Synthesis of arborescent (Dendritic) polystyrenes via controlled inimer‐type reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene and 4‐vinylbenzyl dithiobenzoate, a RAFT‐based inimer (initiator‐monomer), is described. Controlled polymerization was achieved in bulk conditions using thermal initiation at 110 °C to give arborescent polystyrene (arbPSt). The number‐average molecular weights of the polymers increased linearly with conversion and were much higher than theoretically calculated for a linear polymerization, reaching M_n = 364,000 g/mol with M_w/M_n = 2.65. Branching analysis by NMR showed an average of 3.5 branches per chain. SEC data, which were similar to those measured in arborescent polyisobutylene, supported the architectural analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7621–7627, 2008     

Large Cyclodextrins

The existence of large cyclodextrins, cyclic -D-(1 4) glucans with a degree of polymerisation higher than eight, has been proven during the past decade. A number of 4- -glucanotransferases have been shown to be able to produce large cyclodextrins consisting of up to several hundred glycosyl units, from both amylose and amylopectin. Large cyclodextrins with degree of polymerisation up to 31 have been isolated to purity by use of elaborate purification schemes, enabling studies of their structural and complex forming properties. The solid state structures of the large cyclodextrins with a degree of polymerisation 10, 14 and 26, respectively, have revealed interesting new structural features of this family of molecules. This review summarises the studies of the large cyclodextrins, a varied and highly interesting group of molecules.     

The effect of short chain branching on the rheological and thermal properties of olefin: α-olefin copolymers

An important method of the modification of the properties of polyethylene and polypropylene is the copolymerisation with -olefins. The -olefin behaves as a short branch in the structure, and the rheological and thermal properties of copolymers change significantly. A new method is suggested to evaluate the rheological and thermal properties of copolymers on the basis of homopolymer properties, by introducing a short branch degree parameter. The zero shear viscosity, plateau modulus, fractional free volume, reptation tube diameter, glass transition temperature and thermodynamical melting point were calculated.     

Some Long-Range Dependence Processes Arising from Fluctuations of Particle Systems

Several long-range dependence, self-similar Gaussian processes arise from asymptotics of some classes of spatially distributed particle systems and superprocesses. The simplest examples are fractional Brownian motion and sub-fractional fractional Brownian motion, the latter being intermediate between Brownian motion and fractional Brownian motion. In this paper we focus mainly on long-range dependence processes that arise from occupation time fluctuations of immigration particle systems with or without branching, and we study their properties. Some long-range dependence non-Gaussian processes that appear in a similar way are also mentioned. Mathematics Subject Classifications (2000) Primary 60G15, 60G18; secondary 60F17, 60G20, 60J80.Research partially supported by CONACyT grant 37130-E (Mexico).     

用微扰QCD方法研究B(s)→Φρ衰变

用微扰QCD对B(s)→Φρ衰变进行了研究,考虑了因子化和非因子化图的贡献,得出了B(s)→Φρ衰变的分支比以及纵向极化衰变、横向极化衰变之比,所得到的结果与现在的实验数据吻合.     

用微扰QCD方法研究B（s） →Фρ 衰变

用微扰QCD对B（s） →Фρ 衰变进行了研究，考虑了因子化和非因子化图的贡献，得出了B（s） →Фρ 衰变的分支比以及纵向极化衰变、横向极化衰变之比，所得到的结果与现在的实验数据吻合．     

Study of semileptonic decays Bs→Ds1(2536)l(v) and Bs→Ds2(2573)l(v) in the CQM model

Based on the assumption that Ds1 (2536) and Ds2 (2573) belong to T doublet (1+,2+),we calculate the semileptonic decays of Bs to Ds1(2536) and Ds2(2573) in terms of the Constituent Quark Meson (CQM)model.For Bs→Ds1(2536)+l(v) and Bs→Ds2(2573)+l(v),the order of magnitude of the obtained branching ratios is 10-3.Our numerical results of the semileptonic decays of Bs to Ds1(2536) and Ds2(2573) are large,which implies that two semileptonic decays should be seen in future experiments.     

Electron impact excitation of high-lying states in the tungsten atom

The extended crossed-beam method has been used to study excitation of high-lying levels in the tungsten atom. 40 excitation cross sections of WI spectral lines have been measured for exciting electron energy 50 eV. Two optical excitation functions were recorded in the electron energy range 0–200 eV. The results obtained were used to calculate the total excitation cross sections of 24 odd WI energy levels. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 283–288, May–June, 2007.     

超--α对称稳定过程的局部灭绝性

考虑初始测度为Ｌｅｂｅｓｇｕｅ测度μ的超α－对称稳定（记为α－ＳＳ）过程,其分枝特征为ψ（ｘ,ｚ）＝－γ（ｘ）ｚ＾１＋β（０〈β≤１）。本文研究这类超过程的局部灭绝性。运用纯分析的方法我们首先得到了局部灭绝的一个充分条件,借助这一条件,对较特殊的γ（ｘ）＝（１＋│ｘ│）＾θ（θ〈βｄ）,证明了与之联系的超α－ＳＳ过程存在局部灭绝的临界值θ＾＊,同时给出它的一个上界βｄ－α。若γ（ｘ）≡１,这意味着     

Occupation Time Fluctuations in Branching Systems

We consider particle systems in locally compact Abelian groups with particles moving according to a process with symmetric stationary independent increments and undergoing one and two levels of critical branching. We obtain long time fluctuation limits for the occupation time process of the one- and two-level systems. We give complete results for the case of finite variance branching, where the fluctuation limits are Gaussian random fields, and partial results for an example of infinite variance branching, where the fluctuation limits are stable random fields. The asymptotics of the occupation time fluctuations are determined by the Green potential operator G of the individual particle motion and its powers G ²,G ³, and by the growth as t of the operator and its powers, where T _t is the semigroup of the motion. The results are illustrated with two examples of motions: the symmetric -stable Lévy process in , and the so called c-hierarchical random walk in the hierarchical group of order N (0<c<N). We show that the two motions have analogous asymptotics of G _t and its powers that depend on an order parameter for their transience/recurrence behavior. This parameter is =d/–1 for the -stable motion, and =log c/log(N/c) for the c-hierarchical random walk. As a consequence of these analogies, the asymptotics of the occupation time fluctuations of the corresponding branching particle systems are also analogous. In the case of the c-hierarchical random walk, however, the growth of G _t and its powers is modulated by oscillations on a logarithmic time scale.