271 research outputs found
Do Girls and Boys Perceive Themselves as Equally Engaged in School? The Results of an International Study from 12 Countries
This study examined gender differences in student engagement and academic
performance in school. Participants included 3420 students (7th, 8th, and 9th
graders) from Austria, Canada, China, Cyprus, Estonia, Greece, Malta, Portugal,
Romania, South Korea, the United Kingdom, and the United States. The results
indicated that, compared to boys, girls reported higher levels of engagement in
school andwere rated higher by their teachers in academic performance. Student
engagement accounted for gender differences in academic performance, but
gender did not moderate the associations among student engagement, academic
performance, or contextual supports. Analysis of multiple-group structural
equation modeling revealed that perceptions of teacher support and parent
support, but not peer support, were related indirectly to academic performance
through student engagement. This partial mediation model was invariant across
gender. The findings from this study enhance the understanding about the
contextual and personal factors associated with girls' and boys' academic
performance around the world
Temperatures of Exploding Nuclei
Breakup temperatures in central collisions of 197Au + 197Au at bombarding
energies E/A = 50 to 200 MeV were determined with two methods. Isotope
temperatures, deduced from double ratios of hydrogen, helium, and lithium
isotopic yields, increase monotonically with bombarding energy from 5 MeV to 12
MeV, in qualitative agreement with a scenario of chemical freeze-out after
adiabatic expansion. Excited-state temperatures, derived from yield ratios of
states in 4He, 5Li, 6Li, and 8Be, are about 5 MeV, independent of the
projectile energy, and seem to reflect the internal temperature of fragments at
their final separation from the system.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 10 pages, RevTeX with 4 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Crystalline structures and crystallization behaviors of poly(L-lactide) in poly(L-lactide)/graphene nanosheet composites
GNS existence in PLLA favors α′ crystal formation more than α crystal formation resulting in a shift of α′–α crystal formation transition toward high Tcs.</p
Breakup Density in Spectator Fragmentation
Proton-proton correlations and correlations of protons, deuterons and tritons
with alpha particles from spectator decays following 197Au + 197Au collisions
at 1000 MeV per nucleon have been measured with two highly efficient detector
hodoscopes. The constructed correlation functions, interpreted within the
approximation of a simultaneous volume decay, indicate a moderate expansion and
low breakup densities, similar to assumptions made in statistical
multifragmentation models.
PACS numbers: 25.70.Pq, 21.65.+f, 25.70.Mn, 25.75.GzComment: 11 pages, LaTeX with 3 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Time Scales in Spectator Fragmentation
Proton-proton correlations and correlations of p-alpha, d-alpha, and t-alpha
from spectator decays following Au + Au collisions at 1000 AMeV have been
measured with an highly efficient detector hodoscope. The constructed
correlation functions indicate a moderate expansion and low breakup densities
similar to assumptions made in statistical multifragmentation models. In
agreement with a volume breakup rather short time scales were deduced employing
directional cuts in proton-proton correlations.
PACS numbers: 25.70.Pq, 21.65.+f, 25.70.MnComment: 8 pages, with 5 included figures; To appear in the proceedings of the
CRIS 2000 conference; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Thermal and Chemical Freeze-out in Spectator Fragmentation
Isotope temperatures from double ratios of hydrogen, helium, lithium,
beryllium, and carbon isotopic yields, and excited-state temperatures from
yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were
determined for spectator fragmentation, following collisions of 197Au with
targets ranging from C to Au at incident energies of 600 and 1000 MeV per
nucleon. A deviation of the isotopic from the excited-state temperatures is
observed which coincides with the transition from residue formation to
multi-fragment production, suggesting a chemical freeze-out prior to thermal
freeze-out in bulk disintegrations.Comment: 14 pages, 10 figures, submitted to Phys. Rev. C, small changes as
suggested by the editors and referee
Breakup Temperature of Target Spectators in Au + Au Collisions at E/A = 1000 MeV
Breakup temperatures were deduced from double ratios of isotope yields for
target spectators produced in the reaction Au + Au at 1000 MeV per nucleon.
Pairs of He and Li isotopes and pairs of He and H
isotopes (p, d and d, t) yield consistent temperatures after feeding
corrections, based on the quantum statistical model, are applied. The
temperatures rise with decreasing impact parameter from 4 MeV for peripheral to
about 10 MeV for the most central collisions.
The good agreement with the breakup temperatures measured previously for
projectile spectators at an incident energy of 600 MeV per nucleon confirms the
observed universality of the spectator decay at relativistic bombarding
energies. The measured temperatures also agree with the breakup temperatures
predicted by the statistical multifragmentation model. For these calculations a
relation between the initial excitation energy and mass was derived which gives
good simultaneous agreement for the fragment charge correlations.
The energy spectra of light charged particles, measured at =
150, exhibit Maxwellian shapes with inverse slope parameters much
higher than the breakup temperatures. The statistical multifragmentation model,
because Coulomb repulsion and sequential decay processes are included, yields
light-particle spectra with inverse slope parameters higher than the breakup
temperatures but considerably below the measured values. The systematic
behavior of the differences suggests that they are caused by
light-charged-particle emission prior to the final breakup stage.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 29 pages, TeX with 11 included figures; Revised version accepted for
publication in Z. Phys. A Two additional figure
Layer-dependent optically-induced spin polarization in InSe
Optical control of spin in semiconductors has been pioneered using
nanostructures of III-V and II-VI semiconductors, but the emergence of
two-dimensional van der Waals materials offers an alternative low-dimensional
platform for spintronic phenomena. Indium selenide (InSe), a group-III
monochalcogenide van der Waals material, has shown promise for opto-electronics
due to its high electron mobility, tunable direct bandgap, and quantum
transport. There are predictions of spin-dependent optical selection rules
suggesting potential for all-optical excitation and control of spin in a
two-dimensional layered material. Despite these predictions, layer-dependent
optical spin phenomena in InSe have yet to be explored. Here, we present
measurements of layer-dependent optical spin dynamics in few-layer and bulk
InSe. Polarized photoluminescence reveals layer-dependent optical orientation
of spin, thereby demonstrating the optical selection rules in few-layer InSe.
Spin dynamics are also studied in many-layer InSe using time-resolved Kerr
rotation spectroscopy. By applying out-of-plane and in-plane static magnetic
fields for polarized emission measurements and Kerr measurements, respectively,
the -factor for InSe was extracted. Further investigations are done by
calculating precession values using a model,
which is supported by \textit{ab-initio} density functional theory. Comparison
of predicted precession rates with experimental measurements highlights the
importance of excitonic effects in InSe for understanding spin dynamics.
Optical orientation of spin is an important prerequisite for opto-spintronic
phenomena and devices, and these first demonstrations of layer-dependent
optical excitation of spins in InSe lay the foundation for combining
layer-dependent spin properties with advantageous electronic properties found
in this material.Comment: 11 pages, 6 figures, supplemental materia
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