Growth of thin Si oxide in a cyclic oxygen plasma environment below 200 °C

The growth of Si oxide by means of a cyclic radio-frequency (rf) plasma oxidation process has been explored in a low temperature range of 100-200 °C. The growth mechanism exhibits Cabrera-Mott (CM) oxidation, that is, the transport of mobile ionic species is assisted by an electric field. The low activation energy of 0.3 eV is attributed to the small size of O⁻ and the assistance of the electric field. The oxide becomes off-stoichiometric as one approaches to the exterior surface of the oxide layer.     

Quasi‐random graphs with given degree sequences

It is now known that many properties of the objects in certain combinatorial structures are equivalent, in the sense that any object possessing any of the properties must of necessity possess them all. These properties, termed quasirandom, have been described for a variety of structures such as graphs, hypergraphs, tournaments, Boolean functions, and subsets of Z _n, and most recently, sparse graphs. In this article, we extend these ideas to the more complex case of graphs which have a given degree sequence. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008     

Multiboson Realization of Two-Mode q-Boson Algebra with suq (2) Covariance

The multiboson realization of two-mode q-boson algebra with su _q (2) covarianceis constructed. A new quantum deformation of su(2) algebra is presented by useof this realization.     

Effects of chain length distribution on viscoelastic properties of entangled linear polymers: Blending laws for binary blends

The reptation idea of de Gennes and the tube model theory of Doi and Edwards are extended to explain the terminal viscoelastic properties of binary blends in the highly entangled state of two linear monodisperse polymers with different molecular weights M₁ and M₂. A modified tube model is proposed that considers the significance of the constraint release by local tube renewal in accounting for the relaxation process of the higher molecular weight chain. Its relaxation by both reptation and the constraint release is remodeled as the disengagement by pure reptation of an equivalent primitive chain. From knowledge of the longest relaxation times of the blend components, the stress equation is formulated from which blending laws of viscoelastic properties for the binary blends are derived. To force better agreement between theory and experiment at the pure monodisperse limits of the blends, a crude treatment to include the effect of contour-length fluctuation in the equivalent-chain model is also discussed. Theoretical predictions of the zero-shear viscosity and steady-state shear compliance are shown to be in good agreement with literature data on undiluted polystyrenes and polybutadienes over a wide range of the blend composition and M₂/M₁ ratio. The asymptotic of the laws for blends with M₂/M₁ → 1 and 0 are comparable to those from the relaxation spectrum proposed by others earlier on the basis of the tube model.     

Benders decomposition for a class of variational inequalities

This paper examines Benders decomposition for a useful class of variational inequality (VI) problems that can model, e.g., economic equilibrium, games or traffic equilibrium. The dual of the given VI is defined. Benders decomposition of the original VI is derived by applying a Dantzig–Wolfe decomposition procedure to the dual of the given VI, and converting the dual forms of the Dantzig–Wolfe master and subproblems to their primal forms. The master problem VI includes a new cut at each iteration, with information from the latest subproblem VI, which is solved by fixing the “difficult” variables at values determined by the previous master problem. A scalar parameter called the convergence gap is calculated at each iteration; a negative value is equivalent to the algorithm making progress in that the last master problem solution is made infeasible by the new cut. Under mild conditions, the convergence gap approaches zero in the limit of many iterations. With a more restrictive condition that still admits many useful models, a zero value of the convergence gap implies that the master problem has found a solution of the VI. A small model of competitive equilibrium of three commodities in two regions serves as an illustration.     

Synthesis of diblock copolymers containing both polydiene and polyalcohol blocks

A wide range of functional diblock copolymers containing both functional polymer and hydrocarbon polymer, have been prepared by the combination of anionic polymerization and borane chemistry. The distinctive hydroboration reactivity between various polydienes enables us to selectively functionalize one polydiene segment in diblock copolymers which contain two different polydiene segments. In turn, the hydroborated polymers are valuable intermediate compounds which can be converted to a whole family of functional polymers with a variety of other functionalities under mild reaction conditions. The hydroxylated diblock copolymer is used as an example to demonstrate the chemistry. The two-phase nature of these copolymers is also shown by the observation of two distinctive glass transition temperatures associated with the individual polymer segments.     

Non‐Alkaloidal Constituents from the Stem of Ficus Septica

Seven triterpenes, two lignans, and twelve other known compounds were isolated from the non‐alkaloidal fractions of the stem of Ficus septica Among these triterpenoids, a rare triterpene skeleton derivative, 13,27‐cycloursan‐3β‐ylacetate was isolated from natural sources for the first time. All the structures of these compounds were elucidated by spectroscopic methods.     

SYNTHESIS AND CHARACTERIZATION OF NOVEL REACTIVE POLYORGANOSILOXANE CONTAINING NITRO GROUPS*

 A novel reactive polyorganosiloxane containing nitro groups was first prepared by acid-catalyzed equilibration polymerization. The monomer, 3-(4-nitrophenoxy)propylmethyldichlorosilane (NPPMS), was synthesized by hydrosilylation reaction with dicyclopentadienylplatinum(II) chloride (Cp₂PtC1₂) catalyst in high yield. The synthesized polynitroorganosiloxane, which has potential application as a precursor for synthesizing advanced functional polymers, was characterized by FTIR, ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR, vapor pressure osmometry (VPO) and gel permeation chromatography (GPC).