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BEM simulation of compressible fluid flow in an enclosure induced by thermoacoustic waves
Leopold Škerget, Jure Ravnik, 2009, original scientific article

Abstract: The problem of unsteady compressible fluid flow in an enclosure induced by thermoacoustic waves is studied numerically. Full compressible set of Navier-Stokes equations are considered and numerically solved by boundary-domain integral equations approach coupled with wavelet compression and domain decomposition to achieve numerical efficiency. The thermal energy equation is written in its most general form including the Rayleigh and reversible expansion rate terms. Both, the classical Fourier heat flux model and wave heat conduction model are investigated. The velocity-vorticity formulation of the governing Navier-Stokes equations is employed, while the pressure field is evaluated from the corresponding pressure Poisson equation. Material properties are taken to be for the perfect gas, and assumed to be pressure and temperature dependent.
Keywords: compressible fluid flow, boundary element method, thermoacoustic waves, velocity-vorticity fomulation
Published: 31.05.2012; Views: 1353; Downloads: 64
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Wave motion in infinite inhomogeneous waveguides
Igor Špacapan, Miroslav Premrov, 2003, original scientific article

Abstract: The analysis of wave motion in infinite homogeneous waveguides, having a complicated cross-section and/or an irregular inclusion, is a rather difficult task for the majority of available methods, especially when striving for accurate results. In contrast, this presented procedure performed in the frequency domain, is simple to apply. It yields correct results because the radiation conditions are considerably accurately satisfied, and it offers a clear parametric insight into wave motion. This procedure uses the FE modelling of an analysed section of the waveguide. It is based on the decomposition of wave motion, distinguishing propagating and non-propagating wavemodes by solving the eigenvalue problem. The presented examples demonstrate the effectiveness of this procedure, whilst a comparison between computed and analytical results demonstrates its accuracy.
Keywords: waves, wavemodes, waveguides, inhomogeneity, finite element method, parametric analysis, radiation conditions, eigenvalue problem, frequency domain
Published: 01.06.2012; Views: 1404; Downloads: 39
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Cellular diversity promotes intercellular Ca[sup]2+ wave propagation
Marko Gosak, 2009, original scientific article

Abstract: Calcium ions are an important second messenger in living cells. Calcium signals in form of waves serve as a means of intercellular communication and thus represent a vibrant subject for experimental and theoretical investigations. Here we study the role of cellular variability on the occurrence of ▫$Ca^{2+}$▫ wave propagation in a net of diffusively coupled cells. Dynamics of individual cells is simulated by a mathematical model for ▫$Ca^{2+}$▫ oscillations. Structural diversity of cells is introduced via variations of the bifurcation parameters, which signify cell sensitivity for external stimulation. Remarkably, for sufficient values of variability ▫$Ca^{2+}$▫ waves emerge, which are mostly ordered for intermediate variability strength. We analyze the spatial profile via the autocorrelation function, which confirms aresonance-like response due to the cellular variability. Thus, the reported phenomenon is a novel observation of diversity-induced spatial coherence resonance in a tissue-like media.
Keywords: dynamic systems, waves, calcium oscillations, resonance, diversity-induced resonance, cellular variability, coupled cells, intracellular processes
Published: 07.06.2012; Views: 981; Downloads: 11
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Emergence of target waves in paced populations of cyclically competing species
Luo-Luo Jiang, Tao Zhou, Matjaž Perc, Xin Huang, Bing-Hong Wang, 2009, original scientific article

Abstract: We investigate the emergence of target waves in a cyclic predator-prey model incorporating a periodic current of the three competing species in a small area situated at the center of a square lattice. The periodic current acts as a pacemaker, trying to impose its rhythm on the overall spatiotemporal evolution of the three species. We show that the pacemaker is able to nucleate target waves that eventually spread across the whole population, whereby three routes leading to this phenomenon can be distinguished depending on the mobility of the three species and the oscillation period of the localized current. First, target waves can emerge due to the synchronization between the periodic current and oscillations of the density of the three species on the spatial grid. The second route is similar to the first, the difference being that the synchronization sets in only intermittently. Finally, the third route toward target waves is realized when the frequency of the pacemaker is much higher than that characterizing the oscillations of the overall density of the three species. By considering the mobility and frequency of the current as variable parameters, we thus provide insights into the mechanisms of pattern formation resulting from the interplay between local and global dynamics in systems governed by cyclically competing species.
Keywords: cyclical interactions, target waves, spatial games, diversity
Published: 30.06.2017; Views: 570; Downloads: 224
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Critical and supercritical spatiotemporal calcium dynamics in beta cells
Marko Gosak, Andraž Stožer, Rene Markovič, Jurij Dolenšek, Matjaž Perc, Marjan Rupnik, Marko Marhl, 2017, original scientific article

Abstract: A coordinated functioning of beta cells within pancreatic islets is mediated by oscillatory membrane depolarization and subsequent changes in cytoplasmic calcium concentration. While gap junctions allow for intraislet information exchange, beta cells within islets form complex syncytia that are intrinsically nonlinear and highly heterogeneous. To study spatiotemporal calcium dynamics within these syncytia, we make use of computational modeling and confocal high-speed functional multicellular imaging. We show that model predictions are in good agreement with experimental data, especially if a high degree of heterogeneity in the intercellular coupling term is assumed. In particular, during the first few minutes after stimulation, the probability distribution of calcium wave sizes is characterized by a power law, thus indicating critical behavior. After this period, the dynamics changes qualitatively such that the number of global intercellular calcium events increases to the point where the behavior becomes supercritical. To better mimic normal in vivo conditions, we compare the described behavior during supraphysiological non-oscillatory stimulation with the behavior during exposure to a slightly lower and oscillatory glucose challenge. In the case of this protocol, we observe only critical behavior in both experiment and model. Our results indicate that the loss of oscillatory changes, along with the rise in plasma glucose observed in diabetes, could be associated with a switch to supercritical calcium dynamics and loss of beta cell functionality.
Keywords: beta cells, islets of Langerhans, self-organized criticality, intercellular dynamics, calcium waves, glucose oscillations, computational model, confocal calcium imaging
Published: 23.01.2018; Views: 485; Downloads: 222
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Mean grain size as a function of spectral amplitude: a new regression law for marine sediment cores
Nelly Zanette, Darinka Battelino, 2017, original scientific article

Abstract: Geophysics has been developed in order to supply indicative estimations in soil mechanics like the grain size distribution of finely grained soils as day, silt and fine sands. The paper describes the attempt to characterize porous and saturated marine sediments with a non destructive technique which is the acoustic wave, in order to determine the correlation with geotechnical measurements. The characterization of physical parameters of marine sediments was based on research methods which permit to describe the parameters defining different types of sediment and zones of sedimentation; to determine fundamental parameters that influence the propagation of the acoustic waves in saturated and porous means; to define quick and indicative methods for characterization of physical parameters of analysed means. The acoustic measurements were carried out at SACLANT-NATO of La Spezia (I), where the Vertical Multi Sensor Core Logger (V-MSCL) was used. The results of acoustic tests were compared to the grain size curves of the sediments and the propagation characteristics such as velocity, density, porosity and absorption of experimentally determined data. The analyses are based 011 various mathematical models presented in. literature, in order to predict and to describe physical mechanisms of the wave propagation using a simplification of the sediment structure. The target of the study was to determine a new mathematical law that linked the mean grain size to a directly measurable parameter such as the spectral amplitude, and to offer the possibility to obtain the first indicative value of the sediment mean grain size. The determined exponential law represents an innovative and quick approach to determine a physical characteristic of saturated and porous sediments such as the grain size in a non destructive way based on the spectral analysis of the wave propagation form.
Keywords: soil mechanics, marine sediments, finely grained soil, acoustic waves, grain size curve
Published: 17.05.2018; Views: 292; Downloads: 29
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Innovative solution principles of wave problems in horizontaly layered medias
Andrej Štrukelj, Andrej Umek, Tomaž Pliberšek, 2006, original scientific article

Abstract: The paper presents engineeringly reasonable transformation of surface displacements of horizontally layered half-space. The latter shows in the half-space present types of waves. It is shown that surface waves are expressed through residuums in poles of the integrand and the volume waves are expressed as integrals along corresponding branch cuts. The singularity which always appears in the basic singular solution in elastodynamics is in this case exactly excluded. In the second part of the paper the behaviour of Stonely waves is investigated in greater detail. It is shown that in the case of layers of finite thickness their appearance and velocities depends not onlyon the material characteristics of neighbouring layers but also on their thickness.
Keywords: geomechanics, horizontally layered halfspace, volume waves, surface waves, Green`s function, Stonely waves
Published: 17.05.2018; Views: 394; Downloads: 30
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Automatic S-phase arrival identification for local earthquakes
Izidor Tasič, Franc Runovc, 2009, original scientific article

Abstract: In the case of a strong local earthquake, a quick report about the earthquake’s location is expected. Such reports are usually performed automatically, where the identification of the seismic-phase arrival of the various seismic waves on the seismogram is the most important task. For this purpose, numerous detecting methods for the first P-wave arrival identification and determination are used. But in some cases, where the number of seismic stations in a local seismic network is very small, an automatic reading of the S-wave arrival is required. An algorithm for the automatic picking of the S wave arrival from three-component seismic data has been developed. Three parameters of the signal are calculated from these data and the S phase arrival is declared when the product of the three parameters increases above a reference level. Such a so-called S-phase picker is used to automatically analyze the data from local earthquakes in Slovenia's seismic network.
Keywords: seismic waves, P and S waves, analysis of seismogram data, automatic picking of the S-wave arrival, seismic station, seismic network
Published: 06.06.2018; Views: 229; Downloads: 26
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Yielding in the isotropic compression of Porto silty sand
Miguel Ferreira Amaral, Sara Rios, António Viana da Fonseca, 2012, original scientific article

Abstract: The yielding locus of a well-graded silty sand was analysed by means of isotropic compression tests and scanning electron microscopy (SEM). The tests were performed with precise instrumentation, for internal and external strain measurements, and shear-wave velocity measurements by means of bender elements. Finally, aiming at an accurate evaluation of the yield stress, four different methods were applied – two quite well know and the other two being innovative – leading to interesting conclusions.
Keywords: silty sand, yield point, isotropic compression, high pressure, seismic waves
Published: 13.06.2018; Views: 161; Downloads: 38
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The Revelation of Virginia Woolf`s Existentialist Aesthetics in the novels To the Lighthouse and The Waves
Maša Sitar, 2018, master's thesis

Abstract: My thesis is that Virginia Woolf subverts the conventional notion of time and in refusing to accept the chronological sequence of time, adopts Henri Bergson's time philosophy. The common ground between these two authors is analysed through their interest in human consciousness, their epistemological interest in the interaction between memory and perception, their adoption of a specific world-view and the importance of imagery in strengthening thematic content. Woolf’s treatment of philosophical concepts of time, memory and intuition indicates that she is predominately influenced by Bergson. Though not conclusive, the analysis may contribute to our understanding of Woolf’s fiction and illuminate certain aspects of Woolf's work. Using Woolf's novels To the Lighthouse and The Waves as primary texts to elucidate the human experience of time, provides sufficient evidence to prove that Woolf’s system of ideas relies on Bergsonian time philosophy; in particular, the research aims to prove that Woolf fully adhered to his conceptualization of dualist temporality and built her fiction upon Bergsonian dualisms. In this context, we unravel the importance of unity, continuity, epiphany and intuition. These concepts are used to explore the unified experience of time and hold the key to temporal illumination, for in illuminating transience, Woolf also illuminates the manner of transcending it. Thus, she creates a viewpoint that discloses continuity and unfolds in unity. By combining apparently irreconcilable dualisms, she reveals the Bergsonian idea of the multiplicity of conscious states and surpasses the absurdity of life; in other words, this philosophy provides Woolf with a key to answering the existential question of the meaning of life.
Keywords: Virginia Woolf, Henri Bergson, existentialism, modernism, To the Lighthouse, The Waves, dualisms, time, duration, multiplicity, consciousness, unity, continuity, epiphany, and intuition.
Published: 08.01.2019; Views: 230; Downloads: 55
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