Temperature characteristics of optical parameters of phthalocyanine LB films and spin-coated films

The LB films and spin-coated films of tetra-neopentoxy phthalocyanine zinc (TNPPcZn) were prepared and annealed at different temperatures. Their refractive index (n) and extinction coefficient (k) were measured by p-polarized reflectance. The similar value of n and k, as well as similar changing tendency of it and k at varied annealing temperatures, was found between LB films and spin-coated films. In addition, the absorption curves of TNPPcZn LB films and spin-coated films in visible range at different annealing temperature were investigated. The results indicate that the changing tendency of the extinction coefficient of two kinds of TNPPcZn films obtained from two methods mentioned above were coincident. When the annealing temperature increased to 150 degrees C, the monomers of TNPPcZn films transformed to aggregates, n(f) and k(f) of the films increased. Further, n(f) and k(f) decreased as aggregates changed back to monomers again at the annealing temperature of 300 degrees C. The experimental results coincide well with the theoretical analysis. (C) 2004 Elsevier B.V. All rights reserved.

非饱和膨胀土力学特性及其工程处置研究

The unsaturated expansive soil is a hotspot and difficulty in soil mechanics inland and outland. The expansive soil in our China is one of the widest in distributing and greatest in area, and the disaster of expansive soil happens continually as a result. The soil mechanics test, monitor, numerical simulation and engineering practice are used to research swell and shrinkage characteristic, edge strength characteristic and unsaturated strength characteristic of Mengzi expansive soil. The seep and stability of the slope for expansive soil associated with fissure are analyzed and two kinds of new technique are put forward to be used in expansive soil area, based on disaster mechnics proposed of the slope.The technique of reinforcement in road embankment is optimized also. Associated with engineering geology research of Mengzi expansive soil, mineral composition, chemical composition, specific area and cation content, dissolubility salt and agglutinate, microcosmic fabric characteristic, cause of formation and atmosphere effect depth are analyzed to explain the intrinsic cause and essence of swell and shrinkage for expansive soil. The rule between swell-shrinkage and initial state, namely initial water content, initial dry density and initial pressure, can be used to construction control. Does Response model is fit to simulate the rule, based on ternary regression analysis. It has great meaning to expansive soil engineering in area with salt or alkali. The mechanics under CD, CU and GCU of expansive soil is researched by edge surface theory to explain the remarkable effect of consolidation pressure, initial dry density, initial water content, cut velocity, drainage and reinforcement to the edge strength characteristic. The infirm hardening stress strain curves can be fitted with hyperbola model and the infirm softening curves can be fitted with exponential model. The normalization theory can be used to reveal the intrinsic unity of the otherness which is brought by different methods to the shear strength of the same kinds of samples. The unsaturated strain softening characteristic and strength envelope of remolding samples are researched by triaxial shear test based on suction controlled, the result of which is simulated by exponential function. The strength parameters of the unsaturated samples are obtained to be used in the unsaturated seep associated with rainfall. The elasticity and plasticity characters of expansive soil are researched to attain the model parameters by using modified G-A model. The humidification destroy characteristic of expansive soil is discussed to research the disaster mechanism of the slope with the back pressure increasing and suction decreasing under bias pressure consolidation. The indoor and outdoor SWCCs are measured to research the effect factors and the rule between different stress and filling environment. The moisture absorption curves can express the relationship between suction and water content in locale. The SWCCs of Mengzi expansive soil are measured by GDS stress path trixial system. The unsaturated infiltration function is gained to research seep and stability of the slope of expansive soil. The rainfall infiltration and ability of slope considering multifarious factors are studied by analyzing fissure cause of Mengzi expansive soil. The mechanism of the slope disaster is brought forward by the double controlling effect between suction and fissure. Two new kinds of technique are put forward to resolve disaster of expansive soil and the technique of reinforcement on embankment is optimized, which gives a useful help to solving engineering trouble.

Three-photon absorption-induced fluorescence and optical limiting effects in a fluorene derivative

This paper reports on the steady-state fluorescence, three- photon absorption-induced fluorescence emission and subsequently induced optical limiting behaviour of a fluorene derivative with D-pi-D structural motifs. The lifetime of the steady-state fluorescence is 0.903 ns. Large optical limiting behaviour induced by 3PA has also been demonstrated, and the nonlinear absorption coefficient gamma derived from 3PA fitting curves is 5.92 x 10(-20) cm(3)/W-2 and the corresponding molecular 3PA cross-section sigma(3)' is 1.14 x 10(-76) cm(6) s(2).

Dynamic P-I and P-V Curves for Semiconductor Lasers and Modulators

In this paper, we propose the dynamic P-V curve for modulator and P-I curve for laser diode, and present a simple approach to deriving the curves from the small-signal frequency responses measured using a microwave network analyzer. The linear response range, modulation efficiency, optimal driving conditions at different frequency can, therefore, be determined. It is demonstrated that the large-signal performance of electro-absorption (EA) modulator and the directly modulated semiconductor lasers can be predicted from the dynamic curved surface. Experiments show a good agreement between the evaluated characteristics and the measured large-signal performance.

Identification of nonlinear dynamic systems: Time-frequency filtering and skeleton curves

The nonlinear behavior varying with the instantaneous response was analyzed through the joint time-frequency analysis method for a class of S. D. O. F nonlinear system. A masking operator an definite regions is defined and two theorems are presented. Based on these, the nonlinear system is modeled with a special time-varying linear one, called the generalized skeleton linear system (GSLS). The frequency skeleton curve and the damping skeleton curve are defined to describe the main feature of the non-linearity as well. Moreover, an identification method is proposed through the skeleton curves and the time-frequency filtering technique.

Can stress-strain relationships be obtained from indentation curves using conical and pyramidal indenters?

Applying the scaling relationships developed recently for conical indentation in elastic-plastic solids with work-hardening, we examine the question of whether stress-strain relationships of such solids can be uniquely determined by matching the calculated loading and unloading curves with that measured experimentally. We show that there can be multiple stress-strain curves for a given set of loading and unloading curves. Consequently, stress-strain relationships may not be uniquely determined from loading and unloading curves alone using a conical or pyramidal indenter.

Experimental Study on Dynamic Properties of High Strength Fiber Clusters

In this paper, the dynamic behaviors of several kinds of high strength fibers, including Kevlar, UHMPE, glass fibers, carbon fibers etc., are investigated experimentally, with a Split Hopkinson Tension Bar (SHTB). The effect of strain rate on the modulus, strength, failure strain and failure characteristics of fibers, under impact loading, is analyzed with the relative stress vs. strain curves. At the same time, the mechanism about the rate dependence of mechanical behaviors of various fibers is discussed based on the understanding on the microstructures and deformation models of materials. Some comments are also presented on the decentralization of experimental results, and a new method called traveling wave method is presented to increase the experimental accuracy. Research results obtained in this paper will benefit to understand the energy absorption and to build up the constitutive law of protective materials reinforced by high strength fibers.

Further analysis of indentation loading curves: Effects of tip rounding on mechanical property measurements

The effects of indenter tip rounding on the shape of indentation loading curves have been analyzed using dimensional and finite element analysis for conical indentation in elastic-perfectly plastic solids. A method for obtaining mechanical properties from indentation loading curves is then proposed. The validity of this method is examined using finite element analysis. Finally, the method is used to determine the yield strength of several materials for which the indentation loading curves are available in the literature.

Partition Energy Absorption of Axially Crushed Aluminum Foam-Filled Hat Sections

The "interaction effect" between aluminum foam and metal column that takes place when foam-filled hat sections (top-hats and double-hats) are axially crushed was investigated in this paper. Based on experimental examination, numerical simulation and analytical models, a systemic approach was developed to partition the energy absorption quantitatively into the foam filler component and the hat section component, and the relative contribution of each component to the overall interaction effect was therefore evaluated. Careful observation of the collapse profile found that the crushed foam filler could be further divided into two main energy-dissipation regions: densified region and extremely densified region. The volume reduction and volumetric strain of each region were empirically estimated. An analytical model pertinent to the collapse profile was thereafter proposed to find the more precise relationship between the volume reduction and volumetric strain of the foam filler. Combined the superfolding element model for hat sections with the current model according to the coupled method, each component energy absorption was subsequently derived, and the influence of some controlling factors was discussed. According to the finite element analysis and the theoretical modeling, when filled with foam, energy absorption was found to be increased both in the hat section and the foam filler, whereas the latter contributes predominantly to the interaction effect. The formation of the extremely densified region in the foam filler accounts for this effect.

Predictions for Partial-Dislocation-Mediated Processes in Nanocrystalline Ni by Generalized Planar Fault Energy Curves: An Experimental Evaluation

Generalized planar fault energy (GPFE) curves have been used to predict partial-dislocation-mediated processes in nanocrystalline materials, but their validity has not been evaluated experimentally. We report experimental observations of a large quantity of both stacking faults and twins in nc Ni deformed at relatively low stresses in a tensile test. The experimental findings indicate that the GPFE curves can reasonably explain the formation of stacking faults, but they alone were not able to adequately predict the propensity of deformation twinning.

Analysis of indentation loading curves obtained using conical indenters

Using dimensional analysis and finite-element calculations we determine the functional form of indentation loading curves for a rigid conical indenter indenting into elastic-perfectly plastic solids. The new results are compared with the existing theories of indentation using conical indenters, including the slip-line theory for rigid-plastic solids, Sneddon's result for elastic solids, and Johnson's model for elastic-perfectly plastic solids. In the limit of small ratio of yield strength (Y) to Young's modulus (E), both the new results and Johnson's model approach that predicted by slip-line theory for rigid-plastic solids. In the limit of large Y/E, the new results agree with that for elastic solids. For a wide range of Y/E, some difference is found between Johnson's model-and the present result. This study also demonstrates the possibilities and limitations of using indentation loading curves to extract fundamental mechanical properties of solids.

Theermal Stress and Fracture in Transparent Optical Materials due to Laser Energy-Absorption by a Defect

利用热弹性理论分析了在光学材料中由于缺陷吸收激光能量引起的温度和热应力分布,并且针对一个简单的裂纹模型分析了热应力产生的应力强度因子,给出了一些主要参数对于应力强度因子的影响的规律。

Time-Frequency Analysis of Nonlinear Systems: The Skeleton Linear Model and the Skeleton Curves

The joint time-frequency analysis method is adopted to study the nonlinear behavior varying with the instantaneous response for a class of S.D.O.F nonlinear system. A time-frequency masking operator, together with the conception of effective time-frequency region of the asymptotic signal are defined here. Based on these mathematical foundations, a so-called skeleton linear model (SLM) is constructed which has similar nonlinear characteristics with the nonlinear system. Two skeleton curves are deduced which can indicate the stiffness and damping in the nonlinear system. The relationship between the SLM and the nonlinear system, both parameters and solutions, is clarified. Based on this work a new identification technique of nonlinear systems using the nonstationary vibration data will be proposed through time-frequency filtering technique and wavelet transform in the following paper.

Fracture Mechanisms And Size Effects Of Brittle Metallic Foams: In Situ Compression Tests Inside Sem

In situ compressive tests on specially designed small samples made from brittle metallic foams were accomplished in a loading device equipped in the scanning electron microscopy (SEM). Each of the small samples comprises only several cells in the effective test zone (ETZ), with one major cell in the middle. In such a system one can not only obtain sequential collapse-process images of a single cell and its cell walls with high resolution, but also correlate the detailed failure behaviour of the cell walls with the stress-strain response, therefore reveal the mechanisms of energy absorption in the mesoscopic scale. Meanwhile, the stress-strain behaviour is quite different from that of bulk foams in dimensions of enough large, indicating a strong size effect. According to the in situ observations, four failure modes in the cell-wall level were summarized, and these modes account for the mesoscopic mechanisms of energy absorption. Paralleled compression tests on bulk samples were also carried out, and it is found that both fracturing of a single cell and developing of fracture bands are defect-directed or weakness-directed processes. The mechanical properties of the brittle aluminum foams obtained from the present tests agree well with the size effect model for ductile cellular solids proposed by Onck et al. (C) 2008 Elsevier Ltd. All rights reserved.

Numerical Partition of Energy Absorption of Foam-filled Top-Hat and Double-Hat Sections

The interaction effect, i.e., the contribution of each component to the total energy absorption of an axially crushed foam-filled hat section was investigated quantitatively via numerical simulation. The FE results were first verified by experimental work of aluminum foam-filled top-hat and double-hat sections, then the contribution of foam-fillers and that of hat sections to the overall energy absorption were quantitatively obtained, respectively. When foam-filled, increase in energy absorption was found both in hat section component and foam-filler component, whereas the latter contributes predominantly to the interaction effect.