Pair Of Paths Research Articles

Application of <formula formulatype="inline"><tex Notation="TeX">${p}$</tex></formula>-Cycle Protection for the Substation Communication Network Under SRLG Constraints

In order to improve the security and stability of the intelligent substation communication networks, a novel shared risk link group (SRLG) weighted -cycle algorithm (SWCA) is proposed by considering the diversity of different substation links and the associated fiber core. The proposed approach is dedicated to solve the problems of multiple failures by sharing risk analysis. Hybrid integer linear programming and heuristic algorithm implementation are presented to reduce the complexity of optimizing bandwidth allocation under SRLG constraints. The performance of bandwidth utilization, service reject rate, and protection resource redundancy is investigated under the dynamic traffic environment, and the optimum SRLG number is discussed. The experimental results from two demonstration networks with randomly set SRLGs show that SWCA can reserve more bandwidths and, therefore, more service requests can be served at the expense of protection redundancy. Completely separated SRLG protection will decrease simultaneous failure probability of the working path and protection path and, thus, improve the survivability of the substation communication network compared with the classical capacitated iterative design algorithm-grow and shortest path pair protection method. Meanwhile, the approach can restore multiple failures within intelligent substation commu- nication networks, and can therefore enhance the survivability of the electric power communication network.

Survivable Virtual Infrastructure Mapping With Dedicated Protection in Transport Software-Defined Networks [Invited

Efficiently mapping multiple virtual infrastructures (VIs) onto the same physical substrate with survivability is one of the fundamental challenges related to network virtualization in transport software-defined networks (T-SDNs). In this paper, we study the survivable VI mapping problem in T-SDNs with the objective of minimizing the VI request blocking probability. In particular, we address the subproblems of modulation selection and spectrum allocation in the process of provisioning optical channels to support virtual links, taking into consideration the optical layer constraints such as the transmission reach constraint and the spectral continuity constraint. We propose an auxiliary-graph-based algorithm, namely, parallel VI mapping (PAR), to offer dedicated protection against any single physical node or link failure. More specifically, the PAR algorithm can jointly optimize the assignments of mapping the primary and backup VIs by adopting the modified Suurballe algorithm to find the shortest pair of node-disjoint paths for each virtual link. Through extensive simulations, we demonstrate that the PAR algorithm can significantly reduce the VI request blocking probability and improve the traffic-carrying capacity of the networks, compared to the baseline sequential VI mapping approaches.

Survivable Path Sets: A New Approach to Survivability in Multilayer Networks

We consider the problem of survivability in multilayer networks. In single-layer networks, a pair of disjoint paths can be used to provide protection for a source–destination pair. However, this approach cannot be directly applied to layered networks where risk-disjoint paths may not always exist. In this paper, we take a new approach, which is based on finding a set of paths that may not be disjoint but together will survive any single risk. We start with two-layered communication networks, where the risks are fiber failures. We prove that in general, finding the minimum survivable path set (MSPS) is NP-hard, whereas if we restrict the length of paths the problem can be solved in polynomial time. We formulate the problem as an integer linear program (ILP), and use this formulation to develop heuristics and approximation algorithms. Moreover, we study the minimum cost survivable path set problem, where the cost is the number of fibers used, and thus, nonadditive. Finally, we generalize the survivability problem to the networks with more than two layers. By applying our algorithms for survivable path set, we assess the survivability of communication networks that operate relying on power from a power grid.

Two Heuristics for Calculating a Shared Risk Link Group Disjoint Set of Paths of Min-Sum Cost

A shared risk link group (SRLG) is a set of links which share a common risk of failure. Routing protocols in Generalized MultiProtocol Label Switching, using distributed SRLG information, can calculate paths avoiding certain SRLGs. For single SRLG failure an end-to-end SRLG-disjoint path pair can be calculated, but to ensure connection in the event of multiple SRLG failures a set with more than two end-to-end SRLG-disjoint paths should be used. Two heuristic, the Conflicting SRLG-Exclusion Min Sum (CoSE-MS) and the Iterative Modified Suurballes's Heuristic (IMSH), for calculating node and SRLG-disjoint path pairs, which use the Modified Suurballes's Heuristic, are reviewed and new versions (CoSE-MScd and IMSHd) are proposed, which may improve the number of obtained optimal solutions. Moreover two new heuristics are proposed: kCoSE-MScd and kIMSHd, to calculate a set of $$k$$k node and SRLG-disjoint paths, seeking to minimize its total cost. To the best of our knowledge these heuristics are a first proposal for seeking a set of $$k\, (k>2)$$k(k>2) node and SRLG-disjoint paths of minimal additive cost. The performance of the proposed heuristics is evaluated using a real network structure, where SRLGs were randomly defined. The number of solutions found, the percentage of optimal solutions and the relative error of the sub-optimal solutions are presented. Also the CPU time for solving the problem in a path computation element is reported.

Survivable Inter-Domain Routing Based on Topology Aggregation With Intra-Domain Disjointness Information in Multi-Domain Optical Networks

In a network in which multiple domains are defined due to geographical and/or administrative reasons, only a limited amount of domain information is exchanged by domain service providers. Topology aggregation is a method used to facilitate this limited information exchange. The amount of information provided for each domain may vary based on the technical and management decisions taken by the service provider. For instance, some domains may choose to provide only a single shortest path between two border nodes, while another may be able to provide a pair of disjoint paths with minimum total cost. In such cases, end-to-end protected path routing needs to facilitate and use different amounts of domain information provided by domain service providers in order to find the best solution. In this work, we propose several approaches that help find a pair of disjoint end-to-end paths that may traverse multiple domains from source to destination and result in minimum total cost. These approaches include methods for inter-domain information exchange that carry costs of disjoint paths within a domain. The performance of minimizing the total cost of a pair of end-to-end paths is investigated. Finally, the blocking probabilities of these various approaches due to the existence of trap topologies in the network are also discussed.

Survivable Inter-Domain Routing Based on Topology Aggregation With Intra-Domain Disjointness Information in Multi-Domain Optical Networks

In a network in which multiple domains are defined due to geographical and/or administrative reasons, only a limited amount of domain information is exchanged by domain service providers. Topology aggregation is a method used to facilitate this limited information exchange. The amount of information provided for each domain may vary based on the technical and management decisions taken by the service provider. For instance, some domains may choose to provide only a single shortest path between two border nodes, while another may be able to provide a pair of disjoint paths with minimum total cost. In such cases, end-to-end protected path routing needs to facilitate and use different amounts of domain information provided by domain service providers in order to find the best solution. In this work, we propose several approaches that help find a pair of disjoint end-to-end paths that may traverse multiple domains from source to destination and result in minimum total cost. These approaches include methods for inter-domain information exchange that carry costs of disjoint paths within a domain. The performance of minimizing the total cost of a pair of end-to-end paths is investigated. Finally, the blocking probabilities of these various approaches due to the existence of trap topologies in the network are also discussed.

Resilient arcs and node disjointness in diverse routing

In multi-layer networks protection can be provided at multiple layers. Hence some links at an upper layer may be resilient because they are protected at a lower layer. We will designate as resilient arc at a given layer, an arc which has some form of protection at an underlaying layer. When path diversity is used at an upper layer, and resilient arcs are taken into account, it may not be necessary for the considered paths to be fully disjoint.We solve a problem of finding the shortest node-disjoint pair of paths that can share resilient arcs. It is assumed that a network consists of a set of nodes and a set of arcs. Moreover, a number of available arcs are resilient. Our goal is to find the shortest pair of paths such that they share only those nodes that are incident to shared resilient arcs. Moreover, we assume that the resulting paths cannot contain loops, and costs of shared resilient arcs are counted only once towards the objective function.In the paper we present two novel algorithms solving the above problem, and two supporting algorithms that are utilized as subroutines. We implement the proposed algorithms and compare them to an MIP approach.

A comparison of l- and d-Asp and Asn α-radicals a case study for atropisomerism

Asp radical has enantiomeric d and l form, due to axis chirality. This pair of degenerate minima is occurring on a single 4D-Ramachandran Potential Energy Hyper Surface (PEHS). The βD and βL radicals are interconverted on a pair of enantiotopic paths of the 4D-PEHS each of which has a lower and a higher transition state. These barriers are always higher for the Asp in comparison to those of the Asn radical.

Automatic detection of the carotid lumen axis in B-mode ultrasound images

A new approach is introduced for the automatic detection of the lumen axis of the common carotid artery in B-mode ultrasound images. The image is smoothed using a Gaussian filter and then a dynamic programming scheme extracts the dominant paths of local minima of the intensity and the dominant paths of local maxima of the gradient magnitude with the gradient pointing downwards. Since these paths are possible estimates of the lumen axis and the far wall of a blood vessel, respectively, they are grouped together into pairs. Then, a pattern of two features is computed from each pair of paths and used as input to a linear discriminant classifier in order to select the pair of paths that correspond to the common carotid artery. The estimated lumen axis is the path of local minima of the intensity that belongs to the selected pair of paths. The proposed method is suited to real time processing, no user interaction is required and the number of parameters is minimal and easy to determine.The validation was performed using two datasets, with a total of 199 images, and has shown a success rate of 99.5% (100% if only the carotid regions for which a ground truth is available are considered). The datasets have a large diversity of images, including cases of arteries with plaque and images with heavy noise, text or other graphical markings inside the artery region.

Comparison of near-field acoustic coherent backscattering simulations with optics theory and experiments

Remote discrimination of fish schools from other scatterers in the water column is important for environmental awareness and monitoring, and for a variety of sonar applications. Depending on the school's geometry and number of fish, and the fish's scattering characteristics, there may be preferential backscatter of sound, a phenomenon known as coherent backscatter enhancement (CBE). Thus, the presence and characteristics of CBE could help in discriminating fish schools from other objects. For CBE, the addition of in-phase scattered waves from the propagation path pairs yields a scattered intensity enhancement of a factor of two in the direction opposite to that of the incident wave. However, prior simulations based on the Foldy (1945) equations have suggested the enhancement may be greater than a factor of two for relatively large closely spaced scatterers. This presentation re-examines this topic and provides new CBE simulation results for near field scattering from finite-sized aggregations of point scatterers. Comparisons are made with equivalent results from the optics experiments of Wolf and Maret (1985) and the theory of Akkermans et al. (1986). Extension of this effort to comparisons of CBE from single frequency and broadband pulse illumination is anticipated. [Sponsored by the Office of Naval Research.]

Position-Dependent Diffusion of Light in Disordered Waveguides

We present direct experimental evidence for position-dependent diffusion in open random media. The interference of light in time-reversed paths results in renormalization of the diffusion coefficient, which varies spatially. To probe the wave transport inside the system, we fabricate two-dimensional disordered waveguides and monitor the light intensity from the third dimension. Change the geometry of the system or dissipation limits the size of the loop trajectories, allowing us to control the renormalization of the diffusion coefficient. This work shows the possibility of manipulating wave diffusion via the interplay of localization and dissipation.

A Novel Orthogonally Activated Double-hall Device

Abstract The offset and its temperature drift are almost fully compensated in a novel design orthogonally activated silicon double-Hall device. The proposed sensor consist two functionally integrated three-contact Hall elements sharing the same transducer region with rectangular shape and common central electrode. Two pairs equal in value but opposites in direction supply currents are formed by the structure symmetry and using equal resistors. In an orthogonal magnetic field, the Lorentz force deviate the pairs of current paths in opposite directions. The Hall elements have almost equal offsets, the offset temperature drifts are perfectly matched and Hall voltages are equal in value but of opposite sign. The output signal is given by subtraction of two output voltages using a circuitry with three op-amps. The residual offset was about 140 times lower than the individual ones in the range – 10 °C ≤ T ≤ 80 °C and the magnetic-field depended signal is almost doubled.

Exploiting classical decoherence in dissipative quantum dynamics: Memory, phonon emission, and the blip sum

The mechanisms that lead to the quenching of the coherence of a quantum system interacting with a dissipative environment are analyzed within the path integral/influence functional framework. Classical and quantum contributions are identified and linked to stimulated and spontaneous phonon emission processes. Three ways of exploiting decoherence in numerical calculations are discussed. The first is based on the decay of memory effects with time separation and leads to well-known iterative quasi-adiabatic propagator path integral (i-QuAPI) schemes. The other two mechanisms exploit the prominent role of classical decoherence. Removal of classical memory is possible through the introduction of auxiliary variables, leading to efficient and accurate quantum–classical path integral (QCPI) methods. A third way is proposed, which involves systematic corrections to the fully incoherent limit. An efficient procedure for summing all paths associated with ‘blips’ (short off-diagonal path pair segments) is described. The ideas are illustrated with numerical calculations of tunneling dynamics.

Domain-Disjoint Routing Based on Topology Aggregation for Survivable Multidomain Optical Networks

In a multidomain network, topology aggregation (TA) may be adopted to provide limited information regarding intradomain connectivity without revealing detailed topology information. If the TA information does not include details on the mapping of aggregated links in the TA over the physical topology, then physical disjointness cannot be guaranteed in the case in which two interdomain paths traverse the same domain through different aggregated links. Thus, in order to provide survivability over multiple domains, it may be necessary to find two domain-disjoint paths in the multidomain network. In this paper, we propose an algorithm for finding domain-disjoint working and backup paths for a multidomain connection request. The algorithm modifies the original multidomain network topology by adding cyclic structures that enable the direct application of Bhandari's algorithm to find a pair of diverse paths with minimum total cost over the modified topology. We give detailed analysis of various scenarios that may occur during the routing procedure, and the corresponding performance of our approach in these scenarios. We show that our approach can achieve good performance in finding domain-disjoint paths with minimum total cost.

A Spatially Explicit Model of Functional Connectivity for the Endangered Przewalski’s Gazelle (Procapra przewalskii) in a Patchy Landscape

BackgroundHabitat fragmentation, associated with human population expansion, impedes dispersal, reduces gene flow and aggravates inbreeding in species on the brink of extinction. Both scientific and conservation communities increasingly realize that maintaining and restoring landscape connectivity is of vital importance in biodiversity conservation. Prior to any conservation initiatives, it is helpful to present conservation practitioners with a spatially explicit model of functional connectivity for the target species or landscape.Methodology/Principal FindingsUsing Przewalski’s gazelle (Procapra przewalskii) as a model of endangered ungulate species in highly fragmented landscape, we present a model providing spatially explicit information to inform the long-term preservation of well-connected metapopulations. We employed a Geographic Information System (GIS) and expert-literature method to create a habitat suitability map, to identify potential habitats and to delineate a functional connectivity network (least-cost movement corridors and paths) for the gazelle. Results indicated that there were limited suitable habitats for the gazelle, mainly found to the north and northwest of the Qinghai Lake where four of five potential habitat patches were identified. Fifteen pairs of least-cost corridors and paths were mapped connecting eleven extant populations and two neighboring potential patches. The least-cost paths ranged from 0.2 km to 26.8 km in length (averaging 12.4 km) and were all longer than corresponding Euclidean distances.Conclusions/SignificanceThe model outputs were validated and supported by the latest findings in landscape genetics of the species, and may provide impetus for connectivity conservation programs. Dispersal barriers were examined and appropriate mitigation strategies were suggested. This study provides conservation practitioners with thorough and visualized information to reserve the landscape connectivity for Przewalski’s gazelle. In a general sense, we proposed a heuristic framework for species with similar biological and ecological characteristics.

Near- and far-field simulations of coherent backscattering from scatterers in finite sized aggregations

Classification of scatterers is a difficult but important step in active sonar applications. Active sonar signals in an ocean environment are scattered by surface roughness, and volume inhomogeneities in the bottom and water column. Fish schools may be important water-column clutter sources and, under some circumstances, may preferentially backscatter sound because of acoustic coherent backscattering enhancement (CBE). Here, the addition of in-phase scattered waves from propagation path pairs can readily explain a scattered intensity enhancement of a factor of two in the direction opposite to that of the incident wave. This presentation describes CBE simulations for finite sized aggregations of point scatterers using the Foldy (1945) equations that show much larger enhancements are possible in the far-field of the scattering aggregation. The simulations are validated in the near field with the theory from Akkermans et al. (1986), and with existing CBE optics and acoustics experiments from Wolf and Maret (1985) and Aubry et al. (2007). The dependence of the width of the CBE backscattered peak in the far-field is reported. Extension of these results to sonar pulse scattering from schools of fish is also very briefly discussed. [Work supported by the Office of Naval Research.]

SRLG-Aware Topology Aggregation for Survivable Multi-domain Optical Networks

In multi-domain optical networks, due to confidentiality and management considerations, it may be infeasible to exchange complete domain state information among domains. Topology aggregation (TA) is a widely adopted technique for aggregating a domain's detailed topology into simpler aggregated topology with limited information. In order to generate an abstracted topology that is more survivable against failures, the TA approach may also consider the presence of shared risk link groups (SRLGs), each of which defines a set of links that may fail simultaneously. We propose SRLG-aware topology aggregation approaches that can help to find a pair of inter-domain paths with a minimum set of common SRLGs. We find that constructing an aggregated topology while taking into account the SRLG distribution can help in developing a more survivable aggregated multi-domain network. Moreover, exchanging SRLG information prior to constructing the TA further increases the survivability of the aggregated topology. The performance of various TA schemes, such as single node, star, and full mesh, is also investigated.

Atropisomerism of the Asn α Radicals Revealed by Ramachandran Surface Topology

C radicals are typically trigonal planar and thus achiral, regardless of whether they originate from a chiral or an achiral C-atom (e.g., C-H + (•)OH → C• + H2O). Oxidative stress could initiate radical formation in proteins when, for example, the H-atom is abstracted from the Cα-carbon of an amino acid residue. Electronic structure calculations show that such a radical remains achiral when formed from the achiral Gly, or the chiral but small Ala residues. However, when longer side-chain containing proteogenic amino acid residues are studied (e.g., Asn), they provide radicals of axis chirality, which in turn leads to atropisomerism observed for the first time for peptides. The two enantiomeric extended backbone structures, •βL and •βD, interconvert via a pair of enantiotopic reaction paths, monitored on a 4D Ramachandran surface, with two distinct transition states of very different Gibbs-free energies: 37.4 and 67.7 kJ/mol, respectively. This discovery requires the reassessment of our understanding on radical formation and their conformational and stereochemical behavior. Furthermore, the atropisomerism of proteogenic amino acid residues should affect our understanding on radicals in biological systems and, thus, reframes the role of the D-residues as markers of molecular aging.

Multi-Objective Cross-Layer Optimization for Selection of Cooperative Path Pairs in Multihop Wireless Ad hoc Networks

This paper focuses in the selection of an optimal path pair for cooperative diversity based on cross-layer optimization in multihop wireless ad hoc networks. Cross-layer performance indicators, including power consumption, signal-to-noise ratio, and load variance are optimized using multi-objective optimization (MOO) with Pareto method. Consequently, optimization can be performed simultaneously to obtain a compromise among three resources over all possible path pairs. The Pareto method is further compared to the scalarization method in achieving fairness to each resource. We examine the statistics of power consumption, SNR, and load variance for both methods through simulations. In addition, the complexity of the optimization of both methods is evaluated based on the required computing time.

Reliability evaluation of a multistate network subject to time constraint under routing policy

A multistate network is a stochastic network composed of multistate arcs in which each arc has several possible capacities and may fail due to failure, maintenance, etc. The quality of a multistate network depends on how to meet the customer's requirements and how to provide the service in time. The system reliability, the probability that a given amount of data can be transmitted through a pair of minimal paths (MPs) simultaneously under the time constraint, is a proper index to evaluate the quality of a multistate network. An efficient solution procedure is first proposed to calculate it. In order to further enhance the system reliability, the network administrator decides the routing policy in advance to indicate the first and the second priority pairs of MPs. The second priority pair of MPs takes charge of the transmission duty if the first fails. The system reliability under the routing policy can be subsequently evaluated.