Triterpenoids and Some Other Constituents from Spiraea Formosana

The ethanol extract of the stems of Spiraea formosana has been shown to contain triterpenes: friedelin (II), glutinol (III). β-amyrin (IV); 10-nonacosanol (I) and a mixture of sitosterol and campesterol. They were identified by chemical reactions, spectral data and compared with authentic samples (except 10-nonacosanol).     

Contention-Based Airtime Usage Control in Multirate IEEE 802.11 Wireless LANs

In a multirate wireless LAN, wireless/mobile stations usually adapt their transmission rates to the channel condition. It is difficult to control each station's usage of network resources since the shared channel can be overused by low transmission-rate stations. To solve this problem, we propose a distributed control of stations' airtime usage which 1) always guarantees each station to receive a specified share of airtime, and 2) keeps service for individual stations unaffected by other stations' transmission rates. Such airtime control enables service differentiation or quality of service (QoS) support. Moreover, it can achieve a higher overall system throughput. The proposed airtime usage control exploits the Enhanced Distributed Channel Access (EDCA) of the IEEE 802.11e standard . Two control mechanisms are proposed: one based on controlling the station's arbitration inter-frame space (AIFS) and the other based on the contention window size. We show how the stations' airtime usage is related to the AIFS and contention window size parameters. Using this relation, two analytical models are developed to determine the optimal control parameters. Unlike the other heuristic controls or analytical models, our model provides handles or parameters for quantitative control of stations' airtime usage. Our evaluation results show that a precise airtime usage control can be achieved in a multirate wireless LAN     

A novel synthesis of 1,2-diphosphorylbenzenes

Synthesis of phosphorylchloroacetylenes, diphosphorylacetylenes and the Diels-Alder reactions of the latter to produce $\text{o}$-diphosphorylbenzenes are described.     

Diagnosis of single faults in bitonic sorters

Bitonic sorters have recently been proposed to construct along with banyan networks the switching fabric of future broadband networks. Unfortunately, a single fault in a bitonic sorter may have disastrous consequences for the switching system. Therefore, a bitonic sorter must be proved to be free of faults before it can be used. We study the topological properties of bitonic sorters and present an efficient fault diagnosis procedure to detect, locate, and identify the fault type of single faults. Our diagnosis procedure can detect most single faults in two tests. Faults which cannot be detected in two tests can always be detected in four tests. Several binary search techniques are developed to locate a faulty sorting element (i.e. a 2×2 sorter)     

Plasma damage and photo-annealing effects of thin gate oxides andoxynitrides during O2 plasma exposure

Plasma-induced damage effects of oxides and oxynitrides are studied using metal-oxide-semiconductor (MOS) test capacitors in an O ₂ plasma environment inside a capacitive-coupled parallel plate RF etcher. Damage to both covered and sidewall-exposed samples are compared. As expected, it was found that as the exposure time was increased, more damage to the oxide was observed. Furthermore, N₂ O-samples showed better immunity to O₂-plasma damage than the thermally grown O₂ samples during O₂ plasma exposure. However, the edge-intensive sidewall-exposed structures showed surprisingly less damage than the fully covered structures after a fixed plasma exposure time. This reduced damage effect for the sidewall-exposed structures is believed to be due to an in situ annealing as the result of the photoelectron injection by low-energy UV light interacting with the substrate. The in situ annealing does not occur in the fully covered structure since the low-energy UV light is blocked by the thick polysilicon gate. The results indicate that plasma damage evaluation using fully covered capacitors alone cannot be used to predict the actual damage in CMOS integrated circuits where there are almost always exposed thin oxide structures     

Convergence of the control parameterization Ritz method for nonlinear optimal control problems

This paper studies the local convergence properties of the control parameterization Ritz method in which the control variable is approximated over a finite-dimensional subspace. The nonlinear free-endpoint optimal control problem is considered, and error bounds are derived for both the cost functional and state-control convergence. Explicit error bounds are obtained for the particular case of approximations over spline spaces. On specializing the general results to the linear-quadratic regulator problem, global convergence results are obtained. Computational results supporting the theoretically derived error bounds are presented.This research was supported by the University Grants Committee of New Zealand.