Optimized partitioning of a wavelength distributed data interfacering network

A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized     

Dynamic Waveband Switching in WDM Mesh Networks Based on a Generic Auxiliary Graph Model

Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings.     

secG and temperature modulate expression of azide-resistant and signal sequence suppressor phenotypes of Escherichia coli secA mutants

SecA is a dynamic protein that undergoes ATP-dependent membrane cycling to drive protein translocation across the Escherichia coli inner membrane. To understand more about this process, azide-resistant (azi) and signal sequence suppressor (prlD) alleles of secA were studied. We found that azide resistance is cold sensitive because of a direct effect on protein export, suggesting that SecA-membrane interaction is regulated by an endothermic step that is azide inhibitable. secG function is required for expression of azide-resistant and signal sequence suppressor activities of azi and prlD alleles, and in turn, these alleles suppress cold-sensitive and export-defective phenotypes of a secG null mutant. These remarkable genetic observations support biochemical data indicating that SecG promotes SecA membrane cycling and that this process is dependent on an endothermic change in SecA conformation.     

Selective monitoring of peptidase activities with synthetic polypeptide substrates and polyion-sensitive membrane electrode detection

A novel method to monitor specific peptidase activities in biological samples as complex as undiluted plasma/blood is described. The approach is based on the design of synthetic polypeptide substrates in which di- or triarginine sequences are linked to each other via one or more other amino acids recognized specifically by the peptidase to be determined. Detection of chymotrypsin and renin activities using synthetic substrates P4 (F-R-R-R-F-V-R-R-F-NH2) and P5 (R-R-R-L-L-R-R-L-L-R-R-R), respectively, serves to demonstrate the principles of this new assay system. A polyion-sensitive membrane electrode, prepared by doping polymer films with dinonylnaphthalene-sulfonate (DNNS), is shown to exhibit significant nonequilibrium electromotive force (EMF) responses toward these and other polycationic substrates at microgram/milliliter levels under physiological conditions. The same electrode, however, exhibits much smaller total EMF response toward the shorter fragments of the synthetic peptides generated by peptidase activity; hence, the addition of peptidase to a solution containing the synthetic substrate yields a change in electrode EMF response, the rate of which is proportional to the activity of peptidase present. Other synthetic polycationic peptides as well as natural polycationic peptides (e.g., protamine) that lack specific cleavage sites for chymotrypsin and renin, yet are detected by the DNNS-based membrane electrode, do not elicit any significant change in EMF response in the presence of the peptidases, confirming the feasibility and utility of the proposed bioanalytical method.     

Determinants and outcomes of electronic data interchange diffusion

Protagonists of electronic data interchange (EDI), a specific form of inter organizational systems (IOS), claim that it has the potential to dramatically alter the exchange of business documents and business operations (particularly material procurement and sales functions) in a number of industries. Drawing upon past research on innovation diffusion and information systems (IS) implementation, this study examines the role of key innovation and organizational factors in influencing the extent to which EDI is diffused within organizations, and whether more extensive diffusion leads to improved organizational outcomes. Two senior executives (one from the IS and the other from selling/buying function) from over 200 large American companies participated in the field study. The path analyses results indicate that compatibility and relative advantage (two of the three classical innovation attributes), championing, scope for use of EDI within the firm's task environments, and being an early adopter determine the extent to which EDI gets internally diffused through greater integration with other IS applications within the organization. Technical compatibility, top management support and being an early adopter emerge as the key variables influencing the extent to which EDI gets externally diffused through greater external diffusion of business transactions with trading partners. The results also indicate that greater internal as well as external diffusion of EDI facilitates improved organizational outcomes that was measured on six dimensions such as implementation success, organizational performance, influence on market structure, standardization of transactions, etc     

Mixing matrix estimation using discriminative clustering for blind source separation

Mixing matrix estimation in instantaneous blind source separation (BSS) can be performed by exploiting the sparsity and disjoint orthogonality of source signals. As a result, approaches for estimating the unknown mixing process typically employ clustering algorithms on the mixtures in a parametric domain, where the signals can be sparsely represented. In this paper, we propose two algorithms to perform discriminative clustering of the mixture signals for estimating the mixing matrix. For the case of overdetermined BSS, we develop an algorithm to perform linear discriminant analysis based on similarity measures and combine it with K-hyperline clustering. Furthermore, we propose to perform discriminative clustering in a high-dimensional feature space obtained by an implicit mapping, using the kernel trick, for the case of underdetermined source separation. Using simulations on synthetic data, we demonstrate the improvements in mixing matrix estimation performance obtained using the proposed algorithms in comparison to other clustering methods. Finally we perform mixing matrix estimation from speech mixtures, by clustering single source points in the time-frequency domain, and show that the proposed algorithms achieve higher signal to interference ratio when compared to other baseline algorithms.     

Internet messaging: An examination of the impact of attitudinal,normative, and control belief systems

While instant messaging (IM) has been very popular among teenagers and college students for social and recreation communication, its use in corporate settings has been limited. We examined the factors that influence the intention to use and actual use of IM. A research model was developed based on diffusion of innovation and Socio-psychological theories. The model examined the influence of seven variables in three belief structures (the attitudinal, normative, and control). The model was empirically validated using a field survey of 349 respondents. The results indicated that five of the seven variables explained about 41% of the variance in the intention to use IM. The five significant variables were: utilitarian beliefs, hedonic beliefs, subjective norms, critical mass, and ease of use. Affiliation motivation was not significant and social belief had a negative impact on intention. As expected, intention to use had a significant influence on actual usage.     

Consumer Selection of E-Commerce Websites in a B2C Environment: A Discrete Decision Choice Model

Despite the suggestions of friction-free information availability, considerable price dispersions for the same product are not uncommon across online retailers in the business-to-consumer (B2C) segment. Online customers do not necessarily always buy from the site with the lowest price, suggesting that other forces are at work. This paper presents and empirically examines a model that proposes that Web site value in terms of (perceived) Web site quality as well as awareness of the site and consumer differences (on price sensitivity) are key variables in explaining online consumer behavior in their choice of Web site despite the existence of price dispersions. Two hundred ninety-three students participated in a series of controlled laboratory experiments making use of two different types of products in terms of complexity and expensiveness (Canon digital camera Powershot S400 and digital versatile disc full-screen edition of Star Wars: Episodes I and II) that required them to interact with three different real-world Web sites offering each of these two branded products and make their decision on which of the three Web sites they will chose to buy the product from. The prices varied across the Web sites, as did the quality of the sites on various dimensions and site awareness of the participants. Conditional logit models of discrete choice for each of the two product types indicate differential influences of Web site quality dimensions and price sensitivity. A number of interesting implications emerge, and pointers to further extensions of the research theme are discussed.