The effect of partial substitution of Ni by Mg on the structural, magnetic and spectroscopic properties of the double perovskite Sr2NiTeO6.

In this report, the structural, magnetic and spectroscopic properties of the freeze-drying synthesized Sr2Ni1-xMgxTeO6 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxides are analyzed by means of X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD), electron paramagnetic resonance, diffuse reflectance and magnetic susceptibility. The XRPD and NPD data analysis using the mode-crystallography approach have revealed that at room temperature (RT), all the compositions are monoclinically distorted with the space group I2/m. The high and low temperature analyses have shown that these materials suffer a series of three structural phase transitions. The EPR results have shown that the spectra of all the compositions are centred at g≈ 2.28, indicating a slightly distorted octahedral environment of Ni(2+), which is in agreement with the crystal structure analysis. The increase of the Mg(2+) content in Sr2Ni1-xMgxTeO6, provokes a decrease of the dipolar interaction effects and thus, the resonance becomes narrower. This resonance does not completely disappear which leads to the idea that the long-range magnetic order is not completely established when x≥ 0.3. The substitution of the Ni(2+) (S = 1) ions by Mg(2+) (S = 0) ions, also induces a weakening of the antiferromagnetic interactions, which is reflected in the diminishing of the absolute value of θ and the Néel temperature TN. The magnetic structure determination revealed the existence of an antiferromagnetic coupling for x- and z-spin components of the nickel atoms.

Synthesis, structural, magnetic and phase-transition studies of the ferromagnetic La2CoMnO6 double perovskite by symmetry-adapted modes.

A powdered La2CoMnO6 double perovskite was synthesized by the solid-state reaction method, and its crystal structure was investigated by (mode-crystallography) Rietveld analysis using X-ray and neutron powder diffraction data. La2CoMnO6 material is a monoclinic perovskite at room temperature, adopting the space group P21/n (a(-)a(-)b(+)), , c ≈ 2ap and Z = 2. The P21/n phase can be described effectively by three distortion modes (GM4(+), X3(+), X5(+)) of the Fm3[combining macron]m (a(0)a(0)a(0)) parent phase. The comparative study of the material and those in the Ln2CoMnO6 and Ln2NiMnO6 families has shown a general trend in nearly all the materials, has served to select a common direction in the sub-space spanned by X5(+), tri-linearly coupled to the order parameters of the cubic to monoclinic first order phase transition. This direction has been used to parametrize the refinements and to perform reliable refinements in the high-temperature intermediate distorted trigonal phase, R3[combining macron] (a(-)a(-)a(-)), for which only one effectively acting irrep has been deduced: GM5(+), physically a tilt of the oxygen sharing octahedra of Co and Mn. Its temperature evolution up to the prototype cubic phase has been fitted in the framework of the Landau Theory of Phase Transitions, showing a behavior typical of a tricritical point. The low-temperature neutron powder diffraction data have served to solve the magnetic structure: three indistinguishable ferromagnetic models with the space groups P21/n and P2/n' are proposed.

Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1-xMgxTeO6 (x = 0.1, 0.2 and 0.5).

The structural and magnetic properties of a series of ordered double perovskites with the formula Sr(2)Co(1-x)Mg(x)TeO(6) (x = 0.1, 0.2 and 0.5) are investigated by X-ray diffraction, low temperature neutron diffraction, electron paramagnetic resonance and magnetic susceptibility. The progressive substitution of the paramagnetic Co(2+) high spin ion by the diamagnetic Mg(2+), of about the same size, induces changes in the room temperature crystal structure, from a distorted P2(1)/n phase for the undoped Sr(2)CoTeO(6) oxide to the I4/m of the end member (Sr(2)MgTeO(6)). These perovskites experience structural transitions on heating, the temperature at which the transitions occur being smaller as x increases. The novel approach of mode-crystallography is used for the analysis. All oxides show antiferromagnetic exchange interactions between Co(2+) ions but the long range antiferromagnetic order is not achieved for the phase with x = 0.5. The low temperature neutron diffraction data have been evaluated using a full symmetry analysis. Results are consistent with an unquenched orbital contribution of a high spin Co(2+) ion.

Structural study of SrPrZnRuO6, SrPrCoRuO6, SrPrMgRuO6 and SrPrNiRuO6 double perovskite oxides by symmetry-adapted mode analysis.

Powder SrPrZnRuO6, SrPrCoRuO6, SrPrMgRuO6 and SrPrNiRuO6 double perovskites were synthesized by the solid-state reaction method, and their crystal structure was investigated by Rietveld analysis (using the symmetry-mode procedure) by x-ray, synchrotron and neutron powder diffraction data. SrPrMRuO6 materials are monoclinic perovskites at room temperature, adopting the space group P21/n, [Formula: see text], c ≈ 2ap, Z = 2. The unit cell parameters increase through the series as the B-cation size increases. The tilting of the octahedra is associated with irreducible representations GM(+)4 and X(+)3. In the studied series, Sr(2+)/Pr(3+) are in eight-fold coordination and are displaced from the center of the Sr/PrO8 polyhedron along [010] by the X(+)5(A10) mode. The size of the first coordination sphere of Sr/Pr increases and the second coordination sphere reduces with temperature, suggesting an actual change in coordination. While changing the interatomic distances, the distortion of the structure diminishes, as observed in distortion mode amplitudes and octahedral tilt angles. The temperature driven [Formula: see text] phase transition was observed for Ni and Mg materials at ≈1025 K and 950 K, respectively. Tilting of the octahedra in the trigonal phase is associated with GM(+)4, which is the unique active mode associated with the not experimentally observed [Formula: see text] phase transition.

Mode-crystallography analysis and magnetic structures of SrLnFeRuO6 (Ln = La, Pr, Nd) disordered perovskites.

The crystal and magnetic structures of SrLnFeRuO(6) (Ln = La, Pr, Nd) double perovskites have been investigated. All compounds crystallize with an orthorhombic Pbnm structure at room temperature. These materials show complete chemical disorder of Fe and Ru cations for all compounds. The distortion of the structure, relative to the ideal cubic perovskite, has been decomposed into distortion modes. It has been found that the primary modes of the distortion are octahedral tilting modes: R(4)(+) and M(3)(+). The crystal structure of SrPrFeRuO(6) has been studied from room temperature up to 1200 K by neutron powder diffraction. There is a structural phase transition from orthorhombic (space group Pbnm) to trigonal (space group R3c) at T = 1075 K. According to group theory no second-order transition is possible between these symmetries. Magnetic ordering for all the compounds is described by the magnetic propagation vector (0,0,0). SrPrFeRuO(6) shows ferrimagnetic order below ca 475 K, while SrLaFeRuO(6) (below ca 450 K) and SrNdFeRuO(6) (below ca 430 K) exhibit canted-antiferromagnetic order. The magnetic moments at low temperatures are m(Fe/Ru) = 1.88 (3)µ(B) for SrLaFeRuO(6) (2 K), m(Pr) = 0.46 (4)µ(B) and m(Fe/Ru) = 2.24µ(B) for SrPrFeRuO(6) (2 K), and m(Fe/Ru) = 1.92µ(B) for SrNdFeRuO(6) (10 K).

Growth and characterization of Pb3Ni1.5Mn5.5O15 single crystal.

Single crystals of the mixed valence compound Pb3Ni1.5Mn5.5O15 were successfully grown. Polarized Raman spectroscopy revealed that they belong to the point group D(3d), in accordance with single-crystal x-ray diffraction data which were refined within the trigonal space group P3c1 (No. 165), with lattice parameters a = 9.941(3) Å and c = 13.543(3) Å. Strongly anisotropic long range magnetic order is established below 65 K.

Crystal growth and twinned crystal structure of Sr2CaWO6.

Single crystals of Sr(2)CaWO(6) have been prepared by sintering at high temperature. Powder samples were compressed into rods and heated up to 1953 K. This seems a promising new route for further studies of the structure and physical properties of double perovskites. The structural model of Sr(2)CaWO(6) includes a quantitative description of the twinning shown by the diffraction pattern that should be present in almost any single-crystal specimen for this type of compound.

[Anatomical landmarks and surgical limits in the suboccipital transmeatal approach to the acoustic neuroma]. / Referencias anatómicas y límites quirúrgicos en el abordaje suboccipital transmeatal del neurinoma acústico.

INTRODUCTION: To completely remove the intracanalicular portion of the acoustic neuroma through the retrosigmoid approach, we must open the posterior wall of the internal auditory canal (IAC). Therefore, drilling the IAC is one of the key steps we need to take in the transmeatal surgical approach. Nevertheless, there are no clear anatomical landmarks to identify structures such as the semicircular canals, the jugular bulb or air cells. The individual anatomical variations and those caused by the tumour itself make preoperative evaluation essential if we wish to avoid complications such as deafness, cerebrospinal fluid leakage, bleeding and air embolism. OBJECTIVE: We describe here the personal experience of the senior author (EU) in drilling the posterior wall of the IAC, with special reference to the anatomical landmarks and surgical limits in the suboccipital approach to the intracanalicular portion of the acoustic neuromas. MATERIAL AND METHODS: This work is based on anatomical data obtained from drilling human temporal bones obtained from cadavers, along with our experience with 20 patients who were operated on for acoustic neuroma using Samii's technique. RESULTS: We did not operate on any purely intracanalicular neurinomas using this approach. Two tumors were grade II (up to 20mm in diameter), 12 were grade III and 6 were grade IV. We did not drill far enough in any of these cases to be able to see the fundus of the IAC, which was confirmed by postoperative CT. Despite this, the tumor was considered to be completely removed in 17 cases. There was no mortality and we has no major complications as a result of drilling the IAC such as cerebrospinal fluid leakage or air embolism. we cannot guarantee that hearing loss of postoperative deafness, which were the norm except in one case of grade II, were caused by nervous, ischemic or labyrinthine lesions. CONCLUSION: In our material it was not possible to completely expose the IAC fundus using a retrosigmoid approach without injury to labyrinth. The areas in which the risk of secondary complications is greatest when drilling are the inferior wall and the IAC fundus. The medial extension of the suboccipital craniotomy makes drilling the intrameatal tumor exposure easier. There are no intraoperative landmarks to locate the petrous structures while drilling the IAC except for those provided by the surgeon's own experience.

Referencias anatómicas y límites quirúrgicos en el abordaje suboccipital transmeatal del neurinoma acústico / Anatomical landmarks and surgical limits in the suboccipital transmeatal approach to the acoustic neuroma

Introducción. En la extirpación completa del neurinoma acústico por vía suboccipital retrosigmoidea, es obligada la apertura de la pared posterior del conducto auditivo interno (CAI). Por lo tanto, uno de los pasos clave en el abordaje quirúrgico transmeatal es el fresado del CAL Sin embargo, no existen claras referencias anatómicas intraoperatorias para la identificación de estructuras tales como los canales semicirculares, el golfo de la vena yugular o las celdas aéreas. Las variaciones anatómicas individuales y las producidas por el propio tumor, obligan en cada caso a una correcta planificación preoperatoria, si queremos evitar complicaciones secundarias a su lesión yatrógena (cofosis, licuorrea, hemorragia y embolismo aéreo).Objetivo: Se expone la experiencia del primer autor firmante (EU) en el fresado del CAI con especial referencia a la topografía anatómica y límites quirúrgicos en el abordaje suboccipital retrosigmoideo a la porción intracanalicular del neurinoma acústico. Material y métodos. Este trabajo está basado en datos anatómicos obtenidos del fresado de huesos temporales normales extraídos de material autópsico junto a nuestra experiencia sobre 20 pacientes intervenidos de neurinoma acústico siguiendo la técnica y protocolo de Samii. Resultados. No hemos intervenido por esta vía ningún tumor puramente intracanalicular. 2 casos han sido de grado II (hasta 20mm de diámetro), 12 de grado III y 6 casos de grado IV En ningún caso se ha llegado a fresar tanto como para visualizar el fondo del CAI, lo que se confirmó con el TAC postoperatorio; a pesar de ello en 17 casos se ha considerado la extirpación como completa. No ha existido mortalidad y no hemos tenido complicaciones mayores atribuidas al fresado del CAI, como licuorrea o embolismo aéreo. No podemos asegurar que la hipoacusia o la cofosis postoperatoria, que han sido la regla excepto en un caso de grado II, haya sido causada por lesión nerviosa, laberíntica o isquémica. Conclusiones. En nuestro material no ha sido posible la exposición completa del fondo del CAI por vía retrosigmoidea sin lesionar alguna estructura laberíntica. Las zonas de mayor riesgo de complicaciones secundarias al fresado son la pared inferior y el fondo del CAL La extensión medial de la craniectomía suboccipital facilita al fresado y a la exposición tumoral intrameatal. No existen referencias intraoperatorias para localizar las estructuras petrosas durante el fresado del CAI excepto la propia experiencia del cirujano (AU)

Midazolam coma for refractory status epilepticus in children.

OBJECTIVE: To implement and retrospectively evaluate a therapeutic algorithm for the treatment of refractory status epilepticus with midazolam coma. METHODS: Eight consecutive patients with refractory status epilepticus were mechanically ventilated. Their arterial and central venous blood pressures were continuously monitored by indwelling vascular catheters. These patients were also continuously monitored by a 16-channel video electroencephalogram (EEG). A midazolam bolus of 0.15 mg/kg was administered, and a continuous infusion of 1-2 microg/kg/min was started. If seizures continued, the infusion was increased every 15 mins by 1-2 microg/kg/min. If seizures stopped and/or burst suppression was achieved, the patients continued to receive that dose for 48 hrs and were then weaned by decrements of 1-2 microg/kg/min every 15 mins. RESULTS: The patients' ages ranged from 17 days to 16 yrs, and they had various underlying diseases. In five of the eight patients, cessation of seizures occurred before achieving burst suppression on EEG, in two patients, cessation occurred during burst suppression, and in one patient, no response before or during burst suppression was encountered. The maximal midazolam doses required to achieve cessation of seizures and/or burst suppression, whichever came first, ranged from 4-24 microg/kg/min, with a mean of 14 +/- 6 microg/kg/min. The patients maintained stable cardiovascular function while receiving the maximal dose of midazolam and did not require inotropic support. CONCLUSION: Midazolam infusion, as per our described algorithm, is effective in terminating refractory status epilepticus. This treatment is not associated with cardiovascular instability, even at doses resulting in burst suppression. In the majority of cases, cessation of seizures occur before burst suppression is achieved on EEG.

[Prognosis of pediatric rhabdomyosarcoma. Review of literature and a case report]. / Pronóstico de los rabdomiosarcomas infantiles. Revisión de la literatura al respecto. Presentación de un caso.

Rhabdomyosarcomas (RMS) are responsible for 5% to 10% of childhood cancers. In children, they are the most common sarcoma of the head and neck, urogenital tract, and limbs. We report a case of botryoid type rhinopharyngeal RMS in a 14-year-old girl which had a favorable outcome. The prognostic factors of RMS were reviewed.