For a supercapacitor electrode, carbon-based materials have received great attention for their high surface area and stability. In this work, sustainable and cost-effective synthesis of boron-doped activated biomass-derived carbon from the stems of Prosopis juliflora has been reported for supercapacitor applications. The activation by KOH creates pores and boron induces p-type doping in the carbon matrix. The material gave a higher specific capacitance of 307.14 F/g at a current density of 0.5 A/g. The symmetric supercapacitor device delivered 156.29 F/g of specific capacitance with 98.1% of energy efficiency. The observed energy and power densities were 7.81 Wh/Kg and 150 W/Kg, respectively. The device was further studied with stability test for 1000 charge/discharge cycles and showed 98.6% of capacitance retention and 97.9% of coulombic efficiency.
A key performance parameter of a manufacturing network or supply chain is its cycle time; the time that a typical item spends in the network. A previous simulation study on a semiconductor assembly and test facility showed that cycle times could be reduced by having smooth input and service rates. This suggested that there is a “cycle time principle” that, for a system with a specified throughput or input rate, the shortest cycle times are obtained when the input and service rates do not vary over time. We prove that this principle is true for the M/G/1 and M/M/s queueing systems and Jackson networks. The analysis involves establishing several results on the concavity of waiting time probabilities and the convexity of expected waiting times and queue lengths, as functions of input and service rates. These results also have natural uses in other optimization problems. 相似文献
The transport layer in the network protocol stack serves as a liaison between the application and the underlying network. Any quality of service provided by the network thus has to be effectively translated by the transport layer protocol in order to be enjoyed by the applications. In this article, we argue for a fundamental rethinking of the transport layer design to facilitate such QoS delivery. We identify the key requirement for a QoS enabling transport layer protocol as the ability to effectively handle multiplicity in terms of user differentiation levels, network resources, and service models. However, TCP, the transport layer protocol predominantly used in the Internet, is unable to support such multiplicity due to its single-state design. We extend TCP to a parallel transport layer protocol called parallel TCP (pTCP) that can tackle the different dimensions of multiplicity, and hence enable varying classes of QoS to applications. We discuss the applicability of pTCP in three specific domains with different levels of network support for QoS, and present simulation results substantiating our arguments. 相似文献
Synthesis of WC–Co nanocomposites generally involves gas-phase carburization. A novel approach in which a polymer precursor such as polyacrylonitrile serves as an in situ carbon source has been developed. The WC–Co nanocomposites formed are characterized by X-ray powder diffraction and electron microscopy. Nearly phase pure WC–Co nanocomposites with a particle size of 50–80 nm have been obtained. The phase purity of the products is strongly influenced by the synthesis and processing conditions such as the firing temperature, time, and atmosphere. 相似文献
we present a medium access control (MAC) protocol for ad hoc networks with multiple input multiple output (MIMO) links. MIMO links provide extremely high spectral efficiencies in multipath channels by simultaneously transmitting multiple independent data streams in the same channel. MAC protocols have been proposed in related work for ad hoc networks with other classes of smart antennas such as switched beam antennas. However, as we substantiate in the paper, the unique characteristics of MIMO links coupled with several key optimization considerations, necessitate an entirely new MAC protocol. We identify several advantages of MIMO links, and discuss key optimization considerations that can help in realizing an effective MAC protocol for such an environment. We present a centralized algorithm called stream-controlled medium access (SCMA) that has the key optimization considerations incorporated in its design. Finally, we present a distributed SCMA protocol that approximates the centralized algorithm and compare its performance against that of baseline protocols that are CSMA/CA variants. 相似文献
This paper proposes a new control method for the constant-frequency control of power factor correcting boost power converter using a sinewave template modulated PWM signal which eliminates the need for instantaneous measurement of the line current for the switching control of the boost converter. The control strategy is based on the notion that the line current can be forced to trace a deterministic waveform such as a sinusoid by considering the implicit model of the sinewave in the boost converter controller structure. The modulating sinewave template is generated using the line voltage, the boost converter output voltage and the load current. The paper provides the analysis and the design of the controller and presents simulation and implementation results to demonstrate its effectiveness 相似文献