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.

Sonar automatic target recognition for underwater UXO remediation

Abstract: Automatic target recognition (ATR) for unexploded ordnance (UXO) detection and classification using sonar data of opportunity from open oceans survey sites is an open research area. The goal here is to develop ATR spanning real-aperture and synthetic aperture sonar imagery. The classical paradigm of anomaly detection in images breaks down in cluttered and noisy environments. In this work we present an upgraded and ultimately more robust approach to object detection and classification in image sensor data. In this approach, object detection is performed using an in-situ weighted highlight-shadow detector; features are generated on geometric moments in the imaging domain; and finally, classification is performed using an Ada-boosted decision tree classifier. These techniques are demonstrated on simulated real aperture sonar data with varying noise levels.

Capacity Fade of 26650 Lithium-Ion Phosphate Batteries Considered for Use Within a Pulsed-Power System’s Prime Power Supply

Abstract: There is considerable need for a mobile, reliable, efficient, and compact prime power supply for use in a host of directed energy applications. Recent improvements in the energy and power density of electrochemical lithium-ion batteries have made them a very viable option for these types of applications where fast and rep-rate operation is of interest. Despite the proven ability of lithium-ion batteries to source high currents, it is still unclear how they age when they are used to repeatedly source high-rate currents in a pulsed manner, as they must when used in a repetitive rate prime power supply. Similarly, it is unclear how elevated rate recharge affects the life of the battery. Research has been performed at University of Texas at Arlington in which high-power, 2.6 Ah lithium-ion batteries have been repeatedly discharged and recharged at high pulsed rates. This paper will discuss the potential of lithium-ion batteries for use in these applications and will present experimental results performed when two 2.6 Ah cells were both discharged at 28 A (10.8C) and recharged at 9 A (3.5C) to 2.5 and 2.0 V, respectively.

A comparative in situ X-ray absorption spectroscopy study of nanophase V2O5 aerogel and ambigel cathodes

Abstract: We examined the evolution of the oxidation state and atomic structure of V in nanophase V 2 O 5 aerogel and ambigel cathodes under in situ conditions using X-ray absorption spectroscopy (XAS). We show that the oxidation state of V in V 2 O 5 aerogel and ambigel cathodes heated under vacuum (100 μ Torr) at 220°C for 16 h is similar to that of V in a commercially obtained sample of orthorhombic V 2 O 5 . However, the local structure of V in aerogel and ambigel V 2 O 5 has a higher degree of local symmetry relative to orthorhombic V 2 O 5 and/or the average V-O bond length is greater than that of orthorhombic V 2 O 5 . Furthermore, we show that during the first cycle of discharge, the degree of Li insertion (x in Li x V 2 O 5 ) for the ambigel cathode is greater than that of the aerogel cathode (x = 3.06 for the ambigel cathode compared to x=2.68 for the aerogel cathode) for the same cut-off voltage. Accordingly, the observed V K-edge energy shift for the fully discharged ambigel cathode is greater than that observed for the fully discharged aerogel cathode, and hence, the extent of reduction of pentavalent V is greater for the ambigel cathode. In both cases, the extent of reduction of the V is consistent with the amount of Li inserted (i. e., Li x V 2 O 5 ). Initially, pentavalent V is reduced to tetravalent V in the intercalation range 0 2). Analyses of Fourier transform data reveal that V has a higher degree of local symmetry in the discharged state relative to that of the charged state.

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. >

Ab initio studies of crystalline nitromethane under high pressure.

Abstract: We have studied the mechanical compressibility and band structure of solid nitromethane both in equilibrium and compressed states using Hartree-Fock and density functional theory (DFT) with atom-centered all-electron linear combination of atomic orbitals basis sets. Hartree-Fock calculations with a 6-21G basis set, uncorrected for basis set superposition error, gave the best agreement with experimental compression studies. These results may be due to the cancellation of basis set superposition error with dispersion force errors. The equilibrium DFT band gap is comparable to the lowest-energy feature in electron-impact spectroscopy of nitromethane but underpredicts the optical absorption gap; we interpret these features in terms of the presence of tightly bound excitons. Only minor changes in the gap are observed under hydrostatic compression.