Rod Orientation Research Articles

The haptic oblique effect in the perception of rod orientation by blind adults.

The haptic perception of vertical, horizontal, +45 degrees oblique, and +135 degrees oblique orientations was studied in completely blind adults. The purpose was to determine whether the variations of the gravitational cues provided by the arm-hand system during scanning would affect the manifestation of the oblique effect (lower performance in oblique orientations than in vertical-horizontal ones) as they did in blindfolded sighted people (Gentaz & Hatwell, 1996). In blindfolded sighted adults, the oblique effect was reduced or absent when the magnitude of gravitational cues was decreased. If visual experience participated in the haptic oblique effect, we should observe no oblique effect in early blind subjects in the conditions of manual exploration where late blind and blindfolded sighted manifest this effect. The magnitude of gravitational cues was therefore varied by changing gravity constraints, whereas the variability of these cues was varied by changing the plane in which the task was performed: horizontal (low variability) and frontal (high variability). Early and late blind adults were asked to explore haptically a rod and then to reproduce its orientation ipsilaterally in one of two exploratory conditions in each plane. In the horizontal plane, the oblique effect was absent, whatever the gravity constraints, in both groups (early and late blind subjects). In the frontal plane, the oblique effect was present, whatever the gravity constraints, in both groups. Taken together, these results showed that, in blind people, the variability of gravitational cues played a role in the haptic oblique effect; no effect of previous visual experience was observed.

Enamel subsurface damage due to tooth preparation with diamonds.

In clinical tooth preparation with diamond burs, sharp diamond particles indent and scratch the enamel, causing material removal. Such operations may produce subsurface damage in enamel. However, little information is available on the mechanisms and the extent of subsurface damage in enamel produced during clinical tooth preparation. The aim of this study, therefore, was to investigate the mechanisms of subsurface damage produced in enamel during tooth preparation by means of diamond burs, and to examine the dependence of such damage on enamel rod orientation, diamond particle size, and removal rate. Subsurface damage was evaluated by a bonded-interface technique. Tooth preparation was carried out on two enamel rod orientations, with four clinical diamond burs (coarse, medium, fine, and superfine) used in a dental handpiece. The results of this study showed that subsurface damage in enamel took the form of median-type cracks and distributed microcracks, extending preferentially along the boundaries between the enamel rods. Microcracks within individual enamel rods were also observed. The median-type cracks were significantly longer in the direction parallel to the enamel rods than perpendicular to the rods. Preparation with the coarse diamond bur produced cracks as deep as 84 +/- 30 microns in enamel. Finishing with fine diamond burs was effective in crack removal. The crack lengths in enamel were not significantly different when the removal rate was varied. Based on these results, it is concluded that subsurface damage in enamel induced by tooth preparation takes the form of median-type cracks as well as inter- and intra-rod microcracks, and that the lengths of these cracks are sensitive to diamond particle size and enamel rod orientation, but insensitive to removal rate.

A Liquid Crystal Based Polymer for Applications in MMW Modulation Devices

A new liquid crystal monomer, the diacrylate of a bis phenyi diazene, was synthesized. It was polymerized to form both unoriented and oriented polymer solids–the latter in the presence of a magnetic field. The millimeter wave birefringence was measured for a polymeric rod, whose macroscopic orientation was perpendicular to its long axis, using a waveguide version of the Mach-Zehnder interferometer, and the measured δn was 0.075 at 30 GHz. The mechanical strength of oriented and unoriented polymer plates was measured. The tensile modulus in the direction parallel to the oriented axis was 6.8×108 N/m2, which was about 4 times that of the same material without macroscopic orientation. The torsional rigidity modulus of a thin rod (orientation perpendicular to its length) was measured to be of the order 107 N/m4. Both the large dielectric anisotropy and high mechanical strength make the oriented polymer potentially suitable for application in a novel class of millimeter wave modulation devices.

Molecular dynamics simulation of a single-component molecular composite: poly(p-phenylene benzobisthiazole)/meta-poly(aryl ether ketone) block copolymer

Molecular dynamics simulations were performed with a model of a single-component molecular composite in the form of a block copolymer composed of poly( p -phenylene benzobisthiazole) rigid-rod and flexible meta -poly(aryl ether ketone) subunits. The molecular composite concept, applied to improve the compressive strength of rigid-rod polymers and to improve their solubility, relies on a uniform distribution of rods in a coil-like matrix. Pair distribution functions, orientation correlation functions and correlation volumes calculated from equilibrium dynamics trajectories of bulk copolymer, coil homopolymer and rigid-rod homopolymer systems imply that, while inter-rod spacing is only slightly increased in the copolymer, correlation of rod orientation is greatly reduced but to a somewhat lesser extent than previously found for a graft copolymer composed of identical subunits. Conformations of the flexible blocks extend to accommodate the partial rod alignment. The block copolymer topology appears to be a viable alternative to the hairy-rod graft copolymer as a single-component molecular composite.

The spatial inhomogeneity of rodlike polymeric systems subject to simple shear flow

AbstractA novel simulation approach has been developed by the combination of Brownian dynamics and Lebwohl‐Lasher nematogen potential, by which we have made preliminary investigation on the spatial inhomogeneity of nematic rodlike polymeric system with planar surface anchoring and subject to simple shear flow. Some rheological behaviors such as the damped oscillation of stresses with time or the negative first normal stress difference at moderate shear rate find good agreement with previous experimental observations reported in literature. The distribution function of rod orientation takes on “breathe‐like” time‐evolution and is verified not Gaussian‐featured. The layered director, order parameter, shear stress and first normal stress difference have also been calculated by statistics, and most importantly, all of these statistic quantities show spatial distribution in different layers and corresponding distribution functions are time‐dependent. Therefore, our simulation implies the complicated pattern formation and pattern evolution in this system. It is, hence, very meaningful to further study the spatial inhomogeneity of rodlike polymers under shear flow extensively both in theory and in experiment.

Transitions to Ordered Phases in Systems Containing Rod-like Particles: II. Continuum Monte Carlo Approach versus Discrete Lattice Models

Abstract The predictions of the new continuous-placement Monte Carlo (CMC) approach described in the preceding paper are compared with the results obtained from the discrete lattice model (DLM) of Flory and Ronca. The comparison is made for two-dimensional, monodisperse, athermal systems. For this purpose, we have adapted the Flory-Ronca model to two dimensions, gaining additional insight into the justification for one of the numerical correction factors used in that model. The CMC and DLM approaches both predict that a uniform (flat) distribution of rod orientations in the anisotropic phase is associated with a first-order isotropic-to-nematic transition, while normally distributed orientations lead to a continuous transition with increasing rod concentration. The two models also agree qualitatively with respect to the relative free energies of different rod orientation distributions in the anisotropic phase. However, the DLM assigns disproportionately high entropy to short rods (especially at high conce...

Erosion—corrosion of 316 stainless steel rods immersed in a bubbling fluidized bed

A fluidized bed was operated in the bubbling regime with sand to determine the effects of process variables on in-bed metal wastage due to erosion and/or corrosion of immersed 316 stainless steel (SS) rods. Weight loss as a result of erosion was determined by conducting experiments with air at room temperature and high fluidizing velocities (erosion-dominated). Weight loss due mainly to corrosion was determined by carrying out wear tests at 500°C and relatively low gas velocity (corrosion-dominated). by comparing the total weight loss obtained from the tests at high temperature and high gas velocity conditions (erosion—corrosion-dominated) with the sum of weight losses from erosion-dominated and corrosion-dominated studies, it was found that there was a synergistic effect between corrosion and erosion, i.e. erosion and corrosion took place simultaneously and interacted in a way leading to accelerated wear of the 316 SS rods. The wear rates increased with increasing temperature and excess gas velocity and were also affected by rod orientation in that wear rates of vertical rods were less than those of horizontal rods under identical test conditions. In all cases, wear rates were less than 3.0 nm/h in the radial direction.

Conformational and dynamic effects of pendant‐PEK chains on rigid‐rod polymers by molecular dynamics simulation

AbstractMolecular dynamics simulations were performed with models of a single‐component ‘hairy‐rod’ molecular composite composed of flexible meta poly(aryl ether ketone) (mPEK) chains (the ‘hairs’) grafted to a poly(p‐phenylene benzobisthiazole) (PBZT) rigid‐rod backbone. The molecular‐composite concept, conceived to circumvent solubility problems and improve compressive strength of PBZT, relies on an even distribution of rods in a coil‐like matrix. Two‐molecule simulations show that the pendant mPEK chains associate with the rods causing large bends in the rod backbone. Simulations of bulk systems imply that the mPEK chains greatly reduce the correlation of rod orientation without altering rod spacing. Radial distribution and orientation correlation functions as well as correlation volumes are computed.

Monte Carlo methods for polymer chains in two ‐ dimensional geometries (polymers at surfaces and interfaces)

AbstractCoarse‐grained models of polymers at interfaces can be defined such that their treatment by Monte Carlo simulation is most convenient and efficient for the problem at hand. This simulation strategy is briefly illustrated with three examples: (1) The orientational ordering of rigid rod‐like polymers grafted to a surface, where “table methods” can be used, applying a fine discretization of the angles describing rod orientation. (2) Surface enrichment of one species in a polymer blend is treated by a semi‐grand‐canonical technique. (3) The number of configurations and structure of a star polymer attached with its center to a wall is studied by a “growth technique” generalizing simple sampling methods.

Multimeridional apparent frontoparallel plane: relation between stimulus orientation angle and compensating tilt angle.

The classical apparent frontoparallel plane (AFPP) setting is typically obtained by having the subject move a series of parallel rods farther or closer until they line up in a plane perceived to be parallel to the face plane. If there is a size difference between the two ocular images, the AFPP setting defined by the rods will exhibit a tilt from the objective frontoparallel plane, about an axis parallel to the rods. The multimeridional apparent frontoparallel plane (MAFPP) is an extension of this procedure to rod orientations other than the vertical meridian. In previous studies, it was found that oblique tilt angle settings corresponding to rod orientations of 45 degrees and 135 degrees are equal to square root 2 times the tilt angle for the vertical rod orientation for the same interocular magnification difference along the meridian perpendicular to the rods. In this study, we measured the tilt angles produced by a series of oblique rod orientations between 15 degrees and 165 degrees, inclusive. Throughout the 150 degrees range tested, the tilt angles were found to be consistently proportional to the cosecant of the rod orientation angle, the factor square root 2 previously used being a specific example of this relation. Within this range, neither empirical cues nor the induced effect cause the cosecant relation to break down. It is suggested that the MAFPP procedure can be applied more extensively than previously anticipated.

Role of the inertia tensor in perceiving object orientation by dynamic touch.

Ss wielded an occluded L-shaped rod and attempted to perceive the direction in which the rod was pointing with respect to the hand. The pattern of the rod's different resistances to rotation in different directions, quantified by the inertia tensor, changes systematically with the rod's orientation. Perception of orientation by wielding is possible if the tissue deformation consequences of the rod's inertia tensor are detectable. It was shown that perceived orientation was a linear function of actual orientation for both free and restricted wielding and for rods of different-size branches. The eigenvectors of the inertia tensor were implicated as the basis for this haptic perceptual capability. Results were discussed in reference to information-perception specificity and its implications for effortful or dynamic touch.

The cGMP-gated channel of the rod photoreceptor cell characterization and orientation of the amino terminus.

The molecular properties and orientation of the cGMP-gated cation channel of bovine rod outer segment membranes were studied using biochemical and immunochemical methods. Western blots labeled with anti-channel monoclonal antibodies indicate that the channel has a subunit Mr of 63,000 in bovine rod outer segment membranes prepared in the presence and absence of protease inhibitors and in rod outer segments from other mammalian retinas. The channel has an apparent Mr of 78,000 in both COS-1 cells and Xenopus oocytes expressing the cloned cDNA. NH2-terminal sequence analysis indicates that the lower Mr of the channel in rod outer segments is caused by the absence of the first 92 amino acids predicted by cDNA sequence analysis. Immunofluorescent and immunogold labeling has confirmed that the 63,000 form of the channel is present in rod outer segments. These results indicate that photoreceptor cell-specific co-translational or post-translational cleavage of the NH2-terminal segment of the channel occurs prior or during the incorporation of the channel into the rod outer segment plasma membrane. Immunogold labeling studies using site-directed antibodies also indicate that the NH2-terminal segment of the rod outer segment channel is exposed on the cytoplasmic side of the plasma membrane.

Entropy of Rodlike Particles: Continuum versus Lattice Representations

Abstract The computationally tractable discrete lattice model is compared to a more realistic representation of rodlike particles, which allows continuous variation of rod position and orientation. This continuous-placement Monte Carlo method provides a measurement of the combinatoric entropy of rod configurations. Comparisons reveal that the discrete lattice model overestimates the entropy of short rods and of disordered phases. Three fundamental reasons for these predictive errors are discussed.

Factorial Design: Binocular and Monocular Depth Perception in Vertical and Horizontal Stimuli

This article describes a factorial experiment that is useful as a laboratory exercise in a research methods course. In the Howard–Dolman depth perception apparatus, two vertical rods are adjusted, using binocular or monocular vision, so they appear equidistant from the observer. The two rods can also be oriented horizontally, which allows a factorial design combining the factors of Viewing Condition (binocular and monocular) and Rod Orientation (vertical and horizontal). The exercise illustrates the nature of an interaction and the necessity of an additional analysis of simple main effects. It also provides a basis for understanding a perceptual problem in the real world—the difficulty of localizing horizontally extended stimuli such as power lines.

Recent Advances in Morphology and Mechanical Properties of Rigid-Rod Molecular Composites

ABSTRACTRigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. The concept of using a rigid-rod, extended chain polymer to reinforce a ductile polymer matrix at the molecular level has been demonstrated with morphological and mechanical property studies for aromatic heterocyclic systems, but new materials systems and processing techniques will be required to produce thermoplastic or thermoset molecular composites. Improved characterization and modeling will also be required. In this regard, new results on modeling of mechanical properties of molecular composites are presented and compared with experimental results. The Halpin-Tsai equations from ‘shear-lag’ theory of short fiber composites predict properties reasonably well when using the theoretical modulus of rigid-rod molecules in aromatic heterocyclic systems, but newer matrix systems will require consideration of matrix stiffness, desired rod aspect ratio, and rod orientation distribution. Application of traditional and newer morphological characterization techniques are discussed. The newer techniques include: Raman light scattering, high resolution and low voltage SEM, parallel EELS in TEM, synchrotron radiation in X-ray scattering, and ultrasound for integrity studies. The properties of molecular composites and macroscopic composites are compared and it is found that excellent potential exists for use of molecular composites in structural applications including engineering plastics, composite matrix resins, and as direct substitutes for fiber reinforced composites.

Disturbances of spatial perception in children

Spatial perception was tested in 12 children with a localized brain lesion by means of the rod orientation test, line orientation test and facial recognition test. Only children with a lesion of the right hemisphere showed a disturbance of spatial perception.

Spatial disorientation in Parkinson's disease: no effect of levodopa substitution therapy.

In 22 patients with idiopathic Parkinson's disease, we tested spatial orientation with the rod orientation test, before and after levodopa substitution therapy was started. In both situations an impairment of spatial orientation could be demonstrated: levodopa did not improve this impairment.

Development of visual and tactile rod orientation in children

Two groups of neurologically normal children (total number 64), aged from 4 to 13 years, were examined with the rod orientation test. In the second group, the line orientation test and finger tapping were also studied in addition to the rod orientation test. On the rod orientation test, the mean error rates decreased with age in both groups, and from the age of 10 the children performed as well as normal adults. In the period (ages 4–7 years) in which the greatest change in performance on the visual part of the rod orientation test had taken place (63%), a much smaller change occurred in the tapping frequency (23%). Thus the development of motor skills does not seem to be directly related to the development of spatial perception. The line orientation test did not show any developmental profile.

The influence of finite extensibility of the chains on the orientation behaviour of a polymer network

The chains of a deformed polymer network can only be extended up to their contour lengthL. In this work, it is assumed that the chain vector initially undergoes an affine deformation, and then subsequently a pseudo-affine rod orientation as soon as it is fully extended. The density distribution of the chain vectors $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{r} $$ forr<L is approximated by an affinely deforming Gaussian distribution. We calculate the proportion of fully extended chains, their orientation distribution, the Hermans' orientation factor of the segments for both the fully extended and the partially extended chains, and the strain birefringence for this phantom network model. We take into account that the lack of further extension of the fully extended chains results in an excess strain in the partially extended network chains. This leads to non-affine orientation behaviour, and relates the finite extensibility of the chains to the finite elasticity of the network.

Spatial disorientation as an early symptom of Parkinson's disease.

In 44 consecutive outpatients with idiopathic Parkinson's disease (PD) without levodopa substitution therapy, we tested spatial orientation. Spatial orientation was impaired on the rod orientation test in 43 patients, on the line orientation test in 7 patients, and on the facial recognition test in 17 patients. There was no correlation between severity of spatial disorientation and age, length of illness, verbal WAIS score, or severity of PD. Impairment of spatial orientation is part of PD even in mild cases.