Mechanisms and inorganic byproducts of trihalomethane compounds sonodegradation

Organic pollutants can be sonodegraded by two pathways: pyrolysis, oxidation by free radicals, or the combination of both. The sonolytic degradation mechanisms and byproducts formation of aqueous trihalomethanes (THMs) were investigated at acoustic frequency of 20 kHz. The main sonodegradation mechanism of the chloroform, dichlorobromomethane, dibromochloromethane, and bromoform was found to be pyrolysis. The sonolysis degradation pathway of iodoform is free radicals oxidation. Hydrogen peroxide, nitrate, chloride, bromide, iodide, and iodate ions were detected and quantified as the inorganic products of the THMs sonication. A total of 48% TOC removal was achieved after a 180-min sonication of the THMs mixture.     

Tight bounds for prefetching and buffer management algorithms forparallel I/O systems

The I/O performance of applications in multiple-disk systems can be improved by overlapping disk accesses. This requires the use of appropriate prefetching and buffer management algorithms that ensure the most useful blocks are accessed and retained in the buffer. In this paper, we answer several fundamental questions on prefetching and buffer management for distributed-buffer parallel I/O systems. First, we derive and prove the optimality of an algorithm, P-min, that minimizes the number of parallel I/Os. Second, we analyze P-con, an algorithm that always matches its replacement decisions with those of the well-known demand-paged MIN algorithm. We show that P-con can become fully sequential in the worst case. Third, we investigate the behavior of on-line algorithms for multiple-disk prefetching and buffer management. We define and analyze P-Iru, a parallel version of the traditional LRU buffer management algorithm. Unexpectedly, we find that the competitive ratio of P-Iru is independent of the number of disks. Finally, we present the practical performance of these algorithms on randomly generated reference strings. These results confirm the conclusions derived from the analysis on worst case inputs     

Fault-tolerant VLSI sorters

Parallel sorting algorithms have been proposed for VLSI implementation. Random defects in the silicon wafer and fabrication errors render processors in the wafer faulty, and may cause these algorithms to fail despite a significant number of nonfaulty processors. This paper presents twofault-tolerant pipelined sorting algorithms that would work on a wafer comprised of faulty and nonfaulty processors. Both the algorithms useO(n) processors and requireO(n) time to sortn elements.P. J. Varman's research was supported by an IBM Faculty Development Award, I. V. Ramakrishnan's by the ONR Grant N00014-84-K-0530 and NSF Grant ECS-84-04399, and D. S. Fussell's by NSF Grant MCS-8104017.     

Simulator sickness in patients with neck pain and vestibular pathology during virtual reality tasks

Immersion in virtual environments can cause simulator sickness (SS). Further, head and neck movement in interactive virtual reality (VR) assessment and training stimulates the vestibular and cervical afferent systems that can cause dizziness in subjects with neck pain and vestibular pathology. This cross-sectional, observational, study investigated SS and factors that may influence this between 20 neck pain, 14 vestibular pathology and 20 asymptomatic control subjects. Pre-VR questionnaires included a visual symptom scale and dizziness intensity. SS measures included the simulator sickness visual analogue scale and the simulator sickness questionnaire. Significantly greater incidence of any SS and higher values were found in the vestibular and neck pain groups compared to the control group in selected SS measures. No significant differences were found when comparing SS measures between the vestibular and neck pain groups. Significant mild-to-moderate correlations for the entire population were found between both SS measures to pre-VR visual symptoms and dizziness intensity. SS levels in neck pain and vestibular populations are comparable and higher than asymptomatic individuals. Dizziness and visual disturbances may be associated with an increase in severity of SS in these clinical populations.     

Inactivation of E. coli, B. subtilis spores, and MS2, T4, and T7 phage using UV/H2O2 advanced oxidation

The goal of this study was to evaluate the potential of an advanced oxidation process (AOP) for microbiocidal and virucidal inactivation. The viruses chosen for this study were bacteriophage MS2, T4, and T7. In addition, Bacillus subtilis spores and Escherichia coli were studied. By using H(2)O(2) in the presence of filtered ultraviolet (UV) irradiation (UV/H(2)O(2)) to generate wavelengths above 295nm, the direct UV photolysis disinfection mechanism was minimized, while disinfection by H(2)O(2) was also negligible. Virus T4 and E. coli in phosphate buffered saline (PBS) were sensitive to >295nm filtered UV irradiation (without H(2)O(2)), while MS2 was very resistant. Addition of H(2)O(2) at 25mg/l in the presence of filtered UV irradiation over a 15min reaction time did not result in any additional disinfection of virus T4, while an additional one log inactivation for T7 and 2.5 logs for MS2 were obtained. With E. coli, only a slight additional effect was observed when H(2)O(2) was added. B. subtilis spores did not show any inactivation at any of the conditions used in this study. The OH radical exposure (CT value) was calculated to present the relationship between the hydroxyl radical dose and microbial inactivation.     

Dispersion Stability and Tribological Characteristics of TiO2/SiO2 Nanocomposite-Enriched Biobased Lubricant

The stable dispersion of nano-additives is highly desirable for the effective lubrication performance of nanolubricants. The compatibility of base oil with selected nano-additives is required for uniform and stable dispersion. This research evaluated the dispersion stability and tribological characteristics of nano-TiO₂/SiO₂ (average particle size 50 nm) as an additive in a biobased lubricant. The wear protection and friction reducing characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring–cylinder liner sliding tests. Surface analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy, were used to characterize the worn surfaces. Results showed that the nanolubricants demonstrated appreciable dispersion capability in the absence of a surfactant and an improvement in load-carrying capacity, antiwear behavior, and friction reduction capability.     

Degradation and by-product formation of diazinon in water during UV and UV/H(2)O(2) treatment

Kinetics and degradation products resulting from the application of UV and UV/H(2)O(2) to the US EPA Contaminant Candidate List pesticide diazinon were studied. Batch experiments were conducted with both monochromatic (low pressure [LP] UV 253.7 nm) and polychromatic (medium pressure [MP] UV 200-300 nm) UV sources alone or in the presence of up to 50 mg l(-1) H(2)O(2), in a quasi-collimated beam apparatus. Degradation of diazinon by both UV and UV/H(2)O(2) exhibited pseudo first order reaction kinetics, and quantum yield of 8.6 x 10(-2) and 5.8 x 10(-2) mol E(-1) for LP and MP lamps respectively. Photolysis studies under MP UV lamp showed 2-isopropyl-6-methyl-pyrimidin-4-ol (IMP) to be the main degradation product of diazinon at aqueous solution pH values of 4, 7 and 10. Trace levels up to 1.8 x 10(-3) microM of diazinon oxygen analogue diethyl 2-isopropyl-6-methylpyrimidin-4-yl phosphate (diazoxon) were detected only during the UV/H(2)O(2) reaction. Decay of both products was observed, as the UV/H(2)O(2) reaction prolonged, yet no mineralization was achieved over the UV fluence levels examined. Photolysis kinetics, quantum yield and UV/H(2)O(2) degradation of the reaction product IMP was determined using MP UV lamp at pH values of 4, 7 and 10.     

Sonolytic Destruction of Trihalomethanes by Ultrasonic Irradiation

Ultrasonic irradiation was employed for the degradation of trihalomethanes (THMs) CHCl₃, CHBrCl₂, CHBr₂Cl, CHBr₃, and CHI₃. The effects of various reaction and sonication conditions on the sonodegradation of THMs were examined and explained by the principles of sonochemistry. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and power of 18.4 W. The sonodegradation rate of the THMs increased with increasing the solution temperature or the acoustic intensity, whereas aqueous solution pH, solute concentration up to 10 mg/L, and water quality did not affect the sonolytic destruction of the THMs. Ultrasonic removal of CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃ was not affected by the presence of other compounds as a mixture in the aqueous solution, while CHI₃ sonolysis was enhanced. Hydrogen peroxide, nitrate, chloride, bromide, and iodide were identified and quantified as the reaction inorganic products. Degradation rates and efficiencies followed the decreasing order of: CHCl₃ > CHBrCl₂ > CHBr₂Cl > CHBr₃ > CHI₃, while the electrical energy consumed per liter of contaminated aqueous solution treated was found to be in inverse order.