Rensselaer Polytechnic Institute

About: Rensselaer Polytechnic Institute is a education organization based out in Troy, New York, United States. It is known for research contribution in the topics: Terahertz radiation & Finite element method. The organization has 19024 authors who have published 39922 publications receiving 1414699 citations. The organization is also known as: RPI & Rensselaer Institute.

Turning carbon nanotubes from exceptional heat conductors into insulators.

Abstract: Thermal conductivity ($\ensuremath{\kappa}$) of isolated carbon nanotubes (CNTs) is higher than the $\ensuremath{\kappa}$ of diamond; however, in this Letter we show that the $\ensuremath{\kappa}$ of a packed bed of three-dimensional random networks of single and multiwall CNTs is smaller than that of thermally insulating amorphous polymers. The thermoelectric power ($\ensuremath{\Sigma}$) of the random network of CNTs was also measured. The $\ensuremath{\Sigma}$ of a single wall nanotube network is very similar to that of isolated nanotubes and, in contrast with $\ensuremath{\kappa}$, $\ensuremath{\Sigma}$ shows a strong dependence on the tube diameter.

Pulsed second-harmonic generation in nonlinear, one-dimensional, periodic structures

Abstract: We present a numerical study of second-harmonic (SH) generation in a one-dimensional, generic, photonic band-gap material that is doped with a nonlinear ${\ensuremath{\chi}}^{(2)}$ medium. We show that a 20-period, 12-\ensuremath{\mu}m structure can generate short SH pulses (similar in duration to pump pulses) whose energy and power levels may be 2--3 orders of magnitude larger than the energy and power levels produced by an equivalent length of a phase-matched, bulk medium. This phenomenon comes about as a result of the combination of high electromagnetic mode density of states, low group velocity, and spatial phase locking of the fields near the photonic band edge. The structure is designed so that the pump pulse is tuned near the first-order photonic band edge, and the SH signal is generated near the band edge of the second-order gap. This maximizes the density of available field modes for both the pump and SH field. Our results show that the ${\ensuremath{\chi}}^{(2)}$ response is effectively enhanced by several orders of magnitude. Therefore, mm- or cm-long, quasi-phase-matched devices could be replaced by these simple layered structures of only a few micrometers in length. This has important applications to high-energy lasers, Raman-type sources, and frequency up- and down-conversion schemes.

Nonlinear behavior of soft clays during cyclic loading

Abstract: A new stress- strain model that accounts for the nonlinear and degradation characteristics in soft clays due to cyclic loading is developed based on the results of cyclic tests on specimens of San Francisco Bay Mud. The model parameters were obtained from controlled-strain tests and the model was extended for an arbitrary cyclic loading history, such as that occurring during earthquakes, and was used to predict stress-strain response of controlled-stress tests. The main features of the proposed model include: (1)During every cycle, the stress-strain behavior of the soil is defined by a backbone curve and by the Masing criterion; (2)the backbone curve is represented by the Ramberg-Osgood formulation; (3)the ordinates of the backbone curve decrease (degrade) during cyclic loading by an amount measured by a degradation index that represents an irreversible degradation process in the structure of the soil; and (4)the rate of degradation is controlled essentially by the amplitude of the cyclic strain.