关键词： chain transfer reaction   chemical miscibility   crosslinking structure   dynamical mechanical property   free-radical   cationic ring-opening hybrid polymerization   photopolymerization   polymerization kinetics  

摘要： The effects of polymerization kinetics and chemical miscibility on the crosslinking structure and mechanical properties of polymers cured by visible-light initiated free-radical/cationic ring-opening hybrid photopolymerization are determined. A three-component initiator system is used and the monomer system contains methacrylates and epoxides. The photopolymerization kinetics is monitored in situ by Fourier transform infrared-attenuated total reflectance. The crosslinking structure is studied by modulated differential scanning calorimetry and dynamic mechanical analysis. X-ray microcomputed tomography is used to evaluate microphase separation. The mechanical properties of polymers formed by hybrid polymerization are comparable to the control formed by free-radical polymerization. These investigations mark the first time that the benefits of the chain transfer reaction between epoxy and hydroxyl groups of methacrylate, on the crosslinking network and microphase separation during hybrid visible-light initiated photopolymerization, have been determined.

关键词： Cement hydrate   force field   mechanical characteristics   molecular dynamics  

摘要： Molecular dynamics studies towards assessing the bulk properties of the mineralogical array of cement hydrates such as calcium silicate hydrates (C-S-H) and calcium hydroxide (CH) have been conducted. In the case of C-S-H, closely related structures of minerals such as Tobermorite (9, 11, 14) angstrom and Jennite are taken for MD simulations, as they have similarities with C-S-H in terms of its mineralogical array. COMPASS force field with appropriate set parameters such as cut-off distances, micro-canonical ensembles was employed for the smooth running of simulations. Different supercells for the mineral systems were created and studied further. Results show the calculated mechanical properties of cement hydrates, which form an important input for developing computational model for cement hydrate systems for assessing the physico-chemical and mechanical characteristics.

关键词： Redox   Kinetics   Catalysis   Surface   Adsorption  

摘要： Methylene Green (MG), a thiazine dye, is catalytically reduced by N2H4 in presence of palladium nanoparticles (Pdn) in buffer media. The observed rate, k(o) increases with increase in [Pdn], [N2H4] and pH but decrease with increase in ionic strength (maintained with NaNO3). Unlike other thiazine dyes, the catalyzed reduction of MG shows an induction period which is caused by the restructuring of Pdn surface. The rate of adsorbate-induced surface restructuring which increase with increase in [N2H4] but independent of [MG], suggest that only N2H4 is adsorbed on Pdn surface during the catalyzed reaction. Interestingly, NO3 ions are also adsorbed on the Pdn surface and turn the surface negatively charged. The reductant, N2H4 is adsorbed on this negatively charged Pdn surface before it reacts with MG. The surface restructuring energy of Pdn, though is constant (78.8 +/- 1.6 kJ M-1) over the temperature range of 288-313 K but the activation energy for the catalyzed reduction varies with temperatures. The convex Arrhenius plot illustrates that activation energy is different in lower (288-304 K, 123.8 +/- 12.6 kJ M-1) and higher temperature range (304-313 K, 69.2 +/- 2.1 kJ M-1) and around the inversion temperature, Tinv (304 K) a change in the nature of transition state takes place. (C) 2015 Elsevier B.V. All rights reserved.

关键词： COPEPODA   REPRODUCTION   CHEMICALS -- Physiological effect   PETROLEUM -- Environmental aspects   ELECTRON-hole droplets  

摘要： Conflicting reports on the contribution of chemical dispersants on crude oil dispersion toxicity have been published, This can partly be ascribed to the influence of dispersants on the physical properties of the oil in different experimental conditions. In the present study the potential contribution of dispersants to the reproductive effects of dispersed crude oil in the marine copepod Calanus finmarchicus (Gunnerus) was isolated by keeping the oil concentrations and oil droplet size distributions comparable between parallel chemically dispersed (CD, dispersant:oil ratio 1:25) and mechanically dispersed oil (MD, no dispersant) exposures. Female copepods were exposed for 96 h to CD or MD in oil concentration range of 0.2-5.5 mg.L-1 (THC, C-5-C-36) after which they were subjected to a 25-day recovery period where production of eggs and nauplii were compared between treatments. The two highest concentrations, both in the upper range of dispersed oil concentrations reported during spills;caused a lower initial production of eggs/nauplii for both MD and CD exposures. However, copepods exposed to mechanically dispersed oil exhibited compensatory reproduction during the last 10 days of the recovery period, reaching control level of cumulative egg and nauplii production whereas females exposed to a mixture of oil and dispersant did not.

摘要： Two-dimensional and Doppler-derived echocardiographic data on normal St. Jude Medical and Carbomedic mechanical aortic valve prosthesis function have been reported but remain ***:Comprehensive retrospective two-dimensional and Doppler echocardiographic assessment of normal 19- and 21-mm bileaflet mechanical aortic valve prostheses was performed early after ***:For the 295 prostheses, the mean (range) of values were as follows: mean gradient, 20 mmHg (5-59 mmHg); effective orifice area, 1.5 cm2 (0.2-2.8 cm2), and indexed effective orifice area, 0.8 cm2/m2 (0.3-1.7 cm2/m2). Dimensionless index was > 0.25 in 294 (99%) prostheses. Acceleration time was <100 ms in 290 (98%) prostheses. Acceleration time to ejection time ratio was <0.40 in 289 (98%) prostheses. Severe prosthesis patient mismatch was present in 23/54 (43%) of 19-mm prostheses and 57/241 (24%) of 21-mm prostheses (p=0.005).Conclusion:This study establishes parameters defining the distribution of values for Doppler-derived hemodynamic data with normal 19- and 21-mm St. Jude Medical and Carbomedics bileaflet mechanical aortic valve prostheses. Prostheses with hemodynamic values outside these parameters are likely dysfunctional; however, prosthesis dysfunction may be present even when hemodynamic values are within these ***: Demographic and Echocardiographic Characteristics

关键词： Self diffusion   Amorphous metals   Molecular dynamics   Crystal structure   Stress strain relations  

摘要： The mechanical and dynamical properties of ZrSi and ZrSi2 bulk metallic glasses (BMGs) have been investigated by molecular dynamics simulation. The Honeycutt-Anderson (HA) index analysis indicates that the major indexes in ZrSi and ZrSi2 bulk metallic glasses are 1551, 1541, and 1431, which refers to the liquid structure. For uniaxial tension, the results show that the ZrSi and ZrSi2 BMGs are more ductile than their crystal counterparts. The evolution of the distribution of atomic local shear strain clearly shows the initialization of shear transformation zones (STZs), the extension of STZs, and the formation of shear bands along a direction 45 degrees from the tensile direction when the tensile strain gradually increases. The self-diffusion coefficients of ZrSi and ZrSi2 BMGs at temperatures near their melting points were calculated by the Einstein equation according to the slopes of the MSD profiles at the long-time limit. Because the HA fraction summation of icosahedral-like structures of ZrSi BMG is higher than that of ZrSi2 BMG, and these local structures are more dense, the self-diffusion coefficients of the total, Zr, and Si atoms of ZrSi2 BMG are larger than those of ZrSi BMG. This can be attributed to the cage effect, where a denser local structure has a higher possibility of atoms jumping back to form a backflow and then suppress atomic diffusivity. For ZrSi2 BMG, the self-diffusion coefficient of Si increases with temperature more significantly than does that of Zr, because more open packing rhombohedra structures are formed by the Si-Si pair. (C) 2015 AIP Publishing LLC.

关键词： siRNA   Drug delivery   Nanomedicine   PLGA   DOTAP   Sustained release  

摘要： Understanding the delivery dynamics of nucleic acid nanocarriers is fundamental to improve their design for therapeutic applications. We investigated the carrier structure-function relationship of lipid-polymer hybrid nanoparticles (LPNs) consisting of poly(DL-lactic-co-glycolic acid) (PLGA) nanocarriers modified with the cationic lipid dioleoyltrimethyl-ammoniumpropane (DOTAP). A library of siRNA-loaded LPNs was prepared by systematically varying the nitrogen-to-phosphate (N/P) ratio. Atomic force microscopy (AFM) and cryo-transmission electron microscopy (cryo-TEM) combined with small angle X-ray scattering (SAXS) and confocal laser scanning microscopy (CLSM) studies suggested that the siRNA-loaded LPNs are characterized by a core-shell structure consisting of a PLGA matrix core coated with lamellar DOTAP structures with siRNA localized both in the core and in the shell. Release studies in buffer and serum-containing medium combined with in vitro gene silencing and quantification of intracellular siRNA suggested that this self-assembling core-shell structure influences the siRNA release kinetics and the delivery dynamics. A main delivery mechanism appears to be mediated via the release of transfection-competent siRNA-DOTAP lipoplexes from the LPNs. Based on these results, we suggest a model for the nanostructural characteristics of the LPNs, in which the siRNA is organized in lamellar superficial assemblies and/or as complexes entrapped in the polymeric matrix. (C) 2015 Elsevier B. V. All rights reserved.

关键词： STRAINS & stresses (Mechanics)   CYTOKINESIS   PROTEIN-protein interactions   CELL motility   MOLECULAR motor proteins   PROTEIN structure   PROTEIN crosslinking  

摘要： Cell-shape changes associated with processes like cytokinesis and motility proceed on several-second timescales but are derived from molecular events, including protein-protein interactions, filament assembly, and force generation by molecular motors, all of which occur much faster [1-4]. Therefore, defining the dynamics of such molecular machinery is critical for understanding cell-shape regulation. In addition to signaling pathways, mechanical stresses also direct cytoskeletal protein accumulation [5-7]. A myosin-II-based mechanosensory system controls cellular contractility and shape during cytokinesis and under applied stress [6, 8]. In Diciyostelium, this system tunes myosin II accumulation by feedback through the actin network, particularly through the crosslinker cortexillin I. Cortexillin-binding IOGAPs are major regulators of this system. Here, we defined the short timescale dynamics of key cytoskeletal proteins during cytokinesis and under mechanical stress, using fluorescence recovery after photobleaching and fluorescence correlation spectroscopy, to examine the dynamic interplay between these proteins. Equatorially enriched proteins including cortexillin I, IQGAP2, and myosin II recovered much more slowly than actin and polar crosslinkers. The mobility of equatorial proteins was greatly reduced at the furrow compared to the interphase cortex, suggesting their stabilization during cytokinesis. This mobility shift did not arise from a single biochemical event, but rather from a global inhibition of protein dynamics by mechanical-stress-associated changes in the cytoskeletal structure. Mechanical tuning of contractile protein dynamics provides robustness to the cytoskeletal framework responsible for regulating cell shape and contributes to cytokinesis fidelity.

关键词： 电子机械制动   制动力   估测   特性曲线   温度  

摘要： 针对汽车电子机械制动系统(EMB)控制机构中制动力传感器测量制动力存在的不足,运用传热学理论和有限元方法,结合实验对刹车片温度场、热性能、热分布规律及冷却过程进行分析,建立了考虑快速制动和冷却过程条件下估测刹车片温度和制动力的模型。根据模型模拟出EMB特性曲线并用实验进行了验证。实验证明建立的模型准确可行。

关键词： Pro/E   Mechanica   动力学分析   敏感度分析   优化设计  

摘要： 链传动由于其传动可靠、结构简单,在农业机械中获得广泛应用。在工厂化水产养殖中应用的链斗式过滤装置中,作为链传动中关键零件,链轮受到工作环境恶劣、复杂载荷等因素影响,齿根磨损严重而失效。为增加链轮寿命、减少应力集中,利用Pro/E平台建立链轮的三维模型,并应用Pro/E Mechanica进行动力学分析,进行链轮设计的结构优化,在减轻其重量的同时,使链轮受力基本均匀,减少应力集中和变形。通过对链轮做全局敏感度分析表明:齿顶圆弧半径的增加削弱了最大应力的增长;最大应力随凸缘直径的增加而减小。最后以质量最小为目标函数对两个重要参数在合理范围内进行优化得到的最佳设计:当齿顶圆弧直径与凸缘直径分别为14mm、54.952 3mm时,模型质量最小为3.408kg,模型的质量减少了4.48%。