Vibrational Frequency Analysis Research Articles

Development of sensitive napthaquinone-pyridine hydrazone based chemosensor for the colorimetric detection of Cu2+ ion in an aqueous solution

A novel naphthoquinone-pyridine hydrazone (NQPH) based chemosensor was synthesized through the condensation reaction of 2-hydroxynaphthoquinone aldehyde and 2-pyridine carboxylic acid hydrazide. The aqueous buffered solution of NQPH quickly changes color from orange to green upon addition of Cu²⁺ ions with appearance of new absorption band at 452 nm. The UV–vis titration indicated binding constant (K) of chemosensor NQPH with Cu²⁺ was determined to be 2.5 × 104 M⁻¹ (log K = 5.39), and the detection limit for Cu²⁺ ions was found to be 4.35 µM. Analysis using a Job plot based on UV–vis data, along with mass spectrometry, indicated a 1:1 stoichiometry between NQPH and Cu²⁺. Density Functional Theory (DFT) calculations were used to determine the minimum energy conformations, molecular properties and vibrational frequency analysis of NQPH and its Cu²⁺ complex. The DFT results showed the reduction in the HOMO-LUMO gap when NQPH interact with Cu²⁺, indicating intramolecular charge transfer (ICT). The practical application of NQPH was demonstrated by creating test strips for the naked-eye detection of Cu²⁺ and by measuring Cu²⁺ in real water samples.

APPLICATION OF OPTICAL IMAGING METHODS FOR MONITORING VIBRATIONS OF BRIDGE ROAD STRUCTURES

The paper discusses methods for non-contact optical diagnostics of the condition of span constructions of bridge structures. A comparison was made of the capabilities of visualizing vibrations using the laser speckle image correlation method and the photomodulation holographic method when conducting tests on a road bridge. The results of visualization of various traffic conditions of the bridge over the Burunduk channel on the Tomsk bypass road were obtained and analyzed. Relative movements were determined and frequency analysis of vibrations of the span of the bridge structure was carried out. Analysis of the results of the experiments confirmed the possibility and effectiveness of using the photomodulation holographic method for visualizing the movements and vibrations of road infrastructure construction objects.

Effect of chalcogen atoms on the electronic band gaps of the quinoxaline containing donor-acceptor-donor type semiconducting polymers: a systematic DFT investigation.

Due to the widely known positive contributions of the quinoxaline group in organic semiconductors, we conducted a fully computational study using quantum mechanical methods to investigate the effect of quinoxaline in the electron acceptor unit with the combination of different chalcogen atoms on the band gap of a series of donor-acceptor-donor type conjugated polymers. Using density functional theory, we mainly calculated the electronic band gap values of the structures containing four different chalcogen atoms (O, S, Se, and Te) in the electron donor and acceptor units. While chalcogendiazoloquinoxaline groups were used as the electron acceptor units, furan, thiophene, selenophene, and tellurophene were used as the donor units. Our theoretical results showed that the use of heavy chalcogen atoms in both donor and acceptor units resulted in a low band gap. Besides this, the effect of heavy chalcogen atoms used in the electron donor units is much more pronounced compared to the ones used in the acceptor units. More importantly, our findings proved that the inclusion of the chalcogendiazoloquinoxaline group instead of benzochalcogenadiazole as the acceptor unit significantly decreases the electronic band gap of the conjugated polymer. The lowest band gap was found to be 0.10eV for the 4,9-di(tellurophen-2-yl)-[1,2,5]telluradiazolo[3,4-g]quinoxaline polymer. Conformational analysis of the monomers and their corresponding oligomers was performed at the B3LYP/LANL2DZ level of theory. Then, long-range corrected hybrid functional LC-BLYP in a combination with the LANL2DZ basis set was utilized for the calculation of electronic properties and HOMO and LUMO energy gaps of monomers and oligomers through the reoptimization of the lowest energy conformers obtained from the B3LYP/LANL2DZ calculations in the previous step. All energy minimum structures were confirmed through vibrational frequency analysis at both calculation levels. The Gaussian 09 rev. D.01 software was used for all calculations, and GaussView 5.0.9 for visualizations.

Theoretical study of a series of 1,2-diazete based trinitromethyl derivatives as potential energetic compounds.

Explosive properties of novel potential high energy density materials of a series of 1,2-diazete-based molecules with trinitromethyl functional group were investigated computationally. All the sixty seven molecules were optimised to obtain their molecular geometries and electronic structures. Electrostatic potential analysis was also carried out in the determination of different parameters. The calculations indicate that the majority of the compounds have high positive heat of formations, high density and good detonation performance greater than that of traditional energetic materials like RDX and HMX. They are also having comparable values of impact sensitivity. These features promise their potential to be used as energetic materials for future applications. Most of the designed molecules are having high positive oxygen balance values so that the study of these molecules can also be extended as potential candidates for oxidisers in solid propellants. Optimisation and vibrational frequency analysis of the studied molecules were done with density functional theory using B3LYP/aug-cc-pVDZ as the basis set to zero imaginary frequencies using Gaussian 09. Electrostatic potential analysis were carried using the Multiwfn program.

Suppression of wake-induced galloping of tandem cylinders by helical strakes

Helical strakes as a classic passive control method for vortex-induced vibration (VIV), have been extensively studied, but wake-induced galloping (WIG) control of three tandem cylinders has received no previous attention. The current wind tunnel experimental study tries to fill this gap in the context of mechanical science. WIG of three tandem cylinders considering different structures of helical strakes is modeled and investigated. Helical strakes with varying heights G, pitches P, and cross-sectional shapes (square “S”, involute “I”, and D-shaped “D”) are first designed. Wind tunnel tests are conducted to experimentally study the dynamics responses of tandem cylinders (m*ξ = 0.09) at different spacings, and three vibration modes are obtained. This study delves into the characterization and quantification of the impact of various parameters of helical strakes on WIG of three tandem cylinders. These aspects, scarcely addressed in existing research, are thoroughly explored through statistical analysis, focusing on vibration amplitude, vibration frequency, and wavelet analysis. It is found that helical strakes can effectively suppress the multi-frequency vibration instability of bare cylinders. For wind speeds below 6 m/s, the "S" helical strakes achieves a vibration suppression efficiency of up to 665 %; Three-dimensional computational fluid dynamics (3D-CFD) demonstrate the coupling effect in the flow field, revealing that the "S" helical strakes has a greater impact on boundary layer formation than the "D" helical strakes; Reducing the pitch of the helical strakes can enhance the disturbance ability of the spanwise position, thereby increasing its suppression effect. This work improves vibration reduction and sheds light on how the helical strakes' cross-section controls vibrations in the tandem cylinders.

Prediction of Soil Erosion Using 3D Point Scans and Acoustic Emissions

Over half of the approximately 12,000 earthen watershed dams sponsored by the USDA have exceeded their planned 50-year service life. Age, land use changes, extreme weather events, structural deterioration, and sedimentation filling flood pools pose increased risks of dam incidents and potential failures. Among various mechanisms leading to integrity issues, soil erosion is of particular concern due to its potential to occur with little warning. The objective of this research is to determine if soil erosion can be predicted using acoustic emissions. A simulated dam overtopping experiment was replicated in a test flume with dimensions of 0.61 m by 4.27 m (2 ft. by 14 ft.) with a 13.7% slope and a 0.15 m (6 in) layer of inorganic clay (USCS CL) compacted at 17.4% moisture content. A constant flow discharge of 0.07 m3/s (2.37 cfs) was applied to induce erosion. The test was performed until complete failure of the test section occurred. Throughout the experiment, a sonar radar, a 3D scanning total station, and an accelerometer were used to monitor the water level, erosion levels, and vibrations, respectively. The frequency analysis of the water-induced vibrations was compared to measured erosion volumes to determine if in situ vibrations can predict erosion. The results revealed a linear relationship between erosion volume and time, with noticeable changes in the frequency domains as erosion progressed. The outcomes of this research have the potential to provide real-time insights into the integrity of earthen dams concerning erosion, offering a valuable tool for monitoring and maintenance.

Efficient Method for Numerical Calculations of Molecular Vibrational Frequencies by Exploiting Sparseness of Hessian Matrix.

Molecular vibrational frequency analysis plays an important role in theoretical and computational chemistry. However, in many cases, the analytical frequencies are unavailable, whereas frequency calculations using conventional numerical methods are very expensive. In this work, we propose an efficient method to numerically calculate the frequencies. Our main strategies are to exploit the sparseness of the Hessian matrix and to construct the N-fold two-variable potential energy surfaces to fit the parabola parameters, which are later used for the construction of Hessian matrices. A set of benchmark calculations is performed for typical molecules of different sizes and complexities using the proposed method. The obtained frequencies are compared to those calculated with the analytical methods and conventional numerical methods. It is shown that the results yielded with the new method are in very good agreement with corresponding accurate values (with a maximum error of ∼20 cm-1), while the required computation resource is largely reduced compared to that required by conventional numerical methods. For medium-sized molecules, the calculational scaling is lowered to O(N1.6) (this work) from that of O(N2) (conventional numerical methods). For even larger molecules, more computational savings can be achieved, and the scaling is estimated to be quasilinear with respect to the molecular size.

Mechanism of dimethyldichlorosilane preparation by NH2-MIL-53(Al)@γ-Al2O3 core-shell catalyst before and after AlCl3 modification

The irreplaceable silicone materials among the high-tech industry is dimethyldichlorosilane, a monomer whose by-products generated in the synthesis step can be recycled through disproportionation reactions. In this paper, the catalytic activities of NH2-MIL-53(Al)@γ-Al2O3 with Brønsted acid active sites and AlCl3/NH2-MIL-53(Al)@γ-Al2O3 core-shell catalysts with Lewis acid active sites were investigated and compared for the disproportionation to prepare dimethyldichlorosilane by means of the M06-2X/Def2-TZVP hybrid functional method. The results given for structure, energy, vibrational frequency, IRC values, bond order, ELF and LOL analysis were matched. The results showed that AlCl3/NH2-MIL-53(Al)@γ-Al2O3 core-shell catalyst with Lewis acid was more active.

Mechanistic insights into the adsorption and dissociation of nitrogen oxides on nickel phosphide (Ni2P) catalysts

The escalating concern regarding nitrogen oxides (NOx) emissions, linked to environmental challenges like smog, acid rain, ozone depletion, and global warming, necessitates effective strategies for their mitigation. DeNOx processes, including selective catalytic reduction (SCR), offer potential solutions, but costly precious metal catalysts hinder a widespread implementation. Alternatively, earth-abundant element compounds, particularly transition metal phosphides (TMPs), such as nickel phosphides (Ni2P), have garnered interest due to their promising catalytic performance. This study employed first-principles density functional theory (DFT) methods to investigate the catalytic properties of the (0001) Ni2P surface concerning NOx adsorption and dissociation. Both NO and NO2 are found to exhibit strong reactivity towards Ni2P-(0001)’s surface at the hollow triple-Ni sites, forming stable conjugated structures. Bader charge analysis indicates significant charge transfers during NOx adsorption from the interacting surface to the NOx, resulting in elongated N–O bond lengths, confirmed by vibrational frequency analyses. The dissociation process of NO2 was found to be both thermodynamically and kinetically favorable, with more heat being released than the subsequent NO dissociation’s activation barrier, resulting in a self-sustaining overall reaction. These insights provide valuable knowledge for designing efficient and sustainable Ni2P-based catalytic systems to address NOx emissions in environmental and industrial applications.

First principles study of quantum dots-sensitized solar cells using Type-II core/shell quantum dots as efficient sensitizers

Type-II core/shell quantum dots (QDs) present a promising avenue for enhancing the stability and performance of quantum dot-sensitized solar cells (QDSSCs) by reducing charge carrier recombination through the mitigation of trap states and enhancing charge carrier separation. This paper reports first-principles studies on diverse core/shell QDs consisting of group II-VI elements, namely, ZnSe/CdS, ZnTe/CdSe, CdTe/CdS, ZnTe/CdS, CdTe/CdSe, ZnTe/CdTe and ZnTe/ZnSe. The geometric and electronic properties of these QDs were investigated using first-principles density functional theory. The core/shell structures of each quantum dot were optimized, and their energy stability was confirmed through vibrational frequency analysis. The highest occupied molecular orbital principally constituted by S, Se, or Te states, while the states from the shell form the lowest unoccupied molecular orbital. Calculations of optical absorptions and structure optimization after electron transition were conducted using time-dependent density functional theory. The feasibility of type-II core/shell QDs as sensitizers for QDSSCs was assessed by examining absorption spectrum, electron injection, and electron-hole recombination. The results demonstrated that ZnTe/CdSe not only effectively balanced the competition between absorption range and electron injection channels, but also provided a clear advantage in electron–hole separation. Consequently, ZnTe/CdSe holds significant promise as a viable sensitizer for QDSSCs.

Microwave Synthesized Hydrophilic 4‐Oxo‐2‐phenylquinazoline‐3(4H)–carboximidamide and –Carboxamide as Privileged Small Molecule Scaffolds with Anti‐HIV‐1 Activities

AbstractOpportunistic infections like tuberculosis (TB) are prevalent in HIV‐infected individuals. In an approach to introducing an industrial‐scale microwave‐assisted production of agents having both antiviral and antibacterial properties, a set of hydrophilic 2,3‐substituted quinazolinones, 4‐oxo‐2‐phenylquinazoline‐3(4H)‐carboximidamide (Qg) and 4‐oxo‐2‐phenylquinazoline‐3(4H)‐carboxamide (Qu), were afforded in encouraging yields. They were obtained by treating 2‐benzamidobenzoyl chloride with guanidine hydrochloride or urea in the presence of potassium carbonate in DMF. DFT calculations were employed for geometrical optimization and vibrational frequency analysis of the compounds. Free energies of solvation (ΔGsol) of Qg, and Qu calculated using DFT lend evidence in support of their hydrophilicity The anti‐HIV‐1 activities of the small‐molecule quinazolinone derivatives Qg and Qu were investigated. The synthons under in vitro conditions inhibit the entry of HIV in receptor cells with low cytotoxicity (EC50=50.53 nM for Qu and EC50=97.92 nM for Qg). The study identifies the antiviral properties of the two benzo‐fused pyrimidine derivatives, which were earlier reported to have antitubercular activity. Our findings indicate the scope for further synthetic explorations of these quinazolinone scaffolds that can lead to developing promising alternatives in drug design, pharmaceutics, and clinical research.

Ab Initio Approach to the Structure, Vibrational Properties, and Electron Binding Energies of H2S∙∙∙SO2.

The present study employs high-level ab initio calculations to investigate the structure, vibrational frequencies, and electronic properties of H2S∙∙∙SO2. The analysis of vibrational frequencies reveals an intramolecular vibrational energy transfer phenomenon, where energy from the stretching modes of H2S is transferred to the ν1s mode of SO2. At the CCSD(T)/aug-cc-pVQZ level, the interaction energy between H2S and SO2 is predicted to be 2.78 kcal/mol. Electron propagator theory calculations yield a HOMO-LUMO gap of 8.24 eV for H2S∙∙∙SO2. Furthermore, by utilizing ab initio results for the adiabatic ionization energy and electron affinity, the electrophilicity of H2S∙∙∙SO2 is estimated to be 2.01 eV. This value is similar to the electrophilicity of SO2, suggesting comparable reactivity and chemical behavior. The non-covalent interaction (NCI) analysis of the H2S∙∙∙SO2 complex emphasizes the significant contribution of non-covalent van der Waals interactions in its energetic stabilization.

Impact Pressure Influence of Flood on Bridge Deck under Sediment Deposition Conditions: An Experimental Study

This paper investigates the impact of sediment deposition and inflow conditions on horizontal impact pressure and frequency analysis of bridge deck vibrations during flooding. Flooding-induced pressure and vibrations contribute to bridge collapse, and sediment deposition influences water flow and impact pressure. The study explores the relationship between sediment deposition height and impact pressure, revealing a significant increase as sediment approaches 50% of bridge deck clearance. Sediment amplifies impact pressure response to flow velocity changes. The dimensionless sediment deposition height has a greater influence on impact pressure compared to the inflow Froude number. Two distinct frequencies, dominant and secondary, are identified for impact pressure and water level fluctuations. Dominant frequencies positively correlate with sediment deposition height and Froude number, indicating an increasing trend. Secondary frequencies remain stable (0.31–0.58 Hz). These findings enhance understanding of flow dynamics and bridge–flow interaction in sediment-deposited channels, providing theoretical support for evaluating and managing disasters related to bridges in such environments. Overall, this research contributes to the field of bridge engineering and supports improved design and maintenance practices for bridges exposed to sediment-deposited channels.

The Non-Linear Excitation Load-Sharing Method of a High-Powered Nuclear Planetary Gear Train

The paper primarily employs the 3D calculation method of the helical gear-meshing line and meshing position, in addition to the traditional method of the gear-meshing stiffness calculation. This analysis and correction of load-sharing are beneficial for improving the assembly process of high-powered critical equipment. The dynamic models of rigid–flexible coupling, velocity–torque, and the meshing force of planetary gear trains in nuclear power plants are established based on the principles of gear dynamic characteristics. Based on an analysis of the vibration characteristics of a planetary gear train, a load-sharing method for the planetary gear train is proposed. This uniform load-sharing method is explored under different modification values to provide a reference for load-sharing research on high-powered key equipment. In this paper, a dynamic simulation analysis of the gearbox system is conducted, using virtual prototype software to study the load-sharing performance of the planetary gear system. Furthermore, via a vibration frequency analysis of the gear mesh force, the causes of planetary gear train vibration are discussed, particularly their impact on planetary load. This provides a basis for the assembly process of a nuclear power circulation pump gearbox, ensuring that the gearbox for the circulation pump has a longer life that meets the 40-year service life requirement, and provides a foundation for the study of planetary load characteristics.

Frequency Analysis of Vibrations in Terms of Human Exposure While Driving Military Armoured Personnel Carriers and Logistic Transportation Vehicles

Military heavy vehicle drivers experience low-frequency vibrations that are associated with fatigue, drowsiness, and other adverse health effects. The existing research papers focus on performing different types of analysis, but few use advance signal processing tools based on recurrence plot representation; therefore, the main goal of this paper is to assess the whole-body vibration (WBV) and hand-arm vibration (HAV) exposure of a driver, comparing armoured personnel carriers and cargo destined vehicles. For this purpose, the power of a signal distributed over its frequency was analysed using power spectral density (PSD) and diagonal line quantification (DLQ) analysis. According to the results, in the case of the cargo vehicle, the driver experienced vibration dose values of frequency weighted acceleration above the limits during all three experimental tests, with a maximum value of 26.802 m/s2, whereas the results in the case of the armoured personnel carrier are below the 5 m/s2 limit imposed by the ISO 5349-2 standard. From the developed tests it was observed that, to protect the driver against the fatigue induced by the vibrations of the vehicle body, it is necessary to provide an elastic and also damping linkage between the vehicle and the driver’s seat. This is the only way to ensure the needed protection and it is, by far, the least expensive.

Pyrolysis and kinetic study of dimethyl methylphosphonate (DMMP) by synchrotron photoionization mass spectrometry

Pyrolysis experiments of dimethyl methylphosphonate (DMMP) were carried out in a jet stirred reactor (JSR) coupled to synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at 1 atm, from 900 to 1200 K, to quantitatively measure the mole fraction profiles of DMMP and its pyrolysis products. Furthermore, theoretical calculations were carried out. Geometry optimization and vibrational frequency analysis were conducted for DMMP unimolecular and isomerization reactions at the MN15/6-311+G(2df,2p) level of theory, and kinetic calculations were performed using the kinetic code of MESS. The results show that DMMP mainly undergoes isomerization channels to form its isomers before decomposing into pyrolysis products. This is different from the DMMP decomposition channels adopted in the literature models. The kinetic model of DMMP in the literature was modified and improved by adding newly calculated reactions and their rate constants and updating the rate constants of unimolecular reactions for DMMP as well based on computations. Some rate tuning of reactions by 5 or 10 factors has been tried in model development to better describe the experimental measurements. Finally, the model developed by this work showed much better prediction of DMMP consumption and major species production than the prediction by literature models. In addition, the updated model was validated against various previous experimental data (CO mole fraction distributions in the shock tube, the flame speed and species mole fraction distributions in the premixed flame), and the satisfactory validation results indicate the reliability of the DMMP model that was improved in this work. This preliminary work laid a foundation to further study the combustion properties and to develop the kinetic model of organophosphorus compounds.

The frequency analysis of the gun barrel vibration based on road simulation test

Aiming at the problem that the gun barrel vibration affects the firing accuracy during tank moving, based on the road simulation test, under the excitation of the different road levels (C, D and E), the acceleration vibration response curves of the barrel under different road levels and different vehicle speeds were obtained by arranging acceleration sensors on the barrel surface. Based on the power spectrum analysis method, the frequency response characteristics of the barrel vibration were analyzed, and the main frequency of barrel vibration during moving is obtained. It has been shown that, the main frequency of the barrel response is mainly distributed in three frequency ranges: 1~3Hz, 14~15Hz and 24~26Hz. The main frequency of the barrel vibration is different with different roads. The main frequency of the barrel response is mainly in the frequency range of 1~3Hz under C level road, and in the frequency range of 1~3Hz and 24~26Hz under D lever road. And under the E level road, the main frequency of barrel response is within the three frequency ranges of 1~3Hz, 14~15Hz and 24~26Hz. And the main frequency is 25Hz as the measuring point is far away from the muzzle. The results will provide support for obtaining the vibration characteristics of barrel as tank moving and explaining the vibration response law of the barrel.

Ultrasonic, transport and vibrational frequency analysis of non-aqueous peptide + electrolyte solutions

Ultrasonic method finds extensive application in investigating various physicochemical parameters involving molecular interactions in liquid mixtures. The density, viscosity and ultrasonic velocity measurements were carried out in non-aqueous peptide and electrolyte solutions at different concentrations and temperatures to illustrate the intermolecular interactions prevailing in the solutions. The main transport parameters such as adiabatic compressibility, internal pressure and free volume have been computed using the measured values. These parameters were utilized to interpret the intermolecular interactions existing in the mixture of glycyl-glycine and potassium ascorbate in non-aqueous formamide medium. The ultrasonic results are corroborated with the vibrational frequency analysis of the peptide and ascorbate solutions.

An analysis of nonlinear thickness vibration frequencies of multi-layered film bulk acoustic resonators

The fast reduction of the physical size of film bulk acoustic wave resonators as a layered structure implies the intensification of the electric field which can induce large deformation in the functioning state of devices as a circuit element. Consequently, the nonlinear behavior of the resonator and accompanying properties are to be included and evaluated in the development and optimization for performance improvement. With this objective, the nonlinear formulation of a multilayered film bulk acoustic resonator is presented for the analysis of vibration frequencies and mode shapes with the consideration of larger mechanical deformation. The dominantly linear relationship between the voltage or deformation and frequency is obtained to understand the nonlinear behavior and properties which have been subjected to extensive research analytically and experimentally to satisfy the application needs in all modes of communications and network technology.

Experimental and theoretical insights into structural features of methyl (E)-3-(3,4,5-trimethoxybenzylidene)dithiocarbazate with molecular docking and ADMET studies

A new Schiff base, methyl (E)-3-(3,4,5-trimethoxybenzylidene)dithiocarbazte (MTD), was successfully synthesized from a condensation reaction of methyldithiocarbazate with 3,4,5-trimethoxybenzaldehyde. The structure of MTD was confirmed by single-crystal X-ray, NMR, FTIR, TGA, UV-Vis and mass spectroscopy techniques. The Hirshfeld surface analysis of the MTD crystal structure showed dominant H⋅⋅⋅H contacts in the molecular system. Bond lengths and bond angles of the theoretical MTD structure optimized by density functional theory (DFT) using B3LYP label with 6-31G+(d,p) basis set showed excellent agreement with those of the crystal structure. The IR spectra calculated from ground-state vibrational frequency analysis and the UV-Vis spectra from time-dependent density functional theory correlate well with their respective experimental spectra. The results of frontier molecular orbitals (FMO), density of states and global descriptors such as chemical hardness, chemical potential, electrophilic index and chemical softness derived from FMOs with MTD optimized structure revealed that MTD is soft, polarizable, reactive and prone to intramolecular charge transfer. Close observation of frontier molecular orbital map indicated the N, S, O heteroatoms, phenyl ring and p‑methoxy group in negative potential regions while the rest of the molecule was in positive regions. Natural bond orbital analyses concluded that MTD is 98.085% Lewis structure. The molecular docking score result of MTD and Streptococcus pneumoniae protein (PDB code: 3OBH), which is very close to that of standard drugs (trimethoprim and sulfamethoxazole), suggests a potential drug candidature of MTD. The absorption, distribution, metabolism, excretion and toxicity (ADMET) study predicted the good drug-like character of MTD.