Multi-agent quality of experience control

International Journal of Control, Automation and Systems - In the framework of the Future Internet, the aim of the Quality of Experience (QoE) Control functionalities is to track the personalized...     

Multiple pole residue approach for 3D BEM analysis of mathematical degenerate and non‐degenerate materials

In this paper we develop an alternative boundary element method (BEM) formulation for the analysis of anisotropic three‐dimensional (3D) elastic solids. Our implementation is based on the derivation of explicit expressions for the fundamental solution displacements and tractions, of general validity for any class of anisotropic materials, by means of Stroh formalism and Cauchy's residue theory. The resulting fundamental solution remains valid for mathematical degenerate cases when Stroh's eigenvalues are coincident, meanwhile it does not exhibit numerical instabilities for quasi‐degenerate cases when Stroh's eigenvalues are nearly equal. A multiple pole residue approach is followed, leading to general explicit expressions to evaluate the traction fundamental solution for poles of m‐multiplicity. Despite the existence of general displacement solutions in the literature, and for the sake of completeness, the same approach as for the traction solution is considered to derive the displacement fundamental solution as well. Based on these solutions, an explicit BEM approach for the numerical solution of 3D linear elastic problems for solids with general anisotropic behavior is presented. The analysis of cracked anisotropic solids is also considered. Details on the numerical implementation and its validation for degenerate cases are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Single p-type/intrinsic/n-type silicon nanowires as nanoscale avalanche photodetectors

We report the controlled synthesis of axial modulation-doped p-type/intrinsic/n-type (p-i-n) silicon nanowires with uniform diameters and single-crystal structures. The p-i-n nanowires were grown in three sequential steps: in the presence of diborane for the p-type region, in the absence of chemical dopant sources for the middle segment, and in the presence of phosphine for the n-type region. The p-i-n nanowires were structurally characterized by transmission electron microscopy, and the spatially resolved electrical properties of individual nanowires were determined by electrostatic force and scanning gate microscopies. Temperature-dependent current-voltage measurements recorded from individual p-i-n devices show an increase in the breakdown voltage with temperature, characteristic of band-to-band impact ionization, or avalanche breakdown. Spatially resolved photocurrent measurements show that the largest photocurrent is generated at the intrinsic region located between the electrode contacts, with multiplication factors in excess of ca. 30, and demonstrate that single p-i-n nanowires function as avalanche photodiodes. Electron- and hole-initiated avalanche gain measurements performed by localized photoexcitation of the p-type and n-type regions yield multiplication factors of ca. 100 and 20, respectively. These results demonstrate the significant potential of single p-i-n nanowires as nanoscale avalanche photodetectors and open possible opportunities for studying impact ionization of electrons and holes within quasi-one-dimensional semiconductor systems.     

Identification of the flavonoid fraction in saffron spice by LC/DAD/MS/MS: Comparative study of samples from different geographical origins

The flavonoid fraction in saffron spice has been analysed, for the first time, by LC-DAD-MS/MS ESI and five kaempferol derivatives have been found. Compounds such as kaempferol-3-sophoroside, kaempferol-3-sophoroside-7-glucoside and kaempferol-3,7,4′-triglucoside were tentatively identified, whereas other compounds, such as kaempferol tetrahexoside and kaempferol-3-dihexoside were detected. Saffron samples from different geographical origins were clearly separated by their kaempferol 3-sophoroside contents that were able to explain 100% of the variance when a discriminant test was carried out.     

A generalized approach to the analysis of voltage stability in electric power systems

In this paper a new method for analysing the voltage stability problem in electric power systems is presented. The approach starts with a linearized model in state space form of a multi-machine power system, then rigorous voltage stability conditions are derived on the basis of a suitable aggregated model of the original system capable of retaining the dynamics of voltages at generator and load nodes.The approach allows a systematic individualization of all the dynamic factors which affect voltage instability phenomena and suggests the appropriate representation which has to be adopted for each dynamic component of the system.The validity and usefulness of the suggested method are illustrated by carrying out simulation studies on a sample power system.     

Milankovitch’s Theorie der Druckkurven: Good mechanics for masonry architecture

During the nineteenth century many studies on the theory of the thrust line were written in connection with the stability of masonry structures. However, a general treatment of the theory of the thrust line from both a mechanical and mathematical point of view may be found only in the contributions of the Serbian scholar Milutin Milankovitch, published between 1904 and 1910 and substantially unknown to the historians of mechanics applied to architecture. This paper aims at presenting Milankovitch’s theory and discussing its improvements with respect to the previous literature on the subject.