CH3NH3PbI3 perovskite solar cells with a mesoporous TiO2 layer and spiro-MeOTAD as a hole transport layer (HTL) with three different CH3NH3I concentrations (0.032 M, 0.044 M and 0.063 M) were ...investigated. Strong variations in crystal size and morphology resulting in diversified cell efficiencies (9.2%, 16.9% and 12.3%, respectively) were observed. The physical origin of this behaviour was analysed by detailed characterization combining current-voltage curves with photo- and electroluminescence (PL and EL) imaging as well as light beam induced current measurements (LBIC). It was found that the most efficient cell shows the highest luminescence and the least efficient cell is most strongly limited by non-radiative recombination. Crystal size, morphology and distribution in the capping layer and in the porous scaffold strongly affect the non-radiative recombination. Moreover, the very non-uniform crystal structure with multiple facets, as evidenced by SEM images of the 0.032 M device, suggests the creation of a large number of grain boundaries and crystal dislocations. These defects give rise to increased trap-assisted non-radiative recombination as is confirmed by high-resolution μ-PL images. The different imaging techniques used in this study prove to be well-suited to spatially investigate and thus correlate the crystal morphology of the perovskite layer with the electrical and radiative properties of the solar cells and thus with their performance.
As a geological hazard, landslides cause extensive property damage and sometimes result in loss of life. Thus, it is necessary to assess areas that are vulnerable to future landslide events to ...mitigate potential damage. For this purpose, change detection analysis and a generalized additive model were applied to investigate potential landslide occurrences within the Sacheoncheon area, Korea. An unsupervised change detection analysis based on multi-temporal object-based segmentation of high-resolution remote sensing data and thresholding wad adopted to detect landslide-prone areas. Landslide susceptibility was predicted on the basis of detected landslide areas and GIS-based spatial databases. The generalized additive model, which can deal with categorical and continuous data as well as model the continuous data as a nonlinear smoothing function, was used for landslide susceptibility analysis. As a result, the unsupervised change detection scheme was able to detect 83% of actual landslide areas. The generalized additive model provided a superior predictive capability compared with the traditional generalized linear model.
In this paper, the effect of pulse current changes in the Pulsed Current Gas Tungsten Arc Welding (PCGTAW) on the various properties of dissimilar welding of AISI 316L-AISI 310S stainless steels was ...investigated. 10 mm thickness steel sheets were joined by the PCGTAW process with the background current (Ib) of 55, 70 and 85A, as well as the peak current (Ip) of 110, 130 and 150A. Then, optical microscopy (OM) and Field Emission Scanning Electron Microscopy (FE-SEM) techniques were used to study the microstructural evolution in different areas of the welded joints. Also, tensile, Charpy impact and Vickers microhardness tests were used to evaluate the effect of the pulsed current changes on mechanical properties. Finally, the fracture surfaces of Charpy impact and tensile tests samples were studied by FE-SEM. The weld metal (WM) microstructure consisted of austenite dendrites together with a low amount of delta ferrite in the grain-boundaries. Results also showed that by increasing Ib and decreasing Ip, the microstructure of the WM was changed from columnar dendritic to coaxial, and a very fine, dendritic one. This condition led to the reduction of the size of the dendrites and the amount of delta ferrite ingrain boundaries of the WM, as well as a reduction in the width of Unmixed Zone (UMZ) area. Moreover, all the welded joints were fractured from the AISI 316L stainless steels side. However, the results of the Charpy impact and microhardness tests showed that with the above variation in the welding parameters, hardness value and fracture energy of the WM increased significantly. Fractography of the surfaces showed a completely ductile fracture for both tensile and Charpy impact tests samples.
Direct pulp capping involves the placement of dental materials directly onto vital pulp tissues after deep caries removal to stimulate the regeneration of reparative dentin. This physical barrier ...will serve as a “biological seal” between these materials and the pulp tissue. Although numerous direct pulp capping materials are available, the use of small bioactive compounds that can potently stimulate and expedite reparative dentin formation is still underexplored. Here, the authors compared and evaluated the pro-osteogenic and pro-odontogenic effects of 4 small bioactive compounds— phenamil (Phen), purmorphamine (Pur), genistein (Gen), and metformin (Met). The authors found that these compounds at noncytotoxic concentrations induced differentiation and mineralization of preosteoblastic MC3T3-E1 cells and preodontoblastic dental pulp stem cells (DPSCs) in a dose-dependent manner. Among them, Phen consistently and potently induced differentiation and mineralization in vitro. A single treatment with Phen was sufficient to enhance the mineralization potential of DPSCs in vitro. More importantly, Phen-treated DPSCs showed enhanced odontogenic differentiation and mineralization in vivo. Our study suggests that these small bioactive compounds merit further study for their potential clinical use as pulp capping materials.
Ribosomes trapped on mRNAs during protein synthesis need to be rescued for the cell to survive. The most ubiquitous bacterial ribosome rescue pathway is trans-translation mediated by tmRNA and SmpB. ...Genetic inactivation of trans-translation can be lethal, unless ribosomes are rescued by ArfA or ArfB alternative rescue factors or the ribosome-associated quality control (RQC) system, which in Bacillus subtilis involves MutS2, RqcH, RqcP and Pth. Using transposon sequencing in a trans-translation-incompetent B. subtilis strain we identify a poorly characterized S4-domain-containing protein YlmH as a novel potential RQC factor. Cryo-EM structures reveal that YlmH binds peptidyl-tRNA-50S complexes in a position analogous to that of S4-domain-containing protein RqcP, and that, similarly to RqcP, YlmH can co-habit with RqcH. Consistently, we show that YlmH can assume the role of RqcP in RQC by facilitating the addition of poly-alanine tails to truncated nascent polypeptides. While in B. subtilis the function of YlmH is redundant with RqcP, our taxonomic analysis reveals that in multiple bacterial phyla RqcP is absent, while YlmH and RqcH are present, suggesting that in these species YlmH plays a central role in the RQC.
The applications of hydrated layered polysilicates, particularly magadiite, have rapidly expanded from selective cation adsorption to fabrication of nanomaterials even without full understanding of ...their adsorption reactions. This study has successfully elucidated the distinguished adsorption behavior of magadiite, spontaneous nanoparticle formation coupled with selective adsorption reactions. Magadiite exhibited highly reliable and selective adsorption, especially for Cu2+ and Pb2+. The adsorbed heavy metal cations besides Cu2+ and Pb2+ were spontaneously and systematically transformed into the corresponding hydroxide nanoparticles exclusively on the crystal edges and the nanoparticles ultimately sprouted out of the crystals on full growth. Cation selectivity is explained by the compatibility of the interlayer silanol configuration with coordination of the adsorbed cations whereas spontaneous nanoparticle formation by the changes of the silanol configuration through the grafting reaction of the adsorbed cations is due to the high flexibility of the silicate frameworks. These unique adsorption behaviours of hydrated layered polysilicates, particularly magadiite, provide a new strategy not only for developing advanced purification/retrieval technologies but also for tailor-making various nanoparticles.
Crack-free nanocrystalline rutile TiO2 films with thicknesses of up to 12 μm were prepared and characterized in connection with their application to dye-sensitized solar cells. The ...photoelectrochemical properties of the rutile-based solar cell are compared with those of the anatase-based cell. Scanning electron microscopy (SEM) shows that the rutile films consist of homogeneously distributed rod-shaped particles with an average dimension of 20 × 80 nm. Both the thickness and the morphology of the rutile films have a strong influence on the photoelectrochemical properties of the solar cells. Measurements of the incident monochromatic photon-to-current conversion efficiency (IPCE) as a function of film thickness imply that a significant fraction of light in the spectral region below 600 nm is absorbed in the first few microns of the dye-covered films due to strong light absorption by the dye. At longer wavelengths, where the dye absorbs weakly, the IPCE increases in direct proportion to the film thickness, suggesting that the electron-injection rate throughout the cell approaches homogeneity. The open-circuit photovoltage (V oc) shows only a small change with film thickness, which is attributed to the compensating effect associated with the dependence of the number of dye molecules and recombination centers on the surface area. For the same film thickness, the photocurrent−voltage responses of the dye-sensitized rutile and anatase films at one-sun light intensity are remarkably close. Their V oc is essentially the same, whereas the short-circuit photocurrent of the rutile-based cell is only about 30% lower than that of the anatase-based cell. The lower photocurrent of the rutile film correlates with a lesser amount of adsorbed dye, owing to a smaller surface area per unit volume compared with that of the anatase film. Intensity-modulated photocurrent spectroscopy and SEM studies indicate that electron transport is slower in the rutile layer than in the anatase layer due to differences in the extent of interparticle connectivity associated with the particle packing density.
Fully recrystallized Cu-4 at.%Al alloy and Cu-11 at.%Al alloy with grain sizes ranging from 0.5 μm to 80 μm were fabricated by cold rolling and annealing. Tensile tests showed that yield strength, ...ultimate tensile strength and uniform elongation of the two Cu–Al alloys had linear relationships with the inverse square root of the grain size, and both the tensile strength and uniform elongation were ameliorated with decreasing the stacking fault energy. The strain-hardening curves of the Cu-4 at.%Al alloy shifted slightly with increasing the grain size, but the strain-hardening curves of the Cu-11 at.%Al alloy were very sensitive to the grain size. Microstructures of both alloys deformed to different tensile strains showed that the Cu-4 at.%Al alloy was favored by dislocation slip; in contrast, dislocation slip, stacking faults and deformation twins were widely observed in the Cu-11 at.%Al alloy, and their roles changed at different strain levels in the specimens with different grain sizes. Finally, mechanisms of achieving high strength and ductility in low-SFE materials were analyzed based on the strain-hardening behavior and deformation patterns. Optimal grain size ranges of 0.2–1 μm for the Cu-4 at.%Al alloy and 1–3 μm for the Cu-11 at.%Al alloy were proposed to achieve superior comprehensive mechanical properties.
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A binder‐free nanocrystalline TiO2 paste with high viscosity (see Figure) has been developed using non‐thermal sintering conditions to deposit a TiO2 film with good interparticle connectivity. A ...dye‐sensitized TiO2 film dried at 150 °C demonstrates an overall conversion efficiency of 3.52 % under AM 1.5 (1000 W m–2) illumination. The binder‐free TiO2 paste is expected to be utilizable in flexible dye‐sensitized solar cells.
In this investigation, dissimilar welded joints of AISI 316 L and AISI 310S stainless steels were produced using continuous and pulsed modes current of the gas tungsten arc welding process. A filler ...metal type ER309L was used to strengthen the welded joints. The fracture mode of the tensile and Charpy impact test samples was studied using a field emission scanning electron microscope (FE-SEM). Results showed that the welded joints were broken in the 316 L steel side during the tensile test due to the presence of lower alloying elements in this steel compared with the AISI 310S stainless steel. As well, microhardness and Charpy impact tests results showed that changing the welding current from continuous to the pulsed one increased the values of these two mentioned attributes. Fractography analysis, performed on the fracture surfaces of both joints, showed a completely ductile fracture under both tensile and Charpy impact tests. Moreover, microstructural observations showed that the weld metal (WM) structure was austenitic-ferritic (AF) and contained columnar and equiaxed dendrites. Changing the welding current from the continuous to the pulsed one led to the transformation of the columnar dendrites to the very fine equiaxed dendrites. This welding current variation reduced the dendrite size of the WM and decreased the area of the unmixed zone (UMZ). Finally, XRD results indicated that austenite was the predominant phase in the welded joints.
•Microstructural observations indicated that austenite was the predominant phase in the WM and the BMs.•Pulsed current increased delta ferrite distribution in the WM & changed columnar dendrites to fine/equiaxed morphology.•The welded joints of both welding current modes were broken from the 316L steel side during tensile tests.•Microhardness results pointed out that hardness values were ascending from both BMs towards the center of the WM.•Fractography analysis of the joints depicted a completely ductile fracture with the dimple characteristic.
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