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  • 1
    ISSN: 0894-9166
    Keywords: mixed BEM / FEM formulation ; fundamental solution ; free vibration ; bodies of revolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this paper the functionu=Ψrsinθ in cylindrical coordinates (r,θ,z) is introduced into the equation for free torsional vibration of bodies of revolution (whereΨ=v / r represents the angle of twist). With the static fundamental solution (−1 /R) a mixed BEM / FEM equation is derived. The domain integral term in the equation is discretized by Serendipity elements instead of commonly used constant value finite elements in the literature. The equation is an algebraic eigenvalue one. The dynamic fundamental solution (e 1λR /R) is also used for deriving the other mixed BEM / FEM equation. An appropriate iterative solution procedure is described. An algebraic eigenvalue equation can be obtained and its solution accuracy is almost interior meshing independent. A number of examples are studied. The results show the good economy and high accuracy of the algorithms proposed.
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  • 2
    ISSN: 1600-5368
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In the title compound, C21H16N2O, the molecule is nearly planar, with a dihedral angle of 11.2 (1)° between the benzaldehyde and fluorene moieties. The attached methoxy group makes an angle of 3.6 (4)° with the benzaldehyde moiety.
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  • 3
    ISSN: 1600-5368
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Schiff base ligand in the title complex, [Ni(C15H22N3S2)2], lost a proton from its tautomeric thiol form and coordinated to Ni(II) via the mercapto S and β-N atoms. The geometry around the Ni atom is square planar with two equivalent Ni—N and Ni—S bonds. The two phenyl rings and the coordination moieties are in one plane forming an extensive electronic delocalization system. The structure is governed by C—H...S and C—H...N hydrogen bonds, leading to the formation of centrosymmetric dimers.
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Social gliding motility in Myxococcus xanthus depends on the presence of Type IV pili. To begin to examine the role of pili in social motility, 17 mutants were identified which had lost social motility, but still expressed pili. Four of these mutants carry point mutations which mapped to a locus upstream of the recently identified pilS, pilR, and pilA genes. Sequencing of this locus revealed a gene with homology to pilT from Pseudomonas aeruginosa. Sequencing of the four point mutations revealed that they occurred within the M. xanthus pilT locus. A markerless deletion within M. xanthuspilT, similar to the four point mutations, disrupted social gliding behaviour but did not interfere with pilus formation or pilus-dependent cell–cell agglutination. Using time-lapse videomicroscopy, residual social motility was observed in dsp− strains (known to be deficient in fibril but not pilus production); this was not observed in a ΔpilTdsp− double mutant. Two genes flanking pilT were also sequenced, and found to have homology to pilB and pilC from P. aeruginosa. Markerless deletions within these genes caused both pilus and social-motility defects. These results indicate that M. xanthuspilB and pilC are required for pilus biogenesis, while pilT is required for assembled pili to play their role in social motility. Thus, pilB, pilT, pilC, pilS, pilR and pilA form a contiguous cluster of pil genes required for social motility.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 559-564 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive deposition epitaxial growth of iron silicides on Si(110) has been investigated by in situ observation of reflection high-energy electron diffraction. The formation of several phases of iron silicides: simple cubic cursive-epsilon-FeSi, β-FeSi2, γ-FeSi2, and/or FeSi1+x (0≤x≤1) in a CsCl structure have been observed and their crystallographic orientations have been identified. By depositing Fe at 600 °C and annealing at 730 °C for 60 min, β-FeSi2 is formed in islands with facet planes β-FeSi2(1¯00)//Si(221) and β-FeSi2(1¯00)//Si(221¯), and a base plane β-FeSi2(4¯10)//Si(110). The peculiar β-FeSi2(4¯10) plane acts as a matching face because of its better lattice matching to the Si(110) surface than the other planes. © 1996 American Institute of Physics.
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We have evaluated GABAA receptor function during treatment of 1-methyl-4-phenylpridinium (MPP+) using patch-clamp perforated whole-cell recording techniques in acutely dissociated dopaminergic (DAergic) neurons from rat substantia nigra compacta (SNc). γ-Aminobutyric acid (GABA), glutamate or glycine induced inward currents (IGABA, IGlu, IGly) at a holding potential (VH) of −45 mV. The IGABA was reversibly blocked by the GABAA receptor antagonist, bicuculline, suggesting that IGABA is mediated through the activation of GABAA receptors. During extracellular perfusion of MPP+ (1–10 μm), IGABA, but neither IGlu nor IGly, declined (termed run-down) with repetitive agonist applications, indicating that the MPP+-induced IGABA run-down occurred earlier than IGly or IGlu under our experimental conditions. The MPP+-induced IGABA run-down can be prevented by a DA transporter inhibitor, mazindol, and can be mimicked by a metabolic inhibitor, rotenone. Using conventional whole-cell recording with different concentrations of ATP in the pipette solution, IGABA run-down can be induced by decreasing intracellular ATP concentrations, or prevented by supplying intracellular ATP, indicating that IGABA run-down is dependent on intracellular ATP concentrations. A GABAA receptor positive modulator, pentobarbital (PB), potentiated the declined IGABA and eliminated IGABA run-down. Corresponding to these patch-clamp data, tyrosine hydroxylase (TH) immunohistochemical staining showed that TH-positive cell loss was protected by PB during MPP+ perfusion. It is concluded that extracellular perfusion of MPP+ induces a functional run-down of GABAA receptors, which may cause an imbalance of excitation and inhibition of DAergic neurons.
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Heterologous expression of functional, nicotinic acetylcholine receptors (nAChR) in mammalian cells has been difficult to achieve or optimize, even for nAChR containing only one kind of subunit. In this study, we determined effects of lowered temperature or of exposure to the protein synthesis inhibitor cycloheximide (CHX) on cell surface expression of homomeric α7-nAChR in transfected SH-EP1 human epithelial cells. We found that incubation of cells for 2 days at 25°C or in the presence of 0.5–2 μg/mL of CHX caused ∼four- or ∼eight-fold increases, respectively, in surface binding sites for 125I-labeled α-bungarotoxin (I-Bgt). These increases were accompanied by increases in peak whole-cell current responses to nicotinic agonists. Either treatment lowered protein synthesis and cell proliferation, but experiments using puromycin indicated that a reduction in protein synthesis or cell proliferation per se was not sufficient to increase surface binding. I-Bgt binding to whole-cell membrane pools increased in response to either treatment, suggesting that the increase in surface binding was due, at least in part, to an increase in intracellular receptor levels. The cyclophilin inhibitor cyclosporin A reduced surface expression in untreated as well as CHX- or 25°C-treated cells. The results suggest practical means for increasing cell surface and functional expression of α7-nAChR. Although these effects are not simply due to protein synthesis inhibition or reduced cell proliferation, they do involve an increase in intracellular receptor pool size.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2375-2395 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional theory of vorticity dynamics on an incompressible viscous and immiscible fluid–fluid interface, or interfacial vorticity dynamics for short, is presented as a counterpart of the vorticity dynamics on an arbitrarily curved rigid wall [J. Fluid Mech. 254, 183 (1993)]. General formulas with arbitrary Reynolds numbers Re are derived for determining (1) how much vorticity exists on an interface S, (2) how much vorticity is created from S and sent into the fluid per unit area in per unit time, and (3) the force and moment acted on a closed interface by the created vorticity thereon. The common feature and fundamental difference between interfacial vorticity dynamics and its rigid-wall counterpart are analyzed. In particular, on a free surface, the primary driving mechanism of vorticity creation is the balance between the shear stress (measured by tangent vorticity) and the tangent components of the surface-deformation stress alone, which results in a weak creation rate of O (Re−1/2) at large Re. Therefore, the exact form of the theory with its full complexity is of importance mainly at low Reynolds numbers, especially in understanding the small-scale coherent structures of interfacial turbulence. The vorticity creation rate at high-Re approximations, including an interfacial boundary layer of finite thickness and the limit of Re→∞ (the so-called Euler limit), is also studied, both allowing for a rotational inviscid outer flow. While for the former this leads to a generalization of Lundgren's theory [in Mathematic Aspects of Vortex Dynamics, edited by R. E. Caflish (SIAM, Philadelphia, PA, 1989), pp. 68–79] and amounts to solving a linear boundary-layer problem, for the latter the creation rate can be directly obtained from an inviscid solution, leading to a dynamic evolution equation of interfacial vortex sheet. In three dimensions, a vortex sheet may bifurcate into a normal vorticity field, upon which the dependence of the sheet velocity is determined. A few examples are examined to illustrate different aspects and approximation levels of the general theory. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 627-635 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In Reynolds-average Navier–Stokes equation it is the divergence of Reynolds stress tensor, i.e., the turbulent force, rather than the tensor itself, is to be simulated and partially modeled. Thus, directly working on turbulent force could bring significant simplification. In this paper a novel exact equation for incompressible turbulent force f is derived: (∂/∂t −ν∇2)f=∇⋅S, where ν is the molecular viscosity and all source terms in tensor S to be modeled are vortical. The dominant mechanism is the advection and stretching (with an opposite sign) of a "pseudo-Lamb vector" by fluctuating velocity field. No coupling with pressure is involved. The equation follows from a study of the mean fluctuating Lamb vector and kinetic energy, which constitute the turbulent force. Both constituents are governed by the same kind of equations as f. This innovative turbulent-force equation is similar to Lighthill's acoustic analogy and naturally calls one's attention to studying the vortical sources of turbulent force. The methodology described here may lead to turbulence models which provide more complete treatment than that of two-equation models, but relatively easier computation than that of second-order closures. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 503-505 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that the dissipation rate of a Newtonian fluid with constant shear viscosity has three constituents from dilatation, vorticity, and surface strain. The last one, being associated with the most complicated manners of fluid deformation, only contributes to the change of internal energy but not that of kinetic energy. The distinction of these dissipation constituents is used to identify typical compact flow structures at high Reynolds numbers, such as shock waves, thin vortex layers, and filaments. This identification is of particular interest in studying turbulence structures. We then cast the incompressible version of the simplified kinetic-energy transport equation to a novel form, which is free from the work rate done by surface stresses but in which the full dissipation reenters. This result is of relevance to the physical routes via which turbulent energy is transferred to small scales. © 1999 American Institute of Physics.
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