High temperature behaviour of magnetron sputtered nanocrystalline titanium aluminium nitride coatings

This paper is to study the thermal stability of nanocrystalline ternary nitride coatings at elevated temperatures. Nanocrystalline titanium aluminium nitride coatings were produced by reactive magnetron co-sputtering on glass substrates and AISI H13 tool steel substrates with nitrogen pressures of 0.4 and 0.65 mTorr (0.053 and 0.086 Pa) respectively. Heat treatment was applied to the coatings at temperatures up to 1000C. It was found that an unexpected grain refinement occurred in the coatings deposited at 0.4 mTorr nitrogen pressure after the heat treatment. a stronger development of TiN(TiAIN (200) component was also evident at temperatures above 800C. With a finer and densified grain struicture, the hardness of the coatings increased substantially from ~1700 to 2300HV

The field theoretic derivation of the contact value theorem in planar geometries and its modification by the Casimir effect

The contact value theorem for Coulomb gases in planar or film-like geometries is derived using a Hamiltonian field theoretic representation of the system. The case where the film is enclosed by a material of different dielectric constant to that of the film is shown to contain an additional Casimir-like term which is generated by fluctuations of the electric potential about its mean-field value.Comment: Link between Sine-Gordon and Coulomb gas pressures via subtraction of self interaction terms included. Discussion of results within Debye-Huckel approximation included. Added reference

Consequences of anisotropy in electrical charge storage: application to the characterization by the mirror method of TiO2 rutile

This article is devoted first to anisotropic distributions of stored electric charges in isotropic materials, second to charge trapping and induced electrostatic potential in anisotropic dielectrics. On the one hand, we examine the case of anisotropic trapped charge distributions in linear homogeneous isotropic (LHI) insulators, obtained after an electron irradiation in a scanning electron microscope. This injection leads to the formation of a mirror image

EBSD investigations of Equal Channel Angular Extruded copper

Development of nano- and submicron-structured materials has attracted significant research interest in the last ten years [1, 2]. Most recently, an innovative technology called the Equal Channel Angular Extrusion (ECAE) process has demonstrated its capability of producing nano- and submicronstructured metallic alloys with substantial strength improvement [3-8]. ECAE adopts the principle of mechanical attrition and imposes very heavy shear deformation on bulk materials without causing major dimensional changes of the extruded products [3]. It has been suggested that this technology has great advantages over the conventional mechanical attrition of ball milling because it can produce large sized samples free of any residual porosity

Elastic constants of 3-, 4- and 6-connected chiral and anti-chiral honeycombs subject to uniaxial in-plane loading

Finite Element models are developed for the in-plane linear elastic constants of a family of honeycombs comprising arrays of cylinders connected by ligaments. Honeycombs having cylinders with 3, 4 and 6 ligaments attached to them are considered, with two possible configurations explored for each of the 3- (trichiral and anti-trichiral) and 4- (tetrachiral and anti-tetrachiral) connected systems. Honeycombs for each configuration have been manufactured using rapid prototyping and subsequently characterised for mechanical properties through in-plane uniaxial loading to verify the models. An interesting consequence of the family of 'chiral' honeycombs presented here is the ability to produce negative Poisson's ratio (auxetic) response. The deformation mechanisms responsible for auxetic functionality in such honeycombs are discussed

Description beyond the mean field approximation of an electrolyte confined between two planar metallic electrodes

We study an electrolyte confined in a slab of width $W$ composed of two grounded metallic parallel electrodes. We develop a description of this system in a low coupling regime beyond the mean field (Poisson--Boltzmann) approximation. There are two ways to model the metallic boundaries: as ideal conductors in which the electric potential is zero and it does not fluctuate, or as good conductors in which the average electric potential is zero but the thermal fluctuations of the potential are not zero. This latter model is more realistic. For the ideal conductor model we find that the disjoining pressure is positive behaves as $1/W^3$ for large separations with a prefactor that is universal, i.e. independent of the microscopic constitution of the system. For the good conductor boundaries the disjoining pressure is negative and it has an exponential decay for large $W$. We also compute the density and electric potential profiles inside the electrolyte. These are the same in both models. If the electrolyte is charge asymmetric we find that the system is not locally neutral and that a non-zero potential difference builds up between any electrode and the interior of the system although both electrodes are grounded.Comment: 16 pages, 5 figures, added a new appendix B and a discussion on ideal conductors vs. good conductor

The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6

We present a detailed analysis of the distance determination for one intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance Project. Stars along the line of sight to G139.6+47.6 are examined for the presence of sodium absorption attributable to the cloud, and the distance bracket is established by astrometric and spectroscopic parallax measurements of demonstrated foreground and background stars. We detail our strategy regarding target selection, observational setup, and analysis of the data, including a discussion of wavelength calibration and sky subtraction uncertainties. We find a distance estimate of 129 (+/- 10) pc for the lower limit and 257 (+211-33) pc for the upper limit. Given the high number of stars showing absorption due to this IVC, we also discuss the small-scale covering factor of the cloud and the likely significance of non-detections for subsequent observations of this and other similar IVC's. Distance measurements of the remaining targets in the DDO IVC project will be detailed in a companion paper.Comment: 10 pages, 6 figures, LaTe

Construction and validation of a questionnaire to assess student satisfaction with mathematics learning materials

Sixth Edition Technological Ecosystems for Enhancing MulticulturalityMathematics is an essential branch for the scientific development and its study is mandatory in most university degrees. However, currently the level of academic performance and motivation of students to learn this science is not the desired one. The students can use different learning tools inside and outside the math classroom, enhancing the quality of the learning materials that are designed essentially to facilitate the learning of mathematics. The present research project aims to determine the validity and reliability of a measurement instrument that allows theassessment of the satisfaction of the students with the availablelearning materials. To fulfill the objectives of this research, the method of survey was used. A study with a quantitative approach was developed, which led to the design and validation of a questionnaire by a group of 7 experts. The validation closed after applying a pilot study with 728 students. It concluded positively, obtaining nine factors that coincide with the revision of the literature: technological quality, quality of content, visual quality, didactic significance, adequacy of content, relationship between theory and practice, involvement, contribution to learning, relevance and interaction between educational actors. The results of this questionnaire provide to the international scientific community with relevant information for the design, selection, and use of study materials in the classrooms, which will contribute to raising the levels of student engagement, and their academic performance in mathematics, secondaril

A random walk through the dynamics of homogeneous vapor-liquid nucleation

A method of calculating rates of homogeneous vapor-liquid nucleation based on Langevin dynamics of a few relevant degrees of freedom on a free-energy surface is proposed. The surface is obtained here from simulation and from a semi empirical expression. The mass and friction coefficients are derived from atomistic umbrella-sampling molecular-dynamics simulations. The calculated nucleation rate agrees with atomistic simulations for one particular state point of the Lennard-Jones fluid. The present method is about four orders of magnitude more computationally efficient than the direct atomistic simulation of the transmission coefficient.David M. Huang and Phil Attar

Hydrophobic interactions: an overview

We present an overview of the recent progress that has been made in understanding the origin of hydrophobic interactions. We discuss the different character of the solvation behavior of apolar solutes at small and large length scales. We emphasize that the crossover in the solvation behavior arises from a collective effect, which means that implicit solvent models should be used with care. We then discuss a recently developed explicit solvent model, in which the solvent is not described at the atomic level, but rather at the level of a density field. The model is based upon a lattice-gas model, which describes density fluctuations in the solvent at large length scales, and a Gaussian model, which describes density fluctuations at smaller length scales. By integrating out the small length scale field, a Hamiltonian is obtained, which is a function of the binary, large-length scale field only. This makes it possible to simulate much larger systems than hitherto possible as demonstrated by the application of the model to the collapse of an ideal hydrophobic polymer. The results show that the collapse is dominated by the dynamics of the solvent, in particular the formation of a vapor bubble of critical size. Implications of these findings to the understanding of pressure denaturation of proteins are discussed.Comment: 10 pages, 4 figure