A constitutive model of thermoviscoelastic semicrystalline shape memory polymer considering viscous dissipation in the amorphous phase

Mathematical modeling has increasingly recognized as a powerful tool that could aid the understanding of shape memory behavior in semicrystalline shape memory polymer (SMP). Up to now, studies have not fully taken into account the viscous effect of the amorphous phase in the whole shape memory cycle, which causes a more realistic prediction of the SMP behavior. In this work, a constitutive thermoviscoelastic model was developed to predict the thermomechanical behavior of semicrystalline SMP. The simulated results of the proposed model for a typical uniaxial deformation were compared with the case having no dissipation effect, also with experimental data. The accuracy improvements in the results of the stress–strain trends together with fixing ratio and recovery ratio obtained from the modified model were significant. The results were in good agreement with the experimental data. The modified model revealed a real and more accurate trend by considering viscous dissipation.     

Post-buckling optimization of two-dimensional functionally graded porous beams

International Journal of Mechanics and Materials in Design - In the present study, an attempt is made to present the governing equations on the post-buckling of two-dimensional (2D) FGP beams and...     

The latent heat recovery from boiler exhaust flue gas using shell and corrugated tube heat exchanger: A numerical study

The excessively increasing environmental concerns along with reducing fossil fuel resources introduce the trend of increasing the efficiency of boiler via implementing waste heat recovery. In the present study, the potential of latent heat recovery is investigated in the middle‐size boiler exhaust flue gas using the shell and corrugated tube heat exchanger. The main purpose of the present study is efficiency growth in flue gases using latent heat recovery of the steam energy. The heat recovery analysis is evaluated by a validated computational fluid dynamics model by a commercial software. For this study, the effect of different tube arrangements, number of tubes, and flow direction in the shell on heat transfer and pressure drop were investigated. The results showed that in‐line arrangement of the tubes in the shell presents better thermal performance and also high pressure drop among the other arrangements. As a result, by considering the thermal performance and pressure drop, radial arrangement shows higher performance. According to the obtained results from Section 2 of the present study, by considering the radial arrangement of tubes in the shell, as the number of tube rises, the thermal performance declines.     

Treatment of phosphoric acid sludge for rare earths recovery II: effect of sonication and flocculant solution temperature on settling rate

The effect of sonication on sludge exhibited a faster settling rate. Sonication creates acoustic cavitation preparing the slurry for better interaction with flocculant and generating faster settlement. Five samples of flocculants were conditioned at 25, 50, 60, 75 and 100° C for settlement. The flocculant conditioned at 60°C had the best performance in terms of settlement. However, further increase in temperature damaged polymer chains of the flocculant decreasing its effectiveness. ICP analysis showed sonicated samples trapped 11% more rare earth elements (REEs) in their residue and that temperature above 60º C is not favorable for the flocculant preparation in terms of coagulation.     

Evaluation of the fouling phenomenon in the membrane clarification of black mulberry juice

Mixed cellulose ester (MCE) flat membranes were used to clarify black mulberry juice, the yield of which was limited by fouling. The effects of membrane pore size (0.025, 0.1 and 0.22 μm), transmembrane pressure (0.5, 1, 1.5 and 200 kPa), and cross‐flow velocity (0.1, 0.2, 0.3 and 0.4 m s^?1) on membrane fouling were evaluated; the results showed that fouling increased with increased pore size and pressure, and decreased with increased velocity. Analysis of different resistances showed that both reversible and irreversible fouling resistances have an important role in fouling‐resistance changes. There is no cake resistance in all processes. Microstructure analysis of membrane using scanning electron microscopy confirmed the theory that intermediate blocking was the dominant fouling mechanism in MCE 0.025 μm, and standard blocking was the dominant mechanism in MCE 0.1 and 0.22 μm.     

A Simple Method for Measuring Intrinsic Blocking Temperature in Superparamagnetic Nanomaterials

Temperature-dependent magnetic flux density (B) data, clearly exhibiting a transition temperature called intrinsic blocking temperature for some metallic samples in zero field cooled-warmed (ZFC-W) curves without employing an external magnetic field, has been obtained by a simple method. The reasons of the increase and decrease in the measured B-field at low temperature in zero magnetic-field were discussed. Co, CoPt₃ and Co/Au, CoPt₃/Au core-shell nanoparticles, prepared by the reverse-micelle microemulsion method, were used as test materials. The blocking temperature was measured at a cusp of the measured magnetic field, B (produced by the sample), versus the temperature curve during warming up of the sample from a very low temperature (≤15 K) to room temperature. All the samples showed a blocking temperature at 45, 50, 40, and 42 K, respectively, for Co, CoPt₃, Co/Au, and CoPt₃/Au nanoparticles. A completely intrinsic behavior of the sample’s magnetic moment was revealed by our method since no applied external field was used, yielding a truly spontaneous magnetization behavior.     

Coordination Polymer to Atomically Thin,Holey, Metal‐Oxide Nanosheets for Tuning Band Alignment

Holey 2D metal oxides have shown great promise as functional materials for energy storage and catalysts. Despite impressive performance, their processing is challenged by the requirement of templates plus capping agents or high temperatures; these materials also exhibit excessive thicknesses and low yields. The present work reports a metal‐based coordination polymer (MCP) strategy to synthesize polycrystalline, holey, metal oxide (MO) nanosheets with thicknesses as low as two‐unit cells. The process involves rapid exfoliation of bulk‐layered, MCPs (Ce‐, Ti‐, Zr‐based) into atomically thin MCPs at room temperature, followed by transformation into holey 2D MOs upon the removal of organic linkers in aqueous solution. Further, this work represents an extra step for decorating the holey nanosheets using precursors of transition metals to engineer their band alignments, establishing a route to optimize their photocatalysis. The work introduces a simple, high‐yield, room‐temperature, and template‐free approach to synthesize ultrathin holey nanosheets with high‐level functionalities.     

Fabrication of a thermally actuated tunable grating and its application as a CO2 laser beam profile analyzer

We propose a thermally actuated tunable grating for measuring the beam profile of a CO(2) laser. The grooves of a transmissive grating are filled with a liquid whose refractive index depends on temperature. A visible laser as a probe and a CO(2) laser as a heat source are illuminated on the grating. The CO(2) laser is absorbed, and depending on its beam profile, a temperature profile is induced on the grating. The refractive index of the heated liquid is changed, resulting in a change of efficiency of the grating for the probe laser. By using the 1st orders of diffraction in a 4f imaging system, the beam profile of the CO(2) laser is imaged onto a CCD camera by the probe laser.     

Metronidazole-loaded glass ionomer dental cements

The incorporation of antibiotics in glass ionomer cements (GICs) for the treatment of periodontal diseases has been considered as an effective therapeutic strategy. In this research, metronidazole was added to silanized glass fiber-reinforced GICs. The fiber-reinforced cements containing antibiotic were made by adding 6.0 w% silanized E-glass fibers and 3.0 w% metronidazole to the GIC powder. The GIC reinforced with 6.0 w% silanized fibers showed maximum values of 57 MPa, 2.1 GPa, and 1.3 MPa‧m^0.5 for the flexural strength, flexural modulus, and fracture toughness, respectively. The release of metronidazole showed a two-step release in which about 65% of total amount was released in the first 24 hours. Antibacterial test exhibited no bacteria number (CFU/mL) in the presence of GIC containing metronidazole. In addition, gene expression of Streptococcus mutans was performed by real-time PCR method. Based on PCR results, metronidazole significantly reduced the gtfB and gtfC genes expression, related to adherence and biofilm formation, up to 98% after 7 days in comparison to the control one (P < .001). According to the obtained results, GICs reinforced with silanized fibers containing metronidazole are effective in inhibiting bacteria associated with caries and also acceptable mechanical properties for the development of the next generation of restoration dental materials.