Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers

The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase -- the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like ``pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two

Light scattering study of the “pseudo-layer” compression elastic constant in a twist-bend nematic liquid crystal

The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or “pseudo-layers”, each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining “layer” compression and bending ought to be characterized by an effective layer compression elastic constant Beff and average director splay constant Keff1. The magnitude of Keff1 is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, Beff could differ substantially from the typical value of ∼10⁶ Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the “pseudo-layer” structure of the TB phase with Beff in the range 10³–10⁴ Pa. We show additionally that the temperature dependence of Beff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director

ANALYSIS OF RESULTS OF RESEARCHES OF ELECTROTECHNOLOGICAL TREATMENT OF THE COTTON TROUBLE UP TO THE FIRST CROP COLLECTION

This article discusses the electrophysical characteristics of plants, more precisely the disclosure of the mechanism of electrical action on the plant through the study of the specific electrical resistance, as well as the task of developing the technological parameters of the electro-technological processing of crops. Knowledge of current value is given, passing through the minted and the rest of the cotton, determination of the negative impact of electrotechnological stamping of cotton on growth and development, yield, by electrotechnological method, including studies of the minted part of cotton, the death of the leaves, the seeds of the pests, the absence of a negative impact on the remaining non-minted part of the cotton by the proposed spark discharge according to the method of coining. To study the electrical effect of a high-voltage spark discharge on cotton, an electrical circuit of a laboratory setup has been developed

Hypothalamic-Pituitary Complications in Patients with Covid-19

The article discusses the traditions of building hydraulic structures in difficult terrain since ancient times. The unique characteristics of the landscape and socio-economic conditions in the territory of Uzbekistan have led to the development of hydrotechnical structures from the simplest local building materials - stone, wood, clay. In the past, it was possible to build large irrigation facilities, create dams, distribution irrigation facilities, etc., to transport water over difficult terrain. A large part of the experience of the past does not lose its importance even today, especially in the rural areas. Therefore, hydraulic engineering deserves the attention of modern researchers

Results of comparative studies of tillage technologies when sowing repeated crops

The article presents the main results of comparative experimental studies of traditional (plowing, chisel-growing) and energy-saving (strip) tillage in Uzbekistan when sowing re-crops after harvesting winter cereal

Combined tool for improving arid pastures

The purpose of the study is to substantiate the advantages of the combined tool developed by the authors for improving pastures. The device of a tool for improving pastures is given. The results of comparative tests of existing guns and a mock-up sample of a combined gun are presented. During field experiments, fuel consumption, unit performance, soil crumbling, hardness, humidity, and soil density were determined. The calculation of the technical and economic indicators of the tool was carried out. According to the results of tests and calculations, it was found that the combined tool surpasses the existing tools used to improve pastures in terms of the main technical and economic indicators. At the same time, the developed tool allows to increase labor productivity by 6.1 times and reduce fuel consumption by 84.7%. As a result, annual labor savings amount to 823.1 people • h, operating costs will decrease by 82.5%