Switched reluctance motor drive without direct rotor position sensing

A closed-loop control technique based on monitoring phase current risetime for switched reluctance (SR) motors without direct rotor-position sensors has been studied and implemented successfully. In this technique the variation in incremental phase inductance in a SR motor is used to detect rotor position. A control circuit for current-waveform-based rotor position detection has been implemented using hard-wire digital circuits. Torque-speed and system-efficiency characteristics resulting from the application of the method to a 4-kW, four-phase SR motor with an IGBT drive are presented.

Direct growth of horizontally aligned carbon nanotubes between electrodes and its application to field-effect transistors

This paper presents direct growth of horizontally aligned carbon nanotubes (CNTs) between two predefined various inter-spacing up to tens of microns of electrodes (pads) and its use as CNT field-effect transistors (CNT-FETs). The catalytic metals were prepared, consisting of iron (Fe), aluminum (Al) and platinum (Pt) triple layers, on the thermal silicon oxide substrate (Pt/Al/Fe/SiO2). Scanning electron microscopy measurements of CNT-FETs from the as-grown samples showed that over 80% of the nanotubes are grown across the catalytic electrodes. Moreover, the number of CNTs across the catalytic electrodes is roughly controllable by adjusting the growth condition. The Al, as the upper layer on Fe electrode, not only plays a role as a barrier to prevent vertical growth but also serves as a porous medium that helps in forming smaller nano-sized Fe particles which would be necessary for lateral growth of CNTs. Back-gate field effect transistors were demonstrated with the laterally aligned CNTs. The on/off ratios in all the measured devices are lower than 100 due to the drain leakage current. ©2010 IEEE.

Simultaneous pulse compression and jitter reduction at 10GHz using novel self-seeding gain-switched DFB laser incorporating a DILM

A novel scheme using a 10 GHz gain-switched DFB laser with simultaneous pulse width and jitter compression allows generation of 380fs pulses with both system limited 150fs jitter and 30 dB extinction ratio. ©1999 Optical Society of America.

The direct field boundary impedance of two-dimensional periodic structures with application to high frequency vibration prediction.

Large sections of many types of engineering construction can be considered to constitute a two-dimensional periodic structure, with examples ranging from an orthogonally stiffened shell to a honeycomb sandwich panel. In this paper, a method is presented for computing the boundary (or edge) impedance of a semi-infinite two-dimensional periodic structure, a quantity which is referred to as the direct field boundary impedance matrix. This terminology arises from the fact that none of the waves generated at the boundary (the direct field) are reflected back to the boundary in a semi-infinite system. The direct field impedance matrix can be used to calculate elastic wave transmission coefficients, and also to calculate the coupling loss factors (CLFs), which are required by the statistical energy analysis (SEA) approach to predicting high frequency vibration levels in built-up systems. The calculation of the relevant CLFs enables a two-dimensional periodic region of a structure to be modeled very efficiently as a single subsystem within SEA, and also within related methods, such as a recently developed hybrid approach, which couples the finite element method with SEA. The analysis is illustrated by various numerical examples involving stiffened plate structures.

Direct observation of the structural component of the metal-insulator phase transition and growth habits of epitaxially grown VO2 nanowires.

We have grown epitaxially orientation-controlled monoclinic VO2 nanowires without employing catalysts by a vapor-phase transport process. Electron microscopy results reveal that single crystalline VO2 nanowires having a [100] growth direction grow laterally on the basal c plane and out of the basal r and a planes of sapphire, exhibiting triangular and rectangular cross sections, respectively. In addition, we have directly observed the structural phase transition of single crystalline VO2 nanowires between the monoclinic and tetragonal phases which exhibit insulating and metallic properties, respectively, and clearly analyzed their corresponding relationships using in situ transmission electron microscopy.

The role of direct observation in predicting climatic change

The National Oceanic and Atmospheric Administration Center for Ocean Analysis and Prediction (COAP) in Monterey, California, has assembled information to suggest how NOAA's facilities for observing the ocean and atmosphere might be applied to studies of paleoclimate. This effort resulted, indirectly, in several projects that combine direct observations of the ocean/atmosphere system with studies of past climate of the Pacific region. This article considers concepts that link the two kinds of investigations. It defines the thesis that direct observation of systems that generate paleoclimatic information is the nexus upon which understanding of climatic variability begins and upon which prediction of climate and global change depends.