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Articles 331 - 353 of 353

Full-Text Articles in Physics

Measurement And Modeling Of Light Transmission Through Turbid Media, Alois (Al) J. Adams, Michael Fahrenwald, Long Do Jan 2007

Measurement And Modeling Of Light Transmission Through Turbid Media, Alois (Al) J. Adams, Michael Fahrenwald, Long Do

Journal of the Arkansas Academy of Science

No abstract provided.


Modeling Redox-Based Magnetohydrodynamics In Three-Dimensional Microfluidic Channels, Hussameddine S. Kabbani, Aihua Wang, Xiaobing Luo, Shizhi Qian Jan 2007

Modeling Redox-Based Magnetohydrodynamics In Three-Dimensional Microfluidic Channels, Hussameddine S. Kabbani, Aihua Wang, Xiaobing Luo, Shizhi Qian

Mechanical Engineering Faculty Publications

RedOx-based magnetohydrodynamic MHD[1] flows in three-dimensional microfluidic channels are investigated theoretically with a coupled mathematical model consisting of the Nernst-Planck equations for the concentrations of ionic species, the local electroneutrality condition for the electric potential, and the Navier-Stokes equations for the flow field. A potential difference is externally applied across two planar electrodes positioned along the opposing walls of a microchannel that is filled with a dilute RedOx electrolyte solution, and a Faradaic current transmitted through the solution results. The entire device is positioned under a magnetic field which can be provided by either a permanent magnet or an ...


Interaction Of Water With Cap-Ended Defective And Non-Defective Small Carbon Nanotubes, Jose L. Rivera, J. L. Rico, Francis W. Starr Jan 2007

Interaction Of Water With Cap-Ended Defective And Non-Defective Small Carbon Nanotubes, Jose L. Rivera, J. L. Rico, Francis W. Starr

Division III Faculty Publications

No abstract provided.


The Effect Of Nanoparticle Shape On Polymer-Nanocomposite Rheology And Tensile Strength, Scott T. Knauert, Jack F. Douglas, Francis W. Starr Jan 2007

The Effect Of Nanoparticle Shape On Polymer-Nanocomposite Rheology And Tensile Strength, Scott T. Knauert, Jack F. Douglas, Francis W. Starr

Division III Faculty Publications

No abstract provided.


Three-Dimensional Structure Of Cdx (X= Se, Te) Nanocrystals By Total X-Ray Diffraction, S. K. Pradhan, Z. T. Deng, F. Tang, Y. Ren, Peter Moeck, V. Petkov Jan 2007

Three-Dimensional Structure Of Cdx (X= Se, Te) Nanocrystals By Total X-Ray Diffraction, S. K. Pradhan, Z. T. Deng, F. Tang, Y. Ren, Peter Moeck, V. Petkov

Physics Faculty Publications and Presentations

The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiationx-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research.


Exafs Characterization Of Dendrimer‐Derived Pt/Γ‐Al2O3, A. Siani, Oleg S. Alexeev, Christopher T. Williams, Harry J. Ploehn, Michael D. Amiridis Jan 2007

Exafs Characterization Of Dendrimer‐Derived Pt/Γ‐Al2O3, A. Siani, Oleg S. Alexeev, Christopher T. Williams, Harry J. Ploehn, Michael D. Amiridis

Faculty Publications

The various steps involved in the preparation of a Pt/γ‐Al2O3 material using hydroxyl‐terminated generation four (G4OH) PAMAM dendrimers as templates were monitored by EXAFS. The results indicate that Cl ligands in the Pt precursors (H2PtCl6 and K2PtCl4) were partially replaced by aquo ligands upon hydrolysis to form [PtCl3(H2O)3]+ and [PtCl2(H2O)2] species. After interaction of such species with G4OH, Cl ligands from the first coordination shell of Pt were further replaced by nitrogen atoms from the dendrimer interior, indicating ...


Transmission Electron Goniometry And Its Relation To Electron Tomography For Materials Science Apoplications, Peter Moeck, P. Fraundorf Nov 2006

Transmission Electron Goniometry And Its Relation To Electron Tomography For Materials Science Apoplications, Peter Moeck, P. Fraundorf

Physics Faculty Publications and Presentations

Aspects of transmission electron goniometry are discussed. Combined with high resolution phase contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) in the atomic number contrast (Z-STEM) or the phase contrast bright field mode, transmission electron goniometry offers the opportunity to develop dedicated methods for the crystallographic characterization of nanocrystals in three dimensions. The relationship between transmission electron goniometry and electron tomography for materials science applications is briefly discussed. Internet based java applets that facilitate the application of transmission electron goniometry for cubic crystals with calibrated tilt-rotation and double-tilt specimen holders/goniometers are mentioned. The so called cubic-minimalistic ...


Image-Based Nanocrystallography With Online Database Support, Peter Moeck, Ján Zahornadsky, Boris Dusek Jan 2006

Image-Based Nanocrystallography With Online Database Support, Peter Moeck, Ján Zahornadsky, Boris Dusek

Physics Faculty Publications and Presentations

The crystallographic phase and morphology of many materials change with the crystal size so that new needs arise to determine the crystallography of nanocrystals. Direct space high-resolution phase-contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) when combined with tools for image-based nanocrystallography in two (2D) and three (3D) dimensions possess the capacity to meet these needs. After a concise discussion of lattice-fringe visibility spheres and maps, this paper discusses lattice-fringe fingerprinting in 2D and tilt protocol applications. On-line database developments at Portland State University (PSU) that support image-based nanocrystallography are also mentioned.


Lattice Fringe Fingerprinting In Two Dimensions With Database Support, Peter Moeck, B. Seipel, R. Bjorge, P. Fraundorf Jan 2006

Lattice Fringe Fingerprinting In Two Dimensions With Database Support, Peter Moeck, B. Seipel, R. Bjorge, P. Fraundorf

Physics Faculty Publications and Presentations

A brief introduction to lattice fringe fingerprinting in two dimensions (2D) with database support is given. The method is employed for the identification of the crystal phase of a small ensemble of nanocrystals. The enhanced viability of this method in aberration-corrected transmission electron microscopes (TEMs) and scanning TEMs (STEMs) is also illustrated.


Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson Oct 2005

Progress Towards Terahertz Acoustic Phonon Generation In Doping Superlattices, Thomas E. Wilson

Physics Faculty Research

Progress is described in experiments to generate coherent terahertz acoustic phonons in silicon doping superlattices by the resonant absorption of nanosecond-pulsed far-infrared laser radiation. Future experiments are proposed that would use the superlattice as a transducer in a terahertz cryogenic acoustic reflection microscope with sub-nanometer resolution.


Magneto-Optical Spectra Of Closely Spaced Magnetite Nanoparticles, Damon Allen Smith, Yu A. Barnakov, B L. Scott, S A. White, Kevin L. Stokes Jan 2005

Magneto-Optical Spectra Of Closely Spaced Magnetite Nanoparticles, Damon Allen Smith, Yu A. Barnakov, B L. Scott, S A. White, Kevin L. Stokes

Physics Faculty Publications

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe

3O4 smagnetited nanoparticles s8-nm diameterd and polysmethylmethacrylated . Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for sdilute compositesd to 540 nm concentrated . We present a theory based on the discrete-dipole approximation which accounts for

optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental ...


Cofe2o4 Nanostructures With High Coercivity, J S. Jung, J H. Lim, K H. Choi, S L. Oh, Y R. Kim, S H. Lee, D A. Smith, K L. Stokes, L Malkinski, C J. O'Connor Jan 2005

Cofe2o4 Nanostructures With High Coercivity, J S. Jung, J H. Lim, K H. Choi, S L. Oh, Y R. Kim, S H. Lee, D A. Smith, K L. Stokes, L Malkinski, C J. O'Connor

Physics Faculty Publications

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4).. We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside ...


Making Sense Of Nanocrystal Lattice Fringes, P. Fraundorf, Wentao Qin, Peter Moeck, Eric Mandell Jan 2005

Making Sense Of Nanocrystal Lattice Fringes, P. Fraundorf, Wentao Qin, Peter Moeck, Eric Mandell

Physics Faculty Publications and Presentations

The orientation dependence of thin-crystal lattice fringes can be gracefully quantified using fringe-visibility maps, a direct-space analog of Kikuchi maps [Nishikawa and Kikuchi, Nature (London) 121, 1019 (1928)]. As in navigation of reciprocal space with the aid of Kikuchi lines, fringe-visibility maps facilitate acquisition of crystallographic information from lattice images. In particular, these maps can help researchers to determine the three-dimensional lattice of individual nanocrystals, to 'fringe-fingerprint' collections of randomly oriented particles, and to measure local specimen thickness with only a modest tilt. Since the number of fringes in an image increases with maximum spatial-frequency squared, these strategies (with help ...


Boron-Rich Semiconducting Boron Carbide Neutron Detector, Andrew D. Harken, Ellen E. Day, Brian W. Robertson, Shireen Adenwalla Jan 2005

Boron-Rich Semiconducting Boron Carbide Neutron Detector, Andrew D. Harken, Ellen E. Day, Brian W. Robertson, Shireen Adenwalla

Shireen Adenwalla Papers

Data on the neutron detection capabilities of a variety of boron carbide/Si heterojunction diodes is presented. The pulse height spectra are compared with previously measured conversion layer devices and the variations in shape and position of the peaks are discussed.


Science And Engineering Of Nanoparticle-Polymer Composites: Insights From Computer Simulation, Francis W. Starr, Sharon C. Glotzer Jan 2004

Science And Engineering Of Nanoparticle-Polymer Composites: Insights From Computer Simulation, Francis W. Starr, Sharon C. Glotzer

Division III Faculty Publications

No abstract provided.


Science And Engineering Of Nanoparticle-Polymer Composites: Insights From Computer Simulation, Francis W. Starr, Sharon C. Glotzer Dec 2003

Science And Engineering Of Nanoparticle-Polymer Composites: Insights From Computer Simulation, Francis W. Starr, Sharon C. Glotzer

Francis Starr

No abstract provided.


Self-Assembly Of Fept Nanoparticles Into Nanorings, Weilie L. Zhou, Jibao He, Jiye Fang, Tuyet-Anh Huynh, Trevor J. Kennedy, Kevin L. Stokes, Charles J. O'Connor Jan 2003

Self-Assembly Of Fept Nanoparticles Into Nanorings, Weilie L. Zhou, Jibao He, Jiye Fang, Tuyet-Anh Huynh, Trevor J. Kennedy, Kevin L. Stokes, Charles J. O'Connor

Physics Faculty Publications

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the

{100} and {111}

crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area ...


Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang Jan 2003

Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang

Physics Faculty Publications

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite.


Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu Jan 2002

Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu

Physics Faculty Publications

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core ...


121.6 Nm Radiation Source For Advanced Lithography, Jianxun Yan, Ashraf El-Dakrouri, Mounir Laroussi, Mool C. Gupta Jan 2002

121.6 Nm Radiation Source For Advanced Lithography, Jianxun Yan, Ashraf El-Dakrouri, Mounir Laroussi, Mool C. Gupta

Electrical & Computer Engineering Faculty Publications

A vacuum ultraviolet (VUV) light source based on a high-pressure cylindrical dielectric barrier discharge (DBD) has been developed. Intense and spectrally clean Lyman-α line at 121.6 nm was obtained by operating a DBD discharge in neon with a small admixture of hydrogen. The spectrum, optical power, stability, and efficiency of the source were measured. The influence of the gas mixture and total gas pressure on the VUV intensity has been investigated. Maximum optical power of 3.2 W and spectral width 0.03 nm was achieved. Power stability of 2% for 100 h of operation has also been obtained ...


Bistable Operation Of A Two-Section 1.3-Mm Inas Quantum Dot Laser—Absorption Saturation And The Quantum Confined Stark Effect, Xiaodong Huang, A. Stintz, Hua Li, Audra Rice, G. T. Liu, L.F. Lester, Julian Cheng, K.J. Malloy Mar 2001

Bistable Operation Of A Two-Section 1.3-Mm Inas Quantum Dot Laser—Absorption Saturation And The Quantum Confined Stark Effect, Xiaodong Huang, A. Stintz, Hua Li, Audra Rice, G. T. Liu, L.F. Lester, Julian Cheng, K.J. Malloy

Faculty Publications

Room temperature, continuous-wave bistability was observed in oxide-confined, two-section, 1.3- m quantum-dot (QD) lasers with an integrated intracavity quantum-dot saturable absorber. The origin of the hysteresis and bistability were shown to be due to the nonlinear saturation of the QD absorption and the electroabsorption induced by the quantum confined Stark effect.


Modeling The High-Speed Switching Of Far-Infrared Radiation By Photoionization In A Semiconductor, Thomas E. Wilson May 1999

Modeling The High-Speed Switching Of Far-Infrared Radiation By Photoionization In A Semiconductor, Thomas E. Wilson

Physics Faculty Research

Data from an earlier study [T. Vogel et al., Appl. Opt. 31, 329 (1992)] on the subnanosecond switching of 119-μm radiation in high-resistivity silicon by pulsed UV laser radiation, is compared with a refined one-dimensional numerical multilayer model accounting for the generation, recombination, and diffusion of the free carriers on the resulting far-infrared optical properties of the silicon. The inclusion of recent measurements for carrier-density and temperature-dependent transport parameters leads to improved agreement between experiment and theory.


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 ...