28,176 research outputs found
Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud
We have carried out near-infrared spectroscopic observations of 23 very
low-luminosity young stellar object (YSO) candidates and 5 their companions in
Heiles Cloud 2, one of the densest parts of the Taurus molecular cloud. Twelve
objects were confirmed as YSOs by Br gamma feature. The effective temperatures
of the YSOs and of the companions are estimated from the 2.26 micron feature,
the 2.21 micron feature, and the H2O band strengths. Detailed comparisons of
our photometric and spectroscopic observations with evolutionary tracks on the
HR diagram suggest some objects to be very low-mass YSOs.Comment: 15 pages, 19 figures. PASJ accepte
Entanglement Spectra of the quantum hard-square model: Holographic minimal models
We study the entanglement properties of a quantum lattice-gas model for which
we can find the exact ground state (of the Rokhsar-Kivelson type). The ground
state can be expressed as a superposition of states, each of which is
characterized by a particle configuration with nearest-neighbor exclusion. We
show that the reduced density matrix of the model on a ladder is intimately
related to the transfer matrix of the classical hard-square model. The
entanglement spectra of the model on square and triangular ladders are critical
when parameters are chosen so that the corresponding classical hard-square
models are critical. A detailed analysis reveals that the critical theories for
the entanglement Hamiltonians are minimal conformal field theories. We
further show that the entanglement Hamiltonian for the triangular ladder is
integrable despite the fact that the original quantum lattice-gas model is
non-integrable.Comment: 10 pages, 8 figure
Fertility decline, baby boom and economic growth
We present new data documenting the secular decline in fertility in the states of the United States, the dramatic convergence in fertility, child schooling, parental schooling, survival probabilities. In addition we document the disparate nature of the Baby Boom in the United States. There were two different regimes, a large Baby Boom and a Small Baby Boom. The large Baby Boom regions also had the smallest increase in child schooling, whereas the small Baby Boom regions had the largest increase in child schooling. We present suggestive evidence that falling mortality risk is strongly positively correlated with falling fertility, rising education levels of parents is strongly negatively related to fetility, and that population density is negatively related to fertility. Finally we show the robust negative correlation of mortality risk on child schooling attainment, and positve correlation of population density and child schooling attainment.mortality; density; fertility decline; baby boom; economic growth
Strong Magnetization Measured in the Cool Cores of Galaxy Clusters
Tangential discontinuities, seen as X-ray edges known as cold fronts (CFs),
are ubiquitous in cool-core galaxy clusters. We analyze all 17 deprojected CF
thermal profiles found in the literature, including three new CFs we
tentatively identify (in clusters A2204 and 2A0335). We discover small but
significant thermal pressure drops below all nonmerger CFs, and argue that they
arise from strong magnetic fields below and parallel to the discontinuity,
carrying 10%-20% of the pressure. Such magnetization can stabilize the CFs, and
explain the CF-radio minihalo connection.Comment: PRL accepted, additional control tests adde
Observational Test of Environmental Effects on The Local Group Dwarf Spheroidal Galaxies
In this paper, we examine whether tidal forces exerted by the Galaxy or M31
have an influence on the Local Group dwarf spheroidal galaxies (dSphs) which
are their companions. We focus on the surface brightness profiles of the dSphs,
especially their core radii because it is suggested based on the numerical
simulations that tidal disturbance can make core radii extended. We examine the
correlation for the dSphs between the distances from their parent galaxy (the
Galaxy or M31) and the compactnesses of their surface brightness profiles by
using a parameter ``C'' defined newly in this paper. Consequently, we find no
significant correlation. We make some remarks on the origin of this result by
considering three possible scenarios; tidal picture, dark matter picture, and
heterogeneity of the group of dSphs, each of which has been often discussed to
understand fundamental properties and formation processes of dSphs.Comment: 14 pages LaTeX, 2 PostScript figures, to appear in ApJ Letter
Singlet-triplet splitting, correlation and entanglement of two electrons in quantum dot molecules
Starting with an accurate pseudopotential description of the single-particle
states, and following by configuration-interaction treatment of correlated
electrons in vertically coupled, self-assembled InAs/GaAs quantum
dot-molecules, we show how simpler, popularly-practiced approximations, depict
the basic physical characteristics including the singlet-triplet splitting,
degree of entanglement (DOE) and correlation. The mean-field-like
single-configuration approaches such as Hartree-Fock and local spin density,
lacking correlation, incorrectly identify the ground state symmetry and give
inaccurate values for the singlet-triplet splitting and the DOE. The Hubbard
model gives qualitatively correct results for the ground state symmetry and
singlet-triplet splitting, but produces significant errors in the DOE because
it ignores the fact that the strain is asymmetric even if the dots within a
molecule are identical. Finally, the Heisenberg model gives qualitatively
correct ground state symmetry and singlet-triplet splitting only for rather
large inter-dot separations, but it greatly overestimates the DOE as a
consequence of ignoring the electron double occupancy effect.Comment: 13 pages, 9 figures. To appear in Phys. Rev.
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