About

R. Ravi is the Andris A. Zoltners Professor of Business and a Professor of Operations Research and Computer Science at the Tepper School of Business. His academic role involves research and teaching in the fields of operations research, computer science, and business. His work is aligned with the strategic vision of the Tepper School, which emphasizes the intersection of business, technology, and analytics, contributing to thought leadership in artificial intelligence, machine learning, and their applications in management science and organizational behavior.

Research topics

• Computer Science
• Business
• Microeconomics
• Accounting
• Advertising
• Statistics
• Finance
• Mathematics
• Internet privacy
• World Wide Web
• Economics

Selected publications

• The Telephone k-Multicast Problem

  Algorithmica · 2026-03-02

  preprintOpen accessSenior author

  Abstract We consider minimum time multicasting problems in directed and undirected graphs: given a root node and a subset of t terminal nodes, multicasting seeks to find the minimum number of rounds within which all terminals can be informed with a message originating at the root. In each round, the telephone model we study allows the information to move via a matching from the informed nodes to the uninformed nodes. Since minimum time multicasting in digraphs is poorly understood compared to the undirected variant, we study an intermediate problem in undirected graphs that specifies a target $$k &lt; t$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>k</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mi>t</mml:mi> </mml:mrow> </mml:math> , and requires that only k of the terminals be informed in the minimum number of rounds. For this problem, we improve the implications of the previous results and obtain a multiplicative approximation factor of $$\tilde{O}(t^{1/3})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>O</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mrow> <mml:mo>(</mml:mo> <mml:msup> <mml:mi>t</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> . For the directed version, we obtain an additive $$\tilde{O}(k^{1/2})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>O</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mrow> <mml:mo>(</mml:mo> <mml:msup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> approximation algorithm (with a polylogarithmic multiplicative factor). Our algorithms are based on reductions to the related problems of finding k -trees of minimum poise (sum of maximum degree and diameter) and applying a combination of greedy network decomposition techniques and set covering under partition matroid constraints. We also study the problem of bounded degree Directed Steiner Tree, for which we obtain improved polylogarithmic approximations for the special case of bounded treewidth graphs. This extends prior work on the Group Steiner Tree problem.

  PublisherOA PDFDOI

• The Telephone k-Multicast Problem

  Algorithmica · 2026-03-02

  articleOpen accessSenior author

  Abstract We consider minimum time multicasting problems in directed and undirected graphs: given a root node and a subset of t terminal nodes, multicasting seeks to find the minimum number of rounds within which all terminals can be informed with a message originating at the root. In each round, the telephone model we study allows the information to move via a matching from the informed nodes to the uninformed nodes. Since minimum time multicasting in digraphs is poorly understood compared to the undirected variant, we study an intermediate problem in undirected graphs that specifies a target $$k &lt; t$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>k</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mi>t</mml:mi> </mml:mrow> </mml:math> , and requires that only k of the terminals be informed in the minimum number of rounds. For this problem, we improve the implications of the previous results and obtain a multiplicative approximation factor of $$\tilde{O}(t^{1/3})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>O</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mrow> <mml:mo>(</mml:mo> <mml:msup> <mml:mi>t</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> . For the directed version, we obtain an additive $$\tilde{O}(k^{1/2})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>O</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mrow> <mml:mo>(</mml:mo> <mml:msup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> approximation algorithm (with a polylogarithmic multiplicative factor). Our algorithms are based on reductions to the related problems of finding k -trees of minimum poise (sum of maximum degree and diameter) and applying a combination of greedy network decomposition techniques and set covering under partition matroid constraints. We also study the problem of bounded degree Directed Steiner Tree, for which we obtain improved polylogarithmic approximations for the special case of bounded treewidth graphs. This extends prior work on the Group Steiner Tree problem.

  PublisherOA PDFDOI

• Insulin resistance induced by obesity: Mechanisms, metabolic implications and therapeutic approaches

  Molecular Biology Reports · 2026-02-04 · 7 citations

  articleOpen access

  Obesity-induced insulin resistance is an escalating global health challenge that substantially contributes to the development of metabolic disorders, including type 2 diabetes mellitus and cardiovascular disease. This narrative review critically examines the molecular and cellular mechanisms linking excess adiposity to impaired insulin action, with a particular focus on adipose tissue dysfunction, chronic low-grade inflammation, and oxidative stress. A comprehensive literature search was conducted using PubMed, ScienceDirect, and Google Scholar, covering preclinical and clinical studies published primarily over the past two decades. Evidence indicates that adipocyte hypertrophy and hypoxia promote excessive free fatty acid release, ectopic lipid accumulation, and lipotoxicity, thereby disrupting insulin signalling pathways. Numerous clinical studies report that obesity triggers chronic, low-grade inflammation in the liver and pancreas, activating pathways such as NF-κB and SOCS proteins, thereby disrupting insulin signalling. Concurrently, obesity-associated inflammation drives immune cell infiltration and macrophage polarization toward a pro-inflammatory phenotype, further exacerbating insulin resistance and metabolic dysregulation. This review also synthesizes current therapeutic strategies targeting these mechanisms, including insulin-sensitizing agents, anti-inflammatory therapies, glucagon-like peptide-1 receptor agonists, and sodium-glucose cotransporter 2 inhibitors, as well as emerging approaches. Future perspectives highlight the growing relevance of personalized medicine, pharmacogenomics, digital health tools, and gene-based interventions in improving therapeutic precision. A deeper understanding of these interconnected pathways is essential for developing effective strategies to mitigate obesity-related insulin resistance and its global metabolic consequences.

  PublisherOA PDFDOI

• Engineering thiolated polyethoxylated surfactants for mucoadhesive and biointeractive lipid-based drug delivery systems: Molecular design, performance, and translational potential

  Colloids and Surfaces B Biointerfaces · 2026-02-24 · 1 citations

  articleOpen access

  Thiolated polyethoxylated surfactants have emerged as functional excipients in advanced drug delivery systems due to their unique ability to form covalent disulfide bonds with cysteine-rich mucin subdomains. The introduction of thiol/sulfhydryl (-SH) groups onto the surfactant surface can enhance mucoadhesion and prolongs mucosal residence; however, these interactions are highly context-dependent, governed by factors such as the mucosal redox state, the pKa of the thiol groups, and the steric accessibility of mucin cysteine. This review provides a comprehensive overview of mucosal barriers and the fundamental principles of mucoadhesion, emphasizing the biochemical interactions between thiolated polyethoxylated surfactants and mucin glycoproteins. The chemistry, synthetic strategies, characterization techniques, and thiol quantification assays are systematically discussed to elucidate the structure–function relationship governing their performance. Furthermore, the review highlights the integration of thiolated surfactants into various lipid-based systems, including solid lipid nanoparticles, nanostructured lipid carriers, nanoemulsions, and self-emulsifying drug delivery systems, with an emphasis on formulation design, mechanistic insights, and performance outcomes. Safety, biocompatibility, and regulatory considerations are critically examined to evaluate their translational readiness. Finally, the review identifies existing research gaps and future opportunities, underscoring thiolated polyethoxylated surfactants as a promising, biointeractive platform for advanced mucoadhesive and biointeractive drug delivery technologies. • Thiolated polyethoxylated surfactants introduce reactive surface sulfhydryl groups. • Covalent thiol–mucin bonding can enhance mucoadhesion and residence at mucosal sites. • Thiolation alters interfacial behavior, colloidal stability, and potential pathways for drug absorption. • Synthetic strategies and analytical methods for thiol quantification are critically outlined. • Integration into SLNs, NLCs, SEDDS and nanoemulsions offers the potential to improve drug bioavailability. • Regulatory, safety and biocompatibility challenges for clinical translation are examined.

  PublisherDOI

• The Steiner path aggregation problem

  Information Processing Letters · 2025-09-26

  articleOpen accessSenior author

  In the Steiner Path Aggregation Problem , our goal is to aggregate paths in a directed network into a single arborescence without significantly disrupting the paths. In particular, we are given a directed multigraph with colored arcs, a root, and k terminals, each of which has a monochromatic path to the root. Our goal is to find an arborescence in which every terminal has a path to the root, and its path does not switch colors too many times. We give an efficient algorithm that finds such a solution with at most 2 log 4 3 ⁡ k color switches. Up to constant factors this is the best possible universal bound, as there are graphs requiring at least log 2 ⁡ k color switches. • The guarantees of the classic heavy path decomposition are extended to general graphs, within a constant factor. • Dipaths from terminals to a root are aggregated into a single arborescence. • With monochromatic dipaths, the arborescence paths switch colors at most log times. • The algorithm iteratively extends paths of active terminals without allowing cycles.

  PublisherDOI

• Hardware vs. Software Implementation of Warp-Level Features in Vortex RISC-V GPU

  ArXiv.org · 2025-05-06

  preprintOpen access

  RISC-V GPUs present a promising path for supporting GPU applications. Traditionally, GPUs achieve high efficiency through the SPMD (Single Program Multiple Data) programming model. However, modern GPU programming increasingly relies on warp-level features, which diverge from the conventional SPMD paradigm. In this paper, we explore how RISC-V GPUs can support these warp-level features both through hardware implementation and via software-only approaches. Our evaluation shows that a hardware implementation achieves up to 4 times geomean IPC speedup in microbenchmarks, while software-based solutions provide a viable alternative for area-constrained scenarios.

  PublisherOA PDFDOI

• Next Generation Adaptive Artificial Intelligence Systems for Inclusive Societal and Economic Transformation in Smart Communities

  Advances in computer science research · 2025-01-01

  book-chapter
  PublisherDOI

• The Nonstationary Newsvendor with (and Without) Predictions

  Manufacturing & Service Operations Management · 2025-03-04 · 2 citations

  articleSenior author

  Problem definition: The classic newsvendor model yields an optimal decision for a “newsvendor” selecting a quantity of inventory under the assumption that the demand is drawn from a known distribution. Motivated by applications such as cloud provisioning and staffing, we consider a setting in which newsvendor-type decisions must be made sequentially in the face of demand drawn from a stochastic process that is both unknown and nonstationary. All prior work on this problem either (a) assumes that the level of nonstationarity is known or (b) imposes additional statistical assumptions that enable accurate predictions of the unknown demand. Our research tackles the Nonstationary Newsvendor without these assumptions both with and without predictions. Methodology/results: In the setting without predictions, we first design a policy that we prove (via matching upper and lower bounds) achieves order-optimal regret; ours is the first policy to accomplish this without being given the level of nonstationarity of the underlying demand. We then, for the first time, introduce a model for generic (i.e., with no statistical assumptions) predictions with arbitrary accuracy and propose a policy that incorporates these predictions without being given their accuracy. We upper bound the regret of this policy and show that it matches the best achievable regret had the accuracy of the predictions been known. Managerial implications: Our findings provide valuable insights on inventory management. Managers can make more informed and effective decisions in dynamic environments, reducing costs and enhancing service levels despite uncertain demand patterns. This study advances understanding of sequential decision-making under uncertainty, offering robust methodologies for practical applications with nonstationary demand. We empirically validate our new policy with experiments based on three real-world data sets containing thousands of time-series, showing that it succeeds in closing approximately 74% of the gap between the best approaches based on nonstationarity and predictions alone. History: This paper was selected as part of the 1RR initiative between the M&amp;SOM Journal and the MSOM Society. This particular paper was part of the 2024 MSOM Service Operations SIG Conference. Funding: L. An and B. Moseley were supported in part by a Google Research Award, an Infor Research Award, a Carnegie Bosch Junior Faculty Chair, NSF [Grants CCF-2121744 and CCF-1845146] and ONR [Grant N000142212702]. Supplemental Material: The online appendix is available at https://doi.org/10.1287/msom.2024.1168 .

  PublisherDOI

• Approximately Packing Dijoins via Nowhere-Zero Flows

  COMBINATORICA · 2025-06-01

  articleOpen accessSenior author

  Abstract In a digraph, a dicut is a cut where all the arcs cross in one direction. A dijoin is a subset of arcs that intersects each dicut. Woodall conjectured in 1976 that in every digraph, the minimum size of a dicut equals to the maximum number of disjoint dijoins. However, prior to our work, it was not even known whether at least 3 disjoint dijoins exist in an arbitrary digraph whose minimum dicut size is sufficiently large. By building connections with nowhere-zero (circular) k -flows, we prove that every digraph with minimum dicut size $$\tau $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>τ</mml:mi> </mml:math> contains $$\left\lfloor \frac{\tau }{k}\right\rfloor $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mfrac> <mml:mi>τ</mml:mi> <mml:mi>k</mml:mi> </mml:mfrac> </mml:mfenced> </mml:math> disjoint dijoins if the underlying undirected graph admits a nowhere-zero (circular) k -flow. The existence of nowhere-zero 6-flows in 2-edge-connected graphs (Seymour 1981) directly leads to the existence of $$\left\lfloor \frac{\tau }{6}\right\rfloor $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mfrac> <mml:mi>τ</mml:mi> <mml:mn>6</mml:mn> </mml:mfrac> </mml:mfenced> </mml:math> disjoint dijoins in a digraph with minimum dicut size $$\tau $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>τ</mml:mi> </mml:math> , which can be found in polynomial time as well. The existence of nowhere-zero circular $$\frac{2p+1}{p}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>p</mml:mi> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> <mml:mi>p</mml:mi> </mml:mfrac> </mml:math> -flows in 6 p -edge-connected graphs (Lovász et al. 2013) directly leads to the existence of $$\left\lfloor \frac{\tau p}{2p+1}\right\rfloor $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mfrac> <mml:mrow> <mml:mi>τ</mml:mi> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>p</mml:mi> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mfrac> </mml:mfenced> </mml:math> disjoint dijoins in a digraph with minimum dicut size $$\tau $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>τ</mml:mi> </mml:math> whose underlying undirected graph is 6 p -edge-connected. We also discuss reformulations of Woodall’s conjecture into packing strongly connected orientations.

  PublisherOA PDFDOI

• Advanced Real Estate Price Forecasting Using Multivariate Long Short-Term Memory Networks

  2025-03-28

  article

  Forecasting real estate prices is critical in making financial decisions, formulating investment strategies, and designing plans for urban development. Predictive models can enable stakeholders to detect the market's future trends and make meaningful decisions. Forecasting methods often fail to extract complex nonlinear patterns from economic indicators, interest rates, population, and regional trends in the real estate market. The paper proposes a multivariate LSTM network for advanced real estate price forecasting. The input features under consideration for the proposed model are longitude, latitude, median age of housing, total rooms, total bedrooms, population, households, median income, median house value, and ocean proximity. The multivariate technique offers a better facility for capturing time dependency and relations between varied variables. Therefore, the model performs well in correctly predicting house price fluctuations. This model was tested on housing prices in different regions and related economic indicators. We evaluate the performance of our model in terms of actual versus predicted prices and residual plots. We used cross-validation. The model proved robust and efficient in pricing predictions under different market conditions. All the standard metrics, including RMSE, MAE, and R-squared values, proved the Multivariate LSTM model is highly effective. However, the promising result would have been bettered further if sentiment analysis was incorporated with the dataset-the same thing that would have also improved the precision of the model.

  PublisherDOI

Recent grants

• Approximation Algorithms for Network Optimization

  NSF · $251k · 2007–2011

• New Directions in Approximation Algorithms

  NSF · $188k · 2004–2008

• Preliminary Algorithmic Foundations for Ranking Quizzes and Students from Student-sourced Quizzes

  NSF · $148k · 2016–2018

• AF: SMALL: Approximation Algorithms Matching Integrality Gaps for Network Design

  NSF · $400k · 2015–2019

• AF: Small: Approximation Algorithms for Network Design

  NSF · $350k · 2012–2015

Frequent coauthors

• Anupam Gupta

  Mercer University

  41 shared

• Viswanath Nagarajan

  Karpagam Academy of Higher Education

  34 shared

• Amitabh Sinha

  25 shared

• Philip N. Klein

  Providence College

  24 shared

• Madhav Marathe

  21 shared

• Guy E. Blelloch

  Carnegie Mellon University

  16 shared

• Russell Schwartz

  Carnegie Mellon University

  16 shared

• Mohit Singh

  Georgia Institute of Technology

  15 shared