•Capacity weighted spectral partitioning is used to find capacity bottlenecks in transport networks.•The significance of the second smallest eigen value and corresponding vector of the graph ...Laplacian (normalized or otherwise) is explained.•An improvement to Cheeger's inequality is derived.•Results are presented for a 5-node illustrative example, the Sioux Falls road network and the Gifu Prefecture road network.•A new method is offered for transport planners and network designers to identify potential transport network bottlenecks in the absence of demand information.
Transport networks operating at or near capacity are vulnerable to disruptions, so flow bottlenecks are potent sources of vulnerability. This paper presents an efficient method for finding transport network cuts, which may constitute such bottlenecks. Methods for assessing network vulnerability found in the literature require origin-destination demands and path assignment. However, in transport network planning and design, demand information is often missing, out of date, partial or inaccurate. Capacity weighted spectral partitioning is proposed to identify potential flow bottlenecks in the network, without reference to demand information or path assignments. This method identifies the network cut with least capacity, taking into account the relative sizes of the sub-networks either side of the cut. Spectral analysis has the added advantage of tractability, even for large networks, as shown by numerical examples for a five-node illustrative example, the Sioux Falls road network and the Gifu Prefecture road network.
•Recent research on cybersecurity in logistics and supply chain is reviewed.•Research on cybersecurity in logistics and supply chain is in its early stages.•Research on cybersecurity in logistics ...management is insufficient.•Studies on real-time recovery and aftermath measures are scarce.•Blockchain is in its infancy in the transport and logistics sector.
Technological applications have increasingly improved the quality of services in the logistics industry. However, the adoption of internet-based technologies has increased the attack surface in the logistics environment. Such attacks could negatively impact both logistics and overall supply chain performance. This paper reviews studies on measures that enhance cybersecurity in logistics and supply chain management. Several key findings and potential research directions are presented in relation to research on cybersecurity in logistics and supply chain management. These findings are: (1) Existing studies rarely use real cybersecurity data; (2) Studies focusing on cybersecurity in logistics are scarce although logistics plays an important role in supply chains; (3) There is only a limited number of papers adopting quantitative research approaches to study cybersecurity in logistics and supply chain management; (4) While a few studies focus on real-time recovery and aftermath measures, most studies focus on precautionary measures; (5) Blockchain technologies are still in their infancy in the transport and logistics sector; (6) Most studies use one-way encryption schemes that overlook the potential threats in a future dominated by quantum computing techniques; (7) Studies on information security and digital forensic investigation are scarce.
This paper proposes an equilibrium model to characterize the bilateral searching and meeting between customers and taxis on road networks. A taxi driver searches or waits for a customer by ...considering both the expected searching or waiting time cost and ride revenue, and a customer seeks a taxi ride to minimize full trip price. We suppose that the bilateral taxi–customer searching and meeting occurs anywhere in residential and commercial zones or at prescribed taxi stands, such as an airport or a railway station. We propose a meeting function to spell out the search and meeting frictions that arise endogenously as a result of the distinct spatial feature of the area and the taxi–customer moving decisions. With the proposed meeting function and the assumptions underlying taxi–customer search behaviors, the stationary competitive equilibrium achieved at fixed fare prices is determined when the demand of the customers matches the supply of taxis or there is market clearing at the prevailing searching and waiting times in every meeting location. We establish the existence of such an equilibrium by virtue of Brouwer’s fixed-point theorem and demonstrate its principal operational characteristics with a numerical example.
I begin by revisiting Lawrence’s reading of Dana’s Two Years before the Mast reading it not as a critique of Dana but as a Lawrencian fiction in which the sea plays a central symbolic role. As ...Lawrence reflects on the vital relation of the human and the non-human, the sea seems to represent its destructive possibilities which Dana and Melville variously encounter, and thereby allow Lawrence to explore. In the Dana essay it is especially necessary, but not easy, to hold in focus the competing levels of the literal and scientific, on the one hand, and the metaphorical and visionary on the other. Sometimes the relation is strained as I suggest occurs in the flogging episode but this double vision is the basis for appreciating Lawrence’s representation of the sea.
This paper proposes a frequency-based assignment model that considers travellers probability of finding a seat in their perception of route cost and hence also their route choice. The model ...introduces a “fail-to-sit” probability at boarding points with travel costs based on the likelihood of travelling seated or standing. Priority rules are considered; in particular it is assumed that standing on-board passengers will occupy any available seats of alighting passengers before newly boarding passengers can fill any remaining seats. At the boarding point passengers are assumed to mingle, meaning that FIFO is not observed, as is the case for many crowded bus and metro stops, particularly in European countries. The route choice considers the common lines problem and an user equilibrium solution is sought through a Markov type network loading process and the method of successive averages. The model is first illustrated with a small example network before being applied to the inner zone of London’s underground network. The effect of different values passengers might attach to finding a seat are illustrated. Applications of the model for transit planning as well as for information provision at the journey planner stage are discussed.
•This paper addresses the issue of cyber security in logistics management.•A budget constrained demon game is proposed against a quantal response adversary.•The proposed demon game model addresses ...the issue of asset dependency in a network.•The solution is a strategy for defending assets in a digital logistics network.•A method of successive average based algorithm is developed to solve the model.
Interest in cyber security in logistics and supply chain management has grown, but this has not been matched by academic research. Increasingly, the logistics industry is implementing the Internet-of-Things (IoT), namely sensors and actuators, to collect data, process orders and deliver materials and/or products. This automation reduces human errors in processing orders and enhances the efficiency of order deliveries. However, this can be interrupted by attacks from cyberspace, especially from the Internet. In this paper, we propose a novel attacker–defender model against a quantal response (QR) adversary to protect critical assets by considering the defending budget and the asset dependency. Each asset in the solution is represented by its security level indicating its desirability for being protected. Due to the non-convexity of our model, we propose a Method of Successive Average heuristic with randomised initial conditions (MSAR) to obtain a promising solution.
•A new location-routing problem with pick-up stations (LRP-PS) is proposed.•Two extend models of LRP-PS after relaxing the two strategies are provided.•Some properties of the LRP-PS optimal solution ...are proved.•A branch-and-price algorithm is developed to solve the LRP-PS exactly.
In catering to the needs of the growing e-commerce demand and environmentally friendly urban delivery solutions, package delivery companies are increasingly focusing on user experience and sustainable operations, such as alternative delivery methods (e.g., pick-up stations) and green delivery vehicles (e.g., electric vehicles). We consider designing a location-routing problem with pick-up stations (LRP-PS) where the location of pick-up stations to open and the delivery plan of green vehicles (GVs) are optimized simultaneously. The purpose is to satisfy the total demand while minimizing the sum of opening cost and handling cost of pick-up stations and the fixed cost and routing cost of GVs. Then, we present a compact mixed-integer programming formulation to define the LRP-PS and reveal some interesting properties of the optimal solution. We propose an effective branch-and-price (B&P) algorithm to solve the LRP-PS, which is demonstrated to outperform greatly commercial branch-and-cut solvers such as CPLEX in the computational study. Finally, through a comprehensive analysis of several key parameters (e.g., coverage ranges of pick-up stations and battery driving ranges of GVs), we assess the impact of pick-up stations on this last-mile distribution system and provide some helpful business insights for package delivery companies.
Abstract
Quantifying air–sea exchanges of enthalpy and momentum is important for understanding and skillfully predicting tropical cyclone intensity, but the magnitude of the corresponding wind ...speed–dependent bulk exchange coefficients is largely unknown at major hurricane wind speeds greater than 50 m s−1. Since direct turbulent flux measurements in these conditions are extremely difficult, the momentum and enthalpy fluxes were deduced via absolute angular momentum and total energy budgets. An error analysis of the methodology was performed to quantify and mitigate potentially significant uncertainties resulting from unresolved budget terms and observational errors. An analysis of six missions from the 2003 Coupled Boundary Layers Air–Sea Transfer (CBLAST) field program in major hurricanes Fabian and Isabel was conducted using a new variational technique. The analysis indicates a near-surface mean drag coefficient CD of 2.4 × 10−3 with a 46% standard deviation and a mean enthalpy coefficient CK of 1.0 × 10−3 with a 40% standard deviation for wind speeds between 52 and 72 m s−1. These are the first known estimates of CK and the ratio of enthalpy to drag coefficient CK/CD in major hurricanes. The results suggest that there is no significant change in the magnitude of the bulk exchange coefficients estimated at minimal hurricane wind speeds, and that the ratio CK/CD does not significantly increase for wind speeds greater than 50 m s−1.
This paper studies job assignments for automated guided in container terminal settings under various conditions of uncertainty. An introduction to their operation is provided, along with a flexible ...dispatching algorithm, suitable for real-time control of AGVs. Using these concepts a new AGV dispatching approach is developed, capable of operating under uncertain conditions within a detailed container terminal model. Several performance indicators are presented, focused on generic features of vehicle operations as well the assessment of uncertainty levels inside the terminal. From the results of the simulation experiments, it is found that the proposed technique outperforms well known heuristics and alternative algorithms.
•The largest eigenvalue of the weighted adjacency matrix measures network connectivity.•Adding a link always increases the largest eigenvalue of the adjacency matrix.•A max-min integer optimization ...model is proposed to maximize the largest eigenvalue.•Results for the world container shipping network are presented.•First to use the eigenvector centrality to improve shipping network connectivity.
Container shipping accounts for most of the world merchandise trade. Better maritime connectivity leads to lower freight rates and greater economic growth. This paper presents a novel max–min integer optimization model to facilitate better shipping network connectivity by analysing the largest eigenvalue and its corresponding eigenvector of the (asymmetric) frequency weighted adjacency matrix. An algorithm is presented that can quickly identify which link not currently in the container shipping network would best improve its connectivity. A demand matrix is not required by this method of analysis and network symmetry is not assumed. The method could strengthen direct connection between port pairs.
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