Amplification Of Modes Research Articles

Equilibration of Baroclinic Instability in Westward Flows

Abstract We explore the dynamics of baroclinic instability in westward flows using an asymptotic weakly nonlinear model. The proposed theory is based on the multilayer quasigeostrophic framework, which is reduced to a system governed by a single nonlinear prognostic equation for the upper layer. The dynamics of deeper layers are represented by linear diagnostic relations. A major role in the statistical equilibration of baroclinic instability is played by the latent zonally elongated modes. These structures form spontaneously in baroclinically unstable systems and effectively suppress the amplification of primary unstable modes. Special attention is given to the effects of bottom friction, which is shown to control both linear and nonlinear properties of baroclinic instability. The reduced-dynamics model is validated by a series of numerical simulations.

Erbium-doped circular photonic crystal fiber design for the amplification of 20 OAM modes

We propose a fiber design consisting of ring-shaped erbium-doped core surrounded by circularly arranged holes of varying radius in fused silica glass to amplify higher-order orbital angular momentum (OAM) modes. We numerically demonstrate simultaneous amplification of 20 OAM modes ( l = 5 , 6, 7, 8, 9) with more than 20 dB gain at 1550 nm wavelength while having differential modal gain of 0.12 dB. We also demonstrate amplification of modes over the C-band with gain excursion of less than 2 dB, differential modal gain of less than 0.2 dB, and noise figure less than 4.2 dB. The proposed erbium-doped fiber amplifier would be useful in high-data-rate space-division multiplexing optical-communication systems.

Dual-labeling ratiometric electrochemical strategy initiated with ISDPR for accurate screening MecA gene

An outstanding dual-labeling ratiometric electrochemical biosensor based on isothermal strand displacement polymerization reaction (ISDPR) for highly sensitive and selective detection of mecA gene has been proposed. Concretely, in the presence of mecA gene, the addition of methylene blue (MB)-labeled primer and polymerase induced recycling amplification to change the structure of the ferrocene (Fc)-labeled hairpin probe, thereby releasing abundant target gene to realize the signal amplification and dual-signal output. Through this process, the electrochemical responses of Fc (IFc) and MB (IMB) were both substantially reduced and increased proportionally, ensuring that the value of IMB/IFc can accurately reflect the true detection level of mecA gene. Benefiting from the “signal-on/off” strategy, the fabricated biosensor exhibited outstanding sequence specificity to discriminate mismatched mecA gene, which verified to be 2.72 times that of single-label detection for perfect match/single base mismatch (PM/MM) discrimination ratio. This strategy effectively integrated the advantages of signal amplification and ratiometric modes, making the biosensor exhibit a broad working range with 10 fM - 3000 pM and a limit of detection (LOD) with 3.33 fM (S/N = 3). Moreover, the proposed biosensor has good feasibility for mecA gene determination in water samples due to acceptable recoveries (95–115%) and repeatability relative standard deviations (RSD) value of 4%. This will provide a powerful sensing platform for improving accuracy and decreasing background signal of sensor for ARGs screening in environmental monitoring.

Modal Decomposition and Linear Modeling of Swirl Fluctuations in the Mixing Section of a Model Combustor Based on Particle Image Velocimetry Data

Abstract In order to determine the flame transfer function of a combustion system, different mechanisms have been identified that need to be modeled. This study focuses on the generation and propagation of one of these mechanisms, namely, the swirl fluctuations downstream of a radial swirl combustor under isothermal conditions. Swirl fluctuations are generated experimentally by imposing acoustic perturbations. Time-resolved longitudinal and crosswise particle image velocimetry (PIV) measurements are conducted inside the mixing tube and combustion chamber to quantify the evolution of the swirl fluctuations. The measured flow response is decomposed using spectral proper orthogonal decomposition to unravel the contributions of different dynamical modes. In addition a resolvent analysis is conducted based on the linearized Navier–Stokes equations to reveal the intrinsically most amplified flow structures. Both, the data-driven and analytic approach, show that inertial waves are indeed present in the flow response and an inherent flow instability downstream of the swirler, which confirms recent theoretical works on inertial waves. However, the contribution of the identified inertial waves to the total swirl fluctuations turns out to be very small. This is suggested to be due to the very structured forcing at the swirler and the additional amplification of shear-driven modes. Overall, this work confirms the presence of inertial waves in highly turbulent swirl combustors and evaluates its relevance for industry-related configurations. It further outlines a methodology to analyze and predict their characteristics based on mean fields only, which is applicable for complex geometries of industrial relevance.

Material point method for large-deformation modeling of coseismic landslide and liquefaction-induced dam failure

In this study, Material Point Method (MPM) is improved to simulate coseismic slope stability and liquefaction-induced embankment failure under earthquake loading. First, by using elastic or elastoplastic models, topographic amplification and different slope failure modes are analyzed considering the effects of slope geometry, soil properties and excitation frequencies etc. The MPM model is then applied to predict a cascading slope failure process, including triggering, shear band formation, runoff and final deposition. Finally, a fully nonlinear bounding surface soil model is implemented in the two-phase soil-water coupled MPM framework to investigate the liquefaction mechanism and associated dam failure using two case histories. The numerical results are generally comparable with the post-failure profiles obtained from field investigation, which highlight the advantage of MPM in handling liquefaction-induced large deformation. The MPM shows great promise to quantitatively assess risk and consequence associated with seismic slope failure and soil liquefaction, thereby, advance the performance-based engineering design and analysis.

Perturbation Analysis of Nonlinear Stages in Hypersonic Transition

Linear theory continues to play a critical role in extracting the underlying primary instability dynamics of boundary layer transition. However, such methods have difficulty in isolating the dynamics of secondary instabilities, which dominate the later stages of transition. A Floquet analysis can bridge this gap; however, typical matrix-based approaches can be cumbersome to implement in general compressible scenarios. We address this difficulty by developing a matrix-free perturbation technique to extract the three-dimensional linearized secondary dynamics of compressible inhomogeneous flowfields. The method can be implemented into traditional Navier-Stokes codes in a straightforward manner. It is then used to examine the transition mechanism in a hypersonic boundary layer saturated by a second-mode instability. The linear response of the time-periodic basic-state is shown to precisely identify the non-parallel amplification and breakdown of oblique modes that disintegrate the boundary layer. It also correctly predicts the fundamental resonance mechanism that leads to transition.

Dynamics of a bipolarised Nd : YAG laser with partially polarised pump radiation

We propose a model of a bipolarised Nd : YAG laser with partially polarised pump radiation, providing competitive amplification of polarisation modes. A new type of instability is predicted, similar to the one that was first observed in []. The possibility of experimental verification of predictions is discussed.

Torsional wave focusing in cylindrical structures with the conformal gradient-index phononic crystal lens

We present torsional wave focusing in cylindrical structures integrated with conformal gradient-index phononic crystal (GRIN-PC) lenses. The mechanical lens modifies the refractive characteristics of propagating waves along the axial direction such that the torsional wave energy focuses at a desired point with an increased amplitude. In this paper, our main goal is to exploit the GRIN-PC concept for amplification of the fundamental torsional wave mode, namely, T(0,1), which is especially favorable in the guided wave ultrasonic testing of pipelines and can extend important structural information over long-range pipelines. To this end, we first study d35 piezoelectric transducer arrays through multiphysics simulations coupling piezoelectric and solid mechanics models and determine the optimal number of transducers to achieve the excitation of torsional plane wave. Two-dimensional Fourier transform as well as the tangential displacement histories around the pipe circumference at various axial positions verify the pure T(0,1) excitation, which is validated with experiments. Next, we design, fabricate, and numerically and experimentally study the conformal GRIN-PC for T(0,1) mode focusing in a range of ultrasonic frequencies, from 30 to 50 kHz. Measurements show that the amplitude of the torsional wave mode is amplified by 39% at the focal point with the presence of the GRIN-PC lens.

Improvement on the manipulation of a single nitrogen-vacancy spin and microwave photon at single-quantum level

It remains a great challenge to realize direct manipulation of a nitrogen-vacancy (NV) spin at the single-quantum level with a microwave (MW) cavity. As an alternative, a hybrid system with the spin–phonon–photon triple interactions mediated by a squeezed cantilever-type harmonic resonator is proposed. According to the general mechanical parametric amplification of this in-between phonon mode, the direct spin–phonon and photon–phonon couplings are both exponentially enhanced, which can even further improve the coherent manipulation of a single NV spin and MW photon with a higher efficiency. In view of this triple system with enhanced couplings and the additional sideband adjustable designs, this scheme may provide a more efficient phonon-mediated platform to bridge or manipulate the MW quantum and a single electron spin coherently. It is also hoped to evoke wider applications in the areas of quantum state transfer and preparation, ultrasensitive detection and quantum nondestructive measurement, etc.

Resonant particle creation by a time-dependent potential in a nonlocal theory

Considering an exactly solvable local quantum theory of a scalar field interacting with a δ-shaped time-dependent potential we calculate the Bogoliubov coefficients analytically and determine the spectrum of created particles. We then show how these considerations, when suitably generalized to a specific nonlocal “infinite-derivative” quantum theory, are impacted by the presence of nonlocality. In this model, nonlocality leads to a significant resonant amplification of certain modes, leaving its imprint not only in the particle spectrum but also in the total number density of created particles.

Flow destabilization and nonlinear solutions in low aspect ratio, corrugated duct flows

Flows through narrow, rectangular ducts, with width to height aspect ratio below the established linear stability threshold of 3.2 and modified with grooves on top and bottom walls, are investigated. The primary objective of the current work lies in reintroduction of the linear destabilization mechanism, which is not present for the case of low aspect ratio rectangular ducts, via geometrical modifications of boundaries. The flow is assumed periodic in the streamwise- and bounded by sidewalls in the spanwise-direction. Applied geometrical modifications consist of two wavelengths of sinusoidal grooves running parallel to the flow direction. The current analysis starts with a brief characterization of flows through rectangular ducts and recalls some canonical results on hydrodynamic stability in such flows. In the second part, we illustrate that grooved geometries may lead to the onset of unstable modes in the form of waves traveling downstream, in the case of narrow ducts, already at relatively low values of the Reynolds number. The work is concluded with a concise characterization of flow states resulting from amplification of unstable modes into the nonlinear regime.

Influence of initial phase on subharmonic resonance in an incompressible boundary layer

The influence of the initial phase of fundamental and subharmonic waves on subharmonic resonance is investigated for an incompressible boundary layer with zero and adverse pressure gradients. Parabolized stability equation analyses are carried out for various combinations of the initial phases of fundamental and subharmonic waves. The amplification of subharmonic and higher modes is found to depend strongly on the initial phases, and this dependence is consistent with observations from previous experimental studies. There exists a certain combination of initial phases that leads to resonance or anti-resonance condition (i.e., maximum or minimum growth, respectively). For all combinations of the initial phases, the phase dependence appears to be a function of a single parameter that represents the initial phase difference between the fundamental and subharmonic waves. The amplification in the subharmonic resonant interaction depends on the initial phase difference rather than the individual initial phase of the fundamental or subharmonic wave. In the downstream direction, the phase difference changes from the initial value and eventually converges to a specific value approximately ranging from 80° to 90°, regardless of the initial phase difference. This transient behavior does not start until the subharmonic wave enters the parametric resonant stage, which yields double-exponential growth. The qualitative characteristic of the phase dependence remains unchanged for the fundamental frequencies and spanwise wavenumbers as well as for the pressure gradients studied. The method of analysis and results contribute to the physical foundations of controlling boundary-layer transition dominated by the subharmonic resonance.

Thermally Induced Mode Amplification Characteristics of Large Mode Area Segmented Cladding Fiber

A model of amplifier based on large mode area (LMA) segmented cladding fiber (SCF) is proposed. High order modes (HOMs) filtering effect and thermal-induced modal evolution characteristics are theoretically investigated by the few-mode steady state rate equations and heat conduction equation. Simulation results show that an amplifier based on ytterbium doped SCF presents much better HOMs suppression and mode beam quality than the amplifier based on conventional step-index fiber when achieving single-mode operation by coiling fiber. Furthermore, heat load generating in the core of ytterbium doped SCF can change the pre-designed refractive index profile through the thermo-optic effect, which induces evolution of mode amplification characteristics, including mode loss decreasing and mode area shrinking. And the co-pumping amplifier ytterbium doped SCF is more advantageous to get large mode area of fundamental mode at the output end, while single-mode operation is achieved much more effectively in the counter-pumping amplifier. These results can provide guidance in the design of high-power single-mode fiber amplifier based on rare-earth doped LMA-SCF.

Velocity and temperature fluctuations in a high-speed shock–turbulence interaction

Abstract

Parametric amplification and dispersion characteristics of optical phonon mode in a semiconductor magnetoplasma

Using the classical hydrodynamic model of semiconductor plasmas, the parametric amplification and dispersion characteristics of optical phonon mode in a semiconductor magnetoplasma are investigated analytically. An expression for effective complex second-order optical susceptibility ( $${\chi } _{e}^{(2)} =({\chi }_{e}^{(2)} )_{r} +i({\chi }_{e}^{(2)} )_{i} )$$ is obtained under off-resonant laser irradiation. The analysis deals with qualitative behaviour of threshold pump amplitude ( $${\xi }_{0,\mathrm{th}})$$ for the onset of parametric excitation, anomalous parametric dispersion (via $$({\chi }_{e}^{(2)} )_{r} )$$ and parametric gain coefficient ( $$g_\mathrm{para} $$ via $$({\chi }_{e}^{(2)} )_{i} )$$ with respect to externally applied magnetostatic field ( $$B_{0} )$$ for different values of doping concentration ( $$n_{0} )$$ . Numerical estimates are made for n-InSb–CO $$_{\mathrm {2}}$$ laser system at 77 K. The analysis offers three achievable resonance conditions at which $${\xi }_{0,\mathrm{th}} $$ reduces whereas $$g_\mathrm{para} $$ enhances by two orders of magnitude. The lowering in $${\upxi }_{0,th} $$ and enhancement in $$g_\mathrm{para} $$ , under proper selection of $$B_{0} $$ and $$n_{0} $$ , confirms the chosen nonlinear medium as a potential candidate material for the fabrication of efficient optical parametric amplifiers. The negative and positive enhanced parametric dispersion may be of potential use in the study of squeezed state generation as well as in group velocity dispersion in semiconductor magnetoplasmas.

Development of a collective scattering system and its application to the measurement of multiscale fluctuations in KSTAR plasmas

A four-channel collective scattering system (CSS) has been developed to extend the current turbulence measurement capability (poloidal wavenumber 3 cm−1) beyond the ion gyroscale in the KSTAR tokamak. By utilizing a 300 GHz probe beam and four-channel detector array, the CSS can measure electron density fluctuations of four distinct poloidal wavenumbers from 14 to 26 cm−1 at a high sampling rate (typically 10 MS s−1). In between discharges the radial measurement location can be varied from the plasma center to the outer edge with the remote control of the optical system. In this paper, the details of the major components and laboratory evaluation of the optical system are described. Several initial measurements such as (1) the broadband turbulence reduction during L–H transition, (2) the broadband turbulence increase in H-mode when the amplitude of edge-localized mode crashes is reduced by increased density, (3) the amplification of a quasi-coherent mode by additional heating in high-performance H-mode, and (4) the appearance of high-frequency magnetohydro-dynamical modes during slow L–H transition, are briefly presented. The possibility of the CSS as a hybrid system (of a scattering system and fluctuation interferometer), which complicates the interpretation of the CSS data, is also discussed.

Resonant amplification of intrinsic magnon modes and generation of new extrinsic modes in a two-dimensional array of interacting multiferroic nanomagnets by surface acoustic waves.

Using time-resolved magneto-optical Kerr effect (TR-MOKE) microscopy, we demonstrate surface-acoustic-wave (SAW) induced resonant amplification of intrinsic spin-wave (SW) modes, as well as generation of new extrinsic or driven modes at the SAW frequency, in a densely packed two-dimensional array of elliptical Co nanomagnets fabricated on a piezoelectric LiNbO3 substrate. This system can efficiently serve as a magnonic crystal (MC), where the intrinsic shape anisotropy and the strong inter-element magnetostatic interaction trigger the incoherent precession of the nanomagnets' magnetization in the absence of any bias magnetic field, giving rise to the 'intrinsic' SW modes. The magnetoelastic coupling leads to a rich variety of SW phenomena when the SAW is launched along the major axis of the nanomagnets, such as 4-7 times amplification of intrinsic modes (at 3, 4, 7 and 10 GHz) when the applied SAW frequencies are resonant with these frequencies, and the generation of new extrinsic modes at non-resonant SAW frequencies. However, when the SAW is launched along the minor axis, a dominant driven mode appears at the applied SAW frequency. This reveals that the magnetoelastic coupling between SW and SAW is anisotropic in nature. Micromagnetic simulation results are in qualitative agreement with the experimental observations and elucidate the underlying dynamics. Our findings lay the groundwork for bias-field free magnonics, where the SW behavior is efficiently tuned by SAWs. It has important applications in the design of energy efficient on-chip microwave devices, SW logic, and extreme sub-wavelength ultra-miniaturized microwave antennas for embedded applications.

弯曲限模对大模场光纤横模不稳定效应的影响

The effect of transverse mode instability has gradually become the primary problem that causes laser beam quality degradation and limits power scaling of high-power fiber lasers. This paper conducts a series of study on the transverse mode instability (TMI) in large mode area (LMA) fiber based on a co-pumped all-fiberized narrow linewidth high power amplification platform. According to the calculation results of the coupled mode equations, the nonlinear coupling strength between the LP01 and LP11 modes of the LMA fiber 25/400 μm is the largest, which directly induces the TMI. In order to suppress the generation and amplification of the LP11 mode at the main amplifier, the fiber coiling method was used as an operational mode filtering technique to achieve mode control. The threshold of TMI increased from 1000 W to 1600 W while reducing the bending radius of the main amplifier gain fiber from 6 cm to 5 cm, and the other output performance of the fiber laser was hardly affected. This provides a powerful experimental reference for us to build an actual narrow linewidth, high power, all-fiberized laser system.

Quasinormal-Mode Perturbation Theory for Dissipative and Dispersive Optomechanics.

Despite the several novel features arising from the dissipative optomechanical coupling, such effect remains vastly unexplored due to the lack of a simple formalism that captures non-Hermiticity in the engineering of optomechanical systems. In this Letter, we show that quasinormal-mode-based perturbation theory is capable of correctly predicting both dispersive and dissipative optomechanical couplings. We validate our model through simulations and also by comparison with experimental results reported in the literature. Finally, we apply this formalism to plasmonic systems, used for molecular optomechanics, where strong dissipative coupling signatures in the amplification of vibrational modes could be observed.

A 10-kS/s 625-Hz-Bandwidth 65-dB SNDR Second-Order Noise-Shaping SAR ADC for Biomedical Sensor Applications

This paper introduces a low-power noise-shaping SAR ADC which is suitable for biomedical sensor applications. In this ADC, a low power consumption and area-efficient integrator is proposed, which is comprised of several switches, replica capacitors and a dynamic amplifier (DA). With a mode control logic circuit, the comparator in the ADC is reused as an amplifier for three times (three amplification phases) in a single conversion period to save area and power consumption. With the introduction of the first amplification phase, the additional capacitance can be greatly reduced without increasing overall kT/C noise. The second and third amplification phases decouple NTF zeros from the attenuation factor, allowing further area reduction. The comparator in amplification mode is designed more robust than prior arts. Fabricated in 0.18μm CMOS process, the prototype ADC has a 7-bit DAC and occupies a core area of 0.12mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Operating at 10kS/s, it consumes 90nW from a 1-V supply. At an OSR of 8, the SAR ADC achieves 65dB SNDR resulting in a FoMs of 163.5dB, and a FoMw of 50fJ/conv.-step.