11,875 research outputs found
Holocene Climate in Coastal Peru: Potential Implications for Climate Dynamics during the Hypsithermal Period
This pilot study will analyze stable isotopes in planktic foraminifera in sediment cores off the coast of Peru for the Holocene interval. In many regions of the world the early Holocene is believed to have been a time of warmer-than modern temperatures. Data derived from Peruvian middens give conflicting evidence as to whether this period was somewhat warmer or cooler than today. The foraminiferal data should provide a record of sea surface temperatures and seasonal upwelling along coastal Peru throughout the Holocene, including the period of human coastal settlement
Numerical Solution of an Extra-wide Angle Parabolic Equation through Diagonalization of a 1-D Indefinite Schr\"{o}dinger Operator with a Piecewise Constant Potential
We present a numerical method for computing the solution of a partial
differential equation (PDE) for modeling acoustic pressure, known as an
extra-wide angle parabolic equation, that features the square root of a
differential operator. The differential operator is the negative of an
indefinite Schr\"{o}dinger operator with a piecewise constant potential. This
work primarily deals with the 3-piece case; however, a generalization is made
the case of an arbitrary number of pieces. Through restriction to a judiciously
chosen lower-dimensional subspace, approximate eigenfunctions are used to
obtain estimates for the eigenvalues of the operator. Then, the estimated
eigenvalues are used as initial guesses for the Secant Method to find the exact
eigenvalues, up to roundoff error. An eigenfunction expansion of the solution
is then constructed. The computational expense of obtaining each eigenpair is
independent of the grid size. The accuracy, efficiency, and scalability of this
method is shown through numerical experiments and comparisons with other
methods.Comment: 27 pages, 13 figure
Evidence for extended IR emission in NGC2798 and NGC6240
Extended emission at 10 and 20 microns can be used to distinguish starbursts from monsters as the underlying energy source driving the luminous infrared emission in the central regions of galaxies. The spatial extent of the mid infrared emission in the interacting galaxy NCG 2798 and the merger NGC 6240 were investigated. The 10 and 20 micron profiles of the IR source in NGC 2798 are significantly wider than beam profiles measured on a standard star, supporting a starburst interpretation of its IR luminosity. For NGC 6240 there is marginal evidence for an extended 10 micron source, suggesting that a significant fraction of its IR luminosity could be produced by a burst of star formation
R2 Bounds for Predictive Models: What Univariate Properties Tell us About Multivariate Predictability
A long-standing puzzle in macroeconomic forecasting has been that a wide variety of multivariate models have struggled to out-predict univariate models consistently. We seek an explanation for this puzzle in terms of population properties. We derive bounds for the predictive R2 of the true, but unknown, multivariate model from univariate ARMA parameters alone. These bounds can be quite tight, implying little forecasting gain even if we knew the true multivariate model. We illustrate using CPI inflation data
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