Switch-on transient behavior of vanadium phthalocyanine based organic transistors

The authors investigated the switch-on transient properties of p-type vanadium phthalocyanine (VOPc) transistors, which were fabricated by weak epitaxy growth on ordered para-sexiphenyl (p-6P) layer. The overshoot phenomenon of drain current had been observed in the VOPc/p-6P transistors, which was explained by the filling of carriers in traps of organic films. The small overshoot value of about 35% and transient duration time of 2 ms demonstrated the low trap concentration in organic films, which were comparable to the reported hydrogenated amorphous-silicon thin-film transistors. Therefore, the VOPc/p-6P transistors can be applied in active matrix liquid crystal display as switch elements.

Instabilities and transient behaviors of a liquid film flowing down a porous inclined plane

The nonmodal linear stability of a falling film over a porous inclined plane has been investigated. The base flow is driven by gravity. We use Darcy's law to describe the flow in the porous medium. A simplified one-sided model is used to describe the fluid flow. In this model, the influence of the porous layer on the flow in the film can be identified by a parameter beta. The instabilities of a falling film have traditionally been investigated by linearizing the governing equations and testing for unstable eigenvalues of the linearized problem. However, the results of eigenvalue analysis agree poorly in many cases with experiments, especially for shear flows. In the present paper, we have studied the linear stability of three-dimensional disturbances using the nonmodal stability theory. Particular attentions are paid to the transient behavior rather than the long time behavior of eigenmodes predicted by traditional normal mode analysis. The transient behaviors of the response to external excitations and the response to initial conditions are studied by examining the pseudospectral structures and the energy growth function G(t) Before we study the nonmodal stability of the system, we extend the results of long-wave analysis in previous works by examining the linear stabilities for streamwise and spanwise disturbances. Results show that the critical conditions of both the surface mode and the shear mode instabilities are dependent on beta for streamwise disturbances. However, the spanwise disturbances have no unstable eigenvalue. 2010 American Institute of Physics. [doi:10.1063/1.3455503]

Behavior of crystalline silicon under huge electronic excitations: A transient thermal spike description

Recent experimental works devoted to the phenomena of mixing observed at metallic multilayers Ni/Si irradiated by swift heavy ions irradiations make it necessary to revisit the insensibility of crystalline Si under huge electronic excitations. Knowing that Ni is an insensitive material, such observed mixing would exist only if Si is a sensitive material. In order to extend the study of swift heavy ion effects to semiconductor materials, the experimental results obtained in bulk silicon have been analyzed within the framework of the inelastic thermal spike model. Provided the quenching of a boiling ( or vapor) phase is taken as the criterion of amorphization, the calculations with an electron-phonon coupling constant g(300 K) = 1.8 x 10(12) W/cm(3)/K and an electronic diffusivity D-e(300 K) = 80 cm(2)/s nicely reproduce the size of observed amorphous tracks as well as the electronic energy loss threshold value for their creation, assuming that they result from the quenching of the appearance of a boiling phase along the ion path. Using these parameters for Si in the case of a Ni/Si multilayer, the mixing observed experimentally can be well simulated by the inelastic thermal spike model extended to multilayers, assuming that this occurs in the molten phase created at the Ni interface by energy transfer from Si. (C) 2009 Elsevier B. V. All rights reserved.

Growth Mechanism And Corrosion Behavior Of Ceramic Coatings On Aluminum Produced By Autocontrol Ac Pulse Peo

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate. (C) 2008 Elsevier B.V. All fights reserved.

Thermal fatigue on pistons induced by shaped high power laser. Part I: Experimental study of transient temperature field and temperature oscillation

Thermal fatigue behavior is one of the foremost considerations in the design and operation of diesel engines. It is found that thermal fatigue is closely related to the temperature field and temperature fluctuation in the structure. In this paper, spatially shaped high power laser was introduced to simulate thermal loadings on the piston. The incident Gaussian beam was transformed into concentric multi-circular beam of specific intensity distribution with the help of diffractive optical element (DOE), and the transient temperature fields in the piston similar to those under working conditions could be achieved by setting up appropriate loading cycles. Simulation tests for typical thermal loading conditions, i.e., thermal high cycle fatigue (HCF) and thermal shock (or thermal low cycle fatigue, LCF) were carried out. Several important parameters that affect the transient temperature fields and/or temperature oscillations, including controlling mode, intensity distribution of shaped laser, laser power, temporal profile of laser pulse, heating time and cooling time in one thermal cycle, etc., were investigated and discussed. The results show that as a novel method, the shaped high power laser can simulate thermal loadings on pistons efficiently, and it is helpful in the study of thermal fatigue behavior in pistons. (C) 2007 Elsevier Ltd. All rights reserved.

Crack growth by grain boundary cavitation in the transient and extensive creep regimes

Crack growth due to cavity growth and coalescence along grain boundaries is analyzed under transient and extensive creep conditions in a compact tension specimen. Account is taken of the finite geometry changes accompanying crack tip blunting. The material is characterized as an elastic-power law creeping solid with an additional contribution to the creep rate arising from a given density of cavitating grain boundary facets. All voids are assumed present from the outset and distributed on a given density of cavitating grain boundary facets. The evolution of the stress fields with crack growth under three load histories is described in some detail for a relatively ductile material. The full-field plane strain finite element calculations show the competing effects of stress relaxation due to constrained creep, diffusion and crack tip blunting. and of stress increase due to the instantaneous elastic response to crack growth. At very high crack growth rates the Hui-Riedel fields dominate the crack tip region. However. the high growth rates are not sustained for any length of time in the compact tension geometry analyzed. The region of dominance of the Hui-Riedel field shrinks rapidly so that the near-tip fields are controlled by the HRR-type field shortly after the onset of crack growth. Crack growth rates under various conditions of loading and spanning the range of times from small scale creep to extensive creep are obtained. We show that there is a strong similarity between crack growth history and the behaviour of the C(t) and C(t) parameters. so that crack growth rates correlate rather well with C(t) and C(t). A relatively brittle material is also considered that has a very different near-tip stress field and crack growth history.

Transient flow patterns and bubble slug lengths in parallel microchannels with oxygen gas bubbles produced by catalytic chemical reactions

Transient flow patterns and bubble slug lengths were investigated with oxygen gas (O-2) bubbles produced by catalytic chemical reactions using a high speed camera bonded with a microscope. The microreactor consists of an inlet liquid plenum, nine parallel rectangular microchannels followed by a micronozzle, using the MEMS fabrication technique. The etched surface was deposited by the thin platinum film, which is acted as the catalyst. Experiments were performed with the inlet mass concentration of the hydrogen peroxide from 50% to 90% and the pressure drop across the silicon chip from 2.5 to 20.0 kPa. The silicon chip is directly exposed in the environment thus the heat released via the catalytic chemical reactions is dissipated into the environment and the experiment was performed at the room temperature level. It is found that the two-phase flow with the catalytic chemical reactions display the cyclic behavior. A full cycle consists of a short fresh liquid refilling stage, a liquid decomposition stage followed by the bubble slug flow stage. At the beginning of the bubble slug flow stage, the liquid slug number reaches maximum, while at the end of the bubble slug flow stage the liquid slugs are quickly flushed out of the microchannels. Two or three large bubbles are observed in the inlet liquid plenum, affecting the two-phase distributions in microchannels. The bubble slug lengths, cycle periods as well as the mass flow rates are analyzed with different mass concentrations of hydrogen peroxide and pressure drops. The bubble slug length is helpful for the selection of the future microreactor length ensuring the complete hydrogen peroxide decomposition. Future studies on the temperature effect on the transient two-phase flow with chemical reactions are recommended.

A Review of Studies on the Mechanical Behavior of Microcellular Plastics

对微孔泡沫塑料力学行为的研究文献进行了综述,简单介绍了微孔泡沫塑料的制备和表征方法,重点介绍了微孔泡沫塑料力学性能的研究工作,其中也包括作者近期在该领域的一些工作。这些工作主要讨论了微孔泡沫塑料的压缩、拉伸、冲击、疲劳和黏弹性效应。最后：给出了对该领域工作的一些讨论和展望。

Size-dependent inelastic behavior of particle-reinforced metal-matrix composites

The strengthening behavior of particle-reinforced metal-matrix composites (MMCp) is primarily attributed to the dislocation strengthening effect and the load-transfer effect. To account for these two effects in a unified way, a new hybrid approach is developed in this paper by incorporating the geometrically necessary dislocation strengthening effect into the incremental micromechanical scheme. By making use of this hybrid approach, the particle-size-dependent inelastic deformation behavior of MMCp is given. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

Effects of Microstructural Heterogeneity on the Spallation Behavior of Materials

It is of utmost importance to understand the spallation behaviour of heterogeneous materials. In this paper, a driven nonlinear threshold model with stress fluctuation is presented to study the effects of microstructural heterogeneity on continuum damage evolution. The spallation behavior of heterogeneity material is analyzed with this model. The heterogeniety of mesoscopic units is characterized in terms of Weibull modulus m of strength distibution and stress fluctuation parameter k. At high stress, the maximum damage increases with m; while at low stress, the maximum damage decreases. In addition, for low stress, severe stress fluctuation causes higher damage; while for high stress, causes lower damage.

Indentation Creep Behavior in Ce-Based Bulk Metallic Glasses at Room Temperature

The room temperature creep behaviors of Ce-based bulk metallic glasses were examined by the use of nanoindentation. The creep rate and creep rate sensitivity of Ce-based BMGs were derived from indentation creep curves. The low creep rate sensitivity of Ce-based BMGs indicates that the room temperature creep is dominated by localized shear flow. The experimental creep curves can be described by a generalized Kelvin model. Furthermore, the creep retardation spectrum is calculated for the Ce-based metallic glasses. The results showed that creep retardation spectrum consists of two relatively separated peaks with the well defined characteristic relaxation times.

Dynamic behavior of a cylindrical crack in a functionally graded interlayer under torsional loading

In this paper the problem of a cylindrical crack located in a functionally graded material (FGM) interlayer between two coaxial elastic dissimilar homogeneous cylinders and subjected to a torsional impact loading is considered. The shear modulus and the mass density of the FGM interlayer are assumed to vary continuously between those of the two coaxial cylinders. This mixed boundary value problem is first reduced to a singular integral equation with a Cauchy type kernel in the Laplace domain by applying Laplace and Fourier integral transforms. The singular integral equation is then solved numerically and the dynamic stress intensity factor (DSIF) is also obtained by a numerical Laplace inversion technique. The DSIF is found to rise rapidly to a peak and then reduce and tend to the static value almost without oscillation. The influences of the crack location, the FGM interlayer thickness and the relative magnitudes of the adjoining material properties are examined. It is found among others that, by increasing the FGM gradient, the DSIF can be greatly reduced.

Formation, Thermal Stability and Deformation Behavior of Graphite-Flakes Reinforced Cu-based Bulk Metallic Glass Matrix Composites

Graphite-flake reinforced Cu47Ti34Zr11 Ni-8 bulk metallic glass matrix composite was fabricated by water-cooled copper mould cast. Most of the graphite flakes still keep unreacted and distribute uniformly in the amorphous matrix except that some reactive wetting occurs by the formation of TiC particles around the flakes. It reveals that the presence of graphite flakes does not affect the onset of the glass transition temperature, crystallization reaction and liquidus of the metallic glass. The resulting material shows obvious serrated flow and higher fracture strength under room temperature compressive load, comparing with the monolithic bulk metallic glass (BMG). Three types of interaction between the shear bands and graphite flakes, namely, shear band termination, shear bands branching and new shear bands formation near the graphite flakes can be observed by quasi-static uniaxial compression test and bonded interface technique through Vickers indentation.

3D Anisotropic Elastoplastic-Damage Model and its Application in Simulating the Behavior of Rock Materials

A 3D anisotropic elastoplastic-damage model was presented based on continuum damage mechanics theory. In this model, the tensor decomposition technique is employed. Combined with the plastic yield rule and damage evolution, the stress tensor in incremental format is obtained. The derivate eigenmodes in the proposed model are assumed to be related with the uniaxial behavior of the rock material. Each eigenmode has a corresponding damage variable due to the fact that damage is a function of the magnitude of the eigenstrain. Within an eigenmodes, different damage evolution can be used for tensile and compressive loadings. This model was also developed into finite element code in explicit format, and the code was integrated into the well-known computational environment ABAQUS using the ABAQUS/Explicit Solver. Numerical simulation of an uniaxial compressive test for a rock sample is used to examine the performance of the proposed model, and the progressive failure process of the rock sample is unveiled.