Research Interests

 Numerical Optimization
 Machine Learning
 Data Assimilation
 Numerical methods for inverse problems, PDE  constrained optimization, reduced order optimization methods
 Adjointbased spacetime adaptive solution algorithms for sensitivity analysis and inverse problems
 Numerical methods (theory, algorithms and computer programs) for optimal control problems governed by PDEs and by variational inequalities
 Bayesian methods and uncertainty quantification
 Optimal design of experiments for nonlinear inverse problems
Numerical optimization
 Local methods
 Global methods
 Nonsmooth and derivative free methods
 Linear and nonlinear programming
Machine Learning
 Ridge, Lasso, Least Angle regression
 Linear Discriminant Analysis, Logistic Regression, Support Vector Machine
 Feature selection methods: BestSubset Selection, Forward and BackwardStepwise Selection
 Gaussian Process
 Neural Networks
Data Assimilation
 Variational (adjoint based), ensemble and hybrid based Data Assimilation techniques
 Data Assimilation using WRF, MPAS, GSI, WRFDA
 Impact of observation and model errors to various quantity of interest
Bayesian Methods and Uncertainty Quantification
 Markov Chain Monte Carlo
 Hamiltonian Monte Carlo
 Delayed Rejection Adaptive Metropolis
 Differential Evolution Adaptive Metropolis
Reduced Order Modelling
 Projection Based ReducedOrder Modelling
 Proper Orthogonal Decomposition
 Discrete Emperical Interpolation Method (DEIM)
 Gappy POD
 Missing Point Estimation
Applied mathematics
 Fluid dynamics
 Atmospheric and numerical weather prediction models
 Nuclear nonproliferation
 Population dynamics
 Immunological models
 Portfolio optimization and factor models



Publications / Scholar Activities

Articles in Conference proceedings, Journals and Magazines
2019
 R. Stefanescu, A. Sandu, A GoalOriented Adaptive Discrete Empirical
Interpolation Method
, Technical Report.
 R. Stefanescu, J. Hite, J. Cook, R. Smith, and J. Mattingly, SurrogateBased Robust Design for a NonSmooth Radiation Source Detection Problem
, Algorithms, 12(6), 113.
2018
 A. Moosavi, R. Stefanescu, A. Sandu, Multivariate predictions of local reducedordermodel errors and dimensions
, International Journal for Numerical Methods in Engineering, volume 113, number 3, pages 512533
 R. Stefanescu, A. Moosavi, A. Sandu, Parametric domain decomposition for accurate reduced order models: Applications of MPLROM methodology
, Journal of Computational and Applied Mathematics, volume 340, pages 629644
 R. Stefanescu, J. Hite, J. Cook, R. Smith, and J. Mattingly, SurrogateBased Robust Design for a NonSmooth Radiation Source Detection Problem
, Submitted to Inverse Problems in Science and Engineering.
2017
 R. Stefanescu, K. Schmidt, J. Hite, R. Smith, and John Mattingly, Hybrid
optimization and Bayesian inference techniques for a nonsmooth radiation
detection problem
, International Journal for Numerical Methods in Engineering, volume 111, issue 10, pages 955982.
 G. Dimitriu, R. Stefanescu, I.M. Navon, Comparative Numerical Analysis Using ReducedOrder Modeling Strategies for Nonlinear LargeScale Systems
, Journal of Computational and Applied Mathematics, volume 310, pages 3243.
 R. Stefanescu, A. Sandu, Efficient approximation of sparse Jacobians for
timeimplicit reduced order models
, International Journal for Numerical Methods in Fluids, volume 83, issue 2, pages 175–204.
 A. Attia, R. Stefanescu, A. Sandu, The ReducedOrder Hybrid Monte Carlo
Sampling Smoother
, International Journal for Numerical Methods in Fluids, volume 83, issue 1, pages 28–51.
 A. Moosavi, R. Stefanescu, A. Sandu, Multivariate predictions of local reducedordermodel errors and dimensions
, International Journal for Numerical Methods in Engineering, Early View.
2016
 R. Stefanescu, B. Noack and A. Sandu, Model reduction and inverse problems and data assimilation with geophysical applications. A special issue in honor of I. Michael Navon's 75th birthday
, International Journal for Numerical Methods in Fluids, volume 82, no 10, pages 625630.
 R. Stefanescu, J. Hite, R. Smith, and J. Mattingly, Surrogate Based Robust Design for a NonSmooth Radiation Problem
, Technical Report.
 R. Stefanescu, K. Schmidt, J. Hite, R. Smith, and J. Mattingly, Hybrid optimization and Bayesian inference techniques for a nonsmooth radiation detection problem
, Submitted to International Journal for Numerical Methods in Engineering.
 A. Moosavi, R. Stefanescu, and A. Sandu, Multivariate Predictions of Local Parametric ReducedOrder Models Characteristics and Their Applications
, Accepted by Computer Methods in Applied Mechanics and Engineering.
 A. Attia, R. Stefanescu, and A. Sandu, The reducedorder hybrid Monte Carlo sampling smoother
, International Journal for Numerical Methods in Fluids, Early View.
 R. Stefanescu, and A. Sandu, Efficient approximation of Sparse Jacobians for timeimplicit reduced order models
, International Journal for Numerical Methods in Fluids, Early View.
 G. Dimitriu, R. Stefanescu, and M. Navon, Comparative numerical analysis using reducedorder modeling strategies for nonlinear largescale systems
, Journal of Computational and Applied Mathematics, Volume 310, Pages 32–43.
 R. Stefanescu, Optimal Asset Allocation Strategies
, SSRN report.
2015
 A. Attia, R. Stefanescu, A. Sandu, The ReducedOrder Hybrid Monte Carlo Sampling Smoother,
Submitted to International Journal for Numerical Methods in Fluids.
 F.X. Le Dimet, I.M. Navon and R. Stefanescu, Variational Data Assimilation : Optimization and Optimal Control,
To appear in Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications (Vol. III), "A Memorial Volume for Yoshi K. Sasaki", edited by Seon Ki Park and to be published by SpringerVerlag.
 A. Moosavi, R. Stefanescu, A. Sandu, Efficient Construction of Local Parametric Reduced Order Models Using Machine Learning Techniques
,Submitted to Computer Methods in Applied Mechanics and Engineering.
 R. Stefanescu, A. Sandu, Efficient approximation of sparse Jacobians for timeimplicit reduced order models
,Submitted to Applied Mathematics and Computation.
 R. Stefanescu, A. Sandu, I.M. Navon POD/DEIM ReducedOrder Strategies
for Efficient Four Dimensional Variational Data Assimilation
, Journal of Computational Physics, Volume 295, pages 569595.
 G. Dimitriu, R. Stefanescu and I.M. Navon, PODDEIM Approach on dimension reduction of a multispecies hostparasitoid system, Ann. Acad. Rom., Sci. Ser. Math. Appl., Vol. 7, No. 1.
2014
 R. Stefanescu, A. Sandu, Efficient approximation of sparse Jacobians for timeimplicit reduced order models
,Submitted to International Journal for Numerical Methods in Engineering.
 R. Stefanescu, A. Sandu, I.M. Navon POD/DEIM ReducedOrder Strategies
for Efficient Four Dimensional Variational Data Assimilation
, Submitted to Journal of Computational Physics.
 R. Stefanescu, A. Sandu, I.M. Navon Comparison of POD reduced order strategies for the nonlinear 2D Shallow
Water Equations , International Journal for Numerical Methods in Fluids, Volume 76, Issue 8, pages 497521.
 G. Dimitriu, T. Lorenzi, R. Stefanescu Evolutionary dynamics of cancer cell populations under immune selection pressure and optimal control of chemotherapy , Math. Mod. Nat. Phen., 9, Pages 88104.
 G. Dimitriu, I.M. Navon and R. Stefanescu, Application of a PODDEIM Approach for Dimension Reduction of a Diffusive PredatorPrey System with Allee effect,Lecture Notes in Computer Science, LargeScale Scientific Computing, LNCS 8353, Vol 42, Pages 373381, Lirkov et al.(Eds.),Springer Verlag.
2013
 R. Stefanescu, I.M. Navon, Max Marchand, Henry Fuelberg 1D+4DVAR data assimilation of lightning with WRFDA system using nonlinear observation operators , Submitted to Monthly Weather Review.
 R. Stefanescu, I.M. Navon, POD/DEIM Nonlinear model order reduction of an ADI implicit shallow water equations model, Journal of Computational Physics, Vol 237 , pp 95114.
 R. Stefanescu, M.C. Pogan. Optimal Control in Chemotherapy of a Viral Infection, Annals of the Alexandru Ioan Cuza University  Mathematics. Volume 59, Issue 2, Pages 321338, ISSN (Print) 12218421, DOI: 10.2478/v1015701200392.
 R. Stefanescu, B.R. Noack, I.M. Navon, Discrete empirical selection of indices algorithm for treatment of nonlinear terms in FEM Galerkin models for parameterized PDEs. Applications to parametric reduced order models. To be submitted to Siam Journal on Numerical Analysis.
 R. Stefanescu, I.M. Navon, POD/DEIM 4DVAR Data Assimilation of the Shallow Water Equation Model. To be submitted to Siam Journal on Scientific Computing.
2012
 R. Stefanescu, I.M. Navon, Trust region adaptive POD/EIM 4DVar for a finiteelement shallow water equations model., To be submitted.
 R. Stefanescu, G. Dimitriu, Numerical Optimal Harvesting for an AgeDependent PreyPredator System, Numerical Functional Analysis and Optimization, Volume 33, Issue 6, 661679.
2011
 G. Dimitriu, R. Stefanescu, Numerical Procedures for Data Assimilation in Air Pollution Models, Bul. Inst. Politehnic Iasi, 57(61), No. 1, 83110.
 N. Apreutesei, G. Dimitriu, R. Stefanescu, Time optimal control problem for predatorprey systems, Bul. Inst. Politehnic Iasi, 57 (61), No. 2, 1928
2010
 Razvan Stefanescu, Gabriel Dimitriu, Numerical Simulations of ReactionDiffusion Systems Arising in Chemistry Using Exponential Integrators, LNCS, No. 5910, 621628, SpringerVerlag, Berlin Heidelberg.
 Gabriel Dimitriu, Narcisa Apreutesei, Razvan Stefanescu, Numerical Simulations with Data Assimilation Using an Adaptive POD Procedure, LNCS, No. 5910, 165172, SpringerVerlag, Berlin Heidelberg.
2009
 Sebastian Anita, Viorel Arnautu, Razvan Stefanescu, Numerical Optimal Harvesting for a Periodic AgeStructured Population Dynamics with Logistic Terms, Numerical Functional Analysis and Optimization, Volume 30 Issue 3 & 4, 183198.
 Viorel Arnautu, Razvan Stefanescu, The Numerical Solution for an Elliptic Control Problem, SYNASC 2008, 173177, IEE Computer Society Press, Los Alamos.
 Razvan Stefanescu, Gabriel Dimitriu,Numerical Approximation of a Free Boundary Problem for a Prey  Predator Model, LNCS, No. 5434, 548555, SpringerVerlag, Berlin Heidelberg..
 Gabriel Dimitriu, Razvan Stefanescu, Numerical Experiments for ReactionDiffusion Equations Using Exponential Integrators, LNCS, Nr. 5434, 249256, SpringerVerlag, Berlin Heidelberg.
2008
 Viorel Arnautu, Gina Dura, Razvan Stefanescu, Numerical Simulations for the Inverse Stefan Problem, Mathematical Models for Continuous Steel Casting Process Workshop, Dunarea de Jos University, Galati.
 Razvan Stefanescu, Gina Dura, Numerical Algorithms for a Second Order Elliptic BVP, Annals (Analele Stiintifice) of Al. I. Cuza University, Mathematics (Matematica), Tome LIII, fasc.1, 103118, Iasi.



Academic Background

2005  2010 (January, 29), Faculty of Mathematics, Al. I. Cuza University, Iasi, Romania
Ph.D., thesis: Numerical Algorithms for the Approximation of Elliptic PDEs and Applications
2003  2005, Faculty of Mathematics, Al. I. Cuza University, Iasi, Romania
M.Sc. in Mathematical Modeling, dissertation: Applications in Financial Mathematics using Black  Scholes equation
1999  2003, Faculty of Mathematics, Al. I. Cuza University, Iasi, Romania
B.Sc., thesis: ObjectOriented Programming Applications, A Linear Algebraic Library 


Work Experience

August 2015  Now  Postdoctoral Scholar, North Carolina State University, Department of Mathematics, Raleigh, North Carolina, USA
National Nuclear Security Administration (USA) grant supporting the Consortium for Nonproliferation Enabling Capabilities.
July 2013  August 2015  Postdoctoral Scholar, Virginia Tech, Department of Computer Science, Blacksburg, Virginia, USA
National Science Foundation project: A Fully Discrete Framework for the Adaptive Solution of Inverse Problems
February 2011  June 2013  Postdoctoral Scholar, Florida State Universiy, Department of Scientific Computing, Florida, USA
National Oceanic and Atmospheric Administration project: Data Assimilation of lightning in WRF4D VAR
using nonlinear observation operators
May 2009  February 2011, Assistant Researcher, Faculty of Automatic Control and Computers, Gh. Asachi Technical University, Iasi, Romania
October 2007March 2009  Assistant Researcher, Faculty of Mathematics, Al. I. Cuza University, Iasi, Romania
Teaching:
July 2013  August 2015  Researcher Associate, Numerical Optimization Classes, Department of Computer Science, Virginia Tech, Blacksburg, Virginia, USA
January 2011  June 2013  Postdoctoral Scholar, Data Assimilation, Optimization and Preconditioning Methods Classes, Department of Scientific Computing, Florida State University, Tallahassee, Florida, USA
March 2008  February 2011  Assistant Professor, Statistics and Computer Science Classes, Faculty of Pharmacy, Department of Mathematics and Scientific Computing, Universiy of Medicine and Pharmacy Gr. T. Popa, Iasi, Romania
October 2006  June 2007  Teaching Assistant, ObjectOriented Programming Classes in C++, Faculty of Mathematics, Al. I. Cuza University, Iasi, Romania



Honors

 2011  Who's Who in the World (28th Edition)



Applications and resources developed

 4DVar Data Assimilation of lightning observation using incremental WRFDA
 1D+4DVar Data Assimilation of lightning observation using incremental WRFDA



Languages

Romanian (native), English (fluent), French (some) 


Experience in Research Programs

 August 2015  now, member of National Nuclear Security Administration (USA) grant supporting the Consortium for Nonproliferation Enabling Capabilities
 July 2013  August 2015, member of National Science Foundation project, A Fully Discrete Framework for the Adaptive Solution of Inverse Problems
 2011  June 2013, member of National Oceanic and Atmospheric Administration project, Data Assimilation of lightning in WRF4D VAR using nonlinear observation operators
 2009  2011, 2009  2011 , member of IDEI project, No. 342/2009, CNCSIS, Nonlinear Evolution Equation, Theoretical Aspects and Applications to Life and Environmental Sciences
 2007  2008, director of TD project, 201 no. 569/2007, CNCSIS, Numerical Algorithms for the Approximation of Elliptic PDE and Applications.



International Conference Talks

 ORNL MUSE / CNEC SAM Workshop, Oak Ridge National Laboratory, December 2015, Stochastic and Deterministic Techniques for Locating Sources from Multiple Detector Responses.
 United States Naval Research Laboratory, Stennis Space Center, Oceanography Division, October 2015, POD/DEIM Nonlinear model order reduction of an ADI implicit shallow water equations model .
 Applied Mathematics Graduate Student Seminar, Department of Mathematics, North Carolina State University, September 2015, POD/DEIM Nonlinear model order reduction of an ADI implicit shallow water equations model.
 Differential Equations Seminar, Department of Mathematics, North Carolina State University, September 2015, POD/DEIM ReducedOrder Strategies for Efficient Four Dimensional Variational Data Assimilation .
 Workshop on Meteorological Sensitivity Analysis and Data Assimilation, June 2015, Roanoke, West Virginia, ReducedOrder Strategies for Efficient 4DVar Data Assimilation.
 NASA Goddard Space Flight Center Seminar, April 2015, Efficient approaches for 4DVar Data Assimilation Systems.
 Computational Mathematics Seminar, Department of Mathematics, University of Pittsburgh, April 2015, POD/DEIM ReducedOrder Strategies for Efficient Four Dimensional Variational Data Assimilation.
 SIAM CS&E, Salt Lake City, March 2015, Aposteriori error estimates for Reduced Order Models and adaptive DEIM strategies.
 Mechanical Engineering Department Seminar, University of South Carolina, February 2015, Towards Next Generation of Data Assimilation Systems .
 13th International Symposium on Multiscale, Multifunctional and Functionally Graded Materials, October 1922, 2014, Taua Resort, SP, Brazil, Solution of Optimization Problems with Adaptive and Reduced Order Models. .
 European Geosciences Union, General Assembly, Vienna, Austria, April 2014, Reduced Order POD/DEIM 4D Var Data Assimilation .
 Inverse Problem Seminar, Math Department, Virginia Tech, February 2014, POD/DEIM Strategies for Reduced Data Assimilation Systems .
 Sixth Symposium on Data Assimilation, University of Maryland, Washington, D.C, USA, October 2013, Variational data assimilation of lightning with WRFDA system using nonlinear observation operators.
 GLM Science Meeting National Space Science and Technology Center, The University of Alabama in Huntsville, September 2013, Variational Data Assimilation of Lightning With WRFDA System Using Nonlinear Observation Operators.
 SIAM Conference on Computational Science & Engineering (CSE13), Boston, MA, USA, 2013, POD/DEIM 4DVAR Data Assimilation of the Shallow Water Equation Model.
 Centre d'études aérodynamiques et thermiques  Université de Poitiers  Ecole Nationale Supérieure de Mécanique et d'aérotechnique, Poitiers, France, Trust region adaptive POD/EIM 4DVar for a finiteelement shallow water equations model .
 The 6th Computational Expo, Florida State University, Tallahassee, FL, USA, 2012, Data Assimilation of Lightning in WRF 3/4D VAR Using Observation Operators.
 JCSDA 9th Workshop on Satellite Data Assimilation, University of Maryland, Washington, DC, Usa, 2011, Data Assimilation of Lightning in WRF 4D VAR Using Observation Operators and 1D+4D VAR.
 The 18th Conference on Applied and Industrial Mathematics, Iasi, Romania, October 1417, 2010, Optimal control in treatment strategy of HIV infection.
 7th International Conference on LargeScale Scientific Computations, Sozopol, Bulgaria, 48 Iunie 2009, Numerical Simulations of ReactionDiffusion Systems Arising in Chemistry Using Exponential Integrators.
 10th International Symposium on Symbolic and Numeric Algorithms for Scientific Computing, Timisoara, Romania, 2629 Septembrie 2008, The Numerical Solution for an Elliptic Control Problem.
 International Exploratory Workshop, Differential Equations and Applications in Life Sciences, Iasi, Romania, September 5 7, 2008, Numerical approach of a semilinear parabolic problem with free boundary problem for a predatorprey model
 4th International Conference on Numerical Analysis and Its Applications, Lozenetzs, Bulgaria, 1620 iunie, 2008, Numerical Approximation of a Free Boundary Problem for a Prey  Predator Model.



Courses Attended

 Basic WRF Tutorial, 11  15 July 2011, NCAR Foothills Laboratory, Boulder, Colorado, Usa.
 WRF DA Tutorial, 2022 July 2011, NCAR Foothills Laboratory, Boulder, Colorado, Usa.
