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Gao, Heng, Jörn W. F. Venderbos, Youngkuk Kim i Andrew M. Rappe. "Topological Semimetals from First Principles". Annual Review of Materials Research 49, nr 1 (lipiec 2019): 153–83. http://dx.doi.org/10.1146/annurev-matsci-070218-010049.
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We review recent theoretical progress in the understanding and prediction of novel topological semimetals. Topological semimetals define a class of gapless electronic phases exhibiting topologically stable crossings of energy bands. Different types of topological semimetals can be distinguished on the basis of the degeneracy of the band crossings, their codimension (e.g., point or line nodes), and the crystal space group symmetries on which the protection of stable band crossings relies. The dispersion near the band crossing is a further discriminating characteristic. These properties give rise to a wide range of distinct semimetal phases such as Dirac or Weyl semimetals, point or line node semimetals, and type I or type II semimetals. In this review we give a general description of various families of topological semimetals, with an emphasis on proposed material realizations from first-principles calculations. The conceptual framework for studying topological gapless electronic phases is reviewed, with a particular focus on the symmetry requirements of energy band crossings, and the relation between the different families of topological semimetals is elucidated. In addition to the paradigmatic Dirac and Weyl semimetals, we pay particular attention to more recent examples of topological semimetals, which include nodal line semimetals, multifold fermion semimetals, and triple-point semimetals. Less emphasis is placed on their surface state properties, their responses to external probes, and recent experimental developments.
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Margańska, Magdalena, Marek Szopa i Eldot zbieta Zipper. "Symmetric and asymmetric dispersion relation in graphene". Journal of Physics: Conference Series 30 (28.02.2006): 302–6. http://dx.doi.org/10.1088/1742-6596/30/1/036.
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Engström, C., i M. Wang. "Complex dispersion relation calculations with the symmetric interior penalty method". International Journal for Numerical Methods in Engineering 84, nr 7 (25.10.2010): 849–63. http://dx.doi.org/10.1002/nme.2926.
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Namouni, F. "Inclination pathways of planet-crossing asteroids". Monthly Notices of the Royal Astronomical Society 510, nr 1 (26.11.2021): 276–91. http://dx.doi.org/10.1093/mnras/stab3405.
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ABSTRACT Long-term statistical simulations of the past evolution of high-inclination Centaurs showed that their orbits tend to be polar with respect to the Solar system’s invariable plane over a large semimajor axis range in trans-neptunian space. Here, we lay the analytical foundation of the study of the inclination pathways of planet-crossing asteroids that explains these findings. We show that the Tisserand relation partitions the inclination–semimajor axis parameter space of the three-body problem into distinct regions depending on the asteroid’s Tisserand parameter T or equivalently its orbital inclination I∞ far from the planet. The Tisserand relation shows that asteroids with I∞ > 110° (T < −1) cannot be injected inside the planet’s orbit. Injection on to retrograde orbits and high-inclination prograde orbits occurs inside the inclination corridor 45° ≤ I∞ ≤ 110° (−1 ≤ T ≤ 2). Inclination dispersion across the inclination pathway for moderate and high inclinations is explained by the secular perturbations from the planet and is smallest for polar orbits. When a planet-crossing asteroid temporarily leaves the inclination pathway, its long-term evolution still depends on its Tisserand parameter as evidenced by its eccentricity dispersion. Simulations of asteroid orbits using the equations of motion with Neptune as the perturbing planet confirm these results for moderate to high inclinations, forward and backward in time because the Tisserand relation is time-independent. The Tisserand inclination pathways will provide important constraints on comet delivery from the outer Solar system as well as on the possible presence of unknown planets in trans-neptunian space.
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Froes, D., M. Arana, J. P. Sinnecker i L. C. Sampaio. "Magnetoelastic modes in Néel domain walls". Journal of Applied Physics 132, nr 22 (14.12.2022): 223908. http://dx.doi.org/10.1063/5.0128775.
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Spin wave propagation over long distances in confined ferromagnetic strip lines exhibiting magnetoelasticity opens up promising perspectives for device applications. Domain walls as natural spin wave channels increase the spin wave propagation distance. We calculate the magnetic and elastic modes through micromagnetic simulations and the dispersion relation of strip lines containing a Néel wall. We show that at the crossing points in the dispersion relation, two behaviors are observed: an anticrossing gap when a strong coupling is present or a gapless point when the magnetoelastic feedback cycle is not fulfilled. For the Néel wall-confined magnetic mode, the magnetic and elastic waves oscillate independently forming a gapless crossing point. For the domain modes, both behaviors are found. We discuss the gap existence based on the symmetry of the eigenmodes.
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Babović, V. M., B. A. Aničin i D. M. Davidović. "The Square Root Approximation to the Dispersion Relation of the Axially-symmetric Electron Wave on a Cylindrical Plasma". Zeitschrift für Naturforschung A 52, nr 10 (1.10.1997): 709–12. http://dx.doi.org/10.1515/zna-1997-1004.
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Abstract This paper suggests the use of a simple square root approximation to the dispersion relation of axially-symmetric electron surface waves on cylindrical plasmas. The point is not merely to substitute the exact expression for the dispersion relation which involves a number of Bessel functions with a more tractable analytical approximant, but to cast the dispersion relation in a form useful in the comparison with other waves, such as water surface gravity waves and the associated tide-rip effect. The square root form of the dispersion relation is also of help in the analysis of surfactron plasmas, as it directly predicts a linear roll-off of electron density in the discharge.
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KOLLAR, MARCUS. "CONSTRUCTION OF A DISPERSION RELATION FROM AN ARBITRARY DENSITY OF STATES". International Journal of Modern Physics B 16, nr 23 (10.09.2002): 3491–501. http://dx.doi.org/10.1142/s0217979202011937.
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The dispersion relations of energy bands in solids are characterized by their density of states, but a given density of states may originate from various band structures. We show how a spherically symmetric dispersion can be constructed for any one-band density of states. This method is applied to one-, two- and three-dimensional systems. It also serves to establish that any one-band spectrum with finite bandwidth can be obtained from a properly scaled dispersion relation in the limit of infinite dimensions.
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Adachi, Yukio, i Chiaki Hirose. "A Study of the Crossing Angle in Condensed-Phase CARS". Applied Spectroscopy 43, nr 1 (styczeń 1989): 61–65. http://dx.doi.org/10.1366/0003702894201950.
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A novel method of tuning the crossing angle, that is, the phase-matching condition, in condensed-phase CARS measurements has been presented. The method enables us to tune the phase-matching condition by simply tilting the sample cell with no need for adjusting the crossing angle of excitation laser beams over the range of about 600 cm−1.To this end, a relation between the crossing angle and the frequency difference between the two excitation lasers, which is associated with the Raman shift, has been derived in the normal dispersion region and has been experimentally examined.
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Chapman, C. J., i S. V. Sorokin. "The finite-product method in the theory of waves and stability". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, nr 2114 (21.10.2009): 471–91. http://dx.doi.org/10.1098/rspa.2009.0255.
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This paper presents a method of analysing the dispersion relation and field shape of any type of wave field for which the dispersion relation is transcendental. The method involves replacing each transcendental term in the dispersion relation by a finite-product polynomial. The finite products chosen must be consistent with the low-frequency, low-wavenumber limit; but the method is nevertheless accurate up to high frequencies and high wavenumbers. Full details of the method are presented for a non-trivial example, that of anti-symmetric elastic waves in a layer; the method gives a sequence of polynomial approximations to the dispersion relation of extraordinary accuracy over an enormous range of frequencies and wavenumbers. It is proved that the method is accurate because certain gamma-function expressions, which occur as ratios of transcendental terms to finite products, largely cancel out, nullifying Runge’s phenomenon. The polynomial approximations, which are unrelated to Taylor series, introduce no spurious branches into the dispersion relation, and are ideal for numerical computation. The method is potentially useful for a very wide range of problems in wave theory and stability theory.
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Chapman, C. J., i S. V. Sorokin. "The deferred limit method for long waves in a curved waveguide". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, nr 2200 (kwiecień 2017): 20160900. http://dx.doi.org/10.1098/rspa.2016.0900.
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This paper presents a technique, based on a deferred approach to a limit, for analysing the dispersion relation for propagation of long waves in a curved waveguide. The technique involves the concept of an analytically satisfactory pair of Bessel functions, which is different from the concept of a numerically satisfactory pair, and simplifies the dispersion relations for curved waveguide problems. Details are presented for long elastic waves in a curved layer, for which symmetric and antisymmetric waves are strongly coupled. The technique gives high-order corrections to a widely used approximate dispersion relation based a kinematic hypothesis, and determines rigorously which of its coefficients are exact.
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Sajadian, Sedighe, Sohrab Rahvar i Fatemeh Kazemian. "Mass–Velocity Dispersion Relation by Using the Gaia Data and Its Effect on Interpreting Short-duration and Degenerate Microlensing Events". Astronomical Journal 164, nr 3 (24.08.2022): 112. http://dx.doi.org/10.3847/1538-3881/ac82e9.
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Abstract Gravitational microlensing, the lensing of stars in the Milky Way with other stars, has been used for exploring compact dark matter objects, exoplanets, and black holes. The duration of microlensing events, the so-called Einstein crossing time, is a function of distance, mass, and velocities of lens objects. Lenses with different ages and masses might have various characteristic velocities inside the Galaxy and this might lead to our misinterpretation of microlensing events. In this work, we use the Gaia archived data to find a relation between the velocity dispersion and mass, and the age of stars. This mass–velocity dispersion relation confirms the known age–velocity relation for early-type and massive stars, and additionally reveals a dependence of stellar velocity dispersion on the mass for low-mass and late-type stars at a 2σ–3σ level. By considering this correlation, we simulate short-duration microlensing events due to brown dwarfs. From this simulation, we conclude that lens masses are underestimated by ∼2.5%–5.5% while modeling short-duration and degenerate microlensing events with the Bayesian analysis.
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Meshcheryakov, V. A. "Dynamic Form of Static Dispersion Relations and Projective Spaces". International Journal of Modern Physics A 12, nr 01 (10.01.1997): 249–54. http://dx.doi.org/10.1142/s0217751x97000360.
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The S-matrix in the static limit of a dispersion relation has a finite order N and is a matrix of meromorfic functions of energy ω in the plane with cuts (-∞, -1],[+1, = ∞). In the elastic case it reduces to N functions Si(ω) conncted by the crossing symmetry matrix A. The problem of analytical continuation of Si(ω) from the physical sheet to unphysical ones can be treated as a nonlinear system of difference equations. It is shown that a global analysis of this system can be carried out effectively in projective spaces PN and PN+1. The connection between spasec PN and PN+1 is discussed.
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Castanié, A., D. Felbacq i B. Guizal. "Surface Plasmon - Guided Mode strong coupling". Advanced Electromagnetics 1, nr 2 (9.10.2012): 85. http://dx.doi.org/10.7716/aem.v1i2.87.
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It is shown that it is possible to realize strong coupling between a surface plasmon and a guided mode in a layered structure. The dispersion relation of such a structure is obtained through the S-matrix algorithm combined with the Cauchy integral technique that allows for rigorous computations of complex poles. The strong coupling is demonstrated by the presence of an anticrossing in the dispersion diagram and simultaneously by the presence of a crossing in the loss diagram. The temporal characteristics of the different modes and the decay of the losses in the propagation of the hybridized surface plasmons are studied.
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Pudjaprasetya, S. R., I. Magdalena i S. S. Tjandra. "A Nonhydrostatic Two-Layer Staggered Scheme for Transient Waves due to Anti-Symmetric Seabed Thrust". Journal of Earthquake and Tsunami 11, nr 01 (marzec 2017): 1740002. http://dx.doi.org/10.1142/s1793431117400024.
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The development of transient waves generated by bottom motion is studied numerically in this work. A nonhydrostatic numerical scheme, based on solving the two-dimensional Euler equations using two-layer approximation for the vertical direction, is implemented. The dispersion relation of this scheme is shown to agree with the analytical dispersion relation over a wide range of [Formula: see text], where [Formula: see text] denotes the wave number and [Formula: see text] the characteristic water depth. To ensure that a good balance between nonlinearity and dispersion is accommodated by the scheme, the propagation of a solitary wave (undisturbed in shape) was simulated. Our next focus was on the simulation of transient waves generated by bottom motion. After conducting a benchmark test against Hammack’s experimental results for downward bottom motion, an anti-symmetric bottom thrust was considered. The resulting transient waves developed different behavior depending on the water depth. Finally, to mimic the December 2004 tsunami, a seabed motion was generated over Aceh bathymetry. This simulation showed that a package of wave trains developed and propagated towards the Aceh coast, and exhibited inter alia the feature of shoreline withdrawal often observed.
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Pu, Jin, Kai Lin, Xiao-Tao Zu i Shu-Zheng Yang. "Modified Fermions Tunneling Radiation from Nonstationary, Axially Symmetric Kerr Black Hole". Advances in High Energy Physics 2019 (22.07.2019): 1–7. http://dx.doi.org/10.1155/2019/5864042.
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In this paper, by applying the deformed dispersion relation in quantum gravity theory, we study the correction of fermions’ tunneling radiation from nonstationary symmetric black holes. Firstly, the motion equation of fermions is modified in the gravitational space-time. Based on the motion equation, the modified Hamilton-Jacobi equation has been obtained by a semiclassical approximation method. Then, the tunneling behavior of fermions at the event horizon of nonstationary symmetric Kerr black hole is investigated. Finally, the results show that, in the nonstationary symmetric background, the correction of Hawking temperature and the tunneling rate are closely related to the angular parameters of the horizon of the black hole background.
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Liu, Tianshi, i Haiming Zhang. "Asymptotic analysis for dispersion relations and travel times in noise cross-correlations: spherically symmetric case". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, nr 2218 (październik 2018): 20180382. http://dx.doi.org/10.1098/rspa.2018.0382.
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The cross-correlations of ambient noise or earthquake codas are massively used in seismic tomography to measure the dispersion curves of surface waves and the travel times of body waves. Such measurements are based on the assumption that these kinematic parameters in the cross-correlations of noise coincide with those in Green's functions. However, the relation between the cross-correlations of noise and Green's functions deserves to be studied more precisely. In this paper, we use the asymptotic analysis to study the dispersion relations of surface waves and the travel times of body waves, and come to the conclusion that for the spherically symmetric Earth model, when the distribution of noise sources is laterally uniform, the dispersion relations of surface waves and the travel times of SH body-wave phases in noise correlations should be exactly the same as those in Green's functions.
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Zhang, Xuewei, Shaobin Liu, Kun Liao i Jian Lou. "Surface plasmonic waveguide and ultra-wideband bandpass filter using double-layered glide symmetric corrugated lines". Journal of Physics D: Applied Physics 55, nr 27 (19.04.2022): 275104. http://dx.doi.org/10.1088/1361-6463/ac63ff.
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Abstract In this paper, an ultra-wideband high-efficiency bandpass filter based on a surface plasmonic waveguide (SPW) is proposed. The novel SPW consists of double-sided glide symmetric periodic corrugated metal. The dispersion characteristics of the double-layered glide symmetric SPW are analyzed. By using glide symmetry technology, the dispersion curve for the two lowest-order modes of the proposed SPW is a degeneracy at the Brillouin zone boundary, resulting in a higher propagation constant than the traditional symmetric structure with the same geometry. The dispersion relation of the SPW when glide symmetric conditions are broken is also investigated. Based on the proposed double-layered glide symmetric SPW, we design a bandpass filter working in an ultrawide range of frequencies. To realize the high-efficient transmission of the bandpass filter, the matching structure composed of double-layer grooves with gradient variation is designed for the effective mode conversion of quasi-transverse electromagnetic waves and spoof surface plasmonic polariton. The upper cutoff frequency of the passband can be tuned by adjusting the geometric parameters of the corrugated metal unit, and the lower cutoff frequency can be controlled by modifying the coupling distance with the bottom layer. A prototype of an ultra-wideband bandpass filter has been manufactured and measured, showing a reasonable agreement with simulations. The proposed novel UWB bandpass filter with glide symmetry can be widely used in microwave and millimeter wave related communication systems, and may play an important role in the fabrication of advanced plasma functional devices and circuits.
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Li, Xiao‐Ping, Wolfgang Schott i Horst Rüter. "Frequency‐dependent Q‐estimation of Love‐type channel waves and the application of Q‐correction to seismograms". GEOPHYSICS 60, nr 6 (listopad 1995): 1773–89. http://dx.doi.org/10.1190/1.1443911.
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We present the absorption dispersion relation of Love‐type channel waves for a simple, symmetric, homogenous, three‐layered, linear elastic model assuming that the quality factors of coal [Formula: see text] and country rock [Formula: see text] are constant. We introduce complex propagation functions into the known dispersion relation describing most of the properties of the Love‐ type channel waves. The complex dispersion relation is expanded into power series of [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text] factor of the Love‐type channel wave). The real part of the ensuing dispersion relation gives the usual dispersion relation. The imaginary part yields the frequency relation between the quality factor of Love‐type channel waves and the constant quality factors of coal and rock. In this case, [Formula: see text] depends on the frequency because the phase velocity is a function of frequency. Therefore, the attenuation coefficient is a nonlinear function of frequency. The analysis of the analytical result shows that at high frequencies the Love‐type channel wave energy is completely propagating inside the coal seam, and hence its propagation is determined by the physical properties of the coal alone. As the frequency approaches zero, the Love‐type channel wave energy is completely propagating in the rock, since the thickness of the coal is small compared to the wavelength of the channel wave, and hence the channel wave does not “see” the coal seam. The spectral ratio method is used to estimate the frequency‐dependent quality factor [Formula: see text] of Love‐type channel waves. This technique is demonstrated by applying it first to synthetic data and then to data of a well‐designed transmission survey. Finally, we use the estimated [Formula: see text] to derive an inverse Q‐operator and apply it for Q‐correction to both data sets.
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SROCZYNSKI, ZBIGNIEW. "AN INVESTIGATION INTO THE FERMILAB APPROACH TO HEAVY QUARKS ON THE LATTICE". International Journal of Modern Physics A 16, supp01c (wrzesień 2001): 1231–33. http://dx.doi.org/10.1142/s0217751x01009399.
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We use a space-time asymmetric O(a) improved fermion action and fix the asymmetry non-perturbatively to restore the relativistic dispersion relation. We compute spectra and matrix elements of quarkonia and heavy-light mesons and compare with results obtained using a symmetric action with the Fermilab interpretation i.e. that the physics of heavy lattice quarks depends solely on their kinetic mass. We provide additional evidence to support this.
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Yimer, Desalegn Tefera, Pooran Singh i Chernet Amente Geffe. "The effect of anisotropic field on magnon dispersion of antiferromagnetic metal fluoride materials". AIP Advances 13, nr 4 (1.04.2023): 045117. http://dx.doi.org/10.1063/5.0147034.
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This article investigates the dynamics of spin waves in two sublattice antiferromagnetic (AFM) system spins’ interaction and magnon dispersion relation. The analysis is done starting with a standard model that includes a uniaxial magnetic anisotropy field. Quantum field theory is employed in formulating the problem, and double-time temperature-dependent Green function technique is used to obtain magnon dispersion, whereby random phase approximation is considered to decouple and diagonalize the higher order terms. At low temperatures and long wavelength approximation, dispersion of uniaxial symmetric AFM crystal lattice of metallic fluoride materials, such as MnF2, FeF2, and RbMnF3, is analyzed for illustration. Our findings indicate that as the anisotropic field increases, the magnon dispersion vs wave vector k gradually varies, attempts linearity from being curved, and attains a sinusoidal structure when extended further in the first Brillouin zone. Perhaps, these results are useful to understand the feature of magnon dispersion of stable similar AFM materials for practical application.
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Horikawa, Yo. "Exponential dispersion relation and its effects on unstable propagating pulses in unidirectionally coupled symmetric bistable elements". Communications in Nonlinear Science and Numerical Simulation 17, nr 7 (lipiec 2012): 2791–803. http://dx.doi.org/10.1016/j.cnsns.2011.11.002.
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Colquitt, D. J., M. J. Nieves, I. S. Jones, A. B. Movchan i N. V. Movchan. "Localization for a line defect in an infinite square lattice". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, nr 2150 (8.02.2013): 20120579. http://dx.doi.org/10.1098/rspa.2012.0579.
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Localized defect modes generated by a finite line defect composed of several masses, embedded in an infinite square cell lattice, are analysed using the linear superposition of Green's function for a single mass defect. Several representations of the lattice Green's function are presented and discussed. The problem is reduced to an eigenvalue system and the properties of the corresponding matrix are examined in detail to yield information regarding the number of symmetric and skew-symmetric modes. Asymptotic expansions in the far field, associated with long wavelength homogenization, are presented. Asymptotic expressions for Green's function in the vicinity of the band edge are also discussed. Several examples are presented where eigenfrequencies linked to this system and the corresponding eigenmodes are computed for various defects and compared with the asymptotic expansions. The case of an infinite defect is also considered and an explicit dispersion relation is obtained. For the case when the number of masses within the line defect is large, it is shown that the range of the eigenfrequencies can be predicted using the dispersion diagram for the infinite chain.
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GRUNEBERG, J., i H. KEITER. "SELF-CONSISTENT PERTURBATION EXPANSIONS FOR SINGLE-IMPURITY-EXCHANGE-MODELS". International Journal of Modern Physics B 09, nr 26 (30.11.1995): 3429–87. http://dx.doi.org/10.1142/s0217979295001361.
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Combining self-consistent perturbation theory with conventional renormalization group equations, a new systematic approach to Kondo-type models is developed, which yields analytical expressions for universal quantities like pseudofermion exponents and large effective couplings, usually out of reach from perturbative calculations. The new approach is related to the parquet-treatment of the x-ray-edge-singularity by Noziéres and coworkers in the late sixties and makes no use of a linearization of the band-electron-dispersion-relation, which is crucial for the Bethe Ansatz, conformal field theory, or numerical renormalization group treatment of the models. In addition it covers 1/N2-corrections to the well-known Non-Crossing-Approximation.
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Ass'ad, A. I., i H. S. Ashour. "TE Magnetostatic Surface Waves in Symmetric Dielectric Negative Permittivity Material Waveguide". Advances in Condensed Matter Physics 2009 (2009): 1–5. http://dx.doi.org/10.1155/2009/867638.
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Nonlinear magnetostatic surface wave in a slab waveguide structure has been investigated. The design consisted of dielectric film between two thick nonlinear nonmagnetic negative permittivity material (NPM) layers. A dispersion relation for TE nonlinear Magnetostatic surface waves (NMSSWs) has been derived into the proposed structure and has been numerically investigated. Effective refractive index decreases with thickness and frequency increase have been found. Effective refractive index decrease with optical nonlinearity increase and switching to negative values of effective refractive index at a certain value of optical nonlinearity have been found. This meant that the structure behaved like a left-handed material over certain range. We found that the power flow was changing by changing the operating frequency, the dielectric film thickness, and the optical nonlinearity. Also, the effective refractive index and power flow attained constant values over certain values of dielectric constant values.
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Han, Qiyu, i Ru-Shan Wu. "A one-way dual-domain propagator for scalar qP-waves in VTI media". GEOPHYSICS 70, nr 2 (marzec 2005): D9—D17. http://dx.doi.org/10.1190/1.1884826.
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In this paper, we present an anisotropic one-way propagator for modeling and imaging quasi-P (qP) waves in transversely isotropic media with a vertically symmetric axis (VTI media). We derive the dispersion relation for a scalar qP-wave using elastic wave equations for anisotropic media. By applying a rational approximation to the dispersion relation, we obtain a one-way, dual-domain, scalar qP-wave propagator for heterogeneous VTI media. The propagator includes a phase-shift term and both phase-screen and large-angle correction terms. The phase-shift term is implemented in the wavenumber domain, while the other terms are implemented in the space domain. Fourier transformations are used to shuttle the wavefield between the two domains. This propagator can be used to propagate qP-wavefields within an isotropic or a VTI medium, with either medium containing lateral heterogeneities. Error analysis of the impulse response and dispersion relations demonstrates that the propagator is accurate and stable and has a wide-angle capability. The application of the propagator to the imaging of qP-wave data with VTI models which contain complex structures and large perturbations of velocity and anisotropy results in excellent image quality. This demonstrates the potential value of the propagator for use in modeling and imaging qP-wavefields within strongly heterogeneous VTI media.
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Radwan, Ahmed E., i Mourad F. Dimian. "Note on magneto-hydrodynamic gravitational stability of a double fluids interface". Canadian Journal of Physics 86, nr 3 (1.03.2008): 477–85. http://dx.doi.org/10.1139/p07-165.
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The magneto–gravitational stability of double-fluid interface is discussed. The pressure in the unperturbed state is not constant because the self-gravitating force is a long-range force. The dispersion relation is derived and discussed. The self-gravitating model is unstable in the symmetric mode m = 0 (m is the transverse wave number), while it is stable in all other states. The effects of the densities, the liquid-fluid radii ratios, and the electromagnetic force on the stability of the present model are identified for all wavelengths.PACS Nos.: 47.35.Tv, 47.65.–d, 04.40.–b
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Lopin, Igor P. "Symmetric wave modes in coronal flux tubes with magnetically twisted layer". Monthly Notices of the Royal Astronomical Society 505, nr 2 (12.05.2021): 1878–90. http://dx.doi.org/10.1093/mnras/stab1355.
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ABSTRACT The properties of axisymmetric magnetohydrodynamic wave modes are studied for the model of coronal magnetic tube, consisting of a central cord with homogeneous axial magnetic field, surrounded by an annulus with twisted magnetic field. This model mimics the coronal loops with radially localized magnetic twist. The derived dispersion relation is solved numerically. A number of limiting cases are examined analytically. The two families of axisymmetric modes are found to exist in the model. The first one includes an infinite number of fast-sausage modes (FSMs), modified by the twist and the second one is a set of modes with frequencies, lying in a narrow band, closed to Alfvén frequency of a twisted layer ωA0. The fundamental FSM (the mode of the lowest radial order) exists as a trapped mode for the entire range of axial wavenumbers. Its phase speed is always below the Alfvén speed of a magnetically twisted layer. This mode has a weak dispersion in the range of long and intermediate wavelengths. The higher radial order FSMs were found to be less sensitive to the presence of the magnetic twist. Both the fundamental FSM in the case of a weak magnetic twist and a set of symmetric modes for arbitrary twist have very similar frequencies, which are nearly equal to ωA0. This property implies that aforementioned wave modes behave like Alfvén torsional modes in the twisted annulus and like the radial modes in the untwisted core and environment, moreover they are strongly coupled. The main results of the study are discussed in the framework of their applications to coronal seismology.
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Lee, Jeong Ki, Young H. Kim i Ho Chul Kim. "Group Velocity of Lamb Wave S0 Mode in Laminated Unidirectional CFRP Plates". Key Engineering Materials 297-300 (listopad 2005): 2213–18. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2213.
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The elastic waves in the isotropic plate are dispersive waves with the characteristics of Lamb wave, however, S0 symmetric mode is less dispersive in the frequency region less than the first cut-off frequency. In the anisotropic plates such as CFRP plates, the propagation velocities vary with the directions as well as the dispersion of the Lamb wave, and the phase velocity direction does not accord with the group velocity direction. The phase velocity direction is equivalent the wave vector direction, while the group velocity direction is equivalent the energy flow direction. In this work, the group velocity dispersion curves were obtained by the dispersion relation of the Lamb wave in unidirectional CFRP plate with an orthotropic structure. The group velocities of the S0 symmetric mode in the frequency region less than the first cut-off frequency were corrected by applying the slowness surface. The propagation velocities of Lamb wave were decided by measuring the arrival time of the Lamb wave signals received with the two pinducers varying the propagating direction in the laminated unidirectional CFRP plates of 8, 16 and 24 plies having a volume fraction of 67%. The measured velocities are better agreement with corrected group velocity curve, except near the fiber direction at the cusp region. When the propagating direction is not accorded with the principal axis, the direction of the group velocities inclines toward the fiber direction in the unidirectional CFRP plates, suggesting that the energy propagates preferentially toward fiber direction.
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Evseev, Dmitry A., Svetlana V. Eliseeva, Dmitry I. Sementsov i Anatolij M. Shutyi. "A Surface Plasmon–Polariton in a Symmetric Dielectric Waveguide with Active Graphene Plates". Photonics 9, nr 8 (19.08.2022): 587. http://dx.doi.org/10.3390/photonics9080587.
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A theoretical study of the plasmon modes’ characteristics is carried out in a structure consisting of two active graphene layers separated by a dielectric barrier layer. A general dispersion relation is obtained, the numerical analysis of which reveals the possibility of controlling the parameters of amplified surface modes in the region of graphene negative conductivity. In particular, their dispersion is controlled by changing the chemical potential of the graphene layers. For antisymmetric plasmons, their dependence on the barrier layer parameters was revealed. An increase in the chemical potential makes it possible to expand the region of existence of the amplified plasmons, which is accompanied not only by an increase in the amplification coefficient but also by a shift to the region of higher frequencies of the amplified modes. For the first time, modal bistability was also demonstrated in a limited frequency range for antisymmetric plasmons, due to the appearance of additional modes, in which the phase velocity decreases sharply near the cutoff, and the group velocities of the modes entering the bistability turn out to be opposite in sign. The frequency dependences of the real and imaginary parts of the plasmon propagation constant are analyzed, the distributions of wave fields in the structure are plotted, and the frequency dependence of the depth of the plasmon–polariton is given.
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Jost, Andreas, Michel Bendias, Jan Böttcher, Ewelina Hankiewicz, Christoph Brüne, Hartmut Buhmann, Laurens W. Molenkamp i in. "Electron–hole asymmetry of the topological surface states in strained HgTe". Proceedings of the National Academy of Sciences 114, nr 13 (9.03.2017): 3381–86. http://dx.doi.org/10.1073/pnas.1611663114.
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Topological insulators are a new class of materials with an insulating bulk and topologically protected metallic surface states. Although it is widely assumed that these surface states display a Dirac-type dispersion that is symmetric above and below the Dirac point, this exact equivalence across the Fermi level has yet to be established experimentally. Here, we present a detailed transport study of the 3D topological insulator-strained HgTe that strongly challenges this prevailing viewpoint. First, we establish the existence of exclusively surface-dominated transport via the observation of an ambipolar surface quantum Hall effect and quantum oscillations in the Seebeck and Nernst effect. Second, we show that, whereas the thermopower is diffusion driven for surface electrons, both diffusion and phonon drag contributions are essential for the hole surface carriers. This distinct behavior in the thermoelectric response is explained by a strong deviation from the linear dispersion relation for the surface states, with a much flatter dispersion for holes compared with electrons. These findings show that the metallic surface states in topological insulators can exhibit both strong electron–hole asymmetry and a strong deviation from a linear dispersion but remain topologically protected.
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Liu, Yong-Qiang, Zhongru Ren, Hongcheng Yin, Jinhai Sun i Liangsheng Li. "Dispersion Theory of Surface Plasmon Polaritons on Bilayer Graphene Metasurfaces". Nanomaterials 12, nr 11 (25.05.2022): 1804. http://dx.doi.org/10.3390/nano12111804.
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Surface plasmon polaritons (SPPs) on the graphene metasurfaces (GSPs) are crucial to develop a series of novel functional devices that can merge the well-established plasmonics and novel nanomaterials. Dispersion theory on GSPs is an important aspect, which can provide a basic understanding of propagating waves and further guidance for potential applications based on graphene metamaterials. In this paper, the dispersion theory and its modal characteristics of GSPs on double-layer graphene metasurfaces consisting of the same upper and lower graphene micro-ribbon arrays deposited on the dielectric medium are presented. In order to obtain its dispersion expressions of GSP mode on the structure, an analytical approach is provided by directly solving the Maxwell’s equations in each region and then applying periodical conductivity boundary onto the double interfaces. The obtained dispersion expressions show that GSPs split into two newly symmetric and antisymmetric modes compared to that on the single graphene metasurface. Further, the resultant dispersion relation and its propagating properties as a function of some important physical parameters, such as spacer, ribbon width, and substrate, are treated and investigated in the Terahertz band, signifying great potentials in constructing various novel graphene-based plasmonic devices, such as deeply sub-wavelength waveguides, lenses, sensors, emitters, etc.
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Isakov, Serguei B., i Susanne Viefers. "Model of Statistically Coupled Chiral Fields on the Circle". International Journal of Modern Physics A 12, nr 10 (20.04.1997): 1895–914. http://dx.doi.org/10.1142/s0217751x97001195.
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Starting from a field theoretical description of multicomponent anyons with mutual statistical interactions in the lowest Landau level, we construct a model of interacting chiral fields on the circle, with the energy spectrum characterized by a symmetric matrix gαβ with nonnegative entries. Being represented in a free form, the model provides a field theoretical realization of (ideal) fractional exclusion statistics for particles with linear dispersion, with gαβ as a statistics matrix. We derive the bosonized form of the model and discuss the relation to the effective low-energy description of the edge excitations for Abelian fractional quantum Hall states in multilayer systems.
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Deck-Léger, Zoé-Lise, Xuezhi Zheng i Christophe Caloz. "Electromagnetic Wave Scattering from a Moving Medium with Stationary Interface across the Interluminal Regime". Photonics 8, nr 6 (5.06.2021): 202. http://dx.doi.org/10.3390/photonics8060202.
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This paper extends current knowledge on electromagnetic wave scattering from bounded moving media in several regards. First, it complements the usual dispersion relation of moving media, ω(θk) (θk: phase velocity direction, associated with the wave vector, k), with the equally important impedance relation, η(θS) (θS: group velocity direction, associated with the Poynting vector, S). Second, it explains the interluminal-regime phenomenon of double-downstream wave transmission across a stationary interface between a regular medium and the moving medium, assuming motion perpendicular to the interface, and shows that the related waves are symmetric in terms of the energy refraction angle, while being asymmetric in terms of the phase refraction angle, with one of the waves subject to negative refraction, and shows that the wave impedances of the two transmitted waves are equal. Third, it generalizes the problem to the case where the medium moves obliquely with respect to the interface. Finally, it highlights the connection between this problem and a spacetime modulated medium.
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HUANG, WEN-DENG, SHU-YI WEI i YA-JIE REN. "THE QUASI-CONFINED OPTICAL PHONONS IN WURTZITE SYMMETRY MULTIPLE QUANTUM WELLS". Modern Physics Letters B 20, nr 22 (30.09.2006): 1367–81. http://dx.doi.org/10.1142/s0217984906011384.
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Within the framework of the dielectric-continuum model and Loudon's uniaxial crystal model, the equation of motion for p-polarization field in wurtzite multiplayer symmetry heterostructures are solved for the quasi-confined phonon (QC) modes. The polarization eigenvector, the dispersion relation, and the electron-QC interaction Fröhlich-like Hamiltonian are derived by using the transfer-matrix method. The analytical theory and formulas can be directly applied to the single quantum well (QW) and multiple quantum wells (QWs), and superlattices (SLs). The dispersion relations and the electron-QC coupling strength are investigated for a wurtzite GaN/Al 0.15 Ga 0.85 N single QW. The results show that there are infinite branches of the dispersion curve with definite symmetry with respect to the center of the QW structure. The confinement of the quasi-confined phonons in the QW leads to a quantization of qz,j characterized by an integer m that defines the order of corresponding quasi-confined modes. The QC modes are more dispersive for decreasing m. The QC modes display an interface behavior in the barrier and a confined behavior in the well. When q⊥ is small, the symmetric modes have more contribution to electron-QC interaction than the antisymmetric modes.
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Farrar, J. Thomas. "Observations of the Dispersion Characteristics and Meridional Sea Level Structure of Equatorial Waves in the Pacific Ocean". Journal of Physical Oceanography 38, nr 8 (1.08.2008): 1669–89. http://dx.doi.org/10.1175/2007jpo3890.1.
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Abstract Spectral techniques applied to altimetry data are used to examine the dispersion relation and meridional sea level structure of wavelike variability with periods of about 20 to 200 days in the equatorial Pacific Ocean. Zonal wavenumber–frequency power spectra of sea surface height, when averaged over about 7°S–7°N, exhibit spectral peaks near the theoretical dispersion curves of first baroclinic-mode equatorial Kelvin and Rossby waves. There are distinct, statistically significant ridges of power near the first and second meridional-mode Rossby wave dispersion curves. Sea level variability near the theoretical Kelvin wave and first meridional-mode Rossby wave dispersion curves is dominantly (but not perfectly) symmetric about the equator, while variability near the theoretical second meridional-mode Rossby wave dispersion curve is dominantly antisymmetric. These results are qualitatively consistent with expectations from classical or shear-modified theories of equatorial waves. The meridional structures of these modes resemble the meridional modes of equatorial wave theory, but there are some robust features of the meridional profiles that were not anticipated. The meridional sea level structure in the intraseasonal Kelvin wave band closely resembles the theoretically expected Gaussian profile, but sea level variability coherent with that at the equator is detected as far away as 11.75°S, possibly as a result of the forced nature of these Kelvin waves. Both first and second meridional-mode Rossby waves have larger amplitude in the Northern Hemisphere. The meridional sea level structure of tropical instability waves closely resembles that predicted by Lyman et al. using a model linearized about a realistic equatorial zonal current system.
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Simo, Attila, Flaviu Mihai Frigura-Iliasa, Mihaela Frigura-Iliasa, Petru Andea i Sorin Musuroi. "Service Limits for Metal Oxide Varistors Having Cylindrical Symmetry as Function of the Ambient Temperature". Symmetry 14, nr 7 (30.06.2022): 1351. http://dx.doi.org/10.3390/sym14071351.
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This article presents an original experimental method applied to assess the stability limits of a given Metal Oxide Varistor (MOV), with cylindrical symmetry (cylinder or disk shape), as a direct relation between the ambient temperature and the service rated voltage, in the permanent operational regime. As the crossing current of a certain varistor is heavily influenced by its physical temperature, we must find an empirical relationship between these two parameters for a symmetrical configuration. Each ambient temperature can increase the temperature reference and any higher voltage will also produce an increased current, causing a uncontrolled runaway heating process, in an avalanche model. We tried to eliminate any references to technical dimensions or device values, focusing on material parameters. In the case of a symmetric MOV, we will consider the load coefficient, which is the ratio between the service DC voltage and the nominal DC opening voltage. By using experimental measurements and a simple mathematical model, we will establish the relation between the critical load coefficient and the ambient temperature in the case of symmetrical MOVs. This procedure could be applied to the design of more performant and safe surge arrester devices using existing MOVs, for all voltage levels and symmetrical configurations.
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Wu, Qilong, Meysam Bagheri Tagani, Qiwei Tian, Sahar Izadi Vishkayi, Li Zhang, Long-Jing Yin, Yuan Tian, Lijie Zhang i Zhihui Qin. "Symmetry breaking induced bandgap opening in epitaxial germanene on WSe2". Applied Physics Letters 121, nr 5 (1.08.2022): 051901. http://dx.doi.org/10.1063/5.0103367.
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Germanene has attracted much attention because the material was predicted to host Dirac fermions. However, the synthesis of germanene is still in its infancy; moreover, the predicted tiny bandgap induced by the spin–orbit coupling is far from practical applications for nanoelectronic devices. Herein, quasi-freestanding germanene with linear dispersion relation of the band structure is well grown on a WSe2/Au(100) substrate. Band structure calculations reveal that the interaction of germanene with the substrate destroys the sublattice symmetry. The energy-dependent contribution of σ orbitals responsible for band crossing at the Fermi level around the Γ point induces asymmetric density of states at the Dirac point. Upon annealing in ultra-high vacuum, we observe a bandgap opening in germanene of about ∼0.17 eV, which is attributed to a sublattice symmetry breaking in germanene and the emergence of a net electric field. This work provides an effective method to tune or tailor the electronic properties of germanene, paving the way to germanene-based field-effect applications.
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Keto, Eric, George B. Field i Eric G. Blackman. "A turbulent-entropic instability and the fragmentation of star-forming clouds". Monthly Notices of the Royal Astronomical Society 492, nr 4 (28.01.2020): 5870–77. http://dx.doi.org/10.1093/mnras/staa230.
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ABSTRACT The kinetic energy of supersonic turbulence within interstellar clouds is subject to cooling by dissipation in shocks and subsequent line radiation. The clouds are therefore susceptible to a condensation process controlled by the specific entropy. In a form analogous to the thermodynamic entropy, the entropy for supersonic turbulence is proportional to the log of the product of the mean turbulent velocity and the size scale. We derive a dispersion relation for the growth of entropic instabilities in a spherical self-gravitating cloud and find that there is a critical maximum dissipation time-scale, about equal to the crossing time, that allows for fragmentation and subsequent star formation. However, the time-scale for the loss of turbulent energy may be shorter or longer, for example, with rapid thermal cooling or the injection of mechanical energy. Differences in the time-scale for energy loss in different star-forming regions may result in differences in the outcome, for example, in the initial mass function.
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Shirasaki, Masato, Eiichi Egami, Nobuhiro Okabe i Satoshi Miyazaki. "Stacked phase-space density of galaxies around massive clusters: comparison of dynamical and lensing masses". Monthly Notices of the Royal Astronomical Society 506, nr 3 (12.07.2021): 3385–405. http://dx.doi.org/10.1093/mnras/stab1961.
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ABSTRACT We present a measurement of average histograms of line-of-sight velocities over pairs of galaxies and galaxy clusters. Since the histogram can be measured at different galaxy-cluster separations, this observable is commonly referred to as the stacked phase-space density. We formulate the stacked phase-space density based on a halo-model approach so that the model can be applied to real samples of galaxies and clusters. We examine our model by using an actual sample of massive clusters with known weak-lensing masses and spectroscopic observations of galaxies around the clusters. A likelihood analysis with our model enables us to infer the spherical-symmetric velocity dispersion of observed galaxies in massive clusters. We find the velocity dispersion of galaxies surrounding clusters with their lensing masses of $1.1\times 10^{15}\, h^{-1}\,{\rm M}_{\odot }$ to be $1180^{+83}_{-70}\, \mathrm{km\,s^{-1}}$ at the 68 per cent confidence level. Our constraint confirms that the relation between the galaxy velocity dispersion and the host cluster mass in our sample is consistent with the prediction in dark-matter-only N-body simulations under General Relativity. Assuming that the Poisson equation in clusters can be altered by an effective gravitational constant of Geff, our measurement of the velocity dispersion can place a tight constraint of $0.88 \lt G_\mathrm{eff}/G_\mathrm{N} \lt 1.29\, (68{{\ \rm per\ cent}})$ at length-scales of a few Mpc about 2.5 Giga years ago, where GN is the Newton’s constant.
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Oberti, Chiara, i Renzo L. Ricca. "On torus knots and unknots". Journal of Knot Theory and Its Ramifications 25, nr 06 (maj 2016): 1650036. http://dx.doi.org/10.1142/s021821651650036x.
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A comprehensive study of geometric and topological properties of torus knots and unknots is presented. Torus knots/unknots are particularly symmetric, closed, space curves, that wrap the surface of a mathematical torus a number of times in the longitudinal and meridian direction. By using a standard parametrization, new results on local and global properties are found. In particular, we demonstrate the existence of inflection points for a given critical aspect ratio, determine the location and prescribe the regularization condition to remove the local singularity associated with torsion. Since to first approximation total length grows linearly with the number of coils, its nondimensional counterpart is proportional to the topological crossing number of the knot type. We analyze several global geometric quantities, such as total curvature, writhing number, total torsion, and geometric ‘energies’ given by total squared curvature and torsion, in relation to knot complexity measured by the winding number. We conclude with a brief presentation of research topics, where geometric and topological information on torus knots/unknots finds useful application.
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Ginzburg, Sivan, i Eugene Chiang. "Heavy-metal Jupiters by major mergers: metallicity versus mass for giant planets". Monthly Notices of the Royal Astronomical Society 498, nr 1 (19.08.2020): 680–88. http://dx.doi.org/10.1093/mnras/staa2500.
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ABSTRACT Some Jupiter-mass exoplanets contain ${\sim}100\, {\rm M}_{\hbox{$\oplus $}}$ of metals, well above the ${\sim}10\, {\rm M}_{\hbox{$\oplus $}}$ typically needed in a solid core to trigger giant planet formation by runaway gas accretion. We demonstrate that such ‘heavy-metal Jupiters’ can result from planetary mergers near ∼10 au. Multiple cores accreting gas at runaway rates gravitationally perturb one another on to crossing orbits such that the average merger rate equals the gas accretion rate. Concurrent mergers and gas accretion implies the core mass scales with the total planet mass as Mcore ∝ M1/5 – heavier planets harbour heavier cores, in agreement with the observed relation between total mass and metal mass. While the average gas giant merges about once to double its core, others may merge multiple times, as merger trees grow chaotically. We show that the dispersion of outcomes inherent in mergers can reproduce the large scatter in observed planet metallicities, assuming $3{-}30\, {\rm M}_{\hbox{$\oplus $}}$ pre-runaway cores. Mergers potentially correlate metallicity, eccentricity, and spin.
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Martini, Eduardo, André V. G. Cavalieri i Peter Jordan. "Acoustic modes in jet and wake stability". Journal of Fluid Mechanics 867 (28.03.2019): 804–34. http://dx.doi.org/10.1017/jfm.2019.148.
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Motivated by recent studies that have revealed the existence of trapped acoustic waves in subsonic jets (Towne et al., J. Fluid Mech., vol. 825, 2017, pp. 1113–1152), we undertake a more general exploration of the physics associated with acoustic modes in jets and wakes, using a double vortex-sheet model. These acoustic modes are associated with eigenvalues of the vortex-sheet dispersion relation; they are discrete modes, guided by the vortex sheet; they may be either propagative or evanescent; and under certain conditions they behave in the manner of acoustic-duct modes. By analysing these modes we show how jets and wakes may both behave as waveguides under certain conditions, emulating ducts with soft or hard walls, with the vortex-sheet impedance providing effective ‘wall’ conditions. We consider, in particular, the role that upstream-travelling acoustic modes play in the dispersion-relation saddle points that underpin the onset of absolute instability. The analysis illustrates how departure from duct-like behaviour is a necessary condition for absolute instability, and this provides a new perspective on the stabilising and destabilising effects of reverse flow, temperature ratio and compressibility; it also clarifies the differing symmetries of jet (symmetric) and wake (antisymmetric) instabilities. An energy balance, based on the vortex-sheet impedance, is used to determine stability conditions for the acoustic modes: these may become unstable in supersonic flow due to an energy influx through the shear layers. Finally, we construct the impulse response of flows with zero and finite shear-layer thickness. This allows us to show how the long-time wavepacket behaviour is indeed determined by interaction between Kelvin–Helmholtz and acoustic modes.
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Vexler, M. I., A. Kuligk i B. Meinerzhagen. "Simulation of hole and electron tunnel currents in MIS devices adopting the symmetric Franz-type dispersion relation for the charged carriers in thin insulators". Solid-State Electronics 53, nr 3 (marzec 2009): 364–70. http://dx.doi.org/10.1016/j.sse.2009.01.014.
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Srivastava, Ankit, i Sia Nemat-Nasser. "Overall dynamic properties of three-dimensional periodic elastic composites". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, nr 2137 (21.09.2011): 269–87. http://dx.doi.org/10.1098/rspa.2011.0440.
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This article presents a method for the homogenization of three-dimensional periodic elastic composites. It allows for the evaluation of the averaged overall frequency-dependent dynamic material constitutive tensors relating the averaged dynamic field variable tensors of velocity, strain, stress and linear momentum. Although the form of the dynamic constitutive relation for three-dimensional elastodynamic wave propagation has been known, this is the first time that explicit calculations of the effective parameters (for three dimensions) are presented. We show that for three-dimensional periodic composites, the overall compliance (stiffness) tensor, as produced directly by our formulation, is Hermitian, regardless of whether the corresponding unit cell is geometrically or materially symmetric. Overall, mass density is shown to be a tensor and, like the overall compliance tensor, always Hermitian. The average strain and linear momentum tensors are, however, coupled, and the coupling tensors are shown to be each others' Hermitian transpose. Finally, we present a numerical example of a three-dimensional periodic composite composed of elastic cubes periodically distributed in an elastic matrix. The presented results corroborate the predictions of the theoretical treatment illustrating the frequency dependence of the constitutive parameters. We also show that the effective properties calculated in this paper satisfy the dispersion relation of the composite.
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Bužavaitė-Vertelienė, Ernesta, Vilius Vertelis i Zigmas Balevičius. "The experimental evidence of a strong coupling regime in the hybrid Tamm plasmon-surface plasmon polariton mode". Nanophotonics 10, nr 5 (24.02.2021): 1565–71. http://dx.doi.org/10.1515/nanoph-2020-0660.
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Abstract Total internal reflection ellipsometry was employed for the excitation and study of hybrid Tamm plasmon-surface plasmon polaritons mode. Simple optical methodology using optical filters to cut the part of incident light spectra was proposed. Using optical filters measured energy spectra was divided into two parts where in each range only one branch of the hybrid TPP-SPP plasmonic mode was excited directly by the incident light. Present experimental studies have shown, that if the investigated system is in strong coupling, this is always enough to excite only one component of the hybrid excitation. Thus, its dispersion relation will be the same as when the excitation is done with a whole spectrum. In the case of the TPP-SPP hybrid mode where strong coupling is realized only in p-polarized light, the fitting results have shown that the strongest coupling was at the point where the noninteracting TPP and SPP curves should be crossing. The obtained Rabi splitting for the hybrid TPP and SPP modes in BK7 prism/1D PC TiO2/SiO2 (60 nm/110 nm)/TiO2 (30 nm)/Au (40 nm) multilayered structure was about 105 meV.
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Drdlová, Martina, Michal Frank, Jaroslav Buchar i Radek Řídký. "Evaluation of Mechanical Properties of Glass/Epoxy Syntactic Foams Containing Carbon Nanotubes and Nanosilica". Advanced Materials Research 1124 (wrzesień 2015): 51–56. http://dx.doi.org/10.4028/www.scientific.net/amr.1124.51.
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The effect of multi-wall carbon nanotubes and nanoSiO2content on physico-mechanical properties of glass microspheres-epoxy resin composite, designed for blast energy absorbing applications, was evaluated experimentally. Specific porous lightweight foam with high volume fraction of microspheres (70 vol.%) was prepared and modified by 1 to 5 vol.% of multi-wall carbon nanotubes and nanosilica (nanoSiO2). Two types of microsperes with different wall thickness and strength were used. The quality of dispersion of nanoparticles was evaluated in relation to the mixing procedure using scanning electron microscope observation. The compressive and flexural strength tests were conducted at quasi-static load. The mixtures containing nanosilica exhibited an increasing trend in both flexural and compressive strength with increasing nanoparticle content up to 4 vol.%. The addition of carbon nanotubes also increased flexural strength (again up to 4 vol%, crossing this concentration, the significant drop was observed), whereas the compressive strength was affected at lower level. Nanoparticle modification is more effective in the foams with higher thickness and thus strength. The evaluation of test results showed that the properties of glass/epoxy foams can be tailored by adding nanoscale fillers.
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NITSCHE, J. M., i G. K. BATCHELOR. "Break-up of a falling drop containing dispersed particles". Journal of Fluid Mechanics 340 (10.06.1997): 161–75. http://dx.doi.org/10.1017/s0022112097005223.
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The general purpose of this paper is to investigate some consequences of the randomness of the velocities of interacting rigid particles falling under gravity through viscous fluid at small Reynolds number. Random velocities often imply diffusive transport of the particles, but particle diffusion of the conventional kind exists only when the length characteristic of the diffusion process is small compared with the distance over which the particle concentration is effectively uniform. When this condition is not satisfied, some alternative analytical description of the dispersion process is needed. Here we suppose that a dilute dispersion of sedimenting particles is bounded externally by pure fluid and enquire about the rate at which particles make outward random crossings of the (imaginary) boundary. If the particles are initially distributed with uniform concentration within a spherical boundary, we gain the convenience of approximately steady conditions with a velocity distribution like that in a falling spherical drop of pure liquid. However, randomness of the particle velocities causes some particles to make an outward crossing of the spherical boundary and to be carried round the boundary and thence downstream in a vertical ‘tail’. This is the nature of break-up of a falling cloud of particles.A numerical simulation of the motion of a number of interacting particles (maximum 320) assumed to act as Stokeslets confirms the validity of the above picture of the way in which particles leak away from a spherical cluster of particles. A dimensionally correct empirical relation for the rate at which particles are lost from the cluster involves a constant which is indeed found to depend only weakly on the various parameters occurring in the numerical simulation. According to this relation the rate at which particles are lost from the blob is proportional to the fall speed of an isolated particle and to the area of the blob boundary. Some photographs of a leaking tail of particles in figure 5 also provide support for the qualitative picture.
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Zappa, Giuseppe, Valerio Lucarini i Antonio Navarra. "Baroclinic Stationary Waves in Aquaplanet Models". Journal of the Atmospheric Sciences 68, nr 5 (1.05.2011): 1023–40. http://dx.doi.org/10.1175/2011jas3573.1.
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Abstract An aquaplanet model is used to study the nature of the highly persistent low-frequency waves that have been observed in models forced by zonally symmetric boundary conditions. Using the Hayashi spectral analysis of the extratropical waves, the authors find that a quasi-stationary wave 5 belongs to a wave packet obeying a well-defined dispersion relation with eastward group velocity. The components of the dispersion relation with k ≥ 5 baroclinically convert eddy available potential energy into eddy kinetic energy, whereas those with k < 5 are baroclinically neutral. In agreement with Green’s model of baroclinic instability, wave 5 is weakly unstable, and the inverse energy cascade, which had been previously proposed as a main forcing for this type of wave, only acts as a positive feedback on its predominantly baroclinic energetics. The quasi-stationary wave is reinforced by a phase lock to an analogous pattern in the tropical convection, which provides further amplification to the wave. It is also found that the Pedlosky bounds on the phase speed of unstable waves provide guidance in explaining the latitudinal structure of the energy conversion, which is shown to be more enhanced where the zonal westerly surface wind is weaker. The wave’s energy is then trapped in the waveguide created by the upper tropospheric jet stream. In agreement with Green’s theory, as the equator-to-pole SST difference is reduced, the stationary marginally stable component shifts toward higher wavenumbers, while wave 5 becomes neutral and westward propagating. Some properties of the aquaplanet quasi-stationary waves are found to be in interesting agreement with a low frequency wave observed by Salby during December–February in the Southern Hemisphere so that this perspective on low frequency variability, apart from its value in terms of basic geophysical fluid dynamics, might be of specific interest for studying the earth’s atmosphere.
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Dimmock, A. P., M. A. Balikhin, S. N. Walker i S. A. Pope. "Dispersion of low frequency plasma waves upstream of the quasi-perpendicular terrestrial bow shock". Annales Geophysicae 31, nr 8 (9.08.2013): 1387–95. http://dx.doi.org/10.5194/angeo-31-1387-2013.
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Abstract. Low frequency waves in the foot of a supercritical quasi-perpendicular shock front have been observed since the very early in situ observations of the terrestrial bow shock (Guha et al., 1972). The great attention that has been devoted to these type of waves since the first observations is explained by the key role attributed to them in the processes of energy redistribution in the shock front by various theoretical models. In some models, these waves play the role of the intermediator between the ions and electrons. It is assumed that they are generated by plasma instability that exist due to the counter-streaming flows of incident and reflected ions. In the second type of models, these waves result from the evolution of the shock front itself in the quasi-periodic process of steepening and overturning of the magnetic ramp. However, the range of the observed frequencies in the spacecraft frame are not enough to distinguish the origin of the observed waves. It also requires the determination of the wave vectors and the plasma frame frequencies. Multipoint measurements within the wave coherence length are needed for an ambiguous determination of the wave vectors. In the main multi-point missions such as ISEE, AMPTE, Cluster and THEMIS, the spacecraft separation is too large for such a wave vector determination and therefore only very few case studies are published (mainly for AMPTE UKS AMPTE IRM pair). Here we present the observations of upstream low frequency waves by the Cluster spacecraft which took place on 19 February 2002. The spacecraft separation during the crossing of the bow shock was small enough to determine the wave vectors and allowed the identification of the plasma wave dispersion relation for the observed waves. Presented results are compared with whistler wave dispersion and it is shown that contrary to previous studies based on the AMPTE data, the phase velocity in the shock frame is directed downstream. The consequences of this finding for both types of models that were developed to explain the generation of these waves are discussed.
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Itano, Toshihisa, i Akira Kasahara. "Effect of Top and Bottom Boundary Conditions on Symmetric Instability under Full-Component Coriolis Force". Journal of the Atmospheric Sciences 68, nr 11 (1.11.2011): 2771–82. http://dx.doi.org/10.1175/jas-d-11-09.1.
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Abstract The linear stability of a zonal flow confined in a domain within horizontal top and bottom boundaries is examined under full consideration of the Coriolis force. The basic zonal flow is assumed to be in thermal wind balance with the density field and to be sheared in both vertical and horizontal directions under statically and inertially stable conditions. By imposing top and bottom boundary conditions in this framework, the number of wave modes increases to four, instead of two in an unbounded domain, as already reported in studies on internal gravity waves. The four modes are classified into two pairs of high- and low-frequency modes: the high modes are superinertial and the low modes are subinertial. The discriminant of symmetric instability is nevertheless determined by the sign of the potential vorticity of the basic zonal flow, as in the case of an unbounded domain. The solutions satisfying the top and bottom boundary conditions are interpreted as the superposition of incident and reflected waves, revealing that the neutral solutions consist of two neutral plane waves with oppositely directed vertical group velocities. This may explain why the properties of wave behavior, such as the instability criteria, remain the same in both the bounded and unbounded domains, although the manifestation of wave activity, such as the order of dispersion relation, is quite different in the two cases. Furthermore, the slope of the constant momentum surface, the slope of the isopycnic surface including the nontraditional effect of the Coriolis force, and the ratio between the frequencies of gravity and inertial waves form an essential set of parameters for symmetric motion. The combination of these dimensionless quantities determines the fundamental nature of symmetric motions, such as stability, regardless of boundary conditions with and without the horizontal component of the planetary vorticity.