2,283 research outputs found
A method to polarise antiprotons in storage rings and create polarised antineutrons
An intense circularely polarised photon beam interacts with a cooled
antiproton beam in a storage ring. Due to spin dependent absorption cross
sections for the reaction gamma+antiproton > pi- + antineutron a built-up of
polarisation of the stored antiprotons takes place. Figures-of-merit around 0.1
can be reached in principle over a wide range of antiproton energies. In this
process antineutrons with Polarisation > 70% emerge. The method is presented
for the case of 300 MeV/c cooled antiproton beam
Hypoxia‐induced vascular endothelial growth factor expression causes vascular leakage in the brain
Formation of cerebral oedema caused by vascular leakage is a major problem in various injuries of the CNS, such as stroke, head injury and high‐altitude illness. A common feature of all these disorders is the fact that they are associated with tissue hypoxia. Hypoxia has therefore been suggested to be an important pathogenic factor for the induction of vascular leakage in the brain. Vascular endothelial growth factor (VEGF) is known as the major inducer of angiogenesis. Originally, however, it was described as a vascular permeability factor. As VEGF gene expression was shown to be upregulated by hypoxia, increased VEGF expression may link hypoxia and vascular leakage in the CNS in vivo. To delineate the role of VEGF in vascular leakage in the brain, we studied the effect of hypoxia on VEGF expression and vascular permeability in the brains of mice in vivo. Hypoxic exposure led to a significant increase in the levels of VEGF mRNA and protein in mouse brain that correlated with the severity of the hypoxic stimulus. Measurement of vascular permeability using the fluorescent marker sodium fluorescein revealed a two‐fold increase in fluorescence intensity in hypoxic brains, indicative of significant vascular leakage. Inhibition of VEGF activity by a neutralizing antibody completely blocked the hypoxia‐induced increase in vascular permeability. In conclusion, our data show that VEGF is responsible for hypoxia‐induced augmentation in vascular leakage following tissue hypoxia. Our findings might provide the basis for new therapeutic concepts for the treatment of cerebral oedem
Field-induced domain wall propagation: beyond the one-dimensional model
We have investigated numerically the field-driven propagation of
perpendicularly magnetized ferromagnetic layers. It was then compared to the
historical one-dimensional domain wall (DW) propagation model widely used in
spintronics studies of magnetic nanostructures. In the particular regime of
layer thickness (h) of the order of the exchange length, anomalous velocity
peaks appear in the precessional regime, their shape and position shifting with
h. This has also been observed experimentally. Analyses of the simulations show
a distinct correlation between the curvature of the DW and the twist of the
magnetization vector within it, and the velocity peak. Associating a
phenomenological description of this twist with a four-coordinate DW
propagation model, we reproduce very well these kinks and show that they result
from the torque exerted by the stray field created by the domains on the
twisted magnetization. The position of the peaks is well predicted from the
DW's first flexural mode frequency, and depends strongly on the layer
thickness. Comparison of the proposed model to DW propagation data obtained on
dilute semiconductor ferromagnets GaMnAs and GaMnAsP sheds light on the origin
of the measured peaks
- …