Macroscopic Anisotropy and Symmetry Breaking in the Pyrochlore Antiferromagnet Gd2_{2}Ti2_{2}O7_{7}}

In the Heisenberg antiferromagnet $Gd_2Ti_2O_7$, the exchange interactions are geometrically frustrated by the pyrochlore lattice structure. This ESR study reveals a strong temperature dependent anisotropy with respect to a [111] body diagonal below a temperature $T_A=80$ K, despite the spin only nature of the $Gd^{3+}$ ion. Anisotropy and symmetry breaking can nevertheless appear through the superexchange interaction. The presence of short range planar correlation restricted to specific Kagom\'{e} planes is sufficient to explain the two ESR modes studied in this work.Comment: 4 pages, 5 figure

Thinking in action: Need for cognition predicts self-control together with action orientation

Need for Cognition describes relatively stable interindividual differences in cognitive motivation. Previous research has shown relations of Need for Cognition to Self-Control–a capacity that can be broadly defined as resistance to temptation–yet, the processes underlying this relation remain unclear. One explanation for the prediction of Self-Control by Need for Cognition can be an increased motivation to invest cognitive effort with higher levels of Need for Cognition. Another possible link could be that individual differences in the implementation of Self-Control intentions may play a moderating or mediating role for the predictive value of Need for Cognition. Such individual differences in the self-motivated initiation and maintenance of intentions are described by dispositional Action Orientation. Therefore, in the present study, Action Orientation was examined with regard to its possible role in explaining the relation of Need for Cognition to Self-Control. In a sample of 1209 young adults, Self-Control was assessed with two different self-report instruments and moderation and mediation models of the relationship between Need for Cognition, Action Orientation, and Self-Control were tested. While there was no evidence for a moderating role of Action Orientation in explaining the relation of Need for Cognition and Self-Control, Action Orientation was found to partly mediate this relation with a remaining direct effect of Need for Cognition on Self-Control. These results add to the conceptual understanding of Need for Cognition and demonstrate the relevance of trait variables to predict Self-Control

Observing the emergence of chaos in a many-particle quantum system

Accessing the connection between classical chaos and quantum many-body systems has been a long-standing experimental challenge. Here, we investigate the onset of chaos in periodically driven two-component Bose-Einstein condensates, whose small quantum uncertainties allow for exploring the phase space with high resolution. By analyzing the uncertainties of time-evolved many-body states, we find signatures of elliptic and hyperbolic periodic orbits generated according to the Poincar\'e-Birkhoff theorem, and the formation of a chaotic region at increasing driving strengths. The employed fluctuation analysis allows for probing the phase-space structure by use of only short-time quantum dynamics.Comment: 5+2 pages, 4 figure

HLA-G: expression in human keratinocytes in vitro and in human skin in vivo

Classical, polymorphic major histocompatibility complex class I molecules are expressed on most nucleated cells.They present peptides at the cell surface and, thus, enable the immune system to scan peptides for their antigenicity. The function of the other, nonclassical class I molecules in man is controversial. HLA-G which has been shown by transfection experiments to be expressed at the cell surface, is only transcribed in placental tissue and in the fetal eye.Therefore, a role of HLA-G in the control of rejection of the allogeneic fetus has been discussed. We found that HLA-G expression is induced in keratinocytes by culture in vitro. Three different alternative splicing products of HLA-G can be detected: a full length transcript, an mRNA lacking exon 3 and a transcript devoid of exon 3 and 4. Reverse transcription followed by polymerase chain reaction also revealed the presence of HLA-G mRNA in vivo in biopsies of either diseased or healthy skin

Magnetic properties of HO2 thin films

We report on the magnetic and transport studies of hafnium oxide thin films grown by pulsed-laser deposition on sapphire substrates under different oxygen pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these thin films appear to depend on the oxygen pressure during growth: the film grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is conducting, with a positive Hall signal, while those grown under higher oxygen pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic ferromagnetic signal could be attributed to the HfO2 films, irrespective of the oxygen pressure during the deposition.Comment: 1

Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsO1−x_{1-x}Fx_{x}

The electrical resistivity, crystalline structure and electronic properties calculated from the experimentally measured atomic positions of the compound SmFeAsO$_{0.81}$F$_{0.19}$ have been studied up to pressures ~20GPa. The correlation between the pressure dependence of the superconducting transition temperature (Tc) and crystallographic parameters on the same sample shows clearly that a regular FeAs$_{4}$ tetrahedron maximizes Tc, through optimization of carrier transfer to the FeAs planes as indicated by the evolution of the electronic band structures.Comment: 15pages, 4 figure

On the appearance of hyperons in neutron stars

By employing a recently constructed hyperon-nucleon potential the equation of state of \beta-equilibrated and charge neutral nucleonic matter is calculated. The hyperon-nucleon potential is a low-momentum potential which is obtained within a renormalization group framework. Based on the Hartree-Fock approximation at zero temperature the densities at which hyperons appear in neutron stars are estimated. For several different bare hyperon-nucleon potentials and a wide range of nuclear matter parameters it is found that hyperons in neutron stars are always present. These findings have profound consequences for the mass and radius of neutron stars.Comment: 12 pages, 12 figures, RevTeX4; summary and conclusions are strengthened, to appear in PR

High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2-xSrxNiO4-\delta (x = 1 and 1.4)

Oxygen nonstoichiometry, electrical conductivity and thermal expansion of La2 xSrxNiO4-\delta phases with high levels of strontium substitution (1 =< x =< 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20-1050 degrees C. These phases retain the K2NiF4-type structure of La2NiO4 (tetragonal, space group I4/mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La2NiO4$\pm$\delta in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni3+/Ni4+ to a Ni2+/Ni3+ equilibrium on heating