6,445 research outputs found
On Measuring Condensate Fraction in Superconductors
An analysis of off-diagonal long-range order in superconductors shows that
the spin-spin correlation function is significantly influenced by the order if
the order parameter is anisotropic on a microscopic scale. Thus, magnetic
neutron scattering can provide a direct measurement of the condensate fraction
of a superconductor. It is also argued that recent measurements in high
temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped
regime is added. Other corrections are mino
Making the small oblique parameters large
We compute the oblique parameters, including the three new parameters ,
and introduced recently by the Montreal group, for the case of one
scalar multiplet of arbitrary weak isospin and weak hypercharge . We
show that, when the masses of the heaviest and lightest components of the
multiplet remain constant, but increases, the oblique parameter and
the three new oblique parameters increase like , while only
increases like . For large multiplets with masses not much higher than , the oblique parameters and may become much larger than
and .Comment: 9 pages, standard LATEX, 3 figures available from the authors, report
CMU-HEP93-17 and DOE-ER/40682-4
Model study of a surfactant on the GaAs(100) surface
Cataloged from PDF version of article.Based on the facts that: (a) the transverse acoustic vibrational branch frequency is softened at the Brillouin zone boundaries of crystalline GaAs; (b) at the surface, the Ga-As bond is stronger than Ga-Te bond; and (c) the requirement that the final bond orientation of the Te surfactant should be rotated by 90degrees with respect to its initial orientation, we carried out a model study of an exchange process in epitaxial growth of GaAs (100). Even with very restrictive conditions imposed on the atomic movements, this study explains why Te is an effective surfactant for this type of growth. (C) 2002 Elsevier Science B.V. All rights reserved
Gender Diversity in the UK Construction Industry
For many years, there has been an assumption that the UK construction industry is devoid of gender diversity. Part of this assumption was predicated on the representation of
workers in construction sites, who are predominantly male. However, there are many positions in the construction industry that are not public-facing, and the question is whether the assumption that males fill most of these roles is also true. This issue has existed in the construction industry for many years; it appears that placing the sole onus on construction companies to employ more women may not be producing the desired level of progress. This research aim to establish whether clients can influence gender diversity in the construction industry with an objective of determining the current position of inequality in the construction industry; and existing incentives and frameworks. The research adopted an exploratory approach, with data collected through existing literature and records of 20 major construction companies, followed by interviews with Six individuals working for UK construction companies and clients of varying sizes. The study will awaken the construction industry and how it can initiate new proposals or support schemes that have worked previously, to encourage more
women to join the construction industry. It reveals that clients have an important role to play if the construction industry is to improve on gender diversity through contractual commitments that could be monitored regularly throughout the duration of a project
Finite-Size Studies on the SO(5) Symmetry of the Hubbard Model
We present numerical evidence for the approximate SO(5) symmetry of the
Hubbard model on a 10 site cluster. Various dynamic correlation functions
involving the operators, the generators of the SO(5) algebra, are studied
using exact diagonalisation, and are found to possess sharp collective peaks.
Our numerical results also lend support on the interpretation of the recent
resonant neutron scattering peaks in the YBCO superconductors in terms of the
Goldstone modes of the spontaneously broken SO(5) symmetry.Comment: 4 pages, Rev-Tex, includes 2 eps figure
High energy spin excitations in YBa_2 Cu_3 O_{6.5}
Inelastic neutron scattering has been used to obtain a comprehensive
description of the absolute dynamical spin susceptibility
of the underdoped superconducting cuprate YBa_2 Cu_3 O_{6.5} ()
over a wide range of energies and temperatures ( and ). Spin excitations of two different
symmetries (even and odd under exchange of two adjacent CuO_2 layers) are
observed which, surprisingly, are characterized by different temperature
dependences. The excitations show dispersive behavior at high energies.Comment: 15 pages, 5 figure
Endurance of SN 2005ip after a decade: X-rays, radio, and H-alpha like SN 1988Z require long-lived pre-supernova mass loss
SN2005ip was a TypeIIn event notable for its sustained strong interaction
with circumstellar material (CSM), coronal emission lines, and IR excess,
interpreted as shock interaction with the very dense and clumpy wind of an
extreme red supergiant. We present a series of late-time spectra of SN2005ip
and a first radio detection of this SN, plus late-time X-rays, all of which
indicate that its CSM interaction is still strong a decade post-explosion. We
also present and discuss new spectra of geriatric SNe with continued CSM
interaction: SN1988Z, SN1993J, and SN1998S. From 3-10 yr post-explosion,
SN2005ip's H-alpha luminosity and other observed characteristics were nearly
identical to those of the radio-luminous SN1988Z, and much more luminous than
SNe1993J and 1998S. At 10 yr after explosion, SN2005ip showed a drop in
H luminosity, followed by a quick resurgence over several months. We
interpret this variability as ejecta crashing into a dense shell located at
around 0.05 pc from the star, which may be the same shell that caused the IR
echo at earlier epochs. The extreme H-alpha luminosities in SN2005ip and
SN1988Z are still dominated by the forward shock at 10 yr post-explosion,
whereas SN1993J and SN1998S are dominated by the reverse shock at a similar
age. Continuous strong CSM interaction in SNe~2005ip and 1988Z is indicative of
enhanced mass loss for about 1e3 yr before core collapse, longer than Ne, O, or
Si burning phases. Instead, the episodic mass loss must extend back through C
burning and perhaps even part of He burning.Comment: 14 pages, 8 figs. accepted in MNRA
Are Asians comfortable with discussing death in health valuation studies? A study in multi-ethnic Singapore
BACKGROUND
To characterize ease in discussing death (EID) and its influence on health valuation in a multi-ethnic Asian population and to determine the acceptability of various descriptors of death and "pits"/"all-worst" in health valuation.
METHODS
In-depth interviews (English or mother-tongue) among adult Chinese, Malay and Indian Singaporeans selected to represent both genders and a wide range of ages/educational levels. Subjects rated using 0–10 visual analogue scales (VAS): (1) EID, (2) acceptability of 8 descriptors for death, and (3) appropriateness of "pits" and "all-worst" as descriptors for the worst possible health state. Subjects also valued 3 health states using VAS followed by time trade-off (TTO). The influence of sociocultural variables on EID and these descriptors was studied using univariable analyses and multiple linear regression (MLR). The influence of EID on VAS/TTO utilities with adjustment for sociocultural variables was assessed using MLR.
RESULTS
Subjects (n = 63, 35% Chinese, 32% Malay, median age 44 years) were generally comfortable with discussing death (median EID: 8.0). Only education significantly influenced EID (p = 0.045). EID correlated weakly with VAS/TTO scores (range: VAS: -0.23 to 0.07; TTO: -0.14 to 0.11). All subjects felt "passed away", "departed" and "deceased" were most acceptable (median acceptability: 8.0) while "sudden death" and "immediate death" were least acceptable (median acceptability: 5.0). Subjects clearly preferred "all-worst" to "pits" (63% vs. 19%, p < 0.001).
CONCLUSION
Singaporeans were generally comfortable with discussing death and had clear preferences for several descriptors of death and for "all-worst". EID is unlikely to influence health preference measurement in health valuation studies
Resonant Spin Excitation in an Overdoped High Temperature Superconductor
An inelastic neutron scattering study of overdoped Bi_2Sr_2CaCu_2O_{8+\delta}
$ (T_c = 83 K) has revealed a resonant spin excitation in the superconducting
state. The mode energy is E_res=38 meV, significantly lower than in optimally
doped Bi_2Sr_2CaCu_2O_{8+\delta} (T_c = 91 K, E_ res =43 meV). This
observation, which indicates a constant ratio E_res /k_B T_c \sim 5.4, helps
resolve a long-standing controversy about the origin of the resonant spin
excitation in high-temperature superconductors.Comment: final version: PRL 86, 1610 (2001
Effect of Nonmagnetic Impurities on the Magnetic Resonance Peak in YBa2Cu3O7
The magnetic excitation spectrum of a YBa_2 Cu_3 O_7 crystal containing 0.5%
of nonmagnetic (Zn) impurities has been determined by inelastic neutron
scattering. Whereas in the pure system a sharp resonance peak at E ~ 40 meV is
observed exclusively below the superconducting transition temperature T_c, the
magnetic response in the Zn-substituted system is broadened significantly and
vanishes at a temperature much higher than T_c. The energy-integrated spectral
weight observed near q = (pi,pi) increases with Zn substitution, and only about
half of the spectral weight is removed at T_c
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