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Search Results: 1 - 10 of 200056 matches for " E. Hernández Laguna "
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Cambio temporal en la huella ecológica de la región de Murcia y su uso como indicador de desertificación
E. Hernández Laguna,F. López Bermúdez
Papeles de Geografía , 2004,
Abstract: Numerosos estudios han alertado sobre el proceso de desertifi cación en la Región de Murcia, en el Sureste de la Península Ibérica. Su clima semiárido junto con la defi ciente gestión de sus fértiles suelos, son responsables de la degradación de sus recursos naturales. La Huella Ecológica de una población es una medida de la presión sobre la tierra en términos de hectáreas de tierra per capita necesarias para el sostenimiento de dicha población dada la tecnología usada. Junto con la biocapacidad de la tierra, HE mide la sostenibilidad del territorio. En este trabajo, se mide la HE de la Región de Murcia para dos a os consecutivos, 1995 y 2001. Un claro paralelismo es observado entre la variación de este indicador y la desertifi cación.
Solid Particle Erosion Behaviour of TiN Coating on AISI 4140 Steel  [PDF]
J. R. Laguna-Camacho, J. E. Escalante-Martínez, R. Cruz-Vicencio, J. V. Méndez-Méndez, I. Arzate-Vázquez, I. Hernández-Romero, M. Vite-Torres
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2014, DOI: 10.4236/jsemat.2014.41001
Abstract:

In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45

Estudio comparativo de un indicador de desertificación para zonas agrícolas semi-áridas, Cuenca del Guadalentín, Sureste de Espa a
E. Hernández Laguna,F. López Bermúdez,A. Romero Díaz,F. Belmonte Serrato
Papeles de Geografía , 2000,
Abstract: El trabajo calcula un indicador de desertificación para zonas agrícolas, determinado por la ratio entre producción agrícola total y el consumo de fertilizantes inorgánicos (N, P y K), para la agricultura espa ola, para la Región de Murcia y dentro de ésta para el Valle del río Guadalentín. Los resultados muestran como este indicador es válido para determinar procesos de desertificación provocados por prácticas agrícolas insostenibles e inducir estudios más profundos de degradación del suelo.
Decoloración de alginato de sodio extraído de las algas pardas marinas del género Sargassum con el uso de peróxido de hidrógeno
Regalado, Erik L.;Laguna, Abilio;Torres, Mabel;Sabatier, Juan D.;Hernández, Margarita;Ferrer, Anselmo E.;Nogueiras, Clara;
Química Nova , 2007, DOI: 10.1590/S0100-40422007000100002
Abstract: hydrogen peroxide bleaching of sodium alginate from seaweeds oh the sargassum genus was studied. the influence of h2o2 concentration (percentage of h2o2 on a dry weight alginate basis, w/w) and naoh/h2o2 ratio (% naoh/% h2o2, both referred to a dry weight alginate basis, w/w) on the molecular weight, color removal and content of fe3+ ions of bleached alginate samples was investigated by uv and ir spectroscopies, colorimetric determination of fe3+ ions and vapor pressure osmometry. higher yield, purity and molecular weight of alginate were obtained using 3% (or less) of hydrogen peroxide and a naoh/h2o2 ratio of 1.2 for bleaching.
La huella ecológica del cultivo del olivo en Espa a y su aplicabilidad como indicador de agricultura sostenible
E. Hernández Laguna,F. López Bermúdez,F. Alonso Sarría,C. Conesa García
Papeles de Geografía , 2004,
Abstract: El cultivo del olivo ocupa vastas superficies en las tierras mediterráneas constituyendo parte esencial de su paisaje. Es el principal cultivo arbóreo mediterráneo y de Espa a, con grandes repercusiones ecológicas, socio-económicas y culturales. Con el objetivo de determinar la sostenibilidad ecológica del cultivo, y el riesgo de desertificación, se aplica el cálculo del indicador de huella ecológica (HE), se lo compara con la biocapacidad (BP) del olivar en el campo espa ol y se determina si existe déficit ecológico (DE). Además de estos indicadores, se calculan para dos tecnologías de cultivo: el laboreo con suelo desnudo y el no laboreo, hallándose que la huella ecológica discrimina bien ambas técnicas de cultivo.
Instrumentación y dise?o de una fuente de alto voltaje para fabricar rejillas de fibra óptica mediante la técnica de arco eléctrico
Hernández-García, J.C.;Estudillo-Ayala, J.M.;Rojas-Laguna, R.;Mata Chávez, R.I.;Martínez-Ríos, A.;Gutiérrez, J.G.;Trejo-Durán, M.;Vargas-Rodríguez, E.;Andrade-Lucio, J.A.;Alvarado-Méndez, E.;
Revista mexicana de física , 2010,
Abstract: in this work we present the instrumentation and construction of a source of high voltage, the source is controlled by the communication port input/output of a card of acquisition of data, we used programming language labview?, is a tool for the design of acquisition systems, instrumentation and control. the source was utilize for to fabricate long period grating of optical fibers by means of inducing an electric arc with the point by point procedure, with this source is have low cost in the fabrication, this is 80 % down of technique with others devices. the instrument has a panel of virtual control to modify the time of duration of the arch, the voltage and the electric current applied to the optic fiber by means of two electrodes. the gratings were fabricated with smf-28. these gratings can be used with optical fiber lasers as optical filters and in the implementation of optical sensors.
Cyanopolyynes as Organic Molecular Wires in the Interstellar Medium  [PDF]
Raul G. E. Morales, Carlos Hernández
International Journal of Astronomy and Astrophysics (IJAA) , 2012, DOI: 10.4236/ijaa.2012.24030
Abstract: Cyanopolyynes (H[C≡C]n-CN or HC2n+1N, where n = 1, 2, 3, …, n) are commonly observed in the interstellar medium (ISM) as well as in the envelopes of carbon-rich stars. These linear molecular structures can be well described with a one-dimensional conduction model, which considers the scattering processes of electrons through the charge transfer conduction bridge of the H[C≡C]n-molecular wire containing the CN group as an electron-acceptor terminal unit. Therefore, our results using this model enable a better understanding of the longest molecules observed in interstellar space and provide new insight into why these particular cyanopolyynes reach a maximum length, such as is observed from astronomical experimental spectral data and cosmological chemical models. Dipole moments and geometrical parameters of these cyanopolyynes were obtained from ab initio molecular orbital calculations using the restricted Hartree-Fock approach and 6-311G* basis set, in order to obtain the inner resistance as a new parameter of chemical reaction feasibility for this molecular series. Using this last molecular parameter, we have been able to analyze the possibility of identifying long molecular species that can be found under local thermodynamic equilibrium in some ISM such us HC25H, HC27H, and HC29N, which have not been observed at present.
Expected Radial Column Density of Methylcyanopolyynes in CW Leonis (IRC+10216)  [PDF]
Raul G. E. Morales, Carlos Hernández
International Journal of Astronomy and Astrophysics (IJAA) , 2015, DOI: 10.4236/ijaa.2015.53018
Abstract: Methylcyanopolyynes (CH3-[C≡C]n-CN) are a particular kind of linear molecular wires, where the first three oligomers have been detected in the interstellar medium, particularly in CW Leonis (IRC + 10216), as well as in the envelopes of carbon-rich stars in a similar way to the unsubstituted cyanopolyynes. Based on the projected natural distribution in cold clouds under LTE, we have determined the radial column density of new expected methylcyanopolyynes to be present in CW Leonis (IRC + 10216). By following, we have made use of the inner molecular resistances of the internal charge transfer process presenting in these oligomeric species in order to determine the reactivity trends between them. Therefore, geometrical parameters and dipole moments determinations for these methylcyanopolyynes involving the n = 1 to 14 molecular species were obtained from Ab initio molecular orbital calculations by means of a GAUSSIAN Program, using a restricted Hartree-Fock approach and 6-311G* basis set. Our results present a similar behavior observed in cyanopolyynes, where this series reaches a saturation level at the 14th oligomer with a maximum dipole moment of 8.21 ± 0.01 (Debyes). Thus, this molecular wire model permits us to comprehend how these methylcyanopolyynes reach a maximum length in such chemical environment, in agreement to the astronomical observations and cosmological chemical models. The following CH3C9N and CH3C11N oligomers in CW Leonis should be expected near to 3.52 × 1010 [cm2] and 1.82 × 1010 [cm2], respectively.
Influencia de la inestabilidad modulacional en la generación de un espectro continuo en fibras ópticas con pulsos de nanosegundos
Gutiérrez, J.G.;Vargas-Trevi?o, M.;Romero-Salazar, C.;Hernández Flores, O. A.;Kuzin, E.A.;Ibarra-Escamilla, B.;Grajales-Couti?o, R.;Rojas-Laguna, R.;Estudillo-Ayala, J.M.;Vargas-Rodríguez, E.;Gutiérrez-Zainos, F.;
Revista mexicana de física , 2009,
Abstract: in this work the influence of modulational instability on the supercontinuum generation in standard optical fibers in the anomalous dispersión regime is reported. a 30 ns pump pulse with wavelength equal to 1549 nm from a directly modulated dfb laser was used. results show that the spectrum broadening is due to modulational instability and self frequency shift. the spectrum broadening was depending of fiber length and pump power.
Estudio experimental sobre la evolución de los efectos no lineales que generan un espectro supercontinuo en fibras de cristal fotónico usando pulsos con duración de ns
Hernández-García, J. C.;Estudillo-Ayala, J.M.;Rojas-Laguna, R;Pottiez, O;Mata-Chavez, R.I.;Delgado-Negrete, J.M.;Vargas-Rodríguez, E;Andrade-Lucio, J.A.;
Revista mexicana de física , 2011,
Abstract: this paper presents the experimental study on the spectral evolution of a pump pulse spread into two different types of microstructures with solid core in photonic crystal fiber (pcf). we use as pumping source a laser q-switched nd: yag operating in the regime of nanosecond pulses (6 ns) with a central wavelength of 1064 nm, a repetition rate of 20 hz and an energy of ~ 180 mj. supercontinuum spectrum evolution is presented for a range of variation of input power between 0.05 mw to 1.86 mw at the input of the pcf. we analyze the pulse broadening explains the nonlinear phenomena involved in the process generation of new frequencies that appear in the input pulse. an important aspect is based on the development of an optical scheme which is capable of providing adequate control over the coupling of light at the input of the pcf and prevents the damage to the fibers used in this work. as it is known, the pulses generated by the laser q-switch nd:yag are very intense and can damage the pcf used, for this reason, the development of optical scheme was essential to obtain the spectra of supercontinuum generated in each of the pcf (spectra that have with a spectral width of ~ 705 nm and ~ 1100 nm). finally, this paper describes the possible potential applications that can be implemented with the type of spectrum generated in each fiber.
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