Search results for "Energy engineering"
showing 10 items of 1099 documents
Irreversibility of the threshold field for dendritic flux avalanches in superconductors
2010
Hysteretic effects are seen in the upper and lower threshold fields for the appearance of dendritic flux instabilities, first explained in Yurchenko et al. [Phys. Rev. B 76 (2007) 092504], in NbN-films. We have measured the threshold fields at increasing and decreasing applied fields at different temperatures and proposed a mechanism explaining how the hysteresis arises by analyzing the field profiles inside the sample.
History dependence of the magnetization of thin HTSC films: an explanation for distorted SQUID signals
1997
Abstract The magnetizations of thin film disk-shaped type-II superconductors in perpendicular magnetic fields are considered by aid of Mikheenko's critical state model which has been corrected by Zhu for the case of a time-varying periodic field. This paper presents the application of this scheme to an arbitrary nonperiodic time dependence H ( t ). We calculate the influence of field inhomogeneities in a magnetometer on the current density distribution of a disk-shaped type-II superconductor. The resulting SQUID pickup signals and magnetic moments are compared to measurements performed on a 200 nm thick YBa 2 Cu 3 O 7 film in the irreversible regime of the phase diagram. Theory and experime…
Fluxon dynamics by microwave surface resistance measurements in MgB2
2003
Field-induced variations of the microwave surface resistance, Rs(H), have been investigated in high-density ceramic MgB2. At low temperatures, several peculiarities of the Rs(H) curves cannot be justified in the framework of models reported in the literature. We suggest that they are ascribable to the unconventional vortex structure in MgB2, related to the presence of two gaps. On the contrary, the results near Tc can be accounted for by the Coffey and Clem model, with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account.
Microwave second-harmonic response of ceramic MgB2 samples
2005
Nonlinear microwave response of different ceramic MgB2 samples has been investigated by the technique of second-harmonic emission. The second-harmonic signal has been investigated as a function of temperature, DC magnetic field and input microwave power. The attention has mainly been devoted to the response at low magnetic fields, where nonlinear processes arising from motion of Abrikosov fluxons are ineffective. The results show that different mechanisms are responsible for the nonlinear response in the different ranges of temperature. At low temperatures, the nonlinear response is due to processes involving weak links. At temperatures close to Tc, a further contribution to the harmonic em…
Vortex-creep activation energy in YBa2Cu3O7/PrBa2Cu3O7 superlattices
2010
Abstract YBa 2 Cu 3 O 7 /PrBa 2 Cu 3 O 7 (YBCO/PBCO) superlattices with a different ratio of the superconducting and insulating layer thicknesses were prepared by high pressure dc sputtering. The vortex-creep activation energy U 0 was determined by analyzing the in-plane resistive transition of 200 μm wide bridges with the external magnetic field B oriented along the c axis. It was found that U 0 is proportional to the thickness of the YBCO layers, and does only weakly depend on the PBCO layer thickness, when the latter exceeds two unit cells. We observed a change in the variation of U 0 with the current I in the specimen: U 0 exhibits a plateau in the low- I region, then decreases signific…
Polymer solution processing of (Bi, Pb)SrCaCuO
1991
Abstract A simple polymer processing route to the 110 K phase (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor has been developed. The influence of the polymer to metal starting ratio, as well as the sintering temperature and time on the quality of the resulting superconducting powders has been studied by XRD, a.c. susceptibility and resistivity measurements. Microstructure of ceramic compacts has been studied by SEM, and qualitatively analysed by EDS for compositional homogeneity. The results indicate that the polymer synthesis route described here may offer a good alternative to the conventional solid state preparation methods towards attaining homogeneous 110 K superconductor powder withi…
New frontiers in sustainable energy production and storage
2015
Evidently, one of the most effective ways to reduce CO2 emissions consists in the deployment of renewable energies, with the advantage of securing and expanding the energy supplies of a given country. The main problem that arises is due to the intermittent temporary character of many renewable resources like solar and wind. For this reason, it has been recently concluded that in case of high integration of renewables into the distribution grid (more than about 30% of the electricity mix), the implementation of energy storage systems together with smart grids is necessary. Therefore, renewable energies for large scale power production in country would usually require the availability of a su…
Continuous Professional Training and the Situation of Labour Market in Romania
2013
Abstract This study is part of a wider research carried out in recent years, in North-East Moldova – important socio-economic region of Romania – ancient Romanian culture and civilization hearth. It addresses issues of human capital development in the context of sustainable development of the City Suceava and Botosani. This study addresses the issue of human resource development, focusing on continuous training and employment. It is known that the development is based on the human resource, so there must be local responsabilities in terms of skilled labour and increase the adaptability of environamental changes. The results obtained from the research will reflect some of the practical steps…
Ways of Promoting Cultural Ecotourism for Local Communities in Sibiu Area
2014
Abstract Now, Romanian tourism is being confronted with problems of infrastructure and image, and this is a reason we consider that the chance of sustainable development of this area is being represented by promoting niche tourism, namely cultural ecotourism. In an age of globalization, the authentic cultural patrimony is that which makes the difference and represents an opportunity for sustainable development of local communities. The essence of sustainable development is represented by the harmonious integration of economic development, by responsible governing, by ensuring the social cohesion and community man - nature. By the attested value cultural ecotourism can become a touristic pro…
Introduction: Energy, Policy and the Environment: Modeling Sustainable Development for the North
2011
Climate change is unequivocal (IPCC 2007) and it has brought questions of energy and the environment to the forefront. It is unclear to what extent the traditional environmental concern and environmental policy suffice in addressing issues such as climate change while global greenhouse gases continue to increase at a steady rate, as does the depletion of fossil fuels. Ensuring the availability of energy is the key to maintaining current levels of well-being in societies and growth in the global economy. Given that production and utilization of energy and the environment are inherently interlinked, energy policies and changes in economic structures, which focus on alternative modes of energy…