Reliability models for computer systems: An overview including dataflow graphs

The reliability of a system is the probability that the system will perform its intended mission under given conditions. This paper provides an overview of the approaches to reliability modelling and identifies their strengths and weaknesses. The models discussed include structure models, simple stochastic models and decomposable stochastic models. Ignoring time-dependence, structure models give reliability as a function of the topological structure of the system. Simple stochastic models make direct use of the properties of underlying stochastic processes, while decomposable models consider more complex systems and analyse them through subsystems. Petri nets and dataflow graphs facilitate the analysis of complex systems by providing a convenient framework for reliability analysis.     

Mathematical modeling of mixing phenomena in a gas stirred liquid bath

A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate, bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial vessels has been demonstrated. Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur     

A real-time road pricing system: The case of a two-link parallel network

A real-time road pricing system in the case of a two-link parallel network is proposed in this paper. The system that is based on a combination of Dynamic Programming and Neural Networks makes “on-line” decisions about road toll values. In the first phase of the proposed model, the best road toll sequences during certain time period are calculated off-line for many different patterns of vehicle arrivals. These toll sequences are computed using Dynamic Programming approach. In the second phase, learning from vehicle arrival patterns and the corresponding optimal toll sequences, neural network is trained. The results obtained during on-line tests are close to the best solution obtained off-line assuming that the arrival pattern is known.     

Further characterisation of protease inhibitors from pigeon pea (cajanus cajan (l) millsp) seeds

Cajanus trypsin inhibitor (CTI) and Cajanus trypsin-chymotrypsin inhibitor (CTCI) previously purified from cv TAT-10 were further characterised. The modification of the inhibitors revealed the presence of lysine at the trypsin reactive site in both CTI and CTCI. Modification of tyrosine at the reactive site of CTCI did not abolish chymotrypsin inhibition suggesting the presence of leucine or phenylalanine as reported in other chymotrypsin inhibitors. CTCI did not contain tryptophan. Dissociation constants for the inhibitors with bovine trypsin were in the region of 0.69 nmol (CTCI) and 0.029 nmol (CTI). Although the protease inhibitors lost their inhibitory activity on exposure to 2-mercaptoethanol they remained attached to the enzyme. The inhibitors were not very effective against the protease from Helicoverpa armigera which is a serious field pest of Cajanus. Dissociation constants for the inhibitors with the larval enzyme were in the region of 100 nmol.     

Finite element crack growth algorithm for dynamic fracture

A new finite element crack growth algorithm has been developed to simulate dynamic fracture. In this algorithm, pseudo elements with very high initial density are placed below the crack plane and the density is reduced to zero in a gradual manner as the crack passes the element. A number of linear elastic and elasto-viscoplastic problems have been carried out to test the new algorithm. The results are compared with some of the existing crack growth models.     

A mathematical framework for algorithm-based fault-tolerant computing over a ring of integers

In this work, we establish a complete mathematical framework for algorithm-based fault-tolerant computing for data vectors defined over a ring of integers. The ring of integers consists of integers {0,1,…,M−1} and all the arithmetic operations are performed modulo the integerM, which is assumed to be composite. The importance of the work lies in the suitability of modulo arithmetic in certain computational environments. Lack of an underlying Galois field,GF(q), presents a unique challenge to this framework. We develop the theory and algorithms for single as well as multiple fault correction and detection. We also analyze the parallel and serial nature of the encoder and decoder configurations. Certain known but rather old results in the theory of numbers dealing with linear congruences and matrix algebra are also described and extended further using mathematical terminology that modern-day researchers are expected to be familiar with.     

Sequentially Enhanced Electrokinetic Remediation of Heavy Metals in Low Buffering Clayey Soils

This paper presents the results of an experimental investigation undertaken to evaluate different purging solutions to enhance the removal of multiple heavy metals, particularly chromium, nickel, and cadmium, from a low buffering clay, specifically kaolin, during electrokinetic remediation. Experiments were conducted on kaolin spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, which simulate typical electroplating waste contamination. A total of five different tests were performed to investigate the effect of different electrode purging solutions on the electrokinetic remedial efficiency. A constant DC voltage gradient of 1 V/cm was applied for all the tests. The removal of heavy metals from the soil using tap water as the purging solution was very low. When 1 M acetic acid was used as the purging solution in the cathode, the removal of chromium, nickel, and cadmium was increased to 20, 19, and 13%, respectively. Using 0.1 M ethylene diamine tetraacetic acid as the purging solution in the cathode, 83% of the initial Cr was removed; however, the nickel and cadmium removal was very low. A sequentially enhanced electrokinetic remediation approach involving the use of water as a purging solution at both the anode and cathode initially, followed by the use of acetic acid as the cathode purging solution and a NaOH alkaline solution as the anode purging solution was tested. This sequential approach resulted in a maximum removal of chromium, nickel, and cadmium of 68–71, 71–73, and 87–94%, respectively. This study shows that the sequential use of appropriate electrode purging solutions, rather than a single electrode purging solution, is necessary to remediate multiple heavy metals in soils using electrokinetics.     

Prediction of the effects on dynamic response due to distributed structural modification with additional degrees of freedom

The aim of this study is to investigate means of efficiently assessing the effects of distributed structural modification on the dynamic properties of a complex structure. The dynamic properties of the modified structure can be determined by experimental testing or numerical simulation, both of which are complex, expensive and time-consuming. Assuming that the original dynamic characteristics are already established and that the modification is a relatively simple attachment, the modified dynamic properties may be determined numerically without solving the equations of motion of the full-modified structure. The frequency response functions (FRFs) of the modified structure can be computed by coupling the original FRFs and a delta dynamic stiffness matrix for the modification introduced. The validity of this approach is investigated by applying it to a cantilever beam to which a smaller beam is attached as modification. The original FRFs were obtained experimentally as well as numerically. The delta dynamic stiffness matrix was determined numerically by modeling the attachment and part of the original structure including the attachment points. The FRFs of the modified beam were then computed. Good agreement is obtained by comparing the results to the FRFs of the modified beam determined experimentally as well as by numerical modeling of the complete modified structure.     

Ionic mass transfer measurements in the case of submerged multijets impinging on to a flat surface

In the case of submerged multijets impinging on to a flat surface, the limiting current densities were measured at microelectrodes, fixed flush with the target surface using diffusion controlled electrode reactions (i.e. reduction of ferricyanide ion). The height of the multijet distributor from the target surface (Y) was varied from 5 to 9 cm. The numbers of holes of the distributor (N) studied were 76 and 141. The variation of mass transfer data with radial distance reveals the existence of two different regions, i.e. the impingement region and the wall jet region. The mass transfer rate increased with increase in Y in the impingement region. The effect of Y is negligible in the wall jet region. Decrease in N decreases the mass transfer rate in both the regions. The data are correlated separately for the two regions.