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991.
用准经典轨线方法研究了处于振动激发态的硅原子团簇与硅原子团簇碰撞的反应动力学,计算表明,对于Si4+Si3反应,当反应物团簇处于振动激发态时,有利于生成更小团簇的碎片,而对生成Si6+Si及Si5+Si2的影响不大。 相似文献
992.
993.
Santi Tungprapa Tanarinthorn Puangparn Monchawan Weerasombut Ittipol Jangchud Porntiva Fakum Somsak Semongkhol Chidchanok Meechaisue Pitt Supaphol 《Cellulose (London, England)》2007,14(6):563-575
This paper reports an investigation of the effects of solvent system, solution concentration, and applied electrostatic field
strength (EFS) on the morphological appearance and/or size of as-spun cellulose acetate (CA) products. The single-solvent
systems were acetone, chloroform, N,N
-dimethylformamide (DMF), dichloromethane (DCM), methanol (MeOH), formic acid, and pyridine. The mixed-solvent systems were
acetone–DMAc, chloroform–MeOH, and DCM–MeOH. Chloroform, DMF, DCM, MeOH, formic acid, and pyridine were able to dissolve CA,
forming clear solutions (at 5% w/v), but electrospinning of these solutions produced mainly discrete beads. In contrast, electrospinning of the solution of
CA in acetone produced short and beaded fibers. At the same solution concentration of 5% (w/v) electrospinning of the CA solutions was improved by addition of MeOH to either chloroform or DCM. For all the solvent systems
investigated smooth fibers were obtained from 16% (w/v) CA solutions in 1:1, 2:1, and 3:1 (v/v) acetone–DMAc, 14–20% (w/v) CA solutions in 2:1 (v/v) acetone–DMAc, and 8–12% (w/v) CA solutions in 4:1 (v/v) DCM–MeOH. For the as-spun fibers from CA solutions in acetone–DMAc the average diameter ranged between 0.14 and 0.37 μm
whereas for the fibers from solutions in DCM–MeOH it ranged between 0.48 and 1.58 μm. After submersion in distilled water
for 24 h the as-spun CA fibers swelled appreciably (i.e. from 620 to 1110%) but the physical integrity of the fibrous structure
remained intact. 相似文献
994.
T. Datta Samanta S. Laskar D. Nayak S. Lahiri 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):323-325
Binding ability of mercury, thallium, lead and bismuth with Erythrina variegata seed protein have been investigated using tracer packet technique. Due to the lack of standard methods, inter-comparisons
have been made among three different approaches, like trichloroacetic acid (TCA) precipitation, isoelectric precipitation
and dialysis of protein after incubation with the metals. Good agreement was observed for all the cases except that of lead. 相似文献
995.
A density functional theory is proposed for an inhomogeneous hard-core Yukawa (HCY) fluid based on Rosenfeld's perturbative method. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-core repulsion and a quadratic functional Taylor expansion for the long-ranged attractive or repulsive interactions. To test the established theory, grand canonical ensemble Monte Carlo simulations are carried out to simulate the density profiles of attractive and repulsive HCY fluid near a wall. Comparison with the results from the Monte Carlo simulations shows that the present density functional theory gives accurate density profiles for both attractive and repulsive HCY fluid near a wall. Both the present theory and simulations suggest that there is depletion for attractive HCY fluid at low temperature, but no depletion is found for repulsive HCY fluid. The calculated results indicate that the present density functional theory is better than those of the modified version of the Lovett-Mou-Buff-Wertheim and other density functional theories. The present theory is simple in form and computationally efficient. It predicts accurate radial distribution functions of both attractive and repulsive HCY fluid except for the repulsive case at high density, where the theory overestimates the radial distribution function in the vicinity of contact. 相似文献
996.
用峰鉴别技术反相高效液相色谱法测定火锅汤料中微量吗啡 总被引:3,自引:0,他引:3
本文报道了以峰鉴别技术为定性依据的测定火锅汤料中微量吗啡的反相高效液相色谱法。本法采用改良的Stas-otto法分离提取复杂样品中的微量吗啡。由于采用峰鉴别技术,增加了定性参数,大大提高了定性方法的准确性。本法简便、快速。最低检出浓度为0.04mg/L。在数十例样品分析中,与其它仪器分析结果比照,非常符合。 相似文献
997.
硝酸镧与冠醚(2, 2)配合物的晶体及电子结构研究 总被引:1,自引:0,他引:1
用X-射线单晶衍射法测定了硝酸镧与冠醚(2,2)配合物的晶体结构,发现其具有与报道的Eu(NO_3)_3(2,2)配合物不同的配位方式.晶体属于三斜晶系,空间群P(?),晶胞参数为a=10.312(2)(?);b=12.745(3)(?);c=8.917(2)(?);α=103.79(2)°;β=112.73(2)°;γ=83.68(2)°;V=1049.5(5)(?)~3;F(000)=587.88;Z=2.结构用重原子法解出;R值为0.0292.用INDO法计算了配合物的净电荷分布,电子结构、键级.结果表明,镧与配位原子间的键具有一定程度的共价性.镧的5d轨道对共价性的贡献最大,而4f轨道基本上不参与成键.La-N比La-O(醚)间存在较强的作用,增大了配合物的稳定性. 相似文献
998.
Semiconductor quantum dots (QD) are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. In comparison with organic dyes and fluorescent proteins, QD are emerging as a new class of fluorescent labels with improved brightness, resistance against photobleaching and multicolor fluorescence emission. These properties could improve the sensitivity of biological detection and imaging by at least 10- to 100-fold. Further development in high-quality near-infrared-emitting QD should allow ultrasensitive and multicolor imaging of molecular targets in deep tissue and living animals. Here, we discuss recent developments in QD synthesis and bioconjugation, applications in molecular and cellular imaging as well as promising directions for future research. 相似文献
999.
Oxide ceramic masses react to simple shearing with hardening (peptisation: increase in the shear stress with the shear deformation).
In the present study the correlation between the increase in the shear stress and the porosity, agglomeration processes and
the type of flow are analysed. For this purpose oxide ceramic masses are tested in a shear device especially developed for
pastes and analysed by rheometric experiments, NMR methods and particle size analysis. The results support the hypothesis
that structural changes (hardening, increase in the mean porosity) of the material during the peptisation mainly depend on
the magnitude and not on the kind of the energy input and thus of the type of flow. The fraction of bound (more generally,
the immobilised) water increases with the shear displacement. Also crushing of primary particles could be observed. Both the
crushing of solid particles causing an increased solid surface and the formation of a three-dimensional gel structure are
microscopic effects capable of resulting in the binding or retaining water. On a macroscopic scale these phenomena cause hardening.
Magnetic resonance imaging visualises flow-induced agglomerates, which form owing to the shear flow and increase the porosity
averaged over the whole sample. After the shear experiment rolls of paste can be seen which indicate that the general assumption
of a plane shear flow in the shear device is not warrantable.
Received: 19 July 2001 Accepted: 25 October 2001 相似文献
1000.
本文采用GF-AAS加平台技术,基体改进剂,测定了中药片仔癀,六味地黄丸中铬、铅和镉的含量,铬、铅和镉的线性范围分别为0-0.8ng/mL,0-50ng/mL,0-5ng/mL,回收率分别为102-103%,99-101%,97.5-98%,本方法简便快速、准确。 相似文献