Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites

Lead halide perovskites have rapidly emerged as candidate materials for high-performing solar cells, but show serious issues related to long-term stability. Methylammonium (MA) lead perovskites with mixed iodide-bromide compositions, MAPb(I1-xBrx)3, are reported to exhibit improved stability, but the origin of such behavior is not fully understood. Here, we report new insights into the degradation properties of MAPb(I1-xBrx)3 using ab initio simulations and a range of spectroscopic techniques. Absorbance spectroscopy shows that as the Br content increases, the material stability toward oxygen and light increases. Isothermal gravimetric analysis and time-resolved single photon counting show that the amount of oxygen incorporation into perovskite films decreases significantly with increasing Br content. Ab initio simulations indicate that the degradation reaction involving superoxide species is energetically exothermic for pure MAPbI3 but becomes less favorable with increasing Br content with an endothermic energy for pure MAPbBr3, suggesting that the degradation of MAPbBr3 in the presence of oxygen and light is unfavorable. The simulations indicate shorter N-H...Br hydrogen bonds between the MA+ cation and Br ions, which would promote greater structural stability upon bromide substitution. Thin-film passivation with iodide salts is shown to enhance the stabilities of mixed-halide perovskite films and solar cell devices. The greater fundamental understanding of mixed iodide-bromide systems gained from this study is important for the future design of stable perovskite solar cells.</p

Net-Shape Manufacturing using Hybrid Selective Laser Melting/Hot Isostatic Pressing

Purpose The purpose of this study is to develop a manufacturing technology using hybrid selective laser melting/hot isostatic pressing (SLM/HIP) process to produce full density net-shape components more rapidly and at lower cost than processing by SLM alone. Design/methodology/approach Ti-6Al-4V powder was encapsulated in situ by the production of as-SLMed shell prior to the HIP process. After HIPping, the SLM shell is an integral part of the final component. Finite element (FE) modelling based on pure plasticity theory of porous metal coupled with an iterative procedure has been adopted to simulate HIPping of the encapsulated Ti-6Al-4V powder and SLMed shell. Two demonstrator parts have been modelled, designed, produced and experimentally validated. Geometrical analysis and microstructural characterisation have been carried out to demonstrate the efficiency of the process. Findings The FE model is in agreement with the measured data obtained and confirms that the design of the shell affects the resulting deformed parts. In addition, the scanning electron microscope (SEM) and Electron backscatter diffraction EBSD (EBSD) of the interior and exterior parts reveal a considerably different grain structure and crystallographic orientation with a good bonding between the SLMed shell and HIPped powder. Originality/value An approach to improve SLM productivity by combining it with HIP is developed to further innovate the advanced manufacturing field. The possibility of the hybrid SLS/HIP supported by FEA simulation as a net shape manufacturing process for fabrication of high performance parts has been demonstrated. </jats:sec

Exact Synchronization for Finite-State Sources

We analyze how an observer synchronizes to the internal state of a finite-state information source, using the epsilon-machine causal representation. Here, we treat the case of exact synchronization, when it is possible for the observer to synchronize completely after a finite number of observations. The more difficult case of strictly asymptotic synchronization is treated in a sequel. In both cases, we find that an observer, on average, will synchronize to the source state exponentially fast and that, as a result, the average accuracy in an observer's predictions of the source output approaches its optimal level exponentially fast as well. Additionally, we show here how to analytically calculate the synchronization rate for exact epsilon-machines and provide an efficient polynomial-time algorithm to test epsilon-machines for exactness.Comment: 9 pages, 6 figures; now includes analytical calculation of the synchronization rate; updates and corrections adde

Developing evidence-based resources for evaluating postgraduate trainees in the biomedical sciences

Postgraduate trainees elevate the academic strength of institutions by conducting research, promoting innovation, securing grant funding, training undergraduate students, and building alliances. Rigorous and systematic program evaluation can help ensure that postgraduate training programs are achieving the program’s intended outcomes. The purpose of this project was to develop evidence-based evaluation tools that could be shared across federally funded biomedical training programs to enhance program evaluation capacity. This manuscript describes the evidence-based process used to determine program evaluation needs of these programs at a research-intensive university. Using a multi-phased sequential exploratory mixed methods approach, data were collected from trainees, employers, leaders, and program directors. Data analyses included document analysis of program plans, inductive coding of focus groups and interviews, and descriptive analysis of surveys. Two overarching categories–Trainee Skills and Program Characteristics—were identified including six themes each. Program directors prioritized communication, social and behavioral skills, and collaboration as the trainee skills that they needed the most help evaluating. Furthermore, program directors prioritized the following program characteristics as those that they needed the most help evaluating: training environment, trainee outcomes, and opportunities offered. Surveys, interview scripts, and related resources for the categories and themes were developed and curated on a publicly available website for program directors to use in their program evaluations

Sustained vigilance is negatively affected by mild and acute sleep loss reflected by reduced capacity for decision making, motor preparation, and execution

© 2018 Sleep Research Society. Study Objectives The behavioral and cognitive consequences of severe sleep deprivation are well understood. Surprisingly, relatively little is known about the neural correlates of mild and acute sleep restriction on tasks that require sustained vigilance for prolonged periods of time during the day. Methods and Results Event-related potential (ERP) paradigms can reveal insight into the neural correlates underlying visual processing and behavioral responding that is impaired with reduced alertness, as a consequence of sleep loss. Here, we investigated the impact of reduced vigilance following at-home mild sleep restriction to better understand the associated behavioral consequences and changes in information processing revealed by ERPs. As expected, vigilance was reduced (e.g. increased lapses and response slowing) that increased over the course of the experiment in the sleep restricted (5 hr sleep) compared with the sleep-extension (9 hr sleep) condition. Corresponding to these lapses, we found decreased positivity of visually evoked potentials in the Sleep Restriction vs. Sleep Extension condition emerging from 316 to 449 ms, maximal over parietal/occipital cortex. We also investigated electrophysiological signs of motor-related processing by comparing lateralized readiness potentials (LRPs) and found reduced positivity of LRPs in the Sleep Restriction vs. Sleep Extension condition at 70-40 ms before, and 115-158 ms after a response was made. Conclusions These results suggest that even a single night of mild sleep restriction can negatively affect vigilance, reflected by reduced processing capacity for decision making, and dulls motor preparation and execution

A new approach to develop palladium-modified Ti-based alloys for biomedical applications

A new powder mixing/coating technique combined with selective laser melting (SLM) or hot isostatic pressing has been used to modify Ti-6Al-4V (Ti64) with Pd with the aim of further improving its corrosion resistance. The modified alloy samples were characterised in terms of porosity, surface structure, microstructure and composition using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electron microprobe analysis (EPMA). Their corrosion properties were evaluated via electrochemical tests and the mechanical properties measured via tensile tests. Using a new physical powder mixing technique, Pd was homogeneously distributed among the base Ti alloy powder particles without damaging their sphericity. After HIPing Pd is mainly located at grain boundaries while during SLM Pd has dissolved into the matrix. The porosity in the as-SLMed samples and surface roughness both increase continuously with increased laser scanning speed. Pd did not cause significant improvement in tensile properties but did enhance corrosion resistance in 2 M HCl by shifting the corrosion potential into the passive region of Ti64. The current work suggested that the new approach is a feasible route of synthesising modified alloys with both chemical and microstructural homogeneity as well as improved performance for biomedical application

Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass

Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T pulsed magnetic fields. The CF effective mass is found to increase approximately linearly with the effective field $B^*$, in agreement with our earlier work at lower fields. For a $B^*$ of 14 T it reaches $1.6m_e$, over 20 times the band edge electron mass. Data from all fractions are unified by the single parameter $B^*$ for all the samples studied over a wide range of electron densities. The energy gap is found to increase like $\sqrt{B^*}$ at high fields.Comment: Has final table, will LaTeX without error

The U.S. Inland Creel and Angler Survey Catalog (CreelCat): Development, Applications, and Opportunities

Inland recreational fishing, defined as primarily leisure-driven fishing in freshwaters, is a popular pastime in the USA. State natural resource agencies endeavor to provide high-quality and sustainable fishing opportunities for anglers. Managers often use creel and other angler survey data to inform state- and waterbody-level management efforts. Despite the broad implementation of angler surveys and their importance to fisheries management at state scales, regional and national coordination among these activities is minimal, limiting data applicability for larger-scale management practices and research. Here, we introduce the U.S. Inland Creel and Angler Survey Catalog (CreelCat), a first-of-its-kind, publicly available national database of angler survey data that establishes a baseline of national inland recreational fishing metrics. We highlight research and management applications to help support sustainable inland recreational fishing practices, consider cautions, and make recommendations for implementation

System-level integration tools for laser-based powder bed fusion enabled process chains

A multi-setup additive manufacturing (AM) platform that integrates the powder bed fusion (PBF) technology with a range of complementary pre- and post-processing steps has the potential to be an appealing and flexible production solution for addressing the technical requirements of the existing and new products. Especially, such multi-step manufacturing solutions could overcome the limitations of standalone additive, subtractive, replication and surface engineering processes by reinforcing their complementary capabilities. However, the lack of specially developed system-level tools to address interoperability issues in integrating PBF with other technologies leads to high uncertainty and overall risk in producing parts that incorporate geometries with different manufacturing requirements, e.g. parts with areas that can be cost-effectively machined while others require AM solutions. To address such open issues, this paper presents the development of generic hardware and software integration tools that can improve the system level performance of AM enabled process chains. In particular, the research reports the design and implementation of modular workpiece holding system and quality control strategy that can warrant the production of parts encompassing structures with distinctly different manufacturing requirements. An experimental validation of the proposed tools was performed to assess their capabilities in producing parts with high accuracy and repeatability. The results demonstrate that their synergistic utilisation can lead to significant improvements in producing AM sections on top of pre-machined preforms in regards to their positional accuracy and repeatability. It was observed that the positional accuracy in the hybrid additive-subtractive parts was improved thirtyfold with the system level tools from 0.604mm and 0.442mm to 21 μm and 10 μm along X and Y axes, respectively