Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings

We investigate the low-temperature properties of the one-dimensional spin-1 Heisenberg model with geometric fluctuations induced by aperiodic but deterministic coupling distributions, involving two parameters. We focus on two aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is to understand how these geometric fluctuations modify the physics of the (gapped) Haldane phase, which corresponds to the ground state of the uniform spin-1 chain. We make use of different adaptations of the strong-disorder renormalization-group (SDRG) scheme of Ma, Dasgupta and Hu, widely employed in the study of random spin chains, supplemented by quantum Monte Carlo and density-matrix renormalization-group numerical calculations, to study the nature of the ground state as the coupling modulation is increased. We find no phase transition for the Fibonacci chain, while we show that the 6-3 chain exhibits a phase transition to a gapless, aperiodicity-dominated phase similar to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is verified for random spin-1 chains, we show that different adaptations of the SDRG scheme may lead to different qualitative conclusions about the nature of the ground state in the presence of aperiodic coupling modulations.Comment: Accepted for publication in Physical Review

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

Alginate nanohydrogels as a biocompatible platform for the controlled release of a hydrophilic herbicide

The large-scale application of volatile and highly water-soluble pesticides to guarantee crop production can often have negative impacts on the environment. The main loss pathways are vapor drift, direct volatilization, or leaching of the active substances. Consequently, the pesticide can either accumulate and/or undergo physicochemical transformations in the soil. In this scenario, we synthesized alginate nanoparticles using an inverse miniemulsion template in sunflower oil and successfully used them to encapsulate a hydrophilic herbicide, i.e., dicamba. The formulation and process conditions were adjusted to obtain a unimodal size distribution of nanohydrogels of about 20 nm. The loading of the nanoparticles with dicamba did not affect the nanohydrogel size nor the particle stability. The release of dicamba from the nanohydrogels was also tested: the alginate nanoparticles promoted the sustained and prolonged release of dicamba over ten days, demonstrating the potential of our preparation method to be employed for field application. The encapsulation of hydrophilic compounds inside our alginate nanoparticles could enable a more efficient use of pesticides, minimizing losses and thus environmental spreading. The use of biocompatible materials (alginate, sunflower oil) also guarantees the absence of toxic additives in the formulation

Quantifying public transport reliability from a passenger perspective by using operational data

Urban public transport has been developed during the last years, trying to achieve its growth to provide better social, economic and environmental benefits. The reliability of public transport is a key determinant when considering the quality of the service. From a passengers’ perspective, service reliability it’s a key factor to attract and retain passengers in the long term. Since public transport is able to improve and ensure accessibility and livability of cities and since public transport might create a reduction of the negative impacts of increased car mobility, an increase in quality of public transport is necessary. Reliability has been defined from different aspects of bus services in many studies. Buffer time indicators have been the preferred ones to analyze reliability since they reflect passenger-focused attributes. However, passenger’s perception is lost from the time when it takes into account the total travel time. Using AVL system data (automatic vehicle location) and GoCard (automated fare collection) data, which provides the progress of each vehicle as well as passenger loadings, has enabled the analysis of service reliability from the passenger’s perception. All these data was analyzed to make an accurate assessment of the service reliability, comparing different measures. The selected measure was used to investigate the reliability performance for some of the Brisbane bus operations

El movimiento en la ejecución de recalces con inyección armada. Análisis de tres casos con movimientos previos

We can produce movements in a structure when we have an intervention in its foundation. This movement is higher if the building has a previous movement if it is cause for degree and pathologic causes. In this paper we study the results of the analysis in the application of a technique of intervention in the foundation of an existing building. The technique for underpinning is by reinforced grouting. We present three histories cases over buildings that have previously differential settlements of pathological origin for a prolonged period of time. Its underpinning was with this technique. The study is based on knowledge of the movements are obtained by controlling the application of underpinning of each of the three examples. We have unified the criteria used for analysis to compare the results. The main conclusion is that the 3 buildings used in the study respond similarly to the actions executed. Therefore, we consider this behaviour as the normal response of the soil in these cases.En la intervención en la cimentación de una edificación se pueden producir movimientos en la estructura sobre rasante, más en los casos en los que el edificio ya sufre un movimiento previo, normalmente de carácter patológico. En el presente trabajo se estudia el resultado del estudio realizado en la aplicación de una técnica concreta de intervención: las inyecciones armadas. Como muestra se presenta el análisis de tres casos en los que se ha intervenido en su cimentación mediante esta técnica, y con la premisa que los tres sufrían movimientos continuados por un largo periodo de tiempo previo. El análisis parte del seguimiento de los movimientos datados en el control realizado en la ejecución del recalce de cada edificio, unificando los criterios de análisis, para luego realizar la comparación entre los resultados. Como principal conclusión, se obtiene que los edificios responden de un modo similar ante la actuación ejecutada en ellos pudiendo por tanto considerarse tal comportamiento como la respuesta “normal” del sistema de tratamiento de terreno en estos casos