Search results for "Anharmonicity"

Sound attenuation and anharmonic damping in solids with correlated disorder

2010

We study via self-consistent Born approximation a model for sound waves in a disordered environment, in which the local fluctuations of the shear modulus G are spatially correlated with a certain correlation length The theory predicts an enhancement of the density of states over Debye's omega(2) law (boson peak) whose intensity increases for increasing correlation length, and whose frequency position is shifted downwards as lg. Moreover, the predicted disorder-induced sound attenuation coefficient r(k) obeys a universal scaling law F(k) = f (ke) for a given variance of G. Finally, the inclusion of the lowest-order contribution to the anharmonic sound damping into the theory allows us to rec…

Anharmonic elasticity theory for sound attenuation in disordered solids with fluctuating elastic constants

2010

Subharmonic excitation of the eigenmodes of charged particles in a Penning trap

2004

When parametrically excited, a harmonic system reveals a nonlinear dynamical behaviour which is common to non-deterministic phenomena. The ion motion in a Penning trap -- which can be regarded as a system of harmonic oscillators -- offers the possibility to study anharmonic characteristics when perturbed by an external periodical driving force. In our experiment we excited an electron cloud stored in a Penning trap by applying an additional quadrupole r.f. field to the endcaps. We observed phenomena such as individual and center-of-mass oscillations of an electron cloud and fractional frequencies, so-called subharmonics, to the axial oscillation. The latter show a characteristic threshold b…

Conformational substates and dynamic properties of carbonmonoxy hemoglobin.

2003

Heme pocket dynamics of human carbonmonoxy hemoglobin (HbCO) is studied by Fourier transform infrared spectroscopy. The CO stretching band at various temperatures in the interval 300-10 K is analyzed in terms of three taxonomic A substates; however, in HbCO the band attributed to the A(1) taxonomic substate accounts for approximately 90% of the total intensity in the pH range 8.8-4.5. Two different regimes as a function of temperature are observed: below 160 K, the peak frequency and the bandwidth of the A(1) band have constant values whereas, above this temperature, a linear temperature dependence is observed, suggesting the occurrence of transitions between statistical substates within th…

Density functional theory (DFT) prediction of structural and spectroscopic parameters of cytosine using harmonic and anharmonic approximations

2015

The applicability of popular and efficient B3LYP hybrid density functional and medium-size Pople-type basis set in combination with computationally expensive anharmonic model to obtain more accurate theoretical structure, vibrational frequencies and GIAO NMR parameters of cytosine was tested. We report on prediction of cytosine equilibrium (R e ) and rovibrationally averaged (R v ) structures and vibrational frequencies in the gas phase and DMSO solution using density functional theory combined with 6-311++G** basis set. The harmonic and anharmonic vibrational frequencies (using second-order vibrational perturbation theory, VPT2) were critically discussed. In comparison with initial harmoni…

Local dynamics of DNA probed with optical absorption spectroscopy of bound ethidium bromide

1997

We have studied the local dynamics of calf thymus double-helical DNA by means of an "optical labeling" technique. The study has been performed by measuring the visible absorption band of the cationic dye ethidium bromide, both free in solution and bound to DNA, in the temperature interval 360-30 K and in two different solvent conditions. The temperature dependence of the absorption line shape has been analyzed within the framework of the vibronic coupling theory, to extract information on the dynamic properties of the system; comparison of the thermal behavior of the absorption band of free and DNA-bound ethidium bromide gave information on the local dynamics of the double helix in the prox…

Incoherent elastic and quasi-elastic neutron scattering investigation of hemoglobin dynamics.

2005

In this work we investigate the dynamic properties of hemoglobin in glycerolD(8)/D(2)O solution using incoherent elastic (ENS) and quasi-elastic (QENS) neutron scattering. Taking advantage of complementary energy resolutions of backscattering spectrometers at ILL (Grenoble), we explore motions in a large space-time window, up to 1 ns and 14 A; moreover, in order to cover the harmonic and anharmonic protein dynamics regimes, the elastic experiments have been performed over the wide temperature interval of 20-300 K. To study the dependence of the measured dynamics upon the protein quaternary structure, both deoxyhemoglobin (in T quaternary conformation) and carbonmonoxyhemoglobin (in R quater…

The Equilibrium Structure of Benzene

2000

The re structure of benzene is revised on the basis of high-level quantum chemical calculations at the CCSD(T)/cc-pVQZ level as well a reanalysis of the experimental rotational constants using computed vibrational corrections. A least-squares fit to empirically determined Be constants yields re(CC) = 1.3914 ± 0.0010 A and re(CH) = 1.0802 ± 0.0020 A; the latter distance is significantly shorter than the best previous estimate based on experimental data. Comparison of computed rg and rz distances with experiment as well as considerations of bond lengthening due to anharmonicity are consistent with the estimated re distance, indicating that the recommended structural parameters are very accura…

Anharmonicity-induced polaron relaxation in GaAs/InAs quantum dots

2002

The anharmonicity-induced relaxation of a polaron in a quantum dot is analyzed using the Davydov diagonalization method, including the coherent renormalization of the relevant third-order phonon interaction. The resulting relaxation time for a small GaAs/InAs self-assembled quantum dot turns out to be a few times longer than that found previously by a perturbative method.

Theory of the elliptical Penning trap

2008

Abstract An ideal “Elliptical Penning Trap” is an ideal cylindrically symmetric Penning trap with an additional electrostatic quadrupolar potential ∝ κ ( x 2 − y 2 ) . This configuration is here investigated for arbitrary strength κ of the additional potential. Aside from the decoupled axial motion the system is characterized by a generalized cyclotron and a generalized magnetron frequency. While the former depends only weakly on κ , the magnetron frequency decreases rapidly with increasing κ , vanishing at a maximum value κ max ⁡ which represents the stability limit for the magnetron motion. Magnetron orbits are elliptical, with their numerical excentricity tending toward unity as κ approa…