Impact of Thermal Aging on the Microstructure Evolution and Mechanical Properties of Lanthanum-Doped Tin-Silver-Copper Lead-Free Solders

The authors would like to thank Ste´phanie Blanc (Electrical Engineer at Schlumberger) for her useful contribution to the project, Claude Guyomard and Olivier Naegelen (Arts et Me´tiers ParisTech) for the die design and sample casting, respectively, and Jean-Marc Raulot for his enriching discussions.An extensive study is made to analyze the impact of pure lanthanum on the microstructure and mechanical properties of Sn-Ag-Cu (SAC) alloys at high temperatures. Different compositions are tested; the temperature applied for the isothermal aging is 150 C, and aging times of 10 h, 25 h, 50 h, 100 h, and 200 h are studied. Optical microscopy with cross-polarized light is used to follow the grain size, which is refined from 8 mm to 1 mm for as-cast samples and is maintained during thermal aging. Intermetallic compounds (IMCs) present inside the bulk Sn matrix affect the mechanical properties of the SAC alloys. Due to high-temperature exposure, these IMCs grow and hence their impact on mechanical properties becomes more significant. This growth is followed by scanning electron microscopy, and energy-dispersive spectroscopy is used for elemental mapping of each phase. A significant refinement in the average size of IMCs of up to 40% is identified for the as-cast samples, and the coarsening rate of these IMCs is slowed by up to 70% with no change in the interparticle spacing. Yield stress and tensile strength are determined through tensile testing at 20 C for as-cast samples and after thermal aging at 150 C for 100 h and 200h. Both yield stress and tensile strength are increased by up to 20% by minute lanthanum doping

A Correction to the Immirizi Parameter of SU(2) Spin Networks

The elegant predictions of loop quantum gravity are obscured by the free Immirizi parameter. Dreyer (2003), considering the asymptotic quasinormal modes spectrum of a black hole, proposed that the Immirizi parameter may be fixed by letting the j=1 transitions of spin networks as the dominant processes contributing to the black hole area, as opposed to the expected j=1/2 transitions. This suggested that the gauge group of the theory might be SO(3) rather than SU(2). Corichi (2003), maintaining SU(2) as the underlying gauge group, and invoking the principle of local fermion-number conservation, reported the same value of the Immirizi parameter for j=1 processes as obtained by Dreyer. In this note, preserving the SU(2) structure of the theory, and considering j=1 transitions as the dominant processes, we point out that the value of the Immirizi parameter is in fact twice the value reported by these authors. We arrive at this result by assuming the asymptotic quasinormal modes themselves as dynamical systems obeying SU(2) symmetry.Comment: 7 page

Parenting styles and their impact on children’s academic self-concept, behavioural problems and executive functions

Parental styles have a significant impact on children’s developmental outcomes. It could be argued that negative parenting characteristics, including strictness, neglect, control, punishment, and lack of support potentially impact child academic self-concept, behavioural problems as well as child’s cognitive abilities. The current thesis examines this question in Kurdish primary school children. This thesis comprises 6 chapters: Chapter 1 and 2 consist of an introduction and literature review about the topic. Chapter 3 reports study 1 which examines parenting styles and their relationship with academic self-concept and behavioural problems. This chapter also considers whether academic self-concept serves as a mediator in the relationship between parenting styles and behavioural problems. In support of previous studies, results indicate a vital role of parenting styles on children’s academic self-concept and behavioural problems among Kurdish children. The results also indicate that academic self-concept serves as a significant mediator in the relationship between parenting styles with prosocial behaviour and internalising problems. Chapter 4 reports study 2, which is an intervention study. This study tests the impact of Systematic Training for Effective Parenting (STEP) programme to improve parenting styles and decrease parental stress. After three months a follow-up study was carried out in order to examine the effectiveness of the STEP programme. It was found that the intervention was effective in promoting parenting styles and reducing the level of parental stress in Kurdish mothers. The follow-up study showed that the changes were sustained over a three months period. However, contrary to expectation, no significant statistical differences were found in academic self-concept and behavioural problems between children whose mothers attended STEP and others whose mothers did not attend. Chapter 5 reports study 3 in which the individual differences in executive functions based on the parental monitoring and hyperactivity expressed by children was investigated. Additionally, a moderating role of parental monitoring in the relationship between children’s executive function and hyperactivity was performed in this study. Results indicated that children subjected to poor parental monitoring and showing a high level of hyperactivity had difficulties in inhibitory control, accuracy, processing speed and task persistence compared with the matched sample. PROCESS analysis indicated a significant moderating role of parental monitoring in the association between accuracy, verbal inhibition and task persistence with hyperactivity. The last chapter, Chapter 6, summarizes the findings of the empirical studies and provides the discussion, conclusion, limitations, implications and suggestions for future research

Construction Quality Perception of Construction Professionals and Their Expectations from a Quality Improvement Technique in Pakistan

The complexity arises in defining the construction quality due to its perception, based on inherent market conditions and their requirements, the diversified stakeholders itself and their desired output. A quantitative survey based approach was adopted in this constructive study. A questionnaire based survey was conducted for the assessment of construction Quality perception and expectations in the context of quality improvement technique. The survey feedback of professionals of the leading construction organizations/companies of Pakistan construction industry were analyzed. The financial capacity, organizational structure, and construction experience of the construction firms formed basis for their selection. After statistical analysis of survey feedback it was found reliable and valid for the inferential purpose to the target population of construction professionals. The quality perception was found to be project scope oriented, considered as an excess cost for a construction project and keeping the rework minimum by qualifying the required quality tests, keeping the defects minimum by ensuring the specifications of supplied material. Any quality improvement technique was expected to address the financial aspects of the construction project for the employer and contractor, by increasing the profitability through reduction in overall cost, reduction in time, reduction in defects and improving the productivity in a construction project. The study is beneficial for the construction professionals to assess the prevailing construction quality perception and the expectations from implementation of any quality improvement technique in construction projects. Keywords :Construction Quality, Perception, Expectations,  Improvement Techniqu

Distributed Algorithm for Parallel Edit Distance Computation

The edit distance is the measure that quantifies the difference between two strings. It is an important concept because it has its usage in many domains such as natural language processing, spell checking, genome matching, and pattern recognition. Edit distance is also known as Levenshtein distance. Sequentially, the edit distance is computed by using dynamic programming based strategy that may not provide results in reasonable time when input strings are large. In this work, a distributed algorithm is presented for parallel edit distance computation. The proposed algorithm is both time and space efficient. It is evaluated on a hybrid setup of distributed and shared memory systems. Results suggest that the proposed algorithm achieves significant performance gain over the existing parallel approach

Impact of Global Economic Meltdown on Property Development in Bauchi, Nigeria

The global economic meltdown is a situation in which the economy of a country experiences a sudden downturn brought on by a financial crisis. This global recession was caused by so many factors, thus, inflation rate, exchange rate, interest rate, unemployment rate, etc. This paper examined the impact of the global economic meltdown on property development in Bauchi, Nigeria. Data for the study are mainly primary in the form of questionnaires administered. The study had property development as an endogenous variable while a high-interest rate and unemployment rate as exogenous variables to measure the constructs. Multiple Regression were used to analyze the data. Among the study, findings are that high relationship exists between the two predictor variables (High-Interest Rate & Unemployment Rate) and dependent variable (property Development) where ‘R’ of 0.724 means the correlation is about 72 %; with R2 of 0.052 indicate that 5.2 % correlation, the analysis also depict in coefficient table that high-interest rate has more influence on dependent variable (PD) than unemployment rate. The analysis signified that the impact of the global economic meltdown has a positive effect on the dependent variable. Based on the findings, the study recommended governments and financial institutions intervention to curb the impediment of property development in Bauchi, Nigeria