Conservation of dielectric constant upon amorphization in perovskite oxides

We report calculations indicating that amorphous RAO$_3$ oxides, with R and A trivalent cations, have approximately the same static dielectric constant as their perovskite crystal phase. The effect is due to the disorder-activated polar response of non-polar crystal modes at low frequency, which compensates a moderate but appreciable reduction of the ionic dynamical charges. The dielectric response was studied via density-functional perturbation theory. Amorphous samples were generated by molecular dynamics melt-and-quench simulations.Comment: 5 pages, 3 figure

A rare cause of dysphagia due to retropharyngeal foregut duplication cyst: case report and review of the literature

Background: The retropharyngeal space is a deep compartment of the head and neck region which extends from the base of the skull to the mediastinum, between the posterior pharyngeal wall and vertebral muscles, delimited laterally by carotid sheaths. Pathological processes of the retropharyngeal space are rarely encountered, generally are isolated and painless masses often cystic, and they usually originate from branchial arch anomalies, but only in rare cases, they turn out to be foregut duplication cysts. Foregut duplication cyst is rare congenital malformations arising along primitively derived alimentary tract during the first trimester in the developing embryo, mostly seen in the thorax and abdomen, with just few cases reported in the head and neck region. We report an extremely rare case of a foregut duplication cyst lined with respiratory epithelium located in the retropharyngeal space, at the level of the oropharynx, of an adult patient with dysphagia surgically treated, and we also made an analysis of the published literature about this very uncommon condition. Case presentation: A 63-year-old male patient with chronic dysphagia was diagnosed with a retropharyngeal cystic lesion, which was surgically treated. Final pathologic evaluation confirmed the diagnosis of a rare foregut duplication cyst lined with respiratory epithelium. A review of the pertaining published literature about the head and neck foregut duplication cysts was made, with a particular emphasis on retropharyngeal ones. Conclusions: Retropharyngeal foregut duplication cysts are a very rare congenital cyst of the head and neck. Clinical symptoms such as dysphagia and dyspnea should be evaluated with fibrolaryngoscopy, and CT and MRI scans are of great significance for definitive diagnosis, which should include the possibility of a foregut duplication cyst in the differential diagnosis. Surgical excision is the elective treatment for this lesion, in order to prevent complications including infection and compression symptoms or eventually malignant transformation

Detrended fluctuation analysis for fractals and multifractals in higher dimensions

One-dimensional detrended fluctuation analysis (1D DFA) and multifractal detrended fluctuation analysis (1D MF-DFA) are widely used in the scaling analysis of fractal and multifractal time series because of being accurate and easy to implement. In this paper we generalize the one-dimensional DFA and MF-DFA to higher-dimensional versions. The generalization works well when tested with synthetic surfaces including fractional Brownian surfaces and multifractal surfaces. The two-dimensional MF-DFA is also adopted to analyze two images from nature and experiment and nice scaling laws are unraveled.Comment: 7 Revtex pages inluding 11 eps figure

Gray Matter Pathology in MS: A 3-Year Longitudinal Study in a Pediatric Population

RESULTS: At T0, GMf did not differ between cMS and NC (P .18), while it was lower in patients with aMS compared with both NCs (P .001) and patients with cMS (P .001). The number of patients with CLs, as well as CL number and volume, were higher in patients with aMS than in those with cMS (P .001). At T3, -GMf was higher in both patients with cMS (1.6% 0.5%; range 0.7%–3.4%; P .001) and aMS (1.6% 0.6%; range 0.6%–3.4%; P .001) compared with NCs (0.7% 0.2%; range 0.4%–1.1%), whereas no difference was observed between patients with cMS and aMS (P .93). -GMf significantly correlated with increased CL volume (cMS: r 0.46; aMS: r 0.48) and with the appearance of new CLs (cMS: r 0.51; aMS: r 0.49). CONCLUSIONS: Our findings suggest that focal (CLs) and diffuse (atrophy) GM damage are strictly associated with the biologic onset of MS, and proceed linearly and partly independently of WM pathology. ABBREVIATIONS: aMS adult-onset multiple sclerosis; CL cortical lesion; cMS childhoodonset multiple sclerosis; EDSS Expanded Disability Status Scale; GM gray matter; GMf gray matter fraction; -GMf delta gray matter fraction; -GMf_1 delta gray matter fraction at T1; -GMf_2 delta gray matter fraction at T2; -GMf_3 delta gray matter fraction at T3; NC healthy control; T0 baseline; T2WMLV T2 white matter lesion volum

Non-local density correlations as signal of Hawking radiation in BEC acoustic black holes

We have used the analogy between gravitational systems and non-homogeneous fluid flows to calculate the density-density correlation function of an atomic Bose-Einstein condensate in the presence of an acoustic black hole. The emission of correlated pairs of phonons by Hawking-like process results into a peculiar long-range density correlation. Quantitative estimations of the effect are provided for realistic experimental configurations.Comment: Strongly revised version. 5 pages, 3 eps figure

Elasticity of arrested short-ranged attractive colloids: homogeneous and heterogeneous glasses

We evaluate the elasticity of arrested short-ranged attractive colloids by combining an analytically solvable elastic model with a hierarchical arrest scheme into a new approach, which allows to discriminate the microscopic (primary particle-level) from the mesoscopic (cluster-level) contribution to the macroscopic shear modulus. The results quantitatively predict experimental data in a wide range of volume fractions and indicate in which cases the relevant contribution is due to mesoscopic structures. On this basis we propose that different arrested states of short-ranged attractive colloids can be meaningfully distinguished as homogeneous or heterogeneous colloidal glasses in terms of the length-scale which controls their elastic behavior.Comment: 3 figures, revised version, to appear in Physical Review Letter

Magnetic stress as a driving force of structural distortions: the case of CrN

We show that the observed transition from rocksalt to orthorhombic P$_{nma}$ symmetry in CrN can be understood in terms of stress anisotropy. Using local spin density functional theory, we find that the imbalance between stress stored in spin-paired and spin-unpaired Cr nearest neighbors causes the rocksalt structure to be unstable against distortions and justifies the observed antiferromagnetic ordering. This stress has a purely magnetic origin, and may be important in any system where the coupling between spin ordering and structure is strong.Comment: 4 pages (two columns) 4 figure

Multipartite entanglement in three-mode Gaussian states of continuous variable systems: Quantification, sharing structure and decoherence

We present a complete analysis of multipartite entanglement of three-mode Gaussian states of continuous variable systems. We derive standard forms which characterize the covariance matrix of pure and mixed three-mode Gaussian states up to local unitary operations, showing that the local entropies of pure Gaussian states are bound to fulfill a relationship which is stricter than the general Araki-Lieb inequality. Quantum correlations will be quantified by a proper convex roof extension of the squared logarithmic negativity (the contangle), satisfying a monogamy relation for multimode Gaussian states, whose proof will be reviewed and elucidated. The residual contangle, emerging from the monogamy inequality, is an entanglement monotone under Gaussian local operations and classical communication and defines a measure of genuine tripartite entanglement. We analytically determine the residual contangle for arbitrary pure three-mode Gaussian states and study the distribution of quantum correlations for such states. This will lead us to show that pure, symmetric states allow for a promiscuous entanglement sharing, having both maximum tripartite residual entanglement and maximum couplewise entanglement between any pair of modes. We thus name these states GHZ/$W$ states of continuous variable systems because they are simultaneous continuous-variable counterparts of both the GHZ and the $W$ states of three qubits. We finally consider the action of decoherence on tripartite entangled Gaussian states, studying the decay of the residual contangle. The GHZ/$W$ states are shown to be maximally robust under both losses and thermal noise.Comment: 20 pages, 5 figures. (v2) References updated, published versio

Distributed coherent manipulation of qutrits by virtual excitation processes

We propose a scheme for the deterministic coherent manipulation of two atomic qutrits, trapped in separate cavities coupled through a short optical fibre or optical resonator. We study such a system in the regime of dispersive atom-field interactions, where the dynamics of atoms, cavities and fibre operates through virtual population of both the atomic excited states and photonic states in the cavities and fibre. We show that the resulting effective dynamics allows for the creation of robust qutrit entanglement, and thoroughly investigate the influence of imperfections and dissipation, due to atomic spontaneous emission and photon leakage, on the entanglement of the two qutrits state.Comment: 15 pages, 4 figure

Anomalous relaxations and chemical trends at III-V nitride non-polar surfaces

Relaxations at nonpolar surfaces of III-V compounds result from a competition between dehybridization and charge transfer. First principles calculations for the (110) and (10$\bar{1}$0) faces of zincblende and wurtzite AlN, GaN and InN reveal an anomalous behavior as compared with ordinary III-V semiconductors. Additional calculations for GaAs and ZnO suggest close analogies with the latter. We interpret our results in terms of the larger ionicity (charge asymmetry) and bonding strength (cohesive energy) in the nitrides with respect to other III-V compounds, both essentially due to the strong valence potential and absence of $p$ core states in the lighter anion. The same interpretation applies to Zn II-VI compounds.Comment: RevTeX 7 pages, 8 figures included; also available at http://kalix.dsf.unica.it/preprints/; improved after revie