Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn5Ge3.

The phase of the quantum-mechanical wave function can encode a topological structure with wide-ranging physical consequences, such as anomalous transport effects and the existence of edge states robust against perturbations. While this has been exhaustively demonstrated for electrons, properties associated with the elementary quasiparticles in magnetic materials are still underexplored. Here, we show theoretically and via inelastic neutron scattering experiments that the bulk ferromagnet Mn5Ge3 hosts gapped topological Dirac magnons. Although inversion symmetry prohibits a net Dzyaloshinskii-Moriya interaction in the unit cell, it is locally allowed and is responsible for the gap opening in the magnon spectrum. This gap is predicted and experimentally verified to close by rotating the magnetization away from the c-axis with an applied magnetic field. Hence, Mn5Ge3 realizes a gapped Dirac magnon material in three dimensions. Its tunability by chemical doping or by thin film nanostructuring defines an exciting new platform to explore and design topological magnons. More generally, our experimental route to verify and control the topological character of the magnons is applicable to bulk centrosymmetric hexagonal materials, which calls for systematic investigation.

Wettability of chlorhexidine treated non-carious and caries-affected dentine.

BACKGROUND: The wettability of a surface is a prerequisite for adhesion and the type of dentine plays an important role in this property. This study evaluated the effect of different excipients of chlorhexidine (CHX) on sound and caries-affected dentine wettability. METHODS: Flat dentine surfaces were prepared (n = 100) and artificial caries was induced in half of the sample. For each substrate, sound and caries-affected dentine, surfaces were assigned to five groups: (1) smear-covered dentine; (2) smear-free dentine saturated with water; (3) ethanol; (4) 1% CHX in water; or (5) 1% chlorhexidine in ethanol. The infected dentine was ground with 320-grit silicon carbide paper to the level of affected dentine. The smear layer was removed with acid, followed by rinsing, blot drying and the application of each solution (60 seconds). Single Bond 2 was applied to each surface and contact angles were measured using a goniometer. Data were analysed by ANOVA and Student­Newman­Keuls (a = 0.05). RESULTS: Contact angles were higher on sound dentine, regardless of the treatment. For sound and caries-affected dentine significantly higher angles were obtained on smear-covered dentine. Acid-etched dentine saturated with ethanol and ethanol/CHX resulted in significantly lower angles but only for sound dentine. Neither water and water/CHX nor ethanol and ethanol/CHX solutions differ with respect to dentine wettability. CONCLUSIONS: Caries-affected dentine wettability is higher than sound dentine, and chlorhexidine does not influence this property.

[Acromegaly with the sleep apnea syndrome]. / Acromegalia com síndrome de apneia do sono.

The authors present the clinical of a male patient aged 45 years whose main complaints were loud snoring and excessive daytime sleepiness. Polysomnographic study revealed a sleep obstructive apnea syndrome with an apnea/hypopnea index of 86.5. After being treated with nasal continuous positive air pressure, (12 cm H2O), the apneas ended and sleep architecture was corrected. Physical examination also indicated the presence of an acromegaly, and therefore, the patient was subjected to endocrinological and cerebral imagiological studies; the diagnosis confirmed it as a predisposing factor to the sleep breathing disorder. A brief literature review about the incidence of sleep apnea syndrome in acromegaly is also made; the authors conclude that there is still the need for a systematic screening of sleep breathing disorders in acromegalic patients in order to optimise the treatment and prognosis of this disorders.