218 research outputs found
Illiquid Capital: Are Conservation Easement Payments Reinvested in Farms?
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
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
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 () with
an activation energy . 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
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
Utilizing a novel and exact inversion scheme, we determine the complex linear
conductivity 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 and the dynamical scaling of
above and below provide clear evidence for a
continuous phase transition at to a generic superconducting state. Based
on the vortex-glass scaling model, the resulting critical exponents and
are close to those frequently obtained on films by other means and
associated with an 'isotropic' vortex glass. The field effect on
can be related to the increase of the glass coherence length,
.Comment: 8 pages (5 figures upon request), revtex 3.0, APK.94.01.0
Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry
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
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
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
The role of the nucleon resonances () in 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
limit of the constituent quark model, the employed and 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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