Macromolecular structure and viscoelastic response of the organic framework of nacre in Haliotis rufescens: A perspective and overview

Nanoindentation probing on nacre obtained from Haliotis rufescens shells has demonstrated that nacre displays a combined viscoplastic-viscoelastic time dependent response. Additionally, it is found that the moisture/water content of nacre contributes to its time dependent behavior and overall mechanical properties. Detailed finite element simulations allow for the determination of constitutive parameters used to calibrate specific time dependent material models which are, in turn, compared to those found via independent measurement as reported in the literature. The results lead to a new paradigm for nacre’s attractive structural composite behavior and thereby to new potential pathways for biomimetics

The well-posedness of the Cauchy problem for self-interacting vector fields

We point out that the initial-value (Cauchy) problem for self-interactingvector fields presents the same well-posedness issues as for first-orderderivative self-interacting scalar fields (often referred to as $k$-essence).For the latter, suitable strategies have been employed in the last few years tosuccessfully evolve the Cauchy problem at the level of the infrared theory,without the need for an explicit ultraviolet completion. We argue that the verysame techniques can also be applied to self-interacting vector fields, avoidinga number of issues and "pathologies" recently found in the literature.<br

Ultrastructure of the Interlamellar Membranes of the Nacre of the Bivalve Pteria hirundo, Determined by Immunolabelling

The current model for the ultrastructure of the interlamellar membranes of molluscan nacre imply that they consist of a core of aligned chitin fibers surrounded on both sides by acidic proteins. This model was based on observations taken on previously demineralized shells, where the original structure had disappeared. Despite other earlier claims, no direct observations exist in which the different components can be unequivocally discriminated. We have applied different labeling protocols on non-demineralized nacreous shells of the bivalve Pteria. With this method, we have revealed the disposition and nature of the different fibers of the interlamellar membranes that can be observed on the surface of the nacreous shell of the bivalve Pteria hirundo by high resolution scanning electron microscopy (SEM). The minor chitin component consists of very thin fibers with a high aspect ratio and which are seemingly disoriented. Each fiber has a protein coat, which probably forms a complex with the chitin. The chitin-protein-complex fibers are embedded in an additional proteinaceous matrix. This is the first time in which the sizes, positions and distribution of the chitin fibers have been observed in situ.AJOM was financed by a PhD Grant of the FPI program from the Spanish Ministerio de Ciencia e Innovación; TCB's PhD Grant belonged to the FPU Program of the same Ministry. AJOM and AGC were supported by Projects CGL2010-20748-C02-01 and CGL2013-48247-P of the mentioned Ministry, and RNM6433 of the Consejería de Economía, Innovación y Ciencia of the Junta de Andalucía. The European COST Action TD0903 contributed via two Short Term Scientific Missions to AJOM in FM's lab in Dijon

Quantifying pulsed laser induced damage to grapheme

As an emerging optical material, graphene’s ultrafast dynamics are often probed using pulsed lasers yet the region in which optical damage takes place is largely uncharted. Here, femtosecond laser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged area has a linear correlation with the optical fluence. These results demonstrate local modification of sp2-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm2, an order-of-magnitude lower than measured and theoretical ablation thresholds

Wear behaviour of WC plasma sprayed coatings wi th micro and nanostructured powders

El objetivo de este trabajo es estudiar el comportamiento a desgaste de distintos recubrimientos de WC sobre acero inoxidable mediante proyección por plasma atmosférico. Se proyectan dos tipos de polvos comerciales con base cobalto (12 %) y níquel (10 %), con el objeto de analizar la influencia de la matriz e incluso del espesor del recubrimiento. Los recubrimientos obtenidos se caracterizan microestructuralmente por microscopía electrónica de barrido y difracción de rayos X. La caracterización tribológica de los recubrimientos se realiza mediante ensayos pin-on-disc contra bolas cerámicas de alúmina (2.400 HV) y nitruro de silicio (1.600 HV), sin lubricación, obteniéndose las tasas de desgaste y la evolución del coeficiente de rozamiento. Las pistas de desgaste y los residuos generados se caracterizaron mediante Microscopía Electrónica de Barrido, MEB. Los resultados muestran diferentes mecanismos de desgaste en cada par de material ensayado en función de la matriz y de la naturaleza de la bola empleada en el ensayo, encontrándose mayores tasas de desgaste con bola de nitruro de silicio. En una segunda fase, se obtienen recubrimientos, con dos polvos base cobalto cuyos tamaños de partícula son micrométrico y nanométrico, respectivamente, con el objetivo de estudiar la influencia del tamaño de partícula inicial sobre las propiedades a desgaste del recubrimiento. Los resultados obtenidos ponen de manifiesto una mayor resistencia al desgaste de los recubrimientos obtenidos con polvos nanoestructurados, bajo condiciones de carga elevadas, mientras que para cargas bajas ambos recubrimientos presentan un comportamiento similar a pesar de las diferencias microestructurales apreciadasThe aim of the present work is the study of wear behaviour of different WC coatings deposited on stainless steel substrate by means of atmospheric plasma spraying (APS). Two types of WC commercial powders, with different metal binder (12% Cobalt and 10% Nickel) have been deposited in order to analyse the influence of the metal matrix and thickness of the coating in tribological properties.The microstructure of the depositions was characterized using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). On the other hand, tribology characterization of the coatings was made by pin-on-disk wear tests against alumina (2400HV) and silicon nitride (1600HV) ceramic balls, without lubrication. Wear rates and friction coefficient evolution have been calculated. Finally, wear tracks and wear debris have been analysed with the help of SEM.The results of each pair of tested materials show different mechanisms of wear related to the nature of the ball that has been used, obtaining higher wear rates with silicone nitride ball..In a second phase of the study, in order to examine the influence of the initial particle size on the wear properties of the coatings, cobalt based coatings have been analysed with different initial particle size (micrometric and nanometric particles).Results show that nanostructured coatings have higher wear resistance than microstrutured ones for high loads. However for low loads, behaviour is similar in spite of the microstructural differences appreciate

Study of erosion behaviour of conventional and nanostructured WC-12Co coatings sprayed by atmospheric plasma

Thermal sprayed WC-Co coatings are used extensively to enhance the wear resistance of a wide range of engineering components. In this paper, erosive resistance of plasma atmospheric sprayed WC-12Co coatings has been evaluated. Solid particle erosion tests were conducted on these coatings at different angles of impact with silica and alumina abrasives of size 250 µm. Coatings have been deposited by using micrometric and nanometric agglomerated powders, employing H2 and He as plasmogen gas. In order to determine the erosion regime (ductile or brittle), the influence of impact angle on the erosion rate has been studied. Optical microscope and FESEM have been used to analyze the eroded surface. The influence of the plasmogen gas and the powder employed on the erosive behaviour of the coating has been evaluated. An attempt to connect the erosive behaviour with mechanical properties and microstructure has been made. Hardness has been determined by means of several measurements of Vickers microhardness; fracture toughness has been estimated through indentation method. Identification of phases has been made by means of X Ray diffractio

Extraordinary linear dynamic range in laser-defined functionalized graphene photodetectors

Graphene-based photodetectors have demonstrated mechanical flexibility, large operating bandwidth, and broadband spectral response. However, their linear dynamic range (LDR) is limited by graphene's intrinsichot-carrier dynamics, which causes deviation from a linear photoresponse at low incident powers. At the same time, multiplication of hot carriers causes the photoactive region to be smeared over distances of a few micro-meters, limiting the use of graphene in high-resolution applications. We present a novel method for engineer-ing photoactive junctions in FeCl3-intercalated graphene using laser irradiation. Photocurrent measured at these planar junctions shows an extraordinary linear response with an LDR value at least 4500 times larger than that of other graphene devices (44 dB) while maintaining high stability against environmental contamination without the need for encapsulation. The observed photoresponse is purely photovoltaic, demonstrating complete quenching of hot-carrier effects. These results pave the way toward the design of ultrathin photode-tectors with unprecedented LDR for high-definition imaging and sensing.Comment: 44 pages, includes supplementar

Scalar-field Pressure in Induced Gravity with Higgs Potential and Dark Matter

A model of induced gravity with a Higgs potential is investigated in detail in view of the pressure components related to the scalar-field excitations. The physical consequences emerging as an artifact due to the presence of these pressure terms are analysed in terms of the constraints parting from energy density, solar-relativistic effects and galactic dynamics along with the dark matter halos.Comment: 26 pages, 3 figures, Minor revision, Published in JHE

Investigation of the Epitaxial Graphene/p-SiC Heterojunction

There has been significant research in the study of in-plane charge-carrier transport in graphene in order to understand and exploit its unique electrical properties; however, the vertical graphene–semiconductor system also presents opportunities for unique devices. In this letter, we investigate the epitaxial graphene/p-type 4H-SiC system to better understand this vertical heterojunction. The I–V behavior does not demonstrate thermionic emission properties that are indicative of a Schottky barrier but rather demonstrates characteristics of a semiconductor heterojunction. This is confirmed by the fitting of the temperature-dependent I–V curves to classical heterojunction equations and the observation of band-edge electroluminescence in SiC