Pseudoclassical mechanics for the spin-0 and -1 particles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Thermodynamics of quasi-particles at finite chemical potential

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

Search for Long-Lived Charged Massive Particles with the D0 Detector

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Challenging the weak cosmic censorship conjecture with charged quantum particles

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

Search for Charged Massive Long-Lived Particles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for heavy stable charged particles in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of jet fragmentation into charged particles in pp and PbPb collisions at root s(NN)=2.76 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for new physics with long-lived particles decaying to photons and missing energy in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Scaling invariance for the escape of particles from a periodically corrugated waveguide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Recurrence of particles in static and time varying oval billiards

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Scaling investigation for the dynamics of charged particles in an electric field accelerator

Some dynamical properties of an ensemble of trajectories of individual (non-interacting) classical particles of mass m and charge q interacting with a time-dependent electric field and suffering the action of a constant magnetic field are studied. Depending on both the amplitude of oscillation of the electric field and the intensity of the magnetic field, the phase space of the model can either exhibit: (i) regular behavior or (ii) a mixed structure, with periodic islands of regular motion, chaotic seas characterized by positive Lyapunov exponents, and invariant Kolmogorov-Arnold-Moser curves preventing the particle to reach unbounded energy. We define an escape window in the chaotic sea and study the transport properties for chaotic orbits along the phase space by the use of scaling formalism. Our results show that the escape distribution and the survival probability obey homogeneous functions characterized by critical exponents and present universal behavior under appropriate scaling transformations. We show the survival probability decays exponentially for small iterations changing to a slower power law decay for large time, therefore, characterizing clearly the effects of stickiness of the islands and invariant tori. For the range of parameters used, our results show that the crossover from fast to slow decay obeys a power law and the behavior of survival orbits is scaling invariant. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772997]

Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Temperature dependence and magnetocrystalline anisotropy studies of self-assembled L1(0)-Fe55Pt45 ferromagnetic nanocrystals

Temperature dependence and uniaxial magnetocrystalline anisotropy properties of the chemically synthesized 4 nm L1(0)-Fe55Pt45 nanoparticle assembly by a modified polyol route are reported. As-prepared nanoparticles are superparamagnetic presenting fcc structure, and annealing at 550 degrees C converts the assembly into ferromagnetic nanocrystals with large coercivity (H-C>1 T) in an L1(0) phase. Magnetic measurements showed an increasing in the ferromagnetically ordered fraction of the nanoparticles with the annealing temperature increases, and the remanence ratio, S=M-R/M-S congruent to 0.76, suggests an (111) textured film. A monotonic increase of the blocking temperature T-B, the uniaxial magnetocrystalline anisotropy constant K-U, and the coercivity H-C with increasing annealing temperature was observed. Magnetic parameters indicate an enhancement in the magnetic properties due to the improved Fe55Pt45 phase stabilizing, and the room-temperature stability parameter of 67, which indicates that the magnetization should be stable for more than ten years, makes this material suitable for ultrahigh-density magnetic recording application.(c) 2007 American Institute of Physics.

Colloidal particles: Spherical yttrium iron garnet

The purpose of this work is to obtain spherical particles YIG from micrometric to nanometric scales. The spherical particles were obtained from cation hydrolysis in acid medium by adding urea or ammonia in order to carry out a homogeneous nucleation process up to 90 degrees C. Different composition and morphology were achieved by changing reactant concentrations, precipitation agent and stabilizing agent. X-ray diffractometry, electrophoretic mobility, transmission and scanning electron microscopies were carried out on these particles to investigate the phase identification, mobility, morphology and particle size. Crystalline YIG, with spherical characteristics, was obtained. The surface potential presented different characteristics for different dispersion media.

Size distributions of fine silicate and other particles in Masaya's volcanic plume

Direct-sampling and remote-sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d <10 mu m) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d similar to 1.15 mu m. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as similar to 10(11) s(-1), equivalent to similar to 55 kg d(-1). Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(mu m) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d similar to 1 mu m. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as similar to 10(17) s(-1), equivalent to similar to 5.5 Mg d(-1) where d < 4 mu m.