PVC membrane potentiometric sensor based on 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline-phane for selective determination of neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.     

Modeling and analysis of an extrinsic Fabry-Perot interferometer cavity

A schematic representation of optical feedback between two resonator mirrors undergoing a phase shift each round trip as a function of the separation of the mirrors is studied. A transfer function modeling of the extrinsic Fabry-Perot interferometer (EFPI) is presented. Nyquist analysis has been used to forecast the operational stability and possibility of interference in an EFPI. The analysis with two perfectly parallel surfaces of the cavity shows efficient interference. The performance when there is some tilt between the two mirrors in the cavity is also studied and is presented. In this case some restricted interference is found.     

Computer simulation of injection molding

The injection-molding process consists of three consecutive stages: filling, packing, and cooling. In order to obtain some insight into the phenomena involved in the process, and particularly in order to evaluate the moldability of certain resins and to predict the microstructure and properties of products molded therefrom, a number of workers have employed a variety of techniques based on mathematical simulation of the process. Mathematical simulation involves writing the relevant continuity, momentum, and energy equations governing the system, with appropriate boundary and initial conditions representing the prevailing conditions in the cavity and delivery channels. In order to obtain meaningful solutions to the above equations, detailed information is required regarding the thermodynamic, thermal, and rheological properties of the resin. Moreover, the prediction of the microstructure and ultimate properties of the molded article requires a knowledge of the morphological, crystallization, and orientation phenomena that take place under the influence of the thermo-mechanical history experienced by the resin. The complexity of the equations involved results in the utilization of a number of simplifying assumptions and the resort to computer simulation and numerical solutions of these equations. A variety of numerical schemes based on finite difference and finite element methods has been employed by various researchers.     

Kinetics and thermal characterization of thermoset cure

The differential scanning calorimeter (Perkin-Elmer DSC-1) is used to characterize the cure of a general-purpose polyester during isothermal and scanning experiments. The technique is based on a new proposed model for the kinetics of isothermal cure. The model yields results which are in good agreement with experimental isothermal rate of reaction and integral heat of reaction data. It also gives some information about the residual reactivity of the sample after an isothermal cure experiment. With the aid of the proposed kinetic model, it is possible to obtain integral heats of reaction and rates of heat generation at different temperatures during a scanning experiment. The difference between the rate of heat input to the sample and the heat of reaction at any instant during scanning may be used to calculate the specific heat of the sample at the same instant. Specific heat data show two maxima during each scanning experiment. These maxima may be associated with transitions occurring during cure in the melt and rubbery states.     

Kinetics of anodic oxide-film growth on titanium—II. Neutral and alkaline media

Anodic charging curves have been measured on Ti in Na₂SO₄, NaCl, NaNO₃, NaH₂PO₄, Na₂H PO₄, Na₃PO₄ and NaOH solutions in the cd range 5–35 μA/cm². Formation rates are calculated in the region below O₂ evolution. The results indicate the high-field approximation, with linearity between the reciprocal capacitance and log (cd). Data are recorded for the parameters A and B, the field and the activation distance. While B is independent of solution composition, A depends on the nature of anion and the pH. This behaviour is related to the partial dissolution of the oxide films. Use is made of the charge/potential relations to construct the potential/log (cd) curves. These allow estimation of the pre-immersion oxide thickness, giving a result of about 5 Å.     

Cause and effect in the weathering of plastics

In most instances, the study of the weatherability of plastics follows empirical schemes that show little correlation with the actual effects of outdoor exposure. A more reliable analysis must be based on a knowledge of the factors in the weather which affect plastic properties and of the modes of interaction between these factors and the plastic material. It is shown that both the factors of the weather and the kinetics of polymer degradation may be expressed in a quantitative manner suitable for analytical treatment. Furthermore, it is shown that the analytical approach yields predictions which are in qualitative agreement with the results of actual outdoor exposure. Finally, some new techniques are proposed for more reliable predictions of long-term outdoor weatherability on the basis of laboratory studies.     

RO,MSF and VTE/VC Desalination: A comparative evaluation

For sea water conversion in single-purpose plants, reverse osmosis (RO) is shown to be more economical than multistage flash (MSF) desalination over a wide range of unit size and fuel cost. Attention is focussed on vertical tube evaporation/vapor compression (VTE/VC) a self-contained, low-energy consuming thermal process which is potentially competitive with RO.     

Capillary viscometry: A complete analysis including pressure and viscous heating effects

Capillary viscometers have been used extensively, because of their simplicity and reliability, to measure the viscosity of fluids over a wide range of shear rates. However, in capillary flow, the shear rate is not uniform throughout the capillary, a pressure gradient is established in the direction of flow, and the temperature of the fluid is nonuniform due to viscous dissipation. In the present work, a general, simple and practical method is proposed for correcting for the effects of pressure variation and viscous dissipation in determining the viscosity of polymer melts at high pressures. The method essentially involves the estimation of temperature, pressure, shear rate, and shear stress under a variety of experimental conditions at a predetermined point in the capillary. As such, it may be considered as a generalized extension of the classical Rabinowitsch-Mooney method for estimating true viscosity in capillary flow.     

Obtaining silicide free spacers by optimizing sputter etch for deep submicron CMOS processes

In this paper, we have shown that the sputter etch before cobalt deposition during the silicide processing of a deep submicron CMOS device fabrication needs to be optimized in order to eliminate a detrimental origin of gate (G) to source (S)/drain (D) bridging. It is known that Co cannot reduce even a thin layer of native oxide. Therefore, it is necessary to ensure that Co is deposited on a very clean Si surface. To ensure this, an in-situ sputter etch is commonly conducted before Co deposition. It is observed that this sputter etch process can sputter Si from the S/D area and deposit them on the sidewall spacer (SWS). This sputtered Si in turn will react with deposited Co and form silicide. The worst case leakage currents from poly-Si to composite for long (10 m) and narrow (0.18 micron) poly lines are shown to be on the order of milliampere. Transmission electron microscope (TEM) micrographs included show the existence of cobalt silicide layers (/spl sim/8 nm thick) over sidewall spacer. The silicide thickness on the sidewall spacer is correlated with resistance value calculated from current and voltage (I-V) measurements. The need for optimizing the sputter etch recipe has been validated by TEM and I-V measurements.     

Demand assignment for light-route TDMA

With the fluctuating inter-nodal traffic levels that characterize light-route networks, demand assignment (DA) provides the means of increasing the system's effective capacity. This paper focuses on the application of DA in light-route TDMA, and proposes a control architecture that is well-suited to service of heterogeneous traffic. The major advantage of the proposed architecture is its benefit from both the efficient resource management typical of centralized schemes, and the shorter response times of distributed schemes. The impact of the assignment algorithm on the grade of service to heterogeneous populations, and the difficulty in quantifying this impact are also addressed. Results from analytical and simulation models illustrating resource utilization are presented.