433 research outputs found
A First Comparison of the responses of a He4-based fast-neutron detector and a NE-213 liquid-scintillator reference detector
A first comparison has been made between the pulse-shape discrimination
characteristics of a novel He-based pressurized scintillation detector
and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field
neutron and gamma-ray source and a high-resolution scintillation-pulse
digitizer. In particular, the capabilities of the two fast neutron detectors to
discriminate between neutrons and gamma-rays were investigated. The NE-213
liquid-scintillator reference cell produced a wide range of scintillation-light
yields in response to the gamma-ray field of the source. In stark contrast, due
to the size and pressure of the He gas volume, the He-based
detector registered a maximum scintillation-light yield of 750~keV to
the same gamma-ray field. Pulse-shape discrimination for particles with
scintillation-light yields of more than 750~keV was excellent in the
case of the He-based detector. Above 750~keV its signal was
unambiguously neutron, enabling particle identification based entirely upon the
amount of scintillation light produced.Comment: 23 pages, 7 figures, Nuclear Instruments and Methods in Physics
Research Section A review addresse
Overcoming High Energy Backgrounds at Pulsed Spallation Sources
Instrument backgrounds at neutron scattering facilities directly affect the
quality and the efficiency of the scientific measurements that users perform.
Part of the background at pulsed spallation neutron sources is caused by, and
time-correlated with, the emission of high energy particles when the proton
beam strikes the spallation target. This prompt pulse ultimately produces a
signal, which can be highly problematic for a subset of instruments and
measurements due to the time-correlated properties, and different to that from
reactor sources. Measurements of this background have been made at both SNS
(ORNL, Oak Ridge, TN, USA) and SINQ (PSI, Villigen, Switzerland). The
background levels were generally found to be low compared to natural
background. However, very low intensities of high-energy particles have been
found to be detrimental to instrument performance in some conditions. Given
that instrument performance is typically characterised by S/N, improvements in
backgrounds can both improve instrument performance whilst at the same time
delivering significant cost savings. A systematic holistic approach is
suggested in this contribution to increase the effectiveness of this.
Instrument performance should subsequently benefit.Comment: 12 pages, 8 figures. Proceedings of ICANS XXI (International
Collaboration on Advanced Neutron Sources), Mito, Japan. 201
Tagging fast neutrons from an 241Am/9Be source
We report on an investigation of the fast-neutron spectrum emitted by
241Am/9Be. Well-understood shielding, coincidence, and time-of-flight
measurement techniques are employed to produce a continuous, polychromatic,
energy-tagged neutron beam.Comment: 17 pages, 7 figures, submitted to Journal of Applied Radiation and
Isotope
VIPAR, a quantitative approach to 3D histopathology applied to lymphatic malformations.
BACKGROUND: Lack of investigatory and diagnostic tools has been a major contributing factor to the failure to mechanistically understand lymphedema and other lymphatic disorders in order to develop effective drug and surgical therapies. One difficulty has been understanding the true changes in lymph vessel pathology from standard 2D tissue sections. METHODS: VIPAR (volume information-based histopathological analysis by 3D reconstruction and data extraction), a light-sheet microscopy-based approach for the analysis of tissue biopsies, is based on digital reconstruction and visualization of microscopic image stacks. VIPAR allows semiautomated segmentation of the vasculature and subsequent nonbiased extraction of characteristic vessel shape and connectivity parameters. We applied VIPAR to analyze biopsies from healthy lymphedematous and lymphangiomatous skin. RESULTS: Digital 3D reconstruction provided a directly visually interpretable, comprehensive representation of the lymphatic and blood vessels in the analyzed tissue volumes. The most conspicuous features were disrupted lymphatic vessels in lymphedematous skin and a hyperplasia (4.36-fold lymphatic vessel volume increase) in the lymphangiomatous skin. Both abnormalities were detected by the connectivity analysis based on extracted vessel shape and structure data. The quantitative evaluation of extracted data revealed a significant reduction of lymphatic segment length (51.3% and 54.2%) and straightness (89.2% and 83.7%) for lymphedematous and lymphangiomatous skin, respectively. Blood vessel length was significantly increased in the lymphangiomatous sample (239.3%). CONCLUSION: VIPAR is a volume-based tissue reconstruction data extraction and analysis approach that successfully distinguished healthy from lymphedematous and lymphangiomatous skin. Its application is not limited to the vascular systems or skin. FUNDING: Max Planck Society, DFG (SFB 656), and Cells-in-Motion Cluster of Excellence EXC 1003
The Interplay between PolyQ and Protein Context Delays Aggregation by Forming a Reservoir of Protofibrils
Polyglutamine (polyQ) diseases are inherited neurodegenerative disorders caused by the expansion of CAG codon repeats, which code for polyQ in the corresponding gene products. These diseases are associated with the presence of amyloid-like protein aggregates, induced by polyQ expansion. It has been suggested that the soluble aggregates rather than the mature fibrillar aggregates are the toxic species, and that the aggregation properties of polyQ can be strongly modulated by the surrounding protein context. To assess the importance of the protein carrier in polyQ aggregation, we have studied the misfolding pathway and the kinetics of aggregation of polyQ of lengths above (Q41) and below (Q22) the pathological threshold fused to the well-characterized protein carrier glutathione S-transferase (GST). This protein, chosen as a model system, is per se able to misfold and aggregate irreversibly, thus mimicking the behaviour of domains of naturally occurring polyQ proteins. We prove that, while it is generally accepted that the aggregation kinetics of polyQ depend on its length and are faster for longer polyQ tracts, the presence of GST alters the polyQ aggregation pathway and reverses this trend. Aggregation occurs through formation of a reservoir of soluble intermediates whose populations and kinetic stabilities increase with polyQ length. Our results provide a new model that explains the toxicity of expanded polyQ proteins, in which the interplay between polyQ regions and other aggregation-prone domains plays a key role in determining the aggregation pathway
Five-Year Change in Visceral Adipose Tissue Quantity in a Minority Cohort: The Insulin Resistance Atherosclerosis Study (IRAS) Family Study
Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams
The response of a position-sensitive Li-glass scintillator detector being
developed for thermal-neutron detection with 6 mm position resolution has been
investigated using collimated beams of thermal neutrons. The detector was moved
perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and
vertical steps. Scintillation was detected in an 8 X 8 pixel multi-anode
photomultiplier tube on an event-by-event basis. In general, several pixels
registered large signals at each neutron-beam location. The number of pixels
registering signal above a set threshold was investigated, with the
maximization of the single-hit efficiency over the largest possible area of the
detector as the primary goal. At a threshold of ~50% of the mean of the
full-deposition peak, ~80% of the events were registered in a single pixel,
resulting in an effective position resolution of ~5 mm in X and Y. Lower
thresholds generally resulted in events demonstrating higher pixel
multiplicities, but these events could also be localized with ~5 mm position
resolution.Comment: 23 pages, 8 figure
Kinetics and thermodynamics of salt-dependent T7 gene 2.5 protein binding to single- and double-stranded DNA
Bacteriophage T7 gene 2.5 protein (gp2.5) is a single-stranded DNA (ssDNA)-binding protein that has essential roles in DNA replication, recombination and repair. However, it differs from other ssDNA-binding proteins by its weaker binding to ssDNA and lack of cooperative ssDNA binding. By studying the rate-dependent DNA melting force in the presence of gp2.5 and its deletion mutant lacking 26 C-terminal residues, we probe the kinetics and thermodynamics of gp2.5 binding to ssDNA and double-stranded DNA (dsDNA). These force measurements allow us to determine the binding rate of both proteins to ssDNA, as well as their equilibrium association constants to dsDNA. The salt dependence of dsDNA binding parallels that of ssDNA binding. We attribute the four orders of magnitude salt-independent differences between ssDNA and dsDNA binding to nonelectrostatic interactions involved only in ssDNA binding, in contrast to T4 gene 32 protein, which achieves preferential ssDNA binding primarily through cooperative interactions. The results support a model in which dimerization interactions must be broken for DNA binding, and gp2.5 monomers search dsDNA by 1D diffusion to bind ssDNA. We also quantitatively compare the salt-dependent ssDNA- and dsDNA-binding properties of the T4 and T7 ssDNA-binding proteins for the first time
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