I am an Assistant Professor in the Department of Computer Science at Stevens Institute of Technology. I completed my Ph.D (Aug. 22') from the Department of Computer Science at Virginia Tech advised by Prof. Naren Ramakrishnan and Prof. Anuj Karpatne. My primary research focus entails developing machine learning models that also incorporate scientific knowledge (along with data) governing a process of interest. This area of research is termed Science-Guided Machine Learning (SGML). I am especially interested in leveraging scientific domain knowledge to improve model generalization, decision interpretability and reduce the negative effects of data paucity and noise. Most recently, I've been focused on leveraging machine learning techniques to address challenges in physics (specifically computational fluid dynamics) to alleviate the cost of expensive simulations using science-guided machine learning models.

My other areas of research interest include:

  1. Transfer Learning & Domain Adaptation

  2. Multi-task & Meta Learning

  3. Time-series Forecasting & Anomaly Detection (especially in the context of Cyber-Physical Systems)

  4. Intelligent Disaster Management

  5. Disease Modeling (COVID-19, Influenza-Like-illnesses).

Prior to starting my Ph.D., I was part of the Big Data and Personalization team at The Washington Post and was primarily focused on developing and maintaining news article recommendation systems and online content optimization tools using multi-armed bandits.

Selected Publications

Generating flow fields (such as pressure and velocity fields) in 3D space is a fundamental task in computational fluid dynamics (CFD), with applications across a vast spectrum of science and engineering problems. An important class of fluid flow problems in CFD is multi-phase flow, where dispersed solid particles are present in the fluid flow. Despite recent developments in deep learning (DL) for CFD applications, current state-of-the-art is still unable to model 3D flow fields, especially in multi-phase flow settings.

It is with this goal that we introduce PhyFlow, a novel physics-guided deep learning architecture for modeling 3D multi-phase fluid flows, designed to mimic the popular projection method for solving fluid flows in CFD simulations. We demonstrate that PhyFlow, generates high quality flow fields and yields a 49.61% improvement over other state-of-the-art baselines. We also test the quality of PhyFlow based fields by employing them in downstream tasks like particle drag force prediction and demonstrate state-of-the-art results, improving upon the previous best models by 9.89%. Finally, we demonstrate the consistency of PhyFlow predictions with known underlying physics governing equations. Our source code and data are available online at: tinyurl.com/e5mrerb7 .

Timely forecasting of diseases like influenza, helps health organizations and policymakers by allowing them adequate preparation time for decision making. However, due to the non-trivial dynamics of influenza seasonal progression, effective influenza forecasting still remains a challenge despite increasing research interest. The forecasting challenge is further heightened amidst the COVID-19 pandemic, when the influenza-like illness (ILI) counts are affected by various factors such as symptomatic similarities with COVID-19 and shift in healthcare seeking patterns of the general population. Hence, historical influenza forecasting models are unable to adapt to this new trend. Therefore, we present CALI-Net, a neural transfer learning architecture, that uses novel knowledge distillation techniques to 'steer' a historical disease forecasting model to new scenarios where flu and COVID-19 co-exist. CALI-Net allows this automatic adaptation of ILI forecasts by learning to emphasize learning from either COVID-related signals or from historical forecasting models at appropriate times. Through our CALI-Net framework, we are able to effectively exploit representations from historical ILI forecasting models and historical ILI data as well as the limited COVID-related signals.

Physics-based simulations are often used to model and understand complex physical systems in domains like fluid dynamics. Such simulations although used frequently, often suffer from inaccurate or incomplete representations either due to their high computational costs or due to lack of complete physical knowledge of the system. In such situations, it is useful to employ machine learning to fill the gap by learning a model of the complex physical process directly from simulation data. However, as data generation through simulations is costly, we need to develop models being cognizant of data paucity issues. In such scenarios it is helpful if the rich physical knowledge of the application domain is incorporated in the architectural design of machine learning models. We can also use information from physics-based simulations to guide the learning process using aggregate supervision to favorably constrain the learning process. In this paper, we propose PhyNet , a deep learning model using physics-guided structural priors and physics-guided aggregate supervision for modeling the drag forces acting on each particle in a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM). We conduct extensive experiments in the context of drag force prediction and showcase the usefulness of including physics knowledge in our deep learning formulation.

In recent years, the large amount of labeled data available has also helped tend research toward using minimal domain knowledge, e.g., in deep neural network research. However, in many situations, data is still limited and of poor quality. Can domain knowledge be useful in such settings? Here, we propose domain adapted neural networks (DANN) to explore how domain knowledge can be integrated into model training for deep networks. In particular, we incorporate loss terms for knowledge available as monotonicity constraints and approximation constraints. We evaluate our model on both synthetic data generated using the popular Bohachevsky function and a real-world dataset for predicting oxygen solubility in water. In both situations, we find that our DANN model outperforms its domain-agnostic counterpart, yielding an overall mean performance improvement of 19.5%, with a worst and best-case performance improvement of 4% and 42.7% respectively.

Recent hurricane events have caused unprecedented amounts of damage on critical infrastructure systems and have severely threatened our public safety and economic health. The most observable (and severe) impact of these hurricanes is the loss of electric power in many regions, which causes breakdowns in essential public services. Understanding power outages and how they evolve during a hurricane provides insights on how to reduce outages in the future, and how to improve the robustness of the underlying critical infrastructure systems. In this paper, we propose a novel scalable segmentation with explanations framework to help experts understand such datasets. Our method,CnR(Cut-n-Reveal), first finds a segmentation of the outage sequences based on the temporal variations of the power outage failure process so as to capture major pattern changes.This temporal segmentation procedure is capable of accounting for both the spatial and temporal correlations of the underlying power outage process. CnR also provides a novel explanation optimization formulation to find an intuitive explanation of the segmentation, such that the explanation highlights the culprit time-series of the change in each segment. Through extensive experiments, we have demonstrated that our method consistently outperforms competitors in multiple real datasets with ground truth. We further demonstrate results on real county-level power outage data from several recent hurricanes (Matthew, Harvey, Irma) and show that CnR recovers important, non-trivial and actionable patterns for domain experts, while baselines typically do not give meaningful results.

Cyber physical systems (CPSs) are today ubiquitous in urban environments. Such systems now serve as the backbone to numerous critical infrastructure applications, from smart grids to IoT installations. Scalable and seamless operation of such CPSs requires sophisticated tools for monitoring the time series progression of the system, dynamically tracking relationships, and issuing alerts about anomalies to operators. We present an online monitoring system (illiad) that models the state of the CPS as a function of its relationships between constituent components, using a combination of model-based and data-driven strategies. In addition to accurate inference for state estimation and anomaly tracking,illiad also exploits the underlying network structure of the CPS (wired or wireless) for state estimation purposes. We demonstrate the application of illiad to two diverse settings: a wireless sensor motes application and an IEEE 33-bus microgrid.

Publications

  • Muralidhar, N., Zubair, A., Weidler, N., Gerdes, R., & Ramakrishnan, N. Contrastive Graph Convolutional Networks for Hardware Trojan Detection in Third Party IP Cores. In Proceedings of the 14th IEEE International Symposium on Hardware-Oriented Security and Trust (IEEE HOST) 2021.

  • Muralidhar, N., Bu, J., Cao, Z., Raj, N., Ramakrishnan, N., Tafti, D., & Karpatne, A., “Phyflow: Physics-guided deep learning for generating interpretable 3D flow fields,” In Proceedings of the 21st IEEE International Conference on Data Mining (ICDM), IEEE, 2021.

  • Rodriguez, A.*,Muralidhar, N.,*, Adhikari, B., Tabassum, A., Ramakrishnan, N., & Prakash B.A. Steering a Historical Disease Forecasting Model Under a Pandemic: Case of Flu and COVID-19. AAAI 2021

  • Rodriguez, A.*,Muralidhar, N.,*, Adhikari, B., Tabassum, A., Ramakrishnan, N., & Prakash B.A. Steering a Historical Disease Forecasting Model Under a Pandemic: Case of Flu and COVID-19. NeurIPS Machine Learning in Public Health (MLPH) Workshop, Virtual Event. December 2020

  • Muralidhar, N., Mayer, B., Self, N., Kondoju, P., Tonshal, B., Schmotzer, J., & Ramakrishnan,N. RAD: Rapid Automobile Data Analytics Framework for Structured Data. In Proceedings of the 9th SIGKDD International Workshop on Urban Computing (UrbComp 2020).

  • Muralidhar, N., Bu, J., Cao, Z., He, L., Ramakrishnan, N., Tafti, D., & Karpatne, A. (2020).Physics-Guided Deep Learning for Drag Force Prediction in Dense Fluid-Particulate Systems. BigData, 8(5), 431-449.(Impact Factor: 3.644)

  • Muralidhar, N., Tabassum, A., Chen, L., Chinthavali, S., Ramakrishnan, N., & Prakash, B. A. (2020). Cut-n-Reveal: Time Series Segmentations with Explanations. ACM Transactions on Intelligent Systems and Technology (TIST), 11(5), 1-26. (Impact Factor: 3.971)

  • Muralidhar, N., Bu, J., Cao, Z., He, L., Ramakrishnan, N., Tafti, D., & Karpatne, A. "Physics Guided Learning for Particle Drag Force Estimation in Multi Phase Fluid Flow." Proceedings of the 3rd Workshop on Physics Informed Machine Learning 2020.

  • Muralidhar, N., Bu, J., Cao, Z., He, L., Ramakrishnan, N., Tafti, D., & Karpatne, A. (2020). PhyNet: Physics Guided Neural Networks for Particle Drag Force Prediction in Assembly. In Proceedings of the 2020 SIAM International Conference on Data Mining (pp. 559-567). Society for Industrial and Applied Mathematics. [CODE]

  • Muralidhar, N., Muthiah, S., Nakayama, K., Sharma, R., & Ramakrishnan, N. (2019, December). Multivariate Long-Term State Forecasting in Cyber-Physical Systems: A Sequence to SequenceApproach. In 2019 IEEE International Conference on Big Data (IEEE Big Data) (pp. 543-552).

  • Muralidhar, N., Muthiah, S., & Ramakrishnan, N. (2019). DyAt Nets:Dynamic Attention Networks for State Forecasting in Cyber-Physical Systems. In Proceedings of the Twenty-Eighth International Joint Conference on Artificial Intelligence, IJCAI-19. International Joint Conferences on Artificial Intelligence Organization, 3180–3186. https://doi.org/10.24963/ijcai.2019/441 [CODE]

  • Muralidhar, N., Islam, M.R., Marwah, M., Karpatne, A., & Ramakrishnan, N. (2018) Incorporating Prior Domain Knowledge into Deep Neural Networks. In 2018 IEEE International Conference on Big Data (Big Data), pp. 36-45. IEEE, 2018.

  • Muralidhar, N., Wang, C., Self, N., Momtazpour M., Nakayama, K., Sharma, R., & Ramakrishnan, N. (2018) illiad: Intelligent invariant and anomaly detection in cyber-physical systems. ACM Transactions on Intelligent Systems and Technology (TIST) 9, no. 3 (2018): 35. (Impact Factor: 3.971)

  • Muralidhar, N., Rangwala H., & Han E.H. Recommending Temporally Relevant News Content from Implicit Feedback Data. In 2015 IEEE 27th International Conference on Tools with Artificial Intelligence (ICTAI), pp. 689-696. IEEE, 2015.

Selected Honors & Awards

  • First Place Prize COVID-19 Symptom Data Challenge organized by Catalyst Health & Facebook . . . . . 2020

  • Second Place Prize in COVID-19 Grand Challenge Hosted by C3.ai . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2020

  • Top 33% Ranking Reviewer Appreciation (International Conference on Machine Learning) . . . . . . . . . . . 2020

  • Invited Member of τβπ Honor Society (Virginia Tech Chapter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2020-present

  • Invited Life Member of ΦKΦ Honor Society (Virginia Tech Chapter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2017-present

  • National Science Foundation Urban Computing Fellowship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2016-2018

  • Award for Academic Excellence - Dept. of Comp. Sci, George Mason University . . . . . . . . . . . . . . . . . . . 2015

Contact: nik90 at vt dot edu