2,085 research outputs found
Multidimensional relativistic MHD simulations of Pulsar Wind Nebulae: dynamics and emission
Pulsar Wind Nebulae, and the Crab nebula in particular, are the best cosmic
laboratories to investigate the dynamics of magnetized relativistic outflows
and particle acceleration up to PeV energies. Multidimensional MHD modeling by
means of numerical simulations has been very successful at reproducing, to the
very finest details, the innermost structure of these synchrotron emitting
nebulae, as observed in the X-rays. Therefore, the comparison between the
simulated source and observations can be used as a powerful diagnostic tool to
probe the physical conditions in pulsar winds, like their composition,
magnetization, and degree of anisotropy. However, in spite of the wealth of
observations and of the accuracy of current MHD models, the precise mechanisms
for magnetic field dissipation and for the acceleration of the non-thermal
emitting particles are mysteries still puzzling theorists to date. Here we
review the methodologies of the computational approach to the modeling of
Pulsar Wind Nebulae, discussing the most relevant results and the recent
progresses achieved in this fascinating field of high-energy astrophysics.Comment: 29 pages review, preliminary version. To appear in the book
"Modelling Nebulae" edited by D. Torres for Springer, based on the invited
contributions to the workshop held in Sant Cugat (Barcelona), June 14-17,
201
Precursor Plerionic Activity and High Energy Gamma-Ray Emission in the Supranova Model of Gamma-Ray Bursts
The supranova model of gamma-ray bursts (GRBs), in which the GRB event is
preceded by a supernova (SN) explosion by a few months to years, has recently
gained support from Fe line detections in X-ray afterglows. A crucial
ingredient of this model yet to be studied is the fast-rotating pulsar that
should be active during the time interval between the SN and the GRB, driving a
powerful wind and a luminous plerionic nebula. We discuss some observational
consequences of this precursor plerion, which should provide important tests
for the supranova model: 1) the fragmentation of the outlying SN ejecta
material by the plerion and its implications for Fe line emission; and 2) the
effect of inverse Compton cooling and emission in the GRB external shock due to
the plerion radiation field. The plerion-induced inverse Compton emission can
dominate in the GeV-TeV energy range during the afterglow, being detectable by
GLAST from redshifts and distinguishable from self-Compton
emission by its spectrum and light curve. The prospects for direct detection
and identification of the precursor plerion emission are also briefly
considered.Comment: ApJ vol.583, in pres
The calibers of the common femoral, popliteal, and posterior tibialis arteries: a statistical investigation in 100 healthy subjects by color Doppler ultrasonography.
Characteristics and homogeneity of N6-methylation in human genomes.
A novel DNA modification, N-6 methylated deoxyadenosine (m6dA), has recently been discovered in eukaryotic genomes. Despite its low abundance in eukaryotes, m6dA is implicated in human diseases such as cancer. It is therefore important to precisely identify and characterize m6dA in the human genome. Here, we identify m6dA sites at nucleotide level, in different human cells, genome wide. We compare m6dA features between distinct human cells and identify m6dA characteristics in human genomes. Our data demonstrates for the first time that despite low m6dA abundance, the m6dA mark does often occur consistently at the same genomic location within a given human cell type, demonstrating m6dA homogeneity. We further show, for the first time, higher levels of m6dA homogeneity within one chromosome. Most m6dA are found on a single chromosome from a diploid sample, suggesting inheritance. Our transcriptome analysis not only indicates that human genes with m6dA are associated with higher RNA transcript levels but identifies allele-specific gene transcripts showing haplotype-specific m6dA methylation, which are implicated in different biological functions. Our analyses demonstrate the precision and consistency by which the m6dA mark occurs within the human genome, suggesting that m6dA marks are precisely inherited in humans
The original calibre of the lower limbs arteries as a possible risk factor for complications of atherosclerosis: a statistical investigation in 90 subjects by echocolor-doppler.
Acylphosphatase stimulates Ca2+-transport and Ca2+-dependent ATPase activity in cardiac sarcoplasmic reticulum
Elevated insulin sensitivity and -cell function during pregnancy in mothers of growth-restricted newborns
Stimulation of cardiac sarcoplasmic reticulum calcium pump by acylphosphatase: relationship to phospholamban phosphorylation.
Abstract Ca2+ transport by cardiac sarcoplasmic reticulum is tightly coupled with the enzymatic activity of Ca2+-dependent ATPase, which forms and decomposes an intermediate phosphoenzyme. Heart sarcoplasmic reticulum Ca2+ pump is regulated by cAMP-dependent protein kinase (PKA) phospholamban phosphorylation, which results in a stimulation of the initial rates of Ca2+ transport and Ca2+ ATPase activity. In the present studies we found that acylphosphatase from heart muscle, used at concentrations within the physiological range, actively hydrolyzes the phosphoenzyme of cardiac sarcoplasmic reticulum Ca2+ pump, with an apparent Km on the order of 10−7 M, suggesting an high affinity of the enzyme for this special substrate. In unphosphorylated vesicles acylphosphatase enhanced the rate of ATP hydrolysis and Ca2+ uptake with a concomitant significant decrease in apparent Km for Ca2+ and ATP. In vesicles whose phospholamban was PKA-phosphorylated, acylphosphatase also stimulated the rate of Ca2+ uptake and ATP hydrolysis but to a lesser extent, and the Km values for Ca2+ and ATP were not significantly different with respect to those found in the absence of acylphosphatase. These findings suggest that acylphosphatase, owing to its hydrolytic effect, accelerates the turnover of the phosphoenzyme intermediate with the consequence of an enhanced activity of Ca2+ pump. It is known that phosphorylation of phospholamban results in an increase of the rate at which the phosphoenzyme is decomposed. Thus, as discussed, a competition between phospholamban and acylphosphatase effect on the phosphoenzyme might be proposed to explain why the stimulation induced by this enzyme is less marked in PKA-phosphorylated than in unphosphorylated heart vesicles
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