Crystalline Morphology and Nonisothermal Crystallization Behaviors of iPP/PcBR Blends

Isotactic polypropylene/poly(cis‐butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. The influence of PcBR content on crystalline morphology and nonisothermal crystallization behaviors of iPP was investigated by polarized optical microscopy (POM), small angle light scattering (SALS), and differential scanning calorimetry (DSC). The POM showed that an increase of PcBR ranging from 10 vol% to 40 vol% led to less perfection of spherulites, vaguer boundaries between spherulites, and smaller spherulite size, which was quantitatively validated by SALS. The presence of PcBR also remarkably affected the nonisothermal crystallization behaviors of iPP. An addition of PcBR caused higher crystallization peak temperature and a faster crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak temperature moved to lower temperature and the crystallization rate increased as the cooling rate increased. The Ozawa and combined Avrami and Ozawa equations were used to describe the nonisothermal crystallization process of iPP and blends. The combined Avrami and Ozawa equation was more appropriate for the crystallization of the blends. Crystallization activation energy of iPP and blends was calculated by the Kissinger equation; the result showed that crystallization activation energy decreased as the content of PcBR increased from 30 vol% to 40 vol%.     

Synthesis and crystal structure of α,β-unsaturated ketone: 3,3′-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[1-(2-pyridyl)-2-propen-1-one]

The title compound, C₃₀H₂₄N₂O₄, 3,3′-[1,2-ethanediyl-bis(oxy-2,1-phenylene)]bis[1-(2-pyridyl)-2-propen-1-one] was synthesized and characterized by elemental analysis, FT-IR spectra, ¹H NMR, and X-ray single-crystal diffraction. In the molecule, the pyridine plane and the adjacent phenyl plane are almost coplanar with the dihedral angle of 3.07°, while the dihedral angle between the mean planes of the two asymmetric units is 67.56°. The crystal packing is stabilized by weak intermolecular C-H...N and C-H...O hydrogen bonds, C-H...π and π...π stacking interactions.     

Time-varying human mobility patterns with metapopulation epidemic dynamics

In this paper, explicitly considering the influences of an epidemic outbreak on human travel, a time-varying human mobility pattern is introduced to model the time variation of global human travel. The impacts of the pattern on epidemic dynamics in heterogeneous metapopulation networks, wherein each node represents a subpopulation with any number of individuals, are investigated by using a mean-field approach. The results show that the pattern does not alter the epidemic threshold, but can slightly lower the final average density of infected individuals as a whole. More importantly, we also find that the pattern produces different impacts on nodes with different degree, and that there exists a critical degree _kc$k_c$. For nodes with degree smaller than _kc$k_c$, the pattern produces a positive impact on epidemic mitigation; conversely, for nodes with degree larger than _kc$k_c$, the pattern produces a negative impact on epidemic mitigation.     

NUCLEATE POOL BOILING HEAT TRANSFER OF BINARY MIXTURES WITH DIFFERENT BOILING RANGES

The nucleate pool boiling heat transfer data on a smooth flat surface were measured for three binary mixtures of HC600a/HFC134a, HC600a/HC290, and HC600a/HFC23. Much effort was made to investigate the influence of the boiling range on the pool-boiling heat transfer performance. From the experimental results, the HC600a/HFC23 mixture with a wide boiling range showed lower heat transfer coefficients (HTCs) than the mixture with a narrow boiling range such as HC600a/HFC134a and HC600a/HC290 systems. The measured data were also compared with the results predicted by five well-known correlations. It can be found that the average deviation is less than 25% for mixtures with narrow boiling ranges, but a larger deviation for mixtures with wide boiling ranges.     

The C 1 wavelet method for numerical solutions of the Neumann problem

In this article we use the C ¹ wavelet bases on Powell-Sabin triangulations to approximate the solution of the Neumann problem for partial differential equations. The C ¹ wavelet bases are stable and have explicit expressions on a three-direction mesh. Consequently, we can approximate the solution of the Neumann problem accurately and stably. The convergence and error estimates of the numerical solutions are given. The computational results of a numerical example show that our wavelet method is well suitable to the Neumann boundary problem.     

Superconvergence and a posteriori error estimates for the Stokes eigenvalue problems

In this paper we consider the finite element approximation of the Stokes eigenvalue problems based on projection method, and derive some superconvergence results and the related recovery type a posteriori error estimators. The projection method is a postprocessing procedure that constructs a new approximation by using the least squares strategy. The results are based on some regularity assumptions for the Stokes equations, and are applicable to the finite element approximations of the Stokes eigenvalue problems with general quasi-regular partitions. Numerical results are presented to verify the superconvergence results and the efficiency of the recovery type a posteriori error estimators.     

Formation and photoluminescence of Y2O3–H3BO3:Eu3+ powders by mechanical alloying

Y₂O₃–H₃BO₃:Eu³⁺ powders were synthesized by the mechanical alloying (MA) method, and their structural and photoluminescent characteristics were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG/DTA), and luminescence spectrophotometer. The crystallite size of the powder mixture milling for 30 minutes (min) by the Willaimson–Hall method was approximately 58.8 nm with strain of 0.00141; overall, the internal strain increased with the milling time (t_m). The morphology of the powder mixture with t_m, as observed by SEM, divided into three different stages: agglomeration (0 < t_m ≤ 30 min), disintegration (30min < t_m ≤ 120 min), and homogenization (120min < t_m ≤ 300 min). The transition temperature and the weight reduction rate of the sample powders were 645.58 °C and 2.851%, respectively. Furthermore, the photoluminescence of the powder mixture excited to 240 nm by a zenon discharge lamp (20 kW) was detected near 592 nm(⁵D_o → ⁷F₁), 613 nm, 628  (⁵D_o → ⁷F₂), and 650 nm (⁵D_o → ⁷F₃).     

Null testing toroidal surface and biconic surface with cylinder compensator

Toroidal surface and biconic surface are employed increasingly, however their profile cannot be null tested easily for they are non-rotationally symmetrical. Null testing method with cylinder compensator is proposed to solve this problem. The theory of this method is revealed. The errors of this method are present. Three typical testing optical systems with cylinder compensator are demonstrated at last. The design results and total error indicate that this method is feasible.     

3-D simulation of soot formation in a direct-injection diesel engine based on a comprehensive chemical mechanism and method of moments

Here, we propose both a comprehensive chemical mechanism and a reduced mechanism for a three-dimensional combustion simulation, describing the formation of polycyclic aromatic hydrocarbons (PAHs), in a direct-injection diesel engine. A soot model based on the reduced mechanism and a method of moments is also presented. The turbulent diffusion flame and PAH formation in the diesel engine were modelled using the reduced mechanism based on the detailed mechanism using a fixed wall temperature as a boundary condition. The spatial distribution of PAH concentrations and the characteristic parameters for soot formation in the engine cylinder were obtained by coupling a detailed chemical kinetic model with the three-dimensional computational fluid dynamic (CFD) model. Comparison of the simulated results with limited experimental data shows that the chemical mechanisms and soot model are realistic and correctly describe the basic physics of diesel combustion but require further development to improve their accuracy.     

A fractal interpretation of size effects on the strength of metallic glasses

Yielding strength of metallic glasses in the uniaxial tensile and compressive tests is scale-dependent, which is attributed to the self-similar distribution of atomic cluster and free volume in the work. In contrast with the Weibull statistical theory previously employed in scaling phenomena of metallic glasses, fractal scaling laws are for the first time applied to describe the size effect inherent to the material disorder. Especially, the Multifractal Scaling Law (MFSL) originally proposed for quasi-brittle materials is used to interpret some experimental data in the literature. The best-fitted parameters (_fy$f_{\mathrm{y}}$ and l_ch) from the MFSL are in good consistency with the bulk yielding strength and the shear band size of metallic glasses observed in the alternative approaches or experiments. The fractal size effect laws provide insight into not only the scaling phenomena, but also further engineering strength predictions and designs.