Showing papers on "Impulse (physics) published in 2011"

Impulsive anti-periodic boundary value problem for nonlinear differential equations of fractional order

Abstract: In this paper, we prove the existence and uniqueness of solutions for an anti-periodic boundary value problem of nonlinear impulsive differential equations of fractional order α ∈ ( 2 , 3 ] by applying some well-known fixed point theorems. Some examples are presented to illustrate the main results.

Stabilizing Effects of Impulses in Discrete-Time Delayed Neural Networks

Abstract: This brief studies the global exponential stability of the equilibrium point of discrete-time delayed Hopfield neural networks (DHNNs) with impulse effects by using difference inequalities. We shall consider the stabilizing effects of impulses when the corresponding impulse-free DHNN is even not asymptotically stable. The obtained results characterize the aggregated effects of impulses and deviation of the impulse-free DHNN from its equilibrium point on the exponential stability of the whole system. It is shown that, because of effects of impulses, the impulsive discrete-time DHNN may be exponentially stable even if the evolution of impulse-free component deviates from its equilibrium point exponentially.

An ionization region model for high-power impulse magnetron sputtering discharges

Abstract: A time-dependent plasma discharge model has been developed for the ionization region in a high-power impulse magnetron sputtering (HiPIMS) discharge. It provides a flexible modeling tool to explore ...

Flow structures and hydrodynamic force during sediment entrainment

Abstract: [1] An experimental investigation of the role of coherent structures and their effect on hydrodynamic forces responsible for inception of sediment motion has been carried out using a laboratory flume. Two types of experiments, namely, movable and fixed ball, were conducted using spherical roughness element beds with particle image velocimetry used to measure the instantaneous flow velocity field. Movable ball experiments revealed the predominance of large sweep structures at the instant of entrainment for both shielded and exposed particles. Fixed ball experiments involving simultaneous measurements of hydrodynamic forces and velocity on the particle at entrainment conditions revealed the significance of impulse in initiating sediment entrainment such that an optimum combination of force and duration is required to produce the threshold impulse. Short-duration lift forces of magnitudes greater than the submerged weight are thought to be responsible for partial lifting of the completely shielded particle. Quadrant analysis and probability distribution function plots of the dominant hydrodynamic force reveal the higher probability of occurrence of high-magnitude force induced by sweep (Q4) events.

Design and application of an integrated electro-optic sensor for intensive electric field measurement

Abstract: Impulse electric field measurement should satisfy some special requirements such as intensive signal amplitude, appropriate insulation, broadband response, and small size. Three types of integrated electro-optic sensors, designed and fabricated for measuring intensive impulse electric field, was implemented in this paper. The theoretical concerns and specific characteristics of these integrated electro-optic sensors were illustrated in terms of their structures and key parameters. The time domain input/output characteristic and frequency response of the sensors were examined too. Comparison of the time domain characteristics of these sensors revealed that the mono-shield sensor was more efficient than those with antennas in measurable amplitudes, which is critical for high electric field measurement in gas breakdown research. In addition, the application of the sensor in the lightning impulse experiment upon air gap not only verify the existence of streamer charge but also ensured that this sensor is expected to be widely used in transient measurement investigations such as the measurement of lightning electric field, air breakdown procedure, and maybe surface discharge.

Differentiation of benign from malignant liver masses with Acoustic Radiation Force Impulse technique.

Abstract: ObjectiveThe objective of the study was to determine the performance of Acoustic Radiation Force Impulse (ARFI) imaging to differentiate benign from malignant liver masses, both of hepatocellular origin and metastases, by quantification of their stiffness.MethodsThis study has institutional review b

Entrainment of coarse grains in turbulent flows: An extreme value theory approach

Abstract: [1] The occurrence of sufficiently energetic flow events characterized by impulses of varying magnitude is treated as a point process. It is hypothesized that the rare but extreme magnitude impulses are responsible for the removal of coarse grains from the bed matrix. This conjecture is investigated utilizing distributions from extreme value theory and a series of incipient motion experiments. The application of extreme value distributions is demonstrated for both the entire sets of impulses and the maxima above a sufficiently high impulse quantile. In particular, the Frechet distribution is associated with a power law relationship between the frequency of occurrence and magnitude of impulses. It provides a good fit to the flow impulses, having comparable performance to other distributions. Next, a more accurate modeling of the tail of the distribution of impulses is pursued, consistent with the observation that the majority of impulses above a critical value are directly linked to grain entrainments. The peaks over threshold method is implemented to extract conditional impulses in excess of a sufficiently high impulse level. The generalized Pareto distribution is fitted to the excess impulses, and parameters are estimated for various impulse thresholds and methods of estimation for all the experimental runs. Finally, the episodic character of individual grain mobilization is viewed as a survival process, interlinked to the extremal character of occurrence of impulses. The interarrival time of particle entrainment events is successfully modeled by the Weibull and exponential distributions, which belong to the family of extreme value distributions.

Dynamic roughness perturbation of a turbulent boundary layer

Abstract: The zero-pressure-gradient turbulent boundary layer over a flat plate was perturbed by a temporally oscillating, spatial impulse of roughness, and the downstream response of the flow field was interrogated by hot-wire anemometry and particle-image velocimetry. The key features common to impulsively perturbed boundary layers, as identified in Jacobi & McKeon (J. Fluid Mech., 2011), were investigated, and the unique contributions of the dynamic perturbation were isolated by contrast with an appropriately matched static impulse of roughness. In addition, the dynamic perturbation was decomposed into separable large-scale and small-scale structural effects, which in turn were associated with the organized wave and roughness impulse aspects of the perturbation. A phase-locked velocity decomposition of the entire downstream flow field revealed strongly coherent modes of fluctuating velocity, with distinct mode shapes for the streamwise and wall-normal velocity components. Following the analysis of McKeon & Sharma (J. Fluid Mech., vol. 658, 2010, pp. 336–382), the roughness perturbation was treated as a forcing of the Navier–Stokes equation and a linearized analysis employing a modified Orr–Sommerfeld operator was performed. The experimentally ascertained wavespeed of the input disturbance was used to solve for the most amplified singular mode of the Orr–Sommerfeld resolvent. These calculated modes were then compared with the streamwise and wall-normal velocity fluctuations. The discrepancies between the calculated Orr–Sommerfeld resolvent modes and those experimentally observed by phase-locked averaging of the velocity field were postulated to result from the violation of the parallel flow assumption of Orr–Sommerfeld analysis, as well as certain non-equilibrium effects of the roughness. Additionally, some difficulties previously observed using a quasi-laminar eigenmode analysis were also observed under the resolvent approach; however, the resolvent analysis was shown to provide reasonably accurate predictions of velocity fluctuations for the forced Orr–Sommerfeld problem over a portion of the boundary layer, with potential applications to designing efficient flow control strategies. The combined experimental and analytical effort provides a new opportunity to examine the non-equilibrium and forcing effects in a dynamically perturbed flow.

Noncontact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy.

Abstract: When a femtosecond laser pulse (fsLP) is focused through an objective lens into a culture medium, an impulsive force (fsLP-IF) is generated that propagates from the laser focal point (Of) in a micron-sized space. This force can detach individual adherent cells without causing considerable cell damage. In this study, an fsLP-IF was reflected in the vibratory movement of an atomic force microscopy (AFM) cantilever. Based on the magnitude of the vibration and the geometrical relationship between Of and the cantilever, the fsLP-IF generated at Of was calculated as a unit of impulse [N-s]. This impulsive force broke adhesion molecule-mediated intercellular interactions in a manner that depended on the adhesion strength that was estimated by the cell aggregation assay. The force also broke the interactions between streptavidin-coated microspheres and a biotin-coated substrate with a measurement error of approximately 7%. These results suggest that fsLP-IF can be used to break intermolecular and intercellular interactions and estimate the adhesion strength. The fsLP-IF was used to break intercellular contacts in two biologically relevant cultures: a coculture of leukocytes seeded over on an endothelial cell monolayer, and a polarized monolayer culture of epithelial cells. The impulses needed to break leukocyte–endothelial and interepithelial interactions, which were calculated based on the geometrical relationship between Of and the adhesive interface, were on the order of 10-13 and 10-12 N-s, respectively. When the total impulse at Of is well-defined, fsLP-IF can be used to estimate the force required to break intercellular adhesions in a noncontact manner under biologically relevant conditions.

Reproducibility of shear wave velocity measurements by acoustic radiation force impulse imaging of the liver: a study in healthy volunteers.

Abstract: OBJECTIVES The purposes of this study were to investigate interobserver reproducibility using acoustic radiation force impulse imaging and to develop an acoustic radiation force impulse scoring system. METHODS Fifty healthy volunteers with normal liver function test values were selected for the study. Shear wave velocity measurements, expressed in meters per second, were taken in a deep portion of liver segment 6. Two observers with different levels of experience performed the measurements independently and blindly. RESULTS All of the measurements taken by the 2 observers were valid, even in volunteers with a body mass index of greater than 28 kg/m(2). The results point to very good interobserver reproducibility of shear wave velocity measurements, with an intraclass coefficient correlation of 0.86 (P < .001). CONCLUSIONS The results of this study show that shear wave velocity measurements using the acoustic radiation force impulse technique and a standardized protocol are accurate and reproducible.

Spherical Fidelity Patterns of UWB Antennas

Abstract: The time domain radiation properties of UWB antennas are analyzed, especially the angular dependent impulse distortion, with respect to the signal transmitted in the main beam direction, is investigated. The correlation properties of the radiated pulses are determined by the so called fidelity F. The fidelity F is together with the peak pulse amplitude P a powerful tool for the characterization of impulse radiating antennas. The results are applied to two different UWB antennas, a Vivaldi antenna and a Bow-tie antenna. The spatial regions with good correlation and high peak power are determined for both by measurements for verification. The results are vital for UWB impulse communications, and for UWB Radar as well.

Numerical and Experimental Investigation of Grounding Electrode Impulse-Current Dispersal Regularity Considering the Transient Ionization Phenomenon

Abstract: This paper presents a numerical method, combined the finite element method in the spatial domain with the finite difference time domain, to calculate the transient impulse response of grounding systems considering the ionization phenomenon. In this numerical method, space-time variable soil resistivity is used to simulate the soil ionization phenomenon where soil resistivity is controlled according to its relationship with the local instantaneous value of the electric field and no a priori hypothesis on the geometrical shape of the ionized region around the electrodes is necessary. Based on the widely accepted principle of dimensional similarity, this paper makes simulated experimental investigations on the impulse-current dispersal regularity of grounding electrodes with various structures. The proposed numerical scheme is validated by comparing computed results with experimental results and simulation results in literature. Based on the measurement and simulation results, the impulse response regularity of grounding electrodes is discussed and the effect of ionization on human and installations safety is reported.

Stabilization of Switched Systems With Nonlinear Impulse Effects and Disturbances

Abstract: In this note, we investigate the stabilization of switched systems with nonlinear impulse effects and disturbances. Based on the estimate on transition matrices and Gronwall inequality, feedback laws are designed to achieve the exponential stability of the closed-loop system with arbitrary switching frequency.

Internal current measurements in high power impulse magnetron sputtering

Abstract: The transport of charged particles in a high power impulse magnetron sputtering (HiPIMS) discharge is of considerable interest when optimizing this promising deposition technique with respect to de ...

High-frequency interference in low strain integrity testing of large-diameter pipe piles

Abstract: The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transient point load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing is deduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domain velocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various points suffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence of vibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point mainly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors affecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that the larger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The least high-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increase of pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modulus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width and larger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geometrical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditions such as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on the external conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some external measures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adopting suitable receiving point.

Fractional-order impulse response of the respiratory system

Abstract: This paper presents the measurement, frequency-response modeling and identification, and the corresponding impulse time response of the human respiratory impedance and admittance. The investigated adult patient groups were healthy, diagnosed with chronic obstructive pulmonary disease and kyphoscoliosis, respectively. The investigated children patient groups were healthy, diagnosed with asthma and cystic fibrosis, respectively. Fractional order (FO) models are identified on the measured impedance to quantify the respiratory mechanical properties. Two methods are presented for obtaining and simulating the time-domain impulse response from FO models of the respiratory admittance: (i) the classical pole-zero interpolation proposed by Oustaloup in the early 90s, and (ii) the inverse discrete Fourier Transform (DFT). The results of the identified FO models for the respiratory admittance are presented by means of their average values for each group of patients. Consequently, the impulse time response calculated from the frequency response of the averaged FO models is given by means of the two methods mentioned above. Our results indicate that both methods provide similar impulse response data. However, we suggest that the inverse DFT is a more suitable alternative to the high order transfer functions obtained using the classical Oustaloup filter. Additionally, a power law model is fitted on the impulse response data, emphasizing the intrinsic fractal dynamics of the respiratory system.

Comparison of pseudo-random binary sequence and square-wave transient controlled-source electromagnetic data over the Peon gas discovery, Norway

Abstract: We discuss the problem of source control in controlled‐source electromagnetic (CSEM) surveying and compare and contrast equal energy transient square‐wave and transient pseudo‐random binary sequence source signatures for the same towed‐streamer electromagnetic survey line over the Peon gasfield in the Norwegian sector of the North Sea. The received response of the transient square‐wave data was 11 dB greater than that of the pseudo‐random binary sequence data, due to diffusive attenuation of higher frequencies present in the more broadband pseudo‐random binary sequence signature. Deconvolution of the pseudo‐random binary sequence data recovers the total impulse response function, increases the signal‐to‐noise ratio by 32.6 dB and separates most of the air wave from the earth impulse response by the causality principle. The recovered impulse responses have more detailed information in the frequency domain than the transient square‐wave data. The pseudo‐random binary sequence data were acquired with a 10 Hz source bit rate but contain no information about the Peon gasfield at frequencies above 2 Hz. The bit rate could have been reduced to 4 Hz, increasing the signal energy below 2 Hz by 150% and thus, potentially, increasing the signal‐to‐noise ratio by a further 4 dB. Because the total earth impulse response can be recovered from the broad‐bandwidth pseudo‐random binary sequence data, further time‐domain processing may be applied, including correlated noise removal, which can increase the signal‐to‐noise ratio by as much as 20 dB, and air wave removal using the causality principle. The information in the arrival time of the peak of the earth response provides the potential for traveltime to resistivity mapping to provide a starting model for inversion.

A twin unidirectional impulse turbine for wave energy conversion

Abstract: A twin unidirectional impulse turbine has been proposed in order to enhance the performance of wave energy plant. This turbine system uses two unidirectional impulse turbines and their flow direction is different from each other. However, the turbine characteristics have not been clarified to date. The performances of a unidirectional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study. Then, efficiency of the twin impulse turbine have been estimated by a quasi-steady analysis using experimental results.