Articles de revues : « Resistive wall impedance »

1

Okoor, Sondos, A. M. Al-Khateeb et I. M. Odeh. « Longitudinal coupling impedance for particle beams with Gaussian charge distributions in the longitudinal and transverse directions ». Canadian Journal of Physics 88, n^o 8 (août 2010) : 597–605. http://dx.doi.org/10.1139/p10-036.

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The longitudinal coupling impedance is obtained analytically for a smooth and resistive cylindrical pipe of finite wall thickness. We assumed a particle beam with Gaussian charge distribution in the longitudinal and transverse directions. For wall thicknesses d less than the skin depth, the impedance increases because of coupling with the vacuum outside the pipe, while for thicknesses d nearly of the order of the skin depth, the impedance becomes independent of the wall thickness. The resistive wall impedance decreases with increasing wall conductivity and it has its maximum values at low frequencies. By increasing beam energies, the space charge impedance decreases while the resistive wall contribution increases. Gaussian and uniform beams have nearly the same impedance at low energy, independent of the wall thickness, while at higher energies obvious differences are observed at wall thicknesses below the skin penetration depth.

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kim, Eun San, Su-Youn Lee et Ji-Gwang Hwang. « Effects of Resistive Wall Impedance in PLS-II Storage Ring ». Journal of the Korean Physical Society 56, n^o 6(1) (15 juin 2010) : 1957–59. http://dx.doi.org/10.3938/jkps.56.1957.

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Nakamura, N. « Resistive-wall impedance effects for the new KEK Light Source ». Journal of Physics : Conference Series 874 (juillet 2017) : 012069. http://dx.doi.org/10.1088/1742-6596/874/1/012069.

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Hantos, Z., B. Daroczy, B. Suki et S. Nagy. « Low-frequency respiratory mechanical impedance in the rat ». Journal of Applied Physiology 63, n^o 1 (1 juillet 1987) : 36–43. http://dx.doi.org/10.1152/jappl.1987.63.1.36.

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modified forced oscillatory technique was used to determine the respiratory mechanical impedances in anesthetized, paralyzed rats between 0.25 and 10 Hz. From the total respiratory (Zrs) and pulmonary impedance (ZL), measured with pseudorandom oscillations applied at the airway opening before and after thoracotomy, respectively, the chest wall impedance (ZW) was calculated as ZW = Zrs - ZL. The pulmonary (RL) and chest wall resistances were both markedly frequency dependent: between 0.25 and 2 Hz they contributed equally to the total resistance falling from 81.4 +/- 18.3 (SD) at 0.25 Hz to 27.1 +/- 1.7 kPa.l–1 X s at 2 Hz. The pulmonary compliance (CL) decreased mildly, from 2.78 +/- 0.44 at 0.25 Hz to 2.36 +/- 0.39 ml/kPa at 2 Hz, and then increased at higher frequencies, whereas the chest wall compliance declined monotonously from 4.19 +/- 0.88 at 0.25 Hz to 1.93 +/- 0.14 ml/kPa at 10 Hz. Although the frequency dependence of ZW can be interpreted on the basis of parallel inhomogeneities alone, the sharp fall in RL together with the relatively constant CL suggests that at low frequencies significant losses are imposed by the non-Newtonian resistive properties of the lung tissue.

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BANE, K. L. F. « WAKEFIELDS OF SUB-PICOSECOND ELECTRON BUNCHES ». International Journal of Modern Physics A 22, n^o 22 (10 septembre 2007) : 3736–58. http://dx.doi.org/10.1142/s0217751x07037391.

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We discuss wakefields excited by short bunches in accelerators. In particular, we review some of what has been learned in recent years concerning diffraction wakes, roughness impedance, coherent synchrotron radiation wakes, and the resistive wall wake, focusing on analytical solutions where possible. As examples, we apply formulas for these wakes to various parts of the Linac Coherent Light Source (LCLS) project. The longitudinal accelerator structure wake of the SLAC linac is an important ingredient in the LCLS bunch compression process. Of the wakes in the undulator region, the dominant one is the resistive wall wake of the beam pipe.

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Al-Khateeb, A., R. W. Hasse, O. Boine-Frankenheim et I. Hofmann. « Screening of the resistive-wall impedance by a cylindrical electron plasma ». New Journal of Physics 10, n^o 8 (6 août 2008) : 083008. http://dx.doi.org/10.1088/1367-2630/10/8/083008.

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Casalbuoni, S., M. Migliorati, A. Mostacci, L. Palumbo et B. Spataro. « Beam heat load due to geometrical and resistive wall impedance in COLDDIAG ». Journal of Instrumentation 7, n^o 11 (9 novembre 2012) : P11008. http://dx.doi.org/10.1088/1748-0221/7/11/p11008.

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Akbar, Noreen Sher, et S. Nadeem. « Mathematical analysis of Phan-Thien–Tanner fluid model for blood in arteries ». International Journal of Biomathematics 08, n^o 05 (13 août 2015) : 1550064. http://dx.doi.org/10.1142/s1793524515500643.

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In the present paper, we have studied the blood flow through tapered artery with a stenosis. The non-Newtonian nature of blood in small arteries is analyzed mathematically by considering the blood as Phan-Thien–Tanner fluid. The representation for the blood flow is through an axially non-symmetrical but radially symmetric stenosis. Symmetry of the distribution of the wall shearing stress and resistive impedance and their growth with the developing stenosis is another important feature of our analysis. Exact solutions have been evaluated for velocity, resistance impedance, wall shear stress and shearing stress at the stenosis throat. The graphical results of different type of tapered arteries (i.e. converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest.

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Casalbuoni, S., M. Migliorati, A. Mostacci, L. Palumbo et B. Spataro. « Erratum : beam heat load due to geometrical and resistive wall impedance in COLDDIAG ». Journal of Instrumentation 7, n^o 12 (20 décembre 2012) : E12001. http://dx.doi.org/10.1088/1748-0221/7/12/e12001.

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Akbar, Noreen Sher. « Blood flow of Carreau fluid in a tapered artery with mixed convection ». International Journal of Biomathematics 07, n^o 06 (novembre 2014) : 1450068. http://dx.doi.org/10.1142/s1793524514500685.

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This research is concerned with the mathematical modeling and analysis of blood flow in a tapered artery with stenosis. The analysis has been carried out in the presence of heat and mass transfer. Constitutive equation of Carreau fluid has been invoked in the mathematical formulation. The representation of blood flow is considered through an axially non-symmetrical but radially symmetric stenosis. Symmetry of the distribution of the wall shearing stress and resistive impedance and their growth with the developing stenosis is given due attention. Solutions have been obtained for the velocity, temperature, concentration, resistance impedance, wall shear stress and shearing stress at the stenosis throat. Graphical illustrations associated with the tapered arteries namely converging, diverging and non-tapered arteries are examined for different parameters of interest. Streamlines have been plotted and discussed.

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Akbar, Noreen Sher. « Metallic nanoparticles analysis for the blood flow in tapered stenosed arteries : Application in nanomedicines ». International Journal of Biomathematics 09, n^o 01 (2 novembre 2015) : 1650002. http://dx.doi.org/10.1142/s1793524516500029.

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Blood flow model is recycled to study the influence of magnetic field and nanoparticles in tapered stenosed arteries. The metallic nanoparticles for the blood flow with water as base fluid are not explored so far. The representation for the blood flow is through an axially non-symmetrical but radially symmetric stenosis. Symmetry of the distribution of the wall shearing stress and resistive impedance and their growth with the developing stenosis is another important feature of our analysis. Exact solutions have been evaluated for velocity, resistance impedance, wall shear stress and shearing stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e. converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest for pure water and Copper water ( Cu -water).

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Hara, T., T. Tanaka, T. Tanabe, X. M. Maréchal, H. Kitamura, P. Elleaume, B. Morrison, J. Chavanne, P. Van Vaerenbergh et D. Schmidt. « SPring-8 in-vacuum undulator beam test at the ESRF ». Journal of Synchrotron Radiation 5, n^o 3 (1 mai 1998) : 406–8. http://dx.doi.org/10.1107/s0909049597014325.

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Before the commissioning of SPring-8, the in-vacuum hybrid undulator developed at SPring-8 had been brought to the ESRF for the first beam test in the summer of 1996. The purpose of this test was to investigate the influence of the in-vacuum undulator on the beam and check its vacuum system. However, heating by the resistive wall impedance turned out to be a critical issue for the in-vacuum undulators.

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Wang, Y. T., N. Wang, H. S. Xu et G. Xu. « Tune shift due to the quadrupolar resistive-wall impedance of an elliptical beam pipe ». Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment 1029 (avril 2022) : 166414. http://dx.doi.org/10.1016/j.nima.2022.166414.

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Yee-Rendon, B., Y. H. Chin, H. Kuboki, M. Schenk et T. Toyama. « Updated model of the resistive wall impedance for the main ring of J-PARC ». Journal of Physics : Conference Series 1067 (septembre 2018) : 062009. http://dx.doi.org/10.1088/1742-6596/1067/6/062009.

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Hill, A. A., D. R. Surat, R. S. Cobbold, B. L. Langille, L. Y. Mo et S. L. Adamson. « A wave transmission model of the umbilicoplacental circulation based on hemodynamic measurements in sheep ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 269, n^o 5 (1 novembre 1995) : R1267—R1278. http://dx.doi.org/10.1152/ajpregu.1995.269.5.r1267.

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Electrical analog models of the umbilical circulation were developed based on hemodynamic measurements in fetal sheep. The umbilical artery was represented by a transmission line and the placenta by a resistive load. Model predictions of input impedance and pressure and flow waveforms agreed with in vivo measurements under baseline conditions, following placental embolization, and during angiotensin II infusion. A unique positive impedance phase observed at the heart rate frequency under baseline conditions was best explained by the unusual viscoelastic properties of the umbilical arterial wall and small load reflections. Furthermore, a short, less vasoactive segment of the umbilical artery in the retroperitoneal space had a large impact on the input impedance of the umbilical circulation, which was particularly apparent when the artery was constricted during angiotensin II infusion. The model indicated that reflections arising near the approximate location where the first arterial branches leave the main umbilical artery have a measurable impact on impedance spectra when load reflections are low.

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Lee, Jaeyu, M. H. Chun, G. J. Kim, D. C. Shin, D. T. Kim et S. Shin. « Bunch-by-bunch position measurement and analysis at PLS-II ». Journal of Synchrotron Radiation 24, n^o 1 (1 janvier 2017) : 163–67. http://dx.doi.org/10.1107/s1600577516018154.

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A bunch-by-bunch measurement system has been developed at Pohang Light Source II. The system consists of a four-channel button pick-up, 20 GHz sampling oscilloscope and an 800 MHz low-pass digital filter. Upon measuring a bunch-by-bunch spatio-temporal beam motion matrix over many turns, singular-value decomposition analysis is used to reveal the dominant coupled-bunch modes. The system can diagnose injection oscillations due to kicker errors and the effect of resistive-wall impedance that gives rise to instability during operation.

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Talebi Motlagh, S., J. Rahighi, F. Zamani et F. Saeidi. « The resistive wall impedance and the effects of the non-evaporable getter thickness in an ultra-low emittance ring ». Journal of Instrumentation 18, n^o 01 (1 janvier 2023) : P01028. http://dx.doi.org/10.1088/1748-0221/18/01/p01028.

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Abstract In modern particle accelerators with ultra-low emittance, the vacuum chambers are designed based on Non-Evaporable Getter (NEG)-coated vacuum chambers. The thickness of the NEG coating plays a critical role in the dynamic beam effects. So, in this paper, the longitudinal and transverse impedance of a copper chamber coated with a NEG are investigated, and the effects of the NEG thickness over a wide range of frequencies have been studied. A good selection of NEG layer thickness could minimize the coating effects on the longitudinal and transverse beam impedance. The numerical results in this work show that the beam dynamic effects could be minimal with selecting a NEG coating thickness of about 1 μm.

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18

Pascal, L., E. Piot et G. Casalis. « A New Implementation of the Extended Helmholtz Resonator Acoustic Liner Impedance Model in Time Domain CAA ». Journal of Computational Acoustics 24, n^o 01 (mars 2016) : 1550015. http://dx.doi.org/10.1142/s0218396x15500150.

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The application of wall acoustic lining is a major factor in the reduction of aircraft engine noise. The extended Helmholtz Resonator (EHR) impedance model is widely used since it is representative of the behavior of realistic liners over a wide range of frequencies. Its application in time domain CAA methods by means of [Formula: see text]-transform has been the subject of several papers. In contrast to standard liner modeling in time domain CAA, which consists in imposing a boundary condition modeling both the cavities and the perforated sheet of the liner, an alternative approach involves adding the cavities to the computational domain and imposing a condition between these cavities and the duct domain to model the resistive sheet. However, the original method may not be used for broadband acoustics since it implements an impedance condition with frequency independent resistance. This paper describes an extension of this method to implement the EHR impedance model in a time domain CAA method.

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AKBAR, NOREEN SHER. « HEAT AND MASS TRANSFER EFFECTS ON CARREAU FLUID MODEL FOR BLOOD FLOW THROUGH A TAPERED ARTERY WITH A STENOSIS ». International Journal of Biomathematics 07, n^o 01 (janvier 2014) : 1450004. http://dx.doi.org/10.1142/s1793524514500041.

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In the current critique, we deliberate the blood flow through narrowing vein with a stenosis in the manifestation of heat and mass transmission. The non-Newtonian flora of blood in small veins are examined mathematically by demonstrating the blood as Carreau fluid. The illustration for the blood flow is debated through an axially irregular but outward regular stenosis. Regularity in the dissemination of the fortification clipping stress and resistive impedance and their evolution with the emerging stenosis is a new significant feature of our investigation. Analytical solutions have been appraised for "velocity, temperature, concentration, resistance impedance, wall shear stress and shearing stress at the stenosis throat". The graphical consequences of different types of tapering arteries (i.e. "converging tapering, diverging tapering, non-tapered artery") have been studied for dissimilar constraints of attention. Rivulet shapes have been strategized for different parameters at the culmination of the article.

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Zin, W. A., A. Boddener, P. R. Silva, T. M. Pinto et J. Milic-Emili. « Active and passive respiratory mechanics in anesthetized dogs ». Journal of Applied Physiology 61, n^o 5 (1 novembre 1986) : 1647–55. http://dx.doi.org/10.1152/jappl.1986.61.5.1647.

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In six spontaneously breathing anesthetized dogs (pentobarbital sodium, 30 mg/kg) airflow, volume, and tracheal and esophageal pressures were measured. The active and passive mechanical properties of the total respiratory system, lung, and chest wall were calculated. The average passive values of respiratory system, lung, and chest wall elastances amounted to, respectively, 50.1, 32.3, and 17.7 cmH2O X l-1. Resistive pressure-vs.-flow relationships for the relaxed respiratory system, lung, and chest wall were also determined; a linear relationship was found for the former (the total passive intrinsic resistance averaged 4.1 cmH2O X l-1 X s), whereas power functions best described the others: the pulmonary pressure-flow relationship exhibited an upward concavity, which for the chest wall presented an upward convexity. The average active elastance and resistance of the respiratory system were, respectively, 64.0 cmH2O X l-1 and 5.4 cmH2O X l-1 X s. The greater active impedance reflects pressure losses due to force-length and force-velocity properties of the inspiratory muscles and those due to distortion of the respiratory system from its relaxed configuration.

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Ruggiero, Francesco. « Resistive wall impedance as derivative of the electric capacitance for a beam pipe of arbitrary cross section ». Physical Review E 53, n^o 3 (1 mars 1996) : 2802–6. http://dx.doi.org/10.1103/physreve.53.2802.

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Nagaoka, Ryutaro, et Karl L. F. Bane. « Collective effects in a diffraction-limited storage ring ». Journal of Synchrotron Radiation 21, n^o 5 (27 août 2014) : 937–60. http://dx.doi.org/10.1107/s1600577514015215.

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This paper gives an overview of collective effects that are likely to appear and possibly limit the performance in a diffraction-limited storage ring (DLSR) that stores a high-intensity ultra-low-emittance beam. Beam instabilities and other intensity-dependent effects that may significantly impact the machine performance are covered. The latter include beam-induced machine heating, Touschek scattering, intra-beam scattering, as well as incoherent tune shifts. The general trend that the efforts to achieve ultra-low emittance result in increasing the machine coupling impedance and the beam sensitivity to instability is reviewed. The nature of coupling impedance in a DLSR is described, followed by a series of potentially dangerous beam instabilities driven by the former, such as resistive-wall, TMCI (transverse mode coupling instability), head–tail and microwave instabilities. In addition, beam-ion and CSR (coherent synchrotron radiation) instabilities are also treated. Means to fight against collective effects such as lengthening of the bunch with passive harmonic cavities and bunch-by-bunch transverse feedback are introduced. Numerical codes developed and used to evaluate the machine coupling impedance, as well as to simulate beam instability using the former as inputs are described.

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Kim, Mi, Sungwoo Lee, Inug Yoon, Geon Kook, Yeon Jung, Sarah Bawazir, Cesare Stefanini et Hyunjoo Lee. « Polypyrrole/Agarose Hydrogel-Based Bladder Volume Sensor with a Resistor Ladder Structure ». Sensors 18, n^o 7 (14 juillet 2018) : 2288. http://dx.doi.org/10.3390/s18072288.

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Chronic monitoring of bladder activity and urine volume is essential for patients suffering from urinary dysfunctions. However, due to the anatomy and dynamics of the bladder, chronic and precise monitoring of bladder activity remains a challenge. Here, we propose a new sensing mechanism that measures the bladder volume using a resistive ladder network with contact switches. Instead of measuring the impedance between the electrode continuously, the proposed sensor provides a digitized output (‘on’ or ‘off’) when the bladder volume reaches a certain threshold value. We present simple proof-of-concept sensors which compare the discrete-mode operation to the continuous-mode operation. In addition, by using multiple pairs of this contact-mode switch in a resistor ladder structure, we demonstrate monitoring of the bladder volume in four discrete steps using an idealized balloon and an ex vivo pig’s bladder. We implemented the resistive ladder network using a conductive polypyrrole/agarose hydrogel composite which exhibits a Young’s modulus comparable to that of the bladder wall. Compared to the continuous-mode operation, the proposed sensing mechanism is less susceptible to drift due to material degradation and environmental factors.

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Chakravarty, Santabrata, et Prashanta Kumar Mandal. « Unsteady Flow of a Two-Layer Blood Stream Past a Tapered Flexible Artery under Stenotic Conditions ». Computational Methods in Applied Mathematics 4, n^o 4 (2004) : 391–409. http://dx.doi.org/10.2478/cmam-2004-0022.

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Abstract The mechanics of the blood flow in a flexible tapered artery with stenosis is studied from the viewpoint of a mathematical model. The flowing blood is represented by a two-fluid model, consisting of a core region of suspension of all erythrocytes assumed to be characterized by a Casson fluid and a peripheral plasma layer free from cells of any kind as a Newtonian fluid. The moving wall of the artery is treated as an anisotropic, linear viscoelastic incompressible circular cylindrical membrane cell. The effect of the surrounding connective tissues on the motion of the artery wall is also given due attention. The unsteady flow mechanism, subjected to a pulsatile pressure gradient has been solved using the finite difference scheme by exploiting the appropriate physically realistic prescribed conditions. The present model is also employed to study the effect of taper angle, the wall deformation, the severity of the stenonis, the viscosity of the peripheral layer, and the non-Newtonian rheology of streaming blood on the dynamic flow field. Finally, the numerical illustration presented at the end of the paper provides an effective quantitative measure of the flux, the resistive impedance and the wall shear stress through their graphical representations and also a few comparisons with the existing results have been made in order to validate the applicability of the present model.

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Thamrin, Cindy, Peter D. Sly et Zoltán Hantos. « Broadband frequency dependence of respiratory impedance in rats ». Journal of Applied Physiology 99, n^o 4 (octobre 2005) : 1364–71. http://dx.doi.org/10.1152/japplphysiol.00383.2005.

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Past studies in humans and other species have revealed the presence of resonances and antiresonances, i.e., minima and maxima in respiratory system impedance (Zrs), at frequencies much higher than those commonly employed in clinical applications of the forced oscillation technique (FOT). To help understand the mechanisms behind the first occurrence of antiresonance in the Zrs spectrum, the frequency response of the rat was studied by using FOT at both low and high frequencies. We measured Zrs in both Wistar and PVG/c rats using the wave tube technique, with a FOT signal ranging from 2 to 900 Hz. We then compared the high-frequency parameters, i.e., the first antiresonant frequency (far,1) and the resistive part of Zrs at that frequency [Rrs(far,1)], with parameters obtained by fitting a modified constant-phase model to low-frequency Zrs spectra. The far,1 was 570 ± 43 (SD) Hz and 456 ± 16 Hz in Wistar and PVG/c rats, respectively, and it did not shift with respiratory gases of different densities (air, heliox, and a mixture of SF6). The far,1 and Rrs(far,1) were relatively independent of methacholine-induced bronchoconstriction but changed significantly with increasing transrespiratory pressures up to 20 cmH2O, in the same way as airway resistance but independently of changes to tissue parameters. These results suggest that, unlike the human situation, the first antiresonance in the rat is not primarily dependent on the acoustic dimensions of the respiratory system and can be explained by interactions between compliances and inertances localized to the airways, but this most likely does not include airway wall compliance.

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MISHRA, SHAILESH, NARENDRA KUMAR VERMA et S. U. SIDDIQUI. « A SUSPENSION MODEL FOR BLOOD FLOW THROUGH A CATHETERIZED ARTERY ». International Journal of Biomathematics 05, n^o 05 (17 juin 2012) : 1250033. http://dx.doi.org/10.1142/s1793524511001714.

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The present work is concerned with the analysis of an axi-symmetric flow of blood through coaxial tubes where the outer tube has an axially symmetric mild stenosis and the inner tube has a balloon which is axi-symmetric in nature. The mild stenosis approximation is used to solve the present problem. The effect of the volume fraction density of the particles, the maximum height attained by the balloon, the radius of the inner tube, which keeps the balloon in position k, and the axial displacement of the balloon have been studied. Flow parameters such as the resistive impedance, the wall shear stress distribution in the stenotic region and its magnitude at the stenosis throat have been computed for different parameters. It is observed that the resistance to flow decreases with increasing values of the axial displacement of the balloon, while the resistance to flow increases with the volume fraction density of the particles, the radius of the inner tube, which keeps the balloon in position k, and the maximum height attained by the balloon. The wall shear stress distribution in the stenotic region possesses a character similar to the resistance to flow with respect to any parameter.

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Kochi, T., S. Okubo, W. A. Zin et J. Milic-Emili. « Chest wall and respiratory system mechanics in cats : effects of flow and volume ». Journal of Applied Physiology 64, n^o 6 (1 juin 1988) : 2636–46. http://dx.doi.org/10.1152/jappl.1988.64.6.2636.

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The effects of inspiratory flow rate and inflation volume on the resistive properties of the chest wall were investigated in six anesthetized paralyzed cats by use of the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rw,min) and overall dynamic inspiratory impedance (Rw,max), which includes the additional pressure losses due to time constant inequalities within the chest wall tissues and/or stress adaptation. These results, together with our previous data pertaining to the lung (Kochi et al., J. Appl. Physiol. 64: 441–450, 1988), allowed us to determine Rmin and Rmax of the total respiratory system (rs). We observed that 1) Rw,max and Rrs,max exhibited marked frequency dependence; 2) Rw,min was independent of flow (V) and inspired volume (delta V), whereas Rrs,min increased linearly with V and decreased with increasing delta V; 3) Rw,max decreased with increasing V, whereas Rrs,max exhibited a minimum value at a flow rate substantially higher than the resting range of V; 4) both Rw,max and Rrs,max increased with increasing delta V. We conclude that during resting breathing, flow resistance of the chest wall and total respiratory system, as conventionally measured, includes a significant component reflecting time constant inequalities and/or stress adaptation phenomena.

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Mandal, P. K. « AN UNSTEADY ANALYSIS OF NONLINEAR TWO‐LAYERED 2D MODEL OF PULSATILE FLOW THROUGH STENOSED ARTERIES ». Mathematical Modelling and Analysis 8, n^o 3 (30 septembre 2003) : 229–46. http://dx.doi.org/10.3846/13926292.2003.9637226.

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The effects of red cell concentration and peripheral layer viscosity on physiological characteristics of pulsatile flow in presence of mild stenosis are investigated. The flowing blood is represented by a two‐fluid model, consisting of a core region of suspension of all the erythrocytes assumed to be non‐Newtonian (inhomogeneous Newtonian) and a peripheral plasma layer free from cells of any kind as a Newtonian fluid. In the realm of the flow characteristics of blood the viscosity is taken to be a function of hematocrit in a manner that it varies radially only in the central core characterising its non‐Newtonian behaviour while it remains constant in the plasma region. The arterial wall motion and its effect on local fluid mechanics is also incorporated in the present theoretical study. Finite difference scheme has been used to solve the unsteady Navier‐Stokes equations in cylindrical coordinates assuming axial symmetry under laminar conditions, so that the problem effectively becomes two‐dimensional. The nonlinear terms appearing in the Navier‐Stokes equations governing blood flow are accounted for. Finally, the numerical illustration presented at the end of the paper provides an effective measure of the flux, the resistive impedance and the wall shear stress quantitatively in order to validate the applicability of the present model.

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AL-KHATEEB, AHMED, et NOUF AL-SALEEM. « LONGITUDINAL COUPLING IMPEDANCE FOR PARTICLE BEAMS OF PARABOLIC TRANSVERSE CHARGE ISTRIBUTION MOVING IN A RESISTIVE CULINDRICAL BEAM-PIPE OF FINITE WALL THICKENS ». Al-Azhar Bulletin of Science 27, Issue 1-B (1 juin 2016) : 11–18. http://dx.doi.org/10.21608/absb.2016.60511.

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Rooz, E., T. F. Wiesner et R. M. Nerem. « Epicardial Coronary Blood Flow Including the Presence of Stenoses and Aorto-Coronary Bypasses—I : Model and Numerical Method ». Journal of Biomechanical Engineering 107, n^o 4 (1 novembre 1985) : 361–67. http://dx.doi.org/10.1115/1.3138570.

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A computer model and numerical method for calculating left epicardial coronary blood flow has been developed. This model employs a finite-branching geometry of the coronary vasculature and the one-dimensional, unsteady equations for flow with friction. The epicardial coronary geometry includes the left main and its bifurcation, the left anterior descending and left circumflex coronary arteries, and a selected number of small branches. Each of the latter terminate in an impedance, whose resistive component is related to intramyocardial compression through a linear dependence on left ventricular pressure. The elastic properties of the epicardial arteries are taken to be non-linear and are prescribed by specifying the local small-disturbance wave speed. The model allows for the incorporation of multiple stenoses as well as aorto-coronary bypasses. Calculations using this model predict pressure and flow waveform development and allow for the systematic investigation of the dependence of coronary flow on various parameters, e.g., peripheral resistance, wall properties, and branching pattern, as well as the presence of stenoses and bypass grafts. Reasonable comparison between calculations and earlier experiments in horses has been obtained.

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Zhang, Leigang, Shuai Guo et Qing Sun. « An Assist-as-Needed Controller for Passive, Assistant, Active, and Resistive Robot-Aided Rehabilitation Training of the Upper Extremity ». Applied Sciences 11, n^o 1 (31 décembre 2020) : 340. http://dx.doi.org/10.3390/app11010340.

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Clinical studies have demonstrated that robot-involved therapy can effectively improve the rehabilitation training effect of motor ability and daily behavior ability of subjects with an upper limb motor dysfunction. This paper presents an impedance-based assist-as-needed controller that can be used in robot-aided rehabilitation training for subjects with an upper extremity dysfunction. Then, the controller is implemented on an end-effector upper extremity rehabilitation robot which could assist subjects in performing training with a spatial trajectory. The proposed controller enables subjects’ arms to have motion freedom by building a fault-tolerant region around the rehabilitation trajectory. Subjects could move their upper limb without any assistance within the fault-tolerant region while the robot would provide assistance according to the subjects’ functional ability when deviating from the fault-tolerant region. Besides, we also put forward the stiffness field around the fault-tolerant region to increase the robot’s assistance when subjects’ hand is moving outside the fault-tolerant region. A series of columnar rigid walls would be constructed in the controller according to the subjects’ functional ability, and the stiffness of the wall increases as the motion performance deteriorates. Furthermore, the controller contains five adjustable parameters. The controller would show different performances by adjusting these parameters and satisfy the requirement of robot-aided rehabilitation training at different rehabilitation stages such as passive, assistant, active, and resistant training. Finally, the controller was tested with an elderly female participant with different controller parameters, and experimental results verified the correctness of the controller and its potential ability to satisfy the training requirements at different rehabilitation stages. In the close future, the proposed controller in this work is planned to be applied on more subjects and also patients who have upper limb motor dysfunctions to demonstrate performance of the controller with different parameters.

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Burattini, Roberto, et Paola Oriana Di Salvia. « Development of systemic arterial mechanical properties from infancy to adulthood interpreted by four-element windkessel models ». Journal of Applied Physiology 103, n^o 1 (juillet 2007) : 66–79. http://dx.doi.org/10.1152/japplphysiol.00664.2006.

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Aortic impedance data of infants, children and adults (age range 0.8–54 yr), previously reported by others, were interpreted by means of three alternative four-element windkessel models: W4P, W4S, and IVW. The W4P and W4S are derived from the three-element windkessel (W3) by connecting an inertance ( L) in parallel or in series, respectively, with the aortic characteristic resistance ( Rc). In the IVW, L is connected in series with a viscoelastic windkessel (VW). The W4S and IVW (same input impedance) fit the data best. The W4S, however, suffers from the assumption that Rc is part of total peripheral resistance ( Rp). The IVW model offers a new paradigm for interpretation of resistive properties in terms of viscous ( Rd) properties of vessel wall motion, distinguished from Rp. Results indicated that rapid reduction of Rd/ Rp during early development is functional to modulation of decay time constant (τd) of pressure in diastole, such that normalization over heart period (τd/T) is independent of body size. Estimates of total arterial compliance ( C) vs. age were fitted by a bell-shaped curve with a maximum at 33 yr. With body weight (BW) factored out by normalization, the C/BW data scattered about a bell-shaped curve centered at 66 mmHg. Inertance was significantly higher in pediatric patients than in adults, in accordance with a lower cross-sectional area of the vasculature, commensurate to a lower aortic flow. Changes of arterial properties appear functional to control the ratio of pulsatile power to active power and keep arterial efficiency as high as 97% in infants and children.

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Le Brun, Grégoire, Margo Hauwaert, Audrey Leprince, Karine Glinel, Jacques Mahillon et Jean-Pierre Raskin. « Electrical Characterization of Cellulose-Based Membranes towards Pathogen Detection in Water ». Biosensors 11, n^o 2 (21 février 2021) : 57. http://dx.doi.org/10.3390/bios11020057.

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Paper substrates are promising for development of cost-effective and efficient point-of-care biosensors, essential for public healthcare and environmental diagnostics in emergency situations. Most paper-based biosensors rely on the natural capillarity of paper to perform qualitative or semi-quantitative colorimetric detections. To achieve quantification and better sensitivity, technologies combining paper-based substrates and electrical detection are being developed. In this work, we demonstrate the potential of electrical measurements by means of a simple, parallel-plate electrode setup towards the detection of whole-cell bacteria captured in nitrocellulose (NC) membranes. Unlike current electrical sensors, which are mostly integrated, this plug and play system has reusable electrodes and enables simple and fast bacterial detection through impedance measurements. The characterized NC membrane was subjected to (i) a biofunctionalization, (ii) different saline solutions modelling real water samples, and (iii) bacterial suspensions of different concentrations. Bacterial detection was achieved in low conductivity buffers through both resistive and capacitive changes in the sensed medium. To capture Bacillus thuringiensis, the model microorganism used in this work, the endolysin cell-wall binding domain (CBD) of Deep-Blue, a bacteriophage targeting this bacterium, was integrated into the membranes as a recognition bio-interface. This experimental proof-of-concept illustrates the electrical detection of 107 colony-forming units (CFU) mL−1 bacteria in low-salinity buffers within 5 min, using a very simple setup. This offers perspectives for affordable pathogen sensors that can easily be reconfigured for different bacteria. Water quality testing is a particularly interesting application since it requires frequent testing, especially in emergency situations.

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Teeter, J. P., G. M. Saidel et J. M. Fouke. « Contribution of large airway to the input impedance of the respiratory system ». Journal of Applied Physiology 70, n^o 2 (1 février 1991) : 650–57. http://dx.doi.org/10.1152/jappl.1991.70.2.650.

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To evaluate the contribution of the large airway to total respiratory impedance, we develop a one-dimensional model of pressure and flow in these airways by coupling conservation of mass and momentum equations with the geometric information obtained by the acoustic reflection technique. We use this model to calculate the impedance of the respiratory system distal to the carina from impedance data estimated at the airway opening by the forced oscillation technique. Simulations show that the real part of the impedance distal to the carina is uniformly decreased from the impedance at the airway opening, indicating a resistive loss, while the imaginary part is increased as a function of frequency. We estimate parameter values for a six-parameter two-compartment lung model and for a three-parameter reduction of this model before and after the application of the upper airway data to the impedance spectrum. Although compliance terms seem to be minimally affected by the manipulation of the data, resistance and inertance terms are influenced in a fashion that suggests that the resistive contribution of the upper airway to total respiratory impedance is significant. Furthermore it appears that the elastic nature of the walls of the upper airway also impact on estimates of total respiratory impedance at the airway opening.

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Niedermayer, U., et O. Boine-Frankenheim. « Analytical and numerical calculations of resistive wall impedances for thin beam pipe structures at low frequencies ». Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment 687 (septembre 2012) : 51–61. http://dx.doi.org/10.1016/j.nima.2012.05.096.

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Chakravarty, S., P. K. Mandal et A. Mandal. « NUMERICAL SIMULATION OF UNSTEADY TWO-LAYERED PULSATILE BLOOD FLOW IN A STENOSED FLEXIBLE ARTERY : EFFECT OF PERIPHERAL LAYER VISCOSITY ». Mathematical Modelling and Analysis 9, n^o 2 (30 juin 2005) : 99–114. http://dx.doi.org/10.3846/13926292.2004.9637245.

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The present paper deals with a theoretical investigation of blood flow in an arterial segment in the presence of stenosis. The streaming blood is treated to be composed of two different layers ‐ the central core and the plasma. The former is considered to be non‐Newtonian liquid characterised by the Power law model, while the latter is chosen to be Newtonian. The artery is simulated as an elastic (moving wall) cylindrical tube. The unsteady flow mechanism of the present study is subjected to a pulsatile pressure gradient arising from the normal functioning of the heart. The time‐variant geometry of the stenosis has been accounted for in order to improve resemblance to the real situation. The unsteady flow mechanism, subjected to pulsatile pressure gradient, has been solved using finite difference scheme by exploiting the physically realistic prescribed conditions. An extensive quantitative analysis has been performed through numerical computations of the flow velocity, the flux, the resistive impedances and the wall shear stresses, together with their dependence with the time, the input pressure gradient and the severity of the stenosis, presented graphically at the end of the paper in order to illustrate the applicability of the model under consideration. Special emphasis has been made to compare the existing results with the present ones and found to have a good agreement. Straipsnyje nagrinejamas kraujo srauto tekejimas esant stenozei. Nagrinejamas dvisluoks‐nis kraujo tekejimas. Arterija modeliuojama kaip vamzdis su elastinemis sienelemis. Kraujo srauto nestacionaruma sukelia širdies veikla. Skaitinis sprendinys randamas baigtiniu skirtumu metodu. Atlikta kokybine skaitiniu sprendiniu analize iliustruojanti greičiu, srautu, sieneles itampu priklausomybe laike. Skaitiniai rezultatai pakankamai gerai patvirtina eksperimentinius duomenis.

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Shobuda, Yoshihiro. « Two-dimensional resistive-wall impedance with finite thickness : its mathematical structures and their physical meanings ». Progress of Theoretical and Experimental Physics, 22 mars 2022. http://dx.doi.org/10.1093/ptep/ptac053.

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Abstract When the skin depth is greater than the chamber thickness for relativistic beams, the two-dimensional longitudinal resistive-wall impedance of a cylindrical chamber with a finite thickness decreases proportionally to the frequency. The phenomenon is commonly interpreted as electro-magnetic fields leaking out of the chamber over a frequency range. However, the relationship between the wall current on the chamber and the leakage fields from the chamber is unclear because the naive resistive-wall impedance formula does not dynamically express how the wall current converts to the leakage fields when the skin depth exceeds the chamber thickness. A prestigious textbook [1] re-expressed the resistive-wall impedance via a parallel circuit model with the resistive-wall and inductive terms to provide a dynamic picture of the phenomenon. However, there are some flaws in the formula. From a fundamental standpoint, this study highlights them and provides a more appropriate and rigorous picture of the longitudinal resistive-wall impedance with finite thickness. To demonstrate their physical meaning, we re-express the longitudinal impedance for non-relativistic beams, as well as the transverse resistive-wall impedance including space charge impedance based on a parallel circuit model.

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Stupakov, Gennady. « Resistive wall impedance of an insert ». Physical Review Special Topics - Accelerators and Beams 8, n^o 4 (18 avril 2005). http://dx.doi.org/10.1103/physrevstab.8.044401.

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Wang, N., et Q. Qin. « Resistive-wall impedance of two-layer tube ». Physical Review Special Topics - Accelerators and Beams 10, n^o 11 (28 novembre 2007). http://dx.doi.org/10.1103/physrevstab.10.111003.

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Zimmermann, Frank, et Katsunobu Oide. « Resistive-wall wake and impedance for nonultrarelativistic beams ». Physical Review Special Topics - Accelerators and Beams 7, n^o 4 (9 avril 2004). http://dx.doi.org/10.1103/physrevstab.7.044201.

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Migliorati, M., L. Palumbo, C. Zannini, N. Biancacci et V. G. Vaccaro. « Resistive wall impedance in elliptical multilayer vacuum chambers ». Physical Review Accelerators and Beams 22, n^o 12 (12 décembre 2019). http://dx.doi.org/10.1103/physrevaccelbeams.22.121001.

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Wang, Y. T., N. Wang, Q. Qin, G. Xu et S. Yue. « Resistive-wall impedance of an elliptical multilayer beam pipe ». Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment, juin 2022, 166928. http://dx.doi.org/10.1016/j.nima.2022.166928.

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Tian, Xudong, Tuo Liu, Tiantian Wang, Jie Zhu et Chih-Yung Wen. « Double-layer acoustic metasurface for the suppression of the Mack second mode in hypersonic boundary-layer flow ». Physics of Fluids, 20 juin 2022. http://dx.doi.org/10.1063/5.0096772.

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An acoustic metasurface consisting of two layers of perforated plates is proposed for suppression of the Mack second mode in hypersonic boundary-layer flow. The upper layer with very tiny holes is permeable to acoustic waves and hardly alters the background hypersonic boundary-layer flow, offering rather low resistive and inductive components of surface acoustic impedance. The bottom layer with large and sparse square holes is attached to a rigid wall surface and forms a periodic array of chambers, each covering multiple holes of the upper layer, which can adjust the impedance phase by working as a capacitive component. Based on a linear stability analysis of hypersonic boundary-layer instability, such an acoustic metasurface satisfying the required surface impedance is designed and numerically investigated. The results show that the metasurface can efficiently suppress the Mack second mode over a relatively wide bandwidth. This work provides an alternative strategy for the design of porous walls for hypersonic boundary-layer stabilization.

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Shobuda, Yoshihiro, et Kaoru Yokoya. « Resistive wall impedance and tune shift for a chamber with a finite thickness ». Physical Review E 66, n^o 5 (6 novembre 2002). http://dx.doi.org/10.1103/physreve.66.056501.

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Macridin, Alexandru, Panagiotis Spentzouris et James Amundson. « Nonperturbative algorithm for the resistive wall impedance of general cross-section beam pipes ». Physical Review Special Topics - Accelerators and Beams 16, n^o 12 (5 décembre 2013). http://dx.doi.org/10.1103/physrevstab.16.121001.

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Balbekov, V. « Transverse modes and instabilities of a bunched beam with space charge and resistive wall impedance ». Physical Review Special Topics - Accelerators and Beams 15, n^o 5 (21 mai 2012). http://dx.doi.org/10.1103/physrevstab.15.054403.

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Krkotić, Patrick, Nikki Tagdulang, Sergio Calatroni, Juan Manuel O'Callaghan et Montse Pont. « Potential impedance reduction by REBCO coated conductors as beam screen coating for the future circular hadron collider ». Europhysics Letters, 12 décembre 2022. http://dx.doi.org/10.1209/0295-5075/acaac3.

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Abstract The Future Circular Collider study creates a conceptual design for a post-LHC particle accelerator using 16T superconducting dipoles to achieve collision energies of up to 100TeV in a 90km circumference ring. A copper-coated beam screen, similar to that used in the LHC, is planned. However, the undertaken research indicates that copper at the high working temperature of 50K has a strong influence on the accelerator's performance, particularly at injection energy. In this work, we relate the experimentally determined properties of REBCO-coated conductors with their potential performance in the FCC-hh beam screen. Specifically, we use a round pipe approximation to demonstrate that a beam screen coated with a combination of REBCO and copper can have a much lower resistive wall impedance than one using only copper. The reduction is substantial (several orders of magnitude), and is observed in both the longitudinal and transverse wall impedance. Such a reduction has important effects on beam stability, operating costs, potential reduction in beam screen size, and lowering the stringent specifications of the 16T magnets required for the Future Circular Hadron Collider.

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Niedermayer, Uwe, Oliver Boine-Frankenheim et Herbert De Gersem. « Space charge and resistive wall impedance computation in the frequency domain using the finite element method ». Physical Review Special Topics - Accelerators and Beams 18, n^o 3 (26 mars 2015). http://dx.doi.org/10.1103/physrevstab.18.032001.

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Migliorati, M., E. Belli et M. Zobov. « Impact of the resistive wall impedance on beam dynamics in the Future Circular e+e− Collider ». Physical Review Accelerators and Beams 21, n^o 4 (24 avril 2018). http://dx.doi.org/10.1103/physrevaccelbeams.21.041001.

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Thirugnanasambandam, Mirunalini, Tejas Canchi, Senol Piskin, Christof Karmonik, Ethan Kung, Prahlad G. Menon, Stephane Avril et Ender A. Finol. « Design, Development, and Temporal Evaluation of a Magnetic Resonance Imaging-Compatible In Vitro Circulation Model Using a Compliant Abdominal Aortic Aneurysm Phantom ». Journal of Biomechanical Engineering 143, n^o 5 (4 mars 2021). http://dx.doi.org/10.1115/1.4049894.

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Abstract Biomechanical characterization of abdominal aortic aneurysms (AAAs) has become commonplace in rupture risk assessment studies. However, its translation to the clinic has been greatly limited due to the complexity associated with its tools and their implementation. The unattainability of patient-specific tissue properties leads to the use of generalized population-averaged material models in finite element analyses, which adds a degree of uncertainty to the wall mechanics quantification. In addition, computational fluid dynamics modeling of AAA typically lacks the patient-specific inflow and outflow boundary conditions that should be obtained by nonstandard of care clinical imaging. An alternative approach for analyzing AAA flow and sac volume changes is to conduct in vitro experiments in a controlled laboratory environment. In this study, we designed, built, and characterized quantitatively a benchtop flow loop using a deformable AAA silicone phantom representative of a patient-specific geometry. The impedance modules, which are essential components of the flow loop, were fine-tuned to ensure typical intraluminal pressure conditions within the AAA sac. The phantom was imaged with a magnetic resonance imaging (MRI) scanner to acquire time-resolved images of the moving wall and the velocity field inside the sac. Temporal AAA sac volume changes lead to a corresponding variation in compliance throughout the cardiac cycle. The primary outcome of this work was the design optimization of the impedance elements, the quantitative characterization of the resistive and capacitive attributes of a compliant AAA phantom, and the exemplary use of MRI for flow visualization and quantification of the deformed AAA geometry.

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