Revealing the atomistic mechanisms for the high-temperature mechanical behavior of materials is important for optimizing their properties for service at high-temperatures and their thermomechanical ...processing. However, due to materials microstructure's dynamic recovery and the absence of available in situ techniques, the high-temperature deformation behavior and atomistic mechanisms of materials are difficult to evaluate. Here, we report the development of a microelectromechanical systems-based thermomechanical testing apparatus that enables mechanical testing at temperatures reaching 1556 K inside a transmission electron microscope for in situ investigation with atomic-resolution. With this unique technique, we first uncovered that tungsten fractures at 973 K in a ductile manner via a strain-induced multi-step body-centered cubic (BCC)-to-face-centered cubic (FCC) transformation and dislocation activities within the strain-induced FCC phase. Both events reduce the stress concentration at the crack tip and retard crack propagation. Our research provides an approach for timely and atomic-resolved high-temperature mechanical investigation of materials at high-temperatures.
•The rainy season was the key period when land use landscape pattern affected the river water chemistry.•The sub-watershed scale was the core scale that affects river water chemistry as a whole.•The ...“source-sink” functions of the same land use type changes with the change of scale.•Forestland and grassland have obvious interception effect on soil erosion at riparian scale.
The impact of the land use landscape pattern on river hydrochemistry has significant scale effects. It is the premise and foundation of landscape optimization and the conservation of water resources to accurately identify the core scale of the landscape pattern impacting on river hydrochemistry. Taking Binggou River Basin in the source region of Shiyang River Basin as the study area, this paper selected the three spatial scales of catchment area, buffer zone, and riparian zone, and the relationships between land use types and landscape indices and river hydrochemical characteristics were analyzed at different spatio-temporal scales using redundancy analysis. The results showed that the hydrochemistry characteristics of Binggou River Basin had strong temporal variability, and the rainy season was the key period when the land use landscape pattern affected the river hydrochemistry. The sub-watershed and riparian scales were the core scales of influence of the landscape pattern on river hydrochemistry in Binggou River Basin. In particular, the landscape pattern index contributed the most to the river hydrochemistry at the sub-watershed scale on the whole, which was the core scale affecting river hydrochemistry. The “source” or “sink” functions of the same land use type also changed as the scale changed. Forest land showed weak “source” effect at the sub-watered scale, but a strong interception effect on the soil erosion process at the riparian scale, which is a typical “sink” landscape.
Abstract
Background:
New generation antidepressant therapies, including serotonin-norepinephrine reuptake inhibitor (SNRIs) and selective serotonin reuptake inhibitors (SSRIs) were introduced in the ...late 1980s; however, few comprehensive studies compared the benefits and risks of various contemporary treatments for major depressive disorder (MDD) in pediatric patients.
Objective:
Multiple-treatments meta-analysis (MTM) was conducted to assess efficacy, acceptability, and safety of contemporary interventions in children and adolescents with MDD.
Methods:
Cochrane Library, AMED, CINAHL, EMBASE, LiLACS, MEDLINE, PSYCINFO, PSYNDEX, and Journal of Medicine and Pharmacy databases were searched for randomized controlled trials (RCTs) comparing medicinal interventions (citalopram, escitalopram, fluoxetine, mirtazapine, paroxetine, sertraline, venlafaxine), cognitive behavioral therapy (CBT), combined fluoxetine with CBT, and placebo treatment for acute MDD from January 1988 to March 2013. Treatment success, dropout rate, and suicidal ideation/attempt outcomes were measured. Bayesian methods were used to conduct a MTM including age and funding subgroups.
Results:
A total of 21 RCTs (4969 participants) were identified. Combined fluoxetine/CBT exhibited the highest efficacy, with fluoxetine alone superior to CBT, paroxetine, sertraline, citalopram, escitalopram, and placebo treatment. Sertraline, paroxetine, escitalopram, and venlafaxine showed superior acceptability to fluoxetine and combined fluoxetine/CBT. Combined fluoxetine/CBT combination was less safe, though CBT was safer than fluoxetine alone. Combined fluoxetine/CBT, fluoxetine, and mirtazapine exhibited the highest efficacy; sertraline, escitalopram, venlafaxine, and paroxetine were the best tolerated; and mirtazapine and venlafaxine were the safest.
Conclusions:
Sertraline and mirtazapine exhibited optimally balanced efficacy, acceptability, and safety for first-line acute treatment of child and adolescent MDD.
Scientifically evaluating the influence of ecological restoration projects on the water conservation function (WCF) of regional ecosystems is the foundation for formulating regional ecological ...restoration policies and optimizing and adjusting ecological restoration projects. In this paper, we considered fully the runoff generation and confluence process in the Qilian Mountains with the actual situation of the basin and re-rated the parameter Z to improve the simulation accuracy of InVEST model. On this basis, the impact of ecological restoration project on the WCF in the upper reaches of Shiyang River Basin (SRB) in the eastern part of Qilian Mountains was quantified. The results showed that, on the whole, the water conservation depth (WCD) of forest land was the largest (138.5 mm) and that of cultivated land was the smallest (24.78 mm), while the water conservation coefficient of forest land was also the largest (93.36%) and that of unused land was the smallest (16.67%). From 1986 to 2018, the WCD showed an increasing trend in the upper reaches of SRB, among them, the WCD in the western tributaries increased faster than that in the eastern tributaries from 1986 to 2000. The significantly increased areas were mainly distributed in the middle reaches of the western tributaries and the river source areas of the eastern tributaries, while the significantly decreased areas were mainly distributed in the river source areas of the western tributaries and the cultivated land expansion area in the middle reaches of the eastern tributaries. From 2000 to 2018, the WCD of the eastern tributaries increased more than that of the western tributaries. The significantly increased areas were mainly distributed in the four eastern tributaries, and the significantly decreased areas were scattered in the middle and lower reaches of each tributary. From 1986 to 2000, the overall influence of land use change on the increase in WCD was negative, while the influence of climate and land use change on the increase in water conservation were both positive from 2000 to 2018. The influence of land use change on WCD was different in different tributaries. Among them, that of the western tributaries (except the Dongda River) was positive in two different periods, while that of the eastern tributaries (except the Xiying River) was changed from negative to positive. The implementation of ecological restoration project was one of the main reasons for the improvement of WCF in Qilian Mountains from 2000 to 2018, with a contribution of 9.04%. In the future, the protection and restoration of decreased areas of WCF should be strengthened, and the Z value determined in this paper is expected to be applied in the arid inland river basins of northwest China.
Increasing the service temperature of TiAl intermetallics is the main challenge for the development of next-generation aircraft. Dispersion-strengthening, an effective means to further improve the ...high-temperature performance of metals, fails to implement in TiAl intermetallics due to difficulties in interface optimization. Here, we successively fabricate a TiAl naocomposite with fully lamellar microstructures and homogeneously dispersed Ti2AlC nanoprecipitates via spark plasma sintering. The composite consisted of semicoherent interfaces among γ-TiAl/Ti2AlC precipitates/α2-Ti3Al, in addition to continuous polysynthetic nanotwins. Strong pinning effects as well as strain-induced nanoscale TiCr2 precipitation uplift the operation temperature of TiAl nanocomposites by more than 50 °C. Furthermore, we experimentally proved that semicoherent interfaces among in situ Ti2AlC precipitates and its surrounding matrix serve as oxygen diffusion barrier during isothermal oxidization and significantly drop down the mass gain of TiAl nanocomposites during operation, making the present nanocomposite a highly potential candidate for use as light-weight structural materials in automotive and aerospace industries.
A flexible, dense, defect-free, highly adhesive, and highly dissociation energy-rich protective coating is essential to enhance the atomic oxygen (AO) resistance of polymeric materials in a low Earth ...orbit (LEO). In this work, a dense, defect-free hybrid HMDSO/SiO2 thin film coating with compositional gradients on the surface of polyimide was synthesized using vacuum-ultraviolet (VUV) irradiation. The effects of VUV irradiation on the morphology, optical transmittance, and chemical components of plasma-polymerized HMDSO (pp-HMDSO) thin-film coatings deposited on the polyimide surface were investigated in depth. There were no defects such as cracks and holes in the surface morphology of pp-HMDSO films after VUV irradiation, but the surface roughness increased slightly, and the corresponding optical transmittance decreased slightly. The chemical components of pp-HMDSO films were changed in the depth direction starting from the top of the surface, forming hybrid HMDSO/SiO2 thin films with compositional gradients. The component gradient HMDSO/SiO2 composite coating further enhanced the atomic oxygen resistance of the polyimide due to the surface layer of the UV-modified coating enriched with high dissociation energy SiO x material. Therefore, this work provides a facile UV-induced synthesis method to prepare dense, defect-free, and highly dissociation energy-rich protective gradient coatings, which are promising not only for excellent AO protection in LEO but also for potential application in water–oxygen barrier films.
Novel triangularly arranged needle-shaped precipitates in zirconium based alloys were firstly observed and systematically investigated, which were indexed as single hexagonal structured ω phase while ...obeying the orientation relationship with the α phase matrix: {0001}α∥{112‾0}ω and <112‾0>α∥ ω. In particular, viewed along 0001ω zone axis, the ω phase needles were 60° triangularly arranged and paralleled to (21‾1‾0)ω, (112‾0)ω and (1‾21‾0)ω planes, respectively. Based on electron microscopy analysis, a model for understanding the formation of these precipitates was proposed: planar periodicity distribution of dissimilar atoms in these ω phase needles resulted in the needle-shaped morphology as well as the triangular arrangement.
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•Needle-shaped ω phase with 60° arrangement in zirconium based alloy was firstly reported.•Crystallography of the ω phase was systematically investigated through electron microscopy.•Planar distribution of germanium was confirmed, which resulted in the triangular arrangement.
Previous molecular simulations and experiments suggest that grain boundaries (GBs) serve as dislocation sources in nanocrystalline metals. Although a large number of studies have been carried out, ...direct experimental evidence of dislocation nucleation from GBs has rarely been achieved. In this work, we performed in situ transmission electron microscopy (TEM) observations for a Pt nanocrystalline film with an average grain size of ~10 nm during tensile deformation. This study revealed direct evidence of dislocation nucleation at the GBs at the atomic scale. This is different from the common hypothesis predicted by molecular dynamic simulations that only partial dislocations are emitted from GBs in small-grained structures.
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•The atomic-scale plastic deformation mechanism in a nano Pt film with a mean grain size of 10 nm were studied by in situ TEM.•The dislocation nucleation at grain boundaries was directly revealed at the atomic scale.•The dislocations were identified to be full dislocations.
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