The effect of pressure on GRIN lenses

The changes of the optical power of Gradient Index (GRIN) lenses occurring in hydrostatic pressures of the range of 0-2 GPa are investigated. The measurements of the position of the waist of the semiconductor laser beam revealed the increase of the optical power of the lenses with increasing pressure. The use of the special plano-concave lenses insensitive to the changes of the refractive index of the pressure medium allowed to attribute the changes to the increasing index gradient in GRIN material. The effect has been explained within the frame of Mueller’s theory of photoelasticity. The findings have been then confirmed in experiments with the plano-planar and plano-convex lenses of the same materials.     

The rise and decline in the United States of impregnated paperinsulated metallic sheathed cable, solid-type. I. The rise

Paper-insulated lead cable (PILC) has had an impressive history of service. Many of the cables installed earlier in this century are still performing well. Because of this and because of tradition, PILC is still being manufactured and sold today. This article outlines a history of the development and the improvements in the technology of manufacturing lead/paper cables as well as the history of the companies involved. A future article will discuss some of the reasons for the decline in the installation of lead/paper cable     

Deep level transient spectroscopy of hole traps related to CdTe self-assembled quantum dots embedded in ZnTe matrix

The capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements have been made on a Schottky Ti-ZnTe (p-type) diode containing CdTe self-assembled quantum dots (QD) and control diode without dots. The C-V curve of the QD diode exhibits a characteristic step associated with the QD states whereas the reference diode shows ordinary bulk behavior. A quasistatic model based on the self-consistent solution of the Poisson's equation is used to simulate the capacitance. By comparison of the calculated C-V curve with the experimental one, hole binding energy at the QD states is found to be equal about 0.12 eV. The results of DLTS measurements for the sample containing QDs reveal the presence of a low-temperature peak which is not observed for the control diode. Analysis of its behavior at different bias conditions leads to the conclusion that this peak may be related to the hole emission from the QD states to the ZnTe valence band. Its thermal activation energy obtained from related Arrhenius plot equals to 0.12 eV in accordance with the energy obtained from the Poisson's equation. Thus based on the C-V and DLTS studies it may be concluded that the thermal activation energy of holes from the QD states to the ZnTe valence band in the CdTe/ZnTe QD system is equal about 0.12 eV.     

Are Two Heads Better than One? On the Effectiveness of Pair Programming

Pair programming is a collaborative approach that makes working in pairs rather than individually the primary work style for code development. Because PP is a radically different approach than many developers are used to, it can be hard to predict the effects when a team switches to PP. Because projects focus on different things, this article concentrates on understanding general aspects related to effectiveness, specifically project duration, effort, and quality. Not unexpectedly, our meta-analysis showed that the question of whether two heads are better than one isn't precise enough to be meaningful. Given the evidence, the best answer is "it depends" - on both the programmer's expertise and the complexity of the system and tasks to be solved. Two heads are better than one for achieving correctness on highly complex programming tasks. They might also have a time gain on simpler tasks. Additional studies would be useful. For example, further investigation is clearly needed into the interaction of complexity and programmer experience and how they affect the appropriateness of a PP approach; our current understanding of this phenomenon rests chiefly on a single (although large) study. Only by understanding what makes pairs work and what makes them less efficient can we take steps to provide beneficial work conditions, to avoid detrimental conditions, and to avoid pairing altogether when conditions are detrimental. With the right cooks and the right combination of ingredients, the broth has the potential to be very good indeed.     

What Do We Know about Agile Software Development?

From 1,996 studies available in the agile software development literature, the authors identified 36 research studies of acceptable rigor, credibility, and relevance to include in a systematic review of empirical evidence for agile development's benefits and limitations. The review results suggest that despite some limitations, agile development can improve job satisfaction, project productivity, and customer satisfaction.     

A Systematic Review of Theory Use in Software Engineering Experiments

Empirically based theories are generally perceived as foundational to science. However, in many disciplines, the nature, role and even the necessity of theories remain matters for debate, particularly in young or practical disciplines such as software engineering. This article reports a systematic review of the explicit use of theory in a comprehensive set of 103 articles reporting experiments, from of a total of 5,453 articles published in major software engineering journals and conferences in the decade 1993-2002. Of the 103 articles, 24 use a total of 40 theories in various ways to explain the cause-effect relationship(s) under investigation. The majority of these use theory in the experimental design to justify research questions and hypotheses, some use theory to provide post hoc explanations of their results, and a few test or modify theory. A third of the theories are proposed by authors of the reviewed articles. The interdisciplinary nature of the theories used is greater than that of research in software engineering in general. We found that theory use and awareness of theoretical issues are present, but that theory-driven research is, as yet, not a major issue in empirical software engineering. Several articles comment explicitly on the lack of relevant theory. We call for an increased awareness of the potential benefits of involving theory, when feasible. To support software engineering researchers who wish to use theory, we show which of the reviewed articles on which topics use which theories for what purposes, as well as details of the theories' characteristics     

Evidence-based software engineering for practitioners

Software managers and practitioners often must make decisions about what technologies to employ on their projects. They might be aware of problems with their current development practices (for example, production bottlenecks or numerous defect reports from customers) and want to resolve them. Or, they might have read about a new technology and want to take advantage of its promised benefits. However, practitioners can have difficulty making informed decisions about whether to adopt a new technology because there's little objective evidence to confirm its suitability, limits, qualities, costs, and inherent risks. This can lead to poor decisions about technology adoption. Software engineers might make incorrect decisions about adopting new techniques it they don't consider scientific evidence about the techniques' efficacy. They should consider using procedures similar to ones developed for evidence-based medicine. Software companies are often under pressure to adopt immature technologies because of market and management pressures. We suggest that practitioners consider evidence-based software engineering as a mechanism to support and improve their technology adoption decisions.     

Evaluating Pair Programming with Respect to System Complexity and Programmer Expertise

A total of 295 junior, intermediate, and senior professional Java consultants (99 individuals and 98 pairs) from 29 international consultancy companies in Norway, Sweden, and the UK were hired for one day to participate in a controlled experiment on pair programming. The subjects used professional Java tools to perform several change tasks on two alternative Java systems with different degrees of complexity. The results of this experiment do not support the hypotheses that pair programming in general reduces the time required to solve the tasks correctly or increases the proportion of correct solutions. On the other hand, there is a significant 84 percent increase in effort to perform the tasks correctly. However, on the more complex system, the pair programmers had a 48 percent increase in the proportion of correct solutions but no significant differences in the time taken to solve the tasks correctly. For the simpler system, there was a 20 percent decrease in time taken but no significant differences in correctness. However, the moderating effect of system complexity depends on the programmer expertise of the subjects. The observed benefits of pair programming in terms of correctness on the complex system apply mainly to juniors, whereas the reductions in duration to perform the tasks correctly on the simple system apply mainly to intermediates and seniors. It is possible that the benefits of pair programming will exceed the results obtained in this experiment for larger, more complex tasks and if the pair programmers have a chance to work together over a longer period of time