Control of morphological properties of porous biodegradable scaffolds processed by supercritical CO2 foaming

A low cost supercritical CO₂ foaming rig with a novel design has been used to prepare fully interconnected and highly porous biodegradable scaffolds with controllable pore size and structure that can promote cancellous bone regeneration. Porous polymer scaffolds have been produced by plasticising the polymer with high pressure CO₂ and by the formation of a porous structure following the escape of CO₂ from the polymer. Although, control over pore size and structure has been previously reported as difficult with this process, the current study shows that control is possible. The effects of processing parameters such as CO₂ saturation pressure, time and temperature and depressurisation rate on the morphological properties, namely porosity, pore interconnectivity, pore size and wall thickness- of the scaffolds have been investigated. Poly(d,l)lactic acid was used as the biodegradable polymer. The surfaces and internal morphologies of the poly(d,l)lactic acid scaffolds were examined using optical microscope and micro computed tomography. Preosteoblast human bone cells were seeded on the porous scaffolds in vitro to assess cell attachment and viability. The scaffolds showed a good support for cell attachment, and maintained cell viability throughout 7 days in culture. This study demonstrated that the morphology of the porous structure can be controlled by varying the foaming conditions, allowing the porous scaffolds to be used in various tissue engineering applications.     

Electrocatalytic oxidation of methanol on the nickel–cobalt modified glassy carbon electrode in alkaline medium

In this work, Ni–Co alloy coating on the surface of glassy carbon (GC) electrode was performed by cyclic voltammetry. The results showed that the deposition of Ni–Co is an anomalous process. The deposition bath was prepared according to the metal ion Ni/Co ratio of 4:1 using NiSO₄·7H₂O and CoSO₄·8H₂O, and the total concentration of all solutions was 40.0 mM. The pH of the bath solution was adjusted at 2.0 using boric acid at room temperature. The modified electrode was conditioned by potential recycling in a potential range of 100–700 mV (vs. Ag/AgCl) by cyclic voltammetric method in an alkaline solution. The Ni–Co modified electrode showed a higher activity towards methanol oxidation in the Ni (III) and Co (IV) oxidation states. Cyclic voltammetry was used for the electrochemical characterization of the Ni–Co modified electrode and the mechanism of methanol oxidation is proposed. The result of double steps chronoamperometry shows that the methanol electrooxidation is an irreversible reaction. Moreover, the effects of various parameters such as mole ratio of Ni–Co in the alloy in modification step, potential scan rate, methanol concentration and solution temperature on the electro-oxidation of methanol have also been investigated.     

Ring-Shaped Lateral Bracing System for Steel Structures

Buckling of compression members has a great impact on the reduction of energy dissipation capacity and ductility of the structural system such as concentrically braced frame systems (CBFs). As well, direct connection of tensile and compression members to beams and designation of the link beam as a fuse, and the formation of plastic hinges in the link beam in eccentrically braced systems (EBFs) endanger the safety of this type structural systems. This paper introduces a new ring-shaped lateral bracing system so-called the Shami lateral bracing system (SLBs) which removes the common tensile and compressive members along with their connections to the structure. As a substitute, SLBs introduces a new element with proper ductility and energy dissipation capacity and could be an appropriate alternative to the existing systems. Because of the high degree of statically indeterminacy of the proposed system, the structural stiffness does not lead to a steep reduction after the formation of the first plastic hinge. The performance of this lateral system is evaluated by numerical modeling, and the results show that the structures resist against the lateral loads with acceptable seismic performance. It seems that this system in comparison with CBF and EBF systems may not be cost-effective for bending of the ring, welding, etc., but from the seismic performance points of view, it has good performance.     

Sulfur removal of gas oil using ultrasound-assisted catalytic oxidative process and study of its optimum conditions

Ultrasound-assisted oxidative desulfurization process (UAOD) was applied to reduce sulfur compounds of gas oil containing various types of sulfur content. The environmental regulation requires a very deep desulfurization to eliminate the sulfur compounds. UAOD is a promising technology with lower operating cost and higher safety and environmental protection. For the first time the typical phase transfer agent (tetraoctyl-ammonium-bromide) was replaced with isobutanol because using isobutanol is much more economical than TOAB, imposing no contamination. The reaction was carried out at optimal point with various temperatures, in single-, two- and three step-procedures, investigating the effect of gradual increase of H₂O₂ and TOAB being used instead of isobutanol. Total sulfur concentration in oil phase was analyzed by ASTM-D3120 method. The highest removal of about 90% for gas oil containing 9,500 mg/kg of sulfur was achieved in three-steps during 17 minutes of process at 62±2 °C when 180.3 mmol of H₂O₂ was used and extraction carried out by methanol.     

The effect of EEMAO processing on surface mechanical properties of the TiO2–ZrO2 nanostructured composite coatings

We report fabrication of TiO₂–ZrO₂ nanostructured composite coatings by EPD-Enhanced MAO (EEMAO) technique on titanium substrates where especial emphasis was placed on improving the surface hardness of the substrates and establishing a microstructure-property correlation. Based on the XRD and the EDX results, the layers consisted of anatase, rutile, monoclinic zirconia, and tetragonal zirconia. It was observed that the anatase/rutile and tetragonal/monoclinic zirconia rations increased with the processing time and the electrolyte concentration. The zirconia content also increased with the processing time and the electrolyte concentration. XPS technique was also employed to further confirm the surface chemical composition and stoichiometry of the layers. A uniform distribution of zirconia across the titania matrix was evident in the SEM images. The surface hardness of the TiO₂-ZrO₂ composite layers was observed to increase with the zirconia concentration. Employing EEMAO technique, the surface harness of the titanium substrates was successfully improved from ∼190 Hv to ∼700 Hv.     

Omega-3 Fatty Acid Composition of Persian Gulf Fishes

The aim of this study was to investigate the content of omega-3 fatty acids in Persian Gulf fishes. The fishes were collected from Persian Gulf and the content of fatty acids in the head, muscle, and liver of fishes were determined. Quantitative analysis of fatty acids was performed by gas chromatography (GC) and methylmyristate was used as the reference material. GC and mass spectrometer (GC- mass) was applied for qualitative analysis and cod liver oil with all of omega-3 fatty acids was used as standard. Ghezel ala, Zamin kan-e-dom navari and Sorkhu mahi had maximum levels of omega-3 in total body. Halva Sefid, Gish-e-deraz baleh and Shamshiri were poor sources of omega-3. The liver of fish had the most content of omega-3 fatty acids followed by muscle and head, respectively.     

The effect of sliding speed and amount of loading on friction and wear behavior of Cu–0.65 wt.%Cr alloy

Friction and wear behavior of a peak aged Cu–0.65 wt.%Cr alloy was investigated. The friction and wear experiments were run under ambient conditions with a pin-on-disk tribometer. Experiments were performed using various applied normal loads and sliding velocities. The tribological behavior of the studied alloy was discussed in terms of friction coefficient, wear loss and wear mechanism.Friction coefficient and wear loss have shown large sensitivity to the applied normal load and the sliding velocity. At the sliding velocity of 0.3 m/s weight loss increased from 6.9 to 51 mg by increasing the normal load from 20 to 40 N. At higher sliding velocity minimum weight loss is achieved at 60 N normal load. So it can be seen that with increasing normal load wear rate decreases due to the formation of a continuous tribofilm which consists of Fe–Cu intermetallic. Varying of friction coefficients in different conditions of normal load and sliding velocity is correlated to the wear behavior.The analysis of worn surfaces by XRD and SEM showed that an increase in normal load and sliding velocity creates an intermetallic wear-induced layer, which modifies the wear behavior of the alloy. The XRD result indicates that new phase of Cu_9.9Fe_0.1 is generated on worn surfaces of the pin specimens during the wear tests. There is a significant correlation between the micrograph of worn surfaces and the wear rate of specimens.     

Analysis of cold expanded fastener holes subjected to short time creep: Finite element modelling and fatigue tests

The beneficial effects of cold expansion have been well documented in previous studies, yet the performance of cold expanded plates exposed to elevated temperatures is an area of technical interest. In this research, finite element (FE) simulations along with experimental fatigue tests have been carried out to investigate the effect of exposure to elevated temperature on residual stress distribution and subsequent fatigue life of cold expanded fastener holes. According to the obtained results, creep stress relaxation occurs due to exposure to 120 °C for 50 h. FE results demonstrate a non-uniform residual stress relaxation regime through the plate thickness around the cold expanded hole and the fatigue test results show that the subsequent fatigue lives have significantly decreased.     

Composite Living Fibers for Creating Tissue Constructs Using Textile Techniques

The fabrication of cell‐laden structures with anisotropic mechanical properties while having a precise control over the distribution of different cell types within the constructs is important for many tissue engineering applications. Automated textile technologies for making fabrics allow simultaneous control over the color pattern and directional mechanical properties. The use of textile techniques in tissue engineering, however, demands the presence of cell‐laden fibers that can withstand the mechanical stresses during the assembly process. Here, the concept of composite living fibers (CLFs) in which a core of load bearing synthetic polymer is coated by a hydrogel layer containing cells or microparticles is introduced. The core thread is drawn sequentially through reservoirs containing a cell‐laden prepolymer and a crosslinking reagent. The thickness of the hydrogel layer increases linearly with to the drawing speed and the prepolymer viscosity. CLFs are fabricated and assembled using regular textile processes including weaving, knitting, braiding, winding, and embroidering, to form cell‐laden structures. Cellular viability and metabolic activity are preserved during CLF fabrication and assembly, demonstrating the feasibility of using these processes for engineering functional 3D tissue constructs.     

Genetic-based minimum classification error mapping for accurate identifying Peer-to-Peer applications in the internet traffic

In this paper, we propose a hybrid approach using genetic algorithm and neural networks to classify Peer-to-Peer (P2P) traffic in IP networks. We first compute the minimum classification error (MCE) matrix using genetic algorithm. The MCE matrix is then used during the pre-processing step to map the original dataset into a new space. The mapped data set is then fed to three different classifiers: distance-based, K-Nearest Neighbors, and neural networks classifiers. We measure three different indexes, namely mutual information, Dunn, and SD to evaluate the extent of separation of the data points before and after mapping is performed. The experimental results demonstrate that with the proposed mapping scheme we achieve, on average, 8% higher accuracy in classification of the P2P traffic compare to the previous solutions. Moreover, the genetic-based MCE matrix increases the classification accuracy more than what the basic MCE does.