342 research outputs found
Modelling Production Risk in Small Scale Subsistence Agriculture
In this paper we are investigating how production risk may influence the way a risk averse producer like a subsistence farmer chooses optimal input levels. Risk averse producers will take into account both the mean and the variance of output, and therefore we expect them to choose input levels which differ form the optimal input level of risk neutral producers. Production risk is of particular importance in developing countries, since variance in production here may have grave consequences for the farmer and his family. To model the production decision problem under such circumstances we have made use of the fact that production risk can be treated as heteroskedasticity. Our analysis is based on a dataset obtained from a survey on smallholders in the Kilimanjaro region in Tanzania. Since evidence of output risk in inputs is found, we reestimate the mean and variance function using a maximum likelihood estimator, and correct the standard errors to provide valid inference.Farm Management,
Evaluating a framework of theoretical hypotheses for animation learning
This paper presents a set of theoretical hypotheses suggesting various relationships between didactical setting and learning effects with animations. Particularly, we investigated whether individual flow-control adequately provides didactical means to reduce the cognitive load imposed by animations. We did not find an effect of individual flow control, probably due to the fact that this learning condition was embedded in a setting where not enough verbal information was offered together with the graphical animation. Overall the multimedia effects found in this study are in line with known principles of didactical multimedia design. Further, this study sheds light on theoretical aspects involved in the complex interaction between learning content, presentation, learning and resulting knowledg
Level density and gamma strength function in 162-Dy from inelastic 3-He scattering
Complementary measurements have been performed for the level density and
gamma strength function in 162-Dy using inelastic 3-He scattering. Comparing
these results to previous measurements using the 163-Dy(3-He,alpha) reaction,
reveals that the measured quantities above 1.5 MeV do not depend significantly
on the nuclear reaction chosen.Comment: 15 pages, including 7 figure
Critical temperature for quenching of pair correlations
The level density at low spin in the 161,162-Dy and 171,172-Yb nuclei has
been extracted from primary gamma rays. The nuclear heat capacity is deduced
within the framework of the canonical ensemble. The heat capacity exhibits an
S-formed shape as a function of temperature, which is interpreted as a
fingerprint of the phase transition from a strongly correlated to an
uncorrelated phase. The critical temperature for the quenching of pair
correlations is found at Tc=0.50(4) MeV.Comment: 8 pages including 4 figures, different method to extract Tc,
different figures, text partly rewritte
Level density and thermal properties in rare earth nuclei
A convergent method to extract the nuclear level density and the gamma-ray
strength function from primary gamma-ray spectra has been established.
Thermodynamical quantities have been obtained within the microcanonical and
canonical ensemble theory. Structures in the caloric curve and in the heat
capacity curve are interpreted as fingerprints of breaking of Cooper pairs and
quenching of pairing correlations. The strength function can be described using
models and common parameterizations for the E1, M1 and pygmy resonance
strength. However, a significant decrease of the pygmy resonance strength at
finite temperatures has been observed.Comment: 15 pages including 8 figures. Proceedings article for the conference
Nuclear Structure and Related Topics, Dubna, Russia, June 6-10, 200
Pairing Reentrance Phenomenon in Heated Rotating Nuclei in the Shell Model Monte Carlo Approach
Rotational motion of heated 72-Ge is studied within the microscopic Shell
Model Monte Carlo approach. We investigate the the angular momentum alignment
and nuclear pairing correlations associated with J-pi Cooper pairs as a
function of the rotational frequency and temperature. The reentrance of pairing
correlations with temperature is predicted at high rotational frequencies. It
manifests itself through the anomalous behavior of specific heat and level
density.Comment: 4 pages; 4 figure
Observation of Thermodynamical Properties in the Dy, Er and Yb Nuclei
The density of accessible levels in the (He,) reaction has
been extracted for the Dy, Er and Yb nuclei. The
nuclear temperature is measured as a function of excitation energy in the
region of 0 -- 6 MeV. The temperature curves reveal structures indicating new
degrees of freedom. The heat capacity of the nuclear system is discussed within
the framework of a canonical ensemble.Comment: 12 pages, 4 figures include
Microcanonical entropies and radiative strength functions of V
The level densities and radiative strength functions (RSFs) of V
have been extracted using the (He,) and
(He,He) reactions, respectively. From the level
densities, microcanonical entropies are deduced. The high -energy part
of the RSF is described by the giant electric dipole resonance. A significant
enhancement over the predicted strength in the region of MeV is seen, which at present has no theoretical explanation.Comment: 16 pages including 9 figure
Quasicontinuum -decay of Zr: benchmarking indirect () cross section measurements for the -process
Nuclear level densities (NLDs) and -ray strength functions
(SFs) have been extracted from particle- coincidences of the
Zr()Zr and Zr()Zr
reactions using the Oslo method. The new Zr SF data, combined
with photonuclear cross sections, cover the whole energy range from ~MeV up to the giant dipole resonance at ~MeV. The wide-range SF data display structures at ~MeV, compatible with a superposition of the spin-flip
resonance and a pygmy resonance. Furthermore, the SF shows a
minimum at ~MeV and an increase at lower -ray
energies. The experimentally constrained NLDs and SFs are shown to
reproduce known () and Maxwellian-averaged cross sections for
Zr using the {\sf TALYS} reaction code, thus serving as a benchmark
for this indirect method of estimating () cross sections for Zr
isotopes.Comment: 10 pages and 9 figure
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