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.

Sn-polymetallic greisen-type deposits associated with late-stage rapakivi granites, Brazil: fluid inclusion and stable isotope characteristics

Tin-polymetallic greisen-type deposits in the Itu Rapakivi Province and Rondonia Tin Province, Brazil are associated with late-stage rapakivi fluorine-rich peraluminous alkali-feldspar granites. These granites contain topaz and/or muscovite or zinnwaldite and have geochemical characteristics comparable to the low-P sub-type topaz-bearing granites. Stockworks and veins are common in Oriente Novo (Rondonia Tin Province) and Correas (Itu Rapakivi Province) deposits, but in the Santa Barbara deposit (Rondonia Tin Province) a preserved cupola with associated bed-like greisen is predominant. The contrasting mineralization styles reflect different depths of formation, spatial relationship to tin granites, and different wall rock/fluid proportions. The deposits contain a similar rare-metal suite that includes Sri (+/-W, +/-Ta, +/-Nb), and base-metal suite (Zn-Cu-Pb) is present only in Correas deposit. The early fluid inclusions of the Correas and Oriente Novo deposits are (1) low to moderate-salinity (0-19 wt.% NaCl eq.) CO2-bearing aqueous fluids homogenizing at 245-450 degreesC, and (2) aqueous solutions with low CO2, low to moderate salinity (0-14 wt.% NaCl eq.), which homogenize between 100 and 340 T. In the Santa Barbara deposit, the early inclusions are represented by (1) low-salinity (5-12 wt.% NaCl eq.) aqueous fluids with variable CO2 contents, homogenizing at 340 to 390 T, and (2) low-salinity (0-3 wt.% NaCl eq.) aqueous fluid inclusions, which homogenize at 320380 degreesC. Cassiterite, wolframite, columbite-tantalite, scheelite, and sulfide assemblages accompany these fluids. The late fluid in the Oriente Novo and Correas deposit was a low-salinity (0-6 wt.% NaCl eq.) CO2-free aqueous solution, which homogenizes at (100-260 degreesC) and characterizes the sulfide fluorite-sericite association in the Correas deposit. The late fluid in the Santa Barbara deposit has lower salinity (0-3 wt.% NaCl eq.) and characterizes the late-barren-quartz, muscovite and kaolinite veins. Oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240-450 degreesC, and 1,0-2.6 kbar fluid pressure at Correas and Oriente Novo. The hydrogen isotope composition of breccia-greisen, stockwork, and vein fluids (delta(18)O quartz from 9.9parts per thousand to 10.9parts per thousand, deltaDH(2)O from 4.13parts per thousand to 6.95parts per thousand) is consistent with a fluid that was in equilibrium with granite at temperatures from 450 to 240 degreesC. In the Santa Barbara deposit, the inferred temperatures for quartz-pods and bed-like greisens are much higher (570 and 500 degreesC, respectively), and that for the cassiterite-quartz-veins is 415 degreesC. The oxygen and hydrogen isotope composition of greisen and quartz-pods fluids (delta(18)O(qtz-H2O)=5.5-6.1parts per thousand) indicate that the fluid equilibrated with the albite granite, consistent with a magmatic origin. The values for mica (delta(18)O(mica-H2O)=33-9.8parts per thousand) suggest mixing with meteoric water. Late muscovite veins (delta(18)O(qtz-H2O)=-6.4parts per thousand) and late quartz (delta(18)O(mica-H2O)=-3.8parts per thousand) indicate involvement of a meteoric fluid. Overall, the stable isotope and fluid inclusion data imply three fluid types: (1) an early orthomagmatic fluid, which equilibrated with granite; (2) a mixed orthomagmatic-meteoric fluid; and (3) a late hydrothermal meteoric fluid. The first two were responsible for cassiterite, wolframite, and minor coluChange in the redox conditions related to mixing-of magmatic and meteoric fluids favored important sulfide mineralization in the Correas deposit. (C) 2004 Elsevier B.V. All rights reserved.

THE FLUID SYSTEMS FOR THE SLD CHERENKOV RING IMAGING DETECTOR

We describe the design and operation of the fluid delivery, monitor and control systems for the SLD barrel Cherenkov Ring Imaging Detector (CRID). The systems deliver drift gas (C2H6+TMAE), radiator gas (C5F12+N2) and radiator liquid (C6F14). MeasUred critical quantities such as electron lifetime in the drift gas and ultra-violet (UV) transparencies of the radiator fluids, together with the operational experience, are also reported.

Greenhouse gas balance due to the conversion of sugarcane areas from burned to green harvest in Brazil

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

Evaluation of in vitro gas production of roughages and their mixtures using the curves subtraction method

The in vitro gas production of four single roughages and their paired combinations (1:1 on dry matter basis) were evaluated. Two roughage samples (100 mg) per treatment were fermented with ruminal fluid during a 48 h incubation period. Total 48 h gas volumes of fermentation dry matter (DM), neutral detergent fiber (NDF) and soluble compounds in neutral detergent (NDS) were for sugarcane = 16.8, 11.2, 6.9 mL; sugarcane + corn silage = 20.1, 12.6, 9.1 mL; sugarcane + 60-day elephantgrass = 16.5, 17.6 mL; sugarcane + 180-day elephantgrass = 13.8, 8.2, 5.9 mL; corn silage = 18.8, 16.8, 4.7 mL; corn silage + 60-day elephantgrass = 16.3, 15.4, 2.4 mL; corn silage + 180-day elephantgrass = 16.1, 11.8, 4.2 mL; 60-day elephantgrass = 16.9, 19.0 mL and 180-day elephantgrass = fermented 10.7, 12.2 mL, respectively. The NDS gas production was not possible to estimate for sugarcane + 60-day elephantgrass, 60-day elephantgrass and 180-day elephantgrass. The present data shows that the curves subtraction method can be an option to evaluate the contribution of the soluble fractions in roughages to digestion kinetics. However, this method underestimates the NDS gas contribution when roughages are low in crude protein and soluble carbohydrates. It is advisable to directly apply the two-compartmental mathematical model to the digestion curves for roughage DM, when determining the NDS gas volume and the digestion rate. This method is more straightforward and accurate when compared to the curve subtraction method. Non-structural carbohydrates combined with fiber and protein promoted a positive associative effect in sugarcane + corn silage (50:50) mixture. Therefore, it can be concluded that the soluble fraction of roughages greatly contributes to gas production. (C) 2004 Elsevier B.V. All rights reserved.