关键词： Density functional theory (DFT)   Molecular dynamics (MD)   Single-walled carbon nanotube (SWCNT)   Boron-nitride nanotube (BNNT)   Mechanical properties  

摘要： This study investigates the effect of encapsulating a golden fullerene (Au-32) cluster on the mechanical properties of a single-walled carbon nanotube (SWCNT) and a boron-nitride nanotube (BNNT). First, the geometrical parameters of the nanopeapods were optimized using the density functional theory (DFT) method. The DFT results demonstrated that the strength of interaction between the Au-32 cage and a BNNT was stronger than that between the Au-32 cage and SWCNT. The molecular dynamics (MD) method was then applied to calculate mechanical properties such as Young's modulus, failure stress, and failure strain using a stress-strain plot. The mechanical results indicated that encapsulating the Au-32 cluster reduced the Young's modulus and failure stress of both a SWCNT and BNNT, whereas the failure strain did not observably change. To validate these results, a C-60 cage was inserted inside an SWCNT in the most exothermic situation. The MD calculation indicated that, similar to the effect of Au-32 in the Au-32-nanotube peapod, C-60 reduced the mechanical properties of the SWCNT. (C) 2018 American Society of Civil Engineers.

关键词： Cardiovascular disease   Computer simulation   Mock circulation loop   Lumped parameter   Mechanical circulatory support   Pumps, heart-assist  

摘要： The Virtual Mock Loop, a versatile virtual mock circulation loop, was developed using a lumped-parameter model of the mechanically assisted human circulatory system. Inputs allow specification of a variety of continuous-flow pumps (left, right, or biventricular assist devices) and a total artificial heart that can self-regulate between left and right pump outputs. Hemodynamic inputs were simplified using a disease-based input panel, allowing selection of a combination of cardiovascular disease states, including systolic and diastolic heart failure, stenosis, and/or regurgitation in each of the four valves, and high to low systemic and pulmonary vascular resistance values. The menu-driven output includes a summary of hemodynamic parameters and graphical output of selected flows, pressures, and volumes in the heart's four chambers as well as in the pulmonary artery and aorta. New tools to augment experimental research on implantable heart-assist devices and to increase our understanding of patient-specific pump interactions are in high demand. The purpose of this ongoing study is to demonstrate the use of a system analysis computer simulation to explore and better comprehend the interactions of mechanical circulatory support pumps with a more extensive combination of patient-specific or simulation conditions than can be established by practical experimentation. Usability is an important factor in constructing computer models for research purposes, and among our primary objectives in creating this simulation model were to make it as portable and useful as possible outside the lab environment, by people not involved in the creation of its operational software.

ISBN: (纸本)9787568047869

关键词： Free energy   QM/MM   Molecules   Solvents   Hydration  

摘要： The solvation of carbon dioxide in solution represents a key step for the capture and fixation CO2 in nature, which may be further influenced by the formation of (bi)carbonate species and/or the formation of CO2 clusters in solution. The latter processes are strongly dependent on the exact environment of the liquid state (e.g., pH value, solvated ions, etc.) and may interfere with the experimental determination of structural, dynamical, and thermodynamic properties. In this work a hybrid quantum mechanical/molecular mechanical (QM/MM) simulation approach at correlated ab initio level of theory resolution-of-identity second-order Moller-Plesset Perturbation Theory (RI-MP2) has been applied in the framework of thermodynamic integration (TI) to study structure, dynamics, and the hydration free energy of a single carbon dioxide molecule in aqueous solution. A detailed analysis of the individual QM/MM potential energy contributions demonstrate that the overall potential remains highly consistent over the entire sampling phase and that no artificial contributions are influencing the determination of the hydration free energy. The latter value of 0.01 +/- 0.92 kcal/mol was found in very good agreement with the values of 0.06 and 0.24 kcal/mol obtained via quasi-chemical theory and experimental measurements, respectively. In order to obtain detailed information about the C- and O-c-water interaction, conically restricted regions with respect to the main axis of the CO2 molecule have been employed in structural analysis. The presented data not only provide detailed information about the hydration properties of CO2 but act as a critical validation of the simulation technique, which will be beneficial in the study of nonaqueous solvents such as pure and aqueous NH3 solutions, which have been suggested as potential candidates to capture CO2 from anthropogenic sources.

关键词： alpha-Glucosidase   Flavonoid   Geraniaceae   Geranium asphodeloides   Tannin  

摘要： Some Geranium species have been used to treat diabetes. To evaluate the scientific basis of this ethnopharma-cological use, we aimed to isolate potent alpha-glucosidase inhibitory metabolites of Geranium asphodeloides Burm. through in vitro bioactivity-guided fractionation. All the tested extracts showed high alpha-glucosidase inhibitory effect compared to acarbose. Among the tested extracts, the ethyl acetate subextract showed the highest activity with an IC50 value of 0.85 +/- 0.01 mu M. A hydrolysable tannin, 1,2,4 tri-O-galloyl-beta-D-glucopyranose (1), and five flavonoid glycosides, kaempferol-3-O-alpha-rhamnopyranoside (2), kaempferol-3-O-alpha-rabinofuranoside (3), quercetin-3-O-beta-glucopyranoside (4), quercetin-3-O-alpha-rhamnopyranoside (5), and quercetin-3-O-alpha-rhamnofuranoside (6), were isolated from the ethyl acetate subextract. Their structures were identified by 1D- and 2D-NMR experiments. 1 exhibited the highest alpha-glucosidase inhibitory effect, approximately 61 times more potent than positive control, acarbose, with an IC50 value of 0.95 +/- 0.07 mu M. Also, 2 was more potent than acarbose. An enzyme kinetics analysis revealed that compounds 2, 3 and 4 were competitive, whereas 1 and 6 uncompetitive inhibitors. Molecular docking studies were performed to get insights into inhibition mechanisms of the isolated compounds in the light of the enzyme kinetic studies using various binding sites of the enzyme model.

关键词： Graphene oxide (GO)   Cement composites   Hydration   Pore structure   Calcium silicate hydrate (C-S-H) gels  

摘要： The effects of graphene oxide (GO) on the hydration kinetics, pore structure, mechanical properties, and the structure of calcium silicate hydrate (C-S-H) gels were systematically investigated by combinatorial techniques. GO can accelerate the cement hydration, refine the pore structure and increase the polymerization degree of C-S-H gels due to the nucleation effects of GO. The specific surface area of cement paste and the number of gel pores were reduced with the addition of GO. A 3D network structure of GO modified C-S-H gels was originally proposed based on the obtained results that GO could intercalate into the interlayer space of C-S-H gels through ionic bonding with Ca2+ and fill in the gel pores. A small fraction of GO (0.022 wt%) increased the 28 d compressive strength by 16.31%-25.60% at a various water to cement ratios, indicating that GO is a potential nano-reinforcing material for cement composites. The results would provide a well understanding of the reinforcing mechanisms of GO in cement composites and pave a pathway for the design of high-performance cement composites. (C) 2018 Elsevier Ltd. All rights reserved.

摘要： Several regimes of motion are evident in red blood cells (RBCs) under shear flow and are known to be controlled by the shear flow rate and by the deformability of the cell. Above a certain shear flow rate, healthy RBCs present a fluidized regime analogous to that of a droplet: the membrane adopts a tank-treading motion, i.e. rotates around the centre of mass of the cell, and its orientation oscillates around a mean value (Fig. 1). This motion is not observed in rigid RBCs which keep the same regime of motion as with low shear flow rate. The transition from one motion to the other depends on several intrinsic parameters including membrane viscosity, elasticity and cytoplasmic viscosity. Sickle cell disease (SCD) is a hereditary hemolytic anemia due to the presence of mutant hemoglobin, Hb S, which tends to polymerize in RBCs, reducing its deformability and resulting ultimately in RBC sickling. We postulate that SCD may affect RBCs capacity to adopt the tank-treading motion. Thanks to microfluidic chips coupled with high speed video, we studied the fraction of RBCs displaying a tank-treading motion (% of TT) at moderate shear stresses (0.4-0.6 Pa), in homozygous SCD patients (n=30) and in normal subjects (n=12). At the time of sampling, SCD patients were in steady state (no vaso-occlusive crisis or other acute complications) and not transfused for at least 3 months. Around 3 microL of total blood were necessary for each measurement. RBCs were studied under atmospheric conditions and exhibited the normal discoid shape. We showed first that the % of TT is significantly different in SCD patients compared to controls, with no overlap between the values of each groups (respectively 70.4±12.9% versus 98.6±0.9%). Second, measurements performed on different cells fractions isolated by cell density or in the presence of different NaCl concentrations, showed that the % of TT cells is sensitive to cell density and hydration status, both in normal subjects and in SCD patients. Fi

关键词： Bark beetle   Ips   Disturbance interaction   Picea abies   Wind disturbance   Root rot  

摘要： Interaction of disturbance agents may cause cascading effects in forests. The three most important disturbance agents of Norway spruce (Picea abies) in northern Europe are Heterobasidion root rot, wind and the European spruce bark beetle (Ips typographus). In this study, we present a mechanistic individual agent based model to simulate the dynamics of the bark beetle and integrate it in the simulation framework WINDROT to further study the interactive dynamics of root rot, wind and bark beetles. We carried out model performance analysis concluding that the model is sensitive to the parameters of optimal bark thickness for reproduction. Stand level interaction between wind and bark beetle disturbances was also evaluated against field data. The stand level simulations show the interaction between the disturbance agents;the root rot increases wind disturbance and bark beetles benefit from wind fallen trees. No direct interaction was found in the simulation study between the root rot and bark beetles. Further experimental research and large scale simulation studies are needed to better understand the underlying mechanisms in the interaction between the disturbance agents.

关键词： C3S   C-S-H   Nano-indentation   SEM/EDX/BSE   Ca/Si ratio   Molecular dynamics  

摘要： Calcium silicate hydrate (C-S-H) is the most important hydration product in cementitious material. Due to its complexity, the investigation on its mechanical properties is still in progress. In this study, synthesized C3S was utilized to produce relatively pure C-S-H gels with two different water/solid ratios. Then mechanical properties of the C-S-H were measured and characterized by nano-indentation and SEM/EDX/BSE. Two types of C-S-H with Ca/Si ratio around 1.8 were observed through statistical analysis of the indentation modulus (Er) and hardness (H). The looser one possessing lower Er around 25-30 GPa while the denser one possesses higher Er of 35.9 GPa. Both phases have higher stiffness than those of high density (HD) and low density (LD) phase obtained from cement pastes. Furthermore, molecular dynamics provides mechanical understanding of C-S-H gel at nano-scale. Based on the crystal structure of tobermorite 11 angstrom, 64 models with Ca/Si ratios from 1.3 to 2.0 were constructed for uniaxial tension test. The stiffness and cohesive strength of the C-S-H gel are greatly influenced by Ca/Si ratio, water content and nano-porosity. With increasing Ca/Si ratio from 1.3 to 2.0, long silicate chains were broken to shorter ones and more water molecules penetrated into defect regions. The destroyed silicate skeleton and the "hydrolytic weakening" effect resulted in the reduction of the mechanical properties of C-S-H gels. Concurrently considering the intrinsic porosity and chemical compositions, the appropriate micromechanical models are utilized to upscale the molecular properties to higher level. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Vegetables  

摘要： As a new type of machine, field vegetable power machinery can realize different pre-harvest mechanization operations. The frame is subjected to various loads during field operations, which is accompanied by dynamic load. It is necessary to carry out strength research and optimization design of the frame. The multi-objective topology optimization design method based on field measured strain data was studied. HyperWorks software was used to carry out finite element analysis of the frame, the stress distribution under static stress analysis conditions was obtained, and the fatigue damage hotspot of the frame was determined. On the basis of data analysis, the strain gauges were pasted, and the dynamic strain test system was set up to collect the load time history under typical working conditions of field vegetable power machinery. The measured strain time history data was preprocessed, and the force of the frame under the corresponding working conditions was analyzed. The load spectrum was compiled by nCode software, and the fatigue analysis and life prediction of the frame were performed. Based on the analysis and life prediction, the topology optimization was proposed, and a multi-objective topology optimization mathematical model with multiple frame conditions and dynamic low-order natural frequency response was constructed to carry out lightweight design. The test results showed that the fatigue life at the cross weld of the frame was 7.5×104 h, the fatigue life was the shortest among the 15 points, which met the service life requirement, and the overall structural strength of the frame was over-designed. The optimized frame quality was reduced by 443.55 kg, which was reduced by 53.47%. © 2018, Chinese Society of Agricultural Machinery. All right reserved.