Search

We present an efficient approach to evaluate the size dependency of elastic and plastic properties of metallic polycrystalline materials. Specifically, we consider different volume fractions of ferrite and martensite phases for the construction of three macroscopic domains. Statistical Volume Elements (SVEs) of different sizes are extracted from these domains using the moving window method. Linear and Crystal Plasticity (CP) simulations provide elastic and plastic properties of the SVEs such as the bulk and shear moduli, yield strength, and hardening modulus. We use a variation-based criterion to determine the Representative Volume Element (RVE) size of these properties. This RVE size corresponds to a size beyond which the given property can be idealized as homogeneous. We also use anisotropy indices and an additional RVE size criterion to determine the size limits beyond which these properties can be idealized as isotropic. Numerical results show that the plastic properties often reach their homogeneity and isotropy limits at larger sizes compared to elastic properties. This effect is more pronounced for the hardening modulus compared to the yield strength. [ABSTRACT FROM AUTHOR]

This research investigated the synthesis of thermoplastic polyurethane (TPU) with a hard segment content (HSC) of 30% weight. The chain extender, the polyols, and the diisocyanate utilized 1,4-butanediol (BDO), and the polycaprolactone diol (PCL-diol) with molecular weights of 2000, 4000, and 10,000 and isophorone diisocyanate (IPDI), respectively. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (1H-NMR), and X-ray diffraction (XRD) were used to examine the chemical microstructure and physical properties of PCL diol and thermoplastic polyurethanes (TPUs). The molecular weight of the PCL diol as soft segments affected the crystallinity and glass transition temperature (Tg) of TPUs. An increase in PCL diol molecular weight resulted in a reduction in elongation at failure and an increase in ultimate tensile strength. This study was conducted to investigate the permeability and the permselectivity of CO2 and N2 gases over pressure ranges (3 to 9 atm). It was determined that the gas permeability of each sample increased in response to an increase in the pressure of the supplying gas. An elevation in the molecular weight of PCL-diols in TPU samples resulted in a reduction in selectivity and an increase in CO2 and N2 gas permeability. Although IPDI is a non-aromatic cyclic diisocyanate with a significant impact on thermoplastic polyurethane phase morphology, the goal of this paper is to create a change in the molecular weight of PCL-diol and investigate the effect of molecular weight on the resulting morphology as well. [ABSTRACT FROM AUTHOR]

Microalgae have been mentioned as a promising feedstock for biodiesel production. In this study, microalgae Chlorella vulgaris (MCV) was cultivated in a bioreactor with wastewater. After biodiesel production from MCV oil via transesterification reaction, chemical and physical properties of MCV methyl ester were evaluated with regular diesel and ASTM standard. Besides, engine performance and exhaust emissions of CI engine fuelled with the blends of diesel-biodiesel were measured. The GC-MS analysis showed that oleic and linoleic acids were the main fatty acid compounds in the MCV methyl ester. Engine test results revealed that the use of biodiesel had led to a major decrease in CO and HC emissions and a modest reduction in CO2 emissions, whereas there was a minor increase in NOx emissions. Furthermore, there was a slight decrease in the engine power and torque while a modest increase in brake specific fuel consumption which are acceptable due to exhaust emissions reduction. The experimental results illustrate considerable capabilities of applied MVC biodiesel as an alternative fuel in diesel engines to diminish the emissions.

Selective laser melting (SLM) is an additive manufacturing technique commonly used in the rapid prototyping of components. The complexity of the SLM microstructure poses a unique challenge to deriving effective mechanical properties at different length scales. Representative volume elements (RVEs) are often used to homogenize the material properties of composites. Instead of RVEs, we use statistical volume elements (SVEs) to homogenize the elastic and fracture properties of the material. This relates the inherent variation of a material's microstructure to the variation in its mechanical properties at different observation scales. The convergence to the RVE limit is examined from two perspectives: the stability of the mean value as the SVE size increases for the mean-based approach, and the tendency of the normalized variation in homogenized properties to zero as the SVE size increases for the variation-based approach. Fracture properties tend to make the RVE limit slower than do elastic properties from both perspectives. There are also differences between vertical (normal to printing plane) and horizontal (in-plane) properties. While the elastic properties tend to make the RVE limit faster for the horizontal direction, i.e., having a smaller variation and more stable mean value, the fracture properties exhibit the opposite effect. We attributed these differences to the geometry of the melt pools. [ABSTRACT FROM AUTHOR]

The radiative transfer equation (RTE) is an integro-differential equation that describes the radiation energy absorbing, emitting, and scattering in both space and angle, which can be up to five-dimensional problems. It is difficult for a RTE solver to satisfy both accuracy and efficiency (less computational resources) for such high dimensional problems. In this paper, an iterative solver for one-dimensional cylindrical radiative transfer problems using the space-angle discontinuous Galerkin (DG) method is developed to achieve both accuracy and efficiency. The iterative solver is based on the angular decomposition (AD) scheme, which slices the spatial-angular domain into slabs and decouples the angular integration between slabs. Both Jacobi and successive over-relaxation (SOR) iterative schemes are investigated by numerical analysis and examples. The comparison of the two iterative schemes suggests that an appropriate relaxation factor for the SOR method may accelerate the convergence. Finally, the iterative scheme is more efficient than the direct solution of the system both in terms of memory usage and computational time, especially for finer meshes. [ABSTRACT FROM AUTHOR]

Khalil Ansarin1, Siavoush Abedi1, Reza Ghotaslou1, Mohammad Hossein Soroush1, Kamyar Ghabili1, Kenneth R Chapman21Tuberculosis and Lung Disease Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; 2Asthma and Airway Centre, Toronto Western Hospital, University Health Network, Toronto, ON, CanadaBackground: Mycoplasma pneumoniae is an organism that reportedly has a strong relationship to asthma. However, asthma severity and location of airway obstruction have not been compared between asthmatic patients with and without evidence for remote mycoplasma infection.Objectives: The aim of this research was to study the relationship between previous M. pneumoniae infections in asthmatic patients and presence of any predilection for the involvement of central or peripheral airways, the severity of the disease, and asthma control.Methods: Sixty-two patients with asthma were assessed by a validated asthma control test (ACT). All patients underwent spirometry and lung volume studies by body plethysmography. The forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC) were measured. An oropharyngeal swab was obtained for polymerase chain reaction analysis to detect the mycoplasma antigen. Moreover, blood samples were obtained to measure the titration of antimycoplasma immunoglobulin M (IgM) and IgG antibodies. The asthmatic patients with a positive IgG for mycoplasma and negative PCR and negative IgM antibody were considered to have remote history of mycoplasma infection. The relationship between the asthma control using ACT score and pulmonary function variables were compared in patients with and without evidence for remote mycoplasma infection.Results: The incidence of postnasal drip was higher among the patients with asthma who had no evidence for remote mycoplasma infection (61.3% vs 32%, P = 0.035). The median ACT score was 16.5 (11–22) and 20 (13.75–24) in patients with and without remote M. pneumoniae infection, respectively (P > 0.05). In addition, the medians of the predicted values of the pulmonary function test parameters (FEV1, FEV1/FVC, FRC, FRC/TLC, RV/TLC, maximal mean expiratory flow 25%–75%, forced expiratory flow [FEF] 50%, and FEF 75%) and actual values of 5 Hz and 20 Hz resistance were not different between asthmatic patients with and without evidence of mycoplasma infection (P > 0.05).Conclusions: The present study revealed that the asthma control status and parameters of lung function tests did not differ between asthmatic patients with and without evidence of chronic M. pneumoniae infection. The latter indicates the similar location of airway obstruction and comparable severity of asthma between the two groups.Keywords: Mycoplasma pneumoniae, asthma, asthma control test, airway, pulmonary function test