关键词： Denture   Denture cleaning methods   Poly(methyl methacrylate)   Low-cost powered toothbrush   C. albicans biofilm  

摘要： Purpose: To investigate the effects of using a low-cost powered toothbrush for cleaning on dental prostheses made of heat polymerized poly(methyl methacrylate), PMMA. Methods: Heat cured PMMA specimens beam with the dimensions of 45.0 mm x 6.5 mm x 4.5 mm were fabricated. The specimens were kept in water storage at 37 degrees C constant temperature for 0, 1, 7, 15, 30 and 60 days and randomly assigned for testing or control. Test specimens underwent brushing by using a powered toothbrush at an applied force of 2.00 N for 22 min with water as medium. Surface roughness measurement (R-a), flexural strength and efficacy of brushing to remove coated Candida albicans biofilm were investigated. Results: The results of the mean surface roughness value and the flexural strength were analysed by using two-way ANOVA and Tukey post hoc test at 5% significance level. In general, the specimens showed no significant changes in flexural strength after brushing. However, the flexural strength and the surface roughness value were significantly lower in specimens group after 7 days in water storage compared to the control. SEM micrographs of post-brushed specimens revealed satisfactory removal of C. albicans biofilm. Conclusion: A low-cost powered toothbrush together with a liquid medium successfully removed C. albicans biofilm on dental acrylic PMMA-based prostheses, without compromising the mechanical properties. (C) 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.

关键词： Baltic Sea   energy budget models   fisheries models   food dependence   ontogenetic niche shifts   physiologically structured population models   size structure   trophic configuration  

摘要： Food-dependent growth and size-dependent interactions form cornerstones in the dynamics of fish populations. Using two freshwater examples, we illustrate the importance of considering both these cornerstones for understanding system dynamics. Moreover, a proper understanding of the dynamics requires mechanistic linkages between individual-, population-, and community-level processes based on mass conservation principles. In one example, we further find that quantitative predictions of individual-level energy flows are essential for understanding the community dynamics. This mechanistic approach to understanding system dynamics is generally not reflected in fisheries models as an overview shows that only half of them incorporate food-dependent growth, and none fully observe the principles of mass conservation. As a marine example we examine patterns in the Baltic Sea system and show that no relationship between cod growth and sprat biomass is present related to the low size resolution in prey fish. Linking individual cod performance to its resource base is complicated by the many prey types cod uses over its life cycle. We conclude that an ecological perspective including size-and food-dependent processes is vital for ecosystem-based fisheries management making necessary a proper description of the interactive trophic structure as a result of mechanistic linkages between individual, population, and community processes.

关键词： Protein Mutation   Steered Molecular Dynamics   Cell Adhesion Molecule   Mechanical Stiffness  

摘要： In different types of cancer, mutations in protein level lead to impaired structure and function. The epithelial cadherin plays a major role in the consistency of cell-cell adhesion and inhibits cancer progression. Reduced expression level of E-cadherin accompanied by the expression of mutated E-cadherin result in loss of cell adhesion and tendency to invade. To quantify the extent of effect of such mutations on mechanical properties of E-cadherin, we used steered molecular dynamics simulation. Since the mutations occur in different extracellular domains, each domain was modeled separately and two methods of simulations were implemented on the wild-type and mutated structures in gastric and prostate carcinomas. Another mutation was constructed to comply with original sequencing of the protein. Among different variables, number of hydrogen bonds and solvent accessible surface area were mostly influential. Alterations within the protein structure caused both stiffening and softening of the protein depending on the location of mutations and the nature of change in the protein structure. Substitution of a single amino acid induced by mutation considerably changed mechanical stiffness of a single domain. Deletion of four residues in a domain noticeably reduced the stiffness. Results may contribute to proper understanding of mechanisms involved in progression of cancer.

关键词： Polymer gels   Molecular dynamics simulation   Mechanical properties  

摘要： Computational modeling was utilized to design complex polymer networks and gels which display enhanced and tunable mechanical properties. Our approach focuses on overcoming traditional design limitations often encountered in the formulation of simple, single polymer networks. Here, we use a coarse-grained model to study an end-linked flexible polymer network diluted with branched polymer solvent chains, where the latter chains are composed of rigid side-chains or "spikes" attached to a flexible backbone. In order to reduce the entropy penalty of the flexible polymer chains these rigid "spikes" will aggregate into clusters, but the extent of aggregation was shown to depend on the size and distribution of the rigid side-chains. When the "spikes" are short, we observe a lower degree of aggregation, while long "spikes" will aggregate to form an additional secondary network. As a result, the tensile relaxation modulus of the latter system is considerably greater than the modulus of conventional gels and is approximately constant, forming an equilibrium zone for a broad range of time. In this system, the attached long "spikes" create a continuous phase that contributes to a simultaneous increase in tensile stress, relaxation modulus and fracture resistance. Elastic properties and deformation mechanisms of these branched polymers were also studied under tensile deformation at various strain rates. Through this study we show that the architecture of this branched polymer can be optimized and thus the elastic properties of these advanced polymer networks can be tuned for specific applications. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Computational fluid dynamics CFD   Bileaflet mechanical heart valve   Blood damage   Thromboembolic potential   Pediatric flows  

摘要： Despite pressing needs, there are currently no FDA approved prosthetic valves available for use in the pediatric population. This study is performed for predictive assessment of blood damage in bileaflet mechanical heart valves (BMHVs) with pediatric sizing and flow conditions. A model of an adult-sized 23 mm St. Jude Medical (SJM) Regent" valve is selected for use in simulations, which is scaled in size for a 5-year old child and 6-month old infant. A previously validated lattice-Boltzmann method (LBM) is used to simulate pulsatile flow with thousands of suspended platelets for cases of adult, child, and infant BMHV flows. Adult BMHV flows demonstrate more disorganized small-scale flow features, but pediatric flows are associated with higher fluid shear stresses. Platelet damage in the pediatric cases is higher than in adult flow, highlighting thrombus complication dangers of pediatric BMHV flows. This does not necessarily suggest clinically important differences in thromboembolic potential. Highly damaged platelets in pediatric flows are primarily found far downstream of the valve, as there is less flow recirculation in pediatric flows. In addition, damage levels are well below expected thresholds for platelet activation. The extent of differences here documented between the pediatric and adult cases is of concern, demanding particular attention when pediatric valves are designed and manufactured. However, the differences between the pediatric and adult cases are not such that development of pediatric sized valves is untenable. This study may push for eventual approval of prosthetic valves resized for the pediatric population. Further studies will be necessary to determine the validity and potential thrombotic and clinical implications of these findings. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： composites   degradation   flame retardance   kinetics   mechanical properties  

摘要： Addition of particulates into laminates has been found to influence thermal and mechanical properties. Composite laminates of epoxy-high density polyethylene (HDPE) fabric-clay were prepared by reinforcing clay in the range of 0.1-0.7 phr into epoxy-HDPE fabric laminates. These laminates are characterized for their mechanical, thermal, and flame retardant performances. With the addition of clay, an increase was found in impact resistance, tensile strength, flexural strength, and Young's modulus to an extent of 0.2 phr clay, after which there is a decrease in these properties. The thermal stability is found to decrease with the addition of clay. The improved mechanical properties are obtained at the slight expense of thermal stability. UL-94 tests indicate a reduction in the burning rate. Morphology of the broken samples indicate better dispersion at lower clay load and tactoid formation at higher clay loading. These materials have potential applications in agriculture, construction, and decorative purposes. (C) 2014 Wiley Periodicals, Inc.

关键词： High-strength Al81.8Ni9.2Co4.8Y3.1Zr1.1 alloy   Nanostructured intermetallics   Nanocrystalline-embedded alloys   Microhardness   EDX line mapping analysis   Crystallization kinetics  

摘要： High-strength nanocrystalline-embedded-alloy was successfully fabricated by the consolidation of melt-spun amorphous ribbons of Al81.8Ni9.2Co4.8Y3.1Zr1.1. The as-melt amorphous spun, the annealed and the fully dense nanocrystalline extruded specimens were investigated using XRD, HRTEM, SAED, EDX line mapping, microhardness, compression tests, SEM at fractured surfaces and the crystallization's kinetics were determined from DSC. XRD, in good accordance with HRTEM, SAED and the associated EDX line mapping analysis, revealed the merely amorphous nature of the as- melt spun ribbons and confirmed bearing of nanocrystalline-embedded phases in the annealed and extruded specimens with the remaining of some amorphous phase. HRTEM and SAED revealed that annealing at 275 degrees C resulted in the formation of short-range ordered regions of fcc alpha-Al nanoparticles and intermetallic nanocrystalline-embedded grains of 5-10 nm that grown to 20-50 nm after extrusion. DSC showed that the as- melt spun ribbons crystallize at three stages in contrast to one late stage shown by the extruded sample. Crystallization kinetics of the as- spun ribbons yielded crystallization activation energy (E-c) of 143.4 and 36 kJ/mol for the first and second crystallization peaks respectively. The extruded specimen showed improved strength of 550 at a load of 50 g while the as- melt spun ribbons indicated lower hardness of 367 at a similar load. The ultimate compressive stress of the extruded specimen reached 800 MPa with 0.66% strain and Young's modulus of 1.26 GPa. SEM micrographs of the fracture surface showed a transgranular failure with a dimpled surface reflecting the microplasticity of the final product. Improved mechanical properties and thermal stability of the nanocrystalline-embedded-specimen are due to the nanoparticle strengthening effect of the very hard and non-deformable nanosized alpha-aluminumand Al-based intermetallic nanograins that are densely formed during the annealing, extrusi

关键词： Nanoclays   Polymer-matrix composites (PMCs)   Environmental degradation   Computational mechanics  

摘要： In this study, the moisture related hygroscopic characteristics and mechanical properties of polymer-clay nanocomposites (PCNs) were investigated using molecular dynamics (MD) simulations and experiments as a function of the weight fraction of nanoclay. The hygroscopic and mechanical properties including the moisture saturation amount, moisture diffusivity, work of adhesion, and elastic modulus of the PCNs were studied using MD simulations and compared to experimental results as a function of the nanoclay content. It was demonstrated that the proposed MD simulation technique can be successfully used for the prediction of the effects of the nanoclay on the moisture diffusion characteristics as well as mechanical improvements of PCNs. It is expected that the simulation technique applied in this work can be widely used to evaluate the performances of nanocomposite materials. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： 农业机械   安全   割草机   剪草机   灌木   收获机械   AGRICULTURAL MACHINERY   AGRICULTURAL MACHINES   SECURITY   SAFETY   GRASS MOWERS   MOWERS   LAWN TRIMMERS   GRASS SHEARS   LAWN MOVERS   LAWN-MOWERS   SHRUBS   HARVEST EQUIPMENT   HARVESTING EQUIPMENT   HARVESTING MACHINES  

标准号: GB 19725.2-2014

摘要： GB 19725的本部分规定了以内燃机为背负动力源并将机械动力传递至切割附件的便携式割灌机和割草机的设计、结构和使用方面的安全要求及其试验方法,本部分提出了消除或减少使用整机所产生的各种危害的方法,规定了由生产厂家提供的安全操作方面有关资料的要求。本部分和第1部分的相关章节(见4.1)涉及了在正常使用以及合理的、制造商可预见的误用整机时所有与整机相关的严重危险、危险情况及严重危害事件,背负式动力装置引起的全身振动危害除外。本部分适用于在其颁布实施后生产的产品。本部分不适用于安装非整体金属刀片结构的机器,例如甩链或甩刀刀片。

关键词： 林业   林业设备   控制   符号   标记   标志   图形符号   农用设备   园艺设备   农用拖拉机  

标准号: GB/T 4269.4-2014

摘要： GB/T 4269的本部分规定了 ISO 6814所界定的林业机械的操作者控制符号和其他标记。本部分给出的符号和其他标记适用于伐木归堆机、抓钩式集材机和木材装载机,也适用于专用链锯、平衡支撑装置和绞盘机。