1,133 research outputs found
Beyond the project cycle: an evaluation of agroforestry adoption and diffusion over the medium term in a south Indian village
Few studies explicitly assess the temporal and spatial dynamics of agroforestry adoption occurring beyond the project cycle. Where ex-post evaluations are published, abandonment of introduced agroforestry after project cessation is often reported. This paper presents an analysis of agroforestry adoption in a poor, peri-urban village in semi-arid south India, where 97 % of initial adopters had retained their plots six to eight years after implementation. The intervention was facilitated by BAIF, an Indian non-governmental organisation specialising in natural resource management. The complex technological package promoted was known as �wadi� and comprised fruit trees planted in crop fields, with a boundary of multi-purpose trees and integrated soil and water conservation measures. Sixty four agroforestry plots belonging to 43 households were surveyed in 2010/11 and interviews were held with both adopting and non-adopting farmers. Beyond retention, a quarter of adopters had expanded the practice on to additional areas of land and some diffusion to initially non-adopting farmers had also occurred. Adopters were found to have modified the practice to suit their own objectives, capabilities and constraints, highlighting that adoption is more than a simple binary choice. The study demonstrates the importance of external support for adoption of agroforestry. The intervention was not, however, especially pro-poor with adoption occurring disproportionately among relatively wealthier households with larger landholdings. Where poorer households adopted, this tended to occur later. Participation was entirely voluntary and, by 2011, conversion of suitable farmland to agroforestry had reached 18 %; while beneficial to individual adopters, this patchy coverage arguably limits the potential for enhanced ecosystem service provision at landscape-scale
Can Personal Exposures to Higher Nighttime and Early‐Morning Temperatures Increase Blood Pressure?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/89493/1/j.1751-7176.2011.00545.x.pd
Cover crops improve ground cover in a very dry season
Take home messages
• Previous trials have shown cover crops can increase stored fallow water and improve crop performance and returns in northern farming systems
• A cover crop in a long fallow (14 months) in a dry season allowed improved ground cover with no net deficit in soil water. The extra ground cover improved the opportunity to deep plant wheat.
• A cover crop in a short fallow had a water cost that translated to a yield penalty.
• When the sorghum stopped growing in dry conditions it continued to use water, for no biomass (or cover) increase when it wasn’t sprayed out
Spin Dynamics in the Magnetic Chains Arrays of Sr14Cu24O41: a Neutron Inelastic scattering Investigation
Below about 150 K, the spin arrangement in the chain arrays of Sr14Cu24O41 is
shown to develop in two dimensions (2D). Both the correlations and the
dispersion of the observed elementary excitations agree well with a model of
interacting dimers. Along the chains, the intra- and inter-dimer distances are
equal to 2 and about 3 times the distance (c) between neighboring Cu ions.
While the intra-dimer coupling is J about 10 meV, the inter-dimer couplings
along and between the chains are of comparable strenght, J// about -1.1 meV and
Jperp about 1.7 meV, respectively. This remarkable 2D arrangement satisfies the
formal Cu valence of the undoped compound. Our data suggest also that it is
associated with a relative sliding of one chain with respect to the next one,
which, as T decreases, develops in the chain direction. A qualitative analysis
shows that nearest inter-dimer spin correlations are ferromagnetic, which, in
such a 2D structure, could well result from frustration effects.Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, date of receipt 29 June
199
The stellar population content of the thick disk and halo of the Milky Way analogue NGC 891
We present deep ACS images of 3 fields in the edge-on disk galaxy NGC 891,
which extend from the plane of the disk to 12 kpc, and out to 25 kpc along the
major axis. The photometry of individual stars reaches 2.5 magnitudes below the
tip of the RGB. We use the astrophotometric catalogue to probe the stellar
content and metallicity distribution across the thick disk and spheroid of NGC
891. The CMDs of thick disk and spheroid population are dominated by old RGB
stars with a wide range of metallicities, from a metal-poor tail at [Fe/H] ~
-2.4 dex, up to about half-solar metallicity. The peak of the MDF of the thick
disk is at -0.9 dex. The inner parts of the thick disk, within 14 kpc along the
major axis show no vertical colour/metallicity gradient. In the outer parts, a
mild vertical gradient of Delta(V-I)/Delta|Z| = 0.1 +/- 0.05 kpc^-1 is
detected. This gradient is however accounted for by the mixing with the metal
poor halo stars. No metallicity gradient along the major axis is present for
thick disk stars, but strong variations of about 0.35 dex around the mean of
[Fe/H] = -1.13 dex are found. The properties of the asymmetric MDFs of the
thick disk stars show no significant changes in both the radial and the
vertical directions. The stellar populations at solar cylinder-like distances
show strikingly different properties from those of the Galaxy, suggesting that
the accretion histories of both galaxies have been different. The spheroid
population shows remarkably uniform stellar population properties. The median
metallicity of the halo stellar population shows a shallow gradient from about
-1.15 dex in the inner parts to -1.27 dex at 24 kpc distance from the centre.
Similar to the thick disk stars, large variations around the mean relation are
present.Comment: 19 pages, 19 figures, accepted for publication in MNRA
Cosmological Galaxy Formation Simulations Using SPH
We present the McMaster Unbiased Galaxy Simulations (MUGS), the first 9
galaxies of an unbiased selection ranging in total mass from 5
M to 2 M simulated using n-body smoothed
particle hydrodynamics (SPH) at high resolution. The simulations include a
treatment of low temperature metal cooling, UV background radiation, star
formation, and physically motivated stellar feedback. Mock images of the
simulations show that the simulations lie within the observed range of
relations such as that between color and magnitude and that between brightness
and circular velocity (Tully-Fisher). The greatest discrepancy between the
simulated galaxies and observed galaxies is the high concentration of material
at the center of the galaxies as represented by the centrally peaked rotation
curves and the high bulge-to-total ratios of the simulations determined both
kinematically and photometrically. This central concentration represents the
excess of low angular momentum material that long has plagued morphological
studies of simulated galaxies and suggests that higher resolutions and a more
accurate description of feedback will be required to simulate more realistic
galaxies. Even with the excess central mass concentrations, the simulations
suggest the important role merger history and halo spin play in the formation
of disks.Comment: 16 pages, 16 figures, submitted to MNRAS, movies available at
http://mugs.mcmaster.ca . Comments welcome
The Star Formation History in The Far Outer Disc of M33
The outer regions of disc galaxies are becoming increasingly recognized as
key testing sites for models of disc assembly and evolution. Important issues
are the epoch at which the bulk of the stars in these regions formed and how
discs grow radially over time. To address these issues, we use Hubble Space
Telescope Advanced Camera for Surveys imaging to study the star formation
history (SFH) of two fields at 9.1 and 11.6 kpc along M33's northern major
axis. These fields lie at ~ 4 and 5 V-band disc scale-lengths and straddle the
break in M33's surface brightness profile. The colour-magnitude diagrams (CMDs)
reach the ancient main sequence turnoff with a signal-to-noise ratio of ~ 5.
From detailed modelling of the CMDs, we find that the majority of stars in both
fields combined formed at z < 1. The mean age in the inner field, S1, is ~ 3
+/- 1 Gyr and the mean metallicity is [M/H] ~ -0.5 +/- 0.2 dex. The star
formation history of S1 unambiguously reveals how the inside-out growth
previously measured for M33's inner disc out to ~ 6 kpc extends out to the disc
edge at ~ 9 kpc. In comparison, the outer field, S2, is older (mean age ~ 7 +/-
2 Gyr), more metal-poor (mean [M/H] ~ -0.8 +/- 0.3 dex), and contains ~ 30
times less stellar mass. These results provide the most compelling evidence yet
that M33's age gradient reverses at large radii near the disc break and that
this reversal is accompanied by a break in stellar mass surface density. We
discuss several possible interpretations of this behaviour including radial
stellar mixing, warping of the gaseous disc, a change in star formation
efficiency, and a transition to another structural component. These results
offer one of the most detailed views yet of the peripheral regions of any disc
galaxy and provide a much-needed observational constraint on the last major
epoch of star formation in the outer disc.Comment: 15 pages, 9 figures, accepted to MNRAS, hi-res version available at
http://www.roe.ac.uk/~mkb/astroph/m33hires.pd
Feedback and the Formation of Dwarf Galaxy Stellar Halos
Stellar population studies show that low mass galaxies in all environments
exhibit stellar halos that are older and more spherically distributed than the
main body of the galaxy. In some cases, there is a significant intermediate age
component that extends beyond the young disk. We examine a suite of Smoothed
Particle Hydrodynamic (SPH) simulations and find that elevated early star
formation activity combined with supernova feedback can produce an extended
stellar distribution that resembles these halos for model galaxies ranging from
= 15 km s to 35 km s, without the need for accretion of
subhalos.Comment: 15 pages, 15 figures, accepted MNRA
Bacteroides fragilis requires the ferrous-iron transporter FeoAB and the CobN-like proteins BtuS1 and BtuS2 for assimilation of iron released from heme
The intestinal commensal and opportunistic anaerobic pathogen Bacteroides fragilis has an essential requirement for both heme and free iron to support growth in extraintestinal infections. In the absence of free iron, B. fragilis can utilize heme as the sole source of iron. However, the mechanisms to remove iron from heme are not completely understood. In this study, we show that the inner membrane ferrous iron
transporter ∆feoAB mutant strain is no longer able to grow with heme as the sole source of iron. Genetic complementation with the feoAB gene operon completely restored growth. Our data indicate that iron is removed from heme in the periplasmic space, and the released iron is transported by the FeoAB system. Interestingly, when B. fragilis utilizes iron from heme, it releases heme-derived porphyrins by a dechelatase activity which is upregulated under low iron conditions. This is supported by the findings showing that formation of heme-derived porphyrins in the ∆feoAB mutant and the parent strain increased 30-fold and fivefold (respectively) under low iron conditions compared to iron replete conditions. Moreover, the btuS1 btuS2 doublemutant strain (lacking the predicted periplasmic, membrane anchored CobN-like proteins) also showed growth defect with heme as the sole source of iron, suggesting that BtuS1 and BtuS2 are involved in heme-iron assimilation. Though the dechelatase mechanism remains uncharacterized, assays performed in bacterial crude extracts show that BtuS1 and BtuS2 affect the regulation of the dechelatase-specific activities in an iron-dependent manner. These findings suggest that the mechanism to extract iron from heme in Bacteroides requires a group of proteins, which spans the
periplasmic space to make iron available for cellular functions
The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way
It has been known for a long time that the satellite galaxies of the Milky
Way (MW) show a significant amount of phase-space correlation, they are
distributed in a highly inclined Disc of Satellites (DoS). We have extended the
previous studies on the DoS by analysing for the first time the orientations of
streams of stars and gas, and the distributions of globular clusters within the
halo of the MW. It is shown that the spatial distribution of MW globular
clusters classified as young halo clusters (YH GC) is very similar to the DoS,
while 7 of the 14 analysed streams align with the DoS. The probability to find
the observed clustering of streams is only 0.3 per cent when assuming isotropy.
The MW thus is surrounded by a vast polar structure (VPOS) of subsystems
(satellite galaxies, globular clusters and streams), spreading from
Galactocentric distances as small as 10 kpc out to 250 kpc. These findings
demonstrate that a near-isotropic infall of cosmological sub-structure
components onto the MW is essentially ruled out because a large number of
infalling objects would have had to be highly correlated, to a degree not
natural for dark matter sub-structures. The majority of satellites, streams and
YH GCs had to be formed as a correlated population. This is possible in tidal
tails consisting of material expelled from interacting galaxies. We discuss the
tidal scenario for the formation of the VPOS, including successes and possible
challenges. The potential consequences of the MW satellites being tidal dwarf
galaxies are severe. If all the satellite galaxies and YH GCs have been formed
in an encounter between the young MW and another gas-rich galaxy about 10-11
Gyr ago, then the MW does not have any luminous dark-matter substructures and
the missing satellites problem becomes a catastrophic failure of the standard
cosmological model.Comment: 21 pages, 8 figures, 2 tables. Accepted for publication in MNRAS. An
animation of Figure 5 can be found at http://youtu.be/nUwxv-WGfH
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