An Experimental Research of Natural Circulation Heat Transfer for PRHR Heat Exchanger in AP1000

The heat transfer characteristics of the PRHR （passive residual heat removal） HX （heat exchanger） are very important to reactor design and safety assessment of AP1000. The purpose of the present experiment was to obtain the natural circulation data in HX to research the heat transfer behavior. The PRHR HX was simulated by three C-type tubes with prototype sizes immerged in a cooling tank. Separate-effect tests of natural circulation in HX tubes have been performed within wide conditions which could cover the operation conditions in AP1000. The experiment provided lots of important data to indicate heat transfer phenomena of PRHR HX. The test conditions were calculated by RELAP5/MOD3.3. The calculation results agreed well with the experiment. RELAP5 could be applied with proper correlations to analyze the heat transfer in PRHR HX under the test conditions.

A Physical Core-Loss Model for Laminated Magnetic Sheet Steels

A full-frequency instant core-loss equation built from the induction physical model of magnetic materials, where the iron loss, eddy loss, and hysteresis loss no longer have an integral term, and this new equation provides high simulation accuracy and performs dynamic core loss analysis on non-sinusoidal or pulse magnetic fields. The simulation examples use a high-grade electrical steel sheet 65CS400 by Epstein experimental data covering magnetic field 0.1 - 1.8 T and frequency 50 - 5000 Hz, and the average error of the simulated core loss is less than 4%. Since the simulation is converged by magnetic physical parameters, so the physical relevance of the similar laminated materials can be compared with the coefficient results. .

柚木离体快速繁殖技术

从优良柚木林段选取3～4 a生优良单株,从中选取无病虫害的幼嫩侧芽,经表面消毒后接种到无菌培养基上,侧芽萌发率达70%～80%.切取新芽进行增殖,30～40 d为一周期,增殖系数为2～3倍.当侧芽增殖到足够数量时,转移到生根培养基上,生根率超过80%～90%.植株移栽成活率达80%～90%.几个月后植株便可种植到大田.

Squeeze casting of aluminum alloy A380: Microstructure and tensile behavior

A380 alloy with a relatively thick cross-section of 25 mm was squeeze cast using a hydraulic press with an applied pressure of 90 MPa. Microstructure and tensile properties of the squeeze cast A380 were characterized and evaluated in comparison with the die cast counterpart. Results show that the squeeze cast A380 possesses a porosity level much lower than the die cast alloy, which is disclosed by both optical microscopy and the density measurement technique. The results of tensile testing indicate the improved tensile properties, specifically ultimate tensile strength(UTS: 215.9 MPa) and elongation(Ef: 5.4%), for the squeeze cast samples over those of the conventional high-pressure die cast part(UTS: 173.7 MPa, Ef: 1.0%). The analysis of tensile behavior shows that the squeeze cast A380 exhibits a high tensile toughness(8.5 MJ·m-3) and resilience(179.3 k J·m-3) compared with the die cast alloy(toughness: 1.4 MJ·m-3, resilience: 140.6 k J·m-3), despite that, during the onset of plastic deformation, the strain-hardening rate of the die cast specimen is higher than that of the squeeze cast specimens. The microstructure analyzed by the scanning electron microscopy(SEM) shows that both the squeeze and die cast specimens contain the primary α-Al, Al2 Cu, Al5 Fe Si phase and the eutectic Si phase. But, the Al2 Cu phase present in the squeeze cast alloy is relatively large in size and quantity. The SEM fractography evidently reveals the ductile fracture features of the squeeze cast A380 alloy.

Influence of coke structure on coke quality using image analysis method

The quality of coke affects the performance of the blast furnace, factors affecting coke quality include coal properties, coal charge granulometry and carbonization conditions. The coke properties in elude the size analysis, cold strength (Micum Indices-M4(). MI0) and hot strength (Coke Reactivity Index-CRI, Coke Strength after Reaction-CSR) properties and structural properties such as coke structure and texture. Structural properties comprise the porosity, pore-cell wall thickness and pore sizes, while textures consist of the carbon forms in the coke. In present work, advanced method such as image analysis method was used to interpret coke microstructure. Conventional methods such as determination of coke porosity by measurement of real and apparent density and mercury porosimetry have a number of limitations. Coke size, magnification, number of image frames captured, process of pellet preparations and coke properties such as M4(), M|0, CRI and CSR (low, medium and high values) were taken as variables for experimental purposes. The coke structure parameters such as porosity, length, perimeter, breadth, roundness, pore-wall thickness and pore size distribution of the pores were determined by image analysis method. This method provided average porosity in addition to pore-wall thickness and pore-size distribution. The pore wall thickness measuremenl by image analysis method provided significant correlations with M40, CRI and CSR values. This explained the usability of image analysis for coke structure measurement.

Antioxidant Capacities and Main Reducing Substance Contents in 110 Fruits and Vegetables Eaten in China

The aim of this study was to screen strongly-antioxidant fruits and vegetables and supply practical diet guidance for the public. We used 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric-reducing antioxidant potential (FRAP), 2,2’-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and total reducing power (TRP) assays to investigate antioxidant activities in 110 fruits and vegetables. To analyze the correlation between antioxidant capacities and main reducing substance contents, total phenolic, flavonoid and vitamin C contents were assessed. The results showed great variation in antioxidant activity, and fifteen fruits and vegetables possessed the strongest antioxidant capacities: Toona sinensis, hawthorn, jujube, lotus root, persimmon, red plum, black plum, chilli pepper, star fruit, strawberry, blueberry, cherry, peach, pomegranate and great burdock. Total phenolic contents showed higher correlation with antioxidant capacity when using FRAP and TRP assays than when using the DPPH or ABTS assay. Phenolics and flavonoids, rather than vitamin C, contributed to antioxidant potential in most fruits and vegetables.

Treatment effect investigation of underground continuous impervious curtain application in water-rich strata

Serious shaft lining failures often occur when shaft linings are constructed by passing them through the deep topsoil of Quaternary strata. This approach also leads to the formation of an aquifer at the bottom.Based on the theory of the additional stress which is the main reason for these failures, this study focuses on the treatment effect of underground continuous impervious curtain(UCIC) in terms of different factors, namely, the location, shape, range, and width, by using numerical simulation. Results show that the UCIC can reduce the stress concentration in the shaft lining formed in the bottom aquifer. The UCIC can also reinforce the shaft lining at different angles and can be applied in actual situations. The strength factors of the inner surface of the shaft lining increase after the UCIC are used. The material strength and width of the UCIC show an obvious effect on the stability of the shaft lining. Results proved that the UCIC could effectively strengthen the stability of the shaft lining when it was built in the aquifer or built in the aquifer and above and below the layer.

Effects of the Residues of Cuscuta campestris and Mikania micrantha on Subsequent Plant Germination and Early Growth

Cuscuta campestris, a dodder, can parasitize and suppress a scrambling herbaceous to semi-woody perennial vine, Mikania micrantha, one of the most destructive weeds in the world. To assess the effects of the mixed residue of C. campestris and M. micrantha on the subsequent plant community, we conducted a one-year experiment on the germination and seedling growth of subsequent plant community after the application of C. campestris. Seven treatments of varying proportions of C. campestris and M. mierantha residue on 21 subject trees and shrubs, which were commonly found in South China, resulted in a germination rate of 35.3% for all 8 715 seeds from 18 species, ranging from 5.7 to 81.9%; the remaining 3 species failed to germinate. ANOVA analysis showed that the residue did not affect the germination, growth, or mortality of the trees and shrubs. The germinated C. campestris seeds from the residue coiled the seedlings of most of the species, but less than 4% host death caused by C. campestris. In addition, the residue did not affect the germination of the herbaceous seedlings originating from the loam, and the similarity coefficients of the germinated seedlings between the treatments were very high. These results suggested that the residue had no negative impact on the germination and early seedling stages of the tree, shrub and grass species of the subsequent plant community. The use of C. campestris residue had a positive effect on the growth of M. micrantha, but it did not change the trend of M. micrantha being suppressed because re-parasitization occurred soon after the growth restarted. No negative effect was detected on the other species as a result of the parasitization of C. campestris or by the use of the mixed residue. This suggests that C. campestris is likely to be an effective and promising ecologically safe native herbaceous agent for controlling M. micrantha.

The Effects of Shade Tree Types on Light Variation and Robusta Coffee Production in Vietnam

Vietnam is well-known as the second largest global coffee producer and the largest worldwide exporter of Robusta coffee. However, the Robusta coffee sector in Vietnam is facing many problems, including low quality, high external inputs and water shortages as a result of shade tree eradication. A six-month research project was conducted that focused on effects of shaded tree types on variation of light intensity and aspects of Robusta production. Three shade tree species at different planting densities and shade provision were investigated, including 46 trees of Durian ha–1 (14% shade), 35 trees of Sennaha–1 (17% shade), and 60 trees of Leucaena ha–1 (34% shade), and unshaded site (Open) was used as a control. The study found that light intensity declined 50% with Durian, 58% with Senna and 60% with Leucaena compared with the Open site (2096 μmol?m–2?s–1). Within the coffee canopy, a significant decline in light intensity was observed from the top of the canopy to the bottom. The percentage of light at the middle (90 cm above ground) and bottom (30cm) levels of the coffee canopy was declined by 81% and 88% respectively for the Open site, and 86% and 92% for the Leucaena site. There were no differences in the number of flowers branch–1 tree–1 and fruit set between shaded and unshaded coffee sites. However, a significant difference in first fruit drop was observed.

Review of Non-Newtonian Mathematical Models for Rheological Characteristics of Viscoelastic Composites

This study presents an overview of viscoelastic characteristics of biocomposites derived of natural-fibre-reinforced thermoplastic polymers and predictive models have been presented in order to understand their rheological behavior. Various constitutive equations are reviewed for a better understanding of their applicability to polymer melt in determining the viscosity. The models to be investigated are the Giesekus-Leonov model, the Upper Convected Maxwell (UCM) model, the White-Metzner model, K-BKZ model, the Oldroyd-B model, and the Phan-Thien-Tanner models. The aforementioned models are the most powerful for predicting the rheological behavior of hybrid and green viscoelastic materials in the presence of high shear rate and in all dimensions. The Phan-Thien Tanner model, the Oldroyd-B model, and the Giesekus model can be used in various modes to fit the relaxation modulus accurately and to predict the shear thinning as well as shear thickening characteristics. The Phan-Thien Tanner, K-BKZ, Upper convected Maxwell, Oldroyd-B, and Giesekus models predicted the steady shear viscosity and the transient first normal stress coefficient better than the White-Metzner model for green-fibre-reinforced thermoplastic composites.

Filtered-OFDM——Enabling Flexible Waveformfor the 5G Cellular Networks

To deal with the expected diversification on traffic types, the fundamental waveform of the upcoming5 G standard must be sufficiently flexible. In the 4th generation wireless networks(e.g., cellular LTE and Wi- Fi802.11ac), orthogonal frequency division multiplexing(OFDM) has been widely adopted to combat frequency selectivity and thus improve the spectrum efficiency. Holding various advantages such as backward compatibility with LTE, ease of hardware implementation, time-localized low-latency transmission and straightforward combination with multi-antenna transmission, OFDM will remain as an important waveform candidate for 5G. However,OFDM alone appears to be insufficient in terms of the requirements faced by 5G waveform, such as high flexibility to accommodate different waveform numerologies for an efficient support of diversified traffic types and channel characteristics. In this work, we present a new waveform format, named as filtered-OFDM(f-OFDM) and illustrate its potential and benefits for serving as the underlying waveform of 5G.

Microstructure and properties of Cu-0.6Cr alloy after vacuum continuous casting

To promote the solution of chromium in copper and the purity of copper-chromium(Cu-Cr) alloy,vacuum continuous casting(VCC) process was employed to fabricate the Cu-Cr alloy required for electrode material. Cu-0.6Cr(containing 0.6%(mass fraction) chromium) alloy bar with a diameter of 12 mm was cast with a constant rate of 250 mm/min. The microstructure,mechanical properties,and physical properties were discussed. After solid solution strengthening and aging treatments,Cu-0.6Cr alloy fabricated by VCC process has higher tensile strength(σ≥314 MPa),elongation rate(δ≥34%),conductivity(≥80.5% IACS),and hardness(80 HRB) compared to the as-cast alloy.

分析型透射电子显微术在材料工业中的应用:双相不锈钢断裂韧性的研究(英文)

不同的热加工工艺导致双相不锈钢2205(50/50铁素体/奥氏体)产生了不同的断裂韧性,尤其是断裂韧性降至不可接受的低值。本文通过分析透射电子显微镜研究其显微结构,对这种现象提供了解释。尤其是对断裂韧性的急剧变化提出了试验上的观察与分析,获得正确且有效的解决此类问题的方法。β-Cr2N相沿{110}α原子平面析出是导致断裂韧性降低,特别是在低温下的断裂韧性大幅降低的根本原因。因为在韧性至脆性转变温度时形变的机制为位错的移动性,而沿{110}α原子平面析出的β-Cr2N相阻碍了位错的运动,导致α铁素体的脆性,从而使材料整体脆化。材料经1200℃退火随即空气冷却到室温之后,断裂韧性恢复到正常值,是由β-Cr2N相的溶解所致。α-Fe(Cr)→α-Fe+α′-Cr相变(又常称为在475℃失稳分解)导致断裂韧性在低温与室温下都急剧下降是由富铬的铁素体α′-Cr固有的脆性所引起。将材料加热致800℃后随即急冷至室温后,断裂韧性恢复到正常值。这是由于材料经加热将α-Fe+α′-Cr相溶解并经急冷而避免了α-Fe(Cr)→α-Fe+α′-Cr相变的再发生。本研究中观察到的析出相的尺寸均为纳米量级,只有应用分析透射电子显微镜后才可得以同时获得其形态、化学成分以及晶体学的结果,从而解释断裂韧性变化的根本的原因,并找出解决问题的办法。

Effect of Lithium Chloride on the Fibre Length Distribution, Processing Temperature and the Rheological Properties of High-Yield-Pulp-Fibre-Reinforced Modified Bio-Based Polyamide 11 Composite

The aim of this work was to investigate the effect of lithium chloride (LiCl) on the fibre length distribution, melting temperature and the rheological characteristics of high yield pulp fibre reinforced polyamide biocomposite. The inorganic salt lithium chloride (LiCl) was used to decrease the melting and processing temperature of bio-based polyamide 11. The extrusion method and Brabender mixer approaches were used to carry out the compounding process. The densities and fibre content were found to be increased after processing using both compounding methods. The HYP fibre length distribution analysis realized using the FQA equipment showed an important fibre-length reduction after processing by both techniques. The rheological properties of HYP-reinforced net and modified bio-based polyamide 11 “PA11” (HYP/PA11) composite were investigated using a capillary rheometer. The rheological tests were performed in function of the shear rate for different temperature conditions. The low-temperature process compounding had higher shear viscosity;this was because during the process the temperature was low and the mixing and melting were induced by the high shear rate created during compounding process. Experimental test results using the extrusion process showed a steep decrease in shear viscosity with increasing shear rate, and this melt-flow characteristic corresponds to shear-thinning behavior in HYP/PA11, and this steep decrease in the melt viscosity can be associated to the hydrolyse reaction of nylon for high pulp fibre moisture content at high temperature. In addition to the low processing temperature, the melt viscosity of the biocomposite using the Brabender mixer approach increases with increasing shear rate, and this stability in the increase even at high shear rate for high pulp moisture content is associated to the presence of inorganic salt lithium chloride which creates the hydrogen bonds with pulp during the compounding process.

Studies on Mechanical and Wear Properties of Al6061/Beryl Composites

Beryl-Al6061 alloy composites having 2-12 wt% of beryl particles were fabricated by liquid metallurgy (stir cast) method. The tensile and wear properties of beryl-Al6061 composites have been evaluated and compared with its base alloy. The results revealed that the Al6061-10 wt% of beryl composites shows an improvement of 15.38% in tensile strength and specific wear rate decreases by 8.9% at normal load of 9.81N when compared to matrix i.e. base alloy. Significant improvement in tensile properties and hardness are noticed as the wt% of the beryl particles increases. The microstructures of the composites were studied to know the uniform dispersion of the beryl particles in matrix. It has been observed that addition of beryl particles significantly improves ultimate tensile strength and hardness properties as compared with that of unreinforced matrix.

Association mapping of quantitative trait loci for yield-related agronomic traits in rice(Oryza sativa L.)

High yield in rice mainly depends on large grain weight, ideal plant architecture and proper flowering time adapting to various geographic regions. To help achieve higher yield, phenotype variations of heading date（HD）, plant architecture and grain shape in a panel of 416 rice accessions were investigated in this study. A total of 143 markers including 100 simple sequence repeat（SSR） markers and 43 gene-tagged markers were employed in association mapping to detect quantitative trait loci（QTL） responsible for these variations. Among the 7 subpopulations, POP5 in japonica group showed the largest values of HD and grain width（GW）, but the smallest values of grain length（GL） and grain length to width ratio（GLW）. Among the six indica groups, POP7 had the largest values of HD, GL, GLW, and 1 000-grain weight（TGW）. A total of 27 QTLs were detected underlying these phenotypic variations in single year, while 12 of them could be detected in 2006 and 2007. GS3 marker was closely associated with GL, GW and GLW, and widely distributed in different groups. The starch synthesis related gene markers, SSI, SSIIa, SBE1, AGPL4, and ISA1, were linked to plant height（PH）, panicle length（PL）, flag leaf length（FLL）, GW, and GLW. The SSR markers, RM267, RM340 and RM346, were linked to at least two traits. Therefore, these new markers will probably be used to improve rice grain yield or plant architecture when performing marker-assisted selection of proper alleles.

Modeling the Rheological Characteristics of Flexible High-Yield Pulp-Fibre-Reinforced Bio-Based Nylon 11 Bio-Composite

The aim of this work was to develop a mathematical model to investigate the rheological characteristics of viscoelastic pulp-fibre composite materials. The rheological properties of High-Yield Pulp (HYP) reinforced bio-based Nylon 11 (Polyamide 11) (PA11) composite (HYP/PA11) were investigated using a capillary rheometer. Novel predicted multiphase rheological-model-based polymer, fibre, and interphasial phases were developed. Rheological characteristics of the compo-site components influence the development of resultant microstructures;this in turn affects mechanical characteristics of a multiphase composite. The main rheological characteristics of polymer materials are viscosity and shear rate. Experimental and theoretical test results of HYP/PA11 show a steep decrease in apparent viscosity with increasing shear rate, and this melt-flow characteristic corresponds to shear-thinning behavior in HYP/PA11. The non-linear mathematical model to predict the rheological behavior of HYP/PA11 was validated experimentally at 200°C and 5000 S-1?shear rate. Finally, predicted and experimental viscosity results were compared and found to be in a strong agreement.

Evaluation of the Influence of Fibre Aspect Ratio and Fibre Content on the Rheological Characteristic of High Yield Pulp Fibre Reinforced Polyamide 11 “HYP/PA11” Green Composite

The rheological behavior of composites made with low-density polyamide 11 (PA11) and high yield pulp fibre (HYP) is evaluated. The rheological properties of high-yield, pulp-reinforced bio- based Nylon 11 HYP/PA11 composite were investigated using a capillary rheometer. The rheological tests were realized in function of the shear rate for different temperature conditions. The experimental results showed that identically for fibre content and aspect ratio, the shearing effects decreased as the temperature increased;that is, the HYP/PA11 became more non-Newtonian in the higher temperature region, which corresponds to the high pseudoplasticity of the HYP/PA11. At low HYP content, the shear viscosity is expected to increase rapidly with increasing concentrations of the fibres because of the rapidly increasing interactions between particles as they become more closely packed. However, at very high fibre content, random anisotropic structure of the fibres in polymer melts is created. The increase in shear viscosity is greater at lower shear rates, where fibre and polymer molecules are not completely oriented.

Control strategies for aircraft airframe noise reduction

With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft＇s approach to landing phase. Noise control efforts have therefore been extensively focused on the airframe noise problems in order to further reduce aircraft overall noise. In this review, various control methods explored in the last decades for noise reduction on airframe components including high-lift devices and landing gears are summarized. We introduce recent major achievements in airframe noise reduction with passive control methods such as fairings, deceleration plates, splitter plates, acoustic liners, slat cove cover and side-edge replacements, and then discuss the potential and control mechanism of some promising active flow control strategies for airframe noise reduction, such as plasma technique and air blowing/suction devices. Based on the knowledge gained throughout the extensively noise control testing, a few design concepts on the landing gear, high-lift devices and whole aircraft are provided for advanced aircraft low-noise design. Finally, discussions and suggestions are given for future research on airframe noise reduction.

Configuration and Setting of Protections for Wind Farm Collector System

Compared with traditional synchronous generators, wind turbine generators are different in electricity generation principles, control modes and integration topologies, which makes their fault characteristics change a lot. This, consequently, brings challenges regarding the behavior of protections for wind farm collector systems. In this paper, based on a practical wind farm, configuration and setting of relay protections for such a collector system is analyzed and determined systematically in consideration of the selectivity and sensitivity of the protections. Results show that misoperation of overcurrent relay and zero sequence overcurrent relay of the non-fault collector line occurs, and bus differential relay of collector bus cannot remove the single-phase-to-ground fault. In order to solve the problems, a novel substation-area protection for collector system is proposed and its operation mechanism is discussed.