The Landau-Lifshitz-Bloch equation for ferrimagnetic materials

We derive the Landau-Lifshitz-Bloch (LLB) equation for a two-component magnetic system valid up to the Curie temperature. As an example, we consider disordered GdFeCo ferrimagnet where the ultrafast optically induced magnetization switching under the action of heat alone has been recently reported. The two-component LLB equation contains the longitudinal relaxation terms responding to the exchange fields from the proper and the neighboring sublattices. We show that the sign of the longitudinal relaxation rate at high temperatures can change depending on the dynamical magnetization value and a dynamical polarisation of one material by another can occur. We discuss the differences between the LLB and the Baryakhtar equation, recently used to explain the ultrafast switching in ferrimagnets. The two-component LLB equation forms basis for the largescale micromagnetic modeling of nanostructures at high temperatures and ultrashort timescales

X-ray Diffraction Study of the NaF – LiF – LnF3 (Ln=La,Nd) Eutectic Composition in the Liquid and Solid States

The ternary eutectic alloy with the composition 33 mol % NaF+53 mol % LiF+14 mol % NdF3 has been studied in the liquid and solid states using differential thermal analysis and X-ray diffraction at room and high temperatures. The obtained results demonstrate that the eutectic alloy undergoes no phase transformations at temperatures from 298 K to melting point. Analysis of RMC models of the melt indicates that there is no dense non-crystalline packing of the fluorine anions in contrast to the eutectic NaF—LiF—LaF3 melt

Кашель в постковидный период: клинические наблюдения

Among the extensive list of manifestations of post COVID syndrome, cough is often found. Most researchers interpret its character as post infection. In some patients, post infection cough becomes productive, and combined mucoactive therapy is required for effective treatment. Since the onset of the pandemic, clinical descriptions of spontaneous pneumothorax have accumulated in the literature. The risk of this complication is present even in patients who are not burdened with chronic lung diseases, as well as those who are breathing spontaneously. The study of the mechanisms of development of spontaneous pneumothorax in COVID-19 is necessary for the development of further therapeutic and preventive measures. Traction bronchiectasis occurs in 27 – 52.5% of cases of new coronavirus infection. Changes in the structure of the bronchi predispose to chronic cough and recurrent infections. Respiratory viral infection has been considered in the past as a trigger for bronchial asthma. There is controversy over the new coronavirus. Asthma has been suggested as a protective factor in COVID-19, due to the specific inflammation profile that protects patients. In some patients who have had COVID-19, the cough is due to hyperventilation syndrome. To explain it, a hypothesis of impaired respiratory control was proposed. The paper presents clinical examples illustrating a wide range of pathological conditions accompanied by cough. Possible relationships between cough and previous coronavirus infection are discussed.Среди обширных проявлений постковидного синдрома нередко встречается кашель. Большинство исследователей трактуют его характер как постинфекционный. У части больных постинфекционный кашель приобретает продуктивный характер и для эффективного лечения требуется комбинированная мукоактивная терапия. Также с начала пандемии в литературе накопилось достаточно клинических наблюдений спонтанного пневмоторакса. Риск этого осложнения присутствует даже у пациентов, не отягощенных хроническими заболеваниями легких, а также при самостоятельном дыхании. Изучение механизмов развития спонтанного пневмоторакса при COVID-19 необходимо для разработки дальнейших терапевтических и профилактических мероприятий. Тракционные бронхоэктазы встречаются в 27−52,5 % случаев новой коронавирусной инфекции (НКИ). Изменение структуры бронхов предрасполагает к хроническому кашлю и рецидивирующим инфекциям. Респираторная вирусная инфекция в прошлом рассматривалась в качестве триггера бронхиальной астмы (БА), однако в отношении НКИ существуют разногласия, при этом благодаря особому профилю воспаления, который предохраняет больных БА от НКИ, БА рассматривается в качестве защитного фактора при COVID-19. У некоторых больных, перенесших COVID-19, кашель обусловлен гипервентиляционным синдромом, для объяснения которого предложена гипотеза о нарушении дыхательного контроля. В работе представлены клинические наблюдения, иллюстрирующие широкий круг патологических состояний, сопровождающихся кашлем. Обсуждаются возможные взаимосвязи кашля с перенесенной НКИ

Formation of ultrashort triangular pulses in optical fibers

Specialty shape ultrashort optical pulses, and triangular pulses in particular, are of great interest in optical signal processing. Compact fiber-based techniques for producing the special pulse waveforms from Gaussian or secant pulses delivered by modern ultrafast lasers are in demand in telecommunications. Using the nonlinear Schr¨odinger equation in an extended form the transformation of ultrashort pulses in a fiber towards triangular shape is characterized by the misfit parameter under variety of incident pulse shapes, energies, and chirps. It is shown that short (1-2 m) conventional single mode fiber can be used for triangular pulse formation in the steady-state regime without any pre-chirping if femtosecond pulses are used for pumping. The pulses obtained are stable and demonstrate linear chirp. The ranges and combinations of the pulse parameters found here will serve as a guide for scheduling the experiments and implementation of various all-fiber schemes for optical signal processing

Configurational entropy of magnetic skyrmions as an ideal gas

The study of thermodynamics of topological defects is an important challenge to understand their underlying physics. Among them, magnetic skyrmions have a leading role for their physical properties and potential applications in storage and neuromorphic computing. In this paper, the thermodynamic statistics of magnetic skyrmions is derived. It is shown that the skyrmion free energy can be modelled via a parabolic function and the diameters statistics obeys the Maxwell-Boltzmann distribution. This allows for making an analogy between the behavior of the distribution of skyrmion diameters statistics and the diluted gas Maxwell-Boltzmann molecules distribution at thermodynamical equilibrium. The calculation of the skyrmion configurational entropy, due to thermally-induced changes of size and shape of the skyrmion, is essential for the determination of thermal fluctuations of the skyrmion energy around its average value. These results can be employed to advance the field of skyrmionics.Comment: Main text 26 pages and 6 figures. Supplementary Information 4 page