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Transmission Electronic Microscopy (transmission + electronic_microscopy)
Selected AbstractsTwo-Dye Core/Shell Zeolite Nanoparticles: A New Tool for Ratiometric pH MeasurementsADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Tristan Doussineau Abstract The preparation of core/shell nanoparticles that enable ratiometric pH measurement is described. The core of the nanoparticles consists of a zeolite- , matrix that exhibits a 3-hydroxyflavone reference dye within the porous network. Coating an amorphous silica shell containing a fluorosensor around the zeolite through the Stöber process provides pH sensitivity to the nanoparticles. Morphological characterization (dynamic light scattering, transmission electronic microscopy) demonstrates the control of the sensing silica shell around the zeolite cores, leading to highly monodisperse spherical nanoparticles, while structural characterization (wide-angle X-ray diffraction, nitrogen adsorption) shows the amorphous character of the shell. Spectral characterization via UV/Vis absorption and steady-state fluorescence shows good pH sensitivity of the resulting nanosensors with a pKa suitable for bioanalytical applications. [source] Cell wall modifications during osmotic stress in Lactobacillus caseiJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2005M. Piuri Abstract Aims:, To study the modification of the cell wall of Lactobacillus casei ATCC 393 grown in high salt conditions. Methods and Results:, Differences in the overall structure of cell wall between growth in high salt (MRS + 1 mol l,1 NaCl; N condition) and control (MRS; C condition) conditions were determined by transmission electronic microscopy and analytical procedures. Lactobacillus casei cells grown in N condition were significantly larger than cells grown under unstressed C condition. Increased sensitivity to mutanolysin and antibiotics with target in the cell wall was observed in N condition. Purified cell wall also showed the increased sensitivity to lysis by mutanolysin. Analysis of peptidoglycan (PG) from stressed cells showed that modification was at the structural level in accordance with a decreased PG cross-link involving penicillin-binding proteins (PBP). Nine PBP were first described in this species and these proteins were expressed in low percentages or presented a modified pattern of saturation with penicillin G (Pen G) during growth in high salt. Three of the essential PBP were fully saturated in N condition at lower Pen G concentrations than in C condition, suggesting differences in functionality in vivo. Conclusions:, The results show that growth in high salt modified the structural properties of the cell wall. Significance and Impact of Study:, Advances in understanding the adaptation to high osmolarity, in particular those involving sensitivity to lysis of lactic acid bacteria. [source] Synthesis and characterization of cobalt nano-particles through microwave polyol processAICHE JOURNAL, Issue 6 2009Wen-Tung Cheng Abstract This article aims to synthesize and character cobalt nano-particles through microwave polyol process. At first, cobalt acetate is used as precursor to synthesize cobalt nano-particles by microwave assisted ethylene glycol in the presence of polyvinylpyrrolidone (PVP) as capping agent. As measured from ion-coupled plasma (ICP) and thermo-gravimetric analysis (TGA), the yields of as-synthesized cobalt particles in average diameters of 40 and 81 nm verified by transmission electronic microscopy (TEM), are 71 and 85%, respectively; and the structure of as-synthesized cobalt nano-particle is a face-center cubic structure analyzed by X-ray diffraction (XRD). Finally, the as-synthesized cobalt nano-particle modified by oleic acid is dispersed in kerosene to character magnetic property. As measured by vibration sample magnetometer (VSM), the saturation magnetisms of cobalt nano-particles with average diameters of 40 and 81 nm are 39.1 and 29.5 emu/g, respectively, in solution. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] An environmentally-relevant mixture of organochlorines and its vehicle control, dimethylsulfoxide, induce ultrastructural alterations in porcine oocytesMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 1 2006Céline Campagna Abstract Organochlorine chemicals accumulate in the environment, particularly in the Arctic, and constitute potential developmental hazards to wildlife and human health. Although some of their harmful effects are recognized, their mechanisms of action within the target cells need to be better understood. This study was designed to test the hypothesis that an environmentally-relevant organochlorine mixture alters oocyte ultrastructure in the porcine model. Immature cumulus,oocyte complexes (COCs), partially cultured (18 hr) COCs without treatment or exposed to the organochlorine mixture or its vehicle (0.1% dimethysulfoxide; DMSO) during culture were processed for light and transmission electronic microscopy (TEM). The organochlorines induced major ultrastructural changes in the COCs: decreased density of the lipid droplets, increased smooth endoplasmic reticulum (SER) volume and increased interactions among SER, mitochondria, lipid droplets and vesicles. We suggest that these ultrastructural changes facilitate energy formation necessary to produce metabolizing enzymes. Other ultrastructural changes may reflect some degree of organochlorine toxicity: fewer gap junctions and decreased electron density of the cortical granules. Unexpectedly, the DMSO control treatment also induced similar ultrastructural changes, but to a lesser degree than the organochlorine mixture. This study is the first to demonstrate the effect of environmental contaminants on mammalian oocyte ultrastructure. Mol. Reprod. Dev. © 2005 Wiley-Liss, Inc. [source] Observations on surface morphologies and dislocations of a-plane GaN grown by metal organic chemical vapor depositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007T. S. Ko Abstract In this study, we grew non-polar a-plane GaN thin films on r-plane sapphire using a series of growth conditions by metal-organic chemical vapor deposition. The results showed that high temperature and low-pressure conditions benefited two-dimension growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best surface morphology with an excellent mean roughness of 10.5 Ĺ was obtained. The different thickness AlN as a nucleation layer and the different ,/, ratio were also considered. The results revealed that the surface morphology would get worse when the thickness of nucleation layer and ,/, ratio were away from the values of optimal condition. The observation of transmission electronic microscopy shown the lowest density of threading dislocations was 1.85×1010/cm2. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of exfoliated polyamide 6,6/organically modified montmorillonite nanocomposites by in situ interfacial polymerizationPOLYMER COMPOSITES, Issue 6 2007M. Tarameshlou Polyamide 6,6 (PA 6,6)/organically modified montmorillonite (OMMT) nanocomposites were prepared by a novel method, using direct interfacial polymerization of an aqueous hexamethylene diamine and a nonaqueous adipoyl chloride in dichloromethane solution containing different amounts of OMMT dispersed nanoparticles. The state of dispersion of OMMT in the PA 6,6 matrix was investigated by means of X-ray diffraction, as well as transmission electronic microscopy. The results indicated that the OMMT nanoparticles were dispersed homogeneously and nearly exfoliated in the PA 6,6 matrix. The random arrangement of clay platelets in the PA 6,6 matrix, exfoliation, and intercalation of clays between the PA 6,6 matrix were distinguished. The amount of the incorporated OMMT in the PA 6,6 matrix was determined by means of TGA technique. Furthermore it was found that addition of a small amount of OMMT dramatically improved the thermal stability of PA 6,6. The TGA thermograms of all the synthesized nanocomposite samples showed an interesting unexpected lag in the weight loss at high temperatures, which could be another evidence for formation of fully exfoliated nanocomposites structures, with improved thermal stability. Nucleating effect of the OMMT nanoparticles and their influence on crystallization behavior of PA 6,6 was confirmed by DSC. Finally it is concluded that the in situ interfacial polycondensation is a suitable method for synthesis of nanocomposites with well dispersed structures and enhanced properties. POLYM. COMPOS., 28:733,738, 2007. © 2007 Society of Plastics Engineers [source] Synthesis, characterization and properties of organoclay-modified polyurethane/epoxy interpenetrating polymer network nanocompositesPOLYMER INTERNATIONAL, Issue 3 2006Qingming Jia Abstract organoclay-modified polyurethane/epoxy interpenetrating network nanocomposites (oM-PU/EP nanocomposites) were prepared by adding organophilic montmorillonite (oMMT) to interpenetrating polymer networks (IPNs) of polyurethane and epoxy resin (PU/EP) which had been prepared by a sequential polymerization technique. Wide-angle X-ray diffraction (WAXD) and transmission electronic microscopy (TEM) analysis showed that the interpenetrating process of PU and EP improved the exfoliation and dispersion degree of oMMT. The effects of the NCO/OH ratio (isocyanate index), the weight ratio of PU/EP and oMMT content on the phase structure and the mechanical properties of the oM-PU/EP nanocomposites were studied by tensile testing and scanning electronic microscopy (SEM). Water absorption tests showed that the PU/EP interpenetrating networks and oMMT had synergistic effects on improvement in the water resistance of the oM-PU/EP nanocomposites. Differential scanning calorimetry (DSC) analysis showed that PU was compatible with EP and that the glass transition temperature (Tg) of the oM-PU/EP nanocomposites increased with the oMMT content up to 3 wt%, and then decreased with further increasing oMMT content. The thermal stability of these nanocomposites with various oMMT contents was studied by thermogravimetric analysis (TGA), and the mechanism of thermal stability improvement was discussed according to the experimental results. Copyright © 2005 Society of Chemical Industry [source] | |||||||||||||