Design Curves for Transient Heat Flow in Semiconductor Devices

We have ]performed a numerical simulation of heat flow in a cylindrical solid having a ,geometry typical of semiconductor devices. We present curves of temperature as a function of time, normalized to the thermal constants and the surface herat flux. These curves can be used in the design of serniconductor devices where transient or steady state temperature rise is a consideration

Development of Process Technology for GaAs E/D MODFET Logic Circuits

The GaAs MODFET device is one of the prominent candidates for very high speed circuit applications. This thesis presents the MODFET DCFL inverter and other logic circuit design and process development. Working circuits of E/D type inverters, three input NAND and NOR logic gates and ring oscillators are reported

Investigation of a Resistive-Gate MESFET Contiguous Domain Oscillator

The goal of this research is to investigate a novel microwave oscillator — the MESFET version contiguous domain oscillator. By combining the transferred electron effect in GaAs material with the two dimensional electrostatics in the device, a series of contiguous electron packets can be generated in the channel of a resistive gate MESFET. Therefore this novel device can eliminate some restraints which are suffered by the presently existing oscillators, and provides unique new features for oscillators: a wide range of oscillation frequency (from a few tens of GHz to a hundred GHz), an ideal current source, instantaneous frequency tuning, compatibility with the presently existing planar semiconductor integration technology, etc. This investigation is composed of two parts. The first pa rt is to use various semiconductor processing technologies to fabricate the devices which can supply an ideal electrostatic condition for the electrons in the channel; the second part is the device characterization; which includes power output, frequency tunability, and the relationship between device performance and device parameters

Experiments in Interrupted Growth Molecular Beam Epitaxy Technology

From a device structure standpoint it would be advantageous to sandwich laterally defined features between layers of epitaxially grown material. In silicon this is commonly dope by growing the bottom layer, patterning the desired feature, and growing a second layer. Unfortunately, this process has not been practical in GaAs for the same reason that there is no true MOS technology in GaAs: The. GaAs surface is irreparably damaged when it is exposed to the atmosphere leading to the formation of undesirable interface states. Heterojunction FET\u27s are feasible only because high quality epilayers are grown during a single run in an ultrahigh vacuum environment. Standard growth methods allow for variation of doping and material content only in one direction, normal to the wafer surface. Varying the material in more than one dimension without the use of prohibitively exotic equipment requires removal of the wafer from the growth apparatus for lateral processing between material growths. Thus the problem that this thesis attempts to address: How to protect a GaAs surface during a lateral processing step and initiate regrowth leaving behind an electrically invisible restart interface. The potential applications of the development of a successful interrupted growth scheme for GaAs are numerous and far reaching. Specifically it would allow the fabrication of advantageous device geometries that are not possible under single material growth runs. Although this thesis deals exclusively with ion implanted interrupted growth by Molecular Beam Epitaxy, some of the concepts arid theories can be extended to other growth methods. It is both a review of previous work and a report of our attempts at Purdue to fabricate the first interrupted growth HIGFET\u27s and MISFET\u27s. Mechanisms behind the success and failure of GaAs interrupted growth are discussed and several experiments involving passivation materials and new interrupted growth schemes are propose

A study of vision screening for kindergarteners

A study of vision screening for kindergartener

Mini-mast CSI testbed user's guide

The Mini-Mast testbed is a 20 m generic truss highly representative of future deployable trusses for space applications. It is fully instrumented for system identification and active vibrations control experiments and is used as a ground testbed at NASA-Langley. The facility has actuators and feedback sensors linked via fiber optic cables to the Advanced Real Time Simulation (ARTS) system, where user defined control laws are incorporated into generic controls software. The object of the facility is to conduct comprehensive active vibration control experiments on a dynamically realistic large space structure. A primary goal is to understand the practical effects of simplifying theoretical assumptions. This User's Guide describes the hardware and its primary components, the dynamic characteristics of the test article, the control law implementation process, and the necessary safeguards employed to protect the test article. Suggestions for a strawman controls experiment are also included

Modelling and simulation of Space Station Freedom berthing dynamics and control

A large-angle, flexible, multibody, dynamic modeling capability has been developed to help validate numerical simulations of the dynamic motion and control forces which occur during berthing of Space Station Freedom to the Shuttle Orbiter in the early assembly flights. This paper outlines the dynamics and control of the station, the attached Shuttle Remote Manipulator System, and the orbiter. The simulation tool developed for the analysis is described and the results of two simulations are presented. The first is a simulated maneuver from a gravity-gradient attitude to a torque equilibrium attitude using the station reaction control jets. The second simulation is the berthing of the station to the orbiter with the station control moment gyros actively maintaining an estimated torque equilibrium attitude. The influence of the elastic dynamic behavior of the station and of the Remote Manipulator System on the attitude control of the station/orbiter system during each maneuver was investigated. The flexibility of the station and the arm were found to have only a minor influence on the attitude control of the system during the maneuvers

Copy-number variation in BMPR2 is not associated with the pathogenesis of pulmonary arterial hypertension

<p>Abstract</p> <p>Background</p> <p>Copy-number variations (CNVs) are structural variations in the genome involving 1 kb to 3 mb of DNA. CNV has been reported within intron 1 of the <it>BMPR2 </it>gene. We propose that CNV could affect phenotype in familial and/or sporadic pulmonary arterial hypertension (PAH) by altering gene expression.</p> <p>Methods</p> <p>97 human DNA samples were obtained which included 24 patients with familial PAH, 18 obligate carriers (<it>BMPR2 </it>mutation positive), 20 sporadic PAH patients, and 35 controls. Two sets of primers were designed within the CNV, and two sets of control primers were designed outside the CNV. Quantitative PCR was performed to quantify genomic copies of CNV and control sequences.</p> <p>Results</p> <p>A CNV in <it>BMPR2 </it>was present in one African American negative control subject.</p> <p>Conclusion</p> <p>We conclude that the CNV in intron 1 in <it>BMPR2 </it>is unlikely to play a role in the pathogenesis of either familial or sporadic PAH.</p> <p>Trial Registration</p> <p>NIH NCT00091546.</p

Chaste: an open source C++ library for computational physiology and biology

Chaste - Cancer, Heart And Soft Tissue Environment - is an open source C++ library for the computational simulation of mathematical models developed for physiology and biology. Code development has been driven by two initial applications: cardiac electrophysiology and cancer development. A large number of cardiac electrophysiology studies have been enabled and performed, including high performance computational investigations of defibrillation on realistic human cardiac geometries. New models for the initiation and growth of tumours have been developed. In particular, cell-based simulations have provided novel insight into the role of stem cells in the colorectal crypt. Chaste is constantly evolving and is now being applied to a far wider range of problems. The code provides modules for handling common scientific computing components, such as meshes and solvers for ordinary and partial differential equations (ODEs/PDEs). Re-use of these components avoids the need for researchers to "re-invent the wheel" with each new project, accelerating the rate of progress in new applications. Chaste is developed using industrially-derived techniques, in particular test-driven development, to ensure code quality, re-use and reliability. In this article we provide examples that illustrate the types of problems Chaste can be used to solve, which can be run on a desktop computer. We highlight some scientific studies that have used or are using Chaste, and the insights they have provided. The source code, both for specific releases and the development version, is available to download under an open source Berkeley Software Distribution (BSD) licence at http://www.cs.ox.ac.uk/chaste, together with details of a mailing list and links to documentation and tutorials

Decay of isolated surface features driven by the Gibbs-Thomson effect in analytic model and simulation

A theory based on the thermodynamic Gibbs-Thomson relation is presented which provides the framework for understanding the time evolution of isolated nanoscale features (i.e., islands and pits) on surfaces. Two limiting cases are predicted, in which either diffusion or interface transfer is the limiting process. These cases correspond to similar regimes considered in previous works addressing the Ostwald ripening of ensembles of features. A third possible limiting case is noted for the special geometry of "stacked" islands. In these limiting cases, isolated features are predicted to decay in size with a power law scaling in time: A is proportional to (t0-t)^n, where A is the area of the feature, t0 is the time at which the feature disappears, and n=2/3 or 1. The constant of proportionality is related to parameters describing both the kinetic and equilibrium properties of the surface. A continuous time Monte Carlo simulation is used to test the application of this theory to generic surfaces with atomic scale features. A new method is described to obtain macroscopic kinetic parameters describing interfaces in such simulations. Simulation and analytic theory are compared directly, using measurements of the simulation to determine the constants of the analytic theory. Agreement between the two is very good over a range of surface parameters, suggesting that the analytic theory properly captures the necessary physics. It is anticipated that the simulation will be useful in modeling complex surface geometries often seen in experiments on physical surfaces, for which application of the analytic model is not straightforward.Comment: RevTeX (with .bbl file), 25 pages, 7 figures from 9 Postscript files embedded using epsf. Submitted to Phys. Rev. B A few minor changes made on 9/24/9