5,596 research outputs found
Electronic structure and Fermi surface tolopogy of NaCoO
We construct an effective Hamiltonian for the motion of T2g highly correlated
states in NaxCoO2. We solve exactly a multiband model in a CoO6 cluster with
electronic occupation corresponding to a nominal Co valence of either +3 or +4.
Using the ensuing ground states, we calculate the effective O mediated hopping
t=0.10 eV between many-body T2g states, and estimate the direct hopping t'~0.04
eV. The trigonal splitting 3D=0.315 eV is taken from recent quantum chemistry
calculations. The resulting effective Hamiltonian is solved using a generalized
slave-boson mean-field approximation. The results show a significant band
renormalization and a Fermi surface topology that agrees with experiment, in
contrast to predictions using the local-density approximation.Comment: 4 pages, 2 figure
An exact sequence for contact- and symplectic homology
A symplectic manifold with contact type boundary induces
a linearization of the contact homology of with corresponding linearized
contact homology . We establish a Gysin-type exact sequence in which the
symplectic homology of maps to , which in turn maps to
, by a map of degree -2, which then maps to . Furthermore, we
give a description of the degree -2 map in terms of rational holomorphic curves
with constrained asymptotic markers, in the symplectization of .Comment: Final version. Changes for v2: Proof of main theorem supplemented
with detailed discussion of continuation maps. Description of degree -2 map
rewritten with emphasis on asymptotic markers. Sec. 5.2 rewritten with
emphasis on 0-dim. moduli spaces. Transversality discussion reorganized for
clarity (now Remark 9). Various other minor modification
NUMERICAL MIXING PLANE STUDIES WITH VALIDATION FOR AERO-ENGINE CENTRIFUGAL COMPRESSOR DESIGN
The unsteady high-speed flow in centrifugal compressor stages tests current limitations of modeling techniques due to high degrees of curvature, adverse pressure gradients, and three-dimensional turbulent boundary layers. The current study presents experimental and numerical validation studies of predictions for a centrifugal compressor stage with a tandem impeller and fish-tail discrete passage diffuser using the mixing plane approach presently used for the design of these stages. Assessments are made of predictions with a more accurate geometry representation than has been modeled previously and with a number of turbulence closure models including the k — e, SST, SST-RM, and RSM-SSG models. Comparison with measured performance parameters seems to indicate better predictions by the RSM-SSG and SST models. For further validation of the numerical modeling, the latest results of a laser Doppler velocimetry study are presented and compared to numerical predictions, yielding good agreement at stage inlet and exit
The Management of Performance Anxiety with Beta-Adrenergic Blocking Agents
Performance anxiety consists of several symptoms experienced in the context of public performance and is classified in DSM-III-R under social phobia. Performance anxiety must be distinguished from panic disorder, generalized social phobia, and generalized anxiety disorder. Performance anxiety symptoms can be detrimental to both performer and performance. These symptoms can be controlled by the judicious use of beta-adrenergic blocking agents. The use of beta-adrenergic blocking agents should be considered as part of a psychiatric stress-management program for these patients
Le rôle des facteurs institutionnels dans la décision d’externaliser
Notre étude démontre le rôle de facteurs institutionnels dans le recours à l\u27externalisation. Pour ce faire, nous exploitons les principes développés par les auteurs néo-institutionnels. Une étude empirique a été menée auprès d\u27organisations évoluant dans le secteur de la métallurgie. Les résultats obtenus mettent en évidence que l\u27environnement institutionnel conditionne les dirigeants dans la décision d\u27externaliser une activité et que ce choix est déterminé par un phénomène de mimétisme. Si la logique économique caractérise la décision d\u27exter-naliser, nous ne pouvons pas rejeter complè-tement qu\u27elle relève d\u27une logique non économique. La recherche de légitimité, autre principe néo-institutionnel, est moins clairement établie
The "exterior approach" applied to the inverse obstacle problem for the heat equation
International audienceIn this paper we consider the " exterior approach " to solve the inverse obstacle problem for the heat equation. This iterated approach is based on a quasi-reversibility method to compute the solution from the Cauchy data while a simple level set method is used to characterize the obstacle. We present several mixed formulations of quasi-reversibility that enable us to use some classical conforming finite elements. Among these, an iterated formulation that takes the noisy Cauchy data into account in a weak way is selected to serve in some numerical experiments and show the feasibility of our strategy of identification. 1. Introduction. This paper deals with the inverse obstacle problem for the heat equation, which can be described as follows. We consider a bounded domain D ⊂ R d , d ≥ 2, which contains an inclusion O. The temperature in the complementary domain Ω = D \ O satisfies the heat equation while the inclusion is characterized by a zero temperature. The inverse problem consists, from the knowledge of the lateral Cauchy data (that is both the temperature and the heat flux) on a subpart of the boundary ∂D during a certain interval of time (0, T) such that the temperature at time t = 0 is 0 in Ω, to identify the inclusion O. Such kind of inverse problem arises in thermal imaging, as briefly described in the introduction of [9]. The first attempts to solve such kind of problem numerically go back to the late 80's, as illustrated by [1], in which a least square method based on a shape derivative technique is used and numerical applications in 2D are presented. A shape derivative technique is also used in [11] in a 2D case as well, but the least square method is replaced by a Newton type method. Lastly, the shape derivative together with the least square method have recently been used in 3D cases [18]. The main feature of all these contributions is that they rely on the computation of forward problems in the domain Ω × (0, T): this computation obliges the authors to know one of the two lateral Cauchy data (either the temperature or the heat flux) on the whole boundary ∂D of D. In [20], the authors introduce the so-called " enclosure method " , which enables them to recover an approximation of the convex hull of the inclusion without computing any forward problem. Note however that the lateral Cauchy data has to be known on the whole boundary ∂D. The present paper concerns the " exterior approach " , which is an alternative method to solve the inverse obstacle problem. Like in [20], it does not need to compute the solution of the forward problem and in addition, it is applicable even if the lateral Cauchy data are known only on a subpart of ∂D, while no data are given on the complementary part. The " exterior approach " consists in defining a sequence of domains that converges in a certain sense to the inclusion we are looking for. More precisely, the nth step consists, 1. for a given inclusion O n , in approximating the temperature in Ω n × (0, T) (Ω n := D \ O n) with the help of a quasi-reversibility method, 2. for a given temperature in Ω n × (0, T), in computing an updated inclusion O n+1 with the help of a level set method. Such " exterior approach " has already been successfully used to solve inverse obstacle problems for the Laplace equation [5, 4, 15] and for the Stokes system [6]. It has also been used for the heat equation in the 1D case [2]: the problem in this simple case might be considered as a toy problem since the inclusion reduces to a point in some bounded interval. The objective of the present paper is to extend the " exterior approach " for the heat equation to any dimension of space, with numerical applications in the 2D case. Let us shed some light on the two steps o
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