223 research outputs found
Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment
Results obtained with a triple GEM detector operated in pure CF4 with and
without a reflective CsI photocathode are presented. The detector operates in a
stable mode at gains up to 10^4. A deviation from exponential growth starts to
develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation
when the total charge is ~ 2 10^7 e and making the structure relatively robust
against discharges. No aging effects are observed in the GEM foils after a
total accumulated charge of ~ 10 mC/cm^2 at the anode. The ion back-flow
current to the reflective photocathode is comparable to the electron current to
the anode. However, no significant degradation of the CsI photocathode is
observed for a total ion back-flow charge of ~ 7 mC/cm^2.Comment: 14 pages, 11 figures, Submitted to NIM
GEM Operation in Negative Ion Drift Gas Mixtures
The first operation of GEM gas gain elements in negative ion gas mixtures is
reported. Gains up to several thousand were obtained from single-stage GEMs in
carbon disulfide vapor at low pressure, and in mixtures of carbon disulfide
with Argon and Helium, some near 1 bar total pressure.Comment: 7 pages, 3 figure
Infrared enhanced analytic coupling and chiral symmetry breaking in QCD
We study the impact on chiral symmetry breaking of a recently developed model
for the QCD analytic invariant charge. This charge contains no adjustable
parameters, other than the QCD mass scale , and embodies asymptotic
freedom and infrared enhancement into a single expression. Its incorporation
into the standard form of the quark gap equation gives rise to solutions for
the dynamically generated mass that display a singular confining behaviour at
the origin. Using the Pagels-Stokar method we relate the obtained solutions to
the pion decay constant , and estimate the scale parameter ,
in the presence of four active quarks, to be about 880 MeV.Comment: 14 pages, 3 figures; to appear in J. Phys.
A Novel UV Photon Detector with Resistive Electrodes
In this study we present first results from a new detector of UV photons: a
thick gaseous electron multiplier (GEM) with resistive electrodes, combined
with CsI or CsTe/CsI photocathodes. The hole type structure considerably
suppresses the photon and ion feedback, whereas the resistive electrodes
protect the detector and the readout electronics from damage by any eventual
discharges. This device reaches higher gains than a previously developed
photosensitive RPC and could be used not only for the imaging of UV sources,
flames or Cherenkov light, for example, but also for the detection of X-rays
and charged particles.Comment: Presented at the International Workshop on Resistive Plate Chambers,
Korea, October 200
Properties of Groove Chambers
Groove chambers with different pitch and gap height have been tested. Gas
amplifications of the order of a few times 10 have been obtained.
Combining a groove structure with a GEM pre-amplification foil a gas gain of
10 was reached. The device is robust and can be produced at low cost in
large sizes by a laser technique
Evaluation of a CTA-based convolutional neural network for infarct volume prediction in anterior cerebral circulation ischaemic stroke
Background Computed tomography angiography (CTA) imaging is needed in current guideline-based stroke diagnosis, and infarct core size is one factor in guiding treatment decisions. We studied the efficacy of a convolutional neural network (CNN) in final infarct volume prediction from CTA and compared the results to a CT perfusion (CTP)-based commercially available software (RAPID, iSchemaView). Methods We retrospectively selected 83 consecutive stroke cases treated with thrombolytic therapy or receiving supportive care that presented to Helsinki University Hospital between January 2018 and July 2019. We compared CNN-derived ischaemic lesion volumes to final infarct volumes that were manually segmented from follow-up CT and to CTP-RAPID ischaemic core volumes. Results An overall correlation of r = 0.83 was found between CNN outputs and final infarct volumes. The strongest correlation was found in a subgroup of patients that presented more than 9 h of symptom onset (r = 0.90). A good correlation was found between the CNN outputs and CTP-RAPID ischaemic core volumes (r = 0.89) and the CNN was able to classify patients for thrombolytic therapy or supportive care with a 1.00 sensitivity and 0.94 specificity. Conclusions A CTA-based CNN software can provide good infarct core volume estimates as observed in follow-up imaging studies. CNN-derived infarct volumes had a good correlation to CTP-RAPID ischaemic core volumes.Peer reviewe
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Hybrid Textures of Neutrinos
We present numerical and comprehensive analyses of the sixty hybrid textures
of neutrinos, which have an equality of matrix elements and one zero. These
textures are possibly derived from the discrete symmetry. Only six textures
among sixty ones are excluded by the present experimental data. Since there are
many textures which give similar predictions, the textures are classified based
on the numerical results. The neutrinoless double beta decay is also examined
in these textures. Our results suggest that there remain still rich structures
of the neutrino mass matrix in the phenomenological point of view.Comment: 19 pages, 9 figures; analytical discussions added, table and
reference adde
The virtual cathode chamber
We describe the operating principle and the first experimental results obtained with gas micro-strip detectors realized with anodes only on the active side, the multiplying field being provided from the back-plane and drift electrodes. For high rate operation, the detector has to be implemented on electron conducting supports, with resistivity around 10 cm. By construction, the ³Virtual Cathode Chamber² is not subjected to the possibility of discharges between anodes and cathodes, thus avoiding one of the most dangerous problems met with standard micro-strip chambers
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