CliqueStream: an efficient and fault-resilient live streaming network on a clustered peer-to-peer overlay

Several overlay-based live multimedia streaming platforms have been proposed in the recent peer-to-peer streaming literature. In most of the cases, the overlay neighbors are chosen randomly for robustness of the overlay. However, this causes nodes that are distant in terms of proximity in the underlying physical network to become neighbors, and thus data travels unnecessary distances before reaching the destination. For efficiency of bulk data transmission like multimedia streaming, the overlay neighborhood should resemble the proximity in the underlying network. In this paper, we exploit the proximity and redundancy properties of a recently proposed clique-based clustered overlay network, named eQuus, to build efficient as well as robust overlays for multimedia stream dissemination. To combine the efficiency of content pushing over tree structured overlays and the robustness of data-driven mesh overlays, higher capacity stable nodes are organized in tree structure to carry the long haul traffic and less stable nodes with intermittent presence are organized in localized meshes. The overlay construction and fault-recovery procedures are explained in details. Simulation study demonstrates the good locality properties of the platform. The outage time and control overhead induced by the failure recovery mechanism are minimal as demonstrated by the analysis.Comment: 10 page

Kerr effect as a tool for the investigation of dynamic heterogeneities

We propose a dynamic Kerr effect experiment for the distinction between dynamic heterogeneous and homogeneous relaxation in glassy systems. The possibility of this distinction is due to the inherent nonlinearity of the Kerr effect signal. We model the slow reorientational molecular motion in supercooled liquids in terms of non-inertial rotational diffusion. The Kerr effect response, consisting of two terms, is calculated for heterogeneous and for homogeneous variants of the stochastic model. It turns out that the experiment is able to distinguish between the two scenarios. We furthermore show that exchange between relatively 'slow' and 'fast' environments does not affect the possibility of frequency-selective modifications. It is demonstrated how information about changes in the width of the relaxation time distribution can be obtained from experimental results.Comment: 23 pages incl. 6 figures accepted for publication in The Journal of Chemical Physic

The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals

The thermal history and internal structure of chondritic planetesimals, assembled before the giant impact phase of chaotic growth, potentially yield important implications for the final composition and evolution of terrestrial planets. These parameters critically depend on the internal balance of heating versus cooling, which is mostly determined by the presence of short-lived radionuclides (SLRs), such as aluminum-26 and iron-60, as well as the heat conductivity of the material. The heating by SLRs depends on their initial abundances, the formation time of the planetesimal and its size. It has been argued that the cooling history is determined by the porosity of the granular material, which undergoes dramatic changes via compaction processes and tends to decrease with time. In this study we assess the influence of these parameters on the thermo-mechanical evolution of young planetesimals with both 2D and 3D simulations. Using the code family I2ELVIS/I3ELVIS we have run numerous 2D and 3D numerical finite-difference fluid dynamic models with varying planetesimal radius, formation time and initial porosity. Our results indicate that powdery materials lowered the threshold for melting and convection in planetesimals, depending on the amount of SLRs present. A subset of planetesimals retained a powdery surface layer which lowered the thermal conductivity and hindered cooling. The effect of initial porosity was small, however, compared to those of planetesimal size and formation time, which dominated the thermo-mechanical evolution and were the primary factors for the onset of melting and differentiation. We comment on the implications of this work concerning the structure and evolution of these planetesimals, as well as their behavior as possible building blocks of terrestrial planets.Comment: 19 pages, 11 figures, 5 tables; accepted for publication in Icarus; for associated video files, see http://timlichtenberg.net/2015_porosity.html or http://dx.doi.org/10.1016/j.icarus.2016.03.00

The System: A Multilevel Social Service Simulation

Community psychology practice competencies emerged in an effort to provide guidance to the field of community psychology and training programs seeking to provide students with meaningful opportunities to develop a depth and breadth of practice skills. As a teacher of community psychology practice over the past eleven years, the author has consistently faced challenges in teaching the Ecological Perspectives, listed as number 1 under Foundational Principles – “The ability to articulate and apply multiple ecological perspectives and levels of analysis in community practice” (Dalton, & Wolfe, 2012, p. 10). This paper describes a multilevel social service simulation exercise as a teaching tool for community psychology practice competencies within an academic setting. The simulation focuses on Ecological Perspectives and the role of Social Power Dynamics in Systems Change. Suggested curricular content is also included to follow the simulation debriefing

The System: A Multilevel Social Service Simulation

Community psychology practice competencies emerged in an effort to provide guidance to the field of community psychology and training programs seeking to provide students with meaningful opportunities to develop a depth and breadth of practice skills. As a teacher of community psychology practice over the past eleven years, the author has consistently faced challenges in teaching the Ecological Perspectives, listed as number 1 under Foundational Principles – “The ability to articulate and apply multiple ecological perspectives and levels of analysis in community practice” (Dalton, & Wolfe, 2012, p. 10). This paper describes a multilevel social service simulation exercise as a teaching tool for community psychology practice competencies within an academic setting. The simulation focuses on Ecological Perspectives and the role of Social Power Dynamics in Systems Change. Suggested curricular content is also included to follow the simulation debriefing

Nonlinear structures of strongly coupled complex plasmas in the proximity of a presheath/sheath edge

The formation of a steady-state nonlinear potential structure of a double-layer type near the presheath/sheath edge of a plasma discharge is theoretically investigated in complex plasmas containing Boltzmann electrons, cold fluid ions and strongly coupled microparticles. Equilibrium of the particles is provided by the electrostatic force and an effective 'dust pressure' associated with electrostatic interactions between the highly charged grains. The results are of importance for complex plasma experiments in microgravity conditions, for thermophoretically levitated configurations and for processing plasmas loaded by nanometer-sized microparticles

Dipolar spin correlations in classical pyrochlore magnets

We study spin correlations for the highly frustrated classical pyrochlore lattice antiferromagnets with O(N) symmetry in the limit T->0. We conjecture that a local constraint obeyed by the extensively degenerate ground states dictates a dipolar form for the asymptotic spin correlations, at all N $\ne$ 2 for which the system is paramagnetic down to T=0. We verify this conjecture in the cases N=1 and N=3 by simulations and to all orders in the 1/N expansion about the solvable N=infinity limit. Remarkably, the N=infinity formulae are an excellent fit, at all distances, to the correlators at N=3 and even at N=1. Thus we obtain a simple analytical expression also for the correlations of the equivalent models of spin ice and cubic water ice, I_h.Comment: 4 pages revtex

Coupling SPH and thermochemical models of planets: Methodology and example of a Mars-sized body

Giant impacts have been suggested to explain various characteristics of terrestrial planets and their moons. However, so far in most models only the immediate effects of the collisions have been considered, while the long-term interior evolution of the impacted planets was not studied. Here we present a new approach, combining 3-D shock physics collision calculations with 3-D thermochemical interior evolution models. We apply the combined methods to a demonstration example of a giant impact on a Mars-sized body, using typical collisional parameters from previous studies. While the material parameters (equation of state, rheology model) used in the impact simulations can have some effect on the long-term evolution, we find that the impact angle is the most crucial parameter for the resulting spatial distribution of the newly formed crust. The results indicate that a dichotomous crustal pattern can form after a head-on collision, while this is not the case when considering a more likely grazing collision. Our results underline that end-to-end 3-D calculations of the entire process are required to study in the future the effects of large-scale impacts on the evolution of planetary interiors.Comment: 29 pages, 10 figures, accepted for publication in Icaru

One of the northernmost records of Eleocharis mamillata subsp. mamillata (Cyperaceae) in Europe, and the first discovery in Murmansk Region (Russia)

We report the first locality (67°55’13” N, 33°39’73” E) in Murmansk Region of Eleocharis mamillata H. Lindb. f. subsp. mamillata. The species distribution range in Europe extends to nearly 68° N attested by one older (1924) record in Finland and two recent ones (2008–2009) in Norway. The new site at a similar latitude in Lapponia Imandrae in Russia is briefly described. It is proposed to include this species in the next regional Red Data Book in the group ”In need of monitoring”