The Classification of Flats in {\boldsymbol {PG}}({\bf 9,2}) which are External to the Grassmannian {\cal G}_{\bf 1,4,2}

Constructions are given of different kinds of flats in the projective space $PG(9,2)={\mathbb P}(\wedge^{2}V(5,2))$ which are external to the Grassmannian ${\cal G}_{\bf 1,4,2}$ of lines of PG(4,2). In particular it is shown that there exist precisely two GL(5,2)-orbits of external 4-flats, each with stabilizer group ?31:5. (No 5-flat is external.) For each k=1,2,3, two distinct kinds of external k-flats are simply constructed out of certain partial spreads in PG(4,2) of size k+2. A third kind of external plane, with stabilizer ?2³:(7:3), is also shown to exist. With the aid of a certain ‘key counting lemma’, it is proved that the foregoing amounts to a complete classification of external flats.     

Agropine,a new amino acid derivative from crown gall tumours

Agropine, an unusual compound produced in plant tumours was shown by mass spectrometry and proton and carbon-13 nmr spectroscopy to be a bicyclic derivative of glutamic acid and a hexitol sugar.     

Magnetic susceptibility measurements of dilute MgEu alloys

Magnetic susceptibility measurements of strain-free dilute alloys of Eu in Mg indicate that the Eu is predominantly divalent with ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ ground state. The analysis indicates no solid solubility of Eu in Mg.     

X-ray laser gain from Bragg reflection in relativistic electronbeam channel radiation systems

The application of distributed feedback by Bragg reflections in electron-beam channeling X-ray lasers is investigated. Expressions for low-threshold gain are derived for this cavity mirror structure in single crystals and are shown to have possible application in reducing beam high-current requirements by many orders of magnitude     

Investigation of the saturation properties of gyroamplifiers

The saturation properties of a TE_0n gyroamplifier are investigated using a particle-in-cell numerical code. The effect of beam velocity spread is analyzed. It is found that for velocity spread of up to 5%, the reduction in efficiency can be compensated by extending the interaction length. A numerical optimization of efficiency enhancement using a tapered magnetic field was demonstrated. A change in the saturation mechanism from phase trapping to thermalization using the suggested tapering was observed     

The intersection of a matroid and a simplicial complex

A classical theorem of Edmonds provides a min-max formula relating the maximal size of a set in the intersection of two matroids to a ``covering" parameter. We generalize this theorem, replacing one of the matroids by a general simplicial complex. One application is a solution of the case of a matroidal version of Ryser's conjecture. Another is an upper bound on the minimal number of sets belonging to the intersection of two matroids, needed to cover their common ground set. This, in turn, is used to derive a weakened version of a conjecture of Rota. Bounds are also found on the dual parameter--the maximal number of disjoint sets, all spanning in each of two given matroids. We study in detail the case in which the complex is the complex of independent sets of a graph, and prove generalizations of known results on ``independent systems of representatives" (which are the special case in which the matroid is a partition matroid). In particular, we define a notion of -matroidal colorability of a graph, and prove a fractional version of a conjecture, that every graph is -matroidally colorable.

The methods used are mostly topological.

     

可编程芯片：拼合成一个模拟解决方案

可配置模拟IC已经出现了多年,表面看来对市场的影响不及其数字同胞FPGA（现场可编程门阵列）。不过,当前的经济形势却使可编程模拟标准产品的概念突然显现出吸引力。一些需求能很好地适合这些器件的优点：保持在某个产品领域的设计前沿,不花费很多的设计成本,并且不存在会影响任何一个设计进入量产的最终用户需求。这样的日子可能为时不远了。     

A globally linearly convergent method for pointwise quadratically supportable convex–concave saddle point problems

We study the Proximal Alternating Predictor–Corrector (PAPC) algorithm introduced recently by Drori, Sabach and Teboulle [8] to solve nonsmooth structured convex–concave saddle point problems consisting of the sum of a smooth convex function, a finite collection of nonsmooth convex functions and bilinear terms. We introduce the notion of pointwise quadratic supportability, which is a relaxation of a standard strong convexity assumption and allows us to show that the primal sequence is R-linearly convergent to an optimal solution and the primal-dual sequence is globally Q-linearly convergent. We illustrate the proposed method on total variation denoising problems and on locally adaptive estimation in signal/image deconvolution and denoising with multiresolution statistical constraints.