Structural phase transition and dielectric relaxation in Pb(Zn1/3Nb2/3)O3 single crystals

The structure and the dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN) crystal have been investigated by means of high-resolution synchrotron x-ray diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in the frequency range of 100 Hz - 1 MHz). At high temperatures, the PZN crystal exhibits a cubic symmetry and polar nanoregions inherent to relaxor ferroelectrics are present, as evidenced by the single (222) Bragg peak and by the noticeable tails at the basis of the peak. At low temperatures, in addition to the well-known rhombohedral phase, another low-symmetry, probably ferroelectric, phase is found. The two phases coexist in the form of mesoscopic domains. The para- to ferroelectric phase transition is diffused and observed between 325 and 390 K, where the concentration of the low-temperature phases gradually increases and the cubic phase disappears upon cooling. However, no dielectric anomalies can be detected in the temperature range of diffuse phase transition. The temperature dependence of the dielectric constant show the maximum at higher temperature (Tm = 417 - 429 K, depending on frequency) with the typical relaxor dispersion at T < Tm and the frequency dependence of Tm fitted to the Vogel-Fulcher relation. Application of an electric field upon cooling from the cubic phase or poling the crystal in the ferroelectric phase gives rise to a sharp anomaly of the dielectric constant at T 390 K and diminishes greatly the dispersion at lower temperatures, but the dielectric relaxation process around Tm remains qualitatively unchanged. The results are discussed in the framework of the present models of relaxors and in comparison with the prototypical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3.Comment: PDF file, 13 pages, 6 figures collected on pp.12-1

Feasibility Study of Pumping Cycle Kite Power System Implication in Scotland UK

To meet the worldwide requirements of carbon emission reduction, the European Council set a target for 15% of final energy consumption in the UK to come from renewable energy by 2020. In the UK, the Climate Change Act (2008) set a target for the reduction of 80% of carbon emissions by 2050. The biggest renewable energy sources in the UK are bioenergy, wind, solar and hydro. The UK is located in a windy area and is one of the top locations in the world for wind power, often considered to be the best in Europe. Since the 1980’s, the number of wind farms has increased greatly. Wind turbines extract wind energy from 100 metres above the ground. Airborne Wind Energy (AWE) systems enable the extraction of more energy from the wind at elevated altitudes beyond 150 meters using a technique termed pumping cycle kite power system. Scotland is the most suitable location for the implementation of AWE systems in the UK. In this work, the annual energy production of such a pumping cycle kite power system in Scotland was analysed using Luchsinger’s analytical models. The annual energy production was found to be over 3.4MWh/m2 in all five locations in Scotland

Viability of Airborne Wind Energy in the United Kingdom

To meet the worldwide requirements of carbon emission reduction, the European Council has set the UK a 15% energy target to come from renewable energy by 2020. The biggest renewable energy sources in the UK are bioenergy, wind, solar and hydro. The UK is located in prime geography, considered to be the best in Europe, for harvesting and over the last three decades, the number of wind farms has increased greatly. However, the interaction of wind speed and structural strength have limited the height of platform-based wind turbines to a maximum height of around 100 m. Airborne Wind Energy (AWE) systems enable the extraction of more energy from the wind at elevated altitudes beyond 150 meters using a device termed a kite. A method is required to determine suitable locations for AWE system implementation. In this work, a regional feasibility study is conducted to establish an ideal suitable location to implement the AWE system. Extensive work has been carried out to assess the electricity costs and energy savings, area availability as well as regional airborne wind energy power densities at different regions within the UK. A standardised method has been developed to assess the viability of AWE in various geographical locations. It was found that Scotland was the most suitable location for the implementation of an AWE systems due to the high wind power density in this region and existing high costs of electricity thus greater potentials for energy cost savings. This is the pre-print version of an article printed in the Journal of Thermal Science and Engineering Applications, published by the American Society of Mechanical Engineers. The full published version is available online at: http://thermalscienceapplication.asmedigitalcollection.asme.org/journal.asp

Guiding optical flows by photonic crystal slabs made of dielectric cylinders

We investigate the electromagnetic propagation in two-dimensional photonic crystals, formed by parallel dielectric cylinders embedded a uniform medium. The frequency band structure is computed using the standard plane-wave expansion method, while the propagation and scattering of the electromagnetic waves are calculated by the multiple scattering theory. It is shown that within partial bandgaps, the waves tend to bend away from the forbidden directions. Such a property may render novel applications in manipulating optical flows. In addition, the relevance with the imaging by flat photonic crystal slabs will also be discussed.Comment: 5 pages, 5 figure

Closed-Loop Evaluation of an Embedded Visual Servo System

No abstract