1,467 research outputs found
Single-dot Spectroscopy of GaAs Quantum Dots Fabricated by Filling of Self-assembled Nanoholes
We study the optical emission of single GaAs quantum dots (QDs). The QDs are fabricated by filling of nanoholes in AlGaAs and AlAs which are generated in a self-assembled fashion by local droplet etching with Al droplets. Using suitable process parameters, we create either uniform QDs in partially filled deep holes or QDs with very broad size distribution in completely filled shallow holes. Micro photoluminescence measurements of single QDs of both types establish sharp excitonic peaks. We measure a fine-structure splitting in the range of 22–40μeV and no dependence on QD size. Furthermore, we find a decrease in exciton–biexciton splitting with increasing QD size
On the generalized Davenport constant and the Noether number
Known results on the generalized Davenport constant related to zero-sum
sequences over a finite abelian group are extended to the generalized Noether
number related to the rings of polynomial invariants of an arbitrary finite
group. An improved general upper bound is given on the degrees of polynomial
invariants of a non-cyclic finite group which cut out the zero vector.Comment: 14 page
Costs and cost-effectiveness of delivering intermittent preventive treatment through schools in western Kenya
BACKGROUND: Awareness of the potential impact of malaria among school-age children has stimulated investigation into malaria interventions that can be delivered through schools. However, little evidence is available on the costs and cost-effectiveness of intervention options. This paper evaluates the costs and cost-effectiveness of intermittent preventive treatment (IPT) as delivered by teachers in schools in western Kenya. METHODS: Information on actual drug and non-drug associated costs were collected from expenditure and salary records, government budgets and interviews with key district and national officials. Effectiveness data were derived from a cluster-randomised-controlled trial of IPT where a single dose of sulphadoxine-pyrimethamine and three daily doses of amodiaquine were provided three times in year (once termly). Both financial and economic costs were estimated from a provider perspective, and effectiveness was estimated in terms of anaemia cases averted. A sensitivity analysis was conducted to assess the impact of key assumptions on estimated cost-effectiveness. RESULTS: The delivery of IPT by teachers was estimated to cost US 0.25 per child) whilst recurrent costs accounted for 86.8% (US 29.84 and the cost per case of Plasmodium falciparum parasitaemia averted was US 24.60 and 40.32 when the prices of antimalarial drugs and delivery costs were varied. Cost-effectiveness was most influenced by effectiveness of IPT and the background prevalence of anaemia. In settings where 30% and 50% of schoolchildren were anaemic, cost-effectiveness ratios were US$ 12.53 and 7.52, respectively. CONCLUSION: This study provides the first evidence that IPT administered by teachers is a cost-effective school-based malaria intervention and merits investigation in other settings
High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument
We present the results of N-band spectro-interferometric observations of the
silicate carbon star IRAS08002-3803 with the MID-infrared Interferometric
instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the
European Southern Observatory (ESO). The observations were carried out using
two unit telescopes (UT2 and UT3) with projected baseline lengths ranging from
39 to 47 m. Our observations of IRAS08002-3803 have spatially resolved the
dusty environment of a silicate carbon star for the first time and revealed an
unexpected wavelength dependence of the angular size in the N band: the
uniform-disk diameter is found to be constant and ~36 mas (72 Rstar) between 8
and 10 micron, while it steeply increases longward of 10 micron to reach ~53
mas (106 Rstar) at 13 micron. Model calculations with our Monte Carlo radiative
transfer code show that neither spherical shell models nor axisymmetric disk
models consisting of silicate grains alone can simultaneously explain the
observed wavelength dependence of the visibility and the spectral energy
distribution (SED). We propose that the circumstellar environment of
IRAS08002-3803 may consist of two grain species coexisting in the disk:
silicate and a second grain species, for which we consider amorphous carbon,
large silicate grains, and metallic iron grains. Comparison of the observed
visibilities and SED with our models shows that such disk models can fairly --
though not entirely satisfactorily -- reproduce the observed SED and N-band
visibilities. Our MIDI observations and the radiative transfer calculations
lend support to the picture where oxygen-rich material around IRAS08002-3803 is
stored in a circumbinary disk surrounding the carbon-rich primary star and its
putative low-luminosity companion.Comment: 15 pages, 8 figures, accepted for publication in A&
The structure and evolution of M51-type galaxies
We discuss the integrated kinematic parameters of 20 M51-type binary
galaxies. A comparison of the orbital masses of the galaxies with the sum of
the individual masses suggests that moderately massive dark halos surround
bright spiral galaxies. The relative velocities of the galaxies in binary
systems were found to decrease with increasing relative luminosity of the
satellite. We obtained evidence that the Tully-Fisher relation for binary
members could be flatter than that for local field galaxies. An enhanced star
formation rate in the binary members may be responsible for this effect. In
most binary systems, the direction of orbital motion of the satellite coincides
with the direction of rotation of the main galaxy. Seven candidates for distant
M51-type objects were found in the Northern and Southern Hubble Deep Fields. A
comparison of this number with the statistics of nearby galaxies provides
evidence for the rapid evolution of the space density of M51-type galaxies with
redshift Z. We assume that M51-type binary systems could be formed through the
capture of a satellite by a massive spiral galaxy. It is also possible that the
main galaxy and its satellite in some of the systems have a common cosmological
origin.Comment: 8 pages, 4 figures, to be published in Astronomy Letter
Phototriggered release of tetrapeptide AAPV from coumarinyl and pyrenyl cages
Ala-Ala-Pro-Val (AAPV) is a bioactive tetrapeptide that inhibits human neutrophil elastase (HNE), an enzyme involved in skin chronic inflammatory diseases like psoriasis. Caged derivatives of this peptide were prepared by proper N- and C-terminal derivatisation through a carbamate or ester linkage, respectively, with two photoactive moieties, namely 7-methoxycoumarin-2-ylmethyl and pyren-2-ylmethyl groups. These groups were chosen to assess the influence of the photosensitive group and the type of linkage in the controlled photorelease of the active molecule. The caged peptides were irradiated at selected wavelengths of irradiation (254, 300, and 350 nm), and the photolytic process was monitored by HPLC-UV. The results established the applicability of the tested photoactive groups for the release of AAPV, especially for the derivative bearing the carbamate-linked pyrenylmethyl group, which displayed the shortest irradiation times for the release at the various wavelengths of irradiation (ca. 4 min at 254 nm, 8 min at 300 nm and 46 min at 350 nm).Thanks are due to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for
financial support to the portuguese NMR network (PTNMR, Bruker Avance III 400-
Univ. Minho), FCT and FEDER (European Fund for Regional Development)-
COMPETE-QREN-EU for financial support through the Chemistry Research Centre of
the University of Minho (Ref. UID/QUI/00686/2013 and UID/QUI/0686/2016). A PhD
grant to A.M.S. (SFRH/BD/80813/2011) is also acknowledged.info:eu-repo/semantics/publishedVersio
Assembling a global database of malaria parasite prevalence for the Malaria Atlas Project
BACKGROUND: Open access to databases of information generated by the research community can synergize individual efforts and are epitomized by the genome mapping projects. Open source models for outputs of scientific research funded by tax-payers and charities are becoming the norm. This has yet to be extended to malaria epidemiology and control. METHODS: The exhaustive searches and assembly process for a global database of malaria parasite prevalence as part of the Malaria Atlas Project (MAP) are described. The different data sources visited and how productive these were in terms of availability of parasite rate (PR) data are presented, followed by a description of the methods used to assemble a relational database and an associated geographic information system. The challenges facing spatial data assembly from varied sources are described in an effort to help inform similar future applications. RESULTS: At the time of writing, the MAP database held 3,351 spatially independent PR estimates from community surveys conducted since 1985. These include 3,036 Plasmodium falciparum and 1,347 Plasmodium vivax estimates in 74 countries derived from 671 primary sources. More than half of these data represent malaria prevalence after the year 2000. CONCLUSION: This database will help refine maps of the global spatial limits of malaria and be the foundation for the development of global malaria endemicity models as part of MAP. A widespread application of these maps is envisaged. The data compiled and the products generated by MAP are planned to be released in June 2009 to facilitate a more informed approach to global malaria control
Comparative Analysis of Gene Content Evolution in Phytoplasmas and Mycoplasmas
Phytoplasmas and mycoplasmas are two groups of important pathogens in the bacterial class Mollicutes. Because of their economical and clinical importance, these obligate pathogens have attracted much research attention. However, difficulties involved in the empirical study of these bacteria, particularly the fact that phytoplasmas have not yet been successfully cultivated outside of their hosts despite decades of attempts, have greatly hampered research progress. With the rapid advancements in genome sequencing, comparative genome analysis provides a new approach to facilitate our understanding of these bacteria. In this study, our main focus is to investigate the evolution of gene content in phytoplasmas, mycoplasmas, and their common ancestor. By using a phylogenetic framework for comparative analysis of 12 complete genome sequences, we characterized the putative gains and losses of genes in these obligate parasites. Our results demonstrated that the degradation of metabolic capacities in these bacteria has occurred predominantly in the common ancestor of Mollicutes, prior to the evolutionary split of phytoplasmas and mycoplasmas. Furthermore, we identified a list of genes that are acquired by the common ancestor of phytoplasmas and are conserved across all strains with complete genome sequences available. These genes include several putative effectors for the interactions with hosts and may be good candidates for future functional characterization
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