Vibrational Band Structure Research Articles

Study of the bending vibration characteristic of phononic crystals beam-foundation structures by Timoshenko beam theory

Vibration problems wildly exist in beam-foundation structures. In this paper, finite periodic composites inspired by the concept of ideal phononic crystals (PCs), as well as Timoshenko beam theory (TBT), are proposed to the beam anchored on Winkler foundation. The bending vibration band structure of the PCs Timoshenko beam-foundation structure is derived from the modified transfer matrix method (MTMM) and Bloch's theorem. Then, the frequency response of the finite periodic composite Timoshenko beam-foundation structure by the finite element method (FEM) is performed to verify the above theoretical deduction. Study shows that the Timoshenko beam-foundation structure with periodic composites has wider attenuation zones compared with homogeneous ones. It is concluded that TBT is more available than Euler beam theory (EBT) in the study of the bending vibration characteristic of PCs beam-foundation structures with different length-to-height ratios.

Effects of rotated square inserts on the longitudinal vibration band gaps in thin phononic crystal plates

Longitudinal vibration of thin phononic crystal plates with a hybrid square-like array of square inserts is investigated. The plane wave expansion method is used to calculate the vibration band structure of the plate. Numerical results show that rotated square inserts can open several vibration gaps, and the band structures are twisted because of the rotation of inserts. Filling fraction and material of the insert affect the change law of the gap width versus the rotation angles of square inserts.

Synthesis and characterization studies of MgO:CuO nanocrystals by wet-chemical method

In this report, we examine the progress in adapting these nanomaterials for several predominantly photonics device fabrication by wet-chemical method. Nanocomposite of magnesium oxide (MgO) with copper oxide (CuO) doped nanoparticles were characterized by X-ray powder diffraction (XRD) and the observed peaks are quite agreeable with the pure phase cubic structure. High-resolution transmission electron microscopic (HR-TEM) results reveal that the resultant nanopowders are porous and agglomerated with polycrystalline nano-entities. Field emission of selected-area electron diffraction (SAED) studies showed that the average size of the nanoparticles were 20nm. Photoluminescence spectra of MgO:CuO were investigated, showing emission peaks around 375nm relating to new energy levels induced by defects or defect levels generation and confocal micro-Raman images indicated that the chemical molecular vibrational band structure and morphology of the product which is spherical shaped nanoparticles with an average particle size of ∼25nm with standard deviation. The electrochemical response of MgO:CuO which is proves that the nano-copper/magnesium has high functionality due to the small size and it has higher electrochemical activity without any modifications.

Nuclear structure of N = 86 isotones of Ce, Nd, Sm and Gd

The collectivity in the low-energy spectra of N = 86 isotones of Ce, Nd, Sm and Gd is studied vis-a-vis their vibrational band structure. The energy level pattern and the E2 transition rates are compared with the predictions of the microscopic dynamic pairing plus quadrupole model plus 5DCH (Bohr-Mottelson view). The role of the Z = 64 subshell in the increase of ground band level energies with increasing Z , and the different effects on the B(E2) values are illustrated. The subshell energy gap versus the occupation of Nilsson single-particle orbits is discussed. A brief discussion of the different current microscopic collective models is also given.

Multi-phonon scattering processes in one-dimensional anharmonic biological superlattices: Understanding the dissipation of mechanical waves in mineralized tissues

The scattering of elastic waves in a one dimensional phononic (PnC) crystal composed of alternate collagen and hydroxy-apatite constituent layers is studied. These superlattices are metaphors for mineralized tissues present in bones and teeth. The collagen is treated as an open system elastic medium with water content which can vary depending on the level of stress applied. The open system nature of the collagen–water system leads to a non-linear stress–strain response. The finite difference time domain method is employed to investigate the propagation of non-linear mechanical waves through the superlattice. The spectral energy density method enables the calculation of the non-linear vibrational wave band structure. The non-linearity in the mechanical response of the collagen–water system enables a variety of multi-phonon scattering processes resulting in an increase in the number of channels for the dissipation of elastic waves and therefore for the dissipation of mechanical energy. These results provide an explanation for the relationship between bone fragility and decreased hydration.

Bending vibration band structure of phononic crystal beam by modified transfer matrix method

The bending vibration band structure of phononic crystal (PC) beam is solved by a unified formulation of the modified transfer matrix (MTM) method in this paper. The improvement of MTM method is the introduction of constitutive matrix U and matrix of derivative functions V, which standardizes and simplifies the deduction by the matrix operation. The band structure of an epoxy-aluminum PC Timoshenko beam is calculated by both MTM method and plane wave expansion (PWE) method. The results show that the present MTM method has a great advantage in the precision of the result. In addition, the formulation of transfer matrix derived from Timoshenko beam condition is a general form which is also suitable for other general beam structures just by replacing corresponding matrices.

Identification of multi-phononγ-vibrational bands in odd-Z105Nb

Background: The odd-$Z$ ${}^{105}$Nb nucleus is located in the $A=100$ neutron-rich region. The study of multi-phonon vibrational band structures is important for understanding nuclear structure in this region.Purpose: To search for multi-phonon $\ensuremath{\gamma}$-vibrational bands in ${}^{105}$Nb.Methods: The high spin states of ${}^{105}$Nb have been studied by measuring the prompt $\ensuremath{\gamma}$ rays emitted in the spontaneous fission of ${}^{252}$Cf. The data analysis is carried out using triple- and four-fold $\ensuremath{\gamma}$ coincidence methods.Results: A new level scheme of ${}^{105}$Nb is established. The yrast band has been confirmed, and three new collective bands have been identified. Compared with previous results, a total of 14 new levels and 36 new $\ensuremath{\gamma}$ transitions are observed. Two bands built on 625.9 keV and 1231.9 keV levels are proposed as one-phonon- and two-phonon $\ensuremath{\gamma}$-vibrational bands, respectively. The evidences for supporting assignments of the multi-phonon $\ensuremath{\gamma}$-vibrational bands have been discussed. Triaxial projected shell model calculations for the $\ensuremath{\gamma}$-vibrational band structures are found in good agreement with the experimental data, thus further supporting the $\ensuremath{\gamma}$-vibrational interpretations for the experimental results in ${}^{105}$Nb.Conclusions: The one-phonon- and two-phonon $\ensuremath{\gamma}$-vibrational bands have been identified in ${}^{105}$Nb. Our results provide new data to systematically understand the characteristics of the multi-phonon $\ensuremath{\gamma}$-vibrational bands in the $A=100$ neutron-rich region.

Hybridization of surface waves with organic adlayer librations: a helium atom scattering and density functional perturbation theory study of methyl-Si(111).

The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation theory. The Rayleigh wave dispersion relation of CH3- and CD3-terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom time-of-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH3- and CD3-terminated Si(111) surfaces exhibited a nonsinusoidal line shape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface.

A modified transfer matrix method for the study of the bending vibration band structure in phononic crystal Euler beams

We introduce a modified transfer matrix (MTM) method for the calculation of the bending vibration band structure of one-dimensional phononic crystal (PC) Euler beams. A particular combination of hyperbolic functions and triangular functions is introduced to transform the state parameters of the transfer matrix (TM) method into four initial parameters, which have the explicit meanings of the displacement, rotation angle, bending moment and shear force at one beam end. The method is used to calculate the band structures of two PC Euler beams constructed from aluminum–Lucite and 100 kinds of materials. The effectiveness and high efficiency of the MTM method are demonstrated by the results. Several advantages make it a proper choice for the calculation of the bending vibration band structure of PC Euler beams.

Stark spectrum simulation for X2Y4 molecules: Application to the ν12 band of ethylene in a high-silica zeolite

The influence of an electric field of silicalite-1-zeolite on the FTIR vibrational absorption spectrum of ethylene has been simulated and compared to experimental spectra. The presence of silicalite-1 produces a global shift and a change of the structure of vibrational bands. To explain the global shift of the ν(12) band (CH(2) scissor mode) and therefore to estimate an effective average field produced by silicalite-1, Stark calculations were performed. These calculations were based on a tensorial formalism implemented in the D(2h)TDS-ST package [M. Sanzharov, M. Rotger, C. Wenger, M. Loëte, V. Boudon, and A. Rouzée, J. Quant. Spectrosc. Radiat. Transf. 112, 41 (2011)]. The value of the field obtained using tensorial formalism (8-11 GV/m) is compared with values obtained using ab initio calculations. A theory of the molecular alignment in the electric field using tensorial formalism is also developed to model the interaction of ethylene in contact with a zeolite environment.

Polymerization of C60 Fullerene Films Under Doping by Indium Atoms

The crystal structure of C60 fullerene films doped with indium was studied. Formation of new phases was observed. The lattice parameters of these phases decrease at penetration of indium atoms into the film. The character of the fine structure of vibrational bands of the high-temperature phase doped with indium evidences for amplification of molecular interaction.

High-spin structure and multiphononγvibrations in very neutron-richRu114

High-spin levels of the neutron-rich $^{114}\mathrm{Ru}$ have been investigated by measuring the prompt $\ensuremath{\gamma}$ rays in the spontaneous fission of $^{252}\mathrm{Cf}$. The ground-state band and one-phonon $\ensuremath{\gamma}$-vibrational band have been extended up to 14${}^{+}$ and 9${}^{+}$, respectively. Two levels are proposed as the members of a two-phonon $\ensuremath{\gamma}$-vibrational band. A back bending (band crossing) has been observed in the ground-state band at $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\approx}$ 0.40 MeV. Using the triaxial deformation parameters, the cranked shell model calculations indicate that this back bending in $^{114}\mathrm{Ru}$ should originate from the alignment of a pair of ${h}_{11/2}$ neutrons. Triaxial projected shell model calculations for the $\ensuremath{\gamma}$-vibrational band structures of $^{114}\mathrm{Ru}$ are in good agreement with the experimental data. However, when using the oblate deformation parameters, both of the above-calculated results are not in agreement with the experimental data.

Structure of vibrational bands of the [formula omitted] (53P1), B3[formula omitted] (53P1) transitions in CdAr and CdKr studied by optical–optical double resonance method

Isotopic and rotational structures of the (υ′,υ″)=(13,5), (14,5), (16,5) and (υ′,υ″)=(0,1)–(6,1) vibrational bands of the E3Σ+←A3Π0+ and E3Σ+←B3Σ1+ transitions in CdAr, respectively, as well as the (υ′,υ″)=(21,9) of the E3Σ+←A3Π0+ transition in CdKr were investigated using free-jet expansion beam and laser excitation. An optical–optical double resonance process was employed from the X1Σ0++ to the E3Σ+ Rydberg via the A3Π0+ or B3Σ1+ intermediate electronic state. The structure of the bands with resolved isotopic structure was analyzed including their rotational structure. Analysis and simulation of the bands provided values for vibrational and rotational characteristics of the states. The analysis extended our previous low-resolution studies performed for the E3Σ+←A3Π0+ and E3Σ+←B3Σ1+ transitions.

Fine band structure of the vibrational spectra of fullerite C60 and enhancement of intermolecular interaction in high-temperature phase

The fine structure of the fundamental vibrational bands and some combination tones of fullerite C60 in its IR absorption and reflection spectra, as well as in Raman spectra, has been studied. This structure is due to the overlapping components of Davydov and isotopic splittings and the removal of vibrational degeneracy with symmetry lowering. It is shown that for IR Fu(i) bands (i = 1–4) and low-frequency Hg(1) and Ag(1) bands in the Raman spectrum the splittings at room temperature exceed those for the low-temperature phase. The enhancement of intermolecular interaction at elevated temperatures is explained by the nonequilibrium vibrational excitation of the medium as a result of nonlinear interaction of vibrational modes and by the change in the electronic states.

Two-dimensional electronic and vibrational band structure of uniaxially strained graphene fromab initiocalculations

We present an in-depth analysis of the electronic and vibrational band structure of uniaxially strained graphene by ab initio calculations. Depending on the direction and amount of strain, the Fermi crossing moves away from the $K$ point. However, graphene remains semimetallic under small strains. The deformation of the Dirac cone near the $K$ point gives rise to a broadening of the 2D Raman mode. In spite of specific changes in the electronic and vibrational band structure the strain-induced frequency shifts of the Raman active ${E}_{2g}$ and 2D modes are independent of the direction of strain. Thus, the amount of strain can be directly determined from a single Raman measurement.

THE INFRARED SPECTRUM OF PROTONATED NAPHTHALENE AND ITS RELEVANCE FOR THE UNIDENTIFIED INFRARED BANDS

The gas phase infrared spectrum of protonated naphthalene is measured in a cold supersonic beam using mass-selected photodissociation spectroscopy and the messenger atom method. Sharp vibrational band structure is measured throughout the 800-3200 cm–1 region for comparison to the unidentified infrared bands (UIRs). Protonated naphthalene exhibits strong bands at 3.5, 6.2, 7.7, and 8.6 μm that correspond to prominent UIR features. The 6.2 μm feature provides one of the first examples in laboratory spectra for an intense vibrational band at this wavelength. It arises from an allyl-type carbon ring distortion, which is a direct consequence of the perturbation on aromatic rings resulting from protonation in the σ configuration. The 3.5 and 7.7 μm features correspond to the stretches and scissors motion of the aliphatic CH2 group, which also follow directly from protonation. Other strong bands seen at 6.6 and 6.9 μm do not coincide with the strongest UIR features. Protonated naphthalene itself is not a perfect match for the UIR spectra, but it strongly suggests that larger H+PAH species are prominent among the UIR carriers.

Detailed theoretical and experimental description of normal Auger decay in O2

The normal Auger electron spectrum of the O2 molecule is assigned in detail on the basis of ab initio valence configuration interaction (CI) wavefunctions. Potential energy curves of the ground state, the core-ionized states and the doubly charged final states are calculated and Auger decay rates are obtained with the one-centre approximation. Using the lifetime vibrational interference method, band shapes are obtained for all contributions to the Auger spectrum. The calculated Auger electron spectrum allows us to identify all features observed experimentally. Significant differences to previous assignments are reported. A quantitative simulation of the spectrum is given on the basis of a curve-fitting procedure, in which the energetic positions and intensities of the theoretical bands were optimized. Besides providing a basis for a refined analysis of the spectrum, the fit allows us to assess the accuracy of the calculation. As expected for this level of theory, the absolute accuracy of the valence CI energies is found to be about 0.3 eV. The inherent error of the one-centre transition rates is less than 5% of the most intense transition in the spectrum. The frequently questioned one-centre Auger transition rates are shown to be rather appropriate if applied with reasonable wavefunctions and if the vibrational band structure of the molecular spectrum is properly taken into account.

Lateral interactions and nonequilibrium in adsorption and desorption. Part 1. Experimental results for (2 × 2)-(3O + NO)/Ru(0 0 1)

Extending earlier vibrational spectroscopy and thermal desorption measurements on this system, its geometrical structure and its adsorption/desorption kinetics have been investigated in detail. The adsorption and desorption of NO proceed, with little influence on the 3O template, on its (2 × 2) lattice of empty hcp sites. The desorption kinetics, with splitting of the TPD spectra into two peaks, are far from the expected behavior for independent sites. Also, the vibrational band structure shows dispersion beyond dipole–dipole interactions. So, despite the quite large NO–NO distance and their screening by the O atoms, there is clear evidence for static and dynamic lateral interactions which should be extractable from the data. A qualitative analysis suggests that these interactions are due to elastic coupling between the positions and vibrations, respectively, of the O and NO adsorbates. However, quantitative conclusions cannot be drawn directly as the kinetic data cannot be interpreted in a quasiequilibrium approach, as would be the normal procedure, due to the presence of strong nonequilibrium effects. The lack of internal equilibration is presumably caused by slow diffusion. The results are sufficiently complete and detailed to justify the effort of theoretical modeling with the aim to quantitatively describe both the lateral interactions and the nonequilibrium effects.

Excitation of octupole, beta- and gamma-vibration band levels of 238U by inelastic neutron scattering

Experimental data on inelastic neutron scattering are analyzed in a Hauser–Feshbach–Moldauer approach with a coupled-channel estimates of the direct reaction contribution. For the direct excitation of the ground state rotational band levels with J π = 0 + , 2 + , 4 + , 6 + , 8 + the rigid rotator model was used, whereas for the direct excitation of members of the β-, γ- ( K π = 0 2 + , 0 3 + , 2 + ) and first octupole band ( K π = 0 − ) a soft-deformable rotator model was used. Quadrupole, octupole, hexadecapole and gamma-deformation parameters are defined by consistent analysis of excited rotational–vibrational band structures and excitation cross sections of the relevant levels. Structures evident in measured neutron emission spectra for E n ∼ 1 – 6 MeV are correlated with excitation of levels of K π = 0 − and K π = 0 2 + , 0 3 + , 2 + bands.

Aspects of nuclear physics research at iThemba LABS, South Africa

A summary of recent results of research at iThemba LABS is given. This includes high-resolution measurements of the fine structure of isoscalar giant quadrupole resonances, a new programme to measure fusion barrier distributions for reactions leading to the formation of superheavy elements, measurements of high-energy γ-rays from (p,γ) reactions using the AFRODITE array of HpGe clover detectors, and a comparison of the vibrational band structures of 160Yb, measured with the AFRODITE array, with the X(5)-β2n model. A summary of future developments is given.