Mean polarizability of molecules and anisotropy of the Lorentz tensor upon a nematic-smectic a phase transition: Their behavior in a homologous series

Experimental values of the mean polarizability of molecules, [`(g)]\bar \gamma , and components of the Lorentz tensor, L <sub>j</sub> , in the nematic and smectic A phases are obtained for a homologous series of n-alkyl-p-(4-ethoxybenzylideneamino)-α-methylcinnamates. Dependences of the [`(g)]\bar \gamma and L _j values on the mesophase temperature, the orientational order parameter S of molecules, and the number n in the homologous series are revealed. The quadratic dependence of [`(g)]\bar \gamma (S) in the nematic and smectic phases is established that is invariant with respect to the nematic-smectic A transition. Polarizability densities of the molecular core and the alkyl chain are found from the monotone decreasing dependence [`(g)]\bar \gamma (n)/v (where v is volume per one molecule) in the smectic phase. The presence (or absence) of the odd-even alternation of L _j (n) in the nematic (smectic) phase is shown. A monotone decrease in the Lorentz tensor anisotropy L with an increase in n is revealed in the smectic phase, and limiting values L _j (n → ∞) are determined.     

Anisotropy of the local field of the light wave in cholesteric liquid crystals

The experimental values of the L _j components of the Lorentz tensor have been obtained for the first time for the quasinematic layer of the cholesteric phase and in the smectic phase A for homologs of cholesteric fatty ethers using the dispersion dependences of the refraction indices for the planar texture of cholesteric liquid crystals (CLCs). The dependence of the L _j components on the homolog number, mesophase temperature, the magnitude of birefringence, and the change in the orientational ordering of molecules in the cholesteric phase and at the cholesteric-smectic A phase transition was determined. Isotropization of the Lorentz tensor L and the local field tensor f was found for CLCs when the birefringence of LCs and the anisotropy of molecular polarizability decreased simultaneously. The anisotropy Δf was found to be negative for the quasinematic layer of CLCs and the smectic phase in the visible range of the spectrum. The values of L _j , obtained with known local field models for CLCs and smectics A, gave positive Δf irrespective of the chemical structure of molecules, optical anisotropy of LCs, and the spectral region, which contradicts to the experiment.     

Anisotropy of dipole-dipole interactions in ferroelectric langmuir films of poly(vinylidene fluoride-trifluoroethylene)

The Lorentz tensor components L _j for poly(vinylidene fluoride-trifluoroethylene, 70/30) Langmuir-Blodgett films in the ferroelectric phase are determined experimentally. The results indicate that intralayer dipole-dipole interaction between the segments of the polymer is stronger than interlayer interaction. This conclusion agrees with the absence of the critical film thickness below which ferroelectricity would cease to exist.     

Experimental solution of the local-field problem in discotic liquid crystals

Polarized light-absorption spectra are obtained for single-domain planar-oriented samples of the discotic D _ho . Previously predicted spectral effects induced by resonant dipole-dipole interactions of the molecules are observed. New methods for determining the parameters of the local field in the D ho phase are developed which take into account the mixing of the molecular excitations. It is shown that the two-dimensional crystalline ordering of the molecular columns decreases the anisotropy of the local field for this phase. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 1, 30–35 (10 July 1999)     

Low‐Level Laser Therapy and Sodium Diclofenac in Acute Inflammatory Response Induced by Skeletal Muscle Trauma: Effects in Muscle Morphology and mRNA Gene Expression of Inflammatory Markers

Pharmacological therapy is widely used in the treatment of muscle injuries. On the other hand, low‐level laser therapy (LLLT) arises as a promising nonpharmacological treatment. The aim of this study was to analyze the effects of sodium diclofenac (topical application) and LLLT on morphological aspects and gene expression of biochemical inflammatory markers. We performed a single trauma in tibialis anterior muscle of rats. After 1 h, animals were treated with sodium diclofenac (11.6 mg g^‐1 of solution) or LLLT (810 nm; continuous mode; 100 mW; 3.57 W cm^?2; 1, 3 or 9 J; 10, 30 or 90 s). Histological analysis and quantification of gene expression (real‐time polymerase chain reaction—RT‐PCR) of cyclooxygenase 1 and 2 (COX‐1 and COX‐2) and tumor necrosis factor‐alpha (TNF‐α) were performed at 6, 12 and 24 h after trauma. LLLT with all doses improved morphological aspects of muscle tissue, showing better results than injury and diclofenac groups. All LLLT doses also decreased (P < 0.05) COX‐2 compared to injury group at all time points, and to diclofenac group at 24 h after trauma. In addition, LLLT decreased (P < 0.05) TNF‐α compared both to injury and diclofenac groups at all time points. LLLT mainly with dose of 9 J is better than topical application of diclofenac in acute inflammation after muscle trauma.     

Optical and structural anisotropy of a uniaxial nematic consisting of biaxial molecules with internal rotation

A relation is established between the refractive indices of a uniaxial nematic liquid crystal (LC) consisting of biaxial molecules with internal rotation and the properties of molecules and their structural ordering. It is shown that the correlation between the conformation degree of freedom associated with internal rotation of π-conjugate molecular fragments and the orientation degrees of freedom of the molecules as a whole leads to the existence of two mixed parameters of orientation-conformation order, which contribute to the optical anisotropy of the LC along with the parameters of the conformation and orientation order of the molecules. The effect of the correlation of the molecular degrees of freedom on the values of these order parameters and the properties of molecular polarizability is analyzed. The dependence of the polarizability of molecules on their orientation ordering in the LC is explained.     

Modeling processes of thermal decomposition of hydrocarbon fuels in heated channels

We introduce a mathematical model of the nonequilibrium process of thermal decomposition of hydrocarbon fuel in heated channels of a ramjet combustion chamber cooling system. This mathematical model is based on describing the process using intermediate asymptotics formed when taking into account the equilibrium gas composition, which is determined using open source software for calculating the equilibrium state of the chemical reaction products. A procedure was introduced allowing at different stages of the process of thermal decomposition of fuel to separate kinetically irreversible and reversible chemical reactions and to exclude from consideration chemical reactions which remained incomplete in a limited size engine. We present the features of the process of thermal decomposition of liquid and solid fuels which can be used in high-speed aircraft engines.     

Kinetics and mechanism of cyclohexene hydrocarbomethoxylation catalyzed by a Pd(II) complex

The kinetics of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid (TSA) is reported. The reaction is first-order with respect to cyclohexene and TSA and of order 0.5 with respect to Pd(PPh₃)₂Cl₂. The reaction rate as a function of CO pressure or methanol or PPh₃ concentration passes through an extremum. The chloride anion inhibits the reaction. A mechanism involving cationic hydride complexes as intermediates is suggested. A rate equation is set up by the quasi-steady-state treatment of experimental data.