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Light-induced halide segregation limits the bandgap tunability of mixed-halide perovskites for tandem photovoltaics. Here we report that light-induced halide segregation is strain-activated in MAPb(I 1−x Br x ) 3 with Br concentration below approximately 50%, while it is intrinsic for Br concentration over approximately 50%. Free-standing single crystals of CH 3 NH 3 Pb(I 0.65 Br 0.35 ) 3 (35%Br) do not show halide segregation until uniaxial pressure is applied. Besides, 35%Br single crystals grown on lattice-mismatched substrates (e.g. single-crystal CaF 2 ) show inhomogeneous segregation due to heterogenous strain distribution. Through scanning probe microscopy, the above findings are successfully translated to polycrystalline thin films. For 35%Br thin films, halide segregation selectively occurs at grain boundaries due to localized strain at the boundaries; yet for 65%Br films, halide segregation occurs in the whole layer. We close by demonstrating that only the strain-activated halide segregation (35%Br/45%Br thin films) could be suppressed if the strain is properly released via additives (e.g. KI) or ideal substrates (e.g. SiO 2 ). Mixed-halide perovskites are of interest for photovoltaic devices, but light-induced halide segregation obstructs bandgap tuning and is not fully understood. Here the authors study the effects of strain and iodide/bromide ratio on light-induced halide segregation in mixed-halide perovskites.

Cholecystokinin receptors, CCK A R and CCK B R, are important neurointestinal peptide hormone receptors and play a vital role in food intake and appetite regulation. Here, we report three crystal structures of the human CCK A R in complex with different ligands, including one peptide agonist and two small-molecule antagonists, as well as two cryo-electron microscopy structures of CCK B R–gastrin in complex with G i2 and G q , respectively. These structures reveal the recognition pattern of different ligand types and the molecular basis of peptide selectivity in the cholecystokinin receptor family. By comparing receptor structures in different conformational states, a stepwise activation process of cholecystokinin receptors is proposed. Combined with pharmacological data, our results provide atomic details for differential ligand recognition and receptor activation mechanisms. These insights will facilitate the discovery of potential therapeutics targeting cholecystokinin receptors. Structures of human cholecystokinin receptors in complex with various ligands or G-proteins reveal how different ligand types are recognized and the basis of peptide selectivity in this receptor family, and suggest a stepwise activation mechanism.

Many studies have considered the prevalence of dementia in mainland China, Hong Kong and Taiwan. However, area level estimates have not been produced. This study examines area differences across mainland China, Hong Kong and Taiwan adjusting for the effect of methodological factors with the aim of producing estimates of the numbers of people with dementia in these areas. A search of Chinese and English databases identified 76 dementia prevalence studies based on samples drawn from mainland China, Hong Kong and Taiwan between 1980 and 2012. A pattern of significantly decreasing prevalence was observed from northern, central, southern areas of mainland China, Hong Kong and Taiwan. Area variations in dementia prevalence were not explained by differences in methodological factors (diagnostic criteria, age range, study sample size and sampling method), socioeconomic level or life expectancy between areas. The results of meta-analysis were applied to current population data to provide best estimate. Based on the DSM-IV diagnostic criteria, the total number of people aged 60 and over with dementia in mainland China, Hong Kong and Taiwan is 8.4 million (4.6%, 95% CI: 3.4, 5.8) and in northern, central and southern areas are 3.8 (5.1%, 95% CI: 4.1, 6.1), 3.2 (4.4%, 95% CI: 3.2, 5.6) and 1.2 (3.9%, 95% CI: 2.3, 5.4) million respectively. These estimates were mainly based on the studies existing in highly developed areas and potentially affected by incomplete and insufficient data. The findings of this review provide a robust estimate of area differences in dementia prevalence. Application of the estimated prevalence to population data reveals the number of people with dementia is expected to double every 20 years, areas in mainland China will be facing the greatest dementia challenge.

Doping can change the band structure of semiconductors, thereby affecting their electrical, optical, and magnetic properties. In this study, we describe the synthesis of two-dimensional (2D) Se-doped Cr 2 S 3 (Se-Cr 2 S 3 ) nanosheets using the chemical vapor deposition method. In these semiconductor nanosheets, the Se doping concentration can be controlled by tuning the Se/S mass ratio in the precursor. At the doping concentrations of 10.05% and 2.05%, the room temperature conductivity and mobility were increased by nearly 4 and 2 orders of magnitude, respectively. In addition, the response time of an ultrathin Se-Cr 2 S 3 photo-detector was 200 times shorter than that of an undoped Cr 2 S 3 nanosheet photodetector. 4.07%-Se-Cr 2 S 3 nanosheets show ferrimagnetic behavior with a Curie temperature of ∼200 K, which is 80 K higher than that of undoped Cr 2 S 3 nanosheets. A density functional theory calculation indicated that the Se doping can induce the formation of intercalated Cr vacancies in Se-Cr 2 S 3 and enhance its metallic characteristics. Our results demonstrated that Se-Cr 2 S 3 has significant potential in future electronic, optoelectronic, and spintronic devices.

In the production process of maize, the uniformity of maize sowing is one of the main factors affecting maize yield. The effect of soil coverage and the compaction process on sowing uniformity, as the final link in determining the seed bed position, needs to be further investigated. In this paper, the parameters between soil particles and boundaries are calibrated using the Plackett–Burman test and the central composite design. Furthermore, based on the DEM–MBD coupling, the influence of soil coverage and the compaction process on the seed position of the seeding monomer at different forward speeds are analysed. It was found that the adhesion between the soil and the soil-touching component can have a significant effect on the contact process between the component and the soil. Therefore, the EEPA model was used to analyse the soil–component interaction process and the contact parameters between the soil and components were obtained for the calibration. Further, based on the above work, it was found that before and after mulching, the displacement of seed particles of all shapes in the longitudinal direction increased significantly with the increase in the advancement speed of the sowing unit, while the displacement of seed particles in the transverse and sowing depth directions decreased with the increase in the advancement speed of the unit. In addition, before and after suppression, as the forward speed of the sowing unit increased, the displacement of seed particles of all shapes in the longitudinal and transverse directions gradually increased, and the displacement of seed particles of all shapes in the direction of the sowing depth decreased; the disturbance of seed displacement by the mulch suppression process was not related to seed shape. As the operating speed of the seeding unit increased, the mulching compaction process significantly reduced the sowing uniformity of maize seeds. This paper provides a theoretical basis for the next step in optimising the structure and working process of the soil coverage and the compaction.

Mix-dimensional van der Waals heterostructures (vdWHs) have inspired worldwide interests and efforts in the field of ad-vanced electronics and optoelectronics. The fundamental understanding of interfacial charge transfer is of vital import-ance for guiding the design of functional optoelectronic applications. In this work, type-Ⅱ0D-2D CdSe/ZnS quantum dots/MoS2 vdWHs are designed to study the light-triggered interfacial charge behaviors and enhanced optoelectronic performances. From spectral measurements in both steady and transient states, the phenomena of suppressed photolu-minescence (PL) emissions, shifted Raman signals and changed PL lifetimes provide strong evidences of efficient charge transfer at the 0D-2D interface. A series of spectral evolutions of heterostructures with various QDs overlapping concentrations at different laser powers are analyzed in details, which clarifies the dynamic competition between exciton and trion during an efficient doping of 3.9×1013 cm?2. The enhanced photoresponses (1.57×104 A·W–1) and detectivities (2.86×1011 Jones) in 0D/2D phototransistors further demonstrate that the light-induced charge transfer is still a feasible way to optimize the performance of optoelectronic devices. These results are expected to inspire the basic understand-ing of interfacial physics at 0D/2D interfaces, and shed the light on promoting the development of mixed-dimensional op-toelectronic devices in the near future.

The volume versus temperature relations for Ni 3 Si and Ni 3 Ge are obtained by using the first principles calculations combined with the quasiharmonic approach. Based on the equilibrium volumes at temperature T, the temperature dependence of the elastic constants, generalized stacking fault energies and generalized planar fault energies of Ni 3 Si and Ni 3 Ge are investigated by first principles calculations. The elastic constants, antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies and twinning energy decrease with increasing temperature. The twinnability of Ni 3 Si and Ni 3 Ge are examined using the twinnability criteria. It is found that their twinnability decrease with increasing temperature. Furthermore, Ni 3 Si has better twinnability than Ni 3 Ge at different temperatures.

The image dislocation method is used to construct the governing equation of dislocations in nanofilms. The classical Peierls-Nabarro equation can be recovered when the thickness of nanofilm is taken to be infinite. In order to determine the core width and Peierls stress of dislocations, the unstable stacking fault energies of Al and Cu nanofilms are calculated via the first-principle methods. It is found that surface effect can increase the Peierls stresses of screw dislocations in Al and Cu nanofilms.

Vertical transistors—in which the channel length is determined by the thickness of the semiconductor—are of interest in the development of next-generation electronic devices. However, short-channel vertical devices are difficult to fabricate, because the high-energy metallization process typically results in damage to the contact region. Here we show that molybdenum disulfide (MoS 2 ) vertical transistors with channel lengths down to one atomic layer can be created using a low-energy van der Waals metal integration technique. The approach uses prefabricated metal electrodes that are mechanically laminated and transferred on top of MoS 2 /graphene vertical heterostructures, leading to vertical field-effect transistors with on–off ratios of 26 and 10 3 for channel lengths of 0.65 nm and 3.60 nm, respectively. Using scanning tunnelling microscopy and low-temperature electrical measurements, we show that the improved electrical performance is the result of a high-quality metal–semiconductor interface, with minimized direct tunnelling current and Fermi-level pinning effect. The approach can also be extended to other layered materials (tungsten diselenide and tungsten disulfide), resulting in sub-3-nm p-type and n-type vertical transistors. Molybdenum disulfide vertical transistors with channel lengths down to one atomic layer can be made with metal electrodes using a mechanical van der Waals transfer process that leads to a high-quality metal–semiconductor interface.

The aim of this study was to systematically search literature and conduct a meta-analysis comparing the clinical efficacy and safety of Evolut R and Sapien 3 valves for transcatheter aortic valve implantation (TAVI). The PubMed, Biomed Central, Scopus, Cochrane library and Google scholar databases were searched for articles published up to June, 2019. A total of 5 studies were included. In total, 795 patients underwent TAVI with Evolut R, while 665 patients received the Sapien 3 valve in the included studies. Overall device success with Evolut R was 95.7% and with Sapien 3 was 94.2%. Pooled data indicated no significant differences between the 2 valves (OR, 1.12; 95% CI, 0.66-1.89; P=0.68; I2=0%). No significant differences were observed in the incidence of none to mild paravalvular leakage between the 2 groups (OR, 1.71; 95% CI, 0.83-3.54; P=0.14; I2=0%). Both mean [random; mean difference (MD) = −3.96; 95% CI, −4.61 to −3.31; P<0.00001, I2=0%] and peak (random; MD = −6.85; 95% CI, −8.22 to −5.48; P<0.00001, I2=0%) aortic valve gradients were significantly lower with Evolut R. No significant differences were observed in the 30-day mortality (OR, 1.32; 95% CI, 0.45-3.87; P=0.62; I2=0%) or 30-day stroke outcomes (OR, 0.76; 95% CI, 0.32-1.81; P=0.54; I2=0%) between the 2 devices. On the whole, the findings of this study indicate that Evolut R and Sapien 3 valves may be comparable in terms of device success and short-term complications. The differences between the 2 devices for post-operative moderate to severe paravalvular leak and permanent pacemaker implantation remain unclear. There is thus a need for a large multi-center randomized controlled trial to provide stronger evidence on this subject.