No description available.

<p dir="ltr">A key challenge in the assessment of the stability of fractures in rock is the identification of precursory geophysical signatures of shear failure. Accurate estimation and prediction of shear failure along rock discontinuities is crucial to prevent failure of geotechnical structures and potential natural hazards, such as landslides and earthquakes. Active seismic monitoring, such as compressional (P) and shear (S) waves, has been used to monitor the evolution of contact area and contact stress along rock discontinuities. Past laboratory experiments determined that changes in the amplitude of the transmitted, reflected, and converted P- and S-waves can be used to assess local changes in contact area and fracture specific stiffness, and to identify precursory events to shear failure of rock fractures. Those studies have identified the peaks (maxima or minima) in wave amplitudes as the seismic precursors to shear failure. Past studies were performed on dry artificial rock discontinuities with homogeneous and well-matched contact surfaces. However, in nature, rock discontinuities are not always homogeneous and well-matched, and are often found below the water table. In addition, at large depths, e.g. in enhanced geothermal systems (EGS), fractures are subjected to high temperatures.</p><p dir="ltr">The objectives of this research are to: (1) characterize the geophysical response of rock fractures during shear for dry and saturated conditions at room temperature, and saturated conditions at elevated temperatures; and (2) detect and identify seismic signatures of shear failure/slip for each of the three conditions. To achieve the goal of the research, a novel shear test apparatus was designed and built to test saturated jointed rock specimens under normal and shear loading, with a back pressure and at elevated temperatures, while also being capable of housing seismic transducers to monitor simultaneously the mechanical and geophysical response of the rock joints during shear. The system consisted of a sealed and heated pressure chamber and a biaxial compression frame. The pressure chamber was also used to perform B-value tests on cylindrical rock specimens to determine the minimum magnitude of back pressure required for fluid saturation.</p><p dir="ltr">Laboratory direct shear tests were performed on tension-induced fractures in Indiana limestone and Sierra White granite specimens with non-homogeneous rough contact surfaces. The contact surfaces were created by axial splitting of prismatic rock blocks. Shear tests were conducted on the rock fractures at a constant displacement rate in the pressure chamber, which enabled control of effective normal stress, pore water pressure, and temperature. During the tests, transmitted and converted P- and S-waves propagated across rock fractures and their changes in wave amplitude were monitored to assess the evolution of local contact areas during shear and detect precursory changes in wave amplitudes prior to shear failure.</p><p dir="ltr">Seismic precursors were observed in the wave amplitude data from all tests conducted under the three conditions. Precursors were most identifiable in the transmitted S-wave data. For all three conditions, the transmitted S-wave showed the same form of a seismic precursor; a peak (maximum) in wave amplitude was observed prior to the peak shear strength, as local contact surfaces interlocked and failed before macroscopic shear failure. However, the transmitted P-wave and converted waves (P-to-S and S-to-P) exhibited different behavior compared to the transmitted S-wave and depended on the test conditions. While, for dry conditions, the transmitted P-wave and converted waves still exhibited seismic precursors as peaks in their wave amplitudes, they did not display an observable peak for saturated fractures at room temperature, but rather either a very slight increase or a continuous reduction in amplitude. Instead of observable peaks, an abrupt change in the rate of reduction in the transmitted P-wave and converted amplitudes was observed that either coincided or occurred close to the peak in the transmitted S-wave amplitude. Thus, an onset of dramatic change in the reduction rate can be also taken as a seismic precursor to shear failure. This phenomenon can be explained by the large stiffness of the highly incompressible fluid, water, which leads to a decrease in P-wave sensitivity to changes in the normal fracture stiffness that arise from rock asperities under saturated conditions.</p><p dir="ltr">Even though the seismic wave amplitude generally contains a seismic precursor to shear failure, some exceptions exist: the wave amplitudes also depend on the local characteristics of the frictional area. No peak or seismic precursor in wave amplitude is observed prior to failure when the contact area between the fractures surfaces decreases because of dilation/opening. In addition, a delay peak in amplitude after shear failure may be observed when the fracture surfaces contain an initial large void or aperture in the region probed by the sensor. These exceptions may occur at a relatively low effective normal stress (2 MPa) and may disappear when a better contact has been established between the fracture surfaces by increasing the effective stress. Direct shear tests under an effective stress of 6 MPa, but at 50^oC, showed that both the transmitted P-waves and converted waves exhibited peaks in their amplitudes prior to the failure. However, these exceptions still require further exploration for the systematic identification and detection of seismic precursors.</p><p dir="ltr">The research shows that seismic monitoring is an effective tool to monitor the shear behavior of discontinuities, to provide an assessment of the local behavior of the frictional surface under the transducer, and to predict failure of the discontinuity. It can be used for dry, saturated discontinuities and for a wide range of pore pressures and temperatures. Other potential applications include fault monitoring, and even possibly earthquake prediction with additional research.</p>

Structurally precision graphene nanoribbons (GNRs) are promising candidates for next-generation nanoelectronics due to their intriguing and tunable electronic structures. GNRs with hybrid edge structures often confer them unique geometries associated with exotic physicochemical properties. Herein, a novel type of cove-edged GNRs with periodic short zigzag-edge segments is demonstrated. The bandgap of this GNR family can be tuned using an interplay between the length of the zigzag segments and the distance of two adjacent cove units along the opposite edges, which can be converted from semiconducting to nearly metallic. A family member with periodic cove-zigzag edges based on N = 6 zigzag-edged GNR, namely 6-CZGNR-(2,1), is successfully synthesized in solution through the Scholl reaction of a unique snakelike polymer precursor (10) that is achieved by the Yamamoto coupling of a structurally flexible S-shaped phenanthrene-based monomer (1). The efficiency of cyclodehydrogenation of polymer 10 toward 6-CZGNR-(2,1) is validated by FT-IR, Raman, and UV–vis spectroscopies, as well as by the study of two representative model compounds (2 and 3). Remarkably, the resultant 6-CZGNR-(2,1) exhibits an extended and broad absorption in the near-infrared region with a record narrow optical bandgap of 0.99 eV among the reported solution-synthesized GNRs. Moreover, 6-CZGNR-(2,1) exhibits a high macroscopic carrier mobility of ∼20 cm2 V–1 s–1 determined by terahertz spectroscopy, primarily due to the intrinsically small effective mass (m*e = m*h = 0.17 m0), rendering this GNR a promising candidate for nanoelectronics.

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on March 10, 2010). Vita. Thesis advisor: Lorson, Christian L. "December 2008" Includes bibliographical references

Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The successful preparation and structural characterization of a number of N,N-dialkyl-N’-benzoyl(thio)selenourea ligands is described; where the intermolecular interactions are characterized by the presence of Resonance Assisted Hydrogen Bonding (RAHB), π- π interactions between neighbouring benzene residues only being evident amongst the longer alkyl chain derivatives. The first structural characterization of an asymmetrically substituted N,N-dialkyl- N’-benzoylselenourea ligand reveals an increased stability of the Z isomer in the solid state, this being reflected by the sulfur analogue. Attempts to synthesise N,N-dicyclohexyl-N’-benzoylselenourea led to the isolation and structural characterization of a novel 1,3,5-oxaselenazine salt and dicyclohexylaminobenzoate. The first structural characterization of a “bipodal” N,N-dialkyl-N’-benzoylselenourea ligand, 3,3,3’,3’-tetrabutyl-1,1’- isophthaloylbis(selenourea), reveals RAHB in the crystal lattice similar to that exhibited by the “monopodal” analogue, N,N-dibutyl-N’-benzoylselenourea. The successful complexation of the N,N-dialkyl-N’-benzoyl(thio)selenourea ligands to a number of different transition metal ions is reported allowing the preparation of several potential single source precursors. Coordination through the O and Se/S donor atoms to Pd(II) results in the formation of square planar metal complexes, with a cis conformation, several of which could be structurally characterized. In particular, the first structural elucidation of an asymmetrically substituted N,N-dialkyl-N’-benzoylselenourea metal complex, cis-bis(N-benzyl-N-methyl-N’- benzoylselenoureato)palladium(II) indicates the increased stability of the EZ isomer in the solid state. Structural elucidation of the novel (N,N-diphenyl-N’-benzoylselenoureato)cadmium(II) reveals a bimetallic complex in the solid state, where the expected 2:1 ligand : metal ratio is maintained, and the two Cd(II) centres are 5 and 6 coordinated, with O and Se donor atoms. Multinuclear Nuclear Magnetic Resonance (NMR) Spectroscopy has been employed in the thorough characterisation of the potential single source precursors, 77Se NMR spectroscopy indicating a decreased shielding of the 77Se nucleus as the “hardness” of the central metal ion increases i.e. Pd(II) > Zn(II) > Cd(II). Use of 113Cd NMR spectroscopy indicates the preferential binding of N,N-diethyl-N’- benzoylselenourea to Cd(II) over that of its sulfur analogue, and initial studies suggest a form of chelate metathesis taking place in solution. 31P NMR spectroscopy is used to gain insight into the formation of cis-bis(N,N-diethyl-N’- benzoylselenoureato)Pt(II). Thermolysis of (N,N-diethyl-N’-benzoylselenoureato)cadmium(II) and its sulfur analogue led to the successful synthesis of CdSe and CdS quantum dots respectively, where thermolysis over a range of temperatures allows a degree of size control over the resulting nanoparticles. The effect of precursor alkyl chain length on nanoparticle morphology was investigated for both the N,N-dialkyl-N’-benzoylthio- and –selenoureas. A correlation between the two for the (N,N-dialkyl-N’-benzoylselenoureato)Cd(II) complexes is described and possible growth mechanisms are discussed. Preliminary investigations into the use of other N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes as single source precursors reveal that both (N,N-diethyl-N’-benzoylselenoureato)Zn(II) and its sulfur analogue show potential as single source precursors for the formation of ZnO and ZnS nanoparticles respectively. Initial studies into the use of N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes as single source precursors for the synthesis of core-shell nanoparticles is briefly described. The Aerosol Assisted Chemical Vapour Deposition (AACVD) of several N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes is reported, where both (N,N-diethyl-N’-benzoylselenoureato)Cd(II) and its sulfur analogue allow the deposition of crystalline CdSe and CdS respectively. The AACVD of (N,N-diethyl-N’- benzoylselenoureato)Zn(II) leads to the deposition of crystalline ZnSe, ZnS being deposited by (N,N-diethyl-N’-benzoylthioureato)Zn(II). The deposition of heazelwoodite (Ni3S2) with varying morphologies results from the AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Ni(II). Thermal annealing of the amorphous material deposited by the AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Pd(II), allows the formation of highly crystalline palladium. The deposition of metallic platinum using cis-bis(N,N-diethyl-N’-benzoylthioureato)Pt(II) is described as well as the deposition of crystalline Pd17Se15 from cis-bis(N,N-diethyl-N’-benzoylselenoureato)Pd(II). This, to the best of our knowledge, is the first time that AACVD has been performed, using the N,N-dialkyl-N’- benzoyl(thio)selenourea metal complexes as single source precursors, in addition, we believe it to be the first time that palladium selenide has been deposited using the AACVD technique.

Les mécanismes développementaux qui spécifient le nombre et le phénotype laminaire des neurones du cortex cérébral jouent un rôle essentiel dans l’établissement de la cytoarchitecture corticale. Le nombre de neurones dans chaque couche d'une aire donnée est déterminé par le taux de production neuronale, qui dépend étroitement de l'équilibre entre les divisions prolifératives et différenciatives. Des observations clés suggèrent que la durée de la phase G1 (TG1) ferait partie intégrante d'un mécanisme cellulaire régulant le mode de division des précurseurs du cortex. Nous avons testé cette hypothèse par l'accélération expérimentale de la progression dans la phase G1 de précurseurs corticaux de souris in vivo, via la surexpression des cyclines E1 et D1. A E15, la réduction de TG1 promeut la rentrée dans le cycle cellulaire aux dépens de la différenciation neuronale, résultant en une modification de la cytoarchitecture du cortex adulte. Des données de modélisation confirment que les effets induits par la réduction de TG1 sont médiés par des changements du mode de division. Les effets de la surexpression des cyclines E1 et D2 à E13 sont plus modérés qu'à E15, indiquant des différences intrinsèques entre les précurseurs corticaux précoces et tardifs. La mesure des phases du cycle cellulaire des populations de précurseurs corticaux à l’aide de différentes techniques révèle un niveau important d’hétérogénéité et souligne la nécessité de prendre en compte la diversité des précurseurs co‐existant dans les zones germinales du télencéphale. / In the cerebral cortex, area‐specific differences in neuron number and phenotype are distinguishing features both within and across species. The developmental mechanisms that specify the number of neurons and their laminar fate are instrumental in specifying cortical cytoarchitecture. Neuron number in layers and areas correlate with changes in the rate of neuron production, largely determined by the balance between proliferative and differentiative divisions in cortical precursors. Key observations suggest a concerted regulation between the duration of the G1 phase (TG1) and mode of division and have led to the hypothesis that TG1 could be an integral part of a cellular mechanism regulating the mode of division of cortical precursors. To test this hypothesis we experimentally accelerated TG1 in mouse cortical precursors in vivo, via the forced expression of cyclinE1 and cyclinD1. At E15, TG1 reduction promoted cell‐cycle re‐entry at the expense of differentiation and led to cytoarchitectural modifications. Modeling confirms that the TG1‐induced changes in neuron production and laminar fate are mediated via the changes in the mode of division. Forced expression of G1 cyclins was also applied to early cortical precursors. The effects of cyclinD1 and cyclinE1 up‐regulation at E13 were milder than those observed at E15, pointing to intrinsic differences between early and late cortical precursors. The used of various techniques to measure cell‐cycle kinetics in distinct precursor populations underlined the necessity of taking the full diversity of neural precursors co‐existing in the GZ of the telencephalon into account when performing cellcycle kinetics analysis.

Este trabalho objetivou o estudo de rotas de formação de metabólitos secundários utilizando precursores isotopicamente marcados com 13C. Os experimentos de crescimento com adição de [1-13C]acetato, [1,2-13C2]acetato e [U-13C315N1]-L-cisteína para o fungo do ambiente marinho Penicillium sp. DRF2 mostrou que as ciclotiocurvularinas são provenientes da rota de formação de policetídeos e pela incorporação de L-cisteína, depois da transformação desta em 3-mercaptopiruvato. Os resultados sugerem que a formação das ciclotiocurvularinas provém de um processo de detoxificação da &alpha;,&beta;-desidrocurvularina. O estudo do metabolismo secundário de Aspergillus sp. DLM3-8, também do ambiente marinho, mostrou que o seu perfil metabólico produzido em experimentos de crescimento sob diferentes condições é constante. Os experimentos de incorporação de precursores isotopicamente marcados com 13C na naftoquinonaimina, produzida por Aspergillus sp. DLM3-8 foram inconclusivos, indicando que outras abordagens experimentais devem ser realizadas para se investigar a biossíntese deste metabólito. / This investigation aimed investigated the formation routes of secondary metabolites using 13C-labelled precursors. Feeding experiments with [1-13C]acetate, [1,2-13C2]acetate and [U-13C315N1]-L-cysteine within the growth medium of the marine-derived fungi Penicillium sp. DRF2 showed that cyclothiocurvularins are derived from polyketides and from the incorporation of a L-cysteine residue, after its transformation into 3-mercaptopyruvate. The results suggest that the formation of cyclothiocurvularins is derived from a detoxification process of&alpha;,&beta;-dehydrocurvularin. Investigation of the secondary metabolism of a marine-derived Aspergillus sp. DLM3-8 indicated a stable metabolic profile under a variety of growth conditions. Feeding experiments with 13C-labelled precursors for the biosynthesis investigation of naphthoquinoneimine were inconclusive, indicating that other methodologies should be envisaged in order to investigate the biosynthesis of this metabolite.

O objetivo desta dissertação foi estudar a produção de pós de titanato de alumínio - tialita - pelo processo sol-gel associado à aspersão térmica por plasma. Foram investigados 3 tipos de solventes (etilenoglicol, álcool etílico e água) para a obtenção de um pó com características adequadas para a aplicação por aspersão ténnica a plasma. Os pós foram preparados por co-precipitação de sais inorgânicos de titânio e alumínio através da desestabilização das soluções com uma base forte. Os produtos obtidos foram então secos, calcinados em diferentes temperaturas, observando a evolução das fases. Alternativamente, pós pré-calcinados foram submetidos à aspersão térmica a plasma contra um recipiente com água, e contra um substrato de aço baixo carbono, proporcionando um resfriamento rápido. Os pós obtidos foram caracterizados por análises terrnodiferenciais (ATD) e termogravimétricas (ATG), análise granulométrica por difração de laser, análise da evolução de fases em função da temperatura de calcinação (e após aspersão térmica) por difração de raios X, análise da homogeneidade química e morfologia das partículas utilizando microscopia eletrônica de varredura (MEV) com o auxílio de espectrômetro de energia dispersiva (EDS). Os resultados mostraram que é possível obter, via sol-gel, matérias-primas adequadas para a formação da fase tialita após calcinação a temperaturas acima de 1300°C ou calcinando-se a cerca de 600°C e aspergindo em chama plásmica. Os diferentes solventes utilizados proporcionaram a produção de pós com diferentes morfologias e graus de homogeneidade química. Os pós apresentaram uma distribuição de titânio e alumínio na mesma partícula, sendo que a utilização de etilenoglicol corno solvente levou à maior homogeneidade. Com menores taxas de aquecimento nas calcinações (150Kfh), em temperaturas entre 800 e 1200°C, ocorre a segregação desses elementos com formação e crescimento de grãos de rutila e coríndon. Já com o rápido aquecimento e resfriamento, característicos da aspersão térmica por chama plásmica, a fase final preponderante é a tialita, tanto com resfriamento em água quanto no resfriamento sobre um substrato. / This work has the purpose of studying the production of a ceramic powder of aluminurn titanate - tialita - by sol-gel process associated with plasma spraying. Three kinds of solvents (ethyleneglicol, ethyl alcohol, and distillated water) were investigated in order to obtain a powder with adequate characteristics to be used as feedstock in plasma spray technique. The powders were made by co-prectpttation of inorganic salts of titanium and aluminurn through destabilization of the solutions using a strong base. The products obtained were dried, calcinated at different temperatures with attention to the phase evolution. Alternately, powders pré-calcinated were submitted to plasma thermal spraying in water and in a low-carbon steel substrate, providing an intense cooling rate. The powders obtained were characterized by differential thermal analysis (DT A) and thermogravimetric analysis (TGA), particle size analysis by laser diffraction, phase evaluation in function of calcinations temperature by X ray diffraction, chemical homogeneity and particle morphology using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The results showed that is possible obtain, by sol-gel, adequate feedstock to formation of tialita phase after calcinations at temperatures above 1300°C, or calcining at temperatures near 600°C followed by thermal spraying with plasma flame. The different kinds of solvents used, propitiated the production of powders with different morphologies and degrees of chemical homogeneity. With low heating rates in calcinations (150Kih), at temperatures between 800°C and 1200°C, occurs the segregation of aluminum and titaniurn with formation and growing of corundum and rutile phases. Since with fast heating and cooling propitiate by plasma spraying, the preponderant final phase is tialite in the substrate (water or metallic) aspersion.

Submitted by Ariane de França Mescoloto null (rianefm@gmail.com) on 2017-02-25T15:53:15Z No. of bitstreams: 1 Dissertação_Ariane_2017.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-03-07T14:05:43Z (GMT) No. of bitstreams: 1 mescoloto_af_me_araiq.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) / Made available in DSpace on 2017-03-07T14:05:43Z (GMT). No. of bitstreams: 1 mescoloto_af_me_araiq.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) Previous issue date: 2017-02-20 / Materiais híbridos orgânico-inorgânicos, constituídos pela combinação de componentes orgânicos e inorgânicos, são homogêneos, apresentam propriedades diferenciadas que refletem a natureza química dos componentes pelos quais foram formados, e são utilizados em diversas aplicações tecnológicas como catalisadores, sensores eletroquímicos, dispositivos ópticos e revestimentos protetores. Este trabalho foi realizado em duas etapas. Primeiramente, foi realizada a síntese e caracterização de um copolímero derivado do politiofeno, P(HTcoAAT), contendo ácido 3-tiofeno-acético (AAT) e 3-hexiltiofeno (HT), sintetizado via copolimerização oxidativa com cloreto férrico e caracterizado químico-estruturalmente por FTIR e RMN 1H e termicamente por TG/DTG. Em seguida, foram preparados filmes híbridos via sol-gel por spin-coating utilizando três óxidos inorgânicos: óxido de silício, titânio e zinco, os quais foram caracterizados opticamente por Espectroscopia no UV-vis e Fluorescência, e morfologicamente por AFM e MEV, além das caracterizações já citadas anteriormente. Os resultados químico-estruturais obtidos comprovaram a eficiência da metodologia usada para a preparação do copolímero e dos híbridos, permitindo a obtenção de matérias com propriedades ópticas interessantes. / Organic-inorganic hybrid materials, formed from organic and inorganic compounds combination, present specific properties that reflect the chemical nature of each precursor compound, and are used for several technological application such as catalists, electrochemical sensors, optical devices and barrier films. This work comprehends two steps: first of all the synthesis of a copolymer derived from polythiophene, P(HTcoTAA) containing 3-thiophene acetic acid (TAA) and 3-hexylthiophene (HT), it was performed from oxidative copolymerization with ferric chloride, and resulting materials characterized by FTIR and 1H NMR spectroscopy and TG/DTG thermal analyses. Following hybrid films from silicium, titanium and zinc oxides were prepared by sol-gel spin-coating and had its optical and morphological characteristics evaluated by UV-vis and Fluorescence spectroscopy, and AFM and SEM microscopy, besides the other characterization before cited. The obtained chemical-structural results show that the used methodology was efficient to prepare both the copolymer and the hybrids, allowing to materials presenting striking optical properties.

Made available in DSpace on 2014-12-17T15:41:43Z (GMT). No. of bitstreams: 1 JoseEMS.pdf: 2230919 bytes, checksum: f0f4e57c89f3eae4282c6daae0fe0aba (MD5) Previous issue date: 2008-04-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / It was synthesized different Ni1-xMgxFe2O4 (0,2 &#8804; x &#8804; 0,7) compositions by use of citrate precursor method. Initially, the precursory citrates of iron, nickel and magnesium were mixed and homogenized. The stoichiometric compositions were calcined from 350?C to 1200?C at ambient atmosphere or in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, magnetic measures and reflectivity using the wave guide method. I was observed pure magnetic phase formation between 350?C and 500?C, with formation of ferrite and hematite after 600?C at ambient atmosphere. The calcined powder at argon atmosphere formed pure ferromagnetic phase at 1100?C and 1200?C. The Rietveld analyses calculated the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (11-66 nm), that at 900?C/3h presents micrometric sizes (0,45 - 0,70 Om). The better magnetization results were 54 Am2/Kg for x= 0,2 composition, calcined at 350?C/3h and 30 min, and 55,6 Am2/Kg for x= 0,2 1200?C, calcined in argon. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The materials presented absorption less or equal the 50 % in ranges specific frequency. As for the 2,0 and 3,0 thickness (in 11,0 - 11,8 GHz), the reflectivity of the x= 0,3, 0,5 and 0,4 compositions, all calcined at 900?C/3h showed agreement with MS and O. Various factors contribute for the final radiation absortion effect, such as, the particle size, the magnetization and the polymer characteristics in the MARE composition. The samples that presented better magnetization does not obtaining high radiation absorption. It is not clear the interrelaction between the magnetization and the radiation absorption in the strip of frequencies studied (8,2 - 12,4 GHz) / Foram sintetizadas diferentes composi??es da ferrita Ni1-xMgxFe2O4 com (0,2 &#8804; x &#8804; 0,7) pelo uso do m?todo dos citratos precursores. Para se obter a fase estequiom?trica Ni1-xMgxFe2O4, inicialmente foram misturados e homogeneizados os citratos precursores de ferro, n?quel e magn?sio. As composi??es estequiom?tricas foram calcinadas entre as temperaturas de 350?C e 1200?C, em atmosfera ambiente ou de arg?nio. Os p?s calcinados foram caracterizados por DRX, TGA/DTG, FTIR, medidas magn?ticas e refletividade pelo m?todo de guia de ondas. Foi observada a forma??o de fase pura ferrimagn?tica entre 350?C e 500?C, formando ferrita e hematita ap?s 600?C, em atmosfera ambiente. O p? calcinado em atmosfera de arg?nio formou fase ferrimagn?tica pura em 1100?C e 1200?C. A an?lise pelo m?todo de Rietveld calculou o n?vel de ocupa??o dos c?tions e o tamanho de cristalito. A an?lise obteve tamanhos de cristais nanom?tricos, (11 - 66 nm), que a 900?C/3h apresentam tamanhos microm?tricos (0,45 0,70 Om). Os melhores resultados de magnetiza??o foram 54 Am2/Kg para a composi??o x= 0,2, calcinada a 350?C/3h e 30 min, e 55,6 Am2/Kg para x= 0,2 a 1200?C, calcinada em arg?nio. As histereses mostraram um perfil de materiais magn?ticos moles. Dois processos de magnetiza??o foram considerados, o superparamagnetismo a baixa temperatura e a forma??o de dom?nios magn?ticos em altas temperaturas. Os materiais apresentaram absor??o igual ou inferior a 50 % em faixas de freq??ncias espec?ficas. Para as espessuras 3,0 e 2,0 mm (em 11-11,8 GHz), as refletividades das composi??es x= 0,3, x= 0,5 e x= 0,4, todas a 900?C/3h demonstraram concord?ncia com MS e O. V?rios fatores contribuem para o efeito final de absor??o de radia??o, tais como, o tamanho de part?culas, a magnetiza??o, e as caracter?sticas do pol?mero na composi??o do MARE. As amostras que apresentaram maiores magnetiza??es n?o atingiram alta absor??o de radia??o. N?o ficou esclarecido a interrela??o entre a magnetiza??o e a absor??o de radia??o na faixa de freq??ncia estudada (8,2 12,4 GHz)