From fracture to fragmentation: discrete element modeling -- Complexity of crackling noise and fragmentation phenomena revealed by discrete element simulations

Discrete element modelling (DEM) is one of the most efficient computational approaches to the fracture processes of heterogeneous materials on mesoscopic scales. From the dynamics of single crack propagation through the statistics of crack ensembles to the rapid fragmentation of materials DEM had a substantial contribution to our understanding over the past decades. Recently, the combination of DEM with other simulation techniques like Finite Element Modelling further extended the field of applicability. In this paper we briefly review the motivations and basic idea behind the DEM approach to cohesive particulate matter and then we give an overview of on-going developments and applications of the method focusing on two fields where recent success has been achieved. We discuss current challenges of this rapidly evolving field and outline possible future perspectives and debates

Winning strategies in congested traffic

One-directional traffic on two-lanes is modeled in the framework of a spring-block type model. A fraction $q$ of the cars are allowed to change lanes, following simple dynamical rules, while the other cars keep their initial lane. The advance of cars, starting from equivalent positions and following the two driving strategies is studied and compared. As a function of the parameter $q$ the winning probability and the average gain in the advancement for the lane-changing strategy is computed. An interesting phase-transition like behavior is revealed and conclusions are drawn regarding the conditions when the lane changing strategy is the better option for the drivers.Comment: 5 pages, 5 figure

Convergence of general iteration schemes

AbstractIn this paper the convergence of general iteration algorithms defined by point-to-set maps is examined first. Special practical convergence conditions are then derived from the general theory

Out-of-equilibrium critical dynamics at surfaces: Cluster dissolution and non-algebraic correlations

We study nonequilibrium dynamical properties at a free surface after the system is quenched from the high-temperature phase into the critical point. We show that if the spatial surface correlations decay sufficiently rapidly the surface magnetization and/or the surface manifold autocorrelations has a qualitatively different universal short time behavior than the same quantities in the bulk. At a free surface cluster dissolution may take place instead of domain growth yielding stationary dynamical correlations that decay in a stretched exponential form. This phenomenon takes place in the three-dimensional Ising model and should be observable in real ferromagnets.Comment: 4 pages, 4 figure

Hazai szárazföldi ászkarákfajok (Isopoda, Oniscidea) tipizálása két nagyváros, Budapest és Baltimore (ÉK Amerika) összehasonlításának példájával

Munkánkban kísérletet tettünk az ászkarákfajok természetvédelmi szempontú felosztására jellemző élőhelyük és elterjedési adataik alapján. Kategóriáink: természetközeli élőhelyeken élő NR („natural-rare”), kis abundanciával jellemezhető fajok; NF („natural-frequent”) természetközeli élőhelyeken, gyakori fajok; DR („disturbed-rare”) – zavart élőhelyeken, kis egyedszámban előfordulók; DF („disturbed- frequent”) – antropogén habitatok nagy abundanciájú, rendszerint szünantróp fajai; G („generalist”) – minden típusú élőhelyen előfordulható fajok; U („uncertain”) – kevés adat miatt nem tipizálhatóak. Ezen beosztás alapján az utóbbi években faunánkra újként kimutatott fajok kétharmada a DR kategóriába tartozik, ami az idegen faunaelemek felgyorsult betelepülését, a biodiverzitás homogenizálódó tendenciáját igazolja. Baltimore (ÉK Amerika) és Budapest Isopoda faunáját összevető esettanulmányunkban kimutattuk, hogy míg a vizsgált tengeren túli fauna 11 behurcolt fajból áll, addig Budapesten összesen 27 fajból, aminek 33%-a betelepült

Magnetic resonance in the antiferromagnetic and normal state of NH_3K_3C_60

We report on the magnetic resonance of NH_3K_3C_60 powders in the frequency range of 9 to 225 GHz. The observation of an antiferromagnetic resonance below the phase transition at 40 K is evidence for an antiferromagnetically ordered ground state. In the normal state, above 40 K, the temperature dependence of the spin-susceptibilty measured by ESR agrees with previous static measurements and is too weak to be explained by interacting localized spins in an insulator. The magnetic resonance line width has an unusual magnetic-field dependence which is large and temperature independent in the magnetically ordered state and decreases rapidly above the transition. These observations agree with the suggestion that NH_3K_3C_60 is a metal in the normal state and undergoes a Mott-Hubbard metal to insulator transition at 40 K.Comment: 4 pages, 5 figures. Submitted to Phys. Rev.