Process control: Domains, disciplines and cognitive difficulties

The underlying stratum of domains, representations and disciplines makes the study of process control challenging. In this article the authors classify and provide specific remedies for addressing the underlying common difficulties faced by novices in the field of process control. The authors also share content that might be of direct value to practicing engineers. Engineers can use the “identifying similarities and differences” strategy for improving understanding of labels and identifiers such as excitation and DC gain, but the focus needs to be on discerning subtle rather than gross differences. Good practical examples serve as helpful learning aids for complex concepts such as anti reset-windup and non-minimum phase zero but are not easy to find. For big universal ideas such as causality and stability, the authors found a narrative style, linking content to learners’ prior knowledge and use of metaphors - three techniques missing from most standard textbooks - to be useful for overcoming the cognitive barriers.     

Toughening of dimethacrylate resins by addition of ultra high molecular weight polyethylene (UHMWPE) particles

The effects of the addition of UHMWPE particles, of nominal 〈80 μm〉 size, on the fracture toughness, flexural modulus and strength of composites made with dimethacrylate resins (60/40 wt/wt BisGMA-TEGMA) were investigated as a function of volume fraction of UHMWPE (0-60 vol%) and particle surface treatment. Interfacial shear strengths (τ) were measured via microbond shear strength tests using Spectra900™ (UHMWPE) fibers and BisGMA-TEGMA beads. τ increased by a factor of 4 compared with untreated UHMWPE, and surface treated particles improved the mechanical properties of the composite. Fracture toughness (K_IC) and flexural modulus (E) increased with increased volume fraction of UHMWPE, with maximum K_IC/E increases (at 60 vol%) of 238%/25% compared with the neat resin. SEM images showed debonding as well as yielding and fibrillation of the UHMWPE particles, suggesting that these were significant toughening mechanisms.     

Potential of solar home-lighting system in rural western India

The states of Maharastra and Gujarat in Western India are among the largest consumers of electricity. Rural homes are hit by power shortages due to ever increasing demand of electricity. Solar home-lighting system (SHS) is the ideal solution and is prudent as a self-reliant source. The study takes into account the number of villages-households-population and the existing electricity structure to determine the potential. The systems will be supplied through financing schemes involving Government and NGOs. Rural technicians would be trained to maintain the systems. This will serve as a pilot model for the country, to be extended to other states, later.     

Catalytic diastereoselective hydrogenation of (>S)-proline-modified anthranilic acid

The hydrogenation of (S)-proline-modified anthranilic acid was studied on Rh and Ru catalysts. The hydrogenation occurred with a very high diastereoselectivity but a moderate chemoselectivity. In general, the carbon-supported catalysts exhibited a higher activity but a lower diastereoselectivity than the alumina-supported catalysts. The use of water as the solvent instead of ethanol resulted in higher activities but lower diastereoselectivities. Rh- and Ru-based homogeneous catalysts gave a comparable selectivity but a lower activity than their heterogeneous counterparts. This revised version was published online in November 2006 with corrections to the Cover Date.     

Chemical storage of solar energy kinetics of heterogeneous SO3 and H2O reaction—Reaction analysis and reactor design

The first energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the formation of H₂SO₄(l) from H₂O(g) and SO₃(g). It has been determined that the optimum way to accomplish this is by the use of a double pipe tubular reactor. In this paper, a mathematical model for the reactor is presented, applied to the three reaction zones, and a method of numerical solution discussed. Three horizontal pilot-scale configurations, 0.234 × 10⁶ to 5.863 × 10⁶ kJ/h energy release, are discussed and sizing presented. Also, the results for a vertical configuration are presented. The need for additional work on two-phase gas-liquid flow in condensing systems and in annuli has been identified. The most important conclusion is that a high temperature can be achieved in the reactor by the use of a front end adiabatic section followed by nonadiabatic sections to recover the heat released.     

Accumulation of intracellular carbon reserves in relation to chloramphenicol biosynthesis by Streptomyces venezuelae

Two chloramphenicol-producing strains of Streptomyces venezuelae accumulated small amounts of polyhydroxybutyrate during exponential growth; the compound disappeared from the mycelium as the cultures entered stationary phase. Depletion of polyhydroxybutyrate coincided with chloramphenicol production but the amount of polymer stored in the mycelium was insufficient to supply the precursor requirement for biosynthesis of the antibiotic. Accumulation of polyhydroxybutyrate in the S. venezuelae strains was appreciably lower than in two other streptomycetes examined. Glycogen and lipids accumulated in the mycelium of S. venezuelae 13s during the stationary phase, after nitrogen depletion; under the culture conditions used, they were the principal storage compounds in S. venezuelae. Trehalose was absent from the mycelium in vegetative cultures grown under nonsporulating conditions but it was abundant in spores obtained from submerged and surface cultures. Glycogen and polyhydroxybutyrate were absent from spores.     

Dual work function metal gate CMOS technology using metalinterdiffusion

In this letter, we propose a new metal-gate CMOS technology that uses a combination of two metals to achieve low threshold voltages for both n- and p-MOSFET's. One of the gate electrodes is formed by metal interdiffusion so that no metal has to be etched away from the gate dielectric surface. Consequently, this process does not disturb the delicate thin gate dielectric and preserves its uniformity and integrity. This new technology is demonstrated for the Ti-Ni metal combination that produces gate electrodes with 3.9 eV and 5.3 eV work functions for n-MOS and p-MOS devices respectively     

New findings in the occurrence of false-healing in plasticencapsulated microcircuits using scanning acoustic microscopy

“False-healing” refers to the occasionally observed reduction of delamination in plastic encapsulated microcircuits, In previous studies, “false-healing” was reported only at the leadframe-plastic interface. It was thought that the chemical contaminants present in the flux enter the package and form corrosive products which fill up the internal air gaps. This paper reports on some new findings in the occurrence of false-healing in plastic packages using scanning acoustic microscopy. This study found that false-healing also occurs in instances where there was no exposure to corrosive media. Additionally, false healing was observed at the die-plastic interface, where chemical contaminants could not reach. Alternate explanations for this phenomenon are suggested and its impact on damage assessment of plastic encapsulated microcircuits is discussed     

Two-stage anaerobic digestion process for complete inactivation of enteric bacterial pathogens in human night soil.

Anaerobic digestion offers a good alternative for human waste treatment. However, the fate of enteric bacterial pathogens present in human night soil (HNS) remains a major concern for hygienic safety of the process. A two-stage anaerobic digestion process, consisting of separate acidogenic and methanogenic digesters, was designed and its efficacy in the inactivation of Salmonella typhi was compared to a single-stage digestion process. In a single-stage digestion, complete pathogen inactivation was achieved only in the digesters with high levels of volatile fatty acids (VFA approximately equal to 18,000 mg/l) and acidic pH (approximately equal to 6.0). These digesters, however, showed drastic reduction in methane yield. In the two-stage digestion process, S. typhi was completely inactivated in the acidogenic digester and the methanogenic digester was free from the pathogen even after receiving a daily dose of the pathogen. The process also achieved complete inactivation of other enteric pathogens, viz., Shigella dysenteriae and Vibrio cholerae. The two-stage process was efficient in biogas generation from HNS. Thus, the two-stage process ensures complete hygienic safety in anaerobic digestion of human night soil.     

Multilayer differential discrete ordinate method for inhomogeneous participating media

This paper presents a multilayer differential discrete ordinate method to solve the radiative transfer equation for an absorbing, emitting and scattering inhomogeneous plane parallel medium. This method reduces the integro-differential equation into a set of coupled first order ordinary differential equations with two point boundary conditions on using a suitable quadrature scheme. These equations are then solved numerically. Numerical validation of the method for gray medium is done by comparing the results obtained with benchmark cases available in the literature. Validation for a non-gray medium is done by considering a problem concerning radiative transfer from the atmosphere. The brightness temperature at the top of the atmosphere is calculated at various frequencies and validated with those obtained by several other numerical methods.