Resonance Poles Research Articles

The continuum spectrum of hypernuclear trios

The spectrum of hypernuclear trios composed of a Λ baryon and two nucleons is the subject of an ongoing experimental campaign, aiming to study the interaction of the Λ particle with a neutron, and the 3-body Λ-nucleon-nucleon force. In this manuscript we utilize baryonic effective field theory at leading order, constrained to reproduce the available low energy light hypernuclear data, to study the continuum spectrum of such hypernuclear trios. Using the complex scaling method and the inverse analytic continuation in the coupling constant method we find the existence of a virtual state in the ΛnpJπ=3/2+ channel, leading to cross-section enhancement near threshold. For the ΛnnJπ=1/2+ channel we predict a resonance state. Depending, however, on the value of the ΛN scattering length, the resonance pole moves from the physical to the unphysical complex energy sheet within the experimental bounds.

Differential cross sections for neutron-proton scattering in the region of the d*(2380) dibaryon resonance

Differential cross sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized n⃗p scattering performed in the energy region of the d*(2380) dibaryon resonance covering the range of beam energies Tn=0.98−1.29 GeV (s=2.32−2.44 GeV). The experiment was carried out with the WASA-at-COSY setup having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp→np+pspectator. In this way the np differential cross section σ(Θ) was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power Ay(Θ) measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled D33−G33 waves.Received 3 April 2020Accepted 9 June 2020DOI:https://doi.org/10.1103/PhysRevC.102.015204Published 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. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNucleon induced nuclear reactionsNucleon-nucleon interactionsParticle interactionsPhysical SystemsBaryonsHadronsParticles & FieldsNuclear Physics

Dual-mode SICL bandpass filter with via based perturbation technique for K u -band

This Letter presents a dual-mode substrate integrated coaxial line (SICL) based bandpass filter for K u -band application. The proposed bandpass filter is realised by exciting the even and odd modes in an SICL ring resonator. A novel perturbation technique to control the coupling between orthogonal modes is realised by varying the width of the outer conductor formed by metallic vias in this planar coaxial line. Further, the effect of perturbation length and inset on resonant frequency and attenuation pole is studied. The two transmission zeros produced close to the pass band provide excellent selectivity and reject spurious frequencies up to 1.9 f o . The proposed SICL based filter is manufactured using low cost PCB fabrication process. Experimental results indicate an insertion loss of 1.18 dB and a 3 dB bandwidth of 360 MHz centred at 13.83 GHz. The self packaged SICL filter occupying only 0.31 λ g 2 lateral area is suitable for implementation in densely integrated systems.

Tracking Control of Nanopositioning Stages Using Parallel Resonant Controllers for High-Speed Nonraster Sequential Scanning

The resonant controller (RC), as a promising candidate for high-speed nonraster nanopositioning applications, can track the sinusoidal reference with zero steady-state error. This article presents a controller composed of several RCs in parallel for tracking nonraster sequential scanning trajectories. The selection for each RC in the parallel array is based on two considerations: one is the spectrum of the reference signal and the other is the harmonics caused by the nonlinearities of the nanopositioning stage. The performance of RC is highly dependent on the accurate placement of the resonant poles, but unfortunately, many existing digital implementation methods could cause a deviation of the resonant poles from their initial locations. To address this problem, a modified Tustin (MTus) method is proposed in this article to implement the controller with better accuracy. Furthermore, the fractional-order (FO) calculus is introduced to improve the transient performance of the RCs. To validate the proposed methods, a comprehensive examination of several types of the nonraster sequential scanning trajectories with a wide frequency range has been carried out on a nanopositioning stage. The results have been compared with other methods, showing that the tracking errors are reduced significantly under the controller implemented by the MTus method especially in high-frequency conditions and that the application of the FO calculus reduces the settling time of the controller by more than 30% in most cases. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The demand for high-speed atomic force microscope (AFM) increases rapidly. However, the commonly used raster trajectory limits the achievable scan speed of the AFM. An effective way to improve the scanning and imaging speed of the AFM is the application of the sequential nonraster scanning methods. The trajectories of sequential nonraster scanning patterns mainly composed of few sinusoid signals with different frequencies. Therefore, the resonant controller (RC) is introduced in this article as it is capable to track the sinusoidal reference with zero steady-state error. Several RCs are selected first based on the spectrum analysis of the reference and the consideration of the harmonics caused by the system nonlinearities, and then, they are connected in parallel to form the controller for precise tracking of the reference. In order to realize the digital implementation of the designed controller, a modified Tustin discretization method is proposed, which ensures the accurate resonant pole placement of the RC and thus maintains the tracking performance of the RC. In addition, the fractional-order (FO) calculus is introduced to speed up the convergence of the designed controller while preserving the tracking accuracy, and this parallel-structure FO RC (PSFORC) design can be implemented to other systems that require high-speed and high-accuracy tracking of the periodic signals.

Experimental Evaluation of SiC Mosfets in Comparison to Si IGBTs in a Soft-Switching Converter

Silicon-carbide (SiC) mosfet s have shown superior characteristics to Si IGBTs, bringing in significant performance improvement such as enabling more compact, higher efficiency converters that are not feasible with conventional Si IGBTs. Currently, there is a lack of systematic and conclusive investigation into soft-switching inverters using SiC mosfet s in comparison to Si IGBTs. This article, therefore, presents a comparative evaluation of a soft-switching inverter, i.e., the auxiliary resonant commutated pole inverter (ARCPI) using SiC mosfet s or Si IGBTs. The switching transition, switching device current stress, neutral point ripple current, electromagnetic interference (EMI), efficiency, and cost are compared on identical ARCPI setups, i.e., with the same printed circuit boards and under identical driving conditions (gate drivers). Experimental results show that the ARCPI using SiC mosfet s has better performance than that using Si IGBTs due to its faster switching speed. First, the ARCPI using SiC mosfet s performs full zero-voltage switching and the switching transition behavior is more predictable. Unlike Si IGBTs, SiC mosfet s have no turn- off tail current and forward voltage drop during switching transitions. Second, the ARCPI using SiC mosfet s endures less current stress and smaller ripple current in dc-link capacitors. Third, the ARCPI using SiC mosfet s exhibits better EMI performance and higher efficiency. Specifically, a maximum 20 dB μ V harmonic reduction can be achieved around 800 kHz and a 3.1% improvement in efficiency can be achieved at 6 kW.

Properties of the Expansion of the Decaying Wave Solution in Terms of Resonant States

We consider the formulation of quantum decay in terms of resonant states and complex poles of the outgoing Green’s function of the problem to discuss some properties of the decaying wave solution that exhibit its non-Hermitian character and hence illustrate its departure from the standard formalism of quantum mechanics.

Interaction between dielectric particles enhances the Q factor.

We consider resonant modes of two dielectric identical particles which can be classified as symmetric and anti symmetric combinations of the resonant modes of individual particles. We show that an approaching of two particles gives rise to an avoided crossing of resonant poles because of interaction between the disks. That in turn results in strong enhancement of the quality factor factor of two disks compared to isolated disks.

Stability enhancement strategy of virtual synchronous generator for cascaded multilevel converter based energy storage system under weak grid conditions

Considering that the low-voltage and small capacity ratings of the traditional distributed energy storage system (ESS) cannot meet the increasing capacity of distributed generations, this study describes a cascaded multilevel converter-based ESS. In addition, the virtual synchronous generator (VSG) as a promising solution to enhance the system's inertia is studied. However, some studies indicate that VSG suffers from the inherent resonance near synchronous frequency under weak grid conditions, which may result in power oscillation and even deteriorate the system stability. In this work, the resonance mechanism is investigated with an established wide-band small-signal dynamic model. It is revealed that the resonance poles caused by the small impedance ratio on the AC side introduce a phase lag jump of 180°, which decreases the phase margin of VSG, leading to synchronous power oscillation (SPO). The influence of control parameters on the power oscillation is investigated with the eigenvalue analysis method. Accordingly, a differential feedforward compensation-based SPO suppression strategy is proposed. The stability margins are significantly enhanced with this method. The validity of the SPO analysis and suppression method is verified with simulation and a 10 kW experimental prototype.

Exploring the unknown Lambda-neutron interaction

No published \LambdaΛn scattering data exist. A relativistic heavy-ion experiment has suggested that a \LambdaΛnn bound state was seen. However, several theoretical analyses have cast serious doubt on the bound-state assertion. Nevertheless, there could exist a three-body \LambdaΛnn resonance. Such a resonance could be used to constrain the \LambdaΛn interaction. We discuss \LambdaΛnn calculations using nn and \LambdaΛn pairwise interactions of rank-one, separable form that fit effective range parameters of the nn system and those hypothesized for the as yet unobserved \LambdaΛn system based upon four different \LambdaΛN potentials. The use of rank-one separable potentials allows one to analytically continue the \LambdaΛnn Faddeev equations onto the second complex energy plane in search of resonance poles, by examining the eigenvalue spectrum of the kernel of the Faddeev equations. Although each of the potential models predicts a \LambdaΛnn sub-threshold resonance pole, scaling of the \LambdaΛn interaction by as little as \sim∼5% does produce a physical resonance. This suggests that one may use photo-(electro-)production of the \LambdaΛnn system from tritium as a tool to examine the strength of the \LambdaΛn interaction.

Modal expansion of optical far-field quantities using quasinormal modes

We discuss an approach for modal expansion of optical far-field quantities based on quasinormal modes (QNMs). The issue of the exponential divergence of QNMs is circumvented by contour integration of the far-field quantities involving resonance poles with negative and positive imaginary parts. A numerical realization of the approach is demonstrated by convergence studies for a nanophotonic system.

Thermal behaviors of light scalar resonances at low temperatures

We study the thermal properties of the lowest multiplet of the QCD light-flavor scalar resonances, including the $f_0(500)/\sigma$, $K_{0}^{*}(700)/\kappa$, $f_0(980)$ and $a_0(980)$, in the framework of unitarized $U(3)$ chiral perturbation theory. After the successful fits to the meson-meson scattering inputs, such as the phase shifts and inelasticities, we obtain the unknown parameters and further calculate the resonance poles and their residues at zero temperature. By including the finite-temperature effects in the unitarized meson-meson scattering amplitudes, the thermal behaviors of the scalar resonance poles in the complex energy plane are studied. The masses of $\sigma$ and $\kappa$ are found to considerably decrease when increasing the temperatures, while their widths turn out to be still large when the temperatures reach around $200$ MeV. In contrast, both the masses and widths of the $f_0(980)$ and $a_0(980)$ are only slightly changed.

Cross section for γn→π0n measured at the Mainz A2 experiment

The $\gamma n \to \pi^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $\gamma n \to \pi^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to \gamma n$ at the resonance poles are determined for the first time.

A monatomic chain with an impurity in mass and Hooke constant

In this paper, a diatomic chain composed of classical harmonic oscillators and an impurity with different mass and Hooke constant is studied by means of the recurrence relations method. The Laplace transform of the momentum autocorrelation function of the impurity has three pairs of resonant poles and three separate branch cuts; however, one pair of poles was found nonphysical, so only two pairs of poles contribute to the momentum autocorrelation function. The three branch cuts give the acoustic and optical branches that are given by a convolution of a sum of sines and an expansion of even-order Bessel functions. The expansion coefficients are integrals of a Jacobian elliptic function along the real axis in a complex plane for the acoustic branch and those along a contour parallel to the imaginary axis for the optical branch, respectively. The ergodicity of momentum of the impurity is also discussed.

System Model and Performance Evaluation of Single-Stage Buck–Boost-Type Manitoba Inverter for PV Applications

This article presents a control methodology for a recently proposed single-stage buck–boost-type inverter in photovoltaic (PV) applications. A wide range of input voltage is covered, and the dc power is effectively converted into the grid power within a single-stage system. However, from the topological characteristics, a ${ C\!L}$ filter is always formed at the system output, which results in a resonance pole in the control system. In the PV system, the panel output voltage keeps varying. Under the traditional control method, stability issues may occur, which poses a challenge to controller design. Thus, targeting PV applications, a comprehensive control methodology is presented in this article. Under such a control scheme, a high-quality ac grid power is guaranteed and the power conversion is maintained in a stable manner. Meanwhile, the maximum power point (MPP) of PV panels is always tracked and no additional current sensor is required in the MPP tracking (MPPT) design. In this article, a detailed system analysis is presented, which includes the system modeling and the stability evaluation. The performance of the presented control methodology is experimentally verified in a 750-W PV inverter platform. Both steady state and dynamic characteristics are in good agreement with theoretical knowledge.

Scattering amplitudes and contour deformations

We employ a scalar model to exemplify the use of contour deformations when solving Lorentz-invariant integral equations for scattering amplitudes. In particular, we calculate the onshell 2 -> 2 scattering amplitude for the scalar system. The integrals produce branch cuts in the complex plane of the integrand which prohibit a naive Euclidean integration path. By employing contour deformations, we can also access the kinematical regions associated with the scattering amplitude in Minkowski space. We show that in principle a homogeneous Bethe-Salpeter equation, together with analytic continuation methods such as the Resonances-via-Pad\'e method, is sufficient to determine the resonance pole locations on the second Riemann sheet. However, the scalar model investigated here does not produce resonance poles above threshold but instead virtual states on the real axis of the second sheet, which pose difficulties for analytic continuation methods. To address this, we calculate the scattering amplitude on the second sheet directly using the two-body unitarity relation which follows from the scattering equation.

A 2-kV Charge-Based ZVS Three-Level Inverter

Industrial applications, e.g., semiconductor manufacturing equipment, require power converters providing high power with high precision and bandwidth. This article presents a three-level flying capacitor resonant pole inverter configuration that combines high output power and high switching frequency with reduced switch voltage stress. A multilevel modulation strategy is applied to minimize conduction losses, which, in addition, guarantees zero-voltage switching (ZVS) for the entire operating range to reduce switching losses. The proposed multilevel converter configuration is compared with an existing two-level configuration by simulation. Increasing the number of voltage levels results in lower total losses and increased linearity of the generated output current. Experimental results acquired with a hardware prototype validate the fast switching of high voltage, proper functioning of the multilevel modulation strategy, and achieving of ZVS. Improvements of the theoretical analysis are presented to compensate for delays in the system and deviating parameter values. Results obtained with a compensated system indicate a relatively high accuracy and linearity of the generated output current of the inverter.

Damping the tail of the Woods–Saxon potential

Cutting of the tail of the Woods–Saxon (WS) potential influences the distribution of the poles of the [Formula: see text]-matrix considerably. A new attempt is made here to correct the tail of the cut-off WS potential in order to bring the positions of the poles closer to the WS potential without cut. New types of strictly finite range potentials are introduced in which the tail of the WS and the generalized Woods–Saxon (GWS) potentials are modified to damp them at their ends. This damping affects the energies of the bound and narrow resonant states weakly. The resonant pole positions in the new potentials were affected more significantly and the new pole positions became closer to that of the GWS potential without cut. However, the cut-off effect cannot be diminished completely. The new potentials belong to the [Formula: see text] function class.

Complex-energy analysis of proton-proton fusion

An analysis of the astrophysical $S$ factor of the proton-proton weak capture ($\mathrm{p}+\mathrm{p}\rightarrow {}^2\mathrm{H}+\mathrm{e}^++\nu_{\mathrm{e}}$) is performed on a large energy range covering solar-core and early Universe temperatures. The measurement of $S$ being physically unachievable, its value relies on the theoretical calculation of the matrix element $\Lambda$. Surprisingly, $\Lambda$ reaches a maximum near $0.13~\mathrm{MeV}$ that has been unexplained until now. A model-independent parametrization of $\Lambda$ valid up to about $5~\mathrm{MeV}$ is established on the basis of recent effective-range functions. It provides an insight into the relationship between the maximum of $\Lambda$ and the proton-proton resonance pole at $(-140-467\,\mathrm{i})~\mathrm{keV}$ from analytic continuation. In addition, this parametrization leads to an accurate evaluation of the derivatives of $\Lambda$, and hence of $S$, in the limit of zero energy.

Analytical version of the resonance coupled-channel model for D + T → 5He** → α + n reaction and its application for the description of low-energy D-T and D- 3He scattering

The purpose of the present paper is the formulation of the analytical version of the resonance coupled-channel model (RCCM) originally developed for D + T → 5He** → α + n nuclear fusion reaction. The integral in the denominator of the Breit-Wigner type is examined in the expression for S-matrix elements of binary processes in this model. Imaginary part of this integral determines the energy-dependent decay width for the near-threshold channel. It is demonstrated that this integral can be calculated explicitly with the Binet representation for the ψ-function (the logarithmic derivation of the gamma function). As the result the explicit expression for the S-matrix elements in the form of analytical functions of the channel momenta are obtained and the equivalence of the RCCM and the effective range approximation (Landau – Smorodinsky – Bethe approximation) is established on this basis. This allows expressing the parameters of the RCCM through the model independent system characteristics: the complex scattering length and the complex effective range. Several sets of model parameters of both approaches that provide a good description of the measured data on D + T → α + n reaction and D-T elastic scattering are derived. By this means we find the location of the S – matrix poles on different Riemann sheets which corresponds to Jπ = (3/2)+ state of 5He and 5Li nuclei. In particular, the location of the resonance (R) and shadow (S) poles is determined: 5He**: ZR = 46.9 – i37.2 (keV) ZS = 81.7 – i3.5 (keV) 5Li**: ZR = 205.7 – i146.8 (keV) ZS = 264.4 + i112.0 (keV). Our results agree well with previous findings. The possible generalizations of the results obtained are discussed.

Vector mesons as dynamical resonances in the Bethe–Salpeter framework

We present the first dynamical calculation of the ρ-meson as a resonance in the Dyson–Schwinger/Bethe–Salpeter framework by including explicit two-pion exchange in addition to the t-channel one-gluon exchange of rainbow-ladder in the interaction kernel. The width is determined from the imaginary part of the resonance pole and is generated by the singularity structure of the integrand, treated by means of suitable path deformations. We find the resonant mass and width to be 640 MeV and 100 MeV respectively, corresponding to a coupling constant gρππ=5.7; repulsive corrections beyond rainbow-ladder are expected to bring these in line with experiment. Furthermore we present the dependence of these parameters on the pion mass and compare with results from lattice QCD.