Variations in radioactivity of phosphate rocks from different sites in Central Eastern Desert of Upper Egypt

Natural radionuclides in the phosphate rock samples collected from Wadi Batur, Wadi Hegaza and Gabal Abu Had at Eastern Desert were determined using a high resolution 7-ray spectrometer. The experimental results concerning 226Ra, 232Th and their daughters are presented. Analyses of the measured spectra show that 226Ra is distinguished with remarkable activities with average values ranging from 22.4 to 558 Bq/kg, while 232Th activity concentration is in the range of 9.7 to 92.8 Bq/kg. The results of the analyses were found to be in a good agreement with the data obtained by others.     

A pseudo-fully stressed design approach for optimum design of steel frames

An iterative approach based on the fully-stressed design concept employing scaling to find an efficient search path to the optimum design is developed for statically indeterminate elastic frames subjected to behavioural constraints on member stresses and nodal displacements, and side constraints on member sizes. In this approach the fully stressed solution, which recognizes only the stress constraints, is scaled to the boundary of the feasible design region by employing the other constraints on the structure. The inactive constraints in an iteration are identified by the Kuhn-Tucker conditions. The computed stresses of the inactive constraints, for the time being, are considered to be the allowable values in order to develop a pseudo-fully stressed solution with a new set of allowable stresses. Convergence takes places when the normalized change in the value of the objective function between the scaled and unsealed pseudo-fully stressed designs is less than a specified tolerance. The method employs the established relationships between sectional area, section modulus and moment of inertia of W-shapes to express the objective and constraint functions in terms of one design variable for each member. The efficiency and accuracy of the method in optimization of structural steel frames is demonstrated by sample problems designed for stress, displacement and minimum size constraints. The algorithm is verified against published results.     

Inhibition of Aluminum Alloy Corrosion in 0.5 M Nitric Acid Solution by 4-4-Dimethyloxazolidine-2-thione

The corrosion inhibition of Al-Alloy (Al2024) in 0.5 M nitric acid solution at 30 °C was achieved using 4-4-dimethyloxazolidine-2-thione (DMT) as a corrosion inhibitor. The electrochemical performance of the DMT was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization measurements, and scanning electron microscopic study (SEM). The results indicated that DMT acts as an inhibitor for Al2024 in 0.5 M nitric acid. Polarization curves indicated that DMT was a mixed-type inhibitor. Inhibition efficiencies were observed to be increased with an increase in DMT concentration and attains approximately to 93.4% at 2 mM of DMT in 0.5 M nitric acid. The adsorption of DMT model on Al2024 surface obeyed in accordance with Langmuir adsorption isotherm model. The value of the free energy of adsorption ΔG _ads indicated that the adsorption of DMT molecule was a spontaneous process and was typical of physical and chemical adsorption.     

Feasibility of using various photovoltaic systems for window-type air-conditioning units under hot-arid climates

This paper reports on the feasibility of using various Photovoltaic (PV) systems namely; Grid PV (GPV), Stand-Alone PV (SAPV), Grid PV Wind (GPVW) and PV Wind (PVW) for supplying the power requirements of a window-type air-conditioning system or other small loads. It was found that the GPVW system is the best system to meet the load requirement of a window-type air-conditioning system under the climatic conditions of Oman with values ranging from $39,500 to $56,500 for the capital cost and $9,000 to $33,000 for the total net capital cost depending on the wind speed. These values are attractive for remote off grid applications.     

Estimating the uncertainty in the estimated mean area under the ROC curve of a classifier

This article considers the problem of binary classification and its assessment in a distribution-free approach. We estimate the area under the ROC curve (a more general performance metric than the error rate) of a classifier using a bootstrap-based estimator. We then use the method of the influence function to estimate the uncertainty of that estimate from the very same bootstrap samples. Monte Carlo trials show that small-sample estimates can be obtained with little bias.     

Robust wireless location over fading channels

This paper develops an estimation algorithm for the time and amplitude of arrival of a known transmitted sequence over a single-path fading channel. The algorithm is optimized to enhance robustness to fast channel fading and low signal-to-noise ratio (SNR) conditions, which are common in wireless location applications. The paper also presents a noise and fading bias correction technique for amplitude of arrival estimation that improves the estimation accuracy significantly. The proposed algorithm is then applied to the case of code-division multiple-access (CDMA) wireless location finding for which the paper gives simulation results that demonstrate significant estimation accuracy improvement over known algorithms.     

An implementation of distributed shared memory

Shared memory is a simple yet powerful paradigm for structuring systems. Recently, there has been an interest in extending this paradigm to non-shared memory architectures as well. For example, the virtual address spaces for all objects in a distributed object-based system could be viewed as constituting a global distributed shared memory. We propose a set of primitives for managing distributed shared memory. We present an implementation of these primitives in the context of an object-based operating system as well as on top of Unix.     

Diurnal changes in radionuclides uptake by phytoplankton in small scale ecosystems

A continuous release of cesium-134 and strontium-85 into a simulated river system was maintained for more than 3 weeks for the purpose of evaluating the influence of photosynthetic oxygen production on cesium and strontium uptake. The flow rates and radioisotope concentration were maintained at a constant input throughout the experiment.The flow through time in the model river system was 6 h. Samples were taken from various stations every 4 h over a 36 h time interval. Temperature, dissolved oxygen, as well as other routine measurements were made. Samples were processed for plankton count and radioactivity in both the suspended phytoplankton and the water.The uptake of ¹³⁴Cs by phytoplankton was related to diurnal photosynthetic production of oxygen and a linear relationship exists between rate of change in ¹³⁴Cs concentration and the rate of net photosynthetic oxygen production.     

Needle track seeding following percutaneous ethanol injection for treatment of hepatocellular carcinoma

We report two cases of needle track seeding in the subcutaneous tissue and intercostal muscles following percutaneous ethanol injection for the treatment of hepatocellular carcinoma. In one patient, tumor seeding was observed 11 months after a total of 12 alcohol injections, and in the other patient, tumor seeding was observed 30 months after a total of 18 alcohol injections. The cases reported in the literature are discussed.     

Soot formation in gas turbines using heavy fuels. 1

The aim of this study was to determine the impact of the broadening of fuel specifications on the performance of a gas turbine combustor, particularly on soot formation and oxidation, and flame tube durability. Tests were conducted with a fully-developed combustor system, the main measurements comprising total radiation, exhaust smoke and temperatures at different locations. Five fuels were used: kerosine, as aviation fuel; gas oil, as the current industrial gas turbine fuel and possible future aviation fuel; R25 (where 25 is the volume percentage of residual fuel oil in the blend with gas oil), as equivalent to crude oil now in use in many utility gas turbines; and also R50 and R70 to represent future heavier fuels. Combustor pressures were 0.3, 0.7 and 1.0 MPa. Inlet air temperatures were 313, 390 and 460 K. Primary zone air/fuel mass ratios were 12, 15 and 25. Total air/fuel ratios were 60 and 120. Attempts were made to develop a mathematical model of the soot formation-oxidation processes that occur in the system, and to include in the model some parameters to represent the change in fuel properties. In this paper, comparison of the soot formation predictions of the model with the experimental data is seen to be favourable, particularly at full power conditions.