Showing papers by "École Polytechnique Fédérale de Lausanne published in 1977"

Light emission by magnetic and electric dipoles close to a plane interface. I. Total radiated power

Abstract: Expressions for the total power radiated by magnetic and electric dipoles of arbitrary orientation located in a medium 1 at distance z0 from the interface to a homogeneous or planar stratified medium 2 are derived. A relation between the normalized powers radiated by magnetic and electric dipoles is established. For a homogeneous loss-free medium 2, curves of the normalized powers L(z0)/L∞ radiated by magnetic and electric dipoles versus the normalized distance z0/λ1 are presented for different values of the relative refractive index n = n2/n1 as the only parameter. The computer calculations are compared with analytical expressions derived for small and large distances. For n > 1, the contribution of the evanescent waves to the radiated power is calculated separately. We show that the classical results for the normalized radiated power yield the correct normalized spontaneous emission rates from an excited atomic state for electric and magnetic dipole transitions, respectively. We point out that the results for the electric dipole also give the change of the total power scattered by a small dielectric scattering particle when it is placed close to an interface.

Light emission by magnetic and electric dipoles close to a plane dielectric interface. II. Radiation patterns of perpendicular oriented dipoles

Abstract: We have derived analytical expressions for the angular distribution P(α) of the power radiated by magnetic or electric dipoles located at distance z0 from a dielectric interface and oriented perpendicular to it. For dipoles in the rarer medium very close to the interface, evanescent waves in the dipoles’ near field give rise to strong radiation into the denser medium. The resulting large maximum of P(α) shows characteristic differences for magnetic and electric dipoles when the relative refractive index of the two dielectrics is greater than √2. For dipoles lying on the interface a symmetry relation is established connecting the power distributions P(α) for the values n and 1/n of the relative refractive index.

Oxygen transfer coefficients by dynamic model moment analysis

Abstract: A new method to estimate the oxygen transfer coefficient (KLa) from the experimental dynamic response data is presented. Employing a linear model which allows for gas phase, diffusion film, and oxygen electrode dynamics, the first moment of the response curve is simply related to the sum of the model parameters. Two separate experiments are used to characterize the measurement dynamics and to measure the unknown KLa parameter. The simple calculation procedure involves only measuring the area above the response curves.

Raman scattering and structural properties of MoO3

Abstract: MoO3 e una struttura a strati ortorombica con 4 molecole per cella unitaria. Si presentano le proprieta infrarosse e di Raman delle vibrazioniq=0. Si identificano gli automodi degli strati debolmente accoppiati sulla base delle proprieta di simmetria e di un modello qualitativo di polarizzabilita del legame. I risultati sono piu in accordo con la coordinazione tetraedrale piuttosto che ottoedrale delle molecole di ossigeno attorno al molibdeno. Si puo descrivere lo strato base come una organizzazione parallela di catene moderatemente interagenti, in qualche modo simili alle strutture a catena del CrO3. MoO3 представляет орторомбическую слоистую структуру с четырьмя молекулами в элементарной ячейке. Исследуются инфракрасные и рамановские свойства колебанийq=0. Идентифицируются собственные моды слабо связанных слоев на основе свойств симметрии и качественной модели поляризуемости связи. Полученные результаты соответствуют тетраэдральному, а не октаэдральному расположению атомов кислорода вокруг молибдена. Основной слой может быть изображен как параллельная структура умеренно взаимодействующих цепочек, отчасти похожих на структуру цепочек CrO3.

N-methylmethyleneimine and ethylideneimine: Gas- and matrix-infrared spectra, AB initio calculations and thermodynamic properties

Abstract: Gas- and matrix spectra of CH 3 N:CH 2 (I) produced by controlled pyrolysis of N-trimethyl hexahydro-s-triazine and matrix spectra of CH 3 CH:NH (II) and its d s modification produced by photolysis in Ar matrices have been measured. A set of ab initio SCF LCAO calculations for both the cis and trans isomer of II, of I and of the isomers CH 2 :CHNH 2 and CH 2 NHC H 2 is given. For I and II assignments of the vibrational spectra, sets of harmonic force constants as well as statistical thermodynamic functions and thermodynamic data of their interconversion are presented.

Approximation of the spectrum of a non-compact operator given by the magnetohydrodynamic stability of a plasma

Abstract: The study of the magnetohydrodynamic stability of a plasma leads to a problem of determination of the spectrum of a non-compact selfadjoint operatorA. The spectrum ofA will be approximated by the eigenvalues ofA h , whereA h is a linear operator approximatingA in a finite dimensional space (finite element method) andh is a parameter which tends to zero. Generally the spectrum ofA h "pollutes" spectrum ofA, i.e. for eachh there exists an eigenvalue ?h ofA h which, ash tends to zero, converges to ? which is not in the spectrum ofA. We present here a sufficient condition on the finite dimensional spaces used, in order to obtain good approximation properties of the spectrum ofA and, especially, the "non-pollution" property.

Juvenile hormone in larval diapause of the codling moth,Laspeyresia pomonella L. (Lepidopterae, Tortricidae)

Abstract: Whereas in last instar larvae ofL. pomonella kept under long-day-conditions (LD), the JH-titer is temporarily reduced to zero, it stays relatively high in short-day-conditioned (SD) larvae which enter diapause. Application of JH or a juvenoid to LD-larvae results in diapause, if the treated insects are kept under SD-conditions. From these results it is concluded that inL. pomonella diapause is initiated by a relatively high titer of JH during the last larval instar.

Immunochemical investigation of four Saprolegnia species with parasitic activity in fish: Serological and kinetic characterization of a chymotrypsin-like activity.

Abstract: The antigenic structure of four aquatic Phycomycetes of the genusSaprolegnia with parasitic activity in fish was analyzed with immunoelectrophoresis and double diffusion techniques. It is shown that these serological tests might represent a valuable criterion for the identification of the fourSaprolegnia species:S. parasitica, S. ferax, S. delica, andS. diclina. A specific chromogenic reaction revealed the presence of a protease with chymotrypsin-like activity among the precipitation arcs obtained after immunoelectrophoresis. Analysis of this proteolytic activity by kinetic assay methods confirmed the results of the serological tests. Moreover estimates of the quantity of enzyme present in the cellular extract and in the culture medium were obtained. A possible relationship between the proteolytic activity and the host-parasite interaction was discussed.

Magnetic excitations in Nd Al 2

Abstract: The magnetic excitation spectrum of the ferromagnet Nd${\mathrm{Al}}_{2}$ has been studied at 4.2 K by neutron inelastic scattering. Three acoustical, three optical branches, and partly a fourth optical branch have been resolved. Crystal-field and exchange parameters have been obtained by analyzing the results in terms of a pseudoboson theory that includes all ten levels of the free-ion ground state of ${\mathrm{Nd}}^{3+}$. A good description of the observed excitation energies and intensities is obtained. The reliability of the model parameters is supported by internal consistency checks and by comparison with various physical properties of Nd${\mathrm{Al}}_{2}$. The interatomic exchange parameters exhibit a Ruderman-Kittel-Kasuya-Yosida-like qualitative behavior.

The effect of phosphoenolpyruvate on the retention of calcium by liver mitochondria

Abstract: The ability of mitochondria to accumulate large amounts of Ca*+ via a specific carrier in the inner membrane is extensively documented [ 1,2]. The release of Ca2+ from mitochondria ofheart and some other excitable tissues probably occurs via a second carrier, that exchanges Na’ for Ca2+ [3,4]. The mechanism of Ca2+ release from other mitochondria that lack the Na+-Ca2+ exchange, e.g., liver is obscure. Some [S-7] have presented evidence for a second Ca2+ carrier in liver mitochondria, albeit not exchanging Na+, which catalyses release, whereas others [8] have concluded that efflux occurs by reversal of the influx process. In addition, considerable attention has been given to the release of Ca2+ from mitochondria by exogenously added phosphoenolpyruvate (PEP) [9-l 11. However, whether or not the phenomenon of the PEP-induced release of Ca2+ has the qualities of a physiological release mechanism, has not been investigated thorougly. This is the subject of the present paper. In particular, it is shown that the phenomenon is associated with a collapse of the electrical potential difference across the inner membrane, which permits release of Ca2+ via reversal of the energy-linked influx process.

Elastic properties of KCN and K(CN)1−xClx

Abstract: The elastic functions c11 and c44 of KCN are measured by the ultrasonic pulse-echo method and by Brillouin scattering in the cubic phase below room temperature and between 60 and 100 K in phases II and III. The elastic softening of c44 in the cubic phase can well be described by a linear strain—order parameter coupling. The same formalism explains the beginning softening of (c11—c12)/2, data of which are taken from the literature. It is shown that the interaction among CN groups is mediated by the lattice strain. Measurements of c44 in mixed crystals KCN/KCl indicate a strong shift of the stability limit of the cubic phase to lower values by replacing CN with Cl. Die elastischen Funktionen c11 and c44 von KCN werden mit Hilfe der Pulsechomethode und mittels Brillouinstreuung in der kubischen Phase unterhalb Zimmertemperatur sowie in den Phasen II und III zwischen 60 und 100 K gemessen. Das elastische Weichwerden von c44 last sich gut durch eine lineare Kopplung zwischen Deformation und Ordnungsparameter beschreiben. Der gleiche Formalismus erklart das ebenfalls einsetzende Weichwerden von (c11 — c12)/2, wofur Daten der Literatur entnommen wurden. Es wird gezeigt, das die Wechselwirkung zwischen den CN-Gruppen uberwiegend durch die Deformation des Gitters vermittelt wird. Messungen von c44 an Mischkristallen KCN/KCl zeigen eine starke Verschiebung der Temperatur der Stabilitatsgrenze der kubischen Phase zu niedrigeren Werten, wenn CN durch Cl ersetzt wird.

High temperature UV absorption and recombination of methyl radicals in shock waves

Abstract: The UV absorption of CH 3 and CD 3 in the 2 A′ 1 ← 2 A″ 2 electrinic transition has been studied in shock wave experiments using the fast thermal decomposition of azomethane at T >1300 K as the radical source. With a spectral resolution λ (FWHM)=1.6 nm, the maximum effective decadic absorption coefficients at T =1400 K are, near 216 nm e max (CH 3 )=(1.8±0.6)·10 6 cm 2 mol −1 and e max (CD 3 )=(2.0±0.7)·10 6 cm 2 mol −1 . Calculations on the temperature and bandwidth dependence of the spectra show that these results agree well with room temperature data. The recombinantion rate coefficients for the reactions CH 3 +CH 3 (+Ar)→C 2 H 6 (+Ar) and CD 3 +CD 3 (+Ar)→C 2 D 6 (+Ar) have been measured at [Ar]=2·10 −6 −2·10 −4 mol cm −3 in the falloff range near the high pressure limit. Extrapolation gives k H, ∞ =(2.9±1.5)·10 −11 cm 3 s −1 , and k D, ∞ =(3.2±1.7)·10 −11 cm 3 s −1 at 1400 K. The temperature dependence of the rate coefficients obtained by combination with room temperature data agrees well with predictions of the statistical adiabatic channel model but is in conflict with conventional RRKM calculations. A direct observation of the equilibrium C 2 H 6 →2CH 3 gives agreement with the “high” value for H o o (87.76 kcal mol −1 ). The thermal decomposition of azomethane between 850 and 1200 K, the kinetics of methyl radicals at T

Kinetics and intramolecular dynamics of photoradical in solution: An ESR, MESR and quantum chemical study

Abstract: Generation of radicals of glyoxal from photolysis in aprotic solvents is reported. In benzene solution radical X and in toluene solution three radicals