Topological layout of links for optimizing the s-t reliability in a computer communication system

Large-scale Computer Communication Networks (CCN) are coming into use primarily because of the economy achieved through resource sharing. A fundamental consideration in the design of a CCN is the reliability between any pair of nodes and the maximum permissible cost, these characteristics being largely dependent upon the topological layout of the links, their costs and reliabilities. In this paper, having the knowledge of the locations of the various computer centres (nodes), maximum permissible cost of installing the links and the possible position of links, an heuristic algorithm for obtaining an optimal network topology which gives the maximum s-t reliability is presented. The method is general and is easily computerizable.     

Density dependence of solar emission lines of Si(X) and S(XII)

We have used the statistical equilibrium equation for the optically thin medium, under steadystate condition, to calculate the relative populations of 15 levels of Si(X) and S(XII) as functions of electron density at the temperature of maximum ion-abundances. The processes taken into account are collisional electron impact and radiative transitions. Proton excitation and deexcitation between the two levels of the ground state have also been accounted for. These populations are used to calculate the emissivities and intensity ratios.     

A focussed review of scheduling in services

The paper first outlines the special characteristics of services, as compared to those of the manufacturing systems. The second section stresses that each of the service systems has its own major primary objective/objectives, but such primary objectives are invariably in conflict with the well-known cost-minimization objective of manufacturing systems. The paper also discusses the variety of legal, union, and budgetary constraints which must not be violated by the service-system managers under any circumstances. Finally, the paper lists eleven different types of service systems, showing for each the unique constraints, the special sets of conflicting objectives as designated by their respective managements, and the commonly used techniques, methods and procedures. The most important and the most frequently referenced articles related to each type of system are indicated.     

Computer-communication network reliability: Trends and issues

People working in Computer-communication networks usually distinguish between the entire system and the communications subnet. The former includes the latter plus the terminals, devices and computer intercommunication via the subnet. This logically includes the resident processes that control or interface with the subnet. Greater computer communication network reliability can obviously be achieved by maximizing the reliability of its constituent components i.e. hardware, software, and communication network. The network reliability can be improved by exploiting the redundancies that are either inherent due to network topology or can be provided in the network. This paper presents a comprehensive discussion of issues involved and trends prevailing in producing reliable hardware; reliable software; and reliable computer communication network while reviewing techniques available for preventing, detecting, diagnosing, correcting and recovering from malfunctions.     

Facile Tetrahydropyranylation of Alcohols and Phenols Using Anhydrous Calcium Chloride under Mild and Neutral Conditions

Summary.  Treatment of 3,4-dihydro-2H-pyran with various alcohols and phenols in the presence of a catalytic amount of anhydrous calcium chloride in dichloromethane furnished tetrahydropyranyl ethers under almost neutral conditions. Corresponding author. E-mail: bandgar_bp@yahoo.com Received January 25, 2002; accepted (revised) March 20, 2002     

Markov ratio decision processes

A finite-state Markov decision process, in which, associated with each action in each state, there are two rewards, is considered. The objective is to optimize the ratio of the two rewards over an infinite horizon. In the discounted version of this decision problem, it is shown that the optimal value is unique and the optimal strategy is pure and stationary; however, they are dependent on the starting state. Also, a finite algorithm for computing the solution is given.     

Reliability Indices for Topological Design of Computer Communication Networks

Incorporating network reliability parameter in the design of reliable computer communication networks makes the computations prohibitive. Interdependence among network topological parameters does not permit the design of a maximally reliable network using any one of the parameters and thus, there arises a real need for a composite reliability index which gives a more realistic assessment of network reliability. After discussing experimental results regarding the effects of various topological parameters on network reliability, we present two heuristic reliability indices which give a fair indication of overall reliability. A design procedure for reliable computer communication network based on local search technique incorporating these reliability indices is suggested. Having only one composite reliability index which is very simple to evaluate saves computation while designing maximally reliable computer networks as compared to the existing techniques based on several reliability measures.     

A Note on the Operator Equation Generalizing the Notion of Slant Hankel Operators

The operator equation λM_zX = XM_(zk), for k ≥ 2, λ∈ C, is completely solved.Further, some algebraic and spectral properties of the solutions of the equation are discussed.     

Cadmium–halide and mixed cadmium–halide–dicyanamide polymers mediated by ancillary 2-aminoalkyl-pyridine ligands: Synthesis,X-ray single crystal structures and luminescence property

A series of mixed halide–dicyanamide and halide complexes of cadmium(II) mediated by 2-aminoalkyl-pyridine ligands [2-aminomethylpyridine (ampy) and 2-aminoethylpyridine (aepy)] have been synthesized. Five of them, [CdCl(dca)(aepy)]_n (1), [CdBr(dca)(ampy)]_n (2), [CdCl(dca)(ampy)]_n (3) (dca = dicyanamide); [CdI₂(aepy)]_n (4), and [CdI₂(ampy)]_n (5), (dca = dicyanamide) have been characterized by X-ray single crystal structure analysis. The structural determination shows that the compounds are 1D coordination polymers, with the exception of 3 that gives origin to a 2D sheet-like network. The ampy and aepy ligands (also with the occurrence of dca anions in 1–3) reveal to be useful ancillary fragments for the construction of unprecedented Cd–halide polymeric species. The crystal packing shows that the dimensionality of all compounds is enlarged to 2D, and 3D in the case of complex 3, through π–π interactions occurring between the pyridine rings. All the species exhibit interesting luminescence property in solution as well in solid state which is originated from ligand-centered π–π^∗ transitions. The fluorescence band maxima and fluorescence efficiency (in methanol) are found to be dependent not only on the pyridine ligand but also on the type of halide, and the co-ligand. Solid state luminescent study implies that π–π interactions occurring between pyridine rings are also important in controlling the fluorescence intensity. Amongst the synthesized complexes reported, complex 5 exhibits the highest fluorescence efficiency in methanol.