A parameter uniform fitted mesh method for a weakly coupled system of two singularly perturbed convection-diffusion equations

In this paper, a boundary value problem for a singularly perturbed linear system of two second order ordinary differential equations of convection- diffusion type is considered on the interval [0, 1]. The components of the solution of this system exhibit boundary layers at 0. A numerical method composed of an upwind finite difference scheme applied on a piecewise uniform Shishkin mesh is suggested to solve the problem. The method is proved to be first order convergent in the maximum norm uniformly in the perturbation parameters. Numerical examples are provided in support of the theory

Non-Darcy flow characteristics of water as influenced by clay concentration

The flow of water through saturated samples of montmorillonite and kaolinite was studied to help clarify the existence and nature of non-Darcian flow. No threshold gradients were found in any of the samples studied. Non-Darcy flow was found in 9, 30 and 40 weight percent montmorillonite samples but not in a 50 weight percent montmorillonite or in kaolinite samples. The possible causes of the non-Darcian flow are discussed. A refined technique using a pressure transducer was developed to measure hydraulic conductivities. The hydraulic conductivities of several types of samples under varying conditions were measured. Transport equations for convective diffusion in porous media were derived and tested for capillaries, porous diaphragms, sand columns and clay plugs.U.S. Department of the InteriorU.S. Geological SurveyOpe

The Ghost in the Machine: Inferring Machine-Based Strategies from Observed Behavior

We introduce a procedure to infer the repeated-game strategies that generate actions in experimental choice data. We apply the technique to set of experiments where human subjects play a repeated Prisoner's Dilemma. The technique suggests that two types of strategies underly the data

Aerosol Data Sources and Their Roles within PARAGON

We briefly but systematically review major sources of aerosol data, emphasizing suites of measurements that seem most likely to contribute to assessments of global aerosol climate forcing. The strengths and limitations of existing satellite, surface, and aircraft remote sensing systems are described, along with those of direct sampling networks and ship-based stations. It is evident that an enormous number of aerosol-related observations have been made, on a wide range of spatial and temporal sampling scales, and that many of the key gaps in this collection of data could be filled by technologies that either exist or are expected to be available in the near future. Emphasis must be given to combining remote sensing and in situ active and passive observations and integrating them with aerosol chemical transport models, in order to create a more complete environmental picture, having sufficient detail to address current climate forcing questions. The Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) initiative would provide an organizational framework to meet this goal

Searches for Extremely Metal Poor Galaxies using ALFALFA-selected Dwarf Galaxies

We present a study of nearby dwarf galaxies selected from the ALFALFA blind HI survey. A primary goal of the project was to utilize a non-standard selection method with the hope of detecting previously unrecognized extremely metal-poor (XMP) galaxies. The study was motivated by the recent discovery of two XMP galaxies $-$ Leo P and Leoncino $-$ which were both originally found via the ALFALFA survey. We have obtained narrowband H$\alpha$ images for 42 dwarf systems, many of which are located in the local void in front of the Pisces-Perseus Supercluster. Spectra for eleven of the best candidates resulted in the determination of metal abundances for ten of the systems. None were found to be extremely metal poor, although one system (AGC 123350) was found to have an oxygen abundance of log(O/H)+12 = 7.46, or $\sim$6\% solar. One of the galaxies in our sample exhibits a high oxygen abundance for its luminosity, suggesting the possibility that it may have a tidal origin.Comment: 21 pages, 11 figures, 4 table

NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist

Tables of ^1H and ^(13)C NMR chemical shifts have been compiled for common organic compounds often used as reagents or found as products or contaminants in deuterated organic solvents. Building upon the work of Gottlieb, Kotlyar, and Nudelman in the Journal of Organic Chemistry, signals for common impurities are now reported in additional NMR solvents (tetrahydrofuran-d_8, toluene-d_8, dichloromethane-d_2, chlorobenzene-d_5, and 2,2,2-trifluoroethanol-d_3) which are frequently used in organometallic laboratories. Chemical shifts for other organics which are often used as reagents or internal standards or are found as products in organometallic chemistry are also reported for all the listed solvents