Suppressing Near-Receiver Scattered Waves from Seismic Land Data

When upcoming body waves travel through a heterogeneous near-surface region, the continuity of the wavefront can be diminished by scattering. We discuss a multichannel method to predict and subtract near-receiver scattered waves, such that the continuity and trace-to-trace coherency of wavefronts increases. We apply this method to a part from a field-data set which was acquired in an area with significant near-surface scattering. We show that the method increases trace-to-trace coherency in a reflection event. Moreover, application of our method improves the results obtained from application of a dip filter only, because we remove parts of the scattered wave with apparent velocities that are typically passed by the pass-zone of the dip filter.Shell GameChangerDutch Technology Foundation (STW)Shell International Exploration and Production, Inc

Hydrologic analysis of the Headwaters Lamprey River Watershed using water isotopes

The Headwaters Lamprey River Watershed (HLRW) is located in southeastern New Hampshire, a region projected to experience rapid population growth and increased water stress. In order to better understand groundwater flowpaths and residence times within the HLRW, this study employs stable water isotopes as natural tracers. For the period of June 2006 through October 2007, over 200 total water samples of groundwater, surface water, precipitation, and infiltration were collected and analyzed for stable hydrogen and oxygen isotopes. Based on analysis of isotopic and hydrometric data, the groundwater system is interpreted to be comprised of three distinct but interconnected reservoirs: a shallow groundwater reservoir which does not directly contribute to stream flow at the watershed outlet and has a mean residence time greater than 9 years; a very shallow groundwater reservoir, which is fed by the shallow system, flows through surface water bodies and wetlands with a mean residence time of approximately 1.5 months, and is the primary source of baseflow in the stream network; and a deep groundwater reservoir. The findings have significant implications for the interpretation of biogeochemical mass balance models in the Lamprey River Watershed

A Short Note on Modeling Wave Propagation in Media with Multiple Sets of Fractures

Wave propagation and scattering in fractured formations have been modeled with finite-difference programs and the use of equivalent anisotropic media description of discrete fractures. This type of fracture description allows a decomposition of the compliance matrix into two parts: one accounts for the background medium and another accounts for the fractures. The compliance for the fractures themselves can be a sum of compliances of various fracture sets with arbitrary orientations. Non-orthorgonality of the fractures, however, complicates the compliance matrix. At the moment, we can model an orthorhombic medium (9 independent elastic constants) with the two orthogonal fracture sets. However, if the fractures are non-orthogonal, this results in more general anisotropy (monoclinic) for which we need to specify 11 independent parameters.. Theoretical formulation shows that the finite difference program can be extended to simulate wave propagation in monoclinic media with little additional computational and storage cost.United States. Dept. of Energy (Award No. DE-FC26-02NT15346)Massachusetts Institute of Technology. Earth Resources Laborator

Quantum Hall Ferromagnetism in a Two-Dimensional Electron System

Experiments on a nearly spin degenerate two-dimensional electron system reveals unusual hysteretic and relaxational transport in the fractional quantum Hall effect regime. The transition between the spin-polarized (with fill fraction $\nu = 1/3$) and spin-unpolarized ($\nu = 2/5$) states is accompanied by a complicated series of hysteresis loops reminiscent of a classical ferromagnet. In correlation with the hysteresis, magnetoresistance can either grow or decay logarithmically in time with remarkable persistence and does not saturate. In contrast to the established models of relaxation, the relaxation rate exhibits an anomalous divergence as temperature is reduced. These results indicate the presence of novel two-dimensional ferromagnetism with a complicated magnetic domain dynamic.Comment: 15 pages, 5 figure

Excitation Energy Dependence of the Exciton Inner Ring

We report on the excitation energy dependence of the inner ring in the exciton emission pattern. The contrast of the inner ring is found to decrease with lowering excitation energy. Excitation by light tuned to the direct exciton resonance is found to effectively suppress excitation-induced heating of indirect excitons and facilitate the realization of a cold and dense exciton gas. The excitation energy dependence of the inner ring is explained in terms of exciton transport and cooling.Comment: 5 pages, 4 figure