224 research outputs found
Management of Banana Xanthomonas Wilt: Evidence from impact of adoption of cultural control practices in Uganda
Banana Xanthomonas Wilt (BXW) is an important emerging and non-curable infectious plant pathogen in sub-Saharan Africa that can cause up to 100% yield loss, negatively impacting sustainable access to food and income to more than 100 million banana farmers. This study disentangles adopters into partial and full adopters to investigate the factors that are relevant to sustain the adoption process of BXW control practices and quantifies the impact of adopting the practices. Data from a randomly selected sample of 1200 banana farmers in Uganda where the disease is endemic was used. A multinomial logit model was used to determine the factors affecting adoption of control practices and augmented inverse probability weighting was employed to estimate the impacts of adoption on banana productivity and sales. Results show that training a woman farmer and having diverse sources of information about BXW control practices increased adoption of the control practices and reduced the disease incidences. Farmers who adopted all the recommended control practices achieved significantly the highest values of banana production and sales. We conclude that improving information access through farmers’ preferred communication channels, having women-inclusive trainings, and a combination of cultural practices are effective ways for sustaining adoption of the control practices
Spin-Induced Disk Precession in Sagittarius A*
In Sgr A* at the Galactic center, by far the closest and easiest supermassive
black hole we can study, the observational evidence is increasingly pointing to
the presence of a compact, hot, magnetized disk feeding the accretor. In such
low-Mach-number plasmas, forces arising, e.g., from pressure gradients in the
plasma, can altogether negate the warping of disks around Kerr black holes
caused by the Bardeen-Petterson effect and can lead to coherent precession of
the entire disk. In this Letter, we present for the first time highly detailed
3D SPH simulations of the accretion disk evolution in Sgr A*, guided by
observational constraints on its physical characteristics, and conclude that
indeed the Bardeen-Petterson effect is probably absent in this source. Given
what we now understand regarding the emission geometry in this object, we
suggest that a ~ 50-500-day modulation in Sgr A*'s spectrum, arising from the
disk precession, could be an important observational signature; perhaps the ~
106-day period seen earlier in its radio flux, if confirmed, could be due to
this process. On the other hand, if future observations do not confirm this
long modulation in Sgr A*'s spectrum, this would be an indication that either
the disk size or orientation is very different from current estimates, or that
the black hole is not spinning at all (unlikely), or that our current
understanding of how it produces its radiative output is incorrect.Comment: 14 pages, 3 figures; small changes to sections 2.1 and 3; accepted
for publication in Ap
Super stellar clusters with a bimodal hydrodynamic solution: an Approximate Analytic Approach
We look for a simple analytic model to distinguish between stellar clusters
undergoing a bimodal hydrodynamic solution from those able to drive only a
stationary wind. Clusters in the bimodal regime undergo strong radiative
cooling within their densest inner regions, which results in the accumulation
of the matter injected by supernovae and stellar winds and eventually in the
formation of further stellar generations, while their outer regions sustain a
stationary wind. The analytic formulae are derived from the basic hydrodynamic
equations. Our main assumption, that the density at the star cluster surface
scales almost linearly with that at the stagnation radius, is based on results
from semi-analytic and full numerical calculations. The analytic formulation
allows for the determination of the threshold mechanical luminosity that
separates clusters evolving in either of the two solutions. It is possible to
fix the stagnation radius by simple analytic expressions and thus to determine
the fractions of the deposited matter that clusters evolving in the bimodal
regime blow out as a wind or recycle into further stellar generations.Comment: 5 pages, 4 figures, accepted by A&
The effect of 12C + 12C rate uncertainties on s-process yields
The slow neutron capture process in massive stars (the weak s-process)
produces most of the s-only isotopes in the mass region 60 < A < 90. The
nuclear reaction rates used in simulations of this process have a profound
effect on the final s-process yields. We generated 1D stellar models of a 25
solar mass star varying the 12C + 12C rate by a factor of 10 and calculated
full nucleosynthesis using the post-processing code PPN. Increasing or
decreasing the rate by a factor of 10 affects the convective history and
nucleosynthesis, and consequently the final yields.Comment: Conference proceedings for the Nuclear Physics in Astrophysics IV
conference, 8-12 June 2009. 4 pages, 3 figures. Accepted for publication to
the Journal of Physics: Conference Serie
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