Efficient geometric framework for 3D images modeling

El objetivo de este artículo es explorar la implementación de una reconstrucción real de imágenes en 3D utilizando el álgebra geométrica (AG). Con ello queremos mostrar la utilidad del AG para la representación de estructuras y el desarrollo de algoritmos para las aplicaciones de computer graphics , y especialmente para otras aplicaciones de ingeniería, como el modelado de imágenes en 3D. Una primera consecuencia es la obtención de un eficiente entorno de modelado para su implementación en un hardware programable. Los resultados obtenidos muestran que utilizando AG, los cálculos son menos complejos y se materializan como simples operaciones geométricas. El modelo obtenido para el hardware puede ser implementado como un paso siguiente en la reconstrucción de imágenes en 3D. Este artículo pone de manifiesto el potencial del AG para optimizaciones e implementaciones altamente eficientes.The objective of this paper is exploring implementation of a realistic images reconstruction 3D using geometric algebra (GA). We illustrate the suitability of GA for representing structures and developing algorithms in computer graphics, especially for engineering applications as 3D images modeling. A first consequence is to propose an efficient framework model to be implemented in hardware programmable. The obtained results showed that using GA, the computations are less complex and shows as simple computations geometrical operations. The obtained model to hardware can be implemented as a next step in 3D image reconstruction. We also include the potential of GA for optimizations and highly efficient implementations.Peer Reviewe

Screening of herbicides in grain legumes: pre-emergence herbicides in faba beans

Ante la escasez de herbicidas autorizados en leguminosas, se realizaron dos ensayos en habas con 10 herbicidas elegidos por estar autorizados en otras leguminosas o en otros países. Ninguno de los productos resultó totalmente eficaz y selectivo. Algunos de los herbicidas de preemergencia autorizados en España en habas para grano resultaron menos eficaces contra las malas hierbas y produjeron mayor fitotoxicidad que otros no autorizados. Así mismo, productos autorizados en Francia resultaron fitotóxicos en nuestras condiciones. Los mejores resultados seguido de ixosaben y aclonifen. Sin embargo será necesario ajustar dosis y buscar otras alternativas, como combinaciones de productos o estrategias de control para mejorar las eficacias y la selectividad, y sobre todo elegir los productos en función de las especies de malas hierbas dominantes en cada finca.Faced with a shortage of herbicides in legumes, two trials were conducted in faba beans to evaluate 10 herbicides elected by being authorized in other legumes or in other countries. None of the product was completely effective and selective. Some of the pre-emergence herbicides authorized in Spain for grain faba beans were less effective against weeds and produced more phytotoxicity than others not authorized. Likewise, products authorized in France turned out quite phytotoxic in our conditions. The best results were obtained with metribuzin by its effective weed control and low phytotoxicity, followed by ixosaben and aclonifen. However it will be necessary to adjust dose, to look for other alternatives, such as combinations of products or control strategies to improve effectiveness and selectivity, and above all choose the products depending on the species of dominant weeds in each farm

Numerical study of the aerodynamics of sound sources in a bass-reflex port

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The aim of this paper is to study the aerodynamics phenomena of a bass-reflex port that causes noise in the audible frequency range. After discarding structural and mechanical vibration issues, the hypothesis considered is that vortex shedding is the source of the noise. Experimental and numerical evidences of the vortex, an analysis of its noise and the similarities between real and simulated performance are presented. The numerically simulated cases with the original geometry are excited at different frequencies and with modifications of the port geometry. Likewise, the internal performance of an enclosure with a closed port was simulated. The simulations have been performed with axisymmetrical geometries using the open-source OpenFOAM® toolbox. Moreover, experimental measurements were carried out. First, acoustic signal experiments were done to analyse the response of the bass-reflex ports. Secondly, a structure vibration measurement was conducted in order to exclude the cabinet structure vibration as a source of the noise in question. A good agreement was found between numerical and experimental results, especially in the frequency band of the detected noise, i.e. the 1000–1500 Hz range. Despite no remarkable improvement being made with the geometry changes explored, the presented CFD approach has proved a useful and cost-effective tool to address this kind of phenomenon.Peer ReviewedPostprint (published version

On the soliton width in the incommensurate phase of spin-Peierls systems

We study using bosonization techniques the effects of frustration due to competing interactions and of the interchain elastic couplings on the soliton width and soliton structure in spin-Peierls systems. We compare the predictions of this study with numerical results obtained by exact diagonalization of finite chains. We conclude that frustration produces in general a reduction of the soliton width while the interchain elastic coupling increases it. We discuss these results in connection with recent measurements of the soliton width in the incommensurate phase of CuGeO_3.Comment: 4 pages, latex, 2 figures embedded in the tex

Domain excitations in spin-Peierls systems

We study a model of a Spin-Peierls material consisting of a set of antiferromagnetic Heisenberg chains coupled with phonons and interacting among them via an inter-chain elastic coupling. The excitation spectrum is analyzed by bosonization techniques and the self-harmonic approximation. The elementary excitation is the creation of a localized domain structure where the dimerized order is the opposite to the one of the surroundings. It is a triplet excitation whose formation energy is smaller than the magnon gap. Magnetic internal excitations of the domain are possible and give the further excitations of the system. We discuss these results in the context of recent experimental measurements on the inorganic Spin-Peierls compound CuGeO$_3$Comment: 5 pages, 2 figures, corrected version to appear in Phys. Rev.

Origin of spin-gap in CaV4_4O9_9: effect of frustration and lattice distortion

We study the origin of spin-gap in recently discovered material CaV$_4$O$_9$. We analyze the spin-$1/2$ Heisenberg model on the $1/5$ depleted square lattice with nearest neighbor (nn) and next nearest neighbor (nnn) interactions, in terms of the singlet and triplet states of the 4-spin plaquettes and 2-spin dimers. Phase diagram of the model is obtained within a linear ``spin-wave"-like approximation, and is shown to agree well with the earlier results of QMC simulations for nn interactions. We further propose that the special lattice structure of CaV$_4$O$_9$ naturally leads to lattice distortions, which enhances the spin-gap via a spin-Peierls mechanism.Comment: 4 pages, RevTex, 2 postscript figures. Latex file and figures have been uuencode

Thermal Conductivity of the Spin Peierls Compound CuGeO_3

The thermal conductivity of the Spin-Peierls (SP) compound CuGeO_3 was measured in magnetic fields up to 16 T. Above the SP transition, the heat transport due to spin excitations causes a peak at around 22 K, while below the transition the spin excitations rapidly diminish and the heat transport is dominated by phonons; however, the main scattering process of the phonons is with spin excitations, which demonstrates itself in an unusual peak in the thermal conductivity at about 5.5 K. This low-temperature peak is strongly suppressed with magnetic fields in excess of 12.5 T.Comment: 6 pages, including 2 postscript figure

Tolerance of human embryonic stem cell derived islet progenitor cells to vitrification-relevant solutions

We have previously shown that human embryonic stem cell derived islet progenitors (hESC-IPs), encapsulated inside an immunoprotective device, mature in vivo and ameliorate diabetes in mice. The ability to cryopreserve hESC-IPs preloaded in these devices would enhance consistency and portability, but traditional ‘slow freezing’ methods did not work well for cells encapsulated in the device. Vitrification is an attractive alternative cryopreservation approach. To assess the tolerance of hESC-IPs to vitrification relevant conditions, we here are reporting cell survival following excursions in tonicity, exposure to fifteen 40% v/v combinations of 4 cryoprotectants, and varied methods for addition and elution. We find that 78% survival is achieved using a protocol in which cells are abruptly (in one step) exposed to a solution containing 10% v/v each dimethyl sulfoxide, propylene glycol, ethylene glycol, and glycerol on ice, and eluted step-wise with DPBS + 0.5 M sucrose at 37 °C. Importantly, the hESC-IPs also maintain expression of the critical islet progenitor markers PDX-1, NKX6.1, NGN3 and NEURO-D1. Thus, hESC-IPs exhibit robust tolerance to exposure to vitrification solutions in relevant conditions

Removal of Phenolic Compounds from Water Using Copper Ferrite Nanosphere Composites as Fenton Catalysts

The authors affiliated to the University of Jaén (Department of Inorganic and Organic Chemistry) acknowledge financial support from the Spanish Ministry of Economy, Industry and Competitiveness and from FEDER (Project CTQ2016-80978-C2-1-R). L. Mateus thanks the Asociación Universitaria Iberoamericana de Postgrado (AUIP) and University of Jaén for their grant and financial support.Copper ferrites containing Cu+ ions can be highly active heterogeneous Fenton catalysts due to synergic effects between Fe and Cu ions. Therefore, a method of copper ferrite nanosphere (CFNS) synthesis was selected that also permits the formation of cuprite, obtaining a CFNS composite that was subsequently calcined up to 400 °C. Composites were tested as Fenton catalysts in the mineralization of phenol (PHE), p-nitrophenol (PNP) and p-aminophenol (PAP). Catalysts were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and magnetic measurements. Degradation of all phenols was practically complete at 95% total organic carbon (TOC) removal. Catalytic activity increased in the order PHE < PNP < PAP and decreased when the calcination temperature was raised; this order depended on the electronic effects of the substituents of phenols. The as-prepared CFNS showed the highest catalytic activity due to the presence of cubic copper ferrite and cuprite. The Cu+ surface concentration decreased after calcination at 200 °C, diminishing the catalytic activity. Cuprite alone showed a lower activity than the CFNS composite and the homogeneous Fenton reaction had almost no influence on its overall activity. CFNS activity decreased with its reutilization due to the disappearance of the cuprite phase. Degradation pathways are proposed for the phenols.This research was funded by Spanish Ministry of Economy, Industry and Competitiveness and FEDER (grant number CTQ2016-80978-C2-1-R), Asociación Universitaria Iberoamericana de Postgrado (AUIP) and University of Jaén

Spectrum of elementary and collective excitations in the dimerized S=1/2 Heisenberg chain with frustration

We have studied the low-energy excitation spectrum of a dimerized and frustrated antiferromagnetic Heisenberg chain. We use an analytic approach, based on a description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. Additional singlet (S=0) and triplet (S=1) modes are found as two-particle bound states of the elementary triplets. We have also calculated the contributions of the elementary and collective excitations into the spin structure factor. Our results are in excellent agreement with exact diagonalizations and dimer series expansions data as long as the dimerization parameter $\delta$ is not too small ($\delta>0.1$), i.e. while the elementary triplets can be treated as localized objects.Comment: 18 pages, 13 figure