PCL/β-AgVO3 nanocomposites obtained by solvent casting as potential antimicrobial biomaterials

The adhesion of microorganisms on biomaterials can impair its effective application. The addition of antimicrobial agents is a promising alternative to overcome this limitation. In this work, films of polycaprolactone (PCL) and nanostructured β-AgVO₃ (SV) were produced by solvent casting with 0.1, 0.5, and 1.0 wt% of SV. The effect of SV on the structure of PCL was investigate using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The antimicrobial activity of the films against Staphylococcus aureus and Escherichia coli was evaluated by the agar diffusion method and by direct contact test. FTIR confirmed the presence of SV into the PCL films, with chemical interaction between them. SEM showed that SV nanorods were well dispersed and with good interfacial adhesion with PCL. XRD diffraction and Raman spectroscopy showed that the presence of SV increased the number of nucleation sites, reducing the size of crystallites and increasing the amorphous domains in the PCL matrix, consequently reducing crystallinity. This behavior was confirmed by DSC, which showed a reduction in the crystallinity with increasing SV content. Films with 1 wt% of SV showed antimicrobial activity against Staphylococcus aureus in direct contact test.     

Analysis of the conditions for the worst case switching activity in integrated circuits

Relentless advances in IC technologies have fueled steady increases on fabricated component density and working frequencies. As feature sizes decrease to nanometer scales, an increase in switching activity per unit of area and time is observed. When extreme switching activity occurs in a small region of an integrated circuit, malfunctions may be triggered that compromise behavior. This can be either a consequence of a decrease in bias levels in the power grid caused by IR-Drop, or due to unexpected glitching on gates’ outputs caused by ground bounce. For proper circuit verification, both conditions have to be accurately estimated and accounted for. Achieving this in an accurate manner for a large circuit is a very challenging problem. In this paper we propose and compare methods for the identification of the conditions leading to extreme situations of switching activity in integrated circuits. Our approach is based on both spatial and time partitioning which are used to address the accuracy and computational requirements. We propose a method for determining the exact conditions for worst case switching activity in a small circuit area during a short time interval. We then show how this method can be combined with partitioning to allow for accurate full circuit verification.     

Accumulation and apparent recovery of N,P and K after the incorporation of gliricidia and manure in intercropping during the cultivation of corn–cowpea–cotton

Fertilization with manure is widely adopted by farmers in the semiarid region of northeastern Brazil, although the quantity of available manure is limited. Thus, among other alternatives, gliricidia has been used as an additional source of organic fertilizer. The objective of this study was to evaluate the accumulation and apparent recovery of N, P and K after using different forms of gliricidia and manure application in the intercropping of corn, cowpea and cotton in three crop cycles in the semi-arid northeast region of Brazil. The following treatments were used: gliricidia incorporated into the soil before planting; gliricidia spread on the surface of the soil at 45 days after planting; manure and gliricidia incorporated into the soil before planting; manure incorporated into the soil before planting and gliricidia spread on the surface of the soil at 45 days after planting; manure incorporated into the soil before planting; and no addition of organic fertilizer (control). Accumulations followed the same pattern as biomass production but differed greatly from the concentrations. Low apparent recoveries were obtained in the first and second cycles, and high apparent recoveries were obtained in the third cycle. The nutrient balances indicated that the incorporation of gliricidia before planting or spread on the surface does not meet crop needs. The incorporation of manure as well as manure and gliricidia when applied on the surface, were able to meet growth needs and maintain soil fertility.     

An integrated semantics for reasoning about SysML design models using refinement

SysML is a variant of UML for systems design. Several formalisations of SysML (and UML) are available. Our work is distinctive in two ways: a semantics for refinement and for a representative collection of elements from the UML4SysML profile (blocks, state machines, activities, and interactions) used in combination. We provide a means to analyse and refine design models specified using SysML. This facilitates the discovery of problems earlier in the system development lifecycle, reducing time, and costs of production. Here, we describe our semantics, which is defined using a state-rich process algebra and implemented in a tool for automatic generation of formal models. We also show how the semantics can be used for refinement-based analysis and development. Our case study is a leadership-election protocol, a critical component of an industrial application. Our major contribution is a framework for reasoning using refinement about systems specified by collections of SysML diagrams.     

Requirements engineering in software product line engineering

Many attempts have been made to increase the productivity and quality of software products based on software reuse. Software product line practice is one such approach, one that focuses on developing a family of products which have a majority of features in common. Hence, there are numerous requirements that are common across the family, but others are unique to individual products. Traditional requirements engineering methods were conceived to deal with single product requirements and are usually not flexible enough to address the needs arising from reusing requirements for a family of products. There is also the additional burden of correctly identifying and engineering both product-line-wide requirements and product-specific requirements as well as evolving them. Therefore, in this special issue, we want to highlight the importance and the role of requirements engineering for product line development as well as to provide insights into the state of the art in the field.     

Vibrations of axially moving flexible beams made of functionally graded materials

Problems related to the vibrations of axially moving flexible beams made of functionally graded materials are addressed. The problem of an axially moving beam may be interpreted as a telescopic system in which the mass is not constant, the mechanism of elastic deformation is transverse bending. A thin-walled beam with annular cross-section is analyzed, in which a continuously graded variation in the composition of ceramic and metal phases across the wall thickness with a simple power law is considered. In this paper a finite element scheme is employed to obtain numerical approximations to the variational equation of the problem. Normally, finite element approaches use fixed-size elements, however, for this kind of problems the increase of the number of elements, step by step as the mass enters, is a cumbersome task. For this reason an approach based on a beam-element of variable domain is adopted. The length of the element is a prescribed function of time. Results highlighting the effects of the beam flexibility, tip mass and material constituents on the dynamics of the axially moving beams are presented and the corresponding conclusions are given.     

Improved Production of Cyclodextrins by Alkalophilic Bacilli Immobilized on Synthetic or Loofa Sponges

This study aimed to improve the production of β-cyclodextrin (β-CD) by microbial cells immobilized on synthetic or loofa sponges both with and without the use of alginate or chitosan. The most suitable matrix for the immobilization of Bacillus firmus strain 7B was synthetic sponge and for Bacillus sphaericus strain 41 was loofa sponge. After 330 days of storage, the β-CD production by Bacillus firmus and Bacillus sphaericus remained at around 41% and 49%, respectively, of initial levels. After 24 days of immobilization on loofa sponge, Bacillus sphaericus strain 41 achieved an improved operational stability, reaching 86.6 mM β-CD after 20 days of production, compared to only 32.8 mM of β-CD produced by free Bacillus sphaericus strain 41 cells. The expected increase in β-CD production by immobilized cells of Bacillus firmus strain 7B on synthetic sponge for 4 days was not statistically different to that for cells immobilized for 24 days. The application of this process on an industrial scale using loofa sponge, an inexpensive and renewable matrix, will allow the stable production of β-CD.