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1Author    Heidrun Amm, Maren Grigutsch, Ralf StannariusRequires cookie*
 Title    Spatio-temporal Analysis of Electroconvection in Nematics  
 Abstract    We investigate electroconvection in nematic liquid crystals by means of optical microscopy. Time resolved optical images are used to study the director dynamics. For the first time we present instant images in the dielectric regime. A numerical simulation of the optical transmission patterns is performed on the basis of Fermat's principle. In the instant images of dielectric rolls, the periodicity of the observed optical pattern is equal to the wavelength Ao of the convection rolls. The well known low contrast 'stationary' optical texture observed in conventional experiments results from time averaging of these instant images; its wavelength is Ao/2. 
  Reference    Z. Naturforsch. 53a, 117—126 (1998); received December 10 1997 
  Published    1998 
  Keywords    Liquid Crystals, Pattern Formation, Electrohydrodynamic Instability, Optical Microscopy 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0117.pdf 
 Identifier    ZNA-1998-53a-0117 
 Volume    53 
2Author    Hans MeinhardtRequires cookie*
 Title    Cooperation of Compartments for the Generation of Positional Information  
 Abstract    A mechanism is proposed for pattern formation in developmental subfields. In application to imaginal disks, the compartmentalization appears as a prerequisite for the generation of posi­ tional information in the proximo-distal dimension. Cooperation of three or four compartments in the production of a morphogen leads to a cone-shaped morphogen distribution, since a high production rate of the morphogen is possible only at the intersection of compartment borders. The local concentration of the cone-shaped distribution is a measure for the distance from this center and can be used as positional information. In agreement with the experimental observa­ tions, the model predicts that (i) the distalmost structures are formed at the intersection of compartment borders; (ii) distal transformation occurs whenever cells of all compartments come close to each other; (iii) distal transformation does not require a complete set of circumferential structures; (iv) mutants exist in which the positional information and not the response of the cells is altered and (v) no distal to proximal intercalation of missing leg segments occur. Regeneration and formation of supernumerary insect legs can be explained as well. Simple molecular reaction can account for this type of pattern formation. The "complete circle rule" of French, Bryant and Bryant (Science 193,969-981 (1976)) for distal transformation may be simplified by a "coopera­ tion of compartments" rule. 
  Reference    Z. Naturforsch. 35c, 1086—1091 (1980); received July 21 1980 
  Published    1980 
  Keywords    Positional Information, Imaginal Disk, Compartments, Pattern Formation 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-1086.pdf 
 Identifier    ZNC-1980-35c-1086 
 Volume    35 
3Author    Rainer Gilles, Lothar JaenickeRequires cookie*
 Title    Differentiation in Volvox carteri: Study of Pattern Variation of Reproductive Cells  
 Abstract    Asexual spheroids of the multicellular green alga Volvox are composed o f two types o f cells: non-flagellated reproductive gonidia and Chlamydomonas-\ike flagellated somatic cells. They are committed by a differentiating cleavage during embryogenesis. The gonidia o f the adult spheroids form a symmetrical pattern consisting o f four layers o f four gonidia each; their position is established already in the embryos by the gonidial initials. Whereas, generally, the 16-gonidia pattern is assumed to be the basic one, most o f the spheroids have fewer gonidia (down to 8). The nine possible gonidial patterns (8 to 16 gonidia) are described and correlated to the gonidial stem cells which have been differentiated. Defects in gonidial pattern are o f particular interest, since any model of differentiation has to explain not only the basic pattern formed, but also its systematic variations. Our study shows that the pattern reduction is by no means random, but governed by an intrinsic mechanism which shifts the first unequal cleavage from the 32-celled stage to the 16-celled stage. All the patterns formed can be deduced from cleavage pathways involving non-synchronous differentiation of the stem cells. Thus, pattern formation can be correlated to timing and spacing signals regulating events during embryogenesis. 
  Reference    Z. Naturforsch. 37c, 1023—1030 (1982); received June 1 1982 
  Published    1982 
  Keywords    Volvox carteri, Differentiation, Embryogenesis, Cell Lineages, Pattern Formation 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-1023.pdf 
 Identifier    ZNC-1982-37c-1023 
 Volume    37 
4Author    Rudolf WinklbauerRequires cookie*
 Title    Growth Control and Pattern Regulation in the Lateral Line Systems of Xenopus  
 Abstract    In Xenopus, the supraorbital lateral line system consists of a periodic pattern of lateral line organs which is formed by the regular fragmentation of a streak-like primordium. The pattern forming mechanism which subdivides the primordium into individual organs is not capable of adjusting to the variable size of the system. Nevertheless, the number of organs per supraorbital system tends to be held constant. This is achieved by regulating the growth of the system in an appropriate manner. 
  Reference    Z. Naturforsch. 43c, 294—300 (1988); received December 22 1987 
  Published    1988 
  Keywords    Growth Control, Pattern Formation, Lateral Line System Xenopus 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0294.pdf 
 Identifier    ZNC-1988-43c-0294 
 Volume    43 
5Author    Stefan Reimann, Rapporteur, JoaquinM. Fuster, Alfred Gierer, Gottfried Mayer-Kress, Titus Neumann, Pieter Roelfsem, Stefan Rotter, Gregor Schöner, Achim Stephan, Eiion Vaadia, Henrik WalterRequires cookie*
 Title    Group Report: Emergent Properties of Natural and Artificial Systems* On the Meanings of Emergence  
  Reference    Z. Naturforsch. 53c, 770—774 (1998); received April 16 1998 
  Published    1998 
  Keywords    Emergence, Pattern Formation, Self-Organization, Pre-Determinism 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0770.pdf 
 Identifier    ZNC-1998-53c-0770 
 Volume    53 
6Author    J. Ackermann, T. KirnerRequires cookie*
 Title    Parasites and Pattern Formation  
 Abstract    Biological information is coded in replicating molecules. To maintain a given amount of in-formation a cooperative interaction between these molecules is essential. The main problem for the stability of a system of prebiotic replicators are emerging parasites. Stabilization against such parasites is possible if space is introduced in the model. Complex patterns like spiral waves and self-replicating spot patterns have been shown to stabilize such systems. Stability of replicating systems, however, occurs only in parameter regions were such complex patterns occur. We show that parasites are able to push such systems into a parameter region were life is possible. To demonstrate this influence of parasites on such systems, we introduce a parasitic species in the Gray-Scott model. The growing concentration of parasites will kill the system, and the cooperative Gray-Scott system will be diluted out in a well mixed flow reactor. While considering space, in the model stabilizing pattern formation in a narrow parameter region is possible. We demonstrate that the concentration of the parasitic species is able to push the system into a region were stabilizing patterns emerge. 
  Reference    Z. Naturforsch. 54a, 146—152 (1999); received December 15 1998 
  Published    1999 
  Keywords    Pattern Formation, Reaction-Diffusion, Molecular Evolution, Parasites, Coevolution, Cooperation 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0146.pdf 
 Identifier    ZNA-1999-54a-0146 
 Volume    54 
7Author    HansH. Diebner3, O. Tf\, Adolf Mathias3, Horst Prehnc, Marco Rohrbacha, Sven Sahle3Requires cookie*
 Title    Control and Adaptation of Spatio-temporal Patterns  
 Abstract    We apply a recently introduced cognitive system for dynamics recognition to a two-dimensional array of coupled oscillators. The cognitive system allows for both the control and the adaptation of spatio-temporal patterns of that array of oscillators. One array that shows Turing-pattems in a self-organizational manner is viewed as an externally presented dynamics (stimulus) which is mapped onto a mirror dynamics, whereby the latter is capable to simulate (simulus). Two of the parameters of the stimulus are thereby regarded to be unknown and have to be estimated by the cognitive system. The cognitive system itself consists of dynamical modules that are stimulated by the external dynamics in the sense of Pyragas' external force control mechanism and thereby yield measures of how good they match the stimulus. These measures are used as weights to construct the simulus. The adaptation process is performed "on the fly", i. e., without the storage of data. The proposed cognitive system, therefore, is a prominent candidate for the construction of a control device for a permanent real time observation of an external dynamical system in order to interfere instantaneously when necessary. 
  Reference    Z. Naturforsch. 56a, 663—669 (2001); received August 21 2001 
  Published    2001 
  Keywords    Adaptive Systems, Cognitive Systems, Pattern Formation, Brain Dynamics, Force Control 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0663.pdf 
 Identifier    ZNA-2001-56a-0663 
 Volume    56