6,177 research outputs found
On-farm adoption of irrigation technologies in two irrigated valleys in Central Chile : the effect of relative abundance of water resources
This paper examines the adoption of irrigation technologies and the underlying diversity in terms of intensity of adoption in 2 irrigated valleys in Central Chile. Results show a low and narrow range of adoption, with only 30 % of farmers adopting technologies. Through a Latent Class Analysis, 2 types of farmers were identified, a small group comprising moderate to intensive users, and a second one consisting of the majority of farmers mostly constrained in natural capital. Furthermore, the econometric analysis indicates that education, diversification, continuous access to water, and perception of water reliability increase the adoption. Conversely, higher waterland ratios, presence of community reservoirs, and earthen canals reduce the uptake. Overall, the dominance of fruit and horticulture production, access to agricultural credits, and full irrigation of the farm are the main drivers of adoption. The latter is a critical factor, indicating a relative abundance of water resources, which, alongside contextual characteristics, discourages farmers from implementing technologies. The low adoption rate, as well as the hindering factors, will challenge public and private organizations to design and implement policies aiming to improve water reliability and management. To generate incentives and increase awareness on the scarcity of the resource in the light of the predicted reductions in water availability because of climate change will be crucial as well
The ACS Fornax Cluster Survey VII. Half-Light Radii of Globular Clusters in Early-Type Galaxies
We measure the half-light radii of globular clusters (GCs) in 43 galaxies
from the ACS Fornax Cluster Survey (ACSFCS). We use these data to extend
previous work in which the environmental dependencies of the half-light radii
of GCs in early type galaxies in the ACS Virgo Cluster Survey (ACSVCS) were
studied, and a corrected mean half-light radius (corrected for the observed
environmental trends) was suggested as a reliable distance indicator. This work
both increases the sample size for the study of the environmental dependencies,
and adds leverage to the study of the corrected half-light radius as a possible
distance indicator (since Fornax lies at a larger distance than the Virgo
cluster). We study the environmental dependencies of the size of GCs using both
a Principal Component Analysis as well as 2D scaling relations. We largely
confirm the environmental dependencies shown in Jordan et al. (2005), but find
evidence that there is a residual correlation in the mean half-light radius of
GC systems with galaxy magnitude, and subtle differences in the other
correlations - so there may not be a universal correction for the half-light
radii of lower luminosity galaxy GC systems. The main factor determining the
size of a GC in an early type galaxy is the GC color. Red GCs have =
2.8+/-0.3 pc, while blue GCs have = 3.4+/-0.3 pc. We show that for bright
early-type galaxies (M_B < -19 mag), the uncorrected mean half-light radius of
the GC system is by itself an excellent distance indicator (with error ~11%),
having the potential to reach cosmologically interesting distances in the era
of high angular resolution adaptive optics on large optical telescopes.Comment: ApJ in press, 19 pages, 16 figures
A search for massive UCDs in the Centaurus Galaxy Cluster
We recently initiated a search for ultra-compact dwarf galaxies (UCDs) in the
Centaurus galaxy cluster (Mieske et al. 2007), resulting in the discovery of 27
compact objects with -12.2<M_V<-10.9 mag. Our overall survey completeness was
15-20% within 120 kpc projected clustercentric distance. In order to better
constrain the luminosity distribution of the brightest UCDs in Centaurus, we
continue our search by substantially improving our survey completeness
specifically in the regime M_V<-12 mag (V_0<21.3 mag). Using VIMOS at the VLT,
we obtain low-resolution spectra of 400 compact objects with 19.3<V_0<21.3 mag
(-14<M_V<-12 mag at the Centaurus distance) in the central 25' of the Centaurus
cluster, which corresponds to a projected radius of ~150 kpc. Our survey yields
complete area coverage within ~120 kpc. For 94% of the sources included in the
masks we successfully measure a redshift. Due to incompleteness in the slit
assignment, our final completeness in the area surveyed is 52%. Among our
targets we find three new UCDs in the magnitude range -12.2<M_V<-12 mag, hence
at the faint limit of our survey. One of them is covered by archival HST WFPC2
imaging, yielding a size estimate of r_h <= 8-9 pc. At 95% confidence we can
reject the hypothesis that in the area surveyed there are more than 2 massive
UCDs with M_V<-12.2 mag and r_eff <=70 pc. Our survey hence confirms the
extreme rareness of massive UCDs. We find that the radial distributions of
Centaurus and Fornax UCDs with respect to their host clusters' centers agree
within the 2 sigma level.Comment: 9 pages, 7 figures, accepted as Research Note for A&
The ACS Fornax Cluster Survey. IX. The Color-Magnitude Relation of Globular Cluster Systems
We investigate the color-magnitude relation for globular clusters (GCs) --
the so-called "blue tilt" -- detected in the ACS Fornax Cluster Survey and
using the combined sample of GCs from the ACS Fornax and Virgo Cluster Surveys.
We find a tilt of gamma_z=d(g-z)/dz=-0.0257 +- 0.0050 for the full GC sample of
the Fornax Cluster Survey (~5800 GCs). This is slightly shallower than the
value gamma_z=-0.0459 +- 0.0048 found for the Virgo Cluster Survey GC sample
(~11100 GCs). The slope for the merged Fornax and Virgo datasets (~16900 GCs)
is gamma_z=-0.0293 +- 0.0085, corresponding to a mass-metallicity relation of Z
~ M^0.43. We find that the blue tilt sets in at GC masses in excess of M ~
2*10^5 M_sun. The tilt is stronger for GCs belonging to high-mass galaxies (M_*
> 5 * 10^10 M_sun) than for those in low-mass galaxies (M_* < 5 * 10^10 M_sun).
It is also more pronounced for GCs with smaller galactocentric distances. Our
findings suggest a range of mass-metallicity relations Z_GC ~ M_GC^(0.3-0.7)
which vary as a function of host galaxy mass/luminosity. We compare our
observations to a recent model of star cluster self-enrichment with generally
favorable results. We suggest that, within the context of this model, the
proto-cluster clouds out of which the GCs formed may have had density profiles
slightly steeper than isothermal and/or star formation efficiencies somewhat
below 0.3. We caution, however, that the significantly different appearance of
the CMDs defined by the GC systems associated with galaxies of similar mass and
morphological type pose a challenge to any single mechanism that seeks to
explain the blue tilt. We therefore suggest that the merger/accretion histories
of individual galaxies have played a non-negligible role determining the
distribution of GCs in the CMDs of individual GC systems
Food web topology and nested keystone species complexes
Important species may be in critically central network positions in ecological interaction networks. Beyond quantifying
which one is the most central species in a food web, a multi-node approach can identify the key sets of the most central
n species as well. However, for sets of different size n, these structural keystone species complexes may differ in their
composition. If larger sets contain smaller sets, higher nestedness may be a proxy for predictive ecology and efficient
management of ecosystems. On the contrary, lower nestedness makes the identification of keystones more complicated.
Our question here is how the topology of a network can influence nestedness as an architectural constraint. Here, we
study the role of keystone species complexes in 27 real food webs and quantify their nestedness. After quantifying their
topology properties, we determine their keystones species complexes, calculate their nestedness and statistically analyze
the relationship between topological indices and nestedness. A better understanding of the cores of ecosystems is crucial
for efficient conservation efforts and to know which networks will have more nested keystone species complexes would
be a great help for prioritizing species that could preserve the ecosystem’s structural integrity
Kombinatorikus módszerek gráfok és rúdszerkezetek merevségének vizsgálatában = Combinatorial methods in the study of rigidity of graphs and frameworks
A szerkezetek merevsĂ©gi tulajdonságaira vonatkozĂł matematikai eredmĂ©nyek a statikai alkalmazásokon kĂvĂĽl számos más terĂĽleten is hasznosĂthatĂłk. A közelmĂşltban sikerrel alkalmazták ezeket molekulák szerkezetĂ©nek vizsgálataiban, szenzorhálĂłzatok lokalizáciĂłs problĂ©máiban, CAD feladatokban, stb. A kutatás cĂ©lja gráfok Ă©s szerkezetek merevsĂ©gi tulajdonságainak vizsgálata volt kombinatorikus mĂłdszerekkel. Igazoltuk az Ăş.n. Molekuláris SejtĂ©s kĂ©tdimenziĂłs változatát Ă©s jelentĹ‘s elĹ‘relĂ©pĂ©seket tettĂĽnk a molekuláris gráfok háromdimenziĂłs merevsĂ©gĂ©nek jellemzĂ©sĂ©ben is. A globálisan merev, avagy egyĂ©rtelműen realizált gráfok elmĂ©letĂ©t kiterjesztettĂĽk vegyes - hossz Ă©s irány feltĂ©teleket is tartalmazĂł - vegyes gráfokra valamint az egyĂ©rtelműen lokalizálhatĂł rĂ©szekre is. TovábbfejlesztettĂĽk a szĂĽksĂ©ges gráf- Ă©s matroidelmĂ©leti mĂłdszereket. Ăšj eredmĂ©nyeket Ă©rtĂĽnk el a tensegrity szerkezetek, test-zsanĂ©r szerkezetek, valamint a merevsĂ©g egy irányĂtott változatával kapcsolatban is. | The mathematical theory of rigid frameworks has potential applications in various areas. It has been successfully applied - in addition to statics - in the study of flexibility of molecules, in the localization problem of sensor networks, in CAD problems, and elsewhere. In this research project we investigated the rigidity properties of graphs and frameworks by using combinatorial methods. We proved the two-dimensional version of the so-called Molecular Conjecture and made substantial progress towards a complete characterization of the rigid molecular graphs in three dimensions. We generalized the theory of globally rigid (that is, uniquely localized) graphs to mixed graphs, in which lengths as well as direction constraints are given, and to globally rigid clusters, or subgraphs. We developed new graph and matroid theoretical methods. We also obtained new results on tensegrity frameworks, body and hinge frameworks, and on a directed version of rigidity
Posibles consecuencias de los atentados de Madrid
Se ofrece una reflexiĂłn sobre las consecuencias que puedan tener los atentados del 11 de marzo y se proponen algunas medidas para contrarrestar los efectos negativos que puedan derivarse de ellos.
Los atentados de Madrid, cuya autorĂa se atribuye en estos momentos al entramado terrorista de al-Qaeda, pueden convertirse en un Ă©xito estratĂ©gico de la yihad global. Se trata de acciones que refuerzan el discurso y la moral de los yihadistas; pueden dañar la solidez de la coaliciĂłn internacional contra el terrorismo; y pueden perturbar tambiĂ©n la convivencia social en los paĂses con comunidades árabes o musulmanas numerosas. Resulta necesario explorar medidas que ayuden a prevenir dichos efectos
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