Erhaltungsbedingungen und Diagenese fossiler Vogeleischalen aus dem Nördlinger Ries (Miozän, MN6)

Zusammenfassung:Vogeleier und deren Eischalen aus dem Miozän (MN 6) der Ablagerungen des Nördlinger Ries werden hinsichtlich ihrer Erhaltungsbedingungen und Diagenese untersucht. Ein relativ kleines Ei wird aufgrund der Größe und Form sowie der Schalenstruktur den Charadriiformes (Charadriidae?, Scolopacidae?), drei nahe beieinander liegende Eier den Pelecaniformes (Phalacrocorax sp. ?) zugeordnet. Die Eischalen des Nördlinger Ries weisen ein reiches Spektrum an diagenetischen Phänomenen auf: Erhalt einer mineralisierten Membrana testacea, Abdrücke der Membrana testacea auf den basalen Mammillen, Hinweise auf Farbstreifen in den Schalen, mineralisierte primäre und sekundäre Außenschichten, zementierte Porenkanäle und Umkristallisationen der Schale. Die überwiegend frühdiagenetischen kalzitischen Zementationen, die mit dem mikrobiellen Abbau organischer Substanzen in Zusammenhang stehen könnten, scheinen Überlieferung und Transport vollständiger Vogeleier erleichtert oder sogar erst ermöglicht zu haben. Der wahrscheinliche allochthone Charakter der Eier, der sich auch aus den Fundbedingungen in den verkarsteten »Travertinhügeln« (spring mounds) ergibt, wird diskutiert.Abstract:Preservational conditions and diagenesis of avian eggs and eggshells from the Miocene (MN 6) of the Nördlinger Ries (Southern Germany) are studied. One single small egg is assigned, due to shell structure and size and shape of the egg, to the Charadriiformes (Charadriidae?, Scolopacidae?). A cluster of three eggs is assigned to the Pelecaniformes (Phalacrocorax sp. ?). The following taphonomic phenomena of the avian eggshells are described: preservation of a calcified Membrana testacea, reprints of the Membrana testacea at the basal mammillae, mineralized color lines, primary and secondary calcified deposits on the outer surfaces, calcified pore channels and recristallisation of the shell. The early diagenetic processes (cementation) are probably correlated with the microbial decay of organic material (ammonification) within the eggs and are interpreted as being responsible for preservation and transport of the complete bird eggs. The allochthonous character of the eggs, additionally indicated by their deposition and pockets of lacustrine spring mounds, is discussed

Implicit Simulations using Messaging Protocols

A novel algorithm for performing parallel, distributed computer simulations on the Internet using IP control messages is introduced. The algorithm employs carefully constructed ICMP packets which enable the required computations to be completed as part of the standard IP communication protocol. After providing a detailed description of the algorithm, experimental applications in the areas of stochastic neural networks and deterministic cellular automata are discussed. As an example of the algorithms potential power, a simulation of a deterministic cellular automaton involving 10^5 Internet connected devices was performed.Comment: 14 pages, 3 figure

Hyperscaling in the Domany-Kinzel Cellular Automaton

An apparent violation of hyperscaling at the endpoint of the critical line in the Domany-Kinzel stochastic cellular automaton finds an elementary resolution upon noting that the order parameter is discontinuous at this point. We derive a hyperscaling relation for such transitions and discuss applications to related examples.Comment: 8 pages, latex, no figure

Rescue Model for the Bystanders' Intervention in Emergencies

To investigate an effect of social interaction on the bystanders' intervention in emergency situations we introduce a rescue model which includes the effects of the victim's acquaintance with bystanders and those among bystanders. This model reproduces the surprising experimental result that the helping rate tends to decrease although the number of bystanders $k$ increases. The model also shows that given the coupling effect among bystanders, for a certain range of small $k$ the helping rate increases according to $k$ and that coupling effect plays both positive and negative roles in emergencies. Finally we find a broad range of coupling strength to maximize the helping rate.Comment: 10 pages, 4 figure

Quasi-stationary distributions for the Domany-Kinzel stochastic cellular automaton

We construct the {\it quasi-stationary} (QS) probability distribution for the Domany-Kinzel stochastic cellular automaton (DKCA), a discrete-time Markov process with an absorbing state. QS distributions are derived at both the one- and two-site levels. We characterize the distribuitions by their mean, and various moment ratios, and analyze the lifetime of the QS state, and the relaxation time to attain this state. Of particular interest are the scaling properties of the QS state along the critical line separating the active and absorbing phases. These exhibit a high degree of similarity to the contact process and the Malthus-Verhulst process (the closest continuous-time analogs of the DKCA), which extends to the scaling form of the QS distribution.Comment: 15 pages, 9 figures, submited to PR

Closure of Macroscopic Laws in Disordered Spin Systems: A Toy Model

We use a linear system of Langevin spins with disordered interactions as an exactly solvable toy model to investigate a procedure, recently proposed by Coolen and Sherrington, for closing the hierarchy of macroscopic order parameter equations in disordered spin systems. The closure procedure, based on the removal of microscopic memory effects, is shown to reproduce the correct equations for short times and in equilibrium. For intermediate time-scales the procedure does not lead to the exact equations, yet for homogeneous initial conditions succeeds at capturing the main characteristics of the flow in the order parameter plane. The procedure fails in terms of the long-term temporal dependence of the order parameters. For low energy inhomogeneous initial conditions and near criticality (where zero modes appear) deviations in temporal behaviour are most apparent. For homogeneous initial conditions the impact of microscopic memory effects on the evolution of macroscopic order parameters in disordered spin systems appears to be mainly an overall slowing down.Comment: 14 pages, LateX, OUTP-94-24

On Damage Spreading Transitions

We study the damage spreading transition in a generic one-dimensional stochastic cellular automata with two inputs (Domany-Kinzel model) Using an original formalism for the description of the microscopic dynamics of the model, we are able to show analitically that the evolution of the damage between two systems driven by the same noise has the same structure of a directed percolation problem. By means of a mean field approximation, we map the density phase transition into the damage phase transition, obtaining a reliable phase diagram. We extend this analysis to all symmetric cellular automata with two inputs, including the Ising model with heath-bath dynamics.Comment: 12 pages LaTeX, 2 PostScript figures, tar+gzip+u

Vortex Dynamics in Classical Non--Abelian Spin Models

We discuss the abelian vortex dynamics in the abelian projection approach to non-abelian spin models. We show numerically that in the three-dimensional SU(2) spin model in the Maximal Abelian projection the abelian off-diagonal vortices are not responsible for the phase transition contrary to the diagonal vortices. A generalization of the abelian projection approach to SU(N) spin models is briefly discussed.Comment: 7 pages, LaTeX, 1 figure, uses epsf.sty; Introduction is extended and a few references are added; to be published in JETP Let

Random Field and Random Anisotropy Effects in Defect-Free Three-Dimensional XY Models

Monte Carlo simulations have been used to study a vortex-free XY ferromagnet with a random field or a random anisotropy on simple cubic lattices. In the random field case, which can be related to a charge-density wave pinned by random point defects, it is found that long-range order is destroyed even for weak randomness. In the random anisotropy case, which can be related to a randomly pinned spin-density wave, the long-range order is not destroyed and the correlation length is finite. In both cases there are many local minima of the free energy separated by high entropy barriers. Our results for the random field case are consistent with the existence of a Bragg glass phase of the type discussed by Emig, Bogner and Nattermann.Comment: 10 pages, including 2 figures, extensively revise

Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice London model. Motivated by a recent controversy regarding the presence, within this model, of a vortex-liquid regime with longitudinal superconducting coherence over long length scales, we directly compare two different ways to calculate the longitudinal coherence. For an isotropic superconductor, we interpret our results in terms of a temperature regime within the liquid phase in which longitudinal superconducting coherence extends over length scales larger than the system thickness studied. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.