Large DHW solar systems with distributed storage tanks

The thermal behaviour of a central DHW solar system, the design of which is based on a new Central Collection-Separate Storing (CCSS) approach, has been investigated theoretically. The common practice for large DHW solar systems, of employing a central storage and delivery facility, has been shown in the past to exhibit a rather poor performance and considerable heat losses. This is due to the extensive lengths of pipework required for both the transfer of solar energy and the delivery of hot water. The CCSS solar system presented can overcome the above problems by employing separate storage tanks for each family, thus being best suited for multistory buildings. The simulation analysis has revealed a number of interesting features for the system performance: (i) the collected energy is distributed to all users in a fair manner, irrespective of their distance from the collector field and the daily hot water consumption profiles; (ii) an energy saving behaviour is most likely to evolve by most users, since the auxiliary energy consumptions are charged individually (unlike in large DHW solar systems with central water storage and delivery); and (iii) high values of solar fractions, comparable with those attained by thermosiphon systems, have been derived.     

EEG-based BCI and video games: a progress report

This paper presents a systematic review of electroencephalography (EEG)-based brain–computer interfaces (BCIs) used in the video games, a vibrant field of research that touches upon all relevant questions concerning the future directions of BCI. The paper examines the progress of BCI research with regard to games and shows that gaming applications offer numerous advantages by orienting BCI to concerns and expectations of a gaming application. Different BCI paradigms are investigated, and future directions are discussed.     

Efficient, numerically robust characterisation of a large, double-loop antenna array

Arrays of circular, double-loops are treated via a semi-analytical technique, on the basis of a Method of Moments formulation. A Pocklington-type integral equation for the current is derived and discretised via a suitable set of basis functions. The matrix corresponding to the pertinent linear system is found to consist of circulant blocks. The system is therefore analytically solvable, and hence, potential ill-conditioning, encountered in large geometry cases, cannot possibly introduce any numerical instabilities to the calculations. Introduction of a delta gap source as excitation facilitates very efficient computation of the current and input admittance. The algorithm exploits almost exclusively elementary functions and yields results in terms of a set of rapidly convergent series, applicable to extremely large loops. Data for such loops are presented for the first time in literature. The method is expected to lead in the future to very efficient designs of multi-loop arrays.     

Measurement of the electromagnetic field radiating by commercial ESD generators with the Pellegrini target on insulating material

The aim of this work is the investigation of the transient electromagnetic field radiating by two different commercial generators of electrostatic discharges. Measurements of both magnetic and electric field generated by contact electrostatic discharges have been carried out a few centimeters away from the discharge point. In this paper the current transducer, which is used for the measurement of the discharge current is not mounted on a grounded metal plate, but on an insulating material. With this aberration to the Standard a closer simulation to the electromagnetic field produced by the electrostatic discharge generators on the equipment under test is obtained. This experiment is closer to real conditions of electrostatic discharges, which do not involve a metal plate. It is proved by measurements that each generator produces a different transient electromagnetic field, which has different repercussions on the equipment that is tested. Comparisons of the radiating field between the two generators and useful conclusions for the variation of the electromagnetic field are also presented.     

Coherent Structure Dynamics in Turbulent Flows Past In-Stream Structures: Some Insights Gained via Numerical Simulation

Large-scale coherent vortical structures in natural streams and rivers dominate flow and transport processes and impact the stability of stream banks, the diversity and abundance of organisms, and the quality of running waters in aquatic ecosystems. Thus, understanding and being able to model the dynamics of energetic coherent structures in such flows at ecologically relevant scales are crucial prerequisites for developing a science-based ecosystem restoration framework. We review recent progress toward the development of coherent-structure-resolving (CSR) computational fluid dynamics techniques, based on hybrid URANS/LES modeling strategies, for simulating turbulent flows in open-channels with hydraulic structures. CSR simulations of the turbulent horseshoe vortex (THSV) past bed-mounted piers explained the physical mechanism leading to the experimentally documented bimodal velocity fluctuations of the vortex and underscored the importance of the Reynolds number as a key parameter governing the THSV dynamics. Simulations of high Reynolds number flows past surface-piercing, groynelike structures in open channels revealed the complexity of the recirculating region at the upstream face of the groyne, underscored the interaction of the flow in this region with the energetic shear layer shed from the point of separation at the upstream side wall, and demonstrated the importance of flow depth in the vorticity dynamics of such flows. The paper also identifies areas for future work and modeling challenges that need to be addressed for the computational tools to be able to accurately predict flow and transport processes in real-life aquatic environments.     

Oxygen sensors based on a new design concept for amperometric solid state devices

A new design for all-solid amperometric detectors was tested as an oxygen sensor in the 1%–25% v/v concentration range. The design consisted of both the working (WEs) and counter electrodes (CEs) being vacuum-deposited as non-porous Au layers on the same face of a Nafion® membrane and in contact with the gas sample. Both a three-electrode device (the reference electrode being a strip of Ag/AgCl inserted between the two Au layers) and a two-electrode one were tested. In the former case, the sensor exhibited good linearity with oxygen concentration, response times comparable to a commercial sensor but a strong dependence on humidity. The origin of the latter is not due to ohmic losses but rather to the loss of catalytic activity with decreasing water contact in the polymer. The two-electrode device exhibits signal saturation at high oxygen concentrations, which is interpreted by limitations imposed by the CE reactivity. In both cases, oxygen reduction led to an exponential current rise over a wide potential range indicating very high mass transport rates and implying that the electroactive gas reacts at the line formed by the gas/solid electrolyte/metal layer interface.     

AntP2PR: An ant intelligence inspired routing scheme for Peer-to-Peer networks

Unstructured Peer-to-Peer networks consist of an infrastructure-less overlay on top of another network. Most of them use distributed algorithms for all operations, such as resource discovery or connectivity control. Research has shown that a considerable amount of the generated traffic is due to signaling messages. Furthermore, another challenge when implementing a Peer-to-Peer network is avoiding free riders, i.e. users trying to profit from the network without sharing their resources. In this paper a new approach to routing packets in such networks is presented using ant intelligence. Success messages are used as agents and the biological procedure of pheromone trails is used for forwarding new packets used in resource discovery. These agents carry an amount of pheromone which will be added to a pheromone table representing routes to other peers. This approach enables the network to adjust to the dynamic nature of Peer-to-Peer networks where new nodes connect and disconnect continuously. Peers that are free riding will be ultimately isolated from the rest of the network by limiting the number of messages directed to them. The authors have simulated an unstructured Peer-to-Peer network, such as Gnutella, that uses this method and the results are very promising. The amount of traffic used solely for resource discovery is greatly reduced enabling the users to use more bandwidth for transferring content.     

The effect of the hysteresis band on power management strategies in a stand-alone power system

A stand-alone power system that consists of a photovoltaic array and wind generators for the exploitation of renewable energy sources (RES), and that is capable of storing excessive energy in the form of hydrogen via water electrolysis for subsequent use in a polymer electrolyte membrane (PEM) fuel cell is currently being installed at Neo Olvio of Xanthi in Greece. The performance of two power management strategies (PMSs) that utilize a hysteresis band in the operation of the integrated system over a typical 4-month period is assessed. The state-of-charge (SOC) level of the accumulator is the main parameter that governs the operation of the electrolyzer and the fuel cell. The introduction of a hysteresis band in the boundary limits of the SOC of the accumulator provides larger flexibility in the operation of the electrolyzer, the fuel cell, and the accumulator. In this way, the units can be protected from heavy and unnecessary utilization or irregular operation (reduction of frequent start-ups and shut-downs). The simulated results for the implemented PMSs revealed important information about the reliability of the load satisfaction, the total operation time that each subsystem undergoes, as well as about the hydrogen inventory in the integrated system. The study also identified the effect of variation of hysteresis band size on the system performance as an important feature for the development of an integrated control strategy.