Showing papers on "Tilt (optics) published in 1992"

Laser guide star in adaptive optics: the tilt determination problem.

Abstract: The use of laser beacons to create artificial reference stars for adaptive optics has been successfully demonstrated by several experiments (Fugate et al., 1991, Nat., 353; Primmerman et al., 1991, Nat., 353). Nevertheless, laser beacons do not allow the global wave-front tilt determination, which relies then on the availability of a natural reference star. Taking into account the photon noise and the anisoplanatic errors, we compare the performance of adaptive optics correction using natural or artificial (laser) reference star

The role of balance dynamics in the active perception of orientation.

Abstract: The Stoffregen and Riccio (1988) hypothesis that perceived orientation is determined primarily by balance dynamics was tested Perception of orientation was evaluated in the context of a task that required Ss to control the roll orientation of a device in which they were seated The device's direction of balance was manipulated across trials and thus was independent of gravity Eighteen Ss participated in the investigation After each trial, Ss estimated their mean tilt with respect to upright Correlations of perceived tilt with tilt from balance were consistently higher than the correlations with gravity tilt The dominance of balance over gravity depended on the magnitude of tilt from balance

Low-energy configurations of symmetric and asymmetric tilt grain boundaries

Abstract: High-resolution electron-microscopy experiments are combined with computer simulations of tilt grain boundaries (GBs) in Au to investigate the preferred GB planes in ∑ = 9 and ∑ = 11 bicrystals. Th...

Reproducibility of head upright tilt table test results in patients with syncope.

Abstract: Head upright tilt table testing is a promising technique for the evaluation and management of vasovagal (neuroregulatory) syncope. In order to determine the day-to-day reproducibility of results using this technique we performed head upright tilt table testing (with or without graded isoproterenol infusion) in 21 patients (12 males, 9 females, mean age 34 +/- 19.1 years). During the first tilt study a total of 14 patients experienced syncope (six during baseline tilt, mean tilt time 15.8 +/- 7 minutes, eight following tilt with graded isoproterenol infusion, mean tilt time 17.7 +/- 9 minutes) while seven were negative. During the second tilt study (performed 3-7 days following the first study) the results of the first study were duplicated in 19 patients (90%) (six during baseline tilt, mean time 17.5 +/- 8 minutes, eight following graded isoproterenol infusion, mean time 15.9 +/- 7 minutes), however the level of provocation required to provoke syncope differed from that needed in the initial test in five patients (24%). We conclude that the results of head upright tilt table testing with graded isoproterenol infusions can be duplicated in 90% of patients, although some day-to-day variability exists in the degree of provocation necessary to elicit a positive response.

Reproducibility of head-up tilt-table testing for eliciting susceptibility to neurally mediated syncope in patients without structural heart disease.

Abstract: Head-up tilt testing has gained acceptance as a tool for assessing susceptibility to neurally mediated syncopal syndromes (e.g., vasovagal syncope), and is currently being evaluated as a means of testing therapeutic interventions in these conditions. To assess reproducibility of head-up tilt testing and thereby assess the potential of such testing for immediate evaluation of a planned treatment, findings during 2 sequential 80 ° headup tilt tests were compared in 23 patients (age range 6.5 to 74 years) undergoing evaluation of syncope of unknown origin. Upright tilt was performed initially in the absence of drugs, and repeated if necessary during pharmacologic provocation by means of isoproterenol infusions of 1 and 3 μg/min (tilt 1). End points were syncope, maximal tolerated isoproterenol dose, or a tilt duration of 10 minutes. The second tilt test (tilt 2) was conducted after approximately 30 minutes of supine rest using the maximal provocative conditions used in tilt 1. Fifteen of 23 patients (65%) developed syncope in either tilt l or 2, while 8 of 23 (35%) remained asymptomatic. Tilt testing results were concordant (i.e., positive in both tests, or negative in both tests) in 20 of 23 (87%) patients. Concordance was, however, less among tilt-positive patients (12 of 15, 80%) since 3 patients were tilt-positive in tilt 1 only. In the 15 tiltpositive patients, heart rates, systolic and diastolic blood pressures at time of maximal tilt provocation were similar for both tilts (heart rate 1, 67 ± 27; 2, 82 ± 34 beats/min; systolk blood pressure 1: 50 ± 11 mm Hg; 2, 60 ± 21 mm Hg [p = not significant (NS)]; diastolic Wood pressure 1, 27 ± 12 mm Hg; 2, 33 ± 18 mm Hg [p = NS]). Furthermore, time from tilt onset to syncope did not differ in tilt 1 and 2. Among the 15 patients who were tilt-positive in tilt 1, the procedure was tolerated for 3.7 ± 2.1 minutes during the first test compared with 4.5 ± 3.2 minutes in the second test (p = NS). The outcomes were even closer if only patients developing syncope during both tests are considered (tilt 1, 3.7 ± 2.1 minutes vs tilt 2, 3.1 ± 1.8 minutes). Similarly, in the 8 tilt-test negative patients, minimal recorded systolic blood pressure and diastolic blood pressure did not differ in the 2 tests. Thus, upright tilt testing appears to exhibit a relatively high degree of reproducibility when a second study is performed on the same day. Consequently, 2 sequential tilt tests may be useful for assessing the immediate effect of therapeutic interventions on susceptibility to neurally mediated hypotension-bradycardia syndrome.

Imaging apparatus comprising a focus-error and/or tilt detection device

Abstract: An imaging apparatus is described which comprises an imaging system (PL) and a focus detection device for determining a deviation between the image plane of the imaging system and a second plane (WS) on which imaging is to take place. The focus error detection system comprises a radiation source (S) which supplies a beam (bf) having a wide wavelength band, an object grating (G₁) and an image grating (G₂) which are imaged onto each other via the second plane. In the focus detection system a reference beam (br) which is reflected by the outer surface (RP) of the imaging system can be used in combination or not in combination with the wideband beam and the gratings. By using a number of such focus detection systems a tilt detection device can be realised for detecting the position of the second plane (WS) with respect to the image plane.

Wavefront sensor having a lenslet array as a null corrector

Abstract: A wavefront sensor (10) includes a radiation sensor (2) and an array (12) of lenslets (12A) that are optically coupled to the radiation sensor. The array of lenslets has a radiation receiving surface for receiving an incident wavefront and for focussing the wavefront at a plurality of focal positions upon the radiation sensor. Each of the lenslets comprises a diffractive optical element having an optical center that is located at a predetermined point for inducing an equal and opposite tilt to a portion of the wavefront incident on the lenslet. As a result, an aberration within that portion of the wavefront is cancelled. The predetermined point is determined to be equal to and opposite a focal spot shift of the lenslet.

Simple adaptive optical system

Abstract: A system for correcting wavefront distortion includes an eight channel deformable mirror 11 attached to a two-axis, tip/tilt mount 12. The deformable mirror 11 reflects an incoming telescopic wavefront 10 onto a beamsplitter 14. The beamsplitter 14 divides the reflected telescopic wavefront 13 into two separate beams 15, 20. The beam 20 reflected by the beamsplitter 14 may be used for experimentation and measurement. The beam 15 transmitted by the beamsplitter 14 is directed toward a modified Hartmann-Shack wavefront sensor 16. The modified Hartmann-Shack sensor 16 detects the slope of the wavefront at several locations across this transmitted beam 15 and provides analog signals 17 representing these slopes to a series of actuator drive circuits 18. The actuator drive circuits 18 provide excitation signals 19 to actuators 22, 30 on the deformable mirror 11 and the two-axis, tip/tilt mount 12. These actuators 22, 30 facilitate the reforming and repositioning of the deformable mirror 11 so as to correct any incoming wavefront 10 distortion.

Behavior of a first-order smectic-A-smectic-C transition in free-standing liquid-crystal films

Abstract: Free-standing films of the liquid-crystal compound C7 [4-(3-methyl-2-chloropentanoyloxy)-4'-heptyloxybiphenyl], which possesses a first-order smectic-A\char21{}smectic-C transition, are studied. In various films with thicknesses between 2 and 27 molecular layers, the average tilt angle, i.e., the order parameter of the transition, is measured by ellipsometry. In thick films of more than about 15 layers, a first-order transition with a discontinuous jump of the average tilt value is observed at the same temperature at which the smectic-A\char21{}smectic-C transition in the bulk sample occurs; in contrast to the bulk, a finite average tilt remains in the high-temperature phase, indicating that the transition takes place in the interior layers, whereas the surface layers are tilted in the whole temperature range. Films thinner than about 15 layers exhibit instead of the first-order transition a steep but continuous variation of the tilt with temperature. This feature becomes less pronounced with decreasing film thickness and is not observable in the two-layer film, which shows large tilt values in the whole temperature range, indicating the influence of a strong ordering field resulting from surface interactions.

Structure of cells within a mobile communication system

Abstract: A re-use partition of cells in a mobile communication system has an outer cell (30) and an inner cell (20) which is provided in the outer cell (30). An interval of cells using the same channel or the same frequency in the inner cells is shorter than an interval in the outer cells, which is the nature of a re-use partition. Communication between a base station and a mobile station is carried out by using a channel having a higher received level of an outer cell channel or an inner cell channel. A base station has a first beam tilt antenna having tilt angle (Θ out ) for an outer cell (30), and a second beam tilt antenna having tilt angle (Θ in ) so that Θ in is larger than Θ out . A speech channel and a control channel are provided for each of the first antenna and the second antenna.

Normal Palmar Tilt: is Dorsal Tilting Really Normal?:

Abstract: Palmar tilt measured on true lateral radiographs of 100 normal wrists revealed that dorsal palmar tilt is not found in the normal adult, and women generally have a larger palmar tilt (average 12.4°) than men (average 9.3°).

A 360° single‐axis tilt stage for the high‐voltage electron microscope

Abstract: A new type of specimen stage that permits more than 180 degrees of tilting about the axis of a side-entry rod has been developed for a high-voltage electron microscope (HVEM). Roughly cylindrical specimens, with radial dimensions of less than a few micrometers, that can be mounted on the tip of a microneedle or micropipette are applicable. For glass micropipettes, the energy of the 1-MeV beam of the HVEM is sufficient to image specimens through both walls. The stage employs a spindle mechanism that holds these needles or micropipettes coaxial with the tilt axis, allowing the specimen to be rotated without restriction. This arrangement, along with the cylindrical form of the specimen, is an important development for single-axis tomography, because it permits a complete 180 degrees set of projections to be recorded. The angular accuracy of the stage was demonstrated to be within +/- 0.20 degrees, with a cumulative error of less than 1.0 degrees over a 180 degrees span. The new stage was tested using puffball spores mounted on a micropipette. A 180 degrees tilt series was recorded and processed to yield a tomographic three-dimensional reconstruction which was displayed both as a cross-sectional view perpendicular to the tilt axis, and as a shaded surface viewed from different directions. The same computations were repeated using subsets of the tilt series to assess the effect of various amounts of missing information. Visual inspection of a selected cross-section from these reconstructions indicated that limiting the angular range to 160 degrees produced results nearly as good as the full data set. Limiting the range to 140 degrees, however, produced a noticeable geometric distortion, which became increasingly severe with ranges of 120 degrees and 100 degrees.

Cells re-use partition in a mobile communication system

Abstract: A re-use partition of cells in a mobile communication system has an outer cell (30) and an inner cell (20) which is provided in said outer cell (30). Interval of cells using the same channel or the same frequency in inner cells is shorter than interval in outer cells, as nature of re-use partition. Communication between a base station and a mobile station is carried out by using a channel of higher received level of an outer cell channel or an inner cell channel. A base station has a first beam tilt antenna having tilt angle (ϑ out ) for an outer cell (30), and a second beam tilt antenna having tilt angle (ϑ in ) so that ϑ in is larger than ϑ out . A speech channel and a control channel are provided for each of said first antenna and said second antenna.

Electrically remote-controlled mirror assembly

Abstract: The electrically remote-controlled type mirror assembly has a pair of plungers to tilt the mirror body supporting the mirror horizontally and vertically, respectively, within certain pivoting angles. The mirror assembly has a sliding mechanism including another motor to axially slide at least one of these plungers beyond said certain pivoting angles of the mirror body. The sliding mechanism is so arranged as to have no influence on the adjustment of the mirror angle within the certain pivoting angles of the mirror body. Thus, the mirror posture can be changed quickly from the mirror angle adjusted within the certain pivoting angle for ordinary car driving to the mirror angle with which the mirror is tilted further downward, and also the initially adjusted mirror angle can be restored accurately.

Deformable mirrors: design fundamentals, key performance specifications, and parametric trades

Abstract: A wide variety of deformable mirror structures have been studied for wavefront correction since the advent of adaptive optics nearly two decades ago. These structures generally fall into two categories: (1) segmented facesheet and (2) continuous facesheet. The segmented mirror technology features independently activated mirror elements controlled in the piston, tip, and tilt modes. The continuous facesheet designs use discrete electroceramic or electrostatic displacement actuators arranged in either an axial or bimorph position to bend the continuous facesheet. In addition there are two methods of correction: (1) zonal control and (2) modal control. The basic mirror types are discussed and analyzed in terms of wavefront correction capabilities. Curve fitting characteristics are explained in terms of the optical influence function and mirror meshing functions. The continuous facesheet deformable mirror is used as a model to develop basic design equations which are used for parametric trades.

Apparatus and system for positioning a laser beam

Abstract: An apparatus for controlling a high power laser beam for three dimensional operation consists of a mirror and three linear servo-mechanisms to tilt and to translate the mirror. The movement of the linear servo-mechanisms is controlled by a computer numerical control system or programmable logic controller.

Multiaperture overlap-scanning technique for large-aperture test

Abstract: The subaperture test technique developed by J. Wyant et al. revealed a new approach to solve the problem of testing a large optical surface. Unfortunately, uncertainty in the relative pistons and tilts among individual subapertures leaves a considerable measurement error to that method, which becomes an impediment to its practical applications. As is well known, two interferograms, sampled from the same tested surface by different adjustment of an interferometer, must be different in general. However, the difference between these interferograms gives the right information on the relative change of piston and tilt of the reference wavefront during sequential adjustments. Based on that fact, our lab has recently developed the multiaperture overlap-scanning technique (MAOST) for large aperture optics tests, by which a large optical surface is tested by a sequence of scannings of a small aperture with an overlap area. After processing of all sampled interferograms by a special designed software, the full aperture of the tested optical surface will be regained precisely. In this paper, the principle and the mathematical model of MAOST is described, and results of applying MAOST to test two optical flats with an aperture magnification ratio up to 2.6 are also given.

Tilt transitions in Langmuir monolayers of long-chain molecules

Abstract: Molecular dynamics simulations have been used to investigate tilt transitions in a monolayer model of amphiphilic molecules at an air–water interface. Eight simulations were performed at 300 K on monolayers in the density range of 18.5–25 A2/molecule. The model amphiphilic molecules contained 19 pseudoatoms, each representing a methyl or a methylene group, and a head group representing a carboxylate group. Amphiphile–amphiphile interactions were modeled using a new anisotropic united atom model that accounts implicitly for the presence of hydrogen atoms in alkanes; water–amphiphile interactions were modeled using two external potentials that do not constrain the head groups to the interface, allow methylene segments to enter the water, and provide a finite size interface of the same order of magnitude as the size of the experimental water–air interface. The tilt behavior of the monolayer was monitored as a function of molecular area. Tilt angle results and structure factor analysis point to the occurrence of a transition between 20 and 21 A2/molecule from an almost upright to a tilted monolayer. At 21 and 22 A2/molecule, the monolayers do not have a well‐defined tilt order. Upon monolayer expansion to 23 A2/molecule, the molecules become tilted over their nearest neighbors.

Liquid crystal displays of high tilt bias angles

Abstract: Liquid Crystal Display Devices having alignment layers of polyimides which are characterized by pendant perfluorinated chains, preferably linear, and having more than 6 perfluorinated carbon atoms. These alignment layers are capable to provide the Liquid Crystal Display Devices with stable tilt angles of 5 or more degrees.

Study of the molecular tilt angle and the order parameter of a ferroelectric liquid crystal mixture using IR spectroscopy

Abstract: We report measurements of the molecular tilt angle of a ferroelectric liquid crystal mixture (ZLI 3654), using infra-red spectroscopy, and of the optical tilt angle using polarizing microscopy. The molecular tilt angle is found to be approximately the same for different molecular vibrations. The second rank orientational order parameter for the axis of molecular vibrations of different groups of the molecule for homogeneously aligned samples have been determined as a function of temperature. The order parameter depends slightly on the sample thickness and is about 8 per cent higher for a lower thickness (∼ 7 μm) compared to a higher thickness (∼ 12 μm). The order parameter does not change significantly at the SC∗–SA transition. The order parameter of SC∗ is found to be unaffected by the application of a constant electric field. The order parameter for the alkyl chain is found to be about three times lower than for the molecular core.

Titlable optical microscope stage

Abstract: An X-Y microscope stage is provided with a tiltable support for a specimen. The specimen may be tilted about the tilt axis to re-orient the specimen for viewing. The re-orientation of the specimen may require a small adjustment in the X or Y direction and a subsequent refocus of the microscope optics.

Dynamical wavelength selection by tilt domains in thin-film lamellar eutectic growth

Abstract: Tilt domains are dynamical defects of cellular growth fronts consisting of a group of asymmetric cells traveling laterally along the front. We study the dynamics of these defects in thin-film directional solidification of the CBr 4 -C 2 Cl 6 eutectic alloy. We show that the sweeping of the growth front by tilt domains, at a given growth velocity V, brings it into a well-defined «dynamically selected» state. Once this state is reached, the tilt domains travel with a constant width. A sudden increase (decrease) of the growth velocity transforms constant-width tilt domains to growing (shrinking) ones

Image plane tilt in optical systems

Abstract: Mathematical expressions are presented to relate object and image plane tilts in nonaxially symmetrical optical systems. Examples that illustrate the use of these expressions are given. Keystone distortion is described and quantified as a function of image plane tilt.

Focus error detection using an equal path length lateral shearing interferometer

Abstract: This invention provides an equal path length lateral shearing interferometer and its implementation in focus detection devices, particularly for optical data storage devices. The interferometer comprises a beamsplitter and two abutting roof prisms. Shifting the placement of a roof prism along an axis orthogonal to the direction of light propagation and to the peak of the roof creates a lateral shear between the two output beams. Rotation a roof prism about this axis produces a tilt between the two output beams. This creates an interference pattern with a rotational orientation which is a function of the focus of the beam impinging on the optical storage medium. A pattern sensor is provided to adjust the focus of the beam in an accurate and dynamic manner.

Some thermal and paleomagnetic consequences of tilting a batholith

Abstract: If a rock body becomes fully magnetized and then is folded, faulted, or otherwise tilted, its vector of remanent magnetization will tilt with it. However, if a rock body is tilted while it is very hot, and then cools and becomes magnetized, its vector of magnetization will show little if any of the effects of tilt. It is shown, for a wide variety of circumstances, that tilting a large batholith should not be expected to result in equal tilt of that batholith's magnetic direction. This follows from several elementary considerations: (1) Batholiths cool slowly, and slow cooling lowers the blocking-temperature range for acquisition of remanent magnetization. (2) If a tilted block is large (of the order of 25 km in width) and has been tilted through even a moderate angle (25° will do), its “lower” end originally must have been very hot; quite possibly too hot to retain a remanent magnetization. (3) Tilt entails uplift, and uplift rearranges the geothermal gradient. Rapid uplift accompanied by erosion is particularly effective in raising the temperature of the upper levels of the crust, thereby delaying acquisition of magnetization until tilting is nearly complete. Other thermal constraints on the tilting of remanence vectors in batholiths are discussed; in general, it appears that quite special circumstances are required to tilt a large pluton without leaving a clear magnetic record. Few, if any, Cordilleran batholiths studied to date show this kind of evidence of tilt.

Beam tilt antenna

Abstract: PURPOSE: To form two beams separatively radiating on a horizontal plane and to independently set up tilt angles in a vertical face by the two beams. CONSTITUTION: Two adjacent arrays of the 1st and 2nd array antennas 2.1, 2.2 having almost the same constitution are arranged, N hybrid circuits 4 including the 1st and 2nd antenna side terminals and the 1st and 2nd device side terminals are connected to the arrays and the two antenna side terminals of the circuit 4 are provided with branch/coupling characteristics for outputting signals whose phases are mutually different by 90° correspondingly to a signal outputted from one of the device side terminals. This beam tilt antenna is also provided with the 1st and 2nd phase shifters 5.1, 5.2 and the 1st and 2nd power distributors 6.1, 6.2 each of which has N terminals on the antenna side and one terminal on the device side. The beam tilt angles of beams A, B depend respectively on the values of the phase shifters 5.1, 5.2. COPYRIGHT: (C)1994,JPO&Japio