Specific Vibrational Modes Research Articles

Tailoring the resonances of nonlinear mechanical systems

The objective of this paper is the realization of a desired frequency–amplitude dependence of a specific vibration mode of a nonlinear system. To this end, we introduce an additional nonlinearity with an a priori arbitrary mathematical form in the considered system and synthesize its restoring force through optimization. To greatly facilitate the optimization process, the restoring force is optimized piece by piece from low to large motion amplitudes. The suppression of a modal interaction and the enforcement of isochronicity are considered to demonstrate the proposed procedure.

Quality-Factor Enhancing Locations for Substrate Mounted Resonators

An important but often overlooked factor that affects the performance of a meso/micro electro mechanical vibratory sensor is the structural interaction between the sensor's resonator and the substrate on which it is mounted. Situating resonators at node points eliminates this interaction and thereby helps to improve a resonator's quality-factor for a particular mode of vibration. This paper addresses the problem of locating a single degree of freedom spring-mass resonator on a generic cantilever substrate. The loci of natural frequencies obtained when the resonator's mounting location is varied are developed, and the nodal locations are identified. Thereafter a method to obtain these locations from the characteristic equation without solving the associated eigenvalue problem is described. Lookup tables detailing the nodal locations and the corresponding natural frequencies for various resonator parameters are presented. It is found that at these special nodal locations, the magnitude of the power transmitted through anchors is negligible, which ensures minimal structural interaction between the resonator and the substrate.

Mode shape–aided cable force determination using digital image correlation

Assuming the distance between two nodal points of a specific cable vibration mode as the effective length of a pinned–pinned cable, mode shape–aided cable tension estimation methods are employed to estimate the cable force. This article proposes a framework based on digital image correlation technique for remote measurement of the dynamic displacement time history of cables in cable structures. Frequency domain decomposition technique is then used to extract the cable natural frequencies and mode shapes. Identified cable mode shapes are used along with a tensioned pinned–pinned cable model to estimate the cable force. Accuracy of the proposed methodology is investigated using the experimental data coming from a laboratory-scale test setup and hanger cables of a real-world arch bridge.

Absolute configuration and host-guest binding of chiral porphyrin-cages by a combined chiroptical and theoretical approach

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. The chiral porphyrin-cages form complexes with achiral and chiral viologen-guests and upon binding one of the axial enantiomorphs of the guest is bound selectively, as is indicated by induced-electronic-dichroism-spectra in combination with calculations. This host-guest binding also leads to unusual enhanced vibrational circular dichroism, which is the result of a combination of phenomena, such as rigidification of the host and guest structures, charge transfer, and coupling of specific vibration modes of the host and guest. The results offer insights in how the porphyrin cage-compounds may be used to construct a future molecular Turing machine that can write chiral information onto polymer chains.

Quantitative understanding of negative thermal expansion in scandium trifluoride from neutron total scattering measurements

Negative thermal expansion (NTE) - the phenomenon where some materials shrink rather than expand when heated - is both intriguing and useful, but remains poorly understood. Current understanding hinges on the role of specific vibrational modes, but in fact thermal expansion is a weighted sum of contributions from every possible mode. Here we overcome this difficulty by deriving a real-space model of atomic motion in the prototypical NTE material scandium trifluoride, ScF3, from total neutron scattering data. We show that NTE in this material depends not only on rigid unit modes - the vibrations in which the scandium coordination octahedra remain undistorted - but also on modes that distort these octahedra. Furthermore, in contrast with previous predictions, we show that the quasiharmonic approximation coupled with renormalisation through anharmonic interactions describes this behaviour well. Our results point the way towards a new understanding of how NTE is manifested in real materials.

Tailoring \u03c0-conjugation and vibrational modes to steer on-surface synthesis of pentalene-bridged ladder polymers

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. Here we introduce a synthetic protocol based on the search for specific vibrational modes through an appropriate tailoring of the π-conjugation of the precursors, in order to increase the attempt frequency of a chemical reaction. First, we design a 1D π-conjugated polymer on Au(111), which is based on bisanthene monomers linked by cumulene bridges that tune specific vibrational modes. In a second step, upon further annealing, such vibrational modes steer the twofold cyclization reaction between adjacent bisanthene moieties, which gives rise to a long pentalene-bridged conjugated ladder polymer featuring a low bandgap. In addition, high resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, thus confirming the validity of the Glidewell and Lloyd´s rules for aromaticity. This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards π-conjugated polymers with specific structures and properties.

Eco-Friendly Synthesis, Crystal Chemistry, and Magnetic Properties of Manganese-Substituted CoFe2O4 Nanoparticles.

The authors report on the effect of manganese (Mn) substitution on the crystal chemistry, morphology, particle size distribution characteristics, chemical bonding, structure, and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles (NPs) synthesized by a simple, cost-effective, and eco-friendly one-pot aqueous hydrothermal method. Crystal structure analyses indicate that the Mn(II)-substituted cobalt ferrites, Co1–xMnxFe2O4 (CMFO, x = 0.0–0.5), were crystalline with a cubic inverse spinel structure (space group Fd3m). The average crystallite size increases from 8 to 14 nm with increasing Mn(II) content; the crystal growth follows an exponential growth function while the lattice parameters follow Vegard’s law. Chemical bonding analyses made using Raman spectroscopic studies further confirm the cubic inverse spinel phase. The relative changes in specific vibrational modes related to octahedral sites as a function of Mn content suggest a gradual change of measure of inversion of the ferrite lattice at nanoscale dimensions. Small-angle X-ray scattering and electron microscopy revealed a narrow particle size distribution with the spherical shape morphology of the CMFO NPs. The zero-field-cooled and field-cooled magnetic measurements revealed the superparamagnetic behavior of CMFO NPs at room temperature. The sample with x = 0.3 indicates a lower value of blocking temperature (9.16 K) with the improved (maximum) value of saturation magnetization. The results and the structure-composition–property correlation suggest that the economic, eco-friendly hydrothermal approach can be adopted to process superparamagnetic nanostructured magnetic materials at a relatively lower temperature for practical electronic and electromagnetic device applications.

Ab Initio Approach to Femtosecond Stimulated Raman Spectroscopy: Investigating Vibrational Modes Probed in Excited-State Relaxation of Quaterthiophenes.

Femtosecond stimulated Raman spectroscopy (FSRS) is an ultrafast pump-probe technique designed to elucidate excited-state molecular dynamics by means of vibrational spectroscopy. We present a first-principles protocol for the simulation of FSRS that integrates ab initio molecular dynamics with computational resonance Raman spectroscopy. Theoretical calculations can monitor the time-dependent evolution of specific vibrational modes and thus provide insight into the nature of the motion responsible for the experimental FSRS signal, and we apply this technique to study quaterthiophene derivatives. The S1 state of two different quaterthiophene derivatives relaxes via in-phase and out-of-phase stretching modes whose frequencies are coupled to the dihedral backbone angle, such that the spectral evolution reflects the excited-state relaxation toward a planar conformation. The simulated spectra aid in confirming the experimental assignment of the vibrational modes that are probed in the existing FSRS experiments on quaterthiophenes.

Temporary anions of the dielectric gas C3F7CN and their decay channels.

We probe the transient anion states (resonances) in the dielectric gas C4F7N by the electron energy loss spectroscopy and the dissociative electron attachment spectroscopy. The vibrationally inelastic electron scattering leads to two excitation types. The first is the excitation of specific vibrational modes that are assigned with the help of an infrared spectrum of this molecule and quantum chemistry calculations. In the second type of vibrational excitation, the excess energy is randomized via internal vibrational redistribution in the temporary anion, and the electrons are emitted statistically. The electron attachment proceeds in three different regimes. The first is the formation of the parent C4F7N- anion at energies close to 0 eV. The second is a statistical evaporation of the F-atom, leading to the defluorinated anion C4F6N-. Finally, the third is dissociative electron attachment proceeding via the formation of several resonances and leading to a number of fragments. The present data explain the puzzling recent results of the pulsed-Townsend experiments with this gas.

Calibration and Balancing of Multiple Tuned Mass Absorbers for Damping of Coupled Bending-Torsion Beam Vibrations

AbstractFor damping of fully coupled beam vibrations, a three-component tuned mass absorber is proposed, consisting of two translational and a single-rotational absorber, which together target a specific vibration mode. The representation of the interaction with residual nonresonant vibration modes is consistently included by two supplemental terms in the absorber equation, calibrated by frequency matching with the full structural model for vanishing absorber damping. The absorber tuning directly includes these residual terms without approximation when the underlying modal representation is based on the vibration form with absorber masses rigidly attached to the structure. It is demonstrated that the desired damping behavior requires nonhomogeneous absorber balancing, obtained by an approximate method for the relative sizing of each absorber mass.

Synthesis and Characterization of Lithium Iron Phosphate Carbon Composite (LFP/C) using Magnetite Sand Fe3O4

Lithium Ferro Phosphate Carbon Composite (LFP/C) had been synthesized using solid-state reaction method. Magnetite sand Fe3O4 was used as Fe- source in LFP/C synthesized. Calcination temperature of the sample performed at 400, 500, and 600°C. The phase and composition of samples determined by Rietveld analysis of X-ray diffraction (XRD) pattern. The dominant identified phase at 400°C was diphosphate LiFeP2O7, and the others phases were nasicon Li3Fe2(PO4)3 and hematite Fe2O3. As the temperature getting higher the diphosphate phase LiFeP2O7 transform to nasicon Li3Fe2(PO4)3.The chemical bonds, lattice vibration and other structural features of the sample were investigated using FTIR spectroscopy in range of 1400 – 400 cm-1. Specific vibration modes in LFP-1 to LFP-3 for each bonding were shown by the high intense in certain wavenumber.

Synthesis and Characterization of Lithium Iron Phosphate Carbon Composite (LFP/C) using Magnetite Sand Fe3O4

Lithium Ferro Phosphate Carbon Composite (LFP/C) had been synthesized using solid-state reaction method. Magnetite sand Fe 3 O 4 was used as Fe- source in LFP/C synthesized. Calcination temperature of the sample performed at 400, 500, and 600°C. The phase and composition of samples determined by Rietveld analysis of X-ray diffraction (XRD) pattern. The dominant identified phase at 400°C was diphosphate LiFeP 2 O 7 , and the others phases were nasicon Li 3 Fe 2 (PO 4 ) 3 and hematite Fe 2 O 3 . As the temperature getting higher the diphosphate phase LiFeP 2 O 7 transform to nasicon Li 3 Fe 2 (PO 4 ) 3 .The chemical bonds, lattice vibration and other structural features of the sample were investigated using FTIR spectroscopy in range of 1400 – 400 cm -1 . Specific vibration modes in LFP-1 to LFP-3 for each bonding were shown by the high intense in certain wavenumber.

An innovative approach for conducting experimental modal analysis (EMA) in running harmonic for structural modal identification

Abstract This paper presents a novel approach for performing Experimental Modal Analysis (EMA) in running harmonics using the well-established Time Synchronous Averaging (TSA) technique coupled with a newly developed automatic driving impact system. A combination of an electromechanical linear solenoid and force sensor was employed to deliver periodical input on the structure. A phase cancellation strategy was adopted within TSA protocol of the output vibration signals to suppress the harmonic component for a sufficient number of block averages. Evaluation of the results obtained via the new approach with respect to conventional EMA showed high resemblance on the dynamic characteristics (i.e. natural frequency, damping ratio and mode shape). As low as 1.06 Hz shift in natural frequency and 0.07% difference in modal damping were obtained at specific mode of vibration, indicating the reliability of the proposed method to be adopted in getting the modal parameter at operational mode.

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

The coherence of collective modes, such as phonons, and their modulation of the electronic states are long sought in complex systems, which is a cross-cutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polaronic coupling, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal optical (LO) phonons, has been intensely studied yet still debated. This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes and diffusion length. Here we use the intense single-cycle THz pulse with the peak electric field up to $E_{THz}=$1000\,kV/cm to drive coherent band-edge oscillations at room temperature in CH$_3$NH$_3$PbI$_3$. We reveal the oscillatory behavior dominantly to a specific quantized lattice vibration mode at $\omega_{\mathrm{LO}}\sim$4 THz, being both dipole and momentum forbidden. THz-driven coherent dynamics exhibits distinguishing features: the room temperature coherent oscillations at $\omega_{\mathrm{LO}}$ longer than 1 ps in both single crystals and thin films; the {\em mode-selective} modulation of different band edge states assisted by electron-phonon ($e$-$ph$) interaction; {\em dynamic mode splitting} controlled by temperature due to entropy and anharmonicity of organic cations. Our results demonstrate intense THz-driven coherent band-edge modulation as a powerful probe of electron-lattice coupling phenomena and provide compelling implications for polaron correlations in perovskites.

Developing Sustainable Concrete Compaction using a Proposed Multi-vibration Technique

This study seeks to develop a sustainable construction technique based on the introduction of a specific method for improving concrete compressive strength through a proposed multi-vibration compaction method. An experimental program is performed to evaluate the effect of the proposed compaction technique on fresh silica fume concrete undergoing the initial setting. Multi-vibration intends to minimize concrete production cost because it upgrades the compressive strength of the same materials with better utilization of the vibration energy required for compaction. The collected experimental data presented assign relationships among vibration duration, vibration cycles or phases, and compressive strength upgrading of single vibrated, revibrated, and multi-vibrated specimens for analysis and discussion. This study shows that multi-vibration phases, rather than single vibration or revibration techniques, are powerful techniques for improving concrete compressive strength. The results indicated that the existence of an optimum multi-vibration mode was dominated by phase number and vibration duration and confirm the reliability vibration overall time duration recommended by ACI 309 which relates to a single vibration time limit to be considered in the case of multi vibration technique. Multi-vibration Mode 8 (subjected to three vibration phases 10, 20, and 30 sec ) has the best effect for the considered mixtures among the specific vibration modes. The maximum improvement ratio is 1.25, which is associated with the plastic mixture.

Effect of water on excited‐state double proton transfer in 7‐azaindole‐H2O complex: A theoretical study

AbstractThe dynamics of excited‐state double proton transfer (ESDPT) depending on hydrogen bonding of water molecules to the mediating water were studied at the TD‐M06‐2X/6‐31+G(d, p) level. The additional H‐bonding accepting (aW) or donating (dW) water had an effect on the mechanism of ESDPT. The double proton transfer occurred in an asynchronous but concerted protolysis or solvolysis pattern dependence on the aW or dW, respectively. The aW or dW stabilized the corresponding protolysis or solvolysis mechanism, respectively. The extra aW and dW would increase the asynchronicity of proton transfer. The bridging water in ESDPT process needed only one single H‐bond accepting or donating solvent molecule relying on the protolysis or solvolysis mechanism energetically. The specific vibrational modes in the 7AIW‐aW, 7AIW‐dW, and 7AIW‐aW‐dW complexes red‐shifted due to aW or dW.

Examinations of vibration frequency and mode shape variations of quartz crystal plates in a thermal field with strain and kinetic energies

The frequency-temperature behavior has long been analyzed to ensure the smoothness of functioning frequency of a quartz crystal resonator during the temperature variation and maintain its operations in a stable state. It has been proven that vibrations of quartz crystal plates in the thickness-shear mode can be well described by the theory of incremental thermal field in conjunction with the Mindlin plate equations, demonstrating the possibility that vibration frequencies and mode shapes can also be well predicted with the temperature as a targeted variable. By studying the vibrations with temperature changes in a given range, the frequencies and vibration modes can be calculated as a function of temperature, then they can be used in the calculations of both strain and kinetic energies for vibration mode identification or characterization based on energy proportion and changes. The trends of changes of vibration frequency, amplitudes, and energy with temperature variation make it possible for characterization the variations of vibrations and particularly the weakening or enhancement of the dominance of specific vibration modes. With such relations between vibration properties and temperature known, possible analytical tools can be developed to aid the optimal design by avoiding significant mode changes or occurrences of mode conversion.

Harvesting Delayed Fluorescence in Perovskite Nanocrystals Using Spin-Forbidden Mn d States

Optoelectronic devices based on all-inorganic perovskite systems are an energy-efficient source of lighting due to their high photoluminescence quantum yield (QY). However, dominant surface trapping continues to plague the field, despite their high defect tolerance, as evidenced by the several-fold improvements in the external quantum efficiency of perovskite nanocrystals (NCs) upon appropriate surface passivation or physical confinement between high-band-gap materials. Here, we introduce the concept of drip-feeding of photoexcited electrons from an impurity-induced spin-forbidden state to address this major shortcoming. An increased and delayed (about several milliseconds) excitonic QY, Raman spectroscopy demonstrating specific vibrational modes of the PbX6 octahedra, and density functional theory establish the electron back-transfer, signifying an efficient recombination. We term this electron back-transfer from Mn2+ to the host conduction band in this prototypical example of Mn-doped CsPbX3 (X = Cl, Br) NCs through vibrational coupling as vibrationally assisted delayed fluorescence (VADF).

Time-Domain Terahertz Spectroscopy and Solid-State Density Functional Theory Analysis of p-Nitrophenol Polymorphs

Accurate interpretations of THz vibrational spectra using density functional theory (DFT) must account for the often significant thermal expansion exhibited by molecular crystal systems. In this study, the THz spectra of two p-nitrophenol polymorphs were obtained in the spectral bandwidth of 20–95 cm−1, and solid-state DFT was used to assign the observed absorptions to specific vibrational mode characters. Computational treatments of the crystal systems involved comparison of phonon frequencies produced from both fixed- and full-unit cell geometry optimizations using a variety of functional and basis set combinations. Arbitrary frequency scaling was applied to overcome the temperature dependence of unit cell volumes and associated phonon vibrational frequencies. Fully relaxed cell geometries producing contracted cell volumes resulted in a large overestimation of THz vibrational frequencies. Employing appropriate frequency scaling factors to the computed mode frequencies allowed for proper vibrational mode assignments and enhanced the quality of spectral simulations versus fixed-cell calculations. Optimal frequency scalars in the range of 0.675 to 0.827 were determined to best reproduce the THz spectra of the p-nitrophenol polymorphs. This treatment of calculated phonon modes offers the key advantage of eliminating the temperature correlation between the crystal structure data and the THz data acquisition.

Technology Focus: Bits and Bottomhole Assemblies

Technology Focus Drilling vibration continues to preoccupy the industry’s attention, primarily because of its known detrimental effects on operational efficiency, downhole tool reliability, cycle time, and project cost. In addition to drill bits and bottomhole assemblies that have been known to initiate vibrations, researchers have identified several other conditions and factors with similar contributions to vibration initiation. Vibration challenges, if effectively addressed, will have strong positive effects on performance. The debate on whether the industry is doing enough to address vibrations continues to linger. This discussion must be put to rest because the fact is that researchers are passionately obsessed with this challenge. Presently, the focus has shifted from mere awareness to efforts that seek to establish a deeper understanding of this subject. In addition to identifying and characterizing different vibration modes, the current emphasis also delves into their sources. Knowledge gained from these efforts, particularly awareness of the different factors contributing to vibration, is driving development of holistic solutions to the challenge. Numerous initiatives, including downhole tool development for data acquisition, big data and analytics, innovative modeling techniques, and calibration and optimization of modeling results, have been deployed in this effort. Positive results with measurable effects in field operations have been achieved. In all cases, development of effective solutions must start with appropriate characterization and identification of the specific modes of vibration. Its sources must also be established so that developed solutions can be tailored for maximum effectiveness.• The holistic approach has identified borehole spiraling, especially in long lateral sections, as a primary source of vibrations and other drilling challenges. Solutions to address this challenge are currently in development. Yes, we continue to seek effective solutions to address the problem. However, we always encounter new challenges as we drill deeper into harsher environments, increase dogleg-severity requirements, and extend our departures while also drilling highly heterogeneous formations. We cannot stand still; we must keep moving ahead. Recommended additional reading at OnePetro: www.onepetro.org. SPE 196020 Case Studies: Optimizing BHA Performance by Leveraging Data and Advanced Modeling by Mojtaba Shahri, Apache, et al. SPE 194120 Mitigation of Multifrequency Stick/Slip by Zhijie Sun, Halliburton, et al. SPE 194150 Industry’s First PDC Bit Gauge Design for Improved Tracking In North American Horizontal Wells by Reed Spencer, Baker Hughes, a GE Company, et•al.