Showing papers by "Naval Surface Warfare Center published in 1994"

Controlling chaos in the brain

Abstract: In a spontaneously bursting neuronal network in vitro, chaos can be demonstrated by the presence of unstable fixed-point behaviour. Chaos control techniques can increase the periodicity of such neuronal population bursting behaviour. Periodic pacing is also effective in entraining such systems, although in a qualitatively different fashion. Using a strategy of anticontrol such systems can be made less periodic. These techniques may be applicable to in vivo epileptic foci.

Nanowire Array Composites

Abstract: Long, nanometer-size metallic wires can be synthesized by injection of the conducting melt into nanochannel insulating plates. Large-area arrays of parallel wires 200 nanometers in diameter and 50 micrometers long with a packing density of 5 x 108 per square centimeter have been fabricated in this way. When charged, the ends of the wires generate strong, short-range electric fields. The nanowire electric fields have been imaged at high spatial resolution with a scanning force microscope.

A Proposed Three-Dimensional Constitutive Model for Shape Memory Alloys

Abstract: The shape memory alloy (SMA) stress-strain response associated with martensitic twinning hysteresis and austenite-martensite/martensite-austenite superelasticity is modeled using constitutive equations. Compared to the modeling work done on viscoelastic and viscoplastic be havior, this has been an area of limited study. The equations which are presented here express the growth of inelastic strain in a rate-type formulation similar to viscoplastic laws. This constitutive model is obtained by extending a one-dimensional evolutionary model of SMA behavior to three dimensions. The resulting model is then reduced to meet the loading conditions of three special cases: uniaxial loading, shear loading, and non-proportional biaxial loading (combined axial- torsional loading). The model which is being considered, although nonlinear, is relatively simple in that only two evolutionary equations are required to model inelastic strain and a generalized back stress at a material point. Thus the model being presented use...

Satellite Geodesy—Foundations, Methods, and Applications

Abstract: This text is an updated English translation of Satellitengeodasie, a book that was published in German in 1989. The text is the first in many years that attempts to cover the broad spectrum of methods, applications, and systems, both classical and current, that have developed in the field of satellite geodesy. The material is presented in a structure that follows the major observational methods used in satellite geodesy: classical techniques, Doppler, GPS, laser, altimetry, and special methods including satellite-to-satellite tracking, satellite radiometry, and VLBI. Before introducing these observational techniques in detail, the author provides the fundamentals on reference frames, time signal propagation, orbital mechanics and basic applications of satellite geodesy in positioning, gravity field modeling, navigation, marine geodesy, kinematics, and geodynamics. An excellent reference list completes the text.

Experimental observation of on-off intermittency

Abstract: We observe on-off intermittency in a nonlinear electronic circuit tuned near a Hopf bifurcation point. The circuit is driven randomly through the bifurcation point, resulting in intermittent switching between a fixed point (laminar phase) and a limit cycle. The distribution of lengths of laminar phases exhibits -3/2 power law scaling for shorter phases, and an exponential drop for longer phases, due to noise in the system. These results agree with a theoretically predicted distribution. In addition, the crossover from power law to exponential decay obeys the predicted scaling law.

Benchmark problem for beam pointing control of phased array radar against maneuvering targets

Abstract: Presents a benchmark problem for tracking maneuvering targets. The benchmark problem involves beam pointing control of a phased array (agile beam) radar against highly maneuvering targets. A testbed simulation program that includes the effects of target amplitude fluctuations, beamshape, missed detections, finite resolution, target maneuvers, and track loss is described. Limits on the position and maneuverability of the targets are given along with descriptions of six target trajectories. The "best" tracking algorithm is the one that requires the minimum number of radar dwells while satisfying a constraint of 4% on the maximum number of lost tracks.

Atomic structure of amorphous Al100-2xCoxCex (x=8, 9, and 10) and Al80Fe10Ce10 alloys: An XAFS study.

Abstract: The local atomic structure of Co, Fe, and Ce in aluminum-rich amorphous alloys of ${\mathrm{Al}}_{100\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$ (x=8, 9, and 10) and Ce in ${\mathrm{Al}}_{80}$${\mathrm{Fe}}_{10}$${\mathrm{Ce}}_{10}$ has been investigated by x-ray-absorption fine structure (XAFS) spectroscopy. The materials, 1- and 3-\ensuremath{\mu}m-thick films, were prepared by vapor quenching using the dc magnetron sputtering method. We show that the composition of the glass-forming region of these magnetron-sputtered alloys strictly follows the theoretical limit calculated on the basis of the atomic size criterion. From analyses of the XAFS data at the K edges of Co and Fe and the ${\mathit{L}}_{3}$ edge of Ce, the following conclusions with regard to local structure are made. The first coordination sphere of Co in ${\mathrm{Al}}_{100\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$ (x=8, 9, and 10) consists of 5.8 to 6.4 Al atoms at a distance of 2.44 \AA{}. The local coordination sphere for Fe in ${\mathrm{Al}}_{80}$${\mathrm{Fe}}_{10}$${\mathrm{Ce}}_{10}$ consists of 6.4 Al atoms at a distance of 2.47 \AA{}. Ce in both systems appears to be coordinated with roughly 5 and 9 Al atoms at distances of 2.95 and 3.15 \AA{}, respectively. These results are discussed in light of the dense random packing (DRP) of hard spheres model. Both Co-Al and Fe-Al bond lengths are anomalously short (9 and 8 % contraction, respectively) with also anomalously low coordination numbers (45% reduction) from values based on the DRP model using the metallic state radii.These anomalous changes indicate a strong interaction between Co or Fe atoms and the Al atoms which perhaps may be a result of a covalently bonded environment. The Ce-Al distance in both the Al-Co-Ce and Al-Fe-Ce systems, on the other hand, is smaller by only 0.17 \AA{} (a contraction of only 5%) and the coordination number is reduced by only 13% from expected values based on the DRP model. The contraction in the distance and reduction in the coordination number for Ce are much smaller than those values of the Co or Fe and, hence, the local bonding for Ce is likely to be metallic in character.

Image wavelet transforms implemented by discrete wavelet chips

Abstract: Both discrete wavelet transform (DWT) and inverse DWT are implemented using the lossless quadrature mirror filter (QMF) bank The image passing through the finite impulse response QMF filtering becomes blurred and thus requires fewer number of pixels Such a decimation amounts to the critical sampling that leads to the complexity O ( N ) for N data The data compression comes from the permissible bits per pixel dynamic range compression of those filtered images having fewer details The image reconstruction at a telereceiving station is accomplished by means of the inverse DWT Thus, a complete biorthogonal basis of QMF is implemented by a fast wavelet transform chip designed with Verilog HDL and the image processing is demonstrated numerically Adaptive DWT is sketched

X‐Ray Absorption Fine Structure Spectra and the Oxidation State of Nickel in Some of Its Oxycompounds

Abstract: The structure of the higher oxide forms of nickel (where Ni has a valency greater than +2) is interesting from the standpoint of developing advanced nickel batteries for consumer applications and for electric vehicle propulsion. Xanes spectra of nickel K-edge and X-ray diffraction patterns of several nickel oxycompounds were measured. The shift in energy of the Ni K-absorption edge toward higher values correlates well with the increase in the oxidation state of nickel from +2 to +4 in the compounds studied. The inflection point energy of the Ni pre-edge structure shifts approximately 1 eV per unit change in valency. The results provide evidence which support the assignment that the valency of Ni in [beta]-NiOOH is +3; Ni[sub 3]O[sub 2](OH)[sub 4] and commercial nickel peroxide (NiO[sub 2]) likewise contain trivalent nickel. The edge shift for quadrivalent nickel in KNilO[sub 6] is reported for the first time.

Measurement of the Out-of-Plane Shear Response of Thick Section Composite Materials Using the V-Notched Beam Specimen

Abstract: The out-of-plane shear response of thick, unidirectional and crossply, AS4/3501-6 and S2 glass/3501-6 laminates was investigated theoretically and experimentally using V-notched beam (Iosipescu) specimens. Strains were monitored in the specimen test sections using conventional strain gages, moire interferometry and full section strain gages. Crossply laminates exhibited a fairly uniform strain distribution away from the notches, while the unidirectional specimens were characterized by a nonuniform distribution. Measured strains correlated very well with predicted strains from specimen finite element analyses using nonlinear elastic material properties.

Smoothness Implies Determinism: A Method to Detect It in Time Series

Abstract: Continuity on an embedded phase space is enough to imply determinism in time series. Also, it is possible to define infinitely many arbitrary vector fields over an attractor. We exploit this arbitrariness to generate a detector of smoothness and therefore of determinism in time series. We report results of numerical studies of both flow and map examples and of a chaotic experimental system.

Optimization of K-shell emission in aluminum z-pinch implosions: Theory versus experiment.

Abstract: Two sets of [ital z]-pinch experiments were recently completed at the Saturn and Phoenix facilities of Sandia National Laboratories and the Naval Surface Warfare Center, respectively, using aluminum wire arrays of different wire and array diameters. Measurements of the total x-ray yield from the [ital K] shell of aluminum were made. In this paper, a comparison of these measurements is made to both theoretical predictions and to a similar set of earlier measurements that were made at the Double Eagle facility of Physics International Company. These three sets of yield measurements have points of agreement with predicted yields and with each other, but they also show points of mutual disagreement, whose significance is discussed. The data are analyzed using a slightly revised version of a previously published [ital K]-shell yield scaling law, and they support the existence of a reasonably well defined region in (load mass)--(implosion velocity) space in which plasma kinetic energy is efficiently converted into [ital K]-shell x rays. Furthermore, a correlation is observed between the inferred conversion efficiencies and the times in which the implosions occur relative to the times when each generator's short-circuit current reaches its peak value. Finally, unlike the Double Eagle experiments, the largestmore » measured yields in the new experiments were observed to occur at the upper velocity boundary of the efficient emission region. Moreover, the observed yields are in fairly good quantitative agreement with an earlier scaling law prediction of the maximum [ital K]-shell x-ray yield from aluminum as a function of load mass assuming kinetic energy conversion alone.« less

Fractional Fourier transforms, wavelet transforms, and adaptive neural networks

Abstract: A new optical architecture is developed, based on fractional Fourier transforms, that compromises between shift-invariant (frequency) and position-dependent filtering. The analogy of this architecture to wavelet transforms and adaptive neural networks is also presented. The ambiguity and Wigner distribution functions are obtainable from special cases of the filter. The filter design corresponds to the training of the neural networks, and an adaptive learning algorithm is developed based on gradient-descent error minimization and error back propagation. The extension to multilayer architecture is straightforward.

Mathematics of adaptive wavelet transforms: relating continuous with discrete transforms

Abstract: We prove several theorems and construct explicitly the bridge between the continuous and discrete adaptive wavelet transform (AWT). The computational efficiency of the AWT is a result of its compact support closely matching linearly the signal's time-frequency characteristics, and is also a result of a larger redundancy factor of the superposition-mother s(x) (super-mother), created adaptively by a linear superposition of other admissible mother wavelets. The super-mother always forms a complete basis, but is usually associated with a higher redundancy number than its constituent complete orthonormal (CON) bases. The robustness of super-mother suffers less noise contamination (since noise is everywhere, and a redundant sampling by bandpassings can suppress the noise and enhance the signal). Since the continuous super-mother has been created off-line by AWT (using least-mean-squares neural nets), we wish to accomplish fast AWT on line. Thus, we formulate AWT in discrete high-pass (H) and low-pass (L) filter bank coefficients via the quadrature mirror filter (QMF), a digital subband lossless coding. A linear combination of two special cases of the complete biorthogonal normalized (Cbi-ON) QMF [L(z),H(z),L+(z),H+(z)], called α-bank and β-bank, becomes a hybrid aα + bβ-bank (for any real positive constants a and b) that is still admissible, meaning Cbi-ON and lossless. Finally, the power of AWT is the implementation by means of wavelet chips and neurochips, in which each node is a daughter wavelet similar to a radial basis function using dyadic affine scaling.

Adaptive wavelet classification of acoustic backscatter and imagery

Abstract: The utility and robustness of wavelet features is demonstrated through three practical case studies of detecting objects in multispectral electro-optical imagery, sidescan sonar imagery, and acoustic backscatter. Attention is given to choosing proper waveforms for particular applications. Using artificial neural networks (ANNs), evidence is fused from multiple-waveform types that detect local features. The wavelet waveforms and their dilation and shift parameters are adaptively computed with ANNs to maximize classification accuracy. Emphasis is placed on the acoustic backscatter case study, involving detecting a metallic man-made object from natural and synthetic specular clutter with reverberation noise. The synthetic clutter is shown to be a good model for the natural clutter, which appears promising for avoiding huge data collection efforts for natural clutter and for better delineating the classification boundary. The classifier computes the locations, sizes, and weights of Gaussian patches in time-scale space that contain the most discriminatory information. This new approach is shown to give higher classification rates than an ANN with commonly used power spectral features. The new approach also reduces the number of free parameters in the classifier based on all wavelet features, which leads to simpler implementation for applications and to potentially better generalization to test data.

Application of a panel method to hydrodynamics of underwater vehicles

Abstract: A low-order singularity panel method based on Green`s formulation is used to predict the hydrodynamics characteristics of underwater vehicles. The low-order modeling employs constant strength sources and doublets, and the body surface is modeled by quadrilaterals. The method is first applied to predicting the force and moment coefficients of underwater vehicles for the body-alone and finned configurations. Hydrodynamic coefficients of added mass and added moment of inertia are also calculated by modifying the code. Results for several two and three-dimensional bodies show the usefulness of the method for predicting the added mass and added moment of inertia.

On asynchronous data fusion

Abstract: In a multisensor tracking system, sensors often operate asynchronously and provide data at different rates with different communication delays. In this case the sequential processing of the sensor data may be computationally intensive. In addition, due to the inherent delay associated with some sensors, such as a multi-tasking radar, it may not be possible to process the data real time. The present paper presents an approach to deal with asynchronous sensors' data without performing sequential processing, i.e., using a data fusion approach. The result of the paper applies to an arbitrary number of dissimilar sensors. >

Tracking performance of a phased array radar with revisit time controlled using the IMM algorithm

Abstract: Since phased array radars have the ability to perform adaptive sampling of the target trajectory by radar beam positioning, proper control of the radar has the potential for significantly improving many aspects associated with the tracking of multiple maneuvering targets. The technique proposed in this paper uses the Interacting Multiple Model (IMM) algorithm to track maneuvering targets and control the revisit time and pointing of the radar. Since the output of the IMM algorithm better represents the accuracy of the state estimates during a maneuver than that of a single model filter, the IMM algorithm is used to compute an on-line measure of tracking performance to determine the revisit time of the next track update in order to maintain a given level of performance. Algorithms for computing the revisit time and pointing the radar using the output of the IMM algorithm are presented in this paper. Performance comparisons for constant and adaptive data rates are given with measurements provided by a simulated phased array radar. >

Computation of viscous flow around propeller-body configurations: series 60 cb = 0.6 ship model

Abstract: Validation of a viscous-flow method for predicting propeller-hull interaction is provided through detailed comparisons with recent extensive experimental data for the practical three-dimensional configuration of the Series 60 CB = 0.6 ship model. Modifications are made to the K- turbulence model for the present geometry and application. Agreement is demonstrated between the calculations and global and some detailed aspects of the data; however, very detailed resolution of the flow is lacking. This supports the previous conclusion for propeller-shaft configurations and axisymmetric bodies that the present procedures can accurately simulate the steady part of the combined propeller-hull flow field, although turbulence modelling and detailed numerical treatments are critical issues. The present application enables a more critical evaluation through further discussion of these and other relevant issues, such as the use of radial- and angular-varying body-force distributions, the relative importance of turbulence modelling and grid density on the resolution of the harmonics of the propeller inflow, and three-dimensional propeller- hull interaction, including the differences for the nominal and effective inflows and for the resulting steady and unsteady propeller performance. Also, comparisons are made with an inviscid-flow method. Finally, some concluding remarks are made concerning the limitations of the method, requirements and prognosis for improvements, and application to the design of wake-adapted propellers.

Projection Method for Viscous Incompressible Flow on Quadrilateral Grids

Abstract: This paper describes a second-order projection method for the incompressible Navier-Stokes equations on multiply connected domains with a logically rectangular quadrilateral grid. The method uses a second-order fractional step scheme in which one first solves diffusion-convection equations to determine intermediate velocities which are then projected onto the space of divergence-fr ee vector fields. The spatial discretizations are accomplished by formally transforming the equations to a computational space with a uniform grid. The diffusion, pressure gradient, and divergence terms are discretized using standard finite difference approximations. The convection terms are discretized using a second-order Godunov method that provides a robust discretization of these terms at high Reynolds number. Numerical results are presented illustrating the performance of the method.

Filtered kernel density estimation

Abstract: This article describes a multiple-bandwidth version of the kernel estimator for nonparametric probability density estimation, in which the bandwidths are chosen using a set of functions, called filter functions, which determine the support of the density appropriate to the different bandwidths. These filter functions are usually defined using a normal mixture fit to the data. Thus the estimator uses different bandwidths in different regions of the support of the distribution, as controlled by the filter functions. Copyright © 2009 John Wiley & Sons, Inc. For further resources related to this article, please visit the WIREs website.