Static Edge Research Articles

Static/Dynamic Edge Movability Effect on Non-Linear Aerothermoelastic Behavior of Geometrically Imperfect Curved Skin Panel: Flutter and Post-Flutter Analysis

This paper addresses the problem of the aerothermoelastic modeling behavior and analyses of skin curved panels with static and dynamic edge movability effect in high supersonic flow. Flutter and post-flutter behavior will be analyzed toward determining under which conditions such panels will exhibit a benign instability, that is a stable limit cycle oscillation, or a catastrophic instability, that is an unstable LCO. The aerothermoelastic governing equations are developed from the geometrically non-linear theory of infinitely long two dimensional curved panels. Von Kármán non-linear strain-displacement relation in conjunction with the Kirchhoff plate-hypothesis is adopted. A geometrically imperfect curved panel forced by a supersonic/hypersonic unsteady flow is numerically investigated using Galerkin approach. These equations are based on the third-order piston theory aerodynamic for modeling the flow-induced forces. Furthermore, the effects of thermal degradation and Kelvin’s model of structural damping independent of time and temperature are also considered in this model. Computational analysis and discussion of the finding along with pertinent conclusions are presented.

Ripple edge engineering of graphene nanoribbons

It is now possible to produce graphene nanoribbons (GNRs) with atomically defined widths. GNRs offer many opportunities for electronic devices and composites, if it is possible to establish the link between edge structure and functionalization, and resultant GNR properties. Switching hydrogen edge termination to larger more complex functional groups such as hydroxyls or thiols induces strain at the ribbon edge. However, we show that this strain is then relieved via the formation of static out-of-plane ripples. The resultant ribbons have a significantly reduced Young's modulus, which varies as a function of ribbon width, modified band gaps as well as heterogeneous chemical reactivity along the edge. Rather than being the exception, such static edge ripples are likely on the majority of functionalized graphene ribbon edges.

Efficient Energy-Optimal Routing for Electric Vehicles

Traditionally routing has focused on finding shortest paths in networks with positive, static edge costs representing the distance between two nodes. Energy-optimal routing for electric vehicles creates novel algorithmic challenges, as simply understanding edge costs as energy values and applying standard algorithms does not work. First, edge costs can be negative due to recuperation, excluding Dijkstra-like algorithms. Second, edge costs may depend on parameters such as vehicle weight only known at query time, ruling out existing preprocessing techniques. Third, considering battery capacity limitations implies that the cost of a path is no longer just the sum of its edge costs. This paper shows how these challenges can be met within the framework of A* search. We show how the specific domain gives rise to a consistent heuristic function yielding an O(n2) routing algorithm. Moreover, we show how battery constraints can be treated by dynamically adapting edge costs and hence can be handled in the same way as parameters given at query time, without increasing run-time complexity. Experimental results with real road networks and vehicle data demonstrate the advantages of our solution.

α-cluster structure and density waves in oblate nuclei

Pentagon and triangle shapes in Si-28 and C-12 are discussed in relation with nuclear density wave. In the antisymmetrized molecular dynamics calculations, the $K^\pi=5^-$ band in Si-28 and the $K^\pi=3^-$ band in C-12 are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the $K^\pi=0^+$ ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7alpha and 3alpha cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density wave at the edge of the oblate states. In analysis with ideal alpha cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density wave for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density wave. The density wave is enhanced in the Z=N nuclei due to the proton-neutron coherent density waves, while it is suppressed in Z\ne N nuclei.

Weber-Fechner type nonlinear behavior in zigzag edge graphene nanoribbons

Using a continuum Dirac theory, we study the density and spin response of zigzag edge terminated graphene ribbons subjected to edge potentials and Zeeman fields. Our analytical calculations of the density and spin responses of the closed system (fixed particle number) to the static edge fields, show a highly nonlinear Weber-Fechner type behavior where the response depends logarithmically on the edge potential. The dependence of the response on the size of the system (e.g. width of a nanoribbon) is also uncovered. Zigzag edge graphene nanoribbons, therefore, provide a realization of response of organs such as the eye and ear that obey Weber-Fechner law. We validate our analytical results with tight binding calculations. These results are crucial in understanding important effects of electron-electron interactions in graphene nanoribbons such as edge magnetism etc., and also suggest possibilities for device applications of graphene nanoribbons.

Simulation of a tangential soft x-ray imaging system

Tangentially viewing soft x-ray (SXR) cameras are capable of detecting nonaxisymmetric plasma structures in magnetically confined plasmas. They are particularly useful for studying stationary perturbations or phenomenon that occur on a timescale faster than the plasma rotation period. Tangential SXR camera diagnostics are planned for the DIII-D and NSTX tokamaks to elucidate the static edge magnetic structure during the application of 3D perturbations. To support the design of the proposed diagnostics, a synthetic diagnostic model was developed using the CHIANTI database to estimate the SXR emission. The model is shown to be in good agreement with the measurements from an existing tangential SXR camera diagnostic on NSTX.

Providing survivability against jamming attack for multi-radio multi-channel wireless mesh networks

Built upon a shared wireless medium, wireless mesh network is particularly vulnerable to jamming attacks. The ability to recover from attacks and maintain an acceptable level of service degradation is a crucial aspect in the design of a wireless mesh network. To address this issue, this paper investigates the network restoration solutions via the joint design of traffic rerouting, channel re-assignment, and scheduling over a multi-radio multi-channel wireless mesh network. Efficient routing and channel assignment schemes can relieve the interference caused by both the normal network nodes and the jamming nodes. Therefore, based on the necessary conditions of schedulability, we first formulate the optimal network restoration problem as linear programming problem, which gives an upper bound on the achievable network throughput. After we solve the LP problems, we have a set of flows assigned to edges that have been assigned to different channels. And based on the LP solutions, we provide a greedy scheduling algorithm using dynamic channel assignment, which schedules both the network traffic and the jamming traffic. And we further provide a greedy static edge channel assignment algorithm, where a channel is assigned to an edge at the beginning and will remain fixed over all time slots. In particular, we consider two strategies, namely global restoration and local restoration, which can support a range of tradeoffs between the restoration latency and network throughput after restoration. To quantitatively evaluate the impact of jamming attacks during and after restoration, we define two performance degradation indices, transient disruption index ( TDI) and throughput degradation index ( THI). Finally, extensive performance evaluations are performed to study the impact of various jamming scenarios in an example wireless mesh network.

Responses to Lightness Variations in Early Human Visual Cortex

Lightness is the apparent reflectance of a surface, and it depends not only on the actual luminance of the surface but also on the context in which the surface is viewed [1-10]. The cortical mechanisms of lightness processing are largely unknown, and the role of early cortical areas is still a matter of debate [11-17]. We studied the cortical responses to lightness variations in early stages of the human visual system with functional magnetic resonance imaging (fMRI) while observers were performing a demanding fixation task. The set of dynamically presented visual stimuli included the rectangular version of the classic Craik-O'Brien stimulus [3, 18, 19] and a variant that led to a weaker lightness effect, as well as a pattern with actual luminance variations. We found that the cortical activity in retinotopic areas, including the primary visual cortex (V1), is correlated with context-dependent lightness variations.

The velocity of acoustic phonons in crystals with edge dislocations and point impurities

The velocity of longitudinal long-wave phonons in crystals with a small number of randomly distributed static edge dislocations was shown to be the same as in ideal crystals. The correction to the velocity of phonons is determined by their interaction with the field of lattice deformations caused by the presence of dislocations. The field of deformations of dislocation displacements is long-range. In addition, these deformations experience sign reversal when the sign of the coordinate perpendicular to the dislocation line and Burgers vector changes. It follows that a crystal contracts or expands in this direction because of the interaction of phonons with dislocations as the defect deformation sign alters. Such an anisotropic volume (and density) change over the whole crystal should however be balanced somehow. For this reason, the density of samples with edge dislocations should remain constant, and the correction δc to the velocity of phonons should be zero. The procedure for averaging that gives δc = 0 is based on the independence of this macro value from the orientation of phonon momemtum incident on randomly distributed dislocations, the unaveraged correction being a diverging value because of the long-range character of the field of defect deformations. For comparison, the correction to the velocity of phonons in crystals with point impurities was calculated. Lattice deformation caused by such defects is isotropic. For this reason, the mean density of crystals with point impurities and the velocity of phonons in them are different from those in ideal crystals. All calculations were performed using the Dyson equation derived on the basis of the Keldysh diagram technique.

Near-Field and Plane-Wave Electromagnetic Coupling into a Slotted Circular Cylinder: Hard or TE Polarization

An analytically tractable model is proposed in this initial study of the electromagnetic phenomena that control our ability to synthesize, by using a near-field source, the effect of plane-wave coupling through an aperture into the interior of a vehicle under test. An integral equation for the tangential electric field in the slot aperture of a perfectly conducting, infinitesimally thin-walled circular cylinder is solved using a basis set of Chebyshev polynomials that are properly weighted according to the static edge condition. The resulting matrix elements from a Galerkin procedure are computed to high precision upon extracting the logarithmic singularity of the kernel of the integral operator. Exact expressions for the matrix elements, in the form of rapidly convergent series of elementary terms, are constructed by isolating another logarithmic function of the aperture width. A minimization of the mean-square error between the true plane-wave response and that due to a near-field line-source establishes the optimal complex source strength of the near-field source

Dynamic responses of Reissner–Mindlin plates with free edges resting on tensionless elastic foundations

Dynamic response analysis is presented for a Reissner–Mindlin plate with four free edges resting on a tensionless elastic foundation of the Winkler-type and Pasternak-type. The mechanical loads consist of transverse partially distributed impulsive loads and in-plane static edge loads while the temperature field is assumed to exhibit a linear variation through the thickness of the plate. The material properties are assumed to be independent of temperature. The two cases of initially compressed plates and of initially heated plates are considered. The formulations are based on Reissner–Mindlin first-order shear deformation plate theory and include the plate–foundation interaction and thermal effects. A set of admissible functions is developed for the dynamic response analysis of moderately thick plates with four free edges. The Galerkin method, the Gauss–Legendre quadrature procedure and the Runge–Kutta technique are employed in conjunction with this set of admissible functions to determine the deflection-time and bending moment–time curves, as well as shape mode curves. An iterative scheme is developed to obtain numerical results without using any assumption on the shape of the contact region. The numerical illustrations concern moderately thick plates with four free edges resting on tensionless elastic foundations of the Winkler-type and Pasternak-type, from which results for conventional elastic foundations are obtained as comparators. The results confirm that the plate will have stronger dynamic behavior than its counterpart when it is supported by a tensionless elastic foundation.

Random regular graphs with edge faults: Expansion through cores

Let G be a given graph (modelling a communication network) which we assume suffers from static edge faults: That is we let each edge of G be present independently with probability p (or absent with fault probability f = 1−p ). In particular, we are interested in robustness results for the case that the graph G itself is a random member of the class of all regular graphs with given degree d. Here we deal with expansion properties of faulty random regular graphs and show: For fixed d⩾42 and p = κ/d, κ⩾20 , a random regular graph with fault probability f = 1−p contains a linear-size subgraph which is an expander almost surely. This subgraph can be found by a simple linear-time algorithm.

The giant component threshold for random regular graphs with edge faults H. Prodinger

Let G be a given graph (modelling a communication network) which we assume suffers from static edge faults: That is we let each edge of G be present independently with probability p (or absent with fault probabilityf=1−p). In particular, we are interested in robustness results for the case that the graph G itself is a random member of the class of all regular graphs with given degree. Our result is: If the degree d is fixed then p=1/(d−1) is a threshold probability for the existence of a linear-sized component in a faulty version of almost all random regular graphs. We show: If each edge of an arbitrary graph G with maximum degree bounded above by d is present with probability p=λ/(d−1) where λ<1 is fixed then the faulted version of G has only components whose size is at most logarithmic in the number of nodes with high probability. If on the other hand, G is a random regular graph with degree d and p=λ/(d−1) where λ>1 then for almost all G the faulted version of G has a linear size component with high probability. Note that these results imply some kind of optimality of random regular graphs among the class of graphs with the same degree bound. The theme is: Use the known expansion properties of almost all random regular graphs to obtain strong robustness results. This has not been done systematically before.

Effects of seawater absorption on fatigue crack development in carbon/epoxy EDT specimens

Fatigue and static edge delamination tests were performed on [45/0/–45/90] s CFRP laminates. Both dry and seawater presoaked specimens were tested to examine any effect moisture absorption has on fatigue crack development, which was monitored by optical microscopy, scanning electron microscopy and ultrasonic C-scan. Seawater absorption changed the dominant edge-cracking mode from the -45/90 interlaminar delamination in unaged specimens to intralaminar cracking in 90° plies in aged (seawater saturated) specimens. The edge-crack growth rates in both unaged and aged specimens, however, are similar. The effect of moisture absorption on strain energy release rate has been examined, and the change in dominant edge-cracking mode and edge-crack growth have been discussed in terms of strain energy release rate.

Dynamic contact problem for an absolutely rigid plate joined to a rigid slab on an elastic half space

The dynamic contact problem is solved by a method based on use of static determination of the stresses beneath a plate and additional slab. The static mixed edge problem is reduced to the solution of integral equations, and then to determination of the normal stresses on the contact boundary. A sample calculation confirms the effectiveness of reducting vibration by joining slabs to the basic foundation.

Mixed cells in directional solidification of In-doped GaAs; cellular profile and shape-induced stresses

By revealing the built-in rotation striations in In-doped GaAs grown by the Czochralski technique, X-ray topography enables one to follow the time evolution of the solid-liquid interface. The birth, amplification and lateral spreading of morphological instability and the dynamics of formation of the cellular pattern are analysed. Mixed cells, composed of {111} facets linked together by rough parts, are observed to form and continuously increase in size through facet expansion. Besides, critical information on shape-induced stresses and defects is for the first time obtained. Indeed, additional contrast lines show up close to the facet edges, which can be attributed to peaks in the stress field, induced by the very peculiar profile of the rough regions adjacent to the facets. It follows from the observation of cell eliminations that the contrast lines actually separate these rough regions in two parts: one like the classical equilibrium one, i.e. probably as 3/2, with x the distance from the static facet edge, and one created by the dynamical roughening of the facet, whose edges thus recede from their equilibrium positions.

Quantifying edge effect and patch size for multiple-use silviculture — a discussion paper

An argument is presented that the essential difference between even-aged and uneven-aged silviculture lies in the proportion of the patch that is influenced by edge effect. These edge effects may extend well beyond the normally accepted boundary between even-aged and uneven-aged stands. Examples are presented to show that there is not one static edge effect but many dynamic edge effects and that the differences between even-aged and uneven-aged stands are represented by a continuum rather than there being a distinct division between them. In the continuing debate on appropriate forest management practices, the differences between even-aged and uneven-aged silviculture have been oversimplified and are often represented in their extremes. In this paper it is argued that research to quantify the magnitude and the extent of these edge effects is necessary to provide the essential data to design patch sizes to meet specific multiple-use management objectives. The integration of these data would provide the basis for objective trade-offs between various forest values and for the objective evaluation of the long-term impact of different silvicultural practices.

Monocular depth perception from optical flow by space time signal processing

A theory of monocular depth determination is presented. The effect of finite temporal resolution is incorporated by generalizing the Marr-Hildreth edge detected operator —∇ 2 G(r) where ∇ 2 is the Laplacian and G(r) is a two dimensional Gaussian. The constraint that the edge detection operator in space-time should produce zero-crossings at the same place in different channels, i. e. at different resolutions of the Gaussian, led to the conclusion that the Marr-Hildreth operator should be replaced by -□ 2 G(r, t) where □ 2 is the d’Alembertian ∇ 2 -(1/ u 2 ) (∂ 2 /∂ t 2 ) and G(r, t) is a Gaussian in space-time. To ensure that the locations of the zerocrossings are independent o the channel width, G(r, t) has to be isotropic in the sense that the velocity u appearing in the defintion of the d’Alembertian must also be used to relate the scales of length and time in G . However, the new operatior -□ 2 G(r, t) produces two types of zero-crossing for each isolated edge feature in the image I(r, t) . One of these, termed the 'static edge’, corresponds to the position of the image edge at time t as defined by ∇ 2 I(r, t) = 0; the other, called a ‘depth zero’, depends only on the relative motion of the observer and object and is usually found only in the periphery of the field of view. When an edge feature is itself in the periphery of the visual field and these zeros coincide, there is an additional cross-over effect. It is shown how these zero-crossings may be used to infer the depth of an object when the observer and object are in relative motion. If an edge feature is near the centre of the image (i. e. near the focus of expansion), the spatial and temporal slopes of the zeros crossing at the static edge may be used to infer the depth, but, if the edge feature is in the periphery of the image, the cross-over effect enables the depth to be obtained immediately. While the former utilizes sharp spatial and temporal resolution to give detailed three-dimensional information, the cross-over effect relies on longer integration times to give a direct measure of the time-to-contact. We propose that both mechanisms could be used to extract depth information in computer vision systems and speculate on how our theory could be used to model depth perception in early visual processing in humans where there is evidence of both monocular perception of the environment in depth and of looming detection in the periphery of the field of view. In addition it is shown how a number of previous models are included in our theory, in particular the directional sensor proposed by Marr &amp; Ullman and a method of depth determination proposed by Prazdny.

Monocular depth perception from optical flow by space time signal processing.

A theory of monocular depth determination is presented. The effect of finite temporal resolution is incorporated by generalizing the Marr–Hildreth edge detected operator –∇ 2 G ( r ) where ∇ 2 is the Laplacian and G ( r ) is a two-dimensional Gaussian. The constraint that the edge detection operator in space–time should produce zero-crossings at the same place in different channels, i. e. at different resolutions of the Gaussian, led to the conclusion that the Marr–Hildreth operator should be replaced by – □ 2 G ( r , t ) where □ 2 is the d’Alembertian ∇ 2 – (1/ u 2 )(∂ 2 /∂ t 2 ) and G ( r , t ) is a Gaussian in space–time. To ensure that the locations of the zero-crossings are independent of the channel width, G ( r , t ) has to be isotropic in the sense that the velocity u appearing in the defintion of the d’Alembertian must also be used to relate the scales of length and time in G . However, the new operatior –□ 2 G ( r , t ) produces two types of zero-crossing for each isolated edge feature in the image I ( r , t ). One of these, termed the ‘static edge’, corresponds to the position of the image edge at time t as defined by ∇ 2 I ( r , t ) = 0; the other, called a ‘depth zero’, depends only on the relative motion of the observer and object and is usually found only in the periphery of the field of view. When an edge feature is itself in the periphery of the visual field and these zeros coincide, there is an additional cross-over effect. It is shown how these zero-crossings may be used to infer the depth of an object when the observer and object are in relative motion. If an edge feature is near the centre of the image (i. e. near the focus of expansion), the spatial and temporal slopes of the zeros crossing at the static edge may be used to infer the depth, but, if the edge feature is in the periphery of the image, the cross-over effect enables the depth to be obtained immediately. While the former utilizes sharp spatial and temporal resolution to give detailed three-dimensional information, the cross-over effect relies on longer integration times to give a direct measure of the time-to-contact. We propose that both mechanisms could be used to extract depth information in computer vision systems and speculate on how our theory could be used to model depth perception in early visual processing in humans where there is evidence of both monocular perception of the environment in depth and of looming detection in the periphery of the field of view. In addition it is shown how a number of previous models are included in our theory, in particular the directional sensor proposed by Marr &amp; Ullman and a method of depth determination proposed by Prazdny.

Detection of moving edges

A technique requiring only two frames is presented for finding time-varying edges in a dynamic scene. The frames need not be contiguous. The proposed operator picks up moving edge points which are not easily detected with simple static edge operators. The operator includes both change and edge detection in a way that improves overall performance. Also presented are arguments against the use of three-dimensional operators for scenes where the third dimension is temporal rather than spatial.