893 research outputs found
Collectivity in the optical response of small metal clusters
The question whether the linear absorption spectra of metal clusters can be
interpreted as density oscillations (collective ``plasmons'') or can only be
understood as transitions between distinct molecular states is still a matter
of debate for clusters with only a few electrons. We calculate the
photoabsorption spectra of Na2 and Na5+ comparing two different methods:
quantum fluid-dynamics and time-dependent density functional theory. The
changes in the electronic structure associated with particular excitations are
visualized in ``snapshots'' via transition densities. Our analysis shows that
even for the smallest clusters, the observed excitations can be interpreted as
intuitively understandable density oscillations. For Na5+, the importance of
self-interaction corrections to the adiabatic local density approximation is
demonstrated.Comment: 6 pages, 3 figures. To appear in special issue of Applied Physics B,
"Optical properties of Nanoparticles
Static Electric Dipole Polarizabilities of Na Clusters
The static electric dipole polarizability of clusters with
even N has been calculated in a collective, axially averaged and a
three-dimensional, finite-field approach for , including the
ionic structure of the clusters. The validity of a collective model for the
static response of small systems is demonstrated. Our density functional
calculations verify the trends and fine structure seen in a recent experiment.
A pseudopotential that reproduces the experimental bulk bond length and atomic
energy levels leads to a substantial increase in the calculated
polarizabilities, in better agreement with experiment. We relate remaining
differences in the magnitude of the theoretical and experimental
polarizabilities to the finite temperature present in the experiments.Comment: 7 pages, 3 figures, accepted for publication in the European Physical
Journal
Formation, compression and surface melting of colloidal clusters by active particles
We demonstrate with experiments and numerical simulations that the structure and dynamics of a suspension of passive particles is strongly altered by adding a very small (<1%) number of active particles. With increasing passive particle density, we observe first the formation of dynamic clusters comprised of passive particles being surrounded by active particles, then the merging and compression of these clusters, and eventually the local melting of crystalline regions by enclosed active particles. © The Royal Society of Chemistry 2015
Dynamics of conversion of supercurrents into normal currents, and vice versa
The generation and destruction of the supercurrent in a superconductor (S)
between two resistive normal (N) current leads connected to a current source is
computed from the source equation for the supercurrent density. This equation
relates the gradient of the pair potential's phase to electron and hole
wavepackets that create and destroy Cooper pairs in the N/S interfaces. Total
Andreev reflection and supercurrent transmission of electrons and holes are
coupled together by the phase rigidity of the non-bosonic Cooper-pair
condensate. The calculations are illustrated by snapshots from a computer film.Comment: 8 pages, 1 figure, accepted by Phys. Rev.
Active Brownian Motion Tunable by Light
Active Brownian particles are capable of taking up energy from their
environment and converting it into directed motion; examples range from
chemotactic cells and bacteria to artificial micro-swimmers. We have recently
demonstrated that Janus particles, i.e. gold-capped colloidal spheres,
suspended in a critical binary liquid mixture perform active Brownian motion
when illuminated by light. In this article, we investigate in some more details
their swimming mechanism leading to active Brownian motion. We show that the
illumination-borne heating induces a local asymmetric demixing of the binary
mixture generating a spatial chemical concentration gradient, which is
responsible for the particle's self-diffusiophoretic motion. We study this
effect as a function of the functionalization of the gold cap, the particle
size and the illumination intensity: the functionalization determines what
component of the binary mixture is preferentially adsorbed at the cap and the
swimming direction (towards or away from the cap); the particle size determines
the rotational diffusion and, therefore, the random reorientation of the
particle; and the intensity tunes the strength of the heating and, therefore,
of the motion. Finally, we harness this dependence of the swimming strength on
the illumination intensity to investigate the behaviour of a micro-swimmer in a
spatial light gradient, where its swimming properties are space-dependent
Time-dependent quantum transport with superconducting leads: a discrete basis Kohn-Sham formulation and propagation scheme
In this work we put forward an exact one-particle framework to study
nano-scale Josephson junctions out of equilibrium and propose a propagation
scheme to calculate the time-dependent current in response to an external
applied bias. Using a discrete basis set and Peierls phases for the
electromagnetic field we prove that the current and pairing densities in a
superconducting system of interacting electrons can be reproduced in a
non-interacting Kohn-Sham (KS) system under the influence of different Peierls
phases {\em and} of a pairing field. An extended Keldysh formalism for the
non-equilibrium Nambu-Green's function (NEGF) is then introduced to calculate
the short- and long-time response of the KS system. The equivalence between the
NEGF approach and a combination of the static and time-dependent
Bogoliubov-deGennes (BdG) equations is shown. For systems consisting of a
finite region coupled to superconducting semi-infinite leads we
numerically solve the static BdG equations with a generalized wave-guide
approach and their time-dependent version with an embedded Crank-Nicholson
scheme. To demonstrate the feasibility of the propagation scheme we study two
paradigmatic models, the single-level quantum dot and a tight-binding chain,
under dc, ac and pulse biases. We provide a time-dependent picture of single
and multiple Andreev reflections, show that Andreev bound states can be
exploited to generate a zero-bias ac current of tunable frequency, and find a
long-living resonant effect induced by microwave irradiation of appropriate
frequency.Comment: 20 pages, 9 figures, published versio
Polarizibilities as a test of localized approximations to the self-interaction correction
We present applications of the recently introduced ``Generalized SIC-Slater''
scheme which provides a simple Self-Interaction Correction approximation in the
framework of the Optimized Effective Potential. We focus on the computation of
static polarizabilities which are known to constitute stringent tests for
Density Functional Theory. We apply the new method to model H chains, but also
to more realistic systems such as C4 (organic) chains, and less symmetrical
systems such as a Na5 (metallic) cluster. Comparison is made with other SIC
schemes, especially with the standard SIC-Slater one.Comment: 17 pages, 4 figures, 49 reference
Effects of an Integrative Mind-Body-Medicine Group Program on Breast Cancer Patients During Chemotherapy: An Observational Study.
Background: Breast cancer is one of the leading cancers in women in the Western world. Cancer treatment, especially chemotherapy, is often associated with physical and psychosocial side effects.
Objective: To improve the quality of life and manage side effects, a new integrative mind-body-medicine group concept for breast cancer patients receiving chemotherapy was developed and pilot tested.
Methods: Breast cancer patients participated in a 66 hours mind-body-medicine group program tailored to the needs of cancer patients during chemotherapy. The program was integrated into standard care encompassing mindfulness training, yoga, moderate exercise, nutrition, complementary self-help strategies, cognitive restructuring, and acupuncture. Quality of life (EORTC QLQ-C30), depression and anxiety (HADS), stress (PSS-10), and fatigue (BFI) were assessed before and after the program, as well as satisfaction and safety. Analyses were carried out on exploratory basis with paired samples t-tests.
Results: Fifty-seven female patients, aged 51.3±10.5 years, with breast cancer diagnoses were enrolled. After completing the program, global EORTC quality of life was improved (D=9.5; 95%-CI=[2.9|16.1]; p=.005), although the EORTC-symptom scales assessing fatigue (D=9.9; 95%-CI=[1|18.8]; p=.030), nausea (D=7.1; 95%- CI=[0.6|13.6]; p=.031), and dyspnea (D=12.5; 95%-CI=[2.9|22.1]; p=.011) were found to be increased. Stress (D=-3.5; 95%-CI=[-5|-2.1]; p=.000), anxiety (D=-3.8; 95%-CI=[-4.9|-2.7]; p=.000) and depression (D=-3.9; 95%-CI=[-4.9|-2.8]; p=.000) were also found to be significantly reduced. Regarding the severity of (D=0.2; 95%- CI=[-0.8|0.5]; p=.644) and the impairment due to fatigue (D=0.1; 95%-CI=[-0.8|0.6]; p=.696), no significant worsening was observed. Patients were satisfied with the program. No serious adverse events were reported.
Conclusion: Breast cancer patients benefit from an integrative mind-body-medicine group program during chemotherapy regarding the quality of life and psychological symptoms. Randomized controlled trials are warranted
Ionic and electronic structure of sodium clusters up to N=59
We determined the ionic and electronic structure of sodium clusters with even
electron numbers and 2 to 59 atoms in axially averaged and three-dimensional
density functional calculations. A local, phenomenological pseudopotential that
reproduces important bulk and atomic properties and facilitates structure
calculations has been developed. Photoabsorption spectra have been calculated
for , , and to
. The consistent inclusion of ionic structure considerably
improves agreement with experiment. An icosahedral growth pattern is observed
for to . This finding is supported by
photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality
can be requested from the author
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