The challenge of studying perovskite solar cells stability with machine learning

Perovskite solar cells are the most dynamic emerging photovoltaic technology and attracts the attention of thousands of researchers worldwide. Recently, many of them are targeting device stability issues the key challenge for this technology which has resulted in the accumulation of a significant amount of data. The best example is the Perovskite Database Project, which also includes stability related metrics. From this database, we use data on 1,800 perovskite solar cells where device stability is reported and use Random Forest to identify and study the most important factors for cell stability. By applying the concept of learning curves, we find that the potential for improving the models performance by adding more data of the same quality is limited. However, a significant improvement can be made by increasing data quality by reporting more complete information on the performed experiments. Furthermore, we study an in house database with data on more than 1,000 solar cells, where the entire aging curve for each cell is available as opposed to stability metrics based on a single number. We show that the interpretation of aging experiments can strongly depend on the chosen stability metric, unnaturally favoring some cells over others. Therefore, choosing universal stability metrics is a critical question for future databases targeting this promising technolog

Proof systems that take advice

One of the starting points of propositional proof complexity is the seminal paper by Cook and Reckhow [J. Symbolic Logic, 1979], where they defined propositional proof systems as poly-time computable functions which have all propositional tautologies as their range. Motivated by provability consequences in bounded arithmetic, Cook and Krajı´ček [J. Symbolic Logic, 2007] have recently started the investigation of proof systems which are computed by poly-time functions using advice. In this paper we concentrate on three fundamental questions regarding this new model. First, we investigate whether a given language L admits a polynomially bounded proof system with advice. Depending on the complexity of the underlying language L and the amount and type of the advice used by the proof system, we obtain different characterizations for this problem. In particular, we show that this question is tightly linked with the question whether L has small nondeterministic instance complexity. The second question concerns the existence of optimal proof systems with advice. For propositional proof systems, Cook and Krajı´ček gave a surprising positive answer which we extend to all languages. These results show that providing proof systems with advice yields a more powerful model, but this model is also less directly applicable in practice. Our third question therefore asks whether the usage of advice in propositional proof systems can be simplified or even eliminated. While in principle, the advice can be very complex, we show that propositional proof systems with logarithmic advice are also computable in poly-time with access to a sparse NP-oracle. Employing a recent technique of Buhrman and Hitchcock [CCC, 2008] we also manage to transfer the advice from the proof to the proven formula, which leads to a more practical computational model

Learning classes of polynomial abstract identification dimension with an oracle in #SIGMA#_3"P

SIGLEAvailable from TIB Hannover: RR 2036(151) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDeutsche Forschungsgemeinschaft (DFG), Bonn (Germany)DEGerman

Parametrized learnability of k-term DNF and boolean circuits

SIGLEAvailable from TIB Hannover: RR 2036(152) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDeutsche Forschungsgemeinschaft (DFG), Bonn (Germany); Deutscher Akademischer Austauschdienst (DAAD), Bonn (Germany)DEGerman

Alternative Cityscape Visualisation: Drone shooting as a new dimension in urban photography

I was educated as a city planner and an architect. I am not practising any of these professions anymore due to the fact that they do not offer enough freedom during the process of creation. I later turned into an artist using mainly photography as a visual expression tool and a professional photographer shooting architecture and cityscapes. I always had a deep interest in urban photography, un/consciously referring to my educational past. I kept panoramic photography always in my orbit of most used visualisation apparatuses and techniques, in order to be able to construct more comprehensive urban depictions. Roofs, terraces of skyscrapers, observations decks, towers of any kind have usually been my typical platforms, where I have created a remarkably large collection of global cityscapes. It was and still is too expensive to hire a helicopter for a shoot that does not guarantee a commercial return. While I will keep using the above techniques, I feel like I entered a new era in my professional photography practice as I recently acquired a drone. Drones are not that easy to operate and that affordable to buy, if you intend to go highly professional with hi-res camera bodies on-board. You have to have an operator flying an octocopter and yourself in command of the operator telling him/her where to go and what angle to give, in order to end up with the “right” photograph. I preferred a low-priced quadcopter with a rather lower resolution camera, since I can control both the flying gismo and the camera myself. I can now send my eye to the sky, to a sky tier that I personally call “dronosphere”, a layer that is roughly in between 50 - 150 metres. This height gives me a particular viewpoint in between street view and map view. This paper will discuss if drone photography can bring a novel visual language to cityscape and / or street photography

Structure and Performance Evolution of Perovskite Solar Cells under Extreme Temperatures

Metal halide perovskite solar cells may work for application in extreme temperatures, such as those experienced under extraterrestrial conditions. However, device performances in extreme temperatures are poorly investigated. This work systematically explores the performance of perovskite solar cells between amp; 8722;160 and 150 C. In situ grazing incidence wide angle X ray scattering discloses perovskite phase transition and crystal disordering as dominant factors for the temperature dependent device efficiency deterioration. It is shown that perovskite lattice strain and relaxation originating from extreme temperature variations are recoverable, and so are the perovskite structure and photovoltaic performances. This work provides insights into the functioning under extreme temperatures, clarifying bottlenecks to overcome and the potential for extraterrestrial application