698 research outputs found

    Discrete versus continuum modeling of a charged dielectric interface: A first grade test

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    Two main treatments within classical simulations for modeling a charged surface are using explicit, discrete charges and continuous, uniform charges. The computational cost can be substantially reduced if, instead of discrete surface charges, one uses an electric field to represent continuous surface charges. In addition, many electrolyte theories, including the Poisson--Boltzmann theory, are developed on the assumption of uniform surface charge. However, recent simulations have demonstrated with discrete surface charges, one observes much stronger charge reversal, compared to the surfaces with continuous surface charges, when the lattice constant becomes notably larger than the ion diameter. These examples show that the two treatments for modeling a charged dielectric interface can lead to substantially different results. In this short note, we calculate the electrostatic force for a single point charge above an infinite plane, and compare the differences between discrete and continuous representations of surface charges. Our results show that while the continuous, uniform surface charge model gives a quite simple picture, the discrete surface charge model can offer several different cases even for such a simple problem, depending on the respective values of ion size versus lattice spacing and a self-image interaction parameter.Comment: 3 pages, 3 figure

    Performance Analysis of D-MoSK Modulation in Mobile Diffusive-Drift Molecular Communication Relay System

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    Molecular communication (MC) is a new wireless communication technology, which uses molecules as information carriers. Diffusion-based MC is one of the most common MC methods. With the increase of diffusion distance, the molecular signal attenuation is serious, so the traditional communication technology of relay is introduced into the MC system. In this work, a mobile diffusive-drift MC relay model is investigated, in which the depleted molecule shift keying (D-MoSK) modulation is used. The closed-form expression of symbole error rate (SER) and the channel capacity are derived, meanwhile the impacts of several crucial parameters on the performance are discussed comprehensively

    Color Filtering Localization for Three-Dimensional Underwater Acoustic Sensor Networks

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    Accurate localization for mobile nodes has been an important and fundamental problem in underwater acoustic sensor networks (UASNs). The detection information returned from a mobile node is meaningful only if its location is known. In this paper, we propose two localization algorithms based on color filtering technology called PCFL and ACFL. PCFL and ACFL aim at collaboratively accomplishing accurate localization of underwater mobile nodes with minimum energy expenditure. They both adopt the overlapping signal region of task anchors which can communicate with the mobile node directly as the current sampling area. PCFL employs the projected distances between each of the task projections and the mobile node, while ACFL adopts the direct distance between each of the task anchors and the mobile node. Also the proportion factor of distance is proposed to weight the RGB values. By comparing the nearness degrees of the RGB sequences between the samples and the mobile node, samples can be filtered out. And the normalized nearness degrees are considered as the weighted standards to calculate coordinates of the mobile nodes. The simulation results show that the proposed methods have excellent localization performance and can timely localize the mobile node. The average localization error of PCFL can decline by about 30.4% than the AFLA method.Comment: 18 pages, 11 figures, 2 table

    Anomalous diffusion of optical vortices in random wavefields

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    We investigate the dynamic behavior of optical vortices, or phase singularities, in random wavefields and demonstrate the direct experimental observation of the anomalous diffusion of optical vortices. The observed subdiffusion of optical vortices show excellent agreement with the fractional Brownian motion, a Gaussian process. Paradoxically, the vortex displacements are observed exhibiting a non-Gaussian heavy-tailed distribution. We also tune the extent of subdiffusion and non-Gaussianity of optical vortex by varying the viscoelasticity of light scattering media. This complex motion of optical vortices is reminiscent of particles in viscoelastic environments suggesting a vortex tracking based microrheology approach. The fractional Brownian yet non-Gaussian subdiffusion of optical vortices may not only offer insights into the dynamics of phase singularities, but also contribute to the understanding certain general physics, including vortex diffusion in fluids and the decoupling between Brownian and Gaussian

    Multilevel Change of Measure for Complex Digital Options

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    The multilevel Monte Carlo approach introduced by Giles (Operations Research, 56(3):607-617, 2008) aims to achieve greater accuracy for the same computational cost by combining simulations in different levels of discretization. In particular for digital options, previous related work has suggested the conditional expectation approach and the technique of splitting in multiple dimensions. In this paper, we suggest the change of measure approach as an alternative for splitting and analyse its efficiency compared to previous methods in both scalar and multidimensional cases