559 research outputs found
A review of data on abundance, trends in abundance, habitat use and diet of ice-breeding seals in the Southern Ocean
The development of models of marine ecosystems in the Southern Ocean is becoming increasingly important as a means of understanding and managing impacts such as exploitation and climate change. Collating data from disparate sources, and understanding biases or uncertainties inherent in those data, are important first steps for improving ecosystem models. This review focuses on seals that breed in ice habitats of the Southern Ocean (i.e. crabeater seal, Lobodon carcinophaga; Ross seal, Ommatophoca rossii; leopard seal, Hydrurga leptonyx; and Weddell seal, Leptonychotes weddellii). Data on populations (abundance and trends in abundance), distribution and habitat use (movement, key habitat and environmental features) and foraging (diet) are summarised, and potential biases and uncertainties inherent in those data are identified and discussed. Spatial and temporal gaps in knowledge of the populations, habitats and diet of each species are also identified
Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study
The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with
unique properties for future applications. Band structure calculations predict
exclusively majority bands at the Fermi level, thus indicating {100%} spin
polarization there. As one thinks about applications and the design of
functional materials, the influence of chemical disorder in these materials
must be considered. The magnetization, spin polarization, and electronic
structure are expected to be sensitive to structural and stoichiometric
changes. In this contribution, we report on an investigation of the
spin-dependent electronic structure of NiMnSb. We studied the influence of
chemical disorder on the unoccupied electronic density of states by use of the
ab-initio Coherent Potential Approximation method. The theoretical analysis is
discussed along with corresponding spin-resolved Appearance Potential
Spectroscopy measurements. Our theoretical approach describes the spectra as
the fully-relativistic self-convolution of the matrix-element weighted,
orbitally resolved density of states.Comment: JPD submitte
Statistics and Nos\'e formalism for Ehrenfest dynamics
Quantum dynamics (i.e., the Schr\"odinger equation) and classical dynamics
(i.e., Hamilton equations) can both be formulated in equal geometric terms: a
Poisson bracket defined on a manifold. In this paper we first show that the
hybrid quantum-classical dynamics prescribed by the Ehrenfest equations can
also be formulated within this general framework, what has been used in the
literature to construct propagation schemes for Ehrenfest dynamics. Then, the
existence of a well defined Poisson bracket allows to arrive to a Liouville
equation for a statistical ensemble of Ehrenfest systems. The study of a
generic toy model shows that the evolution produced by Ehrenfest dynamics is
ergodic and therefore the only constants of motion are functions of the
Hamiltonian. The emergence of the canonical ensemble characterized by the
Boltzmann distribution follows after an appropriate application of the
principle of equal a priori probabilities to this case. Once we know the
canonical distribution of a Ehrenfest system, it is straightforward to extend
the formalism of Nos\'e (invented to do constant temperature Molecular Dynamics
by a non-stochastic method) to our Ehrenfest formalism. This work also provides
the basis for extending stochastic methods to Ehrenfest dynamics.Comment: 28 pages, 1 figure. Published version. arXiv admin note: substantial
text overlap with arXiv:1010.149
Eliashberg-type equations for correlated superconductors
The derivation of the Eliashberg -- type equations for a superconductor with
strong correlations and electron--phonon interaction has been presented. The
proper account of short range Coulomb interactions results in a strongly
anisotropic equations. Possible symmetries of the order parameter include s, p
and d wave. We found the carrier concentration dependence of the coupling
constants corresponding to these symmetries. At low hole doping the d-wave
component is the largest one.Comment: RevTeX, 18 pages, 5 ps figures added at the end of source file, to be
published in Phys.Rev. B, contact: [email protected]
Late Maastrichtian carbon isotope stratigraphy and cyclostratigraphy of the Newfoundland Margin (Site U1403, IODP Expedition 342)
Earth’s climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma4051 to Ma4057) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4‰) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a ~ 1 Myr period in the late Maastrichtian (67.8–66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change
Born-Oppenheimer Approximation near Level Crossing
We consider the Born-Oppenheimer problem near conical intersection in two
dimensions. For energies close to the crossing energy we describe the wave
function near an isotropic crossing and show that it is related to generalized
hypergeometric functions 0F3. This function is to a conical intersection what
the Airy function is to a classical turning point. As an application we
calculate the anomalous Zeeman shift of vibrational levels near a crossing.Comment: 8 pages, 1 figure, Lette
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
The main concerns of European anaesthesiology postgraduate trainees: A European survey
This is the first study intended to identify the European anaesthesiology trainees' main concerns, to initiate a process of improvement of the training in anaesthesiology by the European Society of Anaesthesiology (ESA). The authors developed an electronic survey which addressed seven different concerns: autonomy transition, technical skills, exchange programs, residency costs, residency workload, employment prospects and educational contents/preparation for the European Diploma in Anaesthesiology and Intensive Care (EDAIC). The survey was disseminated by email to all anaesthesiology trainees registered in ESA and all European National Societies were asked to distribute the survey to their graduating trainees. 665 trainees initiated the survey with a completion rate of 54.6%. The trainees' main concerns were in descending order: educational contents, residency costs, employment prospects, residency workload, exchange programs, technical skills and autonomy transition. This report analyzes the three main concerns in more detail. 68% of respondents were unaware of the existence of the ESA e-learning platform. Other means to improve the preparation for the EDAIC such as a multiple-choice questions book should be developed. The main reason for not becoming an ESA Trainee member was the associated cost and 68% of respondents gave up activities or opportunities during their residency due to economic constraints; 56% of respondents considered emigrating for economic reasons and 28% elected Northern/Central Europe. The results of the present survey may provide additional background information for the development of specific improvements in strategies for training in anaesthesiology. (c) 2018 Elsevier Ltd. All rights reserved
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