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The working conditions of the Scaled Convective Airflow Laboratory Experiment (SCALEX) at Technische Universität Ilmenau and sample experiments are reported. The SCALEX facility is a pressure vessel which allows for downscaling of laboratory experiments up to a factor of 20 by compression of gaseous working fluids, air or sulfur hexafluoride, to change the material properties of the fluid. The requirements and conditions for downscaling of fluid dynamical problems are discussed in detail. Long-term high and low pressure tests are conducted to screen the stability of the experimental environment inside the vessel against pressure and temperature fluctuations. Finally, a Rayleigh–Bénard convection experiment at an aspect ratio 10 is performed inside the SCALEX facility as a proof of concept. The reference experiment was conducted under 4.5 bar pressure for Ra = 1.9 × 105. However, the Rayleigh number could be varied in a wide range of Ra = 104 ... 108. The flow investigation was pursued with stereoscopic particle image velocimetry in horizontal mid-plane through the convection cell. To improve the image quality the cameras were placed inside the pressure cell and tested up to 6 bar. Thus the feasibility of optical flow measurements at elevated pressures is shown. [ABSTRACT FROM AUTHOR]

With the emergence of social coding platforms, collaboration has become a key and dynamic aspect to the success of software projects. In such platforms, developers have to collaborate and deal with issues of collaboration in open‐source software development. Although collaboration is challenging, collaborative development produces better software systems than any developer could produce alone. Several approaches have investigated collaboration challenges, for instance, by proposing or evaluating models and tools to support collaborative work. Despite the undeniable importance of the existing efforts in this direction, there are few works on collaboration from perspectives of developers. In this work, we aim to investigate the perceptions of open‐source software developers on collaborations, such as motivations, techniques, and tools to support global, productive, and collaborative development. Following an ad hoc literature review, an exploratory interview study with 12 open‐source software developers from GitHub, our novel approach for this problem also relies on an extensive survey with 121 developers to confirm or refute the interview results. We found different collaborative contributions, such as managing change requests. Besides, we observed that most collaborators prefer to collaborate with the core team instead of their peers. We also found that most collaboration happens in software development (60%) and maintenance (47%) tasks. Furthermore, despite personal preferences to work independently, developers still consider collaborating with others in specific task categories, for instance, software development. Finally, developers also expressed the importance of the social coding platforms, such as GitHub, to support maintainers, and contributors in making decisions and developing tasks of the projects. Therefore, these findings may help project leaders optimize the collaborations among developers and reduce entry barriers. Moreover, these findings may support the project collaborators in understanding the collaboration process and engaging others in the project. [ABSTRACT FROM AUTHOR]

It is common knowledge that molecular energy level offsets of a type II heterojunction formed at the donor–acceptor interface are considered to be the driving force for photoinduced charge transfer in organic solar cells. Usually, these offsets – present between molecular energy levels of the donor and acceptor – are obtained via cyclic voltammetry (CV) measurements of organic semiconductors cast in a film or dissolved in solution. Simply transferring such determined energy levels from solution or film of single materials to blend films may be obviously limited and not be possible in full generality. Herein, we report various cases of material combinations in which novel non-fullerene acceptors did not yield successful charge transfer, although energy levels obtained by CV on constituting single materials indicate a type II heterojunction. Whilst the integer charge transfer (ICT) model provides one explanation for a relative rise of molecular energy levels of acceptors, further details and other cases have not been studied so far in great detail. By applying energy-resolved electrochemical impedance spectroscopy (ER-EIS) on several donor–acceptor combinations, a Fano-like resonance feature associated with a distinctive molecular energy level of the acceptor as well as various relative molecular energy level shifts of different kinds could be observed. By analyzing ER-EIS and absorption spectra, not only the exciton binding energy within single materials could be determined, but also the commonly unknown binding energy of the CT state with regard to the joint density of states (jDOS) of the effective semiconductor. The latter is defined by transitions between the highest occupied molecular orbitals (HOMO) of the donor and the lowest unoccupied molecular orbitals (LUMO) of the acceptor. Using this technique among others, we identified cases in which charge generation may occur either via uphill or by downhill processes between the charge transfer exciton and the electronic gap of the effective semiconductor. Exceptionally high CT-exciton binding energies and thus low charge generation yields were obtained for a case in which the donor and acceptor yielded a too intimate blend morphology, indicating π–π stacking as a potential cause for unfavorable molecular energy level alignment. [ABSTRACT FROM AUTHOR]

Open source software projects often rely on package management systems that help projects discover, incorporate, and maintain dependencies on other packages, maintained by other people. Such systems save a great deal of effort over ad hoc ways of advertising, packaging, and transmitting useful libraries, but coordination among project teams is still needed when one package makes a breaking change affecting other packages. Ecosystems differ in their approaches to breaking changes, and there is no general theory to explain the relationships between features, behavioral norms, ecosystem outcomes, and motivating values. We address this through two empirical studies. In an interview case study, we contrast Eclipse, NPM, and CRAN, demonstrating that these different norms for coordination of breaking changes shift the costs of using and maintaining the software among stakeholders, appropriate to each ecosystem's mission. In a second study, we combine a survey, repository mining, and document analysis to broaden and systematize these observations across 18 ecosystems. We find that all ecosystems share values such as stability and compatibility, but differ in other values. Ecosystems' practices often support their espoused values, but in surprisingly diverse ways. The data provides counterevidence against easy generalizations about why ecosystem communities do what they do. [ABSTRACT FROM AUTHOR]

Lifecycle assessments suggest preventing halogenated solvents or solvent additives for environmentally friendly polymer solar cells. Thus, the active layers of polymer:fullerene bulk heterojunction solar cells based on poly{[4,8‐bis‐(2‐ethyl‐hexyl‐thiophene‐5‐yl)‐benzo[1,2‐b:4,5‐b0]dithiophene‐2,6‐diyl]‐alt‐[2‐(20‐ethyl‐hexanoyl)‐thieno[3,4‐b]thiophen‐4,6‐diyl]} (PBDTTT‐CT) and the fullerene derivative [6,6]‐phenyl‐C70‐butyric acid methyl ester (PC70BM) are cast from m‐xylene solutions. Ortho‐vanilline is used as a nonhazardous and nontoxic solvent additive. Completed photovoltaic devices are subjected to accelerated laboratory weathering tests. Photovoltaic parameters are periodically obtained from current–voltage recordings of the solar cells twice an hour under well‐defined aging conditions following the International Summit on Organic Photovoltaic Stability (ISOS) protocols. An analysis of aging kinetics reveals the superposition of two individual degradation mechanisms, of which one is assigned to continued intermixing and the other one to the formation of a blocking layer by interfacial segregation. [ABSTRACT FROM AUTHOR]

A novel repair strategy based on decoupled heat source for increasing the productivity of wire-assisted pulsed laser cladding of the '-precipitation strengthening nickel-base superalloys Inconel 738 low carbon (IN 738 LC, base material) and Haynes 282 (HS 282, filler material) is presented. The laser beam welding process is supported by the hot-wire technology. The additional energy is utilized to increase the deposition rate of the filler material by increasing feeding rates and well-defining the thermal management in the welding zone. The simultaneous application of laser pulse modulation allows the precise control of the temperature gradients to minimize the hot-crack formation. Accompanying investigations such as high-speed recordings and numerical simulations allow a generalized statement on the influence of the adapted heat management on the resulting weld seam geometry (dilution, aspect ratio and wetting angle) as well as the formation of hot-cracks and lack of fusion between base and filler material. Statistical analysis of the data--the input parameters like laser pulse energy, pulse shape, hot-wire power and wire-feeding rate in conjunction with the objectives like dilution, aspect ratio, wetting angle and hot-cracking behavior--revealed regression functions to predict certain weld seam properties and hence the required input parameters. [ABSTRACT FROM AUTHOR]

Modern cyber-physical systems (e.g., robotics systems) are typically composed of physical and software components, the characteristics of which are likely to change over time. Assumptions about parts of the system made at design time may not hold at run time, especially when a system is deployed for long periods (e.g., over decades). Self-adaptation is designed to find reconfigurations of systems to handle such run-time inconsistencies. Planners can be used to find and enact optimal reconfigurations in such an evolving context. However, for systems that are highly configurable, such planning becomes intractable due to the size of the adaptation space. To overcome this challenge, in this paper we explore an approach that (a) uses machine learning to find Pareto-optimal configurations without needing to explore every configuration and (b) restricts the search space to such configurations to make planning tractable. We explore this in the context of robot missions that need to consider task timeliness and energy consumption. An independent evaluation shows that our approach results in high-quality adaptation plans in uncertain and adversarial environments. [ABSTRACT FROM AUTHOR]

Abstract: Transparent environments and social‐coding platforms as GitHub help developers to stay abreast of changes during the development and maintenance phase of a project. Especially, notification feeds can help developers to learn about relevant changes in other projects. Unfortunately, transparent environments can quickly overwhelm developers with too many notifications, such that they lose the important ones in a sea of noise. Complementing existing prioritization and filtering strategies based on binary compatibility and code ownership, we develop an anomaly detection mechanism to identify unusual commits in a repository, which stand out with respect to other changes in the same repository or by the same developer. Among others, we detect exceptionally large commits, commits at unusual times, and commits touching rarely changed file types given the characteristics of a particular repository or developer. We automatically flag unusual commits on GitHub through a browser plug‐in. In an interactive survey with 173 active GitHub users, rating commits in a project of their interest, we found that, although our unusual score is only a weak predictor of whether developers want to be notified about a commit, information about unusual characteristics of a commit changes how developers regard commits. Our anomaly detection mechanism is a building block for scaling transparent environments. [ABSTRACT FROM AUTHOR]

We report a comprehensive study probing the influence of polymer blending on the large scale phase separation by the use of electroluminescence imaging (ELI) and light-beam induced current (LBIC) measurements. The study is based on a semi-crystalline and an amorphous analogue of anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE–PPV) copolymer (AnE-PVs) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Since the semi-crystalline polymer AnE-PVab strongly phase separates from PCBM, whereas the amorphous polymer AnE-PVba intimately mixes with PCBM, the phase separation is precisely controlled by blending both polymers in distinct ratios. The analysis of electroluminescence images and light-beam induced current scans allowed us to conclude about the domain size of the phase separated bulk material and intermixed regions, respectively, with the advantage of probing the whole active layer of the device at once. [ABSTRACT FROM AUTHOR]

We present a method for quantitative evaluation of electroluminescence images from thin film solar cells. The method called "quantitative electroluminescence imaging" (QuELI) is based on decoupling local equivalent circuit parameters and allows calculation of the local current-density as well as the local series resistance and saturation current-density. By application of this method to electroluminescence images obtained from polymer-fullerene based solar cells, we show that QuELI allows efficient separation between: (a) properties of the electrodes and their associated interfaces by the local series resistance and (b) properties of the active layer by the saturation current-density. We furthermore reveal large scale lateral phase separation via the strong variation in the saturation current-density, which delivers information on the energetic difference of thermal activation of charge carriers across the effective active band gap. [ABSTRACT FROM AUTHOR]

It is common knowledge that the polymer conformation and its phase separation with fullerene derivatives are delicate issues crucially impacting on the photovoltaic parameters of polymer based solar cells. While strongly intermixed polymer -- fullerene phases presumably provide a large interfacial area and consequently a high quantum efficiency of exciton dissociation, pristine and primarily ordered polymer and fullerene domains may support efficient charge transport and its percolation. To study the aggregation and phase separation behaviour in polymer solar cells we investigated the counterbalancing influences of the polymer solution concentration and its blending ratio with PCBM ([6,6]-phenyl-C[sub 61]-butyric acid methyl ester) on the basis of a semi-crystalline anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymer statistically bearing branched 2-ethylhexyloxy and linear octyloxy side-chains (AnE-PVstat). The polymer aggregation was semi-quantitatively evaluated on the basis of its optical fingerprints and varied with both, the solution and the PCBM concentration, yielding a specific maximum within the parameter range studied. Upon relating photovoltaic parameters to the order within the polymer phase, the counterbalancing effect between charge generation and transport for increasing polymer aggregation is demonstrated, in agreement with sound hypotheses. [ABSTRACT FROM AUTHOR]

Charge generation and recombination processes occurring in ternary photoactive copolymer:copolymer:fullerene blends consisting of different mixing ratios between entirely amorphous and semi-crystalline PPE-PPV copolymers are investigated by transient absorption pump–probe and pump–push photocurrent spectroscopy. The experiments reveal that an excess of semi-crystalline polymer facilitates exciton dissociation into free charge carriers, slows down geminate recombination, and suppresses non-geminate recombination leading to increased short-circuit currents and high fill factors. In contrast, blends utilizing solely the amorphous polymer for their donor phase suffer from a large fraction of sub-nanosecond geminate recombination of interfacially bound charge-transfer states and also from fast non-geminate recombination of free charges, resulting in a significantly reduced photovoltaic performance. However, small fractions of the amorphous polymer blended into the semi-crystalline polymer increase the open-circuit voltage and the fill factor, while keeping the charge generation and recombination parameters largely unaltered in turn leading to an optimized device performance for the ternary PPE-PPV copolymer:copolymer:fullerene blends. [ABSTRACT FROM AUTHOR]

Poly(phenylene ethynylene)- alt-poly(phenylene vinylene)s (PPE-PPVs) with various thiophene units (thiophene, bithiophene, and 3,4-ethylenedioxythiophene) at the X position, with the general backbone design (PhCC XCCPhCHCHPhCHCH), bearing identical solubilizing side chains at the phenylene rings of the polymers, are synthesized to study the effect of this structural alteration on the properties such as the photophysics, the electrochemical properties, the charge-carrier mobility, and the morphology of the materials and its impact on their photovoltaic performance. The polymers are obtained in good yields with reasonable molecular weights and show solubility in ordinary organic solvents required for solution-processing applications. The polymer with a basic thiophene ring at the X positions shows the highest open-circuit voltage ( VOC of 930 mV) and the polymer with a bithiophene unit at the X position shows the highest short-circuit current density and charge-carrier mobility, whereas the polymer with 3,4-ethylenedioxythiophene shows the lowest photovoltaic performance. [ABSTRACT FROM AUTHOR]

Infrared spectra of La2@C80and a series of Ce-based endohedral metallofullerenes (EMFs), including Ce@C82, Ce2@C72, Ce2@C78, and Ce2@C80are reported. DFT calculations are used for their thorough analysis and assignment. The vibrations of the fullerene cages in all studied EMFs differ from those of their empty, charged cage analogues. Furthermore, EMFs with the same carbon cage but different type of encapsulated species also show significant differences in their cage vibrational patterns. These phenomena are explained by a different coupling of the vibrational modes as well as by the different charge distributions in EMFs and empty, isostructural fullerene anions. [ABSTRACT FROM AUTHOR]

ABSTRACT The effect of solvent blending on the performance of an anthracene-containing poly( p-phenylene-ethynylene)-alt-poly( p-phenylene-vinylene) backbone-based donor polymer with asymmetrically substituted branched 2-ethylhexyloxy and methyloxy side-chains in bulk heterojunction solar cells is reported. This copolymer yields relatively high open-circuit voltages with fullerene-based electron acceptors. We systematically studied the thin-film blend morphology and solar cell performance as a function of solvent composition (chlorobenzene to chloroform ratio) and polymer to [6,6]-phenyl C61-butyric acid methylester (PCBM) ratio. We combined photophysical investigations with atomic force microscopy and grazing incidence wide-angle X-ray scattering to elucidate the solid-state morphology in thin films. In the investigated polymer system, the blend morphology becomes independent of the supporting solvent for high PCBM concentrations. Deposition from solvent blends rather than from pure chlorobenzene facilitates the beneficial phase separation between polymer and PCBM, leading to improved charge transport properties (short-circuit currents) at lower PCBM concentrations. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013, 51, 868-874 [ABSTRACT FROM AUTHOR]

SUMMARY Software is changed frequently during its life cycle. New requirements come, and bugs must be fixed. To update an application, it usually must be stopped, patched, and restarted. This causes time periods of unavailability, which is always a problem for highly available applications. Even for the development of complex applications, restarts to test new program parts can be time consuming and annoying. Thus, we aim at dynamic software updates to update programs at runtime. There is a large body of research on dynamic software updates, but so far, existing approaches have shortcomings either in terms of flexibility or performance. In addition, some of them depend on specific runtime environments and dictate the program's architecture. We present JavAdaptor, the first runtime update approach based on Java that (a) offers flexible dynamic software updates, (b) is platform independent, (c) introduces only minimal performance overhead, and (d) does not dictate the program architecture. JavAdaptor combines schema changing class replacements by class renaming and caller updates with Java HotSwap using containers and proxies. It runs on top of all major standard Java virtual machines. We evaluate our approach's applicability and performance in non-trivial case studies and compare it with existing dynamic software update approaches. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A systematic study on the influence of the alkyl side-chain length of C60 based fullerene derivatives in polymer solar cells based on an anthracene-containing poly( p-phenylene-ethynylene)-alt-poly( p-phenylene-vinylene) (PPE-PPV) copolymer (AnE-PV) is reported. It is shown that the alkyl side-chain length of the fullerene derivative strongly correlates with the individual photovoltaic parameters. The most pronounced dependence on the side-chain length is found for the fill factor, spanning the range between 50-72%, which dominantly controls in combination with the short-circuit current the power conversion efficiency. The maximum performance of 4.8% was found for an ethyl terminated side-chain, whereas larger alkyl groups resulted in a gradually decreasing power conversion efficiency. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]

Software product line engineering is an efficient means of generating a family of program variants for a domain from a single code base. However, because of the potentially high number of possible program variants, it is difficult to test them all and ensure properties like type safety for the entire product line. We present a product-line-aware type system that can type check an entire software product line without generating each variant in isolation. Specifically, we extend the Featherweight Java calculus with feature annotations for product-line development and prove formally that all program variants generated from a well typed product line are well typed. Furthermore, we present a solution to the problem of typing mutually exclusive features. We discuss how results from our formalization helped implement our own product-line tool CIDE for full Java and report of our experience with detecting type errors in four existing software product line implementations. [ABSTRACT FROM AUTHOR]

Through implicit invocation, procedures are called without explicitly referencing them. Implicit announcement adds to this implicitness by not only keeping implicit which procedures are called, but also where or when-under implicit invocation with implicit announcement, the call site contains no signs of that, or what it calls. Recently, aspect-oriented programming has popularized implicit invocation with implicit announcement as a possibility to separate concerns that lead to interwoven code if conventional programming techniques are used. However, as has been noted elsewhere, as currently implemented it establishes strong implicit dependencies between components, hampering independent software development and evolution. To address this problem, we present a type-based modularization of implicit invocation with implicit announcement that is inspired by how interfaces and exceptions are realized in JAVA. By extending an existing compiler and by rewriting several programs to make use of our proposed language constructs, we found that the imposed declaration clutter tends to be moderate; in particular, we found that, for general applications of implicit invocation with implicit announcement, fears that programs utilizing our form of modularization become unreasonably verbose are unjustified. [ABSTRACT FROM AUTHOR]