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  • Articles  (36)
  • 2000-2004  (36)
  • 1985-1989
  • 2000  (36)
  • Physics  (36)
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  • Articles  (36)
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  • 2000-2004  (36)
  • 1985-1989
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  • 1
    Electronic Resource
    Electronic Resource
    Return to equilibrium (2000)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 3985-4060 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We study an atom with finitely many energy levels in contact with a heat bath consisting of photons (blackbody radiation) at a temperature T〉0. The dynamics of this system is described by a Liouville operator, or thermal Hamiltonian, which is the sum of an atomic Liouville operator, of a Liouville operator describing the dynamics of a free, massless Bose field, and a local operator describing the interactions between the atom and the heat bath. We show that an arbitrary initial state that is normal with respect to the equilibrium state of the uncoupled system at temperature T converges to an equilibrium state of the coupled system at the same temperature, as time tends to +∞ (return to equilibrium). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.533334
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  • 2
    Electronic Resource
    Electronic Resource
    High-frequency properties of 1.55 μm laterally complex coupled distributed feedback lasers fabricated by focused-ion-beam lithography (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 325-327 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laterally complex coupled distributed feedback lasers have been fabricated by focused-ion-beam lithography on completely grown InGaAsP/InP laser structures emitting at 1.55 μm. The grating definition is based on implantation-enhanced quantum-well intermixing and wet chemical etching and allows the fabrication of complex coupled antiphase gratings without any further overgrowth step. Side-mode suppression ratios of 45 dB and bandwidths for direct modulation beyond 13 GHz were obtained for 300-μm-long devices. The lasers exhibit frequency-modulation response values lower than 200 MHz/mA and feature a low sensitivity to back-reflected light. Preliminary lifetime measurements over 7000 h continuous-wave operation at room temperature show no significant indication for long-time degradation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126965
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  • 3
    Electronic Resource
    Electronic Resource
    Water-chain clusters: Vibronic spectra of 7-hydroxyquinoline⋅(H2O)2 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1192-1203 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass- and isomer-selected S1←S0 resonant two-photon ionization and S1→S0 fluorescence spectra were obtained for the supersonically cooled 7-hydroxyquinoline⋅(H2O)2 cluster. UV/UV-holeburning measurements show that 〉98% of the spectrum is due to a single "water-chain" cluster isomer, although two different tautomers (7-keto- and 7-hydroxyquinoline), two different rotamers (cis- and trans-hydroxy), and two torsional conformers of the chain are possible. Ab initio calculations of structures and vibrations of five different tautomers/ rotamers/ conformers of this cluster are reported. These predict that the cis-7-hydroxyquinoline⋅(H2O)2 "up/down" water-chain form is the most stable cluster. The experimentally observed S0 and S1 state vibrational frequencies agree well with those calculated for this isomer. We find no evidence for either the trans-rotamer or the keto tautomer clusters. S1←S0 excitation leads to contraction of all three hydrogen-bonds along the hydrogen-bonded water chain, inducing intermolecular stretching vibrations, but no proton transfer. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480672
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  • 4
    Electronic Resource
    Electronic Resource
    Water–wire clusters: Vibronic spectra of 7-hydroxyquinoline⋅(H2O)3 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 9032-9043 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The supersonically cooled 7-hydroxyquinoline⋅(H2O)3 cluster was investigated by mass- and isomer-selected S1←S0 resonant two-photon ionization and S1→S0 fluorescence spectroscopy. UV(ultraviolet)/UV-holeburning measurements prove that a single cluster isomer is formed, although different tautomers (7-keto- and 7-hydroxyquinoline), rotamers (cis and trans) and isomers (cyclic and water–wire) are possible. Ab initio calculations of structures and vibrations of different tautomers and isomers of this cluster predict that the cis-enol-7-hydroxyquinoline⋅(H2O)3 "water–wire" cluster is the most stable species. The experimental S0 and S1 inter- and intramolecular vibrational frequencies are in good agreement with the calculated harmonic frequencies. S1←S0 excitation leads to contraction of all four hydrogen bonds along the hydrogen bonded water wire, inducing intense intermolecular stretching vibrations of the O–H(centered ellipsis)O and HO–H(centered ellipsis)N(quinoline) hydrogen bonds which terminate the water–wire. There are no spectroscopic signs of proton transfer. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319352
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  • 5
    Electronic Resource
    Electronic Resource
    Proton transfer in 7-hydroxyquinoline⋅(NH3)n solvent clusters (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 560-565 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass- and isomer-selected S1←S0 resonant two-photon ionization and S1→S0 fluorescence spectra were obtained for the supersonically cooled 7-hydroxyquinoline⋅(NH3)n clusters with n=2–16. For n=2 and 3, the absorption and emission spectra exhibit discrete and narrow bands, characteristic of nonreactive hydrogen bonded ammonia-chain clusters. For n≥4, the S1←S0 R2PI spectra are completely broadened, with an onset at (approximate)355 nm. For n=4–7, a weak fluorescence emission is observed, Stokes-shifted by (approximate)185 nm, with a maximum at (approximate)540 nm, which shows discrete structure on a broad background. From comparison to fluorescence emission observed in bulk solution, we conclude that S1 state enol→keto tautomerization occurs. For the n≥7 or 8 clusters, the fluorescence emission spectra become completely unstructured and shift to the blue, peaking at 435–450 nm. This emission indicates the occurrence of either S1-state proton transfer to the ammonia solvent cluster and formation of the 7-HQ anion, or of the ground-state intracluster enol→keto tautomerization reaction. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480548
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  • 6
    Electronic Resource
    Electronic Resource
    Long-range spin-pairing order and spin defects in quantum spin- ladders (2000)
    Springer
    The European physical journal 14 (2000), S. 439-448 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.27.+a Strongly correlated electron systems; heavy fermions - 75.10.Jm Quantized spin models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: For w-legged antiferromagnetic spin-1/2 Heisenberg ladders, a long-range spin pairing order can be identified which enables the separation of the space spanned by finite-range (covalent) valence-bond configurations into w +1 subspaces. Since every subspace has an equivalent counter subspace connected by translational symmetry, twofold degeneracy, breaking translational symmetry is found except for the subspace where the ground state of w = even belongs to. In terms of energy ordering, (non)degeneracy and the discontinuities introduced in the long-range spin pairing order by topological spin defects, the differences between even and odd ladders are explained in a general and systematic way.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00011053
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  • 7
    Electronic Resource
    Electronic Resource
    Correlation Asymptotics of Classical Lattice Spin Systems with Nonconvex Hamilton Function at Low Temperature (2000)
    Springer
    Annales Henri Poincaré 1 (2000), S. 59-100 
    Details
    ISSN: 1424-0661
    Keywords: Keywords. Correlation Function, Lattice Spin Systems, Exponential Decay, Witten Laplacian.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract. The present paper continues Sjöstrand's study [14] of correlation functions of lattice field theories by means of Witten's deformed Laplacian. Under the assumptions specified in the paper and for sufficiently low temperature, we derive an estimate for the spectral gap of a certain Witten Laplacian which enables us to prove the exponential decay of the two-point correlation function and, further, to derive its asymptotics, as the distance between the spin sites becomes large. Typically, our assumptions do not require uniform strict convexity and apply to Hamiltonian functions which have a single, nondegenerate minimum and no other extremal point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001002
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of cobalt ions on the electrochemical properties of lamellar manganese oxides (2000)
    Springer
    Ionics 6 (2000), S. 470-476 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Evaluation of Co-doping on the electrochemical properties of the sol-gel birnessite and the new lithiated manganese oxide Li0.45MnO2+δ is reported. For both compounds the synthesis of Co-doped materials via a solution technique is described. We demonstrate the interest of Co-doped structures with the selected content of 0.15 Co per mole of oxide as the optimum composition. In the case of Li0.45Mn1−yCoyO2+δ. prepared at 300 °C, a mixture of a lamellar phase and a cubic one is identified while the Co-doped birnessite appears as a single phase. A probable substitution of Mn by Co ions explains the better specific capacity of 185 mAh/g found and the excellent stability observed over 40 cycles in the voltage range 4.2−2.0 V.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02374169
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  • 9
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    High-frequency properties of 1.55 μm laterally complex coupled distributed feedback lasers fabricated by focused-ion-beam lithography (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-07-17
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Nd–Fe–B permanent magnets (thick films) produced by a vacuum-plasma-spraying process (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-05-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics
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