8,075 research outputs found
Progress in Developing Hybrid RPCs: GEM-like Detectors with Resistive Electrodes
We have recently developed an innovative detector of photons and charged
particles: a GEM-like gaseous amplification structure with resistive electrodes
instead of commonly used metallic ones. This novel detector combines the best
property of GEMs- the capability to operate in a cascaded mode and in poorly
quenched gases - and of RPC: the protection against sparks. In this paper will
shortly review our latest achievements in this direction, however the main
focus will be given on a new advanced design that allows to build large area
detectors manufactured by a screen printing technology. The proposed detector,
depending on the applications, can operate either in a GEM mode (electron
multiplications through holes only) or as a hybrid RPC with simultaneous
amplifications in the drift region and in the holes. The possible applications
of this new detector will be discussed
Effect of the Casimir-Polder force on the collective oscillations of a trapped Bose-Einstein condensate
We calculate the effect of the interaction between an optically active
material and a Bose-Einstein condensate on the collective oscillations of the
condensate. We provide explicit expressions for the frequency shift of the
center of mass oscillation in terms of the potential generated by the substrate
and of the density profile of the gas. The form of the potential is discussed
in details and various regimes (van der Waals-London, Casimir-Polder and
thermal regimes) are identified as a function of the distance of atoms from the
surface. Numerical results for the frequency shifts are given for the case of a
sapphire dielectric substrate interacting with a harmonically trapped
condensate of Rb atoms. We find that at distances of , where
thermal effects become visible, the relative frequency shifts produced by the
substrate are of the order and hence accessible experimentally. The
effects of non linearities due to the finite amplitude of the oscillation are
explicitly discussed. Predictions are also given for the radial breathing mode.Comment: 28 pages, 10 figures. Submitted to PR
First observation of Cherenkov rings with a large area CsI-TGEM-based RICH prototype
We have built a RICH detector prototype consisting of a liquid C6F14 radiator
and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having
an active area of 10x10 cm2. One triple TGEM has been placed behind the liquid
radiator in order to detect the beam particles, whereas the other five have
been positioned around the central one at a distance to collect the Cherenkov
photons. The upstream electrode of each of the TGEM stacks has been coated with
a 0.4 micron thick CsI layer.
In this paper, we will present the results from a series of laboratory tests
with this prototype carried out using UV light, 6 keV photons from 55Fe and
electrons from 90Sr as well as recent results of tests with a beam of charged
pions where for the first time Cherenkov Ring images have been successfully
recorded with TGEM photodetectors. The achieved results prove the feasibility
of building a large area Cherenkov detector consisting of a matrix of TGEMs.Comment: Presented at the International Conference NDIP-11, Lyon,July201
R&D results on a CsI-TTGEM based photodetector
The very high momentum particle identification detector proposed for the
ALICE upgrade is a focusing RICH using a C4F10 gaseous radiator. For the
detection of Cherenkov photons, one of the options currently under
investigation is to use a CsI coated Triple-Thick-GEM (CsI-TTGEM) with metallic
or resistive electrodes. We will present results from the laboratory studies as
well as preliminary results of beam tests of a RICH detector prototype
consisting of a CaF2 radiator coupled to a 10x10 cm2 CsI-TTGEM equipped with a
pad readout and GASSIPLEX-based front-end electronics. With such a prototype
the detection of Cherenkov photons simultaneously with minimum ionizing
particles has been achieved for the first time in a stable operation mode
Optimization of graphene-based materials outperforming host epoxy matrices
The degree of graphite exfoliation and edge-carboxylated layers can be controlled and balanced to design lightweight materials characterized by both low electrical percolation thresholds (EPT) and improved mechanical properties. So far, this challenging task has been undoubtedly very hard to achieve. The results presented in this paper highlight the effect of exfoliation degree and the role of edge-carboxylated graphite layers to give self-assembled structures embedded in the polymeric matrix. Graphene layers inside the matrix may serve as building blocks of complex systems that could outperform the host matrix. Improvements in electrical percolation and mechanical performance have been obtained by a synergic effect due to finely balancing the degree of exfoliation and the chemistry of graphene edges which favors the interfacial interaction between polymer and carbon layers. In particular, for epoxy-based resins including two partially exfoliated graphite samples, differing essentially in the content of carboxylated groups, the percolation threshold reduces from 3 wt% down to 0.3 wt%, as the carboxylated group content increases up to 10 wt%. Edge-carboxylated nanosheets also increase the nanofiller/epoxy matrix interaction, determining a relevant reinforcement in the elastic modulus
Two-photon excitation and relaxation of the 3d-4d resonance in atomic Kr
Two-photon excitation of a single-photon forbidden Auger resonance has been observed and investigated using the intense extreme ultraviolet radiation from the free electron laser in Hamburg. At the wavelength 26.9 nm (46 eV) two photons promoted a 3d core electron to the outer 4d shell. The subsequent Auger decay, as well as several nonlinear above threshold ionization processes, were studied by electron spectroscopy. The experimental data are in excellent agreement with theoretical predictions and analysis of the underlying multiphoton processes
Evaluating the impact of policies recommending PrEP to subpopulations of men and transgender women who have sex with men based on demographic and behavioral risk factors.
IntroductionDeveloping guidelines to inform the use of antiretroviral pre-exposure prophylaxis (PrEP) for HIV prevention in resource-limited settings must necessarily be informed by considering the resources and infrastructure needed for PrEP delivery. We describe an approach that identifies subpopulations of cisgender men who have sex with men (MSM) and transgender women (TGW) to prioritize for the rollout of PrEP in resource-limited settings.MethodsWe use data from the iPrEx study, a multi-national phase III study of PrEP for HIV prevention in MSM/TGW, to build statistical models that identify subpopulations at high risk of HIV acquisition without PrEP, and with high expected PrEP benefit. We then evaluate empirically the population impact of policies recommending PrEP to these subpopulations, and contrast these with existing policies.ResultsA policy recommending PrEP to a high risk subpopulation of MSM/TGW reporting condomless receptive anal intercourse over the last 3 months (estimated 3.3% 1-year HIV incidence) yields an estimated 1.95% absolute reduction in 1-year HIV incidence at the population level, and 3.83% reduction over 2 years. Importantly, such a policy requires rolling PrEP out to just 59.7% of MSM/TGW in the iPrEx population. We find that this policy is identical to that which prioritizes MSM/TGW with high expected PrEP benefit. It is estimated to achieve nearly the same reduction in HIV incidence as the PrEP guideline put forth by the US Centers for Disease Control, which relies on the measurement of more behavioral risk factors and which would recommend PrEP to a larger subset of the MSM/TGW population (86% vs. 60%).ConclusionsThese findings may be used to focus future mathematical modelling studies of PrEP in resource-limited settings on prioritizing PrEP for high-risk subpopulations of MSM/TGW. The statistical approach we took could be employed to develop PrEP policies for other at-risk populations and resource-limited settings
The current progress of the ALICE Ring Imaging Cherenkov Detector
Recently, the last two modules (out of seven) of the ALICE High Momentum
Particle Identification detector (HMPID) were assembled and tested. The full
detector, after a pre-commissioning phase, has been installed in the
experimental area, inside the ALICE solenoid, at the end of September 2006. In
this paper we review the status of the ALICE/HMPID project and we present a
summary of the series production of the CsI photo-cathodes. We describe the key
features of the production procedure which ensures high quality photo-cathodes
as well as the results of the quality assessment performed by means of a
specially developed 2D scanner system able to produce a detailed map of the CsI
photo-current over the entire photo-cathode surface.
Finally we present our recent R&D efforts toward the development of a novel
generation of imaging Cherenkov detectors with the aim to identify, in heavy
ions collisions, hadrons up to 30 GeV/c.Comment: Presented at the Imaging-2006 Conference, Stockholm, Sweden, June
200
Verification of Magnitude and Phase Responses in Fixed-Point Digital Filters
In the digital signal processing (DSP) area, one of the most important tasks
is digital filter design. Currently, this procedure is performed with the aid
of computational tools, which generally assume filter coefficients represented
with floating-point arithmetic. Nonetheless, during the implementation phase,
which is often done in digital signal processors or field programmable gate
arrays, the representation of the obtained coefficients can be carried out
through integer or fixed-point arithmetic, which often results in unexpected
behavior or even unstable filters. The present work addresses this issue and
proposes a verification methodology based on the digital-system verifier
(DSVerifier), with the goal of checking fixed-point digital filters w.r.t.
implementation aspects. In particular, DSVerifier checks whether the number of
bits used in coefficient representation will result in a filter with the same
features specified during the design phase. Experimental results show that
errors regarding frequency response and overflow are likely to be identified
with the proposed methodology, which thus improves overall system's
reliability
Search for the Cryptoexotic Member of the Baryon Antidecuplet 1/2+ in the Reactions pi- p --> pi- p and pi- p --> K L
The main goal of this proposal is the search for a narrow cryptoexotic
nucleon resonance by scanning of the pi- p system invariant mass in the region
(1610-1770) MeV with the detection of pi- p and K Lambda decays. The scan is
supposed to be done by the variation of the incident pi- momentum and its
measurement with the accuracy of up to +-0.1% (better than 1 MeV in terms of
the invariant mass in the whole energy range) with a set of proportional
chambers located in the first focus of the magnetooptical channel. High
sensitivity of the method to the resonance under search is shown. The secondary
particles scattered from a liquid hydrogen target are detected by sets of the
wire drift chambers equipped with modern electronics. The time scale of the
project is about 3 years. The budget estimate including manpower, the apparatus
and operation cost, is about 40 million rubles. The beam time required is (4-6)
two week runs on "high" (10 GeV/c) flattop of the ITEP proton synchrotron.Comment: 16 pages, 10 figures. v2: an acknowledge adde
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