Crystal truncation rods in kinematical and dynamical x-ray diffraction theories

Crystal truncation rods calculated in the kinematical approximation are shown to quantitatively agree with the sum of the diffracted waves obtained in the two-beam dynamical calculations for different reflections along the rod. The choice and the number of these reflections are specified. The agreement extends down to at least $\sim 10^{-7}$ of the peak intensity. For lower intensities, the accuracy of dynamical calculations is limited by truncation of the electron density at a mathematically planar surface, arising from the Fourier series expansion of the crystal polarizability

Proton configurations in the hydrogen bonds of KH2PO4 as seen by resonant x-ray diffraction

KH2PO4 (KDP) belongs to the class of hydrogen-bonded ferroelectrics, whose paraelectric to ferroelectric phase transition is driven by the ordering of the protons in the hydrogen bonds. We demonstrate that forbidden reflections of KDP, when measured at an x-ray absorption edge, are highly sensitive to the asymmetry of proton configurations. The change of average symmetry caused by the "freezing" of the protons during the phase transition is clearly evidenced. In the paraelectric phase, we identify in the resonant spectra of the forbidden reflections a contribution related to the transient proton configurations in the hydrogen bonds, which violates the high average symmetry of the sites of the resonant atoms. The analysis of the temperature dependence reveals a change of relative probabilities of the different proton configurations. They follow the Arrhenius law, and the activation energies of polar and Slater configurations are 18.6 and 7.3 meV, respectively

An X-ray study of the Dzyaloshinskii-Moriya interaction in the weak ferromagnet FeBO3

International audienceWe report on the axis, magnitude and direction of the Dzyaloshinskii-Moriya (DM) interaction in the weak ferromagnet FeBO3. The latter relies on the determination of the phase of the magnetic x-ray scattering amplitude. We outline a new technique based on interference with forbidden quadrupole resonant scattering to obtain this phase information

Phase transition of KDP observed by Resonant X-ray Diffraction at forbidden reflections

International audienceWe report observations of space-group-forbidden Bragg reflections in Potassium (KH2PO4), at the potassium K edge. We find clear evidence for a transition from one class of space-group-forbidden reflections, where scattering is ruled out by the electric dipole approximation, to a second class, in the ferroelectric phase, where scattering can proceed due to resonant anisotropy within the dipole approximation. The change of symmetry is clearly evidenced by the sudden change of intensity and energy spectrum of the forbidden reflections

Dzyaloshinskii--Moriya interaction: How to measure its sign in weak ferromagnetics?

Three experimental techniques sensitive to the sign of the Dzyaloshinskii--Moriya interaction are discussed: neutron diffraction, Moessbauer gamma-ray diffraction, and resonant x-ray scattering. Classical examples of hematite (alpha-Fe2O3) and MnCO3 crystals are considered in detailComment: 5 pages, 1 figure; to be published in JETP Letter

Teeth sizes in their correlation with parameters of dentofacial arches and maxillofacial area based on native cranial preparations examination

The work offers a view on the results obtained from a radiological and morphometric study of native preparations obtained from 43 passported skulls with physiological occlusion and normodontia of permanent teeth under neutral position of the jaws and a neutral type of gnathic facial skull. It was found that in patients with physiological occlusion of permanent teeth, skulls with neutral type of gnathic facial part of the cranium as well as neutral jaw relationships proved to be predominant, while the major parameters of the dentofacial arches are determined through mesial-distal diameters of the teeth

Comment on "X-ray resonant scattering studies of orbital and charge ordering in Pr1-xCaxMnO3"

In a recent published paper [Phys. Rev. B 64, 195133 (2001)], Zimmermann et al. present a systematic x-ray scattering study of charge and orbital ordering phenomena in the Pr1-xCaxMnO3 series with x= 0.25, 0.4 and 0.5. They propose that for Ca concentrations x=0.4 and 0.5, the appearance of (0, k+1/2, 0) reflections are originated by the orbital ordering of the eg electrons in the a-b plane while the (0, 2k+1, 0) reflections are due to the charge ordering among the Mn3+ and Mn4+ ions. Moreover, for small Ca concentrations (x<0.3), the orbital ordering is only considered and it occurs at (0, k, 0) reflections. A rigorous analysis of all these resonance reflections will show the inadequacy of the charge-orbital model proposed to explain the experimental results. In addition, this charge-orbital model is highly inconsistent with the electronic balance. On the contrary, these reflections can be easily understood as arising from the anisotropy of charge distribution induced by the presence of local distortions, i.e. due to a structural phase transition.Comment: 10 pages, 2 figures.To be published Phys. Rev.

Foreign Body of the Right Main Bronchus with Tracheal Perforation (Case Report)

The article describes a rare case of a foreign body removal from the tracheobronchial tree of a child. In the acute period of aspiration, the girl developed severe hypoxia, a terminal condition caused by the standing of a foreign body in the infraglottic space, a spasm of the vocal cords and obstruction of the lumen of the respiratory tract. In emergency tracheal intubation in a medical institution at the place of residence, the foreign body was moved more distally, which allowed to restore lung ventilation, stabilize the child’s condition and transport her to a specialized medical institution where X-ray and endoscopic examination were performed. It was found that the one-year-old patient had a screw cap tightly wedged into the lumen of the right main bronchus, and the screw’s opposite sharp end punched the left wall of the trachea above its carina. There was a potentially high risk of perforation of the main vessels of the mediastinum with massive bleeding and an unfavorable outcome. Endoscopic removal of a foreign body was technically impossible due to the peculiarity of its transverse arrangement and perforation of the wall, which served as an indication for emergency thoracotomy. A longitudinal sternotomy was performed, providing good access to the distal trachea, the main bronchi and the great vessels. Then we performed transverse bronchotomy in the initial part of the right main bronchus on half of its circumference, removed the foreign body, sutured the wall of the bronchus. The length of the extracted self-drilling screw was 35 millimeters. Postoperative early and late periods went without complications. At follow-up, mucosal surface of the right main bronchus was pink, the vascular pattern was visible, the bronchus was freely passable, not deformed