11,829 research outputs found
Semiparametric Analysis of the Socio-Demographic and Spatial Determinants of Undernutrition in Two African Countries
We estimate semiparametric regression models of chronic undernutrition (stunting) using the 1992 Demographic and Health Surveys (DHS) from Tanzania and Zambia. We focus particularly on the influence of the child's age, the mother's body mass index, and spatial influences on chronic undernutrition. Conventional parametric regression models are not flexible enough to cope with possibly nonlinear effects of the continuous covariates and cannot flexibly model spatial influences. We present a Bayesian semiparametric analysis of the effects of these two covariates on chronic undernutrition. Moreover, we investigate spatial determinants of undernutrition in these two countries. Compared to previous work with a simple fixed effects approach for the influence of provinces, we model small scale district specific effects using flexible spatial priors. Inference is fully Bayesian and uses recent Markov chain Monte Carlo techniques
Riding the Yield Curve: Diversification of Strategies
Riding the yield curve, the fixed-income strategy of purchasing a longer-dated security and selling before maturity, has long been a popular means to achieve excess returns compared to buying-and-holding, despite its implicit violations of market efficiency and the pure expectations hypothesis of the term structure. This paper looks at the historic excess returns of different strategies across three countries and proposes several statistical and macro-based trading rules which seem to enhance returns even more. While riding based on the Taylor Rule works well even for longer investment horizons, our empirical results indicate that, using expectations implied by Fed funds futures, excess returns can only be increased over short horizons. Furthermore, we demonstrate that duration-neutral strategies are superior to standard riding on a risk- adjusted basis. Overall, our evidence stands in contrast to the pure expectations hypothesis and points to the existence of risk premia which may be exploited consistently.Term Structure, Interest Rates, Market Efficiency, Taylor Rule
Spectroscopic and photometric studies of white dwarfs in the Hyades
The Hyades cluster is known to harbour ten so-called classical white dwarf
members. Numerous studies through the years have predicted that more than twice
this amount of degenerate stars should be associated with the cluster. Using
the PPMXL catalog of proper motions and positions, a recent study proposed 17
new white dwarf candidates. We review the membership of these candidates by
using published spectroscopic and photometric observations, as well as by
simulating the contamination from field white dwarfs. In addition to the ten
classical Hyades white dwarfs, we find six white dwarfs that may be of Hyades
origin and three more objects that have an uncertain membership status due to
their unknown or imprecise atmospheric parameters. Among those, two to three
are expected as field stars contamination. Accurate radial velocity
measurements will confirm or reject the candidates. One consequence is that the
longstanding problem that no white dwarf older than ~340 Myr appears to be
associated with the cluster remains unsolved.Comment: 14 pages, 9 figures, accepted for publication in the Astronomy and
Astrophysics journa
Anomalous resistance overshoot in the integer quantum Hall effect
In this work we report experiments on defined by shallow etching narrow Hall
bars. The magneto-transport properties of intermediate mobility two-dimensional
electron systems are investigated and analyzed within the screening theory of
the integer quantized Hall effect. We observe a non-monotonic increase of Hall
resistance at the low magnetic field ends of the quantized plateaus, known as
the overshoot effect. Unexpectedly, for Hall bars that are defined by shallow
chemical etching the overshoot effect becomes more pronounced at elevated
temperatures. We observe the overshoot effect at odd and even integer plateaus,
which favor a spin independent explanation, in contrast to discussion in the
literature. In a second set of the experiments, we investigate the overshoot
effect in gate defined Hall bar and explicitly show that the amplitude of the
overshoot effect can be directly controlled by gate voltages. We offer a
comprehensive explanation based on scattering between evanescent incompressible
channels.Comment: 7 pages and 5 figure
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