Influência de variáveis de processo sobre a cinética de secagem de abóbora (Cucurbita moschata)

Pós-graduação em Engenharia e Ciência de Alimentos - IBILCE

Desidratação de polpa de manga em leito de espuma com e sem intermitência térmica

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

Effects of edible coatings on convective drying and characteristics of the dried pineapple

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento e estudo de materiais híbridos siloxano-poli(óxipropileno) para liberação prolongada do cloridrato de propranolol

Pós-graduação em Química - IQ

Mass transport in polymers

The study of mass transport in polymeric membranes has grown in importance due to its potential application in many processes such as separation of gases and vapors, packaging, controlled drug release. The diffusion of a low molecular weight species in a polymer is often accompanied by other phenomena like swelling, reactions, stresses, that have not been investigated in all their aspects yet. Furthermore, novel materials have been developed that include inorganic fillers, reactive functional groups or ions, that make the scenery even more complicated. The present work focused on the experimental study of systems where the diffusion is accompanied by other processes; suitable models were also developed to describe the particular circumstances in order to understand the underlying concepts and be able to design the performances of the material. The effect of solvent-induced deformation in polymeric films during sorption processes was studied since the dilation, especially in constrained membranes, can cause the development of stresses and therefore early failures of the material. The bending beam technique was used to test the effects of the dilation and the stress induced in the polymer by penetrant diffusion. A model based on the laminate theory was developed that accounts for the swelling and is able to predict the stress that raise in the material. The addition of inorganic fillers affects the transport properties of polymeric films. Mixed matrix membranes based on fluorinated, high free volume matrices show attractive performances for separation purposes but there is a need for deeper investigation of the selectivity properties towards gases and vapors. A new procedure based on the NELF model was tested on the experimental data; it allows to predict solubility of every penetrant on the basis of data for one vapor. The method has proved to be useful also for the determination of the diffusion coefficient and for an estimation of the permeability in the composite materials. Oxygen scavenging systems can overcome lack of barrier properties in common polymers that forbids their application in sensitive applications as food packaging. The final goal of obtaining a membrane almost impermeable to oxygen leads to experimental times out of reach. Hence, a simple model was developed in order to describe the transport of oxygen in a membrane with also reactive groups and analyze the experimental data collected on SBS copolymers that show attractive scavenging capacity. Furthermore, a model for predicting the oxygen barrier behavior of a film formed as a blend of OSP in a common packaging material was built, considering particles capable of reactions with oxygen embedded in a non-reactive matrix. Perfluorosulphonic acid ionomers (PFSI) are capturing attention due to a high thermal and chemical resistance coupled with very peculiar transport properties, that make them appropriate to be used in fuel cells. The possible effect of different formation procedure was studied together with the swelling due to water sorption since both water uptake and dilation can dramatically affect the fuel cells performances. The water diffusion and sorption was studied with a FTIR-ATR spectrometer that can give deeper information on the bonds between water molecules and the sulphonic hydrophilic groups and, therefore, on the microstructure of the hydrated ionomer.

Fine control of drug delivery for cochlear implant applications

Cochlear implants are neuroprostheses that are inserted into the inner ear to directly electrically stimulate the auditory nerve, thus replacing lost cochlear receptors, the hair cells. The reduction of the gap between electrodes and nerve cells will contribute to technological solutions simultaneously increasing the frequency resolution, the sound quality and the amplification of the signal. Recent findings indicate that neurotrophins (NTs) such as brain derived neurotrophic factor (BDNF) stimulate the neurite outgrowth of auditory nerve cells by activating Trk receptors on the cellular surface (1–3). Furthermore, small-size TrkB receptor agonists such as di-hydroxyflavone (DHF) are now available, which activate the TrkB receptor with similar efficiency as BDNF, but are much more stable (4). Experimentally, such molecules are currently used to attract nerve cells towards, for example, the electrodes of cochlear implants. This paper analyses the scenarios of low dose aspects of controlled release of small-size Trk receptor agonists from the coated CI electrode array into the inner ear. The control must first ensure a sufficient dose for the onset of neurite growth. Secondly, a gradient in concentration needs to be maintained to allow directive growth of neurites through the perilymph-filled gap towards the electrodes of the implant. We used fluorescein as a test molecule for its molecular size similarity to DHF and investigated two different transport mechanisms of drug dispensing, which both have the potential to fulfil controlled low-throughput drug-deliverable requirements. The first is based on the release of aqueous fluorescein into water through well-defined 60-μm size holes arrays in a membrane by pure osmosis. The release was both simulated using the software COMSOL and observed experimentally. In the second approach, solid fluorescein crystals were encapsulated in a thin layer of parylene (PPX), hence creating random nanometer-sized pinholes. In this approach, the release occurred due to subsequent water diffusion through the pinholes, dissolution of the fluorescein and then release by out-diffusion. Surprisingly, the release rate of solid fluorescein through the nanoscopic scale holes was found to be in the same order of magnitude as for liquid fluorescein release through microscopic holes.

Community Structurein Soil Porous System.

Soil is well recognized as a highly complex system. The interaction and coupled physical, chemical, and biological processes and phenomena occurring in the soil environment at different spatial and temporal scales are the main reasons for such complexity. There is a need for appropriate methodologies to characterize soil porous systems with an interdisciplinary character. Four different real soil samples, presenting different textures, have been modeled as heterogeneous complex networks, applying a model known as the heterogeneous preferential attachment. An analytical study of the degree distributions in the soil model shows a multiscaling behavior in the connectivity degrees, leaving an empirically testable signature of heterogeneity in the topology of soil pore networks. We also show that the power-law scaling in the degree distribution is a robust trait of the soil model. Last, the detection of spatial pore communities, as densely connected groups with only sparser connections between them, has been studied for the first time in these soil networks. Our results show that the presence of these communities depends on the parameter values used to construct the network. These findings could contribute to understanding the mechanisms of the diffusion phenomena in soils, such as gas and water diffusion, development and dynamics of microorganisms, among others.

White and gray matter development in human fetal, newborn and pediatric brains

Brain anatomy is characterized by dramatic growth from the end of the second trimester through the neonatal stage. The characterization of normal axonal growth of the white matter tracts has not been well-documented to date and could provide important clues to understanding the extensive inhomogeneity of white matter injuries in cerebral palsy (CP) patients. However, anatomical studies of human brain development during this period are surprisingly scarce and histology-based atlases have become available only recently. Diffusion tensor magnetic resonance imaging (DTMRI) can reveal detailed anatomy of white matter. We acquired diffusion tensor images (DTI) of postmortem fetal brain samples and in vivo neonates and children. Neural structures were annotated in two-dimensional (2D) slices, segmented, measured, and reconstructed three-dimensionally (3D). The growth status of various white matter tracts was evaluated on cross-sections at 19-20 gestational weeks, and compared with 0-month-old neonates and 5- to 6-year-old children. Limbic, commissural, association, and projection white matter tracts and gray matter structures were illustrated in 3D and quantitatively characterized to assess their dynamic changes. The overall pattern of the time courses for the development of different white matter is that limbic fibers develop first and association fibers last and commissural and projection fibers are forming from anterior to posterior part of the brain. The resultant DTNIRI-based 3D human brain data will be a valuable resource for human brain developmental study and will provide reference standards for diagnostic radiology of premature newborns. (c) 2006 Elsevier Inc. All rights reserved.

MRI pressure and stress measurement in novel homogeneous soft solids

This paper presents MRI measurements of a novel semi solid MR contrast agent to pressure. The agent is comprised of potassium chloride cross linked carageenan gum at a concentration of 2% w/v, with micron size lipid coated bubbles of air at a concentration of 3% v/v. The choice for an optimum suspending medium, the methods of production and the preliminary MRI results are presented herein. The carageenan gum is shown to be ideally elastic for compressions relating to volume changes less than 15%, in contrast to the inelastic gellan gum also tested. Although slightly lower than that of gellan gum, carageenan has a water diffusion coefficient of 1.72×10-9 m2.s-1 indicating its suitability to this purpose. RARE imaging is performed whilst simultaneously compressing test and control samples and a maximum sensitivity of 1.6% MR signal change per % volume change is found which is shown to be independent of proton density variations due to the presence of microbubbles and compression. This contrast agent could prove useful for numerous applications, and particularly in chemical engineering. More generally the method allows the user to non-invasively image with MRI any process that causes, within the solid, local changes either in bubble size or bubble shape. © 2008 American Institute of Physics.

Analysis of the moisture effect on the mechanical behaviour of an adhesively bonded joint under proportional multi-axial loads

The objective of the study is to identify the 3D behaviour of an adhesive in an assembly, and to take into account the effect of ageing in a marine environment. To that end, three different tests were employed. Gravimetric analyses were used to determine the water diffusion kinetics in the adhesive. Bulk tensile tests were performed to highlight the effects of humid ageing on the adhesive behaviour. Modified Arcan tests were performed for several ageing times to obtain the experimental database which was necessary to identify constitutive models. A Mahnken-Schlimmer type model was determined for the unaged state according to a procedure developed in a previous study. This identification used inverse techniques. It was based on the unaged modified Arcan results and on a coupling between an optimisation routine and finite-element analysis. Then, a global inverse identification procedure was developed. Its aim was to relate the unaged parameters to the moisture concentration and overcome the difficulties usually associated with ageing of bonded assemblies in a humid environment: a non-uniformity of the stress state and a gradient of mechanical properties in the adhesive. This procedure was similar to the one used in the first part but needed modified Arcan results for several ageing times. It also required an initial assumption for the evolution of the Mahnken-Schlimmer parameters with the moisture concentration.

Arsenic Geochemitry in Warm Spring Ponds: New Field and Experimental Results

Silver Bow Creek (SBC) flows into the Warm Springs Ponds Operable Unit (WSPOU), where various containment cells are used to precipitate copper and other metals (e.g., Cd, Cu, Mn, Pb, Zn). Lime is added seasonally to increase the pH and assist in removal of metals from the water column. Although the WSPOU is effective at removing copper and other cationic trace metals, concentrations of dissolved arsenic exiting the facility are often above the site specific standard, 20 20 ug/L, during low-flow periods each summer and fall. This thesis is a continuation of arsenic geochemistry studies by Montana Tech in the WSPOU. Field work focused on Pond 3, the largest and first in the series of treatment ponds. Shallow groundwater was sampled from 8 PVC piezometers located near the south end of Pond 3. Three sediment pore-water diffusion samplers (“peepers”) were also deployed at the south end of Pond 3 to examine vertical gradients in chemistry in the top 25 cm of the pond sediment. In general, the pH and Eh values of the shallow groundwater and sediment pore-water were less than in the pond water. Concentrations of arsenic were generally higher in subsurface water, and tended to pass through a maximum (up to 530 g/L) about 10 cm below the sediment-water interface. In the peeper cells, there was a strong positive correlation between dissolved As and dissolved Fe, and an inverse correlation with sulfate. Therefore, the zone of arsenic release corresponds to a zone of bacterial Fe and sulfate reduction in the shallow, organic-rich sediment. Redox speciation of arsenic shows that arsenate (As(V)) is dominant in the pond, and arsenite (As(III)) is dominant in the subsurface water. A series of laboratory experiments with pH adjustment were completed using SBC water collected near the inlet to the WSPOU as well as water and shallow sediment collected from Pond 3. Water ± sediment mesocosms were set up in 1-L Nalgene bottles (closed system) or a 20-L aquarium (open system), both with continuous stirring. The pH of the mesocosm was adjusted by addition of NaOH or HNO3 acid. The closed system provided better pH control since the water was not in contact with the atmosphere, which prevented exchange of carbon dioxide. In both the closed and open systems, dissolved arsenic concentrations either decreased or stayed roughly the same with increase in pH to values > 11. Therefore, the release of dissolved As into the treatment ponds in low-flow periods is not due to changes in pH alone. All of these results support the hypothesis that the arsenic release in WSPOU is linked to microbial reduction of ferric oxide minerals in the organic-rich sediment. Upwards diffusion of dissolved As from the sediment pore-water into the pond water is the most likely explanation for the increase in As concentration of the WSPOU in low-flow periods.

Diffusion anomaly and dynamic transitions in the Bell-Lavis water model

In this paper we investigate the dynamic properties of the minimal Bell-Lavis (BL) water model and their relation to the thermodynamic anomalies. The BL model is defined on a triangular lattice in which water molecules are represented by particles with three symmetric bonding arms interacting through van der Waals and hydrogen bonds. We have studied the model diffusivity in different regions of the phase diagram through Monte Carlo simulations. Our results show that the model displays a region of anomalous diffusion which lies inside the region of anomalous density, englobed by the line of temperatures of maximum density. Further, we have found that the diffusivity undergoes a dynamic transition which may be classified as fragile-to-strong transition at the critical line only at low pressures. At higher densities, no dynamic transition is seen on crossing the critical line. Thus evidence from this study is that relation of dynamic transitions to criticality may be discarded. (C) 2010 American Institute of Physics. [doi:10.1063/1.3479001]

Surface treatment of reinforced concrete in marine environment: Influence on chloride diffusion coefficient and capillary water absorption

There are currently many types of protective materials for reinforced concrete structures and the influence of these materials in the chloride diffusion coefficient still needs more research. The aim of this paper is to study the efficacy of certain surface treatments (such as hydrophobic agents, acrylic coating, polyurethane coating and double systems) in inhibiting chloride penetration in concrete. The results indicated that all tested surface protection significantly reduced the sorptivity of concrete (reduction rate > 70%). However, only the polyurethane coating was highly effective in reducing the chloride diffusion coefficient (reduction rate of 86%). (C) 2008 Elsevier Ltd. All rights reserved.

Nmr imaging of the diffusion of water into poly(tetrahydrofurfuryl methacrylate-co-hydroxyethyl methacrylate)

0Nuclear magnetic resonance (n.m.r.) imaging was used to study the ingress of water into poly(tetrahydrofurfuryl methacrylate-co-hydroxyethyl methacrylate). The study offers strong evidence that the diffusion is Fickian in nature. The diffusion coefficient, D, obtained by fitting the underlying diffusion profile, attainable from the images, according to the equation for Fickian diffusion, is 1.5 x 10(-11) m(2) s(-1), which is in good correlation with the value of 2.1 x 10(-11) m(2) s(-1), obtained from mass uptake measurements. Additionally, from the T-2-weighted images, Superimposed features observed in addition to the underlying Fickian diffusion profiles were shown to have a longer spin-spin relaxation time, T-2. This Suggests the presence of two types of water within the polymer matrix; a less mobile phase of absorbed water that is interacting strongly with the polymer matrix and a more mobile phase of absorbed water residing within the cracks observed in the environmental scanning electron micrograph. (C) 1997 Elsevier Science Ltd.