Quantization of (2+1)-spinning particles and bifermionic constraint problem

This work is a natural continuation of our recent study in quantizing relativistic particles. There it was demonstrated that, by applying a consistent quantization scheme to the classical model of a spinless relativistic particle as well as to the Berezin-Marinov model of a 3 + 1 Dirac particle, it is possible to obtain a consistent relativistic quantum mechanics of such particles. In the present paper, we apply a similar approach to the problem of quantizing the massive 2 + 1 Dirac particle. However, we stress that such a problem differs in a nontrivial way from the one in 3 + 1 dimensions. The point is that in 2 + 1 dimensions each spin polarization describes different fermion species. Technically this fact manifests itself through the presence of a bifermionic constant and of a bifermionic first-class constraint. In particular, this constraint does not admit a conjugate gauge condition at the classical level. The quantization problem in 2 + 1 dimensions is also interesting from the physical viewpoint (e.g., anyons). In order to quantize the model, we first derive a classical formulation in an effective phase space, restricted by constraints and gauges. Then the condition of preservation of the classical symmetries allows us to realize the operator algebra in an unambiguous way and construct an appropriate Hilbert space. The physical sector of the constructed quantum mechanics contains spin-1/2 particles and antiparticles without an infinite number of negative-energy levels, and exactly reproduces the one-particle sector of the 2 + 1 quantum theory of a spinor field.

Chronopotentiometric stripping analysis using gold electrodes, an efficient technique for mercury quantification in natural waters

This paper proposes a simple methodology for mercury quantification in natural water by stripping chronopotentiometry at constant current, using gold (film) electrodes constructed from recordable CDs in stationary cell. The proposed method allows the direct measurement of labile mercury in natural waters. To quantify total mercury, a robust and low cost UV irradiation system was developed for the degradation of organic constituents of water. The proposed system presents such advantages as excellent sensitivity, low cost, versatility, and smaller dimensions (portability for on-field applications) when compared with other techniques (ICP, GFAAS, fluorimetry) traditionally utilized for mercury quantification. A large linear region of responses was observed, situated over the range 0.02 - 200 μ g L-1. Various experimental parameters were optimized and the system allowed quantifications in natural samples, with detection limit of 8 ng L-1 and excellent reproducibility (RSD of 1.4% for 48 repetitive measurements using a 10 μ g L-1 mercury solution). Different metal ions were evaluated, including copper, as possible interferences on stripping mercury signals. Applications of the new method were demonstrated for the analysis of certified and groundwater samples spiked with a known amount of mercury and for the quantification of methylmercury in synthetic oceanic water, originally utilized for fishes contamination experiment.

Ferritin in iron containing granules from the fat body of the honeybees Apis mellifera and Scaptotrigona postica

It is already known that the behaviour of the honeybee Apis mellifera is influenced by the Earth's magnetic field. Recently it has been proposed that iron-rich granules found inside the fat body cells of this honeybee had small magnetite crystals that were responsible for this behaviour. In the present work, we studied the iron containing granules from queens of two species of honeybees (A. mellifera and Scaptotrigona postica) by electron microscopy methods in order to clarify this point. The granules were found inside rough endoplasmic reticulum cisternae. Energy dispersive X-ray analysis of granules from A. mellifera showed the presence of iron, phosphorus and calcium. The same analysis performed on the granules of S. postica also indicated the presence of these elements along with the additional element magnesium. The granules of A. mellifera were composed of apoferritin-like particles in the periphery while in the core, clusters of organised particles resembling holoferritin were seen. The larger and more mineralised granules of S. postica presented structures resembling ferritin cores in the periphery, and smaller electron dense particles inside the bulk. Electron spectroscopic images of the granules from A. mellifera showed that iron, oxygen and phosphorus were co-localised in the ferritin-like deposits. These results indicate that the iron-rich granules of these honeybees are formed by accumulation of ferritin and its degraded forms together with elements present inside the rough endoplasmic reticulum, such as phosphorus, calcium and magnesium. It is suggested that the high level of phosphate in the milieu would prevent the crystallisation of iron oxides in these structures, making very unlikely their participation in magnetoreception mechanisms. They are most probably involved in iron homeostasis. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

HELICITY WAVE-FUNCTIONS FOR MASSLESS AND MASSIVE SPIN-2 PARTICLES

Starting from general properties of a spin-2 field, we construct helicity wave functions in the framework of the Weyl-van der Waerden spinor formalism. We discuss here the cases of massless and massive spin-2 particles.

Red and blue emissions of europium doped gadolinium silicate from porous silica matrix and hydroxide carbonate with spherical shaped particles

In this work, Eu(III) and Eu(II) doped gadolinium silicates has been obtained as compact tubes starting from spherical gadolinium hydroxide carbonate using the pores of silica matrix as support and its surface as reagent. Eu(III) doped gadolinium silicate with hexagonal phase shows an interesting visible shifted charge transfer band when compared to disilicate with orthorhombic phase that was also obtained. Eu(II) gadolinium silicate has been prepared using CO atmosphere presenting an intense blue emission. The divalent europium system shows a potential application as an UV-blue converter. The samples were characterized by scanning electron microscopy (SEM), X-ray powder diffractometry (XRD) and photoluminescence spectroscopy. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Characterisation of sugar cane combustion particles in the Araraquara region, Southeast Brazil

Biomass burning is an important primary and secondary source of aerosol particles. The presence of carbonaceous particles in the respirable size range makes the study of this fraction important in view of possible health and climatic effects. The annual burning of sugar cane plantations causes emission of huge amounts of pyrogenic particles. Aerosol samples were collected in Araraquara city, São Paulo state, Brazil, during the harvest season for fine and coarse particles and bulk; they were analysed by electron-probe microanalysis, including facilities for low-Z element determination (low-Z EPMA) and by energy-dispersive X-ray fluorescence (EDXRF), in order to investigate the elemental composition of individual particles and bulk samples, respectively. Numerical analysis of the EPMA results by hierarchical clustering shows high contributions of carbonaceous particles that can be distinguished mainly in two different types: biogenic and carbon-rich. Additionally, two significant contributions of aluminosilicate particles were identified: as rather pure aluminosilicates or mixed with carbonaceous species. The EDXRF results are compatible with those of aerosol particles in Amazon, which is nowadays one of the main sources of biogenic particles in the world.

Preparation and properties of colloidal particles. Silica on yttrium iron garnet

Various properties of particles can be altered by coating them with a layer of different chemical composition. Yttrium iron garnet (YIG) particles has been coated with silica for control of their sintering, corrosion resistance, and stabilization of magnetic properties. This silica cover was obtained by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. This material was characterized by transmission (TEM) electron microscopy, (XEDS) X-ray energy-dispersive spectrometry, (XPS) X-ray photoemission spectroscopy and (VSM) vibrating sample magnetometry. YIG was heterocoagulated by silica as indicated by TEM micrographies. XPS measurements indicated that only binding energy for silicon and oxygen was found on the silica shell, which confirms that the YIG was covered. The values of the saturation magnetization differ from the heterocoagulated system to well-crystallized YIG.

Spherical particles of phenolic resin treated with iron oxide

This paper describes the preparation and characterization of phenolic resins' thermospheres covered by a magnetic phase of iron oxide. The thermospheres were prepared by allowing phenol and formaldehyde to react under dispersion polymerization conditions and the iron oxide phase was incorporated in situ onto the phenolic resin particles by adding concentrated NH3 to FeCl2 in DMSO. This reaction was conducted at 70 degrees C under nitrogen atmosphere in a controlled temperature vessel, and the modified resin was isolated and dried in vacuo. Both pure and modified resins were characterized by DRX, TG- DTA, and MEV/ EDX. The modified particles were attracted by a magnetic field, indicating the fixation of magnetic iron oxide. No diffraction peaks were observed in DRX analysis; thermal analysis ( DTA) of both pure and modified resins presented exothermic events between 300 and 680 degrees C, and 300 and 570 degrees C, respectively, indicating the microstructure of the resin was modified after the treatment. Thermogravimetric analysis ( TGA) of the pure resin registered a 2.0% residue, compared to 8.0% for the modified resin. These residues correspond to about 7.0% of fixed iron oxide. MEV/ EDX analyses confirm the modification of the resins by the process of fixing iron oxide.

The reproductive biology of Cybistax antisyphilitica (Bignoniaceae), a characteristic tree of the South American savannah-like "Cerrado" vegetation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Methods to estimate the number of surface nucleation sites on glass particles

Based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, we propose two new models to describe the crystallisation kinetics of glass particles and use them to determine the density of nucleation sites, N(s), on glass powders. We tested these models with sintered compacts of diopside glass particles using sinter-crystallisation treatments at 825 degrees C (T(g)similar to 727 degrees C), that covered from null to almost 100% crystallised volume time fraction. We measured and compared the evolution of the crystallised volume fractions by optical microscopy and x-ray diffraction. Then we fit our expressions to experimental data using Ns and R (the average particle radius) as adjustable parameters. For comparison, we also fit to our data existing expressions that describe the crystallised volume fraction in glass powders. We demonstrate that all the methods allow one to estimate N(s) with reasonable accuracy. For our ground and water washed diopside glass powder, N(s) is between 10(10)-10(11) sites.m(-2). The reasonable agreement between experimental and adjusted R confirms the consistency of all five models tested. However, one of our equations does not require taking into account the change of crystallisation mode from 3-dimensional to 1-dimensional, and this is advantageous.

Frequency upconversion properties of Tm3+ doped TeO2-ZnO glasses containing silver nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Metal-Organic Semiconductor Nanostructures for Surface-Enhanced Raman Scattering

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Non-leachable highly luminescent ordered mesoporous SiO2 spherical particles

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of the heat treatment on the nucleation of silver nanoparticles in Tm3+ doped PbO-GeO2 glasses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Field profiles of bulk plasmon polariton modes in layered systems containing a metamaterial

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)