2,091 research outputs found
Spin and orbital frustration in MnSc_2S_4 and FeSc_2S_4
Crystal structure, magnetic susceptibility, and specific heat were measured
in the normal cubic spinel compounds MnSc_2S_4 and FeSc_2S_4. Down to the
lowest temperatures, both compounds remain cubic and reveal strong magnetic
frustration. Specifically the Fe compound is characterized by a Curie-Weiss
temperature \Theta_{CW}= -45 K and does not show any indications of order down
to 50 mK. In addition, the Jahn-Teller ion Fe^{2+} is orbitally frustrated.
Hence, FeSc_2S_4 belongs to the rare class of spin-orbital liquids. MnSc_2S_4
is a spin liquid for temperatures T > T_N \approx 2 K.Comment: 4 pages, to be published in Physical Review Letter
Random walks - a sequential approach
In this paper sequential monitoring schemes to detect nonparametric drifts
are studied for the random walk case. The procedure is based on a kernel
smoother. As a by-product we obtain the asymptotics of the Nadaraya-Watson
estimator and its as- sociated sequential partial sum process under
non-standard sampling. The asymptotic behavior differs substantially from the
stationary situation, if there is a unit root (random walk component). To
obtain meaningful asymptotic results we consider local nonpara- metric
alternatives for the drift component. It turns out that the rate of convergence
at which the drift vanishes determines whether the asymptotic properties of the
monitoring procedure are determined by a deterministic or random function.
Further, we provide a theoretical result about the optimal kernel for a given
alternative
OGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge
We report the discovery of a giant planet in the OGLE-2017-BLG-1522
microlensing event. The planetary perturbations were clearly identified by
high-cadence survey experiments despite the relatively short event timescale of
days. The Einstein radius is unusually small, mas, implying that the lens system either has very low mass or
lies much closer to the microlensed source than the Sun, or both. A Bayesian
analysis yields component masses and source-lens
distance , implying that this is a
brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location
that is also consistent with the relatively low lens-source relative proper
motion . The projected
companion-host separation is , indicating that
the planet is placed beyond the snow line of the host, i.e., . Planet formation scenarios combined with the small
companion-host mass ratio and separation suggest that the
companion could be the first discovery of a giant planet that formed in a
protoplanetary disk around a brown dwarf host.Comment: 20 pages, 6 figure
Autonomous clustering using rough set theory
This paper proposes a clustering technique that minimises the need for subjective
human intervention and is based on elements of rough set theory. The proposed algorithm is
unified in its approach to clustering and makes use of both local and global data properties to
obtain clustering solutions. It handles single-type and mixed attribute data sets with ease and
results from three data sets of single and mixed attribute types are used to illustrate the
technique and establish its efficiency
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