23,567 research outputs found
Including nonlocality in exchange-correlation kernel from time-dependent current density functional theory: Application to the stopping power of electron liquids
We develop a scheme for building the scalar exchange-correlation (xc) kernel
of time-dependent density functional theory (TDDFT) from the tensorial kernel
of time-dependent {\em current} density functional theory (TDCDFT) and the
Kohn-Sham current density response function. Resorting to the local
approximation to the kernel of TDCDFT results in a nonlocal approximation to
the kernel of TDDFT, which is free of the contradictions that plague the
standard local density approximation (LDA) to TDDFT. As an application of this
general scheme, we calculate the dynamical xc contribution to the stopping
power of electron liquids for slow ions to find that our results are in
considerably better agreement with experiment than those obtained using TDDFT
in the conventional LDA.Comment: 6 pages, 3 figures, accepted to Phys. Rev.
To let students self-select or not: that is the question for teachers of culturally diverse groups
When students can self-select their group members, a common assumption is that students prefer to select friends from similar cultural backgrounds. However, when teachers randomise students in groups from different cultural backgrounds, students are âforcedâ to work together. The prime goal of this study is to understand the impact of two group selection methods on how students from diverse cultural backgrounds build learning and work-relations, using an innovative quantitative method of Social Network Analysis in a pre-post test manner. In a quasi-experimental study of 2 ËŁ 69 students, in one condition the students were randomly allocated to groups by staff and in the other students were allowed to self-select their group members. The results indicate that students in the self-selected condition primarily selected their friends from a similar cultural background. The learning networks after 14 weeks were primarily predicted by the group allocation and initial friendships. However, students in the random condition developed equally strong internal group relations but more âknowledge spilloversâ outside their group, indicating that the random condition led to positive effects beyond the group
Dynamical Chiral Symmetry Breaking in Unquenched
We investigate dynamical chiral symmetry breaking in unquenched
using the coupled set of Dyson--Schwinger equations for the fermion and photon
propagators. For the fermion-photon interaction we employ an ansatz which
satisfies its Ward--Green--Takahashi identity. We present self-consistent
analytical solutions in the infrared as well as numerical results for all
momenta. In Landau gauge, we find a phase transition at a critical number of
flavours of . In the chirally symmetric phase the
infrared behaviour of the propagators is described by power laws with
interrelated exponents. For and we find small values for the
chiral condensate in accordance with bounds from recent lattice calculations.
We investigate the Dyson--Schwinger equations in other linear covariant gauges
as well. A comparison of their solutions to the accordingly transformed Landau
gauge solutions shows that the quenched solutions are approximately gauge
covariant, but reveals a significant amount of violation of gauge covariance
for the unquenched solutions.Comment: 33 pages, 8 figures, reference added, version to be published in
Phys. Rev.
Dietary Strategies to Optimize Wound Healing after Periodontal and Dental Implant Surgery: An Evidence-Based Review
Methods to optimize healing through dietary strategies present an attractive option for patients, such that healing
from delicate oral surgeries occurs as optimally as possible with minimal patient-meditated complications through improper
food choices. This review discusses findings from studies that have investigated the role of diet, either whole foods
or individual dietary components, on periodontal health and their potential role in wound healing after periodontal surgery.
To date, research in this area has largely focused on foods or individual dietary components that may attenuate inflammation
or oxidant stress, or foster de novo bone formation. These studies suggest that a wide variety of dietary components,
including macronutrients and micronutrients, are integral for optimal periodontal health and have the potential to
accelerate oral wound healing after periodontal procedures. Moreover, this review provides guidance regarding dietary
considerations that may help a patient achieve the best possible outcome after a periodontal procedure
Time-Dependent Density-Functional Theory for the Stopping Power of an Interacting Electron Gas for Slow Ions
Based on the time-dependent density-functional theory, we have derived a
rigorous formula for the stopping power of an {\it interacting} electron gas
for ions in the limit of low projectile velocities. If dynamical correlation
between electrons is not taken into account, this formula recovers the
corresponding stopping power of {\it noninteracting} electrons in an effective
Kohn-Sham potential. The correlation effect, specifically the excitonic one in
electron-hole pair excitations, however, is found to considerably enhance the
stopping power for intermediately charged ions, bringing our theory into good
agreement with experiment.Comment: 4 pages, 1 figure, Accepted to Phys. Rev. B (Rapid Communication
Measures Matter: Scales for Adaptation, Cultural Distance, and Acculturation Orientation Revisited
Building upon existing measures, four new brief acculturation scales are presented, measuring sociocultural adaptation, psychological adaptation, perceived cultural distance, and acculturation orientation. Following good scale reliability in initial samples, the English scales were translated into nine different languages (Chinese, French, German, Italian, Japanese, Portuguese, Spanish, Thai, and Turkish). The translated scales were administered to a large sample of sojourners (N = 1,929), demonstrating good reliability and adequate structural equivalence across languages. In line with existing theory, sociocultural adaptation and psychological adaptation were positively correlated, and showed a negative association with perceived cultural distance. General measures of well-being were correlated with adaptation and distance, with better adaptation relating to higher well-being, and more distance relating to lower well-being. Acculturation orientation toward the home and host culture were measured separately and a weak negative correlation was found between the two, supporting their independence. Arguing against dichotomization, these subscales were analyzed as continuous variables. Regression analysis showed sojourners to be better adapted, if they were oriented more toward the host culture and less toward the home culture. These new scales are proposed as alternatives to existing measures
Molecular line profiles as diagnostics of protostellar collapse: modelling the `blue asymmetry' in inside-out infall
The evolution of star-forming core analogues undergoing inside-out collapse
is studied with a multi-point chemodynamical model which self-consistently
computes the abundance distribution of chemical species in the core. For
several collapse periods the output chemistry of infall tracer species such as
HCO+, CS, and N2H+, is then coupled to an accelerated Lambda-iteration
radiative transfer code, which predicts the emerging molecular line profiles
using two different input gas/dust temperature distributions. We investigate
the sensitivity of the predicted spectral line profiles and line asymmetry
ratios to the core temperature distribution, the time-dependent model
chemistry, as well as to ad hoc abundance distributions. The line asymmetry is
found to be strongly dependent on the adopted chemical abundance distribution.
In general, models with a warm central region show higher values of blue
asymmetry in optically thick HCO+ and CS lines than models with a starless core
temperature profile. We find that in the formal context of Shu-type inside-out
infall, and in the absence of rotation or outflows, the relative blue asymmetry
of certain HCO+ and CS transitions is a function of time and, subject to the
foregoing caveats, can act as a collapse chronometer. The sensitivity of
simulated HCO+ line profiles to linear radial variations, subsonic or
supersonic, of the internal turbulence field is investigated in the separate
case of static cores.Comment: Accepted to MNRAS; 20 pages, 13 fig
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