Designing a road network for hazardous materials shipments

Cataloged from PDF version of article.We consider the problem of designating hazardous materials routes in and through a major population center. Initially, we restrict our attention to a minimally connected network (a tree) where we can predict accurately the flows on the network. We formulate the tree design problem as an integer programming problem with an objective of minimizing the total transport risk. Such design problems of moderate size can be solved using commercial solvers. We then develop a simple construction heuristic to expand the solution of the tree design problem by adding road segments. Such additions provide carriers with routing choices, which usually increase risks but reduce costs. The heuristic adds paths incrementally, which allows local authorities to trade off risk and cost. We use the road network of the city of Ravenna, Italy, to demonstrate the solution of our integer programming model and our path-addition heuristic. © 2005 Elsevier Ltd. All rights reserved

Accurate Calculation of Hazardous Materials Transport Risks

Cataloged from PDF version of article.We propose two path-selection algorithms for the transport of hazardous materials. The algorithms can deal with link impedances that are path-dependent. This approach is superior to the use of a standard shortest path algorithm, common in the literature and practice, which results in inaccuracies

The Network Design Problem with Relays

Cataloged from PDF version of article.The network design problem with relays (NDPR) is defined on an undirected graph G = (V,E,K), where V = {1,...,n} is a vertex set, E = {(i,j):i,j 2 V,i < j} is an edge set. The set K = {(o(k),d(k))} is a set of communication pairs (or commodities): o(k) 2 V and d(k) 2 V denote the origin and the destination of the kth commodity, respectively. With each edge (i,j) are associated a cost cij and a length dij. With vertex i is associated a fixed cost fi of locating a relay at i. The NDPR consists of selecting a subset E of edges of E and of locating relays at a subset V of vertices of V in such a way that: (1) the sum Q of edge costs and relay costs is minimized; (2) there exists a path linking the origin and the destination of each commodity in which the length between the origin and the first relay, the last relay and the destination, or any two consecutive relays does not exceed a preset upper bound k. This article develops a lower bound procedure and four heuristics for the NPDR. These are compared on several randomly generated instances with |V| 6 1002 and |E| 6 1930. 2006 Elsevier B.V. All rights reserved

On the X-Ray Light Curve, Pulsed-Radio Emission, and Spin Frequency Evolution of the Transient Anomalous X-Ray Pulsar Xte J1810--197 During its X-Ray Outburst

We show that: (i) the long-term X-ray outburst light curve of the transient AXP XTE J1810-197 can be accounted for by a fallback disk that is evolving towards quiescence through a disk instability after having been heated by a soft gamma-ray burst, (ii) the spin-frequency evolution of this source in the same period can also be explained by the disk torque acting on the magnetosphere of the neutron star, (iii) most significantly, recently observed pulsed-radio emission from this source coincides with the epoch of minimum X-ray luminosity. This is natural in terms of a fallback disk model, as the accretion power becomes so low that it is not sufficient to suppress the beamed radio emission from XTE J1810-197.Comment: 13 pages, 2 Figures, accepted for publication in Ap

The cost and risk impacts of rerouting railroad shipments of hazardous materials

Cataloged from PDF version of article.Rail shipments of hazardous materials expose the population near the routes to the possibility of an accident resulting in a spill. Rail routes are determined by economic concerns such as route length and the revenue generated for the originating carrier. In this paper we consider an alternate routing strategy that takes accident risks into account. We employ a model to quantify rail transport risk and then use a weighted combination of cost and risk and generate alternate routes. In some cases the alternate routes achieve significantly lower risk values than the practical routes at a small incremental cost. While there are generally fewer rerouting alternatives for rail than for road transport, considering the possible consequences of a train derailment we argue that risk should be taken into account when selecting rail routes and that the cost–risk tradeoffs should be evaluated. © 2007 Elsevier Ltd. All rights reserved

How to unravel pathbreaking trajectories in the left-behind areas of Istanbul?

Entrepreneurial and growth-oriented urban development models see left-behind areas as opportunities in need of redevelopment and upgrading, which can be subjected to speculation. We argue that pathbreaking trajectories emerge during this redevelopment process in distinct ways depending on the adaptive capacity of urban communities and flexibility in the planning practices. Focusing on the squatter areas in Istanbul, we map out pathbreaking trajectories in institutional and policy contexts and unravel societal responses. We conclude that the authoritarian entrepreneurial governance landscape operates in a dual context in which its impacts on re-politicization of urban communities and their engagement with policy networks can vary.</p

Designing a road network for hazardous materials shipments

We consider the problem of designating hazardous materials routes in and through a major population center. Initially, we restrict our attention to a minimally connected network (a tree) where we can predict accurately the flows on the network. We formulate the tree design problem as an integer programming problem with an objective of minimizing the total transport risk. Such design problems of moderate size can be solved using commercial solvers. We then develop a simple construction heuristic to expand the solution of the tree design problem by adding road segments. Such additions provide carriers with routing choices, which usually increase risks but reduce costs. The heuristic adds paths incrementally, which allows local authorities to trade off risk and cost. We use the road network of the city of Ravenna, Italy, to demonstrate the solution of our integer programming model and our path-addition heuristic. © 2005 Elsevier Ltd. All rights reserved

A possible optical counterpart of the X-ray source NuSTARJ053449+2126.0

In this work, we report the observation of a possible optical counterpart to the recently discovered X-ray source NuSTAR J053449+2126.0. To search for an optical counterpart of NuSTAR J053449+2126.0 (J0534 in short), we observed the source with the 1.5-m Telescope (RTT150). Using the B, V, R, and I images of J0534, we detected the possible optical counterpart of J0534 and determined, based on our spectral analysis, the source distance for the first time. J0534 could be a high-redshift member of an Active Galactic Nucleus (AGN) sub-group identified as a quasar. Our analysis favours an accreting black hole of mass $\sim 7\times 10^8 M_{\odot}$ as a power supply for the quasar in J0534. Further observations in optical and other wavelengths are needed to confirm its nature.Comment: 7 pages, 4 figure

Solving the hazmat transport network design problem

In this paper, we consider the problem of network design for hazardous material transportation where the government designates a network, and the carriers choose the routes on the network. We model the problem as a bilevel network flow formulation and analyze the bilevel design problem by comparing it to three other decision scenarios. The bilevel model is difficult to solve and may be ill-posed. We propose a heuristic solution method that always finds a stable solution. The heuristic exploits the network flow structure at both levels to overcome the difficulty and instability of the bilevel integer programming model. Testing on real data shows that the linearization of the bilevel model fails to find stable solutions and that the heuristic finds lower risk networks in less time. Further testing on random instances shows that the heuristically designed networks achieve significant risk reduction over single-level models. The risk is very close to the least risk possible. However, this reduction in risk comes with a significant increase in cost. We extend the bilevel model to account for the cost/risk trade-off by including cost in the first-level objective. The biobjective-bilevel model is a rich decision-support tool that allows for the generation of many good solutions to the design problem. © 2006 Elsevier Ltd. All rights reserved

Integrated routing and scheduling of hazmat trucks with stops en route

We consider an integrated routing and scheduling problem in hazardous materials transportation where accident rates, population exposure, and link durations on the network vary with time of day. We minimize risk (accident probability multiplied by exposure) subject to a constraint on the total duration of the trip. We allow for stopping at the nodes of the network. We consider four versions of this problem with increasingly more realistic constraints on driving and waiting periods, and propose pseudopolynomial dynamic programming algorithms for each version. We use a realistic example network to experiment with our algorithms and provide examples of the solutions they generate. The computational effort required for the algorithms is reasonable, making them good candidates for implementation in a decision-support system. Many of the routes generated by our models do not exhibit the circuitous behavior common in risk-minimizing routes. The en route stops allow us to take full advantage of the time-varying nature of accident probabilities and exposure and result in the generation of routes that are associated with much lower levels of risk than those where no waiting is allowed. © 2007 INFORMS