1,713 research outputs found
Using alterative whole-farm modelling approaches to assess farm enterprise selection, risk and welfare
Using an expected mean-variance model the changes in farm enterprise levels and indirect utility were examined under conditions of risk aversion, budget constraints and gross margin variance. An extension of the comparative statics of the expected mean-variance model was adopted by introducing a budget constraint into the constrained optimisation problem. A 10-year expected mean-variance whole-farm model was solved for a farm in the wheat-sheep zone of Australia to provide an empirical example. Results were obtained using no planning horizon (the static model) and then with a five-year rolling planning horizon (the dynamic model). In addition, enterprise levels were constrained to match levels observed on the farm so as to compare incomes between the constrained and unconstrained models. For a cash constrained, risk averse, farmer it was found that they are likely to have larger expenditures than less risk averse operators in order to obtain the same indirect utility. Enterprise levels differed between the dynamic and static models, and a dynamic model was used to help explain inter-temporal decision-making. Risk aversion reduced the set of possible welfare improving production activities available to a farmer.Whole-farm modelling, enterprise selection, risk., Farm Management, Q12, C61,
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
The crystal structure and the magnetism of BaMnO have been studied by
thermodynamic and by diffraction techniques using large single crystals and
powders. BaMnO is a realization of a spin ladder as the
magnetic interaction is dominant along 180 Mn-O-Mn bonds forming the
legs and the rungs of a ladder. The temperature dependence of the magnetic
susceptibility exhibits well-defined maxima for all directions proving the
low-dimensional magnetic character in BaMnO. The susceptibility and
powder neutron diffraction data, however, show that BaMnO exhibits a
transition to antiferromagnetic order at 184 K, in spite of a full frustration
of the nearest-neighbor inter-ladder coupling in the orthorhombic
high-temperature phase. This frustration is lifted by a remarkably strong
monoclinic distortion which accompanies the magnetic transition.Comment: 9 pages, 8 figures, 2 tables; in V1 fig. 2 was included twice and
fig. 4 was missing; this has been corrected in V
Control of multiferroic domains by external electric fields in TbMnO3
The control of multiferroic domains through external electric fields has been
studied by dielectric measurements and by polarized neutron diffraction on
single-crystalline TbMnO. Full hysteresis cycles were recorded by varying
an external field of the order of several kV/mm and by recording the chiral
magnetic scattering as well as the charge in a sample capacitor. Both methods
yield comparable coercive fields that increase upon cooling.Comment: 12 pages, 6 figure
Magnetoelastic coupling in RETiO3 (RE = La, Nd, Sm, Gd, Y)
A detailed analysis of the crystal structure in RETiO3 with RE = La, Nd, Sm,
Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and
the lattice which cannot be fully attributed to the structural deformation
arising from bond-length mismatch. The TiO6 octahedra in this series are all
irregular with the shape of the distortion depending on the RE ionic radius.
These octahedron distortions vary more strongly with temperature than the tilt
and rotation angles. Around the Ti magnetic ordering all compounds exhibit
strong anomalies in the thermal-expansion coefficients, these anomalies exhibit
opposite signs for the antiferromagnetic and ferromagnetic compounds.
Furthermore the strongest effects are observed in the materials close to the
magnetic cross-over from antiferromagnetic to ferromagnetic order
Intricacies of the Co spin state in SrCoIrO: an x-ray absorption and magnetic circular dichroism study
We report on a combined soft x-ray absorption and magnetic circular dichroism
(XMCD) study at the Co- on the hybrid 3/5 solid state oxide
SrCoIrO with the KNiF structure. Our data
indicate unambiguously a pure high spin state for the Co
(3) ions with a significant unquenched orbital moment
despite the sizeable elongation of the CoO octahedra. Using quantitative
model calculations based on parameters consistent with our spectra, we have
investigated the stability of this high spin state with respect to the
competing low spin and intermediate spin states.Comment: 7 pages, 4 figure
Gain and time resolution of 45 m thin Low Gain Avalanche Detectors before and after irradiation up to a fluence of n/cm
Low Gain Avalanche Detectors (LGADs) are silicon sensors with a built-in
charge multiplication layer providing a gain of typically 10 to 50. Due to the
combination of high signal-to-noise ratio and short rise time, thin LGADs
provide good time resolutions.
LGADs with an active thickness of about 45 m were produced at CNM
Barcelona. Their gains and time resolutions were studied in beam tests for two
different multiplication layer implantation doses, as well as before and after
irradiation with neutrons up to n/cm.
The gain showed the expected decrease at a fixed voltage for a lower initial
implantation dose, as well as for a higher fluence due to effective acceptor
removal in the multiplication layer. Time resolutions below 30 ps were obtained
at the highest applied voltages for both implantation doses before irradiation.
Also after an intermediate fluence of n/cm, similar
values were measured since a higher applicable reverse bias voltage could
recover most of the pre-irradiation gain. At n/cm, the
time resolution at the maximum applicable voltage of 620 V during the beam test
was measured to be 57 ps since the voltage stability was not good enough to
compensate for the gain layer loss. The time resolutions were found to follow
approximately a universal function of gain for all implantation doses and
fluences.Comment: 17 page
Incommensurate spin correlations in highly oxidized cobaltates LaSrCoO
We observe quasi-static incommensurate magnetic peaks in neutron scattering
experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states
that have been reported to be paramagnetic. This enables us to measure the
magnetic excitations in this highly hole-doped incommensurate regime and
compare our results with those found in the low-doped incommensurate regime
that exhibit hourglass magnetic spectra. The hourglass shape of magnetic
excitations completely disappears given a high Sr doping. Moreover, broad
low-energy excitations are found, which are not centered at the incommensurate
magnetic peak positions but around the quarter-integer values that are
typically exhibited by excitations in the checkerboard charge ordered phase.
Our findings suggest that the strong inter-site exchange interactions in the
undoped islands are critical for the emergence of hourglass spectra in the
incommensurate magnetic phases of La2-xSrxCoO4.Comment: http://www.nature.com/articles/srep25117
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