The influence of wall orientation and exterior surface solar absorptivity on time lag and decrement factor in the Greek region

The aim of this study is to determine how time lag and decrement factor are affected by wall orientation and exterior surface solar absorptivity, for specific climatic conditions. Their influence forms a non-sinusoidal periodical forcing function that simulates suitably the outdoor temperature fluctuations. This novel approach, allows the predictability of building's thermal response in an efficient way. The investigation is carried out for various insulated opaque wall formations comprising typical material elements, during the summer period in the mild Greek region. This study that allows proper building planning procedures, at the very early stages of the envelope design, presents great importance. The analysed configurations are assumed to have an orientation that corresponds to each compass point. In addition, the solar absorptivity of surface coatings is assumed to be varying from 0 to 1. The transient thermal analysis is obtained via a thermal circuit that models accurately the fundamental heat transfer mechanisms on both boundaries and through the multi-layered wall configurations. Moreover, the mathematical formulation and solution of this lumped model is achieved in discrete time steps by adopting the non-linear nodal method. The simulation results are focused on the single and combined effects of orientation and solar absorptivity on the dynamic thermal characteristics of various wall configurations.     

Overall reliability determination of computer networks with hierarchical routing strategies

This paper determines the overall reliability of a computer network in which hierarchical routing strategies are used for the communication between its nodes.An exact method is presented which is followed by three fast computer techniques corresponding to three different routing policies. The first two give the exact value for the overall reliability while the third provides a lower bound which is very close to the exact reliability value. The main advantages of these techniques are the important savings in computation time and available memory. The developed algoriths are very useful in the overall reliability evaluation of large networks or many interconnected subnetworks.     

Assessing the determinants of local acceptability of wind-farm investment: A choice experiment in the Greek Aegean Islands

This paper aims at analysing the factors, which motivate communities to resist the installation of wind farms in their vicinity. To this end, the choice experiment methodology was employed in communities in two Greek Aegean Islands to assess the determinants of preferences towards different wind-farm projects. Unlike other studies, the willingness to accept welfare measure was adopted. The results of our analysis show that the conservation status of the area where the wind farms are to be installed, along with the governance characteristics of the planning procedure are the most important determinants of local community welfare in relation to wind farms. In contrast to other studies, we find that the physical attributes of wind farms appear to be of less relative importance from a local community welfare point of view. Implications for the EU's future energy policy are drawn.     

A rapid smart approach for reliability and failure mode analysis of memories and large systems

This paper presents a novel system simulation methodology based on the known Monte Carlo technique, used for reliability and failure mode analysis of complex and large systems. The presented approach, called “state-merging and assorted random-testing” (SMART), is particularly applicable to systems involving different types of clusters of identical components, and is ideally suited for simulation of huge memories and similar systems. Simulators based on this approach are insensitive to the number of system components, system reliability or the number of associated spares or standby units, and thus they afford an extremely small simulation time compared to the accelerated Monte Carlo simulation time.     

Experimental approach to the contribution of plant-covered walls to the thermal behaviour of building envelopes

The use of vegetation has an important impact on the thermal performance of buildings and on the modification of the urban climate as well, both in winter and summer. Plants absorb a significant amount of solar radiation for their growth and biological functions, functioning as a solar barrier that prevents solar radiation absorption extensively. Their utilization is essential and can considerably improve the microclimate of the built environment. Vegetation planted to cover the external surface of a building is common practice in urban areas. However, up to now, it has not been fully approved as an energy-saving method. Climbers can provide a cooling potential on the building surface, which is very important during the hot periods of the year, especially in warm climates. Hence, the peak temperatures that appear are essentially lower, in addition to the decrease of heat flow losses. In this study the thermal analysis concerns two equivalent building floors that incorporate non-covered and covered with plants wall sections (insulated wall surfaces), respectively. The investigation is carried out during the cooling period in the Greek region. A comparison between the bare and plant-covered surface sections of the walls is conducted via an experimental setup (stationary method). Results are focused on the developed temperature variations and dynamic thermal characteristics of wall surfaces for both cases under investigation. As it is shown, the contribution of plant-covered wall sections is important so that the thermal behaviour of the building envelope can be improved.     

The influence of the zone's indoor temperature settings on the cooling/heating loads for fixed and controlled ventilation

In this study, the thermal performance and the energy requirements of a building single-zone are investigated for both the cooling and heating seasons by employing a thermal-network model. The model has six primary heat-flow paths, in order to take into account the position of insulation in the building envelope, and two secondary paths for the ventilation and the cooling/heating unit. The desired indoor temperature of the zone is defined by a pair of preset points of a thermostat. The energy demands and the resulting indoor temperature variations are determined for fixed ventilation as well as for temperature-controlled ventilation. Computer results for both seasons show how the combined influence of slab structure formations, the desired indoor temperature and ventilation control affect the cooling and heating loads.     

Determination of combinational logic circuit reliability through generation of fault diagnosis tests

This paper investigates the relationships between a given set of excitation vectors and the test sets for faults occuring in combinational circuits, in order to obtain new conditions for determining the redundant cubes of terminal states. The analysis presented is concluded with two new algorithms for the evaluation of combinational logic circuit reliability.     

Optimum Redundancy of Repairable Modules

The design of modules to have some redundant functions in order to minimize module production cost is analysed. Upon production modules with failed functions are either discarded or repaired. If some functions have 2 elements in parallel, the production cost of a module can be minimized if modules are discarded or repaired, depending on the number of redundant functions, number of functions per module, element costs and element quality. The number of failed functions above which the module is discarded rather than repaired is calculated using a simple computer algorithm.     

Design and analysis of a self-testing-and-repairing random access memory “STAR–RAM” with error correction

This paper presents the philosophy and design of a fault-tolerant dynamically-reconfigurable random access memory (RAM) system with a built-in Self-Testing-And-Repairing “STAR” engine. The STAR engine, supported by SEC–DED capability, provides on-line fault detection, correction, analysis and repair without destroying useful data stored in the memory. Reliability analysis of the presented system has been accomplished using a SMART simulation approach[1], and results show significant reliability enhancement over SEC–DED RAM designs. The memory system employs a hardware parallel address-comparison mechanism for rapid processing of incoming addresses during normal read/write operations to minimize memory access delay. The flexible STAR architecture and the low hardware overhead enables utilization of the proposed approach in VLSI memory chips as well as in WSI and large memory modules.     

An Algorithm for Evaluating Overall Reliability of Special Tree-Networks

The overall reliability of networks composed of trees, cycles and semi-cycles is determined using a computer algorithm. An n-node cycle contains n nodes and links forming a single loop; an n-node semi-cycle has more than one loop, but reduces to a cycle upon the removal of one link. The algorithm identifies all cycles and semi-cycles and determines iteratively the overall reliability using a simple formula and Bayesian decomposition.