Showing papers on "Tilt (optics) published in 1999"

Human responses to upright tilt: a window on central autonomic integration

Abstract: 1. We examined interactions between haemodynamic and autonomic neural oscillations during passive upright tilt, to gain better insight into human autonomic regulatory mechanisms. 2. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in nine healthy young adults. Subjects breathed in time with a metronome at 12 breaths min-1 (0.2 Hz) for 5 min each, in supine, and 20, 40, 60, 70 and 80 deg head-up positions. We performed fast Fourier transform (and autoregressive) power spectral analyses and integrated low-frequency (0.05-0.15 Hz) and respiratory-frequency (0. 15-0.5 Hz) spectral powers. 3. Integrated areas of muscle sympathetic bursts and their low- and respiratory-frequency spectral powers increased directly and significantly with the tilt angle. The centre frequency of low-frequency sympathetic oscillations was constant before and during tilt. Sympathetic bursts occurred more commonly during expiration than inspiration at low tilt angles, but occurred equally in expiration and inspiration at high tilt angles. 4. Systolic and diastolic pressures and their low- and respiratory-frequency spectral powers increased, and R-R intervals and their respiratory-frequency spectral power decreased progressively with the tilt angle. Low-frequency R-R interval spectral power did not change. 5. The cross-spectral phase angle between systolic pressures and R-R intervals remained constant and consistently negative at the low frequency, but shifted progressively from positive to negative at the respiratory frequency during tilt. The arterial baroreflex modulus, calculated from low-frequency cross-spectra, decreased at high tilt angles. 6. Our results document changes of baroreflex responses during upright tilt, which may reflect leftward movement of subjects on their arterial pressure sympathetic and vagal response relations. The intensity, but not the centre frequency of low-frequency cardiovascular rhythms, is modulated by the level of arterial baroreceptor input. Tilt reduces respiratory gating of sympathetic and vagal motoneurone responsiveness to stimulatory inputs for different reasons; during tilt, sympathetic stimulation increases to a level that overwhelms the respiratory gate, and vagal stimulation decreases to a level below that necessary for maximal respiratory gating to occur.

General formula for coupling-loss characterization of single-mode fiber collimators by use of gradient-index rod lenses

Abstract: A general formula for determining the coupling loss between two single-mode fiber collimators with the simultaneous existence of separation, lateral offset and angular tilt misalignments, and spot-size mismatch is theoretically derived by use of the Gaussian field approximation. Based on this general formula, the formulas for coupling losses that are due to the misalignment of insert separation, lateral offset, and angular tilt are given. The formula for the coupling loss that is due to Gaussian spot-size mismatch of two single-mode collimators is also given. Good agreement between these formulas and experimental results is demonstrated with gradient-index rod lens-based fiber collimators operating in the 1300-nm band.

Frequency locking a laser to an optical cavity by use of spatial mode interference.

Abstract: We present a novel technique to frequency lock a laser to an optical cavity. This technique, tilt locking, utilizes a misalignment of the laser with respect to the cavity to produce a nonresonant spatial mode. By observing the interference between the carrier and the spatial mode one can obtain a quantum-noise-limited frequency discriminator. Tilt locking offers a number of potential benefits over existing locking schemes, including low cost, high sensitivity, and simple implementation.

Automatic storm finding weather radar

Abstract: An automatic storm finding weather radar is disclosed that uses a storm finding algorithm to automatically control the weather radar to eliminate manual control. The storm finding algorithm uses the 0° C. isotherm altitude where precipitation is most likely to first occur to calculate an altitude search layer to find storms. The storm finding algorithm calculates the antenna upper and lower tilt angles and the number of scans to search the altitude search layer. A list of useable antenna tilt values is formed to drive the antenna controller. The antenna controller scans the antenna at the lower tilt angle and then moves to the next tilt angle until the search is complete. The search is then repeated using any new data.

Experimental evidence of the effects of non-Kolmogorov turbulence and anisotropy of turbulence

Abstract: We have observed experimental evidence of the effects of non-Kolmogorov turbulence (NKT) on wavefront tilt. In addition, we have observed the anisotropy of the horizontal and vertical tilt components caused by the anisotropy of turbulence near the telescope. We developed an experimental method, which allowed us to eliminate telescope vibration and isolate the atmospheric tilt from the star Polaris. The spatial and temporal statistics of the wavefront tilt were determined by using aperture masks having diameters in the range from 0.1 m up to 3.5 m. The measured dependencies of the tilt variance on the aperture diameter deviate from the prediction based on the Kolmogorov model. These dependencies have a knee, where the tilt variance approaches a constant level determined by NKT. Anisotropy was observed when comparing the X and Y components of wavefront tilt. On average the horizontal outer scale of turbulence estimated from the tilt statistics is larger than the vertical one by a factor of 2-3. Local topographical features and the telescope dome affect the outer scale with the result that the outer scale measured at the 1 .5 m telescope is smaller than that at the 3 .5 m telescope. The tilt power spectra have a c2/3 andf"3 behavior in the intermediate and high frequency range, respectively, which is predicted by the Kolmogorov model. In the low frequency range, the spectra do not obey the prediction of existing theoretical models. In this range the power spectra of the horizontal tilt exceed that for vertical tilt as a consequence of anisotropy of turbulence. The tilt temporal correlation scale increases with increasing aperture size. For the large apertures the tilt correlation scale is ofthe order of a few seconds.

Preliminary experimental evidence of anisotropy of turbulence and the effect of non-Kolmogorov turbulence on wavefront tilt statistics

Abstract: We report preliminary results ofwavefront tilt measurements for the star Polaris at the Starfire Optical Range 3.5 m telescopeat Kirtland AFB in Albuquerque, NM. We measured full aperture gradient tilt by using five pupil masks representing aperturediameters from O.lm to 3.5 m. Two optical configurations were exploited. In the first configuration, five images of Polariswere recorded simultaneously on one camera frame. The telescope was operated in its normal sidereal pointing mode. In thesecond configuration, pupil masks were changed sequentially. Additional measurements were collected with the telescopebolted to attempt to mitigate the effects of mount jitter. The coordinate system of the tilt measurements was rotated so thatthe cross-correlation coefficient between X- and Y— axis tilt components (b) is equal to zero. Several interesting results wereobtained. We observed amsotropy of the statistics of wavefront tilt. The observed one-axis tilt variances are unequal and thehorizontal tilt variance is consistently greater than the vertical one. We believe these effects are due to anisotropy of the largescale structure of turbulence. The estimates of the outer scale of turbulence support this conclusion. Also, we observed someevidence of the effects of non-Kolmogorov turbulence (NKT) on wavefront tilt. The measured tilt variance vs. aperturediameter curve has a knee beyond which the tilt variance no longer decreases for larger diameters. In the low and highfrequency range the tilt power spectra obey thef213 andf"3 power law, respectively. The tilt temporal correlation scale forthe 3.5 m aperture is on the order ofO.4 sec.Keywords: atmospheric turbulence, optical propagation, tilt, outer scale, anisotropy, measurements, turbulence model

Near-field seismic displacement and tilt associated with the explosive activity of Stromboli

Abstract: Broadband seismic recordings in the near-field of Strombolian explosions, at 500 m distance, show pronounced effects of tilt. The tilt signal is predominant in the horizontal components beyond about 50 s period while it is negligible in the vertical component. The waveform of the tilt signal at the seismometer output is a double time integral of the waveform due to ground displacement. Since the waveform of the displacement is known from the vertical component, the waveform of the tilt signal in the horizontal seismogram can be reconstructed and both contributions can be separated from each other with a linear regression. We have analyzed data recorded in the summit region of Stromboli in 1995 and 1996. The regional tilt can be determined from the differential vertical displacement between instruments a few tens of meters apart. Local tilts determined with individual instruments scatter around the regional value, most probably due to local strain-tilt-coupling. Mogi's (1958) formulae for a pressure source in a homogeneous halfspace are used to interpret the results. The source displaces a volume of several tens of cubic meters of the surrounding rock before the explosive discharge; typical volumes were 25 m3 in July 1995 and 60 m3 in September 1996.

Selected direction lighting device

Abstract: A lighting device is constructed with LED light sources and a power control to project light along a selected direction throughout an angular range of tilt of the lighting device about a vertical. The power control includes a tilt switch or tilt sensor which is responsive to the angular displacement of the lighting device about a vertical plane. A plurality of beams are arranged to project a plurality of oblique light beams. If during its deployment the lighting device is angularly displaced about the vertical, the power control means selectively energizes the beam which projects a light beam including the selected direction when the lighting device is angularly displaced. The divergence of the selected light beam from the selected direction when the light is vertical counterbalances the effect resulting from the angular displacement of the lighting device about the vertical permitting the light beam emerging from the lighting device to emerge directed along the selected direction throughout a range of angular tilt of the lighting device.

A flexible binomial option pricing model

Abstract: This article develops a flexible binomial model with a “tilt” parameter that alters the shape and span of the binomial tree. A positive tilt parameter shifts the tree upward while a negative tilt parameter does exactly the opposite. This simple extension of the standard binomial model is shown to converge with any value of the tilt parameter. More importantly, the binomial tree can be recalibrated through the tilt parameter in order to position nodes relative to the strike price or barrier of an option. The rate of convergence is improved as a result. © 1999 John Wiley & Sons, Inc. Jrl Fut Mark 19: 817–843, 1999

Method and apparatus for implementing automatic tilt control of a radar antenna on an aircraft

Abstract: A method and apparatus for automatically controlling the tilt of a radar antenna to avoid ground clutter returns while scanning the weather formations of most interest. In one embodiment a terrain database is utilized to determine tilt angles for different terrain cells. The tilt angle is determined starting at the aircraft position and working out to the radar range. If a tilt angle for a more distant cell is less than for a nearer cell it is ignored taking shadowing into account. In another embodiment the weighted tilt angle frequencies are entered into a histogram and the histogram is scanned to obtain a tilt angle resulting in an acceptable amount of ground clutter.

The polar cusp location and its dependence on dipole tilt

Abstract: Polar cusp crossings at high altitudes are seen in the POLAR data as decreases in the magnetic field and increases in magnetosheath-like plasma. Close to 500 polar cusp crossings identified from the magnetic field, low-energy electron and ion data observed by POLAR, are used to determine the statistical location of the polar cusp. When compared with Tsyganenko's 1989 vacuum model with an ellipsoidal magnetopause [Tsyganenko, 1989], the medians of the cusp crossings are located between the magnetic field lines with invariant latitudes of 80° and 82°. Statistically the shape of the polar cusp in this region is consistent with this model although there is much scatter around the median value. The position of the cusp is significantly dependent on the dipole tilt angle. When dipole tilts more toward the Sun, the cusp moves more poleward to higher invariant latitude from 77.2° at −30° tilt, to 80.0° at 0° tilt, to 81.8° at 30° or roughly 1° for every 14° of tilt.

Effects of tilt of the gravito-inertial acceleration vector on the angular vestibuloocular reflex during centrifugation.

Abstract: Effects of tilt of the gravito-inertial acceleration vector on the angular vestibuloocular reflex during centrifugation. Interaction of the horizontal linear and angular vestibuloocular reflexes (l...

Lateral-shift variable aberration generators.

Abstract: We describe and analyze an optical device capable of generating tilt, defocus, astigmatism, coma, and spherical aberration wave-front deformation. This optical device consists of a pair of aspheric plates that produce aberrations by laterally shifting one plate relative to the other. The surface descriptions of these optical plates are provided, and their aberration-inducing properties are verified with ray-tracing software. In addition, we examine the versatility and the limitations of using variable aberration generators and provide insight into how aberrations may be controlled by a simple lateral shift. The device may find application in aberration control in lens systems that are nonrotationally symmetric.

Measurement of Kodaikanal white-light images – IV. Axial Tilt Angles of Sunspot Groups

Abstract: The Kodaikanal sunspot data set, covering the interval 1906–1987, is used in conjunction with the similar Mount Wilson sunspot data set, covering the interval 1917–1985, to examine characteristics of sunspot group axial tilt angles. Good agreement is demonstrated between various results derived from the two independent data sets. In particular, the tendency for sunspot groups near the average tilt angle to be larger than those far from the average tilt angle is confirmed. Similarly the faster residual rotation rate for groups near the average tilt angle is also confirmed. Other confirmations are made for the relationships between latitude drift of sunspot groups and tilt angle, polarity separations, and axial expansion. Evidence is presented that tilt angles averaged over these long time intervals differ between the north and south hemispheres by about 1.4 deg. It is suggested that residual tilt angles show a slight systematic variation with phase in the activity cycle.

Double tilt and rotate specimen holder for a transmission electron microscope

Abstract: A side-entry specimen holder for transmission electron microscopy is provided. The specimen holder is capable of rotating a specimen and tilting it in two axes. The specimen, when mounted in the holder, can be tilted in the plus/minus direction of the X-axis, the plus/minus direction of the Y-axis, and simultaneously have the ability of 360° rotation in the axis of the electron beam to permit alignment of microstructural features of the specimen for optimal viewing and analysis.

Compound floating pivot micromechanisms

Abstract: A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use compound floating pivot structures to attain far greater tilt angles than are practical using other micromechanical techniques. The new mechanisms are also capable of bi-directional tilt about multiple axes.

Head tilt during driving.

Abstract: In order to distinguish between the use of visual and gravito-inertial force reference frames, the head tilt of drivers and passengers were measured as they went around corners at various speeds. The visual curvature of the corners were thus dissociated from the magnitude of the centripetal forces (0.30-0.77 g). Drivers' head tilts were highly correlated with the visually-available estimate of the curvature of the road (r2=0.86) but not with the centripetal force (r2<0.1). Passengers' head tilts were inversely correlated with the lateral forces (r2=0.3-0.7) and seem to reflect a passive sway. The strong correlation of the tilt of drivers' heads with a visual aspect of the road ahead, supports the use of a predominantly visual reference frame for the driving task.

Wavelength characteristic control method of optical transmission power by raman amplification, wavelength multiplex optical communication system using the same, and light amplifier

Abstract: PROBLEM TO BE SOLVED: To automatically compensate the wavelength characteristic of optical transmission power and to improve transmission characteristic, without damaging respective channel light beams by compensating the wavelength characteristic for a WDM(wavelength multiplex) signal light where the wavelength characteristic is generated in optical transmission power thorough the use of the gain wavelength characteristic of Raman amplification. SOLUTION: A Raman amplification generation part 2 Raman-amplifies WDM signal light from a tilt generation part 1. Thus, a wavelength characteristic (tilt), generated in optical transmission power between channels, is compensated and optical transmission power between the channels is made uniform in the tilt generation part 1. A tilt monitor part 3 monitors the wavelength characteristic of optical transmission power, by using a part of WDM signal light outputted from the Raman amplification generation part 2. A Raman amplification control part 4 adjusts the power of Raman excitation light in the Raman amplification generation part 2 according with the monitor result of the tilt monitor part 3. Thus, the gain wavelength characteristic of Raman amplification is controlled, so that the wavelength characteristic of optical transmission power is flattened.

Automated optical measurement apparatus and method

Abstract: An automated apparatus and method for measuring properties of optical components based on wavefront sensing and analysis. A wavefront of predetermined profile is directed at a surface to be measured so that it is more or less distorted in accordance with the shape of the surface and the distorted wavefront is sensed and analyzed. From the information derived from the distorted wavefront and other knowledge of the relationship between the surface and position of the wavefront of predetermined profile, the shape of the surface maybe inferred along with other properties such as radius of curvature, focal length, conic constants, asphericity, toricity, tilt, and decentering. Concave, convex, cylindrical, and flat parts may be measured along with wavefront errors in bandpass transmitting components such as lenses, filters, and windows.

Single rotating polygon mirror with adjacent facets having different tilt angles

Abstract: A single rotating polygon mirror with adjacent facets having different tilt angles reflects and splits the scanning beam to multiple photoreceptors in a raster output scanning (ROS) system. The mirror can have two or four alternating facets with different tilt angles. Two different light beams form two different light sources can be reflected and split from the polygon mirror contemporaneously to multiple photoreceptors. The split beams from the polygon mirror facets can share a common f-theta scan lens.

Optical recording and reproducing apparatus, tilt adjusting method appropriate therefor, and recording control method

Abstract: An optical recording and reproducing apparatus for adjusting a tilt of an optical pickup in accordance with an amount of jitter of a reproduction signal, a tilt adjusting method therefor, and a recording control method. The optical recording and reproducing apparatus includes an optical pickup having an object lens, a tilt adjusting unit for adjusting a tilt angle of the object lens, a jitter detecting unit for detecting an amount of jitter of a reproducing signal generated by the optical pickup from a disk, and a tilt controlling unit for minimizing the amount of jitter by feeding the amount of jitter detected by the jitter detecting unit back to the tilt adjusting unit. According to the optical recording and reproducing apparatus, there is no need for a space in which a displacement sensor detecting the tilt angle of the optical pickup faces the disk.

Partial mixing of opposite chirality in a bent-shaped liquid crystal molecular system

Abstract: Layer structure and electrooptical switching were studied in a bent-shaped achiral liquid crystal molecule, P-12-PIMB. By the application of a dc field during slow cooling from the isotropic phase to the highest temperature smectic phase, B2, large uniform domains of about 0.5 mm diameter were obtained. A tilted antiferroelectric structure was confirmed in the B2 phase by means of texture observations and switching current measurements. The molecular tilt angle was found to be independent of temperature and was 34°. In addition, domains with a smaller apparent tilt angle were also observed, suggesting that layers with different senses of chirality coexist in the domain.

Tilt detection device, optical disc device, and tilt control method

Abstract: A tilt detection device detects an inclination (tilt angle) of the recording surface of an optical disc with respect to the optical axis of the light beam. The device has an optical head for directing a light beam onto the optical disc, a photo detector for receiving light reflected from the optical disc, and a tilt detector for detecting inclination of the recording surface of the optical disc with respect to the optical axis of the light beam by a signal output from the photo detector.

Minimum protrusion mechanically beam steered aircraft array antenna systems

Abstract: Low-protrusion array antennas enable reception of satellite signals by airliners in flight. Prior systems using a beam normal to an array face required a 70° array tilt for reception from a satellite at 20° elevation (i.e., tilt angle is complementary angle (90°−β) of satellite angle (β) of elevation). Compared to that 70° array tilt for reception from a satellite at 20° elevation, disclosed antennas require an array tilt of only 25° (90°−β−α=25°). This is accomplished by providing a beam at a fixed acute angle (α) to the array face (e.g. 45 degrees). A side-by-side linear array 16 of slotted waveguide radiator columns 18 provides a pencil beam at a fixed acute angle of 45° to array aperture, for example. By action of tilting motor 42 to mechanically tilt the array of slotted waveguides over a range of ±25° from horizontal, the beam can be scanned from 20° elevation to 70° elevation. Azimuth rotator motor 30 provides 360° beam pointing in azimuth. A television satellite can thus be tracked by an aircraft mounted antenna with only about a 5 inch above-fuselage protrusion.