Attainable regions of reactive distillation—Part III. Complex reaction scheme: Van de Vusse reaction

The main underlying principle behind the application of reactive distillation (RD) for selectivity enhancement is to facilitate the separation of selected components and favorably manipulate the composition profiles in the reactive zone to expedite the desired reaction. In this paper, a geometric approach of attainable region (AR), which is already developed for conventional reactor network, is extended further to include few representative RD configurations. We define new RD building blocks and the corresponding composition vectors that indicate a need of networking of RD units among themselves and with conventional reactors to enlarge the set of attainable compositions. A model reaction scheme of van de Vusse type ) is studied as an illustrative example and an algorithm is developed to obtain the attainable region for the given kinetics, feed composition and relative volatilities. In almost all the different cases, which are studied by varying the kinetics and volatility pattern, network consisting of RD units performs better than the conventional reactor network.     

Effects of Platinum on the Hot Corrosion Behavior of Hf-Modified �á�-Ni3Al?+?��-Ni-Based Alloys

The establishment of a protective ??-Al₂O₃ scale is critical for providing high temperature protection from oxidation and hot corrosion, thereby improving lifetimes of advanced gas turbine engine components. Recent work by our group has shown that a wide range of Pt + Hf-modified ?á?-Ni₃Al + ??-Ni alloy compositions form a very adherent and slow-growing Al₂O₃ scale and exhibit excellent oxidation resistance. The main thrust of the present study was to understand the effects of Pt addition on the Type I (900 °C) and Type II (705 °C) hot corrosion (HC) behavior of model Hf-modified ?á? + ?? alloy compositions. The salt used to bring about hot corrosion was Na₂SO₄. It was found that the Type I HC resistance of ?á? + ?? alloys improved with up to about 10 at.% Pt addition, but then decreased significantly with increasing Pt content up to 30 at.% (the maximum level studied); however, under Type II HC conditions the resistance of ?á? + ?? alloys progressively improved with increasing Pt content up to 30 at.%. The effect of pre-oxidation on hot corrosion resistance was also examined, and the results indicated that pre-oxidation generally improved Type II HC resistance for the test duration studied.     

Sputtered ferroelectric thin films for dynamic random access memory applications

Abstract

A low thermal budget (with 550°C annealing) process with Ti-compensation for sputtered ferroelectric PZT thin films has been developed. PZT films with a composition near the morphotrophic phase boundary (Zr/Ti = 53/47) annealed at 550°C for 1 hr in a N₂ ambient exhibits high charge storage density and low leakage current density, which are the important requirements of dielectric materials for ULSI DRAM cells. It was also found that Ti compensated films show good fatigue endurance in comparison with non-Ti compensated films.     

Stepping toward standard methods of small-signal parameterextraction for HBTs

An improved HBT small-signal parameter extraction procedure is presented in which all the equivalent circuit elements are extracted analytically without reference to numerical optimization. Approximations required for simplified formulae used in the extraction routine are revised, and it is shown that the present method has a wide range of applicability, which makes it appropriate for GaAs and InP-based single and double HBTs. Additionally, a new method is developed to extract the total delay time of HBTs at low frequencies, without the need to measure h₂₁ at very high frequencies and/or extrapolate it with -20 dB/dec roll-off. The existing methods of finding the forward transit time are also modified to improve the accuracy of this parameter and its components. The present technique of parameter extraction and delay time analysis is applied to an InGaP/GaAs DHBT and it is shown that: (1) variations of all the extracted parameters are physically justifiable; (2) the agreement between the measured and simulated S- and Z-parameters in the entire range of frequency is excellent; and (3) an optimization step following the analytical extraction procedure is not necessary. Therefore, we believe that the present technique can be used as a standard extraction routine applicable to various types of HBTs     

Enhanced visible green and 1.5 μm radiative emission of Er~(3+) ions in Li_2O-PbO-Al_2O_3-B_2O_3 glasses for photonic applications

A series of Er~(3+) ions doped lithium lead alumino borate(LiPbAlB) glasses were synthesized via melt quench method and their structural,physical and optical properties were studied.Judd-Ofelt theory in correlation with the emission and absorption profiles was performed for the measurement of various radiative parameters for different transitions of Er~(3+) doped glasses.The as-prepared glasses show deep green(550 nm) as well as NIR(1532 nm) emission at 380 and 980 nm excitation wavelengths,respectively.The intensity of emission spectra increases with Er~(3+) ions concentration up to 1.5 mol% and beyond quenching is observed.The Dexter theory applied to the emission profiles reveals the interaction between Er~(3+)ions as dipole-dipole in nature.CIE color coordinates are found to fall in the green region of the visible spectrum.It is observed that 1.5 mol% of Er~(3+) ions concentration is optimum to exhibit the maximum quantum efficiency,branching ratios,gain bandwidth,emission cross-section,gain crosssection and aptly suitable for visible and NIR photonic applications.     

Potential of Sr4Al14O25: Eu2+,Dy3+ inorganic oxide-based nanophosphor in Latent fingermark detection

In this paper, the potential of the Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor is explored to visualize the latent fingermarks. The nanophosphor has been synthesized using self-propagating high temperature synthesis and shows intense luminescence and strong long after glow properties. These nano particles have been characterized for their particle size, crystalline phase, and photoluminescent properties. The calculated PL CIE co-ordinates (0.138, 0.359) correspond to the blue–green shade. Different porous, non-porous, as well as slightly non-smooth surfaces are taken and successfully tested for latent fingerprints development with the prepared Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ fluorescent nanophosphor powder. Present nano powder is advantageous to use on luminescent or multicolored surfaces as it gives greater contrast and also eliminates the problem of background interferences with the friction ridges due to its strong long after glow property. The results are very good when latent fingerprints were developed on the currency notes with optical variable ink and highly fluorescent pattern areas.     

Analysis of a Multiphase Induction Machine Under Fault Condition in a Phase-Redundant A.C. Drive System

Phase-redundancy is a unique technique for improving the reliability of large variable speed AC drives. This technique, derived from the concept of parallel-redundancy, is based on the capability of a multiphase machine to start and continue running with one or more of its many stator phases open or short circuited with lower performance. Structural unbalance in the machine following loss of excitation is the main source of performance degradation. This paper, therefore, presents a simple generalized approach to analyze the dynamic as well as steady-state behavior of a multiphase induction machine during fault condition in a phase-redundant AC drive system. The key analytical results have been experimentally verified by tests conducted on a laboratory prototype.     

Rolling element bearing design through genetic algorithms

The design of rolling element bearings has been a challenging task in the field of mechanical engineering. While most of the real aspects of the design are never disclosed by bearing manufacturers, the common engineer is left with no other alternative than to refer to standard tables and charts containing the bearing performance characteristics. This paper presents a more viable method to solve this problem using genetic algorithms (GAs). Since the algorithm is basically a guided random search, it weakens the chances of getting trapped in local maxima or minima. The method used has yielded improved performance parameters than those catalogued in standard tables.     

INNOVATIVE TESTS TO PREDICT THE STRENGTH AND TYPE OF ASPHALT-AGGREGATE BONDS

ABSTRACT

This paper discusses two techniques to characterize the type and measure the strength of asphalt-aggregate bonds. The Modified Lottman Test is commonly used to measure the physical strength of asphalt-aggregate bonds. Under certain conditions bonds may become weak due to chemical factors that are not accounted for in the Modified Lottman Test. In order to measure the chemical strength of the bond, a chemical preconditioning stage was introduced prior to performing the Modified Lottman Test. During this stage a compacted mix pill was exposed to an environment that was rich in either OH^?- or H^plus; ions. Such high or low pH conditions affect bonding reactions that are reversible in nature, and thereby expose the chemical weakness of the bond. Results show that different antistrip agents react differently to such conditions. The paper also discusses the effect of mix curing on bond strength under these limiting pH conditions. The other technique discussed in this paper, U a test that characterizes different aggregates in terms of their reactivity with aspnaltic components, which subsequently helps identify those aggregates that would form strong bonds with asphalt. It was observed that even within limestones aggregates, different types reacted to a different extent, and thereby, could be easily characterized