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Search Results: 1 - 10 of 398440 matches for " F.J. Espinoza-Beltran "
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Caracterización de nanopartículas magnéticas de CoFe2o4 y CoZnFe2O4 preparadas por el método de coprecipitación química
J. Lopeza,F.J. Espinoza-Beltran,G. Zambrano,M.E. Gómez
Revista mexicana de física , 2012,
Abstract: Por el método de coprecipitación química a partir de sales de Co(II), ZnSO4 y Fe(III), en un medio alcalino preparamos nanopartículas magnéticas de CoFe2O4 y de CoZnFe2O4. Las muestras en polvo de CoFe2O4 las caracterizamos estructuralmente, por difracción de rayos X, mostrando la presencia del pico m′as intenso en 2μ = 41.3928± (Co K 1) correspondiente a la orientación cristalográfica (311) de la fase espinel inversa del CoFe2O4 El tama o medio del cristal de las nanopartículas de CoFe2O4 y CoZnFe2O4 determinado a partir del ancho del pico a la mitad de la altura de la reflexión del pico (311) usando la aproximación de Scherrer fue calculado en 11.4 y 7.0 (§ 0.2) nm, respectivamente. Estudios de Microscopia Electrónica de Transmisión (TEM) permitieron determinar el tama o de las nanopartículas de CoZnFe2O4. La espectroscopia de infrarrojo con transformada de Fourier FTIR fue usada para confirmar la formación de enlaces Fe O, permitiendo identificar la presencia de la estructura espinel de la ferrita. Las propiedades magn′eticas fueron investigadas usando un magnetómetro de muestra vibrante (VSM), a temperatura ambiente. Aquí, la muestra presento un comportamiento superparamagnético, determinado por el ciclo de histéresis. Por último, debido a que el ciclo de histéresis de la ferrita de CoZnFe2O4 es muy peque o, las nanopartículas magnéticas pueden ser consideradas como un material magnético blando. Estas nanopartículas magnéticas tienen interesantes aplicaciones tecnológicas en biomedicina dado su biocompatibilidad, en nanotecnología y en la preparación de ferrofluidos.
Propiedades ferroeléctricas de películas delgadas de GeSbTe
Gervacio Arciniega, J.J.;Prokhorov, E.;Espinoza Beltrán, F.J.;
Revista mexicana de física , 2011,
Abstract: the aim of this work is to investigate and compare ferroelectrical properties of thin gesbte films with composition ge4sb1te5 (with well defined ferroelectrical properties) and ge2sb2te5 using impedance, optical reflection, xrd, dsc and piezoresponse force microscopy techniques. the temperature dependence of the capacitance in both materials shows an abrupt change at the temperature corresponding to ferroelectric-paraelectric transition and the curie-weiss dependence. in ge2sb2te5 films this transition corresponds to the end from a nacl-type to a hexagonal transformation. piezoresponse force microscopy measurements found ferroelectric domains with dimension approximately equal to the dimension of grains.
Propiedades ferroeléctricas de películas delgadas de GeSbTe
J.J. Gervacio Arciniega,E. Prokhorov,F.J. Espinoza Beltrán
Revista mexicana de física , 2011,
Abstract: El objetivo de este trabajo es investigar y comparar las propiedades ferroeléctricas de películas delgadas de Ge4Sb1Te5 (con propiedades ferroeléctricas bien definidas) y Ge2Sb2Te5 usando técnicas de impedancia, reflexión óptica, XRD, DSC y de microscopia de fuerza por piezorrespuesta. La dependencia de la capacitancia con la temperatura en ambos materiales muestra un cambio abrupto a la temperatura que corresponde a la transición ferroeléctrico-paraeléctrico y la dependencia tipo Curie-Weiss. En las películas de Ge2Sb2Te5 esta transición corresponde al fin de la transformación de la estructura tipo NaCl a la hexagonal. La microscopia de fuerza por piezorespuesta halló dominios ferroeléctricos de dimensiones aproximadamente iguales a la de los granos.
Desarrollo de un nanomaterial base TiFe, como electrodo para baterías recargables tipo NiMH, obtenido por aleado mecánico de alta energía
López-Báez, I.;Espinoza-Beltrán, F.J.;Barreiro-Rodríguez, G.;
Revista mexicana de física , 2006,
Abstract: in this work the development of electrodes type a-b (a: ti; b: fe, co, ni) is presented starting from nanostructured alloys for rechargeable batteries also secondary calls. the purpose of the employment of a metallic alloy in form of nanometric powder like electrode is that its great surface allows making more efficient the electrochemical processes. the methodology that is used for the development of these materials consists in: to use the high energy mechanic alloying, because it is very practical and we can obtain a grain size of nanometric order in relatively short times; to examine their physiochemical characteristic (morphology, composition); to determine the hydrogen absorption/desorption behavior; and to evaluate their yield characteristics like hydride electrodes in an electrolytic cell.
The use of ketamine in cancer palliation
F.J Smith
Southern African Journal of Anaesthesia and Analgesia , 2007,
Abstract: Cancer pain is caused by continuous tissue injury, which may be due to surgery, infiltration of the surrounding organs including nerves, as well as from mucositis after chemo- or radiotherapy. Nerve involvement, chronic opioid therapy and continuous nociceptive input cause hyperalgesia. Chronic stimulation of the dorsal root neurons leads to hyperalgesia and resistance (tolerance) to μ opioid analgesics (hyperalgesia-tolerance). The NMDA receptor antagonist ketamine reverses tolerance to morphine. Ketamine aggravates the sedative effect of opioids and other drugs used for neuropathic pain, such as sodium valproate and amitriptyline. The pain experienced by cancer patients needs a multimodal approach, including ketamine. Although ketamine appears to be a useful analgesic, the literature dealing with ketamine as an analgesic lacks randomised controlled trials.
Soil Patterns Associated with the Major Geological Units of the Kruger National Park
F.J. Venter
Koedoe : African Protected Area Conservation and Science , 1986, DOI: 10.4102/koedoe.v29i1.525
Abstract: The dominant soil types of the Kruger National Park and their interrelationships with parent material, topography and climate are discussed. The geogenetic and topogenetic nature of the soils are manifested in the strong correlations between recurrent soil patterns, major geological units and terrain morphology. The soils are categorised into seven major classes on the basis of the parent material from which they developed. General soil patterns within the major classes are discussed.
Soeklig op die Klerksdorp-kompleks
F.J. Potgieter
Koers : Bulletin for Christian Scholarship , 1969, DOI: 10.4102/koers.v37i2.1302
Abstract: Al vyf blanke universiteite van Transvaal is op die een of ander wyse gemoeid met die beplanningsnavorsingsprojek in die Klerksdorpse gebied wat op die oomblik aan die gang is. Vir dié navorsing het die Staat R18,000 bewillig, verskillende myngroepe altesaam R6,000, en plaaslike owerhede R1,500. En in die komitee wat beheer oor die navorsing uitoefen, is twee staatsdepartemente verteenwoordig, afgesien natuurlik van die verteenwoordiging van die betrokke universiteite.
Geografie en sy verhouding tot beplanning
F.J. Potgieter
Koers : Bulletin for Christian Scholarship , 1967, DOI: 10.4102/koers.v35i2.1374
Abstract: As die geografie hom besig hou met die studie van die aarde as woonplek van die mens, soos die meeste geograwe waarskynlik aanvaar, is dit logies dat die klem in die vak van tyd tot tyd sal verskuif namate die mens se tegnologiese vordering enersyds verandering aanbring in die onderlinge verhoudings van die samestellende dele van die menslike omgewing, en andersyds in die steeds veranderende wyse waarop die mens die aarde bewoon.
Constructing a spreadsheet simulation model of Chuck-a-luck: An application of logical functions
Rispoli, F.J.
Spreadsheets in Education , 2004,
Abstract: Chuck-a-luck is an inviting game played at carnivals in the Midwestern United States and England. A player picks a number from 1 to 6 and an operator rolls three dice. If the number chosen by the player comes up on all three dice, the player wins $3; if it comes up on two of the three dice, the player wins $2; if it comes up on one of the three dice, the player wins $1. Only if the chosen number does not appear at all does the player pay anything, which is just $1. We would like to know if Chuck-a-luck is a fair game, and what is its average payoff? In addition, we are interested in simulating this game using logical functions built into spreadsheet software as well as other computer programming languages.
i=0 (Information has no intrinsic meaning)
F.J. Miller
Information Research: an international electronic journal , 2002,
Abstract: This paper was written mainly to help identify some contradictions that can be found in the notion of knowledge management though its application is wider-ranging. The author suggests that knowledge - that is to say 'what we know' - can scarcely be understood and managed even by ourselves, much less by means of sophisticated information and communications (ie groupware and shareware) technologies. We have progressed from the industrial age through the information age into what is being promoted as the 'golden age' of knowledge and, in the process, we've been led to believe that information contains meaning - rather than just standing for, provoking or evoking meaning in others. The paper argues that unless we take the trouble to face and understand the significance and implications of i=0 (ie that information has no intrinsic meaning) and that knowledge is the uniquely human capability of making meaning from information - ideally in face-to-face relationships with other human beings - we may never emerge into any 'golden' age at all! The consequences of i=0 for communications, learning, safety, quality, management (itself), and winning work are also discussed.
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