1,893 research outputs found
A search for millimetric emission from Gamma Ray Bursts
We have used the 2- year Differential Microwave Radiometer data from the
COsmic Background Explorer (COBE) satellite to systematically search for
millimetric (31 - 90 GHz) emission from the Gamma Ray Bursts (GRBs) in the
Burst And Transient Source Experiment (BATSE) GRB 3B catalog. The large
beamsize of the COBE instrument (7 degs FWHM) allows for an efficient search of
the large GRB positional error boxes, although it also means that fluxes from
(point source) GRB objects will be somewhat diluted. A likelihood analysis has
been used to look for a change in the level of millimetric emission from the
locations of 81 GRB events during the first two years (1990 & 1991) of the COBE
mission. The likelihood analysis determined that we did not find any
significant millimetric signal before or after the occurance of the GRB. We
find 95% confidence level upper limits of 175, 192 and 645 Jy or, in terms of
fluxes, of 9.6, 16.3 and 54.8 10^{-13} erg/cm^2/s, respectively at 31, 53 and
90 GHz. We also look separately at different classes of GRBs, including a study
of the top ten (in peak flux) GRBs, the "short burst" and "long burst" subsets,
finding similar upper limits. While these limits may be somewhat higher than
one would like, we estimate that using this technique with future planned
missions could push these limits down to \sim 1 mJy.Comment: 21 pages, 5 figures, to be published in The Astrophysical Journa
Imipenem resistance in clinical Escherichia coli from Qom, Iran
OBJECTIVE: The emergence of metallo-\u3b2-lactamase-producing Enterobacteriaceae is a worldwide health concern. In this study, the first evaluation of MBL genes, bla IMP and bla VIM , in Escherichia coli resistant to imipenem isolated from urine and blood specimens in Qom, Iran is described. Three hundred urine and blood specimens were analysed to detect the presence of E. coli. Resistance to imipenem and other antimicrobials was determined by disk diffusion and MIC. MBL production was screened using CDDT. PCR was also carried out to determine the presence of bla IMP and bla VIM genes in imipenem-resistant isolates.
RESULTS: In total, 160 E. coli isolates were collected from March to May 2016. According to disk diffusion, high-level of resistance (20%) to cefotaxime was observed, whereas the lowest (1%) was detected for tetracycline. In addition, five isolates showed resistance to imipenem with a MIC\u2009 65\u20094 \ub5g/mL. CDDT test confirmed that five isolates were MBL-producing strains, but no bla IMP and bla VIM genes were detected. Results of this study show a very low level of resistance to imipenem in our geographical area
COBE Observations of the Microwave Counterparts of Gamma Ray Bursts
We have used the data from the COBE satellite to search for delayed microwave
emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large beam
of COBE is well matched to the large positional uncertainties in the GRB
locations, although it also means that fluxes from (point source) GRB objects
will be diluted. In view of this we are doing a statistical search of the GRBs
which occurred during the currently released COBE DMR data (years 1990 and
1991), which overlap GRBs recorded by GRO. Here we concentrate on
just the top 10 GRBs (in peak counts/second). We obtain the limits on the
emission by comparing the COBE fluxes before and after the GRB at the GRB
location. Since it is thought that the microwave emission should lag the GRB
event, we have searched the GRB position for emission in the few months
following the GRB occurrence.Comment: 5 pages, LaTE
Cars Diagnostic on a PhotochemicalReactor for IR Laser Induced Production of Si and Si3N4 Powders
In a flow reactor a low power (up to 50 W) CW CO2 laser tuned at 944,19 cm−1 has been focussed in order
to produce Si and Si3N4 ultrafine powders from SiH4 and SiH4/NH3 mixtures.Among possible on-line optical diagnostics, two different CARS techniques have been used to monitor
the excitation process and to measure average reaction temperatures in collinear geometry. In broad-band
CARS at low resolution (≈6.0 cm−1) the reactant temperature is measured from the attenuation of the
corresponding integrated peak intensity below and at the dissociation threshold. In narrow-band
experiments the temperature reached by the dissociating reactants below and above the threshold is
inferred from the spectral shape (measured with 0.2 cm−1 resolution) of the envelope of rovibrational
CARS transitions involved.Results obtained at the threshold for SiH4 dissociation are in agreement with previous data on gas-phase
pyrolysis in a thermal process. For the SiH4/NH3 reaction the difficulty in obtaining stoichiometric Si3N4
has been related to the cooling effect of large NH3 addition to the SiH4 warmed up in the laser absorption
Photon Self-Induced Spin to Orbital Conversion in TGG crystal at high laser power
In this paper, we present experimental evidence of a newly discovered
third-order nonlinear optical process Self-Induced Spin-to-Orbital Conversion
(SISTOC) of the photon angular momentum. This effect is the physical mechanism
at the origin of the depolarization of very intense laser beams propagating in
isotropic materials. The SISTOC process, like self-focusing, is triggered by
laser heating leading to a radial temperature gradient in the medium. In this
work we tested the occurrence of SISTOC in a terbium gallium garnet (TGG) rod
for an impinging laser power of about 100~W. To study the SISTOC process we
used different techniques: polarization analysis, interferometry and tomography
of the photon orbital angular momentum. Our results confirm, in particular,
that the apparent depolarization of the beam is due to the occurrence of
maximal entanglement between the spin and orbital angular momentum of the
photons undergoing the SISTOC process. This explanation of the true nature of
the depolarization mechanism could be of some help in finding novel methods to
reduce or to compensate for this usually unwanted depolarization effect in all
cases where very high laser power and good beam quality are required.Comment: 6 pages, 10 figures, submitte
Spin-orbit hybrid entanglement of photons and quantum contextuality
We demonstrate electromagnetic quantum states of single photons and of
correlated photon pairs exhibiting "hybrid" entanglement between spin and
orbital angular momentum. These states are obtained from entangled photon pairs
emitted by spontaneous parametric down conversion, by employing a -plate for
coupling the spin and orbital degrees of freedom of a photon. Entanglement and
contextual quantum behavior (that is also non-local, in the case of photon
pairs) is demonstrated by the reported violation of the
Clauser-Horne-Shimony-Holt inequality. In addition a classical analog of the
hybrid spin-orbit photonic entanglement is reported and discussed.Comment: 5 pages, 3 figure
COMPASS: a 2.6m telescope for CMBR polarization studies
COMPASS (COsmic Microwave Polarization at Small Scale) is an experiment devoted to measuring the polarization of the CMBR. Its design and characteristics are presented
Novel hydroxyapatite-TiO2 composite material for photocatalytic degradation of diclofenac
info:eu-repo/semantics/publishedVersio
Carcinoma cells activate AMP-activated protein kinase-dependent autophagy as survival response to kaempferol-mediated energetic impairment.
Kaempferol, a dietary cancer chemopreventive polyphenol, has been reported to trigger apoptosis in several tumor histotypes, but the mechanism underlying this phenomenon is not fully understood. Here, we demonstrate that in HeLa cells, kaempferol induces energetic failure due to inhibition of both glucose uptake and Complex I of the mitochondrial respiratory chain. As adaptive response, cells activate autophagy, the occurrence of which was established cytofluorometrically, upon acridine orange staining, and immunochemically, by following the increase of the autolysosome-associated form of the microtubule-associated protein light chain 3 (LC3-II). Autophagy is an early and reversible process occurring as survival mechanisms against apoptosis. Indeed, chemical inhibition of autophagy, by incubations with monensin, wortmannin, 3-methyladenine, or by silencing Atg5, significantly increases the extent of apoptosis, which takes place via the mitochondrial pathway, and shortens the time in which the apoptotic markers are detectable. We also demonstrate that autophagy depends on the early activation of the AMP-activated protein kinase (AMPK)/mTOR-mediated pathway. The overexpression of dominant negative AMPK results in a decrease of autophagic cells, a decrement of LC3-II levels, and a significant increase of apoptosis. Experiments performed with another carcinoma cell line yielded the same results, suggesting for kaempferol a unique mechanism of action
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