67 research outputs found
Removal of Cr(VI) from Waters by Multi-Walled Carbon Nanotubes: Optimization and Kinetic Investigations
The adsorption of chromium(VI) from aqueous solutions onto multi-walled carbon nanotubes (MWCNTs) has been investigated under various experimental conditions of initial metal concentration, agitation speed, aqueous pH, temperature and adsorbent dosage to assess the equilibrium and kinetic parameters. It was found that the kinetic data were fitted with the pseudo-first- and pseudo-second-order models, whereas the chromium(VI) adsorption data were fitted with the Langmuir and Freundlich equilibrium models to give the characteristic parameters of each model. According with the evaluation, both isotherm models are useful to represent the measured adsorption data. The adsorption of chromium(VI) is also dependent on the temperature, and the corresponding thermodynamic parameters including ΔH°, ΔG° and ΔS° were estimated from the experimental data, indicating the exothermic and non-spontaneous nature of the metal adsorption onto the MWCNTs. Chromium(VI) desorption was investigated by the use of aqueous hydrazine sulfate solutions
Revisión de algoritmos para modelización de equilibrios de distribución de metales en procesos de extracción líquido-líquido
10 pages, 5 figures, 2 tables, 1 appendix.[EN] This work focuses on general guidelines to be considered for application of least-squares
routines and artificial neural networks (ANN) in the estimation of metal distribution
equilibria in liquid-liquid extraction process. The goal of the procedure in the statistical
method is to find the values of the equilibrium constants (K¡) for the reactions involved in
the metal extraction which minimizes the differences between experimental distribution
coefficient (Dgxp) and theoretical distribution coefficients according to the mechanism
proposed (Dt^^gor)- Iri the first part of the article, results obtained with the most frequently
routine reported in the bibliography are compared with those obtained using the algorithms
previously discussed. In the second part, the main features of a single back-propagation
neural network for the same purpose are discussed, and the results obtained are compared
with those obtained with the classical methods.[ES] El trabajo presenta las líneas generales a considerar para la estimación del equilibrio de
distribución de metales en procesos de extracción líquido-líquido, según dos métodos:
algoritmo clásico de mínimos cuadrados y redes neuronales artificiales. El objetivo del
procedimiento, en el caso del método estadístico, es encontrar los valores de las constantes
de equilibrio (KJ para las reacciones involucradas en la extracción del metal, que
minimizan las diferencias entre el coeficiente de distribución experimental y el coeficiente
de distribución teórico, de acuerdo al mecanismo propuesto. En la primera parte del artículo
se comparan los resultados obtenidos a partir de los algoritmos usados más habitualmente
en la bibliografía, con los datos obtenidos mediante el algoritmo previamente descrito. En
la segunda parte, se presentan las características fundamentales para aplicar una red
neuronal sencilla con algoritmo hack-propagatioriy y los resultados obtenidos se comparan
con los de los métodos clásicos.Peer reviewe
Obtained and characterization of composite materials W-Cu for electrical contact
9 páginas, 5 figuras, 4 tablas.-- Nota técnica.[ES] En el Centro de Investigaciones Metalúrgicas (CIME), cubano, se fabrican por
pulvimetalurgia, calzos de material compuesto volframio-cobre, que se utilizan en los
contactos eléctricos de los paneles de control de las grúas pórtico que operan en el puerto
de Ciudad de La Habana. El material base que se utiliza contiene un 70 % en masa de polvo
de cobre electrolítico y polvo de volframio (30 %), que se obtiene por reducción del óxido
de volframio. Los polvos se someten a las etapas de mezclado, prensado y sinterización
obteniéndose un material compuesto con las fases metálicas formadas por partículas libres
de volframio ocluidas en una matriz de cobre, que no interaccionan entre sí. Este material
compuesto proporciona al calzo de ajuste las siguientes propiedades: alta temperatura de
fusión, alta electrotermoconductividad y resistencia a la corrosión, alta resistencia
mecánica y a la erosión eléctrica, baja soldabilidad y estabilidad durante su explotación. Sin
embargo, al no reaccionar las partículas de volframio con el cobre, el material compuesto
comenzará a fundir a la temperatura del cobre; por otro lado y, por la misma razón la
resistencia a la corrosión debe ser similar a la del cobre puro. Los calzos de ajuste se fijan a
los cuerpos de cobre de alta pureza mediante una soldadura de una aleación de plata, la cual
no afecta las buenas cualidades del cobre, como elasticidad, resistencia a la tracción,
conductividad térmica y eléctrica, así como resistencia a la corrosión.[EN] In the Cuban Metallurgical Research Center (CIME), are manufactured by powder
metallurgy, shims of adjustment of a W-Cu composite material, that are used in the
electrical contacts of the panels of control of the portico derricks that operate in the port
of Havana City. The base material used has a composition of 70 % in mass electrolytic
copper powder and wolfram powder of (30 %) that is obtained by reduction from the oxide
from wolfram. The powders are submitted to the stages of mixed, pressed and agglomeration
and is obtained a composite material with free particles of W occluded in a counterfoil of
Cu matrix, that do not interact and they provide the following properties: high melting
temperature, high electro and thermo conductivity and corrosion resistance, high
mechanical and electrical strengtheners, decrease weldability and stability during their
development. However, when not reacting the volframio particles with the copper, the
compound material will begin to fuse to the temperature of the copper, on the other hand
and for the same reason the resistance to the corrosion should be similar to that of the pure
copper. The shims of adjustment are fixed to the bodies of high purity copper welding with
a silver alloy, the one which provides the maximum qualities of the Cu, as elasticity,
breaking strength, thermal and electrical conductivities, as well corrosion resistance.Peer reviewe
Obtention and characterization of ferrous chloride FeCl_2•4H_2O from water pickling liquors
As a hazardous waste, water pickling liquors must be properly treated. An alternative consists of promoting the formation of ferrous salts from this residue due to their higher ferrous content. Since FeCl_2•4H_2O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl_2•4H_2O crystals were obtained from water pickling liquors. Their structural and morphological characteristics were investigated by X-ray diffraction, scanning electron microscopy as well as Mossbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals changed in colour from green to more yellowish. As such, the aged sample was also evaluated, and their structural characteristics were compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl_2•4H_2O structure, which is not modified with the aging of the sample
Low Latency Estimation of Motor Intentions to Assist Reaching Movements along Multiple Sessions in Chronic Stroke Patients: A Feasibility Study
A corrigendum on
Low Latency Estimation of Motor Intentions to Assist Reaching Movements along Multiple
Sessions in Chronic Stroke Patients: A Feasibility Study
by Ibáñez, J., Monge-Pereira, E., Molina-Rueda, F., Serrano, J. I., del Castillo, M. D., Cuesta-Gómez,
A., et al. (2017). Front. Neurosci. 11:126. doi: 10.3389/fnins.2017.00126. In the recently published article, there were incorrect and missing contents in the
Acknowledgments section
Population-based multicase-control study in common tumors in Spain (MCC-Spain): rationale and study design
Introduction: We present the protocol of a large population-based case-control study of 5 common tumors
in Spain (MCC-Spain) that evaluates environmental exposures and genetic factors.
Methods: Between 2008-2013, 10,183 persons aged 20-85 years were enrolled in 23 hospitals and primary
care centres in 12 Spanish provinces including 1,115 cases of a new diagnosis of prostate cancer,
1,750 of breast cancer, 2,171 of colorectal cancer, 492 of gastro-oesophageal cancer, 554 cases of chronic
lymphocytic leukaemia (CLL) and 4,101 population-based controls matched by frequency to cases by age,
sex and region of residence. Participation rates ranged from 57% (stomach cancer) to 87% (CLL cases) and
from 30% to 77% in controls. Participants completed a face-to-face computerized interview on sociodemographic
factors, environmental exposures, occupation, medication, lifestyle, and personal and family
medical history. In addition, participants completed a self-administered food-frequency questionnaire
and telephone interviews. Blood samples were collected from 76% of participants while saliva samples
were collected in CLL cases and participants refusing blood extractions. Clinical information was recorded
for cases and paraffin blocks and/or fresh tumor samples are available in most collaborating hospitals.
Genotyping was done through an exome array enriched with genetic markers in specific pathways. Multiple
analyses are planned to assess the association of environmental, personal and genetic risk factors
for each tumor and to identify pleiotropic effects.
Discussion: This study, conducted within the Spanish Consortium for Biomedical Research in Epidemiology
& Public Health (CIBERESP), is a unique initiative to evaluate etiological factors for common cancers
and will promote cancer research and prevention in Spain.The study was partially funded by the “Accion Transversal
del Cancer”, approved on the Spanish Ministry Council on the
11th October 2007, by the Instituto de Salud Carlos III-FEDER
(PI08/1770, PI08/0533, PI08/1359, PS09/00773, PS09/01286,
PS09/01903, PS09/02078, PS09/01662, PI11/01403, PI11/01889,
PI11/00226, PI11/01810, PI11/02213, PI12/00488, PI12/00265,
PI12/01270, PI12/00715, PI12/00150), by the Fundación Marqués
de Valdecilla (API 10/09), by the ICGC International Cancer Genome
Consortium CLL, by the Junta de Castilla y León (LE22A10-2), by
the Consejería de Salud of the Junta de Andalucía (PI-0571), by the
Conselleria de Sanitat of the Generalitat Valenciana (AP 061/10),
by the Recercaixa (2010ACUP 00310), by the Regional Government
of the Basque Country by European Commission grants FOOD-CT-
2006-036224-HIWATE, by the Spanish Association Against Cancer
(AECC) Scientific Foundation, by the The Catalan Government
DURSI grant 2009SGR1489
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