Symmetry and plate-like convection in fluids with temperature-dependent viscosity

We explore the instabilities developed in a fluid in which viscosity depends on temperature. In particular, we consider a dependency that models a very viscous (and thus rather rigid) lithosphere over a convecting mantle. To this end, we study a 2D convection problem in which viscosity depends on temperature by abruptly changing its value by a factor of 400 within a narrow temperature gap. We conduct a study which combines bifurcation analysis and time-dependent simulations. Solutions such as limit cycles are found that are fundamentally related to the presence of symmetry. Spontaneous plate-like behaviors that rapidly evolve towards a stagnant lid regime emerge sporadically through abrupt bursts during these cycles. The plate-like evolution alternates motions towards either the right or the left, thereby introducing temporary asymmetries on the convecting styles. Further time-dependent regimes with stagnant and plate-like lids are found and described.Comment: 19 pages, 8 figures. arXiv admin note: text overlap with arXiv:1302.073

Bifurcations and dynamics in convection with temperature-dependent viscosity in the presence of the O(2) symmetry

We focus the study of a convection problem in a 2D setup in the presence of the O(2) symmetry. The viscosity in the fluid depends on the temperature as it changes its value abruptly in an interval around a temperature of transition. The influence of the viscosity law on the morphology of the plumes is examined for several parameter settings, and a variety of shapes ranging from spout to mushroom shaped is found. We explore the impact of the symmetry on the time evolution of this type of fluid, and find solutions which are greatly influenced by its presence: at a large aspect ratio and high Rayleigh numbers, traveling waves, heteroclinic connections and chaotic regimes are found. These solutions, which are due to the symmetry presence, have not been previously described in the context of temperature dependent viscosities. However, similarities are found with solutions described in other contexts such as flame propagation problems or convection problems with constant viscosity also under the presence of the O(2) symmetry, thus confirming the determining role of the symmetry in the dynamics.Comment: 21 pages, 10 figure

Estimation of uncertainty in analytical balances. Comparison of mass measurements performed in analytical balances (LATU-1999)

The current paper provides the details of the main sources of uncertainty that occur when conventional mass determinations are performed in analytical balances. The data presented correspond to the calibration of 18 analytical balances that belong to LATU, together with the detailed quantification of each of the sources of uncertainty. The results of a comparison of conventional mass measurement performed in those balances with a Teflon sample are assessed, considering their uncertainty values. Conclusions are subsequently drawn on conventional mass measurement´s reproducibility in analytical balances in LATU

Atomic-scale characterization of single and double layers of InAs and InAlAs Stranski-Krastanov quantum dots

We report a detailed structural characterization of single and double layers of InAs and InAlAs quantum dots (QDs) and their wetting layers (WLs) by atomic force microscopy (AFM) and cross-sectional scanning tunneling microscopy (X-STM). The X-STM analysis with atomic resolution showed that the InAlAs WL consists of two distinct layers: a bottom part where all the Al atoms of the InAlAs alloy settled, and a top part containing exclusively In and Ga atoms. The QDs formed from the InAlAs layer contains no Al atoms at all and lie on top of the Al-rich WL. In the double layers of QDs, the InAlAs QDs were used as a seed to influence the nucleation of the InAs QDs grown on top. A gradual decrease in the density of the top InAs QDs was observed in the AFM images with increasing thickness of the GaAs spacer. The X-STM images showed that both QDs layers were completely intermixed for a 2-nm-thick spacer, while effective strain-induced stacking of both types of QDs was observed for a GaAs spacer thickness of 4 nm. However, both QD layers were completely decoupled for a GaAs spacer thickness of 8 nm and could thus be treated as individual layers

Factores que influyen en la calidad de las reinas de abejas (A. mellifera) criadas artificialmente

During the period 2003-2007 three experimental assays were carried out in order to evaluate the influence of some factors like number of cup cells introduced, the season and the substrate used, on the quality of queen bees produced in the queen bees breeding place of Provincial Foundation of Apiculture of Camagüey, located at the northeastern of the city. The quality of the queen bees was determined starting from the standards of weight, phenotypic characteristics and level of acceptation according to the strain used. In the case of the number of cells introduced, it was concluded that the best variant is using 30 cup cells/ breeding hive which gave the greatest weights taken after the starting of the oviposition (236 mg/animal). The period of the year influenced on the quality of queen bees, with significant differences at favor of March to May and after that in October, while the substrates used during the transfer, in the case honey, honey + royal jelly (50-50) and royal jelly, the last one showed better results in relation to the weight, phenotypic characteristics and acceptation of the animals. It was concluded that there is a remarkable influence of studied factors on the quality of queen bees obtained in the breeding place. It is recommended that the best found variants be applied at the level of foundation.Durante el período de 2003 a 2007 se realizaron tres ensayos experimentales para evaluar la influencia de algunos factores, como el número de copas celdas introducidas, la época del año y el sustrato utilizado, en la calidad de las reinas obtenidas en el criadero de reinas del Establecimiento Provincial de Apicultura de Camagüey, situado al noreste de esta ciudad. La calidad de las reinas se determinó a partir de los patrones de peso, características fenotípicas y nivel de aceptación, de acuerdo con la raza utilizada. En el caso del número de celdas introducidas, se obtuvo que la mejor variante es la de 30 copas celdas/colmena criadora, que logró los mayores pesos tomados luego de comenzada la ovoposición (236 mg/animal). El período del año influyó en la calidad de las reinas, con diferencias significativas a favor de los meses de marzo hasta mayo y posteriormente en octubre, mientras que de los sustratos utilizados en el trasvase, en este caso la miel, miel con jalea real (50-50) y jalea real, está última mostró resultados superiores en cuanto al peso de los animales, sus características fenotípicas y aceptación. Se concluye que existe una marcada influencia de los factores estudiados en la calidad de las reinas obtenidas en el criadero, y se recomienda que se apliquen a nivel del establecimiento las mejores variantes encontradas

Biological treatment of solid wastes from the tobacco industry for enzyme production

Aiming at the production of enzymes using solid wastes from the tobacco industry, the solid fermentation kinetics of Aspergillus niger and Aspergillus terreus using waste of dark tobacco and Virginia tobacco as substrate were characterized. The efficiency of the fermentation process was evaluated by determining the enzymatic activity of the three enzymes that constitute the cellulose enzymatic system (CMCase, PFase and Xylanase). The results obtained led to the establishment of the best initial conditions of fermentation and the selection of the most efficient microorganism for enzyme production. The best results were obtained with Aspergillus terreus for both tobacco residues. In the case of black tobacco, the best incubation temperature was 31 ºC for the enzymes CMCase and Xylanase and 36 ºC for the PFase and initial pH 5.5 for the three enzymes. For the Virginia tobacco, the best incubation temperature and initial pH are the same for the three enzymes, 36 ºC and 5.5 respectively. The biological activity of the fermented tobacco residues was evaluated being the highest rate of inhibition of microbial growth – 72% - obtained with the residue of Virginia tobacco treated with Aspergillus niger

Forage production and bromatological composition of Gliricidia sepium (Jacq) Kunth ex Walp

Forage production and bromatologic composition of Gliricidia sepium (Jacq) Kunth ex Walp were evaluated on cattle raising serpentine soils from the Livestock Center Noel Fernández in Camagüey, Cuba. Data were processed by the statistical package SPSS, and mean and standard deviation were determined. G. sepium foliage levels were significant (3,68 kg/a/cut for green matter and 1,33 kg/a/cut for dry matter) and raw protein levels were satisfactory (13,2 %)