Interference Oscillations Research Articles

Identification of Sub-Synchronous Oscillation Mode Based on HO-VMD and SVD-Regularized TLS-Prony Methods

To reduce errors in sub-synchronous oscillation (SSO) modal identification and improve the accuracy and noise resistance of the traditional Prony algorithm, this paper focuses on SSOs caused by the integration of doubly fed induction generators (DFIGs) with series compensation into the grid. A novel SSO modal identification method based on the hippopotamus optimization–variational mode decomposition (HO-VMD) and singular value decomposition–regularized total least squares–Prony (SVD-RTLS-Prony) algorithms is proposed. First, the energy ratio function is used for real-time monitoring of the system to identify oscillation signals. Then, to address the limitations of the VMD algorithm, the HO algorithm’s excellent optimization capabilities were utilized to improve the VMD algorithm, leading to preliminary denoising. Finally, the SVD-RTLS-improved Prony algorithm was employed to further suppress noise interference and extract oscillation characteristics, allowing for the accurate identification of SSO modes. The performance of the proposed method was evaluated using theoretical and practical models on the Matlab and PSCAD simulation platforms. The results indicate that the algorithms effectively perform denoising and accurately identify the characteristics of SSO signals, confirming its effectiveness, accuracy, superiority, and robustness against interference.

EXPERIMENTAL STUDY ON TWO-PHASE NONLINEAR OSCILLATION BEHAVIOR OF MINIATURIZED GRAVITATIONAL HEAT PIPE

An experimental study on oscillation behavior of vapor-liquid two-phase flow in an ethanol-filled aluminum miniaturized gravitational heat pipe with parallel rectangular channels is carried out. The nonlinear oscillation behavior and oscillation characteristics of two-phase flow in the oscillation state are qualitatively analyzed. In addition, the nonlinear oscillation characteristic of the wall temperature is revealed. Furthermore, the influence of heat load on temperature oscillation characteristics is further analyzed. The research shows that the independent oscillation in a single channel characterized by the random formation and oscillation of liquid plug in a single channel is the typical oscillation behavior of two-phase flow under medium heat load (<i>Q</i> = 28 W). In addition, the interaction on oscillation of liquid plugs between adjacent channels is small. For high heat load (<i>Q</i> = 45 W), the vapor pressure difference at both ends of the liquid plug has a more important role in promoting the liquid plug, the superposition of the liquid plug oscillation in single channel and the oscillation between adjacent channels forms the interference oscillation in adjacent channels. For interference oscillation in adjacent channels, under coupling erosion of the liquid plug in a single channel and the liquid plugs in adjacent channels, with increase of heat load (<i>Q</i> increases from 38 W to 45 W), the dominant frequency of oscillation for independent oscillation in a single channel increases (from 2.5 Hz to 4.2 Hz), and the larger driving force caused by heat load increase enhances the oscillation of liquid plug in a single channel and weakens the oscillation of liquid plug in different channels for interference oscillation in adjacent channels.

Movement-related beta and gamma oscillations indicate parallels and disparities between Alzheimer's disease and HIV-associated neurocognitive disorder

People with HIV (PWH) often develop HIV-related neurological impairments known as HIV-associated neurocognitive disorder (HAND), but cognitive dysfunction in older PWH may also be due to age-related disorders such as Alzheimer's disease (AD). Discerning these two conditions is challenging since the specific neural characteristics are not well understood and limited studies have probed HAND and AD spectrum (ADS) directly. We examined the neural dynamics underlying motor processing during cognitive interference using magnetoencephalography (MEG) in 22 biomarker-confirmed patients on the ADS, 22 older participants diagnosed with HAND, and 30 healthy aging controls. MEG data were transformed into the time-frequency domain to examine movement-related oscillatory activity and the impact of cognitive interference on distinct stages of motor programming. Both cognitively impaired groups (ADS/HAND) performed significantly worse on the task (e.g., less accurate and slower reaction time) and exhibited reductions in frontal and cerebellar beta and parietal gamma activity relative to controls. Disease-specific aberrations were also detected such that those with HAND exhibited weaker gamma interference effects than those on the ADS in frontoparietal and motor areas. Additionally, temporally distinct beta interference effects were identified, with ADS participants exhibiting stronger beta interference activity in the temporal cortex during motor planning, along with weaker beta interference oscillations dispersed across frontoparietal and cerebellar cortices during movement execution relative to those with HAND. These results indicate both overlapping and distinct neurophysiological aberrations in those with ADS disorders or HAND in key motor and top-down cognitive processing regions during cognitive interference and provide new evidence for distinct neuropathology.

Optimal reception of multiple phase shift keying and quadrature amplitude modulation signals with non-coherent processing of harmonic interference

Objectives . Analysis of the reception noise immunity of multiple phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM) signals has demonstrated a significant reduction in the quality of reception of discrete information due to the presence of various types of non-fluctuating interference in a radio communication channel including targeted harmonic interference. Therefore, the development of algorithms for compensating the influence of such forms of interference is an urgent task. While various methods for combatting this kind of interference, these vary in terms of their effectiveness. The aim of the present work is to synthesize and analyze the optimal algorithm for the reception of M-PSK and M-QAM signals with incoherent processing of harmonic interference. Methods . Various statistical radio engineering and computer simulation methods were used in accordance with optimal signal reception theory. Results . Synthesis and analysis of the optimal algorithm for receiving M-PSK and M-QAM signals with incoherent processing of harmonic interference were carried out. In addition to calculating the correlation integrals in the receiver, it is necessary to form weight coefficients, whose value depends on the correlation of the interference oscillation (extracted from the received mixture) with a sample of the interference stored in the receiver. The dependences of the bit error probability on the signal-to-noise ratio, interference detuning, and inaccuracy in setting the frequency and level of the interference sample in the receiver were obtained. It is shown that the higher the gain in the noise immunity of reception, the greater the intensity of the harmonic interference. Conclusions . The synthesized receiver circuit effectively compensates for harmonic interference. However, the efficiency of its operation depends on the detuning of the harmonic interference relative to the center frequency of the spectrum of the useful signal. The scheme for incoherent processing of harmonic interference remains operational even with small (within ±10%) inaccuracies in setting the frequency and the level of the interference copy in the receiver.

Nonequilibrium Hanbury Brown-Twiss interferometry: Theory and application to binary stars

Intensity interferometry based on Hanbury Brown and Twiss's seminal experiment for determining the radius of the star Sirius formed the basis for developing the quantum theory of light. To date, the principle of this experiment is used in various forms across different fields of quantum optics, imaging, and astronomy. Although the technique is powerful, it has not been generalized for objects at different temperatures. Here, we address this problem using a generating functional formalism by employing the $P$-function representation of quantum-thermal light. Specifically, we investigate the photon coincidences of a system of two extended objects at different temperatures using this theoretical framework. We show two unique aspects in the second-order quantum coherence function: interference oscillations and a long-baseline asymptotic value that depends on the observation frequency, temperatures, and size of both objects. We apply our approach to the case of binary stars and discuss the advantages of measuring these two features in an experiment. In addition to the estimation of the radii of each star and the distance between them, we also show that the present approach is suitable for the estimation of temperatures as well. To this end, we apply it to the practical case of binary stars Luhman 16 and Spica $\ensuremath{\alpha}$ Vir. We find that for currently available telescopes, an experimental demonstration is feasible in the near term. Our work contributes to the fundamental understanding of intensity interferometry of quantum-thermal light and can be used as a tool for studying two-body thermal emitters, from binary stars to extended objects.

Measuring Quantum Geometric Tensor of Non-Abelian System in Superconducting Circuits

Topology played an important role in physics research during the last few decades. In particular, the quantum geometric tensor that provides local information about topological properties has attracted much attention. It will reveal interesting topological properties but have not been measured in non-Abelian systems. Here, we use a four-qubit quantum system in superconducting circuits to construct a degenerate Hamiltonian with parametric modulation. By manipulating the Hamiltonian with periodic drivings, we simulate the Bernevig–Hughes–Zhang model and obtain the quantum geometric tensor from interference oscillation. In addition, we reveal its topological feature by extracting the topological invariant, demonstrating an effective protocol for quantum simulation of a non-Abelian system.

Optical-field-induced Electron Emission in a dc-Biased Nanogap

We construct an analytical formulation for nonlinear photoelectron emission in a dc-biased metallic nanovacuum gap triggered by a laser field, by exactly solving the one-dimensional time-dependent Schr\"odinger equation. We theoretically investigate the photoelectron energy spectra and emission current from left- and right-side surfaces of the asymmetric nanojunction with various dc biases, laser fields, and gap distances. The underlying photoemission mechanisms transitioning form multiphoton over-barrier emission to photon-assisted field tunneling, and the spatiotemporal dynamics of electron transport inside the gap are analyzed in detail. Our calculation shows applying a dc field could greatly reduce the interference oscillation in the transmission current in the nanogap, due to the shift of dominant emission away from the multiphoton over-barrier regime. Our results demonstrate that, besides the dc bias, varying the gap spacing could strongly influence the rectification on the photoelectron emission in a dc-biased metal-vacuum-metal gap. Our study provides useful guideline to the design of ultrafast nanogap-based signal rectification devices, such as photoelectron emitters and photodetectors, by choosing an optimal combination of dc bias, gap spacing, and material properties.

Optical theorem of an infinite circular cylinder in weakly absorbing media

The conventional optical theorem cannot consider losses of host media. As a fundamental problem of light scattering, the generalized optical theorem of an infinite cylinder embedded in a weakly absorbing host is studied in this paper. Using the analytical way, we derive the generalized far-field and distance-independent extinction efficiencies per unit length of the cylinder under normally incident p- and s-polarized waves, which reduce to the conventional formulas in the transparent host media. For large cylinders, the increasing absorption of the host medium leads to an increasing amplitude of interference oscillation and the emergence of negative extinction, which is similar to that for spheres. Furthermore, the absorption of the host medium is proved to destroy the morphology-dependent resonance structure in extinction and suppress the electric field resonance inside the cylinder. For small cylinders in a weakly absorbing host medium, we present the conditions for negative extinction and quantitatively analyze the differences in extinction between the absorbing host medium and the nonabsorbing counterpart. It is found that the ratio of the extinction from the generalized theory to conventional formulas depends only on the refraction indices of the cylinder and the host medium. The results for small cylinders are rather sensitive to the state of polarization of the light. By illustrating the significant differences between the generalized optical theorem and the conventional theory with a specific case of a Ge cylinder in polyethylene, we show the non-negligible impacts of the absorption of the host media on the optical extinction of the cylinder for the two polarizations.

Fiber Optic SMS Sensor for Simultaneous Measurement of Strain and Curvature

The article presents a fiber-optic sensor based on a singlemode-multimode-singlemode (SMS) structure for simultaneous measurement of strain and curvature. It is shown that the simultaneous demodulation of strain and curvature can be realized using the Fourier analysis of the recorded interference oscillations. Keywords: optical fiber sensors, intermode interference, single mode-multimode-single mode, stretching, bending.

Fiber Optic SMS Sensor for Simultaneous Measurement of Strain and Curvature

The article presents a fiber-optic sensor based on a singlemode-multimode-singlemode (SMS) structure for simultaneous measurement of strain and curvature. It is shown that the simultaneous demodulation of strain and curvature can be realized using the Fourier analysis of the recorded interference oscillations. Keywords: optical fiber sensors, intermode interference, single mode-multimode-single mode, stretching, bending.

Interference oscillations in the optical response of a hybrid-aligned nematic with a surface disclination line to a pulsed magnetic field

The propagation of light through a hybrid-aligned nematic layer with a surface disclination line is investigated in a pulsed magnetic field. The experimental dependences of light intensity I on time t accompanied by interference oscillations are presented. The shift and expansion of the interference extrema as functions of the magnetic field pulse length during the reaction are shown. The I ( t ) dependence for the relaxation process is calculated with allowance for scattering. The calculated I ( t ) dependence agrees well with the experimental dependence over the entire hybrid-aligned nematic layer, except for the surface layer.

Ellipsometric thermometry in molecular beam epitaxy of mercury cadmium telluride

Low temperature in situ control in the technology of HgCdTe layers growing by MBE is a key requirement for obtaining structures of high quality. Spectroscopic ellipsometry seems to be one of the suitable technique for solving this problem. The present paper proposes ellipsometric methods for determining the temperature in the process of pre-epitaxial heat treatment of the samples. The proposed methods are based on the temperature dependence of the optical constants spectra of the CdTe buffer layer. The first method uses the temperature shift of the absorption edge, which is determined from the onset of interference oscillations. It turned out to be resistant to experimental errors and its accuracy proved to be 3–5 °C. The second method is based on comparing the measured and reference spectra. It is much more sensitive to the temperature, but depends strongly on the accuracy of ellipsometric measurements. The combined use of both methods ensures a temperature sensitivity of the order of 1 °C and an accuracy of 3–5 °C.

Terahertz spectroscopy analysis of human corneal sublayers.

.Significance: Corneal diseases is a major cause of reversible blindness in the world. Monitoring the progression of human corneal edema or corneal scarring to prevent the disease entering into the end stage is crucial.Aim: We present a method for sensing human corneal composition at different depths, namely focused on the epithelium and stromal layer, using high-sensitivity terahertz (THz) broadband spectroscopy.Approach: From the proposed methodology, the THz temporal and absorption spectra of human corneas at different edema stages have been studied. THz wave signals were collected from the direct reflection and four other collection points along the THz wave propagation direction as reviewed from the simulation THz electrical field.Result: Our results show that the epithelium layer acts as a good barrier to maintain hydration level of the stroma, and the quality of the epithelium can be used to predict the level of corneal swelling in corneal edema. At the detection points near to the incident point, the THz frequency spectra demonstrated interference oscillation behavior. At the final edema observing time, results showed that the epithelium lose its barrier properties. The intactness of the epithelium can be used to predict the edema severity in the final stage. When the detection points are further away from the incident point, the THz spectra are believed to contain information from stromal layer. Stromal absorption spectra demonstrated correlation with optical coherence tomography thickness results.Conclusion: The hydration concentration from stromal layer was further quantitatively calculated. At the end of the experiment, all the corneal hydration levels reach to the same value which shows that the edema hydration has reached maximum saturation. The information of individual sublayers of the cornea is obtained by characterizing noninvasively with the use of THz spectroscopy. To our knowledge, this is the first report of using THz for noninvasive characterization of sublayers of the cornea.

Волоконно-оптический датчик на основе межмодового интерферометра с одномодовым подключением для одновременного измерения изгиба и растяжения

The article presents a fiber-optic sensor based on a singlemode-multimode-singlemode (SMS) structure for simultaneous measurement of strain and curvature. It is shown that the simultaneous demodulation of strain and curvature can be realized using the Fourier analysis of the recorded interference oscillations

Determination of the parameters of coherent magneto-optical layers on a finite absorbing substrate from thermal radiation spectra

A possibility of determining the parameters of a coherent magneto-optical layer on a finite incoherent absorbing substrate by analyzing the spectra of its thermal radiation (TR) has been investigated. On the example of a plane-parallel InAs semiconductor plate silver-coated on the back surface, it has been shown that a complex analysis of TR spectra, both without and with the presence of magnetic field, makes it possible to determine the thickness, optical, magneto-optical and electric parameters of the layer. Algorithms for the calculation and analysis of TR spectra are adduced, which simplify determination of layer parameters and increase the accuracy of results. Comparing the position of the extremes of the experimental zero-field spectrum with the theoretical calculations, the thickness of the sample and the plasma oscillation frequency in the used semiconductor have been determined. The analysis of the relative contrast of interference oscillations in the TR spectrum in the magnetic field using previously defined parameters enabled to ascertain the spectral dependence of the Faraday rotation angle and to determine the concentration, effective mass and type of current carriers. It has been assumed, that such analysis of luminescence spectra also allows determining the parameters of magneto-optical layers and structures.

Gate-Modulated Quantum Interference Oscillations in Sb-Doped Bi2Se3 Topological Insulator Nanoribbon

Topological insulator nanoribbons (TI NRs) provide a useful platform to explore the phase-coherent quantum electronic transport of topological surface states, which is crucial for the development of topological quantum devices. When applied with an axial magnetic field, the TI NR exhibits magnetoconductance (MC) oscillations with a flux period of h/e, i.e., Aharonov-Bohm (AB) oscillations, and h/2e, i.e., Altshuler-Aronov-Spivak (AAS) oscillations. Herein, we present an extensive study of the AB and AAS oscillations in Sb doped Bi$_2$Se$_3$ TI NR as a function of the gate voltage, revealing phase-alternating topological AB oscillations. Moreover, the ensemble-averaged fast Fourier transform analysis on the Vg dependent MC curves indicates the suppression of the quantum interference oscillation amplitudes near the Dirac point, which is attributed to the suppression of the phase coherence length within the low carrier density region. The weak antilocalization analysis on the perpendicular MC curves confirms the idea of the suppressed coherence length near the Dirac point in the TI NR.

Adjustable Quantum Interference Oscillations in Sb-Doped Bi2Se3 Topological Insulator Nanoribbons.

Topological insulator (TI) nanoribbons (NRs) provide a platform for investigating quantum interference oscillations combined with topological surface states. One-dimensional subbands formed along the perimeter of a TI NR can be modulated by an axial magnetic field, exhibiting Aharonov-Bohm (AB) and Altshuler-Aronov-Spivak (AAS) oscillations of magnetoconductance (MC). Using Sb-doped Bi2Se3 TI NRs, we found that the relative amplitudes of the two quantum oscillations can be tuned by varying the channel length, exhibiting crossover from quasi-ballistic to diffusive transport regimes. The AB and AAS oscillations were discernible even for a 70 μm long channel, while only the AB oscillations were observed for a short channel. Analyses based on ensemble-averaged fast Fourier transform of MC curves revealed exponential temperature dependences of the AB and AAS oscillations, from which the circumferential phase-coherence length and thermal length were obtained. Our observations indicate that the channel length in a TI NR can be a useful control knob for tailored quantum interference oscillations, especially for developing topological hybrid quantum devices.

Blind Witnesses Quench Quantum Interference without Transfer of Which-Path Information.

Quantum computation is often limited by environmentally-induced decoherence. We examine the loss of coherence for a two-branch quantum interference device in the presence of multiple witnesses, representing an idealized environment. Interference oscillations are visible in the output as the magnetic flux through the branches is varied. Quantum double-dot witnesses are field-coupled and symmetrically attached to each branch. The global system—device and witnesses—undergoes unitary time evolution with no increase in entropy. Witness states entangle with the device state, but for these blind witnesses, which-path information is not able to be transferred to the quantum state of witnesses—they cannot “see” or make a record of which branch is traversed. The system which-path information leaves no imprint on the environment. Yet, the presence of a multiplicity of witnesses rapidly quenches quantum interference.

Light interference in a hybrid-aligned nematic layer with nonordered surface disclination lines

The propagation of a laser beam through a hybrid-aligned nematic layer with a surface disclination line has been investigated. A model of the light interference has been developed to consider the scattering by the structural inhomogeneities. The analytical expression that includes the factor characterizing an exponential decrease in the light scattering has been obtained. The dependence of the intensity of light transmitted through the layer on the magnetic field has been measured. The dependence has been accompanied by the interference oscillations. The theoretical expression is consistent with the experiment, which confirms the correctness of the model concepts.

Scattering by a charged sphere embedded in an absorbing medium

An absorbing host medium and surface conductivity of a charged sphere are two emerging factors that influence electromagnetic scattering and play a role in tuning optical properties of the sphere. In this paper, we study a general case of the light scattering by a charged sphere embedded in an absorbing host medium. Combining the two established Lorentz-Mie theories which apply to the absorbing host medium and the charged sphere, we calculate the far-field extinction efficiency factor and the electric field amplitude. Our results show that amplifying effect of the increasing absorption of host medium on the interference oscillations of the extinction efficiency factor is opposite to the damping effect of the increasing surface conductivity. On the electric field amplitude, the increasing absorption of the host medium enhances the backscattering field in contrast to the front-scattering field. However, the increasing surface conductivity induces a size-parameter dependent change on the pattern of the field distribution and the magnitude of the field.