Chelliah Sriskandarajah

• Texas A&M University

Robotic mobile fulfillment (RMF) systems automate storage and transportation within fulfillment centers while still relying on human pickers. We focus on two key performance metrics in these systems, aiming to minimize overall completion time (OCT) as the primary objective and the number of required robots (NRR) as a secondary objective. We investi...

We study the U.S. Coin Supply Chain from both the demand and supply side perspectives to improve coin circulation in the economy. More specifically, we provide an operating policy for Depository Institutions (DIs) to improve their efficiency in packaging, distributing, coordinating, and managing the inventory of coins. We further propose a new poli...

We study an optimal matching problem in the context of dual‐donor organ exchange, where a portion of two living donors' organs are transplanted to a single patient. This dual‐donor transplant technique is becoming more widespread for lung and liver transplants. However, multiple medical compatibility criteria pose a serious challenge for matching a...

Problem definition: We develop a framework to plan capacity in each of three sequential stages for ambulatory surgery centers (ASCs). The interdependence of activities, their stochastic durations, and the uncertainties in patient-mix pose significant challenges to managing the capacity of each activity and to achieving a smooth patient ow by coordi...

This research studies the logistics and inventory planning problem encountered at an oilfield services company whose supply chain consists of suppliers, a Hybrid Cross-Dock (HCD) facility, and production facilities. The HCD provides an option for the company to store inventory for a period of time without incurring inventory holding costs. This res...

Explosive growth in the number of users on various social media platforms has transformed the way firms strategize their marketing activities. To take advantage of the vast size of social networks, firms have now turned their attention to influencer marketing wherein they employ independent influencers to promote their products on social media plat...

Applications of cloud computing are increasing as companies shift from on-premise IT environments to public, private, or hybrid clouds. Consequently, cloud providers use capacity planning to maintain the capacity of computing resources (instances) required to meet the dynamic nature of computing demand (queries). However, there is a trade-off betwe...

With the rapid growth of cloud computing, firms face a dizzying array of choices and pricing structures for performing their computing tasks on the cloud. Unlike captive computing resources, cloud computing occurs as a pay-as-you-go contract, similar to the provision of electricity. We develop a method to reduce the rental cost of completing a give...

This study explores whether and how lower variations in clinical practice relate to hospital operational performance. This relation is critical to the overall search for pathways that will allow the healthcare industry to bend the cost curve, implying significant implications for practice and regulators. We define practice variation as all variatio...

Can adopting multiple revenue streams secure long-term sustainability of HIEs? Healthcare information exchanges (HIEs) facilitate information sharing among participating healthcare practices. Despite HIEs’ pivotal role in improving healthcare delivery, many struggle to be financially sustainable in the long run. As a practical and implementable sol...

Job shop scheduling with a bank of machines in parallel is important from both theoretical and practical points of view. Herein we focus on the scheduling problem of minimizing the makespan in a flexible two‐center job shop. The first center consists of one machine and the second has k parallel machines. An easy‐to‐perform approximate algorithm for...

We study a generalized location‐routing problem in which the key decisions are made by supply chain partners with conflicting objectives. The context of our problem is the irradiation by electron beam (eBeam) of fresh produce imported from Mexico to reduce the threat of insects and pests to U.S. agriculture. Because too few irradiation facilities e...

We study a coin supply chain problem in the context of improving efficiency. While most consumer products are distributed in one direction, coins are recirculated and reused through the economy. The Federal Reserve System (FRS), the central banking system of the U.S., plays a crucial role in managing the U.S. Coin Supply Chain (CSC). It spends a si...

Operating rooms (ORs) are the greatest source of revenues for hospitals and also their largest cost centers. When scheduling surgeries, hospitals face a trade‐off between the need to conduct planned elective surgeries and the need to be responsive to emergency cases. However, scheduling ORs, especially at Level‐1 trauma hospitals, is challenging du...

Problem Definition: We develop a framework to plan capacity for ambulatory surgery centers (ASCs) typically consisting of three sequential stages. The problem is to determine the capacity in each stage that efficiently covers possible daily patient demand and to coordinate the three stages of a patient's visit. The objective is to minimize the tota...

Explosive growth in the number of users on various social media platforms has transformed the way firms strategize their marketing activities. To take advantage of the vast size of social networks, firms have now turned their attention to influencer marketing wherein they employ independent influencers to promote their products on social media plat...

A robotic cell is a set of machines or processing centres served by a robot or a set of robots. Robotic cells can be classified by certain physical and operating characteristics such as robot type (single- or dual-gripper), robot travel-time (constant, additive or Euclidean) and types of parts processed (no-wait, interval processing time or free-pi...

We study outpatient appointment block scheduling policies for single providers under conditions of patient heterogeneity in service times and patient no-shows. The objective is to find daily appointment schedules that minimize a weighted sum of patients’ waiting time, the physician's idle time, and the physician's overtime. We contribute by suggest...

Many automated manufacturing systems use robotic cells, which consist of a set of machines served by a robot. Robotic cells with a single-gripper robot have been extensively studied in the literature. By contrast, cells with a dual-gripper robot, although more productive, have received less attention, perhaps because of their inherent complexity. W...

The performance of a retail store depends on its ability to attract customer traffic, match labor with incoming traffic, and convert the incoming traffic into sales. Retailers make significant investments in marketing activities (such as advertising) to bring customers into their stores and in-store labor to convert that traffic into sales. Thus, a...

We optimize a large country's currency supply network for its central bank. The central bank provides currency to all branches (who in turn serve consumers and commerce) through its network of big vaults, regional vaults, and retail vaults. The central bank intends to reduce its total transportation cost by enlarging a few retail vaults to regional...

Even though more and more transactions and payments are conducted electronically, physical currency (banknotes and coins) still plays an essential role in commerce and trade, and it is expected to maintain its dominance in the near future. Over the past decade, several studies have analyzed various currency supply chains across the world. This stud...

The online movie rental industry in the United States has grown at a rapid pace during the past decade. Netflix and Blockbuster are two prime examples of companies that operate in this arena, each with a large subscriber base. These two companies employ two standard methods for movie delivery: streaming and DVD-by-mail services. Although the indust...

Online personalization has become quite prevalent in recent years, with firms able to derive additional profits from such services. As the adoption of such services grows, firms implementing such practices face some operational challenges. One important challenge lies in the complexity associated with the personalization process and how to deploy a...

We study the logistics problem faced by Regional Branches (RBs) of a central bank in managing the currency supply under security concerns. While making banknote supply decisions to Sub-Branches (SBs), the management of RB must achieve two goals simultaneously: (1) guarantee that each SB has sufficient inventories of all denominations of banknotes t...

The Federal Reserve System of the United States is making changes to its cash recirculation policy to reduce depository institutions’ (banks’) overuse of its cash processing services. These changes will affect operating policies and costs at many institutions having large cash businesses and, in turn, impact cash transportation and logistics provid...

We consider the problem of optimally allocating contiguous rectangular presentation spaces in order to maximize revenues. Such problems are encountered in the arrangement of products in retail shelf-space and in the design of feature advertising displays or webpages. Specifically, we allow (i) the shape of a product's presentation to have a vertica...

Line extensions-variants of existing products with new appearances, functions, or forms-constitute a significant fraction of products launched each year. While line extensions typically share components with existing products, they can also cannibalize the demand of existing products. The choice of an appropriate set of line extensions is an import...

This article considers the problems of scheduling operations in single-gripper and dual-gripper bufferless robotic cells in which the arrangement of machines is circular. The cells are designed to produce identical parts under the free-pickup criterion with additive intermachine travel time. The objective is to find a cyclic sequence of robot moves...

We study a supply planning problem in a manufacturing system with two stages. The first stage is a remanufacturer that supplies two closely-related components to the second (manufacturing) stage, which uses each component as the basis for its respective product. The used products are recovered from the market by a third-party logistic provider thro...

The online movie rental industry in the United States has grown at a rapid pace during the past decade. Netflix and Blockbuster are two prime examples of companies that operate in this arena, each with a large subscriber base. These two companies employ two standard methods for movie delivery: streaming and DVD-by-mail services. Although the indust...

Motivated by interactions with two reverse-logistics firms, we analyse the trade-off between two product-recovery approaches: recycling and remanufacturing. We consider a manufacturer who produces and markets a product with the objective of maximising profit. A unit of the product consists of two modules: A and B. After recovery, Module A can be re...

We develop, in this article, a sales model for movie and game products at Blockbuster. The model assumes that there are three sales components: the first is from consumers who have already committed to purchasing (or renting) a product (e.g., based on promotion of, or exposure to, the product prior to its launch); the second comes from consumers wh...

We study a problem faced by a secure‐logistics provider (SLP) of maximizing profit by jointly pricing the services of fit‐sorting and transporting cash along with the design of the supporting logistics network, in a market consisting of a population of Depository Institutions (DIs). The need to jointly price the services assumes significance becaus...

Abstract We study conflict and cooperation issues in a two-stage production system. The objective of the first stage is to minimize the sum of the completion times of all n jobs, denoted by P, j=1 Cj(σ1). The second stage’s objective is to minimize the number of tardy jobs, denoted by N(σ2); σ1 and σ2 are, respectively, the preferred schedules – th...

A dedicated subnetwork (DSN) refers to a subset of lanes, with associated loads, in a shipper's transportation network, for which resources—trucks, drivers, and other equipment—are exclusively assigned to accomplish shipping requirements. The resources assigned to a DSN are not shared with the rest of the shipper's network. Thus, a DSN is an autono...

A national recycling and waste management company provides periodic services to its customers from over 160 service centers. The services are performed periodically in units of weeks over a planning horizon. The number of truck-hours allocated to this effort is determined by the maximum weekly workload during the planning horizon. Therefore, minimi...

Blockbuster Inc., a chain of VHS, DVD, Blu-ray, and video game rental stores, has developed a highly specialized distribution network. The company maintains a single distribution center in which it receives products from suppliers, and processes and packs them for shipping to stores across the United States. The volumes of particular products and t...

The effective local reuse of physical cash by depository institutions (DIs) is the primary goal of the new cash recirculation policy of the Federal Reserve System (Fed) of the United States. These guidelines, implemented since July 2007, encourage the reuse of cash by (i) penalizing a DI for the practice of cross shipping, the near-simultaneous dep...

We study zero‐inventory production‐distribution systems under pool‐point delivery. The zero‐inventory production and distribution paradigm is supported in a variety of industries in which a product cannot be inventoried because of its short shelf life. The advantages of pool‐point (or hub‐and‐spoke) distribution, explored extensively in the literat...

Line extensions – variants of existing products with new appearances, functions, or forms – constitute a significant fraction of products launched each year. While line extensions typically share components with existing products and, therefore, require lower development costs (as compared to new products), they can also cannibalize the demand of e...

Although the impact of layout on the productivity of manufacturing systems is well recognized, a quantification of this impact is an issue that is often ignored or crudely approximated in practice. When evaluating competing layouts for a manufacturing system, the trade-off between their relative benefits and their relative costs underlines the need...

Cluster tools (also referred to as robotic cells) are extensively used in semiconductor wafer fabrication. We consider the problem of scheduling operations in an m-machine cluster tool that produces identical parts (wafers). Each machine is equipped with a unit-capacity input buffer and a unit-capacity output buffer. The machines and buffers are se...

The explosive growth in the variety and size of social networks has focused attention on searching these networks for useful structures. Like the Internet or the telephone network, the ability to efficiently search large social networks will play an important role in the extent of their use by individuals and organizations alike. However, unlike th...

We assess the benefits of implementing a dual-arm robot in a flow shop manufacturing cell. Such a robot has the ability to tend (unload or load) two adjacent machines simultaneously. This significantly changes the analysis required to find sequences of robot actions that maximize a cell’s throughput. For cells processing identical parts, we identif...

The overuse of its currency processing operations by depository institutions (DIs) has motivated the Federal Reserve (Fed) to propose new currency recirculation guidelines. The Fed believes that DIs should play a more active role in recirculating fit (i.e., usable) currency so that the societal cost of providing currency to the public is minimized....

We consider the problem of scheduling operations in a robotic cell processing a single part type. Each machine in the cell has a one-unit input buffer and a one-unit output buffer. The machines and buffers are served by one single gripper robot. The domain considered is free-pickup cells with additive inter-machine travel time. The processing const...

This paper analyzes the tradeoff between (demand) substitution costs and (production) changeover costs in a discrete-time production-inventory setting using a two-product dynamic lot-sizing model with changeover, inventory carrying, and substitution costs. We first show that the problem is poly-nomially solvable and then develop several insights in...

A job-shop with two machine centers with the second one consisting of k parallel machines is considered. An approximate algorithm for minimizing schedule length in the job shop with unit time operations in the first machine center and k time-units operations in the second is proposed. The algorithm has the absolute worst case error bound of k-1. Th...

One of the distinctive features of sites on the Internet is their ability to gather enormous amounts of information regarding their visitors, and use this information to enhance a visitor’s experience by providing personalized information or recommendations. In providing personalized services a website is typically faced with the following tradeoff...

The overuse of its currency processing facilities by depository institutions (DIs) has motivated the Federal Reserve (Fed) to impose its new cash recirculation policy. This overuse is characterized by the practice of cross-shipping, where a DI both deposits and withdraws cash of the same denomination in the same business week in the same geographic...

A few weeks before the start of a major season, movie distributors arrange a private screening of the movies to be released during that season for exhibitors and, subsequently, solicit bids for these movies (from exhibitors). Since the number of such solicitations far exceeds the number of movies that can be feasibly screened at a multiplex (i.e.,...

A Dedicated Subnetwork (DSN) refers to a subset of lanes with associated loads in a shipper's transportation network, for which a fleet of resources – trucks, drivers, and other equipment – is exclusively assigned to carry out all shipping requirements. The resources assigned to a DSN are not shared for shipping in the rest of the shipper's network...

Interval robotic cells with several processing stages (chambers) have been increasingly used for diverse wafer fabrication processes in semiconductor manufacturing. Processes such as low-pressure chemical vapor deposition, etching, cleaning and chemical-mechanical planarization, require strict time control for each processing stage. A wafer treated...

We study conflict and cooperation issues in a two-stage production system. The objective of the first stage is to minimize the sum of the completion times of all n jobs. The second stage's objective is to minimize the number of tardy jobs; There is an intermediate buffer connecting the first and the second stage. If required, jobs are re-sequenced...

We establish the computational complexity of the problem of minimizing makespan in a flowshop, where each jobs requires a pallet the entire time, from the start of its first operation until the completion of the last operation. We prove that the problem is NP-hard in the strong sense for m greater than or equal to 2 and K greater than or equal to 3...

This paper studies a two stage supply chain with a dominant upstream partner. Manufacturer is the dominant partner and operates in a Just-in-Time environment. Production is done in a single manufacturing line capable of producing two products without stopping the production for switching from one product to the other. The manufacturer imposes const...

We address the scheduling of operations in a robotic cell that produces multiple part-types. The objective is to obtain a cyclic schedule—a sequence of robot moves and an ordering of the parts—that minimizes the long-run average time to produce a part or, equivalently, maximizes the throughput. We consider two different models that are currently us...

We consider the problem of scheduling operations in bufferless robotic cells that produce identical parts using either single‐gripper or dual‐gripper robots. The objective is to find a cyclic sequence of robot moves that minimizes the long‐run average time to produce a part or, equivalently, maximizes the throughput. Obtaining an efficient algorith...

We consider the scheduling of ground station support times to low Earth orbit (LEO) satellites with overlapping visibilities. LEO satellites typically complete a revolution around the Earth in less than four hours at an altitude of a few hundred miles and are part of the critical infrastructure for natural resource management, crop yield estimation...

In this paper we study the time complexities of some two- and three-stage no-wait flowshop makespan scheduling problems where, in some stage, all the jobs require a constant processing time and the stage may consist of parallel identical machines. Polynomial time algorithms are presented for certain problems, while several others are proved to be s...

Constant travel-time robotic cells with a single gripper robot and with one or more machines at each processing stage have been studied in the literature. By contrast, cells with a dual gripper robot, although more productive, have so far received scant attention, perhaps due to their inherent complexity. We consider the problem of scheduling opera...

A Dallas-based telephone manufacturer, that imports semi-finished products from a supplier in Malaysia, wants to develop a risk mitigation plan to minimise the operational risk it may face due to supply disruptions at a US port. Disruptions at the port can render the supply unavailable for a considerable period of time, resulting in a loss of busin...

RFID presents a great opportunity for leaders to take their supply chain performance to a superior level. However, it does not come without risks which could delay the adoption of this technology. In this paper, we propose a framework for companies to identify their role, typical pain points and performance metrics to focus on to maximize impact. I...

The combination of parallel machines and multiple dual gripper robots has become increasingly prevalent in modern manufacturing with robotic cells. However, there has been no previous study of the design and scheduling challenges faced by managers who employ these complex cells. The benefit of implementing dual grippers in cells with multiple robot...

We study the benefits of coordinated decision making in a supply chain consisting of a manufacturer, a distributor, and several retailers. The distributor bundles finished goods produced by the manufacturer and delivers them to the retailers to meet their demands. The distributor is responsible for managing finished goods inventory. An optimal prod...

In this paper, we deal with the problem of sequencing parts and robot moves in a robotic cell where the robot is used to feed machines in the cell. The robotic cell, which produces a set of parts of the same or different types, is a flow-line manufacturing system. Our objective is to maximize the long-run average throughput of the system subject to...

Part-orienting systems are employed in many manufacturing environments to feed work parts in correct orientation for proper operations. A part-orienting system is a serial arrangement of orienting devices; the selection and ordering of these devices is an important design aspect that is addressed in this paper. In addition, a parallel configuration...

The integrated production and transportation scheduling problem (PTSP) with capacity constraints is common in many industries. An optimal solution to PTSP requires one to simultaneously solve the production scheduling and the transportation routing problems, which requires excessive computational time, even for relatively small problems. In this st...

Recently, an agile software development technique called extreme programming has caught the attention of practitioners and researchers in the software industry. A core practice of extreme programming is pair programming, where two developers work on the same piece of code. We introduce the problem of assigning pairs of developers to modules so as t...

We consider the problem of grooming in all-optical networks to maximize traffic. We present an integer-programming formulation while constraining the number of optical transceivers at each node, the link load, and the capacity of each lightpath. Based on the structural properties of the problem, we develop a heuristic based on a column-generation t...

New currency recirculation guidelines implemented by the Federal Reserve System (Fed) of the United States are intended to reduce the overuse of its currency processing services by depository institutions (banks). These changes are expected to have a signiflcant impact on operating policies at those depository institutions that handle large volumes...