218 research outputs found

    Illiquid Capital: Are Conservation Easement Payments Reinvested in Farms?

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    Agricultural conservation easements have positive externalities but few studies examine the supply-side. This paper explores whether easements may also overcome a credit-market failure, as banks may not be lending based on the full developed value of land. Original survey data test our research hypotheses and show profitable owners and nonoperators to be using easement payments to extract capital from their land by using the preservation programs as a bank. The results also show that the unprofitable owners and operators are reinvesting in their agricultural enterprises. Both results are consistent with an underlying credit-market failure, and the latter suggests that easements may provide indirect efficiency enhancement. The results suggest an integration of policies on agricultural finance and land preservation might lead to improved efficiency

    Dependence of the Superconducting Transition Temperature of MgB2 on Pressure to 20 GPa

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    The dependence of Tc on nearly hydrostatic pressure has been measured for an isotopically pure (11B) MgB2 sample in a helium-loaded diamond-anvil-cell to nearly 20 GPa. Tc decreases monotonically with pressure from 39.1 K at ambient pressure to 20.9 K at 19.2 GPa. The initial dependence is the same as that obtained earlier (dTc/dP = -1.11(2) K/GPa) on the same sample in a He-gas apparatus to 0.7 GPa. The observed pressure dependence Tc(P) to 20 GPa can be readily described in terms of simple lattice stiffening within standard phonon-mediated BCS superconductivity.Comment: 9 pages, 3 figure

    Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta

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    In previous studies on a number of under- and overdoped high temperature superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta}, the transition temperature T_c has been found to change with time in a manner which depends on the sample's detailed temperature and pressure history. This relaxation behavior in T_c is believed to originate from rearrangements within the oxygen sublattice. In the present high-pressure studies on HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation effects in strongly under- and overdoped samples (Tc4050KT_c\simeq 40 - 50 K) with an activation energy EA(1bar)0.80.9eVE_{A}(1 bar) \simeq 0.8 - 0.9 eV. For overdoped HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of +11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an anomalous result for high-T_c superconductors in the present pressure range, giving evidence for a change in the electronic and/or structural properties near 0.4 GPa

    Observing Long Colour Flux Tubes in SU(2) Lattice Gauge Theory

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    We present results of a high statistics study of the chromo field distribution between static quarks in SU(2) gauge theory on lattices of volumes 16^4, 32^4, and 48^3*64, with physical extent ranging from 1.3 fm up to 2.7 fm at beta=2.5, beta=2.635, and beta=2.74. We establish string formation over physical distances as large as 2 fm. The results are tested against Michael's sum rules. A detailed investigation of the transverse action and energy flux tube profiles is provided. As a by-product, we obtain the static lattice potential in unpreceded accuracy.Comment: 66 pages, 29 figures, uuencoded latex file with epsfigures (450 K), supplementary full colour figures are available via ftp, CERN-TH.7413/94 (extended version

    Universality of Frequency and Field Scaling of the Conductivity Measured by Ac-Susceptibility of a Ybco-Film

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    Utilizing a novel and exact inversion scheme, we determine the complex linear conductivity σ(ω)\sigma (\omega ) from the linear magnetic ac-susceptibility which has been measured from 3\,mHz to 50\,MHz in fields between 0.4\,T and 4\,T applied parallel to the c-axis of a 250\,nm thin disk. The frequency derivative of the phase σ/σ\sigma ''/\sigma ' and the dynamical scaling of σ(ω)\sigma (\omega) above and below Tg(B)T_g(B) provide clear evidence for a continuous phase transition at TgT_g to a generic superconducting state. Based on the vortex-glass scaling model, the resulting critical exponents ν\nu and zz are close to those frequently obtained on films by other means and associated with an 'isotropic' vortex glass. The field effect on σ(ω)\sigma(\omega) can be related to the increase of the glass coherence length, ξgB\xi_g\sim B.Comment: 8 pages (5 figures upon request), revtex 3.0, APK.94.01.0

    Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry

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    For polycrystalline RuSr2GdCu2O8 (Ru-1212), distinct peaks have been reported in d.c. magnetization in the superconducting state of the sample. Sr2GdRuO6 (Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in the same temperature regime. Based on measurements performed on both bulk and powdered samples of Ru-1212 and Sr-2116, we exclude the possibility, that the observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities. The effect is related to the superconductivity of Ru-1212, but it is not an intrinsic property of this compound. We provide evidence that the observation of magnetization peaks in the superconducting state of Ru-1212 is due to flux motion generated by the movement of the sample in an inhomogeneous field, during the measurement in the SQUID magnetometer. We propose several tests, that help to decide, whether the features observed in a SQUID magnetization measurement of Ru-1212 represent a property of the compound or not.Comment: 22 pages, 9 figure

    Testing "microscopic" theories of glass-forming liquids

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    We assess the validity of "microscopic" approaches of glass-forming liquids based on the sole k nowledge of the static pair density correlations. To do so we apply them to a benchmark provided by two liquid models that share very similar static pair density correlation functions while disp laying distinct temperature evolutions of their relaxation times. We find that the approaches are unsuccessful in describing the difference in the dynamical behavior of the two models. Our study is not exhausti ve, and we have not tested the effect of adding corrections by including for instance three-body density correlations. Yet, our results appear strong enough to challenge the claim that the slowd own of relaxation in glass-forming liquids, for which it is well established that the changes of the static structure factor with temperature are small, can be explained by "microscopic" appr oaches only requiring the static pair density correlations as nontrivial input.Comment: 10 pages, 7 figs; Accepted to EPJE Special Issue on The Physics of Glasses. Arxiv version contains an addendum to the appendix which does not appear in published versio

    The status of GEO 600

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    The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode

    Nucleon resonances in omega photoproduction

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    The role of the nucleon resonances (NN^*) in ω\omega photoproduction is investigated by using the resonance parameters predicted by Capstick and Roberts [Phys. Rev. D {\bf 46}, 2864 (1992); {\bf 49}, 4570 (1994)]. In contrast with the previous investigations based on the SU(6)×O(3){SU}(6) \times {O}(3) limit of the constituent quark model, the employed NγNN^* \to \gamma N and NωNN^* \to \omega N amplitudes include the configuration mixing effects due to the residual quark-quark interactions. The contributions from the nucleon resonances are found to be significant relative to the non-resonant amplitudes in changing the differential cross sections at large scattering angles and various spin observables. In particular, we suggest that a crucial test of our predictions can be made by measuring the parity asymmetry and beam-target double asymmetry at forward scattering angles.Comment: 18 pages, REVTeX, 8 figures, to appear in Phys. Rev.
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