Structural Investigation of Activated Lattice Oxygen in Ce1-xSnxO2 and Ce1-x-ySnxPdyO2-delta by EXAFS and DFT calculation

Substitution of Sn4+ ion in CeO2 creates activated oxygen in Ce0.8Sn0.2O2 leading to higher oxygen storage capacity compared to Ce0.8Zr0.2O2. With Pd ion substitution in Ce0.8Sn0.2O2,activation of oxygen is further enhanced as observed from the H-2/TPR study. Both EXAFS analysis and DFT calculation reveal that in the solid solution Ceexhibits 4 + 4 coordination, Sri exhibits 4 + 2 + 2 coordination and Pd has 4 + 3 coordination. While the oxygen in the First four coordination with short M-O bonds are strongly held in the lattice, the oxygens in the second and higher coordinations with long M-O bonds are weakly bound, and they are the activated oxygen ill the lattice. Bond valence analysis shows that oxygen with valencies as low its 1.65 are created by the Sn and Pd ion Substitution. Another interesting observation is that H-2/TPR experiment of Ce1-xSnxO2 shows a broad peak starting from 200 to 500 degrees C, while the same reduction is achieved in a single step at similar to 110 degrees C in presence Pd2+ on. Substitution of Pd2+ ion thus facilitates synergistic reduction of the catalyst at lower temperature. We have shown that simultaneous reduction of the Ce4+ and Sr4+ ions by Pd-0 is the synergistic interaction leading to high oxygen storage capacity at low temperature.

Microneurovascular free muscle transfer with cross-over nerve grafts in facial reanimation

Microneurovascular free muscle transfer with cross-over nerve grafts in facial reanimation Loss of facial symmetry and mimetic function as seen in facial paralysis has an enormous impact on the psychosocial conditions of the patients. Patients with severe long-term facial paralysis are often reanimated with a two-stage procedure combining cross-facial nerve grafting, and 6 to 8 months later with microneurovascular (MNV) muscle transfer. In this thesis, we recorded the long-term results of MNV surgery in facial paralysis and observed the possible contributing factors to final functional and aesthetic outcome after this procedure. Twenty-seven out of forty patients operated on were interviewed, and the functional outcome was graded. Magnetic resonance imaging (MRI) of MNV muscle flaps was done, and nerve graft samples (n=37) were obtained in second stage of the operation and muscle biopsies (n=18) were taken during secondary operations.. The structure of MNV muscles and nerve grafts was evaluated using histological and immunohistochemical methods ( Ki-67, anti-myosin fast, S-100, NF-200, CD-31, p75NGFR, VEGF, Flt-1, Flk-1). Statistical analysis was performed. In our studies, we found that almost two-thirds of the patients achieved good result in facial reanimation. The longer the follow-up time after muscle transfer the weaker was the muscle function. A majority of the patients (78%) defined their quality of life improved after surgery. In MRI study, the free MNV flaps were significantly smaller than originally. A correlation was found between good functional outcome and normal muscle structure in MRI. In muscle biopsies, the mean muscle fiber diameter was diminished to 40% compared to control values. Proliferative activity of satellite cells was seen in 60% of the samples and it tended to decline with an increase of follow-up time. All samples showed intramuscular innervation. Severe muscle atrophy correlated with prolonged intraoperative ischaemia. The good long-term functional outcome correlated with dominance of fast fibers in muscle grafts. In nerve grafts, the mean number of viable axons amounted to 38% of that in control samples. The grafted nerves characterized by fibrosis and regenerated axons were thinner than in control samples although they were well vascularized. A longer time between cross facial nerve grafting and biopsy sampling correlated with a higher number of viable axons. P75Nerve Growth Factor Receptor (p75NGFR) was expressed in every nerve graft sample. The expression of p75NGFR was lower in older than in younger patients. A high expression of p75NGFR was often seen with better function of the transplanted muscle. In grafted nerve Vascular Endothelial Growth Factor (VEGF) and its receptors were expressed in nervous tissue. In conclusion, most of the patients achieved good result in facial reanimation and were satisfied with the functional outcome. The mimic function was poorer in patients with longer follow-up time. MRI can be used to evaluate the structure of the microneurovascular muscle flaps. Regeneration of the muscle flaps was still going on many years after the transplantation and reinnervation was seen in all muscle samples. Grafted nerves were characterized by fibrosis and fewer, thinner axons compared to control nerves although they were well vascularized. P75NGFR and VEGF were expressed in human nerve grafts with higher intensity than in control nerves which is described for the first time.

Observation of Peierls transition in nanowires (diameter similar to 130 nm) of the charge transfer molecule TTF-TCNQ synthesized by electric-field-directed growth

We report the growth of nanowires of the charge transfer complex tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) with diameters as low as 130 nm and show that such nanowires can show Peierls transitions at low temperatures. The wires of sub-micron length were grown between two prefabricated electrodes (with sub-micron gap) by vapor phase growth from a single source by applying an electric field between the electrodes during the growth process. The nanowires so grown show a charge transfer ratio similar to 0.57, which is close to that seen in bulk crystals. Below the transition the transport is strongly nonlinear and can be interpreted as originating from de-pinning of CDW that forms at the Peierls transition.

Characterization of DNA Strand Transfer Promoted by Mycobacterium smegmatis RecA Reveals Functional Diversity with Mycobacterium tuberculosis RecA†

The RecA-like proteins constitute a group of DNA strand transfer proteins ubiquitous in eubacteria, eukarya, and archaea. However, the functional relationship among RecA proteins is poorly understood. For instance, Mycobacterium tuberculosis RecA is synthesized as a large precursor, which undergoes an unusual protein-splicing reaction to generate an active form. Whereas the precursor was inactive, the active form promoted DNA strand transfer less efficiently compared to EcRecA. Furthermore, gene disruption studies have indicated that the frequencies of allele exchange are relatively lower in Mycobacterium tuberculosis compared to Mycobacterium smegmatis. The mechanistic basis and the factors that contribute to differences in allele exchange remain to be understood. Here, we show that the extent of DNA strand transfer promoted by the M. smegmatis RecA in vitro differs significantly from that of M. tuberculosis RecA. Importantly, M. smegmatis RecA by itself was unable to promote strand transfer, but cognate or noncognate SSBs rendered it efficient even when added prior to RecA. In the presence of SSB, MsRecA or MtRecA catalyzed strand transfer between ssDNA and varying lengths of linear duplex DNA with distinctly different pH profiles. The factors that were able to suppress the formation of DNA networks greatly stimulated strand transfer reactions promoted by MsRecA or MtRecA. Although the rate and pH profiles of dATP hydrolysis catalyzed by MtRecA and MsRecA were similar, only MsRecA was able to couple dATP hydrolysis to DNA strand transfer. Together, these results provide insights into the functional diversity in DNA strand transfer promoted by RecA proteins of pathogenic and nonpathogenic species of mycobacteria.

Functional transfer of Salmonella pathogenicity island 2 to Salmonella bongori and Escherichia coli.

The type III secretion system (T3SS) encoded by the Salmonella pathogenicity island 2 (SPI2) has a central role in systemic infections by Salmonella enterica and for the intracellular phenotype. Intracellular S. enterica uses the SPI2-encoded T3SS to translocate a set of effector proteins into the host cell, which modify host cell functions, enabling intracellular survival and replication of the bacteria. We sought to determine whether specific functions of the SPI2-encoded T3SS can be transferred to heterologous hosts Salmonella bongori and Escherichia coli Mutaflor, species that lack the SPI2 locus and loci encoding effector proteins. The SPI2 virulence locus was cloned and functionally expressed in S. bongori and E. coli. Here, we demonstrate that S. bongori harboring the SPI2 locus is capable of secretion of SPI2 substrate proteins under culture conditions, as well as of translocation of effector proteins under intracellular conditions. An SPI2-mediated cellular phenotype was induced by S. bongori harboring the SPI2 if the sifA locus was cotransferred. An interference with the host cell microtubule cytoskeleton, a novel SPI2-dependent phenotype, was observed in epithelial cells infected with S. bongori harboring SPI2 without additional effector genes. S. bongori harboring SPI2 showed increased intracellular persistence in a cell culture model, but SPI2 transfer was not sufficient to confer to S. bongori systemic pathogenicity in a murine model. Transfer of SPI2 to heterologous hosts offers a new tool for the study of SPI2 functions and the phenotypes of individual effectors.

Microtribology and Friction-Induced Material Transfer in Layered MoS2 Nanoparticles Sprayed on a Steel Surface

Frictional performance of molybdenum disulfide (MoS2) particles sprayed on a substrate is investigated in a ball-on-disc tribometer. The ability of large (similar to 2 mu m) and small (similar to 50 nm) particles to generate low-friction transfer film is investigated with a view to elucidate the requirement for film formation. Particle migration, particle stability in the contact region, oxidation potential, and particle adhesion to the substrate are explored within a span of operating parametersp; normal load, and sliding velocity. It is found that the larger particles are able to migrate to the contact to raise a homogeneous but nonuniform low-friction transfer film that flows plastically to yield large contact areas, which aid in wear protection. Within the present load and speed range, the inability of small particles to stay in the contact region and undergo basal slip militates against the formation of a low-friction transfer film.

Effect of Bottom Bubbling Conditions on Surface Reaction Rate in Oxygen-Water System

In secondary steelmaking, the enhancement of the reaction rate in the low carbon period during the decarburization of steel is considered the most effective method to produce ultralow carbon steel. In a previous study, it was revealed that the surface reaction is dominant during the final stage of the actual refining process. In order to improve the surface reaction rate, it is necessary to enlarge the reaction region, which is usually achieved by increasing the plume eye area. In this study, water model experiments were carried out to estimate the influence of bottom stirring conditions on the gas-liquid reaction rate; for this purpose, the deoxidation rate during the bottom bubbling process was measured. Five types of nozzle configurations were used to study the effect of the plume eye area on the reaction rate at various gas flow rates. The results reveal that the surface reaction rate is influenced by the gas flow rate and the plume eye area. An empirical correlation was developed for the reaction rate and the plume eye area. This correlation was applied to estimate the gas-liquid reaction rate mat the bath surface.

A Methanol-Tolerant Carbon-Supported Pt-Au Alloy Cathode Catalyst for Direct Methanol Fuel Cells and Its Evaluation by DFT

A Pt-Au alloy catalyst of varying compositions is prepared by codeposition of Pt and Au nanoparticles onto a carbon support to evaluate its electrocatalytic activity toward an oxygen reduction reaction (ORR) with methanol tolerance in direct methanol fuel cells. The optimum atomic weight ratio of Pt to Au in the carbon-supported Pt-Au alloy (Pt-Au/C) as established by cell polarization, linear-sweep voltammetry (LSV), and cyclic voltammetry (CV) studies is determined to be 2:1. A direct methanol fuel cell (DMFC) comprising a carbon-supported Pt-Au (2:1) alloy as the cathode catalyst delivers a peak power density of 120 mW/cm2 at 70 °C in contrast to the peak power density value of 80 mW/cm2 delivered by the DMFC with carbon-supported Pt catalyst operating under identical conditions. Density functional theory (DFT) calculations on a small model cluster reflect electron transfer from Pt to Au within the alloy to be responsible for the synergistic promotion of the oxygen-reduction reaction on a Pt-Au electrode.

A direct borohydride fuel cell employing Prussian Blue as mediated electron-transfer hydrogen peroxide reduction catalyst

A direct borohydride-hydrogen peroxide fuel cell employing carbon-supported Prussian Blue (PB) as mediated electron-transfer cathode catalyst is reported. While operating at 30 °C, the direct borohydride-hydrogen peroxide fuel cell employing carbon-supported PB cathode catalyst shows superior performance with the maximum output power density of 68 mW cm−2 at an operating voltage of 1.1 V compared to direct borohydride-hydrogen peroxide fuel cell employing the conventional gold-based cathode with the maximum output power density of 47 mW cm−2 at an operating voltage of 0.7 V. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDAX) suggest that anchoring of Cetyl-Trimethyl Ammonium Bromide (CTAB) as a surfactant moiety on carbon-supported PB affects the catalyst morphology. Polarization studies on direct borohydride-hydrogen peroxide fuel cell with carbon-supported CTAB-anchored PB cathode exhibit better performance with the maximum output power density of 50 mW cm−2 at an operating voltage of 1 V than the direct borohydride-hydrogen peroxide fuel cell with carbon-supported Prussian Blue without CTAB with the maximum output power density of 29 mW cm−2 at an operating voltage of 1 V.

The oxygen migration in the apatite-type lanthanum silicate with the cation substitution

A theoretical model is proposed to determine the effects of Si substitution with Al on the oxygen diffusion in apatite-type lanthanum silicates based on density-functional theory (DFT) calculations for La10(SiO 4)4(AlO4)2O2. Substitution changes the stable configuration for excess oxygen from the split interstitial to a new cluster form with the original cluster. Al doping completely changes the migration mechanism from the interstitialcy one, which was proposed for the La9.33(SiO4)6O2 starting material, to a mechanism which contains an interstitial process. Nevertheless, the migration barrier is calculated to be 0.81 eV, which indicates small changes in oxygen conduction and is consistent with the observations. The present study indicates that the cation substitution on silicon site alone does not promise the improvement of the oxide ion conduction in the lanthanum silicate.

Position preference and diffusion path of an oxygen ion in apatite-type lanthanum silicate La9.33Si6O26: A density functional study

Using density functional theory, we investigated the position preference and diffusion mechanisms of interstitial oxygen ions in lanthanum silicate La9.33Si6O26, which is an apatite-structured oxide and a promising candidate electrolyte material for solid oxide fuel cells. The reported lanthanum vacancies were explicitly taken into account by theoretically determining their arrangement with a supercell model. The most stable structures and the formation energies of oxygen interstitials were determined for each charged state. It was found that the double-negatively charged state is stable over a wide range of the Fermi level, and that the excess oxygen ions form split interstitials with the original oxygen ions, while the neutral and the single-negatively charged states preferably form molecular oxygen. These species were found near the lanthanum vacancy site. The theoretically determined migration pathway along the c-axis essentially follows an interstitialcy mechanism. The obtained migration barrier is sensitive to the charge state, and is also affected by the lanthanum vacancy. The barrier height of the double-negatively charged state was calculated to be 0.58 eV for the model structure, which is consistent with the measured activation energy.

Vacuum ultraviolet/atomic oxygen erosion resistance of amorphous Si0.26C0.43N0.31 coating

An amorphous silicon carbonitride (Si1-x-yCxN y, x = 0:43, y = 0:31) coating was deposited on polyimide substrate using the magnetron-sputtering method. Exposure tests of the coated polyimide in atomic oxygen beam and vacuum ultraviolet radiation were performed in a ground-based simulator. Erosion kinetics measurements indicated that the erosion yield of the Si0.26C0.43N0.31 coating was about 1.5x and 1.8 × 10-26 cm3 /atom during exposure in single atomic oxygen beam, simultaneous atomic oxygen beam, and vacuum ultraviolet radiation, respectively. These values were 2 orders of magnitude lower than that of bare polyimide substrate. Scanning electron and atomic force microscopy, X-ray photoelectron spectrometer, and Fourier transformed infrared spectroscopy investigation indicated that during exposures, an oxide-rich layer composed of SiO2 and minor Si-C-O formed on the surface of the Si 0.26C0.43N0.31 coating, which was the main reason for the excellent resistance to the attacks of atomic oxygen. Moreover, vacuum ultraviolet radiation could promote the breakage of chemical bonds with low binding energy, such as C-N, C = N, and C-C, and enhance atomic oxygen erosion rate slightly.

Tribological properties of γ-Y2Si2O7 ceramic against AISI 52100 steel and Si3N4 ceramic counterparts

Reciprocating ball-on-flat dry sliding friction and wear experiments have been conducted on singlephase γ-Y2Si2O7 ceramic flats in contact with AISI 52100 bearing steel and Si3N4 ceramic balls at 5-15N normal loads in an ambient environment. The kinetic friction coefficients of γ-Y2Si2O7 varied in the range over 0.53-0.63 against AISI 52100 steel and between 0.51-0.56 against Si3N4 ceramic. We found thatwear occurred predominantly during the running-in period and it almost ceased at the steady friction stage. The wear rates of γ-Y2Si2O7 were in the order of 10-4mm3/(N m). Besides, wear debris strongly influenced the friction and wear processes. The strong chemical affinity between γ-Y2Si2O7 and AISI 52100 balls led to a thick transfer layer formed on both contact surfaces of the flat and counterpart ball, which changed the direct sliding between the ball and the flat into a shearing within the transfer layer. For the γ-Y2Si2O7/Si3N4 pair, a thin silica hydrate lubricant tribofilm presented above the compressed debris entrapped in the worn track and contact ball surface. This transfer layer and the tribofilm separated the sliding couple from direct contact and contributed to the low friction coefficient and wear rate.