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ARTICLE INFO Keywords: Agrocybe cylindracea Antiproliferative activity Edible mushroom HIV-1 reverse transcriptase Laccase ABSTRACT A laccase, with HIV-1 reverse transcriptase inhibitory activity ([IC.sub.50]= 12.7 µM) and antiproliferative activity against HepG2 [...]

The clustered atomistic-continuum method (CACM) comprising of the clustered atom method (CAM) and the atomistic-continuum method (ACM) based on the Newtonian transient finite element approach, is applied to analyze the mechanical features of the long-chain double stranded DNA (dsDNA) molecule under the axial stretching and lateral unzipping. It is indicated that the sequential difference can initiate the various mechanical characteristics and the dsDNA CACM model can simulate the dsDNA under different loading/boundary conditions in silico.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2004.08.007 Byline: G.Q. Zhang (a), K.K. Lai (b) Keywords: Genetic algorithms; Path relinking; Warehouse layout Abstract: Path relinking is a method to generate new solution by exploring trajectories that connect high quality solutions. In this paper, a class of new hybrid heuristics are proposed by combining a genetic algorithm and path relinking and applying these to a multiple-level warehouse layout problem. Parallel and series combinations to integrate crossover and mutation operations of a genetic algorithm with path relinking are investigated. We proposed position and sequence based path relinking methods to connect two solutions, which are either elites or ones selected randomly. Extensive experiments are carried out to compare the performance of the new heuristics. Author Affiliation: (a) Department of Industrial and Manufacturing Systems Engineering, University of Windsor, Windsor, Canada N9B 3P4 (b) Department of Management Sciences, City University of Hong Kong, Kowloon, Hong Kong Article History: Received 30 June 2003; Accepted 18 June 2004

The combined usage of path relinking and genetic algorithms for avoiding warehouse layout problems is discussed.

In microelectronic industry, thin polymer layers are one of the more commonly used product constituents. Examples are glue layers, coatings, and dielectric layers. The thicknesses of these films vary from a few tens of nanometers to over a hundred micrometers. Since at film thicknesses below 100 nm the thermal and mechanical properties start to deviate from those in the bulk, adequate characterization techniques are required. In the present paper we will report the results of an extensive literature search on the state-of-the-art of thermo-mechanical thin film characterization methods, such as the substrate curvature test, nanoindentation technique, bulge test, and impulsive stimulated thermal scattering. [DOI: 10.1115/1.2070092]

SiLK is a polymer material developed for use as a thin-film dielectric in the interconnect structure of high-density integrated circuits. Among others, its thermomechanical properties play a dominant role for the integrity and reliability of the interconnect during processing, testing, and use. Being a polymer, SiLK may show viscoelastic (time-dependent) behavior. In this paper, we use nanoindentation techniques in combination with analytical and finite element modeling (FEM) to determine the viscoelastic properties of a thin SiLK film on a silicon substrate. Indentation-creep experiments show that this SiLK film indeed responds in a viscoelastic way. This may be caused by the non fully cross-linked test samples prepared using nonstandard processing. Using the FEM simulation, we find that the behavior of this thin SiLK film can be described with a linear viscoelastic model up to the characteristic stress and strain levels of approximately 200 MPa and 3%, respectively. For higher stress and strain levels, the response becomes nonlinear. The results are validated with independent indentation load-unload measurements. [DOI: 10.1115/1.1938990]

A complete vapor pressure model based on a micromechanics approach is developed in this paper. The model can be extended to calculate the initial vapor pressure as traction loading subjected to the interfaces after the delamination. The impact of the vapor pressure induced expanison on the material's deformation is discussed. [DOI: 10.1115/1.1939027]

The thermo-mechanical integration of polymer films requires a precise knowledge of material properties. Nanoindentation is a widely used testing method for the determination of material properties of thin films such as Young's modulus and the hardness. An important assumption in the analysis of the indentation is that the indented medium is a semi-infinite plane or half space, i.e., it has an 'infinite thickness. 'In nanoindentation the analyzed material is often a thin film that is deposited on a substrate. If the modulus ratio is small, (soft film on hard substrate) and the penetration depth is small too, then the Hertzian assumption does not hold. We investigate this situation with spherical and conical indentation. Measurement results are shown using spherical indentation on a viscoelastic thin polymer film and a full visco-elastic characterization is presented. [DOI: 10.1115/1.1846065]

In this paper, an 'interfacial boundary volume' based damage criterion was proposed in combination with the modified Coffin-Manson model to predict solder fatigue. This criterion assumes that mainly, the behavior of the thin solder layer at chip pad interface contributes to the solder fatigue, not the whole solder joint or the averaged strains from randomly selected elements. The damage parameter was thus calculated by averaging the visco-plastic strain range over the interfacial boundary layer volume in the solder and later related to the corresponding fatigue life of experimental test through least-squares curves fitting to determine the empirical coefficients in the Coffin-Manson equation. As a demonstrator, the solder joint fatigue in wafer level chip scale packaging under thermal shock loading was analyzed. An appropriate constitutive relation from Darveaux was used to model the inelastic deformation of the solder alloy, and the different stress-strain responses resulting from different designs were calculated. The analysis results were used to develop the empirical fatigue model based on the interfacial boundary volume damage criterion and then this fatigue model was used for prediction. The fatigue lives of chip scale packaging with variable solder land size and component size were analyzed using this model. The prediction results match well with those from experimental tests. For this demonstrator, it was also shown that the empirical model based on the interfacial boundary volume criterion was more accurate than the models obtained from other strain averaging methods.

For reliable virtual thermo-mechanical prototyping of electronic packages appropriate descriptions of the mechanical behavior of the constituent materials are essential. In many packages molding compounds are used for encapsulation and underfill to provide environmental protection and/or to improve the package thermal mechanical reliability. Therefore, among others, the availability of appropriate constitutive models for various epoxy-molding compounds is one of the requirements for computational prototyping. As there is a large variability of available molding compounds, it is essential to be able to experimentally establish the model parameters in an efficient manner Because of the implied simplicity, linear visco-elastic models combined with the time-temperature superposition theory are mostly used in thermo-mechanical simulations. Among the various experimental possibilities to efficiently establish the model parameter functions, in the present paper the use of unidirectional creep testing is worked out for a chosen molding compound. Here isothermal one-day creep experiments at different temperatures (ranging below and above the glass transition temperature of the compound) are performed. The tensile creep compliance and the time-dependent Poisson's ratio of the material at different temperatures are successfully used to construct visco-elastic master curves. As the Poisson's ratio shows a significant change during a creep or relaxation test, its effect in partly constraint situations (as in packages) will be evident. Therefore it is not reliable to approximate this variable using a constant value. Further, the visco-elastic model of the material is implemented in a finite element program and verified by means of a shear stress relaxation experiment and a creep experiment both under nonisothermal conditions. Moreover, the effect of the creep behavior of the molding compound on the packaging process stress field and its evolution is investigated. Substantial cost saving was realized by package design optimization based on the reliable prediction of the packaging process stresses.

This paper investigates the effect of the anisotropic behavior of the die and the time--and temperature-dependent behavior of epoxy molding compound on the packaging induced stresses for a quad flat package. Finite element (FE) simulations using isotropic and anisotropic properties of the die are carried out, respectively, and the results are compared. Creep experiments were performed at different temperatures ranging from -65[degrees]C to 230[degrees]C to obtain the long-term master curves and the related shift factors for the creep compliance of the molding compound. FE models which incorporate the viscoelastic constitutive relation of the material are constructed to simulate the thermo-mechanical stresses caused by the packaging processes. The influences of both the chip anisotropy and the viscoelastic behavior of the molding compound on the packaging induced stresses are discussed.

Interface delamination failure caused by thermomechanical loading and mismatch of thermal expansion coefficients and other material properties is one of the important failure modes occurring in electronic packages, thus a threat for package reliability. To solve this problem, both academic institutions and industry have been spending tremendous research effort in order to understand the inherent failure mechanisms and to develop advanced and reliable experimental and simulation methodologies, thus to be able to predict and to avoid interface delamination before physical prototyping. Various damage mechanisms can be involved and can result in interface delamination phenomena. These are not all sufficiently addressed and/or reported so far, probably because of the complexities caused by the occurrence of strong geometric and materials nonlinearities. One of the phenomena being insufficiently understood so far is the so-called buckling-driven delamination of thin metalic layers on ceramic substrates. This phenomenon will be discussed in the present paper.

The present study focuses on the development of reliable response surface models (RSM's) for the major packaging processes of a typical electronic package. The major objective is to optimize the product/process designs against the possible failure mode of vertical die cracks. First, the finite element mode (FEM)-based physics of failure models are developed and the reliability of the predicted stress levels was verified by experiments. In the development of reliable thermo-mechanical simulation models, both the process (time and temperature) dependent material nonlinearity and geometric nonlinearity are taken into account. Afterwards, RSM's covering the whole specified geometric design spaces are constructed. Finally, these RSM's are used to predict, evaluate, optimize, and eventually qualify the thermo-mechanical behavior of this electronic package against the actual design requirements prior to major physical prototyping and manufacturing investments.

A flexible model for computing one-dimensional, unsteady manifold gas dynamics in single-cylinder spark-ignition and diesel engines has been developed. The numerical method applies an explicit, finite volume formulation and a shock-capturing total variation diminishing scheme. The numerical model has been validated against the method of characteristics for valve flows without combustion prior to coupling with combustion engine simulations. The coupling of the gas-dynamics model with single-cylinder, spark-ignition and diesel engine modules is accomplished using the graphical MATLAB-SIMULINK environment. Comparisons between predictions of the coupled model and measurements shows good agreement for both spark ignition and diesel engines. Parametric studies demonstrating the effect of varying the intake runner length on the volumetric efficiency of a diesel engine illustrate the model use. [DOI: 10.1115/1.1560708]

Thermo-setting polymers are widely used as underfill materials to improve the reliability of electronic packages. In the design phase, the influence of underfill applications on reliability is often judged through thermal and mechanical simulations, under assumed operating conditions. Because of lacking insight into the mechanical processes due to polymer curing, the impact of processing induced residual stress fields is often neglected. To investigate the evolution of stress and strain fields during the curing process it is important to assume a more appropriate starting point for subsequent process modeling Furthermore, study of possible damage originating from the fabrication process then comes within reach. To facilitate future analysis of stress and strain fields during the curing process a cure dependent constitutive relation is assumed. An approximate investigation method for the process-dependent mechanical properties, based on Dynamic Mechanic Analysis (DMA), is developed. As an illustration the parameter identification is performed for a selected epoxy resin. [DOI: 10.1115/1.1459471]