16,932 research outputs found
Municipal commonage and implications for land reform: A profile of commonage users in Philippolis, Free State, South Africa
This paper reports on a survey of municipal commonage users, which was undertaken in Philippolis in the southern Free State, in May 2005. The survey showed that a significant number of commonage users are committed to their farming enterprises, as shown by five proxy indicators: Their readiness to plough their income into their farming enterprises; their sale of livestock; their desire for more land, and their willingness to pay rental to secure such land; their desire to farm on their own; and their desire to own their own land. The paper reflects on the significance of commonage in the context of the South African government’s land reform policy, and argues that commonage can transcend survivalist or subsistence production, and can be used as a “stepping stone” for emergent farmers to access their own land parcels. Finally, the paper argues that, if commonage is to become a key part in a “step-up” strategy of land reform, then appropriately sized land parcels should be made available for commonage users, to enable them to “exit” from commonage use and invest in smallholdings or small farms.Land Economics/Use,
Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.
The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products
Motion and contrast enhancement separation model reconstruction from partial measurements in dynamic MRI
We propose a motion and contrast enhancement separation
model in dynamic magnetic resonance imaging (MRI). Furthermore, the
reconstruction is done from partial measurements to achieve faster dynamic
MR imaging. The algorithm minimizes a linear combination of
three terms, a data fitting functional and two regularization functionals
corresponding to the nuclear and ℓ1 norm. The proposed method
is tested on simulated and real dynamic datasets. This paper suggests
an image reconstruction model that directly induces clinically-relevant
informations from partial measurements
On the precision of chiral-dispersive calculations of scattering
We calculate the combination (the Olsson sum rule)
and the scattering lengths and effective ranges , and ,
dispersively (with the Froissart--Gribov representation) using, at
low energy, the phase shifts for scattering obtained by Colangelo,
Gasser and Leutwyler (CGL) from the Roy equations and chiral perturbation
theory, plus experiment and Regge behaviour at high energy, or directly, using
the CGL parameters for s and s. We find mismatch, both among the CGL
phases themselves and with the results obtained from the pion form factor. This
reaches the level of several (2 to 5) standard deviations, and is essentially
independent of the details of the intermediate energy region ( GeV) and, in some cases, of the high energy behaviour assumed. We discuss
possible reasons for this mismatch, in particular in connection with an
alternate set of phase shifts.Comment: Version to appear in Phys. Rev. D. Graphs and sum rule added. Plain
TeX fil
On the Bethe Ansatz for the Jaynes-Cummings-Gaudin model
We investigate the quantum Jaynes-Cummings model - a particular case of the
Gaudin model with one of the spins being infinite. Starting from the Bethe
equations we derive Baxter's equation and from it a closed set of equations for
the eigenvalues of the commuting Hamiltonians. A scalar product in the
separated variables representation is found for which the commuting
Hamiltonians are Hermitian. In the semi classical limit the Bethe roots
accumulate on very specific curves in the complex plane. We give the equation
of these curves. They build up a system of cuts modeling the spectral curve as
a two sheeted cover of the complex plane. Finally, we extend some of these
results to the XXX Heisenberg spin chain.Comment: 16 page
Failure time and microcrack nucleation
The failure time of samples of heterogeneous materials (wood, fiberglass) is
studied as a function of the applied stress. It is shown that in these
materials the failure time is predicted with a good accuracy by a model of
microcrack nucleation proposed by Pomeau. It is also shown that the crack
growth process presents critical features when the failure time is approached.Comment: 13 pages, 4 figures, submitted to Europhysics Letter
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