Center for Nonlinear Studies
Center for Nonlinear Studies
News Article | February 16, 2017
Abstract: Francis (Frank) Alexander, a physicist with extensive management and leadership experience in computational science research, has been named Deputy Director of the Computational Science Initiative at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, effective February 1. Alexander comes to Brookhaven Lab from DOE's Los Alamos National Laboratory, where he was the acting division leader of the Computer, Computational, and Statistical Sciences (CCS) Division. During his more than 20 years at Los Alamos, he held several leadership roles, including as leader of the CCS Division's Information Sciences Group and leader of the Information Science and Technology Institute. Alexander first joined Los Alamos in 1991 as a postdoctoral researcher at the Center for Nonlinear Studies. He returned to Los Alamos in 1998 after doing postdoctoral work at the Institute for Scientific Computing Research at DOE's Lawrence Livermore National Laboratory and serving as a research assistant professor at Boston University's Center for Computational Science. "I was drawn to Brookhaven by the exciting opportunity to strengthen the ties between computational science and the significant experimental facilities-the Relativistic Heavy Ion Collider, the National Synchrotron Light Source II, and the Center for Functional Nanomaterials [all DOE Office of Science User Facilities]," said Alexander. "The challenge of getting the most out of high-throughput and data-rich science experiments is extremely exciting to me. I very much look forward to working with the talented individuals at Brookhaven on a variety of projects, and am grateful for the opportunity to be part of such a respected institution." In his new role as deputy director, Alexander will work with CSI Director Kerstin Kleese van Dam to expand CSI's research portfolio and realize its potential in data-driven discovery. He will serve as the primary liaison to national security agencies, as well as develop strategic partnerships with other national laboratories, universities, and research institutions. His current research interest is the intersection of machine learning and physics (and other domain sciences). "We are incredibly happy that Frank decided to join our CSI team," said Kleese van Dam. "With his background in high-performance computing, data science, and computational and statistical physics, he is the ideal fit for Brookhaven." Throughout his career, Alexander has worked in a variety of areas, including nonequilibrium physics and computational physics. More recently, he has focused on the optimal design of experiments as part of the joint DOE/National Cancer Institute collaboration on cancer research, as well as on uncertainty quantification and error analysis for the prediction of complex systems' behavior. Alexander has served on many committees and advisory panels, including those related to DOE's Laboratory Directed Research and Development [http://science.energy.gov/lp/laboratory-directed-research-and-development/] program. Currently, he is on DOE's Computational Research Leadership Council and the editorial board of Computing in Science & Engineering Magazine. Alexander received his PhD in physics in 1991 from Rutgers University and a BS in mathematics and physics in 1987 from The Ohio State University. About Brookhaven National Laboratory Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Nayyar I.H.,Center for Nonlinear Studies |
Nayyar I.H.,National Center for Nanosciences and Technology of China |
Nayyar I.H.,University of Central Florida |
Batista E.R.,Center for Nonlinear Studies |
And 5 more authors.
Journal of Chemical Theory and Computation | Year: 2013
Five different Density Functional Theory (DFT) models (ranging from pure GGA to long-range-corrected hybrid functionals) were used to study computationally the nature of the self-trapped electronic states in oligophenylene vinylenes. The electronic excitations in question include the lowest singlet (S1) and triplet (T1 †) excitons (calculated using Time Dependent DFT (TD-DFT) method), positive (P +) and negative (P-) polarons, and the lowest triplet (T1) states (computed with the Self-Consistent Field (SCF) scheme). The polaron formation (spatial localization of excitations) is observed only with the use of range-corrected hybrid DFT models including long-range electronic exchange interactions. The extent of localization for all studied excitations is found to be invariant with respect to the size of the oligomer chain in their corresponding optimal geometries. We have analyzed the interdependence between the extent of the geometrical distortion and the localization of the orbital and spin density, and have observed that the localization of the P+ and P- charged species is quite sensitive to solvent polarization effects and the character of the DFT functional used, rather than the structural deformations. In contrast, the localization of neutral states, S1 and T1 †, is found to follow the structural distortions. Notably, T1 excitation obtained with the mean field SCF approach is always strongly localized in range-corrected hybrid DFT models. The molecular orbital energetics of these excitations was further investigated to identify the relationship between state localization and the corresponding orbital structure. A characteristic stabilization (destabilization) of occupied (virtual) orbitals is observed in hybrid DFT models, compared to tight-binding model-like orbital filling in semilocal GGA functionals. The molecular and natural orbital representation allows visualization of the spatial extent of the underlying electronic states. In terms of stabilization energies, neutral excitons have higher binding energies compared to charged excitations. In contrast, the polaronic species exhibit the highest solvation energies among all electronic states studied. © 2012 American Chemical Society.
News Article | February 22, 2017
LOS ALAMOS, N.M., Feb. 22, 2017--In a new study published today in the journal PLOS ONE, Los Alamos National Laboratory scientists have taken a condensed matter physics concept usually applied to the way substances such as ice freeze, called "frustration," and applied it to a simple social network model of frustrated components. They show that inequality of wealth can emerge spontaneously and more equality can be gained by pure initiative. It's a computer-modeling exploration of the 19th-century Horatio Alger theme, whereby a motivated young person overcomes poor beginnings and lives the "rags to riches" life thanks to strength of character. "Most theories of wealth inequality rely on social stratification due to income inequality and inheritance," said Cristiano Nisoli, of the Physics of Condensed Matter and Complex Systems group at Los Alamos and lead author of the study. "We consider, however, the possibility that in our more economically fluid world, novel, direct channels for wealth transfer could be available, especially for financial wealth." The work stems from Los Alamos research into computational material science, with broader applications to materials physics, energy security and weapons physics. In this case, the study's authors used computer modeling to conceptualize the situation of a set of agents, endowed with opportunities to acquire available wealth. As Nisoli describes it, "we assume that the possession of wealth endows the user with the power to attract more wealth." The team of Benoit Mahault (visiting from Université Paris Saclay), Avadh Saxena and Nisoli divided the problem into three sets of problems: The first set of results shows that in a static society--where the allocation of opportunities does not change in time--the "law of the jungle" allows anyone to gain wealth from or lose it to anyone else. Relative chaos ensues. The second set of results also pertains to static societies, but ones in which transactions of wealth are regulated. People cannot gain or lose wealth from just anybody, but only from their neighbors in the network in which they are linked. This scenario leads to substantially more fairness in the mathematical benchmark cases of Erdös models for random networks and of Barabasi-Albert algorithms for scale-free networks. However, marked differences between the two appear when it comes to overall rather than subjective fairness. The third set of results pertains to dynamic societies. Maintaining the overall wealth level as fixed, the researchers allow agents to freely shift links among themselves as their own initiative drives them. This is where the concepts of power, frustration and initiative, previously benchmarked on static markets, become crucial. Their interplay results in a complex dynamic. At a low level of initiative, results converge to more or less ameliorated inequality where the power of wealth concentrates and wins. At high initiative levels, results converge to strong equality where power never concentrates. For initiative levels somewhere in between, we see the interplay of three emergent social classes: lower, middle and upper. Said Nisoli, "If driven by power alone, the market evolution reaches a static equilibrium characterized by the most savage inequality. Power not only concentrates wealth, but reshapes the market topology to concentrate the very opportunities to acquire wealth on only a few agents, who now amass all the wealth of the society." This equilibrium scenario however, does not take into account personal frustration and initiative to act. If those elements are introduced, at sufficient initiative, a cyclical dynamic of three social classes emerges. "Periodically, a long 'time of inequality' is contrasted by the patient effort of the middle class to rise up, to bring down the upper class and to merge with it. When that finally happens, however, the situation proves unstable: a single egalitarian class forms for a brief time, only to be soon disrupted by the appearance of difficult-to-predict 'black swan' economic events. The power of the latter, now competing against unfrustrated and thus demotivated agents of an egalitarian class, wins easily and a new time of inequality is brought in as a new middle class emerges while the upper-class rises," Nisoli explained. To encapsulate the concept, he said, "We learn from this analysis that in our admittedly simplified model, equality can be improved either by proper engineering of a static market topology, which seems impracticable, or by dynamic emergent reshaping of the market via sufficient individual initiative to act upon frustration." But a successful society, with reduced frustration and improved equality, does not continue for long. "Equality is short lived, we find, as the disappearance of frustration that follows equality removes the fundamental drive toward equality. Perhaps a key element in preventing the cyclical return of inequality would be memory, which is absent from our framework. But then, is it present in a real society?" The paper, "Emergent Inequality and Self-Organized Social Classes in a Network of Power and Frustration," appears in this week's PLOS ONE. Link: http://journals. This research was funded by the U.S. Department of Energy, the Los Alamos National Laboratory Center for Nonlinear Studies, the Los Alamos Institute for Materials Science and Laboratory Directed Research and Development. Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, BWX Technologies, Inc. and URS Corporation for the Department of Energy's National Nuclear Security Administration. Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and global security concerns.
Dorfler F.,University of California at Los Angeles |
Jovanovic M.R.,University of Minnesota |
Chertkov M.,Center for Nonlinear Studies |
Bullo F.,University of California at Santa Barbara
IEEE Transactions on Power Systems | Year: 2014
Inter-area oscillations in bulk power systems are typically poorly controllable by means of local decentralized control. Recent research efforts have been aimed at developing wide-area control strategies that involve communication of remote signals. In conventional wide-area control, the control structure is fixed a priori typically based on modal criteria. In contrast, here we employ the recently-introduced paradigm of sparsity-promoting optimal control to simultaneously identify the optimal control structure and optimize the closed-loop performance. To induce a sparse control architecture, we regularize the standard quadratic performance index with an ℓ1- penalty on the feedback matrix. The quadratic objective functions are inspired by the classic slow coherency theory and are aimed at imitating homogeneous networks without inter-area oscillations. We use the New England power grid model to demonstrate that the proposed combination of the sparsity-promoting control design with the slow coherency objectives performs almost as well as the optimal centralized control while only making use of a single wide-area communication link. In addition to this nominal performance, we also demonstrate that our control strategy yields favorable robustness margins and that it can be used to identify a sparse control architecture for control design via alternative means. © 2014 IEEE.
Li H.,Center for Nonlinear Studies |
Chernyak V.Y.,Wayne State University |
Tretiak S.,Center for Nonlinear Studies |
Tretiak S.,Los Alamos National Laboratory
Journal of Physical Chemistry Letters | Year: 2012
The exciton scattering (ES) method allows efficient calculations of spectroscopic observables in large low-dimensional conjugated molecular systems. To compute the transition dipoles between the ground and excited electronic states, we should extract the ES dipole parameters from quantum chemistry calculations in simple molecular fragments. In this manuscript, we show how to retrieve these parameters from any reference quantum chemistry model that uses an arbitrary nonorthogonal and possibly overcomplete atomic orbital basis set. Our approach relies on the natural atomic orbital (NAO) representation, in which the basis functions are orthonormal and the atom-like character is preserved. We apply the ES approach, combined with the NAO analysis to optical spectra of branched phenylacetylene oligomers. Absorption spectra predicted by the ES method demonstrate close agreement with the results of direct quantum chemistry calculations, when the Time-Dependent Density Functional Theory (TD-DFT) being used as a reference. This testifies applicability of a variety of quantum-chemical techniques, where the NAO population analysis can be conducted, for the ES framework. © 2012 American Chemical Society.
Chundawat S.P.S.,Michigan State University |
Bellesia G.,Theoretical Biology and Biophysics |
Bellesia G.,Center for Nonlinear Studies |
Uppugundla N.,Michigan State University |
And 11 more authors.
Journal of the American Chemical Society | Year: 2011
Conversion of lignocellulose to biofuels is partly inefficient due to the deleterious impact of cellulose crystallinity on enzymatic saccharification. We demonstrate how the synergistic activity of cellulases was enhanced by altering the hydrogen bond network within crystalline cellulose fibrils. We provide a molecular-scale explanation of these phenomena through molecular dynamics (MD) simulations and enzymatic assays. Ammonia transformed the naturally occurring crystalline allomorph Iβ to IIII, which led to a decrease in the number of cellulose intrasheet hydrogen bonds and an increase in the number of intersheet hydrogen bonds. This rearrangement of the hydrogen bond network within cellulose IIII, which increased the number of solvent-exposed glucan chain hydrogen bonds with water by 50%, was accompanied by enhanced saccharification rates by up to 5-fold (closest to amorphous cellulose) and 60 - 70% lower maximum surface-bound cellulase capacity. The enhancement in apparent cellulase activity was attributed to the "amorphous-like" nature of the cellulose IIII fibril surface that facilitated easier glucan chain extraction. Unrestricted substrate accessibility to active-site clefts of certain endocellulase families further accelerated deconstruction of cellulose IIII. Structural and dynamical features of cellulose IIII, revealed by MD simulations, gave additional insights into the role of cellulose crystal structure on fibril surface hydration that influences interfacial enzyme binding. Subtle alterations within the cellulose hydrogen bond network provide an attractive way to enhance its deconstruction and offer unique insight into the nature of cellulose recalcitrance. This approach can lead to unconventional pathways for development of novel pretreatments and engineered cellulases for cost-effective biofuels production. © 2011 American Chemical Society.
Hinnell A.C.,University of Arizona |
Ferr T.P.A.,University of Arizona |
Vrugt J.A.,Center for Nonlinear Studies |
Vrugt J.A.,University of California at Irvine |
And 4 more authors.
Water Resources Research | Year: 2010
There is increasing interest in the use of multiple measurement types, including indirect (geophysical) methods, to constrain hydrologic interpretations. To date, most examples integrating geophysical measurements in hydrology have followed a three-step, uncoupled inverse approach. This approach begins with independent geophysical inversion to infer the spatial and/or temporal distribution of a geophysical property (e.g., electrical conductivity). The geophysical property is then converted to a hydrologic property (e.g., water content) through a petrophysical relation. The inferred hydrologic property is then used either independently or together with direct hydrologic observations to constrain a hydrologic inversion. We present an alternative approach, coupled inversion, which relies on direct coupling of hydrologic models and geophysical models during inversion. We compare the abilities of coupled and uncoupled inversion using a synthetic example where surface-based electrical conductivity surveys are used to monitor one-dimensional infiltration and redistribution. Through this illustrative example, we show that the coupled approach can provide significant reductions in uncertainty for hydrologic properties and associated predictions if the underlying model is a faithful representation of the hydrologic processes. However, if the hydrologic model exhibits structural errors, the coupled inversion may not improve the hydrologic interpretation. Despite this limitation, our results support the use of coupled hydrogeophysical inversion both for the direct benefits of reduced errors during inversion and because of the secondary benefits that accrue because of the extensive communication and sharing of data necessary to produce a coupled model, which will likely lead to more thoughtful use of geophysical data in hydrologic studies. © 2010 by the American Geophysical Union.
Liu Y.,Center for Nonlinear Studies |
Liu Y.,Los Alamos National Laboratory |
Liu Y.,Jet Propulsion Laboratory |
Ecke R.E.,Center for Nonlinear Studies |
Ecke R.E.,Los Alamos National Laboratory
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011
We present local temperature measurements of turbulent Rayleigh- Bénard convection with rotation about a vertical axis. The fluid, water with Prandtl number about 6, was confined in a cell with a square cross section of 7.3×7.3 cm2 and a height of 9.4 cm. Temperature fluctuations and boundary-layer profiles were measured for Rayleigh numbers 1×107
Aluie H.,Los Alamos National Laboratory |
Aluie H.,Center for Nonlinear Studies |
Li S.,Los Alamos National Laboratory |
Li H.,Los Alamos National Laboratory
Astrophysical Journal Letters | Year: 2012
The physical nature of compressible turbulence is of fundamental importance in a variety of astrophysical settings. We investigate the question: "At what scales does the mechanism of pressure-dilatation operate?" and present the first direct evidence that mean kinetic energy cascades conservatively beyond a transitional "conversion" scale range despite not being an invariant of the dynamics. We use high-resolution 10243 subsonic and transonic simulations. The key quantity we measure is the pressure-dilatation cospectrum, E PD(k), where we show that it decays at a rate faster than k -1 in wavenumber in at least the subsonic and transonic regimes. This is sufficient to imply that mean pressure-dilatation acts primarily at large scales and that kinetic and internal energy budgets statistically decouple beyond a transitional scale range. However, we observe that small-scale dynamics remains highly compressible locally in space and that the statistical decoupling in the energy budgets is unrelated to the existence of a subsonic scale range. Our results suggest that an extension of Kolmogorov's inertial-range theory to compressible turbulence is possible. © 2012. The American Astronomical Society. All rights reserved..
Zhong W.-R.,Jinan University |
Zhong W.-R.,Center for Nonlinear Studies |
Hu B.,Center for Nonlinear Studies |
Hu B.,University of Houston
Physical Review B - Condensed Matter and Materials Physics | Year: 2010
We report on the first molecular device of heat pump modeled by a T-shape Frenkel-Kontorova lattice. The system is a three-terminal device with the important feature that the heat can be pumped from the low-temperature region to the high-temperature region through the third terminal. The pumping action is achieved by applying a stochastic external force that periodically modulates the atomic temperature. The temperature, the frequency, and the system size dependence of heat pump are briefly discussed. © 2010 The American Physical Society.