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Automated Generation and Evaluation of JMH Microbenchmark Suites From Unit Tests
No full textPerformance is a crucial non-functional requirement of many software systems. Despite the widespread use of performance testing, developers still struggle to construct and evaluate the quality of performance tests. To address these two major challenges, we implement a framework, dubbed ju2jmh, to automatically generate performance microbenchmarks from JUnit tests and use mutation testing to study the quality of generated microbenchmarks. Specifically, we compare our ju2jmh generated benchmarks to manually written JMH benchmarks and to automatically generated JMH benchmarks using the AutoJMH framework, as well as directly measuring system performance with JUnit tests. For this purpose, we have conducted a study on three subjects (Rxjava, Eclipse-collections, and Zipkin) with 454\ua0K source lines of code (SLOC), 2,417 JMH benchmarks (including manually written and generated AutoJMH benchmarks) and 35,084 JUnit tests. Our results show that the ju2jmh generated JMH benchmarks consistently outperform using the execution time and throughput of JUnit tests as a proxy of performance and JMH benchmarks automatically generated using the AutoJMH framework while being comparable to JMH benchmarks manually written by developers in terms of tests’ stability and ability to detect performance bugs. Nevertheless, ju2jmh benchmarks are able to cover more of the software applications than manually written JMH benchmarks during the microbenchmark execution. Furthermore, ju2jmh benchmarks are generated automatically, while manually written JMH benchmarks requires many hours of hard work and attention; therefore our study can reduce developers’ effort to construct microbenchmarks. In addition, we identify three factors (too low test workload, unstable tests and limited mutant coverage) that affect a benchmark’s ability to detect performance bugs. To the best of our knowledge, this is the first study aimed at assisting developers in fully automated microbenchmark creation and assessing microbenchmark quality for performance testing
Hilbert-Schmidt regularity of symmetric integral operators on bounded domains with applications to SPDE approximations
Get PDFRegularity estimates for an integral operator with a symmetric continuous kernel on a convex bounded domain are derived. The covariance of a mean-square continuous random field on the domain is an example of such an operator. The estimates are of the form of Hilbert--Schmidt norms of the integral operator and its square root, composed with fractional powers of an elliptic operator equipped with homogeneous boundary conditions of either Dirichlet or Neumann type. These types of estimates have important implications for stochastic partial differential equations on bounded domains as well as their numerical approximations, which couple the regularity of the driving noise with the properties of the differential operator. The main tools used to derive the estimates are properties of reproducing kernel Hilbert spaces of functions on bounded domains along with Hilbert--Schmidt embeddings of Sobolev spaces. Both non-homogenenous and homogeneous kernels are considered. Important examples of homogeneous kernels covered by the results of the paper include the class of Mat\ue9rn kernels
Methodology to geometrically age human body models to average and subject-specific anthropometrics, demonstrated using a small stature female model assessed in a side impact
No full textThe aged population has been associated with an increased risk of injury in car-crash, creating a critical need for improved assessment of safety systems. Finite element human body models (HBMs) have been proposed, but require representative geometry of the aged population and high mesh quality. A new hybrid Morphing-CAD methodology was applied to a 26-year-old (YO) 5th percentile female model to create average 75YO and subject-specific 86YO HBMs. The method achieved accurate morphing targets while retaining high mesh quality. The three HBMs were integrated into a side sled impact test demonstrating similar kinematic response but differing rib fracture patterns
Melt processable cellulose fibres engineered for replacing oil-based thermoplastics
Get PDFIf cellulosic materials are to replace materials derived from non-renewable resources, it is necessary to overcome intrinsic limitations such as fragility, permeability to gases, susceptibility to water vapour and poor three-dimensional shaping. Novel properties or the enhancement of existing properties are required to expand the applications of cellulosic materials and will create new market opportunities. Here we have overcome the well-known restrictions that impede melt-processing of high cellulose content composites. Cellulose fibres, partially derivatised to dialcohol cellulose, have been used to manufacture three-dimensional high-density materials by conventional melt processing techniques, with or without the addition of a thermoplastic polymer. This work demonstrates the use of melt processable chemically modified cellulose fibres in the preparation of a new generation of highly sustainable materials with tuneable properties that can be tailored for specific applications requiring complex three-dimensional parts
Enhanced electrochromic switching contrast in the blue by 3,4-propylenedioxypyrrole - Implementation on structural colors
Get PDFRecent advances in nanofabrication technologies have enabled new ways to produce structural colors. By combining nanofabrication methods, it is possible to integrate electrochromic materials with the nanostructures, which enable electrical tuning of the colors and thus new types of reflective displays. Previous work has shown high quality colors and high switching contrast in general. However, so far the intensity modulation has always been more limited in the blue. In this work we prepare blue structural colors and synthesize films of an electrochromic polymer (PProDOP) that is optimized for high contrast in this spectral region. A protocol for electropolymerization of PProDOP on gold surfaces is presented. The polymer films are shown to follow Lambert-Beer behavior and can provide up to 75% contrast (difference in transmittivity). On blue nanostructures, the reflectivity can be modulated with a contrast of 50%, which is a considerable improvement in comparison with previous work. The results presented here should be useful for electrochromic or other electro-optical devices operating in the blue spectral region
Numerical study on transient aerodynamic characteristics of high-speed trains during the opening of braking plates based on dynamic-overset-grid technology
No full textThe safety of high-speed trains is considerably compromised by increasing speed trends. Thus, braking plate technology has been applied to high-speed trains. The purpose of this study is to clarify the evolution law of the flow field of the vehicle during the opening of the braking plate and analyze the influence of the plate movement on the aerodynamic performance of the train. In this study, the flow field was computed using incompressible Navier–Stokes equations and the shear-stress transport (SST)\ua0k–ω turbulence model, and the unsteady flow over the opening brake plates was simulated using moving overlapping grids and dual time-stepping. The numerical method was verified through comparison with wind tunnel data (error <8%). The results reveal that the upstream braking plate significantly decreases the aerodynamic forces of the downstream plate during opening of the plates and causes the aerodynamic drag of the downstream braking plate to fluctuate significantly when it increases. The operation of the braking plate produces a small increase in the drag force of the train body (2.6%), but it significantly decreases the lift force of the train body (by up to 94%), especially during the opening of the braking plates. The flow field in the upper part of the train is significantly changed by the opening of the braking plate. In particular, the pressure in the cavity of the braking device changes sharply, and the surface is subjected to a large pulse pressure
Application of high-frequency mechanical impact treatment for fatigue strength improvement of new and existing bridges
Get PDFThis thesis investigates the application of High-Frequency Mechanical Impact (HFMI) treatment for fatigue strength improvement of weldments in existing and new bridges. In the former case, the welds have already been subjected to fatigue loading and accumulated damage before treatment. A fatigue testing program is set up, comprising welded specimens subjected to fatigue loading before HFMI treatment to investigate the efficiency of HFMI treatment on existing structures. Moreover, additional fatigue test results are collected from the literature and analyzed. HFMI treatment is found to be very efficient in extending the fatigue lives of existing structures regardless of the accumulated fatigue damage prior to treatment, given that any surface cracks, if exist, have not grown more than 2.25 mm in depth. For practical applications, HFMI treatment is only recommended if the critical details are verified to be free of any surface cracks. Remelting the surface with a tungsten electrode before HFMI treatment is another solution which has rarely been studied on existing structures. Therefore, several experimental investigations are conducted including fatigue testing, measurement of residual stress, hardness testing and scanning the welds topography to study the effect of combining these two post-weld treatment techniques. The combined treatment is found to be efficient as it induces higher and deeper compressive residual stress and local hardening. These aspects are all considered in numerical simulations conducted to investigate the fatigue behaviour of new and existing weldments treated using this combination. The results verify the superiority of the combined treatment to both individual treatments (TIG & HFMI). Nonetheless, because of the complexity associated with TIG remelting, the combination is only suggested for existing structures containing shallow fatigue cracks which can be fused by a tungsten electrode. One major hindrance to applying HFMI treatment on weldments in steel bridges is the lack of design rules and recommendations such as consideration of stress ratio (mean stress) and overloads.\ua0 Therefore, a correction factor (λHFMI) to account for the mean stress effect is derived. This factor is used to magnify the design stress range for fatigue verification of HFMI-treated welded details existing in road and railway bridges. λHFMI is calibrated using measured traffic data that includes millions of vehicles and hundreds of trains. In addition, the characteristic load combination associated with the serviceability limit state is found to be the most appropriate for verifying the maximum stresses in road bridges. Based on the work conducted in this thesis, a complete methodology is proposed for the design and assessment of HFMI-treated welded details in new and existing steel bridges. Finally, the effect of corrosion on the performance of HFMI-treated weldments is studied by analyzing collected test results. Despite the observed reduction in fatigue endurance of HFMI-treated details due to the removal of top layers improved by residual stresses, the obtained fatigue lives are still longer than the design lives assigned for new welded details even in extreme corrosion conditions. However, corrosion protection and removal of sharp HFMI groove edges via light grinding are still necessary to reduce the susceptibility of weldments to corrosion
Retrofitting WASP to a RoPax vessel - design, performance and uncertainties
Get PDFWind-assisted propulsion (WASP) is one of the most promising ship propulsion alternatives\ua0that radically reduce greenhouse gas emissions and are available today. Using the example of a\ua0RoPax ferry, this study presents the performance potential of WASP systems under realistic weather\ua0conditions. Different design alternatives and system layouts are discussed. Further, uncertainties in\ua0the performance prediction ofWASP systems are analyzed. Included in the analysis are the sail forces\ua0as well as the aero- and hydrodynamic interaction effects, i.e., the sail–sail and sail–deck interaction as\ua0well as the drift and yaw of the ship. As a result, this study provides guidelines on the most important\ua0parameters when designing and modeling aWASP ship. Finally, the study presents an analysis of the\ua0expected accuracy of the employed empirical/analytical performance prediction model ShipCLEAN
Linking scores from two written receptive English academic vocabulary tests—The VLT-Ac and the AVT
Get PDFThe academic section of the Vocabulary Levels Test (VLT-Ac) and the Academic Vocabulary Test (AVT) both assess meaning-recognition knowledge of written receptive academic vocabulary, deemed central for engagement in academic activities. Depending on the purpose and context of the testing, either of the tests can be appropriate, but for research and pedagogical purposes, it is important to be able to compare scores achieved on the two tests between administrations and within similar contexts. Based on a sample of 385 upper secondary school students in university-preparatory programs (independent CEFR B2-level users of English), this study presents a comparison model by linking the VLT-Ac and the AVT using concurrent calibration procedures in Item Response Theory. The key outcome of the study is a score comparison table providing a means for approximate score comparisons. Additionally, the study showcases a viable and valid method of comparing vocabulary scores from an older test with those from a newer one
Sodium reduction in foods: Challenges and strategies for technical solutions
Get PDFIn many parts of the world, sodium consumption is higher than recommended levels, representing one of the most important food-related health challenges and leading to considerable economical costs for society. Therefore, there is a need to find technical solutions for sodium reduction that can be implemented by food producers and within food services. The aims of this review are to discuss the barriers related to sodium reduction and to highlight a variety of technical solutions. The barriers relate to consumer perception, microbiology, processing, and physicochemistry. Existing technical solutions include inhomogeneous salt distribution, coated salt particles, changing particle sizes and forms, surface coating, multisensory combinations, sodium replacements, double emulsions, adapted serum release by microstructure design, and adapted brittleness by microstructure design. These solutions, their implementation and the associated challenges, and applicable product categories are described. Some of these solutions are ready for use or are in their early development stages. Many solutions are promising, but in most cases, some form of adaptation or optimization is needed before application in specific products, and care must always be taken to ensure food safety. For instance, further research and innovation are required in the dynamic evolution of saltiness perception, consumer acceptance, the binding and migration of sodium, juiciness, microbiological safety, and the timing of salt addition during processing. Once implemented, these solutions will undoubtedly support food producers and food services in reducing sodium content and extend the application of the solutions to different foods