1,283 research outputs found
Signatures of Discontinuity in the Exchange-Correlation Energy Functional Derived from the Subband Electronic Structure of Semiconductor Quantum Wells
The discontinuous character of the exact exchange-correlation energy
functional of Density Functional Theory is shown to arise naturally in the
subband spectra of semiconductor quantum wells. Using an \emph{ab-initio}
functional, including exchange exactly and correlation in an exact partial way,
a discontinuity appears in the potential, each time a subband becomes
slightly occupied. Exchange and correlation give opposite contributions to the
discontinuity, with correlation overcoming exchange. The jump in the
intersubband energy is in excellent agreement with experimental data.Comment: 5 pages, 3 figure
Anelastic relaxation and La NQR in LaSrCuO around the critical Sr content x=0.02
Anelastic relaxation and La NQR relaxation measurements in
LaSrCuO for Sr content x around 2 and 3 percent, are presented
and discussed in terms of spin and lattice excitations and ordering processes.
It is discussed how the phase diagram of LaSrCuO at the
boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02)
could be more complicate than previous thought, with a transition to a
quasi-long range ordered state at T = 150 K, as indicated by recent neutron
scattering data. On the other hand, the La NQR spectra are compatible
with a transition to a conventional AF phase around T = 50 K, in agreement with
the phase diagram commonly accepted in the literature. In this case the
relaxation data, with a peak of magnetic origin in the relaxation rate around
150 K at 12 MHz and the anelastic counterparts around 80 K in the kHz range,
yield the first evidence in LaSrCuO of freezing involving
simultaneously lattice and spin excitations. This excitation could correspond
to the motion of charged stripes.Comment: 10 pages, 8 figure
Kohn-Sham Exchange Potential for a Metallic Surface
The behavior of the surface barrier that forms at the metal-vacuum interface
is important for several fields of surface science. Within the Density
Functional Theory framework, this surface barrier has two non-trivial
components: exchange and correlation. Exact results are provided for the
exchange component, for a jellium metal-vacuum interface, in a slab geometry.
The Kohn-Sham exact-exchange potential has been generated by using
the Optimized Effective Potential method, through an accurate numerical
solution, imposing the correct boundary condition. It has been proved
analytically, and confirmed numerically, that ; this conclusion is not affected by the inclusion of correlation
effects. Also, the exact-exchange potential develops a shoulder-like structure
close to the interface, on the vacuum side. The issue of the classical image
potential is discussed.Comment: Phys. Rev. Lett. (to appear
Novel properties of the Kohn-Sham exchange potential for open systems: application to the two-dimensional electron gas
The properties of the Kohn-Sham (KS) exchange potential for open systems in
thermodynamical equilibrium, where the number of particles is non-conserved,
are analyzed with the Optimized Effective Potential (OEP) method of Density
Functional Theory (DFT) at zero temperature. The quasi two-dimensional electron
gas (2DEG) is used as an illustrative example. The main findings are that the
KS exchange potential builds a significant barrier-like structure under slight
population of the second subband, and that both the asymptotic value of the KS
exchange potential and the inter-subband energy jump discontinuously at the
one-subband (1S) -> two-subband (2S) transition. The results obtained in this
system offer new insights on open problems of semiconductors, such as the
band-gap underestimation and the band-gap renormalization by photo-excited
carriers.Comment: 7 pages, 3 figures, uses epl.cls(included), accepted for publication
in Europhysics Letter
Ursodeoxycholic acid improves bilirubin but not albumin in primary biliary cirrhosis: further evidence for nonefficacy.
BACKGROUND/AIM: In randomised controlled trials (RCTs) of ursodeoxycholic acid (UDCA), although serum bilirubin is frequently reduced, its effect on disease progression and mortality is unclear. As serum albumin is an established independent prognostic marker, one might expect less deterioration of serum albumin values in a UDCA-treated group. We therefore modelled the typical evolution of serum bilirubin and albumin levels over time in UDCA-untreated patients and compared it with the observed levels in UDCA RCTs. METHODS: Multilevel modelling was used to relate the evolution of serum albumin to serum bilirubin and time since patient referral. For each considered RCT, the derived model was used to predict the relationship between final mean serum albumin and bilirubin concentration, adjusted for mean serum albumin at referral and followup duration. RESULTS: Five RCTs were eligible in terms of available data, of which two had long followup. In all trials, serum albumin did not significantly differ between UDCA- and placebo-treated patients, despite the UDCA effect on serum bilirubin. Therefore, there is no evidence over time for changes or maintenance of albumin levels for UDCA-treated patients above the levels predicted for placebo-treated patients. CONCLUSIONS: Our findings suggest that UDCA does not alter serum albumin in a way that is consistent with its effect on serum bilirubin. Therefore, reductions in serum bilirubin of UDCA-treated PBC do not parallel another validated and independent prognostic marker, further questioning the validity of serum bilirubin reduction with UDCA as a surrogate therapeutic marker
Raising Self-Awareness and Developing Intercultural Competence by Activating Personal Filters
All individuals are fitted with filters which affect their experience of the world, and which depend on various factors, including personal traits and cultural influences. Language is a reflection of the self, and of the culture and people it belongs to, thus when learning a new language each individual is approaching a different identity and culture with personal filters which act on the learning process. Learning involves approaching something new and inevitably leads to some change, which may occur without conscious awareness but is affected by the individualâs attitude towards novelty and diversity.This joint project involved learners of English (Parma University) and of Italian (University of Salzburg) as L2, and aimed at indirectly testing these filters. The objectives were to verify if their filters are subtly expressed in their way of seeing themselves, their own language and culture, and the âotherâ language and culture, and also raise their awareness of them. This hopefully is a stepping stone towards discovering aspects of their personality, developing sensitivity to differences and recognizing factors to be exploited to become more efficient learners
Observation of the cluster spin-glass phase in La_{2-x}Sr_{x}CuO_{4} by anelastic spectroscopy
An increase of the acoustic absorption is found in La_{2-x}Sr_{x}CuO_{4} (x =
0.019, 0.03 and 0.06) close to the temperatures at which freezing of the spin
fluctuations in antiferromagnetic-correlated clusters is expected to occur. The
acoustic absorption is attributed to changes of the sizes of the quasi-frozen
clusters induced by the vibration stress through magnetoelastic coupling.Comment: LaTeX, 2 PostScript figures, submitted to Phys. Rev.
Reasons Why Patients Failed Vaccinations Vs Influenza and Pneumococcus. Monocentric Cross-Sectional Study
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