Potentiometric determination of the gibbs energies of formation of SrZrO3 and BaZrO3

The Gibbs free energies of formation of strontium and barium zirconates have been determined in the temperature range 960 to 1210 K using electrochemical cells incorporating the respective alkaline-earth fluoride single crystals as solid electrolytes. Pure strontium and barium monoxides were used in the reference electrodes. During measurements on barium zirconate, the oxygen partial pressure in the gas phase over the electrodes was maintained at a low value of 18.7 Pa to minimize the solubility of barium peroxide in the monoxide phase. Strontium zirconate was found to undergo a phase transition from orthorhombic perovskite to) with space group Cmcm; D-2h(17) to tetragonal perovskite (t) having the space group 14/mcm; D-4h(18) at 1123 (+/- 10) K. Barium zirconate does not appear to undergo a phase transition in the temperature range of measurement. It has the cubic perovskite (c) structure. The standard free energies of formation of the zirconates from their component binary oxides AO (A = Sr, Ba) with rock salt (rs) and ZrO2 with monoclinic (m) structures can be expressed by the following relations:SrO (rs) + ZrO2 (m) --> SrZrO3 (o) Delta G degrees = -74,880 - 14.2T (+/-200) J mol(-1) SrO (rs) + ZrO2 (m) --> SrZrO3 (t) Delta G degrees = -73,645 - 15.3T (+/-200) J mol(-1) BaO (rs) + ZrO2 (m) --> BaZrO4 (c) Delta G degrees = -127,760 - 1.79T (+/-250) J mol(-1) The results of this study are in reasonable agreement with calorimetric measurements reported in the literature. Systematic trends in the stability of alkaline-earth zirconates having the stoichiometry AZrO(3) are discussed.

Gibbs energies of formation of intermetallic phases in the systems Pt Mg, Pt Ca and Pt Ba and some applications

The standard Gibbs energies of formation of platinum-rich intermetallic compounds in the systems Pt-Mg, Pt-Ca, and Pt-Ba have been measured in the temperature range of 950 to 1200 K using solid-state galvanic cells based on MgF2, CaF2, and BaF2 as solid electrolytes. The results are summarized by the following equations: ΔG° (MgPt7) = −256,100 + 16.5T (±2000) J/mol ΔG° (MgPt3) = −217,400 + 10.7T (±2000) J/mol ΔG° (CaPt5) = −297,500 + 13.0T (±5000) J/mol ΔG° (Ca2Pt7) = −551,800 + 22.3T (±5000) J/mol ΔG° (CaPt2) = −245,400 + 9.3T (±5000) J/mol ΔG° (BaPt5) = −238,700 + 8.1T (±4000) J/mol ΔG° (BaPt2) = −197,300 + 4.0T (±4000) J/mol where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group ILA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr2O3 in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and “FeO.”

Phase relations in the system SrO-Y2O3-CuO-O2 and CaO-Y2O3-CuO-O2 at 1173 K

Phase relations in the systems SrO-Y2O3-CuO-O2 and CaO-Y2O3-CuO-O2 at 1173 K were established by equilibrating different compositions in flowing oxygen gas at a pressure of 1.01 × 105 Pa. The quenched samples were examined by optical microscopy, X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX), and electron spin resonance (ESR). In the system SrO-Y2O3-CuO-O2, except for the limited substitution of Y3+ for Sr2+ ions in the ternary oxide Sr14Cu24O41, no new quaternary phase was found to be stable. The compositions corresponding to the solid solution Sr14−xYxCu24O41 and the compound SrCuO2+δ lie above the plane containing SrO, Y2O3, and CuO,displaced towards the oxygen apex. However, in the system CaO-Y203-CuO-O2 at 1173 K, all the condensed phases lie on the plane containing CaO, Y203, and CuO, and a new quaternary oxide YCa2Cu306.s is present. The quaternary phase has a composition that lies at the center of the nonstoichiometric field of the analogous phase YBa2Cu307_~ in the BaO-Y203-CuO-O2 system. The compound YCa2Cu306.s has the tetragonal structure and does not become superconducting at low temperature. Surprisingly, phase relations in the three systems CaO-Y203-CuO-O2, SrO-Y203-CuO-O2, and BaO-Y203-CuO-O2 are found to be quite different.

Fabrication of Transparent BaNaB9O15 Glass-Microcrystal Composites

Transparent glasses in the BaO-Na2O-B2O3 (BNBO) system were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by x-ray powder diffraction (XRD) and differential thermal analysis (DTA), respectively. Cyclic heat treatment of the as-quenched glasses yielded transparent glass-microcrystal composites. The volume fraction of the crystallites and their sizes could be easily controlled by this process. Heat-treated samples were highly transparent owing to the minimum mismatch between the refractive indices of the crystallites and the glass residual matrix. BNBO samples that were heat treated at 540A degrees C for 4 h for 10 cycles were found to be 60% to 70% transparent in the 500 nm to 900 nm wavelength range.

Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity.

Kramers Escape Rate in Nonlinear Diffusive Media

In this paper, we study nonlinear Kramers problem by investigating overdamped systems ruled by the one-dimensional nonlinear Fokker-Planck equation. We obtain an analytic expression for the Kramers escape rate under quasistationary conditions by employing

Efectos del hombre grande (Quassia amara), tabaco (Nicotiana tabacum) y neem (Azadirachta indica) en el control de garrapatas del ganado bovino en la Finca Puerto Rico, municipio de Matiguás, departamento de Matagalpa

Con la finalidad de buscar alternativas con productos de origen natural para el control de garrapatas en bovinos, se realizó un experimento en la finca "Puerto Rico" localizada en las coordenadas 12" 48'18" latitud norte y 85" 23' 39" longitud oeste, en la comarca las Limas a llKms del municipio de Matiguás, departamento de Matagalpa, Nicaragua, donde se usaron extractos de las plantas: hombre grande (Quassia amara), tabaco (Nicotiana tabacum) y neem (Azadirachta indica), al 0.15% para evaluar su efecto acaricida. Se utilizó un diseño completamente aleatorio (DCA), para lo cual se tomaron 60 novillos que se dividieron en 4 grupos conformados por 15 animales cada uno, a los que se les aplicó los tratamientos con las plantas antes mencionadas y un grupo que no recibió ningún tratamiento y que fue considerado como testigo, la aplicación de los tratamientos se hizo por medio de baños por aspersión con mochila de fumigar a los 1 y 21 días. Se realizó recuento de garrapatas antes de realizar el primer baño a los animales y a los 7, 21 y 30 días post tratamiento. El análisis estadístico se hizo utilizando el programa SAS (Stadistic Analisis System), con el cual se realizó análisis de varianza (ANDEVA). Cuando se determinó que existían diferencias significativas en las fechas de recuento, áreas de recuento y tratamientos aplicados, se procedió a realizar separaciones de medias con la prueba de Duncan. De los 3 productos utilizados en el experimento, por el comportamiento demostrado entre cada periodo aplicado, el extracto acuoso de tabaco demostró ser el más efectivo, siguiéndolo en orden de importancia el extracto acuoso de hombre grande y por último el extracto acuoso de aceite de neem al 0.15%.

Dermatofitosis en caninos procedentes de dos barrios de Managua, atendidos en la clínica Emergencia Veterinaria, agosto – septiembre 2014

El presente estudio de caso, se realizó para la valoración de la presencia de la dermatofitosis en especies caninas, siendo las especies más comunes Microsporum y Trichopyton. El estudio se realizó en la Clínica “Emergencias Veterinarias” ubicada en el casco urbano de Managua” para obtener un diagnóstico definitivo se realizó el diagnóstico clínico tomando en cuenta el historial de los pacientes, sintomatología y lesiones: pústula, pápula, eritema, descamación, costra, alopecia, pelo quebradizo, foliculítis así como factores predisponente: factores ambientales, humedad, ph, edad, raza, sexo, individuo, realizando el diagnóstico por laboratorio en tres pacientes. Las muestras fueron remitidas al laboratorio veterinario con los siguientes estudios clínicos ; Raspado de piel por KoH al 10% Y 20%, determinaron la presencia de estructuras micóticas asociadas a hifas y levaduras en el caso N°1, estructuras asociadas a artrosporas e hifas en el caso N°2, y estructuras asociadas a hifas y levaduras en el caso N°3, además se realizó un control de crecimiento de contaminantes en agar Sabouraud con glucosa al 2%, donde se observó por caracterización macroscópica el crecimiento de contaminantes en mayor abundancia en el caso N°3. Una vez obtenidos los resultados se procesaron las muestras en Dermatofitos Test Medium (Urano Test Dermatofitos) donde se observó que el caso N°1 y caso N°3 dieron negativo a DTM, el caso N°2 resulto ser positivo y se prosiguió a la caracterización microscópica del agente por tinción de contraste, donde se identificó al Microsporum gypseum como el agente causal de la lesión y como factores predisponentes se verificaron los ambientales y la edad del paciente, la aplicación de tratamiento fue de forma tópico y sistémico a través de fungicida o fungistático , baño con clorhexidina y miconazol 1 vez a la semana por 6 semanas , ketoconazol en tableta a una dosis de 10 mg /kg/día por 30 días , dándola en la comida para conseguir un ph gástrico acido, regulador del sistema inmune (caseína) 1 tableta al día por 30 días, vitamina ADɜE intramuscular . Palabras claves: Canino; Dermatofitos; Microsporum; Trichophyton; Raspado de piel; Cultivo micotico.

Orthotropy rescaling and implications for fracture in composites

For most practically important plane elasticity problems of orthotropic materials, stresses depend on elastic constants through two nondimensional combinations. A spatial rescaling has been found to reduce the orthotropic problems to equivalent problems in materials with cubic symmetry. The latter, under favorable conditions, may be approximated by isotropic materials. Consequently, solutions for orthotropic materials can be constructed approximately from isotropic material solutions or rigorously from cubic ones. The concept is developed to gain insight into the interplay between anisotropy and finite geometry. The inherent simplicity of the solutions allows a variety of technical problems to be addressed efficiently. Included are stress concentration related cracking, effective contraction of orthotropic material specimens, crack deflection onto easy fracture planes, and surface flaw induced delamination.

竹纤维增强树脂复合材料及其微观形貌

Unconventional spin texture of a topologically nontrivial semimetal Sb(110)

9 p.

Chemical and mineralogical characterization of micro-inclusions in diamonds

Secondary-ion mass spectrometry (SIMS), electron probe analysis (EPMA), analytical scanning electron microscopy (SEM) and infrared (IR) spectroscopy were used to determine the chemical composition and the mineralogy of sub-micrometer inclusions in cubic diamonds and in overgrowths (coats) on octahedral diamonds from Zaire, Botswana, and some unknown localities.

The inclusions are sub-micrometer in size. The typical diameter encountered during transmission electron microscope (TEM) examination was 0.1-0.5 µm. The micro-inclusions are sub-rounded and their shape is crystallographically controlled by the diamond. Normally they are not associated with cracks or dislocations and appear to be well isolated within the diamond matrix. The number density of inclusions is highly variable on any scale and may reach 10^(11) inclusions/cm^3 in the most densely populated zones. The total concentration of metal oxides in the diamonds varies between 20 and 1270 ppm (by weight).

SIMS analysis yields the average composition of about 100 inclusions contained in the sputtered volume. Comparison of analyses of different volumes of an individual diamond show roughly uniform composition (typically ±10% relative). The variation among the average compositions of different diamonds is somewhat greater (typically ±30%). Nevertheless, all diamonds exhibit similar characteristics, being rich in water, carbonate, SiO_2, and K_2O, and depleted in MgO. The composition of micro-inclusions in most diamonds vary within the following ranges: SiO_2, 30-53%; K_2O, 12-30%; CaO, 8-19%; FeO, 6-11%; Al_2O_3, 3-6%; MgO, 2-6%; TiO_2, 2-4%; Na_2O, 1-5%; P_2O_5, 1-4%; and Cl, 1-3%. In addition, BaO, 1-4%; SrO, 0.7-1.5%; La_2O_3, 0.1-0.3%; Ce_2O_3, 0.3-0.5%; smaller amounts of other rare-earth elements (REE), as well as Mn, Th, and U were also detected by instrumental neutron activation analysis (INAA). Mg/(Fe+Mg), 0.40-0.62 is low compared with other mantle derived phases; K/ AI ratios of 2-7 are very high, and the chondrite-normalized Ce/Eu ratios of 10-21 are also high, indicating extremely fractionated REE patterns.

SEM analyses indicate that individual inclusions within a single diamond are roughly of similar composition. The average composition of individual inclusions as measured with the SEM is similar to that measured by SIMS. Compositional variations revealed by the SEM are larger than those detected by SIMS and indicate a small variability in the composition of individual inclusions. No compositions of individual inclusions were determined that might correspond to mono-mineralic inclusions.

IR spectra of inclusion- bearing zones exhibit characteristic absorption due to: (1) pure diamonds, (2) nitrogen and hydrogen in the diamond matrix; and (3) mineral phases in the micro-inclusions. Nitrogen concentrations of 500-1100 ppm, typical of the micro-inclusion-bearing zones, are higher than the average nitrogen content of diamonds. Only type IaA centers were detected by IR. A yellow coloration may indicate small concentration of type IB centers.

The absorption due to the micro-inclusions in all diamonds produces similar spectra and indicates the presence of hydrated sheet silicates (most likely, Fe-rich clay minerals), carbonates (most likely calcite), and apatite. Small quantities of molecular CO_2 are also present in most diamonds. Water is probably associated with the silicates but the possibility of its presence as a fluid phase cannot be excluded. Characteristic lines of olivine, pyroxene and garnet were not detected and these phases cannot be significant components of the inclusions. Preliminary quantification of the IR data suggests that water and carbonate account for, on average, 20-40 wt% of the micro-inclusions.

The composition and mineralogy of the micro-inclusions are completely different from those of the more common, larger inclusions of the peridotitic or eclogitic assemblages. Their bulk composition resembles that of potassic magmas, such as kimberlites and lamproites, but is enriched in H_2O, CO_3, K_2O, and incompatible elements, and depleted in MgO.

It is suggested that the composition of the micro-inclusions represents a volatile-rich fluid or a melt trapped by the diamond during its growth. The high content of K, Na, P, and incompatible elements suggests that the trapped material found in the micro-inclusions may represent an effective metasomatizing agent. It may also be possible that fluids of similar composition are responsible for the extreme enrichment of incompatible elements documented in garnet and pyroxene inclusions in diamonds.

The origin of the fluid trapped in the micro-inclusions is still uncertain. It may have been formed by incipient melting of a highly metasomatized mantle rocks. More likely, it is the result of fractional crystallization of a potassic parental magma at depth. In either case, the micro-inclusions document the presence of highly potassic fluids or melts at depths corresponding to the diamond stability field in the upper mantle. The phases presently identified in the inclusions are believed to be the result of closed system reactions at lower pressures.

Infrared luminescence properties of bismuth-doped barium silicate glasses

Infrared (IR) luminescence covering 1.1 to similar to 1.6 mu m wavelength region was observed from bismuth-doped barium silicate glasses, excited by a laser diode at 808 nm wavelength region, at room temperature. The peak of the IR luminescence appears at 1325 nm. A full width half-maximum (FWHM) and the lifetime of the fluorescence is more than 200 nm and 400 mu s, respectively. The fluorescence intensity increases with Al2O3 content, but decreases with BaO content. We suggest that the IR luminescence should be ascribed to the low valence state of bismuth Bi2+ or Bi+, and Al3+ ions play an indirect dispersing role for the infrared luminescent centers.

Plan de marketing de una PYME: Eder Rodamientos

El objetivo del presente documento es realizar un Plan de Marketing para una PYME. La empresa analizada es Rodamientos Eder SA que se dedica a la producción de rodamientos para otras empresas industriales. Fabrican rodamientos para muchos sectores diferentes, pero me voy a circunscribir en la línea de rodamientos para mamparas de baño.

Plasma loop and strapping field dynamics: reproducing solar eruptions in the laboratory

Coronal mass ejections (CMEs) are dramatic eruptions of large, plasma structures from the Sun. These eruptions are important because they can harm astronauts, damage electrical infrastructure, and cause auroras. A mysterious feature of these eruptions is that plasma-filled solar flux tubes first evolve slowly, but then suddenly erupt. One model, torus instability, predicts an explosive-like transition from slow expansion to fast acceleration, if the spatial decay of the ambient magnetic field exceeds a threshold.

We create arched, plasma filled, magnetic flux ropes similar to CMEs. Small, independently-powered auxiliary coils placed inside the vacuum chamber produce magnetic fields above the decay threshold that are strong enough to act on the plasma. When the strapping field is not too strong and not too weak, expansion force build up while the flux rope is in the strapping field region. When the flux rope moves to a critical height, the plasma accelerates quickly, corresponding to the observed slow-rise to fast-acceleration of most solar eruptions. This behavior is in agreement with the predictions of torus instability.

Historically, eruptions have been separated into gradual CMEs and impulsive CMEs, depending on the acceleration profile. Recent numerical studies question this separation. One study varies the strapping field profile to produce gradual eruptions and impulsive eruptions, while another study varies the temporal profile of the voltage applied to the flux tube footpoints to produce the two eruption types. Our experiment reproduced these different eruptions by changing the strapping field magnitude, and the temporal profile of the current trace. This suggests that the same physics underlies both types of CME and that the separation between impulsive and gradual classes of eruption is artificial.