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Search Results: 1 - 10 of 540308 matches for " M. L. Pitt "
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Applications of Langmuir Films in Integrated Optics
C. W. Pitt,L. M. Walpita
Active and Passive Electronic Components , 1977, DOI: 10.1155/apec.3.191
Abstract:
The SAMPLE Experiment and Weak Nucleon Structure
E. J. Beise,M. L. Pitt,D. T. Spayde
Physics , 2004, DOI: 10.1016/j.ppnp.2004.07.002
Abstract: One of the key elements to understanding the structure of the nucleon is the role of its quark-antiquark sea in its ground state properties such as charge, mass, magnetism and spin. In the last decade, parity-violating electron scattering has emerged as an important tool in this area, because of its ability to isolate the contribution of strange quark-antiquark pairs to the nucleon's charge and magnetism. The SAMPLE experiment at the MIT-Bates Laboratory, which has been focused on s-sbar contributions to the proton's magnetic moment, was the first of such experiments and its program has recently been completed. In this paper we give an overview of some of the experimental aspects of parity-violating electron scattering, briefly review the theoretical predictions for strange quark form factors, summarize the SAMPLE measurements, and place them in context with the program of experiments being carried out at other electron scattering facilities such as Jefferson Laboratory and the Mainz Microtron.
Recent advances with THGEM detectors
S. Bressler,L. Arazi,L. Moleri,M. Pitt,A. Rubin,A. Breskin
Physics , 2013, DOI: 10.1088/1748-0221/8/12/C12012
Abstract: The Thick Gaseous Electron Multiplier (THGEM) is a simple and robust electrode suitable for large area detectors. In this work the results of extensive comparative studies of the physical properties of different THGEM-based structures are reviewed. The focus is on newly suggested THGEM-like WELL configurations as well as on recently developed characterization methods. The WELL structures are single-sided THGEM electrodes directly coupled to different anode readout electrodes. The structures differ by the coupling concept of the bottom THGEM electrode to the metallic readout pads: a Thick WELL (THWELL) with direct coupling; the Resistive WELL (RWELL) and the Segmented Resistive WELL (SRWELL) coupled through thin resistive films deposited on insulating sheets and a Resistive-Plate WELL (RPWELL) coupled through a plate of high bulk resistivity. The results are compared to that of traditional double-sided THGEM electrodes followed by induction gaps - in some cases with moderate additional multiplication within the gap. We compare the different configurations in terms of gain, avalanche extension, discharge-rate and magnitude as well as rate capabilities over a broad dynamic range - exploiting a method that mimics highly ionizing particles in the laboratory. We report on recent studies of avalanche distribution in THGEM holes using optical readout.
Laboratory studies of THGEM-based WELL structures with resistive anodes
L. Arazi,M. Pitt,S. Bressler,L. Moleri,A. Rubin,A. Breskin
Physics , 2013, DOI: 10.1088/1748-0221/9/04/P04011
Abstract: In this work we investigate three variants of single amplification-stage detector elements; they comprise THGEM electrodes closed at their bottom with metallic or resistive anodes to form WELL-type configurations. We present the results of a comparative study of the Thick-WELL (THWELL), Resistive-WELL (RWELL) and Segmented Resistive WELL (SRWELL), focusing on their performance in terms of spark-quenching capability, gain variation with position and counting rate, pulse shapes and signal propagation to neighboring readout pads; the study included both 30x30 and 100x100 mm$^2$ detectors. It was shown that the WELL structures with resistive anodes offer stable operation even in a highly ionizing environment, with effective spark quenching, as well as higher gain than the standard THGEM/induction-gap configuration. Cross talk between neighboring readout pads was shown to be effectively eliminated in the segmented detector with a conductive grid underneath the resistive layer. The latter multiplier should allow for the design of very thin detectors, e.g. sampling elements in digital hadronic calorimeters planned for experiments in future linear colliders.
Optical readout: a tool for studying gas-avalanche processes
A. Rubin,L. Arazi,S. Bressler,A. Dery,L. Moleri,M. Pitt,D. Vartsky,A. Breskin
Physics , 2013, DOI: 10.1088/1748-0221/8/08/P08001
Abstract: Optical recording of avalanche-induced photons is an interesting tool for studying basic physics processes in gaseous detectors. In this work we demonstrate the potential of optical readout in avalanche-propagation investigations in Thick Gas Electron Multipliers (THGEMs) operated with Ne/CF4 (95/5). We present the results of direct measurements, with single- and cascaded-THGEM detectors irradiated with soft x-rays, of the hole-multiplicity and avalanche asymmetry within holes, as a function of detector parameters. Further study directions are discussed.
A concept for laboratory studies of radiation detectors over a broad dynamic-range: instabilities evaluation in THGEM-structures
S. Bressler,L. Moleri,L. Arazi,E. Erdal,A. Rubin,M. Pitt,A. Breskin
Physics , 2013, DOI: 10.1088/1748-0221/9/03/P03005
Abstract: A simple methodology for evaluating the dynamic-range of gas avalanche detectors in the laboratory is presented and discussed. It comprises two tools: a charge injector of tunable gain which transfers radiation-induced amplified electron swarms to the investigated detector to mimic events with well defined primary-ionization spectra, and a systematic approach for measuring the detector's discharge probability. The methodology, applicable to a broad range of detectors, is applied here for instability studies in various single-stage THGEM and THGEM-WELL structures. The results indicate upon a somewhat larger attainable dynamic range in a single-stage THGEM operated with additional multiplication in the induction gap.
First studies with the Resistive-Plate WELL gaseous multiplier
A. Rubin,L. Arazi,S. Bressler,L. Moleri,M. Pitt,A. Breskin
Physics , 2013, DOI: 10.1088/1748-0221/8/11/P11004
Abstract: We present the results of first studies of the Resistive Plate WELL (RPWELL): a single-faced THGEM coupled to a copper anode via a resistive layer of high bulk resistivity. We explored various materials of different bulk resistivity (10^9 - 10^12 Ohm cm) and thickness (0.4 - 4 mm). Our most successful prototype, with a 0.6 mm resistive plate of ~10^9 Ohm cm, achieved gains of up to 10^5 with 8 keV x-ray in Ne/5%CH4; a minor 30% gain drop occurred with a rate increase from 10 to 10^4 Hz/mm^2. The detector displayed a full "discharge-free" operation--even when exposed to high primary ionization events. We present the RPWELL detector concept and compare its performance to that of other previously explored THGEM configurations--in terms of gain, its curves, dependence on rate, and the response to high ionization. The robust Resistive Plate WELL concept is a step forward in the Micro-Pattern Gas-Detector family, with numerous potential applications.
LENS as a Probe of Sterile Neutrino Mediated Oscillations
C. Grieb,J. M. Link,M. L. Pitt,R. S. Raghavan,D. Rountree,R. B. Vogelaar
Physics , 2007,
Abstract: Sterile neutrino ($\nu_s$) conversion in meter scale baselines can be sensitively probed using mono-energetic, sub-MeV, flavor pure $\nu_e$'s from an artificial MCi source and the unique technology of the LENS low energy solar $\nu_e$ detector. Active-sterile {\em oscillations} can be directly observed in the granular LENS detector itself to critically test and extend results of short baseline accelerator and reactor experiments.
Significance of spatial variability in precipitation for process-oriented modelling: results from two nested catchments using radar and ground station data
B. O. L. Demars, D. M. Harper, J.-A. Pitt,R. Slaughter
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2005,
Abstract: In-river phosphorus retention alters the quantity and timings of phosphorus delivery to downstream aquatic systems. Many intensive studies of in-river phosphorus retention have been carried out but generally on a short time scale (2-4 years). In this paper, monthly water quality data, collected by the Environment Agency of England and Wales over 12 years (1990-2001), were used to model daily phosphorus fluxes and monthly in-river phosphorus retention in the lowland calcareous River Wensum, Norfolk, UK. The calibrated model explained 79% and 89% of the observed variance before and after phosphorus control, respectively. A split test revealed that predicted TP loads were in good agreement with observed TP loads (r2=0.85), although TP loads were underestimated under high flow conditions. During relatively dry years, there was no net export of phosphorus from the catchment. High retention of phosphorus occurred, particularly during the summer months, which was not compensated for, by subsequent higher flow events. This was despite a relatively modest critical discharge (Q) above which net remobilisation occur. Phosphorus removal from the effluent at two major STWs (Sewage Treatment Works) reduced phosphorus retention but not the remobilisation. This may indicate that the presence of impoundments and weirs, or overbank flows may have more control on the phosphorus dynamics under high flow conditions. Further phosphorus remedial strategies will be necessary to prevent downstream risks of eutrophication occurring independently of the unpredictable variability in weather conditions. More research is also needed to quantify the impact of the weir and overbank flows on phosphorus dynamics.
Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution
B. O. L. Demars,D. M. Harper,J.-A. Pitt,R. Slaughter
Hydrology and Earth System Sciences Discussions , 2005,
Abstract: In-river phosphorus retention alters the quantity and timings of phosphorus delivery to downstream aquatic systems. Many intensive studies of in-river phosphorus retention have been carried out but generally on a short time scale (2-4 years). In this paper, monthly water quality data, collected by the Environment Agency of England and Wales over 12 years (1990-2001), were used to model daily phosphorus fluxes and monthly in-river phosphorus retention in the lowland calcareous River Wensum, Norfolk, UK. The effectiveness of phosphorus stripping at two major sewage treatment works was quantified over different hydrological conditions. The model explained 78% and 88% of the observed variance before and after phosphorus control, respectively. During relatively dry years, there was no net export of phosphorus from the catchment. High retention of phosphorus occurred, particularly during the summer months, which was not compensated for, by subsequent higher flow events. The critical discharge (Q) above which net remobilisation would occur, was only reached during few, high flow events Q25-Q13. Phosphorus removal from the effluent at two major STWs (Sewage Treatment Works) reduced the phosphorus catchment mass balance variability by 20-24% under the Q99-Q1. range of flow conditions. Although the absorbing capacity of the catchment against human impact was remarkable, further phosphorus remedial strategies will be necessary to prevent downstream risks of eutrophication occuring independently of the unpredictable variability in weather conditions.
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