Research

Major Research Interests:

Mathematical models in the social, behavioral, biological, epidemiological, and environmental sciences and of problems of communications and transportation; theory of measurement; homeland security and in particular stadium and large venue security, natural disasters, maritime cyber security, supply chains, and homeland security aspects of global environmental change; utility, decision making and social choice; socially responsible algorithms; graph theory, combinatorics and their applications; applications of AI in stadiums, ports, transportation; mathematical psychology; precollege education.

Selected List of Research Centers and Institutes I am or Have Been Associated With

Description of Specific Research Topics

Research: Mathematical Social Sciences

From my days as an undergraduate at Dartmouth, through work with Bob Norman and John Kemeny, I have been fascinated by the applications of mathematical sciences methods to problems of psychology, sociology, economics, and other areas in the social and behavioral sciences. As a graduate student at Stanford, under the influence of Pat Suppes and Dana Scott, I focused on topics that would become a career-long interest: preference, utility, subjective probability, loudness, etc.  My papers explore fundamental ideas concerning nontransitive indifference, axioms for subjective expected utility, small group sociology models of balanced signed graphs and consistent marked graphs, and the theory of role assignments, as well as behavioral responses to bioterrorism events. Some of my invited talks about this work have been at meetings of such organizations as the European Mathematical Psychology Group in Brussels and in Luxembourg and the Society for Mathematical Psychology in Ann Arbor, and at International Conferences on Ordinal and Symbolic Data Analysis in Darmstadt and Amherst.

Research: Theory of Measurement

As a graduate student, I became interested in the problem of putting measurement on a firm mathematical foundation, with the aim of developing foundational approaches to measurement in the social and behavioral sciences. I learned about the representational theory of measurement from some of the key founders of that theory, Pat Suppes, R. Duncan Luce, Amos Tversky, and Dave Krantz, and my book Measurement Theory, with Applications to Decisionmaking, Utility, and the Social Sciences on the subject remains in use even though it has not been updated since its appearance in 1979. In representational measurement, National Medal of Science Winner Duncan Luce and I produced axioms for extensive measurement, which involves the analysis of homomorphisms of ordered algebraic systems. My paper on laws of exchange arose from the desire to put measurement of environmental pollutants, in particular noise, on a mathematical foundation, and developed fundamental relationships among three central concepts, extensive measurement, conjoint measurement, and qualitative probability measurement. My primary interest in measurement theory has been on the meaningfulness of statements using scales of measurement, a topic which deals with the uniqueness of a measurement representation, and I have applied the theory of meaningfulness to problems of psychophysics, epidemiology and public health, conservation biology, intelligent machines, emergency management, border security. With Alexis Tsoukias and Helen Roberts, I worked on notions of meaningfulness dealing with body mass indices and air pollution indices. Janos Aczel and I used methods of functional equations to characterize the possible forms of scientific laws and the possible merging or averaging functions. Among my invited talks on measurement theory were one at the First International Conference on Algorithmic Decision Theory in Venice and one at the Workshop on Fundamental Logical Concepts of Measurement in Turin, Italy. I have given numerous invited lecture series in this area, for example at MAA Mathfest and the INFORMS National meeting,

Research: Mathematics of Planet Earth: Ecology, Environment, Epidemiology, Energy

While at the RAND Corporation in the late 1960s and early 1970s, I became interested in environmental problems, and that has led to a career-long interest in mathematical approaches to problems facing the planet.  I chose to make “Mathematique de la planete Terre the subject of my speech when I was awarded an honorary doctorate at the University of Paris – Dauphine in 2013, and I have taken a leadership role (along with Hans Kaper and Christiane Rousseau and others) of the world-wide initiative “Mathematics of Planet Earth” (MPE). This included organization of a 25-workshop program at DIMACS starting in 2013. A 2019 book edited together with Hans Kaper is devoted to MPE. A 2022 book Mathematics for Action: Supporting Science-based Decision-making I co-edited with Kaper and Rousseau and others was devoted to examples in which the mathematical sciences methods were used to address progress toward achieving the UN Sustainable Development Goals for the planet. My research publications have developed graph-theoretical models of disease spread, studied the measurement of biodiversity, and introduced the concept of bioconsensus, which explores the use of consensus methods developed in the context of voting, decision making, and other areas of the social and behavioral sciences to problems of taxonomy and evolutionary biology, and molecular biology. I also edited five books on energy modeling, including a SIAM book on the topic, and helped develop a DIMACS special focus on Energy and Algorithms. My measurement theory work has also emphasized topics of conservation biology, landscape ecology, and public health. In 2001, I initiated a 10-year DIMACS special focus on Mathematical and Computational Epidemiology, with the great assistance of a number of leading scientists including in particular National Medal of Science winner Simon Levin. That program led to important new ideas and fields such as economic epidemiology, syndromic surveillance, and combinatorial group testing. It included 64 workshops, working group meetings, and tutorials and introduced hundreds of people to topics such as climate and disease, co-evolution of hosts and pathogens, vaccination strategies, and disease clusters. Resilience of natural systems and of human systems is threatened by a variety of disruptions. This has led me to organize a series of workshops on sustainability such as the one on Mathematical and Statistical Challenges for Sustainability in 2010 that led to a book on that topic edited with Midge Cozzens. It has also led me to explore models of resilience of networks, and to edit a book, Resilience in the Digital Age, together with my Russian colleague Igor Sheremet. Some of my lectures in this area were at workshops on Conservation Biology in Hoedspruit, South Africa; on Modeling the Impact of Policy Options during Public Health Crises in Banff, Canada; on Landscape Ecology and Sustainability in Durban, South Africa; on Evidence-based Policy Making in Paris; on Mathematical Modeling of Infectious Diseases in Stellenbosch, South Africa; on Smart Cities in Paris; on the Smart Grid at Lehigh University; and on Information and Communication Technologies for Sustainability in Salt Lake City.

Research: Applications of Graph Theory/Combinatorics

My contributions to graph theory have primarily been on or arising from applications of the subject. I was told by Vera Sos that my 1976 book Discrete Mathematical Models, with Applications to Social, Biological and Environmental Problems, introduced the distinguished Hungarian graph theory community to the applied side of the subject. I have analyzed models of preference and indifference through the study of semiorders and indifference graphs, interval graphs, boxicity, cubicity, and their variants. I got interested in the connection between food webs and the corresponding graphs that represent competition, wrote a variety of papers on such variants as double competition graphs, (i,j)-competition graphs, and phylogeny graphs, and introduced competition numbers that arise from the study of which food webs have competition graphs that are interval graphs. My exposure to the radio frequency assignment problem led me to study a variety of variants of graph coloring such as T-coloring, which I introduced with Midge Cozzens, and list coloring. I studied such applications of these variants as traffic light phasing, scheduling, fleet assignment, and DNA mapping. I was also fascinated by the problem of making all streets in a city one-way in order to improve traffic flow and air quality and, together with my Chinese colleague Yonghua Xu, wrote a series of detailed papers on orientations of edges of a graph that would make it strongly connected – allowing for cars following one way streets to reach any place from any other place.

During a sabbatical visit to Bell Labs, I worked with Peter Fishburn, whom I had met during my time at the RAND Corporation when we wrote a widely cited paper on dimension of partial orders that helped launch a huge area of research. While at Bell Labs, we started on a long-lasting collaboration that explored a variety of sequences of integers arising from problems in measurement theory such as comparative judgments of probability and uniqueness of representability. In a series of papers, we introduced combinatorial and number-theoretic properties of Van Lier sequences, regular sequences, elementary sequences, sub-Fibonacci sequences, and two-sided general Fibonacci sequences. Fishburn and I also collaborated on graph theoretical problems (L(2,1) colorings) and utility theory. I have more joint papers with Fishburn than with any other collaborator.

I was invited to give the 1977 CBMS-NSF Lectures at Colby College and this led to my book Graph Theory and its Applications to Problems of Society, published by SIAM. I was invited to give a 6-lecture series on my work on applied graph theory and combinatorics at the ORSA national meeting in 1985, and to give plenary talks about it at a wide variety of meetings, for example the International Conference 2000 — The Year of Mathematics (on the occasion of the 50th anniversary of the Mathematical Institute of the Hungarian Academy of Sciences and the 150th Anniversary of the Academy), in Budapest in 2000; an international conference on Combinatorial and Computational Mathematics in Pohang, S. Korea; and the First International Symposium on Combinatorics in Seoul, S. Korea. I also gave the Rota Lecture at a Conference on Interconnections among Codes, Designs, Graphs and Molecular Biology in Hsinchu, Taiwan, in 2002.

Research: Data Science

Through DIMACS, I helped to plan multi-year special focus programs on Massive Data Sets (1997-1999) and on Data Analysis and Mining (2001-2006). My co-edited book Graphs and Discovery resulted from the latter. Homeland security challenges have also led me to get involved in data science. Starting shortly after 9-11, the intelligence community invited researchers with relevant NSF funding to a series of meetings to see how we could be of help. The result was that with support from the intelligence community through funding provided to NSF, I worked with Paul Kantor and David Madigan and others on the development of Bayesian multiple regression tools for natural language processing. Both the DHS centers that I have led, DyDAn and CCICADA, are data science centers, and have fostered a great deal of data science research.  I have studied connections between data science and resilience. I co-edited a book Resilience in the Digital Age) with my Russian colleague Igor Sheremet; Igor and I met when we both served as representatives to the Scientific Advisory Committee of the International Institute for Applied Systems Science (IIASA), the organization founded by the U.S. and Russia during the Cold War and aimed at collaborations through science. I have studied the role of AI, in particular robots, in responding to disasters, which is one of the topics in the book. I have helped organize three workshops on social responsibility of algorithms and wrote a paper on fairness of face recognition for animals. My work in this area has led to invitations to give a plenary talk at the International Conference on Data Intensive Systems Analysis for Geohazard Studies, Sochi, Russia, in 2016, and a keynote talk at the International Conference on Global Challenges and Data-driven Science, Saint Petersburg, Russia, in October 2017. In 2019, I founded the DATA-INSPIRE Institute at Rutgers (DATA science for INtelligent Systems and People Interaction that integrates Research and Education activities), under support from the NSF program called TRIPODS (Transdisciplinary Research in Principles of Data Science), and through that Institute worked on applications of intelligent machines to emergency management. When the pandemic hit, I organized a group of over 30 Rutgers faculty from across the campus to form the Rutgers AI & Pandemics Initiative and led the AI & Pandemics research group on supply chains.

Research: Homeland Security

The September 11 attacks on the World Trade Center led to my creating and taking leadership of the Rutgers Homeland Security Research Initiative and the New Jersey Universities Homeland Security Research Consortium. The 2002 anthrax attacks soon after September 11 led to great concerns about bioterrorism. I was able to pivot the DIMACS special focus on Mathematical and Computational Epidemiology that I was leading toward mathematical methods to defend against bioterrorist attacks. Such initiatives were rewarded when Rutgers was awarded a Department of Homeland Security University Center of Excellence in 2006, the Center for Dynamic Data Analysis (DyDAn), and then in 2009, a second DHS Center of Excellence, the Command, Control, and Interoperability Center for Advanced Data Analysis (CCICADA), which I continue to lead. Through CCICADA, I have interacted with the highest levels of DHS and the homeland security enterprise nationwide and worldwide. See specific topics for more details of my homeland security research.

Homeland Security Research: Stadiums and Event Venues

My work on security at sports stadiums and large entertainment venues led to a series of reports on best practices for stadium security that were posted on the DHS website and have been widely used by the NFL, NBA, NH, Major League Baseball, Major League Soccer, NASCAR, and other professional sports. As one example, these guides were cited as of great assistance in improving safety at Comerica Park (Detroit Tigers) and design of the new Little Caesars Arena (Detroit Red Wings). This also led to papers on models for patron screening and experimental designs for testing walkthrough metal detectors (WTMDs) that caught the interest of the National Institute of Standards and Technology and led to revised WTMD standards. As a result of the stadium security work, I was invited to give a plenary talk to the NFL security directors national security summit in 2014 and later to the Big Ten Emergency Management and Special Events conference organized by Big Ten security directors. My work on simulation of crowd evacuation at sports stadiums was cited in Congressional testimony about Super Bowl XLVIII by the security director at MetLife Stadium in NJ.

Homeland Security Research: Transportation Facilities

The simulation of crowd evacuation at sports stadiums led to a project on simulation of crowd behavior at the world’s busiest bus terminal, the Port Authority Bus Terminal in New York City, with emphasis on crowd management during terminal redesign and on evacuation. It led to a paper in the Visual Computer Journal and a variety of projects on safety and security at transit facilities. I was invited to give a plenary talk about the bus terminal work and related stadium security work at a Public Area Security Summit organized by the TSA and the National Protection and Programs Directorate of DHS. I was involved in later transit facility modeling through projects led by Rutgers colleagues Jie Gong and Peter Jin. They built digital twins for NJ Transit terminals in Hoboken and Secaucus and, at the invitation of NJ Transit and MetLife Stadium, investigated the crucial role of the Secaucus station in funneling crowds to and from the FIFA World Cup events held at MetLife. Through the SENTRY work, I also started to interact with other surface transportation systems, e.g., WMATA in Washington, DC and BART in the Bay Area.

Homeland Security Research: Coast Guard Projects

My homeland security research also led to interactions with the Commandant and Vice Commandant of the US Coast Guard – I hosted both at Rutgers/CCICADA. Early projects led to research on large combinatorial optimization problems arising from assigning the Coast Guard’s boats to their boat stations and aircraft to aircraft stations. In the case of boats, the resulting model  promised to save the Coast Guard up to $120M. The aircraft work led to a conference paper joint with Coast Guard authors that won a best paper award. I organized the first symposium on Maritime Cyber Security in 2015, which was a major factor in the launching of the field of maritime cyber. During the symposium, the Vice Commandant of the Coast Guard unveiled the Coast Guard’s cyber security strategy and posed research challenges for the university community. I became the lead of a university-Coast Guard maritime cyber security research initiative that eventually led to my co-editing the first book on Maritime Cyber Security. My research on integrated cyber and physical attacks, both in the maritime domain and on sports stadiums, led to an invitation to give a keynote talk at a NATO maritime cyber security conference in Crete in 2019, a featured talk at the Annual Meeting of the Society for Naval Architects and Marine Engineers in Providence in 2018, and a plenary talk at the International Conference on Cyber Security, Fordham University in 2015. I have also written a series of papers on sequential decision-making algorithms for inspecting containers at ports and for detecting nuclear contraband in cities. Work with the Coast Guard and CBP on container inspection built on Boolean function models and decision trees and led to a series of papers. My work with the Coast Guard has also included research on fisheries regulation violations, hoax calls, risk assessment, and, most recently, to a major project on modeling complex disruptions to the marine transportation system. The hoax calls work led to application of a newly-developing field of voice forensics, and this led to identification and arrest of a serial hoax caller who had cost the Coast Guard $500,000 in unnecessary helicopter searches. I cannot take credit for doing this work myself – it was primarily the work of Rita Singh at CMU – but I made the connection.

Homeland Security Research: The Marine Transportation System

Recently, work with the Coast Guard has centered around complex disruptions to the marine transportation system (MTS). With partners at Arizona State, USC, and Ohio State, and key leadership from Adam Rose and retired USCG Captain Andrew Tucci, we developed methods to understand the consequences of multiple disruptions and identify effective mitigation tactics, and a decision-support tool for use by USCG and others to improve risk management. I worked with people at leading ports around the country (LA-Long Beach, New York/New Jersey, Houston, and the Great Lakes), numerous USCG components and many other agencies, e.g., US Army Corps of Engineers, Maritime Administration, US Committee on the MTS (CMTS, run by Dept. of Transportation), FEMA, Port Authority of NY/NJ, and companies such as Maher Terminals, Vitol, and Maersk. One highlight paper coming out of this work studied a complex disruption starting with low water on the Mississippi River resulting from climate change, followed by a failure of a key lock and dam on the river, and also a change in fertilizer imports at the Port of New Orleans. This paper illustrates another interest of mine: The homeland security aspects of climate change. That is also reflected in initial investigations of impact of climate change on indigenous people in Alaska and on ways to use drones to get early warning of potential permafrost disruption leading to a landslide. Another paper studied a three-part complex disruption starting with a labor strike, followed by loss of electric power due to a wildfire, and then a terrorism incident at a container terminal. A third paper involved the disruption to the Port of New York/New Jersey, starting with a background of warehouse shortages having increased terminal dwell time, followed by a container ship catching fire and blocking a key channel in the port, and then a malware attack on a terminal operating system in the Port of New York New Jersey. In all these examples, we built detailed models and analyzed economic impacts, both direct and indirect. I gave invited presentations on this work to numerous USCG officers and groups, the Committee on the Marine Transportation System, a FEMA Committee, the Cybersecurity and Infrastructure Security Agency (CISA) Resilience Services Branch, the government-wide Committee on the Continuity of the Economy, and various interagency committees. One highlight of this work was an invitation to brief the USCG Board of Inquiry in November 2024 after the Baltimore Bridge collapse in March 2024. One of my papers arising from this project won a best paper award.

Research: Supply Chains, with emphasis on Homeland Security Issues

With colleagues from Rutgers Industrial Engineering and elsewhere, in particular Elsayed Elsayed, I developed a risk-based methodology to enable quantitative comparisons of relative risk of different information and communications technology (ICT) supply chain threat scenarios and identify potentially useful countermeasures for different scenarios. This work led to a series of papers, for example in the journal Manufacturing Letters. DHS concern about supply chain disruption led me to organize an initiative involving 11 different DHS COEs on supply chains that turned into an emphasis on supply chains during COVID. During 2020-2021, this led to 7 workshops and heavy engagement of the private sector. One of the workshops, the one on enhanced supply chain crime during the pandemic, led to a project in which we developed methods to model, detect, and mitigate active, pending, or past criminal disruptions of a supply chain. The project, in collaboration with the DHS center of excellence CISA based at George Mason, and including key partners Alok Baveja, Ben Melamed, and Weiwei Chen from the Rutgers Business School, identified likely attack points, developed indicators that can alert authorities about a pending, active, or past attack, and recommendations to mitigate identified vulnerabilities and reduce attack impacts. The project modeled supply chains from four industries: pharmaceuticals, medical devices, solar arrays, and meat packing, working with people from Pfizer, Johnson & Johnson, Merck, Edwards Life Science, Lockheed, and Smithfield Foods, and papers from the project appeared in such journals at the J. of Simulation. My interest in supply chains continues and led to my organizing a workshop on AI-powered automation in ports.

Research: Artificial Intelligence, with emphasis on Homeland Security Issues

My first venture into Artificial Intelligence and homeland security was in developing a project, organized with Vivek Singh, with US Citizenship and Immigration Services, that aimed to automate the detection of anomalies and inconsistencies in immigration form submissions, leveraging AI techniques to identify erroneously filled immigration forms, incorrect document submissions, as well as falsification in documents such as marriage certificates or birth certificates, and enabling faster and more robust adjudication of cases and improved customer service. Unfortunately, the funding for this project was cut off by DOGE after only a few months. However, I recently organized a workshop on AI-powered Automation in Ports, which included participants from some of the world’s most advanced ports, those in Antwerp, Hamburg, and Rotterdam – leaders I met through our marine transportation work in the last few years. My new project on AI and homeland security, together with Vivek Singh, is examining the emerging vulnerabilities created by the rapid deployment of AI systems at sports and entertainment venues, where AI is now beginning to be embedded in areas such as access control, crowd management, vehicle screening, threat alerts, and personalized patron engagement. As the U.S. prepares for major mass‑gathering events such as the 2028 Los Angeles Olympics, the increased use of semi‑autonomous and autonomous AI systems raises concerns that the very tools designed to enhance security and improve the patron experience could be exploited by terrorists or homegrown violent extremists at these large events and more generally at a wide variety of sports and entertainment venue events nationwide. The project aims to identify how AI is currently used or planned to be used in venues, assess the autonomy of these systems, analyze the new vulnerabilities they introduce, determine the skills and resources adversaries would need to exploit them, and develop actionable countermeasures aligned with DHS, CISA, and NIST guidance.

Miscellaneous Homeland Security Research

My research work on homeland security has covered a wide variety of other topics. A sampling: nuclear detection using taxicabs rather than police cars (with Domestic Nuclear Detection Office); information sharing for law enforcement applications (with Office of the Director of National Intelligence); identity and access management; cargo transport inspections; shelter and transportation for unaccompanied minors crossing the border (with CBP and HHS); drone detection (with various NY and NJ law enforcement agencies) and MetLife Stadium; flood mitigation (with FEMA); layered defense; resource allocation (with Coast Guard).