Dominant conduction mechanism and the effects of device temperature on electrical characteristics of Al/ZnPc/n-Si structures

Aluminum/Zinc Phthalocyanine/n-Si metal semiconductor contact with organic interfacial layer has been developed and characterized by Current-Voltage-Temperature (I-V-T) measurements for the study of its junction and charge transport properties. The junction parameters, such as diode ideality factor (n), barrier height (φ_b) and series resistance (R_S), of the device were found to shift with device temperature. The diode ideality factor was found to increase with the device temperature up to 323 K. However, a decreasing trend in the value of n was observed beyond this temperature. The barrier height and series resistance were found to increase and decrease, respectively with increasing device temperature. The peak of interface state energy distribution curves was shifted, in terms of Ess-Ev value, from 0.622 eV to 0.827 eV with 52 meV activation energy of the charge carriers. The data analysis implies that the Fermi level of the organic interfacial layer shifts as function of device temperature. In terms of dominant conduction mechanism, the I-V-T data analysis confirms the relationship log (IV⁴) ∝V^1/2 with the device temperature in the range of 313-343 K and the Poole-Frenkel type is found to be the dominant conduction mechanism for the hybrid device.     

The effects of welding parameters on the weldability of different materials using brazing alloy fillers

The objectives of the study were to investigate the microwelding conditions related to diffusion mechanism and elemental migration metallurgical and microscopy investigation, and to establish the fundamental corrosion mechanism on the properties of small welding and brazing areas that consist different materials. This study focuses on the weldability of Ti /Ni using microspot brazing technology by selection of brazing condition current, 2, 2.5, 3, 3.5 and 4 kA, voltage 2 V, load 60 N and welding time 25–50 ms, this welding condition effective on brazing temperature optimization this condition. Ti and Ni were selected as base metals. Four types of metal fillers were used as filler foils, sandwiched between Ti/Ni. First type of metal fillers was, 65Ni–35Cu foil, melting point 846 °C; the second was, 71Ag–28Cu–1Mg foil, melting point 775 °C; the third was, 80Ag–18Cu–2Ti foil, melting point 782 °C; and fourthly was, 73Ni–18Cr–9Si foil, melting point 917 °C. The electrode tip face chosen was circuitous in form. All brazed joint were made by microspot brazing method. Brazing was done under normal atmospheric condition.     

Predicting Shrinkage Stress Field in Concrete Slab on Elastic Subgrade

Concrete is a material that changes volumetrically in response to moisture and temperature variations. Frequently, these volumetric changes are prevented by restraint from the surrounding structure, resulting in the development of tensile stresses. This paper provides a method for computing the stress and displacement fields that develop in response to this restraint by considering the concrete slab as a plate resting on an elastic foundation. The interface between the slab and the foundation is capable of simulating all cases between complete perfect bond and perfect compression∕zero tension bond to permit debonding. In addition, stress relaxation is considered in the concrete to account for the reduction in stress due to creep∕relaxation-related phenomena. For this reason, the stress-strain relationship and equilibrium equations have been considered in the rate or differential form. The history-dependent equilibrium equations are obtained by integrating the differential equations with respect to time. An example is presented to illustrate the favorable correlation that exists between the predicted behavior of the plate model and finite-element modeling.     

Influence of Specimen Size∕Geometry on Shrinkage Cracking of Rings

This paper presents experimental evidence to show that a size∕geometry dependence is observed in the shrinkage cracking behavior of restrained concrete structures. A theoretical model is developed to explain this behavior. First, a solution is presented to compute the stress and displacement fields of an aging, linear, viscoelastic cylinder by assuming that a uniformly distributed shrinkage strain is perfectly restrained in the radial direction at the internal surface of the cylinder. Second, a fracture mechanics failure criterion is implemented to develop time and geometry-dependent tensile stress resistance (strength) curves. Third, this model is used to illustrate the role of specimen size∕geometry and material composition on the failure response. Finally, experimentally measured ages of cracking are compared with the theoretical modeling predictions.     

Model predictive control for the reactant concentration control of a reactor

The reactant concentration control of a reactor using Model Predictive Control (MPC) is presented in this paper. Two major difficulties in the control of reactant concentration are that the measurement of concentration is not available for the control point of view and it is not possible to control the concentration without considering the reactor temperature. Therefore, MIMO control techniques and state and parameter estimation are needed. One of the MIMO control techniques widely studied recently is MPC. The basic concept of MPC is that it computes a control trajectory for a whole horizon time minimising a cost function of a plant subject to a dynamic plant model and an end point constraint. However, only the initial value of controls is then applied. Feedback is incorporated by using the measurements/estimates to reconstruct the calculation for the next time step. Since MPC is a model based controller, it requires the measurement of the states of an appropriate process model. However, in most industrial processes, the state variables are not all measurable. Therefore, an extended Kalman filter (EKF), one of estimation techniques, is also utilised to estimate unknown/uncertain parameters of the system. Simulation results have demonstrated that without the reactor temperature constraint, the MPC with EKF can control the reactant concentration at a desired set point but the reactor temperator is raised over a maximum allowable value. On the other hand, when the maximun allowable value is added as a constraint, the MPC with EKF can control the reactant concentration at the desired set point with less drastic control action and within the reactor temperature constraint. This shows that the MPC with EKF is applicable to control the reactant concentration of chemical reactors.     

Logic Design Validation via Simulation and Automatic Test Pattern Generation

We investigate an automated design validation scheme for gate-level combinational and sequential circuits that borrows methods from simulation and test generation for physical faults, and verifies a circuit with respect to a modeled set of design errors. The error models used in prior research are examined and reduced to five types: gate substitution errors (GSEs), gate count errors (GCEs), input count errors (ICEs), wrong input errors (WIEs), and latch count errors (LCEs). Conditions are derived for a gate to be testable for GSEs, which lead to small, complete test sets for GSEs; near-minimal test sets are also derived for GCEs. We analyze undetectability in design errors and relate it to single stuck-line (SSL) redundancy. We show how to map all the foregoing error types into SSL faults, and describe an extensive set of experiments to evaluate the proposed method. These experiments demonstrate that high coverage of the modeled errors can be achieved with small test sets obtained with standard test generation and simulation tools for physical faults.     

Methodology to Obtain True Thermal Conductivity of Low Porosity Food Powders

ABSTRACT: A technique was developed to measure, at a porosity close to zero, the true thermal conductivity of food powders. Samples of low porosities were prepared by mechanically compressing the food powder using a hydraulic press at pressures up to 3.035 × 10⁵ kPa (abs) in specially designed stainless steel cylinders with a dummy probe in place. Variation in porosity of the samples was less than 5%. Thermal conductivity was measured as a function of porosity (0.086 to 0.7), moisture content (0 to 37%, dry basis), and temperature (30 to 150 °C) by the thermal conductivity probe method. The thermal conductivity values decreased with an increase in porosity and increased with an increase in moisture content and temperature.     

Monte Carlo evaluation of derivative-based global sensitivity measures

A novel approach for evaluation of derivative-based global sensitivity measures (DGSM) is presented. It is compared with the Morris and the Sobol’ sensitivity indices methods. It is shown that there is a link between DGSM and Sobol’ sensitivity indices. DGSM are very easy to implement and evaluate numerically. The computational time required for numerical evaluation of DGSM is many orders of magnitude lower than that for estimation of the Sobol’ sensitivity indices. It is also lower than that for the Morris method. Efficiencies of Monte Carlo (MC) and quasi-Monte Carlo (QMC) sampling methods for calculation of DGSM are compared. It is shown that the superiority of QMC over MC depends on the problem's effective dimension, which can also be estimated using DGSM.     

Heavy metal accumulation in different varieties of wheat (Triticum aestivum L.) grown in soil amended with domestic sewage sludge

The concentrations of heavy metals (HMs) in plants served to indicate the metal contamination status of the site, and also revealed the abilities of various plant species to take up and accumulate them from the soil dressed with sewage sludge. A study to comprehend the mobility and transport of HMs from soil and soil amended with untreated sewage sludge to different newly breaded varieties of wheat (Anmol, TJ-83, Abadgar and Mehran-89) in Pakistan. A pot-culture experiment was conducted to study the transfer of HMs to wheat grains, grown in soil (control) and soil amended with sewage sludge (test samples). The total and ethylenediaminetetraaceticacid (EDTA)-extractable HMs in agricultural soil and soil amended with domestic sewage sludge (SDWS) and wheat grains were analysed by flame atomic absorption spectrometer/electrothermal atomic absorption spectrometer, prior to microwave-assisted wet acid digestion method. The edible part of wheat plants (grains) from test samples presented high concentration of all HMs understudy (mgkg(-1)). Significant correlations were found between metals in exchangeable fractions of soil and SDWS, with total metals in control and test samples of wheat grains. The bio-concentration factors of all HMs were high in grains of two wheat varieties, TJ-83 and Mehran-89, as compared to other varieties, Anmol and Abadgar grown in the same agricultural plots.