12,282 research outputs found
Denitrification and availability of carbon and nitrogen in a well-drained pasture soil amended with particulate organic carbon
A well-drained soil in N-fertilized dairy pasture was amended with particulate organic carbon (POC), either sawdust or coarse woody mulch, and sampled every 4 wk for a year to test the hypothesis that the addition of POC would increase denitrification activity by increasing the number of microsites where denitrification occurred. Overall mean denitrifying enzyme activity (DEA), on a gravimetric basis, was 100% greater for the woody mulch treatment and 50% greater for the sawdust treatment compared with controls, indicating the denitrifying potential of the soil was enhanced. Despite differences in DEA, no difference in denitrification rate, as measured by the acetylene block technique, was detected among treatments, with an average annual N loss of ā¼22 kg N haā»Ā¹ yrā»Ā¹ Soil water content overall was driving denitrification in this well-drained soil as regression of the natural log of volumetric soil water content (VWC) against denitrification rate was highly significant (r Ā² = 0.74, P < 0.001). Addition of the amendments, however, had significant effects on the availability of both C and N. An additional 20 to 40 kg N haā»Ā¹ was stored in POC-amended treatments as a result of increases in the microbial biomass. Basal respiration, as a measure of available C, was 400% greater than controls in the sawdust treatment and 250% greater than controls in the mulch. Net N mineralization, however, was significantly lower in the sawdust treatment, resulting in significantly lower nitrate N levels than in the control. We attribute the lack of measured response in denitrification rate to the high temporal variability in denitrification and suggest that diffusion of nitrate may ultimately have limited denitrification in the amended treatments. Our data indicate that manipulation of denitrification by addition of POC may be possible, particularly when nitrate levels are high, but quantifying differences in the rate of denitrification is difficult because of the temporal nature of the process (particularly the complex interaction of N availability and soil water content)
Simulating Hamiltonian dynamics using many-qudit Hamiltonians and local unitary control
When can a quantum system of finite dimension be used to simulate another
quantum system of finite dimension? What restricts the capacity of one system
to simulate another? In this paper we complete the program of studying what
simulations can be done with entangling many-qudit Hamiltonians and local
unitary control. By entangling we mean that every qudit is coupled to every
other qudit, at least indirectly. We demonstrate that the only class of
finite-dimensional entangling Hamiltonians that aren't universal for simulation
is the class of entangling Hamiltonians on qubits whose Pauli operator
expansion contains only terms coupling an odd number of systems, as identified
by Bremner et. al. [Phys. Rev. A, 69, 012313 (2004)]. We show that in all other
cases entangling many-qudit Hamiltonians are universal for simulation
Entropy Balance and Dispersive Oscillations in Lattice Boltzmann Models
We conduct an investigation into the dispersive post-shock oscillations in
the entropic lattice-Boltzmann method (ELBM). To this end we use a root finding
algorithm to implement the ELBM which displays fast cubic convergence and
guaranties the proper sign of dissipation. The resulting simulation on the
one-dimensional shock tube shows no benefit in terms of regularization from
using the ELBM over the standard LBGK method. We also conduct an experiment
investigating of the LBGK method using median filtering at a single point per
time step. Here we observe that significant regularization can be achieved.Comment: 18 pages, 4 figures; 13/07/2009 Matlab code added to appendi
The Galaxy Proximity Effect in the Lyman-alpha Forest
Hydrodynamic cosmological simulations predict that the average opacity of the
Ly-alpha forest should increase in the neighborhood of galaxies because
galaxies form in dense environments. Recent observations (Adelberger et al.
2002) confirm this expectation at large scales, but they show a decrease of
absorption at comoving separations Delta_r <~ 1 Mpc/h. We show that this
discrepancy is statistically significant, especially for the innermost data
point at Delta_r <= 0.5 Mpc/h, even though this data point rests on three
galaxy-quasar pairs. Galaxy redshift errors of the expected magnitude are
insufficient to resolve the conflict. Peculiar velocities allow gas at comoving
distances >~ 1 Mpc/h to produce saturated absorption at the galaxy redshift,
putting stringent requirements on any ``feedback'' solution. Local
photoionization is insufficient, even if we allow for recurrent AGN activity
that keeps the neutral hydrogen fraction below its equilibrium value. A simple
``wind'' model that eliminates all neutral hydrogen in spheres around the
observed galaxies can marginally explain the data, but only if the winds extend
to comoving radii ~1.5 Mpc/h.Comment: 4 pages, 1 figure; To appear in proceedings of the 13th Annual
Astrophysics Conference in College Park, Maryland, The Emergence of Cosmic
Structure, eds. S.Holt and C. Reynolds, (AIP
EMERGING BUSINESSES: THE SOUTH AFRICAN WINE INDUSTRY CASE
Emerging economies such as South Africa, only a few years out of apartheid, have been feeling the strains of socio-political change. While South Africa has experienced political reform, economic reform and access are slow to come. Currently, South Africa is the 7th largest producer of wine in the world. Although this industry is impressive, the apartheid era production practices have caused primarily the European consumers and media to be vocal about this issue. However, this concern has spread to other regions. The South African government and wine industry must respond to the external and internal market pressures and minimize transaction costs. Both entities want to increase wine exports and expand market share, however, given the socio-economic and political climate in the country neither knows how to manage this difficult process which emanates from deeply rooted distrust of groups within the country. Socio-political constraints facing previously disadvantaged groups (PDG) as emerging business owners need to be understood; and, measures which could be undertaken by government and industry need to be identified. The objectives of this research were to identify: institutional constraints and transaction costs faced by PDGs aspiring toward production and leadership roles in the wine industry; ways the government can collaborate with the KWV to build social capital and promote PDG ownership in the wine industry, thus minimizing social conflict; and, identify industry strategies to increase exports and international market share under the "New South Africa" banner. This analysis was based on primary and secondary data and information gathered on site. Several potential solutions were suggested for ways to include PDGs in the South African wine market while minimizing the impact on the market shares of existing producers. It is anticipated that the window of opportunity to increase exports and involve PDG is quite small.Agribusiness,
E-democracy: exploring the current stage of e-government
Governments around the world have been pressured to implement e-Government programs in order to improve the government-citizen dialogue. The authors of this article review prior literature on such efforts to find if they lead to increased democratic participation ("e-Democracy") for the affected citizens, with a focus on the key concepts of transparency, openness, and engagement. The authors find that such efforts are a starting point toward e-Democracy, but the journey is far from complete
On the Evolutionary History of Stars and their Fossil Mass and Light
The total extragalactic background radiation can be an important test of the
global star formation history (SFH). Using direct observational estimates of
the SFH, along with standard assumptions about the initial mass function (IMF),
we calculate the total extragalactic background radiation and the observed
stellar density today. We show that plausible SFHs allow a significant range in
each quantity, but that their ratio is very tightly constrained. Current
estimates of the stellar mass and extragalactic background are difficult to
reconcile, as long as the IMF is fixed to the Salpeter slope above 1 Msun. The
joint confidence interval of these two quantities only agrees with that
determined from the allowed range of SFH fits at the 3-sigma level, and for our
best-fit values the discrepancy is about a factor of two. Alternative energy
sources that contribute to the background, such as active galactic nuclei
(AGN), Population III stars, or decaying particles, appear unlikely to resolve
the discrepancy. However, changes to the IMF allow plausible solutions to the
background problem. The simplest is an average IMF with an increased
contribution from stars around 1.5--4 Msun. A ``paunchy'' IMF of this sort
could emerge as a global average if low mass star formation is suppressed in
galaxies experiencing rapid starbursts. Such an IMF is consistent with
observations of star-forming regions, and would help to reconcile the fossil
record of star formation with the directly observed SFH.Comment: 21 pages, 7 figures, 3 tables; submitted to Monthly Notice
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