320 research outputs found
Dopant-dependent impact of Mn-site doping on the critical-state manganites: R0.6Sr0.4MnO3 (R=La, Nd, Sm, and Gd)
Versatile features of impurity doping effects on perovskite manganites,
SrMnO, have been investigated with varying the doing
species as well as the -dependent one-electron bandwidth. In
ferromagnetic-metallic manganites (=La, Nd, and Sm), a few percent of Fe
substitution dramatically decreases the ferromagnetic transition temperature,
leading to a spin glass insulating state with short-range charge-orbital
correlation. For each species, the phase diagram as a function of Fe
concentration is closely similar to that for SrMnO
obtained by decreasing the ionic radius of site, indicating that Fe doping
in the phase-competing region weakens the ferromagnetic double-exchange
interaction, relatively to the charge-orbital ordering instability. We have
also found a contrastive impact of Cr (or Ru) doping on a spin-glass insulating
manganite (=Gd). There, the impurity-induced ferromagnetic magnetization is
observed at low temperatures as a consequence of the collapse of the inherent
short-range charge-orbital ordering, while Fe doping plays only a minor role.
The observed opposite nature of impurity doping may be attributed to the
difference in magnitude of the antiferromagnetic interaction between the doped
ions.Comment: 7 pages, 6 figure
Non-linear electrical response in a non-charge-ordered manganite: Pr0.8Ca0.2MnO3
Up to now, electric field induced non-linear conduction in the Pr(1-x)CaxMnO3
system has been ascribed to a current-induced destabilization of the charge
ordered phase. However, for x<0.25, a ferromagnetic insulator state is observed
and charge-ordering is absent whatever the temperature. A systematic
investigation of the non-linear transport in the ferromagnetic insulator
Pr0.8Ca0.2MnO3 shows rather similar results to those obtained in charge ordered
systems. However, the experimental features observed in Pr0.8Ca0.2MnO3 are
distinct in that the collapse of the CO energy gap can not be invoked as
usually done in the other members of the PCMO system. We propose
interpretations in which the effectiveness of the DE is restored upon
application of electric field.Comment: 6 pages, 5 figure
Synchronization of multi-phase oscillators: An Axelrod-inspired model
Inspired by Axelrod's model of culture dissemination, we introduce and
analyze a model for a population of coupled oscillators where different levels
of synchronization can be assimilated to different degrees of cultural
organization. The state of each oscillator is represented by a set of phases,
and the interaction --which occurs between homologous phases-- is weighted by a
decreasing function of the distance between individual states. Both ordered
arrays and random networks are considered. We find that the transition between
synchronization and incoherent behaviour is mediated by a clustering regime
with rich organizational structure, where some of the phases of a given
oscillator can be synchronized to a certain cluster, while its other phases are
synchronized to different clusters.Comment: 6 pages, 5 figure
Spin versus Lattice Polaron: Prediction for Electron-Doped CaMnO3
CaMnO3 is a simple bi-partite antiferromagnet(AF) which can be continuously
electron-doped up to LaMnO3. Electrons enter the doubly degenerate E_g subshell
with spins aligned to the S=3/2 core of Mn^4+ (T_2g^3)$. We take the Hubbard
and Hund energies to be effectively infinite. Our model Hamiltonian has two E_g
orbitals per Mn atom, nearest neighbor hopping, nearest neighbor exchange
coupling of the S=3/2 cores, and electron-phonon coupling of Mn orbitals to
adjacent oxygen atoms. We solve this model for light doping. Electrons are
confined in local ferromagnetic (FM) regions (spin polarons) where there
proceeds an interesting competition between spin polarization (spin polarons)
which enlarges the polaron, and lattice polarization (Jahn-Teller polarons)
which makes it smaller. A symmetric 7-atom ferromagnetic cluster (Mn_7^27+) is
the stable result, with net spin S=2 relative to the undoped AF. The distorted
oxygen positions around the electron are predicted. The model also predicts a
critical doping x_c=0.045 where the polaronic insulator becomes unstable
relative to a FM metal.Comment: 9 pages with 7 embedded postscript figures and 2 table
Glucocorticoids for acute urticaria: study protocol for a double-blind non-inferiority randomised controlled trial
INTRODUCTION: This study protocol describes a trial designed to investigate whether antihistamine alone in patients with acute urticaria does not increase the 7-day Urticaria Activity Score (UAS7) in comparison with an association of antihistamine and glucocorticoids and reduces short-term relapses and chronic-induced urticaria.
METHODS AND ANALYSIS: This is a prospective, double-blind, parallel-group, multicentre non-inferiority randomised controlled trial. Two-hundred and forty patients with acute urticaria admitted to emergency department will be randomised in a 1:1 ratio to receive levocetirizine or an association of levocetirizine and prednisone. Randomisation will be stratified by centre. The primary outcome will be the UAS7 at day 7. The secondary outcomes will encompass recurrence of hives and/or itch at day 7; occurrence of spontaneous hives or itch for >6 weeks; patients with angioedema at day 7, and 2, 6, 12 and 24 weeks; new emergency visits for acute urticaria recurrences at days 7 and 14, and 3 months; Dermatology Life Quality Index at days 7 and 14, and 3 and 6 months; and Chronic Urticaria Quality of Life Questionnaire at 6 weeks.
ETHICS AND DISSEMINATION: The protocol has been approved by the and will be carried out in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. A steering committee will oversee the progress of the study. Findings will be disseminated through national and international scientific conferences and publication in peer-reviewed journals.
TRIAL REGISTRATION NUMBER: NCT03545464
Resonant photoemission spectroscopy study of insulator-to-metal transition in Cr- and Ru-doped Nd_{1/2}A_{1/2}Mn_{1-y} O_{3} (A=Ca, Sr)
Electronic structures of very dilute Cr- or Ru-doped Nd_{1/2}A_{1/2}MnO_{3}
(NAMO; A=Ca, Sr) manganites have been investigated using the Mn and Cr 2p -> 3d
resonant photoemission spectroscopy (PES). All the Cr- and Ru-doped NAMO
systems exhibit the clear metallic Fermi edges in the Mn e_g spectra near E_F,
consistent with their metallic ground states. The Cr 3d states with t^3_{2g}
configuration are at ~ 1.3 eV below E_F, and the Cr e_{g} states do not
participate in the formation of the band near E_F. Cr- and Ru-induced
ferromagnetism and insulator-to-metal transitions can be understood with their
measured electronic structures.Comment: 4 pages, 4 figure
E-retailing ethics in Egypt and its effect on customer repurchase intention
The theoretical understanding of online shopping behaviour has received much attention. Less focus has been given to the formation of the ethical issues that result from online shopper interactions with e-retailers. The vast majority of earlier research on this area is conceptual in nature and limited in scope by focusing on consumers’ privacy issues. Therefore, the purpose of this paper is to propose a theoretical model explaining what factors contribute to online retailing ethics and its effect on customer repurchase intention. The data were analysed using variance-based structural equation modelling, employing partial least squares regression. Findings indicate that the five factors of the online retailing ethics (security, privacy, non- deception, fulfilment/reliability, and corporate social responsibility) are strongly predictive of online consumers’ repurchase intention. The results offer important implications for e-retailers and are likely to stimulate further research in the area of e-ethics from the consumers’ perspective
Global CO2 fluxes inferred from surface air-sample measurements and from TCCON retrievals of the CO2 total column
We present the first estimate of the global distribution of CO2surface fluxes from 14 stations of the Total Carbon Column Observing Network (TCCON). The evaluation of this inversion is based on 1) comparison with the fluxes from a classical inversion of surface air-sample-measurements, and 2) comparison of CO2mixing ratios calculated from the inverted fluxes with independent aircraft measurements made during the two years analyzed here, 2009 and 2010. The former test shows similar seasonal cycles in the northern hemisphere and consistent regional carbon budgets between inversions from the two datasets, even though the TCCON inversion appears to be less precise than the classical inversion. The latter test confirms that the TCCON inversion has improved the quality (i.e., reduced the uncertainty) of the surface fluxes compared to the assumed or prior fluxes. The consistency between the surface-air-sample-based and the TCCON-based inversions despite remaining flaws in transport models opens the possibility of increased accuracy and robustness of flux inversions based on the combination of both data sources and confirms the usefulness of space-borne monitoring of the CO2 column.It was co-funded by the European Commission under the EU Seventh Research Framework Programme (grants agreements 218793, MACC, and 212196, COCOS
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