Derivative Corrections Research Articles

Coupling Analysis of Electromagnetic Vibration and Noise of FeCo-Based Permanent-Magnet Synchronous Motor

Addressing the problem of the vibration and noise of a permanent-magnet synchronous motor (PMSM), this paper optimizes the structure of a permanent-magnet motor rotator, introduces the electromagnetic-structure-acoustic coupling calculation model, and optimizes the motor rotator to reduce the vibration and noise of a permanent-magnet motor. Using the theory of Maxwell’s stress equation, the radial electromagnetic force on the stator teeth of the permanent-magnet motor is deduced and analyzed, and the correctness of the analysis calculation is verified by using the finite element multi-physical field coupling method. Based on the deduced analytical expression of the radial electromagnetic force, the sources of the radial electromagnetic force for each order and the frequency of the permanent-magnet motor are summarized. A 12-slot, 8-pole, permanent-magnet motor is taken as an example. A calculation model considering the spatial distribution of the radial electromagnetic force and the electromagnetic vibration of an iron-cobalt-based stator is established. The harmonic response of the electromagnetic vibration of the motor is analyzed, and a modal analysis is carried out. The optimized acceleration vibration noise cascade of the FeCo-based permanent-magnet drive motor under load is given. The correctness and validity of the theoretical derivation and simulation are verified by experiments.

Topology of black hole thermodynamics in Gauss-Bonnet gravity

Thermodynamics of black holes in anti de Sitter (AdS) spacetimes typically contains critical points in the phase diagram, some of which correspond to the first order transition ending in a second order one. Following the recent proposal in [arXiv:2112.01706] on using Duan's $\phi$-mapping theory, we classify the critical points of six dimensional charged Gauss-Bonnet black holes in AdS spacetime. We find that the higher derivative corrections from Gauss-Bonnet gravity do not change the topological class of critical points in charged black holes in AdS, unlike the case of Born-Infeld corrections noted earlier. The connection between the topological nature of critical points and existence of first order phase transitions breaks down in a certain parameter regime. A resolution is proposed by treating the novel and conventional critical points as phase creation and phase annihilation points, respectively. Examples are provided to support the proposal.

General double monodromy inflation

We revisit the roller-coaster cosmology based on multiple stages of monodromy inflation. Working within the framework of effective flux monodromy field theory, we include the full range of strong coupling corrections to the inflaton sector. We find that flattened potentials $V\ensuremath{\sim}{\ensuremath{\phi}}^{p}+\ensuremath{\cdots}$ with $p\ensuremath{\lesssim}1/2$, limited to $N\ensuremath{\lesssim}25\ensuremath{-}40$ $e$-folds in the first stage of inflation, continue to fit the cosmic microwave background. They yield $0.96\ensuremath{\lesssim}{n}_{s}\ensuremath{\lesssim}0.97$ and produce relic gravity waves with $0.006\ensuremath{\lesssim}r\ensuremath{\lesssim}0.035$, in full agreement with the most recent bounds from BICEP/Keck. The nonlinear derivative corrections generated by strong dynamics in effective field theory (EFT) also lead to equilateral non-Gaussianity ${f}_{\mathrm{NL}}^{\mathrm{eq}}\ensuremath{\simeq}\mathcal{O}(1)\ensuremath{-}\mathcal{O}(10)$, close to the current observational bounds. Finally, in the multistage roller coaster, an inflaton--hidden sector $U(1)$ coupling can produce a tachyonic chiral vector background, which converts rapidly into tensors during the short interruption by matter domination. The produced stochastic gravity waves are chiral, and so they may be clearly identifiable by gravity wave instruments like LISA, Big Bang Observer, Einstein Telescope, NANOgrav, or SKA, depending on the precise model realization. We also point out that the current attempts to resolve the ${H}_{0}$ tension using early dark energy generically raise ${n}_{s}$. This might significantly alter the impact of BICEP/Keck data on models of inflation.

Analysis of rotor winding interturn short circuits affected by the initial dynamic eccentricity in large synchronous condensers

To investigate the effect of initial dynamic eccentricity on the rotor winding turn-to-turn short circuit (RWISC) in a large synchronous condenser, this paper uses the study object of a 300 MVar dual water intercooler condenser. Firstly, the air gap flux density characteristics, unbalanced magnetic pull (UMP) and stator circulating current of the condenser under single and compound faults are derived theoretically. Then, a phase-modulated field-circuit coupling model is constructed using Anosoft software. It is used to simulate and analyse the condenser. Finally, the operation of the condenser was simulated with the SDF-9 experimental setup, and the correctness of the theoretical derivation and simulation analysis was verified. The results show that the initial dynamic eccentricity of the condenser has a cutting effect on the fault characteristics generated by the RWISC. The 2nd harmonic of air gap flux density and stator circulating current and the fundamental wave of UMP decrease and increase with eccentricity. This study can provide theoretical guidance to eliminate disturbing factors to improve the accuracy of RWISC diagnosis in large synchronous condensers.

Adaptive Aggregate Transmission for Device-to-Multi-Device Aided Cooperative NOMA Networks

The integration of device-to-device (D2D) communications with cooperative non-orthogonal multiple access (NOMA) can achieve superior spectral efficiency. However, the mutual interference caused by D2D communications may prevent NOMA from diverging its high spectral efficiency advantage. Meanwhile, the low adaptability of the fixed transmission strategy can decrease the reliability of the cell-edge user (CEU). To further improve the spectral efficiency, we investigate a device-to-multi-device (D2MD) assisted cooperative NOMA system, where two cell-center users (CCUs) and one CEU are paired as a D2MD cluster. Specifically, the base station directly serves the two CCUs while communicating with the CEU via one CCU. Moreover, we propose an adaptive aggregate transmission scheme using dynamic superposition coding, pre-designing the decoding orders and prior information cancellation for the D2MD assisted cooperative NOMA system to enhance the reliability of the CEU. We provide the closed-form expressions for the outage probability, diversity order, outage throughput, ergodic sum capacity, average spectral efficiency, and spectral efficiency scaling over Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> fading channels under perfect and imperfect successive interference cancellation. The numerical results validate the correctness of the analytical derivations and the effectiveness of the proposed scheme.

Effect of static alignment deviation on coupling efficiency and beam quality of water beam fiber.

In this paper, the problems of decreasing coupling efficiency and energy distribution divergence of water beam fiber caused by static alignment deviation are studied. Based on the basic conditions of coupling between laser and water beam fiber, the mathematical model of coupling efficiency of water beam fiber is established, and the calculation equation of coupling efficiency is modified. The variation of coupling efficiency and energy distribution of water beam fiber under the influence of static alignment deviation is analyzed by numerical simulation, and the correctness of theoretical derivation and simulation model is verified by experiments. The results show that the lateral deviation changes the transmission path of laser in the water beam fiber to a large extent, and its influence on the energy distribution in the water beam fiber is greater than that of longitudinal deviation and angular deviation.

Higher-dimensional symmetry of AdS2×S2 correlators

It was recently shown that IIB supergravity on AdS5×S5 enjoys 10d conformal symmetry and that superstring theory on this background can be described using a 10d scalar effective field theory. In this paper we adapt these two complementary approaches to correlators of hypermultiplets in AdS2×S2. In particular, we show that 4-point correlators of 1/2-BPS operators in the 1d boundary can be computed using 4d conformal symmetry and a 4d effective action in the bulk. The 4d conformal symmetry is realised by acting with Casimirs of SU(1, 1|2), and is generically broken by higher derivative corrections. We point out similar structure underlying α′ corrections to IIB supergravity in AdS5×S5. In particular, while the α′3 corrections can be written in terms of a sixth order Casimir acting on a 10d conformal block, similar structure does not appear in higher-order corrections. We note however that a specific combination of higher derivative corrections can give rise to Witten diagrams with higher dimensional symmetry at the integrand level, with breaking then arising from the measure.

Dimensional reduction of higher derivative heterotic supergravity

Higher derivative couplings of hypermultiplets to 6D, N = (1, 0) supergravity are obtained from dimensional reduction of 10D heterotic supergravity that includes order α′ higher derivative corrections. Reduction on T4 is followed by a consistent truncation. In the resulting action the hyperscalar fields parametrize the coset SO(4, 4)/(SO(4) × SO(4)). While the SO(4, 4) symmetry is ensured by Sen’s construction based on string field theory, its emergence at the field theory level is a nontrivial phenomenon. A number of field redefinitions in the hypermultiplet sector are required to remove several terms that break the SO(4) × SO(4) down to its SO(4) diagonal subgroup in the action and the supersymmetry transformation rules. Working with the Lorentz Chern-Simons term modified 3-form field strength, where the spin connection has the 3-form field strength as torsion, is shown to simplify considerably the dimensional reduction.

NOMA-Based Overlay Cognitive Satellite-UAV-Terrestrial Networks with Multiple Primary Users

Satellite communication is becoming more and more significant in present and future communication systems for its unique advantages of strong survivability and seamless coverage, which can offset the defects of terrestrial communication such as being restricted by terrain and little coverage. Moreover, unmanned aerial vehicle (UAV)-assisted communication is considered as a promising development direction due to its flexibility and expansibility in the integrated satellite-terrestrial networks (ISTN). In addition, to overcome the spectrum shortage and low spectrum utilization problems, cognitive radio and nonorthogonal multiple access (NOMA) has been widely utilized to enhance spectrum efficiency, which is considered as the key technologies of the next generation communication. In this regard, our paper investigates the performance of cognitive satellite-UAV-terrestrial networks with NOMA scheme and multiple primary users. Specifically, the exact expressions of outage probability (OP) and ergodic capacity for both primary network and secondary network are derived. To gain further views, the asymptotic expression of OP and diversity orders for the two networks are provided. Finally, through numerical simulations, the correctness of the theoretical derivations is verified and the influences of critical variables on system indexes are also analyzed.

ABJM at strong coupling from M-theory, localization, and Lorentzian inversion

We study the stress tensor multiplet four-point function in the 3d maximally supersymmetric ABJ(M) theory with Chern-Simons level k = 2, which in the large N limit is holographically dual to weakly coupled M-theory on AdS4 × S7/ℤ2. We use the Lorentzian inversion to compute the 1-loop correction to this holographic correlator coming from Witten diagrams with supergravity R and the first higher derivative correction R4 vertices, up to a finite number of contact terms that contribute to low spins where the inversion formula does not converge. We find a precise match with the corresponding terms in the 11d M-theory S-matrix by taking the flat space limit, which is not sensitive to these contact terms. We then conjecturally fix these contact terms by analytically continuing the inversion formula below its expected range of convergence, and verify this conjecture using supersymmetric localization. Finally, we compare some of the 1-loop CFT data to non-perturbative in N bounds from the numerical conformal bootstrap, which we compute at unprecedently high accuracy, and find that the 1-loop corrections saturate the bounds in the large N regime, which extends the previously observed match at tree level.

Equivalence of JT gravity and near-extremal black hole dynamics in higher derivative theory

Two derivative Jackiw-Teitelboim (JT) gravity theory captures the near-horizon dynamics of higher dimensional near-extremal black holes, which is governed by a Schwarzian action at the boundary in the near-horizon region. The partition function corresponding to this boundary action correctly gives the statistical entropy of the near-extremal black hole. In this paper, we study the thermodynamics of spherically symmetric four-dimensional near-extremal black holes in presence of arbitrary perturbative four derivative corrections. We find that the near-horizon dynamics is again captured by a JT-like action with a particular namely R2 higher derivative modification. Effectively the theory is described by a boundary Schwarzian action which gets suitably modified due to the presence of the higher derivative interactions. Near-extremal entropy, free energy also get corrected accordingly.

Comparison of Gaussian process regression, partial least squares, random forest and support vector machines for a near infrared calibration of paracetamol samples

In this article, we analyze the near-infrared (NIR) spectra of fifty-eight (58) commercial tablets of 500 mg of paracetamol from different origins (that is, with different batch numbers) in the local markets in Bamako. The NIR spectra were recorded in the spectral range 930 nm-1700 nm. The samples are divided into forty-eight (48) samples forming the set of calibration (training set) and ten (10) samples used as the validation or test set. To perform multivariate calibration, we apply-three nonlinear regression techniques (Gaussian processes regression (GPR), Random Forest (RF), Support vector machine (KSVM)), along with the traditional linear partial least-squares regression (PLSR) to several data pretreatments of the 58 samples. The results show that the three nonlinear regression calibrations have better prediction performance than PLS as far as RMSE is concerned. To decide the best regression model, we avoid R2 since this quantity is not a good parameter for this purpose. We will instead consider RMSE when comparing the different multivariate models. Additionally, to assess the impact of data preprocessing, we apply the above regression techniques to the original data, Multi-scattering correction (MSC), standard variate normalization (SNV) correction, smoothing correction, first derivative (FD), and second derivative correction (SD). The overall results reveal that Gaussian Processes Regression (GPR) applied to smooth correction gives the lowest RMSEP = 2.303053e-06 for validation (prediction) and RMSEC = 2.112316e-06 for calibration. In our investigation, one also notices that the developed GPR model is more accurate and exhibits enhanced behavior no matter which data preprocessing is used. All in all, GPR can be seen as an alternative powerful regression tool for NIR spectra of paracetamol samples. The statistical parameters of the proposed model are compared to the results of some other models reported in the literature.

Vibration pile driving system based on Sliding Mode Control

The sliding mode variable structure synchronous control of vibration pile driving system driven by double DC motors is studied. Firstly, the model of double machine driven vibratory pile driving system is established, and the theoretical derivation of system synchronization and stability is carried out. Secondly, the sliding mode variable structure control method is used to realize the phase speed synchronous control of two motors in the vibration system. Finally, Simulink is used to verify the correctness of the theoretical derivation, and the vibration displacement of the pile driving system is simulated and analyzed. The research shows that the sliding mode variable structure control can realize the synchronous control of the double machine driven vibratory pile driving system, which provides a theoretical and practical engineering basis for the design of this type of vibratory pile driving system.

Equilibria and Bogdanov‐Takens Bifurcation Analysis in the Bazykin’s Predator‐Prey System

In the paper, we proposed a Bazykin’s predator‐prey system to explore the equilibrium point and Bogdanov‐Takens bifurcation problems. Firstly, we derived some key parameter threshold conditions to ensure that the Bazykin’s predator‐prey system had a multiple focus of multiplicity one, weak focus of order 2, cusps of codimension 2 and a degenerate Bogdanov‐Takens singularity (focus or center case) of codimension 3. Furthermore, the distinction of two types of codimension 2 cusps was also discussed, which showed that the threshold of the two types of cusps could exhibit a cusp, which was a special case of the mentioned degenerate Bogdanov‐Takens singularity (focus or center case) of codimension 3. Secondly, we systematically calculated that the Bazykin’s predator‐prey system could undergo two types of Bogdanov‐Takens bifurcations of codimension 2 and a degenerate focus type Bogdanov‐Takens bifurcation of codimension 3. Finally, some numerical examples were implemented to verify the correctness and feasibility of mathematical theory derivation, which also directly showed all possible equilibrium points and Bogdanov‐Takens bifurcations of Bazykin’s predator‐prey system. In a word, all the research results could play an important theoretical support role in the study of controlling cyanobacteria bloom.

Transfer Mechanism Analysis of Injected Voltage Harmonic and its Effect on Current Harmonic Regulation in FOC PMSM

Harmonic injection method is widely used in the suppression of current harmonic and torque ripple in field-oriented control (FOC) permanent magnet synchronous motor (PMSM) servo system. However, under some working conditions of FOC PMSM, the harmonic injection method fails to suppress the current harmonics and causes oscillation. To analyze the cause of oscillation, the transfer mechanism of injected voltage harmonic is analyzed in this article, and the relation between injected voltage harmonic and current harmonic is derived. The theoretical analysis results show that the relation between harmonics will change with motor speed and parameters of FOC PMSM. When the relation between harmonics is reversed, the existing harmonic injection method will fail and cause harmonic oscillation. To solve this problem, a simple improvement of the harmonic injection method is proposed in this article based on the proposed close-loop model. The correctness of the mathematical derivation and the effectiveness of the proposed method is evaluated by experiment and simulation.

\u03b1\u2032-corrections to near extremal dyonic strings and weak gravity conjecture

We construct non-extremal dyonic string solutions in 6D minimal supergravity where the leading higher derivative corrections arise from either the type IIA string theory compactified on K3 or the heterotic string theory compactified on 4-torus. The thermodynamical quantities and Euclidean actions of the strings are computed. In the near extremal regime, we calculate the force felt by a probe fundamental string in the background of the macroscopic dyonic string with leading α′ corrections. We find that in both the IIA and heterotic setups, away from extremality, the attractive force overwhelms the repulsive force. However, close to extremality, the α′ corrections can reduce the attractive force in the isoentropic process, where the charges are fixed. This feature may be used as a new constraint for supergravity models with consistent quantum gravity embedding, in cases where the extremal limit coincides with the BPS limit and the higher derivative corrections do not affect the mass-to-charge ratio. By contrast, the α′ corrections can enhance the attractive force in the isothermal or isoenergetic processes.

Performance analysis of Radar detection for fluctuating targets based on coherent demodulation

Stealth targets have extremely small Radar Cross Section (RCS) and fluctuating echoes. For these kinds of fluctuating targets, the detection performance of non-coherent detection is more and more difficult to meet the requirements. The coherent detection with better performance than non-coherent detection, can detect slow fluctuation target, but can't detect fast fluctuation target. In view of the insufficient performance of radar, based on the previous work, this paper applies the coherent demodulation technology in communication systems to radar detection for fluctuating targets. The theoretical expressions of fluctuating targets coherent demodulation detection (FTCDD) method are derived, and the detection probability of Swerling targets is calculated. The correctness of the theoretical derivation is verified by simulation, and the radar detection performance is analyzed under different false alarm probability and Barker code lengths. Proposed method has better performance than non-coherent detection and can meet all fluctuation models.

Secrecy performance of mixed single-input multiple-output-FSO/single-input multiple-output-RF networks with energy harvesting.

In this paper, we study the secrecy performance of an energy-harvested relaying assisted free space optical-radio frequency (FSO-RF) network. In particular, a single-beam source sends an optical signal to a multi-aperture relay over an FSO channel, and then the relay converts it into an RF signal and adopts a decode-and-forward protocol to forward it to a multi-antenna destination under the wiretapping of a multi-antenna eavesdropper. We assume that the relay is power constrained, and it requires to harvest energy from a power beacon to assist the information transmission. It is also assumed that the FSO link and all RF links are subject to gamma-gamma fading with atmospheric turbulence and Rayleigh fading, respectively. Analytical expressions for secrecy outage probability (SOP) and the probability of strictly positive secrecy capacity are derived. In addition, the asymptotic expression for SOP is obtained to present insight into secrecy performance at high signal-to-noise ratio regimes. Finally, Monte Carlo simulations verify the correctness of the theoretical derivations.

Fundamental Limits of Full-Duplex Spectrum Sharing Under Peak Interference Power Constraint

Cognitive radio (CR) and full-duplex (FD) have received extensive attention and research due to their high spectrum efficiency, which can effectively solve the problem of low spectrum efficiency in current communication systems. Based on CR and FD techniques, in this paper, a FD spectrum sharing CR networks is considered, in which both secondary users (SU1 and SU2) are each equipped with dual antennas, one antenna is used to transmit signals, and the other antenna is used to receive signals at the same time and frequency. Under peak interference power and peak transmit power constraints, we analysis the ergodic sum capacity and the outage probability based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks. Furthermore, under no peak transmit power constrain and perfect self-interference cancellation (SIC), based on the FD spectrum sharing CR networks and the conventional spectrum sharing CR networks, the closed-form expressions of the theoretical performance upper bound of the ergodic sum capacity and the outage probability are derived by two lemmas and four propositions. Accurate mathematical analysis display, under the same bandwidth, the upper bound of ergodic sum capacity for the full-duplex spectrum sharing CR networks is twice as much as the traditional spectrum sharing CR networks, and the FD spectrum sharing CR networks based on SU1, also has better performance upper bound on the outage probability than the traditional spectrum sharing CR networks. Simulations results also validate that, the FD spectrum sharing CR networks obtains better communication performance than the conventional spectrum sharing CR networks, especially when the mean of self-interference channel power gain is small. Finally, we also can see that the simulation performance upper bound is completely consistent with the theoretical analysis performance upper bound, whether in the FD spectrum sharing CR networks or the conventional spectrum sharing CR networks. So also verifies the correctness of the theoretical performance upper bound derivation.

Modular invariant holographic correlators for mathcal{N} = 4 SYM with general gauge group

We study the stress tensor four-point function for mathcal{N} = 4 SYM with gauge group G = SU(N), SO(2N + 1), SO(2N) or USp(2N) at large N . When G = SU(N), the theory is dual to type IIB string theory on AdS5× S5 with complexified string coupling τs, while for the other cases it is dual to the orbifold theory on AdS5× S5/ℤ2. In all cases we use the analytic bootstrap and constraints from localization to compute 1-loop and higher derivative tree level corrections to the leading supergravity approximation of the correlator. We give perturbative evidence that the localization constraint in the large N and finite complexified coupling τ limit can be written for each G in terms of Eisenstein series that are modular invariant in terms of τs ∝ τ, which allows us to fix protected terms in the correlator in that limit. In all cases, we find that the flat space limit of the correlator precisely matches the type IIB S-matrix. We also find a closed form expression for the SU(N) 1-loop Mellin amplitude with supergravity vertices. Finally, we compare our analytic predictions at large N and finite τ to bounds from the numerical bootstrap in the large N regime, and find that they are not saturated for any G and any τ , which suggests that no physical theory saturates these bootstrap bounds.