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Institution

Naval Surface Warfare Center

FacilityWashington D.C., District of Columbia, United States
About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.


Papers
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TL;DR: In this paper, a second-order projection method for the incompressible Navier-Stokes equations on multiply connected domains with a logically rectangular quadrilateral grid is described, where diffusion, pressure gradient, and divergence terms are discretized using standard finite difference approximations.
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.

24 citations

Journal ArticleDOI
TL;DR: In this article, the oxidation state and local structure of hydrated ambigel V 2 O 5.0.5H 2 O composite cathodes cycled in a nonaqueous electrolyte lithium cell were monitored by X-ray absorption spectroscopy under in situ conditions.
Abstract: We examined the oxidation state and local structure of hydrated ambigel V 2 O 5 .0.5H 2 O composite cathodes cycled in a nonaqueous electrolyte lithium cell. Changes in the oxidation state and local structure were monitored by X-ray absorption spectroscopy under in situ conditions. The cathodes had initial discharge capacities in the range 440-480 mAh/g, which correspond to an intercalation of 3.1-3.4 Li per V 2 O 5 .0.5H 2 O. Analyses of X-ray absorption near-edge structure data reveal that the average oxidation state of vanadium for discharged cathodes increased with cycling in the range of 1-17 cycles and then remained unchanged with further cycling. The oxidation state for charged cathodes remained relatively unchanged with cycling in the range of 1-40 cycles. The lack of strong contributions from higher coordination spheres in the Fourier transforms of extended X-ray absorption fine structure spectra of charged and discharged cathodes indicate that the amorphous nature of the material is retained during cycling. However, a significant increase in the amplitude of the V-O contribution is observed with prolonged cycling for both discharged and charged cathodes, which is likely due to the formation of irreversible phases with increased local symmetry for the V-O coordination geometry. The observed results for the ambigel material cycled in the range of 1-16 cycles are consistent with results previously observed for an aerogel material.

24 citations

Journal ArticleDOI
TL;DR: In this article, a finite element (FE) method was used to predict the scattered pressure near the outer surface of the target, and then this local target response was propagated via a Helmholtz integral to distant observation points.
Abstract: In March 2010, a series of measurements were conducted to collect synthetic aperture sonar (SAS) data from objects placed on a water–sediment interface. The processed data were compared to two models that included the scattering of an acoustic field from an object on a water–sediment interface. In one model, finite-element (FE) methods were used to predict the scattered pressure near the outer surface of the target, and then this local target response was propagated via a Helmholtz integral to distant observation points. Due to the computational burden of the FE model and Helmholtz integral, a second model utilizing a fast ray model for propagation was developed to track time-of-flight wave packets, which propagate to and subsequently scatter from an object. Rays were associated with image sources and receivers, which account for interactions with the water–sediment interface. Within the ray model, target scattering is reduced to a convolution of a free-field scattering amplitude and an incident acoustic field at the target location. A simulated or measured scattered free-field pressure from a complicated target can be reduced to a (complex) scattering amplitude, and this amplitude then can be used within the ray model via interpolation. The ray model permits the rapid generation of realistic pings suitable for SAS processing and the analysis of acoustic color templates. Results from FE/Helmholtz calculations and FE/ray model calculations are compared to measurements, where the target is a solid aluminum replica of an inert 100-mm unexploded ordnance (UXO).

24 citations

Journal ArticleDOI
TL;DR: In this article, a conformal nanoscale coatings of Na+-birnessite manganese oxide (MnOx) produced via redox reaction between aqueous permanganate (NaMnO4·H2O) and the carbon surfaces of fiber-paper-supported carbon nanofoams are converted to LiMn2O4 spinel through topotactic exchange of Na + for Li+ in the as-deposited lamellar birnessite, followed by mild thermal treatments to complete the transformation to spinel
Abstract: Conformal nanoscale coatings of Na+-birnessite manganese oxide (MnOx) produced via redox reaction between aqueous permanganate (NaMnO4·H2O) and the carbon surfaces of fiber-paper-supported carbon nanofoams are converted to LiMn2O4 spinel through topotactic exchange of Na+ for Li+ in the as-deposited lamellar birnessite, followed by mild thermal treatments to complete the transformation to LiMn2O4. The evolution of the birnessite-to-spinel conversion is verified with X-ray diffraction, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy, electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The mild conditions used to convert birnessite to spinel ensure that the conformal nanoscale nature of the oxide coating is retained throughout the macroscopically thick (170 μm) carbon nanofoam substrate during the conversion process. The architecture of the LiMn2O4–carbon nanofoam facilitates rapid ion/electron transport, enabling the LiMn2O4 to insert and extract Li+ from aqueous electrolytes at scan rates as high as 25 mV s−1, and with a relaxation time of 37 s as derived from electrochemical impedance. This architectural expression of nanoscale LiMn2O4 delivers full theoretical capacity (148 mA h g−1) at 2 mV s−1.

24 citations


Authors

Showing all 2860 results

NameH-indexPapersCitations
James A. Yorke10144544101
Edward Ott10166944649
Sokrates T. Pantelides9480637427
J. M. D. Coey8174836364
Celso Grebogi7648822450
David N. Seidman7459523715
Mingzhou Ding6925617098
C. L. Cocke513128185
Hairong Qi503279909
Kevin J. Hemker4923110236
William L. Ditto431937991
Carey E. Priebe434048499
Clifford George412355110
Judith L. Flippen-Anderson402056110
Mortimer J. Kamlet3910812071
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20233
20227
202172
202071
201982
201884