Manganese based layered oxides with modulated electronic and thermodynamic properties for sodium ion batteries

Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, the Jahn–Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na0.833[Li0.25Mn0.75]O2 can not only suppress the Jahn–Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials

Robust and Agile System against Fault and Anomaly Traffic in Software Defined Networks

The main advantage of software defined networking (SDN) is that it allows intelligent control and management of networking though programmability in real time. It enables efficient utilization of network resources through traffic engineering, and offers potential attack defense methods when abnormalities arise. However, previous studies have only identified individual solutions for respective problems, instead of finding a more global solution in real time that is capable of addressing multiple situations in network status. To cover diverse network conditions, this paper presents a comprehensive reactive system for simultaneously monitoring failures, anomalies, and attacks for high availability and reliability. We design three main modules in the SDN controller for a robust and agile defense (RAD) system against network anomalies: a traffic analyzer, a traffic engineer, and a rule manager. RAD provides reactive flow rule generation to control traffic while detecting network failures, anomalies, high traffic volume (elephant flows), and attacks. The traffic analyzer identifies elephant flows, traffic anomalies, and attacks based on attack signatures and network monitoring. The traffic engineer module measures network utilization and delay in order to determine the best path for multi-dimensional routing and load balancing under any circumstances. Finally, the rule manager generates and installs a flow rule for the selected best path to control traffic. We implement the proposed RAD system based on Floodlight, an open source project for the SDN controller. We evaluate our system using simulation with and without the aforementioned RAD modules. Experimental results show that our approach is both practical and feasible, and can successfully augment an existing SDN controller in terms of agility, robustness, and efficiency, even in the face of link failures, attacks, and elephant flows

Development of Cloud-Based UAV Monitoring and Management System

Unmanned aerial vehicles (UAVs) are an emerging technology with the potential to revolutionize commercial industries and the public domain outside of the military. UAVs would be able to speed up rescue and recovery operations from natural disasters and can be used for autonomous delivery systems (e.g., Amazon Prime Air). An increase in the number of active UAV systems in dense urban areas is attributed to an influx of UAV hobbyists and commercial multi-UAV systems. As airspace for UAV flight becomes more limited, it is important to monitor and manage many UAV systems using modern collision avoidance techniques. In this paper, we propose a cloud-based web application that provides real-time flight monitoring and management for UAVs. For each connected UAV, detailed UAV sensor readings from the accelerometer, GPS sensor, ultrasonic sensor and visual position cameras are provided along with status reports from the smaller internal components of UAVs (i.e., motor and battery). The dynamic map overlay visualizes active flight paths and current UAV locations, allowing the user to monitor all aircrafts easily. Our system detects and prevents potential collisions by automatically adjusting UAV flight paths and then alerting users to the change. We develop our proposed system and demonstrate its feasibility and performances through simulation

Teaching-Learning Activity Modeling Based on Data Analysis

Numerous studies are currently being carried out on personalized services based on data analysis to find and provide valuable information about information overload. Furthermore, the number of studies on data analysis of teaching-learning activities for personalized services in the field of teaching-learning is increasing, too. This paper proposes a learning style recency-frequency-durability (LS-RFD) model for quantified analysis on the level of activities of learners, to provide the elements of teaching-learning activities according to the learning style of the learner among various parameters for personalized service. This is to measure preferences as to teaching-learning activity according to recency, frequency and durability of such activities. Based on the results, user characteristics can be classified into groups for teaching-learning activity by categorizing the level of preference and activity of the learner

Pseudocapacitive Behavior and Ultrafast Kinetics from Solvated Ion Cointercalation into MoS2 for Its Alkali Ion Storage

The popularization of electric vehicles and the increasing use of electronic devices highlight the importance of fast charging technology. The charging process of lithium secondary battery is basically limited by a series of processes on the anode side, which include desolvation of lithium ions as well as lithium diffusion through SEI and the anode material. These series of reactions are kinetically sluggish, leading to insufficient power density. Therefore, to unravel this problem, we need to either accelerate each step or skip over some of the steps to make the whole charging process shorter. A solvated ion cointercalation into graphite has turned out to successfully exclude both desolvation of lithium ions and SEI film formation to achieve high kinetics with graphite. Herein, the solvated ion cointercalation into MoS2 demonstrated that it can help to remove desolvation of alkali ions as well as SEI formation, and thereby ultrahigh kinetics and long-term cyclability are attained by the characteristic pseudocapacitive behavior irrespective of the charge/discharge mechanism of anode materials. This phenomenon occurred between 1 and 3 V with MoS2 anode in a novel electrolyte (i.e., 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethoxyethane/tetraglyme (DME/TGM, v/v = 3:1 by volume)). In detail, its capacity retentions slightly decreased from 95.9% to 91.8%, 89.7%, 87.7%, 84.8%, 77.0%, 67.9%, and 55.1% as current densities increased from 0.1 to 0.2, 0.5, 1, 2, 5, 10, and 20 A g(-1), respectively. Meanwhile, it delivered a capacity retention of 90.6% even after 2000 cycles at 1 A g(-1). Interestingly, MoS2 with solvated ion cointercalation can display much higher capacity (273.5 mAh g(-1)) than that of graphite (<120 mAh g(-1)). As a result of the investigation on its reaction mechanism, the solvated ion cointercalation was validated to occur during the discharge process in MoS2 anode and thus induce pseudocapactive sodiation as well as exclude SEI film formation. This research may help to suggest an alternative way to enhance the kinetics of anode materials for high-power alkali ion batteries.

Multifunctionalities of Graphene for Exploiting a Facile Conversion Reaction Route of Perovskite CoSnO3 for Highly Reversible Na Ion Storage

Transition-metal oxides are promising anode materials for sodium ion batteries (SIBs) and have attracted a great deal of attention because of their natural abundance and high theoretical capacities. However, they suffer from low conductivity and large volumetric/structural variation during sodiation/desodiation processes, leading to unsatisfactory cycling stability and poor rate capability. This study proposes a novel conversion reaction using CoSnO3 (CSO) nanocubes uniformly wrapped in graphene nanosheets, which are fabricated using a wet-chemical strategy followed by low-temperature heat treatment. This optimized composite exhibits durable cyclability and high rate capability, which can be attributed to the strong interaction between reduced graphene oxide and CSO through its surface oxygen moieties. It develops a facile conversion reaction route, thereby leading to SnO2 formation during charging. This interactive phenomenon further contributes to improving the reaction kinetics and restraining the volume expansion during cycling. This study may provide a facile approach for addressing irreversible conversion of high-capacity oxide materials toward advanced SIBs

CNT@Ni@Ni–Co silicate core–shell nanocomposite: a synergistic triple-coaxial catalyst for enhancing catalytic activity and controlling side products for Li–O2 batteries

A great challenge in the application of carbon-based materials to Li-O-2 batteries is to prevent the formation of carbonate-based side products, thereby extending the cycle life of Li-O-2 batteries. Herein, for the first time, CNT@Ni@NiCo silicate core-shell nanocomposite is designed and used as a cathode catalyst in Li-O-2 batteries. This nanocomposite shows a promising electrochemical performance with a discharge capacity of 10 046 mA h g(cat)(-1) and a low overpotential of 1.44 V at a current density of 200 mA g(cat)(-1), and it can sustain for more than 50 cycles within the voltage range of 2-4.7 V. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations prove that the formation of Li2CO3 and other side products are prevented, likely due to the encapsulation of CNTs by NiCo silicates and Ni nanoparticles, which may help decompose the side products. Finally, the synergistic effects, which are contributed by the high electrical conductivity of CNTs, high surface area, the high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of NiCo silicate, and the simple decomposition of side products by Ni nanoparticles enable outstanding performance of the CNT@Ni@NiCo silicate core-shell nanocomposite as a cathode catalyst for Li-O-2 batteries

Achieving outstanding Li+-ORR and -OER activities via edge- and corner-embedded bimetallic nanocubes for rechargeable Li-O-2 batteries

The shape of catalysts has been regarded as a crucial physical factor to determine its catalytic activity in various applications. However, very little is known about the catalyst shape dependent activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the cathode of Li-O-2 battery. Hence, we synthesized Pt3Co nanocube (NC) for the comparison with Pt3Co nanoparticle (NP) by regulating the ratio of reducer (hexadecanediol; HDD) amount. Consequently, we could report on very high capacity (10,000 mA h g(carbon)(-1)), superb rate capability (3500 mA h g(caribon)(-1) at 2000 mA g(caribon)(-1)) and high reversibility of Lithium-O-2 batteries using Pt3Co NC catalysts. Particularly, the Pt3Co NCs catalyst exhibited a low OER potential of 3.1 V, providing the highest round trip efficiency of similar to 86.5% at a current density of 200 mA g(caribon)(-1) which is much superior to NPs catalyst. (C) 2015 Elsevier Ltd. All rights reserved.

Anisotropic surface modulation of Pt catalysts for highly reversible Li-O 2 batteries: High index facet as a critical descriptor

The surface structure of solid catalysts has been regarded as a critical descriptor for determining the catalytic activities in various applications. However, structure-dependent catalytic activities have been rarely understood for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) within Li-O-2 batteries. Here, we succeeded in the preparation of a Pt catalyst with an anisotropic structure and demonstrated its high catalytic activity in nonaqueous Li-O-2 batteries. The cathode incorporating Pt exposed with high-index {411} facets showed greatly enhanced ORR and OER performance in comparison to commercial Pt/C cathode. The anisotropic Pt catalyst improved ORR activity with a large capacity of 12 985 mAh g(carbon)(-1), high rate performance, and stable cyclic retention up to 70 cycles with the capacity limited to 1000 mAh g(carbon)(-1) Furthermore, the anisotropic Pt catalyst exhibited high round-trip efficiency of similar to 87% with a low OER potential (3.1 V) at a current density of 200 mA g(carbon)(-1) Our first-principles calculations revealed that the high-index facets, which contain step edge, kink, and ledge sites, are significantly more reactive than the lown terms of surface energy and O-binding energy.