604 research outputs found
Benzoxazine-based phosphinated bisphenols and their application in preparing flame-retardant, low dielectric cyanate ester thermosets
This work reveals a facile, one-pot synthesis of phosphinated bisphenols (1-2) from a nucleophilic addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) to diaminophenylmethane-and diaminophenylether-based benzoxazines (P-ddm and P-oda). A reaction mechanism including active hydrogen abstraction, ring-opening, and nucleophilic addition was proposed for the synthesis. Phosphinated dicyanate esters (3-4) were prepared based on bisphenols (1-2), and were copolymerized with a commercially available dicyanate ester of bisphenol A (BACY). The properties such as glass transition temperature, coefficient of thermal expansion, thermal decomposition temperature, water absorption, and flame retardancy of the resulting thermosets were evaluated. Experimental data show that incorporating (3-4) into BACY enhances the flame retardancy, dimensional stability and dielectric properties with small penalty to the thermal properties. A thermoset with T-g 241 degrees C, CTE 50 ppm per degrees C, D-k 3.01 (1 GHz), T-d (5%), N-2: 407 degrees C, and UL-94 V-0 rating can be achieved via this approach
Effective Dynamic Range in Measurements with Flash Analog-to-Digital Convertor
Flash Analog to Digital Convertor (FADC) is frequently used in nuclear and
particle physics experiments, often as the major component in big multi-channel
systems. The large data volume makes the optimization of operating parameters
necessary. This article reports a study of a method to extend the dynamic range
of an 8-bit FADC from the nominal value. By comparing the integrated
pulse area with that of a reference profile, good energy reconstruction and
event identification can be achieved on saturated events from CsI(Tl) crystal
scintillators. The effective dynamic range can be extended by at least 4 more
bits. The algorithm is generic and is expected to be applicable to other
detector systems with FADC readout.Comment: 19 pages, 1 table, 10 figure
26: A critical contribution of donor -173G/C polymorphism of macrophage migration inhibitory factor gene to the development of chronic graft versus host disease
Studies of Prototype CsI(Tl) Crystal Scintillators for Low-Energy Neutrino Experiments
Crystal scintillators provide potential merits for the pursuit of low-energy
low-background experiments. A CsI(Tl) scintillating crystal detector is being
constructed to study low-energy neutrino physics at a nuclear reactor, while
projects are underway to adopt this technique for dark matter searches. The
choice of the geometrical parameters of the crystal modules, as well as the
optimization of the read-out scheme, are the results of an R&D program.
Crystals with 40 cm in length were developed. The detector requirements and the
achieved performance of the prototypes are presented. Future prospects for this
technique are discussed.Comment: 32 pages, 14 figure
Prospects of Scintillating Crystal Detector in Low-Energy Low-Background Experiments
Scintillating crystal detector offers potential advantages in low-energy
(keV-MeV range) low-background experiments for particle physics and
astrophysics. The merits are discussed using CsI(Tl) crystal as illustrations.
The various physics topics which can be pursued with this detector technology
are summarized. A conceptual design for a generic detector is presented.Comment: 20 pages, 1 tables, 7 figures, submitted to Astroparticle Physic
Measurement of the Intrinsic Radiopurity of Cs-137/U-235/U-238/Th-232 in CsI(Tl) Crystal Scintillators
The inorganic crystal scintillator CsI(Tl) has been used for low energy
neutrino and Dark Matter experiments, where the intrinsic radiopurity is an
issue of major importance. Low-background data were taken with a CsI(Tl)
crystal array at the Kuo-Sheng Reactor Neutrino Laboratory. The pulse shape
discrimination capabilities of the crystal, as well as the temporal and spatial
correlations of the events, provide powerful means of measuring the intrinsic
radiopurity of Cs-137 as well as the U-235, U-238 and Th-232 series. The event
selection algorithms are described, with which the decay half-lives of Po-218,
Po-214, Rn-220, Po-216 and Po-212 were derived. The measurements of the
contamination levels, their concentration gradients with the crystal growth
axis, and the uniformity among different crystal samples, are reported. The
radiopurity in the U-238 and Th-232 series are comparable to those of the best
reported in other crystal scintillators. Significant improvements in
measurement sensitivities were achieved, similar to those from dedicated
massive liquid scintillator detector. This analysis also provides in situ
measurements of the detector performance parameters, such as spatial
resolution, quenching factors, and data acquisition dead time.Comment: 28 pages, 12 figure
Massive Charged Scalar Quasinormal Modes of Reissner-N\"ordstrom Black Hole Surrounded by Quintessence
We evaluate the complex frequencies of the normal modes for the massive
charged scalar field perturbations around a Reissner-N\"ordstrom black hole
surrounded by a static and spherically symmetric quintessence using third order
WKB approximation approach. Due to the presence of quintessence, quasinormal
frequencies damp more slowly. We studied the variation of quasinormal
frequencies with charge of the black bole, mass and charge of perturbating
scalar field and the quintessential state parameter.Comment: 9 pages, 9 figures and one tabl
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
Scintillation Counters for the D0 Muon Upgrade
We present the results of an upgrade to the D0 muon system. Scintillating
counters have been added to the existing central D0 muon system to provide
rejection for cosmic ray muons and out-of-time background, and to provide
additional fast timing information for muons in an upgraded Tevatron.
Performance and results from the 1994-1996 Tevatron run are presented.Comment: 30 pages, 25 postscript figure
Nonequilibrium Josephson effect in mesoscopic ballistic multiterminal SNS junctions
We present a detailed study of nonequilibrium Josephson currents and
conductance in ballistic multiterminal SNS-devices. Nonequilibrium is created
by means of quasiparticle injection from a normal reservoir connected to the
normal part of the junction. By applying a voltage at the normal reservoir the
Josephson current can be suppressed or the direction of the current can be
reversed. For a junction longer than the thermal length, , the
nonequilibrium current increases linearly with applied voltage, saturating at a
value equal to the equilibrium current of a short junction. The conductance
exhibits a finite bias anomaly around . For symmetric
injection, the conductance oscillates -periodically with the phase
difference between the superconductors, with position of the minimum
( or ) dependent on applied voltage and temperature. For
asymmetric injection, both the nonequilibrium Josephson current and the
conductance becomes -periodic in phase difference. Inclusion of barriers
at the NS-interfaces gives rise to a resonant behavior of the total Josephson
current with respect to junction length with a period . Both
three and four terminal junctions are studied.Comment: 21 pages, 19 figures, submitted to Phys. Rev.
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