Validação do método de análise de espectrofotómetria de absorção atómica/emissão de chama para determinação de minerais na fermentação de medronho (Arbustus unedo L.)

Dissertação mest., Qualidade em análises, Universidade do Algarve, 2006

Effects of sulphurization time on Cu2ZnSnS4 absorbers and thin films solar cells obtained from metallic precursors

We report the results of a study of the sulphurization time effects on Cu2ZnSnS4 absorbers and thin film solar cells prepared from dc-sputtered tackedmetallic precursors. Three different time intervals, 10 min, 30min and 60 min, at maximum sulphurization temperature were considered. The effects of this parameter' change were studied both on the absorber layer properties and on the final solar cell performance. The composition, structure, morphology and thicknesses of the CZTS layers were analyzed. The electrical characterization of the absorber layer was carried out by measuring the transversal electrical resistance of the samples as a function of temperature. This study shows an increase of the conductivity activation energy from 10 meV to 54meV for increasing sulphurization time from 10min to 60min. The solar cells were built with the following structure: SLG/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Ni:Al grid. Several ac response equivalent circuit models were tested to fit impedance measurements. The best results were used to extract the device series and shunt resistances and capacitances. Absorber layer's electronic properties were also determined using the Mott–Schottky method. The results show a decrease of the average acceptor doping density and built-in voltage, from 2.0 1017 cm−3 to 6.5 1015 cm−3 and from 0.71 V to 0.51 V, respectively, with increasing sulphurization time. These results also show an increase of the depletion region width from approximately 90 nm–250 nm.

Investigations into the determinations of hydride-forming elements

Analytical methods for the determination of trace amounts of germanium, tin and arsenic were established using hydride generation coupled with direct current plasma atomic emission spectrometry. A continuous gas flowing batch system for the hydride generation was investigated and was applied to the determination of germanium(Ge), tin(Sn), antimony(Sb) and lead(Pb) (Preliminary results suggest that it is also applicable to arsenic)As) ). With this system, the reproducibility of signals was improved and the determination was speeded up, compared with the conventional batch type hydride generation system. Each determination was complete within one minute. Interferences from a number of transition metal ions, especially from Pd(II), Pt(IV), Ni(II), Cu(II), Co(II), and Fe(II, III), have proven to be very serious under normal conditions, in the determination of germanium, tin, and arsenic. These interference effects were eliminated or significantly reduced in the presence of L-cystine or L-cysteine. Thus, a 10-1000 fold excess of Ni(II), Cu(II), Co(II), Fe(II), Pt(IV), Pd(II), etc. can be tolerated without interference, In the presence of L-cystine or L-cysteine, compared with absence of interference reducing agent. The methods for the determination of Ge, Sn, and As were examined by the analyses of standard reference materials. Interference effects from the sample matrix, for example, in transition metal-rich samples, copper, iron and steel, were eliminated by L-cystine (for As and Sn) and by LI cysteine (for Ge). The analysis of a number of standard reference materials gave excellent results of As and Sn contents in agreement with the certified values, showing there was no systematic interference. The detection limits for both germanium and tin were 20 pg ml- I . Preliminary studies were carried out for the determination of antimony and lead. Antimony was found to react with NaBH4, remaInIng from the previous determinations, giving an analytical signal. A reversed injection manner, i.e., injection of the NaBH4 solution prior to the analyte solution was used to avoid uncertainty caused by residual NaBH4 present and to ensure that an excess of NaB H4 was available. A solution of 0.4% L-cysteine was found to reduce the interference from selected transition metal ions, Co(II), Cu(II), Ni(II) and Pt(IV). Hydrochloric acid - hydrogen peroxide, nitric acid - ammonium persulphate, and potassium dichromate malic acid reaction systems for lead hydride generation were compared. The potassium dichromate - malic acid reaction medium proved to be the best with respect to reproducibility and minimal interference. Cu(II), Ni(II), and Fe(II) caused strong interference In lead determinations, which was not reduced by L-cysteine or Lcystine. Sodium citrate, ascorbic acid, dithizone, thiosemicarbazide and penicillamine reduced interferences to some extent. Further interference reduction studies were carried out uSIng a number of amino acids, glycine, alanine, valine, leucine and histidine, as possible interference reducing agents in the determination of germanium. From glycine, alanine, valine to leucine, the interference reduction effect in germanium determinations decreased. Histidine II was found to be very promising In the reduction of interference. In fact, histidine proved more efficient than L-cystine and L-cysteine In the reduction of interference from Ni(II) in the determination of germanium. Signal enhancement by easily ionized elements (EIEs), usually regarded as an interference effect in analysis by DCP-AES, was studied and successfully applied to advantage in improving the sensitivity and detection limit in the determination of As, Ge, Sn, Sb, and Pb. The effect of alkali and alkaline-earth elements on the determination of the above five hydride forming elements was studied. With the appropriate EIE, a signal enhancement of 40-115% was achieved. Linear calibration and good reproducibility were also obtained in the presence of EIEs. III

Lithium Containing Complex Metal Oxides and Metal phosphates:Investigations on their synthesis and various characterizations for rechargeable lithium battery applications

The work presented in the thesis is centered around two important types of cathode materials, the spinel structured LixMn204 (x =0.8to1.2) and the phospho -oIivine structured LiMP04 (M=Fe and Ni). The spinel system LixMn204, especially LiMn204 corresponding to x= 1 has been extensively investigated to understand its structural electrical and electrochemical properties and to analyse its suitability as a cathode material in rechargeable lithium batteries. However there is no reported work on the thermal and optical properties of this important cathode material. Thermal diffusivity is an important parameter as far as the operation of a rechargeable battery is concerned. In LixMn204, the electronic structure and phenomenon of Jahn-Teller distortion have already been established theoretically and experimentally. Part of the present work is an attempt to use the non-destructive technique (NDT) of photoacoustic spectroscopy to investigate the nature of the various electronic transitions and to unravel the mechanisms leading to the phenomenon of J.T distortion in LixMn204.The phospho-olivines LiMP04 (M=Fe, Ni, Mn, Co etc) are the newly identified, prospective cathode materials offering extremely high stability, quite high theoretical specific capacity, very good cycIability and long life. Inspite of all these advantages, most of the phospho - olivines especially LiFeP04 and LiNiP04 show poor electronic conductivity compared to LixMn204, leading to low rate capacity and energy density. In the present work attempts have been made to improve the electronic conductivity of LiFeP04 and LiNiP04 by adding different weight percentage MWNT .It is expected that the addition of MWNT will enhance the electronic conductivity of LiFeP04 and LiNiP04 with out causing any significant structural distortions, which is important in the working of the lithium ion battery.

Comment on "Reappraisal of experimental values of third-order elastic constants of some cubic semiconductors and metals"

In a recent paper A. S. Johal and D. J. Dunstan [Phys. Rev. B 73, 024106 (2006)] have applied multivariate linear regression analysis to the published data of the change in ultrasonic velocity with applied stress. The aim is to obtain the best estimates for the third-order elastic constants in cubic materials. From such an analysis they conclude that uniaxial stress data on metals turns out to be nearly useless by itself. The purpose of this comment is to point out that by a proper analysis of uniaxial stress data it is possible to obtain reliable values of third-order elastic constants in cubic metals and alloys. Cu-based shape memory alloys are used as an illustrative example.

El municipio

Este documento se inicia con el estudio del entorno m??s inmediato al ni??o: la calle, el barrio, la localidad, para luego ir ampliando su estudio a otros espacios como el municipio, la comunidad aut??noma, la regi??n, etc. Sigue el siguiente gui??n: esquema conceptual, bloques conceptuales, contenidos, actividades (relaci??n de actividades y gu??a de la visita al Ayuntamiento); se ofrecen ideas y materiales en forma de fichas para profundizar en el tema, del tipo de localizaci??n en un croquis, los servicios de un barrio, encuesta a los habitantes del barrio, localizaci??n en el plano, el concepto de Gij??n y sus parroquias, el censo, estudio de la poblaci??n, los impuestos municipales. El objetivo fundamental es dar a conocer el Ayuntamiento como ??rgano administrativo y gestor de los recursos del municipio. Este material se edita dentro de 'HABITAR', programa did??ctico para el estudio del medio, que ofert?? el Ayuntamiento de Gij??n a la comunidad educativa. El documento en s??, viene precedido por la presentaci??n de los principios educativos y otros de procedimiento que gu??an el programa.

Valoraci??n de la gravedad de las situaciones de desprotecci??n infantil por los profesionales de los servicios de protecci??n infantil

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CPA Comunicador Personal Adaptable

Premios de Accesibilidad ASPAYM 2009. Premios Sociedad de la Informaci??n 2008: Mejor iniciativa para la reducci??n de la brecha digital. Menci??n de honor en los Premios Nacionales de Innovaci??n Educativa 2004

CPA comunicador para autistas y TGDS

Menci??n honor??fica de Innovaci??n Educativa 2004

Una Investigació sobre la formació del pensament històric a través de les representacions històriques de l'alumnat

El treball que presentem recull els resultats d’una recerca sobre l’ensenyament i l’aprenentatge de la història a l’educació secundària. El professorat participant forma part del grup GREDICS (Grup de Recerca en Didàctica de les Ciències Socials), de la Universitat Autònoma de Barcelona, així com també professorat d’educació secundària de centres educatius de Catalunya. La recerca ha estat finançada dins el projecte ARIE de la Generalitat de Catalunya. Va començar el curs 2005-06 i ha continuat fins l’actualitat amb diversos projectes. L’objectiu fonamental d’aquesta recerca qualitativa ha estat indagar en els coneixements històrics dels/les adolescents al finalitzar l’educació obligatòria, saber com ho han aprés i com l’utilitzen per situar-se al seu món i en els seus projectes de futur. Ens hem centrat fonamentalment en les representacions històriques de l’alumnat, en especial les escrites, encara que a l’actualitat estem treballant amb altres tipus de representacions històriques, per exemple les audiovisuals que es poden produir per mitjà d’eines informàtiques

Funcionalidad y niveles de integraci??n de las TIC para facilitar el aprendizaje escolar de car??cter constructivista

Resumen tomado del autor

La formaci?? del professorat de p??rvuls segons les disposicions i reials decrets de la segona meitat del segle. 'La formaci??n del profesorado de p??rvulos seg??n las disposiciones y reales decretos de la segunda mitad del siglo'

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La did??ctica del entorn. 'La did??ctica del entorno'

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Pedagog??a de rincones y pr??ctica psicomotriz : hacia una l??nea coherente de trabajo en la Educaci??n Infantil

Los objetivos que se han marcado en el presente proyecto son :-Facilitar el desarrollo global e integral del ni??o, respetando su proceso evolutivo. -Llevar un proyecto de trabajo com??n en los cuatro preescolares basado en la pedagog??a de rincones y en la pr??ctica psicomotriz. -Intentar llevar una coordinaci??n efectiva entre Preescolar y el ciclo inicial. La metodolog??a por rincones requiere espacios f??sicos amplios donde desarrollar las actividades que se propongan. Se establecieron doce rincones diferentes que abarcaban tres tipos de espacios: manipulativo, cognitivo-conceptual y simb??lico. Aplicado a 81 ni??os/as de Preescolar de 4 y 5 a??os pertenecientes al Colegio P??blico de Ba??aderos. Resultados: se han promovido caminos indirectos que han estimulado al ni??o a que construyera su propio aprendizaje; se han respetado los ritmos evolutivos y las diferencias individuales del alumnado; se han favorecido y potenciado los h??bitos de autonom??a e independencia del adulto; se cubri?? la necesidad de juego permanente; se estimul?? la capacidad de expresi??n oral y afectiva; se consigui??, en fin, que el ni??o desarrollara global e ??ntegramente respetando su proceso evolutivo. En cuanto a la coordinaci??n de Preescolar con el ciclo inicial, no pudo llevarse a cabo debido a la inestabilidad del profesorado existente en el ciclo inicial. As?? pues, en general, se valora positivamente la consecuci??n de este proyecto.

Ideolog??a y Educaci??n Religiosa en los libros de lectura de la Escuela de la Restauraci??n Espa??ola

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