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91.
Measurements on thin layers of cholesteric liquid crystals with a cyclic polysiloxane backbone show the usual angle dependence of the reflection wavelength, namely a shift to shorter wavelengths with increasing angle of observation. By mixing these liquid-crystalline side chain polymers with suitable pigments or dyes or by choice of a suitable coloured background, a red shift of the reflection colour with increasing angle can be obtained. 相似文献
92.
Stability constants and thermodynamic values for the complex formation of alkali ions by crown ethers, diaza crown ethers and cryptands have been measured by means of potentiometric and calorimetric titrations in acetone as solvent. The interactions between the ligands and solvent molecules play an important role for the complex formation. Cryptands form the most stable complexes with alkali ions if inclusion complexes are formed. Even in the case that the salts are not completely dissociated in acetone the presence of ion pairs does not influence the calculated values of the stability constants. 相似文献
93.
H-J. Deu en P. V. Shibaev R. Vinokur T. Bj rnholm K. Schaumburg K. Bechgaard V. P. Shibaev 《Liquid crystals》1996,21(3):327-340
A number of new chiral binaphthol (BN) derivatives with different substituents R,R' in the 6,6'-positions in open (BN-diethylethers) and bridged forms (BN-acetals) have been synthesized. The syntheses of the chiral 6,6'-disubstituted-2,2'-diethoxy-1,1'-binaphthyls (R,R' = -CH'CHCHO, -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh)) and the chiral 9,14-disubstituted-dinaphtho [2,1-d:1',2'-f][1,3] dioxepins with R,R' = -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh) are reported for the first time. The possible liquid crystalline properties and molar twisting powers (βM) in three different nematic liquid crystals (LCs) of the BN derivatives were investigated. Derivatives with spatially extended substituents in the 6,6'-positions (e.g. styryl or vinyl) show unusually high molar twisting power (up to 124.5μm-1). A direct correlation between the magnitude of βM and the length of the substituents was found. Bridged forms, in which the dihedral angle θ between the naphthyl moieties is ≊ 54°, show higher twisting power than the corresponding open forms, where θ is allowed to vary around 90° resulting in an equilibrium between transoid and cisoid forms. From the different temperature dependencies of βM of the open and bridged BNs, a molecular model was developed relating the molecular conformation and twisting power. Although no mesophase was found in any of the compounds synthesized, they can be considered as important precursors for the synthesis of potential chiral BN-containing LCs. 相似文献
94.
Within the band gap of a semiconductor no electronic propagating states are allowed, but there exist evanescent states which govern charge transport such as tunneling. In this Letter, we address the issue of their spin dependence in III-V semiconductors. Taking into account the spin-orbit interaction, we treat the problem using a k . p 14 x 14 Hamiltonian that we numerically compute for GaAs. Our results show that the removed spin degeneracy in the band gap can lead to giant energy splittings and induces forbidden zones in space where evanescent states are suppressed. 相似文献
95.
The scattering matrix was measured for a flat microwave cavity with classically chaotic dynamics. The system can be perturbed by small changes of the geometry. We define the "scattering fidelity" in terms of parametric correlation functions of scattering matrix elements. In chaotic systems and for weak coupling, the scattering fidelity approaches the fidelity of the closed system. Without free parameters, the experimental results agree with random matrix theory in a wide range of perturbation strengths, reaching from the perturbative to the Fermi golden rule regime. 相似文献
96.
Weissenrieder J Kaya S Lu JL Gao HJ Shaikhutdinov S Freund HJ Sierka M Todorova TK Sauer J 《Physical review letters》2005,95(7):076103
The structure of a thin single crystalline SiO(2) film grown on Mo(112) has been studied by scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. In excellent agreement with the experimental results, density functional theory calculations show that the film consists of a two-dimensional network of corner sharing [SiO(4)] tetrahedra, with one oxygen of each tetrahedron binding to the protruding Mo atoms of the Mo(112) surface. 相似文献
97.
Ohtsubo T Bosch F Geissel H Maier L Scheidenberger C Attallah F Beckert K Beller P Boutin D Faestermann T Franczak B Franzke B Hausmann M Hellström M Kaza E Kienle P Klepper O Kluge HJ Kozhuharov C Litvinov YA Matos M Münzenberg G Nolden F Novikov YN Portillo M Radon T Stadlmann J Steck M Stöhlker T Sümmerer K Takahashi K Weick H Winkler M Yamaguchi T 《Physical review letters》2005,95(5):052501
We report the first measurement of a ratio lambda(beta(b))/lambda(beta(c)) of bound-state ((lambda(beta(b))) and continuum-state (lambda(beta(c))) beta(-)-decay rates for the case of bare 207Tl81+ ions. These ions were produced at the GSI fragment separator FRS by projectile fragmentation of a 208Pb beam. After in-flight separation with the Brho-deltaE-Brho method, they were injected into the experimental storage-ring ESR at an energy of 400.5A MeV, stored, and electron cooled. The number of both the 207Tl81+ ions and their bound-state beta(-)-decay daughters, hydrogen-like 207Pb81+ ions, were measured as a function of storage time by recording their Schottky-noise intensities. The experimental result, lambda(beta(b))/lambda(beta(c)) = 0.188(18), is in very good agreement with the value of 0.171(1) obtained from theory employing spectra of allowed transitions. 相似文献
98.
Litvinov YA Bürvenich TJ Geissel H Novikov YN Patyk Z Scheidenberger C Attallah F Audi G Beckert K Bosch F Falch M Franzke B Hausmann M Kerscher T Klepper O Kluge HJ Kozhuharov C Löbner KE Madland DG Maruhn JA Münzenberg G Nolden F Radon T Steck M Typel S Wollnik H 《Physical review letters》2005,95(4):042501
The FRS-ESR facility at GSI provides unique conditions for precision measurements of large areas on the nuclear mass surface in a single experiment. Values for masses of 604 neutron-deficient nuclides (30 < or = Z < or = 92) were obtained with a typical uncertainty of 30 microu. The masses of 114 nuclides were determined for the first time. The odd-even staggering (OES) of nuclear masses was systematically investigated for isotopic chains between the proton shell closures at Z = 50 and Z = 82. The results were compared with predictions of modern nuclear models. The comparison revealed that the measured trend of OES is not reproduced by the theories fitted to masses only. The spectral pairing gaps extracted from models adjusted to both masses, and density related observables of nuclei agree better with the experimental data. 相似文献
99.
Ariando Darminto D Smilde HJ Leca V Blank DH Rogalla H Hilgenkamp H 《Physical review letters》2005,94(16):167001
Phase-sensitive order parameter symmetry test experiments are presented on the electron-doped high-T(c) cuprate Nd(2-x)Ce(x)CuO(4-y). These experiments have been conducted using zigzag-shaped thin film Josephson structures, in which the Nd(2-x)Ce(x)CuO(4-y) is connected to the low-T(c) superconductor Nb via an Au barrier layer. For the optimally doped as well as for the overdoped Nd(2-x)Ce(x)CuO(4-y), a clear predominant d(x2-y2)-wave behavior is observed at T=4.2 K. Both compounds were also investigated at T=1.6 K, presenting no indications for a change to a predominant s-wave symmetry with decreasing temperature. 相似文献
100.
Bobbenkamp R Paladini A Russo A Loesch HJ Menéndez M Verdasco E Aoiz FJ Werner HJ 《The Journal of chemical physics》2005,122(24):244304
In a crossed molecular-beam study we have measured angular and time-of-flight distributions of the product LiF from the reaction Li + HF(upsilon = 0)-->LiF + H at various collision energies ranging from 97 to 363 meV for three markedly different rotational state distributions of HF obtained at nozzle temperatures close to 315, 510, and 850 K. Particularly, for the low and intermediate collision energies we observe significant effects of the varying j-state populations on the shape of the product angular distributions. At 315 K an additional feature appears in the angular distributions which is interpreted as being due to scattering from HF dimers. The experimental data are compared with simulations of the monomer reaction based on extensive quasiclassical trajectory calculations on a new state-of-the-art ab initio potential energy surface. We find an overall good agreement between the theoretical simulations and the experimental data for the title reaction, especially at the highest HF nozzle temperature. 相似文献