4,170 research outputs found

    Electronic ground states of Fe2+_2^+ and Co2+_2^+ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

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    The 6Π^6\Pi electronic ground state of the Co2+_2^+ diatomic molecular cation has been assigned experimentally by x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. Three candidates, 6Φ^6\Phi, 8Φ^8\Phi, and 8Γ^8\Gamma, for the electronic ground state of Fe2+_2^+ have been identified. These states carry sizable orbital angular momenta that disagree with theoretical predictions from multireference configuration interaction and density functional theory. Our results show that the ground states of neutral and cationic diatomic molecules of 3d3d transition elements cannot generally be assumed to be connected by a one-electron process

    Direct Observation of High-Spin States in Manganese Dimer and Trimer Cations by X-ray Magnetic Circular Dichroism Spectroscopy in an Ion Trap

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    The electronic structure and magnetic moments of free Mn2+_2^+ and Mn3+_3^+ are characterized by 2p2p x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results show directly that localized magnetic moments of 5 μB\mu_B are created by 3d5(6S)3d^5 (^6\mathrm{S}) states at each ionic core, which are coupled in parallel to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly-occupied 4s4s derived orbital with an unpaired spin. This leads to total magnetic moments of 11 μB\mu_B for Mn2+_2^+ and 16 μB\mu_B for Mn3+_3^+, with no contribution of orbital angular momentum

    The internal Josephson effect in a Fermi gas near a Feshbach resonance

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    We consider a two-component system of Fermi atoms and molecular bosons in the vicinity of a Feshbash resonance. We derive an effective action for the system, which has a term describing coherent tunneling of the molecular bosons into Cooper pairs and vice versa. In the equilibrium state, global phase coherence may be destroyed by thermal or quantum phase fluctuations. In the non-equilibrium regime, the system may show an internal AC Josephson effect leading to real time oscillations in the number of molecular bosons.Comment: 5 pages, 2 figure

    Phase Modulated Thermal Conductance of Josephson Weak Links

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    We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference (ϕ\phi) of the superconducting leads. Branch conversion processes, low-energy Andreev bound states near the contact and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature and disorder, on the phase modulation of the conductance are reported. For high-transmission weak links, D1D\to 1, the formation of an Andreev bound state at ϵb=Δcos(ϕ/2)\epsilon_{\text{\tiny b}}=\Delta\cos(\phi/2) leads to suppression of the density of states for the continuum excitations that transport heat, and thus, to a reduction in the conductance for ϕπ\phi\simeq\pi. For low-transmission (D1D\ll 1) barriers resonant scattering at energies ϵ(1+D/2)Δ\epsilon\simeq(1+D/2)\Delta leads to an increase in the thermal conductance as TT drops below TcT_c (for phase differences near ϕ=π\phi=\pi).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for Ricatti amplitude

    Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

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    The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion

    Postural control and head stability during natural gaze behaviour in 6- to 12-year-old children

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    We investigated how the influence of natural exploratory gaze behaviour on postural control develops from childhood into adulthood. In a cross-sectional design, we compared four age groups: 6-, 9-, 12-year-olds and young adults. Two experimental trials were performed: quiet stance with a fixed gaze (fixed) and quiet stance with natural exploratory gaze behaviour (exploratory). The latter was elicited by having participants watch an animated short film on a large screen in front of them. 3D head rotations in space and centre of pressure (COP) excursions on the ground plane were measured. Across conditions, both head rotation and COP displacement decreased with increasing age. Head movement was greater in the exploratory condition in all age groups. In all children—but not in adults—COP displacement was markedly greater in the exploratory condition. Bivariate correlations across groups showed highly significant positive correlations between COP displacement in ML direction and head rotation in yaw, roll, and pitch in both conditions. The regularity of COP displacements did not show a clear developmental trend, which indicates that COP dynamics were qualitatively similar across age groups. Together, the results suggest that the contribution of head movement to eye-head saccades decreases with age and that head instability—in part resulting from such gaze-related head movements—is an important limiting factor in children's postural control. The lack of head stabilisation might particularly affect children in everyday activities in which both postural control and visual exploration are require

    Indizierte Prävention von Alkoholabhängigkeit und –missbrauch:Motivational Interviewing versus Feedback only ; eine randomisierte kontrollierte Studie

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    Die randomisierte kontrollierte Studie untersucht, ob die isolierten oder kombinierten Kurzinterventionen Motivational Interviewing und Feedback erfolgreich den riskanten Alkoholkonsum oder die daraus resultierenden Konsequenzen reduzieren können. Die Überlegenheit der Interventionen gegenüber einer Kontrollgruppe wurde unter strenger Kontrolle der Manualtreue überprüft. Die Teilnehmer (N = 98) absolvierten nach einem standardisiertem Screening ein umfangreiches Assessment und nahmen an einer der folgenden Interventionen teil: (1) Feedback, (2) MI, (3) Feedback + MI, (4) Kontrollgruppe. Die Follow-up-Untersuchungen zeigten nach 4 und 8 Wochen eine signifikante Reduktion des Alkoholkonsums in allen Gruppen (N = 90), nicht aber eine Reduktion der Konsequenzen des Konsums. Gründe für die mangelnde Überlegenheit der Kurzinterventionen gegenüber der Kontrollgruppe können im Screening, dem umfangreichen Assessment, der Stichprobe oder den Interventionen selber liegen
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