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

The Fiction of Architectural Identity in Contemporary Morocco

On 14 January 1986, H.M. Hassan II, the late King of Morocco, delivered a speech on architecture. The speech was addressed to a small gathering of architects selected by the Ministry of the Interior as representatives of their profession. The King of Morocco, unlike Prince Charles, was a true ruler and his speech was not meant as an art critique. Rather, it was intended to clarify a new incipient politics of urban design. This new politics, which intended to promote a return to 'traditional' architectural culture, was in open contradiction to the former official discourse of modernization. How can one understand this return to traditional forms? Was this an index of failure in the process of modernization initiated by the state after Independence, or rather an issue of strong societal resistance towards modernization, calling for a new politics of urban design

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

Non-Markovian dynamics in a spin star system: The failure of thermalization

In most cases, a small system weakly interacting with a thermal bath will finally reach the thermal state with the temperature of the bath. We show that this intuitive picture is not always true by a spin star model where non-Markov effect predominates in the whole dynamical process. The spin star system consists a central spin homogeneously interacting with an ensemble of identical noninteracting spins. We find that the correlation time of the bath is infinite, which implies that the bath has a perfect memory, and that the dynamical evolution of the central spin must be non- Markovian. A direct consequence is that the final state of the central spin is not the thermal state equilibrium with the bath, but a steady state which depends on its initial state.Comment: 8 page

LANDSLIDE SUSCEPTIBILITY MAPPING IN THE MUNICIPALITY OF OUDKA, NORTHERN MOROCCO: A COMPARISON BETWEEN LOGISTIC REGRESSION AND ARTIFICIAL NEURAL NETWORKS MODELS

The Rif is among the areas of Morocco most susceptible to landslides, because of the existence of relatively young reliefs marked by a very important dynamics compared to other regions. These landslides are one of the most serious problems on many levels: social, economic and environmental. The increase in the frequency and impact of landslides over the past decade has demonstrated the need for an in-depth study of these phenomena, allowing the identification of areas susceptible to landslides. The main objective of this study is to identify the optimal method for the mapping of the area susceptible to landslides in municipality of Oudka. This area has been marked by the largest landslide in the region, caused by heavy rainfall in 2013. Two Statistical Methods i) Regression Logistics (LR) ii) Artificial Neural Networks (ANN), were used to create a landslide susceptibility map. The realization of this susceptibility map required, first, the mapping of old landslides by the aerial photography, the data of the geological map and by the data obtained using field surveys using GPS. A total of 105 landslides were mapped from these various sources. 50% of this database was used for model building and 50% for validation. Eight independent landslide factors are exploited to detect the most sensitive areas: altitude, slope, aspect, distance of faults, distance streams, distance from roads, lithology and vegetation index (NDVI). The results of the landslide susceptibility analysis were verified using success and prediction rates. The success rate (AUC&thinsp;=&thinsp;0.918) and the prediction rate (AUC&thinsp;=&thinsp;0.901) of the LR model is higher than that of the ANN model (success rate (AUC&thinsp;=&thinsp;0.886) and prediction rate (AUC&thinsp;=&thinsp;0.877). These results indicate that the Regression Logistic (LR) model is the best model for determining landslide susceptibility in the study area.</p

Modulated Entanglement Evolution Via Correlated Noises

We study entanglement dynamics in the presence of correlated environmental noises. Specifically, we investigate the quantum entanglement dynamics of two spins in the presence of correlated classical white noises, deriving Markov master equation and obtaining explicit solutions for several interesting classes of initial states including Bell states and X form density matrices. We show how entanglement can be enhanced or reduced by the correlation between the two participating noises.Comment: 9 pages, 4 figures. To be published in Quantum Information Processing, special issue on Quantum Decoherence and Entanglemen