Electric field distortions in structures of the twist bend nematic (NTB) phase of a bent-core liquid crystal

Dielectric spectroscopy of a twist bend nematic phase of an achiral bent core liquid crystalline compound under DC bias is used to investigate its response to electric field. Two collective relaxation processes are revealed, these are assigned to distortions of helicoidal structure by the external bias field. Frequency of the mode depends primarily on the helicoidal angle and has anomalous, softening- like behaviour at the nematic to the twist bend nematic transition. A coupling of dielectric anisotropy with electric field gives rise to a new equilibrium periodic structure in the time scale involved. The modulus of the wave vector gradually vanishes on increasing the bias field (except for the initial behaviour, which is just the opposite). Transition from the twist bend to the splay bend structure is clearly observed by a sudden drop in the frequency of this mode, which decreases almost linearly with increasing field. Results agree with predictions from current models for the periodically distorted a twist bend nematic phase.Comment: 14 PAGES, 7 FIGURES, submitted to Physical Review Letter

Modulatory Effects of L- Tyrosine on Neurobehavioural Consequences of Combat Stress in Rats

The paper presents the results of a study conducted to elucidate tile potentiality of tyrosine, aprecursor of catecholaminergic neurotransmitters, against combat stress-associated behavioural changes and brain catecholamine status in an animal model. The results obtained showed that stressimpaired the performance on Morris water maze (MWM) in saline-injected rats and concurrentlylowered norepinephrine (NE) levels in brain. This could be due to decreased dopamine J3-hydroxylase(DBH) activity and increased monoamine oxidase (MAO) activity. On the contrary, there was asignificant improvement in post-stress performance in MWM test in animals receiving tyrosine.Stress-induced increase in catecholamine metabolites, homovanillic acid and vanillylmandelic acid inbrain was prevented by treatment with tyrosine. The present fmdings imply that precursor availabilitycould be a limiting factor to sustain intensified catecholamine synthesis during stress and hencesupplementation of L-tyrosine could be beneficial to improve performance during stres

A review paper on R&D efforts in assessing the traffic noise on highways

In rapidly urbanizing country like India, the transportation sector is growing in a fast pace and the number of vehicles on Indian roads is increasing at a rate of more than 7% per annum. This has led to over crowded roads and pollution. Transportation sector is one of the major contributors to noise in urban area, which contributes 55% of total noise on highway. In view of this, it is essential to study highway noise with respect to various causative factors. Hence, various noise prediction models have been developed, throughout the world to assess its impact on to the society and the human beings. These traffic noise prediction models differ in some respects, but the overall methodology is similar. All the noise prediction models consists of evaluating basic noise levels and making series of adjustments to take into account geometric, traffic flow, barrier data etc. In this paper, noise prediction models of U.S.A. and U.K. (FHWA and CORTON) along with the research efforts on noise in Indian context has been studied and discussed

The NTB phase in an achiral asymmetrical bent-core liquid crystal terminated with symmetric alkyl chains

The characteristics of the twist-bend nematic (NTB) phase of an achiral asymmetrical rigid bent-core liquid crystal (LC), the ends of which are terminated by symmetric alkyl chains, are reported. The nematic�nematic phase transition and its properties are studied by differential scanning calorimetry (DSC), polarising microscopy and the electro-optic techniques. Large domains of opposite handedness are observed in the absence of the external field in the NTB phase. Another set of periodic striped pattern consisting of domains with sharp boundaries is formed when a high-frequency electric field with a magnitude above its threshold is applied across a planarly aligned cell. The neighbouring domains are of opposite chirality. The temperature dependence of the heliconical angle θ0 is determined from the birefringence measurements using Haller�s extrapolation technique. This material shows lower values of the heliconical angle (~9.3° at a temperature of 155°C within the NTB phase) when compared with the previously reported dimer-based twist-bend nematic LCs (31°±3°). © 2016 Informa UK Limited, trading as Taylor & Francis Group

Nematic twist-bend phase with nanoscale modulation of molecular orientation

A state of matter in which molecules show a long-range orientational order and no positional order is called a nematic liquid crystal. The best known and most widely used (for example, in modern displays) is the uniaxial nematic, with the rod-like molecules aligned along a single axis, called the director. When the molecules are chiral, the director twists in space, drawing a right-angle helicoid and remaining perpendicular to the helix axis; the structure is called a chiral nematic. Here using transmission electron and optical microscopy, we experimentally demonstrate a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend. The oblique helicoids have a nanoscale pitch. The new twist-bend nematic represents a structural link between the uniaxial nematic (no tilt) and a chiral nematic (helicoids with right-angle tilt)

Nematic Twist-Bend Phase with Nanoscale Modulation of Molecular Orientation

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Electrooptic, pyroelectric and dielectric spectroscopic studies of nematic and twist bend nematic phases of achiral hockey-shaped bent-core liquid crystal

Experimental and theoretical investigations of the twist-bend nematic (NTB) phase in liquid crystals have recently received significant attention for reasons of unusual and interesting characteristics of the NTB. Though NTB was predicted to exist for rigid bent-core LCs by Ivan Dozov in 2001, nevertheless it has unambiguously been proven to exist only in a few bent-core systems so far. Here the characteristics of both the nematic (N) and NTB phases are investigated for a hockey shaped achiral rigid bent-core LC, called BCI, in planar and homeotropic aligned cells, using polarizing optical microscopy, electro-optics, pyroelectricity and wide band dielectric spectroscopy. Spontaneous polarization measured for a bias field of 2.2 V/μm of a chiral domain using the pyroelectric effect is found to be only ∼5 nC/cm2. A measurement of the spontaneous polarization using pyroelectricity in general is unaffected by the sample’s dc conductivity except when its conductance dominates the admittance. As helix of NTB is partially unwound by the field, results lead to the identification of NTB as polar and chiral. The first and the second harmonics of the applied field are observed of higher amplitudes in NTB and N phases, respectively. The hockey-shaped bent-core system exhibits a large negative dielectric anisotropy over a wide range of temperatures than observed for any other compound so far. The large negative dielectric anisotropy is the highly desirable characteristic parameter of the NTB for exploring the field induced phases at relatively lower field strengths. The orientational order parameter characteristically jumps at the N-NTB transition temperature. The complex dielectric permittivity is measured as a function of frequency in the range 1 Hz to 10 MHz, the analysis of results reveales two collective modes in the dielectric spectra. Amplitude of the lower frequency mode is much higher than of higher frequency, former is assigned to the hydrodynamic mode q=qzz^ with z-dependent rotation of the heloconical director n^(r), this in turn involves compression and dilation of the pseudo-layers. The higher frequency mode corresponds to fluctuations of the tilt director and closer to the transition temperature, it exhibits a typical soft mode characteristic feature

Biaxial order parameter in the homologous series of orthogonal bent-core smectic liquid crystals

The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of S and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-APA) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that S in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large

Cross center single-cell RNA sequencing study of the immune microenvironment in rapid progressing multiple myeloma

Despite advancements in understanding the pathophysiology of Multiple Myeloma (MM), the cause of rapid progressing disease in a subset of patients is still unclear. MM\u27s progression is facilitated by complex interactions with the surrounding bone marrow (BM) cells, forming a microenvironment that supports tumor growth and drug resistance. Understanding the immune microenvironment is key to identifying factors that promote rapid progression of MM. To accomplish this, we performed a multi-center single-cell RNA sequencing (scRNA-seq) study on 102,207 cells from 48 CD13

Flexoelectric Behaiour of a Bimesogenic Liquid Crystal

The effective flexoelectric coefficient and flexoelectric polarization are investigated for a bimesogenic liquid crystal CBC11CB with a twist bend nematic phase (Ntb). The effective flexoelectric coefficients for CBC11CB in the ordinary nematic phase (N) are obtained to be much larger in comparison to conventional calamitics, and is almost twice higher for CBC11CB than that reported for another odd symmetric bimesogen. The flexoelectric polarization (Pf) in the N phase is found to be almost 2.5 times higher than in rod-like molecules. Additionally, Pf is obtained to be much larger in the Ntb phase than in the nematic phas