2,538 research outputs found
Influence of sodium fluorsilicate addition on manganese minerals and quartz floatability with sodium oleate.
Esse trabalho apresenta e discute resultados de ensaios de microflota??o e determina??o de potencial zeta dos minerais rodonita, rodocrosita e quartzo, na presen?a de fluorsilicato e oleato de s?dio em pH 9 e pH 11. Verificou-se que, para concentra??es de Na2SiF6 abaixo de 10mg/L, houve maior depress?o do quartzo em rela??o ? rodonita no valor de pH 9 e que a flotabilidade da rodocrosita foi pouco afetada para os valores de pH 9 e 11. Resultados de medidas de potencial zeta versus pH indicaram que o ponto isoel?trico da rodonita (pH=2,8) coincidiu com o reportado em literatura, enquanto que os valores determinados para quartzo (pH<2,0) e rodocrosita (pH=10,8) apresentaram pequena diverg?ncia. Para os tr?s minerais, a presen?a de oleato e/ou silicato de s?dio foi capaz de tornar mais negativa a magnitude do potencial zeta dos tr?s minerais em meio b?sico. Fundamentando-se nos resultados experimentais e, tamb?m, na especia??o dos reagentes estudados (oleato e fluorsilicato de s?dio), foi poss?vel fazer infer?ncias sobre mecanismos de adsor??o dos mesmos sobre os tr?s minerais de interesse.This work presents and discusses results from zeta potential measurements and flotation response of rhodonite, rhodochrosite and quartz, in the presence of sodium fluorsilicate and sodium oleate. At concentrations of Na2SiF6 smaller than 10mg/L, at pH 9, quartz is more intensively depressed than rhodonite, whereas the flotation response of rhodochrosite is slightly affected either at pH 9 or pH 11. Results from measurements of zeta potential versus pH indicate that IEP of rhodonite (pH=2.8) is similar to those reported in literature, whereas the value o IEP of quartz (pH<2.0) and rhodochrosite (pH=10,8) differ slightly from literature. Zeta potential of rodonite, quartz and rhodochrosite, in the presence of sodium fluorsilicate and/or sodium oleate, become more negative at basic medium. Based on the experimental results and collector (sodium oleate) plus depressant (sodium fluorsilicitate) speciation, some inference on the adsorption mechanisms of these reagents upon rhodonite, quartz and rhodochrosite is maintained
Geometries of Light and Shadows, from Piero della Francesca to James Turrell
This chapter addresses the problem of representing light and shadow in the artistic culture, from its uncertain beginnings, related to the studies on conical linear perspective in the Fifteenth Century, to the applications of light projection in the installations of contemporary art.
Here are examined in particular two works by two artists, representing two different conceptual approaches to the perception and symbolism of light and shadow. The first is the so-called Brera Madonna by Piero della Francesca, where the image projected from a luminous radiation is employed with a narrative purpose, supporting the apparently hidden script of the painting and according to the artist\u2019s own speculations about perspective as a means to clarify the phenomenal world.
The second is one of James Turrell\u2019s Dark Spaces installations, where quantum electrodynamics interpretation of light is taken into account: for Turrell, light is physical and thus can shape spaces where the visitors, or viewers, can \u201csee themselves seeing.\u201d In his body of work, perceptual deceptions are carefullyproduced by the interaction of the senses with his phenomenal staging of light and darkness, but a strong symbolic component is always present, often related to his own speculative interests.
In both cases, light and shadow, through their geometries, emphasize both phenomenal and spiritual contents of the work of art, intended as a device to expand the perception and the knowledge of the viewer
Linkage disequilibrium and population structure in wild and cultivated populations of rubber tree (Hevea brasiliensis).
Abstract: Among rubber tree species, which belong to the Hevea genus of the Euphorbiaceae family, Hevea brasiliensis (Willd. ex Adr.de Juss.) Muell. Arg. is the main commercial source of natural rubber production worldwide. Knowledge of the population structure and linkage disequilibrium (LD) of this species is essential for the efficient organization and exploitation of genetic resources. Here, we obtained single-nucleotide polymorphisms (SNPs) using a genotyping-by-sequencing (GBS) approach and then employed the SNPs for the following objectives: (i) to identify the positions of SNPs on a genetic map of a segregating mapping population, (ii) to evaluate the population structure of a germplasm collection, and (iii) to detect patterns of LD decay among chromosomes for future genetic association studies in rubber tree. A total of 626 genotypes, including both germplasm accessions (368) and individuals from a genetic mapping population (254), were genotyped. A total of 77,660 and 21,283 SNPs were detected by GBS in the germplasm and mapping populations, respectively. The mapping population, which was previously mapped, was constructed with 1,062 markers, among which only 576 SNPs came from GBS, reducing the average interval between two adjacent markers to 4.4 cM. SNPs from GBS genotyping were used for the analysis of genetic structure and LD estimation in the germplasm accessions. Two groups, which largely corresponded to the cultivated and wild populations, were detected using STRUCTURE and via principal coordinate analysis. LD analysis, also using the mapped SNPs, revealed that non-random associations varied along chromosomes, with regions of high LD interspersed with regions of low LD. Considering the length of the genetic map (4,693 cM) and the mean LD (0.49 for cultivated and 0.02 for wild populations), a large number of evenly spaced SNPs would be needed to perform genome-wide association studies in rubber tree, and the wilder the genotypes used, the more difficult the mapping saturation
High-resolution genetic map and QTL analysis of growth-related traits of Hevea brasiliensis cultivated under suboptimal temperature and humidity conditions
Rubber tree (Hevea brasiliensis) cultivation is the main source of natural rubber worldwide and has been extended to areas with suboptimal climates and lengthy drought periods; this transition affects growth and latex production. High-density genetic maps with reliable markers support precise mapping of quantitative trait loci (QTL), which can help reveal the complex genome of the species, provide tools to enhance molecular breeding, and shorten the breeding cycle. In this study, QTL mapping of the stem diameter, tree height, and number of whorls was performed for a full-sibling population derived from a GT1 and RRIM701 cross. A total of 225 simple sequence repeats (SSRs) and 186 single-nucleotide polymorphism (SNP) markers were used to construct a base map with 18 linkage groups and to anchor 671 SNPs from genotyping by sequencing (GBS) to produce a very dense linkage map with small intervals between loci. The final map was composed of 1,079 markers, spanned 3,779.7 cM with an average marker density of 3.5 cM, and showed collinearity between markers from previous studies. Significant variation in phenotypic characteristics was found over a 59-month evaluation period with a total of 38 QTLs being identified through a composite interval mapping method. Linkage group 4 showed the greatest number of QTLs (7), with phenotypic explained values varying from 7.67 to 14.07%. Additionally, we estimated segregation patterns, dominance, and additive effects for each QTL. A total of 53 significant effects for stem diameter were observed, and these effects were mostly related to additivity in the GT1 clone. Associating accurate genome assemblies and genetic maps represents a promising strategy for identifying the genetic basis of phenotypic traits in rubber trees. Then, further research can benefit from the QTLs identified herein, providing a better understanding of the key determinant genes associated with growth of Hevea brasiliensis under limiting water conditions
Precipitation of a layered double hydroxide comprising Mg2+ and Al3+ to remove sulphate ions from aqueous solutions.
This work presents an alternative route to remove sulphate ions from aqueous solutions, which is simple and fast,
and its efficiency of sulphate removal is slightly influenced by temperature (26 ?C?70 ?C) and pH (4?12). The
lowest residual sulphate concentration was about 60 mg L?1, which was observed in continuous experiments
using wastewater (26 ?C, pH 6 and initial sulphate concentration of 630 mg L?1). All these outcomes together
have not been observed in the current most used processes of sulphate precipitation, i.e. gypsum and ettringite
precipitation. Sulphate removal experiments were carried out in the batch and continuous systems using synthetic
solutions. In these conditions, about 75% of sulphate ions were removed for an initial ion concentration of
1800 mg L?1. A continuous test was also performed using a wastewater sample in addition to a synthetic solution.
The system reached steady-state conditions after four residence times (40 min) in the experiment with
synthetic solutions, whereas three residence times (30 min) were necessary for the tests with the wastewater
(initial sulphate concentration of 630 mg L?1). In the latter case, the sulphate removal efficiency was approximately
90%. The characterisation of the experimentally precipitated solids was carried out by DRX, FTIR, SEMEDS,
elemental analysis and thermal analysis. These techniques showed that, except in pH 4, the sulphate removal
process occurred due to the precipitation of a layered double hydroxide, comprising Mg2+ and Al3+ as its
metallic ions and nitrate (due to the salts used for precipitation) and sulphate anions occupying its interlayer
space
The Evolution of Social Orienting: Evidence from Chicks (Gallus gallus) and Human Newborns
Converging evidence from different species indicates that some newborn vertebrates, including humans, have visual predispositions to attend to the head region of animate creatures. It has been claimed that newborn preferences for faces are domain-relevant and similar in different species. One of the most common criticisms of the work supporting domain-relevant face biases in human newborns is that in most studies they already have several hours of visual experience when tested. This issue can be addressed by testing newly hatched face-na\uefve chicks (Gallus gallus) whose preferences can be assessed prior to any other visual experience with faces
First report of Rhodnius montenegrensis (Hemiptera: Reduviidae: Triatominae) infection by Trypanosoma rangeli
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
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