Linear viscoelasticity of immiscible blends: The application of creep

A new method to characterize the long-time linear relaxation mechanisms of immiscible blends based on creep experiment was developed. Small-amplitude oscillatory shear and incomplete creep/recovery experiments were combined to characterize immiscible blends of polypropylene with dispersed droplets of polystyrene. An experimental protocol was defined such that the full creep compliance function could be obtained while minimizing morphological changes. Dynamic experiments were performed to characterize the shorter time relaxation processes, and creep and recovery measurements were used to detect the longer time portions of the relaxation spectra. Extended retardation and relaxation spectra were constructed by combining these data. It was found that using this technique, very long-time relaxation peaks which were inaccessible with dynamic experiments alone could be detected. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4720081]

Linking origin of the electric field-assisted beta-PbF2 crystallization in lead oxyfluoroborate glasses below T (g) to simultaneous cathode/anode-compensated electrochemical reactions

Full validation of the electrochemical mechanisms so far postulated as driving force of electric field-assisted non-spontaneous crystallization development in given glasses has suffered experimental restrictions. In this work, we looked into origin of this phenomenon in lead oxyfluoroborate glasses, resulting in beta-PbF2 growth even below the corresponding glass transition temperatures, through achieving a systematic study of not only Pt,Ag/Glass/Ag,Pt- but also Pt,Ag/Glass/YSZ:PbF2/Ag,Pt-type cells, where YSZ:PbF2 represents a two-phase system (formed by Y2O3-doped ZrO2 and PbF2). It is demonstrated that crystallization induction in these glasses involves Pb2+ ions reduction at the cathode, the phenomenon being, however, confirmed only when the F- ions were simultaneously also able to reach the anode for oxidation, after assuring either a direct glass-anode contact or percolation pathways for free fluoride migration across the YSZ:PbF2 mixtures. A further support of this account is that the electrochemically induced beta-PbF2 phase crystallizes showing ramified-like microstructure morphology that arises, accordingly, from development of electroconvective diffusion processes under electric field action.

Sintering and Microwave Properties of Zirconium Tin Titanate Doped with Select Oxides

Zirconium tin titanate (ZST) is often used as a dielectric resonator for the fabrication of microwave devices. Pure compositions do not sinter easily by solid state sintering; therefore, sintering ZST requires sintering aids capable of creating defects that could improve diffusion processes and/or promote liquid phase sintering. The mechanisms by which the additives influence the microstructure and, consequently, the ZSTs dielectric properties are not very clear. The effects of ZnO, Bi2O3, and La2O3, on the stoichiometry and dielectric properties of ZST sintered at different temperatures were investigated in this study.

Development of enzymic time-temperature integrators with rapid detection for evaluation of continuous HTST pasteurization processes

The assessment of the thermal process impact in terms of food safety and quality is of great importance for process evaluation and design. This can be accomplished from the analysis of the residence time and temperature distributions coupled with the kinetics of thermal change, or from the use of a proper time-temperature integrator (TTI) as indicator of safety and quality. The objective of this work was to develop and test enzymic TTIs with rapid detection for the evaluation of continuous HTST pasteurization processes (70-85 degrees C, 10-60 s) of low-viscosity liquid foods, such as milk and juices. Enzymes peroxidase, lactoperoxidase and alkaline phosphatase in phosphate buffer were tested and activity was determined with commercial reflectometric strips. Discontinuous thermal treatments at various time-temperature combinations were performed in order to adjust a first order kinetic model of a two-component system. The measured time-temperature history was considered instead of assuming isothermal conditions. Experiments with slow heating and cooling were used to validate the adjusted model. Only the alkaline phosphatase TTI showed potential to be used for the evaluation of pasteurization processes. The choice was based on the obtained z-values of the thermostable and thermolabile fractions, on the cost and on the validation tests. (C) 2012 Elsevier Ltd. All rights reserved.

Deep chlorophyll maximum and upper ocean structure interactions: Case of the Guinea Thermal Dome

Deep Chlorophyll Maximum (DCM) modifies the upper ocean heat capture distribution and thus impacts water column temperature and stratification, as well as biogeochemical processes. This energetical role of the DCM is assessed using a 1 m-resolution 1D physical-biogeochemical model of the upper ocean, using climatological forcing conditions of the Guinea Dome (GD). This zone has been chosen among others because a strong and shallow DCM is present all year round. The results show that the DCM warms the seasonal thermocline by +2 degrees C in September/October and causes an increase of heat transfer from below into the mixed layer (ML) by vertical diffusion and entrainment, leading to a ML warming of about 0.3 degrees C in October. In the permanent thermocline, temperature decreases by up to 2 degrees C. The result is a stratification increase of the water column by 0.3 degrees C m(-1) which improves the thermocline realism when compared with observations. At the same time, the heating associated with the DCM is responsible for an increase of nitrate (+300%, 0.024 mu M), chlorophyll (+50%, 0.02 mu g l(-1)) and primary production (+45%: 10 mg C m(-2) day(-1)) in the ML during the entrainment period of October. The considered concentrations are small but this mechanism could be potentially important to give a better explanation of why there is a significant amount of nitrate in the ML. The mechanisms associated with the DCM presence, no matter which temperature or biogeochemical tracers are concerned, are likely to occur in a wide range of tropical or subpolar regions; in these zones a pronounced DCM is present at least episodically at shallow or moderate depths. These results can be generalized to other thermal dome regions where relatively similar physical and biogeochemical structures are encountered. After testing different vertical resolutions (10 m, 5 m, 2.5 m, 1 m and 0.5 m), we show that using at least a 1 to vertical resolution model is mandatory to assess the energetical importance of the DCM.

Patterns and processes of diversification in a widespread and ecologically diverse avian group, the buteonine hawks (Aves, Accipitridae)

Buteonine hawks represent one of the most diverse groups in the Accipitridae, with 58 species distributed in a variety of habitats on almost all continents. Variations in migratory behavior, remarkable dispersal capability, and unusual diversity in Central and South America make buteonine hawks an excellent model for studies in avian evolution. To evaluate the history of their global radiation, we used an integrative approach that coupled estimation of the phylogeny using a large sequence database (based on 6411 bp of mitochondrial markers and one nuclear intron from 54 species), divergence time estimates, and ancestral state reconstructions. Our findings suggest that Neotropical buteonines resulted from a long evolutionary process that began in the Miocene and extended to the Pleistocene. Colonization of the Nearctic, and eventually the Old World, occurred from South America, promoted by the evolution of seasonal movements and development of land bridges. Migratory behavior evolved several times and may have contributed not only to colonization of the Holarctic, but also derivation of insular species. In the Neotropics, diversification of the buteonines included four disjunction events across the Andes. Adaptation of monophyletic taxa to wet environments occurred more than once, and some relationships indicate an evolutionary connection among mangroves, coastal and varzea environments. On the other hand, groups occupying the same biome, forest, or open vegetation habitats are not monophyletic. Refuges or sea-level changes or a combination of both was responsible for recent speciation in Amazonian taxa. In view of the lack of concordance between phylogeny and classification, we propose numerous taxonomic changes. (C) 2009 Elsevier Inc. All rights reserved.

Use of Gas Diffusion Electrode for the In Situ Generation of Hydrogen Peroxide in an Electrochemical Flow-By Reactor

Hydrogen peroxide is a powerful oxidant that finds application in several areas, but most particularly in the treatment of industrial wastewaters. The aim of the present study was to investigate the effects of applied potential and electrolyte flow conditions on the in situ generation of hydrogen peroxide in an electrochemical flow-by reactor with a gas diffusion electrode (GDE). The electrolyses were performed in an aqueous acidic medium using a GDE constructed with conductive black graphite and polytetrafluoroethylene (80:20 w/w). Under laminar flow conditions (flow rate = 50 L/h), hydrogen peroxide was formed in a maximum yield of 414 mg/L after 2 h at -2.25 V vs Pt //Ag/AgCl (global rate constant = 3.1 mg/(L min); energy consumption = 22.1 kWh/kg). Under turbulent flow (300 L/h), the maximum yield obtained was 294 mg/L after 2 h at -1.75 V vs Pt//Ag/AgCl (global rate constant = 2.5 mg/ (L min); energy consumption = 30.1 kWh/kg).

Weakly anomalous diffusion with non-Gaussian propagators

A poorly understood phenomenon seen in complex systems is diffusion characterized by Hurst exponent H approximate to 1/2 but with non-Gaussian statistics. Motivated by such empirical findings, we report an exact analytical solution for a non-Markovian random walk model that gives rise to weakly anomalous diffusion with H = 1/2 but with a non-Gaussian propagator.

End-to-end Distance Distribution in Fluorescent Derivatives of Bradykinin in Interaction with Lipid Vesicles

Cellular membranes have relevant roles in processes related to proteases like human kallikreins and cathepsins. As enzyme and substrate may interact with cell membranes and associated co-factors, it is important to take into account the behavior of peptide substrates in the lipid environment. In this paper we report an study based on energy transfer in two bradykinin derived peptides labeled with the donor-acceptor pair Abz/Eddnp (ortho-aminobenzoic acid/N-[2,4-dinitrophenyl]-ethylenediamine). Time-resolved fluorescence experiments were performed in phosphate buffer and in the presence of large unilamelar vesicles of phospholipids, and of micelles of sodium dodecyl sulphate (SDS). The decay kinetics were analyzed using the program CONTIN to obtain end-to-end distance distribution functions f(r). Despite of the large difference in the number of residues the end-to-end distance of the longer peptide (9 amino acid residues) is only 20 % larger than the values obtained for the shorter peptide (5 amino acid residues). The proline residue, in position 4 of the bradykinin sequence promotes a turn in the longer peptide chain, shortening its end-to-end distance. The surfactant SDS has a strong disorganizing effect, substantially broadening the distance distributions, while temperature increase has mild effects in the flexibility of the chains, causing small increase in the distribution width. The interaction with phospholipid vesicles stabilizes more compact conformations, decreasing end-to-end distances in the peptides. Anisotropy experiments showed that rotational diffusion was not severely affected by the interaction with the vesicles, suggesting a location for the peptides in the surface region of the bilayer, a result consistent with small effect of lipid phase transition on the peptides conformations.

Residence Time Distribution Models Derived from Non-Ideal Laminar Velocity Profiles in Tubes

The theoretical E-curve for the laminar flow of non-Newtonian fluids in circular tubes may not be accurate for real tubular systems with diffusion, mechanical vibration, wall roughness, pipe fittings, curves, coils, or corrugated walls. Deviations from the idealized laminar flow reactor (LFR) cannot be well represented using the axial dispersion or the tanks-in-series models of residence time distribution (RTD). In this work, four RTD models derived from non-ideal velocity profiles in segregated tube flow are proposed. They were used to represent the RTD of three tubular systems working with Newtonian and pseudoplastic fluids. Other RTD models were considered for comparison. The proposed models provided good adjustments, and it was possible to determine the active volumes. It is expected that these models can be useful for the analysis of LFR or for the evaluation of continuous thermal processing of viscous foods.

Average control of Markov decision processes with Feller transition probabilities and general action spaces

This paper studies the average control problem of discrete-time Markov Decision Processes (MDPs for short) with general state space, Feller transition probabilities, and possibly non-compact control constraint sets A(x). Two hypotheses are considered: either the cost function c is strictly unbounded or the multifunctions A(r)(x) = {a is an element of A(x) : c(x, a) <= r} are upper-semicontinuous and compact-valued for each real r. For these two cases we provide new results for the existence of a solution to the average-cost optimality equality and inequality using the vanishing discount approach. We also study the convergence of the policy iteration approach under these conditions. It should be pointed out that we do not make any assumptions regarding the convergence and the continuity of the limit function generated by the sequence of relative difference of the alpha-discounted value functions and the Poisson equations as often encountered in the literature. (C) 2012 Elsevier Inc. All rights reserved.

Exploration time of static images implying different body movements causes time distortions

Studies of subjective time have adopted different methods to understand different processes of time perception. Four sculptures, with implied movement ranked as 1.5-, 3.0-, 4.5-, and 6.0-point stimuli on the Body Movement Ranking Scale, were randomly presented to 42 university students untrained in visual arts and ballet. Participants were allowed to observe the images for any length of time (exploration time) and, immediately after each image was observed, recorded the duration as they perceived it. The results of temporal ratio (exploration time/time estimation) showed that exploration time of images also affected perception of time, i.e., the subjective time for sculptures representing implied movement were overestimated.\

ESTIMATING REACTION CONSTANTS BY AB INITIO MOLECULAR MODELING: A STUDY ON THE OXIDATION OF PHENOL TO CATECHOL AND HYDROQUINONE IN ADVANCED OXIDATION PROCESSES

Molecular modeling is growing as a research tool in Chemical Engineering studies, as can be seen by a simple research on the latest publications in the field. Molecular investigations retrieve information on properties often accessible only by expensive and time-consuming experimental techniques, such as those involved in the study of radical-based chain reactions. In this work, different quantum chemical techniques were used to study phenol oxidation by hydroxyl radicals in Advanced Oxidation Processes used for wastewater treatment. The results obtained by applying a DFT-based model showed good agreement with experimental values available, as well as qualitative insights into the mechanism of the overall reaction chain. Solvation models were also tried, but were found to be limited for this reaction system within the considered theoretical level without further parameterization.

Skin Penetration Time-Profiles for Continuous 810nm and Superpulsed 904nm Lasers in a Rat Model

Objective: The purpose of this study was to investigate the rat skin penetration abilities of two commercially available low-level laser therapy (LLLT) devices during 150 sec of irradiation. Background data: Effective LLLT irradiation typically lasts from 20 sec up to a few minutes, but the LLLT time-profiles for skin penetration of light energy have not yet been investigated. Materials and methods: Sixty-two skin flaps overlaying rat's gastrocnemius muscles were harvested and immediately irradiated with LLLT devices. Irradiation was performed either with a 810 nm, 200mW continuous wave laser, or with a 904 nm, 60mW superpulsed laser, and the amount of penetrating light energy was measured by an optical power meter and registered at seven time points (range, 1-150 sec). Results: With the continuous wave 810nm laser probe in skin contact, the amount of penetrating light energy was stable at similar to 20% (SEM +/- 0.6) of the initial optical output during 150 sec irradiation. However, irradiation with the superpulsed 904 nm, 60mW laser showed a linear increase in penetrating energy from 38% (SEM +/- 1.4) to 58% (SEM +/- 3.5) during 150 sec of exposure. The skin penetration abilities were significantly different (p < 0.01) between the two lasers at all measured time points. Conclusions: LLLT irradiation through rat skin leaves sufficient subdermal light energy to influence pathological processes and tissue repair. The finding that superpulsed 904nm LLLT light energy penetrates 2-3 easier through the rat skin barrier than 810nm continuous wave LLLT, corresponds well with results of LLLT dose analyses in systematic reviews of LLLT in musculoskeletal disorders. This may explain why the differentiation between these laser types has been needed in the clinical dosage recommendations of World Association for Laser Therapy.

Fiber architecture in remodeled myocardium revealed with a quantitative diffusion CMR tractography framework and histological validation

Background: The study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts. Methods: Diffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy. Results: In normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 +/- 0.16 in normal hearts to 0.22 +/- 0.08 in the remote zone of the remodeled hearts (p<0.05). This was confirmed histologically by the reduction of HA in the subepicardium from -52.03 degrees +/- 2.94 degrees in normal hearts to -37.48 degrees +/- 4.05 degrees in the remote zone of the remodeled hearts (p < 0.05). Conclusions: A significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium, but involves all layers of the myocardium. Tractography-based quantification, performed here for the first time in remodeled hearts, may provide a framework for assessing regional changes in the left ventricle following infarction.