User Heterogeneity and Bi-criteria System Optimum

For a traffic network with fixed demand of heterogeneous users in terms of their different values of time (VOT), the system performance can be measured either in time unit by the total system travel time (in short, system time), or in monetary unit by the total system travel cost (in short, system cost). Thus we have two different objectives for network optimization, i.e., to minimize system time and to minimize system cost, which naturally gives rise to a bi-objective minimization problem. A Pareto optimum of this bi-objective optimization problem represents a bi-criteria system optimum for network optimization in the sense that, at each Pareto optimum, neither system time nor system cost can be further reduced without increasing the other one. In this paper, we prove that any Pareto optimum can be decentralized into multi-class user equilibrium by positive anonymous link tolls. We then bound the system performance gap when optimized by the two different criteria. Specifically, we provide answers to the following questions: when system time is minimized, how far could the corresponding system cost deviate from its minimum value; conversely, when system cost is minimized, how far could the corresponding system time deviate from its minimum value; and more generally, how far can the system time and system cost at a given bi-criteria Pareto optimum deviate from their respective single-criterion based system optimum

Bounded Rationality and Irreversible Network Change

A network change is said to be irreversible if the initial network equilibrium cannot be restored by revoking the change. The phenomenon of irreversible network change has been observed in reality. To model this phenomenon, we develop a day-to-day dynamic model whose fixed point is a boundedly rational user equilibrium (BRUE) flow. Our BRUE based approach to modeling irreversible network change has two advantages over other methods based on Wardrop user equilibrium (UE) or stochastic user equilibrium (SUE). First, the existence of multiple network equilibria is necessary for modeling irreversible network change. Unlike UE or SUE, the BRUE multiple equilibria do not rely on non-separable link cost functions, which makes our model applicable to real-world large-scale networks, where well-calibrated non-separable link cost functions are generally not available. Second, travelers\u27 boundedly rational behavior in route choice is explicitly considered in our model. The proposed model is applied to the Twin Cities network to model the flow evolution during the collapse and reopening of the I-35W Bridge. The results show that our model can to a reasonable level reproduce the observed phenomenon of irreversible network change

Pareto-improving and revenue-neutral congestion pricing schemes in two-mode traffic networks

This paper studies a Pareto-improving and revenue-neutral congestion pricing scheme on a simple two-mode (highway and transit) network: this scheme aims at simultaneously improving system performance, making every individual user better off, and having zero total revenue. Different Pareto-improving situations are explored when a two-mode transportation system serves for travel groups with different value-of-time (VOT) distributions. Since the congestion pricing scheme suggested here charges transit users negative tolls and automobile users positive tolls, it can be considered as a proper way to implement congestion pricing and transit subsidy in one step, while offsetting the inequity for the poor. For a general VOT distribution of commuters, the condition of Pareto-improving is established, and the impact of the VOT distribution on solving the inequity issue is explored. For a uniform VOT distribution, we show that a Pareto-improving and revenue-neutral pricing scheme always exists for any target modal split pattern that reduces the total system travel time

Distribution channel strategies in a mixed market

This paper studies equilibrium channel strategies in a mixed market with a public firm and a private firm. The public firm is concerned with social welfare, while the private firm aims to maximize its own profit. Each firm decides whether to adopt an integrated or a decentralized channel. We examine two standard market competition modes, Bertrand and Cournot. Within each competition mode, we consider two typical vertical contracts, wholesale-price and two-part tariff contracts. Our results suggest that equilibrium channel structures depend on the market competition mode, the vertical contract form, and the level of product substitutability. Specifically, the channel strategy of the private firm depends mainly on the vertical contract form: under a two-part tariff contract, the private firm always chooses decentralization; under a wholesale-price contract, the private firm chooses integration for most scenarios except for highly substitutable products under Bertrand competition (i.e., under very intense competition). The channel strategy of the public firm depends mainly on the competition mode: under Bertrand competition, the public firm always chooses decentralization; under Cournot competition, the public firm always chooses the opposite of the private firm׳s strategy

A strategic analysis of incorporating CSR into managerial incentive design

A strategic analysis is conducted to incorporate corporate social responsibility (CSR) considerations into managerial incentive design in a duopoly where each firm comprises an owner and a manager. Consumer surplus is adopted to represent the firms' CSR concerns and a CSR-related incentive is introduced to accommodate both profit and consumer surplus. Bertrand and Cournot competition modes are discussed with the firms' products being complementary, independent, or substitutable. We first examine the equilibrium of CSR-related incentive design and, then, analyze how CSR-related incentives affect the firms' profitability and CSR performance, measured by consumer surplus and social welfare

The Effect of Bacteria on Seed Germination in Sorghum and Rape Under Cadmium and Petroleum Conditions

A large amount of oil hydrocarbons and heavy metals have been discharged into the environment and caused soil polluted. Petroleum and cadmium in soil accumulated in crops and lead to threaten human healthy through the food chain. In this experiment, seeds of sorghum and rape were germinated in deferent concentrations of petroleum and cadmium, and the effect of Peptococcus activus sp. SH3-3-9 on the germination was studied. The results showed that petroleum and cadmium inhibited seeds germination, and the effects were stronger as their concentrations increased. Peptococcus activus sp.SH3-3-9 had the role of enhancing seed germination, which indicates it has high potential in plant-microbial remediation of petroleum and cadmium in soil

Droplet feature extraction from images obtained from spray drying process

The Studienarbeit "Droplet feature extraction from images obtained from spray drying process" described a method that can extracting a droplet from an image. Features like axes-lengths and area of the droplet could also be calculated. At first several image pre-processing methods such as sobel filter and morphological operations have been discussed. After that different ways for compositing these methods have been introduced and the effect of these ways has been discussed. The function for calculating the droplet's properties has also been introduced. The result has been evaluated, then the algorithm was set. Edge detection, morphological operation and features extraction were the necessary steps in the algorithm. The algorithm was tested on several regular shapes, and it worked well. Ways to improve this algorithm has also been discussed. The amount of memory usage and processing time have been analyzed. Two functions in the first algorithm required reading whole image beforehand, thus two alternative methods have been introduced. The result was analyzed and evaluated. The advantage and disadvantage of this modified algorithm were discussed

Bounding the inefficiency of logit-based stochastic user equilibrium

Bounding the inefficiency of selfish routing has become an emerging research subject. A central result obtained in the literature is that the inefficiency of deterministic User Equilibrium (UE) is bounded and the bound is independent of network topology. This paper makes a contribution to the literature by bounding the inefficiency of the logit-based Stochastic User Equilibrium (SUE). In a stochastic environment there are two different definitions of system optimization: one is the traditional System Optimum (SO) which minimizes the total actual system travel time, and the other is the Stochastic System Optimum (SSO) which minimizes the total perceived travel time of all users. Thus there are two ways to define the inefficiency of SUE, i.e. to compare SUE with SO in terms of total actual system travel time, or to compare SUE with SSO in terms of total perceived travel time. We establish upper bounds on the inefficiency of SUE in both situations

A Link-Based Day-to-Day Traffic Assignment Model

Existing day-to-day traffic assignment models are all built upon path flow variables. This paper demonstrates two essential shortcomings of these path-based models. One is that their application requires a given initial path flow pattern, which is typically unidentifiable, i.e., mathematically nonunique and practically unobservable. In particular, we show that, for the path-based models, different initial path flow patterns constituting the same link flow pattern generally gives different day-to-day link flow evolutions. The other shortcoming of the path-based models is the path-overlapping problem. That is, the path-based models ignore the interdependence among paths and thus can give very unreasonable results for networks with paths overlapping with each other. These two path-based problems exist for most (if not all) deterministic day-to-day dynamics whose fixed points are the classic Wardrop user equilibrium. To avoid the two path-based problems, we propose a day-to-day traffic assignment model that directly deals with link flow variables. Our link-based model captures travelers\u27 cost-minimization behavior in their path finding as well as their inertia. The fixed point of our link-based dynamical system is the classic Wardrop user equilibrium