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Vibration and stability of two tubes in crossflow

Description: Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in crossflow can be predicted.
Date: August 1, 1997
Creator: Zhu, S.; Chen, S.S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

On the unsteady-motion theory of magnetic forces for maglev

Description: Motion-dependent magnetic forces are the key elements in the study of magnetically levitated vehicle (maglev) system dynamics. This paper presents an experimental and analytical study that will enhance their understanding of the role of unsteady-motion-dependent magnetic forces and demonstrate an experimental technique that can be used to measure those unsteady magnetic forces directly. The experimental technique provides a useful tool to measure motion-dependent magnetic forces for the prediction and control of maglev systems.
Date: February 1, 1996
Creator: Chen, S.S.; Zhu, S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Dynamic stability experiment of Maglev systems

Description: This paper presents dynamic stability experiments on maglev systems and compares with predictions calculated by a nonlinear dynamic computer code. Instabilities of an electrodynamic system (EDS)-type vehicle model were obtained from both experimental observations and computer simulations for a five-degree-of-freedom maglev vehicle moving on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of maglev systems.
Date: December 31, 1995
Creator: Cai, Y.; Chen, S.S.; Zhu, S. & Rote, D.M.
Partner: UNT Libraries Government Documents Department

Vibration and stability of two tubes in crossflow

Description: Two tubes in tandem and normal to flow are studied on the basis of the unsteady flow theory. Motion-dependent fluid forces are measured in a water channel for the pitch-to-diameter ratio of 1.35. From the measured fluid forces, fluid damping and stiffness are calculated as a function of reduced flow velocity and several Reynolds numbers. Once fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of two tubes in cross flow can be predicted.
Date: July 1, 1995
Creator: Zhu, S. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Flow-induced vibration of tubes in crossflow

Description: This paper presents an unsteady flow theory for flow-induced vibration of tubes in crossflow. It includes a general description of motion-dependent fluid forces, characteristics of fluid-force coefficients, and mathematical models. The detailed results are presented for the constrained mode in the lift direction of various tube arrangements.
Date: June 1, 1995
Creator: Chen, S.S.; Cai, Y. & Zhu, S.
Partner: UNT Libraries Government Documents Department

Morphology and microstructure of (111) crystalline CeO{sub 2} films grown on amorphous SiO{sub 2} substrates by pulsed-laser ablation

Description: The surface morphology and microstructure of (111)-oriented CeO{sub 2} thin films, grown on amorphous fused silica (SiO{sub 2} substrates by low-energy-ion-beam assisted pulsed laser ablation, have been studied by atomic force microscopy (AFM) and x-ray diffraction (XRD). These CeO{sub 2} films are aligned with respect to a single in-plane axis despite being deposited on an amorphous substrate. There is a honeycomb-like growth morphology to the films and island-growth can be observed in thicker films. These islands, inside of which are high density of honeycomb-like clusters, are separated by a void network with {approximately}700 nm width. However, on the surface of the thinnest film ({approximately}3 nm), only very small clusters (diameter <60 nm) appear, and the boundaries of the void network are undefined, which implies that the film is just beginning to coalesce into clusters (grains). The combined AFM images and XRD pattern suggest these clusters probably are the initial seeds for the subsequent island growth. Based on these results, the growth mechanism of oriented CeO{sub 2} films on amorphous fused silica substrates is discussed.
Date: November 1, 1994
Creator: Zhu, S.; Lowndes, D.H.; Budai, J.D.; Thundat, T.; Norton, D.P. & Warmack, R.J.
Partner: UNT Libraries Government Documents Department

Magnetic damping for maglev

Description: Magnetic damping is one of the important parameters to control the response and stability of maglev systems. An experimental study is presented to measure the magnetic damping using a direct method. A plate attached to a permanent magnet levitated on a rotating drum was tested to investigate the effect of various parameters on magnetic damping such as conductivity, gap, excitation frequency, and oscillation amplitude. The experimental technique is capable of measuring all magnetic damping coefficients, some of which can not be measured by an indirect method.
Date: December 31, 1994
Creator: Chen, S.S.; Zhu, S.; Cai, Y. & Rote, D.M.
Partner: UNT Libraries Government Documents Department

On the Unsteady-Motion Theory of Magnetic Forces for Maglev

Description: Motion-dependent magnetic forces are the key elements in the study of magnetically levitated vehicle (maglev) system dynamics. In the past, most maglevsystem designs were based on a quasisteady-motion theory of magnetic forces. This report presents an experimental and analytical study that will enhance our understanding of the role of unsteady-motion-dependent magnetic forces and demonstrate an experimental technique that can be used to measure those unsteady magnetic forces directly. The experimental technique provides a useful tool to measure motion-dependent magnetic forces for the prediction and control of maglev systems.
Date: November 1993
Creator: Chen, Shoei-Sheng; Zhu, S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Experiment on Fluidelastic Instability of Loosely Supported Tube Arrays in Crossflow

Description: A tube array supported by baffle plates in crossflow may be subjected to fluid-elastic instability in the tube-support-plate-inactive mode. An experimental study is presented to characterize the tube motion. Three series of tests were performed to measure tube displacements as a function of flow velocity for different clearances. The motion was examined by root-mean-square values of tube displacements, power spectral densities, phase planes, Poincare maps, and Lyapunov exponents. The experimental data agree reasonably well with the analytical model, based on the unsteady flow theory.
Date: June 1993
Creator: Chen, Shoei-Sheng; Zhu, S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Identification of root cause of vibration of a liquid-gallium-cooled silicon monochromator and recommendations for abatement

Description: Perfect single crystals of silicon are used to monochromate the high-intensity X-ray beams in the Advanced Photon Source at Argonne National Laboratory. Depending on the crystal geometry and the insertion device, the crystal may absorb anywhere from several hundred watts to in excess of a thousand watts. To minimize the thermal distortions in the crystal, this heat must be efficiently removed. Several approaches to this problem are being developed at the APSP including the use of inclined-crystal geometries, cryogenic cooling, liquid-gallium cooling, thin crystals, and the use of diamond. Most of these approaches require coolant flow within the crystals themselves. One issue of concern is the flow-induced vibrations. Two series of tests were performed earlier for a near-prototypical gallium-cooled crystal. This LS note describes a series of tests to measure the general vibration response characteristics of a complete liquid-gallium-cooled inclined-crystal monochromator system.
Date: August 1, 1994
Creator: Chen, S.S.; Zhu, S.; Wambsganss, M.W.; Jendrzejczyk, J.A. & Lee, W.K.
Partner: UNT Libraries Government Documents Department

Dynamic Stability Experiment of Maglev Systems

Description: This report summarizes the research performed on Maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also documents magnetic-force data obtained from both measurements and calculations. Because dynamic instability is not acceptable for any commercial Maglev system, it is important to consider this phenomenon in the development of all Maglev systems. This report presents dynamic stability experiments on Maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an electrodynamic system (EDS)-type vehicle model were obtained from both experimental observations and computer simulations for a five-degree-of-freedom Maglev vehicle moving on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of Maglev systems.
Date: April 1995
Creator: Cai, Y.; Rote, D. M.; Mulcahy, T. M.; Wang, Z.; Chen, Shoei-Sheng & Zhu, S.
Partner: UNT Libraries Government Documents Department

Motion-Dependent Fluid Forces Acting on Tube Arrays in Crossflow

Description: Motion-dependent fluids forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluid-elastic instability of tube arrays in crossflow. Once the guideline, based on the unsteady flow theory, can be developed for fluid-elastic instability of tube arrays crossflow.
Date: June 1993
Creator: Chen, Shoei-Sheng; Zhu, S. & Jendrzejczyk, J. A.
Partner: UNT Libraries Government Documents Department

Stable and Vibrational Octupole Modes in Mo, Xe, Ba, La, Ce and Nd

Description: Evidence is presented for stable octupole deformation in neutron-rich nuclei, bounded by Z = 54-58 and N = 85-92. To either side of this region negative parity bands built on more vibrational type octupole modes are observed in {sup 140}Ba and {sup 152,154}Nd. The largest stable octupole deformation ({beta}{sub s} {approximately} 0.1) is found in {sup 144}Ba{sub as}. The theoretically predicted quenching ({beta}{sub s} {approximately} 0) of stable octupole deformation at higher spins is found in {sup 140}Ba. There is good agreement between theory and experiment for the strongly varying electric dipole moments as a function of mass for {sup 142-141}Ba. In odd-A {sup 142}Ba and odd-Z {sup 140}La, we observe parity doublets, two pairs of positive and negative parity bands with opposite spins. In {sup 145}La a strong coupled ground band with symmetric shape coexists with the asymmetric octupole shape which stabilizes above about spin 19/2. In {sup 145,147}La a strong reduction in E2 strength around 25/2 from band crossing is observed. The isotope {sup 109}Mo was identified and a new region of stable uctpole deformation is identified in {sup 107,108}Mo centered around N = 64-66 as earlier predicted. This is the first case of stable uctpole deformation involving only one pair of orbitals.
Date: May 18, 1998
Creator: Gore, P.M.; Hamilton, J.H.; Hwang, J.K.; Jones, E.F.; Peker, L.K.; Ramayya, A.V. et al.
Partner: UNT Libraries Government Documents Department

Report of the 2005 Snowmass Top/QCD Working Group

Description: This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the t tbar threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings are reviewed. New results concerning the potential of a 500 GeV e+e collider for measuring Wtb couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a gamma gamma collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.
Date: January 17, 2006
Creator: Juste, A.; Kiyo, Y.; Petriello, F.; Teubner, T.; Agashe, K.; Batra, P. et al.
Partner: UNT Libraries Government Documents Department

Orientation-dependent critical currents in Y sub 1 Ba sub 2 Cu sub 3 O sub 7-x epitaxial thin films: Evidence for intrinsic flux pinning

Description: For YBCO epitaxial thin films the basal plane transport critical current density J{sub c}, flowing perpendicular to an applied magnetic field H, depends sensitively on the orientation of the crystal with respect to H. In particular, J{sub c} is sharply peaked and greatly enhanced when H is precisely parallel to the copper-oxygen planes. Experiments on a series of epitaxial monolithic and superconductor-insulator multilayer thin films provide clear evidence that the enhancement is a bulk, rather than surface or thin sample, phenomenon. Measurements of the orientation dependence are presented and compared with a model of intrinsic flux pinning'' by the layered crystal structure.
Date: January 1, 1990
Creator: Christen, D.K.; Klabunde, C.E.; Feenstra, R.; Lowndes, D.H.; Norton, D.P.; Budai, J.D. et al.
Partner: UNT Libraries Government Documents Department

Nuclear shape and structure in neutron-rich 110,111Tc

Description: The structure of Tc nuclei is extended to the moreneutron-rich regions based on measurements of prompt gamma rays from thespontaneous fission of 252Cf at Gammasphere. The level scheme of N=67neutron-rich (Z=43) 110Tc is established for the first time and that of111Tc is expanded. The ground-state band of 111Tc reaches theband-crossing region and the new observation of the weakly populatedalpha = -1/2 member of the band provides important information ofsignature splitting. The systematics of band crossings in the isotopicand isotonic chains and a CSM calculation suggest that the band crossingof the gs band of 111Tc is due to alignment of a pair of h11/2 neutrons.The best fit to signature splitting, branching ratios, and excitations ofthe ground-state band of 111Tc by RTRP model calculations result in ashape of epsilon2 = 0.32 and gamma = -26 deg. for this nucleus. Itstriaxiality is larger than that of 107Tc, to indicate increasingtriaxiality with increasing neutron number. The identification of theweakly-populated "K+2 satellite" band provides strong evidence for thelarge triaxiality of 111Tc. In 110Tc the four lowest-lying levelsobserved are very similar to those in 108Tc. At an excitation of 478.9keV above the lowest state observed, ten states of a delta I = 1 band areobserved. This band is very analogous to the delta I = 1 bands in106,108Tc, but it has greater signature splitting at higherspins.
Date: February 2, 2006
Creator: Luo, Y.X.; Hamilton, J.H.; Rasmussen, J.O.; Ramayya, A.V.; Stefanescu, I.; Hwang, J.K. et al.
Partner: UNT Libraries Government Documents Department

Shape trends and triaxiality in neutron-rich odd-mass Y and Nbisotopes

Description: New level schemes of Y and Nb isotopes are proposed based on measurements of prompt gamma rays from 252Cf fission at Gammasphere. Shape trends regarding triaxiality and quadrupole deformations are studied.
Date: September 28, 2004
Creator: Luo, Y.X.; Rasmussen, J.O.; Gelberg, A.; Stefanescu, I.; Hamilton, J.H.; Ramayya, A.V. et al.
Partner: UNT Libraries Government Documents Department

Level structure of 141Ba and 139Xe and the level systematics of N=85 even-odd isotones

Description: New level schemes of {sup 141}Ba and {sup 139}Xe are proposed from the analyses of spontaneous-fission gamma data from our {sup 252}Cf spontaneous fission Gammasphere runs of 1995 and 2000. By analogy with the N = 85 even-odd isotones {sup 149}Gd, {sup 147}Sm, and {sup 145}Nd, spins and parities were assigned to the observed excited states in {sup 141}Ba and {sup 139}Xe. It appears that spherical shell model neutron excitations plus octupolephonons are an appropriate basis at the lower end of the bands. Going to higher spins it is clear that the soft rotor involving valence protons as well as neutrons becomes increasingly important in the configurations. Level systematics in the N = 85 even-odd isotones from Gd(Z=64) through Te(Z=52), are discussed. The excitation systematics and smooth trends of the analogous levels support the spin and parity assignment for excited levels observed in {sup 141}Ba and {sup 139}Xe. The level systematics and the comparison with neighboring even-even isotopes indicate that quadrupole and octupole collectivity play roles in {sup 141}Ba and {sup 139}$Xe. From Gd(Z=64) through Te(Z=52), increasing excitation energies of the 13/2{sup +} states and lowering relative intensities of the positive parity bands in the N = 85 even-odd isotones may indicate that the octupole strength is becoming weaker for the isotones when approaching the Z = 50 closed shell.
Date: January 31, 2002
Creator: Luo, Y.X.; Rasmussen, J.O.; Hamilton, J.H.; Ramayya, A.V.; Hwang, J.K.; Beyer, C.J. et al.
Partner: UNT Libraries Government Documents Department