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Search Results: 1 - 10 of 3905 matches for " Tomas Godoy "
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Existence and multiplicity of positive solutions for a singular problem associated to the p-Laplacian operator
Carlos Aranda,Tomas Godoy
Electronic Journal of Differential Equations , 2004,
Abstract: Consider the problem $$ -Delta_{p}u=g(u) +lambda h(u)quadhbox{in }Omega $$ with $u=0$ on the boundary, where $lambdain(0,infty)$, $Omega$ is a strictly convex bounded and $C^{2}$ domain in $mathbb{R}^{N}$ with $Ngeq2$, and 1 less than $pleq2$. Under suitable assumptions on $g$ and $h$ that allow a singularity of $g$ at the origin, we show that for $lambda$ positive and small enough the above problem has at least two positive solutions in $C(overline{Omega})cap C^{1}(Omega)$ and that $lambda=0$ is a bifurcation point from infinity. The existence of positive solutions for problems of the form $-Delta_{p}u=K(x) g(u)+lambda h(u)+f(x)$ in $Omega$, $u=0$ on $partialOmega$ is also studied.
Existence of strictly positive solutions for sublinear elliptic problems in bounded domains
Tomas Godoy,Uriel Kaufmann
Mathematics , 2013,
Abstract: Let $\Omega$ be a smooth bounded domain in $\mathbb{R}^{N}$ and let $m$ be a possibly discontinuous and unbounded function that changes sign in $\Omega$. Let $f:\left[ 0,\infty\right) \rightarrow\left[ 0,\infty\right) $ be a continuous function such that $k_{1}\xi^{p}\leq f\left(\xi\right) \leq k_{2}\xi^{p}$ for all $\xi\geq0$ and some $k_{1},k_{2}>0$ and $p\in\left(0,1\right) $. We study existence and nonexistence of strictly positive solutions for nonlinear elliptic problems of the form $-\Delta u=m\left(x\right) f\left(u\right) $ in $\Omega$, $u=0$ on $\partial\Omega$.
A minimax formula for the principal eigenvalues of Dirichlet problems and its applications
Tomas Godoy,Jean-Pierre Gossez,Sofia R. Paczka
Electronic Journal of Differential Equations , 2007,
Abstract: A minimax formula for the principal eigenvalue of a nonselfadjoint Dirichlet problem was established in [8,18]. In this paper we generalize this formula to the case where an indefinite weight is present. Our proof requires less regularity and, unlike that in [8,18], does not rely on semigroups theory nor on stochastic differential equations. It makes use of weighted Sobolev spaces. An application is given to the study of the uniformity of the antimaximum principle.
Seasonal Differences in Visitor Perceptions: A Comparative Study of Three Mountainous National Parks in Central Europe  [PDF]
Tomas Gorner, Martin Cihar
Journal of Environmental Protection (JEP) , 2011, DOI: 10.4236/jep.2011.28120
Abstract: This paper compares the views and attitudes of visitors to three key mountain national parks and Biosphere Reserves: Sumava National Park (Sumava NP, Czech Republic), Krkonose National Park (KRNAP, Czech Republic) and Karkonoski Park Narodowy (KPN, Poland). A large numbers of people visit these destinations both in the summer (e.g. hikers and cyclists) and in the winter (e.g. hikers and skiers), which threatens sustainability and creates problems regarding the management of these areas. A comprehensive understanding of visitor use, including visitors’ attitudes and perceptions, is fundamental for effective park management. Most research in these national parks is carried out during the summer season, therefore different results in the winter season are expected. Using a standardised socio-environmental survey we attempt to find seasonal differences between visitors and their opinions. A total of 2252 questionnaires were gathered. There were 13 common questions for these three national parks, three of them yielded significantly different results between the two seasons (visitors’ nationality, type of accommodation and financial costs). Other differences were detected in one or two national parks.
House Dust Mite Allergy Models—Reliability for Research of Airway Defensive Mechanisms  [PDF]
Tomas Buday, Jana Plevkova
Open Journal of Molecular and Integrative Physiology (OJMIP) , 2014, DOI: 10.4236/ojmip.2014.43004
Extensive research of respiratory physiology and diseases of the airways and lungs provides better understanding of mechanisms of diseases and it is a source of new data with potential clinical application. The majority of the data in the field of airway defensive reflexes were obtained from guinea pig model, as the most convenient one. Neurophysiology and neuropharma-cology of the cough reflex—which is exclusively mediated by the vagus nerve, share close similarities between guinea pigs and humans. The models used to study pathological processes and their influence on airway-defensive reflexes use sensitization with ovalbumin—the protein from chicken egg, which does not mimic allergies within human respiratory system. House dust mites (HDM) (Dermatophagoides pteronyssius and Dermatophagoides farinae) represent frequent human aeroallergens, however the HDM models are used considerably less than ovalbumin models. The primary objective of this review is to focus on already validated models of HDM-induced airway diseases to see, whether some of them are suitable to study mechanisms of peripheral cough plasticity in a condition of HDM-induced pathological processes. The main purpose of future use and validation of HDM model is to produce higher ability to translate the results obtained in animal models to human cough research.
Endogenous GUS-like activity in Capsicum chinense Jacq
Solís-Ramos,Laura Yesenia; González-Estrada,Tomas; Andrade-Torres,Antonio; Godoy-Hernández,Gregorio; Casta?o de la Serna,Enrique;
Electronic Journal of Biotechnology , 2010,
Abstract: the gene uida, codes for β-glucuronidase, which is one of the reporters more frequently utilized in transgenic plants. however, this can only be use if the selected organism does not present endogenous gus-like activity. in tissues of c. chinense we found a gus-like activity showing different levels of intensity. histochemical screening showed that endogenous gus-like activity decreased, or reduced significantly, in almost all tissues with exception of stament, when phosphate buffer was adjusted to ph 8. subsequently, c. chinense zygotic embryo explants were transient transformed with agrobacterium tumefaciens lba4404 (pcambia2301) and plantlets regenerated were histochemically stained in phosphate buffer ph 8. observations of incubated tissues of c. chinense regenerants showed blue staining, suggesting expression of uida. incubated tissues of non-transformed regenerants did not show blue staining in phosphate buffer ph 8. the results show that for transformation experiments of c. chinense with uida gene, ph 8 is recommended for histochemical staining.
Introducing Engineering Students to Historical/Cultural Perspectives through Story-Centered On-Line Learning  [PDF]
Luis A Godoy
Creative Education (CE) , 2011, DOI: 10.4236/ce.2011.22009
Abstract: Several authors argued that history of science should be an integral part of science education; however, there are many obstacles to carry out an implementation within this approach, including that lecturers normally lack a necessary historical background (a situation that is largely aggravated in engineering faculties), and the impossi- bility of including new courses or credits in an already tight curriculum. The development of on-line modules that engineering students can work outside their normal schedule of classes, introducing historical/cultural per- spectives, is presented in this paper. E-learning and knowledge management strategies are used in the context of science education at undergraduate and graduate levels. The approach is based on learning-by-doing in a virtual environment, and specifically presents story-centered activities, in which the student is faced with a problem and plays the role of an expert to provide a solution to the case. The specific case considered develops in the form of a controversy concerning the origin of the studies of column buckling. Two sets of information are available for navigation in the module: specific information that the student can explore (containing historical material di- rectly connected to the case provided), and more general information (providing the historical/cultural context to the problem). A first application has been made with civil engineering students, who had to write a two-page white paper as a consequence of their work on the problem. The interest generated in the participating students and the positive evaluation of their experience seems to indicate that this type of activity can serve to enhance traditional engineering lectures by incorporating a historical dimension. The present web-based approach could be extended to tackle similar conflicts in fields for which there is ample documentation available in the literature or in other historical episodes which may lead to rich discussions.
A Basis for Causal Scattering Waves, Relativistic Diffraction in Time Functions  [PDF]
Salvador Godoy, Karen Villa
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.710107
Abstract: Relativistic diffraction in time wave functions can be used as a basis for causal scattering waves. We derive such exact wave function for a beam of Dirac and Klein-Gordon particles. The transient Dirac spinors are expressed in terms of integral defined functions which are the relativistic equivalent of the Fresnel integrals. When plotted versus time the exact relativistic densities show transient oscillations which resemble a diffraction pattern. The Dirac and Klein-Gordon time oscillations look different, hence relativistic diffraction in time depends strongly on the particle spin.
Sphingoid Base Metabolism in Yeast: Mapping Gene Expression Patterns Into Qualitative Metabolite Time Course Predictions
Tomas Radivoyevitch
Comparative and Functional Genomics , 2001, DOI: 10.1002/cfg.106
Abstract: Can qualitative metabolite time course predictions be inferred from measured mRNA expression patterns? Speaking against this possibility is the large number of ‘decoupling’ control points that lie between these variables, i.e. translation, protein degradation, enzyme inhibition and enzyme activation. Speaking for it is the notion that these control points might be coordinately regulated such that action exerted on the mRNA level is informative of action exerted on the protein and metabolite levels. A simple kinetic model of sphingoid base metabolism in yeast is postulated. When the enzyme activities in this model are modulated proportional to mRNA expression levels measured in heat shocked yeast, the model yields a transient rise and fall in sphingoid bases followed by a permanent rise in ceramide. This finding is in qualitative agreement with experiments and is thus consistent with the aforementioned coordinated control system hypothesis.
Simulation Study of Building Integrated Solar Liquid PV-T Collectors
Tomas Matuska
International Journal of Photoenergy , 2012, DOI: 10.1155/2012/686393
Abstract: Influence of building integration of polycrystalline PV modules on their performance and potential for use of active liquid cooling by use of BIPV-T collectors has been investigated by simulation analysis with a detailed model. Integration of PV modules into building envelope could reduce the annual production of electricity by a rate above 5% and negatively influence lifetime due to thermal stresses induced by high operation temperatures above 100°C in the case of warm climate and above 90°C in moderate climate. Two configurations of unglazed PV-T collectors (low-tech, high-tech) and their ability to eliminate overheating of BIPV module have been discussed. Simulation study on combined heat and electricity production from given BIPV-T collectors has been presented for three typical applications (5°C: primary circuits of heat pumps; 15°C: cold water preheating; 25°C: pool water preheating). Thermal output of unglazed BIPV-T collectors is up to 10 times higher than electricity. Electricity production could be up to 25% higher than BIPV (without cooling) for warm climate and up to 15% in moderate climate. 1. Introduction Utilization of solar energy being a scarce energy source needs a large area of south-facing collecting surfaces. Rational use of building envelopes for the collection of solar energy and its conversion to required energy carrier results into integration of active solar devices into the building envelope structure and leads to multifunctional or hybrid solar collector configurations combining several purposes (heat and electricity generation, daylighting, and air-liquid) in a single unit [1]. The integration of solar collectors into building envelope instead of separate installation represents a transition from the concept of envelope considered as an energy loss to envelope being an energy source—energy active envelope—which actually means a way to solar active buildings. As photovoltaic modules are getting more and more common in sustainable buildings in order to compensate the electricity consumption by electricity production on site, the combination of photovoltaic and solar thermal technology in hybrid PV-T collectors could represent a step further with combined heat and power production (solar cogeneration). Standard commercial PV modules cannot convert more than 15% of incident solar radiation to electricity, the rest of energy is converted to waste heat which increases temperature of PV cell. The rise of PV cell temperature affects negatively the efficiency of photovoltaic solar/electricity conversion. Aesthetically preferred
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