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Articles 91 - 106 of 106
Full-Text Articles in Mechanical Engineering
Optimizing Fiber Cross-Sectional Shape For Improving Stability Of Air–Water Interface Over Superhydrophobic Fibrous Coatings, B. Emami, Hooman Vahedi Tafreshi
Optimizing Fiber Cross-Sectional Shape For Improving Stability Of Air–Water Interface Over Superhydrophobic Fibrous Coatings, B. Emami, Hooman Vahedi Tafreshi
Mechanical and Nuclear Engineering Publications
In this letter, a mathematical force-balance formulation is developed that can be used to predict the critical pressure, the hydrostaticpressure above which the surface starts to depart from the non-wetting state, for superhydrophobicsurfaces comprised of highly aligned fibers (e.g., biased AC-electrospun coatings) with arbitrary cross-sectional shapes. We have also developed a methodology for optimizing the fiber cross-sections to maximize the critical pressure of the surface, using the Euler–Lagrange equation. A case study is presented to better demonstrate the application of our method.
Predicting Shape And Stability Of Air–Water Interface On Superhydrophobic Surfaces Comprised Of Pores With Arbitrary Shapes And Depths, B. Emami, Dr. Hooman Vahedi Tafreshi, M. Gad-El-Hak, Gary C. Tepper
Predicting Shape And Stability Of Air–Water Interface On Superhydrophobic Surfaces Comprised Of Pores With Arbitrary Shapes And Depths, B. Emami, Dr. Hooman Vahedi Tafreshi, M. Gad-El-Hak, Gary C. Tepper
Mechanical and Nuclear Engineering Publications
An integro-differential equation for the three dimensional shape of air–water interface on superhydrophobicsurfaces comprised of pores with arbitrary shapes and depths is developed and used to predict the static critical pressure under which such surfaces depart from the non-wetting state. Our equation balances the capillary forces with the pressure of the air entrapped in the pores and that of the water over the interface. Stability of shallow and deep circular, elliptical, and polygonal pores is compared with one another and a general conclusion is drawn for designing pore shapes for superhydrophobicsurfaces with maximum stability.
Effect Of Fiber Orientation On Shape And Stability Of Air-Water Interface On Submerged Superhydrophobic Electrospun Thin Coatings, B. Emami, H. Vahedi Tafreshi, M. Gad-El-Hak, G. C. Tepper
Effect Of Fiber Orientation On Shape And Stability Of Air-Water Interface On Submerged Superhydrophobic Electrospun Thin Coatings, B. Emami, H. Vahedi Tafreshi, M. Gad-El-Hak, G. C. Tepper
Mechanical and Nuclear Engineering Publications
To better understand the role of fiber orientation on the stability of superhydrophobicelectrospun coatings under hydrostaticpressures, an integro-differential equation is developed from the balance of forces across the air–water interface between the fibers. This equation is solved numerically for a series of superhydrophobicelectrospun coatings comprised of random and orthogonal fiber orientations to obtain the exact 3D shape of the air–water interface as a function of hydrostaticpressure. More important, this information is used to predict the pressure at which the coatings start to transition from the Cassie state to the Wenzel state, i.e., the so-called critical transition pressure. Our results indicate …
Predicting Shape And Stability Of Air–Water Interface On Superhydrophobic Surfaces With Randomly Distributed, Dissimilar Posts, B. Emami, Hooman Vahedi Tafreshi, M. Gad-El-Hak, Gary C. Tepper
Predicting Shape And Stability Of Air–Water Interface On Superhydrophobic Surfaces With Randomly Distributed, Dissimilar Posts, B. Emami, Hooman Vahedi Tafreshi, M. Gad-El-Hak, Gary C. Tepper
Mechanical and Nuclear Engineering Publications
A mathematical framework developed to calculate the shape of the air–water interface and predict the stability of a microfabricated superhydrophobicsurface with randomly distributed posts of dissimilar diameters and heights is presented. Using the Young–Laplace equation, a second-order partial differential equation is derived and solved numerically to obtain the shape of the interface, and to predict the critical hydrostatic pressure at which the superhydrophobicity vanishes in a submersed surface. Two examples are given for demonstration of the method’s capabilities and accuracy.
Bennett Clocking Of Nanomagnetic Logic Using Multiferroic Single-Domain Nanomagnets, Jayasimha Atulasimha, Supriyo Bandyopadhyay
Bennett Clocking Of Nanomagnetic Logic Using Multiferroic Single-Domain Nanomagnets, Jayasimha Atulasimha, Supriyo Bandyopadhyay
Mechanical and Nuclear Engineering Publications
The authors show that it is possible to rotate the magnetization of a multiferroic (strain-coupled two-layer magnetostrictive-piezoelectric)nanomagnet by a large angle with a small electrostatic potential. This can implement Bennett clocking [Int. J. Theor. Phys.21, 905 (1982)] in nanomagnetic logic arrays resulting in unidirectional propagation of logic bits from one stage to another. This method is potentially more energy efficient than using spin-transfer torque for magnetization rotation. For realistic parameters, it is shown that a potential of ∼0.2 V applied to a multiferroicnanomagnet can rotate magnetization by nearly 90° to implement Bennett clocking.
Hydrothermal Preparation Of Gd+3 -Doped Titanate Nanotubes: Magnetic Properties And Photovoltaic Performance, Hoda S. Hafez, M Saif, James T. Mcleskey Jr., M.S.A. Abdel-Mottaleb, I S. Yahia, T Story, W Knoff
Hydrothermal Preparation Of Gd+3 -Doped Titanate Nanotubes: Magnetic Properties And Photovoltaic Performance, Hoda S. Hafez, M Saif, James T. Mcleskey Jr., M.S.A. Abdel-Mottaleb, I S. Yahia, T Story, W Knoff
Mechanical and Nuclear Engineering Publications
Pure and Gd+3 -doped titanate nanotubes (TNTs) materials were synthesized by a hydrothermal method. Their morphology, optical properties, thermal stability, and magnetic properties were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV-Vis spectroscopy, thermal analysis, and magnetic measurements. It was found that doping renders Gd+3-TNT visible light active and results in smaller crystallite size and larger surface area as well as higher thermal stability compared to pure titanate nanotubes. The estimated magnetic moments point to presence of weak antiferromagnetic interaction. Application of the prepared Gd+3-TNT for modifying conventional photoanodes in polymer solar cells was attempted. Preliminary results show …
Nanostructured Solid-State Hybrid Photovoltaic Cells Fabricated By Electrostatic Layer-By-Layer Deposition, Rolf Kniprath, James T. Mcleskey Jr., Jürgen P. Rabe, Stefan Kirstein
Nanostructured Solid-State Hybrid Photovoltaic Cells Fabricated By Electrostatic Layer-By-Layer Deposition, Rolf Kniprath, James T. Mcleskey Jr., Jürgen P. Rabe, Stefan Kirstein
Mechanical and Nuclear Engineering Publications
We report on the fabrication of hybrid organic/inorganic photovoltaic cells utilizing layer-by-layer deposition of water-soluble polyions and nanocrystals. A bulk heterojunction structure was created consisting of alternating layers of the p-conductive polythiophene derivative poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] and n-conductive TiO2nanoparticles. We fabricated working devices with the heterostructure sandwiched between suitable charge carrier blocking layers and conducting oxide and metal electrodes, respectively. We analyzed the influence of the thickness and nanostructure of the active layer on the cell performance and characterized the devices in terms of static and transient current response with respect to illumination and voltage conditions. We observed reproducible and stable photovoltaic …
A Realistic Modeling Of Fluid Infiltration In Thin Fibrous Sheets, Sudhakar Jaganathan, Hooman Vahedi Tafreshi, Behnam Pourdeyhimi
A Realistic Modeling Of Fluid Infiltration In Thin Fibrous Sheets, Sudhakar Jaganathan, Hooman Vahedi Tafreshi, Behnam Pourdeyhimi
Mechanical and Nuclear Engineering Publications
In this paper, a modeling study is presented to simulate the fluid infiltration in fibrous media. The Richards’ equation of two-phase flow in porous media is used here to model the fluid absorption in unsaturated/partially saturated fibrous thin sheets. The required consecutive equations, relative permeability, and capillary pressure as functions of medium’s saturation are obtained via fiber-level modeling and a long-column experiment, respectively. Our relative permeability calculations are based on solving the Stokes flow equations in partially saturated three-dimensional domains obtained by imaging the sheets’ microstructures. The Richards’ equation, together with the above consecutive correlations, is solved for fibrous media …
Correlation Of Tellurium Inclusions And Carrier Lifetime In Detector Grade Cadmium Zinc Telluride, Ezzat S. Elshazly, Gary C. Tepper
Correlation Of Tellurium Inclusions And Carrier Lifetime In Detector Grade Cadmium Zinc Telluride, Ezzat S. Elshazly, Gary C. Tepper
Mechanical and Nuclear Engineering Publications
Carrier lifetimes and telluriuminclusion densities in detector grade cadmiumzinc telluride crystals grown by the high pressure Bridgman method were optically measured using pulsed laser microwavecavity perturbation and infrared microscopy. Excess carriers were produced in the material using a pulsed laser with a wavelength of 1064 nm and pulse width of 7 ns, and the electronic decay was measured at room temperature. Spatial mapping of lifetimes and defect densities in cadmiumzinc telluride was performed to determine the relationship between telluriumdefect density and trapping. A strong correlation was found between the volume fraction of telluriuminclusions and the carrier trapping time.
Electrokinetic Separation Of Co-Solutes Into Bimodal Fibers By Electrospinning, Chunya Wu, Shinobu Nagata, Gary C. Tepper, James T. Mcleskey Jr.
Electrokinetic Separation Of Co-Solutes Into Bimodal Fibers By Electrospinning, Chunya Wu, Shinobu Nagata, Gary C. Tepper, James T. Mcleskey Jr.
Mechanical and Nuclear Engineering Publications
Composite and chemically/physically distinct fibers of sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) and polyethylene oxide (PEO) were formed by electrospinning from a homogeneous aqueous solution containing PTEBS and PEO co-solutes. Composite nanofibers of diameter of ∼60nm were electrospun from an aqueous solution. The addition of ammonium hydroxide (NH4OH) to the water solution resulted in “bimodal” electrospun fibers consisting of distinct large diameter white PEO fiber segments and small diameter black PTEBS fiber segments. The optical absorptionspectrum of the composite PTEBS/PEO nanofibers did not exhibit the characteristic peak around 460nm, which is present in the bulk spectrum.
Geometrical Modeling Of Fibrous Materials Under Compression, Benoit Maze, Hooman Vahedi Tafreshi, Behnam Pourdeyhimi
Geometrical Modeling Of Fibrous Materials Under Compression, Benoit Maze, Hooman Vahedi Tafreshi, Behnam Pourdeyhimi
Mechanical and Nuclear Engineering Publications
Many fibrous materials such as nonwovens are consolidated via compaction rolls in a so-called calendering process. Hot rolls compress the fiber assembly and cause fiber-to-fiber bonding resulting in a strong yet porous structure. In this paper, we describe an algorithm for generating three dimensional virtual fiberwebs and simulating the geometrical changes that happen to the structure during the calendering process. Fibers are assumed to be continuous filaments with square cross sections lying randomly in the x or y direction. The fibers are assumed to be flexible to allow bending over one another during the compression process. Lateral displacement is not …
An Electrospray-Based, Ozone-Free Air Purification Technology, Gary Tepper, Royal Kessick, Dmitry Pestov
An Electrospray-Based, Ozone-Free Air Purification Technology, Gary Tepper, Royal Kessick, Dmitry Pestov
Mechanical and Nuclear Engineering Publications
A zero-pressure-drop, ozone-free air purification technology is reported. Contaminated air was directed into a chamber containing an array of electrospray wick sources. The electrospray sources produce an aerosol of tiny, electrically charged aqueous droplets.Charge was transferred from the droplets onto polar and polarizable species in the contaminated air stream and the chargedcontaminants were extracted using an electric field and deposited onto a metal surface. Purified air emerged from the other end of the chamber. The very small aqueous electrospray droplets completely evaporate so that the process is essentially dry and no liquid solvent is collected or recirculated. The air purification …
Hybrid Solar Cells From Water-Soluble Polymers, James T. Mcleskey Jr., Qiquan Qiao
Hybrid Solar Cells From Water-Soluble Polymers, James T. Mcleskey Jr., Qiquan Qiao
Mechanical and Nuclear Engineering Publications
We report on the use of a water-soluble, light-absorbing polythiophene polymer to fabricate novel photovoltaic devices. The polymer is a water-soluble thiophene known as sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] or PTEBS. The intention is to take advantage of the properties of conjugated polymers (flexible, tunable, and easy to process) and incorporate the additional benefits of water solubility (easily controlled evaporation rates and environmentally friendly). The PTEBS polythiophene has shown significant photovoltaic response and has been found to be effective for making solar cells. To date, solar cells in three different configurations have been produced: titanium dioxide (TiO2) bilayer cells, TiO2 bulk heterojunction solar …
Water-Soluble Polythiophene∕Nanocrystalline Tio2 Solar Cells, Qiquan Qiao, James T. Mcleskey Jr.
Water-Soluble Polythiophene∕Nanocrystalline Tio2 Solar Cells, Qiquan Qiao, James T. Mcleskey Jr.
Mechanical and Nuclear Engineering Publications
We report the characteristics of polymer∕nanocrystalline solar cells fabricated using an environmentally friendly water-soluble polythiophene and TiO2 in a bilayer configuration. The cells were made by dropping the polymer onto a TiO2nanocrystallinefilm and then repeatedly sweeping a clean glass rod across the polymer as it dried. The devices showed an open circuit voltage of 0.81 V, a short circuit current density of 0.35mA/cm2, a fill factor of 0.4, and an energy conversion efficiency of 0.13%. The water-soluble polythiophene showed significant photovoltaic behavior and the potential for use in solar cells.
Characteristics Of Water-Soluble Polythiophene: Tio2 Composite And Its Application In Photovoltaics, Qiquan Qiao, Lianyong Su, James Beck, James T. Mcleskey Jr.
Characteristics Of Water-Soluble Polythiophene: Tio2 Composite And Its Application In Photovoltaics, Qiquan Qiao, Lianyong Su, James Beck, James T. Mcleskey Jr.
Mechanical and Nuclear Engineering Publications
We have studied the characteristics of composites of an environmentally friendly water-soluble polythiophene sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) and TiO2. We observed that the ultraviolet-visible absorption spectrum of low molecular weight PTEBS is redshifted possibly due to the formation of aggregates. Cyclic voltammetry reveals the values of highest occupied molecular orbitals and lowest unoccupied molecular orbitals for PTEBS. A factor of 7 in photoluminescence quenching indicates that the exciton dissociation and charge separation occur successfully at the PTEBS: TiO2 (1:1 by weight) interface. This enhances the possibility that the separated charges will reach the electrodes before recombining. Scanning electron micrograph images show …
Microscale Polymeric Helical Structures Produced By Electrospinning, Royal Kessick, Gary C. Tepper
Microscale Polymeric Helical Structures Produced By Electrospinning, Royal Kessick, Gary C. Tepper
Mechanical and Nuclear Engineering Publications
Microscale helical coils consisting of a composite of one conducting and one nonconducting polymer were produced using electrospinning. The nonconducting polymer was poly(ethylene oxide) and the conducting polymer was poly(aniline sulfonic acid). The coil structures were studied over a range of processing conditions and fiber composition. The data suggest that the helical structures are formed due to viscoelastic contraction upon partial neutralization of the charged fibers. Polymeric microcoils may find applications in microelectromechanical systems, advanced optical components, and drug delivery systems.