1,675 research outputs found
Comparison of reduced models for blood flow using Runge-Kutta discontinuous Galerkin methods
One-dimensional blood flow models take the general form of nonlinear
hyperbolic systems but differ greatly in their formulation. One class of models
considers the physically conserved quantities of mass and momentum, while
another class describes mass and velocity. Further, the averaging process
employed in the model derivation requires the specification of the axial
velocity profile; this choice differentiates models within each class.
Discrepancies among differing models have yet to be investigated. In this
paper, we systematically compare several reduced models of blood flow for
physiologically relevant vessel parameters, network topology, and boundary
data. The models are discretized by a class of Runge-Kutta discontinuous
Galerkin methods
Subcritical open channel flows in four branch intersections
International audience[1] Subcritical flow in an intersection composed of four similar orthogonal channels has been studied experimentally in a configuration with two inflows and two outflows for a wide range of experimental conditions. The results have been used to develop a relationship between the incoming flow rates and the flow distribution in the two outlet channels, based on the conservation of discharge and momentum in the intersection, and suitable stage-discharge relationships for the downstream controls in the outflow channels. A final equation is provided by an empirical correlation for the outflow in one of the channels, based on the experimental data obtained from these experiments; this correlation agrees with all the available data to within 65%. It is shown how the resulting set of equations can be used to compute the discharge distribution in any similar intersection, given the incoming flow rates and some form of stage-discharge relationship for the outlet conditions
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The effect of formulations and experimental conditions on in vitro human skin permeation: data from updated EDETOX database
In vitro methods are commonly used in order to estimate the extent of systemic absorption of chemicals through skin. Due to the wide variability of experimental procedures, types of skin and data analytical methods, the resulting permeation measures varies significantly between laboratories and individuals. Inter-laboratory and inter-individual variations with the in vitro measures of skin permeation lead to unreliable extrapolations to in vivo situations. This investigation aimed at a comprehensive assessment of the available data and development of validated models for in vitro skin flux of chemicals under various experimental and vehicle conditions. Following an exhaustive literature review, the human skin flux data were collated and combined with those from EDETOX database resulting in a dataset of a total of 536 flux reports. Quantitative structure-activity relationship techniques combined with data mining tools were used to develop models incorporating the effects of permeant molecular structure, properties of the vehicle, and the experimental conditions including the membrane thickness, finite/infinite exposure, skin pre-hydration and occlusion. The work resulted in statistically valid models for estimation of the skin flux from varying experimental conditions, including relevant real-world mixture exposure scenarios. The models indicated that the most prominent factors influencing flux values were the donor concentration, lipophilicity, size and polarity of the penetrant, and the melting and boiling points of the vehicle, with skin occlusion playing significant role in a non-linear way. The models will aid assessment of the utility of dermal absorption data collected under different conditions with broad implications on transdermal delivery research. © 2012 Elsevier B.V. All rights reserved
Characteristics of the recirculation cell pattern in a lateral cavity
River hydrodynamicsInteraction with structure
Herschel GASPS spectral observations of T Tauri stars in Taurus: unraveling far-infrared line emission from jets and discs
At early stages of stellar evolution young stars show powerful jets and/or
outflows that interact with protoplanetary discs and their surroundings.
Despite the scarce knowledge about the interaction of jets and/or outflows with
discs, spectroscopic studies based on Herschel and ISO data suggests that gas
shocked by jets and/or outflows can be traced by far-IR (FIR) emission in
certain sources. We want to provide a consistent catalogue of selected atomic
([OI] and [CII]) and molecular (CO, OH, and HO) line fluxes observed in
the FIR, separate and characterize the contribution from the jet and the disc
to the observed line emission, and place the observations in an evolutionary
picture. The atomic and molecular FIR (60-190 ) line emission of
protoplanetary discs around 76 T Tauri stars located in Taurus are analysed.
The observations were carried out within the Herschel key programme Gas in
Protoplanetary Systems (GASPS). The spectra were obtained with the
Photodetector Array Camera and Spectrometer (PACS). The sample is first divided
in outflow and non-outflow sources according to literature tabulations. With
the aid of archival stellar/disc and jet/outflow tracers and model predictions
(PDRs and shocks), correlations are explored to constrain the physical
mechanisms behind the observed line emission. The much higher detection rate of
emission lines in outflow sources and the compatibility of line ratios with
shock model predictions supports the idea of a dominant contribution from the
jet/outflow to the line emission, in particular at earlier stages of the
stellar evolution as the brightness of FIR lines depends in large part on the
specific evolutionary stage. [Abridged Abstract]Comment: 37 pages, 27 figures, accepted for publication in A&
Efficient Multiphysics Design Workflow of Synchronous Reluctance Motors
This paper proposes a new design strategy for Synchronous Reluctance machines, with cooperative design in the two environments SyR-e and Motor-CAD. The paper proposes to use the open-source SyR-e for initial, equation based design of the machine. Then, the design is validated and refined in Motor-CAD, in multiple physical domains. This synergy complements both design environments and turns into a comprehensive design package, not yet available in the literature, assembling accessible design equations, magnetic and mechanical FEA and drive operating profiles evaluation to the trademark thermal analysis of Motor-CAD. The cooperative design strategy is described in the paper with reference to the case of a Pure Synchronous Reluctance motor prototype for vehicular tractio
Herschel PACS Observations and Modeling of Debris Disks in the Tucana-Horologium Association
We present Herschel PACS photometry of seventeen B- to M-type stars in the 30
Myr-old Tucana-Horologium Association. This work is part of the Herschel Open
Time Key Programme "Gas in Protoplanetary Systems" (GASPS). Six of the
seventeen targets were found to have infrared excesses significantly greater
than the expected stellar IR fluxes, including a previously unknown disk around
HD30051. These six debris disks were fitted with single-temperature blackbody
models to estimate the temperatures and abundances of the dust in the systems.
For the five stars that show excess emission in the Herschel PACS photometry
and also have Spitzer IRS spectra, we fit the data with models of optically
thin debris disks with realistic grain properties in order to better estimate
the disk parameters. The model is determined by a set of six parameters:
surface density index, grain size distribution index, minimum and maximum grain
sizes, and the inner and outer radii of the disk. The best fitting parameters
give us constraints on the geometry of the dust in these systems, as well as
lower limits to the total dust masses. The HD105 disk was further constrained
by fitting marginally resolved PACS 70 micron imaging.Comment: 15 pages, 7 figures, Accepted to Ap
Numerical method of characteristics for one-dimensional blood flow
Mathematical modeling at the level of the full cardiovascular system requires
the numerical approximation of solutions to a one-dimensional nonlinear
hyperbolic system describing flow in a single vessel. This model is often
simulated by computationally intensive methods like finite elements and
discontinuous Galerkin, while some recent applications require more efficient
approaches (e.g. for real-time clinical decision support, phenomena occurring
over multiple cardiac cycles, iterative solutions to optimization/inverse
problems, and uncertainty quantification). Further, the high speed of pressure
waves in blood vessels greatly restricts the time step needed for stability in
explicit schemes. We address both cost and stability by presenting an efficient
and unconditionally stable method for approximating solutions to diagonal
nonlinear hyperbolic systems. Theoretical analysis of the algorithm is given
along with a comparison of our method to a discontinuous Galerkin
implementation. Lastly, we demonstrate the utility of the proposed method by
implementing it on small and large arterial networks of vessels whose elastic
and geometrical parameters are physiologically relevant
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