663 research outputs found
Chiral Speciation in Terrestrial Pulmonate Snails
On the basis of data in the literature, the percentages of dextral versus sinistral species of snails have been calculated for western Europe, Turkey, North America (north of Mexico), and Japan. When the family of Clausiliidae is represented, about a quarter of all snail species may be sinistral, whereas less than one per cent of the species may be sinistral where that family does not occur. The number of single-gene speciation events on the basis of chirality, resulting in the origin of mirror image species, is not closely linked to the percentage of sinistral versus dextral species in a particular region. Turkey is nevertheless exceptional by both a high percentage of sinistral species and a high number of speciation events resulting in mirror image species. Shell morphology and genetic background may influence the ease of chirality-linked speciation, whereas sinistrality may additionally be selected against by internal selection. For the Clausiliidae, the fossil record and the recent fauna suggest that successful reversals in coiling direction occurred with a frequency of once every three to four million years
Ab initio Molecular Dynamics in Adaptive Coordinates
We present a new formulation of ab initio molecular dynamics which exploits
the efficiency of plane waves in adaptive curvilinear coordinates, and thus
provides an accurate treatment of first-row elements. The method is used to
perform a molecular dynamics simulation of the CO_2 molecule, and allows to
reproduce detailed features of its vibrational spectrum such as the splitting
of the Raman sigma+_g mode caused by Fermi resonance. This new approach opens
the way to highly accurate ab initio simulations of organic compounds.Comment: 11 pages, 3 PostScript figure
Cosmological parameters from large scale structure - geometric versus shape information
The matter power spectrum as derived from large scale structure (LSS) surveys
contains two important and distinct pieces of information: an overall smooth
shape and the imprint of baryon acoustic oscillations (BAO). We investigate the
separate impact of these two types of information on cosmological parameter
estimation, and show that for the simplest cosmological models, the broad-band
shape information currently contained in the SDSS DR7 halo power spectrum (HPS)
is by far superseded by geometric information derived from the baryonic
features. An immediate corollary is that contrary to popular beliefs, the upper
limit on the neutrino mass m_\nu presently derived from LSS combined with
cosmic microwave background (CMB) data does not in fact arise from the possible
small-scale power suppression due to neutrino free-streaming, if we limit the
model framework to minimal LambdaCDM+m_\nu. However, in more complicated
models, such as those extended with extra light degrees of freedom and a dark
energy equation of state parameter w differing from -1, shape information
becomes crucial for the resolution of parameter degeneracies. This conclusion
will remain true even when data from the Planck surveyor become available. In
the course of our analysis, we introduce a new dewiggling procedure that allows
us to extend consistently the use of the SDSS HPS to models with an arbitrary
sound horizon at decoupling. All the cases considered here are compatible with
the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio
Theoretical investigation of carbon defects and diffusion in α-quartz
The geometries, formation energies, and diffusion barriers of carbon point defects in silica (α-quartz) have been calculated using a charge-self-consistent density-functional based nonorthogonal tight-binding method. It is found that bonded interstitial carbon configurations have significantly lower formation energies (on the order of 5 eV) than substitutionals. The activation energy of atomic C diffusion via trapping and detrapping in interstitial positions is about 2.7 eV. Extraction of a CO molecule requires an activation energy <3.1 eV but the CO molecule can diffuse with an activation energy <0.4 eV. Retrapping in oxygen vacancies is hindered—unlike for O2—by a barrier of about 2 eV
Band structure and optical properties of germanium sheet polymers
The band structure of H-terminated Ge sheet polymers is calculated using density-functional theory in the local density approximation and compared to the optical properties of epitaxial polygermyne layers as determined from reflection, photoluminescence, and photoluminescence excitation measurements. A direct band gap of 1.7 eV is predicted and a near resonant excitation of the photoluminescence is observed experimentally close to this energy
Enriched biodiversity data as a resource and service
Background: Recent years have seen a surge in projects that produce large volumes of structured, machine-readable biodiversity data. To make these data amenable to processing by generic, open source “data enrichment” workflows, they are increasingly being represented in a variety of standards-compliant interchange formats. Here, we report on an initiative in which software developers and taxonomists came together to address the challenges and highlight the opportunities in the enrichment of such biodiversity data by engaging in intensive, collaborative software development: The Biodiversity Data Enrichment Hackathon.
Results: The hackathon brought together 37 participants (including developers and taxonomists, i.e. scientific professionals that gather, identify, name and classify species) from 10 countries: Belgium, Bulgaria, Canada, Finland, Germany, Italy, the Netherlands, New Zealand, the UK, and the US. The participants brought expertise in processing structured data, text mining, development of ontologies, digital identification keys, geographic information systems, niche modeling, natural language processing, provenance annotation, semantic integration, taxonomic name resolution, web service interfaces, workflow tools and visualisation. Most use cases and exemplar data were provided by taxonomists.
One goal of the meeting was to facilitate re-use and enhancement of biodiversity knowledge by a broad range of stakeholders, such as taxonomists, systematists, ecologists, niche modelers, informaticians and ontologists. The suggested use cases resulted in nine breakout groups addressing three main themes: i) mobilising heritage biodiversity knowledge; ii) formalising and linking concepts; and iii) addressing interoperability between service platforms. Another goal was to further foster a community of experts in biodiversity informatics and to build human links between research projects and institutions, in response to recent calls to further such integration in this research domain.
Conclusions: Beyond deriving prototype solutions for each use case, areas of inadequacy were discussed and are being pursued further. It was striking how many possible applications for biodiversity data there were and how quickly solutions could be put together when the normal constraints to collaboration were broken down for a week. Conversely, mobilising biodiversity knowledge from their silos in heritage literature and natural history collections will continue to require formalisation of the concepts (and the links between them) that define the research domain, as well as increased interoperability between the software platforms that operate on these concepts
Eosinophils Are Important for Protection, Immunoregulation and Pathology during Infection with Nematode Microfilariae
Eosinophil responses typify both allergic and parasitic helminth disease. In helminthic disease, the role of eosinophils can be both protective in immune responses and destructive in pathological responses. To investigate whether eosinophils are involved in both protection and pathology during filarial nematode infection, we explored the role of eosinophils and their granule proteins, eosinophil peroxidase (EPO) and major basic protein-1 (MBP-1), during infection with Brugia malayi microfilariae. Using eosinophil-deficient mice (PHIL), we further clarify the role of eosinophils in clearance of microfilariae during primary, but not challenge infection in vivo. Deletion of EPO or MBP-1 alone was insufficient to abrogate parasite clearance suggesting that either these molecules are redundant or eosinophils act indirectly in parasite clearance via augmentation of other protective responses. Absence of eosinophils increased mast cell recruitment, but not other cell types, into the broncho-alveolar lavage fluid during challenge infection. In addition absence of eosinophils or EPO alone, augmented parasite-induced IgE responses, as measured by ELISA, demonstrating that eosinophils are involved in regulation of IgE. Whole body plethysmography indicated that nematode-induced changes in airway physiology were reduced in challenge infection in the absence of eosinophils and also during primary infection in the absence of EPO alone. However lack of eosinophils or MBP-1 actually increased goblet cell mucus production. We did not find any major differences in cytokine responses in the absence of eosinophils, EPO or MBP-1. These results reveal that eosinophils actively participate in regulation of IgE and goblet cell mucus production via granule secretion during nematode-induced pathology and highlight their importance both as effector cells, as damage-inducing cells and as supervisory cells that shape both innate and adaptive immunity
Constructing living buildings: a review of relevant technologies for a novel application of biohybrid robotics
Biohybrid robotics takes an engineering approach to the expansion and exploitation of biological behaviours for application to automated tasks. Here, we identify the construction of living buildings and infrastructure as a high-potential application domain for biohybrid robotics, and review technological advances relevant to its future development. Construction, civil infrastructure maintenance and building occupancy in the last decades have comprised a major portion of economic production, energy consumption and carbon emissions. Integrating biological organisms into automated construction tasks and permanent building components therefore has high potential for impact. Live materials can provide several advantages over standard synthetic construction materials, including self-repair of damage, increase rather than degradation of structural performance over time, resilience to corrosive environments, support of biodiversity, and mitigation of urban heat islands. Here, we review relevant technologies, which are currently disparate. They span robotics, self-organizing systems, artificial life, construction automation, structural engineering, architecture, bioengineering, biomaterials, and molecular and cellular biology. In these disciplines, developments relevant to biohybrid construction and living buildings are in the early stages, and typically are not exchanged between disciplines. We, therefore, consider this review useful to the future development of biohybrid engineering for this highly interdisciplinary application.publishe
Cosmological parameters constraints from galaxy cluster mass function measurements in combination with other cosmological data
We present the cosmological parameters constraints obtained from the
combination of galaxy cluster mass function measurements (Vikhlinin et al.,
2009a,b) with new cosmological data obtained during last three years: updated
measurements of cosmic microwave background anisotropy with Wilkinson Microwave
Anisotropy Probe (WMAP) observatory, and at smaller angular scales with South
Pole Telescope (SPT), new Hubble constant measurements, baryon acoustic
oscillations and supernovae Type Ia observations.
New constraints on total neutrino mass and effective number of neutrino
species are obtained. In models with free number of massive neutrinos the
constraints on these parameters are notably less strong, and all considered
cosmological data are consistent with non-zero total neutrino mass \Sigma m_\nu
\approx 0.4 eV and larger than standard effective number of neutrino species,
N_eff \approx 4. These constraints are compared to the results of neutrino
oscillations searches at short baselines.
The updated dark energy equation of state parameters constraints are
presented. We show that taking in account systematic uncertainties, current
cluster mass function data provide similarly powerful constraints on dark
energy equation of state, as compared to the constraints from supernovae Type
Ia observations.Comment: Accepted for publication in Astronomy Letter
Water oxidation at hematite photoelectrodes: the role of surface states
Hematite (α-Fe2O3) constitutes one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Its inherent drawbacks related to the long penetration depth of light and poor charge carrier conductivity are being progressively overcome by employing nanostructuring strategies and improved catalysts. However, the physical–chemical mechanisms responsible for the photoelectrochemical performance of this material (J(V) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by atomic layer deposition to study the photoelectrochemical properties of this material under water-splitting conditions. We employed impedance spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity, and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. The charging of this surface state under illumination is also related to the shift of the measured flat-band potential. These findings demonstrate the utility of impedance spectroscopy in investigations of hematite electrodes to provide key parameters of photoelectrodes with a relatively simple measurement
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