1,656 research outputs found
Temperature Dependence of Interlayer Magnetoresistance in Anisotropic Layered Metals
Studies of interlayer transport in layered metals have generally made use of
zero temperature conductivity expressions to analyze angle-dependent
magnetoresistance oscillations (AMRO). However, recent high temperature AMRO
experiments have been performed in a regime where the inclusion of finite
temperature effects may be required for a quantitative description of the
resistivity. We calculate the interlayer conductivity in a layered metal with
anisotropic Fermi surface properties allowing for finite temperature effects.
We find that resistance maxima are modified by thermal effects much more
strongly than resistance minima. We also use our expressions to calculate the
interlayer resistivity appropriate to recent AMRO experiments in an overdoped
cuprate which led to the conclusion that there is an anisotropic, linear in
temperature contribution to the scattering rate and find that this conclusion
is robust.Comment: 8 pages, 4 figure
Analytical calculation of the Green's function and Drude weight for a correlated fermion-boson system
In classical Drude theory the conductivity is determined by the mass of the
propagating particles and the mean free path between two scattering events. For
a quantum particle this simple picture of diffusive transport loses relevance
if strong correlations dominate the particle motion. We study a situation where
the propagation of a fermionic particle is possible only through creation and
annihilation of local bosonic excitations. This correlated quantum transport
process is outside the Drude picture, since one cannot distinguish between free
propagation and intermittent scattering. The characterization of transport is
possible using the Drude weight obtained from the f-sum rule, although its
interpretation in terms of free mass and mean free path breaks down. For the
situation studied we calculate the Green's function and Drude weight using a
Green's functions expansion technique, and discuss their physical meaning.Comment: final version, minor correction
A WZW model based on a non-semi-simple group
We present a conformal field theory which desribes a homogeneous four
dimensional Lorentz-signature space-time. The model is an ungauged WZW model
based on a central extension of the Poincar\'e algebra. The central charge of
this theory is exactly four, just like four dimensional Minkowski space. The
model can be interpreted as a four dimensional monochromatic plane wave. As
there are three commuting isometries, other interesting geometries are expected
to emerge via duality.Comment: 8 pages, phyzzx, IASSNS-HEP-93/61 Texable versio
In-situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects
Combined in-situ x-ray photoemission spectroscopy, scanning tunnelling
spectroscopy and angle resolved photoemission spectroscopy of molecular beam
epitaxy grown Bi2Te3 on lattice mismatched substrates reveal high quality
stoichiometric thin films with topological surface states without a
contribution from the bulk bands at the Fermi energy. The absence of bulk
states at the Fermi energy is achieved without counter doping. We observe that
the surface morphology and electronic band structure of Bi2Te3 are not affected
by in-vacuo storage and exposure to oxygen, whereas major changes are observed
when exposed to ambient conditions. These films help define a pathway towards
intrinsic topological devices.Comment: 8 pages, 5 figure
Degenerate Bose liquid in a fluctuating gauge field
We study the effect of a strongly fluctuating gauge field on a degenerate
Bose liquid, relevant to the charge degrees of freedom in doped Mott
insulators. We find that the superfluidity is destroyed. The resulting metallic
phase is studied using quantum Monte Carlo methods. Gauge fluctuations cause
the boson world lines to retrace themselves. We examine how this world-line
geometry affects the physical properties of the system. In particular, we find
a transport relaxation rate of the order of 2kT, consistent with the normal
state of the cuprate superconductors. We also find that the density excitations
of this model resemble that of the full tJ model.Comment: 4 pages. Uses RevTeX, epsf, multicols macros. 5 postscript figure
Penrose Limits and Non-local theories
We investigate Penrose limits of two classes of non-local theories, little
string theories and non-commutative gauge theories. Penrose limits of the
near-horizon geometry of NS5-branes help to shed some light on the high energy
spectrum of little string theories. We attempt to understand renormalization
group flow in these theories by considering Penrose limits wherein the null
geodesic also has a radial component. In particular, we demonstrate that it is
possible to construct a pp-wave spacetime which interpolates between the linear
dilaton and the AdS regions for the Type IIA NS5-brane. Similar analysis is
considered for the holographic dual geometry to non-commutative field theories.Comment: 27 pages, LaTeX; v2: added reference
Feasibility study for a numerical aerodynamic simulation facility. Volume 1
A Numerical Aerodynamic Simulation Facility (NASF) was designed for the simulation of fluid flow around three-dimensional bodies, both in wind tunnel environments and in free space. The application of numerical simulation to this field of endeavor promised to yield economies in aerodynamic and aircraft body designs. A model for a NASF/FMP (Flow Model Processor) ensemble using a possible approach to meeting NASF goals is presented. The computer hardware and software are presented, along with the entire design and performance analysis and evaluation
Efficacy of infant simulator programmes to prevent teenage pregnancy: a school-based cluster randomised trial in Western Australia
Background: Infant simulator-based programmes seek to prevent teenage pregnancy. They are utilised in western and developing countries but, despite growing popularity, there is no published evidence of their long-term impact. The aim of this trial was to investigate the effect of such a programme, the Virtual Infant Parenting (VIP) Programme, on the pregnancy outcomes of birth and induced abortion.
Methods: Fifty-seven of 66 eligible schools (86%) in Perth, Western Australia enrolled in the pragmatic clustered (by school) randomised trial (ISRCTN24952438) with even randomisation to the intervention and control groups. Between 2003 and 2006, the VIP programme was administered to 1,267 girls in the intervention schools, while 1,567 girls in the control schools received the standard health education curriculum. Participants were aged 13-15 years and were followed until age 20 via data linkage to hospital medical and abortion clinic records. Log binomial and Cox proportional hazards regression was used to test for differences in pregnancy rates between study groups. Findings: Compared to girls
Findings: Compared to girls in the control group, a higher proportion of girls in the intervention group recorded at least one birth (7.6%, n=97; 4·3%, n=67) or at least one abortion as the first pregnancy event (8.9%, n=113; 6.4%, n=101). After adjustment for potential confounding, the intervention group had a higher overall pregnancy risk (RR = 1·36, 95% CI 1.10–1·67, p=0.003) compared to the control group. Similar results were obtained using proportional hazard models (HR = 1.35, 95% CI 1.10–1·67, p=0·016).
Interpretation: The infant-simulator based VIP Programme did not achieve its aim of reducing teenage pregnancy. Girls in the intervention group were more likely to experience a birth or an induced abortion than those in the control group before turning 20 years of age.
Funding: The Health Promotion Research Foundation of Western Australia (Healthway), Lotteries WA, the Western Australian Department of Education and Training and the Western Australian Department of Health
Universal distribution of transparencies in highly conductive Nb/AlO/Nb junctions
We report the observation of the universal distribution of transparencies,
predicted by Schep and Bauer [Phys. Rev. Lett. {\bf 78}, 3015 (1997)] for dirty
sharp interfaces, in uniform Nb/AlO/Nb junctions with high specific
conductance ( Ohmcm). Experiments used the BCS density of
states in superconducting niobium for transparency distribution probing.
Experimental results for both the dc curves at magnetic-field-suppressed
supercurrent and the Josephson critical current in zero magnetic field coincide
remarkably well with calculations based on the multimode theory of multiple
Andreev reflections and the Schep-Bauer distribution.Comment: 4 pages, 4 figures, references adde
Landau Theory of the Finite Temperature Mott Transition
In the context of the dynamical mean-field theory of the Hubbard model, we
identify microscopically an order parameter for the finite temperature Mott
endpoint. We derive a Landau functional of the order parameter. We then use the
order parameter theory to elucidate the singular behavior of various physical
quantities which are experimentally accessible.Comment: 4 pages, 2 figure
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