Search

Software features are intuitive entities used to abstract and manage the functionalities of a software system, for instance, in product-line engineering and agile software development. Nonetheless, developers rarely make features explicit in code, which is why they have to perform costly program comprehension and particularly feature location to (re-)gain knowledge about the code. In a previous paper, we conducted an experiment on how explicit feature traces impact developers’ program comprehension by facilitating feature location. We found that annotating features in code improved program comprehension, while decomposing them into classes had a negative impact. Additionally, but not reported in that paper, we were concerned with understanding whether the different traces would impact developers’ memory regarding the code and its features. To this end, we repeatedly asked our participants questions about the code on different levels of detail within time periods of two weeks. Since developers’ memory decays over time, we expected that our participants would provide fewer correct answers over time, with differences depending on the feature traces in their code. Unfortunately, the actual results were inconclusive and up for interpretation, particularly due to challenges in designing an experiment on developers’ memory. In this paper, we discuss our experimental design, the null results, and challenges for improving the methodology of future studies in this direction.

Although machine learning (ML) methods have already been well described in science, the transfer into manufacturing business practice is only slowly taking place. One of the reasons is that current research is lacking a comprehensive analysis of working ML methods and their characteristics. Therefore, this paper systematically analyzes successfully implemented ML solutions to facilitate the design process for future machine learning systems (MLS) implementations in manufacturing companies. First, a systematic literature review based on 18 scientific publications is conducted to confirm the lacks assumed. Second, 15 MLS approaches are analyzed based on a technology framework to solve the shortcomings identified and extract further findings.In total, we identified two general MLS design patterns. Furthermore, we extracted seven suitable data and data model requirements as well as technology potentials. The results show that theory-based ML approaches are often based on linear methods requiring low-dimensional data, e.g. in image recognition. This points towards the hypothesis, that the application of non-linear ML methods processing high-dimensional data could increase the number of possible use cases. Thus, further high technology potentials regarding the application of MLS in the manufacturing industry would arise.

Photodarkening in rare-earth doped fibers has been subject of intense research over the last decade as the main issue limiting high power performance and long-term stability of fiber lasers.Regarding our previous and most recent experiments on Yb-doped silica fibers, the relationship between photodarkening mitigation and fiber heat load will be discussed for the most prominent co-dopants. The main focus of attention will be paid on the mitigation of photodarkening by co-doping with aluminium and cerium. Beside this, we dedicate ourselves on the thermal properties of NIR-pumped fibers and show that, especially for high pump intensities, methods of PD mitigation can also result in a temperature enhancement of the active fiber. This can even become a critical issue for high power laser performance, e.g. by lowering the thermal mode instability threshold of LMA fibers.

Intel's novel Software Guard eXtensions (SGX) enable secure and trusted execution of services, thereby paving the way to outsource sensitive data processing to external data centers. While SGX promises trusted execution close to native speed, frequent I/O operations and memory usage beyond a hardware-dependent threshold of currently 92 MiB result in substantial performance degradation. For memory-intensive workloads such as key-value stores and databases these penalties can be prohibitively high. We present STANlite – an in-memory database engine for SGX-enabled secure data processing in rack-scale environments. STANlite performs efficient user-level paging, whenever a database workload requires more space than the performance-friendly in-memory state size. Furthermore, STANlite smartly combines the properties of Remote Direct Memory Access (RDMA) and SGX to reduce the overhead of network-based I/O operations. While SGX usually provides confidentiality and integrity at the same time, STANlite enables a purely integrity preserving data management mode for additional performance. Finally, STANlite features a small trusted computing base and is memory-efficient, as it extends SQLite, a database for embedded use. We evaluated STANlite in terms of query response time. It outperforms a vanilla SGX-based SQLite version by 1.79x for microbenchmarks and 2.44x for TPC-C.

Owing to their high beam quality and enormous power scalability, Yb-doped fiber lasers and amplifiers are currently employed for many scientific and industrial applications. However, photodarkening losses and high operating temperatures can limit their performance or even destroy the laser itself. PD loss reduces the laser efficiency during run-time of fiber laser. Technically, this problem can be compensated by enhancing the pump power. But it has been shown that beyond the quantum defect caused by the Stokes shift, also PD losses contribute to the heat load of a fiber laser and thereby can cause damage at high power. Another consequence of heat load is the significant reduction of the beam quality as well as the transverse mode instability threshold [1]. The appropriate solution for overcoming this limitation is the drastic reduction of PD, which can be achieved by co-doping, e.g. with phosphorous, aluminium and cerium.

At present, the combination of high peak power and near diffraction-limited beam quality is essential for high-power pulsed fiber laser systems combining nanosecond pulses with multi-kilohertz repetition rates. In standard fiber amplifier, parasitic nonlinear effects limit further power scaling due to the small active fiber core. Therefore the scaling to larger effective mode areas (LMA) is a promising solution to suppress nonlinear optical effects and to scale up the peak power [1, 2]. However increasing the fiber core size can severely degrade the fundamental mode operation and beam quality due to the excitation of higher order modes.

Researchers perform empirical studies in industry to gain qualitative insights into a real-world problem. However, common critics are the diversity and selection process of participants. To address these issues, we propose to improve the integration of question-answering systems into empirical study. In this paper, we i) describe approaches to conduct studies in such systems, ii) exemplify corresponding challenges, and iii) discuss their potential. We illustrate the approaches on existing works in which they were partly implemented to show that they can succeed.

Program comprehension is an important aspect of developing and maintaining software, as programmers spend most of their time comprehending source code. Thus, it is the focus of many studies and experiments to evaluate approaches and techniques that aim to improve program comprehension. As the amount of corresponding work increases, the question arises how researchers address program comprehension. To answer this question, we conducted a literature review of papers published at the International Conference on Program Comprehension, the major venue for research on program comprehension. In this article, we i) present preliminary results of the literature review and ii) derive further research directions. The results indicate the necessity for a more detailed analysis of program comprehension and empirical research.

Follow-the-sun is an approach to develop software by handing off the progress to different time zones as the day passes. Hence, this approach allows companies to work on a project 24 hours a day, potentially reducing its time-to-market. However, several challenges, such as time zone differences or handing off work, are often reported. In this paper, we describe a case study on a follow-the-sun approach that was applied in a German company. During the approach, we did rarely face the aforementioned challenges but experienced different ones. For this reason, the company put its approach on hold but benefited from the learned lessons. Overall, we report on a partly successful follow-the-sun approach and identify five important practices.

A software product-line comprises a set of products that share a common set of features. These features can be reused to customize a product to satisfy specific needs of certain customers or markets. As the number of possible products increases exponentially for new features, testing all products is infeasible. Existing testing approaches reduce their effort by restricting the number of products (sampling) and improve their effectiveness by considering the order of tests (prioritization). In this paper, we propose a cluster-based prioritization technique to sample similar products with respect to the feature selection. We evaluate our approach using feature models of different sizes and show that cluster-based prioritization can enhance the effectiveness of product-line testing.

This paper discusses the results of the RETHINK big Project, a 2-year Collaborative Support Action funded by the European Commission in order to write the European Roadmap for Hardware and Networking optimizations for Big Data. This industry-driven project was led by the Barcelona Supercomputing Center (BSC), and it included large industry partners, SMEs and academia. The roadmap identifies business opportunities from 89 in-depth interviews with 70 European industry stakeholders in the area of Big Data and predicts the future technologies that will disrupt the state of the art in Big Data processing in terms of hardware and networking optimizations. Moreover, it presents coordinated technology development recommendations (focused on optimizations in networking and hardware) that would be in the best interest of European Big Data companies to undertake in concert as a matter of competitive advantage. This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement n° 619788. It has also been supported by the Spanish Government (grant SEV2015-0493 of the Severo Ochoa Program), by the Spanish Ministry of Science and Innovation (contract TIN2015-65316) and by Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272).

A challenge in building monolithic fiber laser light sources is the characterization of their optical components, especially of the fiber Bragg gratings (FBG) within the actively doped fiber, which define the resonator. We propose an experimental technique to characterize such FBG under pumping conditions directly during FBG inscription. The observed dynamics are discussed considering different absorption processes, taking place during inscription and pumping. Furthermore, we study the laser performance at different pump powers and discuss observed changes in the laser spectra.

A modern tendency is to perform condition-based rather than time-based maintenance on power transformers. This requires the use of diagnostic measurements to know the condition of the tap changer and to determine when and what kind of maintenance is necessary. In addition, diagnostic measurements on OLTCs can be used for the pre-failure detection of defects not seen during maintenance and to assess the condition of parts that are not easily accessible. A number of diagnostic tests can be performed and utilities combine different tests to determine its need for maintenance. Several utilities apply dynamic resistance measurement (DRM) to OLTCs during regular maintenance. Results showed that DRM is sensitive to major degradation mechanisms in on-load tap changers.

With the advent of new contact-less sensors for forensic investigations of latent fingerprint traces, the authors see the need for a benchmarking framework to evaluate existing devices and promising combinations of data acquisition and signal processing techniques. This paper extends the existing benchmarking framework from [1] by categorizing it into properties from a forensic point-of-view (end-user) and a technical point-of-view (scientific-user) and applies a known differential image technique for the subjective evaluation of which traces are visible. We show exemplary results for a chromatic white light (CWL) sensor for the surface quality assessment, using and comparing the experimental setup of 10 surfaces from [1] and additional 10 surfaces, including real-world objects, to determine its potential for detecting latent fingerprints. Using a differential image approach, the particular influence of sensor noise signals is analyzed, showing that this differential approach cannot always be considered as an ideal filter for fingerprint pattern detection.

An on-load tap changer (OLTC) is prone to many different defects and degradation mechanisms due to its continuous operation under load condition. A high load current and high operation temperature accelerate the process of contact wear. Contacts erode due to the fact that under certain conditions the contacts develop a resistive layer due to hot insulation oil. As a major cause of OLTC failure, these defects might take place after some years of operation and their frequency increases with the operation time. Regular maintenance is applied due to degradation of the insulation oil. Dynamic resistance measurement (DRM) can be conducted during this maintenance to measure the resistance of the OLTC when it operates. The measurement results provide important information for assessing the actual condition of the OLTC. This paper aims to analyze the effect of test parameters on DRM results from service-aged OLTCs and describes the implementation of DRM in OLTC condition assessment. Two test parameters were selected for observation: the test current amplitude and the circuit resistance. Their amplitude was varied during laboratory experiments as well as on-site after regular maintenance. To quantify the various measurement results, an analytical tool using 4 performance parameters has been developed. Finally for interpretation, with the help of a three dimensional classification system which is presented in this paper, the actual condition of OLTCs can be identified during maintenance activities.

Resistance measurements on power transformers are a widely accepted method for finding winding defects. Continuity of the tap changer contacts can also be checked when the on-load tap changer (OLTC) is operated during the resistance measurement. Resistance measurements that also record the resistance during OLTC operation are called dynamic resistance measurements. This off-line diagnostic method can be used during regular maintenance to assess the condition of OLTC parts not accessible for inspection. Besides condition assessment of inaccessible parts of the OLTC, this method can also be used to detect maintenance errors that could lead to failure. In particular, these measurements are very helpful in finding contact discontinuity, mechanical defects that influence the operation of the tap changer contacts, problems with the switch time and the transition resistors and can find contact degradation in an early stage.

Resistance measurements on power transformers are offline diagnostic methods that are performed without opening the transformer main tank. In case the power transformer is equipped with an on-load tap changer (OLTC), this resistance measurement can be used to find degradation and defects inside the OLTC. Many OLTC defects as well as contact degradation can be measured by means of dynamic resistance measurements, which is a resistance test during OLTC operation. A low (DC) test current through the on-load tap changer is used during dynamic resistance measurements. This method is in particular sensitive to maintenance errors, contact degradation and contact timing problems. In general, distinction can be made between defects that interrupt the current through the OLTC, defects that affect the timing of the OLTC contacts and contact degradation resulting in abnormal contact resistance.

This paper discusses the recently developed analysis method for service aged power transformers equipped with an OLTC: dynamic resistance measurements (DRM). Because the on-load tap changer contributes to many power transformer failures the emphasis is on OLTC diagnosis. Off-line diagnosis of on-load tap changers during regular maintenance can detect maintenance errors and assess the condition of OLTC parts not accessible for inspection. DRM can be valuable to on-load tap changer (OLTC) condition assessment because of the large variety of defects and OLTC degradation mechanisms that can be found. This paper deals with the results that can be measured with DRM. Besides undisturbed DRM-data, most common deviations originating from degraded and defect tap changers will be discussed. It is explained how these different types of defects appear in the DRM results. The location and shape of the deviation can be used to find the cause and importance of the defect. A subdivision is made between OLTC's in good condition, OLTC's with increased contact resistance, OLTC's with open contacts and OLTC's with deviating switch times. By doing so, an overview of possible DRM results is gained. The seriousness of the defects is also discussed in this paper. Differences between the DRM results of different types of OLTC's will be discussed by showing results of DRM tests. Most graphs presented in this paper are recorded on service-aged OLTC's in the Dutch utility grid. Some measurement results are performed during experiments in a high voltage laboratory.

Static resistance measurements on power transformers give an indication about increased contact resistances of the OLTC. Increased contact resistances can also be measured by means of a dynamic resistance measurement (DRM). This paper elaborates on condition diagnosis of electrical contacts of in-tank high-speed resistor tap changers using DRM. DRM uses a low test current through the on-load tap changer to detect increased contact resistances and current interruptions. The difference with static resistance measurements is that the tap changer is switched through all its tap positions during the test. The test current gets no change to fully stabilize due to the inductance of the transformer windings. DRM is therefore less accurate then static resistance measurements but contains more information about the type and location of tap changer defect. This contribution will show that more defects on OLTC's can be found with DRM compared to static resistance tests: the additional value of DRM compared to static winding resistance measurements is discussed. Secondly, important topics that should be considered when performing dynamic resistance measurements are discussed, like the effect of the test current amplitude, the secondary short-circuit and circuit resistance. Simulation results and experimental data are presented to make the reader familiar with the pros and cons of dynamic resistance measurements.

Photodarkening (PD) is a very critical factor for the long-term stability of Yb fiber lasers and amplifiers, especially for the high power range. There have been done a lot of investigations to develop reliable techniques to examine the PD evolution in optical fibers (e.g. [1]) and to understand this pump-induced process. A reliable comparison of different fiber types is only possible on the basis of measurements approaching the PD equilibrium [2], and moreover, the knowledge of this “worst case” of PD loss is most desirable for fiber applications under defined conditions to predict the long-term performance of commercial devices.

The main task of the interlock system is to prevent any damage of the costly components of the RF station. The implementation of the interlock must also guarantee a maximum uninterrupted time of operation which implies the implementation of self diagnostics and repair strategies on a modular basis. Additional tasks include collection and temporary storage of status information of individual channels; transfer of this information to the higher level control system, and also the implementation of slow control functions.

Tools support is crucial for the acceptance of a new programming language. However, providing such tool support is a huge investment that can usually not be provided for a research language. With FeatureIDE, we have built an IDE for AHEAD that integrates all phases of feature-oriented software development. To reuse this investment for other tools and languages, we refactored FeatureIDE into an open source framework that encapsulates the common ideas of feature-oriented software development and that can be reused and extended beyond AHEAD. Among others, we implemented extensions for FeatureC++ and FeatureHouse, but in general, FeatureIDE is open for everybody to showcase new research results and make them usable to a wide audience of students, researchers, and practitioners.

Several Yb-doped laser active fibers manufactured by the new technology described below were successfully tested in different fiber laser setups. The promising results are discussed in comparison to laser active fibers made by MCVD-technique.