Experimental study of the stability and dynamics of a two-dimensional ideal vortex under external strain

2018 ◽  
Vol 848 ◽  
pp. 256-287 ◽  
Author(s):  
N. C. Hurst ◽  
J. R. Danielson ◽  
D. H. E. Dubin ◽  
C. M. Surko
Keyword(s):  
Ideal Fluid ◽  
Experimental Studies ◽  
Quantitative Agreement ◽  
Two Dimensions ◽  
Global Dynamics ◽  
Two Dimensional ◽  
Plasma Dynamics ◽  
Electron Plasmas ◽  
Precise Control ◽  
The Stability

The dynamics of two-dimensional (2-D) ideal fluid vortices is studied experimentally in the presence of an irrotational strain flow. Laboratory experiments are conducted using strongly magnetized pure electron plasmas, a technique which is made possible by the isomorphism between the drift–Poisson equations describing plasma dynamics transverse to the field and the 2-D Euler equations describing an ideal fluid. The electron plasma system provides an excellent opportunity to study the dynamics of a 2-D Euler fluid due to weak dissipation and weak 3-D effects, simple diagnosis and precise control. The plasma confinement apparatus used here was designed specifically to study vortex dynamics under the influence of external flow by applying boundary conditions in two dimensions. Additionally, vortex-in-cell simulations are carried out to complement the experimental results and to extend the parameter range of the studies. It is shown that the global dynamics of a quasi-flat vorticity profile is in good quantitative agreement with the theory of a piecewise-constant elliptical patch of vorticity, including the equilibria, dynamical orbits and stability properties. Deviations from the elliptical patch theory are observed for non-flat vorticity profiles; they include inviscid damping of the orbits and modified stability limits. The dependence of these phenomena on the flatness of the initial profile is discussed. The relationship of these results to other theoretical, numerical and experimental studies is also discussed.

Improving the Computational Efficiency of Stability Prediction in Milling Employing the Two-Dimensional Bisection Method

2016 ◽  
Author(s):  
Yakun Xie ◽  
Xiaojian Zhang ◽  
Sijie Yan ◽  
Han Ding
Keyword(s):  
Computational Efficiency ◽  
Computation Time ◽  
Stability Diagram ◽  
Two Dimensions ◽  
Bisection Method ◽  
Two Dimensional ◽  
Stability Prediction ◽  
Stability Calculation ◽  
The Stability ◽  
Analytical Time

This paper presents an effective method to improve the computational efficiency of stability prediction in milling based on the two-dimensional bisection method. Contrasted with the traditional semi-analytical time-domain methods, the proposed method for stability prediction only checks the eigenvalues of less nodes on the parameter plane with the two-dimensional bisection method, so that, the computational efficiency of stability can be improved. The novel method for milling stability calculation is comprised of the bisection method in two dimensions and the numerical integration method [NIM], its validity is testified by the comparison of the stability diagram and computation time in contrast to the NIM. The computation demonstrates that the calculated stability diagram by using the presented method agrees well with the result of NIM, while the computation time of the stability diagram can reduce to 1/4 to 3/4 compared with the original methods.

scholarly journals A two-dimensional propensity score matching method for longitudinal quasi-experimental studies: A focus on travel behavior and the built environment

2020 ◽  
pp. 239980832098230
Author(s):  
Haotian Zhong ◽  
Wei Li ◽  
Marlon G Boarnet
Keyword(s):  
Propensity Score ◽  
Built Environment ◽  
Propensity Score Matching ◽  
Treatment Effect ◽  
Travel Behavior ◽  
Experimental Studies ◽  
Two Dimensions ◽  
Superior Performance ◽  
Two Dimensional ◽  
Matching Method

The lack of longitudinal studies of the relationship between the built environment and travel behavior has been widely discussed in the literature. This paper discusses how standard propensity score matching estimators can be extended to enable such studies by pairing observations across two dimensions: longitudinal and cross-sectional. Researchers mimic randomized controlled trials and match observations in both dimensions to find synthetic control groups that are similar to the treatment group and to match subjects across before- and after-treatment periods. We call this a two-dimensional propensity score matching method. This method demonstrates superior performance for improving treatment effect estimation based on Monte Carlo evidence. A near-term opportunity for such matching is identifying the treatment effect of transportation infrastructure on travel behavior.

scholarly journals The effect of pulsation frequency on transition in pulsatile pipe flow

2018 ◽  
Vol 857 ◽  
pp. 937-951 ◽  
Author(s):  
Duo Xu ◽  
Marc Avila
Keyword(s):  
Pipe Flow ◽  
Experimental Studies ◽  
Quantitative Agreement ◽  
Transition To Turbulence ◽  
Pulsation Frequency ◽  
Pipe Length ◽  
Pulsation Amplitude ◽  
Frequency Regime ◽  
Pulsatile Flows ◽  
The Stability

Pulsatile flows are common in nature and in applications, but their stability and transition to turbulence are still poorly understood. Even in the simple case of pipe flow subject to harmonic pulsation, there is no consensus among experimental studies on whether pulsation delays or enhances transition. We here report direct numerical simulations of pulsatile pipe flow at low pulsation amplitude$A\leqslant 0.4$. We use a spatially localized impulsive disturbance to generate a single turbulent puff and track its dynamics as it travels downstream. The computed relaminarization statistics are in quantitative agreement with the experiments of Xuet al. (J. Fluid Mech., vol. 831, 2017, pp. 418–432) and support the conclusion that increasing the pulsation amplitude and lowering the frequency enhance the stability of the flow. In the high-frequency regime, the behaviour of steady pipe flow is recovered. In addition, we show that, when the pipe length does not permit the observation of a full cycle, a reduction of the transition threshold is observed. We obtain an equation quantifying this effect and compare it favourably with the measurements of Stettler & Hussain (J. Fluid Mech., vol. 170, 1986, pp. 169–197). Our results resolve previous discrepancies, which are due to different pipe lengths, perturbation methods and criteria chosen to quantify transition in experiments.

scholarly journals Unifying description of competing orders in two-dimensional quantum magnets

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Xue-Yang Song ◽  
Chong Wang ◽  
Ashvin Vishwanath ◽  
Yin-Chen He
Keyword(s):  
Quantum Electrodynamics ◽  
Spatial Dimension ◽  
Magnetic Monopoles ◽  
Two Dimensions ◽  
Dirac Fermions ◽  
Two Dimensional ◽  
Quantum Magnets ◽  
Two Dimensional Materials ◽  
Ordered Phases ◽  
The Stability

Abstract Quantum magnets provide the simplest example of strongly interacting quantum matter, yet they continue to resist a comprehensive understanding above one spatial dimension. We explore a promising framework in two dimensions, the Dirac spin liquid (DSL) — quantum electrodynamics (QED3) with 4 Dirac fermions coupled to photons. Importantly, its excitations include magnetic monopoles that drive confinement. We address previously open key questions — the symmetry actions on monopoles on square, honeycomb, triangular and kagome lattices. The stability of the DSL is enhanced on triangular and kagome lattices compared to bipartite (square and honeycomb) lattices. We obtain the universal signatures of the DSL on triangular and kagome lattices, including those of monopole excitations, as a guide to numerics and experiments on existing materials. Even when unstable, the DSL helps unify and organize the plethora of ordered phases in correlated two-dimensional materials.

Granular hydrodynamics and pattern formation in vertically oscillated granular disk layers

2008 ◽  
Vol 597 ◽  
pp. 119-144 ◽  
Author(s):  
JOSÉ A. CARRILLO ◽  
THORSTEN PÖSCHEL ◽  
CLARA SALUEÑA
Keyword(s):  
Numerical Scheme ◽  
Granular Flows ◽  
Quantitative Agreement ◽  
Vertical Vibration ◽  
Two Dimensions ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Faraday Waves ◽  
Periodic Patterns ◽  
Hydrodynamic Description

The goal of this study is to demonstrate numerically that certain hydrodynamic systems, derived from inelastic kinetic theory, give fairly good descriptions of rapid granular flows even if they are way beyond their supposed validity limits. A numerical hydrodynamic solver is presented for a vibrated granular bed in two dimensions. It is based on a highly accurate shock capturing state-of-the-art numerical scheme applied to a compressible Navier–Stokes system for granular flow. The hydrodynamic simulation of granular flows is challenging, particularly in systems where dilute and dense regions occur at the same time and interact with each other. As a benchmark experiment, we investigate the formation of Faraday waves in a two-dimensional thin layer exposed to vertical vibration in the presence of gravity. The results of the hydrodynamic simulations are compared with those of event-driven molecular dynamics and the overall quantitative agreement is good at the level of the formation and structure of periodic patterns. The accurate numerical scheme for the hydrodynamic description improves the reproduction of the primary onset of patterns compared to previous literature. To our knowledge, these are the first hydrodynamic results for Faraday waves in two-dimensional granular beds that accurately predict the wavelengths of the two-dimensional standing waves as a function of the perturbation's amplitude. Movies are available with the online version of the paper.

MANY-ELECTRON SCREENING EFFECT ON THE STABILITY CRITERIA OF AN ALL-COUPLING OPTICAL BIPOLARON IN TWO DIMENSIONS

1993 ◽  
Vol 07 (16) ◽  
pp. 1071-1081 ◽  
Author(s):  
ASHOK CHATTERJEE ◽  
SHREEKANTHA SIL
Keyword(s):  
Effective Mass ◽  
Carrier Concentration ◽  
Variational Calculation ◽  
Two Dimensions ◽  
Electron Screening ◽  
Two Dimensional ◽  
Stability Criteria ◽  
Screening Effect ◽  
The Stability ◽  
The Many

We perform an all-coupling variational calculation to study the many-electron screening effect on the stability criteria of a two-dimensional singlet optical bipolaron. We also show how the effective mass and the size of the bipolaron would depend on the carrier concentration.

Polymers on a Random Liquid Surface

1989 ◽  
Vol 177 ◽  
Author(s):  
Bertrand Duplantier
Keyword(s):  
Surface Tension ◽  
Critical Exponents ◽  
Degrees Of Freedom ◽  
Liquid Membrane ◽  
Theoretical Study ◽  
Liquid Surface ◽  
Experimental Studies ◽  
Two Dimensions ◽  
Two Dimensional ◽  
Universal Values

ABSTRACTWe report a recent theoretical study of polymers moving on a random two-dimensional fluid surface. The metric of the liquid membrane is free to fluctuate and these new degrees of freedom couple to those of the polymers - as a result, the critical exponents describing the polymers are changed, but are nevertheless related to those in two dimensions. The relation to possible experimental studies on membranes with vanishing surface tension, which should search for new universal values of exponents u and 7, is discussed.

Quantitative Diameter Measurements of Chromatin and TMV Fibers in the Freeze-Dried State

1988 ◽  
Vol 46 ◽  
pp. 170-171
Author(s):  
B. D. Athey ◽  
A. L. Stout ◽  
M. F. Smith ◽  
J. P. Langmore
Keyword(s):  
Reliable Method ◽  
Fiber Diameter ◽  
Quantitative Agreement ◽  
One Dimension ◽  
Fiber Axis ◽  
Two Dimensional ◽  
Fiber Density ◽  
Variable Diameter ◽  
Freeze Dried ◽  
Expected Values

Although there is general agreement that Inactive chromosome fibers consist of helically packed nucleosomes, the pattern of packing is still undetermined. Only one of the proposed models, the crossed-linker model, predicts a variable diameter dependent on the length of DNA between nucleosomes. Measurements of the fiber diameter of negatively-stained and frozen- hydrated- chromatin from Thyone sperm (87bp linker) and Necturus erythrocytes (48bp linker) have been previously reported from this laboratory. We now introduce a more reliable method of measuring the diameters of electron images of fibrous objects. The procedure uses a modified version of the computer program TOTAL, which takes a two-dimensional projection of the fiber density (represented by the micrograph itself) and projects it down the fiber axis onto one dimension. We illustrate this method using high contrast, in-focus STEM images of TMV and chromatin from Thyone and Necturus. The measured diameters are in quantitative agreement with the expected values for the crossed-linker model for chromatin structure

The “Big Two” in Political Communication

2013 ◽  
Vol 44 (2) ◽  
pp. 117-128 ◽  
Author(s):  
Mauro Bertolotti ◽  
Patrizia Catellani ◽  
Karen M. Douglas ◽  
Robbie M. Sutton
Keyword(s):  
Political Communication ◽  
Experimental Studies ◽  
Two Dimensions ◽  
Political Sophistication

In two experimental studies (conducted in Britain and Italy), participants read about a politician answering to leadership- versus morality-related allegations using either downward counterfactuals (“things could have been worse, if ...”) or upward counterfactuals (“things could have been better, if ...”). Downward messages increased the perception of the politician’s leadership, while both downward and upward messages increased morality perception. Political sophistication moderated the effect of message direction, with downward messages increasing perceived morality in low sophisticates and upward messages increasing perceived morality in high sophisticates. In the latter group, the acknowledgment of an intent to take responsibility mediated morality judgment. Results were consistent across different countries, highlighting previously unexplored effects of communication on the perception of the “Big Two” dimensions.

Urbanicity, City Delegations, and Two-Dimensional Liberalism

2018 ◽  
Author(s):  
Thomas K. Ogorzalek
Keyword(s):  
National Level ◽  
Two Dimensions ◽  
Political Order ◽  
Two Dimensional ◽  
Local Institutions ◽  
Horizontal Integration ◽  
National Politics ◽  
United Front ◽  
Strategies For Success

This theoretical chapter develops the argument that the conditions of cities—large, densely populated, heterogeneous communities—generate distinctive governance demands supporting (1) market interventions and (2) group pluralism. Together, these positions constitute the two dimensions of progressive liberalism. Because of the nature of federalism, such policies are often best pursued at higher levels of government, which means that cities must present a united front in support of city-friendly politics. Such unity is far from assured on the national level, however, because of deep divisions between and within cities that undermine cohesive representation. Strategies for success are enhanced by local institutions of horizontal integration developed to address the governance demands of urbanicity, the effects of which are felt both locally and nationally in the development of cohesive city delegations and a unified urban political order capable of contending with other interests and geographical constituencies in national politics.

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