scholarly journals The impact of a local perturbation on global properties of a turbulent wake

2009 ◽  
Vol 21 (7) ◽  
pp. 071701 ◽  
Author(s):  
Vladimir Parezanović ◽  
Olivier Cadot
Keyword(s):  
Turbulent Wake ◽  
Local Perturbation ◽  
Global Properties ◽  
The Impact

Experimental sensitivity analysis of the global properties of a two-dimensional turbulent wake

2012 ◽  
Vol 693 ◽  
pp. 115-149 ◽  
Author(s):  
Vladimir Parezanović ◽  
Olivier Cadot
Keyword(s):  
Turbulent Wake ◽  
Base Pressure ◽  
Recirculation Region ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Recirculation Bubble ◽  
Global Properties ◽  
Bubble Length ◽  
The Impact ◽  
Control Cylinder

AbstractThe sensitivity of the global properties of a two-dimensional turbulent wake produced by the separated flow of a ‘D’-shaped cylinder at $\mathit{Re}= 13\hspace{0.167em} 000$ is investigated experimentally using a small circular control cylinder as a local disturbance. The height of the main cylinder is $D= 25~\mathrm{mm} $ and control cylinders are of diameters $d= 0. 04D$ and $d= 0. 12D$, the former being smaller than the shear layer thickness detaching from the main cylinder, while the latter is larger. In both cases, the control cylinder is able to modify the global frequency, base pressure and spanwise velocity correlation. The results are presented as sensitivity maps. Reynolds stresses spatial structure and the recirculation bubble length are examined in detail when the control cylinder is displaced vertically across the wake at a fixed downstream location. It is found that the increase of the recirculation bubble length is accompanied by a damping of Reynolds stresses with a downstream shift of their spatial structures together with the base pressure increase. The global frequency can be either decreased or increased independently of the bubble length modification. The sensitivity of these global properties is interpreted on the basis of the ability of the control cylinder to change the size of the formation region of the Kármán vortex street by interacting with the primary detached shear layers. The corresponding physical mechanisms are discussed. The impact of a two-dimensional control cylinder on the three-dimensional properties of the wake is examined through spanwise correlation. This is found to be improved whenever the control cylinder is placed inside the recirculation region of the main cylinder wake.

Ancient Bug Bites on Ancient Plants Record Forest Ecosystem Response to Environmental Perturbations

2013 ◽  
Vol 19 ◽  
pp. 157-174 ◽  
Author(s):  
Ellen D. Currano
Keyword(s):  
Trophic Interactions ◽  
Insect Herbivory ◽  
Fossil Flora ◽  
Local Perturbation ◽  
Insect Damage ◽  
Ecosystem Response ◽  
Insect Feeding ◽  
First Case ◽  
The Impact

Leaf-compression fossils with insect feeding traces are unique in providing rich, direct evidence of two levels in a fossil food web. Plant-insect associations dominate terrestrial trophic interactions, emphasizing the need to understand their ecological and evolutionary history. This paper first discusses methods of recognizing insect herbivore damage on fossil leaves and quantifying fossil insect herbivory. By conducting an unbiased insect damage census, damage frequency (percent of leaves with insect feeding damage), percent of leaf surface area removed by insects, and damage diversity (the number of discrete damage morphotypes, or DTs, found on a fossil flora or individual host plant) can all be measured. Three examples of responses of past plant-insect trophic interactions to environmental stresses are examined. In the first case study, late Oligocene fossil floras from Ethiopia document forest response to local perturbation and key characteristics to recognize disturbance in the plant fossil record. The second case study considers the terrestrial ecosystem response to the catastrophic global perturbation at the Cretaceous–Paleogene boundary. In the third case study, the impact of past global warming events—including the Paleocene–Eocene Thermal Maximum—on insect herbivory is discussed. Productive avenues for further research include: insect damage studies conducted outside the North American Cretaceous and Paleogene, actualistic and taphonomic studies of insect herbivory, and tighter collaboration across paleobotany, paleoentomology, botany, and entomology.

Sensitivity and Robustness of Hydrodynamic Mooring Models

2002 ◽  
Vol 124 (4) ◽  
pp. 179-189 ◽  
Author(s):  
Joa˜o Paulo J. Matsuura ◽  
Michael M. Bernitsas ◽  
Luis O. Garza-Rios ◽  
Kazuo Nishimoto
Keyword(s):  
Design Methodology ◽  
Higher Order ◽  
Systematic Change ◽  
Mooring System ◽  
University Of Michigan ◽  
First Order ◽  
Global Properties ◽  
Higher Order Terms ◽  
The University ◽  
The Impact

Various hydrodynamic maneuvering models are available for modeling the slow motion horizontal plane dynamics of mooring and towing systems. In previous work, we compared four representative and widely used maneuvering models and assessed them based on the design methodology for mooring systems developed at the University of Michigan. In this paper, we study the impact of experimental uncertainties in the maneuvering coefficients on mooring system dynamic analysis. Uncertainties in higher order coefficients may even result in sign change as measured by different experimental facilities. This may indicate lack of robustness in maneuvering modeling. In our recent work, maneuvering models were classified in two schools of thought, each having a different set of coefficients subject to uncertainties. The first school is represented by the Abkowitz (A-M) and the Takashina (T-M) models, and the second by the Obokata (O-M) and the Short Wing (SW-M) models. The design methodology developed at the University of Michigan uses time independent global properties of mooring system dynamics to compare the maneuvering models, and assess their sensitivity and robustness. Equilibria, bifurcation sequences and associated morphogeneses, singularities of bifurcations, and secondary equilibrium paths are such global properties. Systematic change of important coefficients in each model shows that, for both schools of thought, sensitivity to first order terms is high while sensitivity to higher order terms is low. Accuracy in measurement of first order terms is high while accuracy in measurement of higher order terms is low. These two tendencies reduce each other’s impact, providing acceptable robustness.

GLOBAL PROPERTIES OF BIOMIMETIC MEMBRANES: PERSPECTIVES ON MOLECULAR FEATURES

2006 ◽  
Vol 01 (01) ◽  
pp. 57-84 ◽  
Author(s):  
GEORG PABST
Keyword(s):  
Molecular Level ◽  
Local Perturbation ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Analysis Techniques ◽  
Biomimetic Membranes ◽  
Molecular Features ◽  
Global Properties ◽  
Complementary Techniques ◽  
Dynamic Scattering

Global properties of biological model membranes such as, e.g., structure or elasticity, are known to be closely related to their local features. If a membrane active compound interacts with the membrane assembly, the membrane will primarily be affected on the local, molecular level. The local perturbation may than, through some coupling, translate into a global adjustment of the membrane. In order to address this coupling x-ray and neutron diffraction data analysis techniques have been developed that allow accurate monitoring of changes in global properties. This offers new perspectives on molecular membrane features that in combination with complementary techniques, such as differential scanning calorimetry, spectroscopy or dynamic scattering lead to a better understanding of biomimetic membranes. The present article reviews these aspects giving application examples for single- and multicomponent membranes, respectively.

scholarly journals Impact of magnetic activity on inferred stellar properties of main-sequence Sun-like stars

2021 ◽  
Vol 502 (4) ◽  
pp. 5808-5820
Author(s):  
Alexandra E L Thomas ◽  
William J Chaplin ◽  
Sarbani Basu ◽  
Ben Rendle ◽  
Guy Davies ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Frequency Separation ◽  
Near Surface ◽  
Global Properties ◽  
Modelling Analysis ◽  
Inclination Angles ◽  
Stellar Properties ◽  
Oscillation Frequencies ◽  
Frequency Ratios ◽  
The Impact

ABSTRACT The oscillation frequencies observed in Sun-like stars are susceptible to being shifted by magnetic activity effects. The measured shifts depend on a complex relationship involving the mode type, the field strength, and spatial distribution of activity, as well as the inclination angle of the star. Evidence of these shifts is also present in frequency separation ratios that are often used when inferring global properties of stars in order to avoid surface effects. However, one assumption when using frequency ratios for this purpose is that there are no near-surface perturbations that are non-spherically symmetric. In this work, we studied the impact on inferred stellar properties when using frequency ratios that are influenced by non-homogeneous activity distributions. We generate several sets of artificial oscillation frequencies with various amounts of shift and determine stellar properties using two separate pipelines. We find that for asteroseismic observations of Sun-like targets we can expect magnetic activity to affect mode frequencies that will bias the results from stellar modelling analysis. Although for most stellar properties this offset should be small, typically less than 0.5 per cent in mass, estimates of age and central hydrogen content can have an error of up to 5 per cent and 3 per cent, respectively. We expect a larger frequency shift and therefore larger bias for more active stars. We also warn that for stars with very high or low inclination angles, the response of modes to activity is more easily observable in the separation ratios and hence will incur a larger bias.

scholarly journals Inferring the Hidden Cascade Infection over Erdös-Rényi (ER) Random Graph

Electronics ◽  
2021 ◽  
Vol 10 (16) ◽  
pp. 1894
Author(s):  
Jaeyoung Choi
Keyword(s):  
Random Graph ◽  
Control Strategies ◽  
Effective Control ◽  
Recovery Algorithm ◽  
Global Properties ◽  
Diffusion Dynamics ◽  
Partially Observed ◽  
Underlying Network ◽  
The Impact ◽  
Recovery Problem

Finding hidden infected nodes is extremely important when information or diseases spread rapidly in a network because hints regarding the global properties of the diffusion dynamics can be provided, and effective control strategies for mitigating such spread can be derived. In this study, to understand the impact of the structure of the underlying network, a cascade infection-recovery problem is considered over an Erdös-Rényi (ER) random graph when a subset of infected nodes is partially observed. The goal is to reconstruct the underlying cascade that is likely to generate these observations. To address this, two algorithms are proposed: (i) a Neighbor-based recovery algorithm (NBRA(α)), where 0≤α≤1 is a control parameter, and (ii) a BFS tree-source-based recovery algorithm (BSRA). The first one simply counts the number of infected neighbors for candidate hidden cascade nodes and computes the possibility of infection from the neighbors by controlling the parameter α. The latter estimates the cascade sources first and computes the infection probability from the sources. A BFS tree approximation is used for the underlying ER random graph with respect to the sources for computing the infection probability because of the computational complexity in general loopy graphs. We then conducted various simulations to obtain the recovery performance of the two proposed algorithms. As a result, although the NBRA(α) uses only local information of the neighboring infection status, it recovers the hidden cascade infection well and is not significantly affected by the average degree of the ER random graph, whereas the BSRA works well on a local tree-like structure.

scholarly journals The Impact of Turbulence on Physics of the Geomagnetic Tail

2021 ◽  
Vol 8 ◽  
Author(s):  
Elizaveta E. Antonova ◽  
Marina V. Stepanova
Keyword(s):  
Data Analysis ◽  
Plasma Sheet ◽  
Large Scale ◽  
Turbulent Transport ◽  
Turbulent Wake ◽  
Plasma Transport ◽  
Turbulent Fluctuations ◽  
Vast Amount ◽  
Geomagnetic Tail ◽  
The Impact

There is a vast amount of evidence that suggests that the geomagnetic tail is like a turbulent wake behind an obstacle. Large-scale vortices in the wake are able to generate turbulent transport that takes place both along the plasma sheet, in the X and Y directions, and across the plasma sheet, in the Z direction. Thus, turbulent fluctuations in all directions should be taken into consideration when analyzing plasma transport in the plasma sheet, and stability of the plasma sheet configurations. In this review, we summarize and discuss the main results of large and middle scale magnetospheric turbulence yielded by data analysis and modeling. We also identify changes in the description of the magnetospheric dynamics connected with the existence of turbulent fluctuations in the tail.

Asteroseismology: The Impact of Solar Space Observations

1993 ◽  
Vol 137 ◽  
pp. 43-50
Author(s):  
H.S. Hudson
Keyword(s):  
Solar Flares ◽  
Coronal Holes ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Small Bodies ◽  
Solar Observations ◽  
Global Properties ◽  
Stellar Convection ◽  
Technical Report ◽  
The Impact

AbstractObservations from space relevant to solar global properties (oscillations, magnetic activity, etc.) are helpful both scientifically and technically in preparing for stellar observations. This paper summarizes the results from the main previous experiments (ACRIM, SOUP, and IPHIR), and also give an initial technical report from the SXT instrument on board Yohkoh, launched in August 1991. The solar observations to date demonstrate the existence of several mechanisms for low–level variability: spots, faculae, the photospheric network, granulation, and p–mode oscillations. The observations of oscillations have been particularly helpful in setting limits on solar interior rotation. In addition to the solar processes, stars of other types may have different mechanisms of variability. These may include the analogues of coronal holes or solar flares, modes of oscillation not detected in the Sun, collisions with small bodies, duplicity, and probably mechanisms not invented yet but related in interesting ways to stellar convection and magnetism.

scholarly journals New Results on the Magellanic Clouds

1994 ◽  
Vol 161 ◽  
pp. 489-496 ◽  
Author(s):  
D. Hatzidimitriou
Keyword(s):  
Chemical Evolution ◽  
Large Scale ◽  
Magellanic Clouds ◽  
Wide Field ◽  
Spatial Motion ◽  
Field Techniques ◽  
Global Properties ◽  
The Impact

Recent results on global properties of the Magellanic Clouds are reviewed, with particular emphasis on the impact of wide-field techniques on their study. The subjects discussed include large-scale surveys of different tracers of intermediate age and old populations in the Clouds and new data on their chemical evolution, kinematics and spatial motion.

scholarly journals The Intersection of Regional Anesthesia and Cancer Progression: A Theoretical Framework

2020 ◽  
Vol 27 (1) ◽  
pp. 107327482096557
Author(s):  
Aaron R. Muncey ◽  
Sephalie Y. Patel ◽  
Christopher J. Whelan ◽  
Robert S. Ackerman ◽  
Robert A. Gatenby
Keyword(s):  
Inflammatory Response ◽  
Regional Anesthesia ◽  
Cancer Progression ◽  
Surgical Stress ◽  
Volatile Anesthetic ◽  
Theoretical Framework ◽  
Neuraxial Anesthesia ◽  
Local Perturbation ◽  
The Impact

The surgical stress and inflammatory response and volatile anesthetic agents have been shown to promote tumor metastasis in animal and in-vitro studies. Regional neuraxial anesthesia protects against these effects by decreasing the surgical stress and inflammatory response and associated changes in immune function in animals. However, evidence of a similar effect in humans remains equivocal due to the high variability and retrospective nature of clinical studies and difficulty in directly comparing regional versus general anesthesia in humans. We propose a theoretical framework to address the question of regional anesthesia as protective against metastasis. This theoretical construct views the immune system, circulating tumor cells, micrometastases, and inflammatory mediators as distinct populations in a highly connected system. In ecological theory, highly connected populations demonstrate more resilience to local perturbations but are prone to system-wide shifts compared with their poorly connected counterparts. Neuraxial anesthesia transforms the otherwise system-wide perturbations of the surgical stress and inflammatory response and volatile anesthesia into a comparatively local perturbation to which the system is more resilient. We propose this framework for experimental and mathematical models to help determine the impact of anesthetic choice on recurrence and metastasis and create therapeutic strategies to improve cancer outcomes after surgery.

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