High Energy Cosmic-ray Diffusion in Molecular Clouds: A Numerical Approach

The propagation of high-energy cosmic rays through giant molecular clouds constitutes a fundamental process in astronomy and astrophysics. The diffusion of cosmic-rays through these magnetically turbulent environments is often studied through the use of energy-dependent diffusion coefficients, although these are not always well motivated theoretically. Now, however, it is feasible to perform detailed numerical simulations of the diffusion process computationally. While the general problem depends upon both the field structure and particle energy, the analysis may be greatly simplified by dimensionless analysis. That is, for a specified purely turbulent field, the analysis depends almost exclusively on a single parameter -- the ratio of the maximum wavelength of the turbulent field cells to the particle gyration radius. For turbulent magnetic fluctuations superimposed over an underlying uniform magnetic field, particle diffusion depends on a second dimensionless parameter that characterizes the ratio of the turbulent to uniform magnetic field energy densities. We consider both of these possibilities and parametrize our results to provide simple quantitative expressions that suitably characterize the diffusion process within molecular cloud environments. Doing so, we find that the simple scaling laws often invoked by the high-energy astrophysics community to model cosmic-ray diffusion through such regions appear to be fairly robust for the case of a uniform magnetic field with a strong turbulent component, but are only valid up to $\sim 50$ TeV particle energies for a purely turbulent field. These results have important consequences for the analysis of cosmic-ray processes based on TeV emission spectra associated with dense molecular clouds.Comment: Accepted for publication in The Astrophysical Journa

Electronic and magnetic excitations in the "half-stuffed" Cu--O planes of Ba2_2Cu3_3O4_4Cl2_2 measured by resonant inelastic x-ray scattering

We use resonant inelastic x-ray scattering (RIXS) at the Cu L$_3$ edge to measure the charge and spin excitations in the "half-stuffed" Cu--O planes of the cuprate antiferromagnet Ba$_2$Cu$_3$O$_4$Cl$_2$. The RIXS line shape reveals distinct contributions to the $dd$ excitations from the two structurally inequivalent Cu sites, which have different out-of-plane coordinations. The low-energy response exhibits magnetic excitations. We find a spin-wave branch whose dispersion follows the symmetry of a CuO$_2$ sublattice, similar to the case of the "fully-stuffed" planes of tetragonal CuO (T-CuO). Its bandwidth is closer to that of a typical cuprate material, such as Sr$_2$CuO$_2$Cl$_2$, than it is to that of T-CuO. We interpret this result as arising from the absence of the effective four-spin inter-sublattice interactions that act to reduce the bandwidth in T-CuO.Comment: 10 pages, 8 figure

Spin-Orbit-Induced Orbital Excitations in Sr2RuO4 and Ca2RuO4: A Resonant Inelastic X-ray Scattering Study

High-resolution resonant inelastic X-ray scattering (RIXS) at the oxygen K-edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4. In combination with linear dichroism X-ray absorption spectroscopy, the ruthenium 4d-orbital occupation and excitations were probed through their hybridization with the oxygen p-orbitals. These results are described within a minimal model, taking into account crystal field splitting and a spin-orbit coupling \lambda_{so}=200~meV. The effects of spin-orbit interaction on the electronic structure and implications for the Mott and superconducting ground states of (Ca,Sr)2RuO4 are discussed.Comment: accepted in PRB 201

Domain Dynamics of Magnetic Films with Perpendicular Anisotropy

We study the magnetic properties of nanoscale magnetic films with large perpendicular anisotropy comparing polarization microscopy measurements on Co_28Pt_72 alloy samples based on the magneto-optical Kerr effect with Monte Carlo simulations of a corresponding micromagnetic model. We focus on the understanding of the dynamics especially the temperature and field dependence of the magnetisation reversal process. The experimental and simulational results for hysteresis, the reversal mechanism, domain configurations during the reversal, and the time dependence of the magnetisation are in very good qualitative agreement. The results for the field and temperature dependence of the domain wall velocity suggest that for thin films the hysteresis can be described as a depinning transition of the domain walls rounded by thermal activation for finite temperatures.Comment: 7 pages Latex, Postscript figures included, accepted for publication in Phys.Rev.B, also availible at: http://www.thp.Uni-Duisburg.DE/Publikationen/Publist_Us_R.htm

Nanoscale piezoelectric response across a single antiparallel ferroelectric domain wall

Surprising asymmetry in the local electromechanical response across a single antiparallel ferroelectric domain wall is reported. Piezoelectric force microscopy is used to investigate both the in-plane and out-of- plane electromechanical signals around domain walls in congruent and near-stoichiometric lithium niobate. The observed asymmetry is shown to have a strong correlation to crystal stoichiometry, suggesting defect-domain wall interactions. A defect-dipole model is proposed. Finite element method is used to simulate the electromechanical processes at the wall and reconstruct the images. For the near-stoichiometric composition, good agreement is found in both form and magnitude. Some discrepancy remains between the experimental and modeling widths of the imaged effects across a wall. This is analyzed from the perspective of possible electrostatic contributions to the imaging process, as well as local changes in the material properties in the vicinity of the wall

An objective, markerless videosystem for staging facial palsy

Background: The clinical classification of unilateral peripheral facial palsy (UPFP) is still based on subjective conventional methodology, leaving several missing points for an exact depiction of face deformity. Aim of the study: To propose a new objective, video recording method that relies on mathematical algorithms allowing the software to recognize numerical points on the face surface that would be indicative of facial nerve impairment, without positioning of markers on the face. Material and methods: Patients with UPFP of different House-Brackman (HB) degrees, from II to V, have been evaluated after video recording during two selected facial movements (forehead frowning and smiling) by a software trained to recognize the face points as numbers. Numerical parameters in millimeters have been obtained as indicative values of the shifting of the face points, and the shifting ratio between the healthy (denominator) and the affected side (numerator), i.e. the asymmetry index for the two movements taken into consideration. Results: For each HB grade, specific ranges of asymmetry index have been identified with a positive correlation for shift differences and negative correlation for asymmetry indexes. Conclusions: The use of the present objective system enabled the identification of numerical ranges of asymmetry index between the healthy and the affected side, that were found to be consistent with the outcome from the subjective methods currently in use

Molecular and clinical studies in five index cases with novel mutations in the GLA gene

Fabry disease is a metabolic and lysosomal storage disorder caused by the functional defect of the α-galactosidase A enzyme; this defect is due to mutations in the GLA gene, that is composed of seven exons and is located on the long arm of the X-chromosome (Xq21–22). The enzymatic deficit is responsible for the accumulation of glycosphingolipids in lysosomes of different cellular types, mainly in those ones of vascular endothelium. It consequently causes a cellular and microvascular dysfunction. In this paper, we described five novel mutations in the GLA gene, related to absent enzymatic activity and typical manifestations of Fabry disease. We identified three mutations (c.846_847delTC, p.E341X and p.C382X) that lead to the introduction of a stop codon in positions 297, 341 and 382. Moreover we found a missense mutation (p.R227P) in the exon 5 of the GLA gene and a single point mutation (c.639 + 5 G > T) occurring five base pairs beyond the end of the exon 4. These mutations have never been found in our group of healthy control subjects > 2300. The studied patients presented some clinical manifestations, such as cornea verticillata, hypo-anhidrosis, left ventricular hypertrophy, cerebrovascular disorders and renal failure, that, considering the null enzymatic activity, suggest that the new mutations reported here are related to the classic form of Fabry disease. The identification of novel mutations in patients with symptomatology referable to FD increases the molecular knowledge of the GLA gene and it gives clinicians an important support for the proper diagnosis of the disease

Damped spin excitations in a doped cuprate superconductor with orbital hybridization

A resonant inelastic x-ray scattering study of overdamped spin excitations in slightly underdoped La2−x Srx CuO4 (LSCO) with x = 0.12 and 0.145 is presented. Three high-symmetry directions have been investigated: (1) the antinodal (0,0) → ( 1 ,0), (2) the nodal (0,0) → ( 1 , 1 ), and (3) the zone-boundary direction 2 4 4 ( 1 1 1 2 ,0) → ( 4 ,4 ) connecting these two. The overdamped excitations exhibit strong dispersions along (1) and (3), whereas a much more modest dispersion is found along (2). This is in strong contrast to the undoped compound La2CuO4 (LCO) for which the strongest dispersions are found along (1) and (2). The t − t i − t ii − U Hubbard model used to explain the excitation spectrum of LCO predicts—for constant U/t —that the dispersion along (3) scales with (t i/t )2. However, the diagonal hopping t i extracted on LSCO using single-band models is low (t i/t ∼ −0.16) and decreasing with doping. We therefore invoked a two-orbital (dx2 −y2 and dz2 ) model which implies that t i is enhanced. This effect acts to enhance the zone-boundary dispersion within the Hubbard model. We thus conclude that hybridization of dx2 −y2 and dz2 states has a significant impact on the zone-boundary dispersion in LSCO

The Stability of the Suggested Planet in the nu Octantis System: A Numerical and Statistical Study

We provide a detailed theoretical study aimed at the observational finding about the nu Octantis binary system that indicates the possible existence of a Jupiter-type planet in this system. If a prograde planetary orbit is assumed, it has earlier been argued that the planet, if existing, should be located outside the zone of orbital stability. However, a previous study by Eberle & Cuntz (2010) [ApJ 721, L168] concludes that the planet is most likely stable if assumed to be in a retrograde orbit with respect to the secondary system component. In the present work, we significantly augment this study by taking into account the observationally deduced uncertainty ranges of the orbital parameters for the stellar components and the suggested planet. Furthermore, our study employs additional mathematical methods, which include monitoring the Jacobi constant, the zero velocity function, and the maximum Lyapunov exponent. We again find that the suggested planet is indeed possible if assumed to be in a retrograde orbit, but it is virtually impossible if assumed in a prograde orbit. Its existence is found to be consistent with the deduced system parameters of the binary components and of the suggested planet, including the associated uncertainty bars given by observations.Comment: 11 pages, 10 figures, 3 tables; Monthly Notices of the Royal Astronomical Society (in press