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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Relativistická teorie elektronového transportu v magnetických vrstvách / Relativistic Theory of Electron Transport in Magnetic Layers

Sýkora, Rudolf January 2012 (has links)
Title: Relativistic Theory of Electron Transport in Magnetic Layers Author: Rudolf Sýkora Department / Institute: Institude of Theoretical Physics Supervisor of the doctoral thesis: doc. RNDr. Ilja Turek, DrSc., Department of Condensed Matter Physics Abstract: We review the density-functional theory (DFT) in detail using the Levy Lieb ap- proach. The Kohn Sham scheme is discussed, starting from the simplest spinless non- relativistic case, then including spin and considering potential spin magnetism, and finally deriv- ing the full Kohn Sham Dirac relativistic scheme. The Linear Muffin-Tin Orbital (LMTO) method for electronic-structure calculation is presented, together with mentioning the necessary changes to include the spin-orbit (SO) interaction effects to an otherwise scalar-relativistic (SR) theory. Derivation of an electronic-conductance formula for a layered system is given, based on the Landauer scattering picture and using simple non-equilibrium Green functions. The formal- ism is applied to layered metallic systems of light elements Co, Ni, Cu elements, and to layered systems with a tunnelling barrier, Fe/MgO/Ag and Fe/GaAs/Ag. The effects of the SO interac- tion on the Giant Magnetoresistance (GMR) ratio and/or the Tunnelling Anisotropy Magnetore- sistance (TAMR) for these systems are discussed....
412

Electrical transport properties of URhGe and BiPd at very low temperature

Barraclough, Jack Matthew January 2015 (has links)
URhGe has garnered interest recently as one of the few known ferromagnetic superconductors. The superconductivity in this material appears to arise from magnetic fluctuations rather than phonons, and take a triplet form which is remarkably resistant to field. In this thesis, a number of measurements on the material are presented. Some probe the Fermiology, with strong evidence appearing for a model which as both light open sheets and heavy, small, closed pockets. The open sheets, associated with chains of real-space electron density running along the b axis, dominate the conductivity in most circumstances. Evidence for their existence arises from the general large and non-saturating magnetoresistance, and from the unusual observation of negative temperature coefficient of resistance at high fields. The closed pockets have provided a few Shubnikov-de Haas oscillations, but mostly they remain inferred from the high specific heat γ and their role in the magnetism. In order to better probe the superconductivity, a high precision low noise DC resistance measurement bridge was built using a SQUID. Along with conventional measurements, this provides evidence that the two pockets of superconductivity on the phase diagram are the same phase. The re-entrance an be understood simply as a result of magnetic field being a tuning parameter, but also suppressing bulk superconductivity through orbital limiting. The SQUID bridge allowed the detection of domain wall superconductivity linking up these two pockets. The SQUID bridge was also used to study the highly structured superconducting transition in BiPd. This material lacks inversion symmetry in its crystal structure, so is a good candidate for unusual forms of superconductivity. Here again non-bulk superconductivity is considered the most likely cause for the structure. Unusual and distinctive IV curves have been measured, and a simple model of inhomogeneous conductivity channels with different critical currents is proposed as an explanation.
413

Determinação de órbitas com o GPS através de mínimos quadrados recursivo com rotações de Givens

Silva, Aurea Aparecida da [UNESP] January 2001 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2001Bitstream added on 2014-06-13T19:06:44Z : No. of bitstreams: 1 silva_aa_me_guara.pdf: 449677 bytes, checksum: 4be6e3535fba004c9b44ce9da9bf8c3a (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O Sistema de Posicionamento Global oferece um poderoso e relativamente barato processo para se determinar órbitas de satélites artificiais da Terra. Este trabalho apresenta um método de determinação de órbita para satélites com um receptor GPS a bordo. Medidas de pseudo-distância são usadas para estimar o vetor de estado. O estimador considerado é o método dos mínimos quadrados recursivo, através de rotações ortogonais de Givens, com a finalidade de evitar problemas numéricos e de inversão de matrizes. É considerado a modelagem das forças devido ao geopotencial de alto grau e ordem. Resultados indicam que a precisão em posição melhor que 10 m foi obtido usando dados reais do satélite Topex (com um mínimo de duas horas de dados - aproximadamente um período orbital). O resíduo de pseudo-distância teve um desvio padrão cerca de 5 m. / The Global Positioning System is a powerful and low cost process to compute orbits for some artificial Earth satellites. This work presents a method of orbit determination for satellites with an onboard GPS receiver. Pseudo-ranges are used in the measurements equations for the orbit estimator. The estimator considered is the recursive least squares method, numerically improved with orthogonal Givens rotations and thus avoiding problems concerning inversion of matrices. Up to high order geopotential perturbations are taken into account. Results indicate that precision better than 10 m is easily obtained using batches of one orbital period for the TOPEX satellite (two hours of orbital period). Standard deviation of about 5 m resulted for the residuals.
414

Avaliação tomográfica de fraturas orbitárias unilaterais tratadas por meio de malhas de titânio e validação da fisiopatologia do trauma orbitário por meio de elementos finitos /

Moura, Lucas Borin January 2018 (has links)
Orientador: Valfrido Antonio Pereira Filho / Resumo: Fraturas orbitárias apresentam alta prevalência, ocasionando alterações estéticas e funcionais com repercussão clínica. A severidade dos defeitos orbitários é dependente da sua extensão, morfologia e localização, sendo que as alterações do volume orbitário estão intimamente relacionadas com a presença de enoftalmia e de diplopia. Desta forma, o tratamento objetiva restabelecer a anatomia e o volume orbitário prévio ao trauma. Atualmente, o material mais utilizado para a reconstrução orbitária é a malha de titânio convencional, sendo que a combinação de outras técnicas, como assistência por endoscopia e utilização de biomodelos, pode otimizar o tratamento. Em relação à fisiopatologia do trauma orbitário, dois mecanismos estão historicamente estabelecidos, mecanismo hidráulico e trauma direto ao rebordo orbitário. Entretanto, o completo entendimento das características da distribuição de forças de cada mecanismo ainda não está esclarecido. Desta forma, este trabalho teve o objetivo de realizar uma análise tomográfica de fraturas orbitárias unilaterais tratadas por meio de malhas de titânio convencionais; confeccionar um modelo digital da cavidade orbitária para a simulação dinâmica dos mecanismos de trauma orbital; e reportar a otimização do tratamento de fraturas orbitárias pela associação de técnicas com endoscopia transantral e biomodelos. / Abstract: Orbital fractures are high prevalent, and result in aesthetic and functional impairments. The severity of orbital defects is related with the extension, morphology and location. The orbital volume changes are intimately associated with the presence of enophthalmos and diplopia. Therefore, the treatment must reestablish the orbital anatomy and volume. Presently, the most applied material for orbital reconstruction is the conventional titanium mesh, and the association of other techniques, such as endoscopic assistance and the use of printed models, can optimize the treatment. About the orbital trauma pathophysiology, two mechanisms are historically established - hydraulic and buckling mechanisms. However, the complete understanding of the features of stress distribution of each mechanism are not clear. Thus, the aim of this work is to perform a tomographic evaluation of unilateral orbital fractures treated with conventional titanium mesh; to create a digital model of the orbital cavity for a dynamic simulation of the mechanisms of orbital trauma; and to report the optimization of treatment of orbital fractures by the association of techniques, with transantral endoscopy and printed model. / Doutor
415

Schémas de Hilbert invariants et théorie classique des invariants / Invariant Hilbert Schemes and classical invariant theory

Terpereau, Ronan 05 November 2012 (has links)
Pour toute variété affine W munie d'une opération d'un groupe réductif G, le schéma de Hilbert invariant est un espace de modules qui classifie les sous-schémas fermés de W, stables par l'opération de G, et dont l'algèbre affine est somme directe de G-modules simples avec des multiplicités finies préalablement fixées. Dans cette thèse , on étudie d'abord le schéma de Hilbert invariant, noté H, qui paramètre les sous-schémas fermés GL(V)-stables Z de W=n1 V oplus n2 V^* tels que k[Z] est isomorphe à la représentation régulière de GL(V) comme GL(V)-module. Si dim(V)<3,on montre que H est une variété lisse, et donc que le morphisme de Hilbert-Chow gamma: H -> W//G est une résolution des singularités du quotient W//G. En revanche, si dim(V)=3, on montre que H est singulier. Lorsque dim(V)<3, on décrit H par des équations et aussi comme l'espace total d'un fibré vectoriel homogène au dessus d'un produit de deux grassmanniennes. On se place ensuite dans le cadre symplectique en prenant n1=n2 et en remplaçant W par la fibre en 0 de l'application moment mu: W -> End(V). On considère alors le schéma de Hilbert invariant H' qui paramètre les sous-schémas contenus dans mu^{-1}(0). On montre que H' est toujours réductible, mais que sa composante principale Hp' est lisse lorsque dim(V)<3. Dans ce cas, le morphisme de Hilbert-Chow est une résolution (parfois symplectique) des singularités du quotient mu^{-1}(0)//G. Lorsque dim(V)<3, on décrit Hp' comme l'espace total d'un fibré vectoriel homogène au dessus d'une variété de drapeaux. Enfin, on obtient des résultats similaires lorsque l'on remplace GL(V) par un autre groupe classique (SL(V), SO(V), O(V), Sp(V)) que l'on fait opérer d'abord dans W=nV, puis dans la fibre en 0 de l'application moment. / Let W be an affine variety equipped with an action of a reductive group G. The invariant Hilbert scheme is a moduli space which classifies the G-stable closed subschemes of W such that the affine algebra is the direct sum of simple G-modules with previously fixed finite multiplicities. In this thesis, we first study the invariant Hilbert scheme, denoted H. It parametrizes the GL(V)-stable closed subschemes Z of W=n1 V oplus n2 V^* such that k[Z] is isomorphic to the regular representation of GL(V) as GL(V)-module. If dim(V)<3, we show that H is a smooth variety, so that the Hilbert-Chow morphism gamma: H -> W//G is a resolution of singularities of the quotient W//G. However, if dim(V)=3, we show that H is singular. When dim(V)<3, we describe H by equations and also as the total space of a homogeneous vector bundle over the product of two Grassmannians. Then we consider the symplectic setting by letting n1=n2 and replacing W by the zero fiber of the moment map mu: W -> End(V). We study the invariant Hilbert scheme H' which parametrizes the subschemes included in mu^{-1}(0). We show that H' is always reducible, but that its main component Hp' is smooth if dim(V)<3. In this case, the Hilbert-Chow morphism is a resolution of singularities (sometimes a symplectic one) of the quotient mu^{-1}(0)//G. When dim(V)=3, we describe Hp' as the total space of a homogeneous vector bundle over a flag variety. Finally, we get similar results when we replace GL(V) by some other classical group (SL(V), SO(V), O(V), Sp(V)) acting first on W=nV, then on the zero fiber of the moment map.
416

Dynamique du déplacement de parois magnétiques dans les couches ultra-minces à forte interaction spin-orbite / Domain wall motion dynamics in ultra-thin layers magnetic memory with strong spin-orbite interaction

Jué, Emilie 18 December 2013 (has links)
L'étude du déplacement des parois de domaines magnétiques au moyen d'un courant électrique, par couple de transfert de spin, a généré beaucoup d'intérêt ces dernières années, notamment depuis que de nouveaux dispositifs de mémoires magnétiques utilisant cet effet ont été proposés. Récemment, un nouveau mécanisme capable de propager les parois sous courant avec une grande efficacité a été mis en évidence dans les matériaux tri-couches à anisotropie perpendiculaire et à fort couplage spin-orbite. La compréhension de ce mécanisme, appelé couple de spin-orbite, reste néanmoins loin d'être acquise, tout comme son effet sur la propagation des parois de domaines.L'objectif de ce travail de thèse était d'étudier l'influence de ce couple de spin-orbite sur la dynamique des parois. Pour cela, j'ai étudié expérimentalement le déplacement de paroi sous l'action d'un courant et d'un champ magnétique dans une tri-couche de Pt/Co/AlOx en présence d'un champ magnétique planaire, utilisé pour modifier la structure interne de la paroi et ainsi moduler l'action du couple de spin-orbite sur la dynamique de celle-ci. Ce travail a permis de mettre en évidence l'existence d'un effet asymétrique dans la dynamique de la paroi pour ce type de système.Pour expliquer ce résultat, nous avons proposé une nouvelle structure de paroi dans les matériaux ultra-minces à anisotropie perpendiculaire, résultant de l'interaction Dzyaloshinskii-Moriya. En combinant des calculs analytiques et des simulations micro-magnétiques, la dynamique d'une telle paroi a été étudiée et comparée aux résultats expérimentaux. Enfin, toujours dans le but d'expliquer l'effet asymétrique observé expérimentalement, une seconde interprétation basée sur la présence d'un mécanisme d'amortissement anisotrope a également été proposée. / The study of current-induced magnetic domain wall motion through spin transfer torque has attracted a lot of attention in recent years, especially since new magnetic memories devices based on this effect have been proposed. Recently, a new mechanism allowing for highly efficient current-induced domain wall motion has been discovered in ultrathin asymmetric materials with perpendicular magnetic anisotropy and high spin-orbit coupling. However this mechanism, named spin-orbit torque, and its effect on domain wall motion are not yet well understood.The objective of this work was to study the influence of this spin-orbit torque on domain wall motion. For that, I have studied field- and current-induced domain wall motion in Pt/Co/AlOx trilayer, in the presence of an in-plane magnetic field. This work allowed highlighting the existence of an asymmetric effect in the domain-wall dynamics of this system.In order to explain this result, we have proposed a new kind of domain wall structure, resulting from Dzyaloshinskii-Moriya interaction in materials with perpendicular magnetic anisotropy and high spin-orbit coupling. Using analytic calculations and micro-magnetic simulations, this domain wall dynamics has been studied and compared to the experimental results. Finally, a second approach based on the presence of an anisotropic damping mechanism has also been proposed to explain the asymmetric effect observed experimentally.
417

Bloqueio retrobulbar com levobupivacaína e lidocaína em gatos

Xavier, Gustavo Delfino 19 February 2014 (has links)
The objective of this study was to assess the effect of retrobulbar anesthesia in cats with levobupivacaine chloride 0.5% and lidocaine chloride 2% without vasoconstrictor. Fourteen cats were divided into two groups and underwent preanesthetic medication with acepromazine maleate and propofol. Retrobulbar block was performed in the medial corner of the eyelids of the right eyeball with levobupivacaine hydrochloride (Group I) and lidocaine (Group II) without vasoconstrictor. We evaluated the M0 moments i.e. six hours prior to PAM, M1:15 minutes after PAM, when it was taken the anesthetic, as well as the periods M2: 15, M3: 30, M4: M5: 45 and M6: 60 minutes after the anesthetic block. The duration of block with lidocaine was 50 minutes, and 65 minutes with levobupivacaine without change in systolic blood pressure. Anesthetic promoted block of the corneal and the oculocephalic reflexes, being that the loss of sensibility and return of the corneal reflexes were faster with the levobupivacaine than with the lidocaine. No changes in the coloration of the eyelid and bulbar conjunctivae and decentralization of the globe were noted. Anesthetics caused retrobulbar anesthesia in cats, being that 0.5% levobupivacaine promotes appearance of rash in the bulbar and the eyelid conjunctivae, greater reduction in tear production and increased intraocular pressure. Anesthetics are not able to restrict the palpebral reflexes, but they may be used for intraocular surgery. / Objetivo desta pesquisa foi avaliar os efeitos da anestesia retrobulbar em gatos com cloridrato de levobupivacaína 0,5% e cloridrato de lidocaína 2%, sem vasoconstritor. Quatorze gatos foram separados em dois grupos e submetidos à medicação pré-anestésica com maleato de acepromazina e posterior anestesia com propofol. Realizou-se bloqueio retrobulbar no canto medial das pálpebras do bulbo ocular direito com cloridrato de levobupivacaína 0,5% (Grupo I) e lidocaína 2% (Grupo II), sem vasoconstritor. Avaliou-se os momentos M0: seis horas antes da MPA, M1: 15 minutos após a MPA, quando foi feita a administração do anestésico. Assim como nos períodos M2: 15, M3: 30, M4: 45 e M5: 60 minutos após bloqueio anestésico. A duração do bloqueio com lidocaína foi de 50 minutos, e de 65 com a levobupivacaína, sem variação da pressão arterial sistólica. Os anestésicos promoveram bloqueio dos reflexos corneano e oculocefálico, sendo que com a levobupivacaína ocorreu perda da sensibilidade e retorno dos reflexos corneanos mais rápidos que a lidocaína. Não foram notadas alterações na coloração da conjuntiva palpebral e bulbar e descentralização do bulbo ocular. Os anestésicos ocasionaram anestesia retrobulbar em gatos, sendo que levobupivacaína promove aparecimento de prurido na conjuntiva bulbar e palpebral, maior redução na produção de lágrima e aumento da pressão intraocular. Os anestésicos no bloqueio retrobulbar não são capazes de restringir os reflexos palpebrais, porém podem ser indicados para cirurgias intra-oculares. / Mestre em Ciências Veterinárias
418

Relaxation de spin dans les semi-conducteurs dopés et dans les nanostructures à base de semi-conducteurs / Spin relaxation in doped semiconductors and semiconductor nanostructures

Intronati, Guido Alfredo 24 April 2013 (has links)
Dans cette thèse nous considérons un semi-conducteur de GaAs dopé, où nous étudions la relaxation du spin du côté métallique de la transition metal-isolant. Nous considérons deux types différents d'interaction de spin-orbite. Le premier d'entre eux est associé aux impuretés et l'autre est de type Dresselhaus. La dynamique du spin est traitée à travers une formulation analytique basée sur la diffusion du spin de l'électron, et un calcul numérique de la durée de vie du spin.Ensuite, nous considérons une boîte quantique hébergée dans un nanofil de matériau InAs (avec une structure cristalline de type wurtzite), afin d'étudier l'effet de l'interaction spin-orbite sur les états propres du système. Nous développons ici une solution analytique pour la boîte quantique en incluant l'interaction spin-orbite (de type Dresselhaus propre à la structure wurtzite). Nous avons calculé le facteur g effectif, ainsi que la relaxation du spin dûe aux phonons acoustiques, en utilisant les potentiels d'interaction electron-phonon propres à la structure wurtzite. / In the first part of this thesis we consider a doped GaAs semiconductor and study the spin relaxation on the metallic side of the metal-insulator transition. We take into account two different types of spinorbit coupling, the first of them being associated to the presence of extrinsic impurities, while the other one is the Dresselhaus coupling. To tackle the spin dynamics problem, we develop an analytical formulation based on the spin diffusion of an electron in the metallic regime of conduction of the impurity band. The full derivation provides us with an expression for the spin-relaxation time ,which is free of adjustable parameters. We complement this approach and back our analytical results with the numerical calculation of the spin lifetime.In the second part of the thesis we consider a quantum dot hosted in an InAs nanowire (with awurtzite crystalline structure) and study the effect of spin-orbit coupling on the eigenstates of the zero-dimensional system. We develop here an exact analytical solution for the quantum dot, takinginto account the proper effective spin-orbit coupling for this type of material. We focus on the Dresselhaus coupling, which presents a cubic-in-k term, along with a linear term, characteristic of wurtzite materials. A Zeeman interaction from an external magnetic field is included as well and we compute the effective g-factor as a function of the dot size. Finally, we calculate the spin-relaxation due to acoustic phonons, taking into account the phonon potentials corresponding to the wurtzite structure.
419

O acoplamento spin-órbita no estudo de fases topológicas em uma rede hexagonal de baricentros / The spin-orbit coupling in the study of topological phases in a hexgonal lattice of barycenter

Carlos Augusto Mera Acosta 22 April 2013 (has links)
Neste trabalho foram estudadas as fases topológicas não triviais presentes em sistemas formados pela deposição de átomos de grafeno. Encontramos que quando um átomo hibridiza fortemente com o grafeno, apresenta um momento magnético e um forte spin-órbirta é possível a formação de uma rede hexagonal de baricentros que efetivamente gera uma estrutura de bandas característica de um efeito hall quântico anômalo. Especificamente, determinamos que o Ru satisfaz estas características. Quando este metal é depositado em uma configuração triangular no grafeno ocorrem picos na densidade de estados localizados no centro geométrico (baricentro) dos triângulos formados pelos Ru. Estes picos estão distribuídos de forma hexagonal e efetivamente geram uma estrutura de bandas que nas proximidades do nível de Fermi apresenta uma configuração de spin característica do efeito Hall quântico anômalo. Adicionalmente, encontramos que o sistema composto pela absorção de Ba ou Sr no grafeno favorece a formação do efeito Hall quântico de spin. Neste sistema, o acoplamento spin-órbita (SOC) gera um gap mais de 1000 vezes maior ao período no grafeno prístino. Para o estudo destes sistemas, implementamos no código SIESTA a aproximação on-site do acoplamento spin-órbita via o formalismo dos pseudopotenciais relativísticos de norma conservada. Nossa implementação foi testada a partir do estudo de fenômenos já conhecidos: i) o strong spin-splitting gerado no grafeno pela adsorção de Au, ii) o efeito hall quântico de spin no poço quântico de HgTe/CdTe e, iii) a formação de estados topológicos na superfície do Bi2Se3 e as fases magnéticas deste material com átomos de Mn adsorvidos. / In this work, were studied the non-trivial topological phases present in systems formed by deposition of atoms in graphene. We found that when an atom hybridizes strongly with grapheme, has a magnetic moment and a strong spin-orbit it is possible the formation of a hexagonal network of barycentres that effectively generates a structure band characteristic of a quantum anomalous Hall effect. Specifically, we determined that Ru satisfies these characteristics. When this metal is deposited in a triangular configuration in grapheme, peaks occur in the density of localized states in the geometric center (centroid) of the triangles formed by Ru. These peaks are distributed in a hexagonal structure and effectively generates a band structure that near the Fermi level has a spin configuration characteristic of the spin quantum Hall effect anomalous. Additionally, we found that the system composed by the adsorption of Ba or Sr in grapheme, promotes the formation of spin quantum Hall effect. In this system, the spin-orbit coupling (SOC) generates a gap more than 1000 times grater that predicted in pristine praphene. To study these systems, wu implemented in the code SIESTA the on-site approach of the spin-orbit coupling throught the formalism of norm conserved relativistic pseudo potentials. Our implementation was tested from the study of phenomena already known: i) the strong spin-splitting generated in graphene by adsorption of Au, ii) the quantum spin Hall effect in quantum well of HgTe / CdTe and, iii) formation of topological states in the surface of Bi2Se3 and the magnetic of this material with Mn atoms adsorved.
420

Uso da dopplerfluxometria arterial renal, periférica e orbital em jovens portadores de anemia falciforme : associação com biomarcadores de hemólise

Ferrão, Thiago de Oliveira 23 October 2015 (has links)
Sickle cell anemia (SCA), homozygous form of sickle cell disease, is the most common hereditary hemoglobinopathy, characterized by the production of abnormal hemoglobin (HbS) which, in deoxygenated state, deforms and hardens the red cells with multisystemic manifestations. The clinical complications can be grouped in two subphenotypes: vasculopathy and viscosity-vaso-occlusion. Vasculopathy is associated to hemolysis intensity and contributes to chronic dysfunction of several organs, with endothelial participation. Endothelial dysfunction is associated to hemolysis laboratory markers (hemoglobin level, reticulocyte count, lactate dehydrogenase and bilirubin levels) and can manifest as abnormal vascular reactivity in visceral, peripheral and central blood flow studies, assessed by Doppler ultrasound. The aim of this study was to investigate the arterial vascular resistance state in the kidneys, lower limbs and orbits by means of dopplervelocimetry in SCA patients, and its relationship with hemolysis biomarkers. Two groups were examined in this cross-sectional study. One group consisted of 71 outpatients with SCA; the other group was a control group, consisting of 32 age- and sex-matched, apparently healthy subjects. All participants were assessed by means of Doppler ultrasound and laboratory tests. All biomarkers were abnormal in the SCA patients compared with the control subjects (p < 0.0001). Doppler sonography evaluation revealed altered velocities and elevated resistance indices RI (resistive index) and PI (pulsatility index) in SCA group compared to control group (p < 0.0001). The relationship analysis between hemolysis biomarkers and vascular resistance indices showed significant association. In the kidneys, strong inverse correlation was observed between hemoglobin level and RI and PI in all arteries; moderate direct correlation was detected between lactate dehydrogenase and the resistance indices in segmental arteries. In the lower limbs, moderate direct correlation was observed between reticulocyte count and peak systolic velocity (PSV) in the anterior tibial and posterior tibial arteries; strong inverse correlation was detected between hemoglobin and PSV in all arteries. In orbits, moderate direct correlation was found between reticulocyte count and resistance indices in ophthalmic artery; and strong inverse correlation was observed between hemoglobin and RI and PI in the central retinal artery. This research demonstrated that arterial vascular resistance in the kidneys, lower limbs and orbits, assessed by means of Doppler ultrasound, is elevated in SCA patients, and shows moderate to strong correlation with hemolysis biomarkers. / Anemia falciforme (AF), forma homozigótica da doença falciforme, é uma das hemoglobinopatias hereditárias mais comuns, caracterizada pela produção de hemoglobina anormal (HbS) que, no estado desoxigenado, deforma e enrijece as hemácias, promovendo manifestações multissistêmicas. As complicações clínicas podem ser agrupadas em dois subfenótipos: vasculopatia e viscosidade-vaso-oclusão. A vasculopatia está associada à intensidade da hemólise e contribui para a disfunção crônica de diversos órgãos, com a participação do endotélio. A disfunção endotelial está associada a marcadores laboratoriais de hemólise (hemoglobina, contagem de reticulócitos, desidrogenase láctica e bilirrubinas) e pode manifestar-se como reatividade vascular anormal em estudos de fluxo sanguíneo visceral, periférico e central, avaliado por ultrassonografia Doppler. O objetivo deste trabalho foi investigar o estado de resistência vascular arterial nos rins, membros inferiores e órbitas por meio de dopplervelocimetria em portadores de AF, e sua relação com biomarcadores de hemólise. Dois grupos foram examinados neste estudo transversal. Um grupo consistiu de 71 pacientes portadores de AF; o outro, controle, formado por 32 sujeitos saudáveis, pareados por gênero e idade. Todos os participantes foram avaliados por meio de ultrassonografia Doppler e de testes laboratoriais. Todos os biomarcadores foram anormais nos portadores de AF em comparação aos controles (p < 0,0001). A avaliação dopplerfluxométrica evidenciou velocidades alteradas e índices de resistência vascular IR (índice de resistência) e IP (índice de pulsatilidade) elevados no grupo AF em relação ao grupo controle (p < 0,0001). A análise da relação entre os marcadores de hemólise e os índices de resistência vascular mostrou associação significativa. Nos rins, forte correlação inversa foi observada entre nível de hemoglobina e IR e IP em todas as artérias; moderada correlação direta foi encontrada entre desidrogenase láctica e os índices de resistência nas artérias segmentares. Nos membros inferiores, moderada correlação direta foi detectada entre contagem de reticulócitos e velocidade de pico sistólico nas artérias tibial anterior e tibial posterior; forte correlação inversa foi observada entre hemoglobina e velocidade de pico sistólico em todas as artérias. Nas órbitas, moderada correlação direta foi encontrada entre contagem de reticulócitos e os índices de resistência na artéria oftálmica; e forte correlação inversa foi detectada entre hemoglobina e IR e IP na artéria central da retina. O trabalho demonstrou que a resistência vascular arterial dos rins, membros inferiores e órbitas, aferida por meio de dopplervelocimetria, é elevada em portadores de AF, com moderada a forte correlação com os biomarcadores de hemólise.

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