Application of an asymmetrical four point bend shear test to solder joints

The asymmetrical four-point bend shear (AFPB) test method was used to measure the shear strength and creep properties through the stress relaxation experiments using three different Pb-free solder joint compositions in an assolidified condition. Since it was difficult to shear the uniform specimens and the local bending usually occurs at the inner loading points, the notches were introduced at the joint line to preferentially weaken this region. The stress analysis by finite element modeling showed that the straight notches transform the parabolic shear stress distribution in the uniform specimen into a relatively uniform shear distribution along the bond line in the notched specimens. Therefore, the shear strength results from the notched specimens are expected to be much more accurate. Experiments showed that both the Sn-3.6Ag-1Cu (wt.%) and Sn-3.6Ag-1Cu-0.45Co joints have superior strength and creep properties as compared to the Sn-3.5Ag joint. However, there was no statistical difference between the shear strength of the Sn-3.6Ag-1Cu and Sn-3.6Ag-1Cu-0.45 Co joints. Moreover, the difference between the creep resistance of these two types of joints was small.     

A performance and implementation comparison of bidirectional anddual bus 2-D WDM multiple-plane optical interconnections with row-columnmultihop network structures

Bidirectional and dual bus wavelength division multiplexing (WDM) two-dimensional (2-D) multiple-plane optical interconnections with row-column multihop network structures using vertical-cavity surface-emitting lasers (VCSELs) and wavelength-selective detectors are analyzed and compared in terms of the expected number of hops (switching delay) and practical implementation considerations. The bidirectional WDM optical interconnection significantly reduces the necessary implementation hardware while maintaining the performance very closely compared to the dual bus architecture. Both WDM structures show significant performance improvements even when only three to five wavelengths are used. Also, the multihop efficiency is analyzed with the consideration of both electrical hops and optical hops     

Information Capacity of Nonlinear Wavelength Division Multiplexing Fiber Optic Transmission Line

We report the first determination of the impact of optical nonlinearities on the information capacity of a fiber optic transmission channel. By modeling interchannel interference in a nonlinear wavelength division multiplexing transmission system as multiplicative Gaussian noise, we show that the information capacity is reduced below the Shannon capacity of the linear communications channel. For systems of practical interest, this imposes a fundamental limitation on the spectral efficiency of optical data transmission.     

The new method of Academic Review: implications for engineering

The UK Quality Assurance Agency for Higher Education is introducing a new procedure, the Academic Review for assessing the quality of education provision. This paper discusses the similarities and differences between; the Academic Review (introduced in Scotland in October 2000) and the Subject Review system that has run in England and Northern Ireland since September 1995. It identifies issues that are specific to Engineering departments and considers how to interpret the scores between the two systems     

Improved epoxy nano-composite tube-sheets for membrane applications

This article provides details of research work which aims to increase the range of applications in which membranes can be used by improving the epoxies used to form tube-sheets, making them more chemically and thermally stable, more resistant to organic solvents, and with improved mechanical properties.     

Semantic, phonological, and hybrid veridical and false memories in healthy older adults and in individuals with dementia of the Alzheimer type.

Five groups of participants [young, healthy old, healthy old-old, very mild dementia of the Alzheimer type (DAT), and mild DAT] studied 12-item lists of words that converged on a critical nonpresented word (cold) semantically (chill, frost, warm, ice), phonologically (code, told, fold, old), or in a hybrid list of both (chill, told, warm, old). The results indicate that (a) veridical recall decreased with age and dementia; (b) recall of the nonpresented items increased with age and remained fairly stable across dementia; and (c) false recall varied by list type, with hybrid lists producing superadditive effects. For hybrid lists, individuals with DAT were 3 times more likely to recall the critical nonpresented word than a studied word. When false memory was considered as a proportion of veridical memory, there was an increase in relative false memory as a function of age and dementia. Results are discussed in terms of age- and dementia-related changes in attention and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Justice at the millennium: A meta-analytic review of 25 years of organizational justice research.

The field of organizational justice continues to he marked by several important research questions, including the size of relationships among justice dimensions, the relative importance of different justice criteria, and the unique effects of justice dimensions on key outcomes. To address such questions, the authors conducted a meta-analytic review of 183 justice studies. The results suggest that although different justice dimensions are moderately to highly related, they contribute incremental variance explained in fairness perceptions. The results also illustrate the overall and unique relationships among distributive, procedural, interpersonal, and informational justice and several organizational outcomes (e.g., job satisfaction, organizational commitment, evaluation of authority, organizational citizenship behavior, withdrawal, performance). These findings are reviewed in terms of their implications for future research on organizational justice. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Predicting Shrinkage Stress Field in Concrete Slab on Elastic Subgrade

Concrete is a material that changes volumetrically in response to moisture and temperature variations. Frequently, these volumetric changes are prevented by restraint from the surrounding structure, resulting in the development of tensile stresses. This paper provides a method for computing the stress and displacement fields that develop in response to this restraint by considering the concrete slab as a plate resting on an elastic foundation. The interface between the slab and the foundation is capable of simulating all cases between complete perfect bond and perfect compression∕zero tension bond to permit debonding. In addition, stress relaxation is considered in the concrete to account for the reduction in stress due to creep∕relaxation-related phenomena. For this reason, the stress-strain relationship and equilibrium equations have been considered in the rate or differential form. The history-dependent equilibrium equations are obtained by integrating the differential equations with respect to time. An example is presented to illustrate the favorable correlation that exists between the predicted behavior of the plate model and finite-element modeling.     

Influence of Specimen Size∕Geometry on Shrinkage Cracking of Rings

This paper presents experimental evidence to show that a size∕geometry dependence is observed in the shrinkage cracking behavior of restrained concrete structures. A theoretical model is developed to explain this behavior. First, a solution is presented to compute the stress and displacement fields of an aging, linear, viscoelastic cylinder by assuming that a uniformly distributed shrinkage strain is perfectly restrained in the radial direction at the internal surface of the cylinder. Second, a fracture mechanics failure criterion is implemented to develop time and geometry-dependent tensile stress resistance (strength) curves. Third, this model is used to illustrate the role of specimen size∕geometry and material composition on the failure response. Finally, experimentally measured ages of cracking are compared with the theoretical modeling predictions.     

Section Properties for Latticed Members of San Francisco–Oakland Bay Bridge

This paper focuses on the determination of section properties of latticed members for seismic retrofit of the San Francisco–Oakland Bay Bridge. To consider actual section integrity for a latticed member, the concept of reduction factors βm for moment of inertia and βt for torsional constant is introduced to account for the shear flow transferring capacity of lacing bars or battens and their connections. A set of formulas is proposed for calculating section properties required for seismic analysis and capacity determination. The validity of the proposed section properties is confirmed by a finite-element analysis of a latticed member. It is found that the proposed simple procedure closely resembles the finite-element analysis results. The proposed method is also supported by the recent 1∕2 scale model test of the SFOBB laced member at UNR.