bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Computations of Flow in Constricted and Wavy Nano Channels
Authors: Marsh D. D. , Vanka S. P. , Jasiuk I. M. , Knothe Tate M. L.
Published: July 2010

This paper explores flow in complex nano-sized channels by use of molecular dynamics. Due to the small nature of these channels and to better capture wall effects, non-equilibrium molecular dynamics simulations were performed. Straight, constricted and sawtooth channels were studied. The function used for modeling the particle interactions is the Lennard-Jones 6–12 potential. Stochastic boundary conditions are used in conjunction with periodic boundary conditions in a 3D domain. Computational enhancements including cell subdivision and neighbor listing provide increased efficiency. The channels were homogeneous in the depth dimension and the results were averaged in the depth direction in order to improve averages. Velocity profiles at several locations were computed and are presented in the paper. The eventual goal of this research is to study the effects of time-dependent inflow and pressure drops so as to understand the flow in nano channels in the human bone.
Control of Internal Stress for High Quality Nickel Large Area Mold Inserts
Authors: Park D. S. , Singh V. , You B. H. , Kim N. , Chen P.-C. , Soper S. A. , Nikitopoulos D. E. , Goettert J. , Murphy M. C.
Published: July 2010

Metallic large area mold inserts (LAMIs) are essential for the replication of polymer microfluidic devices. Successful molding of micro- or nanoscale features over large areas is dependent on improving the dimensional control of the mold inserts, particularly those fabricated by electrodeposition using the LIGA or UV-LIGA processes. A systematic approach to controlling the internal stress of the nickel deposits, which was essential for predicting the final flatness of the LAMIs prior to electroplating, was carried out. The internal stress of the nickel deposits from a nickel sulfamate solution was estimated using a bent strip stress measurement method after maintaining electroplating chemicals and conditions and reducing contamination. Over-electroplating of the nickel LAMIs was performed on SU-8 electroplating molds on 150 mm diameter Si wafers. Detailed characterization of the nickel LAMIs to determine the relationship between the overall flatness of the LAMIs and the internal stress identified a suitable process window in terms of the current densities (10–20 mA/cm2) and the internal stress (−8.3 ∼ −3.0 MPa) for the high quality nickel LAMIs with an overall flatness of 100 μm.
Mechanical Properties of NiAl Nanocomposite Intermetallic Alloys With Varying Porosity
Authors: Hunt Emily M. , Murty Pilaka
Published: July 2010

Recent advancements in the field of nano-technology focused attention on developing materials with new and useful characteristics. In particular, there is interest in designing nanocomposite thermites for combustion synthesis applications. The composite material consists of nano-scale particles that are in nearly atomic scale proximity but constrained from reaction until triggered. Once initiated, the reaction will become self-sustaining and a new intermetallic alloy product will be produced. An example of this type of reaction is between Ni and Al such that a nickel-aluminide alloy is produced (Eq. (1) [1].
Size Effect on Strength and Lifetime Distributions of Quasibrittle Structures
Authors: Bazˇant Zdeneˇk P. , Le Jia-Liang
Published: July 2010

Engineering structures such as aircraft, bridges, dams, nuclear containments and ships, as well as computer circuits, chips and MEMS, should be designed for failure probability < 10−6–10−7 per lifetime. The safety factors required to ensure it are still determined empirically, even though they represent much larger and much more uncertain corrections to deterministic calculations than do the typical errors of modern computer analysis of structures. The empirical approach is sufficient for perfectly brittle and perfectly ductile structures since the cumulative distribution function (cdf) of random strength is known, making it possible to extrapolate to the tail from the mean and variance. However, the empirical approach does not apply to structures consisting of quasibrittle materials, which are brittle materials with inhomogeneities that are not negligible compared to structure size. This paper presents a refined theory on the strength distribution of quasibrittle structures, which is based on the fracture mechanics of nanocracks propagating by activation energy controlled small jumps through the atomic lattice and an analytical model for the multi-scale transition of strength statistics. Based on the power law for creep crack growth rate and the cdf of material strength, the lifetime distribution of quasibrittle structures under constant loads is derived. Both the strength and lifetime cdf’s are shown to be size- and geometry-dependent. The theory predicts intricate size effects on both the mean structural strength and lifetime, the latter being much stronger. The theory is shown to match the experimentally observed systematic deviations of strength and lifetime histograms of industrial ceramics from the Weibull distribution.
Microthruster Knife-Edge Thrust Stand
Authors: Lee John , Huang Adam
Published: July 2010

Nano- and picosatellites are small satellites that are a more affordable alternative to larger satellites. Nanosats are satellites with a mass ranging from 1kg to 10kg while picosats have a mass that ranges from 0.1kg to 1kg. In addition to their cost, the smaller satellites have the advantage that they are able to carry out missions that would be difficult for a larger satellite. These advantages include using formations to gather data from multiple points and in-orbit inspection of larger satellites. Nano/picosats can be fabricated or procured for under $25k and launched into space for around another $40–60k which makes the total pre-mission expenditures for the satellite under $100k. Currently these satellites have a limited ability to orient themselves and cannot perform orbital maneuvers. For example a satellite could potentially use electro-magnetically charged coils in conjunction with earth’s magnetic field to orient themselves. The problems with the current methods of orientation are they are extremely slow in damping out oscillations due to low power and cannot execute out of orbit maneuvers. Thus, once a satellite is deployed from its launcher it is on a set orbit and cannot change its orbital elements on-command for the duration of its mission, limiting their use for science missions. Thus, it would be extremely beneficial for the nano- and pico-satellite community if a micro propulsion system capable of full-authority attitude control and orbital maneuver is developed. This paper describes the development of a cost-effective thrust stand for cold gas micro thruster development work. The thrust stand design is a static pendulum supported by a razor blade knife edge sitting on top of a silicon V-groove chip. The thrust measurement used is direct technique using a 1-axis strain gauge load cell at 25gm full-scale and resolutions in the order of 10 micro-g. Future possibilities include implementing a electromagnetic force compensation balance to improve sensing resolution.
Effect of Matrix Crystallinity on Nanocomposite Properties
Authors: Shofner Meisha L. , Kaur Jasmeet , Lee Ji Hoon
Published: July 2010

The properties of two nanocomposite systems with semi-crystalline matrices were reported. Differences in achievable dispersion and thermomechanical properties were related to the matrix crystallinity. A lesser amount of matrix crystallinity aided in dispersion and led to greater mechanical reinforcement at temperatures above the glass transition.
Dielectrophoretic Separation of Microparticles in Curved Microchannels
Authors: Zhu Junjie , Tzeng Tzuen-Rong Jeremy , Xuan Xiangchun Schwann
Published: July 2010

Particle (both biological and synthetic) separation is important for a wide range of applications in industry, biology, and medicine. In microfluidic devices particles have been separated based on either extrinsic labels (e.g., fluorescence- and magnetic-activated sorting) or intrinsic properties (e.g., size, charge, density, etc.). The latter may take place in a batchwise or continuous-flow process. The batch-process separation typically includes filtration, chromatography, and electrophoresis. In the continuous-flow separation, an external force field (e.g., acoustic, electrical, magnetic, and optical, etc.) acts on particles at an angle to the flow direction and deflects them to different flow paths [1]. Here we introduce a continuous particle separation technique in electrokinetic flow through curved microchannels. This separation results from the cross-stream dielectrophoretic motion induced by channel curvatures [2]. It eliminates the use of in-channel micro-electrodes or micro-obstacles that are required in present dielectrophoresis-based particle separation techniques [3].
Project STARSHINE (Student Tracked Atmospheric Research Satellite for Heuristic International Networking Experiment)
Authors: Moore R. Gilbert
Published: July 2010

Four spherical STARSHINE Aluminum nano-satellites, covered by laser retroreflectors and by up to 1500 small mirrors that were ground and polished by thousands of students all over the world, have been built by a voluntary consortium of educational institutions, private companies, government laboratories and individuals. Three of these satellites were launched into orbit by NASA during the peak of Solar Cycle 23 in the 1999 to 2001 time period. Two of them were deployed into orbit from Space Shuttle orbiters launched from the Kennedy Space Center, and one was deployed from an Athena expendable launch vehicle launched from Kodiak, Alaska. A fourth satellite is sitting in storage, awaiting launch during Solar Maximum 24 a few years from now. These satellites were tracked by radars of the U.S. Space Command, by lasers in the International Laser Ranging Network, and by the unaided eyes of students at sites all over the world. Their observations were reported to the U.S. Naval Research Laboratory, where orbital dynamicists and solar-terrestrial physicists have used them to determine the density of the upper atmosphere in the altitude range of 300–500 km and to improve their computational codes for predicting the future orbital positions of satellites.
Radial Pre-Concentration With a Planar Nanoporous Film
Authors: Scarff Brent , Escobedo Carlos , Sinton David
Published: July 2010

Electrokinetic flow in microchannels in the vicinity of charged membranes or nanochannels gives rise to a polarization phenomena that can be used to control analyte. Utilizing this concept this paper focuses on a novel method to trap and pre-concentrate an analyte surrounded by a radial planar Nafion membrane. Numerical simulations are conducted to demonstrate the exclusion enrichment phenomena and the relative effect of the convective component on concentration and electric fields is demonstrated. Preliminary experimental results demonstrate the promise of the concept.
Length Scale Effects in Materials Deformation of Nano and Microscale Au Structures
Authors: Lian Jie , Wang Junlan
Published: July 2010

In this study, intrinsic size effect — strong size dependence of mechanical properties — in materials deformation was investigated by performing atomistic simulation of compression on Au (114) pyramids. Sample boundary effect — inaccurate measurement of mechanical properties when sample size is comparable to the indent size — in nanoindentation was also investigated by performing experiments and atomistic simulations of nanoindentation into nano- and micro-scale Au pillars and bulk Au (001) surfaces. For intrinsic size effect, dislocation nucleation and motions that contribute to size effect were analyzed for studying the materials deformation mechanisms. For sample boundary effect, in both experiments and atomistic simulation, the elastic modulus decreases with increasing indent size over sample size ratio. Significantly different dislocation motions contribute to the lower value of the elastic modulus measured in the pillar indentation. The presence of the free surface would allow the dislocations to annihilate, causing a higher elastic recovery during the unloading of pillar indentation.
Dynamic Optical Investigations of Hypervelocity Impact Damage
Authors: Lamberson Leslie E. , Rosakis Ares J.
Published: July 2010

Hypervelocity impact is a rising concern in spacecraft missions where man-made debris in low-earth orbit as well as micrometeroids have the potential to damage not only the structural components, but also the optical, electrical, and thermal components of a space asset. Little has been investigated regarding damage mechanisms and dynamic fracture mechanics resulting from a hypervelocity impact in-situ. Two optical techniques, the methods of photoelasticity and caustics, in conjunction with high-speed photography are used to examine stress waves from impact of unloaded plates, as well as pre-cracked and pre-loaded plates in tension. The resulting photographs are analyzed to extract information regarding stress wave interactions, crack speeds and the dynamic stress field ahead of the moving cracks.
Effect of Interface Geometry on Fracture Parameters at Corrugated Interface
Authors: Desyatova Anastasia S. , Dzenis Yuris A.
Published: July 2010

Interfaces are ubiquitous in both natural and synthetic structural materials. Materials ultimate performance is often determined by interfacial properties (as a weak link). One aspect that is expected to substantially affect crack propagation at interfaces is interfacial geometry. Several works were devoted to the investigation of surface pretreatment influence on the fracture parameters and adhesive strength [1–4]. They showed substantial effect of interfacial micro- and nano-roughness on fracture toughness. However, the experiments to date were performed on random interfaces and it was often difficult to separate chemical and geometric effects.
Thermal Conductivity of Graphene Layers Encased in Oxide
Authors: Chen Zhen , Jang Wanyoung , Bao Wenzhong , Lau Chun Ning , Dames Chris
Published: July 2010

Experimental knowledge of the heat flow along graphene layers encased by oxide is essential for future graphene-based nanoelectronics, interconnects, and thermal management structures. We used a “heat spreader method” to study the heat dissipation performance of encased graphene. Fitting the experimental data with a three-dimensional finite-element method (FEM) allows the in-plane thermal conductivity of the graphene layers to be extracted. The method is validated on samples with metal films of known thermal conductivity, as determined from electrical resistance measurements and the Wiedemann-Franz law.
A Crash Prediction Algorithm Using a Particle Filter and Bayesian Decision Theory
Authors: Kim Taewung , Jeong Hyun-Yong
Published: July 2010

Active safety systems have been developed in automotive industry, and a tracking algorithm and a threat assessment algorithm are needed in such systems to predict the collision between vehicles. It is difficult to track a threat vehicle accurately because of lack of information on a threat vehicle and the measurement noise which does normally not follow Gaussian distribution. Therefore, there is an uncertainty whether the collision will occur or not. Particle filtering is widely used for nonlinear and non-Gaussian tracking problems, and statistical decision theory can be used to make an optimal decision in an uncertain case. In this study, a crash prediction algorithm has been developed using a particle filter and statistical decision making.
Investigation and Modification of Frequency Response Function Using Digital Fourier Analysis for High Speed Dynamic Testing Facility
Authors: Thorbole Chandrashekhar K. , Raju Keshavanarayana S.
Published: July 2010

The increasing application of composites in the aviation and automobile industry demands a better understanding of composite material behavior under high loading rate. This shall provide a better insight of actual loads on occupants while preserving livable crashworthy structure. In this study, a high stroke rate MTS servo-hydraulic testing machine is used to characterize the behavior of composite materials at high strain rates. At higher stroke rates, the output of the load detection system acquired by the load cell deviates from the true load-time wave form of the specimen. This is due to the convolution of the structural response of the detection system with the true characteristic of the specimen. To identify the true nature of the specimen load-time behavior, the de-convolution of the detection system response is necessary to restore the specimen characteristic wave form closer to its true behavior. The convolution of data set in the time domain is a time consuming process which explains the benefit of using the frequency domain; as the convolution in time domain corresponds to multiplication in the frequency domain. This process requires the transformation of the time domain data to frequency domain data via Fast Fourier Transform (FFT). In the frequency domain the complex division of the Fourier transfer of the detection system output with frequency response function of the detection system shall provide the true complex input characteristic. This paper elaborates the methodology utilized for obtaining the Frequency Response Function (FRF) of the load detection system using digital Fourier analysis with a single input/output data set. This also emphasizes precautions and guidelines for improving results with FFT to obtain true FRF measurements of the load detection system. The FRF obtained is successfully used to identify the actual specimen wave form characteristic. This is achieved by extracting the structural response of the load detection system from the load cell output.
Low Velocity Punch-Shear Response of Nanoclay and Graphite Platelet Reinforced Vinyl Ester Plates, Laminated Face Sheets and Sandwich Composites
Authors: Pramanik Brahmananda , Mantena P. Raju
Published: July 2010

Focus of our research is on developing stronger, safer and more cost-effective structures for the new generation naval ships; especially nanoparticle reinforced glass/carbon polymeric based composites and structural foams for blast/shock/impact mitigation. Punch-shear test at low velocity impact is significant for mechanical characterization. Gama et al. [1] performed QS-PST experimental methodology to define elastic energy and absorbed energies of composites as a function of penetration displacement. This paper describes the punch-shear response of nanoparticle reinforced vinyl ester plates, laminated face sheets and sandwich composites using Dynatup 8250 drop-weight impact test system according to ASTM D3763 Standard [2]. Low-velocity tests were performed on 4″ × 4″ square plate specimens with fixed circular boundary condition and impacted by a hemispherical-head plunger with added mass. The impact load, displacement, energy plots and visual inspection of the post damaged specimens depicted the failure characteristics and punch shear response of these composites.
The Effect of Clay/Epoxy Debonding to the Mechanical Properties of Nanocomposites
Authors: Park J. Y. , Fay T. A.
Published: July 2010

Analytical equations using micro- and continuum mechanics approach that can effectively estimate the mechanical properties of polymer composite materials containing clay nanoparticle fillers were developed. Various modeling techniques using the micromechanical approach were investigated, including conventional micromechanical models. An analytical model was proposed based on the consideration of the effects of imperfect bonding between the nanoparticles and the matrix in the composite materials. The mechanical properties of the considered nanocomposites were estimated, and the estimated values were validated using the experimentally determined mechanical properties. For the experimental program, clay/epoxy nanocomposite specimen were fabricated and tested. The developed model was also compared with the conventional and previously developed micromechanical models.
Drawing of Spatially Oriented Electrospun Fibers
Authors: Sun Z. , Knopf J. , Deitzel J. M. , Gillespie J. W.
Published: July 2010

A simple approach to electrospinning has been developed that enables the collection of polymer, ceramic, and multiphase composite fibers, in quantity, with a high degree of spatial orientation. It has been demonstrated that a careful choice of solvent effectively eliminates the onset of the characteristic “bending” instability that is commonly associated with the electrospinning process. This allows collection of spatially oriented submicron electrospun fibers on a rotating drum without the need for elaborate mechanical or electrostatic manipulation of the electrospinning jet and/or collection target. Fibers have been electrospun from a series of model polyethylene oxide/CHCL3 solutions with a range of conductivities. The experimental data confirms theoretical predictions that the onset of the bending instability is a function of the available “free” charge in the solution, which in turn is strongly influenced by the dielectric constant of the solvent. The results show that fiber orientation becomes random as the conductivity increases, indicating the need for the surface charge density to exceed a critical threshold in order for the bending instability to initiate. Furthermore, it has been demonstrated that fiber diameter can be effectively controlled by controlling drum take-up speed. This method has been experimentally demonstrated with other low dielectric constant solvents and other common polymer, ceramic, composite materials.
Guiding the Nonmagnetic Particles by Magnetic Nanoparticles in a Microfluidic Device Using External Magnetic Fields
Authors: Asmatulu R. , Zhang B. , Nuraje N.
Published: July 2010

A microfluidic device was fabricated via UV lithography technique to separate nonmagnetic fluoresbrite carboxy microspheres (∼4.5 μm) from the ferrofluids made of magnetic nanoparticles (∼10 nm). A mixture of microspheres and ferrofluid was injected to lithographically developed Y shape micro channels, and then by applying the external magnet field, the fluoresbrite carboxy microspheres and ferrofluids were clearly separated into different channels because of the magnetic force acting on those nonmagnetic particles. During the fabrication, a number of different parameters, such as UV exposure times, UV power level and photoresist thickness were tested to optimize for our needs. In addition, in the magnetic field testing, different pumping speeds, and particle concentrations associated with the various distances between the magnet and the microfluidic system were studied for an efficient separation.
Reliability of Electrostatically Driven Resonant Sensors Under Mechanical Shock
Authors: Ibrahim Mahmoud I. , Younis Mohammad I.
Published: July 2010

This paper presents a theoretical and experimental investigation of the response of electrostatically actuated parallel-plate resonators when subjected to mechanical shock. Resonators are commonly employed in resonant sensors, where they are operated at low pressure for enhanced sensitivity making their response to external disturbances such as shock a critical issue. A single-degree-of-freedom system is used to model a resonator, which is electrostatically driven by a DC load superimposed to an AC harmonic load. Simulation results are demonstrated in a series of shock spectra that help indicate the combined influence of shock, DC, and AC loads. The effect of the shock duration coinciding with the AC harmonic frequency is investigated. It is concluded that accounting for the electrostatic forces, especially the AC load, is crucial when addressing the reliability and performance of resonators against shock. It is found that for specific shock and AC excitation conditions, the resonator may experience early dynamic pull-in instability. Experimental work has been conducted on a capacitive sensor to verify the obtained theoretical results. The sensor is mounted on top of a small shaker and then both are placed inside a vacuum chamber. Acceleration pulses were applied on the sensor while powered by DC and AC load. The response of the device was monitored using a laser-Doppler vibrometer. The experimental results were compared to the theoretical results and were found to be in good agreement.
Nonlinear Dynamic of Cantilever Functionally Graded Plates Under the Thermalmechanical Loads
Authors: Hao Yu-xin , Zhang Wei , Wang Jian-hua
Published: July 2010

An analysis on nonlinear dynamic of a cantilevered functionally graded materials (FGM) plate which subjected to the transverse excitation in the uniform thermal environment is presented for the first time. Materials properties of the constituents are graded in the thickness direction according to a power-law distribution and assumed to be temperature dependent. In the framework of the Third-order shear deformation plate theory, the nonlinear governing equations of motion for the functionally graded materials plate are derived by using the Hamilton’s principle. For cantilever rectangular plate, the first two vibration mode shapes that satisfy the boundary conditions is given. The Galerkin’s method is utilized to discretize the governing equations of motion to a two-degree-of-freedom nonlinear system under combined thermal and external excitations. By using the numerical method, the two-degree-of-freedom nonlinear system is analyzed to find the nonlinear responses of the cantilever FGMs plate. The influences of the thermal environments on the nonlinear dynamic response of the cantilevered FGM plate are discussed in detail through a parametric study.
Motor Coach/Bus Crashworthiness Systems: Occupant Retention
Authors: Batzer Stephen A. , Beltran David , Herndon G. Grant , Thorbole Chandrashekhar K. , Ziejewski Mariusz
Published: July 2010

Destructive testing of the complete motor coach/bus restraint system to include seatbelts, side glazing, and greenhouse structure was performed with the objective being to determine the overall rollover crashworthiness in this accident mode. During motor coach/bus rollovers, the roof and pillar structures may deform due to friction and body forces initiated by ground and roadway contact. Body deformation, as well as interaction of the glass with rocks and other debris on the ground and roadway, may lead to catastrophic glazing failure, opening a portal for occupant partial or complete ejection. Despite the relatively high occupant capacity of motor coaches/buses, many commercial designs provide seatbelt restraints only for the purpose of securing wheelchairs and the driver, providing no seatbelt restraints for occupants in passenger positions. Rollover testing was performed on a modified commuter motor coach/bus to determine the effectiveness of the seatbelts as primary restraints, and also on several energy absorbing window designs to determine their efficacy as secondary restraints. The results showed that properly fixated laminated glass and other designs were capable of fully retaining both belted and unbelted occupants during the staged collision. This testing showed that structural roof members and occupant retention glazing systems are feasible solutions for the purpose of occupant retention. The physical testing was complemented by simulations of this accident showing that the loading received by the occupants is not injurious.
An Intelligent Detection and Classification System of Faulty Bearings
Authors: Marichal G. N. , Arte´s M. , Garci´a-Prada J. C.
Published: July 2010

Rolling bearings are widely used in domestic and industrial applications. Most of the industrial machinery often includes this kind of elements. Because of that, it is important to devise predictive maintenance tools in order to detect defects in the bearings and to avoid failure of the machinery. The number of rolling elements and their positions in the load zone change with bearing rotation, producing a periodical variation of the total stiffness of the bearing assembly. Hence, the bearing generates vibrations. When a bearing has a defect, these vibrations are increased. In this paper, a detection and classification system of fault bearings is presented. This system is based on the frequency domain response and the application of a Neuro-Fuzzy method. In the literature, different approaches in the frequency domain have been proposed. In this paper, a particular Neuro-Fuzzy approach has been chosen, given its learning properties and its capability of expressing the resultant detection and classification system by rules. A certain amount of trials have been carried out and it has been concluded that several Neuro-Fuzzy systems in a cascade configuration is a better option to solve the classification problem than other classification methods. In addition to, the results of these initial trials have determined the modifications of the learning phase suggested in this paper. The Neuro-Fuzzy systems with the proposed modifications and only two outputs improve the system performance and the rule association capability. Different results of the proposed approach are shown, where satisfactory results have been achieved.
Analytical Solutions for Effective Transverse Mechanical Properties and Performance of Radially Loaded Nanotube Based Nanocomposites
Authors: Askari Davood , Ghasemi-Nejhad Mehrdad N.
Published: July 2010

It is frequently reported that carbon nanotubes (CNTs) can be filled with various materials in different states to create nanocomposites. These nanocomposite tubes are often incorporated in another host material for further reinforcement to attain properties enhancements. The objective of this paper is to introduce exact analytical close form solutions for the prediction of effective transverse Young’s modulus and Poisson ratio of a matrix-filled nanotube (i.e., a representative element of nanotube reinforced nanocomposites) as well as its mechanical behavior (i.e., displacements, strains and stress distributions) when it is subjected to externally applied uniform radial pressure. In this work, both the nanotube and its filler material are considered to be generally cylindrical orthotropic. For no loss of generality, no plain strain condition is used and axial strain is also taken into consideration to obtain a more precise set of solutions. Analytical formulae are developed based on the principles of linear elasticity and continuum mechanics and then exact solutions are obtained for displacements, strains and stress distributions within the domain of each individual constituent. To validate and verify the accuracy of the closed form solutions obtained from the analytical approach, a 3-D model of a matrix-filled CNT is generated and solved for displacements, strains and stresses numerically, using finite element method. Excellent agreements were achieved between the results obtained from the analytical and numerical methods verifying the analytically obtained exact solutions.
Nanoindentation, Nanoscratch and Wear Studies on Nanoscale Multilayer TiN/CrN Coatings
Authors: Konchady Manohar S. , Yarmolenko Sergey , Pai Devdas M. , Sankar Jag
Published: July 2010

In the present study, multilayer TiN/CrN coatings at different bilayer thicknesses have been deposited on silicon (100) and 316 stainless steel substrates using reactive DC magnetron sputtering technique. Nanoindentation, nanoscratch and ball-on-disk tribometer tests were used to characterize the films. Nanoindentation measurements showed enhancement in hardness values for all multilayer coatings with maximum hardness reaching 34 GPa which is about 45% improvement over the rule of mixtures. Nanoscratch tests revealed higher critical loads for multilayer coatings compared to monolayer TiN and CrN coatings. The tribometer tests showed better sliding wear performance for TiN/CrN superlattices.
Fabrication of Novel Single-Chamber Solid Oxide Fuel Cells Towards Green Technology
Authors: Yang Man , Xu Zhigang , Desai Salil , Kumar Dhananjay , Sankar Jagannathan
Published: July 2010

Solid Oxide Fuel Cell (SOFC) is a green energy technology that offers a cleaner and more efficient alternative to fossil fuels. The fabrication of miniaturized device structure for fuel cell manufacturing is a viable method for improving their efficiency. In this research, single chamber-SOFC with inter-digitized structure of electrolyte and electrodes has been developed by two novel methods. In the deposition method, the SC-SOFC design patterns were created with photolithography and micro-structured thin film electrolytes and electrodes were prepared with pulsed laser deposition (PLD). In the direct-writing method, micro-structured electrodes were injected on electrolyte substrates. These studies showed good potential of manufacturing methods for fabricating novel type of fuel cell design.
Mechanism of Cell Transport in a Microchannel With Binding Between Cell Surface and Immobilized Biomolecules
Authors: Waghmare Prashant R. , Mitra Sushanta K.
Published: July 2010

Recent trends in micro and nano fabrication techniques have opened a new era for microfluidic based immunosensing devices. In immunosensing microfluidic device, the buffer solution transports the different biomolecules and cells. The interaction between the cell and surface of the microchannel takes place during this transport. In the present study, the effect of interaction between the cell and the immobilized biomolecule on the cell transport is analyzed theoretically. A single cell transport is studied with the interaction between the cell surface and the microchannel wall. The type of immobilized biomolecule on the surface and the surface properties of the cell decide the interaction force between cell and biomolecule. In the present analysis, the interaction force between the cell and modified microchannel is considered as a bond force between ligand and receptor. The bond force is equated as an additional rolling friction to investigate the effect of bond force on the cell transport behavior. The coefficient of rolling friction is determined through non-dimensional analysis. The non-dimensional governing equation is solved to investigate the effect of different operation parameters on cell velocity. The cell velocity experiences a resistance while attaining the maximum velocity. This resistance depends on different operating parameters and forces acting on the cell. It is observed that, higher cell density delays the attainment of maximum cell velocity. It is also observed that, the value of maximum cell velocity is function of Reynolds number and bond length. Finally, it is demonstrated that, the bond density and contact area have no effect on the cell velocity behavior beyond the maximum bond density.
Deformation and Energy Absorption Characteristics of Thin-Walled Structures
Authors: Elmarakbi Ahmed , Fielding Niki
Published: July 2010

In this paper, to investigate the design of an energy absorbing street pole, a study of axial crush behaviour of metal thin longitudinal tubes (columns) are investigated along with a number of variables such as cross-sectional shape, shell thickness, as well as the velocity affects on columns. Tests have been carried out on the effects of bedded crumple initiators placed a various heights from the top of the column, in determining the desired value of peak load reduction, along with the effect in energy absorption of the column. With the conclusion of the desired variables for the design of an energy absorbing column, the columns are placed 90 degrees to that of the base of the model street column. Simulation of frontal impact of a vehicle and street column are analysed and compared to that of the energy absorbing street column concept. Studies are carried out by numerical simulation via the explicit finite element code LS-DYAN. Results compare the absorbed energy and the deflection of each variable, and recommend best design for the column structure which improved vehicle crashworthiness.
Reducing the Noise Generated During Air-Arc Gouging Can Be as Simple as Flipping a Switch
Authors: Durkt George
Published: July 2010

The Mine Safety and Health Administration (MSHA) has been evaluating the job/task of air-arc gouging performed by mine shop welders. Air-arc gouging is the process of melting an old weld with a carbon based electrode (rod) and blowing the molten metal away with compressed air. Noise levels of 115 dBA or higher can be generated in this process. Three acoustical field evaluations were conducted at mine shops comparing both Constant Current (CC) and Constant Voltage (CV) techniques for air-arc gouging. The results indicate that by using the CV technique, the average overall A-Weighted Sound Pressure Level (SPLA) was reduced by as much as 8 dBA from an average of 117.6 dBA to 109.3 dBA. As might be expected, dosimeter results indicated that the rate of noise accumulation was also reduced utilizing the CV technique. The average accumulation rate decreased from 4.5 percent Dose per minute for CC at varying air pressures to 2.0 percent Dose per minute for CV at 80 psig.
Badge-Type Noise Dosimeters Used in the Mining Industry
Authors: Homer John P.
Published: July 2010

Currently, a number of manufacturers have developed and made commercially available badge-type (cordless) noise dosimeters. Previous studies conducted by the Mine Safety and Health Administration (MSHA) revealed that microphone size and placement/orientation significantly influence measurement error. The badge-type design houses the microphone within a significantly larger casing than does the traditional corded-type dosimeter. This presents concern that badge-type designs may significantly inhibit measurement accuracy. The purpose of this study is to evaluate the casing of various badge-type dosimeters in order to discern conditions and assess the extent to which the badge-type design contributes toward measurement error in comparison with the traditionally used corded dosimeter. For this, a series of laboratory measurements were conducted employing various commercially available badge-type casings and corded counterparts. Corresponding results are summarized and extended to conclusions regarding the effect of microphone casing design, badge-type versus corded, on measurement accuracy for personal noise dosimetry.
Effect of Mechanical Deformation on Electrical Percolation of CNT Polymer Composites
Authors: Baniassadi Majid , Ghazavizadeh Akbar , Safdari Masoud , Garmestani Hamid , Ahzi Said
Published: July 2010

Electrical and mechanical characterization of carbon nanotube (CNT) reinforced composites has long drawn the attention of researchers. Electrical conductivity of CNTs accounts for electrical properties of their composites. Conductivity of insulating polymers is achieved at relatively low volume fractions of CNTs. The lowest volume fraction of CNTs required for conductivity is called percolation threshold. This threshold is affected by the mechanical loading of the composite. In this computer study, the CNT sticks are scattered randomly within a sample block using the algorithm of Monte-Carlo. Subjected to mechanical loading, the sticks are displaced using the method of Mori-Tanaka. Then the diagrams of mechanical strain versus volume fraction at percolation threshold are drawn. The results show that by applying tensile stresses the percolation can be achieved at lower volume fractions compared to the unloaded state.
Mechanical Properties of Aluminum Foam-Polymer Multifunctional Hybrid Materials
Authors: Hadley James R. , Rayess Nassif E. , Dukhan Nihad , Houston Dan Q.
Published: July 2010

A hybrid material consisting of an interpenetrating phase composite of aluminum foam and thermoplastic polymer was made and tested for its basic tensile mechanical properties. The material was made by injection molding a polymer (two polypropylenes and an acetal were used) through a Duocell aluminum foam (10% relative density and 10, 20 and 40 pores per inch linear densities). The material is referred to as an Aluminum Foam Polymer Composite (AFPC) and involves the aluminum foam and the polymer occupying the same volume. The continuous, interconnected morphologies of the two phases (aluminum foam and polymer) sets this type of material apart from regular composites. The AFPC exhibited an increase in stiffness, a reduction in strength and less ductility than the parent polymer. A basic mathematical model and a discussion of the physics were used to shed some light on the behavior of this material.
Molecular Dynamics Simulations of Thermal Conductivity of Bi2Te3 Nanowires
Authors: Qiu Bo , Sun Lin , Ruan Xiulin
Published: July 2010

In this paper, by employing the previously developed two-body interatomic potentials for bismuth telluride, molecular dynamics (MD) simulations are used to describe the thermoelectric properties, namely the lattice thermal conductivity, of Bi2Te3 nanowires. Cylindrical nanowires with both smooth surface and sawtooth surface roughness are studied, aiming at revealing the effects of phonon confinement in 1-D structures, phonon boundary scatterings and surface roughness on the lattice thermal conductivity of Bi2Te3 nanowires. In the end, the influence of various phonon scattering mechanisms on the nanostructures under study are summarized, possible paths to reduce lattice thermal conductivity in nanostructured Bi2Te3, which is favorable for enhancing thermoelectric performance, are pointed out.
Design Considerations for Harvesting Vibration Energy at MEMS Scale: Review
Authors: Challa Vinod R. , Fisher Frank T.
Published: July 2010

Vibration based energy harvesting has wide potential applications in areas such as wireless sensors networks and ultra low power devices. While there have been various technologies through which vibration energy has been harvested, there is a considerable need to improve the power density of such devices. Recently, efforts have been made in developing MEMS scale devices as they would have increased power density and also provide ease of integration with wireless sensors and low power electronic devices. The aim of this paper is to present the generic and specific design considerations for vibration energy harvesting at the MEMS scale for electrostatic, electromagnetic and piezoelectric techniques. The effect of external load such as load resistance employed for peak power output on the total damping in the system is discussed. The typical MEMS scale vibrating structures such as cantilever beam, fixed-fixed beam and membrane are also presented.
Temperature Distribution Analysis in Plates Joined by Friction Stir Welding
Authors: Pacheco Mauricio Rangel , Kabche Jean Paul , Thesi Ivan , Diesel Fabiano Nunes
Published: July 2010

Friction Stir Welding (FSW) is a solid-state welding process which generates heat through mechanical friction between a moving workpiece and a fixed component, in order to plastically combine materials. This process has been gaining considerable attention due to several key advantages, which include: good mechanical properties of the combined materials after welding, absence of toxic fumes and molten material spatter, low environmental impact, and low concentration of defects while allowing a large variation of parameters and materials. Although a reasonable number of experimental investigations on FSW are available in the literature, numerical modeling of this process has not been performed on a large scale. In that light, this paper presents a numerical investigation of the temperature distribution in plates welded by FSW, using finite element analysis. The finite element model developed includes friction between the workpiece and the fixed component, as well as the corresponding heat dissipation that results from plastic deformation of the material. The model was found appropriate for estimating important welding characteristics, such as the heat-affected zone (HAZ), and their sensitivity to various welding parameters.
An Unstructured Finite Volume Method for Incompressible Flows With Complex Immersed Boundaries
Authors: Sun Lin , Mathur Sanjay R. , Murthy Jayathi Y.
Published: July 2010

A numerical method is developed for solving the 3D, unsteady, incompressible flows with immersed moving solids of arbitrary geometrical complexity. A co-located (non-staggered) finite volume method is employed to solve the Navier-Stokes governing equations for flow region using arbitrary convex polyhedral meshes. The solid region is represented by a set of material points with known position and velocity. Faces in the flow region located in the immediate vicinity of the solid body are marked as immersed boundary (IB) faces. At every instant in time, the influence of the body on the flow is accounted for by reconstructing implicitly the velocity the IB faces from a stencil of fluid cells and solid material points. Specific numerical issues related to the non-staggered formulation are addressed, including the specification of face mass fluxes, and corrections to the continuity equation to ensure overall mass balance. Incorporation of this immersed boundary technique within the framework of the SIMPLE algorithm is described. Canonical test cases of laminar flow around stationary and moving spheres and cylinders are used to verify the implementation. Mesh convergence tests are carried out. The simulation results are shown to agree well with experiments for the case of micro-cantilevers vibrating in a viscous fluid.
Waves, Buckles, and Homoclinics
Authors: Phani A. Srikantha
Published: July 2010

Dynamic response of lattice structures in linear and nonlinear regime is investigated. In the linear regime, connections between vibration and buckling are revisited in the context of plane wave propagation. The power of wave technique in picking up the correct bifurcation mode and the associated critical load is illustrated. The stability of spatially localised structures arising from homoclinics is examined in the nonlinear regime. Simple analytical results will be presented and illustrated using numerical examples.
Specific Binding of Cancer Cells Using a Microchamber Array Functionalized With Antibodies
Authors: Zheng Xiangjun , Cheung Siu Lun , Wang Lian , Schroeder Joyce A. , Heimark Ronald L. , Baygents James C. , Guzman Roberto , Zohar Yitshak
Published: July 2010

Specific binding of target suspended metastatic cancer cells to an antibody-functionalized surface utilizing a microfluidic device has experimentally been investigated under various conditions. The microfluidic devices, fabricated in silicon using DRIE process, consisted of a 5×5 micochamber array; each 1mm×1mm in area, and 50μm in depth. The oxide surface of the microchammber array was functionalized with various antibodies immobilized on a protein G layer. The microfluidic device design allows accurate counting of cells loaded into each microchamber and, thus, enabling a reliable counting of cells captured from homogeneous suspensions. The effects of cell suspension concentration, incubation times and ambient temperature on cell capture efficiency have been examined. Furthermore, to evaluate the specificity of the cell-surface interaction, several cell cancer types expressing different membrane receptors have been incubated on surfaces functionalized with various counter receptors. Specific binding of up to 100% of the suspended cells is observed when using surfaces functionalized with counter receptors matching the cell receptors; otherwise, non-specific binding of less than 15% of suspended cells is obtained if the functionalized counter receptors do not match the cell receptors.
Extension of Fatigue Exemption Rules in Section VIII, Div 2 Slightly Into the Creep Regime
Authors: Becht Charles , Becht Charles
Published: July 2010

A number of alloys have applications slightly into the creep range that are in cyclic service, such as process reactors. The 2007 edition of Section VIII, Div 2 [1] provides allowable stresses for these materials, which may be controlled by creep properties. However, the fatigue design rules and fatigue exemption rules are not applicable, precluding construction of vessels using these materials at temperatures above 370°C (700°F). This paper provides a simplified approach for exemption of low chrome alloys that are slightly into the creep range from fatigue analysis.