Background-The mechanisms underlying paroxysmal atrial flutter/atrial fibrillation initiation by ectopic foci from various locations are unclear. Methods and Results-We used parallel computational techniques to study an anatomically accurate 3-dimensional atrial structure incorporating a detailed ionic-current model of an atrial myocyte. At the single-cell level, upregulation of the L-type Ca 2ϩ current I Ca,L steepened restitution curves of action potential duration and conduction velocity compared with the control. Spontaneous firings of ectopic foci, coupled with sinus activity, produced dynamic spatial dispersions of repolarization, including discordant alternans, which caused conduction block and reentry only for the elevated I Ca,L case. For each foci location, a vulnerable window for atrial flutter/atrial fibrillation induction was identified as a function of the coupling interval and focus cycle length. For ectopic foci in the pulmonary veins and left atrium, the site of conduction block and reentry gradually shifted, as a function of coupling interval, from the right atrium to the interatrial area and finally to the left atrium. The size of the vulnerable window was largest for pulmonary vein foci, becoming markedly smaller for right atrial foci, especially those near the sinoatrial node. Conclusions-These findings suggest that a mechanism of dynamically induced repolarization dispersion, especially discordant alternans, underlies the induction of atrial flutter/atrial fibrillation by atrial ectopic foci. The sites and likelihood of reentry induction varied according to ectopic focus location and timing, with the largest vulnerable window corresponding to the pulmonary vein region.
We report spontaneous antispiral wave formation in typical reaction-diffusion systems. Our findings qualitatively reproduce a series of phenomena recently observed in a Belousov-Zhabotinsky-type chemical reaction. We found that antispiral waves can occur only near the Hopf bifurcation, when the system is characterized by small amplitude oscillatory (as opposed to excitable) dynamics. For reaction-diffusion systems in the vicinity of the Hopf bifurcation, the specific conditions required for antispiral formation are established here through theoretical analyses and numerical simulations. Thus, this work provides a comprehensive description of the mechanisms underlying antispiral waves in reaction-diffusion systems.
The dynamics of the generation of the various spike trains in neural pacemakers is of fundamental importance to the understanding of neural coding. Recent studies have demonstrated, theoretically and experimentally, that neural pacemakers produce chaotic oscillations. Deeper analyses in several neuronal models have revealed many nonlinear phenomena including periodadding bifurcations whose existence has not been experimentally confirmed. In this letter, we reported that the period-adding bifurcation with chaos was observed in the interspike interval (ISI) series generated by an experimental neural pacemaker when the extracellular calcium concentration was changed or a potassium channel blocker was administered at the site of the pacemaker. We also simulated our experimental discoveries by computing a generalized model of excitable cells. The chaotic phenomenon in the experiment and that in the model were demonstrated and compared using the nonlinear forecasting and surrogate data methods.
As one of the core techniques in 5G, the Internet of Things is more interested than ever. Furthermore, radio frequency identification (RFID) plays a crucial role in Internet of Things development. Although the low-cost RFID system has wide prospect, it has to face with huge challenges because of potential security risks, privacy problems, and efficiency because of its restrictions on processing, storage, and power in RFID tags. One of the possible solutions in secure authentication of the low-cost RFID system is the lightweight RFID authentication protocol. A lightweight RFID mutual authentication protocol with cache in the reader is proposed in this paper, named LRMAPC. The LRMAPC can greatly reduce the computational and transmission cost. Especially, it can reduce computational costs greatly when a large number of tags want to be authenticated. We prove the correctness of LRMAPC using GNY logic. Compared with some existing works, LRMAPC achieves higher efficiency and stronger security. Furthermore, we developed LRMAPC into ULRMAPC, an ultralightweight RFID mutual authentication protocol with cache in the reader. Compared with SASI and Gossamer protocols, ULRMAPC also achieves higher efficiency and stronger security in storage and computation cost.
This paper presents a novel Y shaped fractal defected ground structure (FDGS) for the mutual coupling (MC) reduction between coplanar closely spaced microstrip antennas. The proposed FDGS has band-gap characteristic, which induces the current distribution on the antenna patch. This will contribute to achieving 25 dB MC reduction. When realizing the MC reduction, the antenna efficiency is increased. Moreover, the envelope correlation of the MIMO system is decreased, which helps to increase the MIMO system capacity. 1. INTRODUCTION The mutual coupling (MC) reduction between antenna elements is important in many applications, especially for multiple-input and multiple-output (MIMO) communication systems [1, 2]. The MIMO communication system employs multiple antennas at both the transmitter and receiver, which rely on multiple antennas to offer increases in capacity without the need for additional power or spectrum [3]. However, when the antenna elements in the MIMO communication system are closely spaced, the high MC level between antennas will degrade the antenna performance as well as the MIMO system performance. Therefore, the MC reduction between closely spaced antenna elements in the MIMO communication system is very important in application [4]. The MC reduction between the closely spaced antennas is difficult to achieve [5-7]. By etching the elliptical split-ring resonators placed horizontally between the antennas, the 19 dB MC reduction between two closely spaced antennas with center-to-center distance 0.25λ 0 is achieved in [8]. An efficient technique based on a T-shaped slot is introduced in [9] to reduce the MC between closely spaced PIFAs (Planar Inverted-F Antennas) for MIMO mobile terminals, and the isolation of above 40 dB is realized. The isolation of more than 36.5 dB is achieved by a slot on the ground plane [10], which operates at 2.4 GHz with an inter-PIFA spacing of center-to-center distance 0.063λ 0. By the etched slot structure in a ground plane [11], the isolation of more than 20 dB is achieved between two parallel PIFAs with center-to-center 0.115λ 0. A dumb-bell-like DGS reducing the MC between closely-packed antennas is proposed in [12], and the 18 dB MC reduction is achieved between antennas with center-to-center distance 0.45λ 0. Except for the MC reduction between PIFAs, approaches for the MC reduction between closely placed microstrip antennas also have been studied. The designs of the folded split-ring resonators etched in the ground plane are proposed for the MC reduction between microstrip antennas [13]. A reduction of more than 30 dB MC between microstrip antennas with a very close distance 0.27λ 0 (center-to-center) is obtained. The microstrip antennas loaded with the coupled split ring resonators are presented in [14], and about 10 dB MC reduction is realized of the antenna elements in the case of 0.27λ 0 inter-element spacing. By inserting the band-gap waveguided metamaterials between two microstrip antennas with the center-to-center distance 0.35λ 0 , about 6 dB MC reduction is...
Abstract:Carbon emissions calculation at the sub-provincial level has issues in limited data and non-unified measurements. This paper calculated the life cycle energy consumption and carbon emissions of the building industry in Wuhan, China. The findings showed that the proportion of carbon emissions in the construction operation phase was the largest, followed by the carbon emissions of the indirect energy consumption and the construction material preparation phase. With the purpose of analyzing the contributors of the construction carbon emissions, this paper conducted decomposition analysis using Logarithmic Mean Divisia Index (LMDI). The results indicated that the increasing buidling area was the major driver of energy consumption and carbon emissions increase, followed by the behavior factor. Population growth and urbanization, to some extent, increased the carbon emissions as well. On the contrary, energy efficiency was the main inhibitory factor for reducing the carbon emissions. Policy implications in terms of low-carbon construction development were highlighted.
Recently it was found that noise could help improve human detection of sensory stimuli via stochastic-resonance-type behavior. Specifically, the ability of an individual to detect a weak tactile stimulus could be enhanced by adding a certain amount of noise. Here we propose, from the perspective of classical signal detection theory, a simple and general model to elucidate the mechanism underlying this phenomenon. We demonstrate that noise-mediated enhancements and decrements in human sensation can be well reproduced by our model. The predicted upper bound of the performance improvement by adding noise is also consistent with the experimental data. We suggest additional experiments to further test the model.
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