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  • American Institute of Physics (AIP)  (15)
  • Nature Publishing Group  (4)
  • Rio de Janeiro: Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Departamento de Economia
  • 2005-2009
  • 1990-1994  (19)
  • 1965-1969
  • 1945-1949
  • 1993  (19)
Collection
Publisher
Years
  • 2005-2009
  • 1990-1994  (19)
  • 1965-1969
  • 1945-1949
Year
  • 1
    Electronic Resource
    Electronic Resource
    A spectrometer for the measurement of reflectance-difference spectra (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2147-2152 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a spectrometer (visible-ultraviolet photon energy range) for the measurement of reflectance-difference spectra of cubic semiconductors. The spectrometer employs a photoelastic modulator to modulate the polarization of the light incident on the sample and allows for a simple procedure to correct the measured spectra for parasitic components associated with such modulation. The instrument reported has a higher throughput than more conventional setups. To illustrate the spectrometer performance we report on reflectance-difference spectra of (001) oriented GaAs single crystals doped with silicon donors at a level of 1018/cm3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143952
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic properties of a novel molecular-based magnetic compound containing a copper (II) monomer, a copper (II) dimer, and a ladder-like copper (II) chain (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1918-1921 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent results concerning synthetic, structural, and magnetic work on 3,4,9,10-perylenetetracarboxylic acid complexes of copper (II) are discussed. To date, the Cu(II)/PTCA/dien system has yielded two compositionally different crystalline products. Compound 1, [Cu3(dien)3(PTCA)(H2O)3](ClO4)22H2O represents the extremely rare case of three different molecular complexes of Cu(II), bound to the same ligands but with different stoichiometries, in the same compound. The magnetic lattice is comprised of three molecular substructures: complex 1a is a monomeric cation, [Cu(dien)(H2O)2]2+; complex 1b is a charge-neutral dimer, [Cu2(dien)2-(PTCA)(H2O)2]; and complex 1c a charge-neutral, infinite ladder-like chain structure, ∞1[Cu2(dien)2(PTCA)]n. Single crystal x-ray analysis of compound 2, [Cu2(dien)2(PTCA)(H2O)2]12H2O, reveals its structure simply consists of isolated, neutral dimers similar in structure to complex 1b. Magnetic susceptibility data in the temperature range 1.7–300 K shows the dimeric unit in 2 to be a weakly exchange-coupled antiferromagnetic dimer (−0.6 cm−1) and suggests that exchange interactions are indeed propagated through the PTCA anion over a Cu.....Cu separation of 15.7 A(ring). This result, in addition to the expected Curie paramagnetism of monomer 1a, affords the ladder-like chain 1c to be characterized as a chain of antiferromagnetically exchange-coupled ferromagnetic dimers (+12 cm−1). Long range ordering is not observed down to 1.7 K. Compound 1 is the first example of a molecular-based magnetic material that contains three different homonuclear magnetic molecules; a monomer, a dimer, and a ladder-like chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354774
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis, crystal structure, and magnetic properties, of a Cu(II) solid state compound derived from the 3,4,9,10-perylenetetracarboxylate anion and diethylenetriammine (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5397-5397 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several strategies have been used to develop novel magnetic materials. One of these is the simultaneous use of at least two different ligands, one an oxygen donor and the other a nitrogen donor. With this approach, using the optically interesting oxygen donor, 3,4,9,10-perylenetetracarboxylate anion (petca), and the tridentate nitrogen donor ligand, diethylenetriamine (dien), we recently reported1 the synthesis of the solid state Cu(II) compound, [Cu5(dien)5(petca)2H2O4] (ClO4)2⋅2H2O (1). This compound contains three different copper species, a chain [Cu2 (dien)2(petca)n, a dimer [Cu2(dien)2(petca)(H2O)2] and a monomer [Cu(dien)(H2O)2] and several exchange pathways. We wish to report, that the dimeric units in 1 have been isolated. The structure of the compound [Cu2(dien)2(petca)H2O)2]⋅13H2O (2), has been determined by an x-ray single-crystal diffraction study. Two different dimers are present in the unit cell: isolated dimer units, surrounded by water molecules; and dimers connected through hydrogen bonds in a way that resembles the chains in 1. In both cases, the Cu(II) ion is coordinated to one oxygen from the petca anion, the three nitrogen atoms of the dien, and a water molecule, in a nearly square planar geometry. The magnetic properties of this compound relate to these structural features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353693
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of substrate preparation on smectic liquid crystal alignment: A structural study (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3299-3304 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Octylcyanobiphenyl, a bilayer smectic A liquid crystal at room temperature, was deposited on gratings, grids, and flat surfaces, and was studied using high-resolution x-ray scattering at shallow angles of incidence. One surface of the film was in contact with air and the other was in contact with the glass or silicon substrate, which had been treated with one of two different silane solutions. At the air interface, surface tension forces caused the liquid crystal molecules to align perpendicularly with respect to the plane of the substrate. Competing with the liquid crystal–air interface, which is a strong aligner, a grating at the liquid crystal–substrate interface can produce distortions in the smectic layering which results in excess elastic energy and favors alignment parallel to the substrate and the grooves. Our results show that in films less than ∼30 μm thick, the homeotropic orientation was maintained throughout the film due to the constraint of perpendicular alignment at the air interface. However, for thicker films on gratings, Bragg scattering from molecules lying parallel to the grooves was observed. The free-air surface was thus the strongest aligning force, followed by the surface topology, while surface anchoring was not found to play a role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352978
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  • 5
    Electronic Resource
    Electronic Resource
    Pseudospectral double excitation configuration interaction (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7081-7085 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a pseudospectral formulation of the single reference, closed shell double excitation configuration interaction method using a generator state self-consistent electron pair approach. The method scales as O(n2N3), compared to the conventional scaling of O(n2N4+n3N3). In no case tested does the pseudospectral energy differ by more than 0.35 mhartree from the conventional result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464751
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  • 6
    Electronic Resource
    Electronic Resource
    Erratum: Pseudospectral full configuration interaction [J. Chem. Phys. 97, 1876 (1992)] (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4238-4238 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466235
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  • 7
    Electronic Resource
    Electronic Resource
    Application of the time-dependent Hartree grid–configuration interaction method to the desorption of diatomic molecules from solid surfaces (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9629-9636 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study UV laser induced photodesorption of diatomic molecules from solid surfaces by means of the time-dependent Hartree grid–configuration interaction (TDHG–CI) method [J. Chem. Phys. 93, 4740 (1990)]. Converged partial and total absorption cross sections are computed in several cases to demonstrate the flexibility and accuracy of the method. Comparison to TDHG results without CI corrections is also made. The failure of simple TDHG dynamics to reproduce state resolved rotational cross sections in various strong coupling limits is noted as a justification for the development of TDHG–CI algorithms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465496
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  • 8
    Electronic Resource
    Electronic Resource
    Fiber-optic based analog signal delivery system with automatic remote control (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1182-1186 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and development of equipment for remote transducer output signal delivery is described which is based on a fiber-optic transmission-reception system employing subcarrier angular modulation for true direct current coupling, high linearity, and low noise behavior. Also, a fiber-based digital uplink for controlling the remote transmitter is presented which provides gain/attenuation programming, calibration signal insertion, battery test, and turn on/stand-by, both manual and automatically using and embedded computer controller. Performance measurements are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144115
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  • 9
    Electronic Resource
    Electronic Resource
    Gauge invariance of systems with first-class constraints (1993)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 5646-5658 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The infinitesimal canonical transformations which map solutions of the total Hamiltonian equations of motion into each other are investigated. For that, the generating function Ψ of such transformations should satisfy certain conditions. In general, Ψ is a function which depends on the coordinates, the momenta, and the Lagrange multipliers λ. However, it is shown that the requirement of independence of the function Ψ on the Lagrange multipliers is sufficient for the existence of gauge invariant transformations in the Lagrange formalism. It is shown that the condition that the Poisson brackets between Ψ and all the primary first-class constraints are a linear combination of the latter ones provides the λ independence of the function Ψ. The existence of such a λ-independent function Ψ is proven for some systems. In particular, this is proven for the relevant case of systems having primary and secondary first-class constraints. The authors suggest the possibility that for some specific systems a λ-independent generating function Ψ cannot be constructed. This conclusion concerns the systems with more than primary and secondary constraints.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530275
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  • 10
    Electronic Resource
    Electronic Resource
    The quantum relativistic harmonic oscillator: Spectrum of zeros of its wave functions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 2926-2935 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The distribution of zeros of the wave functions of the quantum relativistic harmonic oscillator is studied. An analytic approximate expression for this distribution is derived within the framework of the WKB approximation. Using potential theory techniques, it is proved that this WKB approach gives the right asymptotic distribution, which is explicitly calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530105
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