44 research outputs found
The quiet Sun's magnetic flux estimated from CaIIH bright inter-granular G-band structures
We determine the number density and area contribution of small-scale
inter-granular calcium-II bright G-band structures in images of the quiet Sun
as tracers of kilo-Gauss magnetic flux-concentrations.
In a 149" x 117" G-band image of the disk center at the activity minimum,
7593 small inter-granular structures ['IGS']were segmented with the
`multiple-level tracking' pattern recognition algorithm ['MLT_4']. The
scatter-plot of the continuum versus the G-band brightness shows the known
magnetic and non-magnetic branches. These branches are largely disentangled by
applying an intrinsic Ca-II excess criterion. The thus obtained 2995 structures
contain 1152 G-band bright points ['BP'] and 1843 G-band faint points ['FP'].
They show a tendency of increasing size with decreasing G-band excess, as
expected from the `hot wall' picture. Their Ca-H and G-band brightness are
slightly related, resembling the known relation of Ca-II and magnetic field
strength. The magnetic flux density of each individual BP and FP is estimated
from their G-band brightness according to MHD-model calculations.
The entity of BP and FP covers the total field-of-view ['FOV'] with a number
density of 0.32/Mm^2 and a total area contribution of 2.0%. Their individual
calibrations yield a mean flux density of 20 Mx/cm^2 in the entire FOV and 13
Mx/cm^2 for inter-network regions
Drawing as Epistemic Practice in Architectural Design
The essay deals with drawing as a genuine form of knowledge in architectural design. Drawing is described as an epistemic practice enmeshed with historically changing, material spaces of knowledge.Starting with a brief examination of historic philosophical positions on the epistemicity of drawing, the essay tries to sketch out a tentative heuristic of the epistemic features of drawing from the perspective of symbol and media theory.In the last part, with reference to Nelson Goodman’s distinction between analogue and digital symbol systems, the digitalization of drawing is critically reviewed. The main point is to emphasize that the transformation of drawing into digital drawing formats always consist of a translation.It is crucial to take the challenges stemming from the indeterminacy of translation (W.v.O. Quine) into consideration in order to understand both the epistemic restrictions and the potentials of drawing under the conditions of the rising digital habitat
Properties of simulated sunspot umbral dots
Realistic 3D radiative MHD simulations reveal the magneto-convective
processes underlying the formation of the photospheric fine structure of
sunspots, including penumbral filaments and umbral dots. Here we provide
results from a statistical analysis of simulated umbral dots and compare them
with reports from high-resolution observations. A multi-level segmentation and
tracking algorithm has been used to isolate the bright structures in synthetic
bolometric and continuum brightness images. Areas, brightness, and lifetimes of
the resulting set of umbral dots are found to be correlated: larger umbral dots
tend to be brighter and live longer. The magnetic field strength and velocity
structure of umbral dots on surfaces of constant optical depth in the continuum
at 630 nm indicate that the strong field reduction and high velocities in the
upper parts of the upflow plumes underlying umbral dots are largely hidden from
spectro-polarimetric observations. The properties of the simulated umbral dots
are generally consistent with the results of recent high-resolution
observations. However, the observed population of small, short-lived umbral
dots is not reproduced by the simulations, possibly owing to insufficient
spatial resolution.Comment: Accepted for publication in A&
Discriminant analysis of solar bright points and faculae I. Classification method and center-to-limb distribution
While photospheric magnetic elements appear mainly as Bright Points (BPs) at
the disk center and as faculae near the limb, high-resolution images reveal the
coexistence of BPs and faculae over a range of heliocentric angles. This is not
explained by a "hot wall" effect through vertical flux tubes, and suggests that
the transition from BPs to faculae needs to be quantitatively investigated. To
achieve this, we made the first recorded attempt to discriminate BPs and
faculae, using a statistical classification approach based on Linear
Discriminant Analysis(LDA). This paper gives a detailed description of our
method, and shows its application on high-resolution images of active regions
to retrieve a center-to-limb distribution of BPs and faculae. Bright "magnetic"
features were detected at various disk positions by a segmentation algorithm
using simultaneous G-band and continuum information. By using a selected sample
of those features to represent BPs and faculae, suitable photometric parameters
were identified in order to carry out LDA. We thus obtained a Center-to-Limb
Variation (CLV) of the relative number of BPs and faculae, revealing the
predominance of faculae at all disk positions except close to disk center (mu >
0.9). Although the present dataset suffers from limited statistics, our results
are consistent with other observations of BPs and faculae at various disk
positions. The retrieved CLV indicates that at high resolution, faculae are an
essential constituent of active regions all across the solar disk. We speculate
that the faculae near disk center as well as the BPs away from disk center are
associated with inclined fields
Diagrammatic modelling in design : towards an epistemology of BIM
Die Dissertation befasst sich mit einer erkenntnistheoretischen Untersuchung der Gebäudedatenmodellierung bzw. von building information modelling (BIM) als Entwurfsmedium in der Architektur. Hierzu wird zuerst die Geschichte von BIM als transdisziplinäre, non-lineare Geschichte nachgezeichnet, in der der Transfer von Konzepten und Modellen zwischen Architektur und Informatik den Fokus der Betrachtung abgibt. Sodann wird das architektonische Entwerfen als Erkenntnisprozess beschrieben. Den theoretische Rahmen hierfür bilden die Wissensforschung, der semiotische Pragmatismus und die Urteilstheorie des Modells. In diesem Setting wird dann eine Heuristik von sechs charakteristischen Merkmalen des BIM-basierten Entwerfens herausgearbeitet. Im Anschluss an diese Bestandsaufnahme wird das BIM-basierte Entwerfen als diagrammatisches Modellieren charakterisiert. Dabei wird zuerst die Transformation des architektonischen Entwurfsmodells vom analogen Skalenmodell zum digitalen Informationsmodell beschrieben, und ein pragmatischer Modell-Begriff eingeführt, mit dem die Bedingungen der Beurteilung eines BIM- Modells als Entwurfsmodell analysiert werden. Zum zweiten wird das Interface des BIM-Modells als Diagramm interpretiert. Hierbei wird der Diagramm-Begriff des semiotischen Pragmatismus in Stellung gebracht gegenüber dem des Poststrukturalismus, der vor dem Aufkommen von BIM in der Architektur in den architekturtheoretischen Debatten leitend war, und bis heute fortwirkt.The thesis consists of an epistemological investigation of building information modeling (BIM) as a design medium in architecture. The first part traces the development of BIM from the point of view of a trans-disciplinary, non-linear history. This historical approach is centered around the transfer of concepts, models, and techniques between architecture and informatics. Second, architectonical design is described as an epistemological practice in the framework of knowledge research, semiotic pragmatism, and model theory. Within this framework, a heuristics of six characteristics of BIM-based design is layed out. Following this inventory-taking, in the third part, BIM-based design is described as a process of diagrammatic modeling. First, the historical development from the analogue scale-model to the digital information-model is sketched out, and the BIM-model is analyzed as a design-model based on a pragmatistic model concept where the question about the conditions of the assessment of something as a model for something else is at centre stage. And second, the interface of the BIM-model is interpreted as a diagram in the framework of current diagrammatological research. On this base it is argued for the digram concept of semiotic pragmatism against the diagram concept of post-modernism that was directive in architecture already before the advent of BIM, and continues to be influential to this day
Morphology and evolution of umbral dots and their substructures
Substructures - dark lanes and tails - of umbral dots (UDs) were predicted by
numerical simulations of magnetoconvection. We analyse a 6 h 23 min time series
of broadband images of a large umbra in the active region NOAA 10634, acquired
with the 1-m Swedish Solar Telescope, in the wavelength band around 602 nm. A
43 min part of this series was reconstructed with the MFBD method, reaching a
spatial resolution of 0.14". We measure brightness, size, lifetime, and
horizontal velocities of various umbral structures. Most (90 %) of UDs and
bright point-like features in faint LBs split and merge, and their median
lifetimes are 3.5 or 5.7 min, depending on whether the split or merge event is
considered as the end of their life. Both UDs and features in faint LBs that do
not split or merge are clearly smaller (0.15") than the average size (0.17") of
all features. Horizontal motions of umbral bright small-scale features are
directed either into the umbra or along faint LBs with mean horizontal
velocities of 0.34 km/s. Features faster than 0.4 km/s appear mostly at the
periphery of the umbra. The intensity of dark lanes, measured in four bright
central UDs (CUDs), is by a factor 0.8 lower than the peak intensity of CUDs.
The width of dark lanes is probably less than the resolution limit 0.14". The
characteristic time of substructure changes of UDs is ~4 min. We observe narrow
(0.14") bright and dark filaments connected with PUDs. Usually one dark and two
bright filaments form a 0.4" wide tail attached to one PUD, resembling a short
dark-cored penumbral filament. Our results indicate the similarity between PUDs
and PGs located at the tips of bright penumbral filaments. The features seen in
numerical MHD simulations are consistent with our observations of dark lanes in
CUDs and tails attached to PUDs.Comment: 8 pages, 8 figures, Astronomy & Astrophysics, in pres
Converging and diverging convection around axisymmetric magnetic flux tubes
A numerical model of idealized sunspots and pores is presented, where axisymmetric cylindrical domains are used with aspect ratios (radius versus depth) up to 4. The model contains a compressible plasma with density and temperature gradients simulating the upper layer of the Sun's convection zone. Non-linear magnetohydrodynamic equations are solved numerically and time-dependent solutions are obtained where the magnetic field is pushed to the centre of the domain by convection cells. This central magnetic flux bundle is maintained by an inner convection cell, situated next to it and with a flow such that there is an inflow at the top of the numerical domain towards the flux bundle. For aspect ratio 4, a large inner cell persists in time, but for lower aspect ratios it becomes highly time dependent. For aspect ratios 2 and 3 this inner convection cell is smaller, tends to be situated towards the top of the domain next to the flux bundle, and appears and disappears with time. When it is gone, the neighbouring cell (with an opposite sense of rotation, i.e. outflow at the top) pulls the magnetic field away from the central axis. As this happens a new inner cell forms with an inflow which pushes the magnetic field towards the centre. This suggests that to maintain their form, both pores and sunspots need a neighbouring convection cell with inflow at the top towards the magnetic flux bundle. This convection cell does not have to be at the top of the convection zone and could be underneath the penumbral structure around sunspots. For an aspect ratio of 1, there is not enough space in the numerical domain for magnetic flux and convection to separate. In this case the solution oscillates between two steady states: two dominant convection cells threaded by magnetic field and one dominant cell that pushes magnetic flux towards the central axis
The three-dimensional structure of sunspots II. The moat flow at two different heights
Many sunspots are surrounded by a radial outflow called the moat flow. We
investigate the moat flow at two different heights of the solar atmosphere for
a sunspot whose magnetic properties were reported in the first paper of this
series. We use two simultaneous time series taken with the Transition Region
And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The
field-of-view is centered on the small sunspot NOAA 10886 located near disk
center. Horizontal velocities are derived by applying two different local
correlation tracking techniques. Outflows are found everywhere in the moat. In
the inner moat, the velocities from the UV series are larger than those from
white light, whereas in the outer part of the moat we find the converse result.
The results imply that the white light velocities represent a general outflow
of the quiet sun plasma in the moat, while UV velocities are dominated by small
bright points that move faster than the general plasma flow.Comment: Manuscript accepted by Astronomy & Astrophysic
Brightness, distribution, and evolution of sunspot umbral dots
We present a 106-minute TiO (705.7nm) time series of high spatial and
temporal resolution that contains thousands of umbral dots (UDs) in a mature
sunspot in the active region NOAA 10667 at =0.95. The data were acquired
with the 1-m Swedish Solar Telescope on La Palma. With the help of a multilevel
tracking (MLT) algorithm the sizes, brightnesses, and trajectories of 12836
umbral dots were found and analyzed. The MLT allows UDs with very low contrast
to be reliably identified. Inside the umbra we determine a UD filling factor of
11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a
typical lifetime. Three quarters of the UDs lived for less than 150s and showed
no or little motion. The histogram of the UD diameters exhibits a maximum at
225km, i.e. most of the UDs are spatially resolved. UDs display a typical
horizontal velocity of 420m/s and a typical peak intensity of 51% of the mean
intensity of the quiet photosphere, making them on average 20% brighter than
the local umbral background. Almost all mobile UDs (large birth-death distance)
were born close to the umbra-penumbra boundary, move towards the umbral center,
and are brighter than average. Notably bright and mobile UDs were also observed
along a prominent UD chain, both ends of which are located at the
umbra-penumbra boundary. Their motion started primarily at either of the ends
of the chain, continued along the chain, and ended near the chain's center. We
observed the splitting and merging of UDs and the temporal succession of both.
For the first time the evolution of brightness, size, and horizontal speed of a
typical UD could be determined in a statistically significant way. Considerable
differences between the evolution of central and peripheral UDs are found,
which point to a difference in origin
Automated Detection and Tracking of Solar Magnetic Bright Points
Magnetic Bright Points (MBPs) in the internetwork are among the smallest
objects in the solar photosphere and appear bright against the ambient
environment. An algorithm is presented that can be used for the automated
detection of the MBPs in the spatial and temporal domains. The algorithm works
by mapping the lanes through intensity thresholding. A compass search, combined
with a study of the intensity gradient across the detected objects, allows the
disentanglement of MBPs from bright pixels within the granules. Object growing
is implemented to account for any pixels that might have been removed when
mapping the lanes. The images are stabilized by locating long-lived objects
that may have been missed due to variable light levels and seeing quality.
Tests of the algorithm employing data taken with the Swedish Solar Telescope
(SST), reveal that ~90% of MBPs within a 75"x 75" field of view are detected