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Search Results: 1 - 10 of 324974 matches for " Luis J.; "
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Past, Present and Future Climate of Antarctica  [PDF]
Alvarinho J. Luis
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.46089
Abstract:

Anthropogenic warming of near-surface atmosphere in the last 50 years is dominant over the west Antarctic Peninsula. Ozone depletion has led to partly cooling of the stratosphere. The positive polarity of the Southern Hemisphere Annular Mode (SAM) index and its enhancement over the past 50 years have intensified the westerlies over the Southern Ocean, and induced warming of Antarctic Peninsula. Dictated by local ocean-atmosphere processes and remote forcing, the Antarctic sea ice extent is increasing, contrary to climate model predictions for the 21st century, and this increase has strong regional and seasonal signatures. Models incorporating doubling of present day CO2 predict warming of the Antarctic sea ice zone, a reduction in sea ice cover, and warming of the Antarctic Plateau, accompanied by increased snowfall.

Trends and Interannual Variability of Winds and Turbulent Heat Flux in the Indian Ocean Sector of Southern Ocean during 2000-2009  [PDF]
Alvarinho J. Luis
Atmospheric and Climate Sciences (ACS) , 2014, DOI: 10.4236/acs.2014.42030
Abstract: Using satellite-based wind and sea surface temperature (SST) observations, linear trend and inter-annual variability of wind stress, turbulent heat flux (Q) and wind stress curl are addressed for the Indian Ocean sector of the Southern Ocean (ISO, 0°E - 155°E) for the period 2000-2009. The analysis reveals that spatial mean of Q varies between 70 and 73 Wm-2 in the austral summer and winter, respectively, while the mean wind stress is nearly same at 0.22 Nm-2 for both seasons. The anticyclonic curl dominates the ISO, which increases from 0.15 × 10-7 to 0.35 × 10-7 Nm-3 during the austral summer. The detrended box-mean time series of Q, wind stress, and wind stress curl exhibits a decreasing trend of –6.3 ± 1.6 Wm-2·decade-1, -0.012 ± 0.004 Nm-2·decade-1 and -0.48 ± 0.6 × 10-8 Nm-3·decade-1, respectively. The Empirical Orthogonal Function (EOF) analysis was carried out to study inter-annual variability. EOF-1 of Q captures 25% of the total variance, which mimics the austral summer pattern; its time coefficient is highly and negatively correlated with a 2-month lagged Nino3.4 SST index (r =-0.8 at 95% confidence). EOF-1 of wind stress accounts for 35% of the total variance and its time coefficient is strongly correlated with the Antarctic Oscillation (r= 0.86 at 95% confidence). EOF-1 of wind stress curl captures 15% of the total variance; its time coefficient is correlated to the Nino3.4 SST index (r= 0.65 at 95% confidence) with the former lagging the latter by two years. The repercussions of the weakening trends of the climatic parameters on
Sea Ice Observations in Polar Regions: Evolution of Technologies in Remote Sensing  [PDF]
Praveen Rao Teleti, Alvarinho J. Luis
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.47097
Abstract:

Evolution of remote sensing sensors technologies is presented, with emphasis on its suitability in observing the polar regions. The extent of influence of polar regions on the global climate and vice versa is the spearhead of climate change research. The extensive cover of sea ice has major impacts on the atmosphere, oceans, and terrestrial and marine ecosystems of the polar regions in particular and teleconnection on other processes elsewhere. Sea ice covers vast areas of the polar oceans, ranging from ~18 × 106 km2 to ~23 × 106 km2, combined for the Northern and Southern Hemispheres. However, both polar regions are witnessing contrasting rather contradicting effects of climate change. The Arctic sea ice extent is declining at a rate of 0.53 × 106 km2·decade–1, whereasAntarcticaexhibits a positive trend at the rate of 0.167 × 106 km2·decade–1. This work reviews literature published in the field of sea ice

Hydrodynamics between Africa and Antarctica during Austral Summer of 2008 and 2009: Results of the IPY Project  [PDF]
Alvarinho J. Luis, S. M. Pednekar
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.42046
Abstract:

A hydrographic section between Cape Town,South AfricaandIndiaBay,Antarcticawas sampled by deploying expendable CTD probes during the austral summer of 2008 and 2009. In 2009, the Agulhas Retroflection (AR) Front was displaced southward by 1.5° latitude, while the northern and southern Polar Front meandered southward by 1° and 1.4° latitude, respectively, relative to their positions in 2008. Geostrophic transport, relative to1000 m, indicates that Antarctic Circumpolar Current (ACC) flow decreased by 2.5 Sv in 2009 compared to that in 2008. The anticyclones which are detached from the AR facilitates a transport to the southeast Atlantic Ocean ranging between 8 and 12 Sv. Nearly 50% of the ACC transport is confined to the 100 - 500 m layer. A comparison of water mass distribution for 2008 and 2009 suggests that Mode Water distribution was restricted to 42.5°S and 41.9°S, and the Antarctic Surface Water ex°tended to 57.6°S and 46.6°S, respectivel°. In 2009, the along track Heat Content (HC) and Salt Content (SC) for the upper750 mof the water column decreased each by 1% compared to those in 2008. In the ACC domain, the HC and SC dip by 36% and 40% in 2009, respectively. The HC and SC associated with Agulhas Retroflection Front increase in 2009 by 1% and 2%, respectively, due to an enhanced Agulhas transport of warm and saline water from the tropics by 2%.

Relationship between Fracture Toughness and Fracture Surface Fractal Dimension in AISI 4340 Steel  [PDF]
Luis R. Carney, John J. Mecholsky Jr.
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.44032
Abstract:

This study analyzes the relationship between fracture toughness and the fracture surface fractal dimension for a set of twenty-four CT-type AISI 4340 steel specimens heat treated to a variety of tensile strengths. Specimens were tested in accordance with ASTM E 399. Their respective fracture surfaces were plated, polished, photographed under an SEM in BSE mode and measured according to the Richardson method to obtain fractal dimensions. For brittle materials the limited results are consistent with previous literature: increasing fractal dimension with increasing toughness. For partially or fully ductile materials the results indicate a decrease in fractal dimension with an increase in fracture toughness. The data are modeled using a variation of the function applied to ceramics. Fracture in a ductile mode is characterized by the formation of dimples which exhibit fractal characteristics. The results are discussed in terms of the micromechanisms of fracture.

A Comprehensive Evaluation of PAN-Sharpening Algorithms Coupled with Resampling Methods for Image Synthesis of Very High Resolution Remotely Sensed Satellite Data  [PDF]
Shridhar D. Jawak, Alvarinho J. Luis
Advances in Remote Sensing (ARS) , 2013, DOI: 10.4236/ars.2013.24036
Abstract:

The merging of a panchromatic (PAN) image with a multispectral satellite image (MSI) to increase the spatial resolution of the MSI, while simultaneously preserving its spectral information is classically referred as PAN-sharpening. We employed a recent dataset derived from very high resolution of WorldView-2 satellite (PAN and MSI) for two test sites (one over an urban area and the other over Antarctica), to comprehensively evaluate the performance of six existing PAN-sharpening algorithms. The algorithms under consideration were the Gram-Schmidt (GS), Ehlers fusion (EF), modified hue-intensity-saturation (Mod-HIS), high pass filtering (HPF), the Brovey transform (BT), and wavelet-based principal component analysis (W-PC). Quality assessment of the sharpened images was carried out by using 20 quality indices. We also analyzed the performance of nearest neighbour (NN), bilinear interpolation (BI), and cubic convolution (CC) resampling methods to test their practicability in the PAN-sharpening process. Our results indicate that the comprehensive performance of PAN-sharpening methods decreased in the following order: GS > W-PC > EF > HPF > Mod-HIS > BT, while resampling methods followed the order: NN > BI > CC.

The Role of the Southern Hemisphere Polar Cell on Antarctic Sea Ice Variability  [PDF]
Praveen Rao Teleti, Alvarinho J. Luis
International Journal of Geosciences (IJG) , 2016, DOI: 10.4236/ijg.2016.72010
Abstract: The study explores modes of variability in the Southern Polar Cell and their relationship with known global climate modes and Antarctic sea ice. It is found that Polar Cell is barotropic in nature and 500 hPa geo-potential height (Z500) field can satisfactorily represent variability in the Polar Cell. First, three leading Empirical Orthogonal Function (EOF) modes of Z500account for nearly 80% of observed variability in the Polar Cell. Dominant mode (PC1500) comprises of high pressure divergence zone over Antarctica. Second leading mode (PC2500) is low pressure zone covering Amundsen-Bellingshausen Sea (ABS) similar to ABS low feature. A new climate mode called Polar Coastal Index (PCI) is defined, which describes more than 15% and close to 30% variability of circumpolar trough and ABS low, respectively. Out of four modes defined in this study, only PCI and PC2500show linear trends and clear seasonality. Interestingly, both modes are affected by modulation of ABS low due to tropical ENSO forcing. SAM signature is present in Polar Cell as PC1500shares large variance with it. The largest impact on sea ice comes from PC2500followed by PC1500
Algunas referencias útiles para entender la proyección de la educación nacional al continente y al mundo
Bravo Jáuregui,Luis;
Investigación y Postgrado , 2008,
Abstract: this paper studies how national education was projected to the continent during the years of 1999-2003; through the analysis of a chronology derived of the data base of venezuelan educational memory project; where the most important events associated with the internationalization of venezuelan pedagogy are put in order, because of an international campaign for the eradication of the illiteracy in bolivia. the educational country recognizable in the years of 1999-2003 does not seem to be in the best institutional conditions to export a supposed miracle. however, the international topic appears stronger that in other periods studied, and the educational missions, mainly the robinson i, are consolidated as the most genuine expression of the national educational activity.
El género Obrium Dejean, 1821 (Coleoptera, Cerambycidae, Obriini) en Venezuela
Joly, Luis J.;
Papéis Avulsos de Zoologia (S?o Paulo) , 2010, DOI: 10.1590/S0031-10492010004600001
Abstract: four new species of obrium are described from venezuela: obrium asperatum sp. nov., o. clavijoi sp. nov., o. latecinctum sp. nov. and o. semiduffusum sp. nov. a key to south american species is presented.
On the stability index of minimal and constant mean curvature hypersurfaces in spheres
Alías,Luis J.;
Revista de la Uni?3n Matem??tica Argentina , 2006,
Abstract: the study of minimal and, more generally, constant mean curvature hypersurfaces in riemannian space forms is a classical topic in differential geometry. as is well known, minimal hypersurfaces are critical points of the variational problem of minimizing area. similarly, hypersurfaces with constant mean curvature are also solutions to that variational problem, when restricted to volume-preserving variations. in this paper we review about the stability index of both minimal and constant mean curvature hypersurfaces in euclidean spheres, including some recent progress by the author, jointly with some of his collaborators. one of our main objectives on writing this paper has been to make it comprehensible for a wide audience, trying to be as self-contained as possible.
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