Showing papers on "Tilt (optics) published in 2007"

Assessment of cardiac autonomic modulation during graded head-up tilt by symbolic analysis of heart rate variability.

Abstract: Two symbolic indexes, the percentage of sequences characterized by three heart periods with no significant variations (0V%) and that with two significant unlike variations (2UV%), have been found to reflect changes in sympathetic and vagal modulations, respectively. We tested the hypothesis that symbolic indexes may track the gradual shift of the cardiac autonomic modulation during an incremental head-up tilt test. Symbolic analysis was carried out over heart period variability series (250 cardiac beats) derived from ECG recordings during a graded head-up tilt test (0, 15, 30, 45, 60, 75, and 90 degrees ) in 17 healthy subjects. The percentage of subjects showing a significant linear correlation (Spearman rank-order correlation) with tilt angles was utilized to evaluate the performance of symbolic analysis. Spectral analysis was carried out for comparison over the same series. 0V% progressively increased with tilt angles, whereas 2UV% gradually decreased. The decline of 2UV% was greater than the increase of 0V% at low tilt angles. Linear correlation with tilt angles was exhibited in a greater percentage of subjects for 0V% and 2UV% than for any spectral index. Our findings suggest that symbolic analysis performed better than spectral analysis and, thus, is a suitable methodology for assessment of the subtle changes of cardiac autonomic modulation induced by a graded head-up tilt test. Moreover, symbolic analysis indicates that the changes of cardiac sympathetic and vagal modulations observed during this protocol were reciprocal but characterized by different absolute magnitudes.

Asymmetric tilt grain boundary structure and energy in copper and aluminium

Abstract: Atomistic simulations were employed to investigate the structure and energy of asymmetric tilt grain boundaries in Cu and Al. In this work, we examine the Σ5 and Σ13 systems with a boundary plane rotated about the ⟨ 100 ⟩ misorientation axis, and the Σ9 and Σ11 systems rotated about the ⟨ 110 ⟩ misorientation axis. Asymmetric tilt grain boundary energies are calculated as a function of inclination angle and compared with an energy relationship based on faceting into the two symmetric tilt grain boundaries in each system. We find that asymmetric tilt boundaries with low index normals do not necessarily have lower energies than boundaries with similar inclination angles, contrary to previous studies. Further analysis of grain boundary structures provides insight into the asymmetric tilt grain boundary energy. The Σ5 and Σ13 systems in the ⟨ 100 ⟩ system agree with the aforementioned energy relationship; structures confirm that these asymmetric boundaries facet into the symmetric tilt boundaries. The Σ9 and ...

Structures and energies of Σ 3 asymmetric tilt grain boundaries in copper and aluminium

Abstract: The objective of this research is to use atomistic simulations to investigate the energy and structure of symmetric and asymmetric Σ3 ⟨110⟩ tilt grain boundaries. A nonlinear conjugate gradient algorithm was employed along with an embedded atom method potential for Cu and Al to generate the equilibrium 0 K grain boundary structures. A total of 25 ⟨110⟩ grain boundary structures were explored to identify the various equilibrium and metastable structures. Simulation results show that the Σ3 asymmetric tilt grain boundaries in the ⟨110⟩ system are composed of only structural units of the two Σ3 symmetric tilt grain boundaries. The energies for the Σ3 grain boundaries are similar to previous experimental and calculated grain boundary energies. A structural unit and faceting model for Σ3 asymmetric tilt grain boundaries fits all of the calculated asymmetric grain boundary structures. The significance of these results is that the structural unit and facet description of all Σ3 asymmetric tilt grain boundaries m...

Tilt and decentration of intraocular lenses in vivo from Purkinje and Scheimpflug imaging: Validation study

Abstract: Purpose To measure tilt and decentration of intraocular lenses (IOLs) with Scheimpflug and Purkinje imaging systems in physical model eyes with known amounts of tilt and decentration and patients. Setting Instituto de Optica Daza de Valdes, Consejo Superior de Investigaciones Cientificas, Madrid, Spain. Methods Measurements of IOL tilt and decentration were obtained using a commercial Scheimpflug system (Pentacam, Oculus), custom algorithms, and a custom-built Purkinje imaging apparatus. Twenty-five Scheimpflug images of the anterior segment of the eye were obtained at different meridians. Custom algorithms were used to process the images (correction of geometrical distortion, edge detection, and curve fittings). Intraocular lens tilt and decentration were estimated by fitting sinusoidal functions to the projections of the pupillary axis and IOL axis in each image. The Purkinje imaging system captures pupil images showing reflections of light from the anterior corneal surface and anterior and posterior lens surfaces. Custom algorithms were used to detect the Purkinje image locations and estimate IOL tilt and decentration based on a linear system equation and computer eye models with individual biometry. Both methods were validated with a physical model eye in which IOL tilt and decentration can be set nominally. Twenty-one eyes of 12 patients with IOLs were measured with both systems. Results Measurements of the physical model eye showed an absolute discrepancy between nominal and measured values of 0.279 degree (Purkinje) and 0.243 degree (Scheimpflug) for tilt and 0.094 mm (Purkinje) and 0.228 mm (Scheimpflug) for decentration. In patients, the mean tilt was less than 2.6 degrees and the mean decentration less than 0.4 mm. Both techniques showed mirror symmetry between right eyes and left eyes for tilt around the vertical axis and for decentration in the horizontal axis. Conclusions Both systems showed high reproducibility. Validation experiments on physical model eyes showed slightly higher accuracy with the Purkinje method than the Scheimpflug imaging method. Horizontal measurements of patients with both techniques were highly correlated. The IOLs tended to be tilted and decentered nasally in most patients.

Optical sparse aperture imaging

Abstract: The resolution of a conventional diffraction-limited imaging system is proportional to its pupil diameter. A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area; the latter being desirable, in part, because of the cost of large, monolithic apertures. Performance metrics are defined and used to evaluate several sparse aperture arrays constructed from multiple, identical, circular subapertures. Subaperture piston and/or tilt effects on image quality are also considered. We selected arrays with compact nonredundant autocorrelations first described by Golay. We vary both the number of subapertures and their relative spacings to arrive at an optimized array. We report the results of an experiment in which we synthesized an image from multiple subaperture pupil fields by masking a large lens with a Golay array. For this experiment we imaged a slant edge feature of an ISO12233 resolution target in order to measure the modulation transfer function. We note the contrast reduction inherent in images formed through sparse aperture arrays and demonstrate the use of a Wiener-Helstrom filter to restore contrast in our experimental images. Finally, we describe a method to synthesize images from multiple subaperture focal plane intensity images using a phase retrieval algorithm to obtain estimates of subaperture pupil fields. Experimental results from synthesizing an image of a point object from multiple subaperture images are presented, and weaknesses of the phase retrieval method for this application are discussed.

On the orientation of a designed transmembrane peptide: toward the right tilt angle?

Abstract: The orientation of the transmembrane peptide WALP23 under small hydrophobic mismatch has been assessed through long-time-scale molecular dynamics simulations of hundreds of nanoseconds. Each simulation gives systematically large tilt angles (>30°). In addition, the peptide visits various azimuthal rotations that mostly depend on the initial conditions and converge very slowly. In contrast, small tilt angles as well as a well-defined azimuthal rotation were suggested by recent solid-state 2H NMR studies on the same system. To optimally compare our simulations with NMR data, we concatenated the different trajectories in order to increase the sampling. The agreement with 2H NMR quadrupolar splittings is spectacularly better when these latter are back-calculated from the concatenated trajectory than from any individual simulation. From these ensembled-average quadrupolar splittings, we then applied the GALA method as described by Strandberg et al. (Biophys J. 2004, 86, 3709−3721), which basically derives the ...

Effects of tool tilt angle on tensile strength and fracture locations of friction stir welding of polyethylene

Abstract: The aim of this study was to investigate the effect of tool tilt angle on friction stir welding (FSW) of polyethylene (PE). The samples were longitudinally butt welded with double passes of rotating cylindrical shouldered tool in a milling machine for different tool tilt angles. The welding parameters had significant effects on tensile properties and fracture locations of the welds. The tensile strength decreased with increasing tool tilt angle. The thickness of the welding zone decreased with increasing tool tilt angle which affects the tensile strength. The interface line between weld passes was formed shorter for the higher welding speeds because of the less effect of the frictional heat.

Role of molecular tilt in thermal fluctuations of lipid membranes.

Abstract: Long-wavelength thermal fluctuations of lipid membranes are adequately described by the Helfrich elastic model. On the other hand, fluctuations of wavelengths comparable with bilayer thickness exhibit significant deviations from the prediction of the elastic model and are typically assumed to be dominated by microscopic surface tension due to protrusion of lipid molecules into the solvent. We present evidence that the short-wavelength modes of a lipid membrane are dominated by fluctuations of the tilt of lipid molecules with respect to the membrane normal rather than the microscopic surface tension. We obtain an expression for the spectral intensity of the thermal membrane fluctuations by appealing to the Hamm-Kozlov model, which accounts for both membrane bending and lipid tilt contributions to the total membrane energy but neglects the contributions of the microscopic surface tension. The tilt and the bending fluctuations obtained from our coarse-grained molecular dynamics simulations of a dipalmitoylphosphatidylcholine lipid bilayer show good agreement with the theory. Furthermore, the obtained tilt and bending moduli are in close agreement with experimentally determined values. The magnitude of the microscopic protrusion tension estimated from our simulations is significantly smaller than that of the tilt modulus. These results indicate that the membrane fluctuations can be adequately described by a macroscopic elastic model down to scales of interlipid distance provided one accounts for the tilt fluctuations.

An optimized MEMS-based electrolytic tilt sensor

Abstract: A tilt sensor has been realized based on electrolytic solution, which is filled in a micromachined 400 μm-deep cavity and responded relative to tilt angle due to the gravity. The device consists of anisotropically etched deep cavity to contain electrolytic solution and Au/NiCr metal electrodes to detect the electrical signal formed on non-planar surfaces from the substrate surface to the bottom of the cavity. The tilting motion of the device changes the immersed area of the electrodes in the electrolytic solution and the unbalanced ratio of the elecrical siganal is monitored by the change in its resistance. Injected electrolyte solution should be carefully determined because it must have not only small resistance but also small viscosity. Potassium hydroxide (KOH) solution is chosen as the electrolyte due to the relatively high ionic conductance and it is diluted with methanol for an optimized concentration considering the viscosity. The fabricated electrolytic tilt sensor is excited by an alternating current to prevent electrolysis in the electrolyte-filled cavity and measured by Wheatstone bridge circuit to read the variation of resistance with respect to an incoming inclination. Experiments reveal that the resistance of KOH electrolyte is smallest at 5 wt% in its concentration and 800 Hz in the driving frequency. The tested Micro Electro Mechanical Systems (MEMS)-based electrolytic tilt sensor with KOH solution shows a resolution of approximately 50 mV per 1° of inclination angle change and operating angle range of ±60°. The measured output characteristic of the fabricated MEMS-based electrolytic tilt sensor sustains comparison with other conventional electrolytic tilt sensors. Moreover, MEMS-based sensor prevails in its small size, low cost and possible mass production.

Coupled Tilt and Translational Ground Motion Response Spectra

Abstract: Dynamic response of structures subjected to earthquake-induced base excitations are often simplified by ignoring the tilt components of ground motion. However, close to the earthquake source, tilting of the ground surface may become significant. Based on strong-motion records at the Pacoima Dam-upper left abutment obtained during the 1994 Northridge Earthquake, residual tilt reached 3.1° in the N45°E direction while the dynamic tilt remained higher. This study investigates the consequences of neglecting the effects of the tilt component in ground motions on elastic and inelastic spectral ordinates. A complete equation of motion for a single-degree-of-freedom SDOF oscillator is developed which includes the effects of tilt as the secondary P- effect in addition to inertial force effects due to angular and translation accelerations. The expected values of the largest response peaks are computed for the translational and tilting excitations to investigate the relative contribution of each forcing function. The coupled tilt and translational ground motion response spectrum CTT spectrum is generated considering elastic and inelastic response of SDOF oscillator. The CTT spectrum reflects kinematic characteristics of the ground motion that are not identifiable by the translational ground motion response spectrum alone and therefore emerges as a distinct intensity measure of translational ground motion when it is coupled with dynamic tilting of the ground surface on the order of few degrees.

Particle-beam exposure apparatus with overall-modulation of a patterned beam

Abstract: In a charged-particle exposure apparatus for exposure of a target with a beam of electrically charged particles, the illumination system includes a deflector device adapted to vary the direction of incidence of the illuminating beam upon the pattern definition device, the pattern definition device forms the shape of the illuminating beam into a desired pattern, and the projection optics system projects an image of the beam shape defined in the pattern definition device onto the target; the projection optics system includes a blocking aperture device having an opening and being adapted to block passage of beams traversing outside the opening, namely when the deflector device is activated to tilt the beamlet by a sufficient angle from its non-deflected path, e.g., for blanking out during the process of loading a pattern into the pattern definition device.

Phased array antenna system with electrical tilt control

Abstract: A phased array antenna system with electrical tilt control incorporates a tilt controller (62) for splitting an input signal into three intermediate signals, two of which are delayed by variable delays T1 and T2 relative to the third. A corporate feed (64) contains splitters S3 to S10 and hybrids H1 to H6 for processing the intermediate signals to produce drive signals for elements of an antenna array (66); the drive signals are fractions and vector combinations of the intermediate signals. The tilt controller (62) and the corporate feed (64) in combination impose relative phasing on the drive signals as appropriate for phased array beam steering in response to variable delay of two intermediate signals relative to the third intermediate signal.

Slide and tilt mechanism for a telecommunications panel

Abstract: A mechanism that provides access to a rear termination area of a telecommunications panel. The mechanism including a slide bar that permits the panel to laterally slide, and a tilt element the permits the panel to tilt. The slide bar and tilt element positioning the tilted termination panel over lower adjacent termination panels without contacting cables associated with the lower adjacent termination panels.

Requirements for discrete actuator and segmented wavefront correctors for aberration compensation in two large populations of human eyes.

Abstract: Numerous types of wavefront correctors have been employed in adaptive optics (AO) systems for correcting the ocular wavefront aberration. While all have improved image quality, none have yielded diffraction-limited imaging for large pupils (≥6 mm), where the aberrations are most severe and the benefit of AO the greatest. To this end, we modeled the performance of discrete actuator, segmented piston-only, and segmented piston/tip/tilt wavefront correctors in conjunction with wavefront aberrations measured on normal human eyes in two large populations. The wavefront error was found to be as large as 53 μm, depending heavily on the pupil diameter (2–7.5 mm) and the particular refractive state. The required actuator number for diffraction-limited imaging was determined for three pupil sizes (4.5, 6, and 7.5 mm), three second-order aberration states, and four imaging wavelengths (0.4, 0.6, 0.8, and 1.0 μm). The number across the pupil varied from only a few actuators in the discrete case to greater than 100 for the piston-only corrector. The results presented will help guide the development of wavefront correctors for the next generation of ophthalmic instrumentation.

Arrays of High Tilt-Angle Micromirrors for Multiobject Spectroscopy

Abstract: Micromirror arrays are promising components for generating reflective slit masks in future multiobject spectrographs. The micromirrors, 100 mum times200 mum in size, are etched in bulk single crystal silicon, whereas a hidden suspension is realized by surface micromachining. The micromirrors are actuated electrostatically by electrodes located on a second chip. The use of silicon on insulator (SOI) wafers for both mirror and electrode chip ensures thermal compatibility for cryogenic operation. A system of multiple landing beams has been developed, which latches the mirror at a well-defined tilt angle when actuated. Arrays of 5times5 micromirrors have been realized. The tilt angle obtained is 20deg at a pull-in voltage of 90 V. Measurements with an optical profiler showed that the tilt angle of the actuated and locked mirror is stable with a precision of 1 arcmin over a range of 15 V. This locking system makes the tilt angle independent from process variations across the wafer and, thus, provides uniform tilt angle over the whole array. The surface quality of the mirrors in actuated state is better than 10-nm peak to valley and the local roughness is about 1-nm root mean square

Method and apparatus for changing a display direction of a screen of a portable electronic device

Abstract: A portable electronic device having a display screen capable of changing display directions is disclosed. The portable electronic device, such as a tablet personal computer, includes a tiltmeter, a display direction determining circuit and a display direction changing circuit. The tiltmeter measures a first tilt angle of a first axis of a display screen of the portable electronic device with respect to a horizontal plane, and measures a second tilt angle of a second axis of the display screen of the portable electronic device with respect to the horizontal plane. The display direction determining circuit determines whether or not a display direction of the display screen is to be changed based on the changing conditions generated by the first tilt angle and the second tilt angle as measured by the tiltmeter. The display direction changing circuit changes the display direction of the display screen from a current display direction to a different display direction according to a determination result formed by the display direction determining circuit.

Characterization of metamorphic InxAl1−xAs∕GaAs buffer layers using reciprocal space mapping

Abstract: The depth profiles of metamorphic InxAl1−xAs (0.05

Scala vestibuli pressure and three-dimensional stapes velocity measured in direct succession in gerbil.

Abstract: It was shown that the mode of vibration of the stapes has a predominant piston component but rotations producing tilt of the footplate are also present. Tilt and piston components vary with frequency. Separately it was shown that the pressure gain between ear canal and scala vestibuli was a remarkably flat and smooth function of frequency. Is tilt functional contributing to the pressure in the scala vestibuli and helping in smoothing the pressure gain? In experiments on gerbil the pressure in the scala vestibuli directly behind the footplate was measured while recording simultaneously the pressure produced by the sound source in the ear canal. Successively the three-dimensional motion of the stapes was measured in the same animal. Combining the vibration measurements with an anatomical shape measurement from a micro-CT (CT: computed tomography) scan the piston-like motion and the tilt of the footplate was calculated and correlated to the corresponding scala vestibuli pressure curves. No evidence was found for the hypothesis that dips in the piston velocity are filled by peaks in tilt in a systematic way to produce a smooth middle ear pressure gain function. The present data allowed calculations of the individual cochlear input impedances.

Generation of a flat-top laser beam for gravitational wave detectors by means of a nonspherical Fabry-Perot resonator.

Abstract: We have tested a new kind of Fabry-Perot long-baseline optical resonator proposed to reduce the thermal noise sensitivity of gravitational wave interferometric detectors--the "mesa beam" cavity--whose flat top beam shape is achieved by means of an aspherical end mirror. We present the fundamental mode intensity pattern for this cavity and its distortion due to surface imperfections and tilt misalignments, and contrast the higher order mode patterns to the Gauss-Laguerre modes of a spherical mirror cavity. We discuss the effects of mirror tilts on cavity alignment and locking and present measurements of the mesa beam tilt sensitivity.

Increasing Accuracy of Tilt Measurements

Abstract: We have proposed few effective methods of increasing accuracy of tilt measurements to be performed under quasi-static conditions by means of miniature tilt sensor (built of MEMS accelerometers). They ensure increase of the accuracy of ca. 50%. The methods can be also useful while measuring tilt by means of accelerometers manufactured with application of conventional technologies.

Tilt corrections over complex terrain and their implication for CO2 transport

Abstract: Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations. We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate system and its implication in investigation of CO2 transport are discussed.

Display mounting apparatus

Abstract: The present invention is directed to a display mounting apparatus for mounting a flat screen television monitor or the like to a wall. The mounting apparatus provides four degrees of freedom for the flat screen display in lateral translation, tilt, swivel and pan directions. The combination of two two-link arms, counterbalancing torsion springs and friction mechanisms provides for ±20 degrees in the tilt and swivel directions.

Optical device with tilt and power microlenses

Abstract: A microlens array includes plural powered microlenses or microlens elements for tilting different light-emitting elements or portions of a light-emitting device. Each microlens or microlens element both has optical power, and adjusts the tilt of the wavefront so that in combination the individual microlenses act like a more complex multiple-element optic where each element shifts light from only a portion of the light-emitting device. Such an optical device may be incorporated into eyewear for projecting subtitles or other information above or below a far-away image, such as on a movie screen. Another potential use of the microlens array is for use in a heads-up display. Still another potential use for the microlens array to provide soft focusing of emitted laser light to achieve a target light spot of a desired diameter.

Effect of sample tilt on nanoindentation behaviour of materials

Abstract: Analysis of nanoindentation is based on the elastic solution of a rigid indenter perpendicularly penetrating a flat contact surface. In reality, nanoindentation is often performed on a tilt sample surface due to sample tilt mounting or the existing roughness of a polished or raw surface. In this study, finite element simulations as well as nanoindentation experiments on a fused-quartz sample with different tilt angles were carried out to investigate the influence of sample tilt on nanoindentation behaviour of materials. It was found that sample tilt results in increases in the indentation load, contact area and contact stiffness at the same penetration depth. The contact area increase caused by sample tilt cannot be accounted for by Sneddon's equation, commonly used in nanoindentation analysis. This results in a significant underestimation of indentation projected contact area, which in turn leads to an overestimation of the mechanical properties measured by nanoindentation.

Beaconless stochastic parallel gradient descent laser beam control: numerical experiments.

Abstract: We apply a target-in-the-loop strategy to the case of adaptive optics beam control in the presence of strong atmospheric turbulence for air-to-ground directed energy laser applications. Using numerical simulations we show that in the absence of a cooperative beacon to probe the atmosphere it is possible to extract information suitable for effective beam control from images of the speckled and strongly turbulence degraded intensity distribution of the laser energy at the target. We use a closed-loop, single-deformable-mirror adaptive optics system driven by a target-in-the-loop stochastic parallel gradient descent optimization algorithm minimizing a mean-radius performance metric defined on the image of the laser beam intensity distribution formed at the receiver. We show that a relatively low order 25-channel zonal adaptive optical beam control system controlled in this way is capable of achieving a high degree of turbulence compensation with respect to energy concentration if the tilt can be corrected separately.

Method, medium and apparatus browsing images

Abstract: A method, medium and apparatus browsing images is disclosed. The method browsing images includes sensing acceleration imparted to a portable digital device, and moving an image onto a display area in accordance with a tilt angle of the portable digital device if the sensed acceleration is greater than a first threshold value.

Tilt angle of lipid acyl chains in unilamellar vesicles determined by ellipsometric light scattering

Abstract: Ellipsometric light scattering (ELS) at room temperature is applied to unilamellar vesicles (approximately 50 nm radius) of 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the gel phase and of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) in the liquid-crystaline phase. A high sensitivity of this technique to the local anisotropy is found. From the resulting local birefringence, a lower limit of (29 +/-0.5) degrees for the average tilt angle of the lipid chains of DPPC with respect to the membrane normal is estimated. This tilt angle value is slightly lower than literature values for the tilt angle in oriented lipid multi-bilayers on solid substrates.