Metal-Insulator Transitions in Degenerate Hubbard Models and Ax_xC60_{60}

Mott-Hubbard metal-insulator transitions in $N$-fold degenerate Hubbard models are studied within the Gutzwiller approximation. For any rational filling with $x$ (integer) electrons per site it is found that metal-insulator transition occurs at a critical correlation energy $U_c(N,x)=U_c(N,2N-x)=\gamma(N,x)|\bar{\epsilon}(N,x)|$, where $\bar{\epsilon}$ is the band energy per particle for the uncorrelated Fermi-liquid state and $\gamma(N,x)$ is a geometric factor which increases linearly with $x$. We propose that the alkali metal doped fullerides $A_xC_{60}$ can be described by a 3-fold degenerate Hubbard model. Using the current estimate of band width and correlation energy this implies that most of ${\rm A_xC_{60}}$, at integer $x$, are Mott-Hubbard insulators and ${\rm A_3C_{60}}$ is a strongly correlated metal.Comment: 10 pages, Revte

Celiac disease : from basic insight to therapy development

Celiac disease (CD) is a common disorder of the small intestine caused by intolerance to gluten, proteins found in wheat and related cereals. In this study two major questions were addressed: i) which specific properties of gluten contribute to its disease-inducing characteristics ii) how can gluten toxicity be avoided. We found that CD-related molecule HLA-DQ2 has several features that explain why it can specifically interact with a large array of distinct gluten peptides. We also observed that some of the gluten peptides are being recognized by gluten-specific T cells in quite an unusual way, requiring the presence of a proline at position p-1. Another interesting observation was that the disease-inducing properties of rye and barley could be explained by the cross-reaction of gluten-specific T cells with the homologous peptides from these cereals. Although genetic studies indicated that the gene for prolyl endopeptidase could be involved in the pathogenesis of CD we showed that most likely this gene does not play a role in the disease development. Finally, we demonstrated that prolyl endoprotease from Aspergillus niger could be an effective measure to detoxify gluten in vitro

The Role of Qualitative Data in the Management of Enterprises

The article refers to the issue of the use of qualitative data in management processes. The article was compiled on the basis of the results of surveys on the principles of using qualitative data for management purposes. The research results indicate that in the surveyed enterprises the most frequently used is qualitative data referring to the quality of services and products as well as training materials. This is confirmed by the results referring to the areas of activity of enterprises in which qualitative data is used. The results showed that the share of qualitative data in the decision-making processes is relatively low, especially at the strategic level. Therefore, it seems logical to request for the need to undertake work on tools for ordering qualitative data within individual enterprises

Gaps and excitations in fullerides with partially filled bands : NMR study of Na2C60 and K4C60

We present an NMR study of Na2C60 and K4C60, two compounds that are related by electron-hole symmetry in the C60 triply degenerate conduction band. In both systems, it is known that NMR spin-lattice relaxation rate (1/T1) measurements detect a gap in the electronic structure, most likely related to singlet-triplet excitations of the Jahn-Teller distorted (JTD) C60^{2-} or C60^{4-}. However, the extended temperature range of the measurements presented here (10 K to 700 K) allows to reveal deviations with respect to this general trend, both at high and low temperatures. Above room temperature, 1/T1 deviates from the activated law that one would expect from the presence of the gap and saturates. In the same temperature range, a lowering of symmetry is detected in Na2C60 by the appearance of quadrupole effects on the 23Na spectra. In K4C60, modifications of the 13C spectra lineshapes also indicate a structural modification. We discuss this high temperature deviation in terms of a coupling between JTD and local symmetry. At low temperatures, 1/T$_1$T tends to a constant value for Na2C60, both for 13C and 23Na NMR. This indicates a residual metallic character, which emphasizes the proximity of metallic and insulting behaviors in alkali fullerides.Comment: 12 pages, 13 figure

Proactive academic tutoring? Uniting the pastoral and the professional: a critical approach to the PAT role in the contemporary HEI landscape

This qualitative ethnographic study investigates the effectiveness of the Personal Academic Tutor (PAT) role in supporting student retention and progression from level 4 to level 5 at a widening participation university in the East Midlands, England. The research, framed within an interpretivist paradigm, gathers perspectives through semi-structured interviews with key stakeholders (n = 7), focus groups with level 4 PATs (n = 14), and a survey of level 4 home students (n = 57). The study recognizes the varied implementation of the PAT role across Higher Education Institutions (HEIs), influenced by factors such as university policy, workload, and student demographics. It builds on Earwalker's (1992) three models of personal tutoring (pastoral, professional, and curricular) highlighting the evolution towards a hybrid model combining these approaches. The paper argues for the critical importance of institutional-level implementation and measurement of PAT, using key sector metrics like retention, progression, continuation, and student satisfaction. It posits that the PAT role should enhance the overall student experience and be integral to the academic role within contemporary HEIs. The findings suggest that a multi-faceted approach to PAT, incorporating pastoral and academic support, is vital for improving student outcomes

Structure and properties of a novel fulleride Sm6C60

A novel fulleride Sm6C60 has been synthesized using high temperature solid state reaction. The Rietveld refinement on high resolution synchrotron X-ray powder diffraction data shows that Sm6C60 is isostructural with body-centered cubic A6C60 (A=K, Ba). Raman spectrum of Sm6C60 is similar to that of Ba6C60, and the frequencies of two Ag modes in Sm6C60 are nearly the same as that of Ba6C60, suggesting that Sm is divalent and hybridization between C60 molecules and the Sm atom could exist in Sm6C60. Resistivity measurement shows a weak T-linear behavior above 180 K, the transport at low temperature is mainly dominated by granular-metal theory.Comment: 9 pages, 3 figures, submitted to Phys. Rev. B (March 12, 1999

Evidence for phase formation in potassium intercalated 1,2;8,9-dibenzopentacene

We have prepared potassium intercalated 1,2;8,9-dibenzopentacene films under vacuum conditions. The evolution of the electronic excitation spectra upon potassium addition as measured using electron energy-loss spectroscopy clearly indicate the formation of particular doped phases with compositions K$_x$dibenzopentacene ($x$ = 1,2,3). Moreover, the stability of these phases as a function of temperature has been explored. Finally, the electronic excitation spectra also give insight into the electronic ground state of the potassium doped 1,2;8,9-dibenzopentacene films.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with arXiv:1201.200