Insertional Achilles tendinopathy in patients with Haglund's syndrome: results of computer modeling and biomechanical research

In this study, a biomechanical relationship was found between the pathological process in Haglund syndrome and secondary tendinopathy of the Achilles tendon. We have developed the calculation diagram, created computer models and determined the values of the stress-strain state of the rear foot structures in the normal and with Haglund syndrome. It was found that the maximum stress values are concentrated on the Achilles tendon, but in pathological model the stress values were significantly higher than normal in the whole range of motion of the foot. Normally, maximal stress on the calcaneus is localized on its posterior surface - on the anterior surface of the retrocalcaneal recess. In Haglund syndrome, maximum stress was recorded on the upper surface of the posterior sections of the calcaneus. Haglund syndrome is marked by overloading of the calf muscle. The results of this study explain the development of degenerative changes in the AT in patients with Haglund syndrome. It was also found that the enlarged posterior-upper part of the calcaneus is a factor in the development of insertional Achilles tendinopathy, which should also be considered when choosing further treatment

Quantum Oscillations of Elastic Moduli and Softening of Phonon Modes in Metals

In this paper we present a theoretical analysis of the effect of magnetostriction on quantum oscillations of elastic constants in metals under strong magnetic fields. It is shown that at low temperatures a significant softening of some acoustic modes could occur near peaks of quantum oscillations of the electron density of states (DOS) at the Fermi surface (FS). This effect is caused by a magnetic instability of a special kind, and it can give rise to a lattice instability. We also show that the most favorable conditions for this instability to be revealed occur in metals whose Fermi surfaces include nearly cylindrical segments.Comment: 5 pages, 1 figur

Electrical control of optical orientation of neutral and negatively charged excitons in n-type semiconductor quantum well

We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons.Comment: 18 pages, 4 figure

THE DEVELOPMENT OF LOGICAL THINKING IN JUNIOR STUDENTS THROUGH PROJECT-BASED LEARNING

El artículo da una nueva mirada al método de desarrollo del pensamiento lógico en alumnos de tercer año basado en la correlación entre el modelo original y el que hace posible, a diferencia de los métodos tradicionales, desarrollar el pensamiento del habla, las estructuras intelectuales y las operaciones lógicas de los alumnos de manera más efectiva. . Con la ayuda de los enfoques epistemológico, de actividad sistémica y de entorno, se determina una estrategia para desarrollar el pensamiento lógico de los alumnos a través del aprendizaje basado en proyectos que se basa en la correlación entre el modelo original y el original. Asegura el desarrollo efectivo de a) la actividad intelectual de los escolares b) el pensamiento c) la memoria lógica. El estudio demuestra la efectividad de la tecnología presentada, lo que implica 1) sumergirse en el proyecto, así como especificar sus metas y objetivos; 2) organizar y planificar las actividades de los alumnos; 3) resolver las etapas principales del proyecto; 4) llevar a cabo el proyecto y su presentación; 5) evaluar los resultados. Con base en los datos de la investigación, se destacaron los siguientes criterios: análisis, síntesis, comparación, clasificación, generalización y algunos otros criterios que permitieron determinar tres niveles del desarrollo del fenómeno en cuestión. Nuestro método proporciona una mejora significativa de los resultados de la investigación y garantiza la formación de actividades de investigación, informativas, regulatorias y analíticas de aprendizaje universal (ULA). La evaluación de la efectividad y validez del método propuesto se corrobora mediante cálculos para el criterio de Fisher (criterio φ *). Los resultados comparativos de la investigación antes y después del experimento a alto nivel son 3.564. Los valores empíricos obtenidos de φ * están en el área de significancia. H0 se rechaza (el eje de significancia = 1.64–2.31). Por lo tanto, el método en cuestión tiene un grave impacto en el desarrollo del pensamiento lógico a través del aprendizaje basado en proyectos de alumnos menores.O artigo analisa o método de desenvolver o raciocínio lógico em alunos juniores com base na correlação entre o original e o modelo e possibilita, diferentemente dos métodos tradicionais, desenvolver o raciocínio, estruturas intelectuais e operações lógicas dos alunos de maneira mais eficaz. Com o auxílio das abordagens epistemológicas, de atividade sistêmica e do meio, é determinada uma estratégia para o desenvolvimento do pensamento lógico dos alunos por meio da aprendizagem baseada em projetos, baseada na correlação entre o original e o modelo. Garante o desenvolvimento efetivo de a) atividade intelectual das crianças em idade escolar b) pensamento c) memória lógica. O estudo comprova a eficácia da tecnologia apresentada, que implica 1) imersão no projeto, além de especificar suas metas e objetivos; 2) organização e planejamento das atividades dos alunos; 3) elaboração das principais etapas do projeto; 4) realização do projeto e sua apresentação; 5) avaliando os resultados. Com base nos dados da pesquisa, foram destacados os seguintes critérios: análise, síntese, comparação, classificação, generalização e outros critérios que permitiram determinar três níveis de desenvolvimento do fenômeno em questão. Nosso método fornece uma melhoria significativa dos resultados da pesquisa e garante a formação de atividades de aprendizagem universais (ULAs) informativas, regulatórias e analíticas. A avaliação da eficácia e validade do método proposto é corroborada por cálculos para o critério de Fisher (critério φ *). Os resultados comparativos da pesquisa antes e após o experimento em alto nível são 3.564. Os valores empíricos obtidos de φ * estão na área de significância. H0 é rejeitado (o eixo de significância = 1.64-2.31). Assim, o método em questão tem um sério impacto no desenvolvimento do pensamento lógico através da aprendizagem baseada em projetos de alunos juniores.The article takes a new look at the method of developing logical thinking in junior students based on the correlation between the original and the model and making it possible, unlike traditional methods, to develop students’ speech thinking, intellectual structures, and logical operations more effectively. With the aid of the epistemological, systemic-activity, and milieu approaches, a strategy for developing students’ logical thinking through project-based learning that is premised on the correlation between the original and the model is determined. It ensures the effective development of a) schoolchildren’s intellectual activity b) thinking c) logical memory. The study proves the effectiveness of the presented technology, that implies 1) immersing in the project as well as specifying its goals and objectives; 2) organizing and planning students’ activities; 3) working out the main stages of the project; 4) carrying out the project and its presentation; 5) evaluating the results. Based on the research data, the following criteria were singled out analysis, synthesis, comparison, classification, generalization, and some other criteria, which allowed determining three levels of the development of the phenomenon in question. Our method provides for a significant improvement of the results of the research and ensures the formation of research, informational, regulatory, and analytical universal learning activities (ULAs). The assessment of the effectiveness and validity of the proposed method are corroborated by calculations for the Fisher’s criterion (φ*-criterion). The comparative results of the research before and after the experiment at the high level are 3.564. The obtained empirical values of φ * are in the area of significance. H0 is rejected (the significance axis = 1.64–2.31). Thus, the method in question has a serious impact on the development of logical thinking through project-based learning of junior students

Seeded x-ray free-electron laser generating radiation with laser statistical properties

The invention of optical lasers led to a revolution in the field of optics and even to the creation of completely new fields of research such as quantum optics. The reason was their unique statistical and coherence properties. The newly emerging, short-wavelength free-electron lasers (FELs) are sources of very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse durations on the order of femtoseconds, and are presently considered to be laser sources at these energies. Most existing FELs are highly spatially coherent but in spite of their name, they behave statistically as chaotic sources. Here, we demonstrate experimentally, by combining Hanbury Brown and Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI FEL-2 source does indeed behave statistically as a laser. The first steps have been taken towards exploiting the first-order coherence of FELs, and the present work opens the way to quantum optics experiments that strongly rely on high-order statistical properties of the radiation.Comment: 24 pages, 10 figures, 37 reference

Suppression of electron spin relaxation in Mn-doped GaAs

We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.Comment: 4 pages, 4 figure

Statistical properties of a free-electron laser revealed by the Hanbury Brown and Twiss interferometry

We present a comprehensive experimental analysis of statistical properties of the self-amplified spontaneous emission (SASE) free-electron laser (FEL) FLASH at DESY in Hamburg by means of Hanbury Brown and Twiss (HBT) interferometry. The experiments were performed at the FEL wavelengths of 5.5 nm, 13.4 nm, and 20.8 nm. We determined the 2-nd order intensity correlation function for all wavelengths and different operation conditions of FLASH. In all experiments a high degree of spatial coherence (above 50%) was obtained. Our analysis performed in spatial and spectral domains provided us with the independent measurements of an average pulse duration of the FEL that were below 60 fs. To explain complicated behaviour of the 2-nd order intensity correlation function we developed advanced theoretical model that includes the presence of multiple beams and external positional jitter of the FEL pulses. By this analysis we determined that in most experiments several beams were present in radiating field and in one of the experiments external positional jitter was about 25% of the beam size. We envision that methods developed in our study will be used widely for analysis and diagnostics of the FEL radiation.Comment: 29 pages, 14 figures, 3 table

Diffraction based Hanbury Brown and Twiss interferometry performed at a hard x-ray free-electron laser

We demonstrate experimentally Hanbury Brown and Twiss (HBT) interferometry at a hard X-ray Free Electron Laser (XFEL) on a sample diffraction patterns. This is different from the traditional approach when HBT interferometry requires direct beam measurements in absence of the sample. HBT analysis was carried out on the Bragg peaks from the colloidal crystals measured at Linac Coherent Light Source (LCLS). We observed high degree (80%) spatial coherence of the full beam and the pulse duration of the monochromatized beam on the order of 11 fs that is significantly shorter than expected from the electron bunch measurements.Comment: 32 pages, 10 figures, 2 table

On the Theory of Quantum Oscillations of the Elastic Moduli in Layered Conductors

In this paper we study theoretically how the local geometry of the Fermi surface (FS) of a layered conductor can affect quantum oscillations in the thermodynamic observables. We introduce a concrete model of the FS of a layered conductor. The model permits us to analyze the characteristic features of quantum oscillatory phenomena in these materials which occure due to local anomalies of the Gaussian curvature of the FS. Our analysis takes into account strong interaction among quasiparticles and we study the effect of this interaction within the framework of Fermi-liquid theory. We show that the Fermi-liquid interaction strongly affects the density of states of quasiparticles (DOS) on the FS. As a result DOS can have singularities near the peaks of its oscillations in a strong magnetic field. These singularities can be significantly strengthened when the FS of the layered conductor is locally flattened. This can lead to magnetic and lattice instabilities of a special kind which are considered in the final part of the work.Comment: 11 pages, 2 figures, minor changes in the title are made, published versio