Optimization of micromachined relex klystrons for operation at terahertz frequencies

New micromachining techniques now provide us with the technology to fabricate reflex klystron oscillators with dimensions suitable for operation in the terahertz region of the electromagnetic spectrum. For the success of these devices, accurate designs are required since the optimization of certain parameters is critical to obtaining useful amounts of ac power. Classical models for device design have long been in existence, but these are no longer valid at terahertz frequencies. For this reason, we have developed a simulation tool, specifically aimed at the design of terahertz frequency reflex klystrons. The tool, based on the Monte Carlo algorithm, includes loss mechanisms and takes into account the main peculiarities expected for device operation at terahertz frequencies. In this study, the tool is used to study the influence of the electron beam aperture angle and cavity dimensions (particularly the grid spacing) on ac power generation. The results demonstrate that aperture angles of less than 10 are necessary for the optimization of output power. It is also found that the power output is highly sensitive to the distance between the grids

Using the Spreadsheet as a Tool for Teaching the Fundamentals of Engineering

This paper will demonstrate how the electronic spreadsheet has been used in a freshman level Fundamentals of Engineering course to prepare students for maximizing their analytical skills with the most ubiquitous analytical tool available today.Cockrell School of Engineerin

Housing Market in Malaga: An Application of the Hedonic Methodology

The analysis of the factors that determine the price of the second-hand house, by means of the use of the hedonic methodology, constitutes the central objective of this work. This study has been applied to the market of the house corresponding to the municipality of Malaga (Spain), of where a sample of 1996 transactions, made during 2003, has been selected.This information has been facilitated by a real estate agency. The obtained results have allowed to identify those characteristics of the houses that more affect their price and quantify this influence, valuing it in monetary terms. It has been stated that the contribution of some structural attributes (the floor area, the number of toilets, the presence of private garage or the luminosity of the house) and others of location (proximity to the sea or downtown, and location in a certain zone) affects the price of the house decisively.

Single-atom control of the optoelectronic response in sub-nanometric cavities

By means of ab-initio time dependent density functional theory calculations carried out on an prototypical hybrid plasmonic device (two metallic nanoparticles bridged by a one-atom junction), we demonstrate the strong interplay between photoinduced excitation of localized surface plasmons and electron transport through the single atom. Such an interplay is remarkably sensitive to the atomic orbitals of the junction. Therefore, we show the possibility of a twofold tuning (plasmonic response and photoinduced current across the juntion) just by changing a single atom in the device.Comment: 5 pages, 5 figure

Momentum transfer to small particles by aloof electron beams

The force exerted on nanoparticles and atomic clusters by fast passing electrons like those employed in transmission electron microscopes are calculated and integrated over time to yield the momentum transferred from the electrons to the particles. Numerical results are offered for metallic and dielectric particles of different sizes (0-500 nm in diameter) as well as for carbon nanoclusters. Results for both linear and angular momentum transfers are presented. For the electron beam currents commonly employed in electron microscopes, the time-averaged forces are shown to be comparable in magnitude to laser-induced forces in optical tweezers. This opens up the possibility to study optically-trapped particles inside transmission electron microscopes.Comment: 6 pages, 5 figure

Collective oscillations in optical matter

Atom and nanoparticle arrays trapped in optical lattices are shown to be capable of sustaining collective oscillations of frequency proportional to the strength of the external light field. The spectrum of these oscillations determines the mechanical stability of the arrays. This phenomenon is studied for dimers, strings, and two-dimensional planar arrays. Laterally confined particles free to move along an optical channel are also considered as an example of collective motion in partially-confined systems. The fundamental concepts of dynamical response in optical matter introduced here constitute the basis for potential applications to quantum information technology and signal processing. Experimental realizations of these systems are proposed.Comment: 4 figures. Optics Express (in press

Li and Be depletion in metal-poor subgiants

Original article can be found at: http://www.aanda.org/--Copyright The European Southern Observatory (ESO) DOI : 10.1051/0004-6361:20053182Peer reviewe