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Structure Units (structure + unit)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Prediction of vapor,liquid equilibrium for polymer solutions based on the COSMO-SAC model

AICHE JOURNAL, Issue 10 2010
Li Yang
Abstract To extend the application of the COSMO-SAC model to phase-equilibrium calculations of polymer solutions, a new strategy for estimating the charge-density profile, the cavity volume and the cavity surface area of polymer molecules is proposed by finding reasonable parameters for the corresponding repeating structure units. The molecular parameters for polymers are obtained by summing up the corresponding COSMO calculated values of the repeating units calculated by the algorithms of DMol3 (a density functional theory) or MOPAC (a semi-empirical method). Combining with the COSMO-SAC model, the activities and equilibrium pressures for several typical polymer solutions are satisfactorily predicted indicating that the proposed method can be used for the prediction of vapor,liquid equilibrium of polymer solutions. It was also found that both DMol3 and MOPAC can be used though the results obtained from them are slightly different. The results in this paper show that the method proposed has the potential to predict other phase-equilibrium properties of polymer systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

A Comparative Study of Intraplacental Villous Arteries by Latex Cast Model in vitro and Color Doppler Flow Imaging in vivo,

JOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH (ELECTRONIC), Issue 5 2001
Junwu Mu
Abstract Objective: The purpose of this study was to determine whether color Doppler sonogram can accurately depict the placental vascular structures using a latex cast model of the placental vessels, and to make a nomogram of several blood flow parameters according to the vascular structures. Methods: First, we made 9 latex cast models of placental arteries and performed morphologic observation and measurement. Second, the comparative anatomical observation of placental vessels by color flow mapping was performed for all 9 patients from whom the latex models were made. Third, a total of 102 uncomplicated pregnant women between 18 and 40 weeks gestation were examined by color Doppler imaging. The resistance indices (RI) and peak systolic velocity (PSV) were measured. Results: In the latex cast model of placentas, cotyledons could be differentiated by the presence of independent vascular structure units. First, second, third and fourth branches were noted in one cotyledon. Cotyledons were easily identified and counted by color Doppler imaging. Each cotyledon contained only one first branch of the intraplacental villous artery (IPVA). The number of IPVA-1 on color Doppler imaging was equal to the number of the cotyledon calculated from the latex model. RI exhibited a negative, and PSV a positive correlation with gestational age (p < 0.05 in both cases). At any given gestational age, both RI and PSV in the peripheral arteries were significantly lower (p < 0.01) than those in the upstream arteries. Conclusions: Color Doppler flow sonography is a valuable tool for detecting the blood flow of intraplacental villous arteries in vivo and the images agree with the vascular anatomy of placenta in vitro. These results may also provide the basic parameters for future studies of some complicated pregnancies. [source]

X-ray investigation of CdSe nanowires

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009
Özgül Kurtulu
Abstract CdSe nanowires (NWs) have been prepared by a solution,liquid,solid (SLS) approach using Bi nanocatalysts. Structural characterization has been performed by X-ray powder diffraction providing an admixture of wurtzite and zinc-blende (ZB) structure units separated by different types of stacking faults. The relative contributions of ZB type stacking units within the NWs were determined to be in the order of 3,6% from a set of ratios of reflection intensities appearing in only wurtzite structure to those appearing in both ZB and wurtzite (W) structure. In addition, the anisotropy of domain size within the NWs was evaluated from the evolution of peak broadening for increasing scattering length. The coherence lengths along the growth direction are found to be changing between 16 and 21,nm, smaller than the results obtained from TEM measurement, while the NW diameters are determined to be between 5 and 8,nm which is in good agreement with TEM inspection. [source]

Structure of Ga2O3(ZnO)6: a member of the homologous series Ga2O3(ZnO)m

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2008
Yuichi Michiue
The structure of Ga2O3(ZnO)6 was determined using single-crystal X-ray diffraction techniques in the space group Cmcm. The metal ion sublattice resembles some of the Zn ions in the wurtzite ZnO structure. The oxygen ion sublattice in Ga2O3(ZnO)6 also resembles some of the O ions in ZnO. Structural relationships between Ga2O3(ZnO)6 and ZnO are discussed, illustrating the process for obtaining the centrosymmetric Ga2O3(ZnO)6 structure from the noncentrosymmetric ZnO. Structures of phases in the homologous series Ga2O3(ZnO)m are predicted on the basis of the structural data for Ga2O3(ZnO)6. The structures of even m are constructed by simply extending the structure units seen in Ga2O3(ZnO)6, while those of odd m consist of structure units which are of different types from those used for even m. [source]