Finite element modeling of thermal fatigue and damage of solder joints in a ceramic ball grid array package

A nonlinear finite element model is presented for analyzing the cyclic and thermal fatigue loading and for viscoplastic damage characterization of the lead-tin (Pb-Sn) solder joints in a ceramic ball grid array (CBGA) surface mount package. An approach using a Δ ∈ _eq ⁱⁿ -modified Coffin-Manson equation is proposed to estimate the fatigue life of the solder joints. The Δ ∈ _eq ⁱⁿ represents a saturated equivalent inelastic strain range as determined by the finite element model. The present study shows that the predictied fatigue life and the associated damage mechanism of the solder joint agree reasonably well with the test data for the 18,25, and 32 mm CBGA packages run at a cyclic temperature load of 0°C/100°C with a frequency of 1.5 cycles per hour. Analysis also shows that a preferred failure site is expected to occur in and around the Pb37-Sn63 solder attachment of the solder joint. A time-dependent (creep induced) damage mechanism is found to be more pronounced than the time-independent (plastic deformation) mechanism.     

Forward‐link analysis of a two‐tier CDMA system with imperfect power control

Power control is an effective technique to reduce cochannel interference and increase capacity for cellular radio systems. The purpose of forward‐link power control in a CDMA system is to reduce the amount of interference in neighbouring cells by reducing the total amount of power transmitted. In an underlaying two‐tier system, microcell's capacity is limited by the forward link due to the interference from macrocell's basestation. Therefore, forward‐link power control is required to enhance system capacity and reduce outage probability. In this paper, we study the effect of imperfect forward‐link power control due to the limitation of power transmitted by basestation. Performance measures including capacity, outage probability and service hole area are analysed. Copyright © 2002 John Wiley & Sons, Ltd.     

Advanced integrated battery testing and simulation

The recent rapid expansion in the use of portable electronics, computers, personal data assistants, cellular phones, power tools, and even electric and hybrid vehicles creates a strong demand on fast deployment of battery technologies at an unprecedented rate. To facilitate such a development integrated battery testing and simulation (IBTS) using computer modeling is an effective tool to improve our capability of rapid prototyping battery technology and facilitating concurrent product development. In this paper, we will present a state-of-the-art approach to use IBTS for improvements in battery cell design, operation optimization, and even charge control for advanced batteries.     

HIV seroprevalence in a London same-day testing clinic

OBJECTIVES: To determine the prevalence of HIV infection among people attending a confidential, non-genitourinary medicine based testing clinic that provides HIV antibody test results on the day of consultation. METHODS: Retrospective analysis of data collected on 2635 individuals attending the Same-Day HIV Testing Clinic at the Royal Free Hospital, London between March 1992 and February 1993. RESULTS: A total of 1612 men and 1023 women were tested for HIV antibody. The primary risk for HIV infection was heterosexual (71.7%; 1889 out of 2635) and homosexual contact (24.5%; 646 out of 2635). Fifty-four individuals were given positive HIV test results (46 men, median age 34 years; eight women, median age 27 years). Overall HIV seroprevalence was 2.0% (95% confidence interval, 1.5-2.5). HIV seroprevalence was highest among homosexual men (6.5%; 41 out of 635) and injecting drug users (5.7%; four out of 70). The rates for heterosexual men and women were 0.2% (two out of 915) and 0.7% (seven out of 974), respectively. Of the 54 individuals who were HIV-antibody-positive, 44 were Centers for Disease Control and Prevention stage II/III, eight stage IV and one was tested at the time of seroconversion (stage I; data were not available for one patient). Of the total numbers attending this clinic 27% (702 out of 2635) had previously been tested and received a negative result. Of a total of 54 HIV-antibody-positive individuals, 40% (21) had previously received a negative test result. CONCLUSIONS: The data suggest that seroprevalence amongst homosexual men attending a designated HIV testing clinic in London is lower than that reported by genitourinary clinic based testing sites. The large number of repeat testers who subsequently became infected with HIV suggests that there is a population requiring specific targetting for HIV risk reduction.     

Der Kenics Static Mixer® und seine Anwendungsmöglichkeiten in der Verfahrenstechnik

KENICS Static Mixer® and Its Possible Applications in Processing Operations Development of the KENICS Static Mixer® has facilitated remarkable progress in the in-Line Processing technology. The advantages of this system are: continuous operation, minimum space requirement, exact and reproducible mixing operations, no dead zones, and low energy requirement at optimum mixing. No maintenance is required since there are no moving parts. One single passage enables complete mixing with radial homogenity and minimum of axial differentiation. In contrast to all dynamic mixers, it permits scaling up from experimental model to production plant, which, for the processing engineer, means absolutely reliable planning.     

Dynamics of the data processing sensorimotrice: Contribution of electrophysiology.

In the field of sensorimotor activities, progress achieved over the last 50 yrs have been largely driven by the Reaction Time (RT) paradigm. Contrary to a preconceived notion, data obtained from classical neurophysiology are compatible with both a sequential organization and a parallel organization. Electromyography, EEG, reflexology and neuronal recording techniques have been used in the context of two inference logics. The first logic is based on the study of functional relations between RT and certain neuronal events. The second logic is based on the study of the relationships between RT and intervals resulting from the breakdown of the RT in relation to certain neuronal events. Most studies suggest that in tasks where the stimulus is composed of numerous attributes, information processing operates in parallel. However, when the stimulus is made up of a single attribute, information processing could be operating in a sequential manner. One weakness of this electrophysiological approach is that it has so far only examined relationships between physiological indicators and means RT. The authors propose here to offset these weaknesses by examining functional relationships between RT distribution variances and certain neuronal events linked to information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The adsorbate-adsorbate association model in mixed gas adsorption on homogeneous solid surfaces

We discuss the adsorbate-adsorbate association model which assumes the formation of higher associates on the surface. Association both parallel and normal to the surface is considered. The normal association model together with Brunauer-Emmett-Teller and Gonzalez-Holland assumptions lead to interesting isotherms that describe multilayer adsorption from binary gas mixtures onto homogeneous surfaces.     

The observation of elongation dependent macrovoid evolution in single- and dual-layer asymmetric hollow fiber membranes

We have reported, for the first time, that macrovoids in asymmetric hollow fiber membranes may be completely eliminated at high elongational draws. The evolution of macrovoids vs. elongational draw was observed for both single- and dual-layer hollow fiber membranes. The number of macrovoids and the number of macrovoid layer decrease with an increase in elongational draw ratio, while the dimension of macrovoids varies with increasing elongational draw ratio until the macrovoids are fully eliminated. This study indicates that the elongational stress may play a much more important role than our original thoughts on hollow fiber membrane morphology.     

Controllable fabrication and properties of polypropylene nanofibers

Thermoplastic nanofibers in yarn form were prepared by melt extrusion of immiscible blends of cellulose acetate butyrate (CAB) and thermoplastic polymers and subsequent removal of the CAB matrix. Isotactic polypropylene (iPP) nanofiber, with diameters ranging from 75 to 375 nm, were made by using CAB/iPP blends, with a ratio of 97.5–2.5, and a hot‐drawn ratio of 25 in a twin‐screw extruder. Dispersion of iPP in CAB and shear and elongational deformation are major factors to result in nanosized fibers. The spheres and nanofibers with different diameters of iPP dispersed phases in the CAB matrix can be well controlled by changing the flow field and the blend ratio. Differential scanning calorimeter and wide angle X‐ray diffraction results showed that the nanofibers had lower crystallinity and crystallite thickness compared with bulk iPP. The atomic force microscopy images presented the well‐defined nanofiber morphology and the excellent manipulability of single iPP nanofiber separated from a bundle of iPP nanofibers. POLYM. ENG. SCI., 47:1865–1872, 2007. © 2007 Society of Plastics Engineers     

Screening Mesenchymal Stem Cell Attachment and Differentiation on Porous Silicon Gradients

The profound effects that nanoscale surface topography exerts on cell behavior are highly relevant to the development of advanced biomaterials and to advances in tissue engineering and regenerative medicine. Here, an asymmetric anodization procedure is used to produce n‐type porous silicon (pSi) gradients with pore sizes ranging from tens to hundreds of nanometers in diameter and changes in the ridge nanoroughness from a few to tens nanometers. Rat mesenchymal stem cells (rMSCs) adhere poorly at the regions with small pore size but high ridge roughness. Cell adhesion is increased gradually towards the large pore size but low ridge roughness end of the pSi gradients. Surface topography influences cell differentiation, but not cell proliferation. Osteogenesis of rMSCs is enhanced by porous topography with a ridge roughness lower than 10 nm, while adipogenesis of rMSCs is enhanced on the entire pSi gradient compared with flat Si substrates. The results demonstrate that the gradient format allows in‐depth screening of surface parameters that are important for the control of mammalian cell behavior, thereby advancing the development of new and improved biomaterials for orthopaedic and tissue engineering applications.