Showing papers on "Tilt (optics) published in 2006"

Estimation of pelvic tilt on anteroposterior X-rays—a comparison of six parameters

Abstract: Objective To compare six different parameters described in literature for estimation of pelvic tilt on an anteroposterior pelvic radiograph and to create a simple nomogram for tilt correction of prosthetic cup version in total hip arthroplasty.

Posture detector calibration and use

Abstract: Calibrating a posture detector for a patient's body involves measuring outputs of one or more sensors disposed in relation to the patient's body while the patient assumes a plurality of positions. A transfer matrix is formed having coefficients corresponding to the measured outputs. The transfer matrix defines a relationship between a coordinate system of the one or more sensors and a coordinate system of the patient's body. The body coordinate system is used as a reference coordinate system for posture detection. Posture, including tilt and/or tilt angle, may be determined based on first and second rotational angles defined in relation to the body coordinate system.

Tilts in Strong Ground Motion

Abstract: Most instruments used in seismological practice to record ground mo- tion are pendulum seismographs, velocigraphs, or accelerographs. In most cases it is assumed that seismic instruments are only sensitive to the translational motion of the instrument's base. In this study the full equation of pendulum motion, including the inputs of rotations and tilts, is considered. It is shown that tilting the accelerograph's base can severely impact its response to the ground motion. The method of tilt evaluation using uncorrected strong-motion accelerograms was first suggested by Graizer (1989), and later tested in several laboratory experiments with different strong-motion instruments. The method is based on the difference in the tilt sensi- tivity of the horizontal and vertical pendulums. The method was applied to many of the strongest records of the Mw 6.7 Northridge earthquake of 1994. Examples are shown when relatively large tilts of up to a few degrees occurred during strong earthquake ground motion. Residual tilt extracted from the strong-motion record at the Pacoima Dam-Upper Left Abutment reached 3.1 in N45E direction, and was a result of local earthquake-induced tilting due to high-amplitude shaking. This value is in agreement with the residual tilt measured by using electronic level a few days after the earthquake. The method was applied to the building records from the North- ridge earthquake. According to the estimates, residual tilt reached 2.6 on the ground floor of the 12-story Hotel in Ventura. Processing of most of the strongest records of the Northridge earthquake shows that tilts, if happened, were within the error of the method, or less than about 0.5.

Surface shape measurement by phase-shifting digital holography with a wavelength shift

Abstract: Surface contouring by phase-shifting digital holography is proposed and verified by experiments and numerical simulations. Digital holograms are recorded before and after mode hopping of a laser diode subject to current tuning, and the difference of the reconstructed phases at each wavelength is computed to deliver surface contours of a diffusely reflecting surface. Since normal incidence on the object is employed, the method does not need the removal of the tilt component and is free from the shadowing effect as advantages over the dual-incidence method proposed before by the first author.

Sensing Tilt With MEMS Accelerometers

Abstract: A miniature tilt sensor made of standard microelectromechanical systems accelerometers and with an accuracy of 0.3deg over the full measurement range of pitch and roll is presented. Such sensor performance has been achieved, owing to the application of an original method of determining tilt angles, which is described in this paper. Experimental studies performed on a physical model of the sensor are discussed, and ways on improving the performance of the sensor are briefly introduced

Optimum Tilt Angle for Solar Collectors

Abstract: A solar collector is required to absorb solar radiation and transfer the absorbed energy into a heat transfer fluid with a minimum of heat loss. In assessing the performance of a collector, it is therefore important not only to determine its ability to absorb solar radiation but also to characterize its heat losses. The ability of a collector to absorb solar radiation is largely determined by its optical and geometric properties. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation in tilt angle affects the amount of solar radiation reaching the collector surface. In this study, a mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. It is found that the optimum tilt ...

Orientation and motion sensing in athletic training systems, physical rehabilitation and evaluation systems, and hand-held devices

Abstract: Improved apparatus and methods of sensing or monitoring body orientation and motion and measuring range of motion (ROM) for use in athletic training and physical rehabilitation and evaluation. The apparatus includes a 3-axis sensor, at least one memory, and at least one processor, and is attachable to an object to be monitored. The 3-axis sensor senses a magnitude of tilt along each of a first, second, and third axis, the memory stores data representing the sensed magnitudes of tilt, and the processor processes the data stored in the memory. In one embodiment, the processor determines an angle between each of the first, second, and third axes and a horizontal plane, and selects the two axes corresponding to the two smallest angles between the three axes and the horizontal plane. The processor then generates an indication of the orientation of the object based upon the sensed magnitudes of tilt along the two selected axes.

Synthesis of textured thin piezoelectric AlN films with a nonzero C-axis mean tilt for the fabrication of shear mode resonators

Abstract: A method for the deposition of thin piezo-electric aluminum nitride (AlN) films with a nonzero c-axis mean tilt has been developed. The deposition is done in a standard reactive magnetron sputter deposition system without any hardware modifications. In essence, the method consists of a two-stage deposition process. The resulting film has a distinct tilted texture with the mean tilt of the c-axis varying roughly in the interval 28 to 32 degrees over the radius of the wafer excluding a small exclusion zone at the center of the latter. The mean tilt angle distribution over the wafer has a circular symmetry. A membrane-type shear mode thickness-excited thin film bulk acoustic resonator together with a micro-fluidic transport system has been subsequently fabricated using the two stage AlN de-position as well as standard bulk micro machining of Si. The resonator consisted of a 2-mum-thick AlN film with 200-nm-thick Al top and bottom electrodes. The resonator was characterized with a network analyzer when operating in both air and water. The shear mode resonance frequency was about 1.6 GHz, the extracted device Q around 350, and the electromechanical coupling kt 2 2% when the resonator was operated in air, whereas the latter two dropped down to 150 and 1.8%, respectively, when the resonator was operated in pure water

Tilt sensor with FBG technology and matched FBG demodulating method

Abstract: A tilt measurement structure and signal detection method is proposed based on a self-demodulated fiber-Bragg grating (FBG) sensor, which consists of a couple of matched FBGs and a cantilever-based pendulum clinometer. Compared by the typical matched FBGs demodulating method, of which a sensing FBG and a demodulating filter FBG is placed separately, both matched FBGs of this tilt sensor are attached on the upper and lower surface of only one single pendulum-type cantilever element for simultaneous sensing and demodulating. So the received light power will change due to the split of the two reflected spectrum of FBGs, which is corresponding to the tilt angle. In addition, the cross-sensitivity effect of the FBG-based sensor is automatically solved due to a differential signal process method. Experimental results indicate the feasibility of the proposed idea.

Experimental study of spatial structure of turbulence at Maui Space Surveillance Site (MSSS)

Abstract: We investigated the spatial structure of atmospheric turbulence at Maui Space Surveillance Site (MSSS) using a 3.6 m telescope and a spatial filtering receiver. This receiver simultaneously records four star images on one camera frame. The star images are formed through pupil masks representing aperture diameters of 0.1 m, 0.5m, 1.5 m, and 3.6 m. We determined the camera orientation for each data set by moving the telescope at a given angle in azimuth and elevation. We calculated the horizontal and vertical components of the image centroid and evaluated the statistics of the horizontal and vertical wavefront tilt as a function of the aperture diameter and seeing conditions. We found several evidences of anisotropy of turbulence at MSSS. On four nights we observed that the variance of on-axis horizontal tilt exceeded the variance of the vertical tilt by a factor of 1.3-3.3. We believe that this is due to anisotropy of large-scale turbulence, where the horizontal scale of the turbulent inhomogeneities exceeds their vertical scale. The estimates of the horizontal and vertical turbulence outer scale confirmed this conclusion. In addition, in several data sets the horizontal image spot diameter of the long-exposure star image exceeded the vertical image spot diameter. We also found that large apertures are more likely to have higher anisotropy coefficient values than small apertures. This is because the contribution of small-scale isotropic turbulence to the image centroid reduces with increasing telescope diameter. In the case of isotropic turbulence, the power spectral densities (PSDs) of wavefront tilt are consistent with theoretical models. The telescope vibration modes were observed at 20 Hz. In the case of anisotropic turbulence, the PSDs of the horizontal tilt component have lower slope in the high frequency range, and difference between PSDs for large and small apertures is reduced. The anisotropy of turbulence and atmospheric tilt may affect the design and performance analysis of both active and passive optical systems.

Wide-field Fizeau imaging telescope: experimental results.

Abstract: A nine-aperture, wide-field Fizeau imaging telescope has been built at the Lockheed-Martin Advanced Technology Center. The telescope consists of nine, 125 mm diameter collector telescopes coherently phased and combined to form a diffraction-limited image with a resolution that is consistent with the 610 mm diameter of the telescope. The phased field of view of the array is 1 μrad. The measured rms wavefront error is 0.08 waves rms at 635 nm. The telescope is actively controlled to correct for tilt and phasing errors. The control sensing technique is the method known as phase diversity, which extracts wavefront information from a pair of focused and defocused images. The optical design of the telescope and typical performance results are described.

Spatial Properties of Central Vestibular Neurons

Abstract: We studied the spatial characteristics of 45 vestibular-only (VO) and 12 vestibular-plus-saccade (VPS) neurons in two cynomolgus monkeys using angular rotation and static tilt. The purpose was to d...

Stochastic re-calibration: contextual effects on perceived tilt

Abstract: The human visual system exaggerates the difference between the tilts of adjacent lines or grating patches. In addition to this tilt illusion, we found that oblique flanks reduced acuity for small changes of tilt in the centre of the visual field. However, no flanks—regardless of their tilts—decreased sensitivity to contrast. Thus, the foveal tilt illusion should not be attributed to orientation-selective lateral inhibition. Nor is it similar to conventional crowding, which typically does not impair letter recognition in the fovea. Our observers behaved as though the reference orientation (horizontal) had a small tilt in the direction of the flanks. We suggest that the extent of this re-calibration varies randomly over trials, and we demonstrate that this stochastic re-calibration can explain flank-induced acuity loss in the fovea.

New family of light beams and mirror shapes for future LIGO interferometers

Abstract: Advanced LIGO's present baseline design uses arm cavities with Gaussian light beams supported by spherical mirrors. Because Gaussian beams have large intensity gradients in regions of high intensity, they average somewhat poorly over fluctuating bumps and valleys on the mirror surfaces (thermal noise). Flat-topped light beams (mesa beams) are being considered as an alternative because they average over thermal noise more effectively. However, the proposed mesa beams are supported by nearly-flat mirrors, which experience a very serious tilt instability. In this paper we propose an alternative configuration in which mesa-shaped beams are supported by nearly-concentric spheres, which experience only a weak tilt instability. The tilt instability is analyzed for these mirrors in a companion paper by Savov and Vyatchanin. We also propose a one-parameter family of light beams and mirrors in which, as the parameter alpha varies continuously from 0 to pi, the beams and supporting mirrors get deformed continuously from the nearly-flat-mirrored mesa configuration (FM) at alpha=0, to the nearly-concentric-mirrored mesa configuration (CM) at alpha=pi. The FM and CM configurations at the endpoints are close to optically unstable, and as alpha moves away from 0 or pi, the optical stability improves.

Multi-axis tilt estimation and fall remediation

Abstract: Among other things, a vestibular prosthesis includes a wearable motion sensing system, the motion sensing system generating a motion signal indicative of a motion thereof, wherein the motion includes rotation about two distinct axes; a signal processor in communication with the motion sensing system, the signal processor being configured to generate an estimate of a tilt of the motion sensing system; and an actuator responsive to the estimate of the tilt made by the signal processor.

TEM 10 homodyne detection as an optimal small-displacement and tilt-measurement scheme

Abstract: We present a detailed description of small displacement and tilt measurements of a Gaussian beam using split detectors and ${\mathrm{TEM}}_{10}$ homodyne detectors. Theoretical analysis and an experimental demonstration of measurements of these two conjugate variables are given. A comparison between the experimental efficiency of each scheme proves that the standard split detection is only 64% efficient relative to the ${\mathrm{TEM}}_{10}$ homodyne detection, which is optimal for beam displacement and tilt. We also demonstrate experimentally that squeezed light in the appropriate spatial modes allows measurements beyond the quantum noise limit for both types of detectors. Finally, we explain how to choose the detection scheme best adapted to a given application.

Optical Head Device and Optical Information Recording/Reproducing Device

Abstract: In an optical head device and an optical information recording/reproducing device using the optical head device, by driving a liquid crystal panel 4 a , the liquid crystal panel 4 a produces wave aberration for light on a going path and light on a returning path likewise. Accordingly, when the substrate-thickness deviation or tilt of the disc 7 is corrected, the wave aberration due to the substrate-thickness deviation or tilt of the disc 7 and the wave aberration produced by the liquid crystal panel 4 a are canceled by each other for both of the light on the going path and the light on the returning path, so that no wave aberration remains for the light on the returning path and the phase distribution is not varied.

Experimental and Theoretical Study on the Optimal Tilt Angle of Photovoltaic Panels

Abstract: As a result of global warming people are paying more attention to the use of natural energy, such as solar power As one of the main forms of solar energy, photovoltaic (PV) power generators have been developed rapidly in the past few years Proper installation, especially the tilt angle, directly affects the system's output Determination of the optimal tilt angle of a solar cell module depends on the solar radiation characteristics, season, and reflectivity in the local areaThis paper evaluates the performance of four small PV modules at different tilt angles, and analyzes the relationship of solar radiation power output with tilt angle by using actual measurement data at Kitakyushu city A calculation method for optimal tilt angle is then presented using horizontal and diffuse radiation The method has been verified through comparison with the experimental data In addition, the sensitivity of optimal tilt angle to radiation rate, reflection rate, solar declination and latitude have been studied through parameter analysis

Correcting for topography and the tilt of ground‐penetrating radar antennae

Abstract: Static corrections of radargrams can account for the tilt that the GPR antenna encounters on sites with topography Radargrams that are topography-tilt corrected, show that changes in the imaged locations of subsurface structures can be significant The results of these corrections indicate that tilt corrections are necessary to improve the accuracy in imaging subsurface structures on siteswith significant topographic changesCopyright � 2006 JohnWiley & Sons,Ltd

Quantum measurements of spatial conjugate variables: displacement and tilt of a Gaussian beam.

Abstract: We consider the problem of measurement of optical transverse profile parameters and their conjugate variable. Using multimode analysis, we introduce the concept of detection noise modes. For Gaussian beams, displacement and tilt are a pair of transverse-profile conjugate variables. We experimentally demonstrate the optimal encoding and detection of these variables with a spatial homodyning scheme. Using higher-order spatial mode squeezing, we show the sub-shot-noise measurements for the displacement and tilt of a Gaussian beam.

Steep head-down tilt has persisting effects on the distribution of pulmonary blood flow.

Abstract: Head-down tilt has been shown to increase lung water content in animals and alter the distribution of ventilation in humans; however, its effects on the distribution of pulmonary blood flow in humans are unknown. We hypothesized that head-down tilt would increase the heterogeneity of pulmonary blood flow in humans, an effect analogous to the changes seen in the distribution of ventilation, by increasing capillary hydrostatic pressure and fluid efflux in the lung. To test this, we evaluated changes in the distribution of pulmonary blood flow in seven normal subjects before and after 1 h of 30° head-down tilt using the magnetic resonance imaging technique of arterial spin labeling. Data were acquired in triplicate before tilt and at 10-min intervals for 1 h after tilt. Pulmonary blood flow heterogeneity was quantified by the relative dispersion (standard deviation/mean) of signal intensity for all voxels within the right lung. Relative dispersion was significantly increased by 29% after tilt and remained elevated during the 1 h of measurements after tilt (0.84 ± 0.06 pretilt, 1.09 ± 0.09 calculated for all time points posttilt, P < 0.05). We speculate that the mechanism most likely responsible for our findings is that increased pulmonary capillary pressures and fluid efflux in the lung resulting from head-down tilt alters regional blood flow distribution.

Road bank angle considerations in modeling and tilt stability controller design for narrow commuter vehicles

Abstract: Narrow tilting vehicles that occupy a half width lane can play a big role in addressing traffic congestion problems by effectively doubling the capacity of existing highway lanes. In designing the tilt stability control system of such a vehicle consideration of the road bank angle is crucial since it plays a big role in minimizing the torque requirement of the tilt actuation system. In this paper the dynamic model of a tilting vehicle that takes into account the road bank angle is first developed. Then the design of a direct tilt control scheme that stabilizes the tilt mode of such a vehicle is outlined. Since the controller designed makes use of current road bank angle data, a method is outlined on how to determine the road bank angle from accelerometer readings. Finally simulation results are presented and discussion of the results is given.

Aero-Optic Performance of an Aircraft Forward-Facing Optical Turret

Abstract: The results of three-dimensional calculations are presented for aero-optic analysis of an aircraft forward-facing optical turret. Computational-fluid-dynamics calculations, using a compressibility corrected k-e turbulence model, defined the mean flow properties. Turbulence characteristics were obtained from a three-dimensional "g" law equation that yielded the variance of index-of-refraction fluctuations. The characteristic scale length of the correlation function of the index-of-refraction fluctuations was calculated. Strehl ratios and wave front distortion were computed for the mean flow and turbulence aberrations for four azimuth angles, 0, 45, 90, and 120 deg. For 90 and 120 deg azimuth, a portion of the beam passes through an open cavity with large-scale turbulence and nonuniform mean flow. For the mean flow, the Strehl ratio decreased to 0.001 at 90-deg azimuth after tip, tilt, and best focus were removed for a wavelength of 1.06 μm. The loss of Strehl as a result of turbulence was not as severe. Wind-tunnel measurements of optical path differences scale favorably to this work. In addition, instantaneous far-field intensity plots for instantaneous realizations of turbulence were constructed. A deformable mirror adaptive optics system might improve the Strehl ratio for the mean flow, but probably not for turbulence.