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We study pulse propagation in one-dimensional granular chains of spherical granules. Our goal is to develop an analytic approach that makes it possible to predict pulse properties as a function of time. Our method is based on a binary collision approximation that reduces the problem to collisions involving only two granules at a time. We illustrate theâ€¦ (More)

- Upendra Harbola, Alexandre Rosas, Aldo H. Romero, Massimiliano Esposito, Katja Lindenberg
- Physical review. E, Statistical, nonlinear, andâ€¦
- 2009

We study pulse propagation in one-dimensional chains of spherical granules decorated with small grains placed between large granules. The effect of the small granules can be captured by replacing the decorated chains by undecorated chains of large granules of appropriately renormalized mass and effective interaction between the large granules. This allowsâ€¦ (More)

- Christoph A Marx, Upendra Harbola, Shaul Mukamel
- Physical review. A, Atomic, molecular, andâ€¦
- 2008

Nonlinear optical signals from an assembly of N noninteracting particles consist of an incoherent and a coherent component, whose magnitudes scale ~ N and ~ N(N - 1), respectively. A unified microscopic description of both types of signals is developed using a quantum electrodynamical (QED) treatment of the optical fields. Closed nonequilibrium Green'sâ€¦ (More)

- Italo'Ivo Lima Dias Pinto, Daniel Escaff, Upendra Harbola, Alexandre Rosas, Katja Lindenberg
- Physical review. E, Statistical, nonlinear, andâ€¦
- 2014

Infinite arrays of coupled two-state stochastic oscillators exhibit well-defined steady states. We study the fluctuations that occur when the number N of oscillators in the array is finite. We choose a particular form of global coupling that in the infinite array leads to a pitchfork bifurcation from a monostable to a bistable steady state, the latter withâ€¦ (More)

- Upendra Harbola, Alexandre Rosas, Aldo H. Romero, Katja Lindenberg
- Physical review. E, Statistical, nonlinear, andâ€¦
- 2010

We study pulse propagation in one-dimensional chains of spherical granules decorated with small randomly sized granules placed between bigger monodisperse ones. Such "designer chains" are of interest in efforts to control the behavior of the pulse so as to optimize its propagation or attenuation, depending on the desired application. We show that a recentlyâ€¦ (More)

- Upendra Harbola, Alexandre Rosas, Massimiliano Esposito, Katja Lindenberg
- Physical review. E, Statistical, nonlinear, andâ€¦
- 2009

We study pulse propagation in one-dimensional tapered chains of spherical granules. Analytic results for the pulse velocity and other pulse features are obtained using a binary collision approximation. Comparisons with numerical results show that the binary collision approximation provides quantitatively accurate analytic results for these chains.

Closed expressions for tunneling currents in molecular junctions are derived to the fourth-order in electronphonon coupling. The Keldysh-Schwinger formalism is recast in terms of density matrices in Liouville space, and the calculation only involves forward propagation in real time and is represented by the double sided Feynman diagrams commonly used forâ€¦ (More)

- Christian Van den Broeck, Upendra Harbola, RaÃºl Toral, Katja Lindenberg
- Physical review. E, Statistical, nonlinear, andâ€¦
- 2015

We investigate the relaxation of long-tailed distributions under stochastic dynamics that do not support such tails. Linear relaxation is found to be a borderline case in which long tails are exponentially suppressed in time but not eliminated. Relaxation stronger than linear suppresses long tails immediately, but may lead to strong transient peaks in theâ€¦ (More)

- Jeremy B. Maddox, Upendra Harbola, +4 authors Shaul Mukamel
- The journal of physical chemistry. A
- 2006

Inelastic resonances in the electron tunneling spectra of several conjugated molecules are simulated using the nonequilibrium Greens function formalism. The vibrational modes that strongly couple to the electronic current are different from the infrared and Raman active modes. Spatially resolved inelastic electron tunneling (IET) intensities are predicted.â€¦ (More)