PHOTOREACTIVATION IN THE EXTREME HALOPHILIC ARCHAEBACTERIUM Halobacterium cutirubrum

Abstract— Photoreactivation in the extreme halophilic archaebacterium Halobacterium cutirubrum was studied both in vivo and in vitro. Cells irradiated with ultraviolet (UV)-fluences up to 350 J/m² could be completely photoreactivated, indicating very efficient repair of pyrimidine dimers in UV-irradiated DNA. Dark repair is apparently absent in Halobacterium since liquid holding under non-growth conditions did not influence the survival of UV-irradiated cells, while cells remained completely photoreactivable with no change in the kinetics of photoreactivation. Experiments with Halobacterium isolates of different carotenoid content indicated that carotenoids do not influence either UV-inactivation or photoreactivation. Small differences in the rates of UV-inactivation and photoreactivation could be assigned to the occurrence of gas vesicles. Flash experiments and the temperature dependence of photoreactivation indicated an enzymatical reaction. This was confirmed by in vitro experiments with partially purified photoreactivating enzyme. The in vivo action spectrum of photoreactivation showed a main band in the 400-470 nm region with a maximum at 440 nm. Comparison with action spectra of other microorganisms classified the Halobacterium enzyme as a 8-hydroxy-5-deazaflavin type photoreactivating enzyme.     

金属卟啉催化条件下有机化合物与二氧化碳的电羧化反应Ⅰ. 金属卟啉对苄基氯电羧化催化活性的研究

本文研究了系列金属卟啉对苯基氯(phCH~2Cl)和CO~2电羧化反应的催化活性.用熔点,MS,IR,UV鉴别产物为苯乙酸卟脂,利用高效液相色谱(HPLC)定量分析了羧化产物,选出最佳电羧化电解电位为-1.6v(相对于饱和甘汞电极,vs.SCE,下同). 并对催化活性较高的钴卟啉系列配合物进行了深入研究. 探讨了金属卟啉具有催化活性的原因,认为能形成M(Ⅰ)中间体的金属卟啉配合物.具有较高的催化活性.     

A Dynamical Systems Analysis of Semidefinite Programming with Application to Quadratic Optimization with Pure Quadratic Equality Constraints

This paper considers the problem of minimizing a quadratic cost subject to purely quadratic equality constraints. This problem is tackled by first relating it to a standard semidefinite programming problem. The approach taken leads to a dynamical systems analysis of semidefinite programming and the formulation of a gradient descent flow which can be used to solve semidefinite programming problems. Though the reformulation of the initial problem as a semidefinite pro- gramming problem does not in general lead directly to a solution of the original problem, the initial problem is solved by using a modified flow incorporating a penalty function. Accepted 10 March 1998     

AN APPROXIMATE PROJECTION SCHEME FOR INCOMPRESSIBLE FLOW USING SPECTRAL ELEMENTS

An approximate projection scheme based on the pressure correction method is proposed to solve the Navier–Stokes equations for incompressible flow. The algorithm is applied to the continuous equations; however, there are no problems concerning the choice of boundary conditions of the pressure step. The resulting velocity and pressure are consistent with the original system. For the spatial discretization a high-order spectral element method is chosen. The high-order accuracy allows the use of a diagonal mass matrix, resulting in a very efficient algorithm. The properties of the scheme are extensively tested by means of an analytical test example. The scheme is further validated by simulating the laminar flow over a backward-facing step.     

香菇多糖L-2A的结构表征

从香菇子实体中提取纯化得到香菇多糖级分L-2A,利用紫外光谱、红外光谱、凝胶渗透色谱和气相色谱分析其结构特征.香菇多糖L-2A糖含量为90.14%;重均分子量是2.03×10 5道尔顿;具有D-葡萄吡喃糖构型,单糖组成主要是由吡喃型葡萄糖组成;香菇多糖L-2A多糖含有o-糖苷键,且主要是o-Ser连接方式;具有与刚果红结合的螺旋结构.香菇多糖L-2A为首次从香菇子实体中分离得到.     

Laser-produced plasma ion characteristics in laser ablation of lithium manganate

Laser ablation is widely used to assist in the fabrication of prototype lithium manganate (LiMn₂O₄) thin film structures for Li-ion battery electrodes via the pulsed laser deposition technique. However, films can be considerably Li and/or O deficient, depending the deposition conditions used. Here we present data on the ionic component of laser-produced plasma in laser ablation of lithium manganate with ns excimer laser. Plasma was monitored using an electrical Langmuir ion probe, in time-of-flight mode in conjunction with mass spectrometry to identify the dominant ionic species. Ablation in vacuum at ∼2.5 J cm⁻² revealed the plasma's ionic component was composed primarily of singly charged Li and Mn ions. The time-of-flight data indicates significant deceleration of the plasma when ablation is carried out in an oxygen background gas pressure of the order of 10 Pa. The implications for thin film growth are considered in terms of the possible gas phase interactions and/or thin film re-sputtering yield.     

The coherent scattering function of the reptation model: Simulations compared to theory

We present results of Monte Carlo simulations measuring the coherent structure function of a chain moving through an ordered lattice of fixed topological obstacles. Our computer experiments use chains up to 320 beads and cover a large range of wave vectors and a time range exceeding the reptation time. For additional information we also measured the coherent structure function of internal pieces of the chain. We compare our results i) to the predictions of the primitive chain model, ii) to an approximate form resulting from Rouse motion in a coiled tube, and iii) to our recent evaluation of the full reptation model. i) The primitive chain model can fit the data for times , where T ₂ is the Rouse time of the chain. Besides some phenomenological amplitude factor this fit involves the reptation time T ₃ as a second fit parameter. For the chain lengths measured, the asymptotic behavior is not attained. ii) The model of Rouse motion in a tube, which we have criticized before on theoretical grounds, is shown to fail also on the purely phenomenological level. iii) Our evaluation of the full reptation model yields an excellent fit to the data for both total chains and internal pieces and for all wave vectors and all times, provided specific micro-structure effects of the MC dynamics are negligible. Such micro-structure effects show up for wave vectors of the order of the inverse segment size and enforce the introduction of some phenomenological, wave-vector-dependent prefactor. For the dynamics of the total chain our data analysis based on the full reptation model shows the importance of tube length fluctuations. Universal (Rouse-type) internal relaxation, however, is unimportant. It can be observed only in the form of the diffusive motion of a short central subchain in the tube. Finally, we present a fit formula which in a large range of wave vectors and chain lengths reproduces the numerical results of our theory for the scattering from the total chain.Received: 9 July 2003, Published online: 11 November 2003PACS: 83.10.Kn Reptation and tube theories - 82.35.Lr Physical properties of polymers - 83.10.Rs Computer simulation of molecular and particle dynamics     

Stereochemistry of the vinylogous sN2′ reaction

Theoretical treatment indicates that the stereochemistry of both the vinylogous S_N2′ and 1,6- conjugate elimination reaction will be opposite to that of the S_N2′ and 1,4-conjugate elimination reaction.     

Relation between interface states and temperature behavior of the barrier height of silver contacts on clean cleaved n-type silicon

The properties of silver-silicon interfaces formed by cleaving n-type silicon in ultra high vacuum (UHV) in a stream of evaporating silver atoms were studied. The barrier heights of these contacts were measured at different temperatures by using C-V techniques. All measurements were performed in UHV. The dependence of the barrier height upon temperature did not follow the temperature dependence of the Si band gap as it is usually found. The measured temperature behavior depended on the roughness of the Si surface. The temperature behavior can be explained by assuming a specific band structure of the interface states. For Ag contacts on atomically smooth n-type Si, the interface states were found to be arranged in two bands, one band 4 × 10^?3 eV wide with acceptor type states 0.18 eV below the intrinsic level E_i and a density of 10¹⁷ states/cm² eV, and the other 1 eV wide with donor type states with its upper edge 0.28 eV below E_i, and a density of 4 × 10¹⁴ states/cm²eV.