3,430 research outputs found
Inertial-range kinetic turbulence in pressure-anisotropic astrophysical plasmas
A theoretical framework for low-frequency electromagnetic (drift-)kinetic
turbulence in a collisionless, multi-species plasma is presented. The result
generalises reduced magnetohydrodynamics (RMHD) and kinetic RMHD (Schekochihin
et al. 2009) for pressure-anisotropic plasmas, allowing for species drifts---a
situation routinely encountered in the solar wind and presumably ubiquitous in
hot dilute astrophysical plasmas (e.g. intracluster medium). Two main
objectives are achieved. First, in a non-Maxwellian plasma, the relationships
between fluctuating fields (e.g., the Alfven ratio) are order-unity modified
compared to the more commonly considered Maxwellian case, and so a quantitative
theory is developed to support quantitative measurements now possible in the
solar wind. The main physical feature of low-frequency plasma turbulence
survives the generalisation to non-Maxwellian distributions: Alfvenic and
compressive fluctuations are energetically decoupled, with the latter passively
advected by the former; the Alfvenic cascade is fluid, satisfying RMHD
equations (with the Alfven speed modified by pressure anisotropy and species
drifts), whereas the compressive cascade is kinetic and subject to
collisionless damping. Secondly, the organising principle of this turbulence is
elucidated in the form of a generalised kinetic free-energy invariant. It is
shown that non-Maxwellian features in the distribution function reduce the rate
of phase mixing and the efficacy of magnetic stresses; these changes influence
the partitioning of free energy amongst the various cascade channels. As the
firehose or mirror instability thresholds are approached, the dynamics of the
plasma are modified so as to reduce the energetic cost of bending
magnetic-field lines or of compressing/rarefying them. Finally, it is shown
that this theory can be derived as a long-wavelength limit of non-Maxwellian
slab gyrokinetics.Comment: 61 pages, accepted to Journal of Plasma Physics; Abstract abridge
Increased Time Outdoors Is Followed by Reversal of the Long-Term Trend to Reduced Visual Acuity in Taiwan Primary School Students.
PurposeTo investigate the change in the prevalence of reduced visual acuity (VA) in Taiwanese school children after a policy intervention promoting increased time outdoors.DesignProspective cohort study based on the Taiwan School Student Visual Acuity Screen (TSVAS) by the Ministry of Education in Taiwan.ParticipantsAll school children from grades 1 through 6 were enrolled in the TSVAS from 2001 through 2015.MethodsThe TSVAS requires each school in Taiwan to perform measurements of uncorrected VA (UCVA) on all students in grades 1 through 6 every half year using a Tumbling E chart. Reduced VA was defined as UCVA of 20/25 or less. Data from 1.2 to 1.9 million primary school children each year were collected from 2001 through 2015. A policy program named Tian-Tian 120 encouraged schools to take students outdoors for 120 minutes every day for myopia prevention. It was instituted in September 2010. To investigate the impact of the intervention, a segmented regression analysis of interrupted time series was performed.Main outcome measuresPrevalence of reduced VA.ResultsFrom 2001 to 2011, the prevalence of reduced VA of school children from grades 1 through 6 increased from 34.8% (95% confidence interval [CI], 34.7%-34.9%) to 50.0% (95% CI, 49.9%-50.1%). After the implementation of the Tian-Tian 120 outdoor program, the prevalence decreased continuously from 49.4% (95% CI, 49.3%-49.5%) in 2012 to 46.1% (95% CI, 46.0%-46.2%) in 2015, reversing the previous long-term trend. For the segmented regression analysis controlling for gender and grade, a significant constant upward trend before the intervention in the mean annual change of prevalence was found (+1.58%; standard error [SE], 0.08; P ConclusionsPolicy intervention to promote increased time outdoors in schools was followed by a reversal of the long-term trend toward increased low VA in school children in Taiwan. Because randomized trials have demonstrated outdoor exposure slowing myopia onset, interventions to promote increased time outdoors may be useful in other areas affected by an epidemic of myopia
Towards an Efficient Finite Element Method for the Integral Fractional Laplacian on Polygonal Domains
We explore the connection between fractional order partial differential
equations in two or more spatial dimensions with boundary integral operators to
develop techniques that enable one to efficiently tackle the integral
fractional Laplacian. In particular, we develop techniques for the treatment of
the dense stiffness matrix including the computation of the entries, the
efficient assembly and storage of a sparse approximation and the efficient
solution of the resulting equations. The main idea consists of generalising
proven techniques for the treatment of boundary integral equations to general
fractional orders. Importantly, the approximation does not make any strong
assumptions on the shape of the underlying domain and does not rely on any
special structure of the matrix that could be exploited by fast transforms. We
demonstrate the flexibility and performance of this approach in a couple of
two-dimensional numerical examples
Strengthening the Cohomological Crepant Resolution Conjecture for Hilbert-Chow morphisms
Given any smooth toric surface S, we prove a SYM-HILB correspondence which
relates the 3-point, degree zero, extended Gromov-Witten invariants of the
n-fold symmetric product stack [Sym^n(S)] of S to the 3-point extremal
Gromov-Witten invariants of the Hilbert scheme Hilb^n(S) of n points on S. As
we do not specialize the values of the quantum parameters involved, this result
proves a strengthening of Ruan's Cohomological Crepant Resolution Conjecture
for the Hilbert-Chow morphism from Hilb^n(S) to Sym^n(S) and yields a method of
reconstructing the cup product for Hilb^n(S) from the orbifold invariants of
[Sym^n(S)].Comment: Revised versio
A method for predicting the alkali concentrations in pore solution of hydrated slag cement paste
The Yeast Resource Center Public Image Repository: A large database of fluorescence microscopy images
<p>Abstract</p> <p>Background</p> <p>There is increasing interest in the development of computational methods to analyze fluorescent microscopy images and enable automated large-scale analysis of the subcellular localization of proteins. Determining the subcellular localization is an integral part of identifying a protein's function, and the application of bioinformatics to this problem provides a valuable tool for the annotation of proteomes. Training and validating algorithms used in image analysis research typically rely on large sets of image data, and would benefit from a large, well-annotated and highly-available database of images and associated metadata.</p> <p>Description</p> <p>The Yeast Resource Center Public Image Repository (YRC PIR) is a large database of images depicting the subcellular localization and colocalization of proteins. Designed especially for computational biologists who need large numbers of images, the YRC PIR contains 532,182 TIFF images from nearly 85,000 separate experiments and their associated experimental data. All images and associated data are searchable, and the results browsable, through an intuitive web interface. Search results, experiments, individual images or the entire dataset may be downloaded as standards-compliant OME-TIFF data.</p> <p>Conclusions</p> <p>The YRC PIR is a powerful resource for researchers to find, view, and download many images and associated metadata depicting the subcellular localization and colocalization of proteins, or classes of proteins, in a standards-compliant format. The YRC PIR is freely available at <url>http://images.yeastrc.org/</url>.</p
Silver Nanowire Particle Reactivity with Human Monocyte-Derived Macrophage Cells: Intracellular Availability of Silver Governs Their Cytotoxicity
Silver nanowires (AgNWs) are increasingly being used in the production of optoelectronic devices, with manufacturing processes posing a risk for occupational exposures via inhalation. Although some studies have explored the environmental effects of AgNWs, few data exist on human health effects. Alveolar macrophages are central in the clearance of inhaled fibers from the lungs, with frustrated phagocytosis often stated as a key determinant for the onset of inflammatory reactions. However, the mechanisms through which fully ingested AgNWs interact with, degrade, and transform within primary macrophages over time, and whether the reactivity of the AgNWs arises due to ionic or particulate effects, or both, are poorly understood. Here, a combination of elemental quantification, 3D tomography, analytical transmission electron microscopy (TEM), and confocal microscopy were employed to monitor the uptake, intracellular Ag+ availability, and processing of AgNWs of two different lengths (1 and 10 μm) inside human monocyte-derived macrophages (HMMs). Using AgNO3 and spherical silver nanoparticles (AgNPs) as a comparison, the amount of total bioavailable/intracellular Ag highly correlated to the cytotoxicity of AgNWs. The 10 μm AgNWs were completely internalized in HMMs, with numerous lysosomal vesicles observed in close vicinity to the AgNWs. Following cellular uptake, AgNWs dissolved and transformed intracellularly, with precipitation of AgCl as well as Ag2S. These transformation processes were likely due to AgNW degradation in the acidic environment of lysosomes, leading to the release of Ag+ ions that rapidly react with Cl– and SH– species of the cell microenvironment. Our data suggest that, in HMMs, not only frustrated phagocytosis but also the extent of intracellular uptake and dissolution of AgNWs dictates their cytotoxicity
Wind Energy Forecasting at Different Time Horizons with Individual and Global Models
This paper has been presented at: 14th IFIP International Conference on Artificial Intelligence Applications and InnovationsIn this work two different machine learning approaches have been studied to predict wind power for different time horizons: individual and global models. The individual approach constructs a model for each horizon while the global approach obtains a single model that can be used for all horizons. Both approaches have advantages and disadvantages. Each individual model is trained with data pertaining to a single horizon, thus it can be specific for that horizon, but can use fewer data for training than the global model, which is constructed with data belonging to all horizons. Support Vector Machines have been used for constructing the individual and global models. This study has been tested on energy production data obtained from the Sotavento wind farm and meteorological data from the European Centre for Medium-Range Weather Forecasts, for a 5 × 5 grid around Sotavento. Also, given the large amount of variables involved, a feature selection algorithm (Sequential Forward Selection) has been used in order to improve the performance of the models. Experimental results show that the global model is more accurate than the individual ones, specially when feature selection is used.The authors acknowledge financial support granted by the Spanish Ministry of Science under contract ENE2014-56126-C2-2-R
High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide
Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin–optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron–phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its 4A2 symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with ∼1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins
Collision of millimetre droplets induces DNA and protein transfection into cells
Nonperturbing and simple transfection methods are important for modern techniques used in biotechnology. Recently, we reported that electrospraying can be applied to DNA transfection in cell lines, bacteria, and chicken embryos. However, the transfection efficiency was only about 2%. To improve the transfection rate, physical properties of the sprayed droplets were studied in different variations of the method. We describe a highly efficient technique (30–93%) for introduction of materials such as DNA and protein into living cells by electrospraying droplets of a high conductivity liquid onto cells incubated with the material for transfection. Electric conductivity has a sizable influence on the success of transfection. In contrast, molecular weight of the transfected material, types of ions in the electrospray solution, and the osmotic pressure do not influence transfection efficiency. The physical analysis revealed that collision of cells with millimetre-sized droplets activates intracellular uptake
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