Amending cultures of selenium-resistant bacteria with dimethyl selenone

A possible biological intermediate in the reduction and methylation of selenium oxyanions, dimethyl selenone, was synthesized, and the first experiments involving the amendment of selenium resistant bacterial cultures with this compound are reported. The amount of volatile, reduced selenium-containing species released from these cultures into the headspace is significantly more than that produced in analogous experiments involving sodium selenate amended cultures. Dimethyl selenone is reduced in the presence of dimethyl sulfide and dimethyl disulfide in a complex growth medium, trypticase soy broth with 0.1% nitrate. This reduction occurs whether or not the reduced sulfur compounds are biologically produced.     

Sums of Two Exact Powers

An asymptotic formula is obtained for the number of representations of an element of a finite field as a weighted sum of two prescribed powers of primitive elements. This generalises previous work on sums of primitive elements, including that relating to some conjectures of Golomb.     

Thermoelectric properties of tin clathrates under hydrostatic pressure

We report the temperature dependence of electrical resistance (R) and thermopower (S) of clathrate Cs₈Sn₄₄ under high pressure up to 1.2 GPa. We observe a reversible gap widening, prominent relaxation effect of R, irreversible increase of |S| under high pressure. We also find that the power factor S²σ (σ: electrical conductivity) reaches a maximum at pressure of 0.3 GPa. Comparison of the experimental results with band structure calculations suggests that the intrinsic vacancy in the clathrate structure of Cs₈Sn₄₄ plays an important role in transport properties under high pressure. Measurements on Cs₈Zn₄Sn₄₂, a clathrate which has defects other than vacancies, are compared with Cs₈Sn₄₄. The results indicate that replacing Sn by Zn has similar effect as the intrinsic vacancy on S.     

EXISTENCE AND UNIQUENESS OF LIMIT CYCLE FOR A CLASS OF (2n+1)TH ORDER DIFFERENTIAL SYSTEM

In this paper we consider the problem ofllrmt cycles for thefollowing system【&一y＋6x＋a旷＋a。xy＋a。xy‘＋6xv‘”,(门)!i二 X( 一 by)．Ssstem(1)with k二 b二 0 was studiedin P叩er[1];Ifk 4 0 by transformation:y三 x;V二告;d,二 kdt,system(1)。二。can be trmslated Into the form studiedIn p。per IZ]三 System(1)With口1二 k二 0 W。S Studied ill paper k3]．Ifi System(1;SllPPOSe th。t:(1 ＞2 Is。11 lllteger,k / 0*d 6 / oi(2)。1。2 ＋。5 2 0,this assumption Is the same as that In paper[1];(3)w…     

泛连通图定理和Ore2条件

记Ore2=min{d(y) d(x)|x,y∈V(G),d(x,y)=2}，本得到：若n阶图G的Ore2≥n 1，则G是[5;n]泛连通图。此是比Faudree等人的定理进一步的结果。     

聚乙炔的CH面外振动红外光谱研究

采用从头计算方法，计算了反式和顺式聚乙炔的氢原子在垂直于聚乙炔分子面方向振动的红外光谱，计算表明，Gibson等用红外吸收实验所测得的谱线的确是聚乙炔的CH面外振动产生的谱线，经100℃长时间加热后，顺式聚乙炔变为反式聚炔，但波数为740cm^-1的谱级仍保留5％的强度。     

Backlund transformation and variable separation solutions for the generalized Nozhnik—Novikov—Veselov equation

Using the extended homogeneous balance method, the B?cklund transformation for a (2+1)-dimensional integrable model, the generalized Nizhnik－Novikov－Veselov (GNNV) equation, is first obtained. Also, making use of the B?cklund transformation, the GNNV equation is changed into three equations: linear, bilinear and trilinear form equations. Starting from these three equations, a rather general variable separation solution of the model is constructed. The abundant localized coherent structures of the model can be induced by the entrance of two variable-separated arbitrary functions.     

Use of a long-spacer-side-chain liquid crystalline polysiloxane containing a crown ether as a stationary phase for capillary gas chromatography

A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain.     

受激喇曼散射在掺铒光纤放大器中的影响

本文在分析了均匀掺杂分布式光纤放大器（d－EDFA）的基础上，提出了沿传输方向掺杂浓度单调下降（单变），和降升结合（两变）的两种渐变型分布式光纤放大器，并用传输方程研究了透明传输和最佳掺杂浓度下，受激喇曼散射对均匀、单变和两变型三种d－EDFA的各种特性的影响．