膨胀柱壳恒定应变率的本构关系

考虑到金属柱壳膨胀过程中随机裂纹萌生对测试结果的可能干扰,设计了预置有中心穿透圆孔的柱壳样品,采用多普勒光纤探针测量系统获得了柱壳外壁更优的径向速度历史。基于膨胀柱壳实验中固有的非恒定应变率现象,研究了获得恒定应变率下本构方程的方法,并采用改进后的本构方程确定方法,获得了20钢恒定应变率下的应力应变关系。     

DNA甲基化-非甲基化碱基间堆积作用的理论研究

运用二级Mфller-Plesset(MP2)理论方法和cc-pVDZ基组优化了6-甲基鸟嘌呤(O6-MethylG),4-甲基胸腺嘧啶(O4-MethylT)以及5-甲基胞嘧啶(C5-MethylC)与DNA碱基鸟嘌呤(G),腺嘌呤(A),胞嘧啶(C),胸腺嘧啶(T)之间的堆积构型.在MP2/aug-cc-pVXZ//MP2/cc-pVDZ(X=D,T)水平上,采用完全基组外推方法校正了堆积碱基对间的相互作用能,并用完全均衡校正法(CP)校正了基组重叠误差(BSSE).MP2计算结果表明,DNA碱基甲基化使得嘧啶-嘧啶、嘧啶-嘌呤堆积碱基间的平行旋转角发生明显改变,并使堆积碱基间的相互作用能增大.在MP2/cc-pVDZ计算级别上得到了各堆积碱基对的全电子波函数,并用分子中的原子理论(AIM)分析了堆积碱基对间的弱相互作用.AIM分析结果显示,甲基化增强了堆积碱基间的π-π作用,且甲基氢与相邻碱基间形成H2CH…X(X=O,N,CH3,NH2)等类型的氢键.甲基化损伤使碱基间重叠程度增大、π-π作用增强以及堆积碱基间形成多个氢键,是堆积作用能增加的主要原因.     

1.319μm连续固体锁模激光器

报道了１．３１９μｍＮｄ：ＹＡＧ连续锁模激光器的技术研究。激光器的谐振腔为低热敏腔，用声光振幅调制器作为锁模元件，泵浦腔具有较高的泵浦效率和输出稳定性，获得了重复频率１００ＭＨｚ，平均功率～０．５４Ｗ，脉宽＜１７０ｐｓ的光脉冲。     

复合材料Ⅰ、Ⅱ混合型分层试验研究

通过对T300／5405、1300／913、1300／HD03三种航空材料Ⅰ、Ⅱ混合型分层研究，进一步研究了新的Ⅰ、Ⅱ混合型分层断裂测试的JJ法，并和MMB法进行了比较，发现两者较为吻合。但JJ法耗费试件少，简单易行，操作方便，有利于建立混合型分层的失效判据，它可以适用于不同环境下的混合型分层实验的测试。     

初始应力状态对材料层裂破坏特性影响研究

通过对球面飞片加载条件下的应力/应变状态分析表明采用施加径向应变方法可以近似模拟球面加载的受力过程. 采用过盈配合的热装配方法对平面样品施加了径向预应变,一维平面应变气炮实验结果显示初始预应力(变)明显降低了LY12铝层裂强度. 从空洞长大基本原理出发分析了各向异性受力条件下空洞长大的路径和所消耗能量不同于各向同性应力加载.通过数值模拟对含损伤的材料本构模型进行分析,得到了材料层裂强度与其外部宏观应力场密切相关,也间接的与构型相关的结论.      

固定化Methylomonas Z201细胞：甲烷单加氧酶的活性和稳定性

分别以海藻酸钙和砂子为载体，采用包埋和吸附技术固定化ＭｅｔｈｙｌｏｍｏｎａｓＺ２０１细胞．以丙烯环氧化为指标反应，系统研究固定化对ＭｅｔｈｙｌｏｍｏｎａｓＺ２０１细胞ＭＭＯ活性和稳定性的影响．结果表明，对包埋细胞，合适的负载量和粒径为保留较高ＭＭＯ活性所必需．砂子对细胞的吸附能力中等．外源性电子给体甲酸钠对游离和固定化细胞的ＭＭＯ活性影响不同．固定化细胞的最适ｐＨ值和温度与游离细胞相同，但活化能降低．固定化细胞保留游离细胞ＭＭＯ活性的６０—７０％，操作稳定性、热稳定性、贮存稳定性均有所提高．     

Study of a 35-GHz third-harmonic low-voltage complex cavitygyrotron

A self consistent nonlinear theoretical model for a complex cavity gyrotron with abrupt transitions is presented in this paper. The model accounts for mode conversion in the transition region of the complex cavity through the general theory of modal expansion techniques. The interaction between the electron beam and TE₆₁/TE₆₂ RF field in the step cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different electron beam parameters     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0⩽x⩽0.4, 0⩽y⩽0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

ε-Keggin-based coordination networks: Synthesis, structure and application toward green synthesis of polyoxometalate@graphene hybrids

Four coordination networks based on the {ε-PMo(V)(8)Mo(VI)(4)O(40)(OH)(4)Zn(4)} Keggin unit (εZn) have been synthesized under hydrothermal conditions. (TBA)(3){PMo(V)(8)Mo(VI)(4)O(36)(OH)(4)Zn(4)}[C(6)H(4)(COO)(2)](2) (ε(isop)(2)) is a 2D material with monomeric εZn units connected via 1,3 benzenedicarboxylate (isop) linkers and tetrabutylammonium (TBA) counter-cations lying between the planes. In (TPA)(3){PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)}[C(6)H(3)(COO)(3)] (TPA[ε(trim)](∞)), 1D inorganic chains formed by the connection of εZn POMs, via Zn-O bonds, are linked via 1,3,5 benzenetricarboxylate (trim) ligands into a 2D compound with tetrapropylammonium (TPA) cations as counter-cations. (TBA){PMo(V)(8)Mo(VI)(4)O(40)Zn(4)}(C(7)H(4)N(2))(2)(C(7)H(5)N(2))(2)·12H(2)O (ε(bim)(4)) is a molecular material with monomeric εZn POMs bound to terminal benzimidazole (bim) ligands. Finally, (TBA)(C(10)H(10)N(4))(2)(HPO(3)){PMo(V)(8)Mo(VI)(4)O(40)Zn(4)}(2)(C(10)H(9)N(4))(3)(C(10)H(8)N(4)) (ε(2)(pazo)(4)) is a 1D compound with dimeric (εZn)(2) POMs connected by HPO(3)(2-) ions and terminal para-azobipyridine (pazo) ligands. In this compound an unusual bond cleavage of the central N[double bond, length as m-dash]N bond of the pazo ligand is observed. We report also a green chemistry-type one-step synthesis method carried out in water at room temperature using ε(2)(pazo)(4) and ε(isop)(2) as reducing agent of graphite oxide (GO) to obtain graphene (G). The POM@G hybrids were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, powder X-ray diffraction, energy dispersive X-ray analysis, infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and cyclic voltammetry.     

Increased UV-B Radiation Affects the Viability, Reactive Oxygen Species Accumulation and Antioxidant Enzyme Activities in Maize (Zea mays L.) Pollen

The increase in UV-B radiation reaching the earth's surface has prompted extensive studies on the effects of UV-B on plants. However, most of these studies have not addressed the close characteristics related to future survival of plant populations. The purpose of this study was to investigate the effects of UV-B radiation on reactive oxygen species (ROS) accumulation and antioxidant defense system in relation to germination, tube length and viability of maize pollen. Our results indicate that increased UV-B radiation decreased the pollen germination rate and tube length in vitro and also its fertilization ability in the field. Production of O₂^•− and H₂O₂ increased by UV-B radiation treatment, and their continuous accumulation resulted in lipid peroxidization. The activities of superoxide dismutase, catalase, peroxidase and DPPH-radical scavenging were decreased by increased UV-B radiation. The increased ROS and lipid peroxidization, and decreased activities of the antioxidants may be attributed to the effects of UV-B radiation on pollen germination, tube growth and fertilization ability.