49 research outputs found
Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2
The temperature evolution of the crystal and magnetic structures of
ferroelectric sulfide AgCrS2 have been investigated by means of neutron
scattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition,
from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinic
structure with a polar Cm space group. In addition to being ferroelectric below
TN, the low temperature phase of AgCrS2 exhibits an unconventional collinear
magnetic structure that can be described as double ferromagnetic stripes
coupled antiferromagnetically, with the magnetic moment of Cr+3 oriented along
b within the anisotropic triangular plane. The magnetic couplings stabilizing
this structure are discussed using inelastic neutron scattering results.
Ferroelectricity below TN in AgCrS2 can possibly be explained in terms of
atomic displacements at the magneto-elastic induced structural distortion.
These results contrast with the behavior of the parent frustrated
antiferromagnet and spin-driven ferroelectric AgCrO2
Seasonal variability of the subpolar gyres in the Southern Ocean: a numerical investigation based on transfer operators
The detection of regions in the ocean that are coherent over an extended period of time is a fundamental problem in many oceanic applications. For instance such regions are important for studying the transport of marine species and for the distribution of nutrients. In this study we demonstrate the efficacy of transfer operators in detecting and analysing such structures. We focus first on the detection of the Weddell and Ross Gyre for the four seasons spanning December 2003–November 2004 within the 3-D oceanic domain south of 30° S, and show distinct seasonal differences in both the three-dimensional structure and the persistence of the gyres. Further, we demonstrate a new technique based on the discretised transfer operators to calculate the mean residence time of water within parts of the gyres and determine pathways of water leaving and entering the gyres
Quantitative trait loci for sensitivity to ethanol intoxication in a C57BL/6J × 129S1/SvImJ inbred mouse cross
Individual variation in sensitivity to acute ethanol (EtOH) challenge is associated with alcohol drinking and is a predictor of alcohol abuse. Previous studies have shown that the C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mouse strains differ in responses on certain measures of acute EtOH intoxication. To gain insight into genetic factors contributing to these differences, we performed quantitative trait locus (QTL) analysis of measures of EtOH-induced ataxia (accelerating rotarod), hypothermia, and loss of righting reflex (LORR) duration in a B6 × S1 F2 population. We confirmed that S1 showed greater EtOH-induced hypothermia (specifically at a high dose) and longer LORR compared to B6. QTL analysis revealed several additive and interacting loci for various phenotypes, as well as examples of genotype interactions with sex. QTLs for different EtOH phenotypes were largely non-overlapping, suggesting separable genetic influences on these behaviors. The most compelling main-effect QTLs were for hypothermia on chromosome 16 and for LORR on chromosomes 4 and 6. Several QTLs overlapped with loci repeatedly linked to EtOH drinking in previous mouse studies. The architecture of the traits we examined was complex but clearly amenable to dissection in future studies. Using integrative genomics strategies, plausible functional and positional candidates may be found. Uncovering candidate genes associated with variation in these phenotypes in this population could ultimately shed light on genetic factors underlying sensitivity to EtOH intoxication and risk for alcoholism in humans
Bruch- und Schwerverhalten von Gesteinstrennflaechen mit dazwischenliegenden Materialbruecken
Available from TIB Hannover: RN 6942(33)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Network-based study of Lagrangian transport and mixing
Transport and mixing processes in fluid flows are crucially influenced by coherent structures and the characterization of these
Lagrangian objects is a topic of intense current research. While established
mathematical approaches such as variational methods or transfer-operator-based
schemes require full knowledge of the flow field or at least high-resolution
trajectory data, this information may not
be available in applications. Recently, different computational methods have been proposed to identify coherent behavior in flows
directly from Lagrangian trajectory data, that is, numerical or measured time
series of particle positions in a fluid flow. In this
context, spatio-temporal clustering algorithms have been proven to be very effective for the extraction of coherent sets from sparse
and possibly incomplete trajectory data. Inspired by these recent approaches, we consider an unweighted, undirected network, where
Lagrangian particle trajectories serve as network nodes. A link is established between two nodes if the respective trajectories come
close to each other at least once in the course of time. Classical graph concepts are then employed to analyze the resulting
network. In particular, local network measures such as the node degree, the average degree of neighboring nodes, and the clustering
coefficient serve as indicators of highly mixing regions, whereas spectral graph partitioning schemes allow us to extract coherent
sets. The proposed methodology is very fast to run and we demonstrate its applicability in two geophysical flows – the Bickley jet as
well as the Antarctic stratospheric polar vortex
Eulerian and Lagrangian Perspectives on Turbulent Superstructures in Rayleigh-Bénard Convection
Large-scale computations in combination with new mathematical analysis tools make studies of the large-scale patterns, which are termed turbulent superstructures, in extended turbulent convection flows now accessible. Here, we report recent analyses in the Eulerian and Lagrangian frames of reference that reveal the characteristic spatial and temporal scales of the patterns as a function of Prandtl number, the dimensionless number which relates momentum to temperature diffusion in the working fluid