Robust Power and Subcarrier Allocation for OFDM-based Cognitive Radio Networks Considering Spectrum Sensing Uncertainties

‎In this paper‎, ‎we address power and subcarrier allocation for cooperative cognitive radio (CR) networks in the presence of spectrum sensing errors‎. ‎First‎, ‎we derive the mutual interference of primary and secondary networks affecting each other by taking into account spectrum sensing errors‎. ‎Then‎, ‎taking into account the interference constraint imposed by the cognitive network to the primary user and the power budget constraint of cognitive network‎, ‎we maximize the achievable data rates of secondary users‎. ‎Besides‎, ‎in a multi secondary user scenario‎, ‎we propose a suboptimal but low complexity power and subcarrier allocation algorithm to solve the formulated optimization problem‎. ‎Our numerical results indicate that the proposed power loading scheme increases the cognitive achievable data rates compared to classical power loading algorithms that do not consider spectrum sensing errors‎

Braids of entangled particle trajectories

In many applications, the two-dimensional trajectories of fluid particles are available, but little is known about the underlying flow. Oceanic floats are a clear example. To extract quantitative information from such data, one can measure single-particle dispersion coefficients, but this only uses one trajectory at a time, so much of the information on relative motion is lost. In some circumstances the trajectories happen to remain close long enough to measure finite-time Lyapunov exponents, but this is rare. We propose to use tools from braid theory and the topology of surface mappings to approximate the topological entropy of the underlying flow. The procedure uses all the trajectory data and is inherently global. The topological entropy is a measure of the entanglement of the trajectories, and converges to zero if they are not entangled in a complex manner (for instance, if the trajectories are all in a large vortex). We illustrate the techniques on some simple dynamical systems and on float data from the Labrador sea.Comment: 24 pages, 21 figures. PDFLaTeX with RevTeX4 macros. Matlab code included with source. Fixed an inconsistent convention problem. Final versio

Effects of construction delays on construction project objectives

Delays can be defined as the late completion of works as compared to the planned schedule on the contract. Delays can be avoided or minimized only when their causes are identified. When delay occurred in to our project, it will have adverse consequences on project objectives in terms of time, cost and quality. The aim of the study reported in this paper was to identify the effects of delays that could threat project objectives in construction projects. A comprehensive literature review from various sources through books, conference proceedings, the internet, and civil engineering journals was made to carry out the study. According to delay categories that were contractor related, client related, consultant related, labor related and external related, the results of this study identified the six major effects of delay that were time overrun, cost overrun, dispute, arbitration, total abandonment, and litigation. The study also revealed that time and cost overruns were the frequent effects of delay. It is hoped that this study will become the foundation of further research in the area of project delays and mitigation measures

Acute vigabatrin-phenobarbitone-interaction on exploratory behaviour of rats

Vigabatrin (gamma-vinyl GABA) is an irreversible inh:bitor of the enzyme GABA-transaminase (GABA-T) which is responsible for the catabolism of the major inhibitory neurotransmitter gamma- aminobutyric acid (GABA) in the brain. Vigabatrin causes a several fold increase in the levels of brain GABA. The current study investigated further the effects of acute treatment with vigabatrin (100 mgl kg, i.p.) & phenobarbitone sodium (20 mg/kg, i.p.)f alone and in combination, in two rat behavioural models of exploratory activity: the elevated plus-maze model of anxiety and the open field test of locomotor activity. A single injection of vigabatrin or phenobarbitone alone, produced anxiolytic effects in the elevated plus-maze test and increased locomotor activity in the open field test. In contrast, after the concomitant administration of both drugs, the anxiolytic effects were no longer produced in the elevated plus-maze. The increased locomotor activity was also diminished in both tests of exploratory behaviour. These results shed light on the GABA hypothesis of anxiety, insofar as the increased availability of GABA, resulting from either GABA-T inhibition (vigabatrin) or facilitation of GABA-mediated chloride channels (phenobarbitone), seems to result in an increased emotional reactivity which, however, subsequently disappears during combined treatment.peer-reviewe