Multiscale modeling for the heterogeneous strength of biodegradable polyesters

A heterogeneous method of coupled multiscale strength model is presented in this paper for calculating the strength of medical polyesters such as polylactide (PLA), polyglycolide (PGA) and their copolymers during degradation by bulk erosion. The macroscopic device is discretized into an array of mesoscopic cells. A polymer chain is assumed to stay in one cell. With the polymer chain scission, it is found that the molecular weight, chain recrystallization induced by polymer chain scissions, and the cavities formation due to polymer cell collapse play different roles in the composition of mechanical strength of the polymer. Therefore, three types of strength phases were proposed to display the heterogeneous strength structures and to represent different strength contribution to polymers, which are amorphous phase, crystallinity phase and strength vacancy phase, respectively. The strength of the amorphous phase is related to the molecular weight; strength of the crystallinity phase is related to molecular weight and degree of crystallization; and the strength vacancy phase has negligible strength. The vacancy strength phase includes not only the cells with cavity status but also those with an amorphous status, but a molecular weight value below a threshold molecular weight. This heterogeneous strength model is coupled with micro chain scission, chain recrystallization and a macro oligomer diffusion equation to form a multiscale strength model which can simulate the strength phase evolution, cells status evolution, molecular weight, degree of crystallinity, weight loss and device strength during degradation. Different example cases are used to verify this model. The results demonstrate a good fit to experimental data

Datasheet1_High serum copper as a risk factor of all-cause and cause-specific mortality among US adults, NHANES 2011–2014.pdf

BackgroundSeveral studies have shown that serum copper levels are related to coronary heart disease, diabetes, and cancer. However, the association of serum copper levels with all-cause, cause-specific [including cardiovascular disease (CVD) and cancer] mortality remains unclear.ObjectivesThis study aimed to prospectively examine the association of copper exposure with all-cause, CVD, and cancer mortality among US adults.MethodsThe data for this analysis was obtained from the National Health and Nutrition Examination Survey (NHANES) between 2011 and 2014. Mortality from all-causes, CVD, and cancer mortality was linked to US National Death Index mortality data. Cox regression models were used to estimate the association between serum copper levels and all-cause, CVD, and cancer mortality.ResultsA total of 2,863 adults were included in the main study. During the mean follow-up time of 81.2 months, 236 deaths were documented, including 68 deaths from cardiovascular disease and 57 deaths from cancer. The weighted mean overall serum copper levels was 117.2 ug/L. After adjusting for all of the covariates, compared with participants with low (1st tertile,  0.05).ConclusionsThis prospective study found that serum copper concentrations were linearly associated with all-cause and CVD mortality in US adults. High serum copper levels is a risk factor for all-cause and CVD mortality.</p

Emergence of Novel Polynitrogen Molecule-like Species, Covalent Chains, and Layers in Magnesium–Nitrogen Mg_<i>x</i>N_<i>y</i> Phases under High Pressure

Stable structures and stoichiometries of binary Mg–N compounds are explored at pressures from ambient up to 300 GPa using ab initio evolutionary simulations. In addition to Mg₃N₂, we identified five nitrogen-rich compositions (MgN₄, MgN₃, MgN₂, Mg₂N₃, and Mg₅N₇) and three magnesium-rich ones (Mg₅N₃, Mg₄N₃ and Mg₅N₄), which have stability fields on the phase diagram. These compounds have peculiar structural features, such as N₂ dumbbells, bent N₃ units, planar SO₃-like N­(N)₃ units, N₆ six-membered rings, 1D polythiazyl S₂N₂-like nitrogen chains, and 2D polymeric nitrogen nets. The dimensionality of the nitrogen network decreases as magnesium content increases; magnesium atoms act as a scissor by transferring valence electrons to the antibonding states of nitrogen sublattice. In this context, pressure acts as a bonding glue in the nitrogen sublattice, enabling the emergence of polynitrogen molecule-like species and nets. In general, Zintl–Klemm concept and molecular orbital analysis proved useful for rationalizing the structural, bonding and electronic properties encountered in the covalent nitrogen-based units. Interestingly, covalent six-membered N₆^4– rings containing <i>P</i>–1 (I) MgN₃ phase is recoverable at atmospheric pressure. Moreover, ab initio molecular dynamics analysis reveals the polymeric covalent nitrogen network, poly-N₄^2–, encountered in the high-pressure <i>Cmmm</i> MgN₄ phase can be preserved at ambient conditions. Thus, quenchable MgN₄, stable at pressures above 13 GPa, shows that high energy-density materials based on polymeric nitrogen can be achievable at reduced pressures. The high-pressure phase <i>P</i>–1 (I) MgN₃ with covalent N₆ rings is the most promising HEDM candidate with an energy density of 2.87 kJ·g^–1, followed by <i>P</i>–1 MgN₄ (2.08 kJ·g^–1)

Decomposition Reaction Rate of BCl₃–C₃H₆(propene)–H₂ in the Gas Phase

The decomposition reaction rate in the BCl₃–C₃H₆–H₂ gas phase reaction system in preparing boron carbides was investigated based on the most favorable reaction pathways proposed by Jiang et al. [<i>Theor. Chem. Accs.</i> <b>2010</b>, <i>127</i>, 519] and Yang et al. [<i>J. Theor. Comput. Chem.</i> <b>2012</b>, <i>11</i>, 53]. The rate constants of all the elementary reactions were evaluated with the variational transition state theory. The vibrational frequencies for the stationary points as well as the selected points along the minimum energy paths (MEPs) were calculated with density functional theory at the B3PW91/6-311G­(d,p) level and the energies were refined with the accurate model chemistry method G3­(MP2). For the elementary reaction associated with a transition state, the MEP was obtained with the intrinsic reaction coordinates, while for the elementary reaction without transition state, the relaxed potential energy surface scan was employed to obtain the MEP. The rate constants were calculated for temperatures within 200–2000 K and fitted into three-parameter Arrhenius expressions. The reaction rates were investigated by using the COMSOL software to solve numerically the coupled differential rate equations. The results show that the reactions are, consistent with the experiments, appropriate at 1100–1500 K with the reaction time of 30 s for 1100 K, 1.5 s for 1200 K, 0.12 s for 1300 K, 0.011 s for 1400 K ,or 0.001 s for 1500 K, for propene being almost completely consumed. The completely dissociated species, boron carbides C₃B, C₂B, and CB, have very low concentrations, and C₃B is the main product at higher temperatures, while C₂B is the main product at lower temperatures. For the reaction time 1 s, all these concentrations approach into a nearly constant. The maximum value (in mol/m³) is for the highest temperature 1500 K with the orders of −13, −17, and −23 for C₃B, C₂B, and CB, respectively. It was also found that the logarithm of the overall reaction rate and reciprocal temperature have an excellent linear relationship within 700–2000 K with a correlation coefficient of 0.99996. This corresponds to an apparent activation energy 337.0 kJ/mol, which is comparable with the energy barrier 362.6 kJ/mol of the rate control reaction at 0 K but is higher than either of the experiments 208.7 kJ/mol or the Gibbs free energy barrier 226.2 kJ/mol at 1200 K

Microstructure-based multiphysics modeling for semiconductor integration and packaging

Semiconductor technology and packaging is advancing rapidly toward system integration where the packaging is co-designed and co-manufactured along with the wafer fabrication. However, materials issues, in particular the mesoscale microstructure, have to date been excluded from the integrated product design cycle of electronic packaging due to the myriad of materials used and the complex nature of the material phenomena that require a multiphysics approach to describe. In the context of the materials genome initiative, we present an overview of a series of studies that aim to establish the linkages between the material microstructure and its responses by considering the multiple perspectives of the various multiphysics fields. The microstructure was predicted using thermodynamic calculations, sharp interface kinetic models, phase field, and phase field crystal modeling techniques. Based on the predicted mesoscale microstructure, linear elastic mechanical analyses and electromigration simulations on the ultrafine interconnects were performed. The microstructural index extracted by a method based on singular value decomposition exhibits a monotonous decrease with an increase in the interconnect size. An artificial neural network-based fitting revealed a nonlinear relationship between the microstructure index and the average von Mises stress in the ultrafine interconnects. Future work to address the randomness of microstructure and the resulting scatter in the reliability is discussed in this study