A comparison of phototautomerism in different sites of free-base porphin (H2P) in n-alkane crystals

Selective laser-induced phototautomerism of free-base porphin in different n-alkanes (n-hexane, n-heptane, n-octane, nnonane, n-decane, n-undecane and n-dodecane) has been used to identify tautomer splittings in a number of sites in polycrystalline samples at 2 K. Pairs or lines arising from the two molecular orientations in each site can be reversibly transformed into each other. In the odd n-alkanes the occupation of different sites was not dependent on the rate at which the samples were frozen, but in the even n-alkanes metastable sites were only occupied following rapid quenching.     

Methane production from synthesis gas using a mixed culture ofR. rubrum M. barkeri,and M. formicicum

The components of synthesis gas, CO, H₂, and CO₂, may be converted into CH₄ biologically through either acetate or H₂/CO₂ as intermediates. Of these two routes, conversion through H₂/CO₂ is preferred. This paper presents results of mixed-culture studies employing the photosynthetic bacteriumR. rubrum for converting CO to CO₂ and H₂ by the water gas shift reaction and two methanogens,M. formicicum andM. barkeri, for converting CO₂ and H₂ into CH₄. Results are presented for triculture operation in two types of reactors, the packed bubble column and the trickle-bed reactor.     

The relaxation field for the general case of electrolyte mixtures

The relaxation field for solutions of mixed electrolytes of any type is calculated. the calculation is based on the well-known treatment due to Fuoss-Onsager with the same distance parameter for all the ions in solution. A general conductance-continuity equation has been established and an improved iterative method of calculation, using Laplace transforms, is proposed. The relaxation-field results are derived to the second iteration in the perturbation method of integration.     

The computation of the representation matrices of the generators of the unitary group

A method is presented for the efficient computation of the representation matrices of the unitary group, U(n) in the Gelfand—Tsetlin basis (corresponding to the usual spin-symmetry adapted basis for an N electron CI). The present scheme is conceptually and computationally attractive in that it is formulated directly in terms of Weyl tableaux and also that it permits simultaneous basis vector generation and matrix element evaluation. In addition the basis vectors are ordered so that subsequent restriction to the three dimensional rotation group is facilitated. An illustrative example is also presented.Taken in part from a thesis submitted to the University of London in partial fulfilment of the requirements for the degree of PhD.     

Conformation of Tax-response elements in the human T-cell leukemia virus type I promoter

Background: HTLV I Tax is believed to activate viral gene expression by binding bZIP proteins (such as CRIB) and increasing their affinities for proviral THE target sites. Each 21 by THE target site contains an imperfect copy of the intrinsically bent CRE target site (the TRE core) surrounded by highly conserved flanking sequences. These flanking sequences are essential for maximal increases in DNA affinity and transactivation, but they are not, apparently, contacted by protein. Here we employ non-denaturing gel electrophoresis to evaluate TRE conformation in the presence and absence of bZIP proteins, and to explore the role of DNA conformation in viral transactivation.Results: Our results show that the TRE-1 flanking sequences modulate the structure and modestly increase the affinity of a CREB bZIP peptide for the TRE-1 core recognition sequence. These flanking sequences are also essential for a maximal increase in stability of the CREB-DNA complex in the presence of Tax.Conclusions: The CRE-like TRE core and the TRE flanking sequences are both essential for formation of stable CRIB-TRE-1 and Tax-CREB-TRE-1 complexes. These two DNA segments may have co-evolved into a unique structure capable of recognizing Tax and a bZIP protein.     

三重四极杆电感耦合等离子体质谱(ICP-MS)法测定氧化铕中13种稀土杂质元素

稀土杂质元素直接影响高纯单金属稀土材料的整体性能,是高科技领域许多材料的重要组成部分。通过考察最佳的消解酸量、温度、时间、氧气反应气流量、稀释气流量,建立了基于三重四极杆电感耦合等离子体质谱仪(ICP-MS/MS)直接测定氧化铕中13种稀土杂质元素分析方法。该方法采用0.1%基体直接进样,可以很大程度提高前处理分析效率。利用碰撞模式测定氧化铕稀土中的Y、La、Pr、Nd、Sm、Gd、Tb、Dy、Ho、Er、Yb、Lu元素,氧气质量转移模式测定氧化铕中的Tm,两种模式结合可以有效去除多原子干扰,实现氧化铕的稳定测试分析。通过对氧化铕标准物质（GBW02902）直接测定分析,结果表明,在碰撞和氧气质量转移模式下,各元素线性相关系数（r）均大于 0.9999,方法检出限为0.001~0.023 mg/kg,测试精密度优于1.99%,13种元素的测试值都在认定值的不确定度范围之内。该分析方法操作简单,测试稳定,效率高,为实验室进行氧化铕材料中REE杂质的准确测试分析提供思路和借鉴。     

激光诱导击穿光谱(LIBS)技术在低碳钢铁冶金行业的应用

激光诱导击穿光谱技术(Laser induced breakdown spectroscopy,简称LIBS)是一种基于激光等离子体的发射光谱技术,具有样品制备简单,分析迅速,多元素同时分析,现场在线和远程分析等独特优势,已在钢铁冶金领域取得了越来越广泛的应用与发展。综述了近年来LIBS技术在钢铁冶金领域的应用研究进展,从冶金生产的全流程进行介绍,包括矿石、熔融钢水/铁水、钢铁产品及炉渣和废气分析。同时,还总结了LIBS技术在钢铁冶金领域应用的优点和缺点,并对该技术的应用前景及未来发展方向进行展望。     

蝙蝠喉部发声组织建模及发声机理*

建立蝙蝠发声组织模型对超声机理研究及在智能设备的应用具有重要意义。根据蝙蝠喉部发声组织结构特点,通过有限元方法构建了蝙蝠的3种不同发声组织模型,分析了尺寸、材料力学参数、组织结构和张力4个因素对发声组织特征频率的影响。结果表明,如果用人类声带,按比例缩小构建蝙蝠喉部组织模型,蝙蝠无法发出超声波。构建组织结构含甲状软骨和声带的半鼓状模型和只含声带的条状模型,两种模型的特征频率相近且在合理的参数域内均无法达到超声范围。而含膜条状模型的特征频率可以通过张力进行超声频率的调节,这与文献的实验结果一致。因此,可基于含膜条状模型对蝙蝠喉管发声组织进行建模及其发声机理研究。     

On the character of local electric fields in amorphous semiconductors

On the basis of the agreement of calculated and measured parameters of some amorphous semiconductors, an argument is stated in favour of the central-symmetric type of random local electric fields. A possible mechanism of the transport of electrons is discussed.     

Secure Direct Communication Using Ensembles with the Same Compressed Density Matrix

In this paper, a quantum secure direct communication protocol using ensembles with the same density matrix is proposed. The two communication parties can realize the message transmission using this method through a quantum channel, each bit of information can be transmitted using an ensemble and read out through global measurement.The eavesdropping behavior can be detected through the channel diagnoses.