139 research outputs found
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Cosmogenic neutron production at the Sudbury Neutrino Observatory
Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10-4 cm2/(gĀ·Ī¼), is measured to be 7.28Ā±0.09(stat)-1.12+1.59(syst) in pure heavy water and 7.30Ā±0.07(stat)-1.02+1.40(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB
Accelerating String Set Matching in FPGA Hardware for Bioinformatics Research
<p>Abstract</p> <p>Background</p> <p>This paper describes techniques for accelerating the performance of the string set matching problem with particular emphasis on applications in computational proteomics. The process of matching peptide sequences against a genome translated in six reading frames is part of a proteogenomic mapping pipeline that is used as a case-study. The Aho-Corasick algorithm is adapted for execution in field programmable gate array (FPGA) devices in a manner that optimizes space and performance. In this approach, the traditional Aho-Corasick finite state machine (FSM) is split into smaller FSMs, operating in parallel, each of which matches up to 20 peptides in the input translated genome. Each of the smaller FSMs is further divided into five simpler FSMs such that each simple FSM operates on a single bit position in the input (five bits are sufficient for representing all amino acids and special symbols in protein sequences).</p> <p>Results</p> <p>This bit-split organization of the Aho-Corasick implementation enables efficient utilization of the limited random access memory (RAM) resources available in typical FPGAs. The use of on-chip RAM as opposed to FPGA logic resources for FSM implementation also enables rapid reconfiguration of the FPGA without the place and routing delays associated with complex digital designs.</p> <p>Conclusion</p> <p>Experimental results show storage efficiencies of over 80% for several data sets. Furthermore, the FPGA implementation executing at 100 MHz is nearly 20 times faster than an implementation of the traditional Aho-Corasick algorithm executing on a 2.67 GHz workstation.</p
Constraints on Nucleon Decay via "Invisible" Modes from the Sudbury Neutrino Observatory
Data from the Sudbury Neutrino Observatory have been used to constrain the
lifetime for nucleon decay to ``invisible'' modes, such as n -> 3 nu. The
analysis was based on a search for gamma-rays from the de-excitation of the
residual nucleus that would result from the disappearance of either a proton or
neutron from O16. A limit of tau_inv > 2 x 10^{29} years is obtained at 90%
confidence for either neutron or proton decay modes. This is about an order of
magnitude more stringent than previous constraints on invisible proton decay
modes and 400 times more stringent than similar neutron modes.Comment: Update includes missing efficiency factor (limits change by factor of
2) Submitted to Physical Review Letter
First Neutrino Observations from the Sudbury Neutrino Observatory
The first neutrino observations from the Sudbury Neutrino Observatory are
presented from preliminary analyses. Based on energy, direction and location,
the data in the region of interest appear to be dominated by 8B solar
neutrinos, detected by the charged current reaction on deuterium and elastic
scattering from electrons, with very little background. Measurements of
radioactive backgrounds indicate that the measurement of all active neutrino
types via the neutral current reaction on deuterium will be possible with small
systematic uncertainties. Quantitative results for the fluxes observed with
these reactions will be provided when further calibrations have been completed.Comment: Latex, 7 pages, 10 figures, Invited paper at Neutrino 2000
Conference, Sudbury, Canada, June 16-21, 2000 to be published in the
Proceeding
Modulation of calcification of vascular smooth muscle cells in culture by calcium antagonists, statins, and their combination
Background Vascular calcification is an organized process in which vascular smooth muscle cells (VSMCs) are implicated primarily. The purpose of the present study was to assess the effects of calcium antagonists and statins on VSMC calcification inĀ vitro. Methods VSMC calcification was stimulated by incubation in growth medium supplemented with 10Ā mmol/l Ī²-glycerophosphate, 8Ā mmol/l CaCl2, 10Ā mmol/l sodium pyruvate, 1Ā Ī¼mol/l insulin, 50Ā Ī¼g/ml ascorbic acid, and 100Ā nmol/l dexamethasone (calcification medium). Calcification, proliferation, and apoptosis of VSMCs were quantified. Results Calcium deposition was stimulated dose-dependently by Ī²-glycerophosphate, CaCl2, and ascorbic acid (all PĀ <Ā 0.01). Addition of amlodipine (0.01ā1Ā Ī¼mol/l) to the calcification medium did not affect VSMC calcification. However, atorvastatin (2ā50Ā Ī¼mol/l) stimulated calcium deposition dose-dependently. Combining treatments stimulated calcification to a degree similar to that observed with atorvastatin alone. Both atorvastatin and amlodipine inhibited VSMC proliferation at the highest concentration used. Only atorvastatin (50Ā Ī¼mol/l) induced considerable apoptosis of VSMCs. Conclusion InĀ vitro calcification of VSMCs is not affected by amlodipine, but is stimulated by atorvastatin at concentrations ā„10Ā Ī¼mol/l, which could contribute to the plaque-stabilizing effect reported for statins
Quantitative Analysis of Lipid Droplet Fusion: Inefficient Steady State Fusion but Rapid Stimulation by Chemical Fusogens
Lipid droplets (LDs) are dynamic cytoplasmic organelles containing neutral lipids and bounded by a phospholipid monolayer. Previous studies have suggested that LDs can undergo constitutive homotypic fusion, a process linked to the inhibitory effects of fatty acids on glucose transporter trafficking. Using strict quantitative criteria for LD fusion together with refined light microscopic methods and real-time analysis, we now show that LDs in diverse cell types show low constitutive fusogenic activity under normal growth conditions. To investigate the possible modulation of LD fusion, we screened for agents that can trigger fusion. A number of pharmacological agents caused homotypic fusion of lipid droplets in a variety of cell types. This provided a novel cell system to study rapid regulated fusion between homotypic phospholipid monolayers. LD fusion involved an initial step in which the two adjacent membranes became continuous (<10 s), followed by the slower merging (100 s) of the neutral lipid cores to produce a single spherical LD. These fusion events were accompanied by changes to the LD surface organization. Measurements of LDs undergoing homotypic fusion showed that fused LDs maintained their initial volume, with a corresponding decrease in surface area suggesting rapid removal of membrane from the fused LD. This study provides estimates for the level of constitutive LD fusion in cells and questions the role of LD fusion in vivo. In addition, it highlights the extent of LD restructuring which occurs when homotypic LD fusion is triggered in a variety of cell types
Tissue specific expression of human fatty acid oxidation enzyme genes in late pregnancy
Background: Abnormal fatty acid oxidation (FAO) is associated with maternal and fetal complications during
pregnancy. The contribution of maternal and fetal tissues to FAO capacity during late pregnancy is important to
understand the pathophysiology of pregnancy-associated complications. The aim of this study was to determine
the expression levels of mitochondrial FAO enzymes in maternal and fetal tissues during late normal pregnancy.
Methods: We have measured by Real-time PCR the levels of long- and medium -chain acyl-CoA dehydrogenase
(LCHAD and MCAD), two acyl-CoA dehydrogenases that catalyze the initial step in the mitochondrial FAO spiral.
Results: LCHAD and MCAD were expressed in maternal skeletal muscle, subcutaneous adipose tissue, placenta, and
maternal and fetal blood cells. LCHAD gene expression was four- to 16-fold higher than MCAD gene expression in
placenta, adipose tissue and skeletal muscle. In contrast, MCAD gene expression was ~5-fold higher in fetal blood
than maternal blood (p = 0.02), whereas LCHAD gene expression was similar between fetal blood and maternal
blood (p =0.91).
Conclusions: LCHAD and MCAD are differentially expressed in maternal and fetal tissues during normal late
pregnancy, which may represent a metabolic adaptation in response to physiological maternal dyslipidemia during
late pregnancy.Consejeria de Salud, Junta de AndalucĆa Num Expte: 0269/05
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Measurement of neutron production in atmospheric neutrino interactions at the Sudbury Neutrino Observatory
Neutron production in GeV-scale neutrino interactions is a poorly studied
process. We have measured the neutron multiplicities in atmospheric neutrino
interactions in the Sudbury Neutrino Observatory experiment and compared them
to the prediction of a Monte Carlo simulation using GENIE and a minimally
modified version of GEANT4. We analyzed 837 days of exposure corresponding to
Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy
water. Neutrons produced in atmospheric neutrino interactions were identified
with an efficiency of and , for Phase I and II respectively.
The neutron production is measured as a function of the visible energy of the
neutrino interaction and, for charged current quasi-elastic interaction
candidates, also as a function of the neutrino energy. This study is also
performed classifying the complete sample into two pairs of event categories:
charged current quasi-elastic and non charged current quasi-elastic, and
and . Results show good overall agreement between data and
Monte Carlo for both phases, with some small tension with a statistical
significance below for some intermediate energies
Tests of Lorentz invariance at the Sudbury Neutrino Observatory
Experimental tests of Lorentz symmetry in systems of all types are critical
for ensuring that the basic assumptions of physics are well-founded. Data from
all phases of the Sudbury Neutrino Observatory, a kiloton-scale heavy water
Cherenkov detector, are analyzed for possible violations of Lorentz symmetry in
the neutrino sector. Such violations would appear as one of eight possible
signal types in the detector: six seasonal variations in the solar electron
neutrino survival probability differing in energy and time dependence, and two
shape changes to the oscillated solar neutrino energy spectrum. No evidence for
such signals is observed, and limits on the size of such effects are
established in the framework of the Standard Model Extension, including 40
limits on perviously unconstrained operators and improved limits on 15
additional operators. This makes limits on all minimal, Dirac-type Lorentz
violating operators in the neutrino sector available for the first time
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