Elaboration of Monophasic and Biphasic Calcium Phosphate Coatings on Ti6Al4V Substrate by Pulsed Electrodeposition Current

Calcium phosphate coatings on Ti6Al4V substrates are elaborated by pulsed electrodeposition. The surface morphology and chemical composition of the coatings are characterized by SEM–EDS. The obtained results are systematically confirmed at the nanometre scale using TEM. Moreover, XRD is performed in order to identify the coatings phases. The results show that pulsed electrodeposition allows uniform coatings to be obtained without the holes and craters usually observed with classical electrodeposition. After appropriate heat treatment, these coatings have a biphasic composition of stoichiometric hydroxyapatite and β‐tricalcium phosphate. Moreover, the addition of 9% H₂O₂ to the electrolyte leads to monophasic coatings made of stoichiometric hydroxyapatite. As an indication of the passive nature of the electrodeposited coating, electrochemical potentiodynamic tests are performed in physiological solution in order to determine the corrosion behaviour of these coatings.     

Functionalisation and chemical characterisation of cellulose-derived carbon aerogels

A series of nitrogen- and oxygen-functionalised carbon aerogels was produced from a carbon aerogel derived from cellulose acetate. Samples were oxidised by H₂O₂ or HNO₃ and/or enriched in nitrogen by reaction with gaseous ammonia or co-heating of the carbon aerogel and melamine. Porosity variations and morphology were monitored using N₂ adsorption and helium pycnometry. The surface chemistry was characterised by elemental analysis, FTIR and XPS spectroscopy, pH of the point of zero charge and acid/base titration. The prepared carbons are mainly mesoporous and show a moderate porosity development (S_BET between 160 and 300 m²/g). The applied chemical methods allow producing a wide range of functionalised carbon aerogels differing in terms of oxygen and nitrogen groups, their distribution and basicity. Both oxidation methods introduce a similar amount of oxygen, while the produced carbons differ in term of their acid/base character. Treatment with ammonia produces the most basic materials, which is partly due to the introduction of basic nitrogen groups, but also to the reduction of the acidic oxygen functionalities.     

Interactions between steels and sulphide-producing bacteria—Corrosion of carbon steels and low-alloy steels in natural seawater

Metallic infrastructure immersed in natural seawater is exposed to important corrosion phenomena, which are sometimes characterised by microorganism influenced corrosion. The presence of sulphide-producing bacteria is generally associated with catastrophic cases of material degradation. In this work, commercial steel grades (carbon steels and low-alloy steels) are immersed for approximately 1 year in two types of natural seawater, which contain different concentrations of sulphide-producing bacteria. Gravimetric, microbiological, and electrochemical measurements and corrosion product analyses indicate that in seawater the observed corrosion phenomenon is composed of two different phases. The first phase is characterized by decreased corrosion kinetics correlated with a higher concentration of sessile sulphide-producing bacteria and the formation of sulphur-containing chemical species. The second phase is marked by an increased rate of corrosion. This multidisciplinary study demonstrates the complexity of the interactions between steels and bacteria. The presence of alloying elements in the steel composition affects the rate of corrosion and growth patterns of sessile sulphide-producing bacteria. At the same time, the presence of sulphide-producing bacteria affects in the process of steel corrosion in natural seawater.     

Sequential model identification of reaction systems—The missing path between the incremental and simultaneous approaches

Modeling chemical reaction systems is an important but complex task. The identified kinetic model must be able to explain all the underlying rate processes such as chemical reactions and heat and mass transfers. Traditionally, the modeling task is carried out using a simultaneous approach, which, for model prediction, requires having model candidates for all rate processes. The simultaneous approach leads to statistically optimal parameter estimates in the maximum-likelihood sense, but it can be computationally expensive due to its combinatorial nature. The incremental approach, via either rates or extents, was introduced as an alternative to the simultaneous approach. It is characterized by the fact that each rate process can be modeled individually, that is, independently of the other rate processes. Hence, the incremental approach is computationally more attractive, however, at the price of not guaranteeing statistically optimal parameter estimates. This article proposes a novel sequential approach that combines the advantages of the incremental and simultaneous approaches. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1211–1221, 2019     

Thermoresponsive Complex Coacervate‐Based Underwater Adhesive

Sandcastle worms have developed protein‐based adhesives, which they use to construct protective tubes from sand grains and shell bits. A key element in the adhesive delivery is the formation of a fluidic complex coacervate phase. After delivery, the adhesive transforms into a solid upon an external trigger. In this work, a fully synthetic in situ setting adhesive based on complex coacervation is reported by mimicking the main features of the sandcastle worm's glue. The adhesive consists of oppositely charged polyelectrolytes grafted with thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) chains and starts out as a fluid complex coacervate that can be injected at room temperature. Upon increasing the temperature above the lower critical solution temperature of PNIPAM, the complex coacervate transitions into a nonflowing hydrogel while preserving its volume—the water content in the material stays constant. The adhesive functions in the presence of water and bonds to different surfaces regardless of their charge. This type of adhesive avoids many of the problems of current underwater adhesives and may be useful to bond biological tissues.     

When moderation is mediated and mediation is moderated.

Procedures for examining whether treatment effects on an outcome are mediated and/or moderated have been well developed and are routinely applied. The mediation question focuses on the intervening mechanism that produces the treatment effect. The moderation question focuses on factors that affect the magnitude of the treatment effect. It is important to note that these two processes may be combined in informative ways, such that moderation is mediated or mediation is moderated. Although some prior literature has discussed these possibilities, their exact definitions and analytic procedures have not been completely articulated. The purpose of this article is to define precisely both mediated moderation and moderated mediation and provide analytic strategies for assessing each. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the quantification of quenching transient thermal stresses in brittle solids using Vickers indentations

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Ultra wideband: the radio link of the future?

A new data transmission technique is about to create a revolution in the field of wireless local area networks. This new method, called Ultra Wideband, is based on the transmission of data through the communication channel below the noise floor. It involves transmitting very short duration pulses, which has the effect of spreading the signal energy across a wide frequency range. The objective of this article is to report on the state of the art in this research area, and to outline the main advantages of this promising data transmission method.