scholarly journals Duskside F-region dynamo currents: its relationship with prereversal enhancement of vertical plasma drift

2010 ◽  
Vol 28 (11) ◽  
pp. 2097-2101 ◽  
Author(s):  
J. Park ◽  
H. Lühr ◽  
B. G. Fejer ◽  
K. W. Min
Keyword(s):  
Current Density ◽  
Solar Maximum ◽  
Field Observations ◽  
Longitudinal Variation ◽  
Plasma Drift ◽  
F Region ◽  
Close Relationship ◽  
E Region ◽  
Current Densities ◽  
First Time

Abstract. From magnetic field observations by CHAMP we estimate F-region dynamo current densities near the sunset terminator during solar maximum years from 2001 to 2002. The dynamo currents are compared with the pre-reversal enhancement (PRE) of vertical plasma drift as observed by ROCSAT-1. The seasonal-longitudinal variation of PRE can be largely related to the F-region dynamo current density, with the correlation coefficient reaching 0.74. The correlation can be further improved if we consider a zonal gradient of the E-region Pedersen conductivity, which also depends on season and longitude. It is widely accepted that the F-region dynamo drives PRE near sunset. For the first time, our observations provide confirmation for the close relationship between the F-region dynamo current density and PRE.

scholarly journals Vertical and longitudinal electron density structures of equatorial E- and F-regions

2011 ◽  
Vol 29 (1) ◽  
pp. 81-89 ◽  
Author(s):  
P. S. Brahmanandam ◽  
Y.-H. Chu ◽  
K.-H. Wu ◽  
H.-P. Hsia ◽  
C.-L. Su ◽  
...  
Keyword(s):  
Electron Density ◽  
Phase Relation ◽  
F Region ◽  
Good Consistency ◽  
June Solstice ◽  
December Solstice ◽  
Different Seasons ◽  
E Region ◽  
First Time ◽  
Longitudinal Structures

Abstract. From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.

scholarly journals Intermediate Layers responses to Geomagnetic Activity During the 2009 Deep Solar Minimum Over the Brazilian Low Latitude Sector

2021 ◽  
Author(s):  
Ângela Santos ◽  
Christiano Brum ◽  
Inez Batista ◽  
José Sobral ◽  
Mangalathayil Abdu ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Early Morning ◽  
Low Latitude ◽  
Seasonal Behavior ◽  
F Region ◽  
Intermediate Layers ◽  
Bottom Side ◽  
E Region ◽  
First Time

Abstract. Intermediate layers (ILs) are regions of enhanced electron density located in the ionospheric valley that extends from the peak altitude of the daytime E-region to the bottom side of the F-region. This work presents the daytime behavior of the ILs parameters (the virtual height - h’IL, and the top frequency - ftIL) over the low latitude region of Cachoeria Paulista (CP, 22.42° S; 45° W, I: −34.4°) for the deepest solar minimum of the last 500 years. In such a unique condition, this research reveals for the first time the ILs' quiet state seasonal behavior as well as its responses to moderate changes in the geomagnetic activity. The main results show that even small variations of geomagnetic activity (quantified by the planetary Kp index) are able to modify the dynamics of the ILs parameters. For the first time, it was observed that during the summer, the h’IL decrease rapidly with the increase of geomagnetic activity mainly in the early morning hours. In the following hours, a smoothed rise of the IL was found in all seasons analyzed. Regarding to frequency, it was observed that after 12:00 LT, there is a tendency of it decreased with the increase of the magnetic disturbances, being this characteristic more intense after 16:00 LT, except in the equinox, when little or no response was found during all the interval analyzed. In addition, it stands out that the annual periodicity of the ftIL was observed while the h’IL presents semiannual component.

Low Threshold Current Density 1.5 μm Strained-MQW Laser by n-Type Modulation-Doping

2005 ◽  
Vol 475-479 ◽  
pp. 1663-1668 ◽  
Author(s):  
Rui-ying Zhang ◽  
Wei Wang ◽  
Fan Zhou ◽  
Jing Bian ◽  
Ling-juan Zhao ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Current Density ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Multiple Quantum ◽  
Modulation Doping ◽  
Doping Effects ◽  
Low Threshold ◽  
Current Densities ◽  
First Time

1.5µm n-type modulation-doping InGaAsP/InGaAsP strained multiple quantum wells grown by low pressure metalorganic chemistry vapor decomposition technology is reported for the first time in the world. N-type modulation-doped lasers exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 1052.5 A/cm2 for 1000 µm long lasers with seven quantum wells. The estimated threshold current density for an infinite cavity length was 94.72A/cm2/well, reduced by 23.3% compared with undoped barrier lasers. The n-type modulation doping effects on the lasing characteristics in 1.5µm devices have been demonstrated.

scholarly journals On the relationship between the velocity of E-region HF echoes and <i>E</i>x<i>B</i> plasma drift

2005 ◽  
Vol 23 (2) ◽  
pp. 371-378 ◽  
Author(s):  
A. V. Koustov ◽  
D. W. Danskin ◽  
R. A. Makarevitch ◽  
J. D. Gorin
Keyword(s):  
Phase Velocity ◽  
Hf Radar ◽  
Line Of Sight ◽  
Plasma Drift ◽  
F Region ◽  
Plasma Drifts ◽  
E Region ◽  
Cross Track ◽  
The Relationship ◽  
Large Flow

Abstract. In this study, velocities of E-region HF echoes observed by the Stokkseyri HF radar are compared with ExB plasma drifts in the F-region measured by the DMSP satellites. Events were selected for which the DMSP track projected to the height of 110km was almost perpendicular to the central beams of the radar, resulting in a direct comparison of the cross-track component of the ExB drift and the line-of-sight HF velocity. We found that the typical ratio of HF velocity to the DMSP drift is ~0.35 in a range of DMSP drifts of 0-1700m/s. It is suggested that E-region HF velocities, observed both along the electrojet and at large flow angles, are significantly affected by scatter from the bottom of the electrojet layer where the irregularity phase velocity is expected to be strongly depressed with respect to the ExB flow.

scholarly journals The effect of <i>E</i>-region wave heating on electrodynamical structures

2005 ◽  
Vol 23 (6) ◽  
pp. 2081-2094 ◽  
Author(s):  
J.-M. A. Noël ◽  
J.-P. St.-Maurice ◽  
P.-L. Blelly
Keyword(s):  
Electric Fields ◽  
Plasma Temperature ◽  
Dynamical Response ◽  
Electron Recombination ◽  
F Region ◽  
Wave Heating ◽  
E Region ◽  
Current Densities ◽  
Strong Electric Fields ◽  
Parallel Current

Abstract. We show that heating by large amplitude E-region plasma waves at high latitudes can at times substantially enhance the electro-dynamical response of the ionosphere. This is made manifest through an increase in parallel current densities and parallel electric fields generated at the edge of arcs in the E and lower F-region of the ionosphere, in response to sharp cutoffs in precipitation with an otherwise uniform differential energy flux. The enhancement is rooted in a reduction in electron recombination that occurs in response to higher electron temperatures triggered by the generation of strong electric fields near the edge of the arc. The reduced recombination rate, in turn, leads to enhanced conductivity gradients near the edge of the arc, which, in turn, drives more intense parallel currents and stronger local electric fields. Keywords. Ionosphere (Electric fields and curents; Plasma temperature and density) – Space plasma physics (Numerical simulation studies)

scholarly journals Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations

2013 ◽  
Vol 31 (6) ◽  
pp. 1035-1044 ◽  
Author(s):  
J. Park ◽  
H. Lühr
Keyword(s):  
Magnetic Field ◽  
Ionospheric Plasma ◽  
Wind Effect ◽  
Field Observations ◽  
Republic Of China ◽  
Ion Drift ◽  
Plasma Drift ◽  
F Region ◽  
The Republic ◽  
Westward Drift

Abstract. In this paper we estimate zonal plasma drift in the equatorial ionospheric F region without counting on ion drift meters. From June 2001 to June 2004 zonal plasma drift velocity is estimated from electron, neutral, and magnetic field observations of Challenging Mini-satellite Payload (CHAMP) in the 09:00–20:00 LT sector. The estimated velocities are validated against ion drift measurements by the Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics Instrument (ROCSAT-1/IPEI) during the same period. The correlation between the CHAMP (altitude ~ 400 km) estimates and ROCSAT-1 (altitude ~ 600 km) observations is reasonably high (R &amp;approx; 0.8). The slope of the linear regression is close to unity. However, the maximum westward drift and the westward-to-eastward reversal occur earlier for CHAMP estimates than for ROCSAT-1 measurements. In the equatorial F region both zonal wind and plasma drift have the same direction. Both generate vertical currents but with opposite signs. The wind effect (F region wind dynamo) is generally larger in magnitude than the plasma drift effect (Pedersen current generated by vertical E field), thus determining the direction of the F region vertical current.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

Electron-beam damage of oxides at high current densities

1989 ◽  
Vol 47 ◽  
pp. 634-635
Author(s):  
M. R. McCartney ◽  
J. K. Weiss ◽  
David J. Smith
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Current Density ◽  
Transition Metal Oxides ◽  
Time Resolved ◽  
Rapid Acquisition ◽  
Resolution Electron ◽  
Current Densities ◽  
Electron Stimulated Desorption ◽  
Channel Analyzer

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.

scholarly journals Effect of Plating Current Density on the Ball-On-Disc Wear of Sn-Plated Ni Coatings on Cu Foils

Coatings ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 56
Author(s):  
Ashutosh Sharma ◽  
Byungmin Ahn
Keyword(s):  
Current Density ◽  
Wear Loss ◽  
Wear Properties ◽  
Friction Behavior ◽  
Track Geometry ◽  
Cu Substrates ◽  
Current Densities ◽  
The Impact ◽  
Sliding Distance ◽  
Ball On Disc

Metallic and alloyed coatings are used widely in several decorative and technology-based applications. In this work, we selected Sn coatings plated on Cu substrates for joining applications. We employed two different plating baths for the fabrication of Sn and Ni coatings: acidic stannous sulfate for Sn and Watts bath for Ni layer. The plating current densities were varied from 100–500 mA/cm2. Further, the wear and friction behavior of the coatings were studied using a ball-on-disc apparatus under dry sliding conditions. The impact of current density was studied on the morphology, wear, and coefficient of friction (COF) of the resultant coatings. The wear experiments were done at various loads from 2–10 N. The sliding distance was fixed to 7 m. The wear loss was quantified in terms of the volume of the track geometry (width and depth of the tracks). The results indicate that current density has an important role in tailoring the composition and morphology of coatings, which affects the wear properties. At higher loads (8–10 N), Sn coatings on Ni/Cu had higher volume loss with a stable COF due to a mixed adhesive and oxidative type of wear mechanism.

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