Constant Tilt Research Articles

Modeling the vestibulo-ocular reflex of the squirrel monkey during eccentric rotation and roll tilt.

Model simulations of the squirrel monkey vestibulo-ocular reflex (VOR) are presented for two motion paradigms: constant velocity eccentric rotation and roll tilt about a naso-occipital axis. The model represents the implementation of three hypotheses: the "internal model" hypothesis, the "gravito-inertial force (GIF) resolution" hypothesis, and the "compensatory VOR" hypothesis. The internal model hypothesis is based on the idea that the nervous system knows the dynamics of the sensory systems and implements this knowledge as an internal dynamic model. The GIF resolution hypothesis is based on the idea that the nervous system knows that gravity minus linear acceleration equals GIF and implements this knowledge by resolving the otolith measurement of GIF into central estimates of gravity and linear acceleration, such that the central estimate of gravity minus the central estimate of acceleration equals the otolith measurement of GIF. The compensatory VOR hypothesis is based on the idea that the VOR compensates for the central estimates of angular velocity and linear velocity, which sum in a near-linear manner. During constant velocity eccentric rotation, the model correctly predicts that: (1) the peak horizontal response is greater while "facing-motion" than with "back-to-motion"; (2) the axis of eye rotation shifts toward alignment with GIF; and (3) a continuous vertical response, slow phase downward, exists prior to deceleration. The model also correctly predicts that a torsional response during the roll rotation is the only velocity response observed during roll rotations about a naso-occipital axis. The success of this model in predicting the observed experimental responses suggests that the model captures the essence of the complex sensory interactions engendered by eccentric rotation and roll tilt.

The Effect of Head Tilt on Perception of Self-Orientation While in a Greater than One G Environment

The effect of head tilt on the perception of self-orientation while in a greater than one G environment was studied in nine subjects using the Armstrong Laboratory Dynamic Environment Simulator. After a 12-s stabilization period at a constant head tilt and G level, subjects reported their perception of the horizon by placing their right hand in a position they believed to be horizontal. Head tilt conditions ranged from -30 degrees to +45 degrees pitch over each of three head yaw positions. G levels ranged from one to four and were in the longitudinal axis of the body (Gz). Hand position was recorded in both the pitch and roll body axes. A function of head tilt did improve the fit of a multiple regression model to the collected data in both the pitch and roll axes (P < .05). The best fit was accomplished with a nonlinear function of G and head pitch. When the head remained level but the environment tilted with respect to the G vector (at angles similar to those perceived during head tilt), subjects accurately reported the environmental tilt. Head tilt under G can result in vestibular-based illusionary perception of environmental tilt. Actual environmental tilt is accurately perceived due to added channels of haptic information.

Electro-Optic Properties of an Unusual Guest-Host Liquid Crystal Mixture: A Mauve Anthraquinone Dye in a Ferroelectric Organosiloxane

Abstract We examine here the electro-optic properties of an unusual guest-host liquid crystal mixture of a high contrast anthraquinone dye and a new ferroelectric organosiloxane liquid crystal. From measurements of the transition temperatures, tilt angles, spontaneous polarisations and rotational viscosities, we show that dye concentrations as high as 4% w/w have negligible effect upon the host properties. Furthermore, we show that the mixture, with a constant tilt angle of 36° across its smectic-C* phase range from 50°C down to 10°C, high absorbance and good alignment, produces contrast ratios in the V-V scattering mode of 50:1 or higher, with optical response times of 120 μs or less at 20°C. We argue that the technological implications of mixtures of this type are important, due to their being composed of only two components and having properties surpassing that of commercial optimised mixtures.

The contribution of motion, the visual frame, and visual polarity to sensations of body tilt.

Three types of visual information contribute to the sense of self orientation with respect to gravity: visual polarity of objects with a distinct top and bottom, the principal vertical and horizontal lines of the visual environment, and visual motion. Three visual displays were designed to investigate the contribution of each visual feature to illusory self tilt: a large sphere lined with dots, a cubic room lined with dots, and a furnished room with floor and ceiling. In experiment 1 the dotted room and the furnished room were tilted to various angles about the roll axis of the erect subject who set a visual line and an unseen rod to the apparent vertical. In the dotted room, settings were made either with respect to the nearest surface to the horizontal or with respect to the nearest diagonal of the room. In the furnished room, settings were made with respect to the nearest horizontal wall but not with respect to diagonals. In experiment 2 each of the three displays was rotated at constant velocity and subjects' responses were classified into four categories: illusory self tilt at a constant angle, alternating self tilt with the body becoming erect each time a surface became horizontal, continuous head-over-heels self rotation, and a feeling that the body was supine. Almost all responses were of constant tilt in the sphere. Constant and alternating tilt were the most common responses in the dotted room. In the furnished room 60% of subjects experienced full head-over-heels self rotation.

The effect of biasing electric field on relaxations in FLC investigated by the dielectric and optical methods

Abstract The dielectric and electrooptical responses within the frequency range 30 Hz–100 kHz are used to study the properties of the soft and the Goldstone mode in dependence of bias electric field. It is shown that the soft mode relaxation frequency is linearly bias dependent in both SmA and SmC* phases, the Goldstone mode relaxation frequency is constant for small bias. After the modulated structure is unwound a low frequency mode persists a relaxation frequency of which also linearly increases with increasing bias. This mode is connected with vibration of molecules around the layer normal keeping the constant tilt angle, which could take place in surface layers. The Cole—Cole diagrams constructed from the optical response are obtained for all studied modes in the shape of semicircles, showing all the modes have relaxation character with well defined relaxation frequencies. The bias field dependencies of both optical and dielectric responses in the SmC* phase reflect the unwinding process of the helico...

Gravity wave modulation of gradient drift instabilities in mid‐latitude sporadic E irregularities

Recent E region VHF backscatter echoes observed by the MU radar at mid‐latitudes show quasi‐periodic striations with a fairly constant range vs. time tilt in a RTI display. These features are explained in terms of gravity waves with frequencies close to the Brunt‐Väisälä frequency which modulate the shape of sporadic E layers. The conditions of instability, when the magnetic field has a significant dip angle, is revised. Differing from previous work, we argue that conditions of local gradient drift instability are not sufficient and one has to consider the integrated properties of each magnetic filed tube. Stratified sporadic E layers are stable using this new criteria, unless they are distorted to produce unstable integrated gradients. Gravity waves with phase fronts parallel to the magnetic dip angle are capable of producing such distortion, imposing its own temporal and spatial periodicity on the echoes.

Determination of optimum tilt angle of single and multi rows of photovoltaic arrays for selected sites in Jordan

Abstract Solar radiation measured by the Jordanian Meteorological Department (using actinographs) at six Jordanian sites during some, or most, of the period from 1971 to 1987 has been analysed to determine the monthly, and thus the yearly, optimum tilt angles for both single row and multi-rows of photovoltaic arrays operating in such sites. Also a comparison between the solar energy captured by a stationary mounting structure and that captured by a variable-angle mounting structure is carried out. Relative to structures of constant tilt angle the results obtained show an improvement of 5.6% by using PV-mounting structure of adjustable tilt angle.

精密曲面研摩の研究 工具揺動と研摩面傾き角制御

This paper deals with the tilt angle control, based on the tool oscillation and the effect of tool oscillation for curved surface polishing. The results are as follous. (1) The tilt angle of polished surface can be detected in polishing process from the relationship between tool oscillation and the displacement of a detecting shaft by using the oscillated polishing head. (2) The curved surface is kept horizontal or at a constant tilt angle in polishing process by controlling a tilting table using a detecting signal from the polishing head. (3) The surface quality polished by a orcillated polishing head is superior to that by a polishing head without oscillation, because tool contact area become wider when tool is oscillated.

The Sm-C* structure disclinations in an applied electric field

Abstract Analytic formula for the 8π disclination in SmC structures in an applied electric field is derived in the constant tilt approximation. Qualitative conclusions for 2 π disclinations are found from it. In stronger fields domain walls should appear starting at defect lines. They separate regions of homogeneously ordered molecules in layers.

Ocular torsion on earth and in weightlessness.

Ocular torsion (OT) was measured in human subjects during horizontal linear acceleration on a sled in the laboratory and when emerging from weightlessness during parabolic flights in NASA's KC-135 aircraft. Analysis of the frequency response of OT to sinusoidal horizontal oscillation on earth shows results consistent with constant tilt rate studies and with earlier models based on perception of acceleration. Step responses of OT to lateral acceleration are compared to similar profiles from aircraft tests with no preexisting gravitoinertial force on the otoliths. The sensitivity of OT to rotating wide fields producing vection and to tactile cues is compared for earth and weightlessness. A new instrument for high bandwidth video measurement of OT using a soft-contact-lens target is described.

Distorted twisted nematic liquid-crystal structures in zero field

Leslie’s differential equations describing the orientation of the optic axis through a twisted nematic layer are solved for the case where there is a nonzero tilt bias angle. Three classes of solutions are investigated: the simple solution of constant tilt angle through the layer with uniform twist, symmetric solutions where the tilt angle in the middle of the layer has an extreme value, and antisymmetric solutions where the tilt angle in the middle of the layer is identically zero. These solutions and their corresponding elastic deformation energies are compared for typical values of the splay, twist, and bend elastic constants of nematic liquid crystals. For 90° twisted nematic layers the antisymmetric solution always has a higher elastic energy than the symmetric solution. This result explains why regions of reverse twist are suppressed in twisted nematic display devices which have finite tilt bias angles at both boundaries. Reverse-twisted domains can also be avoided by adding chiral dopants to the nematic mixture and by making layers having total twist angles of less than 90°. The effectiveness of these three techniques is discussed in terms of a comparison of the elastic energy difference between the oppositely twisted configurations.

Light scattering from spherulitic materials

AbstractThe azimuthal angular dependence of the depolarized component of the light scattered from spherulitic materials is derived by an algebraic method that avoids the difficult angular integrations of the usual approach. The result appears as a sum of products of two factors, a molecular factor, that depends only on the structure and the scattering angle θ, and a geometrical factor that depends only on the azimuthal angle ϕ and the scattering angle θ. The molecular factors are evaluated for models of spherulitic structure that assume a constant tilt of the optical polarizability tensor. The radial distribution, in principle, is arbitrary, and an evaluation for the layered spherulite is made. If the tilt angle is ω when the azimuthal patterns depend only on a linear combination of P2(cos ω) and P4(cos ω), where Pn(x) is the Legendre polynomial of order n. In our theory the VH scattering pattern is a four‐leaf clover whose axes are restricted by the theory to be at either 0 or 45° to the polarization directions.

Nuclear Magnetic Resonance Study of Smectic Phases

Abstract Proton NMR spectra of oriented smectic phases of terephtal-bis-(p-n-butylaniline) (TBBA) are reproted. Spectra of the liquid crystal, as well as of methylenechloride dissolved as a probe molecule in this material, were taken. In both cases the behavior as function of temperature and under sample rotation relative to the magnetic field was studied. Each of the smectic A, B and C phases exhibits a typical behavior. That in the smectic C phase can be explained in terms of a model in which the molecular orientation can adjust freely on a cone while maintaining a constant tilt angle with respect to the smectic layers. It is concluded that NMR may be a useful tool in classifying smectic phases.

Anomalous microtilt preceding a local earthquake

abstract The three largest earthquakes to occur within 50 km of San Francisco during 1970 were centered near the community of Danville, California, and spanned a time interval of 50 sec starting on June 12, at 0330 hr GMT. These earthquakes were greater than magnitude 4.0 and were part of a shallow, tightly-clustered earthquake swarm that persisted for approximately 2 months starting in mid-May 1970. During the same period of time, continuous tilt at tidal sensitivity (10−8 radian) was being recorded in two vaults at distances of 25 and 45 km west of the epicentral area. Two types of anomalous tilting preceded the principal events: (1) a long-term (1-month) constant tilt rate of 8 × 10−10 radian/hr that was recorded by both tilt stations and (2) a short-term (1-day) accelerated micro-tilt change which occurred just prior to the events and was most pronounced on the station closest to the epicentral area. Neither type of anomaly was recognized in the post-Danville record. The lack of a strong correlation with meteorological phenomena to account for the long-term coherency between two tilt stations of 25-km separation and the apparent azimuthal correlation of the Berkeley residual tilt vector with the earthquake epicenters suggests that the anomalous tilt preceding the Danville events were tectonic.

Rate of Adaptation under Constant and Varied Optical Tilt

Two groups of 8 Ss each were exposed either to a constant optical tilt (Group C) of 30° for ½ hr. or to a series of prism tilts that varied from 5° to 30° in 5° increments every 5 min. (Group V). The rate of change in level of adaptation per unit time was significantly greater for Group V than Group C. The relation between these results and implications from the assumption of a comparator were discussed.