Thermoelectric behavior of Ruddlesden-Popper series iridates

The goal of this work is studying the evolution of thermoelectric transport across the members of the Ruddlesden-Popper series iridates Srn+1IrnO3n+1, where a metal-insulator transition driven by bandwidth change occurs, from the strongly insulating Sr2IrO4 to the metallic non Fermi liquid behavior of SrIrO3. Sr2IrO4 (n=1), Sr3Ir2O7 (n=2) and SrIrO3 (n=inf.) polycrystals are synthesized at high pressure and characterized by structural, magnetic, electric and thermoelectric transport analyses. We find a complex thermoelectric phenomenology in the three compounds. Thermal diffusion of charge carriers accounts for the Seebeck behavior of Sr2IrO4, whereas additional drag mechanisms come into play in determining the Seebeck temperature dependence of Sr3Ir2O7 and SrIrO3. These findings reveal close relationship between magnetic, electronic and thermoelectric properties, strong coupling of charge carriers with phonons and spin fluctuations as well as relevance of multiband description in these compounds.Comment: main paper + supplementary informatio

Phantom Membrane Microfluidic Cross-Flow Filtration Device for the Direct Optical Detection of Water Pollutants

The diffusion of autonomous sensing platforms capable of a remote large-scale surveillance of environmental water basins is currently limited by the cost and complexity of standard analytical methods. In order to create a new generation of water analysis systems suitable for continuous monitoring of a large number of sites, novel technical solutions for fluid handling and detection are needed. Here we present a microfluidic device hosting a perfluorinated microporous membrane with refractive index similar to that of water, which enables the combination of filtration and label-free sensing of adsorbing substances, mainly pollutants, in environmental water samples. The cross-flow design of the microfluidic device avoids the clogging of the membrane due to particulate, whereas molecules with some hydrophobic moiety contained in the crossing flow are partially retained and their adhesion on the inner surface of the membrane yields an increase of light scattering intensity, which can be easily measured using a simple instrument based on Light Emitting Diode illumination. By cycling sample water and pure water as a reference, we demonstrate the detection of 0.5 microM of a model cationic surfactant and regeneration of the sensing surface. The optical response of the membrane sensor was characterized using a simple theoretical model that enables to quantify the concentration of target molecules from the amplitude and kinetics of the measured binding curves. The device was tested with real water samples containing large amount of environmental particles, without showing clogging of the membrane, and enabling nonspecific quantification of adsorbing substances in a few minutes.This project has received funding from the European Union’s Seventh Framework Programme (FP7) for Research, Technological Development and Demonstration through the NAPES project(grant agreement no. 604241). FBL acknowledges the Ramón y CajalProgramme (Ministerio de Economía y Competitividad), Spain. FBL personally acknowledges to Elkartek (KK-2015/00088) Grant from the Gobierno Vasco and funding support from Gobierno de España, Ministerio de Economia y Competitividad, with Grant No. BIO2016-80417-P and to Marian M. De Pancorbo for letting him to use her laboratory facilities at UPV/EHU. PSA was generously provided byAdhesive Research, Ireland. We thank Aurora Giavazzi for helping in the collection of river water samples

Properties of compositionally graded Ba(1-x)SrxTiO(3) thick films

Compositionally graded thick films (0.4 mm) have been fabricated using the airflow deposition method. Films were made of five layers with different composition Ba1-xSrxTiO(3) (BST, x=0, 0.1, 0.2, 0.3 and 0.4). The layers presented different thicknesses, ranging from 80 to 30 microns, but similar Vickers microhardness. The average particle size of deposited layers was below 500 nm and the density of asdeposited films was about 80% of theoretical. After sintering at 1350 ?C samples presented increaseddensity (>90%) and maintained a compositional gradient. When compared to single-composition BST ceramics, permittivity of graded films was much less dependent on temperature over a wide range, from -50 to 250 ?C. In addition, the films displayed polarisation offset when driven by an alternating field and heated above 50?C

Preparation and characterisation of the Ba(Zr,Ti)O(3) ceramics with relaxor properties

Ba(Zr(x)Ti(1-x))O(3) ceramics with various compositions x in the range (0, 0.5) have been prepared via solid state reaction. Optimum parameters for calcination and sintering have been found in order to obtain pure perovskite phase and high density ceramics. The dielectric data showed a transition from ferroelectric towards relaxor state and a shift of the Curie temperature towards lower values with increasing x. Using the modified Landau model for relaxors, the local order parameter has been calculated. Its temperature dependence shows the increasing of the degree of diffuseness of the phase transition with increasing Zr with a maximum for the composition x=0.35. The model also shows that in the relaxor state the local order parameter has non-zero values even at a few hundreds degrees above the temperature corresponding to the maximum of the dielectric constant. Further, the dielectric data obtained for x=0.35 under field cooling (FC) and zero-field cooling (ZFC) conditions shows a splitting characteristic to the relaxors and spin-glass systems

Phantom membrane microfluidic cross-flow filtration device for the direct optical detection of water pollutants

The diffusion of autonomous sensing platforms capable of a remote large-scale surveillance of environmental water basins is currently limited by the cost and complexity of standard analytical methods. In order to create a new generation of water analysis systems suitable for continuous monitoring of a large number of sites, novel technical solutions for fluid handling and detection are needed. Here we present a microfluidic device hosting a perfluorinated microporous membrane with refractive index similar to that of water, which enables the combination of filtration and label-free sensing of adsorbing substances, mainly pollutants, in environmental water samples. The cross-flow design of the microfluidic device avoids the clogging of the membrane due to particulate, whereas molecules with some hydrophobic moiety contained in the crossing flow are partially retained and their adhesion on the inner surface of the membrane yields an increase of light scattering intensity, which can be easily measured using a simple instrument based on Light Emitting Diode illumination. By cycling sample water and pure water as a reference, we demonstrate the detection of 0.5 \uce\ubcM of a model cationic surfactant and regeneration of the sensing surface. The optical response of the membrane sensor was characterized using a simple theoretical model that enables to quantify the concentration of target molecules from the amplitude and kinetics of the measured binding curves. The device was tested with real water samples containing large amount of environmental particles, without showing clogging of the membrane, and enabling nonspecific quantification of adsorbing substances in a few minutes

Hysteresis and tunability characteristics of Ba(Zr,Ti)O(3) ceramics described by first order reversal curves diagrams

The First Order Reversal Curves (FORC) diagrams are proposed for the characterization of the switching process and the tunability in Ba(ZrxTi1-x)O(3) ceramics with various compositions x in the range (0, 0.5), prepared via solid state reaction. The changes induced by the compositional-induced crossover ferroelectric-to-relaxor state are investigated by monitoring the changes of the FORC diagrams (the coercive and bias fields corresponding to the maximum, ratio of the reversible/irreversible contribution to the polarization, the diffuse character of the FORC distribution). The first derivative of the FORCs related to the tunability is a function of both the applied and reversal fields. The critical fields for the highest tunability were found to be composition-dependent

A bit stickier, a bit slower, a lot stiffer: Specific vs. nonspecific binding of gal4 to dna

Transcription factors regulate gene activity by binding specific regions of genomic DNA thanks to a subtle interplay of specific and nonspecific interactions that is challenging to quantify. Here, we exploit Reflective Phantom Interface (RPI), a label-free biosensor based on optical reflectivity, to investigate the binding of the N-terminal domain of Gal4, a well-known gene regulator, to double-stranded DNA fragments containing or not its consensus sequence. The analysis of RPI-binding curves provides interaction strength and kinetics and their dependence on temperature and ionic strength. We found that the binding of Gal4 to its cognate site is stronger, as expected, but also markedly slower. We performed a combined analysis of specific and nonspecific binding— equilibrium and kinetics—by means of a simple model based on nested potential wells and found that the free energy gap between specific and nonspecific binding is of the order of one kcal/mol only. We investigated the origin of such a small value by performing all-atom molecular dynamics simulations of Gal4–DNA interactions. We found a strong enthalpy–entropy compensation, by which the binding of Gal4 to its cognate sequence entails a DNA bending and a striking conformational freezing, which could be instrumental in the biological function of Gal4

Spontaneous superconducting islands and Hall voltage in clean superconductors

We study a clean superconductor in the Hall configuration, in the framework of a purely dissipative time-dependent Ginzburg--Landau theory. We find situations in which the order parameter differs significantly from zero in a set of islands that appear to form a periodic structure. When the pattern of islands becomes irregular, it moves in or against the direction of the current and a Hall voltage is found. Tiny differences in the initial state may reverse the sign of the Hall voltage. When the average Hall voltage vanishes, the local Hall voltage does not necessarily vanish. We examine the influence that several boundary conditions at the electrodes have on these effects.Comment: 6 pages, Includes additional cases and more detailed result