58,932 research outputs found

    Calibrating ultrasonic test equipment for checking thin metal strip stock

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    Calibration technique detects minute laminar-type discontinuities in thin metal strip stock. Patterns of plastic tape are preselected to include minutely calculated discontinuities and the tape is applied to the strip stock to intercept the incident sonic beam

    Ultrasonics used for high-precision nondestructive inspection of brazed joints

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    Technique detects voids greater than or equal to 0.1016 cm in braze depths of 0.254 cm, detecting voids of smaller dimensions is possible. Internal design ensures control of beam's water path length to within 0.635 cm, this length is critical to system's accuracy

    Selecting a Remedy for Private Racial Discrimination: Statutes in Search of Scope

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    Racial discrimination in the United States has been effectively attacked in both the legislatures and the courts for over a hundred years. Enslavement of blacks in the American South prompted adoption of the thirteenth amendment and the Reconstruction Civil Rights Acts enacted pursuant to the amendment’s enabling clause. These laws sought primarily to elevate the status of the black freedman by granting him rights equal to those enjoyed by white citizens. The most far-reaching of these statutes is 42 U.S.C. § 1981, derived from the Civil Rights Act of 1866, which insures to all persons the same right to make and enforce contracts. This Comment shall attempt to evaluate section 1981’s proper place in the enforcement of civil rights by examining whether section 1981 was intended to benefit whites as well as blacks, the propriety of asserting a section 1981 claim without first seeking recourse under Title VII, and the effect of section 1981 actions by white plaintiffs upon the power of the district courts to impose “affirmative action” decrees

    Ground-based studies of emission-line variability: Recent results for NGC 5548 and future plans

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    Ever since emission-line variability was first detected in AGNs, it has been clearly understood that light-travel time effects in the broadline region (BLR) afford a tool for studying the structure of these spatially unresolved regions. However, only within the last few years has the observational problem become well defined in terms of the sampling rates and quality of data necessary to address the problem correctly. The amount of data required to extract structural information about the BLR from the continuum and emission-line light curves is so considerable that the most promising approach seemed to be to combine the observational efforts. The goal was to work together to produce a large, high-quality database which would then be released to individual investigators for more complete analysis. The cornerstone of this effort, was a joint NASA/ESA/SERC program to monitor the spectrum of NGC 5548 every four days with IUE from December 1988 through August 1988. A concurrent ground-based program was organized in an effort to enhance the scientific return on the project by extending the wavelength coverage and providing higher spectral resolution and signal to noise ratios than would be possible with IUE. It also turned out that the temporal resolution of the ground-based program was somewhat better than the temporal resolution of the IUE program, and the temporal baseline is longer and continues to grow. The database and initial results are presented by Peterson et al., (1991). The important results of the ground-based program are summarized, some additional applications of the existing data are described, and a few comments are made on what can be done in the future to expand on this work

    Thick transducers used for generating short-duration stress pulses in thin specimens

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    By generating short stress pulses with thick transducers, the pulse-echo method for determining sound velocities and acoustic attenuation can be applied to thin specimens. The stress pulses enter a specimen where one pulse is reflected several times before a succeeding pulse enters the specimen


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    Agriculture has recently been noted as a provider of non-market environmental benefits in addition to its traditional recognition as a source of negative externalities from polluting inputs. In this paper, a general equilibrium framework is used to determine optimal land subsidies and input taxes in agriculture. When agriculture generates both amenities and pollution, the optimal subsidy does not equal the net extra-market value of agricultural land. If opened to international trade, a small economy will fully correct externalities, while large economies have an incentive to set policies at non-internalizing levels to exploit terms-of-trade effects.agricultural land use, externalities, international trade, Environmental Economics and Policy, International Relations/Trade,

    Non-Gaussianity in Two-Field Inflation

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    We derive semi-analytic formulae for the local bispectrum and trispectrum in general two-field inflation and provide a simple geometric recipe for building observationally allowed models with observable non-Gaussianity. We use the \delta N formalism and the transfer function formalism to express the bispectrum almost entirely in terms of model-independent physical quantities. Similarly, we calculate the trispectrum and show that the trispectrum parameter \tau NL can be expressed entirely in terms of spectral observables, which provides a new consistency relation unique to two-field inflation. We show that in order to generate observably large non-Gaussianity during inflation, the sourcing of curvature modes by isocurvature modes must be extremely sensitive to the initial conditions, and that the amount of sourcing must be moderate in order to avoid excessive fine-tuning. Under some minimal assumptions, we argue that the first condition is satisfied only when neighboring trajectories through the two-dimensional field space diverge during inflation. Geometrically, this means that the inflaton must roll along a ridge in the potential V for some time during inflation and that its trajectory must turn slightly (but not too sharply) in field space. Therefore, it follows that two-field scenarios with attractor solutions necessarily produce small non-Gaussianity. This explains why it has been so difficult to achieve large non-Gaussianity in two-field inflation, and why it has only been achieved in a narrow class of models like hybrid inflation and certain product potentials where the potential and/or the initial conditions are fine-tuned. Some of our conclusions generalize qualitatively to general multi-field inflation.Comment: Discussion improved, gNL formula and extra figure included, typos corrected, references added. 18 pages, 2 figure

    Toward Precision Measurement of Central Black Hole Masses

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    We review briefly direct and indirect methods of measuring the masses of black holes in galactic nuclei, and then focus attention on supermassive black holes in active nuclei, with special attention to results from reverberation mapping and their limitations. We find that the intrinsic scatter in the relationship between the AGN luminosity and the broad-line region size is very small, ~0.11 dex, comparable to the uncertainties in the better reverberation measurements. We also find that the relationship between reverberation-based black hole masses and host-galaxy bulge luminosities also seems to have surprisingly little intrinsic scatter, ~0.17 dex. We note, however, that there are still potential systematics that could affect the overall mass calibration at the level of a factor of a few.Comment: 10 pages, 2 figures. To be published in the Proceedings of IAU Symposium 267 "Co-Evolution of Central Black Holes and Galaxies

    Comparing the cost-effectiveness of water conservation policies in a depleting aquifer: a dynamic analysis of the Kansas High Plains

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    This research analyzes two groundwater conservation policies in the Kansas High Plains located within the Ogallala aquifer: 1) cost-share assistance to increase irrigation efficiency; and 2) incentive payments to convert irrigated crop production to dryland crop production. To compare the cost-effectiveness of these two policies, a dynamic model simulated a representative irrigator’s optimal technology choice, crop selection, and irrigation water use over time. The results suggest that the overall water-saving effectiveness can be improved when different policy tools are considered under different conditions. High prevailing crop prices greatly reduce irrigators’ incentive to give up irrigation and therefore cause low enrollment and ineffectiveness of the incentive payment program. In areas with low aquifer-saturated thickness, the incentive payment program is more effective, whereas in areas with relatively higher water availability, the cost-share program could be a better choice
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