Intelligent Interactive Tutoring Systemfor Engineering Mechanics

Engineering education has traditionally been imparted through the lecture-tutorial-laboratory paradigm. Education technology in the last few years has tried to make teaching more effective by supplementing the chalkboard teaching with audiovisual aids like overhead∕slide projectors and videos. These are, however, passive teaching tools. Recent advancement in computer multimedia has brought in a new teaching medium. Multimedia education has several advantages; most noticeably, the instructions can be interactive and self-paced to meet the needs of each individual student. The writers have developed an Intelligent Interactive Tutoring System for engineering mechanics for the first-year engineering students at the Nanyang Technological University, Singapore. The main objective of this system was to supplement classroom teaching via intelligent interaction with the computer-based tutoring system. This system is designed to be a self-paced virtual tutor with intelligent, user-friendly interactions. It is intended to be different from the many commercially available computerized textbooks. The prototype system was tried out with about 200 students who had earlier failed the course in the first semester and repeated it in the second semester of academic year 1997–1998. The system received good response from the students. The full version was implemented on the Nanyang Technological University Intranet and the Internet for use by the regular class of more than 1,600 students in both academic years 1998–1999 and 1999–2000.     

Bubble Formation through Reaction at Liquid‐Liquid Interfaces

Slag foaming is an important phenomenon in steelmaking processes with both beneficial as well as negative effects. The present work is part of the wider project on the modelling of slag foaming, with special reference to dynamic conditions. Since bubble formation is the first step to foam formation, the present work was carried out in an attempt to simulate the bubble formation in slag/metal reactions in steelmaking processes by water‐modelling experiments. The bubble formation due to the gas produced through chemical reaction at the interface between oleic acid and sodium bicarbonate solution was systematically monitored. The chemical reaction rate was varied by varying the concentration of sodium bicarbonate. The bubbles were observed to be generated in the heavier aqueous phase just below the water‐oil interface. The bubbles penetrated the interface and escaped through the oil phase. The rate of the reaction was estimated from the volume of the gas that passed the water/oil interface. It was observed that the bubble formation and bubble growth mechanism were influenced by the reaction rate while the bubble size seemed to be unaffected by the reaction rate.     

Investigating Role of Growing Adsorbent Bed in a Dead-End PAC/UF Process

A two-stage mathematical model was developed to describe adsorbate removal in a dead-end powdered activated carbon/ultrafiltration (PAC/UF) membrane process. Para-nitrophenol (PNP) was used as the model organic compound. The first stage accounted for adsorbate removal during transport from the initial PAC contact with the PNP solution to the membrane system, and the second stage accounted for additional PNP removal due to the retention of the PAC in a growing bed on the membrane surface. The PAC adsorptive capacity was described using the Langmuir isotherm, whose parameters were estimated from isotherm experiments. Transport of the PNP through the PAC particle was described using the homogeneous surface diffusion model and the surface diffusivity was estimated from batch experiments. The two stage model predicted the effluent concentrations from the PAC/UF process during the early stages of the experiments, but model improvements are required to more accurately predict the latter stages. A batch model can be used to describe the effluent PNP concentration from the PAC/UF process if dispersion is neglected.     

Stimulating Biological Nitrification via Electrolytic Oxygenation

The feasibility of electric current prompted aerobic biodegradation of NH4+–N in an attached growth bioreactor system is demonstrated. Nitrification was induced at electric current densities of 1.25 and 2.5?mA/cm2 and with pure oxygen supplied at a rate equivalent to 1.25?mA/cm2 when the bioreactor was operated in batch mode at 6 days detention time. About 84% (27?mg/L)?NH4+–N loss was observed at the end of each detention period during all three experimental conditions, indicating that the electric current did not negatively impact the rate of nitrification. Nitrite accumulation was observed during the initial stages of nitrification experiments with 1.25?mA/cm2 current intensity, but nitrite did not accumulate during the other two sets of nitrification experiments. A mathematical model formulated to obtain the rates of biological reactions showed that rates of NH4+–N removal are similar for all aeration conditions. Abiotic experiments showed that NH4+–N was not removed electrolytically and via stripping, confirming that NH4+–N disappearance is due to biological activity.     

Trace elements of soil samples from mining area

The affect of mining activity on the environment has been long of public concern. The present paper deals with the elemental analysis of soil samples from a mine and the area around it, located in E 48°59′ and N 34°11′ in Hamadan province of Iran. Elemental analysis was done using Proton Induced X-ray Emission (PIXE) technique. Spectra analysis and quantification was done using GUPIX software. Besides the major elements Si, P, K, Ca, Mn and Fe the other elements, namely Cl, Ti, V, Cr, Co, Ni, Cu, Zn, Rb, Sr and Pb were also present. Arsenic could be detected in some samples only. The presence of Ba and Ce needs more investigations by other techniques due to overlap of the L X-rays of these elements with the K X-rays of the major elements Mn and Fe, etc. Many elements V, Cr, As and Pb are known to be toxic and needs further understanding and proper handling in the mining process.     

Micro-mechanical Behaviour of AA2014 Alloy During Hot Tensile Testing

Nowadays, critical aircraft application demands high end performance of respective aerospace materials. Al–4.5 %Cu alloy known as duralumin have extensive application on spacecraft, as ring rolled and heat treated condition. However, behaviour of the same alloy at high temperature is always a thirst area to improve the understanding. This paper mainly focussed on the behaviour of duralumin alloy during hot tensile testing. Hot tensile testings were done at six different temperatures ranging from room temperature to 300 °C. Mechanical properties at various temperatures were measured and studied along with the microstructural changes at all experimental conditions. Thermodynamic software package FactSage simulation was employed to identify the precipitates expected to precipitate at high temperature. Important conclusions were drawn from both theoretical and experimental observations.     

Mitochondrial calcium in relaxed and tetanized myocardium

The elemental composition of rat cardiac muscle was determined with electron probe x-ray microanalysis (EPMA) of rapidly frozen papillary muscles and trabeculae incubated with ryanodine (1 microM) in either 1.2 or 10 mM [Ca2+]o-containing solutions, paced at 0.6 Hz or tetanized at 10 Hz. Total mitochondrial calcium increased significantly, by 4.2 mmol/kg dry weight during a 7 s tetanus, only in muscles tetanized in the presence of 10 mM [Ca2+]o when cytoplasmic Ca2+ is 1-4 microM (Backx, P. H., W.-D. Gao, M. D. Azan-Backx, and E. Marban. 1995. The relationship between contractile force and intracellular [Ca2+] in intact rat trabeculae. J. Gen. Physiol. 105:1-19). Comparison of total mitochondrial with free mitochondrial Ca2+ reported in the literature indicates that the total/free ratio is approximately 6000 at physiological or near-physiological levels of total mitochondrial calcium. Increases in free mitochondrial [Ca2+] consistent with regulation of mitochondrial enzymes should be associated with increases in total mitochondrial calcium detectable with EPMA. However, such increases in mitochondrial calcium occur only as the result of prolonged, unphysiological elevations of cytosolic [Ca2+].     

A 4?8 GHz dual gate m.e.s.f.e.t. amplifier

A two-stage dual-gate f.e.t. amplifier with small signal gain of 20 ± 0.75 dB, covering an octave bandwidth (4?8 GHz) and having a dynamic gain control range in excess of 60 dB is reported. The gain frequency response, input and output v.s.w.r. are described as a function of second-gate voltage. The performance of the dual-gate f.e.t. amplifier as a fast r.f. switch is also presented.     

Stochastic behaviour of a two-unit cold standby system with three modes and allowed down time

This paper discusses the stochastic behaviour of a two-unit cold standby redundant system under two very general sets of conditions: (i) each unit of the system having three different modes of working—normal, partial failure and total failure; (ii) breakdown of the system occurring when with both the units in total failure mode, the system is not regarded as failed (the system fails only when the breakdown does not terminate within the allowed down time). Failure-time distributions of units are exponential, whereas repair time distributions are arbitrary. Several reliability characteristics of interest to system designers as well as operations managers have been evaluated.