2,827 research outputs found
The mean curvature of cylindrically bounded submanifolds
We give an estimate of the mean curvature of a complete submanifold lying
inside a closed cylinder in a product Riemannian manifold
. It follows that a complete hypersurface of given
constant mean curvature lying inside a closed circular cylinder in Euclidean
space cannot be proper if the circular base is of sufficiently small radius. In
particular, any possible counterexample to a conjecture of Calabion complete
minimal hypersurfaces cannot be proper. As another application of our method,
we derive a result about the stochastic incompleteness of submanifolds with
sufficiently small mean curvature.Comment: First version (December 2008). Final version, including new title
(February 2009). To appear in Mathematische Annale
Infecção pelo Sugarcane yellow leaf virus causa alterações na eficiência fotossintética e acúmulo de carboidratos nas folhas de cana-de-açúcar
Infection by Sugarcane yellow leaf virus (ScYLV) causes severe leaf symptoms in sugarcane (Saccharum spp.) hybrids, which indicate alterations in its photosynthetic apparatus. To gain an overview of the physiological status of infected plants, we evaluated chlorophyll a fluorescence and gas exchange assays, correlating the results with leaf metabolic surveys, i.e., photosynthetic pigments and carbohydrate contents. When compared to healthy plants, infected plants showed a reduction in potential quantum efficiency for photochemistry of photosystem (PSII) and alterations in the filling up of the plastoquinone (PQ) pool. They also showed reduction in the CO2 net exchange rates, probably as a consequence of impaired quantum yield. In addition, reductions were found in the contents of photosynthetic leaf pigments and in the ratio chlorophyll a/chlorophyll b (chla/chlb). Carbohydrate content in the leaves was increased as a secondary effect of the ScYLV infection. This article discusses the relation of virus replication and host defense responses with general alterations in the photosynthetic apparatus and in the metabolism of infected plants.O vÃrus do amarelecimento foliar da cana-de-açúcar (Sugarcane yellow leaf virus, ScYLV) causa sintomas foliares severos e tÃpicos de infecção por luteovirus, em cana-de-açúcar (Saccharum spp.). Uma vez que alterações no sistema fotossintético da planta seriam esperadas, avaliaram-se a análise da emissão da fluorescência da clorofila a e as trocas gasosas durante a fotossÃntese, relacionando esses dados com análises metabólicas, ou seja, conteúdos de pigmentos fotossintéticos e carboidratos presentes nas folhas. As plantas infetadas apresentaram redução na eficiência quântica fotoquÃmica potencial do fotossistema II (PSII) e alterações no preenchimento do pool de plastoquinona (PQ). Essas plantas apresentaram, também, redução nas taxas de troca lÃquida de CO2, provavelmente em conseqüência da redução na eficiência quântica. Paralelamente, reduções nos conteúdos de pigmentos fotossintéticos foliares e na razão clorofila a/clorofila b (chla/chlb) foram verificadas. Adicionalmente, o conteúdo de açúcares nas folhas foi aumentado, provavelmente como um efeito secundário da infecção viral. A relação entre a replicação viral e as respostas de defesa da hospedeira com as alterações encontradas no aparelho fotossintético e no metabolismo das plantas infetadas é discutida.101
Automatic segmentation of the Foveal Avascular Zone in ophthalmological OCT-A images
Angiography by Optical Coherence Tomography is a non-invasive retinal imaging
modality of recent appearance that allows the visualization of the vascular
structure at predefined depths based on the detection of the blood movement.
OCT-A images constitute a suitable scenario to analyse the retinal vascular
properties of regions of interest, measuring the characteristics of the foveal
vascular and avascular zones. Extracted parameters of this region can be used
as prognostic factors that determine if the patient suffers from certain
pathologies, indicating the associated pathological degree. The manual
extraction of these biomedical parameters is a long, tedious and subjective
process, introducing a significant intra and inter-expert variability, which
penalizes the utility of the measurements. In addition, the absence of tools
that automatically facilitate these calculations encourages the creation of
computer-aided diagnosis frameworks that ease the doctor's work, increasing
their productivity and making viable the use of this type of vascular
biomarkers.
We propose a fully automatic system that identifies and precisely segments
the region of the foveal avascular zone (FAZ) using a novel ophthalmological
image modality as is OCT-A. The system combines different image processing
techniques to firstly identify the region where the FAZ is contained and,
secondly, proceed with the extraction of its precise contour. The system was
validated using a representative set of 168 OCT-A images, providing accurate
results with the best correlation with the manual measurements of two experts
clinician of 0.93 as well as a Jaccard's index of 0.82 of the best experimental
case. This tool provides an accurate FAZ measurement with the desired
objectivity and reproducibility, being very useful for the analysis of relevant
vascular diseases through the study of the retinal microcirculation
Concrete for precast blocks: binary and ternary combination of sewage sludge ash with diverse mineral residue
[EN] This paper proposes binary and ternary combinations of sewage sludge ash (SSA) with fly ash (FA), marble dust (MD) and rice husk ash (RHA) as partial replacements of Portland cement in concretes with a similar dosage to that used in precast blocks, with very dry consistency. Several physical-mechanical tests were carried out on concrete specimens with curing ages of 28 and 90 days: density, water absorption, capillary water absorption, ultrasonic pulse velocity and compressive strength. The combinations of residues significantly improve the properties of the cementitious systems: 30% replacement of Portland cement provides strength values similar to the reference sample, showing the synergetic effects of the combination of the mineral additions. The significance of this research relies on the combined use of the mineral additions as well as the use of them for the precast block industry. The results show synergies among the additions and even that some of them showed relevant improvements when they are used in combination, performing better than when used individually.Baeza-Brotons, F.; Paya Bernabeu, JJ.; Galao, O.; Alberti, MG.; Garcés, P. (2020). Concrete for precast blocks: binary and ternary combination of sewage sludge ash with diverse
mineral residue. Materials. 13(20):1-19. https://doi.org/10.3390/ma13204634S1191320Zabalza Bribián, I., Valero Capilla, A., & Aranda Usón, A. (2011). Life cycle assessment of building materials: Comparative analysis of energy and environmental impacts and evaluation of the eco-efficiency improvement potential. Building and Environment, 46(5), 1133-1140. doi:10.1016/j.buildenv.2010.12.002Lothenbach, B., Scrivener, K., & Hooton, R. D. (2011). Supplementary cementitious materials. Cement and Concrete Research, 41(12), 1244-1256. doi:10.1016/j.cemconres.2010.12.001Ministerio de Agricultura Alimentación y Medio Ambiente http://www.magrama.gob.es/es/calidad-y-evaluacion-ambiental/temas/prevencion-y-gestion-residuos/flujos/lodos-depCyr, M., Coutand, M., & Clastres, P. (2007). Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials. Cement and Concrete Research, 37(8), 1278-1289. doi:10.1016/j.cemconres.2007.04.003Donatello, S., & Cheeseman, C. R. (2013). Recycling and recovery routes for incinerated sewage sludge ash (ISSA): A review. Waste Management, 33(11), 2328-2340. doi:10.1016/j.wasman.2013.05.024Marble Association of Alicante http://www.marmoldealicante.esChen, M., Blanc, D., Gautier, M., Mehu, J., & Gourdon, R. (2013). Environmental and technical assessments of the potential utilization of sewage sludge ashes (SSAs) as secondary raw materials in construction. Waste Management, 33(5), 1268-1275. doi:10.1016/j.wasman.2013.01.004Monzó, J., Payá, J., Borrachero, M. V., & Córcoles, A. (1996). Use of sewage sludge ash(SSA)-cement admixtures in mortars. Cement and Concrete Research, 26(9), 1389-1398. doi:10.1016/0008-8846(96)00119-6Payá, J., Monzó, J., Borrachero, M. V., Amahjour, F., Girbés, I., Velázquez, S., & Ordóñez, L. M. (2002). Advantages in the use of fly ashes in cements containing pozzolanic combustion residues: silica fume, sewage sludge ash, spent fluidized bed catalyst and rice husk ash. Journal of Chemical Technology & Biotechnology, 77(3), 331-335. doi:10.1002/jctb.583Tay, J.-H., & Show, K.-Y. (1994). Municipal wastewater sludge as cementitious and blended cement materials. Cement and Concrete Composites, 16(1), 39-48. doi:10.1016/0958-9465(94)90029-9Donatello, S., Tyrer, M., & Cheeseman, C. R. (2010). Comparison of test methods to assess pozzolanic activity. Cement and Concrete Composites, 32(2), 121-127. doi:10.1016/j.cemconcomp.2009.10.008Research Group in Chemistry Building Materials—Universitat Politècnica de València. Proyecto PEL-CEN http://epsar.cop.gva.es/depuradorasvPeris Mora, E., Payá, J., & Monzó, J. (1993). Influence of different sized fractions of a fly ash on workability of mortars. Cement and Concrete Research, 23(4), 917-924. doi:10.1016/0008-8846(93)90045-bEvolución de las resistencias mecánicas de sistemas ternarios cemento/ceniza volante/ceniza de lodo de depuradora: Efectos puzolánicos complementarios https://www.upv.es/pms2002/Comunicaciones/038 PAYA.PDFCorinaldesi, V., Moriconi, G., & Naik, T. R. (2010). Characterization of marble powder for its use in mortar and concrete. Construction and Building Materials, 24(1), 113-117. doi:10.1016/j.conbuildmat.2009.08.013Influence of Marble and Limestone Dusts as Additives on Some Mechanical Properties of Concrete, SCI RES ESSAYS 2 (2007) 372-379 http://www.academicjournals.org/SREAliabdo, A. A., Abd Elmoaty, A. E. M., & Auda, E. M. (2014). Re-use of waste marble dust in the production of cement and concrete. Construction and Building Materials, 50, 28-41. doi:10.1016/j.conbuildmat.2013.09.005RodrÃguez de Sensale, G. (2006). Strength development of concrete with rice-husk ash. Cement and Concrete Composites, 28(2), 158-160. doi:10.1016/j.cemconcomp.2005.09.005Khan, R., Jabbar, A., Ahmad, I., Khan, W., Khan, A. N., & Mirza, J. (2012). Reduction in environmental problems using rice-husk ash in concrete. Construction and Building Materials, 30, 360-365. doi:10.1016/j.conbuildmat.2011.11.028Madandoust, R., Ranjbar, M. M., Moghadam, H. A., & Mousavi, S. Y. (2011). Mechanical properties and durability assessment of rice husk ash concrete. Biosystems Engineering, 110(2), 144-152. doi:10.1016/j.biosystemseng.2011.07.009Nicoara, A. I., Stoica, A. E., Vrabec, M., Å muc Rogan, N., Sturm, S., Ow-Yang, C., … Vasile, B. S. (2020). End-of-Life Materials Used as Supplementary Cementitious Materials in the Concrete Industry. Materials, 13(8), 1954. doi:10.3390/ma13081954GarcÃa Arenas, C., Marrero, M., Leiva, C., SolÃs-Guzmán, J., & Vilches Arenas, L. F. (2011). High fire resistance in blocks containing coal combustion fly ashes and bottom ash. Waste Management, 31(8), 1783-1789. doi:10.1016/j.wasman.2011.03.017Poon, C.-S., Kou, S., Wan, H., & Etxeberria, M. (2009). Properties of concrete blocks prepared with low grade recycled aggregates. Waste Management, 29(8), 2369-2377. doi:10.1016/j.wasman.2009.02.018Sabai, M. M., Cox, M. G. D. M., Mato, R. R., Egmond, E. L. C., & Lichtenberg, J. J. N. (2013). Concrete block production from construction and demolition waste in Tanzania. Resources, Conservation and Recycling, 72, 9-19. doi:10.1016/j.resconrec.2012.12.003Xiao, R., Ma, Y., Jiang, X., Zhang, M., Zhang, Y., Wang, Y., … He, Q. (2020). Strength, microstructure, efflorescence behavior and environmental impacts of waste glass geopolymers cured at ambient temperature. Journal of Cleaner Production, 252, 119610. doi:10.1016/j.jclepro.2019.119610Xiao, R., Polaczyk, P., Zhang, M., Jiang, X., Zhang, Y., Huang, B., & Hu, W. (2020). Evaluation of Glass Powder-Based Geopolymer Stabilized Road Bases Containing Recycled Waste Glass Aggregate. Transportation Research Record: Journal of the Transportation Research Board, 2674(1), 22-32. doi:10.1177/0361198119898695Antoni, M., Rossen, J., Martirena, F., & Scrivener, K. (2012). Cement substitution by a combination of metakaolin and limestone. Cement and Concrete Research, 42(12), 1579-1589. doi:10.1016/j.cemconres.2012.09.006Scrivener, K., Martirena, F., Bishnoi, S., & Maity, S. (2018). Calcined clay limestone cements (LC3). Cement and Concrete Research, 114, 49-56. doi:10.1016/j.cemconres.2017.08.01
Spatially confined UHF RFID detection with a metamaterial grid
WOS: 000329516700044 (Nº de Acesso Web of Science)The confinement of the detection region is one of the most challenging issues in Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) systems. Here, we propose a new paradigm to confine the interrogation zone of standard UHF RFID systems. Our approach relies on the use of an all-planar metamaterial wire grid to block the radiation field (i.e., the far-field) of the reader antenna, and thereby obtain a spatially well-confined detection region in the near-field. This solution is analytically and numerically investigated, and then experimentally verified through near-field and tag-reading measurements, demonstrating its effectiveness and robustness under external perturbations
Siguiendo la huella de la hibridación en poblaciones de Cistus heterophyllus del RIF marroquÃ
Behaviour of local selections of <i>Eucalyptus viminalis</i> Labill.; australian origins of <i>E.viminalis, E.dunnii</i> Maiden., <i>E.ovata</i> Labill. and <i>E.viminalis</i> local commercial provenance, in Lobos, Buenos Aires Province, Argentine
El objetivo de este trabajo fue comparar las progenies de las selecciones de árboles pertenecientes a rodales de Eucalyptus viminalis ubicados en la Provincia de Buenos Aires, productos comerciales locales de E.viminalis, y orÃgenes especÃÂficos australianos del género Eucalyptus sugeridos y suministrados por CSIRO (División of Forestry and Forest Products. Australia) de acuerdo a las caracterÃsticas edafo-climáticas del sitio de la prueba (el material recomendado correspondió a E. viminalis, E. dunnii y E.ovata). El ensayo fue implantado en Lobos, Provincia de Buenos AÃres, República Argentina a los: 35° 10' Latitud Sud; 59°07' Longitud Oeste; 50 metros sobre el nivel del mar (m snm). Comparando los resultados de los tratamientos y contraponiéndolos con otros similares de la región, las procedencias locales seleccionadas pueden ser consideÂradas como un recurso seminal a tener en cuenta en los futuros planes de desarrollo de la zona. La estabilidad del comportamiento de las mismas y su eventual identificación como «razas locales», sugieren su posible incorporación a los planes de mejoramiento genético. E.dunnii, pese a su restringida área de distribución, presenta un disÃmil comportamiento entre los orÃgenes probados. E.ovata no puede descartarse teniendo en cuenta lo sucedido en las otras especies, por lo tanto deben probarse otros orÃgenes. Mientras se continua la introducción de especies, orÃgenes y procedencias, la superioridad de las selecciones locales sobre los productos utilizados comercialmente en la zona, hace que las primeras se constituyan en el nivel de referencia para fijar las respuestas mÃnimas de los materiales importados y suministrar al productor recursos con cierto grado de mejora.The objective of this work was to compare the progenies of the selections of trees belonging to E.viminalis stands loeated in Buenos Aires province, with australian origins of this species and of E.dunnii and E.ovata in respect of local commercial Products of E.viminalis.The australian material was provided by CSIRO (División of Forestry and Forest Products, Australia) in accordance with climatic and edaphic characteristics of the expermental site. The trial was situated in Lobos, Buenos Aires province, Argentine at 35° 10' South latitude, 59°07' West longitude, 50m. Comparing the treatment results and contrasting them with other similar ones of the región, the local provenance rightly selected can be considered as a seminal resource worthy to be taken into account in the future plans for the zone developmentThe behaviour stability of the local provenances selections and their identification as «local races- suggest the possibility of their incorporation to the genetic improvement plans.E.dunnii, in spite of its restricted native distribution area, presents dissimilar behaviours in its tested origins. E.ovata can't be discarded taking into account what happened to the other species, therefore other origins should be tested. While the introduction of species, origins and provenances continue, local selections can constitute a reference level to establish the importad material mÃnimal responses and to provide the grower with material of a certain level of improvement.Facultad de Ciencias Agrarias y Forestale
Reversed rainbow with a nonlocal metamaterial
WOS:000347171300050 (Nº de Acesso Web of Science)One of the intriguing potentials of metamaterials is the possibility to realize a nonlocal electromagnetic reaction, such that the effective medium response at a given point is fundamentally entangled with the macroscopic field distribution at long distances. Here, it is experimentally and numerically verified that a microwave nonlocal metamaterial formed by crossed metallic wires enables a low-loss broadband anomalous material response such that the refractive index decreases with frequency. Notably, it is shown that an electromagnetic beam refracted by our metamaterial prism creates a reversed microwave rainbow
Automatic Visual Acuity Estimation by Means of Computational Vascularity Biomarkers Using Oct Angiographies
[Abstract] Optical Coherence Tomography Angiography (OCTA) constitutes a new non-invasive ophthalmic image modality that allows the precise visualization of the micro-retinal vascularity that is commonly used to analyze the foveal region. Given that there are many systemic and eye diseases that affect the eye fundus and its vascularity, the analysis of that region is crucial to diagnose and estimate the vision loss. The Visual Acuity (VA) is typically measured manually, implying an exhaustive and time-consuming procedure. In this work, we propose a method that exploits the information of the OCTA images to automatically estimate the VA with an accurate error of 0.1713.Instituto de Salud Carlos III; DTS18/00136Ministerio de EconomÃa y Competitividad; DPI2015-69948-RXunta de Galicia; ED431G/01Xunta de Galicia; ED431C 2016-047Ministerio de Ciencia, Innovación y Universidades; RTI2018-095894-B-I0
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