2,775 research outputs found
HESS J1641-463, a very hard spectrum TeV gamma-ray source in the Galactic plane
HESS J1641-463 is a unique source discovered by the High Energy Stereoscopic
System (H.E.S.S.) telescope array in the multi-TeV domain. The source had been
previously hidden in the extended tail of emission from the bright nearby
source HESS J1640-465. However, the analysis of the very-high-energy (VHE) data
from the region at energies above 4 TeV revealed this new source at a
significance level of 8.5. HESS J1641-463 showed a moderate flux level
F(E > 1 TeV) = (3.64 +/- 0.44_stat +/- 0.73_sys) 10^-13 cm^-2s^-1,
corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard
spectrum with a photon index Gamma = 2.07 +/- 0.1_stat +/- 0.20_sys. The light
curve was investigated for evidence of variability, but none was found on both
short (28-min observation) and long (yearly) timescales. HESS J1641-463 is
positionally coincident with the radio supernova remnant (SNR) G338.5+0.1.
There is no clear X-ray counterpart of the SNR, although Chandra and XMM-Newton
data reveal some weak emission that may be associated. If the emission from
HESS J1641-463 is produced by cosmic ray protons colliding with the ambient
gas, then the proton spectrum extends up to 0.1 PeV (99% confidence level) and
likely to higher energies, > 0.27 PeV (90% confidence level). If this is the
case, then HESS J1641-463 may be a member of a larger source population
contributing to the Galactic cosmic-ray flux around the knee.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Experimental observation of the longitudinal plasma excitation in intrinsic Josephson junctions
We have investigated the current-voltage characteristics (IVCs) of intrinsic
Josephson junctions (IJJs). Recently, it is predicted that the longitudinal
plasma wave can be excited by the parametric resonance in IJJs. Such an
excitation induces a singularity called as breakpoint region around switch back
region in the IVC. We have succeeded in the observation of the breakpoint
region in the IVC of the mesa with 5 IJJs at 4.2 K. Furthermore, it is found
that the temperature dependence of the breakpoint current is in agreement with
the theoretical prediction. This suggests that the wave number of the excited
plasma wave varies with temperature.Comment: 7 pages, 7 figures. Dubna-Nano2008, Accepted for JPCS
Experimental manifestation of the breakpoint region in the current-voltage characteristics of intrinsic Josephson junctions
The experimental evidence of the breakpoint on the current-voltage
characteristics (IVCs) of the stacks of intrinsic Josephson junctions (IJJs) is
presented. The influence of the capacitive coupling on the IVCs of
BiSrCaCuO IJJs has been investigated. At 4.2 K, clear
breakpoint region is observed on the branches in the IVCs. It is found that the
hysteresis observed on the IVC is suppressed due to the coupling compared with
that expected from the McCumber parameter. Measurements agree well with the
results obtained by the theoretical model.Comment: 3 pages, 4 figure
Endogenous Murine Leukemia Viruses: Relationship to XMRV and Related Sequences Detected in Human DNA Samples
Xenotropic-murine-leukemia-virus-related virus (XMRV) was the first gammaretrovirus to be reported in humans. The sequence similarity between XMRV and murine leukemia viruses (MLVs) was consistent with an origin of XMRV from one or more MLVs present as endogenous proviruses in mouse genomes. Here, we review the relationship of the human and mouse virus isolates and discuss the potential complications associated with the detection of MLV-like sequences from clinical samples
Theory for Photon-Assisted Macroscopic Quantum Tunneling in a Stack of Intrinsic Josephson Junctions
We propose a theory for photon-assisted macroscopic quantum tunneling (MQT)
in a stack of capacitively-coupled intrinsic Josephson junctions in which the
longitudinal Josephson plasma, i.e., longitudinal collective phase oscillation
modes, is excited. The scheme of energy-level quantization in the collective
oscillatory states is clarified in the -junction system. When the MQT occurs
from the single-plasmon states excited by microwave irradiation in the
multi-photon process to the uniform voltage state, our theory predicts that the
escape rate is proportional to . This result is consistent with the recent
observation in Bi-2212 intrinsic Josephson junctions.Comment: 5 pages, 2 figure
MWL observations of VHE blazars in 2006
In 2006 the MAGIC telescope observed the well known very high energy (VHE, >
80 GeV) blazars Mrk 421 and Mrk 501 in the course of multi-wavelength
campaigns, comprising measurements in the optical, X-ray and VHE regime. MAGIC
performed additional snapshot observations on Mrk 421 around the MWL campaigns
and detected the source each night with high significance, establishing once
more flux variability on nightly scales for this object. For certain nights,
the integral flux exceeded the one of Crab significantly, whereas the truly
simultaneous observations have been conducted in a rather low flux state. The
MAGIC observations contemporaneous to XMM-Newton revealed clear intra-night
variability. No significant correlation between the spectral index and the flux
could be found for the nine days of observations. The VHE observations of Mrk
501 have been conducted during one of the lowest flux states ever measured by
MAGIC for this object. The VHE and optical light curves do not show significant
variability, whereas the flux in X-rays increased by about 50 %. In this
contribution, the results of the MAGIC observations will be presented in
detail.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Decreased expression of p57KIP2mRNA in human bladder cancer
To identify targets of genetic and epigenetic alterations on chromosome 11p15.5 in human bladder cancer, expression of the imprinted KIP2, IGF2 and H19 genes was studied by quantitative RT-PCR in 24 paired samples of urothelial carcinomas and morphologically normal mucosa obtained by cystectomy, and in bladder carcinoma cell lines. The most frequent alteration in tumour tissue was decreased expression of KIP2 identified in 9/24 (37%) specimens. Decreased IGF2 and H19 mRNA levels were found in five (21%) and three (13%) tumours, respectively. One tumour each overexpressed IGF2 and H19. Loss of H19 expression was only found associated with loss of KIP2 expression, whereas decreased expression of IGF2 mRNA occurred independently. Almost all bladder carcinoma cell lines showed significant changes in the expression of at least one gene with diminished expression of KIP2 mRNA as the most frequent alteration. IGF2 mRNA levels were diminished in several lines, but increased in others. The KIP2 gene could be an important target of genetic and epigenetic alterations in bladder cancer affecting the maternal chromosome 11p15.5. However, reminiscent of the situation in Wilms’ tumours, expression of the IGF2 gene on the paternal chromosome can also be disturbed in bladder cancers. © 2000 Cancer Research Campaig
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