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 & Population. The organization has 19024 authors who have published 39922 publications receiving 1414699 citations. The organization is also known as: RPI & Rensselaer Institute.

Surface Reconstructions and Dimensional Changes in Single-Walled Carbon Nanotubes

Abstract: Dimensional stability is crucial to possible applications of single-walled nanotubes, as their properties are linked to size and topology. We observe nanotubes responding to uniform atom loss, through surface reconstruction and drastic dimensional changes. Experiments using electron irradiation evidence nanotube diameters shrinking from similar to 1.4 to 0.4 nm. Molecular dynamics simulations show that surface reconstruction and size reduction occur through dangling bond saturation, forming nonhexagonal rings and 5-7 defects in the lattice. Nonuniform atom removal results in inhomogeneous tube deformations and local necking, and formation of linear atomic carbon chains in the nanotube body.

A Framework for Web Science

Abstract: This text sets out a series of approaches to the analysis and synthesis of the World Wide Web, and other web-like information structures. A comprehensive set of research questions is outlined, together with a sub-disciplinary breakdown, emphasising the multi-faceted nature of the Web, and the multi-disciplinary nature of its study and development. These questions and approaches together set out an agenda for Web Science, the science of decentralised information systems. Web Science is required both as a way to understand the Web, and as a way to focus its development on key communicational and representational requirements. The text surveys central engineering issues, such as the development of the Semantic Web, Web services and P2P. Analytic approaches to discover the Web's topology, or its graph-like structures, are examined. Finally, the Web as a technology is essentially socially embedded; therefore various issues and requirements for Web use and governance are also reviewed.

Monazite solubility and dissolution kinetics: implications for the thorium and light rare earth chemistry of felsic magmas

Abstract: A series of monazite dissolution experiments was conducted in a hydrous (1–6 wt%) granitic melt at 8 kbar over the temperature range 1,000–1,400° C A polished cube of monazite was immersed in a natural obsidian melt and allowed to partially dissolve Electron microprobe traverses perpendicular to the crystal-melt interface revealed concentration gradients in the LREEs and P Diffusivities of the LREEs and P were calculated from these profiles, yielding the following Arrhenius relations for the LREEs: D=023 exp(−601 kcal mol−1/RT) at 6% water D=230×107 exp(−1221 kcal mol−1/RT) at 1% water These results demonstrate the importance of dissolved water on REE diffusion Phosphorus diffusivities are nearly identical to those of the rare-earths, suggesting that P diffusion charge-compensates REE diffusion The concentration of LREEs required for monazite saturation in these melts is given by the level of dissolved LREEs at the crystal-melt interface These values also show a dependence on dissolved water, with LREEsat=60 ppm at 6% H2O when extrapolated down to 700° C, and LREEsat=30 ppm at 1% H2O Calculated dissolution rates based on the above parameters indicate that minute ( 2% H2O), whereas larger (> 50 μm) crystals will likely be residual over the duration of an anatectic event The low solubility of monazite in this melt suggests that the LREE depletion observed in some felsic differentiation suites may be the result of monazite crystallization Limited experimental and geochemical/petrologic evidence indicates that compositional changes in the melt accompanying differentiation decrease the solubility of monazite drastically Kinetic and chemical constraints may also lead to localized monazite saturation and inclusion in major phases or even other accessories Variations in the REE composition of monazite from different parageneses probably reflects the REE pattern of the parent melt, and may be due to gradational differences in the stability of individual or subgroup REE-complexes as a function of melt composition Particularly important in this regard seems to be the lime+alkali/alumina balance of the melt and its volatile content

Light-emitting diodes

Abstract: Inorganic semiconductor light-emitting diodes (LEDs) are environmentally benign and have found widespread use as indicator lights, mobile displays, large-area displays, signage applications, and lighting applications. The entire visible spectrum can be covered by light-emitting semiconductors: AlGaInP and AlGaInN compound semiconductors are capable of emission in the red-to-yellow wavelength range and violet-to-green wavelength range, respectively. For white light sources based on LEDs, the most common approach is the combination of a blue LED chip with a yellow phosphor. Alternatively, a group of red, green, and blue (RGB) LEDs can be used; such source allows for color tunability. White LEDs are currently used to replace incandescent and fluorescent sources. In this review, the properties of inorganic LEDs will be presented, including emission spectra, electrical characteristics, and current-flow patterns. Structures providing high internal quantum efficiency, namely heterostructures and multiple quantum well structures, will be discussed. Advanced techniques enhancing the external quantum efficiency will be reviewed, including die shaping (chip shaping) and surface roughening. Different approaches to white LEDs will be presented and figures-of-merit such as the color rendering index and luminous efficacy will be explained. Besides visible LEDs, the technical challenges of newly evolving deep ultraviolet (UV) LEDs will be introduced. Finally, the packaging of low-power and high-power LED dies will be discussed.