Mott transition and transport crossovers in the organic compound kappa-(BEDT-TTF)2Cu[N(CN)2]Cl

We have performed in-plane transport measurements on the two-dimensional organic salt kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl. A variable (gas) pressure technique allows for a detailed study of the changes in conductivity through the insulator-to-metal transition. We identify four different transport regimes as a function of pressure and temperature (corresponding to insulating, semiconducting, "bad metal," and strongly correlated Fermi-liquid behaviors). Marked hysteresis is found in the transition region, which displays complex physics that we attribute to strong spatial inhomogeneities. Away from the critical region, good agreement is found with a dynamical mean-field calculation of transport properties using the numerical renormalization group technique.     

Density functional theoretical study of Cun, Aln (n = 4-31) and copper doped aluminum clusters: Electronic properties and reactivity with atomic oxygen

A DFT study of the electronic properties of copper doped aluminum clusters and their reactivity with atomic oxygen is reported. Firstly we performed calculations for the pure Cu_n and Al_n (n = 4, 9, 10, 13, 25 and 31) clusters and we determined their atomization energy for some frozen conformations at the B3PW91 level. The calculated work functions and M-M (M = Cu, Al) bond energies of the largest clusters are comparable with experimental data. Secondly, we focused our attention on the change of the electronic properties of the systems upon the substitution of an Al atom by a Cu one. This latter stabilizes the system as the atomization energy of the 31-atoms cluster increases of 0.31 eV when the substitution is done on the surface and of 1.18 eV when it is done inside the cluster. We show that the electronic transfer from the Al cluster to the Cu atom located at the surface is large (equal to 0.7 e⁻) while it is negligible when Cu is inserted in the Al_n cluster. Moreover, the DOS of the Al₃₁ and Al₃₀Cu systems are compared. Finally, the chemisorption energies of atomic oxygen in threefold sites of the Al₃₁, Cu₃₁ and Al₃₀Cu clusters are calculated and discussed. We show that the chemisorption energy of O is decreasing on the bimetallic systems compared to the pure aluminum cluster.     

Détection d’un signal certain dans un bruit sphériquement invariant,structure et caractéristiques des récepteurs

In a previous paper (published inAnnales des télécommunications, Fr. (nov.–déc. 1970),25, n° 11–12, pp. 433–439) we have presented the optimal receiver for the detection of a deterministic signal in a spherically invariant noise and pointed out an asymptotic structure of this receiver which is independent of the a priori distribution of the noise. We study here the structure and properties of this optimal receiver by comparison with others systems presented to solve the same problem. In particular we introduce an optimal receiver in the class of constant false alarm probability receivers which is very interesting for applications and is designed with matched filter and automatic gain control (AGC). We notice that these two receivers give the same output signal to noise ratio and cannot be distinguished by means of this criterion. The comparison is achieved by computing the receiver operating curves which show clearly the optimal properties of the asymptotic receiver; but the second one, which is much simpler to design, has in some cases very similar properties. We give an interpretation of this result.     

Au delà d’une vitesse de groupe: vitesse d’onde et vitesse de signal

A radiated field always appears in a dual, spatial and temporal, aspect. Its spatial one is the wave the author would observe at a given time. Its temporal one is the signal he receives at a given point. The aim of this paper is then to determine bulk velocities of both signal and wave — without any limiting assumption on their spectral widths — in case the field is being radiated thru a dispersive medium. A realistic criterion is first adopted that enables an accurate measurement of the instant position of the wave, by means of a definite space-marker (the wave center,). The same criterion also leads to a similar time-marker (the signal center,) that will be used in measuring the receiving time of the signal. By studying the motion of these markers an operator U spontaneously appears beside the phase velocity. This operator has the same analytical expression as the usual group/signal velocity of a wave packet. Therefore U should be also called group velocity. Both group and phase velocities depend on the transmitting medium only. To the travelling wave then corresponds an uniform motion of its wave center, with some wave velocity. The latter consists of the mean of operator U in a state which is associated with the wave structure at the time origin. To the signal, when received by a fixed transductor, also corresponds some signal velocity. Its value is the inverse of the mean of operator U^?1 in a state which is associated with the signal structure at the transmitter. Thus, wave velocity and signal velocity not only depend on the transmitting medium, but depend on the emitted signal form too. However both of them become identified with the group velocity U in the particular case of a very narrow spectrum. Thus agreeing with the usual wave packet. In such a case the group velocity turns out to be the velocity of the very marker that belongs to the amplitude of the transmitted analytic signal. Such an approach also enables us to describe signal distortion in a dispersive medium. By analogy, it leads to relating that distortion to Fresnel diffraction. Outside anomalous zones, the above properties are roughly maintened when attenuation is taken into account in relation to dispersion.     

Algèbres d’opérateurs non bornés sur un espace deHilbert

Sans résumé Travail réalisé à l’Institute de mathématiques de l’Université de Neuchatel, avec l’appui du Fonds national de la Recherche scientifique (rech. 2560 et 3026).     

Détection d’un signal dans un bruit autorégressif gaussien

The detection of a signal is considered when the noise can be modelled by an autoregressive Gaussian process with unknown regression factors. The likelihood ratio test is compared with two adaptative receivers which correspond to an estimation of the noise parameters under hypothesis H₀ and H₁.It appears that the adaptative receivers based upon an estimation under H₁ gives very good results, as do adaptative receivers with a signal free reference in this type of problems.     

Assignment of submillimeter laser lines in CH3I

We propose explanations for three laser lines observed in CH₃I by Dyubko, Svich and Fesenko. Two lines are respectively assigned to (J = 16, K = 6) → (J = 15, K = 6) and (J = 45, K = 6) → (J = 44, K = 6) in the ν₆ = 1 state. Th e third one might be explained as (ν₃ = 2, J = 54, K) → (ν₃ = 2, J = 53, K).     

Ground-state molecular constants of bideuterated methane

A rotational analysis of the satellite bands of the β system of ZrO gives the splittings in the triplet states. For the lowest triplet state X′³Δ, these splittings are:

$\text{δF}{}_{\mathrm{1,2}}\text{= 287.9 ± 0.1 cm}{}^{\mathrm{?1}}\text{,}$

$\text{δF}{}_{\mathrm{2,3}}\text{= 337.6 ± 0.4 cm}{}^{\mathrm{?1}}\text{.}$

     

L'Etude Théorique des Systèmes Périodiques. I. La Méthode LCAO?HCO

The LCAO ? HCO method is described. Starting from classical procedures of quantum chemistry, this method enables the theoretical study of periodic systems. The explicit form of some properties is deduced in the Hückel approximation. This method is compared with the tight-binding approximation and applied to the study of polyenes, polyacenes, and graphite. Finally, the general validity of the process is discussed.