Efficient medium arbitration of FSAN‐compliant GPONs

The steadily rising demand for multimedia and data services, the falling cost and omnipresence of Ethernet and the maturity of passive optical networks (PON) technology, promise to radically change the landscape in the local loop. The heart of a gigabit PON system (recently standardized by FSAN/ITU) is the medium access controller (MAC), which arbitrates access to the upstream link among users with fluctuating traffic demands and effects the multiplexing and concentration policy. At the same time, it has to safeguard the service quality and enforce the parameters agreed in the service level agreements (SLAs) between the users and the service provider. In this paper, a MAC protocol designed to serve any mix of services according to their quality of service (QoS) needs, employing four priority levels along with a high number of logically separate data queues is presented. The architecture and implementation in hardware of a MAC algorithm capable of allocating bandwidth down to a resolution of a byte with QoS differentiation is the focus of this paper. It employs the bandwidth arbitration tools of the FSAN/ITU G.984.3 standard and maps SLA parameters to GPON service parameters to create an efficient, fair and flexible residential access system. Copyright © 2005 John Wiley & Sons, Ltd.     

A stacked chalcopyrite thin‐film tandem solar cell with 1.2 V open‐circuit voltage

CuGaSe₂ (CGS) thin films were prepared on tin‐doped indium oxide (ITO) coated soda‐lime glass substrates by thermal co‐evaporation to fabricate transparent solar cells. The films consisted of columnar grains with a diameter of approximately 1 μm. Some deterioration of the transparency of the ITO was observed after deposition of the CGS film. The CGS solar cells were electrically connected in series with Cu(In,Ga)Se₂ (CIGS) solar cells and mechanically stacked on the CIGS cells to construct tandem cells. The tandem solar cell with the CGS cell as the top cell showed an efficiency of 7.4% and an open‐circuit voltage of 1.18 V (AM 1.5, total area). Copyright © 2003 John Wiley & Sons, Ltd.     

Molecular Origin of the Charge Carrier Mobility in Small Molecule Organic Semiconductors

Small‐molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes to organic photovoltaics. However, the low carrier mobility severely limits their potential, e.g., for large area devices. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment, and polarizability. Presently, quantitative ab initio models to assess the influence of these molecule‐dependent properties are lacking. Here, a multiscale model is presented, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility, and allows for the decomposition of the carrier mobility into molecule‐specific quantities. Molecule‐specific quantitative measures are provided how two single molecule properties, the dependence of the orbital energy on conformation, and the dipole‐induced polarization determine mobility for hole‐transport materials. The availability of first‐principles based models to compute key performance characteristics of organic semiconductors may enable in silico screening of numerous chemical compounds for the development of highly efficient optoelectronic devices.     

Microchips for the Investigation of Thermal and Electrical Properties of Individual Nanowires

This paper focuses on the determination of thermal and electrical properties of individual thermoelectric nanowires, primarily bismuth and bismuth compound nanowires, as functions of their crystallinity, diameter, and composition. For measurements of the Seebeck coefficient and the electrical and thermal conductivity, specially designed microchips have been developed and employed. Finite-element simulations demonstrate that the temperature profiles of the microchips provide suitable temperature gradients for Seebeck-effect measurements and heat-sink conditions for thermal conductivity investigations. First measurements of thermal conductivity of metallic nanowires and of Seebeck coefficients of granular nanowires prepared by focused electron-beam-induced deposition are presented. Some of these results are discussed in the framework of finite-size-effect theory.     

An efficient algorithm for computing the transmission through highly conducting thin sheild in TLM

This paper presents a new method in TLM for very efficient computation of highly conducting thin shielding walls. Firstly, the impulse response of a finite conducting sheet is computed analytically via inverse Laplace transform. Subsequently, a recursive convolution integral is formulated with the analytical impulse response. This allows a very efficient and accurate calculation of the diffusion process through imperfectly conducting walls.     

Synthese von 4-Alkoxy-2-hydroxyphenylketoximen als Metallextraktions-Reagenzien

Synthesis of 4-Alkoxy-2-hydroxyphenyl Ketoximes as Reagents for Metal Extraction The C-Acylation (Friedel-Crafts reaction) of resorcinol with aluminium chloride, the monoetherification in 4-position of the resulting 2,4-dihydroxyphenylketones, and the preparation of oximes ( 8, 9, 10, 11 ) from this ketones were investigated. The compounds obtained are characterized by elemental analysis, and the i.r., u.v. and ¹H-n.m.r. spectra are discussed. Solubility data of some oximes are determined in water, octane and toluene. The extraction properties for copper-(II)-and iron-(III)-ions are measured by isotope methods in relation to the extragent structure, the extraction time and the pH-range.