Magnetic and dielectric properties of multiferroic Eu0.5Ba0.25Sr0.25TiO3 ceramics

Dielectric and magnetic properties of Eu0.5Ba0.25Sr0.25TiO3 are investigated between 10 K and 300 K in the frequency range from 10 Hz to 100 THz. A peak in permittivity revealed near 130 K and observed ferroelectric hysteresis loops prove the ferroelectric order below thistemperature. The peak in permittivity is given mainly by softening of the lowest frequency polar phonon (soft mode revealed in THz and IR spectra) that demonstrates displacive character of the phase transition. Room-temperature X-ray diffraction analysis reveals cubic structure, but the IR reflectivity spectra give evidence of a lower crystal structure, presumably tetragonal I4/mcm with tilted oxygen octahedra as it has been observed in EuTiO3. The magnetic measurements show that the antiferromagnetic order occurs below 1.8 K. Eu0.5Ba0.25Sr0.25TiO3 has three times lower coercive field than Eu0.5Ba0.5TiO3, therefore we propose this system for measurements of electric dipole moment of electron.Comment: Phase Transitions, in pres

Drone-Aided Detection of Weeds: Transfer Learning for Embedded Image Processing

In this article, we address the problem of hogweed detection using a drone equipped with red, green, blue (RGB) and multispectral cameras. We study two approaches: 1) offline detection running on the orthophoto of the area scanned within the mission and 2) real-time scanning from the frame stream directly on the edge device performing the flight mission. We show that by fusing the information from an additional multispectral camera installed on the drone, there is an opportunity to boost the detection quality, which can then be preserved even with a single RGB camera setup by the introduction of an additional convolution neural network trained with transfer learning to produce the fake multispectral images directly from the RGB stream. We show that this approach helps either eliminate the multispectral hardware from the drone or, if only the RGB camera is at hand, boost the segmentation performance by the cost of slight increase in computational budget. To support this claim, we have performed an extensive study of network performance in simulations of both the real-time and offline modes, where we achieve at least 1.1% increase in terms of the mean intersection over union metric when evaluated on the RGB stream from the camera and 1.4% when evaluated on orthophoto data. Our results show that the proper optimization guarantees a complete elimination of the multispectral camera from the flight mission by adding a preprocessing stage to the segmentation network without the loss of quality

Conductivity and dielectric response of carbon based composites in a broad frequency range

Trabajo presentado a la: "19th International Conference on Composite Materials" celebrada en Montreal (Canadá) del 28 de julio al 2 de agosto de 2013.-- et al.Peer Reviewe

A tissue-mimicking phantom with flexible optical properties for studying photoacoustic response of nanoparticles

Photoacoustic imaging (PAI) is a rapidly growing imaging modality, which combines high contrast of optical absorption with deep penetration depth of ultrasound. When combined with endogenous contrast agents based on light-absorbing nanoparticles (NPs), PAI can visualize various biological processes and tissues. Here, we describe a simple experimental setup based on a tissue-mimicking phantom with flexible optical properties for studying photoacoustic (PA) response of NPs. Our approach is based on a polyacrylamide gel phantom with independently variable optical absorption and scattering. The phantom allows one to model and study PA response of contrast agents with diverse spatial distributions and concentrations. To demonstrate high potential of the developed experimental setup, we prepared a phantom with optical properties matching human prostate tissue and performed a PAI of laser-synthesized titanium nitride (TiN) NPs, distributed in a disk-shaped area, located 10 mm under the phantom surface. We believe that our approach will contribute the successful development of clinical PAI with NPs-based contrast agents

Dielectric properties of carbon nanofibre/alumina composites

Carbon nanofibre (CNF)/Al2O3 composites with concentrations between 1 and 9 vol.% of CNF were prepared by the traditional ceramic processing route followed by spark plasma sintering. The dielectric properties of these composites have been studied in a broad frequency range from mHz to the infrared range. Unlike conventional composites, the percolation threshold in this system is more complex depending on the particles topology. Positive and negative variations by several orders of magnitude in the low frequency AC conductivity have been detected for concentrations near the threshold at ∼2 vol.% of CNF. To explain these results, a modified percolation model has been proposed which takes into consideration the effect of the concentration of the filler on the microstructure of the composite. © 2013 Elsevier Ltd. All rights reserved.The authors acknowledge funding through Projects No. 2010CZ0004, MAT2009-14534, MAT2011-29174-C02-01, the Czech Science Foundation Project P204/12/0232 and Czech Ministry of Education (Project MP0902). L. Fernandez-Garcia acknowledges JAE Predoctoral program for PhD grant.Peer Reviewe

Microstructure and dielectric behaviour of carbon nanofibers-alumina nanocomposites

Resumen del póster presentado al 8th International Workshop on Interfaces: "At the boundary between natural and synthetic materials", celebrado en Santiago de Compostela (España) del 26 de junio al 1 de julio de 2011.Carbon nanofibers-Alumina (CNF-Al2O3) nanocomposites are interesting materials because it is possible to design materials with a very wide range of the ac conductivity values. Depending on the amount of CNF the ac conductiviy of these materials ranges bemeen 10(-4) and 10(-14) s/cm and, therefore, they may flnd applications as dissipative materials. In this study, CNF-Al2O3 nanocomposites, in which CNF content was varied between 1 and 4% volume, were synthesized following processing routes: in one case the CNF were ball-milled before mixing with alumina and in the ofher case raw CUNF were used. Depending on thr CNF procesing different microstructures were obtained. In the composites with ball-milled CNF tke scanning electron microscopy images show a homogeneous dispersion of the CNF while in be composites with raw CNF the nanofibers ane highly agglomerated. These differences Ln the microstructure confer the composites dfferent behaviours of ac conductivity: with raw CNF it is not possible to get a fine-tuning of the ac conductivity and the composites present large steps in ac conductivity values in samples with different amount of CNF. On the other hand, the ball-milled CNF composites show reproducible and well-controlled ac conductivity values in a small range, between 8.10(-7) y 9.10(-8) s/cm, at frequencies below 1Hz. The present work reports on the importance of the processing of CNF in the microstructure and the ac conductivity behaviour of the final nanocomposite.Peer Reviewe

Hertz-to-terahertz dielectric response of nanoconfined water molecules

Broad-band dielectric spectroscopy, heat capacity measurements and molecular dynamic simulations are applied to study excitations of interacting electric dipoles spatially arranged in a network with an inter-dipole distance of 5-10 A. The dipoles with magnitude of 1.85 Debye are represented by single H2O molecules located in voids (0.5 nm size) formed by ions of the crystal lattice of cordierite. We discover emergence of nontrivial disordered paraelectric phase of dipolar system with signs of phase transition below 3 K.Comment: 3 pages, 4 figure