On debonding of graded thermal barrier coatings

Thermal barrier coatings generally consist of a metallic substrate which is the primary structural component, a metallic bond coat which serves as oxygen diffusion barrier, a very thin layer of thermally grown oxide and a ceramic top coat that provides the main thermal shielding. Homogeneous ceramic coatings as top coats appear to have certain undesirable features such as high residual and thermal stresses, generally low toughness and relatively poor bonding strength. The new concept of compositional grading of the top coat may help to overcome some of these shortcomings by eliminating the material property discontinuities. A common mode of failure in thermal barrier coatings seems to be the debonding of the top coat. In this study the related interface crack problem for a graded ceramic/metal top coat is considered. It is assumed that the thermophysical properties of the top coat continuously vary between that of the bond coat at the top coat-bond coat interface and that of the ceramic at and near the free surface. The main objective of the study is to examine the influence of the material nonhomogeneity parameters and relative dimensions on the stress intensity factors and the crack opening displacements.     

The use of Bacillus subtilis immobilized on Amberlite XAD-4 as a new biosorbent in trace metal determination

The present work proposes the use of Bacillus subtilis immobilized on Amberlite XAD-4 as new biosorbent in trace metal determination. The procedure is based on the biosorption of Cu and Cd ions on a column of Amberlite XAD-4 resin loaded with dried, dead bacterial components prior to their determination by flame AAS. Various parameters such as pH, amount of adsorbent, eluent type and volume, flow rate of solution and matrix interference effect on the retention of the metal ions have been studied. The optimum pH values of quantitative sorption for Cu and Cd were found to be 7.0 and 7.5, respectively. These metal ions can be desorbed with 1M HCl (recovery, 96-100%). The sorption capacity of the resin was 0.0297 and 0.035 mmol g(-1) for Cu(2+) and Cd(2+), respectively. The tolerance limit of some electrolytes were also studied. This procedure was applied to Cu(2+) and Cd(2+) determination in aqueous solutions, including river and well water systems. In order to evaluate the accuracy of the proposed procedure, the certified reference materials, NRCC-SLRS-4 Riverine water and LGC7162 Strawberry leaves were analyzed.     

A longitudinal study of the moderating role of extraversion: Leader-member exchange, performance, and turnover during new executive development.

Identifying factors that help or hinder new executives in "getting up to speed" quickly and remaining with an organization is vital to maximizing the effectiveness of executive development. The current study extends past research by examining extraversion as a moderator of relationships between leader-member exchange (LMX) and performance, turnover intentions, and actual turnover for an executive sample. The sample consisted of 116 new executives who were surveyed prior to starting their employment and at 3 months postentry. A total of 67 senior executives rated these new executives in terms of overall performance at 6 months postentry. Turnover data were gathered from company records 3 1/2 years later. Hierarchical regression results showed that LMX was not related to performance or turnover intentions for those high in extraversion; but for individuals low in extraversion, there was a relation between LMX, performance, and turnover intentions. Furthermore, survival analyses showed that LMX was only related to turnover-hazard rate for individuals low in extraversion. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Collaboration Environments for Construction: Implementation Case Studies

Although emerging technologies offer the construction industry many opportunities for computer supported collaboration environments, the companies adopting these technologies usually fail in achieving the full benefits from their implementations. The reason for this is found to be focusing too much on the technical factors and ignoring or underestimating the factors related to change, implementation, human and organizational factors, and the roles of the management and end users. Each new information technology (IT) implementation involves some change for the organization and the employees, and is therefore a source of resistance and confusion unless special attention is paid to managing this change. This paper aims to review the related theoretical concepts and previous work on success factors for collaboration environment implementations and failure reasons for IT, and to present the current approaches adopted by construction organizations implementing collaboration environments. In order to achieve these aims, the results of an extensive literature review on general causes of failure in IT implementations are presented, and the key areas to focus on during IT design and implementation are highlighted and explained. The results of exploratory case studies are summarized to show the current IT implementation and collaborative working approaches in the United Kingdom construction industry and interpreted using a systems thinking approach. The paper then concludes with some insights into how construction organizations can improve the implementation of collaboration systems.     

Effect of Sintering Duration on Some Properties of Pure Magnesium

Powder Metallurgy and Metal Ceramics - Tribological and physical properties of pure magnesium (Mg) are investigated during sintering for 2, 4, and 6 h at the temperature of 600°C. The pure...     

Relationships between the presence of Johne's disease and farm and management factors in dairy cattle in England

The data collected by a postal questionnaire sent to 3772 randomly selected dairy farmers in England and the border regions in Wales were used to estimate the relationships between the presence of clinical Johne's disease and farm and management factors associated with that disease. Two binary outcomes (case reported in 1993, case reported in 1994) and 27 predictor variables were considered. Only two variables were consistently and significantly associated with clinical disease in multivariable analysis. Farms on which Channel Island breeds were predominant were associated with an increased risk of reporting disease (odds ratios (ORs) ranged from 10.9 to 12.9). The presence of farmed deer on the farm also increased the risk of reporting disease (ORs ranged from 15.2 to 209.3). There were other significant but inconsistent associations involving the source of replacements, age of first-offering hay, type of concentrate feed to calves, and calving in individual pens when the cows were at grass. Since Johne's disease is predominantly subclinical, these contributing factors may play important roles in switching subclinical infection to overt disease.     

Morphological changes in poly(?-caprolactone) in dense carbon dioxide

Morphological changes that take place in poly(?-caprolactone) upon exposure to carbon dioxide at high pressures have been explored as a function of pressure and temperature. SEM and DSC results point to a competition between CO₂-modulated crystallization and pressure-induced phase separation which leads to unique morphologies. At 293 K, exposure to CO₂ at pressures up to 45 MPa leads to recrystallization resulting in higher level of crystallinity and higher melting temperatures. Highest crystallinity levels along with distinct crystal morphology were observed after exposure to CO₂ at 308 K and 21 MPa. At a higher pressure at this temperature (308 K/34 MPa) polymer undergoes melting, and foaming is achieved during depressurization prior to solidification. At 323 K, the polymer is found to display unique crystal morphology with concave crystal geometry as well as porous domains. The results are discussed in terms of the crystallization and phase separation paths that are followed during exposure to CO₂ and the depressurization stages.     

Packaged hybrid soliton pulse source results 70 terabit.km/secsoliton transmission

A packaged hybrid soliton pulse source is used in a soliton transmission experiment employing sliding-frequency guiding filters. The source shows excellent stability and very clean tuning characteristics. Control of the operating frequency and wavelength are described. Error free transmission at 10 GBit/s is achieved over a distance of 27000 km     

Four channel fibre grating demultiplexer

The authors demonstrate a four channel all-fibre demultiplexer based on a 1×4 fused fibre coupler followed by strong fibre grating passband filters