A running time analysis of an Ant Colony Optimization algorithm for shortest paths in directed acyclic graphs

In this paper, we prove polynomial running time bounds for an Ant Colony Optimization (ACO) algorithm for the single-destination shortest path problem on directed acyclic graphs. More specifically, we show that the expected number of iterations required for an ACO-based algorithm with n ants is for graphs with n nodes and m edges, where ρ is an evaporation rate. This result can be modified to show that an ACO-based algorithm for One-Max with multiple ants converges in expected iterations, where n is the number of variables. This result stands in sharp contrast with that of Neumann and Witt, where a single-ant algorithm is shown to require an exponential running time if ρ=O(n−1−ε) for any ε>0.     

Laser Surface Modification of Carbon Fiber Reinforced Composites

The removal of top resin layer is an essential task prior to adhesive bonding of carbon fiber reinforced polymer (CFRP) composites. This paper investigates the technical feasibility of using a low power continuous wave carbon dioxide laser for removing the top resin layer of CFRP without damaging the underlying fiber. The operating window and damaging threshold were experimentally determined. Irradiating the CFRP surface at a power of 14 W, scanning speed of 880 mm/sec, and a beam overlap of 25% provides an optimal thermal condition for removal of top resin layer. A finite element model was used to explain the removal mechanisms.     

Enhancement of mechanical properties of 3D printed hydroxyapatite by combined low and high molecular weight polycaprolactone sequential infiltration.

A new infiltration technique using a combination of low and high molecular weight polycaprolactone (PCL) in sequence was developed as a mean to improve the mechanical properties of three dimensional printed hydroxyapatite (HA). It was observed that using either high (M _n~80,000) or low (M _n~10,000) molecular weight infiltration could only increase the flexural modulus compared to non-infiltrated HA, but did not affect strength, strain at break and energy at break. In contrast, a combination of low and high molecular infiltration in sequence increased the flexural modulus, strength and energy at break compared to those of non-infiltrated HA or infiltrated by high or low molecular weight PCL alone. This overall enhancement was found to be attributed to the densification of low molecular weight PCL and the reinforcement of high molecular PCL concurrently. The combined low and high molecular weight infiltration in sequence also maintained high osteoblast proliferation and differentiation of the composites at the similar level of the HA. Densification was a dominant mechanism for the change in modulus with porosity and density of the infiltrated HA/PCL composites. However, both densification and the reinforcing performance of the infiltration phase were crucial for strength and toughening enhancement of the composites possibly by the defect healing and stress shielding mechanisms. The sequence of using low molecular weight infiltration and followed by high molecular infiltration was seen to provide the greatest flexural properties and highest cells proliferation and differentiation capabilities.     

One-pot synthesis of wormhole-like mesostructured silica with a high amine loading for enhanced adsorption of clofibric acid

A series of ordered amine-functionalized hexagonal mesoporous silicas (HMS-NH₂) were synthesized successfully via direct co-condensation using dodecylamine as a structure-directing agent in the presence of 3-aminopropyltrimethoxysilane (APS), [aminoethylamino]propyltrimethoxysilane or [(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEEA) as amine group precursors. Tetrahydrofuran was used as the organic solvent to control the interaction and sol–gel reaction of the silica source and aminosilanes. The effect of the type and concentration of the added aminosilanes on the physicochemical properties of the resulting HMS-NH₂ materials were investigated. Thermogravimetric analysis, Fourier-transform infrared spectroscopy and solid-state ²⁹Si nuclear magnetic resonance spectroscopy confirmed a successful functionalization of the HMS surface with different amine groups. X-ray diffraction and transmission electron microscopy indicated that their wormhole-like mesostructured framework was retained after functionalization at a high APS loading level (15 mol%) or using AEEA as the aminosilane precursor. A high degree (88–98%) of aminosilanes was incorporated into the HMS framework, corresponding to an amine concentration of 0.72–2.16 mmol g^?1. The HMS-NH₂ materials had a high surface area (272–627 m² g^?1), a large total pore volume (0.48–1.92 cm³ g^?1) and exhibited an enhanced adsorption capacity for clofibric acid in aqueous solution.