Different Precursors (different + precursor)

Distribution by Scientific Domains


Selected Abstracts


Cortical radial glial cells in human fetuses: Depth-correlated transformation into astrocytes

DEVELOPMENTAL NEUROBIOLOGY, Issue 3 2003
Leonardo C. deAzevedo
Abstract In the human brain, the transformation of radial glial cells (RGC) into astrocytes has been studied only rarely. In this work, we were interested in studying the morphologic aspects underlying this transformation during the fetal/perinatal period, particularly emphasizing the region-specific glial fiber anatomy in the medial cortex. We have used carbocyanine dyes (DiI/DiA) to identify the RGC transitional forms and glial fiber morphology. Immunocytochemical markers such as vimentin and glial fibrillary acidic protein (GFAP) were also employed to label the radial cells of glial lineage and to reveal the early pattern of astrocyte distribution. Neuronal markers such as neuronal-specific nuclear protein (NeuN) and microtubule-associated protein (MAP-2) were employed to discern whether or not these radial cells could, in fact, be neurons or neuronal precursors. The main findings concern the beginning of RGC transformation showing loss of the ventricular fixation in most cases, followed by transitional figures and the appearance of mature astrocytes. In addition, diverse fiber morphology related to depth within the cortical mantle was clearly demonstrated. We concluded that during the fetal/perinatal period the cerebral cortex is undergoing the final stages of radial neuronal migration, followed by involution of RGC ventricular processes and transformation into astrocytes. None of the transitional or other radial glia were positive for neuronal markers. Furthermore, the differential morphology of RGC fibers according to depth suggests that factors may act locally in the subplate and could have a role in the process of cortical RGC transformation and astrocyte localization. The early pattern of astrocyte distribution is bilaminar, sparing the cortical plate. Few astrocytes (GFAP+) in the upper band could be found with radial processes at anytime. This suggests that astrocytes in the marginal zone could be derived from different precursors than those that differentiate from RGCs during this period. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 288,298, 2003 [source]


Reduced Surfactant Uptake in Three Dimensional Assemblies of VOx Nanotubes Improves Reversible Li+ Intercalation and Charge Capacity

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
Colm O'Dwyer
Abstract The relationship between the nanoscale structure of vanadium pentoxide nanotubes and their ability to accommodate Li+ during intercalation/deintercalation is explored. The nanotubes are synthesized using two different precursors through a surfactant-assisted templating method, resulting in standalone VOx (vanadium oxide) nanotubes and also "nano-urchin". Under highly reducing conditions, where the interlaminar uptake of primary alkylamines is maximized, standalone nanotubes exhibit near-perfect scrolled layers and long-range structural order even at the molecular level. Under less reducing conditions, the degree of amine uptake is reduced due to a lower density of V4+ sites and less V2O5 is functionalized with adsorbed alkylammonium cations. This is typical of the nano-urchin structure. High-resolution TEM studies revealed the unique observation of nanometer-scale nanocrystals of pristine unreacted V2O5 throughout the length of the nanotubes in the nano-urchin. Electrochemical intercalation studies revealed that the very well ordered xerogel-based nanotubes exhibit similar specific capacities (235,mA h g,1) to Na+ -exchange nanorolls of VOx (200,mA h g,1). By comparison, the theoretical maximum value is reported to be 240,mA h g,1. The VOTPP-based nanotubes of the nano-urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437,mA h g,1, which is a considerable advance for VOx based nanomaterials and one of the highest known capacities for Li+ intercalated laminar vanadates. [source]


Permeability and Conductivity Studies on Ionomer-Polysilsesquioxane Hybrid Materials

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2006
Chedarampet S. Karthikeyan
Abstract Summary: Hybrid materials based on sulphonated poly(ether ether ketone) (SPEEK, ionomer) and (RSiO1.5)n network (polysilsequioxane) were prepared by sol-gel process. Two different precursors namely aminopropyl trimethoxysilane (APTMS) and imidazoleglycidoxypropyl trimethoxysilane (IGPTMS) were utilized to generate (RSiO1.5)n in SPEEK matrix by sol-gel process. 29Si MAS NMR confirmed the formation of RSiO3/2 network structure inside the matrix. Characterisation of the hybrid materials showed lower methanol and water permeability compared to the plain SPEEK. They are therefore promising materials as membranes for direct methanol fuel cells applications. The hybrid material derived from amino group was more effective in decreasing the permeability than the material derived from imidazole group. However, the proton conductivity of the latter was higher than the material derived from amino group. The results indicate that hybrid material prepared from imidazole containing silane is more suitable as a membrane for direct methanol fuel cell than the one prepared from amino carrying silane because it fulfils the two main requirements, namely low methanol permeability and reasonably good proton conductivity. Figure shows a network of silica phase in SPEEK matrix. [source]


Differences Between Mistimed and Unwanted Pregnancies Among Women Who Have Live Births

PERSPECTIVES ON SEXUAL AND REPRODUCTIVE HEALTH, Issue 5 2004
Denise V. D'Angelo
CONTEXT: Mistimed and unwanted pregnancies that result in live births are commonly considered together as unintended pregnancies, but they may have different precursors and outcomes METHODS: Data from 15 states participating in the 1998 Pregnancy Risk Assessment Monitoring System were used to calculate the prevalence of intended, mistimed and unwanted conceptions, by selected variables. Associations between unintendedness and women's behaviors and experiences before, during and after the pregnancy were assessed through unadjusted relative risks. RESULTS: The distribution of intended, mistimed and unwanted pregnancies differed on nearly every variable examined; risky behaviors and adverse experiences were more common among women with mistimed than intended pregnancies and were most common among those whose pregnancies were unwanted. The likelihood of having an unwanted rather than mistimed pregnancy was elevated for women 35 or older (relative risk, 2.3) and was reduced for those younger than 25 (0.8); the pattern was reversed for the likelihood of mistimed rather than intended pregnancy (0.5 vs. 1.7,2.7). Parous women had an increased risk of an unwanted pregnancy (2.1,4.0) but a decreased risk of a mistimed one (0.9). Women who smoked in the third trimester, received delayed or no prenatal care, did not breastfeed, were physically abused during pregnancy, said their partner had not wanted a pregnancy or had a low-birth-weight infant had an increased risk of unintended pregnancy; the size of the increase depended on whether the pregnancy was unwanted or mistimed CONCLUSION: Clarifying the difference in risk between mistimed and unwanted pregnancies may help guide decisions regarding services to women and infants [source]


Low Temperature Growth of Photoactive Titania by Atmospheric Pressure Plasma

PLASMA PROCESSES AND POLYMERS, Issue 9 2009
John L. Hodgkinson
Abstract Atmospheric pressure glow discharge plasma CVD was used to deposit thin films of titania at 200,°C using two different precursors. The resulting films were characterised using techniques including XPS, RBS and XRD. It was established that annealing at temperatures as low as 275,°C produced crystalline films that were photocatalytically active. When annealed at 300,°C the photoactivity was greater than that of commercially available "self-cleaning" titania films. The effects of the different precursors, annealing times and temperatures on the crystallinity and photoactivity are discussed. [source]


Synthesis of Highly Efficient Ag@AgCl Plasmonic Photocatalysts with Various Structures

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010
Peng Wang
Abstract By means of a simple ion-exchange process (using different precursors) and a light-induced chemical reduction reaction, highly efficient Ag@AgCl plasmonic photocatalysts with various self-assembled structures,including microrods, irregular balls, and hollow spheres,have been fabricated. All the obtained Ag@AgCl catalysts were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and UV-visible diffuse reflectance spectroscopy. The effect of the different morphologies on the properties of the photocatalysts was studied. The average content of elemental Ag in Ag@AgCl was found to be about 3.2,mol,%. All the catalysts show strong absorption in the visible-light region. The obtained Ag@AgCl samples exhibit enhanced photocatalytic activity for the degradation of organic contaminants under visible-light irradiation. The stability of the plasmonic photocatalysts was also investigated in detail. [source]