Bau, Haim H.
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Publication On the Stability and Flow Reversal of an Asymmetrically Heated Open Convection Loop(1981) Bau, Haim H.; Torrance, Kenneth E.Experimental results are reported for a U-shaped, free convection loop. The top of the loop is open to an isothermal reservoir. The horizontal leg and one vertical leg are heated at rates Q1 and Q2, respectively. The loop is filled either with water or a watersaturated porous medium. Symmetric heating and asymmetric heating favouring the ascending leg of the loop both yield stable flows. Asymmetric heating favouring the descending leg leads to stable flows when the ratio Q1/Q2 is above a critical value. Below this critical value, the flow is observed to oscillate with increasing amplitude until the direction of flow in the loop undergoes a reversal. A steady flow follows the reversal. Analytical results include a stability analysis and time-dependent, one-dimensional numerical calculations, both of which compare favourably with experiment.Publication Thick Film Thermistors Printed on Low Temperature Co-fired Ceramic Tapes(2001-10-01) Zhong, Jihua; Bau, Haim HFocuses on the importance of ceramic tapes as a substrate material for hybrid microelectronic circuits. Fabrication of thermal reactor; Importance in monitoring temperature; Utilization of layered manufacturing and rapid prototyping processes.Publication Experiments on the stabilization of the no-motion state of a fluid layer heated from below and cooled from above(1997-07-28) Tang, Jie; Bau, Haim HIt is demonstrated experimentally that through the use of feedback control, it is possible to stabilize the no-motion (conductive) state of a fluid layer confined in a circular cylinder heated from below and cooled from above (the Rayleigh-Bénard problem), thereby postponing the transition from a no-motion state to cellular convection. The control system utilizes multiple sensors and actuators. The actuators consist of individually controlled heaters microfabricated on a silicon wafer which forms the bottom of the test cell. The sensors are diodes installed at the fluid's midheight. The sensors monitor the deviation of the fluid temperatures from preset, desired values and direct the actuators to act in such a way as to eliminate these deviations.Publication Carbon Nanopipettes Characterize Calcium Release Pathways in Breast Cancer Cells(2008-07-03) Schrlau, Michael G; Brailiou, Eugen; Patel, Sandip; Gogotsi, Yury; Dun, Nae J; Bau, Haim HCarbon-based nanoprobes are attractive for minimally-invasive cell interrogation but their application in cell physiology has thus far been limited. We have developed carbon nanopipettes (CNPs) with nanoscopic tips and used them to inject calcium-mobilizing messengers into cells without compromising cell viability. We identify pathways sensitive to cyclic adenosine diphosphate ribose (cADPr) and nicotinic acid adenine dinucleotide phosphate (NAADP) in breast carcinoma cells. Our findings demonstrate the superior utility of CNPs for intracellular delivery of impermeant molecules and, more generally, for cell physiology studies. The CNPs do not appear to cause any lasting damage to cells. Their advantages over the commonly used glass pipettes include smaller size, breakage and clogging resistance, and potential for multifunctionality such as concurrent injection and electrical measurements.Publication Kelvin-Helmhotz Instability for Parallel Flow in Porous Media: A Linear Theory(1982) Bau, Haim H.Two fluid layers in fully-saturated porous media are considered. The lighter fluid is above the heavier one so that in the absence of motion the arrangement is stable and the interface is flat. It is shown that when the fluids are moving parallel to each other at different velocities, the interface may become unstable (the Kelvin-Helmholtz instability). The corresponding conditions for marginal stability are derived for Darcian and non-Darcian flows. In both cases, the velocities should exceed some critical values in order for the instability to manifest itself. In the case of Darcy's flow, however, an additional condition, involving the fluids' viscosity and density ratios, is required.Publication Torsional Sensor Applications in Two-Phase Fluids(1993-09-01) Kim, Jin O.; Bau, Haim H.; Liu, Yi; Lynnworth, Lawrence C.; Lynnworth, Steven A.; Hall, Kimberly A.; Jacobson, Saul A.; Korba, James. A.; Murphy, Robert J.; Strauch, Michael A.; King, Kyle G.A solid corrosion-resistant torsional waveguide of diamond cross section has been developed to sense on-line and in real-time the characteristics of the liquid in which it is submerged. The sensor can measure, among other things, the liquid content of a bubbly medium; the density of adjacent pure liquids; the equivalent density of liquid-vapor mixtures or particulate suspensions; a suspension's concentration; and the liquid level. The sensor exploits the phenomenon that the speed of propagation of a torsional stress wave in a submerged waveguide with a noncircular cross section is inversely proportional to the equivalent density of the liquid in which the waveguide is submerged. The sensor may be used to conduct measurements along distances ranging from 20 mm to 20 m and over a wide range of temperatures and pressures, e.g., from the cryogenic temperature of liquid nitrogen, -196°C, up to hot pressurized water at 300°C and 7 MPa. A self-calibrating three-zone sensor and associated electronics have also been developed to compensate for any sensor inaccuracies due to operation over a wide range of temperature. In some of the water experiments at room temperature, unexpected attenuation of the guided torsional waves was observed. This excess attenuation depends in part on the waveguide's surface finish. It appears to be caused by air microbubbles adhering to the waveguide, imposing one of the practical limits on the maximum sensor length in nondegassed or aerated water.Publication Complex magnetohydrodynamic low-Reynolds-number flows(2003-07-01) Xiang, Yu; Bau, Haim HThe interaction between electric currents and a magnetic field is used to produce body (Lorentz) forces in electrolyte solutions. By appropriate patterning of the electrodes, one can conveniently control the direction and magnitude of the electric currents and induce spatially and temporally complicated flow patterns. This capability is useful, not only for fundamental flow studies, but also for inducing fluid flow and stirring in minute devices in which the incorporation of moving components may be difficult. This paper focuses on a theoretical and experimental study of magnetohydrodynamic flows in a conduit with a rectangular cross section. The conduit is equipped with individually controlled electrodes uniformly spaced at a pitch L. The electrodes are aligned transversely to the conduit's axis. The entire device is subjected to a uniform magnetic field. The electrodes are divided into two groups A and C in such a way that there is an electrode of group C between any two electrodes of group A. We denote the various A and C electrodes with subscripts, i.e., Ai and Ci , where i = 0, ±1, ±2, ... . When positive and negative potentials are, respectively, applied to the even and odd numbered A electrodes, opposing electric currents are induced on the right and left hand sides of each A electrode. These currents generate transverse forces that drive cellular convection in the conduit. We refer to the resulting flow pattern as A. When electrodes of group C are activated, a similar flow pattern results, albeit shifted in space. We refer to this flow pattern as C. By alternating periodically between patterns A and C, one induces Lagrangian chaos. Such chaotic advection may be beneficial for stirring fluids, particularly in microfluidic devices. Since the flow patterns A and C are shifted in space, they also provide a mechanism for Lagrangian drift that allows net migration of passive tracers along the conduit's length.Publication Magneto hydrodynamic (MHD) pump fabricated with ceramic tapes(2002-01-31) Zhong, Jihua; Yi, Mingqiang; Bau, Haim HThe use of Magneto Hydro Dynamics (MHD) to circulate fluids in conduits fabricated with low temperature co-fired ceramic tapes is described. Conduits shaped like toroidal and rectangular loops were fabricated. Electrodes printed on the ceramic substrate along the conduits' walls facilitated transmission of electric currents through the test fluids. When the devices were subjected to a magnetic field, the resulting Lorentz forces propelled the liquids. The paper details the fabrication process and describes experiments with mercury slugs, saline solution, and deionized water. The measured fluid velocities were compared with theoretical predictions.Publication An integrated, self-contained microfluidic cassette for isolation, amplification, and detection of nucleic acids(2010-04-01) Chen, Dafeng; Mauk, Michale; Qiu, Xianbo; Liu, Changchun; Kim, Jitae; Ramprasad, Sudhir; Ongagna, Serge; Abrams, William; Malamud, Daniel; Bau, Haim H; Corstjens, PaulA self-contained, integrated, disposable, sample-to-answer, polycarbonate microfluidic cassette for nucleic acid-based detection of pathogens at the point of care was designed, constructed, and tested. The cassette comprises on-chip sample lysis, nucleic acid isolation, enzymatic amplification (polymerase chain reaction and, when needed, reverse transcription), amplicon labeling, and detection. On-chip pouches and valves facilitate fluid flow control. All the liquids and dry reagents needed for the various reactions are pre-stored in the cassette. The liquid reagents are stored in flexible pouches formed on the chip surface. Dry (RT-)PCR reagents are pre-stored in the thermal cycling, reaction chamber. The process operations include sample introduction; lysis of cells and viruses; solid-phase extraction, concentration, and purification of nucleic acids from the lysate; elution of the nucleic acids into a thermal cycling chamber and mixing with pre-stored (RT-)PCR dry reagents; thermal cycling; and detection. The PCR amplicons are labeled with digoxigenin and biotin and transmitted onto a lateral flow strip, where the target analytes bind to a test line consisting of immobilized avidin-D. The immobilized nucleic acids are labeled with up-converting phosphor (UCP) reporter particles. The operation of the cassette is automatically controlled by an analyzer that provides pouch and valve actuation with electrical motors and heating for the thermal cycling. The functionality of the device is demonstrated by detecting the presence of bacterial B.Cereus, viral armored RNA HIV, and HIV I virus in saliva samples. The cassette and actuator described here can be used to detect other diseases as well as the presence of bacterial and viral pathogens in the water supply and other fluids.Publication An Automated, Pre-Programmed, Multiplexed, Hydraulic Microvalve(2009-09-14) Chen, Dafeng; Kim, Jitae; Bau, Haim H.An automated, pre-programmed, multiplexed hydraulic valve actuator is described. The valve is membrane-based and normally open. In contrast to the membrane-based pneumatic valve, the hydraulic valve uses hydraulic liquid to exert the control pressure. The line pressure is controlled with a roller moving over a prefabricated topology. Multiple rollers, each traversing its own track, are assembled into a single carriage, which can be actuated either manually or with a single computer-controlled motor. A valve manifold and roller actuators are designed, fabricated, and tested to demonstrate three-way valve actuation in a pre-determined sequence. The performance of the valve is evaluated and the utility of the valve in the operation of a micro thermal cycler was demonstrated. Hydraulic controllers of the type described here can be operated either manually or under computer control and provide an inexpensive means of controlling flow in lab-on-a-chip devices.