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Cubic or Not Cubic? Combined Experimental and Computational Investigation of the Short-Range Order of Tin Halide Perovskites
Get PDFTin-based metal halide perovskites with a composition of ASnX3 (where A= MA or FA and X = I or Br) have been investigated by means of X-ray total scattering techniques coupled to pair distribution function (PDF) analysis. These studies revealed that that none of the four perovskites has a cubic symmetry at the local scale and that a degree of increasing distortion is always present, in particular when the cation size is increased, i.e., from MA to FA, and the hardness of the anion is increased, i.e., from Br- to I-. Electronic structure calculations provided good agreement with experimental band gaps for the four perovskites when local dynamical distortions were included in the calculations. The averaged structure obtained from molecular dynamics simulations was consistent with experimental local structures determined via X-ray PDF, thus highlighting the robustness of computational modeling and strengthening the correlation between experimental and computational results
Disciplinary TA:s exploring the reciprocal effects of providing writing feedback in physics
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HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
Get PDFHD 191939 (TOI-1339) is a nearby (d = 54 pc), bright (V = 9 mag), and inactive Sun-like star (G9 V) known to host a multi-planet transiting system. Ground-based spectroscopic observations confirmed the planetary nature of the three transiting sub-Neptunes (HD 191939 b, c, and d) originally detected by TESS and were used to measure the masses for planets b and c with 3\ucf precision. These previous observations also reported the discovery of an additional Saturn-mass planet (HD 191939 e) and evidence for a further, very long-period companion (HD 191939 f). Here, we report the discovery of a new non-transiting planet in the system and a refined mass determination of HD 191939 d. The new planet, HD 191939 g, has a minimum mass of 13.5\ub12.0 M- and a period of about 280 days. This period places the planet within the conservative habitable zone of the host star, and near a 1:3 resonance with HD 191939 e. The compilation of 362 radial velocity measurements with a baseline of 677 days from four different high-resolution spectrographs also allowed us to refine the properties of the previously known planets, including a 4.6\ucf mass determination for planet d, for which only a 2\ucf upper limit had been set until now. We confirm the previously suspected low density of HD 191939 d, which makes it an attractive target for attempting atmospheric characterisation. Overall, the planetary system consists of three sub-Neptunes interior to a Saturn-mass and a Uranus-mass planet plus a high-mass long-period companion. This particular configuration has no counterpart in the literature and makes HD 191939 an exceptional multi-planet transiting system with an unusual planet demographic worthy of future observation
Electrocatalyst materials for low-temperature hydrogen fuel cells
Get PDFFuel cells have emerged as an alternative to satisfy the need of energy systems with net-zero emissions. Although fuel cells date back to the 1800s, it is only during the last decades that research and development has enabled true commercialization. The growing interest in fuel cells implementation goes hand in hand with the decrease in green H2 production cost, which makes fuel cells a cornerstone in promising energy systems based on H2. It is crucial that the transport sector shifts towards inexpensive carbon-free fuel alternatives, which is possible with H2 owing to its high energy density. A broad implementation of fuel cells is, however, impeded by the high cost of fuel cell systems, which can be attributed to the Pt-based catalyst currently used in low-temperature hydrogen fuel cells. As Pt is a scarce expensive material, development of new efficient and inexpensive electrocatalysts is essential for large-scale fuel cells implementation.Although many strategies have been explored to reduce the amount of Pt without compromising the power output and lifetime, electrocatalyst development is currently hindered by the lack of mechanistic understanding. In order to gain a better understanding of the mechanisms behind the electrochemical reactions in proton exchange membrane fuel cells (PEMFC) and anion exchange membrane fuel cells (AEMFC), this thesis delves into both the fabrication and the characterization of electrocatalysts. A versatile platform was established to study model system catalysts with the aim to test electrocatalytic materials and provide reliable comparisons, making their performance rationalizable in terms of geometric and electronic structure. Pt-rare earth metal (REM) alloys were studied with respect to both their activity and stability towards the oxygen reduction reaction (ORR) in PEMFCs. Measurements with different model systems indicated an overall increase in their specific activity, but it was found that the addition of REM could compromise their stability. Different Ag alloys were studied for the ORR in alkaline conditions. It was found that alloying could improve the binding energy of oxygenated species, which enhances their ORR activity. Hydrogen oxidation reaction (HOR) and ORR activity of PdNi annealed thin films in alkaline media were investigated to pinpoint the mechanism behind the increased activity. This provides insights to the fundamental principles that lead to a good catalyst efficiency, which was also tested with the addition of different ionomers. By providing additional insights on the mechanistic aspects of fuel cell reactions, the presented work takes a step in tailoring new electrocatalytic materials that could eventually outperform bare Pt in terms of both activity and stability while reducing the total fuel cell cost
Applying an extended prototype willingness model to predict back seat safety belt use in China
Get PDFThe risk of injury and death in traffic accidents for passengers in the back and front seats can be reduced by utilizing safety belts. However, passengers use back seatbelts far less frequently than those in the front. More investigation is therefore required into the psychological constructs that affect individuals\u27 attitudes toward using back seat belts. In this study, four models were used to analyze individual intentions and actual back seat belt use: the standard theory of planned behavior (TPB); the standard prototype willingness model (PWM); a model that integrates the TPB and PWM constructs; and a model that integrates the TPB construct, PWM constructs, descriptive norms and perceived law enforcement. The results showed that the standard PWM has much more explanatory power than the standard TPB in explaining the variance in behavioral intention and behavior. Incorporating perceived behavioral control (PBC) into the standard PWM did not improve the model fit considerably, while incorporating descriptive norms and perceived law enforcement moderately improved the model fit. Attitude greatly impacted behavioral intention and the use of back seat belts, followed by perceived law enforcement and descriptive norms, while subjective norms, prototype favorability, prototype similarity and PBC had no significant effect
Infinite-dimensional Lie bialgebras and Manin pairs
Get PDFThis PhD thesis is devoted to the theory of infinite-dimensional Lie bialgebra structures as well as their close relatives such as r-matrices and Manin pairs. The thesis is based on three papers.Paper I. The standard structure on an affine Kac-Moody algebra induces a Lie bialgebra structure on the underlying loop algebra and its parabolic subalgebras. We obtain a full classification of the induced twisted Lie bialgebra structures in terms of Belavin-Drinfeld quadruples.First, we prove that the induced structures are pseudo quasi-triangular. Then, using the algebro-geometric theory of the classical Yang-Baxter equation (CYBE), we reduce the problem of classification to the well-known Belavin-Drinfeld list of trigonometric solutions.Paper II. We classify topological Lie bialgebra structures on the Lie algebra of Taylor series g[[x]], where g is a simple Lie algebra over an algebraically closed field F of characteristic 0. We formalize the notion of a topological Lie bialgebra and introduce topological analogues of Manin pairs, Manin triples, Drinfeld doubles and twists. By relating topological Manin pairs with trace extension of F[[x]] we obtain their complete classification. The classification of topological doubles, which was known before, becomes a special case of the classification of Manin pairs. The classification of doubles tells us that there are only three non-trivial doubles over g[[x]], namely g((x))
7(g[x]/x^n g[x]), n ∈ {0, 1, 2}. We prove that topological Lie bialgebra structures on g[[x]] are in one-to-one correspondence with Lagrangian Lie subalgebras of these doubles complementary to the diagonal embedding Δ of g[[x]]. The classification of topological Lie bialgebra structures is then obtained by associating the corresponding Lagrangian subalgebras with algebro-geometric datum. When the underlying field F is the field of complex numbers, the classification becomes explicit.Paper III. In this paper we associate arbitrary subspaces of g((x))
7(g[x]/x^n g[x]) complementary to Δ with so-called series of type (n, s).We prove that skew-symmetric (n, s)-type series are in bijection with Lagrangian subspaces and topological quasi-Lie bialgebra structures on g[[x]]. We classify all quasi-Lie bialgebra structures using the classification of Manin pairs from Paper II.We show that series of type (n, s), solving the generalized CYBE, correspond to Lie subalgebras
ExTrA: Explaining architectural design tradeoff spaces via dimensionality reduction
Get PDFIn software design, guaranteeing the correctness of run-time system behavior while achieving an acceptable balance among multiple quality attributes remains a challenging problem. Moreover, providing guarantees about the satisfaction of those requirements when systems are subject to uncertain environments is even more challenging. While recent developments in architectural analysis techniques can assist architects in exploring the satisfaction of quantitative guarantees across the design space, existing approaches are still limited because they do not explicitly link design decisions to satisfaction of quality requirements. Furthermore, the amount of information they yield can be overwhelming to a human designer, making it difficult to see the forest for the trees. In this paper we present ExTrA (Explaining Tradeoffs of software Architecture design spaces), an approach to analyzing architectural design spaces that addresses these limitations and provides a basis for explaining design tradeoffs. Our approach employs dimensionality reduction techniques employed in machine learning pipelines like Principal Component Analysis (PCA) and Decision Tree Learning (DTL) to enable architects to understand how design decisions contribute to the satisfaction of extra-functional properties across the design space. Our results show feasibility of the approach in two case studies and evidence that combining complementary techniques like PCA and DTL is a viable approach to facilitate comprehension of tradeoffs in poorly-understood design spaces
Boron-Mediated Regioselective Aromatic C−H Functionalization via an Aryl BF2 Complex
Get PDFAn efficient regioselective functionalization of 2-aryl-heteroarenes and aryl aldehydes via an azaaryl BF2 complex has been developed. Mechanistically the reaction comprises fluoride to bromide ligand exchange on an aryl boron species and consecutive C−B bond cleavage to deliver a broad range of functionalized products. The reaction is high yielding, has a broad substrate scope where several different heteroarenes can be functionalized with chloro, bromo, iodo, hydroxyl, amine and BF2 in a highly regioselective fashion. The method can be applied for late-stage functionalization or for rapid skeleton remodeling with for instance cross-couplings
TD Pulse: Assessing the Systematic Management of Technical Debt
No full textTechnical Debt requires the management of several technical and non-technical aspects: process, organization, tools, etc. Software companies must identify where TD is not well managed and where to improve. Based on ten years of research and practice, we have created an effective approach, TD Pulse, to assess Technical Debt Management in large software companies and find critical improvement areas. The approach was used by 232 and evaluated by more than 200 practitioners in three large companies, including Siemens and Zenseact. The results show that our approach is valuable and lightweight. We also share lessons learned from the whole assessment experience
Dynamics of bubbles across scales
Get PDFThis thesis presents numerical investigations of bubbly flow phenomena across a wide range of relevant spatial and temporal scales. The aim is to increase our understanding of a great variety of underlying phenomena and to facilitate improved predictions of bubbly flows at all relevant scales. The investigations start at small spatial scales (size of individual bubbles and below). We focus on the evolution of vapour bubbles by formulating a multiphase Direct Numerical Simulation (DNS) framework and a computationally inexpensive 1D framework, which both consider phase change- and thermal effects. These frameworks are used to study laser-induced thermocavitation bubbles that are a part of a promising technology to achieve good control of the properties of the formed crystals in the crystallisation process. Our findings identify plausible mechanisms that induce crystallisation and give guidelines for selecting suitable system parameters to maintain and control the crystallisation process. We continue to larger scales by focusing on the dynamics of individual rising bubbles. An efficient multiscale methodology is developed in an Eulerian-Lagrangian framework that predicts the liquid-phase fluctuations experienced by a bubble rising in a turbulent flow field. The dynamics and deformation of the bubble due to the liquid-phase fluctuations are resolved using a multiphase DNS framework together with a formulated Moving Reference Frame (MRF) technique. This multiscale approach is useful for studying numerous small-scale processes where bubbles are smaller than the Kolmogorov scales and can be used for bubbles, droplets or particles in both laminar and turbulent flows. We use the developed DNS framework with the MRF to study the lift force acting on deformable bubbles in steady shear flows. We formulate a theoretical framework and support it with DNS to provide a comprehensive explanation for the several identified mechanisms behind the lift force. The findings also elucidate the influence of the shear rate and governing parameters on the lift force. Finally, we study, using DNS, the dynamics and mixing properties of bubbly flows at large spatial scales (size of the entire system). We extract and analyse the dynamics and statistics of passive scalars involving O(10-100) bubbles in periodic domains. The results show a significant influence of the bubble-induced turbulence on the scalar spectra and elucidate the influence of the governing parameters on the scalar dynamics and mixing properties