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Research Collection Lee Kong Chian School Of Business

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Articles 121 - 150 of 276

Full-Text Articles in Operations and Supply Chain Management

On The Design Of Sparse But Efficient Structures In Operations, Zhenzhen Yan, Sarah Yini Gao, Chung Piaw Teo Jul 2018

On The Design Of Sparse But Efficient Structures In Operations, Zhenzhen Yan, Sarah Yini Gao, Chung Piaw Teo

Research Collection Lee Kong Chian School Of Business

It is widely believed that a little flexibility added at the right place can reap significant benefits for operations. Unfortunately, despite the extensive literature on this topic, we are not aware of any general methodology that can be used to guide managers in designing sparse (i.e., slightly flexible) and yet efficient operations. We address this issue using a distributionally robust approach to model the performance of a stochastic system under different process structures. We use the dual prices obtained from a related conic program to guide managers in the design process. This leads to a general solution methodology for the …

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Optimal Stackelberg Strategies For Financing A Supply Chain Through Online Peer-To-Peer Lending, Guang-Xin Gao, Zhi-Ping Fan, Xin Fang, Yun Fong Lim Jun 2018

Optimal Stackelberg Strategies For Financing A Supply Chain Through Online Peer-To-Peer Lending, Guang-Xin Gao, Zhi-Ping Fan, Xin Fang, Yun Fong Lim

Research Collection Lee Kong Chian School Of Business

In recent years, supply chain finance (SCF) through online peer-to-peer (P2P) lending platforms has gained its popularity. We study an SCF system with a manufacturer selling a product to a retailer that faces uncertain demand over a single period. We assume that either the retailer or the manufacturer faces a capital constraint and must borrow capital through an online P2P lending platform. The platform determines a service rate for the loan, the manufacturer sets a wholesale price for the product, and the retailer chooses its order quantity for the product. We identify optimal Stackelberg strategies of the participants in the …

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Dynamic Inventory Pooling Policies To Deliver Differentiated Service, Yuanguang Zhong, Zhichao Zheng, Mabel C. Chou, Chung-Piaw Teo Apr 2018

Dynamic Inventory Pooling Policies To Deliver Differentiated Service, Yuanguang Zhong, Zhichao Zheng, Mabel C. Chou, Chung-Piaw Teo

Research Collection Lee Kong Chian School Of Business

Resource pooling strategies have been widely used in industry to match supply with demand. However, effective implementation of these strategies can be challenging. Firms need to integrate the heterogeneous service level requirements of different customers into the pooling model and allocate the resources (inventory or capacity) appropriately in the most effective manner. The traditional analysis of inventory pooling, for instance, considers the performance metric in a centralized system and does not address the associated issue of inventory allocation. Using Blackwell’s Approachability Theorem, we derive a set of necessary and sufficient conditions to relate the fill rate requirement of each customer …

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Constrained Dual Representation Of Coherent Risk Measures, Marcus Ang, Jie Sun, Qiang Yao Mar 2018

Constrained Dual Representation Of Coherent Risk Measures, Marcus Ang, Jie Sun, Qiang Yao

Research Collection Lee Kong Chian School Of Business

A classical result in risk measure theory states that every coherent risk measure has a dual representation as the supremum of certain expected value over a risk envelope. We study this topic in more detail. The related issues include: (1) Set operations of risk envelopes and how they change the risk measures, (2) The structure of risk envelopes of popular risk measures, (3) Aversity of risk measures and its impact to risk envelopes, and (4) A connection between risk measures in stochastic optimization and uncertainty sets in robust optimization.

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Quadratic Two-Stage Stochastic Optimization With Coherent Measures Of Risk, Jie Sun, Li-Zhi Liao, Brian Rodrigues Mar 2018

Quadratic Two-Stage Stochastic Optimization With Coherent Measures Of Risk, Jie Sun, Li-Zhi Liao, Brian Rodrigues

Research Collection Lee Kong Chian School Of Business

A new scheme to cope with two-stage stochastic optimization problems uses a risk measure as the objective function of the recourse action, where the risk measure is defined as the worst-case expected values over a set of constrained distributions. This paper develops an approach to deal with the case where both the first and second stage objective functions are convex linear-quadratic. It is shown that under a standard set of regularity assumptions, this two-stage quadratic stochastic optimization problem with measures of risk is equivalent to a conic optimization problem that can be solved in polynomial time.

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On Substitutability And Complementarity In Discrete Choice Models, Guiyun Feng, Xiaobo Li, Zizhuo Wang Jan 2018

On Substitutability And Complementarity In Discrete Choice Models, Guiyun Feng, Xiaobo Li, Zizhuo Wang

Research Collection Lee Kong Chian School Of Business

In this paper, we propose the concepts of substitutability and complementarity in discrete choice models. These concepts concern whether the choice probability of one alternative in a choice model increases or decreases with the utility of another alternative, and they play important roles in capturing certain practical choice patterns, such as the halo effect. We study conditions on discrete choice models that will lead to substitutability and complementarity. We also present ways of constructing choice models that exhibit complementary property.

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Technical Note—On The Relation Between Several Discrete Choice Models, Guiyun Feng, Xiaobo Li, Zizhuo Wang Dec 2017

Technical Note—On The Relation Between Several Discrete Choice Models, Guiyun Feng, Xiaobo Li, Zizhuo Wang

Research Collection Lee Kong Chian School Of Business

In this paper, we study the relationship between several well known classes of discrete choice models, i.e., the random utility model (RUM), the representative agent model (RAM), and the semiparametric choice model (SCM). Using a welfare-based model as an intermediate, we show that the RAM and the SCM are equivalent. Furthermore, we show that both models as well as the welfare-based model strictly subsume the RUM when there are three or more alternatives, while the four are equivalent when there are only two alternatives. Thus, this paper presents a complete picture of the relationship between these choice models.

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Inventory Management Based On Target-Oriented Robust Optimization, Yun Fong Lim, Chen Wang Dec 2017

Inventory Management Based On Target-Oriented Robust Optimization, Yun Fong Lim, Chen Wang

Research Collection Lee Kong Chian School Of Business

We propose a target-oriented robust optimization approach to solve a multi-product, multi-period inventory management problem subject to ordering capacity constraints. We assume the demand for each product in each period is characterized by an uncertainty set, which depends only on a reference value and the bounds of the demand. Our goal is to find an ordering policy that maximizes the sizes of all the uncertainty sets such that all demand realizations from the sets will result in a total cost lower than a pre-specified cost target. We prove that a static decision rule is optimal for an approximate formulation of …

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Capacity Management In Agricultural Commodity Processing And Application In The Palm Industry, Onur Boyabatli, Jason Quang Dang Nguyen, Tong Wang Dec 2017

Capacity Management In Agricultural Commodity Processing And Application In The Palm Industry, Onur Boyabatli, Jason Quang Dang Nguyen, Tong Wang

Research Collection Lee Kong Chian School Of Business

This paper examines the capacity investment decisions of a processor that uses a commodity input to produce both a commodity output and a byproduct in the context of agricultural industries. We employ a multi-period model to study the optimal one-time processing and (output) storage capacity investment decisions---in addition to the periodic processing and inventory decisions---when both input and output spot prices as well as production yield are uncertain. We characterize the optimal decisions and perform sensitivity analysis to investigate how spot price uncertainty affects the processor's optimal capacity and profitability. Using a calibration based on the palm industry, we study …

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The Interaction Between Operational Flexibility And Financial Flexibility, Onur Boyabatli, Tiecheng Leng Dec 2017

The Interaction Between Operational Flexibility And Financial Flexibility, Onur Boyabatli, Tiecheng Leng

Research Collection Lee Kong Chian School Of Business

This paper examines the interaction between operational flexibility and financial flexibility in a multi-product business unit that makes operational decisions based on financial resources provided by its parent company (or headquarters). We capture operational flexibility through investment in flexible technology and financial flexibility through higher availability of financial resources. We consider the flexible-versus-dedicated technology choice and capacity investment decisions of a two-product business unit under demand uncertainty in the presence of budget constraints. The unit operates under a capital budget for financing the capacity investment, and an operating budget, which is uncertain in the capacity investment stage, for financing the …

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Combinatorial Multi-Armed Bandit Problem With Probabilistically Triggered Arms: A Case With Bounded Regret, Omer Saritac, Cem Tekin Nov 2017

Combinatorial Multi-Armed Bandit Problem With Probabilistically Triggered Arms: A Case With Bounded Regret, Omer Saritac, Cem Tekin

Research Collection Lee Kong Chian School Of Business

In this paper, we study the combinatorial multi-armed bandit problem (CMAB) with probabilistically triggered arms (PTAs). Under the assumption that the arm triggering probabilities (ATPs) are positive for all arms, we prove that a simple greedy policy, named greedy CMAB (G-CMAB), achieves bounded regret. This improves the result in previous work, which shows that the regret is O (log T) under no such assumption on the ATPs. Then, we numerically show that G-CMAB achieves bounded regret in a real-world movie recommendation problem, where the action corresponds to recommending a set of movies, arms correspond to the edges between movies and …

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Vungle Inc. Improves Monetization Using Big-Data Analytics, Bert De Reyck, Ioannis Fragkos, Yael Gruksha-Cockayne, Casey Lichtendahl, Hammond Guerin, Andre Kritzer Oct 2017

Vungle Inc. Improves Monetization Using Big-Data Analytics, Bert De Reyck, Ioannis Fragkos, Yael Gruksha-Cockayne, Casey Lichtendahl, Hammond Guerin, Andre Kritzer

Research Collection Lee Kong Chian School Of Business

The advent of big data has created opportunities for firms to customize their products and services to unprecedented levels of granularity. Using big data to personalize an offering in real time, however, remains a major challenge. In the mobile advertising industry, once a customer enters the network, an ad-serving decision must be made in a matter of milliseconds. In this work, we describe the design and implementation of an ad-serving algorithm that incorporates machine-learning methods to make personalized ad-serving decisions within milliseconds. We developed this algorithm for Vungle Inc., one of the largest global mobile ad networks. Our approach also …

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Performance Of Cellular Bucket Brigades With Hand-Off Times, Yun Fong Lim Oct 2017

Performance Of Cellular Bucket Brigades With Hand-Off Times, Yun Fong Lim

Research Collection Lee Kong Chian School Of Business

A cellular bucket brigade is a way to coordinate workers along an aisle with work content on both sides. Each worker in a cellular bucket brigade works on one side of the aisle when he proceeds in one direction, and he works on the other side when he proceeds in the reverse direction. Although the cellular bucket brigade eliminates the unproductive walk-back, it requires more hand-offs to assemble a product than a traditional (serial) bucket brigade. These hand-offs may waste significant production capacity as each of them requires an exchange of work, which can be complicated and time-consuming in practice. …

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Transshipment Hub Selection From A Shipper’S And Freight Forwarder’S Perspective, Gang Chen, Waiman Cheung, Sung-Chi Chu, Liang Xu Oct 2017

Transshipment Hub Selection From A Shipper’S And Freight Forwarder’S Perspective, Gang Chen, Waiman Cheung, Sung-Chi Chu, Liang Xu

Research Collection Lee Kong Chian School Of Business

Transshipment hub selection becomes increasingly important to the global logistics community. From the perspectives of shippers and freight forwarders, a selection must align with cost control strategy and sustain service reliability across cooperative service providers. This paper assesses the selection with the options of both sea and air transports, and from the influence of country of origin of the company. Critical factors of transshipment hub selection, both qualitative and quantitative, are identified through focus group discussions. Relative importance of these factors is determined based on collective views of logistics stakeholders. The competitiveness of transshipment hubs is then assessed using an …

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Optimizing (S, S) Policies For Multi-Period Inventory Models With Demand Distribution Uncertainty: Robust Dynamic Programming Approaches, Ruozhen Qiu, Minghe Sun, Yun Fong Lim Sep 2017

Optimizing (S, S) Policies For Multi-Period Inventory Models With Demand Distribution Uncertainty: Robust Dynamic Programming Approaches, Ruozhen Qiu, Minghe Sun, Yun Fong Lim

Research Collection Lee Kong Chian School Of Business

We consider a finite-horizon single-product periodic-review inventory managementproblem with demand distribution uncertainty. We formulate the problemas a dynamic program and prove the existence of an optimal (s, S) policy. Thecorresponding dynamic robust counterpart models are then developed for thebox and the ellipsoid uncertainty sets. These counterpart models are transformedinto tractable linear and second-order cone programs, respectively. Weillustrate the effectiveness and practicality of the proposed robust optimizationapproaches through a numerical study.

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Analyzing The Impact Of Public Transit Usage On Obesity, Zhaowei She, Douglas M. King, Jacobson Sheldon Sheldon Jun 2017

Analyzing The Impact Of Public Transit Usage On Obesity, Zhaowei She, Douglas M. King, Jacobson Sheldon Sheldon

Research Collection Lee Kong Chian School Of Business

The objective of this paper is to estimate the impact of county-level public transit usage on obesity prevalence in the United States and assess the potential for public transit usage as an intervention for obesity. This study adopts an instrumental regression approach to implicitly control for potential selection bias due to possible differences in commuting preferences among obese and non-obese populations. United States health data from the 2009 Behavioral Risk Factor Surveillance System and transportation data from the 2009 National Household Travel Survey are aggregated and matched at the county level. County-level public transit accessibility and vehicle ownership rates are …

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Closed-Form Approximations For Optimal (R, Q) And (S, T) Policies In A Parallel Processing Environment, Marcus Ang, Karl Sigman, Jing-Sheng Song, Hanqin Zhang Jun 2017

Closed-Form Approximations For Optimal (R, Q) And (S, T) Policies In A Parallel Processing Environment, Marcus Ang, Karl Sigman, Jing-Sheng Song, Hanqin Zhang

Research Collection Lee Kong Chian School Of Business

We consider a single-item continuous-review (r, q) inventory system with a renewal demand process and independent, identically distributed stochastic lead times. Using a stationary marked-point process technique and a heavy-traffic limit, we prove a previous conjecture that inventory position and inventory on-order are asymptotically independent. We also establish closed-form expressions for the optimal policy parameters and system cost in heavy-traffic limit, the first of their kind, to our knowledge. These expressions sharpen our understanding of the key determinants of the optimal policy and their quantitative and qualitative impacts. For example, the results demonstrate that the well-known square-root …

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Contract Theory: Impact On Biopharmaceutical Alliance Structure And Performance, Niyazi Taneri, Arnoud De Meyer Jun 2017

Contract Theory: Impact On Biopharmaceutical Alliance Structure And Performance, Niyazi Taneri, Arnoud De Meyer

Research Collection Lee Kong Chian School Of Business

Alliances for new product development have been studied extensively in the operations management literature. Alliances between an innovator and a partner create value by utilizing their complementary capabilities. In this paper, we seek to understand what drives the alliance structure: the choice between collaborative alliances where the parties exert joint efforts and sequential alliances where, for the most part, the partner takes over going forward. Our analysis of a data set of over 2,000 biopharmaceutical alliances reveals our main finding: a key role of operational choices is to address contract theoretic concerns faced by an alliance.We also find that aligning …

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Is Electricity Storage Green? A Study On Commercial Buildings, Yangfang (Helen) Zhou Jun 2017

Is Electricity Storage Green? A Study On Commercial Buildings, Yangfang (Helen) Zhou

Research Collection Lee Kong Chian School Of Business

Electricity storage facilities, such as industrial batteries, are considered the “holy grail” in decarbonizing the electrical grid. They are being widely installed in commercial buildings, e.g., hospitals and shopping centers. We model the problem of managing electricity storage in a commercial building as a Markov Decision Process. Our numerical results, based on models calibrated to the electricity load profiles of 100 commercial buildings in the U.S., show that for every electricity load profile, storage operation may increase carbon emissions.

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Licensing Contracts: Control Rights, Options And Timing, Pascale Crama, Bert De Reyck, Niyazi Taneri Apr 2017

Licensing Contracts: Control Rights, Options And Timing, Pascale Crama, Bert De Reyck, Niyazi Taneri

Research Collection Lee Kong Chian School Of Business

Research and development (R&D) collaborations, common in high-tech industries, are challenging to manage due to technical and market risks as well as incentive problems. We investigate how control rights, options, payment terms and timing allow the innovator to capture maximum value from its R&D collaborations with a marketer. Our study reveals a counterintuitive result; the innovator may, under certain conditions, prefer to grant launch control rights or buy-out options to the marketer despite the fact that both terms restrict its downstream actions. We demonstrate that a menu of contracts is not necessary to address the adverse selection problem as the …

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Managing Production-Inventory Systems With Scarce Resources, Saif Benjaafar, David Chen, Rowan Wang Feb 2017

Managing Production-Inventory Systems With Scarce Resources, Saif Benjaafar, David Chen, Rowan Wang

Research Collection Lee Kong Chian School Of Business

We consider the problem of managing production in a production-inventory system where a firm is subject to an allowance (a limit) on either the amount of input it can use or the amount of output it can produce over a specified compliance period (in addition to being subject to a constraint on the production capacity). Examples of such settings are numerous and include those where limits are placed on the use of scarce natural resources as input or on the amount of waste or harmful pollution generated by production as output. We study the structure of the optimal production policy …

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On Mx / G(M/H)/1 Retrial System With Vacation: Service Helpline Performance Measurement, Wee Meng Yeo, Xue Ming Yuan, Mei Wan Joyce Low Jan 2017

On Mx / G(M/H)/1 Retrial System With Vacation: Service Helpline Performance Measurement, Wee Meng Yeo, Xue Ming Yuan, Mei Wan Joyce Low

Research Collection Lee Kong Chian School Of Business

This paper analyzes an unreliable Mx/ G(M/ H) / 1 retrial system which models a class of practices in m-commerce industry where services are rendered in-situ. We present the closed-form expressions for the important performance indicators of the system, and derive the optimal vacation policies for minimizing the average waiting time of orbiting customers. Under the long run average cost, it turns out that the optimal vacation policy for the server is either single or multiple vacation policy. Numerical experiments are conducted to examine the effect of vacation policy on the queue length and busy period of the system.

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Predicting The Performance Of Queues: A Data Analytic Approach, Kum Khiong Yang, Cayirli Tugba, Mei Wan Low Dec 2016

Predicting The Performance Of Queues: A Data Analytic Approach, Kum Khiong Yang, Cayirli Tugba, Mei Wan Low

Research Collection Lee Kong Chian School Of Business

Existing models of multi-server queues with system transience and non-standard assumptions are either too complex or restricted in their assumptions to be used broadly in practice. This paper proposes using data analytics, combining computer simulation to generate the data and an advanced non-linear regression technique called the Alternating Conditional Expectation (ACE) to construct a set of easy-to-use equations to predict the performance of queues with a scheduled start and end time. Our results show that the equations can accurately predict the queue performance as a function of the number of servers, mean arrival load, session length and service time variability. …

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Appointment Sequencing: Why The Smallest-Variance-First Rule May Not Be Optimal, Qingxia Kong, Chung-Yee Lee, Chung-Piaw Teo, Zhichao Zheng Dec 2016

Appointment Sequencing: Why The Smallest-Variance-First Rule May Not Be Optimal, Qingxia Kong, Chung-Yee Lee, Chung-Piaw Teo, Zhichao Zheng

Research Collection Lee Kong Chian School Of Business

We study the design of a healthcare appointment system with a single physician and a group of patients whose service durations are stochastic. The challenge is to find the optimal arrival sequence for a group of mixed patients such that the expected total cost of patient waiting time and physician overtime is minimized. While numerous simulation studies report that sequencing patients by increasing order of variance of service duration (Smallest-Variance-First or SVF rule) performs extremely well in many environments, analytical results on optimal sequencing are known only for two patients. In this paper, we shed light on why it is …

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Least Squares Approximation To The Distribution Of Project Completion Times With Gaussian Uncertainty, Zhichao Zheng, Karthik Natarajan, Chung-Piaw Teo Nov 2016

Least Squares Approximation To The Distribution Of Project Completion Times With Gaussian Uncertainty, Zhichao Zheng, Karthik Natarajan, Chung-Piaw Teo

Research Collection Lee Kong Chian School Of Business

This paper is motivated by the following question: How to construct good approximation for the distribution of the solution value to linear optimization problem when the random objective coefficients follow a multivariate normal distribution? Using Stein’s Identity, we show that the least squares normal approximation of the random optimal value can be computed by estimating the persistency values of the corresponding optimization problem. We further extend our method to construct a least squares quadratic estimator to improve the accuracy of the approximation; in particular, to capture the skewness of the objective. Computational studies show that the new approach provides more …

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Managing Emergency Department Crowding Through Improved Triaging And Resource Allocation, Kum Khiong Yang, Sean Shao Wei Lam, Joyce M. W. Low, Marcus Eng Hock Ong Sep 2016

Managing Emergency Department Crowding Through Improved Triaging And Resource Allocation, Kum Khiong Yang, Sean Shao Wei Lam, Joyce M. W. Low, Marcus Eng Hock Ong

Research Collection Lee Kong Chian School Of Business

Long waiting times in emergency departments (EDs) not only reduce patients’ perceived quality of care, but also increase crowding which can adversely affect patients’ outcomes. Waiting time has been found to affect patients’ outcomes and is closely associated with delays in the provision of ancillary services to ED patients by the diagnostic/treatment laboratories. The focus of this study is to improve the flow of ED patients by testing alternative triage processes and capacity of physicians, triage nurses and laboratories. Three alternative triage processes are examined for managing the flow of ED patients through shared and dedicated laboratories across different utilization …

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The Impact Of The Potential Entry Of Copycats: Entry Conditions, Consumer Welfare, And Social Welfare, Sarah Y. Gao, Wei Shi Lim, Christopher Tang Aug 2016

The Impact Of The Potential Entry Of Copycats: Entry Conditions, Consumer Welfare, And Social Welfare, Sarah Y. Gao, Wei Shi Lim, Christopher Tang

Research Collection Lee Kong Chian School Of Business

This article examines the implications of the potential entry of a copycat who produces and sells a copycat (i.e., imitation) product that competes with the incumbent product. By analyzing a two-period dynamic noncooperative game between these two firms, we identify conditions under which the copycat can gain successful market entry. More importantly, we find that the potential entry of a copycat creates (implicit) pressure for the incumbent to lower its selling price; hence, it improves consumer welfare. Finally, we identify conditions under which the potential entry of a copycat can increase social welfare (i.e., consumer welfare and the profit of …

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Can S'Pore Be An Icon For Service Productivity?, Arnoud De Meyer Apr 2016

Can S'Pore Be An Icon For Service Productivity?, Arnoud De Meyer

Research Collection Lee Kong Chian School Of Business

The traditional analysis tools or flexible work design deployed in manufacturing may be insufficient in giving a boost to services. For all practical purposes, there are only two ways to create more value per worker and stimulate growth, we need innovation or become more productive.

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Ad Revenue Optimization In Live Broadcasting, Dana G. Popescu, Pascale Crama Apr 2016

Ad Revenue Optimization In Live Broadcasting, Dana G. Popescu, Pascale Crama

Research Collection Lee Kong Chian School Of Business

In live broadcasting, the break lengths available for commercials are not always fixed and known in advance (e.g., strategic and injury time-outs are of variable duration in live sports transmissions). Broadcasters actively manage their advertising revenue by jointly optimizing sales and scheduling policies. We characterize the optimal dynamic schedule in a simplified setting that incorporates stochastic break durations and advertisement lengths of 15 and 30 seconds. The optimal policy is a "greedy" look-ahead rule that accounts for the remaining number of breaks; in this setting, there is no value to perfect information at the scheduling stage, and hence knowing the …

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Electricity Trading And Negative Prices: Storage Vs. Disposal, Yangfang (Helen) Zhou, Alan Scheller-Wolf, Nicola Secomandi, Stephen Smith Mar 2016

Electricity Trading And Negative Prices: Storage Vs. Disposal, Yangfang (Helen) Zhou, Alan Scheller-Wolf, Nicola Secomandi, Stephen Smith

Research Collection Lee Kong Chian School Of Business

Electricity cannot yet be stored on a large scale, but technological advances leading to cheaper and more efficient industrial batteries make grid-level storage of electricity surpluses a natural choice. Because electricity prices can be negative, it is unclear how the presence of negative prices might affect the storage policy structure known to be optimal when prices are only non-negative, or even how important it is to consider negative prices when managing an industrial battery. For fast storage (a storage facility that can both be fully emptied and filled up in one decision period), we show analytically that negative prices can …

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