University of Miami Industrial Assessment Center

This report documents all activity of the University of Miami Industrial Assessment Center (MIIAC) grant awarded by the United States Department of Energy (USDOE) Office of Energy Efficiency and Renewable Energy (EERE) Industrial Technology Program (ITP). This grant was coordinated through a collaborative effort with the Center for Advanced Energy Systems (CAES) located at Rutgers University in New Jersey (www.caes.rutgers.edu) which acted as the program’s Field Manager. The grant’s duration included fiscal years 2003-2006 (September 2002 – August 2006), and operated under the direction of Dr. Shihab Asfour, Director (MIIAC). MIIAC’s main goal was to provide energy assessments for local manufacturing firms. Energy consumption, productivity enhancement, and waste management were the focus of each assessment. Energy savings, cost savings, implementation costs, and simple payback periods were quantified using scientific methodologies and techniques. Over the four-year period of the grant, the total number of industrial assessments conducted was 91, resulting in 604 assessment recommendations and the following savings: 73,519,747 kWh, 435,722 MMBTU, and $10,024,453 in cost savings. A total of 16 undergraduate and graduate students were trained on energy assessment. Companies in over 40 different zip codes were assessed

Tin Whisker Electrical Short Circuit Characteristics Part 2

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has a currently unknown probability associated with it. Due to contact resistance electrical shorts may not occur at lower voltage levels. In this experiment, we study the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From this data we can estimate the probability of an electrical short, as a function of voltage, given that a free tin whisker has bridged two adjacent exposed electrical conductors. In addition, three tin whiskers grown from the same Space Shuttle Orbiter card guide used in the aforementioned experiment were cross-sectioned and studied using a focused ion beam (FIB)

Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Developing an Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Tin Whisker Electrical Short Circuit Characteristics

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Effects of frequency and load of lift on endurance time

The purpose of the present study was to determine endurance time for manual lifting tasks which were performed over a wide range of loads (5, 10, 15, and 20 kg) and frequencies (4, 6, 8, and 10 times/min) for a lift from floor to table height. Endurance time was defined in this study as the maximum length of time during which an individual was capable of lifting a given load at a given frequency continuously. The upper limit of endurance time was set to 8 h. Eleven male subjects participated in this study, and the lifting technique utilized with the straight back-bent knees method. The results showed that endurance time was significantly reduced with an increase in frequency or load of lift. The lightest frequency-load combination (4 times/min; 5 kg) was maintained by most of the subjects for 8h. Conversely, the average endurance time for the heaviest frequency-load combination (10 times/min; 20 kg) was about 27 minutes

Discrete wavelet transform: a tool in smoothing kinematic data

Motion analysis systems typically introduce noise to the displacement data recorded. Butterworth digital filters have been used to smooth the displacement data in order to obtain smoothed velocities and accelerations. However, this technique does not yield satisfactory results, especially when dealing with complex kinematic motions that occupy the low- and high-frequency bands. The use of the discrete wavelet transform, as an alternative to digital filters, is presented in this paper. The transform passes the original signal through two complementary low- and high-pass FIR filters and decomposes the signal into an approximation function and a detail function. Further decomposition of the signal results in transforming the signal into a hierarchy set of orthogonal approximation and detail functions. A reverse process is employed to perfectly reconstruct the signal (inverse transform) back from its approximation and detail functions. The discrete wavelet transform was applied to the displacement data recorded by Pezzack et al., 1977. The smoothed displacement data were twice differentiated and compared to Pezzack et al.’s acceleration data in order to choose the most appropriate filter coefficients and decomposition level on the basis of maximizing the percentage of retained energy (PRE) and minimizing the root mean square error (RMSE). Daubechies wavelet of the fourth order (Db4) at the second decomposition level showed better results than both the biorthogonal and Coiflet wavelets (PRE=97.5%, RMSE=4.7 rad s -2). The Db4 wavelet was then used to compress complex displacement data obtained from a noisy mathematically generated function. Results clearly indicate superiority of this new smoothing approach over traditional filters

Finite Element Study to Evaluate the Biomechanical Performance of the Spine After Augmenting Percutaneous Pedicle Screw Fixation With Kyphoplasty in the Treatment of Burst Fractures

Percutaneous pedicle screw fixation (PPSF) is a well-known minimally invasive surgery (MIS) employed in the treatment of thoracolumbar burst fractures (TBF). However, hardware failure and loss of angular correction are common limitations caused by the poor support of the anterior column of the spine. Balloon kyphoplasty (KP) is another MIS that was successfully used in the treatment of compression fractures by augmenting the injured vertebral body with cement. To overcome the limitations of stand-alone PPSF, it was suggested to augment PPSF with KP as a surgical treatment of TBF. Yet, little is known about the biomechanical alteration occurred to the spine after performing such procedure. The objective of this study was to evaluate and compare the immediate post-operative biomechanical performance of stand-alone PPSF, stand-alone-KP, and KP-augmented PPSF procedures. Novel three-dimensional (3D) finite element (FE) models of the thoracolumbar junction that describes the fractured spine and the three investigated procedures were developed and tested under mechanical loading conditions. The spinal stiffness, stresses at the implanted hardware, and the intradiscal pressure at the upper and lower segments were measured and compared. The results showed no major differences in the measured parameters between stand-alone PPSF and KP-augmented PPSF procedures, and demonstrated that the stand-alone KP may restore the stiffness of the intact spine. Accordingly, there was no immediate post-operative biomechanical advantage in augmenting PPSF with KP when compared to stand-alone PPSF, and fatigue testing may be required to evaluate the long-term biomechanical performance of such procedures

Identification and Analysis of Quality Gaps for Online Service Retailers

There has been a steady growth in e-commerce, especially during the past seven years. Online service retailers (OSRs), as e-commerce retailers, continue to invest heavily in the enhancement of the services provided to their customers. This study aims to identify the quality gaps of OSRs and the influential factors that can mitigate each gap. A conceptual model of the quality gaps of OSRs was developed based on an exploratory review of several service quality studies of online retailers. A survey instrument was developed to measure the significance of the quality gaps on customers' willingness to shop online. Data from a total of 253 survey respondents were analyzed using a linear regression model. Four out of nine of the quality gaps (Tactile feedback, On-time Delivery, Sales Information, and Confounding Knowledge Technology) showed statistical significant with regards to customers' willingness to shop online, and the overall model was significant (p < 0.001)