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.

AlGaN Deep-Ultraviolet Light-Emitting Diodes with External Quantum Efficiency above 10%

Abstract: Improvements of the internal quantum efficiency by reduction of the threading dislocation density and of the light extraction by using UV transparent p-type cladding and contact layers, UV reflecting ohmic contact, and chip encapsulation with optimized shape and refractive index allowed us to obtain the external quantum efficiency of 104% at 20 mA CW current with the output power up to 93 mW at 278 nm for AlGaN-based deep-ultraviolet light-emitting diodes grown on sapphire substrates

Stanford University Unstructured (SU 2 ): An open-source integrated computational environment for multi-physics simulation and design

Abstract: This paper describes the history, objectives, structure, and current capabilities of the Stanford University Unstructured (SU 2 ) tool suite. This computational analysis and design software collection is being developed to solve complex, multi-physics analysis and optimization tasks using arbitrary unstructured meshes, and it has been designed so that it is easily extensible for the solution of Partial Differential Equation-based (PDE) problems not directly envisioned by the authors. At its core, SU 2 is an open-source collection of C++ software tools to discretize and solve problems described by PDEs and is able to solve PDE-constrained optimization problems, including optimal shape design. Although the toolset has been designed with Computational Fluid Dynamics (CFD) and aerodynamic shape optimization in mind, it has also been extended to treat other sets of governing equations including potential flow, electrodynamics, chemically reacting flows, and several others. In our experience, capabilities for computational analysis and optimization have improved considerably over the past two decades. However, the ability to integrate the resulting software packages into coupled multi-physics analysis and design optimization solvers has remained a challenge: the variety of approaches chosen for the independent components of the overall problem (flow solvers, adjoint solvers, optimizers, shape parameterization, shape deformation, mesh adaption, mesh deformation, etc) make it difficult to (a) expand the range of applicability to situations not originally envisioned, and (b) to reduce the overall burden of creating integrated applications. By leveraging well-established object-oriented software architectures (using C++) and by enabling a common interface for all the necessary components, SU 2 is able to remove these barriers for both the beginner and the seasoned analyst. In this paper we attempt to describe our efforts to develop SU 2 as an integrated platform. In some senses, the paper can also be used as a software reference manual for those who might be interested in modifying it to suit their own needs. We carefully describe the C++ framework and object hierarchy, the sets of equations that can be currently modeled by SU 2 , the available choices for numerical discretization, and conclude with a set of relevant validation and verification test cases that are included with the SU 2 distribution. We intend for SU 2 to remain open source and to serve as a starting point for new capabilities not included in SU 2 today, that will hopefully be contributed by users in both academic and industrial environments.

New Site Coefficients and Site Classification System Used in Recent Building Seismic Code Provisions

Abstract: Recent code provisions for buildings and other structures (1994 and 1997 NEHRP Provisions, 1997 UBC) have adopted new site amplification factors and a new procedure for site classification. Two amplitude‐dependent site amplification factors are specified: Fa for short periods and Fv for longer periods. Previous codes included only a long period factor S and did not provide for a short period amplification factor. The new site classification system is based on definitions of five site classes in terms of a representative average shear wave velocity to a depth of 30 m (V¯s). This definition permits sites to be classified unambiguously. When the shear wave velocity is not available, other soil properties such as standard penetration resistance or undrained shear strength can be used. The new site classes denoted by letters A ‐ E, replace site classes in previous codes denoted by S1 ‐ S4. Site classes A and B correspond to hard rock and rock, Site Class C corresponds to soft rock and very stiff / ver...

Photonic bands: Convergence problems with the plane-wave method.

Abstract: The problems associated with the poor convergence of the Fourier transform of the hard-sphere dielectric function are discussed. A significant band gap between the eighth and ninth levels has been found for air spheres in fcc. We also consider a periodic array of Gaussian spheres, which converges well and allows a consistent and reliable determination of the general features of photonic bands. It is found that when \ensuremath{\epsilon}(r) is sharply peaked, photonic levels become almost degenerate throughout the Brillouin zone, corresponding to standing waves.

A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey

Abstract: We perform an analysis of spectra and photometry for 22,770 stars included in the third data release (DR3) of the Sloan Digital Sky Survey (SDSS). We measure radial velocities and, based on a model-atmosphere analysis, derive estimates of the atmospheric parameters (effective temperature, surface gravity, and [Fe/H]) for each star. Stellar evolution models are then used to estimate distances. We thoroughly check our analysis procedures using three recently published spectroscopic libraries of nearby stars, and compare our results with those obtained from alternative approaches. The SDSS sample covers a range in stellar brightness of 14 < V < 22, primarily at intermediate galactic latitudes, and comprises large numbers of F- and G-type stars from the thick-disk and halo populations (up to 100 kpc from the galactic plane), therefore including some of the oldest stars in the Milky Way. In agreement with previous results from the literature, we find that halo stars exhibit a broad range of iron abundances, with a peak at [Fe/H] {approx_equal} -1.4. This population exhibits essentially no galactic rotation. Thick-disk G-dwarf stars at distances from the galactic plane in the range 1 < |z| < 3 kpc show a much more compact metallicity distribution, with a maximummore » at [Fe/H] {approx_equal} -0.7, and a median galactic rotation velocity at that metallicity of 157 {+-} 4 km s{sup -1} (a lag relative to the thin disk of 63 km s{sup -1}). SDSS DR3 includes spectra of many F-type dwarfs and subgiants between 1 and 3 kpc from the plane with galactic rotation velocities consistent with halo membership. A comparison of color indices and metal abundances with isochrones indicates that no significant star formation has taken place in the halo in the last {approx} 11 Gyr, but there are thick-disk stars which are at least 2 Gyr younger. We find the metallicities of thick-disk stars to be nearly independent of galactocentric distance between 5 and 14 kpc from the galactic center, in contrast with the marked gradients found in the literature for the thin disk. No vertical metallicity gradient is apparent for the thick disk, but we detect a gradient in its rotational velocity of -16 {+-} 4 km s{sup -1} kpc{sup -1} between 1 and 3 kpc from the plane. We estimate that among the stars in our sample there are over 2000 with an iron abundance [Fe/H] < -2, and over 150 stars with an iron abundance [Fe/H] < -3.« less