Microstructure and mechanical properties of co-continuous metal/ceramic composites obtained from Reactive Metal Penetration of commercial aluminium alloys into cordierite

Co-continuous metal/ceramic composites were obtained by the Reactive Metal Penetration (RMP) method. With the aim of components cost reduction, commercial cordierite preforms and standard aluminium infiltrating alloys (1050, 2011 and 7075) were used in the process. Kinetics of the infiltration reaction, microstructure and mechanical properties of the composites were found to be influenced by both quantity and type of alloying elements. In particular, while Young’s modulus remains quite constant, a marked increase in microhardness is observed with 2011 and 7075 alloys, even if to the detriment of flexural strength.     

A multifractal analysis of fatigue crack growth and its application to concrete

As is well-known, strength of materials is influenced by the specimen or structure size. In particular, several experimental campaigns have shown a decrease of the material strength under static or fatigue loading with increasing structure size, and some theoretical arguments have been proposed to interpret such a phenomenon. As far as fatigue crack growth is concerned, limited information on size effect is available in the literature, particularly for so-called quasi-brittle materials like concrete. In the present paper, by exploiting concepts of fractal geometry, some definitions of fracture energy and stress intensity factor based on physical dimensions different from the classical ones are discussed. A multifractal size-dependent fatigue crack growth law (expressing crack growth rate against stress intensity factor range) is proposed and used to interpret relevant experimental data related to concrete.     

PPy doped PEG conducting polymer films synthesized on LiFePO4 particles

In this work, polyethyleneglycole (PEG) is introduced into polypyrrole (PPy) film coated on LiFePO₄ powder particles to promote the properties of cathode material for lithium-ion batteries. The enhancement of the electrochemical activity by the substitution of a carbon with electrochemically active polymer is investigated. Films of the PPy doped with the PEG were prepared by the chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been added as an additive during polymerization process to improve mechanical and structural properties of the PPy in final PPy/PEG-LiFePO₄ cathode material. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge measurements were employed to characterize the electrochemical properties of PPy/PEG-LiFePO₄ material. The electrochemical performance of PPy-LiFePO₄ electrodes was greatly improved by introduction of PEG into the PPy films. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. The morphology and particle sizes of the prepared cathode powder material were investigated by scanning electron microscopy (SEM) and particle size analysis (PSA). Distribution of PPy and PPy/PEG films onto the LiFePO₄ particles surface was studied by time of flight secondary ion mass spectrometry (TOF-SIMS). In addition to polymeric coating layer on the surface of PPy-LiFePO₄ composite particles, some PPy unequally distributed between the particles was found. The median diameter value is 4.92 μm for PPy-LiFePO₄ sample. TOF-SIMS measurements and SEM images confirmed that thickness of polypyrrole coating on LiFePO₄ particles is about 100 nm.     

Measurement method and results of ice adhesion force on the curved surface of a wind turbine blade

Experimental adhesion force measurements were conducted on accumulated ice on the leading edge of a scaled wind turbine blade in both glaze and rime icing regimes. An apparatus was first designed for specifically measuring the adhesion force of ice on a curved surface at climatic temperature where a vertical force was applied to the mounted structure in the test apparatus. Adhesion force measurements were measured and adhesion pressure calculated for plain and ice-mitigated test specimens. Results are presented for the increase in force of ice adhesion over a curved surface area in proportion to degree centigrade decrease in temperature.     

Why attend school? Chinese immigrant and European American preschoolers' views and outcomes.

The developing views of the purposes of school learning (PSLs) and related achievement among immigrant Chinese preschoolers and their European American (EA) age-mates were examined. Both culture and socioeconomic status (SES) were considered simultaneously, an often neglected research approach to studying Asian children. One hundred and fifty 4-year-olds—50 each of middle-class Chinese (CHM), low-income Chinese (CHL), and EA children—completed 2 story beginnings about school and were also tested for their language and math achievement. Results showed that 4-year-olds held sophisticated PSLs, ranging from intellectual to social and affect benefits. Large cultural and SES differences also emerged. CHM children mentioned more adult expectation and seriousness of learning than EA children who expressed more positive affect for self and compliance with adults. CHL children mentioned fewest PSLs. Achievement scores for oral expression of both immigrant groups were significantly lower than those of EA children despite similar reading and math achievement. Controlling for culture and SES, the authors found that children's articulated intellectual, but not other purposes, uniquely predicted their achievement in all tested domains. Cultural and SES influences on immigrant children are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bismuth oxide-related photocatalysts in green nanotechnology: A critical analysis

A survey addressing the uses of bismuth oxide in photocatalysis is presented. The richness of literature on such a specific topic proves the growing importance of this compound as a valid tool in pollution abatement and environmental decontamination. Many research groups have focused their activity on how to improve the photocatalytic properties of this semiconductor and several solutions have been adopted in the synthesis method, often based on wet-chemical processes. The impressive development of nanoscience helped in understanding and identifying process variables and operative conditions aiming at optimizing the yield of this promising photocatalytic material in the utilization of solar energy.     

Ten years of <Emphasis Type="Italic">Energy Efficiency</Emphasis>: a bibliometric analysis

Energy Efficiency is an international journal dedicated to research topics connected to energy with a focus on end-use efficiency issues. In 2018, the journal celebrates its 10th anniversary. In order to mark it and analyze not only how the journal has been performing over the years, but also which are the trends for academic debate and research in this journal, this article presents a bibliometric overview of the publication and citation structure of the journal during period 2008–2017. The study relies on the Web of Science Core Collection and the Scopus database to collect the bibliographic results. Additionally, the work exploits the visualization of similarities (VOS) viewer software to map graphically the bibliographic material. The research analyses the most cited papers and the most popular keywords. Moreover, the paper studies how the journal connects with other international journals and identifies the most productive authors, institutions, and countries. The results indicate that the journal has rapidly grown over the years, obtained a merited position in the scientific community, with contributions from authors all over the world (with Europe as the most productive region). Moreover, the journal has focused so far mainly on energy efficiency issues in close relationship with policies and incentives, corporate energy efficiency, consumer behavior, and demand-side management programs, with both industrial, building and transport sectors widely involved. Our discussion concludes with suggested future research avenues, in particular towards coordinated efforts from different disciplines (technical, economic, and sociopsychological ones) to address the emerging energy efficiency challenges.     

Variability of intact rock mechanical properties for some metamorphic rock types and its implications on the number of test specimens

Intact rock strength and stiffness properties are commonly used in rock mass mechanical characterization, and their evaluation is usually based on laboratory tests. Due to the variability that affects strength and stiffness parameters, the determination of the number of laboratory-tested specimens required to obtain a reliable reference value is very useful. However, many studies reported in apposite literature focused only on the variability of strength parameters. This study investigates the variability of some of the most important strength and stiffness properties (unconfined compressive strength, indirect tensile strength, tangent and secant Young’s moduli, Poisson’s ratio) by applying statistical methods (statistical decision theory and statistical inference theory). A data set of 451 laboratory tests was used, performed on three rock types. The statistical analyses were applied with the aim of assessing how closely intact rock laboratory data follow a normal distribution and determining the minimum number of specimens required to obtain a reliable average value of the parameters in relation to a targeted precision index for a confidence level of 95 %. The results indicate that the minimum number of samples needed varies depending on rock and test types. Among the stiffness properties, tangent Young’s modulus has a lower variability than both the secant modulus and the Poisson’s ratio, whereas in terms of strength parameters, unconfined compressive strength is subject to greater variability than indirect tensile strength.     

Implementation and optimization of the HySyLab DMFC single cell test station

In this study, the construction and optimization of a low cost home-assembled DMFC single cell test station is described. The station was built using two flow control systems, for gas (air/oxygen) and liquid (methanol), a temperature controller, an electronic load, a milliohm-meter for resistance measurements and a computerized data acquisition system. The experiments were carried out on a 6.25 cm² single cell, built using two graphite plates with triple serpentine channel geometry for both anodic and cathodic flow fields. The cell was equipped with an MEA composed of Nafion 117 as electrolyte, Pt/C based catalyst as cathode and PtRu (1:1)/C as anode. In order to develop a HySyLab internal standard procedure, MEA activation was carefully studied. The activated MEA was used to determine the optimum values of cell operating parameters, such as oxidant flow, methanol flow and temperature.     

Crystallographic Texture Evolution of a Zinc Sheet Subjected to Different Strain Paths

Metallurgical and Materials Transactions A - The use of zinc sheets has largely increased in the last years, fundamentally because of new tendencies in architecture and, at the same time, due to...