains two very similar stars of spectral
type A7-8. Moreover, the third body is orbiting around this pair with period of
about 177 years. Due to the discrepancy of total mass as derived from two
methods, there arises that the third body is maybe also a binary, or some
object with lower luminosity but higher mass than normal main-sequence star.
Another explanation is that the Hipparcos value of parallax is incorrect and
the system is much closer to the Sun.Comment: 6 pages, 4 figures, published in 2012MNRAS.421.1196
Full Elite Sets for Multi-Objective Optimisation
Copyright © 2002 Springer. The final publication is available at link.springer.com5th International Conference on Adaptive Computing in Design and Manufacture (ACDM 2002), Exeter, UK, 16-18 April, 2002Multi-objective evolutionary algorithms frequently use an archive of non-dominated solutions to approximate the Pareto front. We show that the truncation of this archive to a limited number of solutions can lead to oscillating and shrinking estimates of the Pareto front. New data structures to permit efficient query and update of the full archive are proposed, and the superior quality of frontal estimates found using the full archive is illustrated on test problems
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