Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods and Na0.33V2O5 center dot 1.5H(2)O/RGO composite fabricated by a facile one pot synthesis and its lithium storage behavior

In this work, Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods and Na0.33V2O5 center dot 1.5H(2)O/reduced graphene oxide (RGO) composites have been prepared through a facile hydrothermal route in acidic medium at 200 degrees C for 2 days. The hydrothermally derived products have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-Visible spectroscopy, Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and electrochemical discharge-charge cycling in lithium ion battery. XRD pattern exhibits the layered structure of Na0.33V2O5 center dot 1.5H(2)O and the composite shows the presence of RGO at 2 theta = 25.8 degrees. FTIR spectrum shows that the band at 760 cm(-1) could be assigned to a V-OH2 stretching mode due to coordinated water. Raman spectrum shows that the band at 264 cm(-1) is due to the presence of water molecules between the layers. FESEM/TEM micrographs reveal that the products consist of nanorings of inner diameter 5 mu m and thickness of the ring is found to be 200-300 nm. Addition of exfoliated graphene oxide (EGO) destroys the formation of rings. The reduction of EGO sheets into RGO is also evidenced by the red shift of the absorbance peak from 228 nm to 264 nm. In this composite Na0.33V2O5 center dot 1.5H(2)O nanorods may adhere to the surface of RGO and/or embedded in the RGO nanosheets. As a result, an effective three-dimensional conducting network was formed by bridging RGO nanosheets, which can facilitate electron transport effectively and thus improve the kinetics and rate performance of Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods. The Na0.33V2O5 center dot 1.5H(2)O/RGO composites exhibited a discharge capacity of 340 mAh g(-1) at a current density of 0.1 mA g(-1) and also an improved cyclic stability. RGO plays a `flexible confinement' function to enwrap Na0.33V2O5 center dot 1.5H(2)O nanorods, which can compensate for the volume change and prevent the detachment and agglomeration of pulverized Na0.33V2O5 center dot 1.5H(2)O, thus extending the cycling life of the electrode. A probable reaction mechanism for the formation of Na0.33V2O5 center dot 1.5H(2)O nanorings is also discussed. (C) 2012 Elsevier B.V. All rights reserved.

Mobile agent based TCP attacker identification in MANET using the traffic history (MAITH)

TCP attacks are the major problem faced by Mobile Ad hoc Networks (MANETs) due to its limited network and host resources. Attacker traceback is a promising solution which allows a victim to identify the exact location of the attacker and hence enables the victim to take proper countermeasure near attack origins, for forensics and to discourage attackers from launching the attacks. However, attacker traceback in MANET is a challenging problem due to dynamic network topology, limited network and host resources such as memory, bandwidth and battery life. We introduce a novel method of TCP attacker Identification in MANET using the Traffic History - MAITH. Based on the comprehensive evaluation based on simulations, we showed that MAITH can successfully track down the attacker under diverse mobile multi-hop network environment with low communication, computation, and memory overhead.

Sonic hedgehog-Dependent Induction of MicroRNA 31 and MicroRNA 150 Regulates Mycobacterium bovis BCG-Driven Toll-Like Receptor 2 Signaling

Hedgehog (HH) signaling is a significant regulator of cell fate decisions during embryogenesis, development, and perpetuation of various disease conditions. Testing whether pathogen-specific HH signaling promotes unique innate recognition of intracellular bacteria, we demonstrate that among diverse Gram-positive or Gram-negative microbes, Mycobacterium bovis BCG, a vaccine strain, elicits a robust activation of Sonic HH (SHH) signaling in macrophages. Interestingly, sustained tumor necrosis factor alpha (TNF-alpha) secretion by macrophages was essential for robust SHH activation, as TNF-alpha(-/-) macrophages exhibited compromised ability to activate SHH signaling. Neutralization of TNF-alpha or blockade of TNF-alpha receptor signaling significantly reduced the infection-induced SHH signaling activation both in vitro and in vivo. Intriguingly, activated SHH signaling downregulated M. bovis BCG-mediated Toll-like receptor 2 (TLR2) signaling events to regulate a battery of genes associated with divergent functions of M1/M2 macrophages. Genome-wide expression profiling as well as conventional gain-of-function or loss-of-function analysis showed that SHH signaling-responsive microRNA 31 (miR-31) and miR-150 target MyD88, an adaptor protein of TLR2 signaling, thus leading to suppression of TLR2 responses. SHH signaling signatures could be detected in vivo in tuberculosis patients and M. bovis BCG-challenged mice. Collectively, these investigations identify SHH signaling to be what we believe is one of the significant regulators of host-pathogen interactions.

A multi-winding transformer based power converter topology for a growing DC Micro-grid structure

A DC micro-grid essentially consists of power ports, bidirectional power converter and a controller structure that enables the control of dynamic power flow. In this paper, a prototype of a micro-grid structure using a recently proposed multi-winding transformer based power converter has been implemented. The power converter topology is further extended to multiple transformer cores in order to form a growing micro-grid structure. Additionally, modifications have been made in order to incorporate a battery charge controller with the main power circuit. All the other advantages of the power converter and its control scheme are still preserved.

Li diffusion through doped and defected graphene

We investigate the effect of nitrogen and boron doping on Li diffusion through defected graphene using first principles based density functional theory. While a high energy barrier rules out the possibility of Li-diffusion through the pristine graphene, the barrier reduces with the incorporation of defects. Among the most common defects in pristine graphene, Li diffusion through the divacancy encounters the lowest energy barrier of 1.34 eV. The effect of nitrogen and boron doping on the Li diffusion through doped defected-graphene sheets has been studied. N-doping in graphene with a monovacancy reduces the energy barrier significantly. The barrier reduces with the increasing number of N atoms. On the other hand, for N doped graphene with a divacancy, Li binds in the plane of the sheet, with an enhanced binding energy. The B doping in graphene with a monovacancy leads to the enhancement of the barrier. However, in the case of B-doped graphene with a divacancy, the barrier reduces to 1.54 eV, which could lead to good kinetics. The barriers do not change significantly with B concentration. Therefore, divacancy, B and N doped defected graphene has emerged as a better alternative to pristine graphene as an anode material for Li ion battery.

Role of silica nanoparticles in conductivity enhancement of nanocomposite solid polymer electrolytes: (PEG(x) NaBr): ySiO(2)

Nanocomposite solid polymer electrolytes (NCSPEs) with conducting species other than Li ions are being investigated for solid-state battery applications. Pristine solid polymer electrolytes (SPEs) do not show ionic conductivity suitable for batteries. Addition of inert fillers to SPEs is known to enhance the ionic conductivity. In this paper, we present the role of silica nanoparticles in enhancing the ionic conductivity in NCSPEs with sodium as conducting species. Sodium bromide is complexed with the host polyethylene glycol polymer by solution cast method and silica nanoparticles (SiO2, average particle size 7 nm) are incorporated into the complex in small amounts. The composites are characterized by powder XRD and IR spectroscopy. Conductivity measurements are undertaken as a function of concentration of salt and also as a function of temperature using impedance spectroscopy. Addition of silica nanoparticles shows an enhancement in conductivity by 1-2 orders of magnitude. The results are discussed in terms of interaction of nanoparticles with the nonconducting anions.

Transmit Power Control Policies for Energy Harvesting Sensors With Retransmissions

This paper addresses the problem of finding outage-optimal power control policies for wireless energy harvesting sensor (EHS) nodes with automatic repeat request (ARQ)-based packet transmissions. The power control policy of the EHS specifies the transmission power for each packet transmission attempt, based on all the information available at the EHS. In particular, the acknowledgement (ACK) or negative acknowledgement (NACK) messages received provide the EHS with partial information about the channel state. We solve the problem of finding an optimal power control policy by casting it as a partially observable Markov decision process (POMDP). We study the structure of the optimal power policy in two ways. First, for the special case of binary power levels at the EHS, we show that the optimal policy for the underlying Markov decision process (MDP) when the channel state is observable is a threshold policy in the battery state. Second, we benchmark the performance of the EHS by rigorously analyzing the outage probability of a general fixed-power transmission scheme, where the EHS uses a predetermined power level at each slot within the frame. Monte Carlo simulation results illustrate the performance of the POMDP approach and verify the accuracy of the analysis. They also show that the POMDP solutions can significantly outperform conventional ad hoc approaches.

Employing synergistic interactions between few-layer WS2 and reduced graphene oxide to improve lithium storage, cyclability and rate capability of Li-ion batteries

The aim of the contribution is to introduce a high performance anode alternative to graphite for lithium-ion batteries (LiBs). A simple process was employed to synthesize uniform graphene-like few-layer tungsten sulfide (WS2) supported on reduced graphene oxide (RGO) through a hydrothermal synthesis route. The WS2-RGO (80:20 and 70:30) composites exhibited good enhanced electrochemical performance and excellent rate capability performance when used as anode materials for lithium-ion batteries. The specific capacity of the WS2-RGO composite delivered a capacity of 400-450 mAh g(-1) after 50 cycles when cycled at a current density of 100 mA g(-1). At 4000 mA g(-1), the composites showed a stable capacity of approximately 180-240 mAh g(-1), respectively. The noteworthy electrochemical performance of the composite is not additive, rather it is synergistic in the sense that the electrochemical performance is much superior compared to both WS2 and RGO. As the observed lithiation/delithiation for WS2-RGO is at a voltage 1.0 V (approximate to 0.1 V for graphite, Li* /Li), the lithium-ion battery with WS2-RGO is expected to possess high interface stability, safety and management of electrical energy is expected to be more efficient and economic. (C) 2013 Elsevier Ltd. All rights reserved.

Hybrid Energy Harvesting Wireless Systems: Performance Evaluation and Benchmarking

Energy harvesting sensor (EHS) nodes provide an attractive and green solution to the problem of limited lifetime of wireless sensor networks (WSNs). Unlike a conventional node that uses a non-rechargeable battery and dies once it runs out of energy, an EHS node can harvest energy from the environment and replenish its rechargeable battery. We consider hybrid WSNs that comprise of both EHS and conventional nodes; these arise when legacy WSNs are upgraded or due to EHS deployment cost issues. We compare conventional and hybrid WSNs on the basis of a new and insightful performance metric called k-outage duration, which captures the inability of the nodes to transmit data either due to lack of sufficient battery energy or wireless fading. The metric overcomes the problem of defining lifetime in networks with EHS nodes, which never die but are occasionally unable to transmit due to lack of sufficient battery energy. It also accounts for the effect of wireless channel fading on the ability of the WSN to transmit data. We develop two novel, tight, and computationally simple bounds for evaluating the k-outage duration. Our results show that increasing the number of EHS nodes has a markedly different effect on the k-outage duration than increasing the number of conventional nodes.

Enhanced electrochemical performance of graphene nanosheet thin film anode decorated with tin nanoparticles

Graphene nanosheet (GNS) was synthesized by using microwave plasma enhanced CVD on copper substrate and followed by evaporation of tin metal. Scanning and transmission electron microscopy show that nanosize Sn particles are well embedded into the GNS matrix. The composition, structure, and electrochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cyclic voltammetry (CV) and chrono-potentiometry. The first discharge capacity of as-deposited and annealed SnGNS obtained was 1551 mA h/g and 975 mA h/g, respectively. The anodes show excellent cyclic performance and coulombic efficiency.

Speed control of brushed DC motor for low cost electric cars

As petrol prices are going up in developing countries in upcoming decades low cost electric cars will become more and more popular in developing world. One of the main deciding factors for success of electric cars specially in developing world in upcoming decades will be its cost. This paper shows a cost effective method to control the speed of low cost brushed D.C. motor by combining a IC 555 Timer with a High Boost Converter. The main purpose of using High Boost Converter since electric cars needs high voltage and current which a High Boost Converter can provide even with low battery supply.

Boron doped defective graphene as a potential anode material for Li-ion batteries

Graphene with large surface area and robust structure has been proposed as a high storage capacity anode material for Li ion batteries. While the inertness of pristine graphene leads to better Li kinetics, poor adsorption leads to Li clustering, significantly affecting the performance of the battery. Here, we show the role of defects and doping in achieving enhanced adsorption without compromising on the high diffusivity of Li. Using first principles density functional theory (DFT) calculations, we carry out a comprehensive study of diffusion kinetics of Li over the plane of the defective structures and calculate the change in the number of Li atoms in the vicinity of defects, with respect to pristine graphene. Our results show that the Li-C interaction, storage capacity and the energy barriers depend sensitively on the type of defects. The un-doped and boron doped mono-vacancy, doped di-vacancy up to two boron, one nitrogen doped di-vacancy, and Stone-Wales defects show low energy barriers that are comparable to pristine graphene. Furthermore, boron doping at mono-vacancy enhances the adsorption of Li. In particular, the two boron doped mono-vacancy graphene shows both a low energy barrier of 0.31 eV and better adsorption, and hence can be considered as a potential candidate for anode material.

Modelling of Effect of Non-Uniform Current Density on the Performance of Soluble Lead Redox Flow Batteries

Soluble lead acid redox flow battery (SLRFB) offers a number of advantages. These advantages can be harnessed after problems associated with buildup of active material on. electrodes (residue) are resolved. A mathematical model is developed to understand residue formation in SLRFB. The model incorporates fluid flow, ion transport, electrode reactions, and non-uniform current distribution on electrode surfaces. A number of limiting cases are studied to conclude that ion transport and electrode reaction on anode simultaneously control battery performance. The model fits the reported cell voltage vs. time profiles very well. During the discharge cycle, the model predicts complete dissolution of deposited material from trailing edge side of the electrodes. With time, the active surface area of electrodes decreases rapidly. The corresponding increase in current density leads to precipitous decrease in cell potential before all the deposited material is dissolved. The successive charge-discharge cycles add to the residue. The model correctly captures the marginal effect of flow rate on cell voltage profiles, and identifies flow rate and flow direction as new variables for controlling residue buildup. Simulations carried out with alternating flow direction and a SLRFB with cylindrical electrodes show improved performance with respect to energy efficiency and residue buildup. (C) 2014 The Electrochemical Society. All rights reserved.

t-Na-2(VO)P2O7: A 3.8 V Pyrophosphate Insertion Material for Sodium-Ion Batteries

Pyrophosphate oxyanionic framework compounds offer a great platform to investigate new battery materials. In our continuing effort to explore pyrophosphate cathodes for sodium-ion batteries, we report, for the first time, the synthesis and use of tetragonal Na-2(VO)P2O7 as a potential sodium-ion insertion material. This material can be easily prepared by using a conventional solid-state route at a relatively low temperature of 400 degrees C. Stabilizing as a tetragonal structure with an open framework, the material offers pathways for Na+ diffusion. The as-synthesized material, with no further cathode optimization, yields a reversible capacity (Q) approaching 80 mAh g(-1) (Q(Theoretical) = 93.4 mAh g(-1)) involving a one electron V5+/V4+ redox potential located at 3.8 V (vs. Na/Na+). Furthermore, the material exhibits decent rate kinetics and reversibility. Combining green synthesis and moderate electrochemical properties, t-Na-2(VO)P2O7 is reported as a new addition to the growing family of pyrophosphate cathodes for sodium-ion batteries.

Pressure induced manifold enhancement of Li-kinetics in FCC fullerene

The reduction of the diffusion energy barrier for Li in electrodes is one of the required criteria to achieve better performances in Li ion batteries. Using density functional theory based calculations, we report a pressure induced manifold enhancement of Li-kinetics in bulk FCC fullerene. Scanning of the potential energy surface reveals a diffusion path with a low energy barrier of 0.62 eV, which reduces further under the application of hydrostatic pressure. The pressure induced reduction in the diffusion barrier continues till a uniform volume strain of 17.7% is reached. Further enhancement of strain increases the barrier due to the repulsion caused by C-C bond formation between two neighbouring fullerenes. The decrease in the barrier is attributed to the combined effect of charge transfer triggered by the enhanced interaction of Li with the fullerene as well as the change in profile of the local potential, which becomes more attractive for Li. The lowering of the barrier leads to an enhancement of two orders of magnitude in Li diffusivity at room temperature making pressurized bulk fullerene a promising artificial solid electrolyte interface (SEI) for a faster rechargeable battery.