3,064 research outputs found
Possible chiral phase transition in two-dimensional solid He
We study a spin system with two- and four-spin exchange interactions on the
triangular lattice, which is a possible model for the nuclear magnetism of
solid He layers. It is found that a novel spin structure with scalar chiral
order appears if the four-spin interaction is dominant. Ground-state properties
are studied using the spin-wave approximation. A phase transition concerning
the scalar chirality occurs at a finite temperature, even though the
dimensionality of the system is two and the interaction has isotropic spin
symmetry. Critical properties of this transition are studied with Monte Carlo
simulations in the classical limit.Comment: 4 pages, Revtex, 4 figures, to appear in Phys.Rev.Let
Magnetization plateau in a two-dimensional multiple-spin exchange model
We study a multiple-spin exchange model on a triangular lattice, which is a
possible model for low-density solid 3He films. Due to strong competitions
between ferromagnetic three-spin exchange and antiferromagnetic four-spin one,
the ground states are highly degenerate in the classical limit. At least
2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the
SO(3) symmetry. In the magnetization process, we found a plateau at
m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state
with four sublattices). The 1/2-plateau appears due to the strong four-spin
exchange interaction. This plateau survives against both quantum and thermal
fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a
phase transition occurs at a finite temperature. We predict that low-density
solid 3He thin films may show the 1/2-plateau in the magnetization process.
Experimental observation of the plateau will verify strength of the four-spin
exchange. It is also discussed that this magnetization plateau can be
understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos,
to be published in Phys.Rev.B (01 APR 99
Efeito sistêmico de inseticidas sobre a oviposição do ácaro-vermelho Tetranychus desertorum em soja.
On Chinese and Western Family Trees: Mechanism and Performance
Family tree is an efficient data structure to store the kinship information in a family. There are basically two kinds of trees: Western Family Tree (WFT) and Oriental Family Tree such as Chinese Family Tree (CFT). To get an insight of their efficiency in the context of family kinship presentation and information extraction, in this paper we develop WFT and CFT presentation models and search algorithms, comparing their search performance and inherent mechanism. The study reveals that the computational cost is higher in CFT model, but it provides a greater gain in information retrieval and produces more details of the kinship between individuals in the family
High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1
The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic
center. Together with its distance, this makes it one of the most central
globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a
metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest
objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern
of the first stars as well as the early chemical enrichment and early formation
of stellar populations. High-resolution spectra obtained for six stars were
analyzed to derive the abundances of the light elements C, N, O, Na, and Al,
the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba,
La, and Eu.} High-resolution spectra of six red giants that are confirmed
members of the bulge globular cluster HP~1 were obtained with the 8m VLT
UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration.
The spectroscopic parameter derivation was based on the excitation and
ionization equilibrium of FeI and FeII. We confirm a mean metallicity of [Fe/H]
= -1.06~0.10, by adding the two stars that were previously analyzed in HP~1.
The alpha-elements O and Mg are enhanced by about +0.3<[O,Mg/Fe]<+0.5 dex, Si
is moderately enhanced with +0.15<[Si/Fe]<+0.35dex, while Ca and Ti show lower
values of -0.04<[Ca,Ti/Fe]<+0.28dex. The r-element Eu is also enhanced with
[Eu/Fe]~+0.4, which together with O and Mg is indicative of early enrichment by
type II supernovae. Na and Al are low, but it is unclear if Na-O are
anticorrelated. The heavy elements are moderately enhanced, with
-0.20<[La/Fe]<+0.43dex and 0.0<[Ba/Fe]<+0.75~dex, which is compatible with
r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other
hand, appears to be compatible with the spinstar scenario or other additional
mechanisms such as the weak r-process.Comment: 15 pages, 8 figures In press in Astronomy & Astrophysics (2016
Evidence for a Self-Bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D He on Graphite
We made heat-capacity measurements of two dimensional (2D) He adsorbed on
graphite preplated with monolayer He in a wide temperature range (0.1 80 mK) at densities higher than that for the 4/7 phase (= 6.8
nm). In the density range of 6.8 8.1 nm, the 4/7
phase is stable against additional He atoms up to 20% and they are promoted
into the third layer. We found evidence that such promoted atoms form a
self-bound 2D Fermi liquid with an approximate density of 1 nm from the
measured density dependence of the -coefficient of heat capacity. We
also show evidence for the first-order transition between the commensurate 4/7
phase and the ferromagnetic incommensurate phase in the second layer in the
density range of 8.1 9.5 nm.Comment: 6 pages, 4 figure
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