Charge analysis predictions and measurements of storage time for a switching transistor.

Thesis (M.S.)--University of Illinois.

Electrochemical Characterisation of Filter Media Properties and Their Exploitation in Enhanced Filtration

Streaming potential measurements for the surface charge characterisation of different filter media types and materials were used. The equipment was developed further so that measurements could be taken along the surfaces, and so that tubular membranes could also be measured. The streaming potential proved to be a very useful tool in the charge analysis of both clean and fouled filter media. Adsorption and fouling could be studied, as could flux, as functions of time. A module to determine the membrane potential was also constructed. The results collected from the experiments conducted with these devices were used in the study of the theory of streaming potential as an electrokinetic phenomenon. Several correction factors, which are derived to take into account the surface conductance and the electrokinetic flow in very narrow capillaries, were tested in practice. The surface materials were studied using FTIR and the results compared with those from the streaming potentials. FTIR analysis was also found to be a useful tool in the characterisation of filters, as well as in the fouling studies. Upon examination of the recorded spectra from different depths in a sample it was possible to determine the adsorption sites. The influence of an external electric field on the cross flow microflltration of a binary protein system was investigated using a membrane electroflltration apparatus. The results showed that a significant improvement could be achieved in membrane filtration by using the measured electrochemical properties to help adjust the process conditions.

The role of metal ions in selective and sustainable processes

Sustainability and recycling are core values in today’s industrial operations. New materials, products and processes need to be designed in such a way as to consume fewer of the diminishing resources we have available and to put as little strain on the environment as possible. An integral part of this is cleaning and recycling. New processes are to be designed to improve the efficiency in this aspect. Wastewater, including municipal wastewaters, is treated in several steps including chemical and mechanical cleaning of waters. Well-cleaned water can be recycled and reused. Clean water for everyone is one of the greatest challenges we are facing today. Ferric sulphate, made by oxidation from ferrous sulphate, is used in water purification. The oxidation of ferrous sulphate, FeSO4, to ferric sulphate in acidic aqueous solutions of H2SO4 over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and several catalysts were screened: active carbon, active carbon impregnated with Pt, Rh, Pd and Ru. Both active carbon and noble metal-active carbon catalysts enhanced the oxidation rate considerably. The order of the noble metals according to the effect was: Pt >> Rh > Pd, Ru. By the use of catalysts, the production capacities of existing oxidation units can be considerably increased. Good coagulants have a high charge on a long polymer chain effectively capturing dirty particles of the opposite charge. Analysis of the reaction product indicated that it is possible to obtain polymeric iron-based products with good coagulation properties. Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60B100°C and 4B10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe2+ to Fe3+ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe2+ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe2+ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe2+ over active carbon and active carbon-noble metal catalysts. Engineering aspects were closely considered and effort was directed to utilizing existing equipment in the production of the new coagulant. Ferrous sulphate can be catalytically oxidized to produce a novel long-chained polymeric iron-based flocculent in an easy and affordable way in existing facilities. The results can be used for modelling the reactors and for scale-up. Ferric iron (Fe3+) was successfully applied for the dissolution of sphalerite. Sphalerite contains indium, gallium and germanium, among others, and the application can promote their recovery. The understanding of the reduction process of ferric to ferrous iron can be used to develop further the understanding of the dissolution mechanisms and oxidation of ferrous sulphate. Indium, gallium and germanium face an ever-increasing demand in the electronics industry, among others. The supply is, however, very limited. The fact that most part of the material is obtained through secondary production means that real production quota depends on the primary material production. This also sets the pricing. The primary production material is in most cases zinc and aluminium. Recycling of scrap material and the utilization of industrial waste, containing indium, gallium and geranium, is a necessity without real options. As a part of this study plausible methods for the recovery of indium, gallium and germanium have been studied. The results were encouraging and provided information about the precipitation of these valuables from highly acidic solutions. Indium and gallium were separated from acidic sulphuric acid solutions by precipitation with basic sulphates such as alunite or they were precipitated as basic sulphates of their own as galliunite and indiunite. Germanium may precipitate as a basic sulphate of a mixed composition. The precipitation is rapid and the selectivity is good. When the solutions contain both indium and gallium then the results show that gallium should be separated before indium to achieve a better selectivity. Germanium was separated from highly acidic sulphuric acid solutions containing other metals as well by precipitating with tannic acid. This is a highly selective method. According to the study other commonly found metals in the solution do not affect germanium precipitation. The reduction of ferric iron to ferrous, the precipitation of indium, gallium and germanium, and the dissolution of the raw materials are strongly depending on temperature and pH. The temperature and pH effect were studied and which contributed to the understanding and design of the different process steps. Increased temperature and reduced pH improve the reduction rate. Finally, the gained understanding in the studied areas can be employed to develop better industrial processes not only on a large scale but also increasingly on a smaller scale. The small amounts of indium, gallium and germanium may favour smaller and more locally bound recovery.

Molecular properties of the PCO radical: heat of formation and the isomerization pathways

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interactions between 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and gamma-Al2O3 (100) surface calculated by density functional theory

The main aim of this work is to investigate the 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1Im]+[BF4]-) ionic liquid (IL) adsorption on the gamma-Al2O3 (100) by density functional theory calculations to try to rationalize the adsorption as an electrostatic phenomenon. Optimized geometries and interaction energies of IL one-monolayer on the gamma-Al2O3 were obtained on high surface coverage (one cationanion pair per 94.96 nm2). A study of dispersion force was made to estimate its contribution to the adsorption. Overall, the process is ruled by electrostatic interaction between ions and surface. Adsorption of the anion [BF4]- and cation [C4C1Im]+ was also studied by Bader charge analysis and charge density difference for supported and unsupported situations. It is suggested that the IL ions have their charges maintained with significant anion cloud polarization inward to the acid aluminum sites. (c) 2012 Wiley Periodicals, Inc.

Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at √s=8 TeV with the ATLAS detector

An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb−1 of pp collisions at s√=8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced four-top-quark production, pair production of chiral b′-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b′-quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models.

Analyse de la prise en charge médicale et de l'impact économique des patients ayant présentés des coûts extrêmes dans un hôpital universitaire [Analysis of the medical management and the economic impact of patients who have represented extreme costs at a university hospital]

Les coûts de traitement de certains patients s'avèrent extrêmement élevés, et peuvent faire soupçonner une prise en charge médicale inadéquate. Comme I'évolution du remboursement des prestations hospitalières passe à des forfaits par pathologie, il est essentiel de vérifier ce point, d'essayer de déterminer si ce type de patients peut être identifié à leur admission, et de s'assurer que leur devenir soit acceptable. Pour les années 1995 et 1997. les coûts de traitement dépassant de 6 déviations standard le coût moyen de la catégorie diagnostique APDRG ont été identifiés, et les dossiers des 50 patients dont les coûts variables étaient les plus élevés ont été analysés. Le nombre total de patients dont I'hospitalisation a entraîné des coûts extrêmes a passé de 391 en 1995 à 328 patients en 1997 (-16%). En ce qui concerne les 50 patients ayant entraîné les prises en charge les plus chères de manière absolue, les longs séjours dans de multiples services sont fréquents, mais 90% des patients sont sortis de l'hôpital en vie, et près de la moitié directement à domicile. Ils présentaient une variabilité importante de diagnostics et d'interventions, mais pas d'évidence de prise en charge inadéquate. En conclusion, les patients qualifiés de cas extrêmes sur un plan économique, ne le sont pas sur un plan strictement médical, et leur devenir est bon. Face à la pression qu'exercera le passage à un mode de financement par pathologie, les hôpitaux doivent mettre au point un système de revue interne de I'adéquation des prestations fournies basées sur des caractéristiques cliniques, s'ils veulent garantir des soins de qualité. et identifier les éventuelles prestations sous-optimales qu'ils pourraient être amenés à délivrer. [Auteurs] Treatment costs for some patients are extremely high and might let think that medical care could have been inadequate. As hospital financing systems move towards reimbursement by diagnostic groups, it is essential to assess whether inadequate care is provided, to try to identify these patients upon admission, and make sure that their outcome is good. For the years 1995 and 1997, treatment costs exceeding by 6 standard deviations the average cost of their APDRG category were identified, and the charts of the 50 patients with the highest variable costs were analyzed. The total number of patients with such extreme costs diminished from 391 in 1995 to 328 in 1997 (-16%). For the 50 most expensive patients, long stays in several services were frequent, but 90% of these patients left the hospital alive, and about half directly to their home. They presented an important variation in diagnoses and operations, but no evidence for inadequate care. Thus, patients qualified as extreme from an economic perspective cannot be qualified as such from a medical perspective, and their outcome is good. To face the pressure linked with the change in financing system, hospitals must develop an internal review system for assessing the adequacy of care, based on clinical characteristics, if they want to guarantee good quality of care and identify potentially inadequate practice.

Photometric procedure for quantitative analysis of Aflatoxin B1 in peanuts by thin-layer chromatography using charge coupled device detector

A photometric procedure was developed for determination of aflatoxin B1 in peanuts by TLC-CCD technique. The quantification and detection limit were 1.2 μg kg-1 and 0.4 ng per spot, respectively, with mean recovery of 98%. The CCD camera is sufficiently sensitive to detect small changes in spots fluorescence intensity and the results for performance confirmed the efficiency of the method. Another important property of CCD detector is its linearity for a wide range of luminous stimulus determined by analysis of five-point calibration curves using the intensity of AFB1 fluorescence versus AFB1 concentration (0.8 to 4.8 ng per spot). The method was applied to the analysis of thirty nine peanut samples and aflatoxin B1 levels ranged from 16 to 115 μg kg-1. The TLC-CCD and the photometric procedure developed in this study demonstrated to be a simple and efficient tool for quantitative analyses of AFB1 in peanut samples.

Detailed analysis of the charge transfer complex N,N-dimethylaniline-SO(2) by Raman spectroscopy and density functional theory calculations

Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N-dimethylaniline (DMA) and sulfur dioxide (SO(2)). The formation of a deep red oil by the reaction of SO(2) with DMA is an evidence of the charge transfer (CT) nature of the DMA-SO(2) interaction. The DMA -SO(2) normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm(-1), which are enhanced when resonance is approached. These bands are assigned to nu(s)(SO(2)) and nu(phi-N) vibrational modes, respectively, confirming the interaction between SO(2) and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO(2) with the ring pi electrons, which gives rise to a pi-pi* low-energy CT electronic transition, as confirmed by time-dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA-SO(2) spectrum at the B3LYP/6-311++g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb, detect, or even quantify SO(2). Copyright (C) 2009 John Wiley & Sons, Ltd.

Analysis of charge-transport properties in GST materials for next generation phase-change memory devices

The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. The memory subsystem accounts for a significant cost and power budget of a computer system. Current DRAM-based main memory systems are starting to hit the power and cost limit. To resolve this issue the industry is improving existing technologies such as Flash and exploring new ones. Among those new technologies is the Phase Change Memory (PCM), which overcomes some of the shortcomings of the Flash such as durability and scalability. This alternative non-volatile memory technology, which uses resistance contrast in phase-change materials, offers more density relative to DRAM, and can help to increase main memory capacity of future systems while remaining within the cost and power constraints. Chalcogenide materials can suitably be exploited for manufacturing phase-change memory devices. Charge transport in amorphous chalcogenide-GST used for memory devices is modeled using two contributions: hopping of trapped electrons and motion of band electrons in extended states. Crystalline GST exhibits an almost Ohmic I(V) curve. In contrast amorphous GST shows a high resistance at low biases while, above a threshold voltage, a transition takes place from a highly resistive to a conductive state, characterized by a negative differential-resistance behavior. A clear and complete understanding of the threshold behavior of the amorphous phase is fundamental for exploiting such materials in the fabrication of innovative nonvolatile memories. The type of feedback that produces the snapback phenomenon is described as a filamentation in energy that is controlled by electron–electron interactions between trapped electrons and band electrons. The model thus derived is implemented within a state-of-the-art simulator. An analytical version of the model is also derived and is useful for discussing the snapback behavior and the scaling properties of the device.

Charge density analysis for crystal engineering

This review reports on the application of charge density analysis in the field of crystal engineering, which is one of the most growing and productive areas of the entire field of crystallography. While methods to calculate or measure electron density are not discussed in detail, the derived quantities and tools, useful for crystal engineering analyses, are presented and their applications in the recent literature are illustrated. Potential developments and future perspectives are also highlighted and critically discussed.