Broad temperature range ferrielectric liquid crystal as a highly sensitive quadratic electro-optical material.

A chiral smectic liquid crystal in which a ferrielectric phase with a helix pitch p0 less than 125 nm exists over a temperature range of at least from -3°C to +36°C has been developed. Such a wide temperature range (including room temperatures) of the ferrielectric phase with a subwavelength helix pitch has been achieved for the first time, to the best of our knowledge, which creates opportunities for the practical use of ferrielectric liquid crystals. A quadratic electro-optical effect caused by deformations of the helix in an electric field is observed in the ferrielectric phase, and the Kerr coefficient, which reaches almost 200 nm/V2, is significantly higher than the same coefficient for the blue phase and for the smectic C* phase, which means a higher sensitivity of the developed ferrielectric liquid crystal to the electric field. The electro-optical response time does not exceed 300 µs at room temperatures for this ferrielectric liquid crystal.

Comparative Monte-Carlo simulations of charge carrier transport in amorphous molecular solids as given by three most common models of disorder: The dipolar glass, the Gaussian disorder, and their mix.

We have performed Monte-Carlo simulations of the charge carrier transport in a model molecularly doped polymer using three most popular hopping theories (the dipolar glass model, the Gaussian disorder model, and an intermediate between them) in a wide range of applied electric fields and temperatures. Time of flight transients have been computed and analyzed in logarithmic coordinates to study the Poole-Frenkel field dependence, the non-Arrhenius mobility temperature dependence, and the nondispersive versus dispersive current shapes. We also have made an attempt to estimate the total disorder energy directly from simulation data at the lowest electric field thus checking the consistency of the model fitting. Computational results have been compared with the analytical and experimental information available in the literature.

Short bent-core molecules: X-ray, polarization, dielectricity, texture and electro-optics investigations.

Bent-core liquid crystals based on 1,2,4-oxadiazole as a central unit have been the first mesogens to exhibit a ferroelectric response in the nematic phase. This behavior has been widely recognized as due to the presence of smectic-like polar cybotactic clusters permeating the nematic phase. Unfortunately, these compounds exhibited rather high melting points, about 120 °C, due to the presence of four benzene rings in the molecules. Here we describe the synthesis and physical characterization of a new series of BC mesogens, featuring the same bent core as the previous compounds but shorter outer substituents. By keeping only two benzene rings, we were able to lower the melting points to about 70 °C. However, while X-ray diffraction and dielectric spectroscopy measurements confirm the cybotactic nature of the nematic phase of these compounds, polarization and electro-optical measurements ascribe their polar response to flexoelectricity rather than to spontaneous polarization. Finally, texture investigation suggests the biaxiality of the nematic phase, which is indicated also by conoscopic measurements. These results are important for recognizing size and rigidity limitations in designing bent-core liquid crystal molecules suitable for applications.

Multistability in the mixtures of smectic-C

The effect of multistability in the mixtures of smectic-C^{*} materials with compensated twisting power, i.e., the existence of a large number of almost equiprobable states in the same mixture under the same conditions, is analyzed in the framework of elastic continuum theory. A simple molecular model is also considered. It is shown that multistability can follow from the bulk properties of the smectic-C^{*} materials with compensated twisting power, but with high spontaneous polarization. Multistability leads to the formation of ferroelectric domains, in which the director oscillates in space. The length and amplitude of this oscillation is tunable smoothly by an electric field. Theoretical results for the domain length agree completely with the experimental data. A suggestion is made as to why each domain structure is remembered without the energy consumption, when the electric field is abruptly switched off. The structural dependence on material parameters, such as the spontaneous polarization, the elastic constant, and the equilibrium wave number, is predicted.

High frequency hysteresis-free switching in thin layers of smectic-C* ferroelectric liquid crystals.

The insulating layers used for the alignment of ferroelectric liquid crystals (FLC) in electro-optical cells usually have non-negligible thickness and their capacitance determines the type of the director switching caused by a triangular-form external voltage U(tr) . With decreasing frequency of U(tr) , the hysteresis in a switching direction changes from the normal to the abnormal one at a characteristic hysteresis inversion frequency f(i) . In the vicinity of f(i) , the electro-optical response is thresholdless and the optical transmission manifests the V -shape field dependence. The V -shape regime is very interesting for certain applications, in particular to microdisplays due to a possibility of the gray scale realization. However, f(i) has to be enhanced from the usually observed frequency of a few Hz up to the range of hundreds of Hz. To this effect, a special FLC material has been designed and its basic properties (tilt angle, spontaneous polarization, rotational viscosity, and electric conductivity) have been measured over the entire range of the smectic-C* phase. Upon variation of cell parameters (thickness of both the FLC and alignment layers), temperature, and external voltage, the frequency of the V -shape effect as high as 150-1000 Hz (in the temperature range 30-75 degrees C) has been found experimentally. The operating voltage remains lower than 8 V. A quantitative interpretation of these results has been done using the modeling procedure developed earlier [S.P. Palto, Cryst. Rep. 48, 124 (2003)]. The modeling has been performed with the experimental values of the FLC material and the cell parameters and has shown very good agreement with experiment. The key point of this approach is consideration of the internal voltage on the FLC layer, the sign, amplitude, and form of which differ from U(tr) . The results of the modeling allow further improvement of the performance of electro-optical FLC cells for high frequency V-shape effect.

"Thresholdless" hysteresis-free switching as an apparent phenomenon of surface stabilized ferroelectric liquid crystal cells.

The thresholdless, hysteresis-free V-shape electro-optical switching in surface-stabilized ferroelectric liquid crystals, observed usually with a triangular voltage form, has been shown to be rather an apparent and not a real effect. Strictly speaking, it is observed only at one characteristic frequency f(i) and is accompanied by an inversion of the electro-optical hysteresis direction from the normal to the abnormal one. The switching of the director in a liquid crystal layer at f(i), in reality, has a threshold and a normal hysteresis. Even the optical transmittance shows a hysteresis at f(i) when it is plotted as a function of the voltage on the liquid crystal layer and not as a function of the total voltage on the liquid crystal cell which always includes the inner insulating layers. Due to these layers, a voltage divider is formed which includes the capacitance of the insulating layers and the dynamic impedance (capacitance and resistance) of the ferroelectric liquid crystal layer. The new explanation has been confirmed by experiments with different ferroelectric liquid crystal cells combined with external resistors and capacitors and by measurements of a strong dependence of f(i) on the liquid crystal resistance which was varied over three orders of magnitude. A theoretical analysis of the problem has also been made using certain approximations for material parameters and the space dependence of the sine form of the electric field in the liquid crystal layer. The conclusions are qualitatively consistent with the experimental results. Finally, the dynamic problem has been solved numerically by taking into account of all the relevant parameters (in the absence of flow and irregularities in the cell plane) and the obtained results are in excellent correspondence with the experiment. This has been demonstrated for sets of material and cell parameters providing the best V-shape performance.

[Morpho-functional changes in tissues surrounding a gunshot wound]. / Morfofunktsional'nye izmeneniia v tkaniakh, okryzhaiushchikh ognestrel'nuiu ranu.

The authors studied the dynamics of changes of microcirculatory disorders in tissues surrounding the wound canal in experimental animals with gunshot injuries of the soft tissues of the thigh. Tissue radiometry and scanning were used. The damage was found to be regularly distributed in 4 zones of microcirculatory disorders differing also in morphological characteristics on a light and electron level: zone 1 of primary necrosis or traumatic destruction of tissues; zone 2 of secondary necrosis (forms on the 3rd day after the injury); zone 3 of reactive-destructive changes of tissues, which is the source of granulation tissue development (microcirculation in this zone is restored by the end of the 2nd week after the injury); zone 4 of reactive changes in the tissues with complete abatement of microcirculatory disorders by the end of the 1st week after the injury. The obtained data possess theoretical and practical significance.

[Experimental substantiation of a precision technic of creating an interintestinal anastomosis in acute intestinal obstruction]. / Eksperimental'noe obosnovanie pretsizionnoi tekhniki formirovaniia mezhkishechnogo soust'ia pri ostroi kishechnoi neprokhodimosti.

Two kinds of intestinal sutures performed with the use of a precision technique were investigated on models of acute intestinal obstruction. One-row (serous-muscular-submucosal) and two-row (serous-musculo-submucosal and submucosal-mucosal) sutures provide an exact layer-after-layer connection of the intestinal wall layers and a sufficient mechanical firmness of the anastomosis with little traumatization. The dynamics of microcirculation changes in the anastomosis zone was followed with the help of contact intraoperative biomicroscopy. Symptoms of the traumatic inflammation were cupped off within 5 days and changed by reparative processes.

[Patterns characterizing different levels of animal organization]. / O zakonomernostiakh, kharakterizuiushchikh raznye urovni organizatsii zhivotnogo

The article deals with features of the regularities characterizing different levels of organization of the animal body. The cell is not only an integrated but also indivisible organic integrity which is due to the interaction of the nucleus and cytoplasm determining all sides of its vital activity. From this viewpoint the results of experiments on transplantation of the embryo cell nucleus into an enucleated egg of amphibia and the data on somatic hybridization are estimated. All processes of the cell life, their growth, multiplication and differentiation develop within the tissue system and are determined by the regularities of its development. The integrated system of the organism of a multicellular animal unites all the forms of integration of multi-step systemic pattern at different organization levels. Among different categories the systems of tissues and their interaction within the organ are most integrated. The regularities of the tissue development can not be brough to the regularities of the development of the anatomical structure of organs. The integration of cell elements in a tissue system and intertissue relations is the basis of all forms of interdependence in the cell development and the organism structure.