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The East China Sea (ECS) seasonally receives a high organic input due to the terrestrial organic matter influx, which is controlled by the East Asian Summer Monsoon (EASM), and from increased produ...

The Andaman Forearc Basin (AFB) is asymmetric in configuration and filled with a ∼6 km-thick pile of Neogene to Recent sediments (∼4 s in two-way travel time: TWT) with distinct zonation. It shows gradual thinning up to ∼3 km (0.8 s in TWT) towards the eastern end with a seabed gradient of 1:30. Thick deformed sediments ∼2 s (TWT) of the Outerarc are associated with intense faulting and occasional folding caused by recent tectonics. Development of a series of faults within the upwarped sedimentary column of Oligocene top to Recent is observed with a rotated fault block. These features are manifestations of Recent igneous intrusion, and reveal the presence of a mild N–S compressional regime. Its effect on the AFB resulted in further uplift of sediments, which can now be seen as the Invisible Bank. Forward gravity modelling supporting our seismic interpretation reveals that it is associated with igneous intrusion from the Moho (∼9 km depth), and also suggests that continental crust underlies the AFB. Strong Bottom Simulating Reflector (BSR)-like features in the Miocene sediments of Outerarc and Forearc basin at a depth of 0.6 s below the seabed suggest the inferred probable occurrence of gas hydrates in the AFB.

Ba[sub 1[minus]x]Ca[sub x]TiO[sub 3] powders have been prepared using a novel route involving solid-state reaction in a mixture of Ba[sub 1[minus]x]Ca[sub x]CO[sub 3] and TiO[sub 2]. The Ba[sub 1[minus]x]Ca[sub x]CO[sub 3] precursors used in this method were prepared by a chemical coprecipitation route to ensure a uniform supply of Ba and Ca ions during thermochemical reaction with TiO[sub 2]. The compositional homogeneity of Ba[sub 1[minus]x]Ca[sub x]TiO[sub 3] powder prepared by such a semiwet route is compared with those prepared by the conventional dry route, involving thermochemical reaction in a mixture of BaCO[sub 3], CaCO[sub 3], and TiO[sub 2] using principles of X-ray line broadening. It is shown that the powders obtained by the semiwet route possess better compositional homogeneity, over a length scale of 1,800 [angstrom] corresponding to the coherently scattering domain size, than those prepared by the conventional dry route. Microstructural studies have revealed grain sizes of the order of 1 [mu]m and several micrometers, respectively, for ceramics prepared by the semiwet and conventional dry routes. The solid solubility limit of Ca in Ba[sub 1[minus]x]Ca[sub x]TiO[sub 3] ceramics fired at 1,300 C is 16 mol% for samples prepared by the semiwet route while conventionally processed ceramics had a Camore » solid solubility limit of 12 mol% at the same temperature.« less

Ferroelectric phase transition in (Ba,Ca)TiO[sub 3] ceramics has been investigated using dielectric measurements. It is shown that samples prepared using (Ba,Ca)CO[sub 3] precursors exhibit diffuse phase transition (DPT) while those prepared by the conventional route show BaTiO[sub 3]-type sharp transition. The diffuseness of the phase transition is found to increase with increasing calcium content. The critical exponent for the dielectric stiffness [prime](1/[var epsilon][prime]) departs significantly from the mean field value of unity and is shown to increase from 1.21 to 1.86 with increasing calcium content. Arguments are advanced to show that the DPT behavior in these ceramics is inexplicable in terms of either the internal stress model due to the absence of 90[degree] domains in fine-grain ceramics or the compositional inhomogeneity model. It is proposed that DPT behavior is intrinsic to the system and is intimately linked with the appearance of polar phase in the critical regime whose width is shown to increase with increasing Ca content.