A vehicular ad hoc network (VANET) may exhibit a bipolar behavior, i.e., the network can either be fully connected or sparsely connected depending on the time of day or on the market penetration rate ...of the wireless communication devices. In this paper, we use empirical vehicle traffic data measured on 1-80 freeway in California to develop a comprehensive analytical framework to study the disconnected network phenomenon and its network characteristics. These characteristics shed light on the key routing performance metrics of interest in disconnected VANETs, such as the average time taken to propagate a packet to disconnected nodes (i.e., the re-healing time). Our results show that, depending on the sparsity of vehicles or the market penetration rate of cars using Dedicated Short Range Communication (DSRC) technology, the network re-healing time can vary from a few seconds to several minutes. This suggests that, for vehicular safety applications, a new ad hoc routing protocol will be needed as the conventional ad hoc routing protocols such as Dynamic Source Routing (DSR) and Ad Hoc On-Demand Distance Vector Routing (AODV) will not work with such long re-healing times. In addition, the developed analytical framework and its predictions provide valuable insights into the VANET routing performance in the disconnected network regime.
This study presents narrow-band measurements of the mobile vehicle-to-vehicle propagation channel at 5.9 GHz, under realistic suburban driving conditions in Pittsburgh, Pennsylvania. Our system ...includes differential Global Positioning System (DGPS) receivers, thereby enabling dynamic measurements of how large-scale path loss, Doppler spectrum, and coherence time depend on vehicle location and separation. A Nakagami distribution is used for describing the fading statistics. The speed-separation diagram is introduced as a new tool for analyzing and understanding the vehicle-to-vehicle propagation environment. We show that this diagram can be used to model and predict channel Doppler spread and coherence time using vehicle speed and separation.
The smoothed particle hydrodynamics (SPH) method was employed to simulate the heat transfer process in porous media at the pore scale. The effective thermal conductivity of a porous medium can be ...predicted through a simulation experiment of SPH. The accuracy of the SPH simulation experiment was verified by comparing the predicted values with reference values for ideal homogeneous media and multiphase layered media. 3D simulation experiments were implemented in granular media generated by the PFC method. Based on the SPH framework, a concise method was proposed to produce unsaturated media by simulating the wetting process in dry media. This approach approximates the formation of liquid bridges and water films on granules. Through simulation experiments, the empirical formula of the variation in thermal conductivity with the degree of saturation was tested. The results showed that the reciprocal of the normalized thermal conductivity and the reciprocal of the saturation are linearly related, which is in line with the empirical formula proposed by Cote and Konrad.
This article addresses the data‐driven resilient platooning control problem for nonlinear vehicular platooning systems with denial‐of‐service attacks. First, the dynamic linearization technique is ...used for transforming the nonlinear vehicular platooning systems into an equivalent linear data model with robustness. Then, an observer is designed to present the estimation of the pseudo‐partial derivative parameter and a novel model‐free adaptive platooning control (MFAPC) framework is presented by defining a novel vehicular platooning system output. Based on this framework, a novel MFAPC algorithm is designed with an attack compensation mechanism to achieve vehicular platooning control objectives. At last, the effectiveness of the MFAPC algorithm is proved by an example with comparisons.
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This article addresses the dynamic event-triggered (DET) fault-tolerant model-free adaptive platooning control (MFAPC) problem of vehicle platoon systems subject to sensor faults. First of all, a ...novel redefined output is introduced to assist in proving the synchronous tracking of the position and velocity. Based on which, the equivalent dynamic linearization technique is used for transforming the nonlinear vehicular platooning systems into an linear data model. Then, an observer is designed to introduce the estimation of the pseudo-partial derivative (PPD) parameter, which can also eliminate the symbol restriction on it. In addition, a DET mechanism is introduced to save network resources more effectively, and the neural network method is applied to deal with the sensor faults for the safe vehicle driving. Further, a novel DET-based fault-tolerant MFAPC strategy is developed to realize the vehicular position and velocity tracking only using the input-output data. At last, an example is provided to prove the effectiveness of designed MFAPC framework.
The calculation of the probability of a minor outbreak is crucial in analyzing a stochastic epidemic model. For stochastic epidemic models with fixed delays, the linear chain trick is applied to ...transform the delayed models into a family of ODE models with increasing shape parameters. We then prove that the well-established results on the probability of a minor outbreak for continuous-time Markov chain (CTMC) epidemic models also hold for the stochastic epidemic models with fixed delays. All theoretical results are verified by numerical simulations implemented by the delay stochastic simulation algorithm (DSSA) in Python. It is shown that DSSA is able to generate exact realizations for underlying delayed models in the context of mathematical epidemiology, and therefore, provides insights into the effect of delays during the outbreak phases of epidemics.
Organometallic halide perovskite materials have attracted great attention in the past few years owing to their excellent optical properties and solution-processable fabrication. However, the further ...development of these lead-based materials is restricted by the toxic heavy-metal element Pb. Herein, we present a dissolution-recrystallization method to fabricate high-quality lead-free Cs3Bi2I9 perovskite nanosheets film and further explore its potential application in solar cells with three different kinds of hole transport materials. The solar cells based on ultrathin Cs3Bi2I9 nanosheets show remarkable improvement in the photovoltaic performance and a high power conversion efficiency of 3.20% has been achieved in the solar cell with CuI as the hole transport material, which is the highest efficiency value of Bi-based perovskite solar cells that has been reported so far. The Cs3Bi2I9 nanosheets based solar cell with CuI also showed a long-term stability in ambient air. These encouraging results of our work demonstrate the possibility of further improvement of the performance of lead-free perovskite solar cells.
Lead-free, air-stable ultrathin Cs3Bi2I9 perovskite nanosheets were prepared by a dissolution-recrystallization method and applied in high efficient solar cells. Display omitted
•A high-quality lead-free Cs3Bi2I9 ultrathin nanosheets film have been fabricated;•A highest efficiency of 3.20% was achieved for Bi-based all-inorganic solar cells;•The device remaining over 57% of the initial efficiency after keeping for 38 days.
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The unique physicochemical properties of (2D) nanomaterials make them well‐suited for use in sustainable energy applications. Many of these materials can be further improved with vacancy engineering. ...This review details recent progress in the vacancy engineering of ultrathin 2D nanomaterials. For clarity, it mainly focuses on various ultrathin 2D materials in three categories: Xa&XaYb‐, MaXb‐, or MaXbYc‐structured materials. Recently developed vacancies in different types of ultrathin 2D materials, as well as their preparation and characterization, are described. Emphasis is placed on the potential electrochemical energy storage and conversion applications of these materials. This review considers the relationship between vacancy properties and material categories of various ultrathin 2D materials in terms of application requirements, preparation, and characterization techniques. The challenges and future outlook of this promising field are summarized.
Recent progress in vacancy‐contained ultrathin 2D nanomaterials and their energy‐related applications are summarized and highlighted. This review provides a new method for classifying ultrathin 2D materials. Based on this, the influence of vacancy engineering in different types of materials is proposed, which provides guidance for the design of vacancies and materials in different energy‐related fields.
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Epidemiological models with the identical basic reproduction number
may behave differently on both short time scale and long time scale. In this paper, we compare the predicted final sizes for ...several deterministic epidemic models and estimate the probabilities of a minor/major outbreak for continuous-time Markov chain (CTMC) models, all epidemic models have the identical
. It is proved that the final size predicted by the epidemic model with homogeneous mixing is larger than with heterogeneous mixing. For CTMC models with heterogeneous mixing, the probabilities of a minor outbreak initiated by superspreaders and non-superspreaders are calculated and compared. For both deterministic modelling and stochastic modelling, numerical simulations are performed to support the mathematical analysis.
The first visible-light-mediated photoredox oxidative approach for generating carbamoyl radicals from oxamic acids is disclosed. Reaction of the generated carbamoyl radicals with electron-deficient ...alkenes opens efficient access to 3,4-dihydroquinolin-2(1H)-ones under mild conditions through a sequence of intermolecular radical addition, cyclization, and aromatization. The process is compatible with a variety of oxamic acids and electron-deficient alkenes, and a wide variety of 3,4-dihydroquinolin-2(1H)-ones were prepared.
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