Search Results

We examined the in vitro developmental competence of parthenogenetic activation (PA) oocytes activated by an electric pulse (EP) and treated with various concentrations of AZD5438 for 4 h. Treatment with 10 µM AZD5438 for 4 h significantly improved the blastocyst formation rate of PA oocytes in comparison with 0, 20, or 50 µM AZD5438 treatment (46.4% vs. 34.5%, 32.3%, and 24.0%, respectively; P < 0.05). The blastocyst formation rate was higher in the group treated with AZD5438 for 4 h than in the groups treated with AZD5438 for 2 or 6 h (42.8% vs. 38.6% and 37.2%, respectively; P > 0.05). Furthermore, 66.67% of blastocysts derived from these AZD5438-treated PA oocytes had a diploid karyotype. The blastocyst formation rate of PA and somatic cell nuclear transfer (SCNT) embryos was similar between oocytes activated by an EP and treated with 2 mM 6-dimethylaminopurine for 4 h and those activated by an EP and treated with 10 µM AZD5438 for 4 h (11.11% vs. 13.40%, P > 0.05). In addition, the level of maturation-promoting factor (MPF) was significantly decreased in oocytes activated by an EP and treated with 10 µM AZD5438 for 4 h. Finally, the mRNA expression levels of apoptosis-related genes (Bax and Bcl-2) and pluripotency-related genes (Oct4, Nanog, and Sox2) were checked by RT-PCR; however, there were no differences between the AZD5438-treated and non-treated control groups. Our results demonstrate that porcine oocyte activation via an EP in combination with AZD5438 treatment can lead to a high blastocyst formation rate in PA and SCNT experiments.

Accurate prediction of the flow around multi-element airfoil is a prerequisite for improving aerodynamic performance, but its complex flow features impose high demands on turbulence modeling. In this work, delayed detached-eddy-simulation (DDES) and zonal detached-eddy-simulation (ZDES) was applied to simulate the flow past a three-element airfoil. To investigate the effects of numerical dissipation of spatial schemes, the third-order MUSCL and the fifth-order interpolation based on modified Roe scheme were implemented. From the comparisons between the calculations and the available experimental result, third-order MUSCL-Roe can provide satisfactory mean velocity profiles, but the excessive dissipation suppresses the velocity fluctuations level and eliminates the small-scale structures; DDES cannot reproduce the separation near the trailing edge of the flap which lead to the discrepancy in mean pressure coefficients, while ZDES result has better tally with the experiment.

Metallic glasses (MGs) are known to have high strength, but poor ductility. Prior studies have shown that plasticity in MG can be enhanced by significantly reducing their dimension to nanoscale. Here we show that, via the introduction of certain types of crystalline/amorphous interfaces, plasticity of MG can be prominently enhanced as manifested by the formation of ductile “dimples” in a 2 μm thick amorphous CuNb film. By tailoring the volume fraction and architecture of crystalline/amorphous multilayers, tensile fracture surface of MG can evolve from brittle featureless morphology to containing ductile dimples. In situ micropillar compression studies performed inside a scanning electron microscope show that shear instability in amorphous layers can be inhibited by interfaces. The mechanisms for improving plasticity and fracture resistance of MG via interface and size effect are discussed.

The impact of climate change on the variability of local discharge was investigated in a glacierized high mountain catchment located in the source area of the Ürümqi river, northwest China. We used past climate records to drive a hydrological model to simulate the discharge from 2000 to 2008. The model was then used to project future discharge variations for the period 2041–60, based on a regionally downscaled climate-change scenario combined with three stages of glacier coverage (i.e. compared to the glacier coverage in 2008): unchanged glacier size (100% glacierized), recession of half the glacier area (50% glacierized) and complete disappearance of glaciers (0% glacierized). In each scenario, snowmelt will begin half a month earlier and the discharge will increase in May. For the 100% glacierized scenario, the discharge will increase by 66 ± 35% in a smaller (3.34 km2) and more glaciated (50%) catchment and 33 ± 20% in a larger (28.90 km2) and proportionally less glaciated (18%) catchment. If the glacier area reduces by half, the discharge will decrease by 8 ± 5% and 9 ± 6%, respectively. Once the glacier disappears, the discharge will decrease by 58 ± 20% and 40 ± 13%, respectively. Together, the results indicate that a warming climate and the resulting glacier shrinkage will cause significant changes in the volume and timing of runoff.

Melt-SHS (self-propagating high-temperature synthesis), based on the SHS process and oxide reaction method, was used for preparation of TiB2/Al composites. The mass ratio of two reactants, Ti powder/TiO2, in initial powder mixture was varied from 0:1 to 1:0. The results showed that the 5 wt% TiB2/Al composites could be successfully produced by a reaction of aluminum powder, TiO2, and B2O3 in Al melt at 950 °C, while the reaction rate was slow. The addition of titanium powder helps to reduce the content of Al2O3 and destroy the coating structure of Al2O3 covered TiB2 particles, which leads to the acceleration of reaction process and improvement of particle concentration. A significant improvement was that TiB2 particles were dispersively distributed when the mass ratio of Ti powder/TiO2 was 2:3. As a result, the 5 wt% TiB2/Al composites fabricated by melt-SHS process with modified reactants ratio showed excellent tensile properties with the ultimate tensile strength as high as 114.24 MPa. Besides, the composite also showed superior ductility.

Surface texture was prepared on the ASTM1045 steel substrate before spraying. Three texturing patterns (groove pattern, square pattern, and hexagon pattern) were acquired by laser processing to investigate the influence of texturing patterns on the adhesion strength of sprayed coatings. The Ni60 coatings were prepared on the textured surface by atmosphere plasma spraying technology. Scanning electron microscopy and laser 3D microscope were used to characterize the morphology of texturing. The adhesion strength between coating and substrate was examined by the tensile test. Image pro plus software was used to calculate the contact area ratio of the textured substrate. The results show that the texturing processed substrates by laser radiation present plain area between two dimples and the protrusion around texturing, and the contact area between coating and substrate is increased. The adhesion strength of coatings with a groove pattern, a square pattern, and a hexagon pattern is 58, 33, and 47 MPa, respectively. The adhesion strength of sprayed coatings varies with the change of the texturing pattern, and it does not only depend on the contact area ratio but also on the texturing density and the texturing microstructure.

A series CeO2/Al2O3 catalysts was modified with rare earth element (La, Nd, Sm, Gd, and Tm) using extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction (SCR) of NO with NH3 to screen suitable addition of rare earth element. These samples were characterized by X-ray diffraction (XRD), N2 adsorption (N2-BET), NH3 temperature-programmed desorption analyses (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), Raman spectra, pyridine adsorption Fourier-transform infrared (Py-IR) and X-ray photoelectron spectroscopy (XPS), respectively. Results showed that the CeO2/Al2O3 exhibited excellent performance in resisting reactant poisoning caused by vapor and sulfur and the highest catalytic activity (98.35%) at 360 °C when the added Tm/Ce molar ratio is 0.10. The surface acidity of CeO2/Al2O3 catalyst would be enhanced with the addition of rare earth ions. Consequently, rare earth ion was beneficial to catalytic activity at low temperatures and corresponded to similar law. Analysis revealed that the higher number of acid sites and the more Ce3+ were conductive to obtain the excellent NH3-SCR activity.

The selection of young stellar objects (YSOs) based on excess emission in the infrared is easily contaminated by post-main-sequence stars and various types of emission line stars with similar properties. We define in this paper stringent criteria for an efficient selection and classification of stellar sources with infrared excess emission based on combined Two Micron All Sky Survey (2MASS) and AKARI colors.

In order to understand the star formation process under the influence of H ii regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescopes, the physical status of interstellar medium and star formation in these regions have been revealed. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Signs of compressed gas and triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions.

In this work, the high-performance silicon carbide particle SiCp[carbon nanotube (CNT)] hybrid reinforcement is currently explored to develop the advanced metal matrix composites. 17 wt% SiCp(CNT)/Al composites were fabricated by a powder metallurgy technique, in which SiCp(CNT) hybrid reinforcement with various CNT contents (e.g., 3, 6 and 9 wt%) were applied. Effects of CNT content on the morphology of SiCp(CNT) hybrid reinforcement, the microstructural characteristics, and the tensile mechanical behavior of SiCp(CNT)/Al composites were studied as well. Especially, the SiCp(CNT)/Al composites with 6 wt% CNT in SiCp(CNT) hybrid reinforcement exhibited the most significant enhancing effects in the elastic modulus and tensile strength. Meanwhile, the SiCp(CNT)/Al composites produced a synergistic strengthening effect of SiCp and CNT compared to SiCp/Al composites, while the SiCp(CNT)/Al composites with high CNT content in SiCp(CNT) hybrid reinforcement provided weak improvement in the tensile strength and ductility due to the forming agglomeration of CNT in the matrix.

We present a novel route to fabricate 3D nanoporous α-Ti foams by dealloying of TiCu master alloy in solid state using Mg powders. Pure open-cell nanoporous α-Ti foams are fabricated with BET surface area of 34.4 ± 0.8 m2/g and pore size in the range of 2–50 nm. The dealloying using powders is a solid state chemical reaction process to form Cu2Mg phase and Ti/Mg nanocomposites. The constituent of Cu in the TiCu alloy was dissolved into Mg powders thanks to the kinetics of interface reaction and volume diffusion. The pore-forming mechanism is a solid-state interdiffusion process. The ligament coarsening is from 492 to 650 nm with increasing of the dealloying temperature. The hardness and elastic modulus in nanoporous α-Ti foam follow linear decay fit with ligament size increasing. Our results demonstrate a facile strategy for the fabrication of nanoporous Ti foams with novel nanostructures and tailored properties.

The evolution of arid environments in northern China was a major environmental change during the Quaternary. Here we present the dating and environmental proxy results from a 35 m long core (A-WL10ZK-1) collected from the Ulan Buh Desert (UBD), along with supplemental data from four other cores. The UBD is one of the main desert dune fields in China and our results indicate the UBD has undergone complex evolution during the late Quaternary. Most of the present UBD was covered by a Jilantai-Hetao Mega-paleolake lasting until ~ 90 ka ago. A sandy desert environment prevailed throughout the UBD during the last glacial period and early Holocene. A wetland environment characterized by the formation of numerous interdunal ponds in the northern UBD occurred at ~ 8–7 ka, although a dune field persisted in the southern UBD. The modern UBD landscape formed after these wetlands dried up. During the last 2000 years, eolian sand from the Badain Jaran Desert has invaded the northern UBD, while farming and overgrazing resulted in the formation of the eastern UBD. We suggest that the formation of UBD landforms is related to the disintegration of the megalake Jilantai-Hetao and to summer monsoon changes during the last glaciation and Holocene.

A long dust history established using geological archives from dust provenance areas is necessary to understand the role of atmospheric dust in the global climate system better. Core sediments from a closed-basin groundwater-recharged lake in arid Central Asia were investigated using a multi-proxy approach (e.g. 14C AMS dating, pollen, and grain size) to trace the dust history since ~ 15 cal ka BP. Pollen analysis showed that before 7.9 cal ka BP, the vegetation was of desert type. After 7.9 cal ka BP, vegetation density increased, probably due to slightly increased moisture. The Chenopodiaceae-dominated desert expanded rapidly at 4.2–3.8 cal ka BP. Grain-size analysis was conducted for samples of lake deposits, modern aeolian dust, and dust trapped in snow, and the data showed that there was strong aeolian dust deposition at 11.8–11.1, 10.6–8, 6.1–4.9, and after 3.3 cal ka BP. This timing corresponds well with periods of increased terrestrial dust fluxes recorded by Greenland ice cores. Our study may document changes in the location and intensity of the Siberia High. These changes may play a more important role in the history of dust emission in arid Central Asia than previously thought.

In this article, we consider the numerical solution for Poisson's equation in axisymmetric geometry. When the boundary condition and source term are axisymmetric, the problem reduces to solving Poisson's equation in cylindrical coordinates in the two-dimensional (r,z) region of the original three-dimensional domain S. Hence, the original boundary value problem is reduced to a two-dimensional one. To make use of the Mechanical quadrature method (MQM), it is necessary to calculate a particular solution, which can be subtracted off, so that MQM can be used to solve the resulting Laplace problem, which possesses high accuracy order and low computing complexities. Moreover, the multivariate asymptotic error expansion of MQM accompanied with for all mesh widths hi is got. Hence, once discrete equations with coarse meshes are solved in parallel, the higher accuracy order of numerical approximations can be at least by the splitting extrapolation algorithm (SEA). Meanwhile, a posteriori asymptotic error estimate is derived, which can be used to construct self-adaptive algorithms. The numerical examples support our theoretical analysis.

The dynamics of vortical structures in flow over a circular cylinder in the vicinity of a flat plate is investigated using particle image velocimetry (PIV). The cylinder is placed above the flat plate with its axis parallel to the wall and normal to the flow direction. The Reynolds number $Re_{D}$ based on the cylinder diameter  $D$ is 1072 and the gap  $G$ between the cylinder and the flat plate is varied from gap-to-diameter ratio $G/D=0$ to $G/D=3.0$ . The flow statistics and vortex dynamics are strongly dependent on the gap ratio $G/D$ . Statistics show that as the cylinder comes close to the wall ( $G/D\leqslant 2.0$ ), the cylinder wake becomes more and more asymmetric and a boundary layer separation is induced on the flat plate downstream of the cylinder. The wake vortex shedding frequency increases with decreasing $G/D$ until a critical gap ratio (about $G/D=0.25$ ) below which the vortex shedding is irregular. The deflection of the gap flow away from the wall and its following interaction with the upper shear layer may be the cause of the higher shedding frequency. The vortex dynamics is investigated based on the phase-averaged flow field and virtual dye visualization in the instantaneous PIV velocity field. It is revealed that when the cylinder is close to the wall ( $G/D=2.0$ ), the cylinder wake vortices can periodically induce secondary spanwise vortices near the wall. As the cylinder approaches the wall ( $G/D=1.0$ ) the secondary vortex can directly interact with the lower wake vortex, and a further approaching of the cylinder ( $G/D=0.5$ ) can result in more complex interactions among the secondary vortex, the lower wake vortex and the upper wake vortex. The breakdown of vortices into filamentary debris during vortex interactions is clearly revealed by the coloured virtual dye visualizations. For $G/D<0.25$ , the lower shear layer is strongly inhibited and only the upper shear layer can shed vortices. Investigation of the vortex formation, evolution and interaction in the flow promotes the understanding of the flow physics for different gap ratios.

The early Cambrian Period was a key interval in Earth history with regard to changes in both ocean chemistry and animal evolution. Although increasing ocean ventilation has been widely assumed to have played a key role in the rapid appearance, diversification and spatial colonization of early animals, this relationship is in fact not firmly established. Here, we report a high-resolution Fe-C-S-Al-Ti geochemical study of the lower Cambrian Wangjiaping section from an outer-shelf setting of the Yangtze Sea of South China. Iron speciation data document a redox transition from dominantly euxinic to ferruginous conditions during Cambrian Age 3 (c. 521–514 Ma). Interpretation of coexisting pyrite sulphur isotope (δ34Spy) records from Wangjiaping reveals relatively high marine sulphate availability at Wangjiaping. Furthermore, Wangjiaping section shows lower δ34Spy (‒2.1±5.3‰) and lower TOC (2.4±1.1%) values but higher positive correlation (R 2 = 0.66, p < 0.01) between TOC and Fepy/FeHR relative to deeper sections reported previously, suggesting that euxinia developed at Wangjiaping in response to increasing marine productivity and organic matter-sinking fluxes. Our reconstructed redox conditions and fossils at Wangjiaping in comparison with previously well-studied strata in the inner-shelf Xiaotan and Shatan sections suggest that planktonic and benthic planktonic trilobites with bioturbation appeared in the oxic water columns, whereas only planktonic trilobites without bioturbation occurred within the anoxic (even euxinic) water columns during Cambrian Age 3. This finding indicates that spatial heterogeneity of redox conditions in the shelves had an important effect on early animal distribution in the Yangtze Block.

We study the convergence of an Ulm-like Cayley transform method for solving inverse eigenvalue problems which avoids solving approximate Jacobian equations. Under the nonsingularity assumption of the relative generalized Jacobian matrices at the solution, a convergence analysis covering both the distinct and multiple eigenvalues cases is provided and the quadratical convergence is proved. Moreover, numerical experiments are given in the last section to illustrate our results.