1,364 research outputs found
Wetland-based passive treatment systems for gold ore processing effluents containing residual cyanide, metals and nitrogen species
Gold extraction operations generate a variety of wastes requiring responsible disposal in compliance with current environmental regulations. During recent decades, increased emphasis has been placed on effluent control and treatment, in order to avoid the threat to the environment posed by toxic constituents. In many modern gold mining and ore processing operations, cyanide species are of most immediate concern. Given that natural degradation processes are known to reduce the toxicity of cyanide over time, trials have been made at laboratory and field scales into the feasibility of using wetland-based passive systems as low-cost and environmentally friendly methods for long-term treatment of leachates from closed gold mine tailing disposal facilities. Laboratory experiments on discrete aerobic and anaerobic treatment units supported the development of design parameters for the construction of a field-scale passive system at a gold mine site in northern Spain. An in situ pilot-scale wetland treatment system was designed, constructed and monitored over a nine-month period. Overall, the results suggest that compost-based constructed wetlands are capable of detoxifying cyanidation effluents, removing about 21.6% of dissolved cyanide and 98% of Cu, as well as nitrite and nitrate. Wetland-based passive systems can therefore be considered as a viable technology for removal of residual concentrations of cyanide from leachates emanating from closed gold mine tailing disposal facilities
BV analysis for covariant and non-covariant actions
The equivalence between the covariant and the non-covariant version of a
constrained system is shown to hold after quantization in the framework of the
field-antifield formalism. Our study covers the cases of Electromagnetism and
Yang-Mills fields and sheds light on some aspects of the Faddeev-Popov method,
for both the coratiant and non-covariant approaches, which had not been fully
clarified in the literature.Comment: 21 pages, preprint # UTTG-02-93, UB-ECM-PF 93/5. To appear in Phys.
Rev.
Spatial and temporal variability of CO2 emisions in soils under conventional tillage and no-till farming
Agricultural soils can act as a carbon sink depending on the soil management practices employed. As a result of this functional duality, soil management systems are present in international documents relating to climate change mitigation. Agricultural practices are responsible for 14% of total greenhouse gas emissions (GHG’s) (MMA, 2009)(1). Conservation agriculture (CA) is one of the most effective agricultural systems for reducing CO2 emissions, as it increases the sequestration of atmospheric carbon in the soil.
In order to assess the performance of CA in terms of CO2 emissions, a field trial was conducted comparing soil derived CO2 fluxes under No-till (NT) farming and under conventional tillage. Three pilot farms were selected in the cereal-growing area of southern Spain, located in Las Cabezas de San Juan (Seville), Carmona (Seville) and Cordoba. Each pilot farm comprises six experimental plots with an approximate area of five hectares; three of the six plots implement CA practices, while the other three use conventional tillage techniques. The subdivision of each tillage system into 3 plots allowed the simultaneous cropping of the three crops of the wheat-sunflower-legume rotation each year.
Results showed that carbon dioxide emissions were 31 to 91% higher in tilled soils than in untilled soils, and that there was a great seasonal variability of CO2 emissions, as weather conditions also differed considerably for the different sampling periods. In all cases, the CO2 fluxes emitted into the atmosphere were always higher when soil was subject to conventional tillage
Regularized Green's Function for the Inverse Square Potential
A Green's function approach is presented for the D-dimensional inverse square
potential in quantum mechanics. This approach is implemented by the
introduction of hyperspherical coordinates and the use of a real-space
regulator in the regularized version of the model. The application of
Sturm-Liouville theory yields a closed expression for the radial energy Green's
function. Finally, the equivalence with a recent path-integral treatment of the
same problem is explicitly shown.Comment: 10 pages. The final section was expande
NN Scattering: Chiral Predictions for Asymptotic Observables
We assume that the nuclear potential for distances larger than 2.5 fm is
given just by the exchanges of one and two pions and, for the latter, we adopt
a model based on chiral symmetry and subthreshold pion-nucleon amplitudes,
which contains no free parameters. The predictions produced by this model for
nucleon-nucleon observables are calculated and shown to agree well with both
experiment and those due to phenomenological potentials.Comment: 16 pages, 12 PS figures included, to appear in Physical Review
Statistical Mechanics of finite arrays of coupled bistable elements
We discuss the equilibrium of a single collective variable characterizing a
finite set of coupled, noisy, bistable systems as the noise strength, the size
and the coupling parameter are varied. We identify distinct regions in
parameter space. The results obtained in prior works in the asymptotic infinite
size limit are significantly different from the finite size results. A
procedure to construct approximate 1-dimensional Langevin equation is adopted.
This equation provides a useful tool to understand the collective behavior even
in the presence of an external driving force
Distributional extensions of Carollia castanea and Micronycteris minuta from Guatemala, Central America
Field expeditions in 2011 that inventoried the terrestrial vertebrate fauna of two wildlife protected areas in the tropical Caribbean of Guatemala have produced the first confirmed records of two bats for the country: the white-bellied big-eared bat, Micronycteris (Schizonycteris) minuta (Gervais 1856) and the Chesnut short-tailed bat Carollia castanea H. Allen, 1890, both of neotropical distribution and with their current northern limit at Lancetilla, Honduras. The record of M. minuta at Sierra de Caral, Guatemala extends the range of this species 137 km to the west, and the record of C. castanea at Cerro San Gil extends its range 147 km to the west
Interactive groups as didactic methodology in secondary education: Case study at a school in a Learning Community center
Objetivos: Analizar el trabajo en Grupos Interactivos (G.I.) en un centro de la
provincia de Sevilla constituido en Comunidad de Aprendizaje, tras su primer año de puesta
en práctica, desde la perspectiva de voluntarios, docentes y estudiantes. Metodología: La
investigación está basada en la metodología comunicativa, contrastando las vivencias de los
sujetos investigados mediante el diálogo, como base para la creación conjunta de nuevo
conocimiento. Para ello, los datos se han recogido a través la observación directa de las
prácticas realizadas y entrevistas con los docentes. Muestra: 16 estudiantes de 2º curso de la
etapa de Secundaria, el Equipo docente de 2º curso de Secundaria y 5 voluntarias de la
Facultad de Ciencias de la Educación, como apoyo y observadoras en los G.I.
Conclusiones: Mejoras en el rendimiento de los estudiantes, en las relaciones
personales y en la convivencia.Objetive: Analyzes Interactive Groups (G.I.) of a center in Seville that has
formed a Learning Community after a year, from the perspective of volunteers, teachers
and students. Methodology: The study is established in the communication methodology,
contrasting the experiences of the subjects investigated through dialogue, as a basis for the
joint creation of new knowledge. Data has been collected through direct observation of
practices and interviews with teachers. Sample: 16 students in the 2nd year of Secondary
School, team teaching 2nd year of Secondary and five volunteers from the Faculty of
Education, supporting and observers in the GI. Discussion: An improving student
achievement, the personal relationships and the coexistence
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