78 research outputs found
On the kinetics of pack aluminization
A theory of pack aluminization has been formulated by combining gaseous and solid-state diffusion rates. This theory relates the surface composition of the coating and therefore, in principle, the phase morphology and the growth rate of the coating, to pack operating parameters such as pack aluminum density, type of activator, temperature and others. Experimental data on the aluminization of unalloyed nickel in pure aluminum packs obtained to date are in good agreement with the predictions of the theory
On the Long Lasting âCâTypeâ Structures in the Sodium Lidargram: The Lifetime of KelvinâHelmholtz Billows in the Mesosphere and Lower Thermosphere Region
In order to understand the characteristics of longâlasting âCâtypeâ structure in the Sodium (Na) lidargram, six cases from different observational locations have been analyzed. The Na lidargram, collected from lowâ, middleâ, and highâlatitude sites, show long lifetime of the Câtype structures which is believed to be the manifestation of KelvinâHelmholtz (KH) billows in the Mesosphere and Lower Thermosphere (MLT) region. In order to explore the characteristics of the longâlasting Câtype structures, the altitude profile of square of BruntâVĂ€isĂ€lĂ€ frequency in the MLT region has been derived using the temperature profile collected from the Na lidar instruments and the SABER instrument onboard TIMED satellite. It is found to be positive in the Câtype structure region for all the six cases which indicates that the regions are convectively stable. Simultaneous wind measurements, which allowed us to calculate the Richardson numbers and Reynolds numbers for three cases, suggest that the regions where the Câtype structure appeared were dynamically stable and nonturbulent. This paper brings out a hypothesis wherein the low temperature can increase the magnitude of the Prandtl number and convectively stable atmospheric region can cause the magnitude of Reynolds number to decrease. As a consequence, the remnant of previously generated KH billows in nearly âfrozenâinâ condition can be advected through this conducive region to a different location by the background wind where they can sustain for a long time without much deformation. These longâlived KH billows in the MLT region will eventually manifest the longâlasting Câtype structures in the Na lidargram
Signature of Y-forking in ionogram traces observed at low-mid latitude Indian station, New Delhi, during the earthquake events of 2020: ionosonde observations
We have examined ionospheric response to eleven earthquake events measuring less than four on the Richter scale during the year 2020 that occurred in the vicinity of New Delhi (28.6°N, 77.2°E, 42.4°N dip). We have used ionogram traces, manually scaled critical ionospheric layer parameters using SAO explorer obtained from Digisonde along with the O(1D) airglow observations from a multi-wavelength all-sky airglow imager installed at Hanle, Ladakh, India (32.7°N, 78.9°E, 24.1°N dip). Perceptible ionospheric perturbations 2â9 days prior to these earthquake events resulting in more than 250% variation in electron density are observed. We found distortion of ionogram trace in the form of Y forking majorly at New Delhi on the precursor day and after the earthquake event. Traces of Y forked ionograms were also observed at Ahmedabad (23°N, 72°E, 15°N dip) and Trivandrum (8.5°N, 76.9°E, 0.5°N dip). These Y-forked ionograms are one of the first observations during any earthquake events and are looked at as a signature of Travelling Ionospheric Disturbances (TIDs)
Identification of active fossil bubbles based on coordinated VHF radar and airglow measurements
Plasma irregularity structures associated with an Equatorial Spread-F (ESF) event were
recorded by the Indian VHF Radar on 26–27 April 2006 near
midnight hours. The plasma structures were found to be isolated
without having bottomside structure. They moved predominantly
downward and the structures were found to be less turbulent than
their post-sunset counterparts. However, the structures were
characterized by meter-scale size irregularities. These structures
are identified for the first time as plasma depletion structures
using simultaneous, collocated measurements of OI 630.0 nm airglow
intensity variations. The variation of the base height of
ionospheric F layer over dip equator is also presented to buttress
the result. Further, these plasma structures are shown to be
"active fossil bubbles"
Arsenic Speciation in Food and Estimation of the Dietary Intake of Inorganic Arsenic in a Rural Village of West Bengal, India
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