4,985 research outputs found
A site-specific standard for comparing dynamic solar ultraviolet protection characteristics of established tree canopies
A standardised procedure for making fair and comparable assessments of the ultraviolet protection of an established tree canopy that takes into account canopy movement and the changing position of the sun is presented for use by government, planning, and environmental health authorities. The technique utilises video image capture and replaces the need for measurement by ultraviolet radiometers for surveying shade quality characteristics of trees growing in public parks, playgrounds and urban settings. The technique improves upon tree shade assessments that may be based upon single measurements of the ultraviolet irradiance observed from a fixed point of view. The presented technique demonstrates how intelligent shade audits can be conducted without the need for specialist equipment, enabling the calculation of the Shade Protection Index (SPI) and Ultraviolet Protection Factor (UPF) for any discreet time interval and over a full calendar year
A method to construct refracting profiles
We propose an original method for determining suitable refracting profiles
between two media to solve two related problems: to produce a given wave front
from a single point source after refraction at the refracting profile, and to
focus a given wave front in a fixed point. These profiles are obtained as
envelopes of specific families of Cartesian ovals. We study the singularities
of these profiles and give a method to construct them from the data of the
associated caustic.Comment: 12 pages, 5 figure
Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron System
We determine the spin susceptibility in a two dimensional electron system in
GaAs/AlGaAs over a wide range of low densities from 2cm to
4cm. Our data can be fitted to an equation that describes
the density dependence as well as the polarization dependence of the spin
susceptibility. It can account for the anomalous g-factors reported recently in
GaAs electron and hole systems. The paramagnetic spin susceptibility increases
with decreasing density as expected from theoretical calculations.Comment: 5 pages, 2 eps figures, to appear in PR
Fermi edge singularity in neutral electron-hole system
In neutral dense electron-hole (e-h) systems at low temperatures, theory
predicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton
condensation. Optical excitation allows creating e-h systems with the densities
controlled by the excitation power. However, the intense optical excitations
required to achieve high densities cause substantial heating of the e-h system
that prevents the realization of dense and cold e-h systems in conventional
semiconductors. In this work, we study e-h systems created by optical
excitation in separated electron and hole layers. The layer separation
increases the e-h recombination time and, in turn, the density for a given
optical excitation by orders of magnitude and, as a result, enables the
realization of the dense and cold e-h system. We found a strong enhancement of
photoluminescence intensity at the Fermi energy of the neutral dense ultracold
e-h system that evidences the emergence of excitonic Fermi edge singularity due
to the Cooper-pair-like excitons at the Fermi energy
Multilocus sequence types of invasive Corynebacterium diphtheriae isolated in the Rio de Janeiro urban area, Brazil
Invasive infections caused by Corynebacterium diphtheriae in vaccinated and non-vaccinated individuals have been reported increasingly. In this study we used multilocus sequence typing (MLST) to study genetic relationships between six invasive strains of this bacterium isolated solely in the urban area of Rio de Janeiro, Brazil, during a 10-year period. Of note, all the strains rendered negative results in PCR reactions for the tox gene, and four strains presented an atypical sucrose-fermenting ability. Five strains represented new sequence types. MLST results did not support the hypothesis that invasive (sucrose-positive) strains of C. diphtheriae are part of a single clonal complex. Instead, one of the main findings of the study was that such strains can be normally found in clonal complexes with strains related to non-invasive disease. Comparative analyses with C. diphtheriae isolated in different countries provided further information on the geographical circulation of some sequence types
Wannier functions for quasi-periodic finite-gap potentials
In this paper we consider Wannier functions of quasi-periodic g-gap () potentials and investigate their main properties. In particular, we discuss
the problem of averaging underlying the definition of Wannier functions for
both periodic and quasi-periodic potentials and express Bloch functions and
quasi-momenta in terms of hyperelliptic functions. Using this approach
we derive a power series expansion of the Wannier function for quasi-periodic
potentials valid at and an asymptotic expansion valid at large
distance. These functions are important for a number of applied problems
Composite Fermion Wavefunctions Derived by Conformal Field Theory
The Jain theory of hierarchical Hall states is reconsidered in the light of
recent analyses that have found exact relations between projected Jain
wavefunctions and conformal field theory correlators. We show that the
underlying conformal theory is precisely given by the W-infinity minimal models
introduced earlier. This theory involves a reduction of the multicomponent
Abelian theory that is similar to the projection to the lowest Landau level in
the Jain approach. The projection yields quasihole excitations obeying
non-Abelian fractional statistics. The analysis closely parallels the bosonic
conformal theory description of the Pfaffian and Read-Rezayi states.Comment: 4 pages, 1 figur
Superposition in nonlinear wave and evolution equations
Real and bounded elliptic solutions suitable for applying the Khare-Sukhatme
superposition procedure are presented and used to generate superposition
solutions of the generalized modified Kadomtsev-Petviashvili equation (gmKPE)
and the nonlinear cubic-quintic Schroedinger equation (NLCQSE).Comment: submitted to International Journal of Theoretical Physics, 23 pages,
2 figures, style change
Nucleation phenomena in protein folding: The modulating role of protein sequence
For the vast majority of naturally occurring, small, single domain proteins
folding is often described as a two-state process that lacks detectable
intermediates. This observation has often been rationalized on the basis of a
nucleation mechanism for protein folding whose basic premise is the idea that
after completion of a specific set of contacts forming the so-called folding
nucleus the native state is achieved promptly. Here we propose a methodology to
identify folding nuclei in small lattice polymers and apply it to the study of
protein molecules with chain length N=48. To investigate the extent to which
protein topology is a robust determinant of the nucleation mechanism we compare
the nucleation scenario of a native-centric model with that of a sequence
specific model sharing the same native fold. To evaluate the impact of the
sequence's finner details in the nucleation mechanism we consider the folding
of two non- homologous sequences. We conclude that in a sequence-specific model
the folding nucleus is, to some extent, formed by the most stable contacts in
the protein and that the less stable linkages in the folding nucleus are solely
determined by the fold's topology. We have also found that independently of
protein sequence the folding nucleus performs the same `topological' function.
This unifying feature of the nucleation mechanism results from the residues
forming the folding nucleus being distributed along the protein chain in a
similar and well-defined manner that is determined by the fold's topological
features.Comment: 10 Figures. J. Physics: Condensed Matter (to appear
- …