Domain wall damped harmonic oscillations induced by curvature gradients in elliptical magnetic nanowires

Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is crucial for spintronic-based applications demanding the use of DWs as information carriers. This work focuses on the dynamics of a DW displacing along a bent NW with an elliptical shape under the action of spin-polarized electric currents and external magnetic fields. Our results evidence that a curvature gradient induces an exchange-driven effective tangential field responsible for pinning a DW near the maximum curvature point in a NW. The DW equilibrium position depends on the competition between the torques produced by the external stimuli and the curvature-induced effective fields. When the external stimuli are below a certain threshold, the DW follows a damped harmonic oscillation around the equilibrium position. Above this threshold, DW displaces along the NW under an oscillatory translational motion

Chiral spin-transfer torque induced by curvature gradient

This work analyzes the propagation of a transverse domain wall (DW) motion under the action of an electric current along a nanowire (NW) with a curvature gradient. Our results evidence that the curvature gradient induces a chiral spin-transfer torque (CSTT) whose effect on the DW motion depends on the direction along which the DW points. The origin of the CSTT is explained in terms of a position and phase-dependent effective field associated with the DW profile and the electric current direction. Finally, our results reveal that this chiral mechanism can also affect the behavior of other magnetization collective modes, such as spin waves. This work shows the emergence of curvature-induced chiral spin transport and highlights a new phenomenon to be considered for designing spintronic devices.Comment: 7 pages, 3 figure

L-Arginine Is Essential for Pancreatic b-Cell Functional Integrity, Metabolism and Defense From Inflammatory Challenge

In this work, our aim was to determine whether L-arginine (a known insulinotropic amino acid) can promote a shift of b-cell intermediary metabolism favoring glutathione (GSH) and glutathione disulfide (GSSG) antioxidant responses, stimulus–secretion coupling and functional integrity. Clonal BRIN-BD11 b-cells and mouse islets were cultured for 24 h at various L-arginine concentrations (0–1.15 mmol/l) in the absence or presence of a proinflammatory cytokine cocktail (interleukin 1b, tumour necrosis factor a and interferon g). Cells were assessed for viability, insulin secretion, GSH, GSSG, glutamate, nitric oxide (NO), superoxide, urea, lactate and for the consumption of glucose and glutamine. Protein levels of NO synthase-2, AMP-activated protein kinase (AMPK) and the heat shock protein 72 (HSP72) were also evaluated. We found that L-arginine at 1.15 mmol/l attenuated the loss of b-cell viability observed in the presence of proinflammatory cytokines. L-Arginine increased total cellular GSH and glutamate levels but reduced the GSSG/GSH ratio and glutamate release. The amino acid stimulated glucose consumption in the presence of cytokines while also stimulating AMPK phosphorylation and HSP72 expression. Proinflammatory cytokines reduced, by at least 50%, chronic (24 h) insulin secretion, an effect partially attenuated by L-arginine. Acute insulin secretion was robustly stimulated by L-arginine but this effect was abolished in the presence of cytokines. We conclude that L-arginine can stimulate b-cell insulin secretion, antioxidant and protective responses, enabling increased functional integrity of b-cells and islets in the presence of proinflammatory cytokines. Glucose consumption and intermediary metabolism were increased by L-arginine. These results highlight the importance of L-arginine availability for b-cells during inflammatory challeng

Gaussian coordinate systems for the Kerr metric

We present the whole class of Gaussian coordinate systems for the Kerr metric. This is achieved through the uses of the relationship between Gaussian observers and the relativistic Hamilton-Jacobi equation. We analyze the completeness of this coordinate system. In the appendix we present the equivalent JEK formulation of General Relativity -- the so-called quasi-Maxwellian equations -- which acquires a simpler form in the Gaussian coordinate system. We show how this set of equations can be used to obtain the internal metric of the Schwazschild solution, as a simple example. We suggest that this path can be followed to the search of the internal Kerr metric

Global Challenges for Cancer Imaging

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Atomic Configuration of Nitrogen Doped Single-Walled Carbon Nanotubes

Having access to the chemical environment at the atomic level of a dopant in a nanostructure is crucial for the understanding of its properties. We have performed atomically-resolved electron energy-loss spectroscopy to detect individual nitrogen dopants in single-walled carbon nanotubes and compared with first principles calculations. We demonstrate that nitrogen doping occurs as single atoms in different bonding configurations: graphitic-like and pyrrolic-like substitutional nitrogen neighbouring local lattice distortion such as Stone-Thrower-Wales defects. The stability under the electron beam of these nanotubes has been studied in two extreme cases of nitrogen incorporation content and configuration. These findings provide key information for the applications of these nanostructures.Comment: 25 pages, 13 figure

Uso de dentifrícios fluoretados em pré-escolares

Os fluoretos desempenham importante papel na prevenção e no declínio da doença cárie. O uso regular de dentifrícios fluoretados é considerado um dos meios mais eficazes e racionais de prevenção da cárie dentária, pois alia a remoção do biofilme com o contato constante do flúor com o esmalte dentário. Os cremes dentais fluoretados estão indicados para a população em geral, inclusive para crianças menores de nove anos. Sua utilização em crianças em idade pré-escolar, na fase de desenvolvimento do esmalte dentário dos dentes permanentes, requer supervisão pelos responsáveis e utilização de uma pequena quantidade, uma vez que é sabido o risco de desenvolvimento de fluorose dentária por ingestão excessiva de flúor nessa faixa etária, que involuntariamente ingere certa quantidade de dentifrício no momento da escovação dos dentes. Devido à preocupação com a ocorrência de fluorose, alguns profissionais e associações médicas e odontológicas começaram a recomendar que fossem utilizados cremes dentais sem flúor ou com baixa concentração de flúor para crianças em idade pré-escolar. Entretanto, recentemente, em função de achados científicos, essas recomendações têm sido reformuladas. Este trabalho tem como objetivo esclarecer a população acadêmica em relação a utilização dos dentifrícios fluoretados em pré-escolares, relatando que as evidências científicas apontam para seu uso em crianças de tenra idade, e que o risco de fluorose dentária está diretamente ligado à quantidade de dentifrício fluoretado utlizado em cada escovação