The efficiency of ultrasonic oscillations transfer into the load

The results of ultrasonic action to the substances have been presented. It is examined, the correlation between the electrical parameters of ultrasonic equipment and acoustic performances of the ultrasonic field in treating the medium, the efficiency of ultrasonic technological facility, and the peculiarities of oscillations introduced into the load under cavitation development. The correlation between the acoustic powers of oscillations securing the needed level of cavitation and desired technological effect, and the electrical parameters of the ultrasonic facility, first of all, the power, is established. The peculiarities of cavitation development in liquids with different physical-chemical properties (including the molten low-melting metals) have been studied, and the acoustic power of oscillations introduced into the load under input variation of electric power to the generator has been also estimated.     

Effect of sample tilt on nanoindentation behaviour of materials

Analysis of nanoindentation is based on the elastic solution of a rigid indenter perpendicularly penetrating a flat contact surface. In reality, nanoindentation is often performed on a tilt sample surface due to sample tilt mounting or the existing roughness of a polished or raw surface. In this study, finite element simulations as well as nanoindentation experiments on a fused-quartz sample with different tilt angles were carried out to investigate the influence of sample tilt on nanoindentation behaviour of materials. It was found that sample tilt results in increases in the indentation load, contact area and contact stiffness at the same penetration depth. The contact area increase caused by sample tilt cannot be accounted for by Sneddon's equation, commonly used in nanoindentation analysis. This results in a significant underestimation of indentation projected contact area, which in turn leads to an overestimation of the mechanical properties measured by nanoindentation.     

The internal friction of longitudinal oscillations in ferromagnetic materials

The paper deals with the theory of the new magnetomechanical phenomenon in an alternating field [6, 7]. The first part concerns the internal friction of longitudinal oscillations of a ferromagnetic material in the shape of a wire in a constant magnetic field. It is assumed that the medium in which the sample oscillates is conducting and has a certain permeability. Equations defining the magnetic field in the oscillating material are derived from the basic thermodynamic relations. The term describing the non-conservative force component in a complex formulation is used to determine the internal friction. A general relation between the internal friction and the magnetic field is derived, as well as other expressions, which are a simplification of it. The second part of the paper deals with internal friction in an alternating field. It is shown that the solution can be transformed to the sum of the internal frictions of the different harmonic oscillations, which are obtained as a partial solution of the problem on the assumption that the elastic oscillations in interaction with the field oscillations are separated into their harmonic components. The calculation then becomes that of the internal friction considered in the first part of the paper. In this case the internal friction significantly depends on the field amplitude. The functional dependence of the internal friction peak on the frequency of the mechanical oscillations is also calculated. The agreement of the theory with experiment is satisfactory.

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The internal friction of torsional oscillations in ferromagnetic materials

The paper is a continuation of the first part [1] and deals with the internal friction of torsional oscillations of ferromagnetic materials in a static and an alternating magnetic field. The calculation differs considerably from the case of longitudinal oscillations, particularly in the following points. In the first place, the internal friction of torsional oscillations depends quite differently on the dimensions of the sample, and the continuous distribution of magnetic domains and Bloch walls cannot be so easily defined. Secondly, a magnetic field created as a result of eddy currents during torsional oscillations does not penetrate the surroundings, so that the internal friction in an electrically conducting medium is the same as in vacuum. Thirdly, the deformation here is an antisymmetrical function of the field, so that the coefficient is an even function while with longitudinal oscillations it was expressed by an odd function. Despite these different conditions the results are very similar to those with longitudinal oscillations and agree well with experiment. In an alternating magnetic field the internal friction of torsional oscillations has a sharp maximum atH=0.64H _S whereH _S is the saturated value of the field for which magnetoelastic effects disappear.

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The effect of low-frequency oscillations on cardio-respiratory synchronization

We show that the transitions which occur between close orders of synchronization in the cardiorespiratory system are mainly due to modulation of the cardiac and respiratory processes by low-frequency components. The experimental evidence is derived from recordings on healthy subjects at rest and during exercise. Exercise acts as a perturbation of the system that alters the mean cardiac and respiratory frequencies and changes the amount of their modulation by low-frequency oscillations. The conclusion is supported by numerical evidence based on a model of phase-coupled oscillators, with white noise and lowfrequency noise. Both the experimental and numerical approaches confirm that low-frequency oscillations play a significant role in the transitional behavior between close orders of synchronization.     

The physics of small-amplitude oscillation of the vocal folds

A theory of vocal fold oscillation is developed on the basis of the body-cover hypothesis. The cover is represented by a distributed surface layer that can propagate a mucosal surface wave. Linearization of the surface-wave displacement and velocity, and further small-amplitude approximations, yields closed-form expressions for conditions of oscillation. The theory predicts that the lung pressure required to sustain oscillation, i.e., the oscillation threshold pressure, is reduced by reducing the mucosal wave velocity, by bringing the vocal folds closer together and by reducing the convergence angle in the glottis. The effect of vocal tract acoustic loading is included. It is shown that vocal tract inertance reduces the oscillation threshold pressure, whereas vocal tract resistance increases it. The treatment, which is applicable to falsetto and breathy voice, as well as onset or release of phonation in the absence of vocal fold collision, is harmonized with former treatments based on two-mass models and collapsible tubes.     

Mechanical characteristics of Fe-based coating obtained by nanoindentation

In this study, clad layers of iron-based alloy with a nature of self-fluxing were melted on low carbon steel by plasma cladding process. Nanoindentation with atomic force microscopy (AFM) has been used to investigate the mechanical properties of the coating. Hardness and elastic modulus at ultra-low loads were first determined using the method proposed by Giannakopoulos and Suresh (G&S method). The true contact area and mechanical properties were then determined using atomic force microscopy (AFM) combined with the Oliver and Pharr method (new proposed method) as the correction group. The mechanical properties calculated by the two methods showed the same distribution while had deviation in specific values. The effect of surface roughness to the calculated mechanical properties was investigated. Both hardness and elastic modulus were found to exhibit certain surface roughness dependence. When root mean square (RMS) roughness ranged from 2.2 nm to 4.4 nm, hardness calculated by both the methods increased obviously and reached maximums around 4.1 nm. Elastic modulus calculated by G&S method at different RMS showed the same distribution with that of hardness, while reduced elastic modulus obtained by AFM was insensitive to the range of RMS.     

Investigation of the photoplastic effect in vitreous semiconductors by cyclic nanoindentation

The dynamics of photoinduced changes in the internal friction and the Young’s modulus for films in the As-Se system is investigated by cyclic nanoindentation at infralow frequencies. It is revealed that the irradiation of the films leads to an increase in the Young’s modulus, a retardation of relaxation processes, and a decrease in the viscosity and nanohardness of the material. The results obtained are discussed in the framework of the concept of microheterogeneous glass structure.     

The effect of load on guided wave propagation

The motivation for this work is the development of load measurement techniques based on the velocity of propagating guided waves in structural members such as cable and rail. A finite element technique for modelling the dispersion characteristics of guided waves in a waveguide of arbitrary cross section subjected to axial load is presented. The results from the FE model are compared to results obtained from a simple Euler–Bernoulli beam model. A dimensionless measure of the sensitivity of phase and group velocity to load is defined as the fractional change in velocity divided by the applied strain. At frequency waveguide-characteristic-dimension products (fd) of greater than around 1 for phase velocity and 5 for group velocity the sensitivity to strain levels likely to be encountered in engineering materials is strain independent (indicating that the change in velocity is proportional to strain) and decreases with increasing frequency. In this fd range, phase velocity increases under tensile loading and group velocity decreases. For waveguides with simple cross sections, such as plates and circular rods, it is shown that the Euler–Bernoulli beam model provides acceptable results over the majority of the fd range where there is measurable sensitivity to load. However, for waveguides with more complex cross sections such as rail, the Euler–Bernoulli beam model is less satisfactory. In particular, it does not predict the subtleties of the sensitivity of certain modes at high frequencies, nor any sensitivity for the torsional fundamental mode.     

Generation of soliton oscillations in nonlinear quadratic materials

We show analytically and numerically that the generation of long-lasting soliton oscillations in resonant chi(2) optical materials possesses a threshold for the amplitude of a fundamental wave. The persistent oscillations of solitary waves reported by Etrich et al. [Phys. Rev. E 54, 4321 (1996)] are found to appear for finite values of the wave amplitude.     

Atomistic simulations of the effect of a void on nanoindentation response of nickel

Three-dimensional molecular dynamics simulations have been performed to investigate the effect of a void on the nanoindentation of nickel thin film.The radius and depth of the void are varied to explore how they influence the nanoindentation.The simulation results reveal that the presence of a void softens the material and allows for a larger indentation depth at a given load compared to the no void case.The radius and depth of the void have a major effect on the indentation behaviors of the thin film.It is also observed that the void will collapse during the nanoindentation of crystal with void.And when the indentation depth is sufficiently large,the void will disappear.It is found that the indentation depth needed to make the void disappear depends on the void size and location.     

The effect of Zeeman splitting on Shubnikov-de Haas oscillations in two-dimensional systems

A theory of the Shubnikov-de Haas effect is developed for two-dimensional systems in a tilted magnetic field. The conductivity tensor is calculated for an arbitrary ratio r of the Zeeman splitting to the cyclotron splitting. Possible anisotropy of the g factor is taken into account. It is shown that at integer values of r, the main harmonic dominates in the spectrum of Shubnikov-de Haas oscillations and the phase of the oscillations depends on the parity of r. At half-integer values of r, the conductivity oscillations are determined by the harmonics of the second order of smallness.     

The effect of respiratory oscillations in heart rate on detrended fluctuation analysis

Characterization of heart rate using detrended fluctuation analysis (DFA) is impeded by respiratory oscillations. In particular, the short-term exponent measured from 15 to 30 beats is compromised in the DFA. We reconstruct respiratory signal from electrocardiograms and attenuate the respiratory oscillation in the heart rate using a frequency-dependent subtraction approach. We validate this method by applying it to an electrocardiogram signal simulated using a coupled differential equation with the respiratory oscillation modelled using a sine function. The exponent estimated using the proposed approach agreed with the exponent incorporated in the model within a narrow range. In contrast, the exponent obtained from the raw data deviated from the expected value. Furthermore, the exponents obtained for the raw heart rate are smaller than the exponents obtained for the respiration oscillation attenuated heart rate. We apply this approach to heart rate measured from 12 preterm infants that were being treated for prematurity related complications. As observed in the simulated data, we show that compared to the raw heart rate, the respiratory oscillation attenuated heart rate shows higher short-term exponent (p < 0.001).     

MD simulation of the effect of contact area and tip radius on nanoindentation

Nanoindentation,namelydepth-sensingindentation(DSI),involvesforcingarigidindenterwithknowngeometryintothesurfaceofamaterialwhilecontinuouslymonitoringtheloadontheindenter,thedisplacementoftheindenterintothesurface,andthetimeoftheexperiment.Thedepthisthenusedtocalculatetheprojectedareaofcontactforthepurposeofcalculatingthehardnessandelasticmodulus.Infact,variouserrorsareassociatedwiththisprocedure.Oneofthemcomesfromthemeasurementofthepenetrationdepth.Ideally,thepenetrationdepthshouldbecalcula…     

The effect of inhomogeneity on electrostatic oscillations of multi-velocity electron streams

The dispersion relations for electrostatic oscillations of an inhomogeneous beam with a longitudinal velocity spread and of two counter-streaming inhomogeneous beams are investigated. In both cases the effect of the inhomogeneity is to extinguish the discrete spectrum entirely and to make the dispersion function a multivalued analytic function: a pair of branch points is created corresponding to each zero of the dispersion function of the associated homogeneous problem. The zeros themselves do not vanish but move on other sheets of the Riemannian surface of the dispersion function. The result is, physically, that the Landau damping is enhanced and the aperiodic two-beam instability becomes an over-stability.     

Transport characteristics of Rabi oscillations in the two-band superlattices

We investigated the transport characteristics of Rabi oscillations, by using numerical methods, within a two-band tight-binding model driven by dc－ac electric fields. We found that Rabi oscillations make the long-time average current a sharply change, i.e. the current have resonant peaks appearing. Rabi oscillations are destroyed by dephasing; these peaks are the signatures of Rabi oscillations on the current response. The strong interband coupling will change the conditions of Rabi oscillations and, correspondingly, changes the places where the current resonant peaks appear.