Quenched Hadron Spectrum and Decay Constants on the lattice

In this talk we present the results obtained from a study of ${\cal O}(2000)$ (quenched) lattice configurations from the APE collaboration, at $6.0\le\beta\le 6.4$, using both the Wilson and the SW-Clover fermion action. We determine the light hadronic spectrum and the meson decay constants. For the light-light systems we find an agreement with the experimental data of $\sim 5$ for mesonic masses and $\sim 10$ for baryonic masses and pseudoscalar decay constants; a larger deviation is present for the vector decay constants. For the heavy-light decay constants we find $f_{D_s}=237 \pm 16 MeV, f_{D} = 221 \pm 17 MeV (f_{D_s}/f_D=1.07(4)), f_{B_s} = 205 \pm 35 MeV, f_{B} = 180 \pm 32 MeV (f_{B_s}/f_B=1.14(8))$, in good agreement with previous estimates.Comment: 8 pages, latex, Talk given at XXV ITEP Winter School of Physics, Moscow - Russia, 18-27 Feb 199

The second moment of the pion's distribution amplitude

We present preliminary results for the second moment of the pion's distribution amplitude. The lattice formulation and the phenomenological implications are briefly reviewed, with special emphasis on some subtleties that arise when the Lorentz group is replaced by the hypercubic group. Having analysed more than half of the available configurations, the result obtained is \xi^2_L = 0.06 \pm 0.02.Comment: Lattice 99 (matrix elements), 3 page

A study of the deep structure of the energy landscape of glassy polystyrene: the exponential distribution of the energy-barriers revealed by high-field Electron Spin Resonance spectroscopy

The reorientation of one small paramagnetic molecule (spin probe) in glassy polystyrene (PS) is studied by high-field Electron Spin Resonance spectroscopy at two different Larmor frequencies (190 and 285 GHz). The exponential distribution of the energy-barriers for the rotational motion of the spin probe is unambigously evidenced at both 240K and 270K. The same shape for the distribution of the energy-barriers of PS was evidenced by the master curves provided by previous mechanical and light scattering studies. The breadth of the energy-barriers distribution of the spin probe is in the range of the estimates of the breadth of the PS energy-barriers distribution. The evidence that the deep structure of the energy landscape of PS exhibits the exponential shape of the energy-barriers distribution agrees with results from extreme-value statistics and the trap model by Bouchaud and coworkers.Comment: Final version in press as Letter to the Editor on J.Phys.:Condensed Matter. Changes in bol

Numerical investigation of the quantum fluctuations of optical fields transmitted through an atomic medium

We have numerically solved the Heisenberg-Langevin equations describing the propagation of quantized fields through an optically thick sample of atoms. Two orthogonal polarization components are considered for the field and the complete Zeeman sublevel structure of the atomic transition is taken into account. Quantum fluctuations of atomic operators are included through appropriate Langevin forces. We have considered an incident field in a linearly polarized coherent state (driving field) and vacuum in the perpendicular polarization and calculated the noise spectra of the amplitude and phase quadratures of the output field for two orthogonal polarizations. We analyze different configurations depending on the total angular momentum of the ground and excited atomic states. We examine the generation of squeezing for the driving field polarization component and vacuum squeezing of the orthogonal polarization. Entanglement of orthogonally polarized modes is predicted. Noise spectral features specific of (Zeeman) multi-level configurations are identified.Comment: 12 pages 9 figures. Submitted to Physical Review

Somatic embryogenesis and efficient regeneration of Vitis vinifera L. 'Carménère' plants

Research Note

Chemical, thermal and particle distribution analyses of two low-fusing dental porcelains

Low-fusing dental porcelains are commonly used for the fabrication of aesthetic restorations to prevent oxidation of NiCrMo, CoCrMo and titanium substructures. The aim of this study was to characterize one feldspar-based commercial porcelain in order to obtain information on the chemical composition, thermal expansion and particle size distribution. Opaque and dentin commercial porcelains have been selected for this purpose. The chemical analyses were carried out by XRD and X-ray fluorescence. The particle size distribution of the porcelains was measured by a particle analyzer associated to the CILAS 2.56 software. Finally, the thermal expansion was characterized by dilatometry. Analyzing the chemical composition, it was observed that the porcelain presented high ZrO2 content. On the other hand, the majority of the porcelains present larger SiO2 and K2O and lower ZrO2 contents. The XRD diffractograms of the dentine and opaque porcelain samples were similar about presence of the leucite crystalline phase found. The main difference observed between opaque and dentine porcelains was in terms of their opaquer phases. A significant difference in the particle size distribution was observed. The opaque and dentin presented bimodal distribution but the opaque porcelain presented a relatively particle agglomeration. However, the porcelains should have a fine and trimodal particle size distribution which is expected to promote an adequate particle compaction increasing the bulk density and minimizing the porosity after the sintering. Several studies report the importance of a fine and trimodal distribution for one better compaction of particles and reduction of pores in the ceramic microstructure [1, 2]. Results are in accordance with some studies in the literature [1-5]. The thermal expansion between alloy and porcelain was different too. Therefore, the thermal behavior of dental porcelain is important for achieving better metal-ceramic properties of the joint. Mismatch of thermal coefficients between ceramic and metal can weaken the metal-ceramics interface compromising the performance of the restoration.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Resummation of Cactus Diagrams in Lattice QCD

We show how to perform a resummation, to all orders in perturbation theory, of a certain class of gauge invariant diagrams in Lattice QCD. These diagrams are often largely responsible for lattice artifacts. Our resummation leads to an improved perturbative expansion. Applied to a number of cases of interest, this expansion yields results remarkably close to corresponding nonperturbative estimates.Comment: 18 page

A calculation of the Lepage-Mackenzie scale for the lattice axial and vector currents

We calculate the perturbative scales (q*) for the axial and vector currents for the Wilson action, with and without tadpole improvement, using Lepage and Mackenzie's formalism. The scale for the pseudoscalar density (times the mass) is computed as well. Contrary to naive expectation, tadpole improvement reduces q* by only a small amount for the operators we consider. We also discuss the use of a nonperturbative coupling to calculate the perturbative scale.Comment: 13 pages. One postscript figur