480 research outputs found
The processing of ambiguous sentences by first and second language learners of English
This study compares the way English-speaking children and adult second language learners of English resolve relative clause attachment ambiguities in sentences such as The dean liked the secretary of the professor who was reading a letter. Two groups of advanced L2 learners of English with Greek or German as their L1 participated in a set of off-line and on-line tasks. While the participants ' disambiguation preferences were influenced by lexical-semantic properties of the preposition linking the two potential antecedent NPs (of vs. with), there was no evidence that they were applying any structure-based ambiguity resolution strategies of the type that have been claimed to influence sentence processing in monolingual adults. These findings differ markedly from those obtained from 6 to 7 yearold monolingual English children in a parallel auditory study (Felser, Marinis, & Clahsen, submitted) in that the children's attachment preferences were not affected by the type of preposition at all. We argue that whereas children primarily rely on structure-based parsing principles during processing, adult L2 learners are guided mainly by non-structural informatio
Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in CrB
In itinerant ferromagnets, the quenched disorder is predicted to dramatically
affect the ferromagnetic to paramagnetic quantum phase transition driven by
external control parameters at zero temperature. Here we report a study on
Fe-doped CrB, which, starting from the paramagnetic parent, orders
ferromagnetically for Fe-doping concentrations larger than \%. In parent CrB, B nuclear magnetic resonance data reveal
the presence of both ferromagnetic and antiferromagnetic fluctuations. The
latter are suppressed with Fe-doping, before the ferromagnetic ones finally
prevail for . Indications for non-Fermi liquid behavior, usually
associated with the proximity of a quantum critical point, were found for all
samples, including undoped CrB. The sharpness of the ferromagnetic-like
transition changes on moving away from , indicating significant
changes in the nature of the magnetic transitions in the vicinity of the
quantum critical point. Our data provide constraints for understanding quantum
phase transitions in itinerant ferromagnets in the limit of weak quenched
disorder.Comment: 8 pages, 7 figure
Lone Pair Effect, Structural Distortions and Potential for Superconductivity in Tl Perovskites
Drawing the analogy to BaBiO3, we investigate via ab-initio electronic
structure calculations potential new superconductors of the type ATlX3 with A =
Rb, Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. Based on
chemical reasoning, supported by the calculations, we show that Tl-based
perovskites have structural and charge instabilities driven by the lone pair
effect, similar to the case of BaBiO3, effectively becoming A2Tl1+Tl3+X6. We
find that upon hole doping of RbTlCl3, structures without Tl1+, Tl3+ charge
disproportionation become more stable, although the ideal cubic perovskite,
often viewed as the best host for superconductivity, should not be the most
stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped
RbTlCl3, predicted to be most stable in the same tetragonal structure, display
highly analogous calculated electronic band structures.Comment: 5 pages, 5 figure
Premartensite to martensite transition and its implications on the origin of modulation in Ni2MnGa ferromagnetic shape memory alloy
We present here results of temperature dependent high resolution synchrotron
x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our
results show that the incommensurate martensite phase results from the
incommensurate premartensite phase, and not from the austenite phase assumed in
the adaptive phase model. The premartensite phase transforms to the martensite
phase through a first order phase transition with coexistence of the two phases
in a broad temperature interval (~40K), discontinuous change in the unit cell
volume as also in the modulation wave vector across the transition temperature
and considerable thermal hysteresis in the characteristic transition
temperatures. The temperature variation of the modulation wave vector q shows
smooth analytic behaviour with no evidence for any devilish plateau
corresponding to an intermediate or ground state commensurate lock-in phases.
The existence of the incommensurate 7M like modulated structure down to 5K
suggests that the incommensurate 7M like modulation is the ground state of
Ni2MnGa and not the Bain distorted tetragonal L10 phase or any other lock-in
phase with a commensurate modulation. These findings can be explained within
the framework of the soft phonon model
Indium-Gallium Segregation in CuInGaSe: An ab initio based Monte Carlo Study
Thin-film solar cells with CuInGaSe (CIGS) absorber are still
far below their efficiency limit, although lab cells reach already 19.9%. One
important aspect is the homogeneity of the alloy. Large-scale simulations
combining Monte Carlo and density functional calculations show that two phases
coexist in thermal equilibrium below room temperature. Only at higher
temperatures, CIGS becomes more and more a homogeneous alloy. A larger degree
of inhomogeneity for Ga-rich CIGS persists over a wide temperature range, which
may contribute to the low observed efficiency of Ga-rich CIGS solar cells
Field-induced charge symmetry revealed by nuclear magnetic resonance in the topological insulator Bi<sub>2</sub>Te<sub>3</sub>
Nuclear magnetic resonance (NMR) was recently shown to measure the bulk band inversion of Bi2Se3 through changes in the Bi-209 nuclear quadrupole interaction, and the corresponding tensor of the local electric field gradient was found to follow, surprisingly, the direction of the external magnetic field if the sample is rotated. This manifests a hidden property of the charge carriers in the bulk of this topological insulator, which is explored here with another material, Bi2Te3. It is found that two electric field gradients appear to be present at Bi-209, one rests with the lattice, as usual, while a second follows the external field if it is rotated with respect to the crystal axes. These electronic degrees of freedom and their lifetime is believed to be responsible for an alternate quadrupolar relaxation that should lead to other special properties including the electronic specific heat
Residual stress induced stabilization of martensite phase and its effect on the magneto-structural transition in Mn rich Ni-Mn-In/Ga magnetic shape memory alloys
The irreversibility of the martensite transition in magnetic shape memory
alloys (MSMAs) with respect to external magnetic field is one of the biggest
challenges that limits their application as giant caloric materials. This
transition is a magneto-structural transition that is accompanied with a steep
drop in magnetization (i.e., 'delta M') around the martensite start temperature
(Ms) due to the lower magnetization of the martensite phase. In this
communication, we show that 'delta M' around Ms in Mn rich Ni-Mn based MSMAs
gets suppressed by two orders of magnitude in crushed powders due to the
stabilization of the martensite phase at temperatures well above the Ms and the
austenite finish (Af) temperatures due to residual stresses. Analysis of the
intensities and the FWHM of the x-ray powder diffraction patterns reveals
stabilized martensite phase fractions as 97, 75 and 90% with corresponding
residual microstrains as 5.4, 5.6 and 3% in crushed powders of the three
different Mn rich Ni-Mn alloys, namely, Mn1.8Ni1.8In0.4, Mn1.75Ni1.25Ga and
Mn1.9Ni1.1Ga, respectively. Even after annealing at 773 K, the residual stress
stabilised martensite phase does not fully revert to the equilibrium cubic
austenite phase as the magneto-structural transition is only partially restored
with reduced value of 'delta M'. Our results have very significant bearing on
application of such alloys as inverse magnetocaloric and barocaloric materials
Investigation of CoFeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment
This work reports on structural and magnetic investigations of the Heusler
compound CoFeSi. X-Ray diffraction and M\"o\ss bauer spectrometry indicate
an ordered structure. Magnetic measurements by means of X-ray magnetic
circular dichroism and magnetometry revealed that this compound is, currently,
the material with the highest magnetic moment () and Curie-temperature
(1100K) in the classes of Heusler compounds as well as half-metallic
ferromagnets
Magnetic and electric properties of double-perovskites and estimation of their Curie temperatures by ab initio calculations
First principles electronic structure calculations have been carried out on
ordered double perovskites Sr_2B'B"O_6 (for B' = Cr or Fe and B" 4d and 5d
transition metal elements) with increasing number of valence electrons at the
B-sites, and on Ba_2MnReO_6 as well as Ba_2FeMoO_6. The Curie temperatures are
estimated ab initio from the electronic structures obtained with the local
spin-density functional approximation, full-potential generalized gradient
approximation and/or the LDA+U method (U - Hubbard parameter). Frozen
spin-spirals are used to model the excited states needed to evaluate the
spherical approximation for the Curie temperatures. In cases, where the induced
moments on the oxygen was found to be large, the determination of the Curie
temperature is improved by additional exchange functions between the oxygen
atoms and between oxygen and B' and B" atoms.
A pronounced systematics can be found among the experimental and/or
calculated Curie temperatures and the total valence electrons of the transition
metal elements.Comment: 8 pages, 11 figures. Submitted to the Physical Review
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