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In this paper, we investigate the rotation-dominant three-scale singular limit of the initial-value problem to the inviscid rotating stratified Boussinesq equations. We first prove a dispersive decay estimate for the linear propagator of that limit regime, which requires novel techniques involving an elaborate frequency cut-off since the phase function is degenerate on both horizontal and vertical directions in some areas. Using the dispersive decay estimate, we then investigate rigorously the rotation-dominant limit of local strong solutions to Boussinesq equations with ill-prepared initial data. The limiting system is shown to be the two-dimensional incompressible Euler equations coupled with a two-dimensional transport equation but in three spatial dimensions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the incompressible limit of the compressible primitive equations with the effect of gravity. First we prove that the estimates of the local strong solutions to the compressible primitive equations with γ = 2 are uniform to the Mach number. Then we show that the local strong solutions of the system with well-prepared initial data, as well as their time derivatives, converge to those of the inhomogeneous incompressible primitive equations as the Mach number tends to zero. The convergence rates are shown to be identical to the Mach number. [ABSTRACT FROM AUTHOR]

A dispersive decay estimate is proven for the linear propagator of the three-scale rotating stratified Boussinesq equations in the stratification-dominant regime. Because the phase function of that propagator is both singular and degenerate, obtaining the estimate requires novel techniques involving cutting phase-space shells into several pieces and using different methods in each region. Using the decay estimate, we prove the long-time existence of solutions to the initial-value problem for the nonlinear equations and obtain a rate of convergence to the limit system and intermediate asymptotics. [ABSTRACT FROM AUTHOR]

The asymptotics of weak solutions to the Boussinesq equations with no-slip boundary and moderately ill-prepared data is investigated in rotation-dominant limit regime as the Rossby number, the Froude number and the vertical viscosity tend to zero simultaneously. The new ingredient of this paper is to give a first proof of the three scale singular limit coupled with Ekman boundary layer by introducing an asymptotic profile to the original system. [ABSTRACT FROM AUTHOR]

In this paper, we consider the motion of two compressible fluid flows under the interaction of magnetic field in bounded domain. With the help of spectral analysis, we prove the low Mach number limit from global weak solutions of the rescaled system to global weak solutions of the limit system, with ill-prepared initial data. [ABSTRACT FROM AUTHOR]

Singular limits of the rotating stratified Boussinesq equations are considered as the Froude number and Rossby number tend to zero at different rates. The limiting dynamics are validated for the rotation-dominant and the stratification-dominant cases, respectively. Furthermore, the convergence rate estimates are obtained. [ABSTRACT FROM AUTHOR]

We are concerned with two kinds of singular limits of the Cauchy problem to the two-layer rotating shallow water equations as the Rossby number and the Froude number tend to zero. First we construct the uniform estimates for the strong solutions to the system under the condition that the Froude number is small enough. Different from the previously studied cases, the large operator of this model is not skew-symmetric. One of the key new ideas in this paper is to obtain the uniform estimates using the special structure of the system rather than the antisymmetry of the large operator. After that the convergence of the equations with ill-prepared data to a two-layer incompressible Navier-Stokes system is proved with the help of Strichartz estimates constructed in this paper. [ABSTRACT FROM AUTHOR]

In the real world, differential evolution (DE) algorithm can effectively solve optimization problems in engineering; thus, DE has been applied in various fields. However, in complex multimodal problems, DE may encounter stagnation during iterations. Thus, we propose an improved DE algorithm with repulsive behavior, named RBDE. The core idea of RBDE is that offsprings no longer simply learn from the current optima but continue to explore the direction in which the current optimal individual is repelled by poorer individuals. This mechanism increases the diversity of the learning direction of a population. RBDE includes two types of repulsive behaviors: In the first, RBDE selects two parents as the source of repulsion and generates two different repulsive forces to promote the offspring to explore the optimal individual; the other considers that the gradient of the repulsion between the parents is the learning direction of the offspring. The repulsive behavior can effectively alleviate the stagnation of DE when dealing with multimodal problems. To evaluate the performance of RBDE, we use CEC2017 benchmarks to test RBDE and nine other algorithms. The results show that the performance of RBDE is better than that of the other nine algorithms. In addition, RBDE is used to train an artificial neural network and is applied to the optimization problem of four-bar linkages, whose results indicate that the model obtained by RBDE is more accurate than those by the other algorithms. [ABSTRACT FROM AUTHOR]

This paper investigates the physical layer security in a multiple-input-single-output multicast channel, where a common message is transmitted to multiple receivers and only statistical channel state information of the eavesdropper is available. We consider transmitting some artificial noise (AN) along with the information-bearing signal to improve secrecy. To find the optimal AN design, we formulate a secrecy outage probability (SOP) constrained secrecy rate maximization problem. For solving this problem, we adopt a novel transformation of the intractable SOP constraint and establish an efficient algorithm which solves the transformed problem to global optimality. We also propose a low-complexity refinement method to reduce the conservatism incurred by the transformation and an efficient algorithm to find a suboptimal solution when the information-bearing signal is transmitted using single-stream beamforming. Our solution is found to be a valuable generalization of the traditional null-space AN scheme. According to our simulation results, when the number of receivers is less than that of transmit antennas, distributing AN uniformly in the null space of the legitimate channel vectors is near-optimal. When there is no valid null space, transmitting AN will interfere with some legitimate receivers, and the secrecy performance can also be improved with carefully designed AN. [ABSTRACT FROM PUBLISHER]

This paper investigates the slow fading single-antenna wiretap channel with imperfect channel state information (CSI) and studies an on–off transmission scheme with fixed communication rate, secrecy rate, and transmit power for maximizing the secrecy throughput under the constraints of secrecy outage probability (SOP) and reliability outage probability (ROP). We first solve this problem in a special case without ROP constraint for which the optimal secrecy throughput is obtained under SOP constraint. The result for the special case gives us an upper bound for the secrecy throughput with imperfect CSI. With the help of this special case, a general case with ROP constraint is studied. In this case, the problem is transformed into a one-dimensional (1-D) search problem on a finite interval, which can be solved either by the exhaustive 1-D search to obtain the optimal solution or by the golden search method (GSM) to obtain a suboptimal solution. Simulation results are finally presented to validate the theoretical analysis and show that the performance obtained by using the GSM based 1-D search is very close to that of exhaustive 1-D search. [ABSTRACT FROM PUBLISHER]

This paper studies the secure transmission in a multiuser broadcast channel where only the statistical channel state information of the eavesdropper is available. We propose to apply secret dirty-paper coding (S-DPC) in this scenario to support the secure transmission of one user and the normal (unclassified) transmission of the other users. By adopting the S-DPC and encoding the secret message in the first place, all the information-bearing signals of the normal transmission are treated as noise by potential eavesdroppers and thus provide secrecy for the secure transmission. In this way, the proposed approach exploits the intrinsic secrecy of multiuser broadcasting and can serve as an energy-efficient alternative to the traditional artificial noise (AN) scheme. To evaluate the secrecy performance of this approach and compare it with the AN scheme, we propose two S-DPC-based secure transmission schemes for maximizing the secrecy rate under constraints on the secrecy outage probability (SOP) and the normal transmission rates. The first scheme directly optimizes the covariance matrices of the transmit signals, and a novel approximation of the intractable SOP constraint is derived to facilitate the optimization. The second scheme combines zero-forcing dirty-paper coding and AN, and the optimization involves only power allocation. We establish efficient numerical algorithms to solve the optimization problems for both schemes. Theoretical and simulation results confirm that, in addition to supporting the normal transmission, the achievable secrecy rates of the proposed schemes can be close to that of the traditional AN scheme, which supports only the secure transmission of one user. [ABSTRACT FROM PUBLISHER]

This paper studies the design of artificial-noise-aided (AN-aided) secure transmission in slow-fading multiple-input–single-output (MISO) channels. We consider the scenario where a multiantenna transmitter sends messages to a single-antenna legitimate receiver in the presence of multiple noncolluding single-antenna eavesdroppers. It is assumed that the transmitter possesses instantaneous channel state information (CSI) of the legitimate channel but only the statistics of the eavesdropper's channels. Instead of adopting the well-known adaptive and nonadaptive transmission schemes, we consider the newly proposed semiadaptive scheme, in which the communication rate is fixed, and the secrecy rate is adaptively adjusted according to the legitimate channel's CSI. Compared with the adaptive scheme, a major advantage of fixing the communication rate is that the codebook can be fixed, and thus, the encoder and decoder designs are both simplified. We consider a generalized AN-aided beamforming structure, which allows arbitrary beamforming direction. Specifically, we focus on the problem of maximizing the secrecy throughput on the premise of reliable and secure transmission. By solving this problem, the optimal beamforming direction, power-allocation parameters, and secrecy rate are derived in closed form, and the optimal communication rate is obtained numerically. Finally, simulation results are presented to show the performance of the semiadaptive scheme. [ABSTRACT FROM PUBLISHER]

In low-earth-orbit (LEO) satellite-to-ground communication, the size of satellite antennae is limited and the satellite motion trajectory is predictable, which makes the channel state information (CSI) of the satellite-to-ground channel easy to leak and impossible to use to generate a physical layer key. To solve these problems, we propose a key generation method based on multi-satellite cooperation and random perturbation. On the one hand, we use multi-satellite cooperation to form a constellation that services users, in order to increase the equivalent aperture of satellite antennae and reduce the correlation between the legal channel and the wiretap channel. On the other hand, according to the endogenous characteristics of satellite motion, a random perturbation factor is proposed, which reflects the randomness of the actual channel and ensures that the CSI of the legal channel is not leaked due to the predictability of satellite motion trajectory. Simulation results show that the proposed method can effectively reduce the leakage of the legal channel's CSI, which makes the method of physical layer key generation safe and feasible in the LEO satellite-to-ground communication scene. [ABSTRACT FROM AUTHOR]

Stratification-dominant limit for weak solutions to the rotating stratified viscous Boussinesq equations with stress-free boundary is considered when the Froude number and Rossby number tend to zero. Convergence rate estimates are also obtained. [ABSTRACT FROM AUTHOR]

Singular limits of the rotating stratified Boussinesq equations with ill-prepared data are investigated when the Froude number and Rossby number tend to zero at different rates. The reduced systems are derived, respectively, for the rotation-dominant and stratification-dominant cases through the developed three-scale fast averaging method. [ABSTRACT FROM AUTHOR]

Accurate navigation and localization are essential for Autonomous Underwater Vehicles (AUVs). However, the unknown modeling errors and nonlinear errors will affect the AUV positioning accuracy. Meanwhile, the marine environment changes may not be accurately sensed by AUV. Therefore, this paper proposes a Hybrid Model (HM) navigation methodology for AUV to reduce the impact of unknown errors and better predict the future states simultaneously. Firstly, an error correction sub-model based on Sequence to Sequence (Seq2Seq) predicts AUV pseudo displacements. The pseudo displacements are augmented to the observation vector to correct the unknown errors in the state estimation. Secondly, a state regression sub-model based on Gaussian Process Regression (GPR) is utilized to capture the motion trends from the historical data and regress the state variation, which is used to resist the unknown disturbances in the changeable marine environment. The sub-models work parallel with the master model, benefiting from the Interacting Multiple Model (IMM). We compare the performance of the proposed HM to Extended Kalman Filter (EKF), Unscented Kalman Filter (UKF), and IMM-EKF by using the actual experimental data of Sailfish 210 AUV. The experimental results show that the proposed HM algorithm achieves superior navigation accuracy and good fault tolerance capability. • A HM navigation method is proposed to improve AUV navigation accuracy. • An error correction sub-model predicts AUV pseudo displacements. • A state regression sub-model captures the motion trends from historical data. [ABSTRACT FROM AUTHOR]

Magnesium aluminate spinel is of great importance for nuclear industry, and its structure, showing a great impact on properties, is sensitive to the composition. In order to explore the stoichiometric effect on structure and properties of spinels, several different spinel compositions with MgO· n Al 2 O 3 ( n  = 0.5–2.4) were synthesized via solid state reaction. Synthetic samples were characterized by X-ray diffraction, scanning electron microscope and nanoindentation tests. The results of XRD and SEM indicate that the single-phase magnesia alumina spinels have been prepared successfully for the first time ranging from n  = 0.667 to n  = 1.5, which is beyond the previous reported ranges of n ≥ 0.91. The hardness and modulus decrease with increasing n, implying further that the nonstoichiometric spinel crystal structures are likely to exhibit superior mechanical properties. [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed to study the structural properties and defect energetics of orthorhombic Ln 2 TiO 5 (Ln = La, Pr, Nd, Sm, Gd, Dy and Y). The lattice parameters decrease with increasing lanthanide cation radius. The mean 〈Ln 1 -O〉 and 〈Ln 2 -O〉 bond lengths increase systematically by respectively 1.16% and 1.19% from Dy 2 TiO 5 to La 2 TiO 5 . Meanwhile, mean 〈Ti-O〉 bond length increases slightly with increasing Ln cation radius from Y 2 TiO 5 to La 2 TiO 5 . The calculated results of point defect formation energies suggest that Ln 2 -Ti antisite defect is the most energetically favorable defect type for Ln 2 TiO 5 . The trend of Ln 2 -Ti antisite defect formation energy of Ln 2 TiO 5 is precisely consistent with the radiation resistance, as demonstrates by the critical amorphization temperature, which indicates that the formation of Ln 2 -Ti antisite defect may has a significant influence on the radiation behavior of Ln 2 TiO 5 . [ABSTRACT FROM AUTHOR]

In an attempt to investigate the role of ion species in the radiation effects of pyrochlores, polycrystalline Lu 2 Ti 2 O 7 samples, prepared through a standard solid state process, were irradiated with three different ion beams: 400 keV Ne 2+ , 2.7 MeV Ar 11+ and 6.5 MeV Xe 26+ . To characterize the damaged layers in Lu 2 Ti 2 O 7 , the grazing incident X-ray diffraction technique was applied. All the three irradiations induce significant amorphization processes and lattice swelling in Lu 2 Ti 2 O 7 . However, when the ion fluence is converted to a standard dose in dpa, the radiation effects of Lu 2 Ti 2 O 7 show a great dependence on the implanted ion species. The threshold amorphization dose decreases with increasing ion mass and energy. Besides, the amorphization rate, as well as lattice swelling rate, increases with increasing ion mass and energy. That is, the Lu 2 Ti 2 O 7 pyrochlore is more susceptible to amorphization and lattice swelling under heavier ion irradiation. These results are then discussed in the framework of defect configuration and the density of collision cascades based on Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Autonomous Underwater Vehicle (AUV) navigation and localization in the complex and changeable marine environment is crucial and challenging. The inaccurate noise covariance matrix may result in significant prediction errors or even filtering divergence for traditional navigation algorithms. Meanwhile, the outliers in sensor observations also have a substantial adverse effect on the AUV positioning accuracy. Therefore, in this paper, we propose an Improved Interacting Multiple Model-Unscented Kalman Filter (IIMM-UKF) with both adaptivity and robustness for AUV navigation. Firstly, the Variational Bayesian (VB) based UKF algorithm is proposed as adaptive sub-models of IIMM to estimate the time-varying measurement noise covariance adaptively. Secondly, an outliers detector sub-model is proposed to enhance the robustness of IIMM. Gaussian Process Regression (GPR) is used to regress state pseudo values for each sub-model as estimations of the filtering process when the outliers are detected by the residual χ 2 detector. Multiple models work in parallel to achieve high-precision and robust AUV navigation. The performance of the IIMM-UKF algorithm has been evaluated on AUV with simulation and actual experimental data. In sea trials, the average AUV navigation accuracy of the IIMM-UKF is improved by 61.02% compared to EKF, 43.44% compared to UKF, and 35.54% compared to the IMM-UKF. • Multiple models work in parallel to improve the AUV navigation accuracy and robustness. • Adaptive sub-model based on Variational Bayesian. • Outliers detector sub-model based on residual χ 2 and GPR. [ABSTRACT FROM AUTHOR]

• Shoot bending, an effective agronomic measure can promote flowering in apple trees. • The 1,060 up- and 1,079 down-regulated proteins after shoot bending. • Differentially expressed proteins involved in fatty acid and lipid pathways were up-regulated by shoot bending. • Starch synthesis related proteins were down-regulated by shoot bending. • Circadian rhythm- and flowering-related genes were up-regulated by shoot bending. Flowering is an important life cycle stage in apple trees, and young 'Nagafu No. 2' produce limited inferior flower buds. Shoot bending, an effective agronomic measure, is widely used to promote flowering but little is known regarding the underlying molecular mechanisms. Using isobaric tags for relative and absolute quantification LC−MS/MS, 8,585 proteins expressed in buds during flower bud differentiation were identified. The 1,060 up- and 1,079 down-regulated proteins after shoot bending were divided into 7 pattern-based groups: I (22/5), II (30/57), III (34/21), IV (77/61), V (381/452), VI (218/170), and VII (298/313) types. Number of proteins were associated with carbohydrate, fatty acid, and lipid metabolism, as well as hormone, transcription factor, circadian rhythm, and photoperiod and flowering pathways. The differentially expressed proteins involved in fatty acid and lipid pathways were up-regulated by shoot bending, while other proteins that were involved in starch synthesis were down-regulated. In addition, circadian rhythm- and flowering-related genes were up-regulated by shoot bending. This research provides a valuable inventory of proteins involved in floral bud development and contributes to the understanding of the regulatory mechanisms of flower bud differentiation caused by shoot bending in apple trees. [ABSTRACT FROM AUTHOR]