3,372 research outputs found
Role of the ferroelastic strain in the optical absorption of BiVO4
Bismuth vanadate (BiVO4) has recently been under focus for its potential use
in photocatalysis thanks to its well-suited absorption edge in the visible
light range. Here, we characterize the optical absorption of a BiVO4 single
crystal as a function of temperature and polarization direction by reflectance
and transmittance spectroscopy. The optical band gap is found to be very
sensitive to temperature, and to the monoclinic-to-tetragonal ferroelastic
transition at 523K. The anisotropy, as measured by the difference in absorption
edge for light polarized parallel and perpendicular to the principal axis, is
reduced from 0.2 eV in the high-temperature tetragonal phase to 0.1 eV at
ambient temperature. We show that this evolution is dominantly controlled by
the ferroelastic shear strain. These findings provide a route for further
optimization of bismuth-vanadate-based light absorbers in photocatalytic
devices.Comment: 6 pages, 5 figure
Excitation Function of Energy Density and Partonic Degrees of Freedom in Relativistic Heavy Ion Collisions
We estimate the energy density pile-up at mid-rapidity in central Pb+Pb
collisions from 2 - 200 GeV/nucleon. The energy density is decomposed into
hadronic and partonic contributions. A detailed analysis of the collision
dynamics in the framework of a microscopic transport model shows the importance
of partonic degrees of freedom and rescattering of leading (di)quarks in the
early phase of the reaction for lab-energies > 30 GeV/nucleon. In Pb+Pb
collisions at 160 GeV/nucleon the energy density reaches up to 4 GeV/fm^3, 95%
of which are contained in partonic degrees of freedom.Comment: 10 pages, 4 figure
Positive pion absorption on 3He using modern trinucleon wave functions
We study pion absorption on 3He employing trinucleon wave functions
calculated from modern realistic NN interactions (Paris, CD Bonn). Even though
the use of the new wave functions leads to a significant improvement over older
calculations with regard to both cross section and polarization data, there are
hints that polarization data with quasifree kinematics cannot be described by
just two-nucleon absorption mechanisms.Comment: 14 pages, 6 figure
Reaction dynamics in Pb+Pb at the CERN/SPS: from partonic degrees of freedom to freeze-out
We analyze the reaction dynamics of central Pb+Pb collisions at 160
GeV/nucleon. First we estimate the energy density pile-up at mid-rapidity and
calculate its excitation function: The energy density is decomposed into
hadronic and partonic contributions. A detailed analysis of the collision
dynamics in the framework of a microscopic transport model shows the importance
of partonic degrees of freedom and rescattering of leading (di)quarks in the
early phase of the reaction for E > 30 GeV/nucleon. The energy density reaches
up to 4 GeV/fm^3, 95% of which are contained in partonic degrees of freedom. It
is shown that cells of hadronic matter, after the early reaction phase, can be
viewed as nearly chemically equilibrated. This matter never exceeds energy
densities of 0.4 GeV/fm^3, i.e. a density above which the notion of separated
hadrons loses its meaning. The final reaction stage is analyzed in terms of
hadron ratios, freeze-out distributions and a source analysis for final state
pions.Comment: 10 pages, 7 figures, Proceedings of the Erice School on Nuclear
Physics in Erice, Sicily, Italy, September 17 -25 1998; to be published in
Progress in Particle and Nuclear Physics Vol. 4
Antimatter and Matter Production in Heavy Ion Collisions at CERN (The NEWMASS Experiment NA52)
Besides the dedicated search for strangelets NA52 measures light
(anti)particle and (anti)nuclei production over a wide range of rapidity.
Compared to previous runs the statistics has been increased in the 1998 run by
more than one order of magnitude for negatively charged objects at different
spectrometer rigidities. Together with previous data taking at a rigidity of
-20 GeV/c we obtained 10^6 antiprotons 10^3 antideuterons and two antihelium3
without centrality requirements. We measured nuclei and antinuclei
(p,d,antiprotons, antideuterons) near midrapidity covering an impact parameter
range of b=2-12 fm. Our results strongly indicate that nuclei and antinuclei
are mainly produced via the coalescence mechanism. However the centrality
dependence of the antibaryon to baryon ratios show that antibaryons are
diminished due to annihilation and breakup reactions in the hadron dense
environment. The volume of the particle source extracted from coalescence
models agrees with results from pion interferometry for an expanding source.
The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide
with each other and with the thermal freeze-out of hadrons.Comment: 12 pages, 8 figures, to appear in the proceedings of the conference
on 'Fundamental Issues in Elementary Matter' Bad Honnef, Germany, Sept.
25-29, 200
Molecular and Cellular Analysis of the DMA Repair Defect in a Patient in Xeroderma Pigmentosum Complementation Group D Who Has the Clinical Features of Xeroderma Pigmentosum and Cockayne Syndrome
Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are quite distinct genetic disorders that are associated with defects in excision repair of UV-induced DNA damage. A few patients have been described previously with the clinical features of both disorders. In this paper we describe an individual in this category who has unusual cellular responses to UV light. We show that his cultured fibroblasts and lymphocytes are extremely sensitive to irradiation with UV-C, despite a level of nucleotide excision repair that is 30%-40% that of normal cells. The deficiency is assigned to the XP-D complementation group, and we have identified two causative mutations in the XPD gene: a gly→arg change at amino acid 675 in the allele inherited from the patient's mother and a -1 frameshift at amino acid 669 in the allele inherited from his father. These mutations are in the C-terminal 20% of the 760-amino-acid XPD protein, in a region where we have recently identified several mutations in patients with trichothiodystrophy.</p
A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization
This paper describes the design, realization and operation of a prototype
liquid Argon Time Projection Chamber (LAr TPC) detector dedicated to the
development of a novel online monitoring and calibration system exploiting UV
laser beams. In particular, the system is intended to measure the lifetime of
the primary ionization in LAr, in turn related to the LAr purity level. This
technique could be exploited by present and next generation large mass LAr TPCs
for which monitoring of the performance and calibration plays an important
role. Results from the first measurements are presented together with some
considerations and outlook.Comment: 26 pages, 27 figure
The combination of two Salmonella-antigen test systems for reliable diagnostic of Salmonellosis in stockbreeding pigs
Salmonella enterica is a facultative intracellular pathogen that is capable of causing disease in a range of hosts. The genus Salmonella covers more than 2,400 different serotypes, whereof some specific clones have become very dominant in one or more host species and have been able to spread worldwide. Nevertheless, all serotypes must be considered potential human pathogens
Rapid Qualitative Urinary Tract Infection Pathogen Identification by SeptiFast® Real-Time PCR
Background
Urinary tract infections (UTI) are frequent in outpatients. Fast pathogen identification is mandatory for shortening the time of discomfort and preventing serious complications. Urine culture needs up to 48 hours until pathogen identification. Consequently, the initial antibiotic regimen is empirical.
Aim
To evaluate the feasibility of qualitative urine pathogen identification by a commercially available real-time PCR blood pathogen test (SeptiFast®) and to compare the results with dipslide and microbiological culture.
Design of study
Pilot study with prospectively collected urine samples.
Setting
University hospital.
Methods
82 prospectively collected urine samples from 81 patients with suspected UTI were included. Dipslide urine culture was followed by microbiological pathogen identification in dipslide positive samples. In parallel, qualitative DNA based pathogen identification (SeptiFast®) was performed in all samples.
Results
61 samples were SeptiFast® positive, whereas 67 samples were dipslide culture positive. The inter-methodological concordance of positive and negative findings in the gram+, gram- and fungi sector was 371/410 (90%), 477/492 (97%) and 238/246 (97%), respectively. Sensitivity and specificity of the SeptiFast® test for the detection of an infection was 0.82 and 0.60, respectively. SeptiFast® pathogen identifications were available at least 43 hours prior to culture results.
Conclusion
The SeptiFast® platform identified bacterial DNA in urine specimens considerably faster compared to conventional culture. For UTI diagnosis sensitivity and specificity is limited by its present qualitative setup which does not allow pathogen quantification. Future quantitative assays may hold promise for PCR based UTI pathogen identification as a supplementation of conventional culture methods
Heavy ion collisions with non-equilibrium Dirac-Brueckner mean fields
The influence of realistic interactions on the reaction dynamics in
intermediate energy heavy ion collisions is investigated. The mean field in
relativistic transport calculations is derived from microscopic Dirac-Brueckner
(DB) self-energies, taking non-equilibrium effects, in particular the
anisotropy of the local phase space configurations, into account. Thus this
approach goes beyond the local density approximation. A detailed analysis of
various in-plane and out-of-plane flow observables is presented for Au on Au
reactions at incident energies ranging from 250 to 800 A.MeV and the results
are compared to recent measurements of the FOPI collaboration. An overall good
agreement with in-plane flow data and a reasonable description of the
out-of-plane emission is achieved. For these results the intrinsic momentum
dependence of the non-equilibrium mean fields is important. On the other hand,
the local density approximation with the same underlying DB forces as well as a
standard non-linear version of the model are less successful in
describing the present data. This gives evidence of the applicability of self
energies derived from the DB approach to nuclear matter also far from
saturation and equilibrium.Comment: 63 pages Latex, using Elsevier style, 20 ps-figures, to appear in
Nucl. Phys.
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