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Ludwig-Maximilians-Universität München

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  1. 01/01/2007

    Wetland paradise lost: Miocene community dynamics in large herbivorous mammals from the German Molasse Basin.

    Geowissenschaften - Open Access LMU

  2. 01/01/1994

    A gradient method for the quantitative analysis of cell movement and tissue flow and its application to the analysis of multicellular Dictyostelium development

    We describe the application of a novel image processing method, which allows quantitative analysis of cell and tissue movement in a series of digitized video images. The result is a vector velocity field showing average direction and velocity of movement for every pixel in the frame. We apply this method to the analysis of cell movement during different stages of the Dictyostelium developmental cycle. We analysed time-lapse video recordings of cell movement in single cells, mounds and slugs. The program can correctly assess the speed and direction of movement of either unlabelled or labelled cells in a time series of video images depending on the illumination conditions. Our analysis of cell movement during multicellular development shows that the entire morphogenesis of Dictyostelium is characterized by rotational cell movement. The analysis of cell and tissue movement by the velocity field method should be applicable to the analysis of morphogenetic processes in other systems such as gastrulation and neurulation in vertebrate embryos.

  3. 01/01/1994

    A new type of reconstruction on the InSb() surface determined by grazing incidence X-ray diffraction

    The (3×3) reconstruction of the InSb( ) surface has been investigated by grazing incidence X-ray diffraction and scanning tunneling microscopy. The structure is characterized by 6-atom rings on top of a slightly buckled InSb top double layer. Two types of rings have been found, an elliptic ring consisting of 4 In and 2 Sb atoms and a trigonal ring with 3 In and 3 Sb atoms. The bond angles and lengths are consistent with the concept of rehybridization and depolarization which explains the reconstructions of the (111) and (110) surfaces.

  4. 01/01/1994

    Axially linear slopes of composition for “delta” crystals

    “Delta” crystals are solid solutions of miscible materials with large lattice parameter differences which contain high concentration gradients in one direction (parallel to a lattice plane strongly diffracting X-rays). The system GaSb-InSb has been chosen as suitable for study. By means of a “gradient projection method”, the growth of nearly linear composition profiles with relatively steep slopes of the lattice parameter (up to (Δa/ ) / Δz = 8.3% cm-1), adjustable by the temperature gradient, have been performed. However, the grown ingots were not monocrystalline due to the use of too high a growth rate.

  5. 01/01/1994

    Comparison of two approaches to forced convection in crystal growth of II-VI compounds by THM

    Hg1 - xCdxTe and Cd1 - xZnxTe single crystals were grown by the tracwelling heater method (THM), applying two different techniques of artificially stirring the solution zone. Accelerated crucible rotation (ACRT) was used in a vertical growth arrangement and compared a technique with constant rotation around the horizontal axis of the ampoule. The dominant hydrodynamic mechanisms of noth methods are discribed by the rotating disc model and are suggested to be almost identical with respect to the growth conditions at the interface. Convective flow is effectively enhanced adhacent to the growing crystal, where the matter transport is regarded as the rate-limiting step of solution growth. Inclusion density analysis by IR microscopy was used to characterise the crystals of Cd1 - xZnxTe grown at different rates. It was shown that forced convection allows an increase in the crystal growth rate from a few mm day-1 with ACRT or horizontally rotating THM.

  6. 01/01/1994

    Compressibility of titanosilicate melts

    The effect of composition on the relaxed adiabatic bulk modulus (K0) of a range of alkali- and alkaline earth-titanosilicate [X 2 n/n+ TiSiO5 (X=Li, Na, K, Rb, Cs, Ca, Sr, Ba)] melts has been investigated. The relaxed bulk moduli of these melts have been measured using ultrasonic interferometric methods at frequencies of 3, 5 and 7 MHz in the temperature range of 950 to 1600°C (0.02 Pa s s 5 Pa s). The bulk moduli of these melts decrease with increasing cation size from Li to Cs and Ca to Ba, and with increasing temperature. The bulk moduli of the Li-, Na-, Ca- and Ba-bearing metasilicate melts decrease with the addition of both TiO2 and SiO2 whereas those of the K-, Rb- and Cs-bearing melts increase. Linear fits to the bulk modulus versus volume fraction of TiO2 do not converge to a common compressibility of the TiO2 component, indicating that the structural role of TiO2 in these melts is dependent on the identity of the cation. This proposition is supported by a number of other property data for these and related melt compositions including heat capacity and density, as well as structural inferences from X-ray absorption spectroscopy (XANES). The compositional dependence of the compressibility of the TiO2 component in these melts explains the difficulty incurred in previous attempts to incorporate TiO2 in calculation schemes for melt compressibility. The empirical relationship KV-4/3 for isostructural materials has been used to evaluate the compressibility-related structural changes occurring in these melts. The alkali metasilicate and disilicate melts are isostructural, independent of the cation. The addition of Ti to the metasilicate composition (i.e. X2TiSiO5), however, results in a series of melts which are not isostructural. The alkaline-earth metasilicate and disilicate compositions are not isostructural, but the addition of Ti to the metasilicate compositions (i.e. XTiSiO5) would appear, on the basis of modulus-volume systematics, to result in the melts becoming isostructural with respect to compressibility.

  7. 01/01/1994

    Coverage-dependent adsorption sites for K/Cu(001) and Cs/Cu(001) determined by surface X-ray diffraction

    Surface X-ray diffraction has been used to analyze in situ the room-temperature adsorption behaviour and the structure of K and Cs on Cu(100) at submonolayer coverages. Adsorption of K takes place in fourfold hollow sites up to coverages of about 0.25 monolayers (ML), where 1 ML corresponds to 1.53 × 1015 atoms/cm2. At higher coverages the formation of a quasi-hexagonal incommensurate adlayer is observed. In contrast, for Cs adsorption we observe from the very beginning the formation of the quasi-hexagonal structure up to the completion of the adlayer at about 0.30 ML. For K adsorption in the hollow sites we determine an adsorption height, d = 2.25(15) Å, corresponding to an effective K radius of reff = 1.6(1) Å close to the ionic radius of 1.33 Å. We do not observe a change in the effective radius as a function of coverage. For the quasi-hexagonal Cs structure we find an (average) adsorption height d = 2.94 Å corresponding to an effective radius of reff = 2.18 and 1.93 Å, for the limiting ca hollow- and bridge-site adsorption, respectively. The analysis of the superlattice reflections corresponding to the quasi-hexagonal incommensurate structures indicated that the K adlayer is strongly modulated. The first Fourier component of the substrate-induced modulation was determined to u01 = 1.29(3) Å. In contrast, for Cs/Cu(001) static modulation is much less important (u01 0.2 Å). Variation of the Cs adlayer density by changing the substrate temperature allows continuous expansion and contraction of the adsorbate unit cell. No commensurate-incommensurate transition has been observed.

  8. 01/01/1994

    Effects of water content, temperature and pressure on actinide tracer diffusion in melts of haplogranitic composition

    Geowissenschaften - Open Access LMU

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Die Universitätsbibliothek (UB) verfügt über ein umfangreiches Archiv an elektronischen Medien, das von Volltextsammlungen über Zeitungsarchive, Wörterbücher und Enzyklopädien bis hin zu ausführlichen Bibliographien und mehr als 1000 Datenbanken reicht. Auf iTunes U stellt die UB unter anderem eine Auswahl an elektronischen Publikationen der Wissenschaftlerinnen und Wissenschaftler an der LMU bereit.

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