3,223 research outputs found
Macroscopic Anisotropy and Symmetry Breaking in the Pyrochlore Antiferromagnet GdTiO}
In the Heisenberg antiferromagnet , 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 K, despite the spin only nature of
the 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 SmFeAsOF
The electrical resistivity, crystalline structure and electronic properties
calculated from the experimentally measured atomic positions of the compound
SmFeAsOF 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 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\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
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