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Mass Enhancement of Two-Dimensional Electrons in Thin Oxide Si-MOSFETs
No full textWe report in this paper a study of the effective mass in thin oxide Si-MOSFETs, using the temperature dependence of the Shubnikov-de Haas (SdH) effect and following the methodology developed by Smith and Stiles
On Theories for Reacting Immiscible Mixtures
No full textOn some small scale each constituent of an immiscible mixture occupies a separate region of space. Given sufficient time and computing power, we could solve the continuum field equations and boundary conditions for this het erogenous system. This usually represents an enormously difficult task that is well beyond today's computational ca- pabilities. Mixture theories approximate this complex heterogeneous formulation with a set of field equations for an equivalent homoge- neous mat erial. In this work, we compare the theory for immiscible mixtures by Drumheller and Bedford with the theory of Passman, Nunziato, and Walsh. We describe the conditions under which these theories reduce to an equivalent formulation, and we also investigate the differences in their microinertial descriptions. Two variables play special roles in both theories. They are t he true material density and the volume fraction. Here we use a kinematical approach based on two new variables-t he true deformation gradient and the distention gradient. We show how the true deformation gra- dient is connected to the true material density and, in the absence of chemical reactions, the volume fraction is the inverse of the deter- minant of the distention gradient. However, when chemical reactions occur, the distention gradient and the volume fraction are not directly connected. We ako present a mixture model for a granuIar expIosive. This model is based upon the work of Baer and Nunziato, but our theory differs from their work in that we Present a three-dimension-al rnodd, `.. ` - - we cast the constitutive postulates in terms of the distention gradient rather than the volume fraction, and we incorporate elastic-plastic effects into the constitutive description of the solid granules
Z-Pinch Driven Inertial Confinement Fusion Target Physics Research at Sandia National Laboratories
No full textThree hohlraum concepts are being pursued at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (z-pinches) to drive high gain targets capable of yields in the range of 200-1000 MJ. This research is being conducted on SNL'S.Z facility that is capable of driving peak currents of 20 MA in z-pinch loads producing implosion velocities as high as 7.5X 107 cm/s, x-ray energies approaching 2 MJ, and x-ray powers exceeding 200 TW. This paper will discuss each of these hohlraum concepts and will overview the experiments that have been conducted on these systems to date
Analysis of Decentralized Variable Structure Control for Collective Search by Mobile Robots
No full textThis paper presents an analysis of a decentralized coordination strategy for organizing and controlling a team of mobile robots performing collective search. The alpha-beta coordination strategy is a family of collective search algorithms that allow teams of communicating robots to implicitly coordinate their search activities through a division of labor based on self-selected roIes. In an alpha-beta team. alpha agents are motivated to improve their status by exploring new regions of the search space. Beta a~ents are conservative, and reiy on the alpha agents to provide advanced information on favorable regions of the search space. An agent selects its current role dynamically based on its current status value relative to the current status values of the other team members. Status is determined by some function of the agent's sensor readings, and is generally a measurement of source intensity at the agent's current location. Variations on the decision rules determining alpha and beta behavior produce different versions of the algorithm that lead to different global properties. The alpha-beta strategy is based on a simple finite-state machine that implements a form of Variable Structure Control (VSC). The VSC system changes the dynamics of the collective system by abruptly switching at defined states to alternative control laws . In VSC, Lyapunov's direct method is often used to design control surfaces which guide the system to a given goal. We introduce the alpha-beta aIgorithm and present an analysis of the equilibrium point and the global stability of the alpha-beta algorithm based on Lyapunov's method
PDS/PIO: Lightweight Libraries for Collective Parallel I/O
No full textPDS/PIO is a lightweight, parallel interface designed to support efficient transfers of massive, grid-based, simulation data among memory, disk, and tape subsystems. The higher-level PDS (Parallel Data Set) interface manages data with tensor and unstructured grid abstractions, while the lower-level PIO (Parallel Input/Output) interface accesses data arrays with arbitrary permutation, and provides communication and collective 1/0 operations. Higher-level data abstraction for finite element applications is provided by PXI (Parallel Exodus Interface), which supports, in parallel, functionality of Exodus 11, a finite element data model developed at Sandia National Laboratories. The entire interface is implemented in C with Fortran-callable PDS and PXI wrappers
SEACAS Theory Manuals: Part II. Nonlinear Continuum Mechanics
No full textThis report summarizes the key continuum mechanics concepts required for the systematic prescription and numerical solution of finite deformation solid mechanics problems. Topics surveyed include measures of deformation appropriate for media undergoing large deformations, stress measures appropriate for such problems, balance laws and their role in nonlinear continuum mechanics, the role of frame indifference in description of large deformation response, and the extension of these theories to encompass two dimensional idealizations, structural idealizations, and rigid body behavior. There are three companion reports that describe the problem formulation, constitutive modeling, and finite element technology for nonlinear continuum mechanics systems
SEACAS Theory Manuals: Part 1. Problem Formulation in Nonlinear Solid Mechancis
No full textThis report gives an introduction to the basic concepts and principles involved in the formulation of nonlinear problems in solid mechanics. By way of motivation, the discussion begins with a survey of some of the important sources of nonlinearity in solid mechanics applications, using wherever possible simple one dimensional idealizations to demonstrate the physical concepts. This discussion is then generalized by presenting generic statements of initial/boundary value problems in solid mechanics, using linear elasticity as a template and encompassing such ideas as strong and weak forms of boundary value problems, boundary and initial conditions, and dynamic and quasistatic idealizations. The notational framework used for the linearized problem is then extended to account for finite deformation of possibly inelastic solids, providing the context for the descriptions of nonlinear continuum mechanics, constitutive modeling, and finite element technology given in three companion reports
Experimental Demonstration of Guiding and Bending of Electromagnetic Waves in a Photonic Crystal
No full textThe routing and interconnection of optical signals through narrow channels and around sharp corners is important for large-scale all-optical circuit applications. A recent computational result suggests that photonic crystals may offer a novel way of achieving this goal by providing a mechanism for guiding light that is fundamentally different from traditional index guiding. Waveguiding in a photonic crystal, and near 100% transmission of electromagnetic waves around sharp 90o corners were observed experimentally. Bend- ing radii were made smaller than one wavelength
Post Test Analysis of a PCCV Model Dynamically Tested Under Simulated Design-Basis Earthquakes
No full textIn a collaborative program between the United States Nuclear Regulatory Commission (USNRC) and the Nuclear Power Engineering Corporation (NUPEC) of Japan under sponsorship of the Ministry of International Trade and Ihdustry, the seismic behavior of Prestressed Concrete Containment Vessels (PCCV) is being investigated. A 1:10 scale PCCV model has been constructed by NUPEC and subjected to seismic simulation tests using the high performance shaking table at the Tadotsu Engineering Laboratory. A primary objective of the testing program is to demonstrate the capability of the PCCV to withstand design basis earthquakes with a significant safety margin against major damage or failure. As part of the collaborative program, Sandia National Laboratories (SNL) is conducting research in state-of-the-art analytical methods for predicting the seismic behavior of PCCV structures, with the eventual goal of understanding, validating, and improving calculations dated to containment structure performance under design and severe seismic events. With the increased emphasis on risk-informed- regulatory focus, more accurate ch&@erization (less uncertainty) of containment structural and functional integri~ is desirable. This paper presents results of post-test calculations conducted at ANATECH to simulate the design level scale model tests
Advanced Recovery and Integrated Extraction System (ARIES) Fiscal Year 1996 Annual Report
No full textPresident Clinton issued Nonprolferation and Export Control Policy in September 1993 in response to the growing threat of nuclear proliferation. Four months later, in January 1994, President Clinton and Russia's President Yeltsin issued a Joint Statement Between the United States and Russia on Nonprollfieration of Weapons of Mass Destruction and the Means of Their Delivery. President Clinton announced on 1 March 1995, that approximately 200 metric tons of US- origin weapons-usable fissile materials had been declared surplus to US defense needs. The Advanced Recovery and Integrated Extraction System (ARIES) Demonstration Project is one part of the scientific response to President Clinton's promise to reduce the nuclear weapons stockpile. The work accomplished on the ARIES Demonstration Project during fiscal year 1996, 10ctober 1995 through 30 September 1996, is described in this report. The Department of Energy (DOE), by forming the Office of Fissile Materials Disposition (OFMD), has initiated a Fissile Materials Disposition Program. The first step is the disassembly and conversion of weapons pits. Of the 200 metric tons of US surplus fissile material, approximately 50 tons are weapons plutonium, and of these 50 tons, 2/3 is contained in pits. Weapons plutonium wili be extracted from pits, rendered to an unclassified form, and converted to oxide. The plutonium oxide will then be dispositioned either by immobilization in a ceramic matrix or blended with uranium oxide, fabricated into ceramic pellets of mixed oxide (MOX) fuel, and "burned" in a commercial light water reactor. The purpose of ARIES is to demonstrate two major activities: (1) dismantlement of nuclear weapons, and (2) conversion of weapons-grade plutonium into a form required for long-term storage or in preparation for the disposition (immobilization m MOX fuel) that allows for international inspection and verification, and in accordance with safeguards regimes. Plutonium does not have to be declassified before storage; however, declassification allows plutonium to be placed under international safeguards and provides political irreversibility of the material. The OFMD sponsors the ARIES Program. The Los Alamos National Laboratory is the lead laboratory for the ARIES Demonstration Project with support from Lawrence Livermore National Laboratory and Sandia National Laboratories, New Mexico. Also, ARIES is the lead technical activity for nationaI plutonium disposition, as well as a major effort of the Los Alamos Nuclear Materials Disposition Project. The ARIES Project Leader, Timothy O. Nelson, is a technical staff member in the Advanced Technology Group (NMT-6) who is responsible for overall project management and system implementation