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.

Ionizing radiation tolerance of high-performance SiGe HBT's grown by UHV/CVD

Abstract: The ionizing radiation tolerance of high-performance SiGe HBTs, grown by UHV/CVD and optimized for 77 K, has been investigated for the first time. Results at both 300 K and 77 K indicate that this SiGe technology is inherently radiation tolerant without additional processing steps. Perimeter-to-area analysis show parallel shifts in the collector and base current density for total radiation doses below 1.0 Mrad(Si). Relatively minor degradation in the current gain characteristics is observed for SiGe HBTs exposed to 1.0 Mrad(Si) of Co/sup 60/ gamma radiation, indicating that the technology is robust for many applications requiring a high degree of ionizing radiation tolerance. 1/f noise measurements made pre- and post-radiation show the appearance of a generation-recombination center in some of the SiGe HBTs after a total-dose exposure to 10.0 Mrad(Si).

Electrochemical Li-ion storage in defect spinel iron oxides: the critical role of cation vacancies

Abstract: Rechargeable lithium-ion batteries are the preferred power source for consumer electronic devices, but the cost and toxicity of many cathode materials limit their scale-up. Worldwide research efforts are addressing this concern by transitioning from conventional Co- and Ni-based intercalation hosts towards Fe- and Mn-based alternatives. The unfavorable energetics of the Fe2+/3+redox couple and limited Li-insertion capacities render the use of iron oxides impractical. We address this limitation with the defect spinel ferrite γ-Fe2O3 as a model structure for Li-ion insertion by replacing a fraction of the Fe3+ sites with highly oxidized Mo6+ to generate cation vacancies that shift the onset of Li-ion insertion to more positive potentials as well as increase capacity. In the present study, native and Mo-substituted iron oxides are synthesized via base-catalyzed precipitation in aqueous media, yielding nanocrystalline spinel materials that also exhibit short-range disorder characteristic of a proton-stabilized structure. The Mo-substituted ferrite reported herein is estimated to have ∼3× as many cation vacancies as γ-Fe2O3 with a corresponding increase in the Li-ion capacity to >100 mA h g−1 between 4.1 and 2.0 V vs.Li/Li+. This dual enhancement in capacity and insertion potential will enable these and related defect spinel ferrites to be explored as positive electrode materials for lithium batteries, while retaining the cost advantages of a material whose metal composition is still predominately iron based.

Computational assessment of ballistic impact on a high strength structural steel/polyurea composite plate

Abstract: Ballistic impact on a polyurea retrofitted high strength structural steel plate is simulated and validated. A soft material model for polyurea, which is capable of capturing complex mechanical behavior characterized by large strains, hysteresis, rate sensitivity, stress softening (Mullins effect), and deviatoric and volumetric plasticity, is calibrated against several uniaxial tension experiments and a three-dimensional release wave experiment to capture both the material point and bulk behaviors. A porous plasticity model is employed to model the high strength structural steel and localization elements are included to capture adiabatic shear bands and strain localization. The computational capabilities of these models are demonstrated by the prediction of the target plate displacement, which shows excellent agreement with experiments.

System-wide versus component-specific trust using multiple aids.

Abstract: Previous research in operator trust toward automated aids has focused primarily on single aids. The current study focuses on how operator trust is affected by the presence of multiple aids. Two competing theories of multiple-trust are presented. A component-specific trust theory predicts that operators will differentially place their trust in automated aids that vary in reliability. A system-wide trust theory predicts that operators will treat multiple imperfect aids as one "system" and merge their trust across aids despite differences in the aids' reliability. A simulated flight task was used to test these theories, whereby operators performed a pursuit tracking task while concurrently monitoring multiple system gauges that were augmented with perfect or imperfect automated aids. The data revealed that a system-wide trust theory best predicted the data; operators merged their trust across both aids, behaving toward a perfectly reliable aid in the same manner as they did towards unreliable aids.