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 $(xc)$ energy functional of Density Functional Theory is shown to arise naturally in the subband spectra of semiconductor quantum wells. Using an \emph{ab-initio} $xc$ functional, including exchange exactly and correlation in an exact partial way, a discontinuity appears in the $xc$ 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 139^{139}La NQR in La2−x_{2-x}Srx_xCuO4_4 around the critical Sr content x=0.02

Anelastic relaxation and $^{139}$La NQR relaxation measurements in La$_{2-x}$Sr$_x$CuO$_4$ 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 La$_{2-x}$Sr$_x$CuO$_4$ 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 $^{139}$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 La$_{1.98}$Sr$_{0.02}$CuO$_4$ 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 $V_{x}(z)$ 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 $V_{x}(z\to \infty)\to - e^{2}/z$; 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 individual’s 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 ‘other’ 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.