Nonlinear interactions between high-Q optical and acoustic modes in dielectric particles

The interaction between acoustic breathing modes and optical Mie resonances in a spherical particle made of a chalcogenide glass material is investigated by means of rigorous calculations, correct to any order in the acousto-optic coupling parameter. Our results reveal the occurrence of strong effects beyond the linear-response approximation, which lead to enhanced modulation of light by acoustic waves through multiphonon exchange mechanisms when both photons and phonons have a very long lifetime inside the particle

On the Surface Restructuring of Highly Dilute Alloys and its Effects on Catalytic Performance

Recent studies have shown that highly dilute alloys of platinum group metals (PGMs: Pt, Rh, Ir and Pd) with coinage metals (Cu, Au, and Ag) serve as highly selective and coke–resistant catalysts in a number of important chemical reactions. These materials are composed of trace amounts of a PGM or Ni, whose atoms are embedded in a coinage metal surface, and their catalytic behaviour is governed by the size and shape of the surface clusters of PGM atoms. Therefore, establishing a means of control over the topological architecture of highly dilute alloy surfaces is crucial to achieving catalytic performance tailored to a specific application. This Thesis employs density functional theory, kinetic Monte Carlo and microkinetic modelling in order to investigate ways of manipulating the surface architecture of a number of dilute alloy surfaces towards optimal performance for key catalytic reactions. The latter include the direct dissociations of NO, CO2 and N2, and the reverse events, which are important in, among others, emission control technologies. Also examined is the potential of a Ni/Cu dilute alloy for the NO + CO chemistry, and it is demonstrated that the selectivity toward the desired products can be manipulated by tuning the size of the Ni clusters in the ensemble. The results can guide future theoretical, surface science and catalysis studies on highly dilute alloys, towards the development of superior catalysts that can efficiently accelerate chemistries of industrial significance

Energy efficiency parametric design tool in the framework of holistic ship design optimization

Recent International Maritime Organization (IMO) decisions with respect to measures to reduce the emissions from maritime greenhouse gases (GHGs) suggest that the collaboration of all major stakeholders of shipbuilding and ship operations is required to address this complex techno-economical and highly political problem efficiently. This calls eventually for the development of proper design, operational knowledge, and assessment tools for the energy-efficient design and operation of ships, as suggested by the Second IMO GHG Study (2009). This type of coordination of the efforts of many maritime stakeholders, with often conflicting professional interests but ultimately commonly aiming at optimal ship design and operation solutions, has been addressed within a methodology developed in the EU-funded Logistics-Based (LOGBASED) Design Project (2004–2007). Based on the knowledge base developed within this project, a new parametric design software tool (PDT) has been developed by the National Technical University of Athens, Ship Design Laboratory (NTUA-SDL), for implementing an energy efficiency design and management procedure. The PDT is an integral part of an earlier developed holistic ship design optimization approach by NTUA-SDL that addresses the multi-objective ship design optimization problem. It provides Pareto-optimum solutions and a complete mapping of the design space in a comprehensive way for the final assessment and decision by all the involved stakeholders. The application of the tool to the design of a large oil tanker and alternatively to container ships is elaborated in the presented paper

Fault specific GIS based seismic hazard maps for the Attica Region, Greece

Traditional seismic hazard assessment methods are based on the historical seismic records for the calculation of an annual probability of exceedance for a particular ground motion level. A new fault specific seismic hazard assessment method is presented, in order to address problems related to the incompleteness and the inhomogeneity of the historical records and to obtain higher spatial resolution of hazard. This method is applied to the region of Attica, which is the most densely populated area in Greece, as nearly half of the country’s population lives in Athens and its surrounding suburbs, in Greater Athens Area. The methodology is based on a database of 22 active faults that could cause damage to Attica in case of seismic rupture. This database provides information about the faults slip rates, lengths and expected magnitudes. The final output of this method are four fault specific seismic hazard maps, showing the recurrence of expected intensities that each locality in the map has been shaken at. These maps offer a high spatial resolution, as they consider the surface geology. Despite the fact that almost half of the Attica region lies on the lowest seismic risk zone according to the official seismic hazard zonation of Greece, different localities have repeatedly experienced strong ground motions during the last 15 kyrs. Moreover, the maximum recurrence for each intensity occurs in different localities across Attica. Highest recurrence for intensity VII (151-156 times over 15 kyrs, or up to 96 year return period) is observed in the central part of the Athens basin. The maximum intensity VIII recurrence (114 times over 15 kyrs, or up to 131 year return period) is observed in the western part of Attica, while the maximum intensity IX (73-77/15kyrs, or 195 year return period) and X (25-29/15kyrs, or 517 year return period) recurrences are observed near the South Alkyonides fault system, which dominates the strong ground motions hazard in the western part of the Attica mainland

Are we teaching our students what they need to know about ageing? Results from the National Survey of Undergraduate Teaching in Ageing and Geriatric Medicine

Introduction - Learning about ageing and the appropriate management of older patients is important for all doctors. This survey set out to evaluate what medical undergraduates in the UK are taught about ageing and geriatric medicine and how this teaching is delivered. Methods – An electronic questionnaire was developed and sent to the 28/31 UK medical schools which agreed to participate. Results – Full responses were received from 17 schools. 8/21 learning objectives were recorded as taught, and none were examined, across every school surveyed. Elder abuse and terminology and classification of health were taught in only 8/17 and 2/17 schools respectively. Pressure ulcers were taught about in 14/17 schools but taught formally in only 7 of these and examined in only 9. With regard to bio- and socio- gerontology, only 9/17 schools reported teaching in social ageing, 7/17 in cellular ageing and 9/17 in the physiology of ageing. Discussion – Even allowing for the suboptimal response rate, this study presents significant cause for concern with UK undergraduate education related to ageing. The failure to teach comprehensively on elder abuse and pressure sores, in particular, may be significantly to the detriment of older patients

Acousto-optic interaction enhancement in dual photonic-phononic cavities

Light control through elastic waves is a well established and mature technology. The underlying mechanism is the scattering of light due to the dynamic modulation of the refractive index and the material interfaces caused by an elastic wave, the so-called acousto-optic interaction. This interaction can be enhanced in appropriately designed structures that simultaneously localize light and elastic waves in the same region of space and operate as dual optical-elastic cavities, often called phoxonic or optomechanical cavities. Typical examples of phoxonic cavities are multilayer films with a dielectric sandwiched between two Bragg mirrors or, in general, defects in macroscopically periodic structures that exhibit dual band gaps for light and elastic waves. In the present work we consider dielectric particles as phoxonic cavities and study the influence of elastic eigenmode vibrations on the optical Mie resonances. An important issue is the excitation of elastic waves in such submicron particles and, in this respect, we analyze the excitation of high-frequency vibrations following thermal expansion induced by the absorption of a femtosecond laser pulse. For spherical particles, homogeneous thermalization leads to excitation of the particle breathing modes. We report a thorough study of the acousto-optic interaction, correct to all orders in the acousto-optic coupling parameter, by means of rigorous full electrodynamic and elastodynamic calculations, in both time and frequency domains. Our results show that, under double elastic-optical resonance conditions, strong acousto-optic interaction takes place and results in large dynamical shifts of the high-Q optical Mie resonances, manifested through multiphonon exchange mechanisms

GEOTHERMIC STATUS OF THERMOPYLAE - ANTHILI AREA IN FTHIOTIDA PREFECTURE

The purpose of this study was the discovery, identification and evaluation of directly exploitable geothermal fields, in the Thermopylae - Anthili area (100km2 ). After the evaluation and the processing of any preexisting data, followed the surface works, such as further geological mapping, tectonic and stratigraphic correlations and analyses, geothermal impressions, observations at 30 recorded points (springs, drillings, wells) regarding water sampling, chemical analyses, temperature, pH and conductivity measurements, special sampling for Br and isotopes analyses. The in depth works that took place concern geophysical prospecting, loggings, small and large diameter drillings. All the data were digitized and processed in a GIS environment. After correlating all the data collected for the region, a geological - geothermal model was constructed. According to this model, water percolates through permeable formations, joints and faults, gets mixed with the existing salt water, warms up and then ascends to the surface through faults and concentrates on proper reservoirs. Specifically, the region of Damasta where two areas of hot water reservoirs have been identified is of particular geothermal interest. The first, located in Triassic– Jurassic limestones (more than 600m deep), presents the greatest interest in terms of temperature and capacity, while the second (found on the surface and up to 350m deep) is located in Quaternary sediments and the upper formations of the underlying Late Cretaceous limestone