Application of Methanobrevibacter acididurans in anaerobic digestion.

To operate anaerobic digesters successfully under acidic conditions, hydrogen utilizing methanogens which can grow efficiently at low pH and tolerate high volatile fatty acids (VFA) are desirable. An acid tolerant hydrogenotrophic methanogen viz. Methanobrevibacter acididurans isolated from slurry of an anaerobic digester running on alcohol distillery wastewater has been described earlier by this lab. This organism could grow optimally at pH 6.0. In the experiments reported herein, M. acididurans showed better methanogenesis under acidic conditions with high VFA, particularly acetate, than Methanobacterium bryantii, a common hydrogenotrophic inhabitant of anaerobic digesters. Addition of M. acididurans culture to digesting slurry of acidogenic as well as methanogenic digesters running on distillery wastewater showed increase in methane production and decrease in accumulation of volatile fatty acids. The results proved the feasibility of application of M. acididurans in anaerobic digesters.     

Analysis and evaluation of permeability techniques for characterizing fine particles Part II. Measurement of specific surface area

The performance of both steady-state and transient permeameters has been evaluated. A number of standard powders was chosen and their surface areas determined by gas adsorption techniques for comparison with surface areas obtained using permeameters. The powders were chosen to cover a wide range o density (0.92 – 18.7 g/cm³) and surface area (0.06 – 350 m²/g).The effect of particle shape, i.e. needles, spherical particles, flakes and irregularly shaped particles on surface area determined by permeametry has also been studied. A linear relationship between BET surface area and that obtained by using a simple U-tube transient flow permeameter has been obtained over a wide range of particle size and macroporosity.The Fisher Subsieve Sizer was chosen as a typical example of a steady-state permeameter, and a number of shortcomings in this instrument have been found. A simple steady-state permeameter was constructed to evaluate the theoretical model as developed in Part I for atmospheric pressure permeametry, and the model has been found to give good values of external surface areas for powders having an average particle size greater than 2 μm. The effect of slip flow for particles less than 1 μm in diameter has been established for atmospheric pressure permeametry.This paper also presents measurements of specific surface area determined by using a more recent permeameter, namely the Permaran. This instrument performed within a reproducibility of ±7% and produced data in agreement with that taken on similar devices and also with the theoretical analysis presented in Part I.The performance of a Knudsen-flow permeameter has been evaluated, and the instrument has been found to give accurate values of external surface area of fine as well as coarse powders.     

Mn-Doped Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript> Phosphors Synthesis Using Flame Spray Pyrolysis

Zn₂SiO₄:Mn²⁺ particles are used as green phosphors in plasma display panels and cathode ray tubes. In this study, we report the synthesis of zinc silicate phosphors by flame spray pyrolysis using different Zn-sources and under different process conditions. The XRD and luminescence measurement showed the phosphors prepared from Zn-nitrate source to have better crystallinity and emission characteristics. The luminescence properties of the phosphor particles were found to improve both at higher methane flow rates during pyrolysis and at higher annealing temperatures.     

An adjustable work function technology using Mo gate for CMOSdevices

Nitrogen implantation of Mo gate was used to fabricate MOS capacitors and CMOS transistors. Initial studies demonstrate that the work function of Mo is sensitive to nitrogen implantation energy. Mo with (110) orientation exhibits a high work function, making it suitable for bulk p-MOSFET gate electrodes. Nitrogen implantation can be used to lower the Mo work function, making it suitable for n-MOSFET gate electrodes. A gate work function reduction of 0.42 eV was achieved for the n-FETs on CMOS wafers. With further optimization, this single metal gate technology may potentially replace conventional poly-Si gate technology for CMOS and can also be used for multiple-V_T technologies     

Interaction between micro- and macro-mixing during reactions in agitated tanks

The present investigation focusses on the interactions between micro-and macro-mixing in a stirred tank reactor, operated in the semi-batch mode. With long feed times only micromixing controls reaction, but below a critical feed time macroscopic gradients also become important. Experiments generated a coherent data set which can be used as a design guide and also for model validation. A competitive, consecutive azocoupling reaction was carried out, whereby imperfect mixing produces finite values of X_S (yield of secondary product) which can be conveniently used as a mixing index. The influences of feed location, feed rate, stirrer speed, concentrations and vessel size on selectivity were studied. The micromixing model of Baldyga and Bourne (1989) was extended to include interactions between macro-and micro-mixing and should be valid for feed times below the critical value, although not so short as the macromixing time in the vessel. Model predictions were compared with the experimental results.     

A novel elevated source/drain PMOSFET formed by Ge-B/Si intermixing

Driven by strain relaxation, the rapid thermal annealing (RTA) of B-doped Ge on an Si substrate forms graded Si_1-xGe_x layers with B confined inside. Based on this observation of Ge-B/Si intermixing, a novel elevated source/drain (S/D) PMOSFET fabrication process is proposed. The new process consists of three simple steps: (a) selective Ge deposition in S/D regions by conventional LPCVD, (b) B implantation, and (c) RTA for Ge-B/Si intermixing to form S/D extensions to the channel. Fabricated PMOSFETs with sub-100 nm gate lengths display excellent short channel performance     

Equilibrium solubility and permeability of sulfur dioxide in epoxy resin of aliphatic diglycidyl ether

Equilibrium sorption isotherms were obtained for the sulfur dioxide-epoxy resin of aliphatic diglycidyl ether system over a temperature range of 1° to 45°C. The sorption isotherms indicated the presence of Langmuir sorption due to specific interaction. This is uncommon for rubbery polymers, though similar behavior was also observed previously. Zimm-Lundberg's clustering analysis indicated a slight tendency for clustering of the penetrant molecules at low temperatures and higher activities. The number of Langmuir sites for sorption was found to be independent of temperature. The mobilities of the molecules sorbed in Henry's law mode and the Langmuir mode were found to be approximately equal. Predictions of the permeability values for this system are presented and compared with other data from the literature. The temperature dependence of different sorption parameters is presented and discussed in detail.     

Comparative evaluation of tolerance control chart models

A comparative evaluation of two widely used tolerance stack up models is carried out. Experimental metal cutting tests of resultant dimensions obtained under one and two fixturing set-ups are used to test the underlying assumptions behind the Wade and Bourdet tolerance chart models. Resultant dimensions obtained under a single fixturing set up are found to be highly correlated and free of fixturing error; their treatment under the Wade model can thus lead to overly conservative tolerance allocation which may reject an otherwise feasible process plan. The results of the experimental evaluation lend support to the Bourdet deterministic treatment of such resultant dimensions. However, the probabilistic approach proposed by Bourdet does not guarantee a solution.     

Drop breakage in a single-pass through vortex-based cavitation device: Experiments and modeling

Liquid–liquid emulsions are used in many sectors such as personal care, home care, and food products. There is an increasing need for developing compact and modular devices for producing emulsions with desired droplet size distribution (DSD). In this work, we have experimentally and computationally investigated an application of vortex-based hydrodynamic cavitation (HC) device for producing emulsions. The focus is on understanding drop breakage occurring in a single-pass through the considered HC device. The experiments were performed for generating oil-in-water emulsion containing 1%–20% rapeseed oil. The effect of pressure drop across the HC device in the range of 50–250 kPa on drop breakage was examined. DSD of emulsions produced through a single pass was measured using the focussed beam reflectance measurements. Comprehensive computational fluid dynamics (CFD) model based on the Eulerian approach was developed to simulate multiphase cavitating flow. Using the simulated flow, population balance model (PBM) with appropriate breakage kernels was solved to simulate droplet breakage in a vortex-based HC device. The device showed an excellent drop breakage efficiency (nearly 1% which is much higher than other commercial devices such as rotor–stators or sonolators) and was able to reduce mean drop size from 66 to ~15 μm in a single pass. The CFD and PBM models were able to simulate DSD. The presented models and results will be useful for researchers and engineers interested in developing compact devices for producing emulsions of desired DSD.