Experimental testing of thick-walled graphite fiber composite rings

Test results are presented from pressurizing thick-walled, hoop-wound graphite fiber composite rings to very high internal radial pressures. Hydraulic pressures exceeding 275 MPa (40 000 psi) were obtained. The testing was performed on rings wound with two different resins: a cyanate ester and a bismaleimide (BMI) resin. To prevent axial delaminations at these high pressures, a thin bi-directional G11 cloth lining was used inside the rings. The rings were monitored with strain gages and acoustic probes as the pressure was applied. Flaw-free cyanate ester rings survived the testing, indicating that the nominal transverse (radial) compressive strength of hoop-wound rings is higher than 275 MPa (40 000 psi).     

An optimization technique for simultaneous reduction of PAPR and out-of-band power in NC-OFDM-based cognitive radio systems

Noncontiguous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio (CR) systems achieve highly efficient spectrum utilization by transmitting unlicensed users' data on subcarriers of licensed users’ data when they are free. However, there are two disadvantages to the NC-OFDM system: out-of-band power (OBP) and a high peak-to-average power ratio (PAPR). OBP arises due to side lobes of an NC-OFDM signal in the frequency domain, and it interferes with the spectrum for unlicensed users. A high PAPR occurs due to the inverse fast Fourier transform (IFFT) block used in an NC-OFDM system, and it induces nonlinear effects in power amplifiers. In this study, we propose an algorithm called “Alternative Projections onto Convex and Non-Convex Sets” that reduces the OBP and PAPR simultaneously. The alternate projections are performed onto these sets to form an iteration, and it converges to the specified limits of in-band-power, peak amplitude, and OBP. Furthermore, simulations show that the bit error rate performance is not degraded while reducing OBP and PAPR.     

A novel polyurethane modified with biomacromolecules for small-diameter vascular graft applications

There is a growing demand for small-caliber tissue-engineered vascular grafts to replace damaged vessels. Fabricated scaffolds are unable to precisely mimic the mechanical properties of native vessels, provide long-term patency and support cell adhesion and growth, in particular support endothelialization. In this study, a new biodegradable poly(ether ester urethane) urea (PEEUU) was synthesized. The synthesized polyurethane was then functionalized by introducing free amino groups through aminolysis for further surface modification by immobilization of biomacromolecules on the surface of vascular grafts. The modified surfaces were then characterized using attenuated total reflectance-Fourier transform infrared spectroscopy, water contact angle measurement and atomic force microscopy. The mechanical properties of the fabricated scaffolds were analyzed, revealing mechanical properties close to that of the natural vessels. Surface modifications led to improved cell–scaffold interactions, showing appropriate cell attachment and function on the scaffolds. A confluent layer of endothelial cells was formed on biomacromolecule-immobilized PEEUU vascular grafts. The preliminary results of this study demonstrated that the new polyurethane modified with biomacromolecules can be considered as a candidate material for vascular tissue engineering application with capability to support endothelialization of fabricated vascular grafts.     

Extraction of nano-porous silica from hydrosodalite produced via modification of low-grade kaolin for removal of methylene blue from wastewater

BACKGROUND: This work employs low-grade kaolin as raw material in the economical production of nano-porous silica with extended surface area via the hydrothermal acidification of intermediate zeolite composite to remove methylene blue from wastewater. Hydrosodalite fabricated through the modification of meta-kaolin (MK) with sodium aluminate (NaAlO₂) was used as a precursor in the hydrothermal acidification step. RESULTS: The direct conversion of MK to zeolite composite generating a low crystalline phase, containing quartz which was eliminated in the acidification step, exhibited a strong affinity towards dye adsorption. It was indicated that the NaAlO₂/MK ratio could influence the hydrosodalite crystallization as well as adsorption efficiency of the nano-porous silica obtained from acidification of zeolite composite. The nano-porous silica formation involved the ion extraction from hydrosodalite cabbage-like particles, depending on crystallinity of intermediate zeolite composite. CONCLUSION: The mesoporous silica represented the appropriate adsorptive behavior when produced from precursor modified with lower NaAlO₂ content, NaAlO₂/MK = 0.24, attributed to superior specific surface area, 420 m² g⁻¹, with average pore diameter about 3.3 nm. The equilibrium data was better correlated by Redlich–Peterson isotherm. Compared to the surface area of silica powders fabricated from high grade kaolins, Al₂O₃/SiO₂, > 0.83, by the acid-etched strategy, the mesoporous silica produced from the low-grade kaolin by the template free method indicates higher value. © 2020 Society of Chemical Industry     

P75 and S100 gene expression induced by cell-imprinted substrate and beta-carotene to nerve tissue engineering

Here we aimed to differentiate adipose derived stem cells (ADSCs) to Schwann cells (SCs), as one of the major and instrumental cell sources in nerve regeneration, by synergistic application of imprinting method and β-carotene. Accordingly, the topography of Schwann cells was imprinted on poly dimethyl siloxane (PDMS) substrates via mold casting and human ADSCs seeded on substrates; moreover, β-carotene was added to induce hADSCs differentiation. Physiochemical evaluations of PDMS by FTIR spectra presented its silicon-methyl bond (Si CH₃) at 1260 cm⁻¹. Morphology analysis by crystal violet, picrosirus red staining, and SEM images illustrated that MSCs seeded on imprinted substrates have formed SC-like morphology. Furthermore, according to q-PCR and ICC evaluations, SCs specific markers; S100 and P75 in addition of 5 μl β-carotene (BC) were upregulated (p-value<0.001). Also, the expression was detected on the imprinted surfaces without β-carotene to a lesser degree. Our study revealed that Schwann cell imprinted substrates can mimic the morphology and topography of SCs and induce differentiation signals in mesenchymal stem cells (MSCs). In addition, the potency of β-carotene as an organic substance in boosting and stimulating the neural differentiation was demonstrated. Relevantly, the reports have confirmed the synergistic pivotal roles of β-carotene and patterned surfaces in directing MSCs into SC-like cells differentiation without applying expensive and less safe chemical growth factors.     

Micro-scale evolution of mechanical properties of glass-ceramic sealant for solid oxide fuel/electrolysis cells

The structural integrity of the sealant is critical for the reliability of solid oxide cells (SOCs) stacks. In this study, elastic modulus (E), hardness (H) and fracture toughness (K_IC) of a rapid crystallizing glass of BaO–CaO–SiO₂ system termed “sealant G” are reported as determined using an indentation test method at room temperature. A wide range of indentation loads (1 mN–10 N) was used to investigate the load-dependency of these mechanical properties. Values of 95 ± 12 GPa, 5.8 ± 0.2 GPa and 1.15 ± 0.07 MPa m^0.5 were derived for E, H and K_IC using the most suitable indentation loads. An application relevant annealing treatment of 500 h at 800 °C does not lead to a significant change of the mechanical properties. Potential self-healing behavior of the sealant has also been studied by electron microscopy, based on heat treatment of samples with indentation-induced cracks for 70 h at 850 °C. Although the sealant G is considered to be fully crystallized, evidence indicates that its cracks can be healed even in the absence of a dead load.     

ESTIMATION OF TRANSPORT PROPERTIES OF LIQUIDS

Based on the theory of intermolecular forces and the Hildebrand relation, a generalized equation in terms of refractive index is proposed to estimate viscosity, thermal conductivity and diffusion coefficients of liquid non-polar compounds at various temperatures. Analytical equations are provided to estimate transport properties of n-alkanes in terms of molecular weight. Average deviations for all three properties of various hydrocarbons from C⁵ to C²⁰ are within 1 % for a large number of data points. The proposed equation also predicts transport properties of some polar compounds with a reasonable degree of accuracy.     

Design and analysis of a novel mechanical loading machine for dynamic in vivo axial loading

This paper describes the construction of a loading machine for performing in vivo, dynamic mechanical loading of the rodent forearm. The loading machine utilizes a unique type of electromagnetic actuator with no mechanically resistive components (servotube), allowing highly accurate loads to be created. A regression analysis of the force created by the actuator with respect to the input voltage demonstrates high linear correlation (R(2) = 1). When the linear correlation is used to create dynamic loading waveforms in the frequency (0.5-10 Hz) and load (1-50 N) range used for in vivo loading, less than 1% normalized root mean square error (NRMSE) is computed. Larger NRMSE is found at increased frequencies, with 5%-8% occurring at 40 Hz, and reasons are discussed. Amplifiers (strain gauge, linear voltage displacement transducer (LVDT), and load cell) are constructed, calibrated, and integrated, to allow well-resolved dynamic measurements to be recorded at each program cycle. Each of the amplifiers uses an active filter with cutoff frequency at the maximum in vivo loading frequencies (50 Hz) so that electronic noise generated by the servo drive and actuator are reduced. The LVDT and load cell amplifiers allow evaluation of stress-strain relationships to determine if in vivo bone damage is occurring. The strain gauge amplifier allows dynamic force to strain calibrations to occur for animals of different sex, age, and strain. Unique features are integrated into the loading system, including a weightless mode, which allows the limbs of anesthetized animals to be quickly positioned and removed. Although the device is constructed for in vivo axial bone loading, it can be used within constraints, as a general measurement instrument in a laboratory setting.