Showing papers on "Tilt (optics) published in 1976"

Microwave radiating element and antenna array including linear phase shift progression angular tilt

Abstract: A slotted waveguide radiator for an antenna array is arranged to receive microwave energy inputs at either end for producing separate radiated beams and has loading slots having predetermined center-to-center spacings in the longitudinal dimension to provide a predetermined squint angle for each radiated beam which is related to the direction in which energy is fed to the waveguide. The radiator includes means for providing a linear phase shift progression in the signal components radiated from the slots from one end of the waveguide to the other to thereby provide an angular tilt to each radiated beam which is independent of the direction in which energy is fed to the waveguide.

Power spectra requirements for wave-front-compensative systems*

Abstract: The phase degradation of an optical wave front distorted by turbulence in the propagation medium may be corrected in a piecewise-linear fashion by using an array of small circular mirrors. An option in the correction scheme is to compensate for overall tilt separately. We have evaluated power spectra and variances of the piston and tilt motions of the mirror segments as well as the motion of the overall tilt corrector. The form of the spectra for any propagation medium is an aperture integral of the product of the phase-difference power spectrum, describing the medium, and a generalized transfer function, representing the aperture and its segments. In the case of low-power atmospheric propagation, the necessary propagation results are linear in turbulence strength; hence the path may be sectioned into a large number of thin slices. A set of standard curves is found to represent a generalized slice, and the differential contributions may be summed to represent any propagation path. The standard curves, further modeled in terms of power-law dependencies, are practical for use on a desk calculator.

Frequency spectra for the geometric representation of wavefront distortions due to atmospheric turbulence

Abstract: The wavefronts of a point source of radiation that is immersed in a turbulent atmosphere become distorted and deformed as they propagate outward. The phase surfaces incident on an unobscured collecting aperture therefore will not be perfectly spherical, but instead will be aberrated in some way. We have expanded this phase profile in a set of orthonormal functions closely related to the Zernike polynomials and then determined the respective power spectra of the time dependent expansion coefficients. The results show, for all spectra, a sharp cutoff of f^{-11/3} for frequencies f > ( u/2R) , where u is the wind velocity transverse to the point source and the receiver, and R is the aperture radius. In particular, for the tilt component expansion coefficients, this result differs from the usual phase difference power spectra previously used by many workers.

Acceleration error compensated attitude sensing and control apparatus and method

Abstract: A structural body is monitored in angular position about at least one axis by utilizing a tilt sensor responsive to tilt about the one axis and a sensor responsive to angular acceleration of the body about the one axis. The tilt sensor also responds to the tangential component of angular acceleration and the angular acceleration sensor output contains a component which results from linear acceleration sensitivity along a cross axis of the angular acceleration sensor. The cross axis of the angular accelerameter is aligned with the sensitive axis of the tilt sensor and a portion of the tilt sensor output related to the ratio of the two sensor scale factors is injected into the angular acceleration sensor output to cancel the cross axis sensitivity. A portion of the angular acceleration sensor output related to the distance between the one axis and the mounting position of the tilt sensor is injected into the tilt sensor output to cancel the tangential component of angular acceleration.

Tilt angle measurements of nematic phases of cyano-biphenyls aligned by obliquely evaporated films

Abstract: The angle between the nematic director and an aligning surface in contact with a nematic phase is of importance in defining the mechanism of surface alignment of liquid crystals. A new and simple optical method of determining this tilt angle is described, and measurements are reported on a number of homologues of the series 4-n-alkoxy- and 4-n-alkyl-4'-cyano-biphenyl liquid crystals aligned by obliquely evaporated films. The tilt angle is found to depend in a systematic way on the liquid crystal material and also on the composition of the aligning layer.

The Ventral Substrate Response * A New Postural Control Mechanism in Fishes

Abstract: 1. Some fishes show a tendency to orient their ventral side towards a substrate and may thus tilt considerably when swimming near vertical walls or even under the ceiling of caves. This behavior was named theVentral Substrate Response (VSR) and was quantitatively studied in the black croaker (Cheilotrema saturnum, Sciaenidae) and in the weakly electric fishEigenmannia sp. (Rhamphichthyidae). 2. It was determined that theVSR ofC. saturnum is visually guided and that a vertical substrate can induce a tilt of about 64° away from the vertical if illumination is from above (Fig. 2). TheVSR ofEigenmannia sp. can be totally or predominantly guided by the electric sense of these animals and can induce ca. 30° tilt to a 45° tilted bottom (Fig. 4). 3. The amount of tilt displayed is dependent on the distance between the animal and the substrate. Measurable tilt responses inC. saturnum were observed up to a distance of 15 cm. 4. In a second experiment interactions between theDorsal Light Response (DLR) and theVSR were investigated inC. saturnum. It was found that tilt responses induced during aDLR or aVSR can add to each other when having the same direction or can subtract from one another, if opposite in direction. This experiment demonstrates the independence of theVSR- and theDLR-mechanisms. 5. After bilateral forebrain ablationC. saturnum did not show aVSR anymore. ADLR was still performed.

Acceleration measuring device

Abstract: An angular accelerometer incorporates two tilt sensors both connected to a differential amplifier arranged to provide a difference signal which is fed to a first integrator the output of which is fed to a second integrator. The tilt sensors are of the torque balance type. The tilt sensors are spaced from one another in a direction transverse to the direction along which the angular acceleration movement takes place.

Effects of head-down tilt on fluid and electrolyte balance

Abstract: The metabolic effects of -5 deg tilt were studied in eight normal individuals. Exposure to tilt for 24 hr increased sodium excretion and decreased plasma volume. Plasma renin activity and plasma aldosterone levels were not significantly different from supine values during the first 6 hr of tilting, but were increased significantly at the end of the 24-hr tilt period. Creatinine clearance and potassium balance were not affected by the tilt. These findings indicate that head-down tilt induces a sodium diuresis and stimulation of the renin-angiotensin-aldosterone system.

Liquid Crystal Surface Alignment Treatment Giving Controlled Low Angle Tilt

Abstract: We report methods of simultaneous or sequential oblique evaporations of silicon monoxide at angles of 30[ddot] and 5[ddot] to glass substrates. These permit parallel homo-geneous alignment of liquid crystals to be obtained concomitant with a controllable surface tilt angle of the director. The range of tilt angles obtained is from O[ddot] to about 45[ddot] depending on the liquid crystal materials used. The low surface tilts obtained using these methods should be of use in producing improved twisted nemetic display devices.

Short-term average irradiance profile of an optical beam in a turbulent medium

Abstract: The short-term average irradiance profile of a focused laser beam transmitted through a homogeneous-isotropic medium has been determined by using the extended Huygens-Fresnel principle and by modifying the phase structure function to remove tilt. In contrast to previous analysis, no assumption is made regarding the independence of the distribution of phase with tilt removed and the random vector β defining tilt. This analysis applies to the near field of the effective coherent transmitting aperture, where the beam wanders as a whole and does not break up into multiple patches or blobs. Central to the analysis is the short-term average mutual coherence function (MCF) of a spherical wave, which has been determined from the modified phase structure function. Assuming a Kolmogorov spectrum, the modified phase structure function has been determined for three specific aperture functions. These same aperture functions are then used to determine the short-term irradiance profiles. Numerical calculations have been performed, and the results are presented for uniform and Gaussian aperture functions for various values of aperture obscuration and for various strengths of turbulence values. Comparisons are made between the long-term average, short-term average, and Fried’s short-term average irradiance profiles. In particular, on-axis irradiance values and beam spread, as determined by the 1/e points in irradiance, are compared. It is found, in contrast to previous analysis, that the short-term beam spread remains relatively constant as the strength of turbulence becomes large and then increases slowly.

Hydraulically powered marine propulsion tilting system with automatic let-down assembly

Abstract: A marine propulsion device includes a member adapted to be attached to a boat hull, a propulsion assembly connected to the member for vertical swinging movement, a tilt hydraulic cylinder-piston assembly connected between the member and the propulsion assembly and including a tilt cylinder having opposed first and second ends, a pressure fluid supply pump communicating with a control valve, a first conduit communicating between the first tilt cylinder end and the control valve and including a first valve preventing fluid flow from the control valve and releasably preventing fluid flow from the first tilt cylinder end, a second conduit communicating between the first tilt cylinder end and the control valve and including a second valve preventing flow from the first tilt cylinder end and releasably preventing fluid flow from the control valve, together with a let-down assembly including a third conduit communicating between the ends of the tilt cylinder and including a valve arrangement operative for temporarily affording fluid flow from the first end of the tilt cylinder to the second end thereof in response to the generation of relatively high pressure adjacent the second end thereof occurring incident to the striking of an underwater obstacle.

Digitally processed radar speed sensor

Abstract: A Doppler speed sensor for a ground vehicle wherein errors due to vehicle tilt relative to the ground surface and initial mounting angle error are substantially eliminated by using a first antenna with its radiation pattern directed down and forward and a second antenna with its radiation pattern directed down and rearward, so the principal axes of the radiation patterns are 90° apart. A novel digital technique for processing the signals received from such antennas is also disclosed.

Bi-static radar speed sensor

Abstract: A doppler speed sensor for a ground vehicle wherein errors due to perpendicular velocity and vehicle tilt relative to the ground surface are substantially eliminated by utilization of a first receiving antenna having a radiation pattern disposed facing forwardly and covering a portion of the ground surface, and a second receiving antenna having a radiation pattern disposed facing rearwardly and overlapping the first antenna radiation pattern on the ground surface portion.

Effect of Substrate Surface on Alignment of Liquid Crystal Molecules

Abstract: Investigations were made of tilt angles of the molecular long axis in a liquid crystal layer sandwiched between two substrates, which were prepared by evaporating silicon at oblique incidence. Measurements of the dependence on the incident angle were carried out, which showed that the tilt angles varied from 3° to 28.4° for the incident angles ranging from 67° to 86°. Observations of the deposited film surfaces by use of electron microscopy revealed that they had a sawtooth-like structure whose shape also depended on the incident angle. It was suggested that the tilt angle was strongly affected by surface structures of the substrates.

The effect of surface orientation on the operation of multiplexed twisted-nematic devices

Abstract: The voltage and angular dependence of the electro-optic transfer characteristic of a twisted-nematic display are strongly affected by the average orientation (tilt bias) of the liquid-crystal molecules at the solid surfaces enclosing the fluid. A cell made with low tilt bias of the liquid-crystal molecules has a much sharper threshold in its electro-optic transfer curve and much better viewability when operated in a multiplexed mode than a display with a high tilt bias of the liquid-crystal molecules. As an example, a four-digit multiplexed twisted-nematic display of low tilt bias is viewable over a solid angle of about II/2 sr; whereas a high tilt-bias twisted-nematic device operating under the same multiplexing conditions is only viewable over a solid angle of about 0.50 sr.

Single-Site Phase Velocity Measurement

Abstract: Summary Mikumo & Aki attempted to determine phase velocities at a single site using seismometers and strainmeters oriented in the same horizontal direction. For the five earthquakes studied, they found a good agreement with the theoretically predicted velocities for body waves and, in some cases, for surface waves. Rodgers showed that for long periods (> 100 s), horizontal acceleration and tilt cannot easily be separated instrumentally, and King et al. have shown that near-station heterogeneities may result in azimuthal effects not considered by Mikumo & Aki. We rederive the method for single-site phase velocity determinations taking into account both of these effects. Our method uses strain and vertical acceleration measurements because the vertical acceleration record is neither affected by site effects nor contaminated by tilt.

Remotely controlled mirror of variable geometry for small‐angle x‐ray diffraction with synchrotron radiation

Abstract: A total‐reflecting mirror of 120‐cm length was designed and built to focus synchrotron radiation emanating from the electron–positron storage ring at the Stanford Linear Accelerator Center (SPEAR). The reflecting surface is of unpolished float glass. The bending and tilt mechanism allows very fine control of the curvature and selectability of the critical angle for wavelengths ranging from 0.5 to 3.0 A. Elliptical curvature is used to minimize aberrations. The mirror is placed asymmetrically onto the ellipse so as to achieve a tenfold demagnification of the source. The bending mechanism reduces nonelastic deformation (flow) and minimizes strains and stresses in the glass despite its length. Special design features assure stability of the focused image. The mirror reduces the intensity of shorter wavelength harmonics by a factor of approximately 100.

Laboratory investigation of tilt and seismicity anomalies in rock before failure

Abstract: Laboratory measurements of tilt and seismicity anomalies whose time durations are a few milliseconds are shown to precede failure in dry rock specimens. The observed tilt and seismicity behaviour is qualitatively similar to that reported to precede earthquakes. Test results suggest that this precursor time for laboratory specimens of this length may be independent of rock type, in agreement with theoretical predictions and other experimental data on rock failures including earthquakes.

Theory relating to remote electromagnetic probing of a nonuniform-thickness coal seam

Abstract: The effect of lateral inhomogeneities on electromagnetic remote probing of layered structures is considered. The excitation is taken to be an incident transverse electric (TE) plane wave. The fields, the surface admittance, and the wave tilt depend upon the angle of incidence, the distance from the air--coal interface, the electrical contrast, and the layer profile (e.g., sinusoidal, step, or slant profile). Both low- and high-frequency cases are illustrated and compared with corresponding results having no lateral inhomogeneities. Results indicate that the surface admittance and the fields tangential to the surface are ''good'' indicators of the local structure, whereas the field normal to the surface and the wave tilt are not. The wave tilt and the field normal to the surface, however, give good indication of subsurface anomalies. As the observation point is moved away from the air--coal interface, the ''information content'' regarding the lateral inhomogeneities rapidly decreases. Thus, measurements performed on the surface, or measurements dependent upon the fields at the surface, e.g., reflection coefficients, are more sensitive to lateral inhomogeneities than measurements performed away from the surface.

A facile location of goniometer tilt-axis position with respect to a single-crystal electron-diffraction pattern orientation

Abstract: For single-crystal electron-diffraction studies requiring definition of the location of the microscope goniometer tilt axis with respect to the diffraction pattern orientation, a quick calibration can be made taking advantage of the methylene O⊥ (001) subcell diffraction pattern obtained from any of a certain series of isostructural long-chain compounds when they are tilted 30° about the monoclinic b* axis Those crystals giving a symmetric O⊥ (001) diffraction pattern when the stage is tilted 30° have their b* axes parallel to the tilt axis

Multi-dimensional corrective system for long radiation beams

Abstract: A system for correcting misalignment and divergence in a long, propagating beam of radiation as is typically applied through a plurality of chambers to produce isotopically selective photoexcitation in a system for isotope separation. The corrective apparatus comprises a reflective relay system placed at predetermined intervals along the path of propagation of the radiation where correction of alignment and/or divergence are required. The reflective relay includes a concave mirror employed to correct divergence and which receives radiation directed at it by a first plane reflective surface which in turn responds to the radiation on the path of propagation. The concave mirror reflects toward a second plane mirror which in turn reflects the radiation back onto the path of beam propagation with correction of alignment and divergence. The first and second plane reflecting surfaces are adjustable on both tilt and position to permit alignment correction in both angle and displacement of the propagating beam of radiation.

Low-angle tilt boundaries and inhomogeneous current densities in sodium beta alumina

Abstract: Observation of [h k.0] low-angle tilt boundaries in sodium beta alumina is reported. The boundaries have a habit plane close to the (00.1) planes, and are evidence for the existence of dislocations with a Burgers vector component in the [00.1] direction. The indications are that these dislocations dissociate according toc 0[00.1]→1/2c 0[00.1]+1/2c 0[00.1]. Such tilt boundaries can cause micro-inhomogeneities in sodium ion current flow and both enhancement and decrease of conduction plane current density seems possible.

Tilt observations in the Poorman Mine Near Boulder, Colorado

Abstract: Tiltmeters consisting of a servoed bubble trapped under an optical flat are described, together with techniques used for calibrating, orienting, and installing such instruments. The long-term stability of one such (quartz) instrument is such that a 2-μ rad annual tilt of the Poorman Hill can be measured; however, we cannot tell whether an apparently steady tilt of 3 μ rad/yr is real or due to instrumental drift. A beryllium copper instrument drifted at a more rapid but relatively constant rate of 22 μ rad/yr. The two instruments agree at the 10−7-ad level over a 2-month interval, after a linear term has been removed from both records. Earth tide tilts observed with the quartz instrument before and after construction of a concrete block enclosure, and with the beryllium copper instrument at two different sites in close proximity to the quartz instrument, all differ in amplitude and phase. The difference between a pair of observations at a single tidal frequency approximates a periodic unidirectional tilt with maximum excursion near the time of greatest earth strain. For a given pair of observations the direction is the same at all frequencies, but this direction differs for different observation pairs. These differences are ascribed to local tilts generated by tidal strains acting on the geometrical irregularities of the observing site. Tilts due to ocean loads and coupling of strain with local geology and topography have been computed, but it is not possible to calculate the very local site effects owing to the complex and irregular nature of the site. Strain-induced tilts are believed to be the major source of error in tilt measurement; the larger-scale couplings are probably calculable in most cases, but the very local site effects must be avoided by the use of long-base instruments in either tunnels or boreholes.