Time-reversal symmetry breaking and decoherence in chaotic Dirac billiards

In this work, we perform a statistical study on Dirac Billiards in the extreme quantumlimit (a single open channel on the leads). Our numerical analysis uses a large ensembleof random matrices and demonstrates the preponderant role of dephasing mechanisms in suchchaotic billiards. Physical implementations of these billiards range from quantum dots ofgraphene to topological insulators structures. We show, in particular, that the role offinite crossover fields between the universal symmetries quickly leaves the conductance tothe asymptotic limit of unitary ensembles. Furthermore, we show that the dephasingmechanisms strikingly lead Dirac billiards from the extreme quantum regime to thesemiclassical Gaussian regime.     

Stabilization of the Columnar Mesophase of Perylenediimide by Racemic Triple Tails

Whereas perylene tetracarboxdiimides derived from amino‐n‐alkanes if at all only show monotropic (thermodynamically unstable) mesogenic self‐assembly, the hexagonal columnar liquid crystalline state can be stabilized over a broad temperature range with doubly branched, doubly racemic alkyl residues. An improved tendency to homeotropic surface orientation is observed, and the orientation of the liquid crystalline domains is maintained upon cycling through the crystalline state at room temperature.     

Minisci C−H Alkylation of Heteroarenes Enabled by Dual Photoredox/Bromide Catalysis in Micellar Solutions**

Aromatic heterocycles are omnipresent structural motifs in various natural products, pharmaceuticals and agrochemicals. This work describes a photocatalytic Minisci-type C−H functionalization of heteroarenes with non-activated alkyl bromides. The reaction avoids stoichiometric radical-promoters, oxidants, or acids, and is conducted using blue LEDs as the light source. The reactive carbon-centered alkyl radicals are generated by merging the photoredox approach with bromide anion co-catalysis and spatial pre-aggregation of reacting species in the micellar aqueous solutions. The obtained data highlight the critical importance of microstructuring and organization of the components in the reaction mixture.     

Overdamped motion of interacting particles in general confining potentials: time-dependent and stationary-state analyses

By comparing numerical and analytical results, it is shown that a system of interacting particles under overdamped motion is very well described by a nonlinear Fokker-Planck equation, which can be associated with nonextensive statistical mechanics. The particle-particle interactions considered are repulsive, motivated by three different physical situations: (i) modified Bessel function, commonly used in vortex-vortex interactions, relevant for the flux-front penetration in disordered type-II superconductors; (ii) Yukawa-like forces, useful for charged particles in plasma, or colloidal suspensions; (iii) derived from a Gaussian potential, common in complex fluids, like polymer chains dispersed in a solvent. Moreover, the system is subjected to a general confining potential, ??(x)?=?(??|x| ^z )/z (???>?0, z?>?1), so that a stationary state is reached after a sufficiently long time. Recent numerical and analytical investigations, considering interactions of type (i) and a harmonic confining potential (z?=?2), have shown strong evidence that a q-Gaussian distribution, P(x,t), with q?=?0, describes appropriately the particle positions during their time evolution, as well as in their stationary state. Herein we reinforce further the connection with nonextensive statistical mechanics, by presenting numerical evidence showing that: (a) in the case z?=?2, different particle-particle interactions only modify the diffusion parameter D of the nonlinear Fokker-Planck equation; (b) for z????2, all cases investigated fit well the analytical stationary solution P _st(x), given in terms of a q-exponential (with the same index q?=?0) of the general external potential ??(x). In this later case, we propose an approximate time-dependent P(x,t) (not known analytically for z????2), which is in very good agreement with the simulations for a large range of times, including the approach to the stationary state. The present work suggests that a wide variety of physical phenomena, characterized by repulsive interacting particles under overdamped motion, present a universal behavior, in the sense that all of them are associated with the same entropic form and nonlinear Fokker-Planck equation.     

Computation of energy exchanges by combining information theory and a key thermodynamic relation: Physical applications

By considering a simple thermodynamic system, in thermal equilibrium at a temperature T and in the presence of an external parameter A, we focus our attention on the particular thermodynamic (macroscopic) relation . Using standard axioms from information theory and the fact that the microscopic energy levels depend upon the external parameter A, we show that all usual results of statistical mechanics for reversible processes follow straightforwardly, without invoking the Maximum Entropy principle. For the simple system considered herein, two distinct forms of heat contributions appear naturally in the Clausius definition of entropy, . We give a special attention to the amount of heat , associated with an infinitesimal variation at fixed temperature, for which a “generalized heat capacity”, , may be defined. The usefulness of these results is illustrated by considering some simple thermodynamic cycles.     

Thermostatistics of overdamped motion of interacting particles

We show through a nonlinear Fokker-Planck formalism, and confirm by molecular dynamics simulations, that the overdamped motion of interacting particles at T=0, where T is the temperature of a thermal bath connected to the system, can be directly associated with Tsallis thermostatistics. For sufficiently high values of T, the distribution of particles becomes Gaussian, so that the classical Boltzmann-Gibbs behavior is recovered. For intermediate temperatures of the thermal bath, the system displays a mixed behavior that follows a novel type of thermostatistics, where the entropy is given by a linear combination of Tsallis and Boltzmann-Gibbs entropies.     

Simulation of amino acid diffusion across water/hydrophobic interfaces

The mechanism of amino acid transfer across water/hydrophobic interfaces has important biological relevance but is poorly understood. Combined QM/MM simulations show that zwitterionic Gly enters the hydrophobic phase till ca. 1 nm before neutralisation occurs. Interfacial effects significantly affect the relative tautomers stability.     

The impact of interference-aware routing metrics on video streaming in Wireless Mesh Networks

Wireless Mesh Networks form a wireless backbone that provides ubiquitous Internet access and support of multimedia services. In this scenario, traffic crosses multi-hop paths, through mesh routers and gateways, causing high levels of interference. To address this problem, the use of schemes that introduce routing metrics that take into account the characteristics of the interference have been made to improve the application performance. Given the diversity of interference-aware routing metrics for Wireless Mesh Networks, it is necessary to assess the impact of employing these routing metrics on multimedia traffic performance, and in particular, on video streaming. This paper seeks to fill this gap, by using simulation to evaluate the video streaming performance when the most relevant interference-aware routing metrics are used. The degree of video quality can be evaluated from two perspectives, the network viewpoint and the standpoint of the user perception. At the network level, video streaming quality is assessed through IP measures, that is, throughput, delay, jitter and routing overhead. At the user level, ‘Quality of Experience’ metrics are employed to measure the user perception with regard to the video quality. The evaluation of the performance takes account of outdoor and indoor environments. The results of the simulation study have shown that routing metrics based on the information that detects interference using accurate measures achieve a better network and user perception performance. However, depending on the environment (i.e., whether it is indoor or outdoor), all the routing metrics result in a different performance being achieved. Although interference-aware routing metrics affect the performance of both the network and the user levels, there are some cases where they have less impact on the user level, because the user perception parameters are less influenced by the behaviour of the network.