38 research outputs found
Modeling the cosmological co-evolution of supermassive black holes and galaxies: I. BH scaling relations and the AGN luminosity function
We model the cosmological co-evolution of galaxies and their central
supermassive black holes (BHs) within a semi-analytical framework developed on
the outputs of the Millennium Simulation. This model, described in detail in
Croton et al. (2006) and De Lucia & Blaizot (2007), introduces a `radio mode'
feedback from Active Galactic Nuclei (AGN) at the centre of X-ray emitting
atmospheres in galaxy groups and clusters. Thanks to this mechanism, the model
can simultaneously explain: (i) the low observed mass drop-out rate in cooling
flows; (ii) the exponential cut-off in the bright end of the galaxy luminosity
function; and (iii) the bulge-dominated morphologies and old stellar ages of
the most massive galaxies in clusters. This paper is the first of a series in
which we investigate how well this model can also reproduce the physical
properties of BHs and AGN. Here we analyze the scaling relations, the
fundamental plane and the mass function of BHs, and compare them with the most
recent observational data. Moreover, we extend the semi-analytic model to
follow the evolution of the BH mass accretion and its conversion into
radiation, and compare the derived AGN bolometric luminosity function with the
observed one. While we find for the most part a very good agreement between
predicted and observed BH properties, the semi-analytic model underestimates
the number density of luminous AGN at high redshifts, independently of the
adopted Eddington factor and accretion efficiency. However, an agreement with
the observations is possible within the framework of our model, provided it is
assumed that the cold gas fraction accreted by BHs at high redshifts is larger
than at low redshifts.Comment: 15 pages, 7 figures, MNRAS submitte
A Complete Analysis of HA and NA Genes of Influenza A Viruses
BACKGROUND: More and more nucleotide sequences of type A influenza virus are available in public databases. Although these sequences have been the focus of many molecular epidemiological and phylogenetic analyses, most studies only deal with a few representative sequences. In this paper, we present a complete analysis of all Haemagglutinin (HA) and Neuraminidase (NA) gene sequences available to allow large scale analyses of the evolution and epidemiology of type A influenza. METHODOLOGY/PRINCIPAL FINDINGS: This paper describes an analysis and complete classification of all HA and NA gene sequences available in public databases using multivariate and phylogenetic methods. CONCLUSIONS/SIGNIFICANCE: We analyzed 18,975 HA sequences and divided them into 280 subgroups according to multivariate and phylogenetic analyses. Similarly, we divided 11,362 NA sequences into 202 subgroups. Compared to previous analyses, this work is more detailed and comprehensive, especially for the bigger datasets. Therefore, it can be used to show the full and complex phylogenetic diversity and provides a framework for studying the molecular evolution and epidemiology of type A influenza virus. For more than 85% of type A influenza HA and NA sequences into GenBank, they are categorized in one unambiguous and unique group. Therefore, our results are a kind of genetic and phylogenetic annotation for influenza HA and NA sequences. In addition, sequences of swine influenza viruses come from 56 HA and 45 NA subgroups. Most of these subgroups also include viruses from other hosts indicating cross species transmission of the viruses between pigs and other hosts. Furthermore, the phylogenetic diversity of swine influenza viruses from Eurasia is greater than that of North American strains and both of them are becoming more diverse. Apart from viruses from human, pigs, birds and horses, viruses from other species show very low phylogenetic diversity. This might indicate that viruses have not become established in these species. Based on current evidence, there is no simple pattern of inter-hemisphere transmission of avian influenza viruses and it appears to happen sporadically. However, for H6 subtype avian influenza viruses, such transmissions might have happened very frequently and multiple and bidirectional transmission events might exist
A communal catalogue reveals Earth's multiscale microbial diversity
Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe
A communal catalogue reveals Earthâs multiscale microbial diversity
Our growing awareness of the microbial worldâs importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earthâs microbial diversity
Selective Chemical Modification of Graphene Surfaces: Distinction Between Single- and Bilayer Graphene
Large-Scale Synthesis of PbSâTiO<sub>2</sub> Heterojunction Nanoparticles in a Single Step for Solar Cell Application
The demand for low cost solar energy technology calls
for manufacturing processes using economic liquid- or gas-phase synthesis
of the corresponding materials. In this regard, manufacturing of quantum
dot-sensitized solar cells is particularly complicated through multiple-step
preparations. Material pairs such as TiO<sub>2</sub>âPbS heterojunctions
have shown high absorption of visible light and good electron transfer
properties. However, traditional solution processing requires extensive
surface functionalization or the use of surfactants to obtain well-defined
films. Such surfactants, unfortunately, often lower electron hopping/tunneling
in the system (surfactants are usually insulators) and therefore have
to be removed or exchanged before completing device fabrication. Similarly,
the so far presented processes to deposit PbS directly on TiO<sub>2</sub> are very time consuming. In this paper, we present a single-step,
large-scale, operable process to synthesize PbSâTiO<sub>2</sub> heterojunction particles by aerosol synthesis using reducing flame
spray pyrolysis. Nanopowders with different lead sulfide to titanium
dioxide ratios were produced and characterized. Thermodynamic equilibrium
calculations of the gaseous environment during the combustion process
show that the process is robust with regard to usual process changes
or fluctuations. We further showed how this approach allowed us to
vary the structure and size of the PbSâTiO<sub>2</sub> heterojunction
particles, as long as an excess of sulfur species (S/Pb = 2.5) was
applied during processing
Adsorption and Orientation of the Physiological Extracellular Peptide Glutathione Disulfide on Surface Functionalized Colloidal Alumina Particles
Understanding the
interrelation between surface chemistry of colloidal
particles and surface adsorption of biomolecules is a crucial prerequisite
for the design of materials for biotechnological and nanomedical applications.
Here, we elucidate how tailoring the surface chemistry of colloidal
alumina particles (<i>d</i><sub>50</sub> = 180 nm) with
amino (âNH<sub>2</sub>), carboxylate (âCOOH), phosphate
(âPO<sub>3</sub>H<sub>2</sub>) or sulfonate (âSO<sub>3</sub>H) groups affects adsorption and orientation of the model
peptide glutathione disulfide (GSSG). GSSG adsorbed on native, âNH<sub>2</sub>-functionalized, and âSO<sub>3</sub>H-functionalized
alumina but not on âCOOH- and âPO<sub>3</sub>H<sub>2</sub>-functionalized particles. When adsorption occurred, the process
was rapid (â€5 min), reversible by application of salts, and
followed a Langmuir adsorption isotherm dependent on the particle
surface functionalization and ζ potential. The orientation of
particle bound GSSG was assessed by the release of glutathione after
reducing the GSSG disulfide bond and by ζ potential measurements.
GSSG is likely to bind via the carboxylate groups of one of its two
glutathionyl (GS) moieties onto native and âNH<sub>2</sub>-modified
alumina, whereas GSSG is suggested to bind to âSO<sub>3</sub>H-modified alumina via the primary amino groups of both GS moieties.
Thus, GSSG adsorption and orientation can be tailored by varying the
molecular composition of the particle surface, demonstrating a step
toward guiding interactions of biomolecules with colloidal particles
Construction of a viral T2A-peptide based knock-in mouse model for enhanced Cre recombinase activity and fluorescent labeling of podocytes
Podocyte injury is a key event in glomerular disease leading to proteinuria and opening the path toward glomerular scarring. As a consequence, glomerular research strives to discover molecular mechanisms and signaling pathways affecting podocyte health. The hNphs2.Cre mouse model has been a valuable tool to manipulate podocyte-specific genes and to label podocytes for lineage tracing and purification. Here we designed a novel podocyte-specific tricistronic Cre mouse model combining codon improved Cre expression and fluorescent cell labeling with mTomato under the control of the endogenous Nphs2 promoter using viral T2A-peptides. Independent expression of endogenous podocin, codon improved Cre, and mTomato was confirmed by immunofluorescence, fluorescent activated cell sorting Nphs2(pod.T2A.ciCre.T2A.mTomato/wild-type) and protein analyses. Nphs2 mice developed normally and did not show any signs of glomerular disease or off-target effects under. basal conditions and in states of disease. Nphs2(pod.T2A.ciCre.T2A.mTomato/wild-type)-mediated gene recombination was superior to conventional hNphs2.Cre mice-mediated gene recombination. Last, we compared Cre efficiency in a disease model by mating Nphs2(pod.T2A.ciCre.T2A.mTomato/wild-type) and hNphs2.Cre mice to Phb2(fl/fl) mice. The podocyte-specific Phb2 knockout by Nphs2(pod.T2A.ciCre.T2A.mTomato/wild-type) mice resulted in an aggravated glomerular injury as compared to a podocyte-specific Phb2 gene deletion triggered by hNphs2.Cre. Thus, we generated the first tricistronic podocyte mouse model combining enhanced Cre recombinase efficiency and fluorescent labeling in podocytes without the need for additional matings with conventional reporter mouse lines
Electrical Resistivity of Assembled Transparent Inorganic Oxide Nanoparticle Thin Layers: Influence of Silica, Insulating Impurities, and Surfactant Layer Thickness
The electrical properties of transparent, conductive
layers prepared
from nanoparticle dispersions of doped oxides are highly sensitive
to impurities. Production of cost-effective thin conducting films
for consumer electronics often employs wet processing such as spin
and/or dip coating of surfactant-stabilized nanoparticle dispersions.
This inherently results in entrainment of organic and inorganic impurities
into the conducting layer leading to largely varying electrical conductivity.
Therefore, this study provides a systematic investigation on the effect
of insulating surfactants, small organic molecules and silica in terms
of pressure dependent electrical resistivity as a result of different
core/shell structures (layer thickness). Application of high temperature
flame synthesis gives access to antimony-doped tin oxide (ATO) nanoparticles
with high purity. This well-defined starting material was then subjected
to representative film preparation processes using organic additives.
In addition ATO nanoparticles were prepared with a homogeneous inorganic
silica layer (silica layer thickness from 0.7 to 2 nm). Testing both
organic and inorganic shell materials for the electronic transport
through the nanoparticle composite allowed a systematic study on the
influence of surface adsorbates (e.g., organic, insulating materials
on the conducting nanoparticleâs surface) in comparison to
well-known insulators such as silica. Insulating impurities or shells
revealed a dominant influence of a tunneling effect on the overall
layer resistance. Mechanical relaxation phenomena were found for 2
nm insulating shells for both large polymer surfactants and (inorganic)
SiO<sub>2</sub> shells
Efficient Magnetic Recycling of Covalently Attached Enzymes on Carbon-Coated Metallic Nanomagnets
In the pursuit of robust and reusable
biocatalysts for industrial
synthetic chemistry, nanobiotechnology is currently taking a significant
part. Recently, enzymes have been immobilized on different nanoscaffold
supports. Carbon coated metallic nanoparticles were found to be a
practically useful support for enzyme immobilization due to their
large surface area, high magnetic saturation, and manipulatable surface
chemistry. In this study carbon coated cobalt nanoparticles were chemically
functionalized (diazonium chemistry), activated for bioconjugation
(<i>N,N</i>-disuccinimidyl carbonate), and subsequently
used in enzyme immobilization. Three enzymes, ÎČ-glucosidase,
α-chymotrypsin, and lipase B were successfully covalently immobilized
on the magnetic nonsupport. The enzymeâparticle conjugates
formed retained their activity and stability after immobilization
and were efficiently recycled from milliliter to liter scales in short
recycle times