933 research outputs found
Structure and stability of helices in square-well homopolymers
Recently, it has been demonstrated [Magee et al., Phys. Rev. Lett. 96, 207802
(2006)] that isolated, square-well homopolymers can spontaneously break chiral
symmetry and freeze into helical structures at sufficiently low temperatures.
This behavior is interesting because the square-well homopolymer is itself
achiral. In this work, we use event-driven molecular dynamics, combined with an
optimized parallel tempering scheme, to study this polymer model over a wide
range of parameters. We examine the conditions where the helix structure is
stable and determine how the interaction parameters of the polymer govern the
details of the helix structure. The width of the square well (proportional to
lambda) is found to control the radius of the helix, which decreases with
increasing well width until the polymer forms a coiled sphere for sufficiently
large wells. The helices are found to be stable for only a window of molecular
weights. If the polymer is too short, the helix will not form. If the polymer
is too long, the helix is no longer the minimum energy structure, and other
folded structures will form. The size of this window is governed by the chain
stiffness, which in this model is a function of the ratio of the monomer size
to the bond length. Outside this window, the polymer still freezes into a
locked structure at low temperature, however, unless the chain is sufficiently
stiff, this structure will not be unique and is similar to a glassy state.Comment: Submitted to Physical Review
Movers and shakers: Granular damping in microgravity
The response of an oscillating granular damper to an initial perturbation is
studied using experiments performed in microgravity and granular dynamics
mulations. High-speed video and image processing techniques are used to extract
experimental data. An inelastic hard sphere model is developed to perform
simulations and the results are in excellent agreement with the experiments.
The granular damper behaves like a frictional damper and a linear decay of the
amplitude is bserved. This is true even for the simulation model, where
friction forces are absent. A simple expression is developed which predicts the
optimal damping conditions for a given amplitude and is independent of the
oscillation frequency and particle inelasticities.Comment: 9 pages, 9 figure
Using Cold Atoms to Measure Neutrino Mass
We propose a beta decay experiment based on a sample of ultracold atomic
tritium. These initial conditions enable detection of the helium ion in
coincidence with the beta. We construct a two-dimensional fit incorporating
both the shape of the beta-spectrum and the direct reconstruction of the
neutrino mass peak. We present simulation results of the feasible limits on the
neutrino mass achievable in this new type of tritium beta-decay experiment.Comment: 10 pages, 5 figure
Identification of candidate genes affecting chronic subclinical mastitis in Norwegian Red cattle: combining genomeâwide association study, topologically associated domains and pathway enrichment analysis
The aim of this study was to identify genes associated with chronic subclinical mastitis (SCM) in Norwegian Red (NR) cattle. Twelve SCM traits defined based on fixed threshold for testâday somatic cell count (SCC) were, together with lactationâaverage somatic cell score (LSCS) used for association and pathway enrichment analyses. A GWAS was performed on 3795 genotyped NR bulls with 777K SNP data and phenotypic information from 7 300 847 testâday SCC observations from 3 543 764 cows. At 5% chromosomeâwide significance level 36 unique SNP were detected to be associated with one or more of the traits. These SNPs were analysed for linked genes using genomic positions of topologically associated domains (TAD). For the SCM traits with SCC >50 000 and >100 000 cells/ml on two testâdays in a row and LSCS, the same top significant genes were identified â checkpoint clamp loader component (RAD17) and cyclin B1 (CCNB1). The SCM traits with SCC >250 000, 300 000, 350 000 or 400 000 cells/ml on two testâdays in a row and D400 (number of days before the first case with SCC >400 000 cells/ml) displayed similar top significant genes: acylâCoA thioesterase 2 and 4 (ACOT2; ACOT4). For the traits SCM200_3 (SCC >200 000 cells/ml on three testâdays in a row) and SCM150, SCM200 (SCC >150 000; 200 000 cells/ml on two testâdays in a row) a group of chemokine (CâXâC motif) ligand genes and the Fos protoâoncogene, APâ1 transcription factor subunit (FOS) gene, were identified. Further functional studies of these identified candidate genes are necessary to clarify their actual role in development of chronic SCM in NR cattle.publishedVersio
An evaluation of the benefits and harms of antenatal corticosteroid treatment for women at risk of imminent preterm birth or prior to elective Caesarean-section: an individual participant data meta-analysis.:Study protocol
Background: Antenatal corticosteroid treatment (ACT) has been widely accepted as a safe, beneficial treatment which improves outcomes following preterm birth. It has been shown to reduce respiratory distress syndrome and neonatal mortality and is commonly used in threatened or planned preterm delivery, as well as prior to elective Caesarean-section at term. There are some concerns however, that in some cases, ACT is used in patients where clinical benefit has not been established, or may potentially increase harm. Many women who receive ACT do not deliver preterm and the long-term consequences of ACT treatment are unclear. This study aims to evaluate the benefits and harms of ACT using latest trial evidence to allow refinement of current practice. Methods: This study will compare ACT with placebo or non-treatment. Inclusion criteria are: Randomised Controlled Trials (RCT) comparing ACT vs. no ACT (with or without placebo) in all settings. Exclusion criteria are: non-randomised or quasi-randomised studies and studies comparing single vs. multiple courses of ACT. Main outcomes are to evaluate, for women at risk of preterm birth or undergoing planned Caesarean- section, the benefits and harms of ACT, on maternal, fetal, newborn, and long-term offspring health outcomes. The individual participant data (IPD) of identified RCTs will be collected and consecutively synthesised using meta-analysis with both a one-stage model where all IPD is analysed together and a two-stage model where treatment effect estimates are calculated for each trial individually first and thereafter pooled in a meta-analysis. Sub-group analysis will be performed to identify heterogeneous effects of ACT across predefined risk groups. Discussion: Co-opt is the Consortium for the Study of Pregnancy Treatments and aims to complete a robust evaluation of the benefits and harms of ACT. This IPD meta-analysis will contribute to this by allowing detailed interrogation of existing trial datasets. PROSPERO registration: CRD42020167312 (03/02/2020
Single-Photon Molecular Cooling
We propose a general method to cool the translational motion of molecules.
Our method is an extension of single photon atomic cooling which was
successfully implemented in our laboratory. Requiring a single event of
absorption followed by a spontaneous emission, this method circumvents the need
for a cycling transition and can be applied to any paramagnetic or polar
molecule. In our approach, trapped molecules would be captured near their
classical turning points in an optical dipole or RF-trap following an
irreversible transition process
Reflections on a degree initiative: the UK's Birmingham Royal Ballet dancers enter the University of Birmingham
This paper provides an opportunity to share experiences and perceptions of the first 5 years of a degree programme for professional dancers. A partnership developed in the mid-1990s between the UK's Birmingham Royal Ballet and the University of Birmingham, Westhill (now School of Education), to provide a part-time, post-experience, flexible study programme for full-time Company dancers. This is the first 'company customised' higher education programme to dovetail studies around rehearsal, performance and touring schedules. Methodology is based on a narrative by the author, informed by ongoing internal and external evaluations, in-depth interviews with dancers and Company managers, documentation and secondary sources. Outcomes indicate that the programme has made a positive difference to the Company, to the dancers and to the wider education and dance/arts world
Collision statistics in sheared inelastic hard spheres
The dynamics of sheared inelastic-hard-sphere systems are studied using
non-equilibrium molecular dynamics simulations and direct simulation Monte
Carlo. In the molecular dynamics simulations Lees-Edwards boundary conditions
are used to impose the shear. The dimensions of the simulation box are chosen
to ensure that the systems are homogeneous and that the shear is applied
uniformly. Various system properties are monitored, including the one-particle
velocity distribution, granular temperature, stress tensor, collision rates,
and time between collisions. The one-particle velocity distribution is found to
agree reasonably well with an anisotropic Gaussian distribution, with only a
slight overpopulation of the high velocity tails. The velocity distribution is
strongly anisotropic, especially at lower densities and lower values of the
coefficient of restitution, with the largest variance in the direction of
shear. The density dependence of the compressibility factor of the sheared
inelastic hard sphere system is quite similar to that of elastic hard sphere
fluids. As the systems become more inelastic, the glancing collisions begin to
dominate more direct, head-on collisions. Examination of the distribution of
the time between collisions indicates that the collisions experienced by the
particles are strongly correlated in the highly inelastic systems. A comparison
of the simulation data is made with DSMC simulation of the Enskog equation.
Results of the kinetic model of Montanero et al. {[}Montanero et al., J. Fluid
Mech. 389, 391 (1999){]} based on the Enskog equation are also included. In
general, good agreement is found for high density, weakly inelastic systems.Comment: 10 figures, 1 table, 27 page
Persistent microglial activation and synaptic loss with behavioral abnormalities in mouse offspring exposed to CASPR2-antibodies in utero
Gestational transfer of maternal antibodies against fetal neuronal proteins may be relevant to some neurodevelopmental disorders, but until recently there were no proteins identified. We recently reported a fivefold increase in CASPR2-antibodies in mid-gestation sera from mothers of children with intellectual and motor disabilities. Here, we exposed mice in utero to purified IgG from patients with CASPR2-antibodies (CASPR2-IgGs) or from healthy controls (HC-IgGs). CASPR2-IgG but not HC-IgG bound to fetal brain parenchyma, from which CASPR2-antibodies could be eluted. CASPR2-IgG exposed neonates achieved milestones similarly to HC-IgG exposed controls but, when adult, the CASPR2-IgG exposed progeny showed marked social interaction deficits, abnormally located glutamatergic neurons in layers V-VI of the somatosensory cortex, a 16% increase in activated microglia, and a 15-52% decrease in glutamatergic synapses in layers of the prefrontal and somatosensory cortices. Thus, in utero exposure to CASPR2-antibodies led to permanent behavioral, cellular, and synaptic abnormalities. These findings support a pathogenic role for maternal antibodies in human neurodevelopmental conditions, and CASPR2 as a potential target
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