System for detection of the inhomogeneous distribution of magnetic field based on liquid crystals with magnetic nanoparticle

The main objective of this article is to develop the basic technological principles of production of the magnetosensitive layer based on nematic liquid crystals with magnetic nanoparticles as the main component of the system, which allows obtaining a two-dimensional picture of the inhomogeneous distribution of low-frequency magnetic field and to identify the object creating this field. In work are described physical methods which allow to increase sensitivity and to expand a working frequency range of the magneto-sensitive layer based on such liquid crystals. By us it has been shown, that the time of reorientation of director in oriented liquid crystals with magnetic nanoparticles is less than the analogous reorientation time in nonoriented crystals. In work also it is shown, that to significantly increase the speed of reorientation in a magnetic field of the director of liquid crystals with magnetic nanoparticles is possible if submitting an additional magnetic field with given amplitude. This method allows to increase sensitivity to a magnetic field and to receive parametrical amplification of signals in liquid crystals with magnetic nanoparticles. In the conclusion on the basis of liquid crystals with magnetic nanoparticles the scheme of system of detection of inhomogeneous magnetic field is described.

Динамика деформации нематика под действием сильных скрещенных электрического и магнитного полей

A new mode of reorientation of the field of director $$\hat n$$ n ^ of a nematic liquid crystal (LC) encapsulated into a rectangular cell under strong crossed electric ( E ) and magnetic ( B ) fields has been proposed. Numerical calculations performed within the linear generalization of the classical Ericksen–Leslie theory show that transition periodic structures facilitating a decrease in the effective rotational viscosity of a nematic, formed by 4- n -pentyl-4'-cyanobiphenyl (5CB) molecules, may arise during reorientation of $$\hat n$$ n ^ at certain ratios of the moments and momenta per unit volume of the LC phase and when E ≫ E _th. The calculations conducted for 5CB also indicate that the periodic structures formed in a LC cell facilitate a decrease in reorientation time τ_on of the director field.

The force on a boundary in active matter

We present a general theory for determining the force (and torque) exerted on a boundary (or body) in active matter. The theory extends the description of passive Brownian colloids to self-propelled active particles and applies for all ratios of the thermal energy $k_{B}T$ to the swimmer’s activity $k_{s}T_{s}={\it\zeta}U_{0}^{2}{\it\tau}_{R}/6$, where ${\it\zeta}$ is the Stokes drag coefficient, $U_{0}$ is the swim speed and ${\it\tau}_{R}$ is the reorientation time of the active particles. The theory, which is valid on all length and time scales, has a natural microscopic length scale over which concentration and orientation distributions are confined near boundaries, but the microscopic length does not appear in the force. The swim pressure emerges naturally and dominates the behaviour when the boundary size is large compared to the swimmer’s run length $\ell =U_{0}{\it\tau}_{R}$. The theory is used to predict the motion of bodies of all sizes immersed in active matter.

DYNAMIC CONTRAST-ENHANCED MAGNETIC RESONANCE ANGIOGRAPHY OF Gd-TTDA-BOM COMPARED WITH Gd-DTPA IN NORMAL RAT AT 3T

Dynamic contrast-enhanced magnetic resonance angiography (DCE-MRA) is a good modality for the diagnosis of vascular diseases. Contrast agents that produce higher and longer enhancement in vessels are highly valued. The complex of gadolinium with (R,S)-4-carboxy-5,9,12-tris(carboxymethyl)-l-phenyl-2-oxa-5,9,12-triazatridecan-14-oic acid (Gd-TTDA-BOM) possesses a benzyloxymethyl group in the ligand TTDA-BOM with the capability of raising lipophilicity. The Gd-TTDA-BOM complex expresses higher and longer enhancement in mouse liver than that of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) because of its faster water exchange rate, higher reorientation time, and higher lipophilicity. Phantom studies have shown that Gd-TTDA-BOM has expressed with higher affinity to human serum albumin (HSA) than Gd-DTPA. In general, these characteristics might provide an advantage for vascular imaging. To verify this in vivo, a 3T MR scanner was used to investigate the signal enhancement in the aorta of normal rats by DCE-MRA after the bolus injection of Gd-TTDA-BOM and compared this with the injection of Gd-DTPA. Gd-TTDA-BOM expressed higher and longer signal enhancement in the aorta than Gd-DTPA. These results suggest that Gd-TTDA-BOM could provide better image quality than Gd-DTPA as an enhancement agent in DCE-MRA.

Temperature-dependent reorientation dynamics of laser dyes in alkane and alcohol solvents

The rotational dynamics of similar sized coumarin 6 (C6), coumarin 7 (C7), and coumarin 30 (C30) laser dyes has been studied in alkane and alcohol solvents using steady-state and time-resolved fluorescence depolarization methods. The estimated rotational reorientation times of these probes are observed to vary linearly as a function of viscosity over the range of temperatures studied. It is found that the rotational reorientation time measurements of these molecules in alcohol and alkane typically have relaxation times on the order of picoseconds. The rotational reorientation times of the C7 molecule are greater than those of the C6 and C30 molecules. It was observed that C7 rotates faster in both the solvents than C6 and C30, indicating that the effects of the medium and structural differences of molecules lead to slower rotation.

A Vision-Based Embedded Control System for Crystal Reorientation and Inspection

This paper proposes a vision-based embedded motion control system that is developed in our research group. The system is an integration of three subsystems including, an embedded positioning platform, a vision system for inspection and a crystal reorientation system. The system is used as a positioning platform and crystal reorientation system to automate the crystal reorientation process. This process is important in ensuring that the units are correctly oriented for production processes. The focus of this research is placed on how to develop the embedded positioning platform, the crystal reorientation system, and how to improve the system performances including positioning and reorientation accuracy in high speed operation and quality of inspection. A distributed control architecture has been developed using PIC18F4520 microcontrollers. Tests run on the complete system have shown that the system is capable of a minimum indexing time of 1.53 units per second and a reorientation time of 1.42 seconds.