6,959 research outputs found
Biological synthesis of fluorescent nanoparticles by cadmium and tellurite resistant Antarctic bacteria: exploring novel natural nanofactories
Indexación: Web of ScienceBackground: Fluorescent nanoparticles or quantum dots (QDs) have been intensely studied for basic and applied research due to their unique size-dependent properties. There is an increasing interest in developing ecofriendly methods to synthesize these nanoparticles since they improve biocompatibility and avoid the generation of toxic byproducts. The use of biological systems, particularly prokaryotes, has emerged as a promising alternative. Recent studies indicate that QDs biosynthesis is related to factors such as cellular redox status and antioxidant defenses. Based on this, the mixture of extreme conditions of Antarctica would allow the development of natural QDs producing bacteria.
Results: In this study we isolated and characterized cadmium and tellurite resistant Antarctic bacteria capable of synthesizing CdS and CdTe QDs when exposed to these oxidizing heavy metals. A time dependent change in fluorescence emission color, moving from green to red, was determined on bacterial cells exposed to metals. Biosynthesis was observed in cells grown at different temperatures and high metal concentrations. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space. Purified biosynthesized QDs displayed broad absorption and emission spectra characteristic of biogenic Cd nanoparticles.
Conclusions: Our work presents a novel and simple biological approach to produce QDs at room temperature by using heavy metal resistant Antarctic bacteria, highlighting the unique properties of these microorganisms as potent natural producers of nano-scale materials and promising candidates for bioremediation purposes.http://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-016-0477-
Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85
This work is part of a series of papers devoted to investigate the evolution
of cluster galaxies during their infall. In the present article we imaged in
NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z
= 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2
deeper than 2MASS. We use these images to unveil asymmetries in the outskirts
of a sample of bright galaxies and develop a new asymmetry index, alpha_An,
which allows to quantify the degree of disruption by the relative area occupied
by the tidal features on the plane of the sky. We measure the asymmetries for a
subsample of 41 large area objects finding clear asymmetries in ten galaxies,
most of them being in groups and pairs projected at different clustercentric
distances, some of them located beyond R500 . Combining information on the
Hi-gas content of blue galaxies and the distribution of sub-structures across
Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful
tool to confirm that tidal mechanisms are indeed present and are currently
affecting a fraction of galaxies in Abell 85. However, when comparing our deep
NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in
this cluster, we discard the presence of tidal 1 interactions down to our
detection limit. Our results suggest that ram-pressure stripping is at the
origin of such spectacular disruptions. We conclude that across a complex
cluster like Abell 85, environment mechanisms, both gravitational and
hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A
Uncertainty as key element in the analysis of X–ray angiography images
The X–ray angiography images are routinely used to assess the blood vessels. The
acquisition procedure considers a medical imaging system which allows obtaining views of the
vessel while the blood flows thought them. The X–ray source is influenced on the region to be
viewed and then, the projection of the all anatomical structures in the champ of view is shown
through an image intensifier. The information of the blood vessel is impacted for the other
structures. Additionally, the blood and the contrast product required in the acquisition are not
mixed homogeneously, producing artifacts in the images. Finally, the noise is also an impact
factor in the quality of the angiography images. In the coronary vessel case, the branches of the
network are superposed. In this paper, an enhancement procedure to diminish the uncertainty
associated to X–ray angiography images is reported. The relation between two versions of the
angiograms is determined using a fuzzy connector considering that this relation diminishes the
images intrinsic uncertainty. These versions correspond with images filtered with low-pass and
high-pass image filters, respectively. The technique is tested with images of the coronary and
kidney vessels. The qualitative results show a good enhanced of the angiography images
PASANDO REVISTA A LAS TROPAS EN LA LLEGADA DEL REY [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
SEÑOR Y SEÑORA [Material gráfico]
ADQUIRIDA POR EL COLECCIONISTA EN TENERIFE.FOTO SOBRE CARTON DE RETRATO DE SEÑOR Y SEÑORA DE PIE (VISTA DESDE CINTURA)Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
DESFILE REAL [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
CAPILLA MORTUORIA REINA REGENTE EN SANTA ANA [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
The evolution of Dscam genes across the arthropods
<p>Abstract</p> <p>Background</p> <p>One way of creating phenotypic diversity is through alternative splicing of precursor mRNAs. A gene that has evolved a hypervariable form is <it>Down syndrome cell adhesion molecule </it>(<it>Dscam-hv</it>), which in <it>Drosophila melanogaster </it>can produce thousands of isoforms via mutually exclusive alternative splicing. The extracellular region of this protein is encoded by three variable exon clusters, each containing multiple exon variants. The protein is vital for neuronal wiring where the extreme variability at the somatic level is required for axonal guidance, and it plays a role in immunity where the variability has been hypothesised to relate to recognition of different antigens. <it>Dscam-hv </it>has been found across the Pancrustacea. Additionally, three paralogous non-hypervariable <it>Dscam-like </it>genes have also been described for <it>D. melanogaster</it>. Here we took a bioinformatics approach, building profile Hidden Markov Models to search across species for putative orthologs to the <it>Dscam </it>genes and for hypervariable alternatively spliced exons, and inferring the phylogenetic relationships among them. Our aims were to examine whether <it>Dscam </it>orthologs exist outside the Bilateria, whether the origin of <it>Dscam-hv </it>could lie outside the Pancrustacea, when the <it>Dscam-like </it>orthologs arose, how many alternatively spliced exons of each exon cluster were present in the most common recent ancestor, and how these clusters evolved.</p> <p>Results</p> <p>Our results suggest that the origin of <it>Dscam </it>genes may lie after the split between the Cnidaria and the Bilateria and supports the hypothesis that <it>Dscam-hv </it>originated in the common ancestor of the Pancrustacea. Our phylogeny of <it>Dscam </it>gene family members shows six well-supported clades: five containing <it>Dscam-like </it>genes and one containing all the <it>Dscam-hv </it>genes, a seventh clade contains arachnid putative <it>Dscam </it>genes. Furthermore, the exon clusters appear to have experienced different evolutionary histories.</p> <p>Conclusions</p> <p><it>Dscam </it>genes have undergone independent duplication events in the insects and in an arachnid genome, which adds to the more well-known tandem duplications that have taken place within <it>Dscam-hv </it>genes. Therefore, two forms of gene expansion seem to be active within this gene family. The evolutionary history of this dynamic gene family will be further unfolded as genomes of species from more disparate groups become available.</p
Low threshold lasing emissions from a single upconversion nanocrystal.
Cross-relaxation among neighboring emitters normally causes self-quenching and limits the brightness of luminescence. However, in nanomaterials, cross-relaxation could be well-controlled and employed for increasing the luminescence efficiency at specific wavelengths. Here we report that cross-relaxation can modulate both the brightness of single upconversion nanoparticles and the threshold to reach population inversion, and both are critical factors in producing the ultra-low threshold lasing emissions in a micro cavity laser. By homogenously coating a 5-μm cavity with a single layer of nanoparticles, we demonstrate that doping Tm3+ ions at 2% can facilitate the electron accumulation at the intermediate state of 3H4 level and efficiently decrease the lasing threshold by more than one order of magnitude. As a result, we demonstrate up-converted lasing emissions with an ultralow threshold of continuous-wave excitation of ~150 W/cm2 achieved at room temperature. A single nanoparticle can lase with a full width at half-maximum as narrow as ~0.45 nm
LAZARETO DE GANDO [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
- …