13 research outputs found
Too Trivial To Test? An Inverse View on Defect Prediction to Identify Methods with Low Fault Risk
Background. Test resources are usually limited and therefore it is often not
possible to completely test an application before a release. To cope with the
problem of scarce resources, development teams can apply defect prediction to
identify fault-prone code regions. However, defect prediction tends to low
precision in cross-project prediction scenarios.
Aims. We take an inverse view on defect prediction and aim to identify
methods that can be deferred when testing because they contain hardly any
faults due to their code being "trivial". We expect that characteristics of
such methods might be project-independent, so that our approach could improve
cross-project predictions.
Method. We compute code metrics and apply association rule mining to create
rules for identifying methods with low fault risk. We conduct an empirical
study to assess our approach with six Java open-source projects containing
precise fault data at the method level.
Results. Our results show that inverse defect prediction can identify approx.
32-44% of the methods of a project to have a low fault risk; on average, they
are about six times less likely to contain a fault than other methods. In
cross-project predictions with larger, more diversified training sets,
identified methods are even eleven times less likely to contain a fault.
Conclusions. Inverse defect prediction supports the efficient allocation of
test resources by identifying methods that can be treated with less priority in
testing activities and is well applicable in cross-project prediction
scenarios.Comment: Submitted to PeerJ C
Comment on "ferroelectricity-free lead halide perovskites" by A. Gomez, Q. Wang, A. R. Goni, M. Campoy-Quiles and A. Abate, Energy Environ. Sci., 2019, 12, 2537
This article comments on the recent publication ‘‘Ferroelectricity-free lead halide perovskites’’ by Gomez´et al. [DOI: 10.1039/c9ee00884e], in which the authors conclude that both methylammonium lead iodide (MAPbI) and the more advanced Cs(FAMA)Pb(IBr) form non-ferroelectric thin-films. This conclusion is based on measuring the vertical piezoelectric effect by ‘‘direct piezoelectric force microscopy’’ (DPFM) and not seeing any domain patterns or other ferroelectric responses. The authors calibrated their measurement using a bulk reference sample of periodically poled lithium niobate with vertical polarization, which has all-different properties from MAPbI or Cs(FAMA)Pb(IBr) thin-films. In earlier works, it was pointed out that the polarization in large MAPbI grains is vastly oriented in-plane and hence could remain invisible to any probing techniques with vertical sensitivity. In addition, the low spatial resolution of their measurements, the strong measurement noise, potential adventitious water contamination and the use of improper cantilever loads reduces the sensitivity of the measurement setup. This is why the conclusion on MAPbI being non-ferroelectric is not supported by the measurement data
Evolution of ferroelectric domains in methylammonium lead iodide and correlation with the performance of perovskite solar cells
While more and more experimental evidence for the ferroelectricity of methylammonium lead iodide (MAPbI(3)) is being reported in the literature, the scientific community still controversially discusses whether or not the ferroelectric polarization has any influence on the performance of perovskite solar cells. In this work, the evolution of ferroelectric domains and their polarization orientation in MAPbI(3) thin films during thermal annealing are investigated using piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM). Right after deposition and annealing for 5 s, small grains with non-uniform crystal orientation and polarization are formed. During the next 30-60 s, these small grains increase in diameter and large ferroelectric domains with out-of-plane polarization appear. In the annealing regime of several minutes to one hour, these large grains produce uniform domains with alternating in-plane polarization and (110) texture. The corresponding MAPbI(3) solar cells show a distinct performance enhancement and improved operational stability if the ferroelectric polarization is oriented in-plane. In contrast, solar cells with out-of-plane-polarized MAPbI(3) exhibit only moderate fill factors and reduced open-circuit voltages
Ferroelectric Poling of Methylammonium Lead Iodide Thin Films
Seemingly contradictory reports on polar domains and their origin have surrounded the controversial discussion about the ferroelectricity of the methyl ammonium lead iodide (MAPbI) thin films that are commonly employed in perovskite solar cells. In this work, microscopic modulations of the polar domain patterns upon application of an electric poling field are correlated with macroscopic changes to the currents through the MAPbI layer. Piezoresponse force microscopy is used to monitor the widening, narrowing, generation or extinction of polar domains, as well as shifts of the domain walls at room temperature under an in‐plane electric poling field that is applied between two laterally organized electrodes. This poling leads to a net polarization of individual grains and the thin film itself. Macroscopically, this net polarization results in a persistent shift of the diode characteristics that is measured across the channel between the electrodes. Both the modulation of the polar domains upon electric poling and the concurrent persistent shift of the electric currents through the device are the unambiguous hallmarks of ferroelectricity, which demonstrate that MAPbI is a ferroelectric semiconductor
Ferroelectric Properties of Perovskite Thin Films and Their Implications for Solar Energy Conversion
Whether or not methylammonium lead iodide (MAPbI3) is a ferroelectric
semiconductor has caused controversy in the literature, fueled by many
misunderstandings and imprecise definitions. Correlating recent literature
reports and generic crystal properties with the authors’ experimental
evidence, the authors show that MAPbI3 thin-films are indeed semiconducting
ferroelectrics and exhibit spontaneous polarization upon transition from the
cubic high-temperature phase to the tetragonal phase at room temperature.
The polarization is predominantly oriented in-plane and is organized in
characteristic domains as probed with piezoresponse force microscopy.
Drift-diffusion simulations based on experimental patterns of polarized
domains indicate a reduction of the Shockley–Read–Hall recombination of
charge carriers within the perovskite grains due to the ferroelectric built-in field
and allow reproduction of the electrical solar cell properties
Too trivial to test? An inverse view on defect prediction to identify methods with low fault risk
Background: Test resources are usually limited and therefore it is often not possible to completely test an application before a release. To cope with the problem of scarce resources, development teams can apply defect prediction to identify fault-prone code regions. However, defect prediction tends to low precision in cross-project prediction scenarios.
Aims: We take an inverse view on defect prediction and aim to identify methods that can be deferred when testing because they contain hardly any faults due to their code being “trivial”. We expect that characteristics of such methods might be project-independent, so that our approach could improve cross-project predictions.
Method: We compute code metrics and apply association rule mining to create rules for identifying methods with low fault risk (LFR). We conduct an empirical study to assess our approach with six Java open-source projects containing precise fault data at the method level.
Results: Our results show that inverse defect prediction can identify approx. 32–44% of the methods of a project to have a LFR; on average, they are about six times less likely to contain a fault than other methods. In cross-project predictions with larger, more diversified training sets, identified methods are even 11 times less likely to contain a fault.
Conclusions: Inverse defect prediction supports the efficient allocation of test resources by identifying methods that can be treated with less priority in testing activities and is well applicable in cross-project prediction scenarios
Structure-Activity Relationships of Thiazolyl Resorcinols, Potent and Selective Inhibitors of Human Tyrosinase
Tyrosinase inhibitors are of great clinical interest as agents for the treatment of hyperpigmentary disorders; however, most compounds described in the literature lack clinical efficiency due to insufficient inhibitory activity against human tyrosinase (hTyr). Recently, we reported that thiazolyl resorcinols (4-resorcinylthiazol-2-amines and -amides) are both selective and efficacious inhibitors of hTyr in vitro and in vivo. Here, we measured dose-activity profiles of a large number of thiazolyl resorcinols and analogous compounds to better understand the molecular basis of their interaction with hTyr. We show that both the resorcinyl moiety and the thiazole ring must be intact to allow efficient inhibition of hTyr, while the substituents at the thiazole 2-amino group confer additional inhibitory activity, depending on their size and polarity. The results of molecular docking simulations were in excellent agreement with the experimental data, affording a rationale for the structural importance of either ring. We further propose that a special type of interaction between the thiazole sulfur and a conserved asparagine residue is partially responsible for the superior inhibitory activity of thiazolyl resorcinols against hTyr