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  • 1
    Electronic Resource
    Electronic Resource
    Raman scattering evidence of a ferroelastic distortion at 105 K in K2ZnCl4 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6181-6186 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Raman scattering measurements on K2ZnCl4 have been performed from 20 up to 250 K in the lattice mode frequency range and in the Zn–Cl stretching mode region. The splitting of certain modes in the low-frequency region and a change in the slope of the frequency vs temperature plot at 105 K show the existence of a phase transition at this temperature. Characteristic phenomena are also observed for the phase transition near 150 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463726
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  • 2
    Electronic Resource
    Electronic Resource
    Raman scattering evidence of the incommensurability influence on stretching modes in Rb2ZnCl4 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7775-7778 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Temperature dependence of stretching modes are presented for two kinds of Rb2ZnCl4 crystals which exhibit different phase transition sequences. The comparison between both sets of results points out a special behavior of the line which appears below the normal–incommensurate phase transition. Appearance of the incommensurability is observed via the temperature dependence of certain stretching lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460163
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  • 3
    Electronic Resource
    Electronic Resource
    Anisotropic displacive to order–disorder crossover of the orientational phase transition in anthracene-tetracyanobenzene crystal (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7346-7353 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A microscopic model for the orientational instability in charge–transfer anthracene-tetracyanobenzene crystal has been proposed. The model is essentially for one degree of freedom but its properties are the same as that called the pseudospin-phonon model. The essential idea presented here is that a character of a degree of freedom is modulated by intermolecular coupling constants. For crystals, where the couplings are anisotropic, a given degree of freedom can change its character from small (angular) displacements for strong coupling directions (planes) to a discrete, pseudospin variable proper for weak coupling directions. The displacive to order–disorder crossover is seen as a change of character of a degree of freedom due to the strength (anisotropy) of intermolecular couplings. The concept has been elaborated for the anthracene-tetracyanobenzene crystal in order to solve the longstanding controversy concerning the mechanism of the orientational phase transition. The conclusion is that the instability is of a displacive type within (ab) planes of anthracene molecules, where an existing soft librational phonon acts as a modulator for interactions between the planes and triggers an order–disorder instability in the direction perpendicular to the planes. This microscopic picture can explain qualitatively experimental results for the anthracene-tetracyanobenzene crystal and is believed to be applicable to other anisotropic molecular crystals where the crossover can be regulated by pressure or impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456214
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  • 4
    Electronic Resource
    Electronic Resource
    Predictability of normal heart rhythms and deterministic chaos (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 3 (1993), S. 267-276 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evidence for deterministic chaos in normal heart rhythms is examined. Electrocardiograms were recorded of 29 subjects falling into four groups—a young healthy group, an older healthy group, and two groups of patients who had recently suffered an acute myocardial infarction. From the measured R–R intervals, a time series of 1000 first differences was constructed for each subject. The correlation integral of Grassberger and Procaccia was calculated for several subjects using these relatively short time series. No evidence was found for the existence of an attractor having a dimension less than about 4. However, a prediction method recently proposed by Sugihara and May and an autoregressive linear predictor both show that there is a measure of short-term predictability in the differenced R–R intervals. Further analysis revealed that the short-term predictability calculated by the Sugihara–May method is not consistent with the null hypothesis of a Gaussian random process. The evidence for a small amount of nonlinear dynamical behavior together with the short-term predictability suggest that there is an element of deterministic chaos in normal heart rhythms, although it is not strong or persistent. Finally, two useful parameters of the predictability curves are identified, namely, the ‘first step predictability' and the ‘predictability decay rate,' neither of which appears to be significantly correlated with the standard deviation of the R–R intervals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.165990
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  • 5
    Electronic Resource
    Electronic Resource
    Legendre polynomial approach for modeling free-ultrasonic waves in multilayered plates (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3419-3427 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modeled on the Laguerre polynomial approach used for surface acoustic waves, a formulation is presented for the study of free-acoustic wave propagation in layered plates. It uses the Legendre polynomials. Each layer can be of arbitrary anisotropy and piezoelectricity with arbitrary crystal orientation with the only restriction that the parameters of the constituent materials are close to each other. Formulations are given for open-circuit and short-circuit surfaces. Phase velocity dispersion curves, attenuations, power distributions, and field profiles are easily obtained from an algorithm easily implemented on a computer using commercial software. Numerical results are given for AlAs/GaAs multilayered structures which illustrate the capabilities of the described method. Its major advantages are: (i) in a unified formulation, all types of modes, surface modes, interface modes, and plate modes are naturally encompassed. (ii) Large values of the frequency-thickness product as compared to the values allowed by the usual methods may be dealt with. (iii) For propagation loss calculation, the usual multivariable search is avoided since the proposed method naturally works in the complex plane. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369699
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  • 6
    Electronic Resource
    Electronic Resource
    Conceptual advantages and limitations of the Laguerre polynomial approach to analyze surface acoustic waves in semi-infinite substrates and multilayered structures (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 28-34 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laguerre polynomial approach is used to calculate velocities, coupling coefficients, and field distributions of surface acoustic waves in both semi-infinite substrates and multilayered structures. Approximation used in boundary conditions for applying the Laguerre polynomial method is investigated. Effectiveness of the method to calculate the coupling coefficient is checked. Its capabilities with regard to the various types of waves are reviewed. It is shown that Laguerre polynomial method cannot be used to study leaky surface acoustic waves. For true surface acoustic waves it can, but for deep penetration, computing time becomes prohibitive. Laguerre polynomial method is interesting for true surface acoustic waves modes if decay length is of the order of one acoustic wavelength: velocities, coupling coefficient and, continuous field profiles are quite well returned. However, for multilayered structures, very dissimilar parameters of the constituent materials give rise to significant field level discontinuities at the interfaces. It is shown that the Laguerre polynomial method does not return, within reasonable computing time and required memory, these discontinuities of which multiple quantum well-based devices can take advantage. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366697
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  • 7
    Electronic Resource
    Electronic Resource
    Two true surface acoustic waves and other acoustic modes in (110) plane of Li2B4O7 substrate (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3361-3370 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface acoustic waves (SAWs) and other acoustic modes propagating in the (110) plane of Li2B4O7 are investigated by means of the effective surface permittivity (ESP). It is demonstrated that the velocity of all piezoactive SAWs, both true and pseudo, as well as surface skimming bulk waves (SSBWs) can be numerically determined by computing the ESP as a function of acoustic trace slowness. A physical phenomenon not reported has been found for certain propagation directions, namely, simultaneous existence of two true SAWs, both being of the generalized Rayleigh type, together with a pseudo SAW of similar polarization. Propagation velocity, electromechanical coupling coefficient, and decay factor have been verified and confirmed by using two different sets of material constants and two numerical methods. The obtained values and accuracy of SAWs parameters are compared, and the validity conditions discussed. The generalized slowness diagram, plotted for the sagittal plane, enables to determine the total number of SSBW and to interpret the depth penetration properties of SAW. The Nyquist diagram of the ESP is shown to be a more helpful form for identifying a pseudo SAW and for distinguishing it from a SSBW. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371214
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  • 8
    Electronic Resource
    Electronic Resource
    Microscopic model with temperature-dependent interactions for the free molecule and for the trigonal phase of benzil (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3329-3337 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecule of benzil (diphenylethanedione, C14H10O2) has been approximated by a system of rigid segments to model the lowest-frequency part of its vibrational spectrum. The interactions of internal degrees of freedom have been described with the use of phenomenological force constants. The structure of the trigonal (P3121) phase has then been modelled by means of a temperature-dependent atom–atom potential based on thermal motions of atoms. The potential gives the correct account of the softening of an E-symmetry, zone-center mode which underlies the phase transition to the low-temperature monoclinic phase (P21). The low-frequency modes at the zone center, supposed until now to be difference overtones, have been shown to result from a coupling between internal and external degrees of freedom. A low-frequency soft mode at the point M of the zone border has been found, which explains the behavior of observed peaks in diffuse x-ray scattering experiments. The values and the temperature evolution of the effective elastic constants calculated within the model are in a very good agreement with the results of ultrasonic and Brillouin scattering data. The model has been shown insufficient in the description of dielectric and piezoelectric properties of benzil. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471095
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  • 9
    Electronic Resource
    Electronic Resource
    Single-wall carbon nanotube circuits assembled with an atomic force microscope (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3014-3016 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a method to assemble single-wall carbon nanotube (SWNT) circuits using a tapping mode atomic force microscope. Nanotubes can be controllably translated, rotated, cut, and placed on top of one another by varying the tip–sample force, and the tip speed. These operations let us construct complex nanotube circuits, which are contacted using electron beam lithography. We present data from a circuit of two crossed SWNT bundles. The lower bundle behaves as two quantum dots in series, separated by a tunnel barrier created at the junction. Gate voltages can tune the number of charges on each dot and the tunnel barrier transmission. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125218
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  • 10
    Electronic Resource
    Electronic Resource
    Fabrication of nanometer size gaps in a metallic wire (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3828-3830 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a simple shadow mask method to fabricate electrodes with nanometer scale separation. Metal wires with gaps are made by incorporating multiwall carbon nanotubes or single-wall carbon nanotube (SWNT) bundles into a trilayer electron beam lithography process. The simple, highly controllable, and scaleable method has been used to make gaps with widths between 20 and 100 nm and may be extended to gap sizes of 1 nm. We report electron transport measurements of individual SWNTs bridging nanogaps with electrode spacings of approximately 20 nm. Metallic SWNTs exhibit quantum dot behavior with an 80 meV charging energy and a 20 meV energy level splitting. We observe a strong field effect behavior in short semiconducting SWNT segments, evidence for diffusive electron transport in these samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126795
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