270 research outputs found
An Exploratory Graphical Method for Identifying Associations in r x c Contingency Tables
On finding a significant association between rows and columns of an r x c contingency table, the next step is to study the nature of the association in more detail. The use of a scree plot to visualize the largest contributions to Χ2 among all cells in the table in order to determine the nature of the association in more detail is proposed
A computational approach for genome-wide mapping of splicing factor binding sites
A computational method is presented for genome-wide mapping of splicing factor binding sites that considers both the genomic environment and evolutionary conservation
Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium
We model the abundance gradients in the disk of the Milky Way for several
chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba,
La and Eu), and compare our results with the most recent and homogeneous
observational data. We adopt a chemical evolution model able to well reproduce
the main properties of the solar vicinity. We compute, for the first time, the
abundance gradients for all the above mentioned elements in the galactocentric
distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in
the galactocentric distance range 5-17 kpc gives a very good agreement for many
of the studied elements. In addition, we fit very well the data for the
evolution of Lanthanum in the solar vicinity for which we present results here
for the first time. We explore, also for the first time, the behaviour of the
abundance gradients at large galactocentric distances by comparing our results
with data relative to distant open clusters and red giants and select the best
chemical evolution model model on the basis of that. We find a very good fit to
the observed abundance gradients, as traced by Cepheids, for most of the
elements, thus confirming the validity of the inside-out scenario for the
formation of the Milky Way disk as well as the adopted nucleosynthesis
prescriptions.Comment: 11 pages, 9 figures, accepted for publication in A&
Selective injection of magnetic domain walls in Permalloy nanostripes
Selective injection of magnetic domain walls in Permalloy nanostripe
The nature of localization in graphene under quantum Hall conditions
Particle localization is an essential ingredient in quantum Hall physics
[1,2]. In conventional high mobility two-dimensional electron systems Coulomb
interactions were shown to compete with disorder and to play a central role in
particle localization [3]. Here we address the nature of localization in
graphene where the carrier mobility, quantifying the disorder, is two to four
orders of magnitude smaller [4,5,6,7,8,9,10]. We image the electronic density
of states and the localized state spectrum of a graphene flake in the quantum
Hall regime with a scanning single electron transistor [11]. Our microscopic
approach provides direct insight into the nature of localization. Surprisingly,
despite strong disorder, our findings indicate that localization in graphene is
not dominated by single particle physics, but rather by a competition between
the underlying disorder potential and the repulsive Coulomb interaction
responsible for screening.Comment: 18 pages, including 5 figure
Does distance matter? Variations in alternative 3âČ splicing regulation
Alternative splicing constitutes a major mechanism creating protein diversity in humans. This diversity can result from the alternative skipping of entire exons or by alternative selection of the 5âČ or 3âČ splice sites that define the exon boundaries. In this study, we analyze the sequence and evolutionary characteristics of alternative 3âČ splice sites conserved between human and mouse genomes for distances ranging from 3 to 100 nucleotides. We show that alternative splicing events can be distinguished from constitutive splicing by a combination of properties which vary depending on the distance between the splice sites. Among the unique features of alternative 3âČ splice sites, we observed an unexpectedly high occurrence of events in which a polypyrimidine tract was found to overlap the upstream splice site. By applying a machine-learning approach, we show that we can successfully discriminate true alternative 3âČ splice sites from constitutive 3âČ splice sites. Finally, we propose that the unique features of the intron flanking alternative splice sites are indicative of a regulatory mechanism that is involved in splice site selection. We postulate that the process of splice site selection is influenced by the distance between the competitive splice sites
Magnetization reversal signatures in the magnetoresistance of magnetic multilayers
The simultaneous determination of magnetoresistance and vectorial-resolved magnetization hysteresis curves in a spin valve structure reveals distinct magnetoresistive features for different magnetic ïŹeld orientations, which are directly related to the magnetization reversal processes. Measurements performed in the whole angular range demonstrate that the magnetoresistive response originates from the intrinsic anisotropic angular dependence of the magnetization orientation between the two ferromagnetic layers. This also provides direct proof that the spin-dependent scattering in the bulk of the magnetic layers is at the origin of the magnetoresistive signal
Observation of Electron-Hole Puddles in Graphene Using a Scanning Single Electron Transistor
The electronic density of states of graphene is equivalent to that of
relativistic electrons. In the absence of disorder or external doping the Fermi
energy lies at the Dirac point where the density of states vanishes. Although
transport measurements at high carrier densities indicate rather high
mobilities, many questions pertaining to disorder remain unanswered. In
particular, it has been argued theoretically, that when the average carrier
density is zero, the inescapable presence of disorder will lead to electron and
hole puddles with equal probability. In this work, we use a scanning single
electron transistor to image the carrier density landscape of graphene in the
vicinity of the neutrality point. Our results clearly show the electron-hole
puddles expected theoretically. In addition, our measurement technique enables
to determine locally the density of states in graphene. In contrast to
previously studied massive two dimensional electron systems, the kinetic
contribution to the density of states accounts quantitatively for the measured
signal. Our results suggests that exchange and correlation effects are either
weak or have canceling contributions.Comment: 13 pages, 5 figure
C IV absorption in damped and sub-damped Lyman-alpha systems: correlations with metallicity and implications for galactic winds at z~2-3
We present a study of C IV absorption in a sample of 63 damped Lyman-alpha
(DLA) systems and 11 sub-DLAs in the redshift range 1.75<z_abs<3.61, using a
dataset of high-resolution (6.6 km/s FWHM), high signal-to-noise VLT/UVES
spectra. Narrow and broad C IV absorption line components indicate the presence
of both warm, photoionized and hot, collisionally ionized gas. We report new
correlations between the metallicity (measured in the neutral-phase) and each
of the C IV column density, the C IV total line width, and the maximum C IV
velocity. We explore the effect on these correlations of the sub-DLAs, the
proximate DLAs (defined as those within 5 000 km/s of the quasar), the
saturated absorbers, and the metal line used to measure the metallicity, and we
find the correlations to be robust. There is no evidence for any difference
between the measured properties of DLA C IV and sub-DLA C IV. In 25 DLAs and 4
sub-DLAs, covering 2.5 dex in [Z/H], we directly observe C IV moving above the
escape speed, where v_esc is derived from the total line width of the neutral
gas profiles. These high-velocity C IV clouds, unbound from the central
potential well, can be interpreted as highly ionized outflowing winds, which
are predicted by numerical simulations of galaxy feedback. The distribution of
C IV column density in DLAs and sub-DLAs is similar to the distribution in
Lyman Break galaxies, where winds are directly observed, supporting the idea
that supernova feedback creates the ionized gas in DLAs. The unbound C IV
absorbers show a median mass flow rate of ~22(r/40 kpc) solar masses per year,
where r is the characteristic C IV radius. Their kinetic energy fluxes are
large enough that a star formation rate (SFR) of ~2 solar masses per year is
required to power them.Comment: 21 pages, accepted to A&A, Fig 1 downgraded, v2 with proof
corrections made and improved Fig 1
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