1,682 research outputs found
Gate-tunable band structure of the LaAlO-SrTiO interface
The 2-dimensional electron system at the interface between LaAlO and
SrTiO has several unique properties that can be tuned by an externally
applied gate voltage. In this work, we show that this gate-tunability extends
to the effective band structure of the system. We combine a magnetotransport
study on top-gated Hall bars with self-consistent Schr\"odinger-Poisson
calculations and observe a Lifshitz transition at a density of
cm. Above the transition, the carrier density of one
of the conducting bands decreases with increasing gate voltage. This surprising
decrease is accurately reproduced in the calculations if electronic
correlations are included. These results provide a clear, intuitive picture of
the physics governing the electronic structure at complex oxide interfaces.Comment: 14 pages, 4 figure
Adaptive Cartesian meshes for atmospheric single-column models: a study using Basilisk 18-02-16
It is well known that the representation of certain atmospheric conditions in
climate and weather models can still suffer from the limited grid resolution
that is facilitated by modern-day computer systems. Herein we study a simple
one-dimensional analogy to those models by using a single-column model
description of the atmosphere. The model employs an adaptive Cartesian mesh
that applies a high-resolution mesh only when and where it is required. The
so-called adaptive-grid model is described, and we report our findings
obtained for tests to evaluate the representation of the atmospheric boundary
layer, based on the first two GEWEX ABL Study (GABLS) inter-comparison cases.
The analysis shows that the adaptive-grid algorithm is indeed able to
dynamically coarsen and refine the numerical grid whilst maintaining an
accurate solution. This is an interesting result as in reality, transitional
dynamics (e.g. due to the diurnal cycle or due to changing synoptic
conditions) are the rule rather than the exception.</p
Intensity-based analysis of dual-color gene expression data as an alternative to ratio-based analysis to enhance reproducibility
<p>Abstract</p> <p>Background</p> <p>Ratio-based analysis is the current standard for the analysis of dual-color microarray data. Indeed, this method provides a powerful means to account for potential technical variations such as differences in background signal, spot size and spot concentration. However, current high density dual-color array platforms are of very high quality, and inter-array variance has become much less pronounced. We therefore raised the question whether it is feasible to use an intensity-based analysis rather than ratio-based analysis of dual-color microarray datasets. Furthermore, we compared performance of both ratio- and intensity-based analyses in terms of reproducibility and sensitivity for differential gene expression.</p> <p>Results</p> <p>By analyzing three distinct and technically replicated datasets with either ratio- or intensity-based models, we determined that, when applied to the same dataset, intensity-based analysis of dual-color gene expression experiments yields 1) more reproducible results, and 2) is more sensitive in the detection of differentially expressed genes. These effects were most pronounced in experiments with large biological variation and complex hybridization designs. Furthermore, a power analysis revealed that for direct two-group comparisons above a certain sample size, ratio-based models have higher power, although the difference with intensity-based models is very small.</p> <p>Conclusions</p> <p>Intensity-based analysis of dual-color datasets results in more reproducible results and increased sensitivity in the detection of differential gene expression than the analysis of the same dataset with ratio-based analysis. Complex dual-color setups such as interwoven loop designs benefit most from ignoring the array factor. The applicability of our approach to array platforms other than dual-color needs to be further investigated.</p
Children's opinions about organ donation:a first step to assent?
Background: Parents have to decide about organ donation after the death of their child. Although most parents probably would like to respect their child's intentions, parents often are not aware of their child's wishes. This requires insight into children's opinions about donation. Methods: An internet survey that investigated whether Dutch children in the age range of 12 through 15 years had heard about organ donation, what their opinions were on donation and whether the topic had been discussed at home. Questionnaire response rate 38%. Results: Around 99% of 2016 responders had heard about organ donation and about the possibility of becoming a donor, 75% preferred to decide for themselves about donation, 43% had discussed organ donation more than once at home, 66% were willing to donate. The willingness to donate was positively associated with age and socio-economic status. Conclusion: This survey indicates that these children at 12 through 15 years of age are capable and willing to think about organ donation. Thought should be given about how to raise awareness and how to enable parents and children to develop some sort of health literacy concerning the concept of organ donation. Children and their parents should be given adequate opportunities to receive appropriate information, suited to their psychological and moral developmental status
Correlation between Superconductivity, Band Filling and Electron Confinement at the LaAlO-SrTiO Interface
By combined top- and backgating, we explore the correlation of
superconductivity with band filling and electron confinement at the
LaAlO-SrTiO interface. We find that the top- and backgate voltages have
distinctly different effects on the superconducting critical temperature,
implying that the confining potential well has a profound effect on
superconductivity. We investigate the origin of this behavior by comparing the
gate-dependence of to the corresponding evolution of the band filling
with gate voltage. For several backgate voltages, we observe maximum to
consistently coincide with a kink in tuning the band filling for high topgate
voltage. Self-consistent Schr\"odinger-Poisson calculations relate this kink to
a Lifshitz transition of the second subband. These results establish a
major role for confinement-induced subbands in the phase diagram of SrTiO
surface states, and establish gating as a means to control the relative energy
of these states.Comment: 17 pages, 5 figure
Magnetic effects at the interface between nonmagnetic oxides
The electronic reconstruction at the interface between two insulating oxides
can give rise to a highly-conductive interface. In analogy to this remarkable
interface-induced conductivity we show how, additionally, magnetism can be
induced at the interface between the otherwise nonmagnetic insulating
perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the
interface is found, together with a logarithmic temperature dependence of the
sheet resistance. At low temperatures, the sheet resistance reveals magnetic
hysteresis. Magnetic ordering is a key issue in solid-state science and its
underlying mechanisms are still the subject of intense research. In particular,
the interplay between localized magnetic moments and the spin of itinerant
conduction electrons in a solid gives rise to intriguing many-body effects such
as Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, the Kondo effect, and
carrier-induced ferromagnetism in diluted magnetic semiconductors. The
conducting oxide interface now provides a versatile system to induce and
manipulate magnetic moments in otherwise nonmagnetic materials.Comment: Nature Materials, July issu
The JCMT Spectral Legacy Survey: physical structure of the molecular envelope of the high-mass protostar AFGL2591
The understanding of the formation process of massive stars (>8 Msun) is
limited, due to theoretical complications and observational challenges.
We investigate the physical structure of the large-scale (~10^4-10^5 AU)
molecular envelope of the high-mass protostar AFGL2591 using spectral imaging
in the 330-373 GHz regime from the JCMT Spectral Legacy Survey. Out of ~160
spectral features, this paper uses the 35 that are spatially resolved.
The observed spatial distributions of a selection of six species are compared
with radiative transfer models based on a static spherically symmetric
structure, a dynamic spherical structure, and a static flattened structure. The
maps of CO and its isotopic variations exhibit elongated geometries on scales
of ~100", and smaller scale substructure is found in maps of N2H+, o-H2CO, CS,
SO2, CCH, and methanol lines. A velocity gradient is apparent in maps of all
molecular lines presented here, except SO, SO2, and H2CO. We find two emission
peaks in warm (Eup~200K) methanol separated by 12", indicative of a secondary
heating source in the envelope.
The spherical models are able to explain the distribution of emission for the
optically thin H13CO+ and C34S, but not for the optically thick HCN, HCO+, and
CS, nor for the optically thin C17O. The introduction of velocity structure
mitigates the optical depth effects, but does not fully explain the
observations, especially in the spectral dimension. A static flattened envelope
viewed at a small inclination angle does slightly better.
We conclude that a geometry of the envelope other than an isotropic static
sphere is needed to circumvent line optical depth effects. We propose that this
could be achieved in envelope models with an outflow cavity and/or
inhomogeneous structure at scales smaller than ~10^4 AU. The picture of
inhomogeneity is supported by observed substructure in at least six species.Comment: 17 pages; accepted for publication in A&
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