Hydration Study of the System Ca3Al2O6–CaSO4· 2H2O–Ca(OH)2–H2O with and without Citric Acid

Hydration occurring in the system Ca₃Al₂O₆–CaSO₄· 2H₂O–Ca(OH)₂–H₂O has been studied at different temperatures and it was found that the reactions are diffusion controlled. The kinetic data obeyed Jander's equation and the rate of reaction increased with increasing temperature. X-ray diffraction studies and calorimetric measurements show that when gypsum is consumed, ettringite is converted into monosulfate. The rate of this conversion also increased with the increasing temperature and decreased in the presence of citric acid. Spectroscopic studies showed that there was some interaction between citric acid and the cement and that the product of hydration is of colloidal nature. Zeta potential measurements show that retardation of Ca₃Al₂O₆ hydration in the presence of gypsum and Ca(OH)₂ is not due to SO²⁻₄ adsorption. Electrical conductivity and thermoelectric potential measurements of solid Ca₃Al₂O₆ show that Ca₃Al₂O₆ is an n -type semiconductor and contains defects. The retardation of Ca₃Al₂O₆ may be due to poisoning of reaction sites by gypsum and Ca(OH)_2.     

Diffusion coefficient in polymer solutions

Molecular diffusivity of a solute in a solvent may be determined by measuring the extent of dispersion of solute in solvent flowing in a straight circular tube under the conditions of laminar flow. This simple and rapid method for determination of molecular diffusivity in aquous polymer solutions is discussed. Experimental results show a substantial reduction in the solute diffusivity with increase in polymer concentration.     

Predicting external sulphur requirement of alfalfa from sulphate sorption isotherm of Tanzanian soils

For Tanzanian soils dominant in hydrous oxides of iron and amorphous ferri-alumino silicate, a 48-hour (hr) mixing period with the sulphate (SO₄) solution was adequate for a near-equilibrium condition. Although differing in their SO₄ sorption capacity, all the soils sorbed SO₄ at or beyond 1µg ml^–1 sulphur (S) concentration in the supernatant. Hydroxyl (OH) ions were displaced during SO₄ sorption as indicated by a significant positive correlation between the amount of sorbed SO₄ and the difference in pH values determined in 0.1N K₂ SO₄ and 0.1N KCl, i.e. the dpH values.In a greenhouse experiment, alfalfa was grown on eight soils at six adjusted S concentrations. Sulphur deficiency symptoms appeared in the control pots of those soils which were low in native sorbed SO₄, SO₄ sorption capacity and initial soil solution S concentration. Sulphur fertilization increased dry matter (DM) yield as well as response to applied S. The external S concentration, i.e. adjusted S concentration required for 95% of the maximum DM yield, ranged from 0.8 to 8.2µg S ml^–1 with values less than 2.0 on most of the soils. The external S concentration decreased hyperbolically as the SO₄ sorption capacity of the soils increased. The total amount of fertilizer S required to obtain the external S concentration in solution, and at the same time satisfy the SO₄ sorption capacity of the soil at the external S concentration (determined from the sorption isotherm) was defined as the external S requirement for the specified yield level of alfalfa. The external S requirement for 95% of the maximum yield of alfalfa varied from soil to soil due to differences in their capacity and intensity for S nutrition.Part of a thesis by the senior author for the MSc (Agric) degree of the University of Dar es Salaam     

Development of antimicrobial polypropylene sutures by graft copolymerization. II. Evaluation of physical properties,drug release,and antimicrobial activity

Polypropylene (PP) sutures are prepared by the simultaneous radiation grafting of 1‐vinylimidazole (VIm) onto PP monofilament sutures. The tenacity slightly decreases whereas the elongation increases with the increase in the degree of grafting. Thermogravimetric analysis shows that the stability of the sutures is enhanced by the grafting process. The grafted sutures have reasonably good water uptake. They are subsequently immobilized with an antimicrobial drug, ciprofloxacin. The modified suture releases the drug over a period of 4–5 days. The antimicrobial activity of the modified suture is determined against Esherichia coli by the zone of inhibition technique. A clear zone of inhibition is observed around the drug‐containing suture. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3534–3538, 2007     

An efficient approach for face recognition based on common eigenvalues

In this paper, a simple technique is proposed for face recognition among many human faces. It is based on the polynomial coefficients, covariance matrix and algorithm on common eigenvalues. The main advantage of the proposed approach is that the identification of similarity between human faces is carried out without computing actual eigenvalues and eigenvectors. A symmetric matrix is calculated using the polynomial coefficients-based companion matrices of two compared images. The nullity of a calculated symmetric matrix is used as similarity measure for face recognition. The value of nullity is very small for dissimilar images and distinctly large for similar face images. The feasibility of the propose approach is demonstrated on three face databases, i.e., the ORL database, the Yale database B and the FERET database. Experimental results have shown the effectiveness of the proposed approach for feature extraction and classification of the face images having large variation in pose and illumination.     

The C-loss function for pattern classification

This paper presents a new loss function for neural network classification, inspired by the recently proposed similarity measure called Correntropy. We show that this function essentially behaves like the conventional square loss for samples that are well within the decision boundary and have small errors, and L₀ or counting norm for samples that are outliers or are difficult to classify. Depending on the value of the kernel size parameter, the proposed loss function moves smoothly from convex to non-convex and becomes a close approximation to the misclassification loss (ideal 0–1 loss). We show that the discriminant function obtained by optimizing the proposed loss function in the neighborhood of the ideal 0–1 loss function to train a neural network is immune to overfitting, more robust to outliers, and has consistent and better generalization performance as compared to other commonly used loss functions, even after prolonged training. The results also show that it is a close competitor to the SVM. Since the proposed method is compatible with simple gradient based online learning, it is a practical way of improving the performance of neural network classifiers.     

Surface tension and contact angle of herbicide solutions affected by surfactants

Contact angle and surface tension were measured for distilled and hard water solutions of adjuvants, Ortho X-77, Span-20, Sterox-NJ. Surfactant-WK, Triton B-1956, Triton X-114, Tween-20, and Sun Oil 11E. The same parameters were measured for suspensions of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] with and without each adjuvant. All adjuvants reduced surface tension and contact angle of distilled water; Surfactant-WK was most effective and Tween-20 was least effective. Increasing concentration of surfactants from 0 to 0.1% (v/v) gave progressive reduction in surface tension and contact angle while higher concentrations, 0.1 to 2.0% (v/v), had no further effect. Surfactant-WK at 0.1% (v/v) in distilled water reduced the surfact tension from 72.8 dynes/cm to 27 dynes/cm and contact angle from 110° to 41°. An additional increase in Surfactant-WK concentration from 0.1% (v/v) to 2% (v/v) did not further reduce surface tension and contact angle. Sun Oil 11E was identical in behavior except that it was less effective than the surfactants. Water hardness up to 1,000 ppm as Ca ions did not affect surface tension and contact angle in surfactant solutions. An aqueous solution of atrazine had a higher surface tension and contact angle than ametryne in the absence of surfactants. However, these differences were not observed when surfactants were added to either herbicide.     

Crack Growth in Solid Oxide Fuel Cell Materials: From Discrete to Continuum Damage Modeling

This paper addresses the damage and fracture issues of glass and ceramic materials used in solid oxide fuel cells. Analyses of an internal crack and of an interface crack between dissimilar materials were conducted using a modified boundary layer modeling approach. In this approach, fracture is allowed to occur in a small process window situated at an initial crack tip. Elastic displacement crack-tip fields are prescribed as remote boundary conditions. Crack propagation was first modeled discretely. Next, a continuum damage mechanics (CDM) model for brittle materials was developed to capture damage and crack growth in the process window. In particular, the damage model was applied to a glass-ceramic material that had been developed in-house for sealing purposes. Discrete and continuum damage solutions were then compared. Finally, the CDM model was used to determine the crack propagation direction as a function of a mode mixity measure.     

An Experimental Study to Evaluate the Effect of Ambient Temperature during Manual Lifting and Design of Optimal Task Parameters

In the present study, the effect of lifting task parameters on the heart rate and oxygen uptake of workers during manual lifting tasks in different ambient conditions was evaluated. The experiments conducted in two different temperature conditions showed a significantly higher oxygen uptake and heart rate in colder conditions as compared to warmer conditions. Three other factors, namely, load, lifting frequency, and vertical distance were found to significant affect the responses. Various combinations of significant factors were used to calculate oxygen uptake and heart rate. These were then compared with the safe limits as per the maximum aerobic capacity of workers. Based on these comparisons, the safe combinations were identified that can be used to design lifting tasks in varied ambient conditions. The study further concluded that lifting tasks performed in winter should have different relaxation or fatigue allowances built into the cycle time of the task to compensate for higher exertion. © 2011 Wiley Periodicals, Inc.     

Heterogeneous networking

In this article, security challenges related to a mobile heterogeneous networking environment, and the general access patterns are discussed. A novel, unified networking architecture that enables secure heterogeneous networking, both in terms of networks and user devices is discussed. A comprehensive security framework providing a generalized authentication scheme using the Extensible Authentication Protocol (EAP) is then presented, by taking into account existing methods for secure network and device access.