2,562 research outputs found
Study of the radiation hardness of CsI(Tl) scintillation crystals
This paper is devoted to the study of a degradation of CsI(Tl)crystals
scintillation characteristics under irradiation with gamma-quanta at the
uniformly distributed absorbed dose up to 3700 rad. The sample set consisted of
25 crystals of 30 cm long having a truncated pyramid shape and 30 rectangular
crystals of the same length. A large difference in the light output
deterioration caused by the radiation was observed for the samples of the same
shape. A substantial dependence of the average light output loss from the
sample shape is seen as well. On the other hand, the crystals from the same
ingot behave very similarly under irradiation
Two-dimensional negative donors in magnetic fields
A finite-difference solution of the Schroedinger equation for negative donor
centers D^- in two dimensions is presented. Our approach is of exact nature and
allows us to resolve a discrepancy in the literature on the ground state of a
negative donor. Detailed calculations of the energies for a number of states
show that for field strengths less than \gamma=0.117 a.u. the donor possesses
one bound state, for 0.117<\gamma<1.68 a.u. there exist two bound states and
for field strengths \gamma>1.68 a.u. the system possesses three bound states.
Further relevant characteristics of negative donors in magnetic fields are
provided.Comment: 7 pages, 1 figur
Insulating and Conducting Phases of RbC60
Optical measurements were performed on thin films of RbC,
identified by X-ray diffraction as mostly material. The samples were
subjected to various heat treatments, including quenching and slow cooling from
400K. The dramatic increase in the transmission of the quenched samples, and
the relaxation towards the transmission observed in slow cooled samples
provides direct evidence for the existence of a metastable insulating phase.
Slow cooling results in a phase transition between two electrically conducting
phases.Comment: Minor revisions. Submitted to PRB, RevTeX 3.0 file, 2 postscript
figures included, ir_dop
A liquid helium target system for a measurement of parity violation in neutron spin rotation
A liquid helium target system was designed and built to perform a precision
measurement of the parity-violating neutron spin rotation in helium due to the
nucleon-nucleon weak interaction. The measurement employed a beam of low energy
neutrons that passed through a crossed neutron polarizer--analyzer pair with
the liquid helium target system located between them. Changes between the
target states generated differences in the beam transmission through the
polarizer--analyzer pair. The amount of parity-violating spin rotation was
determined from the measured beam transmission asymmetries. The expected
parity-violating spin rotation of order rad placed severe constraints
on the target design. In particular, isolation of the parity-odd component of
the spin rotation from a much larger background rotation caused by magnetic
fields required that a nonmagnetic cryostat and target system be supported
inside the magnetic shielding, while allowing nonmagnetic motion of liquid
helium between separated target chambers. This paper provides a detailed
description of the design, function, and performance of the liquid helium
target system.Comment: V2: 29 pages, 14 figues, submitted to Nucl. Instrum. Meth. B. Revised
to address reviewer comment
Testing Library Specifications by Verifying Conformance Tests
Abstract. Formal specifications of standard libraries are necessary when statically verifying software that uses those libraries. Library specifications must be both correct, accurately reflecting library behavior, and useful, describing library behavior in sufficient detail to allow static verification of client programs. Specification and verification researchers regularly face the question of whether the library specifications we use are correct and useful, and we have collectively provided no good answers. Over the past few years we have created and refined a software engineering process, which we call the Formal CTD Process (FCTD), to address this problem. Although FCTD is primarily targeted toward those who write Java libraries (or specifications for existing Java libraries) using the Java Modeling Language (JML), its techniques are broadly applicable. The key to FCTD is its novel usage of library conformance test suites. Rather than executing the conformance tests, FCTD uses them to measure the correctness and utility of specifications through static verification. FCTD is beginning to see significant use within the JML community and is the cornerstone process of the JML Spec-a-thons, meetings that bring JML researchers and practitioners together for intensive specification writing sessions. This article describes the Formal CTD Process, its use in small case studies, and its broad application to the standard Java class library.
Multiaxial Kitagawa analysis of A356-T6
Experimental Kitagawa analysis has been performed on A356-T6 containing
natural and artificial defects. Results are obtained with a load ratio of R =
-1 for three different loadings: tension, torsion and combined tension-torsion.
The critical defect size determined is 400 \pm 100 \mum in A356-T6 under
multiaxial loading. Below this value, the microstructure governs the endurance
limit mainly through Secondary Dendrite Arm Spacing (SDAS). Four theoretical
approaches are used to simulate the endurance limit characterized by a Kitagawa
relationship are compared: Murakami relationships [Y Murakami, Metal Fatigue:
Effects of Small Defects and Nonmetallic Inclusions, Elsevier, 2002.],
defect-crack equivalency via Linear Elastic Fracture Mechanics (LEFM), the
Critical Distance Method (CDM) proposed by Susmel and Taylor [L. Susmel, D.
Taylor. Eng. Fract. Mech. 75 (2008) 15.] and the gradient approach proposed by
Nadot [Y. Nadot, T. ~Billaudeau. Eng. Fract. Mech. 73 (2006) 1.]. It is shown
that the CDM and gradient methods are accurate; however fatigue data for three
loading conditions is necessary to allow accurate identification of an
endurance limit.Comment: 27 pages, 11 figure
Effects of Impurity Content on the Sintering Characteristics of Plasma-Sprayed Zirconia
Yttria-stabilized zirconia powders, containing different levels of SiO2 and Al2O3, have been plasma sprayed onto metallic substrates. The coatings were detached from their substrates and a dilatometer was used to monitor the dimensional changes they exhibited during prolonged heat treatments. It was found that specimens containing higher levels of silica and alumina exhibited higher rates of linear contraction, in both in-plane and through-thickness directions. The in-plane stiffness and the through-thickness thermal conductivity were also measured after different heat treatments and these were found to increase at a greater rate for specimens with higher impurity (silica and alumina) levels. Changes in the pore architecture during heat treatments were studied using Mercury Intrusion Porosimetry (MIP). Fine scale porosity (<_50 nm) was found to be sharply reduced even by relatively short heat treatments. This is correlated with improvements in inter-splat bonding and partial healing of intra-splat microcracks, which are responsible for the observed changes in stiffness and conductivity, as well as the dimensional changes
Coboson formalism for Cooper pairs used to derive Richardson's equations
We propose a many-body formalism for Cooper pairs which has similarities to
the one we recently developed for composite boson excitons (coboson in short).
Its Shiva diagram representation evidences that Cooper pairs differ from
single pairs through electron exchange only: no direct coupling exists due
to the very peculiar form of the BCS potential. As a first application, we here
use this formalism to derive Richardson's equations for the exact eigenstates
of Cooper pairs. This gives hints on why the dependence of the
-pair ground state energy we recently obtained by solving Richardson's
equations analytically in the low density limit, stays valid up to the dense
regime, no higher order dependence exists even under large overlap, a
surprising result hard to accept at first. We also briefly question the BCS
wave function ansatz compared to Richardson's exact form, in the light of our
understanding of coboson many-body effects
Discovery and Observations of ASASSN-13db, an EX Lupi-Type Accretion Event on a Low-Mass T Tauri Star
We discuss ASASSN-13db, an EX Lupi-type ("EXor") accretion event on the young
stellar object (YSO) SDSS J051011.01032826.2 (hereafter SDSSJ0510)
discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). Using
archival photometric data of SDSSJ0510 we construct a pre-outburst spectral
energy distribution (SED) and find that it is consistent with a low-mass class
II YSO near the Orion star forming region ( pc). We present
follow-up photometric and spectroscopic observations of the source after the
5.4 magnitude outburst that began in September 2013 and ended
in early 2014. These data indicate an increase in temperature and luminosity
consistent with an accretion rate of yr,
three or more orders of magnitude greater than in quiescence. Spectroscopic
observations show a forest of narrow emission lines dominated by neutral
metallic lines from Fe I and some low-ionization lines. The properties of
ASASSN-13db are similar to those of the EXor prototype EX Lupi during its
strongest observed outburst in late 2008.Comment: 14 pages, 4 figures, 1 table. Updated May 2014 to reflect changes in
the final version published in ApJL. Photometric data presented in this
submission are included as ancillary files. For a brief video explaining this
paper, see http://youtu.be/yRCCrNJnvt
Low temperature superlattice in monoclinic PZT
TEM has shown that the strongly piezoelectric material Pb(Zr0.52Ti0.48)O3
separates into two phases at low temperatures. The majority phase is the
monoclinic phase previously found by x-ray diffraction. The minority phase,
with a nanoscale coherence length, is a slightly distorted variant of the first
resulting from the anti-phase rotation of the oxygen octahedra about [111].
This work clears up a recent controversy about the origin of superlattice peaks
in these materials, and supports recent theoretical results predicting the
coexistence of ferroelectric and rotational instabilities.Comment: REVTeX4, 4 eps figures embedded. JPG version of figs. 2&4 is also
include
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