Nanogrooved carbon microtubes for wet three‐dimensional printing of conductive composite structures

Recent advances in three‐dimensional (3D) printing have enabled the fabrication of interesting structures which are not achievable using traditional fabrication approaches. The 3D printing of carbon microtube composite inks allows fabrication of conductive structures for practical applications in soft robotics and tissue engineering. However, it is challenging to achieve 3D printed structures from solution‐based composite inks, which requires an additional process to solidify the ink. Here, we introduce a wet 3D printing technique which uses a coagulation bath to fabricate carbon microtube composite structures. We show that through a facile nanogrooving approach which introduces cavitation and channels on carbon microtubes, enhanced interfacial interactions with a chitosan polymer matrix are achieved. Consequently, the mechanical properties of the 3D printed composites improve when nanogrooved carbon microtubes are used, compared to untreated microtubes. We show that by carefully controlling the coagulation bath, extrusion pressure, printing distance and printed line distance, we can 3D print composite lattices which are composed of well‐defined and separated printed lines. The conductive composite 3D structures with highly customised design presented in this work provide a suitable platform for applications ranging from soft robotics to smart tissue engineering scaffolds. © 2019 Society of Chemical Industry     

Multi-player detection in soccer broadcast videos using a blob-guided particle swarm optimization method

Soccer is the most popular sport around the world, and automatic processing of soccer images is a precious alternative to the manual solutions regarding the explosive growth of soccer videos. A new multi-player detection algorithm in far view frames as an initial step to a wide range of applications, such as player tracking, is addressed in this paper. In the proposed detector, a two-step blob detection (grass-based blob detection followed by an edge-based blob detection) is combined with an efficient search mechanism based on particle swarm optimization (PSO) by assigning sub-swarms to each detected blob. Then, a sub-swarm is initialized and tripled to search for three models corresponding to two teams and the referee. Therefore, the most player-like regions in detected blobs are simultaneously searched by all sub-swarms flying through the solution space, thus expanding the scope of single player detection to multi-player detection. Experimental results demonstrate the efficiency and robustness of the algorithm.     

Synthesis and characterization of novel polyimides containing triazoles units in the main chain by click chemistry

In this study, some polyimides containing triazoles units in the main chain was prepared from the polymerization of dialkynes including imide linkages and diazides in the presence of Cu (I) catalyst in yield of 76.2–87.6%, with inherent viscosity of 0.37–0.53 dL g^?1. The obtained polymers are soluble in polar aprotic solvents such as N,N‐dimethyformamide (DMF), N,N‐dimethyacetamide (DMAc), dimethyl sulfoxide (DMSO), and N‐methyl‐2‐pyrrolidone (NMP). These polymers were characterized using FT‐IR, ¹H‐NMR, and elemental analysis techniques. Their thermal stability was evaluated with thermogravimetric (TGA) analysis and differential scanning calorimetry (DSC) techniques under a nitrogen atmosphere which is indicative of their good thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and high velocity impact performance of a hybrid long carbon/glass fiber/polypropylene thermoplastic composite

This research explores mechanical and high velocity impact response of hybrid long carbon/glass fiber-reinforced polypropylene thermoplastic composites (HLFT) with different fiber lengths. The work examines three hybrid long fiber thermoplastic composites, i.e., 5, 10 and 20 mm. The HLFTs were prepared by a combination of extrusion and pultrusion processes and using a cross-head die. Tensile and Izod impact tests were carried out to evaluate the mechanical performance of each HLFT compound. A gas gun with a spherical projectile was used to conduct high velocity impact tests at three velocities of 144, 205 and 240 m/s. The results showed that internal mixing operation caused extensive reduction in fiber length of all three LFT lengths. Tensile strength, modulus and Izod impact test results were the indications of higher values with increase in HLFT length. Comparison of these results for the HLFT with that of corresponding glass/PP LFTs, adopted from earlier work by Shayan Asenjan et al. (J Compos Mater 53:353–360, 2019), showed better performance of HLFT. The high velocity impact results showed a steady higher impact performance with the increase in HFLT fiber length for all impact velocities tested. Comparison of HLFT high velocity impact performance revealed better results for all impact velocities tested with that of the corresponding glass/PP LFT composite.     

Wavelet correlogram: A new approach for image indexing and retrieval

In this paper, a new algorithm for content-based image indexing and retrieval is presented. The proposed method is based on a combination of multiresolution image decomposition and color correlation histogram. According to the new algorithm, wavelet coefficients of the image are computed first using a directional wavelet transform such as Gabor wavelets. A quantization step is then applied before computing one-directional autocorrelograms of the wavelet coefficients. Finally, index vectors are constructed using these one-directional wavelet correlograms. The retrieval results obtained by application of our new method on a 1000 image database demonstrated a significant improvement in effectiveness and efficiency compared to the indexing and retrieval methods based on image color correlogram or wavelet transform.     

Effects of seawater on AAR expansion of concrete

Recently, AAR was identified in submerged piles of some bridges in tidal waters. Microstructural examination detected chloroaluminate salts in some cracks. To clarify whether seawater had influenced the deterioration an experimental program was planned to examine the effects of sodium chloride on AAR under various curing conditions.Concrete prisms containing either of highly-reactive, slowly-reactive or nonreactive aggregate, and either low or high alkali contents, were stored in saltwater (representing seawater) or at 100% RH, at temperatures of 38, 60 and 80 °C, for expansion measurement over 600 days, after which the temperature for those stored in saltwater was lowered to 23 °C, to check its effect on further expansion, which could be attributed to precipitation of ettringite and/or Ca-chloroaluminate.The results indicate that the type of aggregate and concrete alkali content had the greatest effect on AAR expansion. Exposure to saltwater did not have any significant effect on the AAR expansion.     

Dynamic TDD Fixed Cellular Systems Using Smart and Sectored Antennas

There are many benefits in using time division duplex (TDD) instead of frequency division duplex (FDD) schemes in fixed wireless cellular systems. For example, channel reciprocity for a single carrier frequency used on both uplinks and downlinks will allow easy access to channel state information, reduced complexity of RF design, much higher flexibility in handling dynamic traffic, simpler frequency plan, etc. However, there exists a serious limiting factor in using dynamic TDD (D-TDD) in cellular systems. This is due to a steady interference on an uplink in any cell caused by downlink transmissions in other cells. Simulation results show in D-TDD cellular systems, performance is unacceptable, when an omnidirectional antenna is used at base stations. Simulation results also suggest great potential for smart antennas in achieving substantial performance improvement in fixed D-TDD bandwidth-on-demand wireless systems.     

Threshold value for the number of cells in group technology

The similarity coefficient methods are more flexible in incorporating manufacturing data into the machine cells formation process in group technology. When threshold value is applied it is impossible to consider the restriction of number of cells or pact family. This paper discusses how a function is defined on Similarity coefficients and generates a threshold value which specifies an upper band on number of cells.