Preparation of size-controlled nanoparticles of magnetite

Samples of ferrofluids containing chemically stabilized nanoparticles of magnetite (Fe₃O₄) with tetramethylammonium hydroxide (TMAOH) were prepared by a direct reduction–precipitation method. The influences of aging time and temperature on the size and monodispersion characteristics of the produced nanoparticles were investigated. Transmission electron microscopy, powder X-ray diffraction, Fourier-transform infrared, and magnetization measurements with applied magnetic field up to 2 T were used to characterize the synthesized iron oxides. Raising the temperature of the synthesized material in autoclave affects positively the monodispersion of the nanoparticles, but it was not found to significantly influence the size itself of individual particles.     

Diphenylphosphinoylethylidene (DPE) acetals: an alternative protective strategy in glycochemistry

Diphenylphoshinoylethyne reacts with diols under basic conditions to produce cycloacetalic phosphine oxides. The reaction appears to be general and particularly effective with carbohydrate derivatives. The 2-(diphenylphoshinoyl)ethylidene (DPE) acetals produced are stable in acidic media while they can be cleaved under reductive and/or basic conditions: base-catalyzed transacetalization is a method of choice for their mild and effective deprotection.     

An alternating direction scheme on a nonuniform mesh for reaction-diffusion parabolic problems

In this paper we develop a numerical method for two-dimensionaltime-dependent reaction-diffusion problems. This method, whichcan immediately be generalized to higher dimensions, is shownto be uniformly convergent with respect to the diffusion problems.This method, which can immediately be generalized to higherdimensions, is shown to be uniformly convergent with respectto the diffusion parameter.     

The width of the giant dipole resonance built on excited states of Cu compound nuclei

Continuumγ- ray spectra from the decay of⁵⁹Cu formed at an excitation energy of 100 MeV and angular momenta up to 43? by means of the reaction 190 MeV³²S +²⁷Al have been measured and analyzed. The parameters of the Giant Dipole Resonance (GDR) have been extracted using the statistical model. The derived GDR width confirms the sizeable broadening of this resonance in⁵⁹Cu already reported in our earlier investigation at 77 MeV excitation energy (J_crit=38?). Estimates of the GDR width have been performed in the adiabatic approximation. Predicted values account qualitatively for the experimental data of⁵⁹Cu as well as of the heavier isotope⁶³Cu, in which the broadening was not seen up to 77MeV excitation (J_crit=35?). The present analysis demonstrates the strong sensitivity of the GDR to spin effects in this mass region.     

The population of super- and hyper-deformed structures as a probe for fusion dynamics

Experimental data collected so far demonstrate that the population of superdeformed (SD) structures in nuclei with mass A～150 is influenced by the asymmetry in the entrance channel of the reaction. Furthermore, evidences for the population of hyperdeformed (HD) structures in the same mass region have been obtained only when charged particles are emitted in the evaporation chain. Dynamical model calculations show that in the reactions used to populate SD bands the equilibration times of the compound nuclei are not very sensitive on the mass asymmetry of the entrance channel. A qualitative understanding of both phenomena (SD and HD) is obtained assuming a link between the population of evaporation residues at very high spin and the dynamical hindrance of fission. Recent experimental results obtained in this field at the GASP spectrometer are presented for the case of the¹⁵²Dy nucleus populated in the³⁷Cl+¹²⁰Sn reaction. Proton and alpha particle spectra in coincidence with SD structures have been obtained. A sizeable difference is evidenced between alpha particle spectra in coincidence with SD and normally deformed structures.     

Mineralogical analysis of a weathering mantle derived from tuffite

Mössbauer spectra are presented at 15 and 298 K for magnetically-separated extracts of magnetic soils from a tuffite-derived weathering mantle from Minas Gerais, Brazil. The principal iron-bearing mineral is maghemite in which the degree of Ti or Mg substitution is found to vary with depth. The Mg-maghemite, with lattice parametera ₀=0.838 nm, is a new natural mineral. It is associated with anatase in the magnetic-separates.On leave of absence from Departamento de Química, UFV, 36570-000 ViÇosa (MG), Brazil.