The concept, analysis, and design of series switches for graphene-strip plasmonic waveguides at near infrared frequencies are presented. Switching is achieved by using graphene's field effect to ...selectively enable or forbid propagation on a section of the graphene strip waveguide, thereby allowing good transmission or high isolation, respectively. The electromagnetic modeling of the proposed structure is performed using full-wave simulations and a transmission line model combined with a matrix-transfer approach, which takes into account the characteristics of the plasmons supported by the different graphene-strip waveguide sections of the device. The performance of the switch is evaluated versus different parameters of the structure, including surrounding dielectric media, electrostatic gating and waveguide dimensions.
In this manuscript, we consider an initial-boundary-value problem governed by a (1+1)-dimensional hyperbolic partial differential equation with constant damping that generalizes many nonlinear wave ...equations from mathematical physics. The model considers the presence of a spatial Laplacian of fractional order which is defined in terms of Riesz fractional derivatives, as well as the inclusion of a generic continuously differentiable potential. It is known that the undamped regime has an associated positive energy functional, and we show here that it is preserved throughout time under suitable boundary conditions. To approximate the solutions of this model, we propose a finite-difference discretization based on fractional centered differences. Some discrete quantities are proposed in this work to estimate the energy functional, and we show that the numerical method is capable of conserving the discrete energy under the same boundary conditions for which the continuous model is conservative. Moreover, we establish suitable computational constraints under which the discrete energy of the system is positive. The method is consistent of second order, and is both stable and convergent. The numerical simulations shown here illustrate the most important features of our numerical methodology.
•The existence of positive energy invariants of a damped nonlinear wave equation with Riesz fractional Laplacian is proved.•A dissipation-preserving technique satisfying the same properties of its continuous counterpart is proposed.•The method is consistent, stable, convergent and preserves the positivity of the energy.•Numerical simulations illustrate the capability of the method to dissipate/conserve the energy.
•Mathematical considerations of a SEIQR model to describe the propagation of COVID-19 are proposed.•We derive analytically the reproductive number and the equilibria with and without ...COVID-19.•Necessary and sufficient conditions for the stability of the equilibria are mathematically established.•An efficient nonstandard method to solve the continuous problem is proposed and analyzed.•The numerical simulations confirm the analytical and numerical results derived in this work.
In this manuscript, we develop a mathematical model to describe the spreading of an epidemic disease in a human population. The emphasis in this work will be on the study of the propagation of the coronavirus disease (COVID-19). Various epidemiologically relevant assumptions will be imposed upon the problem, and a coupled system of first-order ordinary differential equations will be obtained. The model adopts the form of a nonlinear susceptible-exposed-infected-quarantined-recovered system, and we investigate it both analytically and numerically. Analytically, we obtain the equilibrium points in the presence and absence of the coronavirus. We also calculate the reproduction number and provide conditions that guarantee the local and global asymptotic stability of the equilibria. To that end, various tools from analysis will be employed, including Volterra-type Lyapunov functions, LaSalle’s invariance principle and the Routh–Hurwitz criterion. To simulate computationally the dynamics of propagation of the disease, we propose a nonstandard finite-difference scheme to approximate the solutions of the mathematical model. A thorough analysis of the discrete model is provided in this work, including the consistency and the stability analyses, along with the capability of the discrete model to preserve the equilibria of the continuous system. Among other interesting results, our numerical simulations confirm the stability properties of the equilibrium points.
Rabalais, N. N., Turner, R. E., Díaz, R. J., and Justić, D. 2009. Global change and eutrophication of coastal waters. – ICES Journal of Marine Science, 66: 1528–1537.The cumulative effects of global ...change, including climate change, increased population, and more intense industrialization and agribusiness, will likely continue and intensify the course of eutrophication in estuarine and coastal waters. As a result, the symptoms of eutrophication, such as noxious and harmful algal blooms, reduced water quality, loss of habitat and natural resources, and severity of hypoxia (oxygen depletion) and its extent in estuaries and coastal waters will increase. Global climate changes will likely result in higher water temperatures, stronger stratification, and increased inflows of freshwater and nutrients to coastal waters in many areas of the globe. Both past experience and model forecasts suggest that these changes will result in enhanced primary production, higher phytoplankton and macroalgal standing stocks, and more frequent or severe hypoxia. The negative consequences of increased nutrient loading and stratification may be partly, but only temporarily, compensated by stronger or more frequent tropical storm activity in low and mid-latitudes. In anticipation of the negative effects of global change, nutrient loadings to coastal waters need to be reduced now, so that further water quality degradation is prevented.
Information theory allows us to investigate information processing in neural systems in terms of information transfer, storage and modification. Especially the measure of information transfer, ...transfer entropy, has seen a dramatic surge of interest in neuroscience. Estimating transfer entropy from two processes requires the observation of multiple realizations of these processes to estimate associated probability density functions. To obtain these necessary observations, available estimators typically assume stationarity of processes to allow pooling of observations over time. This assumption however, is a major obstacle to the application of these estimators in neuroscience as observed processes are often non-stationary. As a solution, Gomez-Herrero and colleagues theoretically showed that the stationarity assumption may be avoided by estimating transfer entropy from an ensemble of realizations. Such an ensemble of realizations is often readily available in neuroscience experiments in the form of experimental trials. Thus, in this work we combine the ensemble method with a recently proposed transfer entropy estimator to make transfer entropy estimation applicable to non-stationary time series. We present an efficient implementation of the approach that is suitable for the increased computational demand of the ensemble method's practical application. In particular, we use a massively parallel implementation for a graphics processing unit to handle the computationally most heavy aspects of the ensemble method for transfer entropy estimation. We test the performance and robustness of our implementation on data from numerical simulations of stochastic processes. We also demonstrate the applicability of the ensemble method to magnetoencephalographic data. While we mainly evaluate the proposed method for neuroscience data, we expect it to be applicable in a variety of fields that are concerned with the analysis of information transfer in complex biological, social, and artificial systems.
•Resource recovery from urban wastewater to promote shift towards a circular economy.•Pilot and full-scale studies show MBBR as suitable system for treated wastewater reuse.•Numerous methods ...developed for nutrient recovery from WWTP’s effluents.
Over the last years, an increasing concern has emerged regarding the eco-friendly management of wastewater. Apart from the role of wastewater treatment plants (WWTPs) for wastewater and sewage sludge treatment, the increasing need of the recovery of the resources contained in wastewater, such as nutrients and water, should be highlighted. This would allow for transforming a wastewater treatment plant (WWTP) into a sustainable technological system.
The objective of this review is to propose a moving bed biofilm reactor (MBBR) as a novel technology that contributes to the circularity of the wastewater treatment sector according to the principles of circular economy. In this regard, this paper aims to consider the MBBR process as the initial step for water reuse, and nutrient removal and recovery, within the circular economy model.
Ionic conductors composed of lanthanide-doped ceria with general formula DyyCe1-yO2-δ (y = 0.05, 0.1 and 0.15) were synthesized by mechanochemistry (mechanical milling), and their electrical ...properties analyzed to be used as solid electrolytes in low-temperature SOFC. Starting oxide reagents were milled at different times in a planetary mill and the evolution of their structures and phases with milling time and temperature (up to 1500 °C) was followed by XRD. Just milled powders were also uniaxially pressed and sintered at different temperatures (1200, 1350 and 1500 °C), and analyzed by FE-SEM, to explore their morphologies as a function of temperature and Dy content. The electrical properties of these materials and undoped commercial CeO2 were analyzed by impedance spectroscopy at different temperatures (200–650 °C) and frequencies (100 Hz - 1 MHz). Results showed that mechanochemistry is a suitable method to obtain the DyyCe1-yO2-δ systems after 20 h of milling, since XRD patterns of these milled powders reveal the formation of fluorite-type cubic solid solutions for all studied compositions. Increasing of temperature generates a higher crystallinity in these materials while the absence of phase transitions in them is corroborated at 1200 °C. Analysis of electrical properties of samples sintered a 1200 °C corroborates the viability of these systems to be used as solid electrolytes in the SOFC technology, being that high dc conductivities (σdc) were obtained for all doped samples, especially for the composition Dy0.1Ce0·9O2-δ, which showed a σdc = 1 × 10−1.91 S cm−1 at 650 °C. This value represents an increase of almost three orders of magnitude for this composition with respect to the undoped CeO2 sample (y = 0, σdc = 1 × 10 −4.83 Scm−1).
•CeO2 doped with Dy was successfully synthesized by a mechanochemical reaction.•All compositions (5, 10 and 15% mol of Dy) show a cubic fluorite-type structure.•Electrical properties of the samples were measured as a function of temperature.•Conductivity (σdc) reaches a maximum of 1 * 10−1.91 Scm−1 (650 °C) for 10% of Dy.•Increasing of σdc is related to the creation of oxygen vacancies in the structure.
Fault slip rate is one of the most crucial parameters to characterize earthquake occurrence in fault‐based seismic hazard assessments (SHA). Accordingly, paleoseismic studies have increasingly ...focused on constraining this parameter in active faults worldwide. We present a comprehensive paleoseismic study in the Alhama de Murcia Fault (AMF), one of the most active faults in SE Spain and source of destructing earthquakes such as the 2011 Mw 5.2 Lorca event. Contrasting with previous studies, we integrate paleoseismic data from four fault strands in the AMF and, based on trench slip analysis and numerical dates, we derive slip rate estimates of each strand over the whole transect and assess their time variability. The AMF has a minimum net slip rate between 1.35+0.16/−0.10 and 1.64+0.16/−0.11 mm/yr for the past 18 ± 1 to 15.2 ± 1.1 ka. These results prove the importance of accounting for the complete sections of a geological structure as they are almost twice the previous estimates for a single fault branch. Slip rate variability is identified in the AMF, with cyclic acceleration‐quiescence patterns that could be related to stress field changes driven by fault interaction or synchronicity with neighboring faults (e.g., Carrascoy). We hope that the data presented here motivates their inclusion into forthcoming fault‐based SHAs. In this regard, limitations related to the lack of paleoseismic data for one fault strand, along with poor characterization of the strike component of slip and insufficient age control of the units for another strand are highlighted and need to be accounted for by modelers.
Key Points
Multi‐site paleoseismic surveys allow to improve the estimations of the geological slip rates in the Alhama de Murcia Fault (AMF)
The AMF shows a geological slip rate between 1.35 and 1.64 mm/yr for the past 18–15 ka
Late Quaternary slip rate fluctuations suggest strain rate variations and highlight possible synchronicities with neighboring faults
•The dynamics of a Riesz space-fractional sine-Gordon equation is investigated numerically.•The system is perturbed harmonically at one end at a frequency in the forbidden band gap.•A sudden increase ...in the amplitude of wave signals absorbed by the system is found above a critical amplitude.•The presence of supratransmission in Riesz space-fractional sine-Gordon systems is established for the first time.
In this work, we consider a (1+1)-dimensional Riesz space-fractional damped sine-Gordon equation defined on a bounded spatial interval. Sinusoidal Dirichlet boundary data are imposed at one end of the interval and homogeneous Neumann conditions at the other. The system is initially at rest in the equilibrium position, and is discretized to simulate its complex dynamics. The method employed in this work is a finite-difference discretization of the mathematical model of interest. Our scheme is throughly validated against simulations on the dynamics of the classical and the space-fractional sine-Gordon equations, which are available in the literature. As the main result of this manuscript, we have found numerical evidence on the presence of the phenomenon of nonlinear supratransmission in Riesz space-fractional sine-Gordon systems. Simulations have been conducted in order to predict its occurrence for some values of the fractional order of the spatial derivative, and a wide range of values of the frequency of the sinusoidal perturbation at the boundary. As far as the author knows, this may be one of the first numerical reports on the existence of nonlinear supratransmission in sine-Gordon systems of Riesz space-fractional order.
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