On the Low-Frequency Transport Processes in a Shallow Coastal Lagoon

Estuaries ◽  
1998 ◽  
Vol 21 (4) ◽  
pp. 754 ◽  
Author(s):  
C. D. Janzen ◽  
K.-C. Wong
Keyword(s):  
Coastal Lagoon ◽  
Low Frequency ◽  
Transport Processes

scholarly journals Monoclinic Li2TiO3 Nano-particles via sol-gel method: Structure and impedance spectroscopy

2019 ◽  
Vol 8 (3) ◽  
pp. 209
Author(s):  
Fatima Zahra Krimech ◽  
Salaheddine Sayouri ◽  
Taj-Edine Lamcharfi ◽  
Fatima Zahra Ahjyaje
Keyword(s):  
Impedance Spectroscopy ◽  
Sol Gel ◽  
Low Frequency ◽  
Transport Processes ◽  
Nano Particles ◽  
Secondary Phases ◽  
Conventional Solid State Reaction ◽  
Gel Method ◽  
Sol Gel Method ◽  
Heat Treated

<p>Pure phase Li<sub>2</sub>TiO<sub>3 </sub>nano-particles were synthesized by the sol-gel method and the structural properties were examined with X-ray diffraction (XRD) technique. The latter showed that these materials, heat treated at relatively low temperature 900°C during 4h compared to the conventional solid-state reaction which calcination temperature is about 900–1100°C for 10 h; crystallize in the monoclinic phase without the presence of secondary phases. The microstructure of the LT ceramic (sintered at 1100°C) were determined by SEM and a good crystalline nature was observed with an average of granular size 2 μm. Moreover, the impedance spectroscopy showed at a higher temperature of 500°C the low-frequency arc due either to the grain boundary or sample-electrode charge transport processes.</p>

Tidal and Low-Frequency Net Displacement in a Coastal Lagoon

Estuaries ◽  
1983 ◽  
Vol 6 (3) ◽  
pp. 180 ◽  
Author(s):  
Ned P. Smith
Keyword(s):  
Coastal Lagoon ◽  
Low Frequency

Mechanisms for nitrogen supply to the Australian North West Shelf

1985 ◽  
Vol 36 (6) ◽  
pp. 753 ◽  
Author(s):  
PE Holloway ◽  
SE Humphries ◽  
M Atkinson ◽  
J Imberger
Keyword(s):  
River Flow ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Transport Processes ◽  
Physical Processes ◽  
Mixing Processes ◽  
North West ◽  
Tidal Motion ◽  
The North

An upper bound for the rate of supply of new nitrate required to maintain the observed primary production on the North West Shelf is estimated to be 0.1 g N m-2 day -1. Nitrate concentrations over the shelf and slope regions are high ( > 100 mg N m-3, in water deeper than - 100 m and usually low (~10 mg N m-3), on the shelf. River flow is weak and carries little nutrient into the shelf waters and so it remains for ocean physical processes to advect and mix the nutrient-rich deep waters onto the shallower shelf regions to meet the nutrient demand. Several mechanisms are reviewed to determine their potential in carrying out the required transport processes. Estimates of the advection of nitrate onto the shelf show that both semi-diurnal tidal flow and low-frequency (periods > 35 h) upwelling events can each contribute approximately half the required demand, providing there is rapid use of nutrients. The upwelling events occur in summer and are associated with reversals of the south-west-flowing Leeuwin Current. Tropical cyclones are also shown to be capable of meeting a small, but significant, portion of the demand through enrichment of the surface layers in the offshelf waters by upwelling and vertical mixing. The enriched water can then be advected onto the shelf. Both tidal and internal tidal motion have the potential to transport nitrate onto the shelf from deeper water through vertical and horizontal mixing processes. However, these processes are difficult to quantify accurately. It is concluded that nitrogen is supplied to this shelf ecosystem by physical processes that are regular throughout the year, as opposed to large sporadic events that occur only once or twice a year.

The origin of fluctuations and cross-field transport in idealized magnetic confinement systems

1981 ◽  
Vol 300 (1456) ◽  
pp. 547-557 ◽  
Keyword(s):  
Electric Fields ◽  
High Frequency ◽  
Scaling Laws ◽  
Scaling Law ◽  
Low Frequency ◽  
Magnetic Confinement ◽  
Upper Bounds ◽  
Transport Processes ◽  
General View ◽  
Long Wavelength

The study of plasma fluctuations and confinement in idealized systems such as octupoles and levitrons has contributed to the understanding of cross-field transport processes. The linear theory of plasma instabilities that cause fluctuations is well developed and can predict growth rates γ and wavelengths θ x around lines of force. However, the theoretical prediction of cross-field transport coefficient D ± is restricted to quasilinear estimates of upper bounds (for example, D = 1 2 γ λ x 2 ) because of the complexity of the full nonlinear calculation. Such quasilinear estimates usually far exceed the measured values and are of limited worth. A general view of the results from octupole and levitron experiments shows that under collisional conditions ( λ ei / L < 0 ) the diffusion coefficient, D , scales in the same way as classical collisional diffusion ( D α n / T e 1 2 B 2 ). Agreement is closely approached in many cases, sometimes even in the presence of fluctuations. Under collisionless conditions ( D α n / T e 1 2 B 2 ), Bohm diffusion scaling ( D α T e / B ) is found in the few cases where the scaling law has been determined. This behaviour is consistent with the general scaling laws of Connor & Taylor (1977) but is not understood in detail. In addition there is evidence, both experimental and theoretical, that long-wavelength low-frequency electric fields (convection cells) can be generated nonlinearly from high-frequency fluctuations and can contribute to cross-field transport

scholarly journals CHANG-ES

2019 ◽  
Vol 632 ◽  
pp. A13 ◽  
Author(s):  
Y. Stein ◽  
R.-J. Dettmar ◽  
M. Weżgowiec ◽  
J. Irwin ◽  
R. Beck ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Flux Density ◽  
Magnetic Field Strength ◽  
Low Frequency ◽  
Transport Processes ◽  
Radio Continuum ◽  
Continuum Emission ◽  
X Ray ◽  
The Magnetic Field

Context. The radio continuum halos of edge-on spiral galaxies have diverse morphologies, with different magnetic field properties and cosmic ray (CR) transport processes into the halo. Aims. Using the Continuum HAloes in Nearby Galaxies – an EVLA Survey (CHANG-ES) radio continuum data from the Karl G. Jansky Very Large Array (VLA) in two frequency bands, 6 GHz (C-band) and 1.5 GHz (L-band), we analyzed the radio properties, including polarization and the transport processes of the CR electrons (CREs), in the edge-on spiral galaxy NGC 4013. Supplementary LOw-Frequency ARray (LOFAR) data at 150 MHz are used to study the low-frequency properties of this galaxy and X-ray data are used to investigate the central region. Methods. We determined the total radio flux densities (central source, disk, halo and total) as well as the radio scale heights of the radio continuum emission at both CHANG-ES frequencies and at the LOFAR frequency. We derived the magnetic field orientation from CHANG-ES polarization data and rotation measure synthesis (RM synthesis). Furthermore, we used the revised equipartition formula to calculate the magnetic field strength. Lastly, we modeled the processes of CR transport into the halo with the 1D SPINNAKER model. Results. The central point source dominates the radio continuum emission with a mean of ∼35% of the total flux density emerging from the central source in both CHANG-ES bands. Complementary X-ray data from Chandra show one dominant point source in the central part. The XMM-Newton spectrum shows hard X-rays, but no clear AGN classification is possible at this time. The radio continuum halo of NGC 4013 in C-band is rather small, while the low-frequency LOFAR data reveal a large halo. The scale height analysis shows that Gaussian fits, with halo scale heights of 1.2 kpc in C-band, 2.0 kpc in L-band, and 3.1 kpc at 150 MHz, better represent the intensity profiles than do exponential fits. The frequency dependence gives clear preference to diffusive CRE transport. The radio halo of NGC 4013 is relatively faint and contributes only 40% and 56% of the total flux density in C-band and L-band, respectively. This is less than in galaxies with wind-driven halos. While the SPINNAKER models of the radio profiles show that advection with a launching velocity of ∼20 km s−1 (increasing to ∼50 km s−1 at 4 kpc height) fits the data equally well or slightly better, diffusion is the dominating transport process up to heights of 1–2 kpc. The polarization data reveal plane-parallel, regular magnetic fields within the entire disk and vertical halo components indicating the presence of an axisymmetric field having a radial component pointing outwards. The mean magnetic field strength of the disk of NGC 4013 of 6.6 μG is rather small. Large-scale vertical fields are observed in the halo out to heights of about 6 kpc. Conclusions. The interaction and the low star formation rate (SFR) across the disk of NGC 4013 probably influence the appearance of its radio continuum halo and are correlated with the low total magnetic field strength. Several observable quantities give consistent evidence that the CR transport in the halo of NGC 4013 is diffusive: the frequency dependence of the synchrotron scale height, the disk/halo flux density ratio, the vertical profile of the synchrotron spectral index, the small propagation speed measured modeled with SPINNAKER, and the low temperature of the X-ray emitting hot gas.

scholarly journals Monoclinic Li2TiO3 Nano-particles via sol-gel method: Structure and impedance spectroscopy

2019 ◽  
Vol 8 (3) ◽  
pp. 209-212
Author(s):  
Fatima Zahra Krimech ◽  
Salaheddine Sayouri ◽  
Taj-Edine Lamcharfi ◽  
Fatima Zahra Ahjyaje
Keyword(s):  
Impedance Spectroscopy ◽  
Sol Gel ◽  
Low Frequency ◽  
Transport Processes ◽  
Nano Particles ◽  
Secondary Phases ◽  
Conventional Solid State Reaction ◽  
Gel Method ◽  
Sol Gel Method ◽  
Heat Treated

Pure phase Li2TiO3 nano-particles were synthesized by the sol-gel method, and the structural properties were examined with X-ray diffraction (XRD) technique. The latter showed that these materials, heat treated at relatively low temperature 900°C during 4h compared to the conventional solid-state reaction which calcination temperature is about 900–1100°C for 10 h; crystallize in the monoclinic phase without the presence of secondary phases. The microstructure of the LT ceramic (sintered at 1100°C) were determined by SEM, and good crystalline nature was observed with an average of granular size 2 μm. Moreover, the impedance spectroscopy showed at a higher temperature of 500°C the low-frequency arc due either to the grain boundary or sample-electrode charge transport processes.

Observations and simulations of electron flux oscillations in response to broadband ULF waves

2020 ◽  
Author(s):  
Xinlin Li ◽  
Theodoros Sarris ◽  
Michael Temerin ◽  
Hong Zhao ◽  
Leng Ying Khoo ◽  
...  
Keyword(s):  
Electron Flux ◽  
Low Frequency ◽  
Transport Processes ◽  
Ulf Waves ◽  
Magnetic Fluctuations ◽  
Radial Transport ◽  
Energy Channel ◽  
Van Allen Probes ◽  
Initial Results ◽  
Energy Channels

&lt;p&gt;It has recently been demonstrated through simulations and observations that flux oscillations of hundreds-keV electrons are produced in the magnetosphere in association with broadband Ultra Low Frequency (ULF) waves (Sarris et al., JGR, 2017). These oscillations are observed in the form of drift-periodic flux fluctuations, but are not associated with drift echoes following storm- or substorm-related energetic particle injections. They are observed in particular during quiet times, and it has been shown that they could indicate ongoing radial transport processes caused by ULF waves. It has also been shown that the width of electron energy channels is a critical parameter affecting the observed amplitude of flux oscillations, with narrower energy channel widths enabling the observation of higher-amplitude flux oscillations; this potentially explains why such features were not observed regularly before the Van Allen Probes era, as previous spacecraft generally had lower energy resolution. We extend these initial results by investigating the association between the observed flux oscillations with the amplitude of electric and magnetic fluctuations in the ULF range and with Phase Space Density gradients, both of which are expected to also affect radial transport rates.&lt;/p&gt;

scholarly journals Actuation of Liquid Flow by Guided Acoustic Waves on Punched Steel Tapes with Protruding Loops

2021 ◽  
Vol 18 (3) ◽  
pp. 534-547
Author(s):  
Alexander Backer ◽  
Johannes Landskron ◽  
Klaus Stefan Drese ◽  
Gerhard Lindner
Keyword(s):  
Liquid Flow ◽  
Acoustic Waves ◽  
Acoustic Streaming ◽  
Low Frequency ◽  
Transport Processes ◽  
Frequency Range ◽  
Flow Profiles ◽  
Sharp Edges ◽  
Plate Waves ◽  
Biomimetic Approach

AbstractIn a biomimetic approach the feasibility of liquid flow actuation by vibrating protruding structures excited via guided acoustic waves is investigated. Inspired by periodically beating cilia the loop part of a punched metallic hook-and-loop tape with tilted protruding loops was used as a waveguide for plate waves in water. Such waves were excited in the frequency range of 110 Hz to 220 Hz by directly coupling the tape to a loudspeaker membrane. A flow generated in the tilt direction of the loops with velocities up to 60 mm·s−1 was visualized by ink droplets deposited on the tape. The phenomenon persisted, when the protruding length of the loops was reduced by decreasing the protrusion angle. However, after closing the punch holes near the loops with sticking tape streaming could not be observed any longer. The same happened with open punch holes when the ink was replaced by glycerol. Low-frequency acoustic streaming around vibrating sharp edges is proposed as an explanation for the observed phenomena. Applications are expected with respect to the modification of flow profiles and the enhancement of transport processes along and across liquid-solid boundaries.

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