Showing papers by "École Polytechnique published in 1974"
TL;DR: In this article, a statistical adiabatic channel model is proposed to calculate the rate of unimolecular processes by means of a simple interpolation procedure, where the coupling between the various vibrational-rotational motions is taken into account.
Abstract: The rate of unimolecular processes is calculated by means of a statistical adiabatic channel model. The rates are mainly determined by the maxima of the channel energies. The channels are constructed by correlating reactant and product states; the channel energies are computed by a simple interpolation procedure. The coupling between the various vibrational-rotational motions is taken into account. The influence of parameters of the potential surface on channel energies and on rate constants is studied. Numerical results for the NO2, CH4, CD4, C2H6 and C2D6 dissociation – recombination kinetics are compared to experimental data. The statistical adiabatic channel model gives similar results as minimum local entropy models. Both these approaches lead to stronger curvatures of k(E) and smaller activation energies for the thermal rate constant k∞ than the corresponding RRKM calculations.
Die Geschwindigkeit unimolekularer Zerfallsreaktionen wird mit Hilfe eines Modells adiabatischer Kanale statistisch berechnet. Wesentlich fur die Reaktionsgeschwindigkeiten sind die Maximalenergien der Kanale, die durch Korrelation von Zustanden der Reaktanten und Produkte und einfache Interpolation bestimmt werden. Die Kopplung der Schwingungs-Rotationsbewegungen wird beachtet. Der Einflus von Potentialflachenparametern auf Kanalenergien und Geschwindigkeitskonstanten wird studiert. Numerische Ergebnisse fur die Dissoziations-Rekombinationskinetik von NO2, CH4, CD4, C2H6 und C2D6 werden mit experimentellen Daten verglichen. Das Modell adiabatischer Kanale ergibt ahnliche Ergebnisse wie Modelle mit aktivierten Komplexen, die an Stellen minimaler Zustandsdichte lokalisiert werden. Beide Ansatze fuhren zu einer starkeren Krummung der k(E)-Kurven und zu geringeren Arrhenius-Aktivierungsenergien fur die thermischen Geschwindigkeitskonstanten k∞ als entsprechende RRKM Rechnungen.
466 citations
TL;DR: In this paper, the Euler equation has been considered by several authors including L. Lichtenstein (1925-30), J. Leray (1932-37), M. Wolibner (1938), T. Ebin and J. Marsden [2] have proved the existence of a local solution in the general case.
348 citations
TL;DR: In this article, a study of the various sources which could give rise to such events reveals that less than 20% could be attributed to neutrons or KL°, and the events behave as expected if they arise from neutral current processes induced by neutrinos and antineutrinos.
295 citations
265 citations
TL;DR: It is shown that presently available chromatographs, when handled with care, are sufficient to allow the separation in a few minutes of compounds that require several thousand plates and that the most critical aspect at present is the detector time constant.
117 citations
TL;DR: In this article, the magneto-stark effect and electronic transport properties on GaSe have been studied and it has been shown that GaSe has nearly isotropic electronic states at the forbidden gap and the valence band anisotropy is anomalous.
112 citations
TL;DR: In this paper, the one-dimensional classical electron gas is considered in detail and it is proved that this system is in a crystalline state, at all temperatures and densities.
106 citations
TL;DR: The low temperature luminescence of GaSe has been measured on a series of single crystals, some of which were doped with tin, copper, zinc, iodine, or cadmium as discussed by the authors.
Abstract: The low temperature luminescence of GaSe has been measured on a series of single crystals, some of which were doped with tin, copper, zinc, iodine, or cadmium. Concentrations and activation energies of the impurities have been determined by electrical measurements. At 4.2 °K, radiative recombination of electron–hole pairs occurs via two channels, whose relative efficiency is governed by the total impurity concentration. The first channel is most efficient in pure crystals. It gives rise to a spectrum dominated by the free exciton lines. The second channel is most efficient in doped crystals. Its spectrum is not sensitive to the chemical nature of the impurities. It is attributed to structural defects which are created by the chemical impurities.
On a mesure la luminescence a basse temperature d'une serie de cristaux de GaSe, dont certains etaient dopes a l'etain, au cuivre, au zinc, au cadmium ou a l'iode. Les concentrations et les energies d'activation des impuretes ont ete determinees par des mesures electriques. A 4.2 °K, les recombinaisons radiatives de paires electron–trou suivent deux canaux distincts, dont l'efficacite relative est determinee par la concentration totale en impuretes. Le premier canal, efficace dans les cristaux purs, donne naissance a un spectre domine par les raies de l'exciton libre. Le second canal est efficace dans les cristaux dopes. Son spectre n'est pas sensible a la nature chimique des impuretes. On attribue ce spectre a des defauts de structure engendres par la presence d'impuretes chimiques.
79 citations
TL;DR: In this paper, a discussion is based on new equation, relating pressure and column length at constant analysis performance parameters (i.e. constant retention time and resolution) with special attention to the question whether there is any other limitation than today's technology to the use of finer particles and higher pressures.
77 citations
TL;DR: In this paper, the authors show that the interaction of holes with non-polar, fully symmetric, optical phonons governs both the Hall mobility of the carriers and the temperature shift of the direct energy gap.
Abstract: In the layered semiconductor GaSe, the interaction of holes with non-polar, fully symmetric, optical phonons governs both the Hall mobility of the carriers and the temperature shift of the direct energy gap. The results are in agreement with theory and indicate that the interaction of charge carriers with acoustic phonons is rather weak.
Dans le seleniure de gallium, un semiconducteur a structure en couches, l'interaction des trous avec des phonons optiques non polaires et totalement symetriques determine la mobilite des porteurs d'une part, et le coefficient de temperature du gap direct d'autre part. Les resultats sont en accord avec la theorie. Ils indiquent que la diffusion des porteurs de charge par les phonons acoustiques est faible.
53 citations
TL;DR: In this article, the photolysis of iodine in the gas phase was studied using laser flash photosynthesis at 6943 A. The dependence of the quantum yield on the pressure has been investigated in the range 0.1-1000 atm for several inert gases.
TL;DR: Theoretical computation and experimental verification of the potential probe position in non homogeneous soil is presented in this article, where the experimental work was carried out on a twin layer laboratory model.
Abstract: Ground electrode resistance measurements are usually done by Fall of Potential method. The potential probe position (0.618 rule) has been calculated for homogeneous soil 1,2]. Theoretical computation and experimental verification of the potential probe position in non homogeneous soil is presented. The experimental work was carried out on a twin layer laboratory model [3,4,6].
TL;DR: In this paper, the authors consider isoclinal relaxed configurations in which the director frame keeps a fixed orientation and define an intermediate relaxed configuration (k), assuming that the element is unloaded and brought back to temperature T °.
TL;DR: In a previous paper as mentioned in this paper, we discussed the strong decrease properties of the truncated correlation functions, taking into account the separation of all particles with respect to each other, and discussed the effect of the separation on the performance of the correlation functions.
Abstract: In a previous paper, “strong” decrease properties of the truncated correlation functions, taking into account the separation of all particles with respect to each other, have been presented and discussed.
01 Jun 1974
TL;DR: In this article, the LRP 83 Reference CRPP-REPORT-1974-001 Record created on 2008-04-18, modified on 2016-08-08 was used.
Abstract: Keywords: LRP 83 Reference CRPP-REPORT-1974-001 Record created on 2008-04-18, modified on 2016-08-08
TL;DR: In this paper, the charge densities of the valence electrons in the semiconducting crystals SnSe 2, PbI 2, GaSe, Se and Te have been determined from calculations of the pseudo-wave functions.
TL;DR: In this article, the authors report the generation of powerful infrared radiation continuously tunable between 14 000 and 2 300 cm -1, where the beam is either the output of a dye laser (with a linewidth of 0.07 cm −1 and a full angle divergence of0.2 mrd) or its Raman shifted components.
TL;DR: In this article, a fast equilibrium between two conformations is studied by variable temperature 13 C NMR for five monosubstituted benzene Cr(CO) 3 complexes, and the complexation does not significantly change the trnasmission of electronic substituent effects to the para position.
TL;DR: In this paper, the biexciton problem is reformulated in the framework of the effective mass approximation in a two-band model with screened interaction and the effects due to electron-hole exchange and permutational symmetries are taken into account.
Abstract: The biexciton problem is reformulated in the framework of the effective-mass approximation in a two-band model with screened interaction. The effects due to electron-hole exchange and permutational symmetries are taken into account. The states of all possible spin multiplets are considered and are shown to obey the exclusion principle. The sequence of the energy levels of the biexciton is examined as a function of the electron-hole effective-mass ratio σ. The electron-hole exchange is shown to give an important correction to the biexciton binding energy. Numerical values are obtained for CdS and CuCl.
01 May 1974
TL;DR: The influence of residual tangential stresses on the apparent hardness of rocks for indentation or wear has been investigated in this paper, with various methods and involving different brittle materials (ordinary or tempered glass, hard rocks).
Abstract: The Influence of Residual Stresses on Rock Hardness
An experimental study with various methods and involving different brittle materials (ordinary or tempered glass, hard rocks), has shown the influence of residual tangential stresses on the apparent hardness of rocks for indentation or wear.
This property allows an improving of the efficiency of drilling machines, by choosing tool shapes leading to the most favourable stress concentrations at the bottom of boreholes.
TL;DR: In this paper, a variational method for approximating the eigenstates of the Hamiltonian in relativistic quantum field theory is introduced, which provides a quantum-mechanical interpretation for solitons, some of which resemble extended particles.
DOI•
01 May 1974TL;DR: Fall-off curves of thermal unimolecular reactions in the strong collision limit and in the general weak collision case are discussed in this paper, where reduced falloff curves are represented in (k 0, k∞)-reduced form interpolating between both the limiting low pressure and the limiting high pressure rate constants k0 and k∆.
Abstract: Fall-off curves of thermal unimolecular reactions in the strong collision limit and in the general weak collision case are discussed. The fall-off curves are represented in (k0, k∞)-reduced form interpolating between both the limiting low pressure and the limiting high pressure rate constants k0 and k∞. In this reduced form fall-off curves are very insensitive to details of the theory and simplified models can be used. Reduced fall-off curves are represented in terms of tabulated Kassel integrals; the two Kassel parameters Sk and Bk are expressed in terms of experimental observables like the apparent activation energies in the low and high pressure limit and the collision efficiency. By this procedure some uncertain parts of the theory of unimolecular reactions can be eliminated from the calculation of fall-off curves.
Fall-off-Kurven thermischer unimolekularer Reaktionen werden fur den Grenzfall starker Stose und fur den allgemeinen Fall schwacher Stose diskutiert. Die Kurven werden in (k0,k∞)-reduzierter Form als Interpolation zwischen den Grenzgeschwindigkeitskonstanten k0 und k∞ im Niederdruck- und im Hochdruckbereich dargestellt. In dieser reduzierten Form sind fall-off-Kurven sehr unempfindlich gegen Details der Theorie, und einfache Modelle konnen verwendet werden. Reduzierte fall-off-Kurven werden mit tabellierten Kassel-Integralen dargestellt; die beiden Kassel-Parameter Sk und Bk werden aus experimentellen Grosen wie den scheinbaren Aktivierungsenergien im Niederdruck- und im Hochdruckbereich und den Stosausbeuten berechnet. Mit dieser Methode konnen Unsicherheiten der Theorie unimolekularer Reaktionen bei der Berechnung von fall-off-Kurven umgangen werden.
TL;DR: A non-commutative extension of certain aspects of classical probability theory is presented in such a manner that the notion of Kolmogorov entropy can be extended to a large class of non-classical dynamical systems.
Abstract: A non-commutative extension of certain aspects of classical probability theory is presented in such a manner that the notion of Kolmogorov entropy can be extended to a large class of non-classical dynamical systems. In particular, the generalized K-entropy so defined is shown to be strictly positive on the class of non-abelian K-flows.
TL;DR: Capillarity is used to recycle cesium in order to increase considerably the time of service of a charge-exchange cell as mentioned in this paper, which increases the cost of the cell.
TL;DR: The salient characteristics of a variety of approaches to individualizing instruction are described and their respective merits with regard to higher education discussed in this paper, including: programmed instruction, computer-assisted instruction and management, information retrieval systems, audio-tutorial and modular instruction, contingency management and contracting, and personalized and individually prescribed instruction.
Abstract: The salient characteristics of a variety of approaches to individualizing instruction are described and their respective merits with regard to higher education discussed. The review includes: programmed instruction, computer-assisted instruction and -management, information retrieval systems, audio-tutorial and modular instruction, contingency management and contracting, and personalized and individually prescribed instruction. While these approaches differ from each other in some respects, they all share an overriding concern for individual differences among students and seek to better adapt instruction to the learner. A section on general issues regarding the degree of individualisation, the role of the professor, institutional support for improving instruction, the role of the student, content and method, evaluation, and the future of individualized instruction concludes the review.
TL;DR: In this article, Lambda and neutral-kaon production is studied in K−p interactions at 3.93 and 14.3 GeV/c, respectively, yielding mainly backward lambdas.
Abstract: Lambda and neutral-kaon production is studied in K−p interactions at 3.93 and 14.3 GeV/c. Topological inclusive cross-sections are given at both energies. Invariant cross-sections for lambdas and neutral kaons are presented as a function of the Feynmanx-variable and are found to decrease in magnitude and vary their shapes with energy. The\(AK\overline K \) production, which represents (9±2)% and (29±3)% of the lambda inclusive cross-section at 3.93 GeV/c and 14.3 GeV/c respectively, yields mainly backward lambdas. The shapes of the transverse-momentum invariant distributions vary withx, but are roughly independent of energy. The lambda polarization is studied as a function ofx at both incident momenta: for fast lambdas it is negative, as observed in reactions where nucleon exchange is dominant.
TL;DR: In this paper, les franges presentent des proprietes interessantes, en particulier celle de n'etre visibles qu'en certains endroits seulement, c'est-a-dire d'etres localisees.
Abstract: La reconstitution simultanee par holographie des images d'un objet avant et pendant une sollicitation mecanique fait apparaitre des franges d'interference. Ces franges presentent des proprietes interessantes, en particulier celle de n'etre visibles qu'en certains endroits seulement, c'est-a-dire d'etre localisees. Ces phenomenes ont deja ete examines en detail par plusieurs auteurs auxquels sont empruntes certains raisonnements. Pour chaque point de la surface du corps, on peut observer les franges avec un systeme optique visant dans une direction variable. Sur une courbe de l'espace est remplie la condition de localisation complete: les ondes se superposant en ces points ont meme difference de phase. Pour chaque direction, on peut aussi donner l'endroit ou le contraste des franges est maximum: on se trouve ainsi sur une surface de localisation partielle. Grâce a un critere sur l'orientation des franges, il est possible de determiner les points de localisation complete et d'en deduire par une relation lin...
TL;DR: In this paper, it was shown that microwave power at 2450 MHz can be applied to a bituminous pavement to a depth of 2 cm (4-5") without overheating the top layer of the asphalt road.
Abstract: It is shown that microwave power at 2450 MHz can be effectively coupled into a bituminous pavement to a depth of ~I2 cm (4–5") without overheating the top layer of the asphalt road. It is therefore possible, without damaging the asphalt surface quality, to completely seal road cracks, so that water infiltration into roadbeds is minimized and frost heave prevented. In the autumn of 1973, microwave power was applied to seal a transverse road crack (24' long, 0.5" wide, and 6" deep) on Highway 20 between Montreal and Quebec City. The repaired surface was exposed to heavy traffic conditions during the 1973–1974 winter, with promising results.
TL;DR: In this article, the authors derived analyticity properties in the non-linear program of general quantum field theory, following the line of the many particle structure analysis due to Symanzik.
Abstract: This is the first of a series of papers devoted to the derivation of analyticity properties in the non-linear program of general quantum field theory, following the line of the “many particle structure analysis” due to Symanzik. In this preliminary paper, “convolution products” are associated with graphs whose verticesv represent generalnv-point functions. Under convergence assumptions in Euclidean directions, it is proved that any such convolution productHG associated with a graphG withN external lines is well defined as an analytic function of the correspondingN four-momentum variables. The analyticity domain ofHG is proved to contain the correspondingN-point “primitive domain” implied by causality and spectrum and the various real boundary values ofHG satisfy all the relevant linear relations. For appropriate boundary values, the convolution products generalize the perturbative Feynmann prescription. As a by-product of this study, it is proved that in any perturbative theory using “superpropagators” with Euclidean convergence, Feynmann amplitudes that satisfy all the requirements of the linear program can be defined without the help of a regularization.