1,390 research outputs found
Pulsed flows at the high-altitude cusp poleward boundary, and associated ionospheric convection and particle signatures, during a cluster - FAST - SuperDARN - sondrestrom conjunction under a southwest
Particle and magnetic field observations during a magnetic conjunction Cluster 1-FAST-Søndrestrøm within the field of view of SuperDARN radars on 21 January 2001 allow us to draw a detailed, comprehensive and self-consistent picture at three heights of signatures associated with transient reconnection under a steady south-westerly IMF (clock angle ≈130◦). Cluster 1 was outbound through the high altitude (∼12RE ) exterior northern cusp tailward of the bifurcation line (geomagnetic Bx>0) when a solar wind dynamic pressure release shifted the spacecraft into a boundary layer downstream of the cusp. The centerpiece of the investigation is a series of flow bursts observed there by the spacecraft, which were accompanied by strong field pertur- bations and tailward flow deflections. Analysis shows these to be Alfven waves. We interpret these flow events as being due to a sequence of reconnected flux tubes, with field-aligned currents in the associated Alfven waves carrying stresses to the underlying ionosphere, a view strengthened by the other observations. At the magnetic footprint of the region of Cluster flow bursts, FAST observed an ion energy- latitude disperison of the stepped cusp type, with individual cusp ion steps corresponding to individual flow bursts. Simultaneously, the SuperDARN Stokkseyri radar observed very strong poleward-moving radar auroral forms (PMRAFs) which were conjugate to the flow bursts at Cluster. FAST was traversing these PMRAFs when it observed the cusp ion steps. The Søndrestrøm radar observed pulsed ionospheric flows (PIFs) just poleward of the convection reversal boundary. As at Cluster, the flow was eastward (tailward), implying a coherent eastward (tailward) motion of the hypothesized open flux tubes. The joint Søndrestrøm and FAST observations indicate that the open/closed field line boundary was equatorward of the convection reversal boundary by ∼2 deg. The unprecedented accuracy of the conjunction argues strongly for the validity of the interpretation of the various signatures as resulting from transient reconnection. In particular, the cusp ion steps arise on this pass from this origin, in consonance with the original pulsating cusp model. The observations point to the need of extending current ideas on the response of the ionosphere to transient reconnection. Specifically, it argues in favor of re-establishing the high-latitude boundary layer downstream of the cusp as an active site of momentum transfer
Antibody mediated neutralization of myelin associated EphrinB3 accelerates CNS remyelination
This is the final version of the article. It was first available from Springer via
http://dx.doi.org/10.1007/s00401-015-1521-1Remyelination in multiple sclerosis (MS) lesions often remains incomplete despite the presence of oligodendrocyte progenitor cells (OPCs). Amongst other factors, successful remyelination depends on the phagocytic clearance of myelin debris. However, the proteins in myelin debris that act as potent and selective inhibitors on OPC differentiation and inhibit CNS remyelination remain unknown. Here, we identify the transmembrane signalling protein EphrinB3 as important mediator of this inhibition, using a protein analytical approach in combination with a primary rodent OPC assay. In the presence of EphrinB3, OPCs fail to differentiate. In a rat model of remyelination, infusion of EphrinB3 inhibits remyelination. In contrast, masking EphrinB3 epitopes using antibodies promotes remyelination. Finally, we identify EphrinB3 in MS lesions and demonstrate that MS lesion extracts inhibit OPC differentiation while antibody-mediated masking of EphrinB3 epitopes promotes it. Our findings suggest that EphrinB3 could be a target for therapies aiming at promoting remyelination in demyelinating disease.This work was supported by the UK MS Society Grant ref: 941/11. MRNK held a NIHR
Clinical Lectureship. KAN was supported by an ERC advanced award
Scaling of the Conductivity with Temperature and Uniaxial Stress in Si:B at the Metal-Insulator Transition
Using uniaxial stress to tune Si:B through the metal-insulator transition we
find the conductivity at low temperatures shows an excellent fit to scaling
with temperature and stress on both sides of the transition. The scaling
functions yield the conductivity in the metallic and insulating phases, and
allow a reliable determination of the temperature dependence in the critical
regions on both sides of the transition
Inhibition of CNS remyelination by the presence of semaphorin 3A
Failure of oligodendrocyteprecursor cell (OPC)differentiationhasbeen recognized asthe leading causeforthefailure ofmyelin regenerationin
diseases such as multiple sclerosis (MS). One explanation for the failure of OPC differentiation in MS is the presence of inhibitory molecules in
demyelinatedlesions.Sofaronly afewinhibitory substrateshavebeenidentifiedinMSlesions.Semaphorin3A (Sema3A), a secretedmemberof
the semaphorin family, can act as repulsive guidance cue for neuronal and glial cells in the CNS. Recent studies suggest that Sema3A is also
expressedin activeMSlesions.However,theimplicationof Sema3A expressioninMSlesions remainsunclear asOPCs are commonlypresentin
chronic demyelinated lesions. In the present study we identify Sema3A as a potent, selective, and reversible inhibitor of OPC differentiation in
vitro. Furthermore, we show that administration of Sema3A into demyelinating lesions in the rat CNS results in a failure of remyelination. Our
results imply an important role for Sema3A in the differentiation block occurring in MS lesions
Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations with Ulysses Observations
The most stringent test of theoretical models of the first-order Fermi
mechanism at collisionless astrophysical shocks is a comparison of the
theoretical predictions with observational data on particle populations. Such
comparisons have yielded good agreement between observations at the
quasi-parallel portion of the Earth's bow shock and three theoretical
approaches, including Monte Carlo kinetic simulations. This paper extends such
model testing to the realm of oblique interplanetary shocks: here observations
of proton and alpha particle distributions made by the SWICS ion mass
spectrometer on Ulysses at nearby interplanetary shocks are compared with test
particle Monte Carlo simulation predictions of accelerated populations. The
plasma parameters used in the simulation are obtained from measurements of
solar wind particles and the magnetic field upstream of individual shocks. Good
agreement between downstream spectral measurements and the simulation
predictions are obtained for two shocks by allowing the the ratio of the
mean-free scattering length to the ionic gyroradius, to vary in an optimization
of the fit to the data. Generally small values of this ratio are obtained,
corresponding to the case of strong scattering. The acceleration process
appears to be roughly independent of the mass or charge of the species.Comment: 26 pages, 6 figures, AASTeX format, to appear in the Astrophysical
Journal, February 20, 199
Clinical significance of VEGF-A, -C and -D expression in esophageal malignancies
Vascular endothelial growth factors ( VEGF)- A, - C and - D are members of the proangiogenic VEGF family of glycoproteins. VEGF-A is known to be the most important angiogenic factor under physiological and pathological conditions, while VEGF-C and VEGF-D are implicated in the development and sprouting of lymphatic vessels, so called lymphangiogenesis. Local tumor progression, lymph node metastases and hematogenous tumor spread are important prognostic factors for esophageal carcinoma ( EC), one of the most lethal malignancies throughout the world. We found solid evidence in the literature that VEGF expression contributes to tumor angiogenesis, tumor progression and lymph node metastasis in esophageal squamous cell carcinoma ( SCC), and many authors could show a prognostic value for VEGF-assessment. In adenocarcinoma (AC) of the esophagus angiogenic properties are acquired in early stages, particularly in precancerous lesions like Barrett's dysplasia. However, VEGF expression fails to give prognostic information in AC of the esophagus. VEGF-C and VEGF-D were detected in SCC and dysplastic lesions, but not in normal mucosa of the esophagus. VEGF-C expression might be associated with lymphatic tumor invasion, lymph node metastases and advanced disease in esophageal SCC and AC. Therapeutic interference with VEGF signaling may prove to be a promising way of anti-angiogenic co-treatment in esophageal carcinoma. However, concrete clinical data are still pending
The Plasma and Suprathermal Ion Composition (PLASTIC) investigation on the STEREO observatories
The Plasma and Suprathermal Ion Composition (PLASTIC) investigation provides the in situ solar wind and low energy heliospheric ion measurements for the NASA Solar Terrestrial Relations Observatory Mission, which consists of two spacecraft (STEREO-A, STEREO-B). PLASTIC-A and PLASTIC-B are identical. Each PLASTIC is a time-of-flight/energy mass spectrometer designed to determine the elemental composition, ionic charge states, and bulk flow parameters of major solar wind ions in the mass range from hydrogen to iron. PLASTIC has nearly complete angular coverage in the ecliptic plane and an energy range from ∼0.3 to 80 keV/e, from which the distribution functions of suprathermal ions, including those ions created in pick-up and local shock acceleration processes, are also provided
Solar wind ion trends and signatures: STEREO PLASTIC observations approaching solar minimum
STEREO has now completed the first two years of its mission, moving from close proximity to Earth in 2006/2007 to more than 50 degrees longitudinal separation from Earth in 2009. During this time, several large-scale structures have been observed in situ. Given the prevailing solar minimum conditions, these structures have been predominantly coronal hole-associated solar wind, slow solar wind, their interfaces, and the occasional transient event. In this paper, we extend earlier solar wind composition studies into the current solar minimum using high-resolution (1-h) sampling times for the charge state analysis. We examine 2-year trends for iron charge states and solar wind proton speeds, and present a case study of Carrington Rotation 2064 (December 2007) which includes minor ion (He, Fe, O) kinetic and Fe composition parameters in comparison with proton and magnetic field signatures at large-scale structures observed during this interval
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