5,245 research outputs found

    The Impact of the Kansas Wheat Breeding Program on Wheat Yields, 1911–2006

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    This paper quantifies advances of the Kansas Agricultural Experiment Station (KAES) wheat breeding program for two time periods: (1) 1911 to 2006 and (2) 1977 to 2006. Using multiple regression, increases in yields of wheat varieties grown in Kansas are quantified, holding growing conditions and other improvements in productivity constant. Differences in KAES variety yields and those released by other public and private breeders are quantified. During the ‘‘new age’’ of wheat breeding (1977–2006), wheat breeding alone is found to have increased yields by 6.182 bushels per acre, or an average increase of 0.206 bushels per year.wheat yield, public wheat breeding, multiplicative heteroscedasticity, economic impact of technological change, Agribusiness, Farm Management, O13, Q16,

    Equation of state of classical Coulomb plasma mixtures

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    We develop analytic approximations of thermodynamic functions of fully ionized nonideal electron-ion plasma mixtures. In the regime of strong Coulomb coupling, we use our previously developed analytic approximations for the free energy of one-component plasmas with rigid and polarizable electron background and apply the linear mixing rule (LMR). Other thermodynamic functions are obtained through analytic derivation of this free energy. In order to obtain an analytic approximation for the intermediate coupling and transition to the Debye-Hueckel limit, we perform hypernetted-chain calculations of the free energy, internal energy, and pressure for mixtures of different ion species and introduce a correction to the LMR, which allows a smooth transition from strong to weak Coulomb coupling in agreement with the numerical results.Comment: 6 pages, 7 figures; Phys. Rev. E. In v.2 after proofreading, minor typos are fixe

    Slow dynamics near glass transitions in thin polymer films

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    The α\alpha-process (segmental motion) of thin polystyrene films supported on glass substrate has been investigated in a wider frequency range from 103^{-3} Hz to 104^4 Hz using dielectric relaxation spectroscopy and thermal expansion spectroscopy. The relaxation rate of the α\alpha-process increases with decreasing film thickness at a given temperature above the glass transition. This increase in the relaxation rate with decreasing film thickness is much more enhanced near the glass transition temperature. The glass transition temperature determined as the temperature at which the relaxation time of the α\alpha-process becomes a macroscopic time scale shows a distinct molecular weight dependence. It is also found that the Vogel temperature has the thickness dependence, i.e., the Vogel temperature decreases with decreasing film thickness. The expansion coefficient of the free volume αf\alpha_f is extracted from the temperature dependence of the relaxation time within the free volume theory. The fragility index mm is also evaluated as a function of thickness. Both αf\alpha_f and mm are found to decrease with decreasing film thickness.Comment: 9 pages, 7 figures, and 2 table

    A simple two-module problem to exemplify building-block assembly under crossover

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    Theoretically and empirically it is clear that a genetic algorithm with crossover will outperform a genetic algorithm without crossover in some fitness landscapes, and vice versa in other landscapes. Despite an extensive literature on the subject, and recent proofs of a principled distinction in the abilities of crossover and non-crossover algorithms for a particular theoretical landscape, building general intuitions about when and why crossover performs well when it does is a different matter. In particular, the proposal that crossover might enable the assembly of good building-blocks has been difficult to verify despite many attempts at idealized building-block landscapes. Here we show the first example of a two-module problem that shows a principled advantage for cross-over. This allows us to understand building-block assembly under crossover quite straightforwardly and build intuition about more general landscape classes favoring crossover or disfavoring it

    GGD 37: An Extreme Protostellar Outflow

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    We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom

    Heat capacity study of BaFe2_{2}As2_{2}: effects of annealing

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    Heat-capacity, X-ray diffraction, and resistivity measurements on a high-quality BaFe2_{2}As2_{2} sample show an evolution of the magneto-structural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 μΩ\mu\Omegacm, with a residual resistance ratio \sim36; the heat-capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of \sim0.15 K, and is unchanged in a magnetic field μ0\mu_{0}H = 14 T. The X-ray and heat-capacity data combined suggest that there is a first order jump in the structural order parameter. The entropy of the transition is reported

    The IRAC Shallow Survey

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    The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions.Comment: To appear in ApJS, Spitzer special issue. For full resolution see http://cfa-www.harvard.edu/irac/publication
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