We have carried out time resolved stroboscopic diffraction experiments on standing surface acoustic waves (SAWs) of Rayleigh type on a LiNbO3 substrate. A novel timing system has been developed and ...commissioned at the storage ring Petra III of Desy, allowing for phase locked stroboscopic diffraction experiments applicable to a broad range of timescales and experimental conditions. The combination of atomic structural resolution with temporal resolution on the picosecond time scale allows for the observation of the atomistic displacements for each time (or phase) point within the SAW period. A seamless transition between dynamical and kinematic scattering regimes as a function of the instantaneous surface amplitude induced by the standing SAW is observed. The interpretation and control of the experiment, in particular disentangling the diffraction effects (kinematic to dynamical diffraction regime) from possible non-linear surface effects is unambiguously enabled by the precise control of phase between the standing SAW and the synchrotron bunches. The example illustrates the great flexibility and universality of the presented timing system, opening up new opportunities for a broad range of time resolved experiments.
In small planktonic organisms, large census sizes (Nc) suggest large effective population sizes (Ne), but reliable estimates are rare. Here, we present Ne/Nc ratios for two freshwater copepod species ...(Eudiaptomus sp.) using temporal samples of multilocus microsatellite genotypes and a pseudo‐likelihood approach. Ne/Nc ratios were very small in both Eudiaptomus species (10−7–10−8). Although we hypothesized that the species producing resting eggs (E. graciloides) had a larger Ne than the other (E. gracilis), estimates were not statistically different (E. graciloides: Ne = 672.7, CI: 276–1949; E. gracilis: Ne = 1027.4, CI: 449–2495), suggesting that the propagule bank of E. graciloides had no detectable influence on Ne.
•Yeast pol η possesses a second PIP motif, which we have named PIP2.•The PIP motifs of pol η bind PCNA with different affinity and kinetics.•The PIP motifs of pol η bind Rad6-Rad18 with different ...affinity and kinetics.•PIP1 likely recruits pol η to translesion synthesis complexes.•PIP2 likely facilitates the dynamics of translesion synthesis complexes.
In translesion synthesis (TLS), specialized DNA polymerases, such as polymerase (pol) η and Rev1, are recruited to stalled replication forks. These polymerases form a multi-protein complex with PCNA, Rad6-Rad18, and other specialized polymerases. Pol η interacts with PCNA and Rev1 via a PCNA-interacting protein (PIP) motif in its C-terminal unstructured region. Here we report the discovery of a second PIP-like motif in the C-terminal region of pol η, which we have designated as PIP2. We have designated the original PIP motif as PIP1. We show that the pol η PIP1 and PIP2 motifs bind PCNA with different affinities and kinetics. PIP1 binds with higher affinity than does PIP2, and PIP1 dissociates more slowly than does PIP2. In addition, we show that the interaction between pol η and Rad6-Rad18 is also mediated by the pol η PIP1 and PIP2 motifs. Again, we show that the affinity and kinetics by which these motifs bind Rad6-Rad18 is different. These findings are significant, because the multiple PIP-like motifs on pol η likely play quite different roles within the multi-protein complex formed at stalled replication forks. PIP1 likely plays a critical role in the recruiting pol η to this multi-protein complex. PIP2, by contrast, likely plays a critical role in maintaining the architecture and the dynamics of this multi-protein complex needed to maximize the efficiency and accuracy of TLS.
The spatial coherence of free-electron laser radiation in the water window spectral range was studied, using the third harmonic (λ<(3rd) = 2.66 nm) of DESY's Free-electron LASer in Hamburg (FLASH). ...Coherent single pulse diffraction patterns of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) multilamellar lipid stacks have been recorded. The intensity histogram of the speckle pattern around the first lamellar Bragg peak, corresponding to the d = 5 nm periodicity of the stack, reveals an average number of transverse modes of M¯ = 3.0 of the 3rd harmonic. Using the lipid stack as a 'monochromator', pulse-to-pulse fluctuations in the third harmonic λ(3rd) have been determined to be 0.033 nm.
Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, ...Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes ofc . 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of . of each parasite species over all samples to form an ' individual parasitation index ' (I sub(PI)), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.
The effect of hard X-ray radiation on the structure and electrostatics of solid-supported lipid multilayer membranes is investigated using a scanning Kelvin probe (SKP) integrated with a high-energy ...synchrotron beamline to enable in situ measurements of the membranes’ local Volta potential (V p) during X-ray structural characterization. The undulator radiation employed does not induce any detectable structural damage, but the V p of both bare and lipid-modified substrates is found to undergo strong radiation-induced shifts, almost immediately after X-ray exposure. Sample regions that are macroscopically distant (∼cm) from the irradiated region experience an exponential V p growth with a characteristic time constant of several minutes. The V p variations occurring upon periodic on/off X-ray beam switching are fully or partially reversible depending on the location and time-scale of the SKP measurement. The general relevance of these findings for synchrotron-based characterization of biomolecular thin films is critically reviewed.
We have studied the packing and collective dynamics of the phospholipid acyl chains in a model membrane composed of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and cholesterol in varied ...phase state. After a structural characterization of this two-component model bilayer using X-ray reflectivity, we have carried out coherent inelastic neutron scattering to investigate the chain dynamics. Both DMPC/cholesterol membranes exhibited much sharper and more pronounced low-energy inelastic excitations than a pure DMPC membrane. In the high-energy regime above 10meV, the insertion of cholesterol into the membrane was found to shift the position of the inelastic excitation towards values otherwise found in the pure lipids gel phase. Thus, the dissipative collective short-range dynamics of the acyl chains is strongly influenced by the presence of cholesterol.
Single hydrogen atoms on the Si(001) surface Radny, M. W.; Smith, P. V.; Reusch, T. C. G. ...
Physical review. B, Condensed matter and materials physics,
10/2007, Letnik:
76, Številka:
15
Journal Article
Limited dispersal distances in plant populations frequently cause local genetic structure, which can be quantified by spatial autocorrelation. In clonal plants, three levels of spatial organization ...can contribute to positive autocorrelation; namely, the neighbourhood of (a) ramets, (b) clone fragments and (c) entire clones. Here we use data from an exhaustive sampling scheme on a clonal plant to measure the contribution of the neighbourhoods of each distinct clonal structure to total spatial autocorrelation. Four plots (256 grid points each) within dense meadows of the marine clonal plant Zostera marina (eelgrass) were sampled for clone structure with nine microsatellite markers ( approximately 80 alleles). We found significant coancestry (f(ij)), at all three levels of spatial organization, even when not allowing for joins between samples of identical genets. In addition, absolute values of f(ij) and the maximum distance with significant positive f(ij) decreased with the progressive exclusion of joins between alike genotypes. The neighbourhood of this clonal plant thus consists of three levels of organization, which are reflected in different kinship structures. Each of these kinship structures may affect the level of biparental inbreeding and the physical distance between flowering shoots and their outcrossing neighbourhood. These results also emphasize the notion that spatial autocorrelation crucially depends on the scale and intensity of sampling.
We have studied single Si dangling bonds on the Si(0
0
1) surface using scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations. The Si dangling bonds are created by the ...chemisorption of single hydrogen atoms forming a Si–Si–H hemihydride. At room temperature, the hemihydride induces static buckling on adjacent Si–Si dimers. In the STM measurements, we observe that the orientation of the static buckling pattern can be reversed with tip-sample bias and influenced by the substrate doping. Our DFT calculations yield a correlation between the electron occupancy of the hemihydride Si dangling bond and the buckling orientation around it.
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