429 research outputs found
High Power Cyclotrons for the Neutrino Experiments DAEδALUS and IsoDAR
DAEδALUS (Decay At rest Experiment for δcp At a Laboratory for Underground Science) has been proposed to measure the value of the CP violating phase delta through the oscillation of low energy muon anti-neutrinos to electron antineutrinos. With a single large detector, three accelerators at different distances enable the oscillation to be measured with sufficient accuracy. We have proposed the superconducting multi-megawatt DAEδALUS Supercinducting Ring Cyclotron (DSRC) as the means of producing the 800 MeV 12 mA protons required, through the acceleration of H2+, ions with highly efficient stripping extraction. The DSRC comprises twin ion sources and injector cyclotrons, followed by a booster. The injector cyclotron can also be used for a separate experiment, IsoDAR (Isotope Decay At Rest) in which low energy protons produce Lithium 8, and thus a very pure electron antineutrino source which can be used to measure, or rule out, short range oscillation to a sterile neutrino. We describe recent developments in the designs of the injector and the booster, and the prospects for the two experiments
Demonstration of a Lightguide Detector for Liquid Argon TPCs
We report demonstration of light detection in liquid argon using an acrylic
lightguide detector system. This opens the opportunity for development of an
inexpensive, large-area light collection system for large liquid argon time
projection chambers. The guides are constructed of acrylic, with TPB embedded
in a surface coating with a matching index of refraction. We study the response
to early scintillation light produced by a 5.3 MeV alpha. We measure coating
responses from 7 to 8 PE on average, compared to an ideal expectation of 10 PE
on average. We estimate the attenuation length of light along the lightguide
bar to be greater than 0.5 m. The coating response and the attenuation length
can be improved; we show, however, that these results are already sufficient
for triggering in a large detector
A Prototype Detector for Directional Measurement of the Cosmogenic Neutron Flux
This paper describes a novel directional neutron detector prototype. The low
pressure time projection chamber uses a mix of helium and CF4 gases. The
detector reconstructs the energy and angular distribution of fast neutron
recoils. This paper reports results of energy calibration using an alpha source
and angular reconstruction studies using a collimated neutron source. The best
performance is obtained with a 12.5% CF4 gas mixture. At low energies the
target for fast neutrons transitions is primarily helium, while at higher
energies, the fluorine contributes as a target. The reconstruction efficiency
is both energy and target dependent. For neutrons with energies less than 20
MeV, the reconstruction efficiency is ~40% for fluorine recoils and ~60% for
helium recoils.Comment: final versio
Does femtosecond time-resolved second-harmonic generation probe electron temperatures at surfaces?
Femtosecond pump-probe second-harmonic generation (SHG) and transient linear
reflectivity measurements were carried out on polycrystalline Cu, Ag and Au in
air to analyze whether the electron temperature affects Fresnel factors or
nonlinear susceptibilities, or both. Sensitivity to electron temperatures was
attained by using photon energies near the interband transition threshold. We
find that the nonlinear susceptibility carries the electron temperature
dependence in case of Ag and Au, while for Cu the dependence is in the Fresnel
factors. This contrasting behavior emphasizes that SHG is not a priori
sensitive to electron dynamics at surfaces or interfaces, notwithstanding its
cause.Comment: 11 pages, 4 figure
Inhibition of liver methionine adenosyltransferase gene expression by 3-methylcolanthrene: protective effect of S-adenosylmethionine
Methionine adenosyltransferase (MAT) is an essential enzyme that catalyzes the synthesis of S-adenosylmethionine (AdoMet), the most important biological methyl donor. Liver MAT I/III is the product of the MAT1A gene. Hepatic MAT I/III activity and MAT1A expression are compromised under pathological conditions such as alcoholic liver disease and hepatic cirrhosis, and this gene is silenced upon neoplastic transformation of the liver. In the present work, we evaluated whether MAT1A expression could be targeted by the polycyclic arylhydrocarbon (PAH) 3-methylcholanthrene (3-MC) in rat liver and cultured hepatocytes. MAT1A mRNA levels were reduced by 50% following in vivo administration of 3-MC to adult male rats (100 mg/kg, p.o., 4 days' treatment). This effect was reproduced in a time- and dose-dependent fashion in cultured rat hepatocytes, and was accompanied by the induction of cytochrome P450 1A1 gene expression. This action of 3-MC was mimicked by other PAHs such as benzo[a]pyrene and benzo[e]pyrene, but not by the model arylhydrocarbon receptor (AhR) activator 2,3,7,8-tetrachlorodibenzo-p-dioxin. 3-MC inhibited transcription driven by a MAT1A promoter-reporter construct transfected into rat hepatocytes, but MAT1A mRNA stability was not affected. We recently showed that liver MAT1A expression is induced by AdoMet in cultured hepatocytes. Here, we observed that exogenously added AdoMet prevented the negative effects of 3-MC on MAT1A expression. Taken together, our data demonstrate that liver MAT1A gene expression is targeted by PAHs, independently of AhR activation. The effect of AdoMet may be part of the protective action of this molecule in liver damage
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
Low-Cycle Fatigue of Ultra-Fine-Grained Cryomilled 5083 Aluminum Alloy
The cyclic deformation behavior of cryomilled (CM) AA5083 alloys was compared to that of conventional AA5083-H131. The materials studied were a 100Â pct CM alloy with a Gaussian grain size average of 315Â nm and an alloy created by mixing 85Â pct CM powder with 15Â pct unmilled powder before consolidation to fabricate a plate with a bimodal grain size distribution with peak averages at 240Â nm and 1.8Â Îźm. Although the ultra-fine-grain (UFG) alloys exhibited considerably higher tensile strengths than those of the conventional material, the results from plastic-strain-controlled low-cycle fatigue tests demonstrate that all three materials exhibit identical fatigue lives across a range of plastic strain amplitudes. The CM materials exhibited softening during the first cycle, similar to other alloys produced by conventional powder metallurgy, followed by continual hardening to saturation before failure. The results reported in this study show that fatigue deformation in the CM material is accompanied by slight grain growth, pinning of dislocations at the grain boundaries, and grain rotation to produce macroscopic slip bands that localize strain, creating a single dominant fatigue crack. In contrast, the conventional alloy exhibits a cell structure and more diffuse fatigue damage accumulation
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