Krichever-Novikov-like bases on punctured Riemann surfaces

Bases of holomorphic -differentials on N-punctured Riemann surfaces of arbitrary genus are constructed. The resulting extension of the Virasoro algebra on N-punctured spheres is displayed explicitly.     

Influence of end reflectivity on gain saturation in a planar distributed feedback laser

An approximate method for the analysis of planar-waveguide distributed-feedback lasers is extended to include a nonvanishing reflectivity at the ends of the structure. An index grating structure with parasitic losses is investigated. An expression for the small-signal gain coefficient ^0MN as a function of the output power P ^MNout normalized to the saturation power P ^s , coupling coefficient K, complex reflectivity R of end reflectors, and waveguide parameters is presented.     

Frequency stability of an optically pumped cesium beam frequency standard

Results obtained in an experimental optically pumped cesium beam frequency standard in which a single semiconductor laser is used for the state selection and the atom detection are reported. The separation between the two interaction regions is equal to 21 cm. This gives a 500 Hz linewidth which is observed with a signal to noise ratio equal to 10,000 in a 1 Hz noise bandwidth. A quartz crystal oscillator is frequency controlled by the atomic transition. The measured short term frequency stability is given by _y()=2×10^–12–1/2 for 1 s<500 s. Prospects for improvement of this frequency stability are discussed.     

XeF和KrF的热催化合成及KrF在含氟高能氧化剂NFBF合成中的应用

本文介绍了一种以氟气和惰性气体为原料合成 Kr F2 和 Xe F2 的热催化合成方法并对合成机理和条件作了简单的讨论 ,利用合成的 Kr F2 作为氟化剂合成了含氟高能氧化剂 NF4BF4,纯度约为 93%,其红外光谱和拉曼光谱基本与文献值吻合。元素分析结果表明产品 NF4BF4中含 B5.8%(mass) ,自由氟原子含量为 9.95%(mass) ,与理论值基本一致 ,此结果也间接证明了 Kr F2 质量的可靠性。粉末状的 Xe F2 经升华 -再结晶纯化后可得纯净晶体产品。     

冬凌草中的新对映-贝壳杉烷二萜化合物

对河南省济源地区产冬凌草[Isodon rubescens(Hemsl.)Hara]再次进行了深入 的研究，从其叶的乙酸乙酯提取物中分离得到了16个化合物，其中1和2为两个新的 7，20-环氧-对映-贝壳杉烷类二萜化合物，其结构通过波谱分析确定为16（S）-羟 甲基-1α，6β，7β，11β-甲羟基-7α，20-环氧-对映-贝壳杉烷-15-酮（1）和 16（R）-羟甲基-1α，6β，7β，14β-四羟基-7α，20-环氧-对映-贝壳杉烷-15- 酮（2），分别命名为冬凌草已素（1）和庚素（2）；其余的已知化合物分别鉴定 为lasiodonin（3），冬凌草甲素（oridonin，4），乙素（ponicidin），丙素（ rubescensin C），丁素（rubescensin D），牛尾草丙素（rabdoternin C），荛 花香茶菜乙素（wikstroemioidin B），enmenol-1α-O-β-D-glucoside， enmenol，胡麻素（pedalitin），水杨酸，乌索酸，β-谷甾醇和胡萝卜甙。     

On copowers of an ordered skew field

It is shown that the double of an ordered skew fieldE over a subfieldK, which is its own bicentralizer, can again be ordered, and a corresponding result for groups is deduced.     

Comparison of Boolean algebras

In this work, some results related to superatomic Boolean interval algebras are presented, and proved in a topological way. Let x be an uncountable cardinal. To each I F00337890_TeX2GIFIE1.gif" alt=" $$ \subseteq$$ " align="middle" border="0"> x, we can associate a superatomic interval Boolean algebra B _I of cardinality x in such a way that the following properties are equivalent: (i) I F00337890_TeX2GIFIE2.gif" alt=" $$ \subseteq$$ " align="middle" border="0"> I F00337890_TeX2GIFIE3.gif" alt=" $$ \subseteq$$ " align="middle" border="0"> x, (ii) B _I is a quotient algebra of B _J, and (iii) there is an homomorphism f from B _J into B _I such that for every atom b of B _I, there is an atom a of B _J satisfying f(a)=b. As a corollary, there are 2 ^x isomorphism types of superatomic interval Boolean algebras of cardinality x. This case is quite different from the countable one.     

On the periodic points of a two-parameter family of maps of the plane

We study the dynamics of a two-parameter family of noninvertible maps of the plane, derived from a model in population dynamics. We prove that, as one parameter varies with the other held fixed, the nonwandering set changes from the empty set to an unstable Cantor set on which the map is topologically equivalent to the shift endomorphism on two symbols. With the help of some numerical work, we trace the genealogies of the periodic points of the family of period 5, and describe their stability types and bifurcations. Among our results we find that the family has a fixed point which undergoes fold, flip and Hopf bifurcations, and that certain families of period five points are interconnected through a codimension-two cusp bifurcation.     

Why is space three-dimensional and how may groups be seen?

First we propose a model of visual perception essentially based on the Keldysh-Chernavsky-Sossinsky three-channel theorem, from which three-dimensionality of space follows. Second, we associate with a system of subgroups H ₁, ..., H_s of a given group G a geometric object, called a group crystal, in order to visualize G. How this notion works is illustrated via the Burnside problem.