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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Carbon disulfide has identical microwave and optical dielectric constants, as well as extremely low optical and microwave loss. These properties make it possible to construct long travelingwave light modulators at microwave frequencies using the Kerr electrooptic effect induced in CS(2) by an electric field propagating on a TEM transmission line.Several experiments with traveling-wave Kerr cells consisting of resonant strip transmission lines immersed in CS(2) are described. A decrease in the microwave power required for modulation by a factor of two, by cooling the modulators to a temperature of -55 degrees C, is demonstrated. Simultaneous modulation of light at two microwave frequencies by excitation of two of the longitudinal modes of the strip line resonator is also described. Relatively high efficiency modulation with long devices of this type is also reported. In these experiments, the microwave power required for large depths of modulation is reduced by almost two orders of magnitude compared to previously reported CS(2) light modulators, and is within less than a factor of two of the calculated power for cells up to 44 cm in length. For longer cells, increasingly larger than predicted powers are required.
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PMID:Carbon disulfide traveling-wave Kerr cells. 2005 98

Carbon-supported bimetallic Au-Pt nanoparticle catalysts with a core-shell structure were prepared by the successive reduction method. UV-vis spectra, TEM, XPS, and XRD techniques were used to characterize the prepared core-shell and the monometallic catalysts. Results of all the physical characterizations showed the continuous growth of the Pt shell on the Au core. The electrocatalytic activities for oxygen reduction were characterized using the rotating disk electrode technique in an acid electrolyte, and were compared with those obtained on a Pt/C catalyst under the same measurement conditions. It was found that these core-shell nanoparticles exhibited the structural characteristics of mainly fcc Au nanocrystals but the electrochemical properties of a Pt surface. The electrocatalytic activities of these core-shell nanoparticles showed a transition from the low activity of Au to the high activity of Pt, and the catalyst with a Au-Pt atomic ratio of 2:1 had a maximized specific mass activity, proving the enhanced Pt utilization with the core-shell structure.
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PMID:Influence of the composition of core-shell Au-Pt nanoparticle electrocatalysts for the oxygen reduction reaction. 2006 Sep 83

Multipotent mesenchymal stem cells (MSCs) have attracted substantial attention in stem cell therapy and tissue engineering due to their ability to be cultured for successive passages and multilineage differentiation. Carbon nanotubes (CNTs) have been proposed to be used as potential biomedical structures for bone formation. Therefore, it is important to study the mechanisms of interaction between MSCs and CNTs. We demonstrated that carboxylated single-walled carbon nanotubes (SWCNTs) and carboxylated multiwalled carbon nanotubes (MWCNTs) inhibited the proliferation, osteogenic differentiation, adipogenic differentiation, and mineralization of MSCs. Oxidative stress assay indicated that reactive oxygen species (ROS) may not be responsible for the observed cytotoxicity of carboxylated CNTs. Quantitative real-time polymerase chain reaction (Q-PCR) experiments confirmed that the expression of osteoblast specific genes and adipocyte differentiation specific genes was greatly attenuated during the differentiation of MSCs in the presence of carboxylated CNTs. TEM images revealed that CNTs might interact with proteins located on the cell membrane or in the cytoplasm, which have a further impact on subsequent cellular signaling pathways. Q-PCR results and Western blot analysis together verified that the inhibition of proliferation and osteogenic differentiation of MSCs may be modulated through a Smad-dependent bone morphogenetic protein (BMP) signaling pathway.
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PMID:Inhibition of proliferation and differentiation of mesenchymal stem cells by carboxylated carbon nanotubes. 2021 64

Carbon nanotubes having large surface area is an interesting material to develop H2-Cl2 fuel cell electrodes. The attempts were made to deposit carbon nanotubes on porous substrates by chemical vapour deposition. Turpentine oil (C10H16) was used as a precursor, decomposed at 1100 degrees C reactor temperature. Nickel, platinum, tin, Ni-Pt, Ni-Sn, Pt-Sn, Ni-Pt-Sn catalysts were used to grow carbon nanotubes. Nickel was deposited with electrodeposition, platinum with sputter coater and tin with vacuum deposition technique. The developed electrodes were characterized by XRD, SEM, TEM, FTIR, and resistivity by van-der Pauw method. Carbon nanotubes have been formed for 0.25 N nickel deposited for 45 and 60 min; 0.5 N, 0.75 N and 1 N nickel deposited for 15 to 60 min, at the interval of 15. Ni-Pt, Ni-Sn, Pt-Sn and Ni-Pt-Sn activated carbon also shows the well grown CNTs. Aqueous H2-Cl2 fuel cell performance was tested with these grown carbon nanotubes. 40% KCl with 1067 mohm(-1) cm(-1) conductivity was used as electrolyte. Linear sweep voltametry shows reduction potential for hydrogen gas. Chronoamperometry results show better half cell performance for nickel, deposited with 1 N, 45 min deposition time period; and combination of Ni-Pt-Sn with 140, and 110-100 mA/cm2 stable current density respectively.
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PMID:Chemical vapor deposited carbon nanotubes for aqueous H2-Cl2 fuel cells. 2035 6

Carbon nanocubes and nanobricks were synthesized by pyrolyzing rice powder at 600 degrees C under nitrogen atmosphere. Purification with concentrated nitric acid introduced approximately 0.1 mol/g of carboxylic acid groups as found by acid-base titrimetric analysis. XRD pattern showed the 0.15 mol/g basic graphitic structure of these nano carbon materials. Their SEM and TEM images revealed cube or brick shaped nano crystals. These nanocrystals are further characterized by FT-IR, Raman, and EDAX analysis. High density wrapping of carboxylated acid groups introduces surface passivation of these nano carbon cubes and nano carbon bricks exhibiting photoluminescence. Solid state electronic spectrum showed several bands in the ultraviolet and visible region and excitation at 336 and 474 nm generates photoluminescence respectively in the ultraviolet and visible region.
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PMID:Carbon nanocubes and nanobricks from pyrolysis of rice. 2035 15

LiFePO4/Carbon nanocomposites with varying amounts of carbon were synthesized using polyol process without any further heating as a post step. The X-ray diffraction patterns of all samples were indexed on the basis of orthorhombic olivine-type structure. The field emission-TEM images of composites with the amount of 3 approximately 15 wt% carbon showed the average sizes of 45 approximately 80 nm with nanorod shape surrounded by carbon. The initial discharge curves of LiFePO4/Carbon show 166, 157, 142, and 119 mAh/g capacities at a current density of 0.1 mA/cm2 in the voltage range of 2.5-4.2 V, respectively, without capacity fading and excellent cycle retentions during the 20 cycles. Especially, the sample of amount of 3 wt% carbon shows the excellent high rate performances at 15 and 30 C rates with high capacity retention compared with previously reported results of high temperature processed results, due to the existence of conductive agents such as carbon which suppresses particle growth and exhibits improved electronic conductivity and lithium ion diffusivity, simultaneously.
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PMID:Synthesis and electrochemical properties of LiFePO4/carbon nanocomposites in polyol medium. 2035 69

Carbon nanotubes (CNTs) have been shown to modify some properties of nanomaterials and to modify chemical reactions confined inside their channels, which are formed by curved graphene layers. Here we studied ammonia synthesis over Ru as a probe reaction to understand the effect of the electron structure of CNTs on the confined metal particles and their catalytic activity. The catalyst with Ru nanoparticles dispersed almost exclusively on the exterior nanotube surface exhibits a higher activity than the CNT-confined Ru, although both have a similar metal particle size. Characterization with TEM, N(2) physisorption, H(2) chemisorption, temperature-programmed reduction, CO adsorption microcalorimetry, and first-principles calculations suggests that the outside Ru exhibits a higher electron density than the inside Ru. As a result, the dissociative adsorption of N(2), which is an electrophilic process and the rate-determining step of ammonia synthesis, is more facile over the outside Ru than that over the inside one.
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PMID:Probing the electronic effect of carbon nanotubes in catalysis: NH(3) synthesis with Ru nanoparticles. 2037 23

Co-naphthalocyanine (CoNPc) was prepared by heat treatment for cathode catalysts to be used in microbial fuel cells (MFCs). Four different catalysts (Carbon black, NPc/C, CoNPc/C, Pt/C) were compared and characterized using XPS, EDAX and TEM. The electrochemical characteristics of oxygen reduction reaction (ORR) were compared by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The Co-macrocyclic complex improves the catalyst dispersion and oxygen reduction reaction of CoNPc/C. The maximum power of CoNPc/C was 64.7 mW/m(2) at 0.25 mA as compared with 81.3 mW/m(2) of Pt/C, 29.7 mW/m(2) of NPc/C and 9.3 mW/m(2) of carbon black when the cathodes were implemented in H-type MFCs. The steady state cell, cathode and anode potential of MFC with using CoNPc/C were comparable to those of Pt/C.
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PMID:Application of Co-naphthalocyanine (CoNPc) as alternative cathode catalyst and support structure for microbial fuel cells. 2065 80

Carbon nanofibers containing linear mesocage arrays were prepared via evaporation induced self-assembly method within AAO template with an average channel diameter of about 25 nm. The TEM results show that the mesocages have an elongated shape in the transversal direction. The results of N2 adsorption-desorption analysis indicate that the sample possesses a cage-like mesoporous structure and the average mesopore size of the sample is about 18 nm.
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PMID:Template synthesis of carbon nanofibers containing linear mesocage arrays. 2067 93

We report a new synthesis of PtRe alloy nanoparticles (NPs) and their electrocatalytic activity for methanol oxidation. PtRe alloy NPs with controlled composition were prepared by a capping agents-based colloidal method. In the synthesis, trioctylamine was used as high-boiling solvent, and oleylamine/oleic acid were employed as capping agents to control the particle size and dispersion. The PtRe NPs were fully characterized by TEM, EDX, XRD and XPS. The as-prepared PtRe NPs had a narrow size distribution, and displayed a good dispersion in hydrocarbon solvents. Carbon-supported PtRe catalysts were prepared by physical deposition of as-prepared particles on carbon powder, followed by the catalytic activation at 400 degrees C in Ar/H2. Electrochemical studies showed the PtRe catalysts had high activity for methanol electrooxidation.
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PMID:Synthesis and characterization of PtRe alloy nanoparticles as electrocatalysts for methanol oxidation. 2112 10


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