A cotunneling mechanism for all-electrical Electron Spin Resonance of single adsorbed atoms

The recent development of all-electrical electron spin resonance (ESR) in a scanning tunneling microscope (STM) setup has opened the door to vast applications. Despite the fast growing number of experimental works on STM-ESR, the fundamental principles remains unclear. By using a cotunneling picture, we show that the spin resonance signal can be explained as a time-dependent variation of the tunnel barrier induced by the alternating electric driving field. We demonstrate how this variation translates into the resonant frequency response of the direct current. Our cotunneling theory explains the main experimental findings. Namely, the linear dependence of the Rabi flop rate with the alternating bias amplitude, the absence of resonant response for spin-unpolarized currents, and the weak dependence on the actual atomic species.Comment: 11 pages, 3 figure

Failure and impact behavior of facade panels made of glass fiber reinforced cement(GRC)

GRC is a cementitious composite material made up of a cement mortar matrix and chopped glass fibers. Due to its outstanding mechanical properties, GRC has been widely used to produce cladding panels and some civil engineering elements. Impact failure of cladding panels made of GRC may occur during production if some tool falls onto the panel, due to stone or other objects impacting at low velocities or caused by debris projected after a blast. Impact failure of a front panel of a building may have not only an important economic value but also human lives may be at risk if broken pieces of the panel fall from the building to the pavement. Therefore, knowing GRC impact strength is necessary to prevent economic costs and putting human lives at risk. One-stage light gas gun is an impact test machine capable of testing different materials subjected to impact loads. An experimental program was carried out, testing GRC samples of five different formulations, commonly used in building industry. Steel spheres were shot at different velocities on square GRC samples. The residual velocity of the projectiles was obtained both using a high speed camera with multiframe exposure and measuring the projectile’s penetration depth in molding clay blocks. Tests were performed on young and artificially aged GRC samples to compare GRC’s behavior when subjected to high strain rates. Numerical simulations using a hydrocode were made to analyze which parameters are most important during an impact event. GRC impact strength was obtained from test results. Also, GRC’s embrittlement, caused by GRC aging, has no influence on GRC impact behavior due to the small size of the projectile. Also, glass fibers used in GRC production only maintain GRC panels’ integrity but have no influence on GRC’s impact strength. Numerical models have reproduced accurately impact tests

Effect of Glass Fiber Hybridization on the Behavior Under Impact of Woven Carbon Fiber/Epoxy Laminates

The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven carbon and glass (S2) fabrics. Specimens with different thicknesses and glass fiber content (from 0 to 21 vol.%) were tested with impact energies in the range 30–245 J and the resulting deformation and fracture micromechanisms were studied using X-ray microtomography. The results of these analyses, together with those of the impact tests (maximum load and energy absorbed), were used to elucidate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall laminate performance under low-velocity impact

Spalling uniaxial strength of Al2O3 at high strain rates

In this article research into the uniaxial tensile strength of Al2O3 monolithic ceramic is presented. The experimental procedure of the spalling of long bars is investigated from different approaches. This method is used to obtain the tensile strength at high strain rates under uniaxial conditions. Different methodologies proposed by several authors are used to obtain the tensile strength. The hypotheses needed for the experimental set-up are also checked, and the requirements of the set-up and the variables are also studied by means of numerical simulations. The research shows that the shape of the projectile is crucial to achieve successfully tests results. An experimental campaign has been carried out including high speed video and a digital image correlation system to obtain the tensile strength of alumina. Finally, a comparison of the test results provided by three different methods proposed by different authors is presented. The tensile strength obtained from the three such methods on the same specimens provides contrasting results. Mean values vary from one method to another but the trends are similar for two of the methods. The third method gives less scatter, though the mean values obtained are lower and do not follow the same trend as the other methods for the different specimens

Efecto de la irradiancia en el crecimiento, fotosíntesis, contenido pigmentario y consumo de nutrientes en cultivos densos de Rhodomonas salina (Wislouch) (Cryptophyceae)

12 páginas, 5 figuras, 2 tablas.[EN] The effects of different incident irradiances on growth, photosynthesis, pigment content and nutrient uptake were studied in dense cultures of the cryptophyte Rhodomonas salina (Wislouch) Hill y Wetherbee. Cells were grown for ten days at different incident irradiances: 11, 33, 75, 260 and 320 ?mol photon m-2s-1. The average pigment content (phycoerythrin and chlorophyll a) was lower when cells were grown at high irradiances (260 and 320 ?mol photon m-2s-1) compared with cells grown under low irradiances (11, 33 and 75 ?mol photon m-2s-1).The maximum photosynthetic rate (Pmax) was maximal at 75 ?mol photon m-2s-1 , decreasing considerably at the highest irradiance in which apparent photosynthetic efficiency per cell and per chlorophyll a unit (ᣥll and ᣨla) also decreased. Results showed that dense cultures of R. salina grew optimally in a range between 75 and 260 ?mol photon m-2s-1 with optimal photosynthetic performance at 75 ?mol photon m-2s-1. Nitrogen and phosphorus depletion occurred as a consequence of the exponential growth, except under the lowest and the highest irradiances (11 and 320 ?mol photon m-2s-1, respectively). Associated to N-limitation, phycoerythrin (PE) and chlorophyll a decreased considerably. It is suggested that R.salina responds to nitrogen-depleted conditions by mobilizing nitrogen from PE, this behaviour being modelled by a relationship between external nitrogen availability and PE mobilization.[ES] En este trabajo se analizan los efectos que diferentes irradiancias incidentes tienen en el crecimiento, características fotosintéticas, contenido pigmentario e incorporación de nutrientes en cultivos densos de la criptofita Rhodomonas salina (Wislouch) Hill y Wetherbee. Con tal fin, se mantuvieron cultivos durante diez días bajo distintas condiciones de luz incidente: 11, 33, 75, 260 y 320 µmol fotón m-2s-1. El contenido pigmentario promedio (ficoeritrina y clorofila a) fue menor en células adaptadas a las mayores irradiancias (260 y 320 µmol fotón m-2s-1) en comparación con las adaptadas a las irradiancias menores (11, 33 y 75 µmol fotón m-2s-1). El valor máximo de fotosíntesis (Pmax) se obtuvo para las células adaptadas a 75 µmol fotón m-2s-1, decreciendo considerablemente para la irradiancia máxima ensayada en la que también la eficiencia fotosintética (ácel. and ácla) fue menor. Los resultados muestran que esta criptofita crece óptimamente en cultivos densos en un rango de irradiancias incidentes entre 75 y 260 µmol fotón m-2s-1, con una actividad fotosintética óptima a 75 µmol fotón m-2s-1. Como consecuencia del crecimiento exponencial de los cultivos, se produjo una desaparición paulatina y prácticamente total del nitrógeno y el fósforo del medio, excepto en los cultivos adaptados a las irradiancias máxima (320 µmol fotón m-2s-1) y minima (11 µmol fotón m-2s-1) empleadas. Asociada a tales condiciones de limitación de nitrógeno se observó una disminución del contenido celular de ficoeritrina y clorofila a, definiéndose una clara relación entre la disponibilidad de nitrógeno externo y la tasa de desaparición de ficoeritrina. Estos resultados sugieren que Rhodomonas salina es capaz de movilizar el nitrógeno asociado a la ficoeritrina como respuesta ante condiciones de baja disponibilidad de dicho nutriente.Este trabajo ha sido financiado por un proyecto CICYT (AMB-0684-CO2-01) del Ministerio de Educación y Cultura, España.Peer reviewe

Texture analysis in an apple progeny through instrumental, sensory and histological phenotyping

Phenotypic analysis of texture traits was performed in an apple progeny by three complementary approaches: two classical instrumental measurements (compression and penetrometry), sensory assessment and histological screening. The progeny was composed of 141 individuals harvested over 2 years. Sensory and instrumental texture were assessed at harvest and after 2 and 4 months of cold storage. Histological screening was performed by combining macro-vision of outer parenchyma sections and image analysis on fruits after 2 months storage. Harvest year was observed to have a major impact on texture phenotypes followed by storage and genetic factors. Principal component analysis of data from the instrumental texture evaluations showed that the two methods complemented each other in characterizing the texture of the apple progeny. Compression parameters correlated better than penetrometry variables with sensory descriptors related to crispness, firmness, and graininess. Cell size distribution differentiated individuals in the apple progeny. It correlated with instrumental texture analyses and with juiciness perception. All measured texture related traits showed that they were all under genetic control with high heritability values. Higher values were obtained for fruits after 2 months storage. These results provide ground for future search of new apple texture QTLs