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

Stamped multilayer graphene laminates for disposable in-field electrodes: application to electrochemical sensing of hydrogen peroxide and glucose

Abstract: A multi-step approach is described for the fabrication of multi-layer graphene-based electrodes without the need for ink binders or post-print annealing. Graphite and nanoplatelet graphene were chemically exfoliated using a modified Hummers’ method and the dried material was thermally expanded. Expanded materials were used in a 3D printed mold and stamp to create laminate electrodes on various substrates. The laminates were examined for potential sensing applications using model systems of peroxide (H2O2) and enzymatic glucose detection. Within the context of these two assay systems, platinum nanoparticle electrodeposition and oxygen plasma treatment were examined as methods for improving sensitivity. Electrodes made from both materials displayed excellent H2O2 sensing capability compared to screen-printed carbon electrodes. Laminates made from expanded graphite and treated with platinum, detected H2O2 at a working potential of 0.3 V (vs. Ag/AgCl [0.1 M KCl]) with a 1.91 μM detection limit and sensitivity of 64 nA·μM−1·cm−2. Electrodes made from platinum treated nanoplatelet graphene had a H2O2 detection limit of 1.98 μM (at 0.3 V), and a sensitivity of 16.5 nA·μM−1·cm−2. Both types of laminate electrodes were also tested as glucose sensors via immobilization of the enzyme glucose oxidase. The expanded nanographene material exhibited a wide analytical range for glucose (3.7 μM to 9.9 mM) and a detection limit of 1.2 μM. The sensing range of laminates made from expanded graphite was slightly reduced (9.8 μM to 9.9 mM) and the detection limit for glucose was higher (18.5 μM). When tested on flexible substrates, the expanded graphite laminates demonstrated excellent adhesion and durability during testing. These properties make the electrodes adaptable to a variety of tests for field-based or wearable sensing applications.

Modeling Towed Cable Systems Dynamics

Abstract: : A method for modeling the dynamics of towed cable systems is described. The cable system is assumed to be a multiple branched system with towed bodies. These bodies may be spheres or more general vehicles having a single plane of symmetry. The motion of the two points of the system is arbitrary. The cable is modeled by a series of rigid cylinders connected end-to- end by spherical joints. It is further assumed that the physical parameters of the system and the external forces acting on it can be lumped at the connecting joints. The towed vehicles are three-dimensional bodies with linear (about a steady-state configuration) time-domain analyses. Examples are used to illustrate the analyses.

Nonlinear Discrete-Time Design Methods for Missile Flight Control Systems

Abstract: : Design methods for discrete-time linear control systems have reached an advanced level of maturity. However, the direct design of nonlinear discrete-time control systems remains to be fully developed. Although textbooks are available on nonlinear control system design literature on discrete-time nonlinear control system design is rather sparse. From an applications point-of-view, discrete-time designs are important because most controllers are implemented using digital computers. Design techniques of interest in this paper are those that permit the synthesis of discrete-time controllers for continuous-time nonlinear dynamic systems. The present work is motivated by the need to implement nonlinear control system designs synthesized using computer-aided design techniques6, 7 onboard missiles. Three different discrete-time control system design techniques have been investigated in the present research. All of them are discrete-time analogs of continuous-time nonlinear system design techniques discussed in the literature. The first approach is the discrete-time version of the state-dependent Riccati equation (SDRE) technique discussed in References 8 and 9. The second design technique is a discrete-time version of the recursive backstepping10 methodology, and employs discretized system dynamics. The third technique is the discrete-time version of the feedback linearization design approach. In this last technique, the system dynamics is first transformed into a linear, time-invariant form through the definition of state variable feedback. The transformed model is then converted into discrete-time form by defining sample-holds at the input and the outputs. The discretized is linear model is then used for control system design. All three techniques have been employed for the design of missile flight control systems. Section II will present each of the design techniques in detail.

Cutting of tantalum: Why it is so difficult and what can be done about it

Abstract: Tantalum has long drawn the ire of machinist, being particularly difficult to cut. Often referred to as being ‘gummy,’ cutting of tantalum is characterized by very thick chips, large cutting forces, and a poor surface finish on the machined surface. These unfavorable attributes of the cutting have usually been attributed to bcc tantalum's high strain-hardening capacity, relative softness, and low thermal conductivity; and a small shear plane angle. Here, we show using in situ high-speed imaging at low speeds, and ex situ chip morphology observations at higher commercial cutting speeds (625 mm/s), that the gummy nature of Ta in cutting, including the large forces and thick chips, is actually due to the prevalence of a highly unsteady plastic flow – sinuous flow – characterized by large-amplitude folding and extensive redundant deformation. The sinuous flow and the associated folding are much more amplified and extreme in tantalum (chip thickness ratio, 30–50), and with different morphology, than that observed in fcc Cu and Al (chip thickness ratio, 10–20), wherein this flow mode was first uncovered. The in situ observations are reinforced by force measurements, and chip morphology and cut-surface characterization. The observations also suggest that the sinuous flow, in the same genre of unsteady mesoscale flow modes such as shear banding and segmented flow, is quite prevalent in cutting of highly strain-hardening metal alloys. By application of a surface-adsorbing (SA) medium, e.g., permanent marker ink, to the initial workpiece surface, we show that sinuous flow can be disrupted and replaced by a more energetically favorable flow mode – segmented flow – with thin chips and >70% reduction in the cutting force. This flow disruption is mediated by a local ductile-to-brittle transition in the deformation zone, due to the action of the SA medium – a mechanochemical (MC) effect in large-strain deformation of metals. Equally importantly, the MC effect and underlying segmented flow are beneficial also for machined surface quality – producing nearly an order of magnitude improvement in the surface finish, creating a surface with minimal residual plastic strain, and reducing level of material pull-out. Thus, by use of the SA medium and triggering the MC effect, a promising new opportunity is demonstrated for improving the machinability of Ta by ameliorating its gumminess. The results could enhance the viability of Ta for applications such as gun barrel liners – applications for which it has been hitherto considered but discarded due to its poor machining characteristics.