Finite size effects in a supercooled medium under nanoscale solicitations

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Finite Size Effects and Cooperativity in a Model Diatomic Supercooled Liquid

We use large scale molecular dynamics simulations to investigate the relation between cooperativity and size e ects in a simple diatomic supercooled liquid. We nd that below a characteristic temperature the transport properties depend on the size of the simulation box. is e ect then increases upon decreasing the temperature. For the model molecules constituting our liquid, the smaller box corresponds to the larger di usion coe cient. us, the size e ects increase the di usion of the liquid with our molecules in opposition with previous results concerning silica and atomic so molecules. As a result, the temperature dependence of the di usion coe cient tends to an Arrhenius law for smaller boxes in our simulations. is result is in agreement with a cooperativity origin of non-Arrhenius behavior and size e ects in fragile supercooled liquids, as a small box cuto cooperative motions thus inducing a constant activation energy. To investigate that picture further we then study the size dependence of cooperative motions in our model liquid.

Gain control network conditions in early sensory coding

Gain control is essential for the proper function of any sensory system. However, the precise mechanisms for achieving effective gain control in the brain are unknown. Based on our understanding of the existence and strength of connections in the insect olfactory system, we analyze the conditions that lead to controlled gain in a randomly connected network of excitatory and inhibitory neurons. We consider two scenarios for the variation of input into the system. In the first case, the intensity of the sensory input controls the input currents to a fixed proportion of neurons of the excitatory and inhibitory populations. In the second case, increasing intensity of the sensory stimulus will both, recruit an increasing number of neurons that receive input and change the input current that they receive. Using a mean field approximation for the network activity we derive relationships between the parameters of the network that ensure that the overall level of activity of the excitatory population remains unchanged for increasing intensity of the external stimulation. We find that, first, the main parameters that regulate network gain are the probabilities of connections from the inhibitory population to the excitatory population and of the connections within the inhibitory population. Second, we show that strict gain control is not achievable in a random network in the second case, when the input recruits an increasing number of neurons. Finally, we confirm that the gain control conditions derived from the mean field approximation are valid in simulations of firing rate models and Hodgkin-Huxley conductance based models

Hopping conduction mechanism and impedance spectroscopy analyses of La0.70Sr0.25Na0.05Mn0.70Ti0.30O3 ceramic

The perovskite sample La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 (LSNM0.70T0.30) was produced via a solid-state route process. The frequency dependence of electrical conduction plot established that according to the Jonscher law. The electrical conduction process was based on both theoretical conduction models assigned to the non-overlapping small polaron tunneling model at low temperatures and correlated barrier hopping mechanism at high temperatures. Detailed investigation of impedance data revealed a non-Debye-type relaxation occurring in the polycrystalline. In addition, the dielectric response confirmed the dominance of the Maxwell–Wagner model and Koop’s phenomenological theory effect in conduction phenomenon. The values of permittivity is high for LSNM0.70T0.30 were observed. These values make this composition interesting for microelectric applications. In the thermal study, the relaxation processes observed by electrical conductivity, impedance, and modulus are associated with singly and doubly ionized oxygen vacancies for the lower and higher temperature, respectively. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Majmaah University, MU: R-2021-121The author would like to thank Deanship of Scientific Research at Majmaah University for supporting this work under Project Number No. R-2021-121

Journal of Applied and Theoretical Physics Research Finite Size Effects and Cooperativity in a Model Diatomic Supercooled Liquid

International audienceWe use large scale molecular dynamics simulations to investigate the relation between cooperativity and size effects in a simple diatomic supercooled liquid. We find that below a characteristic temperature the transport properties depend on the size of the simulation box. This effect then increases upon decreasing the temperature. For the model molecules constituting our liquid, the smaller box corresponds to the larger diffusion coefficient. Thus, the size effects increase the diffusion of the liquid with our molecules in opposition with previous results concerning silica and atomic soft molecules. As a result, the temperature dependence of the diffusion coefficient tends to an Arrhenius law for smaller boxes in our simulations. This result is in agreement with a cooperativity origin of non-Arrhenius behavior and size effects in fragile supercooled liquids, as a small box cutoff cooperative motions thus inducing a constant activation energy. To investigate that picture further we then study the size dependence of cooperative motions in our model liquid

Self-consistent vertical transport calculations in Al(x)Ga1-xN/GaN based resonant tunneling diode

International audienceThe formation of two-dimensional electron gases (2DEGs) at AlxGa1-xN/GaN hexagonal double-barriers (DB) resonant tunneling diodes (RTD) is investigated by numerical self consistent (SC) solutions of the coupled Schrodinger and Poisson equations. Spontaneous and piezoelectric effects across the material interfaces are rigorously taken into account. Conduction band profiles, band edges and corresponding envelope functions are calculated in the AlxGa1-xN/GaN structures and likened to those where no polarization effects are included. The combined effect of the polarization-induced bound charge and conduction band offsets between the hexagonal AIGaN and GaN results in the formation of 2DEGs on one side of the DB and a depletion region on the other side. Using the transfer matrix formalism, the vertical transport (J-V characteristics) in AlGaN/GaN RTDs is calculated with a fully SC calculation in the ballistic regime. Compared to standard calculations where the voltage drop along the structure is supposed to be linear, the SC method leads to strong quantitative changes in the J-V characteristics showing that the applied electric field varies significantly in the active region of the structure. The influences of the aluminum composition and the GaN(AlGaN) thickness layers on the evolution of the current characteristics are also self-consistently investigated and discussed. We show that the electrical characteristics are very sensitive to the potential barrier due to the interplay between the potential symmetry and the barrier height and width. More interestingly, we demonstrate that the figures of merit namely the peak-to-valley ratio (PVR) of GaN/AlGaN RTDs can be optimized by increasing the quantum well width. (C) 2015 Elsevier Ltd. All rights reserved

Study of microbial communities and environmental parameters of seawater collected from three Tunisian fishing harbors in Kerkennah Islands: Statistical analysis of the temporal and spatial dynamics

Surface seawater, collected from three fishing harbors during different seasons of the years 2015, 2016 and 2017, were assessed for physico-chemical analyses. Results showed that seawater was mainly polluted by hydrocarbons and some heavy metals. Microbial communities' composition and abundance in the studied harbors were performed using molecular approaches. SSCP analysis indicated the presence of Bacteria, Archaea and Eucarya, with dominance of the bacterial domain. Illumina Miseq analysis revealed that the majority of the sequences were affiliated with Bacteria whereas Archaea were detected at low relative abundance. The bacterial community, dominated by Proteobacteria, Bacteroidetes, Planctomycetes, Cyanobacteria, Firmicutes, Actinobacteria and Chloroflexi phyla, are known to be involved in a variety of biodegradation/biotransformation processes including hydrocarbons degradation and heavy metals resistance. The main objectives of this study are to assess, for the first time, the organic/inorganic pollution in surface seawater of Kerkennah Islands harbors, and to explore the potential of next generation marine microbiome monitoring to achieve the planning coastal managing strategies worldwide. 2022 Elsevier LtdThe present work was supported by the Tunisian Ministry of Higher Education and Scientific Research and the Hubert Curien Program ( CMCU 15G0808 ) supported by the French Ministry of Foreign Affairs .Scopu