Ryotaro Ozaki

Effect of electrical stress produced by repetitive pulsed power on germination of naked barley seed between point-plane electrodes

This paper presents an experimental study on germination control for naked barley seed by using a repetitive pulsed power technique. Two kinds of tests, localized pulse electric field (PEF) treatment and dielectric barrier discharge (DBD) treatment, are carried out. In the first test, very short mono-polar pulses below 500 ns in width and below 5 kV in heights are applied to the seeds between point-plane electrodes with 500 pps repetition rate for 20 min. A fine stainless needle electrode is inserted into embryo region or endosperm region of the seed to clarify which region should be stressed by the localized PEF for the germination control. The germination rate of the seed after the PEF treatment is compared not only with that of the seed without any treatment (control) but also the seed with sham treatment, which means that the needle tip is inserted without voltage application. Results indicate that there is no effect of the PEF application into the endosperm region of the seed on the germination inhibition. On the other hand, the PEF application into the embryo region has an effect on the germination inhibition if the pulse width is long. In the second test, embryo region of the seed is exposed by the dielectric barrier discharges produced by the polarity-reversed voltage pulses with 100 ns in width. Evans Blue dyeing for the seeds is carried out to clarify the biological activity of the embryo cells. Embryo cell necrosis is caused by the 10 min discharge treatment. On the other hand, necrosis of the seed surface is not observed for the seed after the PEF treatment.

Director orientation of nematic liquid crystal using orientated nanofibers obtained by electrospinning

Nanofibers with diameters less than 1000 nm assembled by electrospinning and with a large surface area per unit mass have been attracting considerable attention and are expected to affect the orientation of liquid crystals (LCs). Firstly, to determine the orientated nanofibers on an indium–tin-oxide (ITO) glass surface, the spectral analysis technique of using fast Fourier transform is applied. Optical observation is performed to confirm the orientation of LC molecules in a twisted nematic LC cell. Finally, optical measurement of an LC cell is carried out to estimate the threshold voltage of the LC in two types of twisted nematic LC cell: one with rubbed polyimide and the other with orientated nanofibers as the alignment layer. A twisted nematic LC is oriented in the cell using orientated nanofibers as the alignment layer and the threshold voltage of this cell agrees with that of the conventional polyimide rubbed cell.

Simultaneous determination of ordinary and extraordinary refractive index dispersions of nematic liquid crystals in the visible and near-infrared regions from an interference spectrum

An improved interference method is proposed to determine ordinary and extraordinary refractive index dispersions of nematic liquid crystals (LCs). In this method, an LC cell coated with a thin metal layer is used as a Fabry-Perot interferometer, which shows us a sharp transmission fringe. To ensure high reliability, the wavelength dispersion of the refractive index of the metal is taken into account in fitting calculation. In spite of measuring ordinary and extraordinary components, the LC cell, polarizers, and other equipment are not rotated during the experiment. The index evaluation from a single spectrum avoids errors depending on the measurement position owing to non-uniformities of molecular orientation and cell thickness because we can obtain the two indices at exactly the same position. This system can adapt to a wide frequency range and does not require any specific wavelength light source or laser. We demonstrate the determination of ordinary and extraordinary refractive index dispersions of a n...

Analyses of Nematic Liquid Crystal Molecule Motion and Response Characteristics in Microstripline-Type Microwave Phase Shifter

In this paper, we propose an improved calculation method for analyzing the three-dimensional motion of nematic liquid crystal molecules in studies of all types of microwave transmission line loaded with a nematic liquid crystal. This method is applied to the analysis of motion of nematic liquid crystal molecules under a nonuniformly distributed electric field generated by asymmetric electrodes in a microstripline structure as a comprehensive example. Then, the dielectric constant distribution of the nematic liquid crystal layer, the effective dielectric constant in a microwave electric field, and the phase shift of a microwave in the microstripline loaded with a nematic liquid crystal are calculated. The rise time, decay time, and phase shift of a microwave phase shifter using a microstripline loaded with a nematic liquid crystal are also calculated. The differences in these response characteristics and their dependences on the width of the center conductor of the microstripline are determined by calculation and confirmed by performing experiments on the microwave phase shifters and an optical experiment on the retardation of the microstripline loaded with a nematic liquid crystal structure.

Optically switchable multi-stopband of non-quarter-wavelength dielectric multilayer using azobenzene polymer liquid crystal

Non-quarter-wave stacked dielectric multilayers including azobenzene polymer liquid crystal layers are investigated in this study. The azobenzene polymer liquid crystal has a photoinduced reversible refractive index based on photoisomerization. By using the reversible refractive-index change, the reflectance of a stopband can be controlled. In this system, the azobenzene molecules change their conformation when they are irradiated with ultraviolet (UV) or visible light. In general, stacking many layers of different thicknesses can produce broadband or multicolor reflections for a dielectric multilayer. However, in a multilayer having thick azobenzene layers, UV or visible light used for controlling photoisomerization hardly reaches the bottom part of the multilayer because the light is mainly absorbed at its top surface. To solve this problem, the dependence on the thickness ratio of the multilayer is investigated and a non-quarter-wave stacked multilayer having RGB reflections is experimentally demonstrated using thin azobenzene layers.

Optical properties of broad stopband of a chiral smectic liquid crystal at highly oblique incidence

The optical properties of stopbands of a ferroelectric liquid crystal (FLC) in a chiral smectic C phase are investigated experimentally and theoretically. Chiral smectic and cholesteric liquid crystals are regarded as pseudo photonic crystals. They exhibit Bragg reflections corresponding to half- and full-pitch bands. The characteristics of the Bragg reflections at oblique incidence are discussed on the basis of numerical calculations. The full-pitch band of an FLC becomes deeper and wider at highly oblique incidence. Using this characteristic, we demonstrated an FLC stopband with independently tunable wavelength and bandwidth by controlling the temperature and incident angle, respectively.

Loss of sciophilous character of crop seeds subjected to barrier discharge produced by repetitive polarity-reversed voltage pulses

This study presents the altered photosensitivity of several sciophilous seeds subjected to non-equilibrium plasma produced by polarity-reversed voltage pulses in ns range. It is well known that the photosensitivity of seeds can classified into two types, sciophilous (light-inhibited) and heliophilous (light-favoured). In this study, three kinds of sciophilous seeds, tomato, daikon radish and eggplant, are used as test samples. Dielectric barrier discharge are repeatedly propagated along the surface of the seeds on a glass barrier between plane-plane electrodes. After the discharge treatment, the seeds are incubated on a wet Alter paper with a dark-room condition for sciophilous plants or with an irradiating condition for heliophilous plants. The cultivation result of tomato seeds, regardless of the discharge treatment time (0, 5, 10, 20, 30 min), is that most of the seeds starts to grow roots within 4 days and then germinate within 1 week in dark-room condition. Both the leaf size and root length after 2 weeks of incubation do not depend on the discharge treatment in dark-room condition. On the other hand, the seeds without discharge treatment have a lower ability for germination in irradiating condition because of their sciophilous properties. However, the germination ratio of the seeds in irradiating condition increases with the increase of the discharge treatment time. This interesting phenomenon implies that the loss of sciophilous characteristics due to molecular structure change of photoreceptor in the seed coat is caused by the repetitive barrier discharges. Results for daikon radish shows the same tendency as tomato seeds. But, the germination of eggplant seeds were inhibited by the discharge treatment. On the other hand, germination ratio for eggplant seeds strongly decreased by the 30 min discharge treatment regardless of the irradiation conditions.

Effect of superposed repetitive pulses onto DC voltage on discharge extension into fog water produced by electrospray

Photographic observations for ionized water droplets from an injection needle subjected to high voltage and for streamer discharge light from the same electrode is a part of a fundamental study on water treatment. The goal of this study is to establish a new plasma treatment method for the decomposition of persistent substance in water by using a pulsed power technique. Repetitive pulsed voltages are superposed onto a dc voltage to extend the streamer discharge propagation into fog water produced by electrospray. The Dynamics of fog water from an injection-needle are observed by a high-speed camera, whereas the discharge light is observed by a still camera. Experiments are done in two cases, dc voltage application without any pulse superpositions and dc voltage application with repetitive pulses. In the first step, only a constant dc voltage is applied to needle-plane electrodes. A remarkable polarity effect on the diffusion of fog water is recognized. It is noted that the diameter of the water droplets for the positive polarity is much smaller than that for the polarity, so that the diffusion area of fog water for the positive polarity becomes large. However, the positive streamer discharge cannot propagate into the gap filled with fog water because of a trade-off relationship between the fog formation and the discharge extension. In the second step, the high voltage pulses are repeatedly superimposed onto the constant dc voltage. The Influence of the pulse width on the streamer propagation capability from a water droplet on the needle tip is studied. Results show that the discharge initiation probability for millisecond pulses superposition is higher than that for nanosecond pulse superposition.

Analysis of Dynamic Response of Permittivity in a Liquid Crystal Cell with Flow

Microwave and millimeter-wave devices including a liquid crystal (LC) are increasingly attractive for the use in adaptive and controllable devices. Various types of microwave phase shifters having an LC transmission line have been studied (e.g. microstripline, coplanar waveguide, and rectangular waveguide). In conventional microwave devices, the response time after removal of voltage is slow because the LC layer in the devices is usually thick. In this study, the time response of the LC permittivity is studied experimentally and theoretically. Experimentally measured response curves having two time constants for decay are examined by using Franks continuum theory with and without the backflow effect.

Dielectric Multilayer Including Azobenzene Polymer Liquid Crystal with Non-quarter-wave Stack

Dielectric multilayer including azobenzene polymer liquid crystal acts as a one-dimensional photonic crystal and has optical-switchable reflection bands. The reflection intensity can be controlled by irradiation of ultraviolet (UV) or visible light, in which the optical switch is based on cis-trans photoisomerization. An increase in the number of layers prevents photoresponse in the multilayer including azobenzen layers because UV or visible light for control cis-trans isomerization hardly reach the bottom of the multilayer due to exponential decay of light intensity. In this study, the multilayer consisting of thin azobenzene layers is investigated. According to numerical calculations, the non-quarter-wave structured multilayer has multiwavelength reflection band. Angular dependence of reflection color from multiwavelength stopband is also studied using the XYZ color space. The non-quarter-wave multilayer suppresses reflection color change compared with conventional quarter-wave multilayer.