Tornado-strength winds interacting with a highway overpass

Analysis of tornado strength winds interacting with a highway overpass structure is presented with emphasis on air flow patterns above and under the bridge. Experiments were performed in a wind tunnel with the scaled geometry of an overpass. Velocity and dynamic pressure measurements were obtained independently at four locations as the overpass was rotated about its vertical axis between air flow angles of approach between 0° and 90°, at 10° increments. Lift and drag forces on the overpass geometry were also measured. To compare various highway overpass locations with the surroundings, the measured dynamic pressure and velocity, drag and lift forces, and drag coefficients at each of the locations and approach angles were examined. It was found that at all locations, the measured velocities never exceeded the freestream velocity of 190.2 ft/s (58 m/s; 130 mph), with the maximum Re occurring above the overpass and between the I-beams. A theoretical maximum pressure drop for the tornado center was calculated to be 0.5 psi for an Enhanced Fujita 2 scale tornado and compared with the highest pressure drop of 0.278 psi, determined from the experiments. Calculated pressure coefficients Cp were mostly \u3c0 and some close to one dynamic head less than ambient. The drag coefficients Cd remain primarily in the laminar region with later transition to turbulence. Using experimental data from the literature, drag forces on an average size man in crouching and laying positions between the overpass I-beams section were determined to be a maximum of 31 lbf

Energy Dissipation and Constitutive Modeling for a Mechanistic Description of Pad Scratching in Chemical-Mechanical Planarization

A thermomechanical model to describe the mechanisms of polishing pad scratching in chemical–mechanical planarization (CMP) has been formulated and investigated. CMP is a necessary process in integrated circuit (IC) fabrication to planarize wafers with nanoscale features after patterned layer deposition. Polishing pad asperities can produce microscale scratches on the wafer surface during CMP, reducing IC manufacturing yields. The constructed thermomechanical model accounts for stresses of the pad and wafer contact and also provides the means to track input energy dissipation during CMP. Tracking energy dissipation offers information about processes that may influence scratch production. This knowledge ultimately produces a greater physical understanding of CMP for the prevention of pad scratching. Polishing pad stress relaxation experiments demonstrate the importance of viscoelastic and plastic strain energy dissipation with its effects on the wafer stress field. Scratch producing ability of the polishing pad is found to decrease with use in CMP, with slurry soaking and increasing polishing time. Mechanical behavior of the polishing pad is demonstrated to differ when in compression and in tension. Compressibility of the pad material is shown to be significant in stress modeling through experimental measurement of polishing pad volume change. Differential scanning calorimetry of used polishing pad samples revealed energy dissipation into the polishing pad surface with increasing polishing time of CMP. Energy dissipation processes influence pad scratching in CMP. Analytical wafer stress field modeling unveils that the scratching ability of a polishing pad decreases when it is less stiff or has a smoother surface

Lead-Free Solder Pull-Off Stress Comparison of a Novel Bump Pull Method with Conventional Hot/Cold Bump Pull Methods

A novel method for directly testing the adhesion strength of three lead-free solders was developed and compared with conventional methods. The Isotraction Bump Pull method utilizes a combination of favorable qualities of the Cold and Hot Bump Pull tests. Solder bumps were generated onto copper printed circuit board substrates using an in-house-fabricated solder bump-on-demand generator. The method uses polymer epoxy to encapsulate solder bumps under uniform tractions, and tested under tension for pull-off stresses. Maximum pull-off stresses for the novel method are: 18MPa (Sn-3.5Ag), 16MPa (SAC 305) and 22MPa (Sn-0.7Cu) and fall at the low end in the literature comparisons. It is suggested that since the copper substrates used in the current work were untreated, that the lower pull-off stress values resulted. Energy Dispersive X-Ray Spectrometry of the newly created faces after fracture shows that brittle fracture of the Intermetallic Compound layer was the mode of failure

PDMS Flow Cell for Monitoring Bacterial Adhesion Capacity of Escherichia coli O157:H7 in Beverages

Aims: To develop and standardize a polydimethylsiloxane (PDMS) flow cells for monitoring bacterial adhesion capacity of biofilm formation by Escherichia coli O157:H7 in Beverages industry. Study Design: PDMS chip was fabricated in house and placed in a metal chamber. The bio-Ferrograph generated different flow rates of bacterial cell suspension in the PDMS cells. Methodology: PDMS flow cells were used to monitor bacteria adhesion capacity of E. coli O157:H7 inoculated into some beverages. The Effect of fluid flow rate and temperature on bacteria adhesion capacity was studied in order to standardize the system. Buffer system of adhesion was modified by varying the concentrations of PBS, Saline concentrations and PH value. The impact of elapsing time and initial number of bacterial cells were investigated. Fluorescence imaging of biofilm formation was also captured. Results: Bacterial adhesion capacity reached the maximum at 0.1 ml/min and then dramatically dropped down when fluid flow rate increases. Maximized adhesion capacity occurred with a buffer system of 0.01M Phosphate buffer, 1.0% NaCl, pH 7.5 at 30°C. A complete linear relationship (R2; 0.9956 - 0.9815) occurred between adhesion capacity of E. coli O157:H7 cells and elapsing time of food beverage. This linear relationship would help to predict and study biofilm formation in fluid and beverage industry. Maximum adhesion capacity occurred with beverages at the following order: skim milk followed by apple juice and then grape juice. Conclusions: PDMS flow cell enables non-destructive, in situ investigation of bacteria adhesion capacity as an initial step for biofilm formation in real time under a wide range of flow rates, nutrient conditions, fluid temperature, and elapsing times. It is inexpensive, simple, disposable, easy-to-use, and can accurately mimic the dynamic flow conditions in beverage industry

Wear of Ultra High Molecular Weight Polyethylene against Synthetic Sapphire as Bearing Coating for Total Joint Replacements

Materials commonly found in hip replacements are a polymer paired with metals or alloys. Tribological behavior of polyethylene bearing surfaces against synthetic sapphire are compared against other bearing combinations to evaluate sapphire as a viable means to lower the incidence of revision surgery by mitigating production of wear debris. Sapphire disks against polyethylene plates were tested utilizing a tribometer. The polyethylene wear rate was found to be 22.6mm3 per year, less than the 40-80mm3 per year typically found in traditional hip replacements. A power law function is presented correlating a decreasing friction coefficient as polyethylene volume loss increases as V0.88. These results show potential for synthetic sapphire as an alternative bearing surface in joint replacement

An Inexpensive Microfluidic PDMS Chip for Visual Detection of Biofilm-forming Bacteria

Aims: Design and assembly of an inexpensive microfluidic PDMS chip for visual detection of cell adhesion and biofilm formation. Study Design: Three different styles of microchannels (2.6, 5.0, and 11.5 μl volumes) were designed, fabricated and tested for adhesion and biofilm formation in a microfluidic system. The pressure drop measurements system includes a bio-Ferrograph connected to the PDMS microchannel via a syringe and a pressure transducer. Methodology: Microfluidic chips were fabricated using Polydimethylsiloxane (PDMS) by means of soft lithography. Different cell densities of E.coli K12 cells were introduced to investigate adhesion and biofilm formation at different time intervals. Stabilization time and hydraulic resistance were obtained via a Bio-Ferrograph connected to a pressure transducer. Results: PDMS microfluidic volume (2.6 μl) failed to generate noticeable biofilm, while slight and greatest yield occurred with PDMS microchannels (5.0, and 11.5 μl), respectively, and could detect as low as 26 cells in 11.5 μl microchannel. As incubation time and/or initial cell density increases, cell adhesion increased, illustrated by crystal violet color intensity. High stabilization time (3 h) didn’t allow for bacterial attachment and cultivation inside the microchannel (2.6 μl) while lower stabilization time (10 min) yielded the highest capacity of cell adhesion in microchannel (11.5 μl). Conclusions: We developed a microfluidic chip with low stabilization time and hydraulic resistance, thus offering more volume for adhesion of bacterial cells and biofilm formation. It allowed bacterial cultivation without any addition of nutrients. The microfluidic chip provides a platform to monitor biofilm growth and can be integrated in situ investigations for biological systems, food biotechnology and other industrial biotechnology applications. This would allow a non-destructive and non-invasive monitoring of the biofilm-forming bacteria inside the PDMS microfluidic chip. This work opens opportunities for further investigations of pressure drop phenomena in microchannels that would otherwise go unnoticed in macro scale measurements

Partnership for International Research and Education in Microfluidic Technology with Applications in Point of Care Diagnostic

This poster summarizes the research highlights of a project conducted as part of an National Science Foundation (NSF) partnership for research and education. The objective of this multidisciplinary, international project was to conduct research on microfluidic technology and applications. The project team is comprised of participants from the University of Rhode Island and the Technical University of Braunschweig in Germany. The research focuses on the following four tasks: Task 1 – Discovery of disease biomarkers; Task 2 –Streaming based microfluidic platform for pumping, mixing, separation and detection; Task 3 – Development of rapid, quantitative and sensitive microfluidic fluorescence immunosensors for point-of-care diagnostics; and Task 4 – Microfluidic ocean based applications. The following elements are examined in Task 3: Enzyme-linked Immunosorbent Assay (ELISA) by manipulation of magnetic beads in microfluidic channel network; development of charged coupled device (CCD) contact imaging system for lab-on-a-chip biosensors for detection of disease biomarkers; a portable and hand-held lab-on-a-chip system for detection of disease biomarkers; on-chip valveless sequential sample loading, mixing, and micro-pneumatic valves; and numerical simulation of microfluidics using dissipative particle dynamics

Tornado-Strength Winds Interacting with a Highway Overpass

Analysis of tornado strength winds interacting with a highway overpass structure is presented with emphasis on air flow patterns above and under the bridge. Experiments were performed in a wind tunnel with the scaled geometry of an overpass. Velocity and dynamic pressure measurements were obtained independently at four locations as the overpass was rotated about its vertical axis between air flow angles of approach between 0 degrees and 90 degrees, at 10 degree increments. Lift and drag forces on the overpass geometry were also measured. To compare various highway overpass locations with the surroundings, the measured dynamic pressure and velocity, drag and lift forces, and drag coefficients at each of the locations and approach angles were examined. It was found that at all locations, the measured velocities never exceeded the freestream velocity of 190.2 ft/s (58 m/s; 130 mph), with the maximum Re occurring above the overpass and between the I-beams. A theoretical maximum pressure drop for the tornado center was calculated to be 0.5 psi for an Enhanced Fujita 2 (EF2) scale tornado and compared with the highest pressure drop of 0.278 psi, determined from the experiments. Calculated pressure coefficients Cp were mostly \u3c 0 and some close to one dynamic head less than ambient. The drag coefficients Cd remain primarily in the laminar region with later transition to turbulence. Using experimental data from the literature, drag forces on an average size man in crouching and laying positions between the overpass I-beams section were determined to be a maximum of 31 lbf