4,704 research outputs found
Incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl, Br) studied by single crystal neutron diffraction
Polarized and unpolarized neutron diffraction studies have been carried out
on single crystals of the coupled spin tetrahedra systems Cu2Te2O5X2 (X=Cl,
Br). A model of the magnetic structure associated with the propagation vectors
k'Cl ~ -0.150,0.422,1/2 and k'Br ~ -0.172,0.356,1/2 and stable below TN=18 K
for X=Cl and TN=11 K for X=Br is proposed. A feature of the model, common to
both the bromide and chloride, is a canted coplanar motif for the 4 Cu2+ spins
on each tetrahedron which rotates on a helix from cell to cell following the
propagation vector. The Cu2+magnetic moment determined for X=Br, 0.395(5)muB,
is significantly less than for X=Cl, 0.88(1)muB at 2K. The magnetic structure
of the chloride associated with the wave-vector k' differs from that determined
previously for the wave vector k~0.150,0.422,1/2 [O. Zaharko et.al. Phys. Rev.
Lett. 93, 217206 (2004)]
Cassiopeia A: dust factory revealed via submillimetre polarimetry
If Type-II supernovae - the evolutionary end points of short-lived, massive
stars - produce a significant quantity of dust (>0.1 M_sun) then they can
explain the rest-frame far-infrared emission seen in galaxies and quasars in
the first Gyr of the Universe. Submillimetre observations of the Galactic
supernova remnant, Cas A, provided the first observational evidence for the
formation of significant quantities of dust in Type-II supernovae. In this
paper we present new data which show that the submm emission from Cas A is
polarised at a level significantly higher than that of its synchrotron
emission. The orientation is consistent with that of the magnetic field in Cas
A, implying that the polarised submm emission is associated with the remnant.
No known mechanism would vary the synchrotron polarisation in this way and so
we attribute the excess polarised submm flux to cold dust within the remnant,
providing fresh evidence that cosmic dust can form rapidly. This is supported
by the presence of both polarised and unpolarised dust emission in the north of
the remnant, where there is no contamination from foreground molecular clouds.
The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which,
coupled with the brief timescale available for grain alignment (<300 yr),
suggests that supernova dust differs from that seen in other Galactic sources
(where f_pol=2-7%), or that a highly efficient grain alignment process must
operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou
Precision control of thermal transport in cryogenic single-crystal silicon devices
We report on the diffusive-ballistic thermal conductance of multi-moded
single-crystal silicon beams measured below 1 K. It is shown that the phonon
mean-free-path is a strong function of the surface roughness
characteristics of the beams. This effect is enhanced in diffuse beams with
lengths much larger than , even when the surface is fairly smooth, 5-10
nm rms, and the peak thermal wavelength is 0.6 m. Resonant phonon
scattering has been observed in beams with a pitted surface morphology and
characteristic pit depth of 30 nm. Hence, if the surface roughness is not
adequately controlled, the thermal conductance can vary significantly for
diffuse beams fabricated across a wafer. In contrast, when the beam length is
of order , the conductance is dominated by ballistic transport and is
effectively set by the beam area. We have demonstrated a uniformity of 8%
in fractional deviation for ballistic beams, and this deviation is largely set
by the thermal conductance of diffuse beams that support the
micro-electro-mechanical device and electrical leads. In addition, we have
found no evidence for excess specific heat in single-crystal silicon membranes.
This allows for the precise control of the device heat capacity with normal
metal films. We discuss the results in the context of the design and
fabrication of large-format arrays of far-infrared and millimeter wavelength
cryogenic detectors
Compaction and dilation rate dependence of stresses in gas-fluidized beds
A particle dynamics-based hybrid model, consisting of monodisperse spherical
solid particles and volume-averaged gas hydrodynamics, is used to study
traveling planar waves (one-dimensional traveling waves) of voids formed in
gas-fluidized beds of narrow cross sectional areas. Through ensemble-averaging
in a co-traveling frame, we compute solid phase continuum variables (local
volume fraction, average velocity, stress tensor, and granular temperature)
across the waves, and examine the relations among them. We probe the
consistency between such computationally obtained relations and constitutive
models in the kinetic theory for granular materials which are widely used in
the two-fluid modeling approach to fluidized beds. We demonstrate that solid
phase continuum variables exhibit appreciable ``path dependence'', which is not
captured by the commonly used kinetic theory-based models. We show that this
path dependence is associated with the large rates of dilation and compaction
that occur in the wave. We also examine the relations among solid phase
continuum variables in beds of cohesive particles, which yield the same path
dependence. Our results both for beds of cohesive and non-cohesive particles
suggest that path-dependent constitutive models need to be developed.Comment: accepted for publication in Physics of Fluids (Burnett-order effect
analysis added
Turbulent length-time scales distributions in hydraulic jumps
Airâwater flow measurements were performed in hydraulic jump flows for a range of inflow Froude numbers. The experiments were conducted in a large-sized facility using phase-detection intrusive probes. The void fraction measurements showed the presence of an advective diffusion shear layer where the air concentration vertical distributions were successfully compared with an analytical solution of the advective diffusion equation for air bubbles. In the airâwater shear layer, a new empirical relationship between the maximum air concentration decay as a function of both the distance from the jump toe and the inflow Froude number was derived. Airâwater turbulent time and length scales were deduced from auto- and cross-correlation analyses based on the method of Chanson (2007). The result provided some characteristic transverse time and length scales of the eddy structures advecting the air bubbles in the developing shear layer. The turbulence time scale data showed an increase with the relative elevation above the bed, as well as some decrease with increasing distance from the toe. The dimensionless integral turbulent length scale Lxz/d1 was closely related to the inflow depth
Managing diversity in organisations: practitioner and academic perspectives: report from a gender in management special interest group research event
Purpose - This report aims to provide a brief summary of the presentations made by researchers and practitioners at the Gender in Management Special Interest Groupâs research event, Managing Diversity in Organisations: Practitioner and Academic Perspectives.
Design/methodology/approach - The research seminar was chaired by Dr. Adelina Broadbridge (University of Stirling) and Dr. Gillian Maxwell (Glasgow Caledonian University), and featured five presentations related to diversity in organisations, with a focus on gender issues. Twenty-five delegates were in attendance.
Findings - The academic research presented provided empirical evidence that women continue to face barriers to career progress in a number of industry sectors. The industry presentations provided examples of organisational efforts to improve diversity both among staff and customers.
Research limitations/implications - More needs to be done to ensure that women enjoy career opportunities equal to those of men in a variety of industry sectors. Even in organisations where women are comparatively well represented, such as
professional services firms, research indicates that they are disadvantaged in terms of career development and progress.
Originality/value - This session provided a valuable opportunity for practitioners and academics to meet and share information regarding the state of diversity in todayâs workplace
A Genome-Wide Association Study for Calving Interval in Holstein Dairy Cows Using Weighted Single-Step Genomic BLUP Approach.
The aim of the present study was to identify genomic region(s) associated with the length of the calving interval in primiparous (n = 6866) and multiparous (n = 5071) Holstein cows. The single nucleotide polymorphism (SNP) solutions were estimated using a weighted single-step genomic best linear unbiased prediction (WssGBLUP) approach and imputed high-density panel (777 k) genotypes. The effects of markers and the genomic estimated breeding values (GEBV) of the animals were obtained by five iterations of WssGBLUP. The results showed that the accuracies of GEBVs with WssGBLUP improved by +5.4 to +5.7, (primiparous cows) and +9.4 to +9.7 (multiparous cows) percent points over accuracies from the pedigree-based BLUP. The most accurate genomic evaluation was provided at the second iteration of WssGBLUP, which was used to identify associated genomic regions using a windows-based GWAS procedure. The proportion of additive genetic variance explained by windows of 50 consecutive SNPs (with an average of 165 Kb) was calculated and the region(s) that accounted for equal to or more than 0.20% of the total additive genetic variance were used to search for candidate genes. Three windows of 50 consecutive SNPs (BTA3, BTA6, and BTA7) were identified to be associated with the length of the calving interval in primi- and multiparous cows, while the window with the highest percentage of explained genetic variance was located on BTA3 position 49.42 to 49.52 Mb. There were five genes including , , , , and inside the windows associated with the length of the calving interval. The biological process terms including alanine transport, L-alanine transport, proline transport, and glycine transport were identified as the most important terms enriched by the genes inside the identified windows
Eulerian simulation of the fluid dynamics of helicopter brownout
A computational model is presented that can be used to simulate the development of the dust cloud
that can be entrained into the air when a helicopter is operated close to the ground in desert or dusty
conditions. The physics of this problem, and the associated pathological condition known as âbrownoutâ
where the pilot loses situational awareness as a result of his vision being occluded by dust suspended in the
flow around the helicopter, is acknowledged to be very complex. The approach advocated here involves
an approximation to the full dynamics of the coupled particulate-air system. Away from the ground, the
model assumes that the suspended particles remain in near equilibrium under the action of aerodynamic
forces. Close to the ground, this model is replaced by an algebraic sublayer model for the saltation and
entrainment process. The origin of the model in the statistical mechanics of a distribution of particles
governed by aerodynamic forces allows the validity of the method to be evaluated in context by comparing
the physical properties of the suspended particulates to the local properties of the flow field surrounding
the helicopter. The model applies in the Eulerian frame of reference of most conventional Computational
Fluid Dynamics codes and has been coupled with Brownâs Vorticity Transport Model. Verification of the
predictions of the coupled model against experimental data for particulate entrainment and transport in
the flow around a model rotor are encouraging. An application of the coupled model to analyzing the
differences in the geometry and extent of the dust clouds that are produced by single main rotor and
tandem-rotor configurations as they decelerate to land has shown that the location of the ground vortex
and the size of any regions of recirculatory flow, should they exist, play a primary role in governing the
extent of the dust cloud that is created by the helicopter
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