We study the critical behavior of a general contagion model where nodes are either active (e.g., with opinion A, or functioning) or inactive (e.g., with opinion B, or damaged). The transitions ...between these two states are determined by (i) spontaneous transitions independent of the neighborhood, (ii) transitions induced by neighboring nodes, and (iii) spontaneous reverse transitions. The resulting dynamics is extremely rich including limit cycles and random phase switching. We derive a unifying mean-field theory. Specifically, we analytically show that the critical behavior of systems whose dynamics is governed by processes (i)-(iii) can only exhibit three distinct regimes: (a) uncorrelated spontaneous transition dynamics, (b) contact process dynamics, and (c) cusp catastrophes. This ends a long-standing debate on the universality classes of complex contagion dynamics in mean field and substantially deepens its mathematical understanding.
Aeolian transport controls landform formations on Earth and other planets and crucially affects the atmospheric system. With elaborate wind tunnel measurements, we find that the aerodynamic ...entrainment rate follows a yet unreported exponential increase in the intermittent regime and only complies with the expected linear law for the condition of continuous entrainment. Subsequently, we propose a model accounting for the effects of turbulence on aerodynamic entrainment based on the distribution of local shear stress to describe the experimental results. We also provide evidence that aerodynamic entrainment can be an efficient way to directly induce a horizontal grain transport comparable to the steady and saturated saltation in unsaturated conditions and should not be ignored. Our findings substantially modify the present interpretation of surface erosion and bear thus important consequences on future soil protection techniques.
Plain Language Summary
It has been recognized that grains can be lifted from the surface through two mechanisms, either ejection due to the impact of grains in saltation or the pull‐out of grains due to aerodynamic entrainment. However, saltation has always been believed to be the dominant mechanism of aeolian sand transport. With elaborate wind tunnel measurements, we find that the aerodynamic entrainment rate follows a yet unreported exponential increase in the intermittent regime and only complies with the expected linear law above the threshold to continuous flow. We also present the first evidence that in fact turbulent grain entrainment contributes as least as much to or even more than the particle flux in the continuous flow regime. Our discovery will open a new avenue of research focusing on aerodynamic grain entrainment and thus significantly influence the research of others. It also represents an essential step toward mastering soil erosion.
Key Points
Two scaling laws are found between aerodynamic entrainment rate of grains and mean surface shear stress in wind tunnel experiments
A predictive model considering turbulence is proposed to explain the aerodynamic entrainment rate
Aerodynamic entrainment is able to cause streamwise grain flux in unsaturated sand stream
Levoglucosan, an important molecular marker for biomass burning, represents an important fraction of the water-soluble organic carbon in atmospheric particles influenced by residential wood burning ...and wildfires. However, particle phase oxidation processes of levoglucosan by free radicals are not well-known. Hence, detailed kinetic studies on the reactivity of levoglucosan with OH, NO3, and SO4 − radicals in aqueous solutions were performed to better understand the levoglucosan oxidation in the deliquescent particles. The data obtained were implemented into a parcel model with detailed microphysics and complex multiphase chemistry to investigate the degradation fluxes of levoglucosan in cloud droplets and in deliquescent particles. The model calculations show that levoglucosan can be oxidized readily by OH radicals during daytime with mean degradation fluxes of about 7.2 ng m−3 h−1 in summer and 4.7 ng m−3 h−1 in winter for a polluted continental plume. This indicates that the oxidation of levoglucosan in atmospheric deliquescent particles is at least as fast as that of other atmospherically relevant organic compounds and levoglucosan may not be as stable as previously thought in the atmosphere, especially under high relative humidity conditions.
Grains in desert sandstorms spontaneously generate strong electrical charges; likewise volcanic dust plumes produce spectacular lightning displays. Charged particle clouds also cause devastating ...explosions in food, drug and coal processing industries. Despite the wide-ranging importance of granular charging in both nature and industry, even the simplest aspects of its causes remain elusive, because it is difficult to understand how inert grains in contact with little more than other inert grains can generate the large charges observed. Here, we present a simple yet predictive explanation for the charging of granular materials in collisional flows. We argue from very basic considerations that charge transfer can be expected in collisions of identical dielectric grains in the presence of an electric field, and we confirm the model's predictions using discrete-element simulations and a tabletop granular experiment. PUBLICATION ABSTRACT
Avoiding a Spanning Cluster in Percolation Models Cho, Y. S.; Hwang, S.; Herrmann, H. J. ...
Science (American Association for the Advancement of Science),
03/2013, Letnik:
339, Številka:
6124
Journal Article
Recenzirano
Odprti dostop
When dynamics in a system proceeds under suppressive external bias, the system can undergo an abrupt phase transition, as can happen when an epidemic spreads. Recently, an explosive percolation (EP) ...model was introduced to understand such phenomena. The order of the EP transition has not been clarified in a unified framework covering low-dimensional systems and the mean-field limit. We introduce a stochastic model in which a rule for dynamics is designed to avoid the formation of a spanning cluster through competitive selection in Euclidean space. We use heuristic arguments to show that in the thermodynamic limit and depending on a control parameter, the EP transition can be either continuous or discontinuous if d < d c and is always continuous if d ≥ d c , where d is the spatial dimension and d c is the upper critical dimension.
Free radical reactions are an important degradation process for organic compounds within the aqueous atmospheric environment. Nevertheless, non-radical oxidants such as hydrogen peroxide and ozone ...also contribute to the degradation and conversion of these substances (Tilgner and Herrmann, 2010). In this work, kinetic investigations of non-radical reactions were conducted using UV / Vis spectroscopy (dual-beam spectrophotometer and stopped flow technique) and a capillary electrophoresis system applying pseudo-first order kinetics to reactions of glyoxal, methylglyoxal, glycolaldehyde, glyoxylic, pyruvic and glycolic acid as well as methacrolein (MACR) and methyl vinyl ketone (MVK) with H2O2 and ozone at 298 K. The measurements indicate rather small rate constants at room temperature of k2nd < 3 M−1 s−1 (except for the unsaturated compounds exposed to ozone). Compared to radical reaction rate constants the values are about 10 orders of magnitude smaller (kOH ~109 M−1 s−1). However, when considering the much larger non-radical oxidant concentrations compared to radical concentrations in urban cloud droplets, calculated first-order conversion rate constants change the picture towards H2O2 reactions becoming more important, especially when compared to the nitrate radical. For some reactions mechanistic suggestions are also given.
Recent experiments on the National Ignition Facility M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013) demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable ...option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α∼3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8×10(15) neutrons, with 20% calculated alpha heating at convergence ∼27×.
Resilience of most critical infrastructures against failure of elements that appear insignificant is usually taken for granted. The World Airline Network (WAN) is an infrastructure that reduces the ...geographical gap between societies, both small and large, and brings forth economic gains. With the extensive use of a publicly maintained data set that contains information about airports and alternative connections between these airports, we empirically reveal that the WAN is a redundant and resilient network for long distance air travel, but otherwise breaks down completely due to removal of short and apparently insignificant connections. These short range connections with moderate number of passengers and alternate flights are the connections that keep remote parts of the world accessible. It is surprising, insofar as there exists a highly resilient and strongly connected core consisting of a small fraction of airports (around 2.3%) together with an extremely fragile star-like periphery. Yet, in spite of their relevance, more than 90% of the world airports are still interconnected upon removal of this core. With standard and unconventional removal measures we compare both empirical and topological perceptions for the fragmentation of the world. We identify how the WAN is organized into different classes of clusters based on the physical proximity of airports and analyze the consequence of this fragmentation.
We present and discuss perspectives of current developments on advanced quantum optical circuits monolithically integrated in the lithium niobate platform. A set of basic components comprising photon ...pair sources based on parametric down conversion (PDC), passive routing elements and active electro-optically controllable switches and polarisation converters are building blocks of a toolbox which is the basis for a broad range of diverse quantum circuits. We review the state-of-the-art of these components and provide models that properly describe their performance in quantum circuits. As an example for applications of these models we discuss design issues for a circuit providing on-chip two-photon interference. The circuit comprises a PDC section for photon pair generation followed by an actively controllable modified mach-Zehnder structure for observing Hong-Ou-Mandel interference. The performance of such a chip is simulated theoretically by taking even imperfections of the properties of the individual components into account.
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