508,368 research outputs found
Complete mitochondrial DNA sequences provide new insights into the Polynesian motif and the peopling of Madagascar
More than a decade of mitochondrial DNA (mtDNA) studies have given the 'Polynesian motif' renowned status as a marker for tracing the late-Holocene expansion of Austronesian speaking populations. Despite considerable research on the Polynesian motif in Oceania, there has been little equivalent work on the western edge of its expansion - leaving major issues unresolved regarding the motif's evolutionary history. This has also led to considerable uncertainty regarding the settlement of Madagascar. In this study, we assess mtDNA variation in 266 individuals from three Malagasy ethnic groups: the Mikea, Vezo, and Merina. Complete mtDNA genome sequencing reveals a new variant of the Polynesian motif in Madagascar; two coding region mutations define a Malagasy-specific sub-branch. This newly defined 'Malagasy motif' occurs at high frequency in all three ethnic groups (13-50%), and its phylogenetic position, geographic distribution, and estimated age all support a recent origin, but without conclusively identifying a specific source region. Nevertheless, the haplotype's limited diversity, similar to those of other mtDNA haplogroups found in our Malagasy groups, best supports a small number of initial settlers arriving to Madagascar through the same migratory process. Finally, the discovery of this lineage provides a set of new polymorphic positions to help localize the Austronesian ancestors of the Malagasy, as well as uncover the origin and evolution of the Polynesian motif itself
Tuning Energy Relaxation along Quantum Hall Channels
The chiral edge channels in the quantum Hall regime are considered ideal
ballistic quantum channels, and have quantum information processing
potentialities. Here, we demonstrate experimentally, at filling factor 2, the
efficient tuning of the energy relaxation that limits quantum coherence and
permits the return toward equilibrium. Energy relaxation along an edge channel
is controllably enhanced by increasing its transmission toward a floating ohmic
contact, in quantitative agreement with predictions. Moreover, by forming a
closed inner edge channel loop, we freeze energy exchanges in the outer
channel. This result also elucidates the inelastic mechanisms at work at
filling factor 2, informing us in particular that those within the outer edge
channel are negligible.Comment: 8 pages including supplementary materia
Proportionate vs disproportionate distribution of wealth of two individuals in a tempered Paretian ensemble
We study the distribution P(\omega) of the random variable \omega = x_1/(x_1
+ x_2), where x_1 and x_2 are the wealths of two individuals selected at random
from the same tempered Paretian ensemble characterized by the distribution
\Psi(x) \sim \phi(x)/x^{1 + \alpha}, where \alpha > 0 is the Pareto index and
is the cut-off function. We consider two forms of \phi(x): a bounded
function \phi(x) = 1 for L \leq x \leq H, and zero otherwise, and a smooth
exponential function \phi(x) = \exp(-L/x - x/H). In both cases \Psi(x) has
moments of arbitrary order.
We show that, for \alpha > 1, P(\omega) always has a unimodal form and is
peaked at \omega = 1/2, so that most probably x_1 \approx x_2. For 0 < \alpha <
1 we observe a more complicated behavior which depends on the value of \delta =
L/H. In particular, for \delta < \delta_c - a certain threshold value -
P(\omega) has a three-modal (for a bounded \phi(x)) and a bimodal M-shape (for
an exponential \phi(x)) form which signifies that in such ensembles the wealths
x_1 and x_2 are disproportionately different.Comment: 9 pages, 8 figures, to appear in Physica
Minimax adaptive tests for the Functional Linear model
We introduce two novel procedures to test the nullity of the slope function
in the functional linear model with real output. The test statistics combine
multiple testing ideas and random projections of the input data through
functional Principal Component Analysis. Interestingly, the procedures are
completely data-driven and do not require any prior knowledge on the smoothness
of the slope nor on the smoothness of the covariate functions. The levels and
powers against local alternatives are assessed in a nonasymptotic setting. This
allows us to prove that these procedures are minimax adaptive (up to an
unavoidable \log\log n multiplicative term) to the unknown regularity of the
slope. As a side result, the minimax separation distances of the slope are
derived for a large range of regularity classes. A numerical study illustrates
these theoretical results
Mapping of periodically poled crystals via spontaneous parametric down-conversion
A new method for characterization of periodically poled crystals is developed
based on spontaneous parametric down-conversion. The method is demonstrated on
crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled
structures, obtained directly under Czochralski growth procedure and designed
for application of OPO in the mid infrared range. Infrared dispersion of
refractive index, effective working periods and wavelengths of OPO were
determined by special treatment of frequency-angular spectra of spontaneous
parametric down-conversion in the visible range. Two-dimensional mapping via
spontaneous parametric down-conversion is proposed for characterizing spatial
distribution of bulk quasi-phase matching efficiency across the input window of
a periodically poled sample.Comment: 19 pages, 6 figure
Adaptive estimation of the transition density of a particular hidden Markov chain
We study the following model of hidden Markov chain: , with a real-valued positive recurrent and stationary
Markov chain and a noise independent of the
sequence having a known distribution. We present an adaptive estimator
of the transition density based on the quotient of a deconvolution estimator of
the density of and an estimator of the density of . These
estimators are obtained by contrast minimization and model selection. We
evaluate the risk and its rate of convergence for ordinary smooth and
supersmooth noise with regard to ordinary smooth and supersmooth chains. Some
examples are also detailed
Magnons in the ferromagnetic Kondo-lattice model
The magnetic properties of the ferromagnetic Kondo-lattice model (FKLM) are
investigated. Starting from an analysis of the magnon spectrum in the spin-wave
regime, we examine the ferromagnetic stability as a function of the occupation
of the conduction band and the strength of the coupling between the
localised moments and the conduction electrons. From the properties of the
spin-wave stiffness the ferromagnetic phase at zero temperature is derived.
Using an approximate formula the critical temperature is calculated as a
function of and .Comment: 15 pages, 6 figures, to appear in phys. stat. sol.
Density functional theory of phase coexistence in weakly polydisperse fluids
The recently proposed universal relations between the moments of the
polydispersity distributions of a phase-separated weakly polydisperse system
are analyzed in detail using the numerical results obtained by solving a simple
density functional theory of a polydisperse fluid. It is shown that universal
properties are the exception rather than the rule.Comment: 10 pages, 2 figures, to appear in PR
Stock markets are not what we think they are: the key roles of cross-ownership and corporate treasury stock
We describe and document three mechanisms by which corporations can influence
or even control stock prices. (i) Parent and holding companies wield control
over other publicly traded companies. (ii) Through clever management of
treasury stock based on buyback programs and stock issuance, stock price
fluctuations can be amplified or curbed. (iii) Finally, history shows a close
interdependance between the level of stock prices on the one hand and merger
and acquisition activity on the other hand. This perspective in which Boards of
Directors of major companies shepherd the market offers a natural
interpretation of the so-called "herd behavior" observed in stock markets. The
traditional view holds that by driving profit expectations, corporations have
an indirect role in shaping the market. In this paper, we suggest that over the
last decades they became more and more the direct moving force of stock
markets.Comment: 9 pages, 3 figures, 1 tabl
Material independent crack arrest statistics
The propagation of (planar) cracks in a heterogeneous brittle material
characterized by a random field of toughness is considered, taking into account
explicitly the effect of the crack front roughness on the local stress
intensity factor. In the so-called strong-pinning regime, the onset of crack
propagation appears to map onto a second-order phase transition characterized
by universal critical exponents which are independent of the local
characteristics of the medium. Propagation over large distances can be
described by using a simple one-dimensional description, with a correlation
length and an effective macroscopic toughness distribution that scale in a
non-trivial fashion with the crack front length. As an application of the above
concepts, the arrest of indentation cracks is addressed, and the analytical
expression for the statistical distribution of the crack radius at arrest is
derived. The analysis of indentation crack radii on alumina is shown to obey
the predicted algebraic expression for the radius distribution and its
dependence on the indentation load
- …