Poly-lactide-co-glycolide microparticle sizes: a rational factorial design and surface response analysis

Microsphere size is a primary determinant of solute release velocity. We present here a rational way for producing PLGA microspheres with different and controlled sizes. The following process variables were studied: Stirring velocity during the second emulsion step, dispersed and continuous phases volume ratio, and poly(vinyl alcohol) concentration in the continuous phase. A full factorial experimental design 2(3) with triplicate at the central point was used to determine the influence of variables on PLGA microsphere mean size. The stirring velocity and poly(vinyl alcohol) concentration were the main variables at 0.95 significance level. An influence of PVA and stirring velocity on microspheres size is observed, there is no correlation for DP/CP volume ratio on size of microspheres. By combining the two variables--the stirring velocity and poly(vinyl alcohol) concentration, the surface response was analyzed. The increase of poly(vinyl alcohol) concentration with concomitant increase on stirring velocity produced microspheres with the lower sized. In contrast the lower poly(vinyl alcohol) concentration and the lower stirring velocity used produced the higher microspheres sized. Uniformly spherical and smooth microspheres (4-15 microm of diameter) were obtained. No significant difference was observed on Ponca S loading within the experimental region. Our results open the possibility of formulating PLGA microspheres with custom sizes performing a minimum of experiments as required for specific applications.     

Nonunitary Lewis Number Effects on the Combustion of a Linear Array of Gaseous Fuel Pockets

The numerical solution for the combustion of an infinite linear array of gaseous fuel pockets in a stagnant oxidizing environment under microgravity conditions is discussed. The gas pocket combustion is described using the generalized Shvab-Zel'dovich formulation with nonunitary Lewis number. The combustion process is considered isobaric and the flow is induced by density gradients due to the heat and mass transfer processes (Stefan flow). The model is based on mass, momentum, excess enthalpy, and mixture fraction conservation equations and considers the Burke-Schumann reaction mechanism and ideal gas behavior. The thermophysical properties, except the density, are assumed constant. The finite-volume method is employed in the numerical solution, using a generalized system of coordinates. A nonstaggered grid is used and the SIMPLEC algorithm is employed to solve the modified pressure-velocity coupling. Nonunitary Lewis number and interaction effects on flame behavior and on the fuel consumption are analyzed. Results show that the nonunitary Lewis number can modify the interaction effects on gas pocket linear array combustion. During the combustion process, the flame can evolve from individual flames around each gas fuel pocket to a merged flame, surrounding the merged fuel region. However, under certain conditions, the merged flame and the merged fuel region can be broken, returning to individual flames around each gas fuel pocket.     

Structural study of a new B-rich phase obtained by partial hydrogenation of 2NaH + MgB2

The structure of an unknown crystalline phase observed during the hydrogen absorption reaction of the powder mixtures 2NaH + MgB₂ at high pressure has been studied by ab-initio structure determination from powder diffraction. The sequence of un-overlapped peaks extracted from the X-ray powder diffraction pattern could be indexed with a primitive cubic cell with lattice parameter a = 7.319 Å. The diffraction patterns of the peaks are matched with the Pa-3 space group. The stoichiometry of the hydrogen absorption reaction suggests the presence of a high-boron content phase in the compound under investigation. Assuming this phase to be composed only by boron atoms and therefore having a density similar to that found for boron polymorphs, the solution with a space group of Pa-3 leads to reasonable B–B interatomic distances.     

Physicochemical and microbiological characterization of the dehydration processing of red pepper fruits for paprika production

In order to determine whether changes in pectin fractions facilitate or not the traditional drying of red pepper fruits (Capsicum annuum L.) and the possible consequences of these changes on the dehydration conditions for paprika processing, that have an impact on the evolution of carotenoid content (responsible for colour), this evolution and other parameters were monitored during a traditional drying process in correlation with the temperature-time combinations used. Evolution of microbial flora was followed to analyse their possible contribution, as an exogenous source, to enzymatic polygalacturonase (PG) activity. Our results indicated that the mild temperature-time regime mediated the selection and proliferation of a microbial flora that contributed to enzymatic PG activity modifying the pectic fraction. The enzymatic activity generated rises in the calcium pectate (CaP) fraction, which favoured the drying of fruit with an initial low content of soluble pectins (SP) and CaP. Thus, the changes in texture helped during the transfer of moisture, facilitating the dehydration process, and therefore, a milder temperature-time regime was required. Consequently, bioactive compounds of the fruit, such as capsorubin, capsanthin and provitamin A carotenoids, remained almost unaltered. On the other hand, when the SP fraction increased during dehydration, the process was delayed, and this was also correlated with a higher content in SP and CaP in fresh fruit, indicating that the fruits were harvested at a later stage of ripeness. In this case a more intense temperature-time regime was needed, negatively affecting the carotenoid content by decreasing it significantly.     

Control electronic platform based on floating-point DSP and FPGA for a NPC multilevel back-to-back converter

Modern energy concepts as Distributed Power Generation are changing the appearance of electric distribution and transmission and challenging power electronics researchers, which try to develop new solutions of electronic controllers. The aim is to enable the implementation of new and more complex control algorithms to verify the last standards related to the grid energy quality for new power converters, and, also, for equipments which nowadays are operating. This paper presents the design, implementation and test of a novel real-time controller for a Neutral Point Clamped (NPC) (three-level) multilevel converter based on a floating-point Digital Signal Processor (DSP) and on a Field-Programmable Gate Array (FPGA), by operating in a cooperative way. Although the proposed system can be readily applied to any power electronic application, in this work, it is focused on the next system: a 150 kVA back-to-back three-level NPC Voltage Source Converter (VSC) for wind power applications.     

Characteristics of Virgin Olive Oils from the Olive Zone of Extremadura (Spain), and an Approximation to their Varietal Origin

We studied the differences in the characteristics that typify virgin olive oils produced in three representative zones of Extremadura: Sierra Norte of Cáceres, Serena–Siberia, and Tierra de Barros. A total of 156 samples from those three zones were assayed for fatty acids, triglycerides, sterols, and erythrodiol + uvaol. Statistically significant differences (p < 0.05) were found between the mean values of the parameters corresponding to the three zones. These profiles were then used to classify the varietal origin of the oils using the discriminant functions that had previously been defined by the authors for these parameters. This classification, together with the production data, confirmed the use of the different varieties of olives in the study zones. The results showed Manzanilla Cacereña to be the most used variety in the Sierra Norte of Cáceres zone, Cornezuelo and Verdial de Badajoz with a slight presence of Picual in the Serena–Siberia zone, and Carrasqueña and Morisca in Tierra de Barros.     

Enhanced fibroblast adhesion and proliferation on electrospun fibers obtained from poly(isosorbide succinate-b-l-lactide) block copolymers

Block copolymers containing isosorbide succinate and l-lactic acid repeating units with different mass compositions were synthesized in two steps: bulk ring-opening copolymerization from l-lactide and poli(isosorbide succinate) (PIS) preoligomer, in the presence of tin(II) 2-ethylhexanoate as catalyst, followed by chain extension in solution by using hexamethylene diisocyanate. Poly(l-lactide) (PLLA) and a chain extension product from PIS were also obtained, for comparison. SEC, ¹H and ¹³C NMR, MALDI-TOFMS, WAXD, DSC, TG, and contact angle measurements were used in their characterization. The incorporation of isosorbide succinate into PLLA main backbone had minor effect on the thermal stability and the T_g of the products. However, it reduced the crystallinity and increased the surface energy in relation to PLLA. Nonwoven mats of the block copolymers and PLLA obtained by electrospinning technique were submitted to fibroblasts 3T3-L1 cell culture. The copolymers presented enhanced cell adhesion and proliferation rate as revealed by MTT assay and SEM images.     

Effect of extrusion on the emulsifying properties of soybean proteins and pectin mixtures modelled by response surface methodology

The objective of this study was to apply response surface methodology to estimate the emulsifying capacity and stability of mixtures containing isolated and textured soybean proteins combined with pectin and to evaluate if the extrusion process affects these interfacial properties. A simplex-centroid design was applied to the model emulsifying activity index (EAI), average droplet size (D_[4,3]) and creaming inhibition (CI%) of the mixtures. All models were significant and able to explain more than 86% of the variation. The high predictive capacity of the models was also confirmed. The mean values for EAI, D_[4,3] and CI% observed in all assays were 0.173 ± 0.015 nm, 19.2 ± 1.0 μm and 53.3 ± 2.6%, respectively. No synergism was observed between the three compounds. This result can be attributed to the low soybean protein solubility at pH 6.2 (<35%). Pectin was the most important variable for improving all responses. The emulsifying capacity of the mixture increased 41% after extrusion. Our results showed that pectin could substitute or improve the emulsifying properties of the soybean proteins and that the extrusion brings additional advantage to interfacial properties of this combination.     

A Lagrangean relaxation approach for QoS networks CFA problems

This paper is about design methodologies for packet networks, under the constraints of end-to-end quality of service (QoS) metrics. The network modeling also considers the dynamics of today's packet networks. We are particularly considering the problem of capacity and flow assignment where the routing assignments and capacities are considered to be decision variables. An efficient Lagrangean relaxation-based heuristic procedure is developed to find bounds and solutions for a corporate virtual private network (VPN), where the traffic is mostly based on TCP connections. Numerical results for a variety of problem instances are reported.     

Analysis and optimal individual pitch control decoupling by inclusion of an azimuth offset in the multiblade coordinate transformation

With the trend of increasing wind turbine rotor diameters, the mitigation of blade fatigue loadings is of special interest to extend the turbine lifetime. Fatigue load reductions can be partly accomplished using individual pitch control (IPC) facilitated by the so‐called multiblade coordinate (MBC) transformation. This operation transforms and decouples the blade load signals in a yaw‐axis and tilt‐axis. However, in practical scenarios, the resulting transformed system still shows coupling between the axes, posing a need for more advanced multiple input multiple output (MIMO) control architectures. This paper presents a novel analysis and design framework for decoupling of the nonrotating axes by the inclusion of an azimuth offset in the reverse MBC transformation, enabling the application of simple single‐input single‐output (SISO) controllers. A thorough analysis is given by including the azimuth offset in a frequency‐domain representation. The result is evaluated on simplified blade models, as well as linearizations obtained from the NREL 5–MW reference wind turbine. A sensitivity and decoupling assessment justify the application of decentralized SISO control loops for IPC. Furthermore, closed‐loop high‐fidelity simulations show beneficial effects on pitch actuation and blade fatigue load reductions.