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Graphs are commonly gridded by triangulation; i.e., the generation of a set of triangles for the points of the graph. This technique can also be used in a coupler to improve the commonality of data interpolation between different horizontal model grids. This paper proposes a new parallel triangulation algorithm, PatCC1 (Parallel triangulation algorithm with Commonality and parallel Consistency, version 1), for spherical and planar grids. Experimental evaluation results demonstrate the efficient parallelization of PatCC1 using a hybrid of MPI and OpenMP. They also show PatCC1 to have greater commonality than existing parallel triangulation algorithms (i.e., it is capable of handling more types of model grids) and that it guarantees parallel consistency (i.e., it achieves exactly the same triangulation result under different parallel settings). [ABSTRACT FROM AUTHOR]

Presents information on a study that provided data on the photopumped laser operation of planar AlAs-GaAs superlattice minidisk lasers. Crystal preparation; Crystal oxidation; Discussion on disk and stripe laser operation.

An improved model to predict the gain increases in traveling-wave tubes (TWTs) during long-term operation is presented. The conventional gain growth model describes the pressure variation in a TWT over its life using an exponential decrease from the initial outgassing level to a constant base pressure. This model often shows an inability to capture the gain change behavior of many tubes during the transition between early life burn-in and long-term operation, leading to a significant underprediction of long-term gain increases. The model is improved here first through the introduction of another pressure-related term associated with desorption of gas from the tube’s inner surfaces that exhibits a t^\mathrm \mathbf -1/2 time dependence. This new pressure dependence is governed by the behavior of a Langmuirian adsorption isotherm. Second, the exponential pressure decay term is separated into two terms associated with early life and long-term operation with different outgassing time constants. The improved model shows a significantly better matching of long-term TWT gain growth data compared to the conventional model. In addition, the improved model predicts a more physical pressure behavior in the TWT with time. [ABSTRACT FROM AUTHOR]

We construct two newarea-preserving projections, which map regular hexagons and regular triangles onto circles. Combination of these projections with the inverse Lambert equal-area projection from the disc to the two hemispheres of a sphere provide bi-directional conversions between uniform planar grids with three-fold and six-fold rotational symmetry and corresponding uniform grids on the sphere. An application example is given for the representation of the channeling-modified back-scattered electron yield for hexagonal titanium. [ABSTRACT FROM AUTHOR]

We consider the problem of partitioning the set of vertices of a given unit disk graph (UDG) into a minimum number of cliques. The problem is NP-hard and various constant factor approximations are known, with the current best ratio of 3. Our main result is a weakly robust polynomial time approximation scheme (PTAS) for UDGs expressed with edge-lengths that either (i) computes a clique partition or (ii) gives a certificate that the graph is not a UDG; for the case (i) it computes a clique partition having size that is guaranteed to be within (1+ ε) of the optimum size if the input is UDG; however if the input is not a UDG it either computes a clique partition as in case (i) with no guarantee on the quality of the clique partition or detects that it is not a UDG. Noting that recognition of UDG's is NP-hard even if we are given edge lengths, our PTAS is a weakly-robust algorithm. Our algorithm can be transformed into an $O(\frac{\log^{*} n}{{\varepsilon}^{O(1)}})$ time distributed PTAS. We consider a weighted version of the clique partition problem on vertex-weighted UDGs that generalizes the problem. We note some key distinctions with the unweighted version, where ideas useful in obtaining a PTAS break down. Yet, surprisingly, it admits a (2+ ε)-approximation algorithm for the weighted case where the graph is expressed, say, as an adjacency matrix. This improves on the best known 8-approximation for the unweighted case for UDGs expressed in standard form. [ABSTRACT FROM AUTHOR]

The performance of robotic systems with parallel kinematics can be evaluated by their kinematic, static, and dynamic properties. These properties are directly used in model-based controllers which potentially offer higher accuracy for robotic systems. Inverse dynamic solution is an essential part of these controllers. In the present work, the inverse dynamics model of a 3-PRR (prismatic-revolute-revolute) planar parallel manipulator based on the natural orthogonal complement (NOC) method is developed. To drive the NOC for the 3-PRR closed-loop systems, the explicit expressions of the loop constraints equations and the associated Jacobian matrices are first obtained. Next the NOC matrix, which is a velocity transformation matrix relating the Cartesian angular/translational velocities of various bodies to the motor joint rates, is calculated. Finally results of the NOC method are compared with simulation of a 3-PRR planar parallel manipulator using two commercial softwares: SimMechanics toolbox of Matlab and COSMOSMotion of SolidWorks. In order to verify the theoretical results, two different configurations for the robot are considered: a horizontal and a vertical. Results of the NOC method as well as the two simulations are compared for the two robot configurations. [ABSTRACT FROM AUTHOR]

A program to adaptively generate equivalent wire-grid structures for electromagnetic simulation of two-dimensional structures has been developed. The main purpose of this program is to simulate planar microstrip-patch antenna designs, using the Numerical Electromagnetics Code in collaboration with a genetic algorithm (GA). In order to demonstrate how this program operates in meshing planar structures, two examples are illustrated, both involving the design of circular-polarized coaxially fed antennas. It is confirmed that the performance of both genetic-algorithm-optimized antennas was excellent. The presented examples show the capability of the proposed program in antenna design using the genetic algorithm. [ABSTRACT FROM AUTHOR]

Abstract: Given a graph and a positive integer , the partition into cliques (pic) decision problem consists of deciding whether there exists a partition of into disjoint subsets such that the subgraph induced by each part is a complete subgraph (clique) of . In this paper, we establish both the NP-completeness of pic for planar cubic graphs and the Max SNP-hardness of pic for cubic graphs. We present a deterministic polynomial time -approximation algorithm for finding clique partitions in maximum degree three graphs. [Copyright &y& Elsevier]

This paper investigates two situations in which the forward kinematics of planar 3-RP_R parallel manipulators degenerates. These situations have not been addressed before. The first degeneracy arises when the three input joint variables ρ1, ρ2, and ρ3 satisfy a certain relationship. This degeneracy yields a double root of the characteristic polynomial in t=tan(φ/2), which could be erroneously interpreted as two coalesce assembly modes. However, unlike what arises in nondegenerate cases, this double root yields two sets of solutions for the position coordinates (x,y) of the platform. In the second situation, we show that the forward kinematics degenerates over the whole joint space if the base and platform triangles are congruent and the platform triangle is rotated by 180 deg about one of its sides. For these “degenerate” manipulators, which are defined here for the first time, the forward kinematics is reduced to the solution of a third-degree polynomial and a quadratic in sequence. Such manipulators constitute, in turn, a new family of analytic planar manipulators that would be more suitable for industrial applications. [ABSTRACT FROM AUTHOR]

There is a hypothesis that a non-selfcentric radially-maximal graph of radius r has at least 3r -1 vertices. Using some recent results we prove this hypothesis for r = 4. [ABSTRACT FROM AUTHOR]

It is proved that if G is multigraph with maximum degree 3, and every submultigraph of G has average degree at most 2 1/2 and is different from one forbidden configuration C4+ with average degree exactly 2 1/2 , then G is totally 4-choosable; that is, if every element (vertex or edge) of G is assigned a list of 4 colours, then every element can be coloured with a colour from its own list in such a way that no two adjacent or incident elements are coloured with the same colour. This shows that the List-Total-Colouring Conjecture, that ch"(G) = χ"(G) for every multigraph G, is true for all multigraphs of this type. As a consequence, if G is a graph with maximum degree 3 and girth at least 10 that can be embedded in the plane, projective plane, torus or Klein bottle, then ch"(G) = χ"(G) = 4. Some further total choosability results are discussed for planar graphs with sufficiently large maximum degree and girth. [ABSTRACT FROM AUTHOR]

Abstract  An experiment performed with the gyrotrons of the TJ-II ECRH system has been performed to influence the gyrotron output radiation with a relatively weak wave returned from an external mechanically modulated reflector. An original method is proposed for directly measuring the wavelength of electromagnetic radiation in the free space. The method has been demonstrated in measurements of the wavelength of a high-power gyrotron radiation in the millimeter wavelength range used for plasma ECR heating in the TJ-II stellarator. [ABSTRACT FROM AUTHOR]

Abstract  Gluck has proven that triangulated 2-spheres are generically 3-rigid. Equivalently, planar graphs are generically 3-stress free. We show that already the K 5-minor freeness guarantees the stress freeness. More generally, we prove that every K r+2-minor free graph is generically r-stress free for 1≤r≤4. (This assertion is false for r≥6.) Some further extensions are discussed. [ABSTRACT FROM AUTHOR]

This paper proves that deploying sensors on grid points to construct a wireless sensor network that fully covers critical grids using minimum sensors (Critical-Grid Coverage Problem) and that fully covers a maximum total weight of grids using a given number of sensors (Weighted-Grid Coverage Problem) are each NP-Complete. [ABSTRACT FROM AUTHOR]

The article presents a study which uses a method for vision-based unmanned aerial vehicles (UAV) motion estimation from multiple planar homographies and the results of the application of the proposed technique. These homographies are computed from matches between features extracted from consecutive images. To reduce the influence of the drift errors in the motion estimation, the homography estimation is refined by using a mosaic that stores past information. The article proposes the use of blob features to obtain natural landmarks.

Abstract: We consider the problem of planar grid generation. This problem can be easily reformulated as an unconstrained optimization problem with the usual variational method. This is a very simple technique to produce grids on planar domains, but it cannot be used in automatic grid generation codes. As a matter of fact, its formulation depends on some parameters, whose right value can disagree considerably among different domains. A simple modification of the variational method is proposed. This modification is mainly based on a linearly constrained optimization problem and it gives a significant increase of the robustness of the method. [Copyright &y& Elsevier]

A comprehensive experimental investigation of the effect of the Reynolds number on the degeneration law for turbulence generated by biplanar and wicker grids is carried out over a wide range of the grid geometry parameters and the flow velocity. It is established that an increase in the flow velocity leads to an increase in the turbulence intensity at a given distance from the biplanar grid and a decrease in the turbulence decay rate downstream of the grid. An empirical relation between the turbulence intensity behind the grid, on the one hand, and the relative distance x/M from the grid and the Reynolds number based on the grid rod diameter and the flow velocity at the grid mesh center, on the other hand, is proposed. For the same relative distance x/M from the grid the intensity of wicker-grid turbulence is higher than in the case of the flow past a biplanar grid. [ABSTRACT FROM AUTHOR]

In digital topology, Euclidean n-space Rn is usually modeled either by the set of points of a discrete grid, or by the set of n-cells in a convex cell complex whose union is Rn. For commonly used grids and complexes in the cases n=2 and 3, certain pairs of adjacency relations (κ,λ) on the grid points or n-cells (such as (4,8) and (8,4) on Z2) are known to be “good pairs.” For these pairs of relations (κ,λ), many results of digital topology concerning a set of grid points or n-cells and its complement (such as Rosenfeld''s digital Jordan curve theorem) have versions in which κ-adjacency is used to define connectedness on the set and λ-adjacency is used to define connectedness on its complement. At present, results of 2D and 3D digital topology are often proved for one good pair of adjacency relations at a time; for each result there are different (but analogous) theorems for different good pairs of adjacency relations. In this paper we take the first steps in developing an alternative approach to digital topology based on very general axiomatic definitions of “well-behaved digital spaces.” This approach gives the possibility of stating and proving results of digital topology as single theorems which apply to all spaces of the appropriate dimensionality that satisfy our axioms. Specifically, this paper introduces the notion of a generic axiomatized digital surface-structure (GADS)—a general, axiomatically defined, type of discrete structure that models subsets of the Euclidean plane and of other surfaces. Instances of this notion include GADS corresponding to all of the good pairs of adjacency relations that have previously been used (by ourselves or others) in digital topology on planar grids or on boundary surfaces. We define basic concepts for a GADS (such as homotopy of paths and the intersection number of two paths), give a discrete definition of planar GADS (which are GADS that model subsets of the Euclidean plane) and present some fundamental results including a Jordan curve theorem for planar GADS. [Copyright &y& Elsevier]

The performance of a binary-coded microgenetic algorithm (GA) applied to planar near-field antenna characterization is analyzed in this paper. The method replaces the antenna with an equivalent model consisting of short dipoles, whose optimization is carried out using different GA strategies. Results of reconstructed far-field patterns from synthetic near-field data and a detailed analysis of the GA-based approach are included. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 422–426, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11237 [ABSTRACT FROM AUTHOR]

Ordered trees are generally drawn using order-preserving planar straight-line grid drawings. We investigate the area-requirements of such drawings and present several results. Let T be an ordered tree with n nodes. We show that: • T admits an order-preserving planar straight-line grid drawing with O(n log n) area. • If T is a binary tree, then T admits an order-preserving planar straight-line grid drawing with O(n loglog n) area. • If T is a binary tree, then T admits an order-preserving upward planar straight-line grid drawing with optimal O(n log n) area. We also study the problem of drawing binary trees with user-specified aspect ratios. We show that an ordered binary tree T with n nodes admits an order-preserving planar straight-line grid drawing with area O(n log n), and any user-specified aspect ratio in the range [1,n/log n]. All the drawings mentioned above can be constructed in O(n) time. [ABSTRACT FROM AUTHOR]

In order to develop field emission cold cathode radiation source devices, a gridded carbon nanotube (CNT) cold cathode electron gun is theoretically and experimentally investigated in this letter. The planar grid and annular CNT cold cathode are used and optimal parameters of a high-compression-ratio electron gun are obtained by particle in cell simulation software. A 4-mA/10-kV annular electron beam with an average radius of 1.75 mm is achieved based on a permanent magnet in the experiment. The area compression ratio of electron beam is $\sim 10.$ [ABSTRACT FROM AUTHOR]

A third-order nonlinear equation for the circuit electric field was formulated for a helix traveling-wave tube under Eulerian fluid-dynamical approximations. The equation was solved by the method of successive approximations and interpreted for circuit power. When the third-order effects were included in the analysis, the saturation behavior of the device, with respect to both interaction length and RF input power, was found to be similar in nature to that predicted by Lagrangian analysis, agreeing well under backed-off conditions. The values of RF input power and interaction length corresponding to saturation found by the present Eulerian method were greater than those found by Lagrangian method. Although the present Eulerian technique has an inherent limitation of accuracy as compared to the Lagrangian one, it does not involve large-scale numerical integration, gives a closed-form solution, and hence becomes less encumbered. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 345–349, 1997. [ABSTRACT FROM AUTHOR]

We show that the high-energy ion irradiation of embedded metallic spherical nanoparticles (NPs) is not limited to their transformation into prolate nanorods or nanowires. Depending on their pristine size, the three following morphologies can be obtained: (i) nanorods, (ii) facettedlike, and (iii) almost spherical nanostructures. Planar silica films containing nearly monodisperse gold NPs (8–100 nm) were irradiated with swift heavy ions (5 GeV Pb) at room temperature for fluences up to 5×1013 cm-2. The experimental results are accounted for by considering a liquid-solid transformation of the premelted NP surface driven by the in-plane stress within the ion-deformed host matrix. This work demonstrates the interest of using ion-engineering techniques to shape embedded nanostructures into nonconventional configurations. [ABSTRACT FROM AUTHOR]

A dual-band planar-slot antenna that operates through a single coplanar waveguide (CPW) port in two 10% wide-frequency bands, one octave apart is presented. An input T-match circuit is used to match the antenna in both bands, without increasing its size and keeping the CPW feed advantages. A case antenna covering the two global system for mobile communications bands (0.88-0.96 GHz and 1.71-1.88 GHz) and the digital enhanced cordless telecommunications band (1.88-1.9 GHz) has been designed, built, and measured, to demonstrate the technique. A proprietary program, based on the method of moments, has been used to analyze and optimize the antenna. [ABSTRACT FROM AUTHOR]

The generation and propagation of a small-amplitude Langmuir pulse excited by a planar grid electrode in a spatially uniform collisionless plasma with a constant flow velocity is studied by solving the linearized Vlasov–Poisson equations. The electrode is transparent to the flow of particles, like a screen or a wire mesh. The particles are assumed to have a Kappa velocity distribution, a reasonable approximation for electron distribution functions in the solar wind. Exact, closed-form solutions are obtained for ${\it\kappa}=1$, the Lorentzian distribution, and for ${\it\kappa}=2$. The explicit form of the solution in the case ${\it\kappa}=2$ has not, to our knowledge, appeared in the literature before. The properties of the solutions are investigated and a practical technique for measuring the bulk flow velocity in plasma experiments is proposed that may be useful for high-accuracy, high-time-resolution measurements of the bulk flow velocity in the solar wind. [ABSTRACT FROM PUBLISHER]

A correction to the article "Simple and Accurate Analytical Model of Planar Grids and High-Impedance Surfaces Comprising Metal Strips or Patches," by Olli Luukkonen and colleagues is presented.