7,211 research outputs found
HESS J1825-137: A pulsar wind nebula associated with PSR B1823-13?
HESS J1825-137 was detected with a significance of 8.1 in the
Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. Both HESS
J1825-137 and the X-ray pulsar wind nebula G18.0--0.7 (associated with the
Vela-like pulsar PSR B1823-13) are offset south of the pulsar, which may be the
result of the SNR expanding into an inhomogeneous medium. The TeV size ( pc, for a distance of 4 kpc) is times larger than the X-ray size,
which may be the result of propagation effects as a result of the longer
lifetime of TeV emitting electrons, compared to the relatively short lifetime
of keV synchrotron emitting electrons. The TeV photon spectral index of can also be related to the extended PWN X-ray synchrotron photon index of
, if this spectrum is dominated by synchrotron cooling. The
anomalously large size of the pulsar wind nebula can be explained if the pulsar
was born with a relatively large initial spindown power and braking index
, provided that the SNR expanded into the hot ISM with relatively low
density ( cm).Comment: 4 pages, 4 figures, to appear in the Proc. of the 29th International
Cosmic Ray Conference, OG Sessio
The GeV-TeV Connection in Galactic gamma-ray sources
Recent observations with atmospheric Cherenkov telescope systems such as
H.E.S.S. and MAGIC have revealed a large number of new sources of
very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated
along the Galactic plane. At lower energies (100 MeV - 10 GeV) the
satellite-based instrument EGRET revealed a population of sources clustering
along the Galactic Plane. Given their adjacent energy bands a systematic
correlation study between the two source catalogues seems appropriate. Here,
the populations of Galactic sources in both energy domains are characterised on
observational as well as on phenomenological grounds. Surprisingly few common
sources are found in terms of positional coincidence and spectral consistency.
These common sources and their potential counterparts and emission mechanisms
will be discussed in detail. In cases of detection only in one energy band, for
the first time consistent upper limits in the other energy band have been
derived. The EGRET upper limits are rather unconstraining due to the
sensitivity mismatch to current VHE instruments. The VHE upper limits put
strong constraints on simple power-law extrapolation of several of the EGRET
spectra and thus strongly suggest cutoffs in the unexplored energy range from
10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for
differences in the source population at GeV and TeV energies will be discussed.
Finally, predictions will be derived for common GeV - TeV sources for the
upcoming GLAST mission bridging for the first time the energy gap between
current GeV and TeV instruments.Comment: (1) Kavli Institute for Particle Astrophysics and Cosmology (KIPAC),
Stanford, USA (2) Stanford University, W.W. Hansen Experimental Physics Lab
(HEPL) and KIPAC, Stanford, USA (3) ICREA & Institut de Ciencies de l'Espai
(IEEC-CSIC) Campus UAB, Fac. de Ciencies, Barcelona, Spain. (4) School of
Physics and Astronomy, University of Leeds, UK. Paper Submitted to Ap
Chapter 02 - From Scroll to Codex: New Technology and New Opportunities
This chapter discusses the shift from writing on scrolls to codices, with emphasis on the cultural influences of this change, especially in the religious sector.https://digitalcommons.wou.edu/history_of_book/1001/thumbnail.jp
Discovery of very high energy gamma-ray emission in the W 28 (G6.4-0.1) region, and multiwavelength comparisons
H.E.S.S. observations of the old-age (>10^4yr; ~0.5deg diameter) composite
supernova remnant (SNR) W 28 reveal very high energy (VHE) gamma-ray emission
situated at its northeastern and southern boundaries. The northeastern VHE
source (HESS J1801-233) is in an area where W 28 is interacting with a dense
molecular cloud, containing OH masers, local radio and X-ray peaks. The
southern VHE sources (HESS J1800-240 with components labelled A, B and C) are
found in a region occupied by several HII regions, including the ultracompact
HII region W 28A2. Our analysis of NANTEN CO data reveals a dense molecular
cloud enveloping this southern region, and our reanalysis of EGRET data reveals
MeV/GeV emission centred on HESS J1801-233 and the northeastern interaction
region.Comment: 4 pages, 3 figures, proceedings of the 30th ICRC, Merida, Mexico,
200
A search for VHE counterparts of Galactic Fermi bright sources and MeV to TeV spectral characterization
Very high-energy (VHE; E>100 GeV) gamma-rays have been detected from a wide
range of astronomical objects, such as pulsar wind nebulae (PWNe), supernova
remnants (SNRs), giant molecular clouds, gamma-ray binaries, the Galactic
Center, active galactic nuclei (AGN), radio galaxies, starburst galaxies, and
possibly star-forming regions as well. At lower energies, observations using
the Large Area Telescope (LAT) onboard Fermi provide a rich set of data which
can be used to study the behavior of cosmic accelerators in the MeV to TeV
energy bands. In particular, the improved angular resolution of current
telescopes in both bands compared to previous instruments significantly reduces
source confusion and facilitates the identification of associated counterparts
at lower energies. In this paper, a comprehensive search for VHE gamma-ray
sources which are spatially coincident with Galactic Fermi/LAT bright sources
is performed, and the available MeV to TeV spectra of coincident sources are
compared. It is found that bright LAT GeV sources are correlated with TeV
sources, in contrast to previous studies using EGRET data. Moreover, a single
spectral component seems unable to describe the MeV to TeV spectra of many
coincident GeV/TeV sources. It has been suggested that gamma-ray pulsars may be
accompanied by VHE gamma-ray emitting nebulae, a hypothesis that can be tested
with VHE observations of these pulsars.Comment: Astronomy and Astrophysics, in press, 17 pages, 12 figures, 5 table
Preclinical Pharmacokinetics, Pharmacodynamics and Safety of Sucroferric Oxyhydroxide.
Sucroferric oxyhydroxide (VELPHORO(®)) is a polynuclear iron-based phosphate binder recently approved for the treatment of hyperphosphataemia in patients with chronic kidney disease (CKD). As a number of the available phosphate binders do not provide the optimal combination of good efficacy, adequate tolerability and low pill burden, sucroferric oxyhydroxide constitutes a promising alternative. Among the attributes of an ideal phosphate binder is minimal absorption and, hence, low risk of systemic toxicity. Accordingly, the iron-releasing properties and absorption, distribution, metabolism and excretion (ADME) profile of sucroferric oxyhydroxide, as well as the possibility of iron accumulation and toxicity, were investigated in a series of preclinical studies. The effect of sucroferric oxyhydroxide on the progression of vascular calcification was also investigated. Sucroferric oxyhydroxide exhibited a high phosphate-binding capacity and low iron-releasing properties across the physiological pH range found in the gastrointestinal tract. In the ADME studies, uptake of (59)Fe-radiolabelled sucroferric oxyhydroxide was low in rats and dogs (<1% from a 50 mg Fe/kg bodyweight dose), with the majority of absorbed iron located in red blood cells. Long-term (up to 2 years) administration of sucroferric oxyhydroxide in rats and dogs was associated with modest increases in tissue iron levels and no iron toxicity. Moreoever, in uraemic rats, sucroferric oxyhydroxide was associated with reduced progression of vascular calcification compared with calcium carbonate. In conclusion, sucroferric oxyhydroxide offers a new option for the treatment of hyperphosphataemia, with a high phosphate-binding capacity, minimal iron release, and low potential for iron accumulation and toxicity
Parameter constraints for high-energy models of colliding winds of massive stars: the case WR 147
We explore the ability of high energy observations to constrain orbital
parameters of long period massive binary systems by means of an inverse Compton
model acting in colliding wind environments. This is particular relevant for
(very) long period binaries where orbital parameters are often poorly known
from conventional methods, as is the case e.g. for the Wolf-Rayet (WR) star
binary system WR 147 where INTEGRAL and MAGIC upper limits on the high-energy
emission have recently been presented. We conduct a parameter study of the set
of free quantities describing the yet vaguely constrained geometry and
respective effects on the non-thermal high-energy radiation from WR 147. The
results are confronted with the recently obtained high-energy observations and
with sensitivities of contemporaneous high-energy instruments like Fermi-LAT.
For binaries with sufficient long periods, like WR 147, gamma-ray attenuation
is unlikely to cause any distinctive features in the high-energy spectrum. This
leaves the anisotropic inverse Compton scattering as the only process that
reacts sensitively on the line-of-sight angle with respect to the orbital
plane, and therefore allows the deduction of system parameters even from
observations not covering a substantial part of the orbit.
Provided that particle acceleration acts sufficiently effectively to allow
the production of GeV photons through inverse Compton scattering, our analysis
indicates a preference for WR 147 to possess a large inclination angle.
Otherwise, for low inclination angles, electron acceleration is constrained to
be less efficient as anticipated here.Comment: 33 pages, 9 figures; accepted by Ap
A multiple scale model for tumor growth
We present a physiologically structured lattice model for vascular tumor growth which accounts for blood flow and structural adaptation of the vasculature, transport of oxygen, interaction between cancerous and normal tissue, cell division, apoptosis, vascular endothelial growth factor release, and the coupling between these processes. Simulations of the model are used to investigate the effects of nutrient heterogeneity, growth and invasion of cancerous tissue, and emergent growth laws
Quantum key distribution using non-classical photon number correlations in macroscopic light pulses
We propose a new scheme for quantum key distribution using macroscopic
non-classical pulses of light having of the order 10^6 photons per pulse.
Sub-shot-noise quantum correlation between the two polarization modes in a
pulse gives the necessary sensitivity to eavesdropping that ensures the
security of the protocol. We consider pulses of two-mode squeezed light
generated by a type-II seeded parametric amplification process. We analyze the
security of the system in terms of the effect of an eavesdropper on the bit
error rates for the legitimate parties in the key distribution system. We also
consider the effects of imperfect detectors and lossy channels on the security
of the scheme.Comment: Modifications:added new eavesdropping attack, added more references
Submitted to Physical Review A [email protected]
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