Dynamic relaxation of the elastic properties of hard carbon films

The effect of enhanced atomic mobility on the growth of hard carbon films was examined. Tetrahedrally bonded amorphous carbon films were deposited by condensing energetic carbon ions using an arc-discharge deposition method. The deposition temperature varied between 50 and 400 °C. The dependence of elastic properties on deposition temperature was examined by determining the frequency-dependent propagation velocity of ultrasonic surface acoustic waves induced by a laser. A remarkable decrease in elastic coefficient was revealed above the deposition temperature of 300 °C and complete relaxation was obtained at 400 °C. This observation was analyzed by using a simple model which was in turn supported by molecular dynamics simulations. The relaxation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associated with the migration of atoms or defects on a growing surface are discussed.Peer reviewe

Role of concerted atomic movements on the diffusion of small islands on fcc(100) metal surfaces

The master equation formalism is used to analytically calculate the center-of-mass diffusion coefficient for small two-dimensional islands on fcc(100) metal surfaces. We consider the case of Cu on Cu(100) containing up to nine atoms, with energetics obtained from semiempirical interaction potentials. In the case where only single-particle processes are taken into account, the analytic results agree well with previous Monte Carlo simulation data. However, when recently proposed many-particle processes are included, in some cases the diffusion coefficients increase by an order of magnitude at room temperatures. Qualitatively, the oscillatory behavior of diffusion as a function of the island size is not affected by the many-particle processes.Peer reviewe

Excimer laser surface modification: Process and properties

Surface modification can improve materials for structural, tribological, and corrosion applications. Excimer laser light has been shown to provide a rapid means of modifying surfaces through heat treating, surface zone refining, and mixing. Laser pulses at modest power levels can easily melt the surfaces of many materials. Mixing within the molten layer or with the gas ambient may occur, if thermodynamically allowed, followed by rapid solidification. The high temperatures allow the system to overcome kinetic barriers found in some ion mixing experiments. Alternatively, surface zone refinement may result from repeated melting-solidification cycles. Ultraviolet laser light couples energy efficiently to the surface of metallic and ceramic materials. The nature of the modification that follows depends on the properties of the surface and substrate materials. Alloying from both gas and predeposited layer sources has been observed in metals, semiconductors, and ceramics as has surface enrichment of Cr by zone refinement of stainless steel. Rapid solidification after melting often results in the formation of nonequilibrium phases, including amorphous materials. Improved surface properties, including tribology and corrosion resistance, are observed in these materials

Segmentation of Striatal Brain Structures from High Resolution PET Images

We propose and evaluate an automatic segmentation method for extracting striatal brain structures (caudate, putamen, and ventral striatum) from parametric 11C-raclopride positron emission tomography (PET) brain images. We focus on the images acquired using a novel brain dedicated high-resolution (HRRT) PET scanner. The segmentation method first extracts the striatum using a deformable surface model and then divides the striatum into its substructures based on a graph partitioning algorithm. The weighted kernel k-means algorithm is used to partition the graph describing the voxel affinities within the striatum into the desired number of clusters. The method was experimentally validated with synthetic and real image data. The experiments showed that our method was able to automatically extract caudate, ventral striatum, and putamen from the images. Moreover, the putamen could be subdivided into anterior and posterior parts. An automatic method for the extraction of striatal structures from high-resolution PET images allows for inexpensive and reproducible extraction of the quantitative information from these images necessary in brain research and drug development

Temperament, character and serotonin activity in the human brain: A positron emission tomography study based on a general population cohort

BackgroundThe psychobiological model of personality by Cloninger and colleagues originally hypothesized that interindividual variability in the temperament dimension ‘harm avoidance’ (HA) is explained by differences in the activity of the brain serotonin system. We assessed brain serotonin transporter (5-HTT) density in vivo with positron emission tomography (PET) in healthy individuals with high or low HA scores using an ‘oversampling’ study design.MethodSubjects consistently in either upper or lower quartiles for the HA trait were selected from a population-based cohort in Finland (n = 2075) with pre-existing Temperament and Character Inventory (TCI) scores. A total of 22 subjects free of psychiatric and somatic disorders were included in the matched high- and low-HA groups. The main outcome measure was regional 5-HTT binding potential (BPND) in high- and low-HA groups estimated with PET and [11C]N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine ([11C]MADAM). In secondary analyses, 5-HTT BPND was correlated with other TCI dimensions.Results5-HTT BPND did not differ between high- and low-HA groups in the midbrain or any other brain region. This result remained the same even after adjusting for other relevant TCI dimensions. Higher 5-HTT BPND in the raphe nucleus predicted higher scores in ‘self-directedness’.ConclusionsThis study does not support an association between the temperament dimension HA and serotonin transporter density in healthy subjects. However, we found a link between high serotonin transporter density and high ‘self-directedness’ (ability to adapt and control one's behaviour to fit situations in accord with chosen goals and values). We suggest that biological factors are more important in explaining variability in character than previously thought.</jats:sec

Properties and challenges of nanolayer coatings

A systematic study was made on MoSi{sub 2}-based nanolayer coatings. Alternating layers with thickness 1-20 nm were prepared by sputtering. Nitrided MoSi{sub 2} has a very high crystallization temperature, >1000 C, and MoSi{sub 2}Nx (x=3-4) can be used as a stable second phase reinforcement or diffusion barrier coatings. Mechanical properties depend strongly on phase and morphology of the layers: hardness and modulus is significantly increased in the crystallization. The nanolayers have much higher hardness but lower modulus (which project higher toughness in the nanolayers). Wear resistance is improved with decreasing layer thickness. Single phase MoSi{sub 2}Nx (x=0-4.2) has a wide range of hardness and modulus with varying N content and annealing, suggesting the possibility of engineering MoSi{sub 2}Nx to produce different material properties for different mechanical applications. Most of this paper is made up of viewographs

Factors that Impact Susceptibility to Fiber-Induced Health Effects

Asbestos and related fibers are associated with a number of adverse health effects, including malignant mesothelioma (MM), an aggressive cancer that generally develops in the surface serosal cells of the pleural, pericardial, and peritoneal cavities. Although approximately 80% of individuals with MM are exposed to asbestos, fewer than 5% of asbestos workers develop MM. In addition to asbestos, other mineralogical, environmental, genetic, and possibly viral factors might contribute to MM susceptibility. Given this complex etiology of MM, understanding susceptibility to MM needs to be a priority for investigators in order to reduce exposure of those most at risk to known environmental carcinogens. In this review, the current body of literature related to fiber-associated disease susceptibility including age, sex, nutrition, genetics, asbestos, and other mineral exposure is addressed with a focus on MM, and critical areas for further study are recommended