Apparent Tilt Research Articles

Field Induced Domains in Antiferroelectric Liquid Crystals

Domain structures at field induced phase transitions of antiferroelectric liquid crystals were investigated by dielectric, electrooptic and light deflection experiments under electric bias fields. Characteristic light deflection phenomena indicating the co-existence of different refractive index domains were observed in antiferroelectric, ferroelectric and ferrielectric phases. Above all, in the chiral smectic Cβ* phase (SmCβ) being considered ferroelectric, the light deflections appeared at zero field after removing the bias and also in two field ranges at which the dielectric constant and the apparent molecular tilt angle showed the step-wise changes. Possible models for the coexisting domains at these induced phase transitions were discussed.

Three-dimensional organization of otolith-ocular reflexes in rhesus monkeys. III. Responses To translation.

The three-dimensional (3-D) properties of the translational vestibulo-ocular reflexes (translational VORs) during lateral and fore-aft oscillations in complete darkness were studied in rhesus monkeys at frequencies between 0.16 and 25 Hz. In addition, constant velocity off-vertical axis rotations extended the frequency range to 0.02 Hz. During lateral motion, horizontal responses were in phase with linear velocity in the frequency range of 2-10 Hz. At both lower and higher frequencies, phase lags were introduced. Torsional response phase changed more than 180 degrees in the tested frequency range such that torsional eye movements, which could be regarded as compensatory to "an apparent roll tilt" at the lowest frequencies, became anticompensatory at all frequencies above approximately 1 Hz. These results suggest two functionally different frequency bandwidths for the translational VORs. In the low-frequency spectrum (<<0.5 Hz), horizontal responses compensatory to translation are small and high-pass-filtered whereas torsional response sensitivity is relatively frequency independent. At higher frequencies however, both horizontal and torsional response sensitivity and phase exhibit a similar frequency dependence, suggesting a common role during head translation. During up-down motion, vertical responses were in phase with translational velocity at 3-5 Hz but phase leads progressively increased for lower frequencies (>90 degrees at frequencies <0.2 Hz). No consistent dependence on static head orientation was observed for the vertical response components during up-down motion and the horizontal and torsional response components during lateral translation. The frequency response characteristics of the translational VORs were fitted by "periphery/brain stem" functions that related the linear acceleration input, transduced by primary otolith afferents, to the velocity signals providing the input to the velocity-to-position neural integrator and the oculomotor plant. The lowest-order, best-fit periphery/brain stem model that approximated the frequency dependence of the data consisted of a second order transfer function with two alternating poles (at 0.4 and 7.2 Hz) and zeros (at 0.035 and 3.4 Hz). In addition to clearly differentiator dynamics at low frequencies (less than approximately 0.5 Hz), there was no frequency bandwidth where the periphery/brain stem function could be approximated by an integrator, as previously suggested. In this scheme, the oculomotor plant dynamics are assumed to perform the necessary high-frequency integration as required by the reflex. The detailed frequency dependence of the data could only be precisely described by higher order functions with nonminimum phase characteristics that preclude simple filtering of afferent inputs and might be suggestive of distributed spatiotemporal processing of otolith signals in the translational VORs.

Electro-Optical and Dielectric Investigations of Antiferroelectric and Ferrielectric Smectic Phases

Dielectric and electro-optical properties of the various antiferroelectric and ferrielectric smectic phases of two compounds of the homologous series MHPnCBC (n = 8,9) have been investigated. MHP9CBC exhibits an unidentified chiral induced SmC subphase (denoted by SmCx*) and shows the phase sequence Cr - SmIA* - SmCA* - SmCγ* - SmC SmCx* - SmC SmCx* - SmA - I. The electro-optical and dielectric properties of the SmC SmCx* phase of MHP9CBC differ distinctly from that of the SmC SmCα* as well as the SmC SmCγ* phase. The electric field - temperature phase diagram was obtained by two methods, measurement of the apparent tilt angle as well as the dielectric loss. The results of both methods are in good agreement. For both compounds a field induced ferrielectric state is observed in a broad temperature range (≊ 10 K) of the SmC SmCA*−phase.

Apparent body tilt and postural aftereffect.

Apparent orientation of the body tilted laterally in the frontal plane was studied with the methods of absolute judgments in four experiments. In Experiment 1, 17 subjects, who maintained the normal adaptation of body to gravity, estimated their body tilts under the condition of seeing the gravitational vertical and under the condition of eliminating it. The results showed that (1) there was not a significant difference between the two conditions and (2) the small tilts of less than 45 degrees were exactly estimated, whereas the large tilts of 45 degrees-108 degrees were overestimated. In Experiment 2, 10 subjects estimated their body tilts under three velocities of a rotating chair on which each subject was placed. Although both body tilt and chair velocity were found to influence tilt estimation, the effect of body tilt was overwhelmingly greater than that of chair velocity. In Experiment 3, 11 subjects adapted their bodies to a 72 degrees left tilt for 10 min and then estimated various body tilts around the adapting tilt. The estimations obtained under the 72 degrees adaptation were lower than those obtained under the 0 degree adaptation, and this reduction was greater for the test tilt that was farther away from the adapting tilt. In Experiment 4, 11 subjects adjusted their own body tilts to designated angles. The results confirmed the outcomes of absolute estimation in Experiments 1-3. From these findings and past literature, the judgments of body tilt were considered to be subserved by a single sensory process that was based on the cutaneous and muscular proprioceptors, rather than the vestibular and joint proprioceptors.

Investigations on the field-induced switching behaviour in an antiferroelectric liquid crystal

The switching currents and field-induced apparent tilt angles in an antiferroelectric liquid crystal, (R)-MHPOBC, were measured. The structural differences among different smectic C* subphases may sensitively reflect the field or temperature dependence of the apparent tilt angle. In a thin cell, the apparent tilt angle was found to change in two steps as a function of field strength in the SmC*alpha and SmC* phases: a steep increase at lower fields and a small linear increase at higher fields. The steep increase in apparent tilt angle is divided into two parts via a plateau in the ferrielectric SmC*gamma phase. Stepwise change with a plateau is also seen in the relation of apparent tilt angle versus temperature under various electric fields. Moreover, the apparent tilt angle in the vicinity of the plateau is almost temperature- and field-independent, implying a preferred orientation of the molecules in the ferrielectric state. The influence of the cell thickness on the structural changes was also investigated.

A broad band antiferroelectric liquid crystalline mixture: Physical properties

Abstract We present a multicomponent antiferroelectric liquid crystalline mixture exhibiting the antiferroelectric SmCa* phase in a broad temperature range from 35°C up to 107°C. Further, the antiferroelectric phase can easily be supercooled so that, for practical purposes, measurements and investigations can be performed at room temperature. Important physical parameters of the mixture such as the spontaneous polarization of the ferroelectric state, the apparent tilt angle and the parameter characteristics of the double hysteresis have been investigated. At room temperature the saturated polarization and the tilt angle have been found to reach values of about 150 nC cm−2 and 30°, respectively. Furthermore a very fast linear electrooptic effect exhibiting switching times about 15 μs at room temperature has been observed at electric field strength below the threshold field for switching to the ferroelectric state.

Dielectric investigation of the polymorphism of a new chiral liquid crystal

In this work we present the results of the complex dielectric constant (e', e'') and of the apparent tilt angle, concerning a new chiral compound exhibiting several smectic mesophases. Four polar smectic C* phases were identified: SCA, SCFI, SC* and SCα. An analysis of the relaxation frequency of the system and the distribution of the relaxation times is also presented.

Ｌａｎｇｍｕｉｒ‐Ｂｌｏｄｇｅｔｔ磁性膜の構造とスピン状態

In order to develop the magnetic thin film, we studied the structure and magnetic properties in the Langmuir-Blodgett (LB) multilayers of transition metal ion-fatty acid salt, using X-ray diffraction and electron paramagnetic resonance (EPR) methods. We found the various orientation as a function of multiplicity of layers in the LB films. In the film having more than four layers, the long molecular axis of fatty acid exhibits an apparent tilt structure; but in the film less than three layers, the molecular axis holds the perpendicular position against the substrate plane. Using the vector EPR measurements, we found the anomalous broadening of line shape due to the exchange interaction between successive layers. We concluded that the LB films of the transition metal ion-fatty acid salts may allow the highly ordered and the low-dimensional magnetic system.

Calculation of overall tilt angles for a double tilt holder in a TEM.

A simple formula has been derived for the tilt angle of a specimen in terms of the two tilt angles of a side entry, double tilt holder in a transmission electron microscope. An expression for calculating the direction of the apparent tilt axis in relation to the observed diffraction pattern has also been derived. The accuracy and reproducibility of specimen tilting has been assessed experimentally.

Novel Switching with Gray Scale in Surface-Stabilized Ferroelectric Liquid Crystal Devices

The apparent tilt angle in surface-stabilized ferroelectric liquid crystals (SSFLCs) is dependent on the applied electric field for monostable and bistable devices. This behavior is attributed to the fact that the director profile of molecules in SSFLC cells is changed by an interaction between spontaneous polarization and the electric field. Based on this behavior, the transmission in SSFLCs can be controlled by the applied voltage, resulting in a smooth voltage-transmission curve.

Simulation of dynamic response to an electric field of surface stabilized antiferroelectric liquid crystals

Abstract Responses of surface stabilized antiferroelectric liquid crystals (SSAFLCs) to an electric field are simulated based on a model of the AFLC phase. The apparent tilt angle, the polarization reversal current and the optical transmission under applied triangular wave voltages are calculated. The results obtained systematically explain the experimental observations fairly well. The effects of parameters such as amplitude and frequency of applied voltages, an antiferroelectric coupling parameter and surface anchoring strength on these phenomena are discussed.

Resonance and local-field effects in the characterization of molecular monolayers by optical second-harmonic generation

Langmuir-Blodgett (LB) monolayers are ideal model systems for testing the design parameters of molecular units for ultrathin film nonlinear optical devices. The second-harmonic response of a mixed liquid crystal-stearic acid monolayer as a function of liquid crystal concentration is used here to measure the local field in the monolayer. The effect of the local field is much larger than the resonance behaviour in this system. The apparent molecular hyperpolarizability β in pure monolayers is reduced by a factor of six due to the local field. The other effect of the local field is to increase the apparent tilt angle of the liquid crystals by up to 30°. These effects are significant in the design of materials for ultrathin film nonlinear optical devices. Determination of the true β values of an isolated chromophore should be made using monolayer films where the active species is diluted by about a factor of 10 by a species with negligible polarizability, having first established that the active species disperses uniformly. In this way the experimental hyperpolarizability may be directly compared, for example, to theoretical values from calculations of isolated molecular clusters.

Devil's staircase formed by competing interactions stabilizing the ferroelectric smectic-C* phase and the antiferroelectric smectic-CA* phase in liquid crystalline binary mixtures.

In order to demonstrate experimentally that the competition between the antiferroelectric and ferroelectric interactions stabilizing Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and Sm${\mathit{C}}^{\mathrm{*}}$ (the pairing energy of the transverse dipole moments in adjacent smectic layers and the packing entropy resulting from the excluded volume effect) produces a variety of antiferroelectric and ferroelectric subphases in the temperature region between antiferroelectric Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and ferroelectric Sm${\mathit{C}}^{\mathrm{*}}$, we have tried to observe the subphases in several binary mixtures of chiral smectic liquid crystals. The subphases were identified by the electric field dependence of cono- scopic figures and the apparent tilt angle as a function of field strength. Systematically changing the mixing ratio of two properly chosen compounds and studying the stability of each subphase, we have substantiated that the subphases between Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and Sm${\mathit{C}}^{\mathrm{*}}$ form a Devil's staircase, Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$). Here, ${\mathit{q}}_{\mathit{T}}$ is an irreducible rational number, which specifies a fraction of the ferroelectric ordering in the antiferroelectric ordering. We have also discussed the relationship of Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$) to the other staircase, Sm${\mathit{C}}_{\mathrm{\ensuremath{\alpha}}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$), that was proposed to exist as a result of the rather macroscopic, electrostatic interaction among two-dimensional spontaneous polarizations in smectic layers.

Experimental determination of the chromatic difference of magnification of the human eye and the location of the anterior nodal point.

Theory predicts that retinal image size will vary with wavelength. However, this chromatic difference of magnification (CDM) is likely to be very small (< 1% between 400 and 700 nm) under natural viewing conditions. There has been only one attempt to measure CDM experimentally, and the results were inconsistent with optical theory. Using a technique described by Ogle [Research in Binocular Vision, Hafner, New York (1964)], which is sensitive to even small interocular differences in retinal image size, we measured the apparent tilts in the frontoparallel plane induced by interocular differences in wavelength. We obtained the ocular CDM by determining the afocal lens magnification necessary to cancel the apparent frontoparallel plane tilt caused by interocular differences in wavelength. We show that (1) the ocular CDM can be considerably less than theoretical model predictions, (2) the relationship among delta Rx (wavelength-dependent refractive error), CDM, and pupil position is consistent with our theoretical model, (3) CDM increases considerably when an artificial pupil in front of the eye is used, (4) the location of the anterior nodal point of the eye may be inferred from the data, and (5) unlike in the case for delta Rx, large intersubjective differences may exist for CDM. The results suggest caution in the use of artificial pupils experimentally with polychromatic stimuli because of amplification of CDM and concomitant losses of image contrast.

Construction of Dynamic Conoscope Observation System Using CCD Camera and Image Processor

In order to study the dynamic behavior of conoscopic images with high precision and high efficiency, we constructed a conoscope observation system using a CCD (charge coupled device) camera and an image processor. We can analyze biaxiality and apparent tilt angle by means of a homeotropic cell operated at 0.1 Hz. We discuss the result obtained in an antiferroelectric liquid crystal, 4-1-(methylheptyloxycarbonyl) phenyl 4'-octyloxy-biphenyl-4-carboxylate (MHPOBC).

Inversion of chirality-dependent properties in optically active liquid crystals

Three new low-molar-mass liquid crystals are reported, each of which shows remarkable phase behaviour. One of the materials exhibits a temperature-dependent unwinding of the helix in the cholesteric (chiral nematic) and chiral smectic C phases. This is the first example of a single, pure material to show both of these inversions. The inversion phenomena were studied in terms of the helical pitch and the electrooptic switching behaviour in the cholesteric phase and in terms of the temperature dependence of the apparent optical tilt angle and the spontaneous polarization in the chiral smectic C phase.

Optical and dielectric properties of antiferroelectric liquid crystals and their surface effects

Abstract A detailed study of the dielectric and optical properties of the ferroelectric liquid crystal material (R)-4′-(3-methoxycarbonyl-2-propoxycarbonyl)phenyl 4-(4-(n-octyloxy)phenyl)benzoate (3MC2PCPOPB) has been carried out. It has been found that an anomalous temperature dependence of the dielectric constant in 3MC2PCPOPB is due to the antiferroelectric and ferrielectric properties. A T(temperature)-E(electric field) phase diagram has been obtained on the basis of the apparent tilt angle measurements. In a thin cell (< 3 μm), both ferroelectric and antiferroelectric domains are simultaneously observed over a wide temperature range, and the complete antiferroelectric phase does not appear even at low temperature. A characteristic texture in which boundary focal conics are aligned parallel to a smectic layer has been observed. The movement of the zig-zag defect line caused by the application of the voltage is also observed.

On the inclination and the axial velocity of spicules

This paper studies two properties of chromospheric spicules: their angular distribution and the plasma velocity along their axes. To investigate the first property, we measured the apparent tilt of spicules at the limb, and then computed their actual distribution in space. This was achieved by solving first kind Fredholm or Volterra integral equations by various methods. The distribution of the axial velocity of the spicule plasma was studied on the basis of two types of observations: (1) the height variation of the spicules as a function of time and (2) the Doppler shift of the spectral lines. The resulting velocity distributions, using the experimental data of these two sets of observations, are quite different. The average velocity based on the Doppler shift measurements (≈ 40 km s−1) is greater than that based on height variation of spicules (≈ 20 km s−1). This is due to the ionization of the material as it penetrates the corona.

Dielectric Behavior and the Devil's Staircase in the SmCα* Phase of an Antiferroelectric Liquid Crystal, 4-(1-methylheptyloxycarbonyl)phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate

We have observed an increase of the dielectric constant under a bias electric field in the SmCA* and SmCα* phases in 4-(1-methylheptyloxycarbonyl) phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate. This implies a field-induced phase transition to the ferrielectric and/or to the ferroelectric phases. The transitions were also clearly observed in the field-induced apparent tilt angles in these phases. The electric-field-induced Devil's staircase was confirmed in the SmCα* phase. Using these observations, a T(temperature)-E(electric field) phase diagram was drawn.

Antiferroelectric Properties and Their Surface Effect in Ferroelectric Liquid Crystal 3MC2PCPOPB

A detailed study of dielectric and optical properties in ferroelectric liquid crystal (R)-4′-3(-methoxycarbonyl-2-propoxycarbonyl)phenyl 4-(4-(n-octyloxy)phenyl)benzoate (3MC2PCPOPB) has been carried out. It has been found that the anomalous temperature dependence of the dielectric constant in 3MC2PCPOPB is due to the antiferroelectric property. In the antiferroelectric phase, five stable states are observed in voltage dependence of apparent tilt angle, and on the basis of those measurements the T(temperature)-E(electric field) phase diagram is obtained. In a thin cell (<3 µm), both ferroelectric and antiferroelectric domains are simultaneously observed at the same temperature over a wide temperature range. Although the ratio of the area of antiferroelectric domains to that of ferroelectric domains gradually increases with decreasing temperature, a complete antiferroelectric phase does not appear even at low temperature.