2,024 research outputs found
China’s agricultural prospects and challenges: Report on scenario simulations until 2030 with the Chinagro welfare model covering national, regional and county level
The report describes prospects and challenges for Chinese agriculture until 2030 under different scenarios, using the Chinagro welfare model. A scenario is defined as a coherent set of assumptions about exogenous driving forces (farm land, population, non-agricultural growth, world prices etc.), derived from the literature and own assessments. Under these assumptions, simulations with the Chinagro model analyze the price-based interaction between the supply
behavior of farmers, the demand behavior of consumers and the determination of trade flows by merchants.
The outcomes from the Baseline scenario seem reassuring in that foreign imports remain moderate relative to China’s size, though quite large as fraction of world trade. It would be possible to feed people as well as animals without excessive imports. There is even a potential for significant export flows of vegetables and fruits. Regarding concerns, the trends in per capita agricultural value added are problematic, because they stay in all regions behind per capita value added outside agriculture, albeit that they are rising steadily. This leads to growing disparity in per capita incomes within and across regions. The mounting environmental pressure from fertilizer losses and unused manure surpluses is another cause of concern. The second scenario, the Trade liberalization scenario, appears to hurt farm incomes more than it benefits them and to raise the gap with non-agriculture, also because food becomes cheaper in urban areas. Hence, it highlights the difficult choice between economic efficiency and poverty alleviation that agricultural policy makers often face. The High income growth scenario reinforces the national food self-sufficiency result of the baseline simulation. Even with meat demand higher than under the baseline, levels of imports remain manageable. The High R&D scenario shows that a considerable reduction in dependence on agricultural imports is possible. However, a substantial part of the gains will accrue to consumers rather than to farmers, due to price reductions. Finally, the Enhanced irrigation scenario shows outcomes similar to those of the high R&D scenario. Here also the agricultural trade balance improves and consumer welfare improves, but farmers have to cope with drops in prices, and those who do not benefit from land improvement, only experience losses through falling prices.
The present report is written at the onset of the CATSEI-project that will analyze policy packages with more specificity and detail after implementing the following model improvements. First, the impact of China’s imports and exports on world markets will be represented explicitly. Second, the developments outside agriculture in rural areas will be accounted for endogenously,
particularly to represent farm revenue from off-farm employment. Third, the trade and transportation margins between farm-gates and markets will be made dependent on the relative flexibility of the actors (farmers, processors, traders) along the chain. Finally, the various
techniques to identify more efficient and more sustainable use of scarce water and nutrients and to address health risks will appear more explicitly
Close binary systems among very low mass stars and brown dwarfs
Using Monte Carlo simulations and published radial velocity surveys we have
constrained the frequency and separation (a) distribution of very low mass star
(VLM) and brown dwarf (BD) binary systems. We find that simple Gaussian
extensions of the observed wide binary distribution, with a peak at 4 au and
0.6< sigma_{log(a/au)}<1.0, correctly reproduce the observed number of close
binary systems, implying a close (a<2.6 au) binary frequency of 17-30 per cent
and overall frequency of 32-45 per cent. N-body models of the dynamical decay
of unstable protostellar multiple systems are excluded with high confidence
because they do not produce enough close binary VLMs/BDs. The large number of
close binaries and high overall binary frequency are also completely
inconsistent with published smoothed particle hydrodynamical modelling and
argue against a dynamical origin for VLMs/BDs.Comment: Proceedings of the workshop on Ultra-Low Mass Star Formation, eds. E.
Martin, A. Magazzu. To appear in Astron. Nach
Pre- and postoperative headache in patients with meningioma
Background
Meningiomas are generally slowly growing intracranial tumors. They are often incidentally diagnosed, given that symptoms may be absent even in cases of an enormous tumor size. Headache is a frequent but not consistent symptom. Therefore, we examined the association between structural, biochemical and histochemical tumor parameters with preoperative as well as postoperative occurrence of headache.
Methods
In our study, we prospectively investigated 69 consecutive patients enrolled for meningioma neurosurgery. Anatomical, histological and biochemical parameters were acquired, and headache parameters were registered from the clinical report and from a questionnaire filled by the patients before neurosurgery. The headache was re-evaluated one year after neurosurgery. The study was designed to exploratively investigate whether there is an association of acquired clinical and biological parameters with the occurrence of preoperative and postoperative headache.
Results
Edema diameter and the proliferation marker MIB-1 were negatively associated with the incidence and intensity of preoperative headache, while the content of prostaglandin E2 in the tumor tissue was positively associated with preoperative headache intensity. Headache was more prevalent when the meningioma was located in the area supplied by the ophthalmic trigeminal branch. Compared to preoperative headache levels, an overall reduction was observed one year postoperative, and patients with a larger tumor had a higher headache remission. In parietal and occipital meningiomas and in those with a larger edema, the percentage of the headache remission rate was higher compared to other locations or smaller edema. Multivariable analyses showed an involvement of substance P and prostaglandin E2 in preoperative headache.
Conclusions
The study demonstrates new associations between meningiomas and headache. The postoperative headache outcome in the presented patient sample is encouraging for the performed neurosurgical intervention. These results should be tested in a prospective study that incorporates all patients with meningiomas
Low-mass companions to Hyades stars
It is now well established that a large fraction of the low-mass stars are
binaries or higher order multiples. Similarly a sizable fraction have giant
planets. In contrast to these, the situation for brown dwarf companions is
complicated: While close systems seem to be extremely rare, wide systems are
possibly more common. In this paper, we present new results on a survey for
low-mass companions in the Hyades. After measuring precisely the radial
velocity of 98 Hyades dwarf stars for 5 years, we have selected all stars that
show low-amplitude long-period trends. With AO-observations of these 14 stars
we found companion candidates around nine of them, where one star has two
companions. The two companions of HIP 16548 have masses between 0.07 to 0.08
Mo, and are thus either brown dwarfs or very low mass stars. In the case of HAN
172 we found a companion with a mass between 0.08 to 0.10 Mo, which is again
between a star and a brown dwarf. The other seven stars all have stellar
companions. In two additional cases, the RV-variations are presumably caused by
stellar activity, and in another case the companion could be a short-period
binary. The images of the remaining two stars are slightly elongated, which
might imply that even these are binaries. Because at least 12 of the 14 stars
showing low-amplitude RV trends turn out to have companions with a mass greater
than 70 MJupiter, or are just active, we finally estimate the number of
companions with masses between 10 MJupiter and 70 MJupiter within 8 AU of the
host stars in the Hyades as less equal 2%.Comment: 10 pages, 10 figure
Extrasolar planets in stellar multiple systems
Analyzing exoplanets detected by radial velocity or transit observations, we
determine the multiplicity of exoplanet host stars in order to study the
influence of a stellar companion on the properties of planet candidates.
Matching the host stars of exoplanet candidates detected by radial velocity or
transit observations with online multiplicity catalogs in addition to a
literature search, 57 exoplanet host stars are identified having a stellar
companion. The resulting multiplicity rate of at least 12 percent for exoplanet
host stars is about four times smaller than the multiplicity of solar like
stars in general. The mass and the number of planets in stellar multiple
systems depend on the separation between their host star and its nearest
stellar companion, e.g. the planetary mass decreases with an increasing stellar
separation. We present an updated overview of exoplanet candidates in stellar
multiple systems, including 15 new systems (compared to the latest summary from
2009).Comment: 11 pages, 4 figures, appendix with 6 tables, accepted for publication
in A&
Characterizing the IYJ Excess Continuum Emission in T Tauri Stars
We present the first characterization of the excess continuum emission of
accreting T Tauri stars between optical and near-infrared wavelengths. With
nearly simultaneous spectra from 0.48 to 2.4 microns acquired with HIRES and
NIRSPEC on Keck and SpeX on the IRTF, we find significant excess continuum
emission throughout this region, including the I, Y, and J bands, which are
usually thought to diagnose primarily photospheric emission. The IYJ excess
correlates with the excess in the V band, attributed to accretion shocks in the
photosphere, and the excess in the K band, attributed to dust in the inner disk
near the dust sublimation radius, but it is too large to be an extension of the
excess from these sources. The spectrum of the excess emission is broad and
featureless, suggestive of blackbody radiation with a temperature between 2200
and 5000 K. The luminosity of the IYJ excess is comparable to the accretion
luminosity inferred from modeling the blue and ultraviolet excess emission and
may require reassessment of disk accretion rates. The source of the IYJ excess
is unclear. In stars of low accretion rate, the size of the emitting region is
consistent with cooler material surrounding small hot accretion spots in the
photosphere. However, for stars with high accretion rates, the projected area
is comparable to or exceeds that of the stellar surface. We suggest that at
least some of the IYJ excess emission arises in the dust-free gas inside the
dust sublimation radius in the disk.Comment: Accepted to ApJ, 31 pages, 21 figure
Optimizing regional cropping systems with a dynamic adaptation strategy for water sustainable agriculture in the Hebei Plain
Unsustainable overexploitation of groundwater for agricultural irrigation has led to rapid groundwater depletion and severe environmental damage in the semi-arid Hebei Plain of China. Field experiments have recommended annual winter fallowing (i.e., forgoing winter wheat production) as the most effective way to replenish groundwater. However, adopting the recommendation across the Hebei Plain would lead to a significant reduction in total wheat production. This research aims to find the most favorable water-sustainable cropping systems for different localities in the Hebei Plain, which at the regional aggregation level maintains the uppermost overall levels of wheat and grain production respectively. Our simulations indicate that in the Hebei Plain, an optimal allocation of a wheat-early maize relay intercropping system and an early maize-winter fallow cropping system across the Hebei Plain could lead to significant water savings while minimizing grain production losses to around 11%. Compared to the prevailing wheat and summer maize cropping system, to prevent a drop in the water table, 39% of the current wheat cropping land would need to be fallowed in winter, reducing irrigation water use by 2639Ă—106m^3. Replacing the prevailing wheat and summer maize cropping system with our optimized allocation system could lead to a 36% increase in total maize production and 39% decrease in total wheat production, resulting in total agricultural irrigation water savings of 2322Ă—106m^3 and a total grain production reduction by 11%. The findings indicate the potential benefits of our cropping system adaptation method to meet the challenge of recovering local groundwater level with the least possible reduction of wheat and total grain production in the Hebei Plain
Retrospective Analysis of Bacterial Cultures Sampled in German Chicken- Fattening Farms During the Years 2011–2012 Revealed Additional VIM-1 Carbapenemase-Producing Escherichia coli and a Serologically Rough Salmonella enterica Serovar Infantis
Carbapenems are last-resort antibiotics used in human medicine. The increased
detection of carbapenem-resistant Enterobacteriaceae (CRE) is therefore
worrying. In 2011 we reported the first livestock-associated VIM-1-producing
Salmonella (S.) enterica serovar Infantis (R3) isolate from dust, sampled in a
German chicken fattening farm. Due to this observation we retrospectively
investigated more than 536 stored bacterial cultures, isolated from 45 chicken
fattening farms during the years 2011 and 2012. After a non-selective
overnight incubation, the bacteria were transferred to selective media.
Escherichia (E.) coli and Salmonella growing on these media were further
investigated, including antibiotic susceptibility testing, carbapenemase gene
screening and whole genome sequencing (WGS). In total, four CRE were found in
three out of 45 investigated farms: Besides R3, one additional Salmonella
(G-336-1a) as well as two E. coli isolates (G-336-2, G-268-2). All but G-268-2
harbored the blaVIM-1 gene. Salmonella isolates R3 and G-336-1 were closely
related although derived from two different farms. All three blaVIM-1-encoding
isolates possessed identical plasmids and the blaVIM-1- containing transposon
showed mobility at least in vitro. In isolate G-268-2, the AmpC beta-lactamase
gene blaCMY-2 but no known carbapenemase gene was identified. However, a
transfer of the phenotypic resistance was possible. Furthermore, G-268-2
contained the mcr-1 gene, combining phenotypical carbapenem- as well as
colistin resistance in one isolate. Carbapenem-resistant Enterobacteriaceae
have been found in three out of 45 investigated chicken flocks. This finding
is alarming and emphasizes the importance of intervention strategies to
contain the environmental spread of resistant bacteria in animals and humans
Investigating Off-shell Stability of Anti-de Sitter Space in String Theory
We propose an investigation of stability of vacua in string theory by
studying their stability with respect to a (suitable) world-sheet
renormalization group (RG) flow. We prove geometric stability of (Euclidean)
anti-de Sitter (AdS) space (i.e., ) with respect to the simplest
RG flow in closed string theory, the Ricci flow. AdS space is not a fixed point
of Ricci flow. We therefore choose an appropriate flow for which it is a fixed
point, prove a linear stability result for AdS space with respect to this flow,
and then show this implies its geometric stability with respect to Ricci flow.
The techniques used can be generalized to RG flows involving other fields. We
also discuss tools from the mathematics of geometric flows that can be used to
study stability of string vacua.Comment: 29 pages, references added in this version to appear in Classical and
Quantum Gravit
MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214
We report on the analysis of high-precision space-based photometry of the
roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three
stars were observed by the MOST satellite for more than 25 days, allowing
unprecedented views of their pulsation. We find previously unknown candidate
frequencies in all three stars. We establish the rotation period of HD 9289
(8.5 d) for the first time and show that the star is pulsating in two modes
that show different mode geometries. We present a detailed analysis of HD
99563's mode multiplet and find a new candidate frequency which appears
independent of the previously known mode. Finally, we report on 11 detected
pulsation frequencies in HD 134214, 9 of which were never before detected in
photometry, and 3 of which are completely new detections. Thanks to the
unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214
can be seen to have a well-defined large frequency spacing similar to the
well-studied roAp star HD 24712 (HR 1217).Comment: 11 pages, 12 figures, accepted for publication in A&
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