Inversion of Sequence of Diffusion and Density Anomalies in Core-Softened Systems

In this paper we present a simulation study of water-like anomalies in core-softened system introduced in our previous publications. We investigate the anomalous regions for a system with the same functional form of the potential but with different parameters and show that the order of the region of anomalous diffusion and the region of density anomaly is inverted with increasing the width of the repulsive shoulder.Comment: 8 pages, 10 figure

Experimental methods for the analysis of the durability behavior of concrete joints

This article addresses the applicability of experimental methods for the evaluation of concrete durability on localized structural weaknesses posed by joints. Three different types of exposure are analyzed: chloride penetration, carbonation, and freeze–thaw attack. First, established experimental methods for the characterization of the durability of plain concrete are presented and their general applicability on concrete joints is discussed. The experimental program focuses on the execution of selected tests on laboratory specimens with and without joints. Indicator tests for both chloride penetration and carbonation are generally feasible, but require attention to specimen preparation. Rapid chloride migration yielded inconclusive results, while uniaxial chloride diffusion coefficient of concrete joints cannot be determined because of the areal extent of profile grinding. For the same reason, the characterization of the resistance to freeze–thaw cycles through surface deterioration is not applicable for concrete joints. The structural damage was instead successfully qualified through direct tension tests

Performance Bottlenecks in Digital Movie Systems

Digital movie systems offer great perspectives for multimedia applications. But the large amounts of data involved and the demand for isochronous transmission and playback are also great challenges for the designers of a new generation of file systems, database systems, operating systems, window systems, video encoder/decoder and networks. Today's research prototypes of digital movie systems suffer from severe performance bottlenecks, resulting in small movie windows, low frame rates or bad image quality (or all of these!). We consider the performance problem to be the most important problem with digital movie systems, preventing their widespread use today. In this paper we address performance issues of digital movie systems from a practical perspective. We report on performance experience gained with the XMovie system and new algorithms and protocols to overcome some of these bottlenecks

Phytochrome Mediated Responses in Agrobacterium fabrum: Growth, Motility and Plant Infection

The soil bacterium and plant pathogen Agrobacterium fabrum C58 has two phytochrome photoreceptors, Agp1 and Agp2. We found that plant infection and tumor induction by A. fabrum is down-regulated by light and that phytochrome knockout mutants of A. fabrum have diminished infection rates. The regulation pattern of infection matches with that of bacterial conjugation reported earlier, suggesting similar regulatory mechanisms. In the regulation of conjugation and plant infection, phytochromes are active in darkness. This is a major difference to plant phytochromes, which are typically active after irradiation. We also found that propagation and motility were affected in agp1− and agp2− knockout mutants, although propagation was not always affected by light. The regulatory patterns can partially but not completely be explained by modulated histidine kinase activities of Agp1 and Agp2. In a mass spectrometry-based proteomic study, 24 proteins were different between light and dark grown A. fabrum, whereas 382 proteins differed between wild type and phytochrome knockout mutants, pointing again to light independent roles of Agp1 and Agp2

Key Amino Acids in the Bacterial (6-4) Photolyase PhrB from Agrobacterium fabrum

Photolyases can repair pyrimidine dimers on the DNA that are formed during UV irradiation. PhrB from Agrobacterium fabrum represents a new group of prokaryotic (6–4) photolyases which contain an iron-sulfur cluster and a DMRL chromophore. We performed site-directed mutagenesis in order to assess the role of particular amino acid residues in photorepair and photoreduction, during which the FAD chromophore converts from the oxidized to the enzymatically active, reduced form. Our study showed that Trp342 and Trp390 serve as electron transmitters. In the H366A mutant repair activity was lost, which points to a significant role of His366 in the protonation of the lesion, as discussed for the homolog in eukaryotic (6–4) photolyases. Mutants on cysteines that coordinate the Fe-S cluster of PhrB were either insoluble or not expressed. The same result was found for proteins with a truncated C-terminus, in which one of the Fe-S binding cysteines was mutated and for expression in minimal medium with limited Fe concentrations. We therefore assume that the Fe-S cluster is required for protein stability. We further mutated conserved tyrosines that are located between the DNA lesion and the Fe-S cluster. Mutagenesis results showed that Tyr424 was essential for lesion binding and repair, and Tyr430 was required for efficient repair. The results point to an important function of highly conserved tyrosines in prokaryotic (6–4) photolyase

Transport von Silbernanopartikeln in natürlich gelagerten Bodensäulen

Die Anzahl der wissenschaftlichen Untersuchungen zum Verbleib von Silbernanopartikeln (Ag-NP) in Böden hat in den letzten Jahren zugenommen. Da die publizierten Ergebnisse darauf hinweisen, dass sie stark durch die gewählten Versuchs- und Randbedingungen beeinflusst werden, bleibt die Bewertung der Mobilität von Silbernanopartikeln in Böden schwierig. Daher sollte der Transport und Verbleib der Ag-NP in dieser Untersuchung unter naturnahe Bedingung, aber mit kontrollierten Rand- und Anfangsbedingungen bestimmt werden. Dazu wurden an zwei Standorten (Sand, Schluff) jeweils acht ungestörte Bodensäulen (Ø 10,2 cm Höhe 16 cm) genommen und in einer Säulenversuchsanlage (SCS, Fa. emc GmbH) untersucht. Drei Säulen dienten jeweils als Parallelen während eine Säule als Kontrolle ohne Zugabe von NP untersucht wurde. Für beide Bodenarten erfolgten Versuche mit gesättigtem und ungesättigtem Fluss. Zur Nachverfolgung des Wasserflusses durch die Säulen wurde dem Beregnungswasser D2O als Tracer zugesetzt. Die Silbergesamtgehalte im Perkolat wurde nach HNO3-Aufschluss und mit ICP-OES/MS analysiert. Die Messung der gelösten Silberfraktion erfolgte nach Ultrazentrifugation mit ICP-MS. Die Größenverteilung von natürlichen Bodenkolloiden und Ag-NP wurde mit Dynamic Light Scattering (Malvern NanoZS) gemessen. Die Ergebnisse bestätigen den Einfluss der Versuchsbedingungen, zeigen aber auch die Bedeutung der Bodenstruktur auf die Mobilität der Ag-NP. Die Variabilität zwischen den Parallelproben ist sehr groß und überschattet mögliche Unterschiede zwischen den Bodenarten. Bevorzugte Fließwege sind wohl die Regel, die frühen Durchbrüche von D2O und Ag-NP bestätigt den präferentiellen Transport von Wasser und Partikeln. Mit Hilfe eines nachträglich durch die Säule perkolierten Farbstoffes (Brillant Blue) wurde Randfluss ausgeschlossen. Unter ungesättigten Bedingungen wird ein deutlich größerer Teil der Ag-NP im Boden zurückgehalten als unter gesättigten Fließbedingungen. Daher wird angenommen, dass die Bodenluft für die Retention der Partikel im Boden wichtig ist

Three-nucleon mechanisms in photoreactions

The $^{12}$C$(\gamma,ppn)$ reaction has been measured for E$_{\gamma}$=150-800 MeV in the first study of this reaction in a target heavier than $^3$He. The experimental data are compared to a microscopic many body calculation. The model, which predicts that the largest contribution to the reaction arises from final state interactions following an initial pion production process, overestimates the measured cross sections and there are strong indications that the overestimate arises in this two-step process. The selection of suitable kinematic conditions strongly suppresses this two-step contribution leaving cross sections in which up to half the yield is predicted to arise from the absorption of the photon on three interacting nucleons and which agree with the model. The results indicate $(\gamma,3N)$ measurements on nuclei may be a valuable tool for obtaining information on the nuclear three-body interaction.Comment: 5 pages, 3 figure

Highly conserved residues Asp-197 and His-250 in Agp1 phytochrome control the proton affinity of the chromophore and Pfr formation

The mutants H250A and D197A of Agp1 phytochrome from Agrobacterium tumefaciens were prepared and investigated by different spectroscopic and biochemical methods. Asp-197 and His-250 are highly conserved amino acids and are part of the hydrogen-bonding network that involves the chromophore. Both substitutions cause a destabilization of the protonated chromophore in the Pr state as revealed by resonance Raman and UV-visible absorption spectroscopy. Titration experiments demonstrate a lowering of the pK(a) from 11.1 ( wild type) to 8.8 in H250A and 7.2 in D197A. Photoconversion of the mutants does not lead to the Pfr state. H250A is arrested in a meta-Rc-like state in which the chromophore is deprotonated. For H250A and the wild-type protein, deprotonation of the chromophore in meta-Rc is coupled to the release of a proton to the external medium, whereas the subsequent proton re-uptake, linked to the formation of the Pfr state in the wild- type protein, is not observed for H250A. No transient proton exchange with the external medium occurs in D197A, suggesting that Asp-197 may be the proton release group. Both mutants do not undergo the photoinduced protein structural changes that in the wild- type protein are detectable by size exclusion chromatography. These conformational changes are, therefore, attributed to the meta-Rc -> Pfr transition and most likely coupled to the transient proton re- uptake. The present results demonstrate that Asp-197 and His-250 are essential for stabilizing the protonated chromophore structure in the parent Pr state, which is required for the primary photochemical process, and for the complete photo-induced conversion to the Pfr state.Fil: von Stetten, David. Technische Universität Berlin; AlemaniaFil: Seibeck, Sven. Freie Universität Berlin.; AlemaniaFil: Michael, Norbert. Freie Universität Berlin.; AlemaniaFil: Scheerer, Patrick. Charité Universitätsmedizin Berlin; AlemaniaFil: Mroginski, Maria Andrea. Technische Universität Berlin; AlemaniaFil: Murgida, Daniel Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Technische Universität Berlin; AlemaniaFil: Krauss, Norbert. Freie Universität Berlin.; AlemaniaFil: Heyn, Maarten P.. Charité Universitätsmedizin Berlin; AlemaniaFil: Hildebrandt, Peter. Technische Universität Berlin; AlemaniaFil: Borucki, Berthold. Freie Universität Berlin.; AlemaniaFil: Lamparter, Tilman. Freie Universität Berlin.; Alemani

Polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei

The polarization degrees of freedom in photoinduced two-nucleon knockout from finite nuclei are studied. It is pointed out that they open good perspectives to study the dynamics of dinucleons in the medium in detail. The ($\gamma,pp$) and ($\gamma,pn$) angular cross sections, photon asymmetries and outgoing nucleon polarizations are calculated for the target nuclei $^{16}$O and $^{12}$C and photonenergies ranging from 100 up to 500 MeV. It is investigated to which degree the two-nucleon emission reaction is dominated by photoabsorption on $^3S_1(T=0)$ proton-neutron and $^1S_0(T=1)$ proton-proton pairs in the nuclear medium. The calculations demonstrate that dominance of $S$ wave photoabsorption in the ($\gamma,pn$) channel does not necessarily imply that the reaction mechanism is similar to what is observed in deuteron photodisintegration.Comment: 27 pages, REVTeX 3.0 with epsf.sty, 11 figures in EPS forma