2,445 research outputs found
Skylab investigation of the upwelling off the Northwest coast of Africa
The upwelling off the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer in quantifying surface chlorophyll concentrations. Photographic images of the S190A Multispectral Camera and the S190B Earth Terrain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192 Multispectral Scanner was used to map sea-surface temperature distributions offshore of Cape Blanc. Correlating ocean color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the upwelling region off Africa
Transport in Almost Integrable Models: Perturbed Heisenberg Chains
The heat conductivity kappa(T) of integrable models, like the one-dimensional
spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite
temperatures as a consequence of the conservation laws associated with
integrability. Small perturbations lead to finite but large transport
coefficients which we calculate perturbatively using exact diagonalization and
moment expansions. We show that there are two different classes of
perturbations. While an interchain coupling of strength J_perp leads to
kappa(T) propto 1/J_perp^2 as expected from simple golden-rule arguments, we
obtain a much larger kappa(T) propto 1/J'^4 for a weak next-nearest neighbor
interaction J'. This can be explained by a new approximate conservation law of
the J-J' Heisenberg chain.Comment: 4 pages, several minor modifications, title change
Mental health in higher education students and non-students: evidence from a nationally representative panel study
Despite increasing policy focus on mental health provision for higher education students, it is unclear whether they have worse mental health outcomes than their non-student peers. In a nationally-representative UK study spanning 2010-2019 (N = 11,519), 17-24 year olds who attended higher education had lower average psychological distress (GHQ score difference = - 0.37, 95% CI - 0.60, - 0.08) and lower odds of case-level distress than those who did not (OR = 0.91, 95% CI 0.81, 1.02). Increases in distress between 2010 and 2019 were similar in both groups. Accessible mental health support outside higher education settings is necessary to prevent further widening of socioeconomic inequalities in mental health
Variation of the glass transition temperature with rigidity and chemical composition
The effects of flexibility and chemical composition in the variation of the
glass transition temperature are obtained by using the Lindemann criteria, that
relates melting temperature with atomic vibrations. Using this criteria and
that floppy modes at low frequencies enhance in a considerable way the average
cuadratic displacement, we show that the consequence is a modified glass
transition temperature. This approach allows to obtain in a simple way the
empirically modified Gibbs-DiMarzio law, which has been widely used in
chalcogenide glasses to fit the changes in the glass transition temperature
with the chemical composition . The method predicts that the constant that
appears in the law depends upon the ratio of two characteristic frequencies (or
temperatures). Then, the constant for the Se-Ge-As glass is estimated by using
the experimental density of vibrational states, and the result shows a very
good agreement with the experimental fit from glass transition temperature
variation
The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity
We analyze a detailed model of a Bose-Einstein condensate trapped in a ring
optical resonator and contrast its classical and quantum properties to those of
a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light
fields and three matter field modes leads to important differences between the
two situations. Specifically, we identify an experimentally realizable region
where the system's behavior differs strongly from that of a BEC in a
Fabry-P\'{e}rot cavity, and also where quantum corrections become significant.
The classical dynamics are rich, and near bifurcation points in the mean-field
classical system, the quantum fluctuations have a major impact on the system's
dynamics.Comment: 11 pages, 11 figures, submitted to PR
Energy landscape and rigidity
The effects of floppy modes in the thermodynamical properties of a system are
studied. From thermodynamical arguments, we deduce that floppy modes are not at
zero frequency and thus a modified Debye model is used to take into account
this effect. The model predicts a deviation from the Debye law at low
temperatures. Then, the connection between the topography of the energy
landscape, the topology of the phase space and the rigidity of a glass is
explored. As a result, we relate the number of constraints and floppy modes
with the statistics of the landscape. We apply these ideas to a simple model
for which we provide an approximate expression for the number of energy basins
as a function of the rigidity. This allows to understand certains features of
the glass transition, like the jump in the specific heat or the reversible
window observed in chalcogenide glasses.Comment: 1 text+3 eps figure
A new web-based genomics resource for bioinformatics analysis of Rhipicephalus (Boophilus) microplus: CattleTickBase
No abstract availabl
On vacuum gravitational collapse in nine dimensions
We consider the vacuum gravitational collapse for cohomogeneity-two solutions
of the nine dimensional Einstein equations. Using combined numerical and
analytical methods we give evidence that within this model the
Schwarzschild-Tangherlini black hole is asymptotically stable. In addition, we
briefly discuss the critical behavior at the threshold of black hole formation.Comment: 4 pages, 4 figure
A Method for Evaluating Local Scour Depth at Bridge Piers due to Debris Accumulation
This is the author accepted manuscript. The final version is available from Thomas Telford via the DOI in this record This paper introduces a novel method for evaluating the effect of debris accumulation on local scour depth at bridge piers. The concept of a debris factor is proposed to replace the current effective and equivalent pier width approaches that have been shown to overestimate debris-induced scour in many instances. The concept enables a simpler, more direct and realistic estimation of the change in local scour depth due to debris since it accounts for (i) debris length (streamwise), width (spanwise) and thickness (depth wise), and (ii) the influence of debris elevation in flow, i.e. is applicable for free-surface debris, submerged debris, or debris resting on the stream bed. The concept works with all existing local scour equations alongside other factors that influence scour depth such as flow angle of attack and pier shape. The mathematical model that underpins the proposed concept is derived through multiple linear regression on experimental data obtained at Exeter and elsewhere. The proposed method is shown to improve accuracy by at least 24% and 5% in comparison to the effective and equivalent pier width approaches, respectively. More importantly, the method is shown to be robust, providing highly consistent results with significantly less uncertainty.Engineering and Physical Sciences Research Council (EPSRC
- …