1,113 research outputs found
The radiation environment over the African continent at aviation altitudes: First results of the RPiRENA-based dosimeter
The radiation environment over the African continent, at aviation altitudes,
remains mostly uncharacterized and unregulated. In this paper we present
initial measurements made by a newly developed active dosimeter on-board
long-haul flights between South Africa and Germany. Based on these initial
tests, we believe that this low-cost and open-source dosimeter is suitable for
continued operation over the Africa continent and can provide valuable
long-term measurements to test dosimteric models and inform aviation policyComment: Accepted to appear in Journal of Space Weather and Space Climat
On the existence of a paramagnetic adduct of Ni(II)-bis-(di-n-butyl-diselenocarbamate). An EPR study
Paramagnetic adduct formation of pyridine with nickel(II)-bis(di-n-butyl-diselenocarbamate) is observed by means of EPR at 27°K. The low value of the zero field splitting and the g-factor are explained by strong spin-orbit interactions and by high covalency typical of the Se4-coordination sphere. © 1973
Multi-band optical-NIR variability of blazars on diverse timescales
To search for optical variability on a wide range of timescales, we have
carried out photometric monitoring of two flat spectrum radio quasars, 3C 454.3
and 3C 279, plus one BL Lac, S5 0716+714, all of which have been exhibiting
remarkably high activity and pronounced variability at all wavelengths. CCD
magnitudes in B, V, R and I pass-bands were determined for 7000 new
optical observations from 114 nights made during 2011 - 2014, with an average
length of 4 h each, at seven optical telescopes: four in Bulgaria, one
in Greece, and two in India. We measured multiband optical flux and colour
variations on diverse timescales. Discrete correlation functions were computed
among B, V, R, and I observations, to search for any time delays. We found weak
correlations in some cases with no significant time lags. The structure
function method was used to estimate any characteristic time-scales of
variability. We also investigated the spectral energy distribution of the three
blazars using B, V, R, I, J and K pass-band data. We found that the sources
almost always follows a bluer-when-brighter trend. We discuss possible physical
causes of the observed spectral variability.Comment: Accepted for publication in MNRAS, 16 pages, 11 figures, 5 tables,
plus supplementary material containing additional figures and tables (please
contact authors for it
Multiwavelength Observations of GX 339-4 in 1996. I. Daily Light Curves and X-ray and Gamma-Ray Spectroscopy
As part of our multiwavelength campaign of GX 339-4 observations in 1996 we
present our radio, X-ray, and gamma-ray observations made in July, when the
source was in a hard state (= soft X-ray low state). The radio observations
were made at the time when there was a possible radio jet. We show that the
radio spectrum was flat and significantly variable, and that the radio spectral
shape and amplitude at this time were not anomalous for this source. Daily
light curves from our pointed observation July 9-23 using OSSE, from BATSE, and
from the ASM on RXTE also show that there was no significant change in the X-
and gamma-ray flux or hardness during the time the possible radio jet-like
feature was seen. The higher energy portion of our pointed RXTE observation
made July 26 can be equally well fit using simple power law times exponential
(PLE) and Sunyaev-Titarchuk (ST) functions. An additional soft component is
required, as well as a broad emission feature centered on 6.4 keV. This may be
an iron line that is broadened by orbital Doppler motions and/or scattering off
a hot medium. Its equivalent width is 600 eV. Our simplistic continuum fitting
does not require an extra reflection component. Both a PLE and a ST model also
fit our OSSE spectrum on its own. Although the observations are not quite
simultaneous, combining the RXTE and CGRO spectra we find that the PLE model
easily fits the joint spectrum. However, the ST model drops off too rapidly
with increasing energies to give an acceptable joint fit.Comment: Submitted to Astrophysical Journal. 25 pages. 11 figure
Time-Dependent Synchrotron and Compton Spectra from Jets of Microquasars
Jet models for the high-energy emission of Galactic X-ray binary sources have
regained significant interest with detailed spectral and timing studies of the
X-ray emission from microquasars, the recent detection by the HESS
collaboration of very-high-energy gamma-rays from the microquasar LS~5039, and
the earlier suggestion of jet models for ultraluminous X-ray sources observed
in many nearby galaxies. Here we study the synchrotron and Compton signatures
of time-dependent electron injection and acceleration, adiabatic and radiative
cooling, and different jet geometries in the jets of Galactic microquasars.
Synchrotron, synchrotron-self-Compton, and external-Compton radiation processes
with soft photons provided by the companion star and the accretion disk are
treated. An analytical solution is presented to the electron kinetic equation
for general power-law geometries of the jets for Compton scattering in the
Thomson regime. We pay particular attention to predictions concerning the rapid
flux and spectral variability signatures expected in a variety of scenarios,
making specific predictions concerning possible spectral hysteresis, similar to
what has been observed in several TeV blazars. Such predictions should be
testable with dedicated monitoring observations of Galactic microquasars and
ultraluminous X-ray sources using Chandra and/or XMM-Newton.Comment: Accepted for publication in ApJ; 37 manuscript pages, including 10
eps figures; uses AASTeX macro
Does the Blazar Gamma-Ray Spectrum Harden with Increasing Flux? Analysis of 9 Years of EGRET Data
The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray
Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars
during its 9 yr lifetime. We conducted an exhaustive search of the EGRET
archives and selected all the blazars that were observed multiple times and
were bright enough to enable a spectral analysis using standard power-law
models. The sample consists of 18 flat-spectrum radio quasars(FSRQs), 6
low-frequency peaked BL Lac objects (LBLs) and 2 high-frequency peaked BL Lac
objects (HBLs). We do not detect any clear pattern in the variation of spectral
index with flux. Some of the blazars do not show any statistical evidence for
spectral variability. The spectrum hardens with increasing flux in a few cases.
There is also evidence for a flux-hardness anticorrelation at low fluxes in
five blazars. The well-observed blazars (3C 279, 3C 273, PKS 0528+134, PKS
1622-297 PKS 0208-512) do not show any overall trend in the long-term spectral
dependence on flux, but the sample shows a mixture of hard and soft states. We
observed a previously unreported spectral hysteresis at weekly timescales in
all three FSRQs for which data from flares lasting for ~(3-4) weeks were
available. All three sources show a counterclockwise rotation, despite the
widely different flux profiles. We analyze the observed spectral behavior in
the context of various inverse Compton mechanisms believed to be responsible
for emission in the EGRET energy range. Our analysis uses the EGRET skymaps
that were regenerated to include the changes in performance during the mission
Lattice-gas model for alkali-metal fullerides: face-centered-cubic structure
A lattice-gas model is suggested for describing the ordering phenomena in
alkali-metal fullerides of face-centered-cubic structure assuming the electric
charge of alkali ions residing in either octahedral or tetrahedral interstitial
sites is completely screened by the first-neighbor C_60 molecules. This
approximation allows us to derive an effective ion-ion interaction. The van der
Waals interaction between the ion and C_60 molecule is characterized by
introducing an additional energy at the tetrahedral sites. This model is
investigated by using a three-sublattice mean-field approximation and a simple
cluster-variation method. The analysis shows a large variety of phase diagrams
when changing the site energy parameter.Comment: 10 twocolumn pages (REVTEX) including 12 PS figure
Human phosphodiesterase 4D7 (PDE4D7) expression is increased in TMPRSS2-ERG positive primary prostate cancer and independently adds to a reduced risk of post-surgical disease progression
background: There is an acute need to uncover biomarkers that reflect the molecular pathologies, underpinning prostate cancer progression and poor patient outcome. We have previously demonstrated that in prostate cancer cell lines PDE4D7 is downregulated in advanced cases of the disease. To investigate further the prognostic power of PDE4D7 expression during prostate cancer progression and assess how downregulation of this PDE isoform may affect disease outcome, we have examined PDE4D7 expression in physiologically relevant primary human samples.
methods: About 1405 patient samples across 8 publically available qPCR, Affymetrix Exon 1.0 ST arrays and RNA sequencing data sets were screened for PDE4D7 expression. The TMPRSS2-ERG gene rearrangement status of patient samples was determined by transformation of the exon array and RNA seq expression data to robust z-scores followed by the application of a threshold >3 to define a positive TMPRSS2-ERG gene fusion event in a tumour sample.
results: We demonstrate that PDE4D7 expression positively correlates with primary tumour development. We also show a positive association with the highly prostate cancer-specific gene rearrangement between TMPRSS2 and the ETS transcription factor family member ERG. In addition, we find that in primary TMPRSS2-ERG-positive tumours PDE4D7 expression is significantly positively correlated with low-grade disease and a reduced likelihood of progression after primary treatment. Conversely, PDE4D7 transcript levels become significantly decreased in castration resistant prostate cancer (CRPC).
conclusions: We further characterise and add physiological relevance to PDE4D7 as a novel marker that is associated with the development and progression of prostate tumours. We propose that the assessment of PDE4D7 levels may provide a novel, independent predictor of post-surgical disease progression
Nature of Intra-night Optical Variability of BL Lacertae
We present the results of extensive multi-band intra-night optical monitoring
of BL Lacertae during 2010--2012. BL Lacertae was very active in this period
and showed intense variability in almost all wavelengths. We extensively
observed it for a total for 38 nights; on 26 of them observations were done
quasi-simultaneously in B, V, R and I bands (totaling 113 light curves), with
an average sampling interval of around 8 minutes. BL Lacertae showed
significant variations on hour-like timescales in a total of 19 nights in
different optical bands. We did not find any evidence for periodicities or
characteristic variability time-scales in the light curves.
The intranight variability amplitude is generally greater at higher
frequencies and decreases as the source flux increases.
We found spectral variations in BL Lacertae in the sense that the optical
spectrum becomes flatter as the flux increases but in several flaring states
deviates from the linear trend suggesting different jet components contributing
to the emission at different times.Comment: 12 Pages, 5 figures, 3 Tables, Accepted for Publication in MNRA
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