One of the major merits of CH3NH3PbI3 perovskite as an efficient absorber material for the photovoltaic cell is its long carrier lifetime. We investigate the role of the intrinsic defects of ...CH3NH3PbI3 on its outstanding photovoltaic properties using density-functional studies. Two types of defects are of interest, i.e., Schottky defects and Frenkel defects. Schottky defects, such as PbI2 and CH3NH3I vacancy, do not make a trap state, which can reduce carrier lifetime. Elemental defects like Pb, I, and CH3NH3 vacancies derived from Frenkel defects act as dopants, which explains the unintentional doping of methylammonium lead halides (MALHs). The absence of gap states from intrinsic defects of MALHs can be ascribed to the ionic bonding from organic–inorganic hybridization. These results explain why the perovskite MALHs can be an efficient semiconductor, even when grown using simple solution processes. It also suggests that the n-/p-type can be efficiently manipulated by controlling growth processes.
•We review the recent drone operations (DO) and drone-truck combined operations (DTCO) research.•We provide a detailed review of optimization models and methods for DTCO.•We identity and summarize ...the barriers to DO and DTCO implementation, found in the literature.•We propose new research directions.
This paper surveys the state-of-the-art optimization approaches in the civil application of drone operations (DO) and drone-truck combined operations (DTCO) including construction/infrastructure, agriculture, transportation/logistics, security/disaster management, entertainment/media, etc. In particular, this paper reviews ongoing research on various optimization issues related to DO and DTCO including mathematical models, solution methods, synchronization between a drone and a truck, and barriers in implementing DO and DTCO. First, the paper introduces DO and DTCO and their applications, and explores some previous works including survey papers. In addition, this paper surveys the state of the art of DO and DTCO studies and discusses the research gaps in the literature. Furthermore, the detailed review of DTCO models and solution methods are reviewed. Finally, future research directions are discussed.
Hybrid perovskites are currently the fastest growing photovoltaic technology, having reached a solar cell efficiency of over 20%. One possible strategy to further improve the efficiency of perovskite ...solar cells is to tune the degree of octahedral tilting of the halide frame, since this in turn affects the optical band gap and carrier effective masses. It is commonly accepted that the ion sizes are the main control parameter influencing the degree of tilting in perovskites. Here we re-examine the origin of octahedral tilts in halide perovskites from systematic first-principles calculations. We find that while steric effects dominate the tilt magnitude in inorganic halides, hydrogen bonding between an organic A-cation and the halide frame plays a significant role in hybrids. For example, in the case of MAPbI3, our calculations suggest that, without the contribution from hydrogen bonding, the octahedra would not tilt at all. These results demonstrate that tuning the degree of hydrogen bonding can be used as an additional control parameter to optimize the photovoltaic properties of perovskites.
Shape memory alloys (SMAs) are smart materials that are widely used to create intelligent devices because of their high energy density, actuation strain, and biocompatibility characteristics. Given ...their unique properties, SMAs are found to have significant potential for implementation in many emerging applications in mobile robots, robotic hands, wearable devices, aerospace/automotive components, and biomedical devices. Here, the state–of–the–art of thermal and magnetic SMA actuators in terms of their constituent materials, form, and scaling effects are summarized, including their surface treatments and functionalities. The motion performance of various SMA architectures (wires, springs, smart soft composites, and knitted/woven actuators) is also analyzed. Based on the assessment, current challenges of SMAs that need to be addressed for their practical application are emphasized. Finally, how to advance SMAs by synergistically considering the effects of material, form, and scale is suggested.
Shape memory alloy (SMA) actuators exhibit complex behaviors through simple structures at various scales. This review analyzes different SMA actuators based on material, form, and scale. With state‐of‐the‐art actuators and limitations of current technologies, this review offers insights into how to synergize these three aspects. It will serve soft and micro‐robotics researchers as a guideline for future developments.
In general, in thermoelectric materials the electrical conductivity σ and thermal conductivity κ are related and thus cannot be controlled independently. Previously, to maximize the thermoelectric ...figure of merit in state-of-the-art materials, differences in relative scaling between σ and κ as dimensions are reduced to approach the nanoscale were utilized. Here we present an approach to thermoelectric materials using tin disulfide, SnS2, nanosheets that demonstrated a negative correlation between σ and κ. In other words, as the thickness of SnS2 decreased, σ increased whereas κ decreased. This approach leads to a thermoelectric figure of merit increase to 0.13 at 300 K, a factor ∼1,000 times greater than previously reported bulk single-crystal SnS2. The Seebeck coefficient obtained for our two-dimensional SnS2 nanosheets was 34.7 mV K(-1) for 16-nm-thick samples at 300 K.
Though Forkhead box P (FOXP) transcription factors comprising of FOXP1, FOXP2, FOXP3 and FOXP4 are involved in the embryonic development, immune disorders and cancer progression, the underlying ...function of FOXP3 targeting CD4 + CD25+ regulatory T (Treg) cells and the dual roles of FOXP proteins as an oncogene or a tumor suppressor are unclear and controversial in cancers to date. Thus, the present review highlighted research history, dual roles of FOXP proteins as a tumor suppressor or an oncogene, their molecular networks with other proteins and noncoding RNAs, cellular immunotherapy targeting FOXP3, and clinical implications in cancer progression.
Mesenchymal stem cell (MSC) is a promising tool for the therapy of immune disorders. However, their efficacy and mechanisms in treating allergic skin disorders are less verified. We sought to ...investigate the therapeutic efficacy of human umbilical cord blood-derived MSCs (hUCB-MSCs) against murine atopic dermatitis (AD) and to explore distinct mechanisms that regulate their efficacy. AD was induced in mice by the topical application of Dermatophagoides farinae. Naïve or activated-hUCB-MSCs were administered to mice, and clinical severity was determined. The subcutaneous administration of nucleotide-binding oligomerization domain 2 (NOD2)-activated hUCB-MSCs exhibited prominent protective effects against AD, and suppressed the infiltration and degranulation of mast cells (MCs). A β-hexosaminidase assay was performed to evaluate the effect of hUCB-MSCs on MC degranulation. NOD2-activated MSCs reduced the MC degranulation via NOD2-cyclooxygenase-2 signaling. In contrast to bone marrow-derived MSCs, hUCB-MSCs exerted a cell-to-cell contact-independent suppressive effect on MC degranulation through the higher production of prostaglandin E2 (PGE2 ). Additionally, transforming growth factor (TGF)-β1 production from hUCB-MSCs in response to interleukin-4 contributed to the attenuation of MC degranulation by downregulating FcεRI expression in MCs. In conclusion, the subcutaneous application of NOD2-activated hUCB-MSCs can efficiently ameliorate AD, and MSC-derived PGE2 and TGF-β1 are required for the inhibition of MC degranulation.
Abstract
Surface reconstruction plays a vital role in determining the surface electronic structure and chemistry of semiconductors and metal oxides. However, it has been commonly believed that ...surface reconstruction does not occur in van der Waals layered materials, as they do not undergo significant bond breaking during surface formation. In this study, we present evidence that charge density wave (CDW) order in these materials can, in fact, cause CDW surface reconstruction through interlayer coupling. Using density functional theory calculations on the 1T-TaS
2
surface, we reveal that CDW reconstruction, involving concerted small atomic displacements in the subsurface layer, results in a significant modification of the surface electronic structure, transforming it from a Mott insulator to a band insulator. This new form of surface reconstruction explains several previously unexplained observations on the 1T-TaS
2
surface and has important implications for interpreting surface phenomena in CDW-ordered layered materials.
To build a deep learning model to diagnose glaucoma using fundus photography.
Cross sectional case study Subjects, Participants and Controls: A total of 1,542 photos (786 normal controls, 467 ...advanced glaucoma and 289 early glaucoma patients) were obtained by fundus photography.
The whole dataset of 1,542 images were split into 754 training, 324 validation and 464 test datasets. These datasets were used to construct simple logistic classification and convolutional neural network using Tensorflow. The same datasets were used to fine tune pre-trained GoogleNet Inception v3 model.
The simple logistic classification model showed a training accuracy of 82.9%, validation accuracy of 79.9% and test accuracy of 77.2%. Convolutional neural network achieved accuracy and area under the receiver operating characteristic curve (AUROC) of 92.2% and 0.98 on the training data, 88.6% and 0.95 on the validation data, and 87.9% and 0.94 on the test data. Transfer-learned GoogleNet Inception v3 model achieved accuracy and AUROC of 99.7% and 0.99 on training data, 87.7% and 0.95 on validation data, and 84.5% and 0.93 on test data.
Both advanced and early glaucoma could be correctly detected via machine learning, using only fundus photographs. Our new model that is trained using convolutional neural network is more efficient for the diagnosis of early glaucoma than previously published models.
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