In this paper, we investigate a multiuser mobile edge computing (MEC)-aided smart Internet of vehicle (IoV) network, where one edge server can help accomplish the intensive calculating tasks from the ...vehicular users. For the MEC networks, most existing works mainly focus on minimizing the system latency to guarantee the user’s quality of service (QoS) through designing some offloading strategies, which, however, fail to consider the pricing from the server and hence fail to take into account the budget constraint from the users. To address this issue, we jointly incorporate the budget constraint into the system design of the MEC-based IoV networks and then propose a joint deep reinforcement learning (DRL) approach combined with the convex optimization algorithm. Specifically, a deep Q-network (DQN) is firstly used to make the offloading decision, and then, the Lagrange multiplier method is employed to allocate the calculating capability of the server to multiple users. Simulations are finally presented to demonstrate that the proposed schemes outperform the conventional ones. In particular, the proposed scheme can effectively reduce the system latency by up to 56% compared to the conventional schemes.
The Nanjing Massacre of 1937 is a historical tragedy that is hard to erase from the collective memory of Nanjing residents. Since 1982, the Nanjing Massacre Memorial Hall and other monuments have ...been established as a Chinese response to the Japanese revision of their high school history textbooks, and these facilities have opened a mnemonic channel for the Nanjing people to link history to reality. In the Nanjing people's traumatic memory, the historical facts of the Nanjing Massacre of the contemporary nationalistic sentiments are entangled and symbiotic. Many survivors have profound factual memory of the massacre, yet they have shown tolerance and forgiveness to the victimizers. While their memory has transcended the primitive stage of retaliation, the traumatic memory of mankind should be transformed into invaluable resource of the human endeavor to pursue peace.
Macroporous 3D carbon doped with nitrogen confined MoOx catalyst was designed and synthesized via a cost-effective manner and firstly expanded to the field of oxidative desulfurization. The catalyst ...exhibited highly excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.9% and sulfur content was wiped out from 800 ppm to 10 ppm.
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Macroporous 3D carbon doped with nitrogen confined Mo catalyst (MoOx@CN) had been prepared by a facile one-step pyrolysis technique using silica as a template and was employed for oxidative desulfurization (ODS) of dibenzothiophene (DBT) in model fuel with H2O2 as oxidant. The effect of different operating conditions (i.e., reaction temperature and time, catalyst dosage, H2O2/DBT (O/S) molar ratio) were also systematic investigated. Under the optimal reaction condition, MoOx@CN catalyst exhibited highly excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.9% and sulfur content was wiped out from 800 ppm to 10 ppm. Due to the robust 3D structure promoting rapid transfer, in addition to the increased number of active sites induced by the Mo vacancies, the catalyst, prepared using chitosan and ammonium heptamolybdate in a mass ratio of 1:0.5, displayed rapid kinetics and low activation energy in the oxidation of dibenzothiophene. Moreover, it exhibited excellent recyclability after five cycles without any obvious decrease in catalytic activity for the oxidative desulfurization reaction.
This paper proposes a bio-inspired hull shape (BHS) for AUV by studying and modeling the body shape of humpback whales. Among factors affecting hydrodynamic characteristics, this paper considers both ...the hull drag and displacement volume to optimize the BHS, which profitably improve the space utilization and voyage of the AUV. The optimization is conducted by a surrogate model using response surface methodology (RSM), during which the translational propagation Latin hypercube design (TPLHD) is adopted to obtain sampling points. In order to verify the optimization results of BHS, the drag computations for BHS and eight typical hull shapes of existing typical or bionic AUVs are performed for comparison under conditions of similar volume, wet surface area, body length and attachments. A scaled-down model of BHS with attachments is then designed, manufactured and carried out a towing tank test. The drag measured in the towing tank test is basically the same as the simulation result, with the average relative error of 3.68% at 4m/s. The result of the shape optimization performed with the RSM is effective. Furthermore, the proposed BHS is highly suitable for underwater vehicles with requirements for longer distance, higher speed or better sensor carrying capacity.
The sailing efficiency of an underwater glider, an important type of marine environment detection and data collection equipment, directly affects its range and duration. The zero-angle-of-attack ...gliding can be achieved by adjusting the wing installation angle to minimize the drag and improve the sailing efficiency, and thus further improving performance of the glider. This paper first presents the dynamic characteristics of a hybrid-driven underwater glider with a certain wing installation angle when it is sailing at zero angle of attack in buoyancy-driven mode and hybrid-driven mode. In buoyancy-driven mode, with a given wing installation angle, the glider can achieve zero-angle-of-attack gliding only at a specific glide angle. In hybrid-driven mode, due to the use of a propulsion system, the specific glide angle that allows the zero-angle-of-attack gliding in buoyancy-driven mode is expanded to a glide angle range bounded by zero degrees. Then, the energy consumption per meter is introduced as an indicator of sailing efficiency, and the effects of glide angle and wing installation angle on sailing efficiency of the zero-angle-of-attack glider in two driving modes are studied under the conditions of given net buoyancy and given speed, respectively. Accordingly, the optimal wing installation angle for maximizing the sailing efficiency is proposed. Theoretical analysis shows that the sailing efficiency of a zero-angle-of-attack glider can be higher than that of a traditional glider. Considering the requirements of different measurement tasks, a higher sailing efficiency can be achieved by setting reasonable parameters and selecting the appropriate driving mode.
Here we experimentally study the microwave absorption and near-field radiation behavior of monolayer and few-layer, large-area CVD graphene in the C and X bands. Artificial stacking of CVD graphene ...reduces the sheet resistance, as verified by non-contact microwave cavity measurements and four-probe DC resistivity. The multilayer stacked graphene exhibits increased absorption determined by the total sheet resistance. The underlying mechanism could enable us to apply nanoscale graphene sheets as optically transparent radar absorbers. Near-field radiation measurements show that our present few-layer graphene patches with sheet resistance more than 600Ω/sq exhibit no distinctive microwave resonance and radiate less electromagnetic power with increasing layers; however, our theoretical prediction suggests that for samples to be practical as microwave antennas, doped multilayer graphene with sheet resistance less than 10Ω/sq is required.
The contact resistance between the bipolar plate (BPP) and the gas diffusion layer (GDL) is an important factor contributing to the power loss in proton exchange membrane (PEM) fuel cells. At present ...there is still not a well-developed method to estimate such contact resistance. This paper proposes two effective methods for estimating the contact resistance between the BPP and the GDL based on an experimental contact resistance–pressure constitutive relation. The constitutive relation was obtained by experimentally measuring the contact resistance between the GDL and a flat plate of the same material and processing conditions as the BPP under stated contact pressure. In the first method, which was a simplified prediction, the contact area and contact pressure between the BPP and the GDL were analyzed with a simple geometrical relation and the contact resistance was obtained by the contact resistance–pressure constitutive relation. In the second method, the contact area and contact pressure between the BPP and GDL were analyzed using FEM and the contact resistance was computed for each contact element according to the constitutive relation. The total contact resistance was then calculated by considering all contact elements in parallel. The influence of load distribution on contact resistance was also investigated. Good agreement was demonstrated between experimental results and predictions by both methods. The simplified prediction method provides an efficient approach to estimating the contact resistance in PEM fuel cells. The proposed methods for estimating the contact resistance can be useful in modeling and optimizing the assembly process to improve the performance of PEM fuel cells.
Hybrid-driven technology, which can improve the sailing performance of underwater gliders (UGs), has been successfully used in ocean observation. However, a hybrid-driven UG (HUG) with an added tail ...propeller is still unable to achieve backward and turning motion with a body length radius, and the hydrodynamic pitch moment acting on the HUG that is mainly caused by the fixed-wing makes it difficult to achieve high-precision attitude control during fixed-depth navigation. To solve this problem, a two-degree-of-freedom bioinspired controllable wing mechanism (CWM) is proposed to improve the maneuverability and cruising ability of HUGs. The CWM can realize five motion modes: modifying the dihedral angle or anhedral angle, changing the frontal area of the wing, switching the wing from horizontal to be a vertical rudder, flapping the wing as propulsion, and rotating the wing as a vector propeller. First, the design process of the CWM is provided, and hydrodynamic forces in each motion mode of three CWMs with different trailing edge sweepback angles (TESA) and attitude angles are analyzed through computational fluid dynamics simulation. The relationship between hydrodynamics and the attitude angles or TESA of the CWM is analyzed. Then, experiments are conducted to measure the hydrodynamics of the CWM when it is in a flapping wing mode and rotating the wing as a vector propeller, respectively. The hydrodynamic forces obtained from the simulation are consistent with data measured by a force sensor, proving the credibility of the simulated hydrodynamics. Subsequently, by applying the results of the hydrodynamic force in this study, the flapping trajectory of the wingtip is planned using the cubic spline interpolation method. Furthermore, two underwater demo vehicles with a pair of CWMs are developed, and experiments are conducted in a water tank, further validating and demonstrating the feasibility of the proposed CWM.
A great amount of work on antennas and propagation for body-centric wireless communication has been studied at frequencies up to X band; however, on-body radio propagation at ...millimeter/sub-millimeter wave frequencies still remains largely unexplored. This paper presents a study of on-body radio propagation at 94 GHz, particularly focusing on the analysis of specific channels such as waist-to-torso and head-to-shoulder links. Measured data are compared with results obtained with numerical simulations emphasizing the sensitivity of the simulated path loss to the positioning of the receivers with respect to the human body.
Accurate quantitative plankton observation is significant for biogeochemistry and environmental monitoring. However, current observation equipment is mostly shipborne, and there is a lack of ...long-term, large-scale, and low-cost methods for plankton observation. This paper proposes a solution to investigate plankton using a Seascan holographic camera equipped with a “Petrel-II” underwater glider for a longer time sequence and at a larger scale. Aiming at the new challenges of low efficiency and low accuracy of holographic image processing after integrating holographic imaging systems and underwater gliders, a novel plankton data analysis method applicable to Digital Holographic Underwater Gliders (DHUG) is proposed. The algorithm has the following features: (1) high efficiency: the algorithm breaks the traditional hologram information extraction order, focusing only on the key regions in the hologram and minimizing the redundant computation; (2) high accuracy: applying the Sobel variance algorithm to the plankton in the hologram to focus the plane extraction significantly improves the focus accuracy; and (3) high degree of automation: by integrating a convolutional neural network, the algorithm achieves a fully automated analysis of the observed data. A sea test in the South China Sea verified that the proposed algorithm could greatly improve the problems of severe plankton segmentation and the low focusing accuracy of traditional information extraction algorithms. It also proved that the DHUG plankton survey has great potential.
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