Non-uniform Edge Research Articles

5 kV, 9.5 A SiC JBS Diodes with Non-Uniform Guard Ring Edge Termination for High Power Switching Application

4H-SiC Junction Barrier Diodes (JBS) diodes were designed, fabricated and tested. The JBS diodes based on a 45μm thick, 1.4×1015cm-3 doped drift layer with multiple non-uniform spacing guard ring edge termination showed a blocking voltage of over 5kV. The 5kV JBS diode has a forward current density of 108A/cm2 at 3.5V and a specific on resistance (RSP_ON) of 25.2mW·cm2, which is very close to the theoretical RSP_ON of 23.3mΩ·cm2. DC I-V measurement of packaged JBS diodes showed a forward current of 100A at a voltage drop of 4.3V. A half-bridge inverter with a bus voltage up to 2.5kV was used to characterize the high power switching performance of SiC JBS diodes. A large inductance load of 1mH was used to simulate the load of a high power AC induction motor. Compared to a Si PIN diode module, the SiC JBS package reduces diode turn-off energy loss by 30% and Si IGBT turn-on energy loss by 21% at room temperature.

Combination Resonance Instability of Curved Panels with Cutout Subjected to Nonuniform Loading with Damping

The dynamic instability of doubly curved panels with a centrally located circular cutout, subjected to nonuniform compressive in-plane harmonic edge loading is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to single (mode) resonances in parametrically excited doubly curved panels with a central circular cutout. The method of multiple scales is used to obtain analytical expressions for the single (mode) and combination resonance instability regions. It is shown that other cases of the combination resonance can be of major importance and yield a significantly enlarged instability region in comparison to the principal instability region. The effects of nonuniform edge loading, centrally located circular cutout, damping, the static, and dynamic load factors on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as single (mode) resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which doubly curved panels cannot become dynamically unstable. A central circular cutout has the destabilizing effect on the dynamic stability behavior of doubly curved panels subjected to nonuniform edge loading. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

Exploration of complex multilayer film growth morphologies: STM analysis and predictive atomistic modeling for Ag on Ag(111)

Scanning tunneling microscopy studies are integrated with development of a realistic atomistic model to both characterize and elucidate the complex mounded morphologies formed by deposition of Ag on Ag(111) at 150 and $180\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Threefold symmetric lateral shapes of islands and mounds are shown to reflect the influence of a nonuniform step edge barrier inhibiting interlayer transport. Modeling of structure at the mound peaks leads to a sensitive estimate of the magnitude of this large barrier.

Modular decomposition of metabolic reaction networks based on flux analysis and pathway projection

The rational decomposition of biochemical networks into sub-structures has emerged as a useful approach to study the design of these complex systems. A biochemical network is characterized by an inhomogeneous connectivity distribution, which gives rise to several organizational features, including modularity. To what extent the connectivity-based modules reflect the functional organization of the network remains to be further explored. In this work, we examine the influence of physiological perturbations on the modular organization of cellular metabolism. Modules were characterized for two model systems, liver and adipocyte primary metabolism, by applying an algorithm for top-down partition of directed graphs with non-uniform edge weights. The weights were set by the engagement of the corresponding reactions as expressed by the flux distribution. For the base case of the fasted rat liver, three modules were found, carrying out the following biochemical transformations: ketone body production, glucose synthesis and transamination. This basic organization was further modified when different flux distributions were applied that describe the liver's metabolic response to whole body inflammation. For the fully mature adipocyte, only a single module was observed, integrating all of the major pathways needed for lipid storage. Weaker levels of integration between the pathways were found for the early stages of adipocyte differentiation. Our results underscore the inhomogeneous distribution of both connectivity and connection strengths, and suggest that global activity data such as the flux distribution can be used to study the organizational flexibility of cellular metabolism. Supplementary data are available at Bioinformatics online.

Cooling and crystallization of fusion cake on a belt former in production of coagulant for water purification

A mathematical model and the method of calculation using a computer of cooling and crystallization of the fusion cake on the belt former is developed by the example of production of water-purifying coagulant. A flat layer of the fusion cake is cooled, and its layer-by-layer crystallization proceeds on both sides. The algorithm of calculation with the use of grid method with a variable nonuniform grid and edge conditions and movable internal boundary conditions is developed.

Dynamic combination resonance characteristics of doubly curved panels subjected to non-uniform tensile edge loading with damping

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading <TEX>$P(t)=P_s+P_d\;{\cos}{\Omega}t$</TEX> is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at <TEX>${\Omega}={\omega}_m+{\omega}_n$</TEX>, (<TEX>${\Omega}$</TEX> is the excitation frequency and <TEX>${\omega}_m$</TEX> and <TEX>${\omega}_n$</TEX> are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at <TEX>${\Omega}=2{\omega}_1$</TEX>, where <TEX>${\omega}_1$</TEX> is the fundamental frequency, other cases of <TEX>${\Omega}={\omega}_m+{\omega}_n$</TEX>, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

Parametric combination resonance instability characteristics of laminated composite curved panels with circular cutout subjected to non-uniform loading with damping

The dynamic instability of laminated composite doubly curved panels with centrally located circular cutout, subjected to non-uniform compressive in-plane harmonic edge loading is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited antisymmetric angle-ply and symmetric cross-ply laminated composite doubly curved panels with central circular cutout. The method of multiple scales is used to obtain analytical expressions for the simple and combination resonance instability regions. It is shown that other cases of the combination resonance can be of major importance and yield a significantly enlarged instability region in comparison to the principal instability region. The effects of non-uniform edge loading, centrally located circular cutout, damping, number of layers, orthotropy, the static load factor and the width-to-thickness ratio on dynamic instability behavior of simply supported laminated composite doubly curved panels are studied. The results show that under localized edge loading, combination resonance instability zones are as important as simple resonance instability zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which doubly curved panels cannot become dynamically unstable. A central circular cutout has the destabilizing effect on the dynamic stability behavior of laminated composite doubly curved panels subjected to non-uniform edge loading. This example of simultaneous excitation of two modes, each oscillating steadily as its own natural frequency, may be of considerable interest in vibration testing of actual structures.

Stability analysis of simply-supported rectangular plates under non-uniform uniaxial compression using rigorous and approximate plane stress solutions

The non-classical problem of buckling of a simply-supported rectangular plate due to various types of non-uniform compressive edge loads is analysed here. For each case, the elasticity solution for the internal in-plane stress field is obtained rigorously using a superposition of Airy's stress functions and also approximately using extended Kantorovich method. Subsequently, the convergent buckling loads are obtained using Galerkin's method. Results are presented to highlight the dependence of the total buckling load and the corresponding buckled shape on the edge load distribution, as well as to illustrate the applicability of the approximate plane stress solutions.

Dynamic analysis of parametrically excited laminated composite curved panels under non-uniform edge loading with damping

The present work deals with the problem of the occurrence of combination resonances in parametrically excited simply supported laminated composite doubly curved panels under non-uniform edge loading. The first-order shear deformation theory is used to model the panels, considering the effects of transverse shear deformation and rotary inertia. Finite element technique is applied for obtaining the non-uniform stress distribution within the curved panels. The method of multiple scale is used to derive the analytical expressions for the instability regions. It is shown that, besides the principal instability region at Ω = 2 ω 1, other cases of Ω = ω m + ω n , related to other modes, can be of major importance and yield a significantly enlarged instability regions. The effects of non-uniform loading, damping, number of layers, orthotropy, thickness and the static load factor on the dynamic instability behavior of the simply supported laminated composite curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is finite critical value of dynamic load factor for each instability region below which the curved panels cannot become unstable.

Responses of a Looming-Sensitive Neuron to Compound and Paired Object Approaches

The lobula giant movement detector (LGMD) and its target neuron, the descending contralateral movement detector (DCMD), constitute a motion-sensitive pathway in the locust visual system that responds preferentially to objects approaching on a collision course. LGMD receptive field properties, anisotropic distribution of local retinotopic inputs across the visual field, and localized habituation to repeated stimuli suggest that this pathway should be sensitive to approaches of individual objects within a complex visual scene. We presented locusts with compound looming objects while recording from the DCMD to test the effects of nonuniform edge expansion on looming responses. We also presented paired objects approaching from different regions of the visual field at nonoverlapping, closely timed and simultaneous approach intervals to study DCMD responses to multiple looming stimuli. We found that looming compound objects evoked characteristic responses in the DCMD and that the time of peak firing was consistent with predicted values based on a weighted ratio of the half size of each distinct object edge and the absolute approach velocity. We also found that the azimuthal position and interval of paired approaches affected DCMD firing properties and that DCMDs responded to individual objects approaching within 106 ms of each other. Moreover, comparisons between individual and paired approaches revealed that overlapping approaches are processed in a strongly sublinear manner. These findings are consistent with biophysical mechanisms that produce nonlinear integration of excitatory and feed-forward inhibitory inputs onto the LGMD that have been shown to underlie responses to looming stimuli.

Failure surfaces for brittle honeycombs with Plateau borders under in-plane biaxial loads

Brittle honeycombs without any macrocrack under in-plane biaxial loads fail by elastic buckling and brittle rupturing of cell edges. The failure surfaces of brittle honeycombs with non-uniform thickness cell edges are affected by the cell-edge modulus of rupture and the distribution of solid between three cell edges and a vertex. In the paper, the non-uniform cross-section of cell edges is taken to be a Plateau border. Meanwhile, the variability of cell-edge modulus of rupture is taken into account by assuming that it follows a Weibull distribution. As a result of those, the failure surfaces of brittle honeycombs with Plateau borders caused by elastic buckling and brittle rupturing for a prescribed survival probability can be generated. The effects of the solid distribution in cell edges, the Weibull modulus and the prescribed survival probability on the failure surfaces of brittle honeycombs are also evaluated.

VIBRATION AND STABILITY BEHAVIOR OF LAMINATED COMPOSITE CURVED PANELS WITH CUTOUT UNDER PARTIAL IN-PLANE LOADS

The present paper is concerned with the vibration, buckling and dynamic instability behavior of laminated composite, cross-ply, doubly-curved panels with a central circular hole subjected to in-plane static and periodic compressive loads. A generalized shear deformable Sanders' theory is used to model the curved panels, considering the effects of transverse shear deformation and rotary inertia. Bolotin's approach is used for studying the dynamic instability regions of doubly-curved panels. The effects of non-uniform edge loads, curvature with different cutout ratios, static and dynamic load factors, and lamination parameters on curved panels are investigated with the results discussed.

Elastic buckling of regular hexagonal honeycombs with plateau borders under biaxial compression

The elastic buckling of regular hexagonal honeycombs with non-uniform thickness cell edges under biaxial compression is numerically analyzed and presented here. A multi-cell honeycomb structure with appropriate periodic boundary conditions was proposed and employed to calculate the biaxial buckling strengths of regular hexagonal honeycombs with plateau borders using finite element analysis. The effects of solid distribution in cell edges on the biaxial buckling strengths of regular hexagonal honeycombs are evaluated and discussed. Numerical FEA results indicate that the biaxial elastic buckling strengths of regular hexagonal honeycombs depend on their relative density, the solid distribution in cell edges and biaxial stress state. Also, the failure surfaces caused by elastic buckling and plastic yielding for regular hexagonal honeycombs under biaxial compression are developed.

The relationship between wafer surface pressure and wafer backside loading in Chemical Mechanical Polishing

To have a good carrier head design, it is important to understand the relationship between wafer surface pressure distribution and wafer backside loading by the carrier head. A theoretical study based on a simplified Chemical Mechanical Polishing (CMP) system is presented in this paper. It shows that, to have a uniform pressure distribution, wafer backside pressure will not be uniform and, theoretically, it is impossible to achieve such loading. It also points out that, contradicting to common understanding, uniform backside pressure will lead to nonuniform wafer surface pressure and edge effect. The presented theory may be used as a tool for further optimization of carrier head design and a base for more realistic modeling on specific tool designs.

Tension buckling and parametric instability characteristics of doubly curved panels with circular cutout subjected to nonuniform tensile edge loading

This paper deals with the study of tensile buckling, vibration, and parametric instability behaviour of doubly curved panels with central circular cutout subjected to uniaxial in-plane partially distributed tensile edge loadings using finite element method. First order shear deformation theory is used to model the curved panels, to consider the effects of the transverse shear deformation and rotary inertia. The vibration analysis for this problem shows that for certain parameters of the tensile loading, the frequencies of the panel initially rise with the load, but begin to decrease with increasing tension, showing the onset of tension buckling. The parametric instability behaviour under tensile periodic edge loading with different load parameters shows that instability regions are influenced by the cutout size, load width and its location.

Creep of hexagonal honeycombs with Plateau borders

The creep of hexagonal honeycombs with non-uniform thickness cell edges is analyzed and presented here. In the paper, the non-uniform cross-section of cell edges is taken to be a Plateau border and the solid making up the cell edges of hexagonal honeycombs is assumed to obey power law creep. A repeating element, composed of three cell edges connected at a vertex with Plateau borders of constant radius and width, is employed to calculate the creep strain rate of hexagonal honeycombs. Analytical results indicate that the creep strain rate of hexagonal honeycombs depends on their relative density and cell geometry, the imposed stress and the creep parameters of solid cell edges. Effects of the solid distribution in cell edges and the creep parameters of solid cell edges on the creep strain rate of hexagonal honeycombs are evaluated. In addition, the microstructure coefficient and exponent constant in the theoretical expression for describing the creep strain rate of regular hexagonal honeycombs are modified to account for the effect of solid distribution in cell edges.

Numerical analysis of the stiffness and strength of regular hexagonal honeycombs with plateau borders

Numerical analysis for the stiffness and strength of regular hexagonal honeycombs with non-uniform thickness cell edges is presented here. The non-uniform cross-section of cell edges is taken to be a Plateau border. Then, the effects of solid distribution in cell edges on the stiffness and strength of regular hexagonal honeycombs are numerically investigated using finite element analysis. Results indicate that the stiffness and strength of regular hexagonal honeycombs are affected significantly by the solid distribution in cell edges, consistent with the findings of existing variable-thickness cell-edge models. However, it is also found that the difference between existing theoretical models and finite element analysis results becomes larger when the relative density of regular hexagonal honeycombs and the solid distribution in cell edges are increased.

A note on the greedy algorithm for the unsplittable flow problem

In a recent paper Chekuri and Khanna improved the analysis of the greedy algorithm for the edge disjoint paths problem and proved the same bounds also for the related uniform capacity unsplittable flow problem. Here we show that their ideas can be used to get the same approximation ratio even for the more general Unsplittable Flow Problem with nonuniform edge capacities.

Dynamic instability of stiffened plates subjected to non-uniform harmonic in-plane edge loading

The dynamic instability characteristics of stiffened plates subjected to in-plane partial and concentrated edge loadings are studied using finite element analysis. In the structural modelling, the plate and the stiffeners are treated as separate elements where the compatibility between these two types of elements is maintained. The method of Hill's infinite determinants is applied to determine the dynamic instability regions. Numerical results are presented to study the effects of various parameters, such as static load factor, aspect ratio, boundary conditions, stiffening scheme and load parameters on the principal instability regions of stiffened plates using Bolotin's method. The results show that location, size and number of stiffeners have a significant effect on the location of the boundaries of the principal instability region.

Parametric resonance of plates in a sheet metal coating process

The vibration of sheet metal during zinc coating processes can lead to non-uniform coating thickness and overall poor product quality. This vibration develops from two principal mechanisms, namely, the run-out associated with the supporting rollers and/or bearings, and the time-varying tension associated with the manufacturing process. This study focuses on the second of these mechanisms (time-varying tension) that becomes significant under conditions leading to parametric resonance. The parametric resonance of the sheet metal is captured in a proposed model of a plate subject to time-varying and non-uniform edge tension. The model accounts for these effects as well as the non-linear stretching of the plate mid-plane as a result of transverse plate vibration. The linear vibration characteristics of the plate are studied first and are then used in deriving a single mode approximation of the non-linear, parametrically excited plate model. A perturbation solution of this model reveals the major parameters that influence parametric resonance in this application. Theoretical results for plate vibration are compared to experimental measurements of sheet metal vibration in a production facility. This comparison demonstrates that the model accurately captures the physical mechanisms responsible for sheet metal vibration and therefore, the physical parameters (such as damping) have the greatest impact on this vibration.