Unusual semiconductor-metal-semiconductor transitions in magnetite Fe3O4 nanoparticles

Magnetite (Fe₃O₄) nanoparticles were successfully prepared by a co-precipitation method. Rietveld refinement on the X-ray diffraction pattern confirmed the development of a single-phase cubic spinel structure with space group Fd3̄m. However, ⁵⁷Fe Mössbauer spectroscopy suggested the presence of Fe³⁺ and Fe^2.5+ (mixed Fe³⁺ and Fe²⁺) ions at the tetrahedral and octahedral sites of the inverse spinel structure, respectively. Impedance spectroscopy measurements showed a discontinues variation in the temperature dependence of the sample's resistive behavior, indicating the appearance of semiconductor–metal–semiconductor like transitions between the temperature range of 293 and 373 K. A similar dual transition was also observed from the dielectric and conductivity measurements around the same temperature regions. The observed unusual transition is explained in term of the competitive effects among the hopping of localized/delocalized and short-range/long-range charge carriers present in the sample. Moreover, the prepared sample exhibits colossal dielectric permittivity (∼10⁶), reduced tangent loss (∼0.2) and moderate conductivity (>10⁻⁶ S cm⁻¹) values, making Fe₃O₄ nanoparticles a potential candidate for electromagnetic absorbing materials.

Herein, we report the existence of a novel semiconductor–metal–semiconductor type transition in Fe₃O₄ nanoparticles by employing impedance spectroscopy techniques.

Soft X-ray refractive index by reconciling total electron yield with specular reflection: experimental determination of the optical constants of graphite

The complex refractive index of many materials is poorly known in the soft X-ray range across absorption edges. This is due to saturation effects that occur there in total-electron-yield and fluorescence-yield spectroscopy and that are strongest at resonance energies. Aiming to obtain reliable optical constants, a procedure that reconciles electron-yield measurements and reflection spectroscopy by correcting these saturation effects is presented. The procedure takes into account the energy- and polarization-dependence of the photon penetration depth as well as the creation efficiency for secondary electrons and their escape length. From corrected electron-yield spectra the absorption constants and the imaginary parts of the refractive index of the material are determined. The real parts of the index are subsequently obtained through a Kramers-Kronig transformation. These preliminary optical constants are refined by simulating reflection spectra and adapting them, so that measured reflection spectra are reproduced best. The efficacy of the new procedure is demonstrated for graphite. The optical constants that have been determined for linearly polarized synchrotron light incident with p- and s-geometry provide a detailed and reliable representation of the complex refractive index of the material near π- and σ-resonances. They are also suitable for allotropes of graphite such as graphene.

[Total inverted shoulder prosthesis and rotator cuff insufficiency: evaluation and determination of anatomical parameters predictive of good functional outcome in 21 shoulders]

OBJECTIVE

Evaluation of the functional results of the Delta 3 inverted shoulder prosthesis and determination of a radio-anatomical index predictive of best functional outcome.

PATIENTS AND METHODS

Retrospective analysis of 19 patients (21 shoulders). Clinical (pain, satisfaction, amplitudes, Constant index) and radiological (acromio-epiphyseal distance) evaluation at a mean follow up of 13.6 months.

RESULTS

Outcomes concerning pain, quality of life and Constant index were good and similar to other series. Few complications were observed. An increase of the acromio-epiphyseal distance of 33 to 50% compared to the non operated side is associated with a good functional result.

CONCLUSION

Our results confirm those of other series and show that Delta 3 inverted prosthesis is an efficient therapeutic alternative in arthropathy with rotator cuff tears. Rehabilitation is fairly short and easy. The increase of the acromio-epiphyseal distance determines the tension of the deltoid muscle and could predict a favorable outcome.

Use of ultrasound and hormone assays in the diagnosis, management, and outcome of twin pregnancy

A study of 79 twin pregnancies was conducted between 1973 and 1976 with particular reference to the use of ultrasound and hormone analysis. There were 17 perinatal deaths, a perinatal mortality rate of 107 per 1000 deliveries. The contributing factors were antepartum anoxia (40%), prematurity (30%), congenital abnormalities (18%), and obstetric trauma (12%). During the period of study there was a complete change in the method of confirming twin pregnancies, ie, in 1973, 84% were confirmed by x-ray and in 1976, 86% by ultrasound. About 40% were diagnosed at 28 weeks' gestation or earlier. The ranges (mean +/- 2 SD) for human placental lactogen (hPL) and urinary estrogens have been established for twin pregnancy, and the value of these measurements in the antenatal management of twin gestations is discussed.