Peter J. Plath

Cell movement and shape are non-random and determined by intracellular, oscillatory rotating waves in Dictyostelium amoebae

We present evidence for a mechanism of eukaryotic cell movement. The pseudopodial dynamics and shape of Dictyostelium discoideum amoebae were investigated using computer-supported video microscopy. An examination of the cell periphery by the novel method of serial circular maps revealed explicit, classical wave patterns, which indicate the existence of intrinsic intracellular oscillations. The patterns are generated by the transit of self-organized, super-positioned, harmonic modes of rotating oscillatory waves (ROWS). These waves are probably associated with the dynamics of intracellular actin polymerisation and depolymerisation. A Karhunen-Loève expansion was conducted on one cell during 10 min of locomotion using points each 10 degrees around the cells boundary. The results show that only 2-3 modes are necessary to describe the most essential features of cell movement and shape. Based on this analysis, a wave model was developed, which accurately simulates the dynamics of cell movement and shape during this time. The model was tested by reconstructing the cells dynamical form by means of the Karhunen-Loève transform. No difference was detected between this reconstruction and the actual cell outline. Although cell movement and shape have hitherto been viewed as random, our results demonstrate that ROWS determine the spatio-temporal expression of pseudopodia, and consequently govern cell shape and movement, non-randomly.

Experimental evidence of homoclinic chaos and type-II intermittency during the oxidation of methanol

Abstract The dynamic behavior of heterogeneous catalytic oxidation of methanol on zeolite supported palladium is studied. By varying the flow rate, the methanol concentration and the temperature, several regimes of periodic and toroidal oscillations are observed. Chaos and type-II intermittency are found near a homoclinic situation. It is shown, that in the case of homoclinic chaos the Grassberger-Procaccia algorithm for dimension estimation fails whereas a near-neighbor algorithm is applicable. For the intermittent behavior the histogram of the lengths of laminar episodes is compared with a distribution derived from a local model. It is suggested that the observed complex behavior is caused by periodic formation and reduction of palladium oxide in connection with heat and mass transport processes within the zeolite matrix.

A non-empirical molecular orbital study on loewenstein's rule and zeolite composition

Abstract The role of the “aluminum avoidance rule” in zeolite frameworks and its relation to the electronic structure and stability of various structural units of alumosilicates were studied by non-empirical SCF—MO techniques. Al—O—Al-type linkages are unstable according to the calculations. The presence of cations in the neighbourhood of T1—O—T2 bridges (T1, T2 = Si or Al) is the least stabilizing when T1 = T2 = Al.

Case study: visualization of laser confocal microscopy datasets

The paper presents an example of how existing visualization methods can be successfully applied-after minor modifications-for allowing new, sometimes unexpected insight into scientific questions, in this case for better understanding of unknown, microscopic biological structures. The authors present a volume rendering system supporting the visualization of LCM datasets, a new microscopic tomographic method allowing for the first time accurate and fast in-vivo inspection of the spatial structure of microscopic structures, especially important in (but not restricted to) biology. The speed, flexibility and versatility of the system allows fast, convenient, interactive operation with large datasets on small computers (workstation or PC). By testing different datasets, they have been able to significantly improve the performance of understanding the internal structure of LCM data. Most important, they have been able to show static and dynamic structures of cells never seen before and allowing significant insight in the cell movement process. Therefore they regard the system as a universal tool for the visualization of such data.

Non-empirical SCF molecular orbital studies on simple zeolite model systems

Abstract Non-empirical molecular orbital studies on the relative stabilities of topologically closed ring clusters H 8 Si 4 O 4 , [H 8 Si 3 AlO 4 ] − and [H 8 Si 2 Al 2 O 4 ] − modelling building units of zeolite frameworks, have been carried out. According to the calculations, AlOAl type bridges are unstable in doubly negative charged species, but can be stabilized in the presence of cations. This stabilization effect increases with increasing cation charge. Several hypothetical bimolecular cluster equilibria are also discussed.

Discrete model for laser driven etching and microstructuring of metallic surfaces.

We present a unidimensional discrete solid-on-solid model evolving in time using a kinetic Monte Carlo method to simulate microstructuring of kerfs on metallic surfaces by means of laser-induced jet-chemical etching. The precise control of the passivation layer achieved by this technique is responsible for the high resolution of the structures. However, within a certain range of experimental parameters, the microstructuring of kerfs on stainless steel surfaces with a solution of H3PO4 shows periodic ripples, which are considered to originate from intrinsic dynamics. The model mimics a few of the various physical and chemical processes involved and within certain parameter ranges reproduces some morphological aspects of the structures, in particular ripple regimes. We analyze the range of values of laser beam power for the appearance of ripples in both experimental and simulated kerfs. The discrete model is an extension of one that has been used previously in the context of ion sputtering and is related to a noisy version of the Kuramoto-Sivashinsky equation used extensively in the field of pattern formation.

Pseudopodium extension and amoeboid locomotion in Dictyostelium discoideum : possible autowave behaviour of F-actin

Abstract Supramolecular patterns of filamentous (F-)actin up to several micrometres across were visualized within projections of locomotory amoebae after cell fixation and staining with phalloidin-rhodamine. The patterns included rings, single and double spirals, some apparently colliding and disintegrating. Cell stimulation with a pulse of the chemoattractant cyclic AMP induced damping oscillations in F-actin ring frequency with a period of 6–7 s. Ring front propagation after stimulation was modelled by Markov and Fourier methods at 3.1–17.5 μm/min, similar to actual cell speed. We argue that the dynamics and detailed morphological correspondence of these F-actin structures to wave patterns in chemical reaction-diffusion systems strongly supports the interpretation that Dictyostelium cytoplasm behaves as an unstable, excitable medium enabling the propagation of self-organized, physico-chemical relaxation oscillations, i.e. autowaves, of reversible F-actin assembly or aggregation — a new state of actin - fundamental to pseudopodium extension, cell locomotion, chemotaxis and other cell functions.

Selforganized Structure Formation in Organized Microstructuring by Laser-Jet Etching

Laser-jet induced wet etching of stainless steel in 5M H3PO4 has been investigated. By this method, it is possible to cut and microstructure metals and alloys that form passive layers in strong etchants. Due to the laser heating of the metal and the adjacent layers of the etchant, the passive layer is removed and an active dissolution of the base metal together with the formation of hydrogen is observed. The reactions are limited by the transport of fresh acid and the removal of dissolved metal. A jet of etchant reduces the transport limitations. For definite ranges of the laser power, the feed velocity and the etchant jet velocity, a regime of periodic structure formation of the kerf, often called ripples, has been found. The ripple length depends on all three parameters. The ripple formation can be brought into correlation with a periodic change of the intensity of the reflected light as well as oscillations of the potential workpiece. It could be shown that the periodic structure formation is connected...

A simple discrete stochastic model for laser-induced jet-chemical etching

Recently developed processes based on laser-induced liquid jet-chemical etching provide efficient methods for high resolution microstructuring of metals. Like in other abrasive techniques (water-jet cutting, laser cutting, ion sputtering etc.) a spontaneous formation of ripples in the surface morphology has been observed depending upon the choice of system parameters. In this paper we present a discrete stochastic model describing the joint action of removal of material by chemical etching and thermally activated diffusion initiated by a moving laser leading to structure formation of a surface. Depending on scan speed and laser power different surface morphologies are observed ranging from rough surface structures to the formation of ripples. The continuum equation associated to the discrete model is shown to be a modified Kuramoto-Sivashinsky equation in a frame comoving with the laser beam. Fourier and wavelet techniques as well as large deviation spectra are used for a characterization of the surfaces.

Mathematical Analysis of Cell Shape

Cell motility involves translocation of the cell’s centroid as well as changes or distortions in the cell’s shape. Clues about the mechanism of cell movement may be obtained from information about its shape changes in time. The changes occur in multiple dimensions and can be highly periodic, however they may elude superficial observation. The techniques outlined in this contribution might help to reveal otherwise undetectable periodic shape changes.