scholarly journals Multiple states for flow through a collapsible tube with discontinuities

2014 ◽  
Vol 761 ◽  
pp. 105-122 ◽  
Author(s):  
A. Siviglia ◽  
M. Toffolon
Keyword(s):  
Past History ◽  
Steady State Solution ◽  
External Pressure ◽  
The Other ◽  
Critical Conditions ◽  
Actual State ◽  
Collapsible Tube ◽  
Set Up ◽  
Parameter Values ◽  
Flow States

AbstractWe study the occurrence of the multiple steady states that flows in a collapsible tube can develop under the effect of: (i) geometrical alterations (e.g. stenosis), (ii) variations of the mechanical properties of the tube wall, or (iii) variations of the external pressure acting on the conduit. Specifically, if the approaching flow is supercritical, two steady flow states are possible in a restricted region of the parameter space: one of these flow states is wholly supercritical while the other produces an elastic jump that is located upstream of the variation. In the latter case the flow undergoes a transition through critical conditions in the modified segment of the conduit. Both states being possible, the actual state is determined by the past history of the system, and the parameter values show a hysteretic behaviour when shifting from one state to the other. First we set up the problem in a theoretical framework assuming stationary conditions, and then we analyse the dynamics numerically in a one-dimensional framework. Theoretical considerations suggest that the existence of multiple states is associated with non-uniqueness of the steady-state solution, which is confirmed by numerical simulations of the fully unsteady problem.

Longitudinal Tension Variation in Collapsible Channels: A New Mechanism for the Breakdown of Steady Flow

1992 ◽  
Vol 114 (1) ◽  
pp. 60-67 ◽  
Author(s):  
T. J. Pedley
Keyword(s):  
Unsteady Motion ◽  
External Pressure ◽  
Collapsible Tube ◽  
Initial Tension ◽  
Viscous Shear Stress ◽  
Flow Reynolds Number ◽  
Viscous Shear ◽  
Upstream Part ◽  
Longitudinal Tension ◽  
Parameter Values

There are several mechanisms potentially involved in the breakdown of steady fluid flow in a collapsible tube under external pressure. Here we investigate one that has received little attention in the past: the fact that the longitudinal tension in the tube wall, T, decreases with distance downstream as a consequence of the viscous shear stress exerted by the fluid. If the tube is long enough, or the initial tension small enough, T may fall to zero before the end of the collapsible tube, and unsteady motion would presumably then ensue; this is what we mean by “breakdown.” We study the phenomenon theoretically, when the flow Reynolds number is of order one, using lubrication theory in a symmetric two-dimensional channel in which the collapsible tube is replaced by membranes occupying a segment of each wall. The resulting nonlinear ordinary differential equations are solved numerically for values of the dimensionless parameters that cover all the qualitatively different types of solution (e.g., in which the channel is distended over all its length, collapsed over all its length, or distended in the upstream part and collapsed downstream). Reducing the longitudinal tension has a marked effect on the shape of the collapsible segment, causing it to become much more deformed for the same flow rate and external pressure. Indeed, the wall slope is predicted to become very large when the downstream tension is very small, so the model is not self-consistent then. Nevertheless, the parameter values for which T becomes zero are mapped out and are expected to be qualitatively useful. The relationships between the values of T during flow and its value before the flow begins is also considered.

scholarly journals A mathematical investigation of different growth rates in simultaneous tumors at two distant sites

2021 ◽  
Author(s):  
Farjana Aktar
Keyword(s):  
Mathematical Model ◽  
Growth Rate ◽  
Simulated Annealing Algorithm ◽  
The Other ◽  
Sensitivity Analyses ◽  
Small Tumour ◽  
System A ◽  
Set Up ◽  
Parameter Values ◽  
The Mathematical Model

Experimental data demonstrates that simultaneous injection of cancer cells at two distinct sites often results in one large and one small tumour. Unbalanced tumour-stimulating inflammation is hypothesized to be the cause of this growth rate separation, causing one tumour to grow faster than the other. Here, a mathematical model for immune recruitment and competition between two cancer sites is developed to explore the role of tumour-promoting inflammation in the observed growth rate separation. Due to the experimental set-up, immune predation may be neglected, focusing the model on tumour-promoting immune actions. A new mathematical model with localized immune recruitment and competition between the two cancer sites is developed using a multi-compartment ODE system. A simulated annealing algorithm is used to fit the model to control data (one tumour burden). Stability and parameter sensitivity analyses are used to explore the mathematical model and parameter space. Next, the two-tumour scenario is predicted by testing parameter values tied to possible biological mechanisms of action. The model predicts that indeed inflammation may be a contributor to growth rate separation observed in simultaneous tumour growth, if one site is pre-inflamed compared to the other.

scholarly journals A mathematical investigation of different growth rates in simultaneous tumors at two distant sites

2021 ◽  
Author(s):  
Farjana Aktar
Keyword(s):  
Mathematical Model ◽  
Growth Rate ◽  
Simulated Annealing Algorithm ◽  
The Other ◽  
Sensitivity Analyses ◽  
Small Tumour ◽  
System A ◽  
Set Up ◽  
Parameter Values ◽  
The Mathematical Model

Experimental data demonstrates that simultaneous injection of cancer cells at two distinct sites often results in one large and one small tumour. Unbalanced tumour-stimulating inflammation is hypothesized to be the cause of this growth rate separation, causing one tumour to grow faster than the other. Here, a mathematical model for immune recruitment and competition between two cancer sites is developed to explore the role of tumour-promoting inflammation in the observed growth rate separation. Due to the experimental set-up, immune predation may be neglected, focusing the model on tumour-promoting immune actions. A new mathematical model with localized immune recruitment and competition between the two cancer sites is developed using a multi-compartment ODE system. A simulated annealing algorithm is used to fit the model to control data (one tumour burden). Stability and parameter sensitivity analyses are used to explore the mathematical model and parameter space. Next, the two-tumour scenario is predicted by testing parameter values tied to possible biological mechanisms of action. The model predicts that indeed inflammation may be a contributor to growth rate separation observed in simultaneous tumour growth, if one site is pre-inflamed compared to the other.

Doctrine and Dialectic in Plato’s Dialogues

2018 ◽  
Author(s):  
Rachana Kamtekar
Keyword(s):  
Methodological Approach ◽  
The Other ◽  
Set Up

Chapter 1 lays out the methodological approach employed throughout the book, which is to pay attention to the dialectical dependence of what the main speaker in the dialogue says on the intellectual problem(s) set up in the dialogue both by himself and the other speakers. To illustrate, Chapter 1 describes Socrates’ use of the method of hypotheses from the Meno and Phaedo to answer questions that go beyond his claims to knowledge in the Republic.

scholarly journals Preparation of alcohol-based handrub in COVID-19 Alsatian cluster

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Elodie Di-Falco ◽  
Johan Bourbon ◽  
Isalyne Sbaffe ◽  
Jean-Daniel Kaiser
Keyword(s):  
Critical Period ◽  
Hospital Management ◽  
Management Team ◽  
The Other ◽  
Packaging Materials ◽  
Local Production ◽  
Technical Grade ◽  
Hand Sanitizer ◽  
Set Up ◽  
Real Challenge

AbstractAlsace, in particular Haut-Rhin, is one of the main clusters of COVID-19 in France. There has been a shortage of essential supplies in the area, especially alcohol-based hand sanitizer. In this context, and in accordance with the decree dated March 6, 2020, our hospital management team asked us to start local production of alcohol-based handrub. This was a real challenge: In one week, we had to implement the production of handrub to meet the needs of a 1,400-bed hospital. The production had to comply with the French preparation guidelines and take place on specific premises, with qualified and calibrated equipment, by qualified staff, under the supervision of a pharmacist. The other big challenge we faced was the supply of pharmaceutical raw and packaging materials. During this particular critical period, all suppliers were out of stock. Here, we describe the organizational set-up and the decisions made, e. g., to use technical-grade ethanol before the publication of the decrees dated March 13 and March 23, 2020.

scholarly journals Two Remarks on Blackwell's Theorem

2008 ◽  
Vol 45 (02) ◽  
pp. 580-586 ◽  
Author(s):  
Ehud Lehrer ◽  
Eran Shmaya
Keyword(s):  
Decision Maker ◽  
Information Structure ◽  
Decision Problem ◽  
Partial Information ◽  
The Other ◽  
Actual State ◽  
Information Structures ◽  
Comparison Of Experiments ◽  
Classical Characterization ◽  
Blackwell's Theorem

In a decision problem with uncertainty a decision maker receives partial information about the actual state via an information structure. After receiving a signal, he is allowed to withdraw and gets zero profit. We say that one structure is better than another when a withdrawal option exists if it may never happen that one structure guarantees a positive profit while the other structure guarantees only zero profit. This order between information structures is characterized in terms that are different from those used by Blackwell's comparison of experiments. We also treat the case of a malevolent nature that chooses a state in an adverse manner. It turns out that Blackwell's classical characterization also holds in this case.

scholarly journals Astronomy to understand a human environment

1998 ◽  
Vol 162 ◽  
pp. 211-213
Author(s):  
S. Isobe
Keyword(s):  
School System ◽  
Environmental Science ◽  
The Other ◽  
Human Environment ◽  
Science Courses ◽  
The Public ◽  
Global Environmental Problems ◽  
Global Environmental ◽  
Set Up ◽  
School Period

Astronomy is an important science in understanding a human environment. However, it is thought by most politicians, economists, and members of the public that astronomy is a pure science having no contribution to daily human activities except a few matters relating to time. The Japanese government is studying a reorganisation of our school system to have 5 school days per week, instead of 6 days per week, and this July its committee made a recommendation to reduce school hours for science and set up new courses for practical computers and environmental science. I currently made a proposal. It is very difficult for most of the school pupils, who will have non-scientific jobs, to understand science courses currently taught in school, because each science is taught independently from the other sciences. Therefore, their knowledge of sciences obtained during their school period does not greatly help their understanding of global environmental problems.

scholarly journals An enhanced set of displacement parameter restraints in CRYSTALS

2018 ◽  
Vol 51 (4) ◽  
pp. 1059-1068 ◽  
Author(s):  
Pascal Parois ◽  
James Arnold ◽  
Richard Cooper
Keyword(s):  
Structural Model ◽  
Rigid Bodies ◽  
Model Parameters ◽  
Coordinate Systems ◽  
Principal Axes ◽  
Anisotropic Displacement Parameters ◽  
Set Up ◽  
Meaningful Relationships ◽  
Parameter Values ◽  
Total Model

Crystallographic restraints are widely used during refinement of small-molecule and macromolecular crystal structures. They can be especially useful for introducing additional observations and information into structure refinements against low-quality or low-resolution data (e.g. data obtained at high pressure) or to retain physically meaningful parameter values in disordered or unstable refinements. However, despite the fact that the anisotropic displacement parameters (ADPs) often constitute more than half of the total model parameters determined in a structure analysis, there are relatively few useful restraints for them, examples being Hirshfeld rigid-bond restraints, direct equivalence of parameters and SHELXL RIGU-type restraints. Conversely, geometric parameters can be subject to a multitude of restraints (e.g. absolute or relative distance, angle, planarity, chiral volume, and geometric similarity). This article presents a series of new ADP restraints implemented in CRYSTALS [Parois, Cooper & Thompson (2015), Chem. Cent. J. 9, 30] to give more control over ADPs by restraining, in a variety of ways, the directions and magnitudes of the principal axes of the ellipsoids in locally defined coordinate systems. The use of these new ADPs results in more realistic models, as well as a better user experience, through restraints that are more efficient and faster to set up. The use of these restraints is recommended to preserve physically meaningful relationships between displacement parameters in a structural model for rigid bodies, rotationally disordered groups and low-completeness data.

Motion of slender bodies in unsteady Stokes flow

2011 ◽  
Vol 688 ◽  
pp. 66-87 ◽  
Author(s):  
Efrath Barta
Keyword(s):  
Stokes Flow ◽  
Slenderness Ratio ◽  
Creeping Flow ◽  
Slender Body Theory ◽  
Wide Range ◽  
Unsteady Stokes Flow ◽  
Slender Bodies ◽  
Set Up ◽  
Micro Organisms ◽  
Parameter Values

AbstractThe flow regime in the vicinity of oscillatory slender bodies, either an isolated one or a row of many bodies, immersed in viscous fluid (i.e. under creeping flow conditions) is studied. Applying the slender-body theory by distributing proper singularities on the bodies’ major axes yields reasonably accurate and easily computed solutions. The effect of the oscillations is revealed by comparisons with known Stokes flow solutions and is found to be most significant for motion along the normal direction. Streamline patterns associated with motion of a single body are characterized by formation and evolution of eddies. The motion of adjacent bodies results, with a reduction or an increase of the drag force exerted by each body depending on the direction of motion and the specific geometrical set-up. This dependence is demonstrated by parametric results for frequency of oscillations, number of bodies, their slenderness ratio and the spacing between them. Our method, being valid for a wide range of parameter values and for densely packed arrays of rods, enables simulation of realistic flapping of bristled wings of some tiny insects and of locomotion of flagella and ciliated micro-organisms, and might serve as an efficient tool in the design of minuscule vehicles. Its potency is demonstrated by a solution for the flapping of thrips.

Statics Analysis of the Mechanical Model of Nucleosome

2011 ◽  
Vol 343-344 ◽  
pp. 661-667 ◽  
Author(s):  
Yun Xue ◽  
De Wei Weng ◽  
Gang Ming Gong
Keyword(s):  
Mechanical Model ◽  
The Other ◽  
Elastic Rod ◽  
Equilibrium Equations ◽  
Constraint Force ◽  
Precession Angle ◽  
Nutation Angle ◽  
Analytic Expression ◽  
Set Up ◽  
Calculated Analysis

Mechanical model of nucleoside and its equilibrium equations are set up, and the mechanical properties on the equilibrium position are analyzed. In the case constraint force and electrostatic attraction between cylinder OH and elastic rod are balanced, the analytic expression of nutation angle of the section and its conditions of existence are given. It is show that the cylinder OH can maintain equilibrium at any range of the precession angle. In the other case when unbanced, there is phenomenon of separation of elastic rod from cylinder OH in the spiral wound 2 circles, and numerical solution of the precession angle at separation points are calculated. Analysis of equilibrium of cylinder H1 illustrates that the generatrix of cylinder H1 and OH are not parallel, and the angle between them is obtained

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