Parametric sensitivity and runaway in chemical reactors

In certain regions of operating conditions, chemical reactors may exhibit parametric sensitivity; i.e., small changes in one or more of the reactor input parameters lead to much larger changes in the output variables. Since such behaviour leads to deleterious performance, it is of practical interest to identify regions of parametric sensitivity in the reactor parameter space. Until recently, this could be done only to describe thermal runaway, and only for those systems where a temperature profile could be defined. Both of these limitations can be removed by consideringthe generalized criterion for parametric sensitivity, whereby sensitivity ofany output of the model toany input can be treated. Applications of the generalized criterion are discussed, with specific examples including pseudohomogeneous and heterogeneous model tubular reactors, a nonisothermal CSTR, and a polymerization reactor. Dedicated to Dr L K Doraiswamy — Gentleman, Scholar, Friend — on his sixtieth birthday.     

Reliability and MTTF analysis of a non repairable parallel redundant complex system under hardware and human failures

This paper deals with the evaluation of point-wise availability and M.T.T.F., of a two-unit standby redundant electronic equipment, incorporating the concept of human failures. Single service facility is available for the service of constant failure. Using the supplementary variable technique, general equations are set up for deriving the above two measures. In addition, steady state availability is also derived and some important graphs have been sketched in the end.     

Reliability and MTTF evaluation of a repairable complex system under waiting

This paper deals with the reliability and mean time to failure (MTTF) evaluation of a complex system under waiting incorporating the concept of hardware failure and human error. Failure rates of the complex system follow exponential time distributions, whereas repair follows a general repair time distribution. Laplace transforms of various state probabilities have been evaluated and then reliability is obtained by the inversion process. A formula for variance of time to failure has also been developed. A particular case is also given to highlight some important results. Moreover, various plots have been sketched at the end.     

Effect of pulsing on reaction outcome in a gas–liquid catalytic packed-bed reactor

A novel experiment is described for studying the effect of flow regime on reaction outcome for a consecutive-parallel reaction. By taking advantage of the convective nature of disturbances that grow into pulses in gas–liquid packed-bed reactors, it is shown that it is possible to compare reaction behavior for pulsing and trickling at the same flow rates. This contrasts previous studies where effects of regime were found, but at different flow rates. This experiment is accomplished by packing the column with mostly inert particles and confining the catalytically active region either near the inlet, where pulses have not yet formed, or near the end where they have developed. It is found that for the reaction of phenylacetylene to styrene and ethylbenzene over a platinum/alumina catalyst, where pulses are present in the bottom of the reactor but not at the top, about a 15% increase in styrene concentration, as an intermediate, occurs under pulsing conditions.     

Potential of fly ash to suppress the susceptible behavior of lime-treated gypseous soil

The use of lime and fly ash to improve the properties of certain types of soil is well established. However, the potential of fly ash to control the adverse effects of lime-treated gypseous/sulphatic soil has not been well investigated. In the present work, an attempt is made to quantify the fly ash content used to suppress the susceptible behavior of lime-treated gypseous soil. Series of one-dimensional swell and compressibility analyses are performed on various combinations of expansive soil with a predominance of montmorillonite mineral containing lime, gypsum (0–6%), and fly ash (0–30%). It is observed that the volume change behavior of the lime-treated gypseous soil is not controlled completely by addition of fly ash. However, the maximum improvement in the volume change behavior of the lime-treated gypseous soil is observed with a 20% fly ash content, and hence, can be taken as the Optimum Fly ash Content (OFC). Micro-analyses revealed that the relative dominance of the change in gradation and the formation of cementitious compounds of different compositions and ettringite crystals are the key factors in controlling the volume change behavior of lime-treated gypseous soil with fly ash. However, several factors, such as the types of minerals present in the soil, the types of fly ash and lime, and other physico-chemical environmental conditions (temperature, method of curing, and so on), are seen in the present study to affect the value of the obtained OFC.     

Nano ZnO grafted on MAA/BA/MMA copolymer: An additive for hygienic coating

Nano ZnO particles were synthesized by treating zinc oxalate with glycol and amines. The treated nano particles were in-situ grafted on methacrylic acid/butyl acrylate/methyl methacrylate via solution polymerization technique to prevent aggregation in the coating. The characterizations of grafted and treated nano ZnO particles were performed by transmission electron microscopy, atomic force spectroscopy, X-ray diffraction and particle size analysis. The outcome of this surface modification and varying concentrations of nano ZnO has helped in establishing it as an antibacterial additive in hygienic coating.     

SAKE: Software attestation for key establishment in sensor networks

This paper presents a protocol called Software Attestation for Key Establishment (SAKE), for establishing a shared key between any two neighboring nodes of a sensor network. SAKE guarantees the secrecy and authenticity of the key that is established, without requiring any prior authentic or secret cryptographic information in either node. In other words, the attacker can read and modify the entire memory contents of both nodes before SAKE executes. Further, to the best of our knowledge, SAKE is the only protocol that can perform key re-establishment after sensor nodes are compromised, because the presence of the attacker’s code in the memory of either protocol participant does not compromise the security of SAKE. Also, the attacker can perform any active or passive attack using an arbitrary number of malicious, colluding nodes. SAKE does not require any hardware modification to the sensor nodes, human mediation, or secure side channels. However, we do assume the setting of a computationally-limited attacker that does not introduce its own computationally-powerful nodes into the sensor network.SAKE is based on Indisputable Code Execution (ICE), a primitive we introduce in previous work to dynamically establish a trusted execution environment on a remote, untrusted sensor node.     

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part I—Experimental Studies

Experimental studies were performed to investigate the role and influence of grain movement on macrosegregation and microstructure evolution during equiaxed solidification. Casting experiments were performed with a grain-refined Al-Cu alloy in a rectangular sand mold. For the aluminum alloy studied, the equiaxed grains are lighter than the bulk melt and thus float up. Experiments were designed to investigate floatation phenomena of equiaxed grains in the presence of thermosolutal convection. Cooling curves were recorded at key locations in both the casting and the chill. Quantitative image analysis and spatial chemical analysis were performed on the solidified casting to observe the chemical and microstructural inhomogeneity created by the melt convection and solid floatation. Several notable features that can be attributed to grain movement were observed in temperature histories, macrosegregation patterns, and microstructures. In our experiments, the floatation of grains influences the thermal conditions and the overall flow direction in the casting cavity. In some cases, the induced flow resulting from the grain movement caused a flow reversal. This in turn influences the solidification direction, microstructure evolution, and the overall macrosegregation behavior.