Suitable Amplitudes Research Articles

Improved Tafel-Based Potentiostatic Approach for Corrosion Rate Monitoring of Reinforcing Steel

Potential step voltammetry (PSV) was introduced in earlier works as an advantageous alternative to traditional methods for measuring corrosion rate in reinforced concrete. The present study aims to improve PSV to maximize its applicability in corrosion rate monitoring, that is, beyond the narrowly-defined steel–concrete systems in which was initially validated. It was therefore identified necessary to address the most suitable PSV pulse amplitudes to accurately obtain the Tafel lines and, therefore, corrosion rate in steel-mortar systems with well-differentiated ohmic drop. PSV findings were compared to reference methods, i.e. Tafel intersection and linear polarization resistance. As a novelty, we propose a procedure to improve the reliability of the PSV-determined Tafel lines, which is based on three protocols (P1, P2 and P3). P1 consists of a specific pulse sequence to accurately characterize the morphology of the polarization curve without disturbing the system. P2 consists of two short pulses for determining the ohmic drop compensation factor. Finally, P3 consists of a simple calculation procedure to accurately adjust the PSV pulse amplitudes (∆V) to the steel–concrete system assessed, thus obviating the need for preset values and, therefore, ensuring accurate corrosion rate results. The procedure proposed is intended to improve PSV with a view to its consolidation as a reliable tool for the unsupervised monitoring of real structures.

Design and Numerical Analysis of Rectangular Sonotrode for Ultrasonic Welding

Ultrasonic welding is a fast, clean and high energy process, no flux or filler metal is required, longer tool life and greater efficiency of a weld can be achieved in just a few seconds. Limited length and thickness of weld are the main drawbacks in this process. Welding of large length and thickness materials leads the ultrasonic welding applications unlimited. The design of the components like booster and sonotrode or horn in ultrasonic welding plays a vital role to improve the length and thickness of the welds by generating uniform amplitudes. In the present work, an ultrasonic sonotrode is designed to improve the weld length with suitable uniform amplitudes on the weld bed surface. The design of sonotrode is significantly difficult to obtain the uniform amplitudes at the large weld length. Here, rectangular sonotrode with multiple slots is designed based on theoretical calculations and numerical analysis is performed to obtain the maximum possible weld lengths with uniform amplitudes at a known operating frequency. The finite element method is used to analyze the actual resonating frequency and amplitude distribution of the sonotrode and obtained the maximum weld length as 400 mm for 15 kHz frequency with 3 slots.
 HIGHLIGHTS
 
 One of the major drawbacks in ultrasonic welding is limited length and thickness of weld. Welding of larger length and thickness improves the ultrasonic welding applications.
 Modal and harmonic analysis conducted in order to find the dynamic behaviour of the sonotrode.
 The increase in the weld length of the sonotrode deviates the amplitude distribution within the sonotrode. To overcome this non-uniform amplitude distribution, longitudinal slots are provided in the sonotrode. Also, these slots reduce the weight of the sonotrode.

Automatic locking of a parametrically resonating, base-excited, nonlinear beam

Described is a closed-loop control scheme capable of stabilizing a parametrically excited nonlinear structure in several vibration modes. By setting the relative phase between the spatially filtered response and the excitation, the open-loop unstable solution branches are stabilized under a 2:1 parametric excitation of a chosen mode of vibration. For a given phase, the closed-loop automatically locks on a limit cycle, through an Autoresonance scheme, at any desired point on the solution branches. Axially driven slender beams and nanowires develop large transverse vibration under suitable amplitudes and frequency base-excitation that are sensitive to small potential coupled field. To utilize such a structure as a sensor, stable and robust operation are made possible by the control scheme. In addition, an optimal operating point with large sensitivity to the sensed potential field can be set using phase as a tunable parameter. Detailed analysis of the dynamical behavior, experimental verifications, and demonstrations sheds light on some features of the system dynamics.

DEM simulation of vibrated packing densification of mono-sized regular octahedral particles

The densification of mono-sized regular octahedral particles under vibration is simulated by a DEM model. The model is validated by physical experiments. The effects of operating parameters including vibration amplitude and frequency are investigated. The obtained packing structures are characterized, and corresponding densification mechanisms are identified. The results indicate that vibration amplitude is more critical for densification compared to frequency, where a wide range of suitable amplitudes exists to realize the dense packing structures. Ordered packing structure exists in boundary region. The central region possesses good particle position randomness and orientation randomness, and the packing density for poured packing (initial loose packing) and vibrated packing (dense packing) in the central region are 0.670 and 0.684, respectively. During densification, contacts and constraints between particles decrease, and the stress within the structure becomes larger. The typical arrangement of neighboring particles is close to but not perfect face to face (F–F) contact. Particles in the boundary region experience more rotations and can form local ordered structures. These structures prevent the relative movement of individual particles but favor their movement as a whole. Particles in the central region have relatively little movement and rotation. The ordered structures formed at boundary is difficult to extend to the central region due to the restricted change of particle contact conditions.

Taming chaos in damped driven systems by incommensurate excitations

The possibility of reducing and even suppressing chaos in dissipative nonautonomous systems by additional incommensurate chaos-suppressing excitations is theoretically demonstrated through the universal example of a perturbed Duffing oscillator by considering rational approximations to the irrational ratio Ω/ω between the chaos-suppressing and chaos-inducing frequencies. For each chosen rational approximation, analytical predictions for the suitable amplitudes and initial phases of the chaos-suppressing excitation are numerically confirmed for small amplitudes and at the predicted suitable initial phases. For the significant case of the golden ratio Φ≡(1+5)/2, we study the structural stability of the suppressory scenario as the respective convergents approximate the irrational ratio Ω/ω=1/Φ. Our theory predicts and numerical simulations confirm that the values of the suitable amplitudes are rather insensitive to high-order convergents. On the contrary, the number and values of the suitable initial phases critically depend on each particular convergent in order to satisfy two requirements: (1) Maximum approximation to the frustration of the homoclinic bifurcation existing in the absence of the chaos-suppressing excitation and (2) maximum survival of a relevant spatio-temporal symmetry of the dynamical equation.

Investigation the Amplitude Uniformity on the Surface of the Wide-Blade Ultrasonic Plastic Welding Horn

Ultrasonic welding has been applied for joining thermoplastic components due to their advantages such as clean, fast and reliable. The basic principle is to use the mechanical energy of ultrasonic frequency vibration to produce the molten pool at the interface of the joined components under high pressure to create solid-state welding joints. Depending on the specific application, the ultrasonic horn is designed to generate suitable amplitudes on the surface of the welding zone. Uniformity of the amplitudes can be a challenge as the welding area increases. Therefore, design a welding horn in order to obtain the uniform amplitudes at the large area is significant difficult. This work presents a method for obtaining the uniform amplitudes at the working surface of the stepped wide-blade horn. Finite element method is used to analyze the amplitude distribution at the horn surface of 250 × 34 mm2 with working frequency of 15 kHz and aluminum alloy 7075. The uniformity of amplitude is obtained by changing the shape of the horn.

Second order sliding mode control for nonlinear affine systems with quantized uncertainty

This paper deals with the design of a Second-Order Sliding Mode (SOSM) control algorithm able to enhance the closed-loop performance depending on the current working conditions. The novelty of the proposed approach is the design of a nonsmooth switching line, based on the quantization of the uncertainties affecting the system. The quantized uncertainty levels allow one to define nested box sets in the auxiliary state space, i.e., the space of the sliding variable and its first time derivative, and select suitable control amplitudes for each set, in order to guarantee the convergence of the sliding variable to the sliding manifold in a finite time. The proposed algorithm is theoretically analyzed, proving the existence of an upperbound of the reaching time to the origin through the considered quantization levels.

Practical methods for generating alternating magnetic fields for biomedical research.

Alternating magnetic fields (AMFs) cause magnetic nanoparticles (MNPs) to dissipate heat while leaving surrounding tissue unharmed, a mechanism that serves as the basis for a variety of emerging biomedical technologies. Unfortunately, the challenges and costs of developing experimental setups commonly used to produce AMFs with suitable field amplitudes and frequencies present a barrier to researchers. This paper first presents a simple, cost-effective, and robust alternative for small AMF working volumes that uses soft ferromagnetic cores to focus the flux into a gap. As the experimental length scale increases to accommodate animal models (working volumes of 100s of cm3 or greater), poor thermal conductivity and volumetrically scaled core losses render that strategy ineffective. Comparatively feasible strategies for these larger volumes instead use low loss resonant tank circuits to generate circulating currents of 1 kA or greater in order to produce the comparable field amplitudes. These principles can be extended to the problem of identifying practical routes for scaling AMF setups to humans, an infrequently acknowledged challenge that influences the extent to which many applications of MNPs may ever become clinically relevant.

A string realisation of Ω-deformed Abelian [formula omitted] theory

The N=2⁎ supersymmetric gauge theory is a massive deformation of N=4, in which the adjoint hypermultiplet gets a mass. We present a D-brane realisation of the (non-)Abelian N=2⁎ theory, and compute suitable topological amplitudes, which are expressed as a double series expansion. The coefficients determine couplings of higher-dimensional operators in the effective supergravity action that involve powers of the anti-self-dual N=2 chiral Weyl superfield and of self-dual gauge field strengths superpartners of the D5-brane coupling modulus. In the field theory limit, the result reproduces the Nekrasov partition function in the two-parameter Ω-background, in agreement with a recent proposal.

Control of coherence transfer via tunneling in quadruple and multiple quantum dots

Transfer and manipulation of coherence among the ground state and indirect exciton states via tunneling in quadruple and multiple quantum dots is analyzed. By applying suitable amplitudes and sequences of the pump and tunneling pulses, a complete transfer of coherence or an arbitrary distribution of coherence of multiple states can be realized. The method, which is an adiabatic passage process, is different from previous works on quantum dot molecules in the way that the population can transfer from the ground state to the indirect exciton states without populating the direct exciton state, and thus no spontaneous emission occurs. This investigation can provide further insight to help the experimental development of coherence transfer in semiconductor structures, and may have potential applications in quantum information processing.

Magnetization reversal of the transverse domain wall confined between two clusters of magnetic impurities in a ferromagnetic planar nanowire

Numerical simulations have been used to investigate the polarity reversal of the transverse domain wall in rectangular magnetic nanowires and the stabilization of the domain wall position after occurring the polarity reversal. In order to control the wall position we have considered two clusters of magnetic impurities, identical and equidistant from the nanowire width axis. Traps of pinning and blocking for the transverse domain wall can be originated from magnetic impurities, consisting of a local variation of the exchange constant. Under suitable excitation amplitudes it is possible to switch the polarity of the transverse domain wall by applying a nanosecond axial magnetic field pulse in a fast and controllable way.

On the shielding of sound from a source near one or two coaxial cones

The shielding of the sound from a source near a cone or two coaxial circular cones is addressed by an exact analytical method, considering free spherical waves satisfying a rigid or impedance boundary condition on the wall of the cone(s); the boundary condition is applied for impedance proportional to the distance from the vertex. The exact solution involves the eigenvalues of the problem that are generally real or complex (not integers), and coincide with the degree of the associated Legendre functions and order of the spherical Bessel functions which specify respectively the latitudinal and radial dependencies of the wave field. These eigenfunctions or ‘conical wave harmonics’ can be chosen in more than one way, e.g. (a) as standing wave modes which are finite at the vertex of the cone(s), but do not satisfy a radiation condition at infinity; (b) as propagating waves satisfying a radiation condition at infinity, and generally singular at the vertex of the cone(s). The method of calculation of eigenvalues and eigenfunctions is presented both for a single cone and two coaxial cones with the same vertex, and arbitrary aperture(s). The method specifies the eigenvalues, and the corresponding radial, azimuthal and latitudinal eigenfunctions. An asymptotic formula is obtained for the eigenvalues which gives reasonable good agreement with the exact results. The eigenvalues and eigenfunctions appear with suitable amplitudes in the Green function representing a monopole source near the vertex of the cone(s). The acoustic field is plotted also for a longitudinal and a transverse dipole and mixed quadrupole source near the vertex.

Uniaxial ratchetting of extruded AZ31 magnesium alloy: Effect of mean stress

The uniaxial ratchetting of extruded AZ31 magnesium alloy was investigated in the cyclic tests with different mean stresses and at room temperature. The prescribed mean stresses and corresponding stress amplitudes were chosen to make the different plastic deformation mechanisms such as dislocation slipping, twinning and detwinning occur individually or simultaneously during the cyclic deformation of the AZ31 magnesium alloy with a hexagonal close packed crystal structure, and then the effect of mean stress on the uniaxial ratchetting of the magnesium alloy was discussed. It is seen that ratchetting occurs in the AZ31 magnesium alloy during the stress-controlled cyclic loading, but different evolution features are observed in the uniaxial ratchetting tests with different mean stresses. Different ratchetting behaviors are determined by the different deformation mechanisms of extruded AZ31 magnesium alloy occurring in the tensile and compressive parts of cyclic loading. A sigmoidal stress–strain hysteresis loop of the magnesium alloy presented in the cyclic tension–compression tests with some suitable mean stresses and stress amplitudes is caused by the twinning/detwinning deformation mechanism, which should be reasonably considered in constructing a cyclic constitutive model to describe the uniaxial ratchetting of magnesium alloys.

Scattering of gap solitons byPT-symmetric defects

The resonant scattering of gap solitons (GS) of the periodic nonlinear Schr\"odinger equation with a localized defect which is symmetric under the parity and the time-reversal (PT) symmetry, is investigated. It is shown that for suitable amplitudes ratios of the real and imaginary parts of the defect potential the resonant transmission of the GS through the defect becomes possible. The resonances occur for potential parameters which allow the existence of localized defect modes with the same energy and norm of the incoming GS. Scattering properties of GSs of different band-gaps with effective masses of opposite sign are investigated. The possibility of unidirectional transmission and blockage of GSs by PT defect, as well as, amplification and destruction induced by multiple reflections from two PT defects, are also discussed.

Cyclic deformation behavior of a medium carbon steel in the VHCF regime

At the Institute of Materials Science and Engineering an ultrasonic testing facility (UTF) for the fatigue assessment in the very high cycle fatigue (VHCF) regime was developed. The UTF allows to control the test and to measure process parameters like generator power and specimen temperature. In load increase tests (LIT), the critical stress amplitude leading to a first rise of the measured physical values is determined and can be used to identify suitable amplitudes for single step tests in the VHCF regime. The individual design of the UTF allows a defined interruption of the fatigue experiment for detailed microscopic investigations.

Noise-induced striped trajectories of Rossler systems

In this paper, the generation of striped trajectories in phase space by noise-injection is considered. With suitable amplitudes of noise, the steady-state system orbits appear in rectangular striped shape. The relationship between the shape (including the range and the number of stripes) and some parameters is discussed. The result shows that noise can also generate the striped shape effectively and simply, which is similar to the newly-discovered striped pattern generated by controlled Rossler systems.

Inhibition of chaotic escape from a potential well by incommensurate escape-suppressing excitations.

Theoretical results are presented concerning the reduction of chaotic escape from a potential well by means of a harmonic parametric excitation that satisfies an ultrasubharmonic resonance condition with the escape-inducing excitation. The possibility of incommensurate escape-suppressing excitations is demonstrated by studying rational approximations to the irrational escape-suppressing frequency. The analytical predictions for the suitable amplitudes and initial phases of the escape-suppressing excitation are tested against numerical simulations based on a high-resolution grid of initial conditions. These numerical results indicate that the reduction of escape is reliably achieved for small amplitudes and at, and only at, the predicted initial phases. For the case of irrational escape-suppressing frequencies, the effective escape-reducing initial phases are found to lie close to the accumulation points of the set of suitable initial phases that are associated with the complete series of convergents up to the convergent giving the chosen rational approximation.

The vortex rope in the draft tube of Francis turbines operating at partial load: a proposal for a mathematical model

The phenomenon under consideration is represented as the superposition of two potential-flow motion fields, endowed with singularities ofhelicoidal shape. In the first field the singularity is a helicoidal vortex (i.e. the circulation around it is finite); in the second one the singularity is a uniform distribution line source, sinusoidally pulsating in time. If the draft tube is rectilinear, the solution pertaining to the first field adequately represents the "rotating perturbation field", devoid of any synchronous component: it is not necessary in this case to assign a finite amplitude to the second flow field. If the draft-tube rectilinear stretch is followed by an elbow, qualitative considerations show that a synchronous component must needs arise. If, moreover, the vortex rope is cavitated, the linear combination (with suitable amplitudes) of the two flow fields allow the total perturbation field to be represented (rotating+ synchronous components). Obviously, a certain number of compatibility conditions have to be satisfied. Those concern on one hand the flow coming out of the runner (and this allows the parameters of the first flow field to be defined), on the other hand the other parts of the hydraulic system (and this leads to determination of the parameters of the second flow field, i.e. of the dynamic amplification of the synchronous excitation tied to the elbow). The main characters of the proposed mathematical model are in qualitative agreement with what is known from tests on reduced scale model or from measurements performed on actual installations. The proposed model, after proper quantitative validation, could provide a useful tool in order to advance comprehension of the phenomena. Moreover, it could be used in order to carry out a correct, reliable transposition from reduced-scale model tests to full-size prototype (it is a well-known fact that such a transposition is nowadays fraught with uncertainties).

Enantiomorph-dependent probability distributions of origin-invariant phases

By integrating joint probability distributions of two related invariant phases with respect to one of the variables over the range 0 to π, enantiomorph-dependent phase indications may be obtained. In the present paper the full potential of such a strategy is described. For probability distributions correct up to and including terms of order N-1, all cases of interest appear to consist of combinations of two invariants with one or two structure factors in common. For each case the joint probability distribution of the phases of such a pair of invariants, given a number of suitable structure-factor amplitudes, is derived. Subsequently, all these distribution functions are integrated from 0 to π with respect to one or other variable, thus exploring the full range of enantiomorph-dependent distributions. The resulting expressions are grouped together according to whether the chosen enantiomorph definer is a triplet, quartet, quintet or higher-order invariant, thereby facilitating their future implementation in direct-methods procedures.

Characterization of the pace-maker current kinetics in calf Purkinje fibres.

Kinetics of the cardiac pace-maker current (if) were studied using high K+, low Na+ solutions under conditions where the current time course could be dissected from other components. Activation of if during relatively large negative pulses is S-shaped, and is approximated by an exponential function of time to the third power. Less-pronounced S-shaped activation occurs at potentials close to the middle of the activation curve (near -70/-80 mV). Here, allowing for the presence of a very slow component, the power required to fit the current activation approaches 1. The comparison between current activation and deactivation at the same potentials shows that although deactivation can be approximated by a single exponential, the two processes have a quite different time dependence, and this difference depends on the membrane potential. This behaviour is not compatible with Hodgkin-Huxley kinetics. While near the half-activation range the current decays with an apparently single exponential time course, at more positive potentials the current deactivation becomes sigmoidal. At least the third power of an exponential is required to fit its time course at potentials positive to about -40 mV. These data imply that both open and closed states correspond to several distinct channel configurations. The 'delay' in the current onset during a hyperpolarization is decreased by applying large, short hyperpolarizations before activation. Suitable pre-pulse durations and/or amplitudes can reduce the subsequent current activation to a single exponential. Records with and without a pre-pulse do not always superimpose. After the activation 'delay' has been removed by a suitable hyperpolarization preceding an activating pulse, the time course of its recovery can be studied by applying depolarizations of given amplitude and variable duration. The time course of the delay recovery does not seem to be linked to the time course of current deactivation recorded at the same voltage. Reduction of the activation 'delay' by conditioning pre-hyperpolarizations does not affect current decay during a subsequent depolarizing pulse. The current decay appears to depend only on the current amplitude reached before a deactivating pulse is applied. This, and the evidence in the preceding paragraph, suggest that the delay recovery and the current deactivation are independent processes. A reaction scheme is proposed, which has been developed on the basis of the experimentally determined kinetic properties of if. The channel model is composed of five gating subunits of three different types, not all independent in their movements.(ABSTRACT TRUNCATED AT 400 WORDS)