bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Numerical Prediction of Current Density for a Constructal Theory-Based Flow Field Pattern
Authors: Damia´n Ascencio C. E. , Herna´ndez Guerrero A. , Escobar Vargas J. A. , Rubio-Arana C. , Elizalde Blancas F. F.
Published: May 2009

This work presents a three-dimensional numerical prediction of the current density for a Proton Exchange Membrane Fuel Cell (PEMFC) with a tree-like pattern, which is observed in the nature, for the flow field channels. The numerical model considers a complete solution of the Navier-Stokes Equation, the species transport equation and two potential field equations; the model is solved using a finite volume technique assuming isothermal and steady state conditions. The three-dimensional model includes the analysis of: current collectors, flow channels, gas diffusion layers, catalyst layers on both sides of the PEMFC (anode and cathode) and a membrane between the two catalyst layers. The contours of the current density are compared to other models found in the technical literature. The results of the model presented here show that the average current density is larger than for conventional models (such as serpentine flow paths). This suggests that more efficient flow field paths could be build with this constructal theory-based pattern for the flow field channels.
Experimental and Numerical Study of Single Bubble Dynamics on a Hydrophobic Surface
Authors: Nam Youngsuk , Warrier Gopinath , Wu Jinfeng , Ju Y. Sungtaek
Published: May 2009

The growth and departure of single bubbles on two surfaces with very different wettability is studied using high-speed video microscopy and numerical simulation. Isolated artificial cavities of approximately 10μm diameter are microfabricated on a bare and a Teflon-coated silicon substrate to serve as nucleation sites. The bubble departure diameter is observed to be almost three times larger and the growth period almost 60 times longer for the hydrophobic surface than for the hydrophilic surface. The waiting period is practically zero for the hydrophobic surface because a small residual bubble nucleus is left behind on the cavity from the previous ebullition cycle. The experimental results are consistent with our numerical simulations. Bubble nucleation occurs on nominally smooth hydrophobic regions with root mean square roughness (Rq) less than 1 nm even at superheat as small as 3 °C. Liquid subcooling significantly affects bubble growth on the hydrophobic surface due to increased bubble surface area. Fundamental understanding of bubble dynamics on heated hydrophobic surfaces will help to develop chemically patterned surfaces with enhanced boiling heat transfer and novel phase-change based micro-actuators and energy harvesters.
SRANS and URANS CFD Simulations of Turbulent VHTR Lower Plenum Flow
Authors: Ridluan A. , Tokuhiro A.
Published: May 2009

Time-dependent and time-independent CFD simulations of the flow through a staggered tube bundle were performed. This flow configuration partially simulates the anticipated flow in the lower plenum of a Very High Temperature Reactor (VHTR) design. To design a nuclear reactor with confidence, one needs strict benchmarking as part of a validation and verification exercise for any and all commercial CFD codes. Thus CFD simulations (FLUENT) of isothermal (at present), periodic flow through a tube bundle using both Steady Reynolds Averaged Navier-Stokes (SRANS) and Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were investigated. Selected turbulence models for a single tube diameter and inlet velocity based Re-number, Re ∼ 1.8 × 104, were investigated. The first-order turbulence models were: a standard k-ε turbulence model, a Renormalized Group (RNG) k-ε model, and lastly, a Shear Stress Transport (SST) k-ε model; the second-order model was a Reynolds Stress Model (RSM). Comparison of CFD simulations against experimental results of Simonin and Barcouda was undertaken at five stations (x, y) locations. Under the SRANS, we found the ability of the models to predict the turbulence stresses (u′u′, v′v′, u′v′) generally marginal to poor. However, upon adapting a concept from Large Eddy Simulation (LES), our URANS simulation with RSM revealed a spatiotemporal, oscillating flow structures in the wake. In contrast, it appears that the URANS with (even a) RNG k-ε model is unable to simulate this flow phenomena. In fact, the data suggests that the RNG k-ε model is too spatiotemporally dissipative. Some aspects of the SRANS versus URANS and using the aforementioned turbulence models will be presented.
Stability Limits of Biogas Jet Diffusion Flames
Authors: Leung T. , Wierzba I.
Published: May 2009

An investigation of the stability limits of biogas jet diffusion flames in a co-flowing air stream was conducted. Stability limits were determined experimentally for two different methane-carbon dioxide mixtures that are of typical biogas composition. Moreover, the effect of jet nozzle diameter was also investigated. It was found that with the presence of a significant amount of CO2 in the fuel as in the case of biogas, the stability limits were very low and the flames can only be stabilized over a very small range of coflowing velocities. As expected, an increase in carbon dioxide concentration resulted in the narrowing of the region of the stable flames. However, it was shown that the flame stability of such mixtures can be enhanced very significantly and over a much wider range of co-flowing air velocities by introducing a small amount of hydrogen in the fuel. Results indicate an increase in the stability limits by approximately fourfold when 10% (by vol.) of hydrogen is added under the same operating conditions. The effect of addition of hydrogen on enhancement of biogas stability is most significant with the initial addition of 10%. The degree of enhancement diminishes with further increase in hydrogen addition from 10% to 30%.
Dual Electrode Capacitive Micromachined Ultrasonic Transducer Array for 1-D Intracardiac Echocardiography (ICE)
Authors: Guldiken Rasim O. , Zahorian Jaime , Karaman Mustafa , Degertekin F. Levent
Published: May 2009

We designed and fabricated a 64 element 1-D linear dual electrode Capacitive Micromachined Ultrasonic Transducer (CMUT) array operating at 9.5 MHz for Intracardiac Echocardiography (ICE). The dual electrode CMUT structure increases the overall sensitivity by 12.6dB (6.2dB in receive sensitivity; 6.4dB in output pressure) when compared to optimized single electrode CMUT. We report peak output pressure of 2.3MPa on the CMUT surface when 170V AC and 180V DC is applied. This significant performance increase makes the CMUT more competitive with their piezoelectric counterparts.
Strategies for Implementing Membrane Models in CFD Codes for PEM Fuel Cell Calculations
Authors: Kamarajugadda Sai , Mazumder Sandip
Published: May 2009

The implementation of phenomenological membrane models within computational fluid dynamics (CFD) codes requires coupling of the conservation equation for water content within the membrane to the conservation equations for species mass outside the membrane. It is common practice to treat water and current transport within the membrane as one-dimensional (1D), i.e., normal to the membrane surface only. The purpose of this study is to investigate the accuracy and efficiency of various strategies of implementing a phenomenological membrane model within the framework of a two-dimensional (2D) CFD code. Springer’s membrane model was compared against two other models available from the literature, and the accuracy of each model was assessed by comparing predicted results against experimental data. Results appear to indicate that the Springer model and the Nguyen and White model over-predict the drying of the membrane, while the Fuller and Newman model provides the best match with experimental data. Following these studies, three strategies for implementation of the membrane model were investigated: (1) 2D transport in membrane, (2) 1D transport in membrane and (3) 1D transport with approximate transport properties. Fuller and Newman’s membrane model was used for these studies. The results obtained using the three approaches were found to be within 4% of each other, while there was no significant difference in the computational time required by the three models, indicating that an analytical 1D transport model for the membrane that uses approximate properties is adequate for describing transport through it.
Modeling Cylinder-to-Cylinder Coupling in Multi-Cylinder HCCI Engines Incorporating Reinduction
Authors: Kulkarni Anup M. , Adi Gayatri H. , Shaver Gregory M.
Published: May 2009

Residual-affected homogeneous charge compression ignition (HCCI) is a promising strategy for decreasing fuel consumption and NOx emissions in internal combustion engines. One practical approach for achieving residual-affected HCCI is by using variable valve actuation to reinduct previously exhausted combustion products. This process inherently couples neighboring engine cylinders as products exhausted by one cylinder may be reinducted by a neighboring one. In order to understand this coupling and its implication for controlling HCCI, this paper outlines a simple physics based model of a multi-cylinder HCCI engine using exhaust reinduction. It is based on a physics based model previously validated for a single cylinder, multi mode HCCI engine. The exhaust manifold model links exhaust gases from one cylinder to those of the other cylinders and also simulates the effect of exhaust reinduction from the previous cycle. Depending on the exhaust manifold geometry and orientation, the heat transfer in the manifold causes a difference in the temperature of the re-inducted product gas across the cylinders. The results show that a subtle difference in the re-inducted exhaust gas temperature results in a dramatic variation in combustion timing (approx. 3 degrees). This model provides a basis for understanding the steady state behavior and also for developing control strategies for multi-cylinder HCCI engines. The paper presents exhaust valve timing induced compression ratio modulation (via flexible valve actuation) as one of the approaches to mitigate the imbalance in combustion timing across cylinders.
Connecting With Industry
Authors: Dues Joseph Francis
Published: May 2009

In an era of tight budgets, Universities must plan their capital spending on lab equipment carefully. This process is even more critical for smaller colleges and satellite locations. To address the problem of a limited budget for lab equipment but a strong need for expanded labs to meet minimum course requirements, faculty contacted local industry to ask for help. The Mechanical Engineering Technology department includes a metallography lab as one of its core learning objectives in the freshman level Materials I course. The metallography lab consists of mounting, grinding, polishing and etching a metallographic specimen to identify features of the specimen’s microstructure. Unfortunately, lab equipment was not available for these tasks at one of the University’s satellite locations. However, through contacts with the school’s Industrial Advisory Board, a local company offered to host the laboratory and allow students to use its metallography facility. Conforma Clad, in New Albany, IN, applies very hard coatings to protect metal surfaces subject to wear and abrasion. For quality control purposes, they perform metallographic examinations of the applied coatings. Conforma Clad engineers demonstrated the preparation of the metallographic specimens and the analysis of their microstructure and then let students prepare and view their own specimens. This experiment showed the students the procedures and equipment needed to create pictures of a metal’s microstructure. By preparing the samples themselves, they gained an appreciation of the skill and technique required to successfully view the microstructure. This paper describes the collaboration the MET faculty used to add laboratory experiments without capital expenditures by connecting with local industry. Students benefited by gaining access to the operations and facilities of a local company as well as the knowledge gained by performing the metallography lab. The paper concludes with an evaluation of the experience and the improvements planned for the coming year.
Multiple Annular Ring Capacitive Micromachined Ultrasonic Transducer Arrays for Forward-Looking Intravascular Ultrasound Imaging Catheters
Authors: Guldiken Rasim O. , Zahorian Jaime , Balantekin Mujdat , Karaman Mustafa , Degertekin F. Levent
Published: May 2009

We investigate multiple-annular-ring CMUT array configuration for forward-looking intravascular ultrasound (FL-IVUS) imaging. This configuration has the potential for independent optimization of each ring and uses the silicon area more effectively without any particular drawback. We designed and fabricated a sample 1mm diameter dual annular ring CMUT test array which consists of 24 transmit and 32 receive elements. For imaging experiments, we designed IC chips that contain 8 transimpedance amplifiers, a multiplexer and a buffer. The real time-pulse echo experiments obtained with designed IC electronics show 26dB Signal to Noise Ratio (SNR) from a 3.5 mm away aluminum reflector in oil. This paper presents our first efforts in obtaining real time imaging with designed IC chips which is one step before CMUT on CMOS implementation.
Multi-Level Phase Shift (MLPS) Control Enabled Variable Displacement Gerotor/Geroler
Authors: Yuan QingHui , Armstrong Brian
Published: May 2009

The research focuses on enabling gerotor/geroler, a traditional fixed displacement device, with the variable displacement capability by integrating electronically controlled digital valves and the corresponding control algorithm. Each digital valve controls polarity of each corresponding chamber of the fixed displacement device. A novel Multi-Level Phase Shift (MLPS) control scheme is developed such that the instantaneous displacement of such a system can be controlled. This control law is characteristic of classifying all the possible valve configuration into several displacement families where the peak value within each family would be identical. Given a desired displacement, both displacement family selection and phase shift technology are utilized to achieve better performance. In the experimental study, MLPS control has been verified, and successfully achieves a closed loop velocity tracking control of a hydraulic geroler motor.
Numerical and Experimental Analysis of McKibben Actuators and Dielectric Elastomer Sensors
Authors: Goulbourne N. C. , Son S.
Published: May 2009

Fiber-reinforced pneumatic actuators have the potential to enable the continually evolving technological fields of flexible control surfaces for aircrafts or aquatic vehicles, compliant limbs and graspers for robots, prosthetics, orthotics, and other human-augmenting systems. The McKibben actuator is a pneumatically actuated cylindrical construct consisting of a flexible rubber bladder sheathed in a fiber network, which garners its impressive contracting force from the inextensible fibers that prevent axial extension when an inflation pressure is applied to the internal bladder. The relationship between the axial deformation and contraction force can be accurately modeled using a large deformation continuum model. Our approach is based on the work of Kydoniefs and Matsikoudi-Iliopoulou. Specifically, numerical solutions are obtained by assuming an Ogden strain energy function for the actuator. The deformed shape of the membrane, the fiber angle and the stress components of the membrane and the fibers are predicted by using the initial shape and elastic material parameters. In this paper, a comparison between experimental and numerical modeling results are compared for various actuator geometries. Furthermore, placing a cylindrical dielectric elastomer sensor in direct contact with the inner surface of the McKibben actuator could facilitate in situ monitoring of actuator strains. To illustrate this principle, an experimental setup was developed to measure the changing capacitance of a cylindrical dielectric elastomer sensor as a function of axial extension. A comparison of the predicted and the measured response provides validation of a proposed numerical model. The effects of the dimensions of the sensor on the sensitivity of capacitance measurements are investigated in this paper.
Investigation of Irreversibilities in the Compression Process for Alternative Refrigerants in a Vapor Compression Refrigeration Cycle
Authors: Kilicarslan Ali , Mu¨ller Norbert
Published: May 2009

Irreversibility analyses during compression process are presented for some refrigerants namely, R290, R134a, R12, R22, and R152a in a vapor compression refrigeration cycle. The effects of evaporator temperature, condenser temperature and isentropic efficiency on the irreversibility rates and exergetic efficiencies of the refrigerants under study are investigated By the means of a computer code that simulates a vapor compression cycle including subcooling and superheating. For all the refrigerants in this study, the irreversibility in the compression process decreased as the evaporator temperature and isentropic efficiency increased and it increased with the increasing values of the condenser temperatures. Exergetic efficiency of the compressor increased as the isentropic efficiency of the compressor increased while it decreased with the increasing values of evaporator temperatures. In the case of increasing evaporator and condenser temperatures, and isentropic efficiency values, R22 and R152a approximately show the same and lowest values of compressor irreversibility while R290 has the lowest values. The compressor irreversibilities and compressor exergetic efficiencies of R12 and R134a placed in the moderate range in the case of increasing evaporator and condenser temperatures, and isentropic efficiency values.
Visco-Elastic Modulus and Intercalation of Polymer Chains in Epoxy Nano-Composites
Authors: Ahuja Suresh K.
Published: May 2009

Polymer nano-composites (PNC) are polymers which are reinforced with less than 5% by volume of nano-sized particles with high aspect ratios (L/h > 300). Compared to conventional composites, where the reinforcement is on the order of microns, the nano-composites are reinforced on the order of a few nanometers with advantages in processing and toughness. Nano-composites of epoxy clay have been studied where epoxy is mixed at high shear rates with clay. In our method of making nano-composites, an epoxy, Diglycidyl ether of bisphenol (DGEBA) A was mixed under high shear with organically modified mica type silicate (OMTS) either of benzyl dimethyl stearyl ammonium (BDSMA) or of methyl bishydroxyethyl stearyl ammonium chloride ion exchange with sodium montmorillonite. Nano-composites of epoxy cured with hexahydrophthalic anhydride (70%) with polyether polyol (25%) were made also under high shear both at 90C and 120C. Heat of reaction and transition temperature of epoxy nano-composite was compared with cured epoxy nano-composite. Analysis by X-Ray Diffraction was used to determine peaks, spacing and interfacial region. Dynamic visco-elastic measurements were used to distinguish between the nano-composites from two organically modified mica type silicates. Effect of increase in concentration and temperature on visco-elastic modulus of nano-composites was analyzed in terms of intercalation of polymer chains.
Pool Boiling Studies on Nano-Textured Surfaces: Impact of High Subcooling
Authors: Sathyamurthi Vijaykumar , Banerjee Debjyoti
Published: May 2009

The effect of surface nano-texturing using Multi-Walled Carbon Nano-Tubes (MWCNT) on pool boiling heat transfer is studied under high subcooling (∼30 °C). Three different substrates were used in this study: a bare silicon wafer (450 μm thick), and two similar silicon wafers coated with 9 μm (Type-A) and 25 μm tall (Type-B) MWCNT. The MWCNT are deposited by Chemical Vapor Deposition (CVD), have diameters ranging between 8–16 nanometers and a randomized center to center pitch ranging between 24–45 nm. PF-5060, a fluorocarbon is used as the test fluid. In the nucleate boiling regime the surface coated with Type-A MWCNT shows a significant enhancement in heat transfer in comparison to the bare silicon wafer and Type-B MWCNT coated wafer. Type-B MWCNT on the silicon substrate results in only a slightly higher heat transfer rate as compared to the bare silicon wafer. The presence of MWCNT seems to disrupt the formation of a stable vapor film thus delaying the onset of film boiling. Based on the experimental results, the following transport mechanisms have been identified for the observed enhancement of pool boiling heat flux on the MWCNT: the enhanced surface area (nano-fin effect), enhanced nucleation, disruption of the “microlayer” region in nucleate boiling, and the high thermal conductivity of MWCNT.
Protection From Oxygen and Moisture Via Thin Oxide Barrier Coating for Organic Electronics
Authors: Lee Hyungsuk , Zhang Guangneng , Cho Junghyun
Published: May 2009

Protection from oxygen and moisture is crucial for organic light emitting diodes (OLED) used in flexible display applications. The surface coating is an effective way to protect the enclosed functional materials and organic substrates in order to ensure their device functionality. Parylene films, which can be vapor deposited at room temperature, are known as a superior conformal polymeric material. In fact, a few attempts have shown that the parylene can be a good barrier coating for the OLED devices. This polymer film cannot, however, provide a long-term reliability due to nature of the polymer degradation in the presence of oxygen and moisture. In order to compensate such a drawback, we have explored the ‘biomimetic’ solution processing to deposit the oxide films on the organic substrate. Oxide films can provide a better protection and more robust surface. In this study, polyethylene terephthalate (PET) commonly used for an organic substrate, is deposited with the TiO2 films with or without the parylene underlying layer. Importantly, the oxide coating is processed at very low temperatures (< 60 °C) in aqueous solution, so the process can avoid premature failure due to high-temperature processes, and is applicable to organic structures, cheap and environment-friendly. In addition, hermeticity tests are devised to measure the moisture and oxygen permeation. Interfacial structure and mechanical properties of the resultant coatings are tested via scanning electron microscope (SEM), atomic force microscope (AFM), optical microscope (OM) and nanoindentation.
Modulated Impulsive Forces for Haptic Rendering of Rigid Contact
Authors: Birch Benjamin , Constantinescu Daniela
Published: May 2009

This paper proposes a method for the passive rendering of trains of impulsive forces to users when users contact hard virtual surfaces with a rigid virtual tool. The goal is to improve the sense of presence in virtual environments through enabling users to perceive various transient dynamics at contact onset. The proposed method computes the impulsive forces in the feedback loop based on Newton’s restitution hypothesis, and superimposes them on traditional penalty-based feedback. The method accounts for the energy transferred between the user and the virtual environment by the penalty forces via re-computing the impulsive forces throughout the duration of the transient dynamics. A preliminary user study shows that the modulated impulses are perceptually distinguishable from haptic rendering of collisions via a single impulse.
Adaptive Robust Control Strategy for Coupled Parallel-Kinematics Piezo-Flexural Micro and Nano-Positioning Stages
Authors: Bashash Saeid , Jalili Nader
Published: May 2009

Multiple-axis parallel kinematics piezo-flexural stages, used in variety of scanning probe microscopy and manipulation applications, suffer not only from the hysteresis nonlinearity and the effects of system dynamics, but also from the nonlinear coupling of one axis action on the motion of the other axes. Motivated by these shortfalls, a Lyapunov-based adaptive robust control methodology is proposed for the simultaneous tracking control of multiple-axis parallel kinematics piezo-flexural micro/nano-positioning systems in the presence of parametric uncertainties and unknown or partially known hysteresis and coupling nonlinearities. For this, a double-axis parallel-kinematics piezo-flexural stage with sub-nanometer resolution capacitive position sensors is considered for the system analysis and controller verification. The hysteresis response and the coupling effect of the stage are studied through a number of experiments, followed by a mathematical formulation for the system nonlinear equation of motion. Adopting the variable structure (sliding mode) control method with a parameter adaptation strategy, an adaptive robust controller is then derived with its asymptotic stability guaranteed through the Lyapunov stability criterion. To avoid the chatter phenomenon, which is a common problem in the sliding mode control, the hard switching function of the controller is replaced by a soft switching function. Through theoretical analysis, it is demonstrated that a parallelogram-type zone of attraction can be explicitly formed for the proposed soft variable structure controller, to which the error phase trajectory converges. Therefore, a uniformly ultimately bounded closed-loop system response is achieved. The proposed controller is eventually implemented on the piezo-flexural stage, demonstrating the effective double-axis tracking control of the stage, even in the absence of a representative hysteresis model and despite parametric uncertainties. Results indicate good agreement between experiments and theoretical developments.
Multiplexed High-Throughput Electrokinetically-Controlled Immunoassay on a Chip for the Detection of Specific Bacterial Antibodies in Human Serum
Authors: Gao Yali , Sherman Philip M. , Sun Yu , Li Dongqing
Published: May 2009

This work presents a multiplexed electrokinetically-controlled heterogeneous immunoassay that can process ten samples in parallel. The immunoassay microchip was soft-lithographically fabricated using poly(dimethylsiloxane) and glass. Controlling parameters of the electrokinetically-driven flow in the microfluidic network was determined by numerically simulating transport processes. Multiple passively adsorbed antigens captured antibodies present in samples, which then bound with TRITC-labeled detection antibodies to generate fluorescent signals. Antibodies against Escherichia coli O157:H7 and Helicobacter pylori were studied as model analytes. After conditions for antigen-coating were optimized, a 24-minute assay detected E. coli O157:H7 antibody in the concentration range of 0.02–10 μg/mL, and H. pylori antibody in the range of 0.1–50 μg/mL. In testing human serum samples, non-specific binding of serum components was effectively suppressed by using 10% (w/v) bovine serum albumin. An accuracy of 100% was achieved in detecting either E. coli O157:H7 antibody or H. pylori antibody from human serum samples. Simultaneous screening of both antibodies was also successfully demonstrated. The immunoassay chip shows an excellent potential for efficiently detecting multiple pathogenic infections in clinical environments.
A Low-Memory Block-Implicit Solver for Coupled Solution of the Species Conservation Equations on an Unstructured Mesh
Authors: Kumar Ankan , Mazumder Sandip
Published: May 2009

Many reacting flow applications mandate coupled solution of the species conservation equations. A low-memory coupled solver was developed to solve the species transport equations on an unstructured mesh. The first step was the decomposition of the domain into sub-domains comprised of geometrically contiguous cells—a process termed internal domain decomposition (IDD). This was done using the binary spatial partitioning (BSP) algorithm. Following this step, for each subdomain, the discretized equations were set up, written in block implicit form, and solved using two different solvers: a direct solver using Gaussian elimination and an iterative solver based on Krylov sub-space iterations, i.e., the Generalized Minimum Residual (GMRES) solver. Overall (outer) iterations were then performed to treat explicitness at sub-domain boundaries and non-linearities in the governing equations. The solver is demonstrated for a simple two-dimensional multi-component diffusion problem involving 5 species. Sample calculations show that the solver with direct solution for each block is most efficient if the number of cells in each block is small—typically tens of cells, while the solver with iterative solution for each block is most efficient if the number of cells is relatively large—typically hundreds of cells. Overall the iterative solution based solver performed best, with maximum efficiency gain of a factor of seven over a block Gauss-Seidel (GS) solver and was found to be comparable or better in efficiency than a block-implicit Alternating Direction Implicit (ADI) solver. The gain in efficiency was found to increase with increase in cell aspect ratios.
Ultra-Sensitive Fluidic Sensors by Integrating Fluidic Circuits and MOSFETs
Authors: Xu Dongyan , Kang Yuejun , Li Dongqing , Li Deyu , Sridhar Manoj , Hmelo Anthony B. , Feldman Leonard C.
Published: May 2009

Nanofluidic sensors have been developed over the past decade and demonstrated the capability of sensing single DNA molecules. One important and promising class of nanofluidic devices detects single molecules by inserting a nanopore or nanochannel between two fluid cells and inducing an ionic current by applying an electric bias across the nanopore or nanochannel. When molecules are translocated through the nanopore/nanochannel, a modulation of the baseline ionic current can be observed. In this scheme, the ionic current modulation is approximately the same as the channel resistance modulation, requiring the channel size to be comparable to the molecules to be detected. Here we report on a new sensing scheme to detect the translocation of particles through a fluidic channel, which amplifies the resistance modulation by up to 75 times. In this scheme, the device connects the gate of a MOSFET with a fluidic circuit and monitors the modulation of MOSFET’s drain current to detect particles. We demonstrate that amplification can be achieved from both the fluidic circuit and the MOSFET. For a 9.86 μm diameter polystyrene bead that occupies 0.7% of the total volume of the sensing channel, results show that the drain current of the MOSFET is blocked by 30–46%. We also demonstrate the capability of this device to distinguish particles with similar sizes but different surface charges as they translocate through the sensing channel. More interestingly, the experiments with CD4+ T lymphocyte cells show another modulation pattern: the MOSFET’s drain current is first enhanced and then blocked, which is not fully understood and needs further investigation. Although at this moment the device is based on microchannels and the particles detected are micron-size beads and cells, we expect that the same scheme can be applied to nanofluidic circuits for single molecule detection.
Planar and Three-Dimensional Microfluidic Fuel Cell Architectures
Authors: Kjeang Erik , Djilali Ned , Sinton David
Published: May 2009

We propose planar and three-dimensional microfluidic fuel cell architectures based on the all-vanadium redox system. These fuel cells operate in a membraneless co-laminar flow configuration and are manufactured by economical microfabrication methods. Graphite rods, also known as mechanical pencil refills, are demonstrated as fuel cell electrodes in a three-dimensional array architecture with unique scale-up capabilities. We also demonstrate unprecedented power density levels by incorporation of porous electrodes in a planar microfluidic fuel cell.
Mobile Learning and Digital Libraries
Authors: Datta Esha , Agogino Alice
Published: May 2009

With the recent advancement of mobile technologies, such as smart phones, digital cameras and PDAs (Personal Digital Assistants), and tablet PCs mobile learning provides opportunities for formal and informal education in a wide range of settings. In particular, the use of mobile technologies to access digital libraries opens up doors for providing unique learning experiences, both inside and outside of the classroom. This paper presents the design and implementation of a mobile learning digital library infrastructure and test applications. We first conducted a user needs analysis of students, educators, and parents in order to understand desirable functional attributes and challenges associated with mobile learning. We translated this needs assessment into a list of twelve functional attributes for digital library infrastructures and mobile device applications that will facilitate informal learning. In order to test out the recommendations, a conceptual design was developed as a lesson plan that uses mobile devices and digital libraries to teach the concept of simple machines. This lesson was implemented during a workshop conducted with students in the TechBridge program, an after school program that introduces girls to technology. The students that participated in this workshop were from less affluent schools and were all members of ethnic groups that are typically underrepresented in the field of engineering. This paper summarizes the needs assessment research, implementation, testing and recommendations for future work. Our goal is to provide recommendations for mobile learning technologies that will increase access and enhance mobile learning experiences for students of all backgrounds.
An AFM-Based Nanomanipulation Model Describing the Atomic Two Dimensional Stick-Slip Behavior
Authors: Landolsi Fakhreddine , Ghorbel Fathi H. , Dabney James B.
Published: May 2009

A new AFM-based nanomanipulation model describing the relevant physics and dynamics at the nanoscale is presented. The nanomanipulation scheme consists of integrated subsystems that are identified in a modular approach. The model subsystems define the AFM cantilever-sample dynamics, the AFM tip-sample interactions, the contact mechanics and the friction between the sample and the substrate. The coupling between these different subsystems is emphasized. The main contribution of the proposed nanomanipulation model is the use of a new 2D dynamic friction model based on a generalized bristle interpretation of one asperity contact. The efficacy of the proposed model to reproduce experimental data is demonstrated via numerical simulations. In fact, the model is shown to describe the 2D stick-slip behavior with the substrate lattice periodicity. The proposed nanomanipulation model facilitates the improvement and extension of each subsystem to further take into account the complex interactions at the nanoscale.
Modeling and Characterization of Biomaterials Spreading Properties in Powder-Based Rapid Prototyping Techniques
Authors: Shanjani Yaser , Toyserkani Ehsan , Wei Christina
Published: May 2009

In this work, the spreading properties of biomaterials, while a counter-rotating roller is used in rapid prototyping machines, are modeled and characterized. For modeling, the slab method is used in which biomaterial geometrical properties are incorporated into the model. A pressure dependent plasticity model is used as a constitutive model for biomaterial powders. In addition, the coulomb friction law for the powder-roller interface boundary is incorporated into the model. Size and shape of powder particles as well as roller rotational and linear velocities are considered within the friction coefficient. Powder bed parameters such as compaction pressure, stress distribution and relative density are predicted using the simulation.
Molecular Dynamics Simulations of Bubble Formation in Nanochannels
Authors: Sridhar Manoj , Hmelo Anthony B. , Feldman Leonard C. , Xu Dongyan , Li Deyu
Published: May 2009

The behavior of confined fluids is of great interest due to the proliferation and applications of micro- and nanofluidic devices. Recent computational and experimental results have shown that fluids exhibit unusual phase change behavior when confined to very small length scales where the fluid physics is dominated by interactions with the confining channel walls. In particular, understanding the liquid-vapor phase transition and bubble nucleation process in confined spaces presents opportunities for making valves and pumps in nanofluidic networks. In this paper, we present molecular dynamics simulations of thermal bubble nucleation in fluids confined in nanochannels. To verify the computational models, bulk argon and bulk water were first modeled under conditions similar to those reported in the literature. The results were similar to those presented in the literature, indicating that our computational models could reproduce published data. We then modeled argon and water systems confined between two parallel silicon plates with nanometer separation. To simulate cases more extensively encountered in reality, we performed Molecular Dynamics (MD) simulations in the isothermal-isobaric (NPT) ensemble by allowing the top silicon plate to move up and down under a constant external pressure during the simulation. For either the nano-confined argon or the nano-confined water system, results indicated no bubble generation under an external pressure of 0.1 MPa, even for temperatures much higher than the boiling temperature of the respective fluids at 0.1 MPa. We also observed that there was no bubble generation in either the argon or water NPT system when the external pressure was reduced to as low as 0.01 MPa. The density of the nano-confined fluids at constant temperature was observed to be independent of external pressure on the system. This suggests that the nanoconfined fluids behave like liquids with low compressibility even at temperatures close to their superheat limit.
Molecular Dynamics Simulations of Water and Ion Structures Near Charged Surfaces
Authors: Xu Dongyan , Li Deyu , Leng Yongsheng
Published: May 2009

Extensive research has been devoted to nanofluidics in the past decade because of its potential applications in single molecule sensing and manipulations. Fundamental studies have attracted significant attention in this research field since the success of nanofluidic devices depends on a thorough understanding of the fluidic, ionic, and molecular behavior in highly confined nano-environments. In this paper, we report on molecular dynamics simulations of the effect of surface charge densities on the ion distribution and the water density profile close to a charged surface. We demonstrate that surface charges not only interact with mobile ions in the electrolyte, but also interact with water molecules due to their polarizability, and hence influence the orientation of water molecules in the near wall region. For the first time, we show that as the surface charge density increases, the water molecules within ∼ 5 Å of the {100} silicon surface will evolve from one layer into two layers. Meanwhile, the orientation of the water molecules is more aligned instead of randomly distributed. This layering effect may have important implications on electroosmotic flow through nanochannels and heat transfer across the solid-liquid interface.
Review: Rod-Shaped Nanoparticle Assembly Using an Electric Field
Authors: Oh Kieseok , Chung Jae-Hyun , Yeo Woonhong , Liu Yaling , Liu Wing Kam
Published: May 2009

Various nanowire or nanotube-based devices have been demonstrated to fulfill the future demands on semiconductor industries and bio/chemical sensors. To fabricate such devices, an electric field-based assembly method has demonstrated a great potential for parallel- and one dimensional assembly of nanowires. In this review paper, the future direction of electric field guided assembly of nanowires is discussed with our recent results. The challenges and opportunities of the assembly are also introduced with the current trends of the nanowire assembly.
An Evaluation Mechanism for Defining Gaps and Overlaps of Product Information Exchange Standards
Authors: Sarigecili Mehmet I. , Baysal Mehmet Murat , Roy Utpal , Rachuri Sudarsan , Sriram Ram D. , Mani Mahesh
Published: May 2009

The need to exchange information between organizations or departments of the same corporation is hampered by interoperability problems that mostly originate from the necessity to comply with diverse standards while using dissimilar applications. Each organization generally uses different standards (both local and international) for products which they produce or use. The differences and similarities of these standards, or gaps and overlaps between these standards create problems when exchanging product information through the product life cycle. Defining gaps and overlaps for these standards will help us better understand the interoperability issues. This will aid in the development of strategies for reducing interoperability problems, thus improving efficient information exchange. In this study, we present different approaches for comparing standards and for identifying gaps and overlaps in standards. A Matrix–based evaluation mechanism developed for this purpose is also described.
Dynamic Model of a Hybrid Hydraulic Actuator Utilizing Different Smart Materials
Authors: Chaudhuri A. , Wereley N. M.
Published: May 2009

There has been a lot of research in the development of a hybrid hydraulic actuator driven by various smart materials. The basic operation of these actuators involves high frequency bidirectional operation of the active material which is converted to unidirectional motion by a set of valves. The response of the actuator also shows resonant peaks similar to that of SDOF mechanical systems and indicates a region of maximum output. At these high driving frequencies, the inertial effects of the fluid mass dominate over the viscous effects and the problem becomes unsteady in nature. Geometrical parameters of the flow path are also important. Due to the high pressures existing inside the actuator and the presence of entrained air, compressibility of the hydraulic oil also has to be taken into account. Hybrid actuators using the magnetostrictive material Terfenol-D and the electrostrictive material PMN have been developed in our laboratory, with hydraulic oil as the working fluid. Several key design parameters, which include output cylinder size, diaphragm thickness, reed valve thickness and tubing diameter, along with operational conditions, like input current and bias pressure within the fluid, have been varied to identify a set of optimum driving conditions. Tests at no-load and with load have been carried out for unidirectional motion of the output piston. To characterize the input driving circuitry and magnetic flux path, we have also carried out dynamic tests with the Terfenol-D rod and analyzed its magnetic circuit (flux density vs. frequency) response. In this paper, we develop a mathematical model of the hydraulic hybrid actuator to show the basic operational principle under no-load and loaded conditions and to describe the resonance phenomenon affecting the system performance. The dynamics of the input driving circuit have been included in the model. The fluid passages have been represented using the transmission line model, giving rise to strongly coupled ordinary differential equations which are solved using a lumped parameter approach. This model is then used to calculate the no-load velocity of the actuator and also its blocked force. Finally, we use the model to find optimal pumping frequency to get highest performance with different active materials and also to predict the pump sizing for desired output velocity and load lifting capability.
Methodologies for System-State Interrogation for Prognostication of Electronics Under Thermo-Mechanical Loads
Authors: Lall Pradeep , Hande Madhura , Bhat Chandan , Suhling Jeff
Published: May 2009

Methodologies for prognostication and health monitoring can significantly impact electronic reliability for applications in which even minimal risk of failure may be unbearable. Presently, health monitoring approaches such as the built-in self-test (BIST) are based on reactive failure diagnostics and unable to determine residual-life or estimate residual-reliability [Allen 2003, Drees 2004, Gao 2002, Rosenthal 1990]. Prognostics health-monitoring (PHM) approach presented in this paper is different from state-of-art diagnostics and resides in the pre-failure-space of the electronic-system, in which no macro-indicators such as cracks or delamination exist. Applications for the presented PHM framework include, consumer applications such as automotive safety systems including front and rear impact protection system, chassis-control systems, x-by-wire systems; and defense applications such as avionics systems, naval electronic warfare systems. The presented PHM methodologies enable the estimation of prior damage in deployed electronics by interrogation of the system state. The presented methodologies will trigger repair or replacement, significantly prior to failure. The approach involves the use of condition monitoring devices which can be interrogated for damage proxies at finite time-intervals. The system’s residual life is computed based on residual-life computation algorithms. Previously, Lall, et. al. [2004, 2005, 2006] have developed several leading indicators of failure. In this paper a mathematical approach has been presented to calculate the prior damage in electronics subjected to cyclic and isothermal thermomechanical loads. Electronic components operating in a harsh environment may be subjected to both temperature variations in addition to thermal aging during use-life. Data has been collected for leading indicators of failure for 95.5Sn4Ag0.5Cu first-level interconnects under both single and sequential application of cyclic and isothermal thermo-mechanical loads. Methodology for the determination of prior damage history has been presented using non-linear least-squares method based interrogation techniques. The methodology presented used the Levenberg-Marquardt Algorithm. Test vehicle includes various area-array packaging architectures soldered on Immersion Ag finish, subjected to thermal cycling in the range of −40°C to 125°C and isothermal aging at 125°C.
On-Line Force Ripple Identification and Compensation in Precision Positioning of Wafer Stages
Authors: Yu Shu-Wen , Mishra Sandipan , Tomizuka Masayoshi
Published: May 2009

This paper presents the design and implementation of a composite controller to reduce the effect of force ripple in a linear motor wafer stage system. The composite controller consists of two components: 1) a PID feedback controller and 2) an adaptive feedforward compensator. The feedback controller is tuned to achieve good transient response and enhanced robustness of the system. Force ripples are a major source of tracking error in linear motor precision positioning systems. An approximation of the nonlinear force ripple model can be obtained by expressing the ripple as the sum of a sequence of sinusoidal harmonics, multiplied by the motor current. The force ripple is first approximated by on-line adaptive estimation of the unknown coefficients associated with each harmonic, and then compensated with a feedforward term. Experimental results on a prototype single degree of freedom wafer stage are presented to show the performance improvement obtained by the proposed control scheme.