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Search Results: 1 - 10 of 4818 matches for " Alfonso Carriazo "
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The curvature tensor of almost cosymplectic and almost Kenmotsu (κ,μ,ν)-spaces
Alfonso Carriazo,Verónica Martín-Molina
Mathematics , 2012, DOI: 10.1007/s00009-013-0246-4
Abstract: We study the Riemann curvature tensor of (\kappa,\mu,\nu)-spaces when they have almost cosymplectic and almost Kenmotsu structures, giving its writing explicitly. This leads to the definition and study of a natural generalisation of the contact metric (\kappa,\mu,\nu)-spaces. We present examples or obstruction results of these spaces in all possible cases.
Generalized (κ,μ)-space forms
Alfonso Carriazo,Verónica Martín-Molina,Mukut Mani Tripathi
Mathematics , 2008, DOI: 10.1007/s00009-012-0196-2
Abstract: Generalized (\kappa ,\mu)-space forms are introduced and studied. We examine in depth the contact metric case and present examples for all possible dimensions. We also analyse the trans-Sasakian case.
The curvature tensor of (\ka,μ,ν)-contact metric manifolds
Kadri Arslan,Alfonso Carriazo,Verónica Martín-Molina,Cengizhan Murathan
Mathematics , 2011, DOI: 10.1007/s00605-015-0762-3
Abstract: We study the Riemann curvature tensor of (\kappa,\mu,\nu)-contact metric manifolds, which we prove to be completely determined in dimension 3, and we observe how it is affected by D_a-homothetic deformations. This prompts the definition and study of generalized (\kappa,\mu,\nu)-space forms and of the necessary and sufficient conditions for them to be conformally flat.
Sasaki-Einstein and paraSasaki-Einstein metrics from (κ,μ)-structures
Beniamino Cappelletti Montano,Alfonso Carriazo,Verónica Martín-Molina
Mathematics , 2011, DOI: 10.1016/j.geomphys.2013.05.001
Abstract: We prove that any non-Sasakian contact metric (\kappa,\mu)-space admits a canonical \eta-Einstein Sasakian or \eta-Einstein paraSasakian metric. An explicit expression for the curvature tensor fields of those metrics is given and we find the values of \kappa and \mu for which such metrics are Sasaki-Einstein and paraSasaki-Einstein. Conversely, we prove that, under some natural assumptions, a K-contact or K-paracontact manifold foliated by two mutually orthogonal, totally geodesic Legendre foliations admits a contact metric (\kappa,\mu)-structure. Furthermore, we apply the above results to the geometry of tangent sphere bundles and we discuss some topological and geometrical properties of (\kappa,\mu)-spaces related to the existence of Eistein-Weyl and Lorentzian Sasakian Einstein structures.
Laboratory projects using inquiry-based learning: an application to a practical inorganic course
Carriazo, José G.;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000600029
Abstract: this paper reports how laboratory projects (lp) coupled to inquiry-based learning (ibl) were implemented in a practical inorganic chemistry course. several coordination compounds have been successfully synthesised by students according to the proposed topics by the lp-ibl junction, and the chemistry of a number of metals has been studied. qualitative data were collected from written reports, oral presentations, lab-notebook reviews and personal discussions with the students through an experimental course with undergraduate second-year students at the universidad nacional de colombia during the last 5 years. positive skills production was observed by combining lp and ibl. conceptual, practical, interpretational, constructional (questions, explanations, hypotheses), communicational, environmental and application abilities were revealed by the students throughout the experimental course.
Thermal and structural study of guava (Psidium guajava L) powders obtained by two dehydration methods
Osorio, Coralia;Carriazo, José G.;Barbosa, Helber;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000400016
Abstract: two food products (powders) were obtained by hot-air drying or lyophilisation methods on the whole guava fruits. the powders were characterised by sensory and thermal analyses (tga-dsc), infrared spectroscopy (ir), x-ray diffraction (xrd) and scanning electron microscopy (sem). thermal, morphological and structural characterisations showed a similar behaviour for the two solids. tga-dsc and ir showed the presence of pectin as the main constituent of solids. a semi-crystalline profile was evidenced by xrd, and lamellar/spherical morphologies were observed by sem. sensory analyses revealed an aroma highly related to guava. these value-added food products are an alternative to process guava and avoid loss during postharvest handling.
CARACTERIZACIóN ESTRUCTURAL Y TEXTURAL DE UNA BENTONITA COLOMBIANA
Carriazo,José; Molina,Rafael; Moreno,Sonia;
Revista Colombiana de Química , 2007,
Abstract: in the present work a colombian bentonite (from valle del cauca) was characterized by x-ray diffraction, spectroscopic techniques (ir, nmr and epr) and textural analysis. the results indicate that dioctahedral (aluminian) smectite is the principal component in the natural material. in addition, both 29si nmr and 27al nmr analysis reveal the isomorphous substitution of al3+ by si4+ in the tetrahedral sheet. the epr study shows iron (iii) in octahedral sheet positions of the clay mineral besides ?nanoclusters? probably in oxides or oxyhydroxides form. the textural analysis indicates that the bentonite is predominantly a mesoporous material.
EVALUACIóN DEL EFECTO DE LA IMPREGNACIóN DE PLATINO SOBRE LAS CARACTERíSTICAS SUPERFICIALES Y ESTRUCTURALES DE UNA ZEOLITA Y
Carriazo,José; Barrera,Mario; Almanza,Ovidio;
Revista Colombiana de Química , 2007,
Abstract: the present paper shows the evaluation of texture, surface and structure changes on a zeolite y employed in the synthesis of solids based on supported platinum. the structure features were analyzed by x-ray diffraction (xrd) whereas the texture and morphologic properties were studied from nitrogen adsorption isotherms (77k) and scanning electron microscopy (sem). in addition, fractal dimension and adsorption potential distribution were determinedall solids. the results show that the synthesis process induces the microporosity formation, maintaining the zeolite structure and without important topographic or energetic alterations on the surface.
CARACTERIZACIóN TéRMICA Y ESPECTROSCóPICA DE ARCILLAS PILARIZADAS CON SOLUCIONES POLIHIDROXOCATIóNICAS DE Al, Ce, Fe
Carriazo,José; Molina,Rafael; Moreno,Sonia;
Revista Colombiana de Química , 2008,
Abstract: this work shows the characterization by ir spectroscopy, thermogravimetric analysis (tga), differential thermal analysis (dta) and nuclear magnetic resonance spectroscopy (29sinmrand 27al nmr) of a set of pillared clays synthesized with al, al-fe, al-ce or al-ce-fe polyhydroxocationic solutions. tgadta analyses indicate a favorable thermal effect (higher thermal stability) when ce, fe or ce-fe are added. ir and 29si nmr results reveal a probable formation of a bond between the alumina pillar and the clay (sio4)-tetrahedral sheet, whereas the 27al nmr does not evidence any isomorphous substitution of iron or cerium in the alumina pillars. moreover, by ir spectroscopy was not observed any structural difference between solids pillared with al and those pillared with al-ce, showing that cerium is possibly incorporated in an independent way to the alumina pillar.
Lactate dehydrogenase activity of rat epididymis and spermatozoa: Effect of constant light
RH Ponce,CS Carriazo,NT Vermouth
European Journal of Histochemistry , 2009, DOI: 10.4081/1624
Abstract: During its passage through the epididymis, the gamete undergoes a process of “maturation” leading to the acquisition of its fertilizing ability. The epididymis displays regional variations in the morphology and metabolic properties of its epithelium which are relevant for the progressive development of mature sperm characteristics. The epididymis has spontaneous peristaltic contractions and receives sympathetic innervation that is modulated by melatonin, a hormone synthesized and released by the pineal gland. Constant lighting disrupts melatonin synthesis and secretion. We have studied the effect of constant light on lactate dehydrogenase (LDH; EC 1.1.1.27) and its isozyme C4 activities and protein content in whole epididymis, epididymal tissue and in spermatozoa from caput and cauda segments. Animals were exposed from birth to an illumination schedule of 14 h light: 10 h dark (group L:D). At 60 days of age one group of animals was submitted to constant light over 50 days (group L:L). In order to test the fertilizing ability, the rats of each group were mated with soliciting estrous females. The percentage of pregnancies in females mated with males maintained in L:L was remarkably lower than those in females mated with males maintained in the L:D photoperiod (44% and 88% respectively). Constant light increased protein concentration and LDH activity in caput as well as in cauda of total epididymis. On the contrary, in epididymal tissue, the protein content decreased in both epididymal sections compared with controls. When enzymatic activity was expressed in Units per spermatozoa, constant light induced a significant reduction of total LDH and LDHC4 in caput and cauda spermatozoa while LDH activity of epididymal tissue was not affected. In spite of the decrease in LDH per sperm cell when rats were exposed to constant light, in total epididymis (epididymis tissue plus sperm cells content) and in spermatozoa, values of enzyme activities expressed per weight unit were higher than those of controls. This is explained by the increase in the amount of stored spermatozoa, both in caput and cauda, produced by exposure of animals to constant light.
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