Cyclostationary crosstalk suppression by decision feedbackequalization on digital subscriber loops

Interference from digital signals in multipair cables has been shown to be cyclostationary under some conditions. This work evaluates the performance of a decision feedback equalizer (DFE) in the presence of cyclostationary interference (CI), intersymbol interference (ISI), and additive white noise (AWN). A comparison between a DFE with CI and one with stationary interference (SI) shows the ability of the DFE to substantially suppress CI. Fractionally spaced and symbol-rate DFE equalizers are also compared and the former is found to yield better performance, especially in the presence of CI. The use of a symbol-rate DFE using an adaptive timing technique that finds the receiver's best sampling phase is proposed for when the fractionally spaced DFE cannot be used because of its complexity. The results also demonstrate the potential benefits of synchronizing central office transmitter clocks, if a fractionally spaced DFE is used at the receiver     

Non-parametric maximum-likelihood channel estimator and detector for OFDM in presence of interference

A maximum-likelihood channel estimator for the orthogonal frequency division multiplexing communication environments, in the presence of interference is discussed here. In a training-based scenario, the channel is estimated based on pilots that precede the transmission of the information. To reduce the number of estimation parameters, the channel is estimated iteratively in time-domain. Since interference from other users provide no useful information, parameters of the interference are neither estimated nor the effect of the interference neglected, instead interference along with Gaussian noise is perceived as non-Gaussian noise process. The algorithm assumes no a priori knowledge about the interfering channel and signal at the receiver, further no assumption on the statistical properties of the interferer is assumed, which makes this algorithm robust. The estimated channel information along with the estimated distribution are then utilised to equalise the subsequent data blocks. The strength of the algorithm is in its robustness to both synchronous and asynchronous interference, which is confirmed by the simulation results for both flat and multipath fading channels in presence of synchronous and asynchronous interference.     

Transient measurements of adsorption and diffusion in H-ZSM-5 membranes

A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H-ZSM-5 tubular membranes and modeled assuming Maxwell-Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N₂ and CO₂ were nearly identical to those measured by calorimetry on H-ZSM-5 powders. The CH₄ isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na-ZSM-5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients D_MS depended on concentration and were higher for higher feed partial pressures. Average D_MS values for the two membranes were 7.5, 5 and 1.5×10⁻¹⁰ m²/s for N₂, CH₄, and CO₂, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.     

Characterising effective eLearning resources

The widespread availability of digital learning resources in a variety of media formats offers the possibility to make a profound difference in education. This potential has not been fully realised for range of interrelated reasons. In this paper we study the key characteristics of learning resources that have proved effective in changing learning and teaching, and relate them to existing frameworks for understanding resources. We outline the relationships between resources, their users, and the way they are used, and explore issues that influence practitioners in choosing a particular resource. Our study is based on a review of resources for e-learning and chemistry in post-compulsory education, undertaken for the UK Joint Information Systems Committees (JISC), as part of a wider study examining ‘The Effectiveness of Resources, Tools and Support Services used by Tutors in Designing and Delivering E-Learning Activities’.     

Development and Analytical Verification of an Integrated 2-D Surface Water—Groundwater Model

DIVAST is a two-dimensional hydrodynamic and water quality numerical model developed for estuarine and coastal modelling. The original model enables the simulation of problems such as pollution and flooding in surface waters. In this paper the existing model is extended to allow the modelling of 2-D groundwater as well as surface water in the same model, using an integrated approach rather than two disparate models. The changes to the original model are summarised and the method of implementation is outlined. The new extended model (DIVAST-SG) is then tested against an analytical solution to verify that the model solves the equations correctly. The model is shown to predict the analytical solution for two different scenarios to within approximately 1 % of the height of flood wave.     

A review of the potential water quality impacts of tidal renewable energy systems

The continued increase in the demand for energy, growing recognition of climate change impacts, high oil and gas prices and the rapid depletion of fossil fuel reserves have led to an increased interest in the mass generation of electricity from renewable sources. Traditionally, this has been pursed through riverine hydropower plants, with onshore wind systems growing steadily in popularity and importance over the years. Other renewable energy resources, which were previously not economically attractive or technically feasible for large scale exploitation, are now being considered to form a significant part of the energy mix. Amongst these, marine and in particular, tidal energy resource has become a serious candidate for undergoing mass exploitation in the near future, particularly in places with a tidal range of 4 m or more. Tidal renewable energy systems are designed to extract the kinetic or potential energy flow and convert it into electricity. This can be achieved by placing tidal stream turbines in the path of high speed tidal currents or through tidal range schemes, where low head turbines are encapsulated in impoundment structures, much like in low head riverine hydropower schemes. It is thought that these systems, when implemented at scales required to generate substantial amounts of electricity, have the potential to significantly alter the tidal flow characteristics, which could have knock-on impacts on the hydro-environment. This review gathers together knowledge from different research areas to facilitate an evaluation of the potential hydro-environmental impacts of tidal renewable energy systems, with a particular focus on water quality. It highlights the relevance of hydro-environmental modelling in assessing potential impacts of proposed schemes and identifies areas where further research is needed. A case study is presented of recent modelling studies undertaken for the Severn Estuary.     

China, 1860: A photographic album by Felice Beato

Abstract

The documentation of wars had become a significant feature of photography by the 1860s. As the camera's advantages became apparent, photographers gradually took the place of the graphic artists and painters who had previously accompanied military and diplomatic missions. The camera could reproduce reality in minute detail and an infinite number of prints were possible from each negative. Its precision as a recorder, coupled with its apparent objectivity, also made it a potentially powerful tool of propaganda.     

Major Physical Features of Long Point Bay and its Watershed

Long Point and the bay it encloses comprise a dynamic and unusual region in Lake Erie's eastern basin. The area is on the northern edge of the Appalachian Geosyncline and is underlain by thick sedimentary rocks of Silurian and Devonian age. Over these lie tills and lacustrine sand and clay deposits. The Norfolk Sand Plain, in the western part of the Long Point Bay area, is well drained and productive, and supports a large tobacco industry. The Haldimand Clay Plain to the east has heavier soils and is better suited to pasturage and cereal crops. Surface water quality is variable, especially in the clay plain, and is adversely affected by nutrient loadings from human activities. Nevertheless, the nearshore waters of the bay are the only nearshore areas in Lake Erie which are classifiable as oligo-mesotrophic, all other areas being mesotrophic to eutrophic. Since settlement in the early 1800s, the local economy has been based on agriculture, commercial fishing, and support for recreational activities at Long Point's parks and beaches. However, new industrial development at Nanticoke may spur further industrial and municipal growth. Associated environmental changes are possible. Long-term environmental monitoring programs have been set up to provide background information for present and future development.     

Evaluation of Decision Feedback Equalization and Viterbi Algorithm Detection for Voiceband Data Transmission--Part I

The application of QAM receivers employing passband decision feedback equalization or Viterbi algorithm detection is considered for high-speed data transmission in voiceband telephone channels. Analytical results for the Viterbi receiver indicate that it can permit digital data transmission with symbol rates exceeding the nominal bandwidth capabilities of the channel. However, it is also shown that the minimum distance of partial response-type impulse responses can substantially decrease due to small demodulation phase errors. Thus, decision feedback receivers may offer more robust performance on channels with phase jitter.