1,653 research outputs found
Reprocessing of CHP datasets (HI 1567 & 1570) and seafloor substrate interpretation for selected areas : Inner Sound off Skye on the west coast of Scotland
This report describes the methodology for the processing of multibeam echosounder
bathymetry, production of multibeam echosounder layers (bathymetry, hillshade, slope, aspect
and rugosity) for display and interpretative purposes. Furthermore, an overview of the sea-bed
substrate interpretation undertaken by the British Geological Survey (BGS) for three selected
areas within Inner Sound off Skye on the west coast of Scotland is provided
A migrant study of pubertal timing and tempo in British-Bangladeshi girls at varying risk for breast cancer
Introduction: Earlier menarche is related to subsequent breast cancer risk, yet international differences in the age and tempo of other pubertal milestones and their relationships with body mass index (BMI) are not firmly established in populations at differing risk for breast cancer. We compared age and tempo of adrenarche, thelarche, pubarche, and menarche in a migrant study of Bangladeshi girls to the United Kingdom (UK) and assessed whether differences by migration were explained by differences in BMI. Methods: Included were groups of Bangladeshi (n =168, British-Bangladeshi (n =174) and white British (n =54) girls, aged 5 to 16 years. Interviewer-administered questionnaires obtained pubertal staging; height and weight were measured. Salivary dehydroepiandrosterone-sulfate concentrations >400 pg/ml defined adrenarche. Median ages of pubertal milestones and hazard ratios (HR) with 95% confidence intervals (CI) were estimated from Weibull survival models. Results: In all three groups, adrenarche occurred earliest, followed by thelarche, pubarche, and finally menarche. Neither median age at adrenarche (Bangladeshi = 7.2, British-Bangladeshi = 7.4, white British = 7.1; P-trend = 0.70) nor at menarche (Bangladeshi = 12.5, BritishBangladeshi = 12.1, white British = 12.6; P-trend = 0.70) differed across groups. In contrast, median age at thelarche (Bangladeshi = 10.7, British-Bangladeshi = 9.6, white British = 8.7; P-trend <0.01) occurred earlier among girls living in the UK. Compared with Bangladeshi girls, HRs (95% CI) for earlier thelarche were 1.6 (1.1 to 2.4) for British-Bangladeshi girls and 2.6 (1.5 to 4.4) for white British girls (P-trend <0.01), but were attenuated after adjustment for BMI (British-Bangladeshi = 1.1 (0.7 to 1.8), white British = 1.7(1.0 to 3.1); Ptrend =0.20). Conclusions: Thelarche occurred earlier, but puberty progressed slower with increasing exposure to the UK environment; differences were partially explained by greater BMI. The growth-environment might account for much of the ethnic differences in pubertal development observed across and within countries
Seabed characterization: developing fit for purpose methodologies
We briefly describe three methods of seabed characterization which are âfit for purposeâ, in
that each approach is well suited to distinct objectives e.g. characterizing glacial
geomorphology and shallow glacial geology vs. rapid prediction of seabed sediment
distribution via geostatistics. The methods vary from manual âexpertâ interpretation to
increasingly automated and mathematically based models, each with their own attributes
and limitations. We would note however that increasing automation and mathematical
sophistication does not necessarily equate to improve map outputs, or reduce the time
required to produce them. Judgements must be made to select methodologies which are
most appropriate to the variables mapped, and according to the extent and presentation
scale of final maps
Anomalous Pseudoscalar-Photon Vertex In and Out of Equilibrium
The anomalous pseudoscalar-photon vertex is studied in real time in and out
of equilibrium in a constituent quark model. The goal is to understand the
in-medium modifications of this vertex, exploring the possibility of enhanced
isospin breaking by electromagnetic effects as well as the formation of neutral
pion condensates in a rapid chiral phase transition in peripheral,
ultrarelativistic heavy-ion collisions. In equilibrium the effective vertex is
afflicted by infrared and collinear singularities that require hard thermal
loop (HTL) and width corrections of the quark propagator. The resummed
effective equilibrium vertex vanishes near the chiral transition in the chiral
limit. In a strongly out of equilibrium chiral phase transition we find that
the chiral condensate drastically modifies the quark propagators and the
effective vertex. The ensuing dynamics for the neutral pion results in a
potential enhancement of isospin breaking and the formation of
condensates. While the anomaly equation and the axial Ward identity are not
modified by the medium in or out of equilibrium, the effective real-time
pseudoscalar-photon vertex is sensitive to low energy physics.Comment: Revised version to appear in Phys. Rev. D. 42 pages, 4 figures, uses
Revte
The Effects of Disorder on the Quantum Hall State
A disorder-averaged Hartree-Fock treatment is used to compute the density of
single particle states for quantum Hall systems at filling factor . It
is found that transport and spin polarization experiments can be simultaneously
explained by a model of mostly short-range effective disorder. The slope of the
transport gap (due to quasiparticles) in parallel field emerges as a result of
the interplay between disorder-induced broadening and exchange, and has
implications for skyrmion localization.Comment: 4 pages, 3 eps figure
Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states
An operator formalism is developed for a description of charged electron-hole
complexes in magnetic fields. A novel unitary transformation of the Hamiltonian
that allows one to partially separate the center-of-mass and internal motions
is proposed. We study the operator algebra that leads to the appearance of new
effective particles, electrons and holes with modified interparticle
interactions, and their coherent states in magnetic fields. The developed
formalism is used for studying a two-dimensional negatively charged
magnetoexciton . It is shown that Fano-resonances are present in the
spectra of internal transitions, indicating the existence of
three-particle quasi-bound states embedded in the continuum of higher Landau
levels.Comment: 9 pages + 2 figures, accepted in PRB, a couple of typos correcte
Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter
We apply the closed-time path integral formalism to study the medium effects
of non-equilibrium gluon matter. We derive the medium modified resummed gluon
propagator to the one loop level in non-equilibrium in the covariant gauge. The
gluon propagator we derive can be used to remove the infrared divergences in
the secondary parton collisions to study thermalization of minijet parton
plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification,
reference adde
Thinking about growth : a cognitive mapping approach to understanding small business development
School of Managemen
Shake-up Processes in a Low-Density Two-Dimensional Electron Gas: Spin-Dependent Transitions to Higher Hole Landau Levels
A theory of shake-up processes in photoabsorption of an interacting
low-density two-dimensional electron gas (2DEG) in strong magnetic fields is
presented. In these processes, an incident photon creates an electron-hole pair
and, because of Coulomb interactions, simultaneously excites one particle to
higher Landau levels (LL's). In this work, the spectra of correlated charged
spin-singlet and spin-triplet electron-hole states in the first hole LL and
optical transitions to these states (i.e., shake-ups to the first hole LL) are
studied. Our results indicate, in particular, the presence of optically-active
three-particle quasi-discrete states in the exciton continuum that may give
rise to surprisingly sharp Fano resonances in strong magnetic fields. The
relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole
gas (2DHG), and shake-ups of isolated negative X^- and positive X^+ trions are
discussed.Comment: 8 pages, 8 figures. References updated, one figure added (Fig. 6).
Accepted in Phys. Rev.
Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations
The infrared behaviour of the medium modified gluon propagator in
non-equilibrium situations is studied in the covariant gauge using the
Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic
screening mass is non-zero at the one loop level whenever the initial gluon
distribution function is non isotropic with the assumption that the
distribution function of the gluon is not divergent at zero transverse
momentum. For isotropic gluon distribution functions, such as those describing
local equilibrium, the magnetic mass at one loop level is zero which is
consistent with finite temperature field theory results. Assuming that a
reasonable initial gluon distribution function can be obtained from a
perturbative QCD calculation of minijets, we determine these out of equilibrium
values for the initial magnetic and Debye screening masses at energy densities
appropriate to RHIC and LHC. We also compare the magnetic masses obtained here
with those obtained using finite temperature lattice QCD methods at similar
temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys.
Rev.
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