8,120 research outputs found
Antiferromagnetism in EuCu2As2 and EuCu1.82Sb2 Single Crystals
Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb
self-flux, respectively. The crystallographic, magnetic, thermal and electronic
transport properties of the single crystals were investigated by
room-temperature x-ray diffraction (XRD), magnetic susceptibility \chi versus
temperature T, isothermal magnetization M versus magnetic field H, specific
heat Cp(T) and electrical resistivity \rho(T) measurements. EuCu2As2
crystallizes in the body-centered tetragonal ThCr2Si2-type structure (space
group I4/mmm), whereas EuCu2Sb2 crystallizes in the related primitive
tetragonal CaBe2Ge2-type structure (space group P4/nmm). The energy-dispersive
x-ray spectroscopy and XRD data for the EuCu2Sb2 crystals showed the presence
of vacancies on the Cu sites, yielding the actual composition EuCu1.82Sb2. The
\rho(T) and Cp(T) data reveal metallic character for both EuCu2As2 and
EuCu1.82Sb2. Antiferromagnetic (AFM) ordering is indicated from the \chi(T),
Cp(T), and \rho(T) data for both EuCu2As2 (T_N = 17.5 K) and EuCu1.82Sb2 (T_N =
5.1 K). In EuCu1.82Sb2, the ordered-state \chi(T) and M(H) data suggest either
a collinear A-type AFM ordering of Eu+2 spins S=7/2 or a planar noncollinear
AFM structure, with the ordered moments oriented in the tetragonal ab plane in
either case. This ordered-moment orientation for the A-type AFM is consistent
with calculations with magnetic dipole interactions. The anisotropic \chi(T)
and isothermal M(H) data for EuCu2As2, also containing Eu+2 spins S=7/2,
strongly deviate from the predictions of molecular field theory for collinear
AFM ordering and the AFM structure appears to be both noncollinear and
noncoplanar.Comment: 21 pages, 22 figures, 4 Table
Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulator EuMn2As2
We report magnetic susceptibility \chi, isothermal magnetization M, heat
capacity C_p and electrical resistivity \rho measurements on undoped EuMn2As2
and K-doped Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2 single crystals with the
trigonal CaAl2Si2-type structure as a function of temperature T and magnetic
field H. EuMn2As2 has an insulating ground state with an activation energy of
52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu+2 spins S=7/2 at
T_N1 = 15 K from C_p(T) and \chi(T) data with a likely spin-reorientation
transition at T_N2 = 5.0 K. The Mn+2 3d5 spins-5/2 exhibit AFM ordering at T_N
= 142 K from all three types of measurements. The M(H) isotherm and \chi(T)
data indicate that the Eu AFM structure is both noncollinear and noncoplanar.
The AFM structure of the Mn spins is also unclear. A 4% substitution of K for
Eu in Eu0.96K0.04Mn2As2 is sufficient to induce a metallic ground state.
Evidence is found for a difference in the AFM structure of the Eu moments in
the metallic crystals from that of undoped EuMn2As2 versus both T and H. For
metallic Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2, an anomalous S-shape T
dependence of \rho related to the Mn magnetism is found. Upon cooling from 200
K, \rho exhibits a strong negative curvature, reaches maximum positive slope at
the Mn T_N ~ 150 K, and then continues to decrease but more slowly below T_N.
This suggests that dynamic short-range AFM order of the Mn spins above the Mn
T_N strongly suppresses the resistivity, contrary to the conventional decrease
of \rho that is only observed upon cooling below T_N of an antiferromagnet.Comment: 21 pages, 22 figures, 4 Table
Physical properties of EuPd2As2 single crystals
The physical properties of self-flux grown EuPd2As2 single crystals have been
investigated by magnetization M, magnetic susceptibility chi, specific heat Cp,
and electrical resistivity rho measurements versus temperature T and magnetic
field H. The crystal structure was determined by powder x-ray diffraction
measurements, which confirmed the ThCr2Si2-type body-centered tetragonal
structure (space group I4/mmm) reported previously. The rho(T) data indicate
that state of EuPd2As2 is metallic. Long-range antiferromagnetic (AFM) ordering
is apparent from the chi(T), Cp(T), and rho(T) measurements. For H \parallel c
the chi(T) indicates two transitions at TN1 = 11.0 K and TN2 = 5.5 K, whereas
for H \perp c only one transition is observed at TN1 = 11.0 K. Between TN1 and
TN2 the anisotropic chi(T) data suggest a planar noncollinear AFM structure,
whereas at T < TN2 the chi(T) and M(H,T) data suggest a spin reorientation
transition in which equal numbers of spins cant in opposite directions out of
the ab plane. We estimate the critical field at 2 K at which all Eu moments
become aligned with the field to be about 22 T. The magnetic entropy at 25 K
estimated from the Cp(T) measurements is about smaller than expected,
possibly due to an inaccuracy in the lattice heat capacity contribution. An
upturn in rho at T < TN1 suggests superzone energy gap formation below TN1.
This behavior of rho(T < TN1) is not sensitive to applied magnetic fields up to
H = 12 T.Comment: 11 pages, 10 figures, 2 tables and 52 references; To appear in J.
Phys.: Condens. Matte
Health Employment, Medical Spending, and Long Term Health Reform
This paper explores the relationships between the growth in the medical workforce in an aging society and employment in other sectors of the economy, based on data from the United States since 1985. Employment in medical services grew, but did not displace employment in other sectors uniformly. Instead, regression analysis shows that medical workforce growth produced contemporaneous reductions in relative employment in the manufacturing, construction, and information sectors, while being associated with growth in other services and public administration. Import penetration and productivity growth mattered, but much of the displacement remains even after controlling for these factors.
Taxation by Auction: Fund-Raising by 19th Century Indian Guilds
We describe a unique institution used by 19th century Indian guilds to raise funds: The guild members agreed that on a particular day all but one of their shops would be shut. An auction would be held to determine which one shop would remain open, and the winning bid would go to the guild funds. We compare this “taxation by auction” mechanism with more conventional tax schemes and show that under certain conditions, not only will a majority of the guild members prefer to be taxed via an auction, but that this form of taxation will be more equitable than other forms.Auctions, Fund-Raising, Indian Guilds, Taxation
Enhancing Energy Minimization Framework for Scene Text Recognition with Top-Down Cues
Recognizing scene text is a challenging problem, even more so than the
recognition of scanned documents. This problem has gained significant attention
from the computer vision community in recent years, and several methods based
on energy minimization frameworks and deep learning approaches have been
proposed. In this work, we focus on the energy minimization framework and
propose a model that exploits both bottom-up and top-down cues for recognizing
cropped words extracted from street images. The bottom-up cues are derived from
individual character detections from an image. We build a conditional random
field model on these detections to jointly model the strength of the detections
and the interactions between them. These interactions are top-down cues
obtained from a lexicon-based prior, i.e., language statistics. The optimal
word represented by the text image is obtained by minimizing the energy
function corresponding to the random field model. We evaluate our proposed
algorithm extensively on a number of cropped scene text benchmark datasets,
namely Street View Text, ICDAR 2003, 2011 and 2013 datasets, and IIIT 5K-word,
and show better performance than comparable methods. We perform a rigorous
analysis of all the steps in our approach and analyze the results. We also show
that state-of-the-art convolutional neural network features can be integrated
in our framework to further improve the recognition performance
Unfree Labour : did indenture reduce labour supply to tea plantations in Assam?
Migration to tea plantations in Assam in the 19th century used indentured contracts. These
contracts differed by conditions of harshness. Migration under the Special Act gained notoriety
by giving tea planter the right of private arrest. Using a new set of migration by types of contract,
the paper assesses if harsh terms of indenture discouraged labour flows. We find that regions
using the harsh contract saw lower response to rise in the price of tea. Disaggregating by types of
recruiter, we find that the response to market recruitment was high in all regions, but response to
recruitment using community networks is statistically insignificant, suggesting that informational
asymmetries may be an explanation for continuing migration despite concerns raised by the
nationalist movement, social reformers and policy makers
Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7
Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been
investigated by ac magnetic susceptibility \chi_ac(T), dc magnetic
susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T)
measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a
spin-glass type freezing behavior near 16 K. Our frequency dependent \chi_ac(T)
data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly
influenced by Ca substitution. The effect of partial nonmagnetic Ca2+
substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic
isovalent Y3+ substituted Dy2-xYxTi2O7 (for low levels of dilution), however
the suppression of spin-freezing behavior is substantially stronger for Ca than
Y. The Cole-Cole plot analysis reveals semicircular character and a single
relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the
insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+
substitution for Dy3+ ions.Comment: 9 pages, 7 figures, 1 tabl
- …