Vibrational Frequencies Research Articles

Characteristics of Vibration Sources and Their Propagation Properties in Shield Construction

The vibration generated during the shield construction process may have an impact on the surrounding environment and structures, so it is particularly important to study the characteristics of its vibration sources and propagation properties. This paper analyzes the characteristics of the main vibration sources of the shield machine during the construction process, including the vibration frequency, amplitude distribution and so on. Through the literature research of various experts and scholars, the change rule of vibration sources under different working conditions is explored, and the propagation characteristics of vibration in the soil body are studied. This study can provide reference basis for vibration control and environmental protection during shield construction. The main conclusions are as follows: 1) the vibration during shield construction is mainly generated by the interaction between the cutter plate and the surrounding rock; 2) the frequency of vibration caused by shield construction is mainly in the range of 0~80Hz, and the amplitude is related to the nature of the excavated soil and the construction parameters; 3) the vibration tends to decrease with the increase of the distance, and the high-frequency vibration propagates faster than the low-frequency attenuation in the soil body.

Frequency identification method based on active aliasing of biprobes blade tip timing without once-per-revolution

Rotary blades are the core components of aeroengines, gas turbines and centrifugal compressors. However, due to the complexity of their work environment, monitoring their health is necessary. Blade tip timing (BTT) is an effective non-contact monitoring method for rotating blades. However, conventional BTT rely heavily on once-per-revolution (OPR) signals, which cannot be accurately obtained in complex environments. At the same time, there is a serious under-sampled problem in the BTT signal. Consequently, the extraction of blade vibration parameters from under-sampled BTT signals without relying on OPR signals remains a research hotspot. In this paper, an active aliasing method based on the vibration difference of the blade is proposed to extract the vibration frequency of the blade. In the proposed method, two BTT probes are used to calculate the blade vibration difference, and time delay estimation is used to estimate the approximate value of the natural frequency at small angle delays. Then, a series of aliasing frequencies are generated under various large angle delays. Next, the estimated natural frequency and aliasing frequency are combined to solve the exact natural frequency value. In addition, numerical simulations demonstrate the effectiveness and robustness of the method. Finally, experimental research was conducted on the BTT experimental platform. As a result, this method can accurately identify the inherent frequency of asynchronous vibration of the blades.

Imaging on surfaces with vibrational sum frequency generation microscopy

Nonlinear spectroscopy has been a valuable technique for probing surfaces for many decades. Still, in the recent past, nonlinear spectroscopy has become a useful tool for imaging monolayers on surfaces. This technique of nonlinear microscopy, more specifically sum frequency generation microscopy, provides both spectral and spatial information with varying resolution, allowing for the surface activity to be monitored and imaged. The following paper highlights the history, theory, and range of experimental advantages sum frequency generation imaging provides, focusing on specific experiments that put those advantages on display.

A thermal flexible rotor dynamic modelling for rapid prediction of thermo-elastic coupling vibration characteristics in non-uniform temperature fields

The flexible rotors within aero-engines operate in complex thermal environments, where temperature influences both the vibration frequency and amplitude. This study establishes a simple thermal flexible rotor dynamics model to rapidly and precisely predict thermo-elastic coupling vibration characteristics within a non-uniform temperature field. The thermal potential energy of the thermal rotor element is derived for any temperature field, and the motion equation is obtained using the Euler-Lagrange equation. Specifically, the generalized vector of an arbitrary point and cross-sectional non-uniform thermal stress of the thermal rotor element are considered in the thermal potential energy. The model's frequency error is <1 % under identical boundary conditions. Numerical findings indicate that thermal stress, temperature-dependent material properties, and the coupling effect collectively reduce the natural frequency (NF), with thermal stress having a more pronounced impact under axial constraint. Additionally, thermal stress and material decrease the amplitude across a broad range of rotation speeds, contrasting with thermal bending. This model will play a key role in the iterative calculation of thermo-elastic coupling vibration control due to its accuracy and simplicity.

Effect of vibration frequency on tribological characteristics of vibration-assisted micro-nano machining

Experimental findings regarding the influence of vibration frequency on the machining outcomes of vibration-assisted machining (VAM) have been inconsistent. This work aims to address this issue through both experimental and theoretical analyses. The results indicate that the circuit's frequency response is the primary source of these discrepancies. When the vibration frequency is less than half the cutoff frequency, the friction force reaches a minimum while the wear volume peaks. The solution of the heat conduction equation demonstrated that the acoustic softening effect drives the softening mechanism in nanoscale VAM. Molecular dynamics (MD) simulations further elucidate the damage mechanisms during the wear process, showing that high-frequency vibrations contribute to achieving high-precision machining.

Cyanide Linkage Isomerization Induced by Cobalt Oxidation-State Changes at a Co-Fe Prussian-Blue Analogue/ZnO Interface.

Understanding the interfacial composition in heterostructures is crucial for tailoring heterogenous electrochemical and photoelectrochemical processes. This work aims to elucidate the structure of a series of Co-Fe Prussian blue analogue modified ZnO (PBA/ZnO) electrodes with interface-sensitive vibrational sum frequency generation (VSFG) spectroscopy. Our measurements revealed, for the first time, a cyanide linkage isomerism at the PBA/ZnO interface, when the composite is fabricated at elevated temperatures. In situ VSFG spectro-electrochemistry measurements correlate the CoII→CoIII oxidation with the flip of the bridging CN ligand from Co-NC-Fe coordination mode to a Co-CN-Fe one. Photoluminescence measurements and X-ray photoelectron spectroscopy reveal that this unprecedented linkage isomerism originates from surface defects, which act as oxidation sites for the PBA. The presence of such surface defects is correlated with the fabrication temperature for PBA/ZnO. Thus, this contribution identifies the interplay between the surface states of the ZnO substrates and the chemical composition of PBA at the ZnO surface, suggesting an easily accessible approach to control the chemical composition of the interface.

Orientation Distribution of Crystalline β-Sheet Domains in Bombyx mori Silk Fiber Studied with Vibrational Sum Frequency Generation Spectroscopy.

Silk fibers have good biocompatibility and mechanical properties, which make them attractive in biomaterial applications as well as textile industries. It is believed that the superior mechanical property is associated with the crystalline β-sheet structure in the fiber; but a deeper understanding of the structure-property relationship is still needed for full exploitation of its physical properties. Especially, accurate information on hydrogen-bonding interactions within β-sheet domains at the nanoscale and their spatial distributions at the mesoscale are critically needed. In this study, we demonstrate the selective detection of crystalline β-sheet domains in Bombyx mori silk fiber using sum frequency generation (SFG) spectroscopy and its use to determine the angular distribution of the β-sheet crystallites with respect to the fiber axis. Numerical simulations of the SFG signal of the amide-I band were carried out using tensors based on the B2 symmetry of the D2 point group and compared with experimental data. This comparison found that the crystalline β-sheet domains are aligned along the fiber axis with a standard deviation of ∼27° and parallel to the fiber surface with a standard deviation of ∼5°. It was also found that the amide bands in the SFG spectra cannot be fully explained with the assumption that the crystalline β-sheet vibrations can be described with the D2 point group. Being able to monitor the amide group vibrations sensitive to both interchain hydrogen bonding and crystallite orientations, SFG analysis has a potential to unveil the structure-mechanical property relationship that may not be readily assessable with other characterization techniques.

EFFECT OF EXTERNAL HARMONIC VIBRATION ON THE FORMATION OF SOLITARY WAVES IN FALLING TWO-LAYER LIQUID FILMS

Abstract We study the influence of a low-frequency harmonic vibration on the formation of the two-dimensional rolling solitary waves in vertically co-flowing two-layer liquid films. The system consists of two adjacent layers of immiscible fluids with the first layer being sandwiched between a vertical solid plate and the second fluid layer. The solid plate oscillates harmonically in the horizontal direction inducing Faraday waves at the liquid–liquid and liquid–air interfaces. We use a reduced hydrodynamic model derived from the Navier–Stokes equations in the long-wave approximation. Linear stability of the base flow in a flat two-layer film is determined semi-analytically using Floquet theory. We consider sub-millimetre-thick films and focus on the competition between the long-wavelength gravity-driven and finite wavelength Faraday instabilities. In the linear regime, the range of unstable wave vectors associated with the gravity-driven instability broadens at low and shrinks at high vibration frequencies. In nonlinear regimes, we find multiple metastable states characterized by solitary-like travelling waves and short pulsating waves. In particular, we find the range of the vibration parameters at which the system is multistable. In this regime, depending on the initial conditions, the long-time dynamics is dominated either by the fully developed solitary-like waves or by the shorter pulsating Faraday waves.

Quantum Nuclear Dynamics on a Distributed Set of Ion-Trap Quantum Computing Systems.

Quantum nuclear dynamics with wavepacket time evolution is classically intractable and viewed as a promising avenue for quantum information processing. Here, we use IonQ, Inc.'s 11-qubit trapped-ion quantum computer, Harmony, to study the quantum wavepacket dynamics of a shared-proton within a short-strong hydrogen-bonded system. We also provide the first application of distributed quantum computing for chemical dynamics problems, where a distributed set of quantum processes is constructed using a tensor network formalism. For a range of initial states, we experimentally drive the ion-trap system to emulate the quantum nuclear wavepacket as it evolves along the potential surface generated from the electronic structure. Following the experimental creation of the nuclear wavepacket, we extract measurement observables such as its time-dependent spatial projection and its characteristic vibrational frequencies to good agreement with classical results. Vibrational eigenenergies obtained from quantum computation are in agreement with those obtained from classical simulations to within a fraction of a kilocalorie per mole, thus suggesting chemical accuracy. Our approach opens a new paradigm for studying the quantum chemical dynamics and vibrational spectra of molecules and also provides the first demonstration of parallel quantum computation on a distributed set of ion-trap quantum computers.

Solvent assisted mechanochemical synthesis, antimicrobial and antioxidant studies of Ni2+, Mn2+, Cr&lt;sup&gt;2+&lt;/sup&gt; , and Cu&lt;sup&gt;2+&lt;/sup&gt; Metal complexes of some ligands derived from l-histidine and l-alanine

Mechanochemistry enables rapid, quantitative reactions to occur at or close to 27℃. It is a one-step process that allows for reactant homogenization, product nucleation, and particle growth. These processes use little or no solvent, making them less wasteful and more environmentally friendly than solvent-based reactions. Ni2+ , Mn2+, Cr2+and Cu2+ metal ions were synthesized by grinding in an agate mortar with pestle using ligands derived from amino acids (Histidine &amp;Alanine) which were further synthesized to form complexes. The entire experiment was carried out by solvent solvent-assisted mechanochemical process and ethanol was used as liquid liquid-assisted solvent. The complexes were characterized by IR spectroscopy, U-V spectroscopy, X-ray analysis, melting point, solubility test, and conductivity measurement. The Solubility test showed that the complexes are soluble in DMSO, DMF, and ethanol and are insoluble in both hexane and tetrachloromethane. The molar conductivity values are in the range of (6.05-28.56) Ω-1cm2mol-1 ) indicating the complexes behave as non-electrolytes. IR analysis showed a vibrational frequency band observed at (1620-1625) cm-1 which is assigned to the ʋ(C=N) of the azomethine, also the new bands M=N, M=O indicate the coordination reaction between the metal and the ligands. The UV visible analysis shows various transitions, the metal complexes showed adsorption bands at λ of 420 and 575nm respectively because of the ligand-to-metal charge transfer (LMCT). The XRD analysis showed that there was a change in phase between the starting material and the product which indicate that a reaction occurred, also the nature of the spectra showed that the compounds are all crystalline. The Antimicrobial activity showed that both the complexes and the ligands have good activity against the bacterial isolates. Antioxidant activity was also tested and the compound appeared to have moderate scavenging activities compared to the reference used. The values indicated that the activities are more pronounced when coordinated with metal ions.

Research on the mechanism of impact of vibrational loads on the bearing capacity of drilling surface conductor

The surface conductor is the first structural pipe in the development of deep-water oil and gas resources, bearing the top load and suspending various casing layers. Vibrational loads can cause soil structural damage and increase pore pressure, reducing the bearing capacity of the surface conductor and threatening the safety and stability of the subsea wellhead. Based on the vertical force analysis of the surface conductor and considering the impact of vibrational loads on soil strength, a model for the vertical bearing capacity of the surface conductor was established. Utilizing the dynamic Winkler model for pile foundation horizontal dynamic response, the surface conductor was simplified as a bending beam subjected to harmonic vibration, and a control equation for lateral deformation of the surface conductor was established. The effects of vibration load amplitude and frequency on the vertical bearing capacity of surface conductors were analyzed through simulation experiments, resulting in an equivalent bearing capacity coefficient for surface conductors ranging from 0.88 to 0.97. Combining the engineering data from a deep-water block in the South China Sea, the reliability of the theoretical calculation model was validated. The analysis indicates that the maximum bending moment of the surface conductor is approximately 6m below the mudline; low-frequency(0.05Hz–0.2Hz) vibrational loads can reduce the ultimate bearing capacity of the surface conductor by 3%–11%, with the effect gradually diminishing over time. This research provides a theoretical basis for the design of surface conductor in deep-water oil and gas wells.

Poroelastic size dependent dynamics of viscoelastic microbeams connected via a viscoelastic layer

This article aims to investigate the dynamics of clamped-clamped porous viscoelastic double microbeams interconnected via a viscoelastic layer within the framework of the modified couple stress theory (MCST). Different types of porosity distributions are considered to examine the material imperfection effects on the dynamics of the double microbeam. A closed-cell porosity model is employed to model the variation of the material properties in the thickness plane. The coupled longitudinal and lateral equations of motion are derived using Hamilton’s principle. The governing equations of motion are solved using the modal decomposition method. The equations of motion are verified against the literature for simplified cases (i.e., a non-porous single viscoelastic microbeam and a porous single microbeam resting on a viscoelastic foundation). The numerical results are validated for simpler versions of the system using the finite element method and against the existing literature for a simplified case of a uniformly distributed porous double macrobeam connected via an elastic layer. Influences of viscoelasticity in the double microbeam, viscoelastic layer, porosity, and small-scale influences on the dynamics of the viscoelastic double microbeams are studied. It was found that increasing the material length-scale factor causes the complex fundamental lateral vibrational frequencies to increase for all the porosity patterns.

Copper(II) succinate: electrochemical synthesis, characterization and application as a precursor for micron-sized copper(II) oxide fibers

A coordination compound of copper(II) with succinic acid was obtained by electrochemical synthesis in media of various compositions. The samples were characterized by methods of quantitative analysis, ESR and IR spectroscopy, synchronous thermal analysis. The vibrational frequencies of copper(II) succinate were calculated by using DFT and the experimental IR spectra were interpreted on the basis of the results. Micro-sized copper(II) oxide fibers were obtained by thermal decomposition of synthesized samples. It was shown that the use of the water–dimethyl sulfoxide system with a volume ratio 1:1 is optimal to achieve the formation of moderately aggregated particles with a distinct filamentous morphology.

Anion photoelectron spectroscopy and chemical bonding of ThS2- and ThSO.

Anion photoelectron spectra of ThSO- and ThS2- were recorded using the third (355nm) harmonic of an Nd-YAG laser; these provided the measured vertical detachment energies of each anion. The experiments are supported by extensive coupled cluster calculations on ThSO, ThSO-, ThS2, and ThS2-, as well as the oxygen congeners ThO2 and ThO2-. The abinitio calculations, which included complete basis set extrapolations, spin-orbit effects using four-component coupled cluster, and higher-order correlation contributions through CCSDT(Q), yielded an adiabatic electron affinity for ThO2 that was within 0.02eV of the previously determined experimental value. The singly occupied molecular orbital (SOMO) in all three anions corresponds primarily to the 7s orbital on Th. Successive substitution of S for each O in ThO2 leads to larger electron affinities and smaller bond angles in the neutral molecules, but larger angles in the anions. As demonstrated by Franck-Condon simulations of the spectra using the CCSD(T) spectroscopic constants, substitution of O by S significantly complicates the resulting detachment spectra due to the lower vibrational frequencies in the sulfur species. Overall the calculated vertical detachment energies are in very good agreement with the experiment. In addition to the adiabatic electron affinities of each species, atomization energies and heats of formation have also been determined via the FPD approach with expected uncertainties of 1-2 kcal/mol.

Synthesis, structural, spectroscopic investigation, Hirshfeld surface analysis and DFT calculation of a new spiro compound including 4-nitroaniline moiety

A new spiro compound, C14H13 N3O6 (NHD) was prepared through the reaction of 6,10-dioxaspiro[4.5]decane-7,9‑dione with diazotized solution of 4-nitroaniline in ethanol. The structural characteristics of NHD were investigated using spectroscopy (FT-IR, UV-is and 1H and 13C NMR) and computational analysis utilizing B3LYP/6–311G(d,p) level. Theoretical and experimental results for optimizing molecular geometry, infrared vibrational frequencies, and UV–Vis spectra were found to be consistent. Hirshfeld surface analysis had been used to explain intermolecular interaction and π···π stacking interactions. 2D fingerprint studies confirmed that O···H/H···O contributions make up the greatest contributors (43.6 %) in NHD. Additionally, (HOMO-LUMO) energies, global reactivity properties, MEP and NBO were investigated at the same level. Finally, NHD is thermally stable up to 195 ℃ according to TG/DTA analysis.

Estimates of natural frequencies for nuclear vibration, and an assessment of the feasibility of selective ultrasound ablation of cancer cells

Selective ablation of cancer cells by ultrasound would be transformative for cancer therapy, but has not yet been possible. A key challenge is that cancerous and non-cancerous cells typically have similar acoustic impedance and are thus indistinguishable as materials in their responses to ultrasound. However, in certain cancers, cytoskeletal and nuclear lamin structures differ between healthy and malignant cells, opening the possibility of exploiting structural differences that manifest as different vibrational responses. To assess the possibility that the nuclei of certain cancerous cells might vibrate at different frequencies, we measured sizes and effective indentation moduli of a range of cancerous and non-cancerous cells from several cell lines and regions of the brain, and estimated the natural frequencies for nuclear vibration. Results suggest a potential difference in natural frequency for nuclear vibration between certain cancerous and non-cancerous cells, on the order of tens of kHz. This gap is potentially sufficient for selective ablation and motivates future experimentation on these specific cell types.

Study on Dynamic Strength Characteristics of Sand Solidified by Enzyme-Induced Calcium Carbonate Precipitation (EICP).

Saturated sand foundations are susceptible to liquefaction under dynamic loads. This can result in roadbed subsidence, flotation of underground structures, and other engineering failures. Compared with the traditional foundation reinforcement technology, enzyme-induced calcium carbonate precipitation technology (EICP) is a green environmental protection reinforcement technology. The EICP technology can use enzymes to induce calcium carbonate to cement soil particles and fill soil pores, thus effectively improving soil strength and inhibiting sand liquefaction damage. The study takes EICP-solidified standard sand as the research object and, through the dynamic triaxial test, analyzes the influence of different confining pressure (σ3) cementation times (CT), cyclic stress ratio (CSR), dry density (ρd), and vibration frequency (f) on dynamic strength characteristics. Then, a modified dynamic strength model of EICP-solidified standard sand was established. The results show that, under the same confining pressure, the required vibration number for failure decreases with the increase in dynamic strength, and the dynamic strength increases with the rise in dry density. At the same number of cyclic vibrations, the greater the confining pressure and cementation times, the greater the dynamic strength. When the cementation times are constant, the dynamic strength of EICP-solidified sand decreases with the increase in the vibration number. When cementation times are 6, the dynamic strength of the specimens with CSR of 0.35 is 25.9% and 32.4% higher than those with CSR of 0.25 and 0.30, respectively. The predicted results show that the model can predict the measured values well, which fully verifies the applicability of the model. The research results can provide a reference for liquefaction prevention in sand foundations.

Non-linear optical properties of hybrid materials of (OLi3) superalkali doped perylene diimide (PDI) derivative: comprehensively study via silico-technique

PDI-Imidazole and PDI-Imidazole combined with OLi3 (OLi3@PDI-Imidazole) were the two types of materials that we examined in this study to see how light behaved in each of the complex. To explore this, we employed the three different method such as rB3LYP/6–31G(d, p) DFT, CAM-B3LYP and WB97XD. The impact of PDI-Imidazole and OLi3@PDI-Imidazole geometries, maximum absorption ( λmax ), FMO, vertical ionization energies ( EVI ), Binding Energies ( Eb ), Hyperpolarizabilities, DOS, Dipole Moments (μ), ESP, EDDM, and Global Reactivity parameters have been examined. The type of contacts as well as the vibrational frequencies of PDI-Imidazole and OLi3@PDI-Imidazole were investigated using NCl, iso-surface, Raman spectroscopy, and IR research. The electron transport characteristics of the OLi3@PDI-Imidazole surface was significantly enhanced in comparison to the PDI-Imidazole surface by lowering the bandgap energies from 1.27 eV to 1.03 eV. In contrast to the pure PDI-Imidazole surface, which had lower values for linear polarizability ( α0 ) (547.08 au) and first hyperpolarizability ( β0 )(201.133au), OLi3@PDI-Imidazole surface displayed significant enhancements in linear polarizability ( α0 = 706.472 au) and first hyperpolarizability ( β0 = 21314.360 au). It was observed by TD-DFT calculations that all the compounds had appreciable improvements in their interaction energies, HOMO–LUMO and UV–vis absorption and vertical ionization potential. Future development of nonlinear optical (NLO) devices has been discovered to benefit from the addition of OLi3 to the PDI-Imidazole surface.

Experimental study on condensing flow and heat transfer characteristics in minichannels under mechanical vibration conditions

Minichannel heat exchangers are often used in the condensers of vehicle air conditioners, and vibration is inevitable in vehicle driving. However, the influence of mechanical vibration on the characteristics of minichannel condensing flow and heat transfer has been rarely studied. Therefore, the experimental study of condensing flow and heat transfer in minichannels under mechanical vibration was carried out in this paper. With R134a as the working medium, the condensation heat transfer coefficient, frictional pressure drop and flow pattern images were measured in the saturation temperature of 40 °C, mass flux density of 200 kg/(m2·s), vapor quality range of 0–1, vibration frequency of 15–50 Hz and amplitude of 0–2.4 mm. For annular flow, intermittent flow and bubble flow, the vibration can enhance the wave of gas-liquid interface, and promote the breakup of long bubbles and the polymerization of small bubbles. Vibration enhances heat transfer in most cases, but weakens heat transfer in some specific cases. The frictional pressure drops under vibration conditions are greater than those under static conditions, which indicates that the influence mechanism of vibration on heat transfer and pressure drop is different. This paper attempts to analyze the complex mechanism of vibration affecting minichannel condensing heat transfer and pressure drop, which provides theoretical support for further study of condenser optimization design under vibration conditions.

Laser Spectroscopic Characterization of Supersonic Jet-Cooled 2,6-Diazaindole (26DAI).

The article presents a comprehensive laser spectroscopic characterization of a nitrogen-rich indole derivative, namely, 2,6-diazaindole (26DAI), in the gas phase. A supersonic jet-cooled molecular beam of 26DAI was characterized using two-color resonant two-photon ionization (2C-R2PI) and laser-induced fluorescence spectroscopy (LIF) to investigate the electronic excitation. The S1 ← S0 origin transition was obtained at 33915 cm-1, which was red-shifted from that of one (indole) and two (7-azaindole) nitrogen-containing indole derivatives by 1317 and 713 cm-1, respectively. The molecular orbital and energy analysis for the S1 ← S0 transition shows the significant stabilization of LUMO on subsequent N-insertion, resulting in the lowering of the S1 ← S0 (ππ*) transition energy. The single vibronic level fluorescence spectrum from the vibrationless S1 state of the molecule was recorded. The spectrum displayed an extensive Franck-Condon activity until 2500 cm-1 for the vibrational modes of the S0 state of the 26DAI molecule. The experimental ground state vibrational frequencies were compared to the calculated ones obtained at three different levels of theories. More accurate results were found at DFT B3LYP-D4 than those at the wave function-based MP2 and CCSD levels of theories. Further, the N-H stretching frequency of 26DAI in the S0 state was measured at 3524 cm-1 using fluorescence-dip infrared (FDIR) spectroscopy. The stability of 26DAI against ionization radiation was probed by measuring the two-color photoionization energy (IE2P) of 26DAI at 71866 cm-1. The IE2P value is significantly higher than those of N-poor counterparts (indole and 7-azaindole). The NBO charges and spin density (SD) values of the 26DAI molecule have shown that electronegative N(6) makes the cationic ground state less stable due to the position of the positive centers on the N atom. The results provided insights into the stability of N-rich biomolecules against photodamage. The current investigation can shed light on nature's way of stabilizing biomolecules with a possible N-insertion mechanism.