Combustion synthesized tetragonal ZrO2: Eu3+ nanophosphors: Structural and photoluminescence studies

Novel crystalline tetragonal ZrO2: Eu3+ phosphors were prepared by a facile and efficient low temperature solution combustion method at 400 +/- 10 degrees C using oxalyl dihydrazide (ODH) as fuel. The powder X-ray diffraction patterns and Rietveld confinement of as formed ZrO2: Eu3+ (1-11 mol%) confirmed the presence of body centered tetragonal phase. The crystallite size estimated from Scherrer's and W-H plots was found to be in the range of 7-17 nm. These results were in good agreement with transmission electron microscopy studies. The calculated microstrain in most of the planes indicated the presence of tensile stress along various planes of the particles. The observed space group (P4(2)/nmc) revealed the presence of cations in the 2b positions (0.75, 0.25, 0.25) and the anions in the 4d positions (0.25, 0.25, 0.45). The optical band gap energies estimated from Wood and Tauc's relation was found to be in the range 4.3-4.7 eV. Photoluminescence (PL) emission was recorded under 394 and 464 nm excitation shows an intense emission peak at 605 nm along with other emission peaks at 537, 592, 605 and 713 nm. These emission peaks were attributed to the transition of D-5(0) -> F-7(J) (J = 0, 1, 2, 3) of Eu3+ ions. The high ratio of Intensity of (D-5(0) -> F-7(2)) and (D-5(0) -> F-7(1)) infers that Eu3+ occupies sites with a low symmetry and without an inversion center. CIE color coordinates indicated the red regions which could meet the needs of illumination devices. (C) 2014 Elsevier B.V. All rights reserved.

Phase transformation of ZrO2:Tb3+ nanophosphor: Color tunable photoluminescence and photocatalytic activities

The current study involves synthesis of a series of Tb3+ doped ZrO2 nanophosphors by solution combustion method using oxalyl dihydrazide as fuel. The as-formed ZrO2:Tb3+ nanophosphors having different concentrations of Tb3+ (1-11 mol%) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Visible spectroscopic techniques and the materials were subjected to photoluminescence and photocatalytic dye decolorization studies. The PXRD analysis indicates the formation of tetragonal symmetry up to 5 mol% concentration of Tb3+. Further increase in Tb3+ concentration has lead to cubic phase formation and the same was confirmed by Rietveld refinement analysis. SEM images revealed that material was highly porous in nature comprising of large voids and cracks with irregular morphology. TEM and SAED images clearly confirm the formation of high quality tetragonal nanocrystals. The emissive properties of nanophosphors were found to be dependent on Tb3+ dopant concentration. The green emission of the material was turned to white emission with the increase of Tb3+ ion concentration. The photocatalytic activities of these nanophosphors were probed for the decolorization of Congo red under UV and Sunlight irradiation. All the photocatalysts showed enhanced activity under UV light compared to Sunlight. The photocatalyst with 7 mol% Tb3+ showed enhanced activity attributed to effective separation of charge carriers due to phase transformation from tetragonal to cubic. The influence of crystallite size and PL on charge carrier trapping-recombination dynamics was investigated. The study successfully demonstrates synthesis of tetragonal and cubic ZrO2:Tb3+ green nanophosphors with superior photoluminescence and photocatalytic activities. (C) 2014 Elsevier B.V. All rights reserved.

Structure, dynamics and thermodynamics of single-file water under confinement: effects of polarizability of water molecules

Various structural, dynamic and thermodynamic properties of water molecules confined in single-wall carbon nanotubes (CNTs) are investigated using both polarizable and non-polarizable water models. The inclusion of polarizability quantitatively affects the nature of hydrogen bonding, which governs many properties of confined water molecules. Polarizable water leads to tighter hydrogen bonding and makes the distance between neighboring water molecules shorter than that for non-polarizable water. Stronger hydrogen bonding also decreases the rotational entropy and makes the diffusion constant smaller than in TIP3P and TIP3PM water models. The reorientational dynamics of the water molecules is governed by a jump mechanism, the barrier for the jump being highest for the polarizable water model. Our results highlight the role of polarizability in governing the dynamics of confined water and demonstrate that the inclusion of polarizability is necessary to obtain agreement with the results of ab initio simulations for the distributions of waiting and jump times. The SPC/E water model is found to predict various water properties in close agreement with the results of polarizable water models with much lower computational costs.

Multispectral Bayesian reconstruction technique for real-time two color fluorescence microscopy

We have developed a real-time imaging method for two-color wide-field fluorescence microscopy using a combined approach that integrates multi-spectral imaging and Bayesian image reconstruction technique. To enable simultaneous observation of two dyes (primary and secondary), we exploit their spectral properties that allow parallel recording in both the channels. The key advantage of this technique is the use of a single wavelength of light to excite both the primary dye and the secondary dye. The primary and secondary dyes respectively give rise to fluorescence and bleed-through signal, which after normalization were merged to obtain two-color 3D images. To realize real-time imaging, we employed maximum likelihood (ML) and maximum a posteriori (MAP) techniques on a high-performance computing platform (GPU). The results show two-fold improvement in contrast while the signal-to-background ratio (SBR) is improved by a factor of 4. We report a speed boost of 52 and 350 for 2D and 3D images respectively. Using this system, we have studied the real-time protein aggregation in yeast cells and HeLa cells that exhibits dot-like protein distribution. The proposed technique has the ability to temporally resolve rapidly occurring biological events.

Effect of Channel Confinement on Mixed Convective Flow Past an Equilateral Triangular Cylinder

The present work investigates the mixed convective flow and heat transfer characteristics past a triangular cylinder placed symmetrically in a vertical channel. At a representative Reynolds number, Re = 100, simulations are carried out for the blockage ratios beta = 1/3; 1/4; and 1/6. Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range -1.0 <= Ri <= 1.0. At a blockage ratio of 1/3, suppression of vortex shedding is found at Ri = 1, whereas von Karman vortex street is seen both at beta = 1/4 and 1/6, respectively. This is the first time that such behavior of blockage ratio past a triangular cylinder in the present flow configuration is reported. Drag coefficient increases progressively with increasing Ri and a slightly higher value is noticed at beta = 1/3. For all b, heat transfer increases with increasing Ri. Flattening of Nu(avg)-Ri curve beyond Ri > 0: 75 is observed at beta = 1/3.

Boron-doped carbon nanoparticles: Size-independent color tunability from red to blue and bioimaging applications

Here, we report the hydrothermal synthesis of boron-doped CNPs (B-CNPs) with different size/atomic percentage of doping and size-independent color tunability from red to blue. The variation of size/atomic percentage of B is achieved by simply varying the reaction time, while the color tunability is obtained by diluting the solution. With dilution, the luminescence spectra are not only blue-shifted, the intensity increases as well. The huge blue-shift in the emission energy (similar to 1 eV) is believed to be due to the increase in the interparticle distance. The quantum yield with optimum dilution is found to increase with boron doping though it is very low as compared to CNPs and nitrogen-doped CNPs. Finally, we show that B-CNPs with a quantum yield of 0.5% can be used for bioimaging applications. (C) 2015 Elsevier Ltd. All rights reserved.

YIn0.9Mn0.1O3-ZnO nano-pigment exhibiting intense blue color with impressive solar reflectance

The current study reports on the synthesis and characterization of a new inorganic nano-pigment with an intense blue color and high solar radiation reflective properties (70%). The nano-pigment YIn0.9Mn0.1O3-ZnO was synthesized by a sol-gel combustion method and characterized with the aid of X-Ray diffraction, Raman spectroscopy, Magnetic susceptibility, Transmission electron microscopy, UV ndash;vis-NIR diffuse reflectance spectroscopy and CIE-1976 L*a*b* color measurements. The Rietveld refinement of the XRD patterns of the developed nano-pigment disclosed the existence of YIn0.9Mn0.1O3 and ZnO in a 1:1 ratio with hexagonal crystal structures. For comparison, YIn0.9Mn0.1O3 was also synthesized by the sol gel combustion route and its optical properties compared with that of YIn0.9Mn0.1O3-ZnO. It is interesting to note that the developed YIn0.9Mn0.1O3-ZnO nano-pigmeht exhibits superior blue hue (b* = -40.55) and solar reflectance (R* = 70%) values as compared to the YIn0.9Mn0.1O3 nano-pigment (b* = -22.28, R* = 50%). Most importantly, the potential utility of the nano-pigment as a ``Cool Pigment'' was demonstrated by coating onto roofing materials like aluminum roofing sheets. (C) 2015 Elsevier Ltd. All rights reserved.

Asymptotic behavior and interpretation of virtual states: The effects of confinement and of basis sets

A real-space high order finite difference method is used to analyze the effect of spherical domain size on the Hartree-Fock (and density functional theory) virtual eigenstates. We show the domain size dependence of both positive and negative virtual eigenvalues of the Hartree-Fock equations for small molecules. We demonstrate that positive states behave like a particle in spherical well and show how they approach zero. For the negative eigenstates, we show that large domains are needed to get the correct eigenvalues. We compare our results to those of Gaussian basis sets and draw some conclusions for real-space, basis-sets, and plane-waves calculations. (C) 2016 AIP Publishing LLC.

Evidence of quantum lateral confinement in side-gated resonant tunnelling diodes formed by patterned substrate regrowth

MBE regrowth on patterned np-GaAs wafers has been used to fabricate GaAs/AlGaAs double barrier resonant tunnel diodes with a side-gate in the plane of the quantum well. The physical diameters vary from 1 to 20 μm. For a nominally 1 μm diameter diode the peak current is reduced by more than 95% at a side-gate voltage of -2 V at 1.5 K, which we estimate corresponds to an active tunnel region diameter of 75 nm ± 10 nm. At high gate biases additional structure appears in the conductance data. Differential I-V measurements show a linear dependence of the spacing of subsidiary peaks on gate bias indicating lateral quantum confinement. © 1996 American Institute of Physics.

Evaluación preliminar de sesenta y tres lineas avanzadas de frijol común (Phaseolus vulgaris L.) de grano color negro en la Estación Experimental La Compañía, Carazo

El experimento fue establecido en la estación experimental “La Compañía”, San Marcos, Departamento de Carazo, Nicaragua, durante la época de postrera (Octubre-Diciembre) de 2003, con los objetivos de identificar genotipos de frijol común (Phaseolus vulgaris L) con mejores resultados en cuanto a rendimiento, evaluar las principales características fenológicas y determinar la incidencia y severidad de las principales enfermedades. Las líneas estudiadas provienen del vivero de adaptación centroamericano de grano negro (VIDAC-Negro-2003). Se utilizó un testigo, la variedad Guaymí; el diseño empleado fue el de ensayo preliminar, el cual consistió en un surco por línea de 3m de longitud con el testigo intercalado cada 9 surcos. Los análisis estadísticos realizados a los datos fueron: media, desviación estándar, coeficiente de variación, distribución de frecuencias y correlaciones Pearson. Entre los caracteres evaluados se midieron 13 variables, 3 sobre fenología, hábito de crecimiento, cinco sobre el rendimiento y sus componentes y enfermedades, entre las cuales se evaluaron mustia hilachosa y mancha de la hoja. Se observaron amplios rangos de comportamiento sobre fenología, rendimiento y sus componentes y enfermedades. Respecto a las variables fenológicas se observaron rangos de 33 a 40 dds en el número de días a floración, los días a madurez fisiológica oscilaron entre 63 y 72 dds y los días a cosecha entre 70 y 83 dds. Respecto al hábito de crecimiento las líneas fueron en su totalidad indeterminadas (IIa y IIb), en su mayoría IIb. En cuanto a los componentes del rendimiento el número de vainas por planta osciló entre 1 y 15.6, el número de granos por vaina entre 3.1 y 6.5, las plantas cosechadas entre 8 y 40 y el peso de 100 granos entre 12.31 y 30.25 g. Respecto al rendimiento relativo osciló entre 7.86205.88 %, encontrándose 15 líneas que superaron al testigo. La mayoría de los materiales presentaron severidad a mustia hilachosa con valores de 1 a 6, para mancha de la hoja la severidad osciló entre 2 y 5.

Caracterización y evaluación de siete genotipos de frijol común grano color rojo (Phaseolus vulgaris L.) en la Estación Experimental La Compañía, Carazo, 2004-2005

El presente ensayo se realizó en el centro experimental La Compañía, San Marcos Departamento de Carazo, Nicaragua en la época de primera (junio–agosto del 2004), con el fín de caracterizar y evaluar el comportamiento de 7 genotipos de frijol rojo, proporcionadas por el Programa Internacional de Viveros de Adaptación y Rendimiento, del Centro Internacional de Agricultura Tropical (CIAT) , en coordinación con el Instituto Nicaragüense de Tecnología Agropecuaria (INTA). Fue establecido un diseño de bloques completamente al azar con tres repeticiones; el tamaño de la muestra fue de 10 plantas para caracteres cuantitativos y para los cualitativos se basó en el aspecto de predominancia de caracteres. Se realizó el análisis de varianza y la separación de medias por Tukey al 95% de confianza para las variables del rendimiento y sus componentes; así como la media, desviación estándar y coeficiente de variación para caracteres relacionados al desarrollo y crecimiento. Fueron evaluados 18 caracteres cuantitativos y 15 cu alitativos. De acuerdo con los resultados la semilla se clasificó como pequeña, con forma ovoidea, alargada ovoidea y arriñonada recta en el lado del hilo, esta última con mayor frecuencia; el grano presentó color, rojo claro con testa brillante y rojo marrón oscuro con testa intermedio, predominan do el color rojo claro con testa brillante. Los análisis estadísticos indican que solo dos genotipos difirieron estadísticamente en cuanto al rendimiento, obteniendo el mayor valor el SRC 1-12-1-43 con 2203.9 kg ha -1 , no mostrando diferencias estadísticas las demás variables relacionadas. Todos los genotipos mostraron hábito de crecimiento arbustivo indeterminado (IIb). Respecto a las variables fenológicas se observaron rangos de 36 a 38 dds para el número de días a floración, los días a madurez fisiológica oscilaron entre 62 y 68 dds y los días a cosecha entre 66 y 72 dds, ubicándose de esta manera como materiales precoces. Todos los materiales presentaron daños de las enfermedades mustia hilachosa ( Thanatephorus cucumeris Frank) y mancha angular ( Isariopsis griseola Sacc) con niveles de severidad intermedia con excepción de los genotipos SRC 1-12-1-43 y MPN 103-25, que mostraron susceptibilidad a la mustia hilachosa; sin embargo estos alcanzaron los mayores rendimientos.

Evaluación de dieciseis genotipos de frijol comun de color negro (Phaseolus vulgaris, L.) en epoca de apante, Yasica Sur, San Ramón, Matagalpa

El presente ensayo se realizó en Yasica Sur, San Ramón, Matagalpa, en época de apante del 23 de Noviembre del 2002 al 24 de Febrero del 2003, con el objetivo de evaluar el comportamiento agronómico de 16 genotipos de fríjol común de grano color negro (Phaseolus vulgaris L.) a las condiciones de la localidad, a fin de encontrar alternativas de materiales genéticos para pequeños y medianos productores de frijol común. Para el estudio se utilizó un diseño experimental unífactorial en bloques completos al azar (B.C.A) con 4 repeticiones y 16 tratamientos. Los resultados de campo se procesaron mediante el programa sistema análisis estadístico (SAS V.8), la prueba de rango múltiple de Tukey al 0.01 por ciento de error para las variables evaluadas y correlación de Person para las mismas variables. Con base en los datos obtenidos se puede afirmarque, los componentes del rendimiento grano por vainas, vainas plantas y peso de 100 granos presentaron diferencias significativas; sin embargo, la variable del rendimiento de los genotipos no muestra diferencias significativas entre sí. El análisis de correlación múltiple efectuado a las variables fenológicas mostró diferencias significativas en días a flor, madurez fisiológica y días a cosechas. Los principales hábitos de crecimiento que se presentaron entre los materiales fueron indeterminados IIb y IIIb, a diferencia del genotipo B2059 con hábito indeterminado Ib. Los genotipos evaluados con relación a enfermedades fúngicas mostraron resistencia a Roya (Uromyces appendiculatus. Pers.Unger.), Mancha angular (Isariopsis griseolas Sacc) y Tizón bacteriano o bacteriosis común (Xanthomonas campestrispv.phaseoli). .