1,205 research outputs found

    Weak decays of 4He-Lambda

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    We measured the lifetime and the mesonic and non-mesonic decay rates of the 4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda. The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n p non-mesonic decay (also referred to as proton-stimulated decay) and was found to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined from the observed numbers of pi-'s and pi0's as Gamma_pi-/Gamma_tot = 0.270 +/- 0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL), respectively. The effects of final-state interactions and possible 3-body Lambda N N decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the non-mesonic branching fractions. The implications of the results of this analysis were considered for the empirical Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.Comment: 15 pages, 11 figures, published in PRC, revised content to match published versio

    Multiple-scattering Modelling of Scattering by Biological Cells

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    Past work on scattering by biological cells has been restricted to unrealistic oversimplified models of cells, or uses slow methods unsuited for calculations involving large numbers of cells or varying illumination. We consider the systematic use of fast, accurate methods for modelling light scattering in realistic complex biological cells. This will allow, for example, the study of light scattering by realistic ensembles of cells, which is immediately applicable to optical cancer detection, and remote sensing of microorganisms. It will also be possible to study light scattering by cells under constantly varying illumination, such as encountered in applications like flow cytometry

    The comparative feeding value of Lindsey 77, alfalfa, and corn silage for finishing beef heifers

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    Data collected on 120 Angus heifers at the Middle Tennessee Experiment Station, Spring Hill, Tennessee, were used to determine the comparative value of hybrid-grass (Lindsey 77), alfalfa and corn silage for finishing beef heifers for slaughter. The heifers were fed a ration of either Lindsey 77, alfalfa or corn silage ad lib, plus limited concentrates for 119 days in Trial I, conducted during the winter of 1966-67, and for 56 days in Trial II conducted during the summer of 1967. The heifers in Trial I were changed to a full-feed of concentrates plus a limited amount of the same silage fed during the previous phase for an additional 50 days. In Trial II, the heifers were changed to a full-feed of concentrates plus limited corn silage for 47 days following the 56-day period of corn silage full-fed. Average daily gains in Trial I were 1.35, 1.60 and 1.73 pounds per head per day during the silage phase and 1.51, 1.50 and 1.58 during the full-feed phase for heifers fed Lindsey 77, alfalfa and corn silage, respectively. In Trial II, average daily gains of the heifers fed Lindsey 77, alfalfa and corn silage were 1.53, 2.07 and 1.67 pounds per head per day during the silage phase and 2.25, 2.20 and 2.15 pounds per head per day during the full-feed period. Heifers fed corn silage gained significantly faster (P \u3c ,05) than those fed alfalfa or Lindsey 77 silage during the winter trial. However, during the summer trial, heifers fed alfalfa silage gained significantly (P \u3c .05) faster than those fed the other two silages. Feed costs per hundred pounds of gain for heifers fed Lindsey 77, alfalfa and corn silage during Trial I were 27.40,27.40, 24.82 and 23.62,respectively,and23.62, respectively, and 21.88, 19.61and19.61 and 21.81, respectively, during Trial II. Average return per head above feed and initial cost was highest from heifers fed corn silage in Trial I and highest from heifers fed alfalfa silage in Trial II. These data indicated that these silages, when fed with a limited amount of concentrates followed by a short full-feed period, could be used profitably for finishing beef heifers. The season of year (winter or summer) may affect the results obtained from corn silage. This could be a result of severe heating and spoilage of corn silage in the feed bunk, which was observed during the summer feeding trial. The lower rate of gain and higher feed requirement per unit of gain of heifer fed Lindsey 77 silage in both trials indicated that this type of silage was less desirable as a component of a finishing ration for beef heifers than either alfalfa or corn silage

    Possible ΔΔ\Delta\Delta dibaryons in the quark cluster model

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    In the framework of RGM, the binding energy of one channel ΔΔ(3,0)\Delta\Delta_{(3,0)}(dd^*) and ΔΔ(0,3)\Delta\Delta_{(0,3)} are studied in the chiral SU(3) quark cluster model. It is shown that the binding energies of the systems are a few tens of MeV. The behavior of the chiral field is also investigated by comparing the results with those in the SU(2) and the extended SU(2) chiral quark models. It is found that the symmetry property of the ΔΔ\Delta\Delta system makes the contribution of the relative kinetic energy operator between two clusters attractive. This is very beneficial for forming the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very important role on binding. The S-wave phase shifts and the corresponding scattering lengths of the systems are also given.Comment: LeTex with 2 ps figure

    Variational calculations of the Λ\Lambda-seperation energy of the Λ17_{\Lambda}^{17}O hypernucleus

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    Variational Monte Carlo calculations have been made for the Λ17_{ \Lambda}^{17}O hypernucleus using realistic two- and three-baryon interactions. A two pion exchange potential with spin- and space-exchange components is used for the Λ\LambdaN potential. Three-body two-pion exchange and strongly repulsive dispersive Λ\LambdaNN interactions are also included. The trial wave function is constructed from pair- and triplet-correlation operators acting on a single particle determinant. These operators consist of central, spin, isospin, tensor and three- baryon potential components. A cluster Monte Carlo method is developed for noncentral correlations and is used with up to four-baryon clusters in our calculations. The three-baryon Λ\LambdaNN force is discussed.Comment: 24 pages, 2 figs available by fax., for publication in Phys. Rev.

    Research on the Geography of Agricultural Change: Redundant or Revitalized?

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    Future research directions for agricultural geography were the subject of debate in Area in the late 1980s. The subsequent application of political economy ideas undoubtedly revived interest in agricultural research. This paper argues that agricultural geography contains greater diversity than the dominant political economy discourse would suggest. It reviews ‘other’ areas of agricultural research on policy, post-productivism, people, culture and animals, presenting future suggestions for research. They should ensure that agricultural research continues revitalized rather than redundant into the next millennium

    Gamma-Ray Spectroscopy of Λ16^{16}_\LambdaO and Λ15^{15}_\LambdaN Hypernuclei via the 16^{16}O(K,π)(K^-, \pi^-) reaction

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    he bound-state level structures of the Λ16^{16}_{\Lambda}O and Λ15^{15}_{\Lambda}N hypernuclei were studied by γ\gamma-ray spectroscopy using a germanium detector array (Hyperball) via the 16^{16}O (K,πγK^-, \pi^- \gamma) reaction. A level scheme for Λ16^{16}_{\Lambda}O was determined from the observation of three γ\gamma-ray transitions from the doublet of states (22^-,11^-) at 6.7\sim 6.7 MeV to the ground-state doublet (11^-,00^-). The Λ15^{15}_{\Lambda}N hypernuclei were produced via proton emission from unbound states in Λ16^{16}_{\Lambda}O . Three γ\gamma -rays were observed and the lifetime of the 1/2+;11/2^+;1 state in Λ15^{15}_{\Lambda}N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin-dependence of the ΛN\Lambda N interaction is discussed. In particular, the measured Λ16^{16}_{\Lambda}O ground-state doublet spacing of 26.4 ±\pm 1.6 ±\pm 0.5 keV determines a small but nonzero strength of the ΛN\Lambda N tensor interaction.Comment: 22 pages, 17 figure
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