Full-Duplex DOCSIS/WirelessDOCSIS Fiber–Radio Network Employing Packaged AFPMs as Optical/Electrical Transducers

A hybrid fiber-radio access network architecture for simultaneous wireline and wireless transmissions of data-over-cable service interface specification (DOCSIS) signals is presented. An all-optical harmonic up-conversion technique using a dual-drive Mach-Zehnder modulator provides the downstream optical signal modulated not only at the intermediate frequency in the 600- to 900-MHz band for wireline transmission but also at the up-converted frequency in the 5.45- to 5.75-GHz band for wireless transmission. An InGaAsP/InGaAsP multiple-quantum-well asymmetric Fabry-Perot modulator/detector has been designed, fabricated, and packaged and has been employed in the base station (BS) as an optical/electrical transducer, simultaneously providing the functions of optical intensity modulation and photodetection. At the BS, the DOCSIS signals are recovered at the wireline and wireless frequencies for the respective feeding of a cable access network or a fixed wireless access network in a highly flexible approach. Full-duplex operation has been demonstrated for both access types in an indoor laboratory environment. In a subsequent small-scale field trial, real-life Internet traffic provided by a local community antenna television system operator has been transported over the present hybrid fiber-radio access network architecture, and simultaneous transmission of both DOCSIS and digital television signals has also been performed.     

A comparative numerical study of hybrid-stabilized argon–water electric arc

The paper presents numerical simulations of the discharge and the near-outlet regions of the hybrid-stabilized argon–water electric arc. Two different numerical methods for solving the set of conservative equations for the continuity, momentum and energy have been applied. The major difference between the results using the two methods occurs in the temperature distribution in arc fringes within the discharge chamber. This fact influences the potential drop, overpressure, reabsorption of radiation and arc efficiency. It is shown that the radial profiles of temperature at the exit nozzle are less influenced by different temperature distribution within the discharge chamber. Comparison with chosen experimental temperature profiles shows very good agreement.     

Design of inductive p-i-n diode matching for optical receivers withincreased bit-rate operation

We have studied matching of a p-i-n photodiode (PD) with a single serial inductive element for broadband operation. The bit rate and rise time may be significantly improved, compared to a device without inductor for nonreturn-to-zero (NRZ) modulation. The matched device offers improved pulse equalization leading to increased receiver sensitivity, and reduces the need for an additional pulse-equalizing filter. The material is presented so that it can serve as a guideline of how the inductor can be included when choosing the thickness of the absorption layer and/or area for a p-i-n PD design, and ends with typical design examples     

Effect of different fermentation parameters on bioethanol production from corn meal hydrolyzates by free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus

BACKGROUND: Bioethanol produced from renewable biomass, such as corn meal, is a biofuel that is both renewable and environmentally friendly. Significant scientific and technological investments will be needed to achieve substitution of conventional fossil fuels with alternative fuels. The ethanol fermentation of enzymatically obtained corn meal hydrolyzates by free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus yeast in a batch system was studied. The initial glucose and inoculum concentration and the time required for the efficient ethanol production were optimized taking into account parameters such as ethanol concentration, ethanol yield, percentage of the theoretical yield of ethanol and volumetric productivity in both immobilized and free cell systems. RESULTS: The yeast cells were immobilized in Ca–alginate by an electrostatic droplet generation method. An optimal initial inoculum concentration of 2% (v/v) and optimal fermentation time of 38 h for both immobilized and free yeasts were determined. An optimal initial glucose concentration of 150 g L^?1 for free system was achieved. At the initial glucose concentration of 176 g L no substrate or product inhibition were achieved with immobilized yeast. CONCLUSION: By immobilization of the yeast into Ca–alginate using the method of electrostatic droplet generation a superior system was realized, which exhibited lower substrate inhibition and higher tolerance to ethanol. The cells of S. cerevisiae var. ellipsoideus yeast entrapped in Ca–alginate showed good physical and chemical stability, and no substrate and product diffusion restrictions were noticed. Copyright © 2008 Society of Chemical Industry     

Modelling and evaluation of building integrated SOFC systems

This study presents the final results of a series of modelling steps which are undertaken for the performance assessment of the building cogeneration and polygeneration systems using solid oxide fuel cell (SOFC). Based on earlier work, generic SOFC cell stack and system models were developed and employed to analyze different SOFC systems configurations for optimal efficiencies, this SOFC system model is used to derive performance input data for transient whole-building and energy system simulation tools which contain simpler SOFC system models. These steps are shortly summarized here. Then the final step, the evaluation of building integrated co- and polygeneration SOFC systems in terms of primary energy demand and CO₂ emissions, employing such tools, is presented here for a polygeneration system with typical heating and cooling loads, and electricity demand profiles, for different SOFC systems, including a comparison to current standard technologies.     

Extended modulation bandwidth of DBR and external cavity lasers byutilizing a cavity resonance for equalization

We have investigated the occurrence of a second resonance frequency in distributed Bragg reflector laser diodes and the high modulation bandwidth resulting from it. The influence of different laser parameters has been theoretically investigated. It is also shown that a similar behavior can be obtained in laser diodes with a passive, low-loss, and gratingless external cavity. The possibilities of large-signal digital modulation are also investigated     

Electron subband structure and controlled valley splitting in silicon thin-body SOI FETs: Two-band k · p theory and beyond

We use a two-band k · p Hamiltonian to describe the subband structure in strained silicon thin films. The model describes the dependence of the transversal effective mass on strain and film thickness. However, it is found that the two-band k · p model is unable to describe recently observed large valley splitting. Therefore a generalization of the model is necessary. To go beyond the k · p theory, an auxiliary tight-binding model defined on a lattice of sites containing two localized orbitals is introduced in such a way that it reproduces the bulk dispersion obtained from the two-band k · p model. Corresponding dispersion relations including strain are obtained. We discuss an alternative mechanism to create and control the valley splitting by applying shear strain. The valley splitting increases with increased shear strain and decreasing film thickness and can be larger than the spin splitting. This makes silicon-based quantum devices promising for future applications in quantum computing.     

Tool life testing in gundrilling: an application of the group method of data handling (GMDH)

Although the known techniques of the design of experiments (DOE) allows significant improvements in the methodology of machining tests, their use in metal cutting is restricted by limited number of variables included into consideration, pre-set model, subjective pre-process decisions and uncertainties in the machining data collected experimentally. This paper introduces an application of a new powerful technique of DOE known as the group method of data handling (GMDH) to the design of tool life experiments that allows avoiding the above-mentioned disadvantages of traditional DOE. As a result of such an application, a mathematical model that correlates tool life in gundrilling of cast iron with various regime and design parameters was obtained. Special care was taken to avoid the influence of the dynamic phenomenon of the gundrilling process on the obtained experimental results. The obtained mathematical model reveals that tool life in gundrilling is a complex function of various regime and design parameters.