On the origin of the ferroelectric ordering in nematic liquid crystals and the electrostatic properties of ferroelectric nematic materials

Possible molecular origin of ferroelectricity in the nematic phase is discussed in detail considering a number of models based on direct dipole–dipole interaction and electrostatic interaction between surface charge densities. A more model which combines dipole–dipole interaction and short-range orientational–translational correlations is also considered. In particular we derive a contribution to the total free energy of the long-range tail of the dipole–dipole interaction potential and show that this contribution depends on the sample shape and on the boundary conditions. As a result this shape-dependent contribution may strongly effect the transition into the ferroelectric phase depending on the actual boundary conditions maintained experimentally. We also consider two conjugated thermodynamic potentials which depend on the electric field in the medium and on the displacement field, respectively. It is shown that the actual polarization corresponds to the minimum of one of these potentials depending on the boundary conditions which may have significant experimental consequences. In the framework of the general Landau de Gennes theory, which employs both potentials, the ferroelectric properties of different nematic cells are considered including the ones with fixed applied voltage and free cells with disconnected electrodes

Orientational ordering and spatial distribution of Janus nanoparticles in lamellae diblock copolymers

Orientational ordering and spatial distribution of rod-like Janus nanoparticles in the lamellae diblock copolymers has been considered using a molecular theory based on simple model of Janus particle with two different interaction centres located at the particle ends. Order parameter and concentration profiles of Janus nanoparticles have been calculated numerically for different values of the nanoparticle length. It has been found that Janus nanoparticles are mainly located in the boundary region between the domains and are orientationally ordered in that region with a high orientational order parameter. This orientational order is induced by the interface and is determined by the different affinities of the two ends of the Janus particle with respect to the monomers of different domains. Comparison with block copolymers doped with symmetric nanoparticles indicates that polymer nanocomposites with Janus particles are expected to possess much larger dielectric anisotropy and thus can be considered as promising anisotropic nanomaterials which can be aligned by the external electric field

Computer simulations of hard pear-shaped particles

We report results obtained from Monte Carlo simulations investi- gating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the trun- cated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like po- tential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3; 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A2 phases.</p

Three in one : mesogenic aromatic acid as a liquid crystal matrix, a chiral dopant in liquid crystals and a stabilizer for nanoparticles

Studies of thermodynamics of the N*-I phase transitions and optical properties of the new liquid crystal - (R)-2-[4″-(trans-4-butylcyclohexyl)-2′-chloro-p-terphenyl-4-oxy] propanoic acid are carried out. The aim of these studies is to analyze the capabilities of that liquid crystal to simultaneously serve as a matrix for inorganic semiconductor nanoparticles (NP) as well as a chiral dopant for liquid crystals and a chiral ligand stabilizing the surface of CdSe NPs. The chiral doping of a nematic liquid crystal was proven by the measurements of selective transmittance of the visible light. The embedding of NPs in a nematic liquid crystal leads to the increase in TN⁎I, which is explained by the shape anisotropy of the NPs. The anisotropy of the ligand shell may result from the interaction between the ligand and LC matrix inducing the change of the spherical shape of the shell toward the ellipsoidal one. TN⁎I of the liquid crystal matrix of (R)-2-[4″-(trans-4-butylcyclohexyl)-2′-chloro-p-terphenyl-4-oxy] propanoic acid (R-MPA) decreases with the embedding of NPs stabilized by the same ligands, which is in a good agreement with prior experimental results and theory, but there exists a considerable quantitative difference

The level of blood plasma mitochondrial DNA upon acute myocardium damage in experiment

The aim of the present investigation is to study the level of plasma mtDNA as a potential marker of cardiomyocyte damage in 2 and 4 h after subcutaneous injection of adrenaline and during the formed morphological alterations of the myocardium (3 days). Methods. Real time PCR. Male Wistar rats were used as the experimental animals. Results. It was shown that during the increase in the activity of cytolysis biomarkers, at the first hours after adrenaline injection, no reliable increase is observed in the level of free circulating blood mtDNA. A tendency of 2.5-fold increase in this parameter was established at the third day after adrenaline injection during the development of acute inflammatory process in the myocardium. On the whole, further researches are needed on the dynamics of mtDNA level upon acute damage of the myocardium in experimental and clinical investigations for unbiased estimation of the prospects of using the parameter in laboratory diagnostics. Keywords: mitochondrial DNA, cardiovascular diseases, adrenaline myocarditis, cytolysis biomarkers.Цель. Изучить уровень мтДНК плазмы крови как возможного маркера повреждений кардиомиоцитов через 2 и 4 ч после подкожной инъекции адреналина и на фоне сформированных морфологических изменений миокарда (3-и сут). Методы. Полимеразная цепная реакция в реальном времени. В экспериментах использовали самцов крыс линии Вистар. Результаты. Показано, что наряду с увеличением активности биомаркеров цитолиза в первые часы после введения адреналина значимого повышения уровня свободно циркулирующей мтДНК крови не происходит. Установлена тенденция к 2,5-кратному возрастанию данного показателя на 3-и сут после инъекции адреналина на фоне развития острого воспалительного процесса в миокарде. Выводы. В целом для объективной оценки перспектив этого показателя в лабораторной диагностике инфаркта миокарда необходимо дальнейшее изучение динамики уровня мтДНК при острых повреждениях миокарда в экспериментальных и клинических исследованиях. Ключевые слова: митохондриальная ДНК, сердечно-сосудистые заболевания, адреналиновый миокардит, биомаркеры цитолиза.Мета. Вивчити рівень мтДНК плазми крові як можливого маркера пошкоджень кардіоміоцитиів через 2 і 4 год після підшкірної ін’єкції адреналіну та на фоні сформованих морфологічних змін міокарда (3-тя доба). Методи. Полімеразна ланцюгова реакція у реальному часі. В експериментах використано самців щурів лінії Вістар. Результати. Показано, що поряд із збільшенням активності біомаркерів цитолізу в перші години після введення адреналіну суттєвого підвищення рівня вільно циркулюючої мтДНК крові не відбувається. Встановлено тенденцію до 2,5-разового зростання даного показника на 3-тю добу після ін’кції адреналіну на фоні розвитку гострого запального процесу в міокарді. Висновки. У цілому для об’єктивної оцінки перспектив цього показника у лабораторній діагностиці інфаркта міокарда необхідно подальше вивчення динаміки рівня мтДНК при гострих ураженнях міокарда в експериментальних і клінічних дослідженнях. Ключові слова: мітохондріальна ДНК, серцево-судинні захворювання, адреналіновий міокардит, біомаркери цитолізу

Pion condensation of quark matter in the static Einstein universe

In the framework of an extended Nambu--Jona-Lasinio model we are studying pion condensation in quark matter with an asymmetric isospin composition in a gravitational field of the static Einstein universe at finite temperature and chemical potential. This particular choice of the gravitational field configuration enables us to investigate phase transitions of the system with exact consideration of the role of this field in the formation of quark and pion condensates and to point out its influence on the phase portraits. We demonstrate the effect of oscillations of the thermodynamic quantities as functions of the curvature and also refer to a certain similarity between the behavior of these quantities as functions of curvature and finite temperature. Finally, the role of quantum fluctuations for spontaneous symmetry breaking in the case of a finite volume of the universe is shortly discussed.Comment: RevTex4; 15 pages, 10 figure

First experimental results obtained using the highpower free electron laser at the siberian center for photochemical research

The first lasing near the wavelength of 140 µm was achieved in April 2003 using a high-power free electron laser (FEL) constructed at the Siberian Center for Photochemical Research. In this paper we briefly describe the design of the FEL driven by an accelerator–recuperator. Characteristics of the electron beam and terahertz laser radiation, obtained in the first experiments, are also presented in the paper.У Сибірському центрі фотохімічних досліджень навесні 2003 року отримана генерація випромінювання з довжиною хвилі 140 мкм на потужному лазері на вільних електронах (ЛВЕ). У роботі коротко описана конструкція ЛВЕ на базі прискорювача рекуператора і представлені результати вимірювання деяких параметрів електронного пучка і терагерцового випромінювання.В Сибирском центре фотохимических исследований весной 2003 года получена генерация излучения с длиной волны 140 мкм на мощном лазере на свободных электронах (ЛСЭ). В работе кратко описана конструкция ЛСЭ на базе ускорителя рекуператора и представлены результаты измерения некоторых параметров электронного пучка и терагерцового излучения

Molecular models for the smectic A–smectic C phase transition in a system of biaxial molecules

A molecular theory of the smectic A-smectic C transition in a system of biaxial molecules is developed in the mean-field approximation. The influence of molecular biaxiality on the transition is considered in detail and it is demonstrated how the biaxial order parameters are induced by the tilt. It is shown that the ordering of biaxial molecules of low symmetry in the smectic C phase is generally described by ten independent orientational order parameters, and there exist three different tilt angles which specify the tilt of three ordering tensors. The order parameters are calculated numerically as functions of temperature for two models of biaxial molecules: molecules with two principal axes and molecules with a pair of off-center transverse dipoles. A substantial difference between the three tilt angles is found, which makes impossible a strict definition of a unique director in the smectic C phase. It is also shown that biaxial interactions may lead to an anomalously weak layer contraction in the smectic C phase. Finally, it is demonstrated that the smectic A-smectic C phase transition may be directly driven by biaxial intermolecular interactions. In this case, the tilt of long molecular axes is not a primary order parameter, and its temperature dependence is very different from convention