Statistical synchronization among participants in real-time multimedia conferencing

In this paper, an algorithm to determine the set of packets generated continuously and periodically from different participants that are arriving at a node either for mixing at the master of a conference, or for simply playing back at a regular participant of a conference, is proposed. The essence of the algorithm is to estimate the expected packet arrival time (or reference time) for each participant. With the reference time at hand, the maximum jitter and the optimum waiting time for a mixer to wait packets from all participants can be determined. An enhancement to improve synchronization which deals with the estimation of the time offsets between the individual periods of the sources and the period of the receiver is also presented. The error of the proposed algorithm is enumerated by the Chernoff bound and demonstrated by simulation and is shown to be acceptable in practical application. The algorithm can also be employed when traffic sources operate with different periods.     

A modified flow enforcement technique for ATM networks

In ATM networks the requirement of providing the negotiated Quality of Service (QOS) needs an efficient flow enforcement technique that will result in preventive congestion control. A very effective technique is the Exponentially Weighted Moving Average (EWMA) method. In this paper, we have suggested improvements to the EWMA and call it the Enhanced EWMA (EEWMA). Simulation results show that the EEWMA is consistently better than the EWMA in most of the situations. We present comparisons of cell loss under various conditions. No theoretical analysis is presented.     

Novel thermally and mechanically stable hydrogel for enzyme immobilization of penicillin G acylase via covalent technique

κ‐Carrageenan hydrogel crosslinked with protonated polyethyleneimine (PEI⁺) and glutaraldehyde (GA) was prepared and evaluated as a novel biocatalytic support for covalent immobilization of penicillin G acylase (PGA). The method of modification of the carrageenan biopolymer is clearly illustrated using a schematic diagram and was verified by FTIR, elemental analysis, DSC, and INSTRON using the compression mode. Results showed that the gels' mechanical strength was greatly enhanced from 3.9 kg/cm² to 16.8 kg/cm² with an outstanding improvement in the gels thermal stability. It was proven that, the control gels were completely dissolved at 35°C, whereas the modified gels remained intact at 90°C. The DSC thermogram revealed a shift in the endothermic band of water from 62 to 93°C showing more gel‐crosslinking. FTIR revealed the presence of the new functionality, aldehydic carbonyl group, at 1710 cm^?1 for covalent PGA immobilization. PGA was successfully immobilized as a model industrial enzyme retaining 71% of its activity. The enzyme loading increased from 2.2 U/g (control gel) to 10 U/g using the covalent technique. The operational stability showed no loss of activity after 20 cycles. The present support could be a good candidate for the immobilization of industrial enzymes rich in amino groups, especially the thermophilic ones. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High-performance polymer alloys of polybenzoxazine and bismaleimide

Two series of high-performance polymer alloys were prepared by mixing typical benzoxine monomers, 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (P-a) or 6,6-(1-methylethyliden)-bis-(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine) (B-a), with a typical bismaleimide, 4,4-bismaleimidodiphenyl methane by various ratios followed by thermal treatment up to 240 °C. DSC and IR of the alloys were examined to follow the curing reaction. These analyses showed that the obtained polymer alloys are AB co-cross-linked polymer networks through the formation of ether linkage between the hydroxyl group of polybenoxazine and the double bond of bismaleimide. Viscoelastic analysis and softening temperature measurement revealed that the polymer alloys have much higher glass transition temperatures than those of each homopolymer. The thermal stability also increased with the increase of bismaleimide content as evidenced by TGA.     

A sensing strategy for the reverse engineering of machined parts

The reverse engineering of machined parts requires sensing an existing part and producing a design (and perhaps a manufacturing process) for it. We have developed a reverse engineering system that has proven effective with a set of machined parts. This paper describes the system, presents some results, and discusses strategy for a new system.This work was supported by ARPA under ARO grant number DAAH04-93-G-0420, DARPA grant N00014-91-J-4123, NSF grant CDA 9024721, and a University of Utah Research Committee grant. All opinions, findings, conclusions or recommendations expressed in this document are those of the authors and do not necessarily reflect the views of the sponsoring agencies.     

An accelerated algorithm for full band electron–phonon scattering rate computation

Computing scattering rates of electrons and phonons stands at the core of studies of electron transport properties. In the high field regime, the interactions between all electron bands with all phonon bands need to be considered. This full band interaction implies a huge computational burden in calculating scattering rates. In this study, a new accelerated algorithm is presented for this task, which speeds up the computation by two orders of magnitude (100 times) and dramatically simplifies the coding. At the same time, it visually demonstrates the physical process of scattering more clearly.     

Bandwidth Adaptive Cache Coherence Optimizations for Chip Multiprocessors

Chip Multiprocessors (CMPs) have different technological parameters and physical constraints than earlier multi-processor systems, which should be taken into consideration when designing cache coherence protocols. Also, contemporary cache coherence protocols use invalidate schemes that are known to generate a high number of coherence misses. This is especially true under producer-consumer sharing patterns that can become a performance bottleneck as the number of cores increases. This paper presents two mechanisms to design efficient and scalable cache coherence protocols for CMPs. First, we propose an adaptive hybrid protocol to reduce coherence misses observed in write-invalidate based protocols. The proposed protocol is based on a write-invalidate scheme. However, adaptively, it can push updates to potential consumers based on observed producer-consumer sharing patterns. Secondly, we extend this adaptive protocol with an interconnection resource aware mechanism. Experimental evaluations, conducted on a tiled-CMP via full-system simulation, were used to assess the performance from our proposed dynamic hybrid protocols. Performance analysis is presented on a set of scientific applications from the SPLASH-2 and NAS parallel benchmark suites. Results showed that the proposed mechanisms reduce cache-to-cache sharing misses up to 48 % and speed up application performance up to 34 %. In addition, the proposed interconnection resource aware mechanism is proven to perform well under varying interconnection utilizations.     

Synthesis and Polymerization of Cationic bis(cyclopentadienyliron)arene Complexes Containing Arylazo Dyes

The synthesis of the title complexes was achieved via the reaction of -p-dichlorobenzene- -cyclopentadienyliron cations with 4,4′-bis(4-hydroxyphenyl)valeric acid to produce the diiron complexes which were then reacted with a number of arylazo dyes to give cationic bis(cyclopentadienyliron)arene complexes containing the arylazo dyes. These iron-containing monomers were subsequently polymerized via nucleophilic aromatic substitution using 1,8-octanedithiol, 4,4′-thiobisbenzenethiol, or bisphenol A to produce the desired coloured cationic organoiron polymers. The weight – average molecular weights were estimated to range from 11,800 to 31,600. UV–vis studies conducted in dimethylformamide (DMF) showed that the metallated polymers exhibited of 412–491 nm. Addition of HCl to the polymer solution caused a bathochromic shift into the range of 515–530 nm. Thermogravimetric analysis (TGA) revealed that the iron moieties were cleaved between 205 and 248 °C while the polyether/thioether backbone degraded between 380 and 613 °C. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (Tg) ranging from 106 to 184°C.This paper is dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contribution to the field of metal-containing polymers.