bluuebunny/crossref_metadata_2025 huggingface dataset:
Corporate Governance, Takeovers, and Top-Management Compensation: Theory and Evidence
Authors: Cyert Richard M. , Kang Sok-Hyon , Kumar Praveen
Published: January 2003

We examine, both theoretically and empirically, top-management compensation in the presence of agency conflicts when shareholders have delegated governance responsibilities to a self-interested Board of Directors (BOD). We develop a theoretical framework that explicitly incorporates the BOD as a strategic player, models the negotiation process between the CEO and the BOD in designing CEO compensation, and considers the impact of potential takeovers by large shareholders monitoring the CEO-BOD negotiations. In equilibrium, internal governance by the BOD and external takeover threats by a large shareholder act as substitutes in imposing managerial control, especially in constraining management's profligacy in awarding equity-based compensation to itself. The model emphasizes factors in the design of compensation contracts that are rarely considered in the literature, such as equity ownership of the largest outside shareholder and the firm's bankruptcy risk. It also provides new perspectives on factors that are often considered in the literature, such as firm size, firm performance, equity ownership of the BOD, and BOD structure. Our empirical tests lend considerable support for our theoretical predictions. Equity ownership of the largest external shareholder, that of the BOD, and the default risk, are strongly negatively related to the size of CEO equity compensation. Consistent with the theoretical model, these factors do not significantly influence the growth of fixed (or non-performance-related) compensation. We also find that the equity ownership of the BOD is more important in managerial compensation control than other BOD related variables, such as BOD size or the proportion of outside directors.
Predicting Equity Liquidity
Authors: Breen William J. , Hodrick Laurie Simon , Korajczyk Robert A.
Published: January 2003

In this paper we develop a measure of liquidity, price impact, which quantifies the change in a firm's stock price associated with its observed net trading volume. For a large set of institutional trades we compare out-of-sample, characteristic-based estimates of price impact to actual price impacts. Predictive predetermined firm characteristics, chosen to proxy for the severity of adverse selection in the equity market, the non-information-based costs of making a market in the stock, and the extent of shareholder heterogeneity, include relative size, historical relative trading volume, institutional holdings, and the inverse of the stock price. We find numerous aspects of trade execution which are significantly related to the price impact forecast error in economically plausible ways: For example, the predicted price impact overestimates the actual price impact for very large trades, for trades executed in a more patient manner, and for trades where the institution pays higher commissions.
Controlling Information Systems Development Projects: The View from the Client
Authors: Kirsch Laurie J. , Sambamurthy V. , Ko Dong-Gil , Purvis Russell L.
Published: January 2003

Increasingly, business clients are actively leading information systems (IS) projects, often in collaboration with IS professionals, and they are exercising a greater degree of project control. Control is defined as all attempts to motivate individuals to achieve desired objectives, and it can be exercised via formal and informal modes. Much of the previous research investigating the choice of control mode has focused on direct reporting relationships between IS project leaders and their superiors in a hierarchical setting. However, the client-IS relationships may take on a variety of forms, including both hierarchical and lateral settings. Moreover, prior research has found that the knowledge of the systems development process is a key antecedent of control, yet clients are unlikely to be as knowledgeable as IS professionals about this process. It is therefore unclear whether prior findings will generalize to the client-IS pair, and the goal of this research is to examine the exercise of control across this relationship. Data were gathered from a questionnaire survey of 69 pairs of clients and IS project leaders. The results are largely consistent with prior research on the antecedents of formal control modes, but they shed new insight on the choice of informal control modes.
Order-Based Backorders and Their Implications in Multi-Item Inventory Systems
Authors: Song Jing-Sheng
Published: January 2003

In a multi-item inventory system, such as an assemble-to-order manufacturing system or an online-retailing system, a customer order typically consists of several different items in different amounts. The average order-based backorders are the average number of customer orders that are not yet completely filled. While this is an important measure of customer satisfaction, it has not been widely studied in the operations management literature. This is largely because its evaluation involves the joint distribution of inventory levels of different items and other intricate relations, which is computationally dreadful. Taking a novel approach, this paper develops a tractable way of evaluating this measure exactly. We also develop easy-to-compute bounds, which require the evaluation of item-based backorders only. Numerical experiments indicate that the average of the lower and upper bounds is very effective.

The exact results show surprisingly simple structures, which shed light on how system parameters affect the performance. Using these results, we study several examples to gain managerial insights. Questions addressed include: What are the implications of item-based inventory planning decisions on the order-based performance? What is the impact of introducing common components on inventory and service trade-offs? Would order-delivery performance be improved if we restrict the number of choices in product configurations?
Quantifying Operational Synergies in a Merger/Acquisition
Authors: Gupta Diwakar , Gerchak Yigal
Published: January 2003

Merger and acquisition activity has increased sharply in the last decade. It seems useful to have models that can help senior managers of bidder firms make informed decisions about the amount of premium, over the target's share prices prevailing prior to merger announcement, that can be justified on the basis of operational synergies. The goal of this article is to capture important parameters from the production side that have a bearing on the valuation of the target's shares. We show that the production characteristics of both the bidder and the target matter in a significant way. For example, if the bidder and target operate in independent markets, the bidder has flexible production facilities but the target's production facilities are inflexible, then an increase in the bidder's demand can make the target less attractive and lower the value of operational synergy.
An Approximate Dynamic Programming Approach to Multidimensional Knapsack Problems
Authors: Bertsimas Dimitris , Demir Ramazan
Published: January 2003

We present an Approximate Dynamic Programming (ADP) approach for the multidimensional knapsack problem (MKP). We approximate the value function (a) using parametric and nonparametric methods and (b)using a base-heuristic. We propose a new heuristic which adaptively rounds the solution of the linear programming relaxation. Our computational study suggests: (a)the new heuristic produces high quality solutions fast and robustly, (b)state of the art commercial packages like CPLEX require significantly larger computational time to achieve the same quality of solutions, (c) the ADP approach using the new heuristic competes successfully with alternative heuristic methods such as genetic algorithms, (d)the ADP approach based on parametric and nonparametric approximations, while producing reasonable solutions, is not competitive. Overall, this research illustrates that the base-heuristic approach is a promising computational approach for MKPs worthy of further investigation.
Adaptive Behavior of Impatient Customers in Tele-Queues: Theory and Empirical Support
Authors: Zohar Ety , Mandelbaum Avishai , Shimkin Nahum
Published: January 2003

We address the modeling and analysis of abandonments from a queue that is invisible to its occupants. Such queues arise in remote service systems, notably the Internet and telephone call centers; hence, we refer to them as tele-queues. A basic premise of this paper is that customers adapt their patience (modeled by an abandonment-time distribution) to their service expectations, in particular to their anticipated waiting time. We present empirical support for that hypothesis, and propose an M/M/m-based model that incorporates adaptive customer behavior. In our model, customer patience depends on the mean waiting time in the queue. We characterize the resulting system equilibrium (namely, the operating point in steady state), and establish its existence and uniqueness when changes in customer patience are bounded by the corresponding changes in their anticipated waiting time. The feasibility of multiple system equilibria is illustrated when this condition is violated. Finally, a dynamic learning model is proposed where customer expectations regarding their waiting time are formed through accumulated experience. We demonstrate, via simulation, convergence to the theoretically anticipated equilibrium, while addressing certain issues related to censored-sampling that arise because of abandonments.
Incorporating Workflow Interference in Facility Layout Design: The Quartic Assignment Problem
Authors: Chiang Wen-Chyuan , Kouvelis Panagiotis , Urban Timothy L.
Published: January 2003

Although many authors have noted the importance of minimizing workflow interference in facility layout design, traditional layout research tends to focus on minimizing the distance-based transportation cost. This paper formalizes the concept of workflow interference from a facility layout perspective. A model, formulated as a quartic assignment problem, is developed that explicitly considers the interference of workflow. Optimal and heuristic solution methodologies are developed and evaluated.
On Uncertainty, Ambiguity, and Complexity in Project Management
Authors: Pich Michael T. , Loch Christoph H. , Meyer Arnoud De
Published: January 2003

This article develops a model of a project as a payoff function that depends on the state of the world and the choice of a sequence of actions. A causal mapping, which may be incompletely known by the project team, represents the impact of possible actions on the states of the world. An underlying probability space represents available information about the state of the world. Interactions among actions and states of the world determine the complexity of the payoff function. Activities are endogenous, in that they are the result of a policy that maximizes the expected project payoff.

A key concept is the adequacy of the available information about states of the world and action effects. We express uncertainty, ambiguity, and complexity in terms of information adequacy. We identify three fundamental project management strategies: instructionism, learning, and selectionism. We show that classic project management methods emphasize adequate information and instructionism, and demonstrate how modern methods fit into the three fundamental strategies. The appropriate strategy is contingent on the type of uncertainty present and the complexity of the project payoff function. Our model establishes a rigorous language that allows the project manager to judge the adequacy of the available project information at the outset, choose an appropriate combination of strategies, and set a supporting project infrastructure—that is, systems for planning, coordination and incentives, and monitoring.
The Market Evolution and Sales Takeoff of Product Innovations
Authors: Agarwal Rajshree , Bayus Barry L.
Published: January 2003

In contrast to the prevailing supply-side explanation that price decreases are the key driver of a sales takeoff, we argue that outward shifting supply and demand curves lead to market takeoff. Our fundamental idea is that sales in new markets are initially low because the first commercialized forms of new innovations are primitive. Then, as new firms enter, actual and perceived product quality improves (and prices possibly drop), which leads to a takeoff in sales. To provide empirical evidence for this explanation, we explore the relationship between takeoff times, price decreases, and firm entry for a sample of consumer and industrial product innovations commercialized in the United States over the past 150 years. Based on a proportional hazards analysis of takeoff times, we find that new firm entry dominates other factors in explaining observed sales takeoff times. We interpret these results as supporting the idea that demand shifts during the early evolution of a new market due to nonprice factors is the key driver of a sales takeoff.
Performance Assessment of the Lead User Idea-Generation Process for New Product Development
Authors: Lilien Gary L. , Morrison Pamela D. , Searls Kathleen , Sonnack Mary , Hippel Eric von
Published: January 2003

Traditional idea generation techniques based on customer input usually collect information on new product needs from a random or typical set of customers. The “lead user process” takes a different approach. It collects information about both needs and solutions from users at the leading edges of the target market, as well as from users in other markets that face similar problems in a more extreme form. This paper reports on a natural experiment conducted within the 3M Company on the effect of the lead user (LU) idea-generation process relative to more traditional methods. 3M is known for its innovation capabilities— and we find that the LU process appears to improve upon those capabilities. Annual sales of LU product ideas generated by the average LU project at 3M are conservatively projected to be $146 million after five years—more than eight times higher than forecast sales for the average contemporaneously conducted “traditional” project. Each funded LU project is projected to create a new major product line for a 3M division. As a direct result, divisions funding LU project ideas are projecting their highest rate of major product line generation in the past 50 years.
Managerial Insights into the Effects of Interactions on Replacing Members of a Team
Authors: Solow Daniel , Vairaktarakis George , Piderit Sandy Kristin , Tsai Ming-chi
Published: January 2003

A mathematical model is presented for studying the effects of interactions among team members on the process of replacing members of a team in an organization. The model provides the ability to control the number of members that interact with each individual on the team. Through the use of analysis and computer simulations, it is shown how the amount of interaction affects the tradeoff between the expected performance and the number of replacements and interviews needed to find a good team using various replacement policies. New managerial insights into this process—such as the fact that it is not necessarily optimal to replace the worst-performing team member—are provided.
Preferred by “All” and Preferred by “Most” Decision Makers: Almost Stochastic Dominance
Authors: Leshno Moshe , Levy Haim
Published: January 2003

While “most” decision makers may prefer one uncertain prospect over another, stochastic dominance rules as well as other investment criteria, will not reveal this preference due to some extreme utility functions in the case of even a very small violation of these rules. Such strict rules relate to “all” utility functions in a given class including extreme ones which presumably rarely represents investors' preference. In this paper we establish almost stochastic dominance (ASD) rules which formally reveal a preference for “most” decision makers, but not for “all” of them. The ASD rules reveal that choices which probably conform with “most” decision makers also solve some debates, e.g., showing, as practitioners claim, an ASD preference for a higher proportion of stocks in the portfolio as the investment horizon increases, a conclusion which is not implied by the well-known stochastic dominance rules.
A Jump-Diffusion Model for Option Pricing
Authors: Kou S. G.
Published: January 2003

Brownian motion and normal distribution have been widely used in the Black–Scholes option-pricing framework to model the return of assets. However, two puzzles emerge from many empirical investigations: the leptokurtic feature that the return distribution of assets may have a higher peak and two (asymmetric) heavier tails than those of the normal distribution, and an empirical phenomenon called “volatility smile” in option markets. To incorporate both of them and to strike a balance between reality and tractability, this paper proposes, for the purpose of option pricing, a double exponential jump-diffusion model. In particular, the model is simple enough to produce analytical solutions for a variety of option-pricing problems, including call and put options, interest rate derivatives, and path-dependent options. Equilibrium analysis and a psychological interpretation of the model are also presented.
Sharing the Wealth: When Should Firms Treat Customers as Partners?
Authors: Anderson Eric T.
Published: January 2003

Marketers often stress the importance of treating customers as partners. A fundamental premise of this perspective is that all parties can be weakly better off if they work together to increase joint surplus and reach Pareto-efficient agreements. For marketing managers, this implies organizing marketing activities in a manner that maximizes total surplus. This logic is theoretically sound when agreements between partners are limitless and costless. In most consumer marketing contexts (business-to-consumer), this is typically not true. The question I ask is should one still expect firms to partner with consumers and reach Pareto-efficient agreements? In this paper, I use the example of a firm's choice of product configuration to demonstrate two effects. First, I show that a firm may configure a product in a manner that reduces total surplus but increases firm profits. Second, one might conjecture that increased competition would eliminate this effect, but I show that in a duopoly firm profits may be increasing in the cost of product completion. This second result suggests that firms may prefer to remain inefficient and/or stifie innovations. Both results violate a fundamental premise of partnering—that firms and consumers should work together to increase total surplus and reach Pareto-efficient agreements. The model illustrates that Pareto-efficient agreements are less likely to occur if negotiation with individual partners is infeasible or costly, such as in business-to–consumer contexts. Consumer marketers in one-to- many marketing environments should be wary of treating customers as partners because Pareto–efficient agreements may not be optimal for their firm.
David vs. Goliath: An Analysis of Asymmetric Mixed-Strategy Games and Experimental Evidence
Authors: Amaldoss Wilfred , Jain Sanjay
Published: January 2003

Mixed strategies are widely used to model strategic situations in diverse fields such as economics, marketing, political science, and biology. However, some of the implications of asymmetric mixed-strategy solutions are counterintuitive. We develop a stylized model of patent race to examine some of these implications. In our model two firms compete to develop a product and obtain a patent. However, one firm values the patent more because of its market advantages, such as brand reputation and distribution network. Contrary to some intuition, we find that the firm that values the patent less is likely to invest more aggressively in developing the product and will also win the patent more often. We argue that the reason for these counterintuitive results is inherent in the very concept of mixed strategy solution. In a laboratory test, we examine whether subjects' behavior conforms to the equilibrium predictions. We find that the aggregate behavior of our subjects is consistent with the game-theoretic predictions. With the help of the experience-weighted attraction (EWA) learning model proposed by Camerer and Ho (1999), we show that adaptive learning can account for the investment behavior of our subjects.We find that the EWA learning model tracks the investment decisions of our subjects well, whether we hold out trials or an entire group of subjects.
Supply Chain Coordination Under Channel Rebates with Sales Effort Effects
Authors: Taylor Terry A.
Published: January 2003

A channel rebate is a payment from a manufacturer to a retailer based on retailer sales to end consumers. Two common forms of channel rebates are linear rebates, in which the rebate is paid for each unit sold, and target rebates, in which the rebate is paid for each unit sold beyond a specified target level. When demand is not influenced by sales effort, a properly designed target rebate achieves channel coordination and a win-win outcome. Coordination cannot be achieved by a linear rebate in a way that is implementable. When demand is influenced by retailer sales effort, a properly designed target rebate and returns contract achieves coordination and a win-win outcome. Other contracts, such as linear rebate and returns or target rebate alone, cannot achieve coordination in a way that is implementable. Contrary to the view expressed in the literature that accepting returns weakens incentives for retailer sales effort, we find that the provision of returns strengthens incentives for effort.
A Structural Approach to Assessing Innovation: Construct Development of Innovation Locus, Type, and Characteristics
Authors: Gatignon Hubert , Tushman Michael L. , Smith Wendy , Anderson Philip
Published: January 2003

We take a structural approach to assessing innovation. We develop a comprehensive set of measures to assess an innovation's locus, type, and characteristics. We find that the concepts of competence destroying and competence enhancing are composed of two distinct constructs that, although correlated, separately characterize an innovation: new competence acquisition and competence enhancement/destruction. We develop scales to measure these constructs and show that new competence acquisition and competence enhancing/destroying are different from other innovation characteristics including core/peripheral and incremental/radical, as well as architectural and generational innovation types. We show that innovations can be evaluated distinctively on these various dimensions with generally small correlations between them. We estimate the impact these different innovation characteristics and types have on time to introduction and perceived commercial success. Our results indicate the importance of taking a structural approach to describing innovations and to the differential importance of innovation locus, type, and characteristics on innovation outcomes. Our results also raise intriguing questions regarding the locus of competence acquisition (internal vs. external) and both innovation outcomes.
Pricing of Information Products on Online Servers: Issues, Models, and Analysis
Authors: Jain Sanjay , Kannan P. K.
Published: January 2003

Online information servers that provide access to diverse databases where users can search for, browse through, and download the information they need have been rapidly increasing in number in the past few years. Online vendors have traditionally charged users for information on the based on the length of the time they were connected to the databases. With hardware and software advances, many online servers have recently started changing their pricing strategies to search-based and/or subscription-fee pricing. This paper examines the various issues involved in pricing these information products, and presents an economic approach to analyze conditions under which the various pricing schemes may prove optimal for the online servers. Our results show that the variation in consumer expertise and valuation of information affects the choice of a pricing strategy by the server. We present general conditions under which subscription-fee pricing is optimal even when consumer demand is inelastic. We also find that, given the cost structures characterizing the market, undifferentiated online servers can compete and coexist in the market each making positive profits. We show that in a competitive setting an increase in costs of online servers can sometimes benefit them by enabling them to differentiate themselves. Our results offer insights into the trends in pricing strategies and may provide an explanation as to why many servers may persist with connect-time strategies.
Competitive One-to-One Promotions
Authors: Shaffer Greg , Zhang Z. John
Published: January 2003

One-to-one promotions are possible when consumers are individually addressable and firms know something about each customer's preferences. We explore the competitive effects of one-to-one promotions in a model with two competing firms where the firms differ in size and consumers have heterogeneous brand loyalty. We find that one-to-one promotions always lead to an increase in price competition (average prices in the market decrease). However, we also find that one-to-one promotions affect market shares. This market-share effect may outweigh the effect of lower prices, benefiting the firm whose market share increases. Our results suggest that of two firms, the firm with the higher-quality product may gain from one-to-one promotions. Our model also has implications for the phenomenon of customer churn, where consumers switch to a less preferred brand due to targeted promotional incentives. We show that churning can arise optimally from firms pursuing a profit-maximizing strategy. Instead of trying to minimize it, the optimal way to manage customer churn is to engage in both offensive and defensive promotions with the relative mix depending on the marginal cost of targeting.
Should Start-up Companies Be Cautious? Inventory Policies Which Maximise Survival Probabilities
Authors: Archibald T. W. , Thomas L. C. , Betts J. M. , Johnston R. B.
Published: January 2003

New start-up companies, which are considered to be a vital ingredient in a successful economy, have a different objective than established companies: They want to maximise their chance of long-term survival. We examine the implications for their operating decisions of this different criterion by considering an abstraction of the inventory problem faced by a start-up manufacturing company. The problem is modelled under two criteria as a Markov decision process; the characteristics of the optimal policies under the two criteria are compared. It is shown that although the start-up company should be more conservative in its component purchasing strategy than if it were a well-established company, it should not be too conservative. Nor is its strategy monotone in the amount of capital it has available. The models are extended to allow for interest on investment and inflation.
Deconstructing the Pioneer's Advantage: Examining Vintage Effects and Consumer Valuations of Quality and Variety
Authors: Bohlmann Jonathan D. , Golder Peter N. , Mitra Debanjan
Published: January 2003

Several studies have demonstrated an order-of-entry effect on market share, suggesting that pioneers outperform later entrants. However, other research has pointed out the limitations of these studies and found evidence that many pioneers fail or have low market share. Given this background, the purpose of this research is to understand the conditions under which pioneers are more likely and also less likely to have an advantage. We propose a game-theoretic model that includes important sources of pioneer advantages as well as disadvantages. Specifically, we incorporate a pioneer advantage due to preemption in markets with heterogeneous tastes. In addition, we incorporate a potential pioneer disadvantage due to technology vintage effects, where later entrants utilizing improved technology can have lower costs and higher quality. The model allows us to evaluate the extent of vintage effects necessary to overcome a pioneer's advantage. Key relationships are found between the magnitude of the pioneer advantage or disadvantage and consumer valuations of product attributes (e.g., variety and quality). We empirically validate the model with vintage effect data in 36 product categories, and measures of consumer valuations of product variety and quality for 12 of these 36 categories. The results show that pioneers do better in product categories where variety is more important and worse in categories where product quality is more important. Pioneers in categories with high vintage effects are shown to have lower market shares and higher failure rates. Similar results appear when analyzing persistence of market leadership over time, further validating our model's major implications. We also present two case studies that illustrate key elements of the model.
Information Sharing in a Supply Chain with Horizontal Competition
Authors: Li Lode
Published: January 2003

This paper examines the incentives for firms to share information vertically in a two-level supply chain in which there are an upstream firm (a manufacturer) and many downstream firms (retailers). The retailers are engaged in a Cournot competition and are endowed with some private information. Vertical information sharing has two effects: "direct effect" due to the changes in strategy by the parties involved in sharing the information and "indirect effect" (or "leakage effect") due to the changes in strategy by other competing firms (who may infer the information from the actions of the informed parties). Both changes would affect the profitability of the firms. We show that the leakage effect discourages the retailers from sharing their demand information with the manufacturer while encouraging them to share their cost information. On the other hand, the direct effect always discourages the retailers from sharing their information. When voluntary information sharing is not possible, we identify conditions under which information can be traded and show how price should be determined to facilitate such information exchange. We also examine the impact of vertical information sharing on the total supply chain profits and social benefits.
Easy Quantification of Improved Spare Parts Inventory Policies
Authors: Thonemann Ulrich W. , Brown Alex O. , Hausman Warren H.
Published: January 2003

This paper presents approximate analytical models to quantify the expected improvement in inventory investment when using a system approach to control inventory as opposed to a simpler item approach. A system approach ensures that a demand-weighted average fill rate is achieved at low inventory investment by assigning low fill rates to parts with high costs and high fill rates to parts with low costs. An item approach does not vary fill rates by parts but assigns identical fill rates to all parts. Using single-parameter functional representations of the skewness of unit costs and average demand across all parts in the system, simple approximate analytical expressions for the required inventory investment are derived for both approaches. The accuracy of the approximations is validated using data from a distribution center for computer spare parts. For these data, the solutions obtained by the approximations are very close to the exact values. The results show that inventory investments can be well approximated as a function of only a few cost and demand parameters. These expressions can be used to determine the percentage reduction in inventory investment for a particular target demand-weighted average fill rate when the superior system approach is used instead of the item approach. For increased ease of use, the percentage reduction in inventory when using a system as opposed to an item approach is computed over a range of realistic values for the key parameters of the model and a quadratic expression is fitted to the data. This fitted expression provides rough guidelines for the anticipated improvement with very limited data needed, prior to detailed modeling or implementation.
Adopting a Plurality Vote Perspective
Authors: Saari Donald G.
Published: January 2003

For three-alternative positional voting and decision methods, it is shown how to decompose the profiles and data sets in a manner which identifies all possible conflict relative to a specified procedure. This approach is illustrated with the plurality vote by characterizing all possible profiles which cause all possible conflicts between the plurality and other pairwise and/or positional procedures. The approach then is used to cast doubt on an often-cited plurality vote property.
Cognitive Foundations of Probability
Authors: Gilboa Itzhak , Schmeidler David
Published: January 2003

Prediction is based on past cases. We assume that a predictor can rank eventualities according to their plausibility given any memory that consists of repetitions of past cases. In a companion paper, we show that under mild consistency requirements, these rankings can be represented by numerical functions, such that the function corresponding to each eventuality is linear in the number of case repetitions. In this paper we extend the analysis to rankings of events. Our main result is that a cancellation condition à la de Finetti implies that these functions are additive with respect to union of disjoint sets. If the set of past cases coincides with the set of possible eventualities, natural conditions are equivalent to ranking events by their empirical frequencies. More generally, our results may describe how individuals form probabilistic beliefs given cases that are only partially pertinent to the prediction problem at hand, and how this subjective measure of pertinence can be derived from likelihood rankings.
A Min-Max Theorem on Feedback Vertex Sets
Authors: Cai Mao-Cheng , Deng Xiaotie , Zang Wenan
Published: January 2003

We establish a necessary and sufficient condition for the linear system {x : Hx ≥ e, x ≥ 0} associated with a bipartite tournament to be totally dual integral, where H is the cycle-vertex incidence matrix and e is the all-one vector. The consequence is a min-max relation on packing and covering cycles, together with strongly polynomial time algorithms for the feedback vertex set problem and the cycle packing problem on the corresponding bipartite tournaments. In addition, we show that the feedback vertex set problem on general bipartite tournaments is NP-complete and approximable within 3.5 based on the min-max theorem.
The Semi-Algebraic Theory of Stochastic Games
Authors: Milman Emanuel
Published: January 2003

The asymptotic behavior of the min-max value of a finite-state zero-sum discounted stochastic game, as the discount rate approaches 0, has been studied in the past using the theory of real-closed fields. We use the theory of semi-algebraic sets and mappings to prove some asymptotic properties of the min-max value, which hold uniformly for all stochastic games in which the number of states and players' actions are predetermined to some fixed values. As a corollary, we prove a uniform polynomial convergence rate of the value of the N-stage game to the value of the nondiscount game, over a bounded set of payoffs.
Achieving Target State-Action Frequencies in Multichain Average-Reward Markov Decision Processes
Authors: Krass Dmitry , Vrieze O. J.
Published: January 2003

In this paper we address a basic problem that arises naturally in average-reward Markov decision processes with constraints and/or nonstandard payoff criteria: Given a feasible state-action frequency vector (“the target”), construct a policy whose state-action frequencies match those of the target vector.

While it is well known that the solution to this problem cannot, in general, be found in the space of stationary randomized policies, we construct a solution that has “ultimately stationary” structure: It consists of two stationary policies where the first one is used initially, and then the switch to the second one is made at a certain random switching time. The computational effort required to construct this solution is minimal.

We also show that our problem can always be solved by a stationary policy if the original MDP is “extended” by adding certain states and actions. The solution in the original MDP is obtained by mapping the solution in the extended MDP back to the original process.
Properties of the Log-Barrier Function on Degenerate Nonlinear Programs
Authors: Wright Stephen J. , Orban Dominique
Published: January 2003

We examine the sequence of local minimizers of the log-barrier function for a nonlinear program near a solution at which second-order sufficient conditions and the Mangasarian-Fromovitz constraint qualification are satisfied, but the active constraint gradients are not necessarily linearly independent. When a strict complementarity condition is satisfied, we show uniqueness of the local minimizer of the barrier function in the vicinity of the nonlinear program solution, and we obtain a semiexplicit characterization of this point. When strict complementarity does not hold, we obtain several other interesting characterizations, in particular, an estimate of the distance between the minimizers of the barrier function and the nonlinear program in terms of the barrier parameter, and a result about the direction of approach of the sequence of minimizers of the barrier function to the nonlinear programming solution.
The Theory of 2-Regularity for Mappings with Lipschitzian Derivatives and its Applications to Optimality Conditions
Authors: Izmailov A. F. , Solodov M. V.
Published: January 2003

We study local structure of a nonlinear mapping near points where standard regularity and/or smoothness assumptions need not be satisfied. We introduce a new concept of 2-regularity (a certain kind of second-order regularity) for a once differentiable mapping whose derivative is Lipschitz continuous. Under this 2-regularity condition, we obtain the representation theorem and the covering theorem (i.e., stability with respect to “right-hand side” perturbations) under assumptions that are weaker than those previously employed in the literature for results of this type. These results are further used to derive a constructive description of the tangent cone to a set defined by (2-regular) equality constraints and optimality conditions for related optimization problems. The class of mappings introduced and studied in the paper appears to be a convenient tool for treating complementarity structures by means of an appropriate equation-based reformulation. Optimality conditions for mathematical programs with (equivalently reformulated) complementarity constraints are also discussed.
Structural Properties of Stochastic Dynamic Programs
Authors: Smith James E. , McCardle Kevin F.
Published: January 2003

In Markov models of sequential decision processes, one is often interested in showing that the value function is monotonic, convex, and/or supermodular in the state variables. These kinds of results can be used to develop a qualitative understanding of the model and characterize how the results will change with changes in model parameters. In this paper we present several fundamental results for establishing these kinds of properties. The results are, in essence, "metatheorems" showing that the value functions satisfy property P if the reward functions satisfy property P and the transition probabilities satisfy a stochastic version of this property. We focus our attention on closed convex cone properties, a large class of properties that includes monotonicity, convexity, and supermodularity, as well as combinations of these and many other properties of interest.
A Second Order Stochastic Network Equilibrium Model, I: Theoretical Foundation
Authors: Watling David
Published: January 2003

Existing models of stochastic network equilibrium route choice in transport networks are able to represent exogenously specified variations in drivers' actual or perceived travel costs, but assume throughout that flows are deterministic. In this paper, a new notion of equilibrium is presented based on stochastic flow variables, in which the impact of variable flows on the variability in travel costs is endogenously handled. Firstly, a very general notion of equilibrium is deduced as a fixed point condition on the joint probability distribution of network flows. Then, an approximation to this condition is derived, which operates by equilibrating moments of order n and below of the joint flow probability distribution, and is termed a Generalized Stochastic User Equilibrium of order n, being denoted GSUE(n). The GSUE(1) model is seen to be a conventional Stochastic User Equilibrium. The paper goes on to focus on the second order model, GSUE(2). Conditions are presented to guarantee the existence of GSUE(2) solutions. Conditions are deduced to guarantee (a) uniqueness of solutions in networks with a single interzonal movement, and (b) proximity of solutions in networks with multiple interzonal movements. Finally, a simple example is presented.
Cannabis and Driving in Older Adults
Authors: Di Ciano Patricia , Rajji Tarek K. , Hong Lauren , Zhao Sampson , Byrne Patrick , Elzohairy Yoassry , Brubacher Jeffrey R. , McGrath Michael , Brands Bruna , Chen Sheng , Wang Wei , Hasan Omer S. M. , Wickens Christine M. , Kaduri Pamela , Le Foll Bernard
Published: January 2024

Importance

Epidemiological studies have found that cannabis increases the risk of a motor vehicle collision. Cannabis use is increasing in older adults, but laboratory studies of the association between cannabis and driving in people aged older than 65 years are lacking.

Objective

To investigate the association between cannabis, simulated driving, and concurrent blood tetrahydrocannabinol (THC) levels in older adults.

Design, Setting, and Participants

Using an ecologically valid counterbalanced design, in this cohort study, regular cannabis users operated a driving simulator before, 30 minutes after, and 180 minutes after smoking their preferred legal cannabis or after resting. This study was conducted in Toronto, Canada, between March and November 2022 with no follow-up period. Data were analyzed from December 2022 to February 2023.

Exposures

Most participants chose THC-dominant cannabis with a mean (SD) content of 18.74% (6.12%) THC and 1.46% (3.37%) cannabidiol (CBD).

Main outcomes and measures

The primary end point was SD of lateral position (SDLP, or weaving). Secondary outcomes were mean speed (MS), maximum speed, SD of speed, and reaction time. Driving was assessed under both single-task and dual-task (distracted) conditions. Blood THC and metabolites of THC and CBD were also measured at the time of the drives.

Results

A total of 31 participants (21 male [68%]; 29 White [94%], 1 Latin American [3%], and 1 mixed race [3%]; mean [SD] age, 68.7 [3.5] years), completed all study procedures. SDLP was increased and MS was decreased at 30 but not 180 minutes after smoking cannabis compared with the control condition in both the single-task (SDLP effect size [ES], 0.30; b = 1.65; 95% CI, 0.37 to 2.93; MS ES, −0.58; b = −2.46; 95% CI, −3.56 to −1.36) and dual-task (SDLP ES, 0.27; b = 1.75; 95% CI, 0.21 to 3.28; MS ES, −0.47; b = −3.15; 95% CI, −5.05 to −1.24) conditions. Blood THC levels were significantly increased at 30 minutes but not 180 minutes. Blood THC was not correlated with SDLP or MS at 30 minutes, and SDLP was not correlated with MS. Subjective ratings remained elevated for 5 hours and participants reported that they were less willing to drive at 3 hours after smoking.

Conclusions and relevance

In this cohort study, the findings suggested that older drivers should exercise caution after smoking cannabis.
Recent Advances in Diverse MXenes‐Based Structures for Photocatalytic CO2 Reduction into Renewable Hydrocarbon Fuels
Authors: Tang Qijun , Li Tianhao , Tu Wenguang , Wang Haiqiang , Zhou Yong , Zou Zhigang
Published: January 2024

Photocatalytic CO2 reduction into renewable hydrocarbon fuels is a green solution to address CO2 emission and energy issues simultaneously. However, the fast recombination of photogenerated charge carriers and the sluggish surface reaction kinetics restrict the efficiency of photocatalytic CO2 reduction. The emergence of 2D MXenes has potential in improving the efficiency of photocatalytic CO2 reduction, owing to their high electrical conductivity, flexible structural properties, and abundant active sites. Hence, this review will concisely summarize and highlight recent advances of MXenes‐based photocatalysts used in photocatalytic CO2 reduction. First, the synthesis and properties of MXenes is briefly introduced. Second, the mechanism of CO2 photoreduction along with the roles of MXenes in photocatalytic CO2 reduction are summarized, including promoting the adsorption of CO2, enhancing the separation of photo‐induced charge carriers, acting as a robust support, and photothermal effect. Third, different kinds of MXenes‐based photocatalysts such as MXenes/metal oxides, MXenes/nitrides, MXenes/LDH, MXenes/perovskite, and MXene‐derived photocatalysts for CO2 reduction are classified via the type of semiconductors. Finally, the challenges and perspectives are also presented, including exploring suitable MXenes via machine learning, uncovering the structure‐activity relationship by in situ, time‐ and space‐resolved characterization techniques, improving anti‐oxidization ability, and scale‐up applications.
Laplace Differentiator Based on Metasurface with Toroidal Dipole Resonance
Authors: Zhou Chen , Chen Yanjie , Li Yao , Li Junjie , Zhao Ruizhe , Tao Chengdong , Liu Chuanbao , Bai Yang , Li Xin , Wang Yongtian , Huang Lingling
Published: January 2024

As an important method of image processing, image differentiation enables edge detection of targets to achieve recognition of object features and information compression and the computation speed can be boosted by optical information techniques. Traditional optical image differentiation methods mainly rely on spatial spectrum filtering by using classical 4f system, while some work focus on 1D or single‐direction differentiation. It is only in recent years that the rapid development of metasurfaces has facilitated image differentiation methods. In this work, a Laplace operation device is demonstrated based on a silicon hollow brick dielectric resonant metasurface for incident light field. The optical transfer function (OTF) required by the optical Laplace operation can be obtained by exciting an angularly selective toroidal dipole (TD) resonance supported by the metasurface. This hollow silicon brick differentiator not only realizes 2D second‐order edge detection but also has a numerical aperture close to 0.4 and a broad working wavelength range >100 nm and can be directly integrated with imaging systems. Such metadevice may be potentially applied in the fields of optical sensing, microscopy, machine vision, biomedical imaging, etc.