Maximum Edge Research Articles

An analytic model for limiting high density LH transition by the onset of the tertiary instability

We perform an analytic study of the tertiary instability driven by a strong excitation of zonal flows during high density low to high (LH) mode transition. The drift resistive ballooning mode is assumed to be a dominant edge turbulence driver. The analysis reproduces main qualitative features of early computational results [Rogers and Drake, Phys. Rev. Lett. 81, 4396 (1998); Guzdar et al., Phys. Plasmas 14, 020701 (2007)], as well as new characteristics of the maximum edge density due to the onset of the tertiary instability. An analytical scaling indicates that the density scaling of LH transition power may be determined by the onset condition of the tertiary instability when the operating density approaches to the Greenwald density.

A Combined Approach to SBIR using Edge Histogram Descriptor with Contourlet Transform

This paper focuses on the problem of efficient and fast retrieval of images from a large database using sketch as query image. Basically searching is based on a descriptor that addresses the asymmetry between binary sketch from the user side and full color image of the database. The working of proposed algorithm is such that query image and full color database images undergo same feature extraction process. Database images will be clustered offline which reduces time complexity on runtime. Further indexing is done which will be used to describe, store and organize image information and to assist people in finding image resources conveniently and quickly. Firstly feature vector extraction is done using contours and then edges will be detected in different orientation using modulus maxima edge detection in contourlet domain. This approach is almost better than existing approaches in many aspects such as compactness of feature vector, simplicity of implementation, retrieval performance and efficient feature extraction less time complexity.

Characterization of InN nanoparticles prepared by laser as photodetector

Indium nitride (InN) nanoparticles (NPs) are a potentially important material for optoelectronic and high speed electronic devices. Using 1064 nm Nd:YAG laser, InN NPs suspension has been prepared by laser ablation of indium target submerged under ammonium hydroxide. FTIR determined the presence of In=N at 1114.8 cm[Formula: see text] symmetric stretching mode, and In–N bending vibration mode appears at 445.5 cm[Formula: see text]. X-ray diffraction (XRD) observed the peaks (101), (110), and (220) as a reflection formation cubic InN, with an average size of 2 nm. Scanning electron microscope (SEM) image shows that the NPs have a spherical shape with particle size in the range 2–20 nm. The transmission spectra of InN NPs suspension have the maximum optical transmission edge at 1378 nm with the band gap energy of 1.2 eV. The current–voltage characteristics of InN/Si heterojunction have a good rectifying property with a spectral responsivity of about 0.797 A/W at 750 nm wavelength.

The extent of edge effects in fragmented landscapes: Insights from satellite measurements of tree cover

Due to deforestation, intact tropical forest areas are increasingly transformed into a mixture of remaining forest patches and human modified areas. These forest fragments suffer from edge effects, which cause changes in ecological and ecosystem processes, undermining habitat quality and the offer of ecosystem services. Even though detailed and long term studies were developed on the topic of edge effects at local scale, understanding edge effect characteristics in fragmented forests on larger scales and finding indicators for its impact is crucial for predicting habitat loss and developing management options. Here we evaluate the spatial and temporal dimensions of edge effects in large areas using remote sensing. First we executed a neighborhood pixel analysis in 11 LANDSAT Tree Cover (LTC) scenes (180×185km each, 8 in the tropics and 3 in temperate forested areas) using tree cover as an indicator of habitat quality and in relation to edge distance. Second, we executed a temporal analysis of LTC in a smaller area in the Brazilian Amazon forest where one larger forest fragment (25,890ha) became completely fragmented in 5years. Our results show that for all 11 scenes pixel neighborhood variation of LTC is much higher in the vicinity of forest edges, becoming lower towards the forest interior. This analysis suggests a maximum distance for edge effects and can indicate the location of unaffected core areas. However, LTC patterns in relation to fragment edge distance vary according to the analyzed region, and maximum edge distance may differ according to local conditions. Our temporal analysis illustrates the change in tree cover patterns after 5years of fragmentation, becoming on average lower close to the edge (between 50 and 100m). Although it is still unclear which are the main causes of LTC edge variability within and between regions, LANDSAT Tree Cover could be used as an accessible and efficient discriminator of edge and interior forest habitats in fragmented landscapes, and become invaluable for deriving qualitative spatial and temporal information of ecological and ecosystem processes.

Approximation and hardness results for the maximum edge q-coloring problem

We consider the problem of coloring edges of a graph subject to the following constraints: for every vertex v, all the edges incident with v have to be colored with at most q colors. The goal is to find a coloring satisfying the above constraints and using the maximum number of colors. Notice that the notion of coloring is different than in the classical edge coloring problem, as neighboring edges can have the same color.This problem has been studied in the past from the combinatorial and algorithmic point of view. The optimal coloring is known for some special classes of graphs. There is also an approximation algorithm for general graphs, which in the case q=2 gives a 2-approximation. However, the complexity of finding the optimal coloring was not known.In this paper, we prove that the problem is NP-Hard for any q≥2. Moreover, we prove that it cannot be approximated within a factor of 1+1/q−ϵ for any ϵ>0 and any q≥2 assuming the unique games conjecture (UGC), or 1+q−2(q−1)2−ϵ for any ϵ>0 and any q≥3 (≈1.19 for q=2) assuming P≠NP. These results hold even when the considered graphs are bipartite.On the algorithmic side, we restrict to the case q=2, since this is the most important in practice and we show a 5/3-approximation algorithm for graphs which have a perfect matching.

An Image Edge Detection Algorithm Based on Improved Wavelet Transform

In this paper, for wavelet modulus maxima edge detection affected by noise largely, we propose an improved image fusion algorithm. Firstly, wavelet denoising and smoothing filter are conducted on the original image. Secondly, making edge detection with wavelet transform modulus maxima edge detection and improved canny edge detection get each of edge detection images. Thirdly, let the wavelet fusion follow some certain fusion rules. Finally, making the inverse wavelet transform reconstruct the fused image. The experimental results show that the fused image combines the advantages of edge detection methods, which is an effective image edge detection method.

Development of a novel combined system of deformation amplification and added stiffness and damping: Analytical result and full scale pseudo-dynamic tests

This research presents the theoretical and experimental development of a new system called: Amplified Added Stiffness and Damping (AASD), which is a combination of an amplifying mechanism and a frictional self-centering damper capable to support large deformations. The operation of the damper is based on the well-known straps with friction principle. A first conceptual single acting device used for validating this principle and comparing the behavior of commercial straps (polyamide, aramid and carbon fiber) was built. Subsequently, two double acting prototypes with carbon fiber straps were built, since this material showed the best performance. Both, the conceptual device and the two prototypes (named as I and II) have shown very stable constitutive relations. Because of its greater simplicity, the “prototype II” represents a technically and economically attractive solution. Furthermore, due to its ability to accommodate large deformation in both directions, it is an ideal device to combine with amplifying mechanisms. A parametric numerical analysis performed on a single-story structure with AASD, showed a wide range of parameters of AASD leading to reductions greater than 40% on displacement response. A full-scale asymmetric one-story steel structure equipped with one AASD was built. The structure was subjected to a variety of tests using a multi-axis pseudo-dynamic equipment recently installed in the Laboratory of Structural Engineering of the Pontificia Universidad Católica de Chile. So far, the authors didn’t find references of a full scale pseudo-dynamic test of this nature. The structure without AASD presented a non-linear behavior mainly due to sliding of the bolted connections of the beams. Pseudo-dynamic seismic response tests were performed considering an artificial ground motion acting in one direction. As expected, and due to the mass eccentricity (20% of its plan length), high concentration of deformations in the flexible edge of the structure without AASD was observed. Conversely, the structure with AASD showed a great plan deformation uniformity (torsional balance), with reductions of nearly 40% in maximum edge deformation, which is consistent with the parametric analysis results. The eccentric lever arm used as amplifying mechanism, which have large amplifying ratio α=11, worked in great accordance with numerical simulations.

Local directional mask maximum edge patterns for image retrieval and face recognition

This study proposes a new feature descriptor, local directional mask maximum edge pattern, for image retrieval and face recognition applications. Local binary pattern (LBP) and LBP variants collect the relationship between the centre pixel and its surrounding neighbours in an image. Thus, LBP based features are very sensitive to the noise variations in an image. Whereas the proposed method collects the maximum edge patterns (MEP) and maximum edge position patterns (MEPP) from the magnitude directional edges of face/image. These directional edges are computed with the aid of directional masks. Once the directional edges (DE) are computed, the MEP and MEPP are coded based on the magnitude of DE and position of maximum DE. Further, the robustness of the proposed method is increased by integrating it with the multiresolution Gaussian filters. The performance of the proposed method is tested by conducting four experiments onopen access series of imaging studies-magnetic resonance imaging, Brodatz, MIT VisTex and Extended Yale B databases for biomedical image retrieval, texture retrieval and face recognition applications. The results after being investigated the proposed method shows a significant improvement as compared with LBP and LBP variant features in terms of their evaluation measures on respective databases.

Fast community detection based on sector edge aggregation metric model in hyperbolic space

By studying the edge aggregation characteristic of nodes in hyperbolic space, Sector Edge Aggregation Metric (SEAM) model is proposed and theoretically proved in this paper. In hyperbolic disk SEAM model determines the minimum angular range of a sector which possesses the maximal edge aggregation of nodes. The set of nodes within such sector has dense internal links, which corresponds with the characteristic of community structure. Based on SEAM model, we propose a fast community detection algorithm called Greedy Optimization Modularity Algorithm (GOMA) which employs greedy optimization strategy and hyperbolic coordinates. GOMA firstly divides initial communities according to the quantitative results of sector edge aggregation given by SEAM and the nodes’ hyperbolic coordinates, then based on greedy optimization strategy, only merges the two angular neighboring communities in hyperbolic disk to optimize the network modularity function, and consequently obtains high-quality community detection. The strategies of initial community partition and merger in hyperbolic space greatly improve the speed of searching the most optimal modularity. Experimental results indicate that GOMA is able to detect out high-quality community structure in synthetic and real networks, and performs better when applied to the large-scale and dense networks with strong clustering.

Solving the maximal matching problem with DNA molecules in Adleman–Lipton model

The maximal matching problem (MMP) is to find maximal edge subsets in a given undirected graph, that no pair of edges are adjacent in the subsets. It is a vitally important NP-complete problem in graph theory and applied mathematics, having numerous real life applications in optimal combination and linear programming fields. It can be difficultly solved by the electronic computer in exponential level time. Meanwhile in previous studies deoxyribonucleic acid (DNA) molecular operations usually were used to solve NP-complete continuous path search problems, e.g. HPP, traveling salesman problem, rarely for NP-hard problems with discrete vertices or edges solutions, such as the minimum vertex cover problem, graph coloring problem and so on. In this paper, we present a DNA algorithm for solving the MMP with DNA molecular operations. For an undirected graph with [Formula: see text] vertices and [Formula: see text] edges, we reasonably design fixed length DNA strands representing vertices and edges of the graph, take appropriate steps and get the solutions of the MMP in proper length range using [Formula: see text] time. We extend the application of DNA molecular operations and simultaneously simplify the complexity of the computation.

On the icosahedron inequality of László Fejes-Tóth

In this paper we deal with the problem of finding the maximal volume polyhedra with a prescribed property and inscribed in the unit sphere. We generalize an inequality (called icosahedron inequality) of L. Fejes-Toth which has the following interesting consequence: the regular icosahedron has maximal volume in the class of the polyhedra having twelve vertices and inscribed in the unit sphere. We give an upper bound for the volume of such star-shaped (with respect to the origin) simplicial polyhedra, whose number of faces, and also the list of the maximal edge lengths of the faces are given. As a consequence of this inequality we prove a conjecture which states that the maximal volume polyhedron spanned by the vertices of two regular simplices with common centroid is the cube. Mathematics subject classification (2010): 52A40, 52A38, 26B15.

Minimum Cost Matching for Autonomous Carsharing

Carsharing programs provide an alternative to private vehicle ownership. Combining car-sharing programs with autonomous vehicles would improve user access to vehicles thereby removing one of the main challenges to widescale adoption of these programs. While the ability to easily move cars to meet demand would be significant for carsharing programs, if implemented incorrectly it could lead to worse system performance. In this paper, we seek to improve the performance of a fleet of shared autonomous vehicles through improved matching of vehicles to passengers requesting rides. We consider carsharing with autonomous vehicles as an assignment problem and examine four different methods for matching cars to users in a dynamic setting. We show how applying a recent algorithm (Scalable Collision-avoiding Role Assignment with Minimal-makespan or SCRAM) for minimizing the maximal edge in a perfect matching can result in a more efficient, reliable, and fair carsharing system. Our results highlight some of the problems with greedy or decentralized approaches. Introducing a centralized system creates the possibility for users to strategically mis-report their locations and improve their expected wait time so we provide a proof demonstrating that cancellation fees can be applied to eliminate the incentive to mis-report location.

Environment modulates population social structure: experimental evidence from replicated social networks of wild lizards

Social structure is a fundamental component of a population that drives ecological and evolutionary processes ranging from parasite transmission to sexual selection. Nevertheless, we have much to learn about factors that explain variation in social structure. We used advances in biologging and social network analysis to experimentally test how the local habitat, and specifically habitat complexity, modulates social structure at different levels in wild populations. Sleepy lizards, Tiliqua rugosa , establish nonrandom social networks that are characterized by avoidance of some neighbours and frequent interactions with one opposite-sex individual. Using synchronous GPS locations of all adult lizards, we constructed social networks based on spatial proximity of individuals. We increased habitat structural complexity in two study populations by adding 100 short fences across the landscape. We then compared the resulting movement behaviour and social structure between these populations and two unmanipulated populations. Social connectivity (network density) and social stability, measured at weekly intervals, were greater in populations with increased habitat structural complexity. The level of agonistic interaction (quantified as scale damage) was also higher, indicating a fitness cost of greater social connectivity. However, some network parameters were unaffected by increased complexity, including disassortative mixing by sex, and at the individual level, social differentiation among associates (coefficient of variation of edge weights) and maximal interaction frequencies (maximal edge weight). This suggests divergent effects of changed ecological conditions on individual association behaviour compared to the resulting social structure of the population. Our results contrast with those from studies of more gregarious species, in which higher structural complexity in the environment relaxed the social connectivity. This shows that the response to altered ecological conditions can differ fundamentally between species or between populations, and we suggest that it depends on their tendency for gregarious behaviour. • We investigated how environmental conditions modulate social structure. • We conducted a replicated experiment in wild lizard populations. • Network density was greater in populations with increased habitat complexity. • Social differentiation at the individual level was unaffected. • Our results suggest divergent effects on the individual and population level.

Extremal problems for colorings of simple hypergraphs and applications

The paper deals with extremal problems concerning colorings of hypergraphs. By using a random recoloring algorithm we show that any n-uniform simple hypergraph H with maximum edge degree at most Δ(H)≤c⋅nrn−1, is r-colorable, where c>0 is an absolute constant. As an application of our proof technique we establish a new lower bound for the Van der Waerden number W(n,r).

The Maximal Length of a Gap between $r$-Graph Turán Densities

The Turán density $\pi(\cal F)$ of a family $\cal F$ of $r$-graphs is the limit as $n\to\infty$ of the maximum edge density of an $\cal F$-free $r$-graph on $n$ vertices. Erdős [Israel J. Math, 2 (1964):183—190] proved that no Turán density can lie in the open interval $(0,r!/r^r)$. Here we show that any other open subinterval of $[0,1]$ avoiding Turán densities has strictly smaller length. In particular, this implies a conjecture of Grosu [arXiv:1403.4653, 2014].

Groups and Embeddings in SL(2, ℂ)

We give results on when a finitely generated torsion-free group does or does not embed in SL(2, ℂ). For instance, if we glue two copies of the figure 8 knot along its torus boundary, then the fundamental group of the resulting closed 3-manifold sometimes embeds in SL(2, ℂ) and sometimes does not, depending on the identification, whereas a graph of free groups with maximal cyclic edge groups need not embed, even if it is word hyperbolic.

Improved algorithms for colorings of simple hypergraphs and applications

The paper deals with extremal problems concerning colorings of hypergraphs. By using a random recoloring algorithm we show that any n-uniform simple (i.e. every two distinct edges share at most one vertex) hypergraph H with maximum edge degree at mostΔ(H)⩽c⋅nrn−1 is r-colorable, where c>0 is an absolute constant.As an application of our proof technique we establish a new lower bound for Van der Waerden number W(n,r), the minimum N such that in any r-coloring of the set {1,…,N} there exists a monochromatic arithmetic progression of length n. We show thatW(n,r)>c⋅rn−1, for some absolute constant c>0.

The complexity of $P$<sub>4</sub>-decomposition of regular graphs and multigraphs

Let G denote a multigraph with edge set E(G), let µ(G) denote the maximum edge multiplicity in G, and let Pk denote the path on k vertices. Heinrich et al.(1999) showed that P4 decomposes a connected 4-regular graph G if and only if |E(G)| is divisible by 3. We show that P4 decomposes a connected 4-regular multigraph G with µ(G) ≤2 if and only if no 3 vertices of G induce more than 4 edges and |E(G)| is divisible by 3. Oksimets (2003) proved that for all integers k ≥3, P4 decomposes a connected 2k-regular graph G if and only if |E(G)| is divisible by 3. We prove that for all integers k ≥2, the problem of determining if P4 decomposes a (2k + 1)-regular graph is NP-Complete. El-Zanati et al.(2014) showed that for all integers k ≥1, every 6k-regular multigraph with µ(G) ≤2k has a P4-decomposition. We show that unless P = NP, this result is best possible with respect to µ(G) by proving that for all integers k ≥3 the problem of determining if P4 decomposes a 2k-regular multigraph with µ(G) ≤⌊2k / 3 ⌋+ 1 is NP-Complete.

MEPSA: minimum energy pathway analysis for energy landscapes.

From conformational studies to atomistic descriptions of enzymatic reactions, potential and free energy landscapes can be used to describe biomolecular systems in detail. However, extracting the relevant data of complex 3D energy surfaces can sometimes be laborious. In this article, we present MEPSA (Minimum Energy Path Surface Analysis), a cross-platform user friendly tool for the analysis of energy landscapes from a transition state theory perspective. Some of its most relevant features are: identification of all the barriers and minima of the landscape at once, description of maxima edge profiles, detection of the lowest energy path connecting two minima and generation of transition state theory diagrams along these paths. In addition to a built-in plotting system, MEPSA can save most of the generated data into easily parseable text files, allowing more versatile uses of MEPSA's output such as the generation of molecular dynamics restraints from a calculated path. MEPSA is freely available (under GPLv3 license) at: http://bioweb.cbm.uam.es/software/MEPSA/ CONTACT: pagomez@cbm.csic.es. Supplementary data are available at Bioinformatics online.

Iterative Monte Carlo simulation with the Compton kinematics-based GEB in a plastic scintillation detector

Plastic scintillators have been used for gamma ray detection in the fields of dosimetry and homeland security because of their desired characteristics such as a fast decay time, a low production cost, availability in a large-scale, and a tissue-equivalence. Gaussian energy broadening (GEB) in MCNP simulation is an effective treatment for tallies to calculate the broadened response function of a detector similarly to measured spectra. The full width at half maximum (FWHM) of a photopeak has been generally used to compute input parameters required for the GEB treatment. However, it is hard to find the photopeak in measured gamma spectra with plastic scintillators so that computation of the input parameters for the GEB has to be taken with another way. In this study, an iterative method for the GEB treated MCNP simulation to calculate the response function of a plastic scintillator is suggested. Instead of the photopeak, Compton maximum and Compton edge were used to estimate energy broadening in the measured spectra and to determine the GEB parameters. In a demonstration with a CsI(Tl) scintillator, the proposed iterative simulation showed the similar gamma spectra to the existing method using photopeaks. The proposed method was then applied to a polystyrene scintillator, and the simulation result were in agreement with the measured spectra with only a little iteration.