Non-linear effects in electron cyclotron current drive applied for the stabilization of neoclassical tearing modes

Due to the smallness of the volumes associated with the flux surfaces around the O-point of a magnetic island, the electron cyclotron power density applied inside the island for the stabilization of neoclassical tearing modes (NTMs) can exceed the threshold for non-linear effects as derived previously by Harvey et al, Phys. Rev. Lett. 62 (1989) 426. We study the non-linear electron cyclotron current drive (ECCD) efficiency through bounce-averaged, quasi-linear Fokker-Planck calculations in the magnetic geometry as created by the islands. The calculations are performed for the parameters of a typical NTM stabilization experiment on ASDEX Upgrade. A particular feature of these experiments is that the rays of the EC wave beam propagate tangential to the flux surfaces in the power deposition region. The calculations show significant non-linear effects on the ECCD efficiency, when the ECCD power is increased from its experimental value of 1 MW to a larger value of 4 MW. The nonlinear effects are largest in case of locked islands or when the magnetic island rotation period is longer than the collisional time scale. The non-linear effects result in an overall reduction of the current drive efficiency for this case with absorption of the EC power on the low field side of the electron cyclotron resonance layer. As a consequence of the non-linear effects, also the stabilizing effect of the ECCD on the island is reduced from linear expectations

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.

Early evolution of electron cyclotron driven current during suppression of tearing modes in a circular tokamak

When electron cyclotron (EC) driven current is first applied to the inside of a magnetic island, the current spreads throughout the island and after a short period achieves a steady level. Using a two equation fluid model for the EC current that allows us to examine this early evolution in detail, we analyze high-resolution simulations of a 2/1 classical tearing mode in a low-beta large aspect-ratio circular tokamak. These simulations use a nonlinear 3D reduced-MHD fluid model and the JOREK code. During the initial period where the EC driven current grows and spreads throughout the magnetic island, it is not a function of the magnetic flux. However, once it has reached a steady-state, it should be a flux function. We demonstrate numerically that if sufficiently resolved toroidally, the steady-state EC driven current becomes approximately a flux function. We discuss the physics of this early period of EC evolution and its impact on the size of the magnetic island.Comment: 12 pages, 7 figure

The sele sentence completion questionnaire: a new instrument for the assessment of personal meaning in research on aging

In this paper, the SELE-instrumenits presented. The SELE-instrument is a sentence completion test and an accompanying coding scheme, which is designed to study cognitions about self and life. The related theoretical construct is the personal meaning system, which encompasses different meaning domains, like "self", "activities" and "social relations", as well as evaluations and time perspectives. It is argued that especially in aging research. it is necessarv to use more oven instruments in studying self-and-life-cognitions. A short history of sentence completion instruments in psychology, is presented in order to better understand the specific contents of the SELE-instrument. The SELE provides sentence stems in the first form singular ("I") combination with verbal factors, which express different combinations of evaluation and time perspective, to which the respondents have to react in their own words. The SELE-instrumenits thus a semi-structured questionnaire, which can be used in large-scale research. The sentence completions are coded with an extensive coding scheme, which is hierarchially and dimensionally organized. Some figures on the coding reliability as well as on the validity and stability of the instrument are presented. The different uses to which the SELE-instrument as been put are described shortly.En este articulo se presenta el instrumento SELE. Este instrumento, que consta de un cuestionario de frases incompletas y un esquema de codificación de respuestas, está diseñado para el estudio de las cogniciones sobre el self y la vida. El constructo teórico al que se aproxima es el sistema de significado personal, sistema que comprende tanto diferentes dominios de significado (por ejemplo el "self", "actividades" o "relaciones sociales") como evaluaciones y perspectivas temporales. Se argumenta que, especialmente en la investigación en envejecimiento, es necesario utilizar instrurnentos de carácter más abierto para el estudio de cogniciones relacionadas con el self y la vida. Por otra parte, para entender mejor los contenidos específicos del SELE, se presenta una breve historia de los instrumentos de frases incompletas en Psicologia. El SELE proporciona estimulos en forma de frases incompletas a los que la persona tiene que contestar en sus propias palabras. Estos estímulos comienzan con un sujeto en primera persona del singular ("Yo") seguido por una forma verbal que expresa diferentes combinaciones de perspectiva temporal y evaluación. Debido a este formato, el SELE es un cuestionario semiestructurado que puede ser utilizado en investigaciones a gran escala. Las respuestas se categorizan mediante un exhaustivo sistema de codificación que está organizado tanto jerárquica como dimensionalmente. En el articulo se presentan algunos resultados en relación con la fiabilidad, la validez y la estabilidad del cuestionario, asi como también se describen brevemente los diferentes usos a los que ha estado dirigido el SELE

New insights into the generalized Rutherford equation for nonlinear neoclassical tearing mode growth from 2D reduced MHD simulations

Two dimensional reduced MHD simulations of neoclassical tearing mode growth and suppression by ECCD are performed. The perturbation of the bootstrap current density and the EC drive current density perturbation are assumed to be functions of the perturbed ux surfaces. In the case of ECCD, this implies that the applied power is ux surface averaged to obtain the EC driven current density distribution. The results are consistent with predictions from the generalized Rutherford equation using common expressions for and . These expressions are commonly perceived to describe only the effect on the tearing mode growth of the helical component of the respective current perturbation acting through the modi cation of Ohm’s law. Our results show that they describe in addition the effect of the poloidally averaged current density perturbation which acts through modi cation of the tearing mode stability index. Except for modulated ECCD, the largest contribution to the mode growth comes from this poloidally averaged current density perturbation

The sele sentence completion questionnaire: a new instrument for the assessment of personal meaning in research on aging

In this paper, the SELE-instrumenits presented. The SELE-instrument is a sentence completion test and an accompanying coding scheme, which is designed to study cognitions about self and life. The related theoretical construct is the personal meaning system, which encompasses different meaning domains, like "self", "activities" and "social relations", as well as evaluations and time perspectives. It is argued that especially in aging research. it is necessarv to use more oven instruments in studying self-and-life-cognitions. A short history of sentence completion instruments in psychology, is presented in order to better understand the specific contents of the SELE-instrument. The SELE provides sentence stems in the first form singular ("I") combination with verbal factors, which express different combinations of evaluation and time perspective, to which the respondents have to react in their own words. The SELE-instrumenits thus a semi-structured questionnaire, which can be used in large-scale research. The sentence completions are coded with an extensive coding scheme, which is hierarchially and dimensionally organized. Some figures on the coding reliability as well as on the validity and stability of the instrument are presented. The different uses to which the SELE-instrument as been put are described shortly.En este articulo se presenta el instrumento SELE. Este instrumento, que consta de un cuestionario de frases incompletas y un esquema de codificación de respuestas, está diseñado para el estudio de las cogniciones sobre el self y la vida. El constructo teórico al que se aproxima es el sistema de significado personal, sistema que comprende tanto diferentes dominios de significado (por ejemplo el "self", "actividades" o "relaciones sociales") como evaluaciones y perspectivas temporales. Se argumenta que, especialmente en la investigación en envejecimiento, es necesario utilizar instrurnentos de carácter más abierto para el estudio de cogniciones relacionadas con el self y la vida. Por otra parte, para entender mejor los contenidos específicos del SELE, se presenta una breve historia de los instrumentos de frases incompletas en Psicologia. El SELE proporciona estimulos en forma de frases incompletas a los que la persona tiene que contestar en sus propias palabras. Estos estímulos comienzan con un sujeto en primera persona del singular ("Yo") seguido por una forma verbal que expresa diferentes combinaciones de perspectiva temporal y evaluación. Debido a este formato, el SELE es un cuestionario semiestructurado que puede ser utilizado en investigaciones a gran escala. Las respuestas se categorizan mediante un exhaustivo sistema de codificación que está organizado tanto jerárquica como dimensionalmente. En el articulo se presentan algunos resultados en relación con la fiabilidad, la validez y la estabilidad del cuestionario, asi como también se describen brevemente los diferentes usos a los que ha estado dirigido el SELE

Redistribution of fast ions during sawtooth reconnection

In a tokamak-based fusion power plant, possible scenarios may include regulated sawtooth oscillations to remove thermalized helium from the core of the plasma. During a sawtooth crash, the helium ash and other impurities trapped in the core are driven by the instability to an outer region. However, in a fusion plasma, high energy ions will represent a significant population. We thus study the behaviour of these energetic particles during a sawtooth. This paper presents the modelling of the redistribution of fast ions during a sawtooth reconnection event in a tokamak plasma. Along the lines of the model for the evolution of the flux surfaces during a sawtooth collapse described in Ya.I. Kolesnichenko and Yu.V. Yakovenko 1996 Nucl. Fusion 36 159, we have built a time-dependent electromagnetic model of a sawtooth reconnection. The trajectories of the ions are described by a complete gyro-orbit integration. The fast particles were evolved from specific initial parameters (given energy and uniform spread in pitch) or distributed initially according to a slowing-down distribution created by fusion reactions. Our modelling is used to understand the main equilibrium parameters driving the motions during the collapse and to determine the evolution of the distribution function of energetic ions when different geometries of reconnection are considered.</p

Aortic pressure wave reconstruction during exercise is improved by adaptive filtering: a pilot study

Reconstruction of central aortic pressure from a peripheral measurement by a generalized transfer function (genTF) works well at rest and mild exercise at lower heart rates, but becomes less accurate during heavy exercise. Particularly, systolic and pulse pressure estimations deteriorate, thereby underestimating central pressure. We tested individualization of the TF (indTF) by adapting its resonance frequency at the various levels of exercise. In seven males (age 44–57) with coronary artery disease, central and peripheral pressures were measured simultaneously. The optimal resonance frequency was predicted from regression formulas using variables derived from the individual’s peripheral pressure pulse, including a pulse contour estimation of cardiac output (pcCO). In addition, reconstructed pressures were calibrated to central mean and diastolic pressure at each exercise level. Using a genTF and without calibration, the error in estimated aortic pulse pressure was −7.5 ± 6.4 mmHg, which was reduced to 0.2 ± 5.7 mmHg with the indTFs using pcCO for prediction. Calibration resulted in less scatter at the cost of a small bias (2.7 mmHg). In exercise, the indTFs predict systolic and pulse pressure better than the genTF. This pilot study shows that it is possible to individualize the peripheral to aortic pressure transfer function, thereby improving accuracy in central blood pressure assessment during exercise

From time-series to complex networks: Application to the cerebrovascular flow patterns in atrial fibrillation

A network-based approach is presented to investigate the cerebrovascular flow patterns during atrial fibrillation (AF) with respect to normal sinus rhythm (NSR). AF, the most common cardiac arrhythmia with faster and irregular beating, has been recently and independently associated with the increased risk of dementia. However, the underlying hemodynamic mechanisms relating the two pathologies remain mainly undetermined so far; thus the contribution of modeling and refined statistical tools is valuable. Pressure and flow rate temporal series in NSR and AF are here evaluated along representative cerebral sites (from carotid arteries to capillary brain circulation), exploiting reliable artificially built signals recently obtained from an in silico approach. The complex network analysis evidences, in a synthetic and original way, a dramatic signal variation towards the distal/capillary cerebral regions during AF, which has no counterpart in NSR conditions. At the large artery level, networks obtained from both AF and NSR hemodynamic signals exhibit elongated and chained features, which are typical of pseudo-periodic series. These aspects are almost completely lost towards the microcirculation during AF, where the networks are topologically more circular and present random-like characteristics. As a consequence, all the physiological phenomena at microcerebral level ruled by periodicity - such as regular perfusion, mean pressure per beat, and average nutrient supply at cellular level - can be strongly compromised, since the AF hemodynamic signals assume irregular behaviour and random-like features. Through a powerful approach which is complementary to the classical statistical tools, the present findings further strengthen the potential link between AF hemodynamic and cognitive decline.Comment: 12 pages, 10 figure