Concave Parts Research Articles

Concave-Convex Adaptive Rejection Sampling

We describe a method for generating independent samples from univariate density functions using adaptive rejection sampling without the log-concavity requirement. The method makes use of the fact that many functions can be expressed as a sum of concave and convex functions. Using a concave-convex decomposition, we bound the log-density by separately bounding the concave and convex parts using piecewise linear functions. The upper bound can then be used as the proposal distribution in rejection sampling. We demonstrate the applicability of the concave-convex approach on a number of standard distributions and describe an application to the efficient construction of sequential Monte Carlo proposal distributions for inference over genealogical trees. Computer code for the proposed algorithms is available online.

A novel variational model for image segmentation

In this paper, we propose a new variational model for image segmentation. Our model is inspired by the complex Ginzburg–Landau model and the semi-norm defined by us. This new model can detect both the convex and concave parts of images. Moreover, it can also detect non-closed edges as well as quadruple junctions. Compared with other methods, the initialization is completely automatic and the segmented images obtained by using our new model could keep fine structures and edges of the original images very effectively. Finally, numerical results show the effectiveness of our model.

Vehicle detection and classification by measuring and processing magnetic signal

This paper presents novel vehicle detection and classification method by measuring and processing magnetic signal based on single micro-electro-mechanical system (MEMS) magnetic sensor. When a vehicle moves over the ground, it generates a succession of impacts on the earth’s magnetic field, which can be detected by single magnetic sensor. The magnetic signal measured by the magnetic sensor is related to the moving direction and the type of the vehicle. Generally, the recognition rate using single sensor detector is not high. In order to improve the recognition rate, a novel feature extraction algorithm and a novel vehicle classification and recognition algorithm are presented. The concavity and convexity areas, and the angles of concave and convex parts of the waveform are extracted. An improved support vector machine (ISVM) classifier is developed to perform vehicle classification and recognition. The effectiveness of the proposed approach is verified by outdoor experiments.

밀착의형 3차원 파라메트릭 모델을 활용한 상반신 원형의 다트 및 절개분리선 설정에 관한 연구

The purpose of this study was to develop a plausible methodology based on experimental data how to set up darts and split lines on 3D parametric body dressed with tight-fit garment. The results were as following: Through the process of making convex hull, the concave parts were straightened to make a convex hull, especially in the center part of bust, under breast part and scapular part. To figure out the optimum positions of darts and split lines, the inflection points of curve ratio were searched along the horizontal polylines of waist and bust. This procedures produced reliable results with low deviation. Using Rapidform, CATIA and Unigraphics, six patches of bodice patterns were drawn and aligned. Paired t-test results showed the outline and area between 3D surface and 2D were not significantly different, meaning this method could be adaptable when flattening 3D surfaces. The amount of waist dart measured on the pattern showed that the highest portion was allocated on 2nd dart(back), followed by 1st dart(back), 1st dart(front), 2nd dart(front)/side dart, and center back dart. A series of findings suggested that curve ration inflection point could be used as a guide to set up darts and split line on 3D parametric model with low deviation.

PART II (Portable ART analyzer)—development of a XRF spectrometer adapted for the study of artworks in the Kunsthistorisches Museum, Vienna

AbstractA portable focused‐beam X‐ray fluorescence (XRF) spectrometer was designed and manufactured taking into account a huge variation in material, size and shape of museum objects. The spectrometer is equipped with a vacuum chamber enclosed with a Kapton‐window allowing the detection of chemical elements from Na upwards, which enables the characterization of glass and enamel objects. Two low‐power X‐ray tubes, one with a Mo‐anode the other with a Cr‐anode, operating from 4 to 50 kV and 0 to 2.5 mA with a maximum power of 50 W and a point focus of about 180 µm can be used as excitation source alternatively. A polycapillary lens with a spot size of 150 µm is used for focusing the primary beam to access small details of the different objects, e.g. fine brush strokes in paintings. The vacuum chamber can be evacuated to about 1 mbar.A miniature camera is installed inside the chamber for inspecting the analyzed area through the Kapton‐window. Two laser pointers mounted inside the chamber coincide with the focal point of the polycapillary at the investigated spot. The excitation and X‐ray fluorescence radiation paths in air are about 1 mm each, minimizing the absorption losses. The spectrometer was designed to maximize the accessibility to all parts of the investigated objects through the use of translation stages and an innovative design of the detection head, especially the vacuum chamber. This article shows the capability of the spectrometer to reach measuring positions in concave parts of objects and presents the determined detection limits of elements. Copyright © 2009 John Wiley & Sons, Ltd.

Surface impedance modeling of PEC targets: application to shape reconstruction

We consider the inverse electromagnetic scattering problem of retrieving the shape of an inaccessible, perfectly electric conducting target from a set of far field measurements and develop a new reconstruction method in which the unknown scatterer is modeled by means of a surface impedance. The basic idea is to approximate the unknown object through a circular impedance cylinder enclosed in it and equipped with a suitable inhomogeneous surface impedance. By doing so, the ill-posedness and the nonlinearity of the underlying problem are then handled separately, through two successive processing steps. In the first step, the inhomogeneous surface impedance of the auxiliary scatterer is reconstructed through the regularized analytical continuation of the measured far-field data. Then, the unknown shape is retrieved through the solution of a nonlinear optimization problem aimed at determining the spatial locations where the field outside of the impedance target vanishes, in agreement with the boundary condition arising onto the unknown target. As demonstrated with several numerical results, the method is robust against uncertainties on data and provides quite accurate results for targets with starlike boundaries having both convex and concave parts.

Numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer in the wake behind a hill

AbstractThis study presents a three‐dimensional numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer behind a hill mounted in a laminar boundary layer. When the thickness of the velocity boundary layer is comparable to the hill height, a hairpin vortex is formed symmetrically to the center of the spanwise direction in the wake. A secondary vortex is formed between the legs, and horn‐shaped secondary vortices appear under the concave parts of the hairpin vortex. When the boundary layer thickness increases, the legs and horn‐shaped secondary vortices move toward the center of the spanwise direction, and thus heat transport and heat transfer increase there. At this time, high‐turbulence areas generated locally move toward the center of the spanwise direction with an increase in the boundary layer thickness. With a further increase in the boundary layer thickness, steady streamwise vortices are formed downstream of the hill, but the heat transfer decreases. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20261

Virtual Haptic Map Using Force Display Device for Visually Impaired

We propose a new virtual haptic map system using a force display device and a GPS receiver. This system can haptically display the roads, city blocks, and buildings which are automatically constructed from a numerical map given in DXF format and the information on current location and orientation from a GPS receiver. Hence this system will be especially useful for supporting outdoor activities of visually impaired persons. Other features of the system are that the map can be customized easily with respect to various characteristics such as a concave-convex shape of the objects or friction of surfaces in accordance with the user's need and that the position and orientation of the map can be changed automatically in real time. To evaluate the usability of this system, recognition experiments using simple virtual haptic maps were conducted by ten blindfolded subjects. In the experiments, recognition rates were compared between two representation methods. In the first method the area of road is concaved, and in the second method it is convexed. As a result, high recognition rates were confirmed in both methods, and it shows that this system has reasonable usability. Additionally, we found that concaved areas were touched for longer time than convexed areas. This suggests that important information is better to be displayed by concave parts. We have also developed a mobile robot system with our virtual haptic map system which is aimed at navigating a visually impaired person and supporting outdoor activity. A preliminary experiment is shown for the validity of this mobile robot system.

Traffic sign shape classification and localization based on the normalized FFT of the signature of blobs and 2D homographies

The main goal of a traffic sign recognition system is the detection and recognition of every traffic sign present in the scene. Frequently, the image processing system is divided into three parts, namely, segmentation, detection and recognition. In this work, we will focus on the detection block, dividing it into two sub-blocks that perform shape classification and localization of the sign, respectively. The classification of the shape is performed by means of the signature of the connected components. Object rotations are tackled with the use of the FFT, and the normalization of the object eccentricity improves the performance in the presence of projection distortions. The effect of occlusions are lowered removing the concave parts of the shape. Finally, we propose a novel algorithm, which computes a 2D homography, to re-orientate the sign for further steps, like sign recognition. Experimental results, evaluated using a huge set of randomly generated synthetic images are also given, showing a great robustness of the algorithm to object scaling, rotation, projective deformation, partial occlusions and noise.

Improved configuration space sampling: Langevin dynamics with alternative mobility

We present a new and efficient method for determining optimal configurations of a large number (N) of interacting particles. We use a coarse-grained stochastic Langevin equation in the overdamped limit to describe the dynamics of this system and replace the standard mobility by an effective space dependent inverse Hessian correlation matrix. Due to the analogy of the drift term in the Langevin equation and the update scheme in Newton's method, we expect accelerated dynamics or improved convergence in the convex part of the potential energy surface Phi. The stochastic noise term, however, is not only essential for proper thermodynamic sampling but also allows the system to access transition states in the concave parts of Phi. We employ a Broyden-Fletcher-Goldfarb-Shannon method for updating the local mobility matrix. Quantitative analysis for one and two dimensional systems shows that the new method is indeed more efficient than standard methods with constant effective friction. Due to the construction, our effective mobility adapts high values/low friction in configurations which are less optimal and low values/high friction in configurations that are more optimal.

Festigkeitstheorien von anisotropen Stoffen mit sprödem Bruchverhalten

Strength-theories of anisotropic materials with brittle rupture. Part 1: Comparison and adjudication of anisotropic strength-criterions by virtue of theoretical considerations. | The sizing of load-bearing anisotropic structures needs strength-criterion theories. Three of these hypothesises from the last century seem to be generally acceptable, so they are adaptable to all anisotropic materials in optional tensional status. A strength surface (a 6-dimensions hyper surface in the place of the stress-components) meets all theories. If they are tough materials, these surfaces can be only convex. Demonstrable – according the tests: the bunging surfaces with brittle rupture materials can content concave parts, too. The bunging relations can be transformed having one site supplementary potential or rather proportional expressions. In this interpretation the thesises of von Mises and of Tsai-Wu affirm the supplementary potential to bunging is constant and depends not on the orientation. The not reconcilable to this approach consequence is not followed by the Ashkenasitheory affirming the accumulated to the break supplementary potential is not constant, but depends on invariants of the stress state, mediately on orientation. These statements apply first of all to wood and wood-based materials, but can be extended to all anisotropic materials with brittle rupture.

Numerical solution of scattering problems using pseudo‐differential impedance operators

AbstractDirect numerical solutions of scattering problems based on boundary‐integral equations are computationally costly at high frequencies. A numerical method is presented that efficiently computes accurate approximations to unknown surface quantities given known surface data (an approximate Dirichlet‐to‐Neumann map). The method is based on a pseudo‐differential impedance operator (PIO) numerically implemented using rational approximations. An example of a PIO is the so‐called on‐surface radiation condition (OSRC) method. For a convex obstacle, the method can be viewed as applying a parabolic equation directly on the surface of a scatterer. In contrast to past OSRCs, the use of rational approximations provides accuracy for wide scattering angles which is needed for grazing angles of incidence. Generalization to impedance operators for two‐dimensional acoustic scatterers with concave parts is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical solution of high-frequency acoustic scattering problems by integral equations preconditioned using pseudo-differential impedance operators

Exact computations of high-frequency scattering by targets or rough surfaces can be challenging because of the large number of unknowns. A compromise can be obtained, however, using approximate Dirichlet-to-Neumann surface operators that are known in pseudo-differential form and efficiently implemented using rational approximations. These operators can be used as preconditioners to obtain well-conditioned iterative algorithms to solve the Helmholtz integral equation. Using these algorithms, we compute scattering by two- and three-dimensional targets, and rough surfaces with smooth concave or convex parts with incident fields near grazing angles of interest. This case is particularly important for underwater acoustics, where sounds field graze the free surface or bottom in shallow water.

Surface nanostructures orienting self-protection of an orthodontic nickel-titanium shape memory alloys wire

Shape memory alloys (SMA) have been applied to a wide variety of applications in a number of different fields such as aeronautical applications, sensors/actuators, medical sciences as well as orthodontics. It is a hot topic to enhance the anti-corrosion ability of orthodontic wires for clinical applications. In this letter, a very nice fractal structure, micro-domains with identical nanometer sized grooves, was obtained on the surfaces of the orthodontic wires with an oxygen plasma and acid corrosion. The concave parts of the grooves were dominated by titanium and convex parts were the same as the bulk wires. The micro-nano fractal structure generated a hydrophobic surface with the largest contact angle to water being about 157°. The titanium dominated nanolayer and the hydrophobicity of the surface resulted in jointly the great improvement of the anti-corrosion ability of the orthodontic wires. Because the fractal structures of the wires were formed automatically when they immersed in acidic environment, hence, the self-protection of the oxygen plasma-treated orthodontic wires in acidic environment indicates their potential applications in orthodontics, and should be also inspirable for other applications of SMA materials.

Evolutionary branching and long-term coexistence of cycling predators: Critical function analysis

It is well known that two predators with different functional responses can coexist on one prey when the system exhibits nonequilibrium dynamics. In this paper, we investigate under which conditions such coexistence is evolutionarily stable, and whether the two predators may evolve from a single ancestor via evolutionary branching. We assume that predator strategies differ in handling time, and hence in the shape of their Holling type II functional response. Longer handling times are costly in terms of lost foraging time, but allow the predator to extract more nutrients from the prey and therefore to produce more offspring per consumed prey. In the analysis, we apply a new method to accommodate arbitrary trade-off functions between handling time and offspring production. Contrary to previous results obtained assuming a particular trade-off [Kisdi, E. and Liu, S., 2006. J. Evol. Biol. 19, 49–58], we find that evolutionary branching of handling time is possible, although it does not appear to be very likely and can be excluded for a class of trade-offs. Evolutionarily stable coexistence of two predators occurs under less restrictive conditions, which are always satisfied when the trade-off function has two strongly concave parts connected by a convex piece.

Acceleration of apatite nucleation on microrough bioactive titanium for bone‐replacing implants

The viability of a new two-step method for obtaining bioactive microrough titanium surfaces for bone replacing implants has been evaluated. The method consists of (1) Grit blasting on titanium surface to roughen it; and (2) Thermo-chemical treating to obtain a bioactive surface with bone-bonding ability by means of nucleating and growing an apatite layer on the treated surface of the metal. The aim of this work is to evaluate the effect of surface roughness and chemical composition of the grit-blasting particles on the ability of the surfaces of nucleating and growing a homogeneous apatite layer. The determination and kinetics of the nucleation and growing of the apatite layer on the surfaces has mainly been studied with environmental scanning electron microscopy (ESEM) and grazing-incidence X-ray diffractometry. The results show that Al(2)O(3)-blasted and thermochemically-treated titanium surfaces accelerates nucleation of the apatite, whereas SiC-blasted and thermochemically-treated titanium surfaces inhibits apatite nucleation, compared with the well studied polished and thermochemically-treated titanium surfaces. The acceleration of the apatite nucleation on the Al(2)O(3)-blasted microrough titanium surfaces is because concave parts of the microroughness that are obtained during grit blasting provides to the rough and bioactive surfaces with a chemical- and electrostatic-favored situation for apatite nucleation. This consists of a high density of surface negative charges (also assisted by the nanoroughness of the surface obtained after the thermochemical treatment) and an increased concentration of the Ca(2+)-ions of the fluid, which have a limited mobility at the bottom of the concave parts.

Heterosporis anguillarum infections in farm cultured eels (Anguilla japonica) in Korea

Ten eels (Anguilla japonica) from a fish farm in Korea were examined and diagnosed with a Heterosporis infection. The gross lesions on the trunk were uneven and the concave parts were pasty. Histopathologically, lyses of the trunk muscles, degenerative muscle fibers and the scattered spores were observed. The sporophorocyst (SPC) contained several spores with a variety of shapes. Some SPC were disrupted and the spores in the SPC were scattered in the muscle tissues. Macrophages existed near the scattered spores. Electron microscopy revealed special structures such as sporophorocyst containing various developmental parasitic stages such as meronts, sporonts, sporophorous vesicles and spores.

Two-dimensional Minkowski sum optimization of ganged stamping blank layouts for use on pre-cut sheet metal for convex and concave parts

With the increasing number of parts that manufacturers need to place on a piece of material such as sheet metal, the need increases for more sophisticated algorithms for part orientation and spacing. With greater part shape complexity, the ability of a skilled worker is challenged to minimize waste. Building on the previous work of Nye, this paper presents a Minkowski sum method for maximizing the number of parts within gangs on a rectangular sheet of material. The example provided uses a simply shaped part to illustrate the presented method, yielding a packing efficiency of 62% that is identical to the efficiency that a skilled worker would produce without the algorithm. The paper also provides results for laying out a more complex part in ganged sections, demonstrating a result that would be difficult for a human to reproduce. This work extends that of Nye by adding practical constraints such as the number of parts that can be blanked at once as well as the amount of horizontal and vertical spacing between ganged blanking sets. Additionally, the paper adds an algorithm for laying out polygons with concave geometries by separating the part into a set of convex polygons. Two examples for optimization, one of a chevron-shaped part and one of a complex shape previously used by Nye [Nye TJ. Stamping strip layout for optimal raw material utilization. Journal of Manufacturing Systems 2000;19(4):239–46] and Choi et al. [Choi JC, Kim BM, Cho HY, Kim C. A compact and practical CAD system for blanking or piercing of irregular-shaped sheet metal products and stator and rotor parts. International Journal of Machine Tools & Manufacture 1998;38:931–63], are provided, demonstrating the existence of a local maximum number of parts that may be stamped within a single ganged blank. The algorithm is extendable to a program that may provide stamping manufacturers with a tool that can maximize the total number of parts stamped on stock sheet metal, or for other tiling problems.

Complex spherical waves and inverse problems in unbounded domains

This work is motivated by the inverse conductivity problem of identifying an embedded object in an infinite slab. The novelty of our approach is that we use complex spherical waves rather than classical Calderón-type functions. For Calderón-type functions, they grow exponentially on one side of a hyperplane and decay exponentially on the other side. Without extra modifications, they are inadequate for treating inverse problems in unbounded domains such as the infinite slab. The obvious reason for this is that Calderón-type functions are not integrable on hyperplanes. So they cannot be used as measurements on infinite boundaries. For complex spherical waves used here, they blow up faster than any given positive polynomial order on the inner side of the unit sphere and decay to zero faster than any given negative polynomial order on the outer side of the unit sphere. We shall construct these special solutions for the conductivity equation in the unbounded domain by a Carleman estimate. Using complex spherical waves, we can treat the inverse problem of determining the object in the infinite slab like the problem in the bounded domain. Most importantly, we can easily localize the boundary measurement, which is of great value in practice. On the other hand, since the probing fronts are spheres, it is possible to detect some concave parts of the object.

An Anatomic Study of the Triquetrum–Hamate Joint

To investigate the articulating surface of the triquetrum-hamate joint (TqH). The carpal bones of 46 wrist specimens were examined. The shape of the TqH joint surfaces were investigated, with focus on variations in the shape of the hamate and corresponding triquetrum and the presence and position of convex and concave surfaces. Two distinct patterns of hamate TqH articular surfaces were identified, designated type I (31 of 46) and type II (15 of 46). The triquetral TqH articular surface also was found to have 2 distinct patterns, designated type A (18 of 46) and type B (15 of 46). Of the triquetrums examined 13 of 46 had characteristics that were a variable mixture of the 2 identifiable triquetral surface types, but these did not have sufficient similarity to constitute a third triquetrum surface type. The corresponding articulation patterns of these joint surfaces showed a strong trend for a type A triquetrum to articulate with a type I hamate (18 of 46 of all joints) and for a type B triquetrum to articulate with a type II hamate (13 of 46 of all joints). No association was seen between lunate types and type I or type II hamates. These findings suggest the existence of 2 distinct TqH joint patterns, which have been termed TqH-1 and TqH-2. There appears to be a spectrum of variation between these 2 identifiable types. As a result, the TqH is best described as a spectrum, with TqH-1 at one end and TqH-2 at the other. A TqH-1 joint is a helicoidal configuration. It is double-faceted, with the hamate and the triquetrum articular surfaces possessing complementary concave and convex parts. A TqH-2 joint has a predominantly oval convex shape, whereas the primarily concave triquetrum is better described as a dish for the flatter hamate. It has no hamate groove or distal ridge.