Normal Vibrations Research Articles

How to Measure the Area of Real Contact of Skin on Glass.

The contact between the fingertip and an object is formed by a collection of micro-scale junctions, which collectively constitute the real contact area. This real area of contact is only a fraction of the apparent area of contact and is directly linked to the frictional strength of the contact (i.e., the lateral force at which the finger starts sliding). As a consequence, a measure of this area of real contact can help probe into the mechanism behind the friction of skin on glass. In this article, we present two methods to measure the variations of contact area; one that improves upon a tried-and-true fingertip imaging technique to provide ground truth, and the other that relies on the absorption and reflection of acoustic energy. To achieve precise measurements, the ultrasonic method exploits a recently developed model of the interaction that incorporates the non-linearity of squeeze film levitation. The two methods are in good agreement ($\rho =0.94$) over a large range of normal forces and vibration amplitudes. Since the real area of contact fundamentally underlies fingertip friction, the methods described in the article have importance for studying human grasping, understanding friction perception, and controlling surface-haptic devices.

Origin of vibrational features in the excitation energy transfer dynamics of perylene bisimide J-aggregates.

We investigate the role of intramolecular normal mode vibrations in the excitation energy transfer (EET) dynamics of perylene bisimide J-aggregates composed of 2 or 25 units using numerically exact methods. The calculations employ a Frenkel exciton Hamiltonian where the ground and excited electronic states of each molecular unit are coupled to 28 intramolecular normal mode vibrations at various temperatures. The electronic populations exhibit strong damping effects, a lengthening of the EET time scale, and complex dynamical patterns, which depend on aggregate length, temperature, as well as electronic and vibrational initial conditions and which are not additive. The early evolution is dominated by high-frequency vibrational modes, but all modes are responsible for the observed dynamics after the initial 25 fs. Overall, we observe significant changes in the electronic populations upon varying the temperature between 0 and 600 K. With a Franck-Condon (FC) initial excitation, a strongly coupled vibrational mode introduces new peaks to the dimer populations, which show very weak temperature sensitivity. The first of these peaks is also seen in the long aggregate, but subsequent recurrences appear strongly quenched and merged. These structures are drastically altered if a non-FC initial condition is assumed. Additional insights are obtained from the diagonal elements of the dimer electronic-vibrational reduced density matrix. We find that the vibronic peaks result from depletion of the crossing region during the early coherent evolution of the vibrational density away from the crossing point, which allows the premature back-transfer of excitation to the initially excited unit.

Signal Identification of Gear Vibration in Engine-Gearbox Systems Based on Auto-Regression and Optimized Resonance-Based Signal Sparse Decomposition

As an essential part of the transmission system, gearboxes are considered as a major source of vibration. Signal identification of gear vibration is necessary for online monitoring of the mechanical systems. However, in engine-gearbox systems, the ignition impact of the engine is strong, so that the gear vibration is generally submerged. To overcome this issue, the resonance-based signal sparse decomposition (RSSD) method is used in this paper based on different oscillatory behaviors of the gear meshing impact and the engine ignition impact. To improve the accuracy of RSSD under interferences, the meshing frequency energy ratio (MF–ER) index is introduced into RSSD to adaptively choose the decomposition parameters. Before applying the RSSD method, the auto-regression (AR) model is used as a pre-whitening step to eliminate the normal gear meshing vibration, which improves the decomposition performance of RSSD. The effectiveness of the proposed AR-ORSSD (AR-based optimized RSSD) algorithm is tested using both simulated signals and measured vibration signals from an engine-gearbox system in a forklift. Comparisons were made with the RSSD algorithm based on a genetic algorithm. Experimental results indicate that the AR-ORSSD algorithm is superior at identifying gear vibration signals especially when under strong interferences.

Experimental study on the velocity-dependent frictional resistance of a rough rock fracture exposed to normal load vibrations

Changes in shear velocity can strengthen or weaken the frictional resistance of joints/faults in natural systems, but the mechanism remains unclear. We investigated the shear behavior of a rough basalt fracture in well-controlled, repeatable shear tests under constant and dynamic normal load conditions at different shear velocities. Normal load vibrations, simulating a dynamic normal load, were applied to the upper block of a fractured basalt sample. Simultaneously, a shear load was applied to the bottom block, providing a constant shear velocity. The peak shear strength increased with increasing shear velocity under constant normal load conditions. The peak shear strength decreased at a lower shear velocity under normal load vibrations. When the shear velocity exceeded the critical value, vc, the peak shear strength increased. The apparent coefficient of friction reduced under normal load vibrations. The reduction in the dynamic coefficient of friction increased with increasing shear velocity. We identified a phase shift between the peak normal load and peak shear load with peak shear load delay (D1) and a phase shift between peak normal load and the peak coefficient of friction with the peak coefficient of friction delay (D2). D1 and D2 were dependent on the quasi-static coefficient of friction and shear velocity, and both decreased with increasing shear velocity. D1 decreased with the increasing quasi-static coefficient of friction, while D2 was almost constant with changes in the quasi-static coefficient of friction. A new shear strength criterion was proposed for a rough joint under a constant shear velocity and normal load vibrations.

Level statistics and Anderson delocalization in two-dimensional granular materials

Contrary to the theoretical predictions that all waves in two-dimensional disordered materials are localized, Anderson localization is observed only for sufficiently high frequencies in an isotropically jammed two-dimensional disordered granular packing of photoelastic disks. More specifically, we have performed an experiment in analyzing the level statistics of normal mode vibrations. We observe delocalized modes in the low-frequency boson-peak regime and localized modes in the high frequency regime with the crossover frequency just below the Debye frequency. We find that the level-distance distribution obeys Gaussian-Orthogonal-Ensemble (GOE) statistics, i.e. Wigner-Dyson distribution, in the boson-peak regime, whereas those in the high-frequency regime Poisson statistics is observed. The scenario is found to coincide with that of harmonic vibrational excitations in three-dimensional disordered solids.

Joint influence of electric field and vibrations on the instability of fluid dielectric layer with free boundary

The joint influence of normal electric field and normal vibrations on the instability of the infinitely deep fluid dielectric layer with free boundary in the approximation of small viscosity was studied. It was shown that normal vibrations increase the value of electrical field strength exciting. The electric field effect on the first resonance zone was also studied. It was shown that for sufficiently small values of Weber number there were such values of electrical field strength that had three or two resonance zones existed instead of one first resonance zone.

Симетрія коливальних станів та електронних π-орбі-талей молекули бензену C6H6. Тонка структура спінза-лежних розщеплень

Iз застосуванням оператора проектування на елементи матриць незвiдних представлень точкової групи симетрiї 6/mmm (D6ℎ) молекули бензену C6H6 побудовано аналiтичнi вирази та векторнi зображення форм всiх її нормальних коливань, у тому числi двократно вироджених. Знайдено характери представлень, що вiдповiдають симетрiї п-електронних орбiталей молекули бензену без урахування спiну електрона та проективних представлень її спiнорних п′-орбiталей. Представлення спiнорних п′-орбiталей молекули бензену C6H6 належать проективному класу K1 та описують тонку структуру вперше встановлених спiнзалежних при врахуваннi спiну електрона розщеплень станiв, вироджених без врахування спiну п-орбiталей.

Vibration characteristics based pre-stress analysis of a quadcopter’s body frame

An Unmanned Aerial Vehicle (UAV) Quadcopter is a Mechatronic device consisting of four propellers. Over the past few years we have seen the tremendous growth in the manufacturing of Quadcopters. It has wide range of applications in engineering as well as in daily routine. Present study focuses on the analysis of a Quadcopter’s body frame, because the body frame supports the mechanical and electronics components of the Quadcopter. The Quadcopter’s body frame is subjected to vibration during the flight; in addition, various forces and payload are applied on the body frame. Therefore, in the present study, a Quadcopter body frame has been analyzed on the bases of vibration frequency in order to determine the most prone areas of failure. Furthermore, the simulation results have been analyzed and compared for the normal and pre-stress vibration conditions.

Online Incipient Fault Detection Method Based on Improved ℓ1 Trend Filtering and Support Vector Data Description

Poor model generalization, missing or false alarms, and heavy dependence on expert’s experience are some of the major problems which exist in traditional incipient fault detection (IFD) methods. An IFD rolling bearing application method based on combination of improved $\lambda _{1}$ trend filtering (L1TF) and support vector data description (SVDD) is proposed. First, spectral distance index and multi-scale dispersion entropy based on normal vibration data, which is sensitive to incipient faults, are extracted. The improved $\lambda _{1}$ trend filter (IL1TF) method is employed for processing the feature values and obtaining a trend factor with less fluctuation and better incipient fault indication ability. Then, after determining the kernel function bandwidth of the SVDD by analyzing the characteristics of the training data, a suitable offline SVDD model is trained. Finally, incipient faults are identified by estimating the distance between the trend factor of the real-time data and the center of the hypersphere in the SVDD model. This method employs full performance of SVDD to detect abnormal data files, while reducing the influence of abnormal data files on the model via IL1TF. Furthermore, the method increases the discrimination between the incipient fault data and the normal data. By utilizing Intelligent Maintenance Systems of University of Cincinnati bearing laboratory data and Chinese petrochemical company’s centrifugal pump bearing engineering data, the effectiveness of the constructed model is demonstrated. In addition, the proposed method is compared against existing representative IFD methods. The results indicate that the method proposed in this paper can solve false alarms and detect incipient failure data files more accurately without depending on the external expert’s experience. This is of great significance for providing guidelines to enterprises which employ predictive maintenance techniques.

DFT Study of Molecular and Electronic Structure of Y, La and Lu Complexes with Porphyrazine and Tetrakis(1,2,5-thiadiazole)porphyrazine.

Electronic and geometric structures of Y, La and Lu complexes with porphyrazine (Pz) and tetrakis(1,2,5-thiadiazole)porphyrazine (TTDPz) were investigated by density functional theory (DFT) calculations and compared. The nature of the bonds between metal atoms and nitrogen atoms has been described using the analysis of the electron density distribution in the frame of Bader’s quantum theory of atoms in molecule (QTAIM). Simulation and interpretation of electronic spectra were performed with use of time-dependent density functional theory (TDDFT) calculations. Description of calculated IR spectra was carried out based on the analysis of the distribution of the potential energy of normal vibrations by natural vibrational coordinates.Sample AvailabilityNot available.

USH2A is a Meissner's corpuscle protein necessary for normal vibration sensing in mice and humans.

Fingertip mechanoreceptors comprise sensory neuron endings together with specialized skin cells that form the end-organ. Exquisitely sensitive, vibration-sensing neurons are associated with Meissner's corpuscles in the skin. In the present study, we found that USH2A, a transmembrane protein with a very large extracellular domain, was found in terminal Schwann cells within Meissner's corpuscles. Pathogenic USH2A mutations cause Usher's syndrome, associated with hearing loss and visual impairment. We show that patients with biallelic pathogenic USH2A mutations also have clear and specific impairments in vibrotactile touch perception, as do mutant mice lacking USH2A. Forepaw rapidly adapting mechanoreceptors innervating Meissner's corpuscles, recorded from Ush2a-/- mice, showed large reductions in vibration sensitivity. However, the USH2A protein was not found in sensory neurons. Thus, loss of USH2A in corpuscular end-organs reduced mechanoreceptor sensitivity as well as vibration perception. Thus, a tether-like protein is required to facilitate detection of small-amplitude vibrations essential for the perception of fine-grained tactile surfaces.

Experimental and DFT studies on structure, spectroscopic and thermal properties of N-Methyl-N,N,N-trioctylammonium chloride ionic liquid

The [Aliquat+][Cl−] ionic liquid (IL) has been structural and vibrationally characterized combining experimental FT-IR, FT-Raman and 1H- and 13C-NMR spectroscopies with theoretical studies based on the hybrid B3LYP/6-31G* method. The theoretical determination of structure of IL in gas phase and aqueous solution by using that level of theory shows three ionic C-H···Cl bonds, as supported by atomic Merz-Kollman (MK) charges, bond orders, natural bond orbital (NBO) and atoms in molecules (AIM) calculations. Hence, a monodentate coordination between the [Aliquat+] cation and Cl anion has been proposed for IL because only one of three ionic C-H···Cl bonds presents higher energy and lower distance. The optimized structure confirmed by NMR measurements has allowed the assignments of 237 normal vibration modes to the bands observed in the infrared and Raman spectra with the aid of scaled quantum mechanical force field (SQMFF) methodology and the normal internal coordinates. The effect of Cl in the IL is the shifting of vibration modes corresponding to the CH2 and CH3 groups, as compared with the cation. The mapped MEP surface evidence a strong concentration of charges around the chloride anion compatible with nucleophilic sites in these regions while the frontier orbital analyses suggest that IL is most reactive than the cation probably due to the low values of both global electrophilicity and nucleophilicity indexes. The thermal stability shows that [Aliquat+][Cl−] start to decompose just above 200°C. Comparisons between [Aliquat+][Cl−] and [Aliquat+][NTf2−] ILs show that the IL containing chloride is most reactive than the other one while [Aliquat+] [NTf2−] is thermally more stable than [Aliquat+][Cl−]. These results suggest that the properties of an IL containing the [Aliquat+] cation are strongly dependent of anion. In addition, the scaled force constants for the [Aliquat+][Cl−] IL are also calculated and compared with the reported for the cation. The Cl anion modifies in notable form the properties of cation.

Reddish-orange emission from sol-gel derived Sm3+-doped Sr2La8(SiO4)6O2 phosphors

In this study, Sr2La8-x(SiO4)6O2:xSm3+ (where x=(0.01 ≤ x ≤ 0.11)) phosphors were prepared successfully via the sol-gel route. Their structural properties were evaluated through fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) measurements. The XRD patterns confirmed the purity of the prepared compound that had an average crystallite size of ∼38.8 nm. From the FTIR spectra, various stretching and bending vibrations of the SiO4 units were identified. The band observed at 540 cm−1 was attributed to the normal vibration mode of La-O. The optical properties of the prepared phosphor were assessed through diffuse reflection spectroscopy and photoluminescence measurements. The diffuse reflectance spectrum exhibited seven peaks from the Sm3+ ions corresponding to f-f transitions from the ground state, 6H5/2, to the excited states, 6G7/2, 4D7/2, 4D3/2, 6P7/2, 4L15/2, 6P3/2, and (4I11/2,4I13/2). Out of all these transitions, the peak at 407 nm is the most prominent, this peak come from the 6H5/2→6P3/2 transition, which offers the maximum absorption. The phosphor’s excitation spectrum revealed a charge-transfer (CT) band that extended from 220 to 270 nm and was centered around 240 nm. The excitation spectra also exhibited several transitions of the Sm3+ ion, among these, the transition corresponding to 403 nm was chosen as the pumping wavelength owing to its prominence. The most intense emission peak was observed at 599 nm, this corresponds to the 4G5/2→6H7/2 transition. This emission’s CIE chromaticity coordinates placed it in the reddish-orange region, suggesting that the titled phosphor is suited for orange-red LEDs and the red component in WLEDs.

Modeling and Load Capacity Analysis of Reciprocating Hybrid Linear Guideway With Annular Groove and Sloped Recesses

Abstract In this work, we research a reciprocating hybrid linear guideway and study its load capacity. This hybrid guideway's bearing surface is designed with an annular groove and two sloped shallow recesses. The analysis is based on modeling by mass-conserving cavitation algorithm (p − θ cavitation algorithm), where a modified smoothing switch function is raised for better convergence. Focusing on the normal direction to reciprocation, the load-guideway system is simplified as a single-degree-of-freedom linear time-varying system and solved by Newmark-β method. Due to the hybrid guideway's time-varying dynamic characteristics, there is a normal vibration in reciprocation. By analyzing two typical load cases in detail, the results indicate that the hybrid guideway has greater load capacity than the hydrostatic guideway, and the normal vibration is small enough for most engineering situations.

INFLUENCE OF PRESSURE ON STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES OF CHOLINE IODIDE

The influence of pressure on structural, electronic, and optical properties of choline iodide is studied within the density functional theory approach using the РВЕ gradient functional, the D3(BJ) dispersion correction, and a basis set of localized orbitals. Elastic constants, parameters of the Birch–Murnaghan equation of state, density of electronic states, and frequencies of normal longwave vibrations are calculated. It is shown that the immediate environment of the iodine atom contains 12 carbon atoms with the shortest O–H⋯I distance equal to 2.486 A. The О–H distance increases slightly together with pressure, and the I–H distance decreases while its linear modulus is an order of magnitude smaller than the bulk modulus under 97 GPa. In contrast to intramolecular vibrations, the pressure shifts of lattice vibrations exceed 10 cm–1/GPa, and their modal Gruneisen parameters are an order of magnitude larger.

Membrane-Sugar Interactions Probed by Low-Frequency Raman Spectroscopy: The Monolayer Adsorption Model.

Small sugars are known to stabilize biological membranes under extreme conditions of freezing and desiccation. The proposed mechanisms of stabilization suggest membrane-sugar interactions to be either attractive or repulsive. To obtain new insight into the problem, we use a recently developed low-frequency Raman scattering approach which allows detecting membrane mechanical vibrations. For model membranes of palmitoyl-oleoyl-glycero-phosphocholine (POPC) hydrated in aqueous sucrose and trehalose solutions, we studied the Raman peak between 12 and 15 cm-1 that is attributed to an eigenmode of the normal mechanical vibrations of a lipid monolayer. For both sugars, similar results were obtained. With an increase in sugar concentration in solution, the frequency position of the peak was found to decrease by ∼13% which was interpreted as a consequence of the membrane thickening due sugar monolayer adsorption on the membrane surface. The concentration dependence of the peak frequency position was satisfactorily described by a Langmuir monolayer adsorption model. It is concluded that, at small sugar concentrations (less than 0.2 M), the membrane-sugar interactions are attractive, while at higher concentrations (more than 0.4 M) the attraction disappears. The data obtained show that one sugar molecule on the surface interacts with approximately 3-4 polar lipid heads.

The effect of the macroscopic surface morphology caused by the uneven wear on friction induced vibration

The effects of the macroscopic surface morphology caused by the uneven wear on friction induced vibration were investigated. The experimental results showed the uneven wear in the sliding direction produced the contact plateaus with large theoretical contact lengths at the leading edge and increased the unstable vibrations. A numerical analysis of the contact pressure distribution in different macroscopic surface morphology indicated variation of contact pressure deteriorated the wear status, thus increased the tendency of unstable vibration. And the stability of the friction system decreased with the changes in the macroscopic surface morphology. The lumped parameter model proved the uneven wear in the sliding direction would decrease the stability of the system and increase the coupling of tangential and normal vibration.

Isotope Effects in the Spectra of Hydrogen-Bonded Complexes. Anharmonic Calculations of Isotopologues of the [F(HF)2]– Complex

The frequencies and intensities for IR absorption bands of symmetric and asymmetric hydrogen-bonded complexes [FL1FL2F]– (L1, L2 = K-meson Ka, proton H, deuteron D, and triton T) are calculated. The equilibrium configuration and the potential energy and dipole moment surfaces of [FL1FL2F]– isotopologues were calculated by the MP2/6-311++G(3df,3pd) method with the basis set superposition error taken into account. The calculations of spectral parameters with allowance for anharmonic interactions of all vibrations were carried out using the second-order vibrational perturbation theory. Variation of L1 and L2 masses over wide limits led to significant changes in the forms of normal vibrations and anharmonic interaction constants upon isotopic substitution. The trends in the changes of spectral parameters were determined both upon transition from one symmetric isotopologue to another and upon transition from symmetric to asymmetric isotopologues. The frequency of the D–F stretching band of [FHFDF]– was predicted in good agreement with experimental information, and the assignment of this band was improved.

Graphite oxide as a polymer-like hydrophilic system with peculiar coordinating properties

Structure-energetic and dynamic characteristics of graphite oxide model segments, as a basic element of which the C54 fragment of a carbon sheet was taken, and their hydration complexes involving a restricted number of water molecules are analyzed. The structure optimization and calculation of normal vibrations were performed at the density functional approximation with the B3LYP hybrid exchange-correlation functional with the basis that involves atomic functions of the 6–31G sets on the skeleton carbon atoms and terminal CH groups of the skeleton and of the 6–31G(d,p) sets on the atoms of all functional groups and water molecules. The ability of the hydroxyl groups of graphite oxide to initiate the reorganization of a three-dimensional H-bonded structure of water into the two-dimensional surface structure and to form very strong hydrogen bonds with water molecules providing their partial ionization was revealed.

Modular path integral for finite-temperature dynamics of extended systems with intramolecular vibrations.

The modular decomposition of the path integral is a linear-scaling, numerically exact algorithm for calculating dynamical properties of extended systems composed of multilevel units with local couplings. In a recent article, we generalized the method to wavefunction propagation in aggregates characterized by non-diagonal couplings between adjacent units. Here, we extend the method to the calculation of reduced density matrices in aggregates where each unit includes an arbitrary number of coupled harmonic bath modes, which may describe intramolecular normal mode vibrations, at finite temperature. The effects of harmonic modes are included through influence functional factors, which involve analytical expressions that we derive. Representative applications to spin arrays described by the Heisenberg Hamiltonian with dissipative interactions and to J-aggregates of perylene bisimide, where all coupled normal modes are treated explicitly, are presented.