5,365 research outputs found
A two-layer shallow water model for bedload sediment transport: convergence to Saint-Venant-Exner model
A two-layer shallow water type model is proposed to describe bedload sediment
transport. The upper layer is filled by water and the lower one by sediment.
The key point falls on the definition of the friction laws between the two
layers, which are a generalization of those introduced in Fern\'andez-Nieto et
al. (ESAIM: M2AN, 51:115-145, 2017). This definition allows to apply properly
the two-layer shallow water model for the case of intense and slow bedload
sediment transport. Moreover, we prove that the two-layer model converges to a
Saint-Venant-Exner system (SVE) including gravitational effects when the ratio
between the hydrodynamic and morphodynamic time scales is small. The SVE with
gravitational effects is a degenerated nonlinear parabolic system. This means
that its numerical approximation is very expensive from a computational point
of view, see for example T. Morales de Luna et al. (J. Sci. Comp., 48(1):
258-273, 2011). In this work, gravitational effects are introduced into the
two-layer system without such extra computational cost. Finally, we also
consider a generalization of the model that includes a non-hydrostatic pressure
correction for the fluid layer and the boundary condition at the sediment
surface. Numerical tests show that the model provides promising results and
behave well in low transport rate regimes as well as in many other situations
Polyhedral study of the 2-dominating set polytope of cycles and cactus graphs
Domination and its variations arise in many applications, in particular in those involving strategic placement of items at vertices of a network. For general graphs these problems are NP-hard, however, domination in graphs has been shown to be polynomially solvable in several graph classes. In this work we consider a generalization of this problem called k-domination in graphs.Sociedad Argentina de Informática e Investigación Operativ
Polyhedral study of the 2-dominating set polytope of cycles and cactus graphs
Domination and its variations arise in many applications, in particular in those involving strategic placement of items at vertices of a network. For general graphs these problems are NP-hard, however, domination in graphs has been shown to be polynomially solvable in several graph classes. In this work we consider a generalization of this problem called k-domination in graphs.Sociedad Argentina de Informática e Investigación Operativ
The multifunctional autophagy pathway in the human malaria parasite, Plasmodium falciparum.
Autophagy is a catabolic pathway typically induced by nutrient starvation to recycle amino acids, but can also function in removing damaged organelles. In addition, this pathway plays a key role in eukaryotic development. To date, not much is known about the role of autophagy in apicomplexan parasites and more specifically in the human malaria parasite Plasmodium falciparum. Comparative genomic analysis has uncovered some, but not all, orthologs of autophagy-related (ATG) genes in the malaria parasite genome. Here, using a genome-wide in silico analysis, we confirmed that ATG genes whose products are required for vesicle expansion and completion are present, while genes involved in induction of autophagy and cargo packaging are mostly absent. We subsequently focused on the molecular and cellular function of P. falciparum ATG8 (PfATG8), an autophagosome membrane marker and key component of the autophagy pathway, throughout the parasite asexual and sexual erythrocytic stages. In this context, we showed that PfATG8 has a distinct and atypical role in parasite development. PfATG8 localized in the apicoplast and in vesicles throughout the cytosol during parasite development. Immunofluorescence assays of PfATG8 in apicoplast-minus parasites suggest that PfATG8 is involved in apicoplast biogenesis. Furthermore, treatment of parasite cultures with bafilomycin A 1 and chloroquine, both lysosomotropic agents that inhibit autophagosome and lysosome fusion, resulted in dramatic morphological changes of the apicoplast, and parasite death. Furthermore, deep proteomic analysis of components associated with PfATG8 indicated that it may possibly be involved in ribophagy and piecemeal microautophagy of the nucleus. Collectively, our data revealed the importance and specificity of the autophagy pathway in the malaria parasite and offer potential novel therapeutic strategies
LAS TIC COMO ESTRATEGIA DIDÁCTICA DENTRO DEL PROCESO EDUCATIVO DE ESTUDIANTES UNIVERSITARIOS SORDOS
El objetivo de la investigación demuestra cómo las Tecnologías de la Información y la Comunicación (TIC) son implementadas como estrategias didácticas dentro del proceso educativo de los estudiantes universitarios sordos. Además, se presenta el significado de TIC, didáctica, aprendizaje significativo como enfoque pedagógico, enmarcado dentro de un modelo constructivista. Igualmente se define discapacidad, sordera, y su clasificación. Adicionalmente se presentan algunas reflexiones bibliográficas de experiencias en universidades de Europa y Colombia donde se evidencia la importancia de las TIC en los procesos educativos con estudiantes sordos, resaltando la importancia de la universidad en la educación inclusiva, intentando la democratización del conocimiento. Al finalizar el artículo se concluye la relevancia de las TIC como estrategia didáctica importante en los procesos educativos de los estudiantes universitarios sordos desde el aprendizaje significativo como enfoque pedagógico
Inflation with a constant ratio of scalar and tensor perturbation amplitudes
The single scalar field inflationary models that lead to scalar and tensor
perturbation spectra with amplitudes varying in direct proportion to one
another are reconstructed by solving the Stewart-Lyth inverse problem to
next-to-leading order in the slow-roll approximation.
The potentials asymptote at high energies to an exponential form,
corresponding to power law inflation, but diverge from this model at low
energies, indicating that power law inflation is a repellor in this case. This
feature implies that a fine-tuning of initial conditions is required if such
models are to reproduce the observations. The required initial conditions might
be set through the eternal inflation mechanism.
If this is the case, it will imply that the spectral indices must be nearly
constant, making the underlying model observationally indistinguishable from
power law inflation.Comment: 20 pages, 7 figures. Major changes to the Introduction following
referee's comments. One figure added. Some other minor changes. No conclusion
was modifie
Bird faunas of the humid montane forests of Mesoamerica: biogeographic patterns and priorities for conservation
The distribution of 335 species of birds in 33 islands of humid montane forest in
Mesoamerica is summarized, and patterns of distribution, diversity and endemism are
analysed. The montane forests of Costa Rica and western Panama far exceed other habitat
islands considered for species-richness, richness of species endemic to Mesoamerica,
and richness of species ecologically restricted to humid montane forests. Other regions,
such as the Sierra Madre del Sur of Guerrero and Oaxaca, the Los Tuxtlas region of
southern Veracruz and the mountains of Chiapas and Guatemala, also hold rich and
endemic avifaunas. Based on patterns of similarity of avifaunas, the region can be divided
into seven regions holding distinctive avifaunas (Costa Rica and western Panama;
northern Central America and northern Chiapas; southern Chiapas; eastern Mexico north
of the Isthmus of Tehuantepec; Sierra Madre del Sur; interior Oaxaca; and Transvolcanic
Belt and Sierra Madre Occidental), which serve as useful guides for the setting of
priorities for conservation action.
Se resumen las distribuciones de 335 especies de aves en 33 islas de bosque humedo de
montana en Mesoamerica, y se analizan patrones de distribution, diversidad y
endemismo. Los bosques montanos de Costa Rica y del oeste de Panama tienen la mas
alta riqueza de especies, riqueza de especies endemicas a Mesoamerica, y riqueza de
especies ecologicamente restringidas a bosque humedo de montana. Otras regiones, tales
como la Sierra Madre del Sur de Guerrero y Oaxaca, la region de Los Tuxtlas y las
montanas de Chiapas y Guatemala, tambien tienen avifaunas ricas en especies y en
endemicas. Basado en patrones de similitud de avifaunas, se puede dividir Mesoamerica
en siete regiones que tienen avifaunas distintas (Costa Rica y el oeste de Panama; el
norte de Centroamerica y el norte de Chiapas; el sur de Chiapas; el este de Mexico; la
Sierra Madre del Sur; el interior de Oaxaca; y el Eje Neovolcanico y la Sierra Madre
Occidental), las cuales pueden servir como guias en el establecimiento de prioridades
para la conservation
Black Holes with Varying Flux: A Numerical Approach
We present a numerical study of type IIB supergravity solutions with varying
Ramond-Ramond flux. We construct solutions that have a regular horizon and
contain nontrivial five- and three-form fluxes. These solutions are
holographically dual to the deconfined phase of confining field theories at
finite temperature. As a calibration of the numerical method we first
numerically reproduce various analytically known solutions including singular
and regular nonextremal D3 branes, the Klebanov-Tseytlin solution and its
singular nonextremal generalization. The horizon of the solutions we construct
is of the precise form of nonextremal D3 branes. In the asymptotic region far
away from the horizon we observe a logarithmic behavior similar to that of the
Klebanov-Tseytlin solution.Comment: 40 pages, 15 figure
A model of impairment and functional limitation in rheumatoid arthritis
BACKGROUND: We have previously proposed a theoretical model for studying physical disability and other outcomes in rheumatoid arthritis (RA). The purpose of this paper is to test a model of impairment and functional limitation in (RA), using empirical data from a sample of RA patients. We based the model on the disablement process framework. METHODS: We posited two distinct types of impairment in RA: 1) Joint inflammation, measured by the tender, painful and swollen joint counts; and 2) Joint deformity, measured by the deformed joint count. We hypothesized direct paths from the two impairments to functional limitation, measured by the shirt-button speed, grip strength and walking velocity. We used structural equation modeling to test the hypothetical relationships, using empirical data from a sample of RA patients recruited from six rheumatology clinics. RESULTS: The RA sample was comprised of 779 RA patients. In the structural equation model, the joint inflammation impairment displayed a strong significant path toward the measured variables of joint pain, tenderness and swelling (standardized regression coefficients 0.758, 0.872 and 0.512, P ≤ 0.001 for each). The joint deformity impairment likewise displayed significant paths toward the measured upper limb, lower limb, and other deformed joint counts (standardized regression coefficients 0.849, 0.785, 0.308, P ≤ 0.001 for each). Both the joint inflammation and joint deformity impairments displayed strong direct paths toward functional limitation (standardized regression coefficients of -0.576 and -0.564, respectively, P ≤ 0.001 for each), and explained 65% of its variance. Model fit to data was fair to good, as evidenced by a comparative fit index of 0.975, and the root mean square error of approximation = 0.058. CONCLUSION: This evidence supports the occurrence of two distinct impairments in RA, joint inflammation and joint deformity, that together, contribute strongly to functional limitations in this disease. These findings may have implications for investigators aiming to measure outcome in RA
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