Synthesis of nickel–rubber nanocomposites and evaluation of their dielectric properties

Nanocomposites based on natural rubber and nano-sized nickel were synthesized by incorporating nickel nanoparticles in a natural rubber matrix for various loadings of the filler. Structural, morphological, magnetic and mechanical properties of the composites were evaluated along with a detailed study of dielectric properties. It was found that nickel particles were uniformly distributed in the matrix without agglomeration resulting in a magnetic nanocomposite. The elastic properties showed an improvement with increase in filler content but breaking stress and breaking strain were found to decrease. Dielectric permittivity was found to decrease with increase in frequency, and found to increase with increase in nickel loading. The decrease in permittivity with temperature is attributed to the high volume expansivity of rubber at elevated temperatures. Dielectric loss of blank rubber as well as the composites was found to increase with temperature.     

Scientists’ perceptions of the social and political implications of their research

We explore an empirical approach to studying the social and political implications of science by gathering scientists’ perceptions of the social impacts of their research. It was found that 78 percent of surveyed scientists from a variety of fields responding to a survey indicated that the research performed in connection with a recent highly cited paper had such implications. Health related implications were the most common, but other types of implications encountered were technological spin-offs, public understanding, economic and policy benefits. Surprisingly many scientists considered the advancement of science itself to be a social implication of their research. The relations of these implications to the field and topics of research are examined, and a mapping of implications gives an overview of the major dimensions of the social impacts of science.     

Exploration of entire range of III–V semiconductors and their device applications

Abstract

Superplastic deformation of certain metallic alloys was first observed almost a century ago but simply remained an interesting metallurgical curiosity until the revelation, in 1962, of work in the former Soviet Union. This led to western research and the suggestion by Backofen that the phenomenon could be practically exploited for the manufacture of sheet components. In turn, this resulted in major work to develop new superplastic alloys, forming machinery and forming techniques. Although superplastic behaviour has now been developed in a wide range of materials, its exploitation has been confined to niche applications. It is only the superplastic alloys of titanium and aluminium that have achieved significant commercial markets. The fact that titanium alloys can combine superplastic forming with diffusion bonding to manufacture multisheet structures has assured the material a secure and growing role in aerospace applications. The high basic cost of titanium has precluded significant use in other markets although this could change if current developments in the titanium extraction process are successful. Superplastically formed aluminium components find application in a far wider range of niche applications. It is suggested that the more recent demonstration of superplastic behaviour at much higher strain rates (HSRS) could allow superplastic forming of aluminium alloys to break out of its niche role. However, significant development would be required to combine the existing fundamental knowledge of HSRS with engineering to define a practical, economic manufacturing route for volume production of the new material.     

Electrodeposition of nanostructured coatings and their characterization—A review

Abstract

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.     

Electrodeposition of nanostructured coatings and their characterization—A review

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.     

Study of standard thermometers and their reproduction of the λ point in liquid helium

Self-calibrated resistance thermometers to be used as standards have been investigated. The heat exchange of the sensor coil with liquid helium per unit coil surface area at 0.3 K is 12 times better than that of a conventional gas-filled thermometer. The exchange is due to Kapitza surface thermal resistance. The λ point in liquid helium filling of the thermometer is reproducible to within 0.1 mK. Translated from Izmeritel’naya Tekhnika, No. 7, pp. 50–52, July, 1999     

Designing of macroporous biocompatible cryogels of PVA–haemoglobin and their water sorption study

Macroporous polymeric materials are three-dimensional porous architectures having enormous utility in the areas of biomedical, biotechnological and separation sciences. Thus realizing the crucial role of macroporous polymeric materials in tissue engineering and allied fields the present paper discusses synthesis, characterization, and blood compatibility study of macroporous cryogels of PVA and haemoglobin. Biocompatible spongy and porous hydrogels of polyvinyl alcohol–haemoglobin have been synthesized by repeated freezing–thawing method and characterized by Infrared (FTIR), and ESEM techniques. The FTIR analysis of prepared cryogels indicated that haemoglobin was introduced into the cryogel possibly via hydrogen bonds formed amongst hydroxyl groups and amino groups present in PVA and haemoglobin, respectively. The ‘cryogels’ were evaluated for their water uptake potentials and influence of various factors such as chemical architecture of the spongy hydrogels, pH and temperature of the swelling bath were investigated on the degree of water sorption by the cryogels. The hydrogels were also swollen in salt solutions and various simulated biological fluids. The effect of drying temperature on its water sorption capacity was also studied. The biocompatibility of the prepared cryogels was judged by in vitro methods of blood-clot formation, percent haemolysis and protein (BSA) adsorption.     

Types of superplasticm-δ curves of Ti-6Al-4V alloy and their intertransformation

The superplasticm- curves of Ti-6Al-4 alloy have been determined at different temperatures and strain rates; all were of them _L=m _max type, and were of either fundamental, descending or ascending types. The latter two types were transformed from the former through the processes ofm _Lm _O, _LO andm _Lm _F, _LF, respectively. The highest total elongation, _F, was 1150% obtained at 950C and 1.55×10^–3 s^–1. The Chin Liu equation has been applied to all types ofm- curves. The parameters characteristic of all types ofm- curves have been obtained and were found to vary with temperature and strain rate. The total elongation, _F, is determined by the resultant effects of all other parameters, not by a singlem value, theoretically considered to be constant and determined practically by a tensile strain of about 30%–50% (m _30%–50%) as usual.Nomenclature C (=k/k _o ) the normalized slope ofm- curve corresponding to - a material constant corresponding to - m strain-rate sensitivity index corresponding to - m _max maximum on them- curve corresponding to _L - m _min minimum on them- curve corresponding to _L - crosshead speed during the tensile test - the strain of the entire stretching process (has same significance as ordinarily adopted ) - _F total elongation at fracture chosen for the present work - _I intermediate strains including _I1, _I2, _I3, ..., _I(i–1), _Ii , _I(i+1), ..., chosen for the present work - _L limit strain separatingm- curves into sections - _O (=0) starting strain - strain rate - flow stress     

Solution-liquid-solid synthesis of CuInSe₂ nanowires and their implementation in photovoltaic devices

CuInSe? (CIS) nanowires were synthesized by solution-liquid-solid (SLS) growth in a high boiling solvent using bismuth nanocrystals as seeds. The nanowires tended to be slightly deficient in In and exhibited either cubic or hexagonal crystal structure, depending on the synthesis conditions. The hexagonal structure, which is not observed in bulk crystals, appears to evolve from large concentrations of twin defects. The nanowires could be compressed into a free-standing fabric or paper-like material. Photovoltaic devices (PVs) were fabricated using the nanowires as the light-absorbing layer to test their viability as a solar cell material and were found to exhibit measurable PV response.     

Compaction of fly ash–aluminum alloy composites and evaluation of their mechanical and acoustic properties

The density and elastic moduli of green compacts can be determined by ultrasonic method with the help of pre-prepared diagrams. In this way, pressing conditions can be taken under control easily. In this study, fly ash particles were used as fillers in an aluminum alloy matrix material. The weight fractions of fly ash in the composites were in the range of 5–30%. The resulting composites were compacted at pressures ranging from 63 MPa to 316 MPa. It was observed that the green density increased with increasing compacting pressure and decreased with increasing weight percent of fly ash particles resulting in lightweight composites. The green compact composites were also tested using an ultrasonic non-destructive evaluation method. Results showed that ultrasonic velocities are a strong function of the density and the fly ash fraction in this material and could be potentially used to predict the density and the fly ash fraction as well as the elastic moduli of the metal matrix composite.     

Construction of TiO₂ hierarchical nanostructures from nanocrystals and their photocatalytic properties

Anatase TiO(2) mesoporous structures with high specific surface areas are of special significance in various applications. In this work, hierarchical anatase TiO(2) materials with flowerlike morphologies have been prepared via a one-step template-free hydrothermal method, by using titanocene dichloride as precursor and EDA as chelating agent in aqueous solution. Particularly, the hierarchical structures are assembled from very thin TiO(2) nanosheets, which are composed of numerous highly crystallized anatase nanocrystals. In addition, the assembled materials own relatively large specific surface areas of 170 m(2)/g, and uniform mesopores of 7 nm. We further demonstrate that the hierarchical TiO(2) materials show very good photocatalytic performance when applied in photodegradation of methylene blue, which should be related to the unique features of hierarchical structures, large specific surface areas and high crystallization degree of the obtained TiO(2) materials. With these features, the hierarchical TiO(2) may find more potential applications in the fields such as dye-sensitized solar cells and lithium ion batteries.     

How realistic are older drivers’ ratings of their driving ability?

One strategy that can be used by older drivers to guard against age-related declines in driving capability is to regulate their driving. This strategy presumes that self-judgments of driving capability are realistic. We found no significant relationships between older drivers’ hazard perception skill ratings and performance on an objective and validated video-based hazard perception test, even when self-ratings of performance on specific scenarios in the test were used. Self-enhancement biases were found across all components of driving skill, including hazard perception. If older drivers’ judgments of their driving capability are unrealistic, then this may compromise the effectiveness of any self-restriction strategies to reduce crash risk.     

Fabrication of PbS nanoparticle-sensitized TiO₂ nanotube arrays and their photoelectrochemical properties

TiO(2) nanotube arrays (NTAs) are modified with PbS nanoparticles by successive ionic layer adsorption and reaction (SILAR) or electrodeposition, with an aim towards tuning the photoelectrochemical cell to the visible region. The PbS modification of the TiO(2) NTAs results in an increase in the visible light adsorption, however the increase in photocurrent is dependent on the modification method. PbS/TiO(2) NTAs prepared by SILAR and electrodeposition show, respectively, photocurrents of 11.02 and 5.72 mA/cm(2). The increase in photocurrent is attributed to enhanced charge separation efficiency and improved electron transport.     

Nucleation and growth of β′magnesium sialons and their composition limits

Previous reports on the solubility of magnesium in -sialons have been conflicting. The present work shows conclusively that crystalline magnesium sialons with the silicon nitride structure do exist. They are formed by crystallization of magnesium sialon glasses at low temperatures. -magnesium sialon crystals nucleate on -sialon nuclei which are themselves formed by precipitation from Mg-Si-Al-O-N liquids at high temperatures. The current results suggest that -magnesium sialons exist only over a limited composition range within the 3M/4X plane of the Mg-Si-Al-O-N system, which is indicative of some form of ordering within the structure. Although the compositions investigated in the present study are unstable with respect to forsterite above about 1000° C, the possibility of producing -magnesium sialons which are stable at much higher temperatures cannot be fully discounted at present.     

Comparison of the superelasticity of different nickel–titanium orthodontic archwires and the loss of their properties by heat treatment

The aim of this work is to describe and compare mechanical properties of eight widely used nickel–titanium orthodontic wires under uniform testing conditions and to determine the influence of the heat treatments on the loss of the superelasticity. Ten archwires from two batches from eight different manufacturers were evaluated. A three-point bending test was performed, in accordance with ISO 15841:2006, on 80 round nickel–titanium archwire segments of 0.016?inch. To obtain a load-deflection curve, the centre of each segment was deflected to 3.1?mm and then unloaded until force became zero. On the unloading curve, deflection at the end of the plateau and forces delivered at that point, and at 3, 2, 1 and 0.5?mm of deflection, were recorded. Plateau slopes were calculated from 3 and from 2?mm of deflection. Data obtained were statistically analysed to determine inter-brand, intra-brand and inter-batch differences (P?<?0.05). The results show that at 2?mm of deflection, maximum differential force exerted among brands [Nitinol SuperElastic (1.999N)—Sentalloy M (1.001?N)] was 0.998?N (102?gf). The Nitinol SuperElastic plateau slope (0.353?N/mm) was the only one that was statistically different from 2?mm of deflection, as compared with the other brand values (0.129–0.155?N/mm). Damon Optimal Force described the gentlest slope from 3?mm of deflection (0.230?N/mm) and one of the longest plateaus. Titanol and Orthonol showed the most notable intra-brand differences, whereas inter-batch variability was significant for Nitinol (Henry Schein), Euro Ni–Ti and Orthonol. Superelasticity degree and exerted forces differed significantly among brands. Superelasticity of Nitinol SuperElastic was not observed, while Damon Optimal Force and Proclinic Ni–Ti Superelástico (G&H) showed the most superelastic curves. Intra-brand and inter-batch differences were observed in some brands. In all cases, the heat treatment at 600?°C produces precipitation in the matrix. The precipitates are rich in titanium and this fact produce changes in the chemical composition of the matrix and the loss of the superelasticity. At 400?°C these precipitates are not produced and the forces delivered by the wires are very similar with wires untreated.     

Quantification of amino acids in fermentation media by isocratic HPLC analysis of their α-hydroxy acid derivatives

In this paper we describe a novel method for quantification of amino acids. First, α-hydroxy acid derivatives of amino acids were formed after reaction with dinitrogen trioxide by the van Slyke reaction. Second, the α-hydroxy acid derivatives were separated on an Aminex HPX-87H column (Bio-Rad) eluted isocratically with 5 mM H(2)SO(4) and quantified by refractive index detection. We were able to measure the reaction products of 13 of the 20 classical amino acids: glycine, l-alanine, l-valine, l-leucine, l-isoleucine, l-methionine, l-serine, l-threonine, l-asparagine, l-glutamine, l-aspartic acid, l-glutamic acid, and l-proline. We obtained linear relationships between the product peak areas and initial amino acid concentration, whereby the concentrations of these amino acids could be quantified on the basis of the quantification of their products. The method can be used to analyze amino acids in parallel with other small molecules, such as sugars or short chain fatty acids, and was used for parallel quantification of glycine, l-alanine, or l-glutamic acid, and glucose uptake in cultures of the heterotrophic dinoflagellate Crypthecodinium cohnii . The method can also be used to quantify other amines, as demonstrated by detection of Tris (2-amino-2-(hydroxymethyl)propane-1,3-diol).     

Mössbauer study of the dynamical properties of some lead borate glasses near their transformation temperature

Calcium-lead-borate glasses containing iron were thoroughly studied by Mössbauer effect spectroscopy aiming to determine both their Debye temperature and their transformation temperature during heating. The obtained Mössbauer effect parameters at room temperature exhibit dispersion of iron ions in a low spin ferric state as modifying cations in a pure amorphous glass matrix. The electric field gradient due to the lattice was stabilized at moderate and high lead oxide content glasses. The high-temperature measurements were carried out between 300 and 750 K under vacuum. It can be concluded that the recoil-free fraction decreased and the mean square amplitude of the Mössbauer atom increased as the temperature was increased. From the Inf againstT curve, the Debye temperature of the solid glass can be calculated (_D = 373.8K). The experimentally determined transformation temperature from this study was found to be 665 K, which may be slightly less than the real value.     

A review of bast fibres and their composites. Part 2 – Composites

Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ～140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). Part 2 of this review will consider the prediction of the properties of natural fibre reinforced composites, manufacturing techniques and composite materials characterisation using microscopy, mechanical, chemical and thermal techniques. The review will close with a brief overview of the potential applications and the environmental considerations which might expedite or constrain the adoption of these composites.     

Multivariate chemometric discrimination of cigarette tobacco blends based on the UV–Vis spectrum of their hydrophilic extracts

The application of UV–Vis spectrophotometry as an alternative or complementary approach to the classification of tobacco products is presented in this work for the first time. Two hundred fifty samples from five different cigarette brands composed of single and mixed tobacco blends were examined for that purpose on the basis of the UV–Vis spectrum of their aqueous extracts. Data transformation based on the normalization of absorbance intensities as a function of sample weight was employed in order to account for differences in the relative intensities of each sample. Principal components analysis (PCA) was used to extract outlier cases and sample classification was then pursued with the aid of discriminant analysis (DA) suggesting that a reduced number of variables (thirteen out of seven hundred initially available) could provide perfect classification (100% correct assignations) of samples containing single tobacco species or different blends and a fair classification of samples with similar composition (80% correct assignations) yielding an overall 95.7% correct classification. To this pursue, classification and regression trees were found to afford perfect classification of all samples using only a few logic rules based on appropriate split conditions at the expense of inserting 15 variables in the model.