Spectral Triples and the Super-Virasoro Algebra

We construct infinite dimensional spectral triples associated with representations of the super-Virasoro algebra. In particular the irreducible, unitary positive energy representation of the Ramond algebra with central charge c and minimal lowest weight h = c/24 is graded and gives rise to a net of even θ-summable spectral triples with non-zero Fredholm index. The irreducible unitary positive energy representations of the Neveu-Schwarz algebra give rise to nets of even θ-summable generalised spectral triples where there is no Dirac operator but only a superderivation.     

Experimental study on oscillating grid turbulence and free surface fluctuation

This paper analyses the interaction between the turbulence and free surface. The phenomenon takes place in many natural flows and industrial processes. In the present experiments, turbulence is generated by a vertically oscillating grid moving beneath the free surface. Fluid velocity has been measured through a hot-film anemometer, and the free surface elevation has been measured by an ultrasonic sensor. Integral length scales and several turbulence estimators have been computed. In order to detect the generation of turbulence near the free surface, the correlation between free surface elevation and the underneath flow velocity has been studied, as well as the time lag between turbulence and free surface. The free surface dynamics has been characterized by a velocity scale and a length scale. The kinetic energy associated with the free surface fluctuations increases with the Reynolds number at a rate depending on the frequency of the grid movement. For Reynolds number larger than ≈1000, however, the relationships collapse to a single curve characterized by a lower rate. The present experiments do not achieve the inertial sub-range in the vertical velocity fluctuations, and the estimated spectrum decays with an exponent smaller than ?3, which is the typical value for the two-dimensional turbulence in the inertial sub-range. The macro length scale, estimated by using the Taylor’s frozen turbulence hypothesis, experiences a decay away from the grid, which follows reasonably well the profile of Thompson and Turner (J Fluid Mechanics 67: 349–368, 1975). The micro length scale reduces immediately beneath the free surface, which can be interpreted by the increase of dissipation rate in the subsurface layer. The classification diagram by Brocchini and Peregrine (J Fluid Mech 449: 225–254, 2001) indicates that most tests fall in the weak turbulence domain, but some tests fall in the wavy domain. The vertical velocity fluctuations and the free surface level show a significant correlation with a negative phase lag, that is, the free surface fluctuations are ahead of the vertical velocity fluctuations.     

Microwave-assisted digestion with a single reaction chamber for mineral fertilizer analysis by inductively coupled plasma optical emission spectrometry

A systematic approach is proposed to evaluate microwave-assisted digestion in a single reaction chamber for the simultaneous determination of elements in the mineral fertilizer and raw material by inductively coupled plasma optical emission spectrometry. A reference material was digested using 12 acid mixtures containing nitric, hydrochloric, orthophosphoric, hydrofluoric or boric acid. Principal components analysis was applied for data treatment. Three digestion procedures based on diluted acids exhibited the most accurate results, with relative errors for reference values ranging from ?15% to +?9%. Limits of quantification were in the range of 0.2?mg cadmium kg^?1 up to 1000?mg aluminum kg^?1.     

Cyto-mechanoresponsive polyelectrolyte multilayer films

Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion.     

Concentration Dependence of the Electric Field Gradient in PbZr1−x Ti x O3 Ceramics

The concentration dependence of the electric field gradient (EFG) in PZT ceramics was studied by Time Differential Perturbed Angular Correlations (PAC) using the ¹⁸¹Ta radioactive probe in samples with x=0.3, 0.5 and 0.8 at room temperature. This phase presents two sites, probably related to defects close to probes, caused by oxygen and lead vacancies. We can also state that both the paraelectric and ferroelectric phases of these systems have two sites with different characteristics and that the high-frequency quadrupolar frequency site presents the highest fraction. The concentration dependence revealed by our results is discussed by comparing the latter with previous PAC studies. This revised version was published online in September 2006 with corrections to the Cover Date.     

Preparation and characterisation of Na2S and ZnSO4 nanoparticles in water/sodium bis(2-ethylhexyl)sulphosuccinate/n-heptane microemulsions

The preparation procedure for nanoparticles of the water-soluble salts Na₂S and ZnSO₄, two commonly used reagents to synthesise ZnS nanoparticles, by evaporation of volatile components of salt-containing water-in-oil microemulsions is described. In suitable conditions, the evaporation leads to the formation of dry salt–surfactant composites and to the formation of Na₂S or ZnSO₄ nanoparticles. It was found that the salt–surfactant composites can be totally redissolved in a dry apolar organic solvent allowing the formation of virtually water-free solutions containing a considerable amount of the water-soluble salts. The presence of nanoparticles in these solutions and in the composites has been proved by small-angle X-ray scattering and transmission electron microscopy, respectively. By mixing these solutions, the solid–solid reaction between Na₂S and ZnSO₄ nanoparticles leading to the formation of very small-sized ZnS nanoparticles has been ascertained by UV spectrophotometry. Received: 09 February 2001 Accepted: 19 March 2001     

Double implantation in silica glass for metal cluster composite formation: a study by synchrotron radiation techniques

Silica glass containing metal clusters is studied for both basic and applied aspects, related to the physics of cluster formation and to the optical properties of these materials. To obtain such composite structure, Cu + Ni, Au + Cu, Au + Ag, Cu + Co, and Cu + Ag sequential implantations in fused silica were realized. The resulting systems, after possible annealing in various atmospheres, were studied by synchrotron radiation-based techniques, namely, extended X-ray absorption fine structure (EXAFS) spectroscopy, grazing incidence X-ray diffraction (GIXRD), and grazing incidence small angle X-ray scattering (GISAXS). The unique potential of these techniques is the capability to investigate dilute (volume fraction of clusters0.01) and very thin (50 nm) systems. In the presented experiment, both pure and alloy clusters in the nanometer range of size were observed to form, pointing out the complexity of the cluster formation process in terms of physical and chemical driving forces.     

Synthesis and structural elucidation of a phthalide analog using NMR analysis and DFT calculations

Phtalides are secondary metabolites found in several fungi with a wide range of biological activities. A novel phthalide analog was synthesized by Diels–Alder reaction between cyclopentadiene and 3,4-dichlorofuran-2(5H)-one. Quantum mechanical calculations were used in conjunction with the spectrometric methods to determine the structure of the title compound. The calculated NMR chemical shifts for eight candidate pairs of enantiomers were compared with the experimental NMR chemical shifts applying the DP4 probability and mean absolute errors methodology. DP4 analysis using ¹H and ¹³C NMR chemical shifts without assignment of the signals presented 100% probability for the correct candidate structure 3d , proving the consistency of the method even without spectra interpretation. Results from theoretical calculation and NMR spectra interpretation were in agreement to the structure of rac-(3aR,4S,4aS,5R,8S,8aR,9R,9aS)-3a,9a-dichloro-3a,4,4a,5,8,8a,9,9a-octahydro-4,9:5,8-dimethanonaphtho[2,3-c]furan-1(3H)-one.