Trapped Modes Research Articles

865. NEPENTHES DUBIA

The history, taxonomic placement, relationships, mode of trapping and cultivation of Nepenthes dubia Danser, an epiphytic fly‐eater from the cloud forests of the Bukit Barisan range of the west coast of Sumatra, are discussed. This is one of the eight species of Sect. Montanae Danser with ‘egg‐cup’ like pitchers. A key is provided to the eight species and they are formally named as Nepenthes Sect. Montanae subsect. Poculae‐ovis.

Effect of nonlinear internal wave on monostatic reverberation in the shallow water region with underwater sound channel

The effect of nonlinear internal wave on reverberation is investigated for the shallow water region having an underwater sound channel, which was observed during SAVEX15 experiment. When source is located near the channel axis, the reverberation from rough bottom is insignificant because of trapped modes not interacting with the bottom. However, when a nonlinear internal wave is present, the reverberation level increases since trapped modes transfer to bottom interacting modes due to sound fluctuation by the nonlinear internal wave. This trend can be explained by the coupled mode equation [(2014). J. Acoust. Soc. Am. 135, 610-625]. To theoretically describe the increase of bottom reverberation, we simplify the situation where two modes are present; one is a trapped mode and the other is bottom interacting mode. In the situation, the trapped mode transfers to the bottom interacting mode after its encounter with the nonlinear internal wave. The bottom reverberation has different patterns and levels before and after the internal wave, and thus, it highly depends on the distance between source/receiver and internal wave.

Gyrokinetic simulation of dissipative trapped electron mode in tokamak edge

The gyrokinetic simulation using the gyrokinetic toroidal code (GTC) is carried out for the dissipative trapped electron mode (DTEM), which is an important source for the electrostatic turbulence in the pedestal of tokamak plasmas. The DTEM instability is identified for the edge plasmas, and its dependence on the wavelength and collisional frequency is obtained by both simulation and theory. It is shown for the first time that the linear gyrokinetic simulation results are fully consistent with that from the analytic theory with edge parameters. This suggests that the GTC code can simulate accurately the DTEM instability in the pedestal. It provides a useful benchmark for verifying gyrokinetic simulation of edge plasmas.

Investigation of the interaction between competing types of nondiffusive transport in drift wave turbulence

Radial transport in turbulence dominated tokamak plasmas has been observed to deviate from classical diffusion in certain regimes relevant for magnetic confinement fusion. These situations at least include near-marginal turbulence, where radial transport becomes superdiffusive and mediated by elongated radial structures (or avalanches) and transport across radially sheared poloidal flows, where radial subdiffusion often ensues. In this paper, the interaction between very different physical ingredients responsible for these two types of nondiffusive dynamics (namely, turbulent profile relaxation close to a local threshold and the interaction with radially sheared zonal flows) is studied in detail in the context of a simple two-dimensional electrostatic plasma fluid turbulence model based on the dissipative trapped electron mode. It is shown that, depending on the relative relevance of each of these ingredients, which can be tuned in various ways, a variety of non-diffusive radial transport behaviors can be found in the system. The results also illustrate the fact that the classical diffusion paradigm is often insufficient to describe turbulent transport in systems with self-generated flows and turbulent profile relaxations.

Free-volume defects investigation of GeS2-Ga2S3-CsI chalcogenide glasses by positron annihilation spectroscopy

The transformation behavior of free-volume defect in (80GeS2-20Ga2S3)100-x (CsI)x (x=0, 5, 10, 15mol%) chalcogenide glasses was studied by employing positron annihilation spectroscopic technique, which could reveal valuable information for in-depth understanding of nano-structural defects in glassy matrix. The results indicate that the structural changes caused by CsI additives can be adequately described by positron trapping modes determined with two-state model. The initial addition of CsI (x=5mol%) led to a void contraction, whereas, the void agglomeration occurred with the increase of CsI and the free-volume defects of the glasses were obviously reduced. The atomic density ρ is inversely proportional to the number of these defects. Meanwhile, the UV cut-off edge shifts toward short-wavelength with increasing of CsI. This study provides the valuable information of defects evolution in GeS2-Ga2S3-CsI glasses.

Methodology and Characterization of Isolation and Preconcentration in a Gas-Filled Digital Linear Ion Guide.

Digital operation of linear ion guides allows them to operate as traps and mass filters by modulating the duty cycles of the two driving waveforms. A gas-filled (5 mTorr) digitally driven quadrupole ion guide was used to demonstrate ion isolation and preconcentration. These abilities allow ion trapping mass spectrometers to be filled to capacity with only ions in the range of interest at essentially any value of m/z. Due to the unique performance characteristics of digitally operated quadrupoles, isolation with purely duty cycle enhanced waveforms was developed with three increasingly sophisticated isolation methods. First, the guide was used as a gas-filled transmission mass filter using the waveform duty cycle to generate a narrow mass window. The second method used broadband trapping to collect ions and translationally cool along the transmission axis before shifting the duty cycle to filter the trapped ions. A subsequent duty cycle change axially ejected the filtered population for measurement. The third method improved resolution by shifting the operating frequency during isolation. The resolving power was optimized with the shift frequency to yield a device limited resolving power of 400 (m/Δm). It is the temporal control of the duration of the isolation process that sets digital waveform based isolation apart from the current technology and that minimizes ion loss even when the mass is very large. Preconcentration by repeated trapping and isolation of an individual charge state was also demonstrated to saturate the ion guide with that charge state. These digital isolation and preconcentration techniques will permit the same isolation resolution (m/Δm) at any value of mass or m/z without significant ion loss as long as the secular frequencies do not significantly overlap while in the trapping mode. It is therefore ideal for the isolation and preconcentration of single charge states of large proteins and complexes.

Trapped modes and resonances in gyrotropic graphene stacks

This paper examines the anomalous electromagnetic wave interactions with gyrotropic graphene-dielectric stacks and characterizes their perturbed wave resonances. Expressions for the dispersion relations, trapped mode condition, and the propagating and evanescent modes in the gyrotropic graphene stack have been derived and numerically quantified. The evanescent modes supported in the ambient medium couple as propagating modes in the gyrotropic graphene-dielectric stack at the discrete frequencies of the trapped modes. Valuation of the resonances in the material tensor and the resonances around the trapped modes that result in transmission anomalies (total transmission and total reflection) and field amplifications in the gyrotropic graphene is described. The effects of the chemical potential and the external magnetic field on the number of discrete trapped modes and subsequently on the transmission resonances are numerically assessed.

Resonances in graphene-dielectric stacks

BackgroundThis paper presents a comprehensive theoretical investigation of the anomalous electromagnetic wave propagation and resonances around the trapped modes embedded in graphene dielectric stacks.ResultsExpressions for the dispersion relation, the condition of the trapped mode, the transmission coefficient, and the instantaneous field components through the graphene stack are derived. Evanescent mode coupling to the graphene-dielectric stack arises at the discrete frequencies of the trapped modes. When the wavevector is perturbed, resonances occur around the trapped modes which results in transmission anomalies and dramatic field amplification in graphene stacks.ConclusionsAnomalous electromagnetic wave propagation and resonances in graphene-dielectric stacks are reconnoitered. The number of the conceivable discrete trapped modes and consequently the resonances in graphene-dielectric stacks can be adjusted by the graphene chemical potential.

Optimization of CFETR baseline performance by controlling rotation shear and pedestal collisionality through integrated modeling

The optimization of a CFETR baseline scenario (Chan et al 2015 Nucl. Fusion 55 023017) with an electron cyclotron (EC) wave and neutral beam (NB) is performed using a multi-dimensional code suite. TGLF and NEO are used to calculate turbulent and neoclassical transport. The evaluation of sources and sinks, as well as the current evolution, are performed using ONETWO, and the equilibrium is updated using EFIT. The pedestal is consistent with the EPED model.Rotation shear is controlled using NB. It has been found that both fusion gain Q and NB power deposited in the edge increase with decreasing NB energy, with NB providing current drive, torque, energy and particle source simultaneously. By using an optimized combination of two NBs, Q can be kept at a high level while the NB edge power is reduced. Pedestal collisionality is controlled to find an optimization path for Q by trading off between the pedestal density and temperature with the pedestal pressure fixed. It has been found that Q increases with pedestal collisionality, while the density peaking factor (DPF) remains almost unchanged. The invariance of DPF can be explained by the change of the dominant type of turbulence from the core to the edge (i.e. trapped electron mode in the core and ion temperature gradient mode at the edge), and collisionality has the opposite effect on particle transport for these two modes. A weaker dependence of DPF on collisionality makes a higher density operation more favorable for fusion gain.

Electromagnetic Tunneling and Resonances in Pseudochiral Omega Slabs

This paper presents theoretical investigation of the electromagnetic wave tunneling and anomalous transmission around the trapped modes in a pseudochiral omega slab. The dispersion relation, the conditions of the trapped modes, and the evanescent wave coupling and tunneling in two different reciprocal pseudochiral omega slab structures are derived. The Berreman’s matrix method is applied to obtain the transmission coefficients across the pseudochiral omega slab. When the structure is perturbed, a resonance phenomenon is detected around the trapped modes. This resonance results in transmission anomalies (total transmission and total reflection) and dramatic field amplifications around the trapped modes. The number of the discrete trapped modes and then the resonance frequencies are prescribed by the parameters of the pseudochiral omega slab such as the value of the omega parameter and its orientation and the slab thickness.

Electromagnetic Coupling and Tunneling Through Chiral Layers

This paper presents a theoretical investigation of electromagnetic wave coupling and tunneling through chiral-chiral interfaces. The dispersion relation, conditions of the trapped modes, and evanescent wave coupling and tunneling in an optically active chiral slab and chiral ambient medium are derived. The transfer matrix method is developed to obtain the transmission and reflection coefficients across the chiral slab. The formation of discrete trapped modes and the continuous interval, where the discrete trapped modes are embedded, are determined by the chirality parameter of the chiral slab. The instantaneous field components, revealed via evanescent wave coupling and tunneling through the chiral slab interfaces, are also reported.

Trapped-wave modes of bodies in channels

Trapped waves can exist in the presence of bodies in open water, and also in channels of finite width. Various examples are found for bodies that support trapped waves in channels, including floating and submerged bodies and bottom-mounted cylinders. Different types of trapping are considered where the body is fixed or free to move in response to the oscillatory pressure. In some cases both types are supported by the same body. In most cases for fixed bodies the fluid motion is antisymmetric about the centreline of the channel, but special body shapes exist where the trapped mode is asymmetric. For free bodies the trapping modes and body motions are symmetric about the centreline if the body is floating or antisymmetric if it is submerged.

테라헤르츠 비대칭 분리고리공진기 메타물질의 높은 품질인자를 위한 공진 특성에 관한 연구

본 논문에서는 높은 감도의 테라헤르츠 센서로 응용이 가능한 고품질 비대칭 분리고리공진기(ASLR: Asymmetric Split-Loop Resonator) 메타물질의 구조적인 비대칭 정도에 따른 ASLR의 공진특성 변화를 전자기 시뮬레이션을 통하여 분석하였다. 특히, ASLR의 구조적 비대칭성은 높은 품질인자를 갖는 파노공진을 발생시키므로 ASLR의 비대칭성 정도에 따라서 ASLR 고유공진과 파노공진의 공진주파수 변화와 투과계수 및 품질인자의 변화를 분석하였다. 또한, ASLR의 구조적 비대칭성에 따른 ASLR의 공진 특성 변화의 원인을 분석하기 위해 표면전류밀도를 계산하여 ASLR 공진의 공진주파수, 투과계수, 그리고 품질인자가 변화하는 이유를 분석하였다. 이를 통하여 ASLR 고유공진의 표면전류밀도는 이중 극자를 형성하여 높은 방사 손실을 가지게 되므로 품질인자가 낮아지게 되고, 파노공진의 표면전류밀도는 닫힌 모드 또는 사중 극자를 형성하여 이중 극자에 비하여 낮은 방사 손실을 가지므로 파노공진 상태의 ASLR이 높은 품질인자를 가지게 됨을 확인하였다. 이러한 ASLR의 파노공진 특성 분석 결과를 바탕으로 메타물질의 비대칭성을 조절하면 높은 품질인자를 가지는 테라헤르츠 고성능 필터 또는 고감도 센서 개발이 가능하다. 이러한 고감도 고성능 테라헤르츠 소자 개발은 테라헤르츠 메타물질의 실질적인 산업 응용을 유도할 것으로 기대한다. A terahertz asymmetric split-loop resonator (ASLR) was analyzed for use in high-sensitivity sensing applications. Its structural asymmetricity induces an asymmetric Fano resonance which has a high quality factor compared to the symmetric eigen-resonance. The variations of the resonant frequency, transmission coefficient, and quality factor of the ASLR in the eigen and Fano resonances are analyzed as a function of its structural asymmetricity. Also, the surface current densities on the ASLR in both resonances are calculated to analyze the main cause of the variations of its transmission characteristics. The surface current of the ASLR in the eigen resonance shows a dipole resonance, which increases the radiation loss and reduces the quality factor. On the other hand, the surface current of the ASLR in the Fano resonance shows a trapped or quadrupole mode which has a low radiation loss. Therefore, the ASLR operated in the Fano resonance has a high quality factor. Terahertz, high-performance filters and high sensitivity sensors can be developed based on our analysis results of the ASLR having a high quality factor. These high-performance devices based on terahertz metamaterials could increase the adoption of terahertz industrial applications.

The effects of near-core convective shells on the gravity modes of the subdwarf B pulsator KIC 10553698A

KIC 10553698A is a hot pulsating subdwarf B (sdB) star observed by the Kepler satellite. It exhibits dipole (l = 1) and quadrupole (l = 2) gravity modes with a clear period spacing structure. The seismic properties of the KIC 10553698A provide a test of stellar evolution models, and offer a unique opportunity to determine mixing processes. We consider mixing due to convective overshooting beyond the boundary of the helium burning core. Very small overshooting ( f = 10^{-6} ) results in a progressive increase in the size of convective core. However, moderate ( f = 10^{-2} ) and small ( f = 10^{-5} ) overshooting both lead to the occurrence of inert outer convective shells in the near-core region. We illustrate that the chemical stratifications induced by convective shells are able to change the g-mode period spacing pattern of a sdB star appreciably. The mean period spacing and trapping of the gravity modes in the model with moderate and small core overshooting are fully consistent with the period spacing trends observed in KIC 10553698A. Atomic diffusion driven by gravitational settling as well as thermal and chemical gradients is applied to reach a better match with the observed period spacings. Models that include small or very small overshooting with atomic diffusion have a decreased lifetime of the extreme horizontal branch phase and produce chemical stratification induced by convective shells during helium burning phase. In addition of being consistent with asteroseismology, their calculated values of the R2 parameter are more compatible with the observed R2 values.

Trapped-mode resonances in a Voigt plasma layer

This paper examines the resonant transmission of electromagnetic waves around the trapped modes of a magnetized plasma layer. Expressions for the dispersion relation, the evanescent wave coupling and tunneling, and the condition of trapped modes in the anisotropic Voigt plasma configuration have been derived and quantified. The transfer matrix method is applied to obtain the transmission coefficients across the plasma layer. When the structure is perturbed, resonance is identified around the embedded trapped modes. This resonance results in transmission anomalies (total transmission and total reflection) and dramatic field amplifications around the trapped modes. The number of discrete trapped modes and then the resonance frequencies are prescribed by the parameters of the plasma layer, such as the plasma frequency, the cyclotron frequency, and the layer thickness.

Novel control modes to improve the performance of rectilinear ion trap mass spectrometer with dual pressure chambers.

The rectilinear ion trap (RIT) has gradually become one of the preferred mass analyzers for portable mass spectrometers because of its simple configuration. In order to enhance the performance, including sensitivity, quantitation capability, throughput, and resolution, a novel RIT mass spectrometer with dual pressure chambers was designed and characterized. The studied system constituted a quadrupole linear ion trap (QLIT) in the first chamber and a RIT in the second chamber. Two control modes are hereby proposed: Storage Quadrupole Linear Ion Trap-Rectilinear Ion Trap (SQLIT-RIT) mode, in which the QLIT was used at high pressure for ion storage and isolation, and the RIT was used for analysis; and Analysis Quadrupole Linear Ion Trap-Rectilinear Ion Trap (AQLIT-RIT) mode, in which the QLIT was used for ion storage and cooling. Subsequently, synchronous scanning and analysis were carried out by QLIT and RIT. In SQLIT-RIT mode, signal intensity was improved by a factor of 30; the limit of quantitation was reduced more than tenfold to 50 ng mL-1, and an optimal duty cycle of 96.4% was achieved. In AQLIT-RIT mode, the number of ions coexisting in the RIT was reduced, which weakened the space-charge effect and reduced the mass shift. Furthermore, the mass resolution was enhanced by a factor of 3. The results indicate that the novel control modes achieve satisfactory performance without adding any system complexity, which provides a viable pathway to guarantee good analytical performance in miniaturization of the mass spectrometer.

Observation of trapped light induced by Dwarf Dirac-cone in out-of-plane condition for photonic crystals**Project supported by Director, CSIR-CGCRI, the DST, Government of India, and the CSIR 12th Plan Project (GLASSFIB), India.

Existence of out-of-plane conical dispersion for a triangular photonic crystal lattice is reported. It is observed that conical dispersion is maintained for a number of out-of-plane wave vectors (kz). We study a case where Dirac like linear dispersion exists but the photonic density of states is not vanishing, called Dwarf Dirac cone (DDC) which does not support localized modes. We demonstrate the trapping of such modes by introducing defects in the crystal. Interestingly, we find by k-point sampling as well as by tuning trapped frequency that such a conical dispersion has an inherent light confining property and it is governed by neither of the known wave confining mechanisms like total internal reflection, band gap guidance. Our study reveals that such a conical dispersion in a non-vanishing photonic density of states induces unexpected intense trapping of light compared with those at other points in the continuum. Such studies provoke fabrication of new devices with exciting properties and new functionalities.

Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry

Linear (local) gyrokinetic predictions of edge microinstabilities in highly shaped, lithiated and non-lithiated NSTX discharges are reported using the gyrokinetic code GS2. Microtearing modes dominate the non-lithiated pedestal top. The stabilization of these modes at the lithiated pedestal top enables the electron temperature pedestal to extend further inwards, as observed experimentally. Kinetic ballooning modes are found to be unstable mainly at the mid-pedestal of both types of discharges, with unstable trapped electron modes nearer the separatrix region. At electron wavelengths, electron temperature gradient (ETG) modes are found to be unstable from mid-pedestal outwards for ηe, exp ∼2.2, with higher growth rates for the lithiated discharge. Near the separatrix, the critical temperature gradient for driving ETG modes is reduced in the presence of lithium, reflecting the reduction of the lithiated density gradients observed experimentally. A preliminary linear study in the edge of non-lithiated discharges shows that the equilibrium shaping alters the electrostatic modes stability, which was found more unstable at high plasma shaping.

Trapped modes in an infinite or semi-infinite tube with a local enlargement

Trapped modes in a hard cylindrical tube with a local axisymmetric enlargement or bulge and filled with a uniform acoustic medium is studied. The governing Helmholtz equation in the cylindrical coordinate system is employed to deal with this problem through the domain decomposition method and matching technique. The trapped modes and the corresponding frequencies less than the threshold frequency or cut-off frequency are derived. It is found that in addition to the fundamental mode, the second- and higher-order trapped modes exist and depend on the geometry parameters of the local bulge. The effects of the bulge radius and width on the frequencies are discussed. The local bulge leads to a decrease of the frequencies and the corresponding vibration mode is localized near the bulge. A multimodal analysis is made and frequency band gap of generalized trapped modes is also studied. A frequency band gap depends on the radius of a bulge and is independent of its width. The obtained results can be extended to analyze bound states in quantum wires.

Scattering of flexural waves by a pit of quadratic profile inserted in an infinite thin plate

An acoustic black hole (ABH) is a pit of power law profile inserted in a plate with internal damping. Such a pit with varying thickness leads to local variations of wave propagation properties and has been found to be an efficient vibration damper. In this paper, the ABH is seen as a penetrable obstacle and is studied through its scattering properties. A wave based model is developed within the framework of the Kirchhoff theory for a thin plate of locally varying thickness. It is shown that analytical solutions can be found in the case of a pit of quadratic profile and for uniform damping properties (without added layer). A major outcome of the model is the derivation of the dispersion relations giving a detailed analysis of the behavior of the waves within the ABH. Particularly, cut-on frequencies below which no wave propagates within the ABH are derived and thus give interpretation of the well known typical ABH efficiency threshold frequency for damping vibrations. The analysis is led from numerical computations of the dispersion curves, the scattering diagrams and the scattering cross-section, which are compared to the case of a simple hole. The results show that the ABH behaves as a resonant scatterer, which is a key outcome of this study. The so-called trapped modes, which describe free damped oscillations of the ABH, are responsible for variations of the scattering cross-section with frequency. These variations are investigated thanks to a parametric study on the geometrical properties of the ABH.