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  • 1
    Electronic Resource
    Electronic Resource
    Separation and analysis of pig pancreatic zymogen granules with free flow electrophoresis and lectins (1994)
    Weinheim : Wiley-Blackwell
    Electrophoresis 15 (1994), S. 572-576 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Purified pig pancreatic zymogen granules were subjected to free flow electrophoresis (FFE) in an acetate buffer system (acetic acid/NaOH, pH 5.5) to detect the presence or absence of more than one population or zymogen granules. Pig pancreatic zymogen granules were purified by differential and density gradient centrifugation and subjected to FFE. Fractions were analyzed for protein, α-amylase (EC 3.2.1.1) and 5′-nucleotidase (EC 3.1.3.5) as marker enzymes for zymogen granule content and membranes, respectively. Only one distinct peak, with coincident α-amylase and 5′-nucleotidase activity, and most protein was detected, which reflects the presence of a single population of intact zymogen granules. This was confirmed by electron microscopy. When the granules were incubated with different lectins before FFE, the one distinct peak representing intact zymogen granules was shifted towards the cathode in the case of concanavalin A (Con A) and Ricinus communis agglutinin 120 (RCA 120). No splitting of the peak occurred. Our results do not support the hypothesis of a coexistence of more than one distinct population of zymogen granules.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150150178
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    Paper (German National Licenses)
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  • 2
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    The JCMT Plane Survey: early results from the {ell} = 30{degrees} field (2015)
    Moore, T. J. T., Plume, R., Thompson, M. A., Parsons, H., Urquhart, J. S., Eden, D. J., Dempsey, J. T., Morgan, L. K., Thomas, H. S., Buckle, J., Brunt, C. M., Butner, H., Carretero, D., Chrysostomou, A., de; Villiers, H. M., Fich, M., Hoare, M. G., Manser, G., Mottram, J. C., Natario, C., Olguin, F., Peretto, N., Polychroni, D., Redman, R. O., Rigby, A. J., Salji, C., Summers, L. J., Berry, D., Currie, M. J., Jenness, T., Pestalozzi, M., Traficante, A., Bastien, P., di; Francesco, J., Davis, C. J., Evans, A., Friberg, P., Fuller, G. A., Gibb, A. G., Gibson, S., Hill, T., Johnstone, D., Joncas, G., Longmore, S. N., Lumsden, S. L., Martin, P. G., Lu'o'ng, Q. N. t., Pineda, J. E., Purcell, C., Richer, J. S., Schieven, G. H., Shipman, R., Spaans, M., Taylor, A. R., Viti, S., Weferling, B., White, G. J., Zhu, M.
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: We present early results from the JCMT (James Clerk Maxwell Telescope) Plane Survey (JPS), which has surveyed the northern inner Galactic plane between longitudes  = 7° and  = 63° in the 850-μm continuum with SCUBA-2 (Submm Common-User Bolometer Array 2), as part of the JCMT Legacy Survey programme. Data from the  = 30° survey region, which contains the massive-star-forming regions W43 and G29.96, are analysed after approximately 40 per cent of the observations had been completed. The pixel-to-pixel noise is found to be 19 mJy beam –1 after a smooth over the beam area, and the projected equivalent noise levels in the final survey are expected to be around 10 mJy beam –1 . An initial extraction of compact sources was performed using the FellWalker method, resulting in the detection of 1029 sources above a 5 surface-brightness threshold. The completeness limits in these data are estimated to be around 0.2 Jy beam –1 (peak flux density) and 0.8 Jy (integrated flux density) and are therefore probably already dominated by source confusion in this relatively crowded section of the survey. The flux densities of extracted compact sources are consistent with those of matching detections in the shallower APEX (Atacama Pathfinder Experiment) Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. We analyse the virial and evolutionary state of the detected clumps in the W43 star-forming complex and find that they appear younger than the Galactic-plane average.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    How chemistry influences cloud structure, star formation, and the IMF (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-02
    Description: In the earliest phases of star-forming clouds, stable molecular species, such as CO, are important coolants in the gas phase. Depletion of these molecules on dust surfaces affects the thermal balance of molecular clouds and with that their whole evolution. For the first time, we study the effect of grain surface chemistry (GSC) on star formation and its impact on the initial mass function (IMF). We follow a contracting translucent cloud in which we treat the gas–grain chemical interplay in detail, including the process of freeze-out. We perform 3D hydrodynamical simulations under three different conditions, a pure gas-phase model, a freeze-out model, and a complete chemistry model. The models display different thermal evolution during cloud collapse as also indicated in Hocuk, Cazaux & Spaans, but to a lesser degree because of a different dust temperature treatment, which is more accurate for cloud cores. The equation of state (EOS) of the gas becomes softer with CO freeze-out and the results show that at the onset of star formation, the cloud retains its evolution history such that the number of formed stars differ (by 7 per cent) between the three models. While the stellar mass distribution results in a different IMF when we consider pure freeze-out, with the complete treatment of the GSC, the divergence from a pure gas-phase model is minimal. We find that the impact of freeze-out is balanced by the non-thermal processes; chemical and photodesorption. We also find an average filament width of 0.12 pc (±0.03 pc), and speculate that this may be a result from the changes in the EOS caused by the gas-dust thermal coupling. We conclude that GSC plays a big role in the chemical composition of molecular clouds and that surface processes are needed to accurately interpret observations, however, that GSC does not have a significant impact as far as star formation and the IMF is concerned.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    The average submillimetre properties of Lyman {alpha} blobs at z = 3 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-26
    Description: Ly α blobs (LABs) offer insight into the complex interface between galaxies and their circumgalactic medium. Whilst some LABs have been found to contain luminous star-forming galaxies and active galactic nuclei that could potentially power the Ly α emission, others appear not to be associated with obvious luminous galaxy counterparts. It has been speculated that LABs may be powered by cold gas streaming on to a central galaxy, providing an opportunity to directly observe the ‘cold accretion’ mode of galaxy growth. Star-forming galaxies in LABs could be dust obscured and therefore detectable only at longer wavelengths. We stack deep Submillimetre Common User Bolometer Array 2 (SCUBA-2) observations of the Small Selected Area 22 h field to determine the average 850 μm flux density of 34 LABs. We measure S 850 = 0.6 ± 0.2 mJy for all LABs, but stacking the LABs by size indicates that only the largest third (area ≥1794 kpc 2 ) have a mean detection, at 4.5, with S 850 = 1.4 ± 0.3 mJy. Only two LABs (1 and 18) have individual SCUBA-2 〉3.5 detections at a depth of 1.1 mJy beam –1 . We consider two possible mechanisms for powering the LABs and find that central star formation is likely to dominate the emission of Ly α, with cold accretion playing a secondary role.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Sub-mm emission line deep fields: CO and [C II] luminosity functions out to z = 6 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-30
    Description: Now that Atacama Large (Sub)Millimeter Array is reaching its full capabilities, observations of sub-mm emission line deep fields become feasible. We couple a semi-analytic model of galaxy formation with a radiative transfer code to make predictions for the luminosity function of CO J =1–0 out to CO J = 6–5 and [C ii ] at redshifts z = 0–6. We find that (1) our model correctly reproduces the CO and [C ii ] emission of low- and high-redshift galaxies and reproduces the available constraints on the CO luminosity function at z ≤ 2.75; (2) we find that the CO and [C ii ] luminosity functions of galaxies increase from z = 6 to z = 4, remain relatively constant till z = 1 and rapidly decrease towards z = 0. The galaxies that are brightest in CO and [C ii ] are found at z ~ 2; (3) the CO J = 3–2 emission line is most favourable to study the CO luminosity and global H 2 mass content of galaxies, because of its brightness and observability with currently available sub-mm and radio instruments; (4) the luminosity functions of high-J CO lines show stronger evolution than the luminosity functions of low-J CO lines; (5) our model barely reproduces the available constraints on the CO and [C ii ] luminosity function of galaxies at z ≥ 1.5 and the CO luminosity of individual galaxies at intermediate redshifts. We argue that this is driven by a lack of cold gas in galaxies at intermediate redshifts as predicted by cosmological simulations of galaxy formation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The JCMT Plane Survey: early results from the {ell} = 30{degrees} field (2015)
    Moore, T. J. T., Plume, R., Thompson, M. A., Parsons, H., Urquhart, J. S., Eden, D. J., Dempsey, J. T., Morgan, L. K., Thomas, H. S., Buckle, J., Brunt, C. M., Butner, H., Carretero, D., Chrysostomou, A., de; Villiers, H. M., Fich, M., Hoare, M. G., Manser, G., Mottram, J. C., Natario, C., Olguin, F., Peretto, N., Polychroni, D., Redman, R. O., Rigby, A. J., Salji, C., Summers, L. J., Berry, D., Currie, M. J., Jenness, T., Pestalozzi, M., Traficante, A., Bastien, P., di; Francesco, J., Davis, C. J., Evans, A., Friberg, P., Fuller, G. A., Gibb, A. G., Gibson, S., Hill, T., Johnstone, D., Joncas, G., Longmore, S. N., Lumsden, S. L., Martin, P. G., Lu'o'ng, Q. N. t., Pineda, J. E., Purcell, C., Richer, J. S., Schieven, G. H., Shipman, R., Spaans, M., Taylor, A. R., Viti, S., Weferling, B., White, G. J., Zhu, M.
    Oxford University Press
    Details
    Publication Date: 2015-09-19
    Description: We present early results from the JCMT (James Clerk Maxwell Telescope) Plane Survey (JPS), which has surveyed the northern inner Galactic plane between longitudes  = 7° and  = 63° in the 850-μm continuum with SCUBA-2 (Submm Common-User Bolometer Array 2), as part of the JCMT Legacy Survey programme. Data from the  = 30° survey region, which contains the massive-star-forming regions W43 and G29.96, are analysed after approximately 40 per cent of the observations had been completed. The pixel-to-pixel noise is found to be 19 mJy beam –1 after a smooth over the beam area, and the projected equivalent noise levels in the final survey are expected to be around 10 mJy beam –1 . An initial extraction of compact sources was performed using the FellWalker method, resulting in the detection of 1029 sources above a 5 surface-brightness threshold. The completeness limits in these data are estimated to be around 0.2 Jy beam –1 (peak flux density) and 0.8 Jy (integrated flux density) and are therefore probably already dominated by source confusion in this relatively crowded section of the survey. The flux densities of extracted compact sources are consistent with those of matching detections in the shallower APEX (Atacama Pathfinder Experiment) Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. We analyse the virial and evolutionary state of the detected clumps in the W43 star-forming complex and find that they appear younger than the Galactic-plane average.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The impact of freeze-out on collapsing molecular clouds (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-18
    Description: Atoms and molecules, and in particular CO, are important coolants during the evolution of interstellar star-forming gas clouds. The presence of dust grains, which allow many chemical reactions to occur on their surfaces, strongly impacts the chemical composition of a cloud. At low temperatures, dust grains can lock up species from the gas phase which freeze out and form ices. In this sense, dust can deplete important coolants. Our aim is to understand the effects of freeze-out on the thermal balance and the evolution of a gravitationally bound molecular cloud. For this purpose, we perform 3D hydrodynamical simulations with the adaptive mesh code flash . We simulate a gravitationally unstable cloud under two different conditions, with and without grain surface chemistry. We let the cloud evolve until one free-fall time is reached and track the thermal evolution and the abundances of species during this time. We see that at a number density of 10 4  cm –3 most of the CO molecules are frozen on dust grains in the run with grain surface chemistry, thereby depriving the most important coolant. As a consequence, we find that the temperature of the gas rises up to ~25 K. The temperature drops once again due to gas–grain collisional cooling when the density reaches a few 10 4  cm –3 . We conclude that grain surface chemistry not only affects the chemical abundances in the gas phase, but also leaves a distinct imprint in the thermal evolution that impacts the fragmentation of a star-forming cloud. As a final step, we present the equation of state of a collapsing molecular cloud that has grain surface chemistry included.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Multimolecular studies of Galactic star-forming regions (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-31
    Description: Molecular emission-line observations of isolated Galactic star-forming regions are used to model the physical properties of the molecular interstellar medium in these systems. Observed line ratios are compared with the results predicted by models that incorporate gas-phase chemistry and the heating by stellar radiation and non-radiative feedback processes. The line ratios of characteristic tracer molecules may be interpreted using the contributions of two distinct components: a cold (40–50 K) and high-density (10 5 –10 5.5  cm –3 ) photon-dominated region (PDR) with a nominal UV flux density and a warm (~300 K) mechanical heating-dominated region (MHDR) with a slightly lower density (10 4.5 –10 5  cm –3 ). The relative contributions of these structural components are used to model the observed line ratios. Ionized species may be better modelled by adopting an increase of the cosmic ray flux towards the Galactic Centre and the sulphur abundance should depleted by a factor of 200–400 relative to solar values. The line ratios of the Galactic sample are found to be very similar to those of the integrated signature of prominent (ultra)luminous IR Galaxies. The PDRs and MHDRs in the isolated Galactic regions may be modelled with slightly higher mean densities than in extragalactic systems and a higher MHDR temperature resulting from non-radiative mechanical heating. Multimolecular studies are effective in determining the physical and chemical properties of star formation regions by using characteristic line ratios to diagnose their environment. The addition of more molecular species will reduce the existing modelling redundancy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The nature of the ISM in galaxies during the star-formation activity peak of the Universe (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-30
    Description: We combine a semi-analytic model of galaxy formation, tracking atomic and molecular phases of cold gas, with a three-dimensional radiative-transfer and line tracing code to study the sub-mm emission from atomic and molecular species (CO, HCN, [C i ], [C ii ], [O i ]) in galaxies. We compare the physics that drives the formation of stars at the epoch of peak star formation (SF) in the Universe ( z  = 2.0) with that in local galaxies. We find that normal star-forming galaxies at high redshift have much higher CO-excitation peaks than their local counterparts and that CO cooling takes place at higher excitation levels. CO line ratios increase with redshift as a function of galaxy star-formation rate, but are well correlated with H 2 surface density independent of redshift. We find an increase in the [O i ]/[C ii ] line ratio in typical star-forming galaxies at z  = 1.2 and z  = 2.0 with respect to counterparts at z  = 0. Our model results suggest that typical star-forming galaxies at high redshift consist of much denser and warmer star-forming clouds than their local counterparts. Galaxies belonging to the tail of the SF activity peak at z  = 1.2 are already less dense and cooler than counterparts during the actual peak of SF activity ( z  = 2.0). We use our results to discuss how future ALMA surveys can best confront our predictions and constrain models of galaxy formation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    How realistic UV spectra and X-rays suppress the abundance of direct collapse black holes (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-07
    Description: Observations of high-redshift quasars at z  〉 6 indicate that they harbour supermassive black holes (SMBHs) of a billion solar masses. The direct collapse scenario has emerged as the most plausible way to assemble SMBHs. The nurseries for the direct collapse black holes are massive primordial haloes illuminated with an intense UV flux emitted by Population II (Pop II) stars. In this study, we compute the critical value of such a flux ( $J_{21}^{\rm crit}$ ) for realistic spectra of Pop II stars through three-dimensional cosmological simulations. We derive the dependence of $J_{21}^{\rm crit}$ on the radiation spectra, on variations from halo to halo, and on the impact of X-ray ionization. Our findings show that the value of $J_{21}^{\rm crit}$ is a few times 10 4 and only weakly depends on the adopted radiation spectra in the range between T rad  = 2 x 10 4 and10 5  K. For three simulated haloes of a few times 10 7 M , $J_{21}^{\rm crit}$ varies from 2 x 10 4 to 5 x 10 4 . The impact of X-ray ionization is almost negligible and within the expected scatter of $J_{21}^{\rm crit}$ for background fluxes of J X, 21 ≤ 0.1. The computed estimates of $J_{21}^{\rm crit}$ have profound implications for the quasar abundance at z  = 10 as it lowers the number density of black holes forming through an isothermal direct collapse by a few orders of magnitude below the observed black hole density. However, the sites with moderate amounts of H 2 cooling may still form massive objects sufficient to be compatible with observations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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