5,028 research outputs found
Scaling behavior of the momentum distribution of a quantum Coulomb system in a confining potential
We calculate the single-particle momentum distribution of a quantum
many-particle system in the presence of the Coulomb interaction and a confining
potential. The region of intermediate momenta, where the confining potential
dominates, marks a crossover from a Gaussian distribution valid at low momenta
to a power-law behavior valid at high momenta. We show that for all momenta the
momentum distribution can be parametrized by a -Gaussian distribution whose
parameters are specified by the confining potential. Furthermore, we find that
the functional form of the probability of transitions between the confined
ground state and the excited state is invariant under scaling of the
ratio , where is the transferred momentum and is the
corresponding excitation energy. Using the scaling variable the
maxima of the transition probabilities can also be expressed in terms of a
-Gaussian.Comment: 6 pages, 5 figure
Lattice dynamics of palladium in the presence of electronic correlations
We compute the phonon dispersion, density of states, and the Gr\"uneisen
parameters of bulk palladium in the combined density functional theory (DFT)
and dynamical mean-field theory (DMFT). We find good agreement with
experimental results for ground state properties (equilibrium lattice parameter
and bulk modulus) and the experimentally measured phonon spectra. We
demonstrate that at temperatures the phonon frequency in the
vicinity of the Kohn anomaly, , strongly decreases.
This is in contrast to DFT where this frequency remains essentially constant in
the whole temperature range. Apparently correlation effects reduce the
restoring force of the ionic displacements at low temperatures, leading to a
mode softening.Comment: minor revision
Electronic Correlations in Vanadium Revealed by Electron-Positron Annihilation Measurements
The electronic structure of vanadium measured by Angular Correlation of
electron-positron Annihilation Radiation (ACAR) is compared with the
predictions of the combined Density Functional and Dynamical Mean-Field Theory
(DMFT). Reconstructing the momentum density from five 2D projections we were
able to determine the full Fermi surface and found excellent agreement with the
DMFT calculations. In particular, we show that the local, dynamic self-energy
corrections contribute to the anisotropy of the momentum density and need to be
included to explain the experimental results
On the superconducting nature of the Bi-II phase of elemental Bismuth
The superconductivity in the Bi-II phase of elemental Bismuth (transition
temperature K at pressure GPa) was studied
experimentally by means of the muon-spin rotation as well as theoretically by
using the Eliashberg theory in combination with Density Functional Theory
calculations. Experiments reveal that Bi-II is a type-I superconductor with a
zero temperature value of the thermodynamic critical field ~mT. The Eliashberg theory approach provides a good agreement
with the experimental and the temperature evolution of .
The estimated value for the retardation (coupling) parameter ( is the logarithmically
averaged phonon frequency) suggests that Bi-II is an intermediately-coupled
superconductor.Comment: 6 pages, 2 figure
Transmission through correlated CuCoCu heterostructures
The effects of local electronic interactions and finite temperatures upon the
transmission across the CuCoCu metallic heterostructure are studied in
a combined density functional and dynamical mean field theory. It is shown
that, as the electronic correlations are taken into account via a local but
dynamic self-energy, the total transmission at the Fermi level gets reduced
(predominantly in the minority spin channel), whereby the spin polarization of
the transmission increases. The latter is due to a more significant
-electrons contribution, as compared to the non-correlated case in which the
transport is dominated by and electrons.Comment: 29 pages, 7 figures, submited to PR
Thermo-mechanic-electrical coupling in phospholipid monolayers near the critical point
Lipid monolayers have been shown to represent a powerful tool in studying
mechanical and thermodynamic properties of lipid membranes as well as their
interaction with proteins. Using Einstein's theory of fluctuations we here
demonstrate, that an experimentally derived linear relationship both between
transition entropy S and area A as well as between transition entropy and
charge q implies a linear relationships between compressibility \kappa_T, heat
capacity c_\pi, thermal expansion coefficient \alpha_T and electric capacity
CT. We demonstrate that these couplings have strong predictive power as they
allow calculating electrical and thermal properties from mechanical
measurements. The precision of the prediction increases as the critical point
TC is approached
Patient reported upper gastro-intestinal symptoms associated with fractionated image-guided conformal radiotherapy for metastatic spinal cord compression
Background and purpose
Palliative radiotherapy is given to sustain or improve quality of life for patients with advanced cancer. Radiotherapy may however result in symptomatic side effects, which may affect the patient negatively. This prospective longitudinal study of 30 patients aimed at investigating the incidence and severity of early toxicity, particularly focusing on dysphagia, esophagitis and mucositis, following fractionated radiotherapy for cervical and thoracic metastatic spinal cord compression (MSCC), as well as determining the relationship between esophageal dose and early upper gastro-intestinal symptoms.
Materials and methods
Thirty patients receiving radiotherapy of 3Gyx10 for MSCC were included in the study. Patients were assessed for a total of 7 weeks from onset of radiotherapy using the Edmonton Symptom Assessment System (ESAS) questionnaire. Upper gastro-intestinal symptoms and severity were assessed from the tenth and eleventh question section of the ESAS questionnaire of “other problems” and how much this affected them. The relationships between the mean and maximum esophageal doses and incidence of dysphagia, esophagitis or mucositis were estimated and dose response curves determined.
Results
Eleven patients reported esophageal symptoms (average duration eleven days, range 1–18 days). Incidence of esophageal toxicity in patients treated at Th8 or above was 79 percent, while no patients treated below Th8 reported any symptoms (p < 0.001). Furthermore, 2 out of 3 patients irradiated at the cervical region reported substantial changes in taste sensation.
Risk of symptoms correlated with both mean and maximum esophageal dose and may be a useful tool in planning radiotherapy for MSCC, potentially reducing early upper gastro-intestinal toxicity
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