Scheduling of unrelated parallel machines: an application to PWB manufacturing

In this paper, we tackle scheduling the bottleneck operation of a Printed Wiring Board (PWB) manufacturing line. The problem may be characterized as unrelated parallel machines and we are interested in several performance measures including: makespan, the average finish time, mean flow time, utilization, the number of lots and the total amount of overtime beyond the release interval. Due to setup reduction techniques employed by the company, setups are negligible, and we construct an Integer Programming (IP) model with a special structure - >unimodularity. Thus, the corresponding linear programming optimal solution always satisfies the integrality constraints. In order to account for multiple objectives of the scheduling system, we introduce preference constraints and bring them into the objective function by Lagrangian Relaxation (LR). We give a heuristic procedure to select constraints to be relaxed, and formulations to determine the Lagrange multipliers. To verify the validity of the proposed method, we compare it with a network model and with a modified FIFO method. The proposed method presents very promising results in terms of our measures of interest.     

Development and characterization of printable PLA/β-TCP bioactive composites for bone tissue applications

In this study, poly(lactic acid) (PLA) and PLA/β-tricalcium phosphate (TCP) biocomposites were developed by melt compounding using an internal melt mixer with three different TCP contents (5, 10, and 25 wt%). A comprehensive analysis of the thermal, rheological, and mechanical properties of these biocomposites was performed. TCP presented proper distribution in the PLA/TCP biocomposites: PLA5TCP and PLA10TCP exhibited rheological behavior similar to that of neat PLA. However, PLA25TCP presented significant agglomeration and reduction in thermal stability. Addition of TCP to the biocomposites enhanced their bioactivity and biocompatibility. The bioactivity assay was conducted by immersing the samples in SBF solution for 7 and 21 days, and the SEM and XRD surface analyses of the PLA/TCP biocomposites presented evidence of carbonated hydroxyapatite formation. The biocompatibility assay was performed using the extract method until 7 days, and PLA10TCP presented improved relative cell viability compared with the control. Finally, since the materials presented suitable thermal and rheological properties, filaments for additive manufacturing (AM) were developed, and they were used to produce screw models for bone-ligament fixation. The 3D printed screws exhibited excellent printability and accuracy. Therefore, the PLA/TCP biocomposites developed can be used in further biomedical applications using AM, namely, guided bone tissue engineering.     

Microscopic evidences that bone marrow mononuclear cell treatment improves sciatic nerve regeneration after neurorrhaphy

Cell therapy constitutes a possibility for improving nerve regeneration, increasing the success of nerve repair. We evaluate the use of mononuclear cells in the regeneration of the sciatic nerve after axotomy followed by end‐to‐end neurorrhaphy. Forty adult male Wistar rats (250–300 g) were divided into four groups: (1) sham, (2) neurorrhaphy: the sciatic nerve was sectioned and repaired using epineural sutures, (3) culture medium: after the suture, received an injection of 10 μL of culture medium into the nerve, and (4) mononuclear cell: after the suture, a concentration of 3 × 10⁶ of mononuclear cell was injected in epineurium region. Mononuclear cells were obtained from the bone marrow aspirates and separated by Ficoll‐Hypaque method. The histological analyses were performed at the 4th postoperative day. The sciatic functional index, histological, and morphometric analyzes were used to evaluate nerve regeneration at the 6th postoperative week. Six rats were used for immunohistochemical analysis on the 4th postoperative day. In the group 4, on the fourth day, the histological analysis demonstrated a more accelerated degenerative process and an increase of the neurotrophic factors was observed. In the 6th week, all the morphometric results of the group 4 were statistically better compared with groups 2 and 3. There was a statistically significant improvement in the sciatic functional index for group 4 compared with groups 2 and 3. Mononuclear cells stimulated nerve regeneration, most probably by speeding up the Wallerian degeneration process as well as stimulating the synthesis of neurotrophic factors. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

Safety performance models for urban intersections in Brazil

This paper presents a modeling effort for developing safety performance models (SPM) for urban intersections for three major Brazilian cities. The proposed methodology for calibrating SPM has been divided into the following steps: defining the safety study objective, choosing predictive variables and sample size, data acquisition, defining model expression and model parameters and model evaluation. Among the predictive variables explored in the calibration phase were exposure variables (AADT), number of lanes, number of approaches and central median status. SPMs were obtained for three cities: Fortaleza, Belo Horizonte and Brasília. The SPM developed for signalized intersections in Fortaleza and Belo Horizonte had the same structure and the most significant independent variables, which were AADT entering the intersection and number of lanes, and in addition, the coefficient of the best models were in the same range of values. For Brasília, because of the sample size, the signalized and unsignalized intersections were grouped, and the AADT was split in minor and major approaches, which were the most significant variables. This paper also evaluated SPM transferability to other jurisdiction. The SPM for signalized intersections from Fortaleza and Belo Horizonte have been recalibrated (in terms of the C_x) to the city of Porto Alegre. The models were adjusted following the Highway Safety Manual (HSM) calibration procedure and yielded C_x of 0.65 and 2.06 for Fortaleza and Belo Horizonte SPM respectively. This paper showed the experience and future challenges toward the initiatives on development of SPMs in Brazil, that can serve as a guide for other countries that are in the same stage in this subject.     

The influence of different zeolitic supports on hydrogen production and waste degradation

The photocatalyst composition affects the chemical–physical properties and directly impacts photocatalytic activity, both in the hydrogen production and degradation of organic contaminants. In this work, the influence of zeolitic structures NaA, NaY, and ZSM-5 combined with a 10% active phase, TiO₂ catalyst doped with 1% copper, and cobalt cocatalysts was tested to mineralize the reactive blue dye (CI250) and to produce hydrogen by photocatalysis under ultraviolet radiation. The band gap energy was affected mainly by the cocatalyst, while the Brunauer-Emmett-Teller method (BET) area was affected by the zeolite structure as well as the X-ray diffraction (XRD). The most active catalyst was the Cu@TiO₂/NaY, which promoted a hydrogen production rate of 240 μmolH₂gcat⁻¹ using 10% ethanol (v/v) aqueous solution as a sacrificial agent and mineralization of 53% of the organic dye, followed by the catalysts impregnated on ZSM-5 zeolites, which had discolouration up to 50% and hydrogen evolution of 92.6 and 109.7 μmolH₂gcat⁻¹ for the catalyst doped with Cu and Co, respectively.