Instabilités de calibration de phase

In very long baseline interferometry, the image reconstruction procedures are very sensitive to the potential instabilities of the phase calibration operation. The analysis presented in this Note reveals that these instabilities are due to the existence of secondary minima (more or less critical) of the phase calibration objective functional. By resolving the corresponding integer ambiguity problems in an appropriate manner, these minima can be explicitly identified and compared. The stability of the self-calibration procedures can thus be easily controlled. To cite this article: A. Lannes, C. R. Physique 4 (2003).     

BEPC de前前后后

 80年代是我国高能物理事业的一个转折点.BEPC按计划高质量地完成,为我国高能物理实验研究提供了一个极其重要的手段;也表明我国的加速器事业已在世界高技术领域中占有了一席之地.BEPC的成就凝聚着几代人的心血.早在1957年,在王淦昌教授的领导下。选派了一批年青的科学家,赴苏学习高能加速器的设计及建造.一年后,在苏联专家的指导下,进行1-2GeV电子同步加速器的设计,这一设计在1958年的大跃进中被认为是保守落后的,而把方案改成15GeV的质子同步加速器.     

Procédure rapide de choix de réseaux d'échangeurs de chaleur

A fast calculation of a reasonable solution for the choice of a heat exchanger network able to make some imposed cooling and warming up tasks, with the use of auxiliary utilities, is developed in this article.This problem boils down to the internal heat exchanger network choice with respect to a constraint limiting the exchange area, maximizing the heat recovery and minimizing the number of stream matching.These internal matches are made one by one with respect to the tasks to be effected at each step. Amongst the possible matches, we have retained the privilegied ones, ie matches saturating a maximum number of constraints. Some procedures are implemented so as to choose among this set of privilegied matches.The illustration with some literature problems shows that an algorithm made up with these procedures carries out a good compromise between the quality of the obtained solution and the computer time.     

BEPC de前前后后

80年代是我国高能物理事业的一个转折点.BEPC按计划高质量地完成,为我国高能物理实验研究提供了一个极其重要的手段;也表明我国的加速器事业已在世界高技术领域中占有了一席之地.BEPC的成就凝聚着几代人的心血.早在1957年,在王淦昌教授的领导下。选派了一批年青的科学家,赴苏学习高能加速器的设计及建造.一年后,在苏联专家的指导下,进行1—2GeV电子同步加速器的设计,这一设计在1958年的大跃进中被认为是保守落后的,而把方案改成15GeV的质子同步加速器.但当时苏联正在建造的加速器最高能量为7GeV,所以这一建议受到了苏联专家的“冷遇”,回答是:如果中方要建造,唯     

Contrôle thermique de parois de chambre de combustion. Banc d'essai du laboratoire aquitain de recherche en aérothermique

Thermal control of combustion chamber walls. LARA's test bench. Convective heat transfer along the wall of a combustion chamber is a major source of concern for a gas turbine engine manufacturer like Turboméca. This topic led to a joint research project with the University of Pau : to this end, a specific test bench with up-to-date means of measurement (IR thermography, laser doppler velocimetry) was created. An initial literature study had shown that multi-hole cooling had not been previously studied with a geometry design close to the real case. The present test facility provides and controls the dynamic and thermal parameters of a combustion chamber and the multi-hole cooling was set up on a flat plate simulating the wall chamber. This plate is submitted on one side to the hot gases resulting from combustion and on the other side to the cooling air flow. Dynamic and thermal entry conditions of the hot and cold flows were carefully controlled and are now presented. The wide possibilities of the testing facility have been explored offering scopes for other experimental studies.     

Effet de condensation lors de l'étalement d'un liquide

The spreading of liquid drops on solids is generally explained by two classes of models: the molecular kinetic approach and the hydrodynamic approach. We propose another approach, complementary to the former, in which condensation of the liquid vapour near the triple line plays a role in spreading.     

Développement de lasers visibles pompés par diode à base de cristaux de Nd:GdCOB autodoubleurs de fréquence

We present the performances of a diode-pumped solid-state laser operating in the visible by self-frequency-doubling. A cw output power of 115 mW at 545 nm has been obtained in a stable concave–concave cavity by using a crystal of Nd:GdCa₄O(BO₃)₃ pumped by a 2 W high-brightness laser diode. In a plano–plano cavity, similar to a microchip laser, we have obtained, for the first time to our knowledge, an output power of 22 mW in the green.     

Mesure de la diffusivité longitudinale de matériaux anisotropes

Measurement of in-plane diffusivity of anisotropic solid samples. Survey of the techniques developed at LEMTA. Three techniques for the measurement of in-plane diffusivity of anisotropic solid samples have been developed at the Laboratory and are presented here :

• •the two directional heat pulse (flash) method with local contact measurement of two temperatures;
• •the fin method with local contact or contactless measurement of two temperatures;
• •the two directional heat pulse method with measurement of the temperature field by an infrared camera and data processing through integral transformations.

     

Quelques nouvelles propriétés de régularité de l'opérateur de Gribov

In this work, we establish new regularity properties for Gribov's operator:H=A ^* A ₊ iA ^*(A+A ^*)A;(,)², whereA ^* andA are the creation and annihilation operators. Particularly, we prove that for all >0,H ^–1 is in the class of Carleman's operatorl ₁₊.     

带弦de夸克

 一、一个佯谬夸克模型不仅清楚地解释了SU₃对称性,而且还能借助SU₆对称性理论,成功地说明强子的各种自旋态.在这里,夸克好像弱束缚在强子里似的.显然,这是一个佯谬,因为从来就没见过夸克从强子中被打出来过.根据夸克模型,人们总想了解强子其它重要的特性,为此,必须在模型里加上一些新假设.一般说来,强子碰撞产生弹性散射,同时产生几种强子.由于接连碰撞,反应截面随能量迅速发生变化,从而表现出共振态存在,或强子激发态存在.     

Identification du coefficient de transfert thermique sur la surface externe d'un échangeur de chaleur à tubes et ailettes planes en fonction de l'humidité de l'air,en l'absence de condensation

The following study, which is rather oriented towards experimentation, shows the influence of the humidity content of air on heat transfer. This first article concerns heat transfer between the external fluid (moist air) and the internal fluid (water containing glycol, whose thermal behavior inside circular tubes is well-known) in a heat exchanger of the same type as those used in automotive air conditioning (horizontal copper tubes and plane aluminium fins), in the absence of condensation. The most difficult part of this experimental work is the measurement and control of the air humidity, since one has to make sure that the measurement incertainties are not significant compared to the precision of the calculation of the heat transfer coefficient. The conclusion is that, for this type of exchanger, the heat transfer coefficient decreases with air humidity in the absence of condensation (dry wall). Some correlations have been developed with respect to the relative air humidity. An analog experimental investigation, but this time carried out in the presence of condensation (partially or completely wetted wall), is about to be completed; the obtained results will be communicated later on.     

Formules de Rayleigh-Schrödinger et transformations de contact pour le problème vibrationnel de CO2

L'hamiltonien vibrationnel de la molécule CO₂ est donné dans la littérature [3, 4]; ses paramètres (constantes du potentiel) ont été déterminés en calculant les valeurs propres par le formalisme des transformations de contact. Nous avons calculé les fonctions propres de cet hamiltonien à l'aide d'un autre formalisme de la théorie des perturbations, le formalisme habituel de Rayleigh-Schrödinger et nous avons établi le lien entre les deux formalismes en calculant les énergies associées à ces fonctions d'onde perturbées. Nous avons montré littéralement et vérifié numériquement que, pour les niveaux non résonnants, les fonctions calculées, jusqu'à l'ordre deux, par les formules de Rayleigh-Schrödinger, permettent d'obtenir des énergies jusqu'au quatrième ordre, identiques à celles obtenues par les deux transformations de contact utilisées pour déterminer les paramètres de l'hamiltonien. Dans le cas de niveaux résonants, cette identification n'est plus possible et nous avons étudié numériquement les différences entre les deux formalismes en calculant, jusqu'au quatrième ordre, les énergies des niveaux d'une triade de Fermi pour différents choix possibles des fonctions d'onde perturbées.

L'ensemble des résultats permet de comprendre pourquoi le calcul des valeurs propres de l'hamiltonien vibrationnel de CO₂, par une méthode autre que celle utilisée pour déterminer ses paramètres, peut conduire à des énergies calculées éloignées des énergies observées.     

Determination de bases de gaussiennes optimales pour les molécules

On montre que l'optimisation des exposants et des paramètres géométriques a une grande importance. En particulier la barrière de rotation de CH₃OH (exp. 1,07 kcal/mole) passe, par optimisation complète en restant dans le cadre du modèle à particules indépendantes de 2,2 kcal/mole à la valeur remarquable de 1,078 kcal/mole.