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Thick electrode was promising to increase the energy density in device (battery or supercapacitor) scale, but always suffered the ion polarization upon high rate discharge. We reported the use of 3D Al foam (current collector) to host graphene (with high surface area but very low packing density) to fabricate 450 ​μm thick electrode with mass loading of 10–15 ​mg ​cm−2. The space confinement effect of Al wires on graphene at any regions offered sufficient ordered diffusion channel of liquids, alleviating the ion polarization significantly, compared to the same thick graphene sheet pasted on 2D Al foil by simulation with COMSOL software. The 100 ​F pouch supercapacitor with ionic liquids at 4 ​V exhibited low contact resistance, high specific capacitance in a wide range of current densities, and simultaneously the volumetric energy density of 18 ​Wh L−1 and the power density of 5 ​kW ​kg−1, far better than those of current commercial device.

Shunpo He,1 Zhenzhen Ye,1 Qingwei Yang,2 Jianzhong Lin,2 Xingyu Chen,2 Zhongjie Chen,2 Liangyi Chen2 1The Graduate School of Fujian Medical University, Fuzhou, People’s Republic of China; 2Department of Neurology, Zhongshan Hospital, Xiamen University, Xiamen, People’s Republic of ChinaCorrespondence: Qingwei Yang; Xingyu ChenDepartment of Neurology, Zhongshan Hospital, Xiamen University, No. 203 of Hubin South Road, Siming District, Xiamen, 361001, People’s Republic of ChinaTel +86 592-2292113Fax +86 592-2590120Email yamgqimgwei@aliyun.com; chemximgyu@163.comBackground and Aim: Transient global amnesia (TGA) was first described by Bender in 1956 and is characterized by sudden, temporary, and anterograde memory loss. This study aimed to explore the possible mechanisms of and lesions responsible for TGA.Methods: Retrospective data were collected from all patients with TGA admitted to Zhongshan Hospital, affiliated with Xiamen University, between October 1, 2011, and October 30, 2018. Information about the TGA condition, previous history, and clinical examination of the TGA and control groups was recorded. Functional magnetic resonance imaging was performed on the patients to explore the possible lesions responsible for TGA.Results: A total of 73 patients with TGA and 73 age- and gender-matched controls were included in the analysis. The differences in the migraine history (9/2, p = 0.038) were statistically significant in both groups, but no statistically significant difference was observed regarding the history of hypertension, diabetes, and other diseases. In addition, seven patients with TGA had lesions located in the hippocampal CA1 region; the dome column and hippocampal CA1 region exist in the same functional loop and play a synergistic role. The average follow-up period in the groups was 36 months. During the follow-up period, no significant differences in cerebral infarction, cerebral hemorrhage, CHD, or TGA attack between the groups were observed.Conclusion: Migraine may be a risk factor of TGA, and cerebral infarction may be one of the pathogeneses. The brain area responsible for TGA may involve a memory loop comprising the hippocampal CA1 region and the fornix column among other parts.Keywords: transient global amnesia, risk factors, magnetic resonance imaging, responsible lesions, prognosis

With the emergence of cloud computing, users are increasingly using storage services of cloud providers to satisfy their storage needs. However, these cloud providers charge at different rates and are not 100% reliable, resulting in occasional service outages. Thus the costs on end users are two folds: (1) cost of storage service, and (2) cost of information loss in cloud service outages. End users require a solution that minimizes the overall cost to balance the storage cost and the probability of successfully retrieving stored objects in cases of provider failures. In this paper, based on the concept of federated cloud agent proposed in our previous work [1], we study the cloud storage management strategy which allows end users to simultaneously deploy storage objects to multiple cloud service providers, based on their unit storage costs and failure behaviors. We propose to use random network coding and a decision model to solve this storage management problem. The random network coding over information objects to be stored in clouds helps simplify the cloud storage management and the decision model forms the foundation of solving the problem in a dynamic environment. We solve the decision model analytically and also propose two practical solutions based on efficient local search algorithms which can achieve near-optimal performance and lower computational complexity. In the experiments, we evaluate the proposed cloud storage strategies against a few reference schemes and find our schemes can achieve a good balance between the information success recovery rate and storage cost.

As the primary productive force, education plays a huge role in the development of modern society. Traditional educational activities mainly focus on the teaching of students’ superficial knowledge and skills, which are no longer able to meet the current society’s demand for talents. At present, it is required to promote the development of in-depth thinking of college students, stimulate their innovation and creativity, and enable students to better contribute to social production. Therefore, it is very important to introduce the concept of deep learning for college students and establish a student-based teaching model. The author mainly uses mobile learning technology to analyze the functional role of mobile learning technology in promoting deep learning activities for college students, and proposes ways to effectively grasp mobile learning technology in future university informatization education activities.

Multi-band orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) technology offers large throughput, low latency and has been adopted in wireless audio/video (AV) network products. The complexity and power consumption, however, are still major hurdles for the technology to be widely adopted. In this paper, we propose a unified synchronizer design targeted for MB-OFDM transceiver that achieves high performance with low implementation complexity. The key component of the proposed synchronizer is a parallel auto-correlator structure in which multiple ACF units are instantiated and their outputs are shared by functional blocks in the synchronizer, including preamble signal detection, time-frequency code identification, symbol timing, carrier frequency offset estimation and frame synchronization. This common structure not only reduces the hardware cost but also minimizes the number of operations in the functional blocks in the synchronizer as the results of a large portion of computation can be shared among different functional blocks. To mitigate the effect of narrowband interference (NBI) on UWB systems, we also propose a low-complexity ACF-based frequency detector to facilitate the design of (adaptive) notch filter in analog/digital domain. The theoretical analysis and simulation show that the performance of the proposed design is close to optimal, while the complexity is significantly reduced compared to existing work.

An analytical framework is developed to study the throughput and routing overhead for proactive and reactive routing strategies in random access mobile ad hoc networks. To characterize the coexistence of the routing control traffic and data traffic, the interaction is modeled as a multi-class queue at each node, where the aggregate control traffic and data traffic are two different classes of customers of the queue. With the proposed model, the scaling properties of the throughput, maximum mobility degree supported by the network and mobility-induced throughput deficiencies are investigated, under both classes of routing strategies. The proposed analytical model can be extended to evaluate various routing optimization techniques as well as to study routing/relaying strategies other than conventional proactive or reactive routing. The connection between the derived throughput result and some well-known network throughput capacity results in the literature is also established.

In order to adapt to time-varying wireless channels, various channel-adaptive schemes have been proposed to exploit inherent spatial diversity in mobile/wireless ad hoc networks where there are usually alternate next-hop relays available at a given forwarding node. However, current schemes along this line are designed based on heuristics, implying room for performance enhancement. To seek a theoretical foundation for improving spatial diversity gain, we formulate the selection of the next-hop as a sequential decision problem and propose a general "optimal stopping relaying (OSR)" framework for designing such next-hop diversity schemes. As a particular example, assuming Rayleigh fading channels, we implement an OSR strategy to optimize information efficiency (IE) in a protocol stack consisting of greedy perimeter stateless routing (GPSR) and IEEE 802.11 MAC protocols. We present mathematical analysis of the proposed OSR together with other strategies in literature for a single forwarding node. In addition, we perform extensive simulations (using QualNet) to evaluate the end-to-end performance of these relaying strategies in a multi-hop network. Both the mathematical and simulation results demonstrate the superiority of OSR over other existing schemes.

With the emergence of cloud computing, users are increasingly using storage services of cloud providers to satisfy their storage needs. However, these cloud providers are not 100% reliable, resulting in periodic service outages. End users require a solution that minimizes the impact of cloud service outages and optimizes the chances of successfully retrieving stored objects in cases of provider failures. In this paper, we propose to build a federated cloud agent, enabling end users to simultaneously deploy storage objects to multiple cloud service providers, based on their unit storage costs and failure probabilities. We study two service provider failure models: the first case assumes that at most one service provider fails at any given time, and the second case assumes that cloud service providers may fail independently with certain probabilities. We cast both scenarios as constrained optimization problems to minimize the overall storage cost while enhancing the chances of recovering all the storage objects in case of service outages. In the experiments, we evaluated the proposed optimal storage schemes against a fixed server deployment strategy and find our schemes can achieve good recovery ratios, while incurring minimal storage costs.

Efficient transmission control (e.g., power/rate control) in the physical layer, link scheduling in the link layer and routing in the network layer are critical design issues of wireless ad hoc networks. By considering both the quality-of-service and the utilization of resources under the temporally correlated uncertainties of the network conditions, a sequential decision framework is proposed for protocol design and layering. By observing that there are usually different performance concerns in the network layer versus lower layers, two correlated sequential decision models for the operations at different layers are proposed. With the decision model in the link and physical layers, scheduling and transmission control are jointly optimized. By adding a decision model in the network layer, the benefit of cross-layer information is quantified and the optimal routing/forwarding strategy is characterized. Practical algorithms based on the proposed decision models are also developed to achieve optimal/near-optimal performance.

We develop an analytical framework to study the throughput and routing overhead for proactive and reactive routing strategies in random access mobile ad hoc networks. To characterize the coexistence of the routing control traffic and data traffic, we model the interaction as a multi-class queue model at each node, where the aggregate control traffic and data traffic are two different classes of customers of the queue. We investigate the scaling property of the throughput, maximum mobility degree supported by the network and mobility-induced throughput deficiencies, under both classes of routing strategies. The proposed analytical model can be extended to incorporate various optimization techniques in routing. We present one exemplary technique and discuss its impacts on the scaling properties of throughput and routing overhead. The connection between the derived throughput result and some well-known network throughput capacity results in the literature is also addressed.

We consider the scenario of distributed data aggregation in wireless sensor networks, where each sensor can obtain and estimate the information of the whole sensing field through local data exchange and aggregation. The intrinsic trade-off between energy and delay in aggregation operations imposes a crucial question on nodes to decide optimal instants for forwarding their samples. The samples could be composed of the information from their own sensor readings or an aggregation of information with other samples forwarded from neighboring nodes. By considering the randomness of the sample arrival instants and the uncertainty of the availability of the multiaccess communication channel due to the asynchronous nature of information exchange among neighboring nodes, we propose a decision process model to analyze this problem and determine the optimal decision policies at nodes with local information. We show that, once the statistics of the sample arrival and the availability of the channel satisfy certain conditions, there exist optimal control-limit type policies which are easy to implement in practice. In the case that the required conditions are not satisfied, we provide two learning algorithms to solve a finite-state approximation model of the decision problem. Simulations on a practical distributed data aggregation scenario demonstrate the effectiveness of the developed policies, which can also achieve a desired energy-delay tradeoff.

In mobile ad hoc networks, relaying is one of the most fundamental functions. In this paper, we analyze the stability of several relaying strategies. By using the notion of node lifetime instead of the commonly used link lifetime, our analysis offers a complementary and unique finding not available in the literature previously. Our results show that a route of parallel relays have a significantly longer lifetime than a route of serial relays although the latter of the two has previously predominated the networking research.

In order to adapt to the time-varying nature of wireless channels, various channel-adaptive schemes have been proposed to exploit inherent spatial diversity in wireless ad hoc networks where there are usually alternate forwarding nodes available at a given forwarding node. However, existing schemes along this line are designed based on heuristics, implying room for performance enhancement. Thereby, to seek a theoretical foundation for improving spatial diversity gain, we formulate the selection of the next-hop relay as a sequential decision problem and derive a general "Optimal Stopping Relaying (OSR)" framework for designing such spatial-diversity schemes. As a particular example, assuming Rayleigh fading channels, we implement an OSR strategy to optimize information efficiency (IE) in a protocol stack consisting of Greedy Perimeter Stateless Routing (GPSR) and IEEE 802.11 MAC protocols. We present an analysis of the algorithm for a single node. In addition, we perform extensive simulations (using QualNet) to evaluate the end-to-end performance of the proposed forwarding strategy. The results demonstrate the superiority of OSR over other existing schemes.

For several decades, research activities in mobile ad hoc networking have predominantly relied on the notion of serial relays where a data packet hops from one node to another in a serial fashion. Recent research activities in signal processing and information theory suggest that parallel relays have a greater potential than serial relays. In this paper, a significant diversity gain of using parallel relays over serial relays is highlighted, the lifetimes of a single-path route of parallel relays and multi-path routes of serial relays are compared, and the routing overheads for each type of routes are also investigated. This study strongly supports that parallel relays have great advantages over serial relays in dense and mobile ad hoc networks.

Ultra-wideband (UWB) systems spread the transmitted signal power over an extremely large frequency band, and the power spectral density of the signal is very low. Due to the wide bandwidth of the transmitted signal, UWB signal energy spreads over the frequency bands allocated to other radio systems. Evaluating the interference issues of these narrowband systems to UWB systems in its overlay band is an important issue for understanding and designing efficient UWB systems. An analysis of the power spectral density (PSD) of generic narrowband signals is presented. The theoretical and simulation results reveal that the bit-error-rate (BER) performance of a direct sequence UWB (DS-UWB) system with a minimum mean square error (MMSE) receiver is robust in the presence of narrowband interference caused by existing applications.

Ultra-wideband (UWB) technology is one of the promising solutions for short-range indoor wireless communication applications. UWB systems spread the transmitted signal power over an extremely large frequency band, and the power spectral density of the signal is very low. Due to the wide bandwidth of the transmitted signal, UWB signal energy will spread over the frequency bands allocated to other radio systems. In order to evaluate the effects of UWB system to narrowband systems (such as IEEE802.11a wireless LAN) in its overlay band, it is important to understand and quantify the power spectral density (PSD) of UWB signal. In this paper, a detailed analysis on the PSD of direct sequence coded UWB (DS-UWB) signal is presented. The theoretical and simulation results reveal that the interfering DS-UWB power can be reduced by regulating UWB chip rate, pulse shape, pulse width and scrambling codes in the frequencies of victim narrowband systems.