Risk factors for PAS disorders in patients with placenta previa.

<p>Risk factors for PAS disorders in patients with placenta previa.</p

Risk factors of postpartum hemorrhage in patients with placenta previa.

<p>Risk factors of postpartum hemorrhage in patients with placenta previa.</p

Polarization-Dependent Optoelectronic Performances in Hybrid Halide Perovskite MAPbX₃ (X = Br, Cl) Single-Crystal Photodetectors

Hybrid organic–inorganic lead halide perovskites (HOIPs) have received significant attention because of their impressive performances in the fields of solar cells and photoelectric detection. In the past five years, great efforts have been made to improve the crystallinity, reduce grain boundaries, and enhance the stabilities of perovskite films. Compared with films, HOIP single crystals possess fewer grain boundaries and stronger optoelectronic properties and can be applied in optoelectronic devices. As the most popular HOIP member, single crystals of MAPbX₃ (X = Br, Cl) are deemed as important candidates for ultraviolet–visible photodetectors, in which the crystal structure anisotropy largely affects the detection performance. In this study, high-quality cubic single crystals of MAPbBr₃ and MAPbCl₃ were successfully grown from solutions. Taking advantages of their smooth (100) facets, planar metal–semiconductor–metal photodetectors were fabricated using Au interdigitated electrodes. The optoelectronic performances under nonpolarized and linearly polarized lights were explored. The optoelectronic performances were dependent on linearly polarized lights. Interestingly, both responsivity and external quantum efficiency were greatly enhanced under the excitation with linearly polarized lights. Moreover, the polarization-related optical absorptions and the electron densities within the (100) plane could be used to interpret different optoelectronic performances of single crystals of MAPbX₃ (X = Br, Cl) under various linearly polarized lights

Highly Efficient Catalytic Ozonization at Ultralow Temperatures of Multicomponent VOCs over the Pt/CeO₂ Catalysts

Industrial flue gas has a great impact on the atmosphere environment and human health, and its emission temperatures are usually below 180 °C, which needs a new technology that can catalyze the removal of the multicomponent VOCs over high-performance catalysts in the presence of ozone. In this work, we prepared the Pt/CeO2 catalysts with different morphologies of Pt particles and investigated their catalytic performance for the ozonization of mixed VOCs (i.e., toluene and chlorobenzene (CB)). Among all of the as-prepared samples, Pt NRs/CeO2 with nanorod-like Pt particles showed excellent catalytic performance for the ozonization of toluene and CB. The T50% (the temperature at VOC conversion = 50%) values for toluene and CB ozonization were 40 and 48 °C at a space velocity of 40,000 mL g–1 h–1, respectively. The results of characterization revealed that the reactive oxygen species involved in the VOC ozonization were mainly the O2– and O22– species, surface oxygen vacancies of CeO2 were the active sites for the conversion of ozone to the reactive oxygen species, and the O2– species was the mainly active oxygen species in the low-temperature VOC oxidation. Furthermore, partial reactive oxygen species reacted with the Ptn+ species to generate more amount of the Pt0 species, and the metallic platinum species was the main active site for the adsorption and activation of toluene and CB. The chemisorbed VOCs at the Pt0 sites reacted with the reactive oxygen species at the interface of Pt and CeO2, resulting in the excellent low-temperature catalytic activity. Compared with the reaction without ozone participation, we find that the participation of ozone can not only decrease the reaction temperature but also reduce the production of toxic byproducts. We are sure that the Pt/CeO2 catalyst is promising in practical application for elimination of the VOCs from industrial flue gas

Scalable Production of Few-Layer Boron Sheets by Liquid-Phase Exfoliation and Their Superior Supercapacitive Performance

Although two-dimensional boron (B) has attracted much attention in electronics and optoelectronics due to its unique physical and chemical properties, in-depth investigations and applications have been limited by the current synthesis techniques. Herein, we demonstrate that high-quality few-layer B sheets can be prepared in large quantities by sonication-assisted liquid-phase exfoliation. By simply varying the exfoliating solvent types and centrifugation speeds, the lateral size and thickness of the exfoliated B sheets can be controllably tuned. Additionally, the exfoliated few-layer B sheets exhibit excellent stability and outstanding dispersion in organic solvents without aggregates for more than 50 days under ambient conditions, owing to the presence of a solvent residue shell on the B sheet surface that provides excellent protection against air oxidation. Moreover, we also demonstrate the use of the exfoliated few-layer B sheets for high-performance supercapacitor electrode materials. This as-prepared device exhibits impressive electrochemical performance with a wide potential window of up to 3.0 V, excellent energy density as high as 46.1 Wh/kg at a power density of 478.5 W/kg, and excellent cycling stability with 88.7% retention of the initial specific capacitance after 6000 cycles. This current work not only demonstrates an effective strategy for the synthesis of the few-layer B sheets in a controlled manner but also makes the resulting materials promising for next-generation optoelectronics and energy storage applications

Design Growth of MAPbI₃ Single Crystal with (220) Facets Exposed and Its Superior Optoelectronic Properties

MAPbI₃ is deemed as the most prominent member in hybrid perovskites family because of its extremely optoelectronic properties. However, some issues and puzzles are still in expectation of their answers, such as stabilities, hysteresis, ferroelectricity, and so on. To bridge the distinctions between MAPbI₃ single crystal and thin films, large-size single crystals are demanded. On the contrary, crystal structure anisotropy-dependent optoelectronic properties is an inevitable topic. A series of large-size MAPbI₃ single crystals with (220) facets exposed were successfully grown, using high concentration solutions and large-size seed crystals to match growth rates of (100) and (220) facets. The optoelectronic properties of photocurrents, responsivity, EQE, and detectivity clearly showed significant anisotropy of optoelectronic properties in MAPbI₃ single crystal. According to ion migration theory, the anisotropy of optoelectronic properties was interpreted. We hope this result will be helpful to guide oriented growth MAPbI₃ thin films

Supercompressible Coaxial Carbon Nanotube@Graphene Arrays with Invariant Viscoelasticity over −100 to 500 °C in Ambient Air

Vertically aligned carbon nanotube (CNT) arrays have been recognized as promising cushion materials because of their superior thermal stability, remarkable compressibility, and viscoelastic characteristics. However, most of the previously reported CNT arrays still suffer from permanent shape deformation at only moderate compressive strains, which considerably restricts their practical applications. Here, we demonstrate a facile strategy of fabricating supercompressible coaxial CNT@graphene (CNT@Gr) arrays by using a two-step route involving encapsulating polymer layers onto plastic CNT arrays and subsequent annealing processes. Notably, the resulting CNT@Gr arrays are able to almost completely recover from compression at a strain of up to 80% and retain ∼80% recovery even after 1000 compression cycles at a 60% strain, demonstrating their excellent compressibility. Furthermore, they possess outstanding strain- and frequency-dependent viscoelastic responses, with storage modulus and damping ratio of up to ∼6.5 MPa and ∼0.19, respectively, which are nearly constant over an exceptionally broad temperature range of −100 to 500 °C in ambient air. These supercompressibility and temperature-invariant viscoelasticity together with facile fabrication process of the CNT@Gr arrays enable their promising multifunctional applications such as energy absorbers, mechanical sensors, and heat exchangers, even in extreme environments

Facile Synthesis of Millimeter-Scale Vertically Aligned Boron Nitride Nanotube Forests by Template-Assisted Chemical Vapor Deposition

There is an increasing amount of research interest in synthesizing boron nitride nanotubes (BNNTs) as well as BN coatings to be used for various applications due to their outstanding mechanical, electrical, and thermal properties. However, vertically aligned (VA) BNNTs are difficult to synthesize and the longest VA-BNNTs achieved to date are up to several tens of microns. Here, we report the synthesis of over millimeters long multiwalled BN coated carbon nanotubes (BN/CNT) and BNNT forests via a facile and effective two-step route involving template-assisted chemical vapor deposition at a relatively low temperature of 900 °C and a subsequent annealing process. The as-prepared BN/CNTs and BNNTs retain the highly ordered vertically aligned structures of the CNT templates as identified by scanning electron microscopy. The structure and composition of the resulting products were studied using transmission electron microscopy, electron energy-loss spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. This versatile BN coating technique and the synthesis of millimeter-scale BN/CNTs and BNNTs pave the way for new applications especially where the aligned geometry of the NTs is essential such as for field-emission, interconnects, and thermal management

Biocompatible Hydroxylated Boron Nitride Nanosheets/Poly(vinyl alcohol) Interpenetrating Hydrogels with Enhanced Mechanical and Thermal Responses

Poly­(vinyl alcohol) (PVA) hydrogels with tissue-like viscoelasticity, excellent biocompatibility, and high hydrophilicity have been considered as promising cartilage replacement materials. However, lack of sufficient mechanical properties is a critical barrier to their use as load-bearing cartilage substitutes. Herein, we report hydroxylated boron nitride nanosheets (OH-BNNS)/PVA interpenetrating hydrogels by cyclically freezing/thawing the aqueous mixture of PVA and highly hydrophilic OH-BNNS (up to 0.6 mg/mL, two times the highest reported so far). Encouragingly, the resulting OH-BNNS/PVA hydrogels exhibit controllable reinforcements in both mechanical and thermal responses by simply varying the OH-BNNS contents. Impressive 45, 43, and 63% increases in compressive, tensile strengths and Young’s modulus, respectively, can be obtained even with only 0.12 wt% (OH-BNNS:PVA) OH-BNNS addition. Meanwhile, exciting improvements in the thermal diffusivity (15%) and conductivity (5%) can also be successfully achieved. These enhancements are attributed to the synergistic effect of intrinsic superior properties of the as-prepared OH-BNNS and strong hydrogen bonding interactions between the OH-BNNS and PVA chains. In addition, excellent cytocompatibility of the composite hydrogels was verified by cell proliferation and live/dead viability assays. These biocompatible OH-BNNS/PVA hydrogels are promising in addressing the mechanical failure and locally overheating issues as cartilage substitutes and may also have broad utility for biomedical applications, such as drug delivery, tissue engineering, biosensors, and actuators

Trimethylamine Borane: A New Single-Source Precursor for Monolayer h‑BN Single Crystals and h‑BCN Thin Films

Due to their exceptional chemical and thermal stabilities as well as electrically insulating property, atomically thin hexagonal boron nitride (h-BN) films have been identified as a promising class of dielectric substrate and encapsulation material for high-performance two-dimensional (2D) heterostructure devices. Herein, we report a facile chemical vapor deposition synthesis of large-area atomically thin h-BN including monolayer single crystals and C-doped h-BN (h-BCN) films utilizing a relatively low-cost, commercially available trimethylamine borane (TMAB) as a single-source precursor. Importantly, pristine 2D h-BN films with a wide band gap of ∼6.1 eV can be achieved by limiting the sublimation temperature of TMAB at 40 °C, while C dopants are introduced to the h-BN films when the sublimation temperature is further increased. The h-BCN thin films displayed band gap narrowing effects as identified by an additional shoulder at 205 nm observed in their absorbance spectra. Presence of N–C bonds in the h-BCN structures with a doping concentration of ∼2 to 5% is confirmed by X-ray photoelectron spectroscopy. The inclusion of low C doping in the h-BN films is expected to result in constructive enhancement to its mechanical properties without significant alteration to its electrically insulating nature. This study provides new insights into the design and fabrication of large-area atomically thin h-BN/h-BCN films toward practical applications and suggests that the range of precursors can be potentially extended to other anime borane complexes as well