Cryogenic zero-gravity prototype vent system

Design, fabrication, and tests of prototype cryogenic zero-gravity heat exchanger vent syste

Gated rotation mechanism of site-specific recombination by ϕC31 integrase

Integrases, such as that of the Streptomyces temperate bacteriophage ϕC31, promote site-specific recombination between DNA sequences in the bacteriophage and bacterial genomes to integrate or excise the phage DNA. ϕC31 integrase belongs to the serine recombinase family, a large group of structurally related enzymes with diverse biological functions. It has been proposed that serine integrases use a “subunit rotation” mechanism to exchange DNA strands after double-strand DNA cleavage at the two recombining att sites, and that many rounds of subunit rotation can occur before the strands are religated. We have analyzed the mechanism of ϕC31 integrase-mediated recombination in a topologically constrained experimental system using hybrid “phes” recombination sites, each of which comprises a ϕC31 att site positioned adjacent to a regulatory sequence recognized by Tn3 resolvase. The topologies of reaction products from circular substrates containing two phes sites support a right-handed subunit rotation mechanism for catalysis of both integrative and excisive recombination. Strand exchange usually terminates after a single round of 180° rotation. However, multiple processive “360° rotation” rounds of strand exchange can be observed, if the recombining sites have nonidentical base pairs at their centers. We propose that a regulatory “gating” mechanism normally blocks multiple rounds of strand exchange and triggers product release after a single round

CARMIL family proteins as multidomain regulators of actin-based motility

CARMILs are large multidomain proteins that regulate the actin-binding activity of capping protein (CP), a major capper of actin filament barbed ends in cells. CARMILs bind directly to CP and induce a conformational change that allosterically decreases but does not abolish its actin-capping activity. The CP-binding domain of CARMIL consists of the CP-interaction (CPI) and CARMIL-specific interaction (CSI) motifs, which are arranged in tandem. Many cellular functions of CARMILs require the interaction with CP; however, a more surprising result is that the cellular function of CP in cells appears to require binding to a CARMIL or another protein with a CPI motif, suggesting that CPI-motif proteins target CP and modulate its actin-capping activity. Vertebrates have three highly conserved genes and expressed isoforms of CARMIL with distinct and overlapping localizations and functions in cells. Various domains of these CARMIL isoforms interact with plasma membranes, vimentin intermediate filaments, SH3-containing class I myosins, the dual-GEF Trio, and other adaptors and signaling molecules. These biochemical properties suggest that CARMILs play a variety of membrane-associated functions related to actin assembly and signaling. CARMIL mutations and variants have been implicated in several human diseases. We focus on roles for CARMILs in signaling in addition to their function as regulators of CP and actin. </jats:p

Differences between the Two Anomalous X-Ray Pulsars: Variations in the Spin Down Rate of 1E 1048.1-5937 and An Extended Interval of Quiet Spin Down in 1E 2259+586

We analysed the RXTE archival data of 1E 1048.1-5937 covering a time span of more than one year. The spin down rate of this source decreases by 30 percent during the observation. We could not resolve the X-ray flux variations because of contamination by Eta Carinae. We find that the level of pulse frequency fluctuations of 1E 1048.1-5937 is consistent with typical noise levels of accretion powered pulsars. Recent RXTE observations of 1E 2259+586 have shown a constant spin down with a very low upper limit on timing noise. We used the RXTE archival X-ray observations of 1E 2259+586 to show that the intrinsic X-ray luminosity times series is also stable, with an rms fractional variation of less than 15 percent. The source could have been in a quiet phase of accretion with a constant X-ray luminosity and spin down rate.Comment: MNRAS in pres

Towards electron transport measurements in chemically modified graphene: The effect of a solvent

Chemical functionalization of graphene modifies the local electron density of the carbon atoms and hence electron transport. Measuring these changes allows for a closer understanding of the chemical interaction and the influence of functionalization on the graphene lattice. However, not only chemistry, in this case diazonium chemistry, has an effect on the electron transport. Latter is also influenced by defects and dopants resulting from different processing steps. Here, we show that solvents used in the chemical reaction process change the transport properties. In more detail, the investigated combination of isopropanol and heating treatment reduces the doping concentration and significantly increases the mobility of graphene. Furthermore, the isopropanol treatment alone increases the concentration of dopants and introduces an asymmetry between electron and hole transport which might be difficult to distinguish from the effect of functionalization. The results shown in this work demand a closer look on the influence of solvents used for chemical modification in order to understand their influence

A CS J = 2 1 survey of the galactic center region

A CS map of the galactic center region is presented consisting of 15,000 spectra covering -1 deg. less than 3. deg. 6 min., -0 deg.4 min. less than b less than 0 deg. 4 min., each having an rms noise of 0.15 K in 1 MHz filters. CS is a high-excitation molecule, meaning that it is excited into emission only when the ambient density is less than n much greater than or approx. 2 x 10 to the 4th power/cu cm CS emission in the inner 2 deg. of the galaxy is nearly as pervasive as CO emission, in stark contrast to the outer galaxy where CS emission is confined to cloud cores. Galactic center clouds are on average much more dense than outer Galaxy clouds. This can be understood as a necessary consequence of the strong tidal stresses in the inner galaxy