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1Author    Ruth Marx, Detlef DoeneckeRequires cookie*
 Title    Binding of Polylysine and Ethidium Bromide to Nucleosomal DNA: Comparison of Biochemical and Electron Microscopical Results  
 Abstract    Ethidium bromide and polylysine interact with nucleosomal D NA and lead to changes o f biochemical properties and to morphological changes as to the distance between the two core particles of a nucleosome dimer. With increasing polylysine concentration, the buoyant density of nucleosomes decreases and the accessibility of the nucleosomal DNA to micrococcal nuclease is lowered. Electron microscopy of polylysine treated nucleosome dimers reveals a shortening of the intemucleosomal distance as compared with controls. Treatment of nucleosomes with ethidium bromide leads to an enhanced accessibility of the nucleosomal DNA to micrococcal nuclease. Electron microscopy reveals an increase in length of the DNA connecting the two nucleosome cores in the presence o f the dye. Both the binding of polylysine and the treatment with ethidium bromide apparently do not affect the histone arrangement within the nucleosome core as suggested by chemical cross-linking o f histones and DNA with formaldehyde, and no obvious morphological changes of the nucleosome cores can be observed. 
  Reference    Z. Naturforsch. 36c, 149—156 (1981); received September 1 1980 
  Published    1981 
  Keywords    Nucleosomes, Polylysine, Ethidium Bromide, Biochemistry, Morphology 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0149.pdf 
 Identifier    ZNC-1981-36c-0149 
 Volume    36 
2Author    Maja Iv, NedjalkaV. Mitova3, E. Handjieva3-Mincho, SimeonS. Anchevb, Popov3Requires cookie*
 Title    Indoid Glucosides from Four Balkan Endemics of the Galium incurvum Group (Rubiaceae)  
 Abstract    The Balkan endemics G. mirum, Galium macedonicum, G. rhodopeum and G. aegeum, from the G. incurvum group, were screened for iridoid glucosides. Eleven known iridoid glucosides were isolated, identified and analysed for the first time in the investigated plants. The main components appeared to be asperuloside and/or the non-acetylated iridoid acids -deacetylasperulosidic acid, scandoside, monotropein. Phylogenetic relationships are discussed. 
  Reference    Z. Naturforsch. 51c, 286—2 (1996); received December 12 1995/February 12 1996 
  Published    1996 
  Keywords    Rubiaceae, Galium, Morphology, Iridoids, Phylogenetic Relationships 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0286.pdf 
 Identifier    ZNC-1996-51c-0286 
 Volume    51 
3Author    Rolf Pfeifer, Christian ScheierRequires cookie*
 Title    Representation in Natural and Artificial Agents: An Embodied Cognitive Science Perspective  
 Abstract    The goal of the present paper is to provide an em bodied cognitive science view on repre­ sentation. Using the fundamental task of category learning, we will demonstrate that this perspective enables us to shed new light on many pertinent issues and opens up new pros­ pects for investigation. The main focus of this paper is on the prerequisites to acquire repre­ sentations of objects in the real world. We suggest that the main prerequisite is embodiment which allows an agent -human, animal or robot -to manipulate its sensory input such that invariances are generated. These invariances, in turn, are the basis o f representation forma­ tion. In other words, the paper does not focus on representations per se, but rather discusses the various processes involved in order to make learning and representation acquisition pos­ sible. The argument structure is as follows. First we introduce two new perspectives on represen­ tation, namely frame-of-reference, and com plete agent. Then we elaborate the complete agent perspective and focus in particular on em bodim ent and situatedness. We argue that embodiment has two main aspects, a dynamic and an information theoretic one. Focusing on the latter, there are a number of implications: Representation can only be understood if the embedding of the neural substrate in the physical agent is known, which includes morphology (shape), positioning and nature of sensors. Because an autonom ous mobile agent in the real world is exposed to a continuously changing high-dimensional stream of sensory stimulation, if it is to learn category distinctions, it first needs a focus o f attention mechanism, and then it must have a way to reduce the dimensionality o f this high-dimensional sensory stream. Learning is very hard because the invariances are typically not found in the sensory data directly -the classical problem of object constancy: it is a so-called type 2 problem. Rather than trying to improve the learning algorithms -which is the standard approach -the em bodied cognitive science view suggests a different approach which focuses on the nature of the data: the agent is not passively exposed to a given data distribution, but, by exploiting its body and through the interaction with the environm ent, it can actually generate the data. More specifically, it can generate correlated data that has the property that it can be easily learned. This learnability is due to redundancies resulting from the appropriate interactions with the environment. Through such interactions, the former type 2 problem is transformed into a type 1 problem, thus reducing the complexity o f the learning task by orders o f magni­ tude. By observing the frame-of-reference problem we will discuss to what extent these in­ variances are reflected -represented -in the "neural substrate", i.e. the internal mechanisms of the agent. It is concluded, that representation is not a concept that can be studied in the abstract, but should be elaborated in the context of concrete agent-environment interactions. These ideas are all illustrated with examples of natural agents and artificial agents. In particu­ lar, we will present a suite of experiments on simulated and real-world artificial agents in­ stantiating the main arguments. 
  Reference    Z. Naturforsch. 53c, 480 (1998); received May 18 1998 
  Published    1998 
  Keywords    E m bodied Cognitive Science, Representation, Sensory-M otor Coordination, Self-Generated Data, Morphology 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0480.pdf 
 Identifier    ZNC-1998-53c-0480 
 Volume    53