A kinetic study of the oxidation of hydroquinone by aqueous suspensions of hausmannite at pH 6 was conducted using an on-line analysis system. Electron transfer between hydroquinone and the oxide was monitored by ultraviolet and electron spin resonance spectroscopy to measure the loss of hydroquinone and the appearance of oxidation products. Although hydroquinone oxidized on the surface of the oxide and the oxide surface was altered after the reduction, hydroquinone and its oxidation products did not adsorb strongly on the surface. At a high concentration of hydroquinone, p-benzosemiquinone free radicals persisted in aqueous solution and were oxidized by dissolved O2. Calculations based on the thermodynamic stabilities of the oxide and the organic species involved show that the formation of p-benzosemiquinone radical by Mn reduction is feasible. The presence of the radicals indicates that the oxidation of hydroquinone by the oxide proceeded by a one-electron transfer process. At high organic/ oxide ratios, an increase in the amount of hausmannite dissolved with increasing hydroquinone concentration suggests that the reduction of the oxide by the organic was not limited to the surface layer of the oxide. At a high concentration of hydroquinone, polymers were detected in solution, suggesting that radical-mediated reactions played a role in the polymerization process. A reaction scheme is proposed to explain the effect of the Mn oxide to hydroquinone ratio on the consumption of O2 and the appearance of quinone, p-benzosemiquinone, and polymers in solution.

The kinetics of hydroquinone oxidation by aqueous suspensions of pure hematite and goethite-ferrihydrite mixtures at pH 6.0, 7.4, and 9 was studied using an on-line analysis system. The electron transfer between hydroquinone and the Fe oxides was monitored by UV-visible and electron spin resonance spectroscopy. The adsorption of organics on the Fe oxide surface was detected by Fourier-transform infrared spectroscopy. For different Fe oxides, a higher surface area was correlated with a greater oxidizing ability and greater adsorption of organics, suggesting that the oxidation reaction was a surface process. A reversal of the initially rapid redox reaction was found in this system, suggesting a delayed release of Fe2+ into solution as the reduction of the Fe oxide proceeded. Redox potential calculations confirmed the thermodynamic favorability of the reaction reversal. A distribution of the reduced state over neighboring Fe atoms on the oxide surface probably was responsible for the initial suppression of Fe2+ release into the aqueous phase. Based upon these observations and detection of the semiquinone radical as an intermediate of hydroquinone oxidation, an inner-sphere one-electron transfer mechanism for the oxidation of hydroquinone at the oxide surface is proposed.

The present study, conducted in collaboration between the Departments of Psychiatry in Swiss Universities and the World Health Organization, had two main goals: to develop assessment methods which could subsequently be used in the Swiss centres in a standard manner; and to make arrangements for continuing collaboration between the centres in Switzerland and the acquisition of new knowledge about the distinctions between depression and cognitive impairment. For this aim, three different groups of elderly patients of either sex were selected during the period of November 1989 to July 1991 for inclusion in the study. The first two groups included the first ten patients of either sex over 60 years of age consecutively contacting the participating institutions and showing depression with or without clinically significant symptoms of cognitive impairment; the control group included patients showing no depression or clinically significant symptoms of cognitive impairment. A total of 125 patients were included in the initial evaluation, 69 of which were reassessed at a seven-month follow up (on average). Each patient was administered a number of clinician-rated or self-report instruments for the assessment of depression, cognitive impairment, disabilities, physical status and onset of disorders. The study has shown that a variety of instruments can be used for the reliable assessment of depression or cognitive impairment in the elderly; but the instruments for the assessment of depression differentiate only poorly between patients with or without cognitive impairment. Because of the importance of identifying both depressed and cognitively impaired patients among the elderly, different assessment instruments targeted at the different symptom clusters need to be administered simultaneously.

Within the past few years, there has been a growing interest in the utilisation of airships for a variety of missions. Studies funded by NASA and the US Navy have shown that modern airships not only could perform certain tasks more economically and silently than other aeronautical vehicles (short-haul passenger and freight transport, and long-duration ocean patrol), but that they could perform unique missions, such as the V/STOL transportation of bulky loads an order of magnitude beyond helicopter capability.

The types of modern airships envisioned fall into two categories: modernised blimps and heavy-load carriers. Blimps are receiving reconsideration for their traditional role of patrol and surveillance because of their fuel efficiency and the development of modern sensing devices which require a quiet, stationary vehicle for deployment.

Optical and tactile single scanning probes usually are used in dimensional metrologyapplications, especially for roughness, form, thickness and surface profile measurements.To perform assessments with nanometre level of accuracy, specific ultra-high precisionmachines have been developed by the National Metrology Institutes (NMIs) such as the LNE,VSL, METAS, SMD, generally in collaboration with industrials and academics partners. Suchdevelopments are not devoted only to NMIs but many industrials develop and commercializetheir own ultra-high precision machines as the IBSPE and TNO companies. All these machinesprovide optical and tactile precise measurements and cover a large domain of applicationsuch as the form’s characterization of optical lenses. In this paper the performance andcapability of ultra-high precision machines of some National Metrology Institutes (LNE,VSL, SMD and METAS) and industrials companies (TNO and IBSPE), involving together in theIND10 European EMRP project titled “Optical and tactile metrology for absolute formcharacterization”, will be detailed. Theirs probing systems and accuracies levels will beevoked. Relevant results especially for measuring optical lenses will be also presentedand discussed.

This paper studies the behavior of second grade viscoelastic fluid past a cavity in a horizontal channel. The effects of Reynolds number, fluid elasticity and the aspect ratio of the cavity on the flow field are simulated numerically. The equations are converted into the vorticity and stream function equations. The solution is obtained by the finite difference method.

The behavior of viscoelastic fluids is quite different from the Newtonian fluid, due to the effects of fluid elasticity. Only one flow pattern appears when the Newtonian fluid past the cavity. However, three kinds of flow patterns appear while the viscoelastic fluids past the cavity by increasing Reynolds number from 20 to 300. The flow field is affected by the fluid elasticity as well as the aspect ratio of the cavity. The transitional flow pattern appears at lower Reynolds number as the higher elasticity fluid past the cavity with larger aspect ratio.

We describe the operation of a repetitive semiconductor opening switch in conjunction with inductive energy storage systems. Different materials and switch configurations are examined. A new method of generating square pulses of nanosecond duration is implemented. It utilizes the opening switch and a current charged transmission line.

In some recent investigations involving certain differential operators for a general family of Lagrange polynomials, Chan el al. encountered and proved a certain summation identity for the Lagrange polynomials in several variables. In the present paper, we derive some generalizations of this summation identity for the Chan-Chyan-Srivastava polynomials in several variables. We also discuss a number of interesting corollaries and consequences of our main results.