1,721,027 research outputs found
Sustainability indicators - a tool for regional co-operation
Get PDFSustainability indicators are more than just numbers. Besides their main function of illustrating the complex vision of sustainability they could support some factors for success of regional co-operation through their development. Today the discussion on indicators and co-operation is mainly separated from each other. Sustainability indicators are developed on all spatial levels from neighbourhoods up to the United Nations. In some cases the indicators are developed but remain unused. Regional co-operations on sustainability are more or less successful. Some fail because of the complexity of the topic and the multitude of people involved in sustainability. Despite the existing problems the necessity of both topics for the implementation of sustainable development is out of question. Some of the problems mentioned could be solved by the linkage of the two topics: indicators are not developed as an end in itself and regional co-operation could become more successful. The improvement of both is possible because important factors for success of co-operation can be supported by the following abilities resulting from the development of indicators: a) consensus building, b) improvement of the quality of basic information, c) definition of quantified aims and priorities, d) comprehensive development of measures, e) recognition of need for action f) evaluation of success. Besides these effects among the co-operating actors indicators development supports the following factors according to the external of the co-operation: g) information on the work of the co-operation (setting up transparency), h) contribution to a new sustainable awareness. Additionally the indicators are enhanced because the people developing and using them have intellectual ownership of them and guarantee that they are more than numbers. Regional co-operation and sustainability indicators become one unit and could be seen as a sustainable regional management system.
Nanoflare statistics in an active region 3D MHD coronal model
No full textAims. We investigate the statistics for the spatial and temporal distribution of the energy input into the corona in a three-dimensional magneto-hydrodynamical (3D MHD) model. The model describes the temporal evolution of the corona above an observed active region. The model is driven by photospheric granular motions that braid the magnetic field lines. This induces currents that are dissipated, thereby leading to transient heating of the coronal plasma. We evaluate the transient heating as subsequent heating events and analyze their statistics. The results are then interpreted in the context of observed flare statistics and coronal heating mechanisms. Observed solar flares and other smaller transients cover a wide range of energies. The frequency distribution of energies follow a power law, the lower end of the distribution given by the detection limit of current instrumentation. One particular heating mechanism is based on the occurrence of so-called nanoflares, i.e. very low-energy deposition events.
Methods. To conduct the numerical experiment we use a high-order finite-difference code that solves the partial differential equations for the conservation of mass, the momentum and energy balance, and the induction equation. The energy balance includes Spitzer heat conduction and optically thin radiative losses in the corona.
Results. The temporal and spatial distribution of the Ohmic heating in the 3D MHD model follows a power law and can therefore be understood as a system in a self-organized critical state. The slopes of the power law are similar to the results based on observations of flares and smaller transients. We find that the coronal heating is dominated by events similar to the so-called nanoflares with energies on the order of 1017 J or 1024 erg
Intermittent heating in the solar corona employing a 3D MHD model
No full textAims. We investigate the spatial and temporal evolution of the heating
of the corona of a cool star such as our Sun in a three-dimensional magneto-hydrodynamic
(3D MHD) model.
Methods. We solve the 3D MHD problem numerically in a box representing
part of the (solar) corona. The energy balance includes Spitzer heat conduction along the
magnetic field and optically thin radiative losses. The self-consistent heating mechanism
is based on the braiding of magnetic field lines rooted in the convective photosphere.
Magnetic stress induced by photospheric motions leads to currents in the atmosphere that
heat the corona through Ohmic dissipation.
Results. While the horizontally averaged quantities, such as heating
rate, temperature, or density, are relatively constant in time, the simulated corona is
highly variable and dynamic, on average reaching the temperatures and densities found in
observations. The strongest heating per particle is found in the transition region from
the chromosphere to the corona. The heating is concentrated in current sheets roughly
aligned with the magnetic field and is transient in time and space. This supports the idea
that numerous small heating events heat the corona, often referred to as nanoflares
Nanoflare Heating in the Solar Corona
No full textWe employ a three dimensional magneto-hydrodynamical (3D MHD) model to investigate the statistics of the spatial and temporal distribution of the coronal heating. The model describes the evolution of the solar corona above an observed Active Region. This model is additionally compared to coronal models where the underlying photospheric magnetic field consists of simplified magnetic configurations. In all models random like photospheric motions braid the magnetic field. This induces currents in the upper atmosphere eventually leading to coronal heating by their dissipation. We analyze the heating process which is in general transient in time and space. We compare the results to observed flare statistics
Investigation of mass flows in the transition region and corona in a three-dimensional numerical model approach
Get PDFContext. The origin of solar transition region redshifts is not completely understood. Current research is addressing this issue by investigating three-dimensional magneto-hydrodynamic models that extend from the photosphere to the corona.
Aims. By studying the average properties of emission line profiles synthesized from the simulation runs and comparing them to observations with present-day instrumentation, we investigate the origin of mass flows in the solar transition region and corona.
Methods. Doppler shifts were determined from the emission line profiles of various extreme-ultraviolet emission lines formed in the range of T = 104−106 K. Plasma velocities and mass flows were investigated for their contribution to the observed Doppler shifts in the model. In particular, the temporal evolution of plasma flows along the magnetic field lines was analyzed.
Results. Comparing observed vs. modeled Doppler shifts shows a good correlation in the temperature range log (T/[K]) = 4.5−5.7, which is the basis of our search for the origin of the line shifts. The vertical velocity obtained when weighting the velocity by the density squared is shown to be almost identical to the corresponding Doppler shift. Therefore, a direct comparison between Doppler shifts and the model parameters is allowed. A simple interpretation of Doppler shifts in terms of mass flux leads to overestimating the mass flux. Upflows in the model appear in the form of cool pockets of gas that heat up slowly as they rise. Their low temperature means that these pockets are not observed as blueshifts in the transition region and coronal lines. For a set of magnetic field lines, two different flow phases could be identified. The coronal part of the field line is intermittently connected to subjacent layers of either strong or weak heating, leading either to mass flows into the loop (observed as a blueshift) or to the draining of the loop (observed as a redshift)
Scaling laws of coronal loops compared to a 3D MHD model of an active region
No full textContext. The structure and heating of coronal loops have been investigated for decades. Established scaling laws relate fundamental quantities like the loop apex temperature, pressure, length, and coronal heating.
Aims. We test these scaling laws against a large-scale 3D magneto-hydrodynamics (MHD) model of the solar corona, which became feasible with current high-performance computing.
Methods. We drove an active region simulation with photospheric observations and find strong similarities to the observed coronal loops in X-rays and extreme-ultraviolet (EUV) wavelength. A 3D reconstruction of stereoscopic observations shows that our model loops have a realistic spatial structure. We compared scaling laws to our model data extracted along an ensemble of field lines. Finally, we fit a new scaling law that represents hot loops and also cooler structures, which was not possible before based only on observations.
Results. Our model data gives some support for scaling laws that were established for hot and EUV-emissive coronal loops. For the Rosner-Tucker-Vaiana (RTV) scaling law we find an offset to our model data, which can be explained by 1D considerations of a static loop with a constant heat input and conduction. With a fit to our model data we set up a new scaling law for the coronal heat input along magnetic field lines.
Conclusions. RTV-like scaling laws were fitted to hot loops and therefore do not predict well the coronal heat input for cooler structures that are barely observable. The basic differences between 1D and self-consistent 3D modeling account for deviations between earlier scaling laws and ours. We also conclude that a heating mechanism by MHD-turbulent dissipation within a braided flux tube would heat the corona stronger than is consistent with our model corona
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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