Efficient algorithms for erasure node placement on slotted dual busnetworks

We study the problem of placing erasure nodes among passive stations in a slotted dual bus network. Erasure nodes are known to improve throughput by allowing slot reuse. It is also known that choices made in locating erasure nodes significantly impact network congestion and overall throughput-especially when traffic patterns exhibit a high degree of locality. We present algorithms to determine optimal placements of erasure nodes that improve upon prior work on this problem: we present simpler and faster polynomial-time algorithms and also consider various useful cost measures. These algorithms can be used to solve related placement problems in which limits on congestion and existing placements are given as input, and the goal is to find the minimum number of erasure nodes required to meet the congestion bound     

Interfacial separation of fibres in fibre reinforced composites

An analytical model is proposed to predict the ultimate tensile strength of fibre-reinforced composites when the failure is governed by fibre debonding.

The analytical analysis is based on the principle of the compliance method in fracture mechanics with the presence of an interfacial crack at the fibre/matrix interface. The model is developed on the basis of the assumption that both the matrix and the fibre behave elastically and the matrix strain at a zone far from the matrix-fibre interface is equal to the composite strain. Furthermore, it is assumed that a complete bond exists between the fibre and the matrix and that the crack faces are traction free.

It is shown that the separation strain energy release rate for fibre-reinforced composites can be obtained for cases with and without the existence of an interfacial crack. Numerical examples are presented and compared with results obtained in the literature by finite element analyses and from experimental tests. The comparison demonstrates the accuracy and the convergence of the model.     

Editorial

Pattern Analysis and Applications -     

TOF-SIMS and principal component analysis characterization of the multilayer surface grafting of small molecules: antibacterial furanones

Furanone compounds (fimbrolides) have attracted interest as antibacterial compounds for use in human health care, for instance, as an antibacterial coating for medical devices to combat device-centered infections. To ensure effectiveness for extended periods of time, they must be immobilized covalently onto a device surface; in this study, this was done via azide/nitrene chemistry and photochemical coupling. However, the detection and quantification of surface-immobilized small molecules such as furanones presents a considerable analytical challenge, yet is necessary for optimization of coatings and reliable interpretation of biological responses. We have utilized the surface sensitivity and chemical specificity of time-of-flight secondary ion mass spectrometry (TOF-SIMS) to characterize each step of the grafting sequence. On account of the complexity of the data, principal component analysis (PCA) was used to interpret and compare spectra. The results demonstrate the utility of TOF-SIMS with PCA for the detection of the surface-grafted small molecules azidoaniline and a brominated furanone; imaging of the bromine ion peaks also enabled assessment of grafting uniformity. Thus, successful multilayer coating and furanone grafting was observed, and substantial and uniform coverage of furanone molecules on the surface. Even multiple grafting steps involving, in the present case, two low molecular weight compounds can readily be disentangled by PCA. The utility of TOF-SIMS analysis with PCA is particularly well illustrated in the present case by the grafting of the furanone molecules, which did not yield a singular unique peak in the positive ion mass spectra, whereas the collective spectral changes elucidated by PCA provided unambiguous verification of successful grafting of this low molecular weight compound.     

Assessment of Al-Madra clay as an adsorbent of copper ions from aqueous solutions

Al-Madra clay, a local, cheap and readily available material in Qatar, was tested for the removal of copper ions from aqueous solutions. Batch experiments of copper ion adsorption onto natural and treated clay in different conditions were undertaken. Different types of activated Al-Madra clay were used, such as Na-clay, Al-clay, thermal-clay and cyclohexane-clay. Thermally treated clay achieved the highest removal of Cu ions, followed by Al-clay, cyclohexane-clay, and finally Na-clay. A maximum of 50% adsorption of copper ions can be achieved using the natural clay while about 72% adsorption can be achieved when the clay is thermally treated. The amount of copper adsorbed by untreated Al-Madra clay was dependent on the process conditions; increasing with an increase in pH and initial metal concentration but decreasing with an increase in sorbent concentration. The increase in temperature from 5 to 50°C resulted in only a very slight increase in copper uptake by untreated Al-Madra clay.      

Synthesis of CdSe nanocrystals in a noncoordinating solvent: effect of reaction temperature on size and optical properties

Colloidal synthesis of high quality CdSe nanocrystals with controllable size and tunable properties have been one of the most important topics of research over the last decade, in view of its huge technological potentials. CdSe is one of the most studied nanocrystals of this category because of its photoluminescence tunability across the visible spectrum. We have synthesized CdSe nanocrystals using CdO precursor in a noncoordinating solvent and studied the effect of the reaction temperature on the size and optical properties of the nanocrystals. The size of the nanocrystals could be varied systematically in the range of 3.5 to 6.6 nm diameter with a remarkably narrow size distribution by controlling only the reaction temperature, without any need for a post-synthesis processing. The band gap and the corresponding band edge emission could be tuned across the entire visible range by tuning the size of the nanocrystals. The narrow width of the photoluminescence emissions of different colours (blue to red) make these nanocrystals a potential candidate for different optical and optoelectronic devices.     

Dropwise Condensation Studies on Multiple Scales

Recent advances in nanotechnology, chemical/physical texturing and thin film coating technology generate definite possibilities for sustaining a dropwise mode of condensation for much longer durations than was previously possible. The availability of superior experimental techniques also leads to deeper understanding of the process parameters controlling the relevant transport phenomena, the distinguishing feature of which is the involvement of a hierarchy of length/time scales, proceeding from nuclei formation, to clusters, all the way to macroscopic droplet ensemble, drop coalescence, and subsequent dynamics. This paper is an attempt to connect and present a holistic framework of modeling and studying dropwise condensation at these multiple scales. After a review of the literature, discussions on the following problems are presented: (i) atomistic modeling of nucleation; (ii) droplet–substrate interaction; (iii) surface preparation; (iv) simulation of fluid motion inside sliding drops; (v) experimental determination of the local/ average heat transfer coefficient; and (vi) a macroscopic model of the complete dropwise condensation process underneath horizontal and inclined surfaces. The study indicates that hierarchal modeling is indeed the way forward to capture the complete process dynamics. The microscopic phenomena at the three-phase contact line, leading to the apparent droplet contact angle, influence the shear stress and heat transfer. The nucleation theory captures the quasi-steady-state behavior quite satisfactorily, although the early atomistic nucleation was not seen to have a profound bearing on the steady-state behavior. The latter is strongly governed by the coalescence dynamics. Visual observation of dropwise condensation provides important information for building hierarchical models.     

A closed loop outsourcing decision model for developing effective manufacturing strategy

The case study deals with aligning production capacity for a US manufacturer of industrial thermal transfer bench-top printer, by exploring various insourcing and outsourcing options based on production, cost and delivery capabilities. A modelling framework is devised which aids in selecting an effective manufacturing strategy that considers key enablers and barriers to successful outsourcing. The proposed model is closed loop, which stresses regular re-evaluation of the existing outsourcing strategy. It models the total product cost for the product currently being manufactured in the US and compares the total costs if it were manufactured offshore in countries such as, Malaysia, China, Slovakia and Mexico. The analysis from the model shows moving manufacturing of the product to Mexico results in the largest business benefit of about $400 savings per unit compared to other countries studied. A closer look at China in the future could be considered as the economic, social and security risks may change enough to warrant re-evaluation of this option. To get a clearer picture of how Mexico rates against Malaysia in the existing state, these risks may be reviewed as an extra data point to finalise the decision to move manufacturing of industrial thermal transfer bench-top printers to Mexico.     

Magnetic nanocomposites for environmental remediation

This article provides an overview of current research activities on the synthesis and applications of magnetic nanocomposites, especially highlights their potential environmental remediations such as heavy metal (Cr, As, Pd, Hg) removal. After a brief introduction of the emergency situation of heavy metal pollution all over the world and current techniques designed to deal with these situations, different synthetic methods to fabricate various types of magnetic nanocomposites will be reviewed. The focus is to reveal the advantages of magnetic nanocomposites as an efficient adsorbent which is able to reduce the heavy metal concentrations well below the EPA requirement. At the same time, the conventional process can be redesigned to be an economic and energetic one without using extra energy to recycle the adsorbent, which is desired for future. This review mainly deals with the heavy metal removal using magnetic nanocomposites, the adsorption behaviors of heavy metal ions on the surface of novel adsorbents are well investigated including the concentration effect of both contaminants and adsorbents, adsorption kinetics, solution pH effect with regards to real application.     

Nanoenergetic Composite of Mesoporous Iron Oxide and Aluminum Nanoparticles

Ordered mesoporous Fe₂O₃ was synthesized using cetyltrimethylammonium chloride (CTAC) and polyethylene glycol octadecyl ether (Brij 76) surfactant templates. The gel time was monitored as a function of the concentration ratio of precursor to the surfactant. As-prepared FeOOH gels were extracted in ethanol to remove the surfactant and calcined at 200–400°C for 6 h so that α-Fe₂O₃ is produced. The FTIR spectra of these gels reveal complete removal of surfactant and water impurities and the presence of Fe-O vibrations. TEM images show ordering of mesopores in the gels prepared using surfactant templating and no ordering of the pores in the gels prepared without surfactant. The gels after calcinations were mixed with aluminum nanoparticles to prepare nanoenergetic composites. The burn rate of the nanocomposites containing ordered mesoporous Fe₂O₃ mixed with Al nanoparticles was compared with the one containing Fe₂O₃ with no ordering of mesopores and Al nanoparticles.