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981.
The critical behaviour of a semi-infiniten-vector model with a surface term (c/2) ∫d Sφ2 is studied in 4-ε dimensions near the special transition. It is shown that all critical surface exponents derive from bulk exponents and η∥, the anomalous dimension of the order parameter at the surface. The surface exponents and the crossover exponent Φ for the variablec are calculated to second order in ε. It is found that Φ does not satisfy the relation Φ=1-ν predicted by Bray and Moore. The order-parameter profilem(z)=<ø> is calculated to first order in ε. In contrast to mean-field theory,m(z) is not flat nor does it satisfy a Neumann boundary condition. General aspects of the field-theoretic renormalization program for systems with surfaces are discussed with particular attention paid to the explanation of the unfamiliar new features caused by the presence of surfaces. 相似文献
982.
Dietrich Braess 《Mathematische Annalen》1974,208(2):133-148
Ohne Zusammenfassung 相似文献
983.
Klaus Praefcke Bernd Kohne Dirk Singer Dietrich Demus Gerhard Pelzl Siegmar Diele 《Liquid crystals》1990,7(4):589-594
Two disc-shaped multialkynyl arene ethers (1 and 2) with unusual thermo-mesomorphic properties are presented. Conoscopic studies show that the nematic phases of these new low molecular weight liquid crystals are biaxial and that the sign of their biaxiality is negative. The diether 2 is the first discotic twin liquid crystal which exhibits a nematic phase. 相似文献
984.
Dietrich Menzel 《Applied Physics A: Materials Science & Processing》1990,51(3):163-171
The aim of this survey is the understanding of the dynamics of medium to high energy excitations in simple condensed systems on very short time scales. For this purpose we examine the modifications of the electronic excitations and their evolution in rare gases (mainly Ar and Kr) due to a nearby metal surface (monolayer case) or by embedding into a rare gas condensate (multilayers). Ionic excitations are shifted to lower energies compared to the gas phase by polarization of the surroundings, while neutral excitations stay constant or are shifted to somewhat higher energies. This decreases the spacing between excitonic and ionic states from both sides. Deexcitation events can be analysed by linewidths for valence excitations, and by comparison of autoionisation and Auger spectra for core excitations. For monolayers, we conclude that excitonic states are unstable relative to ionic states but nevertheless are quite long-lived. For multilayers, only minor modifications relative to the gas phase are usually found. All electronic excitations in Ar and Kr mono- or multilayers lead to desorption of neutrals; core excitations in multilayers also lead to ions and cluster ions. The probable mechanisms in all cases are discussed, and open questions are pointed out. 相似文献
985.
986.
987.
R. Keller G. Güntherodt W.B. Holzapfel M. Dietrich F. Holtzberg 《Solid State Communications》1979,29(11):753-758
The lattice parameter of SmS single crystals has been measured under hydrostatic pressure up to 70 kbar. The fit for the metallic phase by means of the Birch equation gives an unusually large pressure derivative of the bulk modulus B' = 11 and hence a large pressure dependence of B. No change in the nonmagnetic intermediate valence state of Sm is observed up to 24 kbar as concluded from our magnetic susceptibility measurements. Reflectivity measurements under hydrostatic pressure p > 6.5 kbar show a small plasma edge shift (~0.08 eV) towards lower energy upon cooling from 77 to 4.2 K. Hence the low temperature resistivity anomaly is attributed to an enhanced conduction electron scattering. 相似文献
988.
989.
R.Justin RajeshPrem B Bisht 《Journal of luminescence》2002,99(3):301-309
Laser-induced transient grating technique has been used to measure the diffraction efficiency (η) and calculate the third-order nonlinear susceptibility (χ(3)) of some laser dyes. Theoretical simulations have been carried out on η and χ(3) as a function of wavelength covering the spectral range corresponding to the first excited singlet state of the dyes. Theoretically simulated values have been found in agreement to those observed experimentally. The decay profiles for these dyes have been measured by using diffraction of a delayed probe laser pulse to estimate the relaxation times in the excited state. 相似文献
990.
Adjustable YBa2Cu3O7/PbSn point contact Josephson junctions are exposed to a microwave field. The current voltage characteristics of the junctions show microwave-induced constant voltage steps. The power dependence of the current width of the steps is well described by the Bessel function behaviour. This clearly demonstrates the presence of macroscopic quantum effects in the new highT
c
material. 相似文献