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Mass Growth (mass + growth)
Selected AbstractsBody size and food thresholds for zero growth in Dreissena polymorpha: a mechanism underlying intraspecific competitionFRESHWATER BIOLOGY, Issue 12 2008ALEXANDER WACKER Summary 1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low-food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size-related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C0) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C0 = 0.08 mg C L,1) is substantially lower than that for adults (C0 = 0.36 mg C L,1). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature. [source] Supermassive black hole mass functions at intermediate redshifts from spheroid and AGN luminosity functionsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Naoyuki Tamura ABSTRACT Redshift evolution of supermassive black hole mass functions (BHMFs) is investigated up to z, 1. BHMFs at intermediate redshifts are calculated in two ways. One way is from early-type galaxy luminosity functions (LFs); we assume an MBH,Lsph correlation at a redshift by considering a passive evolution of Lsph in the local relationship. The resultant BHMFs (spheroid-BHMFs) from LFs of red-sequence galaxies indicate a slight decrease of number density with increasing redshift at MBH, 107.5,8 M,. Since a redshift evolution in slope and zeropoint of the MBH,Lsph relation is unlikely to be capable of making such an evolution in BHMF, the evolution of the spheroid-BHMFs is perhaps due mainly to the decreasing normalization in the galaxy LFs. We also derive BHMFs from LFs of morphologically selected early-type galaxies. The resultant BHMFs are similar to those from the red-sequence galaxies, but show a small discrepancy at z, 1 corresponding to an increase of supermassive black hole (SMBH) number density by ,0.3 dex. We also investigate how spheroid-BHMFs are affected by uncertainties existing in the derivation in detail. The other way of deriving a BHMF is based on the continuity equation for number density of SMBHs and LFs of active galactic nucleus (AGN). The resultant BHMFs (AGN-BHMFs) show no clear evolution out to z= 1 at MBH, 108 M,, but exhibit a significant decrease with redshift in the lower mass range. Interestingly, these AGN-BHMFs are quite different in the range of MBH, 108 M, from those derived by Merloni (2004), where the fundamental plane of black hole activity is exploited. Comparison of the spheroid-BHMFs with the AGN-BHMFs suggests that at MBH, 108 M,, the spheroid-BHMFs are broadly consistent with the AGN-BHMFs out to z, 1. Although the decrease of SMBH number density with redshift suggested by the spheroid-BHMFs is slightly faster than that suggested by the AGN-BHMFs, we presume this to be due at least partly to a selection effect on the LFs of red-sequence galaxies; the colour selection could miss spheroids with blue colours. The agreement between the spheroid-BHMFs and the AGN-BHMFs appears to support that most of the SMBHs are already hosted by massive spheroids at z, 1 and they evolve without significant mass growth since then. [source] Forming supermassive black holes by accreting dark and baryon matterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Jian Hu ABSTRACT Given a large-scale mixture of self-interacting dark matter (SIDM) particles and baryon matter distributed in the early Universe, we advance here a two-phase accretion scenario for forming supermassive black holes (SMBHs) with masses around ,109 M, at high redshifts z(,6). The first phase is conceived to involve a rapid quasi-spherical and quasi-steady Bondi accretion of mainly SIDM particles embedded with baryon matter on to seed black holes (BHs) created at redshifts z, 30 by the first generation of massive Population III stars; this earlier phase rapidly gives birth to significantly enlarged seed BH masses of during z, 20,15, where ,0 is the cross-section per unit mass of SIDM particles and Cs is the velocity dispersion in the SIDM halo referred to as an effective ,sound speed'. The second phase of BH mass growth is envisaged to proceed primarily via baryon accretion, eventually leading to SMBH masses of MBH, 109 M,; such SMBHs may form either by z, 6 for a sustained accretion at the Eddington limit or later at lower z for sub-Eddington mean accretion rates. In between these two phases, there is a transitional yet sustained diffusively limited accretion of SIDM particles which in an eventual steady state would be much lower than the accretion rates of the two main phases. We intend to account for the reported detections of a few SMBHs at early epochs, e.g. Sloan Digital Sky Survey (SDSS) 1148+5251 and so forth, without necessarily resorting to either super-Eddington baryon accretion or very frequent BH merging processes. Only extremely massive dark SIDM haloes associated with rare peaks of density fluctuations in the early Universe may harbour such early SMBHs or quasars. Observational consequences are discussed. During the final stage of accumulating a SMBH mass, violent feedback in circumnuclear environs of a galactic nucleus leads to the central bulge formation and gives rise to the familiar empirical MBH,,b correlation inferred for nearby normal galaxies with ,b being the stellar velocity dispersion in the galactic bulge; in our scenario, the central SMBH formation precedes that of the galactic bulge. [source] The build-up of haloes within Press,Schechter theoryMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001Will J. Percival Modelling the build-up of haloes is important for linking the formation of galaxies with cosmological models. A simple model of halo growth is provided by Press,Schechter (PS) theory, where the initial field of density fluctuations is smoothed using spherically symmetric filters centred on a given position to obtain information about the likelihood of later collapse on varying scales. In this paper the predicted halo mass growth is compared for three filter shapes: Gaussian, top-hat and sharp k -space. Preliminary work is also presented analysing the build-up of haloes within numerical simulations using a friends-of-friends group finder. The best-fit to the simulation mass function was obtained using PS theory with a top-hat filter. By comparing both the backwards conditional mass function, which gives the distribution of halo progenitors, and the distribution of halo mergers in time, the build-up of haloes in the simulations is shown to be better fitted by PS theory with a sharp k -space filter. This strengthens previous work, which also found the build-up of haloes in simulations to be well matched to PS theory with a sharp k -space filter by providing a direct comparison of different filters and by extending the statistical tools used to analyse halo mass growth. The usefulness of this work is illustrated by showing that the cosmological evolution in the proportion of haloes that have undergone recent merger is predicted to be independent of mass and power spectrum and to only depend upon cosmology. Recent results from observations of field galaxies are shown to match the evolution expected, but are not sufficiently accurate to distinguish usefully between cosmological parameters. [source] Effects of water and nutrient availability on fine root growth in eastern Amazonian forest regrowth, BrazilNEW PHYTOLOGIST, Issue 3 2010Tâmara Thaiz Santana Lima Summary ,Fine root dynamics is widely recognized as an important biogeochemical process, but there are few data on fine root growth and its response to soil resource availability, especially for tropical forests. ,We evaluated the response of fine root dynamics to altered availability of soil water and nutrients in a 20-yr-old forest regrowth in eastern Amazonia. In one experiment the dry season reduction in soil moisture was alleviated by irrigation. In the other experiment, nutrient supply was reduced by litter removal. We used the ingrowth core technique to measure fine root mass growth, length growth, mortality and specific root length. ,Dry-season irrigation had no significant effect on mass and length of live and dead roots, whereas litter removal reduced mass and length of live roots. For both irrigation and litter removal experiments, root growth was significantly greater in the dry season than in the wet season. ,Increased root growth was associated with decreased soil water availability. However, root growth did not increase in response to nutrient reduction in litter removal plots. Overall, our results suggest that belowground allocation may differ according to the type of soil resource limitation. [source] | ||||||||||