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Transformation Rates (transformation + rate)
Selected AbstractsQuantification of Chemical Striae in Inorganic Melts and Glasses through Picture ProcessingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Martin Jensen Chemical striations occur in various types of inorganic melts like lava and glass melts, and affect the physical properties of materials. This paper reports a quantitative study of the chemical striations in iron-rich aluminosilicate melts and glasses. In this study, an integrated method has been established, which consists of sample preparation, image acquiring, Fourier Transformation, and characteristic value determination. The principle of the established method is illustrated by picture processing-based simulation. The extent of the chemical striations and the diffusion length of the striae can be measured using this method. It is found that the extent of the chemical striations is rather sensitive to the melting technique. Furthermore, the impact of chemical diffusion and stirring on the extent of striations is revealed using the picture processing-based simulation approach. The diffusion process eliminates small striae and reduces the intensity of the larger ones. At a constant temperature, the diffusion determines the transformation rate of an inhomogeneous melt into a homogeneous one. During stirring, the size distribution of the large striae becomes broader, but the overall intensity of the striae becomes smaller. [source] Crystal-crystal transformations in isotactic polybutene-1 oriented filaments and in thick molded rodsPOLYMER ENGINEERING & SCIENCE, Issue 6 2001Cheol-Ho Choi This paper reports two related studies of the Form II , Form I crystal-crystal transformation in isotactic polybutene-1. First, it was found that in melt spun filaments, the rate of transformation is higher in filaments possessing higher levels of crystalline orientation. Second, we consider the occurrence of this phase transformation in thick quenched cylindrical rods. It was found that the phase transformation occurs more rapidly in the core than at the surface of the part. It is hypothesized that the mechanism of the higher transformation rate in the core is due to the development of residual quench stresses associated with densification at solidification. These stress levels have been calculated and our results compared with earlier studies. [source] Systematic review of the follow-up of oral dysplasiaCLINICAL OTOLARYNGOLOGY, Issue 3 2006T. Rattay Objectives.,To assess effectiveness, safety, and acceptability of follow-up regimens for oral dysplasia with regards to malignant transformation rate and duration to transformation. Method.,Study design,Systematic literature review with criteria for identifying studies, assessing quality and data extraction. Selection criteria,Cohort studies, case-control studies, or randomised-controlled trials (RCTs). Interventions,Clinical follow-up and surveillance, surgical and non-surgical treatment, modification of aetiological factors. Outcome measures,Malignant transformation rate, predictive value of clinical prognostic indicators. Data collection and analysis,Using selection criteria, we identified published data by electronic searching. The validity of studies and extracted data was independently assessed by two authors. Quantitative data is compared and summarized in a table. Qualitative data is also discussed. Results. There are no RCTs assessing follow-up strategies. Nineteen cohort studies (level II and III evidence) reported follow-up, of which 12 were included in the meta-analysis. The malignant transformation rate varies widely between studies (6.6,36.0%). Surgical treatment appears to be more effective than non-surgical modalities, but recurrence is high. Tobacco and alcohol use, site and histological grade of the lesion are associated with progression to cancer. Conclusions. There is currently no evidence-based or consensus strategy for malignant risk quantification and follow-up of patients with oral dysplasia. We present a follow-up protocol based on best evidence. Large randomised-controlled trials are needed to assess these new strategies, including the use of molecular markers to quantify risk and follow-up these lesions. [source] Low-Temperature Aging Behavior of Alumina-Toughened ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Jens Schneider The corrosion of alumina-toughened zirconia (ATZ) as a consequence of hydrothermal treatment was investigated, especially the transformation kinetics from tetragonal zirconia to the monoclinic phase. For this purpose, polished ATZ specimens (Ra<5 nm) were aged in water vapor at different temperatures ranging from 70° to 134°C. The fraction of the monoclinic phase was determined using X-ray diffraction and Rietveld refinement. The isothermal transformation curves obtained were fitted to the Mehl,Johnson,Avrami equation by least squares. An Arrhenius plot of the fitted transformation rates was used to determine the activation energy and the pre-exponential factor. Following this procedure, the kinetic parameters of the phase transformation were extrapolated down to body temperature and the formation of the monoclinic phase was simulated. In addition, optical interferometry on well-polished specimens (Ra<2 nm) was alternatively used to calculate the monoclinic fraction from the histogram dataset. The results agree very well with those of the X-ray measurements. Additionally, the development of surface roughness with increasing aging time is discussed. [source] LANDSCAPE ATTRIBUTES AS CONTROLS ON GROITHD WATER NITRATE REMOVAL CAPACITY OF RIPARIAN ZONES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2001Arthur J. Gold ABSTRACT: Inherent site factors can generate substantial variation in the ground water nitrate removal capacity of riparian zones. This paper examines research in the glaciated Northeast to relate variability in ground water nitrate removal to site attributes depicted in readily available spatial databases, such as SSUIRGO. Linking site-specific studies of riparian ground water nitrate removal to spatial data can help target high-value riparian locations for restoration or protection and improve the modeling of watershed nitrogen flux. Site attributes, such as hydric soil status (soil wetness) and geomorphology, affect the interaction of nitrate-enriched ground water with portions of the soil ecosystem possessing elevated biogeochemical transformation rates (i.e., biologically active zones). At our riparian sites, high ground water nitrate-N removal rates were restricted to hydric soils. Geomorphology provided insights into ground water flowpaths. Riparian sites located on outwash and organic/alluvial deposits have high potential for nitrate-enriched ground water to interact with biologically active zones. In till deposits, ground water nitrate removal capacity may be limited by the high occurrence of surface seeps that markedly reduce the time available for biological transformations to occur within the riparian zone. To fully realize the value of riparian zones for nitrate retention, landscape controls of riparian nitrate removal in different climatic and physiographic regions must be determined and translated into available spatial databases. [source] A Generic QSAR for Assessing the Bioaccumulation Potential of Organic Chemicals in Aquatic Food WebsMOLECULAR INFORMATICS, Issue 3 2003Abstract This study presents the development of a quantitative-structure activity relationship (QSAR) for assessing the bioaccumulation potential of organic chemicals in aquatic food webs. The QSAR is derived by parameterization and calibration of a mechanistic food web bioaccumulation model. Calibration of the QSAR is based on the derivation of a large database of bioconcentration and bioaccumulation factors, which is evaluated for data quality. The QSAR provides estimates of the bioaccumulation potential of organic chemicals in higher trophic level fish species of aquatic food webs. The QSAR can be adapted to include the effect of metabolic transformation and trophic dilution on the BAF. The BAF-QSAR can be applied to categorize organic chemical substances on their bioaccumulation potential. It identifies chemicals with a log KOW between 4.0 and 12.2 to exhibit BAFs greater than 5,000 in the absence of significant metabolic transformation rates. The BAF-QSAR can also be used in the derivation of water quality guidelines and total maximum daily loadings by relating internal concentrations of organic chemicals in upper trophic fish species to corresponding concentrations in the water. [source] A review of in situ measurement of organic compound transformation in groundwater,,PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 4 2001Sharon K Papiernik Abstract Laboratory assessments of the rate of degradation of organic compounds in groundwater have been criticized for producing unrepresentative results. The potential for organic compounds to be transformed in groundwater has been measured using in situ methods, which avoid problems of attempting to duplicate aquifer conditions in the laboratory. In situ assessments of transformation rates have been accomplished using transport studies and in situ microcosms (ISMs); a review of these methods is given here. In transport studies, organic solutes are injected into an aquifer and the concentrations are monitored as they are transported downgradient. The change in mass of a solute is determined by the area contained under the breakthrough curve (plot of concentration versus time). ISMs isolate a portion of the aquifer from advective flow and act as in situ batch reactors. Experiments using ISMs involve removing water from the ISM, amending it with the solutes of interest, re-injecting the amended water, and monitoring the solute concentrations with time. In both transport and ISM studies, the loss of organic solutes from solution does not allow a distinction to be made between sorptive, abiotic and biotic transformation losses. Biological activity can be chemically suppressed in ISMs and the results from those experiments used to indicate sorption and abiotic loss. Transformation products may be monitored to provide additional information on transformation mechanisms and rates. Published in 2001 for SCI by John Wiley & Sons, Ltd [source] | |||||||||||||