558 research outputs found
The influence of shearāvelocity heterogeneity on ScS2/ScS amplitude ratios and estimates of Q in the mantle
Regional waveforms of deepāfocus TongaāFiji earthquakes indicate anomalous traveltime differences (ScS2āScS) and amplitude ratios (ScS2/ScS) of the phases ScS and ScS2. The correlation between the ScS2āScS delay time and the ScS2/ScS amplitude ratio suggests that shear wave apparent Q in the mantle below the TongaāFiji region is highest when shear wave velocities are lowest. This observation is unexpected if temperature variations were responsible for the seismic anomalies. Using spectral element method waveform simulations for four tomographic models, we demonstrate that focusing and scattering of shear waves by longāwavelength 3āD heterogeneity in the mantle may overwhelm the signal from intrinsic attenuation in longāperiod ScS2/ScS amplitude ratios. The tomographic models reproduce the trends in recorded ScS2āScS difference times and ScS2/ScS amplitude ratios. Although they cannot be ruled out, variations in shear wave attenuation (i.e., the quality factor Q) are not necessary to explain the data.Key PointsThe influence of complex 3āD wave propagation in the mantle on ScS2/ScS amplitude ratiosScS2āScS difference times are delayed and ScS2/ScS amplitude ratios are high on Samoa indicating low wave speeds but no attenuationBody wave amplitudes may be useful for evaluating the accuracy of tomographic models and as complementary data in tomographic inversionsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134191/1/grl54786_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134191/2/grl54786.pd
Improving rainwater-use in Cabo Verde drylands by reducing runoff
Dryland agriculture in Cabo Verde copes with steep slopes, inadequate practices, irregular intense rain, recurrent
droughts, high runoff rates, severe soil erosion and declining fertility, leading to the inefficient use of rainwater.
Maize and beans occupy N80% of the arable land in low-input, low-yielding subsistence farming. Three collaborative
field trialswere conducted in different agroecological zones to evaluate the effects ofwater-conservation techniques
(mulching of crop residue, a soil surfactant and pigeon-pea hedges) combinedwith organic amendments (compost
and animal or green manure) on runoff and soil loss. During the 2011 and 2012 rainy seasons, three treatments and
one control (traditional practice) were applied to 44- and 24-m2 field plots. A local maize variety and two types of
beanswere planted. Runoff and suspended sedimentswere collected and quantified after each daily erosive rainfall.
Runoff occurred for rainfallsā„50mm(slope b10%, loamy Kastanozem),ā„60mm(slopeā¤23%, siltāclayāloam Regosol)
andā„40mm(slopeā¤37%, sandy loam Cambisol). Runoffwas significantly reduced only with themulch treatment
on the slope N10% and in the treatment of surfactant with organic amendment on the slope b10%. Soil loss
reached 16.6, 5.1, 6.6 and 0.4 Mg haā1 on the Regosol (ā¤23% slope) for the control, surfactant, pigeon-pea and
mulch/pigeon-pea (with organic amendment) treatments, respectively; 3.2, 0.9, 1.3 and 0.1 Mg haā1 on the
Cambisol (ā¤37% slope) and b0. 2Mg haā1 for all treatments and control on the Kastanozem(b10% slope). Erosion
was highly positively correlated with runoff. Mulch with pigeon-pea combinedwith an organic amendment significantly
reduced runoff and erosion fromagricultural fields on steep slopes, contributing to improved use of rainwater
at the plot level. Sustainable land management techniques, such as mulching with pigeon-pea hedges and an
organic amendment, should be advocated and promoted for the semiarid hillsides of Cabo Verde prone to erosion
to increase rainwater-use and to prevent further soil degradation
Tomographic filtering of highāresolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95052/1/ggge1509.pd
Seismic and mineralogical structures of the lower mantle from probabilistic tomography
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95386/1/jgrb17106.pd
Cross-talk between signaling pathways leading to defense against pathogens and insects
In nature, plants interact with a wide range of organisms, some of which
are harmful (e.g. pathogens, herbivorous insects), while others are beneficial
(e.g. growth-promoting rhizobacteria, mycorrhizal fungi, and predatory
enemies of herbivores). During the evolutionary arms race between plants
and their attackers, primary and secondary immune responses evolved to
recognize common or highly specialized features of microbial pathogens
(Chisholm et al., 2006), resulting in sophisticated mechanisms of defense
Soil and water conservation strategies and impact on sustainable livelihood in Cape Verde ā Case study of Ribeira Seca watershed
Cape Verde, located off the coast of Senegal in western Africa, is a volcanic archipelago where a combination of
human, climatic, geomorphologic and pedologic factors has led to extensive degradation of the soils. Like other
Sahelian countries, Cape Verde has suffered the effects of desertification through the years, threatening the livelihood
of the islands population and its fragile environment. In fact, the steep slopes in the ore agricultural islands,
together with semi-arid and arid environments, characterized by an irregular and poorly distributed rainy season,
with high intensity rainfall events, make dryland production a challenge. To survive in these fragile conditions,
the stabilization of the farming systems and the maintenance of sustainable yields have become absolute priorities,
making the islands an erosion control laboratory. Soil and water conservation strategies have been a centerpiece of
the government0s agricultural policies for the last half century. Aiming to maintain the soil in place and the water
inside the soil, the successive governments of Cape Verde have implemented a number of soil and water conservation
techniques, the most common ones being terraces, half moons, live barriers, contour rock walls, contour
furrows and microcatchments, check dams and reforestation with drought resistant species. The soil and water
conservation techniques implemented have contributed to the improvement of the economical and environmental
conditions of the treated landscape, making crop production possible, consequently, improving the livelihood
of the people living on the islands. In this paper, we survey the existing soil and water conservation techniques,
analyze their impact on the livelihood condition of the population through a thorough literature review and field
monitoring using a semi-quantitative methodology and evaluate their effectiveness and impact on crop yield in
the Ribeira Seca watershed. A brief discussion is given on the cost and effectiveness of the techniques to reduce
soil erosion and to promote rainfall infiltration. Finally, we discuss the critical governance factors that lead to the
successful implementation of such strategy in a country with scarce natural resources
An acceptor-substrate binding site determining glycosyl transfer emerges from mutant analysis of a plant vacuolar invertase and a fructosyltransferase
Glycoside hydrolase family 32 (GH32) harbors hydrolyzing and transglycosylating enzymes that are highly homologous in their primary structure. Eight amino acids dispersed along the sequence correlated with either hydrolase or glycosyltransferase activity. These were mutated in onion vacuolar invertase (acINV) according to the residue in festuca sucrose:sucrose 1-fructosyltransferase (saSST) and vice versa. acINV(W440Y) doubles transferase capacity. Reciprocally, saSST(C223N) and saSST(F362Y) double hydrolysis. SaSST(N425S) shows a hydrolyzing activity three to four times its transferase activity. Interestingly, modeling acINV and saSST according to the 3D structure of crystallized GH32 enzymes indicates that mutations saSST(N425S), acINV(W440Y), and the previously reported acINV(W161Y) reside very close together at the surface in the entrance of the active-site pocket. Residues in- and outside the sucrose-binding box determine hydrolase and transferase capabilities of GH32 enzymes. Modeling suggests that residues dispersed along the sequence identify a location for acceptor-substrate binding in the 3D structure of fructosyltransferases
Density structure of Earth's lowermost mantle from Stoneley mode splitting observations
Advances in our understanding of Earthās thermal evolution and the style of mantle convection rely on robust seismological constraints on lateral variations of density. The large-low-shear-wave velocity provinces (LLSVPs) atop the coreāmantle boundary beneath Africa and the Pacific are the largest structures in the lower mantle, and hence severely affect the convective flow. Here, we show that anomalous splitting of Stoneley modes, a unique class of free oscillations that are perturbed primarily by velocity and density variations at the coreāmantle boundary, is explained best when the overall density of the LLSVPs is lower than the surrounding mantle. The resolved density variations can be explained by the presence of post-perovskite, chemical heterogeneity or a combination of the two. Although we cannot rule out the presence of a ā¼100-km-thick denser-than-average basal structure, our results support the hypothesis that LLSVPs signify large-scale mantle upwelling in two antipodal regions of the mantle
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