N‐arylhydroxamic acids as mineral collectors for ore‐beneficiation

Several arylhydroxamic acids were synthesized, characterized and tested as collectors in the flotation of a Cu‐Zn sulphide ore. Arylhydroxamic acids floated copper in preference to iron and zinc minerals. Substitution in the N‐phenyl ring increased the efficiency of the collector. However, increase in alkyl‐chain beyond C₆ in the acyl group decreased the flotation efficiency of the collector. N‐butanoylphenylhydroxylamine was found to give the best result and floated about 93 wt% of Cu in about 32 wt% of the feed taken and the collector usage was only about 70 g per tonne of the ore. Pyrite flotation was minimum at pH 11.     

Liquid‐solid mass transfer from horizontal woven screen packing in bubble column reactors

The effect of gas sparging on the rate of mass transfer at horizontal single screen and stacks of closely packed horizontal screens was studied by an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide. Variables studied were: distance between the sparger and the screen, screen characteristics, e.g., mesh number and wire diameter, physical properties of the solution and superficial gas velocity. Screen characteristics were found to have little effect on the rate of mass transfer. The mass transfer measurement at beds of closely packed screens revealed that the mass transfer coefficient decreased below the single screen value with increasing the number of screens per bed. Comparison of the present data with previous results showed that screens produce higher rates of mass transfer than other geometries under otherwise the same conditions. The importance of the present work to the design and operation of catalytic and electrochemical reactors was highlighted.     

Structural, absorption and fluorescence spectral analysis of Pr ions doped zinc bismuth borate glasses

Glasses having composition 20ZnO·xBi₂O₃·(79.5 − x)B₂O₃·0.5Pr₆O₁₁ were prepared by melt quench technique. The amorphous nature of the prepared glass samples was confirmed by X-ray diffraction. The spectroscopic properties of these glasses were investigated by recording optical absorption and fluorescence spectra. The structural investigations of the glasses were carried out by recording the IR spectra. The optical properties of Pr³⁺ ions doped zinc borate glasses with varying concentration of bismuth oxide have been studied. The Judd-Ofelt intensity parameters Ω_λ (λ = 2, 4, 6) and other radiative properties like radiative transition probability, radiative life time, branching ratio and stimulated emission cross-section of the prepared glasses have been calculated. The variation of Ω₂ with Bi₂O₃ content has been attributed to changes in the asymmetry of the ligand field at the rare earth ion site and to the changes in their rare earth oxygen (RE-O) covalency. The branching ratio for ³P₀ → ³F₂ transition is 42% and the predicted spontaneous radiative transition probability rates are fairly high (14,347-14,607 s⁻¹). This is beneficial for lasing emission. The stimulated emission cross-section for all the emission bands has been calculated.     

Disinfecting the Coquitlam Water Supply: Ozone and UV Disinfection

The Greater Vancouver Water District (GVWD) is upgrading its unfiltered Coquitlam water treatment system to meet the updated Health Canada guidelines for providing 3-log reduction or inactivation of Cryptosporidium and Giardia. The existing Coquitlam system, which is designed for peak flows of 1200 ML/d (317 mgd), includes an ozonation facility providing 3 log Giardia inactivation, and a chlorination/corrosion control facility. To meet Health Canada guidelines, a UV disinfection facility will be constructed, which will provide 3-log inactivation of Cryptosporidium and Giardia, and the ozone dosage will be increased to reduce THM and HAA precursors as well as improve UV transmittance. This paper will focus on the conceptual design of the Coquitlam system and the preliminary bench-scale studies that were completed for GVWD as part of the predesign phase of the project.     

Effect of Superimposed Pulsating Flow on Liquid‐Solid Mass Transfer in Fixed Beds

The liquid‐solid mass transfer behaviour of a fixed bed of cylinders has been studied using the dissolution of copper in acidified dichromate solution under pulsating flow conditions. The bed diameter was 100 mm. The depth of the working section was 95 mm and the length and diameter of the cylinders were 19.1 mm. Variables studied were steady flow superficial liquid velocity, and oscillation amplitude and frequency. Data have been correlated as the Sherwood number in terms of Schmidt number and the cylinder Reynolds numbers for steady and oscillatory flow. The form of the correlation permits comparison with literature data for the limiting cases where either of these Reynolds numbers is zero.     

Performance of stop-and-wait protocols over high-delay links

The performance of stop-and-wait protocols over links with high propagation delay such as satellite links is discussed. Primary focus is placed on situations where a large block size is employed to compensate for the loss of throughput caused by the large propagation delay. Possible loss in data intergrity due to undetected errors is investigated. The results show that in most environments, acceptably high throughput can be obtained without sacrificing data integrity.     

On formulation of a reliable cost allocation strategy in centralized computer networks

Centralized networks arise in the context of communications between terminals and a Central processing unit or in the context of the design of local distribution network. The basic problem of cost allocation in a network is: “How much should each user be charged for his portion of the services supplied”? The minimum cost required to connect all the consumers to the central supplier (using arcs of the network) is the length of a shortest spanning tree. The question then is how to divide the total cost of this shortest spanning tree to the consumers. In this paper, we present a relative study of a number of possible cost-allocation methods. Based on the suggested criteria formulated as a tradeoff between the satisfaction of user and company holders, a comparative evaluation is tabulated, which can be used as a qualitative guideline while forming a “reliable” as well as near optimal cost-allocation strategy depending upon the locally prevailing conditions also.     

A theoretical study of the electronic properties of intercalated graphite

We present the results of electronic structure calculations for first and second stages of lithium intercalated graphite (LiC₆ and LiC₁₂). The various stages of Li intercalated graphite all have hexagonal symmetry, where different carbon layers are stacked with C-atoms directly on top of each other (AIAI…), as opposed to natural graphite where the C-layers are staggered (ABAB…). All our calculations have been performed within the framework of the extended tight binding method with Gaussian type basis sets. From the orbital and total densities of states, we conclude that Li-2s electrons are transferred into carbon π-bands. This results in shifting the Fermi level into the region of high density of states (compared with pure graphite) and, hence, to observed metallic behavior. The calculated density of states for LiC₆ and LiC₁₂ is 0.25 and 0.12/(eV C-atom), respectively. Recall that for pure graphite the value is nearly zero and for copper it is 0.29. We also found it instructive to obtain the electronic structure of LiC₆ and LiC₁₂ based on a rigid band model.     

On human reliability trends in digital communication systems

Communication system structure is undergoing a significant change: yesterday's massive collection of discrete devices hardwired into fairly simple architectures is in the process of replacement by tomorrow's highly versatile control system driven by a stored program and the whole scheme implemented with very reliable digital LSI devices. Past experience indicates that the integrity of such systems is likely to be greatly influenced by the mode of interface between these complex, intelligent yet abstract machines and the ordinary human user. This paper first discusses very briefly the future trends in the digital communication systems and then presents a system analysis model in the form of a state diagram which may be used hopefully to study the overall availability behaviour of next generation digital communication systems. The emphasis in this paper is mainly on the human reliability aspects. Man-machine reliability which is fast becoming a practical engineering parameter for reliable system designs is briefly discussed emphasizing a life-cycle oriented system development approach.     

A user-centric evaluation of the readability of privacy policies in popular web sites

This paper reports on a formal subject-based experiment, which seeks to evaluate the readability of privacy policy statements found on the Internet. This experiment uses 50 participants and privacy policies collected from 10 of the most popular web sites on the Internet. It evaluates, using a cloze test, the subjects’ ability to comprehend the content of these privacy policies. The paper also compares its results with the results from previous studies on this topic. In general, it finds that privacy policies are “difficult” to comprehend.