390 research outputs found
Bottom-up Derivation of the Qualitatively Different Behaviors of a Car across Varying Spatio-Temporal Scales: a Study in Abstraction of Goal-Directed Motion
No full textion of Goal-Directed Motion Leo Dorst RWCP Novel Functions: SNN Laboratory Amsterdam, Dept. of Mathematics, Computer Science, Physics and Astronomy, University of Amsterdam, Kruislaan 403, NL-1098 SJ Amsterdam, The Netherlands Abstract. Driving a car involves considering it at different spatio-temporal scales, and somehow leads to behavior such as the parallel parking maneuver, the three-point turn, free Euclidean driving in a desert, following a road, and translationally passing other vehicles at high speed. In the study of autonomous systems, it is desirable to find a representation in which such different behaviors of a single system can be related to each other, and to find precisely how and under what conditions a change of representation and corresponding choice of motions occurs. In this paper, we formulate an abstraction mechanism based on approximations of flows of commutators of vector fields. We apply it to the goaldirected motion of a car and show how the environmental co..
Tutorial Appendix: Structure Preserving Representation of Euclidean Motions Through Conformal Geometric Algebra
No full textUsing conformal geometric algebra, Euclidean motions in n-D are represented as orthogonal transformations of a representational space of two extra dimensions, and a well-chosen metric. Orthogonal transformations are representable as multiple reflections, and by means of the geometric product this takes an efficient and structure preserving form as a ‘sandwiching product’. The antisymmetric part of the geometric product produces a spanning operation that permits the construction of lines, planes, spheres and tangents from vectors, and since the sandwiching operation distributes over this construction, ‘objects’ are fully integrated with ‘motions’. Duality and the logarithms complete the computational techniques.The resulting geometric algebra incorporates general conformal transformations and can be implemented to run almost as efficiently as classical homogeneous coordinates. It thus becomes a high-level programming language which naturally integrates quantitative computation with the automatic administration of geometric data structures.<br/
Reconstructing Rotations and Rigid Body Motions from Exact Point Correspondences Through Reflections
No full textWe describe a new algorithm to reconstruct a rigid body motion from point correspondences. The algorithm works by constructing a series of reflections which align the points with their correspondences one by one. This is naturally and efficiently implemented in the conformal model of geometric algebra, where the resulting transformation is represented by a versor. As a direct result of this algorithm, we also present a very compact and fast formula to compute a quaternion from two vector correspondences, a surprisingly elementary result which appears to be new. <br/
Estimating Motors from a Variety of Geometric Data in 3D Conformal Geometric Algebra
No full textThe motion rotors, or motors, are used to model Euclidean motion in 3D conformalgeometric algebra. In this chapter we present a technique for estimatingthe motor which best transforms one set of noisy geometric objects onto another.The technique reduces to an eigenrotator problem and has some advantages overmatrix formulations. It allows motors to be estimated from a variety of geometricdata such as points, spheres, circles, lines, planes, directions, and tangents; andthe different types of geometric data are combined naturally in a single framework.Also, it excludes the possibility of a reflection unlike some matrix formulations.It returns the motor with the smallest translation and rotation angle whenthe optimal motor is not unique
Square Root and Logarithm of Rotors in 3D Conformal Geometric Algebra Using Polar Decomposition
No full textConformal transformations are described by rotors in the conformal model of geometric algebra (CGA). In applications there is a need for interpolation of such transformations, especially for the subclass of 3D rigid body motions. This chapter gives explicit formulas for the square root and the logarithm of rotors in 3D CGA. It also classifies the types of conformal transformations and their orbits. To derive the results, we employ a novel polar decomposition for the even subalgebra of 3D CGA and an associated norm-like expression. <br/
Home and Mortgage Ownership of the Dutch Elderly: Explaining Cohort, Time and Age Effects
No full textThe relationship between home ownership of Dutch elderly households and age is strongly negative. Other studies suggest that this age gradient should be attributed to a cohort effect. In this paper we investigate where those cohort effects come from. We also observe that mortgage ownership among elderly home-owners increased considerably during the nineties. Using panel data we estimate models explaining home and mortgage ownership by age, cohort, and time effects, as well as other factors. Cohort and time effects are modelled explicitly using macro economic and housing market related variables. We find that the level of GDP per capita when the household head was young is the main factor explaining generation effects in home ownership among the elderly. After accounting for cohort effects it also appears that home ownership decreases slightly with age. Mortgage ownership among elderly home owners rose considerably during the nineties due to house price increases and due to financial innovation in the mortgage market. Cohort effects are also important. A supplementary analysis suggests that those cohort effects are due to the fact that the accidental bequest motive is becoming less important.home ownership, mortgages, cohort effects
Report on shape analysis and matching and on semantic matching
No full textIn GRAVITATE, two disparate specialities will come together in one working platform for the archaeologist: the fields of shape analysis, and of metadata search. These fields are relatively disjoint at the moment, and the research and development challenge of GRAVITATE is precisely to merge them for our chosen tasks. As shown in chapter 7 the small amount of literature that already attempts join 3D geometry and semantics is not related to the cultural heritage domain. Therefore, after the project is done, there should be a clear ‘before-GRAVITATE’ and ‘after-GRAVITATE’ split in how these two aspects of a cultural heritage artefact are treated.This state of the art report (SOTA) is ‘before-GRAVITATE’. Shape analysis and metadata description are described separately, as currently in the literature and we end the report with common recommendations in chapter 8 on possible or plausible cross-connections that suggest themselves. These considerations will be refined for the Roadmap for Research deliverable.Within the project, a jargon is developing in which ‘geometry’ stands for the physical properties of an artefact (not only its shape, but also its colour and material) and ‘metadata’ is used as a general shorthand for the semantic description of the provenance, location, ownership, classification, use etc. of the artefact. As we proceed in the project, we will find a need to refine those broad divisions, and find intermediate classes (such as a semantic description of certain colour patterns), but for now the terminology is convenient – not least because it highlights the interesting area where both aspects meet.On the ‘geometry’ side, the GRAVITATE partners are UVA, Technion, CNR/IMATI; on the metadata side, IT Innovation, British Museum and Cyprus Institute; the latter two of course also playing the role of internal users, and representatives of the Cultural Heritage (CH) data and target user’s group. CNR/IMATI’s experience in shape analysis and similarity will be an important bridge between the two worlds for geometry and metadata. The authorship and styles of this SOTA reflect these specialisms: the first part (chapters 3 and 4) purely by the geometry partners (mostly IMATI and UVA), the second part (chapters 5 and 6) by the metadata partners, especially IT Innovation while the joint overview on 3D geometry and semantics is mainly by IT Innovation and IMATI. The common section on Perspectives was written with the contribution of all
Uno specchio in frantumi. Il teatro della rivoluzione di Ernst Toller e Tankred Dorst
No full textMasse-Mensch. Ein Stück aus der sozialen Revolution des 20. Jahrhunderts di Ernst Toller (1919) è uno dei primi drammi novecenteschi che affrontano il tema del ruolo delle masse nelle rivoluzioni moderne. Quella di Toller in Masse-Mensch è una riflessione politica che mai si distacca da una sperimentazione estetica. Con tale riflessione lo scrittore non si limita a dar voce a una poetica genuinamente espressionista, ma prosegue un discorso ‘letterario’ sulla rivoluzione, inaugurato da Georg Büchner negli anni Trenta dell’Ottocento con Dantons Tod, e al medesimo tempo anticipa forme e concetti di successivi Revolutionsdramen. Partendo da tali premesse, il saggio intende far emergere le tensioni che animano Masse-Mensch e i dilemmi con cui il suo autore si confronta, approfondendo poi i legami del dramma della rivoluzione di Toller con il successivo Toller. Szenen aus einer deutschen Revolution di Tankred Dorst (1968). L’opera di Dorst, scritta sul finire degli anni Sessanta del Novecento e dunque nel momento delle rivolte studentesche, ripercorre le vicende vissute dal Toller storico a Monaco alla fine degli anni Dieci, con l’intento di riprendere tratti fondamentali della poetica di Toller in Masse-Mensch e al contempo di smascherarne aspetti ambigui e paradossali, al confine fra estetica e politica.Scenes from a German Revolution: Ernst Toller and Tankred Dorst
The fact that masses have become the main actors of political and social events (and not at least of
revolutions) was the main topic of Ernst Toller’s play Masse Mensch. Ein Stück aus der sozialen Revolution
des 20. Jahrhunderts. In this play, written in prison during the “German revolution” (1918-1919),
the author brings to stage the dilemma of a revolutionary pacifist idea which has to face the necessity
to use violence for the sake of revolution. Toller tries to elaborate the conflict between ideals
and reality, which he considers impossible to solve, by giving form to it in the experimental form of
his expressionist drama. As a matter of fact, Toller’s Masse Mensch is not only a politically engaged
work, but also an aesthetical experiment, an open and visionary drama, anticipating techniques
and languages of later Revolutionsdramen (e.g. Brecht, Weiß and Müller). It’s not a case that the
German playwright Tankred Dorst (1925-2017) at the end of sixties dedicated his revue Toller. Szenen
aus einer deutschen Revolution to the Munich November-Revolution, focusing on Toller and on his
dilemma. Dorst aims at looking at the November Revolution from a historical and critical distance
and not at least at unmasking its actors as intellectuals “who wanted to make the revolution but
only made literature”. By doing this, Dorst himself works in an experimental way and concentrates
on rhythm as well as on the open and fragmented aesthetical form of his play. Taking also reference
to Dorst’s documentary studies about the Munich Revolution, this contribution would like
to analyse Toller’s Masse Mensch and Dorst’s Toller as innovative aesthetical experiments about the
November Revolution in Germany and at the same time as critical reflections about revolutions in
the times of mass society
Perceived Control and Liveability: Environment and behaviour interaction in two urban villages of Shenzhen
No full textUrban village is a very special type of neighbourhood, created in the fast urbanisation process in Chinese cities like Shenzhen in the past three decades, playing an essential role in accommodating migrant groups, including rural-urban migrant workers and the young professionals. Built by the villagers whose farmland was transformed into urban use, these high-density informal settlements have become places where the daily life of the migrant groups happens. Nowadays, along with the processes of fast urban development and upgrading of industries, urban villages located in the central urban districts are being considered as problematic neighbourhoods that need to be reconstructed. The current model is still based on large-scale redevelopment, replacing the urban villages with new urban functions. In response to such radical approach, this paper will present an alternative argument of maintaining and improving urban villages as arrival cities for migrant groups. It is based on an environmental-behaviour study in the framework of liveability. This study is based on the theory that perceived control over the built environment is an important condition for liveability (Altman 1975, Van Dorst 2011). It indicates the changing life styles inside the urban villages, as well as the way space is socially produced in two urban villages in Shenzhen: Hubei and Baishizhou.UrbanismArchitecture and The Built Environmen
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