scholarly journals Observing Plumes and Overturning Cells with a New Coastal Bottom Drifter

2018 ◽  
Vol 35 (8) ◽  
pp. 1675-1686 ◽  
Author(s):  
Lena M. Schulze Chretien ◽  
Kevin Speer
Keyword(s):  
Ocean Circulation ◽  
Small Scale ◽  
Coastal Environments ◽  
Constant Depth ◽  
Physical Processes ◽  
Apalachicola Bay ◽  
Local Topography ◽  
Tracking Device ◽  
To Receive ◽  
Drifter Trajectory

AbstractA new platform, the Coastal Bottom Drifter, was designed and built to observe near-bottom environments in coastal regions. It is capable of observing properties by drifting near the bottom with a prescribed clearance or at a constant depth of up to 300 m. The platform can observe physical and biochemical parameters, such as temperature, salinity, oxygen, and velocities, and has the capacity to carry additional sensors to measure, for example, pH, turbidity, and nutrients. In addition, it can profile to the surface at chosen intervals and can be deployed for days or up to several months. The integrated Iridium communication allows the user to receive positions and data while the platform is surfaced, as well as send new missions to the instrument. The use of an acoustic bottom-tracking device allows the construction of a drifter trajectory while providing information about ocean circulation. Additionally, the ADCP provides information about suspended particles and possible sediment transport. These measurements are valuable in understanding coastal environments as well as the dominant physical processes that cause mixing and set the conditions for local biological activity. An example deployment in Apalachicola Bay shown in this study demonstrates the ability of the drifter to observe small-scale features, such as overturning cells and plumes of dense water, that are caused by local topography.

Leslie Burrowes: A Young Dancer in Dresden and London, 1930–34

2010 ◽  
Vol 28 (2) ◽  
pp. 153-178 ◽  
Author(s):  
Larraine Nicholas
Keyword(s):  
Modern Dance ◽  
Small Scale ◽  
Cultural Environment ◽  
Home Studio ◽  
To Receive

Leslie Burrowes (1908–1985) was the first British dancer to receive the full diploma of the Wigman School in Dresden and subsequently became Wigman's official UK representative. The letters she wrote to her benefactor, Dorothy Elmhirst, with the addition of my commentary and annotations, provide a lens through which to view the School as she experienced it. Her return to London brought her into a quite different cultural environment. I argue that she energetically launched her career, performing and teaching in her new style and contesting what she considered to be false charges against modern dance. But it appears that, by the end of this period, she had adjusted her expectations, away from solo theatrical recitals (in the Wigman mode) and more towards the education of children and students, and a small-scale but intense programme centred on her home studio.

The diffraction-ray model of single filamentation of femtosecond laser pulses for estimating characteristics of the multiple filamentation domain in air

2021 ◽  
Vol 64 (1) ◽  
pp. 154-164
Author(s):  
A.A. Zemlyanov ◽  
◽  
Y.E. Geints ◽  
O.V. Minina ◽  
◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Laser Beam ◽  
Peak Power ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Small Scale ◽  
Beam Forming ◽  
Physical Processes ◽  
Multiple Filamentation ◽  
Number Increase

The characteristics of the domain of multiple filamentation of femtosecond laser pulses in air were estimated based on the single filamentation model. As the single filamentation model, the diffraction-ray model is considered. It is based on the representation of a laser beam as a set of diffraction-ray tubes nested in each other that do not intersect in space and do not exchange energy with each other. In this situation changes in tubes shape and cross section during propagation demonstrate the effect of physical processes that occur with radiation in the medium. It is shown that the use of this model for interpreting experimental results and predicting effects is effective. In particular, it was demonstrated that the radius of small-scale intensity inhomogeneities in the profile of a centimeter laser beam, forming the domain of multiple filamentation of subterawatt femtosecond laser pulses, is several millimeters. The power in these inhomogeneities varies from several units to several tens of gigawatts. Telescoping the initial laser beam, leading to an increase in its radius, also expands the sizes of the initial small-scale intensity inhomogeneities and reduces the power contained in them. As a result of this, the coordinate of the filamentation beginning shifts along the path from the source of laser pulses. As the peak power in the beam increases, the length of the filaments and their number increase.

scholarly journals Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

2021 ◽  
Vol 8 ◽  
Author(s):  
Xuanye Ma ◽  
Peter Delamere ◽  
Katariina Nykyri ◽  
Brandon Burkholder ◽  
Stefan Eriksson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Test Particle ◽  
Acoustic Waves ◽  
Particle Simulation ◽  
Three Dimensions ◽  
Small Scale ◽  
Physical Processes ◽  
Length Scales ◽  
Ion Species

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

scholarly journals Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽  
2021 ◽  
Vol 34 (1) ◽  
pp. 58-75
Author(s):  
Michel Boufadel ◽  
◽  
Annalisa Bracco ◽  
Eric Chassignet ◽  
Shuyi Chen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Physical Environment ◽  
Large Scale ◽  
Transport Processes ◽  
Small Scale ◽  
Surface Mixed Layer ◽  
Physical Processes ◽  
Mixing Processes ◽  
Near Surface ◽  
Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

scholarly journals Goldilocks mixing in oceanic shear-induced turbulent overturns

2021 ◽  
Vol 928 ◽  
Author(s):  
A. Mashayek ◽  
C.P. Caulfield ◽  
M.H. Alford
Keyword(s):  
Ocean Circulation ◽  
Turbulent Mixing ◽  
Intermediate Phase ◽  
Turbulent Flux ◽  
Geographical Location ◽  
Small Scale ◽  
Supporting Evidence ◽  
Stratified Turbulence ◽  
Wide Range ◽  
Variable Flux

We present a new, simple and physically motivated parameterization, based on the ratio of Thorpe and Ozmidov scales, for the irreversible turbulent flux coefficient $\varGamma _{\mathcal {M}}= {\mathcal {M}}/\epsilon$ , i.e. the ratio of the irreversible rate ${\mathcal {M}}$ at which the background potential energy increases in a stratified flow due to macroscopic motions to the dissipation rate of turbulent kinetic energy $\epsilon$ . Our parameterization covers all three key phases (crucially, in time) of a shear-induced stratified turbulence life cycle: the initial, ‘hot’ growing phase, the intermediate energetically forced phase and the final ‘cold’ fossilization decaying phase. Covering all three phases allows us to highlight the importance of the intermediate one, to which we refer as the ‘Goldilocks’ phase due to its apparently optimal (and so neither too hot nor too cold, but just right) balance, in which energy transfer from background shear to the turbulent mixing is most efficient. The value of $\varGamma _{\mathcal {M}}$ is close to 1/3 during this phase, which we demonstrate appears to be related to an adjustment towards a critical or marginal Richardson number for sustained turbulence ${\sim }0.2\text {--}0.25$ . Importantly, although buoyancy effects are still significant at leading order for the turbulent dynamics during this intermediate phase, the marginal balance in the flow ensures that the turbulent mixing of the (density) scalar is nevertheless effectively ‘locked’ to the turbulent mixing of momentum. We present supporting evidence for our parameterization through comparison with six oceanographic datasets that span various turbulence generation regimes and a wide range of geographical location and depth. Using these observations, we highlight the significance of parameterizing an inherently variable flux coefficient for capturing the turbulent flux associated with rare energetic, yet fundamentally shear-driven (and so not strongly stratified) overturns that make a disproportionate contribution to the total mixing. We also highlight the importance of representation of young turbulent patches in the parameterization for connecting the small scale physics to larger scale applications of mixing such as ocean circulation and tracer budgets. Shear-induced turbulence is therefore central to irreversible mixing in the world's oceans, apparently even close to the seafloor, and it is critically important to appreciate the inherent time dependence and evolution of mixing events: history matters to mixing.

scholarly journals The Lx–Luv–Lradio relation and corona–disc–jet connection in optically selected radio-loud quasars

2020 ◽  
Vol 496 (1) ◽  
pp. 245-268 ◽  
Author(s):  
S F Zhu (朱世甫) ◽  
W N Brandt ◽  
B Luo (罗斌) ◽  
Jianfeng Wu (武剑锋) ◽  
Y Q Xue (薛永泉) ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Small Scale ◽  
Spectral Slope ◽  
Physical Processes ◽  
X Ray ◽  
Accretion Flow ◽  
Radio Jets ◽  
Spectrum Radio ◽  
Uniform Sample

ABSTRACT Radio-loud quasars (RLQs) are more X-ray luminous than predicted by the X-ray–optical/UV relation (i.e. $L_\mathrm{x}\propto L_\mathrm{uv}^\gamma$) for radio-quiet quasars (RQQs). The excess X-ray emission depends on the radio-loudness parameter (R) and radio spectral slope (αr). We construct a uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and αr measurements. We find that steep-spectrum radio quasars (SSRQs; αr ≤ −0.5) follow a quantitatively similar $L_\mathrm{x}\propto L_\mathrm{uv}^{\gamma }$ relation as that for RQQs, suggesting a common coronal origin for the X-ray emission of both SSRQs and RQQs. However, the corresponding intercept of SSRQs is larger than that for RQQs and increases with R, suggesting a connection between the radio jets and the configuration of the accretion flow. Flat-spectrum radio quasars (FSRQs; αr > −0.5) are generally more X-ray luminous than SSRQs at given Luv and R, likely involving more physical processes. The emergent picture is different from that commonly assumed where the excess X-ray emission of RLQs is attributed to the jets. We thus perform model selection to compare critically these different interpretations, which prefers the coronal scenario with a corona–jet connection. A distinct jet component is likely important for only a small portion of FSRQs. The corona–jet, disc–corona, and disc–jet connections of RLQs are likely driven by independent physical processes. Furthermore, the corona–jet connection implies that small-scale processes in the vicinity of supermassive black holes, probably associated with the magnetic flux/topology instead of black hole spin, are controlling the radio-loudness of quasars.

The Large Scale Ocean Circulation and Physical Processes Controlling Pacific-Arctic Interactions

2014 ◽  
pp. 101-132 ◽  
Author(s):  
Wieslaw Maslowski ◽  
Jaclyn Clement Kinney ◽  
Stephen R. Okkonen ◽  
Robert Osinski ◽  
Andrew F. Roberts ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Physical Processes

scholarly journals Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

2014 ◽  
Vol 14 (17) ◽  
pp. 9403-9450 ◽  
Author(s):  
T. Vihma ◽  
R. Pirazzini ◽  
I. Fer ◽  
I. A. Renfrew ◽  
J. Sedlar ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Sea Ice ◽  
Surface Fluxes ◽  
Climate System ◽  
Arctic Climate ◽  
The Arctic ◽  
Small Scale ◽  
Climate Modelling ◽  
Physical Processes ◽  
Made In

Abstract. The Arctic climate system includes numerous highly interactive small-scale physical processes in the atmosphere, sea ice, and ocean. During and since the International Polar Year 2007–2009, significant advances have been made in understanding these processes. Here, these recent advances are reviewed, synthesized, and discussed. In atmospheric physics, the primary advances have been in cloud physics, radiative transfer, mesoscale cyclones, coastal, and fjordic processes as well as in boundary layer processes and surface fluxes. In sea ice and its snow cover, advances have been made in understanding of the surface albedo and its relationships with snow properties, the internal structure of sea ice, the heat and salt transfer in ice, the formation of superimposed ice and snow ice, and the small-scale dynamics of sea ice. For the ocean, significant advances have been related to exchange processes at the ice–ocean interface, diapycnal mixing, double-diffusive convection, tidal currents and diurnal resonance. Despite this recent progress, some of these small-scale physical processes are still not sufficiently understood: these include wave–turbulence interactions in the atmosphere and ocean, the exchange of heat and salt at the ice–ocean interface, and the mechanical weakening of sea ice. Many other processes are reasonably well understood as stand-alone processes but the challenge is to understand their interactions with and impacts and feedbacks on other processes. Uncertainty in the parameterization of small-scale processes continues to be among the greatest challenges facing climate modelling, particularly in high latitudes. Further improvements in parameterization require new year-round field campaigns on the Arctic sea ice, closely combined with satellite remote sensing studies and numerical model experiments.

scholarly journals Mixing Inferred from an Ocean Climatology and Surface Fluxes

2017 ◽  
Vol 47 (3) ◽  
pp. 667-687 ◽  
Author(s):  
Sjoerd Groeskamp ◽  
Bernadette M. Sloyan ◽  
Jan D. Zika ◽  
Trevor J. McDougall
Keyword(s):  
Ocean Circulation ◽  
Climate Models ◽  
Eddy Diffusion ◽  
Surface Fluxes ◽  
Small Scale ◽  
Vertical Variation ◽  
Mixing Coefficient ◽  
Order Of Magnitude ◽  
Ocean Models ◽  
Isopycnal Mixing

AbstractThis study provides observation-based estimates, determined by inverse methods, of horizontal and isopycnal eddy diffusion coefficients KH and KI, respectively, the small-scale mixing coefficient D, and the diathermohaline streamfunction Ψ. The inverse solution of Ψ represents the ocean circulation in Absolute Salinity SA and Conservative Temperature Θ coordinates. The authors suggest that the observation-based estimate of Ψ will be useful for comparison with equivalent diagnostics from numerical climate models. The estimates of KH and KI represent horizontal eddy mixing in the mixed layer and isopycnal eddy mixing in the ocean interior, respectively. This study finds that the solution for D and KH are comparable to existing estimates. The solution for KI is one of the first observation-based global and full-depth constrained estimates of isopycnal mixing and indicates that KI is an order of magnitude smaller than KH. This suggests that there is a large vertical variation in the eddy mixing coefficient, which is generally not included in ocean models. With ocean models being very sensitive to the choice of isopycnal mixing, this result suggests that further investigation of the spatial structure of isopycnal eddy mixing from observations is required.

scholarly journals Multipurpose Energy Saving Manual Compressor for Artisans in African Countries

2018 ◽  
Vol 8 (4) ◽  
Author(s):  
Dr.Isaac Ali Kwasu ◽  
Dr.Aje Tokan ◽  
Engr.M A Bawa
Keyword(s):  
Driving Force ◽  
Storage Tank ◽  
Research Work ◽  
Daily Activities ◽  
Small Scale ◽  
Pilot Test ◽  
Prime Mover ◽  
African Countries ◽  
Air Compressor ◽  
To Receive

This Research work involves the design, fabrication and testing of a manually operated compressor for use of artisans and small scale vulcanizing activities. The developed machine consists of chain sprocket arrangement to a flywheel attached to a pulley which powers the compressor as well as a storage tank to receive air by foot pedaling. The article is an innovative product to meet the needs of rural African Artisans that uses air compressor for their daily activities . The design is such that the chain sprocket provides the compressor with a driving force in conjunction with the flywheel thereby replacing the prime mover. Prototype pilot test carried out on the developed manual air compressor could generates 10 Psi ie 0.69bar-volume of air in 60 seconds. A new design with better parameter of the machine was done to improve it’s proficiency after testing for broad application even for the handicap Artisans.

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