11,372 research outputs found
The cleavage surface of the BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) superconductors: from diversity to simplicity
We elucidate the termination surface of cleaved single crystals of the
BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) families of the high
temperature iron based superconductors. By combining scanning tunneling
microscopic data with low energy electron diffraction we prove that the
termination layer of the Ba122 systems is a remnant of the Ba layer, which
exhibits a complex diversity of ordered and disordered structures. The observed
surface topographies and their accompanying superstructure reflections in
electron diffraction depend on the cleavage temperature. In stark contrast,
Fe_(y)Se_(1-x)Te_(x) possesses only a single termination structure - that of
the tetragonally ordered Se_(1-x)Te_(x) layer.Comment: 4 pages, 4 figure
The Relational Side of Teachers’ Self-efficacy:Assimilation and Contrast Effects of Classroom Relational Climate on Teachers’ Self-Efficacy
Although much is known about the sources of teachers' self-efficacy (TSE), less attention has been paid to the social-contextual specificity of TSE and the processes influencing the relevance of TSE information sources. This study investigated both dyad-level relationships and the classroom relational climate as predictors of TSE at the student and classroom level. Additionally, we explored two competing hypotheses—assimilation and contrast—articulating how teachers use information conveyed by classroom relationship experiences as a heuristic to interpret relationship experiences with individual students as a TSE source. Elementary school teachers (N = 86; 72.05% female) completed the Student–Teacher Relationship Scale and Student-Specific Teacher Self-Efficacy Scale for randomly selected children (N = 687, 50.1% girls, Grades 3–6) from their classes. Doubly latent multilevel structural equation modeling was used to test for associations of Closeness and Conflict with TSE at both the student (L1) and classroom level (L2). Contextual effects, corresponding to associations of classroom-level Closeness and Conflict with TSE above the same associations at the student level, were calculated to test assimilation and contrast hypotheses. At L1, results indicated positive associations between Closeness and TSE and negative associations between Conflict and TSE. At L2, only Conflict was negatively associated with TSE. Consistent with the contrast hypothesis, the contextual effect of Closeness, but not Conflict, was negative and significant. Hence, teachers' judgments of a relatively close classroom relational climate may lead them to perceive relational closeness with individual students in a more negative light, resulting in lower levels of TSE toward these students
The Relational Side of Teachers’ Self-efficacy:Assimilation and Contrast Effects of Classroom Relational Climate on Teachers’ Self-Efficacy
Although much is known about the sources of teachers' self-efficacy (TSE), less attention has been paid to the social-contextual specificity of TSE and the processes influencing the relevance of TSE information sources. This study investigated both dyad-level relationships and the classroom relational climate as predictors of TSE at the student and classroom level. Additionally, we explored two competing hypotheses—assimilation and contrast—articulating how teachers use information conveyed by classroom relationship experiences as a heuristic to interpret relationship experiences with individual students as a TSE source. Elementary school teachers (N = 86; 72.05% female) completed the Student–Teacher Relationship Scale and Student-Specific Teacher Self-Efficacy Scale for randomly selected children (N = 687, 50.1% girls, Grades 3–6) from their classes. Doubly latent multilevel structural equation modeling was used to test for associations of Closeness and Conflict with TSE at both the student (L1) and classroom level (L2). Contextual effects, corresponding to associations of classroom-level Closeness and Conflict with TSE above the same associations at the student level, were calculated to test assimilation and contrast hypotheses. At L1, results indicated positive associations between Closeness and TSE and negative associations between Conflict and TSE. At L2, only Conflict was negatively associated with TSE. Consistent with the contrast hypothesis, the contextual effect of Closeness, but not Conflict, was negative and significant. Hence, teachers' judgments of a relatively close classroom relational climate may lead them to perceive relational closeness with individual students in a more negative light, resulting in lower levels of TSE toward these students
Non-gapped Fermi surfaces, quasiparticles and the anomalous temperature dependence of the near- electronic states in the CMR oxide LaSrMnO with
After years of research into colossal magnetoresistant (CMR) manganites using
bulk techniques, there has been a recent upsurge in experiments directly
probing the electronic states at or near the surface of the bilayer CMR
materials LaSrMnO using angle-resolved photoemission
or scanning probe microscopy. Here we report new, temperature dependent, angle
resolved photoemission data from single crystals with a doping level of
. The first important result is that there is no sign of a pseudogap in
the charge channel of this material for temperatures below the Curie
temperature . The second important result concerns the temperature
dependence of the electronic states. The temperature dependent changes in the
Fermi surface spectra both at the zone face and zone diagonal regions in
-space indicate that the coherent quasiparticle weight disappears for
temperatures significantly above , and that the -dependence of the
T-induced changes in the spectra invalidate an interpretation of these data in
terms of the superposition of a `universal' metallic spectrum and an insulating
spectrum whose relative weight changes with temperature. In this sense, our
data are not compatible with a phase separation scenario.Comment: 6 pages, 4 figure
Nonuniversal Shot Noise in Disordered Quantum Wires with Channel-Number Imbalance
The number of conducting channels for one propagating direction is equal to
that for the other direction in ordinary quantum wires. However, they can be
imbalanced in graphene nanoribbons with zigzag edges. Employing the model
system in which a degree of channel-number imbalance can be controlled, we
calculate the shot-noise power at zero frequency by using the
Boltzmann-Langevin approach. The shot-noise power in an ordinary diffusive
conductor is one-third of the Poisson value. We show that with increasing the
degree of channel-number imbalance, the universal one-third suppression breaks
down and a highly nonuniversal behavior of shot noise appears.Comment: 10 pages, 3 figure
Evolving temporal association rules with genetic algorithms
A novel framework for mining temporal association rules by discovering itemsets with a genetic algorithm is introduced. Metaheuristics have been applied to association rule mining, we show the efficacy of extending this to another variant - temporal association rule mining. Our framework is an enhancement to existing temporal association rule mining methods as it employs a genetic algorithm to simultaneously search the rule space and temporal space. A methodology for validating the ability of the proposed framework isolates target temporal itemsets in synthetic datasets. The Iterative Rule Learning method successfully discovers these targets in datasets with varying levels of difficulty
Kondo hybridisation and the origin of metallic states at the (001) surface of SmB6
SmB6, a well-known Kondo insulator, has been proposed to be an ideal
topological insulator with states of topological character located in a clean,
bulk electronic gap, namely the Kondo hybridisation gap. Seeing as the Kondo
gap arises from many body electronic correlations, this would place SmB6 at the
head of a new material class: topological Kondo insulators. Here, for the first
time, we show that the k-space characteristics of the Kondo hybridisation
process is the key to unravelling the origin of the two types of metallic
states observed directly by ARPES in the electronic band structure of
SmB6(001). One group of these states is essentially of bulk origin, and cuts
the Fermi level due to the position of the chemical potential 20 meV above the
lowest lying 5d-4f hybridisation zone. The other metallic state is more
enigmatic, being weak in intensity, but represents a good candidate for a
topological surface state. However, before this claim can be substantiated by
an unequivocal measurement of its massless dispersion relation, our data raises
the bar in terms of the ARPES resolution required, as we show there to be a
strong renormalisation of the hybridisation gaps by a factor 2-3 compared to
theory, following from the knowledge of the true position of the chemical
potential and a careful comparison with the predictions from recent
LDA+Gutzwiler calculations. All in all, these key pieces of evidence act as
triangulation markers, providing a detailed description of the electronic
landscape in SmB6, pointing the way for future, ultrahigh resolution ARPES
experiments to achieve a direct measurement of the Dirac cones in the first
topological Kondo insulator.Comment: 9 pages, 4 Figures and supplementary material (including Movies and
CORPES13 "best prize" poster
A high resolution, hard x-ray photoemission investigation of La_(2-2x)Sr_(1+2x)Mn_2O_7 (0.30<x<0.50): on microscopic phase separation and the surface electronic structure of a bilayered CMR manganite
Photoemission data taken with hard x-ray radiation on cleaved single crystals
of the bilayered, colossal magnetoresistant manganite La_(2-2x)Sr_(1+2x)Mn_2O_7
(LSMO) with 0.30<x<0.50 are presented. Making use of the increased
bulk-sensitivity upon hard x-ray excitation it is shown that the core level
footprint of the electronic structure of the LSMO cleavage surface is identical
to that of the bulk. Furthermore, by comparing the core level shift of the
different elements as a function of doping level x, it is shown that
microscopic phase separation is unlikely to occur for this particular manganite
well above the Curie temperature.Comment: 7 pages, 5 figure
Near infrared and optical morphology of the dusty galaxy NGC972
Near infrared (NIR) and optical surface photometric analyses of the dusty
galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can
be fitted with a combination of gaussian and exponential profiles,
corresponding to a starburst nucleus and a stellar disk respectively. The
exponential scale length in the B-band is 2.8 times larger than in the K-band,
which implies a central B-band optical depth as high as 11. A bulge is absent
even in the NIR bands and hence the galaxy must be of a morphological type
later than the usually adopted Sb type. Relatively low rotational velocity and
high gas content also favor a later type, probably Sd, for the galaxy. Only one
arm can be traced in the distribution of old stars; the second arm, however,
can be traced in the distribution of dust and HII regions. Data suggest a short
NIR bar, which ends inside the nuclear ring. The slowly rising nature of the
rotation curve rules out a resonance origin of the the nuclear ring. The ring
is most likely not in the plane of the galaxy, given its circular appearance in
spite of the moderately high inclination of the galaxy. The off-planar nature
of the star forming ring, the unusually high fraction (30%) of the total mass
in molecular form, the presence of a nuclear starburst and the asymmetry of
spiral arms, are probably the result of a merger with a gas-rich companion
galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical
Journal, October 199
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