335 research outputs found
Cholinergic cells in the nucleus basalis of mice express the N-methyl-D-aspartate-receptor subunit NR2C and its replacement by the NR2B subunit enhances frontal and amygdaloid acetylcholine levels
It is known that glutamatergic and cholinergic systems interact functionally at the level of the cholinergic basal forebrain. The N-methyl-D-aspartate receptor (NMDA-R) is a multiprotein complex composed of NR1, NR2 and/or NR3 subunits. The subunit composition of NMDA-R of cholinergic cells in the nucleus basalis has not yet been investigated. Here, by means of choline acetyl transferase and NR2B or NR2C double staining, we demonstrate that mice express both the NR2C and NR2B subunits in nucleus basalis cholinergic cells.We generated NR2C-2B mutant mice in which an insertion of NR2B cDNA into the gene locus of the NR2C gene replaced NR2C by NR2B expression throughout the brain. This NR2C-2B mutant was used to examine whether a subunit exchange in cholinergic neurons would affect acetylcholine (ACh) content in several brain structures. We found increased ACh levels in the frontal cortex and amygdala in the brains of NR2C-2B mutant mice. Brain ACh has been implicated in neuroplasticity, novelty-induced arousal and encoding of novel stimuli. We therefore assessed behavioral habituation to novel environments and objects as well as object recognition in NR2C-2B subunit exchange mice. The behavioral analysis did not indicate any gross behavioral alteration in the mutant mice compared with the wildtype mice. Our results show that the NR2C by NR2B subunit exchange in mice affects ACh content in two target areas of the nucleus basalis.
State transitions in the 2001/2002 outburst of XTE J1650-500
We present a study of the X-ray transient and black hole candidate XTE
J1650-500 during its 2001/2002 outburst. The source made two state transitions
between the hard and soft states, at luminosity levels that differed by a
factor of ~5-10. The first transition, between hard and soft, lasted for ~30
days and showed two parts; one part in which the spectral properties evolve
smoothly away from the hard state and another that we identify as the 'steep
power law state'. The two parts showed different behavior of the Fe K emission
line and QPO frequencies. The second transition, from soft to hard, lasted only
\~15 days and showed no evidence of the presence of the 'steep power law
state'. Comparing observations from the early rise and the decay of the
outburst, we conclude that the source can be in the hard state in a range of
more 10^4 in luminosity. We briefly discuss the state transitions in the
framework of a two-flow model.Comment: 4 pages, 5 figures. To appear in Proc. of the II BeppoSAX Meeting:
"The Restless High-Energy Universe" (Amsterdam, May 5-8, 2003), E.P.J. van
den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Ed
A concise review on THGEM detectors
We briefly review the concept and properties of the Thick GEM (THGEM); it is
a robust, high-gain gaseous electron multiplier, manufactured economically by
standard printed-circuit drilling and etching technology. Its operation and
structure resemble that of GEMs but with 5 to 20-fold expanded dimensions. The
millimeter-scale hole-size results in good electron transport and in large
avalanche-multiplication factors, e.g. reaching 10^7 in double-THGEM cascaded
single-photoelectron detectors. The multiplier's material, parameters and shape
can be application-tailored; it can operate practically in any counting gas,
including noble gases, over a pressure range spanning from 1 mbar to several
bars; its operation at cryogenic (LAr) conditions was recently demonstrated.
The high gain, sub-millimeter spatial resolution, high counting-rate
capability, good timing properties and the possibility of industrial production
capability of large-area robust detectors, pave ways towards a broad spectrum
of potential applications; some are discussed here in brief.Comment: 8 pages, 11 figures; Invited Review at INSTR08, Novosibirsk, Feb
28-March 5 200
Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4
An energetic electron passing through liquid helium causes ionization along
its track. The ionized electrons quickly recombine with the resulting positive
ions, which leads to the production of prompt scintillation light. By applying
appropriate electric fields, some of the ionized electrons can be separated
from their parent ions. The fraction of the ionized electrons extracted in a
given applied field depends on the separation distance between the electrons
and the ions. We report the determination of the mean electron-ion separation
distance for charge pairs produced along the tracks of beta particles in
superfluid helium at 1.5 K by studying the quenching of the scintillation light
under applied electric fields. Knowledge of this mean separation parameter will
aid in the design of particle detectors that use superfluid helium as a target
material.Comment: 10 pages, 8 figure
Kahler moduli double inflation
We show that double inflation is naturally realized in K\"ahler moduli
inflation, which is caused by moduli associated with string compactification.
We find that there is a small coupling between the two inflatons which leads to
amplification of perturbations through parametric resonance in the intermediate
stage of double inflation. This results in the appearance of a peak in the
power spectrum of the primordial curvature perturbation. We numerically
calculate the power spectrum and show that the power spectrum can have a peak
on observationally interesing scales. We also compute the TT-spectrum of CMB
based on the power spectrum with a peak and see that it better fits WMAP
7-years data.Comment: 21 pages, 8 figure
States and transitions in black-hole binaries
With the availability of the large database of black-hole transients from the
Rossi X-Ray Timing Explorer, the observed phenomenology has become very
complex. The original classification of the properties of these systems in a
series of static states sorted by mass accretion rate proved not to be able to
encompass the new picture. I outline here a summary of the current situation
and show that a coherent picture emerges when simple properties such as X-ray
spectral hardness and fractional variability are considered. In particular,
fast transition in the properties of the fast time variability appear to be
crucial to describe the evolution of black-hole transients. Based on this
picture, I present a state-classification which takes into account the observed
transitions. I show that, in addition to transients systems, other black-hole
binaries and Active Galactic Nuclei can be interpreted within this framework.
The association between these states and the physics of the accretion flow
around black holes will be possible only through modeling of the full time
evolution of galactic transient systems.Comment: 30 pages, 11 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
On the low-temperature performances of THGEM and THGEM/G-APD multipliers in gaseous and two-phase Xe
The performances of THGEM multipliers in two-phase Xe avalanche mode are
presented for the first time. Additional results on THGEM operation in gaseous
Xe at cryogenic temperatures are provided. Stable operation of a double-THGEM
multiplier was demonstrated in two-phase Xe with gains reaching 600. These are
compared to existing data, summarized here for two-phase Ar, Kr and Xe
avalanche detectors incorporating GEM and THGEM multipliers. The optical
readout of THGEMs with Geiger-mode Avalanche Photodiodes (G-APDs) has been
investigated in gaseous Xe at cryogenic temperature; avalanche scintillations
were recorded in the Near Infrared (NIR) at wavelengths of up to 950 nm. At
avalanche charge gain of 350, the double-THGEM/G-APD multiplier yielded 0.07
photoelectrons per initial ionization electron, corresponding to an avalanche
scintillation yield of 0.7 NIR photons per avalanche electron over 4pi. The
results are compared with those of two-phase Ar avalanche detectors. The
advantages, limitations and possible applications are discussed.Comment: 22 pages, 14 figures. Revised Figs. 10,11 and Table 1. To be
published in JINS
Accretion and ejection in black-hole X-ray transients
Aims: We summarize the current observational picture of the outbursts of
black-hole X-ray transients (BHTs), based on the evolution traced in a
hardness-luminosity diagram (HLD), and we offer a physical interpretation.
Methods: The basic ingredient in our interpretation is the Poynting-Robertson
Cosmic Battery (PRCB, Contopoulos & Kazanas 1998), which provides locally the
poloidal magnetic field needed for the ejection of the jet. In addition, we
make two assumptions, easily justifiable. The first is that the mass-accretion
rate to the black hole in a BHT outburst has a generic bell-shaped form. This
is guaranteed by the observational fact that all BHTs start their outburst and
end it at the quiescent state. The second assumption is that at low accretion
rates the accretion flow is geometrically thick, ADAF-like, while at high
accretion rates it is geometrically thin.
Results: Both, at the beginning and the end of an outburst, the PRCB
establishes a strong poloidal magnetic field in the ADAF-like part of the
accretion flow, and this explains naturally why a jet is always present in the
right part of the HLD. In the left part of the HLD, the accretion flow is in
the form of a thin disk, and such a disk cannot sustain a strong poloidal
magnetic filed. Thus, no jet is expected in this part of the HLD. The
counterclockwise traversal of the HLD is explained as follows: the poloidal
magnetic field in the ADAF forces the flow to remain ADAF and the source to
move upwards in the HLD rather than to turn left. Thus, the history of the
system determines the counterclockwise traversal of the HLD. As a result, no
BHT is expected to ever traverse the entire HLD curve in the clockwise
direction.
Conclusions: We offer a physical interpretation of accretion and ejection in
BHTs with only one parameter, the mass transfer rate.Comment: Accepted for publication in A&
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