403 research outputs found
Phonons from neutron powder diffraction
The spherically averaged structure function \soq obtained from pulsed
neutron powder diffraction contains both elastic and inelastic scattering via
an integral over energy. The Fourier transformation of \soq to real space, as
is done in the pair density function (PDF) analysis, regularizes the data, i.e.
it accentuates the diffuse scattering. We present a technique which enables the
extraction of off-center phonon information from powder diffraction experiments
by comparing the experimental PDF with theoretical calculations based on
standard interatomic potentials and the crystal symmetry. This procedure
(dynamics from powder diffraction(DPD)) has been successfully implemented for
two systems, a simple metal, fcc Ni, and an ionic crystal, CaF. Although
computationally intensive, this data analysis allows for a phonon based
modeling of the PDF, and additionally provides off-center phonon information
from powder neutron diffraction
Response of armour steel plates to localised air blast load : a dimensional analysis
We report on the results of dimensional analyses on the dynamic plastic response of square armour steel plates due to detonation of proximal cylindrical charges and ensued air blast loading. By assuming a generic function for the blast load, which is multiplicative comprising its spatial and temporal parts, a set of 14 dimensionless parameters, representative of the load and plate deformation, were identified and recast in the form of dimensionless functions of stand-off to charge diameter ratio. Parametric studies were performed using commercial code ABAQUS’s module of Finite Element hydrocode using MMALE and MMAE techniques, and combined with regression analyses to quantify the dimensional parameters and the expressions for dimensionless functions. A few numerical studies with various FE mesh types were also performed to validate the transient deflections against the small-scale experiments. For pulse loading due to proximal charges of small orders of stand-off/charge diameter ratio, the magnitude of the transverse deflection increased abruptly with incremental decrease in stand-off, in contradistinction to the plate deformations at higher stand-offs where variations in displacement are smooth. This confirmed the existence of a stand-off at which a transition in behaviour takes place. For stand-off values less than charge diameter, a dimensionless energy absorbing effectiveness factor was considered to investigate the prediction of rupture in the plate corresponding to different charge masses. This factor is measured as a baseline parameter to predict, using solely numerical means, the blast loads which ensue rupture on full-scale prototypes
Orbital and spin chains in ZnV2O4
Our powder inelastic neutron scattering data indicate that \zvo is a system
of spin chains that are three dimensionally tangled in the cubic phase above 50
K due to randomly occupied orbitals of V () ions. Below
50 K in the tetragonal phase, the chains become straight due to
antiferro-orbital ordering. This is evidenced by the characteristic wave vector
dependence of the magnetic structure factor that changes from symmetric to
asymmetric at the cubic-to-tetragonal transition
Storage Device Sizing for a Hybrid Railway Traction System by Means of Bicausal Bond Graphs
In this paper, the application of bicausal bond graphs for system design in electrical engineering is emphasized. In particular, it is shown how this approach is very useful for model inversion and parameter dimensioning. To illustrate these issues, a hybrid railway traction device is considered as a case study. The synthesis of a storage device (a supercapacitor) included in this system is then discussed
Investigation of the spin-glass regime between the antiferromagnetic and superconducting phases in FeSeTe
Using bulk magnetization along with elastic and inelastic neutron scattering
techniques, we have investigated the phase diagram of
FeSeTe and the nature of magnetic correlations in three
nonsuperconducting samples of FeSeTe,
FeSeTe and FeSeTe. A cusp
and hysteresis in the temperature dependence of the magnetization for the
and 0.3 samples indicates spin-glass (SG) ordering below K. Neutron scattering measurements indicate that the spin-glass behavior is
associated with short-range spin density wave (SDW) ordering characterized by a
static component and a low-energy dynamic component with a characteristic
incommensurate wave vector of and an anisotropy
gap of 2.5 meV. Our high -resolution data also show that the
systems undergo a glassy structural distortion that coincides with the
short-range SDW order
The dynamics of grooming interactions: maintenance of partner choice and the consequences of demographic variation for female mandrills
A large body of evidence suggests that female Old World monkeys maintain selective long-term grooming interactions with fitness benefits. The last two decades have produced evidence that the regulation of social interactions among primates can be, in part, explained by the Biological Markets theory, with grooming behaviour as the focus of these studies. Grooming facilitates bonding between individuals, constituting an essential part of the regulation of social relationships among female cercopithecids. In contrast to the well-studied baboons (Papio spp), knowledge about the nature of grooming interactions and their regulation is generally lacking for the large, terrestrial species of mandrills (Mandrillus sphinx). We used a combination of social network analysis tools and well-established methods for assessing partner diversity and reciprocity to characterise grooming networks, partner choice and patterns of trade (be groomed, give grooming) among females in a captive group of mandrills, both within and across two separate observation periods. Our results suggest that, even though the relatively stable conditions of captivity allowed the studied females to maintain selective grooming interactions across time, small scale demographic changes affected the grooming dynamics of the group in accordance with the expectations of the Biological Markets theory. In particular, the maturation and consequent integration of a high ranking female into the group’s grooming network from one period to the next resulted in a more pronounced effect of rank on the regulation of grooming interactions. In addition, the influence of the maturation of a dependent infant on the grooming interactions of his mother were evident between periods. Our results also demonstrate that grooming networks are dynamic and that high ranking individuals are not necessarily the most central in grooming networks. Finally, we discuss the potential of social network analysis to identify cases of social exclusion and its consequences for captive management
Nano-magnetic droplets and implications to orbital ordering in La1-xSrxCoO3
Inelastic cold neutron scattering on LaCoO3 provided evidence for a distinct
low energy excitation at 0.6 meV coincident with the thermally induced magnetic
transition. Coexisting strong ferromagnetic (FM) and weaker antiferromagnetic
(AFM) correlations that are dynamic follow the activation to the excited state,
identified as the intermediate S=1 spin triplet. This is indicative of
dynamical orbital ordering favoring the observed magnetic interactions. With
hole doping as in La1-xSrxCoO3, the FM correlations between Co spins become
static and isotropically distributed due to the formation of FM droplets. The
correlation length and condensation temperature of these droplets increase
rapidly with metallicity due to the double exchange mechanism.Comment: To appear in Phys. Rev. Let
The multidimensionality of female mandrill sociality-A dynamic multiplex network approach
Funding: ASP received funding from the School of Biological Sciences, University of Aberdeen, https://www.abdn.ac.uk/sbs/, and was awarded the Watt Fund via the University of Aberdeen https://www.abdn.ac.uk. These funders do not provide grant numbers. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Data Availability: All relevant data are within the manuscript and its Supporting Information files.Peer reviewedPublisher PD
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