Effects of Contact Line Condition on Excitation of Internal Waves Confined by a Cylindrical Wall

2004 ◽  
Author(s):  
Takahiro Ito ◽  
Jun Shimizu ◽  
Hideyuki Nakayama ◽  
Yutaka Kukita
Keyword(s):  
Internal Waves ◽  
Contact Line ◽  
Wave Excitation ◽  
Fluid Interface ◽  
Cylindrical Wall ◽  
Limited Mobility ◽  
The Waves ◽  
Insight Into ◽  
Line Condition ◽  
Do So

Standing internal waves can be excited when fluids overlaid in a stationary enclosure are subjected to harmonic, vertical oscillations. The oscillatory deformation of the fluid-fluid interface near the wall, due to the limited mobility of the fluid-fluid-wall contact line, can play an important role in the excitation of waves. The contact line may or may not move depending on the amplitude of fluid excitation. When it moves, it may do so only in a limited portion of each cycle. We analyze numerically the wave excitation associated with such nonlinear, intermittent motions of the contact line. The analytical results consistently reproduce the experimental results, and give insight into the interactions between the contact line motions and the waves on the interface.

Internal wave excitation from stratified flow over a thin barrier

1998 ◽  
Vol 377 ◽  
pp. 223-252 ◽  
Author(s):  
BRUCE R. SUTHERLAND ◽  
PAUL F. LINDEN
Keyword(s):  
Internal Wave ◽  
Numerical Simulations ◽  
Internal Waves ◽  
Wavelet Transforms ◽  
Large Amplitude ◽  
Internal Gravity Waves ◽  
Wave Excitation ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Waves

We perform laboratory experiments in a recirculating shear flow tank of non-uniform salt-stratified water to examine the excitation of internal gravity waves (IGW) in the wake of a tall, thin vertical barrier. The purpose of this study is to characterize and quantify the coupling between coherent structures shed in the wake and internal waves that radiate from the mixing region into the deep, stationary fluid. In agreement with numerical simulations, large-amplitude internal waves are generated when the mixing region is weakly stratified and the deep fluid is sufficiently strongly stratified. If the mixing region is unstratified, weak but continuous internal wave excitation occurs. In all cases, the tilt of the phase lines of propagating waves lies within a narrow range. Assuming the waves are spanwise uniform, their amplitude in space and time is measured non-intrusively using a recently developed ‘synthetic schlieren’ technique. Using wavelet transforms to measure consistently the width and duration of the observed wavepackets, the Reynolds stress is measured and, in particular, we estimate that when large-amplitude internal wave excitation occurs, approximately 7% of the average momentum across the shear depth and over the extent of the wavepacket is lost due to transport away from the mixing region by the waves.We propose that internal waves may act back upon the mean flow modifying it so that the excitation of waves of that frequency is enhanced. A narrow frequency spectrum of large-amplitude waves is observed because the feedback is largest for waves with phase tilt in a range near 45°. Numerical simulations and analytic theories are presented to further quantify this theory.

Evaluation of Writing Assignments

2017 ◽  
Vol 6 (2) ◽  
pp. 214
Author(s):  
Anita Jokić
Keyword(s):  
Standardized Tests ◽  
Teaching And Learning ◽  
Task Completion ◽  
Writing Assignments ◽  
Listening Skill ◽  
Job Application ◽  
Written Assignments ◽  
Insight Into ◽  
Teacher’S Responsibilities ◽  
Do So

Teaching English as a foreign language is now one of the most important subjects in Croatian secondary schools since English is one of the three obligatory subjects at 'matura' - standardized tests which the seniors need to pass to graduate. Writing is one of the three parts of the EL exam, the other two being listening and reading. When learning a language, students start from listening skill, move on to speaking and reading and finally to most difficult skill to master: writing. Teaching and learning writing faces a lot of challenges since it requires a lot of time to practice and even more to evaluate and monitor progress. Teacher's responsibilities are to regularly provide opportunities to write, encourage students to learn from their mistakes and promote their success. In order to do so, students should be given clear instructions on evaluation/assessment and concise feedback. Since grading written assignments takes up a lot of time, the author proposes rubrics which can be used to assess various types of writing taught at secondary level (description of place/event/person, letters of complaint, job application, invitation, discursive/opinion/for-and-against essay etc.). Author suggests four fixed rubrics and subdivisions: Task completion, Cohesion / coherence, Grammar and Vocabulary. All rubrics and subdivisions are described in the paper. A survey was also conducted on a sample of 140 students and has given an insight into students’ opinion on importance of assessment and feedback and its influence on their progress.

scholarly journals Designing for international law: The architecture of international organizations 1922–1952

2020 ◽  
pp. 1-22
Author(s):  
Miriam Bak McKenna
Keyword(s):  
New York ◽  
International Law ◽  
International Organizations ◽  
International Organization ◽  
International Labour Organization ◽  
The Relationship ◽  
Physical Manifestation ◽  
Insight Into ◽  
Do So

Abstract Situating itself in current debates over the international legal archive, this article delves into the material and conceptual implications of architecture for international law. To do so I trace the architectural developments of international law’s organizational and administrative spaces during the early to mid twentieth century. These architectural endeavours unfolded in three main stages: the years 1922–1926, during which the International Labour Organization (ILO) building, the first building exclusively designed for an international organization was constructed; the years 1927–1937 which saw the great polemic between modernist and classical architects over the building of the Palace of Nations; and the years 1947–1952, with the triumph of modernism, represented by the UN Headquarters in New York. These events provide an illuminating allegorical insight into the physical manifestation, modes of self-expression, and transformation of international law during this era, particularly the relationship between international law and the function and role of international organizations.

Internal waves in a viscous atmosphere

1975 ◽  
Vol 72 (4) ◽  
pp. 773-786 ◽  
Author(s):  
W. L. Chang ◽  
T. N. Stevenson
Keyword(s):  
Energy Source ◽  
Incompressible Fluid ◽  
Internal Waves ◽  
Infinite Number ◽  
Similarity Solution ◽  
Small Amplitude ◽  
Horizontal Plane ◽  
Two Dimensional ◽  
The Waves ◽  
Isothermal Atmosphere

The way in which internal waves change in amplitude as they propagate through an incompressible fluid or an isothermal atmosphere is considered. A similarity solution for the small amplitude isolated viscous internal wave which is generated by a localized two-dimensional disturbance or energy source was given by Thomas & Stevenson (1972). It will be shown how summations or superpositions of this solution may be used to examine the behaviour of groups of internal waves. In particular the paper considers the waves produced by an infinite number of sources distributed in a horizontal plane such that they produce a sinusoidal velocity distribution. The results of this analysis lead to a new small perturbation solution of the linearized equations.

scholarly journals Emancipation from the Whirlwind: Piety and Rebellion among Jewish-American Post-Holocaust and Christian Liberation Readings of Job

2011 ◽  
Vol 2 (2) ◽  
Author(s):  
David C Tollerton
Keyword(s):  
Modern World ◽  
Jewish American ◽  
Political Opposition ◽  
The Bible ◽  
The Holocaust ◽  
Theologically Conservative ◽  
State Of Israel ◽  
Political Radicalism ◽  
Insight Into ◽  
Do So

This article focuses upon the manner in which the Book of Job’s dissonant messages of theological radicalism and conservatism have been utilised within discussion of two specific episodes of innocent suffering in the modern world – the murder of six million Jews during the Holocaust and the suffering of the oppressed in the developing world. Overlaying the discussion, the following model is proposed: that, firstly, Christian liberation theologians emphasise the more theologically conservative messages that can be drawn from Job while asserting radical political opposition to those who possess power. Conversely, Jewish Holocaust theologians empathise with Job’s more theologically radical elements, yet do so within outlooks committed to conservatively maintaining the security and power of the state of Israel after two thousand years of Jewish powerlessness. This model is tested by focusing upon seven treatments of Job associated with liberation or Holocaust theologies. It is concluded that, although there are significant complications, in broad terms the model largely holds ”“ offering a comparative insight into contextual Christian and Jewish interpretations of the Bible in which political radicalism and theological radicalism are found to be at odds with one another.

Attracting Students to Sales Positions: The Case of Effective Salesperson Recruitment Ads

2018 ◽  
Vol 42 (2) ◽  
pp. 170-190 ◽  
Author(s):  
Dawn R. Deeter-Schmelz ◽  
Andrea L. Dixon ◽  
Robert C. Erffmeyer ◽  
Kyoungmi (Kate) Kim ◽  
Raj Agnihotri ◽  
...  
Keyword(s):  
Academic Programs ◽  
Student Group ◽  
Entry Level ◽  
Study Approach ◽  
Business Colleges ◽  
Job Advertisements ◽  
Job Ads ◽  
Group Characteristics ◽  
Insight Into ◽  
Do So

Given the recent proliferation in sales programs, business colleges face a new set of challenges. Sales competencies are changing rapidly, and firms struggle with identifying and attracting sales candidates on campus. Therefore, it is important that we understand needed competencies and how the content of job advertisements may differentially appeal to various student populations. To do so, we develop a conceptual model, based on signaling theory, that focuses on how students formulate their intention to pursue a given sales position. Our research utilizes a two-study approach. First, we explore the desired entry-level sales skills communicated by employers through job advertisements. Next, we examine both student and advertisement characteristics and their distinct relationships with the satisfaction with the job ad and the intention to apply for a sales position. Our study is unique, as we examine distinct undergraduate groups’ (sales, marketing, other business, and nonbusiness students) responses to sales job advertisements. Our findings demonstrate that differences in job ad clusters and student group characteristics influence the intention to pursue a sales position. Specifically, different student majors perceive job characteristics communicated within job ads differently. As such, our research provides insight into academic programs as well as corporate sales recruiters.

scholarly journals Moving contact line on chemically patterned surfaces

2008 ◽  
Vol 605 ◽  
pp. 59-78 ◽  
Author(s):  
XIAO-PING WANG ◽  
TIEZHENG QIAN ◽  
PING SHENG
Keyword(s):  
Contact Line ◽  
Critical Value ◽  
Diffuse Interface ◽  
Patterned Surfaces ◽  
Fluid Interface ◽  
Two Phase ◽  
Stick Slip ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Wetting Fluid

We simulate the moving contact line in two-dimensional chemically patterned channels using a diffuse-interface model with the generalized Navier boundary condition. The motion of the fluid–fluid interface in confined immiscible two-phase flows is modulated by the chemical pattern on the top and bottom surfaces, leading to a stick–slip behaviour of the contact line. The extra dissipation induced by this oscillatory contact-line motion is significant and increases rapidly with the wettability contrast of the pattern. A critical value of the wettability contrast is identified above which the effect of diffusion becomes important, leading to the interesting behaviour of fluid–fluid interface breaking, with the transport of the non-wetting fluid being assisted and mediated by rapid diffusion through the wetting fluid. Near the critical value, the time-averaged extra dissipation scales as U, the displacement velocity. By decreasing the period of the pattern, we show the solid surface to be characterized by an effective contact angle whose value depends on the material characteristics and composition of the patterned surfaces.

Finite-amplitude internal wavepacket dispersion and breaking

2001 ◽  
Vol 429 ◽  
pp. 343-380 ◽  
Author(s):  
BRUCE R. SUTHERLAND
Keyword(s):  
Numerical Simulations ◽  
Internal Waves ◽  
Large Amplitude ◽  
Finite Amplitude ◽  
Critical Amplitude ◽  
Fully Nonlinear ◽  
Weakly Nonlinear ◽  
The Stability ◽  
The Waves ◽  
Horizontal Wavelength

The evolution and stability of two-dimensional, large-amplitude, non-hydrostatic internal wavepackets are examined analytically and by numerical simulations. The weakly nonlinear dispersion relation for horizontally periodic, vertically compact internal waves is derived and the results are applied to assess the stability of weakly nonlinear wavepackets to vertical modulations. In terms of Θ, the angle that lines of constant phase make with the vertical, the wavepackets are predicted to be unstable if [mid ]Θ[mid ] < Θc, where Θc = cos−1 (2/3)1/2 ≃ 35.3° is the angle corresponding to internal waves with the fastest vertical group velocity. Fully nonlinear numerical simulations of finite-amplitude wavepackets confirm this prediction: the amplitude of wavepackets with [mid ]Θ[mid ] > Θc decreases over time; the amplitude of wavepackets with [mid ]Θ[mid ] < Θc increases initially, but then decreases as the wavepacket subdivides into a wave train, following the well-known Fermi–Pasta–Ulam recurrence phenomenon.If the initial wavepacket is of sufficiently large amplitude, it becomes unstable in the sense that eventually it convectively overturns. Two new analytic conditions for the stability of quasi-plane large-amplitude internal waves are proposed. These are qualitatively and quantitatively different from the parametric instability of plane periodic internal waves. The ‘breaking condition’ requires not only that the wave is statically unstable but that the convective instability growth rate is greater than the frequency of the waves. The critical amplitude for breaking to occur is found to be ACV = cot Θ (1 + cos2 Θ)/2π, where ACV is the ratio of the maximum vertical displacement of the wave to its horizontal wavelength. A second instability condition proposes that a statically stable wavepacket may evolve so that it becomes convectively unstable due to resonant interactions between the waves and the wave-induced mean flow. This hypothesis is based on the assumption that the resonant long wave–short wave interaction, which Grimshaw (1977) has shown amplifies the waves linearly in time, continues to amplify the waves in the fully nonlinear regime. Using linear theory estimates, the critical amplitude for instability is ASA = sin 2Θ/(8π2)1/2. The results of numerical simulations of horizontally periodic, vertically compact wavepackets show excellent agreement with this latter stability condition. However, for wavepackets with horizontal extent comparable with the horizontal wavelength, the wavepacket is found to be stable at larger amplitudes than predicted if Θ [lsim ] 45°. It is proposed that these results may explain why internal waves generated by turbulence in laboratory experiments are often observed to be excited within a narrow frequency band corresponding to Θ less than approximately 45°.

A moving fluid interface. Part 2. The removal of the force singularity by a slip flow

1977 ◽  
Vol 79 (2) ◽  
pp. 209-229 ◽  
Author(s):  
L. M. Hocking
Keyword(s):  
Contact Line ◽  
Slip Flow ◽  
Slip Condition ◽  
Solid Boundary ◽  
Parallel Plates ◽  
Fluid Interface ◽  
Slip Coefficient ◽  
Outer Flow ◽  
Normal Contact ◽  
Two Fluids

If the no-slip condition is used to determine the flow produced when a fluid interface moves along a solid boundary, a non-integrable stress is obtained. In part 1 of this study (Hocking 1976), it was argued that, when allowance was made for the presence of irregularities on the solid boundary, an effective slip coefficient could be found, which might remove the difficulty.This paper examines the effect of a slip coefficient on the flow in the neighbourhood of the contact line. Particular cases which are solved in detail are liquid–gas interfaces at an arbitrary angle, and normal contact of fluids of arbitrary viscosity. The contribution of the vicinity of the contact line to the force on the boundary is obtained.The inner region, near the contact line, must be matched with an outer flow, in which the no-slip condition can be applied, in order to obtain the total value of the force on the boundary. This force is determined for the flow of two fluids between parallel plates and in a pipe, with a plane interface. The enhanced resistance produced by the presence of the interface is calculated, and it is shown to be equivalent to an increase in the length of the column of fluid by a small multiple of the pipe radius.

scholarly journals Visualization is crucial for understanding microbial processes in the ocean

2019 ◽  
Vol 374 (1786) ◽  
pp. 20190083 ◽  
Author(s):  
Marta Sebastián ◽  
Josep M. Gasol
Keyword(s):  
Single Cell ◽  
Metabolic Activity ◽  
Cell Activity ◽  
Level Of Activity ◽  
Single Cell Activity ◽  
Recent Developments ◽  
Insight Into ◽  
Do So

Recent developments in community and single-cell genomic approaches have provided an unprecedented amount of information on the ecology of microbes in the aquatic environment. However, linkages between each specific microbe's identity and their in situ level of activity (be it growth, division or just metabolic activity) are much more scarce. The ultimate goal of marine microbial ecology is to understand how the environment determines the types of different microbes in nature, their function, morphology and cell-to-cell interactions and to do so we should gather three levels of information, the genomic (including identity), the functional (activity or growth), and the morphological, and for as many individual cells as possible. We present a brief overview of methodologies applied to address single-cell activity in marine prokaryotes, together with a discussion of the difficulties in identifying and categorizing activity and growth. We then provide and discuss some examples showing how visualization has been pivotal for challenging established paradigms and for understanding the role of microbes in the environment, unveiling processes and interactions that otherwise would have been overlooked. We conclude by stating that more effort should be directed towards integrating visualization in future approaches if we want to gain a comprehensive insight into how microbes contribute to the functioning of ecosystems. This article is part of a discussion meeting issue ‘Single cell ecology’.

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