A New Method for Getting Rational Approximation for Fractional Order Differintegrals

In this paper a new algorithm is presented to calculate the poles and zeros to approximate a fractional order (FO) differintegral (s^±α,α∈(0,1)) by a rational function on a finite frequency band ω∈(ω_l,ω_h). The constant phase property of the FO differintegral is the basis for development of the algorithm. Interlacing of real poles and zeros is used to achieve the constant phase. The calculations are done using the asymptotic Bode phase plot. A brief investigation is made to get a good approximation for the Bode phase plot. Two design parameters are introduced to keep the average phase close to the desired phase angle and to keep the error within the allowed bounds. A study is done to empirically understand the relationship between the error and the design parameters. The results thus obtained help in the further calculations. The algorithm is computationally simple and inexpensive, and gives a fairly good approximation of fractance frequency response on the specified frequency band.     

A PC-controlled microwave tomographic scanner for breast imaging

This article presents the design and development of a personal computer based controller for a microwave tomographic system for breast cancer detection. The system uses motorized, dual-polarized antennas and a custom-made GUI interface to control stepper motors, a wideband vector network analyzer (VNA) and to coordinate data acquisition and archival in a local MDSPlus database. Both copolar and cross-polar scattered field components can be measured directly. Experimental results are presented to validate the various functionalities of the scanner.     

A novel microfluidic switch for pH control using Chitosan based hydrogels

We report a novel pH-sensitive hydrogel based micro-valve for metered flow that has applications in a laboratory made “Intelligent valving system”. The hydrogel solution was prepared through Chitosan and poly vinyl alcohol in acetic acid and crystallized using gluteraldehyde as the crosslinking agent in the form of thin wafers and it was found to be very sensitive to pH changes. The pore structure of hydrogel was investigated through Field Emission Scanning Electron Microscopy and thin wafers of the gel were physically placed inside PDMS microchannels. Flow metering in these channels was observed by controlled expansion of the hydrogel plug till complete valving was realized. This valving device was further precisely characterized with micro Particle Image Velocimetry using a solution containing fluorescent polymeric micro beads. The principle advantage of this hydrogel device is the smaller range of pH (varying between pH 3 and 7) over which the valving response is observed.     

Optimal monolithic configuration for heat integrated ethanol steam reformer

A design concept for optimal design of monolith catalyst is presented through modeling of transport–kinetic interactions in a monolith catalyst. We argue that reactors employing monolithic catalysts should be based on its optimal choice of geometry. In line with that argument, we present a thorough analysis of the geometrical parameters influencing the performance of non-isothermal reactor operation. In this study, an optimal monolith configuration is estimated to be a combination (d_h, t_w) of (0.9 mm, 0.2 mm) for a compact ethanol reformer to produce hydrogen for portable applications where maximum volumetric reactor activity exists. A three-dimensional modeling framework is developed for the resulting optimal monolithic catalyst design that couples the reforming section with a suitable heat source in a recuperative way. As a result, greater ethanol conversion is obtained from the monolith channels near the periphery of the block. The coupling with combustion could predict the formation of cold and hot spots inside the reactor, their nature being dependent on the flow configuration. Further, the effect of altering the feed inlet operating conditions over the variation of ethanol conversion and temperature inside the reactor is also analyzed. The increase in reforming inlet velocity decreases the outlet conversion and shifts the cold spot, forward and deeper in co-flow configuration. The decreasing inlet feed temperature enhances the transfer of heat, eliminating the cold spot.     

Effect of non‐isothermal processing and moisture content on the anthocyanin degradation and colour kinetics of cherry pomace

Anthocyanins (ACY) and colour changes in cherry pomace under non‐isothermal processing were investigated. Pomace at moisture levels of 70% (MC‐70), 41% (MC‐41) and 25% (MC‐25) was heated at 126.7 °C in a retort for 25, 40 and 60 min. Total ACY, Hunter colour values, total colour difference (ΔE), chroma, hue angle (h°) and browning index (BI) were analysed. Thermal degradation kinetics for colour parameters were determined using zero‐ and first‐order models. ACY degradation increased with heating time and ranged from 34 to 68% for 25 and 60 min heating, respectively. The half‐life of ACY was 38, 33 and 27 min for MC‐70, MC‐41 and MC‐25 pomace, respectively. The ΔE increased with increasing heating time, whereas BI exhibited an inverse trend. Except for ?E for MC‐70, the zero‐order kinetic model showed better fit (R² = 0.85–0.97) to experimental data than the first‐order kinetic model for Hunter colour b values and ?E.     

Mapping Simple Polygons: How Robots Benefit from Looking Back

We consider the problem of mapping an initially unknown polygon of size n with a simple robot that moves inside the polygon along straight lines between the vertices. The robot sees distant vertices in counter-clockwise order and is able to recognize the vertex among them which it came from in its last move, i.e. the robot can look back. Other than that the robot has no means of distinguishing distant vertices. We assume that an upper bound on n is known to the robot beforehand and show that it can always uniquely reconstruct the visibility graph of the polygon. Additionally, we show that multiple identical and deterministic robots can always solve the weak rendezvous problem in which the robots need to position themselves such that all of them are mutually visible to each other. Our results are tight in the sense that the strong rendezvous problem, where robots need to gather at a vertex, cannot be solved in general, and, without knowing a bound beforehand, not even n can be determined. In terms of mobile agents exploring a graph, our result implies that they can reconstruct any graph that is the visibility graph of a simple polygon. This is in contrast to the known result that the reconstruction of arbitrary graphs is impossible in general, even if n is known.     

Modeling of partial oxidation in gas–solids downer reactors

Selective partial oxidations represent an important class of reactions in the process industry. Of particular interest is the partial oxidation of n‐butane to maleic anhydride (MAN), which is arguably the largest commercialized alkane partial oxidation process. Partial oxidation of n‐butane, which uses vanadium phosphorous oxide (VPO) as a heterogeneous catalyst, is believed to operate through a unique mechanism in which lattice oxygen oxidizes n‐butane selectively to MAN. Past work has shown that performing partial oxidation reactions in gas–solids riser configuration is realizable and commercially viable, which has lead to commercialization of this technology in the last decade. Though the riser configuration allows optimal and independent control of the oxidation and reduction steps, the riser unit suffers from solid backmixing at walls, which in turn result into lower conversion, nonoptimal selectivity and diminished overall yield of desired product. In recent years, there has been growing interest in downers involving cocurrent downflow of both solids and gas phases, hence offering relatively uniform flow characteristics. In this contribution, we explore through modeling the implications of effecting partial oxidation reactions in a downer (gas–solids cocurrent downflow) compared to that in a conventional riser reactor (gas–solids cocurrent up flow) operated under equivalent operating conditions. Further, we explore the operational space of downers for these reactions, suggesting ways for improving the productivity of downer for partial oxidation applications. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Physico-chemical characteristics of high performance polymer modified by low and atmospheric pressure plasma

In this work, the effect of low pressure plasma and atmospheric-pressure plasma treatment on surface properties and adhesion characteristics of high performance polymer, Polyether Ether Ketone (PEEK) are investigated in terms of Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Atomic Force Microscopy (AFM). The experimental results show that the PEEK surface treated by atmospheric pressure plasma lead to an increase in the polar component of the surface energy, resulting in improving the adhesion characteristics of the PEEK/Epoxy adhesive system. Also, the roughness of the treated surfaces is largely increased as confirmed by AFM observation. These results can be explained by the fact that the atmospheric pressure plasma treatment of PEEK surface yields several oxygen functionalities on hydrophobic surface, which play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the PEEK/Epoxy adhesive system.     

Effect of Heat Treatment on the Microstructure and Properties of Dense AIN Sintered with Y2O3 Additions

The secondary phase constitution in two sintered AIN ceramics (1.8% and 4.2% Y₂O₃ additions) was studied as a function of heat treatment temperatures between 1750° and 1900°C under pure nitrogen atmosphere. The effect of the phase constitution on the physical properties, such as density, thermal conductivity ( K ), and lattice constants, and on the mechanical properties in three-point bending, was also investigated. Y₃Al₅O₁₂ was found to getter dissolved oxygen from the AIN lattice below 1850°C, but evaporated at 1850°C and above. Y₄Al₂O₉ appeared to sublimate below 1850°C in the atmosphere used in this study. Depending on the secondary phase constitution, heat treatment affected thermal conductivity favorably or adversely. Occasionally, samples with similar lattice oxygen contents were found to have different thermal conductivities, suggesting that factors besides dissolved oxygen can also influence K . Lattice parameter measurements indicated that, within the small range of lattice oxygen concentrations in the AIN samples studied, the c-axis was more sensitive than the a -axis to oxygen content.