杆件局部失稳对钢桁架拱桥整体稳定性的影响

以某城市钢桁架拱桥为研究对象,采用板单元、梁单元、桁架单元等模拟整体有限元模型,分析钢桁架拱桥局部杆件弹塑性稳定性的特征值;通过改变风撑、斜撑、拱肋、吊杆数量及拱肋的刚度和矢跨比等参数,分析成桥状态下局部稳定性对钢桁架拱桥整体稳定性的影响.结果表明:①经计算结构的失稳临界值,杆件局部失稳是钢桁架拱桥失稳的主要影响因素,局部杆件受力能较好地反映结构稳定性承载力.②增加风撑结构的数量可以显著提高结构的稳定性;但当风撑数量足够时,继续增加风撑结构的数量,结构的稳定性并不能得到很大的提高;斜撑的设置对整体稳定性有很大的影响,特别是"K"和"X"斜撑对结构稳定性的影响非常显著.③风撑和拱肋刚度变化对结构的稳定性影响较为显著,吊杆刚度变化对结构的稳定性影响不大.④当矢跨比为1.0/4.0～1.0/5.0时,失稳位置出现在风撑位置;矢跨比为1.0/5.5～1.0/6.0时,失稳位置出现在拱肋弦杆位置;矢跨比主要通过影响局部位置杆件的受力状态影响结构整体的稳定性.     

露温露时和施氮量对稻瘟菌侵染的多元影响及其建模

 在人工气候室条件下研究了露温(DT),露时(DP),和施氮量(N)对稻瘟菌侵染的综合影响。发现这三个因子及其互作对侵染均有明显的作用,在供试条件和范围内,其作用大小为DP > DT > N > DP×DT > DT×N > DP×N > DP×DT×N。并得出了侵染的适合条件范围。本文首次在稻瘟侵染的研究中应用了侵染几率的概念,组建了侵染几率因气象和栽培因子而变的预测式。     

稻瘟菌水平抗性稳定性的研究——品种与小种适合度的分析

在温室条件下,对9个无垂直抗性基因粳稻品种×8个日本标准稻瘟菌株组合测定了侵染几率(IP)、病斑型比例(PB)、病斑扩展速率(LR)和产孢能力(SPC)组分,并据此确定了品种与小种的适合度。方差分析结果表明,除SPC的互作项外,其它组分及类型,方差均达到显著或极显著水平。但品种和小种主效应所占方差更大,从而证实了品种的抗性类型为水平抗性。某些品种在IP、PB及LR组分上反映了小种的专化作用,但因为不同品种在各组分上的抗性反应不同,因此,品种水平抗性的稳定性不能由组分的小种专化作用确定,而须由各组分组成的适合度的小种专化性确定。对品种X小种的适合度进行了互作的多重比较,未发现专化性互作,说明供试品种的水平抗性是稳定的。     

两株气单胞菌的分离与鉴定

从福建省某牛蛙养殖场病死牛蛙和某鸭场病死鸭体内分离到两株细菌，检验结果表明，两株分离菌均为有运动力的革兰氏阴性杆菌。根据其临床症状、细菌培养特性、生化特性、动物回归试验以及溶血试验等一系列试验，研究证明牛蛙感染的病原为嗜水气单胞菌，鸭感染的病原为温和气单胞菌。     

Induction of APOBEC3G ubiquitination and degradation by an HIV-1 Vif-Cul5-SCF complex

Human immunodeficiency virus-1 (HIV-1) Vif is essential for viral evasion of host antiviral factor CEM15/APOBEC3G. We report that Vif interacts with cellular proteins Cul5, elongins B and C, and Rbx1 to form an Skp1-cullin-F-box (SCF)-like complex. The ability of Vif to suppress antiviral activity of APOBEC3G was specifically dependent on Cul5-SCF function, allowing Vif to interact with APOBEC3G and induce its ubiquitination and degradation. A Vif mutant that interacted with APOBEC3G but not with Cul5-SCF was functionally inactive. The Cul5-SCF was also required for Vif function in distantly related simian immunodeficiency virus mac. These results indicate that the conserved Cul5-SCF pathway used by Vif is a potential target for antiviral development.     

“十一五”我国饲料业发展的战略转变

2006年7月26—27日,农业部在山东济南召开了全国饲料工作会议。会议总结了“十五”期间我国饲料业取得的成绩,分析了饲料业发展面临的形势与任务,明确了“十一五”饲料业的发展战略,部署了“十一五”政府的工作重点。本文即对此次会议要点进行了概括总结,以期引导读者了解相关政策并在今后工作中把握宏观方向,有所裨益。     

Nitrogen balance in barrows fed low-protein diets supplemented with essential amino acids

This study was conducted to determine the effect of addition of essential amino acids (EAA) to low-protein diets on N balance in barrows. Thirty barrows (Duroc × Yorkshire) with an initial BW of 36 kg were fed 5 corn- and soybean meal-based diets containing 13.6 to 18.2% crude protein (CP) for 10 d in a randomized complete block design. The 18.2% CP diet was formulated without addition of EAA (Lys, Met or Thr). The other diets contained 13.6 to 16.5% CP and were supplemented with EAA to provide 0.83% true digestible lysine equal to that in the 18.2% CP diet. Fecal, urinary, and total N excretion as well as N retention (g/d) decreased with decreasing dietary CP level (P < 0.01). The apparent digestibility of N was almost the same for the 18.2 and 16.5 CP diets, but the value was 2% higher (P = 0.07) than that for the 13.6% CP diet. These findings indicate that, compared with the 18.2% CP diets, supplementation with three EAA to the lowest-protein diets (13.6 CP) is inadequate for maximum intestinal protein digestion, amino acid absorption, or tissue protein deposition in growing barrows.     

Toxicity and biochemical action of amicarthiazol on citrus canker pathogen, Xanthomonas citri ex Hasse

Inhibitory effects of amicarthiazol, in vitro, against the growth of seven plant bacterial pathogens and its biochemical actions on Xanthomonas citri were investigated. The growth of Erwinia carotovora, Ralstonia solanacearum, and Pseudomonas syringe pv. syringae was not sensitive to amicarthiazol whilst Xanthomonads were all strongly inhibited in NB liquid medium; EC₅₀ of X. citri was 2.63 μg ml⁻¹ and the effectiveness of amicarthiazol depended on the timing of application. The inhibitions on the secretion of gross EPS and gross EPR as well as the activities of amylase, cellulase, and pectase of X. citri were increased with the concentrations of amicarthiazol, whereas the conductivities of the extracellular product suspensions and the protease activity were somewhat accelerated by the concentration less than 10 or 20 μg ml⁻¹ and inhibited only at higher concentration. EPS which was purified from X. citri showed obvious antagonistic effects on the inhibition of amicarthiazol, but not on the inhibition of Cu(OH)₂. The endogenous respirations and the activity of succinic dehydrogenase of X. citri were also inhibited and the inhibitions were increased with the toxic concentrations. Furthermore, the potential induced physiological adaptability of X. citri to amicarthiazol and the comparison with Cu(OH)₂ and carboxin were also discussed.     

土壤容重对生姜生长及产量和品质的影响

以莱芜大姜为试材,研究了容重分别为1.49(CK)、1.36(T1)、1.20(T2)g·cm-3的3种土壤对生姜生长及产量、品质的影响。结果表明,容重较小的土壤,其孔隙度较大,最大持水量较高,有利于生姜植株的生长和产量的提高。生长末期T2的株高、茎粗、分枝数和叶片数分别比CK增加17.9%、14.0%、35.2%和36.1%,单株根、茎、叶、根茎鲜质量分别比CK提高43.3%、24.4%、28.1%和35.2%,收获时CK、T1、T2的产量分别为2534.1、3017.7和3326.8kg·(667m2)-1,处理间差异极显著。此外,生姜根茎干物质、淀粉及挥发油含量随土壤容重降低而降低,而蛋白质、游离氨基酸则相反,粗纤维、可溶性糖及VC含量则基本不受土壤容重的影响。     

复方中草药抗乳炎奶牛饲料添加剂的研制

试验结果显示,所研制的3种新制剂对奶牛乳腺炎均有明显的防治效果,同时对提高产奶量,改善牛乳的品质和风味、降低牛乳中的体细胞数也有显著的效果。