Shape Curvature Research Articles

Geodesic Models With Convexity Shape Prior.

The minimal geodesic models established upon the eikonal equation framework are capable of finding suitable solutions in various image segmentation scenarios. Existing geodesic-based segmentation approaches usually exploit image features in conjunction with geometric regularization terms, such as euclidean curve length or curvature-penalized length, for computing geodesic curves. In this paper, we take into account a more complicated problem: finding curvature-penalized geodesic paths with a convexity shape prior. We establish new geodesic models relying on the strategy of orientation-lifting, by which a planar curve can be mapped to an high-dimensional orientation-dependent space. The convexity shape prior serves as a constraint for the construction of local geodesic metrics encoding a particular curvature constraint. Then the geodesic distances and the corresponding closed geodesic paths in the orientation-lifted space can be efficiently computed through state-of-the-art Hamiltonian fast marching method. In addition, we apply the proposed geodesic models to the active contours, leading to efficient interactive image segmentation algorithms that preserve the advantages of convexity shape prior and curvature penalization.

Identifikasi Keragaman Plasma Nutfah Bunga Telang (Clitoria ternatea L.) Di Provinsi Maluku Utara

The Clitoria ternatea plant which has the common name flower telang is a perennial shrub that has deep and woody roots, slightly upward or upright and climbing stems with a height between 20 - 90 cm, downy hair, three to five leaves, oval leaflets the upper surface is hairless and the lower surface is scattered with hairs, flowering bunches in the armpits with 1-2 flowers, the length of the petiole is up to 4 cm, the petals are purple to almost white, the pods are spun oval, hairless, seeds 3-7 , convex valve, seeds round to ovate, brownish in color. The research objective was to determine the diversity of clitoria ternatea flower plants in North Maluku province and as a breeding material for the development of telang flower plants. This research uses descriptive method with direct observation techniques on the object being observed. Morphological and agronomic character data were obtained through surveys and direct observation of sample plants in the field based on modified telang plant descriptor guidelines (IBPGR, 1983 and e-Floras, 2010). From the research found 14 accessions of Clitoria ternatea in North Maluku Province and showed diversity in leaf color, leaf length, leaf length, leaf width, leaf blade size, leaf shape, leaf stalk length, protective crown size, pod length, pod width. pod color, degree of pod curvature, shape of pod beak curvature, seed color, seed coat glossy, number of seeds / pods, maximum number of ovules / pods, weight of seeds / seeds, weight of seeds / pods. The kinship relationship of 14 accessions, cluster I level of similarity 50.55%, cluster II 60.75% and cluster III 42.31%.Keywords: Telang Flower, Germplasm, Diversity

Separated Liquid–Vapor Flow Analysis in a Mini-Channel with Mesh Walls in the Closed-Loop Two-Phase Wicked Thermosyphon (CLTPWT)

A metallic wire mesh screen, wire diameter of approximately 50 μm, is folded into ~80 “accordion-shaped” mini-channels and placed inside the evaporator package of a novel passive thermal management device for cooling overhead light-emitting diodes (LEDs) used in factory floors and high-bay facilities. The thermal power dissipated via these devices ranges between 75 W and 171 W. The channel walls (screen) wick liquid water from the porous wick (located centrally above the screen) and facilitate its evaporation. The closed-loop tests on this device confirm that the two-phase mixture quality exiting the evaporator is approximately 0.2. This paper presents a steady-state numerical model of this separated liquid–vapor flow in a single mini-rectangular channel (900 μm × 2000 μm, 4 cm long) with wire mesh-screen walls. The primary objective of the model is to estimate the pressure drops occurring in this two-phase flow. The model initially assumes a flat liquid–vapor interface along the channel and uses an iterative approach to estimate its final meniscus shape (curvature). In addition to the temperature distribution along the screen walls, this paper also discusses the velocity and pressure distributions in both liquid and vapor regions. It also helps understand the liquid–vapor interfacial shear in this flow configuration and proposes a flow-limiting condition for the device by predicting flow reversal in the channel.

The Emergence of Tuning to Global Shape Properties of Radial Frequency Patterns in the Ventral Visual Pathway.

Radial frequency (RF) patterns, created by sinusoidal modulations of a circle's radius, are processed globally when RF is low. These closed shapes therefore offer a useful way to interrogate the human visual system for global processing of curvature. RF patterns elicit greater responses than those to radial gratings in V4 and more anterior face-selective regions of the ventral visual pathway. This is largely consistent with work on nonhuman primates showing curvature processing emerges in V4, but is evident also higher up the ventral visual stream. Rather than contrasting RF patterns with other stimuli, we presented them at varied frequencies in a regimen that allowed tunings to RF to be derived from 8 human participants (3 female). We found tuning to low RF in lateral occipital areas and to some extent in V4. In a control experiment, we added a high-frequency ripple to the stimuli disrupting the local contour. Low-frequency tuning to these stimuli remained in the ventral visual stream, underscoring its role in global processing of shape curvature. We then used representational similarity analysis to show that, in lateral occipital areas, the neural representation was related to stimulus similarity, when it was computed with a model that captured how stimuli are perceived. We therefore show that global processing of shape curvature emerges in the ventral visual stream as early as V4, but is found more strongly in lateral occipital regions, which exhibit responses and representations that relate well to perception.SIGNIFICANCE STATEMENT We show that tuning to low radial frequencies, known to engage global shape processing mechanisms, was localized to lateral occipital regions. When low-level stimulus properties were accounted for such tuning emerged in V4 and LO2 in addition to the object-selective region LO. We also documented representations of global shape properties in lateral occipital regions, and these representations were predicted well by a proxy of the perceptual difference between the stimuli.

Bone dysplasia in Hutchinson-Gilford progeria syndrome is associated with dysregulated differentiation and function of bone cell populations.

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder affecting tissues of mesenchymal origin. Most individuals with HGPS harbor a de novo c.1824C > T (p.G608G) mutation in the gene encoding lamin A (LMNA), which activates a cryptic splice donor site resulting in production of the toxic "progerin" protein. Clinical manifestations include growth deficiency, lipodystrophy, sclerotic dermis, cardiovascular defects, and bone dysplasia. Here we utilized the LmnaG609G knock-in (KI) mouse model of HGPS to further define mechanisms of bone loss associated with normal and premature aging disorders. Newborn skeletal staining of KI mice revealed altered rib cage shape and spinal curvature, and delayed calvarial mineralization with increased craniofacial and mandibular cartilage content. MicroCT analysis and mechanical testing of adult femurs indicated increased fragility associated with reduced bone mass, recapitulating the progressive bone deterioration that occurs in HGPS patients. We investigated mechanisms of bone loss in KI mice at the cellular level in bone cell populations. Formation of wild-type and KI osteoclasts from marrow-derived precursors was inhibited by KI osteoblast-conditioned media in vitro, suggesting a secreted factor(s) responsible for decreased osteoclasts on KI trabecular surfaces in vivo. Cultured KI osteoblasts exhibited abnormal differentiation characterized by reduced deposition and mineralization of extracellular matrix with increased lipid accumulation compared to wild-type, providing a mechanism for altered bone formation. Furthermore, quantitative analyses of KI transcripts confirmed upregulation of adipogenic genes both in vitro and in vivo. Thus, osteoblast phenotypic plasticity, inflammation and altered cellular cross-talk contribute to abnormal bone formation in HGPS mice.

Advanced Video-Based Processing for Low-Cost Damage Assessment of Buildings under Seismic Loading in Shaking Table Tests.

This paper explores the potential of a low-cost, advanced video-based technique for the assessment of structural damage to buildings caused by seismic loading. A low-cost, high-speed video camera was utilized for the motion magnification processing of footage of a two-story reinforced-concrete frame building subjected to shaking table tests. The damage after seismic loading was estimated by analyzing the dynamic behavior (i.e., modal parameters) and the structural deformations of the building in magnified videos. The results using the motion magnification procedure were compared for validation of the method of the damage assessment obtained through analyses of conventional accelerometric sensors and high-precision optical markers tracked using a passive 3D motion capture system. In addition, 3D laser scanning to obtain an accurate survey of the building geometry before and after the seismic tests was carried out. In particular, accelerometric recordings were also processed and analyzed using several stationary and nonstationary signal processing techniques with the aim of analyzing the linear behavior of the undamaged structure and the nonlinear structural behavior during damaging shaking table tests. The proposed procedure based on the analysis of magnified videos provided an accurate estimate of the main modal frequency and the damage location through the analysis of the modal shapes, which were confirmed using advanced analyses of the accelerometric data. Consequently, the main novelty of the study was the highlighting of a simple procedure with high potential for the extraction and analysis of modal parameters, with a special focus on the analysis of the modal shape's curvature, which provides accurate information on the location of the damage in a structure, while using a noncontact and low-cost method.

Improved vibration based damage detection in laminated composite plate structures under free and forced modal analysis

Composite materials are widely used in modern structural design and technologies due to their qualified mechanical properties and high stiffness to weight ratio. Fibre breakage (FB) and delamination (Dlm) are the most serious damages in these materials, which led to stiffness reduction and loose of functionality and followed by catastrophic failure of the overall structure. The current study presents an extended evaluation of a recent proposed damage index to confirm its capability to identify and quantify structural damage in much more moderate conditions. It has used an improved technique to analysis the measured mode shape curvature (MSC) of the first three mode shapes under both free and forced vibrations for identifying damage location in laminated carbon fibre-reinforced polymer (CFRP) plate structures. It has confirmed its best finding for optimally diagnosis the damage severity and suppressing the confusion of noise effects in both theoretical and experimental analyses. The results show that the improved damage index can be employed with higher accuracy when compared with previous studies for detecting the exact damage location within the laminated composite structure.

Evaluation of crack locations in beam using artificial neural network‐based modified curvature damage index

AbstractAlthough the frequency response‐curvature methodology is commonly used to detect irregularities in mechanical and civil structures, the artificial neural network‐based frequency response‐curvature damage index method may have good efficacy in the detection and localization of structural damages. By utilizing experimental data sets, a novel method is proposed to pinpoint a saw‐cut damage location and the degree of damage in beam models. Using a dynamic data logger, the frequency response function of a beam model is obtained for altering damage levels at different positions. As frequency response data contains environmental and operational noise, the accuracy of obtained results may get reduced. To improve the accuracy by reducing the noise effect, the experimentally obtained frequency response data is trained through an artificial neural network. Using central difference approximation, the sets of trained modal data are utilized to determine the improved mode shape curvature. The curvature damage index is then obtained by using the improved mode shape curvature for different damaged scenarios to ultimately identify structural damages.

Multiple damage prediction in tubular rectangular beam model using frequency response-based mode shape curvature with back-propagation neural network

In the civil infrastructure, the structures made up of tubular sections played an important role due to an economic point of view, lower self-weight, and stability against functional loads. The periodical maintenance or inspection of the structure is mandatory nowadays to achieve the potential utilization of the structural system. In this study, an experimental, numerical, and analytical study is carried out to investigate the structural fault and its severity in a tubular rectangular beam made up of structural steel. Modal parameters are extracted with the help of a dynamic data logger (B&K) by exciting an impact hammer on model structure and extracting a data with a set of unidirectional accelerometers. First, two displacement mode shapes are extracted using obtained modal parameters. The modal parameters are expected to contain environmental noise during experimentation, so, de-noising is must to obtain noise-free data. Artificial neural network training is utilized to reduce the noise from experimental modal parameters. Using the modified modal parameters, the mode shape curvature is obtained, and so-called modified mode shape curvature (MMSC) is used to calculate the curvature damage index. The curvature damage index is appropriate to investigate multiple fault locations with different fault levels in tubular rectangular beam structures.

Systematic Classification of Curvature and Feature Descriptor of 3D Shape and Its Application to "Complexity" Quantification Methods.

Generative design is a system that automates part of the design process, but it cannot evaluate psychological issues related to shapes, such as "beauty" and "liking". Designers therefore evaluate and choose the generated shapes based on their experience. Among the design features, "complexity" is considered to influence "aesthetic preference". Although feature descriptors calculated from curvature can be used to quantify "complexity", the selection guidelines for curvature and feature descriptors have not been adequately discussed. Therefore, this study aimed to conduct a systematic classification of curvature and a feature descriptor of 3D shapes and to apply the results to the "complexity" quantification. First, we surveyed the literature on curvature and feature descriptors and conducted a systematic classification. To quantify "complexity", we used five curvatures (Gaussian curvature, mean curvature, Casorati curvature, shape index, and curvature index) and a feature descriptor (entropy of occurrence probability) obtained from the classification and compared them with the sensory evaluation values of "complexity". The results showed that the determination coefficient between the quantified and sensory evaluation values of "complexity" was highest when the mean curvature was used. In addition, the Casorati curvature tended to show the highest signal-to-noise ratio (i.e., a high determination coefficient irrespective of the parameters set in the entropy calculation). These results will foster the development of generative design of 3D shapes using psychological evaluation.

Multiple Damage Prediction in Tubular Rectangular Beam Model Using Frequency Response-Based Mode Shape Curvature with Back-Propagation Neural Network

Multiple Damage Prediction in Tubular Rectangular Beam Model Using Frequency Response-Based Mode Shape Curvature with Back-Propagation Neural Network

An fMRI study of visual geometric shapes processing.

Cross-modal correspondence has been consistently evidenced between shapes and other sensory attributes. Especially, the curvature of shapes may arouse the affective account, which may contribute to understanding the mechanism of cross-modal integration. Hence, the current study used the functional magnetic resonance imaging (fMRI) technique to examine brain activity's specificity when people view circular and angular shapes. The circular shapes consisted of a circle and an ellipse, while the angular shapes consisted of a triangle and a star. Results show that the brain areas activated by circular shapes mainly involved the sub-occipital lobe, fusiform gyrus, sub and middle occipital gyrus, and cerebellar VI. The brain areas activated by angular shapes mainly involve the cuneus, middle occipital gyrus, lingual gyrus, and calcarine gyrus. The brain activation patterns of circular shapes did not differ significantly from those of angular shapes. Such a null finding was unexpected when previous cross-modal correspondence of shape curvature was considered. The different brain regions detected by circular and angular shapes and the potential explanations were discussed in the paper.

Rethinking Perturbation Directions for Imperceptible Adversarial Attacks on Point Clouds

Adversarial attacks have been successfully extended to the field of point clouds. Besides applying the common perturbation guided by the gradient, adversarial attacks on point clouds can be conducted by applying directional perturbations, e.g., along normal and along the tangent plane. In this article, we first investigate whether adversarial attacks with these two orthogonal directional perturbations are more imperceptible than that with the gradient-aware perturbation. Second, we investigate the deeper difference between adversarial attacks with these two directional perturbations, and whether they are applicable to the same scenarios. Third, based on the verification results that the above two directional perturbations have different sensitiveness to curvature, we devise a novel normal-tangent attack (NTA) framework with a hybrid directional perturbation scheme that adaptively chooses the direction according to the curvature of the local shape around the point. Extensive experiments on two publicly available data sets, e.g., ModelNet40 and ShapeNet Part, with classifiers in three representative networks, e.g., PointNet++, DGCNN, PointConv, validate the effectiveness of NTA, and the superiority to the state-of-the-art methods.

Numerical investigation on the water entry of curved wedge-shaped sections into waves

The water entry of structures with curved boundaries into waves can be frequently observed in actual operations as they are often exposed to harsh wave conditions. To investigate the problem, a numerical model which can simulate the water entry of complex objects into waves is developed in this paper. Under the framework of Cartesian grid, Volume of Fluid method combined with Piecewise Linear Interface Calculation (VOF-PLIC) are used to capture free surface. In addition, Volume of Solid Based Immersed Boundary Method (VOS-IB) is adopted to treat the body condition. Relaxation zones are applied to generate and absorb waves. After a careful validation, five curvatures and three entry locations are selected to investigate the influences of curvature and entry locations on slamming characteristics. Discoveries can be generally summarized as follows: 1) The arriving moment of force peak is not sensitive to the entry location, but is sensitive to the shape of curvatures because of its significant influence on flow separation. 2) The magnitude of force peak is always the smallest at wave peak, followed by calm water and wave trough, regardless of the shape of curvature. 3) The relative magnitude of the pressure on the left and right sides of body surface is influenced not only by the curvature but also by the entry location, and it changes during the water entry process. 4) Sequence of flow separation on the left and right sides of the body is determined by entry location, not by the curvature.

Kinetostatic Modeling of Continuum Delta Robot With Variable Curvature Continuum Joints

Abstract Continuum robots have attracted lots of attention due to their structural compliance, manipulation dexterity, and design compactness. To extend the application scenarios, a slender continuum robot, the CurviPicker, was developed for low-load medium-speed pick-and-place tasks in a previous study. To improve the payload capacity and positioning accuracy of the CurviPicker, a novel Continuum Delta Robot (CDR) was then proposed with three dual-continuum-joint translators in a preliminary investigation. However, the initial version of the CDR did not fully utilize the bending ranges of its continuum joints. In addition, while being modeled using the constant curvature assumption for the continuum joints, the CDR shows lowered positioning accuracy for heavier objects, as the CDR’s continuum joints diverge from the assumed constant curvature shapes. In this paper, the design of the CDR was re-optimized to enable wider bending ranges of the continuum joints (>90 deg) to generate an enlarged workspace, taking into consideration several possible structural interferences. Furthermore, a kinetostatic model is derived based on the Cosserat rod theory to reduce the positioning errors caused by the external loads. The experimental result showed that the workspace is enlarged to approximately 9.47 × 107 mm3 compared with the volume of 6.57 × 107 mm3 of the initial version. Within this enlarged workspace, the average positioning error with a 1000-g load was reduced to 1.93 mm, compared with 4.43 mm obtained by the previous constant curvature assumption.

Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems.

Fundamental studies have improved understanding of molecular-level properties and behavior in surfactant-oil-water (SOW) systems at equilibrium and under nonequilibrium conditions. However, confusion persists regarding the terms "microemulsion" and "curvature" in these systems. Microemulsion refers to a single-phase system that does not contain distinct oil or water droplets but at least four different structures with globular domains of nanometer size and sometimes arbitrary shape. The significance of "curvature" in such systems is unclear. At high surfactant concentrations (typically 30 wt % or more), a single phase zone has been identified in which complex molecular arrangements may result in light scattering. As surfactant concentration decreases, the single phase is referred to as a bicontinuous microemulsion, known as the middle phase in a Winsor III triphasic system. Its structure has been described as involving simple or multiple surfactant films surrounding more or less elongated excess oil and water phase globules. In cases where the system separates into two or three phases, known as Winsor I or II systems, one of the phases, containing most of the surfactant, is also confusedly referred to as the microemulsion. In this surfactant-rich phase, the only curved objects are micellar size structures that are soluble in the system and have no real interface but rather exchange surfactant molecules with the external liquid phase at an ultrafast pace. The use of the term "curvature" in the context of these complex microemulsion systems is confusing, particularly when applied to merged nanometer-size globular or percolating domains. In this work, we discuss the terms "microemulsion" and "curvature", and the most simple four-dimensional spatiotemporal model is proposed concerning SOW equilibrated systems near the optimum formulation. This model explains the motion of surfactant molecules due to Brownian movement, which is a quick and arbitrary thermal fluctuation, and limited to a short distance. The resulting observation and behavior will be an average in time and in space, leading to a permanent change in the local microcurvature of the aggregate, thus changing the average from micelle-like to inverse micelle-like order over an extremely short time. The term "microcurvature" is used to explain the small variations of globule size and indicates a close-to-zero mean curvature of the surfactant-containing film surface shape.

Modeling Channel Deformation and Pollutant Transport in Rivers in Permafrost Zone with Local Channel Curvature

The results of laboratory and mathematical modeling of pollutant propagation from thawed sources on bank slopes in curvilinear reaches of rivers in permafrost zone are presented. Particular attention is paid to studying the effect of channel deformations caused by thermal erosion on the speed and character of pollutant spot propagation. The laboratory experiments in the hydraulic flume were primarily focused on determining the difference in the deformation dynamics and solute propagation from thawing sources at different shapes of channel curvature for the farther use of these data as input parameters of mathematical model for its verification. The analysis of a series of numerical calculations at a scale of laboratory experiment and an actual natural object suggested the conclusion regarding the effect of channel morphometric characteristics, the hydrological and thermal parameters of water flow, the characteristics of permafrost channel-forming ground on the dynamics of pollutant propagation in curvilinear reaches of the permafrost zone.

Network-Based Characterization of Blood Large-Scale Coherent Motion in the Healthy Human Aorta With 4D Flow MRI.

The need for distilling the hemodynamic complexity of aortic flows into clinically relevant quantities resulted in a loss of the information hidden in 4D aortic fluid structures. To reduce information loss, this study proposes a network-based approach to identify and characterize in vivo the large-scale coherent motion of blood in the healthy human aorta. The quantitative paradigm of the aortic flow as a "social network" was applied on 4D flow MRI acquisitions performed on forty-one healthy volunteers. Correlations between the aortic blood flow rate waveform at the proximal ascending aorta (AAo), assumed as one of the drivers of aortic hemodynamics, and the waveforms of the axial velocity in the whole aorta were used to build "one-to-all" networks. The impact of the driving flow rate waveform and of aortic geometric attributes on the transport of large-scale coherent fluid structures was investigated. The anatomical length of persistence of large-scale coherent motion was the 29.6% of the healthy thoracic aorta length (median value, IQR 23.1%-33.9%). Such length is significantly influenced by the average and peak-to-peak AAo blood flow rate values, suggesting a remarkable inertial effect of the AAo flow rate on the transport of large-scale fluid structures in the distal aorta. Aortic geometric attributes such as curvature, torsion and arch shape did not influence the anatomical length of persistence. The proposed in vivo approach allowed to quantitatively characterize the transport of large-scale fluid structures in the healthy aorta, strengthening the definition of coherent hemodynamic structures and identifying flow inertia rather than geometry as one of its main determinants. The findings on healthy aortas may be used as reference values to investigate the impact of aortic disease or implanted devices in disrupting/restoring the physiological spatiotemporal coherence of large-scale aortic flow.

A novel index for vibration-based damage detection technique in laminated composite plates under forced vibrations: experimental study

In this study, vibration modal analysis has been used to experimentally investigate the detection of fiber breakage (FB) and delamination in laminated composite plates. The modal analysis was performed on two arrangement styles of carbon fiber reinforced polymer (CFRP) laminated plates under forced vibrations. The main contribution in this study is that a new index named Improved Curvature Damage Factor (ICDF) was introduced to detect and localize damages in composite structures. It is a developed version of an earlier index based on the change in mode shape curvature (MSC) of dynamic response. To include the effect of more than one mode shape Cumulative Improved Damage Factor (CICDF) was proposed. The ICDF index was validated with a number of earlier studies that investigated the damage detection in different structures in order to approve the efficiency of this index. A scanning laser vibrometer was also used to experimentally examine the modal-based and forced responses for intact and damaged plates. Various experimental tests were used to verify the advantages of the proposed methodology and its use in structural health monitoring. In addition, the analysis of experimental results showed that the mutation caused by FB is almost double that of the value of delamination peaking.

The shape of the sagittal curvatures of the spine in a high-level acrobatic gymnasts – comparison by sex

Specific loads on the spine and the very young age at which acrobatic gymnastics training is undertaken require monitoring the shape of the spine curvatures in gymnasts to detect possible postural abnormalities. The aim of this descriptive study was to assess and compare the shape of the spine in the sagittal plane in acrobatic gymnasts of both sexes and their associations with demographic and somatic variables. The study group included 159 acrobatic gymnasts aged 12-19 (106 females and 53 males) from 16 European countries. The study was designed as a survey and measurements of somatic variables and the angles of inclination (using the Baseline Bubble inclinometer) at four topographic points of the spine: S1, L5/S1, Th12/L1, C7/Th1. Based on the angles of spinal inclination, the sizes of the sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis (TK) were calculated. Body posture was assessed based on Wolański’s modified typology. The angles of SS and LL were significantly higher in females, and TK did not differ between sexes. Training experience positively correlated only with the size of the SS in both sexes. Age and somatic variables were significantly correlated with the size of the sagittal curvatures, mainly in females. The majority of gymnasts had a normal angle of SS and TK and a flattened LL. The equivalent and lordotic types of body posture were more frequent in females, and the kyphotic type in males. The incorrect body posture was noted in 19.8% of females and 43.4% of males. We concluded that acrobatic gymnasts are not at risk of increasing the size of spinal curvatures in the sagittal plane, but males show a tendency toward flattened LL and kyphotic type of body posture.