The synthesis and characterization of novel coumarin dyes derived from 1,4-diethyl-1,2,3,4-tetrahydro-7-hydroxyquinoxalin-6-carboxaldehyde

1,4-Diethyl-1,2,3,4-tetrahydro-7-hydroxyquinoxalin-6-carboxaldehyde was synthesized and condensed with substituted active methylene compounds to obtain a series of novel coumarin compounds. Solutions of the dyes in various solvents exhibited an orange hue and brilliant fluorescence and displayed high thermal stability, as determined using thermogravimetric analysis. The dye having a heterocyclic benzimidazole ring as an electron withdrawing system was selected as a representative compound for comparison of its spectral characteristics with known analogues.     

On the elastic stability of simply supported anisotropic sandwich panels

Here, the elastic stability behavior of simply supported anisotropic sandwich flat panels subjected to mechanical in-plane loads is investigated using an analytical approach. The formulation is based on first-order shear deformation theory and the shear correction factors employed are based on energy consideration that depends on the lay-up as well as material properties. The governing equations are obtained using the Raleigh–Ritz method assuming a combination of sine and cosine functions in the form of double Fourier series for the displacement fields. The effectiveness of the integrated formulation is tested for global characteristics considering examples related to multi-layered laminates and sandwich panels for which solutions are available.     

Joint Hypothesis Tests for a Unit Root When There is a Break in the Innovation Variance

Abstract. We develop extensions of the Dickey–Fuller F‐statistics for the joint null hypothesis of a unit root that allows for a break in the innovation variance. Our statistics are based on the modified generalized least squares (GLS) strategy outlined in Kim, Leybourne and Newbold [Journal of Econometrics (2002) Vol. 109, pp. 365–387] that requires estimation of the break‐date and corresponding pre‐break and post‐break variances. We derive the asymptotic distribution of the new F‐statistics, tabulate their finite sample and asymptotic critical values, and present finite sample simulation evidence regarding their size and power.     

On-line acquisition of link deformation for the robot of accuracy

No manipulator is rigid. The actual end-effector position deviates from the desired one. For the remedy, compensation methods have been investigated. This paper presents the on-line acquisition method of link deflection and bending angle necessary for compensation methods.     

Modification of styrene–divinylbenzene copolymer by anchoring ferric–dipyridylamine complex

Polystyrene–divinylbenzene (PS–DVB) copolymer was modified by anchoring dipyridylamine (DPA) on it followed by complexation with Fe(III). Under the experimental conditions followed, 9% incorporation of Fe(III) was achieved. PS–DVB–DPA and PS–DVB–DPA–Fe(III) were characterized by IR spectra. Diffuse reflectance spectra for PS–DVB–DPA–Fe(III) and DPA–Fe(III) revealed λ_max at ～ 360 and ～ 310, respectively. This difference could be due to a difference in the nature of the coordinating moieties complexing with Fe(III) in these two systems. Scanning electron micrographs of PS–DVB, PS–DVB–DPA–Fe(III), and heat-treated PS–DVB–DPA–Fe(III) revealed some typical surface features. Thermal stability varied in the order PS–DVB–DPA–Fe(III) > PS–DVB–DPA ?PS–DVB, and DTA showed characteristic exotherms. © 1992 John Wiley & Sons, Inc.     

Effect of hydroperoxide decomposer and slipping agent on recycling of polypropylene

Polypropylene (PP) recycling has always been challenging because the polymer is highly susceptible to thermooxidative degradation during extrusion. Recycled (degraded) PP is normally blended with virgin PP to achieve reasonable mechanical properties after reprocessing operations. However, impurities present in recycled PP tend to degrade even the virgin PP in this process. In this study, standard recycled PP was produced in a laboratory by repeated extrusion and pelletization operations of virgin PP. This material was blended with virgin PP in a ratio from 3 : 7 to 7 : 3. An attempt was made to stabilize the recycled blend by adding a peroxide decomposer (triphenylphosphite, TPP) and a slipping agent (zinc stearate) in contrast to radical scavengers normally used in reprocessing. It was found that by using 0.3–0.5 wt % of TPP and 2 wt % of zinc stearate, this degradation could be effectively attested. Compared to the tensile strength retention of 68% (based on strength of pure virgin PP) of a 60 : 40 (recycled : virgin) PP blend without any stabilizer, a value of 77% was obtained for the same blend with the above‐mentioned stabilizers. This stabilization effect was attributed to decomposition of unstable hydroperoxides to stable compounds in the recycled materials by TPP, and lower generation of new radicals in the presence of zinc stearate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3247–3251, 2004     

Logical models of discrete event systems: A comparative exposition

The increasing complexity of man-made systems calls for new tools and techniques to model them efficiently and at the desired level of abstraction. Well-established modelling paradigms, such as finite state machines, petri nets, communicating sequential processes etc., which are borrowed from the fields of computer science and operations research, often lack certain essential features for capturing discrete event dynamics. New tools such as state charts, timed transition models, finitely recursive processes etc., are evolving to take into account some of these requirements. In this paper we first characterize such systems as well as typical problems related to them. We then discuss and critically evaluate several modelling frameworks through examples. At the end we provide a comparison among the frameworks and directions for future research.     

Effects of active Q enhancement on oscillator phase noise: an analysis

This article describes the effects of active Q enhancement on the performance of monolithic LC oscillator. Phase noise being the most important parameter for oscillators used in communication circuits, a lot of research efforts have been put in the direction of improving phase noise of fully on-chip LC oscillators over the past few years. Poor quality factor (Q) of on-chip passive components, specially that of spiral inductors limit the phase noise performance of LC oscillators. Use of active Q enhancement techniques has been proposed to improve phase noise but has not been proved by rigorous theory or supported by conclusive measurement results and thus require further investigation. In this article, it has been shown that active Q enhancement using transformer coupling, in fact, degrades the phase noise. The conclusion was reached based on theoretical analysis supported by simulation results.