About
Summary
Most of my theoretical research is related to the behavior of complex systems at the interface between physics and the fields of biology and materials science. In particular, my recent work has been dedicated to the studying of the phase ordering phenomena with respect to biological soft matter systems such as polyelectrolyte solutions. Investigations of the nematic ordering in solutions of rigid-rod polyelectrolytes are essential for optimization of technological processes and deeper understanding of physical principles which govern molecular scale phenomena including biological systems of DNA molecules and tobacco mosaic viruses. Motivated by the experimental investigations on the rodlike tobacco mosaic virus (TMV) liquid crystalline ordering, I developed an approximate field theoretical approach beyond the Debye-Hückel approximation and applied it in order to describe the properties of the one-component plasma (OCP) of salt-free similarly charged rodlike polyelectrolyte solutions for all electrostatic couplings from the weak- to the strong-coupling regime. By theory and numerical simulations, I have found that the isotropic phase becomes unstable with reference to the orientational ordering due to both electrostatic and excluded volume interactions. I have described my results in this area in my papers: “Nematic phase emergence in solutions of similarly charged rodlike polyelectrolytes” in the Journal of the Physical Society of Japan 83, 014002 (2014) and “Phase transition in similarly charged rodlike polyelectrolyte solutions”, in Proceedings of the 4th International Symposium on Slow Dynamics in Complex Systems, Sendai, Japan, AIP Conf. Proc. 1518, 558 (2013).
Another particular area of my research is the emergence of minimal living systems from non-living materials and how minimal living systems may support increasingly more evolutionary richness. Novel functionalities in physico-chemical systems can be generated naturally in three ways: (i) by the assembly of structures (equilibrium processes), (ii) by self-organization (non-equilibrium processes), and (iii) by a combination of the two through the evolution of structures. The general approach to create minimal living systems which are defined as protocells, uses coupled self-assembling and self-organizing processes. In my work, I developed a theoretical model of the key open challenge for implementing an integrated functional protocell: how to optimize and realize an independent and robust replication of the protocellular information molecules ? In other words, my analysis sought to determine how to optimize the overall information replication rate dependent on three key experimental parameters: the hybridization energies, the information strand length and the reaction temperature. In my investigation, I employed a model for the minimal ligation-based replication process of a single-stranded template in which the ligation of oligomers is involved in the formation of the complementary replica. I have found that larger oligomer strand length or lower temperature increase the overall template production rate. In the case of product inhibition, if the ligation process is not rate-limiting then it will be the hybridization/dehybridization rates of the oligomers and ligated oligomers that determine the overall template production rate. The protocell inherits its information through the replication processes discussed above. The details are described in the papers: "Generating minimal living systems from non-living materials and increasing their evolutionary abilities" in Philosophical Transactions of the Royal Society B: Biological Sciences 371, 20150440 (2016) and “Protocells: what we have learned about minimal life and evolvability“ in Proceedings of the Artificial Life Conference 2016, Cancun, Mexico, MIT Press, 2016, pages 76-77.
My Ph.D thesis work was dedicated to elucidating the coarsening dynamics of thin films of solids (such as soft polymeric and metallic materials) within a unified model that incorporates long range de-wetting interactions acting across thin films (such as the ubiquitous van der Walls forces). By analytic arguments and simulations, I studied the growth laws of clusters formed in these films due to the de-wetting interactions. I have revealed that long range de-wetting interactions introduce a long lasting early time scaling behavior characterized by a slow growth of the cluster height/lateral size aspect ratio. Such an interesting cluster growth behavior (characterized by a time dependent Young angle) has been indeed seen in experiments, however its physical origin has remained unexplained at that time. My theoretical study explains this phenomenon as an effect of the long range de-wetting interactions acting across thin films. I have described my results in this area in my paper: “Beyond the Young-Laplace model for cluster growth during de-wetting of thin films: Effective coarsening exponents and the role of long range de-wetting interactions”, in Physical Review E 88, 032113 (2013).
I have been interested also in correlated quantum systems. In this area, I studied the dynamical effects that arise from the interaction between electrons by using dynamical density functional theory. I contributed to the development of the formalism known as “current-density functional theory” which expresses the transport properties of electron systems in terms of their current density. My results in this field are emphasized in the paper: “Solving the ultra-nonlocality problem in time-dependent spin-density functional theory”, in Physical Review Letters 90, 066402 (2003).
The study of specific heats of alloys by theory and simulation was another area of interest to me. In my M.S. thesis, I employed the lattice dynamical and Monte Carlo approaches to study the variation of the specific heat of Type I binary metallic alloys with changing the concentration of the minority phase. My study revealed significant deviations from linearity of the low-temperature specific heat, which cannot be explained by the conventional Debye’s low temperature contribution. Rather, they were shown to emerge due to anharmonic phonon vibrations.
Positions
Postdoctoral Researcher Jun 2015 -
FLinT-Center for Fundamental Living Technology, University of Southern Denmark
Biological and Soft Matter Theory: "Generating minimal living systems from non-living materials and increasing their evolutionary abilities", FLinT-Center for Fundamental Living Technology, University of Southern Denmark (SDU), Denmark (advisor: Prof. Steen Rasmussen).
"Generating minimal living systems from non-living materials and increasing their evolutionary abilities"
We review lessons learned about evolutionary transitions from a bottom-up construction of minimal life. We use a particular systemic protocell design process as a starting point for exploring two fundamental questions: (i) how may minimal living systems emerge from non-living materials? and (ii) how may minimal living systems support increasingly more evol- utionary richness? Under (i), we present what has been accomplished so far and discuss the remaining open challenges and their possible solutions. Under (ii), we present a design principle we have used successfully both for our computational and experimental protocellular investigations, and we conjecture how this design principle can be extended for enhancing the evolutionary potential for a wide range of systems.
Steen Rasmussen, Adi Constantinescu and Carsten Svaneborg
"Generating minimal living systems from non-living materials and increasing their evolutionary abilities",
Philosophical Transactions of the Royal Society B: Biological Sciences 371, 20150440 (2016).
DOI:http://dx.doi.org/10.1098/rstb.2015.0440
(impact factor 7.055)
This article is part of the themed issue "The major synthetic evolutionary transitions".
Postdoctoral Research Fellow Sep 2011 - May 2014
Asia Pacific Center for Theoretical Physics, Pohang University of Science and Technology
Biological and Soft Matter Theory: "Phase separation in solutions of charged rodlike polyelectrolytes", Asia Pacific Center for Theoretical Physics (APCTP), South Korea (advisor: Group Leader YongSeok Jho).
"Nematic Phase Emergence in Solutions of Similarly Charged Rodlike Polyelectrolytes"
We extend an approximate theory in order to examine the properties of the one-component plasma (OCP) of similarly charged rodlike polyelectrolytes system from the weak- to the strong-coupling regimes. In addition, Monte Carlo simulations are performed in order to verify the approximate theory. The electrostatic interactions are decomposed into short- and long-range components treated within different approximations. In addition to the Coulomb interactions present within the system, the excluded volume interactions between the charged rods are included in our analysis within a second order virial reference system. By theory and numerical simulation, we find that the isotropic phase becomes unstable with reference to the orientational ordering performed by both electrostatic and excluded volume interactions. Good agreement between theory and numerical simulation is obtained for the conditions investigated.
Adi Constantinescu and YongSeok Jho
“Nematic phase emergence in solutions of similarly charged rodlike polyelectrolytes”,
Journal of the Physical Society of Japan 83, 014002 (2014).
DOI: http://dx.doi.org/10.7566/JPSJ.83.014002
(impact factor 1.585)
Teaching Assistant and PhD Candidate Aug 2003 - Jun 2011
Theoretical Condensed Matter Physics: "Cluster growth during de-wetting of solid thin films: Coarsening exponents and the role of long range de-wetting interactions", West Virginia University, USA (advisor: Prof. Leonardo Golubović).
"Beyond the Young-Laplace model for cluster growth during dewetting of thin films: Effective coarsening exponents and the role of long range dewetting interactions"
Long range dewetting forces acting across thin films, such as the fundamental van der Waals interactions, may drive the formation of large clusters (tall multilayer islands) and pits, observed in thin films of diverse materials such as polymers, liquid crystals, and metals. In this study we further develop the methodology of the nonequilibrium statistical mechanics of thin films coarsening within continuum interface dynamics model incorporating long range dewetting interactions. The theoretical test bench model considered here is a generalization of the classical Mullins model for the dynamics of solid film surfaces. By analytic arguments and simulations of the model, we study the coarsening growth laws of clusters formed in thin films due to the dewetting interactions. The ultimate cluster growth scaling laws at long times are strongly universal: Short and long range dewetting interactions yield the same coarsening exponents. However, long range dewetting interactions, such as the van der Waals forces, introduce a distinct long lasting early time scaling behavior characterized by a slow growth of the cluster height/lateral size aspect ratio (i.e., a time-dependent Young angle) and by effective coarsening exponents that depend on cluster size. In this study, we develop a theory capable of analytically calculating these effective size-dependent coarsening exponents characterizing the cluster growth in the early time regime. Such a pronounced early time scaling behavior has been indeed seen in experiments; however, its physical origin has remained elusive to this date. Our theory attributes these observed phenomena to ubiquitous long range dewetting interactions acting across thin solid and liquid films. Our results are also applicable to cluster growth in initially very thin fluid films, formed by depositing a few monolayers or by a submonolayer deposition. Under this condition, the dominant coarsening mechanism is diffusive intercluster mass transport while the cluster coalescence plays a minor role, both in solid and in fluid films.
Adi Constantinescu, Leonardo Golubović, and Artem Levandovsky
“Beyond the Young-Laplace model for cluster growth during dewetting of thin films: Effective coarsening exponents and the role of long range dewetting interactions”,
Physical Review E 88, 032113 (2013).
DOI: 10.1103/PhysRevE.88.032113
(impact factor 2.326)
Research Assistant Aug 2001 - Jun 2003
University of Missouri, Columbia
Theoretical Condensed Matter Physics: "Time dependent spin density functional theory", University of Missouri-Columbia, USA (advisor: Prof. Giovanni Vignale).
"Solving the Ultranonlocality Problem in Time-Dependent Spin-Density-Functional Theory"
It has been known for some time that the exchange-correlation potential in time-dependent density- functional theory is an intrinsically nonlocal functional of the density as soon as one goes beyond the adiabatic approximation. In this paper we show that a much more severe nonlocality problem, with a completely different physical origin, plagues the exchange-correlation potentials in time-dependent spin-density functional theory. We show how the use of the spin current density as a basic variable solves this problem, and we provide an explicit local expression for the exchange-correlation fields as functionals of the spin currents.
Zhixin Qian, Adi Constantinescu, and Giovanni Vignale
“Solving the ultra-nonlocality problem in time-dependent spin-density functional theory”,
Physical Review Letters 90, 066402 (2003).
DOI: 10.1103/PhysRevLett.90.066402
(impact factor 7.035)
MS Student Sep 1999 - Jul 2001
M.S. Thesis: "On the specific heat of type I binary metallic alloys: a simulation study", University of Bucharest, Romania (advisor: Prof. Ana Ioanid).
BS Student Sep 1993 - Jul 1998
B.S. Thesis: "The Coulomb Green’s function and multi-photon calculations", University of Bucharest, Romania (advisor: Prof. Tudor Marian).
Education
West Virginia University, USA 2003 - 2011
Field of study: Theoretical Condensed Matter Physics
Degree: PhD
Book (My PhD Thesis)
Adi Constantinescu: “Cluster Growth During De-Wetting of Solid Thin Films: Coarsening Exponents and the Role of Long Range De-Wetting Interactions”.
Publisher: ProQuest ISBN: 1249871417 / ISBN-13: 9781249871415
Publication date: 10/18/2012
advisor: Prof. Leonardo Golubović
Coarsening processes play prominent roles in non-equilibrium statistical physics and in applied physical sciences. A new area in this field of statistical physics has emerged from recent experimental revelations that long-range de-wetting forces acting across thin films, such as the fundamental van der Waals interactions, may drive the formation of large clusters (tall multi- layer islands) and pits, observed in thin films of soft materials (polymers), as well as in thin films of liquid and solid metals. Motivated by the experiments, in this Thesis I elucidate the fundamentals of the non-equilibrium statistical mechanics of solid thin films coarsening within a unified model explicitly incorporating de-wetting interactions. By analytic arguments and simulations of the model, I study the growth laws of clusters formed in thin films due to the de-wetting interactions. The ultimate long time-scale cluster growth coarsening exponents are found to depend on the substrate dimensionality, unlike the super-universal exponents encountered in standard coarsening phenomena. Nonetheless, the ultimate cluster growth scaling laws at long times are strongly universal: Short and long range de-wetting interactions yield the same coarsening exponents. However, long range de-wetting interactions, such as the common van der Waals forces, introduce a distinct long lasting early-time scaling behavior characterized by a slow growth of the cluster height/lateral size aspect ratio (i.e., a time-dependent Young angle), and by effective coarsening exponents that depend on cluster size. In this thesis, I develop a theory capable to calculate these effective size-dependent coarsening exponents characterizing the cluster growth in the early-time cross-over regime. Such a pronounced cross- over behavior has been indeed seen in experiments; however its physical origin has remained elusive to this date. My results attribute these observed phenomena to ubiquitous long range de-wetting interactions acting across thin films.
University of Bucharest, Romania 1999 - 2001
Field of study: Theoretical Condensed Matter Physics
Degree: Master
M.S. Thesis: "On the specific heat of type I binary metallic alloys: a simulation study".
advisor: Prof. Ana Ioanid
The study of specific heats of alloys, by theory and simulation, was another area of interest to me. In my M.S. thesis, I employed the lattice dynamical and Monte Carlo approaches to study the variation of the specific heat of Type I binary metallic alloys with changing the concentration of the minority phase. My study revealed significant deviations from linearity of the low-temperature specific heat, which cannot be explained by the conventional Debye’s low temperature contribution. Rather, they were shown to emerge due to anharmonic phonon vibrations.
University of Bucharest, Romania 1993 - 1998
Field of study: Theoretical Condensed Matter Physics
Degree: Bachelor
B.S. Thesis: "The Coulomb Green’s function and multi-photon calculations".
advisor: Prof. Tudor Marian
Skills
(i) Experience in HPC environments:
I have developed my own C\C++ code in order to perform numerical simulations on HPC environment for studying the coarsening growth laws of clusters formed in thin films due to the de-wetting interactions.
(ii) Certifications:
College Teaching Institute-Program for Excellence in Teaching
University of Missouri-Columbia, USA,
January 2003.
(iii) Courses Taught:
As graduate student at University of Missouri-Columbia and West Virginia University I have been involved in teaching a number of different kinds of physics courses at both undergraduate and graduate levels. Most frequent topics have been: Introductory Physics 101-Classical Mechanics (lab course-undergraduate level), Introductory Physics 102-Electricity and Magnetism, Optics (lab course-undergraduate level), Mathematical Methods in Physics (graduate level). At University of Southern Denmark, I am currently teaching the Physical Chemistry Course KE 523 (tutorial class-undergraduate level).
(iV) Languages: Romanian-Native Proficiency, English-Full Professional Proficiency, French-Elementary Proficiency, Korean-Elementary Proficiency, Danish-Elementary Proficiency.
Professional interests
Statistical Mechanics and Condensed Matter Theory: Modern theories of phase transitions; Non-Equilibrium Statistical Mechanics; Phase ordering phenomena; Dynamics of surfaces and interfaces; Theory of many-particle systems in external fields, confined geometry and reduced dimensionality.
Non-Linear Dynamics: Perturbation methods for dynamical systems.
Computational and Numerical Methods: Algorithm development; Large scale numerical simulations; Grid methods for continuum modeling; Molecular Dynamics and Monte Carlo simulations.
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