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Gradual Degradation (gradual + degradation)
Selected AbstractsComputer simulation of flow-sheets for the solvent extraction of uranium: a new route to delay the effect of chemical degradation of the organic phase during uranium recovery from acidic sulfate mediaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2009Alexandre Chagnes Abstract BACKGROUND: The extractants used in solvent extraction processes undergo degradation under thermal, chemical and radiolytical stresses. In the case of uranium plants, tri- n -octylamine, used as an extractant, slowly degrades into di- n -octylamine. Such degradation causes a gradual depletion of the uranium extraction isotherms and as a result, of the efficiency of uranium recovery from feed solutions. The present work highlights a new route to delay this depletion of the extraction efficiency, merely by optimizing the flow-sheets involved in the process. Five flow-sheets have been compared for uranium recovery from acidic sulfate media by a solution of 0.146 mol L,1 tri- n -octylamine in kerosene modified with 5% w/w 1-tridecanol and stripping with a 199 g L,1 Na2CO3 solution. These five flow-sheets include the classical counter-current flow-sheet with four mixers,settlers in extraction and three mixers,settlers in stripping and four unusual combined solvent extraction flow-sheets with two independent extraction stripping loops and with one or two feed inlets. RESULTS: Computer simulation supplied evidence of the strong influence of the studied flow-sheets on the sturdiness of the process. More precisely, the unusual combined solvent extraction flow-sheets appeared to be significantly more efficient than the classical counter-current one and it is shown that an advantage of this can be to delay the negative impact of gradual degradation of tri- n -octylamine on uranium recovery efficiency from acidic sulfate media. CONCLUSION: The replacement of classical counter-current flow-sheets with a unique extraction-stripping loop in unusual combined flow-sheets with two or more independent extraction-stripping loops and with one or more feed inlets is a fruitful approach to delay the periodic addition of fresh tri- n -octylamine necessary for counter-balancing the progressive degradation of the extraction solvent and, as a result, to delay the gradual depletion of the efficiency of uranium recovery. Copyright © 2009 Society of Chemical Industry [source] Physicochemical Changes in Alaska Pollock Surimi and Surimi Gel as Affected by Electron BeamJOURNAL OF FOOD SCIENCE, Issue 1 2004J. JACZYNSKI ABSTRACT: Alaska pollock surimi and surimi gels (cooked) were subjected to various doses of electron beam (e-beam). Shear stress of surimi gels increased as the dose increased up to 6 to 8 kGy and then decreased. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed gradual degradation of myosin heavy chain as the dose increased. The degradation was slower for frozen samples. The integrity of actin was slightly affected by high doses (25 kGy). The amount of sulfhydryl groups and the level of surface hydrophobicity of Alaska pollock surimi decreased as the dose increased, suggesting formation of disulfide bonds and hydrophobic interactions. The sulfhydryl groups and hydrophobicity of surimi gels increased as the dose increased up to 6 kGy and then decreased. [source] Physical and chemical considerations of damage induced in protein crystals by synchrotron radiation: a radiation chemical perspectiveJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2002Peter O'Neill Radiation-induced degradation of protein or DNA samples by synchrotron radiation is an inherent problem in X-ray crystallography, especially at the `brighter' light sources. This short review gives a radiation chemical perspective on some of the physical and chemical processes that need to be considered in understanding potential pathways leading to the gradual degradation of the samples. Under the conditions used for X-ray crystallography at a temperature of <100,K in the presence of cryoprotectant agents, the majority of radiation damage of the protein samples arises from direct ionization of the amino acid residues and their associated water molecules. Some of the chemical processes that may occur at these protein centres, such as bond scission, are discussed. Several approaches are discussed that may reduce radiation damage, using agents known from radiation chemistry to minimize radical-induced degradation of the sample. [source] An experimental study of uniaxial fatigue behavior of an epoxy resin by a new noncontact real-time strain measurement and control systemPOLYMER ENGINEERING & SCIENCE, Issue 6 2007Gang Tao Uniaxial fatigue behavior of an epoxy resin was investigated with a recently established non-contact real-time strain measurement and control system. A relation of strain amplitude vs. fatigue life for fully-reversed strain-range-controlled uniaxial fatigue tests was obtained. Quantitative analyses of evolutions of various mechanical properties (including stress range, elastic modulus, nonlinear stress-strain relation, dissipated strain energy density, etc.) during entire fatigue life period were carried out based on recorded stress-strain data. From the evolution of the stress-strain hysteresis loops, a gradual degradation of modulus and a decrease of nonlinear effect in stress-strain response were observed. It was also found that these two phenomena were independent of the loading control mode (stress-control or strain-range-control) and the mean stress/strain values in the cyclic loading. Fractographic analysis was also performed and the mechanism of crack initiation and propagation of the epoxy material under cyclic loading was investigated. POLYM. ENG. SCI., 47:780,788, 2007. © 2007 Society of Plastics Engineers [source] Dopamine-dependent motor learning: Insight into levodopa's long-duration responseANNALS OF NEUROLOGY, Issue 5 2010Jeff A. Beeler PhD Objective Dopamine (DA) is critical for motor performance, motor learning, and corticostriatal plasticity. The relationship between motor performance and learning, and the role of DA in the mediation of them, however, remain unclear. Methods To examine this question, we took advantage of PITx3-deficient mice (aphakia mice), in which DA in the dorsal striatum is reduced by 90%. PITx3-deficient mice do not display obvious motor deficits in their home cage, but are impaired in motor tasks that require new motor skills. We used the accelerating rotarod as a motor learning task. Results We show that the deficiency in motor skill learning in PITx3(,/,) is dramatic and can be rescued with levodopa treatment. In addition, cessation of levodopa treatment after acquisition of the motor skill does not result in an immediate drop in performance. Instead, there is a gradual decline of performance that lasts for a few days, which is not related to levodopa pharmacokinetics. We show that this gradual decline is dependent on the retesting experience. Interpretation This observation resembles the long-duration response to levodopa therapy in its slow buildup of improvement after the initiation of therapy and gradual degradation. We hypothesize that motor learning may play a significant, underappreciated role in the symptomatology of Parkinson disease as well as in the therapeutic effects of levodopa. We suggest that the important, yet enigmatic long-duration response to chronic levodopa treatment is a manifestation of rescued motor learning. ANN NEUROL 2010;67:639,647 [source] | ||||||||||