284 research outputs found
Study of a Threshold Cherenkov Counter Based on Silica Aerogels with Low Refractive Indices
To identify and in the region of GeV/c, a
threshold Cherenkov counter equipped with silica aerogels has been
investigated. Silica aerogels with a low refractive index of 1.013 have been
successfully produced using a new technique. By making use of these aerogels as
radiators, we have constructed a Cherenkov counter and have checked its
properties in a test beam. The obtained results have demonstrated that our
aerogel was transparent enough to make up for loss of the Cherenkov photon
yield due to a low refractive index. Various configurations for the photon
collection system and some types of photomultipliers, such as the fine-mesh
type, for a read out were also tested. From these studies, our design of a
Cherenkov counter dedicated to separation up to a few GeV/c %in the
momentum range of GeV/c with an efficiency greater than \%
was considered.Comment: 21 pages, latex format (article), figures included, to be published
in Nucl. Instrm. Meth.
IL-12 Production Induced by Agaricus blazei Fraction H (ABH) Involves Toll-like Receptor (TLR)
Agaricus blazei Murill is an edible fungus used in traditional medicine, which has various well-documented medicinal properties. In the present study, we investigated the effects of hemicellulase-derived mycelia extract (Agaricus blazei fraction H: ABH) on the immune system. First, we examined the cytokine-inducing activity of ABH on human peripheral mononuclear cells (PBMC). The results indicated that ABH induced expression of IL-12, a cytokine known to be a critical regulator of cellular immune responses. Flow cytometric analysis demonstrated the induction of IL-12 production by the CD14-positive cell population, consisting of monocytes/macrophages (Mo/MÏ). Furthermore, the elimination of Mo/MÏ attenuated IL-12 production in PBMC. ABH-induced IL-12 production was inhibited by anti-CD14 and anti-TLR4 antibodies but not by anti-TLR2 antibody. The activity of ABH was not inhibited by polymyxin B, while the activity of lipopolysaccharide used as a reference was inhibited. Oral administration of ABH enhanced natural killer (NK) activity in the spleen. These findings suggest that ABH activated Mo/MÏ in a manner dependent on CD14/TLR4 and NK activity
Magic Islands and Barriers to Attachment: A Si/Si(111)7x7 Growth Model
Surface reconstructions can drastically modify growth kinetics during initial
stages of epitaxial growth as well as during the process of surface
equilibration after termination of growth. We investigate the effect of
activation barriers hindering attachment of material to existing islands on the
density and size distribution of islands in a model of homoepitaxial growth on
Si(111)7x7 reconstructed surface. An unusual distribution of island sizes
peaked around "magic" sizes and a steep dependence of the island density on the
growth rate are observed. "Magic" islands (of a different shape as compared to
those obtained during growth) are observed also during surface equilibration.Comment: 4 pages including 5 figures, REVTeX, submitted to Physical Review
Mesoscopic Capacitors: A Statistical Analysis
The capacitance of mesoscopic samples depends on their geometry and physical
properties, described in terms of characteristic times scales. The resulting ac
admittance shows sample to sample fluctuations. Their distribution is studied
here -through a random-matrix model- for a chaotic cavity capacitively coupled
to a backgate: it is observed from the distribution of scattering time delays
for the cavity, which is found analytically for the orthogonal, unitary, and
symplectic universality classes, one mode in the lead connecting the cavity to
the reservoir and no direct scattering. The results agree with numerical
simulations.Comment: 4 pages (Revtex), 4 PS figures. Minor corrections. New e-mail
address: [email protected] [email protected] e-mail
address: [email protected]
Semiclassical theory of shot noise in ballistic n+-i-n+ semiconductor strucutres: relevance of Pauli and long range Coulomb correlations
We work out a semiclassical theory of shot noise in ballistic n+-i-n+
semiconductor structures aiming at studying two fundamental physical
correlations coming from Pauli exclusion principle and long range Coulomb
interaction. The theory provides a unifying scheme which, in addition to the
current-voltage characteristics, describes the suppression of shot noise due to
Pauli and Coulomb correlations in the whole range of system parameters and
applied bias. The whole scenario is summarized by a phase diagram in the plane
of two dimensionless variables related to the sample length and contact
chemical potential. Here different regions of physical interest can be
identified where only Coulomb or only Pauli correlations are active, or where
both are present with different relevance. The predictions of the theory are
proven to be fully corroborated by Monte Carlo simulations.Comment: 15 pages, 11 figures. Title changed and Introduction rewritten.
Accepted for publication in Physical Review
STM and RHEED study of the Si(001)-c(8x8) surface
The Si(001) surface deoxidized by short annealing at T~925C in the ultrahigh
vacuum molecular beam epitaxy chamber has been in situ investigated by high
resolution scanning tunnelling microscopy (STM) and reflected high energy
electron diffraction (RHEED). RHEED patterns corresponding to (2x1) and (4x4)
structures were observed during sample treatment. The (4x4) reconstruction
arose at T<600C after annealing. The reconstruction was observed to be
reversible: the (4x4) structure turned into the (2x1) one at T>600C, the (4x4)
structure appeared again at recurring cooling. The c(8x8) reconstruction was
revealed by STM at room temperature on the same samples. A fraction of the
surface area covered by the c(8x8) structure decreased as the sample cooling
rate was reduced. The (2x1) structure was observed on the surface free of the
c(8x8) one. The c(8x8) structure has been evidenced to manifest itself as the
(4x4) one in the RHEED patterns. A model of the c(8x8) structure formation has
been built on the basis of the STM data. Origin of the high-order structure on
the Si(001) surface and its connection with the epinucleation phenomenon are
discussed.Comment: 26 pages, 12 figure
New constraint on the existence of the mu+-> e+ gamma decay
The analysis of a combined data set, totaling 3.6 \times 10^14 stopped muons
on target, in the search for the lepton flavour violating decay mu^+ -> e^+
gamma is presented. The data collected by the MEG experiment at the Paul
Scherrer Institut show no excess of events compared to background expectations
and yield a new upper limit on the branching ratio of this decay of 5.7 \times
10^-13 (90% confidence level). This represents a four times more stringent
limit than the previous world best limit set by MEG.Comment: 5 pages, 3 figures, a version accepted in Phys. Rev. Let
The MEG detector for decay search
The MEG (Mu to Electron Gamma) experiment has been running at the Paul
Scherrer Institut (PSI), Switzerland since 2008 to search for the decay \meg\
by using one of the most intense continuous beams in the world. This
paper presents the MEG components: the positron spectrometer, including a thin
target, a superconducting magnet, a set of drift chambers for measuring the
muon decay vertex and the positron momentum, a timing counter for measuring the
positron time, and a liquid xenon detector for measuring the photon energy,
position and time. The trigger system, the read-out electronics and the data
acquisition system are also presented in detail. The paper is completed with a
description of the equipment and techniques developed for the calibration in
time and energy and the simulation of the whole apparatus.Comment: 59 pages, 90 figure
Increased epithelial cell proliferation in the ileal pouch mucosa of patients with familial adenomatous polyposis
To eliminate the risk of colorectal cancer in patients with familial adenomatous polyposis (FAP), reconstructive proctocolectomy is performed. Although most colonic mucosa is resected during the ileal pouch anal anastomosis, adenomas and carcinomas may develop in the pouch. This may be caused by altered cell kinetics due to intraluminal changes in the pouch. In 32 patients with FAP, biopsy specimens from the mucosa of the pouch and also of the afferent ileal loop were taken. Tissue sections were immunohistochemically processed with the monoclonal antibodies M30 and MIB-1 to assess apoptotic and proliferative indices, respectively. Cell proliferation was also assessed by a modified sign test. There were no significant differences in apoptotic rates between the mucosa of the pouch and the mucosa of the afferent ileal loop. However, cell proliferation was significantly higher in the mucosa of the pouch vs afferent ileal loop, both by using the quantitative (68.3% vs 61.6%, pâ=â0.001) and semiquantitative methods (pâ<â0.05). Our newly developed semiquantitative approach outperformed previously described methods. The higher cell proliferation in the pouch as compared to the afferent ileal loop may contribute to the increased risk for adenomas and carcinomas in the pouch of patients with FAP and emphasizes the need for regular endoscopic surveillance
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