Application of Semi-Hertzian Approach to Predict the Dynamic Behavior of Railway Vehicles Through a Wear Evolution Model

Wear prediction due to the wheel-rail interaction in a railway vehicle has a significant role in the view of running stability (critical speed), dynamic performance and maintenance scheduling. In this article, we have focused on the estimation of wear distribution on the wheel profile through co-simulation between the vehicle and the wear evolution models, built in the multi-body simulation (MBS) software ADAMS (VI-Rail) and MATLAB environments, respectively. As the shape of the contact patches varies from elliptical to non-elliptical depending upon the contact patch location on the rail and the wheel, the contact forces/stresses are calculated by using a combined formulation of semi-Hertzian approach with modified FASTSIM. The wear distribution is obtained using Archard’s wear model. The wheel profiles are updated after calculating the wear depth for a particular distance travelled by the vehicle. The dynamic behavior of the vehicle with the worn wheel profile is utilized to predict additional wear during a further fixed distance of travel and this profile updating and dynamic simulation process is repeated. The vehicle’s dynamic performance and passenger comfort are evaluated for various levels of wheel wear.     

Structural Elaboration of a Natural Product: Identification of 3,3′‐Diindolylmethane Aminophosphonate and Urea Derivatives as Potent Anticancer Agents

An approach involving rational structural elaboration of the biologically active natural product diindolylmethane (DIM) with the incorporation of aminophosphonate and urea moieties toward the discovery of potent anticancer agents was considered. A four‐step approach for the synthesis of DIM aminophosphonate and urea derivatives was established. These novel compounds showed potent anticancer activities in two representative kidney and colon cancer cell lines, low toxicity to normal cells, higher potency than the parent natural product DIM and etoposide, and potent inhibition of cancer cell migration. Biophysical and immunological studies, including DAPI nuclear staining, western blot analysis with apoptotic protein markers, flow cytometry, immunocytochemistry, and comet assays of the two most potent compounds revealed good efficacies in apoptosis and DNA damage. It was found that down‐regulation of nuclear factor κB (NF‐κB p65) could be an important mode of action in apoptosis, and the two most potent derivatives were found to be more potent than parent compound DIM in the down‐regulation of NF‐κB. Our results show the importance of structural elaboration of DIM by rational incorporation of aminophosphonate and urea moieties to produce potent anticancer agents; they also suggest that this approach using other structurally simple bioactive natural products as scaffolds holds promise for future drug discovery and development.     

Temperature Dependence of Gas–Particle Partitioning of Primary Organic Aerosol Emissions from a Small Diesel Engine

A new experimental technique has been developed to study the gas–particle partitioning behavior of primary organic aerosol (POA) emissions from combustion sources at atmospherically relevant concentrations. The technique involves slowly filling a Teflon chamber with a constant emission source. As aerosol concentrations increase inside the chamber, the gas–particle partitioning of semivolatile organics shifts to the particle phase, thus increasing the fuel-based POA emission factor. The technique allows characterization of partitioning under isothermal conditions and atmospherically relevant concentrations. The technique was evaluated using emissions from a small diesel engine; the measured changes in gas–particle partitioning agreed well with previously published data for this engine measured with a dilution sampler. The temperature dependence of the gas–particle partitioning was investigated by conducting experiments at three different temperatures (15°C, 26°C, and 33°C). Increasing organic aerosol concentration and decreasing temperature increased the fuel-based POA emission factor. The gas–particle partitioning data were fit using absorptive partitioning theory to determine the volatility distribution and enthalpy of vaporization (ΔH _v) of the emissions. We have derived two fits; one using the volatility basis set approach and a second using a two-product model. Both fits are suitable for use in chemical transport models. These fits were tested using previously published thermodenuder data. Partitioning calculations predict that the gas–particle partitioning from POA emissions from this engine vary by about a factor of 4 across the atmospherically relevant range of temperature and organic aerosol concentrations. This underscores the semivolatile nature of POA emissions.

Copyright 2012 American Association for Aerosol Research     

A generalized methodology for optimal configurations of hybrid distillation-pervaporation processes

The aim of this work is to illustrate the structural and parametric optimization of continuous hybrid distillation-pervaporation process with different configurations such as series, parallel, and series-parallel arrangement of pervaporation modules in the pervaporation network, and to propose a generalized methodology for difficult separations. A superstructure representation of hybrid process is considered and the process is modeled and optimized using an MINLP approach. The optimization strategy is to obtain the desired degree of either the retentate or the distillate purity without violating the composition constraints of products and heat exchange policy which minimizes the required membrane area by increasing the flux through the membrane. The structural and operating parameters such as number of trays required, feed tray location, reflux ratio, retentate recycle location, permeate recycle location, membrane feed location, number of pervaporation modules required, target composition (which is directly related to membrane area), and membrane selectivity are optimized for each configuration by minimizing the total annual cost (TAC) for the separation system. The optimization studies have been carried out with General Algebraic Modeling System software (GAMS/SBB/CONOPT) and the results of different configurations have been compared on the basis of TAC required for the separation. A total of three industrial case studies have been dealt with. The separation of isopropanol-water as an azeotropic mixture, propylene-propane as a close boiling mixture (system with a low relative volatility) and acetone-water as a tangent pinch mixture have been studied as representative examples.     

Averaging theory and low-dimensional models for chemical reactors and reacting flows

A novel approach based on the Liapunov-Schmidt technique of bifurcation theory is presented for the spatial averaging of a class of convection-diffusion-reaction models. It is used to derive low-dimensional averaged models for different types of homogeneous and catalytic reactors, as well as coupled homogeneous-heterogeneous systems. For the homogeneous isothermal case, the averaged models consist of a pair of balance equations for each species A_j in terms of the mixing-cup (C_j,m) and spatially averaged (〈C_j〉) concentrations. The first (global) equation traces the evolution of C_j,m with residence time while the second (local) equation, which is independent of the reactor type, gives the local concentration gradient as a difference between C_j,m and 〈C_j〉 in terms of the local variables (such as species diffusivities, shear and reaction rates). For the wall-catalyzed reaction case, the averaged models are described by a pair of equations for each species in terms of C_j,m and the surface concentration C_j,s and are similar to the classical two-phase models of catalytic reactors. For the coupled homogeneous-heterogeneous case, the averaged models consist of three balance equations for each species in terms of C_j,m, 〈C_j〉 and C_j,s, and contain four mass transfer or exchange coefficients. The accuracy, convergence and the region of validity of the averaged models are examined for some special cases. Finally, the usefulness of the averaged models in predicting the reactor behavior is illustrated with an example for each of the three cases, homogeneous, heterogeneous and coupled homogeneous-heterogeneous case.     

Preparation of asymmetric polysulfone/polyimide blended membranes for CO<Subscript>2</Subscript> separation

Asymmetric Flat sheet polysulfone-polyimide (PSF-PI) blended polymeric membranes (with PI content from 5–20%) have been fabricated following phase inversion technique. The membranes have been thoroughly characterized by the measurement of porosity, mechanical properties and also by SEM, FTIR and DSC analyses. With the increase in the PI content, the mechanical properties of the membranes, like Young’s modulus, tensile strength and elongation at break, increased. SEM investigations revealed that the surfaces of fabricated blended membranes possessed adequate homogeneity and their cross-sections showed non-porous top and diminutive porous substructure. From DSC analyses it has been observed that different compositions of the blended membranes exhibited single glass transition temperatures, implying proper compatibility of the polymers. The permeance of CO₂ and CH₄ through the membrane increased with the increase in PI content and it gradually decreased with the increase in the feed pressure in the range of 2–10 bar. Under the present investigation, the membrane with 20% PI content exhibited the maximum selectivity for the separation of CO₂/CH₄ gas mixes.     

Discrete Modeling of Growth of Hairy Roots in a Mist Bioreactor

Hairy root culture is a promising route for large‐scale secondary metabolite production. A discrete model is developed to study the kinetic growth of these valuable roots in a reactor. The growth process is defined to occur in three sequential phases. The elongation rate is modeled as exponential growth with the growth coefficient being dependent on mass transfer coefficient, nutrient concentration difference, and distribution of nutrients in growth and sustenance requirements. Results indicate that the primary root growth is reduced by one‐fifth of its initial growth rate due to the branching process, and the growth of new branches is significantly faster than its primary root growth due to internal transport of nutrients. The model is successfully validated against experimental findings. Its integration with spatio‐temporal variation of nutrients in a reactor will be a crucial input to large‐scale production of hairy roots.     

Compatibilization of polyetherimide/liquid crystalline polymer blend using modified multiwalled carbon nanotubes and polyphosphazene as compatibilizers

In this study, compatibilizing ability of silicone carbide modified multiwalled carbon nanotube (MWCNT) and polyphosphazene for the incompatible polyetherimide/liquid crystalline polymer (LCP) blend was investigated in detail. From rheological study, it was evident that the viscosities of binary and ternary blends were lower than those of the neat polymers, which signifying the great ability of LCP as a processing aid. Field emission scanning electron microscopic analysis revealed that the addition of polyphosphazene and modified MWCNT, together, reduced the average domain size of LCP and improved the filler‐matrix adhesion. Measurement of surface energy from contact angle measurement also point towards the improved interfacial interaction, in presence of compatibilizers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012