Investigation of photophysical, morphological and photovoltaic behavior of poly(p-phenylene vinylene) based polymer/oligomer blends

Two cyano oligo-phenylene-vinylenes [α-CNOPV and β-CNOPV] distinguished by the position of cyano (CN) group at the vinylic double bond were synthesized. The acceptor oligomer CNOPVs were blended with poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) MEH-PPV to achieve α and β blends. The pronounced influence of cyano position on the photophysical and morphological properties of blends was observed through UV-vis absorption, photoluminescence and atomic force microscopy. The optical characterization suggests wider spectral photon harvesting in α blends and more planar conformation of molecules in β blends. The steady-state and time-resolved photoluminescence study provides evidence for efficient energy transfer from α-CNOPV to MEH-PPV. On the other hand, the 3:1 β blend exhibits quenching of PL intensity indicative of charge transfer. In addition, the feasibility of MEH-PPV:CNOPV blends in organic photovoltaic devices have been investigated. The initial device parameters show that power conversion efficiency is as high as 0.05% in β 1:1 devices. The photovoltaic efficiencies were limited by weak exciton dissociation in α blends while poor morphology restricted the efficiency in β blends.     

Modeling the compression-induced morphological behavior of nonwoven materials

Nonwovens have the most complex morphologies in textile materials and they are often being compressed in a range of applications. The morphology of a typical nonwoven is defined in terms of fiber orientation, fiber volume fraction, number of fiber-to-fiber contacts, distance between the contacts, porosity, and pore size distribution. In this study, an attempt has been made to predict the morphological characteristics of nonwoven materials under the state of compression. A concept of compression ratio has been introduced in predicting the fiber volume fraction at a defined level of compression strain that has significantly influenced the other morphological characteristics of nonwoven materials. A mechanistic model of pore size distribution of nonwoven has been proposed by updating the structural and morphological parameters under predefined compressive stresses. A comparison has been made between theoretical and experimental pore size distributions of compressed nonwoven fibrous materials. In addition, the out-of-plane fiber orientation distribution was experimentally obtained by analyzing the two-dimensional (2D) cross-sections of fibers in the thickness direction.     

The role of contact friction in the dynamic breakage behavior of granular materials

Based on the discrete element method, a multi-scale model is employed to investigate the role of contact friction in the dynamic compression responses of brittle granular materials. Four numerical granular samples with different particle friction coefficients ranging from 0.0 to 2.0 are tested and the particle breakage extent is quantified with the Einav breakage index. It is observed that the relationship of the breakage extent with the axial stress is apparently non-monotonic concerning the particle friction coefficient. At the same stress level, the breakage extent exhibits a minimum when the particle friction coefficient is around 0.1 but increases significantly with the particle friction coefficient to both sides. The micro physical origin of this non-monotonic behavior is a distinct transition in dominant particle-breakage modes from tension to shear. Moreover, energy analyses also show non-monotonic evolution of the frictional and damping dissipation with the particle friction coefficient. The joint effect of these two dissipation terms contributes to the non-monotonic behavior of particle breakage. In addition, the accuracy and competence of two frequently-used micro quantities, fraction of sliding contacts and average coordination number, are discussed.

     

IPMC的力输出特性

IPMC(ion-exchange polymer metal composite)离子交换聚合物-金属复合材料)是一种人工肌肉材料,其较低的驱动电压能产生较大的位移变形,研究了IPMC这种智能材料的输出力特性.实验选取了不同电压幅值,不同频率的方波、三角波、正弦波3种波形作为电激励信号,通过力传感器实测了IPMC试样末端的输出力.结果表明,随着电压幅值的增大,其输出力也增大;随着电刺激信号频率的降低,其输出力也增大;而波形对其输出力影响不显著.     

Predicting breakage behavior and particle size of bronze and cast iron machining chips pulverized by jet milling

It has been proposed that the breakage behavior of particulate materials can be described by two material parameters f_mat and W_min. f_mat describes the resistance of the material to fracture in impact pulverization and W_min characterizes the specific energy which a particle can absorb without fracture. It is shown in this study that this concept can be used to quantify breakage behavior of bronze and cast iron chips in jet milling process and also to predict particle size of the jet milled product. Different tin bronze and cast iron chips with varying initial size were pulverized in a target plate jet mill with different velocity. f_mat was found to be in the range of 0.06–0.09 and 0.18–0.25 for bronze and cast iron alloys, respectively. For the cast iron alloys f_mat increased with increasing content of carbon and silicon. Similarly, for the bronze alloys, f_mat increased with increasing tin content. An equation was developed to predict mean particle size of the jet milled chips as a function of the kinetic energy, initial chip size and material parameters. The experimental results of various alloys confirmed that the mean particle size after single and multiple impacts were accurately predicted.     

Modeling and simulation of the effect of fiber breakage on creep behavior of fiber-reinforced metal matrix composites

A theoretical model and computer simulation methodology was developed to predict the effect of fiber fracture on creep behavior of continuous fiber-reinforced metal matrix composites. Initially, a single fiber model was developed based upon the fiber statistical characteristics and a shear-lag analysis to establish the computation simulation route. Then, the methodology was extended to predict the creep behavior of a multiple fiber composite. A failure criterion was also incorporated in the model to predict the rupture life of the composite. A parametric study was also conducted to investigate the effects of properties of the constituents on the longitudinal creep behavior of the SCS-6/Ti composite.     

Influence of high-pressure grinding rolls on physical properties and impact breakage behavior of coarsely sized cement clinker

ABSTRACT

High-pressure grinding rolls (HPGR) are widely used in cement clinker grinding prior to ball milling. The efficiency of HPGR was previously related to two capabilities: (a) efficient stressing mechanism and (b) weakening of particles which lead to finer product sizes after subsequent ball milling. This study aimed to investigate the influence of HPGR on the impact breakage behavior of coarsely sized cement clinker. Drop weight tests were conducted on three single-size samples from both feed and product streams of an industrial HPGR, so as to obtain impact breakage parameters: breakage probability and impact breakage functions. Radiographic, Vickers micro-hardness, BET, SEM, XRD, XRF, and image processing methods were utilized to explain the variations in impact breakage parameters. The product samples were found to have less porosity than feed samples but they contained HPGR-induced micro-cracks. Those cracks are believed to be responsible for lower hardness and higher breakage probability of product particles than of feed ones under impact. However, fragments generated from the product samples by drop weight tests were coarser than those generated from feed samples. That was due to elimination of pores by HPGR action. At excess energy levels, both samples were broken to same extent regardless of structural differences.     

An investigation on the breakage behavior of olivine sand particles: An attainable region technique

This study investigates the breakage behavior of olivine sand particles to identify optimal operating parameters to get products in three different define particle size classes. This was achieved by a Los Angeles abrasion test with different numbers of steel balls (up to 12), weights of steel balls (up to 0.441 kg), and different grinding durations (up to 200 mins). The data obtained were then analyzed using a model-free and equipment-independent attainable region (AR) technique. The findings revealed that the required product fineness is a function of the grinding time, numbers and weight of steel balls, and feed material size. Using 9 steel balls of 0.441 kg, a higher mass fraction of materials in the fine-sized class (?75 μm) was obtained after grinding for 200 mins. The AR technique proved to be a practical approach to optimize olivine particle size during breakage, with a potential application in sustainable soil stabilization projects.     

不同形状涡街发生体流场仿真及特性研究

利用Fluent数值仿真软件对圆柱、梯形柱和一种新型带狭缝圆柱发生体的绕流特性进行对比研究.通过在发生体附近设置检测点,得到静压分布情况.以计算精度和速度为依据,指出适合涡街发生体的计算方法.将带狭缝圆柱作为重点,分析不同发生体绕流产生的涡街信号特性.结果表明,带狭缝圆柱生成的涡街信号强度最高,斯特劳哈尔数线性度好且压力损失较低,因此将带狭缝圆柱用于涡街流量计是可行的.     

Preparation and structural characterization of bismuth ferrite crystals of different morphological types

We have studied conditions for bismuth ferrite, BiFeO₃, crystallization from off-stoichiometric Bi₂O₃-Fe₂O₃ melts, obtained crystals of different morphological types (dendritic and faceted pseudocubic) up to 3 mm in size, and characterized them by a variety of techniques (X-ray diffraction, IR spectroscopy, differential thermal analysis, X-ray structure analysis, and X-ray microanalysis).     

Solvothermal synthesis of nickel nanorods and its magnetic, structural and surface morphological behavior

One-dimensional rod-like nickel nanostructure was fabricated through a simple, efficient and one pot solvothermal approach with hydrazine hydrate and trimethylamine as reducing and morphology directing agents. The phase structure, morphology and magnetic properties of the as-prepared product were extensively characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. X-ray diffraction pattern indicated that the as-synthesized product was nickel with well-crystallized face-centered cubic structure. TEM observation showed that the nickel product consists of rod-like shape with size around 10 nm. Magnetic measurements revealed that the coercive forces of nickel nanorods at 300 K and 4.2 K are 198 Oe and 250 Oe, respectively. Compared with bulk nickel, the nanorods exhibit significant increase in coercive force as a reflection of shape anisotropy. A possible mechanism for the formation of rod-like nanostructure is proposed.     

Investigation of failure behavior of two different types of Zircaloy clad tubes used as nuclear reactor fuel pins

Nuclear reactor fuel pins act as barriers to the release of radioactive fission products to the coolant flowing around these thin-walled tubes and hence they prevent the leakage of radioactivity to the surroundings of reactor core. These tubes are of small thickness in order to have less resistance in the path of heat flow from the fuel to the coolant. Investigation of failure behavior of these fuel clad tubes is of utmost importance to the designers and plant operators in order to ensure the maximum residence time of the fuel bundles inside the reactor core as well as to ensure minimal activity during operation and refueling activities. Various types of zirconium based alloys are used to manufacture these pins. The focus is to obtain better strength, ductility, corrosion resistance, oxidation resistance, and minimal creep including those due to irradiation-assisted damage and deformation processes. Two number of such types of alloys, namely, re-crystallization annealed Zircaloy-2 and stress-relief annealed Zircaloy-4, have been investigated in this work for their fracture behavior. As standard fracture mechanics specimens cannot be machined from these thin-walled tubes, non-standard specimens with axial cracks have been used in this work. Load normalization technique has been used to evaluate crack growth during loading of these specimens. It was observed that the re-crystallization annealed Zircaloy-2 specimens have higher initiation fracture toughness as well as higher resistance to crack growth compared to the other type of specimens. In order to understand the micro-structural aspects of the fracture resistance behavior of these materials, further investigation incorporating optical and transmission electron microscopy have also been carried out. It was concluded that the higher fracture resistance behavior of the re-crystallization annealed Zircaloy-2 specimens can be attributed to the presence of finer grain and sub-grain micro-structure, very low dislocation density and other defects in the material.     

Investigation of annealing behavior of nanocrystalline NiAl

Nanocrystalline NiAl prepared by mechanical alloying and the vacuum heat pressing method has been studied to investigate its thermal stability. Isothermal annealing was conducted at 1000°C. The results show that a significant grain growth takes place from 30 nm at the initial state to 56 nm by annealing for 30 h, then maintains this value regardless of annealing time up to 100 h. Microhardness test results show that the microhardness of the annealed specimens reduces significantly with annealing time up to 5 h and then increases slightly with further annealing due to off-stoichiometry. In addition, positron annihilation spectroscopy has been used to investigate the interfacial defects in the nanocrystalline NiAl specimens. The results show that there are three kinds of defects in the interfacial region of the nano-NiAl alloy, which are monovacancy-sized free volumes, microvoids and large voids. During the present annealing process, the sizes of the three defects have no significant change, but the amount of the defects, especially for monovacancy-sized free volumes and microvoids varies clearly with annealing time.     

Investigation of sisal fibers by atomic force microscopy: morphological and adhesive characteristics

Atomic force microscopy (AFM) was used to study the nanoscale surface chemistry and morphological changes caused by chemical treatment of sisal fibers. Scanning Electron Microscopy (SEM) micrographs indicated that sisal in natura (bundle of fibers) is formed by fibers with diameters of approximately 10 microm. AFM images showed that these fibers consist of microfibrils with diameters varying from 250 to 600 nm, which are made up of nanofibrils of ca. 20 nm in diameter. The adhesion force (pull-off force) between the AFM tip and the fibers surface increased after benzylation, pointing to a decrease in the polar groups on the sisal fiber. The adhesion map measured over a scan range of 3 microm was heterogeneous in samples treated with 40% NaOH and the low adhesion sites disappeared after benzylation. Using an established mathematical model, it was possible to evaluate the increase in adhesion work and consequently in the interaction between the AFM tip and sisal fibers. These results indicated that AFM can detect heterogeneity in the wettability of sisal fibers with nanometer resolution and can be applied in the study of fiber-matrix adhesion in polymer composites.     

Investigation of microstructure and flexural behavior of steel-fiber reinforced concrete

This paper presents microstructure and flexural behavior of steel-fiber reinforced concrete produced with different steel fibers volume fraction and aspect ratio. Prismatic concrete specimens of 100 × 100 × 350 mm were prepared with and without steel fiber. Two different steel fiber types (both is hooked-end) were used by ratio of 0% (control), 0.2, 0.4, 0.6 and 0.8% by volume. Specimens were de-molded after 24 h and cured in water until 7, 28, 56, 180 and 360 days. On the prisms, flexural strength has been defined for every age. The crack widths have also been measured after maximum bearing loads. Microstructure of SFRC was studied by scanning electron microscopy and optical microscopy for 180 aged specimens. The results showed that the polarized microcopy images may be used for observing the bond characteristic of SFRC as alternatively to SEM. A good bond was observed between steel fiber and concrete matrix interface zone by using polarizing microscopy, too. Flexural strength of SFRC increased with the concrete age and fiber volume fraction. Besides, the first crack development significantly decreased by increasing of fiber volume fraction in the all concrete ages.     

C/C复合材料特性对其摩擦磨损性能的影响

在MM-2000环-块摩擦试验机上研究了制备工艺、石墨化度、密度、纤维取向等材料特性对其摩擦磨损性能的影响。研究结果表明，采用化学气相渗透(CVI) 浸渍工艺制备并经过多次浸渍增密且石墨化后的材料具有优良的摩擦磨损特性。石墨化后试样的密度越大，其摩擦磨损性能也越好。一般情况下在载荷适中时，垂直试样的摩擦系数要大于平行试样，而体积磨损量却小于平行试样。C／C复合材料比高强石墨材料更适宜用作航空发动机轴间密封材料。     

Investigation of the breakage parameters of gypsum as dependent on interstitial filling in a laboratory ball mill

Gypsum is an industrial material used in many applications such as building and chemical industry, fertilizer manufacture, medicine and dentistry. In these industries, there is need for finely ground gypsum. Energy consumption is very high in grinding processes. Therefore, the effects on breakage kinetics of powder filling and ball filling were investigated on gypsum samples taken from the Denizli-Honaz region (Turkey), for batch grinding conditions based on a kinetic model. For this purpose, firstly, eight different mono-size fractions between 1.7 and 0.106 mm formed by a \({\surd 2}\) sieve series were obtained. Then, S _i and B _i,j equations were determined from the size distributions at different grinding times, and the model parameters (S _i , a _T , α, γ and \({\phi_{j}}\)) were compared for four different proportions of powder filling (5, 7.5, 10 and 15%), and three different proportions of ball filling (25, 35 and 45%). Finally, model parameters are discussed for each test. From the result of tests, obtained of the effect of ball filling and powder filling on the grinding, it was found our results differed from those of other investigators.     

Photocatalytic behavior of different titanium dioxide layers

Many recently developed applications are related to the photocatalytic behavior of semiconductive oxides. Among the different oxides, titanium dioxide (TiO₂) is one of the most interesting due to its high photocatalytic efficiency towards a great number of reactions and to its hydrophilic properties. Aim of this work is the evaluation and comparison of the photocatalytic properties of different crystalline titanium dioxide films, directly grown on titanium substrates by surface anodization (eventually followed by thermal annealing) and by Pulsed Laser Deposition (PLD) on titanium and silicon substrates, followed by thermal annealing. The structure and morphology of the layers were characterized by Scanning Electron Microscopy and X-Ray Diffraction and photocatalytic tests on stearic acid mineralization were performed. Results showed that the PLD layers possess a higher photocatalytic efficiency than anodized titanium. This can be attributed to the microstructured/microporous morphology of the related surfaces. Instead, PLD TiO₂ layers with a relatively high content of the rutile phase have a reduced photocatalytic efficiency with respect to mainly anatase containing layers.     

人耳对于不同频率成分分离知觉的定量分析

文章中研究了知觉性声源分离的最基本的问题，即听觉对于不同频率成分特征声源的分离知觉。通过三组听觉辨别实验，定量地分析了不同频率成分特征声源与产生分离知觉的关系，得到了描述这种关系的近似函数，提出了听觉对于不同频率成分特征的分离知觉模型。通过听觉辨别实验得出：两种频率成分的On-set和Off-set的偏离是产生分离知觉的主要原因之一；谐波频率成分之间频率发生的偏移也是产生分离知觉的要因之一；要实现实环境下的知觉性声源分离系统，必须研究各个特征量相互作用时产生的综合结果。     

Towards a realistic morphological model for the meso-scale mechanical and transport behavior of cementitious composites

In this work, we investigate the mechanical and transport properties of cementitious composites using a realistic morphological 3D matrix-inclusion-ITZ model for the mesoscale behavior. Assuming a compression damaged plasticity-based behavior for the matrix phase under quasi-static loading, the model is used to determine the effect of inclusion (aggregate) shape, volume fraction and segregation on the mechanical response of the composite specimen under uniaxial loading. We then use the model to evaluate the effect of the previously mentioned variables as well as aggregate intrinsic permeability on the macroscopic permeability of the same composite specimen using a series of non-conforming FE meshes and level set functions to monitor the heterogenities. The model is then applied to a self-compacting concrete (SCC) with a higher volume of cement paste in order to flow more freely and be formed into complex shapes without shaking. However, this elevated fluidity predisposes SCCs to a higher risk of segregation, i.e. separation between the suspending phase and coarse aggregates, which can affect the mechanical behavior of the composite.