State University of New York System

About: State University of New York System is a education organization based out in Albany, New York, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 54077 authors who have published 78070 publications receiving 2985160 citations.

A fast algorithm for two-point seismic ray tracing

Abstract: A new approximate algorithm for two-point ray tracing is proposed and tested in a variety of laterally heterogeneous velocity models. An initial path estimate is perturbed using a geometric interpretation of the ray equations, and the travel time along the path is minimized in a piecewise fashion. This perturbation is iteratively performed until the travel time converges within a specified limit. Test results show that this algorithm successfully finds the correct travel time within typical observational error much faster than existing three-dimensional ray tracing programs. The method finds an accurate ray path in a fully three-dimensional form even where lateral variations in velocity are severe. Because our algorithm utilizes direct minimization of the travel time instead of solving the ray equations, a simple linear interpolation scheme can be employed to compute velocity as a function of position, providing an added computational advantage.

The role of the thalamus in the flow of information to the cortex

Abstract: The lateral geniculate nucleus is the best understood thalamic relay and serves as a model for all thalamic relays. Only 5-10% of the input to geniculate relay cells derives from the retina, which is the driving input. The rest is modulatory and derives from local inhibitory inputs, descending inputs from layer 6 of the visual cortex, and ascending inputs from the brainstem. These modulatory inputs control many features of retinogeniculate transmission. One such feature is the response mode, burst or tonic, of relay cells, which relates to the attentional demands at the moment. This response mode depends on membrane potential, which is controlled effectively by the modulator inputs. The lateral geniculate nucleus is a first-order relay, because it relays subcortical (i.e. retinal) information to the cortex for the first time. By contrast, the other main thalamic relay of visual information, the pulvinar region, is largely a higher-order relay, since much of it relays information from layer 5 of one cortical area to another. All thalamic relays receive a layer-6 modulatory input from cortex, but higher-order relays in addition receive a layer-5 driver input. Corticocortical processing may involve these corticothalamocortical 're-entry' routes to a far greater extent than previously appreciated. If so, the thalamus sits at an indispensable position for the modulation of messages involved in corticocortical processing.

Origin of mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust?

Abstract: To the best of our knowledge, modern adakites have not been documented in a nonarc environment. We report geochemical and isotopic data for Early Cretaceous Anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction. The Anjishan adakitic intrusive rocks, which are exposed in the Ningzhen area of east China, have high Sr/Y and La/Yb ratios coupled with low Yb and Y as well as relatively high MgO contents and Mg numbers (Mg#; 0.4-0.6), similar to products from slab melting. However, low ∈ N d ( t ) values (-6.8 to-9.7) and high ( 8 7 Sr/ 8 6 Sr) i (0.7053-0.7066) are inconsistent with an origin by slab melting. The tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust. High Sr/Y and La/Yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting, implying that the crustal thickness exceeded 40 km in the Early Cretaceous. The present thickness of the crust in the Ningzhen area is only 30 km, and therefore the crust appears to have been thinned by at least ∼10 km since the Early Cretaceous. The relatively high MgO contents and Mg# of the Anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks, possibly coinciding with lower-crustal delamination, which would also account for the observed thinning.