Search Results (72)

As a core power supply component of the more electric aircraft (MEA), the reliability of the permanent magnet synchronous generator (PMSG) is of paramount importance. Phase current reconstruction technology can enhance the redundancy of current sensors, thereby improving system reliability. However, owing to the generally high engine speeds in MEAs, the employment of traditional d-axis current–zero control not only induces DC-link voltage fluctuations but also leads to inaccurate DC-link sampling points and distortion in the reconstructed current. In this paper, a lead-angle flux-weakening control strategy is introduced into the PMSG rectification system. This approach guarantees the normal operation of the current loop when the rotational speed exceeds the rated speed of the PMSG, ensuring the accuracy of the sampling points for phase current reconstruction. To further enhance the reconstruction accuracy, a phase current reconstruction technology based on a linear extended state observer (LESO) is proposed. The LESO not only filters the reconstructed current but also ensures that the observer performance remains robust against PMSG parameter perturbations. Finally, the effectiveness of the proposed method is validated through Hardware-in-the-Loop results. Full article

A ring of classical charge with a charged point particle oscillating within is first analyzed. The charged particle interacts with classical electromagnetic thermal radiation, which causes the particle to fluctuate, while the ring of charge imparts a resonant frequency to the particle’s motion. Oscillations in one direction within the plane of the ring are analyzed. The radius of the ring is slowly altered. The accompanying change in the particle’s average internal energy and the average work done in changing the radius are calculated. This leads to a derivation of the classical electromagnetic zero-point radiation spectrum. Next, the second law of thermodynamics is applied to the entropy to enable a more general derivation of the Wien displacement law. With this derivation, zero-point radiation can be included in the Wien displacement law. Finally the definition of the thermodynamic temperature is emphasized, and methods for performing the needed calculations for the temperature ratio are discussed. Full article

We present a detailed derivation of the quantum and quantum–thermal effective action for non-relativistic systems, starting from the single-particle case and extending to the Gross–Pitaevskii (GP) field theory for weakly interacting bosons. In the single-particle framework, we introduce the one-particle-irreducible (1PI) effective action formalism, taking explicitly into account the choice of the initial quantum state, its saddle-point plus Gaussian-fluctuation approximation, and its finite-temperature extension via Matsubara summation, yielding a clear physical interpretation in terms of zero-point and thermal contributions to the Helmholtz free energy. The formalism is then applied to the GP action, producing the 1PI effective potential at zero and finite temperature, including beyond-mean-field Lee–Huang–Yang and thermal corrections. We discuss the gapless and gapped Bogoliubov spectra, their relevance to equilibrium and non-equilibrium regimes, and the role of regularization. Applications include the inclusion of an external potential within the local density approximation, the derivation of finite-temperature Josephson equations, and the extension to D-dimensional systems, with particular attention to the zero-dimensional limit. This unified approach provides a transparent connection between microscopic quantum fluctuations and effective macroscopic equations of motion for Bose–Einstein condensates. Full article

We have investigated the evolution of CDW states and structural phases in a Cu-deficient Cu_1-δTe (δ = 0.016) by employing high-pressure experiments and first-principles calculations. Raman scattering results reveal that the vulcanite structure at ambient pressure starts to change into the Cu-deficient rickardite (r-CuTe) structure from 6.7 GPa, which then becomes fully stabilized above 8.3 GPa. Resistivity data show that T_CDW1 (≈333 K) is systematically suppressed under high pressure, reaching zero at 5.9 GPa. In the pressure range of 5.2–8.2 GPa, a sharp resistivity drop due to superconductivity occurs at the onset temperature T_C = ~2.0–3.2 K. The maximum T_C = 3.2 K achieved at 5.6 GPa is clearly higher than that of CuTe (2.3 K), suggesting the importance of charge fluctuation in the vicinity of CDW suppression. At 7.5 GPa, another resistivity anomaly appears due to the emergence of a second CDW (CDW2) ordering at T_CDW2 = ~176 K, which exhibits a gradual increase to ~203 K with pressure increase up to 11.3 GPa. First-principles calculations on the Cu-deficient Cu₁₁Te₁₂ with the r-CuTe structure show that including on-site Coulomb repulsion is essential for incurring an unstable phonon mode relevant for stabilizing the CDW2 order. These results point out the important role of charge fluctuation in optimizing the pressure-induced superconductivity and that of Coulomb interaction in creating the competing CDW order in the Cu-deficient CuTe system. Full article

To address the issues of quadrature component attenuation and signal-to-noise ratio (SNR) degradation caused by carrier phase delay in Phase-Generated Carrier (PGC) demodulation, this paper proposes a phase delay compensation method based on sampling-point shift pre-calibration. By establishing a discrete phase offset model, we derive the mathematical relationship between sampling point shift and carrier cycle duration, and introduce a compensation mechanism that adjusts the starting point of the sampling sequence to achieve carrier phase pre-alignment. Theoretical analysis demonstrates that this method restricts the residual phase error to within Δθ_max = πf₀/f_s, thereby fundamentally avoiding the denominator-zero problem inherent in traditional compensation algorithms when θ approaches 45°. Experimental validation using an Extrinsic Fabry–Perot Interferometric (EFPI) ultrasonic sensor shows that, at a sampling rate of 10 MS/s, the proposed pre-alignment algorithm improves the minimum demodulation SNR by 35 dB and reduces phase fluctuation error to 2% of that of conventional methods. Notably, in 1100 consecutive measurements, the proposed method eliminates demodulation failures at critical phase points (e.g., π/4, π/2), which are commonly problematic in traditional techniques. By performing phase pre-compensation at the signal acquisition level, this method significantly enhances the long-term measurement stability of interferometric fiber-optic sensors in complex environments while maintaining the existing PGC demodulation architecture. Full article

A multiscale thermodynamic model is considered, in which cosmological dynamics enforce persistent non-equilibrium conditions through recursive energy exchange across hierarchically ordered subsystems. The internal energy of each subsystem is recursively determined by energetic interactions with its subcomponents, forming a nested hierarchy extending up to cosmological scales. The total energy of the universe is assumed to be constant, imposing global consistency conditions on local dynamics. On the quantum scale, subsystems remain thermodynamically constrained in their accessible state space due to the unresolved energetic embedding imposed by higher-order couplings. As a result, quantum behavior is interpreted as an effective projection of unresolved thermodynamic interactions. In this view, the wave function serves as a mathematical representation of a subsystem’s thermodynamic embedding, summarizing the unresolved energetic couplings with its environment, as shaped by recursive interactions across cosmological and microscopic scales. Phenomena such as zero-point energy and vacuum fluctuations are thereby understood as residual effects of structural energy constraints. Classical mechanics arises as a limiting case under full energetic resolution, while the quantum formalism reflects thermodynamic incompleteness. This formulation bridges statistical mechanics and quantum theory without metaphysical assumptions. It remains fully compatible with standard formalism, offering a thermodynamic interpretation based solely on energy conservation and hierarchical organization. All effects arise from scale-dependent resolution, not from violations of established physics. Full article

Miller’s rule originated as an empirical relation between the nonlinear and linear optical coefficients of materials. It is now accepted as a useful tool for guiding experiments and computational materials discovery, but its theoretical foundation had long been limited to a derivation for the classical Lorentz model with a weak anharmonic perturbation. Recently, we developed a mathematical framework which enabled us to prove that Miller’s rule is equally valid for quantum anharmonic oscillators, despite different dynamics due to zero-point fluctuations and further quantum-mechanical effects. However, our previous derivation applied only to one-dimensional oscillators and to the special case of second- and third-harmonic generation in a monochromatic electric field. Here we extend the proof to three-dimensional quantum anharmonic oscillators and also treat all orders of the nonlinear response to an arbitrary multi-frequency field. This makes the results applicable to a much larger range of physical systems and nonlinear optical processes. The obtained generalized Miller formulae rigorously express all tensor elements of the frequency-dependent nonlinear susceptibilities in terms of the linear susceptibility and thus allow a computationally inexpensive quantitative prediction of arbitrary parametric frequency-mixing processes from a small initial dataset. Full article

The influence of zero-point fluctuations on photon propagation in a vacuum is investigated without using normal ordering and renormalization procedures, but in a frame of the conformally unimodular metric for a description of the fluctuating gravitational field. The complete formula for decoherence time is presented. Full article

Modular multilevel converters (MMCs) are widely used in power-conversion applications, including distributed energy storage integration, because of their scalability, high efficiency, and reduced harmonic distortion. Integrating battery storage systems into MMC submodules using dual active bridge (DAB) converters provides electrical isolation and reduces voltage stress, harmonics, and common-mode issues. However, voltage fluctuations due to the battery state of charge can compromise the zero-voltage switching (ZVS) operation of a DAB and increase the reactive power circulation, leading to higher losses and reduced system performance. To address these challenges, this study investigated an active control strategy for submodule voltage regulation in an MMC with DAB-based battery integration. Assuming single-phase-shift modulation, two control strategies were evaluated. The first strategy regulated the DAB voltage on one side to match the battery voltage on the other, scaled by the high-frequency transformer turns ratio, which facilitated the ZVS operation and reduced the reactive power. The second strategy optimized this voltage to minimize the total power-conversion losses. The proposed control strategies improved the efficiency, particularly at low power levels, achieving several percentage points of improvement compared to maintaining a constant voltage. Full article

The transient operation of pump turbines generates significant flow-induced instabilities, prompting a comprehensive numerical investigation using the SST $k-\omega$ turbulence model to examine these instability effects throughout the complete operating range in turbine mode. This study specifically analyzes the evolutionary mechanisms of unsteady flow dynamics under ten characteristic off-design conditions while simultaneously characterizing the pressure fluctuation behavior within the vaneless space (VS). The results demonstrate that under both low-speed conditions and near-zero-discharge conditions, the VS and its adjacent flow domains exhibit pronounced flow instabilities with highly turbulent flow structures, while the pressure fluctuation amplitudes remain relatively small due to insufficient rotational speed or flow rate. Across the entire turbine operating range, the blade passing frequency (BPF) dominates the VS pressure fluctuation spectrum. Significant variations are observed in both low-frequency components (LFCs) and high-frequency, low-amplitude components (HF-LACs) with changing operating conditions. The HF-LACs exhibit relatively stable amplitudes but demonstrate significant variation in the frequency spectrum distribution across different operating conditions, with notably broader frequency dispersion under runaway conditions and adjacent operating points. The LFCs demonstrate significantly higher spectral density and amplitude magnitudes under high-speed, low-discharge operating conditions while exhibiting markedly reduced occurrence and diminished amplitudes in the low-speed, high-flow regime. This systematic investigation provides fundamental insights into the flow physics governing pump-turbine performance under off-design conditions while offering practical implications for optimizing transient operational control methodologies in hydroelectric energy storage systems. Full article

Any quantum theory of gravity at the quantum gravity scale has the expectation of the existence of a minimal observable length. It is also expected that this fundamental length has a principal role in nature at the quantum gravity scale. From the uncertainty principle that influences the quantum measurement process, the existence of a minimal measurable length can be heuristically deduced. The existence of this minimal measurable length leads to an apparent discretization of spacetime, as distinguishing below this minimal length becomes impossible. In topologically non-trivial cosmological models, the Casimir effect is significant since it alters the spectrum of vacuum fluctuations and leads to a non-zero Casimir energy density. This suggests that the topology of the Universe could influence its vacuum energy, potentially affecting its expansion dynamics. In this sense, the Casimir effect could contribute to the observed acceleration of the Universe’s expansion. Here, we use the Casimir effect to determine the value of the electromagnetic zero-point energy in the Universe, applying it to the regions outside and inside the Universe horizon or Hubble horizon and assuming the existence of this minimal length. The Casimir effect is directly related to the boundary conditions imposed by the geometry and symmetries of the Hubble horizon. The agreement of the obtained value with the observed cosmological constant is not exact and therefore the contribution of non-electromagnetic radiation (gravitational effects) must be take into account. Full article

Zinc oxide (ZnO) has recently gained considerable attention due to its exceptional properties, including higher electron mobility, good thermal conductivity, high breakdown voltage, and a relatively large exciton-binding energy. These characteristics helped engineers to develop low dimensional heterostructures (LDHs)-based advanced flexible/transparent nanoelectronics, which were then integrated into thermal management systems. Coefficients of thermal expansion $\mathsf{\alpha }\left(\mathrm{T}\right),$ phonon dispersions ${\mathsf{\omega }}_{\mathrm{j}}(\overrightarrow{\mathrm{q}})$, and Grüneisen parameters ${\mathsf{\gamma }}_{\mathrm{j}}\left(\overrightarrow{\mathrm{q}}\right)$ can play important roles in evaluating the suitability of materials in such devices. By adopting a realistic rigid-ion model in the quasi-harmonic approximation, this work aims to report the results of a methodical study to comprehend the structural, lattice dynamical, and thermodynamic behavior of zinc-blende (zb) ZnO. Systematic calculations of ${\mathsf{\omega }}_{\mathrm{j}}(\overrightarrow{\mathrm{q}})$, ${\mathsf{\gamma }}_{\mathrm{j}}\left(\overrightarrow{\mathrm{q}}\right),$ and $\mathsf{\alpha }\left(\mathrm{T}\right)$ have indicated negative thermal expansion (NTE) at low T. Soft transverse acoustic shear mode gammas ${\mathsf{\gamma }}_{\mathrm{T}\mathrm{A}}$ at critical points offered major contributions to NTE. Our results of ${\mathsf{\omega }}_{\mathrm{j}}(\overrightarrow{\mathrm{q}})$ at ambient pressure compare reasonably well with Raman scattering spectroscopy measurements and first-principles calculations. By adjusting the layers of materials with positive and negative thermal expansion, it is possible to create LDHs with near-zero $\mathsf{\alpha }\left(\mathrm{T}\right)$. Such a nanostructure might experience a minimal dimensional change with T fluctuations, making it ideal for devices where precise dimensional stability is crucial. Full article

Nuclear quantum effects play a significant role in the dissociation dynamics of HCl ions during collisions with the (H₂O)₄₉ ice cluster. These effects become particularly important when analyzing proton transfer, tunneling, and zero-point energy contributions during the dissociation process. In this study, we investigate the dissociation behavior of HCl when colliding with the (H₂O)₄₉ ice cluster, focusing on the influence of the nuclear quantum effects on the proton transfer mechanism, ionic dissociation rates, and subsequent solvation dynamics. Through a combination of classical molecular dynamics (MD) and ring-polymer molecular dynamics (RPMD) simulations, we explore how quantum fluctuations in the proton’s position alter the dissociation pathway of HCl. The inclusion of nuclear quantum effects reveals enhanced proton mobility, leading to differences in dissociation behavior compared to classical simulations. Our findings indicate that nuclear quantum effects significantly affect the dissociation dynamics, with the proton more readily transferring to the hydrogen-bond network in the (H₂O)₄₉ ice cluster. This study provides insights into the quantum mechanical nature of ionic dissociation in hydrogen-bonded systems and highlights the importance of incorporating nuclear quantum effects for accurate modeling of proton transfer processes in complex environments. Full article

This article introduces a small microwave remote sensing satellite weighing 310 kg, operating in low earth orbit (LEO). It is equipped with an X-band synthetic aperture radar (SAR) antenna, capable of a maximum imaging resolution of 0.6 m. To achieve the objectives of lower cost, reduced weight, minimized power consumption, and enhanced temperature stability, an optimized thermal design method tailored for satellites has been developed, with a particular focus on SAR antennas. The thermal control method of the antenna is closely integrated with structural design, simplifying the thermal design and its assembly process, reducing the resource consumption of thermal control systems. The distribution of thermal interface material (TIM) in the antenna assembly has been carefully calculated, achieving a zero-consumption thermal design for the SAR antenna. And the temperature difference of the entire antennas when powered on and powered off would not exceed 17 °C, meeting the specification requirements. In addition, to ensure the accuracy of antenna pointing, the support plate of antennas requires stable temperature. The layout of the heaters on the board has been optimized, reducing the use of heaters by 30% while ensuring that the temperature variation of the support board remains within 5 °C. Then, an on-orbit thermal simulation analysis of the satellite was conducted to refine the design and verification. Finally, the thermal test of the SAR satellite under vacuum conditions was conducted, involving operating the high-power antenna, verifying that the peak temperature of T/RM is below 29 °C, the temperature fluctuation amplitude during a single imaging task is 10 °C, and the lowest temperature point of the support plate is 16 °C. The results of the thermal simulation and test are highly consistent, verifying the correctness and effectiveness of the thermal design. Full article

Dual-port direct drive wave energy power generation systems (DP-DDWEPGS) have received widespread attention due to their smooth and zero-free output power, compared to single-port direct drive wave energy power generation systems (SP-DDWEPGS) which have the disadvantage of large out-put power fluctuations. To further enhance the performance of the DP-DDWEPGS, optimal power capture control is proposed to achieve maximum power point tracking. Meanwhile, a multiport converter is applied to the DP-DDWEPGS to solve the problem caused by an excessive number of switching devices in the overall system converter. The multiport converter fulfills all the functional requirements of the DP-DDWEPGS while reducing the number of switching devices. However, switch multiplexing of the multiport converter also introduces coupling relationships between each port and the wave force exhibits time-varying characteristics, necessitating advanced control methods with superior fast-tracking capability. Therefore, in this paper, a decoupling duty cycle optimization model predictive control for DP-DDWEPGS is proposed. Based on the characteristics of switching multiplexing, NSC finite control set model predictive control (FCS-MPC) decouples the current prediction and the cost function, reduces the number of candidate voltage vectors in each operation, and shortens the operation time by 70%. To address the issues of high ripple value and increased error due to decoupling in FCS-MPC, duty cycle optimization control is added, greatly reducing the fluctuations in electromagnetic force and power of the permanent magnet linear generator (PMLG). Based on the established simulation model, the feasibility and superiority of the multiport converter and decoupling duty cycle optimization model predictive current control method are verified. Full article