Phacoemulsification can be safely performed by experienced hands in cataractous eyes with PEX. The incidence of intraoperative and immediate post-operative complications in eyes with PEX was not significantly different compared to eyes without PEX in our study. Further studies among a larger population are required.
Ambient noise characteristics are perused to assess the station performance of 27 newly constructed broadband seismic stations across Sikkim Himalaya and adjoining Himalayan foreland basin, installed to study the seismogenesis and subsurface structure of the region. Power spectral densities obtained at each station, compared against the global noise limits, reveal that observed vertical component noise levels are within the defined global limits. However, the horizontal components marginally overshoot the limits due to the tilt effect. Ambient noise conditions significantly vary with different installation techniques, analysis revealing that seismic sensors buried directly in the ground have reduced long-period noise in comparison to pier installations. Tectonic settings and anthropogenic activities are also noted to cause a significant rise across short-period and microseism noise spectrum, varying spatially and temporally across the region. Day-time records higher cultural noise than night-time, while the microseism noise dominates during the monsoonal season. An assessment of the effect of the nationwide lockdown imposed due to COVID-19 pandemic revealed a significant decrease in the short-period noise levels at stations installed across the foreland basin marked with higher anthropogenic activity. Our study summarizes the overall ambient noise patterns, validating the stability and performance of the seismic stations across the Sikkim Himalayas.
Seismic tomography yields information about the 3-D structure of the interior of the Earth. Travel-times of a large number of criss-crossing waves are used for this purpose. A new model of the subducting slab geometry beneath the Himalaya and Burmese arc is proposed by inverting high-quality seismic data using the inversion technique of VanDecar (1991, http://hdl.handle.net/1773/6804). The tomographic results reveal presence of southward plunging remnants of the Indian lithosphere that follow a steep path while descending into the mantle beyond depths of 200 km below the Himalayan arc. Tomographic images below the Burmese arc, do not reveal any signature of a detachment in the subducting slab.
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