Open Access. Powered by Scholars. Published by Universities.®

Nanoscience and Nanotechnology Commons™

Open Access. Powered by Scholars. Published by Universities.®

University of Nebraska - Lincoln

Discipline
Keyword
Publication Year
Publication

Articles 661 - 683 of 683

Full-Text Articles in Nanoscience and Nanotechnology

Task Specific Uncertainty In Coordinate Measurement, R. G. Wilhelm, R. Hocken, H. Schwenke Jan 2001

Task Specific Uncertainty In Coordinate Measurement, R. G. Wilhelm, R. Hocken, H. Schwenke

Department of Mechanical and Materials Engineering: Faculty Publications

Task specific uncertainty is the measurement uncertainty associated with the measurement of a specific feature using a specific measurement plan. This paper surveys techniques developed to model and estimate task specific uncertainty for coordinate measuring systems, primarily coordinate measuring machines using contacting probes. Sources of uncertainty are also reviewed.

Go to article

Order–Disorder Effects In Nitrided Sm–Fe Permanent Magnets, B.E. Meacham, Jeffrey E. Shield, D.J. Branagan May 2000

Order–Disorder Effects In Nitrided Sm–Fe Permanent Magnets, B.E. Meacham, Jeffrey E. Shield, D.J. Branagan

Nebraska Center for Materials and Nanoscience: Faculty Publications

Rapidly solidified Sm11Fe89 was observed to form partially ordered Sm2Fe17. The ordering increased systematically with annealing temperature, reaching an order parameter of 0.8 after annealing at 950 °C for 15 min. The coercivity of the corresponding interstitial compound Sm2Fe17Nx varied with annealing temperature and thus order parameter. The coercivity reached a maximum for an order parameter of 0.45–5, then dramatically decreased as the order increased. This behavior is characteristic of demagnetization controlled by domain wall pinning by antiphase boundaries.

Go to article

Phase Formation In Hypostoichiometric Sm2Fe17 Alloys Modified With Ti And C, Jeffrey E. Shield, B.E. Meacham Feb 2000

Phase Formation In Hypostoichiometric Sm2Fe17 Alloys Modified With Ti And C, Jeffrey E. Shield, B.E. Meacham

Nebraska Center for Materials and Nanoscience: Faculty Publications

The phase formation, crystallization products, microstructure, and magnetic behavior of Fe-rich Sm–Fe alloys modified with Ti and C have been determined. Alloys of nominal composition (Sm 0.11-xFe 0.89+x) 94Ti 3C 3 with x=0, 0.02, and 0.04 were produced by melt spinning. Crystalline phases observed included SmFe 7 and α -Fe and an increasing amorphous fraction was observed with increasing x. Upon crystallization the amorphous fraction converted to Sm2Fe17 and a-Fe, with a grain size of 30 nm for the sample with x=0.02. The magnetic measurements of nitrided alloys …

Go to article

Breakaway Steel Guardrail Post, Dean L. Sicking, John D. Reid, John R. Rohde Nov 1999

Breakaway Steel Guardrail Post, Dean L. Sicking, John D. Reid, John R. Rohde

Department of Mechanical and Materials Engineering: Faculty Publications

A breakaway guardrail post includes upper and lower post sections spaced apart but connected by a breakaway joint. The joint is attached at one end to the upper post by a first fastener set and connected at a second end by a second fasteners set. Upon impact forces being applied to the upper post section, the first fastener fails and the upper post section rotates downwardly.

Go to article

Elastic Wave Propagation And Scattering In Heterogeneous, Anisotropic Media: Textured Polycrystalline Materials, Joseph A. Turner Aug 1999

Elastic Wave Propagation And Scattering In Heterogeneous, Anisotropic Media: Textured Polycrystalline Materials, Joseph A. Turner

Nebraska Center for Materials and Nanoscience: Faculty Publications

The propagation of elastic waves through heterogeneous, anisotropic media is considered. Appropriate ensemble averaging of the elastic wave equation leads to the Dyson equation which governs the mean response of the field. The Dyson equation is given here in terms of anisotropic elastic Green’s dyadics for the medium with and without heterogeneities. The solution of the Dyson equation for the mean response is given for heterogeneities that are weak. The formalism is further specified for the case of equiaxed cubic polycrystalline metals with a single aligned axis. The Green’s dyadics in this case are those for a transversely isotropic medium. …

Go to article

Foundation Sleeve For A Guardrail System, Dean L. Sicking, John D. Reid, John R. Rohde Jul 1999

Foundation Sleeve For A Guardrail System, Dean L. Sicking, John D. Reid, John R. Rohde

Department of Mechanical and Materials Engineering: Faculty Publications

A highway guardrail terminal system having horizontally extending guardrail elements mounted on a plurality of posts. Foundation sleeves having an elongated slit along one side retain and support appropriate guardrail posts. A plurality of stiffing ribs extend across the slit at a distal portion of the tube. The sleeves enable a safer and faster removal of broken guardrail posts after vehicular impact.

Go to article

Adaptive Sampling For Coordinate Metrology, Robert Edgeworth, Robert G. Wilhelm Jul 1999

Adaptive Sampling For Coordinate Metrology, Robert Edgeworth, Robert G. Wilhelm

Department of Mechanical and Materials Engineering: Faculty Publications

An iterative sampling process for dimensional measurement is presented. The strategy is based upon the use of surface normal measurement data to develop an interpolating curve between sample points. The interpolant is used to select subsequent measurement targets iteratively. The process is repeated until the measurement converges to a complete and accurate evaluation of the surface. The required sample size is proportional to part quality. The most accurate parts will require the least sample points; whereas, lower quality parts will require a greater number of total samples. The method is particularly applicable to measurement of complex surfaces with coordinate measuring …

Go to article

Asymptotic Decay Of Radius Of A Weakly Conductive Viscous Jet, A.F. Spivak, Yuris A. Dzenis Nov 1998

Asymptotic Decay Of Radius Of A Weakly Conductive Viscous Jet, A.F. Spivak, Yuris A. Dzenis

Nebraska Center for Materials and Nanoscience: Faculty Publications

Motion of a weakly conductive viscous jet accelerated by an external electric field is considered. Nonlinear rheological constitutive equation applicable for polymer fluids (Oswald–deWaele law) is applied. A differential equation for the variation of jet radius with axial coordinate is derived. Asymptotic variation of the jet radius at large distances from the jet origin is analyzed. It is found that the well-known power-law asymptote for Newtonian fluids with the exponent 1/4 holds for more general class of fluids, i.e., pseudoplastic (shear thinning) and dilatant (shear thickening) fluids with the flow index between 0 and 2. Dilatant fluids with the flow …

Go to article

Processing Of Hydroxylapatite Coatings On Titanium Alloy Bone Prostheses, Michael A. Nastasi, Timothy E. Levine, James W. Mayer, Vincent B. Pizziconi Oct 1998

Processing Of Hydroxylapatite Coatings On Titanium Alloy Bone Prostheses, Michael A. Nastasi, Timothy E. Levine, James W. Mayer, Vincent B. Pizziconi

Department of Mechanical and Materials Engineering: Faculty Publications

Processing of hydroxylapatite Sol-gel films on titanium alloy bone prostheses. A method utilizing non-line-of-Sight ion beam implantation and/or rapid thermal processing to provide improved bonding of layers of hydroxylapatite to titanium alloy Substrates while encouraging bone ingrowth into the hydroxylapatite layers located away from the substrate, is described for the fabrication of prostheses. The first layer of hydroxylapatite is mixed into the Substrate by the ions or rapidly thermally annealed, while Subsequent layers are heat treated or densified using ion implantation to form layers of decreasing density and larger crystallization, with the outermost layers being Suitable for bone ingrowth.

Go to article

The Effect Of Grain Size On Magnetic Properties In Sm2Fe17NX, Jeffrey E. Shield, D.J. Branagan, C.P. Li, R.W. Mccallum May 1998

The Effect Of Grain Size On Magnetic Properties In Sm2Fe17NX, Jeffrey E. Shield, D.J. Branagan, C.P. Li, R.W. Mccallum

Nebraska Center for Materials and Nanoscience: Faculty Publications

The microstructures of melt spun Sm11Fe89 and (Sm11Fe89)94Ti3C3 have been investigated under different solidification conditions. The magnetic properties of the nitrided materials have been related to the observed microstructures. Melt spinning of the Sm11Fe89 alloys resulted in grain sizes at or above the single domain limit. The addition of Ti and C resulted in an order of magnitude refinement in the microstructural scale. The magnetic properties of the samples with grain sizes below the single domain limit decreased with decreasing grain size due to increased intergranular exchange coupling.

Go to article

A Generalized Solidification Model And Microstructural Verification For The Nd–Fe–B–Ti–C System Processed By Rapid Solidification, Matthew J. Kramer, C.P. Li, K.W. Dennis, R.W. Mccallum, C.H. Sellers, D.J. Branagan, Jeffrey E. Shield Apr 1997

A Generalized Solidification Model And Microstructural Verification For The Nd–Fe–B–Ti–C System Processed By Rapid Solidification, Matthew J. Kramer, C.P. Li, K.W. Dennis, R.W. Mccallum, C.H. Sellers, D.J. Branagan, Jeffrey E. Shield

Nebraska Center for Materials and Nanoscience: Faculty Publications

For the Nd2Fe14B (2-14-1) compound, the optimal grain size should be smaller than the size of the single domain size of 150 nm. Transition metal carbides (TMC) also reduce the quench rate necessary to achieve the optimal or overquenched condition. This allows inert gas atomization (IGA) to produce viable magnetic materials. In this article we will demonstrate that optimal microstructure for the 2-14-1 can be produced by IGA with the addition of TiC. Moreover, a solidification model will be presented to show (1) how recalescence is a critical feature to the evolution of the microstructure in …

Go to article

Part Form Errors Predicted From Machine Tool Performance Measurements, R. G. Wilhelm, N. Srinivasan, F. Farabaugh, R. Hocken Jan 1997

Part Form Errors Predicted From Machine Tool Performance Measurements, R. G. Wilhelm, N. Srinivasan, F. Farabaugh, R. Hocken

Department of Mechanical and Materials Engineering: Faculty Publications

Machine tool performance testing, as defined by IS0 230 and ANSI B5.54 has been successfully used to maintain and improve the accuracy and repeatability of production-level machine tools. In this study, a controlled series of experiments have been used to test the efficacy of these performance tests in the prediction of part form errors. Results are shown for flatness, squareness, position, and profile tolerances. The experimental results suggest that standard machine tool performance tests can also be used to predict the “best-case” tolerances that can be achieved for particular part features.

Go to article

Explosive Compaction Of Magnequench Nd–Fe–B Magnetic Powders, S. Guruswamy, M.K. Mccarter, Jeffrey E. Shield, V. Panthanachan Apr 1996

Explosive Compaction Of Magnequench Nd–Fe–B Magnetic Powders, S. Guruswamy, M.K. Mccarter, Jeffrey E. Shield, V. Panthanachan

Nebraska Center for Materials and Nanoscience: Faculty Publications

Magnequench NdFeB powders having high and low rare earth contents were explosively compacted to obtain cylindrical magnets. The magnetic properties were found to be isotropic and were superior to conventionally consolidated isotropic magnets. The (BH) max was 14.7 MGOe and the remanence was 8.7 kG for the explosively compacted magnet with lower rare earth content. X-ray diffraction patterns confirm the explosively compacted magnet to be crystalline and the predominant phase to be the 2-14-1 phase. Transmission electron microscopy examination showed a microstructure to consist of 20–25 nm size equiaxed grains consistent with the magnetic measurements.

Go to article

Process For The Formation Of Wear- And Scuff-Resistant Carbon Coatings, Gerard W. Malaczynski, Xiaohong Qiu, Joseph V. Mantese, Alaa A. Elmoursi, Aboud H. Hamdi, Blake P. Wood, Kevin C. Walter, Michael Nastasi Oct 1995

Process For The Formation Of Wear- And Scuff-Resistant Carbon Coatings, Gerard W. Malaczynski, Xiaohong Qiu, Joseph V. Mantese, Alaa A. Elmoursi, Aboud H. Hamdi, Blake P. Wood, Kevin C. Walter, Michael Nastasi

Department of Mechanical and Materials Engineering: Faculty Publications

A process for forming an adherent diamond-like carbon coating on a workpiece of suitable material such as an aluminum alloy is disclosed. The workpiece is successively immersed in different plasma atmospheres and subjected to short duration, high voltage, negative electrical potential pulses or constant negative electrical potentials or the like so as to clean the surface of oxygen atoms, implant carbon atoms into the surface of the alloy to form carbide com pounds while codepositing a carbonaceous layer on the surface, bombard and remove the carbonaceous layer, and to thereafter deposit a generally amorphous hydrogen-containing carbon layer on the surface …

Go to article

Method Of Making Quasicrystal Alloy Powder, Protectivecoatings And Articles, Jeffrey E. Shield, Alan I. Goldman, Iver E. Anderson, Timothy W. Ellis, R. William Mccallum, Daniel J. Sordelet Jul 1995

Method Of Making Quasicrystal Alloy Powder, Protectivecoatings And Articles, Jeffrey E. Shield, Alan I. Goldman, Iver E. Anderson, Timothy W. Ellis, R. William Mccallum, Daniel J. Sordelet

Department of Mechanical and Materials Engineering: Faculty Publications

A method of making quasicrystalline alloy particulates wherein an alloy is superheated and the meltis atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture.

Go to article

Incorporation Of Zn In Gaas During Organometallic Vapor Phase Epitaxy Growth Compared To Equilibrium, W. Reichert, C.Y. Chen, W.M. Li, Jeffrey E. Shield, R.M. Cohen, D.S. Simons, P.H. Chi Mar 1995

Incorporation Of Zn In Gaas During Organometallic Vapor Phase Epitaxy Growth Compared To Equilibrium, W. Reichert, C.Y. Chen, W.M. Li, Jeffrey E. Shield, R.M. Cohen, D.S. Simons, P.H. Chi

Nebraska Center for Materials and Nanoscience: Faculty Publications

The zinc concentration measured after organometallic vapor phase epitaxy (GMVPE) growth on (100)-oriented GaAs at 700 °C has been compared to the zinc concentration measured after in-diffusion under near-equilibrium conditions. During diffusion, the concentration of Zn 20 nm below the surface was found to vary with PZn1/2, as expected for bulk solid-vapor equilibrium. During growth, the concentration of Zn varied linearly with PZn up to a maximum value which was found to correspond to the solubility limit set by second phase formation, e.g., growth of Zn3As2. Although large differences were observed between …

Go to article

Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky Jan 1995

Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky

Shireen Adenwalla Papers

We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (~nanometers) and large amplitude (~400 µm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature …

Go to article

Nmr And Nqr Study Of The Electronic And Structural Properties Of Al-Cu-Fe And Al-Cu-Ru Quasicrystals, A. Shastri, F. Borsa, D.R. Torgeson, Jeffrey E. Shield, A.I. Goldman Dec 1994

Nmr And Nqr Study Of The Electronic And Structural Properties Of Al-Cu-Fe And Al-Cu-Ru Quasicrystals, A. Shastri, F. Borsa, D.R. Torgeson, Jeffrey E. Shield, A.I. Goldman

Nebraska Center for Materials and Nanoscience: Faculty Publications

27 Al and 63.65Cu NMR measurements are reported for powder samples of stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and their crystalline approximants, and for an Al-Pd-Mn singlegrain quasicrystal. Furthermore, 27Al NQR spectra at 4.2 K have been observed in the Al-Cu-Fe and Al-Cu-Ru samples. From the quadrupole-perturbed NMR spectra at different magnetic fields, and from the zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant was successful in explaining the observed NQR spectra. The average …

Go to article

Icosahedral Phase Stabilities In Al-Cu-Ru Alloys, Jeffrey E. Shield, C. Hoppe, R.W. Mccallum, A.I. Goldman, K.F. Kelton, P.C. Gibbons Feb 1992

Icosahedral Phase Stabilities In Al-Cu-Ru Alloys, Jeffrey E. Shield, C. Hoppe, R.W. Mccallum, A.I. Goldman, K.F. Kelton, P.C. Gibbons

Nebraska Center for Materials and Nanoscience: Faculty Publications

By examining a wide region of the Al-Cu-Ru phase diagram, a thorough analysis of the compositional and thermal stability of the icosahedral phase has been completed. The primary solidification product of rapid solidification was a topologically and chemically disordered icosahedral phase with an extensive compositional region. Crystallization through exothermic events of the as-solidified materials produced crystalline phases, without the formation of the face-centered-icosahedral (FCI) phase. However, the FCI phase does form at higher temperatures through an endothermic reaction, indicating that it is a stable phase of the system, but only at elevated temperatures. Of the alloys studied, the FCI phase …

Go to article

Diffraction Studies On Ni-Co And Ni-Cr Alloy Thin Films, A. R. Sethuraman, R. J. De Angelis, P. J. Reucroft Apr 1991

Diffraction Studies On Ni-Co And Ni-Cr Alloy Thin Films, A. R. Sethuraman, R. J. De Angelis, P. J. Reucroft

Nebraska Center for Materials and Nanoscience: Faculty Publications

Alloy films of Ni-Co and Ni-Cr of compositional ratios 1:1, 1:3, and 3:1 deposited by vapor deposition were studied by Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Results of TEM analysis on the Ni-Co alloy films indicated that the films were face-centered cubic (fee) in structure. XRD results confirmed the TEM observations. TEM analysis of Ni-Cr alloy films showed that the films were bodycentered cubic (bec) in structure. With increase in the Cr content more than 25%, the material contained a higher fraction of an amorphous phase. XRD studies provide limited information owing to the quasi-amorphous structure of the …

Go to article

Automating Tolerance Synthesis: A Framework And Tools, Stephen C.-Y. Lu, Robert G. Wilhelm Jan 1991

Automating Tolerance Synthesis: A Framework And Tools, Stephen C.-Y. Lu, Robert G. Wilhelm

Department of Mechanical and Materials Engineering: Faculty Publications

This paper describes CASCADE-T—a new approach to tolerance synthesis that uses a complete representation of the conditional tolerance relations that exist between features of a part under design. Conditional tolerances are automatically determined from functional requirements and shape information. Tolerance primitives based on the virtual boundary requirements approach to tolerance representation are composed to form more complex tolerance relationships. Artificial intelligence techniques, including a constraint network, frame-based system, and dependency tracking are used to support flexible and detailed computation for tolerance analysis and synthesis.

Go to article

Nondestructive Detection Of An Undeserable Metallic Phase, T1, During Processing Of Alumnum-L Thumalloys, Otto Buck, David J. Bracci, David C. Jiles, Lisa J.H. Brasche, Jeffrey E. Shield, Leonard S. Chumbley Aug 1990

Nondestructive Detection Of An Undeserable Metallic Phase, T1, During Processing Of Alumnum-L Thumalloys, Otto Buck, David J. Bracci, David C. Jiles, Lisa J.H. Brasche, Jeffrey E. Shield, Leonard S. Chumbley

Department of Mechanical and Materials Engineering: Faculty Publications

A method is disclosed for detecting the T1 phase in aluminum-lithium alloys through simultaneous measurement of conductivity and hardness. In employing eddy current to measure conductivity, when the eddy current decreases with aging of the alloy, while the hardness of the material continues to increase, the presence of the T1 phase may be detected.

Go to article

Microcomputer Based Digital Image Processing System Developed To Count And Size Laser-Generated Small Particle Images, K. D. Ahlers, D. R. Alexander Jan 1985

Microcomputer Based Digital Image Processing System Developed To Count And Size Laser-Generated Small Particle Images, K. D. Ahlers, D. R. Alexander

Department of Mechanical and Materials Engineering: Faculty Publications

A microcomputer-based digital image processing system has been developed to count and size laser-generated small particle images. Processing rates of 5 to 600 frames per minute were achieved by utilizing a real-time digital image processor. Particles from 7 to 700 µm in the plane of focus were counted and sized. A major emphasis in this work was to determine the basic problems and limitations involved with using a digital image processing scheme to accurately size particles. Areas that were investigated include the effect of the threshold level on measured particle size, particle boundary diffraction gray-level gradients, and geometric nonlinearities introduced …

Go to article

First Prev