3,688 research outputs found
Classically Integrable Cosmological Models with a Scalar Field
New classes of classically integrable models in the cosmological theories
with a scalar field are obtained by using freedoms of defining time and fields.
In particular, some models with the sum of exponential potentials in the flat
spatial metric are shown to be integrable. The model with the Sine-Gordon
potential can be solved in terms of analytic continuation of the non-periodic
Toda field theory.Comment: 10 pages, Late
Magnetic studies of the lightly Ru doped perovskite rhodates Sr(Ru,Rh)O
The solid solution between the ferromagnetic metal SrRuO and the enhanced
paramagnetic metal SrRhO was recently reported [K. Yamaura et al., Phys.
Rev. B 69 (2004) 024410], and an unexpected feature was found in the specific
heat data at =0.9 of SrRuRhO. The feature was reinvestigated
further by characterizing additional samples with various Ru concentrations in
the vicinity of =0.9. Specific heat and magnetic susceptibility data
indicate that the feature reflects a peculiar magnetism of the doped
perovskite, which appears only in the very narrow composition range
0.850.95.Comment: Accepted for publication in a special issue of Physica B (the
proceedings of SCES04
Comment on "Memory Effects in an Interacting Magnetic Nanoparticle System"
In Phys. Rev. Lett. 91 167206 (2003), Sun et al. study memory effects in an
interacting nanoparticle system with specific temperature and field protocols.
The authors claim that the observed memory effects originate from spin-glass
dynamics and that the results are consistent with the hierarchical picture of
the spin-glass phase. In this comment, we argue their claims premature by
demonstrating that all their experimental curves can be reproduced
qualitatively using only a simplified model of isolated nanoparticles with a
temperature dependent distribution of relaxation times.Comment: 1 page, 2 figures, slightly changed content, the parameters involved
in Figs. 1 and 2 are changed a little for a semi-quantitative comparision
with experimental result
Dynamical breakdown of the Ising spin-glass order under a magnetic field
The dynamical magnetic properties of an Ising spin glass
FeMnTiO are studied under various magnetic fields. Having
determined the temperature and static field dependent relaxation time
from ac magnetization measurements under a dc bias field by a
general method, we first demonstrate that these data provide evidence for a
spin-glass (SG) phase transition only in zero field. We next argue that the
data of finite can be well interpreted by the droplet theory
which predicts the absence of a SG phase transition in finite fields.Comment: 4 pages, 5 figure
Electronic properties of the novel 4d metallic oxide SrRhO3
The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping
studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and
20%, respectively. Although SrRhO3 was chemically compressed, approximately
5.7% by the Ca doping, no significant influence was observed on the magnetic
and electrical properties.Comment: To be published in a special issue of Physica B (the proceedings of
LT23
Bubbling 1/2 BPS Geometries and Penrose Limits
We discuss how to take a Penrose limit in bubbling 1/2 BPS geometries at the
stage of a single function z(x_1,x_2,y). By starting from the z of the AdS_5 x
S^5 we can directly derive that of the pp-wave via the Penrose limit. In that
time the function z for the pp-wave with 1/R^2-corrections is obtained. We see
that it surely reproduces the pp-wave with 1/R^2 terms. In addition we consider
the Penrose limit in the configuration of the concentric rings.Comment: 15 pages, 3 figures, LaTeX, v2:higher order corrections are added,
typos corrected and references added, version to appear in PR
Metallic conductivity and a Ca substitution study of NaRh2O4 comprising a double chain system
The metallic compound NaRh2O4 forms a full range solid solution to the
insulating phase CaRh2O4. At a Na concentration of 0.25 moles per formula unit,
we found an unexpected contribution to the specific heat at low temperature [K.
Yamaura et al. Chem. Mater. 17 (2005) 359]. To address this issue, specific
heat and ac and dc magnetic susceptibilities were additionally measured under a
variety of conditions for the Na0.25 sample. A new set of data clearly indicate
the additional specific heat is magnetic in origin; however, the magnetic
entropy is fairly small (~1 % of Schottky term for a simple splitting doublet),
and there is no other evidence to suggest that a magnetic phase transition is
responsible for the anomalous specific heat.Comment: Accepted for publication in a special issue of Physica B (the
proceedings of SCES05
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