Bulletin of the American Physical Society
2005 TSAPS/AAPT/SPS Joint Fall Meeting
Thursday–Saturday, October 20–22, 2005; Houston, TX
Session A4: Poster Session I |
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Room: Waldorf Astoria Lobby |
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A4.00001: An SEM study on the effect of strain rate on the deformation process of amorphous Cu-Nb alloy thin films using nanoindentation Stephen Myers, Suman Vadlakonda, Reza Mirshams, Rajarshi Banerjee Deformation mechanisms in amorphous alloys have been a topic of great interest recently. Applying different strain rates during nanoindentation using cubecorner indenter tips has shed much light on the mechanisms of deformation in amorphous Cu-Nb thin films. Transformation of a serrated load-displacement curve to a smoother curve with an increase in strain rate has been attributed to the change from discrete to homogeneous plasticity in recent studies. In order to have a better understanding of the deformation mechanisms and to study shear band formation on the surface, a detailed study is done using scanning electron microscopy. Indentation is done at three different strain rates on amorphous Cu-Nb alloy thin films. An attempt is being made to determine a close relation between the surface characteristics and the load - displacement curve. [Preview Abstract] |
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A4.00002: Positron annihilation spectroscopy study of polymers and organic liquids Paul Arpin, C.A. Quarles We have used positron annihilation Doppler broadening spectroscopy and positron annihilation lifetime spectroscopy to investigate properties of several polymers and organic liquids. The Doppler broadening is characterized by the $S$ parameter, which is a measure of the probability of low momentum annihilations in the material. The lifetime spectroscopy is characterized by the ortho-positronium (o-Ps) lifetime and intensity of o-Ps formation. We found that the correlation between the S parameter and the probability of o-Ps formation is dependent on polymer composition and sensitive to oxygen or fluorine present in the polymer. A similar conclusion has also been recently reported by another group.[1] We also found correlations between our results and various physical parameters characterizing the materials. \newline \newline [1] K. Sato, et al, Phys. Rev. B 71, 012201 (2005). [Preview Abstract] |
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A4.00003: Waking an Anemic Giant: Exploring a Recently Discovered Circumnuclear Star Forming Ring Sarah Dorn, Pamela Marcum, Michael Fanelli The disks within spiral galaxies are thought to be regions of quasi-continuous star formation, averaged over long timescales. However, in the case of the barred spiral (Sb) galaxy NGC 4314, a variety of data indicates that this system contains a circumnuclear ring of~recent massive star formation. Stellar population modeling is applied to U, V, and I--band imagery, obtained with the 0.8 meter telescope at McDonald Observatory, to explore the relationship between the strong circumnuclear star birth and the star formation history of the main disk within this object. [Preview Abstract] |
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A4.00004: Binding of Two Photoactive Molecules to Tubulin Lorenzo Brancaleon, Fang Tian The interaction of Tubulin with two porphyrin dyes, meso-terakis(p-sulfonatophenyl)porphyrin (TSPP) and protoporphyrin IX (PPIX), were studied by steady-state and dynamic fluorescence spectroscopy. The shifts of TSPP and PPIX emission maximums upon excitation at 405 nm and 420 nm, respectively, and the increases of the fluorescence intensity are indicators that bindings between the tubulin and the porphyrins occur. The static quenching caused by porprhyrin on the protein's tryptophan yield constants of 1.7 $\times $ 10 $^{5}$ M$^{-1}$ and 5.4 $\times $ 10 $^{4}$ M$^{-1}$ for tubulin-TSPP and tubulin-PPIX respectively. Double logarithmic plots yield a single binding site for the two complexes while the dissociation constants is 6.9 $\times $ 10 $^{-7}$ M for tubulin-TSPP and of 7.8 $\times $ 10 $^{-7}$ M for tubulin-PPIX. Fluorescence Anisotropy Decay confirms the binding of both porphyrins to tubulin. Both porphyrin show a fast correlation time ($<$300 ps) which is due either to remaining free porphyrin in solution or to some rotational freedom within the binding site. The longer correlation time appears to be shorter for TSPP (10 ns) than for PPIX (17 ns). The result present the first study of the molecular interaction between porphyrin and tubulin despite the fact that such interaction was first observed almost ten years ago. [Preview Abstract] |
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A4.00005: Electronic structure and dynamics of microhydrated DNA base clusters Valoris Smith, Elena Samoylova, Thomas Schultz, Hans-Hermann Ritze, I.V. Hertel DNA and DNA bases emerged before the ozone layer was formed and therefore must have inherent properties protecting them upon irradiation with UV rays. These mechanisms might be ultrafast relaxation to the ground state via conical intersections or internal vibrational relaxation. Using gas-phase, femtosecond pump-probe methods, we try to determine which relaxation pathways are energetically favorable after excitation by a UV pump pulse. We also study the impact of microsolvation on the dynamics and electronic state character to bridge the gap between ab initio theory and biologically relevant liquid phase experiments. [Preview Abstract] |
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A4.00006: Study of poly[N-isopropylacrylamide-co-Glycidyl Methacrylate] Particle Size Under the Effects of Varying Phase Ratio, Initiator Dose and Temperature Nicole Fox, Jun Zhou, Zhibing Hu This is a study of the particle size of poly[N-isopropylacrylamide-co-glycidal methacrylate] (p[NIPA-co-GMA]) nanoparticles. The function group of GMA allows it to bond easily with proteins, making it very important in biomedical applications. The effects of varying phase ratios and varying initiator doses on particle size were studied, as well as the temperature dependence of particle size using dynamic light scattering techniques. The kinematic properties of particles at set times after beginning a reaction were studied. [Preview Abstract] |
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A4.00007: Bragg Diffraction as an Indicator of Hydrogel Crystal Uniformity William Estabrook, Tong Cai, Zhibing Hu This is a study on the use of Bragg diffraction from hydrogel crystals to determine characteristics of growth and uniformity of the crystalline structure. One part of the successful application of hydrogels lies in a better understanding of their crystallization process. This can be done by examining the diffraction pattern generated from projecting a laser on a sample during the stages of crystal formation. The typical spacing in a hydrogel crystal is on the order of hundreds to thousands of nanometers, allowing the utilization of visible spectrum lasers for diffraction studies. [Preview Abstract] |
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A4.00008: Planarizing Single-Walled Carbon Nanotube Fibers Michelle Prewitt, Nolan Nicholas, Jae Jang, Erik Haroz, Myung Kim, Hongwei Shan, Richard Smalley Planarization of single-walled carbon nanotube (SWNT) fibers was performed to produce a clean, level fiber surface of open-ended nanotubes. Low pressures, approximately 50 mTorr -- 1.0 Torr, of gas were introduced into the planarizer. The planarizer is a vacuum system that contains the heated catalytic foil and the fiber. The foil and gas react to create an aggressive species that is localized on the foil. Since the end of the fiber can be moved into contact with the foil, carbon and impurities can be removed from the end of the fiber and escape in the gas phase. The effect of change in temperature, pressure, and other variables, were tested to determine conditions that allow the end of the fiber to be etched without damaging the sidewalls of the nanotubes. The clean fibers can then be used for continued growth resembling 1D molecular epitaxy. Raman spectroscopy suggests that continued growth from a fiber produces SWNT that are identical to the ones present in the fiber. Thus, continued growth is a process that can produce specific types of SWNT, which is important because the properties, and therefore uses, of the nanotubes depend on their diameter and chirality. [Preview Abstract] |
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A4.00009: Characterization of MEMS Deformable Mirrors for Wavefront Control in Extreme Adaptive Optics Layra Reza |
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A4.00010: Elastic properties, Mossbauer spectra and phonon density of states in FexCr1-x alloys Tomas Hernandez, Matthew S. Lucas, Brent Fultz The binary alloy of iron and chromium is known to have three magnetic transitions observable at temperatures below 300 K. Our research group has performed inelastic neutron scattering on the samples of FexCr1-x for x = 1, 3, 10, 20, 30 at percent across the magnetic phase transitions to obtain the phonon energy density of states. From these measurements elastic properties and vibrational entropy can be determined. Direct measurements of the elastic constants, i.e. shear and bulk moduli, were done using an ultrasonic technique by measuring sound speeds in the alloys at room temperature. The results are to be compared with the data obtained from the inelastic neutron scattering experiment. Mossbauer spectroscopy, a technique that detects the change in nuclear energy levels caused by electronic interactions was used to detect the magnetic transitions and measure the isomer shift of the alloys in the paramagnetic phase of the different alloy concentrations. [Preview Abstract] |
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A4.00011: Balloon and Satellite Observations of Substorm Activity Brandon Reddell, Edgar Bering The first campaign of the Polar Patrol Balloon (PPB) experiment (1st-PPB) was carried out at Syowa Station in Antarctica during 1990-1991 and 1992-1993. Based on the results of the 1st-PPB experiment, the next campaign (2nd-PPB) was carried out in the austral summer of 2002-2003. This paper will present an overview of substorm, convection and ULF activity during the 2nd-PPB experiment. In that experiment, two balloons were launched for the purpose of upper atmosphere physics observation. Payloads of these 2 flights were identical with each other, and were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. Such a ``Balloon Cluster'' is suitable to observe temporal evolution and spatial distribution of phenomena in the ionospheric regions and boundaries that the balloons traversed during their circumpolar trajectory. Balloon separation varied from 60 to 500 km. More than 20 days of simultaneous fair weather 3-axis electric field data were obtained at geomagnetic latitudes ranging from sub-auroral to the polar cap. This paper will present the observations of substorms that occurred on January 25th, 2003, with emphasis on the temporal and spatial variations. [Preview Abstract] |
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A4.00012: Terrace Width Distributions for Stepped Crystal Surfaces: An Ensemble Approach Ryan P. Jacob, Howard L. Richards For almost 40 years, Terrace Width Distributions (TWDs) for stepped crystal surfaces have been calculated by the Gruber- Mullins (GM) approximation, which is derived from the fluctuations of a single step between two rigid neighbors at fixed positions. Much more recently, the Generalized Wigner Distribution (GWD) has been found to be a better approximation for TWDs. The GWD can be derived from two interacting steps confined in a harmonic well, and it has recently been shown to work well also for systems in which steps alternate in stiffness. Here we use an alternate approach, and consider an ensemble average of GM approximations in which the separation of the neighbors is allowed to change; this can be viewed as the limit in which the stiffness of alternating steps diverge, so the GWD is expected. A characteristic length along the steps must be introduced to perform the ensemble average. This length is in suprisingly good agreement with the length over which Step Position Distributions (SPDs) calculated from Monte Carlo simulation data agree with SPDs derived consistently with the GWD. [Preview Abstract] |
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A4.00013: Investigation of bremsstrahlung radiation from slabs of different thickness with PENELOPE Keith Hayton, C.A. Quarles The computer code system, PENELOPE, performs Monte Carlo simulations of electrons, photons, and positrons transported through different materials. [1] PENSLAB, included with the distribution package as an example of a ``main program'' which the user must write in order to utilize the ``driving program,'' PENELOPE, simulates the path of photons, electrons, and positrons through a slab composed of an arbitrary material. PENSLAB records and calculates detailed information concerning the track of the particle during and after its travel through the slab. We have made some modifications to the PENSLAB code. The goal of the modifications has been to enable the program to collect and record the energy of the emerging particles as a function of solid angle. We will discuss applications of PENSLAB to the study of bremsstrahlung radiation from slabs of various thickness. We will discuss results that we have generated to compare with experiments with 50 keV electrons on Au and Al targets. \newline \newline [1] Llovet, X., Sorbier, L., Campos, C. S., Acosta, E., and Salvat, F., J. Appl. Phys. \textbf{93}, 3844 (2003). [Preview Abstract] |
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A4.00014: Electronic Band Structure Investigation of GaP$_{1-x}$N$_{x}$/GaAs$_{1-x}$N$_{x}$ Superlattices Lattice-matched to Si Wenkai Zhu, Lekhnath Bhusal, Andenet Alemu, Alex Freundlich Strain-balanced GaP$_{1-x}$N$_{x}$/GaAs$_{1-x}$N$_{x}$ short period superlattices can be lattice-matched to the most commonly available Si substrate for many optoelectronic devices. The theoretical investigation of the electronic band structure in the vicinity of the $\Gamma $-point of this superlattices strain-balanced to Si(001) is performed using a transfer matrix method. A six-band Kane Hamiltonian modified with the strain effect and a band anti-crossing model are used to describe the electronic states of the highly strained zinc blende GaP$_{1-x}$N$_{x}$ and GaAs$_{1-x}$N$_{x}$ ternaries. The evolution of the conduction band minima and valence subbands maxima of GaP$_{1-x}$N$_{x}$ and GaAs$_{1-x}$N$_{x}$ as a function of the nitrogen composition indicate the occurrence of a type I band alignment for the superlattice involving the $m_{j}=\pm $3/2, $\pm $1/2 valence subbands (both hole and electron wells in GaAs$_{1-x}$N$_{x})$. The room temperature energy gap between the first electron miniband and the first hole miniband of these short period superlattices is predicted to cover the range of band gap from 1.5eV to 1.8eV. [Preview Abstract] |
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