Microprocessor-Based Control of an Ion Beam Deposition System

A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films.     

On obtaining of a transfer function with complex-conjugate poles of the same Q-factor by fourier approximation

This communication presents a method for obtaining a transfer function with multiple complex conjugate poles. The procedure is based on a special frequency transformation. The function derived from those to be approximated is expanded in a Fourier series with a finite number of terms. The application of the inverse transformation to this truncated series gives an algebraic ratio from which the transfer function with chosen poles can be obtained with known methods.     

More active RC filters using the d.v.c.c.s./d.v.c.v.s.

Novel configurations using a differential-voltage-controlled current source, differential-voltage-controlled voltage source (d.v.c.c.s./d.v.c.v.s.) as the active building block are described. The configurations assume that the active building block is divided into two independent parts initially.     

Simultaneous removal of phosphorus and foulants in a hybrid coagulation/membrane filtration system

At many wastewater treatment plants, chemical addition is required to meet the requirements for discharge of phosphorus. Membrane filtration is an attractive option for removing the chemically precipitated phosphorus, but that process can be impeded by fouling of the membrane by effluent organic matter (EfOM). In the current study, membrane fouling and ortho-P removal were explored in hybrid adsorbent/membrane systems dosed with alum and/or a new aluminum-based adsorbent (heated aluminum oxide particles, HAOPs). HAOPs prevented fouling more effectively than alum did, even though the two adsorbents removed similar amounts of EfOM. The HAOPs were particularly effective when they were pre-deposited on the membrane (as opposed to being mixed into the feed upstream). On the other hand, alum removed ortho-P more efficiently than HAOPs did. Combining both adsorbents in a single membrane system takes advantage of the most attractive features of each, accomplishing good ortho-P removal while simultaneously minimizing fouling. In addition to being potentially applicable directly, the results demonstrate the potential benefits of using multiple coagulants and/or adsorbents in a single hybrid membrane system.     

Modeling a novel ion exchange process for arsenic and nitrate removal

Arsenate and nitrate can be removed quantitatively from drinking water by anion exchange. However, if the raw water contains substantial concentrations of sulfate or nitrate, the resin becomes exhausted quickly, and the requirements for regenerant (brine) can make the process unattractive. Previously, we described a modified ion exchange operating procedure for arsenic removal from solutions containing sulfate that could overcome this problem. This paper extends that work to solutions containing nitrate, and presents a mathematical model for the process. The selectivity coefficient for sulfate over nitrate of a strong base anion exchange resin increased dramatically with increasing ionic strength, partially counteracting the decrease in SO(4)/NO(3) separation factor predicted from mass action considerations. The value of this selectivity coefficient in different solutions can be used in conjunction with mass balances and solid/liquid equilibrium considerations to explore the brine requirement when the modified treatment process is applied to influent waters with various compositions. The modeling results indicate that, for relatively low influent nitrate concentrations, the volume of water treated per unit volume of brine used can be increased greatly by using the modified ion exchange process. At higher influent nitrate concentrations, the modified process remains advantageous, but is less so. The use of separate brine solutions to regenerate the upstream and downstream columns magnifies the benefits of the modified process significantly. If the sulfate in the brine is precipitated as CaSO(4)(s) rather than BaSO(4)(s), the brine usage rate increases by only 30-40%, even though the former solid is orders of magnitude more soluble than the latter.     

Coarse-graining of cohesive zone at interface of amorphous material

This work studies on coarse-graining of the cohesive zone at the interface of an amorphous material. A coarse-grained cohesive zone model is obtained with the aid of homogenization and relaxation method. The amorphous material in atomic scale is homogenized and the effect of its domain volume upon homogenization is investigated through molecular dynamics. The homogenized amorphous material is then utilized for coarse-graining at the interface. Coarse-graining leads to an increase of opening displacement and a decrease of decohesion stress while fracture toughness of the interface is conserved.     

Temperature dependence of screw dislocation mobility on shuffle-set of silicon

Large-scale atomistic simulations are performed in order to observe local behaviors of screw dislocations located on the shuffle set of (111) in single crystal silicon, focusing on the propagation process of the screw dislocations. A quadrupolar arrangement of screw dislocations is utilized to impose the periodic boundary conditions along each of the three spatial directions. With the aid of molecular dynamics simulations, the dislocation mobility is investigated in terms of the critical resolved shear stress. Based on the results from the simulations, we discuss effects of the model size and temperature on the critical resolved shear stress. After choosing the proper model size to reduce undesirable interference between the dislocations, we further estimate the Peierls stress by fitting from a set of the critical resolved shear stresses at various temperatures. Meanwhile, we observe a double kink mechanism in the dislocation propagation which is the most energetically favorable dislocation movement in silicon. We investigate the formation and migration of kink pairs on an undissociated screw dislocation in silicon.     

Comparative study of electrochemical degradation and ozonation of nonylphenol

Treatment of solutions of nonylphenol (NP), Triton X-100 (TrX) and phenol in a flow-through undivided EC reactor equipped with a Co(2+)-promoted PbO(2) anode and a stainless steel cathode was accompanied by consistent changes of absorbance, fluorescence and mass spectra of the effluents, and formation of aldehydes ranging from formaldehyde to decyl aldehyde. Deconvolution of the absorbance spectra of EC-treated NP, TrX and phenol and examination of their fluorescence indicated that the compounds are rapidly degraded in the reactor. For NP, the degradation of the target proceeded via the generation (at current densities <25mA/cm(2)) of benzoquinone intermediates that yielded peaks with m/z ratios 223, 227, 235, and 241D in the mass spectra. Their breakdown at current densities >10mA/cm(2) was accompanied by the release of aldehydes that were predominated by acetaldehyde and formaldehyde. The total yield of aldehydes increased with the current density, but their speciation showed little sensitivity to it. Deconvolution of the absorbance spectra of NP solutions subjected to ozonation, and analysis for reaction by-products formed in these conditions showed the reaction pathway in the latter case was likely to be similar to that observed for the EC treatment.     

Current-voltage conveyor

A four-port active circuit called the current-voltage conveyor (CVC) is proposed and its properties are described. It can be used for realisation of controlled sources, negative impedance convertors and other active elements. It is shown how to obtain summing of voltages and currents using the CVC. The realisation of the CVC with OAs and OTAs is given.