Markov partition in non-hyperbolic interval dynamics

We considerC ² unimodal mapsf such that all periodic points are hyperbolic, the critical point is non-degenerated and non-recurrent, and the Julia set does not contain intervals. We construct a Markov partition for a big part of the Julia set. Then we use it to estimate the limit capacity and Hausdorff dimension of the Julia set.Partially supported by CNPq, S.C.T.-Brazil     

Biosorption of Chromium(III) by Biomass of Seaweed Sargassum sp. in a Fixed-Bed Column

This work aimed at modeling chromium biosorption using the biomass of seaweed Sargassum sp. in a fixed-bed column. The mathematical model used was obtained from the mass balance of the component in the liquid phase and in the biosorbent material. The effects of both axial dispersion in the column and the resistance to mass transfer in the solid were considered for the solution of the partial differential equations of the model, using the Galerkin method on finite elements. To represent the equilibrium data of the batch system the Langmuir isotherm were used. The chromium ion adsorption capacity of the seaweed Sargassum sp., at a temperature of 30°C and pH 3.5, was 2.61 mmol/g. The model performance was evaluated from experimental data obtained at 30°C for flow rates of 2, 6 and 8 mL/min. The parameters of the model, mass transfer and axial dispersion coefficients, were adjusted from these experimental data. The model proved adequate to describe chromium biosorption dynamics in fixed-bed columns.     

Stabilization of HIV/AIDS model by receding horizon control

This work concerns the stabilization of uninfected steady state of an ordinary differential equation system modeling the interaction of the HIV virus and the immune system of the human body. The control variable is the drug dose, which, in turn, affects the rate of infection of CD4⁺ T cells by HIV virus. The feedback controller is constructed by a variant of the receding horizon control (RHC) method. Simulation results are discussed.     

Entropy and ergodic probability for differentiable dynamical systems and their bundle extensions

We answer a problem of Liao [S.T. Liao, Standard systems of differential equations and obstruction sets—from linearity to perturbations, in: System Researches, Proceedings Dedicated to the 85th Anniversary of Qian Xue-Sen, Zhejiang Education Press, Hangzhou, China, 1996, pp. 279-290 (in Chinese)]: A C¹ vector field or a C¹ diffeomorphism on an n-dimensional manifold has equal entropy with that of its bundle extensions. We also prove that each ergodic probability with simple Lyapunov spectrum has at most n²n! covering probabilities on each bundle extension.     

Interaction of Chlorpromazine and Trifluoperazine with Anionic Sodium Dodecyl Sulfate (SDS) Micelles: Electronic Absorption and Fluorescence Studies

The characteristics of binding of two phenothiazine antipsychothic drugs, chlorpromazine (CPZ) and trifluoperazine (TFP), to anionic sodium dodecyl sulfate (SDS) monomers and/or micelles were investigated using electronic absorption and fluorescence spectroscopies. Binding constants K(b) and pK(a) values for the drugs in SDS micelles were estimated using the red shifts of the maximum absorption and changes in absorption upon alkalization or in the presence of surfactant. The pK(a) shift of CPZ due to its interaction with SDS micelles is about 0.7 unit to higher values, as compared to the reported value of pK(a) obtained in buffer around 9.3. For TFP the pK(a) shift is 0.4 unit to higher values compared to that in buffer, reported as 4.0. The electronic absorption spectroscopic data suggest a biphasic interaction as a function of detergent concentration which is quite dependent of the protonation states of the drugs. In the case of TFP a very strong binding takes place when the drug is fully protonated (pH 2.0) and a distinct binding takes place at stoichiometric (low) surfactant concentrations (interaction via surfactant monomers) and at higher concentrations (in the presence of micelles). Static fluorescence probe analysis using pyrene was used to study the nature of the phenothiazine-surfactant premicellar and self-aggregates. The I(3)/I(1) and I(475)/I(1) ratios associated to pyrene fluorescence vibronic bands and excimer intensities ratios, respectively, were monitored for several ratios [SDS]/[drug] and significant changes, dependent of the drug presence and its protonation state, have been observed revealing a hydrophobic microenvironment provided by TFP-SDS aggregates in comparison with CPZ both at pH 7.0 and 4.0. Static anisotropy was also used to monitor the changes of the self-aggregates and micellar packing in the presence of the phenothiazine drugs. In aqueous solutions the anisotropy of the fluorescent probe dipyridamole (DIP) is quite low, being around 0.005 at pH 7.0 and 0.025 at pH 4.0, and the addition of detergent leads to an increase in the values of anisotropy to 0.030 at pH 7.0 and 0.070 at pH 4.0. In the presence of the phenothiazine drugs, and in the premicellar detergent concentration range, the anisotropy of DIP increases to 0.134 and 0.111 (dependent on drug concentration) for CPZ and TFP, respectively, at pH 4.0. These results suggest that the presence of both phenotiazine drugs makes the premicellar aggregates more rigid by decreasing the probe mobility, and are consistent with a more polar localization of the CPZ in the micelles as compared with TFP. At pH 7.0 the anisotropy changes are smaller, suggesting a slight decrease in CMC induced by the phenothiazines. Copyright 2000 Academic Press.     

Transitions between disordered phases in supercooled liquid silicon

We have investigated the transitions between disordered phases in supercooled liquid silicon using computer simulations. The thermodynamic properties were directly obtained from the free energy, which was computed using the recently proposed reversible scaling method. The calculated free energies of the crystalline and liquid phases of silicon at zero pressure, obtained using the environment dependent interatomic potential, are in excellent agreement with the available experimental data. The results show that, at zero pressure, a weak first-order liquid-liquid transition occurs at 1135 K and a continuous liquid-amorphous transition takes place at 843 K. These results are consistent with the existence of a second critical point for the liquid-liquid transition at a negative pressure.     

Amperometric detection of nitrite and nitrate at tetraruthenated porphyrin-modified electrodes in a continuous-flow assembly

The modification of a glassy carbon surface by coating with an electrostatically assembled film of tetraruthenated cobalt porphyrin/(meso-tetra(4-sulphonatephenyl)porphyrinate zinc(II) yields an indicator electrode that allows the determination of nitrite to be performed with a limit of detection of 0.1 μM in a flow injection configuration. The dynamic range extends up to 1000 μM and the repeatability of the measurements was evaluated to be 1.5% with a throughput of 50 samples per hour. The efficiency of the bilayered film to mediate the electron transfer allows the determinations to be performed at a less positive potential (+0.75 V) with enhanced sensitivity. The coating also prevents the surface poisoning and its stability is maintained over several weeks. The same detector was used for determination of nitrate after reduction to nitrite in a reductor column containing copperised cadmium. This method was used for the determination of nitrate and nitrite in mineral water, saliva and cured meats, the results being in agreement with certified values and those obtained by using recommended procedures.     

Development of a rapid and specific assay for detection of busulfan in human plasma by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

A sensitive and specific assay for detection of busulfan in human plasma was developed. The assay is based on rapid isolation of busulfan by liquid-liquid extraction with ethyl acetate, and detection by high-performance liquid chromatography with electrospray ionization and tandem mass spectrometry. 1,6-Bis(methanesulfonyloxy)hexane, a synthesized analogue of busulfan, was used as the internal standard (IS). The acquisition was performed in the multiple reaction monitoring mode; busulfan and the IS were detected with no interferences from plasma matrix. The method was linear over the range 5-2500 ng mL(-1), with r2 > 0.99 and a run time of only 3.5 min. The intra- and inter-assay precisions were in the ranges 2.1-11.9% and 3.2-10.1%, respectively, and the intra- and inter-assay accuracies were 92.2-107.6% and 94.7-104.1%, respectively. The absolute recoveries were 82.0% (20 ng mL(-1)), 90.6% (1000 ng mL(-1)) and 80.0% (2000 ng mL(-1)) for busulfan, and 89.1% for the IS (1000 ng mL(-1)). The limits of detection and quantification were 2 and 5 ng mL(-1), respectively. The validated method was successfully applied to analyze plasma samples obtained from six adults receiving doses of 1 mg kg(-1) in a conditioning regimen prior to bone marrow transplantation. A marked intra-patient variation in busulfan concentrations during the steady state was observed, which limits the application of pharmacokinetic modeling and suggests that continuous therapeutic monitoring is necessary for adequate individualized dosing. In this regard, the present assay brings important advantages relative to other methods described in the literature, i.e., it is highly specific and simple to perform, with a rapid chromatographic run time (3.5 min), and the whole procedure can be completed in 4-5 h, which would permit dose corrections after the third dose allowing earlier and better dosing adjustments towards the target level of busulfan.     

The partial hydrogenation of benzene to cyclohexene by nanoscale ruthenium catalysts in imidazolium ionic liquids

The controlled decomposition of an Ru(0) organometallic precursor dispersed in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)), tetrafluoroborate (BMI.BF(4)) or trifluoromethane sulfonate (BMI.CF(3)SO(3)) ionic liquids with H(2) represents a simple and efficient method for the generation of Ru(0) nanoparticles. TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approximately 57 nm that contain dispersed Ru(0) nanoparticles with diameters of 2.6+/-0.4 nm. These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogenation of alkenes and benzene under mild reaction conditions (4 atm, 75 degrees C). The ternary diagram (benzene/cyclohexene/BMI.PF(6)) indicated a maximum of 1 % cyclohexene concentration in BMI.PF(6), which is attained with 4 % benzene in the ionic phase. This solubility difference in the ionic liquid can be used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PF(6). Selectivities of up to 39 % in cyclohexene can be attained at very low benzene conversion. Although the maximum yield of 2 % in cyclohexene is too low for technical applications, it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles.