Effect Of Shape Change Research Articles

Swimming in an inviscid fluid

We present a set of equations governing the motion of a body due to prescribed shape changes in an inviscid, planar fluid with nonzero vorticity. The derived equations, when neglecting vorticity, reduce to the model developed in Kanso et al. (J Nonlinear Sci 15:255–289, 2005) for swimming in potential flow, and are also consistent with the models developed in Borisov et al. (J Math Phys 48:1–9, 2007), Kanso and Oskouei (J Fluid Mech 800:77–94, 2008), Shasikanth et al. (Phys Fluids 14(3):1214–1227, 2002) for a rigid body interacting dynamically with point vortices. The effects of cyclic shape changes and the presence of vorticity on the locomotion of a submerged body are discussed through examples.

TURBULENT DYNAMOS IN SPHERICAL SHELL SEGMENTS OF VARYING GEOMETRICAL EXTENT

We use three-dimensional direct numerical simulations of the helically forced magnetohydrodynamic equations in spherical shell segments in order to study the effects of changes in the geometrical shape and size of the domain on the growth and saturation of large-scale magnetic fields. We inject kinetic energy along with kinetic helicity in spherical domains via helical forcing using Chandrasekhar-Kendall functions. We take perfect conductor boundary conditions for the magnetic field to ensure that no magnetic helicity escapes the domain boundaries. We find dynamo action giving rise to magnetic fields at scales larger than the characteristic scale of the forcing. The magnetic energy exceeds the kinetic energy over dissipative time scales, similar to that seen earlier in Cartesian simulations in periodic boxes. As we increase the size of the domain in the azimuthal direction we find that the nonlinearly saturated magnetic field organizes itself in long-lived cellular structures with aspect ratios close to unity. These structures tile the domain along the azimuthal direction, thus resulting in very small longitudinally averaged magnetic fields for large domain sizes. The scales of these structures are determined by the smallest scales of the domain, which in our simulations is usually the radial scale. We also find that increasing the meridional extent of the domains produces little qualitative change, except a marginal increase in the large-scale field. We obtain qualitatively similar results in Cartesian domains with similar aspect ratios.

Void Coalescence With and Without Prestrain History

In this study, void coalescence with and without a plastic prestrain history is studied using stress-controlled axisymmetric unit cell models. In addition to spherical voids, both oblate and prolate voids are considered. In the case with prestrain history a uniaxial prestrain up to 10% was applied and the material is thereafter subjected to loadings with constant stress triaxiality. It is found that the microscopic position of the maximum axial stress in void ligament can be taken as an indicator for void coalescence. In the beginning of plastic loading the maximum axial stress occurs at the edge close to the void. With the increase of plastic deformation, the position of maximum axial stress shifts from the void edge to cell boundary and coalescence starts when the position appears at the boundary. It is shown that a prestrain history significantly reduces the void coalescence strain. The prestrain effect on void coalescence depends strongly on the initial void shape. Prestrain history induces both strain hardening and void shape change. The effect of prestrain-induced void shape change on coalescence strain is relatively small while the effect of prestrain-induced local hardening is significant.

Light scattering calculations exploring sensitivity of depolarization ratio to shape changes I Single spores in air

Calculations of the depolarization ratio, D(Theta, lambda) = 1 - (S22)/(S11), for light scattered from an ensemble or cloud of single aerosolized spores in air were studied using the discrete dipole approximation (DDA), sometimes also called the coupled-dipole approximation. Here S(ij) is the appropriate Mueller matrix element for scattering angle Theta and wavelength lambda. The effect of modest shape changes on D(Theta, lambda) was determined. The shapes compared were prolate ellipsoids versus right circular cylinders joined smoothly to end caps consisting of hemispheres of the same diameter as the cylinder. Using the same models, the graphs of (S34)/(S11) versus angle were compared with those for D(Theta, lambda). The latter shows sensitivity to length in some cases we examined, while (S34)/(S11) does not. Size parameters and optical constants suggested by measurements of Bacillus cereus endospores were used. An ensemble of spores was modeled with prolate spheroids. The results of this model were compared with results of a model using the same size and optical parameters, but for capped cylinders. The two models produced distinguishably different results for the same parameters. In calculations for all the graphs shown, averaging over random orientations was performed. Averaging over size distributions similar to those from experimental measurements was performed where indicated. The results show that measurements of D(Theta, lambda) could be quite useful in characterizing the shape of particles in an unknown aerosol and for distinguishing between two likely shapes, but not to reconstruct the shapes from the graphs alone without additional information.

複合材料の巨視的弾性定数に及ぼす楕円体強化基材の形状変化の影響

複合材料の巨視的弾性定数に及ぼす楕円体強化基材の形状変化の影響

Morphological analyses and 3D modeling of the tongue musculature of the chimpanzee (Pan troglodytes)

Knowledge of the comparative anatomy of tongue musculature is crucial to the discussion of the origin and the evolution of speech because of the indispensable role played by this organ in speech. However, the tongue musculature of primates has rarely been studied. In a previous study, the author analyzed human tongue musculature and developed a 3D model of this organ [Takemoto, Journal of Speech, Language, and Hearing Research 44:95-107, 2001]. In this study, the tongue musculature of chimpanzees was examined using methods similar to those used for humans. Results showed that tongue musculature was topologically the same for both humans and chimpanzees. As in humans, the tongue musculature of chimpanzees consisted of inner and outer regions. The inner musculature was composed of serial "structural units," made up of two types of laminae whose fibers were perpendicular to the tongue surface. The outer musculature was a thin layer of fibers oriented parallel to the surface and superficial to the inner musculature. Although the tongue musculature of humans and chimpanzees is similar, the external shapes differ: the chimpanzee tongue is flat, whereas the human tongue is round. Applying the muscular hydrostat theory to the external shape of the tongue suggests that the primary actions of the chimpanzee tongue are protrusion and retrusion, whereas the human tongue can be deformed in the oral cavity with a high degree of freedom. It is hypothesized that the evolution of the external shape of the tongue is one of the factors that led to the development of human speech. The results of this study suggest that modeling based on muscular hydrostatic theory of the effects of changes in external tongue shape on articulatory movements should be included in discussions on the origin of speech.

Color appearance of familiar objects: Effects of object shape, texture, and illumination changes

People perceive roughly constant surface colors despite large changes in illumination. The familiarity of colors of some natural objects might help achieve this feat through direct modulation of the objects' color appearance. Research on memory colors and color appearance has yielded controversial results and due to the employed methods has often confounded perceptual with semantic effects. We studied the effect of memory colors on color appearance by presenting photographs of fruit on a monitor under various simulated illuminations and by asking observers to make either achromatic or typical color settings without placing demands on short-term memory or semantic processing. In a control condition, we presented photographs of 3D fruit shapes without texture and 2D outline shapes. We found that (1) achromatic settings for fruit were systematically biased away from the gray point toward the opposite direction of a fruit's memory color; (2) the strength of the effect depended on the degree of naturalness of the stimuli; and (3) the effect was evident under all tested illuminations, being strongest for illuminations whose chromaticity was closest to the stimulus chromaticity. We conclude that the visual identity of an object has a measurable effect on color perception, and that this effect is robust under illuminant changes, indicating its potential significance as an additional mechanism for color constancy.

The relationship between shape of the skull and bite force in finches

In finches husking time is non-linearly related to the ratio of seed hardness to maximal bite force. Fringillids produce larger bite force and husk relatively hard seeds faster than estrildids of similar size. This is at least partly explained by their relatively larger jaw muscle mass and a difference in husking technique. However, the effect of differences in skull geometry on bite force is unclear. In this study differences in skull morphology that may contribute to the difference in bite force between fringillids and estrildids are analyzed. The shape of the skull was described by the 3D coordinates of a set of landmarks and, after eliminating size, the effect of differences in the shape of the skull on bite force was determined using a static force model. EMG recordings of jaw muscles during seed cracking were used to validate assumptions about the muscle activation patterns used for the static bite force model. The analysis shows that most of the variation in skull geometry is related to differences in size. Although the shape of the skull is highly convergent between fringillids and estrildids, the shape of the skull differs significantly between the two groups. A principal component analysis of the landmark coordinates shows several patterns of allometric shape changes, one of which is expressed more strongly in estrildids than in fringillids. Three characters dominate the effect of shape changes on bite force. Bite force increases with a more caudal position of the quadrate, a more downward inclined beak and a relatively short jugal and palatine. A more downward inclined beak is typically found in estrildids. The height of the upper bill and a number of other changes in skull shape have little effect on bite force. An estimate of the relative contributions of jaw muscle size and skull geometry to the difference in bite force between fringillids and estrildids suggests that the contribution of muscle size is much larger than the contribution of skull geometry.

Controlling the rates of biochemical reactions and signaling networks by shape and volume changes

In biological systems, chemical activity takes place in micrometer- and nanometer-sized compartments that constantly change in shape and volume. These ever-changing cellular compartments embed chemical reactions, and we demonstrate that the rates of such incorporated reactions are directly affected by the ongoing shape reconfigurations. First, we show that the rate of product formation in an enzymatic reaction can be regulated by simple volume contraction-dilation transitions. The results suggest that mitochondria may regulate the dynamics of interior reaction pathways (e.g., the Krebs cycle) by volume changes. We then show the effect of shape changes on reactions occurring in more complex and structured systems by using biomimetic networks composed of micrometer-sized compartments joined together by nanotubes. Chemical activity was measured by implementing an enzymatic reaction-diffusion system. During ongoing reactions, the network connectivity is changed suddenly (similar to the dynamic tube formations found inside Golgi stacks, for example), and the effect on the reaction is registered. We show that spatiotemporal properties of the reaction-diffusion system are extremely sensitive to sudden changes in network topology and that chemical reactions can be initiated, or boosted, in certain nodes as a function of connectivity.

Dynamic PIV flow field analysis of the mechanical mitral bi-leaflet valves: Effect of ventrical shape change

Dynamic PIV flow field analysis of the mechanical mitral bi-leaflet valves: Effect of ventrical shape change

Depletion Interactions in a Cylindric Pipeline with a SmallShape Change

Stressed by external forces, it is possible for a cylindric pipeline tochange into an elliptic pipeline. To expose the effect of small shapechange of the pipeline on the depletion interactions, both the depletionpotentials and depletion forces in the hard sphere systems confined by acylindric pipeline or by an elliptic pipeline are studied by Monte Carlosimulations. The numerical results show that the depletion interactionsare strongly affected by the small change of the shape of the pipelinein a way. Furthermore, it is also found that the depletion interactionswill be strengthened if the short axis of the elliptic pipeline isdecreased.

Effect of small shape changes on the optical response of highly symmetric silicon quantum dots

Ellipsoidal quantum dot structures are proposed and studied with ab inito calculations. A comparison of the formation energy with spherical partners shows small differences. However, electronic and optical properties are distinct. Because electronic states have different sensitivities to aspect ratio changes, selected frontier orbitals are driven into the gap and an overall level shifting allows for absorption in the visible range. Our result shows the importance of both size and shape for the gap engineering of silicon quantum dots.

Protective effect of Ugni molinae Turcz against oxidative damage of human erythrocytes

Ugni molinae Turcz, also known as “Murtilla”, is a plant that grows in the south of Chile. Infusions of its leaves have long been used in traditional native herbal medicine. The chemical composition of the leaves indicates the presence of polyphenols, which have antioxidant properties. In the present work, the antioxidant properties of U. molinae were evaluated in human erythrocytes exposed in vitro to oxidative stress induced by HClO. The experiments were carried out by scanning electron microscopy (SEM) and hemolysis measurements. The SEM observations showed that HClO induced a morphological alteration in the red blood cells from a discoid to an echinocytic form. According to the bilayer couple hypothesis, the formation of echinocytes indicates that HClO was inserted in the outer leaflet of the erythrocyte membrane. However, a concentration as low as 10 μM gallic acid equivalents (GAE) U. molinae aqueous extract neutralized the shape change effect of HClO applied in a concentration as high as 0.25 mM. The significant protection of U. molinae aqueous extract was also shown in the hemolysis experiments. In fact, very low concentrations of the extract considerably reduced the deleterious capacity of HClO to induce hemolysis in red blood cells. It is concluded that the location of the extract components into the membrane bilayer and the resulting restriction on its fluidity might hinder the diffusion of HClO and its consequent damaging effects. This conclusion can also imply that this restriction could apply to the diffusion of free radicals into cell membranes and the subsequent decrease of the kinetics of free radical reactions.

Analytical derivatives technology for structural shape design

The ability to perform and evaluate the effect of shape changes on the stress and modal responses of components is an important ingredient in the “design” of aircraft engine components. The classical design of experiments (DOE)-based approach that is motivated from statistics (for physical experiments) is one of the possible approaches for the evaluation of the component response with respect to design parameters [Myers, Montgomery. Response surface methodology, process and product optimization using design of experiments. John Wiley and Sons, NY (1995)]. As the underlying physical model used for the component response is deterministic and understood through a computer simulation model, one needs to re-think the use of the classical DOE techniques for this class of problems. In this paper, we explore an alternate sensitivity-analysis-based technique where a deterministic parametric response is constructed using exact derivatives of the complex finite-element (FE)-based computer models to design parameters. The method is based on a discrete sensitivity analysis formulation using semi-automatic differentiation (Griewank, SIAM (2000), ADIFOR, Automatic Differentiation of FORTRAN codes http://www-unix.mcs.anl.gov/autodiff/ADIFOR/) to compute the Taylor series or its Pade equivalent for finite-element-based responses. Shape design or optimization in the context of finite element modeling is challenging because the evaluation of the response for different shape requires the need for a meshing consistent with the new geometry. This paper examines the differences in the nature and performance (accuracy and efficiency) of the analytical derivatives approach against other existing approaches with validation on several benchmark structural applications. The use of analytical derivatives for parametric analysis is demonstrated to have accuracy benefits on certain classes of shape applications.

Electro-shape-memory effect in Mn-doped BaTiO 3 single crystals and in situ observation of the reversible domain switching

Very recently a giant electric-field-induced recoverable shape change effect (electro-shape-memory effect) has been found in aged BaTiO 3-based ferroelectric crystals. This effect is supposed to come from a reversible domain-switching process with the restoring force provided by a symmetry-conforming principle of defects. However, the reversible domain switching process itself behind the giant electro-shape-memory effect is yet to be directly verified. In the present study, we performed in situ domain observation during electric field cycling for aged Mn-doped BaTiO 3 single crystals and simultaneously measured its macroscopic properties. It was found that the aged sample shows a reversible domain switching during electric field cycling; this corresponds very well to the electro-shape-memory effect (with a maximum shape change of 0.4%, which is almost half of the theoretical value). This provides a direct mesoscopic evidence for the defect-mediated reversible domain switching mechanism. Moreover, as all these effects stems from aging in ferroelectric state, we further explained that their microscopic origin is symmetry-conforming property of defects, which is completed during aging by defect migration.

The hydrodynamic effects of shape and size change during reconfiguration of a flexible macroalga

Rocky intertidal organisms experience large hydrodynamic forces due to high water velocities created by breaking waves. Flexible organisms, like macroalgae, often experience lower drag than rigid organisms because their shape and size change as velocity increases. This phenomenon, known as reconfiguration, has been previously quantified as Vogel's E, a measure of the relationship between velocity and drag. While this method is very useful for comparing reconfiguration among organisms it does not address the mechanisms of reconfiguration, and its application to predicting drag is problematic. The purpose of this study was twofold: (1) to examine the mechanisms of reconfiguration by quantifying the change in shape and size of a macroalga in flow and (2) to build a mechanistic model of drag for reconfiguring organisms. Drag, frontal area and shape of the intertidal alga Chondrus crispus were measured simultaneously in a recirculating flume at water velocities from 0 to approximately 2 m s(-1). Reconfiguration was due to two separate mechanisms: whole-alga realignment (deflection of the stipe) at low velocities (<0.2 m s(-1)) and compaction of the crown (reduction in frontal area and change in shape) at higher velocities. Change in frontal area contributed more to drag reduction than change in drag coefficient. Drag coefficient and frontal area both decrease exponentially with increasing water velocity, and a mechanistic model of drag was developed with explicit functions to describe these changes. The model not only provides mechanistic parameters with which to compare reconfiguration among individuals and species, but also allows for more reliable predictions of drag at high, ecologically relevant water velocities.

Comparing view sensitivity in shape discrimination with shape sensitivity in view discrimination

In three picture-picture matching experiments, the effects of a view change on our ability to detect a shape change (Experiments 1 and 2) were contrasted with the effects of a shape change on our ability to detect a view change (Experiment 3). In each experiment, both view changes and shape changes influenced performance. However, shape changes had more influence than did view changes in the shape change detection task Conversely, view changes were more influential when the task was to detect view changes. Thus, the participants could often discriminate between the effects of shape changes and the effects of view changes. The disruptive effect of task-irrelevant changes (view changes in the first two experiments; shape changes in the final experiment) does not support Stankiewicz's (2002) claim that information about viewpoint and about shape can be estimated independently by human observers. However, the greater effect of variation in the task-relevant than in the task-irrelevant dimension indicates that the observers were moderately successful at disregarding irrelevant changes.

Leaf area estimation from linear measurements in zucchini plants of different ages

SummarySimple, accurate and non-destructive methods to determine individual leaf areas of plants are a useful tool in physiological and agronomic research. Determining the individual leaf area (LA) of zucchini squash (Cucurbita pepo L.) involves measurements of leaf parameters such as length (L) and width (W), or some combinations of these parameters. Three greenhouse experiments were carried out during Spring-Summer 2001, Spring-Summer 2002 and Summer-Autumn 2003 to compare predictive models for zucchini leaf areas using simple linear measurements that could accommodate the effects of changes in leaf shape during different plant ages. The L:W ratio (leaf shape parameter) of zucchini squash decreased with increasing leaf area and became constant, with a similar pattern between growing seasons. Leaf area was predicted accurately from the product of L and W (R2 = 0.97 and Mean Square Error, MSE = 1,526 cm2), but this model was dependent on plant age. A linear model having W2 as the independent variable provided the most accurate estimate (R2 = 0.98, MSE = 972 cm2) of zucchini LA, independent of plant age. Validation of the model having the W2 of leaves measured in the 2002 and 2003 Experiments showed that the correlation between calculated and measured areas was very high.

A method for aligning trans-tibial residual limb shapes so as to identify regions of shape change

Quantification of the change in shape of a residual limb over time is relevant to the fitting of an external prosthesis. Three algorithms were developed and evaluated to align residual limb shapes: iterative closest points (ICP), mean absolute difference, and weighted surface normals/mean absolute difference. Evaluations were conducted by aligning residual limb shapes with known deformations and transformations with their original shapes. Results showed that ICP did not perform well in that it tended to favor a global distribution of local shape difference rather than localization of the error. The mean absolute difference algorithm performed well as long as the shape difference was localized to one region. Weighted mean surface normals/absolute difference provided the best alignment results, performing well both if shape changes were localized and if they were globally distributed. Mean alignment errors for this method were less than 0.285 mm for each of the three translation directions and less than 0.357 degrees for each of the three rotation directions. This algorithm could be helpful to patients, prosthetists, and researchers developing treatments to overcome the detrimental fitting effects of residual limb shape change.

Calculations of neoclassical viscous damping on flux surfaces near magnetic islands in the Helically Symmetric Experiment

Neoclassical viscous damping rates have been calculated for the helically symmetric experiment [F. S. B. Anderson et al., Fusion Technol. 27, 273 (1995)], concentrating on the effects of magnetic surface shape changes due to magnetic islands. The interaction between the main helical spectral component and magnetic surface shape changes caused by an island chain introduces symmetry breaking spectral components on closed surfaces near the island chain. Results indicate that small islands present in the quasihelically symmetric configuration can give rise to an observable but not problematic deviation from quasisymmetry on surfaces near the islands. These islands can be eliminated via a small reduction in the rotational transform. Large islands can be produced by the introduction of the ι̷=4∕4 resonance inside the last closed magnetic surface. These islands result in not only a significant reduction in the volume of closed nested magnetic surfaces, but also an elevated level of viscous damping on magnetic surfaces adjacent to the islands.