MAPLE-deposited polymer films for improved organic device performance

Matrix-assisted pulsed-laser evaporation (MAPLE) provides a mechanism for layer-by-layer growth to control the polymer–dielectric interface in organic metal–insulator–semiconductor (MIS) diodes and field-effect transistors (FETs). MAPLE-deposited copolymers of polyfluorene (PF) and polythiophene maintain their structural and optical properties, as determined by Raman spectroscopy, absorption, and photoluminescence. These films are further utilized in MIS and FET structures with SiO₂ and other polymer dielectrics. Since common polymer dielectrics prevent spin coating of solution processable polymers due to solubility effects, MAPLE is one of the only deposition techniques for investigating all polymer semiconductor-insulator interfaces. In this paper we present optical and electrical studies of MAPLE-deposited PF and polythiophene films in FETs and MIS structures. The FET carrier mobilities of these devices compare well with spin-coated devices. Capacitance–voltage and conductance–voltage from MIS structures with MAPLE-deposited PF copolymer films yield interface trap densities in the low 10¹² eV⁻¹ cm⁻² range.     

Structural behaviour of fibre metal laminates subjected to a low velocity impact

Structural impact tests were first presented to cover typical fibre metal laminates (FMLs) subjected a low velocity projectile impact,which produced the corresponding load-displacement traces and deformation/failure modes for the validation of numerical models.Finite element (FE) models were then developed to simulate the impact behaviour of FMLs tested.The aluminium (alloy grade 2024-0) layer was modelled as an isotropic elasto-plastic material up to the on-set of post failure stage,followed by shear failu...     

Studies on the impact response of carbon-epoxy laminates with and without buffer-strip layers

The work looks at the dynamic behaviour of laminated carbon-epoxy (C-E) composites with inserted interleaf material. Instrumented impact tests were performed to study the impact response of C-E system containing the interleaved PTFE-coated fabric material. Significant differences were noticed in the trend of the load-time plots. It was inferred that the introduction of small amounts of less adherent layers of material at specific locations causes a decrement in the load carrying capability of this material. An attempt to correlate these trends with the post impact observed failure features has been made in this work.     

Narrow stripe semiconductor laser for improved performance of optical communication systems

A narrow stripe (GaAl) As/GaAs laser is described, which has low source noise, high linearity and an expected life in excess of 20,000 hours. It has a short coherence length compared with a self-focused or refractive index guided laser giving very good modal noise performance. It is suitable for all digital systems and all but the most demanding amplitude modulated analogue systems.     

A simple technique for improved performance of intracavity Fabry-Perot frequency selectors

By placing an intracavity Fabry-Perot transmission etalon between quarter-wave plates it is possible to operate it at normal incidence without spurious oscillation due to reflections from the etalon. The insertion loss and reduced finesse associated with a tilted etalon are thereby avoided. This technique will allow the use of longer etalons thus allowing much greater mode selectivity.     

An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates

Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1] and [2].     

Development of mechanoluminescence technique for impact studies

A new technique called, mechanoluminescence technique, is developed for measuring the parameters of impact. This technique is based on the phenomenon of mechanoluminescence (ML), in which light emission takes place during any mechanical action on solids. When a small solid ball makes an impact on the mechanoluminescent thin film coated on a solid, then initially the elastico ML (EML) intensity increases with time, attains a maximum value I_m at a particular time t_m, and later on it decreases with time. The contact time T_c of ball, can be determined from the relation T_c=2t_c, where t_c is the time at which the EML emission due to compression of the sample becomes negligible. The area from where the EML emission occurs can be taken as the contact area A_c. The maximum compression h is given by h=A_c/(πr), where r is the radius of the impacting ball, and thus, h can be determined from the known values of A_c and r. The maximum force at contact is given by F_m=(2mU₀)/T_c, where m is the mass of the impacting ball and U₀ is the velocity of the ball at impact. The maximum impact stress σ_m can be obtained from the relation, σ_m=F_m/A_c=(2mU₀)/(T_cA_c). Thus, ML provides a real-time technique for determining the impact parameters such as T_c, A_c, h, F_m and σ_m. Using the ML technique, the impact parameters of the SrAl₂O₄:Eu film and ZnS:Mn coating are determined. The ML technique can be used to determine the impact parameters in the elastic region and plastic region as well as fracture. ML can also be used to determine the impact parameters for the collision between solid and liquid, if the mechanoluminescent material is coated on the surface of the solid. The measurement of fracto ML in microsecond and nanosecond range may provide a tool for studying the fragmentations in solids by the impact. Using the fast camera the contact area and the depth of compression can be determined for different intervals of time.     

Automatic tracking improved performance for electro-optical imaging and target acquisition system

Real time electro-optical imaging devices, especially those sensors having standard television format compatibility, have previously been adapted for use in various airborne reconnaissance and fire control systems. Performance requirements of these systems have become particularly stringent in such applications as aircraft-mounted laser designator platforms which are needed to assure a high probability of first-pass target acquisition and engagement. This paper discusses a new generation of microprocessor based digital tracker modules for electro-optical fire control systems.     

Development of an improved energy-based method for residual stress assessment

In this study, an improved energy-based method is proposed to measure the equi-biaxial residual stress of bulk materials using spherical indentation. Through analysis of the load–depth curve and residual indentation profile, two calculation methods of the energy of residual stress are proposed, one of which is determined from the load–depth curve and the other based on the Hertizan theory. Finite element analysis was used to establish their relationship, which is the function of the residual stress and material parameters. According to reverse analysis, the proposed method can be used to quickly and effectively determine residual stress. To verify the model, indentation experiments were performed using a ZHU0.2/Z2.5 testing machine. A comparison with conventional X-ray diffraction results showed that the improved method is suitable for the quantitative assessment of residual stress in industrial facilities.     

Design of composite laminates for optimum frequency response

In this study, natural frequency response of symmetrically laminated composite plates was optimized. An analytical model accounting for bending–twisting effects was used to determine the laminate natural frequency. Two different problems, fundamental frequency maximization and frequency separation maximization, were considered. Fiber orientation angles were chosen as design variables. Because of the existence of numerous local optimums, a global search algorithm, a variant of simulated annealing, was utilized to find the optimal designs. Results were obtained for different plate aspect ratios. Effects of the number of design variables and the range of values they may take on the optimal frequency were investigated. Problems in which fiber angles showed uncertainty were considered. Optimal frequency response of laminates subjected to static loads was also investigated.     

Sn/carbon nanotube composite anode with improved cycle performance for lithium-ion battery

Anode material for lithium-ion battery based on Sn/carbon nanotube (CNT) composite is synthesized via a chemical reduction method. The Sn/CNT composite is characterized by thermogravimetry, X-ray diffraction, and transition electron microscopy. The Sn/CNT composite delivers high initial reversible capacity of 630.5 mAh g^?1 and exhibits stable cycling performance with a reversible capacity of 413 mAh g^?1 at the 100th cycle. The enhanced electrochemical performance of the Sn/CNT composite could be mainly attributed to the well dispersion of Sn nanoparticles on CNT and partially filling Sn nanoparticles inside the CNT. It is proposed that the chemical treatment of CNT with concentrated nitric acid, which cuts carbon nanotube into short pieces and increases the amount of oxygen-functional groups on the surface, plays an important role in the anchoring of Sn nanoparticles on carbon nanotube and inhibiting the agglomeration of Sn nanoparticles during the charge–discharge process.     

Comparative analysis for performance of brown coal combustion in a vortex furnace with improved design

Comparative study of 3D numerical simulation of fluid flow and coal-firing processes was applied for flame combustion of Kansk-Achinsk brown coal in a vortex furnace of improved design with bottom injection of secondary air. The analysis of engineering performance of this furnace was carried out for several operational modes as a function of coal grinding fineness and coal input rate. The preferable operational regime for furnace was found.     

Dynamic characteristics of composite laminates

An exact solution for the vibration of elastic composite laminates in cylindrical bending is presented. Dispersion curves for multi-layer symmetrical and unsymmetrical laminates with materials possessing high and low degrees of anisotropy at various fiber orientations are compared with those obtained from an approximate shear deformation theory. Mode shapes are also drawn for different wavelengths and their variation with fiber orientation is studied. Equations are developed for the wave propagation in an infinite medium consisting of a repeated pair of anisotropic layers by extending the “continuum” theory of Sun, Achenbach and Herrmann. Dispersion characteristics for 0–90° fiber orientations obtained by the “continuum” approach are also compared with those obtained by the exact method. The range of validity of each approximate theory is then assessed.     

Diffraction grating interferometers for mechanical characterisations of advanced fabric laminates

It is demonstrated that two grating interferometers with high spatial resolutions can successfully be applied for the mechanical characterisation of the advanced fabric composite materials. Based on these two techniques, the mechanical properties of two kinds of fabric laminates are obtained without assumption of uniform strain fields to be used in the characterisation approaches using the local strain sensors. The degree of the yarn crimp effects of the two laminates is compared in terms of the out-of-plane displacement derivatives. Especially, it is shown that the grating shearing interferometer is appropriate for the crimped fabric structure requiring a three-dimensional analysis. The modification from moiré interferometer to grating shearing interferometer is performed by introducing a Michelson interferometer modified for image shearing.     

The performance of resilient layers made from recycled rubber fluff for impact noise reduction

This paper reports an investigation of a new kind of material and its acoustical performance. The potential of recycled materials made from rubber fluff for reducing impact noise was assessed according to EN ISO 140-8:1997. The performance of these materials was compared to those of some commercially available underlays.     

The improved performance in the ternary bulk heterojunction solar cells

The ternary blend films have been fabricated via adding 4,4’-N,N’-dicarbazole-biphenyl(CBP,a hole transport material widely used in organic light emitting diodes) into the poly(3-hexylthiophene):[6,6]-phenyl C 61-butyric acid methyl ester(P3HT:PCBM).Despite the wide bandgap(3.1 eV) of the CBP,the solar cell utilizing the optimized P3HT:PCBM:CBP blend film showed an increase of 16% in power conversion efficiency and 25% in short-circuit current than the compared standard P3HT:PCBM blend film.This is attributed to the fact that the addition of the CBP could enhance the aggregation of the P3HT chains and thereby reduce the hole-electron recombination at the interface of P3HT and PCBM.We provide a simple,effective way to improve the performance of P3HT based bulk heterojunction solar cells.     

Binder-free chemical synthesis of ZnFe2O4 thin films for asymmetric supercapacitor with improved performance

Ionics - In this work, a simple, cost-effective, binder-free, and wet chemical successive ionic layer adsorption and reaction (SILAR) method is developed for the growth of ZnFe2O4 thin films on...     

平行流冷凝器性能测试实验台的研制

根据平行流冷凝器性能测试需求,研制了一套冷凝器性能测试实验台,可从空气侧和制冷剂侧测试换热量,两者偏差在5%以内,制冷剂侧换热量进一步验证了测试的准确性。空气侧布置成环路风洞,采取直接引入环境空气与试验工质空气混合的方法进行节能改造,可减少制冷系统的使用、降低能耗。采用PID控制方法,使实验台能满足对温度、压力及风量等技术要求,实现对冷凝器的性能测试。试验证明,实验台能够很好地满足冷凝器的测试需求。