Flows of gas through a protoplanetary gap Casassus, Simon; van der Plas, Gerrit; Sebastian Perez, M ...
Nature,
01/2013, Letnik:
493, Številka:
7431
Journal Article
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The formation of gaseous giant planets is thought to occur in the first few million years after stellar birth. Models predict that the process produces a deep gap in the dust component (shallower in ...the gas). Infrared observations of the disk around the young star HD 142527 (at a distance of about 140 parsecs from Earth) found an inner disk about 10 astronomical units (AU) in radius (1 AU is the Earth-Sun distance), surrounded by a particularly large gap and a disrupted outer disk beyond 140 AU. This disruption is indicative of a perturbing planetary-mass body at about 90 AU. Radio observations indicate that the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology. The high stellar accretion rate would deplete the inner disk in less than one year, and to sustain the observed accretion matter must therefore flow from the outer disk and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk. Here we report observations of diffuse CO gas inside the gap, with denser HCO(+) gas along gap-crossing filaments. The estimated flow rate of the gas is in the range of 7 × 10(-9) to 2 × 10(-7) solar masses per year, which is sufficient to maintain accretion onto the star at the present rate.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dysfunction of cell bioenergetics is a common feature of neurodegenerative diseases, the most common of which is Alzheimer's disease (AD). Disrupted energy utilization implicates mitochondria at its ...nexus. This review summarizes some of the evidence that points to faulty mitochondrial function in AD and highlights past and current therapeutic development efforts. Classical neuropathological hallmarks of disease (β‐amyloid and τ) and sporadic AD risk genes (APOE) may trigger mitochondrial disturbance, yet mitochondrial dysfunction may incite pathology. Preclinical and clinical efforts have overwhelmingly centred on the amyloid pathway, but clinical trials have yet to reveal clear‐cut benefits. AD therapies aimed at mitochondrial dysfunction are few and concentrate on reversing oxidative stress and cell death pathways. Novel research efforts aimed at boosting mitochondrial and bioenergetic function offer an alternative treatment strategy. Enhancing cell bioenergetics in preclinical models may yield widespread favourable effects that could benefit persons with AD.
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This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc
New information and communication technologies (ICTs) provide educators and learners with an innovative learning environment to stimulate and enhance the teaching and learning process. In this ...context, novel educational concepts such as blended learning are being developed. In the present paper, we present the results obtained from a blended learning experience carried out at the University of Granada. A total of 17 groups took part, with 1431 students registered for the 2009–2010 academic year. In this study, we use objective outcomes and the students’ perceptions regarding the blended learning activities performed. The study shows that the use of blended learning has a positive effect in reducing dropout rates and in improving exam marks. Moreover, the students’ perceptions on blended learning are interrelated, with their final marks depending on the blended learning activities, and on the students’ age, background and class attendance rate.
The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy, but the overall spectrum of the EBL ...between 0.1 and 1000 μm has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. This is achieved from the observed evolution of the rest-frame K-band galaxy luminosity function up to redshift 4, combined with a determination of galaxy-SED-type fractions. These are based on fitting Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) templates to a multiwavelength sample of about 6000 galaxies in the redshift range from 0.2 to 1 from the All-wavelength Extended Groth Strip International Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies in that redshift range are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolution of the luminosity densities from the ultraviolet (UV) to the infrared (IR), the evolving star formation rate density of the Universe, the evolving contribution to the bolometric EBL from the different galaxy populations including AGN galaxies and the buildup of the EBL. Our EBL calculations are compared with those from a semi-analytic model, another observationally based model and observational data. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very-high-energy γ-rays due to pair production on the EBL are discussed. It is concluded that the EBL is well constrained from the UV to the mid-IR, but independent efforts from IR and γ-ray astronomy are needed in order to reduce the uncertainties in the far-IR.
This paper provides a review of pyrolysis technologies, focusing on reactor designs and companies commercializing these technologies. The renewed interest in pyrolysis is driven by the potential to ...convert lignocellulosic materials into bio-oil and biochar and the use of these intermediates for the production of biofuels, biochemicals, and engineered biochars for environmental services. This review presents slow, intermediate, fast, and microwave pyrolysis as complementary technologies that share some commonalities in their designs. While slow pyrolysis technologies (traditional carbonization kilns) use wood trunks to produce char chunks for cooking, fast pyrolysis systems process small particles to maximize bio-oil yield. The realization of the environmental issues associated with the use of carbonization technologies and the technical difficulties of operating fast pyrolysis reactors using sand as the heating medium and large volumes of carrier gas, as well as the problems with refining the resulting highly oxygenated oils, are forcing the thermochemical conversion community to rethink the design and use of these reactors. Intermediate pyrolysis reactors (also known as converters) offer opportunities for the large-scale balanced production of char and bio-oil. The capacity of these reactors to process forest and agricultural wastes without much preprocessing is a clear advantage. Microwave pyrolysis is an option for modular small autonomous devices for solid waste management. Herein, the evolution of pyrolysis technology is presented from a historical perspective; thus, old and new innovative designs are discussed together.
In this study, we evaluated the efficacy of various primers for the purpose of DNA barcoding old, pinned museum specimens of blackflies (Diptera: Simuliidae). We analysed 271 pinned specimens ...representing two genera and at least 36 species. Due to the age of our material, we targeted overlapping DNA fragments ranging in size from 94 to 407 bp. We were able to recover valid sequences from 215 specimens, of which 18% had 500‐ to 658‐bp barcodes, 36% had 201‐ to 499‐bp barcodes and 46% had 65‐ to 200‐bp barcodes. Our study demonstrates the importance of choosing suitable primers when dealing with older specimens and shows that even very short sequences can be diagnostically informative provided that an appropriate gene region is used. Our study also highlights the lack of knowledge surrounding blackfly taxonomy, and we briefly discuss the need for further phylogenetic studies in this socioeconomically important family of insects.
A simple and straightforward technique for coating microplate wells with molecularly imprinted polymer nanoparticles (nanoMIPs) to develop assays similar to the enzyme-linked immunosorbent assay ...(ELISA) is presented here for the first time. NanoMIPs were synthesized by a solid-phase approach with an immobilized vancomycin (template) and characterized using Biacore 3000, dynamic light scattering, and electron microscopy. Immobilization, blocking, and washing conditions were optimized in microplate format. The detection of vancomycin was achieved in competitive binding experiments with a horseradish peroxidase–vancomycin conjugate. The assay was capable of measuring vancomycin in buffer and in blood plasma within the range of 0.001–70 nM with a detection limit of 0.0025 nM (2.5 pM). The sensitivity of the assay was 3 orders of magnitude better than a previously described ELISA based on antibodies. In these experiments, nanoMIPs have shown high affinity and minimal interference from blood plasma components. Immobilized nanoMIPs were stored for 1 month at room temperature without any detrimental effects to their binding properties. The high affinity of nanoMIPs and the lack of a requirement for cold chain logistics make them an attractive alternative to traditional antibodies used in ELISA.
•Mathematical model for coronavirus disease that fits well the spread in China.•New θ-SEIHRD model taking into account undetected infections.•Validation of the model with the reported data on ...China.•Estimation of errors when identifying parameters at early stages of the pandemic.•Different scenarios to show the impact of undetected cases on the pandemic.
In this paper we develop a mathematical model for the spread of the coronavirus disease 2019 (COVID-19). It is a new θ-SEIHRD model (not a SIR, SEIR or other general purpose model), which takes into account the known special characteristics of this disease, as the existence of infectious undetected cases and the different sanitary and infectiousness conditions of hospitalized people. In particular, it includes a novel approach that considers the fraction θ of detected cases over the real total infected cases, which allows to study the importance of this ratio on the impact of COVID-19. The model is also able to estimate the needs of beds in hospitals. It is complex enough to capture the most important effects, but also simple enough to allow an affordable identification of its parameters, using the data that authorities report on this pandemic.
We study the particular case of China (including Chinese Mainland, Macao, Hong-Kong and Taiwan, as done by the World Health Organization in its reports on COVID-19), the country spreading the disease, and use its reported data to identify the model parameters, which can be of interest for estimating the spread of COVID-19 in other countries. We show a good agreement between the reported data and the estimations given by our model. We also study the behavior of the outputs returned by our model when considering incomplete reported data (by truncating them at some dates before and after the peak of daily reported cases). By comparing those results, we can estimate the error produced by the model when identifying the parameters at early stages of the pandemic. Finally, taking into account the advantages of the novelties introduced by our model, we study different scenarios to show how different values of the percentage of detected cases would have changed the global magnitude of COVID-19 in China, which can be of interest for policy makers.
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