198 research outputs found
⁶³Cu(n,γ ) cross section measured via 25 keV activation and time of flight
In the nuclear mass range A≈60 to 90 of the solar abundance distribution the weak s-process component is the dominant contributor. In this scenario, which is related to massive stars, the overall neutron exposure is not sufficient for the s process to reach mass flow equilibrium. Hence, abundances and isotopic ratios are very sensitive to the neutron capture cross sections of single isotopes, and nucleosynthesis models need accurate experimental data. In this work we report on a new measurement of the Cu63(n,γ) cross section for which the existing experimental data show large discrepancies. The Cu63(n,γ) cross section at kBT=25 keV was determined via activation with a quasistellar neutron spectrum at the Joint Research Centre (JRC) in Geel, and the energy dependence was determined with the time-of-flight technique and the calorimetric 4πBaF2 detector array DANCE at the Los Alamos National Laboratory. We provide new cross section data for the whole astrophysically relevant energy range
Extended peptide-based inhibitors efficiently target the proteasome and reveal overlapping specificities of the catalytic β-subunits
AbstractBackground: The 26S proteasome is responsible for most cytosolic proteolysis, and is an important protease in major histocompatibility complex class I-mediated antigen presentation. Constitutively expressed proteasomes from mammalian sources possess three distinct catalytically active species, β1, β2 and β5, which are replaced in the γ-interferon-inducible immunoproteasome by a different set of catalytic subunits, β1i, β2i and β5i, respectively. Based on preferred cleavage of short fluorogenic peptide substrates, activities of the proteasome have been assigned to individual subunits and classified as ‘chymotryptic-like’ (β5), ‘tryptic-like’ (β2) and ‘peptidyl-glutamyl peptide hydrolyzing’ (β1). Studies with protein substrates indicate a far more complicated, less strict cleavage preference. We reasoned that inhibitors of extended size would give insight into the extent of overlapping substrate specificity of the individual activities and subunits.Results: A new class of proteasome inhibitors, considerably extended in comparison with the commonly used fluorescent substrates and peptide-based inhibitors, has been prepared. Application of the safety catch resin allowed the generation of the target compounds using a solid phase protocol. Evaluation of the new compounds revealed a set of highly potent proteasome inhibitors that target all individual active subunits with comparable affinity, unlike the other inhibitors described to date. Modification of the most active compound, adamantane-acetyl-(6-aminohexanoyl)3-(leucinyl)3-vinyl-(methyl)-sulfone (AdaAhx3L3VS), itself capable of proteasome inhibition in living cells, afforded a new set of radio- and affinity labels.Conclusions: N-terminal extension of peptide vinyl sulfones has a profound influence on both their efficiency and selectivity as proteasome inhibitors. Such extensions greatly enhance inhibition and largely obliterate selectivity towards the individual catalytic activities. We conclude that for the interaction with larger substrates, there appears to be less discrimination of different substrate sequences for the catalytic activities than is normally assumed based on the use of small peptide-based substrates and inhibitors. The compounds described here are readily accessible synthetically, and are more potent inhibitors in living cells than their shorter peptide vinyl sulfone counterparts
Simulations of the High-Energy Beam-Transport (HEBT) section at FRANZ
The neutron source FRANZ (Frankfurter Neutronenquelle am
Stern-Gerlach-Zentrum), which is currently under construction, will be the neutron source with the highest intensity in the nuclear-astrophysically relevant energy
region. The TraceWin code was used to design the High-Energy Beam-Transport section with regard to the experimental requirements at different target positions
Thermal (n, γ) cross section and resonance integral of 171Tm
Background: About 50% of the heavy elements are produced in stars during the slow neutron capture process.
The analysis of branching points allows us to set constraints on the temperature and the neutron density in the
interior of stars.
Purpose: The temperature dependence of the branch point 171Tm is weak. Hence, the 171Tm neutron capture
cross section can be used to constrain the neutron density during the main component of the s process in thermally
pulsing asymptotic giant branch (TP-AGB) stars.
Methods: A 171Tm sample produced at the ILL was activated with thermal and epithermal neutrons at the
TRIGA research reactor at the Johannes Gutenberg-Universität Mainz.
Results: The thermal neutron capture cross section and the resonance integral have been measured for the first
time to be σth = 9.9 ± 0.9 b and σRI = 193 ± 14 b.
Conclusions: Based on our results, new estimations of the direct capture components’ impact on the
Maxwellian-nAveraged cross sections (MACS) are possible.European Unions’s Seventh Framework Programme (FP/2007-2013
Analysis of Protease Activity in Live Antigen-presenting Cells Shows Regulation of the Phagosomal Proteolytic Contents During Dendritic Cell Activation
Here, we describe a new approach designed to monitor the proteolytic activity of maturing phagosomes in live antigen-presenting cells. We find that an ingested particle sequentially encounters distinct protease activities during phagosomal maturation. Incorporation of active proteases into the phagosome of the macrophage cell line J774 indicates that phagosome maturation involves progressive fusion with early and late endocytic compartments. In contrast, phagosome biogenesis in bone marrow–derived dendritic cells (DCs) and macrophages preferentially involves endocytic compartments enriched in cathepsin S. Kinetics of phagosomal maturation is faster in macrophages than in DCs. Furthermore, the delivery of active proteases to the phagosome is significantly reduced after the activation of DCs with lipopolysaccharide. This observation is in agreement with the notion that DCs prevent the premature destruction of antigenic determinants to optimize T cell activation. Phagosomal maturation is therefore a tightly regulated process that varies according to the type and differentiation stage of the phagocyte
Characterization of the QUartz Photon Intensifying Detector (QUPID) for Noble Liquid Detectors
Dark Matter and Double Beta Decay experiments require extremely low
radioactivity within the detector materials. For this purpose, the University
of California, Los Angeles and Hamamatsu Photonics have developed the QUartz
Photon Intensifying Detector (QUPID), an ultra-low background photodetector
based on the Hybrid Avalanche Photo Diode (HAPD) and entirely made of
ultraclean synthetic fused silica. In this work we present the basic concept of
the QUPID and the testing measurements on QUPIDs from the first production
line. Screening of radioactivity at the Gator facility in the Laboratori
Nazionali del Gran Sasso has shown that the QUPIDs safely fulfill the low
radioactive contamination requirements for the next generation zero background
experiments set by Monte Carlo simulations. The quantum efficiency of the QUPID
at room temperature is > 30% at the xenon scintillation wavelength. At low
temperatures, the QUPID shows a leakage current less than 1 nA and a global
gain of 10^5. In these conditions, the photocathode and the anode show > 95%
linearity up to 1 uA for the cathode and 3 mA for the anode. The photocathode
and collection efficiency are uniform to 80% over the entire surface. In
parallel with single photon counting capabilities, the QUPIDs have a good
timing response: 1.8 +/- 0.1 ns rise time, 2.5 +/- 0.2 ns fall time, 4.20 +/-
0.05 ns pulse width, and 160 +/- 30 ps transit time spread. The QUPIDs have
also been tested in a liquid xenon environment, and scintillation light from
57Co and 210Po radioactive sources were observed.Comment: 15 pages, 22 figure
Neutron activation of Ga and Ga at kBT≈25 keV
Background: About 50% of heavy elements are produced by the slow neutron capture process (s process) in stars. The element gallium is mostly produced during the weak s process in massive stars.
Purpose: Our activation at kT≈25 keV is the first experiment in a series of activation and time-of-flight measurements on Ga and Ga relevant for astrophysics.
Methods: We activated Ga and Ga with a neutron distribution that corresponds to a quasistellar distribution with kT=25 keV at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction Li(p,n). The produced activity was measured via the γ emission by the decaying product nuclei by high-purity germanium detectors.
Results: We provide spectrum-averaged cross sections (SACS) and ratios of the cross sections σ/σ for the neutron spectrum of the activation. We obtain values of σ=(186±12) mb and σ = (112±7) mb, and cross section ratios of σ/σ=0.29±0.02 and σ/σ = 0.17±0.01.
Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for Ga and about 20% lower for Ga
Approaching the Gamow Window with Stored Ions : Direct Measurement of Xe 124 (p,γ) in the ESR Storage Ring
© 2019 American Physical Society. All rights reserved.We report the first measurement of low-energy proton-capture cross sections of Xe124 in a heavy-ion storage ring. Xe12454+ ions of five different beam energies between 5.5 and 8 AMeV were stored to collide with a windowless hydrogen target. The Cs125 reaction products were directly detected. The interaction energies are located on the high energy tail of the Gamow window for hot, explosive scenarios such as supernovae and x-ray binaries. The results serve as an important test of predicted astrophysical reaction rates in this mass range. Good agreement in the prediction of the astrophysically important proton width at low energy is found, with only a 30% difference between measurement and theory. Larger deviations are found above the neutron emission threshold, where also neutron and γ widths significantly impact the cross sections. The newly established experimental method is a very powerful tool to investigate nuclear reactions on rare ion beams at low center-of-mass energies.Peer reviewedFinal Published versio
IgE Mediated Autoallergy against Thyroid Peroxidase – A Novel Pathomechanism of Chronic Spontaneous Urticaria?
Chronic spontaneous urticaria (csU), which is characterized by recurrent episodes
of mast cell-driven wheal and flare-type skin reactions, is often associated with
elevated total IgE levels and thyroid autoimmunity. We speculate that some csU
patients express IgE autoantibodies against thyroid antigens such as thyroid
peroxidase (TPO), which could bind to skin mast cells and induce their
activation.We developed and used a site-directed human IgE capture ELISA to quantify
IgE-anti-TPO. We used this assay and investigated csU patients
(n = 478) and healthy control subjects
(n = 127) for IgE-anti-TPO and then assessed
IgE-anti-TPO-positive and -negative csU patients for clinical and serological
differences. ( = 61%, IgE-anti-TPO:
median 6.67, interquartile range 5.39–8.24). IgE-anti-TPO-positive and
-negative csU patients had very similar distributions of age and gender as well as
disease activity and duration. IgE-anti-TPO-positive csU patients exhibited
significantly higher IgG-anti-TPO levels and lymphocyte counts as well as
decreased C4 complement levels.Our findings show that a sizeable subgroup of csU patients expresses IgE
antibodies against thyroid peroxidase. These autoantibodies could cause
“autoallergic” mast cell activation, a novel pathomechanism of chronic
spontaneous urticaria
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