Zero Frequency Research Articles

Effects of plasma nonuniformity on zero frequency zonal structure generation by drift Alfvén wave instabilities in toroidal plasmas

Abstract The effects of plasma nonuniformity on zero frequency zonal structure (ZFZS) excitation by drift Alfvén wave (DAW) instabilities in toroidal plasmas are investigated using nonlinear gyrokinetic theory. The governing equations describing nonlinear interactions among ZFZSs and DAWs are derived, with the contribution of DAW self-beating and radial modulation accounted for on the same footing, and the physics picture contributing to both channels clarified. The obtained equations are then used to derive the nonlinear dispersion relation, which is then applied to investigate ZFZS generation in several scenarios. In particular, it is found that the condition for zonal flow excitation by the kinetic ballooning mode (KBM) could be sensitive to plasma parameters and a more detailed investigation is needed to understand KBM nonlinear saturation, crucial for bulk plasma transport in future reactors.

Infinite temperature spin dc conductivity of the spin-1/2 XXZ chain

Abstract Using the Bethe ansatz method and the thermodynamic Bethe ansatz equations for the higher-spin integrable XXZ chain, the regular zero frequency contribution to the spin current correlation (spin dc conductivity) is analyzed for the spin-1/2 XXZ chain with the anisotropy 0 ⩽ Δ < 1 . In the high temperature limit, we write down the dressed scattering kernels by one quasi-particle bare energies and exactly evaluate the spin dc conductivity at zero magnetic field, which is proportional to the inverse temperature β at the β → 0 limit. We find that the high temperature proportionality constant σ 0 reg of the spin dc conductivity is discontinuous at all rational numbers of the anisotropy parameter p 0 = π / cos − 1 ⁡ Δ ⩾ 2 with the gap increasing larger than the second power of growing magnetization on one quasi-particle. The isotropic Δ = 1 point is exceptional. Close to this point, σ 0 reg slowly increases in proportion to the first power of the one quasi-particle magnetization. On the other hand, σ 0 reg is proportional to the second power of the same when p 0 approaches irrational numbers.

A novel Short-time Fourier transform-based algorithm for detection of wandering in the patients with Alzheimer’s disease

ABSTRACT As the elderly population rises, the growth rate of age-related diseases such as Alzheimer’s disease and cognitive impairments increases. Wandering is one of the first and the most progressive and challenging behaviors; that manifest with certain patterns in the mobility behavior of the patients in the early stages of the disease. Timely diagnosis of wandering can prevent irreparable damages, including the risk of losing the patient, severe physical injuries caused by accidents, and even death. So far, numerous studies have focused on the development of wandering detection algorithms. Most of these mainly rely on two approaches of extracting features from patients’ trajectory history and estimating the path complexity. Motion signal processing methods have rarely been used in this area. An important consideration for these patients is the instability in their movement behaviors, which has received limited attention in previous research, leading to less compatibility of models with this feature. Therefore, this paper proposes an algorithm based on motion signal processing using the Short-time Fourier transform (STFT). This algorithm detects wandering patterns only by using the patient’s trajectory data and changes in their zero and non-zero frequency components. The efficiency of the proposed algorithm has been evaluated using the Geolife open-source dataset, considering the macro-average of metrics such as accuracy, precision, specificity, recall, and F-score, achieving respective values of 96.38%, 94.89%, 96.36%, 96.36%, and 95.58%. The results have validated the proposed algorithm’s strong performance in diagnosing wandering behavior, which, on one hand, helps prevent adverse consequences and, on the other hand, aids in the diagnosis and predicting the progression of the disease to severe Alzheimer’s stage.

Highly miniaturized dual-band bandpass filter with wide bandwidth and large center frequency ratio

The design of a miniaturized dual-band bandpass filter featuring a broad bandwidth and a high center frequency ratio is demonstrated in this article. A novel symmetrically loaded shunt coupled line with dual stepped impedance stubs has been investigated for the first time and it is utilized to realize a dual-band bandpass filter with seven transmission zeros. The transmission zeros frequencies of the filter response have been theoretically verified using even-odd mode analysis. For experimental validation purposes, a dual-band filter with a center frequency ratio of 4.06 covering 5G applications is implemented using Rogers RT/duroid 5870 substrate and tested. The tested filter has wide 3 dB fractional bandwidths of 53.8% and 17.9% in the first and second passbands, respectively, and has a compact topology of 0.20 × 0.09 λg 2. The full-wave simulated and tested magnitude and group delay responses of the proposed filter are in good congruence.

Overdispersion in gate tomography: Experiments and continuous, two-scale random walk model on the Bloch sphere

Noisy intermediate-scale quantum computers (NISQ) are computing hardware in their childhood, but they are showing high promise and growing quickly. They are based on so-called qubits, which are the quantum equivalents of bits. Any given qubit state results in a given probability of observing a value of zero or one in the readout process. One of the main concerns for NISQ machines is the inherent noisiness of qubits, i.e. the observable frequencies of zeros and ones do not correspond to the theoretically expected probability, as the qubit states are subject to random disturbances over time and with each additional algorithmic operation applied to them. Models to describe the influence of this noise exist. In this study, we conduct extensive experiments on quantum noise. Based on our data, we show that existing noise models lack important aspects. Specifically, they fail to properly capture the aggregation of noise effects over time (or over an algorithm’s runtime), and they are underdispersed. With underdispersion, we refer to the fact that observable frequencies scatter much more between repeated experiments than what the standard assumptions of the binomial distribution would allow for. Based on these shortcomings, we develop an extended noise model for the probability distribution of observable frequencies as a function of the number of gate operations. The model roots back to a known continuous random walk on the (Bloch) sphere, where the angular diffusion coefficient can be used to characterize the standard noisiness of gate operations. Here, we superimpose a second random walk at the scale of multiple readouts to account for overdispersion. Further, our model has known, explicit components for noise during state preparation and measurement (SPAM). The interaction of these two random walks predicts theoretical, runtime-dependent bounds for probabilities. Overall, it is a three-parameter distributional model that fits the data much better than the corresponding one-scale model (without overdispersion), and we demonstrate the better fit and the plausibility of the predicted bounds via Bayesian data-model analysis.

Screened optimally tuned range separated hybrid functional for solvated low bandgap molecular systems.

The description of electronic properties of low bandgap molecular system is often performed by using density functional theory (DFT) and time dependent (TD) DFT calculations with the optimally tuned range-separated hybrid (OT-RSH) functional, as it contains the necessary ingredients to reliably predict charge transfer excitations. However, the range separating parameter (ω) is system-dependent and its optimization, including the chemical environment, is intricate. Refaely-Abramson et al. demonstrated that the gap renormalization in molecular crystals, a ground state property, can be represented by an OT-RSH functional screened by ɛstatic [Phys. Rev. B 88, 081204(R) (2013)], the zero frequency scalar dielectric constant. In this study, we propose the use of an OT-RSH functional screened by the scalar dielectric constant in the high frequency limit (OT-sRSH), ɛ∞, an appropriate constraint for vertical ionization energies or excitations in a dielectric environment. We have performed calculations for S,N-heteroacene derivatives in tetrahydrofuran and dichloromethane. The "unscreened" OT-RSH functional tends to underestimate experimental ionization potentials (IPs) and optical gaps (Egs) by up to 1.5 and 0.5eV, respectively. In contrast, OT-sRSH functional calculations underestimate IPs and Egs by only 0.4 and 0.2eV. We also compared the OT-sRSH results to explicitly solvated OT-RSH functional calculations for oligothiophenes in dioxane, benzene in ammonia, and methylene blue in water. We observe that both the approaches perform similarly for weakly interacting intermolecular systems and deviate for solvent-solute interacting systems, as expected. In conclusion, the OT-sRSH functional can describe molecular systems with environmental polarization effects accurately, a step toward describing realistic molecular systems.

Research on Failure Characteristics of Electric Logistics Vehicle Powertrain Gearbox Based on Current Signal

As a core component of the powertrain system of Electric Logistics Vehicles (ELVs), the gearbox is crucial for ensuring the reliability and stability of ELV operations. Traditional fault diagnosis methods for gearboxes primarily rely on the analysis of vibration signals during operation. This paper presents research on diagnosing gear tooth wear faults in ELV powertrains using motor current signals. Firstly, an experimental test platform was constructed based on the structural principle of the powertrain of ELV models. Subsequently, a pure electric light truck powertrain gearbox with tooth wear was tested. Time–frequency domain analysis, amplitude analysis, ANOVA analysis, kurtosis analysis, and zero−crossing points analysis were used to analyze the U−phase current of the motor connected to the gearbox to study the characteristics of the phase current of the drive motor after tooth wear. The results indicate that while the time–frequency domain characteristics of the U−phase currents are not significantly altered by tooth wear faults, the amplitude, variance, and kurtosis of the current increase with the severity of the wear. Conversely, the number of zero−crossing points decreases. These findings provide valuable insights into new methodologies for diagnosing faults in ELV powertrain systems, potentially enhancing the efficiency and effectiveness of troubleshooting processes.

Exponential tilting for zero-inflated interval regression with applications to cyber security survey data

Abstract Non-negative ordered survey data often exhibit an unusually high frequency of zeros in the first interval. Zero-inflated interval regression models handle the excess of zeros by combining a split probit model and an ordered probit model. In the presence of data violating distributional assumptions, standard inference based on the maximum likelihood method gives biased estimates with large standard errors. In this paper, we consider robust inference based on the exponential tilting methodology for the zero-inflated interval regression model. The application considers data on cyber security to study the relationship between investments in cyber defences and losses from cyber breaches. Robust estimates obtained via tilting clearly show an effect of the investments in reducing the loss amount.

Friction of a driven chain: role of momentum conservation, Goldstone and radiation modes

We analytically study friction and dissipation of a driven bead in a 1D harmonic chain, and analyze the role of internal damping mechanism as well as chain length. Specifically, we investigate Dissipative Particle Dynamics and Langevin Dynamics, as paradigmatic examples that do and do not display translational symmetry, with distinct results: For identical parameters, the friction forces can differ by many orders of magnitude. For slow driving, a Goldstone mode traverses the entire system, resulting in friction of the driven bead that grows arbitrarily large (Langevin) or gets arbitrarily small (Dissipative Particle Dynamics) with system size. For a long chain, the friction for DPD is shown to be bound, while it shows a singularity (i.e. can be arbitrarily large) for Langevin damping. For long underdamped chains, a radiation mode is recovered in either case, with friction independent of damping mechanism. For medium length chains, the chain shows the expected resonant behavior. At the resonance, friction is non-analytic in damping parameter γ, depending on it as γ −1. Generally, no zero frequency bulk friction coefficient can be determined, as the limits of small frequency and infinite chain length do not commute, and we discuss the regimes where ‘simple’ macroscopic friction occurs.

The Zero-Inflated Poisson - Probit regression model: a new model for count data

This paper wishes to propose a new model for count data and it is shortly called a Zero-Inflated Poisson - Probit (ZIP-P) model. The way of setting up for this new model is also based on the traditional model, the Zero-Inflated Poisson (ZIP) model. Note that this new model as well as the ZIP model has a wide range of practical applications and it can be easily applied and analyzed to the real data sets. More specifically, both of these models can be applied very well to count data sets where the frequency of zeros occupies a very high percentage. To achieve the goal of this study, we first recall the construction and general formula of the ZIP model. Then we present the most detailed way for building a new model includes the general formula and related equations necessary for estimating the parameters of the ZIP-P model. In addition, asymptotic results, numerical simulations and analysis of a real data set are also performed in this work. Moreover, we also clarify that this actual data set fits the ZIP-P model better than the other models considered. Finally, several lines of discussions and inferences are made in the study.

Exact closed-form solution for vibration characteristics of multi-span beams on an elastic foundation subjected to axial force

This paper investigates the vibration characteristics of multi-span beams resting on an elastic foundation and subjected to axial forces. A comprehensive analytical expression of the dynamic response of multi-span beams on an elastic foundation that is developed to address various boundary conditions. The vibration equation is derived by employing Newton's second law. By Laplace transformations and the Green's function method, the solution of this governing equation can be obtained. Subsequently, a unified description is implemented for distinct types of boundary conditions using matrix representations. The correctness is verified through reference results and finite element methods (FEM). The effects of different parameters such as support stiffness, foundation elastic and shear layer stiffness, and axial force on the vibration characteristics are analyzed. This study demonstrates two findings: First, there are two thresholds for support stiffness, and the stiffness value is divided into three intervals. In the same interval, multi-span beams show the same properties. Second, for a rigidly supported multi-span beam, the critical axial force with a natural frequency of zero is just the corresponding Euler's buckling load; for elastically supported multi-span beams, the critical axial force falls between the Euler’s buckling load corresponding to single-span and multi-span beams.

Instability in optical injection locking semiconductors lasers using multiparametric bifurcation analysis.

In this paper, we investigate bifurcations of equilibria and transients by using modified rate equations of semiconductor lasers (SCLs) subjected to optical injection. An analytical study is performed to demonstrate some two-parameter bifurcations, inter alia, Bogdanov-Takens and Gavrilov-Guckenheimer bifurcations. A detailed numerical study based on the multiparametric bifurcation method and using 3D-plots and projections reveal a rich locking dynamics of SCLs. In this way, a so-called zero frequency detuning well is highlighted in the vicinity of a Hopf bifurcation confining minimal states of the larger Lyapunov exponent in injection locking curves. Three-parameter bifurcation curves mainly underscore cusp bifurcation and resizing of its multi-equilibrium region by the specific control parameter defined in this model. The bursting phenomenon observed in the transient regime is discussed by using various numerical approaches wherefrom another quantifying method tapping into two-parameter bifurcation analysis is proposed. Thereafter, metastable chaos dynamics supported by spiraling relaxation oscillations is also investigated as well as planar saddle-node bifurcations with three homoclinic orbits for high positive and negative detunings. At last, zero α-factor effects contribute to drastically shrink the unlocking region of SCLs, twofold increase in Hopf bifurcation along with evidencing of complex chaotic sine-shaped and folded torus-shaped attractors.

Signal Feature Extraction Method of Three-Band Infrared Flame Sensor

A three-band infrared flame sensor is designed and experimentally investigated for the analysis of infrared signals from three radiation sources (Flame, man and ambient). The Fourier transform and empirical mode decomposition (EMD) is applied to the analysis of the spectral characteristics, intrinsic modes and energy spectra. The results show that the received flame infrared signal exhibits significant low-frequency and energy characteristics. Near the zero frequency, the received infrared signal energy of the flame, man and ambient is 3.4 × 104 J, 2.8 × 104 J and 2.1 × 104 J, respectively. In this way the flame signal features can be accurately identified from different radiation sources. It can be believed that the results of the three-band infrared sensor presented here are useful guiding significance and practical application value for fire detection.

A dynamic-mode-decomposition-based acceleration method for unsteady adjoint equations at low Reynolds numbers

The computational cost of unsteady adjoint equations remains high in adjoint-based unsteady aerodynamic optimization. In this letter, the solution of unsteady adjoint equations is accelerated by dynamic mode decomposition (DMD). The pseudo-time marching of every real-time step is approximated as an infinite-dimensional linear dynamical system. Thereafter, DMD is utilized to analyze the adjoint vectors sampled from these pseudo-time marching. First-order zero frequency mode is selected to accelerate the pseudo-time marching of unsteady adjoint equations in every real-time step. Through flow past a stationary circular cylinder and an unsteady aerodynamic shape optimization example, the efficiency of solving unsteady adjoint equations is significantly improved. Results show that one hundred adjoint vectors contains enough information about the pseudo-time dynamics, and the adjoint dominant mode can be precisely predicted only by five snapshots produced from the adjoint vectors, which indicates DMD analysis for pseudo-time marching of unsteady adjoint equations is efficient.

Novel Topology and Design for Wideband Bandpass Filter With Frequency- and Attenuation-Reconfigurable In-Band Notch

A novel topology and the design method are proposed for a wideband bandpass filter (BPF) with frequency- and attenuation-reconfigurable in-band notch by engineering the complex frequencies of transmission zeros. The proposed topology consists of a fifth-order wideband BPF and two coupled notch resonators. With the two coupled notch resonators, a pair of complex in-band transmission zeros are formed. By controlling the frequency difference between the two notch resonators, a frequency- and attenuation-reconfigurable notch can be obtained in the passband of the wideband BPF. A matrix analysis method is presented to characterize the frequency- and attenuation-tunable in-band notch precisely. The relationship between complex transmission zeros and in-band attenuation is also investigated. To demonstrate the proposed techniques, a prototype using microstrip and evanescent mode resonators is designed and fabricated. The proposed wideband BPF exhibits a reconfigurable in-band notch with frequency tuning from 1.494 to 2.004 GHz and attenuation tuning from 2 to 79 dB. The simulated and measured results are in good agreement with each other, validating the proposed design and method.

Novel SVPWM for Open Winding PMSM Drives With Simultaneous Common Mode Voltage Control and Full Frequency Zero Sequence Current Suppression

Zero sequence voltage (ZSV) can cause zero sequence current (ZSC), while variation of common mode voltage (CMV) can cause bearing current in an open winding (OW) permanent magnet synchronous machine (PMSM) fed by common dc -bus dual two-level inverters. This article proposes a novel space vector pulsewidth modulation (SVPWM) strategy for simultaneously eliminating CMV variation and suppressing full frequency ZSC harmonics in either linear or over modulation region by optimal selection of switching combinations. The proposed SVPWM can reduce large ZSV ripples and number of switching actions in the conventional CMV control method for the common dc -bus OW drive. Thus, high-frequency ZSC harmonics and switching frequency can be significantly reduced in both linear and over modulation regions. Moreover, the proposed SVPWM can suppress large low-frequency ZSC harmonics induced by the conventional method in over modulation region. The superior performances of CMV variation elimination and full frequency ZSC suppression in the proposed SVPWM are verified by experiments.

A novel power balance control scheme for cascaded H-bridge multilevel converters with battery energy storage

Battery energy stored quasi-Z source cascaded H-bridge based photovoltaic power generation system combines advantages of quasi-z-source inverter, cascaded H-bridge, and battery energy storage system. However, the battery state of charge imbalance between the cascaded H-bridge inverter modules would reduce the system's performance and efficiency and potentially cause the system to fail. An integrated control technique of adaptive state of charge balancing based on gain scheduling and three-phase power balance of third harmonic injection based on fundamental frequency whole zero sequences is suggested for the quasi-Z source cascaded H-bridge battery storage system. Based on the mathematical relationship between the instantaneous state of charge of battery energy stored quasi-z-source cascaded H-bridge and the voltage reference value, this method updates the proportional controller gain in each sampling period. It combines the third harmonic injection method based on the fundamental frequency zero sequence to select the optimal modulation ratio Mn. Rapid state of charge balancing is accomplished without overmodulation while increasing the power balance range and decreasing DC link voltage swings. The simulation results validate the method's usefulness. The simulation results validate the proposed control method for ensuring power distribution between each phase and achieving a balanced state of charge of the battery energy stored quasi-Z source cascaded H-bridge photovoltaic system's battery energy storage.

Terahertz monolithic integrated narrow-band filter based on the silicon carbide substrate

This paper presented a narrow-band terahertz integrated cavity filter based on the silicon carbide (SiC) substrate. By introducing two metalized via-holes in a rectangular integrated cavity, an integrated coupling cavity was built, on the one hand, to operate as a coupling structure; on the other hand, to control the direct coupling between input and output feeding lines, further to control the frequency of the transmission zero. This novel approach was thoroughly investigated with attention paid to the position of the via-holes. Based on this approach, a terahertz narrow-band filter was realized on the semi-insulating SiC substrate, demonstrated good filtering performance, especially the stopband rejection characteristic, and established the groundwork for the production of the terahertz monolithic integrated circuit.

On Nonlinear Oscillations of a Near-Autonomous Hamiltonian System in One Case of Integer Nonequal Frequencies

This paper is concerned with the motions of a near-autonomous two-degree-of-freedom Hamiltonian system, $2\pi$-periodic in time, in a neighborhood of a trivial equilibrium. It is assumed that in the autonomous case, in the region where only necessary (which are not sufficient) conditions for the stability of this equilibrium are satisfied, for some parameter values of the system one of the frequencies of small linear oscillations is equal to two and the other is equal to one. An analysis is made of nonlinear oscillations of the system in a neighborhood of this equilibrium for the parameter values near a resonant point of parameter space. The boundaries of the parametric resonance regions are constructed which arise in the presence of secondary resonances in the transformed linear system (the cases of zero frequency and equal frequencies). The general case and both cases of secondary resonances are considered; in particular, the case of two zero frequencies is singled out. An analysis is made of resonant periodic motions of the system that are analytic in integer or fractional powers of the small parameter, and conditions for their linear stability are obtained. Using KAM theory, two- and three-frequency conditionally periodic motions (with frequencies of different orders in a small parameter) are described.

Security enhanced underwater visible light communication system based on chaotic phase scrambling and conjugate frequency hopping

We propose an encryption technique for underwater visible light communication (UVLC) based on chaotic phase scrambling (PS) and conjugate frequency hopping (CFH). The technique is experimentally tested using an 8-level pulse amplitude modulation (PAM-8) and a 1.2 m underwater link. The security key of the phase scrambling code is generated according to a logistic map, and the frequency hopping is achieved by adding the same zero frequency points to the signal spectrum. The maximum transmission rate of 2.1 Gbit/s is measured with bit-error-rate (BER) below 7% the hard-decision forward error correction (HD-FEC) threshold of 3.8×10-3.