Frequency-tunable metamaterials using broadside-coupled split ring resonators

We present frequency tunable metamaterial designs at terahertz (THz) frequencies using broadside-coupled split ring resonator (BC-SRR) arrays. Frequency tuning, arising from changes in near field coupling, is obtained by in-plane horizontal or vertical displacements of the two SRR layers. For electrical excitation, the resonance frequency continuously redshifts as a function of displacement. The maximum frequency shift occurs for displacement of half a unit cell, with vertical displacement resulting in a shift of 663 GHz (51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of f0). We also discuss the significant differences in tuning that arise for electrical excitation in comparison to magnetic excitation of BC-SRRs

Results from an ethnographically-informed study in the context of test driven development

Background: Test-driven development (TDD) is an iterative software development technique where unit tests are defined before production code. Previous studies fail to analyze the values, beliefs, and assumptions that inform and shape TDD. Aim: We designed and conducted a qualitative study to understand the values, beliefs, and assumptions of TDD. In particular, we sought to understand how novice and professional software developers, arranged in pairs (a driver and a pointer), perceive and apply TDD. Method: 14 novice software developers, i.e., graduate students in Computer Science at the University of Basilicata, and six professional software developers (with one to 10 years work experience) participated in our ethnographicallyinformed study. We asked the participants to implement a new feature for an existing software written in Java. We immersed ourselves in the context of the study, and collected data by means of contemporaneous field notes, audio recordings, and other artifacts. Results: A number of insights emerge from our analysis of the collected data, the main ones being: (i) refactoring (one of the phases of TDD) is not performed as often as the process requires and it is considered less important than other phases, (ii) the most important phase is implementation, (iii) unit tests are almost never up-to-date, (iv) participants first build a sort of mental model of the source code to be implemented and only then write test cases on the basis of this model; and (v) apart from minor differences, professional developers and students applied TDD in a similar fashion. Conclusions: Developers write quick-and-dirty production code to pass the tests and ignore refactoring.Copyright is held by the owner/auther(s)

Adsorption of methylene blue from aqueous solutions by pyrolusite ore

In this study, the adsorption of methylene blue dye was examined by using pyrolusite ore as a low-cost alternative adsorbent source. Pyrolusite, which contains mainly MnO2, is a manganese ore. The effects of the initial concentration of dye, contact time, initial pH of solution, adsorbent dosage, stirring speed of solution, and average particle size of adsorbent on the adsorption of methylene blue were studied. It was found that the percentage of the adsorbed dye increased with increasing the amount of pyrolusite. While the initial dye concentration, initial pH, contact time, stirring speed, particle size, and adsorbent dosage were 25 ppm, 6, 90 min, 250 rpm, 63 µm, and 12 g/l, respectively, the efficiency of dye adsorption on pyrolusite ore was 99%. The isotherm and kinetic studies relating to this adsorption process were also made. It was found that the equilibrium data followed the Langmuir isotherm model while the kinetic of process could be described by the pseudo-second order kinetic model

A Systematic Literature Review and Meta-analysis on Cross Project Defect Prediction

Background: Cross project defect prediction (CPDP) recently gained considerable attention, yet there are no systematic efforts to analyse existing empirical evidence. Objective: To synthesise literature to understand the state-of-the-art in CPDP with respect to metrics, models, data approaches, datasets and associated performances. Further, we aim to assess the performance of CPDP vs. within project DP models. Method: We conducted a systematic literature review. Results from primary studies are synthesised (thematic, meta-analysis) to answer research questions. Results: We identified 30 primary studies passing quality assessment. Performance measures, except precision, vary with the choice of metrics. Recall, precision, f-measure, and AUC are the most common measures. Models based on Nearest-Neighbour and Decision Tree tend to perform well in CPDP, whereas the popular na¨ıve Bayes yield average performance. Performance of ensembles varies greatly across f-measure and AUC. Data approaches address CPDP challenges using row/column processing, which improve CPDP in terms of recall at the cost of precision. This is observed in multiple occasions including the meta-analysis of CPDP vs. WPDP. NASA and Jureczko datasets seem to favour CPDP over WPDP more frequently. Conclusion: CPDP is still a challenge and requires more research before trustworthy applications can take place. We provide guidelines for further research

Conformance Factor in Test-driven Development: Initial Results from an Enhanced Replication

Test-driven development (TDD) is an iterative software development technique where unit-tests are defined before production code. The proponents of TDD claim that it improves both external quality and developers’ productivity. In particular, Erdogmus et al. (i.e., original study) proposed a two-stage model to investigate these claims regarding TDD’s effects. Our aim is to enhance the model proposed in the original study by investigating an additional factor: TDD process conformance. We conducted a close, external replication of the original study accompanied by a correlation analysis to check whether process conformance is related to improvements for the subjects using TDD. We partially confirmed the results of the original study. Moreover, we observed a correlation between process conformance and quality, but not productivity. We found no evidence to support the claim that external quality and productivity are improved by the adoption of TDD compared to test-last development. Finally, conformance to TDD process improves the quality and does not affect productivity. We conclude that the role of process conformance is relevant in studying the quality and productivity-related effects of TDD

On the effects of programming and testing skills on external quality and productivity in a test-driven development context

Background: In previous studies, a model was proposed that investigated how the developers’ unit testing effort impacted their productivity as well as the external quality of the software they developed. Goal: The aim of this study is to enhance the proposed model by considering two additional factors related to the expertise of developers: programming and unit testing skills. The possibility of including such skills in a model that represents the relationship that testing effort has with the developer’s productivity and the product’s external quality was investigated. Method: Data collected from a test-first development task in academic setting was used in order to gauge the relationship between testing effort, external quality, and productivity. Furthermore, Analysis of Covariance (ANCOVA) was utilized to check the impact of developers’ skills on productivity and quality. Result: The results obtained in previous studies were confirmed: there exists a positive effect of testing effort on productivity, but not on quality. Moreover, the developers’ skills have an impact on productivity but none on external quality. Conclusion: Productivity improves with testing effort, a result consistent across previous, similar studies. The role of existing skills is a relevant factor in studying the effects of developers’ unit testing effort on productivity. Nevertheless, more investigations are needed regarding the relationship between unit testing effort and external quality.This research is partially supported by the Academy of Finland with decision no: 278354. The rst author would like to acknowledge ISACA Finland Chapter for the support provided to complete this work

Impact of process conformance on the effects of test-driven development

Context: One limitation of the empirical studies about test-driven development (TDD) is knowing whether the developers followed the advocated test-code-refactor cycle. Research dealt with the issue of process conformance only in terms of internal validity, while investigating the role of other confounding variables that might explain the controversial effects of TDD. None of the research included process conformance as a fundamental part of the analysis. Goal: We aim to examine the impact of process conformance on the claimed effects of TDD on external quality, developers’ productivity and test quality. Method: We used data collected during a previous study to create regression models in which the level of process conformance was used to predict external quality, productivity, and tests thoroughness. Result: Based on our analysis of the available data (n = 22), we observe that neither quality (p – value = 0.21), productivity (p – value = 0.80), number of tests (p – value = 0.39) nor coverage (p – value = 0.09) was correlated with the level of TDD process conformance. Conclusion: While based on a small sample, we raise concerns about how TDD is interpreted. We also question whether the cost of strictly following TDD will pay-off in terms of external quality, productivity, and tests thoroughness.This research has been supported in part by the Academy of Finland with decision/grant no: 278354