3,178 research outputs found
Capacity building during COVID-19: Utilising South Africa’s underutilised international medical graduates
Brain Gene Expression Analysis: a MATLAB toolbox for the analysis of brain-wide gene-expression data
The Allen Brain Atlas project (ABA) generated a genome-scale collection of gene-expression profiles using in-situ hybridization. These profiles were co-registered to the three-dimensional Allen Reference Atlas (ARA) of the adult mouse brain. A set of more than 4,000 such volumetric data are available for the full brain, at a resolution of 200 microns. These data are presented in a voxel-by-gene matrix. The ARA comes with several systems of annotation, hierarchical (40 cortical regions, 209 sub-cortical regions in the whole brain), or non-hierarchical (12 regions in the left hemisphere, with refinement into 94 regions, and cortical layers). The high-dimensional nature of this unique dataset and the possible connection between anatomy and gene expression pose challenges to data analysis. We developed the Brain Gene Expression Analysis Toolbox (downloadable at: www.brainarchitecture.org). The key functionalities include: determination of marker genes for brain regions, statistical analysis of brain-wide co-expression patterns, and the computation of brain-wide correlation maps with cell-type specific microarray data. The auxiliary dataset consisting of cell-type-specific transcriptomes (chapter 4) will be made available in the second version of the toolbox
Chronic inflammation as a manifestation of defects in immunoregulatory networks: implications for novel therapies based on microbial products
Based on a unifying theory presented here, it is predicted that the immune defects resulting in chronic inflammation rather than effective immune responses could be rectified by the therapeutic use of agents prepared from micro-organisms. With appropriate molecular patterns, these should be able to induce protective immunoregulatory networks or to reprogramme defective ones. In contrast to acute inflammation, chronic inflammation appears to have no beneficial role, but is a state of sustained immune reactivity in the presence or progression of a disease process. This results in an escalating cycle of tissue damage followed by unproductive tissue repair, breaks in self-tolerance, malignant transformation or deleterious changes in tissue morphology and function. Such inappropriate immune reactivity is an underlying characteristic, either in initiation or maintenance, of a diverse range of disease states including chronic infection, autoimmunity, allergy, cancer, vascular disease and metabolic alterations. Evidence is presented that the inappropriate immune reactivity is due, at least to some extent, to failures in the establishment of immunoregulatory networks as a result of hygiene-related factors. Such networks are the result of activation of antigen-presenting cells, principally dendritic cells, by molecular patterns of micro-organisms encountered sequentially during life and establishing the "biography" of the immune system.Fil: Bottasso, Oscar Adelmo. Universidad Nacional de Rosario. Facultad de Ciencias Médicas. Instituto de Inmunología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Docena, Guillermo H.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Stanford, J. L.. University College London; Estados UnidosFil: Grange, J. M.. University College London; Estados Unido
Intersublevel Polaron Dephasing in Self-Assembled Quantum Dots
Polaron dephasing processes are investigated in InAs/GaAs dots using
far-infrared transient four wave mixing (FWM) spectroscopy. We observe an
oscillatory behaviour in the FWM signal shortly (< 5 ps) after resonant
excitation of the lowest energy conduction band transition due to coherent
acoustic phonon generation. The subsequent single exponential decay yields long
intraband dephasing times of 90 ps. We find excellent agreement between our
measured and calculated FWM dynamics, and show that both real and virtual
acoustic phonon processes are necessary to explain the temperature dependence
of the polarization decay.Comment: 10 pages, 4 figures, submitted to Phys Rev Let
Fission widths of hot nuclei from Langevin dynamics
Fission dynamics of excited nuclei is studied in the framework of Langevin
equation. The one body wall-and-window friction is used as the dissipative
force in the Langevin equation. In addition to the usual wall formula friction,
the chaos weighted wall formula developed earlier to account for
nonintegrability of single-particle motion within the nuclear volume is also
considered here. The fission rate calculated with the chaos weighted wall
formula is found to be faster by about a factor of two than that obtained with
the usual wall friction. The systematic dependence of fission width on
temperature and spin of the fissioning nucleus is investigated and a simple
parametric form of fission width is obtained.Comment: RevTex, 12 pages including 9 Postscript figure
Towards mirror symmetry \`a la SYZ for generalized Calabi-Yau manifolds
Fibrations of flux backgrounds by supersymmetric cycles are investigated. For
an internal six-manifold M with static SU(2) structure and mirror \hat{M}, it
is argued that the product M x \hat{M} is doubly fibered by supersymmetric
three-tori, with both sets of fibers transverse to M and \hat{M}. The mirror
map is then realized by T-dualizing the fibers. Mirror-symmetric properties of
the fluxes, both geometric and non-geometric, are shown to agree with previous
conjectures based on the requirement of mirror symmetry for Killing
prepotentials. The fibers are conjectured to be destabilized by fluxes on
generic SU(3)xSU(3) backgrounds, though they may survive at type-jumping
points. T-dualizing the surviving fibers ensures the exchange of pure spinors
under mirror symmetry.Comment: 30 pages, 3 figures, LaTeX; v2: references adde
Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission
A theoretical model of one-body nuclear friction which was developed earlier,
namely the chaos-weighted wall formula, is applied to a dynamical description
of compound nuclear decay in the framework of the Langevin equation coupled
with statistical evaporation of light particles and photons. We have used both
the usual wall formula friction and its chaos-weighted version in the Langevin
equation to calculate the fission probability and prescission neutron
multiplicity for the compound nuclei W, Pt, Pb,
Fr, Th, and Es. We have also obtained the contributions
of the presaddle and postsaddle neutrons to the total prescission multiplicity.
A detailed analysis of our results leads us to conclude that the chaos-weighted
wall formula friction can adequately describe the fission dynamics in the
presaddle region. This friction, however, turns out to be too weak to describe
the postsaddle dynamics properly. This points to the need for a suitable
explanation for the enhanced neutron emission in the postsaddle stage of
nuclear fission.Comment: RevTex, 14 pages including 5 Postscript figures, results improved by
using a different potential, conclusions remain unchanged, to appear in Phys.
Rev.
Modeling of mode-locking in a laser with spatially separate gain media
We present a novel laser mode-locking scheme and discuss its unusual
properties and feasibility using a theoretical model. A large set of
single-frequency continuous-wave lasers oscillate by amplification in spatially
separated gain media. They are mutually phase-locked by nonlinear feedback from
a common saturable absorber. As a result, ultra short pulses are generated. The
new scheme offers three significant benefits: the light that is amplified in
each medium is continuous wave, thereby avoiding issues related to group
velocity dispersion and nonlinear effects that can perturb the pulse shape. The
set of frequencies on which the laser oscillates, and therefore the pulse
repetition rate, is controlled by the geometry of resonator-internal optical
elements, not by the cavity length. Finally, the bandwidth of the laser can be
controlled by switching gain modules on and off. This scheme offers a route to
mode-locked lasers with high average output power, repetition rates that can be
scaled into the THz range, and a bandwidth that can be dynamically controlled.
The approach is particularly suited for implementation using semiconductor
diode laser arrays.Comment: 13 pages, 5 figures, submitted to Optics Expres
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