6,318 research outputs found
Band gap control via tuning of inversion degree in CdInS spinel
Based on theoretical arguments we propose a possible route for controlling
the band-gap in the promising photovoltaic material CdInS. Our
\textit{ab initio} calculations show that the experimental degree of inversion
in this spinel (fraction of tetrahedral sites occupied by In) corresponds
approximately to the equilibrium value given by the minimum of the theoretical
inversion free energy at a typical synthesis temperature. Modification of this
temperature, or of the cooling rate after synthesis, is then expected to change
the inversion degree, which in turn sensitively tunes the electronic band-gap
of the solid, as shown here by accurate screened hybrid functional
calculations.Comment: In press in Applied Physics Letters (2012); 4 pages, 2 figures, 1
tabl
Measures of gravitational entropy I. Self-similar spacetimes
We examine the possibility that the gravitational contribution to the entropy
of a system can be identified with some measure of the Weyl curvature. In this
paper we consider homothetically self-similar spacetimes. These are believed to
play an important role in describing the asymptotic properties of more general
models. By exploiting their symmetry properties we are able to impose
significant restrictions on measures of the Weyl curvature which could reflect
the gravitational entropy of a system. In particular, we are able to show, by
way of a more general relation, that the most widely used "dimensionless"
scalar is \textit{not} a candidate for this measure along homothetic
trajectories.Comment: revtex, minor clarifications, to appear in Physical Review
Electrical characterisation of highly doped triangular silicon nanowires
A top-down silicon nanowire fabrication using a combination of optical lithography and orientation dependent etching (ODE) has been developed using Silicon-on Insulator (SOI) as the starting substrate. Initially, the samples were doped with phosphorus using the diffusion process resulting in carrier concentration of 2 X 10 18 cm-3. After the silicon nanowires were
fabricated, they were measured using a dual configuration method which is similar to the four-point
probe measurement technique to deduce its resistivity. The data obtained had suggested that the
doping distribution in the silicon nanowires were lower and this may have been affected by the
surface depletion effect. In addition, with respect to carrier mobility, the effective mobility of
electrons extracted using the four-point probe data had demonstrated that the mobility of carriers in
the silicon nanowire is comparable with the bulk mobility. This is most probably due to the fact that
in this research, the quantum confinement effect on these nanowires is not significant
Uniqueness of static decompositions
We classify static manifolds which admit more than one static decomposition
whenever a condition on the curvature is fullfilled. For this, we take a
standard static vector field and analyze its associated one parameter family of
projections onto the base. We show that the base itself is a static manifold
and the warping function satisfies severe restrictions, leading us to our
classification results. Moreover, we show that certain condition on the
lightlike sectional curvature ensures the uniqueness of static decomposition
for Lorentzian manifolds.Comment: 14 page
Integration of the Friedmann equation for universes of arbitrary complexity
An explicit and complete set of constants of the motion are constructed
algorithmically for Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) models
consisting of an arbitrary number of non-interacting species. The inheritance
of constants of the motion from simpler models as more species are added is
stressed. It is then argued that all FLRW models admit what amounts to a unique
candidate for a gravitational epoch function (a dimensionless scalar invariant
derivable from the Riemann tensor without differentiation which is monotone
throughout the evolution of the universe). The same relations that lead to the
construction of constants of the motion allow an explicit evaluation of this
function. In the simplest of all models, the CDM model, it is shown
that the epoch function exists for all models with , but for
almost no models with .Comment: Final form to appear in Physical Review D1
Yang-Mills fields on CR manifolds
We study pseudo Yang-Mills fields on a compact strictly pseudoconvex CR
manifold.Comment: 52 page
Tonsillar carcinoma spreading metastases to central nervous system – Case report and literature review
We present a case report of a 51-year-old left-handed gentleman with a background of HPV 16-positive tonsil squamous cell carcinoma presenting with tonic-clonic seizure and a radiological diagnosis of secondary metastatic deposits. These were initially treated with Stereotactic RadioSurgery (SRS), and subsequently with surgery. Surgical resection was performed under general anaesthesia with right-sided temporal and parietal approaches. Both the parietal and temporal deposits were removed, while the intraventricular mass was intentionally left to avoid post-op deficits. Adjuvant radiotherapy and chemotherapy were administered post-op. The patient experienced a satisfactory recovery post-op and was re-operated for recurrence 4 months later. He maintained a good quality of life and an excellent performance status throughout, but unfortunately passed away in November 2018 due to septic complications. This case history stresses the difficulty in managing SCC with brain metastatic deposits. There are no current guidelines about the management of patients presenting with such a rare condition. More data is thus desirable in order to better define treatment guidelines and protocols when SCC brain metastases are present
Measurement of the shear strength of a charge-density wave
We have explored the shear plasticity of charge density waves (CDWs) in
niobium triselenide samples with cross-sections having a single
micro-fabricated thickness step. Shear stresses along the step result from
thickness-dependent CDW pinning. For small thickness differences the CDW depins
elastically at the volume average depinning field. For large thickness
differences the thicker, more weakly pinned side depins first via plastic
shear. A simple model describes the qualitative features of our data, and
yields a value for the CDW's shear strength of approximately 9.5*10^3 N/m^2 and
a lower bound for the elastic shear modulus of 2.1*10^4 N/m^2. These values are
orders of magnitude smaller than the CDW's longitudinal modulus but are much
larger than corresponding values for flux-line lattices, and may explain the
relative coherence of the CDW response.Comment: 10 pages, 4 figures, submitted to Physical Review Letter
West Highland White Terriers under primary veterinary care in the UK in 2016: demography, mortality and disorders
The West Highland White Terrier (WHWT) is a relatively common breed in the UK, although Kennel Club registrations have declined in recent years. The VetCompass™ Programme collates de-identified clinical data from primary-care veterinary practices in the UK for epidemiological research. Using VetCompass clinical data, this study aimed to characterise the demography, longevity and common disorders of WHWTs under primary veterinary care in the UK
On paraquaternionic submersions between paraquaternionic K\"ahler manifolds
In this paper we deal with some properties of a class of semi-Riemannian
submersions between manifolds endowed with paraquaternionic structures, proving
a result of non-existence of paraquaternionic submersions between
paraquaternionic K\"ahler non locally hyper paraK\"ahler manifolds. Then we
examine, as an example, the canonical projection of the tangent bundle, endowed
with the Sasaki metric, of an almost paraquaternionic Hermitian manifold.Comment: 13 pages, no figure
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