Efeitos de interface em bicamadas magnéticas acopladas

We have developed a theoretical study of magnetic bilayers composed by a ferromagnetic film grown in direct contact on an antiferromagnetic one. We have investigated the interface effects in this systems due to the interfilms coupling. We describe the interface effects by a Heisenberg like coupling with an additional unidirectional anisotropy. In the first approach we assume that the magnetic layers are thick enough to be described by the bulk parameters and they are coupled through the interaction between the magnetic moments located at the interface. We use this approach to calculate the modified dynamical response of each material. We use the magnetic permeability of the layers (with corrections introduced by interface interactions) to obtain a correlation between the interface characteristics and the physical behavior of the magnetic excitations propagating in the system. In the second model, we calculated an effective susceptibility of the system considering a nearly microscopical approach. The dynamic response obtained by this approach was used to study the modifications in the spectrum of the polaritons and its consequences on the attenuated total reflection (ATR). In addition, we have calculated the oblique reflectivity. We compare our result with those obtained for the dispersion relation of the magnetostatic modes in these systems

Efeitos de interface em bicamadas magnéticas

We study magnetic interface roughness in F/AF bilayers. Two kinds of roughness were considered. The first one consists of isolated defects that divide the substrate in two regions, each one with an AF sub-lattice. The interface exchange coupling is considered uniform and presents a sudden change in the defects line, favoring Neel wall nucleation. Our results show the interface field dependence of the threshold thickness for the reorientation of the magnetization in the ferromagnetic film. Angular profiles show the relaxation of the magnetization, from Neel wall, at the interface, to reoriented state, at the surface. External magnetic field, perpendicular to the easy axis of the substrate, favors the reoriented state. Depending, of the external magnetic field intensity, parallel to the easy axis of the AF, the magnetization profile at surface can be parallel or perpendicular to the field direction. The second one treats of distributed deffects, periodically. The shape hysteresis curves, exchange bias and coercivity were characterized by interface field intensity and roughness pattern. Our results show that dipolar effects decrease the exchange bias and coercivity

Propriedades físicas de bicamadas magnéticas

The magnetic order of bylayers composed by a ferromagnetic film (F) coupled with an antiferromagnetic film (AF) is studied. Piles of coupled monolayers describe the films and the interfilm coupling is described by an exchange interaction between the magnetic moments at the interface. The F has a cubic anisotropy while the AF has a uniaxial anisotropy. We analyze the effects of an external do magnetic field applied parallel to the interface. We consider the intralayer coupling is strong enough to keep parallel all moments of the monolayer an then they are described by one vector proportional to the magnetization of the layer. The interlayer coupling is represented by an exchange interaction between these vectors. The magnetic energy of the system is the sum of the exchange. Anisotropy and Zeeman energies and the equilibrium configuration is one that gives the absolute minimum of the total energy. The magnetization of the system is calculated and the influence of the external do field combined with the interfilm coupling and the unidirectional anisotropy is studied. Special attention is given to the region near of the transition fields. The torque equation is used to study dynamical behavior of these systems. We consider small oscillations around the equilibrium position and we negleet nonlinear terms to obtain the natural frequencies of the system. The dependence of the frequencies with the external do field and their behavior in the phase transition region is analized

Hyperfine interaction in Zn-Al layered double hydroxides intercalated with conducting polymers

Organic-inorganic hybrid materials based on the assembly between inorganic 2D host structure and polymer have received considerable attention in the last few years. This emerging class of materials presents several applications according to their structural and functional properties. Particularly, among others, layered double hydroxides (LDHs) provide the opportunity of preparing new organically modified 2D nanocomposites. Pyrrole carboxylic acid derivatives, namely 4-(lH-pyrrol-1-yl)benzoate, 3-(pyrrol-i-yl)-propanoate,7-(pyrrol-1-yl)-heptanoate, and aniline carboxylic acid derivative, namely 3-aminobenzoic acid, have been intercalated in LDHs of intralamellar composition Zn2Al(OH)(6). The LDHs were synthesized by the co-precipitation method at constant pH followed by hydrothermal treatment for 72 h. The materials were characterized by powder X-ray diffraction patterns (PXRD), transmission electron microscopy (TEM) thermogravimetric analysis (TGA), and electron spin resonance (ESR). The basal spacing found by the PXRD technique gives evidence of the formation of bilayers of the intercalated anions. ESR spectra present a typical signal with a superhyperfine structure with 6 + 1 lines (g = 2.005 +/- 0.0004), which is assigned to the interaction between a carboxylate radical from the guest molecules and a nearby aluminium nucleus (I = 5/2) from the host structure. Additionally, the ESR data suggest that the monomers are connected to each other in limited number after thermal treatment. (c) 2007 Elsevier Ltd. All rights reserved.

Dynamics of meso and thermo citrate synthases with implicit solvation

The dynamics of hydration of meso and thermo citrate synthases has been investigated using the EEF1 methodology implemented with the CHARNM program. The native enzymes are composed of two identical subunits, each divided into a small and large domain. The dynamics behavior of both enzymes at 30 degrees C and 60 degrees C has been compared. The results of simulations show that during the hydration process, each subunit follows a different pathway of hydration, in spite of the identical sequence. The hydrated structures were compared with the crystalline structure, and the root mean square deviation (RMSD) of each residue along the trajectory was calculated. The regions with larger and smaller mobility were identified. In particular, helices belonging to the small domain are more mobile than those of the large domain. In contrast, the residues that constitute the active site show a much lower displacement compared with the crystalline structure. Hydration free energy calculations point out that Thermoplasma acidophilum citrate synthase (TCS) is more stable than chicken citrate synthase (CCS), at high temperatures. Such result has been ascribed to the higher number of superficial charges in the thermophilic homologue, which stabilizes the enzyme, while the mesophilic homologue denatures. These results are in accord with the experimental found that TCS keeps activity at temperatures farther apart from the catalysis regular temperature than the CCS. (c) 2005 Wiley Periodicals, Inc.

Bacterial cellulose-silica organic-inorganic hybrids

Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the preparation of new organic-inorganic hybrids. BC-silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS) at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.% of silica spheres, 20-30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 degrees C and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface. Emission color can be tuned by changing the excitation wavelength.

Desenvolvimento de misturas ternárias para remoção de reboco de fluido de perfuração sintético

The construction of wells is one of the most important activities of the oil industry. The drilling process is the set of activities and operations to design, program and perform the opening thereof. During this process, the cuttings are removed by the drilling fluid, or mud, and carted to the surface. This fluid is injected into the drill string and returns to the surface through the annular space between the well walls and the drill string. After the descent of the column casing, the annular space between the casing string and the walls of the borehole is filled with cement so as to secure the spine and prevent any migration of fluids between the various permeable zones traversed by the well behind of the coating. To ensure the good quality of the cementation scrubbers are used mattresses which are pumped ahead of the cement slurry so as to avoid contamination of the drilling fluid paste, or vice versa, and assist in the removal of plaster, formed by drilling fluid of the borehole walls, thus enabling a better cement bond to the well. Within this context, this work aims to evaluate the efficiency of mattresses scrubbers, the basis of ionic and nonionic surfactants, on the removal of nonaqueous drilling fluid, based on n-paraffin in oil wells, and the compatibility between the Mattress relations washer / drilling fluid bed scrubber / cement paste mattress washer / cement slurry / drilling fluid and the drilling fluid / cement slurry using laboratory tests rheology, thickening time and compressive strength. Also technique was performed X-ray diffraction (XRD) for a more detailed analysis of these mixtures with hydrated cement paste. In compatibility tests the conditions of temperature and pressure used in the same laboratory procedure simulating the conditions of oil wells, the well is considered the depth of 800 m. The results showed that the compositions of the mattress washer nonionic, KMS obtained a 100% efficient in removing the non-aqueous drilling fluid, and the best formulation showed good results with respect to compliance testing

Comportamento hemodinâmico e metabólico do choque hemorrágico: estudo experimental no cão

JUSTIFICATIVA E OBJETIVOS: Diversos modelos experimentais têm sido utilizados para ilustrar as alterações hemodinâmicas e metabólicas que ocorrem durante o choque hemorrágico. O objetivo da pesquisa é o de observar os comportamentos hemodinâmicos e metabólicos que acontecem em um modelo seqüencial e progressivo de choque hemorrágico no cão, verificando quais índices alteram-se mais precocemente. MÉTODO: O estudo foi realizado em 13 cães sob anestesia venosa total com pentobarbital sódico, em normoventilação e previamente esplenectomizados. Os animais não foram hidratados e a velocidade do sangramento foi ditada pela pressão arterial em que o animal se encontrava. Os atributos estudados foram divididos em hemodinâmicos (freqüência cardíaca - FC, pressão arterial média - PAM, índice de resistência vascular sistêmica - IRVS, índice sistólico - IS, índice cardíaco - IC, índice de choque - I.choque, índice de trabalho sistólico do ventrículo esquerdo - ITSVE, pressão capilar pulmonar - PCP, pressão venosa central - PVC) e metabólicos (saturação venosa mista - SvO2, pressão venosa de oxigênio - PvO2, transporte de oxigênio - DO2, consumo de oxigênio - VO2, extração de oxigênio - TEO2, lactato sérico). A coleta de dados e os atributos foram estudados em 6 momentos distintos, sendo M1, o momento controle e os outros momentos correspondentes a decréscimos gradativos de 10% da volemia calculada para cada animal. RESULTADOS: A hemorragia determinou diminuição significativa da FC somente em M6; queda da PAM, IC, IS e ITSVE a cada momento estudado; discreta alteração da PVC e PCP em cada momento; diminuição da PvO2 e da SvO2 nos momentos estudados; redução do DO2, estabilização do VO2 e elevação da TEO2 nos momentos; o índice de choque apresentou elevação até M3, diminuição em M4 e nova elevação até M6; o IRVS elevou-se até M6, ficou inalterado em M5 e apresentou diminuição significativa em M6; o lactato apresentou elevações a partir de M5 e M6. CONCLUSÕES: Considerou-se que a pressão arterial média, freqüência cardíaca, pressão venosa central e pressão capilar pulmonar não refletem o real estado volêmico dos cães no nosso modelo experimental e que o transporte, consumo e a taxa de extração de oxigênio são parâmetros úteis na determinação da reversibilidade e prognóstico do choque hemorrágico.

Perfil Fosfolipídico Pulmonar em Recém-nascidos de Ratas Diabéticas

Objetivo: avaliar as repercussões do diabete materno sobre o perfil fosfolipídico pulmonar de fetos de ratas com diabete moderado e grave pelas dosagens de lecitina (L), esfingomielina (E), fosfatidil-glicerol (PG), fosfatidil-inositol (PI) e relações L/E e PG/PI. Métodos: foram utilizadas 54 ratas Wistar, em idade reprodutiva, introduzidas na seqüência experimental de diabete e prenhez¹. O diabete foi induzido por aloxana (42 mg/kg de peso, iv) e compostos três grupos: controle, diabete moderado (DM, glicemia entre 120 e 200 mg/dl) e diabete grave (DG, níveis superiores a 200 mg/dl). Realizou-se cesárea no 21º dia, os pulmões fetais foram macerados, reunidos em pool e os fosfolipídios dosados por cromatografia em camada delgada unidirecional. Resultados: os pulmões dos filhotes das ratas com diabete moderado tiveram maior peso (0,159 g) e menor concentração de PG (3,0 µg/ml) e PI (3,4 µg/ml) que o grupo controle (0,155 g; 6,8 e 6,7 µg/ml), e as mesmas relações L/E (2,2) e PG/PI (2,0); os pulmões dos filhotes das ratas com diabete grave tiveram menor peso (0,145 g), os mesmos valores das relações L/E (1,9) e PG/PI (2,1) e menor valor de PI (5,1 µg/ml) que o grupo controle. Conclusões: 1) o retardo do amadurecimento pulmonar dos recém-nascidos de ratas com diabete moderado é explicado pelo maior peso pulmonar associado à menor concentração de PG e PI; 2) a aceleração do amadurecimento pulmonar dos recém-nascidos de ratas com diabete grave é explicada pelo menor peso pulmonar associado à mesma concentração de PG e PI.

Gel and porous polyethylene implants for anophthalmic cavity reconstruction-evaluation using the B scan ultrasound

AIM: To evaluate the host response of the gel and porous polyethylene implants in anophthalmic cavities using the B scan ultrasound.METHODS: Thirty-six white rabbits underwent unilateral enucleation with placement of gel or porous polyethylene spheres implants. The animals were submitted to clinical examination weekly and to ultrasound evaluation on 30, 60 and 90 days after surgery.RESULTS: All rabbits with gel polyethylene spheres, except one, showed implant extrusion probably because the gel spheres have hydrated and increased in volume. The B ultrasound of the gel polyethylene implant did not show vessels inside during the following period. Five animals (27.8%) with porous polyethylene spheres presented implant extrusion after 30 days of surgery. According to B ultrasound, the porous polyethylene implant showed irregular and heterogeneous architecture and reflective peaks similar to vascularized tissues.CONCLUSION: More studies are required to determine the ideal volume of gel polyethylene implant necessary to correct the diminished orbital content in the anophthalmic cavity. The B ultrasound effectiveness showed in this study for anophthalmic socket implants evaluation provides useful information for further in vivo studies and might substitute expensive methods of implants vascularization evaluation,

Damage to the central amygdala produces differential encephalic c-fos expression in the water deprivation-partial rehydration protocol

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Central angiotensin II induces sodium bicarbonate intake in the rat

The aim of this work was to test mineral preference in hydrated rats that received a pulse intracerebroventricular (icv(p)) injection of ANG II at a dipsogenic dose (50 ng). The icv(p) ANG II induced a four-fold higher ingestion of 0.15 M NaHCO(3) than of other mineral solutions at palatable concentrations (0.15 M NaCl, 0.05 mM CaCl(2) and 0.01 M KCl) in a five-bottle test with water available in a fifth bottle; water intake was not consistently high in this test. Contrary to what is predicted by the mineralocorticoid/angiotensin II synergy hypothesis, the 0.15 M NaCl intake in the five-bottle test was not enhanced by icvp ANG H preceded by deoxycorticosterone (DOCA) treatment (2.5 mg/day for 3 days); neither was the NaHCO(3) intake. This result contrasted with the vigorous ingestion of both isotonic sodium solutions, but mostly of NaCl, rather than of other fluids, by sodium-depleted (furosemide 10 mg sc + 24 h removal ambient sodium) rats in a sodium appetite test. The results suggest that mineralocorticoid combined to icv(p) ANG II does not simulate the sodium preference shown during sodium appetite. The results also show that a dipsogenic dose of central ANG II induces a reliable ingestion of isotonic sodium bicarbonate in the rat. (C) 2007 Elsevier Ltd. All rights reserved.

Phosphorus magnetic resonance spectroscopy in malformations of cortical development

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Phospholipase A(2) myotoxins from Bothrops snake venoms: Structure-function relationship

Phospholipases A(2) constitute the major components from Bothrops snake venoms and have been extensively investigated not only because they are relatively very abundant in these venoms but mainly because they display a range of many relevant biological effects, including: myotoxic, cytotoxic, edema-inducing, artificial membrane disrupting, anticoagulant, neuromuscular, platelet aggregation inhibiting, hypotensive, bactericidal, anti-HIV, anti-tumoural, anti-malarial and anti-parasitic. The primary structures of several PLA(2)s have been elucidated through direct amino acid sequencing or, inderectly, through the corresponding nucleotide sequencing. Two main subgroups were thus described: (i) Asp49 PLA(2)s, showing low (basic, highly myotoxic) to relatively high (acidic, less or non myotoxic) Ca++-dependent hydrolytic activity upon artificial substrates; (ii) Lys49 PLA(2)s (basic, highly myotoxic) , showing no detectable hydrolytic activity on artificial substrates. Several crystal structures of Lys49 PLAs from genus Bothrops have already been solved, revealing very similar fold patterns. Lack of catalytic activity of myotoxic Lys49-PLA(2)s, first related solely with the fact that Lys49 occupies the position of the calcium ion in the catalyticly active site of Asp49 PLA(2)s, is now also attributed to Lys122 which interacts with the carbonyl of Cys29 hyperpolarising the peptide bond between Cys29 and Gly30 and trapping the fatty acid product in the active site, thus interrupting the catalytic cycle. This hypothesis, supported for three recent structures, is also discussed here. All Asp49 myotoxins showed to be pharmacologically more potent when compared with the Lys49 variants, but phospholipid hydrolysis is not an indispensable condition for the myotoxic, cytotoxic, bactericidal, anti-HIV, anti-parasitic, liposome disrupting or edema-inducing activities. Recent studies on site directed mutagenesis of the recombinant Lys49 myotoxin from Bothrops jararacussu revealed the participation of important amino acid residues in the membrane damaging and myotoxic activities.

Cloning and Identification of a Complete cDNA Coding for a Bactericidal and Antitumoral Acidic Phospholipase A(2) from Bothrops jararacussu Venom

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)