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Are V1 Simple Cells Optimized for Visual Occlusions? A Comparative Study

Jörg Bornschein; Marc Henniges; Jörg Lücke — Wed, 19 Jun 2013 16:26:53 +0200

Abstract: Simple cells in primary visual cortex were famously found to respond to low-level image components such as edges. Sparse coding and independent component analysis (ICA) emerged as the standard computational models for simple cell coding because they linked their receptive fields to the statistics of visual stimuli. However, a salient feature of image statistics, occlusions of image components, is not considered by these models. Here we ask if occlusions have an effect on the predicted shapes of simple cell receptive fields. We use a comparative approach to answer this question and investigate two models for simple cells: a standard linear model and an occlusive model. For both models we simultaneously estimate optimal receptive fields, sparsity and stimulus noise. The two models are identical except for their component superposition assumption. We find the image encoding and receptive fields predicted by the models to differ significantly. While both models predict many Gabor-like fields, the occlusive model predicts a much sparser encoding and high percentages of ‘globular’ receptive fields. This relatively new center-surround type of simple cell response is observed since reverse correlation is used in experimental studies. While high percentages of ‘globular’ fields can be obtained using specific choices of sparsity and overcompleteness in linear sparse coding, no or only low proportions are reported in the vast majority of studies on linear models (including all ICA models). Likewise, for the here investigated linear model and optimal sparsity, only low proportions of ‘globular’ fields are observed. In comparison, the occlusive model robustly infers high proportions and can match the experimentally observed high proportions of ‘globular’ fields well. Our computational study, therefore, suggests that ‘globular’ fields may be evidence for an optimal encoding of visual occlusions in primary visual cortex. Author Summary: The statistics of our visual world is dominated by occlusions. Almost every image processed by our brain consists of mutually occluding objects, animals and plants. Our visual cortex is optimized through evolution and throughout our lifespan for such stimuli. Yet, the standard computational models of primary visual processing do not consider occlusions. In this study, we ask what effects visual occlusions may have on predicted response properties of simple cells which are the first cortical processing units for images. Our results suggest that recently observed differences between experiments and predictions of the standard simple cell models can be attributed to occlusions. The most significant consequence of occlusions is the prediction of many cells sensitive to center-surround stimuli. Experimentally, large quantities of such cells are observed since new techniques (reverse correlation) are used. Without occlusions, they are only obtained for specific settings and none of the seminal studies (sparse coding, ICA) predicted such fields. In contrast, the new type of response naturally emerges as soon as occlusions are considered. In comparison with recent in vivo experiments we find that occlusive models are consistent with the high percentages of center-surround simple cells observed in macaque monkeys, ferrets and mice.

BACL Is a Novel Brain-Associated, Non-NKC-Encoded Mammalian C-Type Lectin-Like Receptor of the CLEC2 Family

Olga Lysenko; Dorothea Schulte; Michel Mittelbronn; Alexander Steinle — Wed, 19 Jun 2013 16:17:43 +0200

Natural Killer Gene Complex (NKC)–encoded C-type lectin-like receptors (CTLRs) are expressed on various immune cells including T cells, NK cells and myeloid cells and thereby contribute to the orchestration of cellular immune responses. Some NKC-encoded CTLRs are grouped into the C-type lectin family 2 (CLEC2 family) and interact with genetically linked CTLRs of the NKRP1 family. While many CLEC2 family members are expressed by hematopoietic cells (e.g. CD69 (CLEC2C)), others such as the keratinocyte-associated KACL (CLEC2A) are specifically expressed by other tissues. Here we provide the first characterization of the orphan gene CLEC2L. In contrast to other CLEC2 family members, CLEC2L is conserved among mammals and located outside of the NKC. We show that CLEC2L-encoded CTLRs are expressed as non-glycosylated, disulfide-linked homodimers at the cell surface. CLEC2L expression is fairly tissue-restricted with a predominant expression in the brain. Thus CLEC2L-encoded CTLRs were designated BACL (brain-associated C-type lectin). Combining in situ hybridization and immunohistochemistry, we show that BACL is expressed by neurons in the CNS, with a pronounced expression by Purkinje cells. Notably, the CLEC2L locus is adjacent to another orphan CTLR gene (KLRG2), but reporter cell assays did neither indicate interaction of BACL with the KLRG2 ectodomain nor with human NK cell lines or lymphocytes. Along these lines, growth of BACL-expressing tumor cell lines in immunocompetent mice did not provide evidence for an immune-related function of BACL. Altogether, the CLEC2L gene encodes a homodimeric cell surface CTLR that stands out among CLEC2 family members by its conservation in mammals, its biochemical properties and the predominant expression in the brain. Future studies will have to reveal insights into the functional relevance of BACL in the context of its neuronal expression.

Postoperative Neurocognitive Dysfunction in Patients Undergoing Cardiac Surgery after Remote Ischemic Preconditioning: A Double-Blind Randomized Controlled Pilot Study

Wed, 19 Jun 2013 16:08:06 +0200

Background: Remote ischemic preconditioning (RIPC) has been shown to enhance the tolerance of remote organs to cope with a subsequent ischemic event. We hypothesized that RIPC reduces postoperative neurocognitive dysfunction (POCD) in patients undergoing complex cardiac surgery. Methods: We conducted a prospective, randomized, double-blind, controlled trial including 180 adult patients undergoing elective cardiac surgery with cardiopulmonary bypass. Patients were randomized either to RIPC or to control group. Primary endpoint was postoperative neurocognitive dysfunction 5–7 days after surgery assessed by a comprehensive test battery. Cognitive change was assumed if the preoperative to postoperative difference in 2 or more tasks assessing different cognitive domains exceeded more than one SD (1 SD criterion) or if the combined Z score was 1.96 or greater (Z score criterion). Results: According to 1 SD criterion, 52% of control and 46% of RIPC patients had cognitive deterioration 5–7 days after surgery (p = 0.753). The summarized Z score showed a trend to more cognitive decline in the control group (2.16±5.30) compared to the RIPC group (1.14±4.02; p = 0.228). Three months after surgery, incidence and severity of neurocognitive dysfunction did not differ between control and RIPC. RIPC tended to decrease postoperative troponin T release at both 12 hours [0.60 (0.19–1.94) µg/L vs. 0.48 (0.07–1.84) µg/L] and 24 hours after surgery [0.36 (0.14–1.89) µg/L vs. 0.26 (0.07–0.90) µg/L]. Conclusions: We failed to demonstrate efficacy of a RIPC protocol with respect to incidence and severity of POCD and secondary outcome variables in patients undergoing a wide range of cardiac surgery. Therefore, definitive large-scale multicenter trials are needed. Trial Registration: ClinicalTrials.gov NCT00877305

Robust Automated Detection of Microstructural White Matter Degeneration in Alzheimer’s Disease Using Machine Learning Classification of Multicenter DTI Data

Wed, 19 Jun 2013 16:00:07 +0200

Diffusion tensor imaging (DTI) based assessment of white matter fiber tract integrity can support the diagnosis of Alzheimer’s disease (AD). The use of DTI as a biomarker, however, depends on its applicability in a multicenter setting accounting for effects of different MRI scanners. We applied multivariate machine learning (ML) to a large multicenter sample from the recently created framework of the European DTI study on Dementia (EDSD). We hypothesized that ML approaches may amend effects of multicenter acquisition. We included a sample of 137 patients with clinically probable AD (MMSE 20.6±5.3) and 143 healthy elderly controls, scanned in nine different scanners. For diagnostic classification we used the DTI indices fractional anisotropy (FA) and mean diffusivity (MD) and, for comparison, gray matter and white matter density maps from anatomical MRI. Data were classified using a Support Vector Machine (SVM) and a Naïve Bayes (NB) classifier. We used two cross-validation approaches, (i) test and training samples randomly drawn from the entire data set (pooled cross-validation) and (ii) data from each scanner as test set, and the data from the remaining scanners as training set (scanner-specific cross-validation). In the pooled cross-validation, SVM achieved an accuracy of 80% for FA and 83% for MD. Accuracies for NB were significantly lower, ranging between 68% and 75%. Removing variance components arising from scanners using principal component analysis did not significantly change the classification results for both classifiers. For the scanner-specific cross-validation, the classification accuracy was reduced for both SVM and NB. After mean correction, classification accuracy reached a level comparable to the results obtained from the pooled cross-validation. Our findings support the notion that machine learning classification allows robust classification of DTI data sets arising from multiple scanners, even if a new data set comes from a scanner that was not part of the training sample.

Le livre du consistoire

Gudrun Petasch — Mon, 17 Jun 2013 11:24:29 +0200

2me protocolle de la justice de la communauté D’Isembourg : commencé le 13˘1 du mois d’aout de lannée 1727 ; contenant 273 feuillets / par Pierre Arnoul Greffier [d]e la justice et communauté

Gudrun Petasch — Mon, 17 Jun 2013 11:19:11 +0200

Sustainable consumption: towards action and impact. : International scientific conference November 6th-8th 2011, Hamburg - European Green Capital 2011, Germany: abstract volume

Fri, 14 Jun 2013 15:54:25 +0200

This volume contains the abstracts of all oral and poster presentations of the international scientific conference „Sustainable Consumption – Towards Action and Impact“ held in Hamburg (Germany) on November 6th-8th 2011. This unique conference aims to promote a comprehensive academic discourse on issues concerning sustainable consumption and brings together scholars from a wide range of academic disciplines.

Übersicht über im Herbst 2003 laufende Forschungsprojekte im E-Finance Lab

Fri, 14 Jun 2013 15:45:21 +0200

Nonthermal phase transitions in semiconductors induced by a femtosecond extreme ultraviolet laser pulse

Nikita Medvedev; Harald O. Jeschke; Beata Ziaja — Fri, 14 Jun 2013 14:57:49 +0200

Part of Focus on High Energy Density Physics. In this paper, we present a novel theoretical approach, which allows the study of nonequilibrium dynamics of both electrons and atoms/ions within free-electron laser excited semiconductors at femtosecond time scales. The approach consists of the Monte-Carlo method treating photoabsorption, high-energy-electron and core-hole kinetics and relaxation processes. Low-energy electrons localized within the valence and conduction bands of the target are treated with a temperature equation, including source terms, defined by the exchange of energy and particles with high-energy electrons and atoms. We follow the atomic motion with the molecular dynamics method on the changing potential energy surface. The changes of the potential energy surface and of the electron band structure are calculated at each time step with the help of the tight-binding method. Such a combination of methods enables investigation of nonequilibrium structural changes within materials under extreme ultraviolet (XUV) femtosecond irradiation. Our analysis performed for diamond irradiated with an XUV femtosecond laser pulse predicts for the first time in this wavelength regime the nonthermal phase transition from diamond to graphite. Similar to the case of visible light irradiation, this transition takes place within a few tens of femtoseconds and is caused by changes of the interatomic potential induced by ultrafast electronic excitations. It thus occurs well before the heating stimulated by electron–phonon coupling starts to play a role. This allows us to conclude that this transition is nonthermal and represents a general mechanism of the response of solids to ultrafast electron excitations.

Zoo Basel Newsletter. 2013, Juni

Fri, 14 Jun 2013 13:50:34 +0200

Integer point sets minimizing average pairwise L1 distance: What is the optimal shape of a town?

Fri, 14 Jun 2013 11:20:05 +0200

An n-town, n[is an element of]N , is a group of n buildings, each occupying a distinct position on a 2-dimensional integer grid. If we measure the distance between two buildings along the axis-parallel street grid, then an n-town has optimal shape if the sum of all pairwise Manhattan distances is minimized. This problem has been studied for cities, i.e., the limiting case of very large n. For cities, it is known that the optimal shape can be described by a differential equation, for which no closed-form solution is known. We show that optimal n-towns can be computed in O(n[superscript 7.5]) time. This is also practically useful, as it allows us to compute optimal solutions up to n=80.

CAST constraints on the axion-electron coupling

Fri, 14 Jun 2013 10:51:38 +0200

In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axiorecombination, the “BCA processes.” Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling gae and axion-photon interaction strength ga using the CAST phase-I data (vacuum phase). For ma <~ 10 meV/c2 we find ga gae < 8.1 × 10−23 GeV−1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission.

4-Nitrophenyl 2-chlorobenzoate

Asma Iqbal; Toheed Akhter; Humaira Masood Siddiqi; Zareen Akhter; Michael Bolte — Fri, 14 Jun 2013 08:39:21 +0200

The aromatic rings in the title compound, C13H8ClNO4, enclose a dihedral angle of 39.53 (3)°. The nitro group is almost coplanar with the ring to which it is attached [dihedral angle = 4.31 (1)°]. In the crystal, molecules are connected by C-H...O hydrogen bonds into chains running along [001]. Key indicators: single-crystal X-ray study; T = 173 K; mean σ(C–C) = 0.002 A°; R factor = 0.044; wR factor = 0.105; data-to-parameter ratio = 18.9.

Electron Supersurface Scattering On Polycrystalline Au

Fri, 14 Jun 2013 08:14:13 +0200

Supersurface electron scattering, i.e., electron energy losses and associated deflections in vacuum above the surface of a medium, is shown to contribute significantly to electron spectra. We have obtained experimental verification (in absolute units) of theoretical predictions that the angular distribution of the supersurface backscattering probability exhibits strong oscillations which are anticorrelated with the generalized Ramsauer-Townsend minima in the backscattering probability. We have investigated 500-eV electron backscattering from an Au surface for an incidence angle of 70° and scattering angles between 37° and 165°. After removing the contribution of supersurface scattering from the experimental data, the resulting angular and energy distribution agrees with the Landau-Goudsmit-Saunderson (LGS) theory, which was proposed about 60 years ago, while the raw data are anticorrelated with LGS theory. This result implies that supersurface scattering is an essential phenomenon for quantitative understanding of electron spectra.

A review of the New World Krisnini (Hemiptera: Cicadellidae: Iassinae) including three genera and six new species

Paul H. Freytag — Thu, 13 Jun 2013 17:55:07 +0200

The tribe Krisnini (Hemiptera: Cicadellidae) is presently known in the New World from three species from Puerto Rico and one species from Dominican Amber, all described in the Old World genus Krisna Baker. The three species from Puerto Rico are being placed in Lipokrisna, new genus, with Krisna insularis Oman as the type species, becoming Lipokrisna insularis (Oman), new combination. The other species in this genus are L. montana (Caldwell) and L. aesta (DeLong) both new combinations. The one species from Dominican amber is placed in the Genus Archiokrisna, new genus, with Krisna garciamarquezi Dietrich as the type species, becoming Archiokrisna garciamarquezi (Dietrich), new combination. The genus, Neokrisna, new genus, is described for six new species from the Dominican Republic, with Neokrisna oncora, new species, as the type species. The other new species in the genus are N. breva, N. decliva, N. libera, N. longula, and N. stena. A key to the species of Neokrisna is included. The three genera are compared with each other and the old World genus Krisna.

Spin modulation instabilities and phase separation dynamics in trapped two-component Bose condensates

Ivana Vidanović; Nicolaas Jan van Druten; Masudul Haque — Thu, 13 Jun 2013 15:01:21 +0200

n the study of trapped two-component Bose gases, a widely used dynamical protocol is to start from the ground state of a one-component condensate and then switch half the atoms into another hyperfine state. The slightly different intra-component and inter-component interactions can then lead to highly non-trivial dynamics, especially in the density mismatch between the two components, commonly referred to as 'spin' density. We study and classify the possible subsequent dynamics, over a wide variety of parameters spanned by the trap strength and by the inter- to intra-component interaction ratio. A stability analysis suited to the trapped situation provides us with a framework to explain the various types of dynamics in different regimes.

Multiple encoding in genetic editions: the case of "Faust"

Gerrit Brüning; Katrin Henzel; Dietmar Pravida — Thu, 13 Jun 2013 14:46:56 +0200

The aim of the present paper is to show how, and to what extent, the standards of critical genetic editions as applied to Goethe's Faust can be attained within a TEI framework. It proposes and argues for the introduction of two separate transcripts: documentary and textual. Despite the apparent disadvantages of multiple encoding, this approach recommends itself for practical reasons (e.g., avoidance of overlapping hierarchies), and it conveniently reflects the idea that any written document must be considered a material object on the one hand and a medium of textual transmission on the other. In the course of the paper, some aspects and problems of chapter 11 of version 2.0.0 of TEI P5 (the definition and use of the elements and and related issues) will be discussed.

ISOE-Newsletter / Institut für sozial-ökologische Forschung. 2013, 3

Thu, 13 Jun 2013 12:55:11 +0200

Inhalt: „The Sound of Cycling“: Das ISOE auf der Velo-city 2013 in Wien +++ Wegweiser Energie-Sanierung: Vom Hauskauf bis zum Einzug +++ Energiesparen leicht gemacht: Forscherteam entwickelt Stromeffizienzklassen für Haushalte +++ Energiewende: Nicht ohne die Bürger! Neues Forschungsprojekt zu zivilgesellschaftlicher Beteiligung +++ Wer entscheidet über Forschung? +++ Controlling in der Siedlungswasserwirtschaft – Neue Konzepte gefragt +++ Fit für die Zukunft: Nachhaltigkeitsstrategien für kommunale Wasser- und Abwasserbetriebe +++ ISOE erhält Auszeichnung „ÖKOPROFIT Betrieb Frankfurt am Main“ +++ Aktuelle Termine +++ Publikationen

Einige Überlegungen zum Netzwerkcharakter des mentalen Lexikons und zu möglichen Konsequenzen für die Didaktik des Fremdsprachenerwerbs

László Kovács — Wed, 12 Jun 2013 14:24:41 +0200

Im Beitrag wird auf aktuelle Ergebnisse der Forschung zum mentalen Lexikon eingegangen. Das mentale Lexikon wird dabei aus der Sicht der Netzwerktheorie untersucht. Der Netzwerkcharakter des mentalen Lexikons hat zur Folge, dass die gelernten Wörter nicht voneinander unabhängig existieren: Sie sind miteinander verknüpft. Diese Verknüpfungen sind nicht gleich stark; zudem ist die Richtung dieser Verknüpfung von großer Bedeutung. Assoziationstests in mehreren Sprachen zeigen, dass dasselbe Wort in verschiedenen Sprachen verschiedene Verknüpfungen hat bzw. dass die Stärke der Verknüpfungen zwischen zwei beliebigen Wörtern von Sprache zu Sprache variiert. Beim Fremdsprachenerwerb und Fremdsprachenunterricht werden diese Unterschiede kaum berücksichtigt. Der vorliegende Beitrag analysiert das mentale Lexikon aus der Perspektive der Netzwerke. Dabei wird das Projekt ConnectYourMind vorgestellt, das in mehreren Sprachen Assoziationsdaten sammelt.

Onomatopoetika : ein vernachlässigtes Gebiet der Sprachwissenschaft und Sprachdidaktik

Georg Schuppener — Wed, 12 Jun 2013 14:13:51 +0200

Der vorliegende Beitrag gibt zunächst einen Überblick über die sprachwissenschaftlichen Zugänge zur Onomatopöie und den derzeitigen Forschungsstand. Danach wird dargestellt, dass Onomatopoetika insbesondere für den Sprachvergleich ein lohnendes, aber bislang noch unzureichend behandeltes Forschungsthema darstellen. Dabei zeigen sich zahlreiche Fragestellungen, die auch für die Sprachdidaktik relevant sind. Auf dieser Grundlage zeigt der Beitrag, wie und warum Onomatopoetika sprachdidaktisch nutzbringend thematisiert werden können.

Jetzt sind aber Männer dran! : Reflexion über neu verwendete maskuline Berufs- und Personenbezeichnungen im Deutschen und im Polnischen

Edyta Grotek — Wed, 12 Jun 2013 14:08:05 +0200

The language, and especially vocabulary, reflects very precise changes taking place in extralinguistic provinces. This article demonstrates the development of masculine names of persons and jobs which until now have been reserved for women, hence in the maternity and education field, comparative - in Polish and German. First, the article presents the systemic possibilities of both languages to mark the gender or gender neutrality. Then, on chosen examples found on Internet forums, it demonstrates how nowadays they are realized in "parole".

Tschechische Äquivalente der deutschen Determinativkomposita : Zum Einsatz von Parallelkorpora für kontrastive linguistische Untersuchungen

Veronika Kotůlková — Wed, 12 Jun 2013 13:53:31 +0200

Der vorliegende Beitrag stellt eine linguistische Studie vor, die zwei nicht nah verwandte Sprachen auf dem Gebiet der Wortbildung vergleicht – das Deutsche und das Tschechische. Das Forschungsziel der Arbeit stellt die Untersuchung deutscher Determinativkomposita und der ihnen entsprechenden Wortbildungskonstruktionen im Tschechischen dar. Es wird eine relativ junge sprachwissenschaftliche Disziplin, die Korpuslinguistik, rein praktisch vorgestellt und die konkreten Ergebnisse der kontrastiven Untersuchung werden präsentiert.

Grammatik und Wirtschaft : Die kontrastive Hypertextgrammatik

Raúl Sánchez Prieto — Wed, 12 Jun 2013 13:45:04 +0200

Um den schwierigen Wettbewerbsbedingungen im internationalen Vergleich entgegentreten zu können, benötigen kleine und mittlere Unternehmen nicht nur den Einsatz moderner Informationstechniken und eine kommerzielle Präsenz im multimedialen und grafikintensiven Teil des Internets, sondern auch eine an den Kunden angepasste Web-Präsenz. In diesem Sinne widmen wir uns in diesem Beitrag der wirtschaftlichen Notwendigkeit einer kontrastiven Hypertextgrammatik. In den letzten Jahren ist dank der zunehmenden Bedeutung des Internets als Handelsplattform eine grammatische Unterdisziplin entstanden, die zur Geschäftsoptimierung kleiner und mittlerer Unternehmen einen beachtlichen Beitrag leisten könnte: die kontrastive Hypertextgrammatik. Wir gehen hier der Frage nach, wie man bei einer kontrastiven hypertextgrammatischen Studie vorgehen könnte.

Entwurf eines Tempussystems des Deutschen : (am Beispiel des Sprachunterrichts Deutsch für ausländische Studierende an deutschen Hochschulen)

Bernd Griebel — Wed, 12 Jun 2013 13:38:32 +0200

Ausländische Studierende an deutschen Hochschulen haben mit dem traditionellen deutschen Tempussystem nach lateinischem Vorbild eine Reihe von Problemen, weil es nicht immer logisch nachvollziehbare Beziehungen zwischen einer grammatischen Tempusform und den Zeitbedeutungen gibt. Nach einer überblicksartigen kritischen Betrachtung der Darstellung des Tempussystems in einigen einschlägigen (Übungs-) Grammatiken und Lehrwerken stellt der Verfasser den Entwurf eines Tempussystems des Deutschen vor, bei dem die klassische Einteilung in 6 Tempusformen zugunsten eines nutzerfreundlicheren Tempussystems aufgegeben wird. Dann werden exemplarisch typischen kommunikativen Aufgaben von Studierenden Tempusformen in Form von Gebrauchsvorschriften, -präferenzen bzw. -möglichkeiten zugeordnet.

Artikulations- und Intonationsveränderungen als Ausdrucksweisen der sozialen Distanz : (Soziale Funktionen phonostilistischer Merkmale in der Konversation)

Miloš Chovan — Wed, 12 Jun 2013 13:33:30 +0200

Die Beschreibungen der phonologischen und phonetischen Gebrauchsmerkmale erschöpfen sich aus der Sicht der informellen Kommunikation bekanntlich vorwiegend in den sprecherbezogenen phonologischen Prozessen, die dominant mit einer durch natürliches Sprechtempo bedingten ausspracheerleichternden Funktion einhergehen. Auch verfügt die moderne Interaktionslinguistik über Kenntnisse einiger linguistischer Funktionen von Intonation. Dennoch wissen wir immer noch sehr wenig über die soziale (d. h. auch strategische) Funktionalität der artikulatorischen und prosodischen (also der segmentalen und suprasegmentalen) Merkmale im Gesprächsverhalten. Dieser Beitrag setzt sich zum Ziel, die kontextsensitiven konversationsphonologischen Sprachmerkmale und ihre soziale Funktionsweise im Alltagsgespräch zu skizzieren. Die Problematik der Herangehensweise an die Erfassung der sozialen Bedeutung von konversationeller Phonetik, Phonologie und Prosodie wird anhand von drei exemplarischen Analysen der Kontextualisierung der sozialen Distanz in den Gesprächen bei verschiedenen informellen Gruppen Jugendlicher beleuchtet.