The rhythm of fountains: the length and time scales of rise height fluctuations at low and high Froude numbers

2013 ◽  
Vol 728 ◽  
pp. 91-119 ◽  
Author(s):  
H. C. Burridge ◽  
G. R. Hunt
Keyword(s):  
Time Scales ◽  
Characteristic Time ◽  
Full Range ◽  
Dimensionless Frequency ◽  
Long Period ◽  
Apparent Length ◽  
Alternative Approach ◽  
Physical Scale ◽  
Velocity Scale ◽  
Rise Height

AbstractThe magnitude and frequency of vertical fluctuations of the top of an axisymmetric miscible Boussinesq fountain forms the focus of this work. We present measurements of these quantities for saline-aqueous fountains in uniform quiescent surroundings. Our results span source Froude numbers $0. 3\leq {\mathrm{Fr} }_{0} \leq 40$ and, thereby, encompass very weak, weak, intermediate and forced classes of fountain. We identify distinct scalings, based on known quantities at the fountain source, for the frequency of fountain height fluctuations which collapse our data within bands of ${\mathrm{Fr} }_{0} $. Notably, our scalings reveal that the (dimensionless) frequency takes a constant value within each band. These results highlight characteristic time scales for the fluctuations which we decompose into a single, physically apparent, length scale and velocity scale within each band. Moreover, within one particular band, spanning source Froude numbers towards the lower end of the full range considered, we identify unexpectedly long-period fluctuations indicating a near balance of inertia and (opposing) buoyancy at the source. Our analysis identifies four distinct classes of fluctuation behaviour (four bands of ${\mathrm{Fr} }_{0} $) and this classification matches well with existing classifications of fountains based on rise heights. As such, we show that an analysis of the behaviour of the fountain top alone, rather than the entire fountain, provides an alternative approach to classifying fountains. The similarity of classifications based on the two different methods confirms that the boundaries between classes mark tangible changes in the physics of fountains. For high ${\mathrm{Fr} }_{0} $ we show that the dominant fluctuations occur at the scale of the largest eddies which can be contained within the fountain near its top. Extending this, we develop a Strouhal number, ${\mathrm{Str} }_{top} $, based on experimental measures of the fountain top, defined such that ${\mathrm{Str} }_{top} = 1$ would suggest the dominant fluctuations are caused by a continual cycle of eddies forming and collapsing at this largest physical scale. For high-${\mathrm{Fr} }_{0} $ fountains we find ${\mathrm{Str} }_{top} \approx 0. 9$.

scholarly journals Characteristics of Large-Scale Orographic Precipitation in a Linear Perspective

2011 ◽  
Vol 12 (1) ◽  
pp. 27-44 ◽  
Author(s):  
Michael Kunz
Keyword(s):  
Time Scales ◽  
Characteristic Time ◽  
Large Scale ◽  
Linear Perspective ◽  
Horizontal Wind ◽  
Small Scale ◽  
Orographic Precipitation ◽  
Observation Data ◽  
Horizontal Wind Speed ◽  
Precipitation Patterns

Abstract Simulations of orographic precipitation over the low mountain ranges of southwestern Germany and eastern France with two different physics-based linear precipitation models are presented. Both models are based on 3D airflow dynamics from linear theory and consider advection of condensed water and leeside drying. Sensitivity studies for idealized conditions and a real case study show that the amount and spatial distribution of orographic precipitation is strongly controlled by characteristic time scales for cloud and hydrometeor advection and background precipitation due to large-scale lifting. These parameters are estimated by adjusting the model results on a 2.5-km grid to observed precipitation patterns for a sample of 40 representative orography-dominated stratiform events (24 h) during a calibration period (1971–80). In general, the best results in terms of lowest rmse and bias are obtained for characteristic time scales of 1600 s and background precipitation of 0.4 mm h−1. Model simulations of a sample of 84 events during an application period (1981–2000) with fixed parameters demonstrate that both models are able to reproduce quantitatively precipitation patterns obtained from observations and reanalyses from a numerical model [Consortium for Small-scale Modeling (COSMO)]. Combining model results with observation data shows that heavy precipitations over mountains are restricted to situations with strong atmospheric forcings in terms of synoptic-scale lifting, horizontal wind speed, and moisture content.

scholarly journals Superconducting fluctuations and characteristic time scales in amorphous WSi

2018 ◽  
Vol 97 (17) ◽  
Author(s):  
Xiaofu Zhang ◽  
Adriana E. Lita ◽  
Mariia Sidorova ◽  
Varun B. Verma ◽  
Qiang Wang ◽  
...  
Keyword(s):  
Time Scales ◽  
Characteristic Time ◽  
Superconducting Fluctuations

scholarly journals From vacant land to urban fallows: a permacultural approach to wasted land in cities and suburbs

2019 ◽  
Vol 26 (1) ◽  
pp. 282 ◽  
Author(s):  
Alex Korsunsky
Keyword(s):  
Pacific Northwest ◽  
Full Range ◽  
Intentional Communities ◽  
Vacant Land ◽  
Residential Areas ◽  
The Pacific ◽  
Alternative Approach ◽  
New Urbanist ◽  
American Cities ◽  
The City

<p>While vacant land in cities has long been considered a sign of decline, a growing literature now suggests that such land can serve valuable social and ecological functions. In this article, I argue that such approaches advocated to date, while beneficial, operate within a New Urbanist framework that is essentially concerned with filling in vacant land with new 'green' projects. Unfortunately, such approaches are limited by a conceptualization of the city that treats inner city vacant lots as paradigmatic and makes invisible the systematic creation of functionally vacant land through zoning and building practices in low-density residential areas. Inspired by degrowth scholarship, I suggest that permaculture may provide the basis for an alternative approach based in the concept of fallowing more suited to the full range of vacant land present in American cities and suburbs. I explore the implications of such an approach through the practice of two permaculture-inspired intentional communities in the Pacific Northwest.</p><strong>Key words: </strong>vacant land, permaculture, New Urbanism, intentional communities, commons, degrowth

scholarly journals Properties of Phase Solitons in an Optically Driven Semiconductor Ring Laser

2019 ◽  
Vol 9 (20) ◽  
pp. 4351
Author(s):  
Ghafour Hashemvand Shakarab ◽  
Reza Kheradmand ◽  
Mohammad Agha Bolorizadeh ◽  
Franco Prati
Keyword(s):  
Time Scales ◽  
Propagation Velocity ◽  
Ring Laser ◽  
Characteristic Time ◽  
Carrier Lifetime ◽  
Large Range ◽  
Semiconductor Ring Laser

A semiconductor ring laser with a long cavity supports propagating localised structures with a chiral charge, named phase solitons. In this paper we study the dependence of the velocity and of the duration of the phase solitons on the characteristic time scales of the laser, namely the photon lifetime and the carrier lifetime. We show numerically that phase solitons are stable over a large range of those parameters and verify that the propagation velocity decreases linearly with the ratio of the carrier lifetime to the photon lifetime, while the duration is proportional to the ratio of the carrier lifetime to the cavity roundtrip time.

JCPDS-lnternational Centre for Diffraction Data Low-Angle Powder Diffraction Study of Silver Behenate

1994 ◽  
Vol 38 ◽  
pp. 99-105
Author(s):  
T. Blanton ◽  
T. Huang ◽  
H. Toraya ◽  
C. Hubbard ◽  
S. Robie ◽  
...  
Keyword(s):  
Data Analysis ◽  
Data Collection ◽  
Diffraction Data ◽  
Calculation Method ◽  
Full Range ◽  
Internal Standard ◽  
Average Crystallite Size ◽  
Long Period ◽  
Diffraction Peaks ◽  
Characterization Of Materials

Abstract As a result of interest in the characterization of materials with large d-spacings and layer periodicities, it has become necessary to develop a low-angle diffraction material which has welldefined diffraction peaks down to very small 2θ angles. The use of silver behenate, CH3(CH2)20COO-Ag, was introduced by one of the authors (TB) at the 1991 International Centre for Diffraction Data (ICDD) Annual Meeting and was shown to have a set of well-defined (001) diffraction peaks down to 1.5° 2θ when using CuKα radiation. The silver behenate diffraction peaks were observed to be slightly asymmetric with relatively long tails at the low angle side of the peaks. The average crystallite size along the c-axis was estimated using the Scherrer equation and was found to be 900 Å. A task group of the JCPDS-ICJDD Data Collection and Analysis Subcommittee was established with the charge of investigating the use of silver behenate as a possible low-angle calibration material for diffraction applications. Utilizing several data collection and data analysis techniques, d001 long-period spacings in the range of 58.219-58.480 Å were obtained. Using the same collected data and one data analysis refinement calculation method resulted in long-period spacing with a range of 58.303-58.425 Å. Data collected using a silicon internal standard and the same singular data analysis calculation method provided d001 values with a range of 58.363-58.381 Å. The formation of a full-range 2θ diffraction sample was also investigated. Silver behenate and inorganic powders were mixed with an epoxy binder to form a permanent sample which provides diffraction peaks over the entire 2θ range of a powder diffractometer.

Characteristic time scales for the adsorption process for fibrinogen on silica

Langmuir ◽  
1992 ◽  
Vol 8 (2) ◽  
pp. 514-517 ◽  
Author(s):  
P. Schaaf ◽  
P. Dejardin ◽  
A. Johner ◽  
A. Schmitt
Keyword(s):  
Time Scales ◽  
Characteristic Time ◽  
Adsorption Process

scholarly journals Clinic is the Basis for a Complete Legal Education: Quality Assurance, Learning Outcomes and the Clinical Method

2015 ◽  
Vol 22 (1) ◽  
pp. 84
Author(s):  
Neil Gold
Keyword(s):  
Learning Outcomes ◽  
Full Range ◽  
Legal Education ◽  
Education Quality ◽  
Clinical Method ◽  
Assessment Of Learning ◽  
Alternative Approach ◽  
To Come ◽  
The Relationship ◽  
Education Quality Assurance

Clinic is the basis for a complete legal education. The time has come to stop treating clinic as a marginal, alternative approach to learning some but not all things requisite for a sound legal education aimed at producing capable practitioners.  It is a powerfully effective, experiential and varied, comprehensive approach to the structure and contents of a legal education. I will argue that given a full interpretation of the term “Clinical Legal Education” (CLE), CLE in its many forms can serve as the model for a legal education. Also, in this paper I will examine the relationship between the learning outcomes we have for a legal education and the learning methods characteristic of a variety of forms of clinical legal education. At another time it will be useful to show how assessment of learning through clinic suits the full range of outcomes as well. There is a discussion of the meaning of the term Clinical Legal Education, as I use it, in Section 6. Some readers may wish to come back to the beginning after reading the section entitled “What is clinical legal education?”.

scholarly journals Meteor radar observations of mesopause region long-period temperature oscillations

2016 ◽  
Vol 14 ◽  
pp. 169-174
Author(s):  
Ch. Jacobi ◽  
N. Samtleben ◽  
G. Stober
Keyword(s):  
Time Scales ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Meteor Radar ◽  
Mesopause Region ◽  
Radar Observations ◽  
Long Period ◽  
Temperature Oscillations ◽  
Wind Measurements

Abstract. Meteor radar observations of mesosphere/lower thermosphere (MLT) daily temperatures have been performed at Collm, Germany since August 2004. The data have been analyzed with respect to long-period oscillations at time scales of 2–30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The oscillations may be considered as the signature of planetary waves. The results are compared with analyses from radar wind measurements. Moreover, the temperature oscillations show considerable year-to-year variability. In particular, amplitudes of the quasi 5-day oscillation have increased during the last decade, and the quasi 10-day oscillations are larger if the equatorial stratospheric winds are eastward.

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