scholarly journals Lagrangian Mixing Dynamics at the Cloudy–Clear Air Interface

2014 ◽  
Vol 71 (7) ◽  
pp. 2564-2580 ◽  
Author(s):  
Bipin Kumar ◽  
Jörg Schumacher ◽  
Raymond A. Shaw
Keyword(s):  
Time Scale ◽  
Three Dimensional ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Droplet Evaporation ◽  
Sample Volume ◽  
Minor Role ◽  
Mixing Dynamics ◽  
Decaying Turbulence ◽  
A Minor

Abstract The entrainment of clear air and its subsequent mixing with a filament of cloudy air, as occurs at the edge of a cloud, is studied in three-dimensional direct numerical simulations that combine the Eulerian description of the turbulent velocity, temperature, and vapor fields with a Lagrangian cloud droplet ensemble. Forced and decaying turbulence is considered, such as when the dynamics around the filament is driven by larger-scale eddies or during the final period of the life cycle of a cloud. The microphysical response depicted in nd − 〈r3〉 space (where nd and r are droplet number density and radius, respectively) shows characteristics of both homogeneous and inhomogeneous mixing, depending on the Damköhler number. The transition from inhomogeneous to homogeneous mixing leads to an offset of the homogeneous mixing curve to larger dilution fractions. The response of the system is governed by the smaller of the single droplet evaporation time scale and the bulk phase relaxation time scale. Variability within the nd − 〈r3〉 space increases with decreasing sample volume, especially during the mixing transients. All of these factors have implications for the interpretation of measurements in clouds. The qualitative mixing behavior changes for forced versus decaying turbulence, with the latter yielding remnant patches of unmixed cloud and stronger fluctuations. Buoyancy due to droplet evaporation is observed to play a minor role in the mixing for the present configuration. Finally, the mixing process leads to the transient formation of a pronounced nearly exponential tail of the probability density function of the Lagrangian supersaturation, and a similar tail emerges in the droplet size distribution under inhomogeneous conditions.

Climatic, Solar, Oceanic, and Geomagnetic Influences on Late-Glacial and Holocene Atmospheric 14C/12C Change

1991 ◽  
Vol 35 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Minze Stuiver ◽  
Thomas F. Braziunas ◽  
Bernd Becker ◽  
Bernd Kromer
Keyword(s):  
Ocean Circulation ◽  
Time Scale ◽  
Late Glacial ◽  
Minor Role ◽  
Activity Levels ◽  
Data Set ◽  
The Holocene ◽  
Spectral Interpretation ◽  
Late Glacial And Holocene ◽  
A Minor

AbstractLate-glacial and Holocene 14C/12C ratios of atmospheric CO2 vary in magnitude from a few per mil for annual/decadal pertubations to more than 10% for events lasting millennia. A data set illuminating 10- to 104-yr variability refines our understanding of oceanic (climatic) versus geomagnetic or solar forcing of atmospheric 14C/12C ratios. Most of the variance in the Holocene atmospheric 14C/12C record can be attributed to the geomagnetic (millennia time scale) and solar (century time scale) influence on the flux of primary cosmic rays entering the atmosphere. Attributing the observed atmospheric 14C/12C changes to climate alone leads to ocean circulation and/or global wind speed changes incompatible with proxy records. Climate-(ocean-)related 14C redistribution between carbon reservoirs, while evidently playing a minor role during the Holocene, may have perturbed atmospheric 14C/12C ratios measurably during the late-glacial Younger Dryas event. First-order corrections to the radiocarbon time scale (12,000–30,000 14C yr B.P.) are calculated from adjusted lake-sediment and tree-ring records and from geomagnetically defined model 14C histories. Paleosunspot numbers (100–9700 cal yr B.P.) are derived from the relationship of model 14C production rates to sunspot observations. The spectral interpretation of the 14C/12C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.

scholarly journals Flow Topology of Three-Dimensional Spherical Flame in Shock Accelerated Flows

2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
Yuejin Zhu ◽  
Lei Yu ◽  
Gang Dong ◽  
Jianfeng Pan ◽  
Zhenhua Pan
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Joint Probability ◽  
Reflected Shock Wave ◽  
Minor Role ◽  
Flow Topology ◽  
Reflected Shock ◽  
Compression And Expansion ◽  
Scale Turbulence ◽  
A Minor

The flow topologies of compressible large-scale distorted flames are studied by means of the analysis of the invariants of the velocity gradient tensor (VGT). The results indicate that compressibility plays a minor role in the distorted flame zone. And the joint probability density function (p.d.f.) of the Q-R diagram appears as a teardrop shape, which is a universal feature of turbulence. Therefore, the distorted flame exhibits the characteristic of large-scale turbulence combustion, especially behind the reflected shock wave, while the p.d.f. of the QS⁎-QW diagram implies that the dissipation is enhanced in the compression and expansion regions, where it is higher than that when P=0. Furthermore, we identify that the flame evolution is dominated by rotation by means of a quantitative statistical study, and the SFS topology is the predominant flow pattern. Not surprisingly, negative dilatation could suppress the unstable topologies, whereas positive dilatation could suppress the stable topologies.

Investigation of Through-Flow Hypothesis in a Turbine Cascade Using a 3D Navier-Stokes Computation

1993 ◽  
Author(s):  
G. Perrin ◽  
F. Leboeuf
Keyword(s):  
Kinetic Energy ◽  
Three Dimensional ◽  
Radial Pressure ◽  
Momentum Balance ◽  
Navier Stokes ◽  
Minor Role ◽  
Passage Vortex ◽  
Spatial Fluctuations ◽  
Flow Variables ◽  
A Minor

The results of a computation, performed with a three-dimensional Navier-Stokes computation at ONERA, have been averaged in the blade-to-blade direction; the spatial fluctuations around the averaged flow variables have also been determined. It has then been possible to estimate all terms in the average components of the momentum equations. The comparison of the two-dimensional balances of these three equations shows that the shear stress play a minor role in the momentum balance, except on the dissipation of the passage vortex kinetic energy downstream of the blade trailing edges. The kinetic energy of the spanwise component of the velocity spatial fluctuations has a very strong influence on the radial pressure gradient; it introduces a convection effect. This is a key effect for all these balances.

scholarly journals Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

2020 ◽  
Vol 13 (2) ◽  
pp. 925-939 ◽  
Author(s):  
Fabiola Ramelli ◽  
Alexander Beck ◽  
Jan Henneberger ◽  
Ulrike Lohmann
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Cloud Droplet ◽  
Sample Volume ◽  
Tethered Balloon ◽  
Wind Speeds ◽  
Boundary Layer Clouds ◽  
Main Component ◽  
Balloon System

Abstract. Conventional techniques to measure boundary layer clouds such as research aircraft are unable to sample in orographically diverse or densely populated areas. In this paper, we present a newly developed measurement platform on a tethered balloon system (HoloBalloon) to measure in situ vertical profiles of microphysical and meteorological cloud properties up to 1 km above ground. The main component of the HoloBalloon platform is a holographic imager, which uses digital in-line holography to image an ensemble of cloud particles in the size range from small cloud droplets to precipitation-sized particles in a three-dimensional volume. Based on a set of two-dimensional images, information about the phase-resolved particle size distribution, shape and spatial distribution can be obtained. The velocity-independent sample volume makes holographic imagers particularly well suited for measurements on a balloon. The unique combination of holography and balloon-borne measurements allows for observations with high spatial resolution, covering cloud structures from the kilometer down to the millimeter scale. The potential of the measurement technique in studying boundary layer clouds is demonstrated on the basis of a case study. We present observations of a supercooled low stratus cloud during a Bise situation over the Swiss Plateau in February 2018. In situ microphysical profiles up to 700 m altitude above the ground were performed at temperatures down to −8 ∘C and wind speeds up to 15 m s−1. We were able to capture unique microphysical signatures in stratus clouds, in the form of inhomogeneities in the cloud droplet number concentration and in cloud droplet size, from the kilometer down to the meter scale.

Primary and secondary instabilities in the wake of a cylinder with free ends

1997 ◽  
Vol 332 ◽  
pp. 295-339 ◽  
Author(s):  
Christophe Dauchy ◽  
Jan Dušek ◽  
Philippe Fraunié
Keyword(s):  
Aspect Ratio ◽  
Limit Cycle ◽  
Three Dimensional ◽  
Secondary Instability ◽  
Instability Threshold ◽  
Three Dimensions ◽  
Finite Cylinder ◽  
Minor Role ◽  
A Minor ◽  
Primary Instability

The wake of a finite cylinder with free ends and an aspect ratio of 21.4 is simulated in three-dimensions and analysed theoretically. Close to the primary-instability threshold, the flow is shown to settle on a limit cycle with a uniform frequency throughout the flow-field. About 20% above the primary-instability threshold, a secondary instability sets in and the limit cycle becomes unstable. The new attractor of the flow can be identified as a limit T2-torus characterized by two incommensurate frequencies. One of them is shown to evolve continuously from the primary-instability frequency, the other one, about 17 times smaller near the secondary-instability threshold, generates a slow modulation of the oscillations in the wake. The limit cycle and the limit torus are described in terms of their Fourier expansion and the spatial distribution of the most relevant Fourier components is investigated. The theoretical analysis and numerical results given shed some light on the mechanisms underlying a number of known but not satisfactorily explained three-dimensional effects in wakes of finite cylinders such as the ambiguity in the dominant Strouhal frequency, the existence of zones with different frequencies spanwise in the wake, the discreteness of coexisting frequencies observed in the wake as well as the spatial uniformity of the beating period. They moreover explain the Reynolds number variation of these effects and identify the recirculation around the cylinder ends as basically responsible for the onset of the secondary instability. The results are compared to the case of a cylinder with aspect ratio of 10.7 to determine the basic trends in aspect ratio dependence. It is shown that qualitatively the same behaviour is obtained, but that the secondary-instability threshold is shifted significantly upward to about twice the primary-instability threshold. Simulations of the wake of a finite NACA wing with incidence show that the form of the cross-section plays a minor role.

Investigation of Throughflow Hypothesis in a Turbine Cascade Using a Three-Dimensional Navier–Stokes Computation

1995 ◽  
Vol 117 (1) ◽  
pp. 126-132
Author(s):  
G. Perrin ◽  
F. Leboeuf
Keyword(s):  
Kinetic Energy ◽  
Three Dimensional ◽  
Radial Pressure ◽  
Momentum Balance ◽  
Navier Stokes ◽  
Minor Role ◽  
Passage Vortex ◽  
Spatial Fluctuations ◽  
Flow Variables ◽  
A Minor

The results of a computation, performed with a three-dimensional Navier–Stokes computation at ONERA, have been averaged in the blade-to-blade direction; the spatial fluctuations around the averaged flow variables have also been determined. It has then been possible to estimate all terms in the average components of the momentum equations. The comparison of the two-dimensional balances of these three equations shows that the shear stress plays a minor role in the momentum balance, except on the dissipation of the passage vortex kinetic energy downstream of the blade trailing edges. The kinetic energy of the spanwise component of the velocity spatial fluctuations has a very strong influence on the radial pressure gradient; it introduces a convection effect. This is a key effect for all these balances.

scholarly journals Low-Temperature-Induced Controllable Transversal Shell Growth of NaLnF4 Nanocrystals

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 654
Author(s):  
Deming Liu ◽  
Yan Jin ◽  
Xiaotong Dong ◽  
Lei Liu ◽  
Dayong Jin ◽  
...  
Keyword(s):  
Reaction Temperature ◽  
Lattice Mismatch ◽  
Shell Growth ◽  
Three Dimensional ◽  
Anisotropic Shell ◽  
Growth Direction ◽  
Minor Role ◽  
Growth Method ◽  
Surface Ligand ◽  
A Minor

Highly controllable anisotropic shell growth is essential for further engineering the function and properties of lanthanide-doped luminescence nanocrystals, especially in some of the advanced applications such as multi-mode bioimaging, security coding and three-dimensional (3D) display. However, the understanding of the transversal shell growth mechanism is still limited today, because the shell growth direction is impacted by multiple complex factors, such as the anisotropy of surface ligand-binding energy, anisotropic core–shell lattice mismatch, the size of cores and varied shell crystalline stability. Herein, we report a highly controlled transversal shell growth method for hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals. Exploiting the relationship between reaction temperature and shell growth direction, we found that the shell growth direction could be tuned from longitudinal to transversal by decreasing the reaction temperature from 310 °C to 280 °C. In addition to the reaction temperature, we also discussed the roles of other factors in the transversal shell growth of nanocrystals. A suitable core size and a relative lower shell precursor concentration could promote transversal shell growth, although different shell hosts played a minor role in changing the shell growth direction.

scholarly journals The structural dynamics of macropinosome formation and PI3-kinase-mediated sealing revealed by lattice light sheet microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shayne E. Quinn ◽  
Lu Huang ◽  
Jason G. Kerkvliet ◽  
Joel A. Swanson ◽  
Steve Smith ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Three Dimensional ◽  
Light Sheet ◽  
Dimensional Structure ◽  
Minor Role ◽  
Membrane Ruffling ◽  
Light Sheet Microscopy ◽  
Pi3k Activity ◽  
Intracellular Organelles ◽  
A Minor

AbstractMacropinosomes are formed by shaping actin-rich plasma membrane ruffles into large intracellular organelles in a phosphatidylinositol 3-kinase (PI3K)-coordinated manner. Here, we utilize lattice lightsheet microscopy and image visualization methods to map the three-dimensional structure and dynamics of macropinosome formation relative to PI3K activity. We show that multiple ruffling morphologies produce macropinosomes and that the majority form through collisions of adjacent PI3K-rich ruffles. By combining multiple volumetric representations of the plasma membrane structure and PI3K products, we show that PI3K activity begins early throughout the entire ruffle volume and continues to increase until peak activity concentrates at the base of the ruffle after the macropinosome closes. Additionally, areas of the plasma membrane rich in ruffling had increased PI3K activity and produced many macropinosomes of various sizes. Pharmacologic inhibition of PI3K activity had little effect on the rate and morphology of membrane ruffling, demonstrating that early production of 3′-phosphoinositides within ruffles plays a minor role in regulating their morphology. However, 3′-phosphoinositides are critical for the fusogenic activity that seals ruffles into macropinosomes. Taken together, these data indicate that local PI3K activity is amplified in ruffles and serves as a priming mechanism for closure and sealing of ruffles into macropinosomes.

scholarly journals Applicability of the VisiSize D30 shadowgraph system for cloud microphysical measurements

2020 ◽  
Author(s):  
Jakub L. Nowak ◽  
Moein Mohammadi ◽  
Szymon P. Malinowski
Keyword(s):  
Size Distribution ◽  
Droplet Diameter ◽  
Strong Dependence ◽  
Field Tests ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Sample Volume ◽  
Number Concentration ◽  
Depth Of Field ◽  
Spatial Homogeneity

Abstract. The commercial shadowgraph system, Oxford Lasers VisiSize D30, originally designed to characterize industrial and agricultural sprays, was tested with respect to the application for measuring cloud microphysical properties, such as droplet size distribution and number concentration. Laboratory experiment with a dense stream of poly-disperse cloud-like droplets indicated strong dependence of the depth of field, thus also sample volume, on particle size. This relationship was determined and a suitable correction method was developed to improve estimations of droplet number concentration and size distribution. Spatial homogeneity of detection probability inside the sample volume and minimum droplet diameter providing uniform detection were examined. The second experiment with mono-disperse droplets produced by Flow-Focusing Monosized Aerosol Generator (FMAG) verified sizing accuracy and demonstrated reasonable agreement between the instruments. Effects of collisions and evaporation of droplets produced by FMAG were observed. Finally, the instrument was applied to sample atmospheric clouds at a ground-based mountain observatory and performed reliably during 3 week long field experiment. Based on the laboratory and field tests, recommendations concerning the use of the instrument for cloud droplet measurements were formulated.

scholarly journals Detailed Streetspace Modelling for Multiple Applications: Discussions on the Proposed CityGML 3.0 Transportation Model

2020 ◽  
Vol 9 (10) ◽  
pp. 603
Author(s):  
Christof Beil ◽  
Roland Ruhdorfer ◽  
Theresa Coduro ◽  
Thomas H. Kolbe
Keyword(s):  
Urban Areas ◽  
Smart Cities ◽  
Three Dimensional ◽  
Data Availability ◽  
Minor Role ◽  
Extensive Literature ◽  
Transportation Model ◽  
Potential Applications ◽  
A Minor ◽  
City Models

In the context of smart cities and digital twins, three-dimensional semantic city models are increasingly used for the analyses of large urban areas. While the representation of buildings, terrain, and vegetation has become standard for most city models, detailed spatio-semantic representations of streetspace have played a minor role so far. This is now changing (1) because of data availability, and (2) because recent and emerging applications require having detailed data about the streetspace. The upcoming version 3.0 of the international standard CityGML provides a substantially updated data model regarding the transportation infrastructure, including the representation of the streetspace. However, there already exist a number of other standards and data formats dealing with the representation and exchange of streetspace data. Thus, based on an extensive literature review of potential applications as well as discussions and collaborations with relevant stakeholders, seven key modelling aspects of detailed streetspace models are identified. This allows a structured discussion of representational capabilities of the proposed CityGML3.0 Transportation Model with respect to these aspects and in comparison to the other standards. Subsequently, it is shown that CityGML3.0 meets most of these aspects and that streetspace models can be derived from various data sources and for different cities. Models generated compliant to the CityGML standard are immediately usable for a number of applications. This is demonstrated for some applications, such as land use management, solar potential analyses, and traffic and pedestrian simulations.

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