Journal articles: 'Fluid analogue'

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Bilic, Neven, and Dijana Tolic. "Analogue cosmology in a hadronic fluid." Facta universitatis - series: Physics, Chemistry and Technology 12, no. 2 (2014): 77–83. http://dx.doi.org/10.2298/fupct1402077b.

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Analog gravity models of general relativity seem promising routes to providing laboratory tests of the foundation of quantum field theory in curved space-time. In contrast to general relativity, where geometry of a spacetime is determined by the Einstein equations, in analog models geometry and evolution of analog spacetime are determined by the equations of fluid mechanics. In this paper we study the analogue gravity model based on massless pions propagating in a expanding hadronic fluid. The analog expanding spacetime takes the form of an FRW universe, with the apparent and trapping horizons defined in the standard way.

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Carvalho, Denise, Ana Rodrigues, Vera Faustino, Diana Pinho, Elisabete Castanheira, and Rui Lima. "Microfluidic Deformability Study of an Innovative Blood Analogue Fluid Based on Giant Unilamellar Vesicles." Journal of Functional Biomaterials 9, no. 4 (December 4, 2018): 70. http://dx.doi.org/10.3390/jfb9040070.

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Blood analogues have long been a topic of interest in biofluid mechanics due to the safety and ethical issues involved in the collection and handling of blood samples. Although the current blood analogue fluids can adequately mimic the rheological properties of blood from a macroscopic point of view, at the microscopic level blood analogues need further development and improvement. In this work, an innovative blood analogue containing giant unilamellar vesicles (GUVs) was developed to mimic the flow behavior of red blood cells (RBCs). A natural lipid mixture, soybean lecithin, was used for the GUVs preparation, and three different lipid concentrations were tested (1 × 10−3 M, 2 × 10−3 M and 4 × 10−3 M). GUV solutions were prepared by thin film hydration with a buffer, followed by extrusion. It was found that GUVs present diameters between 5 and 7 µm which are close to the size of human RBCs. Experimental flow studies of three different GUV solutions were performed in a hyperbolic-shaped microchannel in order to measure the GUVs deformability when subjected to a homogeneous extensional flow. The result of the deformation index (DI) of the GUVs was about 0.5, which is in good agreement with the human RBC’s DI. Hence, the GUVs developed in this study are a promising way to mimic the mechanical properties of the RBCs and to further develop particulate blood analogues with flow properties closer to those of real blood.

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Jusufi, Kimet, and Ali Övgün. "Canonical acoustic thin-shell wormholes." Modern Physics Letters A 32, no. 07 (February 27, 2017): 1750047. http://dx.doi.org/10.1142/s021773231750047x.

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In this paper, we model a canonical acoustic thin-shell wormhole (CATSW) in the framework of analogue gravity systems. In this model, we apply cut and paste technique to join together two spherically symmetric, analogue canonical acoustic solutions, and compute the analogue surface density/surface pressure of the fluid using the Darmois–Israel formalism. We study the stability analyses by using a linear barotropic fluid (LBF), Chaplygin fluid (CF), logarithmic fluid (LogF), polytropic fluid (PF) and finally Van der Waals Quintessence (VDWQ). We show that a kind of analog acoustic fluid with negative energy is required at the throat to keep the wormhole stable. It is argued that CATSW can be a stabile thin-shell wormhole if we choose a suitable parameter values.

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Masovic, Drasko, and Ennes Sarradj. "Derivation of Lighthill’s Eighth Power Law of an Aeroacoustic Quadrupole in Acoustic Spacetime." Acoustics 2, no. 3 (September 8, 2020): 666–73. http://dx.doi.org/10.3390/acoustics2030035.

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Acoustic spacetime is a four-dimensional manifold analogue to the relativistic spacetime with the reference speed of light replaced by the speed of sound. It has been established primarily for the indirect studies of relativistic phenomena by means of their better understood acoustic analogues. More recently, it has also been used for the analytical treatment of sound propagation in various uniform and non-uniform flows of the background fluid. In this paper the analogy is extended and utilized to derive Lighthill’s eight power law for sound generation of an aeroacoustic quadrupole. Adding to the existing analogue theory, propagating sound waves are described in terms of a weak perturbation of the background acoustic spacetime metric. The obtained result proves that the acoustic analogy can be extended to cover both weak perturbation of the fluid due to the sound waves and certain sound generation mechanisms, at least in incompressible low Mach number flows.

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Jacquet, M. J., T. Boulier, F. Claude, A. Maître, E. Cancellieri, C. Adrados, A. Amo, et al. "Polariton fluids for analogue gravity physics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2177 (July 20, 2020): 20190225. http://dx.doi.org/10.1098/rsta.2019.0225.

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Analogue gravity enables the study of fields on curved space–times in the laboratory. There are numerous experimental platforms in which amplification at the event horizon or the ergoregion has been observed. Here, we demonstrate how optically generating a defect in a polariton microcavity enables the creation of one- and two-dimensional, transsonic fluid flows. We show that this highly tuneable method permits the creation of horizons. Furthermore, we present a rotating geometry akin to the water-wave bathtub vortex. These experiments usher in the possibility of observing stimulated as well as spontaneous amplification by the Hawking, Penrose and Zeld’ovich effects in fluids of light. This article is part of a discussion meeting issue ‘The next generation of analogue gravity experiments’.

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Sadek, Samir Hassan, Manuel Rubio, Rui Lima, and Emilio José Vega. "Blood Particulate Analogue Fluids: A Review." Materials 14, no. 9 (May 9, 2021): 2451. http://dx.doi.org/10.3390/ma14092451.

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Microfluidics has proven to be an extraordinary working platform to mimic and study blood flow phenomena and the dynamics of components of the human microcirculatory system. However, the use of real blood increases the complexity to perform these kinds of in vitro blood experiments due to diverse problems such as coagulation, sample storage, and handling problems. For this reason, interest in the development of fluids with rheological properties similar to those of real blood has grown over the last years. The inclusion of microparticles in blood analogue fluids is essential to reproduce multiphase effects taking place in a microcirculatory system, such as the cell-free layer (CFL) and Fähraeus–Lindqvist effect. In this review, we summarize the progress made in the last twenty years. Size, shape, mechanical properties, and even biological functionalities of microparticles produced/used to mimic red blood cells (RBCs) are critically exposed and analyzed. The methods developed to fabricate these RBC templates are also shown. The dynamic flow/rheology of blood particulate analogue fluids proposed in the literature (with different particle concentrations, in most of the cases, relatively low) is shown and discussed in-depth. Although there have been many advances, the development of a reliable blood particulate analogue fluid, with around 45% by volume of microparticles, continues to be a big challenge.

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Paor, Annraoi M. De. "A Fluid Analogy to Mutual Inductance, Based on The Atmospheric Railway." International Journal of Electrical Engineering & Education 29, no. 2 (April 1992): 101–10. http://dx.doi.org/10.1177/002072099202900202.

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A fluid analogy to mutual inductance, based on the atmospheric railway It is shown that the propulsion system for the Kingstown (now Dùn Laoghaire) to Dalkey Atmospheric Railway (1843–1854) is a translational counterpart to an idling turbine analogue for self-inductance. A two-pipeline atmospheric system driving a whirligig is proposed as an analogue for mutual inductance.

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BATISTA, A. B., J. C. FABRIS, S. V. B. GONCALVES, and J. TOSSA. "QUANTUM PERFECT FLUID COSMOLOGICAL MODEL AND ITS CLASSICAL ANALOGUE." International Journal of Modern Physics A 17, no. 20 (August 10, 2002): 2749. http://dx.doi.org/10.1142/s0217751x0201176x.

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The quantization of gravity coupled to a perfect fluid model leads to a Schrödinger-like equation, where the matter variable plays the role of time. The wave function can be determined, in the flat case, for an arbitrary barotropic equation of state p = α ρ; solutions can also be found for the radiative non-flat case. The wave packets are constructed, from which the expectation value for the scale factor is determined. The quantum scenarios reveal a bouncing Universe, free from singularity. Such quantum cosmological perfect fluid models admit a universal classical analogue, represented by the addition, to the ordinary classical model, of a repulsive stiff matter fluid1,2. The existence of this universal classical analogue may imply that this perfect fluid coupled to gravity model is not a real quantum system. The quantum cosmological perfect fluid model is, for a flat spatial section, formally equivalent to a free particle in ordinary quantum mechanics, for any value of α, while the radiative non-flat case is equivalent to the harmonic oscillator. The repulsive fluid needed to reproduce the quantum results is the same in both cases.

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Solovitz, Stephen A., Darcy E. Ogden, Dave Dae-Wook Kim, and Sang Young Kim. "Coupled fluid and solid evolution in analogue volcanic vents." Journal of Geophysical Research: Solid Earth 119, no. 7 (July 2014): 5342–55. http://dx.doi.org/10.1002/2014jb010993.

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Singh, Ksh Newton, N. Pradhan, and Neeraj Pant. "Charge Analogue of Tolman IV Solution for Anisotropic Fluid." International Journal of Theoretical Physics 54, no. 9 (March 17, 2015): 3408–23. http://dx.doi.org/10.1007/s10773-015-2581-7.

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Antonopoulou, Smaragdi, Alexandros Tsoupras, George Baltas, Helen Kotsifaki, Zacharias Mantzavinos, and Constantinos A. Demopoulos. "Hydroxyl-platelet-activating factor exists in blood of healthy volunteers and periodontal patients." Mediators of Inflammation 12, no. 4 (2003): 221–27. http://dx.doi.org/10.1080/09629350310001599666.

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Periodontal diseases are localized chronic inflammatory conditions of the gingival and underlying bone and connective tissue. Platelet-activating factor (PAF), a potent inflammatory phospholipid mediator that has been previously detected in elevated levels in inflamed gingival tissues, in gingival crevicular fluid and in saliva, is implicated in periodontal disease. Our results from previous studies showed that the biologically active phospholipid detected in gingival crevicular fluid is a hydroxyl-PAF analogue. In this study, hydroxyl-PAF analogue was detected for the first time in human blood derived from patients with chronic periodontitis as well as from periodontally healthy volunteers. The hydroxyl-PAF analogue was purified by high-performance liquid chromatography, detected by biological assays and identified by electrospray analysis. In addition, the quantitative determination of PAF and hydroxyl-PAF analogue (expressed as PAF-like activity) showed a statistically significant increase in the ratio of hydroxyl-PAF analogue levels to PAF levels in periodontal patients, suggesting that this bioactive lipid may play a role in oral inflammation.

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12

Tchen, C. M. "Statistical Foundation of the Fluid Analogue of the Soliton Formalism." Physica Scripta 34, no. 4 (October 1, 1986): 289–94. http://dx.doi.org/10.1088/0031-8949/34/4/001.

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13

Carneiro, J., R. Lima, J. B. L. M. Campos, and J. M. Miranda. "A microparticle blood analogue suspension matching blood rheology." Soft Matter 17, no. 14 (2021): 3963–74. http://dx.doi.org/10.1039/d1sm00106j.

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The new suspension-based blood analogue fluid has a long shelf life and matches blood shear and extensional rheologies. Microparticles in the suspension have size and deformability similar to red blood cells.

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Patel, LK, and Sharda S Koppar. "A Charged Analogue of the Vaidya?Tikekar Solution." Australian Journal of Physics 40, no. 3 (1987): 441. http://dx.doi.org/10.1071/ph870441.

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We present here an interior solution of the Einstein-Maxwell equations for a charged static fluid sphere. The physical 3-space t = constant of the solution is spheroidal. The solution is interpreted as an exact relativistic model for a charged superdense star.

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Dueymes, E. "Study of a high-velocity separator on an analogue fluid system." International Journal of Multiphase Flow 19, no. 2 (April 1993): 309–27. http://dx.doi.org/10.1016/0301-9322(93)90005-f.

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Sherman, T. F. "A simple analogue of lung mechanics." Advances in Physiology Education 265, no. 6 (December 1993): S32. http://dx.doi.org/10.1152/advances.1993.265.6.s32.

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A model of the chest and lungs can be easily constructed from a bottle of water, a balloon, a syringe, a rubber stopper, glass and rubber tubing, and clamps. The model is a more exact analogue of the body than the classic apparatus of Hering in two respects: 1) the pleurae and intrapleural fluid are represented by water rather than air, and 2) the subatmospheric "intrapleural" pressure is created by the elasticity of the "lung" (balloon) rather than by a vacuum pump. With this model, students can readily see how the lung is inflated and deflated by movements of the "diaphragm and chest" (syringe plunger) and how intrapleural pressures change as this is accomplished.

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Yu, Xiaoxi, Yuan Li, Yuquan Liu, Yuping Yang, and Yining Wu. "Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures." Polymers 11, no. 8 (August 2, 2019): 1291. http://dx.doi.org/10.3390/polym11081291.

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Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10−2. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.

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Krishnaswami, Govind S., and Sachin S. Phatak. "Higgs mechanism and the added-mass effect." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2176 (April 2015): 20140803. http://dx.doi.org/10.1098/rspa.2014.0803.

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In the Higgs mechanism, mediators of the weak force acquire masses by interacting with the Higgs condensate, leading to a vector boson mass matrix. On the other hand, a rigid body accelerated through an inviscid, incompressible and irrotational fluid feels an opposing force linearly related to its acceleration, via an added-mass tensor. We uncover a striking physical analogy between the two effects and propose a dictionary relating them. The correspondence turns the gauge Lie algebra into the space of directions in which the body can move, encodes the pattern of gauge symmetry breaking in the shape of an associated body and relates symmetries of the body to those of the scalar vacuum manifold. The new viewpoint is illustrated with numerous examples, and raises interesting questions, notably on the fluid analogues of the broken symmetry and Higgs particle, and the field-theoretic analogue of the added mass of a composite body.

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Okumura, T., I. L. Taylor, and T. N. Pappas. "Microinjection of TRH analogue into the dorsal vagal complex stimulates pancreatic secretion in rats." American Journal of Physiology-Gastrointestinal and Liver Physiology 269, no. 3 (September 1, 1995): G328—G334. http://dx.doi.org/10.1152/ajpgi.1995.269.3.g328.

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Thyrotropin-releasing hormone (TRH) stimulates pancreatic exocrine secretion through the vagus nerve when injected into rat cerebrospinal fluid. However, little is known about the exact site of action of TRH in the brain to stimulate pancreatic secretion. Recent neuroimmunochemical and neurophysiological studies suggest that TRH could be a neurotransmitter in the dorsal vagal complex, which sends fibers to the pancreas through the vagus nerve. We therefore hypothesized that TRH may act centrally in the dorsal vagal complex to stimulate pancreatic exocrine secretion. To address this question, a TRH analogue, [1-methyl-(S)-4,5-dihydroorotyl]-L-histidyl-L-prolinamide- NH2, was microinjected into the dorsal vagal complex, and basal pancreatic fluid flow and protein secretion were measured in urethan-anesthetized rats. Microinjection of TRH analogue (0.2-2 ng/site) into the dorsal vagal complex significantly stimulated pancreatic flow and protein output in a dose-dependent manner. As a control, microinjection of the TRH analogue into the brain stem outside the vagal complex failed to stimulate pancreatic secretion. Either bilateral subdiaphragmatic vagotomy or atropine abolished the ability of the TRH analogue to stimulate pancreatic secretion. Our data suggest that TRH acts in the dorsal vagal complex to stimulate pancreatic secretion through vagus-dependent and cholinergic pathways. The dorsal vagal complex may play an important role as a central site for control of the exocrine pancreas.

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Corsi, G., A. De Simone, C. Maurini, and S. Vidoli. "A neutrally stable shell in a Stokes flow: a rotational Taylor's sheet." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, no. 2227 (July 2019): 20190178. http://dx.doi.org/10.1098/rspa.2019.0178.

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In a seminal paper published in 1951, Taylor studied the interactions between a viscous fluid and an immersed flat sheet which is subjected to a travelling wave of transversal displacement. The net reaction of the fluid over the sheet turned out to be a force in the direction of the wave phase-speed. This effect is a key mechanism for the swimming of micro-organisms in viscous fluids. Here, we study the interaction between a viscous fluid and a special class of nonlinear morphing shells. We consider pre-stressed shells showing a one-dimensional set of neutrally stable equilibria with almost cylindrical configurations. Their shape can be effectively controlled through embedded active materials, generating a large-amplitude shape-wave associated with precession of the axis of maximal curvature. We show that this shape-wave constitutes the rotational analogue of a Taylor's sheet, where the translational swimming velocity is replaced by an angular velocity. Despite the net force acting on the shell vanishes, the resultant torque does not. A similar mechanism can be used to manoeuver in viscous fluids.

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HANSRAJ, S., and S. D. MAHARAJ. "CHARGED ANALOGUE OF FINCH–SKEA STARS." International Journal of Modern Physics D 15, no. 08 (August 2006): 1311–27. http://dx.doi.org/10.1142/s0218271806008826.

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We present solutions to the Einstein–Maxwell system of equations in spherically symmetric gravitational fields for static interior space–times with a specified form of the electric field intensity. The condition of pressure isotropy yields three category of solutions. The first category is expressible in terms of elementary functions and does not have an uncharged limit. The second category is given in terms of Bessel functions of half-integer order. These charged solutions satisfy a barotropic equation of state and contain Finch–Skea uncharged stars. The third category is obtained in terms of modified Bessel functions of half-integer order and does not have an uncharged limit. The physical features of the charged analogue of the Finch–Skea stars are studied in detail. In particular, the condition of causality is satisfied and the speed of sound does not exceed the speed of light. The physical analysis indicates that this analogue is a realistic model for static charged relativistic perfect fluid spheres.

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Zhang, Baocheng. "Thermodynamics of Acoustic Black Holes in Two Dimensions." Advances in High Energy Physics 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/5710625.

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It is well-known that the thermal Hawking-like radiation can be emitted from the acoustic horizon, but the thermodynamic-like understanding for acoustic black holes was rarely made. In this paper, we will show that the kinematic connection can lead to the dynamic connection at the horizon between the fluid and gravitational models in two dimensions, which implies that there exists the thermodynamic-like description for acoustic black holes. Then, we discuss the first law of thermodynamics for the acoustic black hole via an intriguing connection between the gravitational-like dynamics of the acoustic horizon and thermodynamics. We obtain a universal form for the entropy of acoustic black holes, which has an interpretation similar to the entropic gravity. We also discuss the specific heat and find that the derivative of the velocity of background fluid can be regarded as a novel acoustic analogue of the two-dimensional dilaton potential, which interprets why the two-dimensional fluid dynamics can be connected to the gravitational dynamics but it is difficult for four-dimensional case. In particular, when a constraint is added for the fluid, the analogue of a Schwarzschild black hole can be realized.

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GONZÁLEZ-FERNÁNDEZ, B., and A. CAMACHO. "FLUID-GRAVITY CORRESPONDENCE UNDER THE PRESENCE OF VISCOSITY." Modern Physics Letters A 27, no. 32 (October 11, 2012): 1250185. http://dx.doi.org/10.1142/s0217732312501854.

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This work addresses the analogy between the speed of sound of a viscous, barotropic, and irrotational fluid and the equation of motion for a non-massive field in a curved manifold. It will be shown that the presence of viscosity implies the introduction, into the equation of motion of the gravitational analogue, of a source term which entails the flow of energy from the non-massive field to the curvature of the spacetime manifold. The stress–energy tensor is also computed and it is found not to be constant, which is consistent with such energy interchange.

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Simon, E. E., C. Merli, J. Herndon, E. J. Cragoe, and L. L. Hamm. "Determinants of ammonia entry along the rat proximal tubule during chronic metabolic acidosis." American Journal of Physiology-Renal Physiology 256, no. 6 (June 1, 1989): F1104—F1110. http://dx.doi.org/10.1152/ajprenal.1989.256.6.f1104.

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The technique of in vivo microperfusion was used to examine the determinants of ammonia entry along the rat proximal tubule under conditions of chronic metabolic acidosis (CMA). When perfused with a 5 mM bicarbonate-containing perfusate, collected fluid ammonia concentrations remained constant with increasing flow rate and thus ammonia entry was highly flow-rate dependent. Ammonia entry was also flow-rate dependent using a 25 mM bicarbonate perfusate but entry reached a plateau as perfusion rate increased. Also, ammonia entry tended to be lower at all perfusion rates with the 25 mM perfusate compared with the 5 mM bicarbonate perfusate, but this was most evident at the highest perfusion rate (45 nl/min). The decline in ammonia entry was associated with increasing collected fluid bicarbonate concentrations, suggesting that there was inhibition of diffusion trapping of ammonia. The effects of Na+-H+ exchange inhibition on ammonia entry were examined using the amiloride analogue, 5-(N-ethyl-N-isopropyl)amiloride. With a 25 mM bicarbonate-containing perfusate, the amiloride analogue caused a significant decrease in bicarbonate reabsorption but a nonsignificant decrease in ammonia entry associated with a significant rise in collected fluid bicarbonate concentration. When the potential effects of decreased diffusion trapping of ammonia were eliminated with 12 and 5 mM bicarbonate-containing perfusates, the analogue had no effect on ammonia entry despite significant inhibition of bicarbonate reabsorption. Thus ammonia entry in CMA is moderately affected by tubule fluid pH but is highly flow-rate dependent. There were no effects of inhibition of Na+-H+ exchange above those expected from inhibition of diffusion trapping of ammonia.

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Dichiarante, Anna M., Ken J. W. McCaffrey, Robert E. Holdsworth, Tore I. Bjørnarå, and Edward D. Dempsey. "Fracture attribute scaling and connectivity in the Devonian Orcadian Basin with implications for geologically equivalent sub-surface fractured reservoirs." Solid Earth 11, no. 6 (November 23, 2020): 2221–44. http://dx.doi.org/10.5194/se-11-2221-2020.

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Abstract. Fracture attribute scaling and connectivity datasets from analogue systems are widely used to inform sub-surface fractured reservoir models in a range of geological settings. However, significant uncertainties are associated with the determination of reliable scaling parameters in surface outcrops. This has limited our ability to upscale key parameters that control fluid flow at reservoir to basin scales. In this study, we present nine 1D-transect (scanline) fault and fracture attribute datasets from Middle Devonian sandstones in Caithness (Scotland) that are used as an onshore analogue for nearby sub-surface reservoirs such as the Clair field, west of Shetland. By taking account of truncation and censoring effects in individual datasets, our multiscale analysis shows a preference for power-law scaling of fracture length over 8 orders of magnitude (10−4 to 104 m) and kinematic aperture over 4 orders of magnitude (10−6 to 10−2 m). Our assessment of the spatial organization (clustering and topology) provides a new basis for up-scaling fracture attributes collected in outcrop- to regional-scale analogues. We show how these relationships may inform knowledge of geologically equivalent sub-surface fractured reservoirs.

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Liotta, Domenico, Andrea Brogi, Giovanni Ruggieri, and Martina Zucchi. "Fossil vs. Active Geothermal Systems: A Field and Laboratory Method to Disclose the Relationships between Geothermal Fluid Flow and Geological Structures at Depth." Energies 14, no. 4 (February 10, 2021): 933. http://dx.doi.org/10.3390/en14040933.

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Comparison between fossil and analogue active geothermal systems permit to obtain key-parameters to define a conceptual model of the area under exploration. The approach is based on structural, kinematic, and fluid inclusions analyses. The fossil system is investigated to describe the distribution of the hydrothermal mineralization as witness of the fluid flow through geological structures and bodies, at depth. Structural and kinematic data (to define the preferential direction of fluid flow) are collected in structural stations and by scan lines and scan boxes on key outcrops. Distribution, length, width of fractures, and hydrothermal veins bring to evaluate permeability in the fossil system and, by analogy, in the deep roots of the active system. Fluid inclusions analysis shed light on density, viscosity, and temperature of the paleo-fluids. Data integration provides the hydraulic conductivity. In active geothermal systems, fieldwork is addressed to paleo-stress analysis with data from recent faults (<2 Ma), to compare with local focal mechanisms. By this, indications on the present fluid pathways are given. The main advantage resides in obtaining parameters normally got after drilling, thus contributing to strengthen the strategy of exploration, de-risking unsuccessful boreholes.

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Das, S., T. Sahoo, and M. H. Meylan. "Flexural-gravity wave dynamics in two-layer fluid: blocking and dead water analogue." Journal of Fluid Mechanics 854 (August 31, 2018): 121–45. http://dx.doi.org/10.1017/jfm.2018.617.

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Flexural-gravity wave characteristics are analysed, in the presence of a compressive force and a two-layer fluid, under the assumption of linearized water wave theory and small amplitude structural response. The occurrence of blocking for flexural-gravity waves is demonstrated in both the surface and internal modes. Within the threshold of the blocking and the buckling limit, the dispersion relation possesses four positive roots (for fixed wavenumber). It is shown that, under certain conditions, the phase and group velocities coalesce. Moreover, a wavenumber range for certain critical values of compression and depth is provided within which the internal wave energy moves faster than that of the surface wave. It is also demonstrated that, for shallow water, the wave frequencies in the surface and internal modes will never coalesce. It is established that the phase speed in the surface and internal modes attains a minimum and maximum, respectively, when the interface is located approximately in the middle of the water depth. An analogue of the dead water phenomenon, the occurrence of a high amplitude internal wave with a low amplitude at the surface, is established, irrespective of water depth, when the densities of the two fluids are close to each other. When the interface becomes close to the seabed, the dead water effect ceases to exist. The theory developed in the frequency domain is extended to the time domain and examples of negative energy waves and blocking are presented.

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Tarafdar, Pratik, and Tapas K. Das. "Dependence of acoustic surface gravity on geometric configuration of matter for axially symmetric background flows in the Schwarzschild metric." International Journal of Modern Physics D 24, no. 14 (December 2015): 1550096. http://dx.doi.org/10.1142/s0218271815500960.

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In black hole evaporation process, the mass of the hole anti-correlates with the Hawking temperature. This indicates that the smaller holes have higher surface gravity. For analogue Hawking effects, however, the acoustic surface gravity is determined by the local values of the dynamical velocity of the stationary background fluid flow and the speed of propagation of the characteristic perturbation embedded in the background fluid, as well as by their space derivatives evaluated along the direction normal to the acoustic horizon, respectively. The mass of the analogue system — whether classical or quantum — does not directly contribute to extremize the value of the associated acoustic surface gravity. For general relativistic axially symmetric background fluid flow in the Schwarzschild metric, we show that the initial boundary conditions describing such accretion influence the maximization scheme of the acoustic surface gravity and associated analogue temperature. Aforementioned background flow onto black holes can assume three distinct geometric configurations. Identical set of initial boundary conditions can lead to entirely different phase-space behavior of the stationary flow solutions, as well as the salient features of the associated relativistic acoustic geometry. This implies that it is imperative to investigate how the measure of the acoustic surface gravity corresponding to the accreting black holes gets influenced by the geometric configuration of the inflow described by various thermodynamic equations of state. Such investigation is useful to study the effect of Einstenian gravity on the nonconventional classical features as observed in Hawking like effect in a dispersive medium in the limit of a strong dispersion relation.

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Jansen, Sebastian V., Indra Müller, Max Nachtsheim, Thomas Schmitz-Rode, and Ulrich Steinseifer. "Ghost Cell Suspensions as Blood Analogue Fluid for Macroscopic Particle Image Velocimetry Measurements." Artificial Organs 40, no. 2 (May 21, 2015): 207–12. http://dx.doi.org/10.1111/aor.12511.

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Pegler, Samuel S., Alexandra S. D. Maskell, Katherine A. Daniels, and Mike J. Bickle. "Fluid transport in geological reservoirs with background flow." Journal of Fluid Mechanics 827 (August 24, 2017): 536–71. http://dx.doi.org/10.1017/jfm.2017.501.

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This paper presents fundamental analysis of the injection and release of fluid into porous media or geological reservoirs saturated by a different fluid undergoing a background flow, and tests the predictions using analogue laboratory experiments. The study reveals new results important for an understanding of the transport of hazardous contaminants through aquifers and the long-term fate of carbon dioxide ($\text{CO}_{2}$) in geological $\text{CO}_{2}$ sequestration. Using numerical and asymptotic analysis, we describe a variety of flow regimes that arise, and demonstrate an almost instantaneous control of injected fluid by the far field conditions in geological reservoirs. For a continuous input, the flow develops a horizontal interface between the injected and ambient fluids. The background flow thereby effectively caps the height of the injected fluid into a shallower region of vertical confinement. For a released parcel of fluid, gravitational spreading is found to become negligible after a short time. A dominant control of the interface by the background pressure gradient arises, and stems from the different velocities at which it drives the injected and ambient fluids individually. Similarity solutions describing these dynamics show that the parcel approaches a slender triangular profile that grows horizontally as $t^{1/2}$, where $t$ is time, a rate faster than relaxation under gravity. Shock layers develop at the front or back of the parcel, depending on whether it is more or less viscous than the ambient fluid. New analytical results describing the long-term effects of residual trapping due to capillary retention are developed, which yield explicit predictions for the time and length scales on which a parcel of $\text{CO}_{2}$ becomes retained. We end by applying our results to geological contexts, concluding that even slight background motion can have considerable implications for long-term transport through the subsurface.

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31

Forté, Martin, Dominique Bouchard, and André Charette. "Fluid Flow Investigation of Die Cast Tensile Test Bars." Solid State Phenomena 116-117 (October 2006): 457–63. http://dx.doi.org/10.4028/www.scientific.net/ssp.116-117.457.

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The fluid flow of an A356 semi-solid aluminum alloy filling a die consisting of four tensile test bars was investigated. Numerical simulations were carried out by implementing a mathematical model in a finite element software. Additional simulations were also obtained with a physical model in which tomato paste was used as the analogue fluid for the semi-solid aluminum. The modeling results were complemented by a series of experiments where tensile test bars were produced from semi-solid aluminum with a high pressure die casting press. The correspondence observed with the two modeling approaches and the casting experiments is discussed along with the effect the die geometry had on the flow patterns.

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32

Sahu, Chunendra K., and M. R. Flynn. "Filling box flows in porous media." Journal of Fluid Mechanics 782 (October 9, 2015): 455–78. http://dx.doi.org/10.1017/jfm.2015.555.

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We report upon a theoretical and experimental investigation of a porous medium ‘filling box’ flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls. The plume outflow initially comprises a pair of oppositely directed gravity currents. The gravity currents propagate horizontally until they reach the lateral sidewalls at $y=\pm L$. The flow then becomes of filling box type, with a vertically ascending ‘first front’ separating discharged plume fluid below from ambient fluid above. The flow details are described analytically by first deriving a new similarity solution for Darcy plumes with $\mathit{Pe}>O(1)$, where $\mathit{Pe}$ is the Péclet number. From the similarity solution so obtained, we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source. Regarding the plume outflow, a similarity solution adopted from Huppert & Woods (J. Fluid Mech., vol. 292, 1995, pp. 55–69) describes the height and front speed of the gravity currents, whereas a semi-implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance. As with high-Reynolds-number filling box flows, that studied here is an example of a coupled problem: the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity. Conversely, discharged plume fluid may be re-entrained into the plume, be it soon or long after reaching the bottom impermeable boundary. To corroborate our model predictions, analogue laboratory experiments are performed with fresh water and salt water as the working fluids. Our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity. Predictions for the gravity current front position and height compare favourably against analogue measured data. Good agreement is likewise noted when considering either the mean elevation or the profile of the first front. Results from this study may be adopted in modelling geological plumes. For example, our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries.

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33

Yanagisawa, K., and Y. Tache. "Intracisternal TRH analogue RX 77368 stimulates gastric histamine release in rats." American Journal of Physiology-Gastrointestinal and Liver Physiology 259, no. 4 (October 1, 1990): G599—G604. http://dx.doi.org/10.1152/ajpgi.1990.259.4.g599.

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The influence of intracisternal injection of the stable thyrotropin-releasing hormone (TRH) analogue RX 77368 on histamine levels in gastric secretion, interstitial fluid of the fundic submucosa, and portal hepatic circulation was investigated in rats. Intracisternal injection of RX 77368 (10-300 ng) induced a dose-related increase in histamine and acid output measured in the gastric secretion of pylorus-ligated, conscious rats. Intracisternal RX 77368 (300 ng) induced within 20 min a significant twofold histamine increase in interstitial fluid sampled from dialysis fibers implanted into the fundic submucosa. Histamine levels in the hepatic portal circulation were also dose dependently increased by RX 77368 injected intracisternally (30-100 ng), whereas intravenous infusion of RX 77368 (300 ng/30 min) did not significantly modify portal histamine levels. Bilateral cervical vagotomy or atropine pretreatment prevented intracisternal RX 77368-induced rise in hepatic portal levels of histamine, whereas purified gastrin monoclonal antibody 9303, injected at a dose blocking gastrin-stimulated acid secretion, had no effect. These results indicate that RX 77368 acts in the brain to increase gastric histamine secretion through vagal-dependent, muscarinic, nongastrin-mediated mechanisms and suggest a possible role of medullary TRH in the vagal regulation of gastric histamine secretion.

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34

Ren, Jie, Xiaopeng Zhu, Pan Xu, Rui Li, Ying Fu, Shuai Dong, Dongting Zhangsun, Yong Wu, and Sulan Luo. "d-Amino Acid Substitution of α-Conotoxin RgIA Identifies its Critical Residues and Improves the Enzymatic Stability." Marine Drugs 17, no. 3 (February 28, 2019): 142. http://dx.doi.org/10.3390/md17030142.

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α-Conotoxin RgIA is a selective and potent competitive antagonist of rat α9α10 nicotinic acetylcholine receptors (nAChR), but it is much less potent towards human α9α10 nAChR. Furthermore, RgIA is susceptible to proteolytic degradation due to containing four arginine residues. These disadvantages greatly limit its use for clinical applications. The purpose of this research was to identify critical stereocenters of RgIA and discover more stable analogues, enhancing its bioavailability by using the d-amino acid scan method. The activity of each variant was investigated against rat and human α9α10 nAChRs, which were expressed in Xenopus oocytes. Experimental assays showed that 14 out of 15 analogues had a substantial reduction in potency towards rat α9α10 nAChR. Noticeably, analogue 13 retained full biological activity compared with RgIA. Meanwhile, two other analogues, 14 and 15, of which l-Args were substituted with d-Args, exhibited a significantly increased potency towards human α9α10 nAChR, although these analogues showed decreased activities against rat α9α10 nAChR. Additionally, these three analogues exhibited a high resistance against enzymatic degradation in human serum and simulated intestinal fluid (SIF). Collectively, our findings suggest that a d-amino acid scan is a useful strategy for investigating how the side-chain chirality of amino acids affects the structure and function of peptides and may facilitate the development of more stable analogues to increase therapeutic potential.

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35

Carusotto, Iacopo. "Superfluid light in bulk nonlinear media." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2169 (September 8, 2014): 20140320. http://dx.doi.org/10.1098/rspa.2014.0320.

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We review how the paraxial approximation naturally leads to a hydrodynamic description of light propagation in a bulk Kerr nonlinear medium in terms of a wave equation analogous to the Gross–Pitaevskii equation for the order parameter of a superfluid. The main features of the many-body collective dynamics of the fluid of light in this propagating geometry are discussed: generation and observation of Bogoliubov sound waves in the fluid of light is first described. Experimentally accessible manifestations of superfluidity are then highlighted. Perspectives in view of realizing analogue models of gravity are finally given.

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36

MARUNO, KEN-ICHI, YASUHIRO OHTA, and MASAYUKI OIKAWA. "NOTE ON THE TWO-COMPONENT ANALOGUE OF TWO-DIMENSIONAL LONG WAVE – SHORT WAVE RESONANCE INTERACTION SYSTEM." Glasgow Mathematical Journal 51, A (February 2009): 129–35. http://dx.doi.org/10.1017/s0017089508004849.

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AbstractAn integrable two-component analogue of the two-dimensional long wave – short wave resonance interaction (2c-2d-LSRI) system is studied. Wronskian solutions of 2c-2d-LSRI system are presented. A reduced case, which describes resonant interaction between an interfacial wave and two surface wave packets in a two-layer fluid, is also discussed.

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37

Empey, Lonnie R., Keith Walker, and Richard N. Fedorak. "Indomethacin worsens and a leukotriene biosynthesis inhibitor accelerates mucosal healing in rat colitis." Canadian Journal of Physiology and Pharmacology 70, no. 5 (May 1, 1992): 660–68. http://dx.doi.org/10.1139/y92-084.

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The implication of leukotrienes as mediators of inflammation and recent evidence that prostaglandin analogues provide a beneficial effect during experimental colitis led to the speculation that (i) leukotrienes may be injurious and (ii) prostaglandins may be protective to colonic mucosa. Using a 2% acetic acid induced rat colitis model, we administered specific cyclooxygenase (indomethacin) and leukotriene biosynthesis inhibitors (MK-886) to examine the effect of endogenous prostaglandins and leukotrienes on colonic macroscopic injury, mucosal inflammation as measured by myeloperoxidase activity, net in vivo intestinal fluid absorption, and colonic PGE2 and LTB4 levels as measured by in vivo rectal dialysis. Indomethacin treatment prior to induction of colitis reduced endogenous mucosal PGE2 levels and exacerbated macroscopic ulceration and net fluid absorption. Addition of the exogenous PGE1 analogue misoprostol to the indomethacin-exacerbated colitis completely healed colonic macroscopic ulceration and inflammation but only partially improved fluid absorptive injury. The specific leukotriene biosynthesis inhibitor MK-886 administered prior to induction of colitis healed macroscopic ulceration and inflammation but not fluid absorptive injury. This mucosal reparative effect of MK-886 occurred at a dose that reduced colonic LTB4 synthesis while concomitantly enhancing PGE2 levels. Combining MK-886 with misoprostol treatment improved not only macroscopic ulceration and inflammation but also provided a synergistic effect that maintained net colonic fluid absorption at noncolitic control levels. These studies suggest that, during the induction of experimental colitis, endogenous prostaglandins play a pivotal role in providing a mucosal healing effect, and that leukotriene biosynthesis inhibitor may manifest part of its beneficial effect by shifting arachidonic acid metabolism towards production of prostaglandins.Key words: cyclooxygenase, eicosanoids, indomethacin, inflammatory bowel disease, leukotrienes, lipoxygenase, MK-886, misoprostol, prostaglandins.

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Montanari, Domenico, Marco Bonini, Giacomo Corti, Andrea Agostini, and Chiara Del Ventisette. "Forced folding above shallow magma intrusions: Insights on supercritical fluid flow from analogue modelling." Journal of Volcanology and Geothermal Research 345 (October 2017): 67–80. http://dx.doi.org/10.1016/j.jvolgeores.2017.07.022.

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39

Agada, S., F. Chen, S. Geiger, G. Toigulova, S. Agar, R. Shekhar, G. Benson, et al. "Numerical simulation of fluid-flow processes in a 3D high-resolution carbonate reservoir analogue." Petroleum Geoscience 20, no. 1 (January 27, 2014): 125–42. http://dx.doi.org/10.1144/petgeo2012-096.

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40

Tripathi, Ashwani S., Bhabani P. Chattopadhyay, and Soumen Das. "Actuation behavior of ionic polymer-metal composite based actuator in blood analogue fluid environment." Polymer-Plastics Technology and Materials 59, no. 12 (April 1, 2020): 1268–76. http://dx.doi.org/10.1080/25740881.2020.1738467.

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41

Dong, Tianyu, Ke Yin, Xiaoke Gao, and Xikui Ma. "Generalized local analogue model for nonlocal plasmonic nanostructures based on multiple-fluid hydrodynamic framework." Journal of Physics D: Applied Physics 53, no. 29 (May 21, 2020): 295105. http://dx.doi.org/10.1088/1361-6463/ab8509.

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42

Elias, Radu M., and Miles G. Johnston. "Modulation of fluid pumping in isolated bovine mesenteric lymphatics by a thromboxane/endoperoxide analogue." Prostaglandins 36, no. 1 (July 1988): 97–106. http://dx.doi.org/10.1016/0090-6980(88)90105-0.

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43

Yuan, T., D. Durox, and E. Villermaux. "An analogue study for flame flickering." Experiments in Fluids 17, no. 5 (September 1994): 337–49. http://dx.doi.org/10.1007/bf01874414.

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44

Shu, Jian-Jun. "A Finite Element Model and Electronic Analogue of Pipeline Pressure Transients With Frequency-Dependent Friction." Journal of Fluids Engineering 125, no. 1 (January 1, 2003): 194–98. http://dx.doi.org/10.1115/1.1522415.

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A finite element model and its equivalent electronic analogue circuit has been developed for fluid transients in hydraulic transmission lines with laminar frequency-dependent friction. Basic equations are approximated to be a set of ordinary differential equations that can be represented in state-space form. The accuracy of the model is demonstrated by comparison with the method of characteristics.

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45

Cohen, Tal, and David Durban. "Longitudinal shock waves in solids: the piston shock analogue." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2164 (April 8, 2014): 20130061. http://dx.doi.org/10.1098/rspa.2013.0061.

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Propagation of longitudinal deformation in hardening elastoplastic solids is investigated by the way of analogy with the shock tube pattern in fluid mechanics. Conditions for the appearance of a shock discontinuity are formulated and steady-state continuous and discontinuous solutions are derived. Field characteristics are then investigated for a representative family of hardening elastoplastic Mises solids accounting for finite strains. A critical limit value of the imposed velocity for the emergence of a shock wave is found and sensitivity to material parameters is assessed. Evaluation of dissipation effects is conducted and field response is compared with other uniaxial stress fields. In agreement with available experimental results, it is established that the field may consist of both an elastic precursor and a plastic shock separated by a continuous elastoplastic range. Or, alternatively, when the imposed velocity is higher, the plastic shock overtakes those regions allowing for a variety of resulting fields.

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46

Huppert, Herbert E., and Andrew W. Woods. "Gravity-driven flows in porous layers." Journal of Fluid Mechanics 292 (June 10, 1995): 55–69. http://dx.doi.org/10.1017/s0022112095001431.

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The motion of instantaneous and maintained releases of buoyant fluid through shallow permeable layers of large horizontal extent is described by a nonlinear advection–diffusion equation. This equation admits similarity solutions which describe the release of one fluid into a horizontal porous layer initially saturated with a second immiscible fluid of different density. Asymptotically, a finite volume of fluid spreads as t1/3. On an inclined surface, in a layer of uniform permeability, a finite volume of fluid propagates steadily alongslope under gravity, and spreads diffusively owing to the gravitational acceleration normal to the boundary, as on a horizontal boundary. However, if the permeability varies in this cross-slope direction, then, in the moving frame, the spreading of the current eventually becomes dominated by the variation in speed with depth, and the current length increases as t1/2. Shocks develop either at the leading or trailing edge of the flows depending upon whether the permeability increases or decreases away from the sloping boundary. Finally we consider the transient and steady exchange of fluids of different densities between reservoirs connected by a shallow long porous channel. Similarity solutions in a steadily migrating frame describe the initial stages of the exchange process. In the final steady state, there is a continuum of possible solutions, which may include flow in either one or both layers of fluid. The maximal exchange flow between the reservoirs involves motion in one layer only. We confirm some of our analysis with analogue laboratory experiments using a Hele-Shaw cell.

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Poyatos, Lourdes, Esther Papaseit, Eulalia Olesti, Clara Pérez-Mañá, Mireia Ventura, Xoán Carbón, Marc Grifell, et al. "A Comparison of Acute Pharmacological Effects of Methylone and MDMA Administration in Humans and Oral Fluid Concentrations as Biomarkers of Exposure." Biology 10, no. 8 (August 17, 2021): 788. http://dx.doi.org/10.3390/biology10080788.

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Considered the β-keto analogue of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy), 3,4-Methylenedioxymethcathinone (methylone) is a synthetic cathinone. Over the years, methylone has been used as a substitute for conventional psychostimulants, such as MDMA. To date, little is known about the human pharmacology of methylone; the only available information has been provided by surveys or published intoxication reports. In the present observational–naturalistic study, we evaluate the acute subjective and physiological effects of methylone after oral self-administration in comparison to MDMA in healthy poly-drug users. Fourteen participants (10 males, 4 females) selected their single oral doses of methylone from 100 to 300 mg (n = 8, mean dose 187.5 mg) or MDMA from 75 to 100 mg (n = 6, mean dose 87.5 mg) based on their experience. Study variables were assessed at 0, 1, 2, and 4 h (h) and included vital signs (non-invasive blood pressure, heart rate, cutaneous temperature) and subjective effects using visual analogue scales (VAS), the 49-item Addiction Research Centre Inventory (ARCI) short form, and the Evaluation of the Subjective Effects of Substances with Abuse Potential (VESSPA-SSE) questionnaire. Additionally, oral fluid concentrations of methylone and MDMA were determined. Acute pharmacological effects produced by methylone followed the prototypical psychostimulant and empathogenic profile associated with MDMA, although they were less intense. Methylone concentrations in oral fluid can be considered a useful biomarker to detect acute exposure in oral fluid. Oral fluid concentrations of MDMA and methylone peaked at 2 h and concentrations of MDMA were in the range of those previously described in controlled studies. Our results demonstrate that the potential abuse liability of methylone is similar to that of MDMA in recreational subjects.

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48

Weydt, Leandra M., Kristian Bär, Chiara Colombero, Cesare Comina, Paromita Deb, Baptiste Lepillier, Giuseppe Mandrone, et al. "Outcrop analogue study to determine reservoir properties of the Los Humeros and Acoculco geothermal fields, Mexico." Advances in Geosciences 45 (September 11, 2018): 281–87. http://dx.doi.org/10.5194/adgeo-45-281-2018.

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Abstract. The Los Humeros geothermal system is steam dominated and currently under exploration with 65 wells (23 producing). Having temperatures above 380 ∘C, the system is characterized as a super hot geothermal system (SHGS). The development of such systems is still challenging due to the high temperatures and aggressive reservoir fluids which lead to corrosion and scaling problems. The geothermal system in Acoculco (Puebla, Mexico; so far only explored via two exploration wells) is characterized by temperatures of approximately 300 ∘C at a depth of about 2 km. In both wells no geothermal fluids were found, even though a well-developed fracture network exists. Therefore, it is planned to develop an enhanced geothermal system (EGS). For better reservoir understanding and prospective modeling, extensive geological, geochemical, geophysical and technical investigations are performed within the scope of the GEMex project. Outcrop analogue studies have been carried out in order to identify the main fracture pattern, geometry and distribution of geological units in the area and to characterize all key units from the basement to the cap rock regarding petro- and thermo-physical rock properties and mineralogy. Ongoing investigations aim to identify geological and structural heterogeneities on different scales to enable a more reliable prediction of reservoir properties. Beside geological investigations, physical properties of the reservoir fluids are determined to improve the understanding of the hydrochemical processes in the reservoir and the fluid-rock interactions, which affect the reservoir rock properties.

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Zhou, Shiwei, and Kui Xiao. "Hawking radiation of analogous acoustic black holes." Modern Physics Letters A 35, no. 28 (July 30, 2020): 2050236. http://dx.doi.org/10.1142/s0217732320502363.

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Propagation of sound waves in a flowing fluid can be viewed as a minimally coupled massless scalar field propagating in curved spacetime. The analogue Hawking radiation from a spherically symmetric acoustic black hole and a (2 + 1)-dimensional rotating acoustic black hole are investigated respectively in Damour–Ruffini’s method. The emission rate and Hawking temperature are obtained, which are related to acoustic black holes parameter.

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Zorzan, C., and P. S. Cally. "Resonant structures within incompressible ideal MHD." Journal of Plasma Physics 47, no. 2 (April 1992): 321–47. http://dx.doi.org/10.1017/s0022377800024259.

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The resonant characteristics of an incompressible ideal MHD fluid are highly structured. To help expose this structure, an equivalent electrical analogue of the MHD system is developed. The model, in the form of a transmission line, makes it possible to identify a number of new and important concepts, one of which is the effective impedance. This in turn enables entire regions of MHD fluid to be replaced with equivalent impedances. When fully exploited, the model also provides a more consistent interpretation of the spectrum of ideal MHD. The discrete Alfvén modes are found to be highly degenerate, while the transition to a discontinuous profile is accompanied by a redistribution of an uncountably infinite number of ‘poles’ from the continuous spectrum and onto the Alfvén modes. In addition, the electrical analogue shows that within a continuously structured fluid the characteristic behaviour is not necessarily dominated by the ‘surface mode’ alone. This view is also supported by the results of a numerical simulation of the linear MHD equations. Depending on the initial conditions, the collective behaviour can have any frequency within the range spanned by the transition zone. The energy itself is monitored using a new pair of energy and flux expressions derived from a variational (Lagrangian) description of the MHD system. Again the electrical model is used to provide a physical interpretation of the individual terms within these expressions. In particular, it allows a partition of the total energy into separate kinetic- and potential-energy terms.

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Journal articles on the topic 'Fluid analogue'

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