Biodegradable hollow microfibres to produce bioactive scaffolds

Biodegradable hollow microfibres containing particles loaded with specific active agents can be potentially employed to produce a special kind of substrate for tissue engineering, able to function as a scaffold and at the same time to act as a drug‐releasing system. Biodegradable hollow microfibres based on poly(lactic acid) were produced by a dry–wet spinning procedure. Drug‐loaded microparticles were prepared by a simple oil‐in‐water emulsion and entrapped inside the fibres. The morphology of both fibres and particles was investigated by scanning electron microscopy. The mechanical and thermal properties of the fibres were investigated by tensile tests and differential scanning calorimetry. In vitro tests were performed to evaluate the release of the drug from the fibres loaded with the particles Copyright © 2004 Society of Chemical Industry     

THE EFFECT OF CATHODIC PROTECTION POTENTIAL ON CORROSION FATIGUE CRACK GROWTH RATE OF AN OFFSHORE STRUCTURAL STEEL

Abstract— Duplicate tests have been performed to determine the effect of cathodic protection potential on corrosion fatigue crack growth rate of a modern offshore structural steel, produced by thermo-mechanically controlled processes. The experiments were carried out using compact tension specimens exposed to artificial seawater at 10°C and subjected to constant amplitude loading at 0.35 Hz. Reproducible results showed that the merits of cathodic protection potentials are strongly dependent on stress intensity ratio R and stress intensity range Δ K . It appears that a specific value of cathodic potential may not give comprehensive protection against corrosion fatigue within the spectrum of variable amplitude loading experienced in service. Fractography showed the initiation of secondary cracks on the fracture surface to be associated with the dissolution of calcium sulphide inclusions, regardless of imposed cathodic potential.     

Optimizing the order picking of a scholar and office supplies warehouse

The warehouse operation planning in the scholar and office supplies industry encompasses the activities of receiving, storing, order picking, and shipping products. The order picking operation is a laborious and capital intensive procedure. Despite the extensive literature to solve practical problems of warehouse routing as a step of the order picking process, the application of general approaches to deal with the routing of the warehouse pickers is not straightforward given the specific conditions and configurations and the singular design and operational policies commonly found in practice. In this paper, we present an optimization approach to the stacker routing problem found in the order picking of a Brazilian scholar and office supplies company. The approach is based on a routing algorithm that solves different integer linear problems to define the optimal routes of the stacker inside the facility. The solutions of several numerical experiments show the potential and effectiveness of the approach, for instance, that only one fifth of the routes actually performed by the company are optimal and that the algorithm application to a real set of batches reduced by more than one fourth the total distance monthly traveled by the stacker.     

Analyzing the Trade-off Between Investing in Service Channels and Satisfying the Targeted User Service for Brazilian Internet Service Providers

The computer connection to the Internet is provided by firms known as internet service providers (ISPs). The simplest mode of physical connection is when the user connects to an ISP's service channel by an ordinary telephone line (dial-up). Finding an available channel may not be an easy task, especially during the peak hours of many Brazilian ISPs. This results in a problem for the ISPs, which is how to achieve the most appropriate trade-off between investing in capacity and satisfying the target user service level. This paper analyzes this trade-off based on a three-step approach: (i) determine user arrival and service processes in chosen periods, (ii) select an appropriate queueing model using some simplifying assumptions, and (iii) generate trade-off curves between system performance measures. To illustrate the application of this approach, some results derived from a case study performed at an ISP in Sao Paulo state are given.     

Interdiffusion in the CuAu thin film system at 25°C to 250°C

Interdiffusion in the Cu-Au system has been studied in the temperature range 25–250°C using conductivity measurements and Auger in-depth composition profiles. Samples were prepared by three different methods: (1) Au was evaporated over evaporated Cu, (2) Au was electroplated over electroplated Cu and (3) Au was electroplated over wrought (bulk) Cu.The conductivity data for both the evaporated and the plated samples could be represented by $\text{ΔG}\text{G}\text{= 0.030{1?exp(?10}{}^5\text{t}\text{k}\text{)} ? (}\text{t}\text{k}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ where G is the conductance, t the time and k is an acceleration factor which is a function of temperature and thickness. Interdiffusion coefficients D? were obtained from the conductivity data by using the measured acceleration factors. These data can also be used to predict sheet conductance changes for reasonable thicknesses of Cu and Au films. Auger composition profiles were obtained by analysis beginning at the original Au-to-air interface and proceeding through the Au film into the Cu. Three distinct regions were found: (1) Cu oxide growth at the original Au surface, (2) a plateau region of a few atomic per cent Cu in the Au film and (3) a zone around the original Au-Cu interface where the Cu concentration rises to 100%. Interdiffusion coefficients were obtained from the Auger profiles based on the concentration gradient at the Au-Cu interface (region (3)).Interdiffusion coefficients obtained from $\text{ΔG}\text{G}$ and from the Auger profiles agreed within a factor of 10 for all three methods of specimen preparation. Over the range 50–250°C the interdiffusion coefficient could be represented by $\text{D}\text{= 2.9 × 10}{}^{\mathrm{?3}}\text{exp(?1.21}\text{eV}\text{kT}\text{) cm}{}^2\text{s}{}^{\mathrm{?1}}$, giving 1.3 × 10^-19 cm² s^-1 at 100°C and 6.2 × 10^-15 cm² s^-1 at 250°C. These values fall within the range of extrapolations of previously published data obtained at higher temperatures.Auger profiles from a Cu ribbon which had been Au plated and stored for 18 years at room temperature prior to analysis were used to obtain an upper limit of 2 × 10^-20 cm² s^-1 for the interdiffusion coefficient at 25°C. Subsequent measurements of D? on this sample at 150–250°C were in agreement with values obtained for the other two types of CuAu specimens. This agreement leads to the conclusion that the room temperature interdiffusion coefficient in the other two types of samples is also less than 2 × 10^-20 cm² s^-1.     

A discrete-time paradigm to evaluate skew performance in amultimedia ATM multiplexer

One of the most important quality-of-service parameters in a multimedia environment is skew, defined as the difference between the delays suffered by the monomedia flows belonging to the same multimedia stream. An analytical paradigm is proposed to evaluate the skew affecting a multimedia traffic stream in an asynchronous transfer mode multiplexer. For this purpose, the emission process of each multimedia source loading the multiplexer is defined as the superposition of heterogeneous correlated emission processes, each of which models one monomedia source as a switched batch Bernoulli process (SBBP). In order to model the intermedia relationships, the transition probabilities in the Markov chain underlying each SBBP are functions of the state of the other monomedia sources. The model is applied to a case study and the dependence of skew performance on some of the source characteristics, such as intermedia correlation, and some of the environment characteristics, such as buffer size, output capacity, and buffer utilization is analyzed and discussed     

Crime hotspot mapping using the crime related factors—a spatial data mining approach

The technique of Hotspot Mapping is widely used in analysing the spatial characteristics of crimes. The spatial distribution of crime is considered to be related with a variety of socio-economic and crime opportunity factors. But existing methods usually focus on the target crime density as input without utilizing these related factors. In this study, we introduce a new crime hotspot mapping tool—Hotspot Optimization Tool (HOT). HOT is an application of spatial data miming to the field of hotspot mapping. The key component of HOT is the Geospatial Discriminative Patterns (GDPatterns) concept, which can capture the differences between two classes in a spatial dataset. Experiments are done using a real world dataset from a northeastern city in the United States and the pros and cons of utilizing related factors in hotspot mapping are discussed. Comparison studies with the Hot Spot Analysis tool implemented by Esri ArcMap 10.1 validate that HOT is capable of accurately mapping crime hotspots.