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991.
The nematic liquid-crystalline phase exhibits average orientational order, with no positional organisation. So-called modulated nematic phases exhibit this same orientational order with an additional spatially periodic modulation of the nematic director, the most common of which is the twist-bend nematic phase. We report a pentaerythritol derived tetrapode which exhibits a nematic-like mesophase at ambient temperature, and we denote this new mesophase ‘NX’ to indicate a nematic phase of unknown structure. X-ray scattering experiments refute the possibility of positional order, yet optical textures are consistent with a periodic structure. We suggest that the mesophase exhibited by this material is a new type of nematic-like mesophase with some form of modulated structure. We find the NX phase to exhibit an electrooptic response consistent with a nematic-like phase. 相似文献
992.
Chong Zhang Qing-Hong Zhang Kou-Lin Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(12):1593-1604
A novel hydrolytic stable CoII–organic framework, namely poly[[bis(2‐amino‐4‐sulfonatobenzoato‐κO1)tetraaquatris{μ‐1,4‐bis[(imidazol‐1‐yl)methyl]benzene‐κ2N3:N3′}dicobalt(II)] tetrahydrate], {[Co(C7H5NO5S)(C14H14N4)1.5(H2O)2]·2H2O}n, ( 1 ), based on multifunctional 2‐amino‐5‐sulfobenzoic acid (H2asba) and the auxiliary flexible ligand 1,4‐bis[(imidazol‐1‐yl)methyl]benzene (bix), was prepared using the solution evaporation method. The purity of ( 1 ) was confirmed by elemental analysis and powder X‐ray diffraction (PXRD) analysis. Complex ( 1 ) shows a novel 1D→2D interpenetrating network, which is further extended into a 3D supramolecular framework with channels occupied by the lattice water molecules. The 2‐amino‐4‐sulfonatobenzoate (asba2?) ligand adopts a monodentate coordination mode. The bix ligands exhibit gauche–gauche (GG) and trans–trans (TT) conformations. A detailed analysis of the solid‐state diffuse‐reflectance UV–Vis spectrum reveals that an indirect band gap exists in the complex. The band structure, the total density of states (TDOS) and the partial density of states (PDOS) were calculated using the CASTEP program. The calculated band gap (Eg) matches well with the experimental one. The complex exhibits a reversible dehydration–rehydration behaviour. Interestingly, gas sorption experiments demonstrate that the new fully anhydrous compound obtained by activating complex ( 1 ) at 400 K shows selective adsorption of CO2 over N2. Complex ( 1 ) retains excellent framework stability in a variety of solvents and manifests distinct solvent‐dependent fluorescence properties. Moreover, the complex shows multiresponsive fluorescence sensing for some nitroaromatics in aqueous medium. 相似文献
993.
Vladimíra Novotná Sergey Stulov Věra Hamplová Martin Cigl Oliva Pacherová 《Liquid crystals》2019,46(7):1035-1042
We report the synthesis and mesomorphic properties of new chiral materials based on (S)-2-methylbutyl lactate group in the chiral chains and a lateral substitution by a chlorine atom in the molecular core. We have studied mesomorphic properties and found that homologues with only one lactate and methylbutyl in the chain exhibit the SmC* phase in a broad temperature range. We established the spontaneous polarisation and tilt angle values. The pitch values are rather small, being within the range 360–450 nm. On the other hand, a homologue with one additional lactate in the chiral part does not exhibit the mesomorphic properties. We have tried to establish the effect of lateral substitution by comparing all studied compounds with previously prepared (S)-2-methylbutyl lactate derivatives with non-substituted molecular core. 相似文献
994.
S. Halder K. Parida S.N. Das S.K. Pradhan S. Bhuyan R.N.P. Choudhary 《Physics letters. A》2018,382(10):716-722
A polycrystalline vanadium doped lead free dielectric material of Bi(Zn2/3V1/3)O3 (BZV) has been prepared using a standard high-temperature solid state reaction technique. Its temperature and frequency dependent capacitive, conductive and resistive characteristics are outlined though experimental investigation. The formation of single phase compound of BZV material with orthorhombic crystal symmetry is identified through X-ray diffraction data analysis, and the homogeneous distribution of grains are realized through scanning electron micrograph. The acquaintance of frequency–temperature dependent electrical parameters with the obtained micrograph provides the experimental evidence of contributions of grain as well as grain boundary in its capacitive and resistive characteristics. The negative temperature coefficient of resistance behaviour of the material is revealed from impedance characteristic, and non-Debye type relaxation has been realized from the Nyquist plot. The charge carriers of this electronic compound have both long & short range order that has been validated from the complex modulus and impedance analysis. The prepared electronic material substantiate some important dielectric features which props up the material as promising component for electronic devices. 相似文献
995.
996.
This paper establishes a continuous-time stochastic asset pricing model in a speculative financial market with fundamentalists and chartists by introducing a noisy fundamental price. By application of stochastic bifurcation theory, the limiting market equilibrium distribution is examined numerically. It is shown that speculative behaviour of chartists can cause the market price to display different forms of equilibrium distributions. In particular, when chartists are less active, there is a unique equilibrium distribution which is stable. However, when the chartists become more active, a new equilibrium distribution will be generated and become stable. The corresponding stationary density will change from a single peak to a crater-like density. The change of stationary distribution is characterized by a bimodal logarithm price distribution and fat tails. The paper demonstrates that stochastic bifurcation theory is a useful tool in providing insight into various types of financial market behaviour in a stochastic environment. 相似文献
997.
998.
Evolution of gluon distribution function from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equation in next-to-leading
order (NLO) at low-x is presented assuming the Regge behaviour of quark and gluon at this limit. We compare our results of gluon distribution
function with MRST2004, GRV98LO and GRV98NLO parametrizations and show the compatibility of Regge behaviour of quark and gluon
distribution functions with perturbative quantum chromodynamics (PQCD) at low-x.
相似文献
999.
We solve several low temperature problems of an infinite range metallic spin glass model. A compensation problem of T 0 divergencies is solved for the free energy which helped to extract the quantum critical behaviour of the spin glass order parameters as a function of δJ = J – Jc (T = 0). The critical value Jc(T = 0) = 3/16pF?1 of the frustrated spin coupling J, which separates spin glass from nonmagnetic (spin liquid) phase, is determined exactly in the static saddle point solution for a semielliptic metallic band model in terms of the density of states at the Fermi level. In addition to the replica-overlap order parameter 〈Qab〉, a ≠ b, the diagonal 〈Qaa〉 is confirmed as order parameter by the result 〈Qaa〉 SP ~ (δJ)β, β = 1, and its susceptibility χaaaa ~(-δJ)?γ with γ = 1/2 at T = 0. The value for γ agrees with the one for the transverse field Ising spin glass. The low γ decay of 〈Qaa〉, ~ T is obtained exactly in the whole quantum disordered phase including the critical value. 相似文献
1000.