Mixing process of two miscible fluids in a lid-driven cavity

The authors gratefully acknowledge the financial support from the National and Key Research and Development Program of China (No.2016YFB0302801), National Natural Science Foundation of China (No.21676007) and Scientific Research and Technology Development Projects of China National Petroleum Corporation (No. 2016B-2605).Peer reviewedPostprin

Mechanisms for drawdown of floating particles in a laminar stirred tank flow

The authors gratefully acknowledge the financial support from the National Key R&D Program of China (2017YFB0306701) and from the National Natural Science Foundation of China (No.21676007).Peer reviewedPostprin

ReaxFF reactive molecular dynamics on silicon pentaerythritol tetranitrate crystal validates the mechanism for the colossal sensitivity

Recently quantum mechanical (QM) calculations on a single Si-PETN (silicon-pentaerythritol tetranitrate) molecule were used to explain its colossal sensitivity observed experimentally in terms of a unique Liu carbon-silyl nitro-ester rearrangement (R_3Si–CH_2–O–R_2 → R_3Si–O–CH_2–R_2). In this paper we expanded the study of Si-PETN from a single molecule to a bulk system by extending the ReaxFF reactive force field to describe similar Si–C–H–O–N systems with parameters optimized to reproduce QM results. The reaction mechanisms and kinetics of thermal decomposition of solid Si-PETN were investigated using ReaxFF reactive molecular dynamics (ReaxFF-RMD) simulations at various temperatures to explore the origin of the high sensitivity. We find that at lower temperatures, the decomposition of Si-PETN is initiated by the Liu carbon-silyl nitro-ester rearrangement forming Si–O bonds which is not observed in PETN. As the reaction proceeds, the exothermicity of Si–O bond formation promotes the onset of NO_2 formation from N–OC bond cleavage which does not occur in PETN. At higher temperatures PETN starts to react by the usual mechanisms of NO_2 dissociation and HONO elimination; however, Si-PETN remains far more reactive. These results validate the predictions from QM that the significantly increased sensitivity of Si-PETN arises from a unimolecular process involving the unusual Liu rearrangement but not from multi-molecular collisions. It is the very low energy barrier and the high exothermicity of the Si–O bond formation providing energy early in the decomposition process that is responsible

Refractive Index-Matched PIV Experiments and CFD Simulations of Mixing in a Complex Dynamic Geometry

Acknowledgment The authors appreciatively acknowledge the financial support from the National Key Research and Development Program of China (No.2016YFB0302801), National Natural Science Foundation of China (No.21676007), the Fundamental Research Funds for the Central Universities (XK1802-1) and the China Scholarship Council.Peer reviewedPostprin

Numerical study of drop behavior in a pore space

Acknowledgements The authors appreciatively acknowledge the financial support from the National Key Research and Development Program of China (No.2016YFB0302801) and the China Scholarship Council. This research has been enabled by the use of computing resources provided by Compute Canada.Peer reviewedPostprin

Prediction of the Chapman–Jouguet chemical equilibrium state in a detonation wave from first principles based reactive molecular dynamics

The combustion or detonation of reacting materials at high temperature and pressure can be characterized by the Chapman–Jouguet (CJ) state that describes the chemical equilibrium of the products at the end of the reaction zone of the detonation wave for sustained detonation. This provides the critical properties and product kinetics for input to macroscale continuum simulations of energetic materials. We propose the ReaxFF Reactive Dynamics to CJ point protocol (Rx2CJ) for predicting the CJ state parameters, providing the means to predict the performance of new materials prior to synthesis and characterization, allowing the simulation based design to be done in silico. Our Rx2CJ method is based on atomistic reactive molecular dynamics (RMD) using the QM-derived ReaxFF force field. We validate this method here by predicting the CJ point and detonation products for three typical energetic materials. We find good agreement between the predicted and experimental detonation velocities, indicating that this method can reliably predict the CJ state using modest levels of computation

Suspension of a Single Sphere in a Stirred Tank with Transitional Flow

ACKNOWLEDGEMENT The authors gratefully acknowledge the financial support from Scientific Research and Technology Development Projects of China National Petroleum Corporation (No.2020B-2512).Peer reviewe

The co-crystal of TNT/CL-20 leads to decreased sensitivity toward thermal decomposition from first principles based reactive molecular dynamics

To gain an atomistic-level understanding of the experimental observation that the cocrystal TNT/CL-20 leads to decreased sensitivity, we carried out reactive molecular dynamics (RMD) simulations using the ReaxFF reactive force field. We compared the thermal decomposition of the TNT/CL-20 cocrystal with that of pure crystals of TNT and CL-20 and with a simple physical mixture of TNT and CL-20. We find that cocrystal has a lower decomposition rate than CL-20 but higher than TNT, which is consistent with experimental observation. We find that the formation of carbon clusters arising from TNT, a carbon-rich molecule, plays an important role in the thermal decomposition process, explaining the decrease in sensitivity for the cocrystal. At low temperature and in the early stage of chemical reactions under high temperature, the cocrystal releases energy more slowly than the simple mixture of CL-20–TNT. These results confirm the expectation that co-crystallization is an effective way to decrease the sensitivity for energetic materials while retaining high performance

Maternal Blood Pressure Rise During Pregnancy and Offspring Obesity Risk at 4 to 7 Years Old: The Jiaxing Birth Cohort.

CONTEXT: Maternal hypertensive disorders during pregnancy are suggested to affect obesity risk in offspring. However, little is known about the prospective association of rise in maternal blood pressure within normal range during pregnancy with this risk for obesity. OBJECTIVE: To clarify the associations of diastolic and systolic blood pressure during pregnancy among normotensive women with the risk for obesity in offspring. DESIGN: Prospective cohort study. SETTING: Southeast China. PARTICIPANTS: Up to 2013, a total of 88,406 mother-child pairs with anthropometric measurements of offspring age 4 to 7 years were included in the present analysis. MAIN OUTCOME MEASURES: Overweight/obesity risk in offspring. RESULTS: Among normotensive women, second- and third-trimester diastolic and systolic blood pressures were positively associated with risk for overweight/obesity in offspring: odds ratios per 10-mm Hg higher second- and third-trimester diastolic blood pressure were 1.05 [95% confidence interval (CI), 1.01 to 1.09] and 1.05 (95% CI, 1.02 to 1.10), respectively, and for systolic blood pressure were 1.08 (95% CI, 1.05 to 1.11) and 1.06 (95% CI, 1.03 to 1.09). Each 10-mm Hg greater rise in blood pressure between first and third trimesters was associated with a higher risk for offspring overweight/obesity: diastolic, 1.06 (95% CI, 1.01 to 1.10); systolic, 1.05 (95% CI, 1.02 to 1.07). Among all women (combining normotensive and hypertensive women), maternal hypertension in the second and third trimesters was associated with 49% and 14% higher risks for overweight/obesity in offspring, respectively. CONCLUSIONS: These results suggest that rise in maternal blood pressure during pregnancy and hypertension during pregnancy, independent of maternal body size before pregnancy, are risk factors for offspring childhood obesity