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1

A distributed shortest path protocol  

NASA Astrophysics Data System (ADS)

We present a distributed protocol for obtaining the shortest paths between all pairs of nodes in a network with weighted links. The protocol is based on an extension of the Dijkstra (centralized) shortest path algorithm and uses collaboration between neighboring nodes to transfer the information needed at the nodes for the successive construction of the shortest paths. A formal description of the protocol is given by indicating the exact algorithm performed by each node. The validation proofs are greatly simplified by separating the communication mechanism from the computation at the nodes, the latter being the transposition of the Dijkstra shortest path algorithm to the decentralized protocol.

Zerbib, F. B. M.; Segall, A.

1981-06-01

2

Shortest path algorithms  

Microsoft Academic Search

Theshortest path problem is considered from a computational point of view. Eight algorithms which solve theshortest path tree problem on directed graphs are presented, together with the results of wide-ranging experimentation designed to compare their relative performances on different graph topologies. The focus of this paper is on the implementation of the different data structures used in the algorithms. A

Giorgio Gallo; Stefano Pallottino

1988-01-01

3

Physarum can compute shortest paths.  

PubMed

Physarum polycephalum is a slime mold that is apparently able to solve shortest path problems. A mathematical model has been proposed by Tero et al. (Journal of Theoretical Biology, 244, 2007, pp. 553-564) to describe the feedback mechanism used by the slime mold to adapt its tubular channels while foraging two food sources s(0) and s(1). We prove that, under this model, the mass of the mold will eventually converge to the shortest s(0)-s(1) path of the network that the mold lies on, independently of the structure of the network or of the initial mass distribution. This matches the experimental observations by Tero et al. and can be seen as an example of a "natural algorithm", that is, an algorithm developed by evolution over millions of years. PMID:22732274

Bonifaci, Vincenzo; Mehlhorn, Kurt; Varma, Girish

2012-06-23

4

Efficient computation of geodesic shortest paths  

Microsoft Academic Search

This paper describes an ecient algorithm for the geodesic shortest path problem, i.e. the problemof nding shortest paths between pairs of points on the surface of a 3-dimensional polyhedron suchthat the path is constrained to lie on the surface of the polyhedron. We use the wavefront methodand show an O(nlog2n) time bound for this problem, when there are O(n) vertices

Sanjiv Kapoor; Hauz Khan

1999-01-01

5

Fuzzy shortest path problems incorporating interactivity among paths  

Microsoft Academic Search

This paper deals with a shortest path problem on a network in which a fuzzy number, instead of a real number, is assigned to each arc length. Such a problem is “ill-posed” because each arc cannot be identified as being either on the shortest path or not. Therefore, based on the possibility theory, we introduce the concept of “degree of

Shinkoh Okada

2004-01-01

6

Faster algorithms for the shortest path problem  

Microsoft Academic Search

Efficient implementations of Dijkstra's shortest path algorithm are investigated. A new data structure, called the radix heap, is proposed for use in this algorithm. On a network with n vertices, m edges, and nonnegative integer arc costs bounded by C, a one-level form of radix heap gives a time bound for Dijkstra's algorithm of O(m + n log C). A

Ravindra K. Ahuja; Kurt Mehlhorn; James B. Orlin; Robert Endre Tarjan

1990-01-01

7

Shortest paths algorithms: theory and experimental evaluation  

Microsoft Academic Search

We conduct an extensive computational study of shortest paths algorithms, including some very recent algorithms. We also suggest new algorithms motivated by the experimental results and prove interesting theoretical results suggested by the experimental data. Our computational study is based on several natural problem classes which identify strengths and weaknesses of various algorithms. These problem classes and algorithm implementations form

Boris V. Cherkassky; Andrew V. Goldberg; Tomasz Radzikt

1994-01-01

8

An Improved Shortest Path Algorithm for Computing One-to-One Shortest Paths on Road Networks  

Microsoft Academic Search

Computing one-to-one shortest paths on road networks is a fundamental work in many practical applications, especially in network and transportation related analyses. Pallottino's graph growth algorithm implemented with two queues (TWO-Q) is recommended as one of the top candidates to this kind of problems in literature. However, as a label-correcting shortest path algorithm, original TWO-Q algorithm begins scan from the

JinFu Leng; Wen Zeng

2009-01-01

9

Approximate Euclidean shortest path in 3-space  

Microsoft Academic Search

Papadimitriou's approximation approach to the Euclidean shortest path (ESP) problem in 3-space is revisited. As this problem is NP-hard, his approach represents an important step towards practical algorithms. Unfortunately, there are non-trivial gaps in the original description. Besides giving a complete treatment, we also give an alternative to his subdivision method which has some nice properties. Among the tools needed

Joonsoo Choi; Jürgen Sellen; Chee-Keng Yap

1994-01-01

10

Shortest paths in synchronized traffic-light networks  

Microsoft Academic Search

The time-constrained shortest path problem is an important generalization of the shortest path problem. The basic feature in time-constrained shortest path problem is considering when a node in the network can be visited under some time constraints. In this paper, a label-setting shortest path algorithm will be proposed to use in the synchronized traffic-light networks which uses the waiting times

Mohammad Khanjary; Karim Faez; Mohammad Reza Meybodi; Masoud Sabaei

2011-01-01

11

A Shortest Path Processor for Traffic Engineering of VPN Services  

Microsoft Academic Search

The shortest path problem is common in many different fields (transportation systems, mechanical systems, etc). Most of the telecommunication industry protocols such as PNNI, OSPF and IISP use Dijkstra's algorithm or Bellman-Ford's algorithm to solve the shortest path problem. Today, the majority of the shortest path computations are performed in software, which is inefficient for real-time applications that are sensitive

Mohamed Abou-Gabal; Raymond Peterkin; Dan Ionescu; C. Lambiri; Voicu Groza

12

Shortest path ray tracing with sparse graphs  

SciTech Connect

A technique for improving the efficiency of shortest path ray tracing (SPR) is presented. The authors analyze situations where SPR fails and provide quantitative measures to assess the performance of SPR ray tracing with varying numbers of nodes. Their improvements include perturbing the ray at interfaces according to Snell's Law, and a method to find correct rays efficiently in regions of low velocity contract. This approach allows the investigator to use fewer nodes in the calculation, thereby increasing the computational efficiency. In two-dimensional (2-D) cross-borehole experiments they find that with their improvements, they need only use 2/3 as many nodes, saving up to 60 percent in time. Savings should be even greater in three dimensions. These improvements make SPR more attractive for tomographic applications in three dimensions.

Fischer, R.; Lees, J.M. (Yale Univ., New Haven, CT (United States). Dept. of Geology and Geophysics)

1993-07-01

13

Shortest paths synthesis for a car-like robot  

Microsoft Academic Search

This paper deals with the complete characterization of the shortest paths for a car-like robot. Previous works have shown that the search for a shortest path may be limited to a simple family of trajectories. Our work completes this study by providing a way to select inside this family an optimal path to link any two configurations. We combine the

P. Soueres; J.-P. Laumond

1996-01-01

14

Fast and accurate estimation of shortest paths in large graphs  

Microsoft Academic Search

Computing shortest paths between two given nodes is a fundamental operation over graphs, but known to be nontrivial over large disk-resident instances of graph data. While a number of techniques exist for answering reachability queries and approximating node distances efficiently, determining actual shortest paths (i.e. the sequence of nodes involved) is often neglected. However, in applications arising in massive online

Andrey Gubichev; Srikanta J. Bedathur; Stephan Seufert; Gerhard Weikum

2010-01-01

15

Shortest path algorithm based on city emergency system  

Microsoft Academic Search

It requires that the savers get to the spot with the quickest speed when the accidents take place in the City Emergency System, therefore the Shortest Path problem is one of the pivotal technology to satisfy the system. This paper put forward a real-time and effective algorithm realization of Shortest Path, according to the characteristics of City Emergency System, taking

Gui-Qin Dou; Yan-Song Zhu; Yu-Min Han

2011-01-01

16

k-Link Shortest Paths in Weighted Subdivisions  

Microsoft Academic Search

We study the shortest path problem in weighted polygonal subdivisions of the plane, with the additional constraint of an upper bound, k, on the number of links (segments) in the path. We prove structural properties of optimal paths and utilize these results to ob- tain approximation algorithms that yield a path having O(k) links and weighted length at most (1

Ovidiu Daescu; Joseph S. B. Mitchell; Simeon C. Ntafos; James D. Palmer; Chee-keng Yap

2005-01-01

17

Distributional properties of stochastic shortest paths for smuggled nuclear material  

SciTech Connect

The shortest path problem on a network with fixed weights is a well studied problem with applications to many diverse areas such as transportation and telecommunications. We are particularly interested in the scenario where a nuclear material smuggler tries to succesfully reach herlhis target by identifying the most likely path to the target. The identification of the path relies on reliabilities (weights) associated with each link and node in a multi-modal transportation network. In order to account for the adversary's uncertainty and to perform sensitivity analysis we introduce random reliabilities. We perform some controlled experiments on the grid and present the distributional properties of the resulting stochastic shortest paths.

Cuellar, Leticia [Los Alamos National Laboratory; Pan, Feng [Los Alamos National Laboratory; Roach, Fred [Los Alamos National Laboratory; Saeger, Kevin J [Los Alamos National Laboratory

2011-01-05

18

I\\/O-Efficiency of Shortest Path Algorithms: An Analysis  

Microsoft Academic Search

To establish the behavior of algorithms in a paging environment, the author analyzes the input\\/output (I\\/O) efficiency of several representative shortest path algorithms. These algorithms include single-course, multisource, and all pairs ones. The results are also applicable for other path problems such as longest paths, most reliable paths, and bill of materials. The author introduces the notation and a model

Bin Jiang; ETH Zurich

1992-01-01

19

The role of convexity for solving some shortest path problems in plane without triangulation  

NASA Astrophysics Data System (ADS)

Solving shortest path problems inside simple polygons is a very classical problem in motion planning. To date, it has usually relied on triangulation of the polygons. The question: "Can one devise a simple O(n) time algorithm for computing the shortest path between two points in a simple polygon (with n vertices), without resorting to a (complicated) linear-time triangulation algorithm?" raised by J. S. B. Mitchell in Handbook of Computational Geometry (J. Sack and J. Urrutia, eds., Elsevier Science B.V., 2000), is still open. The aim of this paper is to show that convexity contributes to the design of efficient algorithms for solving some versions of shortest path problems (namely, computing the convex hull of a finite set of points and convex rope on rays in 2D, computing approximate shortest path between two points inside a simple polygon) without triangulation on the entire polygons. New algorithms are implemented in C and numerical examples are presented.

An, Phan Thanh; Hai, Nguyen Ngoc; Hoai, Tran Van

2013-09-01

20

Optimal shortest path queries in a simple polygon  

Microsoft Academic Search

Let P be a simple polygon with n sides. This paper shows how to preprocess the polygon so that, given two query points p and q inside P, the length of the shortest path inside the polygon from p to q can be found in time &Ogr;(log n). The path itself must be polygonal and can be extracted in additional

Leonidas J. Guibas; John Hershberger

1987-01-01

21

Shortest path based splitting line finding for touching cells  

NASA Astrophysics Data System (ADS)

A shortest path based algorithm is proposed in this paper to find splitting lines for touching cells. Firstly, an initial splitting line is obtained through the distance transform of a marker image and the watershed algorithm. Then, the initial splitting line is separated into different line segments if necessary, and the start and end points of these line segments act as the start and end points of shortest path. Finally, the shortest path algorithm is used to find the splitting line between the start and end points, and the final result of touching cells splitting can be formed by the contour of the touching cells and the splitting lines. Experimental results show that the proposed algorithm is efficient for different types of touching cells.

Bai, Xiangzhi; Sun, Changming; Wang, Peng; Zhou, Fugen

2013-10-01

22

Efficient Algorithms for Shortest Paths in Sparse Networks  

Microsoft Academic Search

Algorithms for finding shortest paths are presented which are faster than algorithms previously known on networks which are relatively sparse in arcs. Known results which the results of this paper extend are surveyed briefly and analyzed. A new implementation for priority queues is employed, and a class of “arc set partition” algorithms is introduced. For the single source problem on

Donald B. Johnson

1977-01-01

23

Wavelength Conversion in Shortest-Path All-Optical Networks  

Microsoft Academic Search

We consider all-optical networks with shortest-path routing that use wavelength- division multiplexing and employ wavelength conversion at specic nodes in order to maximize their capacity usage. We present ecien t algorithms for deciding whether a placement of wavelength converters allows the network to run at maximum capacity, and for nding an optimal wavelength assignment when such a placement of con-

Thomas Erlebach; Stamatis Stefanakos

2003-01-01

24

NP-Completeness Results for All-Shortest-Path Interval Routing  

Microsoft Academic Search

\\u000a \\u000a k-Interval Routing Scheme (k-IRS) is a compact routing method that allows up to k interval labels to be assigned to an arc. A fundamental problem is to characterize the networks that admit k-IRS. Many of the problems related to single-shortest-path k-IRS have already been shown to be NP-complete. For all-shortest-path k-IRS, the characterization problem remains open for k? 1. We

Rui Wang; Francis C. M. Lau; Yan Yan Liu

2004-01-01

25

Computing Point-to-Point Shortest Paths from External Memory  

Microsoft Academic Search

We study the ALT algorithm (19) for the point-to-point shortest path problem in the context of road networks. We suggest improvements to the algorithm itself and to its preprocessing stage. We also develop a memory-ecien t implementation of the algorithm that runs on a Pocket PC. It stores graph data in a ash memory card and uses RAM to store

Andrew V. Goldberg; Renato Fonseca F. Werneck

2005-01-01

26

Average Network Flow Problem: Shortest Path and Minimum Cost Flow Formulations, Algorithms, Heuristics, and Complexity.  

National Technical Information Service (NTIS)

Integrating value focused thinking with the shortest path problem results in a unique formulation called the multiobjective average shortest path problem. We prove this is NP-complete for general graphs. For directed acyclic graphs, an efficient algorithm...

J. D. Jordan

2012-01-01

27

Optimal Shortest Path Queries in a Simple Polygon  

Microsoft Academic Search

Abstract Let P be a simple polygon with n sides. This paper shows how to preprocess,the polygon so that, given two query points p and q inside P, the length of the shortest,path,inside the polygon($#$to q can be found,in time,O(Iogn). The path,itself must,be polygonal and can be extracted,in additional,time proportional,to the number,of turns,it makes.,The preprocessing consists of triangulation,plus a linear

Leonidas J. Guibas; John Hershberger

1989-01-01

28

A Graph Search Heuristic for Shortest Distance Paths  

SciTech Connect

This paper presents a heuristic for guiding A* search for finding the shortest distance path between two vertices in a connected, undirected, and explicitly stored graph. The heuristic requires a small amount of data to be stored at each vertex. The heuristic has application to quickly detecting relationships between two vertices in a large information or knowledge network. We compare the performance of this heuristic with breadth-first search on graphs with various topological properties. The results show that one or more orders of magnitude improvement in the number of vertices expanded is possible for large graphs, including Poisson random graphs.

Chow, E

2005-03-24

29

KSPTH: A Subroutine for the K Shortest Paths in a Sabotage Graph.  

National Technical Information Service (NTIS)

Finding shortest paths in a weighted graph model is one way for a safeguards analyst to locate weaknesses in a facility's barrier and alarm system. KSPTH can be used to rank sabotage paths according to path length so that the K shortest paths can be studi...

B. L. Hulme D. B. Holdridge

1977-01-01

30

Membrane Boundary Extraction Using a Circular Shortest Path Technique  

NASA Astrophysics Data System (ADS)

Membrane proteins represent over 50% of known drug targets. Accordingly, several widely used assays in the High Content Analysis area rely on quantitative measures of the translocation of proteins between intracellular organelles and the cell surface. In order to increase the sensitivity of these assays, one needs to measure the signal specifically along the membrane, requiring a precise segmentation of this compartment. Doing this manually is a very time-consuming practice, limited to an academic setting. Manual tracing of the membrane compartment also confronts us with issues of objectivity and reproducibility. In this paper, we present an approach based on a circular shortest path technique that enables us to segment the membrane compartment accurately and rapidly. This feature is illustrated using cells expressing epitope-tagged membrane proteins.

Sun, Changming; Vallotton, Pascal; Wang, Dadong; Lopez, Jamie; Ng, Yvonne; James, David

2007-11-01

31

Dynamic behavior of shortest path routing algorithms for communication networks  

NASA Astrophysics Data System (ADS)

Several proposed routing algorithms for store and forward communication networks, including one currently in operation in the ARPANET, route messages along shortest paths computed by using some set of link lengths. When these lengths depend on current traffic conditions as they must in an adaptive algorithm, dynamic behavior questions such as stability convergence, and speed of convergence are of interest. This paper is the first attempt to analyze systematically these issues. It is shown that minimum queuing delay path algorithms tend to exhibit violent oscillatory behavior in the absence of a damping mechanism. The oscillations can be damped by means of several types of schemes, two of which are analyzed in this paper. In the first scheme a constant bias is added to the queuing delay thereby providing a preference towards paths with a small number of links. In the second scheme the effects of several past routings are averaged as, for example, when the link lengths are computed and communicated asynchronously throughout the network.

Bertsekas, D. P.

1980-06-01

32

Shortest Paths in a Digitized Map Using a Tile-Based Data Structure,  

National Technical Information Service (NTIS)

The problem addressed here is that of finding the shortest paths between two points within a digitized map. The map contains obstacles which may not be traversed. For this reason, the problem statement is analogous to that of finding shortest paths within...

P. Holmes E. Jungert

1988-01-01

33

Algorithm for shortest path search in Geographic Information Systems by using reduced graphs.  

PubMed

The use of Geographic Information Systems has increased considerably since the eighties and nineties. As one of their most demanding applications we can mention shortest paths search. Several studies about shortest path search show the feasibility of using graphs for this purpose. Dijkstra's algorithm is one of the classic shortest path search algorithms. This algorithm is not well suited for shortest path search in large graphs. This is the reason why various modifications to Dijkstra's algorithm have been proposed by several authors using heuristics to reduce the run time of shortest path search. One of the most used heuristic algorithms is the A* algorithm, the main goal is to reduce the run time by reducing the search space. This article proposes a modification of Dijkstra's shortest path search algorithm in reduced graphs. It shows that the cost of the path found in this work, is equal to the cost of the path found using Dijkstra's algorithm in the original graph. The results of finding the shortest path, applying the proposed algorithm, Dijkstra's algorithm and A* algorithm, are compared. This comparison shows that, by applying the approach proposed, it is possible to obtain the optimal path in a similar or even in less time than when using heuristic algorithms. PMID:24010024

Rodríguez-Puente, Rafael; Lazo-Cortés, Manuel S

2013-07-01

34

Weight functions for shortest path routing of periodically scheduled burst flows  

Microsoft Academic Search

We investgate weighted shortest path routing mechanisms based on Dijkstra’s algorithm to find optimal paths for periodically scheduled burst flows in optical burst switching networks. Our objective is to reduce the flow blocking rate. We propose three dynamic weight functions to estimate the path level flow blocking probability based on wavelength utilization. We evaluate the performance of these weight functions

Li Lei; Srinivas Sampalli

2007-01-01

35

Linear-Time Algorithms for Visibility and Shortest Path Problems Inside Triangulated Simple Polygons  

Microsoft Academic Search

Given a triangulation of a simple polygonP, we present linear-time algorithms for solving a collection of problems concerning shortest paths and visibility withinP. These problems include calculation of the collection of all shortest paths insideP from a given source vertexS to all the other vertices ofP, calculation of the subpolygon ofP consisting of points that are visible from a given

Leonidas J. Guibas; John Hershberger; Daniel Leven; Micha Sharir; Robert Endre Tarjan

1987-01-01

36

The shortest path and spatial decision support system implementation in the context of parcel delivery  

Microsoft Academic Search

The shortest path decision-making had been proved to be critical to a parcel delivery business. This paper first introduces a modular decision support framework, which based on the small and medium enterprise's delivery operation model. It then proposes a Demand-Scheduling-Delivering process chain incorporate the shortest path analysis and decision as its central components. A pilot decision support system for intra-city

Xintong Li; Feng Peng

2010-01-01

37

Efficient shortest-path-tree computation in network routing based on pulse-coupled neural networks.  

PubMed

Shortest path tree (SPT) computation is a critical issue for routers using link-state routing protocols, such as the most commonly used open shortest path first and intermediate system to intermediate system. Each router needs to recompute a new SPT rooted from itself whenever a change happens in the link state. Most commercial routers do this computation by deleting the current SPT and building a new one using static algorithms such as the Dijkstra algorithm at the beginning. Such recomputation of an entire SPT is inefficient, which may consume a considerable amount of CPU time and result in a time delay in the network. Some dynamic updating methods using the information in the updated SPT have been proposed in recent years. However, there are still many limitations in those dynamic algorithms. In this paper, a new modified model of pulse-coupled neural networks (M-PCNNs) is proposed for the SPT computation. It is rigorously proved that the proposed model is capable of solving some optimization problems, such as the SPT. A static algorithm is proposed based on the M-PCNNs to compute the SPT efficiently for large-scale problems. In addition, a dynamic algorithm that makes use of the structure of the previously computed SPT is proposed, which significantly improves the efficiency of the algorithm. Simulation results demonstrate the effective and efficient performance of the proposed approach. PMID:23144039

Qu, Hong; Yi, Zhang; Yang, Simon X

2012-10-23

38

Snell's law and light traveling along the shortest path  

Microsoft Academic Search

the problem to be analyzed follows: Given a starting point s, an ending point t and a set of n Weighted Faces (or regions) in a 2-dimensional space, find the best path from s to t, where the length of the path is defined as the weighted sum of the Euclidean length of the sub paths inside each region. Let

Carlos Lara

2006-01-01

39

Curvature-Constrained Shortest Paths in a Convex Polygon  

Microsoft Academic Search

Let be a point robot moving in the plane, whose path is con- strained to have curvature at most , and let be a convex polygon with vertices. We study the collision-free, optimal path-plann ing problem for moving between two configurations inside (a con- figuration specifies both a location and a direction of travel ). We present an time algorithm

Pankaj K. Agarwal; Therese C. Biedl; Sylvain Lazard; Steve Robbins; Subhash Suri; Sue Whitesides

2002-01-01

40

a Shortest Path Algorithm for a Network with Various Fuzzy Arc Lengths  

NASA Astrophysics Data System (ADS)

We are concerned with the design of a model and an algorithm for computing a shortest path in a network having various types of fuzzy arc lengths. First, we develop a new technique for the addition of various fuzzy numbers in a path using ? -cuts. Then, we propose a regression model for obtaining membership function for the considered addition. Finally, we present a dynamic programming method for finding a shortest path in the network. An example is worked out to illustrate the applicability of the proposed approach.

Tajdin, Ali; Mahdavi, Iraj; Mahdavi-Amiri, Nezam; Sadeghpour-Gildeh, Bahram; Hadighi, Rofideh

2010-06-01

41

A New Algorithm for Finding the Shortest Path Tree Using Competitive Pulse Coupled Neural Network  

Microsoft Academic Search

The competitive pulse coupled neural network (CPCNN) model is proposed based on the pulse coupled neural network (PCNN), the\\u000a properties of pulse wave propagation of the CPCNN are analyzed for the solution of network shortest routing. The setting terms\\u000a of the neuron parameters for the pulse wave propagation along the routing of the shortest path tree (SPT) of network routing

Dongming Zhou; Rencan Nie; Dongfeng Zhao

2008-01-01

42

Greedy partitioned algorithms for the shortest-path problem  

SciTech Connect

A partitioned, priority-queue algorithm for solving the single-source best-path problem is defined and evaluated. Finding single-source paths for sparse graphs is notable because of its definite lack of parallelism-no known algorithm are scalable. Qualitatively, they discuss the close relationship between the algorithm and previous work by Quinn, Chikayama, and others. Performance measurements of variations of the algorithm, implemented both in concurrent and imperative programming languages on a shared-memory multiprocessor, are presented. This quantitative analysis of the algorithms provides insights into the tradeoffs between complexity and overhead in graph-searching executed in high-level parallel languages with automatic task scheduling.

Adamson, P.; Tick, E. (Univ. of Oregon (United States))

1991-08-01

43

Fast shortest path computation in time-dependent traffic networks  

Microsoft Academic Search

In agent based traffic simulations which use systematic relaxation to reach a steady state of the scenario, the performance of the routing algorithm used for finding a path from a start node to an end node in the network is crucial for the overall performance. For example, a systematic re- laxation process for a large scale scenario with about 7.5

Nicolas Lefebvre; ETH Zurich; Michael Balmer

2007-01-01

44

Shortest Paths in Euclidean Space with Polyhedral Obstacles.  

National Technical Information Service (NTIS)

This document considers the problem of finding a minimum length path between two points in Euclidean space which avoids a set (not necessarily convex) polyhedral obstacles; we let n denote the number of the obstacle edges and k denote the number of island...

J. H. Reif J. A. Storer

1985-01-01

45

The approach for shortest paths in fire succor based on component GIS technology  

NASA Astrophysics Data System (ADS)

Fire safety is an important issue for the national economy and people's living. Efficiency and exactness of fire department succor directly relate to safety of peoples' lives and property. Many disadvantages of the traditional fire system have been emerged in practical applications. The preparation of pumpers is guided by wireless communication or wire communication, so its real-time and accurate performances are much poorer. The information about the reported fire, such as the position, disaster and map, et al., for alarm and command was processed by persons, which slows the reaction speed and delays the combat opportunity. In order to solve these disadvantages, it has an important role to construct a modern fire command center based on high technology. The construction of modern fire command center can realize the modernization and automation of fire command and management. It will play a great role in protecting safety of peoples' lives and property. The center can enhance battle ability and can reduce the direct and indirect loss of fire damage at most. With the development of science technology, Geographic Information System (GIS) has becoming a new information industry for hardware production, software development, data collection, space analysis and counseling. With the popularization of computers and the development of GIS, GIS has gained increasing broad applications for its strong functionality. Network analysis is one of the most important functions of GIS, and the most elementary and pivotal issue of network analysis is the calculation of shortest paths. The shortest paths are mostly applied to some emergent systems such as 119 fire alarms. These systems mainly require that the computation time of the optimal path should be 1-3 seconds. And during traveling, the next running path of the vehicles should be calculated in time. So the implement of the shortest paths must have a high efficiency. In this paper, the component GIS technology was applied to collect and record the data information (such as, the situation of this disaster, map and road status et al) of the reported fire firstly. The ant colony optimization was used to calculate the shortest path of fire succor secondly. The optimization results were sent to the pumpers, which can let pumpers choose the shortest paths intelligently and come to fire position with least time. The programming method for shortest paths is proposed in section 3. There are three parts in this section. The elementary framework of the proposed programming method is presented in part one. The systematic framework of GIS component is described in part two. The ant colony optimization employed is presented in part three. In section 4, a simple application instance was presented to demonstrate the proposed programming method. There are three parts in this section. The distributed Web application based on component GIS was described in part one. The optimization results without traffic constraint were presented in part two. The optimization results with traffic constraint were presented in part three. The contributions of this paper can be summarized as follows. (1) It proposed an effective approach for shortest paths in fire succor based on component GIS technology. This proposed approach can achieve the real-time decisions of shortest paths for fire succor. (2) It applied the ant colony optimization to implement the shortest path decision. The traffic information was considered in the shortest path decision using ant colony optimization. The final application instance suggests that the proposed approach is feasible, correct and valid.

Han, Jie; Zhao, Yong; Dai, K. W.

2007-08-01

46

Comparison of k-shortest paths and maximum flow routing for network facility restoration  

Microsoft Academic Search

In the development of technologies for span failure restoration, a question arises about the restoration rerouting characteristics to be specified. In theory, maximal rerouting capacity is obtained with a maximum flow (Max Flow) criterion. However, rerouting that realizes the k-successively shortest link disjoint paths (KSP) may be faster, easier, and, in distributed implementation, more robust than a distributed counterpart for

D. Anthony Dunn; Wayne D. Grover; Mike H. MacGregor

1994-01-01

47

Multicast Routing in Wireless Mesh Networks: Minimum Cost Trees or Shortest Path Trees?  

Microsoft Academic Search

There exist two fundamental approaches to multicast routing: shortest path trees (SPTs) and minimum cost trees (MCTs). The SPT algorithms minimize the distance (or cost) from the sender to each receiver, whereas the MCT algorithms minimize the overall cost of the multicast tree. Due to the very large scale and unknown topology of the Internet, computing MCTs for multicast routing

Uyen Trang Nguyen; Jin Xu

2007-01-01

48

Ports Logistics Cost Optimization with Linear Transportation Cost Function and Shortest Path  

Microsoft Academic Search

Suppose the goods transported in accordance with the shortest path and transportation fixed cost considered in land and sea transport system, the sea and land transport problem is analyzed. And then, mathematical models are established and corresponding algorithm is proposed. The algorithm complex degree is. Furthermore, a computational example is offered to demonstrate the steps and effectiveness of the algorithm.

Cui Wanan; Wei Bin

2011-01-01

49

Linear time algorithms for visibility and shortest path problems inside simple polygons  

Microsoft Academic Search

We present linear time algorithms for solving the following problems involving a simple planar polygon P: (i) Computing the collection of all shortest paths inside P from a given source vertex s to all the other vertices of P; (ii) Computing the subpolygon of P consisting of points that are visible from a segment within P; (iii) Preprocessing P so

Leonidas J. Guibas; John Hershberger; Daniel Leven; Micha Sharir; Robert Endre Tarjan

1986-01-01

50

A genetic algorithm for shortest path routing problem and the sizing of populations  

Microsoft Academic Search

This paper presents a genetic algorithmic approach to the shortest path (SP) routing problem. Variable-length chromosomes (strings) and their genes (parameters) have been used for encoding the problem. The crossover operation exchanges partial chromosomes (partial routes) at positionally independent crossing sites and the mutation operation maintains the genetic diversity of the population. The proposed algorithm can cure all the infeasible

Chang Wook Ahn; Rudrapatna S. Ramakrishna

2002-01-01

51

Heterogeneity-aware shortest path routing: flow holding time, user demand and network state  

Microsoft Academic Search

We investigate possible performance improvements by exploring heterogeneity of traffic characteristics when designing a shortest path routing scheme. First we focus on the effect of the maintenance of the link metrics for connections with different holding times. We found that by using a differentiated routing scheme with respect to connection holding times, one can enhance network performance for a range

SHANCHIEH YANG; XUN SU; GUSTAVO DE VECIANA

2001-01-01

52

Visibility-Graph-Based Shortest-Path Geographic Routing in Sensor Networks  

Microsoft Academic Search

We study the problem of shortest-path geographic routing in a static sensor network. Existing algorithms often make routing decisions based on node information in local neighborhoods. However, it is shown by Kuhn et al. that such a design constraint results in a highly undesirable lower bound for routing performance: if a best route has length c ,t hen in the

Guang Tan; Marin Bertier; Anne-Marie Kermarrec

2009-01-01

53

Fighting organized crimes: using shortest-path algorithms to identify associations in criminal networks  

Microsoft Academic Search

Effective and efficient link analysis techniques are needed to help law enforcement and intelligence agencies fight organized crimes such as narcotics violation, terrorism, and kidnapping. In this paper, we propose a link analysis technique that uses shortest-path algorithms, priority-first-search (PFS) and two-tree PFS, to identify the strongest association paths between entities in a criminal network. To evaluate effectiveness, we compared

Jennifer Jie Xu; Hsinchun Chen

2004-01-01

54

The d-edge shortest-path problem for a Monge graph  

SciTech Connect

A complete edge-weighted directed graph on vertices 1,2,...,n that assigns cost c(i,j) to the edge (i,j) is called Monge if its edge costs form a Monge array, i.e., for all i < k and j < l, c[i, j]+c[k,l]{le} < c[i,l]+c[k,j]. One reason Monge graphs are interesting is that shortest paths can be computed quite quickly in such graphs. In particular, Wilber showed that the shortest path from vertex 1 to vertex n of a Monge graph can be computed in O(n) time, and Aggarwal, Klawe, Moran, Shor, and Wilber showed that the shortest d-edge 1-to-n path (i.e., the shortest path among all 1-to-n paths with exactly d edges) can be computed in O(dn) time. This paper`s contribution is a new algorithm for the latter problem. Assuming 0 {le} c[i,j] {le} U and c[i,j + 1] + c[i + 1,j] {minus} c[i,j] {minus} c[i + 1, j + 1] {ge} L > 0 for all i and j, our algorithm runs in O(n(1 + 1g(U/L))) time. Thus, when d {much_gt} 1 + 1g(U/L), our algorithm represents a significant improvement over Aggarwal et al.`s O(dn)-time algorithm. We also present several applications of our algorithm; they include length-limited Huffman coding, finding the maximum-perimeter d-gon inscribed in a given convex n-gon, and a digital-signal-compression problem.

Bein, W.W. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Computer Science; Larmore, L.L. [California Univ., Riverside, CA (United States). Dept. of Computer Science; Park, J.K. [Sandia National Labs.,Albuquerque, NM (United States)

1992-07-14

55

Scaling of average receiving time and average weighted shortest path on weighted Koch networks  

NASA Astrophysics Data System (ADS)

In this paper we present weighted Koch networks based on classic Koch networks. A new method is used to determine the average receiving time (ART), whose key step is to write the sum of mean first-passage times (MFPTs) for all nodes to absorption at the trap located at a hub node as a recursive relation. We show that the ART exhibits a sublinear or linear dependence on network order. Thus, the weighted Koch networks are more efficient than classic Koch networks in receiving information. Moreover, average weighted shortest path (AWSP) is calculated. In the infinite network order limit, the AWSP depends on the scaling factor. The weighted Koch network grows unbounded but with the logarithm of the network size, while the weighted shortest paths stay bounded.

Dai, Meifeng; Chen, Dandan; Dong, Yujuan; Liu, Jie

2012-12-01

56

Genetic Algorithm for Solving Fuzzy Shortest Path Problem in a Network with mixed fuzzy arc lengths  

NASA Astrophysics Data System (ADS)

We are concerned with the design of a model and an algorithm for computing a shortest path in a network having various types of fuzzy arc lengths. First, we develop a new technique for the addition of various fuzzy numbers in a path using ? -cuts by proposing a linear least squares model to obtain membership functions for the considered additions. Then, using a recently proposed distance function for comparison of fuzzy numbers. we propose a new approach to solve the fuzzy APSPP using of genetic algorithm. Examples are worked out to illustrate the applicability of the proposed model.

Mahdavi, Iraj; Tajdin, Ali; Hassanzadeh, Reza; Mahdavi-Amiri, Nezam; Shafieian, Hosna

2011-06-01

57

Wavelength Conversion in All-Optical Networks with Shortest-Path Routing  

Microsoft Academic Search

We consider all-optical networks with shortest-path routing \\u000a that use wavelength-division multiplexing\\u000a and employ wavelength conversion at specific nodes in order to maximize \\u000a their capacity usage. We present efficient algorithms for deciding whether\\u000a a placement of wavelength converters allows the network to run at maximum\\u000a capacity,\\u000a and for finding an optimal wavelength assignment when such a placement\\u000a of converters is\\u000a known.

Thomas Erlebach; Stamatis Stefanakos

2005-01-01

58

Parallel shortest augmenting path algorithm for the assignment problem. Technical report  

SciTech Connect

We describe a parallel version of the shortest augmenting path algorithm for the assignment problem. While generating the initial dual solution and partial assignment in parallel does not require substantive changes in the sequential algorithm, using several augmenting paths in parallel does require a new dual variable recalculation method. The parallel algorithm was tested on a 14-processor Butterfly Plus computer, on problems with up to 900 million variables. The speedup obtained increases with problem size. The algorithm was also embedded into a parallel branch and bound procedure for the traveling salesman problem on a directed graph, which was tested on the Butterfly Plus on problems involving up to 7,500 cities. To our knowledge, these are the largest assignment problems and traveling salesman problems solved so far.

Balas, E.; Miller, D.; Pekny, J.; Toth, P.

1989-04-01

59

A shortest-path graph kernel for estimating gene product semantic similarity  

PubMed Central

Background Existing methods for calculating semantic similarity between gene products using the Gene Ontology (GO) often rely on external resources, which are not part of the ontology. Consequently, changes in these external resources like biased term distribution caused by shifting of hot research topics, will affect the calculation of semantic similarity. One way to avoid this problem is to use semantic methods that are "intrinsic" to the ontology, i.e. independent of external knowledge. Results We present a shortest-path graph kernel (spgk) method that relies exclusively on the GO and its structure. In spgk, a gene product is represented by an induced subgraph of the GO, which consists of all the GO terms annotating it. Then a shortest-path graph kernel is used to compute the similarity between two graphs. In a comprehensive evaluation using a benchmark dataset, spgk compares favorably with other methods that depend on external resources. Compared with simUI, a method that is also intrinsic to GO, spgk achieves slightly better results on the benchmark dataset. Statistical tests show that the improvement is significant when the resolution and EC similarity correlation coefficient are used to measure the performance, but is insignificant when the Pfam similarity correlation coefficient is used. Conclusions Spgk uses a graph kernel method in polynomial time to exploit the structure of the GO to calculate semantic similarity between gene products. It provides an alternative to both methods that use external resources and "intrinsic" methods with comparable performance.

2011-01-01

60

Structural properties of invasion percolation with and without trapping: Shortest path and distributions  

NASA Astrophysics Data System (ADS)

We study several structural properties including the shortest path l between two sites separated by a Euclidean distance r of invasion percolation with trapping (TIP) and without trapping (NIP). For the trapping case we find that the mass M scales with l as M~ldl with dl=1.510+/-0.005 and l scales with r as l~rdmin with dmin=1.213+/-0.005, whereas in the nontrapping case dl=1.671+/-0.006 and dmin=1.133+/-0.005. These values further support previous results that NIP and TIP are in distinct universality classes. We also study numerically using scaling approaches the distribution N(l,r) of the lengths of the shortest paths connecting two sites at distance r in NIP and TIP. We find that it obeys a scaling form N(l,r)~rdf-1-d minf(l/rdmin). The scaling function has a power-law tail for large x values, f(x)~x-h, with a universal value of h~2 for both models within our numerical accuracy.

Schwarzer, Stefan; Havlin, Shlomo; Bunde, Armin

1999-03-01

61

An Improved Ant Colony Algorithm for the Shortest Path Problem in Time-Dependent Networks  

NASA Astrophysics Data System (ADS)

Research of the shortest path problem in time-dependent networks has important practical value. An improved pheromone update strategy suitable for time-dependent networks was proposed. Under this strategy, the residual pheromone of each road can accurately reflect the change of weighted value of each road. An improved selection strategy between adjacent cities was used to compute the cities' transfer probabilities, as a result, the amount of calculation is greatly reduced. To avoid the algorithm converging to the local optimal solution, the ant colony algorithm was combined with genetic algorithm. In this way, the solutions after each traversal were used as the initial species to carry out single-point crossover. An improved ant colony algorithm for the shortest path problem in time-dependent networks based on these improved strategies was presented. The simulation results show that the improved algorithm has greater probability to get the global optimal solution, and the convergence rate of algorithm is better than traditional ant colony algorithm.

Chang, Qing; Liu, Yongqiang; Xiong, Huagang

62

Freight Network Modeling System. Volume IV. Shortest-Path Analysis and Display user's guide  

SciTech Connect

The Freight Network Modeling System (FNEM) is a general and flexible modeling system designed to have wide applicability to a variety of freight transportation analyses. The system consists of compatible network data bases, data management software, models of freight transportation, report generators, and graphics output. In many studies, a model as comprehensive as FNEM is not required. The second model, Shortest-Path Analysis and Display (SPAD), is a simpler model that optimizes routings of single shipments. The routing criteria that can be used are numerous - including minimizing cost, minimizing delay, minimizing population exposure (useful when considering shipments of hazardous materials), and minimizing accident risk. In addition to the above criteria, the routes can also be restricted to those with clearance for oversized loads or with sufficient load capabilities. SPAD can be used interactively and the routes can be displayed graphically. This volume contains a user's guide for SPAD including preprocessor programs and SPAD execution. 7 figs., 19 tabs.

Not Available

1985-04-01

63

Tubule detection in testis images using boundary weighting and circular shortest path.  

PubMed

In studies of germ cell transplantation, measureing tubule diameters and counting cells from different populations using antibodies as markers are very important. Manual measurement of tubule sizes and cell counts is a tedious and sanity grinding work. In this paper, we propose a new boundary weighting based tubule detection method. We first enhance the linear features of the input image and detect the approximate centers of tubules. Next, a boundary weighting transform is applied to the polar transformed image of each tubule region and a circular shortest path is used for the boundary detection. Then, ellipse fitting is carried out for tubule selection and measurement. The algorithm has been tested on a dataset consisting of 20 images, each having about 20 tubules. Experiments show that the detection results of our algorithm are very close to the results obtained manually. PMID:24110438

Zhang, Chao; Sun, Changming; Davey, Rhonda; Su, Ran; Bischof, Leanne; Vallotton, Pascal; Lovell, David; Hope, Shelly; Lehnert, Sigrid; Pham, Tuan D

2013-07-01

64

2-D/3-D irregular shortest-path ray tracing for multiple arrivals and its applications  

NASA Astrophysics Data System (ADS)

The purpose of this study is to introduce a multistage irregular shortest-path method (ISPM) for tracking multiple seismic arrivals including any combinations of transmissions, reflections (or refractions) and mode conversions in complex 2-D/3-D layered media, incorporating irregular interfaces (or subsurface in 3-D) and velocity discontinuities. The basic principle is to first divide the model into several different layers (using irregular cells near each interface, discontinuity and the Earth's undulating surface topography) and then to apply the multistage technique to trace the multiple arrivals. It is possible to realize the multiple arrival tracking with the multistage scheme because the multiple arrivals are just different combinations or conjugations of the simple incident, transmitted, reflected (or refracted) and mode converted waves via the velocity discontinuities and the interfaces. Benchmark tests against the popular multistage fast marching method (FMM) and the multistage MSPM (modified shortest path method) are undertaken to assess the solution accuracy and the computational efficiency. The results show that the multistage ISPM is advantageous over both the multistage FMM and the multistage MSPM in both solution accuracy and CPU time. Several examples (including the Marmousi model) are used to demonstrate the viability and versatility of the multistage ISPM in heterogeneous media, even in the presence of high-velocity contrasts involving interfaces of relatively high curvature. Applications to the seismological problems, such as traveltime tomography and earthquake location, indicate that it is possible to improve the spatial resolution in traveltime tomography and solution accuracy in earthquake location if later arrival information is combined with the first arrivals.

Bai, Chao-Ying; Huang, Guo-Jiao; Zhao, Rui

2010-12-01

65

SHORTEST PATHS FOR THE REEDS-SHEPP CAR: A WORKED OUT EXAMPLE OF THE USE OF GEOMETRIC TECHNIQUES IN NONLINEAR OPTIMAL CONTROL. 1  

Microsoft Academic Search

We illustrate the use of the techniques of modern geometric optimal control theory by studying the shortest paths for a model of a car that can move forwards and backwards. This problem was discussed in recent work by Reeds and Shepp who showed, by special methods, (a) that shortest path motion could always be achieved by means of trajectories of

J. Sussmann; Guoqing Tang

1991-01-01

66

Fast and accurate global multiphase arrival tracking: the irregular shortest-path method in a 3-D spherical earth model  

NASA Astrophysics Data System (ADS)

The traditional grid/cell-based wavefront expansion algorithms, such as the shortest path algorithm, can only find the first arrivals or multiply reflected (or mode converted) waves transmitted from subsurface interfaces, but cannot calculate the other later reflections/conversions having a minimax time path. In order to overcome the above limitations, we introduce the concept of a stationary minimax time path of Fermat's Principle into the multistage irregular shortest path method. Here we extend it from Cartesian coordinates for a flat earth model to global ray tracing of multiple phases in a 3-D complex spherical earth model. The ray tracing results for 49 different kinds of crustal, mantle and core phases show that the maximum absolute traveltime error is less than 0.12 s and the average absolute traveltime error is within 0.09 s when compared with the AK135 theoretical traveltime tables for a 1-D reference model. Numerical tests in terms of computational accuracy and CPU time consumption indicate that the new scheme is an accurate, efficient and a practical way to perform 3-D multiphase arrival tracking in regional or global traveltime tomography.

Huang, Guo-Jiao; Bai, Chao-Ying; Greenhalgh, Stewart

2013-09-01

67

Performance Analysis of Reactive Shortest Single-path and Multipath Routing Mechanism With Load Balance  

Microsoft Academic Search

Research on multi-path routing protocols to provideimproved throughput and route resilience as compared withsingle-path routing has been explored in details in the contextof wired networks. However, multi-path routing mechanism hasnot been explored thoroughly in the domain of ad hoc networks.In this paper, we analyze and compare reactive single-path andmulti-path routing with load balance mechanisms in ad hoc networks,in terms of

Peter P. Pham; Sylvie Perreau

2003-01-01

68

Constrained shortest link-disjoint paths selection: a network programming based approach  

Microsoft Academic Search

Given a graph G with each link in the graph associated with two positive weights, cost and delay, we consider the problem of selecting a set of k link-disjoint paths from a node s to another node t such that the total cost of these paths is minimum and that the total delay of these paths is not greater than

Ying Xiao; Krishnaiyan Thulasiraman; Guoliang Xue

2006-01-01

69

On Shortest-Path All-Optical Networks without Wavelength Conversion Requirements  

Microsoft Academic Search

In all-optical networks with wavelength division multiplexing, every connection is routed along a certain path and assigned a wavelength such that no two connections use the same wavelength on the same link. For a given set P of paths (a routing), let (P) denote the minimum number of wavelengths in a valid wavelength assignment and let L(P ) denote the

Thomas Erlebach; Stamatis Stefanakos

2003-01-01

70

Robot Group Formations: A Dynamic Programming Approach for a Shortest Path Computation  

Microsoft Academic Search

Rigid formations of mobile robots are to be used for special missions in which the task-execution requires a tight cooperation of all units in the group so as to constrain them to keep preassigned mutual distances. In the paper an algorithm for the optimal path-planning of rigid formations of mobile robots is considered for a case in which the path

Federico Gentili; Francesco Martinelli

2000-01-01

71

Dynamic Ray Shooting and Shortest Paths in Planar Subdivisions via Balanced Geodesic Triangulations  

Microsoft Academic Search

We give new methods for maintaining a data structure that supports ray shooting andshortest path queries in a dynamically-changing connected planar subdivision S. Our approachis based on a new dynamic method for maintaining a balanced decomposition of a simplepolygon via geodesic triangles. We maintain such triangulations by viewing their dual treesas balanced trees. We show that rotations in these trees

Michael T. Goodrich; Roberto Tamassia

1997-01-01

72

'Mini small worlds' of shortest link paths crossing domain boundaries in an academic Web space  

Microsoft Academic Search

Summary  Combining webometric and social network analytic approaches, this study developed a methodology to sample and identify Web\\u000a links, pages, and sites that function as small-world connectors affecting short link distances along link paths between different\\u000a topical domains in an academic Web space. The data set comprised 7669 subsites harvested from 109 UK universities. A novel\\u000a corona-shaped Web graph model revealed

Lennart Björneborn

2006-01-01

73

Closing of interrupted vascular segmentations: an automatic approach based on shortest paths and level sets  

NASA Astrophysics Data System (ADS)

Exact segmentations of the cerebrovascular system are the basis for several medical applications, like preoperation planning, postoperative monitoring and medical research. Several automatic methods for the extraction of the vascular system have been proposed. These automatic approaches suffer from several problems. One of the major problems are interruptions in the vascular segmentation, especially in case of small vessels represented by low intensities. These breaks are problematic for the outcome of several applications e.g. FEM-simulations and quantitative vessel analysis. In this paper we propose an automatic post-processing method to connect broken vessel segmentations. The approach proposed consists of four steps. Based on an existing vessel segmentation the 3D-skeleton is computed first and used to detect the dead ends of the segmentation. In a following step possible connections between these dead ends are computed using a graph based approach based on the vesselness parameter image. After a consistency check is performed, the detected paths are used to obtain the final segmentation using a level set approach. The method proposed was validated using a synthetic dataset as well as two clinical datasets. The evaluation of the results yielded by the method proposed based on two Time-of-Flight MRA datasets showed that in mean 45 connections between dead ends per dataset were found. A quantitative comparison with semi-automatic segmentations by medical experts using the Dice coefficient revealed that a mean improvement of 0.0229 per dataset was achieved. In summary the approach presented can considerably improve the accuracy of vascular segmentations needed for following analysis steps.

Forkert, Nils Daniel; Schmidt-Richberg, Alexander; Säring, Dennis; Illies, Till; Fiehler, Jens; Handels, Heinz

2010-03-01

74

Identification of hepatocellular carcinoma related genes with k-th shortest paths in a protein-protein interaction network.  

PubMed

Hepatocellular carcinoma (HCC) is the most common type of liver cancer worldwide and one of the deadliest cancers in Asia. But at present, effective targets for HCC clinical therapy are still limited. The "guilt by association" rule suggests that interacting proteins share the same or similar functions and hence may be involved in the same pathway. This assumption can be used to identify disease related genes from protein association networks constructed from existing PPI data. Given the close association between Hepatitis B virus and Hepatitis B which may lead to HCC, here we develop a computational method to identify hepatocellular carcinoma related genes based on k-th shortest paths in the protein-protein interaction (PPI) network (we set k = 1, 2 in this study). Finally, we found 33 genes whose p-values were less than 0.05, and most of them have been reported to be involved in HCC tumorigenesis and development. The results also provide a new reference for research into HCC oncogenesis and for development of new strategies for HCC clinical therapies. PMID:24056857

Jiang, Min; Chen, Yukang; Zhang, Yuchao; Chen, Lei; Zhang, Ning; Huang, Tao; Cai, Yu-Dong; Kong, Xiangyin

2013-10-01

75

Adiabatic Berry Phase and Hannay Angle for Open Paths  

NASA Astrophysics Data System (ADS)

We obtain the adiabatic Berry phase by defining a generalised gauge potential whose line integral gives the phase holonomy for arbitrary evolutions of parameters. Keeping in mind that for classical integrable systems it is hardly clear how to obtain the open-path Hannay angle, we establish a connection between the open-path Berry phase and Hannay angle by using the parametrised coherent state approach. Using the semiclassical wavefunction we analyse the open-path Berry phase and obtain the open-path Hannay angle. Further, by expressing the adiabatic Berry phase in terms of the commutator of instantaneous projectors with its differential and using Wigner representation of operators we obtain the Poisson bracket between the distribution function and its differential. This enables us to talk about the classical limit of the phase holonomy which yields the angle holonomy for open paths. An operational definition of the Hannay angle is provided based on the idea of the classical limit of the quantum mechanical inner product. A probable application of the open-path Berry phase and Hannay angle to the wave-packet revival phenomena is also pointed out.

Pati, Arun Kumar

1998-11-01

76

OPEN PATH AMBIENT MEASUREMENTS OF POLLUTANTS WITH A DOAS SYSTEM  

EPA Science Inventory

A differential optical absorption spectrometer (DOAS) has been in operation since August 1991 at the U.S. EPA in RTP, NC. he analyzer unit is located in an environmentally-controlled shelter in the EPA parking lot. our separate open optical paths have been established, ranging fr...

77

Conflict-free shortest-time bidirectional AGV routeing  

Microsoft Academic Search

This paper presents an efficient algorithm for finding conflict-free shortest-time routes for automated guided vehicles moving in a bidirectional flow path network. The proposed algorithm is based on Dijkstra's shortest-path method. It maintains, for each node, a list of time windows reserved by scheduled vehicles and a list of free time windows available for vehicles to be scheduled. We introduce

CHANG W. KIM; J. M. A. TANCHOCO

1991-01-01

78

An advanced open-path atmospheric monitor design  

SciTech Connect

The conceptual design of an open-path atmospheric monitor combines an acousto-optic tunable filter for emission spectroscopy (3-14 {mu}m) with a mid-IR (4.6-5.4 {mu}m) for absorption spectroscopy. It utilizes mostly commercially available components, covers a large area ({approximately}4 km radius), measures the distance to any reflecting object, can take measurements along any line-of-sight, and is eye safe. Of twenty test pollutants it is to detect, the concentrations of all twenty will be measurable via emission spectroscopy and ten by the more sensitive absorption spectroscopy.

Taylor, L.; Suhre, D. [Westinghouse Electric Corp., Pittsburgh, PA (United States); Mech, S. [Westinghouse Hanford Co., Richland, WA (United States)

1996-05-01

79

Completely automated open-path FT-IR spectrometry  

Microsoft Academic Search

Atmospheric analysis by open-path Fourier-transform infrared (OP\\/FT-IR) spectrometry has been possible for over two decades\\u000a but has not been widely used because of the limitations of the software of commercial instruments. In this paper, we describe\\u000a the current state-of-the-art of the hardware and software that constitutes a contemporary OP\\/FT-IR spectrometer. We then describe\\u000a advances that have been made in our

Peter R. Griffiths; Limin Shao; April B. Leytem

2009-01-01

80

An Open-path Laser Transmissometer for Atmospheric Extinction Measurements  

SciTech Connect

A transmissometer is an optical instrument which measures transmitted intensity of monochromatic light over a fixed pathlength. Prototype of a simple laser transmissometer has been developed for transmission (or extinction) measurements through suspended absorbers and scatterers in the atmosphere over tens of meters. Instrument consists of a continuous green diode pumped solid state laser, transmission optics, photodiode detectors and A/D data acquisition components. A modulated laser beam is transmitted and subsequently reflected and returned to the unit by a retroreflecting mirror assembly placed several tens of meters away. Results from an open-path field measurement of the instrument are described.

Chandran, P. M. Satheesh; Krishnakumar, C. P.; Varma, Ravi [Department of Physics, National Institute of Technology Calicut, Calicut, Kerala 673 601 (India); Yuen, Wangki; Rood, Mark J. [Department of Civil and Environmental Engineering, University of Illinois Urbana-Champaign, Urbana (United States)

2011-10-20

81

Dynamical paths and universality in continuous-variable open systems  

NASA Astrophysics Data System (ADS)

We address the dynamics of quantum correlations in continuous-variable open systems and analyze the evolution of bipartite Gaussian states in independent noisy channels. In particular, we introduce the notion of dynamical path through a suitable parametrization for symmetric states and focus attention on phenomena that are common to Markovian and non-Markovian Gaussian maps under the assumptions of weak coupling and the secular approximation. We find that the dynamical paths in the parameter space are universal, that is, they depend only on the initial state and on the effective temperature of the environment, with non-Markovianity that manifests itself in the velocity of running over a given path. This phenomenon allows one to map non-Markovian processes onto Markovian ones and may reduce the number of parameters needed to study a dynamical process, e.g., it may be exploited to build constants of motions valid for both Markovian and non-Markovian maps. Universality is also observed in the value of Gaussian discord at the separability threshold, which itself is function of the initial conditions only, in the limit of high temperature. We also prove the existence of excluded regions in the parameter space, i.e., sets of states that cannot be linked by any Gaussian dynamical map.

Cazzaniga, Andrea; Maniscalco, Sabrina; Olivares, Stefano; Paris, Matteo G. A.

2013-09-01

82

TATP stand-off detection with open path: FTIR techniques  

NASA Astrophysics Data System (ADS)

TATP is a very easy to synthesize [9], sensitive, high explosive [10] and high volatile explosive [1, 3, 7] with great absorption in the IR Spectra [4, 5, 6]. In this project we detect TATP gas traces with open path FTIR - techniques. The first project phase was to construct and build a heatable multi-reflection cell with adjustable optical path length and a heatable intake to evaporate solid TATP samples. In this cell reference TATP - spectra were collected under controlled conditions with a Bruker FTIR system (Typ OPAG 33). The next step was to find out how the TATP gas will be diluted in the ambient air and validate some physical properties which are described inconsistently in literature e.g. evaporation rates. We constructed a special double - T shaped chamber with stabile air conditions. In this chamber the dispersion kinetics of the TATP vapour could be tested. It turned out that the TATP vapours has the tendency to drop down. Therefore the highest TATP - concentrations were measured below the TATP sample. During the investigation for this study it turned out, that some materials scrub the TATP- vapour out of the air, e.g. Metals, fabric, leather. In the second phase of the project successful open path FTIR- measurements were taken in ambient air and will be continued with different system configurations of the OPAG 33 to lower the detection limits. Also successful measurements were taken in indoor ambient air with a Hyper spectral camera (passive FTIR with array sensor) to detect TATP in solid and gaseous phase. This technique allows detecting TATP and identifying the TATP source. The poster shows some selected results of the continued research.

Fischer, C.; Pohl, T.; Weber, K.; Vogel, A.; van Haren, G.; Schweikert, W.

2012-10-01

83

Evaluation of an Open-Path Fourier Transform Infrared Spectrophotometer Using an Exposure Chamber  

Microsoft Academic Search

This study investigated the use of a controlled outdoor exposure chamber to evaluate the accuracy of an open-path Fourier transform infrared (OP-FTIR) spectrometer, using path lengths that are found in the workplace. A range of stable homogenous pollutant concentrations of toluene and cyclohexane were generated in the chamber, multiple backgrounds were taken throughout each sampling day, and open-path measurements were

L. A. Todd

1996-01-01

84

Open-path FTIR measurement of criteria pollutants and other ambient species in an industrial city  

Microsoft Academic Search

Recent improvements in signal processing techniques for Open- Path FTIR (OP-FTIR) have resulted in a dramatic reduction of detection limits for infrared active chemicals including ambient species. These lower detection limits opens the open- path FTIR technology to new applications involving monitoring and analyzing ambient air in urban settings. To test application of OP-FTIR technology to urban applications, an RAM2000TM

Robert H. Kagann; C. D. Wang; King L. Chang; Chung H. Lu

1999-01-01

85

Debugging ants: How ants find the shortest route  

Microsoft Academic Search

Collective foraging in ant colonies is as remarkable in that ants are solving a distributed control and optimization task that is still not fully untravelled. Ants deposit pheromone as they travel, and paths with more pheromone are preferred by succeeding ants. Without any direct communication amongst themselves, ants quickly abandon other trails to concentrate on the shortest one. If the

Jayadeva; Sameena Shah; R. Kothari; Suresh Chandra

2011-01-01

86

PATH  

NSDL National Science Digital Library

Started in the 1970s as an agency to assist men and women in gaining access to a variety of birth control methods, PATH has since expanded its focus to provide "sustainable, culturally relevant [health] solutions, enabling communities worldwide to break longstanding cycles of poor health." The PATH website has more than a dozen videos and slideshows available to visitors at the "Our Multimedia" link near the bottom right hand corner of the homepage. A three-minute video entitled "Better Nutrition For Life" educates visitors about an innovative rice product that could bring greater nutrition to millions of malnourished people where rice is a staple food. The product is Ultra Rice, and is actually fortified pasta that looks, cooks, and tastes like rice, but is fortified with nutrients. The "rice" can be fortified with the needed nutrients the particular population being served is lacking. A slideshow about TB in the Ukraine, explains to visitors why there has been a resurgence of TB in Eastern Europe, and how PATH and its partners set out to help control it throughout the region.

87

Multipollutant concentration measurements around a concentrated swine production facility using open-path FTIR spectrometry  

Microsoft Academic Search

Open-path Fourier transform infrared (OP\\/FTIR) spectrometry was used to measure the concentrations of ammonia, methane, and other atmospheric gases around an integrated industrial swine production facility in eastern North Carolina. Several single-path measurements were made over an 8-day period from 11 to 22 January 1999. Nine different monitoring paths were configured to determine the concentration ranges of ammonia and methane

J. W. Childers; E. L. Thompson; D. B. Harris; D. A. Kirchgessner; M. Clayton; D. F. Natschke; W. J. Phillips

2001-01-01

88

Use of an Open-path FTIR sensor to measure VOCs at the Hanford Site.  

National Technical Information Service (NTIS)

An Open-path Fourier Transform Infrared (OP-FTIR) instrument was used to measure carbon tetrachloride vapor emitted from contaminated soil and monitoring wells in the 200 West Area of the Hanford Site in southeastern Washington State. Historical activitie...

R. H. Kagann J. D. Fancher S. D. Tomich

1994-01-01

89

Simultaneous Measurement of Vaporous and Aerosolized Threats by Active Open Path FTIR.  

National Technical Information Service (NTIS)

The Environmental Protection Agency's open-path Fourier transform infrared (OP-FTIR) activities include passive and active measurements in several stack and fugitive emission monitoring applications. Extensive research has been devoted during the pas...

R. A. Hashmonay R. M. Varma M. Modrak R. H. Kagann P. D. Sullivan

2004-01-01

90

Particulate Matter Measurements using Open-Path Fourier Transform Infrared Spectroscopy.  

National Technical Information Service (NTIS)

Open-path Fourier transform infrared (OP-FTIR) spectroscopy is an accepted technology for measuring gaseous air contaminants. OP-FTIR absorbance spectra acquired during changing aerosols conditions reveal related changes in very broad baseline features. U...

R. A. Hashmonay D. B. Harris

2001-01-01

91

Quality-assurance\\/quality-control issues in open-path FTIR monitoring  

Microsoft Academic Search

Although much effort has been directed toward developing quality assurance\\/quality control procedures in open-path Fourier transform infrared (OP\\/FTIR) monitoring, many issues remain unresolved. Despite efforts in this area, there are still no universally accepted procedures for determining the accuracy and precision of OP\\/FTIR data. When the concentrations of atmospheric species are measured over a long, open path, several factors can

George M. Russwurm; Jeffrey W. Childers

1997-01-01

92

Reimann surfaces with shortest geodesic of maximal length  

Microsoft Academic Search

I describe Riemann surfaces of constant curvature -1 with the property that the length of its shortest simple closed geodesic is maximal with respect to an open neighborhood in the corresponding Teichmüller space. I give examples of such surfaces. In particular, examples are presented which are modelled upon (Euclidean) polyhedra. This problem is a non-Euclidean analogue of the well known

P. Schmutz

1993-01-01

93

Applying Open-Path FTIR with Computed Tomography to Evaluate Personal Exposures. Part 1: Simulation Studies  

Microsoft Academic Search

This paper presents the theoretical background and the numerical evaluation results obtained using computed tomography coupled with open-path Fourier transform infrared (CT-FTIR) measurements to estimate personal exposures. In this simulation study, we first tested the one- dimensional scenario with a five-beam segment geometry. A series of Gaussian plumes and the corresponding path-integrated concentrations (PICs) were simulated. The personal exposures were

CHANG-FU WU; MICHAEL G. YOST; RAM A. HASHMONAY; TIMOTHY V. LARSON; STEVEN E. GUFFEY

2005-01-01

94

Chirped laser dispersion spectroscopy for remote open-path trace-gas sensing.  

PubMed

In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 ?m quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best of our knowledge this is the first demonstration of open-path laser-based trace-gas detection using a molecular dispersion measurement. The prototype sensor achieves a detection limit down to the single-ppbv level and exhibits excellent stability and robustness. The instrument characterization, field deployment performance, and the advantages of applying dispersion sensing to sensitive trace-gas detection in a remote open-path configuration are presented. PMID:23443389

Nikodem, Michal; Wysocki, Gerard

2012-11-28

95

OPEN PATH TUNABLE DIODE LASER ABSORPTION SPECTROSCOPY FOR ACQUISITION OF FUGITIVE EMISSION FLUX DATA  

EPA Science Inventory

Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. EPA has developed a gorund-based optical remote sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transfor...

96

Estimating ammonia and methane emissions from CAFOs using an open-path optical remote sensing technology  

Technology Transfer Automated Retrieval System (TEKTRAN)

The U.S. EPA recently demonstrated the open-path optical remote sensing technology to identify hot spots and estimate mass flux of fugitive gases from closed landfill. The objective of this research is to validate this technology for estimating ammonia and methane emission from concentrated animal f...

97

Combination of Neural Network and SBFM Algorithm for Monitoring VOCs Distribution by Open Path FTIR Spectrometry  

Microsoft Academic Search

In this research, the combination of artificial neural network (ANN) modeling and smooth basis function minimization (SBFM) algorithm were applied to Open Path Fourier transform infrared spectroscopy (OP?FTIR) for monitoring volatile organic compounds' concentration distribution in the air. ANN was utilized to analyze the measured mixture spectra containing chloroform, methanol, and methylene chloride; Then, SBFM was used to reconstruct each

Yibo Ren; Yan Li; Baihua Yu; Junde Wang; Lanping Hu

2007-01-01

98

Measurement of tracer gas distributions using an open-path FTIR system coupled with computed tomography  

Microsoft Academic Search

Optical remote sensing and iterative computed tomography (CT) can be combined to measure the spatial distribution of gaseous pollutant concentrations in a plane. We have conducted chamber experiments to test this combination of techniques using an Open Path Fourier Transform Infrared Spectrometer (OP-FTIR) and a standard algebraic reconstruction technique (ART). ART was found to converge to solutions that showed excellent

Anushka C. Drescher; Michael G. Yost; Doo Y. Park; Steven P. Levine; Ashok J. Gadgil; Marc L. Fischer; William W. Nazaroff

1995-01-01

99

Evaluation of Open-Path FTIR Spectrometers for Monitoring Multiple Chemicals in Air  

Microsoft Academic Search

There has been mounting interest in the use of open-path Fourier transform infrared (OP-FTIR) spectrometers for occupational and environmental air monitoring. Although this technology is gaining acceptance in the environmental field, there has not yet been a comprehensive assessment of instrument performance and the analytical limitations of this method have not been thoroughly delineated. Unlike extractive FTIR spectrometers, calibration of

S. K. Farhat; L. A. Todd

2000-01-01

100

Advances in Data Processing for Open-path Fourier Transform Infrared Spectrometry of Greenhouse Gases  

Technology Transfer Automated Retrieval System (TEKTRAN)

The automated quantification of three greenhouse gases, ammonia, methane and nitrous oxide, in the vicinity of a large dairy farm by open-path Fourier transform infrared (OP/FT-IR) spectrometry at intervals of 5 minutes is demonstrated. Spectral pretreatment, including the detection and correction ...

101

The stable paths problem and interdomain routing  

Microsoft Academic Search

Dynamic routing protocols such as RIP and OSPF essentially implement distributed algorithms for solving the shortest paths problem. The border gateway protocol (BGP) is currently the only interdomain routing protocol deployed in the Internet. BGP does not solve a shortest paths problem since any interdomain protocol is required to allow policy-based metrics to override distance-based metrics and enable autonomous systems

Timothy G. Griffin; F. Bruce Shepherd; Gordon T. Wilfong

2002-01-01

102

SIMULTANEOUS CALIBRATION OF OPEN-PATH AND CONVENTIONAL POINT MONITORS FOR MEASURING AMBIENT AIR CONCENTRATIONS OF SULPHUR DIOXIDE, OZONE, AND NITROGEN DIOXIDE  

EPA Science Inventory

A two-stage dilution system and an associated procedure to simultaneously calibrate both open-path (long-path) and conventional point air monitors have been used successfully during a comparison test study of open-path monitoring systems in Houston during August, 1 993. wo open-p...

103

On-line monitoring of solvent emission rates using an open path FTIR analyser.  

PubMed

Solvent mixture concentrations in paint and resin manufacture were on-line monitored using a portable open path Fourier transform infrared (OP-FTIR) analyser in order to determine solvent emission rates into workspaces. The mean solvent emission rate was 0.46 kg/h in paint production and 0.35 kg/h in resin manufacture. Expressed as emission factor, i.e. evaporated portion of the total solvent mass used, the corresponding values were 0.01% for paint production and 0.1% for resin manufacture. The OP-FTIR instrument together with advanced spectra analysis software facilitated a rapid identification of solvent mixtures and on-line concentration monitoring with good temporal resolution. The analyser seems to be particularly useful in industrial hygiene applications where spatial average concentrations are needed. The further benefit of the open path instrument is that no sampling lines, pumps or sample cells are needed. PMID:12176764

Räisänen, Jouni; Niemelä, Raimo

2002-07-01

104

An open path, fast response infrared absorption gas analyzer for H2O and CO2  

Microsoft Academic Search

An open path infrared absorption based instrument for fast response measurements of H2O and CO2 fluctuations is described. This instrument performed reliably in several field experiments in both terrestrial and marine environments, on both fixed (tower) and mobile (boat, plane) flux platforms. Noise levels for H2O and CO2 concentrations were less than 10 mg\\/m3 and 300 ?g\\/m3, respectively for frequencies

David L. Auble; Tilden P. Meyers

1992-01-01

105

Orthogonal Signal Correction Used for Noise Elimination of Open Path Fourier Transform Infrared Spectra  

Microsoft Academic Search

Open path Fourier transform infrared (OP–FTIR) spectroscopy is qualified in detecting mixtures by multivariate calibration methods such as partial least squares (PLS); however, its applications are still restricted by background noise, which is unavoidable for OP–FTIR spectra and cannot be resolved solely by multivariate calibration methods. Hence OP–FTIR spectra are often pretreated before the data are subjected to the multivariate

Lin Zhang; Liming Zhang; Yan Li; Junde Wang

2005-01-01

106

Applying open-path Fourier transform infrared spectroscopy for measuring aerosols  

Microsoft Academic Search

This paper examines the feasibility of using Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR) to measure aerosols. The extinction spectra of water, ammonium nitrate, and ammonium sulfate aerosols were first simulated with various particle size distributions (geometric mean ranged from 2 to 10 ? m; geometric standard deviation ranged from 1.1 to 2.5) based on the Mie theory. An optimization procedure

Chang-Fu Wu; Yen-Ling Chen; Chih-Chieh Chen; Tzu-Ting Yang; Pao-Erh Chang

2007-01-01

107

Open-path Fourier transform infrared spectrometry characterization of low temperature combustion gases in biomass fuels  

Microsoft Academic Search

Accurate determination of gas concentration emitted during thermal degradation (pyrolysis) of biomass in forest fires is one of the keypoints in recent research on physical-based fire spread models. However, it is a very cumbersome task not well solved by classical invasive sensors and procedures. In this work, a methodology to use open-path Fourier transform-based infrared (OP-FTIR) spectrometry has been applied

A. J. de Castro; A. M. Lerma; F. López; M. Guijarro; C. Díez; C. Hernando; J. Madrigal

2007-01-01

108

International Diffusion of Open Path FTIR Technology and Air Monitoring Methods: Taiwan (Republic of China)  

Microsoft Academic Search

International cooperation and diffusion of environmental technologies is a central goal of the U.S. EPA Environmental Technology Initiative, and is of great interest to many countries. One objective is to exchange knowledge and skills concerning new monitoring technologies. In this case, the technology was open path Fourier Transform Infrared Spectrometry (op-FTIR).Taiwan is a high-technology, newly industrialized country. Because of air

Steven P. Levine

1996-01-01

109

Open-path FTIR measurements at an urban area in Germany  

Microsoft Academic Search

The open-path FTIR (op-FTIR) measurement method has several characteristics, which make the method attractive for monitoring air pollutants in urban areas. In this paper recent op-FTIR measurements at an urban site in Germany are presented. These measurements include the first direct intercomparisons between op-FTIR measurements and an official measurement system of the Environmental State Agency in North- Rhine-Westphalia. These intercomparisons

Konradin Weber; Johannes Weidemann; Guenther van Haren; Torsten Lamp

1995-01-01

110

Imaging open-path Fourier transform infrared spectrometer for 3D cloud profiling  

Microsoft Academic Search

OPTRA and University of North Carolina are developing an imaging open-path Fourier transform infrared (I-OP-FTIR) spectrometer for 3D profiling of chemical and biological agent simulant plumes released into test ranges and chambers. An array of I-OP-FTIR instruments positioned around the perimeter of the test site, in concert with advanced spectroscopic algorithms, enables real time tomographic reconstruction of the plume. The

Julia Rentz Dupuis; David J. Mansur; Robert Vaillancourt; Thomas Evans; Elizabeth Schundler; Lori Todd; Kathleen Mottus

2008-01-01

111

Assessment of data intercomparability and data quality for multiple open-path FTIR systems  

Microsoft Academic Search

There exists little information concerning the quality of data generated from open-path Fourier transform infrared spectrometer (OP-FTIR) systems as applied to measuring toxic air pollutants. The U.S. Environmental Protection Agency, Region VII conducted a study designed to assess the intercomparability and data quality for several OP-FTIR systems. This paper describes the design of the study, presents the resulting data, and

Jody L. Hudson; M. J. Thomas; John R. Helvig; Billy J. Fairless; Ray E. Carter; Glen A. Marotz

1993-01-01

112

Open-path FTIR measurements at an urban area in Germany  

NASA Astrophysics Data System (ADS)

The open-path FTIR (op-FTIR) measurement method has several characteristics, which make the method attractive for monitoring air pollutants in urban areas. In this paper recent op-FTIR measurements at an urban site in Germany are presented. These measurements include the first direct intercomparisons between op-FTIR measurements and an official measurement system of the Environmental State Agency in North- Rhine-Westphalia. These intercomparisons revealed very good results.

Weber, Konradin; Weidemann, Johannes; van Haren, Guenther; Lamp, Torsten

1995-05-01

113

Assessment of data intercomparability and data quality for multiple open-path FTIR systems  

NASA Astrophysics Data System (ADS)

There exists little information concerning the quality of data generated from open-path Fourier transform infrared spectrometer (OP-FTIR) systems as applied to measuring toxic air pollutants. The U.S. Environmental Protection Agency, Region VII conducted a study designed to assess the intercomparability and data quality for several OP-FTIR systems. This paper describes the design of the study, presents the resulting data, and discusses the conclusions reached.

Hudson, Jody L.; Thomas, M. J.; Helvig, John R.; Fairless, Billy J.; Carter, Ray E.; Lane, Dennis D.; Marotz, Glen A.

1993-03-01

114

Open-Path Tunable Diode Laser Absorption Spectroscopy for Acquisition of Fugitive Emission Flux Data  

Microsoft Academic Search

Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. Environmental Protection Agency (EPA) has developed a ground-based optical remote-sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transform infrared spectroscopy (OP–FTIR) has been the primary technique for acquisition of pollutant concentration data used in this emission measurement method.

Eben D. Thoma; Richard C. Shores; Edgar L. Thompson; D. Bruce Harris; Susan A. Thorneloe; Ravi M. Varma; Ram A. Hashmonay; Mark T. Modrak; David F. Natschke; Heather A. Gamble

2005-01-01

115

On-line Monitoring of Solvent Emission Rates Using an Open Path FTIR Analyser  

Microsoft Academic Search

Solvent mixture concentrations in paint and resin manufacture were on-line monitored using a portable open path Fourier transform infrared (OP-FTIR) analyser in order to determine solvent emission rates into workspaces. The mean solvent emission rate was 0.46 kg\\/h in paint production and 0.35 kg\\/h in resin manufacture. Expressed as emission factor, i.e. evaporated portion of the total solvent mass used,

J. RAISANEN; RAIMO NIEMELÄ

2002-01-01

116

Transmission quantification for open path Fourier transform spectroscopy with temperature compensation  

Microsoft Academic Search

This dissertation contains analyses of new methods for determining the concentration and temperature of atmospheric gases from the data generated by an open-path Fourier transform (OP-FTIR) spectrometer. The concept of FTIR and the subset OP-FTIR are explained in terms of the physical instrumentation and the traditional Beer-Lambert Law based absorbance quantification. The important problems of background collection and water vapor

Robert Stiles Crampton

2007-01-01

117

The Exact Subgraph Recoverable Robust Shortest Path Problem  

NASA Astrophysics Data System (ADS)

Passengers of a public transportation system are often forced to change their planned route due to deviation in travel times. Rerouting is mostly done by simple means such as announcements. We introduce a model, in which the passenger computes his optimal route on his mobile device in a given subnetwork according to the actual travel times. Those travel times are sent to him as soon as a delay occurs.

Büsing, Christina

118

Visibility-Polygon Search and Euclidean Shortest Paths  

Microsoft Academic Search

Consider a collection of disjoint polygons in the plane containing a total of n edges. We show how to build, in O(n2) time and space, a data structure from which in O(n) time we can compute the visibility polygon of a given point with respect to the polygon collection. As an application of this structure, the visibility graph of the

Takao Asano; Tetsuo Asano; Leonidas J. Guibas; John Hershberger; Hiroshi Imai

1985-01-01

119

Open path atmospheric spectroscopy using room temperature operated pulsed quantum cascade laser.  

PubMed

We report the application of a distributed feedback quantum cascade laser for 5.8 km long open path spectroscopic monitoring of ozone, water vapor and CO(2). The thermal chirp during a 140 or 200 ns long excitation pulse is used for fast wavelength scanning. The fast wavelength scanning has the advantage of the measured spectra not being affected by atmospheric turbulence, which is essential for long open path measurements. An almost linear tuning of about 0.6 and 1.2 cm(-1) is achieved, respectively. Lines from the nu(3) vibrational band of the ozone spectra centered at 1,031 and 1,049 cm(-1) is used for ozone detection by differential absorption. The lowest column densities (LCD) for ozone of the order of 0.3 ppmm retrieved from the absorption spectra for averaging times less than 20s are better then the LCD value of 2 ppmm measured with UV DOAS systems. The intrinsic haze immunity of mid-IR laser sources is an additional important advantage of mid-IR open path spectroscopy, compared with standard UV-vis DOAS. The third major advantage of the method is the possibility to measure more inorganic and organic atmospheric species compared to the UV-vis DOAS. PMID:16503192

Taslakov, M; Simeonov, V; van den Bergh, H

2006-02-24

120

Feasibility study of detection of hazardous airborne pollutants using passive open-path FTIR  

NASA Astrophysics Data System (ADS)

In recent years open-path FTIR systems (active and passive) have demonstrated great potential and success for monitoring air pollution, industrial stack emissions, and trace gas constituents in the atmosphere. However, most of the studies were focused mainly on monitoring gaseous species and very few studies have investigated the feasibility of detecting bio-aerosols and dust by passive open-path FTIR measurements. The goal of the present study was to test the feasibility of detecting a cloud of toxic aerosols by a passive mode open-path FTIR. More specifically, we are focusing on the detection of toxic organophosphorous nerve agents for which we use Tri-2-ethyl-hexyl-phosphate as a model compound. We have determined the compounds' optical properties, which were needed for the radiative calculations, using a procedure developed in our laboratory. In addition, measurements of the aerosol size distribution in an airborne cloud were performed, which provided the additional input required for the radiative transfer model. This allowed simulation of the radiance signal that would be measured by the FTIR instrument and hence estimation of the detection limit of such a cloud. Preliminary outdoor measurements have demonstrated the possibility of detecting such a cloud using two detection methods. However, even in a simple case consisting of the detection of a pure airborne cloud, detection is not straightforward and reliable identification of the compound would require more advanced methods than simple correlation with spectral library.

Segal-Rosenheimer, M.; Dubowski, Y.; Jahn, C.; Schäfer, K.; Gerl, G.; Linker, R.

2010-04-01

121

Formal Language Constrained Path Problems  

Microsoft Academic Search

Given an alphabet ?, a (directed) graph G whose edges are weighted and ?-labeled, and a formal language L ? ??, the formal-language-constrained shortest\\/simple path problem con- sists of finding a shortest (simple) path p in G complying with the additional constraint that l(p) ? L. Here l(p) denotes the unique word obtained by concatenating the ?-labels of the edges

Christopher L. Barrett; Riko Jacob; Madhav V. Marathe

1998-01-01

122

cPath: open source software for collecting, storing, and querying biological pathways  

PubMed Central

Background Biological pathways, including metabolic pathways, protein interaction networks, signal transduction pathways, and gene regulatory networks, are currently represented in over 220 diverse databases. These data are crucial for the study of specific biological processes, including human diseases. Standard exchange formats for pathway information, such as BioPAX, CellML, SBML and PSI-MI, enable convenient collection of this data for biological research, but mechanisms for common storage and communication are required. Results We have developed cPath, an open source database and web application for collecting, storing, and querying biological pathway data. cPath makes it easy to aggregate custom pathway data sets available in standard exchange formats from multiple databases, present pathway data to biologists via a customizable web interface, and export pathway data via a web service to third-party software, such as Cytoscape, for visualization and analysis. cPath is software only, and does not include new pathway information. Key features include: a built-in identifier mapping service for linking identical interactors and linking to external resources; built-in support for PSI-MI and BioPAX standard pathway exchange formats; a web service interface for searching and retrieving pathway data sets; and thorough documentation. The cPath software is freely available under the LGPL open source license for academic and commercial use. Conclusion cPath is a robust, scalable, modular, professional-grade software platform for collecting, storing, and querying biological pathways. It can serve as the core data handling component in information systems for pathway visualization, analysis and modeling.

Cerami, Ethan G; Bader, Gary D; Gross, Benjamin E; Sander, Chris

2006-01-01

123

Tightening non-simple paths and cycles on surfaces  

Microsoft Academic Search

We describe algorithms to compute the shortest path homo- topic to a given path, or the shortest cycle freely homotopic to a given cycle, on an orientable combinatorial surface. Unlike earlier results, our algorithms do not require the input path or cycle to be simple. Given a surface with complexity n, genus g ? 2, and no boundary, we construct

Éric Colin De Verdière; Jeff Erickson

2006-01-01

124

The Path Planning for Mobile Robot Based on Voronoi Diagram  

Microsoft Academic Search

In order to get the shortest path of the mobile robot, Voronoi diagram has been introduced to the robot path planning in the paper. The paper uses the voronoi diagram method to model the work space, and obtained the global shortest path by the improved Dijkstra algorithm, besides, when dealing with the unknown static obstacles, the paper adopt one method

Huiying Dong; Wenguang Li; Jiayu Zhu; Shuo Duan

2010-01-01

125

Open-path millimeter-wave spectroscopy in the 225--315 GHz range  

SciTech Connect

This paper discusses the development of an open-path millimeter-wave (mm-wave) spectroscopy system in the 225--315 GHz atmospheric window. The new system is primarily a monostatic swept-frequency radar consisting of a mm-wave sweeper, hot-electron-bolometer or Schottky detector, and trihedral reflector. The heart of the system is a Russian backward-wave oscillator (BWO) tube that is tunable over 225--350 GHz. A mm-wave sweeper has been built with the BWO tube to sweep the entire frequency range within 1 s. The chemical plume to be detected is situated between the transmitter/receiver and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring swept-frequency radar signals with and without the plume in the beam path. Because of power supply noise and thermal instabilities within the BWO structure over time, the BWO frequencies fluctuate between sweeps and thus cause errors in baseline subtraction. To reduce this frequency-jitter problem, a quasi-optical Fabry-Perot cavity is used in conjunction with the radar for on-line calibration of sweep traces, allowing excellent baseline subtraction and signal averaging. Initial results of the new system are given for open-path detection of chemicals.

Gopalsami, N.; Bakhtiari, S.; Raptis, A.C. [Argonne National Lab., IL (United States). Energy Technology Div.

1996-10-01

126

On Bounded Distance Decoding, Unique Shortest Vectors, and the Minimum Distance Problem  

Microsoft Academic Search

We prove the equivalence, up to a small polynomial approximation factor Ö{n\\/logn}\\\\sqrt{n\\/\\\\log n}, of the lattice problems uSVP (unique Shortest Vector Problem), BDD (Bounded Distance Decoding) and GapSVP (the decision version of the Shortest Vector Problem). This resolves a long-standing open problem about the relationship\\u000a between uSVP and the more standard GapSVP, as well the BDD problem commonly used in

Vadim Lyubashevsky; Daniele Micciancio

2009-01-01

127

Simultaneous Calibration of Open-Path and Conventional Point Monitors for Measuring Ambient Air Concentrations of Sulfur Dioxide, Ozone, and Nitrogen Dioxide.  

National Technical Information Service (NTIS)

A two-stage dilution system and an associated procedure to simultaneously calibrate both open-path (long-path) and conventional point air monitors have been used successfully during a comparison test study of open-path monitoring systems in Houston during...

F. F. McElroy J. Hodgeson T. A. Lumpkin K. A. Rehme R. K. Stevens

1993-01-01

128

Imaging open-path Fourier transform infrared spectrometer for 3D cloud profiling  

NASA Astrophysics Data System (ADS)

An imaging open-path Fourier transform infrared (I-OP-FTIR) spectrometer is being developed for real-time three-dimensional cloud profiling. The system employs a single modulator and a novel optical configuration which projects an array of angularly dispersed IR beams, each of which exhibits comparable throughput to a single channel OP-FTIR, to an array of respective retroreflector arrays remotely located at the opposite side of the test grid. The return light from each retroreflector array is imaged onto respective detectors that record the spatially-resolved interferograms which are subsequently transformed and analyzed for molecular content via advanced multicomponent algorithms. The result is a capability to sensitively, quantitatively, and simultaneously measure the molecular absorbance and associated concentration-pathlength of an open release plume over a spatial region. Use of two or more I-OP-FTIR sensors around the perimeter of the release allows for tomographic reconstruction of the concentration map of each molecular species contained in the plume. This approach realizes the high sensitivity of an OP-FTIR spectrometer without adding the expense and logistical difficulties associated with installing a large number of spectrometer units required for the cloud profiling application. In addition, the active spectral measurement supports detection in zero temperature contrast conditions where the plume is the same temperature as the background. A further reduction in cost and weight is achieved through the use of low-cost plastic press molded retroreflector arrays to return the spatially dispersed open path beams.

Dupuis, Julia R.; Mansur, David J.; Engel, James R.; Vaillancourt, Robert; Todd, Lori; Mottus, Kathleen

2007-10-01

129

A Unified Approach to Path Problems  

Microsoft Academic Search

A general method is described for solving path problems on directed graphs. Such path problems include finding shortest paths, solving sparse systems of hnear equaUons, and carrying out global flow analysis of computer programs The method consists of two steps First, a collecUon of regular expressions representmg sets of paths m the graph Is constructed This can be done by

Robert Endre Tarjan; TAR JAN

1981-01-01

130

An open path, fast response infrared absorption gas analyzer for H2O and CO2  

NASA Astrophysics Data System (ADS)

An open path infrared absorption based instrument for fast response measurements of H2O and CO2 fluctuations is described. This instrument performed reliably in several field experiments in both terrestrial and marine environments, on both fixed (tower) and mobile (boat, plane) flux platforms. Noise levels for H2O and CO2 concentrations were less than 10 mg/m3 and 300 ?g/m3, respectively for frequencies between 0.005 and 10 Hz. Drifts in instrument output, associated with changes in instrument temperature, are compensated for electronically.

Auble, David L.; Meyers, Tilden P.

1992-05-01

131

TDLAS-based open-path laser hygrometer using simple reflective foils as scattering targets  

NASA Astrophysics Data System (ADS)

We present a new, very simple to use and very easy to align, inexpensive, robust, mono-static optical hygrometer based on tunable diode laser absorption spectroscopy (TDLAS) that makes use of very inexpensive reflective foils as scattering targets at the distant side of the absorption path. Various alternative foils as scattering targets were examined concerning their reflective behaviour and their suitability for TDLAS applications. Using a micro prismatic reflection tape as the optimum scattering target we determined absolute water vapour concentrations employing open path TDLAS. With the reflection tape being in a distance of 75 cm to 1 m (i.e., absorption path lengths between 1.5 and 2 m) we detected ambient H2O concentrations of up to 12,300 ppmv with detectivities of 1 ppm which corresponds to length and bandwidth normalized H2O detection limits of up to 0.9 ppmv m/ sqrt {{Hz}} , which is only a factor of 2 worse than our previous bi-static TDLAS setups (Hunsmann, Appl. Phys. B 92:393-401, 1). This small sensitivity disadvantage is well compensated for by the simplicity of the spectrometer setup and particularly by its extreme tolerance towards misalignment of the scattering target.

Seidel, A.; Wagner, S.; Ebert, V.

2012-11-01

132

Open-path trace gas detection of ammonia based on cavity-enhanced absorption spectroscopy  

NASA Astrophysics Data System (ADS)

A compact open-path optical ammonia detector is developed. A tunable external-cavity diode laser operating at 1.5 ?m is used to probe absorptions of ammonia via the cavity-enhanced absorption (CEA) technique. The detector is tested in a climate chamber. The sensitivity and linearity of this system are studied for ammonia and water at atmospheric pressure. A cluster of closely spaced rovibrational overtone and combination band transitions, observed as one broad absorption feature, is used for the detection of ammonia. On these molecular transitions a detection limit of 100 ppb (1 s) is determined. The ammonia measurements are calibrated independently with a chemiluminescence monitor. Compared to other optical open-path detection methods in the 1-2 ?m region, the present result shows an improved sensitivity for contactless ammonia detection by over one order of magnitude. Using the same set-up, a detection limit of 100 ppm (1 s) is determined for the detection of water at atmospheric pressure.

Peeters, R.; Berden, G.; Apituley, A.; Meijer, G.

133

Quantum cascade laser open-path system for remote sensing of trace gases in Beijing, China  

NASA Astrophysics Data System (ADS)

Exploiting several key characteristics of quantum cascade (QC) lasers, including wide tunability and room-temperature operation, the Quantum Cascade Laser Open-Path System (QCLOPS) was designed for the detection of a range of trace gases and for field deployment in urban environments. Tunability over a wavelength range from 9.3 to 9.8 ?m potentially provides the capability for monitoring ozone, ammonia, and carbon dioxide, a suite of trace gases important for air quality and regional climate applications in urban environments. The 2008 Olympic Games in Beijing, China drew attention to air quality problems in urban environments. Prior to and during the Olympic games, regional air quality modifications through factory shutdowns, car restrictions, and construction halts in Beijing and its surrounding areas created a unique test bed for new sensor technologies such as the QCLOPS sensor. We report the design of this novel, open-path air quality sensor and the results of both laboratory tests and field trials during the 2008 Olympic Games in Beijing, China.

Michel, Anna P. M.; Liu, Peter Q.; Yeung, June K.; Corrigan, Paul; Baeck, Mary Lynn; Wang, Zifa; Day, Timothy; Smith, James A.

2010-11-01

134

Open-path tunable diode laser absorption spectroscopy for acquisition of fugitive emission flux data.  

PubMed

Air pollutant emission from unconfined sources is an increasingly important environmental issue. The U.S. Environmental Protection Agency (EPA) has developed a ground-based optical remote-sensing method that enables direct measurement of fugitive emission flux from large area sources. Open-path Fourier transform infrared spectroscopy (OP-FTIR) has been the primary technique for acquisition of pollutant concentration data used in this emission measurement method. For a number of environmentally important compounds, such as ammonia and methane, open-path tunable diode laser absorption spectroscopy (OP-TDLAS) is shown to be a viable alternative to Fourier transform spectroscopy for pollutant concentration measurements. Near-IR diode laser spectroscopy systems offer significant operational and cost advantages over Fourier transform instruments enabling more efficient implementation of the measurement strategy. This article reviews the EPA's fugitive emission measurement method and describes its multipath tunable diode laser instrument. Validation testing of the system is discussed. OP-TDLAS versus OP-FTIR correlation testing results for ammonia (R2 = 0.980) and methane (R2 = 0.991) are reported. Two example applications of tunable diode laser-based fugitive emission measurements are presented. PMID:15991674

Thoma, Eben D; Shores, Richard C; Thompson, Edgar L; Harris, D Bruce; Thorneloe, Susan A; Varma, Ravi M; Hashmonay, Ram A; Modrak, Mark T; Natschke, David F; Gamble, Heather A

2005-05-01

135

Development of an open path THz transmissometer for deterministic and random propagation studies  

NASA Astrophysics Data System (ADS)

The design of an open-path 320 GHz - 340 GHz coherent transmissometer for experimental measurements of amplitude scintillation, phase scintillation, angle-of-arrival (AoA) fluctuations, and transverse coherence near the 325.1529 GHz water absorption resonance is presented. The system uses a uni-directional transmitter and two phase-coherent receivers with adjustable transverse. The objective of the experiment is to verify and improve existing propagation models for use by designers of applied THz systems for remote sensing, radiolocation, or communications. System stability will be verified using a short range near-ground test path of several ~10's of meters length using a cable for locking the transmitter local oscillator (LO) to the receivers' LOs. This short range configuration, similar to tests conducted at Flatville, Illinois during the 1980s, permits characterization of system errors in all of the above parameters, thus yielding a baseline for the long range experiments. Characterization of the phase-coherent RF link will be studied vis-à-vis anticipated theoretical performance based on the Rytov approximation. The system will then be configured for long term open-path measurements on a 1.78 km elevated link between the University of Colorado at Boulder (CU) and the National Telecommunications and Information Administration (NTIA) Mesa site at the NOAA-NIST campus in Boulder, Colorado. The system will provide long range coherent THz propagation statistics during continuous longduration study of turbulent atmospheric propagation effects over an extensive array of atmospheric conditions in a realistic operational environment.

Scally, Lawrence J.; Gasiewski, Albin J.; Fritz, Jason

2012-05-01

136

Evaluation of open-path FTIR spectrometers for monitoring multiple chemicals in air.  

PubMed

There has been mounting interest in the use of open-path Fourier transform infrared (OP-FTIR) spectrometers for occupational and environmental air monitoring. Although this technology is gaining acceptance in the environmental field, there has not yet been a comprehensive assessment of instrument performance and the analytical limitations of this method have not been thoroughly delineated. Unlike extractive FTIR spectrometers, calibration of OP-FTIR spectrometer systems presents unique problems because the optical beam is exposed to the atmosphere. Therefore, it is difficult to get an adequate clean background and perform evaluation tests used by extractive instruments. One solution to the problem of evaluating an open-path system is to place a sample cell directly in the path of the infrared beam. The purpose of this study was to investigate the use of a specially designed external calibration cell as a tool for laboratory and field evaluation of the accuracy of OP-FTIR spectrometers and to investigate various commonly used instrument performance parameters such as root mean square (RMS) noise, return intensity, instrument precision, and detector saturation. These performance parameters were measured to see if they could be used to predict whether an instrument is operating correctly. Six instruments from the same manufacturer were evaluated with a prototype calibration cell using NIST traceable sulfur hexafluoride, n-hexane, and cyclohexane. Reference concentrations generated in the calibration cell were compared with OP-FTIR spectrometer measured concentrations measured through the cell. Excellent correlation and slopes were obtained for all three chemicals. The instrument performance measures could not be used to predict accuracy. The external calibration cell shows promise as a method of validating the operation of an OP-FTIR spectrometer for quality assurance and for quality control. PMID:11141603

Farhat, S K; Todd, L A

2000-12-01

137

A new low-power, open-path instrument for measuring methane flux by eddy covariance  

NASA Astrophysics Data System (ADS)

This paper describes a new low-power instrument for measuring methane flux by eddy covariance method at sites without grid power. Design and field performance of the LI-7700 Methane Analyzer (LI-COR Biosciences) are examined in this study. The instrument uses 8 W of power in steady-state operation and employs a tunable diode laser in an open Herriott cell configuration with 0.47 m base path and 30 m optical path length. Methane number density is measured using wavelength modulation spectroscopy (WMS) with 2f detection. Typical signal noise is <5 ppb rms at 10 Hz. Corrections for variations in temperature, pressure and water vapor are described. Data losses due to mirror contamination and condensation are minimized by a radiation shield and automatic mirror cleaning system and are shown to be small. Measured spectra and co-spectra are shown to follow the Kaimal model at deployment sites meeting classical criteria, and to follow sensible heat flux co-spectra from the sonic anemometer in most other cases, including difficult ones. Measured fluxes are similar in magnitude to those expected from the literature, and zero flux was measured during both summer and winter at a site known to have fluxes at or very near zero.

McDermitt, D.; Burba, G.; Xu, L.; Anderson, T.; Komissarov, A.; Riensche, B.; Schedlbauer, J.; Starr, G.; Zona, D.; Oechel, W.; Oberbauer, S.; Hastings, S.

2011-02-01

138

Applying open-path FTIR with computed tomography to evaluate personal exposures. Part 1: simulation studies.  

PubMed

This paper presents the theoretical background and the numerical evaluation results obtained using computed tomography coupled with open-path Fourier transform infrared (CT-FTIR) measurements to estimate personal exposures. In this simulation study, we first tested the one-dimensional scenario with a five-beam segment geometry. A series of Gaussian plumes and the corresponding path-integrated concentrations (PICs) were simulated. The personal exposures were estimated as the average of the point estimates calculated from the workers' locations and the concentration profiles reconstructed from the Smooth Basis Function Minimization algorithm. It was found that the running-average PIC updating strategy has similar performance as the spline PIC updating strategy. However, the latter strategy gives delayed estimates of the workers' exposures since it requires additional measurements before and after the time period of interest. In the two-dimensional scenario, we simulated a series of single-mode bivariate Gaussian plumes with a nine-beam radial geometry. The average of the estimated exposures from the CT-FTIR approach was close to the average of the true exposures. The concordance correlation factors between the true and estimated exposures were reasonably good (between 0.50 and 0.58). This study demonstrated that the CT-FTIR approach is feasible for industrial hygiene monitoring. PMID:15604104

Wu, Chang-Fu; Yost, Michael G; Hashmonay, Ram A; Larson, Timothy V; Guffey, Steven E

2004-12-16

139

Open path FTIR detection of threat chemicals in air and on surfaces  

NASA Astrophysics Data System (ADS)

A remote infrared spectroscopy (RIRS) detection system was assembled using a mid infrared (MIR) Fourier Transform interferometer useful in open-path (OP) mode, a reflective infrared telescope and a cryocooled wide band, MCT detector. The system was used for passive mode IR thermal emission measurements and was also coupled to another Newtonian telescope in conjunction with a globar source for active mode measurements. The operation of the system was validated by measuring RIRS spectra of gases (NH3) and condensable vapors: acetone, dichloromethane, methyl ether and acetonitrile. Solid samples were measured by smearing small amounts on aluminum plates after dissolving in appropriate solvents. Highly energetic compounds: TNT, DNT, PETN and RDX were also detected. Experiments of solids on metal surfaces were carried out in passive and active modes. The analyzed samples were placed at different standoff distances up to a maximum of 30 m in active mode and 60 m in passive mode.

Castro-Suarez, John R.; Pacheco-Londoño, Leonardo C.; Ortiz-Rivera, William; Vélez-Reyes, Miguel; Diem, Max; Hernandez-Rivera, Samuel P.

2011-05-01

140

[Monitoring and analysis of urban ozone using open path Fourier transform infrared spectrometry].  

PubMed

An ozone monitoring system was developed by the method of open path Fourier transform infrared (OP-FTIR) spectrometry based on our FTIR spectrometer. In order to improve measurement precision and detection limit, the quantitative analysis was completed to get ozone concentration by combining synthetic background spectrum method which uses information from HITRAN database and instrumental line shape, and nonlinear least squares (NLLSQ) method. The measurement methods for system detection limit were discussed and the result is 1.42 nmol x mol(-1) with sixteen times averages. The authors developed continuous monitoring experiments in the suburban area of Hefei. For the day and month measurement results, the authors analyzed their variations with the generation sources. The result has shown that this system is reliable and precise and can be used as a new device and method for national ozone monitoring. PMID:22295771

Li, Sheng; Gao, Min-guang; Zhang, Yu-jun; Liu, Wen-qing; Xu, Liang; Tong, Jing-jing; Cheng, Si-yang; Jin, Ling; Wei, Xiu-li; Wang, Ya-ping; Chen, Jun

2011-12-01

141

Source selectable path diversity via routing deflections  

Microsoft Academic Search

We present the design of a routing system in which end-systems set tags to select non-shortest path routes as an alternative to explicit source routes. Routers collectively generate these routes by using tags as hints to independently deflect packets to neighbors t hat lie off the shortest-path. We show how this can be done simply, by local extensions of the

Xiaowei Yang; David Wetherall

2006-01-01

142

Open-path Emission Factors Derived from DOAS and FTIR Measurements in the Mexico City Metropolitan Area  

Microsoft Academic Search

Mobile sources are responsible for about 50% of VOC (volatile organic compounds) and about 70% of NOx emissions in the Mexico City Metropolitan Area (MCMA). A novel approach has been developed to derive emission factors for mobile sources that are representative of the overall vehicle fleet, using collocated open-path Differential Optical Absorption Spectroscopy (DOAS) and Fourier Transform Infrared (FTIR) spectroscopic

E. Flores; M. Grutter; B. Galle; J. Mellqvist; J. Samuelsson; B. Knighton; B. T. Jobson; R. Volkamer; L. T. Molina; M. J. Molina

2004-01-01

143

Program Objectives and Status for the U.S.EPA Program on FTIR-Based Open-Path Monitoring.  

National Technical Information Service (NTIS)

The Office of Research and Development of the U.S. EPA supports a methods development program for FTIR-based, open path monitoring of trace gases in the air. This type of system provides an estimate of the average concentration of individual trace gases o...

W. A. McClenny

1997-01-01

144

Monitoring of CO flare emissions using open-path Fourier transform infrared technology  

NASA Astrophysics Data System (ADS)

A pilot study was performed in order to gather data to determine the efficiencies of two nearby CO flares. Each flare stack was about 150 feet high with the thermal rise of the flare raising the resulting plume to about 200 feet. Since there are no routinely accepted methods for determining flare emissions, especially for such high flares, the pilot study was designed to collect the appropriate data using open-path Fourier Transform Infrared (OP-FTIR) technology. There were a number of challenges both in physically setting up the equipment and in evaluating the resulting spectra: (1) The retroreflector needed to be hung on a 300 foot crane in order to have the plume centerlines near the center of the beam. (2) The positions of the crane and main OP-FTIR unit had to be determined in relation to availability of space at the appropriate downwind distances since this was an operating facility. (3) The tracer gases (SF6 and CF4) needed to be released at rates to provide sufficiently high downwind concentrations. (4) Sufficient upwind data needed to be collected to be able to subtract the background CO and CO2 values with enough accuracy to provide data for efficiency calculation. (5) The spectra collected for the beam paths (approximately 300 to 350 m from main unit to retroreflector angled from ground level to approximately 100 meters) traversed a wide range of temperatures and to a certain degree pressures which would affect the determination of the plume concentrations. This paper presents a discussion of these challenges and the degrees to which they were met. Suggestions for improving such studies is also included.

Zwicker, Judith O.; Ringler, Eric; Kagann, Robert H.

1999-02-01

145

A Linear-Time Algorithm for Finding Approximate Shortest Common Superstrings  

Microsoft Academic Search

Approximate shortest common superstrings for a given setR of strings can be constructed by applying the greedy heuristics for finding a longest Hamiltonian path in the weighted graph\\u000a that represents the pairwise overlaps between the strings inR. We develop an efficient implementation of this idea using a modified Aho-Corasick string-matching automaton. The resulting\\u000a common superstring algorithm runs in timeO(n) or

Esko Ukkonen

1990-01-01

146

[Open-path online monitoring of ambient atmospheric CO2 based on laser absorption spectrum].  

PubMed

With the conjunction of tunable diode laser absorption spectroscopy technology (TDLAS) and the open long optical path technology, the system designing scheme of CO2 on-line monitoring based on near infrared tunable diode laser absorption spectroscopy technology was discussed in detail, and the instrument for large-range measurement was set up. By choosing the infrared absorption line of CO2 at 1.57 microm whose line strength is strong and suitable for measurement, the ambient atmospheric CO2 was measured continuously with a 30 s temporal resolution at an suburb site in the autumn of 2007. The diurnal atmospheric variations of CO2 and continuous monitoring results were presented. The results show that the variation in CO2 concentration has an obvious diurnal periodicity in suburb where the air is free of interference and contamination. The general characteristic of diurnal variation is that the concentration is low in the daytime and high at night, so it matches the photosynthesis trend. The instrument can detect gas concentration online with high resolution, high sensitivity, high precision, short response time and many other advantages, the monitoring requires no gas sampling, the calibration is easy, and the detection limit is about 4.2 x 10(-7). It has been proved that the system and measurement project are feasible, so it is an effective method for gas flux continuous online monitoring of large range in ecosystem based on TDLAS technology. PMID:19385195

He, Ying; Zhang, Yu-Jun; Kan, Rui-Feng; Xia, Hui; Geng, Hui; Ruan, Jun; Wang, Min; Cui, Xiao-Juan; Liu, Wen-Qing

2009-01-01

147

Continuous field measurements of ?D in water vapor by open-path Fourier transform infrared spectrometry  

NASA Astrophysics Data System (ADS)

The stable isotopes in atmospheric water vapor contain rich information on the hydrologic cycles and gaseous exchange processes between biosphere and atmosphere. About one-week field experiment was conducted to continuously measure the isotope composition of water vapor in ambient air using an open-path FTIR system. Mixing ratios of H2 16O and HD16O were measured simultaneously. Analysis of water vapor isotopes revealed that the variations of H2 16O and HD16O were highly related. Mixing ratios of both isotopes varied considerably on a daily timescale or between days, with no obvious diurnal cycle, whereas the deuterium isotopic [delta]D showed clear diel cycle. The results illustrated that the correlation between [delta]D and H2O mixing ratio was relatively weak, which was also demonstrated by the Keeling plot analysis with the whole data. Yet the further Keeling analysis on a daily timescale displayed more obvious linear relationship between [delta]D and the total H2O concentration. All daily isotopic values of evapotranspiration source were obtained, with the range between -113.93±10.25‰ and -245.63±17.61‰ over the observation period.

Wang, Wei; Liu, Wenqing; Zhang, Tianshu

2012-12-01

148

Sensitive detection of chemical agents and toxic industrial chemicals using active open-path FTIRs  

NASA Astrophysics Data System (ADS)

Active open-path FTIR sensors provide more sensitive detection of chemical agents than passive FTIRs, such as the M21 RSCAAL and JSLSCAD, and at the same time identify and quantify toxic industrial chemicals (TIC). Passive FTIRs are bistatic sensors relying on infrared sources of opportunity. Utilization of earth-based sources of opportunity limits the source temperatures available for passive chemical-agent FTIR sensors to 300° K. Active FTIR chemical-agent sensors utilize silicon carbide sources, which can be operated at 1500° K. The higher source temperature provides more than an 80-times increase in the infrared radiant flux emitted per unit area in the 7 to 14 micron spectral fingerprint region. Minimum detection limits are better than 5 ?gm/m3 for GA, GB, GD, GF and VX. Active FTIR sensors can (1) assist first responders and emergency response teams in their assessment of and reaction to a terrorist threat, (2) provide information on the identification of the TIC present and their concentrations and (3) contribute to the understanding and prevention of debilitating disorders analogous to the Gulf War Syndrome for military and civilian personnel.

Walter, William T.

149

Orthogonal signal correction used for noise elimination of open path Fourier transform infrared spectra.  

PubMed

Open path Fourier transform infrared (OP-FTIR) spectroscopy is qualified in detecting mixtures by multivariate calibration methods such as partial least squares (PLS); however, its applications are still restricted by background noise, which is unavoidable for OP-FTIR spectra and cannot be resolved solely by multivariate calibration methods. Hence OP-FTIR spectra are often pretreated before the data are subjected to the multivariate calibration model. A new preprocessing technique, orthogonal signal correction (OSC), was presented in this paper. The principle of OSC is to remove the part in X orthogonal to Y, and it is implemented based on PLS and nonlinear iterative partial least squares (NIPALS) algorithm. The approach was applied to three different data sets of PLS model. It performed much better than classical PLS when handling data with noise but comparably when processing on the simulated data. Moreover, OSC could reduce the complexity of model, which would facilitate the interpretation of the models. The results reveal that the proposed method gives much better prediction than the classical PLS and is very promising for the wide use of OP-FTIR. The preprocessing technique, auto-scaling, and second-order derivatives (SOD) were also considered. PMID:15887575

Zhang, Lin; Zhang, Liming; Li, Yan; Wang, Junde

2005-01-01

150

Field evaluation of a method for estimating gaseous fluxes from area sources using open-path Fourier transform infrared.  

PubMed

This paper describes results from the first field experiment designed to evaluate a new approach for quantifying gaseous fugitive emissions of area air pollution sources. The approach combines path-integrated concentration data acquired with any path-integrated optical remote sensing (PI-ORS) technique and computed tomography (CT) technique. In this study, an open-path Fourier transform infrared (OP-FTIR) instrument sampled path-integrated concentrations along five radial beam paths in a vertical plane downwind from the source. A meteorological station collected measurements of wind direction and wind speed. Nitrous oxide (N2O) was released from a controlled area source simulator. The innovative CT technique, which applies the smooth basis function minimization method to the beam data in conjunction with measured wind data, was used to estimate the total flux from the simulated area source. The new approach estimates consistently underestimated the true emission rates in unstable atmospheric conditions and agreed with the true emission rate in neutral atmospheric conditions. This approach is applicable to many types of industrial areas or volume sources, given the use of an adequate PI-ORS system. PMID:11414037

Hashmonay, R A; Natschke, D F; Wagoner, K; Harris, D B; Thompson, E L; Yost, M G

2001-06-01

151

Measuring chemical emissions using open-path Fourier transform infrared (OP-FTIR) spectroscopy and computer-assisted tomography  

Microsoft Academic Search

This paper reports on a field study that was part of a large-scale, multi-seasonal research study with the North Carolina Department of Environment, Health, and Natural Resources, to measure nitrogen emissions from an intensive swine confinement facility. The study measured emission rates using tracer gases and a horizontal network of open-path Fourier transform infrared (FTIR) optical rays placed less than

Lori A. Todd; Mallika Ramanathan; Kathleen Mottus; Robert Katz; Ashley Dodson; Gary Mihlan

2001-01-01

152

Fugitive Coke Oven Gas Emission Profile by Continuous Line Averaged Open-Path Fourier Transform Infrared Monitoring  

Microsoft Academic Search

Although most coke oven research is focused on the emission of polycyclic aromatic hydrocarbons, well-known carcinogens, little has been done on the emission of volatile organic compounds, some of which are also thought to be hazardous to workers and the environment. To profile coke oven gas (COG) emissions, we set up an open-path Fourier transform infrared (OP-FTIR) system on top

Chitsan Lin; Naiwei Liou; Pao-Erh Chang; Jen-Chin Yang; Endy Sun

2007-01-01

153

Use of open-path FTIR monitoring for emission rate assessment of industrial area sources during winter conditions  

Microsoft Academic Search

Open-path Fourier transform-infrared (OP-FTIR) was used to collect emission data for a number of chemical compounds for several area sources at a northwestern industrial facility. The data collected was used in conjunction with meteorological measurements to assess the emission rate of several of the compounds from these area sources. The release of a tracer gas at a known emission rate

Robert J. Kricks; Jerry A. Keely; Robert L. Spellicy; Stephen H. Perry

1999-01-01

154

Evaluation of emissions from remedial activity at a former manufactured gas plant by open-path Fourier transform infrared spectroscopy  

Microsoft Academic Search

Open-path Fourier Transform Infrared Spectroscopy (OP-FTIR) was used to conduct an air monitoring survey at a Fourier manufactured gas plant (FMGP) superfund site. This survey was performed in support and at the request of the Waste Management Division, U.S. EPA, Region VII. A three day study was conducted in which the OP- FTIR instrument was operated at several fenceline locations

Michael F. Davis; Joseph Arello; John R. Helvig; Jody L. Hudson; Melissa D. Tucker; John M. Poholarz; Robert M. Hammaker; William G. Fateley

1995-01-01

155

On the application of Open-Path Fourier Transform InfraRed spectroscopy to measure aerosols: Observations of water droplets  

Microsoft Academic Search

This paper proposes the application of Open-Path Fourier Transform Infra-Red (OP-FTIR) spectroscopy to measure aerosols. A preliminary experiment conducted in a standard shower chamber generated a condensed water aerosol cloud. The OP-FTIR beam acquired spectra through the cloud of water droplets. The authors matched calculated extinction spectra to measured extinction in the spectral range between 500 and 5,000 wavenumbers by

Ram A. Hashmonay; Michael G. Yost

1999-01-01

156

Developing and Evaluating Techniques for Localizing Pollutant Emission Sources with Open-Path Fourier Transform Infrared Measurements and Wind Data  

Microsoft Academic Search

This paper presents the simulation and field evaluation results of two approaches to localize pollutant emission sources with open-path Fourier transform infrared (OPFTIR) spectroscopy. The first approach combined the plume’s peak location information reconstructed from the Smooth Basis Function Minimization (SBFM) algorithm and the wind direction data to calculate source projection lines. In the second approach, the plume’s peak location

Chang-Fu Wu; Ching-Hui Chen; Shih-Ying Chang; Pao-Erh Chang; Ruei-Hou Shie; Lung-Yu Sung; Jen-Chih Yang; Jen-Wei Su; Chang-Tang Chang; Chyow-San Chiou; Je-Lueng Shie; Yu-Min Chang; H. Frey; Kangwook Kim; Shih-Hao Pang; William Rasdorf; Phil Lewis; William Faulkner; Bryan Shaw; Tom Grosch; Rhona Julien; Jonathan Levy; Gary Adamkiewicz; Russ Hauser; John Spengler; Robert Canales; H. Hynes; Thomas Stock; Maria Morandi; Masoud Afshar; Kuenja Chung; Phirun Saiyasitpanich; Tim Keener; Mingming Lu; Fuyan Liang; Soon-Jai Khang; Kang-Shin Chen; Hsin-Kai Wang; Yen-Ping Peng; Wen-Cheng Wang; Chia-Hsiu Chen; Chia-Hsiang Lai; Eugene Kim; Philip Hopke; Le Nghiem; Nguyen Oanh; Michelle Bergin; Armistead Russell; Mehmet Odman; Daniel Cohan; William Chameides

2008-01-01

157

Low Cost Open-Path Instrument for Monitoring Surface Carbon Dioxide at Sequestration Sites Phase I SBIR Final Report  

SciTech Connect

Public confidence in safety is a prerequisite to the success of carbon dioxide (CO2) capture and storage for any program that intends to mitigate greenhouse gas emissions. In that regard, this project addresses the security of CO2 containment by undertaking development of what is called �¢����an open path device�¢��� to measure CO2 concentrations near the ground above a CO2 storage area.

Sheng Wu

2012-10-02

158

Consequences of Uncertainties in CO2 Density for Estimating Net Ecosystem CO2 Exchange by Open-path Eddy Covariance  

NASA Astrophysics Data System (ADS)

Errors in the estimation of CO2 surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol Soc 106:85-100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65-85, (2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements of absolute CO2 density (? c ). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to reliably report ? c and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ? c in a semi-arid climate with large sensible heat fluxes ( H s ) and (wet) mineral deposition. When ?c is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO2 uptake.

Serrano-Ortiz, Penélope; Kowalski, Andrew S.; Domingo, Francisco; Ruiz, Borja; Alados-Arboledas, Lucas

2008-02-01

159

Applying open-path Fourier transform infrared spectroscopy for measuring aerosols.  

PubMed

This paper examines the feasibility of using Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR) to measure aerosols. The extinction spectra of water, ammonium nitrate, and ammonium sulfate aerosols were first simulated with various particle size distributions (geometric mean ranged from 2 to 10 microm; geometric standard deviation ranged from 1.1 to 2.5) based on the Mie theory. An optimization procedure was developed to retrieve the geometric mean and standard deviation of the aerosols size distributions from the spectra, assuming that the complex refractive index is known. To test sensitivity, we also added 4%, 7%, and 10% noise levels to the spectra and compared the reconstruction results. In the experimental study, water aerosols were generated by a two-fluid nozzle inside a cylindrical chamber (3325 cm(3)). The extinction spectrum was collected with a modified FTIR and the size distribution information was retrieved following the same optimization procedure as the one used in the simulation study. The optimization procedure developed in this study reconstructed the size distribution reasonably well for particles with known refractive index (i.e. homogeneous or internally mixed aerosols). The results were robust with the added noise levels up to 10%, after removing inaccurate estimates with the use of the censoring criteria for reconstructed GSD < 1.3, reconstructed GM < 2.5 microm and GSD < 1.5, and reconstructed GM > 10 microm. With regard to externally mixed aerosols, the reconstructed results were sensitive to the noise within the measuring systems, although most ambient aerosols were internally mixed. The reconstructed size distribution in the chamber experiment had a GM of 3.85 microm and GSD of 1.70. The simulation results were applied to support this reconstruction result. We conclude that OP-FTIR can be used to measure aerosols and screen for the right region for a more detailed aerosol measurement campaign. PMID:17616885

Wu, Chang-Fu; Chen, Yen-Ling; Chen, Chih-Chieh; Yang, Tzu-Ting; Chang, Pao-Erh

2007-07-01

160

Emission source strengths of gasoline-filling processes determined by open-path spectroscopic techniques and inverse modeling  

NASA Astrophysics Data System (ADS)

Up to now emission source strengths of diffuse and heterogenous emission of important VOCs are not well known especially from gas stations and gasoline tank farms. To estimate the total emission of these sources non-intrusive measurements were performed by a differential optical absorption spectroscopy (DOAS) system to determine the path- integrated concentrations of exhaust compounds downwind of the source through the whole exhaust plume. Simultaneously, the meteorological parameters were measured for modeling the dispersion of the plume inversely to obtain the emission source strengths of these compounds. The emissions by road traffic were determined by an additional open-path DOAS measurement. Measurement campaigns were performed during different wether conditions and at different sources which were characterized by well defined and easy air flow conditions. The emission source strengths were calculated with the Gaussian model PAL. The determined total emission of gas stations with gasoline vapor recovery system are about 20 mg benzene per kg refueled gasoline and the emission from refueling activities vary between 1 and 9 benzene per kg refueled gasoline depending on the technical behavior of the gasoline vapor recovery system. These values which were found from measurements during times with a and without refueling activities show a high amount of diffuse emissions. The emission rates from a gasoline taken farm were measured on an open path through the middle of that area and a maximum of 8 (mu) g/(m2s) was determined.

Schaefer, Klaus; Stockhause, Martina; Hoffmann, Herbert; Sedlmaier, Achim; Emeis, Stefan M.

1998-12-01

161

Remote measurements of volcanic gases: Applications of open-path Fourier transform infrared spectroscopy  

NASA Astrophysics Data System (ADS)

The composition of volcanic gas plumes depends largely on the chemistry of the degassing magma, the depth of volatile exsolution, and the level of volcanic activity. The ratios between the most common volcanic gases: CO 2, H2O, SO2, HCl and HF, as measured at the surface, can be used to provide information on the evolution of the magma body. My research on volcanic gases has centred on the use of open-path Fourier transform IR spectroscopy (OP-FTIR) and correlation spectroscopy (COSPEC). Remote-sensing techniques rely on the characteristic IR or UV absorbances of natural and/or artificial radiation by different gases. Direct-sampling techniques rely on gases being trapped, dissolved or adsorbed before being analysed by traditional methods, e.g. wet-chemistry, colourimetry, and gas chromatography. The capture of gases is best achieved as close to the source as possible and the suitability of an individual technique depends on: the type of gas to be measured; the location of vent or fumarole; the level of volcanic activity; and the environment in which data are collected. I used OP-FTIR on La Fossa di Vulcano to measure the SO2:HCl mass ratios of gases emitted from the rim and central crater fumaroles, ~4.3-6.1 and 0.9-2.6 respectively. At Mt. Etna, analysis showed that, in 1994, SO2:HCl mass ratios were ~4.9-5.8. A comparative study of lava effusion rates and COSPEC-derived SO2 fluxes for the 1991-1993 Etna eruption showed that variations were generally synchronous. Analyses on Montserrat in June 1996 to show the gas plume to be relatively SO 2 poor, with SO2:HCl mass ratios of <0.5. I have also used HF-SiF4 ratios to estimate gas equilibrium temperatures at La Fossa and Mt. Etna to be ~200°C and ~250-290°C respectively. Historic activity has centred on the twin massifs of Volcán Masaya and Volcán Santiago and is dominated by pit-crater collapses. I propose that the degassing episodes, which occur with no increase in eruptive activity, are related to the convective overturn of magma beneath the craters. (Abstract shortened by UMI.)

Maciejewski, Adam John Henry

162

Propagating Spectroscopic Effects through WPL Terms when Using a Fast Laser-Based Open-Path CH4 Analyzer  

NASA Astrophysics Data System (ADS)

Eddy flux is computed using a covariance between fast changes in gas density and vertical wind speed. The measured changes in gas density happen due to gas flux itself, thermal expansion and contraction of the sampled gas, water vapor dilution, and pressure-related expansions and contractions. These are standard processes described by the Ideal Gas Law and by the Law of Partial Pressures, and are often called density effects. The gas flux is usually corrected for such density effects using Webb-Pearman-Leuning terms (WPL). When gas density is measured by laser spectroscopy, there are also spectroscopic effects affecting measured gas density depending on fluctuations in temperature, water vapor and pressure, in addition to the density effects. The spectroscopic effects are related to changes in the shape of the absorption line due to changes in gas temperature, pressure and the presence of water vapor. These effects are specific for each specific absorption line, and the measurement technique. The majority of density effects and spectroscopic effects are reduced or eliminated in the closed-path analyzers, when: (a) intake tube is very long, (b) gas sample is dried, and (c) pressure fluctuations are very small. However, the use of long intake tubes and drying of the air sample also lead to a significant increase in power demand, and to increased uncertainties due to excess attenuation of the fluctuations of the gas in the drier. Not drying the air sample leads to a need for applying a density correction for dilution, and spectroscopic corrections for gas absorption due to fast fluctuations in water vapor pressure. For both of these corrections water vapor should be measured accurately at high-speed inside the closed-path device, which increases measurements costs. In addition, current fast closed-path analyzers based on laser spectroscopy have to operate under significantly reduced pressures, and require powerful pumps and grid power (400-1500 Watts). Power demands may be why these instruments are often deployed at locations with infrastructure and grid power, and not where the gas is produced. Open-path gas analyzers can require very low-power (e.g., 5-10 Watts), permitting solar-powered deployments, cost-effectively permitting an addition of a single new gas measurement to the present array of CO2 and H2O measurements, and avoiding attenuation of gas fluctuations in the intake tube. These features enable long-term deployments of permanent, portable or mobile open-path flux stations at remote locations with high production of the gas of interest. However, in open-path analyzers, density and spectroscopic effects cannot be neglected. Here we propose a new way to account for spectroscopic effects due to fast fluctuations in air temperature, water vapor and pressure in the same manner as Webb et al. (1980) proposed a way of accounting for respective density effects. Since both density effects and spectroscopic effects are known from Gas Laws and HITRAN, respectively, they can be incorporated into the WPL correction. We use an example of a fast open-path CH4 gas analyzer, the LI-7700, yet the proposed approach would also apply to any closed-path design where fluctuations in temperature, water vapor and pressure are not fully eliminated.

Burba, George; McDermitt, Dayle; Anderson, Tyler; Komissarov, Anatoly

2013-04-01

163

Spin-orbit-path hybrid Greenberger-Horne-Zeilinger entanglement and open-destination teleportation with multiple degrees of freedom  

SciTech Connect

We propose a scheme to generate hybrid Greenberger-Horne-Zeilinger (GHZ) entanglement where multiple photons are entangled in different degrees of freedom of spin, orbital angular momentum (OAM), and path (linear momentum). The generation involves mapping the preliminary OAM entanglement of photon pairs onto their spin-orbit and spin-path degrees of freedom, respectively. Based on the hybrid GHZ entanglement, we demonstrate an open-destination teleportation with multiples degrees of freedom, via which a spin state of a single photon is teleported onto a superposition of multiple photons with the postselection technique and the original information could be read out at any photon in individual spin, OAM, or the linear-momentum state. Our scheme holds promise for asymmetric optical quantum network.

Chen Lixiang [Department of Physics, Xiamen University, Xiamen 361005 (China); State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China); She Weilong [State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275 (China)

2011-03-15

164

On the application of Open-Path Fourier Transform Infra-Red spectroscopy to measure aerosols: Observations of water droplets  

SciTech Connect

This paper proposes the application of Open-Path Fourier Transform Infra-Red (OP-FTIR) spectroscopy to measure aerosols. A preliminary experiment conducted in a standard shower chamber generated a condensed water aerosol cloud. The OP-FTIR beam acquired spectra through the cloud of water droplets. The authors matched calculated extinction spectra to measured extinction in the spectral range between 500 and 5,000 wavenumbers by using Mie theory for spherical particles. The results indicate that size distribution parameters may be retrieved from OP-FTIR spectra acquired over a 1 km optical path with reasonable detection limits on the order of 10 {micro}g{center_dot}m{sup {minus}3} for aerosols with optical properties equivalent to water.

Hashmonay, R.A.; Yost, M.G. [Univ. of Washington, Seattle, WA (United States). Dept. of Environmental Health

1999-04-01

165

Binary Decision Diagrams: A Mathematical Model for the Path-Related Objective Functions  

Microsoft Academic Search

This paper describes a mathematical model for all path length parameters (APL: Average Path Length, LPL: Longest Path Length, and SPL: Shortest Path Length) of Binary Decision Diagrams (BDDs). The proposed model is based on an empirical analysis of randomly generated Boolean functions. The formal core of the developed model is a unique equation for the path-related objective functions over

P. W. C. PRASAD; ALI ASSI; BRUCE MILLS

2006-01-01

166

On path planning: Adaptation to the environment using Fast Marching  

Microsoft Academic Search

This paper presents a novel methodology for fast path planning based on an offline predefined skeleton of the environment by means of the Fast Marching Square method. The FM2 skeleton concept is introduced whose intuition is a set which contains the shortest paths (in terms of time) of a given environment This way, the path planning algorithm is adapted to

Javier V. Gomez; Cesar Arismendit; Santiago Garrido; Luis Moreno

2012-01-01

167

Path planning for a mobile robot  

Microsoft Academic Search

Two problems for path planning of a mobile robot are considered. The first problem is to find a shortest-time, collision-free path for the robot in the presence of stationary obstacles in two dimensions. The second problem is to determine a collision-free path (greedy in time) for a mobile robot in an environment of moving obstacles. The environment is modeled in

Christos Alexopoulos; Paul M. Griffin

1992-01-01

168

Wave-particle interaction in parallel transport of long mean-free-path plasmas along open field magnetic field lines  

NASA Astrophysics Data System (ADS)

A tokamak fusion reactor dumps a large amount of heat and particle flux to the divertor through the scrape-off plasma (SOL). Situation exists either by necessity or through deliberate design that the SOL plasma attains long mean-free-path along large segments of the open field lines. The rapid parallel streaming of electrons requires a large parallel electric field to maintain ambipolarity. The confining effect of the parallel electric field on electrons leads to a trap/passing boundary in the velocity space for electrons. In the normal situation where the upstream electron source populates both the trapped and passing region, a mechanism must exist to produce a flux across the electron trap/passing boundary. In a short mean-free-path plasma, this is provided by collisions. For long mean-free-path plasmas, wave-particle interaction is the primary candidate for detrapping the electrons. Here we present simulation results and a theoretical analysis using a model distribution function of trapped electrons. The dominating electromagnetic plasma instability and the associated collisionless scattering, that produces both particle and energy fluxes across the electron trap/passing boundary in velocity space, are discussed.

Guo, Zehua; Tang, Xianzhu

2012-03-01

169

[Measurements of stable isotopes in atmospheric CO2 and H2O by open-path Fourier transform infrared spectrometry].  

PubMed

The development of spectroscopic techniques has offered continuous measurement of stable isotopes in the ambient air. The method of measuring environmental stable isotopes based on Fourier transform infrared spectrometry (FTIR) is described. In order to verify the feasibility of the method for continuous measurement of the stable isotopes, an open-path FTIR system was used to measure stable isotopes of CO2 and H2O in ambient air directly in a seven-day field experiment, including 12CO2, 3CO2, H2 16O and HD16 O. Also, the time course of carbon isotopic ratio delta13 C and deuterium isotope composition deltaD was calculated. The measurement precision is about 1.08 per thousand for delta13 C and 1.32 per thousand for deltaD. The measured stable isotopes of CO2 and H2O were analyzed on different time scales by Keeling plot methods, and the deuterium isotopic ratios of evapotranspiration were determined. The results of the field experiment demonstrate the potential of the open-path FTIR system for continuous measurement of stable isotopes in the air. PMID:24159837

Wang, Wei; Liu, Wen-Qing; Zhang, Tian-Shu

2013-08-01

170

Walking the Walk: A Path to Support Open Access Publishing [Poster  

Microsoft Academic Search

Scholarly communication is the lifeblood of universities. Threats to the free flow of research and ideas continue to jeopardize the entire academy; however administrators, scholars, and librarians are now pursuing options to reclaim research produced in the academy's domain. One way to do this is with Open Access. Open Access has been a topic of interest and intense depabe for

Linda L. Phillips; Donna Braquet

2009-01-01

171

Efficacy of using multiple open-path Fourier transform infrared (OP-FTIR) spectrometers in an odor emission episode investigation at a semiconductor manufacturing plant  

Microsoft Academic Search

This study evaluated the efficacy of simultaneously employing three open-path Fourier transform infrared (OP-FTIR) spectrometers with 3-day consecutive monitoring, using an odor episode as an example. The corresponding monitoring paths were allocated among the possible emission sources of a semiconductor manufacturing plant and the surrounding optoelectronic and electronic-related factories, which were located in a high-tech industrial park.There was a combined

Yung-Chieh Tsao; Chang-Fu Wu; Pao-Erh Chang; Shin-Yu Chen; Yaw-Huei Hwang

2011-01-01

172

The Longest Shortest Fence and Sharp Poincaré-Sobolev Inequalities  

NASA Astrophysics Data System (ADS)

We prove a long standing conjecture concerning the fencing problem in the plane: among planar convex sets of given area, the disc, and only the disc, maximizes the length of the shortest area-bisecting curve. Although it may look intuitive, the result is by no means trivial since we also prove that among planar convex sets of given area the set which maximizes the length of the shortest bisecting chords is the so-called Auerbach triangle.

Esposito, L.; Ferone, V.; Kawohl, B.; Nitsch, C.; Trombetti, C.

2012-12-01

173

Measurement and study of partial VOCs based on open path FTIR  

NASA Astrophysics Data System (ADS)

This paper describes a long path Fourier transform infrared spectroscopy system which is used to analyze ambient gas. Some VOCs (C2H2, C2H4) are measured with this system in laboratory. As different VOCs has unique infrared absorbing spectrum, we retrieve VOCs concentration based on the nonlinear least square algorithm. The result shows that the system is stable and rapid. The retrieved concentrations are very close to real value. The system can used to monitor and research VOCs in ambient gas.

Tong, Jing-Jing; Liu, Wen-Qing; Gao, Min-Guang; Liu, Zhi-Ming; Xu, Liang; Wei, Xiu-Li; Jin, Ling

2010-05-01

174

Developing and evaluating techniques for localizing pollutant emission sources with open-path Fourier transform infrared measurements and wind data.  

PubMed

This paper presents the simulation and field evaluation results of two approaches to localize pollutant emission sources with open-path Fourier transform infrared (OP-FTIR) spectroscopy. The first approach combined the plume's peak location information reconstructed from the Smooth Basis Function Minimization (SBFM) algorithm and the wind direction data to calculate source projection lines. In the second approach, the plume's peak location was determined with the Monte Carlo methodology by randomly sampling within the beam segment having the largest path-integrated concentration. We first conducted a series of simulation studies to investigate the sensitivity of using different basis functions in the SBFM algorithm. It was found that fitting with the beta and Weibull basis functions generally gave better estimates of the peak locations than with the normal basis function when the plumes were mainly within the OP-FTIR's monitoring line. However, for plumes that were symmetric to the peak position or spread over the OP-FTIR, fitting with the normal basis function gave better performance. In the field experiment, two tracer gases were released simultaneously from two locations and the OP-FTIR collected data downwind from the sources with a maximum beam path length of 97 m. For the first approach, the release locations were within the 0.25- to 0.5-probability area only after the uncertainty of the peak locations was included in the calculation process. The second approach was easy to implement and still performed as satisfactorily as the first approach. The distances from the sources to the best-fit lines (i.e., the regression lines) of the estimated locations were smaller than 10 m. PMID:18939783

Wu, Chang-Fu; Chen, Ching-Hui; Chang, Shih-Ying; Chang, Pao-Erh; Shie, Ruei-Hou; Sung, Lung-Yu; Yang, Jen-Chih; Su, Jen-Wei

2008-10-01

175

SP-NN: A novel neural network approach for path planning  

Microsoft Academic Search

In this paper, a neural network approach named shortest path neural networks (SP-NN) is proposed for real-time on-line path planning. Based on grid-based map and mapping this kind of map to neural networks, this proposed method is capable of generating the globally shortest path from the target position to the start position without collision with any obstacles. The dynamics of

Shuai Li; Max Q. H. Meng; Wanming Chen; Yangming Li; Zhuhong You; Yajin Zhou; Lei Sun; Huawei Liang; Kai Jiang; Qinglei Guo

2007-01-01

176

Efficacy of using multiple open-path Fourier transform infrared (OP-FTIR) spectrometers in an odor emission episode investigation at a semiconductor manufacturing plant.  

PubMed

This study evaluated the efficacy of simultaneously employing three open-path Fourier transform infrared (OP-FTIR) spectrometers with 3-day consecutive monitoring, using an odor episode as an example. The corresponding monitoring paths were allocated among the possible emission sources of a semiconductor manufacturing plant and the surrounding optoelectronic and electronic-related factories, which were located in a high-tech industrial park. There was a combined total odor rate of 43.9% for the three monitoring paths, each comprised of 736 continuous 5-minute monitoring records and containing detectable odor compounds, such as ammonia, ozone, butyl acetate, and propylene glycol monomethyl ether acetate (PGMEA). The results of the logistic regression model indicated that the prevailing south wind and the OP-FTIR monitoring path closest to the emission source in down-wind direction resulted in a high efficacy for detecting odorous samples with odds ratios (OR) of 3.8 (95% confidence interval (CI): 2.9-5.0) and 5.1 (95% CI: 3.6-7.2), respectively. Meanwhile, the odds ratio for detecting ammonia odorous samples was 7.5 for Path II, which was downwind closer to the possible source, as compared to Path III, downwind far away from the possible source. PGMEA could not be monitored at Path II but could be at Path III, indicating the importance of the monitoring path and flow ejection velocities inside the stacks on the monitoring performance of OP-FTIR. Besides, an odds ratio of 5.1 for odorous sample detection was obtained with south prevailing wind comprising 65.0% of the monitoring time period. In general, it is concluded that OP-FTIR operated with multiple paths simultaneously shall be considered for investigation on relatively complicated episodes such as emergency of chemical release, multiple-source emission and chemical monitoring for odor in a densely populated plant area to enhance the efficacy of OP-FTIR monitoring. PMID:21621818

Tsao, Yung-Chieh; Wu, Chang-Fu; Chang, Pao-Erh; Chen, Shin-Yu; Hwang, Yaw-Huei

2011-05-31

177

Measurement of Urban Air Quality by an Open-Path Quantum Cascade Laser Absorption Spectrometer in Beijing During Summer 2008  

NASA Astrophysics Data System (ADS)

The 2008 Olympic Games focused attention on the air quality of Beijing, China and served as an important test-bed for developing, deploying, and testing new technologies for analysis of air quality and regional climate in urban environments. Poor air quality in urban locations has a significant detrimental effect on the health of residents while also impacting both regional and global climate change. As a result, there exists a great need for highly sensitive trace gas sensors for studying the atmosphere of the urban environment. Open-path remote sensors are of particular interest as they can obtain data on spatial scales similar to those used in regional climate models. Quantum cascade lasers (QCLs) can be designed for operation in the mid-infrared (mid-IR) with a central wavelength anywhere between 3 to 24 ?m and made tunable over a wavelength interval of over 0.1 ?m. The Quantum Cascade Laser Open-Path System (QCLOPS) is a mid-infrared laser absorption spectrometer that uses a tunable, thermoelectrically cooled, pulsed Daylight Solutions Inc. QCL for measurement of trace gases. The system is aimed at applications with path lengths ranging from approximately 0.1 to 1.0 km. The system is designed to continuously monitor multiple trace gases [water vapor (H2O), ozone (O3), ammonia (NH3), and carbon dioxide (CO2)] in the lower atmosphere. A field campaign from July to September 2008 in Beijing used QCLOPS to study trace gas concentrations before, during, and after the Olympic Games in an effort to capture changes induced by emissions reduction methods. QCLOPS was deployed at the Institute of Atmospheric Physics - Chinese Academy of Sciences on the roof of a two-story building, at an approximate distance of 2 miles from the Olympic National Stadium ("The Bird's Nest.") QCLOPS operated with an open-path round trip distance of approximately 75 m. The system ran with minimal human interference, twenty-four hours per day for the full campaign period. In order to collect data over numerous absorption peaks belonging to the target gases of H2O, NH3, O3, and CO2, measurements were made at 317 different wavelengths within the full tuning range of the laser (1020 - 1070 cm-1). We present the design of this novel sensor which was successfully built, deployed, and operated with minimal operator intervention for the three month field campaign period. Furthermore, we present the results of the field campaign and the capabilities of the QCLOPS system to measure fluctuations of the trace gases at parts-per-billion levels. The time series data illustrate the changing levels of the trace gases over the campaign period. In addition, data from commercial sensors simultaneously deployed at the field site are presented as a validation of the capabilities of the QCLOPS system. This work was supported by MIRTHE (NSF-ERC #EEC-0540832).

Michel, A. P.; Liu, P. Q.; Yeung, J. K.; Zhang, Y.; Baeck, M. L.; Pan, X.; Dong, H.; Wang, Z.; Smith, J. A.; Gmachl, C. F.

2009-05-01

178

Trace gas emissions from the production and use of domestic biofuels in Zambia measured by open-path Fourier transform infrared spectroscopy  

Microsoft Academic Search

Domestic biomass fuels (biofuels) were recently estimated to be the second largest source of carbon emissions from global biomass burning. Wood and charcoal provide approximately 90% and 10% of domestic energy in tropical Africa. In September 2000, we used open-path Fourier transform infrared (OP-FTIR) spectroscopy to quantify 18 of the most abundant trace gases emitted by wood and charcoal cooking

Isaac T. Bertschi; Robert J. Yokelson; Darold E. Ward; Ted J. Christian; Wei Min Hao

2003-01-01

179

Trace gas emissions from laboratory biomass fires measured by open-path Fourier transform infrared spectroscopy: Fires in grass and surface fuels  

Microsoft Academic Search

The trace gas emissions from six biomass fires, including three grass fires, were measured using a Fourier transform infrared (FTIR) spectrometer coupled to an open-path, multipass cell (OP-FTIR). The quantified emissions consisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, methane, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in this

Jon G. Goode; Robert J. Yokelson; Ronald A. Susott; Darold E. Ward

1999-01-01

180

[Study on the measurement of ambient ammonia in urban area based on open-path DOAS technique].  

PubMed

As a key role in the acid-deposition and the generation of secondary particle matter (PM), measurement of the concentration of atmospheric ammonia in urban area has been attracting the scientists' interests nowadays. After studying the special absorption features of ammonia in short UV wavelength range, detailed concernful issues were put forward in the present paper. The decision of using xenon lamp as the light source was made after the evaluation of measurement of light spectroscopy. Retrieval wavelength band for NH3 was fixed from 204 to 214 nm and optimal method of deducting other interferential gases was also shown. A home-made open-path DOAS (OP-DOAS) system was set up for the measurement of the concentration of atmospheric NH3. The detection limit of such system was calculated with the typical noise level as low as 0.33 microg x m(-3) with the optical path 228 m. Through field experiment in Guangzhou city, such a system can be competent for the online and high time-resolution monitoring of the concentration of atmospheric ammonia. With a significant diurnal variation, the atmospheric ammonia changed from 0.83 to 3.11 microg x m(-3) with the mean value 1.59 microg x m(-3). The representative character of the diurnal variation is that the concentration of NH3 peaks during night while drops to bottom in the daytime. After the error analysis procedure, typical measurement accuracy of such OP-DOAS system was within 10%. PMID:22512193

Wang, Jie; Xie, Pin-hua; Qin, Min; Ling, Liu-yi; Ye, Cong-lei; Liu, Jian-guo; Liu, Wen-qing

2012-02-01

181

Application of the Ant Colony Algorithm for the Path Planning  

Microsoft Academic Search

The paper presents the ant colony algorithm and its application for the path planning. Ant algorithms were designed on the base of the behaviour of real ant colonies. Real ants can always find the shortest way between the nest and the food so one of the most “natural” is the application of the ant colony algorithm in the path planning.

Marcin Pluci?ski

182

Innovative Approach for Measuring Ammonia and Methane Fluxes from a Hog Farm Using Open-Path Fourier Transform Infrared Spectroscopy.  

National Technical Information Service (NTIS)

The paper describes a new approach to quantify emissions from area air pollution sources. The approach combines path-integrated concentration data acquired with any path-integrated optical remote sensing (PI-ORS) technique and computed tomography (CT) tec...

D. B. Harris E. L. Thompson C. A. Vogel R. A. Hashmonay D. Natschke K. Wagoner

2000-01-01

183

Emissions from smoldering combustion of biomass measured by open-path Fourier transform infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Biomass samples from a diverse range of ecosystems were burned in the Intermountain Fire Sciences Laboratory open combustion facility. Midinfrared spectra of the nascent emissions were acquired at several heights above the fires with a Fourier transform infrared spectrometer (FTIR) coupled to an open multipass cell. In this report, the results from smoldering combustion during 24 fires are presented including production of carbon dioxide, carbon monoxide, methane, ethene, ethyne, propene, formaldehyde, 2-hydroxyethanal, methanol, phenol, acetic acid, formic acid, ammonia, hydrogen cyanide, and carbonyl sulfide. These were the dominant products observed, and many have significant influence on atmospheric chemistry at the local, regional, and global scale. Included in these results are the first optical, in situ measurements of smoke composition from fires in grasses, hardwoods, and organic soils. About one half of the detected organic emissions arose from fuel pyrolysis which produces white smoke rich in oxygenated organic compounds. These compounds deserve more attention in the assessment of fire impacts on the atmosphere. The compound 2-hydroxyethanal is a significant component of the smoke, and it is reported here for the first time as a product of fires. Most of the observed alkane and ammonia production accompanied visible glowing combustion. NH3 is normally the major nitrogen-containing emission detected from smoldering combustion of biomass, but from some smoldering organic soils, HCN was dominant. Tar condensed on cool surfaces below the fires accounting for ˜1% of the biomass burned, but it was enriched in N by a factor of 6-7 over the parent material, and its possible role in postfire nutrient cycling should be further investigated.

Yokelson, Robert J.; Susott, Ronald; Ward, Darold E.; Reardon, James; Griffith, David W. T.

1997-08-01

184

Atmospheric ammonia monitoring near Beijing National Stadium from July to October in 2008 by open-path TDLAS system  

NASA Astrophysics Data System (ADS)

Gaseous ammonia is the most abundant alkaline trace gas in the atmosphere. As ammonia plays an important role in acid deposition and aerosol formation, it influences the regional air quality and atmospheric visibility. TDLAS (Tunable Diode Laser Absorption Spectroscopy)is a method to obtain the spectroscopy of single molecule absorption line in the characteristic absorption spectrum region as the characteristic of the distributed feed back (DFB) diode laser with narrow linewidth and tunability, which makes it possible to detect trace-gas qualitatively or quantificationally. The NH3 in-situ monitoring instrument based on TDLAS and long open path technology have been developed combining with wavelength modulation and harmonic detection techniques to obtain the necessary detection sensitivity. This instrument has been used to measure atmospheric NH3 concentration at an urban site near Beijing National Stadium from July to October in 2008, especially in the period of Beijing Olympics and Paralympics. The continuously monitoring results show that the atmospheric NH3 concentration variation has an obvious diurnal periodicity in the urban of Beijing. First of all, the general diurnal variation rule is the concentration decreased to the minimum in the daytime, and then increased to the maximum at night. Moreover, the NH3 peak concentration decreased obviously at the beginning of the Beijing Olympics then it kept descending during the Paralympics. The obtained maximum of NH3 is between 20.31?g/m3 48.54?g/m3 with the daily average concentration between 12.6?g/m327.5?g/m3. During these three months, Air Quality Assurance Scheme for the Olympics (AQASO) was implemented through the joint actions of Beijing Municipal Government and the five neighboring provinces/municipalities in north China. The measures such as auto restriction and plant ejection-decreasing are carried out in Beijing. In conclusion, the open-path TDLAS instrument is suitable for atmospheric trace gases detection on-line with its high resolution, high sensitivity, rapid response time without gas sampling. Also correlation studies have verified the positive effects of measures taken for improving the air quality including restricting ammonia formation.

He, Ying; Zhang, Yujun; Liu, Wenqing; Kan, Ruifeng; Xia, Hui

2009-07-01

185

Formal language constrained path problems  

SciTech Connect

In many path finding problems arising in practice, certain patterns of edge/vertex labels in the labeled graph being traversed are allowed/preferred, while others are disallowed. Motivated by such applications as intermodal transportation planning, the authors investigate the complexity of finding feasible paths in a labeled network, where the mode choice for each traveler is specified by a formal language. The main contributions of this paper include the following: (1) the authors show that the problem of finding a shortest path between a source and destination for a traveler whose mode choice is specified as a context free language is solvable efficiently in polynomial time, when the mode choice is specified as a regular language they provide algorithms with improved space and time bounds; (2) in contrast, they show that the problem of finding simple paths between a source and a given destination is NP-hard, even when restricted to very simple regular expressions and/or very simple graphs; (3) for the class of treewidth bounded graphs, they show that (i) the problem of finding a regular language constrained simple path between source and a destination is solvable in polynomial time and (ii) the extension to finding context free language constrained simple paths is NP-complete. Several extensions of these results are presented in the context of finding shortest paths with additional constraints. These results significantly extend the results in [MW95]. As a corollary of the results, they obtain a polynomial time algorithm for the BEST k-SIMILAR PATH problem studied in [SJB97]. The previous best algorithm was given by [SJB97] and takes exponential time in the worst case.

Barrett, C.; Jacob, R.; Marathe, M.

1997-07-08

186

Parallel transport of long mean-free-path plasmas along open magnetic field lines: Plasma profile variation  

SciTech Connect

Parallel transport of long mean-free-path plasma along an open magnetic field line is characterized by strong temperature anisotropy, which is driven by two effects. The first is magnetic moment conservation in a non-uniform magnetic field, which can transfer energy between parallel and perpendicular degrees of freedom. The second is decompressional cooling of the parallel temperature due to parallel flow acceleration by conventional presheath electric field which is associated with the sheath condition near the wall surface where the open magnetic field line intercepts the discharge chamber. To the leading order in gyroradius to system gradient length scale expansion, the parallel transport can be understood via the Chew-Goldbeger-Low (CGL) model which retains two components of the parallel heat flux, i.e., q{sub n} associated with the parallel thermal energy and q{sub s} related to perpendicular thermal energy. It is shown that in addition to the effect of magnetic field strength (B) modulation, the two components (q{sub n} and q{sub s}) of the parallel heat flux play decisive roles in the parallel variation of the plasma profile, which includes the plasma density (n), parallel flow (u), parallel and perpendicular temperatures (T{sub Parallel-To} and T{sub Up-Tack }), and the ambipolar potential ({phi}). Both their profile (q{sub n}/B and q{sub s}/B{sup 2}) and the upstream values of the ratio of the conductive and convective thermal flux (q{sub n}/nuT{sub Parallel-To} and q{sub s}/nuT{sub Up-Tack }) provide the controlling physics, in addition to B modulation. The physics described by the CGL model are contrasted with those of the double-adiabatic laws and further elucidated by comparison with the first-principles kinetic simulation for a specific but representative flux expander case.

Guo Zehua; Tang Xianzhu [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-08-15

187

Parallel transport of long mean-free-path plasmas along open magnetic field lines: Plasma profile variation  

NASA Astrophysics Data System (ADS)

Parallel transport of long mean-free-path plasma along an open magnetic field line is characterized by strong temperature anisotropy, which is driven by two effects. The first is magnetic moment conservation in a non-uniform magnetic field, which can transfer energy between parallel and perpendicular degrees of freedom. The second is decompressional cooling of the parallel temperature due to parallel flow acceleration by conventional presheath electric field which is associated with the sheath condition near the wall surface where the open magnetic field line intercepts the discharge chamber. To the leading order in gyroradius to system gradient length scale expansion, the parallel transport can be understood via the Chew-Goldbeger-Low (CGL) model which retains two components of the parallel heat flux, i.e., qn associated with the parallel thermal energy and qs related to perpendicular thermal energy. It is shown that in addition to the effect of magnetic field strength (B) modulation, the two components (qn and qs) of the parallel heat flux play decisive roles in the parallel variation of the plasma profile, which includes the plasma density (n), parallel flow (u), parallel and perpendicular temperatures (T? and T?), and the ambipolar potential (?). Both their profile (qn/B and qs/B2) and the upstream values of the ratio of the conductive and convective thermal flux (qn/nuT? and qs/nuT?) provide the controlling physics, in addition to B modulation. The physics described by the CGL model are contrasted with those of the double-adiabatic laws and further elucidated by comparison with the first-principles kinetic simulation for a specific but representative flux expander case.

Guo, Zehua; Tang, Xian-Zhu

2012-08-01

188

Evaluating open-path FTIR spectrometer data using different quantification methods, libraries, and background spectra obtained under varying environmental conditions  

NASA Astrophysics Data System (ADS)

This paper discussed studies performed in a 35 foot outdoor Teflon exposure chamber in Pittsboro, North Carolina. The purpose of this research was to evaluate open-path FTIR data and compare it to a reference method varying several parameters: the method used for quantification, the library used for quantification, and backgrounds representing varying environmental conditions. The reference method used was GC- FID. The chemical evaluated was toluene over the concentration range of 5-30 ppm. Two different quantification methods were used in this analysis: traditional peak area method and interactive subtraction. All quantification was done manually. Two different libraries were used for quantification: the Hanst library (137 ppm-m toluene) and the EPA library (249 ppm-m) toluene. Several concentration data files were analyzed with the original background and then with subsequent backgrounds obtained from that same day. The subsequent backgrounds contained varying amounts of water vapor. The effect on quantification was evaluated. For concentrations of 20 ppm and below there was no significant difference between the peak area and subtraction method. However, for concentrations greater than 20 ppm, the difference between the two methods increased up to 20%. The difference between the EPA and Hanst libraries was statistically insignificant below 25 ppm. At concentrations greater than 15 ppm, the two libraries deviated and the difference ranged from 5% to 10% with the EPA results being higher. Water vapor was found to drastically impact the quantification. The magnitude of the effect varied between quantification methods and libraries.

Tomasko, Maria S.; Todd, Lori A.

1995-05-01

189

Mapping of methane spatial distribution around biogas plant with an open-path tunable diode absorption spectroscopy scanning system  

NASA Astrophysics Data System (ADS)

An open-path tunable diode laser absorption spectroscopy (OP-TDLAS) detector was applied to detect the methane emission from a biogas plant in a dairy farm. Two OP-TDLAS scanning systems were built according to maximum likelihood with expectation minimization (MLEM) and smooth basis function minimization (SBFM) algorithms to reconstruct the two-dimensional (2-D) distribution maps. Six reconstruction maps with the resolution of 30×80 were obtained by the MLEM algorithm with "grid translation method" and three reconstruction maps were obtained by the SBFM algorithm with 2-D Gaussian model. The maximum mixing ratio in the first result was between 0.85 and 1.30 ppm, while it was between 1.14 and 1.30 ppm in the second result. The average mixing ratio in the first result was between 0.54 and 0.49 ppm, and between 0.56 and 0.65 ppm in the second result. The reconstruction results validated that the two algorithms could effectively reflect the methane mixing ratio distribution within the target area. However, with the more simple optical rays and less equipment requirements, the OP-TDLAS scanning system based on SBFM algorithm provides a useful monitoring tool of methane emissions in agricultural production.

Zhang, Shirui; Wang, Jihua; Dong, Daming; Zheng, Wengang; Zhao, Xiande

2013-02-01

190

Real-time 3D path planning for sensor-based underwater robotics vehicles in unknown environment  

Microsoft Academic Search

Studies path planning strategies on real-time 3D near-shortest path planning for sensor-based underwater robotics vehicles (URV) in an unknown environment. The unknown environment includes multiple static obstacles of arbitrary shape. Based on limited sensor vision zone and the URV attitude dynamics, a 3D near-shortest path planning algorithm is developed for the URV in an unknown environment. The control variables are

Nan Ying; Low Eicher; Wang Xunzhang; G. G. L. Seet; M. W. S. Lau

2000-01-01

191

Optimal paths for a car that goes both forwards and backwards  

Microsoft Academic Search

The path taken by a car with a given minimum turning radius has a lower bound on its radius of curvature at each point, but the path has cusps if the car shifts into or out of reverse gear. What is the shortest such path a car can travel between two points if its starting and ending directions are specified?

J. A. Reeds; L. A. Shepp

1990-01-01

192

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: II. Fog and rain  

Microsoft Academic Search

Open-path FT-IR spectra of low-concentration releases of diethyl ether were measured both when a glycol fog was passed into\\u000a the infrared beam and when large water droplets from a lawn sprinkler were sprayed into the beam. It was shown that the glycol\\u000a fog, for which the droplet size was much less than the wavelength of the infrared radiation, gave rise

Limin Shao; Christopher W. Roske; Peter R. Griffiths

2010-01-01

193

Applications of Open-Path Fourier Transform Infrared for Identification of Volatile Organic Compound Pollution Sources and Characterization of Source Emission Behaviors  

Microsoft Academic Search

An open-path Fourier transform infrared spectroscopy (OP-FTIR) system was set up for 3-day continuous line-averaged volatile organic compound (VOC) monitoring in a paint manufacturing plant. Seven VOCs (toluene, m-xylene, p-xylene, styrene, methanol, acetone, and 2-butanone) were identified in the ambient environment. Daytime-only batch operation mode was well explained by the time-series concentration plots. Major sources of methanol, m-xylene, acetone, and

Chitsan Lin; Naiwei Liou; Endy Sun; Edwin Corporan; Matthew DeWitt; Chester Spicer; Michael Holdren; Kenneth Cowen; Alex Laskin; David Harris; Richard Shores; Robert Kagann; Ram Hashmonay; Francesca Sprovieri; Nicola Pirrone; Larry Jacobson; Brian Hetchler; David Schmidt; Richard Nicolai; Albert Heber; Ji-Qin Ni; Steven Hoff; Jacek Koziel; Yuanhui Zhang; David Beasley; David Parker; Roxolana Kashuba; Peter Scheff; Aniket Sawant; David Cocker; J. Miller; Tony Taliaferro; David Diaz-Sanchez; William Linn; Kenneth Clark; Henry Gong; Gustavo Olivares; Johan Strom; Christer Johansson; Lars Gidhagen

2008-01-01

194

Multi-criteria evaluation and least-cost path analysis for optimal haulage routing of dump trucks in large scale open-pit mines  

Microsoft Academic Search

A new raster?based GIS model that combines multi?criteria evaluation and least?cost path analysis was developed to determine the optimal haulage routes of dump trucks in large scale open?pit mines. The model logic can consider multiple criteria simultaneously (i.e. speed, water body, ore body, curve, visibility, haul road maintenance) and can rate the adverse factor scores of truck movement using fuzzy

Yosoon Choi; Choon Sunwoo; Keith C. Clarke

2009-01-01

195

Workplace and Environmental Air Contaminant Concentrations Measured by Open Path Fourier Transform Infrared Spectroscopy: A Statistical Process Control Technique to Detect Changes from Normal Operating Conditions  

Microsoft Academic Search

Open path Fourier transform infrared (OP-FTIR) spectroscopy is a new air monitoring technique that can be used to measure concentrations of air contaminants in real or near-real time. OP-FTIR spectroscopy has been used to monitor workplace gas and vapor exposures, emissions from hazardous waste sites, and to track emissions along fence lines. This paper discusses a statistical process control technique

Maureen Simonds Malachowski; Steven P. Levine; Gary Herrin; Robert C. Spear; Michael Yost; Zhou Yi

1994-01-01

196

Applying Open-Path FTIR with a Bi-Beam Strategy to Evaluate Personal Exposure in Indoor Environments: Experimental Results of a Validation Study  

Microsoft Academic Search

This study evaluated the performance and feasibility of using open-path Fourier transform infrared (OP-FTIR) with a bi-beam strategy to assess personal exposures in workplaces. The bi-beam strategy combines a long beam and a short beam measurement to calculate the average concentration level of the segmented region. A series of experiments was conducted with six human subjects at two workstations inside

Chang-Fu Wu; Michael G. Yost; Janice Varr; Ram A. Hashmonay

2003-01-01

197

Odor Load Investigation for a Pharmaceutical Plant by Open Path Fourier Transform Infrared (OP-FTIR)\\/Environmental Protection Agency Regulatory Dispersion Model (AERMOD)  

Microsoft Academic Search

In this article, a case study was conducted to correlate the odor index and possible pollutants from a pharmaceutical plant based on the odor threshold and Open Path Fourier Transform Infrared (OP-FTIR) technique to model the results using American Meteorological Society\\/Environmental Protection Agency Regulatory Dispersion Model (AERMOD). Although nine different pollutants were obtained from OP-FTIR, the contribution to the detected

Wen-Shing Chang; Shiao-Shing Chen; Jung-Hua Chang; Chih-Hui Tang; Tzi-Chin Chang

2009-01-01

198

Minimum Wheel-rotation Paths for Differential-drive Mobile Robots  

Microsoft Academic Search

The shortest paths for a mobile robot are a fundamental property of the mechanism, and may also be used as a family of primitives for mo- tion planning in the presence of obstacles. This paper characterizes shortest paths for differential-drive mobile robots, with the goal of classifying solutions in the spirit of Dubins curves and Reeds-Shepp curves for car-like robots.

Hamid Reza Chitsaz; Steven M. Lavalle; Devin J. Balkcom; Matthew T. Mason

2006-01-01

199

On path selection for traffic with bandwidth guarantees  

Microsoft Academic Search

Transmission of multimedia streams imposes a minimum-band width requirementon the path being used to ensure end-to-end Qual ity-of- Service (QoS) guarantees. While any shortest-path algorit hm can be used to select a feasible path, additional constraints th at limit resource consumption and balance the network load are neede d to achieve efficient resource utilization. We present a syst ematic evaluation

Qingming Ma; Peter Steenkiste

1997-01-01

200

Intrinsic shortest path length: a new, accurate a priori wirelength estimator  

Microsoft Academic Search

A priori wirelength estimation is concerned with predicting various wirelength characteristics before placement. In this work we propose a novel, accurate estimator of net lengths. We observe that in \\

Andrew B. Kahng; Sherief Reda

2005-01-01

201

A Dynamic Programming Approach to Identifying the Shortest Path in Virtual Learning Environments  

ERIC Educational Resources Information Center

|E-learning has been widely adopted as a promising solution by many organizations to offer learning-on-demand opportunities to individual employees (learners) in order to reduce training time and cost. While successful information systems models have received much attention among researchers, little research has been conducted to assess the…

Fazlollahtabar, Hamed

2008-01-01

202

Recursive Shortest Path Algorithm with Application to Density-integration of Weighted Graphs  

Microsoft Academic Search

Graph theory is increasingly commonly utilised in genetics, proteomics and neuroimaging. In such fields, the data of interest generally constitute weighted graphs. Analysis of such weighted graphs often require the integration of topological metrics with respect to the density of the graph. Here, density refers to the proportion of the number of edges present in that graph. When topological metrics

Cedric E. Ginestet; Andrew Simmons

2011-01-01

203

A constrained shortest-path energy-aware routing algorithm for wireless sensor networks  

Microsoft Academic Search

While traditional routing protocols try to minimize the end-to-end delay or maximize the throughput, most energy-aware routing protocols for wireless sensor networks try to extend the life time of the network by minimizing the energy consumption sacrificing other performance metrics. We introduce a new energy-aware routing protocol that tries to minimize the energy consumption and, at the same time, maintain

Moustafa Youssef; Mohamed Younis; Khaled Arisha

2002-01-01

204

Persistence Search - A New Search Strategy for the Dynamic Shortest Path Problem.  

National Technical Information Service (NTIS)

The research reported in this paper deals with the problem of searching through an unknown terrain by a physical agent such as a robot. The unknown terrain over which the agent will travel is represented by an undirected graph. The agent has no prior know...

M. M. Mayer M. T. Shing

1991-01-01

205

A Dynamic Programming Approach to Identifying the Shortest Path in Virtual Learning Environments  

ERIC Educational Resources Information Center

E-learning has been widely adopted as a promising solution by many organizations to offer learning-on-demand opportunities to individual employees (learners) in order to reduce training time and cost. While successful information systems models have received much attention among researchers, little research has been conducted to assess the success…

Fazlollahtabar, Hamed

2008-01-01

206

The approach for shortest paths in fire succor based on component GIS technology  

Microsoft Academic Search

Fire safety is an important issue for the national economy and people's living. Efficiency and exactness of fire department succor directly relate to safety of peoples' lives and property. Many disadvantages of the traditional fire system have been emerged in practical applications. The preparation of pumpers is guided by wireless communication or wire communication, so its real-time and accurate performances

Jie Han; Yong Zhao; K. W. Dai

2007-01-01

207

Modelling spatial substructure in wildlife populations using an approximation to the shortest path Voronoi Diagram  

Microsoft Academic Search

In the field of conservation biology, accurate population models are important for managing wildlife. It has been acknowledged that spatial structure should form an integral part of such models. Advancement in the power of desktop computers has allowed biologists to construct individual-based, spatially-explicit simulation models to predict the population dynamics of species. These models take into account local interactions and

C. W. Stewart; R. van der Ree

208

Fugitive coke oven gas emission profile by continuous line averaged open-path Fourier transform infrared monitoring.  

PubMed

Although most coke oven research is focused on the emission of polycyclic aromatic hydrocarbons, well-known carcinogens, little has been done on the emission of volatile organic compounds, some of which are also thought to be hazardous to workers and the environment. To profile coke oven gas (COG) emissions, we set up an open-path Fourier transform infrared (OP-FTIR) system on top of a battery of coke ovens at a steel mill located in Southern Taiwan and monitored average emissions in a coke processing area for 16.5 hr. Nine COGs were identified, including ammonia, CO, methane, ethane, ethylene, acetylene, propylene, cyclohexane, and O-xylene. Time series plots indicated that the type of pollutants differed over time, suggesting that different emission sources (e.g., coke pushing, quench tower, etc.) were involved at different times over the study period. This observation was confirmed by the low cross-correlation coefficients of the COGs. It was also found that, with the help of meteorological analysis, the data collected by the OP-FTIR system could be analyzed effectively to characterize differences in the location of sources. Although the traditional single-point samplings of emissions involves sampling various sources in a coke processing area at several different times and is a credible profiling of emissions, our findings strongly suggest that they are not nearly as efficient or as cost-effective as the continuous line average method used in this study. This method would make it easier and cheaper for engineers and health risk assessors to identify and to control fugitive volatile organic compound emissions and to improve environmental health. PMID:17458466

Lin, Chitsan; Liou, Naiwei; Chang, Pao-Erh; Yang, Jen-Chin; Sun, Endy

2007-04-01

209

Use of open-path FTIR monitoring for emission rate assessment of industrial area sources during winter conditions  

NASA Astrophysics Data System (ADS)

Open-path Fourier transform-infrared (OP-FTIR) was used to collect emission data for a number of chemical compounds for several area sources at a northwestern industrial facility. The data collected was used in conjunction with meteorological measurements to assess the emission rate of several of the compounds from these area sources. The release of a tracer gas at a known emission rate and its subsequent measurement with the OP-FTIR allowed for correction of emission rates to account for local effects on the site specific vertical dispersion coefficients used for emission assessments. The methodology for emission rate assessment is presented, and the implications of correcting for site specific vertical dispersion are discussed. Four area source case studies are included for the study. Most of this data was collected during cold temperature conditions, and some of the data collected during the night time hours, this represents one of the first studies of site specific vertical dispersion under these conditions. Possible impacts of these conditions on emission rate determinations will be presented. The effectiveness of OP-FTIR as a tool for area source emission rate assessment will be evaluated. OP-FTIR was employed for data collection because of its ability to detect the compounds of interest accurately and with reasonable levels of detectability. Emission rate determinations were done for process ponds AA, and BB. Fence-line concentration measurements were also made north of pond AA. The on-site study was conducted from 11/10/97 through 11/26/97. The data collected indicated that moderate to significant levels of two target compounds were being emitted by both pond AA and pond BB. Emission rates were estimated using text book dispersion coefficients and found to overestimate actual emission rates based on tracer gas release significantly. One target compound's emission rate was found to also be related to wind speed.

Kricks, Robert J.; Keely, Jerry A.; Spellicy, Robert L.; Perry, Stephen H.

1999-02-01

210

FIELD EVALUATION OF A METHOD FOR ESTIMATING GASEOUS FLUXES FROM AREA SOURCES USING OPEN-PATH FOURIER TRANSFORM INFRARED  

EPA Science Inventory

The paper describes preliminary results from a field experiment designed to evaluate a new approach to quantifying gaseous fugitive emissions from area air pollution sources. The new approach combines path-integrated concentration data acquired with any path-integrated optical re...

211

IP-oriented control of unidirectional-path-switched-ring-based transport networks  

NASA Astrophysics Data System (ADS)

An important requirement in the IP-based control of time-division multiplexing (TDM) optical transport networks is to utilize the in-built protection capabilities of synchronous optical network (SONET) unidirectional path-switched rings (UPSRs) and to automate the UPSR-protected path setup in mixed mesh-ring networks. This requires modifications to existing IP signaling and routing protocols and new processing rules at the network nodes. Here we leverage IP routing and signaling and multiprotocol label switching (MPLS) fast-reroute techniques for accurately advertising UPSR ring topologies to remote nodes and dynamically establishing UPSR-protected paths across a transport network. Our proposal also makes a NUT1-like (nonpreemptible unprotected traffic) feature possible in UPSRs, which allows for efficient utilization of UPSR protection bandwidth. We achieve this by encoding UPSR-specific information in the open shortest-path-first (OSPF) link state advertisements and in signaling messages of the Resource Reservation Protocol (RSVP) with TE extensions. In addition, we modify the signaling and routing state machines at the nodes to interpret and process this information to perform UPSR topology discovery and path computation. The uniqueness of our proposals is that the algorithms and the rules specified here allow for existing IP-based protocols [such as those within the generalized MPLS (GMPLS) framework, which currently applies to mesh networks] to be efficiently adapted for this context while still achieving our objective of exploiting UPSR-protection capabilities.

Sharma, Vishal; Das, Abhimanyu; Chen, Charles

2003-03-01

212

Dispersion of nonlinear group velocity determines shortest envelope solitons  

SciTech Connect

We demonstrate that a generalized nonlinear Schroedinger equation (NSE), which includes dispersion of the intensity-dependent group velocity, allows for exact solitary solutions. In the limit of a long pulse duration, these solutions naturally converge to a fundamental soliton of the standard NSE. In particular, the peak pulse intensity times squared pulse duration is constant. For short durations, this scaling gets violated and a cusp of the envelope may be formed. The limiting singular solution determines then the shortest possible pulse duration and the largest possible peak power. We obtain these parameters explicitly in terms of the parameters of the generalized NSE.

Amiranashvili, Sh.; Bandelow, U.; Akhmediev, N. [Weierstrass Institute for Applied Analysis and Stochastics, Mohrenstrasse 39, D-10117 Berlin (Germany); Optical Sciences Group, Research School of Physics and Engineering, Institute of Advanced Studies, Australian National University, Canberra ACT 0200 (Australia)

2011-10-15

213

A MULTI-PURPOSE OFF-LINE PATH PLANNER BASED ON AN A* SEARCH ALGORITHM  

Microsoft Academic Search

Efficient navigation of an autonomous mobile robot through a majority of which search for shortest euclidean-distance paths for well-defined environment requires the ability of the robot to plan robots free of nonholonomic constraints. For a broad overview of paths. An efficient and reliable planar off-line path planner has been path planning for robots see (Latombe, 1990). Deo and Pang developed

Arturo L. Rankin; Carl D. Crane

214

New insights into volcanic processes at Stromboli from Cerberus, a remote-controlled open-path FTIR scanner system  

NASA Astrophysics Data System (ADS)

The ordinary, low intensity activity of Stromboli volcano is sporadically interrupted by more energetic events termed, depending on their intensity, "major explosions" and "paroxysms". These short-lived energetic episodes represent a potential risk to visitors to the highly accessible summit of Stromboli. Observations made at Stromboli over the last decade have shown that the composition of gas emitted from the summit craters may change prior to such explosions, allowing the possibility that such changes may be used to forecast these potentially dangerous events.In 2008 we installed a novel, remote-controlled, open-path FTIR scanning system called Cerberus at the summit of Stromboli, with the objective of measuring gas compositions from individual vents within the summit crater terrace of the volcano with high temporal resolution and for extended periods. In this work we report the first results from the Cerberus system, collected in August-September 2009, November 2009 and May-June 2010.We find significant, fairly consistent intra-crater variability for CO2/SO2 and H2O/CO2 ratios, and relatively homogeneous SO2/HCl ratios. In general, the southwest crater is richest in CO2, and the northeast crater poorest, while the central crater is richest in H2O. It thus appears that during the measurement period the southwest crater had somewhat more direct connection to a primary, deep degassing system while the central and northeast craters reflect a slightly more secondary degassing nature, with a supplementary, shallow H2O source for the central crater, probably related to puffing activity. Such water-rich emissions from the central crater can account for the lower crystal content of its eruption products, and emphasise the role of continual magma supply to the shallowest levels of Stromboli's plumbing system.Our observations of heterogeneous crater gas emissions and high H2O/CO2 ratios do not agree with models of CO2-flushing, and we show that simple depressurisation during magma ascent to the surface is a more likely model for H2O loss at Stromboli. We highlight that alternative explanations other than CO2 flushing are required to explain distributions of H2O and CO2 amounts dissolved in melt inclusions.We detected fairly systematic increases in CO2/SO2 ratio some weeks prior to major explosions, and some evidence of a decrease in this ratio in the days immediately preceding the explosions, with periods of low, stable CO2/SO2 ratios between explosions otherwise. Our measurements, therefore, confirm the medium term (~ weeks) precursory increases previously observed with MultiGas instruments, and, in addition, reveal new short-term precursory decreases in CO2/SO2 ratios immediately prior to the major explosions. Such patterns, if shown to be systematic, may be of great utility for hazard management at Stromboli's summit.Our results suggest that intra-crater CO2/SO2 variability may produce short-term peaks and troughs in CO2/SO2 time series measured with in-situ MultiGas instruments, due simply to variations in wind direction.

La Spina, A.; Burton, M. R.; Harig, R.; Mure, F.; Rusch, P.; Jordan, M.; Caltabiano, T.

2013-01-01

215

Emission source strengths of gasoline-filling processes determined by open-path spectroscopic techniques and inverse modeling  

Microsoft Academic Search

Up to now emission source strengths of diffuse and heterogenous emission of important VOCs are not well known especially from gas stations and gasoline tank farms. To estimate the total emission of these sources non-intrusive measurements were performed by a differential optical absorption spectroscopy (DOAS) system to determine the path- integrated concentrations of exhaust compounds downwind of the source through

Klaus Schaefer; Martina Stockhause; Herbert Hoffmann; Achim Sedlmaier; Stefan M. Emeis

1998-01-01

216

Tornado Paths  

NSDL National Science Digital Library

This website catalogs all the tornado paths in the United States since 1950. The tornado path data is overlaid onto a Google Maps base for easy browsing and manipulation of the map view. Clicking on individual tornados provides the user with information such as its Fujita rating, the amount of damage caused by the tornado, the size of the path that the tornado made, and the length of time the tornado was on the ground.

Samson, Perry; Michigan, University O.

217

Path Planning for Unmanned Vehicles Using Ant Colony Optimization on a Dynamic Voronoi Diagram  

Microsoft Academic Search

One of the main objectives when planning paths for unmanned vehicles is to minimizing the time of arriving at the given destination while maximizing the safety of the vehicles. If the operational environment is static with perfect information, a safe and shortest path can be generated by applying a traditional optimization algorithm such as A*. However, if the environment is

Yaohang Li; Tao Dong; Marwan Bikdash; Yong-duan Song

2005-01-01

218

Identification of biochemical network modules based on shortest retroactive distances.  

PubMed

Modularity analysis offers a route to better understand the organization of cellular biochemical networks as well as to derive practically useful, simplified models of these complex systems. While there is general agreement regarding the qualitative properties of a biochemical module, there is no clear consensus on the quantitative criteria that may be used to systematically derive these modules. In this work, we investigate cyclical interactions as the defining characteristic of a biochemical module. We utilize a round trip distance metric, termed Shortest Retroactive Distance (ShReD), to characterize the retroactive connectivity between any two reactions in a biochemical network and to group together network components that mutually influence each other. We evaluate the metric on two types of networks that feature feedback interactions: (i) epidermal growth factor receptor (EGFR) signaling and (ii) liver metabolism supporting drug transformation. For both networks, the ShReD partitions found hierarchically arranged modules that confirm biological intuition. In addition, the partitions also revealed modules that are less intuitive. In particular, ShReD-based partition of the metabolic network identified a 'redox' module that couples reactions of glucose, pyruvate, lipid and drug metabolism through shared production and consumption of NADPH. Our results suggest that retroactive interactions arising from feedback loops and metabolic cycles significantly contribute to the modularity of biochemical networks. For metabolic networks, cofactors play an important role as allosteric effectors that mediate the retroactive interactions. PMID:22102800

Sridharan, Gautham Vivek; Hassoun, Soha; Lee, Kyongbum

2011-11-10

219

Open-path TDL-Spectrometry for a Tomographic Reconstruction of 2D H2O-Concentration Fields in the Soil-Air-Boundary-Layer of Permafrost  

NASA Astrophysics Data System (ADS)

The melting of permafrost soils in arctic regions is one of the effects of climate change. It is recognized that climatically relevant gases are emitted during the thawing process, and that they may lead to a positive atmospheric feedback [1]. For a better understanding of these developments, a quantification of the gases emitted from the soil would be required. Extractive sensors with local point-wise gas sampling are currently used for this task, but are hampered due to the complex spatial structure of the soil surface, which complicates the situation due to the essential need for finding a representative gas sampling point. For this situation it would be much preferred if a sensor for detecting 2D-concentration fields of e.g. water vapor, (and in the mid-term also for methane or carbon dioxide) directly in the soil-atmosphere-boundary layer of permafrost soils would be available. However, it also has to be kept in mind that field measurements over long time periods in such a harsh environment require very sturdy instrumentation preferably without the need for sensor calibration. Therefore we are currently developing a new, robust TDLAS (tuneable diode laser absorption spectroscopy)-spectrometer based on cheap reflective foils [2]. The spectrometer is easily transportable, requires hardly any alignment and consists of industrially available, very stable components (e.g. diode lasers and glass fibers). Our measurement technique, open path TDLAS, allows for calibration-free measurements of absolute H2O concentrations. The static instrument for sampling open-path H2O concentrations consists of a joint sending and receiving optics at one side of the measurement path and a reflective element at the other side. The latter is very easy to align, since it is a foil usually applied for traffic purposes that retro-reflects the light to its origin even for large angles of misalignment (up to 60°). With this instrument, we achieved normalized detection limits of up to 0.9 ppmv?m??Hz. For absorption path lengths of up to 2 m and time resolution of 0.2 sec, we attained detection limits of 1 ppmv. Furthermore we realized a wide dynamic range covering concentrations between 200 ppmv and 12300 ppmv. The static spectrometer will now be extended to a spatially scanning TDL sensor using rapidly rotating polygon mirrors. In combination with tomographic reconstruction methods, spatially resolved 2D-fields will be measured and retrieved. The aim is to capture concentration fields with at least 1 m2 spatial coverage with concentration detection faster than 1 Hz rate. We simulated various measurements from typical concentration distributions ("phantoms") and used Algebraic Reconstruction Techniques (ART) to compute the according 2D-fields. The reconstructions look very promising and demonstrate the potential of the measurement method. In the presentation we will describe and discuss the optical setup of the stationary instrument and explain the concept of extending this instrument to a spatially scanning tomographic TDL instrument for soil studies. Further we present first results evaluating the capabilities of the selected ART reconstruction on tomographic phantoms. [1] E. Schuur, J. G. Vogel, K. G. Crummer, H. Lee, J. O. Sickman, and T. E. Osterkamp, "The effect of permafrost thaw on old carbon release and net carbon exchange from tundra.," Nature, vol. 459, no. 7246, pp. 556-9, May 2009. [2] A. Seidel, S. Wagner, and V. Ebert, "TDLAS-based open-path laser hygrometer using simple reflective foils as scattering targets," Applied Physics B, vol. 109, no. 3, pp. 497-504, Oct. 2012.

Seidel, Anne; Wagner, Steven; Dreizler, Andreas; Ebert, Volker

2013-04-01

220

Path Sensitization in Critical Path Problem  

Microsoft Academic Search

Since the delay of a circuit is determined by the delay of its longest sensitizable paths (such paths are called critical paths), the problem of estimating the delay of a circuit is called critical path problem. One important aspect of the critical path problem is to decide whether a path is sensitizable. A framework which allows various previously proposed path

Hsi-chuan Chen; David Hung-chang Du

1991-01-01

221

A Preliminary Path Analysis of Expectancy and Patient-Provider Encounter in an Open-label Randomized Controlled Trial of Spinal Manipulation for Cervicogenic Headache  

PubMed Central

Objective The purpose of this paper is to present a preliminary model to identify the effects of expectancy of treatment success and the patient-provider encounter (PPE) on outcomes in an open-label randomized trial. Methods 80 participants with chronic cervicogenic headache (CGH) were randomized to 4 groups: 2 levels of treatment dose (8 or 16) and 2 levels of therapy from a chiropractor (spinal manipulation or light massage). Providers were instructed to have equal enthusiasm for all care. Structural equation modeling with standardized path coefficients (?) was used in a path analysis to identify the effects of patient expectancy and the PPE on CGH pain. The model included monthly pain from baseline to 12 weeks. Expectancy and PPE were evaluated on Likert scales. The PPE was measured as patient perception of chiropractor enthusiasm, confidence, and comfort with care. Results Baseline patient expectancy was balanced across groups. PPE measures were balanced across groups and consistent over the 8-week treatment period. Treatment and baseline pain had the strongest effects on pain outcomes (|?| =.46 to .59). Expectations had little effect on pain (|?| < .15). The PPE had a weak effect on pain (|?| = .03 to .27) and on subsequent confidence in treatment success (|?| = .09 and .12). Conclusions Encouraging equipoise in the provider-patient encounter and balancing expectancy across treatment groups may protect against some confounding related to the absence of blinding in a randomized controlled trial of pain. In this trial, their effects were found to be small relative to the effects of treatment and baseline values.

Haas, Mitchell; Aickin, Mikel; Vavrek, Darcy

2010-01-01

222

Applications of open-path Fourier transform infrared for identification of volatile organic compound pollution sources and characterization of source emission behaviors.  

PubMed

An open-path Fourier transform infrared spectroscopy (OP-FTIR) system was set up for 3-day continuous line-averaged volatile organic compound (VOC) monitoring in a paint manufacturing plant. Seven VOCs (toluene, m-xylene, p-xylene, styrene, methanol, acetone, and 2-butanone) were identified in the ambient environment. Daytime-only batch operation mode was well explained by the time-series concentration plots. Major sources of methanol, m-xylene, acetone, and 2-butanone were identified in the southeast direction where paint solvent manufacturing processes are located. However, an attempt to uncover sources of styrene was not successful because the method detection limit (MDL) of the OP-FTIR system was not sensitive enough to produce conclusive data. In the second scenario, the OP-FTIR system was set up in an industrial complex to distinguish the origins of several VOCs. Eight major VOCs were identified in the ambient environment. The pollutant detected wind-rose percentage plots that clearly showed that ethylene, propylene, 2-butanone, and toluene mainly originated from the tank storage area, whereas the source of n-butane was mainly from the butadiene manufacturing processes of the refinery plant, and ammonia was identified as an accompanying reduction product in the gasoline desulfuration process. Advantages of OP-FTIR include its ability to simultaneously and continuously analyze many compounds, and its long path length monitoring has also shown advantages in obtaining more comprehensive data than the traditional multiple, single-point monitoring methods. PMID:18581812

Lin, Chitsan; Liou, Naiwei; Sun, Endy

2008-06-01

223

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: II. Fog and rain.  

PubMed

Open-path FT-IR spectra of low-concentration releases of diethyl ether were measured both when a glycol fog was passed into the infrared beam and when large water droplets from a lawn sprinkler were sprayed into the beam. It was shown that the glycol fog, for which the droplet size was much less than the wavelength of the infrared radiation, gave rise to a significant interference such that partial least squares (PLS) regression would only yield reasonable values for the ether concentration if background spectra in which the glycol fog was present were included in the calibration set. On the other hand, target factor analysis (TFA) allowed the presence of the ether to be recognized without precalibration. When large water droplets were present in the beam, any infrared radiation entering the droplet was completely absorbed, so that both PLS and TFA would yield accurate results. PMID:20414770

Shao, Limin; Roske, Christopher W; Griffiths, Peter R

2010-04-23

224

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: I. High-frequency flashes.  

PubMed

Open-path FT-IR spectra were measured while fireworks were emitting smoke and incandescent particles into the infrared beam. These conditions were designed to simulate the appearance of smoke and explosions in a battlefield. Diethyl ether was used to simulate the vapor-phase spectra of G agents such as sarin. The measured interferograms were corrected by a high-pass filter and were rejected when interfering features were of such high frequency that they could not be removed by application of this filter. The concentration of diethyl ether was calculated correctly by partial least squares regression in the absence of fireworks but significant errors were encountered when the spectra of the oxide particles were not included in the calibration set. Target factor analysis allowed the presence of the analyte to be detected even when the incandescent particles were present in the beam. PMID:20401469

Shao, Limin; Roske, Christopher W; Griffiths, Peter R

2010-04-18

225

A critical examination of stoichiometric and path-finding approaches to metabolic pathways.  

PubMed

Advances in the field of genomics have enabled computational analysis of metabolic pathways at the genome scale. Singular attention has been devoted in the literature to stoichiometric approaches, and path-finding approaches, to metabolic pathways. Stoichiometric approaches make use of reaction stoichiometry when trying to determine metabolic pathways. Stoichiometric approaches involve elementary flux modes and extreme pathways. In contrast, path-finding approaches propose an alternative view based on graph theory in which reaction stoichiometry is not considered. Path-finding approaches use shortest path and k-shortest path concepts. In this article we give a critical overview of the theory, applications and key research challenges of stoichiometric and path-finding approaches to metabolic pathways. PMID:18436574

Planes, Francisco J; Beasley, John E

2008-04-24

226

Open path measurements of carbon dioxide and water vapor under foggy conditions - technical problems, approaches and effects on flux measurements and budget calculations  

NASA Astrophysics Data System (ADS)

To estimate carbon dioxide or water vapor fluxes with the Eddy Covariance method high quality data sets are necessary. Under foggy conditions this is challenging, because open path measurements are influenced by the water droplets that cross the measurement path as well as deposit on the windows of the optical path. For the LI-7500 the deposition of droplets on the window results in an intensity reduction of the infrared beam. To keep the strength of the infrared beam under these conditions, the energy is increased. A measure for the increased energy is given by the AGC value (Automatic Gain Control). Up to a AGC threshold value of 70 % the data from the LI-7500 is assumed to be of good quality (personal communication with LICOR). Due to fog deposition on the windows, the AGC value rises above 70 % and stays there until the fog disappears and the water on the windows evaporates. To gain better data quality during foggy conditions, a blower system was developed that blows the deposited water droplets off the window. The system is triggered if the AGC value rises above 70 %. Then a pneumatic jack will lift the blower system towards the LI-7500 and the water-droplets get blown off with compressed air. After the AGC value drops below 70 %, the pneumatic jack will move back to the idle position. Using this technique showed that not only the fog droplets on the window causing significant problems to the measurement, but also the fog droplets inside the measurement path. Under conditions of very dense fog the measured values of carbon dioxide can get unrealistically high, and for water vapor, negative values can be observed even if the AGC value is below 70 %. The negative values can be explained by the scatter of the infrared beam on the fog droplets. It is assumed, that different types of fog droplet spectra are causing the various error patterns observed. For high quality flux measurements, not only the AGC threshold value of 70 % is important, but also the fluctuation of the AGC value in a flux averaging interval. Such AGC value fluctuations can cause severe jumps in the concentration measurements that can hardly be corrected for. Results of fog effects on the LI-7500 performance and its consequences for flux measurements and budget calculations will be presented.

El-Madany, T.; Griessbaum, F.; Maneke, F.; Chu, H.-S.; Wu, C.-C.; Chang, S. C.; Hsia, Y.-J.; Juang, J.-Y.; Klemm, O.

2010-07-01

227

Carbon dioxide and water budget of grazed grassland in Grünschwaige (Munich, Bavaria) measured by EC-method with an open path gas analyzer  

NASA Astrophysics Data System (ADS)

Terrestrial ecosystems like grasslands can act as a sink or source for greenhouse gases (GHG) like carbon dioxide. This is important for scientific and political stakeholders as GHG cause the climate change. The eddy covariance method has become a major tool for quantifying such fluxes. It depends, however, on a number of corrections applied to the measured data. The influence of air density is often considered following the WPL-correction (Webb-Pearman-Leuning), which does not take the heating of the instrument surface into account in contrast to the recently published method by Burba et al. (2008). The aim of the study is the comparison of the influence of the two density correction on the CO2 fluxes. The fluxes of water and carbon dioxide were measured with the eddy covariance method from 2002 to 2008 on a grazed grassland site located in Grünschwaige close to Munich (Bavaria) in the South of Germany. The climate in this area is temperate with an annual precipitation of 800 mm and an annual mean temperature of 9 °C. For eddy covariance measurements an open path CO2/H2O analyzer was used. Wind speed (3D) and temperature were measured by a sonic anemometer. The sensible/latent heat flux and the carbon dioxide flux were calculated and corrected using EdiRe. The application of the two density correction methods resulted in important differences of the carbon dioxide flux. The fluxes corrected according to Burba et al. (2008) indicated small CO2 sinks (= negative net carbon exchange) or even sources while the WPL-correction showed (larger) CO2 sinks. Additionally, with both correction methods the results showed a high sensitivity to weather conditions but the effects were stronger using the correction following Burba et al. (2008). The most important drivers of flux variability were precipitation and temperature. The seasonal pattern of precipitation was important especially during the vegetation period. Drought and heat periods, which lasted at last one month like in 2003 and 2006, lowered evapotranspiration and resulted in lower CO2 sinks or even turned the grassland into a source. This study shows the sensitivity of the carbon dioxide and water vapour fluxes quantified by the eddy covariance method to density correction, which can cause substantial changes in the assessment of the influence of environmental factors on fluxes from grassland. Burba, George G.; McDermitt, Dayle K.; Grelle, Achim; Anderson, Daniel J. and Xu, Liukang (2008): Addressing the influence of instrument surface heat exchange on the measurements of CO2 flux from open-path gas analyzers. Global Change Biology, 14, 1854 - 1876

Vetter, S.; Bernhofer, Ch.; Auerswald, K.

2009-04-01

228

Term Paths  

NSDL National Science Digital Library

Students follow several pathways using anatomical directions on a simulated "body" produced from a copy of a school building's fire evacuation plan. The main hallways are designated as major blood vessels and the various areas of the school, the head, chest, abdomen, etc. Students complete several pathways using anatomical terms as directions. For example, one of my paths begins, "Ex- ot-, ad- superior, ecto- derm-, peri-frontal, circum- rhino-, " which loosely means, exit the ear, go to the superior region, outside the skin, around the frontal region, around the nose. At the end of each path I leave a clue that lets me know the students actually made it. The combined clues form a sentence.

Cynthia Ann Radle (McCullough High School REV)

1995-06-30

229

Trace gas emissions from laboratory biomass fires measured by open-path Fourier transform infrared spectroscopy: Fires in grass and surface fuels  

NASA Astrophysics Data System (ADS)

The trace gas emissions from six biomass fires, including three grass fires, were measured using a Fourier transform infrared (FTIR) spectrometer coupled to an open-path, multipass cell (OP-FTIR). The quantified emissions consisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, methane, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in this study we have now measured smoke composition from fires in each major vegetation class. The emission ratios of the oxygenated compounds, formaldehyde, methanol, and acetic acid, were 1-2% of CO in the grass fires, similar to our other laboratory and field measurements but significantly higher than in some other studies. These oxygenated compounds are important, as they affect O3 and HOx chemistry in both biomass fire plumes and the free troposphere. The OP-FTIR data and the simultaneously collected canister data indicated that the dominant C4 emission was isobutene (C4H8) and not 1-butene. The rate constant for the reaction of isobutene with the OH radical is 60% larger than that of 1-butene. We estimate that 67±9% of the fuel nitrogen was volatilized with the major nitrogen emissions, ammonia, and nitric oxide, accounting for 22±8%.

Goode, Jon G.; Yokelson, Robert J.; Susott, Ronald A.; Ward, Darold E.

1999-09-01

230

Minimum-Risk Path Finding by an Adaptive Amoebal Network  

NASA Astrophysics Data System (ADS)

When two food sources are presented to the slime mold Physarum in the dark, a thick tube for absorbing nutrients is formed that connects the food sources through the shortest route. When the light-avoiding organism is partially illuminated, however, the tube connecting the food sources follows a different route. Defining risk as the experimentally measurable rate of light-avoiding movement, the minimum-risk path is exhibited by the organism, determined by integrating along the path. A model for an adaptive-tube network is presented that is in good agreement with the experimental observations.

Nakagaki, Toshiyuki; Iima, Makoto; Ueda, Tetsuo; Nishiura, Yasumasa; Saigusa, Tetsu; Tero, Atsushi; Kobayashi, Ryo; Showalter, Kenneth

2007-08-01

231

Applying open-path FTIR with a bi-beam strategy to evaluate personal exposure in indoor environments: experimental results of a validation study.  

PubMed

This study evaluated the performance and feasibility of using open-path Fourier transform infrared (OP-FTIR) with a bi-beam strategy to assess personal exposures in workplaces. The bi-beam strategy combines a long beam and a short beam measurement to calculate the average concentration level of the segmented region. A series of experiments was conducted with six human subjects at two workstations inside a chamber. A bi-beam geometry was set up for each workstation. Each subject repeatedly performed two tasks (9 min/task), which were designed to simulate a painting and an assembly task. For each task a tracer gas (N(2)O) was released from a point source near the subject. During each task, while the OP-FTIR collected the N(2)O spectrum, bag samples were collected simultaneously at nose and lapel height. Statistical data analysis applied a general linear model with the bag samples as the dependent variable. Results show that the locations, tasks, and subjects are not significant factors when using OP-FTIR measurements with the bi-beam strategy to estimate personal exposure at the nose height. The model used in this study fits the data reasonably well (R(2)=0.87), and when it is compared with a second set of experimental data, the bias is 0.7 ppm (3%) and the precision is 5.5 ppm. This study demonstrates that the bi-beam sampling strategy may offer a new approach for applying OP-FTIR to industrial hygiene monitoring. PMID:12688842

Wu, Chang-Fu; Yost, Michael G; Varr, Janice; Hashmonay, Ram A

232

Workplace and environmental air contaminant concentrations measured by open path Fourier transform infrared spectroscopy: a statistical process control technique to detect changes from normal operating conditions.  

PubMed

Open path Fourier transform infrared (OP-FTIR) spectroscopy is a new air monitoring technique that can be used to measure concentrations of air contaminants in real or near-real time. OP-FTIR spectroscopy has been used to monitor workplace gas and vapor exposures, emissions from hazardous waste sites, and to track emissions along fence lines. This paper discusses a statistical process control technique that can be used with air monitoring data collected with an OP-FTIR spectrometer to detect departures from normal operating conditions in the workplace or along a fence line. Time series data, produced by plotting consecutive air sample concentrations in time, were analyzed. Autocorrelation in the time series data was removed by fitting dynamic models. Control charts were used with the residuals of the model fit data to determine if departures from defined normal operating conditions could be rapidly detected. Shewhart and exponentially weighted moving average (EWMA) control charts were evaluated for use with data collected under different room air flow and mixing conditions. Under rapidly changing conditions the Shewhart control chart was able to detect a leak in a simulated process area. The EWMA control chart was found to be more sensitive to drifts and slowly changing concentrations in air monitoring data. The time series and statistical process control techniques were also applied to data obtained during a field study at a chemical plant. A production area of an acrylonitrile, 1,3-butadiene, and styrene (ABS) polymer process was monitored in near-real time. Decision logics based on the time series and statistical process control technique introduced suggest several applications in workplace and environmental monitoring. These applications might include signaling of an alarm or warning, increasing levels of worker respiratory protection, or evacuation of a community, when gas and vapor concentrations are determined to be out-of-control. PMID:8012765

Malachowski, M S; Levine, S P; Herrin, G; Spear, R C; Yost, M; Yi, Z

1994-05-01

233

A two-laser beam technique for improving the sensitivity of low frequency open path tunable diode laser absorption spectrometer (OP-TDLAS) measurements  

NASA Astrophysics Data System (ADS)

Open path tunable diode-laser absorption spectroscopy (OP-TDLAS) is a promising technique to detect low concentrations of possible biogenic gases on Mars. This technique finds the concentration of a gas by measuring the amount of laser light absorbed by gaseous molecules at a specific wavelength. One of the major factors limiting sensitivity in the TDLAS systems operating at low modulation frequencies is 1/f noise. 1/f noise is minimized in many spectroscopy systems by the use of high frequency modulation techniques. However, these techniques require complex instruments that include reference cells and other devices for calibration, making them relatively large and bulky. We are developing a spectroscopy system for space applications that requires small, low mass and low power instrumentation, making the high frequency techniques unsuitable. This paper explores a new technique using two-laser beam to reduce the affect of 1/f noise and increase the signal strength for measurements made at lower frequencies. The two lasers are excited at slightly different frequencies. An algorithm is used to estimate the noise in the second harmonic from the combined spectra of both lasers. This noise is subtracted from the signal to give a more accurate measurement of gas concentration. The error in estimation of 1/f noise is negligible as it corresponds to noise level made at much higher frequencies. Simulation results using ammonia gas and two lasers operating at 500 and 510 Hz respectively shows that this technique is able to decrease the error in estimation of gas concentration to 1/6 its normal value.

Mohammad, Israa L.; Anderson, Gary T.; Chen, Youhua

2013-09-01

234

Approximating cycles in a shortest basis of the first homology group from point data  

NASA Astrophysics Data System (ADS)

Inference of topological and geometric attributes of a hidden manifold from its point data is a fundamental problem arising in many scientific studies and engineering applications. In this paper, we present an algorithm to compute a set of cycles from a point data that presumably sample a smooth manifold M\\subset {R}^d. These cycles approximate a shortest basis of the first homology group {\\sf H}_1(M) over coefficients in the finite field {Z}_2. Previous results addressed the issue of computing the rank of the homology groups from point data, but there is no result on approximating the shortest basis of a manifold from its point sample. In arriving at our result, we also present a polynomial time algorithm for computing a shortest basis of {\\sf H}_1({ K}) for any finite simplicial complex { K} whose edges have non-negative weights.

Dey, Tamal K.; Sun, Jian; Wang, Yusu

2011-12-01

235

A disjoint path selection scheme with shared risk link groups in GMPLS networks  

Microsoft Academic Search

This letter proposes a disjoint path selection scheme for generalized multi-protocol label switching (GMPLS) networks with shared risk link group (SRLG) constraints. It is called the weighted-SRLG (WSRLG) scheme. It treats the number of SRLG members related to a link as part of the link cost when the k-shortest path algorithm is executed. In WSRLG, a link that has many

Eiji Oki; Nobuaki Matsuura; Kohei Shiomoto; Naoaki Yamanaka

2002-01-01

236

Shortest Route Models for the Allocation of Inspection Effort on a Production Line  

Microsoft Academic Search

Two shortest route models for determining where to allocate inspection effort on a production line are developed for the cases where this effort is unlimited or limited in its availability. A production line is defined as an ordered sequence of production stages, each stage consisting of a manufacturing operation followed by a potential inspection station. Items flow through the line

Leon S. White

1969-01-01

237

The shortest processing time first (SPTF) dispatch rule and some variants in semiconductor manufacturing  

Microsoft Academic Search

Looking for appropriate dispatch rules for semiconductor fabrication facilities (wafer fabs), practitioners often intend to use the Shortest Processing Time First (SPTF) rule because it is said to reduce cycle times. In our study, we show, however, that this positive effect on cycle times can be achieved in single machine systems but not necessarily in complete wafer fabs. In addition,

Oliver Rose

2001-01-01

238

Optimally computing a shortest weakly visible line segment inside a simple polygon  

Microsoft Academic Search

A simple polygon is said to be weakly internally visible from a line segment lyinginside it if every point on the boundary of the polygon is visible from some point onthe line segment. In this paper, we present an optimal linear-time algorithm for thefollowing problem: Given a simple polygon, either compute a shortest line segmentfrom which the polygon is weakly

Binay K. Bhattacharya; Gautam Das; Asish Mukhopadhyay; Giri Narasimhan

2002-01-01

239

Implementation and efficiency of Moore-algorithms for the shortest route problem  

Microsoft Academic Search

In the last 15 years, a good deal of effort has been devoted to the study of the shortest route problem. More than 200 publications are known but little has been reported concerning relative efficiencies. For a long time the Dijkstra method was considered the most efficient one. Programming work, using different data structures and implementation techniques for several algorithms,

U. Pape

1974-01-01

240

Comprehensive laboratory measurements of biomass-burning emissions: 2. First intercomparison of open-path FTIR, PTR-MS, and GC-MS/FID/ECD  

NASA Astrophysics Data System (ADS)

Oxygenated volatile organic compounds (OVOC) can dominate atmospheric organic chemistry, but they are difficult to measure reliably at low levels in complex mixtures. Several techniques that have been used to speciate nonmethane organic compounds (NMOC) including OVOC were codeployed/intercompared in well-mixed smoke generated by 47 fires in the U.S. Department of Agriculture Forest Service Fire Sciences Combustion Facility. The agreement between proton transfer reaction mass spectrometry (PTR-MS) and open-path Fourier transform infrared spectroscopy (OP-FTIR) was excellent for methanol (PT/FT = 1.04 ± 0.118) and good on average for phenol (0.843 ± 0.845) and acetol (˜0.81). The sum of OP-FTIR mixing ratios for acetic acid and glycolaldehyde agreed (within experimental uncertainty) with the PTR-MS mixing ratios for protonated mass 61 (PT/FT = 1.17 ± 0.34), and the sum of OP-FTIR mixing ratios for furan and isoprene agreed with the PTR-MS mixing ratios for protonated mass 69 (PT/FT = 0.783 ± 0.465). The sum of OP-FTIR mixing ratios for acetone and methylvinylether accounted for most of the PTR-MS protonated mass 59 signal (PT/FT = 1.29 ± 0.81), suggesting that one of these compounds was underestimated by OP-FTIR or that it failed to detect other compounds that could contribute at mass 59. Canister grab sampling followed by gas chromatography (GC) with mass spectrometry (MS), flame ionization detection (FID), and electron capture detection (ECD) analysis by two different groups agreed well with OP-FTIR for ethylene, acetylene, and propylene. However, these propylene levels were below those observed by PTR-MS (PT/FT = 2.33 ± 0.89). Good average agreement between PTR-MS and GC was obtained for benzene and toluene. At mixing ratios above a few parts per billion the OP-FTIR had advantages for measuring sticky compounds (e.g., ammonia and formic acid) or compounds with low proton affinity (e.g., hydrogen cyanide and formaldehyde). Even at these levels, only the PTR-MS measured acetonitrile and acetaldehyde. Below a few ppbv only the PTR-MS measured a variety of OVOC, but the possibility of fragmentation, interference, and sampling losses must be considered.

Christian, T. J.; Kleiss, B.; Yokelson, R. J.; Holzinger, R.; Crutzen, P. J.; Hao, W. M.; Shirai, T.; Blake, D. R.

2004-01-01

241

Efficient path profiling  

Microsoft Academic Search

A path profile determines how many times each acyclic path in a routine executes. This type of profiling subsumes the more common basic block and edge profiling, which only approximate path frequencies. Path profiles have many potential uses in program performance tuning, profile-directed compilation, and software test coverage. This paper describes a new algorithm for path profiling. This simple, fast

Thomas Ball; James R. Larus

1996-01-01

242

Field determination of biomass burning emission ratios and factors via open-path FTIR spectroscopy and fire radiative power assessment: headfire, backfire and residual smouldering combustion in African savannahs  

NASA Astrophysics Data System (ADS)

Biomass burning emissions factors are vital to quantifying trace gases releases from vegetation fires. Here we evaluate emissions factors for a series of savannah fires in Kruger National Park (KNP), South Africa using ground-based open path Fourier transform infrared (FTIR) spectroscopy and an infrared lamp separated by 150-250 m distance. Molecular abundances along the extended open path are retrieved using a spectral forward model coupled to a non-linear least squares fitting approach. We demonstrate derivation of trace gas column amounts for horizontal paths transecting the width of the advected plume, and find, for example, that CO mixing ratio changes of ~0.001 ?mol mol-1 (~10 ppbv) can be detected across the relatively long optical paths used here. We focus analysis on five key compounds whose production is preferential during the pyrolysis (CH2O), flaming (CO2) and smoldering (CO, CH4, NH3) fire phases. We demonstrate that well constrained emissions ratios for these gases to both CO2 and CO can be derived for the backfire, headfire and residual smouldering combustion stages of these savannah fires, from which stage-specific emission factors can then be calculated. Headfires and backfires in general show similar emission ratios and emission factors, but those of the residual smouldering combustion stage can differ substantially (e.g., ERCH4/CO2 up to ~7 times higher than for the flaming stages). The timing of each fire stage was identified via airborne optical and thermal IR imagery and ground-observer reports, with the airborne IR imagery also used to derive estimates of fire radiative energy, thus allowing the relative amount of fuel burned in each stage to be calculated and the "fire averaged" emission ratios and emission factors to be determined. The derived "fire averaged" emission ratios are dominated by the headfire contribution, since the vast majority of the fuel is burned in this stage. Our fire averaged emission ratios and factors for CO2 and CH4 agree with those from published studies conducted in the same area using airborne plume sampling, and we concur with past suggestions that emission factors for formaldehyde in this environment appear substantially underestimated in widely used databases. We also find the emission ratios and factors for CO and NH3 to be somewhat higher than most other estimates, however, we see no evidence to support suggestions of a major overestimation in the emission factor of ammonia. Our data also suggest that the contribution of burning animal (elephant) dung can be a significant factor in the emissions characteristics of certain KNP fires, and indicate some similarities between the time series of fire brightness temperature and modified combustion efficiency (MCE) that supports suggestions that EO-derived fire temperature estimates maybe useful when attempting to remotely classify fire activity into its different phases. We conclude that ground-based, extended open path FTIR spectroscopy is a practical and very effective means for determining emission ratios, emission factors and modified combustion efficiencies at open vegetation fire plumes, allowing these to be probed at temporal and spatial scales difficult to explore using other ground-based approaches. Though we limited our study to five key emissions products, open path FTIR spectroscopy can detect dozens of other species, as has been demonstrated during previous closed-path FTIR airborne deployments in the same study area.

Wooster, M. J.; Freeborn, P. H.; Archibald, S.; Oppenheimer, C.; Roberts, G. J.; Smith, T. E. L.; Govender, N.; Burton, M.; Palumbo, I.

2011-02-01

243

Flight Path Displays.  

National Technical Information Service (NTIS)

Aircraft display technology has advanced to the state where the flight path display, an integrated format on which both the vertical and horizontal path are graphically represented, is feasible. This report researches efforts made to design flight paths f...

D. A. Warner

1979-01-01

244

Translational and structural analysis of the shortest legume ENOD40 gene in Lupinus luteus  

Microsoft Academic Search

Two early nodulin 40 (enod40) genes, ENOD40-1, the shortest legume ENOD40 gene, and ENOD40-2, were isolated from Lupinus luteus, a legume with indeterminate nodules. Both genes were expressed at similar levels during symbiosis with nitrogen-fixing bacteria. ENOD40 phylog- eny clustered the L. luteus genes with legumes forming determinate nodules and revealed pep- tide similarities. The ENOD40-1 small ORF A fused

Jan Podkowinski; Agnieszka Zmienko; Blazena Florek; Pawel Wojciechowski; Agnieszka Rybarczyk; Jan Wrzesinski; Jerzy Ciesiolka; Jacek Blazewicz; Adam Kondorosi; Martin Crespi; Andrzej Legocki

2009-01-01

245

An Island Model Based Ant System with Lookahead for the Shortest Supersequence Problem  

Microsoft Academic Search

In this paper we introduce an Ant Colony Optimisation (ACO) algorithm for the Shortest Common Supersequence (SCS) problem,\\u000a which has applications in production system planning, mechanical engineering and molecular biology. The ACO algorithm is used\\u000a to find good parameters for a heuristic for the SCS problem. An island model with several populations of ants is used for\\u000a the ACO algorithm.

René Michel; Martin Middendorf

1998-01-01

246

Constraint-Based Local Search for Constrained Optimum Paths Problems  

NASA Astrophysics Data System (ADS)

Constrained Optimum Path (COP) problems arise in many real-life applications and are ubiquitous in communication networks. They have been traditionally approached by dedicated algorithms, which are often hard to extend with side constraints and to apply widely. This paper proposes a constraint-based local search (CBLS) framework for COP applications, bringing the compositionality, reuse, and extensibility at the core of CBLS and CP systems. The modeling contribution is the ability to express compositional models for various COP applications at a high level of abstraction, while cleanly separating the model and the search procedure. The main technical contribution is a connected neighborhood based on rooted spanning trees to find high-quality solutions to COP problems. The framework, implemented in COMET, is applied to Resource Constrained Shortest Path (RCSP) problems (with and without side constraints) and to the edge-disjoint paths problem (EDP). Computational results show the potential significance of the approach.

Pham, Quang Dung; Deville, Yves; van Hentenryck, Pascal

247

A strategy for solving static multiple-optimal-path transit network problems  

SciTech Connect

The trip making process using transit versus private automobile differs in the use of time schedules, walking paths, transfer stops, plus issues such as fare and safety. Due to these factors, many of the standard shortest path algorithms do not apply. The purpose of this study is to develop an algorithm and strategy for transit providers to find best alternatives for the user, and to demonstrate how a geographic information system can be used in the development of transit advanced traveler information system (TATIS) to meet these needs. This paper presents a short introduction to TATIS systems, some commonly used algorithms in determining the shortest and multiple paths, and a new strategy that was developed in this study which differs from standard network algorithms. The major features of this proposed algorithm are: (1) Capability of handling multiple modes of transit; (2) providing paths that include walking distances from and to the transit path as well as between transfer points; and (3) provision of multiple optimal paths to allow the user flexibility in choosing a path.

Koncz, N.; Greenfeld, J.; Mouskos, K. [New Jersey Inst. of Tech., Newark, NJ (United States). Dept. of Civil Engineering

1996-05-01

248

G codes for the specification of Pythagorean-hodograph tool paths and associated feedrate functions on open-architecture CNC machines  

Microsoft Academic Search

A new class of machine codes for the specification of Pythagorean-hodograph (PH) curve tool paths, and associated feedrate functions, is proposed. The PH curves are a special family of free-form curves, compatible with the Bézier\\/B-spline representations of CAD systems, that are amenable to real-time interpolation at constant or variable feedrate directly from their exact analytic descriptions. The proposed codes are

Rida T. Farouki; Jairam Manjunathaiah; Guo-Feng Yuan

1999-01-01

249

DISCUSS: Critical Path Analysis  

NSDL National Science Digital Library

This module, by Barrie Baker and Neville Hunt of Coventry University, introduces critical path analysis and addresses the following topics: Networks, Critical paths, Floats, Activity-on-node (AON) networks. Excel spreadsheets are used to provide examples and exercises.

Hunt, Neville; Baker, Barrie

2009-04-23

250

Path planning for UAVs  

Microsoft Academic Search

In this paper, a two step path-planning algorithm for UAVs is proposed. The algorithm generates a stealthy path through a set of enemy radar sites of known location, and provides an intuitive way to trade-off stealth versus path length. In the first step, a suboptimal rough-cut path is generated through the radar sites by constructing and searching a graph based

S. A. Bortoff; E. Hartford

2000-01-01

251

Mobile system for open-path trace gas detection in the mid-infrared using a Raman-shifted Cr:LiSAF source  

NASA Astrophysics Data System (ADS)

Many trace atmospheric gas constituents have optical absorption bands in the 2 - 5 micrometers atmospheric transmission window. Remote sensing of these compounds is possible with an appropriate laser source. We use stimulated Raman scattering in hydrogen to shift pulsed, Cr:LiSAF laser emission from the near infrared to this mid-infrared band. Injection seeding the oscillator with a spectrally narrow, low-power diode laser produces a tunable, spectroscopic grade source. We have combined this laser source with transmitting and receiving optics in order to make double- ended, long-path DIAL measurements. For example, we are able to detect ambient levels of water and methane and trace levels of ethane over a two mile, round-trip path. Spectral control is critical for making these measurements for several reasons. First, the DIAL technique requires a spectrally narrow source to tune across the narrow absorption bands of molecules with absorption features in the 2 - 5 micrometers band. Second, good spectral control allows species-specific detection when there are target species with closely spaced absorption features. Third, strong water vapor and CO2 absorption bands are common throughout the 2 - 5 micrometers band causing large fluctuations in the background transmission. Good spectral control enables species specific detection within this highly variable transmission background.

Wamsley, Paula R.; Weimer, Carl S.; Applegate, Jeffrey T.; Beaton, Stuart P.; Beyer, Brian S.

1999-10-01

252

An Efficient Path Computation Model for Hierarchically Structured Topographical Road Maps  

Microsoft Academic Search

In this paper, we have developed a HiT i (Hierarchical MulTi) graph model for structuring large topographical road maps to speed up the minimum cost route computation. The HiT i graph model provides a novel approach to abstracting and structuring a topographical road map in a hierarchical fashion. We propose a new shortest path algorithm named SP AH, which utilizes

Sungwon Jung; Sakti Pramanik

2002-01-01

253

Walden's Paths - Ensemble Edition  

NSDL National Science Digital Library

WaldenÂs Paths enables users of digital document collections (e.g. the Web) to exploit these documents by reusing them for previously unintended audiences in an academic setting. Authors of paths (usually educators) overlay a linear, directed meta-structure over the Web documents and recontextualize these by adding explanatory text to achieve their curricular goals. Paths do not modifythe structure or content of the Web resources that they include. The creation of a path over pre-organized content (e.g. books, Web pages) to reorganize and associate related information serves to facilitate easy retrieval and communication. WaldenÂs Paths displays the information that the path points to in conjunction with the textual annotations added by the author of the path.

2011-01-04

254

Calibration of an open-path FTIR spectrometer for methane, ethylene, and carbon monoxide using a fixed 20-m multipass cell  

NASA Astrophysics Data System (ADS)

A calibration experiment was performed by the Fachhochschule Duesseldorf in cooperation with the official calibration laboratory of the Environmental State Agency of Northrhine Westphalia. This was the first calibration of an OP-FTIR spectrometer at an official calibration laboratory in Germany. The calibration measurements were carried out along the standard ISO/DIS 9169, 'air quality - determination of performance characteristics of measurement methods'. A multipass cell with a light path of 20m was used. During these measurements the deviation between the calibration gas concentration and the measured concentration increased rapidly with higher concentration. This indicates a nonlinear calibration function of the OP-FTIR spectrometer used here and might be addressed to the used spectral resolution of 1.0 wavenumbers. The calibration measurements are still running for other gases and other OP-FTIR spectrometers.

Lamp, Torsten; Radmacher, M.; Weber, Konradin; Gaertner, A.; Nitz, R.; Broeker, G.

1997-05-01

255

News CERN Celebration: CERN marks 20 years of the Web Workshops: Physics Teachers' Day aired live on Web Teacher Programme: Physics Teachers at CERN 2009 leaves attendees thirsty for more GIREP: Registration open for GIREP '09 Science and Creationism: Telegraph headline leads readers down wrong path Recruitment: Is recession proving to be good news for science teaching? Forthcoming Events  

NASA Astrophysics Data System (ADS)

CERN Celebration: CERN marks 20 years of the Web Workshops: Physics Teachers' Day aired live on Web Teacher Programme: Physics Teachers at CERN 2009 leaves attendees thirsty for more GIREP: Registration open for GIREP '09 Science and Creationism: Telegraph headline leads readers down wrong path Recruitment: Is recession proving to be good news for science teaching? Forthcoming Events

2009-05-01

256

TWINS: THE TWO SHORTEST PERIOD NON-INTERACTING DOUBLE DEGENERATE WHITE DWARF STARS  

SciTech Connect

We report on the detection of the two shortest period non-interacting white dwarf binary systems. These systems, SDSS J143633.29+501026.8 and SDSS J105353.89+520031.0, were identified by searching for radial velocity variations in the individual exposures that make up the published spectra from the Sloan Digital Sky Survey. We followed up these systems with time series spectroscopy to measure the period and mass ratios of these systems. Although we only place a lower bound on the companion masses, we argue that they must also be white dwarf stars. With periods of approximately 1 hr, we estimate that the systems will merge in less than 100 Myr, but the merger product will likely not be massive enough to result in a Type 1a supernova.

Mullally, F.; Badenes, Carles; Lupton, Robert [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Thompson, Susan E., E-mail: fergal@astro.princeton.ed [Department of Physics and Astronomy, University of Delaware, 217 Sharp Lab, Newark, DE 19716 (United States)

2009-12-10

257

A Multilevel Probabilistic Beam Search Algorithm for the Shortest Common Supersequence Problem  

PubMed Central

The shortest common supersequence problem is a classical problem with many applications in different fields such as planning, Artificial Intelligence and especially in Bioinformatics. Due to its NP-hardness, we can not expect to efficiently solve this problem using conventional exact techniques. This paper presents a heuristic to tackle this problem based on the use at different levels of a probabilistic variant of a classical heuristic known as Beam Search. The proposed algorithm is empirically analysed and compared to current approaches in the literature. Experiments show that it provides better quality solutions in a reasonable time for medium and large instances of the problem. For very large instances, our heuristic also provides better solutions, but required execution times may increase considerably.

Gallardo, Jose E.

2012-01-01

258

Path Entanglement of Continuous-Variable Quantum Microwaves  

NASA Astrophysics Data System (ADS)

Path entanglement constitutes an essential resource in quantum information and communication protocols. Here, we demonstrate frequency-degenerate entanglement between continuous-variable quantum microwaves propagating along two spatially separated paths. We combine a squeezed and a vacuum state using a microwave beam splitter. Via correlation measurements, we detect and quantify the path entanglement contained in the beam splitter output state. Our experiments open the avenue to quantum teleportation, quantum communication, or quantum radar with continuous variables at microwave frequencies.

Menzel, E. P.; Di Candia, R.; Deppe, F.; Eder, P.; Zhong, L.; Ihmig, M.; Haeberlein, M.; Baust, A.; Hoffmann, E.; Ballester, D.; Inomata, K.; Yamamoto, T.; Nakamura, Y.; Solano, E.; Marx, A.; Gross, R.

2012-12-01

259

The SunPath  

NSDL National Science Digital Library

This site features an interactive applet that models the Sun's path from a geocentric view. It calculates and visualizes the position of the Sun based on latitude and time, and allows students to simulate the Sun's position and path for an hour, a day, a month or a year.

University, Australian N.

260

Visualizing Paths in Context  

Microsoft Academic Search

Data about movement through a space is increasingly becoming available for capture and analysis. In many applications, this data is captured or modeled as transitions between a small number of areas of interests, or a finite set of states, and these transitions constitute paths in the space. Similarities and differences between paths are of great importance to such analyses, but

Fabio Pellacini; Lori Lorigo; Geri Gay

2006-01-01

261

Agricultural robot path tracking based on predictable path  

Microsoft Academic Search

In order to realize the path tracking of agricultural robot in complex farmland environment and improve its speed and accuracy, a kind of agricultural robot path tracking method based predictable path was put forward in this paper. The definition of predictable path and fitting were presented, the positioning principles and methods were described in detail. The implementation method of path

Chi Gao; Yougang Su; Hui Ma

2010-01-01

262

Path-summation waveforms  

NASA Astrophysics Data System (ADS)

In this paper, we examine an efficient, practical method to calculate approximate, finite-frequency waveforms for the early signals from a point source in 3-D acoustic media with smoothly varying velocity and constant density. In analogy to the use of Feynman path integrals in quantum physics, we obtain an approximate waveform solution for the scalar wave equation by a Monte Carlo summation of elementary signals over a representative sample of all possible paths between a source and observation point. The elementary signal is formed from the convolution of the source time function with a time derivative of the Green's function for the homogeneous problem. For each path, this elementary signal is summed into a time series at a traveltime obtained from an integral of slowness along the path. The constructive and destructive interference of these signals produces the approximate waveform response for the range of traveltimes covered by the sampled paths. We justify the path-summation technique for a smooth medium using a heuristic construction involving the Helmholtz-Kirchhoff integral theorem. The technique can be applied to smooth, but strongly varying and complicated velocity structures. The approximate waveform includes geometrical spreading, focusing, defocusing and phase changes, but does not fully account for multiple scattering. We compare path-summation waveforms with the exact solution for a 3-D geometry involving a low-velocity spherical inclusion, and with finite-difference waveforms for a 2-D structure with realistic, complicated velocity variations. In contrast to geometrical-ray methods, the path-summation approach reproduces finite-frequency wave phenomena such as diffraction and does not exhibit singular behaviour. Relative to the finite-difference numerical method, the path-summation approach requires insignificant computer memory and, depending on the number of waveforms required, up to one to two orders of magnitude less computing time. The sampled paths and associated traveltimes produced by the path summation give a relation between the medium and the signal on the waveform that is not available with finite-difference and finite-element methods. Furthermore, the speed and accuracy of the path-summation method may be sufficient to allow 3-D waveform inversion using stochastic, non-linear, global search methods.

Lomax, Anthony

1999-09-01

263

The path to open-angle glaucoma gene discovery: endophenotypic status of intraocular pressure, cup-to-disc ratio, and central corneal thickness.  

PubMed

PURPOSE. Primary open-angle glaucoma (POAG) is a complex disease with a genetic architecture that can be simplified through the investigation of individual traits underlying disease risk. It has been well studied in twin models, and this study was undertaken to investigate the heritability of some of these key endophenotypes in extended pedigrees. METHODS. These data are derived from a large, multicenter study of extended, Caucasian POAG families from Australia and the United States. The study included 1181 people from 22 extended pedigrees. Variance components modeling was used to determine the heritabilities of maximum intraocular pressure (IOP), maximum vertical cup-to-disc ratio (VCDR), and mean central corneal thickness (CCT). Bivariate quantitative genetic analysis between these eye-related phenotypes and POAG itself was performed to determine whether any of these traits represent true endophenotypes. RESULTS. Heritability estimates for IOP, VCDR, and CCT (0.42, 0.66, and 0.72, respectively) were significant and show strong concordance with data in previous studies. Bivariate analysis revealed that both IOP (RhoG = 0.80; P = 9.6 x 10(-6)) and VCDR (RhoG = 0.76; P = 4.8 x 10(-10)) showed strong evidence of genetic correlation with POAG susceptibility. These two traits also correlated genetically with each other (RhoG = 0.45; P = 0.0012). Alternatively, CCT did not correlate genetically with risk of POAG. CONCLUSIONS. All the proposed POAG-related traits have genetic components. However, the significant genetic correlations observed between IOP, VCDR, and POAG itself suggest that they most likely represent true endophenotypes that could aid in the identification of genes underlying POAG susceptibility. CCT did not correlate genetically with disease and is unlikely to be a useful surrogate endophenotype for POAG. PMID:20237253

Charlesworth, Jac; Kramer, Patricia L; Dyer, Tom; Diego, Victor; Samples, John R; Craig, Jamie E; Mackey, David A; Hewitt, Alex W; Blangero, John; Wirtz, Mary K

2010-03-17

264

An attempt of microwave CT system which discriminates the transmission path by means of time domain measurement.  

PubMed

A microwave-based computed tomography system was developed based on a method that uses time domain measurement to determine the shortest path of propagation components between two antennas. The method calculates shortest path of propagation components by examining mixer output DC components, delivering similar precision as chirp-pulse microwave computed tomography. Because post-mixer signal processing need only concerns DC currents, the effects of overshoot characteristics of baseband filters and the like are removed, simplifying measurement. System circuit composition is also simplified, lowering system costs. This paper provides a theoretical framework for the method, an S-parameter verification of the theory, and an experimental verification using a basic hardware construction. Results showed a restored image from the measurement data, indicating the utility of the method for microwave imaging. PMID:22255201

Tamura, Mutsumi; Ogawa, Takahiro; Miyakawa, Michio

2011-01-01

265

Network performance and integrity enhancement with optical path layer technologies  

NASA Astrophysics Data System (ADS)

Path layer technologies will play a key role in the development of a powerful and failure resilient B-ISDN. So far, they have been based on electrical technologies. This paper highlights WDM/FDM techniques and demonstrates that optical paths can greatly enhance the path layer capability and, therefore, the network performance. It is also shown that effective network failure restoration can be achieved with optical paths. The applicability of the Wavelength Path (WP) technique to global area networks is revealed by comparing different optical path realization techniques. WP's are applied to the national backbone network example to evaluate the require number of wavelength, and to identify optical path concept: the Virtual Wavelength Path (VWP). In the VWP scheme, wavelengths are assigned on a link-by-link basis. In other words, the wavelength assigned to a wavelength path has only local significance. Significant benefits of the VWP such as the simplified path accommodation design within a transmission facility network and the reduced number of wavelengths needed, are elucidated. An optical cross-connect node architecture that enables the VWP's is also proposed. The architecture allows the VWP concept to be realized with commercially available optical technologies. The optical path layer concept proposed in this paper exploits and consolidate the layered transport network architecture and optical technologies, and will open up new opportunities for creating a B-ISDN that is bandwidth abundant and has a high degree of integrity.

Sato, Ken-Ichi; Okamoto, Satoru; Hadama, Hisaya

1994-01-01

266

Tortuous path chemical preconcentrator  

SciTech Connect

A non-planar, tortuous path chemical preconcentrator has a high internal surface area having a heatable sorptive coating that can be used to selectively collect and concentrate one or more chemical species of interest from a fluid stream that can be rapidly released as a concentrated plug into an analytical or microanalytical chain for separation and detection. The non-planar chemical preconcentrator comprises a sorptive support structure having a tortuous flow path. The tortuosity provides repeated twists, turns, and bends to the flow, thereby increasing the interfacial contact between sample fluid stream and the sorptive material. The tortuous path also provides more opportunities for desorption and readsorption of volatile species. Further, the thermal efficiency of the tortuous path chemical preconcentrator is comparable or superior to the prior non-planar chemical preconcentrator. Finally, the tortuosity can be varied in different directions to optimize flow rates during the adsorption and desorption phases of operation of the preconcentrator.

Manginell, Ronald P. (Albuquerque, NM); Lewis, Patrick R. (Albuquerque, NM); Adkins, Douglas R. (Albuquerque, NM); Wheeler, David R. (Albuquerque, NM); Simonson, Robert J. (Cedar Crest, NM)

2010-09-21

267

Follow the Paths  

NSDL National Science Digital Library

In this lesson, younger students will be introduced to the various orbital paths that are used for satellites. Using a globe and a satellite model or a large picture of Earth, the teacher will introduce three types of orbital paths (polar, elliptical, and geosynchronous). The students should be able to define 'satellite', define the three types of orbits, describe how satellites orbit the Earth, and understand how they are slowed down by drag from the atmosphere.

268

Path integrals and parastatistics  

NASA Astrophysics Data System (ADS)

The propagator and corresponding path integral for a system of identical particles obeying parastatistics are derived. It is found that the statistical weights of topological sectors of the path integral for parafermions and parabosons are simply related through multiplication by the parity of the permutation of the final positions of the particles. Appropriate generalizations of statistics are proposed obeying unitarity and factorizability (strong cluster decomposition). The realization of simple maximal occupancy (Gentile) statistics is shown to require ghost states.

Polychronakos, Alexios P.

1996-02-01

269

PathFinder Science  

NSDL National Science Digital Library

PathFinder Science contains research projects about water conservation, tardigrades, a winter bird survey, ozone, ultraviolet light and DNA, global warming, spot removal, lichens, stream monitoring, amphibian biomonitoring, and particulate monitoring. Free registration to the PathFinder Science Network offers the opportunity to be a part of the listserv, upload collaborative project data or publish research work. There are tools and tips to help students publish their research on the web.

270

NLTT 5306: the shortest period detached white dwarf+brown dwarf binary  

NASA Astrophysics Data System (ADS)

We have spectroscopically confirmed a brown dwarf mass companion to the hydrogen atmosphere white dwarf NLTT 5306. The white dwarf's atmospheric parameters were measured using the Sloan Digital Sky Survey and X-shooter spectroscopy as Teff = 7756 ± 35 K and log(g) = 7.68 ± 0.08, giving a mass for the primary of MWD = 0.44 ± 0.04 M? at a distance of 71 ± 4 pc with a cooling age of 710 ± 50 Myr. The existence of the brown dwarf secondary was confirmed through the near-infrared arm of the X-shooter data and a spectral type of dL4-dL7 was estimated using standard spectral indices. Combined radial velocity measurements from the Sloan Digital Sky Survey, X-shooter and the Hobby-Eberly Telescope's High Resolution Spectrograph of the white dwarf give a minimum mass of 56 ± 3 MJup for the secondary, confirming the substellar nature. The period of the binary was measured as 101.88 ± 0.02 min using both the radial velocity data and i'-band variability detected with the Isaac Newton Telescope. This variability indicates `day' side heating of the brown dwarf companion. We also observe H? emission in our higher resolution data in phase with the white dwarf radial velocity, indicating that this system is in a low level of accretion, most likely via a stellar wind. This system represents the shortest period white dwarf+brown dwarf binary and the secondary has survived a stage of common envelope evolution, much like its longer period counterpart, WD 0137-349. Both systems likely represent bona fide progenitors of cataclysmic variables with a low-mass white dwarf and a brown dwarf donor.

Steele, P. R.; Saglia, R. P.; Burleigh, M. R.; Marsh, T. R.; Gänsicke, B. T.; Lawrie, K.; Cappetta, M.; Girven, J.; Napiwotzki, R.

2013-03-01

271

Sampling diffusive transition paths  

SciTech Connect

We address the problem of sampling double-ended diffusive paths. The ensemble of paths is expressed using a symmetric version of the Onsager-Machlup formula, which only requires evaluation of the force field and which, upon direct time discretization, gives rise to a symmetric integrator that is accurate to second order. Efficiently sampling this ensemble requires avoiding the well-known stiffness problem associated with sampling infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with sampling the coarse features of long paths. The fine-features sampling stiffness is eliminated with the use of the fast sampling algorithm (FSA), and the coarse-feature sampling stiffness is avoided by introducing the sliding and sampling (S&S) algorithm. A key feature of the S&S algorithm is that it enables massively parallel computers to sample diffusive trajectories that are long in time. We use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature.

F. Miller III, Thomas; Predescu, Cristian

2006-10-12

272

VDSPT: A Sensor-Actor Coordination Protocol for Wireless Sensor and Actor Network Based on Voronoi Diagram and Shortest Path Tree  

Microsoft Academic Search

Wireless sensor and actor network refers to a group of sensors and actors, which gather information in detection area and perform appropriate actions upon the event area, respectively. Just as in wireless sensor network (WSN), one of the most important objectives of designing coordination protocols in WSAN is to decrease energy consumption and prolong network lifetime. This paper proposes a

Zhicheng Dai; Bingwen Wang; Zhi Li; An Yin

2009-01-01

273

Path efficiency of ant foraging trails in an artificial network.  

PubMed

In this paper we present an individual-based model describing the foraging behavior of ants moving in an artificial network of tunnels in which several interconnected paths can be used to reach a single food source. Ants lay a trail pheromone while moving in the network and this pheromone acts as a system of mass recruitment that attracts other ants in the network. The rules implemented in the model are based on measures of the decisions taken by ants at tunnel bifurcations during real experiments. The collective choice of the ants is estimated by measuring their probability to take a given path in the network. Overall, we found a good agreement between the results of the simulations and those of the experiments, showing that simple behavioral rules can lead ants to find the shortest paths in the network. The match between the experiments and the model, however, was better for nestbound than for outbound ants. A sensitivity study of the model suggests that the bias observed in the choice of the ants at asymmetrical bifurcations is a key behavior to reproduce the collective choice observed in the experiments. PMID:16199059

Vittori, Karla; Talbot, Grégoire; Gautrais, Jacques; Fourcassié, Vincent; Araújo, Aluizio F R; Theraulaz, Guy

2005-09-30

274

C-Testable One-Dimensional ILAs with Respect to Path Delay Faults: Theory and Applications  

Microsoft Academic Search

In this paper we give, for first time in the open literature, sufficient conditions so that a one-dimensional iterative-logic-array (ILA) is C-testable taking into account the path delay fault model. We give also a method for path selection so as all the selected paths can be tested by a constant number of test-vector pairs. The delay of all other paths

Th. Haniotakis; Dimitris Nikolos; Y. Tsiatouhas

1998-01-01

275

Variability in quasar broad absorption line outflows - III. What happens on the shortest time-scales?  

NASA Astrophysics Data System (ADS)

Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in C IV ?1549 BALs in our full multi-epoch sample, which covers time-scales from 0.02 to 8.7 yr in the quasar rest frame. Our sample contains up to 13 epochs of data per quasar, with an average of seven epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales ?2 months. This revealed variability down to the shortest time-scales we probe (8-10 d). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Specific results also depend on the emission and absorption geometries. We consider a range of geometries and use Keplerian rotational speeds to derive a general relationship between the variability times, crossing speeds and outflow locations. Typical variability times of the order of ˜1 yr indicate crossing speeds of a few thousand km s-1 and radial distances ˜1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 d require crossing speeds of 17 000-84 000 km s-1 and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission-line region.

Capellupo, D. M.; Hamann, F.; Shields, J. C.; Halpern, J. P.; Barlow, T. A.

2013-03-01

276

Following the Path  

ERIC Educational Resources Information Center

This article profiles Diane Stanley, an author and illustrator of children's books. Although she was studying to be a medical illustrator in graduate school, Stanley's path changed when she got married and had children. As she was raising her children, she became increasingly enamored of the colorful children's books she would check out of the…

Rodia, Becky

2004-01-01

277

Paths of Innovation  

Microsoft Academic Search

In 1903 the Wright brothers' airplane travelled a couple of hundred yards. Today fleets of streamlined jets transport millions of people each day to cities worldwide. Between discovery and application, between invention and widespread use, there is a world of innovation, of tinkering, improvement and adaptation. This is the world David Mowery and Nathan Rosenberg map out in Paths of

David C. Mowery; Nathan Rosenberg

278

Intrusion Path Analysis.  

National Technical Information Service (NTIS)

The design and implementation of an Intrusion Path Analysis (IPA) function came about as a result of the upgrades to the security systems at the Savannah River Site (SRS), near Aiken, South Carolina. The stated requirements for IPA were broad, leaving opp...

R. D. Hardwick

1989-01-01

279

(Intrusion Path Analysis)  

Microsoft Academic Search

The design and implementation of an Intrusion Path Analysis (IPA) function came about as a result of the upgrades to the security systems at the Savannah River Site (SRS), near Aiken, South Carolina. The stated requirements for IPA were broad, leaving opportunity for creative freedom during design and development. The essential elements were that it: be based on alarm and

Hardwick

1989-01-01

280

Paths to Remarriage  

Microsoft Academic Search

High divorce rates and the traditionally discrepant ages at death for husbands and wives indicate a need for a more complete understanding of the paths to remarriage in contemporary America. This study uses data from the U.S. Bureau of the Census' Current Population Survey to examine the extent and timing of remarriage, social factors associated with remarriage, and the impact

Graham B. Spanier; Paul C. Glick

1980-01-01

281

Path to the Profession  

ERIC Educational Resources Information Center

A growing number of institutions are being more deliberate about bringing in fundraisers who fit the culture of the development department and about assessing skills and providing training that fill specific needs. Development shops are paying more attention to cultivating their staffs, staying attuned to employees' needs and creating career paths…

Coleman, Toni

2012-01-01

282

Automatic sulcal line extraction on cortical surfaces using geodesic path density maps.  

PubMed

We present here a method that is designed to automatically extract sulcal lines on the mesh of any cortical surface. The method is based on the definition of a new function, the Geodesic Path Density Map (GPDM), within each sulcal basin (i.e. regions with a negative mean curvature). GPDM indicates at each vertex the likelihood that a shortest path between any two points of the basins boundary goes through that vertex. If the distance used to compute shortest path is anisotropic and constrained by a geometric information such as the depth, the GPDM indicates the likelihood that a vertex belongs to the sulcal line in the basin. An automatic GPDM adaptive thresholding procedure is proposed and sulcal lines are then defined. The process has been validated on a set of 25 subjects by comparing results to the manual segmentation from an expert and showed an average error below 2mm. It is also compared to our previous reference method in the context of inter-subject cortical surface registration and shows an significant improvement in performance. PMID:22521478

Le Troter, A; Auzias, G; Coulon, O

2012-04-14

283

Group selection management in conifer forests: relationships between opening size and tree growth  

Microsoft Academic Search

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared in 1996 at Blodgett Forest Re- search Station, California, and planted with seedlings of six native species. After 5 years of postharvest growth, heights were measured and analyzed according to species, opening size, and location within opening. The sequence of mean height from tallest to shortest, according

Robert A. York; Robert C. Heald; John J. Battles; Jennifer D. York

2004-01-01

284

Exact train pathing  

Microsoft Academic Search

Suppose we are given a schedule of train movements over a rail network into which a new train is to be included. The origin\\u000a and the destination are specified for the new train; it is required that a schedule (including the path) be determined for\\u000a it so as to minimize the time taken without affecting the schedules for the old

Viswanath Nagarajan; Abhiram G. Ranade

2008-01-01

285

Adaptive Fast Path Architecture  

Microsoft Academic Search

Adaptive Fast Path Architecture (AFPA) is a software architecture that dramatically improves the efficiency, and therefore the capacity, of Web and other network servers. The architecture includes a RAM-based cache that serves static content and a reverse proxy that can distribute requests for dynamic content to multiple servers. These two mechanisms are combined using a ?exible layer-7 (content-based) routing facility.

Elbert C. Hu; Philippe Joubert; Robert B. King; Jason D. Lavoie; John M. Tracey

2001-01-01

286

PATHS groundwater hydrologic model  

SciTech Connect

A preliminary evaluation capability for two-dimensional groundwater pollution problems was developed as part of the Transport Modeling Task for the Waste Isolation Safety Assessment Program (WISAP). Our approach was to use the data limitations as a guide in setting the level of modeling detail. PATHS Groundwater Hydrologic Model is the first level (simplest) idealized hybrid analytical/numerical model for two-dimensional, saturated groundwater flow and single component transport; homogeneous geology. This document consists of the description of the PATHS groundwater hydrologic model. The preliminary evaluation capability prepared for WISAP, including the enhancements that were made because of the authors' experience using the earlier capability is described. Appendixes A through D supplement the report as follows: complete derivations of the background equations are provided in Appendix A. Appendix B is a comprehensive set of instructions for users of PATHS. It is written for users who have little or no experience with computers. Appendix C is for the programmer. It contains information on how input parameters are passed between programs in the system. It also contains program listings and test case listing. Appendix D is a definition of terms.

Nelson, R.W.; Schur, J.A.

1980-04-01

287

Modeling DNA Dynamics by Path Integrals  

NASA Astrophysics Data System (ADS)

Complementary strands in DNA double helix show temporary fluctuational openings which are essential to biological functions such as transcription and replication of the genetic information. Such large amplitude fluctuations, known as the breathing of DNA, are generally localized and, microscopically, are due to the breaking of the hydrogen bonds linking the base pairs (bps). I apply imaginary time path integral techniques to a mesoscopic Hamiltonian which accounts for the helicoidal geometry of a short circular DNA molecule. The bps displacements with respect to the ground state are interpreted as time dependent paths whose amplitudes are consistent with the model potential for the hydrogen bonds. The portion of the paths configuration space contributing to the partition function is determined by selecting the ensemble of paths which fulfill the second law of thermodynamics. Computations of the thermodynamics in the denaturation range show the energetic advantage for the equilibrium helicoidal geometry peculiar of B-DNA. I discuss the interplay between twisting of the double helix and anharmonic stacking along the molecule backbone suggesting an interesting relation between intrinsic nonlinear character of the microscopic interactions and molecular topology.

Zoli, Marco

2013-02-01

288

Portage and Path Dependence*  

PubMed Central

We examine portage sites in the U.S. South, Mid-Atlantic, and Midwest, including those on the fall line, a geomorphological feature in the southeastern U.S. marking the final rapids on rivers before the ocean. Historically, waterborne transport of goods required portage around the falls at these points, while some falls provided water power during early industrialization. These factors attracted commerce and manufacturing. Although these original advantages have long since been made obsolete, we document the continuing importance of these portage sites over time. We interpret these results as path dependence and contrast explanations based on sunk costs interacting with decreasing versus increasing returns to scale.

Bleakley, Hoyt; Lin, Jeffrey

2012-01-01

289

Byrds Flight Path  

NSDL National Science Digital Library

The Ohio State Universitys Library web site notes As a navigational aviator, Byrd pioneered in the technology that would be the foundation for modern polar exploration and investigation. As a decorated and much celebrated hero, Byrd drew popular attention to areas of the world that became focal points of scientific investigation in numerous disciplines. More information about Admiral Richard E. Byrd can be found at (http:--www.lib.ohio-state.edu-arvweb-polar-byrd-byrd.htm). The next animation, #1001, shows Byrds plane as it follows the flight path presented in this animation.

Biddlecome, Tom; Snodgrass, Stuart; Newcombe, Marte; Jezek, Ken

1999-11-08

290

Semiclassical Ehrenfest paths  

NASA Astrophysics Data System (ADS)

Trajectories are a central concept in our understanding of classical phenomena and also in rationalizing quantum mechanical effects. In this work we provide a way to determine semiclassical paths, approximations to quantum averages in phase space, directly from classical trajectories. We avoid the need of intermediate steps, like particular solutions to the Schroedinger equation or numerical integration in phase space by considering the system to be initially in a coherent state and by assuming that its early dynamics is governed by the Heller semiclassical approximation. Our result is valid for short propagation times only, but gives non-trivial information on the quantum-classical transition.

Liberalquino, Rafael; Parisio, Fernando

2013-08-01

291

The Path of Pollution  

NSDL National Science Digital Library

This lesson plan has students follow the path of pollution from the Chernobyl nuclear accident. They will name and locate countries to which radiation traveled and describe how air pollution moves from one area to another. In addition they will compare the chronological sequence of radiation travel with geographic distribution. Provided are: essential elements, objective, focus, a list of materials, background information, procedure, and ideas for extension and evaluation. Links provide the history of the accident and the data required to complete the investigation.

292

The California PATH Database  

NSDL National Science Digital Library

The well known Berkeley Digital Library SunSite, discussed in the February 9, 1996 Scout Report, has recently added a new resource to its collection. The PATH database, maintained by the Harmer E. Davis Transportation Library at the University of California, is "the world's largest bibliographical database pertaining to Intelligent Transportation Systems (ITS)." It is searchable and browsable (Browse by ITS Thesaurus Term), and contains over 9,000 records and abstracts "including monographs, journal articles, conference papers, technical reports, theses and selected media coverage," dating back to the 1940s.

1997-01-01

293

A Comparison of Heuristic and Human Performance on Open Versions of the Traveling Salesperson Problem  

Microsoft Academic Search

We compared the performance of three heuristics with that of subjects on variants of a well-known combinatorial optimization task, the Traveling Salesperson Problem (TSP). The present task consisted of finding the shortest path through an array of points from one side of the array to the other. Like the standard TSP, the task is computationally intractable and, as with the

James N. MacGregor; Edward P. Chronicle; Thomas C. Ormerod

2006-01-01

294

Photodeactivation paths in norbornadiene.  

PubMed

The first high level ab initio quantum-chemical calculations of potential energy surfaces (PESs) for low-lying singlet excited states of norbornadiene in the gas phase are presented. The optimization of the stationary points (minima and conical intersections) and the recalculation of the energies were performed using the multireference configuration interaction with singles (MR-CIS) and the multiconfigurational second-order perturbation (CASPT2) methods, respectively. It was shown that the crossing between valence V2 and Rydberg R1 states close to the Franck-Condon (FC) point permits an easy population switch between these states. Also, a new deactivation path in which the doubly excited state with (?3)(2) configuration (DE) has a prominent role in photodeactivation from the R1 state due to the R1/DE and the DE/V1 conical intersections very close to the R1 and DE minima, respectively, was proposed. Subsequent deactivation from the V1 to the ground state goes through an Olivucci-Robb-type conical intersection that adopts a rhombic distorted geometry. The deactivation path has negligible barriers, thereby making ultrafast radiationless decay to the ground state possible. PMID:23553256

Antol, Ivana

2013-04-03

295

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

SciTech Connect

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, pathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, pathChirp does not require synchronous nor highly stable clocks at the sender and receiver. We test pathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using only a fraction of the number of probe bytes that current state-of-the-art techniques use.

Cottrell, Les

2003-04-30

296

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

Microsoft Academic Search

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing

Les

2003-01-01

297

Nonoptimal Component Placement, but Short Processing Paths, due to Long-Distance Projections in Neural Systems  

PubMed Central

It has been suggested that neural systems across several scales of organization show optimal component placement, in which any spatial rearrangement of the components would lead to an increase of total wiring. Using extensive connectivity datasets for diverse neural networks combined with spatial coordinates for network nodes, we applied an optimization algorithm to the network layouts, in order to search for wire-saving component rearrangements. We found that optimized component rearrangements could substantially reduce total wiring length in all tested neural networks. Specifically, total wiring among 95 primate (Macaque) cortical areas could be decreased by 32%, and wiring of neuronal networks in the nematode Caenorhabditis elegans could be reduced by 48% on the global level, and by 49% for neurons within frontal ganglia. Wiring length reductions were possible due to the existence of long-distance projections in neural networks. We explored the role of these projections by comparing the original networks with minimally rewired networks of the same size, which possessed only the shortest possible connections. In the minimally rewired networks, the number of processing steps along the shortest paths between components was significantly increased compared to the original networks. Additional benchmark comparisons also indicated that neural networks are more similar to network layouts that minimize the length of processing paths, rather than wiring length. These findings suggest that neural systems are not exclusively optimized for minimal global wiring, but for a variety of factors including the minimization of processing steps.

Kaiser, Marcus; Hilgetag, Claus C

2006-01-01

298

Path Integral Simulation of Positronium in Materials  

NASA Astrophysics Data System (ADS)

A path integral Monte Carlo technique is used to simulate positronium (Ps) in an insulator. The primitive propagator is used, with a pair of interacting chains representing the positron and electron. We calculate the energy and radial distribution function for Ps enclosed in a hard, spherical cavity, and the polarizability of the model Ps in the presence of an electrostatic field. The model can be extended to calculate the "pick-off" annihilation rate of the positron within the open volume of an insulating solid.

Bug, Amy L. R.; Sterne, P. A.; Larrimore, Lisa; McFarland, Robert

2000-03-01

299

The optimal selection of processing path based on a genetic algorithm for manufacturing processes in the machine industry  

NASA Astrophysics Data System (ADS)

The focus of this study is path selection for manufacturing processing, such as finding the shortest processing path, in an application of such a printed circuit board in the electronic industry. This paper models this kind of processing path optimization problem by application of a GA algorithm. First, the related problem of math modeling is discussed, such as coding methods, selection of fitness functions, and choice of genetic operators such as a selection operator, crossover operator, reverse operator, mutation operator and related parameters. All of these are used to build a solving model. Then related factor of genetic optimization algorithm such as initial generation, fitness evaluation, computing steps and so on was designed. The results of simulation and comparisons with practical application show that GA is feasible and valid.

Peng, Jinmin; Yan, He; Li, Taifu

2005-12-01

300

New Paths of Learning  

ERIC Educational Resources Information Center

While resources for the gifted are not abundant, many schools do offer classes, programs, services, and/or clubs that broaden student learning beyond the curriculum. What can educators do to expand the horizons of gifted children--to open their minds to new worlds of knowledge and understanding? Programs for gifted students, particularly those…

Smutny, Joan Franklin

2011-01-01

301

New Paths of Learning  

ERIC Educational Resources Information Center

|While resources for the gifted are not abundant, many schools do offer classes, programs, services, and/or clubs that broaden student learning beyond the curriculum. What can educators do to expand the horizons of gifted children--to open their minds to new worlds of knowledge and understanding? Programs for gifted students, particularly those…

Smutny, Joan Franklin

2011-01-01

302

Steered transition path sampling.  

PubMed

We introduce a path sampling method for obtaining statistical properties of an arbitrary stochastic dynamics. The method works by decomposing a trajectory in time, estimating the probability of satisfying a progress constraint, modifying the dynamics based on that probability, and then reweighting to calculate averages. Because the progress constraint can be formulated in terms of occurrences of events within time intervals, the method is particularly well suited for controlling the sampling of currents of dynamic events. We demonstrate the method for calculating transition probabilities in barrier crossing problems and survival probabilities in strongly diffusive systems with absorbing states, which are difficult to treat by shooting. We discuss the relation of the algorithm to other methods. PMID:22779577

Guttenberg, Nicholas; Dinner, Aaron R; Weare, Jonathan

2012-06-21

303

Steered transition path sampling  

NASA Astrophysics Data System (ADS)

We introduce a path sampling method for obtaining statistical properties of an arbitrary stochastic dynamics. The method works by decomposing a trajectory in time, estimating the probability of satisfying a progress constraint, modifying the dynamics based on that probability, and then reweighting to calculate averages. Because the progress constraint can be formulated in terms of occurrences of events within time intervals, the method is particularly well suited for controlling the sampling of currents of dynamic events. We demonstrate the method for calculating transition probabilities in barrier crossing problems and survival probabilities in strongly diffusive systems with absorbing states, which are difficult to treat by shooting. We discuss the relation of the algorithm to other methods.

Guttenberg, Nicholas; Dinner, Aaron R.; Weare, Jonathan

2012-06-01

304

Automatic 3D neuron tracing using all-path pruning  

PubMed Central

Motivation: Digital reconstruction, or tracing, of 3D neuron structures is critical toward reverse engineering the wiring and functions of a brain. However, despite a number of existing studies, this task is still challenging, especially when a 3D microscopic image has low signal-to-noise ratio (SNR) and fragmented neuron segments. Published work can handle these hard situations only by introducing global prior information, such as where a neurite segment starts and terminates. However, manual incorporation of such global information can be very time consuming. Thus, a completely automatic approach for these hard situations is highly desirable. Results: We have developed an automatic graph algorithm, called the all-path pruning (APP), to trace the 3D structure of a neuron. To avoid potential mis-tracing of some parts of a neuron, an APP first produces an initial over-reconstruction, by tracing the optimal geodesic shortest path from the seed location to every possible destination voxel/pixel location in the image. Since the initial reconstruction contains all the possible paths and thus could contain redundant structural components (SC), we simplify the entire reconstruction without compromising its connectedness by pruning the redundant structural elements, using a new maximal-covering minimal-redundant (MCMR) subgraph algorithm. We show that MCMR has a linear computational complexity and will converge. We examined the performance of our method using challenging 3D neuronal image datasets of model organisms (e.g. fruit fly). Availability: The software is available upon request. We plan to eventually release the software as a plugin of the V3D-Neuron package at http://penglab.janelia.org/proj/v3d. Contact: pengh@janelia.hhmi.org

Peng, Hanchuan; Long, Fuhui; Myers, Gene

2011-01-01

305

Stabilizing Intelligent Route Control: Randomized Path Monitoring, Randomized Path Switching or History-Aware Path Switching?  

Microsoft Academic Search

Multihoming Intelligent Route Control (IRC) plays a significant role in improving the performance of Internet accesses. However,\\u000a in a competitive environment, IRC systems may introduce persistent route oscillations, causing significant performance degradation.\\u000a In this study, three design alternatives to cope with this issue are investigated: Randomized Path Monitoring, Randomized\\u000a Path Switching and History-aware Path Switching. The simulation results show that

Alexandre Fonte; José Martins; Marilia Curado; Edmundo Monteiro

2008-01-01

306

Path concentration profile reconstruction of optical remote sensing measurements using polynomial curve fitting procedures  

Microsoft Academic Search

Open path Fourier transform infrared (OP-FTIR) spectroscopy is one of several optical remote sensing (ORS) techniques that can identify and quantify many air pollutants. These instruments provide path-integrated measurements along the scanning beam path. There is a growing interest in gaining spatial resolution from ORS through innovative multiple-beam configurations and mathematical algorithms. In this study, we explored the use of

Chang-fu Wu; Michael G. Yost; Ram A. Hashmonay; Ming-Yi Tsai

2003-01-01

307

Measurements of direct path and folded path optical scintillation path weightings  

NASA Astrophysics Data System (ADS)

A theoretical prediction by Dr. Avihu Ze'evi of the relative contribution to the optical scintillation by different points along the path was described by a weight function for direct and exact folded path spherical wave sources. In an effort to verify this prediction a turbulence chamber was built to allow a controlled turbulence source to be moved and measured at different path positions in conjunction with scintillation measurements. The experimental results follow Dr. Ze'evi's general pattern but both sources are less weighted at the detector end than predicted and the folded path is more heavily weighted at the target end than predicted.

Costantine, A. G.

1983-06-01

308

Path Diversity Aware Interdomain Routing  

Microsoft Academic Search

Abstract—As the Internet becomes the critical information infrastructure for both personal and business applications, fast and reliable routing protocols need to be designed to maintain the performance of those applications in the presence of failures. Today’s interdomain routing protocol, BGP, is known to be slow in reacting and recovering from network failures. Increasing path diversity by advertising multiple paths is

Feng Wang; Lixin Gao

2009-01-01

309

Fracture paths and ultrananocrystalline diamond  

Microsoft Academic Search

We use the simulated fracture of ultrananocrystalline diamond (UNCD) to illustrate how different fracture paths can result in different predictions of system properties. At zero temperature, the system is unable to explore the potential energy surface far from the fracture path being investigated. This can result in misleading predictions for the mechanical properties of UNCD. In non-zero temperature simulations, the

Jeffrey T. Paci; Lipeng Sun; Ted Belytschko; George C. Schatz

2005-01-01

310

Path Analysis: A Brief Introduction.  

ERIC Educational Resources Information Center

Path analysis is presented as a technique that can be used to test on a priori model based on a theoretical conceptualization involving a network of selected variables. This being an introductory source, no previous knowledge of path analysis is assumed, although some understanding of the fundamentals of multiple regression analysis might be…

Carducci, Bernardo J.

311

Obstacle avoidance and path planning  

Microsoft Academic Search

Outlines the state-of-the-art in obstacle avoidance and path planning for industrial robots that is practical on the current generation of computer hardware. Describes practical vehicle planners and planning for manipulators. Summarizes that obstacle avoidance and path planning are techniques with differing goals. Sonar is the standard method of obstacle avoidance systems which is largely limited by the reliability of the

Stephen Cameron

1994-01-01

312

Width change of a planar magma path: implication for the evolution and style of volcanic eruptions  

Microsoft Academic Search

The width change of a planar path filled with magma is analyzed, assuming that the process is controlled by laminar flow of an incompressible viscous magma between movable parallel walls of country rock. The analysis shows that the width of a planar path changes at a rate is proportional to the effective opening pressure, which is defined as the pressure

Yoshiaki Ida

1992-01-01

313

A New Hybrid Iterated Local Search for the Open Vehicle Routing Problem  

Microsoft Academic Search

Open vehicle routing problem (OVRP) aims to design a set of open vehicle routes with the least number of vehicles and the shortest total travel time, for serving a set of geographically distributed customers with known coordinates and demands. In this paper, a new hybrid iterated local search algorithm IVND is proposed for solving the OVRP. The IVND integrates a

Ping Chen; Youli Qu; Houkuan Huang; Xingye Dong

2008-01-01

314

Integrated Flight Path Planning System and Flight Control System for Unmanned Helicopters  

PubMed Central

This paper focuses on the design of an integrated navigation and guidance system for unmanned helicopters. The integrated navigation system comprises two systems: the Flight Path Planning System (FPPS) and the Flight Control System (FCS). The FPPS finds the shortest flight path by the A-Star (A*) algorithm in an adaptive manner for different flight conditions, and the FPPS can add a forbidden zone to stop the unmanned helicopter from crossing over into dangerous areas. In this paper, the FPPS computation time is reduced by the multi-resolution scheme, and the flight path quality is improved by the path smoothing methods. Meanwhile, the FCS includes the fuzzy inference systems (FISs) based on the fuzzy logic. By using expert knowledge and experience to train the FIS, the controller can operate the unmanned helicopter without dynamic models. The integrated system of the FPPS and the FCS is aimed at providing navigation and guidance to the mission destination and it is implemented by coupling the flight simulation software, X-Plane, and the computing software, MATLAB. Simulations are performed and shown in real time three-dimensional animations. Finally, the integrated system is demonstrated to work successfully in controlling the unmanned helicopter to operate in various terrains of a digital elevation model (DEM).

Jan, Shau Shiun; Lin, Yu Hsiang

2011-01-01

315

Integrated flight path planning system and flight control system for unmanned helicopters.  

PubMed

This paper focuses on the design of an integrated navigation and guidance system for unmanned helicopters. The integrated navigation system comprises two systems: the Flight Path Planning System (FPPS) and the Flight Control System (FCS). The FPPS finds the shortest flight path by the A-Star (A*) algorithm in an adaptive manner for different flight conditions, and the FPPS can add a forbidden zone to stop the unmanned helicopter from crossing over into dangerous areas. In this paper, the FPPS computation time is reduced by the multi-resolution scheme, and the flight path quality is improved by the path smoothing methods. Meanwhile, the FCS includes the fuzzy inference systems (FISs) based on the fuzzy logic. By using expert knowledge and experience to train the FIS, the controller can operate the unmanned helicopter without dynamic models. The integrated system of the FPPS and the FCS is aimed at providing navigation and guidance to the mission destination and it is implemented by coupling the flight simulation software, X-Plane, and the computing software, MATLAB. Simulations are performed and shown in real time three-dimensional animations. Finally, the integrated system is demonstrated to work successfully in controlling the unmanned helicopter to operate in various terrains of a digital elevation model (DEM). PMID:22164029

Jan, Shau Shiun; Lin, Yu Hsiang

2011-07-28

316

Initial Studies Toward Real-Time Transmission Path Rating  

SciTech Connect

Demand continues to increase while transmission line construction is being constrained by multiple factors— economic, environmental, and political. Effective and efficient utilization of transmission lines is thus of great importance in an open access environment. Large blocks of power are transferred from areas with inexpensive generation to heavy load demand areas or areas with high generation costs. This results in some transmission paths being loaded closer to their path ratings, which limits further power transfer between areas. Traditionally, rating of important paths was determined off line by assuming the worst-case study scenario; once determined, it could be used for years. With increasing uncertainty arising from rapid growth of renewable energy and smart technologies, path rating studies are needed in near-real time to account for the latest system status and support a reliable and economic power grid. This paper adopts a simplified procedure based on standards of the North American Electric Reliability Corporation (NERC) to determine total transfer capability (TTC) or transfer limit for the purpose of demonstrating the benefits and necessity of real-time path rating. Initial studies are conducted to compute TTC of a two-area test system and a 39-bus test system. Results indicate that path rating can be significantly affected by loading conditions, generator schedules, system topology and other factors.

Singh, Ruchi; Diao, Ruisheng; Cai, Niannian; Huang, Zhenyu; Tuck, Brian; Guo, Xinxin

2012-07-26

317

Triggered plasma opening switch  

Microsoft Academic Search

A triggerable opening switch for a very high voltage and current pulse includes a transmission line extending from a source to a load and having an intermediate switch section including a plasma for conducting electrons between transmission line conductors and a magnetic field for breaking the plasma conduction path and magnetically insulating the electrons when it is desired to open

Mendel

1986-01-01

318

Triggered plasma opening switch  

Microsoft Academic Search

A triggerable opening switch for a very high voltage and current pulse includes a transmission line extending from a source to a load and having an intermediate switch section including a plasma for conducting electrons between transmission line conductors and a magnetic field for breaking the plasma conduction path and magnetically insulating the electrons when it is desired to open

Mendel; Clifford W

1988-01-01

319

Triggered plasma opening switch  

DOEpatents

A triggerable opening switch for a very high voltage and current pulse includes a transmission line extending from a source to a load and having an intermediate switch section including a plasma for conducting electrons between transmission line conductors and a magnetic field for breaking the plasma conduction path and magnetically insulating the electrons when it is desired to open the switch.

Mendel, Clifford W. (Albuquerque, NM)

1988-01-01

320

An introduction to critical paths.  

PubMed

A critical path defines the optimal sequencing and timing of interventions by physicians, nurses, and other staff for a particular diagnosis or procedure. Critical paths are developed through collaborative efforts of physicians, nurses, pharmacists, and others to improve the quality and value of patient care. They are designed to minimize delays and resource utilization and to maximize quality of care. Critical paths have been shown to reduce variation in the care provided, facilitate expected outcomes, reduce delays, reduce length of stay, and improve cost-effectiveness. The approach and goals of critical paths are consistent with those of total quality management (TQM) and can be an important part of an organization's TQM process. PMID:15739581

Coffey, Richard J; Richards, Janet S; Remmert, Carl S; LeRoy, Sarah S; Schoville, Rhonda R; Baldwin, Phyllis J

321

Squeezed States and Path Integrals.  

National Technical Information Service (NTIS)

The continuous-time regularization scheme for defining phase-space path integrals is briefly reviewed as a method to define a quantization procedure that is completely covariant under all smooth canonical coordinate transformations. As an illustration of ...

I. Daubechies J. R. Klauder

1992-01-01

322

Real Time Path Integral Methods  

Microsoft Academic Search

An efficient methodology has been developed for simulating the long-time dynamics of quantum dissipative processes modeled in terms of a system coupled to a multidimensional harmonic bath. The starting point is expression of the path integral in terms of a quasi-adiabatic propagator which allows large time increments. The resulting quasi-adiabatic propagator path integral is evaluated on a system-specific discrete variable

Nancy Makri

1998-01-01

323

The Shortest Period sdB Plus White Dwarf Binary CD-30 11223 (GALEX J1411-3053)  

NASA Astrophysics Data System (ADS)

We report on the discovery of the shortest period binary comprising a hot subdwarf star (CD-30 11223, GALEX J1411-3053) and a massive unseen companion. Photometric data from the All Sky Automated Survey show ellipsoidal variations of the hot subdwarf primary and spectroscopic series revealed an orbital period of 70.5 minutes. The large velocity amplitude suggests the presence of a massive white dwarf in the system (M 2/M ? >~ 0.77) assuming a canonical mass for the hot subdwarf (0.48 M ?), although a white dwarf mass as low as 0.75 M ? is allowable by postulating a subdwarf mass as low as 0.44 M ?. The amplitude of ellipsoidal variations and a high rotation velocity imposed a high-inclination to the system (i >~ 68°) and, possibly, observable secondary transits (i >~ 74°). At the lowest permissible inclination and assuming a subdwarf mass of ~0.48 M ?, the total mass of the system reaches the Chandrasekhar mass limit at 1.35 M ? and would exceed it for a subdwarf mass above 0.48 M ?. The system should be considered, like its sibling KPD 1930+2752, a candidate progenitor for a Type Ia supernova. The system should become semi-detached and initiate mass transfer within ?30 Myr. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program IDs 83.D-0540, 85.D-0866, and 089.D-0864.

Vennes, S.; Kawka, A.; O'Toole, S. J.; Németh, P.; Burton, D.

2012-11-01

324

The difference of brain functional connectivity between eyes-closed and eyes-open using graph theoretical analysis.  

PubMed

To study the differences in functional brain networks between eyes-closed (EC) and eyes-open (EO) at resting state, electroencephalographic (EEG) activity was recorded in 21 normal adults during EC and EO states. The synchronization likelihood (SL) was applied to measure correlations between all pairwise EEG channels, and then the SL matrices were converted to graphs by thresholding. Graphs were measured by topological parameters in theta (4-7?Hz), alpha (8-13?Hz), and beta (14-30?Hz) bands. By changing from EC to EO states, mean cluster coefficients decreased in both theta and alpha bands, but mean shortest path lengths became shorter only in the alpha band. In addition, local efficiencies decreased in both theta and alpha bands, while global efficiencies in the alpha band increased inversely. Opening the eyes decreased both nodes and connections in frontal area in the theta band, and also decreased those in bilateral posterior areas in the alpha band. These results suggested that a combination of the SL and graph theory methods may be a useful tool for distinguishing states of EC and EO. The differences in functional connectivity between EC and EO states may reflect the difference of information communication in human brain. PMID:23690886

Tan, Bo; Kong, Xianxian; Yang, Ping; Jin, Zhenlan; Li, Ling

2013-04-17

325

Heuristically optimal path scanning for high-speed multiphoton circuit imaging  

PubMed Central

Population dynamics of patterned neuronal firing are fundamental to information processing in the brain. Multiphoton microscopy in combination with calcium indicator dyes allows circuit dynamics to be imaged with single-neuron resolution. However, the temporal resolution of fluorescent measures is constrained by the imaging frequency imposed by standard raster scanning techniques. As a result, traditional raster scans limit the ability to detect the relative timing of action potentials in the imaged neuronal population. To maximize the speed of fluorescence measures from large populations of neurons using a standard multiphoton laser scanning microscope (MPLSM) setup, we have developed heuristically optimal path scanning (HOPS). HOPS optimizes the laser travel path length, and thus the temporal resolution of neuronal fluorescent measures, using standard galvanometer scan mirrors. Minimizing the scan path alone is insufficient for prolonged high-speed imaging of neuronal populations. Path stability and the signal-to-noise ratio become increasingly important factors as scan rates increase. HOPS addresses this by characterizing the scan mirror galvanometers to achieve prolonged path stability. In addition, the neuronal dwell time is optimized to sharpen the detection of action potentials while maximizing scan rate. The combination of shortest path calculation and minimization of mirror positioning time allows us to optically monitor a population of neurons in a field of view at high rates with single-spike resolution, ?125 Hz for 50 neurons and ?8.5 Hz for 1,000 neurons. Our approach introduces an accessible method for rapid imaging of large neuronal populations using traditional MPLSMs, facilitating new insights into neuronal circuit dynamics.

Sadovsky, Alexander J.; Kruskal, Peter B.; Kimmel, Joseph M.; Ostmeyer, Jared; Neubauer, Florian B.

2011-01-01

326

Underwater path planing using fast marching algorithms  

Microsoft Academic Search

In this paper, new tools for obstacle avoidance and path planning for underwater vehicles are presented. The authors' technique, based on a level set formulation of the path planning problem, extracts optimal paths from complex and continuous environments in a complete and consistent manner. Fast marching algorithm is known to be efficient for finding cost optimal path in mobile robotics

Clément Pêtrès; Yan Pailhast; Yvan Petilloti; Dave Lanes

2005-01-01

327

Paths, Trees and Cycles in Tournaments  

Microsoft Academic Search

We survey results on paths, trees and cycles in tournaments. The main subjects are hamiltonian paths and cycles, vertex and arc disjoint paths with prescribed endvertices, arc-pancyclicity, oriented paths, trees and cycles in tour- naments. Several unsolved problems are included.

Jørgen Bang-Jensen; Gregory Gutin

328

THE SHORTEST PERIOD sdB PLUS WHITE DWARF BINARY CD-30 11223 (GALEX J1411-3053)  

SciTech Connect

We report on the discovery of the shortest period binary comprising a hot subdwarf star (CD-30 11223, GALEX J1411-3053) and a massive unseen companion. Photometric data from the All Sky Automated Survey show ellipsoidal variations of the hot subdwarf primary and spectroscopic series revealed an orbital period of 70.5 minutes. The large velocity amplitude suggests the presence of a massive white dwarf in the system (M{sub 2}/M{sub Sun} {approx}> 0.77) assuming a canonical mass for the hot subdwarf (0.48 M{sub Sun }), although a white dwarf mass as low as 0.75 M{sub Sun} is allowable by postulating a subdwarf mass as low as 0.44 M{sub Sun }. The amplitude of ellipsoidal variations and a high rotation velocity imposed a high-inclination to the system (i {approx}> 68 Degree-Sign ) and, possibly, observable secondary transits (i {approx}> 74 Degree-Sign ). At the lowest permissible inclination and assuming a subdwarf mass of {approx}0.48 M{sub Sun }, the total mass of the system reaches the Chandrasekhar mass limit at 1.35 M{sub Sun} and would exceed it for a subdwarf mass above 0.48 M{sub Sun }. The system should be considered, like its sibling KPD 1930+2752, a candidate progenitor for a Type Ia supernova. The system should become semi-detached and initiate mass transfer within Almost-Equal-To 30 Myr.

Vennes, S.; Kawka, A.; Nemeth, P. [Astronomicky ustav, Akademie ved Ceske republiky, Fricova 298, CZ-251 65 Ondrejov (Czech Republic); O'Toole, S. J. [Australian Astronomical Observatory, P.O. Box 915, 1670 North Ryde NSW (Australia); Burton, D. [Faculty of Sciences, University of Southern Queensland, Toowoomba, QLD 4350 (Australia)

2012-11-01

329

On the general false path problem in timing analysis  

Microsoft Academic Search

The false path problem is often referred to as the problem of detecting the longest sensitizable path (A path which is not a false path is a sensitizable path). The term “false path” is not clearly defined. In this paper, we first give a clear and precise definition of a false path. Then the general false path problem is formulated.

David Hung-Chang Du; S. H. Yen; Subbarao Ghanta

1989-01-01

330

Hierarchical Encoded Path Views for Path Query Processing: An Optimal Model and Its Performance Evaluation  

Microsoft Academic Search

Efficient path computation is essential for applications such as intelligent transportation systems (ITS) and network routing. In ITS navigation systems, many path requests can be submitted over the same, typically huge, transportation network within a small time window. While path precomputation (path view) would provide an efficient path query response, it raises three problems which must be addressed: 1) precomputed

Ning Jing; Yun-wu Huang; Elke A. Rundensteiner

1998-01-01

331

In-situ Measurements of Tropospheric Hydroxyl Radicals by Folded Long-Path Laser Absorption During the Field Campaign POPCORN  

Microsoft Academic Search

Absolutely calibrated in-situ measurements of tropospheric hydroxyl radicals, formaldehyde, sulfur dioxide, and naphthalene (C10H8) were performed by long-path laser absorption spectroscopy during the field campaign POPCORN. The absorption light path was folded into an open optical multiple reflection cell with a mirror separation of 38.5 m. Using a light path length of 1848 m and an integration time of 200

Uwe Brandenburger; Theo Brauers; Hans-Peter Dorn; Martin Hausmann; Dieter H. Ehhalt

1998-01-01

332

Career Paths of Academic Deans.  

ERIC Educational Resources Information Center

|This paper examines various career paths leading to deanship and considers the implications of the findings for women and minorities who aspire to this position. The paper is part of a larger study of academic deanship conducted by the Center for Academic Leadership at Washington State University between October 1996 and January 1997. Data for…

Wolverton, Mimi; Gonzales, Mary Jo

333

Employer Resource Manual. Project Path.  

ERIC Educational Resources Information Center

|Project Path at Illinois' College of DuPage was established to provide pre-employment training and career counseling for disabled students. To encourage the integration of qualified individuals with disabilities into the workplace, the project compiled this resource manual for area businesses, providing tips for interacting with disabled people…

Kane, Karen R.; Del George, Eve

334

Complexity of Path Forming Games.  

National Technical Information Service (NTIS)

For a number of two player games where players alternately choose the next vertex of a simple or elementary path in a graph, the authors considers the problem to determine whether for a given game instance there is a winning strategy for the first player....

H. L. Bodlaender

1989-01-01

335

Alternative Nuclear Paths To 2050  

Microsoft Academic Search

he circumstances surrounding nuclear power worldwide and the importance that may be given to issues affecting its future development point toward very different alternative paths over the next 50 years. Economic deregulation, lack of competitiveness in some countries, negative public perception and concerns about waste issues suggest that nuclear power might decrease progressively with a potential phase-out of the technology

Ivan Vera; Evelyne Bertel; Geoffrey Stevens

336

Thinking on the Write Path  

ERIC Educational Resources Information Center

The present paper underscores the importance of the cognitive orientation of English as a Foreign Language (EFL) students in their success in writing courses. A few suggestions are made as to how EFL teachers can put their students on the right cognitive path in their writings.

Salmani-Nodoushan, Mohammad Ali

2007-01-01

337

Beam wander experiments: terrestrial path  

Microsoft Academic Search

We report on a set of measurements made in December 2005 by researchers from the University of Central Florida, SPAWAR's Innovative Science and Technology Experiment Facility (ISTEF), Harris Corporation, NASA Kennedy Space Center, and Northrop Grumman. The experiments were conducted on the Shuttle Landing Facility (SLF) at Kennedy Space Center (KSC) over terrestrial paths of 1, 2, and 5 km.

R. L. Phillips; L. C. Andrews; J. Stryjewski; B. Griffis; M. Borbath; D. Galus; G. Burdge; K. Green; C. Kim; D. Stack; C. Harkrider; D. Wayne; D. Hand; J. Kiriazes

2006-01-01

338

Perceived Shrinkage of Motion Paths  

ERIC Educational Resources Information Center

|We show that human observers strongly underestimate a linear or circular trajectory that a luminous spot follows in the dark. At slow speeds, observers are relatively accurate, but, as the speed increases, the size of the path is progressively underestimated, by up to 35%. The underestimation imposes little memory load and does not require…

Sinico, Michele; Parovel, Giulia; Casco, Clara; Anstis, Stuart

2009-01-01

339

The path to adaptive microsystems  

Microsoft Academic Search

Scaling trends in microsystems are discussed frequently in the technical community, providing a short-term perspective on the future of integrated microsystems. This paper looks beyond the leading edge of technological development, focusing on new microsystem design paradigms that move far beyond today's systems based on static components. We introduce the concept of Adaptive Microsystems and outline a path to realizing

John C. Zolper; Michael J. Biercuk

2006-01-01

340

Time optimal paths for high speed maneuvering  

SciTech Connect

Recent theoretical results have completely solved the problem of determining the minimum length path for a vehicle with a minimum turning radius moving from an initial configuration to a final configuration. Time optimal paths for a constant speed vehicle are a subset of the minimum length paths. This paper uses the Pontryagin maximum principle to find time optimal paths for a constant speed vehicle. The time optimal paths consist of sequences of axes of circles and straight lines. The maximum principle introduces concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature of the time optimal paths. We explore the properties of the optimal paths and present some experimental results for a mobile robot following an optimal path.

Reister, D.B.; Lenhart, S.M.

1993-01-01

341

NASA: a path dependent organization  

Microsoft Academic Search

Mission agencies like NASA are complex systems, connecting people with science and technology to accomplish the desired tasks. Path dependence can help explain why NASA and other mission agencies often sacrifice long-term capabilities for short-term survival. The National Aeronautics and Space Act of 1958, followed by President Kennedy’s challenge, catapulted NASA to the moon, encouraged human exploration, and sped up

David Bruggeman

2002-01-01

342

Accelerating cleanup: Paths to closure  

SciTech Connect

This document was previously referred to as the Draft 2006 Plan. As part of the DOE`s national strategy, the Richland Operations Office`s Paths to Closure summarizes an integrated path forward for environmental cleanup at the Hanford Site. The Hanford Site underwent a concerted effort between 1994 and 1996 to accelerate the cleanup of the Site. These efforts are reflected in the current Site Baseline. This document describes the current Site Baseline and suggests strategies for further improvements in scope, schedule and cost. The Environmental Management program decided to change the name of the draft strategy and the document describing it in response to a series of stakeholder concerns, including the practicality of achieving widespread cleanup by 2006. Also, EM was concerned that calling the document a plan could be misconstrued to be a proposal by DOE or a decision-making document. The change in name, however, does not diminish the 2006 vision. To that end, Paths to Closure retains a focus on 2006, which serves as a point in time around which objectives and goals are established.

Edwards, C.

1998-06-30

343

Path integral on star graph  

NASA Astrophysics Data System (ADS)

In this paper we study path integral for a single spinless particle on a star graph with N edges, whose vertex is known to be described by U(N) family of boundary conditions. After carefully studying the free particle case, both at the critical and off-critical levels, we propose a new path integral formulation that correctly captures all the scale-invariant subfamily of boundary conditions realized at fixed points of boundary renormalization group flow. Our proposal is based on the folding trick, which maps a scalar-valued wave function on star graph to an N-component vector-valued wave function on half-line. All the parameters of scale-invariant subfamily of boundary conditions are encoded into the momentum independent weight factors, which appear to be associated with the two distinct path classes on half-line that form the cyclic group Z2. We show that, when bulk interactions are edge-independent, these weight factors are generally given by an N-dimensional unitary representation of Z2. Generalization to momentum dependent weight factors and applications to worldline formalism are briefly discussed.

Ohya, Satoshi

2012-06-01

344

Multiple Paths to Encephalization and Technical Civilizations  

NASA Astrophysics Data System (ADS)

We propose consideration of at least two possible evolutionary paths for the emergence of intelligent life with the potential for technical civilization. The first is the path via encephalization of homeothermic animals; the second is the path to swarm intelligence of so-called superorganisms, in particular the social insects. The path to each appears to be facilitated by environmental change: homeothermic animals by decreased climatic temperature and for swarm intelligence by increased oxygen levels.

Schwartzman, David; Middendorf, George

2011-12-01

345

Lateral Path Controller Design for Autonomous Airship  

Microsoft Academic Search

According to the path control problem for unmanned autonomous airship, the lateral path mathematic model was introduced based on the scheme of control system and a kind of lateral path design method of autonomous airship is proposed based on fuzzy logic and adaptive sliding mode control (ASMC). The movement model and dynamic model of autonomous airship is derived from considering

Guo Jian-guo; Zhou Jun

2010-01-01

346

Quantifying the Causes of Path Inflation  

Microsoft Academic Search

Researchers have shown that the Internet exhibits path inflation - end-to-end paths can be significantly longer than necessary. We present a trace-driven study of 65 ISPs that characterizes the root causes of path inflation, namely topology and routing policy choices within an ISP, between pairs of ISPs, and across the global Inter- net. To do so, we develop and validate

Neil Spring; Ratul Mahajan; Thomas Anderson

2003-01-01

347

Chip layout optimization using critical path weighting  

Microsoft Academic Search

A chip layout procedure for optimizing the performance of critical timing paths in a synchronous digital circuit is presented. The procedure uses the path analysis data produced by a static timing analysis program to generate weights for critical nets on clock and data paths. These weights are then used to bias automatic placement and routing in the layout program. This

A. E. Dunlop; V. D. Agrawal; D. N. Deutsch; M. F. Jukl; P. Kozak; M. Wiesel

1984-01-01

348

Chip layout optimization using critical path weighting  

Microsoft Academic Search

A chip layout procedure for optimizing the performance of critical timing paths in a synchronous digital circuit is presented. The procedure uses the path analysis data produced by a static timing analysis program to generate weights for critical nets on clock and data paths. These weights are then used to bias automatic placement and routing in the layout program. This

A. E. Dunlop; V. D. Agrawal; D. N. Deutsch; M. F. Jukl; P. Kazak

1988-01-01

349

Multilinear decomposition of human walking paths  

Microsoft Academic Search

In a previous work, the authors have shown how the Principal Components Analysis (PCA) of a set of human walking paths provides sufficient information to derive a linear human-like path generator based on examples. The present work aims to provide an analysis of human walking paths from the perspective of multilinear algebra, using the n-mode Singular Value Decomposition (SVD). This

Christian A. Ramirez; M. Castela?n; G. Arechavaleta

2010-01-01

350

Randomized path coloring on binary trees  

Microsoft Academic Search

Motivated by the problem of WDM routing in all-optical networks, we study the following NP-hard problem. We are given a directed binary tree T and a set R of directed paths on T. We wish to assign colors to paths of R, in such way that no two paths that share a directed arc of T are assigned the same

Vincenzo Auletta; Ioannis Caragiannis; Christos Kaklamanis; Pino Persiano

2002-01-01

351

Removing False Paths from Combinational Modules 1  

Microsoft Academic Search

The existence of false paths complicates the task of accurate tim- ing analysis significantly. A technique to remove false paths from a combinational circuit without degrading its performance h as a prac- tical value since topological timing analysis is then good e nough to estimate the performance of false-path-free circuits accu rately. One can think of the KMS algorithm (1)

Yuji Kukimoto; Robert K. Brayton

352

Critical Path-Based Thread Placement for NUMA Systems  

SciTech Connect

Multicore multiprocessors use a Non Uniform Memory Architecture (NUMA) to improve their scalability. However, NUMA introduces performance penalties due to remote memory accesses. Without efficiently managing data layout and thread mapping to cores, scientific applications, even if they are optimized for NUMA, may suffer performance loss. In this paper, we present algorithms and a runtime system that optimize the execution of OpenMP applications on NUMA architectures. By collecting information from hardware counters, the runtime system directs thread placement and reduces performance penalties by minimizing the critical path of OpenMP parallel regions. The runtime system uses a scalable algorithm that derives placement decisions with negligible overhead. We evaluate our algorithms and runtime system with four NPB applications implemented in OpenMP. On average the algorithms achieve between 8.13% and 25.68% performance improvement compared to the default Linux thread placement scheme. The algorithms miss the optimal thread placement in only 8.9% of the cases.

Su, C Y; Li, D; Nikolopoulos, D S; Grove, M; Cameron, K; de Supinski, B R

2011-11-01

353

Hypertext Paths and the World-Wide Web: Experiences with Walden's Paths  

Microsoft Academic Search

Walden's Paths applies the concept of hypertextual paths to the World-Wide Web. Walden's Paths is being developed for use in the K-12 school environment. The heterogene- ity of the Web coupled with the desirability of supporting the teacher-student relationship make this an interesting and challenging project. We describe the Walden's Paths imple- mentation, discuss ...

Richard Furuta; Frank M. Shipman III; Catherine C. Marshall; Donald Brenner; Hao-wei Hsieh

1997-01-01

354

Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism  

Microsoft Academic Search

Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering (TE) Label Switched Paths (LSPs) may be computed by Path Computation Elements (PCEs). Where the TE LSP crosses multiple domains, such as Autonomous Systems (ASes), the path may be computed by multiple PCEs that cooperate, with each responsible for computing a segment of the path. However, in some cases (e.g.,

A. Farrel

355

Diffusion Path Theorems for Ternary Diffusion Couples  

NASA Astrophysics Data System (ADS)

A review is given of 17 theorems concerning diffusion paths in ternary diffusion couples published by Kirkaldy and Brown in 1963. An additional 11 theorems are given herein that were taken from work published on diffusion paths after that time. The new theorems are concerned primarily with diffusion paths that result from crossing multiple-phase regions in an interdiffusion zone. The theorems describe a method for classifying microstructural boundaries between the regions and a catalog of diffusion path features that are unique to each type of boundary. In addition, a proposal is given for how to plot diffusion paths in quaternary and higher order systems.

Morral, John E.

2012-10-01

356

Longest Path Problems on Ptolemaic Graphs  

NASA Astrophysics Data System (ADS)

Longest path problem is a problem for finding a longest path in a given graph. While the graph classes in which the Hamiltonian path problem can be solved efficiently are widely investigated, there are few known graph classes such that the longest path problem can be solved efficiently. Polynomial time algorithms for finding a longest cycle and a longest path in a Ptolemaic graph are proposed. Ptolemaic graphs are the graphs that satisfy the Ptolemy inequality, and they are the intersection of chordal graphs and distance-hereditary graphs. The algorithms use the dynamic programming technique on a laminar structure of cliques, which is a recent characterization of Ptolemaic graphs.

Takahara, Yoshihiro; Teramoto, Sachio; Uehara, Ryuhei

357

Attention trees and semantic paths  

NASA Astrophysics Data System (ADS)

In the last few decades several techniques for image content extraction, often based on segmentation, have been proposed. It has been suggested that under the assumption of very general image content, segmentation becomes unstable and classification becomes unreliable. According to recent psychological theories, certain image regions attract the attention of human observers more than others and, generally, the image main meaning appears concentrated in those regions. Initially, regions attracting our attention are perceived as a whole and hypotheses on their content are formulated; successively the components of those regions are carefully analyzed and a more precise interpretation is reached. It is interesting to observe that an image decomposition process performed according to these psychological visual attention theories might present advantages with respect to a traditional segmentation approach. In this paper we propose an automatic procedure generating image decomposition based on the detection of visual attention regions. A new clustering algorithm taking advantage of the Delaunay- Voronoi diagrams for achieving the decomposition target is proposed. By applying that algorithm recursively, starting from the whole image, a transformation of the image into a tree of related meaningful regions is obtained (Attention Tree). Successively, a semantic interpretation of the leaf nodes is carried out by using a structure of Neural Networks (Neural Tree) assisted by a knowledge base (Ontology Net). Starting from leaf nodes, paths toward the root node across the Attention Tree are attempted. The task of the path consists in relating the semantics of each child-parent node pair and, consequently, in merging the corresponding image regions. The relationship detected in this way between two tree nodes generates, as a result, the extension of the interpreted image area through each step of the path. The construction of several Attention Trees has been performed and partial results will be shown.

Giusti, Christian; Pieroni, Goffredo G.; Pieroni, Laura

2007-03-01

358

Evaluation of guidewire path reproducibility  

PubMed Central

The number of minimally invasive vascular interventions is increasing. In these interventions, a variety of devices are directed to and placed at the site of intervention. The device used in almost all of these interventions is the guidewire, acting as a monorail for all devices which are delivered to the intervention site. However, even with the guidewire in place, clinicians still experience difficulties during the interventions. As a first step toward understanding these difficulties and facilitating guidewire and device guidance, we have investigated the reproducibility of the final paths of the guidewire in vessel phantom models on different factors: user, materials and geometry. Three vessel phantoms (vessel diameters ?4 mm) were constructed having tortuousity similar to the internal carotid artery from silicon tubing and encased in Sylgard elastomer. Several trained users repeatedly passed two guidewires of different flexibility through the phantoms under pulsatile flow conditions. After the guidewire had been placed, rotational c-arm image sequences were acquired (9 in. II mode, 0.185 mm pixel size), and the phantom and guidewire were reconstructed (5123, 0.288 mm voxel size). The reconstructed volumes were aligned. The centerlines of the guidewire and the phantom vessel were then determined using region-growing techniques. Guidewire paths appear similar across users but not across materials. The average root mean square difference of the repeated placement was 0.17±0.02 mm (plastic-coated guidewire), 0.73±0.55 mm (steel guidewire) and 1.15±0.65 mm (steel versus plastic-coated). For a given guidewire, these results indicate that the guidewire path is relatively reproducible in shape and position.

Schafer, Sebastian; Hoffmann, Kenneth R.; Noel, Peter B.; Ionita, Ciprian N.; Dmochowski, Jacek

2008-01-01

359

Evaluation of guidewire path reproducibility.  

PubMed

The number of minimally invasive vascular interventions is increasing. In these interventions, a variety of devices are directed to and placed at the site of intervention. The device used in almost all of these interventions is the guidewire, acting as a monorail for all devices which are delivered to the intervention site. However, even with the guidewire in place, clinicians still experience difficulties during the interventions. As a first step toward understanding these difficulties and facilitating guidewire and device guidance, we have investigated the reproducibility of the final paths of the guidewire in vessel phantom models on different factors: user, materials and geometry. Three vessel phantoms (vessel diameters approximately 4 mm) were constructed having tortuousity similar to the internal carotid artery from silicon tubing and encased in Sylgard elastomer. Several trained users repeatedly passed two guidewires of different flexibility through the phantoms under pulsatile flow conditions. After the guidewire had been placed, rotational c-arm image sequences were acquired (9 in. II mode, 0.185 mm pixel size), and the phantom and guidewire were reconstructed (512(3), 0.288 mm voxel size). The reconstructed volumes were aligned. The centerlines of the guidewire and the phantom vessel were then determined using region-growing techniques. Guidewire paths appear similar across users but not across materials. The average root mean square difference of the repeated placement was 0.17 +/- 0.02 mm (plastic-coated guidewire), 0.73 +/- 0.55 mm (steel guidewire) and 1.15 +/- 0.65 mm (steel versus plastic-coated). For a given guidewire, these results indicate that the guidewire path is relatively reproducible in shape and position. PMID:18561663

Schafer, Sebastian; Hoffmann, Kenneth R; Noël, Peter B; Ionita, Ciprian N; Dmochowski, Jacek

2008-05-01

360

[Botulinum toxin: the misguided path].  

PubMed

Botulinum toxin is widely used and has become a popular mass phenomenon in aesthetic medicine. Considerable scientific data concerning the biopsychosocial impact of botulinum toxin use have become available. The bidirectional interaction of mimic and emotion, described as the facial feedback hypothesis, is particularly influenced, as is mimicry. Furthermore, botulinum toxin can cause dysfunction of face harmony including false laughing or the "frozen face". As a result, complex psychosocial disturbances can occur and may affect social interaction and cause flattening of affect. Thus one must ask whether in the future botulinum toxin will continue to be employed in aesthetic dermatology or perhaps be regarded as a misguided path. PMID:23636411

Harth, W

2013-06-01

361

Path integration: effect of curved path complexity and sensory system on blindfolded walking.  

PubMed

Path integration refers to the ability to integrate continuous information of the direction and distance traveled by the system relative to the origin. Previous studies have investigated path integration through blindfolded walking along simple paths such as straight line and triangles. However, limited knowledge exists regarding the role of path complexity in path integration. Moreover, little is known about how information from different sensory input systems (like vision and proprioception) contributes to accurate path integration. The purpose of the current study was to investigate how sensory information and curved path complexity affect path integration. Forty blindfolded participants had to accurately reproduce a curved path and return to the origin. They were divided into four groups that differed in the curved path, circle (simple) or figure-eight (complex), and received either visual (previously seen) or proprioceptive (previously guided) information about the path before they reproduced it. The dependent variables used were average trajectory error, walking speed, and distance traveled. The results indicated that (a) both groups that walked on a circular path and both groups that received visual information produced greater accuracy in reproducing the path. Moreover, the performance of the group that received proprioceptive information and later walked on a figure-eight path was less accurate than their corresponding circular group. The groups that had the visual information also walked faster compared to the group that had proprioceptive information. Results of the current study highlight the roles of different sensory inputs while performing blindfolded walking for path integration. PMID:22840893

Koutakis, Panagiotis; Mukherjee, Mukul; Vallabhajosula, Srikant; Blanke, Daniel J; Stergiou, Nicholas

2012-07-27

362

Beyond centrality—classifying topological significance using backup efficiency and alternative paths  

NASA Astrophysics Data System (ADS)

In complex networks characterized by broad degree distribution, node significance is often associated with its degree or with centrality metrics which relate to its reachability and shortest paths passing through it. Such measures do not consider availability of efficient backup of the node and thus often fail to capture its contribution to the functionality and resilience of the network operation. In this paper, we suggest the quality of backup (QoB) and alternative path centrality (APC) measures as complementary methods which enable analysis of node significance in a manner which considers backup. We examine the theoretical significance of these measures and use them to classify nodes in social interaction networks and in the Internet AS (autonomous system) graph while applying the valley-free routing restrictions which reflect the economic relationships between the AS nodes in the Internet. We show that both node degree and node centrality are not necessarily evidence of its significance. In particular, we show that social structures do not necessarily depend on highly central nodes and that medium degree nodes with medium centrality measure prove to be crucial for efficient routing in the Internet AS graph. Partial results presented in this paper also appear in the IFIP NETWORKING 2007 Conference.

Shavitt, Yuval; Singer, Yaron

2007-08-01

363

The optomechanical design of AquEYE, an instrument for astrophysics on its shortest timescales at the Asiago Observatory  

NASA Astrophysics Data System (ADS)

This paper describes the ultra-fast photometer AquEYE (the Asiago Quantum Eye) being built for the 182 cm telescope at Cima Ekar, as a prototype for the QuantEYE instrument studied for the ESO OWL. In a way similar to what has been proposed for Quanteye, Aqueye isolates a single object at the center of the telescope field of view, and divides the telescope pupil in four parts. Each sub-pupil is then focused on a Single Photon Avalanche Photodiode capable to tag the arrival time of each photon to better than 50 picoseconds. The counts are acquired via a Time to Digital Converter board and stored in four separate memories. Both in-line and off-line algorithms will be available for data analysis. The designed optical non-imaging solution concentrates all the light collected inside a 3 arcsec field on the 50 micrometer detector square area. Different filters can be inserted in the 4 different optical paths. It is foreseen to utilize the instrument on several different astrophysical problems characterized by rapid variability, including occultations by the Moon, asteroids and KBOs, and extrasolar planet transits.

Barbieri, C.; Naletto, G.; Occhipinti, T.; Tamburini, F.; Giro, E.; D'Onofrio, M.; Sain, E.; Zaccariotto, M.

364

Optimum gradient of mountain paths.  

PubMed

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions. PMID:8594031

Minetti, A E

1995-11-01

365

Evaluation of beam-path configurations for use with a monostatic OP-FTIR capable of rapid beam movement for tomographic reconstruction of gas and vapor concentrations in workplaces  

Microsoft Academic Search

Beam path average data from an open path Fourier transform infrared (OP-FTIR) spectrometer can be used to reconstruct 2D concentration maps of the gas and vapor contaminants in workplaces using computed tomographic (CT) techniques. However, a practical limitation arises because many source and detector units are required to produce a sufficient number of intersecting beam paths in order to reconstruct

Doo Y. Park; Michael G. Yost; Anushka C. Drescher; Ashok J. Gadgil; Yi Zhou; Steven P. Levine

1995-01-01

366

Path tracking control of a manipulator with passive joints  

Microsoft Academic Search

A method is proposed of path tracking control of a manipulator with passive joints, i.e. having no actuators. A desired path is geometrically specified in operational space. The position of the manipulator is controlled to follow the desired path. In this method, a path coordinate system based on the desired path is defined in operational space. The path coordinates consist

Hirohiko ARAI; Kazuo TANIE; Susumu TACHI

1991-01-01

367

OSL—optimal single-loop guide paths for AGVS  

Microsoft Academic Search

This study deals with the Automated Guided Vehicle System guide path design problem. We suggest a single closed loop guide path layout configuration as an alternative to conventional but more complex guide path designs. The benefits of using a simple guide path versus more complicated guide paths are discussed. A procedure for designing an optimal single loop guide path for

J. M. A. TANCHOCOf; DAVID SINRIECH

1992-01-01

368

Integrated assignment and path planning  

NASA Astrophysics Data System (ADS)

A surge of interest in unmanned systems has exposed many new and challenging research problems across many fields of engineering and mathematics. These systems have the potential of transforming our society by replacing dangerous and dirty jobs with networks of moving machines. This vision is fundamentally separate from the modern view of robotics in that sophisticated behavior is realizable not by increasing individual vehicle complexity, but instead through collaborative teaming that relies on collective perception, abstraction, decision making, and manipulation. Obvious examples where collective robotics will make an impact include planetary exploration, space structure assembly, remote and undersea mining, hazardous material handling and clean-up, and search and rescue. Nonetheless, the phenomenon driving this technology trend is the increasing reliance of the US military on unmanned vehicles, specifically, aircraft. Only a few years ago, following years of resistance to the use of unmanned systems, the military and civilian leadership in the United States reversed itself and have recently demonstrated surprisingly broad acceptance of increasingly pervasive use of unmanned platforms in defense surveillance, and even attack. However, as rapidly as unmanned systems have gained acceptance, the defense research community has discovered the technical pitfalls that lie ahead, especially for operating collective groups of unmanned platforms. A great deal of talent and energy has been devoted to solving these technical problems, which tend to fall into two categories: resource allocation of vehicles to objectives, and path planning of vehicle trajectories. An extensive amount of research has been conducted in each direction, yet, surprisingly, very little work has considered the integrated problem of assignment and path planning. This dissertation presents a framework for studying integrated assignment and path planning and then moves on to suggest an exact mathematical model and solution techniques. The approach adopted is based upon the very flexible New Product Development model but also blends many features from other approaches. Solution methods using branch and bound and construction heuristics are developed and tested on several example problems, including a military scenario featuring unmanned air vehicles.

Murphey, Robert A.

369

Sequential path entanglement for quantum metrology.  

PubMed

Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications. PMID:23648653

Jin, Xian-Min; Peng, Cheng-Zhi; Deng, Youjin; Barbieri, Marco; Nunn, Joshua; Walmsley, Ian A

2013-01-01

370

Sequential Path Entanglement for Quantum Metrology  

NASA Astrophysics Data System (ADS)

Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications.

Jin, Xian-Min; Peng, Cheng-Zhi; Deng, Youjin; Barbieri, Marco; Nunn, Joshua; Walmsley, Ian A.

2013-05-01

371

Quantifying Kinetic Paths of Protein Folding  

PubMed Central

We propose a new approach to activated protein folding dynamics via a diffusive path integral framework. The important issues of kinetic paths in this situation can be directly addressed. This leads to the identification of the kinetic paths of the activated folding process, and provides a direct tool and language for the theoretical and experimental community to understand the problem better. The kinetic paths giving the dominant contributions to the long-time folding activation dynamics can be quantitatively determined. These are shown to be the instanton paths. The contributions of these instanton paths to the kinetics lead to the “bell-like” shape folding rate dependence on temperature, which is in good agreement with folding kinetic experiments and simulations. The connections to other approaches as well as the experiments of the protein folding kinetics are discussed.

Wang, Jin; Zhang, Kun; Lu, Hongyang; Wang, Erkang

2005-01-01

372

Semiclassical series from path integrals  

SciTech Connect

We derive the semiclassical series for the partition function in Quantum Statistical Mechanics (QSM) from its path integral representation. Each term of the series is obtained explicitly from the (real) minima of the classical action. The method yields a simple derivation of the exact result for the harmonic oscillator, and an accurate estimate of ground-state energy and specific heat for a single-well quartic anharmonic oscillator. As QSM can be regarded as finite temperature field theory at a point, we make use of the field-theoretic language of Feynman diagrams to illustrate the non-perturbative character of the series: it contains all powers of ({Dirac_h}/2{pi}) and graphs with any number of loops; the usual perturbative series corresponds to a subset of the diagrams of the semiclassical series. We comment on the application of our results to other potentials, to correlation functions and to field theories in higher dimensions.

Carvalho, C. A. A. de; Cavalcanti, R. M. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cx. Postal 68528, CEP 21945-970, Rio de Janeiro, RJ (Brazil); Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States)

1999-07-13

373

The path to adaptive microsystems  

NASA Astrophysics Data System (ADS)

Scaling trends in microsystems are discussed frequently in the technical community, providing a short-term perspective on the future of integrated microsystems. This paper looks beyond the leading edge of technological development, focusing on new microsystem design paradigms that move far beyond today's systems based on static components. We introduce the concept of Adaptive Microsystems and outline a path to realizing these systems-on-a-chip. The role of DARPA in advancing future components and systems research is discussed, and specific DARPA efforts enabling and producing adaptive microsystems are presented. In particular, we discuss efforts underway in the DARPA Microsystems Technology Office (MTO) including programs in novel circuit architectures (3DIC), adaptive imaging and sensing (AFPA, VISA, MONTAGE, A-to-I) and reconfigurable RF/Microwave devices (SMART, TFAST, IRFFE).

Zolper, John C.; Biercuk, Michael J.

2006-06-01

374

Slant path atmospheric extinction measurements  

NASA Astrophysics Data System (ADS)

A commercial Fourier transform spectrometer is being used to collect 0.06/cm 2-14-micron slant path atmospheric spectra using the sun as the source of radiation. Using a Lambert plot approach, 10-15 spectra are collected at different air masses. The logarithm of the intensity versus air mass is used to calculate the extinctance for the atmosphere at arbitrary frequencies within the bandwidth. Over the past three years, spectra have been collected on over 120 days at White Sands Missile Range, NM. Up to a factor of ten variation in the atmospheric extinction is observed at many CO2 laser frequencies which correlate with atmospheric water vapor measurements. Variations in the atmospheric extinction for DF frequencies are smaller and do not correlate with the water vapor measurements.

Gutman, W. M.; Hanley, S. T.; Walters, D. L.

1981-01-01

375

ANALYSIS OF CROSSING PATH CRASH COUNTERMEASURE SYSTEMS  

Microsoft Academic Search

This paper summarizes the results of an analysis of promising countermeasure systems for crossing path crashes, and thus provides a foundation for setting research priorities under the United States (U.S.) Department of Transportation's Intelligent Vehicle Initiative. Crossing path crashes involve one moving vehicle cutting across the path of another, which amounted to 1.72 million police-reported crashes in the U.S. based

Wassim G. Najm; Jonathan A. Koopmann; David L. Smith

376

Optimizing Regular Path Expressions Using Graph Schemas  

Microsoft Academic Search

Several languages, such as LOREL and UnQL, support querying of semi-structured data. Others, such as WebSQL and WebLog, query Web sites. All these languages model data as labeled graphs and use regular path expressions to express queries that traverse arbitrary paths in graphs. Naive execution of path expressions is inefficient, however, because it often requires exhaustive graph search. We describe

Mary F. Fernandez; Dan Suciu

1998-01-01

377

Maximum Flux Transition Paths of Conformational Change.  

PubMed

Given two metastable states A and B of a biomolecular system, the problem is to calculate the likely paths of the transition from A to B. Such a calculation is more informative and more manageable if done for a reduced set of collective variables chosen so that paths cluster in collective variable space. The computational task becomes that of computing the "center" of such a cluster. A good way to define the center employs the concept of a committor, whose value at a point in collective variable space is the probability that a trajectory at that point will reach B before A. The committor "foliates" the transition region into a set of isocommittors. The maximum flux transition path is defined as a path that crosses each isocommittor at a point which (locally) has the highest crossing rate of distinct reactive trajectories. This path is based on the same principle as the minimum resistance path of Berkowitz et al (1983), but it has two advantages: (i) the path is invariant with respect to a change of coordinates in collective variable space and (ii) the differential equations that define the path are simpler. It is argued that such a path is nearer to an ideal path than others that have been proposed with the possible exception of the finite-temperature string method path. To make the calculation tractable, three approximations are introduced, yielding a path that is the solution of a nonsingular two-point boundary-value problem. For such a problem, one can construct a simple and robust algorithm. One such algorithm and its performance is discussed. PMID:20890401

Zhao, Ruijun; Shen, Juanfang; Skeel, Robert D

2010-08-10

378

Applications of Visible Light Path Laser Projector  

Microsoft Academic Search

We proposed and developed a method to visualize the light path of a laser with jetting mists along light axis of a laser pointer.\\u000a The estimation accuracy for the position of a laser spot occluded behind an object was improved when the light path of the\\u000a laser was visualized. In this paper, we propose visible light path laser projector (VLLP)

Nobuchika Sakata; Shu Okamoto; Shogo Nishida

2009-01-01

379

Randomized path coloring on binary trees  

Microsoft Academic Search

Motivated by the problem of WDM routing in all-optical networks, we study the following NP-hard problem. We are given a di- rected binary tree T and a set R of directed paths on T.W e wish to assign colors to paths in R, in such a way that no two paths that share ad irected arc ofT are assigned the

Vincenzo Auletta; Ioannis Caragiannis; Christos Kaklamanis; Pino Persiano

2000-01-01

380

Path instability of a rising bubble.  

PubMed

We model the problem of path instability of a rising bubble by considering the bubble as a spheroidal body of fixed shape, and we solve numerically the coupled fluid-body problem. Numerical results show that this model exhibits path instability for large enough values of the control parameters. The corresponding characteristics of the zigzag and spiral paths are in good agreement with experimental observations. Analysis of the vorticity field behind the bubble reveals that a wake instability leading to a double threaded wake is the primary cause of the path instability. PMID:11800955

Mougin, Guillaume; Magnaudet, Jacques

2001-12-19

381

Making the Stranger's Path Familiar: Environmental Communication that Turns Access into Participation  

ERIC Educational Resources Information Center

Visitors to the FDR Memorial in Washington, D.C., enter the area through ceremonial openings: from the pathway around the reflecting pond of the Jefferson Memorial, or across a small shaded plaza reached from a roadway parallel to the Potomac River. The FDR Memorial itself cannot be seen at the start of either of these paths. It is out there…

Adelman, Clifford

2005-01-01

382

An advanced open path atmospheric pollution monitor for large areas  

SciTech Connect

Over 100 million gallons of radioactive and toxic waste materials generated in weapon materials production are stored in 322 tanks buried within large areas at DOE sites. Toxic vapors occur in the tank headspace due to the solvents used and chemical reactions within the tanks. To prevent flammable or explosive concentration of volatile vapors, the headspace are vented, either manually or automatically, to the atmosphere when the headspace pressure exceeds preset values. Furthermore, 67 of the 177 tanks at the DOE Hanford Site are suspected or are known to be leaking into the ground. These underground storage tanks are grouped into tank farms which contain closely spaced tanks in areas as large as 1 km{sup 2}. The objective of this program is to protect DOE personnel and the public by monitoring the air above these tank farms for toxic air pollutants without the monitor entering the tanks farms, which can be radioactive. A secondary objective is to protect personnel by monitoring the air above buried 50 gallon drums containing moderately low radioactive materials but which could also emit toxic air pollutants.

Taylor, L.; Suhre, D.; Mani, S. [and others

1996-12-31

383

Characterizing Motor Vehicle Fleet Emissions by Open-Path Spectroscopy.  

National Technical Information Service (NTIS)

In this thesis, I present the conceptual combination of the tunnel study with remote sensing. In other words, I present a technique for measuring fleet-averaged modal emissions from a large aggregate population of vehicles (as in a tunnel study), which em...

D. M. Branan

2002-01-01

384

Improved FTIR open-path remote sensing data reduction technique  

Microsoft Academic Search

Progress on the developement of a nonlinear curve fitting computer algorithm for data reduction of optical remote sensing Fourier transform spectrometer (FTS) data is presented. This new algorithm is an adaptation of an existing algorithm employed at the Arnold Engineering Development Center for the analysis of infrared plume signature and optical gas diagnostic data on rocket and turbine engine exhaust.

Bill Phillips; Rick Moyers; Lori T. Lay

1995-01-01

385

A Simple Histone Code Opens Many Paths to Epigenetics  

PubMed Central

Nucleosomes can be covalently modified by addition of various chemical groups on several of their exposed histone amino acids. These modifications are added and removed by enzymes (writers) and can be recognized by nucleosome-binding proteins (readers). Linking a reader domain and a writer domain that recognize and create the same modification state should allow nucleosomes in a particular modification state to recruit enzymes that create that modification state on nearby nucleosomes. This positive feedback has the potential to provide the alternative stable and heritable states required for epigenetic memory. However, analysis of simple histone codes involving interconversions between only two or three types of modified nucleosomes has revealed only a few circuit designs that allow heritable bistability. Here we show by computer simulations that a histone code involving alternative modifications at two histone positions, producing four modification states, combined with reader-writer proteins able to distinguish these states, allows for hundreds of different circuits capable of heritable bistability. These expanded possibilities result from multiple ways of generating two-step cooperativity in the positive feedback - through alternative pathways and an additional, novel cooperativity motif. Our analysis reveals other properties of such epigenetic circuits. They are most robust when the dominant nucleosome types are different at both modification positions and are not the type inserted after DNA replication. The dominant nucleosome types often recruit enzymes that create their own type or destroy the opposing type, but never catalyze their own destruction. The circuits appear to be evolutionary accessible; most circuits can be changed stepwise into almost any other circuit without losing heritable bistability. Thus, our analysis indicates that systems that utilize an expanded histone code have huge potential for generating stable and heritable nucleosome modification states and identifies the critical features of such systems.

Sneppen, Kim; Dodd, Ian B.

2012-01-01

386

Path planning and path tracking control of unmanned ground vehicles (UGVs)  

Microsoft Academic Search

Unmanned ground vehicles (UGVs) will be playing increasingly important role in the future battlefields. How to automatically guide and control UGVs under varying environment conditions represents a challenging issue. This paper presents a novel approach to achieving path planning and path tracking of UGVs under dynamic environments. We apply the topology theory to find the optimal path given any starting

Liguo Weng; D. Y. Song

2005-01-01

387

Path-Goal Theory of Leadership.  

National Technical Information Service (NTIS)

The paper reviews the path-goal theory of leadership. This theory states that a leader's behavior is important for good performance as a function of its impact on subordinates' perceptions of paths to goals and the attractiveness of the goals. When leader...

R. J. House T. R. Mitchell

1975-01-01

388

Cooperative organic mine avoidance path planning  

NASA Astrophysics Data System (ADS)

The JHU/APL Path Planning team has developed path planning techniques to look for paths that balance the utility and risk associated with different routes through a minefield. Extending on previous years' efforts, we investigated real-world Naval mine avoidance requirements and developed a tactical decision aid (TDA) that satisfies those requirements. APL has developed new mine path planning techniques using graph based and genetic algorithms which quickly produce near-minimum risk paths for complicated fitness functions incorporating risk, path length, ship kinematics, and naval doctrine. The TDA user interface, a Java Swing application that obtains data via Corba interfaces to path planning databases, allows the operator to explore a fusion of historic and in situ mine field data, control the path planner, and display the planning results. To provide a context for the minefield data, the user interface also renders data from the Digital Nautical Chart database, a database created by the National Geospatial-Intelligence Agency containing charts of the world's ports and coastal regions. This TDA has been developed in conjunction with the COMID (Cooperative Organic Mine Defense) system. This paper presents a description of the algorithms, architecture, and application produced.

McCubbin, Christopher B.; Piatko, Christine D.; Peterson, Adam V.; Donnald, Creighton R.; Cohen, David

2005-06-01

389

Ray path deviation in a nonhemispherical dome  

Microsoft Academic Search

A calculation is presented for meridional rays of the ray path deviation in a conformal dome in which both the shape of the inner and outer surfaces are specified in detail so as to examine under what conditions the ray path deviation might be minimized by independently adjusting the shape of the inner surface. Specific results are given for the

Richard I. Joseph; Michael E. Thomas

2001-01-01

390

Adaptively Ubiquitous Learning in Campus Math Path  

ERIC Educational Resources Information Center

|The purposes of this study are to develop and evaluate the instructional model and learning system which integrate ubiquitous learning, computerized adaptive diagnostic testing system and campus math path learning. The researcher first creates a ubiquitous learning environment which is called "adaptive U-learning math path system". This system…

Shih, Shu-Chuan; Kuo, Bor-Chen; Liu, Yu-Lung

2012-01-01

391

Modeling Robot Path Planning with CD  

Microsoft Academic Search

Robotic systems are usually built as independent a gents that collaborate to accomplish a specific task. Analysis of robot path planning consists of route plan- ning and path generation. We will show how to apply the Cell-DEVS formalism and the CD++ toolkit for these tasks. We present a Cell -DEVS model for route planning, which, based on the obstacles, finds

Gabriel A. Wainer

2006-01-01

392

Hausdorff Dimension of Operator Stable Sample Paths  

Microsoft Academic Search

The Hausdorff dimension of the sample paths of a stochastic process with stationary independent operator stable increments is computed. With probability one, every sample path has the same dimension, depending on the real parts of the eigenvalues of the operator stable exponent.

Peter Becker-Kern; Mark M. Meerschaert; Hans-Peter Scheffler

2003-01-01

393

Bounding the error of path loss models  

Microsoft Academic Search

In this paper we analyze the efficacy of basic path loss models at predicting median path loss in urban environments. We attempt to bound the practical error of these models and look at how they may hinder practical wireless applications, and in particular dynamic spectrum access networks. This analysis is made using a large set of measurements from production networks

Caleb Phillips; Douglas Sicker; Dirk Grunwald

2011-01-01

394

Paths in m-ary interval trees  

Microsoft Academic Search

We introduce the m-ary interval tree, a random structure that underlies interval division and simultaneous parking problems. Certain significant paths in the m-ary interval trees are considered. When appropriately normed, the length of these paths are shown to converge in distribution to a normal random variable. The work extends the study of incomplete binary interval trees in Itoh and Mahmoud

Mehri Javanian; Hosam M. Mahmoud; Mohammad Vahidi-asl

2004-01-01

395

Diversion path analysis handbook. Volume I. Methodology  

Microsoft Academic Search

Diversion Path Analysis (DPA) is a procedure for analyzing internal controls of a facility in order to identify vulnerabilities to successful diversion of material by an adversary. The internal covert threat is addressed but the results are also applicable to the external overt threat. The diversion paths are identified. Complexity parameters include records alteration or falsification, multiple removals of sub-threshold

M. D. K. Maltese; K. E. Goodwin; J. C. Schleter

1976-01-01

396

Judgments of path, not heading, guide locomotion.  

PubMed

To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient control solution. Here, the authors aim to establish how well observers can pinpoint instantaneous heading and path, by measuring their accuracy when looking at these features while traveling along straight and curved paths. The results showed that observers could identify both heading and path accurately (approximately 3 degrees ) when traveling along straight paths, but on curved paths they were more accurate at identifying a point on their future path (approximately 5 degrees ) than indicating their instantaneous heading (approximately 13 degrees ). Furthermore, whereas participants could track changes in the tightness of their path, they were unable to accurately track the rate of change of heading. In light of these results, the authors suggest it is unlikely that heading is primarily used by the visual system to support active steering. PMID:16478328

Wilkie, Richard M; Wann, John P

2006-02-01

397

Reducing power with dynamic critical path information  

Microsoft Academic Search

Recent research has shown that dynamic information regarding instruction criticality can be used to increase microprocessor performance. Critical path information can also be used in processors to achieve a better balance of power and performance. This paper uses the output of a dynamic critical path predictor to decrease the power consumption of key portions of the processor without incurring a

John S. Seng; Eric S. Tune; Dean M. Tullsen

2001-01-01

398

Analysis of probabilistic roadmaps for path planning  

Microsoft Academic Search

We provide an analysis of a path planning method which uses probabilistic roadmaps. This method has proven very successful in practice, but the theoretical understanding of its performance is still limited. Assuming that a path ? exists between two configurations a and b of the robot, we study the dependence of the failure probability to connect a and b, on:

Lydia E. Kavraki; Mihail N. Kolountzakis; Jean-claude Latombe

1998-01-01

399

Path Planning Algorithms for Agricultural Machines  

Microsoft Academic Search

If the field plot shape is not rectangular and if it contains obstacles, the coverage path planning problem is hard to solve for a non-omnidirectional machine. Scientists have developed several algorithms to solve this coverage path planning problem, but all of them have pros and cons. If the machines were omnidirectional and turning times were decreased to insignificant, the problem

T. Oksanen; A. Visala

2007-01-01

400

Path Integrals in Lattice Quantum Chromodynamics  

NASA Astrophysics Data System (ADS)

I discuss the use of path integrals to study strong-interaction physics from first principles. The underlying theory is cast into path integrals which are evaluated numerically using Monte Carlo methods on a space-time lattice. Examples are given in progress made in nuclear physics.

Lee, F. X.

2008-11-01

401

Fatigue failure paths for offshore platform inspection  

Microsoft Academic Search

A closed- form, reliability-based procedure is developed to identify fatigue failure paths of offshore structures and assess the notional probability of system failure through these paths. The procedure utilizes the Miners rule node fatigue failure reliability model developed by Wirsching. Effects of load redistribution following the fatigue failure of a node on the time to failure of remaining unfailed nodes

Demir I. Karsan; Ashok Kumar

1990-01-01

402

The path dependence of deformation texture development  

SciTech Connect

It is demonstrated for the case of three different strain paths, all of which end up with the same, elongated specimen shape, that the texture developed during straining is path dependent. This is true both for experiments on aluminum polycrystals and for simulations using the LApp code.

Takeshita, T.; Kocks, U.F.; Wenk, H.R.

1987-01-01

403

Evaluation of Calcine Disposition Path Forward  

SciTech Connect

This document describes an evaluation of the baseline and two alternative disposition paths for the final disposition of the calcine wastes stored at the Idaho Nuclear Technology and Engineering Center at the Idaho National Engineering and Environmental Laboratory. The pathways are evaluated against a prescribed set of criteria and a recommendation is made for the path forward.

Birrer, S.A.; Heiser, M.B.

2003-02-26

404

Evaluation of Calcine Disposition - Path Forward  

SciTech Connect

This document describes an evaluation of the baseline and two alternative disposition paths for the final disposition of the calcine wastes stored at the Idaho Nuclear Technology and Engineering Center at the Idaho National Engineering and Environmental Laboratory. The pathways are evaluated against a prescribed set of criteria and a recommendation is made for the path forward.

Steve Birrer

2003-02-01

405

White Noise Path Integrals in Stochastic Neurodynamics  

NASA Astrophysics Data System (ADS)

The white noise path integral approach is used in stochastic modeling of neural activity, where the primary dynamical variables are the relative membrane potentials, while information on transmembrane ionic currents is contained in the drift coefficient. The white noise path integral allows a natural framework and can be evaluated explicitly to yield a closed form for the conditional probability density.

Carpio-Bernido, M. Victoria; Bernido, Christopher C.

2008-06-01

406

Bergman Kernel from Path Integral  

NASA Astrophysics Data System (ADS)

We rederive the expansion of the Bergman kernel on Kähler manifolds developed by Tian, Yau, Zelditch, Lu and Catlin, using path integral and perturbation theory, and generalize it to supersymmetric quantum mechanics. One physics interpretation of this result is as an expansion of the projector of wave functions on the lowest Landau level, in the special case that the magnetic field is proportional to the Kähler form. This is relevant for the quantum Hall effect in curved space, and for its higher dimensional generalizations. Other applications include the theory of coherent states, the study of balanced metrics, noncommutative field theory, and a conjecture on metrics in black hole backgrounds discussed in [24]. We give a short overview of these various topics. From a conceptual point of view, this expansion is noteworthy as it is a geometric expansion, somewhat similar to the DeWitt-Seeley-Gilkey et al short time expansion for the heat kernel, but in this case describing the long time limit, without depending on supersymmetry.

Douglas, Michael R.; Klevtsov, Semyon

2010-01-01

407

Dynamics of dielectric breakdown paths.  

PubMed

We investigate the dynamics and geometry of dielectric breakdown paths of needle defects of arbitrary residual resistivity in an otherwise homogeneous medium using a time-dependent electrical-circuit model. The circuit model consists of a semi-infinite lattice of capacitors in parallel with resistors that break down to a lower (residual) resistance. The breakdown occurs if the local field across a resistor exceeds a critical value for a breakdown delay time. We consider cases where the initial resistance is infinite or finite and where the residual resistance is finite or zero. We consider the model for the case where the applied field reaches the critical value adiabatically. We find that, as in the quasistatic case, the breakdown grows either one dimensionally or spreads with a fractal dimension (bifurcates) depending on the values of residual resistance and breakdown delay time. Also, we find that the propagation velocity of the needle oscillates spontaneously. We give the phase diagram for bifurcation and oscillations. We derive a simplified recursive map approximation to explain this behavior. PMID:16241371

Boksiner, Jeffrey; Leath, P L

2003-06-27

408

Path integral for inflationary perturbations  

NASA Astrophysics Data System (ADS)

The quantum theory of cosmological perturbations in single-field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well-known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anticommuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level three-point and four-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.

Prokopec, Tomislav; Rigopoulos, Gerasimos

2010-07-01

409

Texture of locomotor path: a replicable characterization of a complex behavioral phenotype.  

PubMed

A database of mouse locomotor path in spatial tests can be used to search in silico for behavioral measures that better discriminate between genotypes and are more replicable across laboratories. In this study, software for the exploration of exploration (SEE) was used to search a large database for a novel behavioral measure that would characterize complex movement paths. The database included mouse open-field behavior assessed in 3 laboratories, 7 inbred strains, several pharmacological treatments and hundreds of animals. The new behavioral measure, "path texture", was characterized using the local curvature of the path (the change of direction per unit distance, in degrees/cm) across several spatial scales, starting from scales smaller than the animal's body length and up to the scale of the arena size. Path texture analysis differs from fractal dimension analysis in that it does not assume self-similarity across scales. Path texture was found to discriminate inbred strains with relatively high broad-sense heritability (43%-71%) and high replicability across laboratories. Even genotypes that had similar path curvatures in some scales usually differed in other scales, and self-similarity across scales was not displayed by all genotypes. Amphetamine decreased the path curvature of C57BL/6 mice in small and medium scales, while having no effect on DBA/2J mice. Diazepam dose-dependently decreased the curvature of C57BL/6 mice across all scales, while 2 anxiogenic drugs, FG-7142 and pentylenetetrazole, increased it. Path texture thus has high potential for behavioral phenotyping and the study of drug effects in the mouse. PMID:16176389

Kafkafi, N; Elmer, G I

2005-10-01

410

The Path of Human Evolution  

NASA Astrophysics Data System (ADS)

A complex series of evolutionary steps, contingent upon a dynamic environmental context and a long biological heritage, have led to the ascent of Homo sapiens as a dominant component of the modern biosphere. In a field where missing links still abound and new discoveries regularly overturn theoretical paradigms, our understanding of the path of human evolution has made tremendous advances in recent years. Two major trends characterize the development of the hominin clade subsequent to its origins with the advent of upright bipedalism in the Late Miocene of Africa. One is a diversification into two prominent morphological branches, each with a series of 'twigs' representing evolutionary experimentation at the species or subspecies level. The second important trend, which in its earliest manifestations cannot clearly be ascribed to one or the other branch, is the behavioral complexity of an increasing reliance on technology to expand upon limited inherent morphological specializations and to buffer the organism from its environment. This technological dependence is directly associated with the expansion of hominin range outside Africa by the genus Homo, and is accelerated in the sole extant form Homo sapiens through the last 100 Ka. There are interesting correlates between the evolutionary and behavioral patterns seen in the hominin clade and environmental dynamics of the Neogene. In particular, the tempo of morphological and behavioral innovation may be tracking major events in Neogene climatic development as well as reflecting intervals of variability or stability. Major improvements in analytical techniques, coupled with important new collections and a growing body of contextual data are now making possible the integration of global, regional and local environmental archives with an improved biological understanding of the hominin clade to address questions of coincidence and causality.

Feibel, C. S.

2004-12-01

411

Steering Chiral Swimmers along Noisy Helical Paths  

NASA Astrophysics Data System (ADS)

Chemotaxis along helical paths towards a target releasing a chemoattractant is found in sperm cells and many microorganisms. We discuss the stochastic differential geometry of the noisy helical swimming path of a chiral swimmer. A chiral swimmer equipped with a simple feedback system can navigate in a concentration gradient of chemoattractant. We derive an effective equation for the alignment of helical paths with a concentration gradient which is related to the alignment of a dipole in an external field and discuss the chemotaxis index.

Friedrich, Benjamin M.; Jülicher, Frank

2009-08-01

412

Quickest Paths for Different Network Router Mechanisms  

SciTech Connect

The quickest path problem deals with the transmission of a message of size {sigma} from a source to a destination with the minimum end-to-end delay over a network with bandwidth and delay constraints on the links. We consider four basic modes and two variations for the message delivery at the nodes reacting the mechanisms such as circuit switching, Internet protocol, and their combinations. For each of first three modes, we present O(m{sup 2} + mn log n) time algorithm to compute the quickest path for a given message size {sigma}. For the last mode, the quickest path can be computed in O(m + n log n) time.

Rao, NSV

2000-10-16

413

Middle path for electricity options and sustainable development.  

National Technical Information Service (NTIS)

In a landmark article in Foreign Affairs in October 1976, Amory Lovins presented his vision of two vastly different and seemingly irreconcilable paths that energy provision might take into the future. One path was a ''hard'' path, characterized by extensi...

J. I. Mills J. S. Herring

1994-01-01

414

A chemist building paths to cell biology.  

PubMed

Galileo is reported to have stated, "Measure what is measurable and make measurable what is not so." My group's trajectory in cell biology has closely followed this philosophy, although it took some searching to find this path. PMID:24174456

Weibel, Douglas B

2013-11-01

415

UV Laser Long-Path Absorption Spectroscopy.  

National Technical Information Service (NTIS)

Long path Differential Optical Absorption Spectroscopy (DOAS) using a picosecond UV laser as a light source was developed in our institute. Tropospheric OH radicals are measured by their rotational absorption lines around 308 nm. The spectra are obtained ...

H. Dorn T. Brauers R. Neuroth

1994-01-01

416

Diversion Path Analysis Handbook. Volume I. Methodology.  

National Technical Information Service (NTIS)

Diversion Path Analysis (DPA) is a procedure for analyzing internal controls of a facility in order to identify vulnerabilities to successful diversion of material by an adversary. The internal covert threat is addressed but the results are also applicabl...

M. D. K. Maltese K. E. Goodwin J. C. Schleter

1976-01-01

417

Path integration while ignoring irrelevant movement.  

PubMed

Participants attempted to return to the origin of travel after following an outbound path by locomotion on foot (Experiments 1-3) or in a virtual visual environment (Experiment 4). Critical conditions interrupted the outbound path with verbal distraction or irrelevant, to-be-ignored movements. Irrelevant movement, real or virtual, had greater effects than verbal or cognitive distraction, indicating inability to ignore displacement during path integration. Effects of the irrelevant movement's direction (backward vs. rightward) and location (1st vs. 2nd leg of path) indicated that participants encoded a configural representation of the pathway and then cognitively compensated for the movement, producing errors directly related to the demands of compensation. An encoding-error model fit to the data indicated that backward movement produced downward rescaling, whereas movement that led to implied rotation (rightward on 2nd leg) produced distortions of shape and scale. PMID:10682296

May, M; Klatzky, R L

2000-01-01

418

Expedite Departure Path (EDP) Operational Concept.  

National Technical Information Service (NTIS)

This document describes the operational concept for the Expedite Departure Path (EDP) tool. EDP is part of the Center-TRACON Automation System (CTAS). CTAS provides computer intelligence for planning and controlling arrival and departure traffic within se...

C. W. Johnson D. R. Isaacson K. K. Lee

1999-01-01

419

Path concentration distribution of toluene using remote sensing FTIR and one-dimensional reconstruction method.  

PubMed

A one-dimensional mapping technique coupled with Open-Path remote sensing FTIR was presented in this article. This technique was applied to one of the air toxic volatile organic compounds (VOCs)-toluene. The Path Integrated Concentrations (PICs) of toluene in different path lengths along one beam path were fitted by polynomial fitting method with degrees from 3 to 7. The 6th degree polynomial fitting showed the best fitting result. Moreover, the methods of reconstructing path concentration distribution along the beam path by applying a Gaussian model and the derivative of 6th degree polynomial fitting function were established in this article. The reconstructed concentrations of toluene along the beam path by the two methods were experimentally close. Results showed that the concentration peaks were at 1.05 and 2.40 m from the instrument by applying the Gaussian model with the maximum concentration of 0.85 and 3.19 ppm, and at 0.99 and 2.49 m from the instrument with the maximum concentration of 0.78 and 2.80 ppm by applying the 6th polynomial fitting function. It was obvious that the reconstruction results by these two methods were very close. This approach could be appreciated for its fast calculation, exact peak location orientation and concentration flow tendency mapping. In can be concluded that this method can provide the path concentration distributions of much more releasing gases in a briefly and intuitionistic way. The remote sensing FTIR coupled with these mathematical reconstruction techniques can be applied to the real world environmental and industrial hygiene monitoring, thus works as an alert system for the VOCs pollution. PMID:15663309

Li, Yan; Xu, Houqian; Xue, Rui; Wang, Xiaofei; Ren, Yibo; Wang, Lianjun; Wang, Junde

2005-01-01

420

The prediction of radio-path characteristics  

NASA Astrophysics Data System (ADS)

The paper examines algorithms for the long-term prediction of radio-path characteristics in the ionosphere, the main characteristic being the MUF at a given distance. The proposed approach is based on long-term memories called DATA BANKS. Attention is given to the characteritics of the various banks, including the BANK OF CITIES, the BANK OF RADIO PATHS, the REFERENCE DATA BANK, and the OUTPUT DATA BANK.

Gitina, G. M.; Kalinin, Iu. K.

421

A Path Algorithm for Constrained Estimation  

PubMed Central

Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ?, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online.

Zhou, Hua; Lange, Kenneth

2013-01-01

422

Bond Paths Are Not Chemical Bonds  

NASA Astrophysics Data System (ADS)

This account takes to task papers that criticize the definition of a bond path as a criterion for the bonding between the atoms it links by mistakenly identifying it with a chemical bond. It is argued that the notion of a chemical bond is too restrictive to account for the physics underlying the broad spectrum of interactions between atoms and molecules that determine the properties of matter. A bond path on the other hand, as well as being accessible to experimental verification and subject to the theorems of quantum mechanics, is applicable to any and all of the interactions that account for the properties of matter. It is shown that one may define a bond path operator as a Dirac observable, making the bond path the measurable expectation value of a quantum mechanical operator. Particular attention is given to van der Waals interactions that traditionally are assumed to represent attractive interactions that are distinct from chemical bonding. They are assumed by some to act in concert with Pauli repulsions to account for the existence of condensed states of molecules. It is such dichotomies of interpretation that are resolved by the experimental detection of bond paths and the delineation of their properties in molecular crystals. Specific criticisms of the stabilization afforded by the presence of bond paths derived from spectroscopic measurements performed on dideuteriophenanthrene are shown to be physically unsound. The concept of a bond path as a "bridge of density" linking bonded atoms was introduced by London in 1928 following the definition of the electron density by Schrödinger in 1926. These papers marked the beginning of the theory of atoms in molecules linked by bond paths.

Bader, Richard F. W.

2009-09-01

423

Robust real-time NURBS path interpolators  

Microsoft Academic Search

In a review of the real-time non-uniform rational B-splines (NURBS) path interpolation method in CNC controllers, it was found that none of the NURBS interpolators described in the literature has the necessary robustness against an extreme knot distribution. The problems begin with the calculation of the total length of the NURBS path: most interpolators handle knots as a global curve

W. T. Lei; S. B. Wang

2009-01-01

424

47 CFR 22.515 - Permissible communications paths.  

Code of Federal Regulations, 2012 CFR

...false Permissible communications paths. 22.515...Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED...515 Permissible communications paths. Mobile stations may communicate only with and through base stations....

2012-10-01

425

47 CFR 22.515 - Permissible communications paths.  

Code of Federal Regulations, 2011 CFR

...false Permissible communications paths. 22.515...Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED...515 Permissible communications paths. Mobile stations may communicate only with and through base stations....

2011-10-01

426

Quantum cosmology based on discrete Feynman paths  

SciTech Connect

Although the rules for interpreting local quantum theory imply discretization of process, Lorentz covariance is usually regarded as precluding time quantization. Nevertheless a time-discretized quantum representation of redshifting spatially-homogeneous universe may be based on discrete-step Feynman paths carrying causal Lorentz-invariant action--paths that not only propagate the wave function but provide a phenomenologically-promising elementary-particle Hilbert-space basis. In a model under development, local path steps are at Planck scale while, at a much larger ''wave-function scale'', global steps separate successive wave-functions. Wave-function spacetime is but a tiny fraction of path spacetime. Electromagnetic and gravitational actions are ''at a distance'' in Wheeler-Feynman sense while strong (color) and weak (isospin) actions, as well as action of particle motion, are ''local'' in a sense paralleling the action of local field theory. ''Nonmaterial'' path segments and ''trivial events'' collaborate to define energy and gravity. Photons coupled to conserved electric charge enjoy privileged model status among elementary fermions and vector bosons. Although real path parameters provide no immediate meaning for ''measurement'', the phase of the complex wave function allows significance for ''information'' accumulated through ''gentle'' electromagnetic events involving charged matter and ''soft'' photons. Through its soft-photon content the wave function is an ''information reservoir''.

Chew, Geoffrey F.

2002-10-10

427

Equivalence of trans paths in ion channels  

NASA Astrophysics Data System (ADS)

We explore stochastic models for the study of ion transport in biological cells. Analysis of these models explains and explores an interesting feature of ion transport observed by biophysicists. Namely, the average time it takes ions to cross certain ion channels is the same in either direction, even if there is an electric potential difference across the channels. It is shown for simple single ion models that the distribution of a path (i.e., the history of location versus time) of an ion crossing the channel in one direction has the same distribution as the time-reversed path of an ion crossing the channel in the reverse direction. Therefore, not only is the mean duration of these paths equal, but other measures, such as the variance of passage time or the mean time a path spends within a specified section of the channel, are also the same for both directions of traversal. The feature is also explored for channels with interacting ions. If a system of interacting ions is in reversible equilibrium (net flux is zero), then the equivalence of the left-to-right trans paths with the time-reversed right-to-left trans paths still holds. However, if the system is in equilibrium, but not reversible equilibrium, then such equivalence need not hold.

Alvarez, Juan; Hajek, Bruce

2006-04-01

428

Feedback cancellation for hearing aids fitted to open ear canals  

Microsoft Academic Search

Fitting hearing aids to open ear canals, in spite of its many benefits and increased popularity, is particularly prone to feedback problems. The present study examined the system responses of the feedback path and how effective the feedback signals can be cancelled under the open-canal condition. Compared to a traditional fitting method with earmolds, the open-canal fitting has a smaller

Huanping Dai

2008-01-01

429

Tracking the energy flow along the reaction path  

PubMed Central

We report a comprehensive study of the quantum-state correlation property of product pairs from reactions of chlorine atoms with both the ground-state and the CH stretch-excited CHD3. In light of available ab initio theoretical results, this set of experimental data provides a conceptual framework to visualize the energy-flow pattern along the reaction path, to classify the activity of different vibrational modes in a reactive encounter, to gain deeper insight into the concept of vibrational adiabaticity, and to elucidate the intermode coupling in the transition-state region. This exploratory approach not only opens up an avenue to understand polyatomic reaction dynamics, even for motions at the molecular level in the fleeting transition-state region, but it also leads to a generalization of Polanyi's rules to reactions involving a polyatomic molecule.

Yan, Shannon; Wu, Yen-Tien; Liu, Kopin

2008-01-01

430

Long-length contaminated equipment disposal process path document  

SciTech Connect

The first objective of the LLCE Process Path Document is to guide future users of this system on how to accomplish the cradle-to-grave process for the disposal of long-length equipment. Information will be provided describing the function and approach to each step in the process. Pertinent documentation, prerequisites, drawings, procedures, hardware, software, and key interfacing organizations will be identified. The second objective is related to the decision to lay up the program until funding is made available to complete it or until a need arises due to failure of an important component in a waste tank. To this end, the document will identify work remaining to be completed for each step of the process and open items or issues that remain to be resolved.

McCormick, W.A.

1998-09-30

431

Minimal entropy probability paths between genome families.  

PubMed

We develop a metric for probability distributions with applications to biological sequence analysis. Our distance metric is obtained by minimizing a functional defined on the class of paths over probability measures on N categories. The underlying mathematical theory is connected to a constrained problem in the calculus of variations. The solution presented is a numerical solution, which approximates the true solution in a set of cases called rich paths where none of the components of the path is zero. The functional to be minimized is motivated by entropy considerations, reflecting the idea that nature might efficiently carry out mutations of genome sequences in such a way that the increase in entropy involved in transformation is as small as possible. We characterize sequences by frequency profiles or probability vectors, in the case of DNA where N is 4 and the components of the probability vector are the frequency of occurrence of each of the bases A, C, G and T. Given two probability vectors a and b, we define a distance function based as the infimum of path integrals of the entropy function H( p) over all admissible paths p(t), 0 < or = t< or =1, with p(t) a probability vector such that p(0)=a and p(1)=b. If the probability paths p(t) are parameterized as y(s) in terms of arc length s and the optimal path is smooth with arc length L, then smooth and "rich" optimal probability paths may be numerically estimated by a hybrid method of iterating Newton's method on solutions of a two point boundary value problem, with unknown distance L between the abscissas, for the Euler-Lagrange equations resulting from a multiplier rule for the constrained optimization problem together with linear regression to improve the arc length estimate L. Matlab code for these numerical methods is provided which works only for "rich" optimal probability vectors. These methods motivate a definition of an elementary distance function which is easier and faster to calculate, works on non-rich vectors, does not involve variational theory and does not involve differential equations, but is a better approximation of the minimal entropy path distance than the distance //b-a//(2). We compute minimal entropy distance matrices for examples of DNA myostatin genes and amino-acid sequences across several species. Output tree dendograms for our minimal entropy metric are compared with dendograms based on BLAST and BLAST identity scores. PMID:15133624

Ahlbrandt, Calvin; Benson, Gary; Casey, William

2003-12-02

432

Perfect discretization of reparametrization invariant path integrals  

NASA Astrophysics Data System (ADS)

To obtain a well-defined path integral one often employs discretizations. In the case of gravity and reparametrization-invariant systems, the latter of which we consider here as a toy example, discretizations generically break diffeomorphism and reparametrization symmetry, respectively. This has severe implications, as these symmetries determine the dynamics of the corresponding system. Indeed we will show that a discretized path integral with reparametrization-invariance is necessarily also discretization independent and therefore uniquely determined by the corresponding continuum quantum mechanical propagator. We use this insight to develop an iterative method for constructing such a discretized path integral, akin to a Wilsonian RG flow. This allows us to address the problem of discretization ambiguities and of an anomaly-free path integral measure for such systems. The latter is needed to obtain a path integral, that can act as a projector onto the physical states, satisfying the quantum constraints. We will comment on implications for discrete quantum gravity models, such as spin foams.

Bahr, Benjamin; Dittrich, Bianca; Steinhaus, Sebastian

2011-05-01

433

Oscillatory fracture paths in thin elastic sheets  

NASA Astrophysics Data System (ADS)

We report results on a novel mode of quasi-static oscillatory crack propagation in thin elastic sheets [1]. A cutting tip of width w is perpendicularly driven through a thin brittle polymer film, held along its lateral boundaries, that progressively cuts the material as it advances [2]. For thin enough cutting tips (w < wc with w_c=0.2mm) the fracture path is straight. However, for w > w_c, the crack follows a well defined and highly reproducible oscillatory path. The amplitude and wavelength of the oscillatory crack paths scale linearly with the width of the cutting tip over a wide range of length scales but are independent of both of the cutting speed and the width of the sheet. We develop a model for this phenomena, based on the coupling between crack propagation and out-of-plane deformations of the film, which exhibits behaviour in remarkably good agreement with the experimental crack paths. [1] B. Roman, P.M. Reis, B. Audoly , S. DeVilliers, V. Viguié, D. Vallet, Oscillatory fracture paths in thin elastic sheets C.R. de Mecanique, vol 331, no 12, p. 811--816 (2003). [2] http://www.lmm.jussieu.fr/platefracture/

Reis, Pedro Miguel; Audoly, Basile; Roman, Benoit

2004-03-01

434

Unbiased sampling of lattice Hamilton path ensembles.  

PubMed

Hamilton paths, or Hamiltonian paths, are walks on a lattice which visit each site exactly once. They have been proposed as models of globular proteins and of compact polymers. A previously published algorithm [Mansfield, Macromolecules 27, 5924 (1994)] for sampling Hamilton paths on simple square and simple cubic lattices is tested for bias and for efficiency. Because the algorithm is a Metropolis Monte Carlo technique obviously satisfying detailed balance, we need only demonstrate ergodicity to ensure unbiased sampling. Two different tests for ergodicity (exact enumeration on small lattices, nonexhaustive enumeration on larger lattices) demonstrate ergodicity unequivocally for small lattices and provide strong support for ergodicity on larger lattices. Two other sampling algorithms [Ramakrishnan et al., J. Chem. Phys. 103, 7592 (1995); Lua et al., Polymer 45, 717 (2004)] are both known to produce biases on both 2x2x2 and 3x3x3 lattices, but it is shown here that the current algorithm gives unbiased sampling on these same lattices. Successive Hamilton paths are strongly correlated, so that many iterations are required between statistically independent samples. Rules for estimating the number of iterations needed to dissipate these correlations are given. However, the iteration time is so fast that the efficiency is still very good except on extremely large lattices. For example, even on lattices of total size 10x10x10 we are able to generate tens of thousands of uncorrelated Hamilton paths per hour of CPU time. PMID:17059235

Mansfield, Marc L

2006-10-21

435

Unbiased sampling of lattice Hamilton path ensembles  

NASA Astrophysics Data System (ADS)

Hamilton paths, or Hamiltonian paths, are walks on a lattice which visit each site exactly once. They have been proposed as models of globular proteins and of compact polymers. A previously published algorithm [Mansfield, Macromolecules 27, 5924 (1994)] for sampling Hamilton paths on simple square and simple cubic lattices is tested for bias and for efficiency. Because the algorithm is a Metropolis Monte Carlo technique obviously satisfying detailed balance, we need only demonstrate ergodicity to ensure unbiased sampling. Two different tests for ergodicity (exact enumeration on small lattices, nonexhaustive enumeration on larger lattices) demonstrate ergodicity unequivocally for small lattices and provide strong support for ergodicity on larger lattices. Two other sampling algorithms [Ramakrishnan et al., J. Chem. Phys. 103, 7592 (1995); Lua et al., Polymer 45, 717 (2004)] are both known to produce biases on both 2×2×2 and 3×3×3 lattices, but it is shown here that the current algorithm gives unbiased sampling on these same lattices. Successive Hamilton paths are strongly correlated, so that many iterations are required between statistically independent samples. Rules for estimating the number of iterations needed to dissipate these correlations are given. However, the iteration time is so fast that the efficiency is still very good except on extremely large lattices. For example, even on lattices of total size 10×10×10 we are able to generate tens of thousands of uncorrelated Hamilton paths per hour of CPU time.

Mansfield, Marc L.

2006-10-01

436

Path analysis in genetic epidemiology: a critique.  

PubMed Central

Path analysis, a form of general linear structural equation models, is used in studies of human genetics data to discern genetic, environmental, and cultural factors contributing to familial resemblance. It postulates a set of linear and additive parametric relationships between phenotypes and genetic and cultural variables and then essentially uses the assumption of multivariate normality to estimate and perform tests of hypothesis on parameters. Such an approach has been advocated for the analysis of genetic epidemiological data by D. C. Rao, N. Morton, C. R. Cloninger, L. J. Eaves, and W. E. Nance, among others. This paper reviews and evaluates the formulations, assumptions, methodological procedures, interpretations, and applications of path analysis. To give perspective, we begin with a discussion of path analysis as it occurs in the form of general linear causal models in several disciplines of the social sciences. Several specific path analysis models applied to lipoprotein concentrations, IQ, and twin data are then reviewed to keep the presentation self-contained. The bulk of the critical discussion that follows is directed toward the following four facets of path analysis: (1) coherence of model specification and applicability to data; (2) plausibility of modeling assumptions; (3) interpretability and utility of the model; and (4) validity of statistical and computational procedures. In the concluding section, a brief discussion of the problem of appropriate model selection is presented, followed by a number of suggestions of essentially model-free alternative methods of use in the treatment of complex structured data such as occurs in genetic epidemiology.

Karlin, S; Cameron, E C; Chakraborty, R

1983-01-01

437

Orientation Specificity in Spatial Memory: What Makes a Path Different From a Map of the Path?  

Microsoft Academic Search

Three studies investigated the factors that lead spatial information to be stored in an orientation-specific versus orientation-free manner. In Experiment 1, we replicated the findings of Presson and Hazelrigg (1984) that learning paths from a small map versus learning the paths directly from viewing a world leads to different functional characteristics of spatial memory. Whether the route display was presented

Clark C. Presson; Nina DeLange; Mark D. Hazelrigg

1989-01-01

438

Adaptive path planning algorithm for cooperating unmanned air vehicles  

SciTech Connect

An adaptive path planning algorithm is presented for cooperating Unmanned Air Vehicles (UAVs) that are used to deploy and operate land-based sensor networks. The algorithm employs a global cost function to generate paths for the UAVs, and adapts the paths to exceptions that might occur. Examples are provided of the paths and adaptation.

Cunningham, C T; Roberts, R S

2001-02-08

439

A Genetic Robot Path Planner with Fuzzy Logic Adaptation  

Microsoft Academic Search

The paper develops a combined genetic algorithm and fuzzy logic approach to path planning for a mobile robot operating in rough environments. Path planning consists of a description of the environment using a fuzzy logic framework, and a two-stage planner. A global planner determines the path that optimizes a combination of terrain roughness and path curvature. A local planner uses

Mahmoud Tarokh

2007-01-01

440

Off-axis paths in spherical mirror interferometers  

Microsoft Academic Search

vO = 24r, and g being integers, the rays retrace their paths. These ray paths give rise to additional resonances which were observed. Pictures of the points of reflection are reproduced. The theory is in good agreement with the experi- mental observations. In laser amplifiers these ray paths enable one to obtain long effective path lengths in the active medium

D. Herriott; H. Kogelnik; R. Kompfner

1964-01-01

441

Fermionic path integrals and local anomalies  

NASA Astrophysics Data System (ADS)

No doubt, the subject of path integrals proved to be an immensely fruitful human, i.e. Feynman's idea. No wonder it is more timely than ever. Some even claim that it is the most daring, innovative and revolutionary idea since the days of Heisenberg and Bohr. It is thus likely to generate enthusiasm, if not addiction among physicists who seek simplicity together with perfection. Professor Devreese's long-lasting interest in, if not passion on the subject stems from his firm conviction that, beyond being the tool of choice, path integration provides the key to all quantum phenomena, be it in solid state, atomic, molecular or particle physics as evidenced by the impressive list of publications at the address http://lib.ua.ac.be/AB/a867.html. In this note, I review a pitfall of fermionic path integrals and a way to get around it in situations relevant to the Standard Model of particle physics.

Roepstorff, G.

2003-05-01

442

Molecular path control in zeolite membranes  

PubMed Central

We report molecular simulations of diffusion in confinement showing a phenomenon that we denote as molecular path control (MPC); depending on loading, molecules follow a preferred pathway. MPC raises the important question to which extent the loading may affect the molecular trajectories in nanoporous materials. Through MPC one is able to manually adjust the ratio of the diffusivities through different types of pores, and as an application one can direct the flow of diffusing particles in membranes forward or sideward by simply adjusting the pressure, without the need for mechanical parts like valves. We show that the key ingredient of MPC is the anisotropic nature of the nanoporous material that results in a complex interplay between different diffusion paths as a function of loading. These paths may be controlled by changing the loading, either through a change in pressure or temperature.

Dubbeldam, D.; Beerdsen, E.; Calero, S.; Smit, B.

2005-01-01

443

Quickest Paths for Different Network Router Mechanisms  

SciTech Connect

The quickest path problem deals with the transmission of a message of size {sigma} from a source to a destination with the minimum end-to-end delay over a network with bandwidth and delay constraints on the links. The authors consider four basic modes and two variations for the message delivery at the nodes reflecting the mechanisms such as circuit switching, Internet protocol, and their combinations. For each of the first three modes, they present O(m{sup 2} + mn log n) time algorithm to compute the quickest path for a given message size {sigma}. For the last mode, the quickest path can be computed in O(m + n log n) time.

Rao, N.S.V.; Grimmell, W.C.; Radhakrishnan, S.; Bang, Y.C.

2000-06-01

444

Quantum state of wormholes and path integral  

SciTech Connect

The quantum state of a wormhole can be represented by a path integral over all asymptotically Euclidean four-geometries and all matter fields which have prescribed values, the arguments of the wave function, on a three-surface {ital S} which divides the spacetime manifold into two disconnected parts. The ground-state wave function is picked out by requiring that there be no matter excitations in the asymptotic region. Once the path integrals over the lapse and shift functions are evaluated, the requirement that the spacetime be asymptotically Euclidean can be accomplished by fixing the asymptotic gravitational momentum in the remaining path integral. It is claimed that no wave function exists which corresponds to asymptotic field configurations such that the effective gravitational constant is negative in the asymptotic region. The wormhole wave functions are worked out in minisuperspace models with massless minimal and conformal scalar fields.

Garay, L.J. (Instituto de Optica, Consejo Superior de Investigaciones Cientificas, Serrano 121, E-28006 Madrid (Spain))

1991-08-15

445

Transition-path sampling of -hairpin folding  

NASA Astrophysics Data System (ADS)

We examine the dynamical folding pathways of the C-terminal -hairpin of protein G-B1 in explicit solvent at room temperature by means of a transition-path sampling algorithm. In agreement with previous free-energy calculations, the resulting path ensembles reveal a folding mechanism in which the hydrophobic residues collapse first followed by backbone hydrogen-bond formation, starting with the hydrogen bonds inside the hydrophobic core. In addition, the path ensembles contain information on the folding kinetics, including solvent motion. Using the recently developed transition interface sampling technique, we calculate the rate constant for unfolding of the protein fragment and find it to be in reasonable agreement with experiments. The results support the validation of using all-atom force fields to study protein folding.

Bolhuis, Peter G.

2003-10-01

446

Information Flow Analysis via Path Condition Refinement  

NASA Astrophysics Data System (ADS)

We present a new approach to information flow control (IFC), which exploits counterexample-guided abstraction refinement (CEGAR) technology. The CEGAR process is built on top of our existing IFC analysis in which illegal flows are characterized using program dependence graphs (PDG) and path conditions (as described in [12]). Although path conditions provide an already precise abstraction that can be used to generate witnesses to the illegal flow, they may still cause false alarms. Our CEGAR process recognizes false witnesses by executing them and monitoring their executions, and eliminates them by automatically refining path conditions in an iterative way as needed. The paper sketches the foundations of CEGAR and PDG-based IFC, and describes the approach in detail. An example shows how the approach finds illegal flow, and demonstrates how CEGAR eliminates false alarms.

Taghdiri, Mana; Snelting, Gregor; Sinz, Carsten

447

Better understanding of the species with the shortest Re2(6+) bonds and related Re2)(7+) species with tetraguanidinate paddlewheel structures.  

PubMed

A series of compounds has been made containing quadruply bonded Re2(hpp)4X2 species (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2a]pyrimidine), where X is CF3SO3 (1), CF3CO2 (2), and F (3). The distances of 2.1562(7), 2.1711(5), and 2.1959(4) A for 1-3 show significant effects of the sigma and pi electron donating ability of the axial ligands on the metal-metal distance. With the weakly coordinating triflate ligand the Re-Re distance is the shortest for any quadruple bonded species known. In addition to examining the effects of axial ligands on the Re2(hpp)42+ core, our study of the Re2(hpp)43+ core is being extended beyond the preliminary results previously reported in only one compound [Re2(hpp)4Cl2]PF6 (Dalton Trans. 2003, 1218). We now report the structural characterization by both X-ray and neutron diffraction of the compound [Re2(hpp)4F](TFPB)2, 4 (TFPB = the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), and a detailed study by EPR spectroscopy of [Re2(hpp)4Cl2]PF6 at 9.5, 34.5, and 95 GHz frequencies, using dilute fluid solutions, frozen glass, and neat powder, show that the unpaired electron in the [Re2(hpp)4Cl2]+ ion is in an MO of predominant metal character with little mixing from the guanidinate ligands. PMID:17243673

Cotton, F Albert; Dalal, Naresh S; Huang, Penglin; Ibragimov, Sergey A; Murillo, Carlos A; Piccoli, Paula M B; Ramsey, Chris M; Schultz, Arthur J; Wang, Xiaoping; Zhao, Qinliang

2007-01-23

448

Non-intrusive end-to-end runtime path tracing for J2EE systems  

Microsoft Academic Search

An end-to-end runtime path-tracing approach for J2EE systems has been introduced. The approach is non-intrusive and thus does not require instrumentation of middleware or application source code. The implementation of the system has been realised in the COMPAS Java end-to-end monitoring tool that extends and integrates a number of open source projects. The first set of results shows the performance

T. Parsons; A. Mos; J. Murphy

2006-01-01

449

Augmenting Scan Path SRLs with an XOR Network to Enhance Delay Fault Testing  

Microsoft Academic Search

In this paper, we present a technique to enhance transition delay and stuck-open fault testing in an LSSD environment. To reduce shift dependency in the scan path, thereby improving transition quality, a re-arrangement heuristic combined with a one level XOR network is proposed. The method is hierarchical, combining a simple re-arrangement, heuristic driven local reconfiguration, and finally a circuit modification

Zaifu Zhang; Robert D. Mcleod; Witold Pedrycz

1994-01-01

450

Path planning for everday robotics with SANDROS  

SciTech Connect

We discuss the integration of the SANDROS path planner into a general robot simulation and control package with the inclusion of a fast geometry engine for distance calculations. This creates a single system that allows the path to be computed, simulated, and then executed on the physical robot. The architecture and usage procedures are presented. Also, we present examples of its usage in typical environments found in our organization. The resulting system is as easy to use as the general simulation system (which is in common use here) and is fast enough (example problems are solved in seconds) to be used interactively on an everyday basis.

Watterberg, P.; Xavier, P. [Sandia National Labs., Albuquerque, NM (United States); Hwang, Y. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of)

1997-02-01

451

Practical path planning among movable obstacles  

SciTech Connect

Path planning among movable obstacles is a practical problem that is in need of a solution. In this paper an efficient heuristic algorithm that uses a generate-and-test paradigm: a good'' candidate path is hypothesized by a global planner and subsequently verified by a local planner. In the process of formalizing the problem, we also present a technique for modeling object interactions through contact. Our algorithm has been tested on a variety of examples, and was able to generate solutions within 10 seconds. 5 figs., 27 refs.

Chen, Pang C.; Hwang, Yong K.

1990-09-05

452

Creativity, Spirituality, and Transcendence: Paths to Integrity and Wisdom in the Mature Self. Publications in Creativity Research.  

ERIC Educational Resources Information Center

|This book contains 11 papers on creativity, spirituality, and transcendence as paths to integrity and wisdom in the mature self. The book begins with the paper "Introduction--Creativity in Adulthood: Personal Maturity and Openness to Extraordinary Sources of Inspiration" (Susanne R. Cook-Greuter, Melvin E. Miller). The next four papers, which…

Miller, Melvin E., Ed.; Cook-Greuter, Susanne R., Ed.

453

An exploratory look at supermarket shopping paths  

Microsoft Academic Search

We present analyses of an extraordinary new dataset that reveals the path taken by individual shoppers in an actual grocery store, as provided by RFID (radio frequency identification) tags located on their shopping carts. The analysis is performed using a multivariate clustering algorithm not yet seen in the marketing literature that is able to handle data sets with unique (and

Jeffrey S. Larson; Eric T. Bradlow; Peter S. Fader

2005-01-01

454

A Random Sampling Scheme for Path Planning  

Microsoft Academic Search

Several randomized path planners have been proposed dur ing the last few years. Their attractiveness stems from their applicability to virtually any type of robots, and their empir ically observed success. In this article, we attempt to present a unifying view of these planners and to theoretically explain their success. First, we introduce a general planning scheme that consists of

Jérôme Barraquand; Lydia E. Kavraki; Jean-claude Latombe; Tsai-yen Li; Rajeev Motwani; Prabhakar Raghavan

1997-01-01

455

Graph Minors .XIII. The Disjoint Paths Problem  

Microsoft Academic Search

We describe an algorithm, which for fixed k ? 0 has running time O(|V(G)|3), to solve the following problem: given a graph G and k pairs of vertices of G, decide if there are k mutually vertex-disjoint paths of G joining the pairs.

Neil Robertson; Paul D. Seymour

1995-01-01

456

DPDAT: data path direct access testing  

Microsoft Academic Search

Data Path Direct Access Test, DPDAT, supports efficient structural test of targeted datapath blocks using existing non-datapath DFT features in conjunction with architectural transparency already present in surrounding datapath blocks. This new DFT technique allows ATPG patterns generated at logic block levels to be applied at the full chip without expensive DFT overhead. The results of investigating feasibility on Intel(R)

Kee Sup Kim; Rathish Jayabharathi; Craig Carstens; Praveen Vishakantaiah; Derek Feltham; Adrian Carbine

2001-01-01

457

Applications of Path Compression on Balanced Trees  

Microsoft Academic Search

Several fast algorithms are presented for computing functions defined on paths in trees under various assumpuons. The algorithms are based on tree mampulatton methods first used to efficiently represent equivalence relations. The algorithms have O((m + n)a(m + n, n)) running tunes, where m and n are measures of the problem size and a Is a functional reverse of Ackermann's

Robert Endre Tarjan

1979-01-01

458

SILK: Scout Paths in the Linux Kernel  

Microsoft Academic Search

SILK stands for Scout In the Linux Kernel, and is a port of the Scout operating system to run as a Linux kernel mod- ule. SILK forms a replacement networking subsystem for standard Linux 2.4 kernels. Linux applications create and use Scout paths via the Linux socket interface with virtually no modifications to the applications themselves. SILK pro- vides Linux

Andy Bavier; Thiemo Voigt; Mike Wawrzoniak; Larry Peterson; Per Gunningberg

2001-01-01

459

Path instability of a rising bubble  

NASA Astrophysics Data System (ADS)

Path instability of a rising bubble is studied by carrying out DNS around a freely moving ellipsoidal bubble with a prescribed aspect ratio. The flow field is obtained by solving the full Navier-Stokes equations and the velocity and rotation rate of the bubble are found by solving the Kirchhoff equations in a form suitable to vortical flows. The problem has two control parameters, ie the aspect ratio K and the Galileo number Ga. Beyond a certain critical value K(Ga) or Ga(K), the path of the bubble first bifurcates towards a plane zigzag whose geometrical characteristics are in good agreement with experimental observations. Detailed examination reveals that the transition to the zigzag path occurs through a supercritical Hopf bifurcation when K is set fixed, while it occurs through a more complex process when Ga is set fixed. Ultimately, the zigzag degenerates into a fully helical trajectory, as observed in experiments. Examining the vorticity field reveals a one-to-one correspondance between the topology of the wake and the nature of the path. The competition between creation of vorticity at the bubble surface and evacuation in the wake allows us to propose a consistent scenario for explaining physically the observed transitions.

Magnaudet, Jacques; Mougin, Guillaume

2001-11-01

460

Dynamic path-based software watermarking  

Microsoft Academic Search

Software watermarking is a tool used to combat software piracy by embedding identifying information into a program. Most existing proposals for software watermarking have the shortcoming that the mark can be destroyed via fairly straightforward semantics-preserving code transformations. This paper introduces path-based watermarking, a new approach to software watermarking based on the dynamic branching behavior of programs. The advantage of

C. Collberg; E. Carter; S. Debray; A. Huntwork; J. Kececioglu; C. Linn; M. Stepp

2004-01-01

461

Issues affecting specialty career paths in dermatology.  

PubMed

As the field of medicine changes, physicians deal with ever-increasing challenges and pressures. An overview of broad career paths within the specialty of dermatology is presented and important issues affecting these subspecialty tracks are discussed. These issues include increasing regulatory controls, the medical liability crisis, competitive forces, corporate and global outsourcing threats, managed care, and reimbursement. PMID:18189057

Leonard, Aimee L; Hanke, C William; Bechtel, Mark A; Brownell, Isaac; Buckel, Larry J; Hurwitz, Robert M; Hsiung, Sherry H; Paller, Amy S; Turchan, Kirsten

2007-12-01

462

Folded-path optical analysis gas cell  

DOEpatents

A folded-path gas cell employs an elliptical concave mirror in confronting relationship to two substantially spherical concave mirrors. At least one of the spherical mirrors, and usually both, are formed with an added cylindrical component to increase orthogonal focii coincidence and thereby to increase the radiation energy throughput characteristic of the cell.

Carangelo, Robert M. (Glastonbury, CT); Wright, David D. (Vershire, VT)

1995-01-01

463

Judgments of Path, Not Heading, Guide Locomotion  

Microsoft Academic Search

To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient control solution.

Richard M. Wilkie; John P. Wann

2006-01-01

464

VIPER: an efficient vigorously sensitizable path extractor  

Microsoft Academic Search

Fast and correct timing verification is a critical issue in VLSI design. Several tim-ing verification algorithms have been proposed in the last few years. However, due to the huge computation time needed to eliminate false paths, existing algorithms have difficulty in performing timing verification for large circuits. This paper presents an efficient timing verification algorithm, with a new sensitization criterion,

Hoon Chang; Jacob A. Abraham

1993-01-01

465

LONG PATH LASER OZONE MONITOR EVALUATION  

EPA Science Inventory

The purpose of the study reported here was to evaluate a long path laser air pollution monitor developed for the U.S. Environmental Protection Agency (EPA) by the General Electric (GE) Company. The monitor was known as ILAMS (Infrared Laser Atmospheric Monitoring System) and desi...

466

A Modal Perspective on Path Constraints  

Microsoft Academic Search

We analyze several classes of path constraints for semistructured data and prove a umber of decidability and complexity results for such constraints. While some of these decidability results were known before, we believe that our improved complexity bounds are new. Our proofs are based on techniques from modal logic and automata theory. We believe that our modal logic perspective sheds

Natasha Alechina; Stéphane Demri; Maarten De Rijke

2003-01-01

467

Animation: Path of 2010 Solar Eclipse  

NASA Video Gallery

On Sunday, 2010 July 11, a total eclipse of the Sun is visible from within a narrow corridor that traverses Earth's southern hemisphere. The path of the Moon's umbral shadow crosses the South Pacific Ocean where it makes no landfall except for Mangaia (Cook Islands) and Easter Island (Isla de Pascua).

Jim Wilson

2010-07-09

468

Parallel Path Planning with Multiple Evasion Strategies  

Microsoft Academic Search

Probabilistic path planning driven by a potential eld is a well established technique and has been successfully ex- ploited to solve complex problems arising in a variety of domains. However, planners implementing this approach are rather inecient in dealing with certain types of lo- cal minima occurring in the potential eld, especially those characterized by deep or large attraction basins.

Stefano Caselli; Monica Reggiani; Roberto Sbravati

2002-01-01

469

Scanning path optimization for ultrasound surgery  

Microsoft Academic Search

One of the problems in ultrasound surgery is the long treatment times when large tumour volumes are sonicated. Large tumours are usually treated by scanning the tumour volume using a sequence of individual focus points. During the scanning, it is possible that surrounding healthy tissue suffers from undesired temperature rise. The selection of the scanning path so that the tumour

Matti Malinenyx; Tomi Huttunen; Jari P. Kaipio; Kullervo Hynynen

2005-01-01

470

14 CFR 25.111 - Takeoff path.  

Code of Federal Regulations, 2010 CFR

...500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In additionâ (1) The takeoff path must be based on the procedures prescribed...

2010-01-01

471

14 CFR 25.111 - Takeoff path.  

Code of Federal Regulations, 2010 CFR

...500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In additionâ (1) The takeoff path must be based on the procedures prescribed...

2009-01-01

472

Judgments of Path, Not Heading, Guide Locomotion  

ERIC Educational Resources Information Center

To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient…

Wilkie, Richard M.; Wann, John P.

2006-01-01

473

The Critical Path Program in Taiwan  

Microsoft Academic Search

Taiwan's Critical Path Program facilitates the development process for niche products of new drug and medical devices. The program fosters a favorable regulatory environment by establishing guidance systems and identifying selected index cases for successful stories through achievement-based proactive consultation. A total of 27 index cases were selected from a total of 68 cases submitted. Two index cases have been

Bing Bing Lin; Chih-Hwa Lin; Herng-Der Chern

2009-01-01

474

First Order Paths in Ordered Trees  

Microsoft Academic Search

We give two sucient conditions on XPath like languages for having first order expressivity, meaning that every first order defin- able set of paths in an ordered node-labeled tree is definable in that XPath language. They are phrased in terms of expansions of naviga- tional (sometimes called \\

Maarten Marx

2005-01-01

475

Ambivalent Journey: Teacher Career Paths in Oman  

ERIC Educational Resources Information Center

|This study investigated the career paths of 625 university graduates who prepared to be secondary school teachers in Oman, their assessment of their current work situation, and the extent to which their initial commitment to teaching was related to their subsequent career satisfaction and intention to remain in teaching. While nearly all…

Chapman, David W.; Al-Barwani, Thuwayba; Al Mawali, Fathiya; Green, Elizabeth

2012-01-01

476

Air Path Estimation on Diesel HCCI Engine  

Microsoft Academic Search

In this paper, we address the problem of air path variables estimation for an HCCI engine. Two observers are pro- posed. Both rely on physical assumptions on the com- bustion, but use different sensors. After proving conver- gence in the two cases, we carry out comparisons based on simulation results. We stress the impact of two particu- lar additional sensors

J. Chauvin; N. Petit; P. Rouchon; C. Vigild; Ford Forschungszentrum Aachen

2006-01-01

477

Free Path Lengths in Quasi Crystals  

NASA Astrophysics Data System (ADS)

The Lorentz gas is a model for a cloud of point particles (electrons) in a distribution of scatterers in space. The scatterers are often assumed to be spherical with a fixed diameter d, and the point particles move with constant velocity between the scatterers, and are specularly reflected when hitting a scatterer. There is no interaction between point particles. An interesting question concerns the distribution of free path lengths, i.e. the distance a point particle moves between the scattering events, and how this distribution scales with scatterer diameter, scatterer density and the distribution of the scatterers. It is by now well known that in the so-called Boltzmann-Grad limit, a Poisson distribution of scatterers leads to an exponential distribution of free path lengths, whereas if the scatterer distribution is periodic, the free path length distribution asymptotically behaves as a power law. This paper considers the case when the scatters are distributed on a quasi crystal, i.e. non periodically, but with a long range order. Simulations of a one-dimensional model are presented, showing that the quasi crystal behaves very much like a periodic crystal, and in particular, the distribution of free path lengths is not exponential.

Wennberg, Bernt

2012-06-01