3,692 research outputs found
Phase diagrams of correlated electrons: systematic corrections to the mean field theory
Perturbative corrections to the mean field theory for particle-hole
instabilities of interacting electron systems are computed within a scheme
which is equivalent to the recently developed variational approach to the
Kohn-Luttinger superconductivity. This enables an unbiased comparison of
particle-particle and particle-hole instabilities within the same approximation
scheme. A spin-rotation invariant formulation for the particle-hole
instabilities in the triplet channel is developed. The method is applied to the
phase diagram of the t-t' Hubbard model on the square lattice. At the Van Hove
density, antiferromagnetic and d-wave Pomeranchuk phases are found to be stable
close to half filling. However, the latter phase is confined to an extremely
narrow interval of densities and away from the singular filling, d-wave
superconducting instability dominates
Direct calculation of the hard-sphere crystal/melt interfacial free energy
We present a direct calculation by molecular-dynamics computer simulation of
the crystal/melt interfacial free energy, , for a system of hard
spheres of diameter . The calculation is performed by thermodynamic
integration along a reversible path defined by cleaving, using specially
constructed movable hard-sphere walls, separate bulk crystal and fluid systems,
which are then merged to form an interface. We find the interfacial free energy
to be slightly anisotropic with = 0.62, 0.64 and
0.58 for the (100), (110) and (111) fcc crystal/fluid
interfaces, respectively. These values are consistent with earlier density
functional calculations and recent experiments measuring the crystal nucleation
rates from colloidal fluids of polystyrene spheres that have been interpreted
[Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of
for the hard-sphere system of , slightly lower
than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
The national telephone plan - numbering [1959]
This article was originally published in the Telecommunication Journal of Australia Volume 12 No 1, 1959. It describes one of the basic elements in the design of the system for the long-term development of the Australian telephone service the national numbering plan
Perceptions Of School By Two Teenage Boys With Asperger Syndrome And Their Mothers: A Qualitative Study
This qualitative study aimed to develop an understanding of the challenges faced by teenage boys with Asperger syndrome and their mothers. A case study approach was used to collect data from two 13-year-old boys who have Asperger syndrome and their mothers in Queensland, Australia. Data were collected through the use of semiĀ¬structured interviews. The words of the boys and their mothers provide a valuable insight into the personal experiences and feelings of the parĀ¬ticipants. An inductive approach to data analysis identified four themes: (1) developmental differences; (2) problems associated with the general characteristics of Asperger syndrome (i.e. communication and social difficulties, restricted range of interests, a need for routine); (3) stress; and (4) 'masquerading'. The first three themes relate strongly to the current literature, but the emergence of masquerading is of particular interest in developing a fuller understanding of the experiences of individuals with Asperger syndrome at school
Neutron scattering from a coordination polymer quantum paramagnet
Inelastic neutron scattering measurements are reported for a powder sample of
the spin-1/2 quantum paramagnet . Magnetic neutron
scattering is identified above an energy gap of 1.9 meV. Analysis of the sharp
spectral maximum at the onset indicates that the material is magnetically
quasi-one-dimensional. Consideration of the wave vector dependence of the
scattering and polymeric structure further identifies the material as a
two-legged spin-1/2 ladder. Detailed comparison of the data to various models
of magnetism in this material based on the single mode approximation and the
continuous unitary transformation are presented. The latter theory provides an
excellent account of the data with leg exchange meV and
rung exchange meV.Comment: 10 pages, 11 figures, 1 tabl
Searching for Earth analogues around the nearest stars: the disk age-metallicity relation and the age distribution in the Solar Neighbourhood
The chemical composition of Earth's atmosphere has undergone substantial
evolution over the course of its history. It is possible, even likely, that
terrestrial planets in other planetary systems have undergone similar changes;
consequently, the age distribution of nearby stars is an important
consideration in designing surveys for Earth-analogues. Valenti & Fischer
(2005) provide age and metallicity estimates for 1039 FGK dwarfs in the Solar
Neighbourhood. Using the Hipparcos catalogue as a reference to calibrate
potential biases, we have extracted volume-limited samples of nearby stars from
the Valenti-Fischer dataset. Unlike other recent investigations, our analysis
shows clear evidence for an age-metallicity relation in the local disk, albeit
with substantial dispersion at any epoch. The mean metallicity increases from
-0.3 dex at a lookback time of ~10 Gyrs to +0.15 dex at the present day.
Supplementing the Valenti-Fischer measurements with literature data to give a
complete volume-limited sample, the age distribution of nearby FGK dwarfs is
broadly consistent with a uniform star-formation rate over the history of the
Galactic disk. In striking contrast, most stars known to have planetary
companions are younger than 5 Gyrs; however, stars with planetary companions
within 0.4 AU have a significantly flatter age distribution, indicating that
those systems are stable on timescales of many Gyrs. Several of the older,
lower metallicity host stars have enhanced [alpha/Fe] ratios, implying
membership of the thick disk. If the frequency of terrestrial planets is also
correlated with stellar metallicity, then the median age of such planetary
system is likely to be ~3 Gyrs. We discuss the implications of this hypothesis
in designing searches for Earth analogues among the nearby stars.Comment: Accepted for publication in Ap
Chirped pulse Raman amplification in warm plasma: towards controlling saturation
Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10's - 100's fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies.close0
Inconsistency of the MLE for the joint distribution of interval censored survival times and continuous marks
This paper considers the nonparametric maximum likelihood estimator (MLE) for
the joint distribution function of an interval censored survival time and a
continuous mark variable. We provide a new explicit formula for the MLE in this
problem. We use this formula and the mark specific cumulative hazard function
of Huang and Louis (1998) to obtain the almost sure limit of the MLE. This
result leads to necessary and sufficient conditions for consistency of the MLE
which imply that the MLE is inconsistent in general. We show that the
inconsistency can be repaired by discretizing the marks. Our theoretical
results are supported by simulations.Comment: 27 pages, 4 figure
Comparing the effect of CTG+STan with CTG alone on emergency Cesarean section rate : STan Australian Randomized controlled Trial (START)
The authors would like to thank the women and their babies for participating. We would like to thank all the staff at the WCH, in particular Priya Umampathysivam, Denise Cheetham and Cecilia Heitmann for their assistance in recruitment of participants for START. We would also like to thank the members of the DSMC, Diogo Ayres-de-Campos, Scott Morris and Katherine Lee, for their oversight of START and the Clinical Information Service (CIS) team at the WCH for the comparative hospital dataPeer reviewedPublisher PD
An Evaluation of the Performance and Acceptability of Three LED Fluorescent Microscopes in Zambia: Lessons Learnt for Scale-Up
The World Health Organization recommends the roll-out of light-emitting diode (LED) fluorescent microscopes (FM) as an alternative to light microscopes in resource-limited settings. We evaluated the acceptability and performance of three LED FMs after a short orientation among laboratory technicians from government health centers in Zambia. Sixteen technicians with varied light microscopy experience were oriented to FMs and divided into groups; each group read a different set of 40 slides on each LED FM (Primo Star iLEDā¢, Luminā¢, FluoLEDā¢) and on a reference mercury-vapor FM (Olympus BX41TF). Slide reading times were recorded. An experienced FM technician examined each slide on the Olympus BX41TF. Sensitivity and specificity compared to TB culture were calculated. Misclassification compared to the experienced technician and inter-rater reliability between trainees was assessed. Trainees rated microscopes on technical aspects. Primo Star iLEDā¢, FluoLEDā¢ and Olympus BX41TF had comparable sensitivities (67%, 65% and 65% respectively), with the Luminā¢ significantly worse (56%; p<0.05). Specificity was low for trainees on all microscopes (75.9%) compared to the experienced technician on Olympus BX41TF (100%). Primo Star iLEDā¢ had significantly less misclassification (21.1% p<0.05) than FluoLEDā¢ (26.5%) and Luminā¢ (26.8%) and significantly higher inter-rater reliability (0.611; p<0.05), compared to FluoLEDā¢ (0.523) and Luminā¢ (0.492). Slide reading times for LED FMs were slower than the reference, but not significantly different from each other. Primo Star iLEDā¢ rated highest in acceptability measures, followed by FluoLEDā¢ then Luminā¢. Primo Star iLEDā¢ was consistently better than FluoLEDā¢ and Luminā¢, and performed comparably to the Olympus BX41TF in all analyses, except reading times. The Luminā¢ compared least favorably and was thought unacceptable for use. Specificity and inter-rater reliability were low for all microscopes suggesting that a brief orientation was insufficient in this setting. These results provide important data for resource-limited settings to consider as they scale-up LED FMs
- ā¦