University of Piraeus

About: University of Piraeus is a education organization based out in Piraeus, Attiki, Greece. It is known for research contribution in the topics: Context (language use) & Computer science. The organization has 1731 authors who have published 6209 publications receiving 106699 citations.

Performance of diversity receivers in generalised gamma fading channels

Abstract: The performance of M-ary modulation schemes operating in a generalised gamma fading environment in the presence of additive white Gaussian noise is studied. The multipath fading channel is modelled by the three-parameter generalised gamma distribution, which includes the Rayleigh, Nakagami and Weibull distributions as special cases and the log-normal distribution as a limiting case. The Suzuki distribution can also be adequately approximated by the generalised gamma distribution. The performances of the selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) diversity schemes are considered. Specifically, the exact average symbol error rates (ASER) for coherent multilevel modulation schemes with SC and MRC are derived using the moment generating function-based approach, while the ASER of EGC is obtained by employing the characteristic function-based approach. The analytical results are validated by computer simulation.

A cross country analysis of outward foreign direct investment patterns

Abstract: Purpose – To evaluate the relevance of the source country idiosyncratic factors in determining the firm's foreign direct investment (FDI) propensity and consequently the country's outward FDI position.Design/methodology/approach – A sample containing all countries with positive outward FDI flows for the whole period between 1976 and 1999 is selected. The sample consists of 25 countries and is divided in three groups, namely advanced countries, middle‐income countries and developing countries. An econometric model is estimated for each country group aiming to determine the variables affecting outward FDI position.Findings – Market structure differentiation and openness are the only variables affecting outward FDI in all country groups. Marginal efficiency of capital is the significant variable in advanced and middle‐income countries. All other variables, namely technology, human capital and exchange rate affect outward FDI position of advanced countries.Research limitations/implications – The list of FDI e...

Simulation of autohydrolysis effect on adsorptivity of wheat straw in the case of oil spill cleaning

Abstract: This work deals with the use of chemically modified wheat straw as efficient low-cost adsorbent for combating oil-spills in aquatic environment. The autohydrolyzed wheat straw was produced from the corresponding raw material by autohydrolysis in a PARR batch reactor (autoclave) at 160–240 °C for 0–50 min isothermal reaction time (following a non-isothermal preheating period). Oil adsorbency tests were performed, using diesel and crude oil spills in freshwater and seawater. Diesel and crude oil adsorbency values were found to increase up to a maximum by intensifying the autohydrolysis conditions, i.e., time and temperature. The adsorbency values were estimated by a proposed novel model incorporating the autohydrolysis severity factor R 0 . Optimal modification conditions were found for log R 0 = 5.15 (i.e., 200 °C, 10 min isothermal time period) giving diesel adsorbency up to 6.65 g g −1 and crude oil adsorbency up to 6.91 g g −1 . The maximum adsorbency values were comparable to those of the commonly used commercial adsorbents.

Distributed radio access technology selection for adaptive networks in high‐speed, B3G infrastructures

Abstract: Wireless systems migrate towards the era of ‘Beyond the 3rd Generation’ (B3G). A fundamental facilitator of this vision is the evolution of high speed, adaptive networks, needed for better handling the offered demand and improving resource utilization. Adaptive networks dynamically select their configuration, in order to optimally adapt to the changing environment requirements and conditions. This paper presents optimization functionality that can be used to support network adaptability (cognition-reconfigurability) in a B3G context. The paper starts from the business case that justifies the need for placing research onto adaptive networks and then continues with the management functionality for (re)configuration decisions, which is targeted to the dynamic selection of the appropriate radio access technologies (RATs). RAT selection is modelled through an optimization problem called (RAT, Demand and QoS-Assignment problem—RDQ-A), the solution of which assigns in a distributed manner the available RATs to adaptive Base Station transceivers and the demand (users) to these transceivers and to QoS levels, respectively. The RDQ-A optimization problem is decoupled in several sub-problems and is implemented in phases corresponding to the aforementioned assignments, while efficient custom greedy algorithms are mobilized in each phase for obtaining the optimum assignment. Finally, indicative results from the application of the proposed functionality to a simulated network are presented. Copyright © 2006 John Wiley & Sons, Ltd.