7,635 research outputs found
Nitrogen loss assessment and environmental consequences in the loess soil of China
Attention is focused on fertilizer nitrogen loss and the environmental consequences in Shaanxi Province in loess region of China, including N losses to the atmosphere via ammonia volatilization, nitrification and denitrification, N losses to groundwater by leaching, and crop uptake by roots. Three soils were selected, Entisol, Anthrosol and Luvisol from north, central and south Shaanxi, respectively. Nitrification and NH4+ fixation were measured using a closed chamber method in the laboratory. Denitrification was tested in the laboratory with intact soil cores, C2H2 inhibition techniques. N2O emission was assessed via in situ measurement of N2O in the soil profile and at the soil surface in field experiments. Fertilizer use and crop yields obtained by the farmers were investigated on a large scale in Shaanxi Province. Transformation of fertilizer NH4+ to NO3- was within nine days in the Entisol and Anthrosols, but it took 40 days in Luvisol due to NH4+ fixation by clay minerals. In the pot experiment open to the wind and sunshine with different water content, applied N fertilizer recovery was 74.2% for the Luvisol and 61.3% for the Entisol. The results for the Luvisol showed lower nitrogen recovery as initial soil water content increased. When the fertilizer was incorporated, the recovery was 91.6% at 8% and 68.9% at 28% water content. Recovery increased with increasing soil clay content. Large amount of nitrate was accumulated at 200-400 cm depth in the soil profile and accounted for 362-543, 144-677 and 165-569 kg N ha-1 in terrace and bottom land in north Shaanxi, terrace land in Guanzhong and south Shaanxi, respectively. N2O measurements also showed that N2O spatial variation in the profile could be ranked as, 10 cm < 30 cm < 150 cm < 90 cm < 60 cm. Temporal variation was correlated with rainfall or irrigation. Closed chamber measurements or calculations from profile concentrations resulted in N2O emission of less than 1 kg N2O ha-1 y-1. An investigation showed that soil fertility in the Guanzhong area is high, but yield has not increased with increasing N fertilizer application during the last five years. Over-application of N fertilizer was very common in the Guanzhong area and ranged from 100 to 382 kg N ha-1 for wheat and from 106 to 530 kg N ha-1 for maize. The results of the experiments indicate that the N fertilizer recovery efficiency is about 30% and the consequences of N losses are seriously threatening the environment by leaching to the groundwater and by denitrification to the atmosphere
The XMM Newton spectra of the 2012 outburst of the black-hole candidate 4U 1630-47 revisited
Recent XMM-Newton observations of the black-hole candidate 4U 1630-47 during
the 2012 outburst revealed three relativistically Doppler-shifted emission
lines that were interpreted as arising from baryonic matter in the jet of this
source. Here we reanalyse those data and find an alternative model that, with
less free parameters than the model with Doppler-shifted emission lines, fits
the data well. In our model we allow the abundance of S and Fe in the
interstellar material along the line of sight to the source to be non solar.
Among other things, this significantly impacts the emission predicted by the
model at around 7.1 keV, where the edge of neutral Fe appears, and renders the
lines unnecessary. The fits to all the 2012 XMM-Newton observations of this
source require a moderately broad emission line at around 7 keV plus several
absorption lines and edges due to highly ionised Fe and Ni, which reveal the
presence of a highly-ionised absorber close to the source. Finally, our model
also fits well the observations in which the lines were detected when we apply
the most recent calibration files, whereas the model with the three
Doppler-shifted emission lines does not.Comment: 8 pages, 6 figure
Relabelling Algorithms for Large Dataset Mixture Models
Mixture models are flexible tools in density estimation and classification
problems. Bayesian estimation of such models typically relies on sampling from
the posterior distribution using Markov chain Monte Carlo. Label switching
arises because the posterior is invariant to permutations of the component
parameters. Methods for dealing with label switching have been studied fairly
extensively in the literature, with the most popular approaches being those
based on loss functions. However, many of these algorithms turn out to be too
slow in practice, and can be infeasible as the size and dimension of the data
grow. In this article, we review earlier solutions which can scale up well for
large data sets, and compare their performances on simulated and real datasets.
In addition, we propose a new, and computationally efficient algorithm based on
a loss function interpretation, and show that it can scale up well in larger
problems. We conclude with some discussions and recommendations of all the
methods studied
Linear maps on nonnegative symmetric matrices preserving a given independence number
The independence number of a square matrix , denoted by , is
the maximum order of its principal zero submatrices. Let be the set
of nonnegative symmetric matrices with zero trace, and let be
the matrix with all entries equal to one. Given any integers
with , we prove that a linear map
satisfies and if and only if there is a permutation matrix
such that \phi(X)=P^TXP{~~~~\rm for~ all~}X\in S_n^+.$
- …