Propagation Angle Research Articles

Chromatin jets define the properties of cohesin-driven in vivo loop extrusion

Complex genomes show intricate organization in three-dimensional (3D) nuclear space. Current models posit that cohesin extrudes loops to form self-interacting domains delimited by the DNA binding protein CTCF. Here, we describe and quantitatively characterize cohesin-propelled, jet-like chromatin contacts as landmarks of loop extrusion in quiescent mammalian lymphocytes. Experimental observations and polymer simulations indicate that narrow origins of loop extrusion favor jet formation. Unless constrained by CTCF, jets propagate symmetrically for 1-2 Mb, providing an estimate for the range of invivo loop extrusion. Asymmetric CTCF binding deflects the angle of jet propagation as experimental evidence that cohesin-mediated loop extrusion can switch from bi- to unidirectional and is controlled independently in both directions. These data offer new insights into the physiological behavior of invivo cohesin-mediated loop extrusion and further our understanding of the principles that underlie genome organization.

Computational Investigation on Cracking Behaviors of AerMet 100

AerMet 100 exhibits excellent mechanical properties, proven in previous studies; however, defects may greatly influence the mechanical behavior during the service of the material, which serves as one of the major challenges in the wider application of the material. To quantify the crack evolution process, the in-plane type I crack propagation behavior is comprehensively investigated based on the extended finite element method (XFEM). The crack growth is characterized in terms of the extracted crack propagation angle, stress intensity factor (SIF) in the crack tip, and stress field profiles during the crack propagation process. An extrapolation method is adopted to calculate the SIF, followed by a series of parametric studies on the influence of the governing factors, i.e., initial crack length, initial crack location, initial crack angle, and the crack number through numerical investigation. It is found that the crack propagation angle enlarges monotonously with the increase of the initial crack location, the initial crack length, and the crack number, increases slowly with the growth of initial crack angle, and rapidly enlarges in reverse at about 45°. The SIF in Mode I, KId, gradually decreases with the increase of the initial crack location and the crack number, and nearly keeps steady when the initial crack length and initial crack angle varies. Results provide further understanding of the failure and fracture behavior of AerMet 100 and guide the future application and design of the structures.

Doublet splitting of fusion alpha particle driven ion cyclotron emission

Ion cyclotron emission (ICE) originating from confined populations of fast ions in toroidal fusion plasmas is an important non-invasive, passive diagnostic for current and next-generation devices. The ability to model ICE signals accurately is an essential step towards inferring the characteristics of confined energetic alpha particles or fast neutral beam ions and background plasma. In this paper, the linear growth rates of the magnetoacoustic cyclotron instability, which is the leading explanation for ICE, are calculated in high-resolution 2D space for parameters corresponding to JET Pulse No. 26148. These calculations further highlight the origin of doublet splitting of the cyclotron harmonics and the perceived need to invoke nonlinear interactions with 1D3V particle-in-cell studies to account for lower harmonics with substantial amplitudes. The inclusion of signals of ICE from a well-resolved range of propagation angles can also account for these effects.

Quantum squeezing of vector slow-light solitons in a coherent atomic system

We investigate the squeezing of two-component quantum optical solitons slowly moving in a tripod-type atomic system with double electromagnetically induced transparency (EIT). The evolution of the double probe-field envelopes is governed by a vector quantum nonlinear Schrödinger equation, derived from the coupled Heisenberg-Langevin and Maxwell equations. Quantum fluctuations of vector soliton pairs and atomic spin are analysed by means of a direct perturbation approach. Importantly, we find that the quantum squeezing of vector soliton pairs is generated by the giant Kerr nonlinearity, which is provided by EIT, and the outcome of the squeezing can be optimized by the selection of propagation distance and angle. The atomic spin squeezing is found for short propagation distances. The predicted results offer insights into soliton physics and may be useful for entanglement detection.

Nonlinear dynamical analysis of drift ion acoustic shock waves in Electron-Positron-Ion plasma with adiabatic trapping

Propagation of nonlinear coupled drift ion acoustic shock wave is investigated in an electron–positron-ion (epi) plasma in the presence of fully degenerate adiabatically trapped electrons. A novel complex nonlinear equation with fractional nonlinear terms is formulated. Phase plane theory of planar dynamical system is employed to investigate this nonlinear equation of epi plasma. The variations in nonlinear periodic orbits (NPO), nonlinear heteroclinic orbits (NHO), time series plots and shock profiles are demonstrated by varying the values of different controlling parameters such as the ratio of positron to electron number density, collisional frequency, magnetic field, drift velocity and angle of propagation. It is seen that a pair of shock structures are obtained – which is the most significant result of this work.

Mathematical Modeling of Waves in a Porous Micropolar Fibrereinforced Structure and Liquid Interface

The present investigation envisages on the Mathematical modeling of waves propagating in a porous micropolar fibre-reinforced structure in a half-space and liquid interface. The harmonic method of wave analysis is utilized, such that, the reflection and transmission of waves in the media were modelled and it’s equations of motion analytically derived. It was deduced that incident longitudinal wave in the solid structure yielded four reflected waves given as; quasi–P wave (qLD), quasi–SV wave, quasi–transverse microrotational (qTM) wave and a wave due to voids and one transmitted wave known as the quasi-longitudinal transmitted (qLT) wave. The phase velocity in the liquid medium is independent of angle of propagation as observed. The corresponding amplitude ratios of propagations for both reflected and transmitted waves are analytically derived by employing Snell’s law. The model would prove to be of relevance in the understanding of modeling of the behavior of propagation phenomena of waves in micropolar fibre-reinforecd machination systems resulting in solid/liquid interfaces especially in earth sciences and in particular seismology, amongst others.

Influence of tooth crack parameters on bearing vibration signal of a geared rotor

Fault diagnosis is a mandatory process in modern industry management, because it may reduce costs due to unexpected failures that may occur in machines. It is proposed to study the dynamic effect in the rotor response of gear tooth crack caused by bending stress. As the bearings are the common location to install sensors as accelerometers, the response in their corresponding degrees of freedom is considered. A geared rotor model is assumed for the simulations. This model embraces a detailed finite element discretization, which contemplates five degrees of freedom per node, including torsional rotation. In addition, a time-varying mesh stiffness calculated by the potential energy method is adopted to represent the tooth contact. A crack model is assumed with three input parameters (initial position, propagation angle and depth). A design of experiments was set up to show the influence of each parameter on the system response for three different mean depths. The results analysis pointed out that for a precise parameter identification, all three parameters should be taken into account, because they affect the system response and they also present combined influence.

Experiments and modelling of ultrasonic waves in composite plates under varying temperature

Guided wave (GW) structural health monitoring (SHM) systems offer an attractive solution as an in-situ quasi real-time assessment of structural damage, but their sensitivity and efficiency may be impaired under varied environmental and operational conditions. Thus, virtual tests, such as that based on the Finite Element (FE) method, represent a valid approach for simulating and investigating SHM systems, enabling a substantial reduction in experimental campaigns. In this work, GW propagation characteristics in a carbon fibre-reinforced composite plate are studied under a varying temperature condition, representative of the aeronautics application. At first, GW SHM system was physically tested at room temperature (20°C), and the results were used to calibrate and assess the proposed FE modelling approaches, characterised by different element types and mesh sizes. A temperature independent averaged time compensation factor is proposed to mitigate the numerical data dependency on excitation frequency and propagation angle. Two temperature variations (from 20°C to -50°C, and 20°C to 65°C) were experimentally and numerically considered to investigate the effect of varying temperature on the GW. For all test cases, the compensated numerical data was compared to the experimental results, and discussed in terms of dispersion curves, focusing on the zero-order symmetric, S0, and antisymmetric, A0, modes. Results show that both 2D and 3D FE approaches can accurately predict the changes in GW due to varying temperature, with the group velocity of the A0 mode being less sensitive to temperature variations.

Focusing of inertial waves by a vertically annular forcing

A theory of inertial wave focusing generated by a vertically oscillating slender torus immersed in a uniformly rotating fluid is presented. The analytical solution of the velocity field shows that, under an axisymmetric annular forcing in inviscid rotating fluid, the wave rays form a double cone symmetric about the plane on which the torus is located. At the two vertices of the double cone, the waves are in a shock-like manner focus causing localized surges of energy. After focusing, the waves continue their propagation and form a new inverted cone with the same cone angle, such that both cones are symmetric about the focal point. These results are in good agreement with the experimental and numerical study by Duran-Matute et al. [Phys. Rev. E 87, 041001(R) (2013)]. When friction effects occur, the wave pattern changes substantially and the wave away from the focal point is significantly attenuated so that the symmetry about the focal point is broken. As a consequence, the wave beam widens and the focusing effect becomes weaker with increasing Ekman number (Ek), which indicates the ratio of the viscous force to the Coriolis force. Furthermore, for the same Ek, the focusing effect tends to disappear when the forcing frequency is close to zero or twice the angular velocity of rotating flow. For forcing frequency close to the angular velocity of a rotating fluid, the amplitude of the vertical velocity at the focal point reaches its maximum, which corresponds to a wave propagation angle of 60 degrees.

Research on Vehicle-to-Vehicle MIMO Wireless Channels in Various Tunnels

In this paper, we propose a geometry-based channel model for multiple-input multiple-output (MIMO) vehicle-to-vehicle (V2V) communications in practical tunnel scenarios. In the proposed channel model, the waves transmitted from the transmitter experience line-of-sight (LoS) and non-LoS (NLoS) before arriving at the receiver. The time-varying parameters of the propagation paths and angles are derived to characterize the channel non-stationarity. Furthermore, we derive the correlation property functions of the proposed V2V channel model; they are space cross-correlation functions (CCFs), temporal auto-correlation functions (ACFs), frequency CCFs, as well as the Doppler power spectrum distributions (PSDs). Numerous simulation results of the propagation characteristic for different physical properties of the tunnel, as well as the different motion properties of the transmitter and receiver, are studied and discussed; they demonstrate that the proposed channel model is suitable for describing the practical V2V tunnel communication scenarios.

Metamaterial shields for inner protection and outer tuning through a relaxed micromorphic approach.

In this paper, a coherent boundary value problem to model metamaterials' behaviour based on the relaxed micromorphic model is established. This boundary value problem includes well-posed boundary conditions, thus disclosing the possibility of exploring the scattering patterns of finite-size metamaterial specimens. Thanks to the simplified model's structure (few frequency- and angle-independent parameters), we are able to unveil the scattering metamaterial's response for a wide range of frequencies and angles of propagation of the incident wave. These results are an important stepping stone towards the conception of more complex large-scale meta-structures that can control elastic waves and recover energy. This article is part of the theme issue 'Wave generation and transmission in multi-scale complex media and structured metamaterials (part 1)'.

Experiments on three-dimensional flaw dynamic evolution of transparent rock-like material under osmotic pressure

The dynamic evolution mechanism of intrinsic crack propagation in rocks is a topical and difficult problem in rock mechanics and engineering. Numerous examples of rock mass engineering disasters indicate that the three-dimensional (3D) flaw propagation and evolution process are the internal factors causing geological disasters. A persistent puzzle is the effect of osmotic pressure on the spatial form of crack propagation in compressed rock mass. As the naked eye cannot observe the dynamic evolution process of internal natural crack propagation, we experimented with transparent specimens that have brittle fracture properties similar to those of a rock-like material under frozen conditions. We prefabricated elliptical open cracks in the specimens, on which were applied osmotic pressure through a high-pressure osmotic injection equipment. Through uniaxial and biaxial compression tests, we established a set of compression test steps and methods for intrinsic open-type prefabricated crack specimens under osmotic pressure. Further, we analyzed and compared with the dynamic evolution law of the entire stress–strain process of 3D flaw under osmotic pressure, exploring the effects of different osmotic pressures and crack forms on the crack initiation, penetration, and peak strengths of elliptical open-type cracks. Consequently, the fan-shaped and spiral surface cracks formed by 3D flaw propagation were found for the first time without osmotic pressure. Meanwhile, osmotic pressure accelerated the growth of wrapping wing cracks and inhibited the growth of petal cracks and wrapping anti-wing cracks. Lateral pressure suppressed the vertical propagation of the wing cracks, increased the crack stress and peak strength, and reduced the initial propagation angle of the wing cracks at the long axis end of the prefabricated crack. These findings provide an important basis for expanding the initiation, propagation, evolution, and failure mechanism of 3D flaw under osmotic pressure in natural rock mass.

Instabilities in magnetized inhomogeneous dusty plasmas with the effect of recombination

An analytical formalism to understand the impact of various parameters on evolving instabilities in inhomogeneous collisional dusty plasmas is presented here under the effect of recombination. The basic fluid dynamics for electrons and singly charged cold ions is carried out including recombination and collision at constant rate at the surface of dust particles. Dust particles are considered to be static with unperturbed density. Normal mode analysis method has been used along with linear approximation to get perturbed densities (n i1, n e1) which are used along with quasi-neutrality condition to get perturbed potential using Poisson’s equation to obtain dispersion relation. While other authors have detected instabilities in unmagnetized plasmas, here this method has been successfully realized in presence of static magnetic field at various propagation angle and allowed the straightforward calculation of growth rates of observed instability. An extensive study of the unstable modes has been done which are well discriminated and plotted with respect to different plasma parameters like dust charge, dust density, propagation angle, magnetic field, electrostatic potential along with plasma oscillation wavelength to Debye wavelength ratio. We have observed in the said model that the presence of dust particles and propagation angle of applied magnetic field are affecting significantly the growth rate of instability as compared to magnetic field and recombination.

Investigation on anti-penetration capability of water filled aluminum alloy cell structure to the shaped charge jet

Passive protective armor is reliable and cheap, and is favored by many armored weapons and equipment. However, reports on metal-liquid composite armor are not sufficient and systematic. Based on the shaped charge jet (SCJ), the anti-penetration capabilities of water filled aluminum alloy cell structure were studied. The hourglass cell structure (HCS) was designed according to the shock wave propagation characteristics in liquid, and the expansion-convergence cell structure (E-CCS) was derived. Based on the virtual origin theory, the residual tip velocity of jet after SCJ penetrated the cell structure was calculated. According to the theory of supersonic disturbance propagation, the Mach cone half angle of SCJ shock wave propagation in liquid was defined and corrected. The propagation and reflection behavior of shock wave were discussed to analysis the radial convergence of liquid. Via the Van Leer Arbitrary Lagrangian Euler finite element simulation model verified by experiments, the simulation studies of SCJ penetrated the circular cell structure (CCS), HCS, E-CCS and convergence/expansion multi-cell structure were performed. The results show that HCS has better effect of interfering with SCJ than that of CCS and E-CCS. An important discovery is that when the liquid composite multi-cell structure is penetrated by SCJ, the attacked cell will not affect other cells due to the shock wave has been trapped in a single cell.

Bragg Scattering from a Random Potential.

A potential for propagation of a wave in two dimensions is constructed from a random superposition of plane waves around all propagation angles. Surprisingly, despite the lack of periodic structure, sharp Bragg diffraction of the wave is observed, analogous to a powder diffraction pattern. The scattering is partially resonant, so Fermi's golden rule does not apply. This phenomenon would be experimentally observable by sending an atomic beam into a chaotic cavity populated by a single mode laser.

Optimizing finite-difference scheme in multidirections on rectangular grids based on the minimum norm

The finite-difference (FD) method is widely used in numerical simulation; however, its accuracy suffers from numerical spatial dispersion and numerical anisotropy. The single-direction optimization methods, which optimize the FD coefficients along a single spatial direction, can suppress numerical spatial dispersion, but they are suboptimal for mitigating numerical anisotropy on rectangular grids. We have developed a multidirection optimization method that penalizes approximation errors among all propagation angles on rectangular grids with the minimum norm (i.e., [Formula: see text] norm) to mitigate numerical spatial dispersion and numerical anisotropy simultaneously. Given maximum absolute error tolerance and grid-spacing ratio, we first determine the optimal order of the FD operator in each spatial direction. Then, we penalize approximation errors within the wavenumber-azimuth domain to obtain the optimized FD coefficients. Theoretical analysis and numerical experiments find that our method is superior to single-direction optimization methods in suppressing numerical spatial dispersion and mitigating numerical anisotropy for square and rectangular grids. For homogeneous models with grid-spacing ratios of 1.0 (i.e., square grids), 1.2, and 1.4, the root-mean-square (rms) errors obtained by our method are 77%, 80%, and 72% that of the single-direction optimization method adopting the [Formula: see text] norm, respectively. For the Marmousi model with a grid-spacing ratio of 1.4, the rms error of our method is 36% that of the single-direction optimization method based on the [Formula: see text] norm. Such an evident improvement on error suppression is critical for numerical simulations adopting more flexible grid-spacing ratios.

Fatigue crack propagation simulation method using XFEM with variable-node element

The extended finite element method (XFEM) with the local refinement technique using the variable-node element (VNE) is proposed to simulate the fatigue crack propagation under the cyclic loadings, in which the initially generated coarse mesh around the crack tip is refined after the crack propagation and the VNE is used to connect the refined elements and the adjacent elements. The local refine elements are used to improve the accuracy of stress near the crack tip and it is unnecessary to conform the discretization to the crack surfaces. The maximum tangential stress criterion is used to determine the crack propagation angle θc and the fatigue life is estimated by the Paris law. With this method, the condition number of the global stiffness matrix is alleviated by using the only discontinuous branch enrichment function and the crack increment size can be set flexibly and small enough to reproduce true crack path. Because only the refined mesh around crack tip is updated at each increment step during crack propagation, the simulation cost is much less than that of the method in which global fine mesh is required. Numerical examples of the crack propagation under the monotonic and cyclic loadings are given out and it is demonstrated that the proposed method can calculate the stress intensity factors (SIFs) and predict the crack paths more accurately with the local refine elements near the each crack tip. The proposed method is also suitable to simulate the crack propagation of the functional graded materials under the thermal loadings in the future works, in which the material non-homogeneity near the crack tip requires accurate modeling.

Laser Gaussian beam analysis of structure constant depends on Kolmogorov in turbulent atmosphere for a variable angle of wave propagation

Laser Gaussian beam propagation is important in optical communications; the challenges of the measured constant parameters are varied angle wave propagation, the receiver plan in the slant path of laser Gaussian beam (G) in Kolmogorov gauges, and the effect of the laser in a random medium. At this point, atmospheric turbulence is reputable based on laser Gaussian beam propagation. Moreover, the space propagation of Gaussian beam waves of higher-order Gaussian beam modes has been expanded from the effects of the scintillation index and with different zenith angles between the laser propagator and the detector (receiver) in the ramp path. Furthermore, in the Cartesian coordinate system, the scintillation index in the Kolmogorov standard is evaluated, and it employs two methods; first, Huygens–Fresnel fundamental and, second, random phase screen for work synchronization. Additionally, to analyze the contour parameters of constant construction, the intensity and receiver field is found to compute the high turbulent modes in the atmospheric deposition, which depends on propagation distances. These result in significant reserves in the matlab computation period and serve the imitation for enhancement of the link transmission; therefore, the zenith angle and scintillation index are pretentious by slant beam, and they enhance the performance that makes the comparisons found with fixed structure constant parameters C2n and the propagation distance against the scintillation index.

The anisotropic plasma wave in the plasma turbulence

AbstractIn this paper, the influence of plasma turbulence due to the sheared and body stress flow on the dispersion characteristics of the transverse electromagnetic modes in strongly coupled plasma is analysed. Using kinetic theory and solving the scattering relationship for the Vlasov‐Maxwell system, the influence of plasma turbulence on the growth of the electromagnetic mode is investigated. The minimum value of the stress rate threshold for the growth rate of electromagnetic instability in the linear polarization is higher than that of circular polarization. It is shown that the instability growth rate maximum for the circular polarization is about 100 times higher than that of the linear polarization. In the circular polarization, the value minimum of the shear stress is 1.2 times the minimum volume of the body stress. For the linear polarization, the value minimum of the body stress is 1.5 times the minimum volume of the shear stress. Increasing the density gradient of plasma leads to a higher stress threshold rate, and the range of propagation angles of growing modes is limited. With increasing steps of the density gradient plasma in the low‐density corona, electromagnetic instability occurs at a higher stress flow.

High bandwidth measurements of auroral Langmuir waves with multiple antennas

Abstract. The High-Bandwidth Auroral Rocket (HIBAR) was launched from Poker Flat, Alaska, on 28 January 2003 at 07:50 UT towards an apogee of 382 km in the nightside aurora. The flight was unique in having three high-frequency (HF) receivers using multiple antennas parallel and perpendicular to the ambient magnetic field, as well as very low-frequency (VLF) receivers using antennas perpendicular to the magnetic field. These receivers observed five short-lived Langmuir wave bursts lasting from 0.1–0.2 s, consisting of a thin plasma line with frequencies in the range of 2470–2610 kHz that had an associated diffuse feature occurring 5–10 kHz above the plasma line. Both of these waves occurred slightly above the local plasma frequency with amplitudes between 1–100 µV m−1. The ratio of the parallel to perpendicular components of the plasma line and diffuse feature were used to determine the angle of propagation of these waves with respect to the background magnetic field. These angles were found to be comparable to the theoretical Z-infinity angle that these waves would resonate at. The VLF receiver detected auroral hiss throughout the flight at 5–10 kHz, a frequency matching the difference between the plasma line and the diffuse feature. A dispersion solver, partially informed with measured electron distributions, and associated frequency- and wavevector-matching conditions were employed to determine if the diffuse features could be generated by a nonlinear wave–wave interaction of the plasma line with the lower-frequency auroral hiss waves/lower-hybrid waves. The results show that this interpretation is plausible.