7,420 research outputs found
Transport and thermoelectric properties of the LaAlO/SrTiO interface
The transport and thermoelectric properties of the interface between
SrTiO and a 26-monolayer thick LaAlO-layer grown at high
oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and
in magnetic fields up to 18 T. For 4.2 K, two different electron-like
charge carriers originating from two electron channels which contribute to
transport are observed. We probe the contributions of a degenerate and a
non-degenerate band to the thermoelectric power and develop a consistent model
to describe the temperature dependence of the thermoelectric tensor. Anomalies
in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure
Representation Class and Geometrical Invariants of Quantum States under Local Unitary Transformations
We investigate the equivalence of bipartite quantum mixed states under local
unitary transformations by introducing representation classes from a
geometrical approach. It is shown that two bipartite mixed states are
equivalent under local unitary transformations if and only if they have the
same representation class. Detailed examples are given on calculating
representation classes.Comment: 11 page
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
Clustering properties of a generalised critical Euclidean network
Many real-world networks exhibit scale-free feature, have a small diameter
and a high clustering tendency. We have studied the properties of a growing
network, which has all these features, in which an incoming node is connected
to its th predecessor of degree with a link of length using a
probability proportional to . For , the
network is scale free at with the degree distribution and as in the Barab\'asi-Albert model (). We find a phase boundary in the plane along which
the network is scale-free. Interestingly, we find scale-free behaviour even for
for where the existence of a new universality class
is indicated from the behaviour of the degree distribution and the clustering
coefficients. The network has a small diameter in the entire scale-free region.
The clustering coefficients emulate the behaviour of most real networks for
increasing negative values of on the phase boundary.Comment: 4 pages REVTEX, 4 figure
Visualizing Spacetime Curvature via Gradient Flows I: Introduction
Traditional approaches to the study of the dynamics of spacetime curvature in
a very real sense hide the intricacies of the nonlinear regime. Whether it be
huge formulae, or mountains of numerical data, standard methods of presentation
make little use of our remarkable skill, as humans, at pattern recognition.
Here we introduce a new approach to the visualization of spacetime curvature.
We examine the flows associated with the gradient fields of invariants derived
from the spacetime. These flows reveal a remarkably rich structure, and offer
fresh insights even for well known analytical solutions to Einstein's
equations. This paper serves as an overview and as an introduction to this
approach.Comment: 10 pages twocolumn revtex 4-1 two figures. Final form to appear in
Phys Rev
Final results from the EU project AVATAR: aerodynamic modelling of 10 MW wind turbines
This paper presents final results from the EU project AVATAR in which aerodynamic models are improved and validated for wind turbines on a scale of 10 MW and more. Special attention is paid to the improvement of low fidelity engineering (BEM based) models with higher fidelity (CFD) models but also with intermediate fidelity free vortex wake (FVW) models. The latter methods were found to be a good basis for improvement of induction modelling in engineering methods amongst others for the prediction of yawed cases, which in AVATAR was found to be one of the most challenging subjects to model. FVW methods also helped to improve the prediction of tip losses. Aero-elastic calculations with BEM based and FVW based models showed that fatigue loads for normal production cases were over predicted with approximately 15% or even more. It should then be realised that the outcome of BEM based models does not only depend on the choice of engineering add-ons (as is often assumed) but it is also heavily dependent on the way the induced velocities are solved. To this end an annulus and element approach are discussed which are assessed with the aid of FVW methods. For the prediction of fatigue loads the so-called element approach is recommended but the derived yaw models rely on an annulus approach which pleads for a generalised solution method for the induced velocities
Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion
Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion
allows us to detect sub-shot-noise spatial quantum correlation with up to one
hundred photoelectrons per mode, by means of a high efficiency CCD. The
statistics is performed in single-shot over independent spatial replica of the
system. The paper highlights the evidence of quantum correlation between
symmetrical signal and idler spatial areas in the far field, in the high gain
regime. In accordance with the predictions of numerical calculations the
observed transition from the quantum to the classical regime is interpreted as
a consequence of the narrowing of the down-converted beams in the very high
gain regime.Comment: 4,2 pages, 4 figure
Ground-based remote sensing of an elevated forest fire aerosol layer at Whistler, BC: implications for interpretation of mountaintop chemistry
On 30 August 2009, intense forest fires in interior British Columbia (BC)
coupled with winds from the east and northeast resulted in transport of a
broad forest fire plume across southwestern BC. The physico-chemical and
optical characteristics of the plume as observed from Saturna Island
(AERONET), CORALNet-UBC and the Whistler Mountain air chemistry facility
were consistent with forest fire plumes that have been observed elsewhere in
continental North America. However, the importance of three-dimensional
transport in relation to the interpretation of mountaintop chemistry
observations is highlighted on the basis of deployment of both a <i>CL31</i> ceilometer
and a single particle mass spectrometer (SPMS) in a mountainous setting. The
SPMS is used to identify the biomass plume based on levoglucosan and
potassium markers. Data from the SPMS are also used to show that the
biomass plume was correlated with nitrate, but not correlated with sulphate
or sodium. This study not only provides baseline measurements of biomass
burning plume physico-chemical characteristics in western Canada, but also
highlights the importance of lidar remote sensing methods in the
interpretation of mountaintop chemistry measurements
Towards an Axiomatic Formulation of Noncommutative Quantum Field Theory
We propose new Wightman functions as vacuum expectation values of products of
field operators in the noncommutative space-time. These Wightman functions
involve the -product among the fields, compatible with the twisted
Poincar\'e symmetry of the noncommutative quantum field theory (NC QFT). In the
case of only space-space noncommutativity (), we prove the CPT
theorem using the noncommutative form of the Wightman functions. We also show
that the spin-statistics theorem, demonstrated for the simplest case of a
scalar field, holds in NC QFT within this formalism.Comment: 16 pages, version to appear in J. Math. Phy
Transient obstructive hydrocephalus due to intraventricular hemorrhage: A case report and review of literature
BACKGROUND: Acute transient obstructive hydrocephalus is rare in adults. We describe a patient with intraventricular hemorrhage (IVH) who experienced the delayed development of acute transient hydrocephalus. CASE REPORT: A 33-year-old man with a previously diagnosed Spetzler-Martin Grade 5 arteriovenous malformation presented with severe headache, which was found to be due to IVH. Forty hours after presentation he developed significant obstructive hydrocephalus due to the thrombus migrating to the cerebral aqueduct, and a ventriculostomy placement was planned. However, shortly thereafter his headache began to improve spontaneously. Within 4 hours after onset the headache had completely resolved, and an interval head CT scan revealed resolution of hydrocephalus. CONCLUSIONS: In patients with IVH, acute obstructive hydrocephalus can develop at any time after the ictus. Though a delayed presentation of acute but transient obstructive hydrocephalus is unusual, it is important to be aware of this scenario and ensure that deterioration secondary to thrombus migration and subsequent obstructive hydrocephalus do not occur
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