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Causal Structure Discovery (CSD) is the problem of identifying causal relationships from large quantities of data through computational methods. With the limited ability of traditional association-based computational methods to discover causal relationships, CSD methodologies are gaining popularity. The goal of the study was to systematically examine whether (i) CSD methods can discover the known causal relationships from observational clinical data and (ii) to offer guidance to accurately discover known causal relationships. We used Alzheimer's disease (AD), a complex progressive disease, as a model because the well-established evidence provides a "gold-standard" causal graph for evaluation. We evaluated two CSD methods, Fast Causal Inference (FCI) and Fast Greedy Equivalence Search (FGES) in their ability to discover this structure from data collected by the Alzheimer's Disease Neuroimaging Initiative (ADNI). We used structural equation models (which is not designed for CSD) as control. We applied these methods under three scenarios defined by increasing amounts of background knowledge provided to the methods. The methods were evaluated by comparing the resulting causal relationships with the "gold standard" graph that was constructed from literature. Dedicated CSD methods managed to discover graphs that nearly coincided with the gold standard. For best results, CSD algorithms should be used with longitudinal data providing as much prior knowledge as possible.

The performance of organic–inorganic perovskite-based devices has rapidly increased in recent years, but the poor air-stability of perovskite materials limits their widespread applications. Here we report a strategy to enhance the air-stability of the CH3NH3PbI3 (MAPbI3) perovskite with trilayer graphene on top of it by an anhydrous transfer method. Our morphological characterization shows good adhesion at the interface of the graphene/perovskite film. The time dependent X-ray diffraction spectra of perovskite films demonstrate enhanced stability of graphene-coated films during exposure to the ambient environment. The protected perovskite film is also evidenced by photoluminescence and absorbance measurements. This graphene transfer method without the use of water has the potential to enhance the air-stability of perovskites as well as other moisture sensitive materials. [ABSTRACT FROM AUTHOR]

Abstract: Nonvolatile optoelectronic memories integrated with the functions of sensing, data storage, and data processing are promising for the potential Internet of things (IoT) applications. To meet the requirements of IoT devices, multifunctional memory devices with low power consumption and secure data storage are highly desirable. This study demonstrates an optoelectronic resistive switching memory integrated with sensing and logic operations by adopting organic–inorganic hybrid CH3NH3PbI3−xClx perovskites, which possess unusual defect physics and excellent light absorption. The CH3NH3PbI3−xClx cell exhibits low operation voltage of 0.1 V with the assistance of light illumination, long‐term retention property, and multiple resistance states. Its unique optoelectronic characteristics enable to perform logic operation for inputting one electrical pulse and one optical signal, and detect the coincidence of electrical and optical signal as well. This design provides possibilities for smart sensor in IoT application. [ABSTRACT FROM AUTHOR]

Robust hydrogen evolution reaction (HER) in alkaline solution using a cost-effective catalyst is still a critical challenge for industrial H2O electrolysis. The dramatic depletion of interfacial H2O and hindered OH− diffusion bring about a harsh interfacial environment and thereby lead to sluggish hydrogen evolution. Here we develop heterogeneous catalysts based on defect-rich three-dimensional graphene (M/3D graphene) and achieve improved HER kinetics via surface hydroxyl group modification on the graphene surface. Our theoretical studies suggest that the surface hydroxyl groups derived from the hydroxylation process effectively attract multi-overlayer H2O clusters without any thermodynamic barrier and form a reservoir to continuously supply H2O for catalytic sites. Electrochemical characterizations indicate that the HER kinetics per active electrochemical surface area have been greatly improved after crafting abundant hydroxyl groups on the 3D graphene framework, which can be attributed to sufficient proton donors and an ameliorative interfacial pH environment. Benefiting from the surface hydroxyl group modification, the MoS2/3D graphene structure facilitates the HER at a low onset potential of 60 mV in alkaline medium and exhibits excellent durability after 3000 cycles. This surface modification strategy reveals the importance of interfacial H2O supply in HER kinetics and provides general guidance on designing highly efficient catalysts in alkaline medium. [ABSTRACT FROM AUTHOR]

To alleviate photoinduced charge recombination in semiconducting nanomaterials represents an important endeavor toward high‐efficiency photocatalysis. Here a judicious integration of piezoelectric and photocatalytic properties of organolead halide perovskite CH3NH3PbI3 (MAPbI3) to enable a piezophotocatalytic activity under simultaneous ultrasonication and visible light illumination for markedly enhanced photocatalytic hydrogen generation of MAPbI3 is reported. The conduction band minimum of MAPbI3 is higher than hydrogen generation potential (0.046 V vs normal hydrogen electrode), thereby rendering efficient hydrogen evolution. In addition, the noncentrosymmetric crystal structure of MAPbI3 enables its piezoelectric properties. Thus, MAPbI3 readily responds to external mechanical force, creating a built‐in electric field for collective piezophotocatalysis as a result of effective separation of photogenerated charge carriers. The experimental results show that MAPbI3 powders exhibit superior piezophotocatalytic hydrogen generation rate (23.30 µmol h−1) in hydroiodic acid (HI) solution upon concurrent light and mechanical stimulations, much higher than that of piezocatalytic (i.e., 2.21 µmol h−1) and photocatalytic (i.e., 3.42 µmol h−1) hydrogen evolution rate as well as their sum (i.e., 5.63 µmol h−1). The piezophotocatalytic strategy provides a new way to control the recombination of photoinduced charge carriers by cooperatively capitalizing on piezocatalysis and photocatalysis of organolead halide perovskites to yield highly efficient piezophotocatalysis. [ABSTRACT FROM AUTHOR]

Photovoltachromic cells (PVCCs) are of great interest for the self-powered smart windows of architectures and vehicles, which require widely tunable transmittance and automatic color change under photostimuli. Organolead halide perovskite possesses high light absorption coefficient and enables thin and semitransparent photovoltaic device. In this work, we demonstrate co-anode and co-cathode photovoltachromic supercapacitors (PVCSs) by vertically integrating a perovskite solar cell (PSC) with MoO3/Au/MoO3 transparent electrode and electrochromic supercapacitor. The PVCSs provide a seamless integration of energy harvesting/storage device, automatic and wide color tunability, and enhanced photostability of PSCs. Compared with conventional PVCC, the counter electrodes of our PVCSs provide sufficient balancing charge, eliminate the necessity of reverse bias voltage for bleaching the device, and realize reasonable in situ energy storage. The color states of PVCSs not only indicate the amount of energy stored and energy consumed in real time, but also enhance the photostability of photovoltaic component by preventing its long-time photoexposure under fully charged state of PVCSs. This work designs PVCS devices for multifunctional smart window applications commonly made of glass.

With significant progress in the past decade, semiconductor nanowires have demonstrated unique features compared to their thin film counterparts, such as enhanced light absorption, mechanical integrity and reduced therma conductivity, etc. However, technologies of semiconductor thin film still serve as foundations of several major industries, such as electronics, displays, energy, etc. A direct path to convert thin film to nanowires can build a bridge between these two and therefore facilitate the large-scale applications of nanowires. Here, we demonstrate that methylammonium lead iodide (CH3NH3PbI3) nanowires can be synthesized directly from perovskite film by a scalable conversion process. In addition, with fine kinetic control, morphologies, and diameters of these nanowires can be well-controlled. Based on these perovskite nanowires with excellent optical trapping and mechanical properties, flexible photodetectors with good sensitivity are demonstrated.