Nearby Modes Research Articles

Microstreaming profile of a phospholipid-coated wall-attached microbubble undergoing shape oscillation

Ultrasound-activated microbubbles induce shape oscillation and microstreaming. However, a thorough understanding remains elusive. This study investigated the 3D microstreaming profile of clinically relevant lipid-coated microbubbles undergoing shape oscillation when bound to a wall. Size-controlled biotinylated microbubbles (radius 3–8 μm) were produced by a flow-focusing device and bound to a streptavidin-coated glass. Insonification spanned 85–425 kPa at 25,000 cycles and 1.25 MHz. Two cameras, operating at 5 Mfps and 10 kfps, coupled to a microscope, captured microbubble shape oscillation and cavitation microstreaming, respectively. Astigmatic particle tracking velocimetry measured 3D particle trajectories of 500-nm beads. In the dataset (n = 79), four microstreaming profiles were observed: quadrupole, dipole, radial, and patternless. Modal decomposition revealed that quadrupole patterns resulted from self-interaction of the predominant shape mode, while dipole patterns arose from strong interactions of two nearby modes at the same oscillation frequency. Microstreaming reached 0.002–0.01 m/s at varying acoustic pressures. Quadrupole microstreaming generally induced higher shear stresses than dipole and radial patterns at identical acoustic pressure. A lower shape mode induced higher shear stresses than a higher mode at the same acoustic pressure. The unique microstreaming characteristics yield diverse outcomes in mechanical impact, which could aid efficient therapeutic applications of ultrasound-activated microbubbles.

Wakefield damping in a distributed coupling linear accelerator

The number of cells in a π-mode standing wave (SW) accelerating structure for the Compact Linear Collider (CLIC) project is limited by mode overlap with nearby modes. The distributed coupling scheme avoids mode overlap by treating each cell as independent. Designs of cells suitable for distributed coupling with strong wakefield suppression by waveguide damping have not previously been studied. In this paper we develop a SW cell to be used in a distributed coupling structure that can satisfy the CLIC transverse wake potential limit. From the middle cell of the CLIC-G* traveling wave (TW) structure, a SW cell is designed and then adapted to perform as a cell in a distributed coupling structure. Its wake potentials in an ideal case of open boundaries are reduced to satisfy the wake potential threshold. An electric boundary is added to the model to simulate total reflection at the distribution network. A horizontal coupler cell that connects to the distribution network such that the reflected wakefields remain similar to the open boundary case is simulated. A triplet module which takes advantage of cell-to-cell coupling to reduce reflected wake potential is presented.

Observation of hydrodynamization and local prethermalization in 1D Bose gases.

Hydrodynamics accurately describe relativistic heavy-ion collision experiments well before local thermal equilibrium is established1. This unexpectedly rapid onset of hydrodynamics-which takes place on the fastest available timescale-is called hydrodynamization2-4. It occurs when an interacting quantum system is quenched with an energy density that is much greater than its ground-state energy density5,6. During hydrodynamization, energy gets redistributed across very different energy scales. Hydrodynamization precedes local equilibration among momentum modes5, which is local prethermalization to a generalized Gibbs ensemble7,8 in nearly integrable systems or local thermalization in non-integrable systems9. Although many theories of quantum dynamics postulate local prethermalization10,11, the associated timescale has not been studied experimentally. Here we use an array of one-dimensional Bose gases to directly observe both hydrodynamization and local prethermalization. After we apply a Bragg scattering pulse, hydrodynamization is evident in the fast redistribution of energy among distant momentum modes, which occurs on timescales associated with the Bragg peak energies. Local prethermalization can be seen in the slower redistribution of occupation among nearby momentum modes. We find that the timescale for local prethermalization in our system is inversely proportional to the momenta involved. During hydrodynamization and local prethermalization, existing theories cannot quantitatively model our experiment. Exact theoretical calculations in the Tonks-Girardeau limit12 show qualitatively similar features.

On the link between mechanics and thermal properties: mechanothermics

We report on the theoretical derivation of macroscopic thermal properties (specific heat, thermal conductivity) of an electrically insulating rod connected to two reservoirs, from the linear superposition of its mechanical mode Brownian motions. The calculation is performed for a weak thermal gradient, in the classical limit (high temperature). The development is kept basic as far as geometry and experimental conditions are concerned, enabling an almost fully analytic treatment. In the modeling, each of the modes is subject to a specific Langevin force, which enables to produce the required temperature profile along the rod. The theory is predictive: the temperature gradient (and therefore energy transport) is linked to motion amplitude cross-correlations between nearby mechanical modes. This arises because energy transport is actually mediated by mixing between the modal waves, and not by the modes themselves. This result can be tested on experiments, and shall extend the concepts underlying equipartition and fluctuation–dissipation theorems. The theory links intimately the macroscopic size of the clamping region where the mixing occurs to the microscopic lengthscale of the problem at hand: the phonon mean-free-path. This clamping region, which is key, has received recently a renewed attention in the field of nanomechanics with topical works on ‘phonon shields’ and ‘soft clamping’. We believe that our work should impact the domain of thermal transport in nanostructures, with future developments of the theory toward the quantum regime.

A Synthesis of Mobile Ticketing Applications Used by Commuter Railroads in the United States

Since 2012, many major commuter railroads have deployed mobile ticketing applications (or “apps”) that allow passengers to pay fares directly using their smartphones. In light of this rapid technological change, this research aims to provide a synthesis of the current state of mobile ticketing in the United States. The 14 largest commuter railroads that have launched mobile ticketing apps are compared in four different areas: (1) the ticket validation process; (2) ticket types offered in the mobile app; (3) additional features in the app; and (4) the process for transferring to other modes using the app. The results reveal that all mobile ticketing applications considered in this analysis utilize visual inspection for validation, and that most of them also use quick response (QR) barcodes to validate tickets. Additionally, many of the commuter rail operators examined offer the majority of the ticket types available via traditional fare media in their mobile ticketing apps. The third dimension revealed a large degree of variation in the availability of additional travel-related features, such as trip planners and schedules, in mobile ticketing apps. Last, only a handful of commuter rail operators have fully integrated transfer policies between commuter rail and other nearby transit modes using mobile ticketing, which is an area that warrants further study. These findings are important for other commuter rail and transit operators that are considering deployment of mobile ticketing systems.

Cross-polar reflective linear polarization rotator using anisotropic ultrathin metamaterial

A reflection type linear polarization rotator using L-shaped slot resonator is presented. The proposed metamaterial structure realizes wideband performance (relative bandwidth of 10.35%) due to the overlapping of two nearby resonance modes at 7.54 GHz and 8.03 GHz. The polarization rotation is achieved owing to the structural anisotropy along the two diagonals of the proposed resonator. The polarization conversion ratio (PCR) of the proposed structure is more than 90% in the frequency band of 7.42–8.23 GHz. The proposed structure is competitive in terms of its ultrathin substrate thickness, very low form factor, and wide-angle performance.

A finite Zener-Stroh crack interacting with a blunt crack under in-plane deformations

A Zener-Stroh crack is the name given to a microcrack resulting from the coalescence of edge dislocations along a slip plane. The process by which the crack is initiated was proposed in the first instance by Zener and later examined in detail by Stroh. The Zener-Stroh crack can be thought of as being equivalent, in some sense, to the Griffith crack in classical linear elastic fracture mechanics. We study a finite mode I and II Zener-Stroh crack interacting with a nearby mode I and II blunt crack represented by a parabolic cavity. In this respect, the Zener-Stroh crack can be considered as a coalescence of edge dislocations emitted from the blunt crack. A conformal mapping function is introduced which maps the parabolic boundary onto a straight line in the image plane. By treating the Zener-Stroh crack as a pileup of edge dislocations, two Cauchy singular integral equations are constructed in the image plane. The Gauss-Chebyshev integration formula is applied to numerically solve the resulting singular integral equations. The local mode I and II stress intensity factors at the two tips of the Zener-Stroh crack are determined. We establish conditions on the propagation direction of the Zener-Stroh crack away from or toward the blunt crack. Also established are the conditions for the emission of an edge dislocation from the blunt crack by treating the edge dislocation as a Zener-Stroh crack with infinitesimal length. The dislocation emission criteria from the blunt crack are established here in elementary closed form and will thus be particularly convenient for application in engineering practice.

Thermoacoustic modal instability and its suppression with locally resonant flexible membranes

Thermoacoustic oscillation and instability are a common occurrence in many industrial problems. Investigations on the interplay among different types of modes, their evolution process and coupling with add-on control devices are of vital importance to guide the development of proper control strategies. Using a linear heat release n-τ model inside a duct, these issues are investigated in this paper based on a fully coupled energy-based model. Studies allow the classification and quantification of different types of eigen-modes, as well as their stability and controllability features. Using flush-mounted flexible membranes over the duct wall, possible suppressions of unstable modes and the underlying control mechanisms are revealed with particular focus on cases involving small time delay and interaction indices. Numerical analyses show that thermoacoustic instability of the system can be controlled via creating strong vibro-acoustic coupling, via two different physical processes for acoustic and intrinsic modes. For the former, the acoustic modal pressure distribution should be positively altered in the vicinity of the heat source to create a favorable pressure state scenario, in agreement with Rayleigh criterion. For the latter, control is achieved indirectly through a proper alteration of the nearby acoustic modes, thus affecting their coupling with the targeted intrinsic mode. In both cases, a successful suppression of the thermoacoustic modal instability can be materialized through a proper adjustment of the physical parameters of the membranes and their installation locations.

Direct Observation of Magnon-Phonon Strong Coupling in Two-Dimensional Antiferromagnet at High Magnetic Fields.

We report the direct observation of strong coupling between magnons and phonons in a two-dimensional antiferromagnetic semiconductor FePS_{3}, via magneto-Raman spectroscopy at magnetic fields up to 30Tesla. A Raman-active magnon at 121 cm^{-1} is identified through Zeeman splitting in an applied magnetic field. At a field-driven resonance with a nearby phonon mode, a hybridized magnon-phonon quasiparticle is formed due to strong coupling between the two modes. We develop a microscopic model of the strong coupling in the two-dimensional magnetic lattice, which enables us to elucidate the nature of the emergent quasiparticle. Our polarized Raman results directly show that the magnons transfer their spin angular momentum to the phonons and generate phonon spin through the strong coupling.

Facial reshaping operator for controllable face beautification

Posting attractive facial photos is part of everyday life in the social media era. Motivated by the demand, we propose a lightweight method to automatically and efficiently beautify the shapes of both portrait and non-portrait faces in photos, while allowing users to customize the beautification of individual facial features. Previous methods focus on the beautification of mostly frontal and neutral faces, without incorporating user controllability in the beautification process. To address these restrictions, we propose the Facial Reshaping Operator representation, which is affine-invariant, captures the pairwise geometric configuration of facial landmarks, and allows for efficient face beautification with the user-specified weights of individual facial parts. We also propose an unsupervised beautification method in the operator space of faces, where an input face is iteratively pulled towards a local nearby density mode with improved attractiveness. Our method distinguishes itself from the commercial beautification tools in that it mildly enhances facial shapes without altering makeups or complexions, which complements these tools that lack fine-grained control on the attractiveness of facial shapes for users. The experimental results show that our method improves facial shape attractiveness for a large range of poses and expressions, demonstrating the potential of applicability to photos seen on the social media such as Facebook and Instagram everyday.

Perturbation theories for symmetry-protected bound states in the continuum on two-dimensional periodic structures

On dielectric periodic structures with a reflection symmetry in a periodic direction, there can be antisymmetric standing waves (ASWs) that are symmetry-protected bound states in the continuum (BICs). The BICs have found many applications, mainly because they give rise to resonant modes of extremely large quality-factors ($Q$-factors). The ASWs are robust to symmetric perturbations of the structure, but they become resonant modes if the perturbation is non-symmetric. The $Q$-factor of a resonant mode on a perturbed structure is typically $O(1/\delta^2)$ where $\delta$ is the amplitude of the perturbation, but special perturbations can produce resonant modes with larger $Q$-factors. For two-dimensional (2D) periodic structures with a 1D periodicity, we derive conditions on the perturbation profile such that the $Q$-factors are $O(1/\delta^4)$ or $O(1/\delta^6)$. For the unperturbed structure, an ASW is surrounded by resonant modes with a nonzero Bloch wave vector. For 2D periodic structures, the $Q$-factors of nearby resonant modes are typically $O(1/\beta^2)$, where $\beta$ is the Bloch wavenumber. We show that the $Q$-factors can be $O(1/\beta^6)$ if the ASW satisfies a simple condition.

Environmentally Induced Exceptional Points in Elastodynamics

We study the nature of an environment-induced exceptional point in a non-Hermitian pair of coupled mechanical oscillators. The mechanical oscillators are a pair of pillars carved out of a single isotropic elastodynamic medium made of aluminum and consist of carefully controlled differential losses. The inter-oscillator coupling originates exclusively from background modes associated with the "environment", that portion of the structure which, if perfectly rigid, would support the oscillators without coupling. We describe the effective interaction in terms of a coupled mode framework where only one nearby environmental mode can qualitatively reproduce changes to the exceptional point characteristics. Our experimental and numerical demonstrations illustrates new directions utilizing environmental mode control for the implementation of exceptional point degeneracies. Potential applications include a new type of non-invasive, dfferential atomic force microscopy and hypersensitive sensors for the structural integrity of surfaces.

Finite Element Analysis of Cold Formed Steel Channel Columns with Complex Edge Stiffeners and Web Holes using Abaqus

The present theory work means to think about the numerical examination on models of channel segment with middle and complex edge stiffeners and web gaps under pivotal pressure. A wide scope of parameters, for example, slimness proportion, spine width and thickness have been considered in the investigation. An aggregate of 12 channel models with various parameters, for example, length, thickness and rib width are reenacted. The limited component non-direct examination program ABAQUS V6.14-2 is utilized to reproduce the models. The material properties are acquired from Coupon test. Component type utilized in this non-straight examination is SHELL. A Static, Riks step is utilized to complete examination. The Failure modes, extreme burden and the pressure conveyance around web gaps are inquired about. The relocation parts in every augmentation of burden along X, Y and Z bearings and Rotation segment about X course are gathered. The Von-Mises pressure forms, Deformed shapes and disappointment modes including nearby, horizontal distortional and parallel torsional clasping modes are acquired. The pivotal burden limits of pressure individuals with various parameters are looked at.

Coupling of Acoustic and Intrinsic Modes in 1D Combustor Models

ABSTRACT The work is concerned with the theoretical examination of a new type of thermo-acoustic instability in combustors not reported in the literature. The instability results from linear coupling between the conventional acoustic mode and the recently discovered “flame intrinsic modes.” Within the framework of a 1D model of a quarter wave resonator with the standard model of flame heat release, intrinsic-acoustic mode coupling occurs when the real parts of the frequencies of neighboring acoustic and flame-intrinsic modes at small interaction index are close. While at small the Eigen-functions of close acoustic and flame intrinsic modes clearly exhibit their distinctive identities, with increase of the mode identities become blurred and the Eigen-functions of acoustic modes resemble more and more those of flame intrinsic modes and at a certain become indistinguishable. We refer them as coupled intrinsic-acoustic modes or coupled modes. When the “Rayleigh index” for a coupled mode behaving as an acoustic mode at small is negative, at a larger such a mode can nevertheless become unstable at one of the nearby intrinsic mode frequencies. We find analytically the instability domain due to coupling in the parameter space. Near the instability boundary, we reduce the transcendental dispersion relation to a quadratic or, if higher accuracy is desired, to a quartic equation. These models capture well all four possible coupling scenarios.

Cruciform specimens' experimental analysis in ultrasonic fatigue testing

AbstractIn this paper, two special aluminium cruciform specimens are designed and tested in an ultrasonic fatigue machine. They were designed based on Single‐Input‐Multiple‐Output (SIMO) modal analysis to induce in‐plane biaxial stress combinations (in‐phase tension‐tension [T‐T] and out‐of‐phase compression‐tension [C‐T]) when at resonance at 20 kHz. The geometries were subjected to both numerical analysis and experimental testing to understand if they can indeed create the intended biaxial state of stresses. Both numerical and experimental results showed an impact of nearby resonant modes of noninterest on the correct functioning of the specimens, especially regarding the T‐T specimen where a large deviation from the mode of interest was measured. This means that future work includes re‐designing T‐T specimens taking into account these mode shapes. Only out‐of‐phase specimens demonstrated to work properly and tests until failure were conducted. The first failure results showed to be consistent with literature when out‐of‐phase biaxial stress is applied cyclically.

A mode III Dugdale crack interacting with a non-elliptical inhomogeneity with internal uniform stresses

Using conformal mapping techniques and the theory of Cauchy singular integral equations, we prove that the internal stresses inside a non-elliptical inhomogeneity can remain uniform despite the presence of a nearby finite mode III Dugdale crack in the surrounding matrix which is subjected to a uniform remote loading. Our numerical results indicate that: (i) the existence of the two plastic zones in the vicinity of the “crack tips” significantly influences the non-elliptical shape of the inhomogeneity; (ii) the changes in the two plastic zone length ratios are quite different as the remote loading increases; (iii) at a critical remote loading, one plastic zone vanishes while the other plastic zone occupies practically the entire crack length.

The coupling between inertial and rotational eigenmodes in planets with liquid cores

The Earth is a rapidly rotating body. The centrifugal pull makes its shape resemble a flattened ellipsoid and Coriolis forces support waves in its fluid core, known as inertial waves. These waves can lead to global oscillations, or modes, of the fluid. Periodic variations of the Earth's rotation axis (nutations) can lead to an exchange of angular momentum between the mantle and the fluid core and excite these inertial modes. In addition to viscous torques that exist regardless of the shape of the boundaries, the small flattening of the core-mantle boundary (CMB) allows inertial modes to exert pressure torques on the mantle. These torques effectively couple the rigid-body dynamics of the Earth with the fluid dynamics of the fluid core. Here we present the first high resolution numerical model that solves simultaneously the rigid body dynamics of the mantle and the Navier-Stokes equation for the liquid core. This method takes naturally into account dissipative processes in the fluid that are ignored in current nutation models. We find that the Free Core Nutation (FCN) mode, mostly a toroidal fluid flow if the mantle has a large moment of inertia, enters into resonance with nearby modes if the mantle's moment of inertia is reduced. These mode interactions seem to be completely analogous to the ones discovered by Schmitt (2006) in a uniformly rotating ellipsoid with varying flattening.

Unidirectional emission from a PT -symmetric annular microcavity

The introduction of a scattering center to microdisk lasers has been considered as an effective way to tailor their far-field emissions. However, this approach is practically limited by its nearby modes with higher quality ($Q$) factors and worse directionalities. In this research, by applying the simple concept of parity-time ($\mathcal{P}\mathcal{T}$) symmetry, we demonstrate that the resonances with well-designed directionalities can be selectively excited in optical microcavities. Taking the annular microcavities as examples, the unidirectional laser emissions and single-mode operations have been realized simultaneously by breaking the $\mathcal{P}\mathcal{T}$ symmetry. More interestingly, we find that the $\mathcal{P}\mathcal{T}$-symmetric modulations on the imaginary parts of the refractive index in a circular microdisk can affect the internal ray dynamics and thus generate highly directional laser emission. This research can boost both the fundamental studies and the practical applications of $\mathcal{P}\mathcal{T}$-symmetric systems.

Axisymmetric density waves in Saturn’s rings

Density waves in Saturn's rings are usually tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km from Saturn's spin axis), there are density variations that appear to form an axisymmetric density wave consisting of concentric zones of varying densities that propagate radially through the rings. Axisymmetric waves cannot be generated directly by a satellite resonance, but instead appear to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist just interior to other resonantly confined edges that exhibit a large number of normal modes, including the Dawes ringlet in the outer C ring and the outermost part of the B ring.

Analytical and experimental study on web-crippling behaviour of cold-formed C-section with and without FRP wrapping

Cold-formed sections are widely employed in steel construction because they are lighter and more economical than traditional hot-rolled members. The simple accessibility and reasonable cost of high-quality, low-compound steels, weathering steels and Zinc-covered steels have prompted individuals with high/thickness (h/t) proportions, rendering them significantly more defenseless to nearby clasping mode and to another clasping mode called mutilation and worldwide. There are numerous investigations in progress with regard to local buckling, web-crippling, etc. This paper discusses the web-crippling behaviour of cold-formed sections, which were subjected to various loading conditions like end-one-flange loading, end-two-flange loading, and interior-two-flange loading with and without FRP wrapping. The experimental and analytical results are compared. Moreover, without increasing the thickness of the element, it is proposed to use the FRP on web, to reduce the web-crippling of cold-formed sections.