4,320 research outputs found
Mapping the dynamic interactions between vortex species in highly anisotropic superconductors
Here we use highly sensitive magnetisation measurements performed using a
Hall probe sensor on single crystals of highly anisotropic high temperature
superconductors to study the dynamic interactions
between the two species of vortices that exist in such superconductors. We
observe a remarkable and clearly delineated high temperature regime that
mirrors the underlying vortex phase diagram. Our results map out the parameter
space over which these dynamic interaction processes can be used to create
vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno
The Magellanic Stream and the density of coronal gas in the Galactic halo
The properties of the Magellanic Stream constrain the density of coronal gas
in the distant Galactic halo. We show that motion through ambient gas can
strongly heat Stream clouds, driving mass loss and causing evaporation. If the
ambient gas density is too high, then evaporation occurs on unreasonably short
timescales. Since heating dominates drag, tidal stripping appears to be
responsible for producing the Stream. Requiring the survival of the cloud MS IV
for 500 Myr sets an upper limit on the halo gas density n_H< 10^{-5} cm^{-3} at
50 kpc, roughly a factor of 10 lower than that estimated from the drag model of
Moore & Davis (1994). Implications for models of the evolution of gas in galaxy
halos are discussed.Comment: 4 pages, 1 figure, in press, ApJ
Single-qubit lasing in the strong-coupling regime
Motivated by recent ``circuit QED'' experiments we study the lasing
transition and spectral properties of single-qubit lasers. In the strong
coupling, low-temperature regime quantum fluctuations dominate over thermal
noise and strongly influence the linewidth of the laser. When the qubit and the
resonator are detuned, amplitude and phase fluctuations of the radiation field
are coupled, and the phase diffusion model, commonly used to describe
conventional lasers, fails. We predict pronounced effects near the lasing
transition, with an enhanced linewidth and non-exponential decay of the
correlation functions. We cover a wide range of parameters by using two
complementary approaches, one based on the Liouville equation in a Fock state
basis, covering arbitrarily strong coupling but limited to low photon numbers,
the other based on the coherent-state representation, covering large photon
numbers but restricted to weak or intermediate coupling.Comment: 11 pages, 11 figure
Spatial adiabatic passage in a realistic triple well structure
We investigate the evolution of an electron undergoing coherent tunneling via
adiabatic passage (CTAP) using the solution of the one-dimensional Schroedinger
equation in both space and time for a triple well potential. We find the
eigenspectrum and complete time evolution for a range of different pulsing
schemes. This also provides an example of a system that can be described with
the tools from both quantum optics and condensed matter. We find that while the
quantum optics description of the process captures most of the key physics,
there are important effects that can only be correctly described by a more
complete representation. This is an important point for applications such as
quantum information processing or quantum control where it is common practice
to use a reduced state space formulation of the quantum system in question.Comment: 10 pages, 12 figures (color online) - Published Versio
A framework for power analysis using a structural equation modelling procedure
BACKGROUND: This paper demonstrates how structural equation modelling (SEM) can be used as a tool to aid in carrying out power analyses. For many complex multivariate designs that are increasingly being employed, power analyses can be difficult to carry out, because the software available lacks sufficient flexibility. Satorra and Saris developed a method for estimating the power of the likelihood ratio test for structural equation models. Whilst the Satorra and Saris approach is familiar to researchers who use the structural equation modelling approach, it is less well known amongst other researchers. The SEM approach can be equivalent to other multivariate statistical tests, and therefore the Satorra and Saris approach to power analysis can be used. METHODS: The covariance matrix, along with a vector of means, relating to the alternative hypothesis is generated. This represents the hypothesised population effects. A model (representing the null hypothesis) is then tested in a structural equation model, using the population parameters as input. An analysis based on the chi-square of this model can provide estimates of the sample size required for different levels of power to reject the null hypothesis. CONCLUSIONS: The SEM based power analysis approach may prove useful for researchers designing research in the health and medical spheres
Does early intervention improve outcomes in the physiotherapy management of lumbar radicular syndrome? Results of the POLAR pilot randomised controlled trial
OBJECTIVE: To investigate the feasibility of undertaking a definitive randomised controlled trial (RCT). SETTING: This was a pilot, pragmatic superiority RCT with a qualitative element, recruiting from 14 general practitioner (GP) practices in England. PARTICIPANTS: Patients over 18 years of age presenting to their GP with unilateral lumbar radicular syndrome (LRS), defined as radicular pain and/or neurological symptoms originating from lumbar nerve roots, were eligible to participate in the study, those who did not have a clear understanding of the English language or had comorbidities preventing rehabilitation were ineligible. INTERVENTIONS: Participants were randomised into early intervention physiotherapy or usual care with the former receiving their treatment within 2 weeks after randomisation and the latter 6 weeks postrandomisation. Both groups received a patient-centred, goal-orientated physiotherapy programme specific to their needs. Participants received up to six treatment sessions over an 8-week period. OUTCOME MEASURES: Process outcomes to determine the feasibility of the study and an exploratory analysis of patient-reported outcomes, including self-rated disability, pain and general health, these were collected at baseline, 6, 12 and 26 weeks postrandomisation. RESULTS: 80 participants were recruited in 10 GP practices over 34 weeks and randomised to (early intervention physiotherapy n=42, usual care n=38). Follow-up rates at 26 weeks were 32 (84%) in the usual care and 36 (86%) in the early intervention physiotherapy group. The mean area under the curve (larger values indicating more disability) for the Oswestry Disability Index over the 26 weeks was 16.6 (SD 11.4) in the usual care group and 16.0 (SD 14.0) in the intervention group. A difference of -0.6 (95% CI -0.68 to 5.6) in favour of the intervention group. CONCLUSIONS: The results of the study suggest a full RCT is feasible and will provide evidence as to the optimal timing of physiotherapy for patients with LRS. TRIAL REGISTRATION NUMBER: NCT02618278, ISRCTN25018352
Employing culturally responsive pedagogy to foster literacy learning in schools
In recent years it has become increasingly obvious that, to enable students in schools from an increasingly diverse range of cultural backgrounds to acquire literacy to a standard that will support them to achieve academically, it is important to adopt pedagogy that is responsive to, and respectful of, them as culturally situated. What largely has been omitted from the literature, however, is discussion of a relevant model of learning to underpin this approach. For this reason this paper adopts a socio-cultural lens (Vygotsky, 1978) through which to view such pedagogy and refers to a number of seminal texts to justify of its relevance. Use of this lens is seen as having a particular rationale. It forces a focus on the agency of the teacher as a mediator of learning who needs to acknowledge the learner’s cultural situatedness (Kozulin, 2003) if school literacy learning for all students is to be as successful as it might be. It also focuses attention on the predominant value systems and social practices that characterize the school settings in which students’ literacy learning is acquired. The paper discusses implications for policy and practice at whole-school, classroom and individual student levels of culturally-responsive pedagogy that is based on a socio-cultural model of learning. In doing so it draws on illustrations from the work of a number of researchers, including that of the author
A new search for distant radio galaxies in the southern hemisphere - I. Sample definition and radio properties
This paper introduces a new program to find high-redshift radio galaxies in
the southern hemisphere through ultra-steep spectrum (USS) selection. We define
a sample of 234 USS radio sources with spectral indices alpha_408^843 < -1.0
and flux densities S_408 > 200 mJy in a region of 0.35 sr, chosen by
cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz
Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in
the overlap region -40 deg < delta < -30 deg. We present Australia Telescope
Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each
source, which we use to analyse the morphological, spectral index and
polarization properties of our sample. We find that 85 per cent of the sources
have observed-frame spectral energy distributions that are straight over the
frequency range 408-2368 MHz, and that, on average, sources with smaller
angular sizes have slightly steeper spectral indices and lower fractional
linear polarization. Fractional polarization is anti-correlated with flux
density at both 1400 and 2368 MHz. We also use the ATCA data to determine
observed-frame Faraday rotation measures for half of the sample.Comment: 28 pages, 9 figures, 10 tables, accepted for publication in MNRAS.
Correct version of SUMSS catalogue now noted in Section 2.1.2; analysis and
conclusions unchanged. A higher-resolution version of Figure 1 is available
at http://www.physics.usyd.edu.au/~jess/papers.htm
C. elegans serine-threonine kinase KIN-29 modulates TGFβ signaling and regulates body size formation
BACKGROUND: In C. elegans there are two well-defined TGFβ-like signaling pathways. The Sma/Mab pathway affects body size morphogenesis, male tail development and spicule formation while the Daf pathway regulates entry into and exit out of the dauer state. To identify additional factors that modulate TGFβ signaling in the Sma/Mab pathway, we have undertaken a genetic screen for small animals and have identified kin-29. RESULTS: kin-29 encodes a protein with a cytoplasmic serine-threonine kinase and a novel C-terminal domain. The kinase domain is a distantly related member of the EMK (ELKL motif kinase) family, which interacts with microtubules. We show that the serine-threonine kinase domain has in vitro activity. kin-29 mutations result in small animals, but do not affect male tail morphology as do several of the Sma/Mab signal transducers. Adult worms are smaller than the wild-type, but also develop more slowly. Rescue by kin-29 is achieved by expression in neurons or in the hypodermis. Interaction with the dauer pathway is observed in double mutant combinations, which have been seen with Sma/Mab pathway mutants. We show that kin-29 is epistatic to the ligand dbl-1, and lies upstream of the Sma/Mab pathway target gene, lon-1. CONCLUSION: kin-29 is a new modulator of the Sma/Mab pathway. It functions in neurons and in the hypodermis to regulate body size, but does not affect all TGFβ outputs, such as tail morphogenesis
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