Stabilization of magnetic islands in tokamaks by localized heating and current drive : a numerical approach

This thesis deals with the theory of active stabilization of the so-called Neoclassical Tearing modes (NTMs) in fusion reactors. Hot fuel, in the form of a fully ionized gas (referred to as "plasma"), is confined by a magnetic field with the topology of toroidally nested magnetic surfaces. The NTM is a spontaneous break of this magnetic configuration, leading to a non-symmetric topology characterised by a chain of magnetic islands. Within a magnetic island temperature and pressure are flattened. The NTM onset occurs when the plasma pressure exceeds a certain limit. Since the fusion power is proportional to the pressure squared, NTMs limit the performance of the reactor. Active stabilization of such instabilities can yield an enhanced performance of the fusion reactor of up to 50%. For this reason, it is important to study the mechanisms responsible for their growth and achieve a reliable control strategy. Control and suppression of NTMs is achieved experimentally by depositing highly localized radio-frequency power, in the range of electron cyclotron frequency (EC), at the island location. Qualitatively, the effect of the localized EC power on magnetic islands is twofold: it makes the island formation more difficult, and it compensates for the effect of the temperature flattening inside the island region by a local increase of the temperature and by inducing a current inside the island. These effects are referred to as Electron Cyclotron Resonance Heating (ECRH) and Electron Cyclotron Current Drive (ECCD), respectively. The thesis addresses the stabilizing contribution of ECRH and ECCD, on the temporal evolution of a magnetic island. This model relies on the equation for the evolution of the magnetic island width, the generalized "Rutherford" equation (GRE), which depends on the different driving and stabilizing mechanisms. There are three main open questions that this work tries to answer: the relative merits of ECRH and ECCD, the role of asymmetries in the magnetic island topology and finally the determination of a criterion for full NTM suppression. The research focused at first on the relative merits of each method. The conditions determining the relative importance of ECRH and ECCD are found to depend on the product of two factors, the efficiency with which ECRH or ECCD generates a current inside the magnetic island and a geometrical factor showing essentially different scalings for either ECRH or ECCD. For a fusion reactor like ITER the main stabilizing mechanism for a magnetic island is found to be the ECCD, while ECRH becomes relevant in smaller devices. In the following step an extension of the model allowed to treat asymmetries in the island shape and to discuss their effect on the ECCD and ECRH contribution to the island evolution. This study demonstrates that these deformations have a small or negligible impact on the tearing mode evolution. Opposing claims in the existing literature could be shown to be based on inappropriate approximations or comparisons. The last part of the thesis is devoted to the determination of the requirements for the suppression of a magnetic island. This is usually described by the parameter ¿NTM, defined as the ratio between the local driven current density, responsible for the stabilization of the mode and the local bootstrap current density, the drive of the NTM instability. An extensive analysis allowed to formulate a general criterion for the full NTM suppression in the form of a combined criterion for the maximum allowed width of the EC power density profile and a minimum required EC driven current. The results of this analysis have been used to suggest an improvement of the design of ITER-ECRH system. A moderate increase of the angle with which EC waves are injected into the plasma of up to 5¿ from its present design value is shown to reduce the power requirement by up to 25%. In conclusion, the theoretical work presented in this thesis has provided a comprehensive analysis of the stabilization of a magnetic island by means of the localized heating and driven current. The proposed model verifies and improves criteria for the design of ITER-ECRH system. Finally, it provides a sound theoretical basis for the design of NTM feedback control loops

Potential Response of Soil-Borne Fungal Pathogens Affecting Crops to a Scenario of Climate Change in Europe

A study was carried out on the potential response of soil-borne pathogens causing crop yield losses under a climate change scenario in Europe. A controlled chamber set of experiments was carried out to quantify pathogen response to temperature using pure colonies of three soil-borne fungi, representative of low (Fusarium nivale), medium-high (Athelia rolfsii) and high (Macrophomina phaseolina) temperature requirements. A generic model to simulate fungal growth response to temperature based on these experiments was developed and linked to a soil temperature model component, and to components to simulate soil water content accounting for crop water uptake of potential hosts. Pathogens relative growth was simulated over Europe using the IPCC A1B emission scenario as realization of the Hadley-CM3 global climate model, available from the European Commission and processed for use with biophysical models. The simulations resulting from using the time span centred on 2030 were compared to the baseline, centred on the year 2000, using a sample of 30 years of daily weather. The general trend of soil-borne pathogens response to the scenario of climate change is a relative increase in growth in colder areas of Europe, as a function of their temperature requirements. Projections of F. nivale in the future indicate a relative increase of this winter pathogen of wheat in Northern European countries. A. rolfsii and M. phaseolina, two soil-borne pathogens typical of warmer agricultural areas, could find more favourable conditions in areas of the Central Europe, but they differentiated in Southern Europe where A. rolfsii resulted affected by summer soil temperatures above optimum

The construction of knowledge-based economies versus knowledge societies: The cases of Germany and Singapore

In the past decades, terms such as knowledge-based economy (KBE)\u27, and \u27information/knowledge society\u27 have been adopted by governments worldwide in order to underline their interest in developing their economies and societies further and assure future growth. Many governments used these catchwords as labels for government programs and action plans aiming at economic and social prosperity. This aim of national governments to construct knowledge-based economies, information/knowledge societies, the actions taken and especially the ability or disability to do so, is the topic of this paper. As two cases of comparison act Singapore and Germany. (DIPF/Orig.

Stochastic 0-dimensional Biogeochemical Flux Model: Effect of temperature fluctuations on the dynamics of the biogeochemical properties in a marine ecosystem

We present a new stochastic model, based on a 0-dimensional version of the well known biogeochemical flux model (BFM), which allows to take into account the temperature random fluctuations present in natural systems and therefore to describe more realistically the dynamics of real marine ecosystems. The study presents a detailed analysis of the effects of randomly varying temperature on the lower trophic levels of the food web and ocean biogeochemical processes. More in detail, the temperature is described as a stochastic process driven by an additive self-correlated Gaussian noise. Varying both correlation time and intensity of the noise source, the predominance of different plankton populations is observed, with regimes shifted towards the coexistence or the exclusion of some populations. Finally a Fourier analysis carried out on the time series of the plankton populations shows how the ecosystem responds to the seasonal driving for different values of the noise intensit

Math Skills: a New Look from Functional Data Analysis

: Mental calculations involve various areas of the brain. The frontal, parietal and temporal lobes of the left hemisphere have a principal role in the completion of this typology of tasks. Their level of activation varies based on the mathematical competence and attentiveness of the subject under examination and the perceived difficulty of the task. Recent literature often investigates patterns of cerebral activity through fMRI, which is an expensive technique. In this scenario, EEGs represent a more straightforward and cheaper way to collect information regarding brain activity. In this work, we propose an EEG based method to detect differences in the cerebral activation level of people characterized by different abilities in carrying out the same arithmetical task. Our approach consists in the extraction of the activation level of a given region starting from the EEG acquired during resting state and during the completion of a subtraction task. We then analyze these data through Functional Data Analysis, a statistical technique that allows operating on biomedical signals as if they were functions. The application of this technique allowed for the detection of distinct cerebral patterns among the two groups and, more specifically, highlighted the presence of higher levels of activation in the parietal lobe in the population characterized by a lower performance

Identification of dynamic contact instabilities generated by braking materials

The occurrence of unstable friction-induced vibrations is a major issue for braking manufacturers, as they lead to annoying noise, structure vibrations and brake surface degradation. Understanding the underlying causes of frictional instabilities, arising during the sliding between two bodies, is necessary for developing solutions and countermeasures. For this purpose, in this work, an experimental and numerical investigation of contact instabilities has been performed. Mode coupling and negative friction-velocity slope instabilities have been numerically investigated by both lumped-parameter and finite element models. As well, an experimental campaign has been carried out for recovering the frictional and vibrational response of braking materials under different boundary conditions. The comparison between numerical and experimental results allows validating a new methodology, based on the study of the phase shift between the tangential and normal vibrational responses, in order to distinguish the different types of contact instabilities

Early embryonic development, assisted reproductive technologies, and pluripotent stem cell biology in domestic mammals

Over many decades assisted reproductive technologies, including artificial insemination, embryo transfer, in vitro production (IVP) of embryos, cloning by somatic cell nuclear transfer (SCNT), and stem cell culture, have been developed with the aim of refining breeding strategies for improved production and health in animal husbandry. More recently, biomedical applications of these technologies, in particular, SCNT and stem cell culture, have been pursued in domestic mammals in order to create models for human disease and therapy. The following review focuses on presenting important aspects of pre-implantation development in cattle, pigs, horses, and dogs. Biological aspects and impact of assisted reproductive technologies including IVP, SCNT, and culture of pluripotent stem cells are also addressed. © 2013 Elsevier Ltd

Social interaction and communities of practice in Formative period NW Argentina: a multi-analytical study of ceramics

We present clear production areas for two distinct polychrome wares in the earlier part of the period. Both networks appear to be geographically selective. The connection between Quebrada del Toro and the southern sector of Calchaquí has been now clearly demonstrated and should be considered in future modeling. There existed shared technological style in the core study area throughout the first millennium AD: ordinary wares varied across valleys but minimally, decorated wares were technologically homogenous (intercommunity circulation of clays, pots, knowledge & skills). Results call for a revision of the purported central role of some areas: Ambato clays not found, Condohuasi likely to have been manufactured at Campo del Pucará but other areas cannot be discarded yet. We need to acknowledge the relevance of connections between ?marginal? areas to model social interaction and emergent complexity. A complex and ever-widening network of associations and mutual dependencies demonstrated beyond typological analysis. The diversity of connections revealed in this study shows that communities often avoided the artifacts and iconographies related to so-called centers.Fil: Lazzari, Marisa. University of Exeter; Reino UnidoFil: Pereyra Domingorena, Lucas. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Museo Etnográfico "Juan B. Ambrosetti"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scattolin, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Museo Etnográfico "Juan B. Ambrosetti"; ArgentinaFil: Stoner, Wesley D.. University of Arkansas; Estados UnidosFil: Glascock, Michael D. University of Missouri; Estados Unidos81st Meeting Society for American ArchaeologyOrlandoEstados UnidosSociety for American Archaeolog

Susceptibility, Oviposition Preference, and Biology of Grapholita molesta (Lepidoptera: Tortricidae) in Prunus Spp. Rootstock Genotypes.

Studying the susceptibility of peach trees to Grapholita molesta (Busck) is one of the major steps in the develop- ment of pest-resistant peach varieties. This work evaluated the susceptibility of 55 genotypes of the "Prunus Rootstock Collection" ("Coleção Porta-enxerto de Prunus ") of Embrapa Temperate Climate (Pelotas, Rio Grande do Sul, Brazil) to the natural infestation of G. molesta , assessed the oviposition preference of G. molesta in choice and no-choice bioassays, and estimated the biological parameters and the fertility life table on different Prunus spp. genotypes in the laboratory. Genotypes Prunus kansuensis (Rehder), I-67-52-9, and I-67-52-4 were the most susceptible to G. molesta infestation in the field ( > 60% of branches infested), while 0 Sharpe 0 ( Prunus angustifolia x Prunus spp.) and Prunus sellowii (Koehne) were the least infested (0% of branches infested). In choice and no-choice bioassays, G. molesta preferred to oviposit on P. kansuensis when compared with Sharpe. The Sharpe genotype also showed an antibiosis effect, resulting in negative effects on the fertility life table parameters when compared with the genotypes P. kansuensis and 0 Capdeboscq. 0 The results found in the present study can provide information to initiate a long-term breeding program moving desired G. molesta resistance traits from the rootstock into the Prunus spp. cultivars. Keywords : Rosaceae, insect resistance, antibiosis, antixenosis, oriental fruit mot

Early embryonic development, assisted reproductive technologies, and pluripotent stem cell biology in domestic mammals

Over many decades assisted reproductive technologies, including artificial insemination, embryo transfer, in vitro production (IVP) of embryos, cloning by somatic cell nuclear transfer (SCNT), and stem cell culture, have been developed with the aim of refining breeding strategies for improved production and health in animal husbandry. More recently, biomedical applications of these technologies, in particular, SCNT and stem cell culture, have been pursued in domestic mammals in order to create models for human disease and therapy. The following review focuses on presenting important aspects of pre-implantation development in cattle, pigs, horses, and dogs. Biological aspects and impact of assisted reproductive technologies including IVP, SCNT, and culture of pluripotent stem cells are also addressed. © 2013 Elsevier Ltd