Evolution of ion emission yield of alloys with the nature of the solute. 2: Interpretation

Solid solutions of transition elements in copper, nickel, cobalt, iron, and aluminum matrices were analyzed by observing secondary ion emissions under bombardment with 6.2-keV argon ions. Enchancement of the production of solute-element ions was observed. An ion emission model is proposed according to which the ion yield is governed by the probability of an atom leaving the metal in a preionized state. The energy distribution of the valence electrons of the solute atoms is the bases of the probability calculation

Concerning the Problem of High Depth Resolution Using Ion Sputtering

The inhomogeneity of ion bombardment, the angular dependence of sputtering yields and the crystalline orientation of samples are the three main causes of the degradation of resolution with depth. It is possible to reduce these effects by bombarding at low energy (≈ 1 keV). A low-energy ion-bombardment device is described which has been adapted for use on our sputtered thermal-ion source mass spectrometer

Sputtered Thermal Ion Mass Spectrometry as a New Quantitative Method for In-Depth Analysis

The Sputtered Thermal Ion Mass Spectrometry method (STIMS) consists of collecting a part of the matter sputtered from a solid by ion bombardment into a heated cell where it is reduced into atoms. A thermal ionization process or an electron impact process taking place in the cell yields ions which are extracted and mass analyzed. The composition of the solid is determined from ion intensities after calibration of ionization coefficients. It has been demonstrated that the method has an absolute quantitative character. Applications to elemental quantitative analysis (identification of new compounds in diffusion couples, dust particle analysis) and in-depth analysis of thin layers (unannealed, annealed and amorphous layers) are being developed. We have found that in-depth resolution is better in annealed layers than in unannealed ones, it can be improved by lowering the primary ion energy below 2 keV and it is very good in amorphous materials

Amyloidogenesis of β-2-microglobulin Studied by Mass Spectrometry and Covalent Labeling

Amyloid-forming proteins are implicated in a number of debilitating diseases. While many amyloid-forming proteins are well studied, the early stages of amyloidosis are still not well understood on a molecular level. Covalent labeling, combined with mass spectrometry (CL-MS), is uniquely well suited to provide molecular-level insight into the factors governing the early stages of amyloidosis. This dissertation leverages CL-MS techniques to examine the early stages of β-2-microglobulin (β2m) amyloidosis. β2m is the protein that forms amyloids in the condition known as dialysis-related amyloidosis. An automated CL-MS technique that uses dimethyl(2-hydroxy-5-nitrobenzyl) sulfonium bromide as a labeling reagent was developed and used to measure energy barriers to the initial pre-amyloid structural change of β2m under different amyloid-forming conditions. The results represent the first ever measure of the activation barrier for a structural change initiating amyloid formation. The results also give new mechanistic insight into β2m’s amyloidogenic structural change, particularly the role of Pro32 isomerization. The catalytic nature of Cu(II) as an initiator of the β2m pre-amyloid structural change was confirmed as it significantly lowered the energy barrier to this structural change. It also appears that, when initiated by acid, the Pro32 isomerization may no longer be the rate limiting step in this process. The same technique was further used to investigate the β2m structural change caused by its interaction with an amyloidogenic variant of β2m called ΔN6-β2m, which is missing its first six N-terminal residues. Both primary and secondary nucleation events involved in the β2m/ΔN6-β2m interaction were investigated. The measured barrier for the primary nucleation event seems to indicate that, like the acid induced structural change of β2m, the isomerization of Pro32 may not be the rate determining step. However, the measured barrier for the secondary nucleation event, similar to that of the Cu(II) induced structural change, indicates that the isomerization of Pro32 is the rate determining step. The use of point mutants gives further detail on the crucial residues and regions of the proteins required for a productive interaction to yield amyloids. The new kinetic and thermodynamic information gained in this work yields new insight into the mechanistic details of the biomedically important process of β2m amyloidosis

Global existence and asymptotic behaviour in the future for the Einstein-Vlasov system with positive cosmological constant

The behaviour of expanding cosmological models with collisionless matter and a positive cosmological constant is analysed. It is shown that under the assumption of plane or hyperbolic symmetry the area radius goes to infinity, the spacetimes are future geodesically complete, and the expansion becomes isotropic and exponential at late times. This proves a form of the cosmic no hair theorem in this class of spacetimes

Athletes Who Train on Unstable Compared to Stable Surfaces Exhibit Unique Postural Control Strategies in Response to Balance Perturbations

Background Athletes have been shown to exhibit better balance compared to non-athletes (NON). However, few studies have investigated how the surface on which athletes train affects the strategies adopted to maintain balance. Two distinct athlete groups who experience different types of sport-specific balance training are stable surface athletes (SSA) such as basketball players and those who train on unstable surfaces (USA) such as surfers. The purpose of this study was to investigate the effects of training surface on dynamic balance in athletes compared to NON. Methods Eight NON, eight SSA, and eight USA performed five 20-s trials in each of five experimental conditions including a static condition and four dynamic conditions in which the support surface translated in the anteroposterior (AP) or mediolateral (ML) planes using positive or negative feedback paradigms. Approximate entropy (ApEn) and root mean square distance (RMS) of the center of pressure (CoP) were calculated for the AP and ML directions. Four 3 × 5 (group × condition) repeated measures ANOVAs were used to determine significant effects of group and condition on variables of interest. Results USA exhibited smaller ApEn values than SSA in the AP signals while no significant differences were observed in the ML CoP signals. Generally, the negative feedback conditions were associated with significantly greater RMS values than the positive feedback conditions. Conclusion USA exhibit unique postural strategies compared to SSA. These unique strategies seemingly exhibit a direction-specific attribute and may be associated with divergent motor control strategies

The Effects of Exercise Training on Resting Prostacyclin and Thromboxane A(2) in Older Adults

Ten adult volunteers participated in 16 weeks of cardiovascular exercise training (EG) to determine the effects of training on resting prostacyclin (PGI(2)) and thromboxane A(2) (TXA(2)). Six volunteers of similar age served as sedentary controls (CG). Blood was collected in tubes after training and eicosanoids were measured by standard I-125 RIA methods. Over the 16 weeks of the study, PGI(2) decreased 48% for EG and 33% for CG. There were no between-group differences for PGI(2) values. No significant within-group changes in TXA(2) were found, whereas between-group pretraining TXA(2) values were significantly different. A time main effect for PGI(2) may indicate a seasonal shift in this eicosanoid; however, the additional 15% decrease in PGI(2) for EG may be due to a training-induced reduction in PGI(2) substrate and/or endothelial sensitivity to agonists. The lack of within-group changes in TXA(2) may be due to a combination of high platelet turnover and a training stimulus inadequate to alter platelet function

Structural, AC and DC Electrical Transport Properties of Nano Titania - Polyacrylamide Composite Films

227-237The microstructural features as well as the AC and DC electrical properties of titanium dioxide (titania or TiO2) nanoparticle (NP) filled polyacrylamide (PAM) composite films with filler level (FLs) Varied from 0.02 up to 19.5 Wt % were experimentally studied . SEM images revealed that the composite films with FLs equal to 0.02 and 0.40 Wt % (low FLs) showed homogeneous dispersion of spherical TiO2 NPs, whereas aggregation of the filler was observed at higher FLs. The XRD patterns of these composite films revealed an increase in their amorphousness at low FLs. The activation energy (Ea) determined from Arrhenius equation showed that the composite with FL equal to 0.40 Wt % exhibited the lowest value of Ea (equal to 0.84 eV). Dielectric study revealed that the composite film with FL equal to 0.40 Wt % exhibited the highest value bulk conductivity at room temperature (4.39×10-6S m-1 at 303 K). Hence, the composite sample with FL 0.40Wt %, along with pure PAM, were subjected to a detailed dielectric study at various fixed temperatures ranging from 303K up to 353K. The composite sample with FL 0.40 Wt % showed a maximum bulk conductivity of 1.12×10-4 S m- 1at temperature 353K, while it was 3.45×10-8 S m-1 for pure PAM at 303 K