Tilt Components Research Articles

The visual perception of surface orientation from optical motion.

Observers viewed monocular animations of rotating dihedral angles and were required to indicate their perceived structures by adjusting the magnitude and orientation of a stereoscopic dihedral angle. The motion displays were created by directly manipulating various aspects of the image velocity field, including the mean translation, the horizontal and vertical velocity gradients, and the manner in which these gradients changed over time. The adjusted orientation of each planar facet was decomposed into components of slant and tilt. Although the tilt component was estimated with a high degree of accuracy, the judgments of slant exhibited large systematic errors. The magnitude of perceived slant was determined primarily by the magnitude of the velocity gradient scaled by its direction. The results also indicate that higher order temporal derivatives of the moving elements had little effect on observers' judgments.

Exocentric pointing in three-dimensional space.

A study is reported of an exocentric pointing task in all three dimensions, in near space, with only two visible luminous objects--a pointer and a target. The task of the subject was to aim a pointer at a target. The results clearly show that visual space is not isotropic, since every set direction appeared to consist of two independent components--one in the projection onto a frontoparallel plane (tilt), the other in depth (slant). The tilt component shows a general trend across subjects, an oblique effect, and can be judged monocularly. The slant component is symmetrical in the mid-sagittal plane, requires the use of binocular information, and shows considerable differences between subjects. These differences seem to depend on the amount of binocular information used by each subject. There was a remarkably high level of consistency in the exocentric pointing, despite the absence of environmental cues. The within-subject consistency in the settings of the pointer corresponds to a consistency of about 1 min of arc in disparity of its tip, even though the pointer and target are separated by more than 5 deg.

X-ray topography and diffraction studies of misfit dislocation nucleation in Si-based structures

The combination of different X–ray topography techniques and reciprocal space mapping is used to monitor the early stages of relaxation in silicon–based heterostructures. For lightly doped silicon layers grown on heavily boron–doped 150 mm substrates, Lang transmission topography demonstrates that an orthogonal array of 60°; misfits nucleates only at the wafer periphery. The length of the individual misfit segment depends on the epitaxial layer thickness and on the presence of the orthogonal blocking misfit segments. Double–crystal X–ray topography, with better strain and tilt resolution, allows one to distinguish between the different tilt components of parallel misfit dislocations. Relaxation is quantified using triple–axis X–ray diffraction. Reciprocal space maps around both the (004) and (224) reflections show that the misfits relieve about 38% of the strain. The combination of these X–ray techniques offers insight into the means to reduce dislocation formation and into the fundamental nature of the dislocations themselves.

Torsional eye movements are facilitated during perception of self-motion.

Visual motion in the roll plane elicits torsional optokinetic nystagmus (tOKN) with intermittent periods of illusory, contradirectional self-motion (circularvection, CV). The CV may also have a component of whole-body tilt if the axis of stimulus rotation is not aligned with the direction of gravity. We report how the characteristics of tOKN are affected by the presence of CV. Subjects had their eye movements recorded by VOG whilst viewing a full-field stimulus rotating at 30-60 degrees/s about their naso-occipital axis. They were tested in upright and supine posture and signalled the presence-absence of CV with a pushbutton. In both postures, during CV, tOKN slow-phase gain was found to be enhanced and average torsional eye position shifted in the direction opposite to stimulus rotation. When supine, slow-phase gain was greater than when upright both during the perception of object-motion and during CV. The effects may be explained in terms of a relegation of restraining vestibular input to the torsional oculomotor system during CV and illusory tilt.

Experimental validation of a technique to measure tilt from a laser guide star

We have experimentally demonstrated for what is believed to be the first time a method for sensing wave-front tilt with a laser guide star (LGS). The tilt components of wave fronts were measured synchronously from the LGS by use of a telescope with a 0.75-m effective aperture and from the star Polaris by use of a 1.5-m telescope. The Rayleigh guide star was formed at an altitude of 6 km and at a corresponding range of 10.5 km by projection of a focused beam at Polaris from the full aperture at the 1.5-m telescope. Both telescope mounts were unpowered and bolted in place, allowing us to reduce substantially the telescope vibration. The maximum value of the measured cross-correlation coefficient between the tilt for Polaris and the LGS is 0.71. The variations of the measured cross-correlation coefficient in the range from 0.22 to 0.71 are caused by turbulence at altitudes above 6 km, which was not sampled by the laser beacon but affected tilt for Polaris, the cone effect for turbulence below 6 km, residual mount jitter of the telescopes, and variations of the signal/noise ratio. The results support our concept of sensing atmospheric tilt by observing a LGS with an auxiliary telescope and indicate that this method is a possible solution for the tip-tilt problem.

Transmission electron microscopy study of a low-angle boundary in plastically deformed Ti3SiC2

The dislocation structure of a typical low-angle boundary associated with a kink band in a sample of Ti3SiC2 deformed at room temperature was studied by high-resolution transmission electron microscopy. The boundary had both tilt and twist components. To account for both, the boundary was interpreted to be composed of parallel alternating mixed perfect dislocations with two different Burgers vectors lying in the basal plane at an angle of 120o relative to one another. The boundary twist was provided by having an excess of one type of dislocation. This hitherto unreported structure of a low-angle boundary is attributed to the fact that all dislocations are confined to the basal planes.

Interferometric array illuminator with analysis of nonobservable fringes

Interferometric methods for array generation offer various advantages over diffractive methods. Use of polarizing elements in an interferometric array illuminator results in interesting properties in addition to improving the efficiency considerably from low levels. The array pattern appears as nonobservable fringes that can be observed only with a polarizer, and the interferometer is insensitive to one of the tilt components. A thorough analysis of such an interferometric array illuminator is presented in this paper. Several possible applications of such an interferometer in addition to use as an array illuminator are proposed.

On the waveforms and spectra of glottal flow models

Several glottal flow models have been proposed for speech analysis and synthesis (e.g., LF, Rosenberg, R++, and Klatt). All these models do not use the same number of parameters, or the same name for similar parameters, and it appears difficult to compare their merits. Then, a unified framework for studying the time and frequency domain properties of glottal flow models is proposed. It is shown that all the models can be represented by a common set of five time-domain parameters: three scale parameters (T0, peak amplitude, open quotient), a shape parameter (asymmetry quotient), and a closure continuity parameter. A generating function is computed for each model by normalization of the model with respect to scale parameters and closure continuity parameter. The specific features of each model are represented in its generating function. The spectrum of generating functions is low pass, and its derivative can be characterized by a spectral maximum, coined ‘‘glottal formant.’’ The closure continuity parameter corresponds to a spectral tilt component. The scale parameters are interpreted using scaling properties of the Fourier transform. Then, the glottal flow spectra can be characterized by two breakpoints. Frequencies of these breakpoints can be computed analytically for each model parameter setting.

Computer-Aided Female Screw Grinding without Form Dressing.

Based on the present investigation, a computer-aided female screw grinding method without the form dressing process is proposed, in which a standard-shaped grinding wheel independent of the final hellcold is used. The method uses a simple conical or plain wheel, without limitations on diameter and base angle. The wheel axis is set three-dimensionally at the computed optimum angle of inclination comprising the tilt and swivel angle components of the planned helicoid and wheel. The optimum angle of inclination is determined through simulation of the grinding process and an investigation of the optimum angle of inclination that will give the minimum geometrical error. Through the aid of a computer assuming several geometrical shape of grinding wheel and generation experiments, it is shown that the present female screw generation method is effective and the generated female screw is more accurate than that obtained by normal female screw grinding method.

TEM Study of Defects in Laterally Overgrown GaN Layers

Transmission electron microscopy was applied to study defects in laterally overgrown GaN layers, with initial growth on Al2O3 substrates followed by further growth over SiO2 masks. Dislocations found in the overgrown areas show changes in line direction. Most dislocations propagate along c-planes. In the overgrown material planar defects (faulted loops) are present on c-planes and their presence is most probably related to segregation of excess point defects and impurities present in this material. They appear to be initiated by the fast lateral growth. Some dislocations with screw orientation become helical resulting from climb motion.Formation of voids and also a high dislocation density was observed at the boundaries where two overgrowing fronts meet. Tilt and twist components were observed for these boundaries that were different for different overgrown strips grown in the same crystallographic direction suggesting that the GaN subgrain orientations on the two sides of a SiO2 mask are responsible for the final tilt and twist value.

Incorporating higher-order modal measurements in tilt estimation: natural and laser guide star applications

Tilt compensation performance is generally suboptimal when phase measurements from natural or laser guide stars are used as the conjugate phase in an adaptive optics system. Optimal compensation is obtained when the conjugate-phase coefficients are estimated from beacon measurements, given knowledge of the correlation between the on-axis object phase and the beacon measurements. We apply optimal compensation theory to tilt correction for the case of an off-axis beacon. Because off-axis higher-order modes are correlated with the on-axis tilt components, a performance gain can be realized when the tilt estimator includes higher-order modal measurements. For natural guide star compensation, it is shown that equivalent tilt compensation can be achieved at beacon offsets that are three times larger when higher-order modes through Zernike 15 are used in the tilt estimator. For a laser guide star, although tilt information cannot be measured directly because of beam reciprocity, off-axis higher-order modal measurements can be used to estimate tilt components, leading to a maximum Strehl ratio of approximately 0.3 for the relative aperture diameter D/r(0) = 4 and the relative turbulence outer scale L(0)/D = 10.

Subsurface deformations induced by rainfall and atmospheric pressure: tilt/strain measurements in the NE-Italy seismic area

Tilt and strain measurements are collected in a cave at a depth of 60 m in the Friuli seismic area (NE-Italy) where the topography suddenly reaches a height of 600 m a.s.l. The data are analysed to find a possible correlation between crustal deformations on one side and precipitation and barometric pressure variations on the other. Once the significance of the correlation is established, an attempt is made to give a physical explanation of the detected correlation in the frame of the elasticity theory. A significant areal reduction in strain observations occurs together with a marked rotation of the principal axes in the horizontal plane at the time of rainfall events while no evident signals are revealed in the tilt components. The atmospheric pressure has small influence on the tilt–strain observations, when compared with the effects of rainfall and consequent underground waterflow: referring to large perturbations, atmospheric pressure appears to influence the areal deformations in terms of about 1 nstrain per mbar, an order of magnitude less then that of the hydrologically induced deformation rate, which reaches up to 600 nstrain (in about 1 day) per 120 mm/day rainfall.

Tectonics and sedimentation in the hangingwall of a major extensional detachment: the Devonian Kvamshesten Basin, western Norway

The Middle Devonian Kvamshesten Basin in western Norway is a late‐orogenic basin situated in the hangingwall of the regional extensional Nordfjord–Sogn Detachment Zone. The basin is folded into a syncline with the axis subparallel to the ductile lineations in the detachment zone. The structural and stratigraphic development of the Kvamshesten Basin indicates that the basin history is more complex than hitherto recognized. The parallelism stated by previous workers between mylonitic lineation below the basin and intrabasinal fold axes is only partly reflected in the configuration of sedimentary units and in the time‐relations between deposits on opposing basin margins. The basin shows a pronounced asymmetry in the organization and timing of sedimentary facies units. The present northern basin margin was characterized by bypass or erosion at the earliest stage of basin formation, but was subsequently onlapped and eventually overlain by fanglomerates and sandstones organized in well‐defined coarsening‐upwards successions. The oldest and thickest depositional units are situated along the present southern basin margin. This as well as onlap relations towards basement at low stratigraphic level indicates a significant component of southwards tilt of the basin floor during the earliest stages of deposition. The inferred south‐eastwards tilt was most likely produced by north‐westwards extension during early stages of basin formation. Synsedimentary intrabasinal faults show that at high stratigraphic levels, the basin was extending in an E–W as well as a N–S direction. Thus, the basin records an anticlockwise rotation of the syndepositional strain field. In addition, our observations indicate that shortening normal to the extension direction cannot have been both syndepositional and continuous, as suggested by previous authors. Through most of its history, the basin was controlled by a listric, ramp‐flat low‐angle fault that developed into a scoop shape or was flanked by transfer faults. The basin‐controlling fault was rooted in the extensional mylonite zone. Sedimentation was accompanied by formation of a NE‐ to N‐trending extensional rollover fold pair, evidenced by thickness variations in the marginal fan complexes, onlap relations towards basement and the fanning wedge geometry displayed by the Devonian strata. Further E–W extension was accompanied by N–S shortening, resulting in extension‐parallel folds and thrusts that mainly post‐date the preserved basin stratigraphy. During shortening, conjugate extensional faults were rotated to steeper dips on the flanks of a basin‐wide syncline and re‐activated as strike‐slip faults. The present scoop‐shaped, low‐angle Dalsfjord fault cross‐cut the folded basin and juxtaposed it against the extensional mylonites in the footwall of the Nordfjord–Sogn detachment. Much of this juxtaposition may post‐date sedimentation in the preserved parts of the basin.Basinal asymmetry as well as variations in this asymmetry on a regional scale may be explained by the Kvamshesten and other Devonian basins in western Norway developing in a strain regime affected by large‐scale sinistral strike‐slip subparallel to the Caledonian orogen.

Tem Study of Defects in Laterally Overgrown GaN Layers

AbstractTransmission electron microscopy was applied to study defects in laterally overgrown GaN layers, with initial growth on A12O3 substrates followed by further growth over SiO2 masks. Dislocations found in the overgrown areas show changes in line direction. Most dislocations propagate along c-planes. In the overgrown material planar defects (faulted loops) are present on c-planes and their presence is most probably related to segregation of excess point defects and impurities present in this material. They appear to be initiated by the fast lateral growth. Some dislocations with screw orientation become helical resulting from climb motion.Formation of voids and also a high dislocation density was observed at the boundaries where two overgrowing fronts meet. Tilt and twist components were observed for these boundaries that were different for different overgrown strips grown in the same crystallographic direction suggesting that the GaN subgrain orientations on the two sides of a SiO2 mask are responsible for the final tilt and twist value.

Selectivity of macaque MT/V5 neurons for surface orientation in depth specified by motion.

Area MTN5 in the macaque brain is one of the major cortical regions involved in the analysis of retinal image motion. The majority of the neurons in this cortical area have non-uniform antagonistic surrounds as components of their receptive field complexes. Theoretical studies indicate that such asymmetrical surrounds should enable neurons to extract orientation in depth from motion. Here we show that nearly half of the MTN5 neurons encode the tilt component of the orientation in depth of a plane specified by motion. Furthermore, we show that such selectivity for depth from motion depends on the presence of an asymmetrical surround and on the speed tuning of those asymmetrical surround influences.

Structural and electrical investigations of silicon wafer bonding interfaces

The structure and the electrical properties of Si/Si interfaces obtained by wafer bonding are studied by transmission electron microscopy (TEM), electron-beam-induced current (EBIC) and spreading resistance (SR). Boron-doped Czochralsky-silicon (Cz-Si) (001) wafers and float zone-silicon (FZ-Si) (001) wafers are bonded after hydrophobic cleaning of the surfaces and annealed at 1200 °C for 2 h. The TEM experiments show that these interfaces are made of two dislocation networks: a grid of screw dislocations accommodating the misorientation between the two wafers and a set of 60 ° dislocations compensating a tilt component related to the vicinal surfaces. These dislocations are all located at the interface and no extended defects propagate in the Si wafers. The EBIC experiments show a large electrical activity of the Cz interfaces; SR profiles show a variation of carriers concentration near the interface. Large density of oxide precipitates located at the interface are seen for Cz-Si wafers. EBIC observations performed on FZ wafer show a weak electrical activity which seems to be related to a low content of oxygen in the interface.

Microstructures in high- Jc Tl-1223/Ag tapes

High- T c Tl-1223/Ag tapes with a nominal composition of (Tl 0.93Bi 0.22)(Sr 1.6Ba 0.4)Ca 2Cu 3O x were prepared using the powder-in-tube method combined with the two step reaction method. Their microstructures were examined using scanning and transmission electron microscopy. Tape A ( J c = 5 500 A/cm 2 at 77 K under 0 T) prepared using rolling only has a lower J c than tape B ( J c = 14 000 A/cm 2) prepared using pressing. In both tapes Tl-1223 forms plate-like grains. Although the size of the plates in tape A is larger than those in tape B, their mutual connection is poorer. Many subgrains are formed in each grain with small angle boundaries, which are composed of tilt-type as well as twist-type components in most cases. The boundaries might be considered as effective pinning sites for magnetic flux as far as the tilt component predominates. Additionally, small holes were found at the subgrain boundaries.

Zernike expansions for non-Kolmogorov turbulence

We investigate the expression of non-Kolmogorov turbulence in terms of Zernike polynomials. Increasing the power-law exponent of the three-dimensional phase power spectrum from 2 to 4 results in a higher proportion of wave-front energy being contained in the tilt components. Closed-form expressions are given for the variances of the Zernike coefficients in this range. For exponents greater than 4 a von Karman spectrum is used to compute the variances numerically as a function of exponent for different outer-scale lengths. We find in this range that the Zernike-coefficient variances depend more strongly on outer scale than on exponent and that longer outer-scale lengths lead to more energy in the tilt terms. The scaling of Zernike-coefficient variances with pupil diameter is an explicit function of the exponent.

Method for Ball Screw Generation without Form-Dressing.

This paper deals with the development of a method for ball screw generation. The method is based on a generation process that uses a standard-shaped grinding wheel, instead of a form-grinding process that uses a form-dressed grinding wheel, and requires no extensive form-dressing process. In a newly developed thread-generation system, the wheel axis is set three-dimensionally at the computed optimum angle of inclination, consisting of the tilt and swivel angle components of the planned ball screw and grinding wheel. The optimum angle of inclination that gives the minimum geometrical error is determined by a numerical simulation of the generation process with the aid of a computer. Through the aid of a computer assuming several geometrical shapes of grinding wheel and generation experiments, it is shown that the present ball screw generation method is effective.

Method for Ball Screw Generation without Form- Dressing

This paper deals with the development of a method for ball screw generation. The method is based on a generation process that uses a standard-shaped grinding wheel, instead of a form-grinding process with a form-dressed grinding wheel, and requires no extensive form-dressing process. With the newly developed thread-generation system, the wheel axis is set three-dimensionally at the computed optimum angle of inclination, based on the tilt and swivel angle components of the planned ball screw and grinding wheel. The optimum angle of inclination that gives the minimum geometrical error is determined by a numerical simulation of the generation process with the aid of a computer. The suggested ball screw generation method is shown to be effective by computer simulations with several geometrical shapes of grinding wheels and generation experiments.