A nontrivial bosonic representation of large spin systems at high temperatures

We report on a nontrivial bosonization scheme for spin operators. It is shown that in the large $N$ limit, at infinite temperature, the operators $\sum_{k=1}^N \hat s_{k\pm}/\sqrt{N}$ behave like the creation and annihilation operators, $a^\dag$ and $a$, corresponding to a harmonic oscillator in thermal equilibrium, whose temperature and frequency are related by $\hbar\omega/k_B T=\ln 3$. The $z$ component is found to be equivalent to the position variable of another harmonic oscillator occupying its ground Gaussian state at zero temperature. The obtained results are applied to the Heisenberg XY Hamiltonian at finite temperature.Comment: 12 pages, preprint, we have included a brief discussion of the antiferromagnetic cas

Retrieval of total ozone quantity from high resolution infrared spectra : influence of spectroscopic and physical parameters

In this work, we present the results obtained for total ozone quantity from Jungfraujoch observatory spectrometer using 3 different spectral region

Consequences of Symmetries on the Analysis and Construction of Turbulence Models

Since they represent fundamental physical properties in turbulence (conservation laws, wall laws, Kolmogorov energy spectrum, ...), symmetries are used to analyse common turbulence models. A class of symmetry preserving turbulence models is proposed. This class is refined such that the models respect the second law of thermodynamics. Finally, an example of model belonging to the class is numerically tested

Crystalline and Spectroscopic Experimental Study of the Dinitromesithylen (DNM) Compared with the Theoretical Results

International audienceThe aim by our group is to understand the behavior of the grouping Me starting from the study of mols. having a great symmetry. In this part of work, it is had the cryst. structure of the dinitromesitylen (DNM) who is solved starting from the diffraction of x-​rays starting from a monocrystal at the ambient temp. Parallel to the exptl. study, we undertook theor. calcns. conformation of the insulated mol. of DNM by using the methods of the DFT (D. Functional Theory)​. Calcns. of optimization of the mol. conformation of the DNM by using the chain of program GAUSSIAN03 and functional MPW1PW91, B3LYP level with the 6-​311G and LANL2DZ bases gave a conformation Cs with results very close to the expt. for the lengths and the angles of bond. The computation results obtained starting from the base set (6-​311G) and functional MPW1PW91 give for the conformation of Dinitromesitylen (DNM) a good agreement of about a 1.9​% for the lengths of bond and 1.2​% for the angles of bond compared with the results of the diffraction of x-​rays. Calcns. of Raman and infra-​red spectroscopy undertaken starting from the results of optimization by using same functional MPW1PW91 and B3LYP and the sets of bases 6-​311G LanL2DZ led to the values of frequencies very close to the exptl. results

An Asymptotic Linear Thin-Walled Rod Model Coupling Twist and Bending

A linear one-dimensional model for thin-walled rods with open strongly curved cross-section, obtained by asymptotic methods is presented. A dimensional analysis of the linear three-dimensional equilibrium equations lets appear dimensionless numbers which reflect the geometry of the structure and the level of applied forces. For a given force level, the order of magnitude of the displacements and the corresponding one-dimensional model are deduced by asymptotic expansions. In the case of low force levels, we obtain a one dimensional model whose kinematics, traction and twist equations correspond to Vlassov ones. However this model couples twist and bending effects in the bending equations, at the difference from Vlassov model where the twist angle and the bending displacement are uncoupled.Запропоновано отриману асимптотичним методом одновимірну модель для тонкостінного стержня з відкритим сильно скривленим поперечним перерізом, яка враховує взаємо- зв’язок між скручуванням та згином. За допомогою аналізу розмірностей в лінійних тривимірних рівняннях рівноваги знайдено безрозмірні величини, які характеризують геометрію стержня та рівень прикладених сил. Для заданого рівня сил методом асимптотичного розкладу отримані порядок змі- щень та відповідна одновимірна модель. У випадку низького рівня сил отримано одновимірну модель, кінематичні рівняння, рівняння кручення та згину відповідають моделі Власова. Однак ця модель враховує в рівняннях згину взаємодію між згином і крученням на відміну від моделі Власова, яка таку взаємодію не враховує.Запропоновано отриману асимптотичним методом одновимірну модель для тонкостінного стержня з відкритим сильно скривленим поперечним перерізом, яка враховує взаємо- зв’язок між скручуванням та згином. За допомогою аналізу розмірностей в лінійних тривимірних рівняннях рівноваги знайдено безрозмірні величини, які характеризують геометрію стержня та рівень прикладених сил. Для заданого рівня сил методом асимптотичного розкладу отримані порядок зміщень та відповідна одновимірна модель. У випадку низького рівня сил отримано одновимірну модель, кінематичні рівняння, рівняння кручення та згину відповідають моделі Власова. Однак ця модель враховує в рівняннях згину взаємодію між згином і крученням на відміну від моделі Власова, яка таку взаємодію не враховує

Géométrie généralisée et graduée pour la mécanique

International audienceIn this contribution we will describe some objects of the so-called generalized geometry that appear naturally in the analysis of mechanical systems. In particular we will discuss the Dirac structures that we will illustrate by the example of systems with constraints. Dirac structures generalize simultaneously symplectic and Poisson structures. They provide a convenient framework to give a gemetric description of the so-called port-Hamiltonian systems. Then, we will present a framework which is even more general-the one of differential graded manifolds (also called Q-manifolds). The ultimate goal of this work is to construct numerical methods that preserve these geometric structures, and thus guarantee good physical behavior of the simulated systems.Dans cette communication on va décrire certains objets de la géométrie dite généralisée, qui appa-raissent naturellement dans l'analyse des systèmes mécaniques. En particulier, on présentera les structures de Dirac, que l'on illustrera sur l'exemple des systèmes avec contraintes. Les structures de Dirac généralisent à la fois les structures symplectiques et celles de Poisson. Elles sont le bon cadre pour décrire géométriquement les systèmes dits Hamiltoniens à ports. Nous présenterons aussi une structure plus générale, qui est celle des variétés différentielles graduées (dites aussi Q-variétés). L'objectif final de ce travail est la construction de schémas numériques qui préservent ces structures géométriques et garantissent ainsi un bon comportement physique dans les simulations

Characterization and Analysis of Landslide Evolution in Intramountain Areas in Loja (Ecuador) Using RPAS Photogrammetric Products

This case study focuses on the area of El Plateado near the city of Loja, Ecuador, where landslides with a high impact on infrastructures require monitoring and control. The main objectives of this work are the characterization of the landslide and the monitoring of its kinematics. Four flights were conducted using a remotely piloted aerial vehicle (RPAS) to capture aerial images that were processed with SfM techniques to generate digital elevation models (DEMs) and orthoimages of high resolution (0.05 m) and sufficient accuracy (below 0.05 m) for subsequent analyses. Thus, the DEM of differences (DoD) and profiles are obtained, but a morphometric analysis is conducted to quantitatively characterize the landslide's elements and study its evolution. Parameters such as slope, aspect, topographic position index (TPI), terrain roughness index (TRI), and topographic wetness index (TWI) are analyzed. The results show a higher slope and roughness for scarps compared to stable areas and other elements. From TPI, slope break lines have been extracted, which allow the identification of landslide features such as scarps and toe tip. The landslide shows important changes in the landslide body surface, the retraction of the main scarp, and advances of the foot. A general decrease in average slope and TRI and an increase in TWI are also observed due to the landslide evolution and stabilization. The presence of fissures and the infiltration of rainfall water in the unsaturated soil layers, which consist of high-plasticity clays and silts, contribute to the instability. Thus, the study provides insights into the measurement accuracy, identification and characterization of landslide elements, morphometric analysis, landslide evolution, and the relationship with geotechnical factors that contribute to a better understanding of landslides. A higher frequency of the RPAS surveys and quality of geotechnical and meteorological data are required to improve the instability analysis together with a major automation of the GIS procedures.Private Technical University of Loja PROY_GMIC_128

Time evolution and decoherence of a spin-1/2 particle coupled to a spin bath in thermal equilibrium

The time evolution of a spin-1/2 particle under the influence of a locally applied external magnetic field, and interacting with anisotropic spin environment in thermal equilibrium at temperature $T$ is studied. The exact analytical form of the reduced density matrix of the central spin is calculated explicitly for finite number of bath spins. The case of an infinite number of environmental spins is investigated using the convergence of the rescaled bath operators to normal Gaussian random variables. In this limit, we derive the analytical form of the components of the Bloch vector for antiferromagnetic interactions within the bath, and we investigate the short-time and long-time behavior of reduced dynamics. The effect of the external magnetic field, the anisotropy and the temperature of the bath on the decoherence of the central spin is discussed.Comment: 17 pages, 13 figures (compressed), one table. To appear in Phys. Rev.

Prise en charge tardive des sequelles de fractures du plancher orbitaire

Introduction : Les fractures du plancher orbitaire, sont devenues une pathologie assez fréquente étant donné, l’augmentation du nombre d’accidents de la route. Le plancher orbitaire de part sa constitution anatomique est certainement le maillon faible du cadre orbitaire. Observation : Nous présentons le cas d’un jeune de 35 ans polytraumatisé avec des séquelles de fracture du plancher orbitaire qui ne sera opéré que deux années plus tard, priorité chirurgicale oblige ( le rachis étant opéré en premier) avec les risques certains d’échec de la chirurgie ophtalmologique. Discussion : Les séquelles de ce type de fracture sont exposées, ainsi que les différentes modalités thérapeutiques. L’enophtalmie, la diplopie, les anomalies osseuses et palpébrales constituent autant de séquelles parfois difficiles à prendre en charge. Les voies d’abord chirurgical sont discutées ; l’usage de matériaux tels les implants en hydroxyapatite également. Conclusion : Le traitement des fractures du plancher de l’orbite est actuellement bien codifié et doit toujours être tenté même des années après le traumatisme causal.Mots clés : fracture plancher orbitaire, diplopi

Robustness of spatial Penning trap modes against environment-assisted entanglement

The separability of the spatial modes of a charged particle in a Penning trap in the presence of an environment is studied by means of the positive partial transpose (PPT) criterion. Assuming a weak Markovian environment, described by linear Lindblad operators, our results strongly suggest that the environmental coupling of the axial and cyclotron degrees of freedom does not lead to entanglement at experimentally realistic temperatures. We therefore argue that, apart from unavoidable decoherence, the presence of such an environment does not alter the effectiveness of recently suggested quantum information protocols in Penning traps, which are based on the combination of a spatial mode with the spin of the particle.Comment: 11 pages, 2 figure