| Ceramic Actuators for Smart Materials |
30 JUN 92 |
44 pages |
| Authors:
L. E. Cross; PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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 | In earlier studies a number of phase switching systems had been explored which permit the switching of large electric polarization and the associated high elastic strain. The question to be resolved was whether these large polarization values could be repeatedly switched without associated mechanical or electrical fatigue. Early fatigue was shown to be an electrode problem and with care in electrode application, density control, grain size control and field homogeneity ... |
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| Role of Resuspended Sediments in the Transport and Bioaccumulation of Toxic Organic Contaminants in Nearshore Marine Environment |
31 MAY 92 |
18 pages |
| Authors:
James S. Latimer; James G. Quinn; RHODE ISLAND UNIV NARRAGANSETT GRADUATE SCHOOL OF OCEANOGRAPHY
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| The resuspension - deposition continuum plays a significant part in the distribution of fine grained sediments and associated organic pollutants in aquatic systems. The chemistry of resuspension was investigated during a year long study by submitting a variety of sediments, including relatively contaminated homogenized dredge spoils and moderately contaminated stratigraphically intact sediments, to artificial resuspension using a particle entrainment simulator. Fine grained sediments were entrained into the test cylinder under ... |
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| Preparation of Non-Oxide Ceramics by Pyrolysis of Organometallic Precursors |
25 MAY 92 |
12 pages |
| Authors:
L. V. Interrante; W. R. Schmidt; P. S. Marchetti; G. E. Maciel; RENSSELAER POLYTECHNIC INST TROY NY DEPT OF CHEMISTRY
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| Molecular precursors to non-oxide ceramics are finding increasing interest for applications where conventional processing methods fail to provide the ceramic product in the required purity, microstructure an d/or final form. The thermoplasticity, volatility, solubility, and/or molecular-level homogeneity of such precursor systems can provide, for example: high surface area powders of pure phases or of homogeneous nanocomposites; thin films and coatings by CVD and by pyrolysis of solution-applied precursor films; and ... |
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| Homogeneity of the Photorefractive Effect in Reduced and Unreduced KNbo sub 3 Crystals, |
22 MAY 1992 |
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| Authors:
P. Amrhein; P. Gunter; EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZURICH (SWITZERLAND)
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 | It is obvious that the homogeneity of the photorefractive sensitivity has strong influence devices such as optically driven spatial light modulators (SLM). These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction. ... |
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| Incoherent Light Read-Out of Spectral Holograms, |
22 MAY 1992 |
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| Authors:
A. Debarre; J. C. Keller; J. L. Le Gouet; P. Tchenio; CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE ORSAY (FRANCE)
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| It is known that one has investigated two types of approach to Persistent Spectral Hole Burning (PHB), and to potential application for optical data storage. In both methods, a structure is stored within the inhomogeneously broadened optical absorption line of the guest ions or molecules in a host matrix at low temperature. In the first method, monochromatic laser irradiation results in the reduction of the sample absorption coefficient at a ... |
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| Frequency - Domain Measurements of Spectral Hole Patterns Burned with Phase - Coherent Pulses, |
22 MAY 1992 |
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| Authors:
C. M. Jefferson; Alfred J. Meixner; IBM ALMADEN RESEARCH CENTER SAN JOSE CA
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| Several investigations have shown that in some systems stimulated photon echoes may be obtained over times much longer than the excited state relaxation T(1). It has been claimed that the mechanism for this anomalously long storage time is the formation of a frequency dependent modulation of the ground state population which persists because of spectral hole-burning. Such a population grating produced by coherent multipulse excitation and spectral hole-burning has been ... |
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| Iron-Free Cytochrome C and Myoglobin in Buffer Glass as Weakly-Coupling Mesoscopic Molecular System: Hole-Burning, Absorption and Fluorescence Spectra and their Temperature Properties, |
22 MAY 1992 |
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| Authors:
Toshiro Tani; Youichi Sakakibara; Hisao Takahashi; Kyonosuke Yamamoto; ELECTROTECHNICAL LAB SAKURA (JAPAN)
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| Persistent spectral hole burning is a useful tool to detect zero-Phonon line and Phonon sideband of organic dye molecules doped in glasses and polymers, which are usually covered under Inhomogeneous broadening. These observation bring us information in on the electron-phonon interaction such as Debye-Waller factor a these molecular systems. From the viewpoint of the issue of materials designing for wavelength-multiplexed optical memory and also with naive interest to obtain efficient ... |
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| The Study of Weak Linear Electron-Phonon Coupling in Iron-Free Hemeproteins, |
22 MAY 1992 |
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| Authors:
J. W Lin; T. Tada; S. Saikan; T. Kushida; T. Tani; OSAKA UNIV (JAPAN)
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| The present interest in the PHB optical memories has motivated research into finding materials which have weak electron-phonon coupling between the guest impurity and the host system. The magnitude of the linear electron-phonon coupling strength can be obtained from the Debye-Waller factor, the relative strength of the zero-phonon line and phonon sideband of the homogeneous spectrum. The Debye-Waller factor can be determined readily in crystals; in amorphous solids, however, the ... |
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| Persistent Hole Burning Spectroscopy Applications on Phthalocyanine Langmuir-Blodgett Films, |
22 MAY 1992 |
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| Authors:
F. Adamec; M. Ambroz; E. Brynda; J. Dian; M. Vacha; CHARLES UNIV PRAGUE (CZECHOSLOVAKIA) FACULTY OF MATHEMATICS AND PHYSICS
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| Phthalocyanine Langmuir Blodgett (LB) films represent ultra thin monomolecular layers with molecules in tight contact. Most of the phthalocyanine molecules in LB films are ordered in domains where they occupy well defined (parallel) positions. There is also a minority of non-ordered molecules in off-domain positions in LB films. This fact is well documented in X-ray diffraction and transmission electron diffraction. Moreover, significant inhomogeneous broadening of absorption spectra of LB film ... |
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| Kinetics of Hole Burning in Inhomogeneously Broadened Spectra: the Origin of Nonexponentiality and Problem of Burning Efficiency, |
22 MAY 1992 |
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| Authors:
E. I. Al'shits; B. M. Kharlamov; N. I. Ulitsky; AKADEMIYA NAUK SSSR MOSCOW
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| High inhomogeneous broadening of impurity spectra in amorphous media reflects one type of dispersion, characteristic for disordered systems: dispersion of electronic transition frequency. In Principle, there can exist a pronounced dispersion of other parameters: homogeneous line width (gamma), Debye-Waller factor (alpha), hole burning efficiency(phi), etc. The problem of the burning efficiency dispersion (BED) was extensively discussed in the recent years ( and references therein). The nonexponentiality of the burning kinetics ... |
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| Electro-Optical, Multi-Stable Switches Based on Persistent Spectral Holes, |
22 MAY 1992 |
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| Authors:
David M. Hanson; STATE UNIV OF NEW YORK AT STONY BROOK DEPT OF CHEMISTRY
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| Photochemical or photophysical transformations induced by highly monochromatic laser radiation can drastically reduce the concentration of molecules absorbing at a particular wavelength within an inhomogeneously broadened absorption band. These spectral holes can be broadened, removed, shifted or split by the application of an external electric field under appropriate conditions. This property provides a nonlinear response in sample transmission, absorption, or diffraction and can be coupled with feedback to produce novel ... |
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| Fluorine Spin Diffusion Barrier in Pr3+:LaF3 Observed by Cross Relaxation, |
22 MAY 1992 |
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| Authors:
L. L. Wald; E. L. Hahn; M. Lukac; CALIFORNIA UNIV BERKELEY DEPT OF PHYSICS
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| Photon echo measurements made at 2 OK on the 3H4 - ID2 transition in pr3+:LaF3 show that magnetic dipolar couplings between the Pr and F nuclei account for the 56 kHz homogeneous linewidth of this transition. The homogeneous broadening arises from the enhanced 141 Pr nuclear moment (I=5/2) interacting with the local field fluctuations of the 19 F nuclear moments undergoing mutual spin flip transitions. Such resonant fluctuations should, in ... |
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| Change Analysis and Fisher-Score Change Processes |
MAY 92 |
18 pages |
| Authors:
Emanuel Parzen; TEXAS A AND M UNIV COLLEGE STATION DEPT OF STATISTICS
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| This paper aims to synthesize classical statistical methods and changepoint hypothesis testing and to contribute to solutions of the historical basic applied problem of statistics: distinguish change (of the model) from fluctuation (within the model), the variability expected under homogeneity. Contents are: 0. Goals, (1). Comparison, change analysis as probability study of (X,Y); (2). Asymptotic distributions of sample change processes; (3). One way analysis of variance (AOV); (4). Change analysis ... |
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| Structure/Property Relationships of Siloxane-Based Liquid Crystalline Materials |
MAY 92 |
318 pages |
| Authors:
Timothy J. Bunning; Herbert E. Klei; Jeffery T. Koberstein; Edward T. Samulski; W. W. Adams; WRIGHT LAB WRIGHT-PATTERSON AFB OH
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| The structure/property relationships of a class of cyclic-siloxane based molecules were investigated. X-ray diffraction and electron microscopy techniques were used to initially investigate commercially available pentamethylcyclopentasiloxane rings with various molar ratios of biphenyl-4- allyloxybenzoate and cholesteryl-4-allyloxybenzoate mesogens attached. Results indicated a strong dependence of the X-ray diffraction patterns on the composition of the mesogens. Three dozen new siloxanes with mesogens were synthesized to investigate the packing behavior in more detail. ... |
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| Microwave (Hybrid) Heating of Alumina at 2.45 GHZ: I. Microstructural Uniformity and Homogeneity, |
27 APR 1992 |
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| Authors:
Arindam De; Iftikhar Ahmad; E. Dow Whitney; David E. Clark; FLORIDA UNIV GAINESVILLE DEPT OF MATERIALS SCIENCE AND ENGINEERING
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| Microwave (hybrid) heating (MHH) is a unique combination of microwave (MW)material interaction and conventional radiant/conduction mechanisms that facilitates the attainment of very high heating rates in a 2.45 GHz, multimode MW cavity. Microstructural uniformity and homogeneity of dry-pressed green samples of pure, undoped alumina with (MHH relative to conventional fast firing (CFF) has been studied. The confluence of the two heating mechanisms (with MHH) results in an improved parity in ... |
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| Investigations of Fabrication Tolerances of Narrow Bandwidth Directional Coupler Filters in InP, |
APR 1992 |
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| Authors:
Remigius Zengerle; Ottokar Leminger; DEUTSCHE BUNDESPOST TELEKOM DARMSTADT (GERMANY)
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| Wavelength filters of narrow bandwidth are essential components of future photonic integrated circuits to be used, for example, in dense WDM systems. Based on the principle of asymmetrical directional couplers, there exist several studies and demonstrations in the InGaAsP/InP system. In order to achieve the desired wavelength selectivity in the nanometer range, filters with a length of several millimeters will be needed. The epitaxial layers for these structures are fabricated ... |
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| Comparison of Electromagnetic Propagation Predictions from IREPS and RPO Across a Coastal Transition |
MAR 92 |
89 pages |
| Authors:
Bryce Campbell; Stephan Siletzky; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| The Navy's existing electromagnetic ion prediction software, the Integrated Refractive Effects Prediction System (IREPS), neglects signal leakage from a duct, approximates diffraction, and assumes atmospheric horizontal homogeneity. To ameliorate these deficiencies, the Radio Physics Optics (RPO) program is being developed. This thesis analyzes the significantly different propagation predictions of the two models. RPO predicts significantly shorter propagation ranges in a duct than does IREPS. RPO predicts variations in duct thickness ... |
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| Characterization of Sol-Gel Thin Films of TiO2-PbO, TiO2-Bi2O2-CeO2 Compositions, |
MAR 1992 |
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| Authors:
Michel A. Aegerter; Eliane R. La Serra; ILLINOIS UNIV AT URBANA
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| Single and multilayer sol-gel thin films of TiO2-PbO, Ti02-Bi203 and Ti02- Ceo2 composition were deposited on glasses using the dip coating technique. The precursors included Ti(OPri)4 chemically modified by acetyl acetone and diluted in PriOH and sols of Pb(OAc)2, Bi(NO3)3 5H20 diluted in acetic acid. The Ti02-CeO2 sol was prepared by mixing Ce(NH4)2(NO3)6 in ethanol and then adding Ti(O-iso-C3H7)4.Structure texture and homogeneity of their main constituants was established by XRD, ... |
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| New Developments in Sol-Gel Imaging, |
MAR 1992 |
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| Authors:
Nicholas J. Phillips; LOUGHBOROUGH UNIV OF TECHNOLOGY (UNITED KINGDOM)
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| This paper addresses the properties of sol-gel silica in relation to its potential to provide new devices for optical imaging. Although the sol-gel method opens the door to unprecedented levels of purity of silica materials, it is also beset with problems of the achievement of extreme optical homogeneity. The work reported discusses experiences with sol-gel silica intra cavity elements in ion lasers and new concepts of imaging and laser structures ... |
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| Dynamical Solvent Effects on Activated Electron-Transfer Reactions: Principles, Pitfalls, and Progress |
FEB 92 |
58 pages |
| Authors:
Michael J. Weaver; PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
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| Recent experimental and conceptual progress in our understanding of dynamical solvent effects in activated electron-transfer processes are critically reviewed. Understanding the various influences exerted by the solvating environment upon the kinetics of electron-transfer (ET) processes, either in homogeneous solution or at metal-solution and related interfaces, has long captured the attention of experimentalists and theoreticians alike. These roles have been perceived primarily in terms of energetic factors, whereby the solvent is ... |
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| LOMPOC Valley Diffusion Experiment Analysis - Mt. Iron Comparison and Two Zone Convective Scaling Model |
02 JAN 92 |
115 pages |
| Authors:
C. E. Skupniewicz; R. F. Kamada; S. A. Drake; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF PHYSICS
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| LVDE(Lompoc Valley Diffusion Experiment) was conducted Aug 1989 to assess the potential risk of gaseous releases from the Hypergolic Stockpile and Storage Facility at Vandenberg AFB. Results of the LVDE are compared to the predictive equations of the Mt. Iron Diffusion Tests, conducted at Vandenberg in the 1960's. The Mt. Iron equation parameterizes diffusion with on-base meteorological tower input data. Regression techniques similar to those of Mt. Iron are used ... |
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| Conformal Stereotactic Radiosurgery With Multileaf Collimation |
92 |
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| Authors:
Dale C. Moss; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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| This paper outlines and implements a method of producing dose distributions that conform to any arbitrary, irregularly shaped target by means of dynamic conformal collimation using a multileaf collimator. The method may be summarized in three steps: production of the treatment plan; localization of the target; and the calculation of three dimensional dosimetry. Provision is made for volumetric evaluation of dosimetry with dose volume histograms and complication probability functions. Treatment ... |
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| On the Stability of Finite Plastic Deformations |
92 |
12 pages |
| Authors:
H. M. Zbib; E. C. Aifantis; MICHIGAN TECHNOLOGICAL UNIV HOUGHTON
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| The stability of inelastic deformation and the formation of shear bands are examined by considering a recently developed gradient-dependent theory of elasto-viscoplasticity. The main issues addressed in the present work are the role of viscosity, inertia and higher order strain gradients in providing internal length scales, as well as the effect of back stress (deformation induced anisotropy) and plastic spin (texture development) on the structure of the shear bands in ... |
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| Background Suppression in MAS-NMR |
12 DEC 91 |
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| Authors:
J. L. White; L. W. Beck; D. B. Ferguson; J. F. Haw; TEXAS A AND M UNIV COLLEGE STATION DEPT OF CHEMISTRY
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| We report the use of pulse sequences for suppressing background signals from spinning modules used in magic angle spinning (MAS) NMR. These pulses sequences are based on spatially selective composite 90 deg pulses originally reported by Bax, which provide for no net excitation of spins outside the homogeneous region of the coil. We have achieved essentially complete suppression of background signals originating from our Vespel spinning modules (which uses a ... |
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| Robust Grasp Design Using Grasp Force Focus Positioning |
12 DEC 91 |
209 pages |
| Authors:
Freddie D. Zayas; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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| A three-finger precision grasp is used to rotate a cylindrical object about a threaded post. Three fingered grasps are unique in that the homogeneous solution for the contact forces produces a grasp force focus. Mapping of focus points which meet grasp stability and joint torque criteria results in a usable focus region. The effects of applied torque, contact location, and object position and orientation on usable regions are presented. Stability ... |
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| Mechanisms and Modelling of Environment-Dependent Fatigue Crack Growth in a Nickel Based Superalloys |
12 DEC 91 |
252 pages |
| Authors:
H. Ghonem; D. Zheng; RHODE ISLAND UNIV KINGSTON DEPT OF MECHANICAL ENGINEERING AND APPLIED MECHANI CS
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| At loading frequencies below that of the transitional frequency level, which is typical of mission cycles of jet engines, the elevated temperature fatigue crack growth process in Alloy 718 is viewed to be fully environment-dependent. Of all the crack growth stages, this process, while is the most critical in high temperature application due to its highly accelerated crack growth rate, is the least studied or understood. The objective of this ... |
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| Determination of Bistatic Radar Clutter Power from Topographic Data |
DEC 1991 |
118 pages |
| Authors:
Clyde R. Heddings; AIR FORCE INST OF TECH WRIGHT-PATTERSONAFB OH SCHOOL OF ENGINEERING
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| The purpose of this research was to develop a procedure for estimating the average bistatic radar clutter power from a topographic map using rough surface scattering theory. First, the terrain in the radar target area was divided into sub regions having homogeneous characteristics. A joint Gaussian distribution for the surface heights was fitted from the information contained in the topographic map contour lines for each homogeneous area. From these distributions, ... |
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| Remote Sensing of Trapping Layer Base Height Using ATIS Transmissions |
DEC 91 |
26 pages |
| Authors:
T. M. Vuong; NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
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| This report describes an experiment that examined the method of determining a trapping layer directly from VHF and UHF radio measurements. The experiment used existing radio broadcasts along the coast of southern California. Some strong correlations between the observed signal strengths and the inferred trapping layer base heights of the various radio paths were shown, indicating the height of the trapping layer is an important factor in controlling radio propagation ... |
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| Cost/Benefit Analysis of Commander, Naval Surface Force, U.S. Pacific Fleet's Supply Maintenance Training Team |
DEC 91 |
129 pages |
| Authors:
Carlos D. Buzon Ii; Michael D. Huggins; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| This thesis is an attempt to accomplish a cost/benefit analysis of Commander, Naval Surface Force, U.S. Pacific Fleet's (COMNAVSURFPAC) Supply Maintenance Training Team (SMTT). The effectiveness of the SMTT program is also evaluated. Data were gathered from surveys of current and former Supply Officers of COMNAVSURFPAC ships, with the Shipboard Non-Tactical Automated Data Processing II system installed and which had received all or part of an SMTT assistance visit. Interviews ... |
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| The Effect of Turbulence Ingestion on Propeller Broadband Thrust |
DEC 91 |
51 pages |
| Authors:
C. W. Jiang; M. S. Chang; Y. N. Liu; DAVID TAYLOR RESEARCH CENTER BETHESDA MD SHIP HYDROMECHANICS DEPT
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| This report presents the theoretical prediction of the low frequency unsteady broadband thrust for propellers/rotors in a turbulent flow, such as those on any surface ship. Broadband thrust forces are predicted by the use of a new correlation method and are compared with existing theoretical models based on both correlation and spectrum approaches. In contrast to the available theories, the new theory predicts low blade rate humps and broadband forces ... |
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| Modeling Acoustic Backscatter from the Seafloor by Long-Range Side-Scan Sonar |
DEC 91 |
88 pages |
| Authors:
Anthony P. Lyons; TEXAS A AND M UNIV COLLEGE STATION
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| An existing model of seafloor backscattering was extended to include volume scattering from a random inhomogeneous continuum and scattering from subbottom interfaces. Results of computer simulations with the extended model were compared with values of scattering strength obtained from processed GLORIA data from the Monterey Fan off the coast of California. Regions of well delineated high and low backscatter are seen in the GLORIA imagery. The geoacoustic input parameters for ... |
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| NMLONG: Numerical Model to Simulate Wave Transformation and Longshore Current |
Dec 1991 |
9 pages |
| Authors:
COASTAL ENGINEERING RESEARCH CENTER VICKSBURG MS
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| NMLONG is a PC-based model that calculates wave height, wave angle, mean water surface, and longshore current over an irregular bottom profile that can include longshore bars. The program includes features such as self-contained data entry, default values of model parameters, error trapping, on-line help, and graphics. The major assumptions in NMLONG are longshore homogeneity (straight and parallel bottom contours) and linear wave theory. Potential applications of NMLONG include estimating ... |
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| Theoretical Studies of Homogeneous and Heterogeneous Reactions in Silicon Systems |
19 NOV 91 |
52 pages |
| Authors:
Lionel M. Raff; Donald L. Thompson; OKLAHOMA STATE UNIV STILLWATER DEPT OF CHEMISTRY
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| This report summarizes the results of research conducted under AFOSR support with particular emphasis on investigations carried out during three-year period. The research reviewed includes homogeneous and heterogeneous processes of particular importance in the chemical vapor deposition (CVD) of silicon from silanes and disilanes, the study of chemical processes occurring under conditions of close confinement, non-statistical dynamics and intramolecular energy transfer processes. New methods for (1) obtaining potential energy surfaces ... |
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| Effect of Comproportionation on the Voltammetric Reduction of Methyl Viologen in Low Ionic Strength Solutions |
10 NOV 91 |
18 pages |
| Authors:
John D. Norton; Henry S. White; MINNESOTA UNIV MINNEAPOLIS DEPT OF CHEMICAL ENGINEERING AND MATERIALS SCIENCE
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| A variety of electrochemical methods are available for investigating homogeneous chemical reactions coupled to an initial electron-transfer step. Frequently, these methods are based on varying the mass-transfer rate(s) of reactant or intermediate(s) relative to the rate of chemical reaction. In a recent report, we proposed a new general method using microelectrodes, in low ionic strength solutions, that allows controlled variation of the mass transfer coefficients of charged reactants and intermediates ... |
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| Estimation of the Outer Sphere Contribution to the Activation Parameters for Homogeneous Electron Transfer Reactions Using the Mean Spherical Approximation |
09 NOV 91 |
19 pages |
| Authors:
W. R. Fawcett; L. Blum; PUERTO RICO UNIV RIO PIEDRAS DEPT OF PHYSICS
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| Estimation of the outer sphere contribution to the Gibbs energy and enthalpy of activation for homogeneous electron transfer is described on the basis of the mean spherical approximation (MSA). It is shown that these quantities for spherical reactants are significantly smaller than those estimated by the Born continuum model. MSA estimates and experimental values of the activation enthalpy for the cobaltacene/cobaltacenium cation redox couple are found to agree very well ... |
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| Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. 17. Characterization of Poly(10-((4-Cyano-4'-Biphenyl)oxy) decanyl Vinyl Ether)s by 1-D and 2-D H-NMR Spectroscopy |
30 OCT 91 |
14 pages |
| Authors:
Virgil Percec; Myongsoo Lee; Peter L. Rinaldi; Vincent E. Litman; CASE WESTERN RESERVE UNIV CLEVELAND OH DEPT OF MACROMOLECULAR SCIENCE
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| Since the first examples of mesogenic vinyl ethers and liquid crystalline poly(vinyl ether)s were reported from our laboratory, several research groups became actively engaged in the synthesis of liquid crystalline poly(vinyl ether)s mainly because they can be polymerized by living cationic mechanism. So far, we have elucidated the influence of molecular weight on the phase transitions of poly(omega-((4-cyano-4'-biphenyl)oxy)alkyl vinyl ether)s with alkyl groups from ethyl to undecanyl. Binary copolymerization experiments ... |
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| DURIP Instrumentation Support for High-Latitude Ionospheric Research and the Establishment of a Dual Radar/Dual Frequency Observational Capability at the Millstone Radar Facility |
28 OCT 91 |
7 pages |
| Authors:
John C. Foster; HAYSTACK OBSERVATORY WESTFORD MA
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| Radar receiver and signal processing instrumentation was acquired and fabricated in order to establish a capability for dual 440 MHz and 1390 MHz radar operations at the M.I.T. Millstone Hill research facility. Hardware costs for a duplicate of the MIDAS radar processor were provided. This instrumentation enables a program of simultaneous, high-spatial resolution dual frequency observations of non-thermal and coherent radar backscatter from ionospheric plasma waves and turbulence at both ... |
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| Optimal Shear Correction Factors in Hierarchical Plte Modelling |
07 OCT 91 |
39 pages |
| Authors:
I. Babuska; J. M. d'Harcourt; C. Schwab; MARYLAND UNIV COLLEGE PARK INST FOR PHYSICAL SCIENCE AND TECHNOLOGY
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| This paper addresses the formulation of hierarchical plate models as an optimal (in a clearly defined sense) numerical method which can be easily implemented and is available in the code MSC/PROBE. Special emphasis is placed on the optimal selection of the shear correction factors. It is shown that different measures of accuracy lead to different optimal choices of these factors. The main tool in the analysis is the Fourier transformation. ... |
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| Validation of the Bulk Method for Overwater Optical Refractivity |
OCT 91 |
39 pages |
| Authors:
R. A. Paulus; NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
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| The effects of refraction on optical propagation at low altitudes over the ocean were investigated. A telescope was used to optically track ships to the range at which they disappeared over the horizon. Concurrent bulk meteorological measurements were used with surface-layer theory to model optical refractivity. A ray-trace program, with these profiles of refractivity, was used to calculate maximum intervision range (MIVR). Calculated MIVRs agree well with observations for subrefractive ... |
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| Synthesis, Analysis, and Processing of Fractal Signals |
OCT 1991 |
239 pages |
| Authors:
Gregory W. Wornell; MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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| Fractal geometry arises in a truly extraordinary range of natural and man-made phenomena. The 1/f family of fractal random processes, in particular, are appealing candidates for data modeling in a wide variety of signal processing scenarios involving such phenomena. In contrast to the well-studied family of ARMA processes, 1/f processes are typically characterized by persistent long-term correlation structure. However, the mathematical intractability of such processes has largely precluded their use ... |
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| Computer-Aided Structural Engineering (CASE) Project: Application of Finite Element, Grid Generation, and Scientific Visualization Techniques to 2-D and 3-D Seepage and Groundwater Modeling |
SEP 91 |
257 pages |
| Authors:
Fred T. Tracy; ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS INFORMATION TECHNOLOG Y LAB
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| This report describes new advances in the computational modeling of ground water and seepage using the finite element method (FEM) in conjunction with tools and techniques typically used by the aerospace engineers. The unsolved environmental issues regarding our hazardous and toxic waste problems must be resolved, and significant resources must be placed on this effort. Some military bases are contaminated with hazardous waste that has entered the groundwater domain. A ... |
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| NMR Characterization of Products Formed in Diazotizing Mixtures of Luminol and 3-Amino-L-Tryosine |
25 AUG 91 |
39 pages |
| Authors:
John R. Wright; SOUTHEASTERN OKLAHOMA STATE UNIV DURANT DEPT OF PHYSICAL SCIENCES
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| A diazotized mixture of luminol and 3-amino-L-tyrosine prepared as an acetone-precipitated solid polymerizes slowly (over a period of weeks) yielding a brown, water soluble polymer which migrates electrophoretically as an anion at pH 6. Solutions of this substance in Heavy water or a mixed D2O/deuterated Dimethylsulfoxide solvent present very broadened 1 Hydrogen-nmr resonances, and all attempts to chemically fragment this material into its subunit structures have been unsuccessful. The polymer, ... |
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| Frequency-Independent and Frequency-Dependent Polymer Transitions on Flexural Plate Wave Devices and their Effects on Vapor Sensor Response Mechanisms |
10 AUG 91 |
44 pages |
| Authors:
Jay W. Grate; Stuart W. Wenzel; Richard M. White; NATIONAL AEROSPACE LAB AMSTERDAM (NETHERLANDS)
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| The flexural plate wave device is capable of sensing transition behaviors of homogeneous amorphous polymers applied as thin films to its surface. The changes in polymer properties at the static glass transition temperature are sensed as a change in slope of the frequency-temperature plot. Frequency-dependent relaxation properties are detected with a sigmoidal change in slope of the frequency-temperature plot and a minimum in signal amplitude. The transitions observed using poly(vinyl ... |
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| Modelling the Response of Thick Composite Materials Due to Axisymmetric Shock Loading |
05 AUG 91 |
85 pages |
| Authors:
J. A. Nemes; P. W. Randles; NAVAL RESEARCH LAB WASHINGTON DC
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| Preliminary efforts for developing a methodology to predict the response of thick composite materials to axisymmetric shock loading are presented. Consideration is given to material layups that result in transversely isotropic behavior in the plane of the fibers. The response of thick graphite/ epoxy composite plates subjected to underwater explosive loadings is solved numerically using a transient finite-element code. Both spherical and plane shock waves are considered. Results are compared ... |
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| Damage Mechanisms in Composites |
AUG 91 |
41 pages |
| Authors:
BROWN UNIV PROVIDENCE RI DIV OF ENGINEERING
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| Mechanically induced residual stresses are an inherent feature of permanently deformed metal-matrix composites such as aluminum silicon carbide. The presence of hard SiC reinforcements promotes non homogeneous flow in the matrix, resulting in residual stresses when the applied loads are removed. These residual stresses are potentially important because of the effect on cavitation and other damage mechanisms leading to composite failure. We have attempted to simulate the residual stresses in ... |
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| Various Target Material Failure Mechanisms Observed for Ballistic Penetrations |
AUG 91 |
64 pages |
| Authors:
Timothy G. Farrand; ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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| The failure mechanism of a novel target material is compared to existing armor materials (rolled homogeneous armor, RHA, and high hardness armor, HHA), which exhibit two vastly different failure mechanisms. The RHA steel exhibits large bulk plastic deformation as the penetrator burrows into the target. In contrast, the HHA deforms much less as the strain is localized in very small regions that develop into adiabatic shear bands which 'chip' undeformed ... |
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| Application of Adaptive Nulling to Electromagnetic Hyperthermia for Improved Thermal Dose Distribution in Cancer Therapy |
03 JUL 91 |
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| Authors:
Alan J. Fenn; MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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| Adaptive nulling is applied to the problem of generating a therapeutic thermal dose distribution in electromagnetic hyperthermia treatment of cancer. A system design concept for implementing adaptive hyperthermia is introduced. With the proposed design concept, it may be possible to maximize the applied electric field at a tumor position in th target body and simultaneously minimize or reduce the electric field at target positions where undesired high temperature regions (hot ... |
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| Analysis of Two-Equation Turbulence Models for Recirculating Flows |
JUL 91 |
23 pages |
| Authors:
S. Thangam; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
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| The two-equation K-epsilon model is used to analyze turbulent separated flow past a backward-facing step. It is shown that if the model constants are modified to be consistent with the accepted energy decay rate for isotropic turbulence, the dominant features of the flow field -- namely -- the size of the separation bubble and the streamwise component of the mean velocity, can be accurately predicted. In addition, except in the ... |
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| Development of Turbulence Models for Shear Flows by a Double Expansion technique |
JUL 91 |
27 pages |
| Authors:
V. Yakhot; S. Thangam; T. B. Gatski; S. A. Orszag; C. G. Speziale; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
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| Turbulence models are developed by supplementing the renormalization group (RNG) approach of Yakhot and Orszag with scale expansions for the Reynolds stress and production of dissipation terms. A certain additional expansion parameter is the ratio of the turbulent to mean strain time scale. While low- order expansions appear to provide an adequate description for the Reynolds stress, no finite truncation of the expansion for the production of dissipation term in ... |
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| Electrified Microscopic and Conventional Interfaces between Two Immiscible Electrolyte Solutions |
24 JUN 91 |
40 pages |
| Authors:
Petr Vanysek; NORTHERN ILLINOIS UNIV DE KALB DEPT OF CHEMISTRY
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| Transport studies on interfaces between immiscible phases bridges the field of heterogeneous electrode electrochemistry and that of homogeneous solution chemistry. Early work on liquid/liquid boundary was concerned with large area (order of a square centimeter) interfaces. Recent studies investigate phenomena on interfaces rendered in pores, capillaries and small holes. The behavior of such interfaces in the presence of dodecyl sulfate, forming micelles, is investigated. Voltammetry and amperometry on these small ... |
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