Stainless Steel Surface Nitriding in Open Atmosphere Cold Plasma: Improved Mechanical, Corrosion and Wear Resistance Properties.

This work presents preliminary results regarding improving the mechanical, wear and protective properties (hardness, coefficient of friction, corrosion resistance) of AISI 304 stainless steel surfaces by open atmosphere cold plasma surface treatment method. Comparative evaluations of the morphological, corrosion resistance, mechanical and tribological properties for different periods of treatment (using N2 gas for cold plasma generation in an open atmosphere) were performed. AFM surface analyses have shown significant surface morphology modifications (average roughness, FWHM, surface skewness and kurtosis coefficient) of the treated samples. An improved corrosion resistance of the N2 treated surfaces in open atmosphere cold plasma could be observed using electrochemical corrosion tests. The mechanical tests have shown that the surface hardness (obtained by instrumented indentation) is higher for the 304 stainless steel samples than it is for the un-treated surface, and it decreases gradually for higher penetration depths. The kinetic coefficient of friction (obtained by ball-on-disk wear tests) is significantly lower for the treated samples and increases gradually to the value of the un-treated surface. The low friction regime length is dependent on the surface treatment period, with a longer cold plasma nitriding process leading to a significantly better wear behavior.

Photoluminescence and structural properties of the nitrogen doped TiO2 and the influence of SiO2 and Ag nanoparticles.

Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.

Quantitative assessment of brain glucose metabolic rates using in vivo deuterium magnetic resonance spectroscopy.

Quantitative assessment of cerebral glucose consumption rate (CMRglc) and tricarboxylic acid cycle flux (VTCA) is crucial for understanding neuroenergetics under physiopathological conditions. In this study, we report a novel in vivo Deuterium (2H) MRS (DMRS) approach for simultaneously measuring and quantifying CMRglc and VTCA in rat brains at 16.4 Tesla. Following a brief infusion of deuterated glucose, dynamic changes of isotope-labeled glucose, glutamate/glutamine (Glx) and water contents in the brain can be robustly monitored from their well-resolved 2H resonances. Dynamic DMRS glucose and Glx data were employed to determine CMRglc and VTCA concurrently. To test the sensitivity of this method in response to altered glucose metabolism, two brain conditions with different anesthetics were investigated. Increased CMRglc (0.46 vs. 0.28 µmol/g/min) and VTCA (0.96 vs. 0.6 µmol/g/min) were found in rats under morphine as compared to deeper anesthesia using 2% isoflurane. This study demonstrates the feasibility and new utility of the in vivo DMRS approach to assess cerebral glucose metabolic rates at high/ultrahigh field. It provides an alternative MRS tool for in vivo study of metabolic coupling relationship between aerobic and anaerobic glucose metabolisms in brain under physiopathological states.

Assessing mitochondrial respiration in isolated hearts using (17)O MRS.

The application of (17)O MRI and MRS for the evaluation of cardiac mitochondrial function has been limited because of the challenge of detecting metabolic H(2)(17)O in the vast background of naturally abundant H(2)(17)O. In this study, we have developed a direct (17)O MRS approach to examine the feasibility and sensitivity of detecting metabolically produced H(2)(17)O in isolated rat hearts perfused with (17)O(2)-enriched Krebs-Henseleit buffer containing normal (1.5 mm) and high (2.5 mm) calcium (Ca(2+)) concentrations to induce high workload. Consistent with increased workload at high Ca(2+) concentration, the measured myocardial oxygen consumption rate (MVO(2)) increased by 82%. Dynamic (17)O MRS showed an accelerated increase in the H(2)(17)O signal at high Ca(2+) concentration, suggesting increased mitochondrial production of H(2)(17)O in concordance with the increased workload. A compartment model was developed to describe the kinetics of H(2)(17)O production as a function of MVO(2). The myocardial (17)O(2) consumption rate (MV(17)O(2) was determined by least-squares fitting of the model to the NMR-measured H(2)(17)O concentration. Consistent with the measured MVO(2), the model-determined MV(17)O(2) showed a 92% increase at high Ca(2+) concentration. The increase in metabolic activity at high workload allowed the balance between ATP production and utilization to be maintained, leading to a similar phosphocreatine to ATP ratio. These results demonstrate that dynamic (17)O MRS can provide a valuable tool for the detection of an altered metabolic rate associated with a change in cardiac workload.

In vivo assessment of oxygen consumption via Deuterium Magnetic Resonance.

We present a novel approach to simultaneously measure, in vivo, noninvasively, glucose and oxygen consumption via Deuterium Magnetic Resonance (DMR). Mice are administered deuteriated glucose by intravenous injection. The rate of formation of nascent (deuteriated) mitochondrial water is then measured via DMR. The rate of glucose metabolism and oxygen utilization is assessed by tracking their separate peaks in DMR spectra during dynamic scanning. Further studies will aim to validate these results by comparison with in vivo (17)O-MRI (mitochondrial function), (13)C-MRI and (19)FDG-PET (glucose metabolism) and ex vivo 1H- and 2H-MR, as well as mass spectrometry.

Functional oxygen-17 magnetic resonance imaging and localized spectroscopy.

Functional oxygen-17 magnetic resonance (MR) imaging and localized spectroscopy is defined as the ensemble of MR measurements aiming at in vivo, noninvasive characterization of oxygen transport and utilization. After a brief description of the present status of in vivo 17O-MR, preliminary results are reported on oxygen delivery and consumption in cell suspensions of Saccharomyces cerevisiae. It is shown that parallel 31P-MR at high magnetic fields has an important corroborative value.