Ballistic transport properties across nonuniform strain barriers in graphene

We study the effect of uniaxial strain on the transmission and the conductivity across a strain-induced barrier in graphene. At variance with conventional studies, which consider sharp barriers, we consider a more realistic, smooth barrier, characterized by a nonuniform, continuous strain profile. Our results are instrumental towards a better understanding of the transport properties in corrugated graphene.Comment: High Press. Res., to appea

A Numerical Method for a Nonlocal Form of Richards' Equation Based on Peridynamic Theory

Forecasting water content dynamics in heterogeneous porous media has significant interest in hydrological applications; in particular, the treatment of infiltration when in presence of cracks and fractures can be accomplished resorting to peridynamic theory, which allows a proper modeling of non localities in space. In this framework, we make use of Chebyshev transform on the diffusive component of the equation and then we integrate forward in time using an explicit method. We prove that the proposed spectral numerical scheme provides a solution converging to the unique solution in some appropriate Sobolev space. We finally exemplify on several different soils, also considering a sink term representing the root water uptake

Colloidal CuFeS2 Nanocrystals: Intermediate Fe d-Band Leads to High Photothermal Conversion Efficiency

We describe the colloidal hot-injection synthesis of phase-pure nanocrystals (NCs) of a highly abundant mineral, chalcopyrite (CuFeS2). Absorption bands centered at around 480 and 950 nm, spanning almost the entire visible and near infrared regions, encompass their optical extinction characteristics. These peaks are ascribable to electronic transitions from the valence band (VB) to the empty intermediate band (IB), located in the fundamental gap and mainly composed of Fe 3d orbitals. Laser-irradiation (at 808 nm) of an aqueous suspension of CuFeS2 NCs exhibited significant heating, with a photothermal conversion efficiency of 49%. Such efficient heating is ascribable to the carrier relaxation within the broad IB band (owing to the indirect VB-IB gap), as corroborated by transient absorption measurements. The intense absorption and high photothermal transduction efficiency (PTE) of these NCs in the so-called biological window (650-900 nm) makes them suitable for photothermal therapy as demonstrated by tumor cell annihilation upon laser irradiation. The otherwise harmless nature of these NCs in dark conditions was confirmed by in vitro toxicity tests on two different cell lines. The presence of the deep Fe levels constituting the IB is the origin of such enhanced PTE, which can be used to design other high performing NC photothermal agents.Comment: 12 pages, Chemistry of Materials, 31-May-201

Nonlinear thermomechanical response and constitutive modeling of viscoelastic polyethylene membranes

Thin films of linear low-density polyethylene show a significant time-dependent behavior, strongly reliant on temperature and strain rate effects. A constitutive nonlinear thermo-viscoelastic relation is developed to characterize the response of thin membranes up to yielding, in a wide range of temperatures, strain rates, and mechanical loading conditions. The presented plane stress orthotropic formulation involves the free volume theory of viscoelasticity and the time-temperature superposition principle, necessary to describe non-linearities and non-isothermal conditions. Uniaxial tension tests at constant strain rate and long-duration biaxial inflation experiments have been employed in the calibration of the material parameters. The model has been implemented in the Abaqus finite element code by means of a user-defined subroutine based on a recursive integration algorithm. The accuracy of the constitutive relation has been validated against experimental data of full field diaphragm inflation tests and uniaxial tension, relaxation and cyclic experiments, covering sub-ambient temperatures and strain rate ranges observed during the operation of stratospheric balloons

Design of Al-free and Al-based InGaAs/GaAs strained quantum well 980-nm pump lasers including thermal behavior effects on E/O characteristics

A 2D thermal simulator and a model to evaluate high power lasers characteristics have been developed. With these models it was possible to optimize cavity length of InGaAs/GaAs (Multiple) Quantum Well 980 nm lasers realized both with Al-based and Al-free confining layers. A comprehensive experimental investigation of the influence of cavity length and temperature on the laser emission wavelength has been performed. This allows a fine trimming of the devices to match the Erbium doped fiber absorption bandwidth

Innovation complementarities and firm growth

This article explores the relations between firm growth and a set of four innovation indicators (inhouse R & D, external sourcing, product innovation, and process innovation) that capture the different sources, modes, and outcomes of the innovative strategies adopted by firms. While existing studies tend to focus on the individual effects on growth of each innovation activity, we stress that firms adopt heterogeneous innovation strategies, choosing to perform different combinations of the basic innovation activities. We directly address the empirical question as to whether jointly performing two basic innovation activities boosts sales growth above and beyond the separate contribution of each innovation activity when performed individually. Exploiting a panel of Spanish manufacturing firms observed between 2004 and 2011, we document instances of super-modularity of the growth function, and reveal the presence of complementarities between internal R & D and product innovation, and between product and process innovations. As such, the combination of these three basic innovation activities appears to be the most effective strategy for sustaining growth and market shares, while external sourcing does not appear to make any systematic contribution

Prospects for the detection of electronic pre-turbulence in graphene

Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic pre-turbulence in graphene samples. In particular, pre-turbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100 GHz

Antibacterial β-Glucan/Zinc Oxide Nanocomposite Films for Wound Healing

Advanced antimicrobial biomaterials for wound healing applications are an active field of research for their potential in addressing severe and infected wounds and overcoming the threat of antimicrobial resistance. Beta-glucans have been used in the preparation of these materials for their bioactive properties, but very little progress has been made so far in producing biomedical devices entirely made of beta-glucans and in their integration with effective antimicrobial agents. In this work, a simple and eco-friendly method is used to produce flexible beta-glucan/nanostructured zinc oxide films, using glucans derived from the yeast Saccharomyces cerevisiae. The properties of the films are characterized through scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, infrared and UV–visible spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and water absorption tests. Finally, the antibacterial properties of the nanostructured zinc oxide and of the composite films are assessed against Staphylococcus epidermidis and Escherichia coli, showing a marked effectiveness against the former. Overall, this study demonstrates how a novel bionanocomposite can be obtained towards the development of advanced wound healing devices