Elimination reactions of 1,2-dihalo-2,3,3-trifluorocyclobutanes

Elimination reactions on isomeric mixtures of $\text{cis}$ and $\text{trans}$ 1,2-dihalo-2,3,3-trifluorocyclobutanes are reported. In zinc-promoted dehalogenations a steady decrease in the relative amount of the $\text{trans}$ isomers compared to the $\text{cis}$ isomers occured, with 2,3,3-trifluorocyclobutene as the sole product. The $\text{cis}$ isomers reacted at a faster rate in potassium hydroxide induced eliminations to yield a slight predominance of 1-halo-2,3,3-trifluorocyclobutenes over 3-halo-3,4,4-trifluorocyclobutenes. However, with triethylamine as the inducing base, an increased rate of elimination from the $\text{trans}$ isomers was noted along with almost exclusive formation of 3-halo-3,4,4-trifluorocyclobutenes.     

A. C. conductivity due to intimate pairs of charged defect centres

The influence of the association of charged defects into intimate pairs on a.c. conduction is discussed in the light of the fundamental mechanism being that of the simultaneous hopping of two electrons over the barrier separating two oppositely charged defect centres, the barrier height being correlated with the intersite separation via the Coulomb interaction. The behaviour of chalcogenide glasses is discussed in terms of the present theory, and it is concluded that the existence of two classes of a.c. conductivity behaviour into which these materials generally fall can be simply explained by the predominance of either intimate pairs or non-intimate pairs of charged defect states according to the conditions of preparation.     

坡面流运动方程和有支流入汇时的一维明渠流方程形式

从带源项的圣维南方程出发,根据坡面流特点,分析给出了坡面水流运动方程的基本形式,通过基本的力学分析,指出了通常应用于有支流放汇时的一维明渠流方程存在的问题,并得到了新的方程形式。     

自然弯扭梁广义翘曲坐标的求解

提出了自然弯扭梁受复杂载荷作用时静力分析的一种理论方法,重点在于对控制方程的求解,其中考虑了与扭转有关的翘曲变形和横向剪切变形的影响．在特殊的情况下,可以比较容易地得到这些方程的解答,包括各种内力、应力、应变和位移的计算．算例给出了平面曲梁受水平和垂直分布载荷作用时广义翘曲坐标的求解方法．计算结果表明,求得的应力和位移的理论值和三维有限元结果非常接近．此外,该理论不限于具有双对称横截面的自然弯扭梁,同样可推广至具有一般横截面形状的情况．     

Modelling the impact of dam failure scenarios on flood inundation using SPH

Flooding resulting from collapse of a dam is a highly destructive event. It is important to accurately predict the flow behaviour so that potential mitigation strategies can be investigated for disaster management planning. The meshless SPH method has previously been able to model this class of extreme flow events. In this paper, we extend the method to include modelling of dam wall fragments. Collisions between dam wall fragments, between fragments and terrain and full two-way coupling between fragments and the free surface water flow is included. This gives a method that can specifically investigate the impact of the dam wall failure scenario on the subsequent inundation. The historical St. Francis dam failure is used to demonstrate the impact of including the dam fragments. It also provides a means of quantitatively investigating their effect in terms of arrival time and water height at a downstream power station. The scenario with multiple independently timed failures of different parts of the wall (which closely matches the historical failure) gives excellent agreement with the observed data and gives the best match of all failure scenarios. Traditionally such modelling is performed by solving the two dimensional shallow water equations which is not able to capture the three dimensional nature of the flow in earlier stages of dam flooding. We specifically investigate the three dimensional nature of flow structures and formation of multiple downstream hydraulic jumps. These strongly influence water height and therefore control the extent of flooding of tributary valleys.     

In vitro inhibition of protein glycation and advanced glycation end products formation by hydroethanolic extract and two fractions of Simaba trichilioides roots

Abstract

Long-term hyperglycemia maintenance is responsible for increased protein glycation and formation of advanced glycation end products (AGEs), both are associated with the onset of diabetes mellitus complications. Efforts have been made to discover new agents having antiglycation potential. The aim of this study was to investigate the effects of the hydroethanolic extract and the ethyl acetate and methanolic fractions of Simaba trichilioides roots on the formation of AGEs. In an in vitro model system of protein glycation, incubations with hydroethanolic extract, ethyl acetate or methanolic fractions of S. trichilioides decreased the fluorescent AGEs, and markers of tyrosine and tryptophan oxidation. Protein crosslinking was reduced in the presence of the ethyl acetate fraction of S. trichilioides. Simaba trichilioides roots seem to be a promising source of compounds having ability to prevent glycoxidation changes, with potential applications in complementary therapies for management of diabetic complications.     

Synthesis of micron-scale gold nanochains by a modified citrate reduction method

Gold nanochains ranged from several hundred nanometers to more than 5 μm were synthesized by a modified citrate reduction method. The synthesized nanochains have been characterized by TEM, AFM and UV absorption spectrum. The produced nanochains can be transferred onto the mica surface, and can bear the repeating scan by AFM tip, which may have some potential applications in electronics and catalysis.     

Numerical solution of the St. Venant equations with the MacCormack finite-difference scheme

This paper describes the use of the MacCormack explicit time-spilitting scheme in the development of a two-dimensional (in plan) hydraulic simulation model that solves the St. Venant equations. Various tests devised to assess the performance of the method have been performed and the results are reported. Finally, two industrial applications of the model are presented. The method has been found to be computationally efficient and warrants further development.     

Bundles and foils of WS2 nanotubes

In this paper, the synthesis of multigram portions of WS₂ nanotubes and large foils consisting of aligned nanotubes is described. For this purpose, a fluidized bed reactor, in which WO₃ powder is fed from the top and the reaction gases are blown from below maintaining the powder aloft, is described. The reaction mechanism is briefly discussed. Received: 20 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002