Liquid Titanium Solute Diffusion Measured by Pulsed Ion-Beam Melting

The diffusivities of Sri, Mo, Zr, and Hf in liquid Ti were determined by pulsed ion-beam melting of thin liquid layers. Time-resolved optical reflectance and one-dimensional heat-flow simulations were employed to determine the melt duration. The broadening of nearly Gaussian solute concentration-depth profiles was determined ex situ using Rutherford backscattering spectrometry. Solute diffusivities in the range of 5 to 9 X 10-5 cm2/s were determined at temperatures in the range of 2200 to 2500 K. Calculations of buoyancy and Marangoni convection indicate that convective contamination is unlikely.Engineering and Applied Science

How the interface type manipulates the thermomechanical response of nanostructured metals : A case study on nickel

The presence of interfaces with nanoscale spacing significantly enhances the strength of materials, but also the rate controlling processes of plastic flow are subject to change. Due to the confined grain volumes, intragranular dislocation-dislocation interactions, the predominant processes at the micrometer scale, are replaced by emission of dislocations from and their subsequent accommodation at the interfaces. Both processes not only depend on the interfacial spacing, but also on the atomistic structure of the interface. Hence, a thorough understanding how these processes are affected by the interface structure is required to predict and improve the behavior of nanomaterials. The present study attempts to rationalize this effect by investigating the thermomechanical behavior of samples consisting of three different interfaces. Pure nickel samples with predominant fractions of low- and high-angle as well as twin boundaries with a similar average spacing around 150 nm are investigated using high temperature nanoindentation strain rate jump tests. Depending on the interface structure, hardness, strain rate sensitivity and apparent activation volumes evolve distinctively different with testing temperature. While in case of high-angle boundaries for all quantities a pronounced thermal dependence is found, the other two interface types behave almost athermal in the same temperature range. These differences can be rationalized based on the different interfacial diffusivity, affecting the predominant process of interfacial stress relaxation

Transport Theoretical Description of Collisional Energy Loss in Infinite Quark-Gluon Matter

We study the time evolution of a high-momentum gluon or quark propagating through an infinite, thermalized, partonic medium utilizing a Boltzmann equation approach. We calculate the collisional energy loss of the parton, study its temperature and flavor dependence as well as the the momentum broadening incurred through multiple interactions. Our transport calculations agree well with analytic calculations of collisional energy-loss where available, but offer the unique opportunity to address the medium response as well in a consistent fashion.Comment: 12 pages, updated with additional references and typos correcte

STAR results on medium properties and response of the medium to energetic partons

We report new STAR results on the consequences of highly energetic partons propagating through the medium formed in heavy ion collisions using correlations as an experimental probe. The recent results providing insights about color factor effects and path length dependence of parton energy loss, system size dependence of di-hadron fragmentation functions, conical emission and ridge formation in heavy ion collisions are presented.Comment: STAR Plenary talk at QM2008. Manuscript for the Proceedings of Quark Matter 2008, Jaipur, Indi

The electrochemical behavior of Ti and Ti alloys subjected to pulsed ion beam surface treatment

Pulsed high-energy ion beams have been used to thermally treat Ti and Ti alloy surfaces to alter the electrochemical response. Two regimes have been explored: rapid melt and resolidification, and ion beam mixing. In this report, results from initial studies are presented exploring effect of these two regimes on the electrochemical behavior of Ti and Ti alloys

Polyakov Loops versus Hadronic States

The order parameter for the pure Yang-Mills phase transition is the Polyakov loop which encodes the symmetries of the Z_N center of the SU(N) gauge group. On the other side the physical degrees of freedom of any asymptotically free gauge theory are hadronic states. Using the Yang-Mills trace anomaly and the exact Z_N symmetry we construct a model able to communicate to the hadrons the information carried by the order parameter.Comment: RevTex4 2-col., 6 pages, 2 figures. Typos fixed and added a paragraph in the conclusion