焊管的残余应力测试与研究

通过小孔法与分割法对φ272mm螺旋埋弧焊管和φ380mm对接焊管的残余应力测试,分析探讨了螺旋焊缝、环焊缝以及焊缝热影响区的残余应力分布。研究结果表明,不同工艺焊接成型的圆管,其焊缝纵向均匀为拉应力分布,焊缝横向均为压应力分布,焊缝热影响区的残余应力分布各异。     

Helicity induction on a poly(phenylacetylene) bearing a phosphonate residue by chiral dendrons

A series of optically active dendrons with a primary amino group at the terminal were prepared from L - or D -glutamic acid, and their helicity induction abilities for a poly(phenylacetylene) bearing a phosphonate pendant were characterized with ultraviolet–visible and circular dichroism spectroscopy. The magnitude of the Cotton effects of the polymer induced by the dendrons significantly increased upon complexation with a higher generation dendron. The effect of the chirality of the glutamate residues (L and D ) on the helicity induction was also studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4580–4586, 2004     

Solution properties of exocellular polysaccharides of rhizobium leguminosarum. Static and dynamic light-scattering: Characterization in dilute solution

Three polysaccharides, Rhizobium leguminosarum 8002 EPS(I), Rhizobium trifolii TA1-EPS (II), Rhizobium leguminosarum 127K87 EPS (III), produced by bacteria of Rhizobium genus have been investigated by static and dynamic light scattering combined with chirooptical measurements. All three polymers have the same backbone but differ in the length of the side chains and in the content of minor substituents. An isothermal conformational transition coil → helix was observed with I and II by adding salt (NaCl). The molecular parameters of the polysaccharides in the ordered state were determined by light-scattering data. Increasing the ionic strength a shrinking of the helix was observed accompanied by a corresponding decrease in the radius of gyration. An extraordinary chain stiffness in terms of Kuhn segment lengths was found in both cases, similar to that already observed for other microbial polysaccharides. In the case of III no disorder → order transition was induced by the salt, and the scattering behavior corresponds to that of a rather flexible polymer with a characteristic ratio C_∞ = 24. The incapability of III to form a helical structure is attributed to the effect of the very long side chain. The analysis of the time correlation functions revealed typical flexible chain behavior for all three polysaccharides. This behavior for the two ordered polymers is in agreement with a recent theory by Maggs and is due to bending modes of the rods. ©1995 John Wiley & Sons, Inc.     

Wave Properties of A Free Elliptical Helix Slow-Wave Structure with Arbitrary Eccentricity

This paper gives the investigations of the fundamental wave of a free elliptical helix slow-wave structure (SWS) with arbitrary eccentricity. The wave properties including the phase velocity characteristics, interaction impedance and the longitudinal electric field distribution of this mode has been fully studied. It is found that, when the eccentricity increases, the interaction impedance and the operating frequency of such SWS will be improved, which allows to have a higher gain and operating in a higher frequency band. Furthermore, the field configuration is different from that of a round helix; the azimuthal distribution of the E-field follows with the angular Mathieu function of the first kind, even with mode of zero. In radial, E-field is elliptical surface wave. When the eccentricity tends to zero, all the characteristics will be smoothly degenerates to the case of round helix correspondingly.     

CC型原表面回热器传热与流动数值模拟

对CC型原表面回热器的主换热面附近流场和温度场进行了三维数值模拟。结果表明,传热的强化程度与流动阻力的大小取决于螺旋型二次流动的强弱,影响机理是螺旋型二次流动强烈影响流体的混合和边界层的发展。针对低雷诺数范围流动,通过比较不同结构尺度和换热面布置时传热和流动特性,对换热表面进行了设计优选。     

Synthesis and DNA triplex formation of an oligonucleotide containing an urocanamide

An urocanamide nucleoside designed and previously tested as its protected ribose derivative in aprotic solvents for binding a cytosine-guanine (CG) Watson-Crick base pair was successfully incorporated into a triplex forming oligonucleotide. Binding affinity and specificity of this nonnatural nucleoside were studied in a triple helix with duplex targets containing all four possible Watson-Crick base pairs opposite the nucleoside analog in the third strand. UV melting experiments indicate the formation of a well-defined triplex with specific binding of the urocanamide analog to a CG inversion of the homopurine-homopyrimidine target. However, binding affinities in the triplex are weak and much lower when compared to the canonical base triads.     

Ab initio prediction of helical segments in polypeptides

An ab initio method has been developed to predict helix formation for polypeptides. The approach relies on the systematic analysis of overlapping oligopeptides to determine the helical propensity for individual residues. Detailed atomistic level modeling, including entropic contributions, and solvation/ionization energies calculated through the solution of the Poisson-Boltzmann equation, is utilized. The calculation of probabilities for helix formation is based on the generation of ensembles of low energy conformers. The approach, which is easily amenable to parallelization, is shown to perform very well for several benchmark polypeptide systems, including the bovine pancreatic trypsin inhibitor, the immunoglobulin binding domain of protein G, the chymotrypsin inhibitor 2, the R69 N-terminal domain of phage 434 repressor, and the wheat germ agglutinin.     

Inclusion Compound Formation of Amylose by Sealed-Heating with Salicylic Acid Analogues

The inclusion compounds of linear amylose and salicylic acid analogues preparedby sealed-heating were evaluated by using powder X-ray diffraction and infraredspectroscopy. Sealed-heating of amylose and either salicylamide or benzoic acidinduced the amylose structural change from the 6₁- to the 7₁-helix structure, while sealed-heating with o-toluic acid, o-chlorobenzoic acid and o-nitrobenzoic acid induced the change from the 6₁- to the 8₁-helix structure. In contrast to theresults in the salicylic acid system, the amylose helix type of sealed-heated samplewas not varied by the load of the guest compound, but was fixed only by the guestspecies. No change of the helical structure of amylose depending on the amylose molecular weight was observed. From the comparison of inclusion compound formation among different guest systems, it was found that the higher vapor pressure at 100 °C of the guest resulted in faster inclusion compound formation. The vapor pressure of the guest compound would be an important factor affecting the progress of inclusion compound formation.     

微波辐照对胶原蛋白三股螺旋结构的影响

胶原蛋白的三股螺旋结构是其不同于其他蛋白质的特殊结构，也是其具有特殊功能的基础，然而，胶原的三股螺旋结构易在外界条件的影响下被破坏。目前微波已被越来越多的应用于胶原蛋白的提取和改性过程，但是关于微波辐照对胶原蛋白结构影响的研究还相对较少。首先从牛跟腱中提取胶原蛋白，然后采用0.5 mg·mL-1的胶原蛋白溶液在30 ℃下以微波辐照保温为实验样，水浴加热和未经加热处理为对比样，最后采用紫外-可见光谱、傅里叶变换红外光谱、圆二色谱以及荧光发射光谱等方法，对不同加热方法中胶原蛋白的三股螺旋结构和超分子结构进行表征，研究了微波辐照对胶原蛋白结构的影响。实验结果表明，在低于胶原变性温度的条件下，无论是微波辐照还是水浴加热都不会破坏胶原蛋白的三股螺旋结构，也不会使胶原蛋白变性。但是，与水浴加热相比，微波辐照会对胶原蛋白的聚集行为产生抑制作用。微波辐照对胶原蛋白的作用既有与常规加热相同的热效应，又有常规加热过程中不存在的非热效应，非热效应表现为抑制胶原蛋白的聚集行为。研究结果可为微波场中胶原蛋白结构和性质的变化提供科学依据。