Modeling Oxidation of Soot Particles Within a Laminar Aerosol Flow Reactor Using Computational Fluid Dynamics

This work examines the measurement of surface specific soot oxidation rates with the High Temperature Oxidation-Tandem Differential Mobility Analyzer (HTO-TDMA) method. The Computational Fluid Dynamics package CFD-ACE⁺ is used to understand particle flow, oxidation and size dependent particle losses in the laminar aerosol flow reactor using an Eulerian-Lagrangian framework. Decrease of DMA selected mono-disperse particle size distribution due to oxidation within the aerosol tube is modeled using fitted kinetic soot oxidation parameters. The effects of Brownian diffusion and thermophoresis on particle flow and loss to the reactor walls are evaluated. The position of peak particle diameter, which is used as an indicator to determine oxidation rate, is found to be independent of diffusion, thermophoresis and secondary flow effects, thus validating its use in deriving kinetic soot oxidation parameters. Diffusion does not affect the evolution of particle size distribution within the reactor. However, thermophoresis is found to be the dominant mechanism influencing both shape of particle size distribution and particle loss to the walls of the aerosol reactor. Simulations show reduced effects of secondary recirculating flows on the particle flow trajectories in a vertical furnace as compared to horizontal furnace orientation. This work highlights the importance of making accurate measurements of temperature within the modeling domain. Since gas temperature within the flow tube could not be measured with high radial resolution using radiation shielded thermocouple, the derived soot oxidation rate may be uncertain by a factor of 2. Importantly, CFD simulations suggest that a distribution of temperature and size-dependent particle reactivities may be present in the reactor, requiring further theoretical and experimental investigation.     

Gamma Irradiation Insensitivity of GaAs Schottky Diodes

Guarded Al-and Au-nGaAs Schottky barrier diodes were subjected to Co60 ?-ray irradiation and their electrical characteristics evaluated. These GaAs Schottkys did not exhibit significant change in their I-V and C-V characteristics up to an absorbed dose as high as 1.5 × 107 rads. Diodes that were previously neutron-irradiated with consequent degradation were also subjected to Co60 irradiation, but no synergistic changes were observed.     

Conducting cryogel scaffold as a potential biomaterial for cell stimulation and proliferation

The aim of the study was to demonstrate the potential of the cryogelation technique for the synthesis of the conducting cryogel scaffolds which would encompass the advantages of the cryogel matrix, like the mechanical strength and interconnected porous network as well as the conductive properties of the incorporated conducting polymeric material, polypyrrole. The cryogels were synthesized using different combinations of oxidizing agents and surfactants like, sodium dodecyl sulfate (SDS)/ammonium persulfate (APS), SDS/iron chloride (FeCl₃), cetyl trimethyl ammonium bromide (CTAB)/APS, and CTAB/FeCl₃. The synthesized gels were characterized by scanning electron microscopic analysis for morphology, Fourier transform infrared spectroscopy for analyzing the presence of the polypyrrole (0.5–4 %) as nano-fillers in the gel. It was observed that the presence of these nano-fillers increased the swelling ratio by approximately 50 %. The synthesized conducting cryogels displayed high stress bearing capacity without being deformed as analysed by rheological measurements. The degradation studies showed 12–15 % degradation in 4 weeks time. In vitro studies with conducting and non-conducting cryogel scaffold were carried out to optimize the stimulation conditions for the two cell lines, neuro2a and cardiac muscle C2C12. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed approximately 25 and 15 % increase in the cell proliferation rate for neuro2a and C2C12 cell line, respectively. This was observed at a specific voltage of 100 mV and 2 V, for a specified duration of 2 h and 1 min, respectively for the conducting scaffold as compared to the control. This can play an important role in tissue engineering applications for cell lines where acquiring a high cell number and functionality is desired.     

Application of link adjacency values to detect isomorphism among kinematic chains

The present work deals with problem of detection of isomorphism which is frequently encountered in structural synthesis of kinematic chains. A new method has been proposed using two invariants called as First adjacency chain link string [FACLS] and Second adjacency chain link string [SACLS]. These invariants take into account the degree of links and type of joints and are used as the composite identification number of a KC. The proposed method is easy to compute, reliable and capable of detecting isomorphism in all types of compound KC, i.e. chains of single or multi degree of freedom with simple or multiple joints. This study will help the designer to select the best KC and mechanisms to perform the specified task at conceptual stage of design. Some examples are provided to demonstrate the effectiveness of this method.     

Conservative interpolation on unstructured polyhedral meshes: An extension of the supermesh approach to cell-centered finite-volume variables

A method is presented for conservatively transferring, or remapping, cell-centered variable fields from one mesh to another with second-order accuracy. The method is generally applicable to any polyhedral source or target mesh. Like the work of Farrell et al. [1], which was designed for finite-element computations, the proposed methodology uses a logical supermesh consisting of the intersections of polyhedra from both meshes. The resulting transfer process is well-suited for finite-volume methods that rely on cell-centered variables. The accuracy and efficacy of the new remapping process is demonstrated with numerical experiments and a computational fluid dynamics test.     

A systems engineering approach to validation of a pulmonary physiology simulator for clinical applications

Physiological simulators which are intended for use in clinical environments face harsh expectations from medical practitioners; they must cope with significant levels of uncertainty arising from non-measurable parameters, population heterogeneity and disease heterogeneity, and their validation must provide watertight proof of their applicability and reliability in the clinical arena. This paper describes a systems engineering framework for the validation of an in silico simulation model of pulmonary physiology. We combine explicit modelling of uncertainty/variability with advanced global optimization methods to demonstrate that the model predictions never deviate from physiologically plausible values for realistic levels of parametric uncertainty. The simulation model considered here has been designed to represent a dynamic in vivo cardiopulmonary state iterating through a mass-conserving set of equations based on established physiological principles and has been developed for a direct clinical application in an intensive-care environment. The approach to uncertainty modelling is adapted from the current best practice in the field of systems and control engineering, and a range of advanced optimization methods are employed to check the robustness of the model, including sequential quadratic programming, mesh-adaptive direct search and genetic algorithms. An overview of these methods and a comparison of their reliability and computational efficiency in comparison to statistical approaches such as Monte Carlo simulation are provided. The results of our study indicate that the simulator provides robust predictions of arterial gas pressures for all realistic ranges of model parameters, and also demonstrate the general applicability of the proposed approach to model validation for physiological simulation.     

LIBS based spectroscopic analysis and antidiabetic evaluation of a polyherbal formulation

Although plants have long been a major source of medicine, there is renewed interest in studying the phytochemistry and use of herbal formulations. This paper reports spectroscopic analysis using Laser Induced Breakdown Spectroscopy (LIBS) of a polyherbal formulation, whose antidiabetic activity has also been demonstrated on rat models. LIBS analysis revealed the presence of elements such as Na, K, Mg, Ca, H, O and N. The antidiabetic study showed that amongst the four doses studied (50, 100, 150 and 200 mg/kg bw), the dose of 150 mg/kg bw registered the maximum fall in Blood Glucose Level (BGL) in both normal and diabetic (sub and mild) rats in the Glucose Tolerance Test (GTT) study—normal rats (22 %), sub-diabetic (36.6 %) and mild-diabetic (39 %). The dose of 150 mg/kg also showed the maximum fall of 23.7 % and 22 % in BGL during fasting BGL and GTT studies of normal rats, respectively. The formulation also showed significant antioxidant activity assessed using in vitro assays. The study validates for the first time the therapeutic use of an antidiabetic polyherbal formulation.     

Advances in high-k dielectric gate materials for future ULSI devices

This article discusses recent developments in high dielectric constant gate insulator materials for future ultra-large-scale integration devices below 100 nm. Since conventional gate oxide poses problems as device features are scaled down, it becomes necessary to develop new gate dielectric materials with properties similar to SiO₂ and compatible with current complementary metal-oxide semiconductor technology. As the thickness of silicon dioxide approaches less than 1.5 nm, the leakage current becomes higher than 1 A/cm² and tunnel current increases significantly. Therefore, materials are needed to provide excellent electrical characteristics such as dielectric constant higher than 30, interface-state-density less than 1 × 10¹¹/cm²-eV, tunneling current less than 10 mA/cm², and negligible hysteresis. Many high dielectric constant materials have been reported that could potentially replace SiO₂. These include SiO_xN_y, Ta₂O₅, TiO₂, Y₂O₃, CeO₂, SrTiO₃, Al₂O₃, La₂O₃, and silicates of hafnium and zirconium. These materials exhibit the desired high dielectric constants for applications as gate dielectrics in sub-100 nm silicon technology. However, detailed studies need to be performed to evaluate the compatibility of these materials with the rest of the silicon integrated-circuit manufacturing processes. For more information, contact A. Kumar, Center for Microelectronics Research, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida, 33620, (813) 974-3942; fax (813) 974-6310; e-mail akumar1@eng.usf.edu