RESUMO
The Tilt-depth is a popular approach for determining depths of magnetic sources. As this method is based on the distance between contour levels of the tilt angle, it can lead to inaccurate depth estimates when the contour lines are distorted by the presence of noise. In this paper, we stabilize the Tilt-depth method based on the computation of stable vertical derivative obtained by the ß-VDR method. The presented method is demonstrated on synthetic magnetic anomalies and real magnetic data from the Arabian Shield. The results obtained from the synthetic examples coincide well with the actual depths. These results proved the utility of the presented method in cases where the field is corrupted by noise. The real example shows that the presented method can provide valuable information on subsurface structures of the area where the Tilt-depth estimates are consistent with the result of the horizontal tilt angle. The findings show that the presented method is less sensitive to noise and can provide source edges and depths more clearly and with higher accuracy.
RESUMO
The debatable timing of India-Eurasia collision is based on geologic, stratigraphic, kinematic, and tectonic evidence. However, the collision event disturbed persistent processes, and the timing of disturbance in such processes could determine the onset of India-Eurasia collision precisely. We use the longevity of Southeast Indian Ridge (SEIR)-Kerguelen mantle plume (KMP) interaction cycles along the Ninetyeast ridge (NER) as a proxy to determine the commencement of India-Eurasia collision. The geochemical signature of the KMP tail along the NER is predominantly that of long-term coupling cycles, that was perturbed once by a short-term decoupling cycle. The long-term coupling cycles are mainly of enriched mid-ocean ridge basalts (E-MORBs). The short-term decoupling cycle is mostly derived from two distinct sources, MOR and plume separately, whereas the KMP is still being on-axis. The onset of India-Eurasia collision led to continental materials recycling into the mantle; hence the abrupt enrichment in incompatible elements at ca. 55 Ma, the MOR-plume on-axis decoupling, and the abrupt slowdown in the northward drift of the Indian plate was induced by the onset of India-Eurasia collision, thereafter MOR-plume recoupled.
RESUMO
The baseline data of radioactivity levels in food is one of the main factors for the assessment of resident's health risk. Gross beta and alpha activity was identified for selected commercial freshwater fish species, including 29 types of fish species by a gas-flow proportional detector. The samples were collected from wholesale markets in Hanoi city, Vietnam. The highest gross alpha activity was recorded in blotched snakehead, a pelagic and carnivorous species, and the lowest one was recorded in common carp, a demersal and omnivorous species. Meanwhile, the gross beta activity was much higher than the gross alpha activity with the highest value of gross beta, observed in Wels catfish, a demersal and carnivorous species, and the lowest one found in Mudskipper a demersal, herbivores species. Regarding feeding types, the gross alpha activity was observed in the order of Alcarnivores > Alomnivores > Alherbivores whereas the gross beta was non-distinction. In terms of living behavior, the gross alpha activity in pelagic species was much higher than that in demersal species (Alpelagic > > Aldemersal) and indifferent for gross beta. There was an insignificant relationship between the trophic level with gross beta and alpha activities in freshwater fish species. The calculated annual effective dose ââranged from 0.19 to 1.88 and 0.78 mSv.y-1 on average, being within the limited dose for the public as reported by UNSCEAR in which gross beta activity has a strong correlation with the total annual effective dose.