Fatigue growth of multiple-cracks near a row of fastener-holes in a fuselage lap-joint

The fatigue growth of multiple cracks, of arbitrary lengths, emanating from a row of fastener holes in a bonded, riveted, lap joint in a pressurized aircraft fuselage is studied. The effects of residual stresses due to a rivet misfit, and of plastic deformation near the hole, are included. A Schwartz-Neumann alternating method which uses the analytical solution for a row of multiple colinear cracks in an infinite sheet (the crack-faces being subject to arbitrary tractions), is developed to analyze this MSD problem on a personal computer. It is found that for a range of crack lengths, a phenomena wherein the shorter cracks may grow faster than longer cracks may exist.     

On the behaviour of hygroscopic wheels: Part I – channel modelling

In this paper a detailed mathematical formulation is developed for the numerical modelling of the behaviour of a channel of a hygroscopic compact matrix. A comparison between the detailed version and a simplified one is performed considering a two-dimensional airflow between desiccant parallel plates. The distinct heat and mass transfer phenomena are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption processes. Both physical models take into account the gas side and solid side resistances to heat and mass transfer. The wall domain is treated similarly in both models, by taking into account the simultaneous heat and mass transfer together with the water adsorption/desorption process. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms without hysteresis. The detailed model is based on the solution of the differential equations for the conservation of mass, energy and momentum, assuming that no momentum transport exists in the porous wall domain. In the simplified model, the airflow is treated as a bulk flow, the interaction with the wall being evaluated by using appropriated convective coefficients.Both models are compared in the simulation of a parallel plate channel during an adsorption process. The results show a good agreement for channel lengths greater than 0.1 m. In part II of the paper, the simplified model is adapted to the simulation of the three-dimensional problem in the channel of a hygroscopic rotor, and it is used to perform parametric studies.     

Variational density matrix approach to the temperature-dependent elementary excitation spectrum of two-dimensional liquid4He

Using the variational density matrix method, we obtain a temperature-dependent elementary excitation spectrum for two-dimensional liquid⁴He. For more precise results, we use a Jastrow-Feenberg-type trial wave function and include the contribution of elementary diagrams within the hypernetted chain approximation. The behavior of the excitation spectrum as a function of the temperature and density in two dimensions is similar to that of the bulk system, but has a smaller roton minimum. The roton minimum of the excitation spectrum decreases with increasing temperature and increases with increasing density at low densities but decreases at large densities. The results agree well with Monte Carlo calculations and are closer than pevious theories to experimental measurements of⁴He film adsorbed on substrates.     

Visual tracking using convolutional features with sparse coding

Artificial Intelligence Review - Visual object tracking has become one of the most active research topics in computer vision, and it has been applied in several commercial...     

Spray Coating of 2- and 3-D Solid Substrates Using a Sulfated Polysaccharide for Marine Antifouling Applications

Marine antifouling coating using functional polymers has emerged as an important tool to combat marine fouling. Owing to their natural abundance, polysaccharides represent a more sustainable option than synthetic polymers and carrageenan, a sulfated polysaccharide, is identified as a promising candidate for further research based on its excellent marine antifouling properties. However, existing research has only explored the application of carrageenan-based coatings for 2D objects, using techniques such as spin-coating. Here, a spray-coating method is proposed to apply carrageenan-based coatings to the surfaces of 2- and 3-D objects. The coated surfaces exhibit high stability under various chemical/physical stresses and high resistance to protein adsorption and marine diatom adhesion.     

Leveraging clustering approaches to solve the gray-sheep users problem in recommender systems

Recommender systems apply data mining and machine learning techniques for filtering unseen information and can predict whether a user would like a given item. This paper focuses on gray-sheep users problem responsible for the increased error rate in collaborative filtering based recommender systems. This paper makes the following contributions: we show that (1) the presence of gray-sheep users can affect the performance – accuracy and coverage – of the collaborative filtering based algorithms, depending on the data sparsity and distribution; (2) gray-sheep users can be identified using clustering algorithms in offline fashion, where the similarity threshold to isolate these users from the rest of community can be found empirically. We propose various improved centroid selection approaches and distance measures for the K-means clustering algorithm; (3) content-based profile of gray-sheep users can be used for making accurate recommendations. We offer a hybrid recommendation algorithm to make reliable recommendations for gray-sheep users. To the best of our knowledge, this is the first attempt to propose a formal solution for gray-sheep users problem. By extensive experimental results on two different datasets (MovieLens and community of movie fans in the FilmTrust website), we showed that the proposed approach reduces the recommendation error rate for the gray-sheep users while maintaining reasonable computational performance.     

Estimation and forecasting with logarithmic autoregressive conditional duration models: A comparative study with an application

This paper presents a semi-parametric method of parameter estimation for the class of logarithmic ACD (Log-ACD) models using the theory of estimating functions (EF). A number of theoretical results related to the corresponding EF estimators are derived. A simulation study is conducted to compare the performance of the proposed EF estimates with corresponding ML (maximum likelihood) and QML (quasi maximum likelihood) estimates. It is argued that the EF estimates are relatively easier to evaluate and have sampling properties comparable with those of ML and QML methods. Furthermore, the suggested EF estimates can be obtained without any knowledge of the distribution of errors is known. We apply all these suggested methodology for a real financial duration dataset. Our results show that Log-ACD (1, 1) fits the data well giving relatively smaller variation in forecast errors than in Linear ACD (1, 1) regardless of the method of estimation. In addition, the Diebold–Mariano (DM) and superior predictive ability (SPA) tests have been applied to confirm the performance of the suggested methodology. It is shown that the new method is slightly better than traditional methods in practice in terms of computation; however, there is no significant difference in forecasting ability for all models and methods.     

1D helical ZnII metal–organic polymers: Syntheses,structures and fluorescent properties

Hydrothermal reactions of 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole (pbbm) with ZnCl₂ afford two 1D helical metal–organic polymers {[ZnCl₂(pbbm)] · (H₂O)_1/8}_n (1) and {[Zn(pbbm)₂] · Cl₂ · (H₂O)_1/2}_n (2). Polymer 1 features a 1D single helical architecture, whereas 2 possesses a 1D cationic double helical chain framework. Photoluminescence investigations reveal that both of them display strong emissions in the solid state at room temperature, which could originate from a ligand-to-ligand charge-transfer (LLCT) transition, as confirmed by the molecular orbital (MO) calculations.     

Physical properties and morphology of polycaprolactone/starch/pine‐leaf composites

Polycaprolactone (PCL)/starch and PCL/starch/pine‐leaf composites, which can be possibly applied as biodegradable food packaging materials with natural pine flavor, were prepared and characterized in this study. The effect of incorporating a silane coupling agent at different content levels on the physical properties and morphology of the composites was studied. To investigate the melting behavior of the composites, a differential scanning calorimetry was employed. A universal testing machine was used to investigate the tensile properties of the composites and the water absorption properties of the composites were also investigated. Scanning electron microscope was used to investigate the morphology of the composites. The physical properties and morphology of the PCL/starch and PCL/starch/pine‐leaf composites were largely affected by the composition, especially the content of the silane coupling agent. The silane coupling agent led to a much better interfacial compatibility between the PCL matrix and the fillers and resulted in better physical properties of the composites. The PCL/starch/pine‐leaf composite with the silane coupling agent showed a morphology, indicating a good interfacial adhesion between the PCL matrix and the fillers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 928–934, 2007     

基于Workbench的龙门五轴联动机床多种位姿下的静动态分析

针对龙门机床运行过程中在外载荷影响下因刚度不足而产生的震颤问题,利用Solidworks建立虚拟样机,导入Workbench,并按照实际工况施加预应力对模型进行了结构静力、自由模态和预应力模态分析.结果表明,外载荷使机床的固有频率明显减小,振型变大,因此在实际工作中不可忽视外载荷对机床振动的影响.