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Search Results: 1 - 10 of 115267 matches for " Melisa; Mendoza-Brice?o "
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Investigación de Blastocystis sp. en agua de consumo humano en una población escolar de la zona rural del estado Mérida-Venezuela
Flores-Carrero,Ana Deixy; Pe?a-Contreras,Zulma; Dávila-Vera,Delsy; Colmenares-Sulbarán,Melisa; Mendoza-Briceo,Rosa Virginia;
Kasmera , 2011,
Abstract: in order to determine the presence of blastocystis sp. in drinking water at a rural school in merida, 36 water samples were collected from natural sources that feed the distribution tank and faucets during the months of september, 2008, february and december, 2009, and may, 2010. samples were processed using the technique proposed by suresh et al. (2005). all samples were negative. these results suggest that the water was exempt from blastocystis or that the quantity of viable cysts present in the samples was very low, not permitting reproduction in the culture. this report suggests the importance of using more sensitive techniques to detect low amounts of the organism in drinking water. the study of student water consumption habits at the rural school showed that more than half the population consume boiled water; probably, they are aware that the water source has not been treated for drinking.
Estructuras solitarias de amplitud arbitraria en plasmas a dos temperaturas electrónicas con iones fríos
Mendoza-Briceo, C. A;Luna-Cardozo, M;
Revista mexicana de física , 2006,
Abstract: the compresive and rarefactive ion-acoustic solitary wave of arbitrary amplitude which have been found to coexist in two-electron temperature plasmas, are investigated by the pseudo potential approach. an expression of this pseudo potential have been derived and the range of the parameters space ms, α and μ for the coexistence of these solitary structures are found for the case of cold ion plasma. aditionally, the effect of the parameters space on wave amplitude was studied.
Estructuras solitarias de amplitud arbitraria en plasmas a dos temperaturas electrónicas con iones fríos
C. A. Mendoza-Briceo,M. Luna-Cardozo
Revista mexicana de física , 2006,
Abstract: Este trabajo investiga, utilizando la aproximación del pseudo potencial de Sagdeev, las ondas solitarias iónico-acústicas compresivas y rarefactivas de amplitud arbitraria, las cuales han sido encontradas en plasmas a dos temperaturas electrónicas. Se deriva la expresión del pseudo potencial y se obtienen los rangos de los parametros Ms, α y μ, de coexistencia de las ondas solitarias compresivas y rarefactivas para el caso de un plasma ionico frío. Además se estudió el efecto de estos parámetros sobre la amplitud de las ondas.
Synaptic dimorphism in Onychophoran cephalic ganglia
Pe?a-Contreras,Z; Mendoza-Briceo,R.V;
Revista de Biología Tropical , 2007,
Abstract: the taxonomic location of the onychophora has been controversial because of their phenotypic and genotypic characteristics, related to both annelids and arthropods. we analyzed the ultrastructure of the neurons and their synapses in the cephalic ganglion of a poorly known invertebrate, the velvet worm peripatus sedgwicki, from the mountainous region of el valle, mérida, venezuela. cephalic ganglia were dissected, fixed and processed for transmission electron microscopy. the animal has a high degree of neurobiological development, as evidenced by the presence of asymmetric (excitatory) and symmetric (inhibitory) synapses, as well as the existence of glial cell processes in a wide neuropile zone. the postsynaptic terminals were seen to contain subsynaptic cisterns formed by membranes of smooth endoplasmic reticulum beneath the postsynaptic density, whereas the presynaptic terminal showed numerous electron transparent synaptic vesicles. from the neurophylogenetic perspectives, the ultrastructural characteristics of the central nervous tissue of the onychophora show important evolutionary acquirements, such as the presence of both excitatory and inhibitory synapses, indicating functional synaptic transmission, and the appearance of mature glial cells. rev. biol . trop. 55 (1): 261-267. epub 2007 march. 31.
Numerical simulation of the cooling of a solar flare
César A. Mendoza-Briceo,Leonardo Sigalotti,Neyda Y. A?ez-Parra
Geofísica internacional , 2004,
Abstract: A one-dimensional hydrodynamics code is used to study the cooling of solar flares. The cooling of the flux tube is calculated for the case in which the atmosphere is initially in thermal equilibrium with a maximum temperature of about 107 K. As the system cools, the evolution of the temperature, density, and velocity is calculated as a function of height for different lengths of the loop. We use the cooling function proposed by Hildner (1974), extended to include temperatures lower than 104 K and the Bremsstrahlung effect for values higher than 106 K. It is found that the cooling time increases as the length of the loop is increased. Furthermore, if a spatially-varying energy source is allowed along the loop length, the cooling time differs from the case with no external heating. In particular, it is seen to decrease as the input heating concentrates at the base of the loop.
Synaptic dimorphism in Onychophoran cephalic ganglia
Z Pe?a-Contreras,R.V Mendoza-Briceo
Revista de Biología Tropical , 2007,
Abstract: The taxonomic location of the Onychophora has been controversial because of their phenotypic and genotypic characteristics, related to both annelids and arthropods. We analyzed the ultrastructure of the neurons and their synapses in the cephalic ganglion of a poorly known invertebrate, the velvet worm Peripatus sedgwicki, from the mountainous region of El Valle, Mérida, Venezuela. Cephalic ganglia were dissected, fixed and processed for transmission electron microscopy. The animal has a high degree of neurobiological development, as evidenced by the presence of asymmetric (excitatory) and symmetric (inhibitory) synapses, as well as the existence of glial cell processes in a wide neuropile zone. The postsynaptic terminals were seen to contain subsynaptic cisterns formed by membranes of smooth endoplasmic reticulum beneath the postsynaptic density, whereas the presynaptic terminal showed numerous electron transparent synaptic vesicles. From the neurophylogenetic perspectives, the ultrastructural characteristics of the central nervous tissue of the Onychophora show important evolutionary acquirements, such as the presence of both excitatory and inhibitory synapses, indicating functional synaptic transmission, and the appearance of mature glial cells. Rev. Biol . Trop. 55 (1): 261-267. Epub 2007 March. 31. Estudiamos la ultraestructura de las neuronas y sus sinapsis del ganglio cefálico de un invertebrado poco conocido del phylum Onychophora: Peripatus sedgwicki de los Andes Venezolanos, utilizando para ello la microscopía electrónica de transmisión. La localización taxonómica de los onicóforos ha sido controversial debido a sus características fenotípicas y genotípicas que los relacionan tanto con los anélidos como con los artrópodos. Para este trabajo se estudió el ganglio cefálico de P. sedgwicki de la zona monta osa de El Valle, Mérida, Venezuela. El ganglio cefálico se localiza en la región anterior del animal y fue diseccionado, fijado y luego procesado para microscopía electrónica de transmisión. El estudio ultraestructural permitió observar el alto grado de desarrollo neurobiológico de este grupo. En el ganglio cefálico se observó una amplia zona neuropílica donde se constató la existencia de sinapsis químicas asimétricas y simétricas, las cuales corresponden con sinapsis excitatorias e inhibitorias respectivamente. Se pudo observar en los terminales sinápticos una formación cisternal subsináptica formada por membranas de retículo endoplásmico liso situada por debajo de la densidad postsináptica; también se constató la existencia de prolongaciones g
Estructuras solitarias de amplitud arbitraria en plasmas a dos temperaturas electrónicas con iones fríos
C.A. Mendoza-Briceo,M. Luna-Cardozo
Revista mexicana de física , 2006,
Abstract: The compresive and rarefactive ion-acoustic solitary wave of arbitrary amplitude which have been found to coexist in two-electron temperature plasmas, are investigated by the pseudo potential approach. An expression of this pseudo potential have been derived and the range of the parameters space Ms, and 1 for the coexistence of these solitary structures are found for the case of cold ion plasma. Aditionally, the effect of the parameters space on wave amplitude was studied.
Metabolitos secundarios de líquenes de la zona nival de la Sierra Nevada de Mérida-Venezuela y su papel en la absorción de la radiación ultravioleta
Palacios-Prü, Ernesto,Mendoza-Briceo, Rosa Virginia,Pe?a-Contreras, Zulma,Dávila-Vera, Delsy
Anales del Jardín Botánico de Madrid , 2008,
Abstract: Photochemical analyses of secondary compounds in lichens from the venezuelan andean snow zone were carried out in order to know the absorbance capacity of UV radiation at the UVA, UVB and UVC ranges and to determine its probable UV protective function. Spectrophotometric (UV) and fine layer chromatographic techniques (TLC) were utilized to separate and identify the compounds. UV radiation values were obtained from the Red Bioclimática del Parque Nacional Sierra Nevada de Mérida which constitutes a program supported by the University of Los Andes, Venezuela. Results indicated the existence of 22 species of lichens at the snow zone; 55% of these species showed a strong resistance to UVC radiation, 95% to UVB radiation, whereas the 100% revealed a strong resistance to UVA radiation. The substances that have the highest resistance to UVA and UVB radiation are characterized by having ester bonds among phenolic units depsids and constitute the most abundant products in lichens, whereas the substances having both ester and ether bonds among the two phenolic units depsidones revealed a higher capacity to absorb UVC radiation that could indicate a primitive origin. Se hicieron análisis fotoquímicos de compuestos secundarios presentes en líquenes de la zona nival andina venezolana con la finalidad de conocer su capacidad de absorber las radiaciones ultravioletas UVA, UVB y UVC e inferir en la probable función protectora de estos compuestos ante estas radiaciones. Para la separación e identificación de sustancias se utilizaron técnicas espectrofotométricas (UV) y técnicas de cromatografía de capa fina (TLC). Para el estudio climático de la zona nival se utilizaron registros de la Red Bioclimática del Parque Nacional Sierra Nevada de Mérida, Programa de la Universidad de Los Andes, Venezuela. Los resultados revelaron que, de las 22 especies encontradas, el 55% presentó una resistencia potencial a la radiación UVC, el 95% a la radiación UVB y el 100% a la radiación UVA. Entre las sustancias identificadas, las que presentaron mayor resistencia a las radiaciones UVA y UVB se caracterizan por presentar enlaces tipo éster entre las unidades fenólicas (dépsidos) y constituyen los productos más abundantes en estos líquenes. Mientras que, las sustancias con enlaces tipo éster y éter entre las dos unidades fenólicas (depsidonas), tienen alta capacidad de absorber radiación UVC, lo cual sugiere que el fenómeno de protección podría ser de origen primitivo.
Effects of Aeromonas caviae co-cultured in mouse small intestine
Longa-Briceo,Aurora; Pe?a-Contreras,Zulma; Dávila-Vera,Delsy; Mendoza-Briceo,Rosa Virginia; Palacios-Prü,Ernesto;
Interciencia , 2006,
Abstract: the ultrastructural aspects generated by the interaction between two strains of aeromonas caviae with mouse intestinal mucosa are described. one of the strains was isolated from an asymptomatic patient and the other one from a patient with diarrhea. both strains were separately inoculated in closed cylinders of mouse small intestine and the whole preparations were incubated in eagle?s culture medium. the intestinal cylinders were divided into two groups, one was incubated for 24h and the other for 48h. samples of the co-cultures were processed for analysis using high resolution light microscopy and transmission electron microscopy. the strain isolated from the asymptomatic patient showed variable alterations in the intestinal mucosa, according to the different periods of incubation, whereas the one obtained from the patient with diarrhea always produced severe enteropathogenic effects
Experimental toxicity of Aeromonas spp. In mouse?s small intestine: Ultrastructural aspects
Longa-Briceo,Aurora; Pe?a-Contreras,Zulma; Dávila-Vera,Delsy; Mendoza-Briceo,osa Virginia; Palacios-Prü?,Ernesto;
Interciencia , 2008,
Abstract: ultrastructural aspects of mouse small intestinal tissue cultures infected with aeromonas spp. strains are described. high resolution light and transmission electron microscopy were used to assess the bacterial pathogenic mechanism, the ultrastructural changes that take place during the colonization of the intestinal tract and the interaction of aeromonas spp. with the host epithelium. after 24h of culture, chains of vesicles were seen on the outer surface of the aeromonas? membrane. the vesicles were also found on the enterocyte surface. after 48h of culture, lysis of the epithelial intestinal cells, mononuclear phagocytic cells, phagocytic eosinophils and phagocyted aeromonas were observed.
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