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  • 1
    Digitale Medien
    Digitale Medien
    A confocal fiber-coupled single-lens theta microscope (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2956-2963 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A confocal theta microscope using a single water-immersion objective lens is described. The system is based on the Zeiss Axioplan universal microscope, such that the illumination light is coupled into, and the detected light out of, the microscope optics via optical fibers attached to the reflector slider of the microscope. Conventional wide-field, laser-scanning confocal, confocal theta, and 4Pi-confocal theta microscopy modes are available with the system. As the design can be easily adapted to other microscopes, objective lenses, and wavelengths, it allows confocal theta techniques to be implemented in many standard systems. The design constraints and specifications for the microscope are given, as well as a demonstration of its performance. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149040
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  • 2
    Digitale Medien
    Digitale Medien
    Routine Myocardial Revascularization with the Radial Artery: A Multicenter Experience (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiac surgery 13 (1998), S. 0 
    Details
    ISSN: 1540-8191
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Abstract Background: Current literature documents use of the radial artery (RA) for myocardial revascularization only as an alternative conduit in cases where the saphenous veins have been previously harvested or are unsuitable for use. Large-scale routine clinical use of the RA as the conduit of choice has not been reported. Methods: This prospective study evaluated the harvest of the RA from 933 patients and the subsequent use of the conduit as a preferred coronary artery bypass graft second only to the left internal thoracic artery in 930 of these patients. Results: Unilateral RA harvest was performed in 786 patients and 147 patients had bilateral RA harvest. A total of 1080 RAs were harvested; 214 (19.8%) originated from the dominant forearm. There was a mean of 3.30 ± 0.93 grafts per patient of which 2.43 ± 0.83 were arterial grafts. The mean number of RA grafts was 1.43 ± 0.53. Operative mortality was 2.3% with none due to the RA graft(s). There was no ischemia nor motor dysfunction in the operated hands. Thirty-two (3.4%) patients experienced transient thenar dysesthesia that resolved in 1 day to 6 weeks. Conclusions: Our results demonstrate that routine total or near total arterial myocardial revascularization may be achieved safely and effectively with the use of one or both RAs in conjunction with the internal thoracic artery.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1540-8191.1998.tb01092.x
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  • 3
    Digitale Medien
    Digitale Medien
    Switching of surface-stabilized ferroelectric liquid crystal cells by motion of defects (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1381-1387 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerical calculations are presented on both equilibrium states and switching processes of surface-stabilized ferroelectric liquid crystal cells. Defect mediated switching by Bloch walls and by disclination lines is studied in particular. Our examinations are based on an idealized bookshelf configuration of the molecules with fixed tilt angle of the director. Numerical solutions for the scalar fields both of the director twist angle and the electric potential have been determined in two spatial dimensions, assuming the fields to be constant along the third dimension. In the bulk we employ the full Frank–Oseen energy (i.e., no one-constant approximation) with electric terms added represented by a uniaxial dielectric tensor and the spontaneous polarization. On the surface the director is anchored by a Rapini–Papoular potential with medium anchoring strength. The calculations were performed in high precision with a multigrid method on an adaptive grid. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362937
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  • 4
    Digitale Medien
    Digitale Medien
    High-resolution axial and lateral position sensing using two-photon excitation of fluorophores by a continuous-wave Nd:YAG laser (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 446-448 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The change in position of fluorescent beads captured inside the focal volume of optical tweezers is monitored using fluorescence emission induced by two-photon absorption of a continuous-wave Nd:YAG laser (λ=1064 nm). The displacement of a bead due to interactions with its environment leads to a fluorescence intensity variation that is used to design a novel spatial sensor. We determine changes in the axial position of a CY3-labeled latex bead with a diameter of 1.03 μm to a precision better than 10 nm. At an intensity of 600 mW/ μm2 the two-photon bleaching rate is lower than 50% per 2000 s. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.118134
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  • 5
    Digitale Medien
    Digitale Medien
    Evaluation of a simple method for chopping Penning surface-plasma source H− beams (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1024-1027 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Accumulator rings proposed for use in high-intensity spallation-neutron sources require a chopped beam with ∼100-ns-wide particle-free gaps at 1–2 MHz rates, with fall and rise times ≤20 ns. Chopping the beam directly in the ion source may be an attractive way to provide the desired beam structure. Previous measurements showed that placing a grounded collar in the drift region just before the emission aperture lowers the e−/H− ratio in the Penning surface-plasma source H− beam. We electrically isolated the collar and biased it to modulate the extracted H− current. Positive collar bias decreases the H− beam by up to 90%. The fastest H− current fall and rise times achieved to date are 400 ns and 2 μs, respectively. The current fall time is close to the 300-ns pulser rise time. The current rise time is considerably longer than the 500-ns pulser fall time. Negative collar bias lowers the H− beam by up to 50%. Simulations indicate that the beam time structure will be preserved in transport from the ion source to the radio-frequency quadrupole entrance. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146039
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  • 6
    Digitale Medien
    Digitale Medien
    Molecular dynamics simulations of a Gay–Berne nematic liquid crystal: Elastic properties from direct correlation functions (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3098-3107 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report molecular dynamics simulations of a Gay–Berne nematic liquid crystal at constant temperature and density/pressure using the generalization of an algorithm recently proposed by Toxvaerd [Phys. Rev. E 47, 343 (1993)]. On the basis of these simulations the absolute values of the Oseen–Zöcher–Frank elastic constants K11, K22, and K33 as well as the surface constants K13 and K24 have been calculated ab initio within the framework of the direct correlation function approach of Lipkin et al. [J. Chem. Phys. 82, 472 (1985)]. The angular coefficients of the direct pair correlation function, which enter the final equations, have been determined from the computer simulation data for the pair correlation function of the nematic by combining the Ornstein–Zernike relation and the Wiener–Hopf factorization scheme. The unoriented nematic approximation has been assumed when constructing the reference state of Lipkin et al. By an extensive study of the model over a wide range of temperatures, densities and pressures, very detailed information is provided on the elastic behavior of the Gay–Berne nematic. Interestingly, it is found that the results for the surface elastic constants are qualitatively different from those obtained with the help of analytical approximations for the isotropic direct pair correlation function. For example, the values of the surface elastic constants are partly negative and an order of magnitude smaller than the bulk elasticity. The negative values of the surface constant K13 indicate on the possibility of surface instabilities of the director pattern in a thin, free standing or weakly anchored Gay–Berne nematic liquid crystal. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470268
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  • 7
    Digitale Medien
    Digitale Medien
    Density functional approach to study the elastic constants of biaxial nematic liquid crystals (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1555-1566 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A density functional theory for bulk and surface elastic constants of biaxial nematic liquid crystals is developed. It is based on a functional Taylor expansion of the free energy of a distorted biaxial nematic with respect to the one-particle distribution function. Detailed microscopic expressions for the biaxial elastic constants of bulk and surface deformations are derived by expanding further the distribution functions into symmetry-adapted Wigner matrices. The final expressions depend on generalized orientational order parameters characterizing the biaxial nematic and on expansion coefficients of the direct pair correlation function. The case where the expansions are truncated at the lowest nontrivial order with respect to the momentum index of the Wigner matrices is analyzed in detail. It gives only six distinct, nonzero bulk elastic constants. The mixed elastic constants, which measure distortions of more than one director, vanish within this approximation. As in the uniaxial case, a splay-bend degeneracy for all directors is apparent. The theory is next applied to the biaxial nematic phase recently studied by Biscarini et al. [Phys. Rev. Lett. 75, 1803 (1995)] providing numerical estimates of biaxial elastic constants for the case of thermodynamically stable biaxial ordering. It is shown that the values of the elastic constants connected with secondary directors are much lower than those associated with the primary one. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.476707
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  • 8
    Digitale Medien
    Digitale Medien
    Computer simulation studies of anisotropic systems. XXVII. The direct pair correlation function of the Gay–Berne discotic nematic and estimates of its elastic constants (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7483-7492 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Monte Carlo simulations have been performed for a discotic liquid crystal composed of Gay–Berne particles. On the basis of these simulations for the nematic phase, a subset of the spherical harmonic expansion coefficients of the direct pair correlation function (DPCF) were determined from the pair distribution function (PDF) by solving the Ornstein–Zernike (OZ) equation. This was achieved by generalizing the Wiener–Hopf factorization scheme for the numerical solution of the OZ equation. Only the expansion coefficients gl1,l2,l(r) (lα≤4) of the PDF in the laboratory frame were used when solving the OZ equation; this means that the DPCF so obtained is equivalent to that for a nematic in which the director is randomly distributed. From the DPCF, the scaled Oseen–Zöcher–Frank elastic constants K11*, K22*, and K33*, as well as the surface constant K13*, have been calculated from the subset of expansion coefficients. Generally, we find that K33*〈K11*〈K22*, in agreement with what is expected and found for discotic nematics. These results are quantitatively but not qualitatively different from those calculated with the help of analytical approximations for the the same spherical harmonic expansion coefficients of the direct pair correlation function. For example, the values of the bulk elastic constants determined via the OZ equation are about three times larger than the bulk elasticity obtained with the low density approximation. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.474988
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  • 9
    Digitale Medien
    Digitale Medien
    Erratum: "Molecular dynamics simulations of a Gay–Berne nematic liquid crystal: Elastic properties from direct correlation functions" [J. Chem. Phys. 103, 3098 (1995)] (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1295-1296 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.475326
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  • 10
    Digitale Medien
    Digitale Medien
    Intersection curves of surfaces (1997)
    Bradford : Emerald
    Engineering computations 14 (1997), S. 159-169 
    Details
    ISSN: 0264-4401
    Quelle: Emerald Fulltext Archive Database 1994-2005
    Thema: Technik allgemein
    Notizen: Deals with the development of algorithms to calculate the penetration curves of intersecting bodies. Although starting from ideas of a finite element environment where such procedures can be very helpful when generating complicated meshes, the algorithms also cover requirements of the describing geometry or computer graphics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1108/02644409710157677
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