3,648 research outputs found
Environmental Education and Ecotourists: Experience from the Yucatan Coast, Mexico
Ecotourism is a tourism modality intricately linked to the principles of sustainability, due to its natural offer component and environmental education. The objective of this research is to evaluate the perception of ecotourists present on the coast of Yucatan. From a regional approach, the author selected twenty-five community-based ecotourism ventures (CBET) present in the area and analysed the perception of ecotourists through a questionnaire and its respective statistical analysis with nonparametric tests, and developed a general profile of the ecotourist applying a sociodemographic segmentation and based on a geographical segmentation the author compared the perceptions of two populations: national ecotourists and international ecotourists. The data reveal that the profile of the ecotourist on the coast of Yucatan is similar to that postulated in the literature. In terms of environmental perception the author found a significant difference in both populations, and believed that this difference is because the international market is more critical and demanding. In addition, areas of opportunity were documented in the CBETs in the way they carry out their environmental communication. The author concluded that ecotourism in the region is still an activity in consolidation and although it presents great achievements. It is still not possible to qualify it as a sustainable activity. We call for continuing deepening the studies of ecotourism demand and evaluation of perception, through comparative, longitudinal studies and with new variables that allow new test statistics, to contribute new elements to the ecotourism debate
Polymeric templating synthesis of anatase TiO₂ nanoparticles from low-cost inorganic titanium sources
A novel facile and cost-effective synthesis method for anatase TiO₂ nanoparticles has been developed by using poly-acrylic acid hydrogel as template at room temperature. The newly developed synthesis method avoids the use of hazardous reagents and/or hydrothermal steps, and enables production of highly active TiO₂ nanoparticles from low cost inorganic titanium sources. The synthesized TiO₂ nanoparticles have been studied in several applications including dye-sensitized solar cells as a photoanode as well as in organics degradation of methyl orange in aqueous media. Good photocatalytic performances were obtained in both applications
CXCL12-induced neurotoxicity critically depends on NMDA receptor-gated and L-type Ca2+ channels upstream of p38 MAPK.
BackgroundThe chemokine receptor CXCR4 (CD184) and its natural ligand CXCL12 contribute to many physiological processes, including decisions about cell death and survival in the central nervous system. In addition, CXCR4 is a co-receptor for human immunodeficiency virus (HIV)-1 and mediates the neurotoxicity of the viral envelope protein gp120. However, we previously observed that CXCL12 also causes toxicity in cerebrocortical neurons but the cellular mechanism remained incompletely defined.MethodsPrimary neuronal-glial cerebrocortical cell cultures from rat were exposed to a neurotoxicity-inducing CXCL12 concentration for different times and the activity of the stress-associated mitogen-activated protein kinase p38 (p38 MAPK) was assessed using an in vitro kinase assay. Neurotoxicity of CXCL12 and cellular localization of p38 MAPK was analyzed by immunofluorescence microscopy. Pharmacological inhibition of NMDA-type glutamate receptor-gated ion channels (NMDAR) of L-type Ca2+ channels was employed during 12- and 24-h exposure to neurotoxic amounts of CXCL12 to study the effects on active p38 MAPK and neuronal survival by Western blotting and microscopy, respectively. Neurotoxicity of CXCL12 was also assessed during pharmacological inhibition of p38 MAPK.ResultsHere, we show that a neurotoxic amount of CXCL12 triggers a significant increase of endogenous p38 MAPK activity in cerebrocortical cells. Immunofluorescence and Western blotting experiments with mixed neuronal-glial and neuron-depleted glial cerebrocortical cells revealed that the majority of active/phosphorylated p38 MAPK was located in neurons. Blockade of NMDAR-gated ion channels or L-type Ca2+ channels both abrogated an increase of active p38 MAPK and toxicity of CXCL12 in cerebrocortical neurons. Inhibition of L-type Ca2+ channels with nimodipine kept the active kinase at levels not significantly different from baseline while blocking NMDAR with MK-801 strongly reduced phosphorylated p38 MAPK below baseline. Finally, we confirmed that directly blocking p38 MAPK also abrogated neurotoxicity of CXCL12.ConclusionsOur findings link CXCL12-induced neuronal death to the regulation of NMDAR-gated ion channels and L-type Ca2+ channels upstream of p38 MAPK activation
Affine semigroups having a unique Betti element
We characterize affine semigroups having one Betti element and we compute
some relevant non-unique factorization invariants for these semigroups. As an
example, we particularize our description to numerical semigroups.Comment: 8 pages, 1 figure. To appear in Journal of Algebra and its
Application
Tuning the proximity effect in a superconductor-graphene-superconductor junction
We have tuned in situ the proximity effect in a single graphene layer coupled
to two Pt/Ta superconducting electrodes. An annealing current through the
device changed the transmission coefficient of the electrode/graphene
interface, increasing the probability of multiple Andreev reflections. Repeated
annealing steps improved the contact sufficiently for a Josephson current to be
induced in graphene.Comment: Accepted for publication in Phys. Rev.
Serviço de avaliação genética de reprodutores ovinos. S.A.G.R.O.: resultados de 1998.
Na ovinocultura tipo carne, a premência na busca de um produto com qualidade, em quantidade abundante no menor espaço de tempo possível, é uma realidade para aqueles produtores que desejarem abarcar uma fatia no mercado tão cobiçado da "proteína vermelha".bitstream/item/109844/1/SERVICO-DE-AVALIACAO-GENETICA.pd
Triple-Star Candidates Among the Kepler Binaries
We present the results of a search through the photometric database of
eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for
evidence of hierarchical triple star systems. The presence of a third star
orbiting the binary can be inferred from eclipse timing variations. We apply a
simple algorithm in an automated determination of the eclipse times for all
2157 binaries. The "calculated" eclipse times, based on a constant period
model, are subtracted from those observed. The resulting O-C (observed minus
calculated times) curves are then visually inspected for periodicities in order
to find triple-star candidates. After eliminating false positives due to the
beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39
candidate triple systems were identified. The periodic O-C curves for these
candidates were then fit for contributions from both the classical Roemer delay
and so-called "physical" delay, in an attempt to extract a number of the system
parameters of the triple. We discuss the limitations of the information that
can be inferred from these O-C curves without further supplemental input, e.g.,
ground-based spectroscopy. Based on the limited range of orbital periods for
the triple star systems to which this search is sensitive, we can extrapolate
to estimate that at least 20% of all close binaries have tertiary companions.Comment: 19 pages, 13 figures, 3 tables; ApJ, 2013, 768, 33; corrected Fig. 7,
updated references, minor fixes to tex
The frobenius problem for generalized repunit numerical semigroups
In this paper, we introduce and study the numerical semigroups generated by {a1, a2, . . .} ⊂ N such that a1 is the repunit number in base b > 1 of length n > 1 and ai − ai−1 = a bi−2, for every i ≥ 2, where a is a positive integer relatively prime with a1. These numerical semigroups generalize the repunit numerical semigroups among many others. We show that they have interesting properties such as being homogeneous
and Wilf. Moreover, we solve the Frobenius problem for this family, by giving a closed formula for the Frobenius number in terms of a, b and n, and compute other usual invariants such as the Ap´ery sets,
the genus or the type
Riesgo moral y contratos: cierta evidencia experimental
This paper shows one type of asymmetric information problems, their theoretical implications, the design of contracts that mitigate them, as well as some experimental evidence. Furthermore, by extrapolating the results, the paper tries to illustrate certain macroeconomic implications obtained under a controlled environment.moral risk, contracts, experimental evidence, asymmetric information
Arithmetic varieties of numerical semigroups
In this paper we present the notion of arithmetic variety for numerical
semigroups. We study various aspects related to these varieties such as the
smallest arithmetic that contains a set of numerical semigroups and we exhibit
the root three associated with an arithmetic variety. This tree is not locally
finite; however, if the Frobenius number is fixed, the tree has finitely many
nodes and algorithms can be developed. All algorithms provided in this article
include their (non-debugged) implementation in GAP.Comment: 15 page
- …