A low-power high-performance SiGe BiCMOS 802.11a/b/g transceiver IC for cellular and bluetooth Co-existence applications

This paper describes a high-performance WLAN 802.11a/b/g radio transceiver, optimized for low-power in mobile applications, and for co-existence with cellular and Bluetooth systems in the same terminal. The direct-conversion transceiver architecture is optimized in each mode for low-power operation without compromising the challenging RF performance targets. A key transceiver requirement is a sensitivity of -77 dBm (at the LNA input) in 54 Mb/s OFDM mode while in the presence of a GSM1900 transmitter interferer. The receiver chain achieves an overall noise figure of 2.8/3.2 dB, consuming 168/185 mW at 2.8 V for the 2.4/5GHz bands, respectively. Signal loopback and transmit power detection techniques are used in conjunction with the baseband modem processor to calibrate the transmitter LO leakage and the transceiver I/Q imbalances. Fabricated in a 70 GHz f/sub T/ 0.25-/spl mu/m SiGe BiCMOS technology for system-in-package (SiP) use, the dual-band, tri-mode transceiver occupies only 4.6 mm/sup 2/.     

A joint parametric prediction model for wireless internet traffic using Hidden Markov Model

Addressing performance related issues of networks and ensuring better Quality of Service (QoS) for end-users calls for simple, tractable and realistic traffic models. The work reported here focuses on modelling the Wireless Internet traffic using realistic traffic traces collected over wireless networks and forecasting the end-to-end QoS parameters for the networks. A measurement framework is set-up to collect the QoS parameters and a traffic model is designed based on Hidden Markov Model considering joint distribution of End to End Delay (E2ED or d), Inter-Packet Delay Variation (IPDV) and Packet Size. States are mapped to the four traffic classes namely conversational, streaming, interactive, and background. The model is validated by forecasting QoS parameters and the results are shown to be within the tolerance limit.     

New voltage and current-mode APS using current controlled conveyor

A first-order all-pass section (APS) is introduced employing a single second-generation current conveyor and three passive components. The translinear conveyor version of the circuit employing only two passive components is also proposed. A fully tunable version of the circuit employing two current controlled conveyors (CCCIIs) and a single capacitor is finally derived. All the three versions of APS can be operated both in voltage as well as current mode without changing the circuit configuration. As an application, a quadrature oscillator providing two quadrature currents and two phase-shifted voltage outputs simultaneously, is realized using the proposed APS. RSPICE simulation results for the translinear-C APS, and the translinear-C quadrature oscillator are included to verify the theory.     

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose. This configuration can allow a simple tuning approach where fast and stable electronic wavelength switching is required in a narrow tuning range, on an order between a few tens of picometers to nanometers, without involving any mechanical movement.     

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

The development of pseudocapacitive materials for energy‐oriented applications has stimulated considerable interest in recent years due to their high energy‐storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery‐like to the pseudocapacitive‐like behavior. As a result, it becomes challenging to distinguish “pseudocapacitive” and “battery” materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery‐type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid‐state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state‐of‐the‐art progress in the engineering of active materials is summarized, which will guide for the development of real‐pseudocapacitive energy storage systems.     

Synthesis of quantitative and qualitative evidence for accident analysis in risk-based highway planning

Accident analysis involves the use of both quantitative and qualitative data in decision-making. The aim of this paper is to demonstrate the synthesis of relevant quantitative and qualitative evidence for accident analysis and for planning a large and diverse portfolio of highway investment projects. The proposed analysis and visualization techniques along with traditional mathematical modeling serve as an aid to planners, engineers, and the public in comparing the benefits of current and proposed improvement projects. The analysis uses data on crash rates, average daily traffic, cost estimates from highway agency databases, and project portfolios for regions and localities. It also utilizes up to two motivations out of seven that are outlined in the Transportation Equity Act for the 21st Century (TEA-21). Three case studies demonstrate the risk-based approach to accident analysis for short- and long-range transportation plans. The approach is adaptable to other topics in accident analysis and prevention that involve the use of quantitative and qualitative evidence, risk analysis, and multi-criteria decision-making for project portfolio selection.     

An Approach to Tackle the Threat of Sympathy Trips in Directional Overcurrent Relay Coordination

This paper proposes to introduce additional constraints in the directional overcurrent relay coordination problem to tackle the sympathy trips. This paper attempts to tackle the sympathy trips in which other relay(s) in the system operate(s) earlier in the designated primary relay. The solution to this problem requires the inclusion of some additional constraints, making the coordination problem too complex. This paper proposes to solve the problem in two phases. In the first phase, the problem is solved by a normal coordination procedure and sympathy trips are identified. In the second phase, the proposed additional constraints are imposed only for the sympathy trips identified in the first phase. For the second phase, three approaches for including additional constraints were investigated. This paper includes results of the proposed algorithm for the IEEE 30-bus system. The results amply suggest that one of the three approaches of including additional constraints successfully tackled the problem of sympathy trip     

EFFECTS OF SAWDUST ON BIOGAS PRODUCTION FROM COWDUNG

The biogas generation was performed using cowdung and sawdust in the ratios of 4:1 and 2:1, respectively. The experiments were also conducted using cowdung alone for the comparison purpose. The increase in the amount of sawdust in the mixture of cowdung and sawdust decreases the quantity of gas production. The production of methane up to three weeks is also effected by the amount of sawdust. The nitrogen contents increase and volatile solids decrease with the digestion of waste materials. The thermogravimetric studies of the materials support the biogas generation as the decomposition of particular part of cowdung.     

Choice of sink for air conditioning systems

This Paper presents general correlations to estimate the power demand of different conventional air conditioning (A/C) systems operating under varied climatological conditions. The results have been applied to estimate the peak power demand and annual energy consumption. As a case study, the analysis is applied to Kuwaiti buildings for quantitative assessments using a unit peak cooling load (1 kW_c). Contrary to general understanding and practice the results strongly favour the use of water-cooled systems for both the residential and the non-residential types of buildings.     

ZnS:Sm and ZnS:Cu,Sm electroluminescent phosphors

Electroluminescent ZnS: Sm and ZnS: Cu, Sm phosphors have been prepared and their electroluminescent (el) characteristics have been studied. The time-averagedel brightness follows the Alfrey-Taylor relation over a wide range of frequencies. The constants of this relation have been determined. Theel emission shows one main and one auxiliary peak during each half cycle of the applied voltage. Variation of current with applied voltage has also been investigated.