All Minimal Prime Extensions of Hereditary Classes of Graphs

The substitution composition of two disjoint graphs G1 and G2 is obtained by first removing a vertex x from G2 and then making every vertex in G1 adjacent to all neighbours of x in G2. Let F be a family of graphs defined by a set Z* of forbidden configurations. Giakoumakis [V. Giakoumakis, On the closure of graphs under substitution, Discrete Mathematics 177 (1997) 83–97] proved that F∗, the closure under substitution of F, can be characterized by a set Z∗ of forbidden configurations — the minimal prime extensions of Z. He also showed that Z∗ is not necessarily a finite set. Since substitution preserves many of the properties of the composed graphs, an important problem is the following: find necessary and sufficient conditions for the finiteness of Z∗. Giakoumakis [V. Giakoumakis, On the closure of graphs under substitution, Discrete Mathematics 177 (1997) 83–97] presented a sufficient condition for the finiteness of Z∗ and a simple method for enumerating all its elements. Since then, many other researchers have studied various classes of graphs for which the substitution closure can be characterized by a finite set of forbidden configurations. The main contribution of this paper is to completely solve the above problem by characterizing all classes of graphs having a finite number of minimal prime extensions. We then go on to point out a simple way for generating an infinite number of minimal prime extensions for all the other classes of F∗

Clique separator decomposition of hole-free and diamond-free graphs and algorithmic consequences

AbstractClique separator decomposition, introduced by Whitesides and Tarjan, is one of the most important graph decompositions. A hole is a chordless cycle with at least five vertices. A paraglider is a graph with five vertices a,b,c,d,e and edges ab,ac,bc,bd,cd,ae,de. We show that every (hole, paraglider)-free graph admits a clique separator decomposition into graphs of three very specific types. This yields efficient algorithms for various optimization problems in this class of graphs

Escaping the Slippery Slope: Freedom of Expression and Cyberspace Regulation after the Delfi Case

In June 2015, the European Court of Human Rights delivered the final judgment in the Delfi case, where it upheld the decision of an Estonian court to fine a news portal for hosting anonymous defamatory comments. This controversial judgment has a chilling effect on freedom of expression in cyberspace and paves the way for a slippery slope leading to online censorship. The key policy issue is striking a balance between freedom of expression and other protected interests, including privacy, reputation and national security. This paper argues that holding Internet Service Providers (ISPs) liable for third-party content places a disproportionate burden on them and destabilises the architecture of Web 2.0 to the detriment of human rights. To this end, we argue that a new regulatory approach is necessary to address the rights of ISPs in the attempt to balance freedom of expression with new developments in the need for protection of personal data

Estimating annual buildings ground floors heat losses using a one-dimensional (1-D) numerical model

In this work, an estimation of the annual buildings ground floors heat losses by means of numerical simulations of two different geometrical models (constructional details of buildings ground floors), using a 1-D numerical model, is attempted. Given the three-dimensional (3-D) nature of the heat transfer through the ground, the annual ground floor heat losses are first estimated using a 3-D model, constructed and simulated with the thermal analysis computer programs: "TRISCO" & "VOLTRA". Then, the 3-D model is converted to the 'respective' one-dimensional (1-D) one and the 'equalization' of the two models - for the both cases (geometrical models) - as far as the annual ground floor heat losses per unit surface area are concerned, is done by changing the values of the various simulation parameters of the used computer programs. Furthermore, since the various simulation tools, such as "TAS" thermal analysis software, generally simulate all heat transfer processes in one dimension - those through the ground floors included - and model the soil depth, in particular, to be: 1m, an estimation of the possibly introduced, in this 'methodology', errors is made, by comparing the respective results derived from the 3-D & 1-D numerical models. As far as the 'equalization' of the 1-D & 3-D numerical models is concerned, the results in question 'revealed' that, the (1-D numerical model's) soil depth, primarily and the soil thermal conductivity (A), secondly, are the most significant simulation parameters for the achievement of this aim. Regarding the errors possibly introduced in the process of estimating the annual buildings ground floor heat losses using a 1-D numerical model (with a soil depth value of: 1m), it is shown that, the size of these errors - for the specific models examined in this work - is approximately: -38% for the first and: +59% for the second one and, furthermore, that, the definition of the 'proper' soil depth value depends on the specific numerical model (its geometry, configuration and simulation parameters), as well as, the soil type and its thermal properties, the thermal conductivity being the most significant one. However, given the limited capabilities of "VOLTRA" thermal analysis computer program and of the PCs used for the numerical simulations, as well as, the great differences between the various numerical models (regarding their: geometry, configuration, simulation parameters and soil type/ thermal properties), a generalization of the conclusions presented hereby cannot be defended. Keywords: Annual buildings heat losses via the ground Numerical simulations Thermal analysis computer programs "TRISCO" & "VOLTRA" 'Equalization' of the 1-D & 3-D numerical models Estimating the annual buildings ground floor heat losses using a 1-D numerical model "TAS" thermal analysis software Soil depth (of the 1-D numerical model) Soil thermal conductivity

An examination of the housing market in Crete, Greece A research from a perspective for the developer

This report examines the housing market in Crete. It identifies that house prices are detennined by the supply of housing, the supply of finance, the demand for housing, and confidence rather than by the construction cost. The increasing wealth in Europe, and the increased accessibility with more frequent and cheaper flights attributed most to the increased demand for second homes in Crete. Demand for both first and second home markets in Crete is high and is expected to remain high. From 2000 to 2005, housing stock increased in Crete by 8.2% to meet the demand, while the output of new dwellings increased by 78.4% during the same period. The multi-European clientele of the property market in Crete is making it a multi-source market with potential benefits of high stability and strength. On the other hand, the frequent changes in the planning system create problems to the developers. In the wake of increased foreign involvement in the market, Greek developers would have to form alliances while investing in better marketing strategies. The retirement market, made particularly appealing by retirees' tremendous purchasing power, is quickly becoming the hot housebuilding category

Bi-complement Reducible Graphs

AbstractWe introduce a new family of bipartite graphs which is the bipartite analogue of the class ofcomplement reduciblegraphs orcographs. Abi-complement reduciblegraph orbi-cographis a bipartite graphG=(W∪B,E) that can be reduced to single vertices by recursively bi-complementing the edge set of all connected bipartite subgraphs. Thebi-complementedgraphḠbipofGis the graph having the same vertex setW∪BasG, while its edge set is equal toW×B−E. The aim of this paper is to show that there exists an equivalent definition of bi-cographs by three forbidden configurations. We also propose a tree representation for this class of graphs

A study of PC-based HF Ionospheric Propagation predictions for use in Naval communications

High frequency (HF) ionospheric propagation predictions have been available on mainframe computers since the late 1960s. Since the advent of low cost, computationally powerful personnel computers, several propagation codes have been ported from mainframes to PC's. This study compares results from two versions of the IONCAP and PROPHET HF propagation prediction codes to a database of measured electric field strengths. IONCAP-PC 2.5 predictions were compared to IONCAP-VAX 85.04 predictions and to those from PROPHET 3.2 (PC-version). A database of measured signal strengths from the CCIR containing over 16,000 points or cases was used as a benchmark for comparing code results. For both IONCAP-PC 2.5 and PROPHET 3.2, field strength predictions were low in more than 50% of the cases examined. This was particularly true for PROPHET, which is considered to be a conservative model. PROPHET features quick solution, graphical outputs, and a user-friendly environment, in comparison to IONCAP. IONCAP-PC 2.5, which is an improved version of a previous mainframe IONCAP, produced slightly more accurate predictions than IONCAP 85.04, and substantially better results than those from PROPHET.http://archive.org/details/astudyofpcbasedh1094527747Lieutenant Junior Grade, Hellenic NavyApproved for public release; distribution is unlimited