Naval Surface Warfare Center

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: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Automated detection and classification of sea mines in sonar imagery

Abstract: An advanced capability for automated detection and classification of sea mines in sonar imagery has been developed. The advanced mine detection and classification (AMDAC) algorithm consists of an improved detection density algorithm, a classification feature extractor that uses a stepwise feature selection strategy, a k-nearest neighbor attractor-based neural network (KNN) classifier, and an optimal discriminatory filter classifier. The detection stage uses a nonlinear matched filter to identify mine-size regions in the sonar image that closely match a mine's signature. For each detected mine-like region, the feature extractor calculates a large set of candidate classification features. A stepwise feature selection process then determines the subset features that optimizes probability of detection and probability of classification for each of the classifiers while minimizing false alarms.

High‐Temperature Chemistry and Oxidation of ZrB2 Ceramics Containing SiC, Si3N4, Ta5Si3, and TaSi2

Abstract: The effect of Si 3 N 4 , Ta 5 Si 3 , and TaSi 2 additions on the oxidation behavior of ZrB 2 was characterized at 1200°-1500°C and compared with both ZrB 2 and ZrB 2 /SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB 2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si 3 N 4 -modified ceramics increased with increasing Si 3 N 4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB 2 , with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta 5 Si 3 , 30 vol% TaSi 2 , 35 vol% Si 3 N 4 , or 20 vol% Si 3 N 4 with 10 mol% CrB 2 . These materials exceeded the oxidation resistance of the ZrB 2 /SiC ceramics below 1300°-1400°C. However, the ZrB 2 /SiC ceramics showed slightly superior oxidation resistance at 1500°C.

Thermomechanical response of AL-6XN stainless steel over a wide range of strain rates and temperatures

Abstract: To understand and model the thermomechanical response of AL-6XN stainless steel, uniaxial compression tests are performed on cylindrical samples, using an Instron servohydraulic testing machine and UCSD's enhanced Hopkinson technique. True strains exceeding 40% are achieved in these tests, over the range of strain rates from 0.001/s to about 8000/s, and at initial temperatures from 77 to 1000 K. In an effort to understand the underlying deformation mechanisms, some interrupted tests involving temperature and low- and high-strain rates, are also performed. The microstructure of the undeformed and deformed samples is observed by optical microscopy. The experimental results show: (1) AL-6XN stainless steel displays good ductility (strain >40%) at low temperatures and high-strain rates, with its ductility increasing with temperature; (2) at high-strain rates and 77 K initial temperature, adiabatic shearbands develop at strains exceeding about 40%, and the sample breaks, while at low-strain rates and 77 K, axial microcracks develop at strains close to 50% or greater; (3) dynamic strain aging occurs at temperatures between 500 and 1000 K and at a strain rate of 0.001/s, with the peak value of the stress occurring at about 800 K, and becoming more pronounced with increasing strain and less pronounced with increasing strain rate; and (4) the microstructure of this material evolves with temperature, but is not very sensitive to the changes in the strain rate. Finally, based on the mechanism of dislocation motion, paralleled with a systematic experimental investigation, a physically based model is developed for the deformation behavior of this material, including the effect of viscous drag on the motion of dislocations, but excluding the dynamic strain aging effects. The model predictions are compared with the results of the experiments. Good agreement between the theoretical predictions and experimental results is obtained. In order to verify the model independently of the experiments used in the modeling, additional compression tests at a strain rate of 8000/s and various initial temperatures, are performed, and the results are compared with the model predictions. Good correlation is observed.

Electroless Deposition of Conformal Nanoscale Iron Oxide on Carbon Nanoarchitectures for Electrochemical Charge Storage

Abstract: We describe a simple self-limiting electroless deposition process whereby conformal, nanoscale iron oxide (FeOx) coatings are generated at the interior and exterior surfaces of macroscopically thick (∼90 μm) carbon nanofoam paper substrates via redox reaction with aqueous K2FeO4. The resulting FeOx-carbon nanofoams are characterized as device-ready electrode structures for aqueous electrochemical capacitors and they demonstrate a 3-to-7 fold increase in charge-storage capacity relative to the native carbon nanofoam when cycled in a mild aqueous electrolyte (2.5 M Li2SO4), yielding mass-, volume-, and footprint-normalized capacitances of 84 F g−1, 121 F cm−3, and 0.85 F cm−2, respectively, even at modest FeOx loadings (27 wt %). The additional charge-storage capacity arises from faradaic pseudocapacitance of the FeOx coating, delivering specific capacitance >300 F g−1 normalized to the content of FeOx as FeOOH, as verified by electrochemical measurements and in situ X-ray absorption spectroscopy. The addit...