Validity of Stokes-Einstein Relation in Soft Colloids up to the Glass Transition

We investigate the dynamics of kinetically frozen block copolymer micelles of different softness across a wide range of particle concentrations, from the fluid to the onset of glassy behavior, through a combination of rheology, dynamic light scattering and pulsed field gradient NMR spectroscopy. We additionally perform Brownian dynamics simulations based on an ultrasoft coarse-grained potential, which are found to be in quantitative agreement with experiments, capturing even the very details of dynamic structure factors S(Q, t) on approaching the glass transition. We provide evidence that for these systems the Stokes-Einstein relation holds up to the glass transition; given that it is violated for dense suspensions of hard colloids, our findings suggest that its validity is an intriguing signature of ultrasoft interactions.Comment: 5 pages, 4 figures, Supplementary Information, Accepted to Physical Review Letters (PRL) (2015

The highest-speed local dark matter particles come from the Large Magellanic Cloud

Using N-body simulations of the Large Magellanic Cloud (LMC's) passage through the Milky Way (MW), tailored to reproduce observed kinematic properties of both galaxies, we show that the high-speed tail of the Solar Neighborhood dark matter distribution is overwhelmingly of LMC origin. Two populations contribute at high speeds: 1) Particles that were once bound to the LMC, and 2) MW halo particles that have been accelerated owing to the response of the halo to the recent passage of the LMC. These particles reach speeds of 700-900 km/s with respect to the Earth, near or somewhat higher that the local escape speed of the MW. The high-speed particles follow trajectories similar to the Solar reflex motion, with peak velocities reached in June. For low-mass dark matter, these high-speed particles can dominate the signal in direct-detection experiments, extending the reach of the experiments to lower mass and elastic scattering cross sections even with existing data sets. Our study shows that even non-disrupted MW satellite galaxies can leave a significant dark matter footprint in the Solar Neighborhood.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Glassy phases of the Gaussian Core Model

We present results from molecular dynamics simulations exploring the supercooled dynamics of the Gaussian Core Model in the low- and intermediate-density regimes. In particular, we discuss the transition from the low-density hard-sphere-like glassy dynamics to the high-density one. The dynamics at low densities is well described by the caging mechanism, giving rise to intermittent dynamics. At high densities, the particles undergo a more continuous motion in which the concept of cage loses its meaning. We elaborate on the idea that these different supercooled dynamics are in fact the precursors of two different glass states

Dynamics in binary cluster crystals

As a result of the application of coarse-graining procedures to describe complex fluids, the study of systems consisting of particles interacting through bounded, repulsive pair potentials has become of increasing interest in the last years. A well known example is the so-called Generalized Exponential Model (GEM-$m$), for which the interaction between particles is described by the potential $v(r)=\epsilon\exp[-(r/\sigma)^m]$. Interactions with $m > 2$ lead to the formation of a novel phase of soft matter consisting of cluster crystals. Recent studies on the phase behavior of binary mixtures of GEM-$m$ particles have provided evidence for the formation of novel kinds of alloys, depending on the cross interactions between the two species. This work aims to study the dynamic behavior of such binary mixtures by means of extensive molecular dynamics simulations, and in particular to investigate the effect of the addition of non-clustering particles on the dynamic scenario of one-component cluster crystals. Analogies and differences with the one-component case are revealed and discussed by analyzing self- and collective dynamic correlators.Comment: 17 pages, 8 figures, submitted to JSTA

Integrated Nuclear Knowledge Management System – NUTEMA

Knowledge Management has become one of the most important issues for the nuclear industry. On the one hand, the amount of codifiable knowledge in the nuclear technology area saw a steep increase in the last years; on the other hand, due to the “generation gap” in the nuclear industry it became very challenging to organize the seamless transfer of the noncodifiable knowledge from one generation of engineers to the other. Computer aided systems so far where aiming at to preserve the codifiable knowledge. The present paper introduces a system that should support knowledge management not only dealing with the codifiable part of it, but also address broader aspects (which includes the management of non-codifiable knowledge).- NUTEMA. The integrated nuclear knowledge management system NUTEMA should provide interactive combination of information and methods, but also identifying competences which more adequately fit to a given task, keeping track of keeping skills of the experts within an organization. Application is foreseen in nuclear engineering fields as system design, operation and maintenance plant and process modifications, standardization, certification and even for licensing-related tasks. The system combines an extensively diverse and modular database with computer based simulations including a scientific software platform. NUTEMA is conceived to operate in different modes, for example collecting and retrieving database knowledge, training applications, NPP operations support, computer code applications, and as plant analyzer. This paper will present two examples; one acting as at a supporting tool for typical NPP plant modification: In a second case, application on review and optimization of operational process is described. Despite the provided examples deal with different objectives and methods associated with different stages of an NPP lifetime, (design and operation) both are supported by the integrated nuclear knowledge management system