M-SrFe12O19 and ferrihydrite-like ultrathin nanoplatelets as building blocks for permanent magnets: HAADF-STEM study and magnetic properties

Mixtures of M-type strontium hexaferrite (M-SrFe12O19) and ferrihydrite-like particles were prepared by a microwave-assisted hydrothermal process at 200 °C with heating rates in the range 40–50 °C min-1. The particles exhibited a platelet shape with a diameter comprised between 20 and 200 nm and a thickness between 2 and 5 nm. HAADF-STEM observations and EDS analysis were carried out for a better understanding of nucleation and growth process. EDS showed that most of the particles contained Sr and HAADF-STEM revealed that very thin particles with a hexaferrite core extending over less than a unit cell and with surface disorder crystallized along with well crystallized hexaferrite and defect free ferrihydrite particles. The symmetric multilayer structures (SRS) of the ultrathin particles suggested that the nucleation step of the hexaferrite particles involved clusters containing Sr atoms. In comparison with the M-SrFe12O19 micrometer sized platelets prepared with heating rate of 25 °C min-1, the mixtures of ultrathin hexaferrite- and ferrihydrite-like particles combined after annealing a higher coercivity reaching 465 kA m-1 thanks to the smaller initial particle size and a high magnetization reaching 65 A m2 kg-1 thanks to a limited amount of hematite

Light Deflection by Rotating Regular Black Holes with a Cosmological Constant

Using the Gauss-Bonnet theorem, we compute and examine the deflection angle of light rays by rotating regular black holes with a cosmological constant. By the help of optical geometries, we first deal with the Hayward black holes with cosmological contributions. Then, we reconsider the study of the Bardeen solutions. We inspect the cosmological constant effect on the deflection angle of light rays. Concretely, we find extra cosmological correction terms generalizing certain obtained findings. Using graphical analysis, we provide a comparative discussion with respect to the Kerr solutions. The results confirm that the non-linear electrodynamic charges affect the space-time geometry by decreasing the deflection angle of light rays by such cosmological black holes.Comment: latex, 16 pages, 4 figures. Accepted for publication in Chin. J. Phys 202

Landau mean-field analysis and estimation of the spontaneous magnetization from magnetic entropy change

We investigated the critical exponents for the compounds La1-x□xMnO3 (x = 0.1; 0.2 and 0.3) prepared by the sol–gel method. Our samples show a second- order transition inferred from the positive slope, in accordance with the Banerjee Criterion. Using the slope of different models on the TC, the relative slope (RS) was traced. From this perspective, the best models for the three samples prove to be the mean field and the tricritical mean field models. This model is characterized by critical exponents β, γ and δ which are determined by many methods such as MAP, KF method and critical isotherm analysis. The theoritical methods and experimental results were in good agreement for the three compounds. The universality class has been shown. After determining the spontaneous magnetization for x = 0.2 from (-ΔSM) vs. M2, we detected a good agreement with those obtained from the classical extrapolation of Arrott curves (µ0H/M vs. M2). Furthermore, based on the magnetocaloric effect (MCE), Landau’s theory is valid for the compound x = 0.2.publishe

Les masques trompeurs de la bipolarité: étude de 100 cas

Le trouble bipolaire (TB) est une pathologie dont la prévalence est estimée à 1-2 %. Le diagnostic précoce du trouble constitue un enjeu thérapeutique majeur. L'objectif de ce travail est de déterminer les différents diagnostiques attribués aux patients bipolaires avant de recevoir le diagnostic adéquat et de préciser le délai moyen du retard diagnostique. C'est une étude descriptive transversale portant sur 100 patients atteintsde TB, inclus selon les critères du DSM V, qui ont été vus en consultation ou bien hospitalisés dans le service de psychiatrie de l'hôpital Militaire Avicenne de Marrakech, durant une période de deux ans. L'âge moyen des patients était de 29,5 ans avec une prédominance masculine (80%). 40% de nos patients ont reçu au début un autre diagnostic que celui du TB et le premier diagnostic retenu était celui de l'épisode dépressif majeur dans 36% des cas, suivi de l'accès psychotique aigu dans 28% des cas, la schizophrénie dans 16,8% et le trouble de personnalité dans 10,2%. Le délai moyen du retard diagnostic était de 64 mois. 50% des patients ayant reçu un autre diagnostic avaient consulté au moins un psychiatre et 60% des patients avaient été hospitalisés au moins une fois avant le diagnostic du TB.Les errances diagnostiques du TB sont bien établies, conduisant forcément à un retard de prise en charge adéquate .Ces données devraient alerter les psychiatres pour favoriser un meilleur dépistage de la manie et de l'hypomanie qui restent les éléments clé du diagnostic du TB

Optical properties of an ensemble of G-centers in silicon

We addressed the carrier dynamics in so-called G-centers in silicon (consisting of substitutional-interstitial carbon pairs interacting with interstitial silicons) obtained via ion implantation into a silicon-on-insulator wafer. For this point defect in silicon emitting in the telecommunication wavelength range, we unravel the recombination dynamics by time-resolved photoluminescence spectroscopy. More specifically, we performed detailed photoluminescence experiments as a function of excitation energy, incident power, irradiation fluence and temperature in order to study the impact of radiative and non-radiative recombination channels on the spectrum, yield and lifetime of G-centers. The sharp line emitting at 969 meV ($\sim$1280 nm) and the broad asymmetric sideband developing at lower energy share the same recombination dynamics as shown by time-resolved experiments performed selectively on each spectral component. This feature accounts for the common origin of the two emission bands which are unambiguously attributed to the zero-phonon line and to the corresponding phonon sideband. In the framework of the Huang-Rhys theory with non-perturbative calculations, we reach an estimation of 1.6$\pm$0.1 \angstrom for the spatial extension of the electronic wave function in the G-center. The radiative recombination time measured at low temperature lies in the 6 ns-range. The estimation of both radiative and non-radiative recombination rates as a function of temperature further demonstrate a constant radiative lifetime. Finally, although G-centers are shallow levels in silicon, we find a value of the Debye-Waller factor comparable to deep levels in wide-bandgap materials. Our results point out the potential of G-centers as a solid-state light source to be integrated into opto-electronic devices within a common silicon platform

Deflection angle and Shadows by Black Holes in Starobinsky-Bel-Robinson Gravity from M-theory

Motivated by M-theory compactifications, we investigate optical properties of black holes in the Starobinsky-Bel-Robinsion gravity. Precisely, we study the shadows and the deflection angle of light rays by non-rotating and rotating black holes in such a novel gravity. We start by discussing the shadows of the Schwarzschild-type solutions. As expected, we obtain perfect circular shadows where the size decreases with a stringy gravity parameter denoted by $\beta$. We show that this parameter is constrained by the shadow existence. Combining the Newman-Janis algorithm and the Hamilton-Jacobi mechanism, we examine the shadow behaviors of the rotating solutions in terms of one-dimensional real curves. Essentially, we find various sizes and shapes depending on the rotating parameter and the stringy gravity parameter $a$ and $\beta$, respectively. To inspect the shadow geometric deformations, we investigate the astronomical observables and the energy emission rate. As envisaged, we reveal that $a$ and $\beta$ have an impact on such shadow behaviors. For specific values of $a$, we remark that the obtained shadow shapes share certain similarities with the ones of the Kerr black holes in plasma backgrounds. Using the Event Horizon Telescope observational data, we provide predictions for the stringy gravity parameter $\beta$ which could play a relevant role in M-theory compactifications. We finish this work by a discussion on the behaviors of the light rays near to such four dimensional black holes by computing the deflection angle in terms of a required moduli space.Comment: Latex, 27 pages, 10 figures. Authors in alphabetical orde