The group of local biholomorphisms of ℂ1 and conformal field theory in the operator formalism

Motivated by the operator formulation of conformal field theory on Riemann surfaces, we study the properties of the infinite dimensional group of local biholomorphic transformations (conformal reparametrizations) of ¹ and develop elements of its representation theory.     

Investigation of metabolic changes in irradiated rat brain tissue by means of 1H NMR in vitro relaxation study

The effect of irradiation on concentrations and relaxation behaviour of brain metabolites was studied by means of high-resolution 1H NMR in vitro. The studies were performed on rat brains irradiated with the doses of 20 Gy applied in fractions of 2 Gy. Standard procedures were used to obtain HClO4 extracts of rat brains. The 1H NMR studies of the extracts solutions in D2O were performed using a Varian Inova-300 NMR spectrometer. The integral intensities of the metabolite signals were found to change during the irradiation cycle and after it. These changes are accompanied by the variations in the T1 relaxation times. N-acetylaspartate, glycerophosphocholine, phosphocholine, choline, creatine and phosphocreatine, myoinositol and taurine were analysed as potential markers of irradiation injury.     

3D MR imaging of dental cavities-an in vitro study

A 3D spin-echo (3D SE) pulse sequence was used on a 4.7 T research MRI system to produce images of extracted human first molar tooth placed in CuSO4 water solution. The maximal resolution achieved was 35 x 63 x 300 microm3 in read and two phase directions, respectively. The high-intensity signal from water in solution together with the lack of signal from mineralized tooth tissue produce very good contrast allowing to visualize topography of outer and inner surfaces of the tooth. The 3D MR data were median filtered, binarized and then divided into separate segments corresponding to the inner tooth cavities and the hard tooth tissue. The topography of the root canals was visualized and the canals volume was calculated. The presented technique may be used for quantitative analysis of the root canal cavities shape and volume. The results of such an analysis may be applied for estimation of the quality of the impressional mapping methods in restorative dentistry or as an alternative non-impressional 3D mapping method.     

Model for describing the production of Centauro events and strangelets in heavy-ion collisions

A phenomenological model for describing the production of Centauro events in relativistic heavy-ion collisions is discussed. The model provides quantitative predictions for kinematical variables, for the baryon number, and for the masses of a Centauro fireball and of its decay products. A Centauro fireball decays predominantly into nucleons, strange hyperons, and possibly strangelets. Centauro events in Pb + Pb collisions at the LHC energy are simulated for the CASTOR detector. The signatures of these events are discussed in detail.     

Cosmological constant from quarks and torsion

We present a simple and natural way to derive the observed small, positive cosmological constant from the gravitational interaction of condensing fermions. In the Riemann‐Cartan spacetime, torsion gives rise to the axial–axial vector four‐fermion interaction term in the Dirac Lagrangian for spinor fields. We show that this nonlinear term acts like a cosmological constant if these fields have a nonzero vacuum expectation value. For quark fields in QCD, such a torsion‐induced cosmological constant is positive and its energy scale is only about 8 times larger than the observed value. Adding leptons to this picture could lower this scale to the observed value.     

Ab initio determination of atomic structure and energy of surface states of bare and hydrogen covered GaN (0001) surface — Existence of the Surface States Stark Effect (SSSE)

Density Functional Theory (DFT) calculations indicate that energetically stable structure of clean GaN(0001) surface posses (2 × 1) reconstruction, having every second row of Ga located near plane of N atoms, that gives rise to Ga-related dispersionless surface electronic state, already identified by angle resolved photoelectron spectroscopy (ARPES) measurements [S.S. Dhesi et al. Phys. Rev. B 56 (1997) 10271, L. Plucinski et al. Surf. Sci 507-10 (2002) 223, S. M. Widstrand et al. Surf. Sci. 584 (2005) 169]. The energy reduction in reconstruction proceeds via change of the hybridization of the occupied Ga surface states from sp³ to sp², transforming the empty states to p_z type. It is also shown that the electric subsurface field, modeled in new slab model which allows to simulate electric fields at the semiconductor surfaces [P. Kempisty et al., J. Appl. Phys. 106 (2009) 054901], strongly affects the energy of electronic states of GaN(0001) surfaces. The change of the field may shift the energy of surface states of bare and hydrogen covered GaN(0001) surface, by several eV with respect to the band states. The phenomenon, denoted as Surface States Stark Effect (SSSE), explains various band bending values, measured at differently doped n-type GaN(0001) surfaces. It is shown also that, for the adsorbate density up to one H atom for each Ga surface atom i.e. 1 monolayer coverage (1 ML), the hydrogen adatoms are located at the on-top positions, i.e. directly above Ga atoms. For these adsorbate densities, the H-related quantum surface state is located slightly below the valence band maximum (VBM) in the case of p-type GaN surface. For n-type GaN, the H-related surface state is located deeply in the valence band, about 2 eV below VBM. For higher, 1.25 ML hydrogen coverage, the two H adatoms create either surface attached H₂ ad-molecule (energetically stable) or triple bridge configuration is created (metastable). The H₂ ad-molecule is weekly attached to the surface, having the desorption energy barrier equal to 0.16 eV. For 1.25 ML coverage the DFT results were obtained for p-type GaN only. They show that in the ad-molecule case, a new surface electronic state arises which is located about 6.7 eV below VBM. In the case of the bridge configuration, the bridge related surface state is located closely to the conduction band minimum (CBM).