Frequency Vibrational Modes Research Articles

Nanomechanical pump-probe measurements of insulating electronic states in a carbon nanotube.

Transport measurements have been an indispensable tool in studying conducting states of matter. However, there exists a large set of interesting states that are insulating, often due to electronic interactions or topology, and are difficult to probe via transport. Here, through an experiment on carbon nanotubes, we present a new approach capable of measuring insulating electronic states through their back action on nanomechanical motion. We use a mechanical pump-probe scheme, allowing the detection of shifts in both frequency and dissipation rate of mechanical vibrational modes, in an overall insulating system. As an example, we use this method to probe the non-conducting configurations of a double quantum dot, allowing us to observe the theoretically predicted signature of nanomechanical back action resulting from a coherently tunnelling electron. The technique opens a new way for measuring the internal electronic structure of a growing variety of insulating states in one- and two-dimensional systems.

Study on the dynamic characteristics of piezoelectric inkjet print head with basic excitation methods

In this paper, the dynamic characteristics of piezoelectric inkjet print head were studied by analyzing vibration mode and resonant frequency. The modal analysis was carried out by using the multiphysics simulation software COMSOL. The vibration characteristics of print head were measured. The piezoelectric actuator and print head were excited by two basic excitation methods: fast sine sweep and white noise, respectively. The speed response was measured by the laser Doppler vibrometer and the power spectrum was obtained by using MATLAB software to obtain the first-order resonant frequency. The results show that the first-order mode is most suitable for droplet formation and ejection, and the print head in the working state is indeed under the first-order mode. The fluid–solid coupling effect has great influence on the shape and amplitude of the vibration curve. The presence of liquid lower the peak of the resonant frequency and the severe liquid motion affect the number of peaks of the resonant frequency.

Modeling and first-principles calculation of low-frequency quasi-localized vibrations of soft and rigid As–S nanoclusters

Experimental and theoretical studies were performed on Boson peak of binary AsxS100−x glasses and As–S polycrystalline composites (mixtures of glass with polycrystallites) of different compositions. Low-frequency Raman spectra of six different compositions ranging from As6S94 to As60S40, including the stoichiometric As40S60 composition, were measured in the region of 5–100 cm−1. The Fourier-transform Raman spectra of the As–S samples in the range of 50–600 cm−1 were also measured to reveal the structure of the materials at nanoscale. In addition, density functional theory calculations were performed on different As–S nanoclusters for determination of their low-frequency vibrational modes. The effect of the structural interconnection of the clusters on their vibrational mode frequencies was modeled by attaching different numbers of heavy dummy hydrogen atoms to the dangling bonds of branchy—As2+4/3S5 and 12-membered ring-like As6S6+6/2 nanoclusters. It was found that the vibrational mode frequencies have a U-shaped dependence on the level of interconnection, which correlates with experimental findings on compositional dependence of the Boson peak position in AsxS100−x glasses. The composition dependence of spectral behavior and very low-frequency features detected at low-energy side of the Boson peak in the Raman spectra of As–S samples were also analyzed and their structural origin is discussed.

Расчет динамики решетки кристаллов RFe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=- в квазигармоническом приближении

The lattice dynamic calculations and calculation of temperature dependence of the vibrational frequencies in the quasi-harmonic approximation were carried out for RFe3(BO3)4 crystals (R = Pr, Nd, Tb, Dy, Ho) in high temperature phase R32. It was obtained that in the boundary point Λ of Brillouin zone the frequency of instable vibrational mode, which associated with structural phase transition R32 -> P3121, change intensely with temperature in TbFe3(BO3)4, DyFe3(BO3)4 and HoFe3(BO3)4 crystals. The frequency of “soft” mode stabilizes with temperature increasing and takes a real value. Significant changes in phonon spectra, including in the boundary point Λ, in PrFe3(BO3)4 and NdFe3(BO3)4 crystals with temperature increasing were not observed.

Precise Measurement of Transition Frequencies of Optically Trapped 40Ca19F Molecules

The laser cooling and trapping of molecules have recently been achieved. In this paper, the possibility of precisely measuring the vibrational transition frequencies of optically trapped 40Ca19F mo...

Monte Carlo-Based Finite Element Method for the Study of Randomly Distributed Vacancy Defects in Graphene Sheets

This paper proposed an effective stochastic finite element method for the study of randomly distributed vacancy defects in graphene sheets. The honeycomb lattice of graphene is represented by beam finite elements. The simulation results of the pristine graphene are in accordance with literatures. The randomly dispersed vacancies are propagated and performed in graphene by integrating Monte Carlo simulation (MCS) with the beam finite element model (FEM). The results present that the natural frequencies of different vibration modes decrease with the augment of the vacancy defect amount. When the vacancy defect reaches 5%, the regularity and geometrical symmetry of displacement and rotation in vibration behavior are obviously damaged. In addition, with the raise of vacancy defects, the random dispersion position of vacancy defects increases the variance in natural frequencies. The probability density distributions of natural frequencies are close to the Gaussian and Weibull distributions.

Visible emission spectroscopy of jet-cooled chloro-substituted 2-methylbenzyl radicals

Four isomeric chloro-substituted 2-methylbenzyl radicals were generated from the corona discharge of 3- and 4-chloro-o-xylenes seeded in a large amount of He carrier gas using a technique of corona excited supersonic expansion coupled with a pinhole-type glass nozzle. The observed visible vibronic emission spectra were analyzed to identify the radical species produced in the discharge, from which the production of the 3-, 4-, 5-, and 6-chloro-2- methylbenzyl radicals was confirmed. In addition, we determined the D1 → D0 electronic transition energies and vibrational mode frequencies in the D0 state of the isomeric chloro-substituted 2-methylbenzyl radicals.

Vibration measurement and structural performance evaluation of a 17th century timber guest house in Japan

AbstractTo clarify the actual structural performance of an existing traditional timber structure in Japan, vibration measurements were carried out at a 17th century timber guest house (Gekkouden of Gokokuji temple). The results of the micro tremor measurement, earthquake monitoring, and analysis are discussed in this paper. For minute angles of less than 1/5000 rad, it was revealed through earthquake monitoring that each dominant frequency was strongly dependent on the vibration amplitude. It was also confirmed that the dominant frequencies of the lower vibration modes in 1/1000 rad declined to 65%‐75% of the frequencies obtained through micro tremor measurement. We propose a structural model that consists of a joint spring, column, beam, and hanging wall, based on previously reported experiments. In this study, it was clarified that the dominant frequencies determined by the analysis of the proposed structural model were in good agreement with the frequencies obtained through earthquake monitoring.

Spectroscopic identification of jet-cooled o-ethynylbenzyl radical generated in corona discharge

The vibronically excited but jet-cooled o-ethynylbenzyl radical was generated from precursor, o-ethynyltoluene seeded in a large amount of carrier gas helium using a home-made pinhole-type glass nozzle combined with the technique of corona excited supersonic expansion. The visible vibronic emission spectrum was recorded with a long-path monochromator from the corona discharge of the precursor. By analyzing the observed spectrum, we determined the electronic energy in the D1 → D0 transition and vibrational mode frequencies in the D0 electronic state of the o-ethynylbenzyl radical.

The Application of Scilab Software in Frequency Mode Simulation on the Circular Membrane

Scilab software is utilized for solving physics cases in two dimensional wave equations. This study aims to obtain a frequency mode simulation on the circular membrane so that it can display the wave pattern of each frequency mode. The method is to compare the simulation results with the normal mode circular membrane in each mode in to the theoretical calculation. The simulation has been done by utilizing the physics concept in a wave equation involving cos θ. The function of the wave equation is , assuming that r is the radius of the circle membrane. The value of the vibration frequency mode in theoretical are f<sub>01</sub> = (200.6 ± 2.0) Hz, f<sub>11</sub> = (319.7 ± 3.1) Hz, f<sub>21</sub> = (428.5 ± 4.2) Hz. By using the Scilab program application, the results obtained show that the results frequency mode simulation f<sub>01</sub>, f<sub>11</sub>, dan f<sub>21</sub> are similar to the normal mode in theoretical calculation. Thus, the simulation can be used to visualize waves of two dimensions in vibration and wave learning.

Exploiting the subharmonic parametric resonances of a buckled beam for vibratory energy harvesting

The potential of harvesting vibratory energy via a bistable beam subjected to subharmonic parametric excitations is investigated. The vibrating structure is a buckled beam with two stable equilibria separated by a potential barrier. The beam is subjected to a superposition of a static axial load beyond its buckling load and a harmonic axial excitation whose frequency is around twice the frequency of the buckled beam’s first vibration mode. A macro-fiber composite patch is attached to one side of the beam to convert the strain energy resulting from the beam’s oscillation into electricity. The study considers two regimes of excitations: an amplitude sweep and a frequency sweep. In the first regime, the amplitude of excitation is quasi-statically varied while the excitation frequency is tuned at twice the natural frequency of the first vibration mode. In the second regime, the excitation frequency is swept forward and backward around the subharmonic resonant frequency while the amplitude of excitation is kept constant. A theoretical model which governs the electromechanical coupling of the transverse vibrations of the beam and the output voltage is used to monitor the response as the excitation parameters are changed. An experimental setup is also built and a series of tests is performed to validate the theoretical findings. It is shown that, depending on the amplitude and frequency of excitation, the harvester can perform small-amplitude periodic intra-well motion, intra- and inter-well chaotic motions, as well as periodic inter-well motions. Experimental results also show that, as compared to the classical linear resonance, utilizing the sub-harmonic resonance of a bistable energy harvesters can result in a broadband frequency response.

Accuracy of XH-stretching intensities with the Deng–Fan potential

ABSTRACTOne-dimensional local mode XH-stretching (X = O, F and Cl) vibrational transition frequencies and intensities have been calculated for six small atmospheric relevant molecules. The calculations are done using Morse, Deng–Fan and numeric potentials at the CCSD(T)/aug-cc-pVTZ level of theory. Parameters of the Morse potential are found from the derivatives of the potential energy surface, with respect to the internal XH-stretching displacement coordinate, evaluated at the equilibrium geometry. Parameters of the Deng–Fan potential are obtained using the first two transition frequencies of the Morse potential. The dipole moment functions (DMFs) are represented by a sixth-order polynomial in the displacement coordinate fitted to dipole moment single points calculated with a finite field approach. Analytical matrix elements are derived and used to calculate oscillator strengths for the Morse and Deng–Fan potential. We compare calculated and experimentally determined oscillator strengths and transition frequencies, as well as displacement matrix elements of the different potentials. For the XH-stretching vibrations considered, the Deng–Fan potential predicts absorption intensities considerably better than the Morse potential.

A Method to Precise Determine the Young’s Modulus from Dynamic Measurements

Knowing the mechanical characteristics of materials is crucial for properly interpreting the results attained from experiments. In this paper, we present a method to experimentally determine the Young modulus of various materials by employing multi-modal analysis. The method, which implies finding the structures’ natural frequencies, is based on the resonance test. If the natural frequencies are known, the dynamic Young’s modulus can be extracted from the relation that expresses these frequencies in respect to the stiffness. An advanced signal processing algorithm is proposed for precise frequency evaluation. The algorithm constitutes the core of the method; herein we demonstrate how it is involved to extract the frequencies of several bending vibration modes. Tests were made by involving non-contact and impulsive excitation, respectively, the fist one providing best repeatability.

Overtone series in variable density strings

The vibrational mode frequencies of a taut string depend on the form of its mass distribution. To lowest order, deviations away from a uniform mass density that are even about the center of the string cause shifts in the overtones away from harmonic, while deviations that are odd do not. The problem of determining the overtone series for a given mass distribution is formulated and a full solution is derived for variations in the inverse mass density that are expressed as a Fourier cosine series. Variations arising from a single Fourier component predominantly shift the relative frequency of a single mode, with the 2nth Fourier component shifting the frequency of the nth mode. For a physically reasonable range of mass density variations, the frequency of a mode can typically be shifted by two semitones. Wrapped metal strings with variations in inverse mass density with different Fourier components have been fabricated, characterized, and tested. Light plucking produces overtones in agreement with the model; ordinary plucking produces incommensurate tones at sum and difference frequencies. Overtone series with several different major and minor tones are possible for variations involving more than one Fourier component.

Time-resolved step-scan FTIR difference spectroscopy for the study of photosystem I with different benzoquinones incorporated into the A1 binding site

Time-resolved step-scan FTIR difference spectroscopy has been used to study photosystem I (PSI) with plastoquinone-9 (PQ) and two other benzoquinones (2,6-dimethyl-1,4-benzoquinone and 2,3,5,6-tetrachloro-1,4-benzoquinone) incorporated into the A1 binding site. By subtracting a (P700+A1− − P700A1) FTIR difference spectrum for PSI with the native phylloquinone (PhQ) incorporated from corresponding spectra for PSI with different benzoquinones (BQs) incorporated, FTIR double difference spectra are produced, that display bands associated with vibrational modes of the quinones, without interference from features associated with protein vibrational modes.Molecular models for BQs involved in asymmetric hydrogen bonding were constructed and used in vibrational mode frequency calculations. The calculated data were used to aid in the interpretation and assignment of bands in the experimental spectra. We show that the calculations capture the general trends found in the experimental spectra.By comparing four different FTIR double difference spectra we are able to verify unambiguously bands associated with phyllosemiquinone in PSI at 1495 and 1415 cm−1. We also resolve a previously unrecognized band of phyllosemiquinone at 1476 cm−1 that calculations suggest is due in part to a C4−⃛O stretching mode.For PSI with PQ incorporated, calculations and experiment taken together indicate that the C1−⃛O and C4−⃛O vibrational modes of the semiquinone give rise to bands at 1487 and 1444 cm−1, respectively. This is very distinct compared to PSI with PhQ incorporated.From the calculated and experimental spectra, we show that it is possible to distinguish between two possible orientations of PQ in the A1 protein binding site.

Infrared spectroscopic and computational studies on formamide solutions of Ca2+. Vibrational frequencies of formamide and modes of coordination to Ca2+

Infrared spectroscopy for formamide (FA) solutions of Ca(ClO4)2 shows that both CN stretch (νCN) and CO stretch (νCO) bands of FA undergo upshifts in the presence of Ca2+. Modeling of Ca2+ in FA solutions is accomplished by quantum chemical calculations for Ca2+(FA)n (n = 1–8) complexes with Polarizable Continuum Model (PCM). The calculations indicate that bidentate Ca2+(FA)4 complexes are not consistent with the observed upshift of the νCN band, although a bidentate coordination of four FA molecules via both O and N atoms was assumed in a previous study of the same system. The experimental results are reasonably reproduced by adopting Ca2+(FA)7 and Ca2+(FA)8 complexes with a monodentate coordination of all FA molecules via the O atom. A strong coupling among the CO oscillators is shown to be responsible for the upshifts of the νCO modes despite the O atom coordination.

Analysis of Rotational–Vibrational Transition Frequencies of the HCl Molecule and Its RKR Potentials in the Ground Electronic State

The consistency of all data that have been published to date on the rovibrational line centers of the hydrogen chloride molecule HCl is analyzed. It was revealed that a number of corrections are needed because of systematic inaccuracies in the line center determination. A simultaneous fit of rovibrational transition frequencies was performed in the region from 7.4 to 18075 cm–1. The isotopically independent spectroscopic parameters for calculating rovibrational energy levels in the ground electronic state are determined. The calculated line centers are compared with the HITRAN data. The obtained spectroscopic parameters are used to calculate the turning points (rmin and rmax) of RKR-potentials of HCl isotopologues. The use of experimental data, including the highest vibrational state with Vmax = 8 that lies approximately at half the potential well depth allowed the pointwise potentials to be calculated up to Vmax = 20.

Vibrational assignments and thermodynamic properties of triclinic TATB

We have used the first-principles density-functional theory calculations to study the structural parameters, Raman/IR spectrum, electronic, vibrational, dielectric, thermodynamic and optical properties of TATB. The obtained structural parameters and the vibrational frequencies of the internal modes are consistent with previous results. The results of density of states, bond populations and Mulliken charges are used to analyze the electronic properties and chemical bondings. The vibrational frequencies (in 300–3267 cm−1) are assigned to corresponding vibrational modes. We also used the phonon density of states and quasiharmonic approximation to calculate entropy, enthalpy, heat capacity and Gibbs free energy. Further, the permittivity, refractive index, reflectivity, absorption coefficient, loss function and optical conductivity have been obtained.

Spectroscopic investigation, molecular orbital studies, frequency and solvent dependent NLO properties of (2E)-1-(4-bromophenyl)-3-phenylprop-2-en-1-one

ABSTRACTThe structure and the vibrational frequencies of the fundamental modes of the optimized geometry of (2E)-1-(4-bromophenyl)-3-phenylprop-2-en-1-one (BP3PP) have been determined. A detailed vibrational spectral analysis was carried out and the assignments of the observed bands have been proposed on the basis of potential energy distribution (PED). The UV-Vis spectral analysis has been performed by the TD – DFT method at the CAM-B3LYP/6–31 + G (d) level in gas phase and different solvent phase. Other molecular properties such as ionization energy, electron affinity, chemical potential, global hardness and electrophilicity were also calculated. The static and dynamic (frequency) average polarizability (α), first- and second- order hyperpolarizabilities (β and γ) have been investigated by using the CAM-B3LYP method. The solvent effects on the polarizability (α), first- and second- order hyperpolarizabilities (β and γ) have also been evaluated by IEFPCM model. The results display significant second- and third-order molecular nonlinearity of the title compound.

Optimal synergy between micro and nano scale: Hierarchical all carbon composite fibers for enhanced stiffness, interfacial shear strength and Raman strain sensing

Multifunctional hierarchical reinforcements are fabricated by growing multi walled carbon nanotubes (CNTs) onto carbon fibers (CFs) via chemical vapor deposition. In contrast to typical hybrid multi scale reinforced composites, the biomimetic approach of hierarchical interconnection between CFs and CNTs is followed in order to provide the dimensional confinement required for the effective synergy between the nanophase i.e. the CNTs and the micron phase i.e. the CFs. Compared to the reference CF: (i) ASTM single fiber tensile tests reveal up to 50% increase in tensile modulus together with the expected decrease in tensile strength, (ii) Single Fiber Fragmentation Tests (SFFT) reveal up to 134% enhancement for Interfacial Shear Strength (IFSS), (iii) the frequency of the Raman 2D graphitic vibrational mode with strain shows a strain sensitivity enhancement up to 87.4% and (iv) fractographic investigation shows bridging of the CNTs only for specific growth conditions, which correspond to the optimal IFSS. Furthermore, a direct correlation between the Raman strain sensitivity with the young moduli of the CF and the hierarchical CF-CNT is found, proving the efficient stress transfer from the nano to micron scale in a “composite” fiber. Overall, an optimal synergy between the reinforcing graphitic phases is achieved, attaining for the first time an equivalent stiffness for the CNT reinforcement close to theoretically obtained values. Thus, biomimetic hierarchical reinforcements provide the roadmap for the full exploitation of the unique properties of the nanophase in advanced structural composites.