749 research outputs found
Unstructured un-split geometrical Volume-of-Fluid methods -- A review
Geometrical Volume-of-Fluid (VoF) methods mainly support structured meshes,
and only a small number of contributions in the scientific literature report
results with unstructured meshes and three spatial dimensions. Unstructured
meshes are traditionally used for handling geometrically complex solution
domains that are prevalent when simulating problems of industrial relevance.
However, three-dimensional geometrical operations are significantly more
complex than their two-dimensional counterparts, which is confirmed by the
ratio of publications with three-dimensional results on unstructured meshes to
publications with two-dimensional results or support for structured meshes.
Additionally, unstructured meshes present challenges in serial and parallel
computational efficiency, accuracy, implementation complexity, and robustness.
Ongoing research is still very active, focusing on different issues: interface
positioning in general polyhedra, estimation of interface normal vectors,
advection accuracy, and parallel and serial computational efficiency.
This survey tries to give a complete and critical overview of classical, as
well as contemporary geometrical VOF methods with concise explanations of the
underlying ideas and sub-algorithms, focusing primarily on unstructured meshes
and three dimensional calculations. Reviewed methods are listed in historical
order and compared in terms of accuracy and computational efficiency
The unrestricted Skyrme-tensor time-dependent Hartree-Fock and its application to the nuclear response from spherical to triaxial nuclei
The nuclear time-dependent Hartree-Fock model formulated in the
three-dimensional space,based on the full Skyrme energy density functional and
complemented with the tensor force,is presented for the first time. Full
self-consistency is achieved by the model. The application to the isovector
giant dipole resonance is discussed in the linear limit, ranging from spherical
nuclei (16O, 120Sn) to systems displaying axial or triaxial deformation (24Mg,
28Si, 178Os, 190W, 238U).
Particular attention is paid to the spin-dependent terms from the central
sector of the functional, recently included together with the tensor. They turn
out to be capable of producing a qualitative change on the strength
distribution in this channel. The effect on the deformation properties is also
discussed. The quantitative effects on the linear response are small and,
overall, the giant dipole energy remains unaffected.
Calculations are compared to predictions from the (quasi)-particle random
phase approximation and experimental data where available, finding good
agreement
The use of reinforcement learning algorithms to meet the challenges of an artificial pancreas
Blood glucose control, for example, in diabetes mellitus or severe illness, requires strict adherence to a protocol of food, insulin administration and exercise personalized to each patient. An artificial pancreas for automated treatment could boost quality of glucose control and patients' independence. The components required for an artificial pancreas are: i) continuous glucose monitoring (CGM), ii) smart controllers and iii) insulin pumps delivering the optimal amount of insulin. In recent years, medical devices for CGM and insulin administration have undergone rapid progression and are now commercially available. Yet, clinically available devices still require regular patients' or caregivers' attention as they operate in open-loop control with frequent user intervention. Dosage-calculating algorithms are currently being studied in intensive care patients [1] , for short overnight control to supplement conventional insulin delivery [2] , and for short periods where patients rest and follow a prescribed food regime [3] . Fully automated algorithms that can respond to the varying activity levels seen in outpatients, with unpredictable and unreported food intake, and which provide the necessary personalized control for individuals is currently beyond the state-of-the-art. Here, we review and discuss reinforcement learning algorithms, controlling insulin in a closed-loop to provide individual insulin dosing regimens that are reactive to the immediate needs of the patient
A Two-Field Formulation for Surfactant Transport within the Algebraic Volume of Fluid Method
Surfactant transport plays an important role in many technical processes and
industrial applications such as chemical reactors, microfluidics, printing and
coating technology. High fidelity numerical simulations of two-phase flow
phenomena reveal rich insights into the flow dynamics, heat, mass and species
transport. In the present study, a two-field formulation for surfactant
transport within the algebraic volume of fluid method is presented. The slight
diffuse nature of representing the interface in the algebraic volume of fluid
method is utilized to track the concentration of surfactant at the interface as
a volumetric concentration. Transport of insoluble and soluble surfactants is
investigated by tracking two different concentrations of the surfactant, one
within the bulk of the liquid and the other one at the interface. These two
transport equations are in turn coupled by source terms considering the
ad-/desorption processes at a liquid-gas interface. Appropriate boundary
conditions at a solid-fluid interface are formulated to ensure surfactant
conservation, while also enabling to study the ad-/desorption processes at a
solid-fluid interface. The developed numerical method is verified by comparing
the numerical simulations with well-known analytical and numerical reference
solutions. The presented numerical methodology offers a seamless integration of
surfactant transport into the algebraic volume of fluid method, where the
latter has many advantages such as volume conservation and an inherent ability
of handling large interface deformations and topological changes
Regional but not global temperature variability underestimated by climate models at supradecadal timescales
Knowledge of the characteristics of natural climate variability is vital when assessing the range of plausible future climate trajectories in the next decades to centuries. The reliable detection of climate fluctuations on multidecadal to centennial timescales depends on proxy reconstructions and model simulations, as the instrumental record extends back only a few decades in most parts of the world. Systematic comparisons between model-simulated and proxy-based inferences of natural variability, however, often seem contradictory. Locally, simulated temperature variability is consistently smaller on multidecadal and longer timescales than is indicated by proxy-based reconstructions, implying that climate models or proxy interpretations might have deficiencies. In contrast, at global scales, studies found agreement between simulated and proxy reconstructed temperature variations. Here we review the evidence regarding the scale of natural temperature variability during recent millennia. We identify systematic reconstruction deficiencies that may contribute to differing local and global modelâproxy agreement but conclude that they are probably insufficient to resolve such discrepancies. Instead, we argue that regional climate variations persisted for longer timescales than climate models simulating past climate states are able to reproduce. This would imply an underestimation of the regional variability on multidecadal and longer timescales and would bias climate projections and attribution studies. Thus, efforts are needed to improve the simulation of natural variability in climate models accompanied by further refining proxy-based inferences of variability.This study was undertaken by members of CVAS and 2k Network, working groups of the Past Global Changes (PAGES) Global Research association. This is a contribution to the SPACE ERC, STACY and PALMOD projects. The SPACE ERC project has received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant agreement no. 716092). STACY has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, project no. 395588486). This work has also been supported by the German Federal Ministry of Education and Research (BMBF), through the PalMod project (subprojects 01LP1926B (O.B.), 01LP1926D (M.C.) and 01LP1926C (B.E., P.S. and N.W.)) from the Research for Sustainability initiative (FONA). B.E. is supported by the Heinrich Böll Foundation. E.M.-C. was supported by the PARAMOUR project, funded by the Fonds de la Recherche ScientifiqueâFNRS and the FWO under the Excellence of Science (EOS) programme (grant no. O0100718F, EOS ID no. 30454083). A.H. was supported by a Legacy Grant from the Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage. B.M. was supported by LINKA20102 and the Spanish Ministry of Science and Innovation project CEX2018â000794âS. The work originated from discussions at the CVAS working group of PAGES at a workshop at the Internationales Wissenschaftsforum Heidelberg, which was funded by a Hengstberger Prize. We thank N. Beech, C. Brierley, F. Gonzalez-Rouco and M. MacPartland for comments on earlier drafts of the manuscript. This manuscript uses data provided by the World Climate Research Programmeâs Working Group on Coupled Modelling, which is responsible for CMIP and PMIP. We thank the research groups for producing and kindly making their model outputs, measurements and palaeoclimate reconstructions available to us. Editorial assistance, in the form of language editing and correction, was provided by XpertScientific Editing and Consulting Services. We acknowledge support by the Open Access Publication Funds of Alfred-Wegener-Institut Helmholtz Zentrum fĂŒr Polar- und Meeresforschung.Peer ReviewedPostprint (author's final draft
The effect of pure mitral regurgitation on mitral annular geometry and three-dimensional saddle shape
ObjectiveChronic ischemic mitral regurgitation is associated with mitral annular dilatation in the septal-lateral dimension and flattening of the annular 3-dimensional saddle shape. To examine whether these perturbations are caused by the ischemic insult, mitral regurgitation, or both, we investigated the effects of pure mitral regurgitation (low pressure volume overload) on annular geometry and shape.MethodsEight radiopaque markers were sutured evenly around the mitral annulus in sheep randomized to control (CTRL, n = 8) or experimental (HOLE, n = 12) groups. In HOLE, a 3.5- to 4.8-mm hole was punched in the posterior leaflet to generate pure mitral regurgitation. Four-dimensional marker coordinates were obtained radiographically 1 and 12 weeks postoperatively. Mitral annular area, annular septal-lateral and commissureâcommissure dimensions, and annular height were calculated every 16.7 ms.ResultsMitral regurgitation grade was 0.4 ± 0.4 in CTRL and 3.0 ± 0.8 in HOLE (P < .001) at 12 weeks. End-diastolic left ventricular volume index was greater in HOLE at both 1 and 12 weeks; end-systolic volume index was larger in HOLE at 12 weeks. Mitral annular area increased in HOLE predominantly in the commissureâcommissure dimension, with no difference in annular height between HOLE versus CTRL at 1 or 12 weeks, respectively.ConclusionIn contrast with annular septal-lateral dilatation and flattening of the annular saddle shape observed with chronic ischemic mitral regurgitation, pure mitral regurgitation was associated with commissureâcommissure dimension annular dilatation and no change in annular shape. Thus, infarction is a more important determinant of septal-lateral dilatation and annular shape than mitral regurgitation, which reinforces the need for disease-specific designs of annuloplasty rings
Instrumentation-related uncertainty of reflectance and transmittance measurements with a two-channel spectrophotometer
Spectrophotometers are operated in numerous fields of science and industry for a variety of applications. In order to provide confidence for the measured data, analyzing the associated uncertainty is valuable. However, the uncertainty of the measurement results is often unknown or reduced to sample-related contributions. In this paper, we describe our approach for the systematic determination of the measurement uncertainty of the commercially available two-channel spectrophotometer Agilent Cary 5000 in accordance with the Guide to the expression of uncertainty in measurements. We focus on the instrumentation-related uncertainty contributions rather than the specific application and thus outline a general procedure which can be adapted for other instruments. Moreover, we discover a systematic signal deviation due to the inertia of the measurement amplifier and develop and apply a correction procedure. Thereby we increase the usable dynamic range of the instrument by more than one order of magnitude. We present methods for the quantification of the uncertainty contributions and combine them into an uncertainty budget for the device. © 2017 Author(s)
On two-dimensional surface attractors and repellers on 3-manifolds
We show that if is an -diffeomorphism with a surface
two-dimensional attractor or repeller and is a
supporting surface for , then and
there is such that: 1) is a union
of disjoint tame surfaces such that every is
homeomorphic to the 2-torus . 2) the restriction of to
is conjugate to Anosov automorphism of
On the verge of Umdeutung in Minnesota: Van Vleck and the correspondence principle (Part One)
In October 1924, the Physical Review, a relatively minor journal at the time,
published a remarkable two-part paper by John H. Van Vleck, working in virtual
isolation at the University of Minnesota. Van Vleck combined advanced
techniques of classical mechanics with Bohr's correspondence principle and
Einstein's quantum theory of radiation to find quantum analogues of classical
expressions for the emission, absorption, and dispersion of radiation. For
modern readers Van Vleck's paper is much easier to follow than the famous paper
by Kramers and Heisenberg on dispersion theory, which covers similar terrain
and is widely credited to have led directly to Heisenberg's "Umdeutung" paper.
This makes Van Vleck's paper extremely valuable for the reconstruction of the
genesis of matrix mechanics. It also makes it tempting to ask why Van Vleck did
not take the next step and develop matrix mechanics himself.Comment: 82 page
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