25,332 research outputs found
Two-photon imaging of cell-specific fluorophores in transgenic mice – an exploratory tool to study mechanisms of white matter injury
Relatively little is known about specific pathways leading to structural and functional disruption of axons and glial cells in white matter. Because focal cerebral ischemia in humans damages both gray and white matter, an understanding of white matter injury is important in devising potential therapeutic approaches. We have developed a novel brain slice model from transgenic mice under control of cell-specific promoters to understand interactions between oligodendrocytes and axons under high resolution twophoton microscopy. Our data extends over previous findings the vulnerability of oligodendrocytes and axons both in culture and in slice preparations to glutamate toxicity during stroke and hypoglycemia. Conditions as different as stroke, trauma, perinatal brain injury, and multiple sclerosis may share common mechanisms of white matter injury.N/
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Upgrade to the SHARP EUV mask microscope
The Sharp High-NA Actinic Reticle review Project (SHARP) is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. A potential upgrade to the SHARP microscope is presented. The upgrade includes changing the light path in the instrument from its current off-Axis configuration to an on-Axis configuration. This change allows for an increased working distance of 2.5 mm or more. A central obscuration, added to the zoneplate aperture, blocks stray light from reaching the central part of the image, thus improving the image contrast. The imaging performance of the two configurations is evaluated by means of ray tracing
The Galaxy Octopole Moment as a Probe of Weak Lensing Shear Fields
In this paper, we introduce the octopole moment of the light distribution in
galaxies as a probe of the weak lensing shear field. While traditional
ellipticity estimates of the local shear derived from the quadrupole moment are
limited by the width of the intrinsic ellipticity distribution of background
galaxies, the dispersion in the intrinsic octopole distribution is expected to
be much smaller, implying that the signal from this higher order moment is
ultimately limited by measurement noise, and not by intrinsic scatter. We
present the computation of the octopole moment and show that current
observations are at the regime where the octopole estimates will soon be able
to contribute to the overall accuracy of the estimates of local shear fields.
Therefore, the prospects for this estimator from future datasets like the
Advanced Camera for Survey and the Next Generation Space Telescope are very
promising.Comment: 9 pages, 2 PostScript figures; Submitted to Astrophysical Journa
What is the excess risk of infertility in women after genital chlamydia infection? A systematic review of the evidence
Methods: Twelve databases were searched, limited to peer-reviewed literature published from January 1970 to September 2007. Conference abstracts and reference lists from reviews published since 2000 and from key articles were hand-searched. Studies were selected for review if they met the following criteria: (1) the study population comprised women of child-bearing age (defined as 15–45 years) and incorporated a comparison group of women documented as "chlamydia negative"; (2) the study outcomes included either infertility or successful pregnancy; and (3) the study design was one of the following: cohort, randomised controlled trial, "before and after" study, screening trial and systematic review. Studies were excluded if they described genital infections that either did not include Chlamydia trachomatis or described genital chlamydial co-infection, in which no data were available for C trachomatis infection alone.
Results: 3349 studies were identified by the search. One study satisfied the inclusion criteria, a longitudinal investigation measuring pregnancy rates in adolescent women with and without current chlamydial infection at baseline. That study reported no significant difference in subsequent pregnancy rates; however, it had serious methodological limitations, which restricted its conclusions.
Conclusions: This systematic review demonstrates the absence of valid evidence on the attributable risk of post-infective tubal factor infertility after genital chlamydial infection. The findings contribute empirical data to the growing debate surrounding previous assumptions about the natural history of chlamydial infection in women
Reconstruction of Cluster Masses using Particle Based Lensing I: Application to Weak Lensing
We present Particle-Based Lensing (PBL), a new technique for gravitational
lensing mass reconstructions of galaxy clusters. Traditionally, most methods
have employed either a finite inversion or gridding to turn observational
lensed galaxy ellipticities into an estimate of the surface mass density of a
galaxy cluster. We approach the problem from a different perspective, motivated
by the success of multi-scale analysis in smoothed particle hydrodynamics. In
PBL, we treat each of the lensed galaxies as a particle and then reconstruct
the potential by smoothing over a local kernel with variable smoothing scale.
In this way, we can tune a reconstruction to produce constant signal-noise
throughout, and maximally exploit regions of high information density.
PBL is designed to include all lensing observables, including multiple image
positions and fluxes from strong lensing, as well as weak lensing signals
including shear and flexion. In this paper, however, we describe a shear-only
reconstruction, and apply the method to several test cases, including simulated
lensing clusters, as well as the well-studied ``Bullet Cluster'' (1E0657-56).
In the former cases, we show that PBL is better able to identify cusps and
substructures than are grid-based reconstructions, and in the latter case, we
show that PBL is able to identify substructure in the Bullet Cluster without
even exploiting strong lensing measurements. We also make our codes publicly
available.Comment: Accepted for publication in ApJ; Codes available at
http://www.physics.drexel.edu/~deb/PBL.htm ; 12 pages,9 figures, section 3
shortene
Weak Gravitational Flexion
Flexion is the significant third-order weak gravitational lensing effect
responsible for the weakly skewed and arc-like appearance of lensed galaxies.
Here we demonstrate how flexion measurements can be used to measure galaxy halo
density profiles and large-scale structure on non-linear scales, via
galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation
functions. We describe the origin of gravitational flexion, and discuss its
four components, two of which are first described here. We also introduce an
efficient complex formalism for all orders of lensing distortion. We proceed to
examine the flexion predictions for galaxy-galaxy lensing, examining isothermal
sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric
and elliptical cases. We show that in combination with shear we can precisely
measure galaxy masses and NFW halo concentrations. We also show how flexion
measurements can be used to reconstruct mass maps in 2-D projection on the sky,
and in 3-D in combination with redshift data. Finally, we examine the
predictions for cosmic flexion, including convergence-flexion
cross-correlations, and find that the signal is an effective probe of structure
on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA
An Anderson-Fano Resonance and Shake-Up Processes in the Magneto-Photoluminescence of a Two-Dimensional Electron System
We report an anomalous doublet structure and low-energy satellite in the
magneto-photoluminescence spectra of a two-dimensional electron system. The
doublet structure moves to higher energy with increasing magnetic field and is
most prominent at odd filling factors 5 and 3. The lower-energy satellite peak
tunes to lower energy for increasing magnetic field between filling factor 6
and 2. These features occur at energies below the fundamental band of
recombination originating from the lowest Landau level and display striking
magnetic field and temperature dependence that indicates a many-body origin.
Drawing on a recent theoretical description of Hawrylak and Potemski, we show
that distinct mechanisms are responsible for each feature.Comment: 14 pages including 5 figures. To appear in the April 15th edition of
Phy. Rev. B. rapid com
The Goldberg-Sachs theorem in linearized gravity
The Goldberg-Sachs theorem has been very useful in constructing algebraically
special exact solutions of Einstein vacuum equation. Most of the physical
meaningful vacuum exact solutions are algebraically special. We show that the
Goldberg-Sachs theorem is not true in linearized gravity. This is a remarkable
result, which gives light on the understanding of the physical meaning of the
linearized solutions.Comment: 6 pages, no figures, LaTeX 2
L^p boundedness of the wave operator for the one dimensional Schroedinger operator
Given a one dimensional perturbed Schroedinger operator H=-(d/dx)^2+V(x) we
consider the associated wave operators W_+, W_- defined as the strong L^2
limits as s-> \pm\infty of the operators e^{isH} e^{-isH_0} We prove that the
wave operators are bounded operators on L^p for all 1<p<\infty, provided
(1+|x|)^2 V(x) is integrable, or else (1+|x|)V(x) is integrable and 0 is not a
resonance. For p=\infty we obtain an estimate in terms of the Hilbert
transform. Some applications to dispersive estimates for equations with
variable rough coefficients are given.Comment: 26 page
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