似生物膜系统之六角液相

首度在二维溶致型层状液晶系统中,发现了液相与固相之间存在一“六角方向性”的新状态.这个状态显示了的六角长程有序与似液相的位置相关连特性之特征,而与熟知的二维融化理论所预期的现象有显著的差异.     

New hexatic liquid phase observed in lyotropic thin films

An intermediate surface hexatic phase between the liquid and the crystalline phases has been found for the first time in a lyotropic lamellar liquid-crystal system. This phase is highly unusual in that it has long-range sixfold bond-orientational order but liquidlike nearest-neighbor positional correlations, and could represent a significant departure from our current understanding of defect-mediated melting in two dimensions.     

Chromonic liquid crystalline phase transition involving a biphasic region of nematic and hexagonal phases

We report the results of our studies on the optical and thermal properties of binary mixture of two compounds viz. abietic acid and poly ethylene glycol (PEG). The mixture shows a very interesting co-existent biphasic region of lyotropic nematic (N + I) and intermediate hexagonal (M + I) phases, sequentially when the specimen is cooled from its isotropic phase at different concentrations of abietic acid in PEG. The aggregated molecular size has been confirmed by X-ray studies. The temperature variation of optical anisotropy, electrical conductivity, ultrasonic velocity, and molar and adiabatic compressibility has also been discussed.     

液晶中一种稳定的相态:蓝相

文章描述了胆甾相液晶中蓝相的研究现况．蓝相(BP)是液晶中具有特殊性质的一个相态，它的序参量表现出三维空间周期性．蓝相是出现在一个狭小的温度间隔里(量级为0．1—1K)的稳定相态．文章对已观察到的BPⅠ，BPⅡ，BPⅢ(“雾”相)的性质做了简要的叙述．对研究液晶蓝相的主要理论——Ginzburg-Landau理论(唯象理论)作了介绍，并指出了蓝相研究的实际物理意义。     

Near infrared photoluminescence observed in dilute GaSbBi alloys grown by liquid phase epitaxy

We report the first observation of photoluminescence (PL) from the dilute bismide alloy GaSbBi. Epitaxial layers are grown by liquid phase epitaxy technique onto GaSb (1 0 0) substrates and PL is obtained in the near infrared spectral range (λ ∼ 1.6 μm). Incorporation of 0.2, 0.3 and 0.4 at% Bi to the layer results in a decrease of band gap energy up to 40 meV as well as an increase of luminescence from the sample. Structural analysis confirms the successful incorporation of Bi consistent with an increase in lattice parameter. Raman spectroscopy measurements indicate vibrational modes due to GaBi as well as to free Bi atoms residing at interstitial spaces.     

Birefringence study on lyotropic micellar nematic phase in a binary mixture

We report the results of our studies on optical and thermal properties of two non-mesogenic compounds, namely, didodecyl dimethyl ammonium bromide (DDAB) and glacial acetic acid. The mixture exhibits schlieren texture of lyotropic micellar nematic (N_D), SmA, SmB, and SmG phases, respectively, at different concentrations of DDAB sequentially when the specimen is cooled from isotropic phase. The order parameter (S) of lyotropic micellar nematic (N_D) phase is estimated with the help of temperature dependence of optical anisotropy from the measured values of refractive index and density data. The temperature variation of order parameter of the experimental curve is in agreement with the Mayer–Saupe theoretical curve. The formation of the above phases has been confirmed by optical studies.     

Molecular orientation of lyotropic nematic phase in a mixture of two non-mesogenic compounds

We report the results of our studies on the optical and thermal properties of the mixture of two non-mesogenic compounds, namely, sodium dodecyl sulfate (SDS) and glacial acetic acid (GAA). The mixture exhibits very interesting schlieren texture of lyotropic micellar nematic (N_D) phase, SmA and SmB phases, respectively, at different concentrations of SDS in GAA sequentially when the specimen is cooled from its isotropic phase. The order parameter (S) of the lyotropic micellar nematic (N_D) phase is estimated with the help of temperature dependence of optical anisotropy from the measured values of refractive index and density data. The experimental curve showing the temperature variation of order parameter is very well fitted with the Mayer–Saupe theoretical curve. X-ray studies have also been discussed. The formation of the above phases has been confirmed by optical and differential scanning calorimetry studies.     

Parity-breaking phase transition in tangentially anchored nematic drops

Summary The existence of the parity-breaking phase transition between untwisted and twisted bipolar structures of the tangentially anchored spherical nematic drops has been shown experimentally. Twisted structures behave like the optically active objects in spite of the nonactivity of nematic and isotropic matrix themselves. Temperature dependences of the order parameter (twist angle) have been determined for the drops of 8 CB and 8 OCB. It has been shown that these dependences are very similar to that observed in usual second-order phase transition. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.     

Berry phase in a generalized nonlinear two-level system

In this paper, we investigate the behaviour of the geometric phase of a more generalized nonlinear system composed of an effective two-level system interacting with a single-mode quantized cavity field. Both the field nonlinearity and the atom-field coupling nonlinearity are considered. We find that the geometric phase depends on whether the index k is an odd number or an even number in the resonant case. In addition, we also find that the geometric phase may be easily observed when the field nonlinearity is not considered. The fractional statistical phenomenon appears in this system if the strong nonlinear atom-field coupling is considered. We have also investigated the geometric phase of an effective two-level system interacting with a two-mode quantized cavity field.     

Berry phase in a generalized nonlinear two-level system

In this paper, we investigate the behaviour of the geometric phase of a more generalized nonlinear system composed of an effective two-level system interacting with a single-mode quantized cavity field. Both the field nonlinearity and the atom--field coupling nonlinearity are considered. We find that the geometric phase depends on whether the index $k$ is an odd number or an even number in the resonant case. In addition, we also find that the geometric phase may be easily observed when the field nonlinearity is not considered. The fractional statistical phenomenon appears in this system if the strong nonlinear atom--field coupling is considered. We have also investigated the geometric phase of an effective two-level system interacting with a two-mode quantized cavity field.     

Monitoring the liquid phase concentration by Raman spectroscopy in a polymorphic system

In this work, Raman spectroscopy was successfully used for the quantitative determination of the liquid phase concentration in an aqueous polymorphic system of D‐mannitol. An extensive study has initially been performed to identify the influence of the solid state, e.g. particle size, particle amount, and different polymorphs, on the intensity of the characteristic Raman solute signal. It was found that the existence of solid phase can decrease Raman intensity, and this influence is more significant when the suspension density is higher, e.g. with smaller size and larger amount of particles. Based on this information, a large number of samples were examined by Raman spectroscopy in the form of clear solutions and suspensions. The spectral preprocessing and partial least squares (PLS) regression were then used to relate the solute concentrations to these spectral data, independent of solid state. Several PLS calibration models were developed with different treatments to the spectral data, and the optimized strategy was finally demonstrated. Particularly, a reference peak at 578 cm⁻¹ related to the sapphire in the Raman probe window was innovatively applied to reduce the influences from the equipment and other external variations, with which the full‐spectrum PLS model was seen to give more stable results rather than partial spectral regions. The optimized model was subsequently applied to predict the liquid phase concentration in a multiphase multicomponent dynamic process, the solvent mediated polymorphic transformation (SMPT) of mannitol, and it was shown that the offline measurements and the predicted values were mainly in agreement with one another. Copyright © 2015 John Wiley & Sons, Ltd.