62 research outputs found
An Ultra-Low Background PMT for Liquid Xenon Detectors
Results are presented from radioactivity screening of two models of
photomultiplier tubes designed for use in current and future liquid xenon
experiments. The Hamamatsu 5.6 cm diameter R8778 PMT, used in the LUX dark
matter experiment, has yielded a positive detection of four common radioactive
isotopes: 238U, 232Th, 40K, and 60Co. Screening of LUX materials has rendered
backgrounds from other detector materials subdominant to the R8778
contribution. A prototype Hamamatsu 7.6 cm diameter R11410 MOD PMT has also
been screened, with benchmark isotope counts measured at <0.4 238U / <0.3 232Th
/ <8.3 40K / 2.0+-0.2 60Co mBq/PMT. This represents a large reduction, equal to
a change of \times 1/24 238U / \times 1/9 232Th / \times 1/8 40K per PMT,
between R8778 and R11410 MOD, concurrent with a doubling of the photocathode
surface area (4.5 cm to 6.4 cm diameter). 60Co measurements are comparable
between the PMTs, but can be significantly reduced in future R11410 MOD units
through further material selection. Assuming PMT activity equal to the measured
90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs
with R11410 MOD PMTs will change LUX PMT electron recoil background
contributions by a factor of \times1/25 after further material selection for
60Co reduction, and nuclear recoil backgrounds by a factor of \times 1/36. The
strong reduction in backgrounds below the measured R8778 levels makes the
R11410 MOD a very competitive technology for use in large-scale liquid xenon
detectors.Comment: v2 updated to include content after reviewer comments (Sep 2012
LUXSim: A Component-Centric Approach to Low-Background Simulations
Geant4 has been used throughout the nuclear and high-energy physics community
to simulate energy depositions in various detectors and materials. These
simulations have mostly been run with a source beam outside the detector. In
the case of low-background physics, however, a primary concern is the effect on
the detector from radioactivity inherent in the detector parts themselves. From
this standpoint, there is no single source or beam, but rather a collection of
sources with potentially complicated spatial extent. LUXSim is a simulation
framework used by the LUX collaboration that takes a component-centric approach
to event generation and recording. A new set of classes allows for multiple
radioactive sources to be set within any number of components at run time, with
the entire collection of sources handled within a single simulation run.
Various levels of information can also be recorded from the individual
components, with these record levels also being set at runtime. This
flexibility in both source generation and information recording is possible
without the need to recompile, reducing the complexity of code management and
the proliferation of versions. Within the code itself, casting geometry objects
within this new set of classes rather than as the default Geant4 classes
automatically extends this flexibility to every individual component. No
additional work is required on the part of the developer, reducing development
time and increasing confidence in the results. We describe the guiding
principles behind LUXSim, detail some of its unique classes and methods, and
give examples of usage.
* Corresponding author, [email protected]: 45 pages, 15 figure
Stochastic thermodynamics of holonomic systems
International audienc
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
Internalization of Oncolytic Reovirus by Human Dendritic Cell Carriers Protects the Virus from Neutralization
Purpose: Dendritic cells (DC) may be the most effective way of delivering oncolytic viruses to patients. Reovirus, a naturally occurring oncolytic virus, is currently undergoing early clinical trials; however, intravenous delivery of the virus is hampered by pre-existing antiviral immunity. Systemic delivery via cell carriage is a novel approach currently under investigation and initial studies have indicated its feasibility by using a variety of cell types and viruses. This study addressed the efficacy of human DC to transport virus in the presence of human neutralizing serum. Experimental Design: Following reovirus-loading, DC or T cells were cocultured with melanoma cells with or without neutralizing serum; the melanoma cells were then analyzed for cell death. Following reovirus loading, cells were examined by electron microscopy to identify mechanisms of delivery. The phagocytic function of reovirus-loaded DC was investigated by using labeled tumor cells and the ability of reovirus-loaded DC to prime T cells was also investigated. Results: In the presence of human neutralizing serum DC, but not T cells, were able to deliver reovirus for melanoma cell killing in vitro. Electron microscopy suggested that DC protected the virus by internalization, whereas with T cells it remained bound to the surface and hence accessible to neutralizing antibodies. Furthermore, DC loaded with reovirus were fully functional with regard to phagocytosis and priming of specific antitumor immune responses. Conclusions: The delivery of reovirus via DC could be a promising new approach offering the possibility of combining systemic viral therapy for metastatic disease with induction of an antitumor immune response. Clin Cancer Res; 17(9); 2767-76. (C)2011 AACR.Microscopic imaging and technolog
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