关于动态位错场张量势的规范变换

本文引入并论证了描述动态位错场的张量势(A与B)的规范交换问题,而且证明这种变换可采取这样的形式:B′=B+▽F, A′=A-ρ?/(?t)▽G,x′=x-ρ?/(?t)F,其中x_i=e_iklA_kl。至于F与G,则为带有很大任意性的时空坐标的矢量函数,但它们要满足以下关系式:F=▽×G,▽²F-1/G_t²-(?²/?t²)F=0.进 关键词：     

纳豆激酶分离纯化和酶活性测定的研究进展

该文对纳豆激酶的分离纯化和酶活性测定进行了综述。重点讨论了溶剂沉淀法、柱层析法、磁性微球吸附法、膨胀床法、反相胶束法、三相分割法等分离方法。对酶活性的不同测定方法进行了讨论和比较。提出了将核酸适配体识别技术用于纳豆激酶分离纯化和酶活性测定的可行性。     

Multi length scale analysis of the microstructure in sticky sphere dispersions during shear flow

The effect of shear flow on the microstructure in a weakly aggregated suspension is investigated. Monodisperse small silica particles with a grafted layer of 1-octadecanol are dispersed in n-tetradecane, yielding a thermoreversible sticky sphere model suspension. A combination of small angle light scattering and ultra small and small-angle X-ray scattering techniques have been used, in situ and time resolved, to study the flow-induced anisotropy of the microstructure. In this manner, the length scales from the single particle size to that of the spatial organization of the aggregates can be covered. Harmonic expansion of the structure factor demonstrates that anisotropy develops in the microstructure on all relevant length scales. Possible real space interpretations of the scattering information are discussed in conjunction with implications for the nonlinear rheological behavior.     

Sunfish cationic amphiphiles: toward an adaptative lipoplex morphology

A detailed physicochemical study is presented on a new class of cationic amphiphiles, Sunfish amphiphiles, recently designed, synthesized, and tested for gene delivery. These materials have two hydrophobic tails, connected to the cationic pyridinium headgroup at the 1- and 4-positions. Two extreme morphologies can be visualized, i.e. one by back-folding involving association of both tails at one side of the pyridinium ring and one by independent unfolding of the tails, the two molecular geometries leading to considerable differences in the aggregate morphology. The behavior of six members of the Sunfish family in mixtures with DOPE, applying different conditions relevant for transfection, has been studied by a combination of techniques (DLS, DSC, NMR, SAXS, Cryo-TEM, fluorescence, etc.). The effects of structural parameters such as the presence of unsaturation in the tails and length of the alkyl chains on the properties of the aggregates have been assessed. A correlation of these structural data with cellular transfection efficiencies reveals that the highest transfection efficiency is obtained with those amphiphiles that are easily hydrated, form fluid aggregates, and undergo a transition to the inverted hexagonal phase in the presence of plasmid DNA (p-DNA) at physiological ionic strength.     

Emission cross sections for fully stripped carbon colliding with atomic hydrogen

In the impact velocity range of 0.2–0.6 a.u. we have measured line emission cross sections in the vuv and visible spectral region for collisions of C⁶⁺ with atomic hydrogen. The electron capture goes predominantly into then=4 shell and to a lesser extent into then=5 shell. For the dominant lines there is a good agreement with the molecular, the extended atomic and the unified atomic-molecular orbital calculations of respectively Green et al. [8], Fritsch and Lin [9], and Kimura and Lin [10]. However for transitions originating from then=5 level the measurements strongly support the molecular orbital calculations. Furthermore there are considerable differences between measured and calculated intensities for the lines of non-dominantly populated high-n states (n=7 and 8) and atomic orbital and UDWA calculations.     

Fragmentation of alpha- and beta-alanine molecules by ions at Bragg-peak energies

The interaction of keV He(+), He(2+), and O(5+) ions with isolated alpha and beta isomers of the amino acid alanine was studied by means of high resolution coincidence time-of-flight mass spectrometry. We observed a strong isomer dependence of characteristic fragmentation channels which manifests in strongly altered branching ratios. Despite the ultrashort initial perturbation by the incoming ion, evidence for molecular rearrangement leading to the formation of H(3)(+) was found. The measured kinetic energies of ionic alanine fragments can be sufficient to induce secondary damage to DNA in a biological environment.     

Response of polyatomic molecules to ultrastrong laser- and ion-induced fields

The exposure of molecules to short, ultrastrong electric fields leads to multiple ionization and a subsequent Coulomb explosion. We present a comparative study where uracil molecules are exposed to fields generated by high-power laser pulses (tau approximately 75 fs, I > 10(16) W/cm2) or swift highly charged ions (0.5 MeV Xe25+) representing a half-cycle pulse of less than 10 fs duration. Molecular dynamics and structural information contained in the fragmentation pathways can be assessed separately. Despite the similar field strengths large differences in fragment kinetic energies are found which are related to field shape and duration with the aid of molecular dynamics simulations.     

Near-Edge Soft X-ray Absorption Mass Spectrometry of Protonated Melittin

We have investigated the photoionization and photofragmentation yields of gas-phase multiply protonated melittin cations for photon energies at the K-shell absorption edges of carbon, nitrogen, and oxygen. Two similar experimental approaches were employed. In both experiments, mass selected [melittin+qH]^q+ (q=2–4) ions were accumulated in radiofrequency ion traps. The trap content was exposed to intense beams of monochromatic soft X-ray photons from synchrotron beamlines and photoproducts were analyzed by means of time-of-flight mass spectrometry. Mass spectra were recorded for fixed photon energies, and partial ion yield spectra were recorded as a function of photon energy. The combination of mass spectrometry and soft X-ray spectroscopy allows for a direct correlation of protein electronic structure with various photoionization channels. Non-dissociative single and double ionization are used as a reference. The contribution of both channels to various backbone scission channels is quantified and related to activation energies and protonation sites. Soft X-ray absorption mass spectrometry combines fast energy deposition with single and double ionization and could complement established activation techniques.

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