原状黄土冻融过程抗剪强度劣化机理试验分析

通过对西安Q₃原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验,研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化,大颗粒集粒数量明显减少,小粒径土颗粒所占比重增加,孔隙面积比增加。进一步基于损伤力学理论,得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势,反映出冻融作用一定程度上破坏黄土体的结构强度,但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏,且含水率越高,土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势,且含水率越高,粘聚力衰减幅值和速率越小;粘聚力随含水率增加表现出线性衰减特征,且冻融后粘聚力与含水率的变化规律近似重合;内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势,随含水率升高有增大趋势。基于试验数据规律性,进一步提出了原状黄土粘聚强度劣化模型,该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。     

Effect of cooling rate on high temperature mechanical properties of weathering steel

High temperature mechanical properties are key factors which affect fracture production during deforming process of continuous casting. High temperature properties of weathering steel Q450NQR1 are tested in 3 cooling rates (1.65, 5, 10 ℃/s) using Gleeble thermo-mechanical simulator. Specimens appear austenite dynamic recrystallization at 1 050 ℃, and the ductility reaches the lowest point and the reduction of area approaches 23% at 850 ℃ in 3 cooling rates. As the cooling rate increases, the low ductility area where cracks are easy to be produced in slabs is enlarged and extended towards low temperature, and the ductility troughs are deepened. The increase of the cooling rate decreases the tensile stress and yield stress, while when the cooling rate increases to some degree, it doesn’t affect the stress. The low cooling rate decreases the film or network ferrite producing in austenite grain boundary, and the carbonitride of microalloy is enwrapped in matrix, which is helpful to improve the ductility of steel.     

Static Load Test and Calculation on Multi-tower Cable-Stayed Bridge with Tie-down Cables

The static load test and the finite element analysis of the multi-tower cable-stayed bridge with tie-down cables are carried out. The test and analysis model of the bridge is created by referencing to the actual structure of a Changjiang River bridge. The static mechanical behaviors of such bridge with tie-down cables and the normal multi-tower cable-stayed bridge are comparatively analyzed by the static load test and the finite element analysis. It is shown that the structural system of the cable-stayed bridge with tie-down cables can effectively improve the structural rigidity and reduce the bending moment of the main beams, pylons and piers. According to the results, the best scheme about the location and number of tie-down cables is proposed.     

Influence of Alkali-Silica Reaction on Mechanical Properties of Cementitious Materials

The expansion rate of mortars, prepared with active sand and non-active sand, under alkali-silica reaction (ASR) was recorded. The effects of ASR on mechanical properties of cementitious materials were studied by triaxial compression test. The relation between the microstructure of cementitious materials and the mechanical properties was investigated as well. The results showed that there was a little blade crystals gel formed in a local region near the aggregate in materials prepared with non-active sand. For the quantity of formed gel is small, the expansion effects of ASR are limited. Whereas, thick blade crystals gel layers formed near the aggregate when the active sand prepared materials subjected to ASR. Moreover, the reactive products would lead to cracks and then significantly affects the mechanical properties of mortars. Additionally, the results showed that besides the expansion rate,the ultimate compressive strength and the strain are also effective indexes to estimate the influence of ASR.     

The Study on Intelligent Experimental System of Bio-soft Tissue

According to the especial mechanical properties of bio-soft tissue materials, we design a mechanical test system of bio-soft tissue moterials which is controlled by microcomputer and can execute the post-processing for bio-soft tissue materials. The system can solve better the problems of reliability and accuracy appearing in the test of the mechanical properties for bio-soft tissue materials,and the test is convenient as well as speedy,and provides an effective experimental means for the study of biomechanics.     

Critical Phase Transition of the Two-dimensional Microcanonical Ising Model by Cellular Automata Q2R Method

The authors construct a microcanonical ensemble system and analyzes the phase change of the two-dimensional Ising model Cellular Automata Q2R/WQ2R method. The result indicates that the numerical value simulation can show the spontaneous magnetization of two-dimensional crystal lattice in isolated system. The authors have observed the critical phase transition phenomenon and gotten the critical energy. The simulation of three-dimensional Ising model can be grounded on the method that this article establishes.     

Study on Acoustic Emission of Limestone in Uniaxial Compression Test

In order to study the acoustic emission of rock under compression by means of the rock acoustic parameter dynamic testing system (RAPDTS), some uniaxial compression tests on a kind of limestone from Guangxi Province were carried out. It was concluded that the formations of new micro clefts generated in the rock and the enmargements of existing clefts are the principal factors that cause the acoustic emission.     

长期施用含SO42- 肥料对水稻农艺性状及产量影响

为了研究长期施用含SO4=肥料对水稻水稻农艺性状及产量的影响,对红壤地区农业持续发展和科学研究提供原创性的理论依据,刘更另院士于1975年开始在湖南祁阳官山坪中国农业科学院红壤实验站布置了肥料定位试验。试验设三个处理,即：处理一：SO4=,采用含SO4=化肥：(NH4)2SO4 + K2SO4 + 过磷酸钙。 处理二： Cl- ,采用含Cl- 化肥：NH4Cl + KCl + KH2PO4;处理三：隔离区（CK）。施用化肥NPK。即：尿素 +过磷酸钙+ 氯化钾。 三个处理NPK用量相同。通过32年的长期研究,结果表明：1.长期施用含SO4=肥料对水稻产量没有多大影响;2.长期施用含SO4=肥料能够提高水稻生物产量。据1982-2007年26年的总产量（生物产量）统计,SO4=处理（488653.5kg/hm2）,比CK处理（483862.1 kg/hm2）高4791.4kg/hm2,比Cl-处理（477262.5kg/hm2）高11391.0 kg/hm2。3. 长期施用含SO4=肥料能够增加水稻有效穗,但结实率和千粒重较低。     

Influences of Y on the microstructures and mechanical properties of Mg-12Gd-1Zn-0.6Zr magnesium alloys

To develop Mg-Gd-Y based high-strength alloys and widen the application of magnesium alloys, the effects of Y addition on the microstructure and mechanical properties of Mg-12Gd-1Zn-0.6Zr alloy are investigated by using both optical and electron microscopy,X-ray diffraction (XRD),differential scanning calorimetric (DSC) analysis,and tensile test．The results indicate that adding 2%Y to the Mg-12Gd-1Zn-0.6Zr alloy does not cause an obvious change in the as-cast microstructure of the alloy. However,after adding 3%and 4%Y,the as-cast microstructure of the alloy is coarsened,and simultaneously the morphology of the secondary phases in the alloy is changed from the initial discontinuous fine network to thick skeleton-like frame. Furthermore,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also refine the grains of the as-extruded alloy,and adding 2%and 3%Y can obtain higher refining efficiency than adding 4%Y. In addition,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also effectively improve the ultimate tensile strength and yield strength of the as-extruded alloy,and the ultimate tensile strength,yield strength and elongation of the as-extruded alloy with the addition of 2%Y can reach 348.8 MPa,256.8 MPa and 14.7%,respectively.     

Effect of nitrogen on microstructure and properties of SWRH82B wire rod

The microstructure, mechanical properties, tensile fractures and the precipitation of the second phase of vanadium microalloyed wire rods with different nitrogen contents are studied by hydraulic universal testing machine, scanning electron microscopy(SEM) and transmission electron microscopy(TEM) . The results show that the interlamellar spacing of pearlite is smaller in high nitrogen steel; the high nitrogen steel has higher yield strength, tensile strength and lower elongation and reduction of area; there are more inclusions on the tensile fracture surfaces of the high nitrogen steel; and in high nitrogen steel, the size of precipitation, mainly precipitating at dislocation or the boundary of austenite, is finer than that of low nitrogen steel, what is more, fine V(C,N) particles are concluded in the precipitations.     

Characterization of the Q.Ymym region on wheat chromosome 2D associated with wheat yellow mosaic virus resistance

Yellow mosaic disease, caused by wheat yellow mosaic virus (WYMV), is one of the most serious diseases of winter wheat in Japan and China. A single major QTL for WYMV resistance in the Japanese wheat variety 'Yumechikara', designated Q.Ymym, has been mapped on a 43.6 cM linkage block between the two markers Xcfd233 and Xgwm349 on chromosome 2D. We were able to obtain two recombinants within the block, which facilitated reducing the size of the linkage block. The pseudomolecule sequence of 'Chinese Spring' (CS) indicated that the original Q.Ymym region of 43.6 cM corresponded to 68.5 Mb and the narrowed Q.Ymym region represents a size of 27.3 Mb. The sequence features of the Q.Ymym region were unique in comparison with CS sequences, which may have led to the low recombination rate within the block. The Q.Ymym haplotype block was detected in other WYMV-resistant varieties but not in the susceptible varieties used in this study. The unique sequence structure of the Q.Ymym region allowed the development of co-dominant markers for use in marker-assisted selection.     

流固耦合的多元结构深厚覆盖层透水地基的力学特性

深厚覆盖层多元结构坝基在渗流过程中各土层力学差异明显,分析时关注的具体问题也不尽相同,需要深入研究。基于比奥固结理论,考虑土体的非线性流变以及土体固结变形过程中孔隙度、渗透系数、弹性模量及泊松比的变化;借助ADINA流固耦合模块来模拟西藏达嘎水电站坝基渗流场与应力场耦合过程,分析各层力学特性及相互作用。研究表明,透水性较强的表层土体是渗流主要通道,也是渗流进出区和沉降变形体现区,应在上游采取措施提高其压缩模量,下游区域增设反滤层和排水设施;坝基中的粉细砂层是坝基沉降的主要原因,对坝基沉降起主导作用,同时应注意其液化特性对坝基的不利影响;坝基中的承压含水土层对下游上部结构产生向上顶托力,若位置较深,则破坏性较小;坝基深部土层对整个坝基的渗流破坏影响较小,但对沉降和渗流量的影响不可忽视;表层砂卵砾石层和粉细砂层的渗透系数相差较小时,土层间不会发生接触冲刷。此外,还发现坝基孔隙水压力在快速衰减阶段被消散,期间土体固结较快。垂直防渗墙能有效降低渗透坡降和渗流量,将坝基沉降变形控制在防渗墙上游区域,但上游坝基变形对防渗墙产生较大的水平推力,应加大防渗墙尺寸或者采用辅助渗控措施。     

不同膜上遮挡措施对旱地玉米土壤理化性状及产量的影响

Aiming at the phenomenon of premature senescence of plants under long-term maize plastic film mulching in rainfed and arid regions in Northwest China, adding cooling measures on mulched maize were taken to study the effects of soil temperature change on maize yield formation and analysis the changes of soil physical and chemical properties in topsoil of maize from the perspective of never changing the water conserving function of plastic film, which would provide the theoretical reference for the analysis of the early senescence in the later growth stage of ordinary plastic film maize. This experiment design using Shaandan 609 (SD 609) as tested materials, based on a 2-year field experiment, compared with the effects of three modes, ordinary plastic film mulch + black sunshade net (A), ordinary plastic film mulch + straw (B) and ordinary plastic film mulch (C) on soil temperature, soil nutrients, dry matter mass accumulation yield and water and fertilizer use efficiency in yield. The results were as follows: (1) Adding coverings on plastic film mulching (black sunshade net, straw) can effectively decrease the soil temperature and compactness, especially early stage of maize growth. (2) Compared with the control treatment C, cooling treatment A and treatment B significantly increased the content of organic matter, total nitrogen and total potassium in the later stage of maize growth, and the average partial fertilizer productivity increased by 7.24% and 6.97%, respectively. (3) Cooling treatments can delay the attenuation of green leaf area in the later stage of maize growth, improve the accumulation rate of dry matter and increase the kernel weight of maize. Compared with treatment C, the 2-year average maize yields of cooling treatment A and treatment B were increased by 6.39% and 5.93% and the average water use efficiency by 8.17% and 7.67%, respectively. In rainfed and arid regions in Northwest China, properly reducing the temperature under the film of mulched maize are helpful to improve soil physical and chemical properties, promote the accumulation of dry matter and the formation of yield and improve the high utilization efficiency of fertilizer and water.     

Study on hot compression deformation behavior of a brush alloy Ag-Pd-Cu-X

Hot compression deformation of Ag-Pd-Cu-X alloy is performed on Gleeble-1500 thermal simulator with strain rates of 0.001~0.1 s -1 and temperature at 650~950 ℃. Variations of flow stress and microstructure are investigated. The flow stress constitutive equation of Ag-Pd-Cu-X alloy is established. The results indicate that the dominant softening mechanism shift from dynamic recovery to the dynamic recrystallization with the compression temperature increases from 650 ℃ to 750 ℃,the flow stress exhibits a gradual downward trend. While the alloy deforms at 750~ 950 ℃,and the activation energy is 210.369 kJ/mol. The stress values predicted by the constitutive equation demonstrate well agreement with the experimental results.     

Heat,wheat and CO2: The relevance of timing and the mode of temperature stress on biomass and yield

Atmospheric CO₂ enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat (Triticum aestivum L. cv. Triso) to CO₂ enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO₂ enrichment increased above‐ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (?19%). This adverse effect was, however, compensated by CO₂ enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO₂, but not so at elevated CO₂. Thus, the interactive effects were complex and prediction of future wheat yield under CO₂ enrichment and climate extremes deserves more attention.     

增施CO2对马铃薯植株光合特性及产量的影响

为检验增施CO₂对马铃薯组培苗植株光合特性及微型薯产量的影响,选用马铃薯品种夏坡蒂组培苗为试验材料,于2015年在温室条件下进行了两批次试验。结果表明,增加CO₂浓度可显著增加植株的叶面积、叶片净光合速率和胞间CO₂浓度,且CO₂ 750μmol/mol处理>550μmol/mol处理>CK（空气）,但增加CO₂浓度降低了马铃薯植株叶片气孔导度和蒸腾速率。结果还表明,增施CO₂增加了马铃薯单株结薯数、单个薯重和单株产量,其增幅随CO₂量的增加而增加。上述结果充分证明在温室条件下增施CO₂对加速马铃薯微型薯的繁育有积极作用。     

沟垄覆膜对连作马铃薯土壤酶活性、理化性状及产量的影响

以当地主栽品种“新大坪”为试验材料,采用大田定位试验,研究了平畦不覆膜(CK)、平畦覆膜(T1)、全膜垄播(T2)、全膜沟播(T3)、半膜垄播(T4)、半膜沟播(T5) 6 种栽培模式对连作马铃薯土壤酶活性、理化性状及产量的影响。结果表明,沟垄覆膜栽培可不同程度提高马铃薯连作田土壤过氧化氢酶、脲酶、碱性磷酸酶的活性,其中 T2 对 3 种酶活性的提高效果最为显著;沟垄覆膜可降低土壤 pH,从而改善马铃薯根际土壤的理化性状,且以 T2 对土壤化学性质的改善最为明显,沟垄覆膜可不同程度提高土壤电导率;此外,沟垄覆膜栽培还可以显著提高马铃薯块茎的产量,其中T2 增产幅度最高可达 75%。本研究以期为半干旱地区马铃薯连作障碍的克服及提高马铃薯产量提供理论依据。     

不同土壤改良措施对机械压实酸化蔗地土壤理化性质及微生物群落结构的影响

探讨不同土壤改良措施对土壤物理性质、养分、微生物和甘蔗产量的影响,对机械压实后酸性土壤改良策略的制定具有较为重要的意义。本研究设置添加松土精(B2)、添加生物菌肥(B3)、添加有机肥(B4)、添加生石灰(B5)4种土壤改良处理,以不添加土壤改良剂作为对照(B1),连续2个作物季对蔗地土壤物理性质、养分、微生物和甘蔗产量构成等指标进行研究。结果表明, B4处理可显著降低土壤容重、紧实度、贯入阻力和抗剪强度,提高土壤总孔隙度、通气孔隙度和毛孔孔隙度,其固相容积率显著低于对照,液相容积率显著高于对照,土壤有机质含量、全氮含量得到显著提升, B2、B3处理紧实度和总孔隙度降低,土壤物理性状得到一定改善, B5处理土壤pH值显著提升,土壤酸性得到改善, B3、B5处理土壤有效磷含量得到显著提升。4种土壤改良措施土壤细菌和真菌Shannon指数、Chao1指数和ACE指数均高于对照,均能提升土壤耕层细菌和真菌的物种多样性和物种丰富度,降低土壤细菌中Proteobacteria (变形菌门)和Acidobacteria (酸杆菌门)的相对丰度、真菌中Basidiomycota (担子菌门)的相对丰度...     

Cu2+对花生根土系统和地上部性状的影响

试验表明,花生根际土壤的酶、根系性状和地上部性状对土壤中Cu2+浓度的反应不同.外施不同浓度Cu2+均使根际土壤的脲酶、磷酸酶的活性受到抑制.花生根系活力、根体积和根干重在适量铜浓度(＜200 mg/kg)下表现增加,超过200 mg/kg后均下降;但根瘤数在Cu2+浓度为50 mg/kg时最多.地上部性状和产量性状均在Cu2+浓度为100 mg/kg时表现最好,产量最高.     

Ca2+对过量Fe2+胁迫下水稻保护酶活性及膜脂过氧化的影响

采用水培法研究了不同浓度Ca2+在过量Fe2+胁迫下对水稻生长、保护酶(SOD、POD、CAT)活性及脂质过氧化的影响.结果表明,Fe2+供应正常时,100～300 mg kg-1Ca2+的水培液能不同程度地促进水稻生长,提高SOD、POD活性,而对CAT的影响不大,高钙(400 mg kg-1)供应则会加剧脂质过氧化.在过量Fe2+胁迫下,100～300 mg kg-1Ca2+能较好地促