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Articles 28921 - 28950 of 36694

Full-Text Articles in Physical Sciences and Mathematics

Effect Of Relativistic Many-Electron Interactions On Photoelectron Partial Wave Probabilities, K. W. Mclaughlin, Orhan Yenen, Duane H. Jaecks, Timothy J. Gay, M. M. Sant'anna, D. Calabrese, B. Thaden-Jordan Mar 2002

Effect Of Relativistic Many-Electron Interactions On Photoelectron Partial Wave Probabilities, K. W. Mclaughlin, Orhan Yenen, Duane H. Jaecks, Timothy J. Gay, M. M. Sant'anna, D. Calabrese, B. Thaden-Jordan

Timothy J. Gay Publications

We obtain relative cross sections for the production of photoelectrons with specific angular momentum quantum numbers. These cross sections are obtained from the polarization analysis of the visible fluorescence of ions produced when circularly polarized vacuum ultraviolet radiation photoionizes ground state Ar. The ratio of cross sections for the production of photoelectrons with the same orbital angular momentum but different total angular momenta shows strong deviations from the statistical ratio, demonstrating the importance of relativistic interactions in many-electron photoionization dynamics.

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Anomalous Conductance Distribution In Quasi-One-Dimensional Gold Wires: Possible Violation Of The One-Parameter Scaling Hypothesis, Pritiraj Mohanty, Richard A. Webb Mar 2002

Anomalous Conductance Distribution In Quasi-One-Dimensional Gold Wires: Possible Violation Of The One-Parameter Scaling Hypothesis, Pritiraj Mohanty, Richard A. Webb

Faculty Publications

We report measurements of conductance distribution in a set of quasi-one-dimensional gold wires. The distribution includes the second cumulant or the variance which describes the universal conductance fluctuations, and the third cumulant which denotes the leading deviation. We have observed an asymmetric contribution—or, a nonvanishing third cumulant—contrary to the expectation for quasi-one-dimensional systems in the noninteracting theories in the one-parameter scaling framework, which include the perturbative diagrammatic calculations and the random matrix theory.

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Entanglement And Decoherence Of A Micromechanical Resonator Via Coupling To A Cooper-Pair Box, A. D. Armour, M. P. Blencowe, K. C. Schwab Mar 2002

Entanglement And Decoherence Of A Micromechanical Resonator Via Coupling To A Cooper-Pair Box, A. D. Armour, M. P. Blencowe, K. C. Schwab

Dartmouth Scholarship

We analyze the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper-pair box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the decay of the resonator superposition state due to environmental decoherence.

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Structural Investigation Of Ag-Pd Clusters Synthesized With The Radiolysis Method, Carmen M. Doudna, Massimo F. Bertino, Akira T. Tokuhiro Mar 2002

Structural Investigation Of Ag-Pd Clusters Synthesized With The Radiolysis Method, Carmen M. Doudna, Massimo F. Bertino, Akira T. Tokuhiro

Physics Faculty Research & Creative Works

The structure of Ag-Pd clusters synthesized with the radiolysis method was investigated. The clusters were characterized with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). These techniques showed that the synthesized clusters had face-centered cubic (fcc) crystalline structure and were free of contamination.

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Thermoelectric Properties Of The N-Type Filled Skutterudite Ba0.3co4sb12 Doped With Ni, Jeffrey Dyck, Wei Chen, Ctirad Uher, Lidong Chen, Xinfeng Tang, Toshio Hirai Mar 2002

Thermoelectric Properties Of The N-Type Filled Skutterudite Ba0.3co4sb12 Doped With Ni, Jeffrey Dyck, Wei Chen, Ctirad Uher, Lidong Chen, Xinfeng Tang, Toshio Hirai

Jeffrey Dyck

Synthesis and electrical and thermal transport properties are reported for several filled skutterudite compounds doped with Ni: Ba0.3NixCo4_xSb12 with 0

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Diluted Magnetic Semiconductors Based On Sb2àXvxte3 „0.01ïXï0.03., Jeffrey Dyck, Pavel Hájek, Petr LošŤÁK, Ctirad Uher Mar 2002

Diluted Magnetic Semiconductors Based On Sb2àXvxte3 „0.01ïXï0.03., Jeffrey Dyck, Pavel Hájek, Petr LošŤÁK, Ctirad Uher

Jeffrey Dyck

We report on a diluted magnetic semiconductor based on the [formula] tetradymite structure doped with very low concentrations of vanadium (1—3 at. %). The anomalous transport behavior and robust magnetic hysteresis loops observed in magnetotransport and magnetic measurements are experimental manifestations of the ferromagnetic state in these materials. The [formula] exchange between holes and vanadium [formula] spins is estimated from the behavior of the magnetoresistance. A Curie temperature of at least 22 K is observed for [formula] This discovery offers possibilities for exploring magnetic properties of other tetradymite structure semiconductors doped with a wide range of [formula] transition metals.

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Effect Of Ni On The Transport And Magnetic Properties Of Co1àXnixsb3, Jeffrey Dyck, Wei Chen, Jihui Yang, Gregory P. Meisner, Ctirad Uher Mar 2002

Effect Of Ni On The Transport And Magnetic Properties Of Co1àXnixsb3, Jeffrey Dyck, Wei Chen, Jihui Yang, Gregory P. Meisner, Ctirad Uher

Jeffrey Dyck

The filled skutterudite compounds based on the binary skutterudite [formula] are currently being investigated for their potential applications as thermoelectric materials. One route to optimization of these compounds is by doping on the Co site. An obvious candidate for an n-type dopant is Ni, since it has one more electron in its valence shell than Co. Up to now, however, only high concentrations of Ni in [formula] have been studied; and the valence of Ni in this compound and its influence on the transport and magnetic properties has been an open question. We present electrical resistivity, thermopower, Hall effect, magnetoresistance, …

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Three-Body Dynamics In The Ionization Of Hydrogen By Positron Impact, J. Fiol, Ronald E. Olson Mar 2002

Three-Body Dynamics In The Ionization Of Hydrogen By Positron Impact, J. Fiol, Ronald E. Olson

Physics Faculty Research & Creative Works

Three-body dynamics are investigated for single ionization of hydrogen by 50 and 100 eV positron impact. The momentum distributions of the electron, the projectile and the recoiling target nucleus are investigated. The present results show that, despite the large mass of the target nucleus, it actively participates in the dynamics of the ionizing collisions. In particular, a strong correlation between the positron and the recoil-ion momenta is found, which is especially important at the lower collision energy of this study.

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Superspin-Glass Nature Of Discontinuous Co80Fe20/Al2O3 Multilayers, Sarbeswar Sahoo, O. Petracic, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas Mar 2002

Superspin-Glass Nature Of Discontinuous Co80Fe20/Al2O3 Multilayers, Sarbeswar Sahoo, O. Petracic, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas

Christian Binek Publications

Ferromagnetic single domain particles of CoFe in discontinuous magnetic multilayers [Co80Fe20 (0.9 nm)/ Al2O3(3 nm)] 10 reveal spin-glass ordering below Tg=43.6 K as evidenced by the criticality of the nonlinear susceptibility. Dynamic critical scaling yields exponents zν=8.0 and β=1.0 in both zero and weak applied field, where an Almeida-Thouless line is encountered. In fields exceeding 2 mT a crossover into a chiral glass regime seems to occur.

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Transition From Negative Magnetoresistance Behavior To Positive Behavior In Co20 (Cu1-XGeX)80 Ribbons, J. He, Z.D. Zhang, J. Ping Liu, David J. Sellmyer Mar 2002

Transition From Negative Magnetoresistance Behavior To Positive Behavior In Co20 (Cu1-XGeX)80 Ribbons, J. He, Z.D. Zhang, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20 (Cu1-xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration.

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Anisotropy And Magnetic Field Effects On The Entanglement Of A Two Qubit Heisenberg Xy Chain , G. Lagmago Kamta, Anthony F. Starace Mar 2002

Anisotropy And Magnetic Field Effects On The Entanglement Of A Two Qubit Heisenberg Xy Chain , G. Lagmago Kamta, Anthony F. Starace

Anthony F. Starace Publications

We investigate the entanglement of a two-qubit anisotropic Heisenberg XY chain in thermal equilibrium at temperature T in the presence of an external magnetic field B along the z axis. By means of the combined influences of anisotropic interactions and a magnetic field B, one is able to produce entanglement for any finite T, by adjusting the magnetic field strength. This contrasts with the isotropic interaction or the B = 0 cases, for which there is no entanglement above a critical temperature Tc that is independent of the external B field.

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Controlling Nucleation And Growth Of Nanodroplets In Supersonic Nozzles, Kiril A. Streletzky, Yury Zvinevich, Barbara E. Wyslouzil, Reinhard Strey Mar 2002

Controlling Nucleation And Growth Of Nanodroplets In Supersonic Nozzles, Kiril A. Streletzky, Yury Zvinevich, Barbara E. Wyslouzil, Reinhard Strey

Physics Faculty Publications

We present the first results for a new supersonic nozzle that decouples nucleation and droplet growth, and closely controls the supersaturation and temperature during nucleation. We characterize the expansions using pressure trace measurements, and the aerosol properties using light scattering and small angle neutron scattering. We show that when nucleation and droplet growth are separated, the aerosol number density decreases, the average particle size increases, and the aerosol can be more monodisperse than that formed in a conventional nozzle. Under these conditions, we can estimate the nucleation rate J as a function of supersaturation S and temperature T directly from …

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Sensor Development For Single-Photon Thermoelectric Detectors, Armen Gulian, K. S. Wood, G. G. Fritz, D. Van Vechten, H.-D. Wu, J. S. Horwitz, G. R. Badalyantz, S. R. Harutyunyan, V. H. Vartanyan, S. A. Petrosyan, A. S. Kuzanyan Mar 2002

Sensor Development For Single-Photon Thermoelectric Detectors, Armen Gulian, K. S. Wood, G. G. Fritz, D. Van Vechten, H.-D. Wu, J. S. Horwitz, G. R. Badalyantz, S. R. Harutyunyan, V. H. Vartanyan, S. A. Petrosyan, A. S. Kuzanyan

Mathematics, Physics, and Computer Science Faculty Articles and Research

As we reported earlier [1], thermoelectric detectors can be competitive as nondispersive energy resolving focal-plane instruments in X-ray/UV spectrum. The first generations of prototype devices demonstrated the viability of detector design and provided good agreement between theoretical expectations and experimental data. These devices exploited sensors made of gold with a small fraction of iron impurity. To get the projected high resolution one needs another type of material, namely, lanthanum-cerium hexaborides. We report on the first experimental tests of the feasibility of lanthanum-cerium films as sensor materials. Progress with thin films of these materials argues for the success of these thermoelectric …

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Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky Mar 2002

Effective Index Of Refraction, Optical Rotation, And Circular Dichroism In Isotropic Chiral Liquid Crystals, D. Lacoste, Peter J. Collings, T. C. Lubensky

Physics & Astronomy Faculty Works

This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependence of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric P is much shorter than the wavelength of the light lambda, an approximation that has been made in previous studies of this …

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Nonperturbative Effects In A Rapidly Expanding Quark Gluon Plasma, A. K. Mohanty, P. Shukla, Marcelo Gleiser Mar 2002

Nonperturbative Effects In A Rapidly Expanding Quark Gluon Plasma, A. K. Mohanty, P. Shukla, Marcelo Gleiser

Dartmouth Scholarship

Within first-order phase transitions, we investigate pretransitional effects due to the nonperturbative, large-amplitude thermal fluctuations which can promote phase mixing before the critical temperature is reached from above. In contrast with the cosmological quark-hadron transition, we find that the rapid cooling typical of the relativistic heavy ion collider and large hadron collider experiments and the fact that the quark-gluon plasma is chemically unsaturated suppress the role of nonperturbative effects at current collider energies. Significant supercooling is possible in a (nearly) homogeneous state of quark gluon plasma.

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Visualizing The Phonon Wave Function, Scott C. Johnson, Thomas D. Gutierrez Mar 2002

Visualizing The Phonon Wave Function, Scott C. Johnson, Thomas D. Gutierrez

Physics

A phonon often is described as ‘‘a quantum of lattice vibration,’’ but this description can be difficult to reconcile with the wave functions explored in a typical undergraduate quantum mechanics class. A phonon wave function is similar to the harmonic oscillator wave functions studied in introductory quantum mechanics, except that it is many-dimensional. We suggest a way to visualize the probability density for this very high-dimensional wave function. The resulting pictures are especially clear and intuitive for a coherent state, which is both a good approximation to a sound wave and a discrete analog to laser light. These pictures can …

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Measurement Of The B+ Total Cross Section And B+ Differential Cross Section Dσ/DPT In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Mar 2002

Measurement Of The B+ Total Cross Section And B+ Differential Cross Section Dσ/DPT In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present measurements of the B+ meson total cross section and differential cross section dσ/dpT. The measurements use a 98±4 pb-1 sample of pp̅ collisions at √s=1.8 TeV collected by the CDF detector. Charged B meson candidates are reconstructed through the decay B±→J/ψK± with J/ψ→μ+μ-. The total cross section, measured in the central rapidity region |y|pT(B)> 6.0 GeV/c is 3.6±0.6 (stat⊕ syst), μb. The measured differential cross section is  substantially larger than typical QCD predictions calculated to next-to-leading order.

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Searches For New Physics In Events With A Photon And B-Quark Jet At Cdf, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Mar 2002

Searches For New Physics In Events With A Photon And B-Quark Jet At Cdf, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have searched for evidence of physics beyond the standard model in events that include an energetic photon and an energetic b-quark jet, produced in 85 pb-1 of p̅p collisions at 1.8 TeV at the Tevatron Collider at Fermilab. This signature, containing at least one gauge boson and a third-generation quark, could arise in the production and decay of a pair of new particles, such as those predicted by supersymmetry, leading to a production rate exceeding standard model predictions. We also search these events for anomalous production of missing transverse energy, additional jets and leptons (e, …

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Study Of The Heavy Flavor Content Of Jets Produced In Association With W Bosons In Pp̅ Collisions At √S =1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Mar 2002

Study Of The Heavy Flavor Content Of Jets Produced In Association With W Bosons In Pp̅ Collisions At √S =1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present a detailed examination of the heavy flavor content of the W+ jet data sample collected with the Collider Detector at Fermilab during the 1992–1995 collider run at the Fermilab Tevatron. Jets containing heavy flavor quarks are selected via the identification of secondary vertices or semileptonic decays of b and c quarks. There is generally good agreement between the rates of secondary vertices and soft leptons in the data and in the standard model simulation including single and pair production of top quarks. An exception is the number of events in which a single jet has both a …

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Transport Of Space Environment Electrons: A Simplified Rapid-Analysis Computational Procedure, John E. Nealy, Brooke M. Anderson, Francis Cucinotta, John W. Wilson, Robert Katz, C. K. Chang Mar 2002

Transport Of Space Environment Electrons: A Simplified Rapid-Analysis Computational Procedure, John E. Nealy, Brooke M. Anderson, Francis Cucinotta, John W. Wilson, Robert Katz, C. K. Chang

Robert Katz Publications

A computational procedure for describing transport of electrons in condensed media has been formulated for application to effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The procedure is based on earlier parameterizations established from numerous electron beam experiments. New parameterizations have been derived that logically extend the domain of application to low molecular weight (high hydrogen content) materials and higher energies (~50 MeV). The production and transport of high energy photons (bremsstrahlung) generated in the electron transport processes have also been modeled using tabulated values of photon production cross sections. A primary purpose for …

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Third Quarter Report, Covering January Through March 2002, John Farley Mar 2002

Third Quarter Report, Covering January Through March 2002, John Farley

Transmutation Sciences Materials (TRP)

Progress from June 2001-November 2001 was presented at the winter meeting of the American Nuclear Society in Reno (November 12-15, 2001), and incorporated into a refereed conference proceeding. A copy of the refereed conference proceeding has been provided to Tony Hechanova. In brief, the paper described the new program to examine the corrosive effects of lead-bismuth eutectic (LBE) on steels. We employed various types of surface studies (Scanning Electron Microscope [SEM], and X-ray Photoelectron Spectrometry [XPS]) to examine steel samples that had been exposed to LBE for various lengths of time at various temperatures. The goal is to understand the …

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Parity Violation In Neutron Resonances Of Palladium, D A. Smith, J D. Bowman, Bret E. Crawford, C A. Grossmann, T Haseyama, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, V W. Yuan Mar 2002

Parity Violation In Neutron Resonances Of Palladium, D A. Smith, J D. Bowman, Bret E. Crawford, C A. Grossmann, T Haseyama, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, V W. Yuan

Physics and Astronomy Faculty Publications

Parity violation in p-wave neutron resonances of the palladium isotopes 104, 105, 106, and 108 has been measured by transmission of a longitudinally polarized neutron beam through a natural palladium target. The measurements were performed at the pulsed spallation neutron source of Los Alamos Neutron Science Center. The rms weak interaction matrix elements and the corresponding spreading widths were determined for 104 Pd, 105 Pd, and 106 Pd

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Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik Mar 2002

Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik

Physics Faculty Research & Creative Works

Structural and superconducting properties of (La2.5-xPrxNd0.5)CaBa3Cu7Oz (0≤x≤0.7) compounds have been investigated. Neutron diffraction studies reveal that these crystallize in the triple-perovskite structure (space group P4/mmm) with an oxygen content of 16.6 per formula unit nearly independent of the Pr content. The superconducting transition temperature, Tc, of x = 0 compound is ∼ 79K and decreases almost linearly with increasing x to ∼ 42K for x = 0.7. In order to see if the depression of Tc due to Pr can be compensated by Ca, we examined the compounds (La …

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Collisional Dynamics Of Bi2 A(0U+). Ii. State-To-State Rotational Energy Transfer, Robert E. Franklin, Glen P. Perram Mar 2002

Collisional Dynamics Of Bi2 A(0U+). Ii. State-To-State Rotational Energy Transfer, Robert E. Franklin, Glen P. Perram

Faculty Publications

Rotational-to-translational (R–T) energy transfer within v′=1 of the A(0+u) state of Bi2 has been investigated using spectrally resolved, laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated rotational levels of Bi2(A,v′=1) were observed for helium, neon, and argon collision partners after laser excitation of the high rotational levels J′=171, 201, and 231. Total rotational removal rates from the initially prepared state range from 2.8–8.9×10−10 cm3/molecule s. Collisional population of rotational states with |ΔJ|⩽56 was observed at pressures of 0.09–1.4 Torr. The state-to-state rates are adequately modeled by the energy based statistical power gap …

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Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, R. W. Smith, John R. Hardy Mar 2002

Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, R. W. Smith, John R. Hardy

John R. Hardy Papers

Structural phase transitions in Ca2SiO4 and Sr2SiO4 are investigated by molecular dynamics simulations. The simulations are based on the potentials calculated from the Gordon–Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition γ -α’H and β-α’L - α’H - α in Ca2SiO4, and the transition β-α’ in Sr2SiO4. We find that the α’L phase of Ca2SiO4 is an ax3b x c superstructure of the α’H phase, while the α’H phase …

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The Surface Composition And Spin Polarization Of Nimnsb Epitaxial Thin Films, D. Ristoiu, J.P. Nozières , C.N. Borca, T. Komesu, H.-K. Jeong, Peter A. Dowben Mar 2002

The Surface Composition And Spin Polarization Of Nimnsb Epitaxial Thin Films, D. Ristoiu, J.P. Nozières , C.N. Borca, T. Komesu, H.-K. Jeong, Peter A. Dowben

Peter Dowben Publications

The composition in the surface region of the Heusler alloy NiMnSb has been studied using angle-resolved X-ray photoemission spectroscopy, low-energy electron diffraction and spin-polarized inverse photoemission. The results are consistent with a generally Mn-Sb terminal layer, though the surface composition is very sensitive to preparation. The surface composition has a critical influence on the polarization near the Fermi level in spin-polarized inverse photoemission. Under some conditions, the polarization at the Fermi level for normal incidence inverse photoemission can reach values very close to 100% above background.

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Superconducting Studies On The Ho (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon Mar 2002

Superconducting Studies On The Ho (Ba2-Y Lay) Cu3 Oz (0 ≤ Y ≤0.5) System, Amish G. Joshi, S. K. Malik, William B. Yelon

Physics Faculty Research & Creative Works

Structural and superconducting properties of the Ho(Ba2-yLay)Cu3Oz system, with 0.0≤y≤0.5, have been investigated through neutron diffraction, resistivity and magnetization studies. It is observed that on increasing La in Ho(Ba2-yLay)Cu3Oz, the oxygen occupancy at the O(1) site (at 0, 1/2, 0 in space group Pmmm) decreases and that at the O(5) (1/2, 0, 0) site increases, resulting in a decrease in orthorhombicity. As Ba2+ is replaced by La3+, the oxygen content per formula unit increases beyond 7. The variation in the superconducting transition …

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Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy Mar 2002

Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

Structural phase transitions in Ca2SiO4 and Sr2SiO4 are investigated by molecular dynamics simulations. The simulations are based on the potentials calculated from the Gordon–Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition γ -α’H and β-α’L - α’H - α in Ca2SiO4, and the transition β-α’ in Sr2SiO4. We find that the α’L phase of Ca2SiO4 is an ax3b x c superstructure of the α’H phase, while the α’H phase …

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Fabrication And Cold-Flow Testing Of Subscale Space-Based Laser Geometry, Scott E. Bergren Mar 2002

Fabrication And Cold-Flow Testing Of Subscale Space-Based Laser Geometry, Scott E. Bergren

Theses and Dissertations

The objectives of this research were to build a facility that could simulate the expected fluid flow properties in the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser using cold-flow, and to investigate the performance of the model. A 1/5th scale model was fabricated and mated to a blow-down/vacuum wind tunnel. Using rapid data acquisition and schlieren photography the diffuser was determined to initially produce similar fluid flow to the SBL IFX, but rapidly became subsonic due to a transient normal shock wave formed when the wind tunnel was started.

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Fabrication Techniques For Micro-Optical Device Arrays, Ryan D. Conk Mar 2002

Fabrication Techniques For Micro-Optical Device Arrays, Ryan D. Conk

Theses and Dissertations

Micro-optical devices are vital components of conventional military data storage, sensor, and communication systems. Two types of micro-optical device arrays exist: individually addressable and matrix addressable. The matrix addressable array has a drastically reduced number of metal lines and can potentially be fabricated into large, dense (over 1k elements) arrays. Such arrays are expected to enable the development of extremely high bandwidth optical interconnect systems for future military applications including optical computing and short-haul fiber optical communication systems. I investigate new fabrication techniques for the assembly of dense matrix-addressed arrays of micro-optical devices such as vertical-cavity surface-emitting lasers. Using a …

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