5d-5f Electric-multipole Transitions in Uranium Dioxide Probed by Non-resonant Inelastic X-ray Scattering

Non-resonant inelastic x ray scattering (NIXS) experiments have been performed to probe the 5d-5f electronic transitions at the uranium O(4,5) absorption edges in uranium dioxide. For small values of the scattering vector q, the spectra are dominated by dipole-allowed transitions encapsulated within the giant resonance, whereas for higher values of q the multipolar transitions of rank 3 and 5 give rise to strong and well-defined multiplet structure in the pre-edge region. The origin of the observed non-dipole multiplet structures is explained on the basis of many-electron atomic spectral calculations. The results obtained demonstrate the high potential of NIXS as a bulk-sensitive technique for the characterization of the electronic properties of actinide materials.Comment: Submitted to Physical Review Letters on 31 December 200

On the role of intrinsic disorder in the structural phase transition of magnetoelectric EuTiO3

Up to now the crystallographic structure of the magnetoelectric perovskite EuTiO3 was considered to remain cubic down to low temperature. Here we present high resolution synchrotron X-ray powder diffraction data showing the existence of a structural phase transition, from cubic Pm-3m to tetragonal I4/mcm, involving TiO6 octahedra tilting, in analogy to the case of SrTiO3. The temperature evolution of the tilting angle indicates a second-order phase transition with an estimated Tc=235K. This critical temperature is well below the recent anomaly reported by specific heat measurement at TA\sim282K. By performing atomic pair distribution function analysis on diffraction data we provide evidence of a mismatch between the local (short-range) and the average crystallographic structures in this material. Below the estimated Tc, the average model symmetry is fully compatible with the local environment distortion but the former is characterized by a reduced value of the tilting angle compared to the latter. At T=240K data show the presence of local octahedra tilting identical to the low temperature one, while the average crystallographic structure remains cubic. On this basis, we propose intrinsic lattice disorder to be of fundamental importance in the understanding of EuTiO3 properties.Comment: 13 pages, 8 figures, 2 table

Momentum-dependent charge correlations in YBa2_2Cu3_3O6+δ_{6+\delta} superconductors probed by resonant x-ray scattering: Evidence for three competing phases

We have used resonant x-ray scattering to determine the momentum dependent charge correlations in YBa$_2$Cu$_3$O$_{6.55}$ samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments were carried out on a YBa$_2$Cu$_3$O$_{6.6}$ crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length were found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa$_2$Cu$_3$O$_{6+\delta}$.Comment: 6 pages, 3 figures revised version, to appear in Phys. Rev. Let

High-energy spin and charge excitations in electron-doped copper oxide superconductors

The evolution of electronic (spin and charge) excitations upon carrier doping is an extremely important issue in superconducting layered cuprates and the knowledge of its asymmetry between electron- and hole-dopings is still fragmentary. Here we combine x-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper L3 resonant inelastic x-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone center and deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the {\Gamma}-point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin-excitations (paramagnons) recently observed in hole-doped compounds even at high doping-levels.Comment: 20 page

Role of Chlamydia Trachomatis infection in young men : what we need to know?

Chlamydia Trachomatis infections are the most common sexually transmitted bacterial infections worldwide: Because Chlamydia Trachomatis infections are asymptomatic in approximately 50% of infected men and 70% of infected women, there is a high risk for reproductive tract sequelae and high diffusion of the disease. Recently some studies improved the comprehension of this infection and its natural history highlighting the fact that severe complications can be avoided only by a proper early diagnosis and appropriate treatment. We reviewed the literature related to the new findings in the treatment of Chlamydia Trachomatis infection in sexually active young men. Articles from 1960-2014 were identified through a Medline search using the keywords "Chlamydia Trachomatis" combined with "urethritis", "epididymitis", "prostatitis" "treatment" or "management". Several studies highlighted that Chlamidia are only metabolically active in the host cell and therefore only targeted intracellularly by antibiotics. However, even if the standard therapy includes intracellularly-accumulated antibiotics such as tetracyclines or macrolides, recent evidences highlight the role of quinolones. In particular recent studies hilight the role of prulifloxacin in the treatment of chronic prostatitis patients for improving patient's quality of life and decreasing the IL-8 level. However, there is a need for future studies and to diffuse the knowledge about Chlamydia Trachomatis especially in urological clinical practice, in order to reduce the risk of diagnosis failure

Direct observation of bulk charge modulations in optimally-doped Bi1.5_{1.5}Pb0.6_{0.6}Sr1.54_{1.54}CaCu2_{2}O8+δ_{8+\delta}

Bulk charge density modulations, recently observed in high critical-temperature ($T_\mathrm{c}$) cuprate superconductors, coexist with the so-called pseudogap and compete with superconductivity. However, its direct observation has been limited to a narrow doping region in the underdoped regime. Using energy-resolved resonant x-ray scattering we have found evidence for such bulk charge modulations, or soft collective charge modes (soft CCMs), in optimally doped Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_{2}$O$_{8+\delta}$ (Pb-Bi2212) around the summit of the superconducting dome with momentum transfer $q_{\parallel}\sim0.28$ reciprocal lattice units (r.l.u.) along the Cu-O bond direction. The signal is stronger at $T\simeq T_\mathrm{c}$ than at lower temperatures, thereby confirming a competition between soft CCMs and superconductivity. These results demonstrate that soft CCMs are not constrained to the underdoped regime, suggesting that soft CCMs appear across a large part of the phase diagram of cuprates and are intimately entangled with high-$T_\mathrm{c}$ superconductivity.Comment: 6 pages, 3 figures, 1 tabl

The Acute Effects of Cognitively Demanding Physical Activity on Inhibitory and Affective Responses in Children:An Online-Based Mixed Methods Approach

This online study investigated the acute effects of a cognitively demanding physical activity (CDPA) vs a simple physical activity (SPA) bout on children’s inhibitory and affective responses. Using a counterbalanced within-subjects’ crossover design, thirty-nine participants aged 9–12 years old (29 boys; M(age) = 11 ± 1 years) performed a CDPA and a SPA bout online (via ZOOM) for 15 min. Inhibition (Stroop test) was measured at the baseline, 1 and 30 min following the physical activity (PA) bouts, and self-report measures of affect, mental and physical exertion were taken prior, during and post-PA. Additionally, 31 children took part in semi-structured focus groups to explore the factors affecting their enjoyment. The quantitative results suggest no significant differences on inhibitory responses, affect and physical exertion (all p > 0.05). However, the CDPA induced more mental exertion than the SPA did (p < 0.05). In the focus groups, four themes were identified: physical exertion (e.g., tiredness), social (e.g., teams/groups), environment (e.g., outdoors and competition) and emotional (e.g., fun/enjoyment). Some children (n = 18) reported that the CDPA condition confused them, and to make these activities more interesting and enjoyable, they suggested performing the activities outdoors (n = 15) and including other children as part of a group/team (n = 19). The findings suggest no additional benefit of a cognitively enriched physical activity compared to an SPA bout on the inhibitory responses, affect and enjoyment. Using the instructions provided and given the low cost, the easy administration and the minimal amount of equipment and time involved, either of the approaches may be used in a diversity of contexts (i.e., online, schools or outdoors), and it is worth exploring the effects of these conditions on other aspects of executive function

The Magnetic Structure of DyMn2O5 Determined by Resonant X-ray Scattering

Resonant magnetic x-ray scattering has been used to investigate the magnetic structure of the magnetoelectric multiferroic DyMn2O5. We have studied the magnetic structure in the ferroelectric phase of this material, which displays the strongest ferroelectric polarisation and magnetodielectric effect of the RMn2O5 (where R is a rare earth ion, Y or Bi) family. The magnetic structure observed is similar to that of the other members of the series, but differs in the direction of the ordered moments. In DyMn2O5 both the Dy and Mn moments lie close to the b-axis, whereas in other RMn2O5 they lie close to the a-axis.Comment: 8 pages, 8 figure