Showing papers by "Naval Surface Warfare Center published in 1993"
TL;DR: This work clarifies the roles of such attractors in producing intermittency, and provides examples, and relates them to previous work.
Abstract: On-off intermittency is an aperiodic switching between static, or laminar, behavior and chaotic bursts of oscillation. It can be generated by systems having an unstable invariant (or quasi-invariant) manifold, within which is found a suitable attractor. We clarify the roles of such attractors in producing intermittency, provide examples, and relate them to previous work.
546 citations
TL;DR: The observed size dependence of the melting temperature was in good agreement with the predictions of thermodynamic treatments of melting in finite systems, and allowed the solid-liquid interfacial free energy to be estimated for several different geometrical models.
Abstract: The size-dependent melting and freezing behavior of In metal in porous silica glasses with mean pore diameters between 6 and 141 nm has been studied by differential scanning calorimetry. The melting and freezing temperatures of the pore In were always less than the corresponding bulk values, and varied in inverse proportion to the diameter of the confining silica pores. In the smallest pores the latent heat of fusion was also determined, and found to be about one-third of its bulk value. The observed size dependence of the melting temperature was in good agreement with the predictions of thermodynamic treatments of melting in finite systems, and allowed the solid-liquid interfacial free energy to be estimated for several different geometrical models. The measured latent heat, however, was smaller than expected based on thermodynamic considerations. No evidence for an energy barrier separating the solid from the liquid was found.
197 citations
TL;DR: This paper focuses on the classification of segmented local bright spots as either calcification or noncalcification in mammographic images and seven classifiers (linear and quadratic classifiers, binary decision trees, standard backpropagation network, 2 dynamic neural networks, and a K-nearest neighbor) are compared.
Abstract: Computer-assisted detection of microcalcifications in mammographic images will likely require a multistage algorithm that includes segmentation of possible microcalcifications, pattern recognition techniques to classify the segmented objects, a method to determine if a cluster of calcifications exists, and possibly a method to determine the probability of malignancy. This paper focuses on the first three of these stages, and especially on the classification of segmented local bright spots as either calcification or noncalcification. Seven classifiers (linear and quadratic classifiers, binary decision trees, a standard backpropagation network, 2 dynamic neural networks, and a K-nearest neighbor) are compared. In addition, a postprocessing step is performed on objects identified as calcifications by the classifiers to determine if any clusters of microcalcifications exist. A database of digitized film mammograms is used for training and testing. Detection accuracy of individual and clustered microcalcificat...
192 citations
TL;DR: In this article, the use of a kinematic constraint as a pseudomeasurement in the tracking of constant-speed, maneuvering targets is considered, and a new formulation of the constraint equation is presented, and the rationale for the new formulation is discussed.
Abstract: The use of a kinematic constraint as a pseudomeasurement in the tracking of constant-speed, maneuvering targets is considered. The kinematic constraint provides additional information about the target motion that can be processed as a pseudomeasurement to improve tracking performances. A new formulation of the constraint equation is presented, and the rationale for the new formulation is discussed. The filter using the kinematic constraint as a pseudomeasurement is shown to be unbiased, and sufficient conditions for stochastic stability of the filter are given. Simulated tracking results are given to demonstrate the potential that the new formulation provides for improving tracking performance. >
132 citations
TL;DR: In this paper, the authors proposed a physical model of hole-collection following a heavy-ion strike to explain the development of oxide fields sufficient to cause single-event gate rupture (SEGR) in power MOSFETs.
Abstract: Proposes a physical model of hole-collection following a heavy-ion strike to explain the development of oxide fields sufficient to cause single-event gate rupture (SEGR) in power MOSFETs. It is found that the size of the maximum field and the time at which it is attained are strongly affected by the hole mobility. Oxide fields larger than the intrinsic breakdown strength of the oxide can arise from the holes collecting at the interface and their image charge in the gate electrode. These high fields persist for times of the order of picoseconds. It is not known how long these fields must persist to initiate SEGR. >
90 citations
TL;DR: It is shown how the model, applicable to a trilayer film such as Fe/Cr/Fe or Co/Ru/Co, generates an infinite sum of terms with coefficients A 12 ,B 12 ,... in the coupling energy, extending beyond the Heisenberg-like A 12 term of bilinear coupling between the moments of the ferromagnets.
Abstract: We consider a free-electron model of exchange coupling between transition-metal ferromagnetic films separated by a paramagnetic metal spacer. The minority-spin energy bands in the ferromagnets are matched to those of the paramagnetic spacer. The majority-spin electrons experience a repulsive potential arising from the lack of corresponding states in the spacer. The height of the potential barrier is equal to the exchange-energy gap in the ferromagnets. We show how the model, applicable to a trilayer film such as Fe/Cr/Fe or Co/Ru/Co, generates an infinite sum of terms with coefficients A 12 ,B 12 ,... in the coupling energy, extending beyond the Heisenberg-like A 12 term of bilinear coupling between the moments of the ferromagnets
89 citations
TL;DR: An algorithm is presented to relatively align two 3-D sensors using targets that are tracked by both sensors and estimates and removes sensor biases and sensor frame orientation errors.
Abstract: An algorithm is presented to relatively align two 3-D sensors using targets that are tracked by both sensors. The algorithm estimates and removes sensor biases and sensor frame orientation errors. To illustrate this technique, the alignment algorithm is applied to simulated track data from two sensors. >
87 citations
TL;DR: These new bandpass matched filters show improved discrimination capability with respect to the conventional matched spatial filter and improved signal-to-noise ratio withrespect to the phase-only matched filter.
Abstract: We introduce optical wavelet matched filters that perform the wavelet transforms for edge enhancement and perform correlations between the wavelet coefficients for shift-invariant pattern recognition. These new bandpass matched filters show improved discrimination capability with respect to the conventional matched spatial filter and improved signal-to-noise ratio with respect to the phase-only matched filter.
79 citations
TL;DR: The asymptotic performance of the recursive, nonparametric method, dubbed “adaptive mixtures” for its data-driven development of a mixture model approximation to the true density, is investigated using the method of sieves.
70 citations
TL;DR: In this paper, the properties of two high-power magnetostrictive materials, TbxDy1-x and TbxsDy 1-xFe2 (Terfenol-D), were reviewed.
Abstract: Magnetic materials capable of producing strains greater than 10-3 have received con siderable attention over the last few years. This is partly due to recent interest in fields such as de formable surfaces, active vibration control, and precision machining, where large forces and small displacements are required, and partly due to the commercial availability of the new materials. These magnetostrictive materials have the advantage of functioning under adverse environmental conditions and elevated temperatures, plus the capability to regulate stress and displacements at low frequencies. In this paper, we review the properties of two high power magnetostrictive materials: (1) TbxDy1-x alloys and (2) TbxDy 1-xFe2 (Terfenol-D) alloys (0 ≤ x ≤ 1).
70 citations
01 Jul 1993
TL;DR: In this paper, the authors used finite element analysis to develop J and CTOD estimation strategies appropriate for application to both shallow and deep crack SE(B) specimens, using Ramberg Osgood strain hardening exponents between 4 and 50.
Abstract: Fracture toughness values determined using shallow cracked single edge notch bend, SE(B), specimens of structural thickness are useful for structural integrity assessments. However, testing standards have not yet incorporated formulas that permit evaluation of J and CTOD for shallow cracks from experimentally measured quantities (i.e. load, crack mouth opening displacement (CMOD), and load line displacement (LLD)). Results from two dimensional plane strain finite - element analyses are used to develop J and CTOD estimation strategies appropriate for application to both shallow and deep crack SE(B) specimens. Crack depth to specimen width ( a/W ) ratios between 0.05 and 0.70 are modelled using Ramberg Osgood strain hardening exponents ( n ) between 4 and 50. The estimation formulas divide J and CTOD into small scale yielding ( SSY ) and large scale yielding ( LSY ) components. For each case, the SSY component is determined by the linear elastic stress intensity factor, K I . The formulas differ in evaluation of the LSY component. The techniques considered include: estimating J or CTOD from plastic work based on load line displacement ( A pl | LLD ), from plastic work based on crack mouth opening displacement ( A pl | CMOD ), and from the plastic component of crack mouth opening displacement (CMOD pl ). A pl | CMOD provides the most accurate J estimation possible. The finite - element results for all conditions investigated fall within 9% of the following formula:
TL;DR: In this article, a two-stage alpha-beta-gamma estimator is proposed as an alternative to adaptive gain versions of the alpha, beta and alpha, gamma, and gamma filters for tracking maneuvering targets.
Abstract: The two-stage alpha-beta-gamma estimator is proposed as an alternative to adaptive gain versions of the alpha, beta and alpha, beta, and gamma filters for tracking maneuvering targets. The aim is to achieve fixed-gain, variable dimension filtering. The two-stage alpha-beta-gamma estimator is derived from the two-stage Kalman estimator, and the noise variance reduction matrix and steady-state error covariance matrix are given as a function of the steady-state gains. A procedure for filter parameter selection is also given along with a technique for maneuver response and a gain scheduling technique for initialization. The kinematic constraint for constant speed targets is also incorporated into the two-stage estimator to form the two-stage alpha-beta-gamma-lambda estimator. Simulation results are given to compare the performances of other estimators with that of the alpha-beta-gamma filter. >
TL;DR: A theoretical model for molecular computing in which Boolean logic is implemented in parallel networks of individual MTs interconnected by MAPs and the simulations demonstrate symbolic manipulation in a connectionist system and suggest that MT-MAP networks can perform computation in living cells and are candidates for future molecular computing devices.
Abstract: Adaptive behaviors and dynamic activities within living cells are organized by the cytoskeleton: intracellular networks of interconnected protein polymers which include microtubules (MTs), actin, intermediate filaments, microtubule associated proteins (MAPs) and other protein structures. Cooperative interactions among cytoskeletal protein subunit conformational states have been used to model signal transmission and information processing. In the present work we present a theoretical model for molecular computing in which Boolean logic is implemented in parallel networks of individual MTs interconnected by MAPs. Conformational signals propagate on MTs as in data buses and in the model MAPs are considered as Boolean operators, either as bit-lines (like MTs) where a signal can be transported unchanged between MTs ('BUS-MAP'), or as bit-lines where a Boolean operation is performed in one of the two MAP-MT attachments ('LOGIC-MAP'). Three logic MAPs have been defined ('NOT-MAP, 'AND-MAP', 'XOR-MAP') and used to demonstrate addition, subtraction and other arithmetic operations. Although our choice of Boolean logic is arbitrary, the simulations demonstrate symbolic manipulation in a connectionist system and suggest that MT-MAP networks can perform computation in living cells and are candidates for future molecular computing devices.
TL;DR: In this article, the authors observed up to 8 orders (ital n) in the spectra of parametric x-radiation in the range 5-40 keV, produced by the interaction of a 90 MeV electron beam with mosaic graphite and single silicon crystals.
Abstract: We have observed up to 8 orders ([ital n]) in the spectra of parametric x-radiation (PXR) in the range 5--40 keV, produced by the interaction of a 90 MeV electron beam with mosaic graphite and single silicon crystals. The measured yields and intensity ratios, [ital I]([ital n][ge]2)/[ital I]([ital n]=1), in graphite are not in agreement with the theory of PXR for mosaic crystals. In comparison, the ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals. The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with theoretical predictions.
TL;DR: The 96N mutant of bacteriorhodopsin (BR) has been successfully entrapped in a sol-gel glass and retains it light-sensitive properties when immobilized at pH 9.0.
TL;DR: A generalized formulation of inviscid incompressible hydrodynamics as a system of conservation laws subject to a one-sided density constraint is used as the basis of a numerical algorithm for a variety of hydrodynamic free surface problems as discussed by the authors.
TL;DR: Wavelet applications in turbulence onset, spectrum analyses, fractal aggregates, and bubble-chamber particle-track pattern-recognition problems are indicated but are modeled, in the interest of simplicity, in a one-dimensional example.
Abstract: Given an astrophysical observation with an arbitrary carrier frequency and an unknown scale under an additive white noise, s'(t)\ensuremath{\equiv}s(\ensuremath{\alpha}t)+n(t), its wavelet transform is W'(a,b)\ensuremath{\equiv}(s'(t),${\mathit{h}}_{\mathit{a}\mathit{b}}$(t)), as computed by the inner product with a daughter wavelet ${\mathit{h}}_{\mathit{a}\mathit{b}}$(t)\ensuremath{\equiv}h((t-b)/a)/a. W'(a,b) equals the original transform W(a,b)\ensuremath{\equiv}(s(t),${\mathit{h}}_{\mathit{a}\mathit{b}}$(t)) displaced along the radial direction W'(a,b)=W(\ensuremath{\alpha}a,\ensuremath{\alpha}b) plus noise in the time-scale joint-representation plane. A bank of wedge-shaped detectors collects those displaced transforms W'(a,b) to create a set of invariant features. These features are fed into a two-layer feed-forward artificial neural network, to interpolate discrete sampling, as demonstrated successfully for real-time-signal automatic classification. Useful wavelet applications in turbulence onset, spectrum analyses, fractal aggregates, and bubble-chamber particle-track pattern-recognition problems are indicated but are modeled, in the interest of simplicity, in a one-dimensional example.
TL;DR: In this article, the early reaction chemistry of NTO, (3-Nitro-1,2,4-triazol-5-one) induced by, drop weight impact, shock, heat and radiation has been investigated.
Abstract: The early reaction chemistry of NTO, (3-Nitro-1,2,4-triazol-5-one) induced by, drop weight impact, shock, heat and radiation has been investigated. X-ray photoelectron spectroscopy XPS and chemical ionization mass spectrometry CIMS were employed to observe and identify the partial decomposition products in the damaged samples. Several reaction intermediates have been identified, the focus of the reaction being the single nitro group present on this molecule. XPS spectra indicated in all cases the loss of NO2 concentration in response to damage. Additional chemical states were suggested in the XPS N(ls) spectrum by the appearance of a new peak at a binding energy below that of the triazol ring nitrogens. Mass spectrometry provided the molecularly specific information needed to identify molecular species resulting from the decomposition reactions. Relative to the parent NTO molecule, mass peaks were observed that corresponded to the loss of one O atom, an NO fragment, and a HONO.
TL;DR: In this paper, the authors explore the possibility of modeling such temporal variations of the sunspot number with a deterministic dynamical system of relatively low order, which manifests on/off intermittency in which the cyclic variations of solar activity switch off almost completely for extended periods.
Abstract: A prominent feature of the solar cycle is the rise and fall of the number of sunspots on the surface with a timescale of approximately eleven years. The mathematical description of this behavior is complicated by the interruption of the cycle for 75 years starting around 1650. Similar previous intermissions of this kind are implied by the available data. We explore the possibility of modeling such temporal variations of the sunspot number with a deterministic dynamical system of relatively low order. The system we propose manifests on/off intermittency in which the cyclic variations of the solar activity switch off almost completely for extended periods. We also offer an explanation of the variation of the fluctuating part of the sunspot number over the cycle.
TL;DR: In this paper, an analytic expression for the alpha of an alpha-beta-gamma filter in terms of the tracking index was derived, which permits direct calculation of alpha from a simple analytic expression instead of using numerical techniques.
Abstract: The authors derive an analytic expression for the alpha of an alpha-beta-gamma filter in terms of the tracking index. The result permits a direct calculation of alpha from a simple analytic expression instead of using numerical techniques. >
TL;DR: In this article, a 200 km anomalous topographic zone was discovered using wavelet scale analysis in a 1600 km linear bathymetric profile taken northeast of Hawaii, and spectral analysis of the zone shows that the power in wavelengths shorter than 25 km averages 5-10 times lower than the surrounding topography.
Abstract: A 200 km anomalous topographic zone was discovered using wavelet scale analysis in a 1600 km linear bathymetric profile taken northeast of Hawaii. A spectral analysis of the zone shows that the power in wavelengths shorter than 25 km averages 5–10 times lower than the surrounding topography. Conversely, wavelengths longer than 25 km have 2–3 times greater power than nearby topography. Further research reveals that this low-frequency zone correlates with the eastern flank of a regional bathymetric high which has been described by J. Mammerickx [1981]. Details of the features suggest that this zone is a small, abandoned, slow-spreading rift overprinted by a regional thermal swell. The magnitude of the feature is smaller than other, known, abandoned spreading centers, making it easy to overlook without the application of the wavelet transform.
TL;DR: Two methods are tested for improving multispectral neural network classification: (a) new criterion functions and (b) incorporating contextual information, which yields significant improvements in classification accuracy over the standard least mean squares energy function.
TL;DR: The authors present a resonance scattering analysis of the echoes returned by a submerged, air-filled, elastic spherical shell, and also from a rigid sphere, when they are insonified by sound pulses.
Abstract: The authors present a resonance scattering analysis of the echoes returned by a submerged, air-filled, elastic spherical shell, and also from a rigid sphere, when they are insonified by sound pulses. They consider arbitrary pulsed incidences of any duration, carrier frequency, envelope and shape. The approach is equally effective in the frequency and the time domains. They compare backscattered echoes returned by the structures under study in various instances, which are predicted by exact modal approaches, and by the approximate Kirchhoff method. The effects of pulse duration are examined, and so are the various kinds of resonances that develop when a shell is insonified by extremely narrowband pulses. Also examined is the concept of an impulse sonar, for incident pulses that are short- and broadbanded. An inverse scattering analysis shows how and how well physical target characteristics extracted in situ from the remotely sensed echoes can be used for target identification. Various sample cases are constructed and solved and the results interpreted. >
TL;DR: The structure and magnetic properties of Fe/Cu multilayered films with a constant total Fe thickness of 1050 A but varying Fe-layer thickness from 6.3 to 42 A and varying Cu to Fe thickness ratio from 1 to 3 were investigated using x-ray diffraction, XRD, XAFS, and magnetic measurements.
Abstract: The structure and magnetic properties of Fe/Cu multilayered films with a constant total Fe thickness of 1050 A but varying Fe-layer thickness from 6.3 to 42 A and varying Cu to Fe thickness ratio from 1 to 3 were investigated using x-ray diffraction (XRD), x-ray absorption fine-structure (XAFS) spectroscopy, and magnetic measurements. Samples were prepared at room temperature on mica, glass, and silicon substrates using the dc-magnetron-sputtering method. For films with the same Fe-layer thickness, it was found that the magnetic moment of Fe decreases with increasing thickness ratio of Cu to Fe. For films with a Cu to Fe thickness ratio of 3, it was found that the magnetic moment of Fe decreases with decreasing thickness of the individual Fe layers. XRD and XAFS results revealed that in the multilayered films, Cu has a well-defined fcc structure with minimal amount of structural disorder independent of the individual layer thickness or thickness ratio. On the other hand, quantitative analysis of EXAFS data revealed that the crystal structure of Fe changes with decreasing thickness of the Fe layers from distorted bcc (for 42- and 21-A-thick Fe layers) to fcc (for 10.5- and 6.3-A-thick Fe layers) in films with the Cu layermore » three times thicker than the Fe layer. The single-phase fcc Fe of the 6.3-A Fe/19-A Cu multilayered film was found to have a lattice constant of 3.596 A and is ferromagnetic with a Curie temperature of 210 K and a spontaneous magnetization of [similar to]690 emu/cm[sup 3].« less
01 Nov 1993
TL;DR: In this article, a cone-kernel TFR was proposed to reveal the existence of fine structural details inherent to the signal, which can be used as supplemental information to assess the condition of the machine.
Abstract: Machinery condition has traditionally been assessed by analysis of the spectral energy density of the machine's vibration signal. Examination of time-frequency representations (TFRs) of constant-speed machinery data reveals vibration features that demonstrate variation in frequency over a short time period and thus cannot be adequately characterized by the power spectrum. These features may be used as supplemental information to assess the condition of the machine. Although the spectrogram provides a general indication of the time-varying spectrum, new representations such as the "cone-kernel" TFR reveal the existence of fine structural details inherent to the signal. >
TL;DR: Results indicate that dedicated auxiliary generators driven from propulsion gas turbine engines are the preferred method of powering electric gun PFNs from ship drive-train equipment.
Abstract: Alternative power system architectures and interface technologies for driving high-energy pulsed loads from the propulsion equipment of naval surface combatants are compared. Gas turbine mechanical and gas turbine integrated electric drive propulsion trains are considered as prime power sources. Focus is on the energy path between the ship's prime power and the pulsed load, comparing system candidates on a size, weight, and component cost basis. A capacitor-based pulse forming network (PFN) supplying an electrothermal chemical gun is utilized as the common load for all configurations. Results indicate that dedicated auxiliary generators driven from propulsion gas turbine engines are the preferred method of powering electric gun PFNs from ship drive-train equipment. Auxiliary generator-based systems are compact and lightweight over a wide power range, are equally attractive with both electric and mechanical drive trains, and demonstrate retrofit potential to the current fleet. >
19 Apr 1993
TL;DR: In this paper, the added mass coefficients for two and three-dimensional submerged bodies were calculated using a low-order panel code and the source and dipole strengths, and the panel surface area for each panel, were used to compute the integrals needed for added mass in all six degrees of motions.
Abstract: The added mass coefficients for two and three-dimensional submerged bodies were calculated using a low-order panel code. The source and dipole strengths, and the panel surface area for each panel, were used to compute the integrals needed for added mass in all six degrees of motions. Several applications of this method were used in comparing the results with the theoretical, when available, experimental or other numerical results. The method was found to be successful in predicting the added mass coefficients using relatively low numbers of panels.
TL;DR: Detailed calculations have revealed the atomic displacements by which the clustered vacancies collapse in a body-centered-cubic lattice collapse and stable and stable Burgers-vector dislocations have been identified in dipole configurations.
Abstract: Molecular-dynamics modeling has been used to study the evolution of a dislocation nanostructure from the shock compression of a vacancy cluster in a body-centered-cubic lattice. Detailed calculations have revealed the atomic displacements by which the clustered vacancies collapse. The energetics of the process were also monitored in detail. Stable 〈100〉 and 〈111〉 Burgers-vector dislocations have been identified in dipole configurations. These dislocations relate to a periodic nanodislocation dipole structure proposed in a model by Armstrong, Miller, and Sandusky (AMS) to occur by the reaction of dislocations just behind the shock front. The postshock stability of the AMS dipole nanostructure was also evaluated on a molecular-dynamics basis and the stress-strain behaviors of the crystal for the pre- and postshock compression conditions were compared.