709 research outputs found
Rayleigh superradiance and dynamic Bragg gratings in an end-pumped Bose-Einstein condensate
We study experimentally superradiant Rayleigh scattering from a Bose-Einstein
condensate (BEC) in a new parameter regime where pump depletion and the
exchange of photons between the endfire modes are important. Through
experiments and simulations we show that collective atom light coupling leads
to the self-organized formation of dynamic Bragg gratings within the sample.
These gratings lead to an efficient back-scattering of pump photons and optical
resonator structures within the BEC.Comment: 5 pages, 3 figure
Clozapine-induced agranulocytosis is associated with rare HLA-DQB1 and HLA-B alleles
Clozapine is a particularly effective antipsychotic medication but its use is curtailed by the risk of clozapine-induced agranulocytosis/granulocytopenia (CIAG), a severe adverse drug reaction occurring in up to 1% of treated individuals. Identifying genetic risk factors for CIAG could enable safer and more widespread use of clozapine. Here we perform the largest and most comprehensive genetic study of CIAG to date by interrogating 163 cases using genomewide genotyping and whole-exome sequencing. We find that two loci in the major histocompatibility complex are independently associated with CIAG: a single amino acid in HLA-DQB1 (126Q) (P = 4.7 x 10(-14), odds ratio (OR) = 0.19, 95% confidence interval (CI) = 0.12-0.29) and an amino acid change in the extracellular binding pocket of HLA-B (158T) (P = 6.4 x 10(-10), OR = 3.3, 95% CI = 2.3-4.9). These associations dovetail with the roles of these genes in immunogenetic phenotypes and adverse drug responses for other medications, and provide insight into the pathophysiology of CIAG
Size-dependent spinodal and miscibility gaps for intercalation in nano-particles
Using a recently-proposed mathematical model for intercalation dynamics in
phase-separating materials [Singh, Ceder, Bazant, Electrochimica Acta 53, 7599
(2008)], we show that the spinodal and miscibility gaps generally shrink as the
host particle size decreases to the nano-scale. Our work is motivated by recent
experiments on the high-rate Li-ion battery material LiFePO4; this serves as
the basis for our examples, but our analysis and conclusions apply to any
intercalation material. We describe two general mechanisms for the suppression
of phase separation in nano-particles: (i) a classical bulk effect, predicted
by the Cahn-Hilliard equation, in which the diffuse phase boundary becomes
confined by the particle geometry; and (ii) a novel surface effect, predicted
by chemical-potential-dependent reaction kinetics, in which
insertion/extraction reactions stabilize composition gradients near surfaces in
equilibrium with the local environment. Composition-dependent surface energy
and (especially) elastic strain can contribute to these effects but are not
required to predict decreased spinodal and miscibility gaps at the nano-scale
Spinodal Decomposition and Inflation: Dynamics and Metric Perturbations
We analyse the dynamics of spinodal decomposition in inflationary cosmology
using the closed time path formalism of out of equilibrium quantum field theory
combined with the non-perturbative Hartree approximation. In addition to a
general analysis, we compute the detailed evolution of two inflationary models
of particular importance: lambda Phi^4 new inflation and natural inflation. We
compute the metric fluctuations resulting from inflationary phase transitions
in the slow roll approximation, showing that there exists a regime for which
quantum fluctuations of the inflaton field result in a significant deviation in
the predictions of the spectrum of primordial density perturbations from
standard results. We provide case examples for which a blue tilt to the power
spectrum (i.e. n_s > 1) results from the evolution of a single inflaton field,
and demonstrate that field fluctuations may result in a scalar amplitude of
fluctuations significantly below standard predictions, resulting in a slight
alleviation of the inflationary fine tuning problem. We show explicitly that
the metric perturbation spectrum resulting from inflation depends upon the
state at the outset of the inflationary phase.Comment: 26 pages, 19 figure
In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn+0.8 vol pct TiBâ‚‚
The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiBâ‚‚ intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.The authors are grateful to Industria de Turbo Propulsores, S.A. for supplying the intermetallic blades. Funding from the Spanish Ministry of Science and Innovation through projects MAT2009-14547-C02-01 and MAT2009-14547-C02-02 is acknowledged. The Madrid Regional Government supported this project partially through the ESTRUMAT grant P2009/MAT-1585. C.J.B. acknowledges the support from Grant SAB2009-0045 from the Spanish Ministry of Education for his sabbatical stage in Madrid.Publicad
The violence of peace and the role of education: insights from Sierra Leone
Research on peacebuilding has mushroomed over the last decade and there is a growing interest in the role of education in supporting peacebuilding processes. This paper engages with these debates, UN peacebuilding activities and the location of education initiatives therein, through a case study of Sierra Leone. In the first part, we explore the complex and multi-dimensional nature of violence in post-conflict Sierra Leone. In the second, we critically address the role of education in the conflict and post-conflict period, highlighting education’s centrality as a catalyst to conflict, and then reflect on the failure of the post-conflict reconstruction process to adequately transform the education system into one that could support a process of sustainable peacebuilding. Finally, we conclude by exploring the ways that greater investment and focus, both financial and human, in the education sector might, in the long term, better contribute to a sustainable and socially just peace
Large-scale associations between the leukocyte transcriptome and BOLD responses to speech differ in autism early language outcome subtypes.
Heterogeneity in early language development in autism spectrum disorder (ASD) is clinically important and may reflect neurobiologically distinct subtypes. Here, we identified a large-scale association between multiple coordinated blood leukocyte gene coexpression modules and the multivariate functional neuroimaging (fMRI) response to speech. Gene coexpression modules associated with the multivariate fMRI response to speech were different for all pairwise comparisons between typically developing toddlers and toddlers with ASD and poor versus good early language outcome. Associated coexpression modules were enriched in genes that are broadly expressed in the brain and many other tissues. These coexpression modules were also enriched in ASD-associated, prenatal, human-specific, and language-relevant genes. This work highlights distinctive neurobiology in ASD subtypes with different early language outcomes that is present well before such outcomes are known. Associations between neuroimaging measures and gene expression levels in blood leukocytes may offer a unique in vivo window into identifying brain-relevant molecular mechanisms in ASD
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