Articles you may be interested inSelf-consistent computation of electronic and optical properties of a single exciton in a spherical quantum dot via matrix diagonalization method

The simple shell model which takes account of the polarizability of the ions is improved by including the effect of deformations of the electron shell during the vibrations of the ions. The deformability is introduced in a phenomenological way and it is shown that this ultimately leads to three body interactions between like particles. Because of the inclusion of many body effects the elastic constants do not satisfy in general the Cauchy relation C , , = Cad. The theory is applied to the calculation of the dispersion curves for NaI and the result is compared with the simple shell model curves and with the curves obtained by neutron diffraction experiments. Definite improvement of the agreement for the deformable shell model is noticed.Das einfache Schalenmodell, das die Polarisierbarkeit der Ionen beriicksichtigt, wird durch Einbeziehung der Verformungen der Elektronenschalen wiihrend der Schwingungen der Ionen verbessert. Die Deformierbarkeit wird phiinomenologisch eingefiihrt und es wird gezeigt, daB dies zu einer Dreikorperwechselwirkung zwischen gleichen Teilchen fiihrt. Wegen der Einbeziehung der Vielkorpereffekte erfiillen die elastischen Konstanten im allgemeinen nicht die Cauchy-Relation C , , = C,. Die Theorie wird angewendet zur Berechnung der Dispersionskurven fur NaJ und das Ergebnis wird mit Kurven nach dem einfachen Schalenmodell und mit Kurven, die durch Neutronenbeugungsexperimente erhalten werden, verglichen. Das Model1 mit deformierbaren Schalen zeigt deutlich bessere Vbereinstimmung.

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The longer persistence of the high water level around high tide implies that a storm surge is more likely to coincide with the high tide, leading to a greater chance of destruction. Since the stands are associated with an amplification of the 4-hourly and 6-hourly constituents, storm surges that have a similar period are also likely to amplify more during their passage through the SES.

We have investigated the fluctuation induced conductivity (FIC) of two high-Tc superconductors (HTSC) namely Bi2Sr2Ca1Cu2O8+δ and Y1−xCaxBa2Cu3Oy. The effective medium theory is used to formulate the Aslamazov–Larkin type equations for these polycrystalline superconductors. For the three dimensional case the temperature exponent remains unaltered since both the exponents for the ab plane and c direction FICs in the crystal are same. But the situation is more complex in the two dimensional case where the counterparts in the crystal have different temperature dependencies. The FIC is evaluated and compared with the theoretically obtained values from the model proposed. We have also evaluated the exponents, the coherence lengths, and the crossover temperature. The analysis based on the present model reveals that these two superconductors are similar concerning their nature of fluctuations. The extent of a particular fluctuation region of course differs from one HTSC to another.

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The multiple-scattering theory developed in various ways has significantly contributed to our understanding of the dielectric, mechanical, thermal, and other physical properties of disordered solids mainly in the linear-response regime. Its application has, however, been limited when both nonlinearity and disorder are present. In particular, very little work has been done to treat nonlinear elastic properties of disordered materials apart from the simple constant stress or strain averagingan extreme approximation that is well known to lead to violation of equilibrium condition. Some of our earlier work goes beyond this simple approximation and provides a formal solution of the strain distribution including nonlinearity for an arbitrary disordered solid within the framework of the multiple-scattering theory.Following a similar approach, we propose in this work to develop a general theoretical framework and deduce explicit analytical expression for the third-order elastic constant, which is a generic quantity. As a specific application we have calculated the three independent third-order elastic constants for a particular type of disordered solid, namely, cubic polycrystals following two methods: a perturbative and an approximate self-consistent method developed in the present investigation. These methods have been applied to evaluate third-order elastic constants of eight different materials. The results seem to indicate that for low-anisotropy cases, the two methods give values that closely agree whereas for large anisotropy, they differ. In view of the scarcity of data on the third-order elastic constant of polycrystals, we have also calculated another important nonlinear parameter, namely, the pressure derivative of the secondorder shear modulus, for which accurate measurements are available. In all cases, the calculated values are found to compare favorably with experiment. Lastly it may be mentioned that the method developed is quite general and may be adopted to treat nonlinearity in any tensor property of disordered materials.