Exchange narrowing of NMR line shapes in randomly diluted magnetic systems

An analysis of 19F NMR linewidths in the randomly diluted magnetic system KMnxMg1-xF3 is presented. It is shown that good agreement with measured linewidths can be obtained if in the usual asymptotic spin-diffusion assumption for the spin autocorrelation function 〈Siα(τ)Siα(0)〉avατ-d(x)/2, d(x) is taken to be independent of x above the percolation concentration. Experimental results in the system KNixMg1-xF3 are also presented. These data exhibit striking differences with the behavior of isostructural KMnxMg1-xF3 whose origin is discussed

Effects of a Recurrent Selection Scheme, Applied to an Interspecific Hybrid \u3cem\u3ePennisetum Purpureum\u3c/em\u3e Schum. (Elephantgrass) \u3cem\u3ex Pennisetum Glaucum\u3c/em\u3e (L.) R. Br. Stuntz (Pearl Millet), on Several Seed Quality Parameters

Elephantgrass cultivars and introductions show practically no viable pure seeds and their uses in cultivated grasslands are exclusively dependent on vegetative propagation. Therefore, in large areas, sowing operation costs make unfeasible setting up new pastures. On the other hand, pearl millet is a high seed producer species though presenting some forage constraints (poor forage production, low regrowth potential after cutting or grazing and low field persistence). Recently, an hexaploid interespecific hybrid between the two species was developed (Schank & Diz, 1996), which is able to produce viable pure seeds, in variable amounts according to the genotype considered (Diz & Schank, 1995). This research aimed to check several seed quality parameters in two selected populations, derived from the original F2 interespecific hybrid population

Coevolution creates complex mosaics across large landscapes

The spatial distribution of populations can influence the evolutionary outcome of species interactions. The variation in direction and strength of selection across local communities creates geographic selection mosaics that, when combined with gene flow and genomic processes such as genome duplication or hybridization, can fuel ongoing coevolution. A fundamental problem to solve is how coevolution proceeds when many populations that vary in their ecological outcomes are connected across large landscapes. Here we use a lattice model to explore this problem. Our results show that the complex interrelationships among the elements of the geographic mosaic of coevolution can lead to the formation of clusters of populations with similar phenotypes that are larger than expected by local selection. Our results indicate that neither the spatial distribution of phenotypes nor the spatial differences in magnitude and direction of selection alone dictate coevolutionary dynamics: the geographic mosaic of coevolution affects formation of phenotypic clusters, which in turn affect the spatial and temporal dynamics of coevolution. Because the formation of large phenotypic clusters depends on gene flow, we predict that current habitat fragmentation will change the outcomes of geographic mosaics, coupling spatial patterns in selection and phenotypes1942217229We acknowledge the funding provided by the European Union Seventh Framework Programme (FP7/2007–2013; grant agreement 289384 [L.D.F.]), the São Paulo Research Foundation (grants 2009/54422-8 [P.R.G.], 2016/06054-3 [M.A.M.A.], and 2015/26989-4 [L.D.F.]), the National Council of Scientific and Technological Development (M.A.M.A. and P.L.-C.), and the National Science Foundation (DEB0839853 [J.N.T.]

Spectroscopy of high-lying resonances in 9 Be by the measurement of ( p , p ), ( p , d ), and ( p , α ) reactions with a radioactive 8 Li beam

We measured the 8 Li ( p , p ) 8 Li , 8 Li ( p , d ) 7 Li , and 8 Li ( p , α ) 5 He reactions at low energies using the thick target inverse kinematics method, with a polyethylene [ CH 2 ] n target and a radioactive 8 Li beam available at the Radioactive Ion Beams in Brazil facility of São Paulo. By measuring simultaneously several reaction channels ( p , p ) , ( p , d ) , and ( p , α ) , the still uncertain high-lying resonances of 9 Be , close to the proton threshold, can be studied and their parameters, such as energy, width, and spin parity can be more reliably determined. The experimental excitation functions of the reactions 8 Li ( p , p ) 8 Li , 8 Li ( p , d ) 7 Li , and 8 Li ( p , α ) 5 He were analyzed using the R -matrix theory, which allows us to infer the properties of the resonances. Multichannel R -matrix analysis provides evidence for a significant clustering in the ( p , d ) channel. The experimental data and the multichannel R -matrix analysis will be presented.Fundação de Amparo à Pesquisa do Estado de São Paulo. Brasil. (FAPESP) 2011/15904-7, 2013/22100-7 y 2016/21434-7VI Plan Propio de Investigación de la Universidad de Sevilla. España. (2017–2018

Silicon emissivity as a function of temperature

In this paper we present the temperature-dependent emissivity of a silicon sample, estimated from its cool-down curve in a constant low temperature environment ( ~ 82K). The emissivity value follow a linear dependency in the 120–260 K temperature range. This result is of great interest to the LIGO Voyager gravitational wave interferometer project since it would mean that no extra high thermal emissivity coating on the test masses would be required in order to cool them down to 123 K. The results presented here indicate that bulk silicon itself can have sufficient thermal emissivity in order to cool the 200 kg LIGO Voyager test masses only by radiation in a reasonable short amount of time (less than a week). However, it is still not clear if the natural emissivity of silicon will be sufficient to maintain the LIGO Voyager test masses at the desired temperature (123 K) while removing power absorbed by the test masses. With the present results, a black coating on the barrel surface of the test masses would be necessary if power in excess of 6 W is delivered. However, the agreement we found between the hemispherical emissivity obtained by a theory of semi-transparent Silicon and the obtained experimental results makes us believe that the LIGO Voyager test masses, because of their dimensions, will have effective emissivities around 0.7, which would be enough to remove about 8.6 W (7.5 W) for a shield at 60 K (80 K). This hypothesis may be confirmed in the near future with new measurements

Physical and Quality Seed Traits Observed in New Pigeon Pea (\u3cem\u3eCajanus Cajan\u3c/em\u3e) Hybrids

Pigeon pea seed production may be affected by factors such as % of pure seeds, mean seed weight, incidence of pests and diseases and environmental stresses. Harvested seeds from different cultivars may also vary in germination %, hardseededness and germination speed. Hardseededness (seed coat impermeability to water) commonly occurs in forage legume species (Hopkinson, 1993). There is considerable variation among different entries for seed characters but this is not considered within genetic materials. This research analysed harvested seeds of selected individuals of two segregating F2 pigeon pea populations for the above cited traits and assessed the range of variation for them resulting from the hybridisation process

Semiclassical mechanics of a non-integrable spin cluster

We study detailed classical-quantum correspondence for a cluster system of three spins with single-axis anisotropic exchange coupling. With autoregressive spectral estimation, we find oscillating terms in the quantum density of states caused by classical periodic orbits: in the slowly varying part of the density of states we see signs of nontrivial topology changes happening to the energy surface as the energy is varied. Also, we can explain the hierarchy of quantum energy levels near the ferromagnetic and antiferromagnetic states with EKB quantization to explain large structures and tunneling to explain small structures.Comment: 9 pages. For related works see "http://www.msc.cornell.edu/~clh/clh.html

Environmental Costs of Government-Sponsored Agrarian Settlements in Brazilian Amazonia

Brazil has presided over the most comprehensive agrarian reform frontier colonization program on Earth, in which ~1.2 million settlers have been translocated by successive governments since the 1970's, mostly into forested hinterlands of Brazilian Amazonia. These settlements encompass 5.3% of this ~5 million km2 region, but have contributed with 13.5% of all land conversion into agropastoral land uses. The Brazilian Federal Agrarian Agency (INCRA) has repeatedly claimed that deforestation in these areas largely predates the sanctioned arrival of new settlers. Here, we quantify rates of natural vegetation conversion across 1911 agrarian settlements allocated to 568 Amazonian counties and compare fire incidence and deforestation rates before and after the official occupation of settlements by migrant farmers. The timing and spatial distribution of deforestation and fires in our analysis provides irrefutable chronological and spatially explicit evidence of agropastoral conversion both inside and immediately outside agrarian settlements over the last decade. Deforestation rates are strongly related to local human population density and road access to regional markets. Agrarian settlements consistently accelerated rates of deforestation and fires, compared to neighboring areas outside settlements, but within the same counties. Relocated smallholders allocated to forest areas undoubtedly operate as pivotal agents of deforestation, and most of the forest clearance occurs in the aftermath of government-induced migration