801 research outputs found
Non-uniform carrier density in CdAs evidenced by optical spectroscopy
We report the detailed optical properties of CdAs crystals in a wide
parameter space: temperature, magnetic field, carrier concentration and crystal
orientation. We investigate high-quality crystals synthesized by three
different techniques. In all the studied samples, independently of how they
were prepared and how they were treated before the optical experiments, our
data indicate conspicuous fluctuations in the carrier density (up to 30%).
These charge puddles have a characteristic scale of 100 m, they become
more pronounced at low temperatures, and possibly, they become enhanced by the
presence of crystal twinning. The Drude response is characterized by very small
scattering rates ( meV) for as-grown samples. Mechanical treatment,
such as cutting or polishing, influences the optical properties of single
crystals, by increasing the Drude scattering rate and also modifying the high
frequency optical response. Magneto-reflectivity and Kerr rotation are
consistent with electron-like charge carriers and a spatially non-uniform
carrier density.Comment: Accepted in Physical Review
Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice
As a prototypical self-organization in the system with orbital degeneracy, we
theoretically investigate trimer formation on a triangular lattice, as observed
in LiVO2. From the analysis of an effective spin-orbital coupled model in the
strong correlation limit, we show that the previously-proposed orbital-ordered
trimer state is not the lowest-energy state for a finite Hund's-rule coupling.
Instead, exploring the ground state in a wide range of parameters for a
multiorbital Hubbard model, we find an instability toward a different
orbital-ordered trimer state in the intermediately correlated regime in the
presence of trigonal crystal field. The trimer phase appears in the competing
region among a paramagnetic metal, band insulator, and Mott insulator. The
underlying mechanism is nesting instability of the Fermi surface by a
synergetic effect of Coulomb interactions and trigonal-field splitting. The
results are compared with experiments in triangularlattice compounds, LiVX2
(X=O, S, Se) and NaVO2.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
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Segmentation of British Sign Language (BSL): Mind the gap!
This study asks how users of British Sign Language (BSL) recognize individual signs in connected sign sequences. We examined whether this is achieved through modality-specific or modality-general segmentation procedures. A modality-specific feature of signed languages is that, during continuous signing, there are salient transitions between sign locations. We used the sign-spotting task to ask if and how BSL signers use these transitions in segmentation. A total of 96 real BSL signs were preceded by nonsense signs which were produced in either the target location or another location (with a small or large transition). Half of the transitions were within the same major body area (e.g., head) and half were across body areas (e.g., chest to hand). Deaf adult BSL users (a group of natives and early learners, and a group of late learners) spotted target signs best when there was a minimal transition and worst when there was a large transition. When location changes were present, both groups performed better when transitions were to a different body area than when they were within the same area. These findings suggest that transitions do not provide explicit sign-boundary cues in a modality-specific fashion. Instead, we argue that smaller transitions help recognition in a modality-general way by limiting lexical search to signs within location neighbourhoods, and that transitions across body areas also aid segmentation in a modality-general way, by providing a phonotactic cue to a sign boundary. We propose that sign segmentation is based on modality-general procedures which are core language-processing mechanisms
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Spring School on Language, Music, and Cognition: Organizing Events in Time
The interdisciplinary spring school “Language, music, and cognition: Organizing events in time” was held from February 26 to March 2, 2018 at the Institute of Musicology of the University of Cologne. Language, speech, and music as events in time were explored from different perspectives including evolutionary biology, social cognition, developmental psychology, cognitive neuroscience of speech, language, and communication, as well as computational and biological approaches to language and music. There were 10 lectures, 4 workshops, and 1 student poster session.
Overall, the spring school investigated language and music as neurocognitive systems and focused on a mechanistic approach exploring the neural substrates underlying musical, linguistic, social, and emotional processes and behaviors. In particular, researchers approached questions concerning cognitive processes, computational procedures, and neural mechanisms underlying the temporal organization of language and music, mainly from two perspectives: one was concerned with syntax or structural representations of language and music as neurocognitive systems (i.e., an intrapersonal perspective), while the other emphasized social interaction and emotions in their communicative function (i.e., an interpersonal perspective). The spring school not only acted as a platform for knowledge transfer and exchange but also generated a number of important research questions as challenges for future investigations
Open reduction and internal fixation compared to closed reduction and external fixation in distal radial fractures: A randomized study of 50 patients
Background and purpose In unstable distal radial fractures that are impossible to reduce or to maintain in reduced position, the treatment of choice is operation. The type of operation and the choice of implant, however, is a matter of discussion. Our aim was to investigate whether open reduction and internal fixation would produce a better result than traditional external fixation
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
Genome-wide linkage analysis of 972 bipolar pedigrees using single-nucleotide polymorphisms.
Because of the high costs associated with ascertainment of families, most linkage studies of Bipolar I disorder (BPI) have used relatively small samples. Moreover, the genetic information content reported in most studies has been less than 0.6. Although microsatellite markers spaced every 10 cM typically extract most of the genetic information content for larger multiplex families, they can be less informative for smaller pedigrees especially for affected sib pair kindreds. For these reasons we collaborated to pool family resources and carried out higher density genotyping. Approximately 1100 pedigrees of European ancestry were initially selected for study and were genotyped by the Center for Inherited Disease Research using the Illumina Linkage Panel 12 set of 6090 single-nucleotide polymorphisms. Of the ~1100 families, 972 were informative for further analyses, and mean information content was 0.86 after pruning for linkage disequilibrium. The 972 kindreds include 2284 cases of BPI disorder, 498 individuals with bipolar II disorder (BPII) and 702 subjects with recurrent major depression. Three affection status models (ASMs) were considered: ASM1 (BPI and schizoaffective disorder, BP cases (SABP) only), ASM2 (ASM1 cases plus BPII) and ASM3 (ASM2 cases plus recurrent major depression). Both parametric and non-parametric linkage methods were carried out. The strongest findings occurred at 6q21 (non-parametric pairs LOD 3.4 for rs1046943 at 119 cM) and 9q21 (non-parametric pairs logarithm of odds (LOD) 3.4 for rs722642 at 78 cM) using only BPI and schizoaffective (SA), BP cases. Both results met genome-wide significant criteria, although neither was significant after correction for multiple analyses. We also inspected parametric scores for the larger multiplex families to identify possible rare susceptibility loci. In this analysis, we observed 59 parametric LODs of 2 or greater, many of which are likely to be close to maximum possible scores. Although some linkage findings may be false positives, the results could help prioritize the search for rare variants using whole exome or genome sequencing
Interplay between magnetism and superconductivity and appearance of a second superconducting transition in alpha-FeSe at high pressure
We synthesized tetragonal alpha-FeSe by melting a powder mixture of iron and
selenium at high pressure. Subsequent annealing at normal pressure results in
removing traces of hexagonal beta- FeSe, formation of a rather sharp transition
to superconducting state at Tc ~ 7 K, and the appearance of a magnetic
transition near Tm = 120 K. Resistivity and ac-susceptibility were measured on
the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic
transition visible in ac-susceptibility shifts down under pressure and the
resistive anomaly typical for a spin density wave (SDW) antiferromagnetic
transition develops near the susceptibility anomaly. Tc determined by the
appearance of a diamagnetic response in susceptibility, increases linearly
under pressure at a rate dTc/dP = 3.5 K/GPa. Below 1.5 GPa, the resistive
superconducting transition is sharp; the width of transition does not change
with pressure; and, Tc determined by a peak in drho/dT increases at a rate ~
3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition
develops. This effect cannot be explained by possible pressure gradients in the
sample and is inherent to alpha-FeSe. The dependences drho(T)/dT show a
signature for a second peak above 3 GPa which is indicative of the appearance
of another superconducting state in alpha-FeSe at high pressure. We argue that
this second superconducting phase coexists with SDW antiferromagnetism in a
partial volume fraction and originates from pairing of charge carriers from
other sheets of the Fermi surface
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