188 research outputs found
Improved energy resolution for VHE gamma-ray astronomy with systems of Cherenkov telescopes
We present analysis techniques to improve the energy resolution of
stereoscopic systems of imaging atmospheric Cherenkov telescopes, using the
HEGRA telescope system as an example. The techniques include (i) the
determination of the height of the shower maximum, which is then taken into
account in the energy determination, and (ii) the determination of the location
of the shower core with the additional constraint that the direction of the
gamma rays is known a priori. This constraint can be applied for gamma-ray
point sources, and results in a significant improvement in the localization of
the shower core, which translates into better energy resolution. Combining both
techniques, the HEGRA telescopes reach an energy resolution between 9% and 12%,
over the entire energy range from 1 TeV to almost 100 TeV. Options for further
improvements of the energy resolution are discussed.Comment: 13 Pages, 7 figures, Latex. Astroparticle Physics, in pres
X20CoCrWMo10-9//Co3O4: a Metal-Ceramic Composite with Unique Efficiency Values for Water-Splitting in Neutral Regime
Water splitting allows the storage of solar energy into chemical bonds
(H2+O2) and will help to implement the urgently needed replacement of limited
available fossil fuels. Particularly in neutral environment electrochemically
initiated water splitting suffers from low efficiency due to high
overpotentials caused by the anode. Electro-activation of X20CoCrWMo10-9, a
Co-based tool steel resulted in a new composite material
(X20CoCrWMo10-9//Co3O4) that catalyzes the anode half-cell reaction of water
electrolysis with a so far unequalled effectiveness. The current density
achieved with this new anode in pH 7 corrected 0.1 M phosphate buffer is over a
wide range of overpotentials around 10 times higher compared to recently
developed, up-to-date electrocatalysts and represents the benchmark performance
advanced catalysts show in regimes that support water splitting significantly
better than pH 7 medium. X20CoCrWMo10-9//Co3O4 exhibited electrocatalytic
properties not only at pH 7, but also at pH 13, which is much superior to the
ones of IrO2-RuO2, single-phase Co3O4- or Fe/Ni- based catalysts. Both XPS and
FT-IR experiments unmasked Co3O4 as the dominating compound on the surface of
the X20CoCrWMo10-9//Co3O4 composite. Upon a comprehensive dual beam FIB-SEM
(focused ion beam-scanning electron microscopy) study we could show that the
new composite does not exhibit a classical substrate-layer structure due to the
intrinsic formation of the Co-enriched outer zone. This structural
particularity is basically responsible for the outstanding electrocatalytic OER
performance
Gamma-Hadron Separation Methods for the VERITAS Array of Four Imaging Atmospheric Cherenkov Telescopes
Ground-based arrays of imaging atmospheric Cherenkov telescopes have emerged
as the most sensitive gamma-ray detectors in the energy range of about 100 GeV
and above. The strengths of these arrays are a very large effective collection
area on the order of 100,000 square meter, combined with excellent single
photon angular and energy resolutions. The sensitivity of such detectors is
limited by statistical fluctuations in the number of Cosmic Ray initiated air
showers that resemble gamma-ray air showers in many ways. In this paper, we
study the performance of simple event reconstruction methods when applied to
simulated data of the Very Energetic Radiation Imaging Telescope Array System
(VERITAS) experiment. We review methods for reconstructing the arrival
direction and the energy of the primary photons, and examine means to improve
on their performance. For a software threshold energy of 300 GeV (100 GeV), the
methods achieve point source angular and energy resolutions of sigma[63%]= 0.1
degree (0.2 degree) and sigma[68%]= 15% (22%), respectively. The main emphasis
of the paper is the discussion of gamma-hadron separation methods for the
VERITAS experiment. We find that the information from several methods can be
combined based on a likelihood ratio approach and the resulting algorithm
achieves a gamma-hadron suppression with a quality factor that is substantially
higher than that achieved with the standard methods used so far.Comment: Astroparticle Physics, in press, 22 pages, 10 figure
PuraStat in gastrointestinal bleeding: results of a prospective multicentre observational pilot study
Background: A recently developed haemostatic peptide gel for endoscopic application has been introduced to improve the management of gastrointestinal bleeding. The aim of this pilot study was to evaluate the feasibility, safety, efficacy and indication profiles of PuraStat in a clinical setting.
Methods: In this prospective observational multicentre pilot study, patients with acute non-variceal gastrointestinal bleeding (upper and lower) were included. Primary and secondary application of PuraStat was evaluated. Haemoglobin, prothrombin time, platelets and transfusion behaviour were documented before and after haemostasis. The efficacy of PuraStat was assessed during the procedure, at 3 days and 1 week after application.
Results: 111 patients with acute gastrointestinal bleeding were recruited into the study. 70 percent (78/111) of the patients had upper gastrointestinal bleeding and 30% (33/111) had lower gastrointestinal bleeding. After primary application of PuraStat, initial haemostatic success was achieved in 94% of patients (74/79, 95% CI 88-99%), and in 75% of the patients when used as a secondary haemostatic product, following failure of established techniques (24/32, 95% CI 59-91%). The therapeutic success rates (absence of rebleeding) after 3 and 7 days were 91% and 87% after primary use, and 87% and 81% in all study patients. Overall rebleeding rate at 30 day follow-up was 16% (18/111). In the 5 patients who finally required surgery (4.5%), PuraStat allowed temporary haemostasis and stabilisation.
Conclusions: PuraStat expanded the therapeutic toolbox available for an effective treatment of gastrointestinal bleeding sources. It could be safely applied and administered without complications as a primary or secondary therapy. PuraStat may additionally serve as a bridge to surgery in order to achieve temporary haemostasis in case of refractory severe bleeding, possibly playing a role in preventing immediate emergency surgery
Unbinned deep learning jet substructure measurement in high ep collisions at HERA
The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators with numerous applications in high energy particle and nuclear physics. Looking at electron-proton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the kt jet clustering algorithm. Results are reported at high transverse momentum transfer >150 GeV , and inelasticity 0.2<y<0.7 . The analysis is also performed in sub-regions of Q, thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models
Searches at HERA for Squarks in R-Parity Violating Supersymmetry
A search for squarks in R-parity violating supersymmetry is performed in e^+p
collisions at HERA at a centre of mass energy of 300 GeV, using H1 data
corresponding to an integrated luminosity of 37 pb^(-1). The direct production
of single squarks of any generation in positron-quark fusion via a Yukawa
coupling lambda' is considered, taking into account R-parity violating and
conserving decays of the squarks. No significant deviation from the Standard
Model expectation is found. The results are interpreted in terms of constraints
within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM
and the minimal Supergravity model, and their sensitivity to the model
parameters is studied in detail. For a Yukawa coupling of electromagnetic
strength, squark masses below 260 GeV are excluded at 95% confidence level in a
large part of the parameter space. For a 100 times smaller coupling strength
masses up to 182 GeV are excluded.Comment: 32 pages, 14 figures, 3 table
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