Signal Design for Digital Multiple Access Communications

In this concise paper we examine the signal design problem associated with a multiple access communication channel in which several binary digital links are operated simultaneously over a common channel. Receiver noise is neglected but the channel is confined in dimension, so that signal crosstalk is the only source of bit errors. An encoder is assumed to exist prior to channel transmission for converting the bit waveforms from all transmitters into a common channel signal available to all receivers. The encoder selects the channel signal during each bit so as to maximize the average detection probability per bit, where the average is taken over all links and all possible bit patterns. Two classes of receivers are considered. In the first the receivers are confined to only signal correlations with the corresponding transmitter signals. In the second the encoder and receivers are matched to arbitrary signal sets. For both type receivers, optimal channel signal selection is shown to be related to minimal hamming distance mappings. Values and bounds for the resulting detection probabilities in terms of numbers of transmitters and channel dimension are reported.     

Application of the Cell Method to the Simulation of Unsaturated Flow

The present work shows an alternative to the classical methods to solve the Richards' Equation (RE), used to model flow in unsaturated porous media. This alternative is named Cell Method (CM). The CM is based on a preliminary reformulation of the mathematical model in a partially discrete form, which preserves as much as possible the physical and geometrical content of the original problem, and is made possible by the existence and properties of a common mathematical structure of field theories. The goal is to maintain the focus, both in the modelling and discretization steps, on the physics of the problem. The present work derives the discrete formulation of the RE. Because of the nonlinearities involved, RE is often solved using low-order numerical approximation methods, such as Finite Difference (FDM) or Finite Element Methods (FEM). These types of solution methods are used in many of the existing unsaturated flow codes. We show how the CM can be applied in this problem. We have solved a number of test cases, available in literature, to verify the ability of our model to reproduce these results. We have used the Newton-iterative methods which use iterative linear solvers, such as the Bi-CGSTAB. Numerical results, as it is possible to see in the verification exercise section, show the CM to be effective compared with the classical approaches (FDM and FEM) to solve the flow in unsaturated porous media. The procedure presented here is not peculiar to groundwater hydraulics but also applicable in fluid dynamics, solid mechanics, heat conduction and electromagnetism.     

Sequential decision making with partially ordered preferences

This paper presents new insights and novel algorithms for strategy selection in sequential decision making with partially ordered preferences; that is, where some strategies may be incomparable with respect to expected utility. We assume that incomparability amongst strategies is caused by indeterminacy/imprecision in probability values. We investigate six criteria for consequentialist strategy selection: Γ-Maximin, Γ-Maximax, Γ-Maximix, Interval Dominance, Maximality and E-admissibility. We focus on the popular decision tree and influence diagram representations. Algorithms resort to linear/multilinear programming; we describe implementation and experiments.     

Does skilled migration foster innovative performance? Evidence from British local areas

What is the effect of an increase in the stock of human capital due to skilled immigration on the innovative performance of recipient economies? Combining firm‐level micro‐data with area‐level labour force information, this paper investigates the impact of skilled international migration inflows on firms' product and process innovation in British local labour market areas. The paper supports the evidence in favour of a causal link between immigration and innovation. Results also show that the nature of the innovative process and the typology of innovative activities performed by local firms play a key role in the relation between immigration and innovation.     

Use of microbial fuel cells for soil remediation: A preliminary study on DDE

DDE (2,2-bis (p-chlorophenyl)-1,1-dichloroetylene) is a very persistent and bioaccumulative pesticide and its residues are continuously found in the environment. Among the green remediation strategies for soil recovery, terrestrial Microbial Fuel Cells (MFC) are arousing great interest in scientific community. MFCs transform energy stored in the chemical bonds of organic compounds into electrical energy thanks to exo-electrogen microorganisms naturally occurring in soil, which catalyse oxidation and reduction reactions in the area between two graphite electrodes. This work reports preliminary data on the use of MFCs for promoting soil decontamination from DDE. Several experimental conditions (e.g. addition of compost and open/closed circuit) were applied for assessing how to improve MFC performance in favouring DDE removal. MFCs promoted a significant DDE removal (39%) after 2 months, while at the same time any pesticide decrease was observed in the batch condition. Compost addition stimulated microbial activity and improved MFC performance for a longer time.     

On-farm and postharvest processing sources of bacterial contamination to melon rinds

Multistate and international foodborne illness outbreaks, particularly involving cantaloupe and often involving rare Salmonella spp., have increased dramatically over the past 13 years. This study assessed the sources and extent of melon rind contamination in production fields and at processing and packing facilities. In the spring of 1999, cantaloupe (Cucumis melo L. [reticulatus group] cv. Cruiser) sampled from two sites in the Rio Grande River Valley showed that postharvest-processed melon rinds often had greater plate counts of bacterial contaminants than field-fresh melons. Cantaloupe in the field had 2.5 to 3.5 log CFU g(-1) rind total coliforms by aerobic plate counts, whereas washed melons had 4.0 to 5.0 log CFU g(-1). In the fall of 1999, coliforms on honeydew melons (C. melo [inodorous group] cv. Honey Brew) ranged from 2.6 to 3.7 log CFU g(-1) after processing, and total and fecal coliforms and enterococci never fell below 2.5 log CFU g(-1). A hydrocooler at another site contaminated cantaloupe rinds with up to 3.4 log CFU g(-1) total and fecal enterococci; a secondary rinse with chlorinated water incompletely removed these bacteria. Sources of coliforms and enterococci were at high levels in melon production soils, especially in furrows that were flood irrigated, in standing water at one field, and in irrigation water at both sites. At one processing facility, wash water pumped from the Rio Grande River may not have been sufficiently disinfected prior to use. Because soil, irrigation water, and process water were potential sources of bacterial contamination, monitoring and management on-farm and at processing and packing facilities should focus on water quality as an important control point for growers and packers to reduce bacterial contamination on melon rinds.     

Simulation of dye solar cells: through and beyond one dimension

In this work we present a Computer Aided Design (CAD) software, called TiberCAD, to simulate Dye Sensitized Solar Cells (DSC). DSCs are particularly interesting devices due to their high efficiency (more than 11% on small area and 8% on large area) and long stability. Since their first development, much progress has been made in terms of efficiency, stability, lifespan and engineering of the device. However, the field of DSCs still lacks a complete model able to simulate the entire device over a general domain including all its components. In our model a drift-diffusion set of equations for the different charge carriers coupled to Poisson equation has been implemented within finite element method. The model takes into account also trap assisted transport for electrons in the mesoporous titanium dioxide with a phenomenological model derived from multi-trapping model.     

Switching devices in sol-gel hybrid thin film technology

Development of non-volatile memories based on organic soft materials is one of two main trends in industry for flash-memories. The electrical bistability of such materials makes them ideal candidates for cost-effective, fast programming switching devices. SiO₂-Rose Bengal (bis-triethylammonium) hybrid thin films are reported here together with their characterizations. The technology yields well reproducible films with good current-voltage switching characteristics. Owing to their physical and chemical stability the films are suited to standard micro-photolitography technology, rendering their fabrication cost-effective.     

Performance of Optical Receivers with Avalanche Photodetection

This paper reports the results of a computer study to numerically evaluate the digital performance of an optical receiver with avalanche photodetectors. Exact and approximate APD statistics were implemented and error probabilities in the rangel0^{-1}tol0^{-4}were computed. Both shot-noise and receiver-noise limited conditions were examined, and on-off keying, binary pulse comparison, multilevel intensity, and PPM signaling formats are considered.