基于分布位错法研究多条微裂纹对偏折主裂纹的影响

目的 采用理论方法求解多条微裂纹对偏折主裂纹的影响,重点分析偏折主裂纹尖端的力学行为及微裂纹对主裂纹扩展角度和闭合区域的影响等问题,为实际的工程应用提供理论依据。方法 运用叠加原理将主问题分解成2个子问题,通过材料力学方法求解子问题一;基于分布位错方法求解子问题二。进一步建立关于位错密度的奇异积分方程,利用Gauss-Chebyshev数值求积分法解决位错密度方程的奇异性问题,并通过计算机编写程序,最终得到相关力学参量的数值解。结果 得到了偏折主裂纹附近的应力场以及微裂纹长度、微裂纹个数对偏折主裂纹尖端应力强度因子的影响等相关力学参量。分析了主裂纹不同偏折角度时的闭合区域,以及微裂纹的方位角、微裂纹个数等对偏折主裂纹扩展角度的影响。结论 裂纹面对拉应力有屏蔽作用,导致拉应力在裂纹面附近应力松弛,而裂纹尖端对拉应力有放大作用,随着应力增加将导致裂纹的扩展。一条微裂纹位于主裂纹尖端约–30°<θ<50°时,将使主裂纹尖端应力强度因子增加,促进主裂纹的扩展,而微裂纹位于50°<θ<90°或–90°<θ<–30°时,将使主裂纹尖端应力强度因子减小,抑制主裂纹的扩展。主裂纹尖端应力强度因子随微裂纹长度的增加而变大,随微裂纹与主裂纹间距离的增加而减小。

7000车双燃料汽车滚装船LNG燃料舱布置设计

结合PCTC特点,提出7000 PCTC双燃料滚装船的LNG燃料舱布置方案,进行LNG燃料舱和鞍座设计;运用AM模拟拆分组立,得出装配程序,结果表明,该设计的车辆通行没受到影响,根据载荷分布设计燃料舱和鞍座,通过了强度校核;模拟拆分组立,得出船体分段与鞍座可以实行一体化设计建造,设计方案解决了车辆甲板面积问题,提高了船舶稳性,扩大了先行组立范围,缩短了建造周期,形成了LNG燃料舱船体设计制造方法。

早期雾化吸入布地奈德混悬液预防早产儿支气管肺发育不良的疗效和安全性分析

目的:探讨出生后早期雾化吸入布地奈德混悬液预防早产儿支气管肺发育不良(bronchopulmonary dysplasia,BPD)的疗效和安全性。方法:采用前瞻性随机队列研究设计,将2017年11月至2020年5月某院新生儿科收治的胎龄<32周且在出生后3 d内接受机械通气或经鼻持续气道正压通气的102例早产儿随机分为干预组(n=50)和对照组(n=52),干预组雾化吸入布地奈德混悬液,对照组雾化吸入等量0.9%氯化钠溶液。比较2组主要结局和次要结局。结果:干预组BPD或死亡发生率低于对照组(P<0.05),干预组存活者BPD发病率低于对照组(P<0.05),2组死亡率差异无统计学意义(P>0.05)。干预组中重度BPD发病率低于对照组(P<0.05),2组轻度、中度、重度BPD发病率差异均无统计学意义(P>0.05)。干预组常压氧疗时间和住院时间均少于对照组(P<0.01和P<0.05)。2组并发症发生率、体质量变化值、血红蛋白、血小板、肝肾功能电解质及肺表面活性物质、枸橼酸咖啡因和地塞米松使用率均无统计学意义(P>0.05)。结论:出生后早期雾化吸入布地奈德混悬液可降低机械辅助通气早产儿BPD和中重度BPD的发病率,对死亡率无明显影响,无近期不良反应。

分布位错法研究钢轨表面边缘直裂纹的力学行为

目的钢轨表面损伤机理较为复杂,因此进行相应的理论研究来探究其力学原理,为实际的工程应用提供理论依据。方法利用叠加原理将主问题分解成两个子问题,通过函数拟合得到轮轨接触力,基于弹性力学集中力的Flamant解求解子问题1,基于分布位错技术求解子问题2。进一步建立了两类关于位错密度的积分方程,利用Gauss-Chebyshev数值求积法解决位错密度的奇异积分方程,得到了相关的力学参量。结果得到了列车在含边缘直裂纹钢轨上运行时的最危险位置,以及张开部分裂纹长度和不同类型裂纹的尖端应力强度因子等。分析了不同轮重大小、列车运行状态(稳态滚动和全滑动)等因素对裂尖应力强度因子及张开裂纹长度的影响,还分析了列车运行中裂纹面的滑移等。结论列车稳态滚动于含初始边缘长裂纹的钢轨表面时,以剪切破坏为主,列车所处最危险位置是裂纹位于接触斑边缘附近;全滑动运行时,裂纹面上的应力大小和方向均会发生改变,导致裂纹面状态(张开或闭合)随之改变,裂纹较短时,钢轨表面容易发生沿深度方向的张开型扩展。

考虑塑性的钢轨表面疲劳微裂纹分析

目的研究塑性条件下受重复轮轨荷载的钢轨表面的初始疲劳裂纹行为。方法建立含表面微裂纹的钢轨二维有限元模型,通过耦合裂纹面对应节点达到无裂纹的效果。经过几次循环加载后取消节点耦合设置,达到出现裂纹的效果。分析随着轮轨循环加载钢轨的响应,计算残余应力强度因子,并利用渐进状态(随着循环次数的增加,裂纹尖端区新产生的塑性越来越小,裂尖小范围内塑性不再增加)下的应力强度因子计算初始疲劳裂纹扩展速率。结果有限元模拟中,轮轨荷载循环加载在钢轨上表面,使其产生拉伸残余应力,且随着深度增加,拉伸残余应力越来越小。裂纹萌生后,不同角度的裂纹残余(KI)都随循环次数的增加而减小,但残余(KII)都随循环次数的增加而增大。受残余应力的影响,渐进状态下的钢轨表面初始微裂纹应力强度因子随裂纹角度(θ)的增加而增加。结论钢轨表面的残余应力加快了初始微裂纹的扩展速率,降低了钢轨的使用寿命。

分布位错法研究移动赫兹压力作用下次表面裂纹的力学行为

目的用理论方法来求解复杂工况下的次表面裂纹问题,并分析裂纹尖端的力学行为。方法利用叠加原理将主问题分成两个子问题,基于弹性力学集中力的Flamant解求解子问题一,基于分布位错技术求解子问题二。进一步建立关于位错密度的积分方程,利用Gauss-Chebyshev数值求积法求解此奇异积分方程,得到相关的力学参量。结果得到了裂纹尖端的应力强度因子和靠近上表面裂纹尖端附近产生局部粘着的临界摩擦系数,并分析了裂纹长度、裂纹埋入深度对裂尖应力强度因子及临界摩擦系数的影响。在裂纹埋入深度一定时,两个裂尖的应力强度因子都随裂纹变长而先增加后减小。靠近表面的裂尖更容易发生粘着,裂纹长度越短,裂纹埋入深度越小,越容易粘着。临界摩擦系数随着裂纹长度的增加而缓慢增加,随裂纹埋入深度的增加,近似呈线性增加。结论在赫兹压力作用下,当裂纹长度较短时,裂纹更容易往内部扩展;而当裂纹较长时,裂纹更容易往表面扩展。

Effect of Nitric Oxide on Alleviating Cadmium Toxicity in Rice (Oryza sativa L.)

Nitric oxide （NO） is a gaseous signaling molecule in plants that plays a key role in mediating a wide range of physiological processes and responses to biotic and abiotic stresses. The present study was conducted to investigate the effects of the exogenous application of sodium nitroprusside （SNP）, an NO donor, on cadmium （Cd）-induced oxidative stress and Cd uptake in rice plants. Rice plants were exposed to Cd stress （0.2 mmol L^-1 CdC12） and different concentrations of SNP （0.05, 0.1, 0.2, and 0.4 mmol L^-1）. A SNP concentration of 0.1 mmol L^-1 （SNP 10） significantly reduced the Cd-induced decrease in shoot and root dry weights and leaf chlorophyll concentrations. The addition of NO also reduced the malondialdehyde （MDA）, hydrogen peroxide （H202） and ascorbic acid （ASA） concentrations. However, the reduction in glutathione （GSH） concentration was inhibited by NO treatment. Moreover, NO prevented the Cd-induced increase in antioxidative enzyme activity. The amount of Cd accumulation in rice plants was also influenced by the addition of NO. The NO supplied by the SNP enhanced the Cd tolerance of the rice by increasing the Cd uptake by the roots and decreasing the Cd accumulation by the shoots. However, the application of potassium ferrocyanide （Cd＋Fe） or sodium nitrate and nitrite （Cd＋N） （without NO release）, did not exhibit the effects of the SNP. Furthermore, the effects of the SNP were reversed by the addition of hemoglobin （an NO scavenger）. Our results suggested that exogenous NO was involved in the resistance of rice to Cd-toxicity.

Physicochemical and Sensory Properties of japonica Rice Varied with Production Areas in China

Northeast of China and Jiangsu Province are major production areas of japonica rice in China.Rice from northeast of China is well-known for its good-eating and appearance quality,and that from Jiangsu Province is viewed as inferior.However,little is known concerning the difference in physicochemical and sensory properties of rice between the major two production areas.Analysis of 16 commercial rice samples showed marked differences in physicochemical properties,including chalky grain rate,contents of amylose and protein and pasting properties between the two main areas.Northeastern rice contained more shortchain amylopectin as compared with Jiangsu rice.However,Jiangsu rice is comparable to northeastern rice in terms of sensory quality including overall acceptability and textural properties of springiness,stickiness and hardness as evaluated by trained panel.Our results indicated the limitation of conventional index of physicochemical properties,and suggested the necessity of identification of new factors controlling rice sensory property.In addition,the taste analyzer from Japan demonstrates limitation in distinguishing the differences between northeastern and Jiangsu rice,and therefore needs localization to fit China.

Effects of Nitrogen Fertilization and Genotype on Rice Grain Macronutrients and Micronutrients

High nitrogen （N） input features China＇s intensive rice production system. To elucidate N and genotype effects on accumulation of macronutrients and micronutrients in grains of japonica rice, and to discuss its significance in rice production, a three-year field experiment involving six japonica rice varieties and seven N treatments were performed. Macronutrients （Ca, Mg, K, and Na） and micronutrients （Cu, Fe, Mn, and Zn） concentrations in brown and milled rice were measured using an atomic absorption spectrophotometer. For macronutrients, no consistently significant effect of N was detected in both brown and milled rice. For micronutrients, N showed significant effect, especially in lowering Zn accumulation in brown and milled rice. In addition, N tended to increase Fe concentration in milled rice. Genotype showed larger effect on distribution of minerals in milled rice than N. The high-yielding variety, Wuyunjing 7, accumulated larger proportion of Mg, K, and Zn in the milled rice as compared with the other five varieties and could be of value for rice breeding programs aiming at high nutritional quality. The results demonstrated differences in response to N between macronutrients and micronutrients, and are of significance for coping with ＇hidden hunger＇ both in humans and crops through agronomical practices.

帷幕灌浆试验在基础处理中的作用

帷幕灌浆在水利工程施工中是常见的基础处理方式,施工质量直接影响蓄水安全,为了更好地进行帷幕灌浆施工,帷幕灌浆试验显得尤为关键,灌浆试验确定各项灌浆参数,有效论证灌浆方法在技术上的可行性、施工效果的可靠性、经济上的合理性。通过马岭水利枢纽帷幕灌浆试验工程实例,详细阐述帷幕灌浆试验在基础处理中的重要作用。

帷幕灌浆施工技术在地下厂房岩溶系统中的应用

岩溶系统由于溶蚀裂隙发育、溶洞多、渗透性大等特性,造成了帷幕灌浆灌入浆量大和施工难度较大的特点。结合马岭水利枢纽工程地下厂房岩溶系统帷幕灌浆施工技术,有针对性地分析了在厂房岩溶系统中,如何采取有效的灌浆方法、适当的灌浆参数及岩溶系统灌浆特殊情况处理的措施,以保证岩溶系统中帷幕灌浆质量,提高工程进度,节约灌浆成本。

Analysis of Variations in White-Belly and White-Core Rice Kernels Within a Panicle and the Effect of Panicle Type

This study aims to investigate the variation in occurrence of white-belly rice kernel（WBRK） and white-core rice kernel（WCRK） among different positions within a panicle. Twenty-four M4 mutants involved in four panicle types, namely the compact, intermediate, loose, and chicken foot panicle were used. They derived from a japonica rice cultivar Wuyujing 3. Considerable differences in morphological characters existed among the four types of panicle, especially in panicle length, the secondary branch number and ratio of grain number to total branch length. Marked differences were found in WBRK and WCRK among different positions within a panicle for all types of panicle. In general, grains located on the primary rachis and top rachis branches had higher WBRK and WCRK percentage than those on the secondary rachis and bottom rachis branches. WCRK exhibited larger variation among grain positions than WBRK did. Moreover, there was a significant difference in WCRK/WBRK among grain positions within a panicle, with primary rachis and top rachis branches having higher values than the secondary and bottom rachis. In addition, panicle type showed no significant effect on the pattern of WBRK and WCRK occurrence within a panicle. The results indicated the difference in mechanism of WBRK and WCRK formation in grain position within a panicle, and are valuable for breeding and agronomic practices aimed at lowering chalky grain rate.

不同剂量氨基酸在早期静脉营养中对早产儿血生化指标及耐受性的影响

目的研究不同剂量氨基酸在早期静脉营养中对早产儿血生化指标及耐受性的影响,为临床治疗低体质量早产儿提供数据支持。方法选取2016年6月-2017年6月在该院出生的180例低体质量早产儿作为研究对象。根据随机数字法将早产儿分成高、中、低剂量组,每组60例。各组均常规给予脂肪乳、葡萄糖以及早产儿配方奶等营养物质,另外,每组患儿每日给予不同剂量的氨基酸静脉滴注,高剂量组首日剂量为3.0 g·kg^(-1),每日最高剂量<4.0 g·kg^(-1);中剂量组首日剂量为2.0 g·kg^(-1),每日最高剂量<3.7 g·kg^(-1);低剂量组首日剂量为1.0 g·kg^(-1),每日最高剂量<3.5 g·kg^(-1)。治疗7 d后对比各组疗效相关指标、血生化指标以及各组耐受性。结果高、中剂量组的最大体质量降低值、恢复至正常出生体质量的时间、肠外营养时间以及住院时间均分别明显低于低剂量组,且高剂量组明显低于中剂量组,差异均有统计学意义(均P<0.05)。高、中剂量组的头围增长明显高于低剂量组,且高剂量组又明显高于中剂量组,差异均有统计学意义(均P<0.05)。各组总胆红素(TBIL)、直接胆红素(DBIL)、间接胆红素(IBIL)水平、入院当日的前白蛋白(PA)、入院当日和治疗7 d后的谷草转氨酶(AST)、谷丙转氨酶(ALT)、p H、血肌酐(Cr)水平相比,差异均无统计学意义(均P>0.05)。高、中、低剂量组治疗7 d后PA水平均分别明显高于入院当日,且高、中剂量组明显高于低剂量组,而高剂量组又明显高于中剂量组,差异均有统计学意义(均P<0.05)。高剂量组耐受率均分别明显高于中剂量组和低剂量组,差异均有统计学意义(均P<0.05)。结论大剂量的氨基酸在对低体质量早产儿实施早期静脉营养的过程中疗效明显,且患儿可耐受,临床可考虑对此用药方案进行推广,从而更好地改善早产儿的生存预后。

容器形状和冻结行为对储能效率影响研究

本文采用计算流体力学分析方法,分析了冰储能过程中水的固-液相变行为和由此产生的自然对流现象的特征。特别地,本文着重研究了安装在冰储能器中的换热器周围的冻结行为和桥接过程对储能效率的影响。为了研究冻结行为和桥接过程中产生自然对流对储能效率的影响,改变了容器的高宽比,并采用椭圆形换热器以促进对流的形成。采用潜热与比热相结合的单域计算模型,分析了两椭圆形换热器在冻结过程中的水温分布特征、速度分布特征以及冻结率。研究发现容器内对流方向的趋势是由水的初始温度决定的,并且容器宽度越大,高度越高,冻结率效率越高。