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Showing papers by "Naval Surface Warfare Center published in 2016"


Journal ArticleDOI
TL;DR: This work examines the PIR between alumina and PVDF to further explain the reaction mechanism of the Al/PVDF system and shows a direct correlation between the amount of alumina in the PVDF film and the relative signal intensity of hydrogen fluoride release (HF).
Abstract: Energetic thin films with high mass loadings of nanosized components have been recently fabricated using electrospray deposition. These films are composed of aluminum nanoparticles (nAl) homogeneously dispersed in an energetic fluoropolymer binder, poly(vinylidene fluoride) (PVDF). The nascent oxide shell of the nAl has been previously shown to undergo a preignition reaction (PIR) with fluoropolymers such as polytetrafluoroethylene (PTFE). This work examines the PIR between alumina and PVDF to further explain the reaction mechanism of the Al/PVDF system. Temperature jump (T-jump) ignition experiments in air, argon, and vacuum environments showed that the nAl is fluorinated by gas phase species due to a decrease in reactivity in a vacuum. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC) was used to confirm the occurrence of a PIR, and gas phase products during the PIR and fluorination of nAl were investigated with temperature jump time-of-flight mass spectrometry (T-jump ...

132 citations


Journal ArticleDOI
01 Feb 2016
TL;DR: In this article, a central limit theorem for the components of the largest eigenvectors of the adjacency matrix of a finite-dimensional random dot product graph whose true latent positions are unknown is proved.
Abstract: We prove a central limit theorem for the components of the largest eigenvectors of the adjacency matrix of a finite-dimensional random dot product graph whose true latent positions are unknown. We use the spectral embedding of the adjacency matrix to construct consistent estimates for the latent positions, and we show that the appropriately scaled differences between the estimated and true latent positions converge to a mixture of Gaussian random variables. We state several corollaries, including an alternate proof of a central limit theorem for the first eigenvector of the adjacency matrix of an Erdos-Renyi random graph.

99 citations


Journal ArticleDOI
TL;DR: This mini-review examines the approach to assessments of ship biofouling among sectors (industry, biosecurity and marine science) and the implications for existing and emerging management of bioFouling.
Abstract: Biofouling exerts a frictional and cost penalty on ships and is a direct cause of invasion by marine species. These negative consequences provide a unifying purpose for the maritime industry and biosecurity managers to prevent biofouling accumulation and transfer, but important gaps exist between these sectors. This mini-review examines the approach to assessments of ship biofouling among sectors (industry, biosecurity and marine science) and the implications for existing and emerging management of biofouling. The primary distinctions between industry and biosecurity in assessment of vessels biofouling revolve around the resolution of biological information collected and the specific wetted surface areas of primary concern to each sector. The morphological characteristics of biofouling and their effects on propulsion dynamics are of primary concern to industry, with an almost exclusive focus on the vertical sides and flat bottom of hulls and an emphasis on antifouling and operational performance. In contrast, the identity, biogeography, and ecology of translocated organisms is of highest concern to invasion researchers and biosecurity managers and policymakers, especially as it relates to species with known histories of invasion elsewhere. Current management practices often provide adequate, although not complete, provision for hull surfaces, but niche areas are well known to enhance biosecurity risk. As regulations to prevent invasions emerge in this arena, there is a growing opportunity for industry, biosecurity and academic stakeholders to collaborate and harmonize efforts to assess and manage biofouling of ships that should lead to more comprehensive biofouling solutions that promote industry goals while reducing biosecurity risk and greenhouse gas emissions.

82 citations


Journal ArticleDOI
20 Jun 2016
TL;DR: In this article, a stainless steel bridged structure with a 90° overhang was fabricated using a carbon steel sacrificial support that was later removed through electrochemical etching in 41.5wt.% nitric acid with bubbling O2.
Abstract: Additive manufacturing (AM) offers the ability to fabricate complex metallic structures and shapes in a layer-by-layer process. However, overhanging surfaces often require support structures to be fabricated and minimize thermally induced distortion. Unlike polymer AM processes, soluble sacrificial support materials have not been identified and characterized for metallic materials, and, as a result, support structures in 3D printed metals must be removed using additional machining operations. In this work, we demonstrate that sacrificial metal supports can be fabricated by taking advantage of differences in the chemical and electrochemical stability between different metals. As a demonstration, a stainless steel bridged structure with a 90° overhang was fabricated using a carbon steel sacrificial support that was later removed through electrochemical etching in 41 wt.% nitric acid with bubbling O2. Open circuit potentials and potentiodynamic polarization curves were gathered to verify etch select...

76 citations


Journal ArticleDOI
TL;DR: The authors found that a combination of coaching, classroom instruction, feedback, and experiential training has a significant impact on leader performance, and organizational effectiveness improves for organizations whose leaders received the intervention.
Abstract: Although significant progress has been made in developing leadership theory and understanding the traits, skills, behaviors, and styles that make a good leader, progress in bridging the gap between theory and practice using models of leadership training and development has been slow. This research attempts to answer the question of whether leadership training and development programs in the public sector improve leader and organizational performance. The findings indicate that a combination of coaching, classroom instruction, feedback, and experiential training has a significant impact on leader performance. In addition, organizational effectiveness improves for organizations whose leaders received the intervention. This article enhances our understanding of the impact that training and development can have on leader and organizational outcomes.

76 citations


Proceedings ArticleDOI
07 May 2016
TL;DR: Using computer vision to automatically detect computer screens in photo lifelogs is investigated, and it is shown that the technique could help manage privacy in the upcoming era of wearable cameras.
Abstract: Low-cost, lightweight wearable cameras let us record (or 'lifelog') our lives from a 'first-person' perspective for purposes ranging from fun to therapy. But they also capture private information that people may not want to be recorded, especially if images are stored in the cloud or visible to other people. For example, recent studies suggest that computer screens may be lifeloggers' single greatest privacy concern, because many people spend a considerable amount of time in front of devices that display private information. In this paper, we investigate using computer vision to automatically detect computer screens in photo lifelogs. We evaluate our approach on an existing in-situ dataset of 36 people who wore cameras for a week, and show that our technique could help manage privacy in the upcoming era of wearable cameras.

71 citations


Journal ArticleDOI
TL;DR: In this article, a generic four-cell module was modeled using finite element analysis to determine the sensitivity of module temperatures to cell spacing, and the effects of different heat sink materials and interface qualities were investigated.

68 citations



Journal ArticleDOI
TL;DR: A pioneering study based on a series of experiments on the operation of commercial Time-Division Long-Term Evolution systems in the presence of pulsed interfering signals in the 3550-3650 MHz band demonstrates that LTE communication using low antenna heights was not adversely affected by the pulsing interfering signal operating on adjacent frequencies irrespective of the distance of interfering transmitter.
Abstract: This letter presents a pioneering study based on a series of experiments on the operation of commercial Time-Division Long-Term Evolution (TD-LTE) systems in the presence of pulsed interfering signals in the 3550-3650 MHz band. TD-LTE operations were carried out in channels overlapping and adjacent to the high power SPN-43 radar with various frequency offsets between the two systems to evaluate the susceptibility of LTE to a high power interfering signal. Our results demonstrate that LTE communication using low antenna heights was not adversely affected by the pulsed interfering signal operating on adjacent frequencies irrespective of the distance of interfering transmitter. Performance was degraded only for very close distances (1-2 km) of overlapping frequencies of interfering transmitter.

50 citations


Journal ArticleDOI
TL;DR: In this article, a crosslinked polyurethane elastomer featuring a thermochromic molecular sensor for local temperature analysis is presented, where the thermochrome is a modified donor-acceptor Stenhouse adduct (DASA) that was dispersed homogeneously into the polymer blend in minuscule amounts.
Abstract: We present a crosslinked polyurethane elastomer featuring a thermochromic molecular sensor for local temperature analysis. The thermochrome is a modified donor-acceptor Stenhouse adduct (DASA) that was dispersed homogeneously into the polymer blend in minuscule amounts. Rapid temperature jump measurements in a pyroprobe and impacts in a Hopkinson bar show that the DASA has suitable kinetics for detecting localized temperature increase following impact or rapid heating. The thermochrome retains a signature of the peak temperature in the elastomer, allowing post-mortem mapping of micron-scale temperature localization in materials such as explosive and propellant composites. We demonstrate the concept by using the kinetics of the DASA activation to determine peak temperatures reached during bullet perforation of the polyurethane.

50 citations


Journal ArticleDOI
TL;DR: In this paper, a pioneering study based on a series of experiments on the operation of commercial Time Division Long-Term Evolution (TD-LTE) systems in the presence of pulsed interfering signals in the 3550-3650 MHz band is presented.
Abstract: This paper presents a pioneering study based on a series of experiments on the operation of commercial Time-Division Long-Term Evolution (TD-LTE) systems in the presence of pulsed interfering signals in the 3550-3650 MHz band. TD-LTE operations were carried out in channels overlapping and adjacent to the high power SPN-43 radar with various frequency offsets between the two systems to evaluate the susceptibility of LTE to a high power interfering signal. Our results demonstrate that LTE communication using low antenna heights was not adversely affected by the pulsed interfering signal operating on adjacent frequencies irrespective of the distance of interfering transmitter. Performance was degraded only for very close distances (1-2 km) of overlapping frequencies of interfering transmitter.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the unsteady aerodynamic forcing that occurs near the trailing edge of airfoils with chordwise Reynolds numbers between 2 and 6 million, and developed a new model for estimation of fluctuating surface pressure autospectra beneath two-dimensional turbulent boundary layer flow experiencing an adverse pressure gradient of variable strength.
Abstract: This study investigated the unsteady aerodynamic forcing that occurs near the trailing edge of airfoils with chordwise Reynolds numbers between 2 and 6 million. Static pressure, unsteady surface pressure, and velocity measurements were made throughout the trailing-edge region of an airfoil model with three interchangeable, symmetric trailing-edge sections. The data of the present study were used to develop a new model for estimation of fluctuating surface pressure autospectra beneath two-dimensional turbulent boundary layer flow experiencing an adverse pressure gradient of variable strength. This new model has been used to compare with data from six separate experimental investigations from literature, and has been compared against a separately developed empirical model of the fluctuating surface pressure. Additional empirical modeling of the coherent extents of the fluctuating pressure field in the longitudinal and lateral directions, as well as the convection velocity, is presented as a function of nond...

Journal ArticleDOI
TL;DR: In this article, the 5xxx series alloys are used in marine applications where light weight and increased speed are paramount, providing an optimum combination of as-welded strength and general corrosion resistance.
Abstract: Structural aluminum alloys are used in marine applications where light weight and increased speed are paramount. The 5xxx series alloys are the ideal choice, providing an optimum combination of as-welded strength and general corrosion resistance. A particular concern is sensitization in service. Aluminum is considered sensitized when a nearly continuous network of β phase forms along the grain boundaries. The β phase is anodic to the Al matrix, and, when exposed to sea water and sufficient loading, provides a clear pathway to stress corrosion cracking (SCC). The degree of β-phase precipitation is driven by a combination of time and elevated temperature. For over a decade, SCC of Al superstructures has plagued Navy ships. To address this issue, relevant technologies have been adopted, adapted, and developed to combat this issue. More specifically, the technology areas involve the detection of sensitization, the mitigation of SCC, and the replacement of corrupt materials. The technologies discussed herein a...

Journal ArticleDOI
TL;DR: Giant transmission and reflection of a finite bandwidth are demonstrated at the same wavelength when the electromagnetic wave is incident on a subwavelength array of parity-time (PT) symmetric dimers embedded in a metallic film, indicating that the PT-synthetic plasmonic metafilm can function as a thinfilm PT-plasmonics laser or absorber depending on the tuning parameter.
Abstract: Giant transmission and reflection of a finite bandwidth are demonstrated at the same wavelength when the electromagnetic wave is incident on a subwavelength array of parity-time (PT) symmetric dimers embedded in a metallic film. Remarkably, this phenomenon vanishes if the metallic substrate is lossless while keeping other parameters unchanged. Moreover super scattering can also occur when increasing the loss of the dimers while keeping the gain unchanged. When the metafilm is adjusted to the vicinity of an exceptional point, tuning either the substrate dissipation or the loss of the dimers can lead to supper scattering in stark contrast to what would be expected in conventional systems. In addition, increasing the gain of the dimers can increase the absorption near the exceptional point. These phenomena indicate that the PT-synthetic plasmonic metafilm can function as a thinfilm PT-plasmonic laser or absorber depending on the tuning parameter. One implication is that super radiation is possible from a cavity by tuning cavity dissipation or lossy element inside the cavity.

Journal ArticleDOI
TL;DR: These experiments show that isoprene readily forms SOA in unseeded chamber experiments, even during dark ozonolysis, and reveal that temperature affects SOA yield, volatility, and density formed from isophene.
Abstract: Isoprene is globally the most ubiquitous nonmethane hydrocarbon. The biogenic emission is found in abundance and has a propensity for SOA formation in diverse climates. It is important to characterize isoprene SOA formation with varying reaction temperature. In this work, the effect of temperature on SOA formation, physical properties, and chemical nature is probed. Three experimental systems are probed for temperature effects on SOA formation from isoprene, NO + H2O2 photo-oxidation, H2O2 only photo-oxidation, and dark ozonolysis. These experiments show that isoprene readily forms SOA in unseeded chamber experiments, even during dark ozonolysis, and also reveal that temperature affects SOA yield, volatility, and density formed from isoprene. As temperature increases SOA yield is shown to generally decrease, particle density is shown to be stable (or increase slightly), and formed SOA is shown to be less volatile. Chemical characterization is shown to have a complex trend with both temperature and oxidant...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effects of the size of hollow glass microspheres (20 μm vs. 40 μm) and composition on the energy absorption capacity of the silicate glass foams under both the quasistatic and high-strain rate (∼10^(−3) s^( −1)) loading conditions.
Abstract: This study investigates the effects of the size of hollow glass microspheres (20 μm vs. 40 μm) and composition on the energy absorption capacity of the silicate glass foams under both the quasistatic (∼10^(−3) s^(−1)) and high-strain rate (∼10^3 s^(−1)) loading conditions. These measurements revealed that while the size difference of the hollow glass microspheres and the foam composition have negligible effects on the uniaxial quasistatic response, their effects were significant under the dynamic loading conditions. The results suggest that the smaller glass microspheres (20 μm) dominated the dynamic behavior of the glass foams in comparison to the larger glass microspheres (40 μm), leading to a significant increase of the energy absorption capacity of the 20 μm-based glass foams at high-strain rates. Glass foams exhibited energy absorption capacity of about 54 kJ/kg under the dynamic loading that is greater in comparison to that of the typical metallic and syntactic foams.


Journal ArticleDOI
TL;DR: In this article, the effects of turbulent flow conditions on combustion characteristics for both aluminum and titanium powders were investigated. But the results of the experiments were limited to a single laser beam.

Journal ArticleDOI
TL;DR: In this paper, an Eulerian-Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water is presented, where the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase.
Abstract: Multiphase flows are present in many important fields ranging from multiphase explosions to chemical processing. An important subset of multiphase flow applications involves dispersed materials, such as particles, droplets, and bubbles. This work presents an Eulerian–Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water. Following a large body of multiphase literature, the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase. While the application of these two components of driving force is well accepted in much of the literature, other models exist in which the particle-phase pressure gradient itself drives particle motion. The multiphase model treats all phases as compressible and is derived to ensure adherence to the 2nd Law of Thermodynamics. The governing equations are presented and discussed, and a characteristic analysis shows the model to be hyperbolic, with a degeneracy in the case that the intergranular stress, which is modeled as a configuration pressure, is zero. Finally, results from a two sample problems involving shock-induced particle dispersion are presented. The results agree well with experimental measurements, providing initial confidence in the proposed model.

Journal ArticleDOI
TL;DR: To develop test methods and evaluate survival of Bacillus thuringiensis kurstaki cry− HD‐1 and B. thurringiensis Al Hakam spores after exposure to hot, humid air inside of a C‐130 aircraft.
Abstract: Aim To develop test methods and evaluate survival of Bacillus thuringiensis kurstaki cry(-) HD-1 and B. thuringiensis Al Hakam spores after exposure to hot, humid air inside of a C-130 aircraft. Methods and results Bacillus thuringiensis spores were either pre-inoculated on 1 × 2 or 2 × 2 cm substrates or aerosolized inside the cargo hold of a C-130 and allowed to dry. Dirty, complex surfaces (10 × 10 cm) swabbed after spore dispersal showed a deposition of 8-10 log10 m(-2) through the entire cargo hold. After hot, humid air decontamination at 75-80°C, 70-90% relative humidity for 7 days, 87 of 98 test swabs covering 0·98 m(2) , showed complete spore inactivation. There was a total of 1·67 log10 live CFU detected in 11 of the test swabs. Spore inactivation in the 98 test swabs was measured at 7·06 log10 m(-2) . Conclusions Laboratory test methods for hot, humid air decontamination were scaled for a large-scale aircraft field test. The C-130 field test demonstrated that hot, humid air can be successfully used to decontaminate an aircraft. Significance and impact of the study Transition of a new technology from research and development to acquisition at a Technology Readiness Level 7 is unprecedented.

Journal ArticleDOI
TL;DR: A solid-state four element array gyromagnetic nonlinear transmission line high power microwave system is presented as well as a detailed description of its subsystems and general output capabilities.
Abstract: In this paper, a solid-state four element array gyromagnetic nonlinear transmission line high power microwave system is presented as well as a detailed description of its subsystems and general output capabilities. This frequency agile S-band source is easily adjusted from 2-4 GHz by way of a DC driven biasing magnetic field and is capable of generating electric fields of 7.8 kV/m at 10 m correlating to 4.2 MW of RF power with pulse repetition frequencies up to 1 kHz. Beam steering of the array at angles of ±16.7° is also demonstrated, and the associated general radiation pattern is detailed.

Journal ArticleDOI
TL;DR: Robustness of the coregistration methods and analysis of scene coherence over time is characterized by analysis of repeat pass as well as synthetically modified data sets.
Abstract: In this paper, an automated change detection technique is presented that compares new and historical seafloor images created with sidescan synthetic aperture sonar (SAS) for changes occurring over time. The method consists of a four-stage process: a coarse navigational alignment that relates and approximates pixel locations of reference and repeat–pass data sets; fine-scale coregistration using the scale-invariant feature transform (SIFT) algorithm to match features between overlapping data sets; local coregistration that improves phase coherence; and finally, change detection utilizing a canonical correlation analysis (CCA) algorithm to detect changes. The method was tested using data collected with a high-frequency SAS in a sandy shallow-water environment. Successful results of this multistage change detection method are presented here, and the robustness of the techniques that exploit phase and amplitude levels of the backscattered signals is discussed. It is shown that the coherent nature of the SAS data can be exploited and utilized in this environment over time scales ranging from hours through several days. Robustness of the coregistration methods and analysis of scene coherence over time is characterized by analysis of repeat pass as well as synthetically modified data sets.

Journal ArticleDOI
19 Aug 2016-Chaos
TL;DR: This work extends FTLE to the compressible flow regime so that coherent structures, which travel at convective speeds, can be associated with waves traveling at acoustic speeds and shows that intermittent events are associated with entrainment in the initial roll up region and emissive events downstream of the potential-core collapse.
Abstract: The finite-time Lyapunov exponent (FTLE) technique has shown substantial success in analyzing incompressible flows by capturing the dynamics of coherent structures. Recent applications include river and ocean flow patterns, respiratory tract dynamics, and bio-inspired propulsors. In the present work, we extend FTLE to the compressible flow regime so that coherent structures, which travel at convective speeds, can be associated with waves traveling at acoustic speeds. This is particularly helpful in the study of jet acoustics. We first show that with a suitable choice of integration time interval, FTLE can extract wave dynamics from the velocity field. The integration time thus acts as a pseudo-filter separating coherent structures from waves. Results are confirmed by examining forward and backward FTLE coefficients for several simple, well-known acoustic fields. Next, we use this analysis to identify events associated with intermittency in jet noise pressure probe data. Although intermittent events are known to be dominant causes of jet noise, their direct source in the turbulent jet flow has remained unexplained. To this end, a Large-Eddy Simulation of a Mach 0.9 jet is subjected to FTLE to simultaneously examine, and thus expose, the causal relationship between coherent structures and the corresponding acoustic waves. Results show that intermittent events are associated with entrainment in the initial roll up region and emissive events downstream of the potential-core collapse. Instantaneous acoustic disturbances are observed to be primarily induced near the collapse of the potential core and continue propagating towards the far-field at the experimentally observed, approximately 30° angle relative to the jet axis.

Journal ArticleDOI
TL;DR: In this article, a multidimensional aperture is synthesized by performing a series of circular scans at varying grazing angles around targets and coherently combining the backscattering information from the set of scans to form high-resolution volumetric images.
Abstract: In this paper, volumetric imaging via multipass circular synthetic aperture sonar (CSAS) is demonstrated using an autonomous underwater vehicle (AUV). A multidimensional aperture is synthesized by performing a series of circular scans at varying grazing angles around targets and coherently combining the backscattering information from the set of scans to form high-resolution volumetric images. A data-driven technique for precision alignment of the individual scans comprising the multipass set enables synthesis of a multidimensional array. To beamform in the vertical dimension using the irregular and undersampled multipass aperture, a compressive-sensing-based approach is adopted which is similar to methods used in analogous synthetic aperture radar tomography applications but modified to accommodate for the wider fractional bandwidth of the synthetic aperture sonar (SAS) system. The modification exploits a joint sparsity assumption in the vertical scattering profile at different subbands and adapts a standard joint sparse solving algorithm to the relevant case in which the sparsity profile is common between solution vectors but the sensing matrices are different. Results are shown for a variety of targets, including proud and obliquely buried unexploded ordnance, a 2-1 solid aluminum cylinder, and a steel oil drum.

Journal ArticleDOI
TL;DR: In this paper, a numerical investigation of the bottom pressure and wave elevation generated by a planing hull in finite-depth water is presented, which is based on the discretization of the continuum fields of hydrodynamics through mesh-less particles.

Journal ArticleDOI
TL;DR: In this article, three 26650 LiFePO4 (LFP) cells were cycled using a 40 A pulsed charge/discharge profile to study their performance in high rate pulsed applications.

Journal ArticleDOI
TL;DR: The concomitance of facile fabrication, economic and scalable processing, and high performance-including a reduction in H2O2 decomposition activation energy of 40-50% over conventional material catalysts-paves the way for using these nanostructured microfibers in modern, small-scale underwater vehicle propulsion systems.
Abstract: Micro unmanned underwater vehicles (UUVs) need to house propulsion mechanisms that are small in size but sufficiently powerful to deliver on-demand acceleration for tight radius turns, burst-driven docking maneuvers, and low-speed course corrections. Recently, small-scale hydrogen peroxide (H2O2) propulsion mechanisms have shown great promise in delivering pulsatile thrust for such acceleration needs. However, the need for robust, high surface area nanocatalysts that can be manufactured on a large scale for integration into micro UUV reaction chambers is still needed. In this report, a thermal/electrical insulator, silicon oxide (SiO2) microfibers, is used as a support for platinum nanoparticle (PtNP) catalysts. The mercapto-silanization of the SiO2 microfibers enables strong covalent attachment with PtNPs, and the resultant PtNP–SiO2 fibers act as a robust, high surface area catalyst for H2O2 decomposition. The PtNP–SiO2 catalysts are fitted inside a micro UUV reaction chamber for vehicular propulsion; t...

Journal ArticleDOI
TL;DR: In this article, an inside-out-in system is introduced for rapid lubrication or relubrication of polymeric LIS, which consists of an embedded millichannel liquid distribution network connected to the exterior polymer surface using periodically spaced vias and could be used to lubricate LIS-based personal protective gear.
Abstract: Liquid-infused surfaces (LIS) consist of a porous or textured solid matrix infused with a lubricating liquid. The presence of a thin film of the lubricant on the exterior surface facilitates dramatically the shedding of a wide range of liquids and solids, making LIS potential candidates for a variety of applications. However, before LIS can transition into industrial use, durability issues posed by lubricant depletion need to be addressed. In this paper an ‘inside-out-in’ system is introduced for rapid lubrication or relubrication of polymeric LIS. The system consists of an embedded millichannel liquid distribution network connected to the exterior polymer surface using periodically spaced vias and could be used to, for example, lubricate LIS-based personal protective gear. By using periodic contact angle measurements and spray impingement experiments, the authors show that release of a lubricant using this system leads to diminishing contact angle hysteresis of the exterior LIS surface nearly instantaneo...

Journal ArticleDOI
TL;DR: In this article, the authors introduce and experimentally validate an electromagnetic probability-of-effect assessment tool which statistically assesses the magnitude of a system/subsystem's hardness or safety margin to upset/failure under any level of threat.
Abstract: Future naval radio frequency emitters, particularly radars, will produce shipboard operational electromagnetic environments greater than what are produced today. Presently, hazards of electromagnetic radiation to ordnance and electromagnetic susceptibility certification test methods cannot meet the higher power level requirements and primarily employ deterministic test methods. The purpose of this study is to introduce and experimentally validate an electromagnetic probability-of-effect assessment tool which statistically assesses the magnitude of a system/subsystem's hardness or safety margin to upset/failure under any level of threat. The generalized extreme value and generalized log-logistic distributions are leveraged for enclosure maximum field and device threshold distributions, respectively, and the hardness margin, from structural reliability analysis, is applied for probability-of-effect prediction.

Journal ArticleDOI
TL;DR: Carbon fibers exhibit exceptional properties such as high stiffness and specific strength, making them excellent reinforcements for composite materials, but it is difficult to directly measure their tensile properties and estimates are often obtained by tensioning fiber bundles or composites.
Abstract: Carbon fibers exhibit exceptional properties such as high stiffness and specific strength, making them excellent reinforcements for composite materials. However, it is difficult to directly measure their tensile properties and estimates are often obtained by tensioning fiber bundles or composites. While these macro scale tests are informative for composite design, their results differ from that of direct testing of individual fibers. Furthermore, carbon filament strength also depends on other variables, including the test length, actual fiber diameter, and material flaw distribution. Single fiber tensile testing was performed on high-strength carbon fibers to determine the load and strain at failure. Scanning electron microscopy was also conducted to evaluate the fiber surface morphology and precisely measure each fiber’s diameter. Fiber strength was found to depend on the test gage length and in an effort to better understand the overall expected performance of these fibers at various lengths, statistical weak link scaling was performed. In addition, the true Young’s modulus was also determined by taking the system compliance into account. It was found that all properties (tensile strength, strain to failure, and Young’s modulus) matched very well with the manufacturers’ reported values at 20 mm gage lengths, but deviated significantly at other lengths.