Showing papers on "Tilt (optics) published in 1973"

Short-term average optical-beam spread in a turbulent medium

Abstract: On the basis of the extended Huygens–Fresnel principle, a general expression is derived for the short-term average optical-beam spread, as measured with respect to the instantaneous center of energy of the beam, of an initially coherent optical-beam wave propagating in a weakly inhomogeneous medium. The present analysis applies to the near field of the effective coherent transmitting aperture, where the beam wanders (dances) 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. This quantity is obtained from the corresponding long-term MCF by removing the random tilt of the wave front. Analytic expressions for the short-term beam spread are presented for the case of a Kolmogorov spectrum and the short-term average MCF derived by Fried. As expected, the short-term, turbulence-induced beam spread is always less than the corresponding long-term beam spread. Analytic and numerical results are given for the short-term average irradiance at focal range f, which is always greater than the corresponding long-term average irradiance.

Visual adaptation to tilt and displacement: Sameor different processes?

Abstract: Visual adaptation to tilt and displacement were compared to test whether they were dependent on the same or different processes. Although interocular transfer was essentially complete for both transforms, marked differences occurred between the two kinds of optical transforms in terms of rate of adaptation as a function of exposure time and transform magnitude, level of compensation, and rate of decay. Tilt and displacement appear to be quantitatively different, consistent with the idea of a different locus for each adaptation effect. This conclusion was supported by the absence of a correlation between individual performance under the two transforms. The possibility is discussed that displacement and tilt adaptation involve independent visual systems for the perception of location and form.

Characterization of bicrystals using kikuchi patterns

Abstract: Three parameters, the misorientation angle, misorientation axis, and boundary normal, have been used to describe a general bicrystal,e.g., two adjacent grains, subgrains, or twins. An analysis developed to determine these parameters is presented. The angle and axis of misorientation are calculated from a misorientation matrix obtained from two Kikuchi patterns, one taken from each of the two crystals. To obtain the boundary normal, a specimen tilt is made inside the electron microscope. A rotation matrix specifying the actual specimen tilt is formulated from two Kikuchi patterns taken from the same crystal before and after tilt. With this rotation matrix and the change of projected boundary images before and after tilt, the boundary normal can be calculated. It is demonstrated that 1) for high-angle bicrystals, the misorientation angle may be determined to within ±0.2 deg, and the misorientation axis to within 0.1 deg; 2) for low-angle bicrystals, the misfit angle can be obtained to within ±0.1 deg, and the misfit axis to within 4 deg; and 3) the boundary normals so determined are generally accurate to 2 deg if suitable correction is made for the magnification change resulting from the specimen tilt.

Simultaneous visual adaptation to tilt and displacement: A test of independent processes

Abstract: Change in both visual direction and visual orientation was assessed following simultaneous exposure to both optical displacement and optical tilt. Tilt adaptation when both transforms were present was not different from tilt adaptation when Ss were exposed to optical tilt alone. A slight decrease in displacement adaptation when the transforms were presented simultaneously was found to be attributable to oblique displacement of the straight-ahead point produced when the optic array is first displaced and then rotated. It was concluded that adaptation to both transforms simultaneously is not different from adaptation to each transform separately, consistent with the view that the two kinds of adaptation involve independent visual systems.

Cation displacements and octahedral tilts in NaNbO3 Part I—Determination from x-ray difference reflections

Abstract: The angles of tilt of the anion octahedra in NaNbO3 have been calculated from measurements of the intensities of very weak x-ray difference reflections. Their variation with temperature is shown and compared with values calculated directly from lattice parameter measurements. The Nb displacements have also been calculated from the intensities of difference reflections.

Laser alignment device

Abstract: A projector of a high intensity collimated light beam for alignment use and employs a laser as a light source. A diverging lens expands the fine laser beam and passes it to a damped, pendulously supported, inclined mirror where it is reflected to a double convex condensing lens which acts to condense the beam. A plano-concave lens having its concave surface adjacent to the exit convex surface of the condensing lens is adjustably supported for movement about the center of curvature of the concave surface so as to tilt the planar surface relative to the axis of the entering beam and thus adjust the exit angle of the beam. The adjustment mechanism includes a pair of pivoting arms which contact one another at their free ends and a micrometer adjustment knob for pivoting the arms and providing a digital readout of their inclination which is equal to the beam elevation grade by virtue of the geometry of the mechanism. Once the angle is adjusted the pendulously supported mirror maintains the exit angle of the beam against the small tilts of the housing.

Tidal Tilt Anomalies

Abstract: King and Bilham1 have made an interesting suggestion for a mechanism to explain the large number of published anomalous tidal tilt results. The proposed coupling between the tidal strain and the tidal tilt leads to tilt anomalies of the order of 8 msec for the M2 body tide and, for the loading tide, anomalies depending on the magnitude of the loading strain.

Reproduction of tilt of a cast on a surveyor

Abstract: A method is described by which the tilt of the cast on the surveyor is registered and reproduced. In contrast to others, this method has these advantages: The registration of the tilt is established by using a geometric technique, and it is measured in degrees which designate mathematically the position of the determined plane in relation to the horizontal plane. By the same geometrical method, the tilt can be accurately reproduced at any time. The registration data are listed on the patient's card, and they can be transferred to subsequent casts at any time provided the measurements are not altered. The method is simple, easy to use, and not affected by the shape of the cast. The reproducibility of the tilt is independent of the wear or fracture of the preliminary cast.

Optimal input rates for tilt adaptation.

Abstract: The effect of rate of change in optical tilt on adaptation was investigated by incrementing the level of tilt after every 5-min exposure period for a total of 25 min. The increments were 8, 10, and 12 deg in conditions 1, 2, and 3, respectively. In Experiment I the same subjects took part in all conditions; in Experiment II separate groups were used and the experiment was extended to include ten increments in tilt. In both experiments the rate of growth of adaptation varied inversely with the size of the increment. The results also suggest that higher levels of tilt require more time to process than lower levels and that increments in tilt may actually inhibit further processing when the change occurs too rapidly.

Web aligning apparatus

Abstract: A web aligning apparatus is disclosed wherein a web path correcting tilt frame is mounted for tilting movement between the laterally spaced side plates of the tilt frame support structure. The tilt frame includes a pair of laterally spaced frame members which extend generally longitudinally of the path of travel of the web through the apparatus and which rotatably support a pair of steering rollers therebetween. The axes of the steering rollers extend generally transversely to the path of travel of the web through the apparatus. A pair of elongated links respectively connect the tilt frame members with the support structure side plates and are arranged so that the instantaneous center of rotation of the tilt frame is located outside the perimeter of the tilt frame and shifts along an arcuate path that extends laterally of the path of travel of the web with tilting movements of the tilt frame.

Methods for prediction and evaluation of tidal tilt data from borehole and observatory sites near active faults

Abstract: Tilt has been measured continuously at tidal sensitivity in borehole and observatory sites in the San Francisco Bay region, California. These sites, within a few kilometres of a m ajor fault and the Pacific Ocean, are part of an extensive network measuring strain and microseismicity. Static response of the Presidio site to ocean loading at the M 2 frequency best fits a finite-element model with lower shear modulus in the San Andreas fault zone than in adjacent material at the same depth. The Presidio tilt data exhibit a secular trend less than 3 (rrad/year superim posed on local earthquake and meteorological effects. On two occasions earthquakes (M„ > 4.3) occurred within 55 km of a station and were preceded by anom alous tilt accumulating to 1 ^rad over several days with an accelerated rate of tilt a few hours before the events. The root-mean-square (r.m.s.) difference for two stations of 25 km apart for 700 h before and after one of these events was 5 x 10-8 and 2 x 10 ^ respectively . A similar r.m.s. difference was observed before and after a larger ( M b> 5) but more distant (180 km) earthquake from the same two stations. This latter event did not, however, exhibit the extreme linear slope (10~9 rad/h) of the two earlier earthquakes. Although such anomalies can be correlated with meteorological activity over short periods of time, they do not correlate for periods approaching one month. A transfer function derived during a period w hen there were no local earthquakes can be used for calculating tilt response to surface loading from telemetered meteorological and tilt data. These results can then be input for a prediction beyond the data, and the error in prediction monitored as a final output for instrument performance and potential earthquake hazard.

Apparatus for determining the momentary tilt of a vehicle or craft

Abstract: An apparatus for determining the momentary tilt of a moving vehicle or craft is provided with two translational accelerometers mounted rigidly on or in the vehicle or craft. The output signals of the accelerometers determine the acceleration components (ax, ay) in two, mutually perpendicular, axial directions (x, y) situated in a plane horizontal with respect to the vehicle or craft. From said output signals the low frequency components of two of the three angles ( Alpha , Beta ) defining the momentary tilt are obtained by employing, amongst others, a low-pass filter available for the two signals. The low-frequency components of the third angle ( gamma ) defining the momentary tilt are derived, via a low-pass filter, from a signal which is supplied by a compass and indicates the azimuth position of the vehicle or craft. The apparatus is furthermore provided with three angular accelerometers also mounted rigidly on or in the vehicle or craft, of which accelerometers the output signals determine the angular acceleration ( omega ) which said vehicle or craft is experiencing with respect to its centre of gravity. From said output signals the high frequency components of the three angles ( Alpha , Beta , gamma ) defining the momentary tilt are obtained by using a high-pass filter, available for each of these signals, and a (first) computing device.

Tilt and twist boundaries

Abstract: Tilt and twist components are determined for cubic bicrystals meeting at a planar boundary. It is shown that any boundary is nearly either a twist or tilt boundary, but the distinction between the two types is, in some cases, ambiguous.

Comments on ``Grain boundary contrast in field‐ion microscope images''. II

Abstract: A recent paper by French and Bishop has discussed the field‐ion contrast from a particular grain boundary configuration as a function of increasing angular misorientation, the images being constructed by computer simulation. Although their boundary configuration was pure tilt about [110], the resulting surface contrast displays apparent tilt and twist character because of the oblique surface section of the emitter tip chosen to contain the boundary trace. The present paper aims to distinguish the contrast events occurring in such images as a function of this apparent tilt and twist character and to quantify the expected contrast in terms of the ``ring‐matching'' contrast theory proposed by the present authors.

Watch display switch

Abstract: A tilt sensitive electrical switch wherein an asymmetrically balanced disc mounted on an axis causes electrical contact to be made when it is aligned in the desired activation region (plane); various embodiments are provided for causing electrical contact and for minimizing electrical energy dissipation.

Note on stereophotography with the electron microscope

Abstract: This note points out the applicability of the formula h=p/2M sin omega relating vertical distances h in the sample to parallax p and tilt angle omega , when an arbitrary (not horizontal) axis is used for the rotation (tilt) of the sample between exposures of left- and right-hand plates. Such an axis is usually required with crystalline samples, and may often be desirable with amorphous samples. It also indicates how the photographs may be correctly set up on the stereo viewer and the angle omega calculated, without recording or measuring diffraction patterns, if a calibrated goniometer stage is available, and presents in a simple notation and without approximation the correction required if the parallel projection approximation is not to be made.

Multiple transducer mounting

Abstract: Slotted staves for sonar transducer array elements in which the forward vertical frame is slotted and individual plates for each transducer element are bolted to it. This permits the individual transducer elements to tilt vertically in the slots on removal and eliminates the rotating of the entire transducer assembly as done previously.

Moiré patterns in the electron image of solution‐grown polymer crystals

Abstract: Relative tilt between two similar thin crystals may result in the formation of a moire pattern in the electron image Patterns hitherto interpreted as being parallel moires or rotation moire obtained from overlapping solution-grown polymer crystals are reconsidered, and it is shown that in some cases a tilt model is more acceptable The general features of tilt moire patterns predicted for crystals of this kind are discussed and compared with micrographs appearing in the literature Methods of distinguishing tilt moire patterns are indicated, though it is admitted that such experiments would be difficult to complete in the time limited by destruction of the crystal structure under the action of the electron beam Extinction contours may also sometimes be confused with long-period tilt moire patterns, and again careful experimentation is required for accurate identification The model of the structure of solution-grown polyethylene crystals inferred from a tilt moire interpretation of many of the electron image fringe patterns found in the literature is consistent with that derived from other sources

Centrifugally cast tapered tube - mfd in tilting mould

Abstract: A thin-walled conical, plastics tube with a uniformly thick, fibre-reinforced wall, is mfd with the rotational speed of the mould and/or its angle of tilt being varied both at the start of, and during centrifuging, to suit the material used The process is pref controlled as a function of mould temp