1,594 research outputs found
ORFEUS II Far-UV Spectroscopy of AM Herculis
Six high-resolution (\lambda/\Delta\lambda ~ 3000) far-UV (\lambda\lambda =
910-1210 \AA) spectra of the magnetic cataclysmic variable AM Herculis were
acquired in 1996 November during the flight of the ORFEUS-SPAS II mission. AM
Her was in a high optical state at the time of the observations, and the
spectra reveal emission lines of O VI \lambda\lambda 1032, 1038, C III \lambda
977, \lambda 1176, and He II \lambda 1085 superposed on a nearly flat
continuum. Continuum flux variations can be described as per Gansicke et al. by
a ~ 20 kK white dwarf with a ~ 37 kK hot spot covering a fraction f~0.15 of the
surface of the white dwarf, but we caution that the expected Lyman absorption
lines are not detected. The O VI emission lines have narrow and broad component
structure similar to that of the optical emission lines, with radial velocities
consistent with an origin in the irradiated face of the secondary and the
accretion funnel, respectively. The density of the narrow- and broad-line
regions is n_{nlr} ~ 3\times 10^{10} cm^{-3} and n_{blr} ~ 1\times 10^{12}
cm^{-3}, respectively, yet the narrow-line region is optically thick in the O
VI line and the broad-line region is optically thin; apparently, the velocity
shear in the broad-line region allows the O VI photons to escape, rendering the
gas effectively optically thin. Unexplained are the orbital phase variations of
the emission-line fluxes.Comment: 15 pages, 6 Postscript figures; LaTeX format, uses aaspp4.sty;
table2.tex included separately because it must be printed sideways - see
instructions in the file; accepted on April 17, 1998 for publication in The
Astrophysical Journa
Acquired platelet antagonism: off-target antiplatelet effects of malignancy treatment with tyrosine kinase inhibitors
Platelets can contribute to tumor progression and metastasis. Cancer patients are at increased risk of thrombosis, and advanced stages of cancer are associated with thrombocytosis or increased platelet reactivity. Tyrosine kinase inhibitors (TKIs) are widely used as a targeted strategy for cancer treatment, with the aim of prolonging progression-free survival of the patients. Because of their broad kinase target spectrum, most TKIs inevitably have off-target effects. Platelets rely on tyrosine kinase activity for their activation. Frequently observed side effects are lowering of platelet count and inhibition of platelet functions, whether or not accompanied by an increased bleeding risk. In this review, we aim to give insights into: (i) 38 TKIs that are currently used for the treatment of different types of cancer, either on the market or in clinical trials; (ii) how distinct TKIs can inhibit activation mechanisms in platelets; and (iii) the clinical consequences of the antiplatelet effects of TKI treatment. For several TKIs, the knowledge on affinity for their targets does not align with the published effects on platelets and reported bleeding events. This review should raise awareness of the potential antiplatelet effects of several TKIs, which will be enhanced in the presence of antithrombotic drugs
Linear acceleration emission in pulsar magnetospheres
(abbrev.) Linear acceleration emission occurs when a charged particle is
accelerated parallel to its velocity. We evaluate the spectral and angular
distribution of this radiation for several special cases, including constant
acceleration (hyperbolic motion) of finite duration. Based on these results, we
find the following general properties of the emission from an electron in a
linear accelerator that can be characterized by an electric field E acting over
a distance L: (i) the spectrum extends to a cut-off photon energy ~ LE^2 MeV,
where E is in units of the Schwinger critical field and L in units of the
Compton wavelength of the electron. (ii) the total energy emitted by a particle
traversing the accelerator is in agreement with the standard Larmor formula
(iii) the low frequency spectrum is flat for hyperbolic trajectories, but in
general depends on the details of the accelerator. We also show that linear
acceleration emission complements curvature radiation in the strongly
magnetized pair formation regions in pulsar magnetospheres. It dominates when
the length L of the accelerator is less than the formation length of curvature
photons, which is given by the ratio of the radius of curvature of the magnetic
field lines to the Lorentz factor of the particle. In standard static models of
pair creating regions linear acceleration emission is negligible, but it is
important in more realistic dynamical models in which the accelerating field
fluctuates on a short length-scale.Comment: Accepted for publication in Ap
On the Search for Coherent Radiation from Radio Pulsars
We have examined data from pulsars B0950+08 and B0329+54 for evidence of
temporally coherent radiation using the modified coherence function (MCF)
technique of Jenet et al. (2001). We consider the influence of both
instrumental bandpass and interstellar propagation effects. Even after removal
of the effects due to the instrumental bandpass, we detect a signature in the
MCF of our PSR B0329+54 data which is consistent with the definition of a
coherent signal. However, we model the effects due to interstellar
scintillation for this pulsar and show that it reproduces the observed
signature. In particular, the temporal coherence time is close to the
reciprocal of the decorrelation bandwidth due to diffractive scintillation.
Furthermore, comparison of the coherence times of three pulsars reported by
Jenet et al. (2001) with their expected diffractive decorrelation bandwidths
suggests that the detection of coherence in these pulsars is also likely a
result of interstellar scintillation, and is not intrinsic to the pulsars.Comment: 8 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics (A&A
Soluble adhesion molecules as markers for sepsis and the potential pathophysiological discrepancy in neonates, children and adults
Sepsis is a severe and life-threatening systemic inflammatory response to infection that affects all populations and age groups. The pathophysiology of sepsis is associated with aberrant interaction between leukocytes and the vascular endothelium. As inflammation progresses, the adhesion molecules that mediate these interactions become shed from cell surfaces and accumulate in the blood as soluble isoforms that are being explored as potential prognostic disease biomarkers. We critically review the studies that have tested the predictive value of soluble adhesion molecules in sepsis pathophysiology with emphasis on age, as well as the underlying mechanisms and potential roles for inflammatory shedding. Five soluble adhesion molecules are associated with sepsis, specifically, E-selectin, L-selectin and P-selectin, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. While increased levels of these soluble adhesion molecules generally correlate well with the presence of sepsis, their degree of elevation is still poorly predictive of sepsis severity scores, outcome and mortality. Separate analyses of neonates, children and adults demonstrate significant age-dependent discrepancies in both basal and septic levels of circulating soluble adhesion molecules. Additionally, a range of both clinical and experimental studies suggests protective roles for adhesion molecule shedding that raise important questions about whether these should positively or negatively correlate with mortality. In conclusion, while predictive properties of soluble adhesion molecules have been researched intensively, their levels are still poorly predictive of sepsis outcome and mortality. We propose two novel directions for improving clinical utility of soluble adhesion molecules: the combined simultaneous analysis of levels of adhesion molecules and their sheddases; and taking age-related discrepancies into account. Further attention to these issues may provide better understanding of sepsis pathophysiology and increase the usefulness of soluble adhesion molecules as diagnostic and predictive biomarkers
A burst from the direction of UZ Fornacis with XMM-Newton
The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For
finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT
observations. The source was not detected for the majority of a 22 ksec
exposure with the EPIC cameras, suggesting that the accretion rate either
decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ
For during the observation. Spectral fits favour optically thin, kT = 4.4 keV
thermal emission. Detection of the burst by the on-board Optical Monitor
indicates that this was most probably an accretion event. The 0.1-10 keV
luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from
high state polars and would result from the potential energy release of ~ 10^16
g of gas. There is no significant soft excess due to reprocessing in the white
dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres
- …