24 Matching Results

Search Results

Advanced search parameters have been applied.
in creator/contributor: "United States. Office of Naval Research."  
Results: 1 - 24
open access

Chemical reaction rates using the semiclassical Van-Vleck initialvalue representation

Description: A semiclassical IVR formulation using the Van-Vleck propagator has been used to calculate the flux correlation function and thereby reaction rate constants. This Van-Vleck formulation of the flux-flux correlation function is computationally as simple as the classical Wigner model. However unlike the latter, it has the ability to capture quantum interference/coherence effects. Classical trajectories are evolved starting from the dividing surface that separates reactants and products, and are evo… more
Date: November 29, 2006
Creator: Venkataraman, Charulatha & Miller, William H.
Partner: UNT Libraries Government Documents Department
open access

Efficient Estimators for Quantum Instanton Evaluation of theKinetic Isotope Effects: Application to the Intramolecular HydrogenTransfer in Pentadiene

Description: The quantum instanton approximation is used to compute kinetic isotope effects for intramolecular hydrogen transfer in cis-1,3-pentadiene. Due to the importance of skeleton motions, this system with 13 atoms is a simple prototype for hydrogen transfer in enzymatic reactions. The calculation is carried out using thermodynamic integration with respect to the mass of the isotopes and a path integral Monte Carlo evaluation of relevant thermodynamic quantities. Efficient 'virial' estimators are deri… more
Date: June 13, 2007
Creator: Vanicek, Jiri & Miller, William H.
Partner: UNT Libraries Government Documents Department
open access

Electronic and Optical Properties of Energetic Particle-IrradiatedIn-rich InGaN

Description: We have carried out a systematic study of the effects of irradiation on the electronic and optical properties of InGaN alloys over the entire composition range. High energy electrons, protons, and {sup 4}He{sup +} were used to produce displacement damage doses (D{sub d}) spanning over five orders of magnitude. The free electron concentrations in InN and In-rich InGaN increase with D{sub d} and finally saturate after a sufficiently high D{sub d}. The saturation of carrier density is attributed t… more
Date: April 13, 2005
Creator: Li, S. X.; Yu, K. M.; Jones, R. E.; Wu, J.; Walukiewicz, W.; AgerIII, J. W. et al.
Partner: UNT Libraries Government Documents Department
open access

Linearized Semiclassical Initial Value Time Correlation FunctionsUsing the Thermal Gaussian Approximation: Applications to Condensed PhaseSystems

Description: The linearized approximation to the semiclassical initial value representation (LSC-IVR) has been used together with the thermal Gaussian approximation (TGA) (TGA/LSC-IVR) to simulate quantum dynamical effects in realistic models of two condensed phase systems. This represents the first study of dynamical properties of the Ne13 Lennard-Jones (LJ) cluster in its liquid-solid phase transition region (temperature from 4 K to 14 K). Calculation of the force autocorrelation function shows considerab… more
Date: July 10, 2007
Creator: Liu, Jian & Miller, William H.
Partner: UNT Libraries Government Documents Department
open access

Prediction of strongly-heated internal gas flows

Description: The purposes of the present article are to remind practitioners why the usual textbook approaches may not be appropriate for treating gas flows heated from the surface with large heat fluxes and to review the successes of some recent applications of turbulence models to this case. Simulations from various turbulence models have been assessed by comparison to the measurements of internal mean velocity and temperature distributions by Shehata for turbulent, laminarizing and intermediate flows wit… more
Date: December 31, 1997
Creator: McEligot, D. M.; Shehata, A. M. & Kunugi, Tomoaki
Partner: UNT Libraries Government Documents Department
open access

Modeling the effects of prior infection on vaccine efficacy

Description: We performed computer simulations to study the effects of prior infection on vaccine efficacy. We injected three antigens sequentially. The first antigen, designated the prior, represented a prior infection or vaccination. The second antigen, the vaccine, represented a single component of the trivalent influenza vaccine. The third antigen, the epidemic, represented challenge by an epidemic strain. For a fixed vaccine to epidemic strain cross-reactivities to the vaccine and to the epidemic strai… more
Date: November 1, 1997
Creator: Smith, D. J.; Forrest, S.; Ackley, D. H. & Perelson, A. S.
Partner: UNT Libraries Government Documents Department
open access

Experiments in non-perturbative electron beam characterization with the MIT microwiggler at the Accelerator Test Facility at BNL

Description: We report a new method through which the properties of an electron beam at linac energies may be studied using the spontaneous emission of a microwiggler. The setup is simple and the measurement efficient. A simple set of scaling laws is derived to describe broadening of spontaneous emission in a narrow bandwidth radiation cone. The relations suggest that one can obtain beam divergence from a cone at large angle in a single shot measurement. A systematic series of experiments was performed with… more
Date: November 1, 1996
Creator: Qiu, X.; Babzien, M.; Ben-Zvi, Ilan & Graves, W.
Partner: UNT Libraries Government Documents Department
open access

Algorithms for fusion of multiple sensors having unknown error distributions

Description: The authors presented recent results on a general sensor fusion problem, where the underlying sensor error distributions are not known, but a sample is available. They presented a general method for obtaining a fusion rule based on scale-sensitive dimension of the function class. Two computationally viable methods are reviewed based on the Nadaraya-Watson estimator, and the finite dimensional vector spaces. Several computational issues of the fusion rule estimation are open problems. It would b… more
Date: June 1, 1997
Creator: Rao, N. S. V.
Partner: UNT Libraries Government Documents Department
open access

Status report on Jefferson Lab`s high-power infrared free-electron laser

Description: Jefferson Lab is building a free-electron laser to produce tunable, continuous-wave (cw), kW-level light at 3-6 {mu}m wavelength. A superconducting accelerator will drive the laser, and a transport lattice will recirculate the beam back through the accelerator for energy recovery. Space charge in the injector and coherent synchrotron radiation in magnetic bends will be present, and the machine is instrumented to study these phenomena during commissioning. The wiggler and optical cavity are conv… more
Date: October 1, 1997
Creator: Bohn, C. L.
Partner: UNT Libraries Government Documents Department
open access

A multislit transverse-emittance diagnostic for space-charge-dominated electron beams

Description: Jefferson Lab is developing a 10 MeV injector to provide an electron beam for a high-power free-electron laser (FEL). To characterize the transverse phase space of the space-charged-dominated beam produced by this injector, the authors designed an interceptive multislit emittance diagnostic. It incorporates an algorithm for phase-space reconstruction and subsequent calculation of the Twiss parameters and emittance for both transverse directions at an update rate exceeding 1 Hz, a speed that wil… more
Date: June 1, 1997
Creator: Piot, P.; Song, J. & Li, R.
Partner: UNT Libraries Government Documents Department
open access

Ceramic-silicide composites

Description: The area of ceramic-silicide composites represents a merging of structural ceramics and structural silicides. Such ceramic-silicide composites can possess the desirable characteristics of both classes of compounds. Important structural ceramics are materials such as Si{sub 3}N{sub 4}, SiC, Al{sub 2}O{sub 3}, and ZrO{sub 2}, which possess covalent, ionic, or mixed covalent-ionic atomic bonding. An important structural silicide is MoSi{sub 2}, which possesses mixed covalent-metallic bonding. The … more
Date: December 1, 1998
Creator: Petrovic, J. J.
Partner: UNT Libraries Government Documents Department
open access

Modeling of residual stresses by HY-100 weldments

Description: Residual stress distribution in a HY-100 steel disk, induced by GTA spot welding, was analyzed by finite element (FE) formulations and measured by neutron diffraction (ND). Computations used temperature- dependent thermophysical and mechanical properties. FE model predictions are in good agreement with ND data in far heat affected zone (HAZ) and in base metal. Predicted residual stresses in fusion zone and near HAZ were higher than those measured by ND. This discrepancy was attributed to micros… more
Date: February 1, 1997
Creator: Zacharia, T.; Taljat, B. & Radhakrishnan, B.
Partner: UNT Libraries Government Documents Department
open access

Mechanics of interfacial crack propagation in microscratching

Description: There are two main issues regarding thin film debonding. The first is the nucleation of interfacial cracks, while the second is the propagation of cracks. From a mechanical testing point of view, scratch testing primarily serves to address the former issue, while indentation testing is a method of addressing the latter. A new probing technique has been developed to test thin film mechanical properties. In the Microwedge Scratch Test (MWST), a wedge shaped diamond indenter tip is drawn along a f… more
Date: May 1996
Creator: de Boer, M. P.; Nelson, J. C. & Gerberich, W. W.
Partner: UNT Libraries Government Documents Department
open access

Multiresolution reproducing kernel particle methods in acoustic problems

Description: In the analysis of complex phenomena of acoustic systems, the computational modeling requires special attention for a realistic representation of the physics. As a powerful tool, the finite element method has been widely used in the study of complex systems. In order to capture the important physical phenomena, p-finite elements and/or hp-finite elements are employed. The reproducing kernel particle methods (RKPM) are emerging as an effective alternative due to the elimination of a mesh, and th… more
Date: December 31, 1995
Creator: Liu, W. K.; Chang, C. T.; Chen, Y. & Uras, R. A.
Partner: UNT Libraries Government Documents Department
open access

High temperature structural silicides

Description: Structural silicides have important high temperature applications in oxidizing and aggressive environments. Most prominent are MoSi{sub 2}-based materials, which are borderline ceramic-intermetallic compounds. MoSi{sub 2} single crystals exhibit macroscopic compressive ductility at temperatures below room temperature in some orientations. Polycrystalline MoSi{sub 2} possesses elevated temperature creep behavior which is highly sensitive to grain size. MoSi{sub 2}-Si{sub 3}N{sub 4} composites sh… more
Date: March 1, 1997
Creator: Petrovic, J. J.
Partner: UNT Libraries Government Documents Department
open access

Pulse selection control for the IR FEL photocathode drive laser

Description: The method for current control of a photocathode source is described. This system allows for full remote control of a photocathode drive laser for resulting electron beam currents ranging from less than one microamp to a full current of five milliamps. All current modes are obtained by gating the drive laser with a series of electro-optical cells. The system remotely generates this control signal by assuming a mode of operation with the following properties selectable: Current mode as continuou… more
Date: August 1, 1997
Creator: Jordan, K.; Evans, R. & Garza, O.
Partner: UNT Libraries Government Documents Department
open access

Development of N-layer materials for SNS junction and SQUID applications

Description: Materials characteristics including water reactivity, oxygen loss, electromigration of oxide ions, and interfacial reactivity problems have plagued attempts to produce reliable and reproducible cuprate SNS superconductor junctions. In an effort to solve some of these formidable problems, new N-layer compounds from the family of R{sub 1{minus}x}Ca{sub x}Ba{sub 2{minus}y}La{sub y}Cu{sub 3{minus}z}M{sub z}O{sub 7{minus}{delta}} (R = Y, Gd and Pr; M = Co, Ni and Zn; 0 < x < 0.4; 0 < y < 0.4; 0 < z … more
Date: September 1, 1997
Creator: Zhou, J. P.; McDevitt, J. T. & Jia, Q.
Partner: UNT Libraries Government Documents Department
open access

Adsorption-controlled growth of ferroelectric PbTiO{sub 3} and Bi{sub 4}Ti{sub 3}O{sub 12} films for nonvolatile memory applications by MBE

Description: Epitaxial PbTiO{sub 3} and Bi{sub 4}Ti{sub 3}O{sub 12} thin films have been grown on (100) SrTiO{sub 3} and (100) LaAlO{sub 3} substrates by reactive molecular beam epitaxy (MBE). Titanium is supplied to the film in the form of shuttered bursts each containing a one monolayer dose of titanium atoms for the growth of PbTiO{sub 3} and three monolayers for the growth of Bi{sub 4}Ti{sub 3}O{sub 12}. Lead, bismuth, and ozone are continuously supplied to the surface of the depositing film. Growth of … more
Date: September 1, 1997
Creator: Theis, C. D.; Yeh, J.; Schlom, D. G.; Hawley, M. E. & Brown, G. W.
Partner: UNT Libraries Government Documents Department
open access

Adaptive heterogeneous multi-robot teams

Description: This research addresses the problem of achieving fault tolerant cooperation within small- to medium-sized teams of heterogeneous mobile robots. The author describes a novel behavior-based, fully distributed architecture, called ALLIANCE, that utilizes adaptive action selection to achieve fault tolerant cooperative control in robot missions involving loosely coupled, largely independent tasks. The robots in this architecture possess a variety of high-level functions that they can perform during … more
Date: November 1, 1998
Creator: Parker, L. E.
Partner: UNT Libraries Government Documents Department
open access

Quantum entanglement and the communication complexity of the inner product function

Description: The authors consider the communication complexity of the binary inner product function in a variation of the two-party scenario where the parties have an a priori supply of particles in an entangled quantum state. They prove linear lower bounds for both exact protocols, as well as for protocols that determine the answer with bounded-error probability. The proofs employ a novel kind of quantum reduction from multibit communication problems to the problem of computing the inner product. The commu… more
Date: August 1, 1998
Creator: Cleve, R.; Dam, W. van; Nielsen, M. & Tapp, A.
Partner: UNT Libraries Government Documents Department
open access

Overture: Object-oriented tools for solving CFD and combustion problems

Description: The Overture Framework is an object-oriented environment for solving partial differential equations on serial and parallel architectures. It is a collection of C{sup 2} libraries that enables the use of finite difference and finite volume methods at a level that hides the details of the associated data structures, as well as the details of the parallel implementation. It is based on the A{sup 2}/P{sup 2} array class library and is designed for solving problems on a structured grid or a collecti… more
Date: September 1, 1998
Creator: Brown, D. L. & Henshaw, W. D.
Partner: UNT Libraries Government Documents Department
open access

The controlled growth of perovskite thin films: Opportunities, challenges, and synthesis

Description: The broad spectrum of electronic and optical properties exhibited by perovskites offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired. Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the monolayer-level; its use for the integration of perovskites with similar nanoscale customization appears promising. Composition control and oxidation are often significant cha… more
Date: October 1, 1997
Creator: Schlom, D. G.; Theis, C. D. & Hawley, M. E.
Partner: UNT Libraries Government Documents Department
open access

Experimental results from a DC photocathode electron gun for an IR FEL

Description: A 350 keV DC photocathode gun capable of delivering the high-brightness CW electron beam necessary for Jefferson Lab`s infrared free-electron laser is described. The gun is to be used with a superconducting radiofrequency linac operating at 1.497 GHz and is mode-locked to the 40th subharmonic of the fundamental using a Nd:YLF drive laser. The gun provides 20--25 ps bunches at up to 135 pC/bunch. Experimental measurements of transverse and longitudinal beam properties are presented. Transverse e… more
Date: October 1, 1997
Creator: Kehne, D.; Engwall, D.; Legg, R. & Shinn, M.
Partner: UNT Libraries Government Documents Department
Back to Top of Screen