Magnetocaloric effect in manganites: metamagnetic transitions for magnetic refrigeration

We present a study of the magnetocaloric effect in La5/8-yPryCa3/8MnO3 (y=0.3) and Pr0.5Ca0.09Sr0.41MnO3 manganites. The low temperature state of both ystems is the result of a competition between the antiferromagnetic and ferromagnetic phases. The samples display magnetocaloric effect evidenced in an adiabatic temperature change during a metamagnetic transition from an antiferromagnetic to a ferromagnetic phase . As additional features, La5/8-yPryCa3/8MnO3 exhibits phase separation characterized by the coexistence of antiferromagnetic and ferromagnetic phases and Pr0.5Ca0.09Sr0.41MnO3 displays inverse magnetocaloric effect in which temperature decreases while applying an external magnetic field. In both cases, a significant part of the magnetocaloric effect appears from non-reversible processes. As the traditional thermodynamic description of the effect usually deals with reversible transitions, we developed an alternative way to calculate the adiabatic temperature change in terms of the change of the relative ferromagnetic fraction induced by magnetic field. To evaluate our model, we performed direct measurement of the sample's adiabatic temperature change by means of a differential thermal analysis. An excellent agreement has been obtained between experimental and calculated data. These results show that metamagnetic transition in manganites play an important role in the study of magnetic refrigeration.Comment: Acepted to be published in Applied Physics Letter

Equilibrium tuned by a magnetic field in phase separated manganite

We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y = 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions. Time relaxation effects between 60 and 120K, and the obtained magnetic and resistive viscosities, unveils the dynamic nature of the phase separated state. An experimental procedure based on the derivative of the time relaxation after the application and removal of a magnetic field enables the determination of the otherwise unreachable equilibrium state of the phase separated system. With this procedure the equilibrium phase fraction for zero field as a function of temperature is obtained. The presented results allow a correlation between the distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte

A propensity criterion for networking in an array of coupled chaotic systems

We examine the mutual synchronization of a one dimensional chain of chaotic identical objects in the presence of a stimulus applied to the first site. We first describe the characteristics of the local elements, and then the process whereby a global nontrivial behaviour emerges. A propensity criterion for networking is introduced, consisting in the coexistence within the attractor of a localized chaotic region, which displays high sensitivity to external stimuli,and an island of stability, which provides a reliable coupling signal to the neighbors in the chain. Based on this criterion we compare homoclinic chaos, recently explored in lasers and conjectured to be typical of a single neuron, with Lorenz chaos.Comment: 4 pages, 3 figure

Note: "Lock-in accelerometry" to follow sink dynamics in shaken granular matter

Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental Physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. While the penetration of intruders in two dimensional (2D) laboratory granular beds can be followed using video recording, it is useless in three dimensional (3D) beds of non-transparent materials such as common sand. Here we propose a method to quantify the sink dynamics of an intruder into laterally shaken granular beds based on the temporal correlations between the signals from a reference accelerometer fixed to the shaken granular bed, and a probe accelerometer deployed inside the intruder. Due to its analogy with the working principle of a lock in amplifier, we call this technique Lock in accelerometry (LIA). During Earthquakes, some soils can lose their ability to sustain shear and deform, causing subsidence and sometimes substantial building damage due to deformation or tumblin

Amplificación del efecto destructivo de los desprendimientos rocosos por deslizamiento sobre suelos volcánicos (Tenerife y Madeira)

This work provides geomorphological and geotechnical observations on the amplification of the destructive behaviour of rock falls developed in rocky slopes with a soil rich in organic matter, which are both exposed to high rainfall regimes. The determinant factor of this process would be related to the low geotechnical quality that the organic matter gives to the soil, which experience a sudden change in its fabric related to the dynamic load, similar to those observed in the quick clays in the fjords of Norway

Sustitución del pienso B de ceba por subproductos y derivados de la industria azucarera en la alimentación de cerdos en crecimiento

Twenty growing market swines (Yorkshire-Landrace x Duroc) with a 25,1 kg liveweight and equal number per sex were sam- pled. Swines were arranged according to a randomized block design to study the zootechnical and economical effect of a partial substitution of fattening feedstuff “B” by a mixture of final molasses, torul, yeast, and GARANVER (feed for animals fixed with sugar cane industry wastes, urea and final molasses). Results did not show a significant effect regarding the main traits analyzed, such as: final weight (56,00; 53,75 kg), daily weight gain (550; 534 g/animal), dry matter conversion rate (3,69; 3,84 kg/kg weight gain); and raw protein conversion rate (0,51; 0,54 kg/kg weight gain) for fattening feedstuff “B” and sugar cane industry byprod- ucts and derivatives mixture, respectively. An economical evaluation of costs per ton of liveweight gain, taking into account feed expenses, showed that the experimental feedstuff was cheaper. The results proved the availability of including up to a 60% of sugar cane industry byproducts and derivatives mixture in solid diets due to its suitable zootechnical and economical effects.Se utilizaron 20 cerdos comerciales (Yorkshire-Landrace x Duroc) en crecimiento, con peso vivo de 25,1 kg en igual propor- ción de sexos. Se organizaron en un diseño de bloques al azar, para estudiar el efecto zootécnico y económico de la sustitución parcial del pienso B de ceba por una mezcla de miel final, levadura torula y garanver (alimento para animales compuesto por una mezcla de cachaza, bagacillo, residuales líquidos -ácidos, alcalinos y azucarados-, urea y miel final). Los resultados no mostraron efecto significativo en los principales rasgos estudiados como son: peso final (56,00; 53,75 kg), ganancia diaria de peso (550; 534 g/animal), conversión de materia seca (3,69; 3,84 kg/kg de incremento de peso), y conversión de proteína bruta (0,51; 0,54 kg/kg de incremento de peso), para el pienso B y el que incluye los derivados y subproductos de la industria azucarera, respectivamente. La valoración económica demostró que el pienso experimental resultó más barato con relación al costo de la tonelada de incre- mento de peso vivo, según los gastos de alimentación. Estos resultados demostraron la factibilidad de incluir en dietas sólidas ni- veles del 60 % de alimentos de la industria azucarera con efectos zootécnico y económico aceptables