Densification kinetics of nanocrystalline zirconia powder using microwave and spark plasma sintering--a comparative study

Two-stage densification process of nanosized 3 mol% yttria-stabilized zirconia (3Y-SZ) polycrystalline compacts during consolidation via microwave and spark-plasma sintering have been observed. The values of activation energies obtained for microwave and spark-plasma sintering 260-275 kJ x mol(-1) are quite similar to that of conventional sintering of zirconia, suggesting that densification during initial stage is controlled by the grain-boundary diffusion mechanism. The sintering behavior during microwave sintering was significantly affected by preliminary pressing conditions, as the surface diffusion mechanism (230 kJ x mol(-1)) is active in case of cold-isostatic pressing procedure was applied.     

Effect of Preconstruction Planning Effort on Sheet Metal Project Performance

The complexity of construction industry requires the identification of work tasks and the coordination of interactions among them. As a result, construction planning is considered to be one of the most critical steps toward success and is the main focus of past research. Consequently, little research has been performed regarding the preconstruction planning, which is the planning completed by the contractor in the period between project award and project execution. This paper focuses on sheet metal preconstruction planning, primarily that of mechanical and heating ventilations and air conditioning contractors. The research was completed in three phases: phase one gathered data on the current state of preconstruction planning, phase two developed a model sheet metal preconstruction planning process to be used by sheet metal contractors, and phase three validated the model preconstruction planning process. Based on project data collected for this research, projects that used a planning process similar to the model process performed more successfully—they achieved an average profit margin of 23% while projects that were poorly planned experienced an average profit margin of ?3%.     

Nanosized fibers' effect on adult human articular chondrocytes behavior

Tissue engineering with chondrogenic cell based therapies is an expanding field with the intention of treating cartilage defects. It has been suggested that scaffolds used in cartilage tissue engineering influence cellular behavior and thus the long-term clinical outcome. The objective of this study was to assess whether chondrocyte attachment, proliferation and post-expansion re-differentiation could be influenced by the size of the fibers presented to the cells in a scaffold. Polylactic acid (PLA) scaffolds with different fiber morphologies were produced, i.e. microfiber (MS) scaffolds as well as nanofiber-coated microfiber scaffold (NMS). Adult human articular chondrocytes were cultured in the scaffolds in vitro up to 28 days, and the resulting constructs were assessed histologically, immunohistochemically, and biochemically. Attachment of cells and serum proteins to the scaffolds was affected by the architecture. The results point toward nano-patterning onto the microfibers influencing proliferation of the chondrocytes, and the overall 3D environment having a greater influence on the re-differentiation. In the efforts of finding the optimal scaffold for cartilage tissue engineering, studies as the current contribute to the knowledge of how to affect and control chondrocytes behavior.     

An Ytterbium-doped Monomode Fibre Laser: Broadly Tunable Operation from 1·010 μm to 1·162 μm and Three-level Operation at 974 Nm

Abstract

Continuous-wave laser action has been observed from an ytterbium-doped monomode fibre laser on the three-level transition at 974 nm and on the four-level transition at 1036 nm with slope efficiencies of 67% and 77% respectively, with respect to absorbed power. Tuning behaviour is described, in which polarisation control by means of fibre loops has allowed smooth continuous tuning from 1·010 μm to 1·162 μm.     

Handbook of Laser Science and Technology

A brief account is given of the reasons why the classical notion of resolving power fails to provide a satisfactory quality criterion of optical systems designed to form images of extended objects. The discussion indicates that a quantity here called the structural resolving power, which is formally identical with an assessment proposed independently by Schade (1952) and Fellgett (1953), seems well suited to replace the old notion of resolution limit in evaluating the images of extended objects. On the basis of known results about images by systems with annular apertures, and of the rather close relation between the structural resolving power of an optical system and its information-passing capacity, it is concluded that the image of an extended object showing low-contrast fine structure begins to show visible deterioration when the reduction in the structural resolving power of the optical system by aberrations or by central obstruction reaches about 20 per cent. L'auteur rappelle brièvement les raisons pour lesquelles la notion classique de pouvoir séparateur ne peut fournir un criterium de qualité satisfaisant pour les systèmes optiques calculés pour la formation d'images d'objets étendus. La discussion montre qu'une grandeur appelée ici pouvoir séparateur de structure, tout à fait analogue à une grandeur définie indépendamment par Schade en 1952 et par Fellgett en 1953, semble bien convenir au remplacement de l'ancienne notion de limite de résolution pour l'appréciation des images d'objets étendus. En s'appuyant sur les résultats connus concernant les images formées par des systèmes à ouvertures annulaires et sur la relation étroite existant entre le pouvoir séparateur de structure d'un système optique et sa capacité de transmission d'information, on conclut que l'image d'objets étendus ayant une structure fine faiblement contrastée commence à s'altérer visiblement quand la réduction du pouvoir séparateur de structure du système due aux aberrations ou à une obturation centrale atteint environ 20 %. Es werden kurz die Gründe dargelegt, warum der klassische Begriff des Auflösungsvermögens als Gütekriterium versagt, wenn man ihn auf optische Systeme anwenden will, die für die Abbildung ausgedehnter Objekte bestimmt sind. Eine Grösse, die hier “strukturauflösung” genannt wird und im Wesentlichen mit der von Schade (1952) und Fellgett (1953) vorgeschlagenen Festsetzung übereinstimmt, scheint jedoch gut geeignet zu sein, für die Beurteilung der Abbildung ausgedehnter Objekte die alte Definition des Auflösungsvermögens zu ersetzen. Die bekannten Ergebnisse bei der Abbildung durch Systeme mit ringförmiger Pupille und die enge Beziehung zwischen der Strukturauflösung und der Informationskapazität optischer Systeme lassen schliessen, dass das Bild eines ausgedehnten Objektes mit feinen kontrastarmen Einzelheiten eine deutliche Verschlechterung erst dann zeigt, wann die Strukturauflösung des optischen Systems infolge von Aberrationen oder von einer zentralen Abblendung um 20 % zurückgeht.     

Characterisation of amorphous silica in air-oxidised Ti3SiC2 at 500–1000 °C using secondary-ion mass spectrometry,nuclear magnetic resonance and transmission electron microscopy

In this paper we have described the use of secondary-ion mass spectrometry (SIMS), solid state ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) to detect the existence of amorphous silica in Ti₃SiC₂ oxidised at 500–1000 °C. The formation of amorphous SiO₂ and growth of crystalline TiO₂ with temperature was monitored using dynamic SIMS and synchrotron radiation diffraction. A duplex structure with an outer TiO₂-rich layer and an inner mixed layer of SiO₂ and TiO₂ was observed. Results of NMR and TEM verified for the first time the direct evidence of amorphous silica formation during the oxidation of Ti₃SiC₂ at the temperature range 500–1000 °C.     

Hydration of Nafion® studied by AFM and X-ray scattering

Nafion® is a commercially available perfluorosulphonate cation exchange membrane commonly used as a perm-selective separator in chlor-alkali electrolysers and as the electrolyte in solid polymer fuel cells. This usage arises because of its high mechanical, thermal and chemical stability coupled with its high conductivity and ionic selectivity, which depend strongly on the water content. The membrane was therefore studied in different states of hydration with two complementary techniques: atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) combined with a maximum entropy (MaxEnt) reconstruction. Tapping mode phase imaging was successfully used to identify the hydrophobic and hydrophilic regions of Nafion. The images support the MaxEnt interpretation of a cluster model of ionic aggregation, with spacings between individual clusters ranging from 3 to 5 nm, aggregating to form cluster agglomerates with sizes from 5 to 30 nm. Both techniques indicate that the number density of ionic clusters changes as a function of water content, and this explains why the bulk volumetric swelling in water is observed to be significantly less than the swelling inferred from scattering measurements.     

Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II,III) oxide

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H₂O₂ dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H₂O₂ or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H₂O₂ or by iron oxide surface. Sorption and decolourization rate of RhB as well as H₂O₂ decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural Fe^II content strongly affects the reactivity towards H₂O₂ decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H₂O₂ system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants.