Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite

We present a study on the kinetics of oxygen adsorption and desorption from single-wall carbon nanotube (SWNT) and highly oriented pyrolytic graphite (HOPG) samples. Thermal desorption spectra for SWNT samples show a broad desorption feature peaked at 62 K which is shifted to significantly higher temperature than the low-coverage desorption feature on HOPG. The low-coverage O2 binding energy on SWNT bundles, 18.5 kJ/mol, is 55% higher than that for adsorption on HOPG, 12.0 kJ/mol. In combination with molecular mechanics calculations we show that the observed binding energies for both systems can be attributed to van der Waals interactions, i.e. physisorption. The experiments provide no evidence for a more strongly bound chemisorbed species or for dissociative oxygen adsorption.Comment: 7 pages, 5 figures, 1 tabl

Die Rolle der PML-Kernkörperchen bei der Regulation der MHC Klasse II-Expression

Die Regulation der Lokalisation von Genen im Zellkern ist ein wichtiges Transkriptions-Kontrollelement in Eukaryoten. Für Wirbeltierzellen konnte gezeigt werden, dass bestimmte Gene mit Kernkörperchen assoziieren, wodurch möglicherweise deren Transkriptionsaktivität moduliert wird. Promyelozytische Leukämie (PML)-Körperchen sind Multiproteinkomplexe in Wirbeltierzellkernen, deren Funktion noch nicht geklärt ist. Es ist bekannt, dass diese Körperchen spezifisch mit dem Gen-reichen major histocompatibility (MHC) Gencluster auf Chromosom 6 assoziieren. Diese Genregion enthält eine Vielzahl von Genen für die Immunantwort. Die Frage, ob PML-Proteine bzw. -Körperchen an der Regulation dieser Gene beteiligt sind, blieb bislang unbeantwortet. Aufbauend auf der Beobachtung, dass die Assoziationsrate zwischen PML Körperchen und dem MHC Klasse II-Genlokus spezifisch durch Interferon γ (IFNγ) erhöht wird, zeigt die vorliegende Arbeit, dass IFNγ ebenfalls zu einer Rekrutierung von Faktoren, die die Transkription von MHC II-Genen kontrollieren, an PML-Körperchen führt. Vier der 8 bekannten MHC II-Transkriptionsfaktoren (CIITA, RFXap, RFXb und NFYa) binden an PML-Körperchen. Der MHC Klasse II-Transaktivator (CIITA), der Hauptregulator der MHC II-Gene, wird spezifisch durch die PML-Isoform II an PML-Körperchen rekrutiert. IFNγ verlängert die PML II-vermittelte Anbindung von CIITA an PML-Körperchen, die Verweildauer beträgt mehrere Minuten. Die Senkung der PML-Proteinmenge führt (1) zu einer Verringerung der Transkription einiger, aber nicht aller MHC II-Gene, (2) zur Inhibition der MHC II-Expression auf der Oberfläche von Fibroblasten und (3) zur verringerten IFNγ-induzierten Expression des CIITA. Diese Beobachtungen zeigen, dass PML(-Körperchen) eine Funktion als Koaktivator bei der IFNγ-induzierten MHC II-Expression ausübt. Der zugrundeliegende Mechanismus basiert vermutlich auf der Assoziation der PML-Körperchen mit dem MHC II-Genlokus und der Regulation der CIITA-Menge

Color-charge separation in trapped SU(3) fermionic atoms

Cold fermionic atoms with three different hyperfine states with SU(3) symmetry confined in one-dimensional optical lattices show color-charge separation, generalizing the conventional spin charge separation for interacting SU(2) fermions in one dimension. Through time-dependent DMRG simulations, we explore the features of this phenomenon for a generalized SU(3) Hubbard Hamiltonian. In our numerical simulations of finite size systems, we observe different velocities of the charge and color degrees of freedom when a Gaussian wave packet or a charge (color) density response to a local perturbation is evolved. The differences between attractive and repulsive interactions are explored and we note that neither a small anisotropy of the interaction, breaking the SU(3) symmetry, nor the filling impedes the basic observation of these effects

Staubabscheider in häuslichen Feuerungen

Sehr geehrte Damen und Herren, Biomasse, insbesondere Holz, ist im deutschen Wärmemarkt der mit großem Abstand wichtigste erneuerbare Energieträger. Insbesondere häusliche Holzfeuerungen erfreuen sich einer hohen Beliebtheit. Regionale Wertschöpfung und weitgehende CO2-Neutralität sind die positiven Seiten dieser Entwicklung. Dem gegenüber stehen, insbesondere bei Altanlagen, erhöhte Emissionen von Feinstaub und anderen gasförmigen Schadstoffen. Damit durch den zwingend notwendigen Ausbau der erneuerbaren Energien keine neuen Umweltbelastungen entstehen, wurden in den letzten Jahren die gesetzlichen Grenzwerte für die wichtigsten Schadstoffe stufenweise verringert. Viele moderne Feuerungen sind in der Lage, diese ohne weitere Maßnahmen einzuhalten. In einigen Marktsegmenten können jedoch Feinstaubabscheider eine interessante Möglichkeit darstellen, die geforderten Grenzwerte sicher einzuhalten. Darüber hinaus bieten sich Staubabscheider an, freiwillig einen größeren Beitrag zur Feinstaubemissionsreduktion zu leisten

DNA damage-induced translocation of S100A11 into the nucleus regulates cell proliferation

<p>Abstract</p> <p>Background</p> <p>Proteins are able to react in response to distinct stress stimuli by alteration of their subcellular distribution. The stress-responsive protein S100A11 belongs to the family of multifunctional S100 proteins which have been implicated in several key biological processes. Previously, we have shown that S100A11 is directly involved in DNA repair processes at damaged chromatin in the nucleus. To gain further insight into the underlying mechanism subcellular trafficking of S100A11 in response to DNA damage was analyzed.</p> <p>Results</p> <p>We show that DNA damage induces a nucleolin-mediated translocation of S100A11 from the cytoplasm into the nucleus. This translocation is impeded by inhibition of the phosphorylation activity of PKCα. Translocation of S100A11 into the nucleus correlates with an increased cellular p21 protein level. Depletion of nucleolin by siRNA severely impairs translocation of S100A11 into the nucleus resulting in a decreased p21 protein level. Additionally, cells lacking nucleolin showed a reduced colony forming capacity.</p> <p>Conclusions</p> <p>These observations suggest that regulation of the subcellular distribution of S100A11 plays an important role in the DNA damage response and p21-mediated cell cycle control.</p

Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite

We present a study on the kinetics of oxygen adsorption and desorption from single-wall carbon nanotube ͑SWNT͒ and highly oriented pyrolytic graphite ͑HOPG͒ samples. Thermal-desorption spectra for SWNT samples show a broad desorption feature peaked at 62 K, which is shifted to a significantly higher temperature than the low-coverage desorption feature on HOPG. The low-coverage O 2 binding energy on SWNT bundles ͑18.5 kJ/mol͒ is 55% higher than that for adsorption on HOPG ͑12.0 kJ/mol͒. In combination with molecular mechanics calculations we show that the observed binding energies for both systems can be attributed to van der Waals interactions, i.e., physisorption. The experiments provide no evidence for a more strongly bound chemisorbed species or for dissociative oxygen adsorption

Is spin-charge separation observable in a transport experiment?

We consider a one-dimensional chain consisting of an interacting area coupled to non-interacting leads. Within the area, interaction is mediated by a local on-site repulsion. Using real time evolution within the Density Matrix Renormalisation Group (DMRG) scheme, we study the dynamics of wave packets in this two-terminal transport setup. In contrast to previous works, where excitations were created by adding potentials to the Hamiltonian, we explicitly create left moving single particle excitations in the right lead as the starting condition. Our simulations show that such a transport setup allows for a clear detection of spin-charge separation using time-resolved spin-polarised density measurements.Comment: 5 pages, 4 figures. accepted by Europhysics Letter

Step-wise assembly, maturation and dynamic behavior of the human CENP-P/O/R/Q/U kinetochore sub-complex

Kinetochores are multi-protein megadalton assemblies that are required for attachment of microtubules to centromeres and, in turn, the segregation of chromosomes in mitosis. Kinetochore assembly is a cell cycle regulated multi-step process. The initial step occurs during interphase and involves loading of the 15-subunit constitutive centromere associated complex (CCAN), which contains a 5-subunit (CENP-P/O/R/Q/U) sub-complex. Here we show using a fluorescent three-hybrid (F3H) assay and fluorescence resonance energy transfer (FRET) in living mammalian cells that CENP-P/O/R/Q/U subunits exist in a tightly packed arrangement that involves multifold protein-protein interactions. This sub-complex is, however, not pre-assembled in the cytoplasm, but rather assembled on kinetochores through the step-wise recruitment of CENP-O/P heterodimers and the CENP-P, -O, -R, -Q and -U single protein units. SNAP-tag experiments and immuno-staining indicate that these loading events occur during S-phase in a manner similar to the nucleosome binding components of the CCAN, CENP-T/W/N. Furthermore, CENP-P/O/R/Q/U binding to the CCAN is largely mediated through interactions with the CENP-N binding protein CENP-L as well as CENP-K. Once assembled, CENP-P/O/R/Q/U exchanges slowly with the free nucleoplasmic pool indicating a low off-rate for individual CENP-P/O/R/Q/U subunits. Surprisingly, we then find that during late S-phase, following the kinetochore-binding step, both CENP-Q and -U but not -R undergo oligomerization. We propose that CENP-P/O/R/Q/U self-assembles on kinetochores with varying stoichiometry and undergoes a pre-mitotic maturation step that could be important for kinetochores switching into the correct conformation necessary for microtubule-attachment

Desorption kinetics and interaction of Xe with single-wall carbon nanotube bundles

We present a study on the kinetics of xenon desorption from single-wall carbon nanotube (SWNT) bundles using thermal desorption spectroscopy (TDS). TD-spectra from SWNT samples show a broad desorption feature peaked at significantly higher temperature than the corresponding low-coverage desorption feature on graphite. The observations are explained using a coupled desorption-diffusion (CDD) model, which allows the determination of the low-coverage Xe binding energy for adsorption on SWNT bundles, 27 kJ/mol. This energy is about 25% higher than the monolayer binding energy on graphite, 21.9 kJ/mol. By comparison with molecular mechanics calculations we find that this increase of the binding energy is consistent with adsorption in highly coordinated groove-sites on the external bundle surface.Comment: 8 pages, 5 figure