On associate subgroups of regular semigroups

We describe the structure of a regular semigroup with an associate subgroup the identiy element of which is a mcdial idempotent. As a particular application of this, we obtain the structure of perfect Dubreil-Jacotin semigroups in which the set of residuals of the bimaximum element form a subgroup.     

Thermal characterization and compatibility studies of norfloxacin for development of extended release tablets

Norfloxacin (NFX) is a synthetic antibacterial drug. The development of extended release tablets improves the patients’ comfort and compliance, resulting in lower discontinuation of the therapy; with consequently decrease in bacterial resistance. In the present work, the thermal behavior of NFX was investigated using TG and DSC techniques. Isothermal and non-isothermal methods were employed to determine kinetic data of decomposition process. Compatibility studies between NFX and pharmaceutical excipients, including three hydrophilic polymers were carried out in order to develop a new formulation of NFX to obtain extended release tablets with an approved quality.     

Stability studies on nifedipine tablets using thermogravimetry and differential scanning calorimetry

A new formulation of nifedipine tablets was prepared. The tablets were conditioned in amber-colored glass containers and placed in a climatized room at 40 °C and relative humidity of 75% for 180 days. Differential scanning calorimetry (DSC) and Thermogravimetry (TG) were used in order to evaluate the thermal properties of nifedipine, the excipients and two well-known nifedipine degradation products. There is no evidence of interaction between nifedipine and excipients or degradation products. High performance liquid chromatography (HPLC) was used in the dosage of nifedipine tablets before and after acclimatized exposure. Results show that DSC and TG offer important data for a more detailed assessment of the stability of a pharmaceutical formulation.     

Campedelli surfaces with fundamental group of order 8

Let S be a Campedelli surface (a minimal surface of general type with p _g  = 0, K ² = 2), and an etale cover of degree 8. We prove that the canonical model of Y is a complete intersection of four quadrics . As a consequence, Y is the universal cover of S, the covering group G = Gal(Y/S) is the topological fundamental group π ₁ S and G cannot be the dihedral group D ₄ of order 8. The first author is a member of the Centre for Mathematical Analysis, Geometry and Dynamical Systems, Instituto Superior Técnico, Lisboa. The second is a member of G.N.S.A.G.A.–I.N.d.A.M.     

An analytical approach to the unified solution of kinetic equations in the rarefied gas dynamics. II. Heat transfer problems

The ADO method, an analytical version of the discrete-ordinates method, is used here to solve a heat-transfer problem in a rarefied gas confined in a channel, as well as to solve a half-space problem in order to evaluate the temperature jump at the wall. This work is an extension of a previous work, devoted to flow problems, where the complete development of the solution, which is analytical in terms of the spatial variable, is presented in a way, such that, a wide class of kinetic models are considered, in an unified approach. A series of numerical results are showed and different simulations are used in order to establish a general comparative analysis based on this consistent set of results provided by the same methodology. In particular, numerical results for heat-flow profile, temperature and density perturbations are obtained for channels (walls), defined by different materials, on which different temperatures are imposed.     

Evaluation of a new rigid carbon-castor oil polyurethane composite as an electrode material

Polyurethane resin derived from castor oil was used to prepare a graphite composite intented to be applied in voltammetry. The best graphite/resin content in the composite was evaluated using cyclic voltammetry. The useful potential window was investigated in different electrolytes with pH ranging from 1 to 13, with good results in relation to the glassy carbon electrode. Response of this new electrode material to ferricyanide, hydroquinone, catechol and cadmium(II) ions was investigated in cyclic voltammetry and/or differential pulse voltammetry. The composite showed to be also useful in flow procedures.     

Numerical simulation of the vertical flow in a gas-solid system based on nuclear techniques

The conservation equations for particulate systems were utilized to investigate the fluid-dynamic behavior of a gas-solid mixture flowing along a vertical tube (riser) in a simplified model of a pilot catalytic cracking unit. Nuclear techniques were utilized for the determination of the flow parameters along the riser. The results show a satisfactory agreement between the theoretical data and those obtained by experimental tests.     

Characterization of a soil ilmenite developed from basalt

A natural ilmenite was extracted from the silt fraction of a soil developed from basalt of Minas Gerais State, Brazil. The sample was characterized by chemical analysis, X-ray diffraction, magnetic measurements and Mössbauer spectroscopy. The Mössbauer spectrum at 293 K shows two doublets: a major subspectrum of Fe²⁺ (relative area 74%) and a minor one of Fe³⁺ (26%). An incipient magnetic structure appears at 85 K, with a broadline sextet. These results may be explained by supposing that the separate is a solid solutionxFeTiO₃ · (1–x)Fe₂O₃, withx=0.85, which is magnetically ordered at low temperature. The lattice parameters for this hexagonal structure area=0.5082±0.0001 nm andc=1.398±0.001 nm.On leave of absence from the Departamento de Química, Universidade Federal de ViÇosa, 36570 000 ViÇosa (MG), Brazil.     

Theoretical and experimental investigation of millimeter wave phase fluctuations in an absorption region

The differential phase scintillations between two neighbouring frequencies on the side of the oxygen absorption peak have been measured. The –8/3 slope of the asymptotes to the measured spectra at the lowest and highest scintillation frequencies and the spectral ratio between these asymptotes are in good agreement with the theoretical model proposed.