Mixtures of Hard Ellipsoids and Spheres: Stability of the Nematic Phase

The stability of liquid crystal phases in presence of small amount of non-mesogenic impurities is of general interest for a large spectrum of technological applications and in the theories of binary mixtures. Starting from the known phase diagram of the hard ellipsoids systems, we propose a simple model and method to explore the stability of the nematic phase in presence of small impurities represented by hard spheres. The study is performed in the isobaric ensemble with Monte Carlo simulations

Percolation and orientational ordering in systems of magnetic nanorods

Based on Monte Carlo (MC) computer simulations we study the structure formation of a system of magnetic nanorods. Our model particles consist of fused spheres with permanent magnetic dipole moments, as inspired by recent experiments. The resulting system behaves significantly different from a system of hard (non-magnetic) rods or magnetic rods with a single longitudinal dipole. In particular, we observe for the magnetic nanorods a significant decrease of the percolation threshold (as compared to non-magnetic rods) at low densities, and a stabilization of the high-density nematic phase. Moreover, the percolation threshold is tunable by an external magnetic field.Comment: 11 pages, 12 figure

Translational and rotational dynamics in suspensions of magnetic nanorods

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Using computer simulations we investigate the translational and rotational diffusion of dilute suspensions of magnetic nanorods with and without a (homogeneous) external magnetic field. The magnetic rods are represented as spherocylinders with a longitudinal point dipole at their center and length-to-breadth ratios L/D = 3 or L/D = 9. In the absence of a field, the rods tend to form compact clusters with antiparallel ordering and thus behave very differently to dipolar spheres (L/D = 0), which tend to form head-to-tail chains. Furthermore, for rod-like particles the external field tends to destabilize rather than to support cluster formation. We show that these differences in the aggregation behavior have profound consequences not only in static material properties such as the field-induced magnetization and the zero-frequency susceptibility, but also in the dynamics. In particular, for magnetic rods the translational diffusion constant parallel to the field is larger than the perpendicular one, in contrast to the behavior observed for magnetic spheres. Moreover, the rod-like character greatly affects the shape and the density dependence of the single-particle and collective dipole–dipole time correlation functions and their counterparts in the frequency domain

Performance assessment of an NH3/LINO3 bubble plate absorber applying a semi-empirical model and artificial neural networks

In this study, ammonia vapor absorption with NH3/LiNO3 was assessed using correlations derived from a semi-empirical model, and artificial neural networks (ANNs). The absorption process was studied in an H-type corrugated plate absorber working in bubble mode under the conditions of an absorption chiller machine driven by low-temperature heat sources. The semi-empirical model is based on discretized heat and mass balances, and heat and mass transfer correlations, proposed and developed from experimental data. The ANN model consists of five trained artificial neurons, six inputs (inlet flows and temperatures, solution pressure, and concentration), and three outputs (absorption mass flux, and solution heat and mass transfer coefficients). The semi-empirical model allows estimation of temperatures and concentration along the absorber, in addition to overall heat and mass transfer. Furthermore, the ANN design estimates overall heat and mass transfer without the need for internal details of the absorption phenomenon and thermophysical properties. Results show that the semi-empirical model predicts the absorption mass flux and heat flow with maximum errors of 15.8% and 12.5%, respectively. Maximum errors of the ANN model are 10.8% and 11.3% for the mass flux and thermal load, respectively

Effect of Prosopis flexuosa on understory species and its importance to pastoral management in woodlands of the Central Monte Desert

In the Monte Biogeographic Province, located in the arid region of Argentina, the presence of Prosopis flexuosa DC. produces spatial heterogeneity through edaphic modifications and microclimate changes. This results in vegetation patches differing in species composition and abundance. However, this interaction can be modified by the occurrence of gradients of biotic stress or disturbance intensity. In particular, grazing has been observed to enhance or reduce vegetation heterogeneity. Such complex of interactions could determine forage availability for cattle in one of the driest areas of the Monte Desert. We assessed the effect of Prosopis on understory species and analyzed whether the outcomes of this interaction differed with distance to watering points, as a proxy of grazing intensity, in the Northeast of Mendoza Province, Argentina. We used a two-way factorial design including the following factors: 1) microsite (under the cover of P. flexuosa trees and in intercanopy microsites) and 2) distance to watering points ("near the watering point", 500-700 m away, and "far from the watering point", 3-4 km away). Cover of each species, total cover, bare soil, and litter were recorded, and plant diversity, richness, and evenness were estimated with the modified Point Quadrat method. Results showed that P. flexuosa cover, distance from watering points, and the interaction between them determined species composition, abundance and spatial distribution of understory species, and were, consequently, a determining factor for forage availability. The presence of P. flexuosa enhances carrying capacity by supporting higher abundance of grasses under its canopy. Near watering points, high grazing intensity appears to disrupt the patches formed under P. flexuosa canopies, reducing the differences between microsites.In the Monte Biogeographic Province, located in the arid region of Argentina, the presence of Prosopis flexuosa DC. produces spatial heterogeneity through edaphic modifications and microclimate changes. This results in vegetation patches differing in species composition and abundance. However, this interaction can be modified by the occurrence of gradients of biotic stress or disturbance intensity. In particular, grazing has been observed to enhance or reduce vegetation heterogeneity. Such complex of interactions could determine forage availability for cattle in one of the driest areas of the Monte Desert. We assessed the effect of Prosopis on understory species and analyzed whether the outcomes of this interaction differed with distance to watering points, as a proxy of grazing intensity, in the Northeast of Mendoza Province, Argentina. We used a two-way factorial design including the following factors: 1) microsite (under the cover of P. flexuosa trees and in intercanopy microsites) and 2) distance to watering points ("near the watering point", 500-700 m away, and "far from the watering point", 3-4 km away). Cover of each species, total cover, bare soil, and litter were recorded, and plant diversity, richness, and evenness were estimated with the modified Point Quadrat method. Results showed that P. flexuosa cover, distance from watering points, and the interaction between them determined species composition, abundance and spatial distribution of understory species, and were, consequently, a determining factor for forage availability. The presence of P. flexuosa enhances carrying capacity by supporting higher abundance of grasses under its canopy. Near watering points, high grazing intensity appears to disrupt the patches formed under P. flexuosa canopies, reducing the differences between microsites

Records and distribution of the Afro Asian species Digitonthophagus gazella (Coleoptera: Scarabaeidae: Scarabaeinae) in Argentina

Se cita por primera vez el escarabajo coprófago Digitonthophagus gazella Fabricius (Coleoptera: Scarabaeidae) para Argentina, por lo que se amplía su área de distribución geográfica en Sudamérica. Esta especie de origen afro-asiático fue capturada mediante colecta manual en estiércol de ganado bovino y equino, con trampas de luz y trampas de caída cebadas con estiércol en seis provincias del centro y norte argentino entre los años 2006 y 2009.The occurrence of the dung beetle Digitonthophagus gazella Fabricius (Coleoptera: Scarabaeidae) is reported for the first time for Argentina. The record of this species represents an extension of its geographical range in South America. This species of Afro Asian origin was captured by manual collection in cattle dung, light traps, and dung baited pitfall traps in six provinces of Northern and Central Argentina between 2006 and 2009.Fil: Alvarez Bohle, María Celeste. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas, Naturales y Agrimensura. Laboratorio de Biología de los Artrópodos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Damborsky, Miryam Pieri. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas, Naturales y Agrimensura. Laboratorio de Biología de los Artrópodos; ArgentinaFil: Bar, María E.. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas, Naturales y Agrimensura. Laboratorio de Biología de los Artrópodos; ArgentinaFil: Ocampo, Federico Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentin

Modulation of glycolisis and the pentose phosphate pathway influences porcine oocyte in vitro maturation

Glycolytic and pentose phosphate pathway (PPP) activities were modulated in porcine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM) by the addition of inhibitors or stimulators of key enzymes of the pathways to elucidate their relative participation in oocyte maturation. The activities of glycolysis and PPP were evaluated by lactate production per COC and by the brilliant cresyl blue test, respectively. Glucose uptake per COC and the oocyte maturation rate were also evaluated. Lactate production, glucose uptake and the percentage of oocytes reaching metaphase II decreased in a dose-dependent manner in the presence of the pharmacological (NaF) or the physiological (ATP) inhibitors of glycolysis (p < 0.05). The addition of the physiological stimulator of glycolysis (AMP) caused no effect on lactate production, glucose uptake or the meiotic maturation rate. The pharmacological (6-AN) and the physiological (NADPH) inhibitors of PPP induced a dose-dependent decrease in the percentage of oocytes with high PPP activity and in the nuclear maturation rate (p < 0.05). The physiological stimulator of PPP (NADP) caused no effect on the percentage of oocytes with high PPP activity. The glycolytic and PPP activities of porcine COCs and maturational competence of oocytes seem to be closely related events. This study shows for the first time the regulatory effect of ATP and NADPH as physiological inhibitors of glycolysis and PPP in porcine COCs, respectively. Besides, these pathways seem to reach their maximum activities in porcine COCs during IVM because no further increases were achieved by the presence of AMP or NADP.Fil: Alvarez, Gabriel Martín. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario; ArgentinaFil: Ferretti, E. L.. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; ArgentinaFil: Gutnisky, Cynthia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; ArgentinaFil: Dalvit, Gabriel Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; ArgentinaFil: Cetica, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; Argentin

Active Disturbance Rejection Control for Robot Manipulator

Active Disturbance Rejection Control (ADRC) is a control methodology used in chemical processes, aircraft, motors, and other systems. This paper compares the results of an ADRC controller to a Proportional Integral Derivative controller (PID), applied to two degrees of freedom robots. A Linear Extended State Observer (LESO) is used to reconstruct the state variables and unknown parameters needed to control the position of each link. The ADRC can achieve the tracking position and estimate the velocity of each link. The results of the simulation program are shown