Strain-induced interface reconstruction in epitaxial heterostructures

We investigate in the framework of Landau theory the distortion of the strain fields at the interface of two dissimilar ferroelastic oxides that undergo a structural cubic-to-tetragonal phase transition. Simple analytical solutions are derived for the dilatational and the order parameter strains that are globally valid over the whole of the heterostructure. The solutions reveal that the dilatational strain exhibits compression close to the interface which may in turn affect the electronic properties in that region.Comment: 7 pages, 5 figures, to be published in Physical Review

Driven Intrinsic Localized Modes in a Coupled Pendulum Array

Intrinsic localized modes (ILMs), also called discrete breathers, are directly generated via modulational instability in an array of coupled pendulums. These ILMs can be stabilized over a range of driver frequencies and amplitudes. They are characterized by a pi-phase difference between their center and wings. At higher driver frequencies, these ILMs are observed to disintegrate via a pulsating instability, and the mechanism of this breather instability is investigated.Comment: 5 pages, 6 figure

Surmounting collectively oscillating bottlenecks

We study the collective escape dynamics of a chain of coupled, weakly damped nonlinear oscillators from a metastable state over a barrier when driven by a thermal heat bath in combination with a weak, globally acting periodic perturbation. Optimal parameter choices are identified that lead to a drastic enhancement of escape rates as compared to a pure noise-assisted situation. We elucidate the speed-up of escape in the driven Langevin dynamics by showing that the time-periodic external field in combination with the thermal fluctuations triggers an instability mechanism of the stationary homogeneous lattice state of the system. Perturbations of the latter provided by incoherent thermal fluctuations grow because of a parametric resonance, leading to the formation of spatially localized modes (LMs). Remarkably, the LMs persist in spite of continuously impacting thermal noise. The average escape time assumes a distinct minimum by either tuning the coupling strength and/or the driving frequency. This weak ac-driven assisted escape in turn implies a giant speed of the activation rate of such thermally driven coupled nonlinear oscillator chains

Multipeaked polarons in soft potentials

We consider a minimal coupled charge/excitation-lattice model capturing a competition between linear polaronic self-trapping and the self-focusing effects of a soft nonlinear on-site potential. The standard singlehumped polaron ceases to exist above a critical value of the coupling strength, closely related to the inflection point in the nonlinear potential. For couplings beyond this critical value, we find that successive multihumped polaronic solutions correspond to the lowest-energy stationary states of the system, which may admit interesting quantum resonance behavior.Fil: Fuentes, Miguel Angel. Instituto de Investigaciones Filosóficas - Sadaf; Argentina. University of New Mexico; Estados UnidosFil: Maniadis, P.. Université Pierre et Marie Curie; FranciaFil: Kalosakas, G.. Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory; Estados UnidosFil: Rasmussen, K.. Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory; Estados UnidosFil: Bishop, A. R.. Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory; Estados UnidosFil: Kenkre, V. M.. University of New Mexico; Estados UnidosFil: Gaidedei, Yu B.. Bogolyubov Institute for Theoretical Physics; Ucrani

Ordering mechanisms in triblock copolymers

Maniadis, P., Thompson, R. B., Rasmussen, K. Ø., & Lookman, T. (2004). Ordering mechanisms in triblock copolymers. Physical Review E, 69(3), 031801. https://doi.org/10.1103/PhysRevE.69.031801The ordering mechanisms for an ABC triblock copolymer system are studied using self-consistent field theory. We find a two-phase mechanism, similar to what has been suggested experimentally two-step mecha- nism. Analysis of free energy components shows that the two-phase process comes about through a compe- tition between stretching energy and interfacial energy. The mechanism is found to be sufficiently robust so as to make it potentially useful for device applications.U.S. Department of Energy, W-7405-ENG-36 || European TMP program LOCNET, HPRN-CT-1999-00163

Tight-binding parameters for charge transfer along DNA

We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The $\pi$ molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are discussed and then used for calculating the corresponding wavefunctions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the $\pi$ molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons, which probably indicates that hole transport along DNA is more favorable than electron transport. Our findings are also compared with existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table

Who Said or What Said? Estimating Ideological Bias in Views Among Economists

There exists a long-standing debate about the influence of ideology in economics. Surprisingly, however, there is no concrete empirical evidence to examine this critical issue. Using an online randomized controlled experiment involving economists in 19 countries, we examine the effect of ideological bias on views among economists. Participants were asked to evaluate statements from prominent economists on different topics, while source attribution for each statement was randomized without participants’ knowledge. For each statement, participants either received a mainstream source, an ideologically different less-/non-mainstream source, or no source. We find that changing source attributions from mainstream to less-/non-mainstream, or removing them, significantly reduces economists’ reported agreement with statements. Using a model of Bayesian updating we examine two competing hypotheses as potential explanations for these results: unbiased Bayesian updating versus ideologically-biased Bayesian updating. While we find no evidence in support of unbiased updating, our results are consistent with biased Bayesian updating. More specifically, we find that changing/removing sources (1) has no impact on economists’ reported confidence with their evaluations; (2) similarly affects experts/non-experts in relevant areas; and (3) affects those at the far right of the political spectrum much more significantly than those at the far left. Finally, we find significant heterogeneity in our results by gender, country, PhD completion country, research area, and undergraduate major, with patterns consistent with the existence of ideological bias