Variable Curvature Research Articles

Curvature-Mediated Forces on Elastic Inclusions in Fluid Interfaces.

Heterogeneous fluid interfaces often include two-dimensional solid domains that mechanically respond to changes in interfacial curvature. While this response is well-characterized for rigid inclusions, the influence of solid-like elasticity remains essentially unexplored. Here, we show that an initially flat, elastic inclusion embedded in a curved, fluid interface will exhibit qualitatively distinct behavior depending on its size and stiffness. Small, stiff inclusions are limited by bending and experience forces directed up gradients of Gaussian curvature, in keeping with prior findings for rigid discoids. By contrast, larger and softer inclusions are driven down gradients of squared Gaussian curvature in order to minimize the elastic penalty for stretching. Our calculations of the force on a solid inclusion are shown to collapse onto a universal curve spanning the bending- and stretching-limited regimes. From these results, we make predictions for the curvature-directed motion of deformable solids embedded within a model interface of variable Gaussian curvature.

Lung image registration by featured surface matching method

ABSTRACT The objective is to validate lung image registration using the featured surface matching method. The method can be applied to volume-to-surface deformable image registration, which is the 3D volume image to be deformed and aligned with a 3D surface image. Curvature variation extracts the surface feature. A group of neighbour curvature variations forms a local surface feature. A surface-matching scheme uses the local surface feature to determine the correspondence between two surface points. A finite element model uses the surface point correspondence to propagate the surface displacement into internal tissues and determine the intraoperative landmark locations from the deformed image. The validation uses the publicly available DIRLAB and POPI datasets to assess target registration errors. The work shows that the target registration error is 1.88 ± 1.16 mm, 4.77 ± 2.59 mm, and 4.12 ± 2.22 mm, and the initial error is 4.01 ± 2.91 mm, 11.10 ± 6.98 mm, 11.66 ± 6.23 mm for DIRLAB lung #1, DIRLAB lung #6 and POPI lung #1, respectively. The proposed method outperforms the average of other methods. The proposed novel surface matching method is feasible and validated.

Three-dimensional geometry and topology effects in viscous streaming

Recent studies on viscous streaming flows in two dimensions have elucidated the impact of body curvature variations on resulting flow topology and dynamics, with opportunities for microfluidic applications. Following that, we present here a three-dimensional characterization of streaming flows as functions of changes in body geometry and topology, starting from the well-known case of a sphere to progressively arrive at toroidal shapes. We leverage direct numerical simulations and dynamical systems theory to systematically analyse the reorganization of streaming flows into a dynamically rich set of regimes, the origins of which are explained using bifurcation theory.

Influence of the Linear Interpolation Segment on the Accuracy of Tool’s Outline Characterized by Variable Curvature

Influence of the Linear Interpolation Segment on the Accuracy of Tool’s Outline Characterized by Variable Curvature

Experimental and numerical study on the performance of new prefabricated connections for free-form grid structures

Free-form grid shell structures are widely used for stadiums, airport terminals, exhibition pavilions, shopping malls and warehouses, however, the shape of the grid surface is usually complex. A flexible joint that can adapt to the curvature variation of the free-form surface is therefore important for assembling such structures. To meet the demand of various curvatures for single-layer free-form grid structures, a new type of prefabricated bolted joint is introduced in this paper. A series of in-plane bending tests were conducted to investigate the initial stiffness and the moment resistance of the joints. Coupon tests were carried out to study the material properties and provide parameters for a numerical study. FE models considering the geometric and material nonlinearity were developed and validated by the tests. Parametric studies were then carried out using the developed FE model to investigate the influencing geometric factors of the in-plane behaviours semi-rigid joints. The results demonstrated that the initial in-plane stiffness of the joints is dominantly controlled by the endplate thickness, the side plate thickness, the bolt diameter and the bolt row distance, while the moment resistance of the joint is governed by the endplate thickness, the side plate thickness, the sleeve cross-sections and the bolt row distance. Subsequently, FE analysis was carried out using the validated FE models to investigate the out-of-plane behaviour of the proposed assembled joint. The experimental and numerical study showed that the proposed joint has good rotational capacity and load-bearing resistance, therefore has the potential to be applied in the design and construction of free-form grid structures.

Highly efficient light trapping of clustered silicon nanowires for solar cell applications.

Due to their excellent photoelectric performance, nanostructures have attracted considerable attention in research to improve the power conversion efficiency of thin-film solar cells (TFSCs). Furthermore, cylindrical silicon nanowires (Cy-SiNWs) are regarded as promising candidates for a new generation of TFSCs. On this basis, many new nanostructures derived from conventional Cy-SiNWs have been studied extensively, but most of these structures require high manufacturing accuracy because of their complex morphology. In this paper, an ingenious design of clustered silicon nanowires (Cl-SiNWs) is introduced, whose cross section is similar to the flower shape and consists of four arcs with the same radius. Hence, it requires lower manufacturing difficulty compared with nanostructures with curvature variation of the cross-section profile (i.e., elliptic shape, crescent shape, etc.). In this study, the optical and electrical characterizations are numerically investigated using the finite-difference time-domain method. The numerical simulation shows that the optimized Cl-SiNWs achieve an optical ultimate efficiency (ηul) and circuit current density (Jsc) of 33.66% and 27.54mA/cm2, respectively, with an enhancement of 7.3% over conventional Cy-SiNWs. Further, the ηul and Jsc improve to 42.20% and 34.53mA/cm2 by adding the silicon substrate and silver backreflector. More importantly, the ηul of Cl-SiNWs always obtained a higher value than Cy-SiNWs at a recommended diameter range of 360-560 nm. Therefore, the suggested Cl-SiNWs have exhibited tremendous potential for the future development of low-cost and highly efficient solar cells.

Curvature-Variation-Inspired Sampling for Point Cloud Classification and Segmentation

Point cloud is a discrete and unordered expression of 3D data. A lot of methods have been proposed to solve the problem in 3D object classification and scene recognition. To handle the huge amount of unordered point cloud, down-sampling before processing is needed. The shortage of existing sampling methods is the lack of geometry information consideration, which is essential for point cloud classification and segmentation tasks. Our method is mainly motivated by the observation that points with a high curvature variation can depict the outlines of objects. Thus, we propose a curvature variation based sampling method for point cloud classification and segmentation tasks. We aim to sample points with high curvature variations, which are considered to be more suitable for classification and segmentation tasks than the traditional sampling method. We combine the proposed sampling algorithm with the existing sampling method for multiple information fusion, and a higher accuracy and mean IoU can be achieved. The experimental results verify the advantage of considering curvature variation in classification and segmentation tasks.

A semi analytical method for in-plane free vibrations of arches with a variable curvature

Rayleigh-Ritz method (RRM) is used in this paper in order to investigate the in-plane vibrations of arches with a variable curvature in particular, the frequency parameters and mode shapes. The trial functions are particular solutions of the sixth order differential equation of arch vibrations corresponding to an opening angle equal to one rad. The investigations are made with the follow’s hypotheses: the constant dimensions of the cross-section are small in comparison with the radius, the arch axis is inextensible and the effect of rotary inertia and shear deformation are neglected. The parabolic, catenary, spiral, circular and cycloid arches with different boundary conditions are investigated. The frequency parameters are presented for different types of curved arches with various geometrical properties and boundary conditions and the corresponding mode shapes are plotted. The results are compared with the published literature. The accuracy and relative simplicity of the RRM, applied herein a systematic way with the new choice of trial functions, is established, making it ready to use in more complex situations, such as those of arches with added masses, with non-uniform cross sections or with one or more point supports.

Experimental Studies Into the Beam Parameter Product of GaAs High-Power Diode Lasers

Experimental studies into the beam parameter product (BPP) of 940-980 nm GaAs-based high-power diode lasers are presented. Such lasers exhibit broadening far field and narrowing near field with increasing bias, with BPP increasing tenfold over the diffraction limit. First, spectrally-resolved beam profile measurements of lasers with monolithically-integrated gratings are presented, showing that a reproducible series of spatially-extended optical modes makes up the optical field. Then, changes to the device construction are presented, enabling effects limiting BPP to be inferred and addressed. Process- and package-induced effects can be minimized by design, while the effects of carrier, gain and temperature profiles dominate. Self-heating within the laser stripe raises the refractive index, forming a thermal lens, and the variation in curvature of this lens with bias and device construction directly affects BPP. Temperature non-uniformity along the resonator is also shown to strongly degrade BPP. Moreover, current spreading and the resulting lateral carrier accumulation (LCA) amplify high-order, high-BPP modes, thus degrading BPP for any given thermal lens. This LCA-induced degradation is shown to be suppressed by regrown lateral current-blocking structures. Finally, a flatter thermal lens and lower BPP can be achieved using thermal engineering, via changes to the epitaxial design or device layout.

A Comparative Experiment on Heterogeneous Distributions of Stress Field for Underground Panels With Different Geological Setting in North China

A comparative experiment was carried out to discuss the detectability and influence factors on heterogeneous distributions of the stress field for underground panels in North China. The panels are situated in the center and the eastern margin of the North China plate, having similar layouts and stress states. Seismic surveys were performed before coal extractions, and travel-time topographies for refracted P-waves from stiff roofs were computed with a ray-based inversion. The tomographic distributions of P-wave velocity were interpreted by a K-means clustering to categorize the stress fields. The estimated high-stress anomalies show strong correlations with the monitored dynamic roof ruptures and high-energy microseisms. Besides, the relationship among high-stress areas, geological factors, and mined-out voids is also discussed through feature comparisons, Monte–Carlo simulations, and point process statistics. Our results show that the curvature variations and the mined-out voids are dominant factors that affect the heterogeneous distribution of the stress field in the panels. However, the leading causes of the curvature variations in the small-scale panels are different, but they do follow the large-scale regional patterns of the geological regime.

Design rules for 2D field mediated assembly of different shaped colloids into diverse microstructures.

Assembling different shaped particles into ordered microstructures is an open challenge in creating multifunctional particle-based materials and devices. Here, we report the two-dimensional (2D) AC electric field mediated assembly of different shaped colloidal particles into amorphous, liquid crystalline, and crystalline microstructures. Particle shapes investigated include disks, ellipses, squares, and rectangles, which show how systematic variations in anisotropy and corner curvature determine the number and type of resulting microstructures. AC electric fields induce dipolar interactions to control particle positional and orientational order. Microstructural states are determined via particle tracking to compute order parameters, which agree with computer simulations and show how particle packing and dipolar interactions together produce each structure. Results demonstrate how choice of particle shape and field conditions enable kinetically viable routes to assemble nematic, tetratic, and smectic liquid crystal structures as well as crystals with stretched 4- and 6-fold symmetry. Results show it is possible to assemble all corresponding hard particle phases, but also show how dipolar interactions influence and produce additional microstructures. Our findings provide design rules for the assembly of diverse microstructures of different shaped particles in AC electric fields, which could enable scalable and reconfigurable particle-based materials, displays, and printing technologies.

Resolution-Normalizing Image Stitching for Long-Linear-Array and Wide-Swath Whiskbroom Payloads

Affected by the large and inconsistent geometric distortion deriving from long-linear-array and wide-swath whiskbroom (LWW) imaging and the small overlap area of adjacent images, the conventional stitching methods based on feature matching greatly suffer from the severe misalignment, ghosting effect and distortion in overlapping and non-overlapping areas, respectively. Here, in view of these problems, this letter proposes a resolution-normalizing stitching method for LWW images. Firstly, considering the variation of scan-angle, earth curvature, and pixel position along-track, we establish a resolution characterization model to calculate the accurate ground sampling distance (GSD) anywhere in the field of view. Then, accordingly, the resolution-normalizing method comprising GSD allocation and gray-value interpolation is proposed to re-project the original adjacent images for eliminating the resolution inconsistency along-track. Finally, the normalized images were stitched based on the perspective transformation with matching corresponding pairs. Experimental results evaluated on the images of Thermal Infrared Spectrometer (TIS) aboard Sustainable Development Goals Satellite-1 (SDGSAT-1) show that the stitching accuracy of the proposed method can be around 0.5 pixels, and more importantly, the ghosting effects and projection distortions are reduced effectively.

Analysis of blood flow through curved artery with mild stenosis

Building-up of plaque narrows arteries, decreasing blood flow to the heart, causing chest pain, shortness of breath, or other coronary artery disease signs and symptoms. Implementing Navier–Stokes equations in a cylindrical coordinate system and assuming axial symmetry under laminar flow conditions, the study has been conducted on the two aspects of blood flow dynamics viz., velocity profile and volumetric flow rate of blood around curved stenosis with a variation of curvature of the artery and the stenosis thickness. The blood flow behavior taking different values for the viscosity coefficient has been also studied.

Modeling and Simulation of Temperature Field During Belt Grinding of Inconel 718 Variable Curvature Components Considering Elastic Contact

Modeling and Simulation of Temperature Field During Belt Grinding of Inconel 718 Variable Curvature Components Considering Elastic Contact

Research and Design of Variable Curvature Optical Integrator for Solar Simulator

Research and Design of Variable Curvature Optical Integrator for Solar Simulator

Mandibular Canal Segmentation From CBCT Image Using 3D Convolutional Neural Network With scSE Attention

In dental implant planning, the mandibular canal is an important reference for determining the safe position of the implant. Accurate and automatic segmentation of the mandibular canal from CBCT image is of great significance. However, the variable curvature of the mandibular canal and the blurred borders make the process challenging. At present, the segmentation of mandibular canal is usually carried out by experienced, doctors using manual or semi-automatic methods, which are time-consuming and have poor segmentation consistency. For these issues, this paper proposes a mandibular canal segmentation method based on 3D convolutional neural network. Firstly, a mandibular canal segmentation method based on center line combined with region growth and a mandibular canal clipping method based on fixed points are proposed to improve the efficiency of mandibular canal marking and reduce the imbalance between sample categories, respectively. Thereafter, the scSE attention module was added to the network for reducing irrelevant background information. Finally, an weighted BCE loss function was used to prevent the mental foramen and mandibular foramen areas from participating in the back-propagation calculation, and the network is more focused on the feature learning of the mandibular canal. The experimental results show that the proposed segmentation method achieves good segmentation results, with a Dice score of 85.9% and a 95% Hausdorff distance of 0.5371mm. Compared with other methods, the segmentation method proposed in this paper had a higher accuracy and a faster efficiency, which is expected to play a practical role in dental implants.

Variable Curvature Mirror with Variable Thickness and Its Application in Space-Borne Optical Camera

Variable Curvature Mirror with Variable Thickness and Its Application in Space-Borne Optical Camera

Kinematics Modeling of Soft Manipulator Interacting with Environment Using Segmented Variable Curvature Method

Kinematics Modeling of Soft Manipulator Interacting with Environment Using Segmented Variable Curvature Method

COMPARATIVE ANALYSIS OF PLASTICITY THEORIES UNDER COMPLEX LOADING

Variants of theories of plastic flow under combined hardening, widely used in practical calculations of structures, are considered. A comparative analysis of the variants of theories under complex loading along plane and spatial deformation trajectories is carried out, covering a wide range of trajectories from multi-link polylines to curved trajectories of variable curvature and torsion. Trajectories from medium to large curvature and torsion are considered. The analysis of the research results is carried out in the vector space of A.A. Ilyushin. The plane trajectories of deformations in the form of a square and a curved trajectory of variable curvature in the form of an astroid are considered, as well as the spatial trajectory of deformations of variable curvature and torsion in the form of a helix. The results of calculations are compared with the results of experimental studies on stress response trajectories, scalar and vector properties. Variants of the theories are considered: the isotropic hardening model; the Ishlinski–Prager–Kadashevich–Novozhilov model (linear kinematic hardening + isotropic hardening); a model similar to the Ono–Wang model; the Armstrong-Frederick-Kadashevich model; the Shabosh model with three Armstrong–Frederick–Kadashevich evolutionary equations; the Temis model based on the invariant theory of plasticity; the Cooper model with a three-membered structure the evolutionary equation for kinematic hardening. The material parameters (functions), the closing versions of the theories of plasticity are given. Satisfactory compliance with the experiment for all deformation trajectories is achieved by calculations based on the Shabosh and the Bondar models – the difference between the results of calculations and experiments does not exceed 30% with the best correspondence to the experiment of the Bondar model. It should be noted that the Bondar plasticity model is closed by three parameters of anisotropic hardening and one function of isotropic hardening, and the Shabosh model is closed by six parameters and one function.

New insights on hip bone sexual dimorphism in adolescents and adults using deformation-based geometric morphometrics.

Morphological variation of the human pelvis, and particularly the hip bone, mainly results from both female-specific selective pressure related to the give birth of large-headed newborns, and constraints in both sexes for efficient bipedal locomotion, abdominal stability, and adaptation to climate. Hip bone morphology has thus been extensively investigated using several approaches, although the nuances of inter-individual and sex-related variation are still underappreciated, and the effect of sex on ontogenetic patterns is debated. Here, we employ a landmark-free, deformation-based morphometric approach to explore variation in modern human hip bone shape and size from middle adolescence to adulthood. Virtual surface models of the hip bone were obtained from 147 modern human individuals (70 females and 77 males) including adolescents, and young and mature adults. The 3D meshes were registered by rotation, translation, and uniform scaling prior to analysis in Deformetrica. The orientation and amplitude of deviations of individual specimens relative to a global mean were assessed using Principal Component Analysis, while colour maps and vectors were employed for visualisation purposes. Deformation-based morphometrics is a time-efficient and objective method free of observer-dependent biases that allows accurate shape characterisation of general and more subtle morphological variation. Here, we captured nuanced hip bone morphology revealing ontogenetic trends and sex-based variation in arcuate line curvature, greater sciatic notch shape, pubic body and rami length, acetabular expansion, and height-to-width proportions of the ilium. The observed ontogenetic trends showed a higher degree of bone modelling of the lesser pelvis of adolescent females, while male variation was mainly confined to the greater pelvis.