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Dynamic Study (dynamic + study)
Selected AbstractsA Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C,S,H) GelsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Jorge S. Dolado In this article, we study the polymerization of silicic acids (Si(OH)4) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C,S,H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three-dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca,OH and Si,OH bonds formed, the relationship with commonly used structural models of C,S,H gels, such as 1.4 nm tobermorite and jennite, is discussed. [source] Dynamic Study of Excited State Hydrogen-bonded Complexes of Harmane in Cyclohexane,Toluene Mixtures,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2002Carmen Carmona ABSTRACT Photoinduced proton transfer reactions of harmane or 1-methyl-9H -pyrido[3,4- b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane,toluene mixtures (CY,TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cationlike exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, ,em, 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, ,em, 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H -pyrido[3,4- b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes. [source] Dynamic study of cerebral bioenergetics and brain function using in vivo multinuclear MRS approachesCONCEPTS IN MAGNETIC RESONANCE, Issue 2 2005Wei Chen Abstract One of the greatest merits of nuclear magnetic resonance (NMR) methodology used in biomedical research and clinical settings is its capability of measuring various physiological parameters in vivo. Besides MR imaging (MRI), which has been routinely applied to obtain vital information in living organs at normal and diseased states, in vivo MR spectroscopy (MRS) provides an invaluable tool for determining metabolites, chemical reaction rates, bioenergetics, and their dynamic changes in the human and animals noninvasively. These MRS capabilities are further enhanced at high/ultrahigh magnetic fields because of significant gain in NMR detection sensitivity and improvement in the spectral resolution. Recent progress has shown that in vivo MRS holds great promise in many biomedical research areas,in particular, brain research. This article provides a broad review of (i) in vivo multinuclear MRS approaches, (ii) advanced MRS methodologies, and (iii) MRS applications for determining cerebral metabolism as well as bioenergetics at resting brain state and their dynamic changes in response to brain activation. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 27A: 84-121, 2005 [source] Dynamic study of stacked packaging units by operational modal analysisPACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2010Carlos Bernad Abstract Laboratory simulation of transport vibration has been the object of many studies in recent years due to the financial implications of potential customer claims in respect of damage caused during product distribution and the need for tools for packaging optimization. Most of these works concentrate on the special nature of transport vibrations and how to reproduce them: Power Spectral Density (PSD) profiles related to road and truck characteristics, the non-stationary aspects of the environment, the non-Gaussian characteristics of the recorded vibrations and the best procedures for meaningful laboratory testing. In the present work, a different point of view is applied to the issue. The paper deals with the dynamics of different corrugated stacked packaging units by means of operational modal analysis and a 6 degrees of freedom multi-axis shaker table. The results show the already known non-linear behaviour of the paperboard containers and the natural frequencies and modes likely to appear in the packaging. The relevance of bending-like modes in relation to laboratory testing is discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simplified inelastic seismic analysis of base-isolated structures using the N2 methodEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2010Vojko Kilar Abstract In the paper a simplified nonlinear method has been applied to the analysis of base-isolated structures. In the first part, a three-linear idealization of the capacity curve is proposed. The initial stiffness is defined based on the first yielding point in the superstructure, whereas the secondary slope depends on the failure mechanism of the superstructure. A consequence is a much more pronounced secondary slope, which does not correspond to the presumptions used in the originally proposed N2 method. A parametric nonlinear dynamic study of single degree of freedom systems with different hardening slopes and damping has been performed for an ensemble of seven EC8 spectrum-compatible artificial accelerograms. It was concluded that, in the long-period range, the equal displacement rule could be assumed also for the proposed systems with non-zero post-yield stiffness. In the second part, the proposed idealization was used for the analysis of isolated RC frame buildings that were isolated with different (lead) rubber-bearing isolation systems. The stiffness of the isolators was selected for three different protection levels and for three different ground motion intensities, which have resulted in elastic as well as moderately and fully damaged superstructure performance levels. Three different lateral load distributions were investigated. It was observed that a triangular distribution, with an additional force at the base, works best in the majority of practical cases. It was concluded that the N2 method can, in general, provide a reasonably accurate prediction of the actual top displacement, as well as of the expected damage to the superstructure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Direct dynamic study on the hydrogen abstraction reaction of H2CO with NCOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009Hao Sun A direct ab initio dynamics method is used to investigate the hydrogen-abstraction reaction of H2CO with NCO. The potential energy surface information is obtained at the MP2/6-311G(d,p) level. More accurate single-point energy is refined at the G3(MP2)//MP2/6-311G(d,p) level. Furthermore, the rate constants of reaction H2CO + NCO are evaluated by using the canonical variational transition state theory with small-curvature tunneling contributions over a wide temperature range of 200,2000 K. The calculated reaction enthalpy and rate constants are in good agreement with the available experimental values. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 394,400, 2009 [source] Kinetic and dynamic study of liquid,liquid extraction of copper in a HFMC: Experimentation, modeling, and simulationAICHE JOURNAL, Issue 6 2010M. Younas Abstract In this work, we present the dispersion-free liquid,liquid extraction of copper from aqueous streams in a hollow fiber membrane contactor (HFMC). Copper has been transferred from aqueous solutions to heptane using LIX 84-I (2-hydroxy-5-nonylacetephenone oxime) as extracting agent. In a first step, batch experiments have been performed to identify the extraction kinetics and to measure the partition coefficient of copper aqueous-organic phase system. Then, the continuous recycled-base extraction process has been performed in a HFMC Liqui-Cel® module. The module has been modeled from resistance in series concept to gain the exit concentrations, which are used to develop a dynamic model to calculate the exit concentration of copper from the output of storage tanks. The model has been validated with experimental data at various operating conditions. The integrated process model algorithm was scripted in MATLAB® 7.4 R (a). Simulations have been made for a range of different operating parameters to determine the optimum criterion conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Resovist enhanced MR imaging of the liver: Does quantitative assessment help in focal lesion classification and characterization?JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Lucia Santoro MD Abstract Purpose: To improve characterization of focal liver lesions by a prospective quantitative analysis of percentage signal intensity change, in dynamic and late phases after slow (0.5 mL/s) Resovist administration. Materials and Methods: Seventy-three patients were submitted on clinical indication to MR examination with Resovist. Signal intensity of 92 detected focal lesions (5,80 mm) were measured with regions of interest and normalized to paravertebral muscle in arterial, portal, equilibrium and T1/T2 late phases, by two observers in conference. Five values of percentage variations per patient were obtained and statistically evaluated. Results: The enhancement obtained on dynamic study is more suitable in hemangiomas and focal nodular hyperplasias than in adenomas and hepatocellular carcinomas. To discriminate benign versus malignant lesions on late-phase-T2-weighted images, a cutoff = ,26%, allowed sensitivity and specificity values of 97.4% and 97.7%, respectively. Area under the receiver operating characteristic (ROC) curve was 0.99. To differentiate hemangioma versus all other focal liver lesions, on late-phase-T1-weighted images, a cutoff = +40% permitted sensitivity and specificity values of 90.5% and 98.0%, respectively. Area under the ROC curve was 0.98. Conclusion: Late phase quantitative evaluation after slow Resovist administration, allows to differentiate malignant from benign hepatic masses and hemangiomas from all the others focal liver lesions, on T2-/T1-weighted acquisitions, respectively. J. Magn. Reson. Imaging 2009;30:1012,1020. © 2009 Wiley-Liss, Inc. [source] | ||||||||||||||||