Development, optimization and validation of gas chromatographic fingerprinting of Brazilian commercial gasoline for quality control

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A pH optode based on thymol blue: application to determination of CO2 using flow injection analysis system

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

Fluid dynamics of air in a packed bed: velocity profiles and the continuum model assumption

Air flow through packed beds was analyzed experimentally under conditions ranging from those that reinforce the effect of the wall on the void fraction to those that minimize it. The packing was spherical particles, with a tube-to-particle diameter ratio (D/dp) between 3 and 60. Air flow rates were maintained between 1.3 and 4.44 m3/min, and gas velocity was measured with a Pitot tube positioned above the bed exit. Measurements were made at various radial and angular coordinate values, allowing the distribution of air flow across the bed to be described in detail. Comparison of the experimentally observed radial profiles with those derived from published equations revealed that at high D/dp ratios the measured and calculated velocity profiles behaved similarly. At low ratios, oscillations in the velocity profiles agreed with those in the voidage profiles, signifying that treating the porous medium as a continuum medium is questionable in these cases.

Agarose gel electrophoresis of cerebrospinal fluid proteins of dogs after sample concentration using a membrane microconcentrator technique

Background: Cerebrospinal fluid (CSF) is produced in the cerebral ventricles through ultrafiltration of plasma and active transport mechanisms. Evaluation of proteins in CSF may provide important information about the production of immunoglobulins within the central nervous system as well as possible disturbances in the blood-brain barrier. Objective: the objective of this study was to measure the concentration and fractions of protein in CSF samples using a membrane microconcentrator technique followed by electrophoresis, and to compare the protein fractions obtained with those in serum. Methods: CSF samples from 3 healthy dogs and 3 dogs with canine distemper virus infection were concentrated using a membrane microconcentrator having a 0.5 to 30,000 d nominal molecular weight limit (Ultrafree, Millipore, Billerica, MA, USA). Protein concentration was determined before and after concentration. Agarose gel electrophoresis was done on concentrated CSF samples, serum, and serial dilutions of one of the CSF samples. Results: Electrophoretic bands were clearly identified in densitometer tracings in CSF samples with protein concentrations as low as 1.3 g/dL. The higher CSF protein concentration in dogs with distemper was mainly the result of increased albumin concentration. Conclusion: the microconcentrating method used in this study enables characterization of the main protein fractions in CSF by routine electrophoresis and may be useful for interpreting the underlying cause of changes in CSF protein concentrations

NONLINEAR DIFFUSION PROCESS IN A BENARD SYSTEM AT THE CRITICAL-POINT FOR THE ONSET OF CONVECTION

The evolution equation governing surface perturbations of a shallow fluid heated from below at the critical Rayleigh number for the onset of convective motion, and with boundary conditions leading to zero critical wave number, is obtained. A solution for negative or cooling perturbations is explicitly exhibited, which shows that the system presents sharp propagating fronts.

SURFACE SOLITARY WAVES IN A DOUBLE DIFFUSIVE SYSTEM

We show that a surface solitary wave governed by the Korteweg-de Vries equation can develop in a fluid acted upon by fluxes of heat and of a second diffusive element. This solitary wave appears as a manifestation of a hydrodynamical instability which sets in only when a certain relation involving the parameters of the system is satisfied.

Fabrication and testing of a poly(vinylidene fluoride) (PVDF) microvalve for gas flow control

A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm x 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 mu m, and a voltage of -200 V DC was used to close the device by moving the actuator 20 mu m lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

Effect of a pilot washing system on dicofol levels in orange matrix

An efficient analytical method is described for the analysis of dicofol residues in pulp and orange peel. Samples are mixed with Celite and transferred to chromatographic columns prepacked with silica gel. Dicofol is eluted with ethyl acetate, and the extracts are analyzed by gas chromatography with electron capture detection. Mean recoveries for dicofol at levels of 0.5, 2.0, 5.0, and 10 mg/kg ranged from 87 to 95% with relative standard deviation values between 2.6 and 9.0%. To investigate the effect of a pilot washing system on dicofol residues in oranges, the analytical procedure was applied to samples submitted to different treatments with commercial formulations under field and laboratory conditions. The orange samples with and without washing were analyzed in duplicate, and the results indicated that washing under the described conditions did not allow a complete removal of dicofol residues from orange peel.

A flow-injection-ICP system sequential multielemental analysis with simultaneously mercury(II) preconcentration step

A flow-injection system for multielemental analysis with a mercury(II) preconcentration step using a resin Chelite-S(R)(Serva Feinbiochemica Heidelberg, Part No. 41709) packed minicolumn by inductively coupled plasma atomic emission spectroscopy is described. A mercury reductive elution procedure with a mixture of SnCl2/HCl was used, which allows use of 6 mol/L HCl solution instead of concentrated hydrochoric acid. The main parameters related to ICP operation, such as radio frequency power (950-1750 W), auxiliary argon flow (0.0-1.5 L/min) and spray chamber nebulizer pressure (15-35 psi), were studied. Optimization of the FIA system was reached by defining the best eluent carrier stream (1.4-2.8 mL/min), Hgdegrees carrier stream (10-40 mL min(-1)), loading time (0.5-4.0 min), sample flow rate (1.25-10.0 mL/min), temperature of reactor gas liquid separator (GLS) (25-75 degreesC) and eluent volume (50-350 muL). Throughput is around 30 samples per hour for analytical solutions within the range 50-2500 ng Hg(II)/L. Results from certified material showed good precision (RSD < 3%, n = 12) and no statistical difference was observed for real samples analyzed by AAS and by the proposed system.

SURFACE PERTURBATIONS OF A SHALLOW VISCOUS-FLUID HEATED FROM BELOW AND THE (2+1)-DIMENSIONAL BURGERS-EQUATION

The (2 + 1)-dimensional Burgers equation is obtained as the equation of motion governing the surface perturbations of a shallow viscous fluid heated from below, provided the Rayleigh number of the system satisfies the condition R not-equal 30. A solution to this equation is explicitly exhibited and it is argued that it describes the nonlinear evolution of a nearly one-dimensional kink.

Simplified architecture of a neurofuzzy controller applied on industrial systems for fluid flow control

This work presents a simplified architecture of a neurofuzzy controller for general purpose applications that tries to minimize the processing used in the several stages of hazy modeling of systems. The basic procedures of fuzzification and defuzzification are simplified to the maximum while the inference procedures are computed in a private way. The simplified architecture allows a fast and easy configuration of the neurofuzzy controller and the structuring rules that define the control actions is automatic. Th controller's Limits and performance are standardized and the control actions are previously calculated. For application, the industrial systems of fluid flow control will be considered.

Global yields, chemical compositions and antioxidant activities of clove basil (Ocimum gratissimum L.) extracts obtained by supercritical fluid extraction

Clove basil (Ocimum gratissimum) extracts were obtained with supercritical CO2. Clove basil was cultivated using 0, 4, 8 and 12 kg/m(2) of organic fertilizer and was harvested in four seasons: winter, spring, summer and autumn, in the Southern Hemisphere. The extracts' global yields were determined at 40C and 150 bar for samples from all cultivation conditions and harvesting seasons. For selected samples, the extracts' global yields at 40C were determined for pressures of 100, 150, 200, 250 and 300 bar. The extracts were analyzed by gas chromatography-flame ionization detector. Antioxidant activity (AA) was assessed using the coupled reaction of beta-caroteneand linolenic acid. The extracts' global yields varied from 0.91 to 1.79% (dry basis), and the AAs varied from 62 to 84% compared with the control beta-carotene. Eugenol and beta-selinene were the major compounds. The relative proportion of eugenol varied from 35 to 60%, while the content of beta-selinene remained approximately constant (11.5-14.1%, area). The other substances quantified in the extracts were 1,8 cineole, trans-caryophyllene and alpha-selinene.

ALCOHOL IN CEREBROSPINAL-FLUID (CSF) AND ALCOHOLISM

Alcohol levels were measured in 15 cerebrospinal fluid (CSF) samples and 14 blood samples from grade III and IV male alcoholic patients with signs of nervous system involvement, and compared with levels detected in 11 CSF samples and 11 blood samples from abstemious patients or patients with grade I or II alcoholism whose CSF had been found to be normal by routine analysis (controls). Among the alcoholic patients, alcohol levels were lower in the CSF than in blood, whereas the opposite was true for the controls. The possible mechanisms underlying this difference are discussed and the need for further study of this topic is emphasized.

SEMICLASSICAL THEORY OF MAGNETIZATION FOR A 2-DIMENSIONAL NONINTERACTING ELECTRON-GAS

We compute the semiclassical magnetization and susceptibility of non-interacting electrons, confined by a smooth two-dimensional potential and subjected to a uniform perpendicular magnetic field, in the general case when their classical motion is chaotic. It is demonstrated that the magnetization per particle m(B) is directly related to the staircase function N(E), which counts the single-particle levels up to energy E. Using Gutzwiller's trace formula for N, we derive a semiclassical expression for m. Our results show that the magnetization has a non-zero average, which arises from quantum corrections to the leading-order Weyl approximation to the mean staircase and which is independent of whether the classical motion is chaotic or not. Fluctuations about the average are due to classical periodic orbits and do represent a signature of chaos. This behaviour is confirmed by numerical computations for a specific system.

NONLINEAR SURFACE-WAVE EXCITATIONS IN THE BENARD-MARANGONI SYSTEM

We examine the appearance of surface waves governed by Burgers and Korteweg-de Vries equations in a shallow viscous heated fluid. We consider waves triggered by a surface-tension variation induced by both temperature and concentration gradients. We also establish the range of parameters for which the above-mentioned equations appear.