5,110 research outputs found
High pressure operation of the triple-GEM detector in pure Ne, Ar and Xe
We study the performance of the triple-GEM (Gas Electron Multiplier) detector
in pure noble gases Ne, Ar and Xe, at different pressures varying from 1 to 10
atm. In Ar and Xe, the maximum attainable gain of the detector abruptly drops
down for pressures exceeding 3 atm. In contrast, the maximum gain in Ne was
found to increase with pressure, reaching a value of 100,000 at 7 atm. The
results obtained are of particular interest for developing noble gas-based
cryogenic particle detectors for solar neutrino and dark matter search.Comment: 7 pages, 4 figures. Submitted to Nucl. Instr. and Meth. A as a letter
to the Edito
Study of ion feedback in multi-GEM structures
We study the feedback of positive ions in triple and quadruple Gas Electron
Multiplier (GEM) detectors. The effects of GEM hole diameter, detector gain,
applied voltages, number of GEMs and other parameters on ion feedback are
investigated in detail. In particular, it was found that the ion feedback is
independent of the gas mixture and the pressure. In the optimized multi-GEM
structure, the ion feedback current can be suppressed down to 0.5% of the anode
current, at a drift field of 0.1 kV/cm and gain of 10^4. A simple model of ion
feedback in multi-GEM structures is suggested. The results obtained are
relevant to the performance of time projection chambers and gas
photomultipliers.Comment: 9 pages, 11 figures. Submitted to Nucl. Instr. and Meth.
Infrared scintillation yield in gaseous and liquid argon
The study of primary and secondary scintillations in noble gases and liquids
is of paramount importance to rare-event experiments using noble gas media. In
the present work, the scintillation yield in gaseous and liquid Ar has for the
first time been measured in the near infrared (NIR) and visible region, both
for primary and secondary (proportional) scintillations, using Geiger-mode
avalanche photodiodes (G-APDs) and pulsed X-ray irradiation. The primary
scintillation yield of the fast component was measured to be 17000 photon/MeV
in gaseous Ar in the NIR, in the range of 690-1000 nm, and 510 photon/MeV in
liquid Ar, in the range of 400-1000 nm. Proportional NIR scintillations
(electroluminescence) in gaseous Ar have been also observed; their
amplification parameter at 163 K was measured to be 13 photons per drifting
electron per kV. Possible applications of NIR scintillations in high energy
physics experiments are discussed.Comment: 6 pages, 5 figures. Submitted to Europhysics Letter. Revised Figs. 3
and
Down-regulation of serotonergic genes expression in the raphe nuclei of midbrain under chronic social defeat stress in male mice
Background: 
There is ample experimental evidence supporting the hypothesis that the brain serotonergic system is involved in the control of chronic social defeat stress (CSDS), depression and anxiety. The study aimed to analyze mRNA levels of the serotonergic genes in the raphe nuclei of the midbrain that may be associated with chronic social defeats consistently shown by male mice in special experimental settings. 

Methodology/Principal Findings: 
The serotonergic genes were the Tph2, Sert, Maoa and Htr1a. The Bdnf, Creb, Cphn, Gapdh, Hprt, B2M, 18S and Actb genes were also studied. The experimental groups were composed of male mice with experience of defeats in 21 daily encounters and male mice with the same track record of defeats followed by a no-defeat period without agonistic interactions (relative rest for 14 days). It has been shown that mRNA levels of the Tph2, Maoa, Sert, Htr1a, Bdnf and Creb genes in the raphe nuclei of defeated mice are decreased as compared with the controls. Under CSDS the Cphn, Gapdh, Hprt, B2M, 18S, Actb genes are also down-regulated. The expression of the serotonergic genes as well as the Cphn and Creb genes is not restored to the control level after the 2 weeks of relative rest. mRNA levels of other genes are not recovered to the control levels, although some up-regulation was observed in rested losers. Significant positive correlations were found between the total time of avoidance behavior demonstrated by the 21-day defeaters in agonistic interactions and Sert, Maoa, Bdnf, Gapdh and 18S mRNA levels. 

Conclusions: 
CSDS experience inducing the development of mixed anxious/depression-like state in male mice down-regulates the serotonergic genes expression associated with the synthesis, inactivation and reception of serotonin. The Bdnf and Creb genes as well as the cell and metabolic Cphn, Gapdh, Hprt, B2M, Actb and 18S genes in the midbrain raphe nuclei are also down-regulated under CSDS. Period of relative rest is not enough for most genes to recover expression to the control levels
Photoelectron spectra in strong-field ionization by a high frequency field
We analyze atomic photoelectron momentum distributions induced by bichromatic
and monochromatic laser fields within the strong field approximation (SFA),
separable Coulomb-Volkov approximation (SCVA), and ab initio treatment. We
focus on the high frequency regime -- the smallest frequency used is larger
than the ionization potential of the atom. We observe a remarkable agreement
between the ab initio and velocity gauge SFA results while the velocity gauge
SCVA fails to agree. Reasons of such a failure are discussed.Comment: Completely rewritten paper. Ionization by a two-color field is adde
Molecular implications of prolonged aggression experience: Th, Dat1, Snca and Bdnf gene expression in the ventral tegmental area of the victorious male mice
Th, Dat1, Snca and Bdnf were the genes whose mRNA levels in the ventral tegmental area of the midbrain were measured in male mice that were victorious in 20 daily agonistic interactions and in a group of such victorious mice that had later not been allowed to fight for 14 days. This experiment demonstrated increased Th, Dat1 and Snca but not Bdnf mRNA levels in the former group as compared to the controls. In the latter group, the expression of the Th and Dat1 genes was still enhanced, while the level of Snca mRNA did not differ from that in the controls. These findings suggest that positive fighting experience enhances the expression of the genes concerned with dopaminergic systems and this enhanced expression is preserved for a long time afterwards. Significant positive correlations were found between the level of aggression and Th and Snca mRNA levels in the winners
Decrease of vanillin sucrose intake by victorious and defeated mice: development of anhedonia?
Hedonic reactions to various rewards play a key role in various forms of motivated behavior. The influence of repeated experience of social victories or defeats in daily agonistic interactions between male mice on voluntary consumption of vanillin sucrose solution used as hedonic reinforcer was studied. Intake of vanillin sucrose solution was shown to decrease in the winners and losers exposed to social confrontations as compared with the controls. Three days of deprivation failed to restore the intake of vanillin sucrose solution to the control level in the losers and did so in the winners. The results obtained imply that similar reaction of animals to a hedonic non-drug reinforcer may have different motivational origin depending on positive or negative social experience
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