1,525 research outputs found
Bound-preserving discontinuous Galerkin methods for compressible two-phase flows in porous media
This paper presents a numerical study of immiscible, compressible two-phase
flows in porous media, that takes into account heterogeneity, gravity,
anisotropy, and injection/production wells. We formulate a fully implicit
stable discontinuous Galerkin solver for this system that is accurate, that
respects the maximum principle for the approximation of saturation, and that is
locally mass conservative. To completely eliminate the overshoot and undershoot
phenomena, we construct a flux limiter that produces bound-preserving
elementwise average of the saturation. The addition of a slope limiter allows
to recover a pointwise bound-preserving discrete saturation. Numerical results
show that both maximum principle and monotonicity of the solution are
satisfied. The proposed flux limiter does not impact the local mass error and
the number of nonlinear solver iterations.Comment: 21 pages and 17 figure
Can WFS-T replace SQL ?
Background With the advent of rich internet applications (RIA’s), part of processing has been transferred from the server to the client. However, many geo-spatial applications still require serverside access to a geodatabase to select and manipulate data using SQL. It would be profitable if these actions could be handled by an out of the box serverside component, thus eliminating the need for the development of a custom serverside component. Can OGC standards like WMS and WFS play a role here? Since WFS-T provides select, insert, delete and update methods much like SQL, it was decided to investigate whether the WFS-T implementation specification could replace SQL when developing complex geo-spatial applications. Or is SQL still needed? Method To answer this research question, this approach was tested during the development of several tailor made internet GIS applications: - a wheater and crop growth monitoring system; - a discussion support system for the water domain; - a national cultural heritage portal. Results Filtering and manipulating serverside data by WFS-T using the OpenGIS Filter Encoding Standard (FES) fullfills the needs to a large extent. Almost all of the desired functionality is there. There is one major limitation: FES lacks the ability to define a filter expression based on a joined table. Dependant on the implementation a work around may be available. Xml-schemas support 1-to-many relationships. They can be implemented as a joined table, which as a result can be queried. For larger datasets - a couple of ten thousand records or more - WFS-T tends to end up with a bad performance. Larger datasets should be processed serverside. Downloading large amounts of data and processing them clientside is too time-consuming. Compared to SQL WFS-T has less possibilities to influence the serverside performance. So for performance reasons SQL stays inevitable to handle larger datasets
Single-fluorophore orientation determination with multiview polarized illumination : modeling and microscope design
Author Posting. © Optical Society of America, 2017. This article is posted here by permission of Optical Society of America for personal use, not for redistribution. The definitive version was published in Optics Express 25 (2017): 31309-31325, doi:10.1364/OE.25.031309.We investigate the use of polarized illumination in multiview microscopes for determining the orientation of single-molecule fluorescence transition dipoles. First, we relate the orientation of single dipoles to measurable intensities in multiview microscopes and develop an information-theoretic metric—the solid-angle uncertainty—to compare the ability of multiview microscopes to estimate the orientation of single dipoles. Next, we compare a broad class of microscopes using this metric—single- and dual-view microscopes with varying illumination polarization, illumination numerical aperture (NA), detection NA, obliquity, asymmetry, and exposure. We find that multi-view microscopes can measure all dipole orientations, while the orientations measurable with single-view microscopes is halved because of symmetries in the detection process. We also find that choosing a small illumination NA and a large detection NA are good design choices, that multiview microscopes can benefit from oblique illumination and detection, and that asymmetric NA microscopes can benefit from exposure asymmetry.National Institute of Health (NIH) (R01GM114274, R01EB017293)
The Transiting Exocomets in the HD 172555 System
The Earth is thought to have formed dry, in a part of the Solar Nebula deficient in organic material, and to have acquired its organics and water through bombardment by minor bodies. Observations of this process in well-dated systems can provide insight into the probable origin and composition of the bombarding parent bodies. Transiting cometary activity has previously been reported in Ca II for the late-A member of the 241 Myr old Pictoris Moving Group member, HD 172555(Kiefer et al. 2014). We present HST STIS and COS spectra of HD 172555 demonstrating that the star has chromospheric emission and variable in falling gas features in transitions of silicon and carbon ions at times when no Fe II absorption is seen in the UV data, and no Ca II absorption is seen in contemporary optical spectra. The lack of CO absorption and stable gas absorption at the system velocity is consistent with the absence of a cold Kuiper belt analog (Riviere-Marichalar et al. 2012) in this system. The presence of infall in some species at one epoch and others at different epochs suggests that, like Pictoris, there may be more than one family of exocomets. If perturbed into star-grazing orbits by the same mechanism as for Pic, these data suggest that the wide planet frequency among A-early F stars in the PMG is at least 37.5, well above the frequency estimated for young moving groups independent of host star spectral type
Polar Smectic Films
We report on a new experimental procedure for forming and studying polar
smectic liquid crystal films. A free standing smectic film is put in contact
with a liquid drop, so that the film has one liquid crystal/liquid interface
and one liquid crystal/air interface. This polar environment results in changes
in the textures observed in the film, including a boojum texture and a
previously unobserved spiral texture in which the winding direction of the
spiral reverses at a finite radius from its center. Some aspects of these
textures are explained by the presence of a Ksb term in the bulk elastic free
energy density that favors a combination of splay and bend deformations.Comment: 4 pages, REVTeX, 3 figures, submitted to PR
Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory
Context. Debris discs are thought to be formed through the collisional
grinding of planetesimals, and can be considered as the outcome of planet
formation. Understanding the properties of gas and dust in debris discs can
help us to comprehend the architecture of extrasolar planetary systems.
Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have
provided a valuable dataset for the study of debris discs gas and dust
composition. This paper is part of a series of papers devoted to the study of
Herschel PACS observations of young stellar associations.
Aims. This work aims at studying the properties of discs in the Beta Pictoris
Moving Group (BPMG) through far-IR PACS observations of dust and gas.
Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100
and 160 microns of 19 BPMG members, together with spectroscopic observations of
four of them. Spectroscopic observations were centred at 63.18 microns and 157
microns, aiming to detect [OI] and [CII] emission. We incorporated the new
far-IR observations in the SED of BPMG members and fitted modified blackbody
models to better characterise the dust content.
Results. We have detected far-IR excess emission toward nine BPMG members,
including the first detection of an IR excess toward HD 29391.The star HD
172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding
the short list of debris discs with a gas detection. No debris disc in BPMG is
detected in both [OI] and [CII]. The discs show dust temperatures in the range
55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii
from blackbody models in the range 3 to 82 AU. All the objects with a gas
detection are early spectral type stars with a hot dust component.Comment: 12 pages, 7 figures, 6 table
Anomalous diffusion in polymers: long-time behaviour
We study the Dirichlet boundary value problem for viscoelastic diffusion in
polymers. We show that its weak solutions generate a dissipative semiflow. We
construct the minimal trajectory attractor and the global attractor for this
problem.Comment: 13 page
Dissection of Molecular Assembly Dynamics by Tracking Orientation and Position of Single Molecules in Live Cells
Regulation of order, such as orientation and conformation, drives the function of most molecular assemblies in living cells but remains difficult to measure accurately through space and time. We built an instantaneous fluorescence polarization microscope, which simultaneously images position and orientation of fluorophores in living cells with single-molecule sensitivity and a time resolution of 100 ms. We developed image acquisition and analysis methods to track single particles that interact with higher-order assemblies of molecules. We tracked the fluctuations in position and orientation of molecules from the level of an ensemble of fluorophores down to single fluorophores. We tested our system in vitro using fluorescently labeled DNA and F-actin, in which the ensemble orientation of polarized fluorescence is known. We then tracked the orientation of sparsely labeled F-actin network at the leading edge of migrating human keratinocytes, revealing the anisotropic distribution of actin filaments relative to the local retrograde flow of the F-actin network. Additionally, we analyzed the position and orientation of septin-GFP molecules incorporated in septin bundles in growing hyphae of a filamentous fungus. Our data indicate that septin-GFP molecules undergo positional fluctuations within ∼350 nm of the binding site and angular fluctuations within ∼30° of the central orientation of the bundle. By reporting position and orientation of molecules while they form dynamic higher-order structures, our approach can provide insights into how micrometer-scale ordered assemblies emerge from nanoscale molecules in living cells
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