Monopole Mode Research Articles

Temperature-sensitive hybridization of propagating and localized surface phonon polaritons in polar 4H-SiC nano-resonators

Polar 4H-SiC nano-resonators can host localized surface phonon polaritons (SPhPs) with low optical loss and fully exploit light–matter interactions for promising nanophotonic applications such as surface-enhanced spectroscopies and thermal imaging. To expand the mid-infrared and infrared application spaces, a sound knowledge of temperature effect on infrared dielectric functions and SPhPs of 4H-SiC is required, yet it remains largely unexplored. Herein, we focus on exploiting the temperature influence on dielectric functions, hybridization of propagating and localized SPhPs, and tailed spectral radiation properties of 4H-SiC nanopillar arrays through spectroscopic ellipsometry (SE) measurements as well as multiscale simulations. The 4H-SiC crystal is grown using the physical vapor transport method, and SE experiments measure infrared dielectric functions at temperatures between 300 and 800 K. Finite-element electromagnetic simulations confirm the emerged Monopole and transverse dipoles (TD1 and TD2) resonance modes in 4H-SiC nano-resonators, which agrees with the literature experiment. At high temperatures with strong lattice vibration, the amplitudes of resonant optical absorption peaks gradually decrease and the linewidths broaden, accompanied by the weakened electric resonances. First-principles calculations show that the anharmonic phonon scattering strengthens and less optical phonons are coupled to incident photons as temperature increases. Moreover, the propagating and localized SPhPs’ hybridization and spectral radiation properties of 4H-SiC nanopillar arrays can be largely tailed by modifying the morphology and incident angle of light. This work provides physical insights into the temperature-induced spectral tuning of 4H-SiC nano-resonators and helps exploit their applications in the high-temperature working conditions.

Finite amplitude method on the deformed relativistic Hartree-Bogoliubov theory in continuum: The isoscalar giant monopole resonance in exotic nuclei

Finite amplitude method based on the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc-FAM) is developed and applied to study isoscalar giant monopole resonance in exotic nuclei. Validation of the numerical implementation is examined for $^{208}\textrm{Pb}$. The isoscalar giant monopole resonances for even-even calcium isotopes from $^{40}\textrm{Ca}$ to the last bound neutron-rich nucleus $^{80}\textrm{Ca}$ are calculated, and a good agreement with the available experimental centroid energies is obtained for $^{40-48}\textrm{Ca}$. For the exotic calcium isotopes, e.g., $^{68}\textrm{Ca}$ and $^{80}\textrm{Ca}$, the DRHBc-FAM calculated results are closer to the energy weighted sum rule than the calculations on the harmonic oscillator basis, which highlights the advantages of DRHBc-FAM in describing giant resonances for exotic nuclei. In order to explore the soft monopole mode in the exotic nuclei, the giant monopole resonance for the deformed exotic nucleus $^{200}\textrm{Nd}$ is investigated, where the prolate shape and the oblate shape coexist. A soft monopole mode near 6.0 MeV is found in the prolate case, and another one near 4.5 MeV is found in the oblate case. The transition density of the soft monopole mode shows in phase or out-of-phase vibrations near the surface region, which is generated by quadrupole vibrations.

A Broadband Antenna Based on a Single CRLH TL Unit Cell and a Parasitic Strip for Sub-1GHz DVB and LTE Applications

A Broadband and slim profile antenna based-on a single composite right/left-handed transmission line unit cell and parasitic shorted strip is presented for sub-1 GHz digital video broadcasting and long-term evolution applications (470-970 MHz). It is comprised of an ungrounded coplanar waveguide that feeds a meandered strip (distributed series inductors), which is connected through capacitive coupling (series capacitance) with a virtual small ground, while an upper shorted meandered strip represents a parallel inductor. A shorted meandered strip (parasitic inductor) is added to create a third resonant frequency. A broadband operation is achieved by merging three different resonant modes frequencies (zeroth-order mode and two quarter wavelength monopole modes) to satisfy 6 dB bandwidth criterion. A prototype is constructed and measured in order to verify the achieved results. The results of reflection parameter, gain, efficiency, patterns and bandwidth efficiency product are presented, discussed, and evaluated with respect to literature. The results show that the proposed antenna is a potential candidate for recent broadband digital video broadcasting applications.

Thermodynamic contacts and breathing-mode physics of one-dimensional p -wave Fermi gases in the high-temperature limit

An important tool for understanding the effects of interactions in harmonically trapped atomic gases is the examination of their collective modes. One such mode is the breathing or monopole mode, which is special as it is constrained to occur at twice the harmonic trapping frequency when the interactions are scale invariant. When the interactions are not scale invariant, the frequency of the breathing mode will deviate from twice the trap frequency. The deviation itself depends on the thermodynamic contacts, which describe how the energy changes with the interactions. In this work I examine how the thermodynamic contacts and the breathing mode frequency of a spin-polarized one-dimensional (1D) p-wave Fermi gas depend on the 1D scattering volume, $\ell$, and the effective range, $r$, in the high temperature limit. Such dynamics can be studied in experiments and provide a tool for understanding how the dynamics depend on interactions with a finite effective range.

Deep inelastic collision of two-dimensional anisotropic dipolar condensate solitons

The possibility of generating stable anisotropic solitons in dipolar Bose–Einstein condensates (BECs) leads to a different scenario not possible in a nondipolar BEC with contact interaction. We study the statics and dynamics of anisotropic bright solitons in quasi-two-dimensional BECs consisting of polarized dipolar atoms. We study the collision dynamics of two such solitons at different velocities for different angles between the polarization and collision directions. The collision is found to be quasi elastic at large velocities. At small velocities the collision is inelastic leading to the formation of a coalesced soliton in an excited scissors mode, monopole mode or quadrupole mode. Also, at small velocities, after collision, a large change of direction of motion of the solitons is possible. The investigation is performed through a numerical solution of the underlying mean-field Gross–Pitaevskii equation.

Electrostatic Model for Antenna Signal Generation From Dust Impacts

AbstractDust impacts on spacecraft are commonly detected by antenna instruments as transient voltage perturbations. The signal waveform is generated by the interaction between the impact‐generated plasma cloud and the elements of the antenna–spacecraft system. A general electrostatic model is presented that includes the two key elements of the interaction, namely the charge recollected from the impact plasma by the spacecraft and the fraction electrons and cations that escape to infinity. The clouds of escaping electrons and cations generate induced signals, and their vastly different escape speeds are responsible for the characteristic shape of the waveforms. The induced signals are modeled numerically for the geometry of the system and the location of the impact. The model employs a Maxwell capacitance matrix to keep track of the mutual interaction between the elements of system. A new reduced‐size model spacecraft is constructed for laboratory measurements using the dust accelerator facility. The model spacecraft is equipped with four antennas: two operating in a monopole mode, and one pair configured as a dipole. Submicron‐sized iron dust particles accelerated to >20 km/s are used for test measurements, where the waveforms of each antenna are recorded. The electrostatic model provides a remarkably good fit to the data using only a handful of physical fitting parameters, such as the escape speeds of electrons and cations. The presented general model provides the framework for analyzing antenna waveforms and is applicable for a range of space missions investigating the distribution of dust particles in relevant environments.

Ocean salinity indices of interannual modes in the tropical Pacific

This study investigates the interannual modes of the tropical Pacific using salinity from observations, ocean reanalysis output and CMIP6 products. Here we propose two indices of sea surface salinity (SSS), a monopole mode and a dipole mode, to identify the El Niño—South Oscillation (ENSO) and its diversity, respectively. The monopole mode is primarily controlled by atmospheric forcing, namely, the enhanced precipitation that induces negative SSS anomalies across nearly the entire tropical Pacific. The dipole mode is mainly forced by oceanic dynamics, with zonal current transporting fresh water from the western fresh pool into the western-central and salty water from the subtropics into the eastern tropical Pacific. Under a global warming condition, an increase in the monopole and dipole mode variance indicates an increase in both the central and eastern Pacific El Niño variability. The increase in central Pacific El Niño variability is largely due to enhanced vertical stratification during global warming in the upper layer, with intensified zonal advection. An eastern Pacific El Niño-like warming pattern contributes to the increase in eastern Pacific El Niño, with enhanced precipitation over the central-eastern tropical Pacific.

Mean acoustic fields exerted on a subwavelength axisymmetric particle.

The acoustic radiation force produced by ultrasonic waves is the "workhorse" of particle manipulation in acoustofluidics. Nonspherical particles are also subjected to a mean torque known as the acoustic radiation torque. Together they constitute the mean acoustic fields exerted on the particle. Analytical methods alone cannot calculate these fields on arbitrarily shaped particles in actual fluids and are no longer fit for purpose. Here, a semi-analytical approach is introduced for handling subwavelength axisymmetric particles immersed in an isotropic Newtonian fluid. The obtained mean acoustic fields depend on the scattering coefficients that reflect the monopole and dipole modes. These coefficients are determined by numerically solving the scattering problem. Our method is benchmarked by comparison with the exact result for a subwavelength rigid sphere in water. Besides, a more realistic case of a red blood cell immersed in blood plasma under a standing ultrasonic wave is investigated with our methodology.

Proposal of a gauge-invariant treatment of l = 0, 1-mode perturbations on Schwarzschild background spacetime

A gauge-invariant treatment of the monopole (l = 0) and dipole (l = 1) modes in linear perturbations of the Schwarzschild background spacetime is proposed. Through this gauge-invariant treatment, we derived the solutions to the linearized Einstein equation for these modes with a generic matter field. In the vacuum case, these solutions include the Kerr parameter perturbations in the l = 1 odd modes and the additional mass parameter perturbations of the Schwarzschild mass in the l = 0 even modes. The linearized version of Birkhoff’s theorem is also confirmed in a gauge-invariant manner. In this sense, our proposal is reasonable.

Evolution of soft monopole mode in the even-even nickel isotopes Ni58–68

The finite amplitude method is implemented for covariant density functional theory with the point-coupling functional PC-PK1 for deformed nuclei. The giant monopole resonances for even-even nickel isotopes $^{58\text{--}68}\mathrm{Ni}$ are studied. The experimentally reported soft monopole mode, a distinct form of nuclear compressional mode, for the unstable nucleus $^{68}\mathrm{Ni}$ is well reproduced. The evolution of the soft monopole mode in neutron-rich nickel isotopes is shown. Microscopic analysis of the transition density shows that the soft monopole mode is dominated by neutron vibrations.

Formal Solutions of Any-Order Mass, Angular-Momentum, andDipole Perturbations on the Schwarzschild Background Spacetime

Formal solutions of any-order mass, angular-momentum, dipole perturbations on the Schwarzschild background spacetime are derived in a gauge-invariant manner. Once we accept the proposal in [K. Nakamura, Class. Quantum Grav. {\bf 38} (2021), 145010.], we can extend the gauge-invariant linear perturbation theory on the Schwarzschild background spacetime including the monopole ($l=0$) and dipole ($l=1$) modes to any-order perturbations of the same background spacetime through the arguments in [K. Nakamura, Class. Quantum Grav. {\bf 31} (2014), 135013.]. As a result of this resolution, we reached to a simple derivation of the above formal solutions of any order.

Multiple Integrated Antennas for Wearable Fifth-Generation Communication and Internet of Things Applications

This paper proposes integrating multiple antennas into wearable devices for application in fifth-generation (5G) communications and the Internet of Things (IoT). The frequency bands covered were wireless local area network 2.4-GHz/5-GHz channels (2410–2484 MHz), the global positioning system (1575 MHz), narrowband IoT band 8 (880–960 MHz), Global System for Mobile Communications 850/900, and the 5G frequency range 1 n77/78/79 band (3300–5000 MHz). The antennas were configured as a $2\times2$ multiple-input multiple-output system (MIMO). The antenna resonance contribution integrates the slot mode, monopole mode of the three-dimensional frame, and loop coupling monopole mode. The configuration of the independent matching circuits facilitated the effective control of the desired mode and the coverage of the desired bands. All integrated antennas were placed in a watch device ( $37\times 43\times8$ mm3) with a metal body and a metal strap. An integrated miniaturized antenna was designed. The diversity gain and multiplexing efficiency between the MIMO antennas were 9.97dB and above −2dB, respectively. Favorable diversity performance was confirmed. The channel capacity of the $2\times $ 2 MIMO array was determined to be 8.8 bps/Hz. Moreover, its performance was evaluated through the addition of a hand tissue module. The impact of metal straps on antenna radiation performance was discussed. The specific absorption rate (SAR) was examined, and the best results obtained under an SAR of 1 g and 10 g were 0.25 and 0.58 W/kg, respectively. The findings demonstrate the suitability of the antenna for practical applications in 5G communication systems and the IoT.

Compact Shared Aperture Quasi-Yagi Antenna With Pattern Diversity for 5G-NR Applications

A novel shared aperture planar quasi-Yagi antenna with complementary pattern (as well as polarization) diversity performance is presented for fifth generation (5G)-new radio (NR) application. A shared aperture antenna with high port isolation and a compact size is first proposed by the even-odd mode feedings. Then, by combining the monopole and dipole modes, the novel pattern reconfigurable method is studied step by step using the surface current distribution. By controlling the feeding states of the monopole and dipole elements, a pattern reconfigurable Yagi antenna with four modes (omnidirectional, broadside, and two tilted patterns) is realized. The quasi-Yagi antenna, which exhibits a compact size of 0.511λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.244λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.005λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , is fabricated and measured for experimental verification. The measured -10 dB bandwidth of the four modes all basically covers the 5G-N78 band 3.3-3.8 GHz (14.1%). The measured peak radiation efficiency is greater than 80%. The proposed compact antenna, with the advantages of low-cost, simple design, good bandwidth, and radiation performance, and pattern/polarization reconfigurability, is well situated for 5G-NR communication.

On attempting to automate the identification of mixed dipole modes for subgiant stars

Context. The existence of mixed modes in stars is a marker of stellar evolution. Their detection serves for a better determination of stellar age. Aims. The goal of this paper is to identify the dipole modes in an automatic manner without human intervention. Methods. I used the power spectra obtained by the Kepler mission for the application of the method. I computed asymptotic dipole mode frequencies as a function of the coupling factor and dipole period spacing, as well as other parameters. For each star, I collapsed the power in an echelle diagramme aligned onto the monopole and dipole mixed modes. The power at the null frequency was used as a figure of merit. Using a genetic algorithm, I then optimised the figure of merit by adjusting the location of the dipole frequencies in the power spectrum. Using published frequencies, I compared the asymptotic dipole mode frequencies with published frequencies. I also used published frequencies to derive the coupling factor and dipole period spacing using a non-linear least squares fit. I used Monte-Carlo simulations of the non-linear least square fit to derive error bars for each parameter. Results. From the 44 subgiants studied, the automatic identification allows one to retrieve within 3 μHz, at least 80% of the modes for 32 stars, and within 6 μHz, at least 90% of the modes for 37 stars. The optimised and fitted gravity-mode period spacing and coupling factor are in agreement with previous measurements. Random errors for the mixed-mode parameters deduced from the Monte-Carlo simulation are about 30−50 times smaller than previously determined errors, which are in fact systematic errors. Conclusions. The period spacing and coupling factors of mixed modes in subgiants are confirmed. The current automated procedure will need to be improved upon using a more accurate asymptotic model and/or proper statistical tests.

Retroreflection from a single layer of electromagnetic Helmholtz cavities based on magnetic symmetric dipole modes.

We demonstrate a new electromagnetic mode which is formed by the dynamic interaction between a magnetic quadrupole mode and an electric monopole mode in a two-dimensional electromagnetic Helmholtz cavity. It is termed a magnetic symmetric dipole mode since it shares similarity with a magnetic dipole mode in the sense that their radiation is both overwhelmingly dominant in the forward and backward directions with respect to the incident wave. However, the phase distribution in the two radiation directions is symmetric, in stark contrast to the antisymmetry of magnetic dipole modes. When the Helmholtz cavities are arranged in a line, the incident wave will be reflected back to the source, in other words, retroreflection occurs because of the peculiar properties of magnetic symmetric dipole modes. We show that the retroreflection is quite robust against the disorder of the orientation angle of Helmholtz cavities and there exists a wide tolerance for wavelength and the outer radius of the cavity. With low fabrication demands, this might offer a feasible solution for the design of ultrathin retroreflectors towards device miniaturization and the realization of multiplexing holography.

Observation of a strongly ferromagnetic spinor Bose-Einstein condensate

We report the observation of strongly ferromagnetic F=1 spinor Bose-Einstein condensates of Li7 atoms. The condensates are generated in an optical dipole trap without using magnetic Feshbach resonances, so that the condensates have internal spin degrees of freedom. Studying the nonequilibrium spin dynamics, we have measured the ferromagnetic spin interaction energy and determined the s-wave scattering length difference among total spin f channels to be af=2−af=0=−18(3) Bohr radius. This strong collision-channel dependence leads to a large variation in the condensate size with different spin composition. We were able to excite a radial monopole mode after a spin-flip transition between the |mF=0〉 and |mF=1〉 spin states. From the experiments, we estimated the scattering length ratio af=2/af=0=0.27(6), and determined af=2=7(2) and af=0=25(5) Bohr radii, respectively. The results indicate the spin-dependent interaction energy of our system is as large as 46% of the condensate chemical potential.1 MoreReceived 11 June 2020Accepted 28 August 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.033471Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBose-Einstein condensatesUltracold collisionsAtomic, Molecular & Optical

Aerosol concentrations variability over China: two distinct leading modes

Abstract. Understanding the variability in aerosol concentrations (ACs) over China is a scientific challenge and is of practical importance. The present study explored the month-to-month variability in ACs over China based on simulations of an atmospheric chemical transport model with a fixed emissions level. The month-to-month variability in ACs over China is dominated by two principal modes: the first leading monopole mode and the second meridional dipole mode. The monopole mode mainly indicates enhanced ACs over eastern China, and the dipole mode displays a south–north out-of-phase pattern. The two leading modes are associated with different climatic systems. The monopole mode relates to the 3 months leading the El Niño–Southern Oscillation (ENSO), while the dipole mode connects with the simultaneous variation in the North Atlantic Oscillation (NAO) or the Northern Hemisphere Annular Mode (NAM). The associated anomalous dynamic and thermal impacts of the two climatic variabilities are examined to explain their contributions to the formation of the two modes. For the monopole mode, the preceding ENSO is associated with anomalous convergence, decreased planetary boundary layer height (PBLH), and negative temperature anomalies over eastern China, which are unfavorable for emissions. For the dipole mode, the positive NAO is accompanied by opposite anomalies in the convergence, PBLH, and temperature over southern and northern China, paralleling the spatial formation of the mode. This result suggests that the variations originating from the tropical Pacific and extratropical atmospheric systems contribute to the dominant variabilities of ACs over China.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

Transport controlled by Poincaré orbit topology in a driven inhomogeneous lattice gas

In periodic quantum systems which are both homogeneously tilted and driven, the interplay between drive and Bloch oscillations controls transport dynamics. Using a quantum gas in a modulated optical lattice, we show experimentally that inhomogeneity of the applied force leads to a rich new variety of dynamical behaviors controlled by the drive phase, from self-parametrically-modulated Bloch epicycles to adaptive driving of transport against a force gradient to modulation-enhanced monopole modes. Matching experimental observations to fit-parameter-free numerical predictions of time-dependent band theory, we show that these phenomena can be quantitatively understood as manifestations of an underlying inhomogeneity-induced phase space structure, in which topological classification of stroboscopic Poincar\'e orbits controls the transport dynamics.