2,995 research outputs found
Electronic doping of graphene by deposited transition metal atoms
We perform a phenomenological analysis of the problem of the electronic
doping of a graphene sheet by deposited transition metal atoms, which aggregate
in clusters. The sample is placed in a capacitor device such that the
electronic doping of graphene can be varied by the application of a gate
voltage and such that transport measurements can be performed via the
application of a (much smaller) voltage along the graphene sample, as reported
in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows
us to explain the thermodynamic properties of the device, such as the level of
doping of graphene and the ionisation potential of the metal clusters in terms
of the chemical interaction between graphene and the clusters. We are also
able, by modelling the metallic clusters as perfect conducting spheres, to
determine the scattering potential due to these clusters on the electronic
carriers of graphene and hence the contribution of these clusters to the
resistivity of the sample. The model presented is able to explain the
measurements performed by Pi et al. on Pt-covered graphene samples at the
lowest metallic coverages measured and we also present a theoretical argument
based on the above model that explains why significant deviations from such a
theory are observed at higher levels of coverage.Comment: 16 pages, 10 figure
2b-RAD genotyping for population genomic studies of Chagas disease vectors: Rhodnius ecuadoriensis in Ecuador
Background:
Rhodnius ecuadoriensis is the main triatomine vector of Chagas disease, American trypanosomiasis, in Southern Ecuador and Northern Peru. Genomic approaches and next generation sequencing technologies have become powerful tools for investigating population diversity and structure which is a key consideration for vector control. Here we assess the effectiveness of three different 2b restriction site-associated DNA (2b-RAD) genotyping strategies in R. ecuadoriensis to provide sufficient genomic resolution to tease apart microevolutionary processes and undertake some pilot population genomic analyses.
Methodology/Principal findings:
The 2b-RAD protocol was carried out in-house at a non-specialized laboratory using 20 R. ecuadoriensis adults collected from the central coast and southern Andean region of Ecuador, from June 2006 to July 2013. 2b-RAD sequencing data was performed on an Illumina MiSeq instrument and analyzed with the STACKS de novo pipeline for loci assembly and Single Nucleotide Polymorphism (SNP) discovery. Preliminary population genomic analyses (global AMOVA and Bayesian clustering) were implemented. Our results showed that the 2b-RAD genotyping protocol is effective for R. ecuadoriensis and likely for other triatomine species. However, only BcgI and CspCI restriction enzymes provided a number of markers suitable for population genomic analysis at the read depth we generated. Our preliminary genomic analyses detected a signal of genetic structuring across the study area.
Conclusions/Significance:
Our findings suggest that 2b-RAD genotyping is both a cost effective and methodologically simple approach for generating high resolution genomic data for Chagas disease vectors with the power to distinguish between different vector populations at epidemiologically relevant scales. As such, 2b-RAD represents a powerful tool in the hands of medical entomologists with limited access to specialized molecular biological equipment.
Author summary:
Understanding Chagas disease vector (triatomine) population dispersal is key for the design of control measures tailored for the epidemiological situation of a particular region. In Ecuador, Rhodnius ecuadoriensis is a cause of concern for Chagas disease transmission, since it is widely distributed from the central coast to southern Ecuador. Here, a genome-wide sequencing (2b-RAD) approach was performed in 20 specimens from four communities from Manabí (central coast) and Loja (southern) provinces of Ecuador, and the effectiveness of three type IIB restriction enzymes was assessed. The findings of this study show that this genotyping methodology is cost effective in R. ecuadoriensis and likely in other triatomine species. In addition, preliminary population genomic analysis results detected a signal of population structure among geographically distinct communities and genetic variability within communities. As such, 2b-RAD shows significant promise as a relatively low-tech solution for determination of vector population genomics, dynamics, and spread
Una tentativa de entrevista a Manuel Mur Oti
Castro De Paz, JL.; Pena, JJ. (1993). Una tentativa de entrevista a Manuel Mur Oti. Vértigo. Revista de cine. (8):52-57. http://hdl.handle.net/10251/42995.Importación Masiva5257
Libros de cine
Castro De Paz, JL.; Jaime J. Pena (1991). Libros de cine. Vértigo. Revista de cine. (1):47-48. http://hdl.handle.net/10251/42903.Importación Masiva4748
The 2011 October Draconids outburst-I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth
On 2011 October 8, the Earth crossed the dust trails left by comet 21P/Giacobini-Zinner during its 19th and 20th century perihelion approaches with the comet being close to perihelion. The geometric circumstances of that encounter were thus favourable to produce a meteor storm, but the trails were much older than in the 1933 and 1946 historical encounters. As a consequence the 2011 October Draconid display exhibited several activity peaks with Zenithal Hourly Rates of about 400 meteors h-1. In fact, if the display had not been forecasted, it could have passed almost unnoticed as was strongly attenuated for visual observers due to the Moon. This suggests that most meteor storms of a similar nature could have passed historically unnoticed under unfavourable weather and Moon observing conditions. The possibility of obtaining information on the physical properties of cometary meteoroids penetrating the atmosphere under low geocentric velocity encounter circumstances motivated us to set up a special observing campaign. Added to the Spanish Fireball Network wide-field all-sky and CCD video monitoring, other high-sensitivity 1/2 arcsec black and white CCD videocameras were attached to the modified medium-field lenses for obtaining high-resolution orbital information. The trajectory, radiant and orbital data of October 16 Draconid meteors observed at multiple stations are presented. The results show that the meteors appeared from a geocentric radiant located at α = 263.0 ± 0°.4 and δ =+55.3 ± 0°.3 that is in close agreement with the radiant predicted for the 1873-1894 and the 1900 dust trails. The estimated mass of material from 21P/Giacobini-Zinner delivered to Earth during the 6 h outburst was around950 ±150 kg
The 2011 October Draconids outburst. I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth
On October 8th, 2011 the Earth crossed the dust trails left by comet
21P/Giacobini-Zinner during its XIX and XX century perihelion approaches with
the comet being close to perihelion. The geometric circumstances of that
encounter were thus favorable to produce a meteor storm, but the trails were
much older than in the 1933 and 1946 historical encounters. As a consequence
the 2011 October Draconid display exhibited several activity peaks with
Zenithal Hourly Rates of about 400 meteors per hour. In fact, if the display
had been not forecasted, it could have passed almost unnoticed as was strongly
attenuated for visual observers due to the Moon. This suggests that most meteor
storms of a similar nature could have passed historically unnoticed under
unfavorable weather and Moon observing conditions. The possibility of obtaining
information on the physical properties of cometary meteoroids penetrating the
atmosphere under low-geocentric velocity encounter circumstances motivated us
to set up a special observing campaign. Added to the Spanish Fireball Network
wide-field all-sky and CCD video monitoring, other high-sensitivity 1/2" black
and white CCD video cameras were attached to modified medium-field lenses for
obtaining high resolution orbital information. The trajectory, radiant, and
orbital data of 16 October Draconid meteors observed at multiple stations are
presented. The results show that the meteors appeared from a geocentric radiant
located at R.A.=263.0+-0.4 deg. and Dec.=+55.3+-0.3 deg. that is in close
agreement with the radiant predicted for the 1873-1894 and the 1900 dust
trails. The estimated mass of material from 21P/Giacobini-Zinner delivered to
Earth during the six-hours outburst was around 950+-150 kg.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society, submitted to MNRAS on November 16th, 2012 Accepted for publication
in MNRAS on April 28th, 2013 Manuscript Pages: 21 Tables: 8 Figures: 4
Manuscript associated: "The 2011 October Draconids outburst. II. Meteoroid
chemical abundances from fireball spectroscopy" by J.M. Madiedo is also in
press in the same journa
Colossal Magnetoresistance is a Griffiths Singularity
It is now widely accepted that the magnetic transition in doped manganites
that show large magnetoresistance is a type of percolation effect. This paper
demonstrates that the transition should be viewed in the context of the
Griffiths phase that arises when disorder suppresses a magnetic transition.
This approach explains unusual aspects of susceptibility and heat capacity data
from a single crystal of LaCaMnOComment: 4 page
Libros de cine
Hueso, AL.; Peláez, A.; Castro De Paz, JL.; Pena, JJ. (1992). Libros de cine. Vértigo. Revista de cine. (3):75-79. http://hdl.handle.net/10251/42947.Importación Masiva7579
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