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  • 1
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    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6915-6926 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An optical–optical double resonance experiment has been carried out to study rotationally inelastic collisions of N2 B 3Πg v=3 by argon with initial and final state resolution. Nitrogen molecules in the metastable A state are generated by collisional excitation transfer from metastable argon atoms in a flow system. Specific B state rotational levels are prepared by pulsed pump laser excitation of isolated rotational lines in the B 3Πg–A 3Σ+u (3,0) band near 688 nm. After a short delay, a probe laser interrogates the rotational populations in the B state by fluorescence excitation in the C 3Πu–B 3Πg (0,3) band near 406 nm. Collisional transfer from incident levels in all three spin–orbit manifolds of the B state was investigated. For molecules initially in the F1 (Ω=0) manifold, a preference for conservation of fine-structure label with even ΔJ changes was observed. This propensity is very pronounced for the J=0 level but is considerably relaxed for the higher levels investigated. By contrast, inelastic collisions involving the F2 (Ω=1) and F3 (Ω=2) manifolds do not exhibit a significant propensity to conserve fine-structure label. A slight residual preference for even ΔJ changes is observed in collisional transitions within the F2 manifold. These experimental results are compared to the propensity rules expected for homonuclear 3Π rotationally inelastic collisions, both in the case (a) and (b) limits. The reduction of the predicted propensities by the transition to intermediate case coupling and "orbital-correlated'' scattering is discussed. The latter term refers to the difference potential for the N2–Ar interaction when the N2 unfilled π orbital is in or perpendicular to the triatomic plane. An unsuccessful attempt to detect collisional interelectronic transfer from the B state to the W 3Δu state by G–W laser fluorescence excitation is also reported.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2045-2050 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An optical–optical double resonance technique has been employed for the study of collisional transfer from the CN A 2Π v=8 manifold to X 2Σ+ v=12 with initial and final rotational state resolution. In contrast to our previous studies of vA=3 to vX=7 and vA=7 to vX=11 collisions, no significant even–odd oscillation in the final X state rotational populations was observed for any of the incident A state levels investigated. The absence of this alternation for vA=8 collisions is ascribed to the dependence on CN vibrational coordinate of the off-diagonal matrix element connecting the Σ and Π(A') wave functions describing the CN(A,X)–Ar interaction. For all incident vA=8 levels studied, a preference for formation of X state e vs f levels of a given N was observed.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3860-3868 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional transfer from the A 2Π state of CN has been studied with initial and final state resolution by an optical–optical double resonance technique. Specific rotational levels in the v=7 vibrational manifold of the A state of CN in a flow of several Torr of argon are prepared by pulsed laser excitation in the A–X (7,2) band. After a short time delay, a second laser probes the populations of quantum levels in this vibrational manifold and in the nearly isoenergetic v=11 manifold of the X 2Σ+ state by fluorescence excitation in the overlapped B–A (8,7) and B–X (8,11) bands. The interelectronic A→X transfer rate is found to be comparable to that for purely rotational collisional transitions within the A state for all incident levels studied, regardless of whether or not they possess significant X state character, because of isolated molecule non-Born–Oppenheimer mixing. Reflecting the near homonuclear character of the CN–Ar interaction potentials, the final X state populations exhibited a significant even–odd alternation as a function of the final rotational angular momentum quantum number. These populations could be adequately fit by the sudden scaling relationship for Π→Σ cross sections derived by Alexander and Corey [J. Chem. Phys. 84, 100 (1986)].
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 7098-7105 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional transfer within the CN A 2Π v=3 vibrational manifold and to the X 2Σ+ v=7 manifold has been studied with initial and final rotational state resolution by an optical–optical double resonance technique. Despite the large energy gap between these two manifolds, the interelectronic cross sections are significant for only a relatively small range of ΔJ, and there is no observable propensity for energy resonant, large ΔJ transitions. The even–odd alternation vs N, observed previously in vA=7 collisions [N. Furio, A. Ali, and P. J. Dagdigian, J. Chem. Phys. 85, 3860 (1986)] and indicative of the near homonuclear form of the CN–Ar interaction potentials, is even more pronounced here for vA=3. The relative rate of intraelectronic and interelectronic energy transfer for the vA=3 N=6 F1f initial level was found to be comparable to that for the corresponding vA=7 level, despite the smaller Franck–Condon factor and larger energy gap to the neighboring vX=vA−4 manifold for the former.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 35 (1992), S. 2079-2100 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An infinite boundary element (IBE) is presented for the analysis of three-dimensional potential problems in an unbounded medium. The IBE formulations are done to allow their coupling with the finite element (FE) matrices for finite domains and to obtain the overall matrices without destroying the banded structure of the FE matrices. The infinite body is divided into a number of zones whose contributions are expressed in terms of the nodal quantities at FE nodes by employing suitable decay functions and performing mainly analytical integrations of the boundary element kernels. The continuity and compatibility conditions for the potential and the flux at the FE-IBE interface are developed. The relationships for the contributions of the IBE flux vectors to the FE load vectors are given. The final equations for the IBE are obtained in the usual FE stiffness-load vector form and are easily assembled with the FE matrices for the finite object. A series of numerical examples in heat transfer and electromagnetics were solved and compared with alternative solutions to demonstrate the validity of the present formulations.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 3957-3972 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A damped system eigenvalue analysis of acoustical cavities using the boundary element method is presented. The acoustic boundary element eigenproblem formulation found in the literature is extended to include sound absorption in acoustical cavities. A dissipative term is included in the eigenvalue matrix equation to account for boundary absorption. The resulting damped system eigenvalue problem is solved using a new Lanczos subspace algorithm for quadratic eigenproblems. Since the boundary element matrices are unsym-metric, the Lanczos algorithm presented is in its most general form for unsymmetric quadratic eigenprob-lems. Examples are presented to show the application of the method in computing the eigenfrequencies of acoustic cavities with sound absorption.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new comprehensive acoustic 2-D interface element capable of coupling the boundary element (BE) and finite element (FE) discretizations has been formulated for fluid-structure interaction problems. The Helmholtz equation governing the acoustic pressure in a fluid is discretized using the BE method and coupled to the FE discretization of a vibrating structure that is in contact with the fluid. Since the BE method naturally maps the infinite fluid domain into finite node points on the fluid-structure interface, the formulation is especially useful for problems where the fluid domain extends to infinity. Details of the BE matrix computation process adapted to FE code architecture are included for easy incorporation of the interface element in FE codes. The interface element has been used to solve a few simple fluid-structure problems to demonstrate the validity of the formulation. Also, the vibration response of a submerged cylindrical shell has been computed and compared with the results from an entirely finite element formulation.
    Additional Material: 10 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 343-356 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Numerous engineering problems, especially those in electromagnetics, often require the treatment of the unbounded continua. Mapped infinite elements have been developed for the solution of 3-D magnetic vector potential equations in infinite domain that may be used in conjunction with the standard finite elements. The electromagnetic field equations are written in terms of the magnetic vector potential for the infinite domain, and 3-D mapped infinite eiement formulation based on these equations is presented in detail. A series of magnetostatics and eddy current problems are solved to demonstrate the validity and efficiency of the procedure. These numerical results indicate that the combined finite-infinite element procedure is computationally much more economical for the solution of unbounded electromagnetic problems, especially when using the vector potential formulation, as the number of system equations decreases substantially compared to the finite element only procedure. The present procedure shows promise for the treatment of large practical industrial 3-D eddy current problems with manageable computer resources.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Communications in Applied Numerical Methods 7 (1991), S. 65-77 
    ISSN: 0748-8025
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new analysis technique has been developed to study the non-linear elastic mode interaction in thin-walled beam columns under ground excitation. The technique is capable of handling arbitrary cross-sectional shapes and end conditions. In the analysis of P - Δ effects in the building frames, the technique incorporates the instantaneous loss of stiffness due to local buckling of the individual plates in a rational and convenient manner. The latter is achieved via use of the finite-strip technique which is found to be extremely efficient in the local and post-local buckling analysis of prismatic plate structures. The overall behaviour is modelled by a one-dimensional finite element in which the effects of local buckling are appropriately incorporated. It is observed that moment frames lose stability at an axial load significantly lower than the static buckling load, even for moderate levels of earthquake.
    Additional Material: 12 Ill.
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