Potential theory

In this chapter we will introduce the reader to the techniques of the Boundary Element Method applied to simple Laplacian problems. Most classical applications refer to electrostatic and magnetic fields, but the Laplacian operator also governs problems such as Saint-Venant torsion, irrotational flow, fluid flow through porous media and the added fluid mass in fluidstructure interaction problems. This short list, to which it would be possible to add many other physical problems governed by the same equation, is an indication of the importance of the numerical treatment of the Laplacian operator. Potential theory has pioneered the use of BEM since the papers of Jaswon and Hess. An interesting introduction to the topic is given by Cruse. In the last five years a renaissance of integral methods has been detected. This can be followed in the books by Jaswon and Symm and by Brebbia or Brebbia and Walker.In this chapter we shall maintain an elementary level and follow a classical scheme in order to make the content accessible to the reader who has just started to study the technique. The whole emphasis has been put on the socalled "direct" method because it is the one which appears to offer more advantages. In this section we recall the classical concepts of potential theory and establish the basic equations of the method. Later on we discuss the discretization philosophy, the implementation of different kinds of elements and the advantages of substructuring which is unavoidable when dealing with heterogeneous materials.

Anisotropic magnetoresistive study in bilayer NiFe-NiO for sensor applications

Related with the detection of weak magnetic fields, the anisotropic magnetoresistive (AMR) effect is widely utilized in sensor applications. Exchange coupling between an antiferromagnet (AF) and the ferromagnet (FM) has been known as a significant parameter in the field sensitivity of magnetoresistance because of pinning effects on magnetic domain in FM layer by the bias field in AF. In this work we have studied the thermal evolution of the magnetization reversal processes in nanocrystalline exchange biased Ni80Fe20/Ni-O bilayers with large training effects and we report the anisotropic magnetoresistance ratio arising from field orientation in the bilayer.

Anisotropic magnetoresistive study in bilayer NiFe-NiO for sensor applications

Related with the detection of weak magnetic fields, the anisotropic magnetoresistive(AMR) effect is widely utilized in sensor applications. Exchange coupling between an antiferromagnet (AF) and the ferromagnet (FM) has been known as a significant parameter in the field sensitivity of magnetoresistance because of pinning effects on magnetic domain in FM layer by the bias field in AF. In this work we have studied the thermal evolution of the magnetization reversal processes in nanocrystalline exchange biased Ni80Fe20/Ni-O bilayers with large training effects and we report the anisotropic magnetoresistance ratio arising from field orientation in the bilayer.

Drifting plasma collection by a positive biased tether wire in LEO-like plasma conditions: current measurement and plasma diagnostic

BETs is a three-year project financed by the Space Program of the European Commission, aimed at developing an efficient deorbit system that could be carried on board any future satellite launched into Low Earth Orbit (LEO). The operational system involves a conductive tape-tether left bare to establish anodic contact with the ambient plasma as a giant Langmuir probe. As a part of this project, we are carrying out both numerical and experimental approaches to estimate the collected current by the positive part of the tether. This paper deals with experimental measurements performed in the IONospheric Atmosphere Simulator (JONAS) plasma chamber of the Onera-Space Environment Department. The JONAS facility is a 9- m3 vacuum chamber equipped with a plasma source providing drifting plasma simulating LEO conditions in terms of density and temperature. A thin metallic cylinder, simulating the tether, is set inside the chamber and polarized up to 1000 V. The Earth's magnetic field is neutralized inside the chamber. In a first time, tether collected current versus tether polarization is measured for different plasma source energies and densities. In complement, several types of Langmuir probes are used at the same location to allow the extraction of both ion densities and electron parameters by computer modeling (classical Langmuir probe characteristics are not accurate enough in the present situation). These two measurements permit estimation of the discrepancies between the theoretical collection laws, orbital motion limited law in particular, and the experimental data in LEO-like conditions without magnetic fields. In a second time, the spatial variations and the time evolutions of the plasma properties around the tether are investigated. Spherical and emissive Langmuir probes are also used for a more extensive characterization of the plasma in space and time dependent analysis. Results show the ion depletion because of the wake effect and the accumulation of- ions upstream of the tether. In some regimes (at large positive potential), oscillations are observed on the tether collected current and on Langmuir probe collected current in specific sites.

Multimodal integration of functional and structural brain connectivity. An application to the characterization of Mild Cognitive Impairment

La investigaci��n para el conocimiento del cerebro es una ciencia joven, su inicio se remonta a Santiago Ram��n y Cajal en 1888. Desde esta fecha a nuestro tiempo la neurociencia ha avanzado mucho en el desarrollo de t��cnicas que permiten su estudio. Desde la neurociencia cognitiva hoy se explican muchos modelos que nos permiten acercar a nuestro entendimiento a capacidades cognitivas complejas. Aun as�� hablamos de una ciencia casi en pa��ales que tiene un lago recorrido por delante. Una de las claves del ��xito en los estudios de la funci��n cerebral ha sido convertirse en una disciplina que combina conocimientos de diversas ��reas: de la f��sica, de las matem��ticas, de la estad��stica y de la psicolog��a. Esta es la raz��n por la que a lo largo de este trabajo se entremezclan conceptos de diferentes campos con el objetivo de avanzar en el conocimiento de un tema tan complejo como el que nos ocupa: el entendimiento de la mente humana. Concretamente, esta tesis ha estado dirigida a la integraci��n multimodal de la magnetoencefalograf��a (MEG) y la resonancia magn��tica ponderada en difusi��n (dMRI). Estas t��cnicas son sensibles, respectivamente, a los campos magn��ticos emitidos por las corrientes neuronales, y a la microestructura de la materia blanca cerebral. A lo largo de este trabajo hemos visto que la combinaci��n de estas t��cnicas permiten descubrir sinergias estructurofuncionales en el procesamiento de la informaci��n en el cerebro sano y en el curso de patolog��as neurol��gicas. M��s espec��ficamente en este trabajo se ha estudiado la relaci��n entre la conectividad funcional y estructural y en c��mo fusionarlas. Para ello, se ha cuantificado la conectividad funcional mediante el estudio de la sincronizaci��n de fase o la correlaci��n de amplitudes entre series temporales, de esta forma se ha conseguido un ��ndice que mide la similitud entre grupos neuronales o regiones cerebrales. Adicionalmente, la cuantificaci��n de la conectividad estructural a partir de im��genes de resonancia magn��tica ponderadas en difusi��n, ha permitido hallar ��ndices de la integridad de materia blanca o de la fuerza de las conexiones estructurales entre regiones. Estas medidas fueron combinadas en los cap��tulos 3, 4 y 5 de este trabajo siguiendo tres aproximaciones que iban desde el nivel m��s bajo al m��s alto de integraci��n. Finalmente se utiliz�� la informaci��n fusionada de MEG y dMRI para la caracterizaci��n de grupos de sujetos con deterioro cognitivo leve, la detecci��n de esta patolog��a resulta relevante en la identificaci��n precoz de la enfermedad de Alzheimer. Esta tesis est�� dividida en seis cap��tulos. En el cap��tulos 1 se establece un contexto para la introducci��n de la connect��mica dentro de los campos de la neuroimagen y la neurociencia. Posteriormente en este cap��tulo se describen los objetivos de la tesis, y los objetivos espec��ficos de cada una de las publicaciones cient��ficas que resultaron de este trabajo. En el cap��tulo 2 se describen los m��todos para cada t��cnica que fue empleada: conectividad estructural, conectividad funcional en resting state, redes cerebrales complejas y teor��a de grafos y finalmente se describe la condici��n de deterioro cognitivo leve y el estado actual en la b��squeda de nuevos biomarcadores diagn��sticos. En los cap��tulos 3, 4 y 5 se han incluido los art��culos cient��ficos que fueron producidos a lo largo de esta tesis. Estos han sido incluidos en el formato de la revista en que fueron publicados, estando divididos en introducci��n, materiales y m��todos, resultados y discusi��n. Todos los m��todos que fueron empleados en los art��culos est��n descritos en el cap��tulo 2 de la tesis. Finalmente, en el cap��tulo 6 se concluyen los resultados generales de la tesis y se discuten de forma espec��fica los resultados de cada art��culo. ABSTRACT In this thesis I apply concepts from mathematics, physics and statistics to the neurosciences. This field benefits from the collaborative work of multidisciplinary teams where physicians, psychologists, engineers and other specialists fight for a common well: the understanding of the brain. Research on this field is still in its early years, being its birth attributed to the neuronal theory of Santiago Ramo��n y Cajal in 1888. In more than one hundred years only a very little percentage of the brain functioning has been discovered, and still much more needs to be explored. Isolated techniques aim at unraveling the system that supports our cognition, nevertheless in order to provide solid evidence in such a field multimodal techniques have arisen, with them we will be able to improve current knowledge about human cognition. Here we focus on the multimodal integration of magnetoencephalography (MEG) and diffusion weighted magnetic resonance imaging. These techniques are sensitive to the magnetic fields emitted by the neuronal currents and to the white matter microstructure, respectively. The combination of such techniques could bring up evidences about structural-functional synergies in the brain information processing and which part of this synergy fails in specific neurological pathologies. In particular, we are interested in the relationship between functional and structural connectivity, and how two integrate this information. We quantify the functional connectivity by studying the phase synchronization or the amplitude correlation between time series obtained by MEG, and so we get an index indicating similarity between neuronal entities, i.e. brain regions. In addition we quantify structural connectivity by performing diffusion tensor estimation from the diffusion weighted images, thus obtaining an indicator of the integrity of the white matter or, if preferred, the strength of the structural connections between regions. These quantifications are then combined following three different approaches, from the lowest to the highest level of integration, in chapters 3, 4 and 5. We finally apply the fused information to the characterization or prediction of mild cognitive impairment, a clinical entity which is considered as an early step in the continuum pathological process of dementia. The dissertation is divided in six chapters. In chapter 1 I introduce connectomics within the fields of neuroimaging and neuroscience. Later in this chapter we describe the objectives of this thesis, and the specific objectives of each of the scientific publications that were produced as result of this work. In chapter 2 I describe the methods for each of the techniques that were employed, namely structural connectivity, resting state functional connectivity, complex brain networks and graph theory, and finally, I describe the clinical condition of mild cognitive impairment and the current state of the art in the search for early biomarkers. In chapters 3, 4 and 5 I have included the scientific publications that were generated along this work. They have been included in in their original format and they contain introduction, materials and methods, results and discussion. All methods that were employed in these papers have been described in chapter 2. Finally, in chapter 6 I summarize all the results from this thesis, both locally for each of the scientific publications and globally for the whole work.

Design of a Semi-analytical Method to Describe Plasma-Wall Interactions

Electric probes are objects immersed in the plasma with sharp boundaries which collect of emit charged particles. Consequently, the nearby plasma evolves under abrupt imposed and/or naturally emerging conditions. There could be localized currents, different time scales for plasma species evolution, charge separation and absorbing-emitting walls. The traditional numerical schemes based on differences often transform these disparate boundary conditions into computational singularities. This is the case of models using advection-diffusion differential equations with source-sink terms (also called Fokker-Planck equations). These equations are used in both, fluid and kinetic descriptions, to obtain the distribution functions or the density for each plasma species close to the boundaries. We present a resolution method grounded on an integral advancing scheme by using approximate Green's functions, also called short-time propagators. All the integrals, as a path integration process, are numerically calculated, what states a robust grid-free computational integral method, which is unconditionally stable for any time step. Hence, the sharp boundary conditions, as the current emission from a wall, can be treated during the short-time regime providing solutions that works as if they were known for each time step analytically. The form of the propagator (typically a multivariate Gaussian) is not unique and it can be adjusted during the advancing scheme to preserve the conserved quantities of the problem. The effects of the electric or magnetic fields can be incorporated into the iterative algorithm. The method allows smooth transitions of the evolving solutions even when abrupt discontinuities are present. In this work it is proposed a procedure to incorporate, for the very first time, the boundary conditions in the numerical integral scheme. This numerical scheme is applied to model the plasma bulk interaction with a charge-emitting electrode, dealing with fluid diffusion equations combined with Poisson equation self-consistently. It has been checked the stability of this computational method under any number of iterations, even for advancing in time electrons and ions having different time scales. This work establishes the basis to deal in future work with problems related to plasma thrusters or emissive probes in electromagnetic fields.

Lock-in amplifiers for AMR sensors

Anisotropic magnetoresistive (AMR) magnetic sensors are often chosen as the magnetic transducer for magnetic field sensing in applications with low to moderate magnetic field resolution because of the relative low mass of the sensor and their ease of use. They measure magnetic fields in the order of the Earth magnetic field (with typical sensitivities of 1���/G or 10���2���/��T), have typical minimum detectable fields in order of nT and even 0.1 nT but they are seriously limited by the thermal drifts due to the variation of the resistivity with temperature (���2.5���/��C) and the variation of the magnetoresistive effect with temperature (which affects both the sensitivity of the sensors: ���2.7���/��C, and the offset: ��0.5���/��C). Therefore, for lower magnetic fields, fluxgate vector sensors are generally preferred. In the present work these limitations of AMR sensors are outlined and studied. Three methods based on lock-in amplifiers are proposed as low noise techniques. Their performance has been simulated, experimentally tested and comparatively discussed. The developed model has been also used to derive a technique for temperature compensation of AMR response. The final goal to implement these techniques in a space qualified applied specific integrated circuit (ASIC) for Mars in situ exploration with compact miniaturized magnetometers.

Attenuated T2 relaxation by mutual cancellation of dipole���dipole coupling and chemical shift anisotropy indicates an avenue to NMR structures of very large biological macromolecules in���solution

Fast transverse relaxation of 1H, 15N, and 13C by dipole-dipole coupling (DD) and chemical shift anisotropy (CSA) modulated by rotational molecular motions has a dominant impact on the size limit for biomacromolecular structures that can be studied by NMR spectroscopy in solution. Transverse relaxation-optimized spectroscopy (TROSY) is an approach for suppression of transverse relaxation in multidimensional NMR experiments, which is based on constructive use of interference between DD coupling and CSA. For example, a TROSY-type two-dimensional 1H,15N-correlation experiment with a uniformly 15N-labeled protein in a DNA complex of molecular mass 17 kDa at a 1H frequency of 750 MHz showed that 15N relaxation during 15N chemical shift evolution and 1HN relaxation during signal acquisition both are significantly reduced by mutual compensation of the DD and CSA interactions. The reduction of the linewidths when compared with a conventional two-dimensional 1H,15N-correlation experiment was 60% and 40%, respectively, and the residual linewidths were 5 Hz for 15N and 15 Hz for 1HN at 4��C. Because the ratio of the DD and CSA relaxation rates is nearly independent of the molecular size, a similar percentagewise reduction of the overall transverse relaxation rates is expected for larger proteins. For a 15N-labeled protein of 150 kDa at 750 MHz and 20��C one predicts residual linewidths of 10 Hz for 15N and 45 Hz for 1HN, and for the corresponding uniformly 15N,2H-labeled protein the residual linewidths are predicted to be smaller than 5 Hz and 15 Hz, respectively. The TROSY principle should benefit a variety of multidimensional solution NMR experiments, especially with future use of yet somewhat higher polarizing magnetic fields than are presently available, and thus largely eliminate one of the key factors that limit work with larger molecules.

Curvature Induced by Amyloplast Magnetophoresis in Protonemata of the Moss Ceratodon purpureus1

After gravistimulation of Ceratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrong way response). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (<1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm���3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity.

Magnetars

Recent x-ray observations have shown that a substantial fraction of newly born neutron stars have magnetic fields of several 1014 G. They reveal themselves as soft gamma repeaters and anomalous x-ray pulsars and may account for the missing radio pulsars in young supernova remnants.

Composite fermions and bosons: An invitation to electron masquerade in Quantum Hall

The two-dimensional electron gas formed at the semiconductor heterointerface is a theater for many intriguing plays of physics. The fractional quantum Hall effect (FQHE), which occurs in strong magnetic fields and low temperatures, is the most fascinating of them. The concept of composite fermions and bosons not only is beautiful by itself but also has proved highly successful in providing pictorial interpretation of the phenomena associated with the FQHE.

The universe at z > 5: When and how did the ���dark age������end?

This paper considers how the first subgalactic structures produced the UV radiation that ionized the intergalactic medium before z = 5 and the ���feedback��� effects of the UV radiation on structure formation. The first ���pregalaxies��� may eventually be detectable by their direct UV emission, with characteristic spectral features at Lyman ��; high-z supernovae may also be detectable. Other probes of the intergalactic medium beyond z = 5, and of the epochs of reheating and reionization, are discussed, along with possible links between the diffusion of pregalactic metals and the origin of magnetic fields.

Desenvolvimento de microssensores eletroqu��micos e aplica����es no estudo de processos din��micos interfaciais utilizando microscopia eletroqu��mica de varredura

O trabalho descrito nesta tese mostra de forma detalhada a fabrica����o e caracteriza����o de diferentes microssensores eletroqu��micos os quais t��m sido recentemente utilizados como sondas em grupo de t��cnicas conhecida como Scanning Electrochemical Probe Microscopy (SEPM). Desta forma, a caracteriza����o de superf��cies pode ser feita explorando diferentes fen��menos interfaciais relevantes �� Ci��ncia. Neste sentido, as interfaces de materiais cristalinos como hidroxiapatita (materiais dent��rios) e calcita foram o foco de estudo neste trabalho. Assim, diferentes t��cnicas SEPM foram exploradas no sentido de se obter informa����es relevantes relacionadas aos processos dent��rios, como a eros��o ��cida e hipersensibilidade. Inicialmente, microeletrodos de platina foram desenvolvidos empregando uma metodologia convencional na qual s��o utilizados microfibras encapsuladas em capilares de vidro. Scanning Electrochemical Microscopy (SECM) no modo amperom��trico foi utilizada para obten����o de informa����es com rela����o ��s altera����es de topografia do esmalte dent��rio causadas pelo contato com subst��ncias ��cidas. Adicionalmente, SECM foi empregada no estudo do transporte de esp��cies eletroativas em amostras de dentina e investiga����es relacionadas ao bloqueio dos t��bulos empregando-se cremes dentais comerciais foram realizadas. A permea����o de per��xido de hidrog��nio pela dentina tamb��m foi estudada. Os resultados de SECM foram comparados com imagens SEM obtidas nas mesmas condi����es experimentais. Microeletrodos de membrana ion��fora ��on-seletiva (Ion Selective Microelectrodes-ISMEs) sens��veis a ��ons c��lcio tamb��m foram desenvolvidos e caracterizados, com subsequente aplica����o em SECM no modo potenciom��trico. A dissolu����o ��cida de esmalte bovino (eros��o dent��ria) foi investigada em diferentes valores de pH (2,5; 4,5; 6,8). Al��m disso, o transporte de ��ons c��lcio atrav��s de membranas porosas sint��ticas foi avaliado a uma dist��ncia tip/substrato de 300&#181;m. Altera����es no fluxo de ��ons c��lcio foram correlacionadas em experimentos realizados na presen��a e aus��ncia de campos magn��ticos gerados por nanopart��culas de magnetita incorporadas �� membrana porosa. Microcristais de calcita facilmente sintetizados pelo m��todo de precipita����o foram utilizados como superf��cie modelo para investiga����es interfaciais, cujos resultados podem ser correlacionados aos materiais dent��rios. Desta forma, nanopipetas de vidro preenchidas com eletr��lito suporte foram fabricadas e utilizadas como sonda em Scanning Ion Conductance Microscopy (SICM). O mapeamento topogr��fico de alta resolu����o espacial da superf��cie de um microcristal de calcita foi obtido utilizando o modo de varredura hopping mode. Adicionalmente, sondas multifuncionais ISME-SICM tamb��m foram desenvolvidas e caracterizadas para investiga����es simult��neas com rela����o ��s altera����es topogr��ficas e quantifica����o de ��ons c��lcio sobre a superf��cie de um microcristal de calcita. A adi����o de reagentes ��cidos no canal SICM promoveu a dissolu����o da superf��cie do microcristal, sendo obtidos dados cin��ticos de dissolu����o. Investiga����es em meio neutro tamb��m foram realizadas utilizando a sonda ISME-SICM. Os resultados experimentais obtidos tamb��m foram comparados com aqueles oriundos de simula����o computacional.

Supercondutividade em ligas de Ta1-xZrx

No presente estudo, amostras policristalinas ricas em Ta e com estequiometrias Ta1-xZrx; x < 0.15; foram preparadas atrav��s da mistura apropriada dos elementos met��licos, os quais foram fundidos em forno a arco el��trico sobre uma placa de cobre refrigerada a ��gua e sob atmosfera de arg��nio de alta pureza. Os padr��es de difra����o de raios-X das ligas, como fundidas (as cast) e tratadas termicamente a 850 ��C por 24 h, revelaram a ocorr��ncia de uma estrutura cristalina c��bica de corpo centrada bcc, tipo W, e par��metros de rede que aumentam suavemente com o aumento do teor de Zr nas ligas. Medidas de susceptibilidade magn��tica dc, conduzidas nas condi����es de resfriamento da amostra em campo zero (ZFC) e do resfriamento com o campo magn��tico aplicado (FC), indicaram que supercondutividade volum��trica �� observada abaixo de ~ 5.8, 6.9, 7.0 K em amostras com x = 0.05, 0.08, e 0.10, respectivamente. Essas temperaturas cr��ticas supercondutoras s��o bastante superiores ��quela observada no Ta elementar ~ 4.45 K. Medidas de resistividade el��trica na presen��a de campos magn��ticos aplicados de at�� 9 T confirmaram a temperatura cr��tica supercondutora das amostras estudadas. O campo cr��tico superior Hc2 e o comprimento de coer��ncia E foram estimados a partir dos dados de magnetorresist��ncia. Os valores estimados de Hc2 foram de ~ 0.46, 1.78, 3.85 e 3.97 T, resultando em valores de E ~ 26.0, 13.6, 9.2 e 9.1 nm para as ligas as cast com x = 0.00, 0.05, 0.08 e 0.10, respectivamente. A partir dos dados experimentais do calor espec��fico Cp das ligas, magnitudes estimadas do salto em Cp nas vizinhan��as das transi����es supercondutoras indicaram valores maiores que o previsto pela teoria BCS. Utilizando as equa����es anal��ticas derivadas da teoria do acoplamento forte da supercondutividade foi ent��o proposto que o aumento da temperatura de transi����o supercondutora nas ligas devido a substitui����o parcial do Ta por Zr est�� intimamente relacionado ao aumento do acoplamento el��tron-f��non, visto que a densidade de estados eletr��nicos no n��vel de Fermi foi estimada ser essencialmente constante atrav��s da s��rie Ta1-xZrx com x < 0.10.

S��ntese e caracteriza����o de nanomateriais superparamagn��ticos do tipo core-shell para aplica����o em cat��lise e biomedicina

As diversas aplica����es tecnol��gicas de nanopart��culas magn��ticas (NPM) v��m intensificando o interesse por materiais com propriedades magn��ticas diferenciadas, como magnetiza����o de satura����o (MS) intensificada e comportamento superparamagn��tico. Embora MNP met��licas de Fe, Co e bimet��licas de FeCo e FePt possuam altos valores de MS, sua baixa estabilidade qu��mica dificulta aplica����es em escala nanom��trica. Neste trabalho foram sintetizadas NPM de Fe, Co, FeCo e FePt com alta estabilidade qu��mica e rigoroso controle morfol��gico. NPM de ��xido met��licos (Fe e Co) tamb��m foram obtidas. Dois m��todos de s��ntese foram empregados. Usando m��todo baseado em sistemas nanoheterog��neos (sistemas micelares ou de microemuls��o inversa), foram sintetizadas NPM de Fe3O4 e Co met��lico. Foram empregados surfactantes c��tion-substitu��dos: dodecil sulfato de ferro(III) (FeDS) e dodecil sulfato de cobalto(II) (CoDS). Para a s��ntese das NPM, foram estudados e determinados a concentra����o micelar cr��tica do FeDS em 1-octanol (cmc = 0,90 mmol L-1) e o diagrama de fases pseudotern��rio para o sistema n-heptano/CoDS/n-butanol/H2O. NPM esferoidais de magnetita com3,4 nm de di��metro e comportamento quase-paramagn��tico foram obtidas usando sistemas micelares de FeDS em 1-octanol. J�� as NPM de Co obtidas via microemuls��o inversa, apesar da larga distribui����o de tamanho e baixa MS, s��o quimicamente est��veis e superparamagn��ticas. O segundo m��todo �� baseado na decomposi����o t��rmica de complexos met��licos, pelo qual foram preparadas NPM esf��ricas de FePt e de ��xidos met��licos (Fe3O4, FeXO1-X, (Co,Fe)XO1-X e CoFe2O4) com morfologia controlada e estabilidade qu��mica. O m��todo n��o mostrou a mesma efetividade na s��ntese de NPM de FeAg e FeCo: a liga FeAg n��o foi obtida enquanto que NPM de FeCo com estabilidade qu��mica foram obtidas sem controle morfol��gico. NPM de Fe e FeCo foram preparadas a partir da redu����o t��rmica de NPM de Fe3O4 e CoFe2O4, as quais foram previamente recobertas com s��lica. A s��lica previne a sinteriza����o inter-part��culas, al��m de proporcionar car��ter hidrof��lico e biocompatibilidade ao material. As amostras reduzidas apresentaram aumento dos valores de MS (entre 21,3 e 163,9%), o qual �� diretamente proporcional ��s dimens��es das NPM. O recobrimento com s��lica foi realizado via hidr��lise de tetraetilortosilicato (TEOS) em sistema de microemuls��o inversa. A espessura da camada de s��lica foi controlada variando-se o tempo de rea����o e as concentra����es de TEOS e de NPM, sendo ent��o proposto um mecanismo do processo de recobrimento. Algumas amostras receberam um recobrimento adicional de TiO2 na fase anatase, para o qual foi empregado etilenoglicol como solvente e ligante para forma����o de glicolato de Ti como precursor. A espessura da camada de TiO2 (2-12 nm) �� controlada variando as quantidades relativas entre NPM e o precursor de Ti. Ensaios de hipertermia magn��tica foram realizados para as amostras recobertas com s��lica. Ensaios de hipertermia magn��ticas mostram grande aumento da taxa de aquecimento das amostras ap��s a redu����o t��rmica, mesmo para dispers��es dilu��das de NPM (0,6 a 4,5 mg mL-1). Taxas de aquecimento entre 0,3 e 3,0oC min-1 e SAR entre 37,2 e 96,3 W g-1. foram obtidos. A atividade fotocatal��tica das amostras recobertas foram pr��ximas �� da fase anatase pura, com a vantagem de possuir um n��cleo magn��tico que permite a recupera����o do catalisador pela simples aplica����o de campos magn��ticos externos. Os resultados preliminares dos ensaios de hipertermia magn��tica e fotocat��lise indicam um forte potencial dos materiais aqui relatados para aplica����es em biomedicina e em fotocat��lise.