Object oriented modeling of social networks

The aim of this paper is to explain principles of object oriented modeling in the scope of modeling dynamic social networks. As such, the approach of object oriented modeling is advocated within the field of organizational research that focuses on networks.We provide a brief introduction into the field of social networks and present an overview of existing network models and methods. Subsequently we introduce an elementary problem field in the social sciences in general, and in studies of organizational change and design in particular: the micro-macro link. We argue that the most appropriate way to hadle this problem is the principle of methodological individualism. For social network analysis, to contribute to this theoretical perspective, it should include an individual choice mechanism and become more dynamically oriented. Subsequently, object oriented modeling is advocated as a tool to meet these requirements for social network analysis. We show that characteristics of social systems that are emphasized in the methodological individualistic approach have their direct equivalences in object oriented models. The link between the micro level where actors act, and the macro level where phenomena occur as a consequence and cause of these actions, can be modelled in a straightforward way.     

Optimization of the design of recuperative heat exchangers in the exhaust nozzle of an aero engine

Today the needs for safer, cleaner and more affordable civil aero engines are found to be of great importance. Five years ago, the EU initiated an action for the design and the construction of efficient and environmentally friendly aero engines (EEFAE). One of the major European gas turbine industries, MTU, has presented a new technology for an advanced aero engine design, which uses an alternative thermodynamic cycle. The basis of this cycle is the adoption of a recuperation part with the use of a system of heat exchangers, installed in the exhaust nozzle of the aircraft engine. Thermal energy in the turbine exhaust is used in the recuperator to pre-heat the compressor outlet air before combustion. The benefits of this technique are focused on reduced pollutants and decreased fuel consumption. In this work, the procedure of the optimization of this installation, by means of the imposed pressure drop downstream the aircraft engine and the balanced mass inflow to the heat exchangers is presented. The optimization is based on experimental measurements in laboratory conditions and preliminary 2D CFD modeling for the flow inside the exhaust duct and through the heat exchangers. It is shown that with a careful approach, a better arrangement of the heat exchangers can be achieved in order to have a minimum pressure drop in the exhaust nozzle which can positively affect the engine’s performance.     

An iterative construction of isospectral digraphs

Recently, Storm used generating functions to provide a proof that an infinite family of graphs constructed by Cooper have the same Ihara zeta function. Here, we generalize the construction of that infinite family of graphs to a directed graph construction. A similar generating function proof technique applies, and we exhibit conditions under which our digraphs have the same spectra with respect to the adjacency matrix.     

Perceptual weights in auditory level discrimination

Perceptual weights in level discrimination (also called intensity discrimination) were determined for 3-, 7-, 15-, and 24-component tone complexes with flat spectral envelopes using a correlational paradigm. Each frequency component was randomly and independently perturbed in level oneach presentation. For the target interval, frequency-component levels were additionally increased by the level increment to be detected, deltaL [= 201og10((p + deltap)/p), where p is pressure]. Weights were calculated from the across-trial correlation between the level perturbations for each frequency component and the interval chosen by the listener. Two conditions were investigated: (1) deltaL was equal across frequency components, and (2) deltaL increased progressively across frequency components. For both conditions, data for four listeners usually showed the greatest weight for the highest frequency component. The two-to-four highest frequency components generally were most important for level discrimination. The effect of increasing deltaL progressively with frequency was small and inconsistent. Additional measurements showed that flanking noise maskers designed to mask spread of excitation caused only small and generally unsystematic changes to the weights. Overall, these results indicate that listeners combine information across a wide range of auditory channels to arrive at a decision for level discrimination, but the weighting of channels appears to be suboptimal.     

Fission of a multiphase membrane tube

A common mechanism for intracellular transport is the use of controlled deformations of the membrane to create spherical or tubular buds. While the basic physical properties of homogeneous membranes are relatively well known, the effects of inhomogeneities within membranes are very much an active field of study. Membrane domains enriched in certain lipids, in particular, are attracting much attention, and in this Letter we investigate the effect of such domains on the shape and fate of membrane tubes. Recent experiments have demonstrated that forced lipid phase separation can trigger tube fission, and we demonstrate how this can be understood purely from the difference in elastic constants between the domains. Moreover, the proposed model predicts time scales for fission that agree well with experimental findings.     

A systematic approach to the determination of reducible configurations in the four-color conjecture

Reducibility of configurations is determined by an algorithm programmed on a computer. The effectiveness of the program is improved after implementing results obtained by investigating the algebraic structure of the problem. A comprehensive list of reducible configurations up to the 10-ring level is tabled.     

Synthesis and structure of the p-hydroxybenzoic acid polymer

The synthesis and structure of the p-hydroxybenzoic acid polymer is described. The polymer was successfully prepared from either the phenyl ester of p-hydroxybenzoic acid or from p-acetoxybenzoic acid. With highly purified acetoxybenzoic acid, single crystals of the polymer could be prepared. The structure of the polymer was determined and shown to consist of a double helix where the two chains are in a reversed head-to-tail order. The unit cell dimensions are: a = 17.8 Å and c = 18.4 Å, where c corresponds to the chain length with a repeat distance of three units. The mechanism of polymerization and formation of the single crystal is discussed. The polymer displays a reversible high-temperature crystalline transition at 325–360°C (not a melting point). The transition was characterized by differential thermal analysis, differential calorimetry, thermal expansion coefficient measurements, high-temperature x-ray scans, and dielectric constant determinations. Orientation of the polymer chains during fabrication and changes in the mechanism of oxidative degradation above the crystal transition are described.     

An organoiron approach to the benzophenone appendage of the protein kinase C inhibitor balanol

[formula: see text] A new synthetic route to the benzophenone appendage of balanol, based on sequential iron-assisted nucleophilic aromatic substitution and ring-opening as well as regioselective oxidative cyanation, is described.