Wavelength conversion in WDM networking

Wavelength conversion has been proposed for use in wavelength-division multiplexed networks to improve efficiency. This study highlights systems challenges and performance issues which need to be addressed in order to incorporate wavelength conversion effectively. A review/survey of the enabling technologies, design methods, and analytical models used in wavelength-convertible networks is provided     

Survivable WDM mesh networks

In a wavelength-division-multiplexing (WDM) optical network, the failure of network elements (e.g., fiber links and cross connects) may cause the failure of several optical channels, thereby leading to large data losses. This study examines different approaches to protect a mesh-based WDM optical network from such failures. These approaches are based on two survivability paradigms: 1) path protection/restoration and 2) link protection/restoration. The study examines the wavelength capacity requirements, and routing and wavelength assignment of primary and backup paths for path and link protection and proposes distributed protocols for path and link restoration. The study also examines the protection-switching time and the restoration time for each of these schemes, and the susceptibility of these schemes to multiple link failures. The numerical results obtained for a representative network topology with random traffic demands demonstrate that there is a tradeoff between the capacity utilization and the susceptibility to multiple link failures. We find that, on one hand, path protection provides significant capacity savings over link protection, and shared protection provides significant savings over dedicated protection; while on the other hand, path protection is more susceptible to multiple link failures than link protection, and shared protection is more susceptible to multiple link failures than dedicated protection. We formulate a model of protection-switching times for the different protection schemes based on a fully distributed control network. We propose distributed control protocols for path and link restoration. Numerical results obtained by simulating these protocols indicate that, for a representative network topology, path restoration has a better restoration efficiency than link restoration, and link restoration has a faster restoration time compared with path restoration.     

Analysis of flange joints with elastic bolt

The contact zone and pressure distribution between two elastic plates joined by an elastic bolt and nut are estimated using finite element analysis. Smooth interfacial conditions are assumed in all the regions of contact. Eight node axisymmetric ring elements are used to model the structure. The matrix solution is obtained through frontal technique and this solution technique is shown to be very efficient for the iterative scheme adopted to determine the extent of contact. A parametric study is conducted varying the elastic properties of bolt and plate materials, bolt head diameter and thickness of the plates. The method of approach presented in this paper provides a solution with a realistic idealization of tension flange joints.     

Modified crack closure integral using six-noded isoparametric quadrilateral singular elements

Six-noded, isoparametric serendipity type quadrilateral regular/singular elements are used for the estimation of stress intensity factors (SIF) in linear elastic fracture mechanics (LEFM) problems involving cracks in two-dimensional structural components. The square root singularity is achieved in the six-noded elements by moving the in-side nodes to the quarter point position. The modified crack closure integral (MCCI) method is adopted which could generate accurate estimates of SIF for a relatively coarse mesh. The equations for strain energy release rate and SIF are derived for mixed mode situations using six-noded quadrilateral elements at the crack tip. The model is validated by numerical studies for a centre crack in a finite plate under uniaxial tension, a single edge notched specimen under uniaxial tension, an inclined crack in a finite rectangular plate and cracks emanating from a pin-loaded lug (or lug attachment). The results compare very well with reference solutions available in the literature.     

Sequence and phylogenetic analysis of the Borrelia burgdorferi secA gene

Adamantinoma of long bones is a rare bone tumour with (immuno-) histological features of epithelial cells, surrounded by various amounts of osteofibrous tissue. Recent studies have indicated that cells with an epithelial phenotype are most probably the malignant element. There is still debate as to whether the fibrous part should be designed as a benign neoplastic element of a biphasic tumour or as a reactive non-neoplastic tissue next to an epithelioid bone tumour. The expression of fibroblast growth factor type 2 (FGF-2), epidermal growth factor (EGF), and their respective receptors FGFR-1 and EGFR, as well as the proliferation marker Ki-67, was studied in both constituents of adamantinoma in serial sections of 25 cases by immunohistochemistry. Expression of FGF-2 and its receptor was present in both constituents of adamantinoma, but predominated in the epithelial component. Expression of EGF and its receptor was restricted to the epithelial component of adamantinoma. Comparing osteofibrous dysplasia (OFD)-like adamantinoma with classic epithelial cell-rich adamantinoma, the expression of FGF-2, EGF, and EGFR was more intense and in a higher percentage of cells in classic adamantinoma. Proliferative activity was found nearly exclusively in the epithelial component. These data further substantiate the hypothesis that epithelial cells constitute the proliferating tumour cell population responsible for the malignant behaviour of adamantinoma. The data indicate that during progression, the epithelial cells acquire expression of FGF-2, EGF, and EGFR, accompanied by a higher proliferative activity. Within the epithelial cell population, there exists an autocrine pathway of growth stimulation. Furthermore, these data point to an interaction between the epithelial and fibrous components, in which the epithelial cells additionally stimulate fibrous cell growth via a paracrine pathway involving FGF-2.     

Determinants of EDI adoption in the transportation industry

This study examines the impact of various environmental, organizational, and technological factors on the adoption of innovation in the context of electronic data interchange (EDI). Based on research in information technology (IT) adoption, organizational studies and marketing a comprehensive research model is developed. The model identifies eleven variables, under three broad categories (environmental, organizational, and innovation characteristics), that could potentially influence the adoption of EDI. The research variables are operationalised using multi-item indicators and data collected from a large scale field survey of 950 firms in the trucking industry. A total of 181 firms responded to the survey with near equal number of adopters and non-adopters. Multivariate discriminant analysis is used to determine the impact of each of these variables on EDI adoption. The results of data analysis indicate that four factors are important to discriminate adopters from non-adopters of EDI in the transportation industry. They are: size of the firm, competitive pressure, customer support, and top management support.     

Influence of composition and curing on drying shrinkage of aerated concrete

The process of drying of many materials is accompanied by dimensional changes, which induce cracks in the structure. This phenomenon is particularly significant in acrated concrete owing to its high total porosity and specific surface of pores. The factors influencing drying shrinkage of aerated concrete are widely different from that of normal concrete because of the presence of coarse aggregates in the latter. This paper discusses the results of statistically designed experiments conducted to ascertain the influence of composition on the drying shrinkage of non-autoclaved and autoclaved aerated concrete. Detailed single factor experiments were conducted to assess the influence of basic constituents of the mix on drying shrinkage whereas fractional factorial experiments were used for the interaction effects and the influence of some additives. It was observed that increase in lime-cement ratio and fly ash content increases drying shrinkage. Significant shrinkage reduction is obtained by autoclaving, suggesting that drying shrinkage is predominantly a function of the physical structure of the hydration product.     

Delay analysis of a packet voice multiplexer by the ΣDi/D/1 queue

The performance of a statistical multiplexer whose inputs consist of a superposition of voice packet streams is studied. The delay for such a system is analyzed by solving the ΣD_i/ D/1 queue. The analytic method can be used to find the approximate mean delay for an arbitrarily large number of trunks and the approximate delay distribution when the number of trunks is less than 100. An efficient hybrid simulation of the packet voice multiplexer which can be used to find the delay distribution for a large number of trunks is presented. In addition, easily computable error bounds for the present approximation are provided, and the accuracy of the M/ D/1 approximation is investigated     

Elasto-plastic contact stress analysis of joints subjected to cyclic loading

Rigorous elastic-plastic finite element analysis of joints subjected to cyclic loading is carried out. An incremental-iterative algorithm is developed in a modular form combining elasto-plastic material behaviour and contact stress analysis. For the case of the interference fit, the analysis sequentially carries out insertion of the pin and application of the load on the joint, covering possible initiation of separation (and/or yielding) and progressively the receding/advancing contact at the pin-plate interface. Deformations of both the plate and the pin are considered in the analysis. Numerical examples are presented for the case of an interference fit pin in a large plate under remote cyclic tension, and for an interference fit pin lug joint subjected to cyclic loading. A detailed study is carried out for the latter problem considering the effect of change in contact/separation at the pin-plate interface on local stresses, strains and redistribution of these stresses with the spread of a plastic zone. The results of the study are a useful input for the estimation of the fatigue life of joints.     

An enhanced slew rate source follower

A unity-gain buffer capable of high slew rates in both the positive and negative directions is presented. By sensing the drain current of the common-drain device in an NMOS source follower, the extent of slewing is detected, and the tail current of the source follower is dynamically adjusted. A buffer incorporating this strategy was implemented in a 2 μm p-well process. This buffer has over 4 times the negative-going slew rate and twice the bandwidth of a source follower, while requiring only 13% more static power. Moreover, the output voltage swing range is as large as that of a source follower. With a 20 pF output load, the measured 3-dB bandwidth was 9 MHz. The signal-to-total-harmonic-distortion ratio with 2 V_p-p sinewave input at a frequency of 2 MHz was better than 50 dB