scholarly journals A well-balanced scheme for the simulation tool-kit A-MaZe: implementation, tests, and first applications to stellar structure

2019 ◽  
Vol 630 ◽  
pp. A129 ◽  
Author(s):  
M. V. Popov ◽  
R. Walder ◽  
D. Folini ◽  
T. Goffrey ◽  
I. Baraffe ◽  
...  
Keyword(s):  
Stellar Structure ◽  
Machine Precision ◽  
Slab Geometry ◽  
Stellar Convection ◽  
Multiple Dimensions ◽  
Physically Identical ◽  
Implicit Code ◽  
Short Time ◽  
2D And 3D

Characterizing stellar convection in multiple dimensions is a topic at the forefront of stellar astrophysics. Numerical simulations are an essential tool for this task. We present an extension of the existing numerical tool-kit A-MaZe that enables such simulations of stratified flows in a gravitational field. The finite-volume based, cell-centered, and time-explicit hydrodynamics solver of A-MaZe was extended such that the scheme is now well-balanced in both momentum and energy. The algorithm maintains an initially static balance between gravity and pressure to machine precision. Quasi-stationary convection in slab-geometry preserves gas energy (internal plus kinetic) on average, despite strong local up- and down-drafts. By contrast, a more standard numerical scheme is demonstrated to result in substantial gains of energy within a short time on purely numerical grounds. The test is further used to point out the role of dimensionality, viscosity, and Rayleigh number for compressible convection. Applications to a young sun in 2D and 3D, covering a part of the inner radiative zone, as well as the outer convective zone, demonstrate that the scheme meets its initial design goal. Comparison with results obtained for a physically identical setup with a time-implicit code show qualitative agreement.

scholarly journals Impact of tumor-parenchyma biomechanics on liver metastatic progression: a multi-model approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yafei Wang ◽  
Erik Brodin ◽  
Kenichiro Nishii ◽  
Hermann B. Frieboes ◽  
Shannon M. Mumenthaler ◽  
...  
Keyword(s):  
Time Scales ◽  
Constitutive Relations ◽  
Elastic Tissue ◽  
Metastatic Progression ◽  
Patient Death ◽  
Metastatic Growth ◽  
Tumor Parenchyma ◽  
Short Time ◽  
Model Approach

AbstractColorectal cancer and other cancers often metastasize to the liver in later stages of the disease, contributing significantly to patient death. While the biomechanical properties of the liver parenchyma (normal liver tissue) are known to affect tumor cell behavior in primary and metastatic tumors, the role of these properties in driving or inhibiting metastatic inception remains poorly understood, as are the longer-term multicellular dynamics. This study adopts a multi-model approach to study the dynamics of tumor-parenchyma biomechanical interactions during metastatic seeding and growth. We employ a detailed poroviscoelastic model of a liver lobule to study how micrometastases disrupt flow and pressure on short time scales. Results from short-time simulations in detailed single hepatic lobules motivate constitutive relations and biological hypotheses for a minimal agent-based model of metastatic growth in centimeter-scale tissue over months-long time scales. After a parameter space investigation, we find that the balance of basic tumor-parenchyma biomechanical interactions on shorter time scales (adhesion, repulsion, and elastic tissue deformation over minutes) and longer time scales (plastic tissue relaxation over hours) can explain a broad range of behaviors of micrometastases, without the need for complex molecular-scale signaling. These interactions may arrest the growth of micrometastases in a dormant state and prevent newly arriving cancer cells from establishing successful metastatic foci. Moreover, the simulations indicate ways in which dormant tumors could “reawaken” after changes in parenchymal tissue mechanical properties, as may arise during aging or following acute liver illness or injury. We conclude that the proposed modeling approach yields insight into the role of tumor-parenchyma biomechanics in promoting liver metastatic growth, and advances the longer term goal of identifying conditions to clinically arrest and reverse the course of late-stage cancer.

scholarly journals COVID-19: systematic learning across boundaries requires a conceptual agreement

2021 ◽  
pp. 140349482110270
Author(s):  
Knut Ole Sundnes ◽  
Geir Sverre Braut
Keyword(s):  
Public Health ◽  
Knowledge Base ◽  
External Validity ◽  
Evaluation Research ◽  
The Other ◽  
Basic Knowledge ◽  
Early Publication ◽  
Number Of Publications ◽  
Short Time

The COVID-19 epidemic has revealed a shortage of basic knowledge and understanding of pandemics, especially regarding their dynamics and how to contain them. The results are a host of governments’ decrees and instructions, one replacing the other, often within the same week. It has further, in a truly short time, resulted in an overwhelming number of publications, many of them prioritising early publication over quality. This commentary addresses the concept of structured research related to disasters and how the use of endorsed guidelines will facilitate well-designed evaluation research with improved rigour and external validity, even if applied retrospectively. The outcome should be a solidified knowledge base. Further, the important role of public health efforts is to be highlighted, as their role has proved crucial during the COVID-19 pandemic.

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

A Simple Statistical Theory for Grain Growth in Materials.

1990 ◽  
Vol 209 ◽  
Author(s):  
P. Mulheran ◽  
J.H. Harding
Keyword(s):  
Growth Rate ◽  
Monte Carlo ◽  
Statistical Theory ◽  
Stochastic Model ◽  
Grain Growth ◽  
Three Dimensional ◽  
Monte Carlo Procedure ◽  
Short Time ◽  
2D And 3D ◽  
Good Agreement

A Monte Carlo procedure has been used to study the ordering of both two and three dimensional (2d and 3d) Potts Hamiltonians, further to the work of Anderson et al. For the 3d lattice, the short time growth rate is found to be much slower than previously reported, though the simulated microstructure is in agreement with the earlier studies. We propose a new stochastic model that gives good agreement with the simulations.

Chairman’s remarks

1989 ◽  
Vol 43 (2) ◽  
pp. 97-98
Keyword(s):  
Civil Wars ◽  
Fine Arts ◽  
Intellectual Life ◽  
Cultural Hegemony ◽  
Territorial Expansion ◽  
Isaac Newton ◽  
Mathematical School ◽  
Christiaan Huygens ◽  
Short Time

It was our plan that this meeting should consider some aspects of the changes in material civilization and intellectual life in Britain and the United Provinces resulting from the union of the two Crowns in 1688. A parallel meeting in Amsterdam will devote more attention to politics and the fine arts. In a short time it is impossible to cover many topics and we thought it right to pay some attention to the role of the Stadtholder while not omitting the two great scientific figures of this age, Christiaan Huygens and Isaac Newton. It is tempting to suppose that the replacement of James II on the throne of England by William and Mary, as it ensured the ascendancy of Protestantism, so also it introduced a strong Dutch influence to replace the Frenchification characteristic of the reigns of Charles and James. Did not William, in stemming the territorial expansion of France, also check its cultural hegemony? So far as Britain is concerned the proposition is dubious, for our cultural links with The Netherlands were already strong before 1688, not least because of earlier migrations and the relationships formed during the Civil Wars and their aftermath. In the scientific realm one thinks especially of van Schooten and the Dutch mathematical school, of De Graaf, Swammerdam, Leeuwenhoek and especially Christiaan Huygens.

The role of stimulus comparison in animal perceptual learning: Effects of a distractor placement

2018 ◽  
Vol 71 (12) ◽  
pp. 2488-2496 ◽  
Author(s):  
Sergio A Recio ◽  
Adela F Iliescu ◽  
Isabel de Brugada
Keyword(s):  
Perceptual Learning ◽  
Learning Process ◽  
Time Lapse ◽  
Animal Research ◽  
Learning Effects ◽  
Stimulus Comparison ◽  
Human Research ◽  
Short Time ◽  
Effect Experiment

Research on perceptual learning shows that the way stimuli are presented leads to different outcomes. The intermixed/blocked (I/B) effect is one of these outcomes, and different mechanisms have been proposed to explain it. In human research, it seems that comparison between stimuli is important, and the placement of a distractor between the pre-exposed stimuli interferes with the effect. Results from animal research are usually interpreted in different terms because the type of procedure normally used in animal perceptual learning does not favour comparison. In our experiments, we explore the possibility that a distractor placed between the to-be-discriminated stimuli may interfere with the perceptual learning process in rats. In Experiment 1, two flavoured solutions are presented in an I/B fashion, with a short time lapse between them to favour comparison, showing the typical I/B effect. In Experiment 2, we introduced a distractor in between the solutions, abolishing this effect. Experiment 3 further replicates this by comparing two intermixed groups with or without distractor. The results replicate the findings from human research, suggesting that comparison also plays an important role in animal perceptual learning.

scholarly journals Is the quest to eat healthy a route to enhancing consumer’s food security?

2022 ◽  
Vol 11 (1) ◽  
Author(s):  
William A. Kerr ◽  
Jill E. Hobbs
Keyword(s):  
Food Security ◽  
Supply Chains ◽  
Food Supply ◽  
Food Markets ◽  
Individual Level ◽  
Food Supply Chains ◽  
Multiple Dimensions ◽  
Private Standards ◽  
Regulatory Failure

Abstract Background On an individual level, food security has multiple dimensions and consumers exhibit heterogeneity in the extent to which different attributes matter in their quest for enhanced food security. The aim of this paper is to explain how the quest for individual food security arises and its dynamic nature and its implications for how food security-enhancing attributes are defined and how they are signaled, and for the role of regulators and food supply chains in establishing credible signals. Results The paper finds that the quest for enhanced individual food security is a dynamic process that responds to the disequilibrium that change brings. The changing role of standards and grades as signals in food markets is discussed as a precursor to considering the implications for both market and non-market (regulatory) failure in determining the appropriate role for the public sector in regulating food safety and quality standards and labeling. The rise of private standards is examined, along with a consideration of how these standards differ in terms of scope and objective and their implications for international trade in increasingly globalized food supply chains. Conclusions Despite the growth of private standards, a clear role remains for mandatory public standards, yet challenges arise when these standards differ across countries.

scholarly journals Ineffable Cultures or Material Devices: What Valuation Studies can Learn from the Disappearance of Ensured Solidarity in a Health Care Market

2015 ◽  
Vol 3 (1) ◽  
pp. 45-73 ◽  
Author(s):  
Teun Zuiderent-Jerak ◽  
Stans Van Egmond
Keyword(s):  
Health Care ◽  
Decisive Role ◽  
Cultural Value ◽  
Health Care Market ◽  
A Value ◽  
Dutch Health ◽  
Short Time ◽  
Regulated Competition ◽  
Made In

Valuation studies addresses how values are made in valuation practices. A next - or rather previous - question becomes: what then makes valuation practices? Two oppositional replies are starting to dominate how that question can be answered: a more materially oriented focus on devices of valuation and a more sociologically inclined focus on ineffable valuation cultures. The debate between proponents of both approaches may easily turn into the kind of leapfrog debates that have dominated many previous discussions on whether culture or materiality would play a decisive role in driving history. This paper explores a less repetitive reply. It does so by analyzing the puzzling case of the demise of solidarity as a core value within the recent Dutch health care system of regulated competition. While “solidarity among the insured” was both a strong cultural value within the Dutch welfare-based health system, and a value that was built into market devices by health economists, within a fairly short time “fairness” became of lesser importance than “competition”. This makes us call for a more historical, relational, and dynamic understanding of the role of economists, market devices, and of culture in valuation studies.

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