Influence Of Perturbations Research Articles

A comprehensive RFD-FTC-DCA system for hypersonic vehicles with saturation constraints

A comprehensive RFD-FTC-DCA system is proposed for the hypersonic vehicle with saturation constraints to resist the control surface damage, actuator faults, disturbances and parameter perturbation. Firstly, the hypersonic vehicle fault model is established. Secondly, the robust fault detection (RFD) observer is designed to detect the control surface damage and actuator faults accurately under the influences of disturbances and parameter perturbation. Thirdly, the fault-tolerant control (FTC) law is designed to resist the control surface damage, actuator faults, disturbances and parameter perturbation simultaneously. Finally, a dynamic control allocation (DCA) algorithm is designed to reallocate the FTC law and limit the deflection angle and velocity within saturation constraint. The comparison simulation results are presented to demonstrate that the RFD observer can detect the faults accurately and reduce false alarm rates effectively, the FTC law can resist the control surface damage, actuator faults, disturbances and parameter perturbation simultaneously, and the tracing errors of attack angle, side-slip angle and roll angle are only , and , respectively, and the DCA algorithm can reallocate the FTC law and limit the deflection angle and velocity within saturation values.

A possible signature of the influence of tidal perturbations in dwarf galaxy scaling relations

ABSTRACT Dwarf galaxies are excellent cosmological probes, because their shallow potential wells make them very sensitive to the key processes that drive galaxy evolution, including baryonic feedback, tidal interactions, and ram pressure stripping. However, some of the key parameters of dwarf galaxies, which help trace the effects of these processes, are still debated, including the relationship between their sizes and masses. We re-examine the Fornax Cluster dwarf population from the point of view of isomass-radius–stellar mass relations (IRSMRs) using the Fornax Deep Survey Dwarf galaxy Catalogue, with the centrally located (among dwarfs) $3.63 \mathcal {M}_{\odot }$ pc−2 isodensity radius defining our fiducial relation. This relation is a powerful diagnostic tool for identifying dwarfs with unusual structure, as dwarf galaxies’ remarkable monotonicity in light profile shapes, as a function of stellar mass, reduces the relation’s scatter tremendously. By examining how different dwarf properties (colour, 10th nearest neighbour distance, etc.) correlate with distance from our fiducial relation, we find a significant population of structural outliers with comparatively lower central mass surface density and larger half-light-radii, residing in locally denser regions in the cluster, albeit with similar red colours. We propose that these faint, extended outliers likely formed through tidal disturbances, which make the dwarfs more diffuse, but with little mass-loss. Comparing these outliers with ultra-diffuse galaxies (UDGs), we find that the term UDG lacks discriminatory power; UDGs in the Fornax Cluster lie both on and off of IRSMRs defined at small radii, while IRSMR outliers with masses below $\sim 10^{7.5} \mathcal {M}_{\odot }$ are excluded from the UDG classification due to their small effective radii.

Influences of plasma density perturbations on ion cyclotron resonance heating

The scattering of waves in the ion cyclotron range by plasma density perturbations in the edge has been previously studied by Zhang et al with the help of antenna code RAPLICASOL (2020, Nucl. Fusion, 60, 096001). The further interesting question is whether the density perturbations have an effect on ion cyclotron resonance heating (ICRH) in the core. In this paper, finite element method based 2D full wave code integrating the core with the edge is used to study this issue. The analytical density perturbations are applied to study the influence of density perturbations on field distribution, power deposition, wave coupling, power partition among different species in the core, and the fraction of energy dissipation in the scrape-off layer. The influence of density perturbations becomes global and significant when the poloidal size of the density blob is comparable to the perpendicular wavelength. In addition, the strength of wave scattering is directly proportional to the amplitude and the radial size of the density blob. Finally, a typical experiment on the EAST is chosen and the influence of realistic density perturbations on ICRH is evaluated.

Experimental study of the VFD's speed stabilization processes under torque disturbances

<span lang="EN-US">Maintaining speed with various jumps and changes in load torque is one of the main tasks of variable frequency drives (VFD). The article considers the operation of the VFD under the influence of periodic perturbations of variable frequency and amplitude. The dependence of the transient function of the VFD and the family of frequency characteristics associated with it on the frequency of the stator voltage and slip underlies the methodology for experimental studies of such drives. The traditional method is based on the response to harmonic stimulation and works well for a non-linear system. In the course of the work, it was found that the introduction of dynamic positive feedback (DPF) allows to compensate for disturbances of varying frequency and amplitude. Experiments with a sinusoidal change in the load torque have shown the effectiveness of introducing the DPF in front of conventional sensorless control systems (vector and scalar).</span>

Parametric Stability Score for Local Solutions of Constrained Parametric Nonlinear Programs

AbstractNonlinear optimization problems arise in the context of many engineering processes and other real‐world applications. Depending on the complexity of modeled phenomena and constraints, such problems can feature multiple local solutions of different nature. Primarily, the quality of a solution is measured by the value of an objective function, and hence, one aims to find a global optimum. In many cases, however, additional criteria arise. For instance, nonlinear programs, in addition to decision variables, might depend on parameters undergoing perturbations. Such disturbances might be caused by noisy measurement data, changes in the environment in a real‐time setting or other factors. In this case, apart from good optimality, a practitioner might be interested in the behaviour of a solution under changes in parameters. Recently, the parametric stability score was introduced as a quality measure for solutions of unconstrained problems with respect to the influence of parameter perturbations. In this paper, we extend the concept to constrained optimization problems. The score is defined as the largest magnitude of a perturbation for which the perturbed solution does not deviate from the nominal one beyond an allowed tolerance. Our work is based on the results of parametric sensitivity analysis. This framework enables us to give a formal definition of the parametric stability score and provides tools for its efficient numerical approximation. We illustrate the approach with an example and discuss possible application scenarios for the concept.

Pair breaking in superconductors with strong spin-orbit coupling

We study the influence of symmetry-breaking perturbations on superconductivity in multiorbital materials, with a particular focus on an external magnetic field. We introduce the field-fitness function which characterizes the pair-breaking effects of the perturbation on a given superconducting state. For even-parity superconductors we find that this field-fitness function for an external magnetic field is one, implying that the paramagnetic response is controlled only by a generalized effective $g$ factor. For odd-parity superconductors, the interplay of the effective $g$ factor and the field-fitness function can lead to counterintuitive results. We demonstrate this for $p$-wave pairing in the effective $j=\frac{3}{2}$ electronic states of the Luttinger-Kohn model.

Dry air intrusions link Rossby wave breaking to large-scale dust storms in Northwest Africa: Four extreme cases

Large dust storms in the Saharan desert and the subsequent transport of airborne dust over large distances are a major meteorological hazard. Several mechanisms associated to dust emission, occurring on a range of scales, have been previously documented, notably involving Rossby wave breaking and a low-level jet. However, the mechanistic link between the different features and actual dust concentrations has not been coherently established. Here, using a Lagrangian approach, and the conceptual view of extratropical cyclone airstreams, the role of the dry intrusion airstream for translating the influence of the upper-tropospheric Rossby wave perturbation to near-surface flow conductive for the highest dust concentrations is examined. To this end, four large-scale dust storms that were accompanied by dry intrusions in west Africa are studied. Data from the Copernicus Atmospheric Monitoring Service (validated against AERONET station data) are combined with atmospheric data from reanalysis and objectively-identified Lagrangian trajectories of dry intrusions. Common, coherent structures highlighting the role of dry intrusions link the upper-tropospheric Rossby wave breaks with the lower-tropospheric dry and cold jets. These conditions favor dust uplift and transport along an arc-shaped cold front trailing from a Mediterranean cyclone. Consequently, the southwest side of the front is characterized by the highest near-surface dust concentrations ahead of the dry intrusion outflow, where the Intertropical Discontinuity shifts equatorward by 3 to 7°. The northeast part of the front is, however, accompanied by southerly, warm conveyor belt-like flow transporting the dust northward to the Mediterranean, Middle East and/or Europe at mid and upper-tropospheric levels. While case-to-case variations exists, the central role of dry intrusions in all cases calls for systematic investigation of its occurrence as a predictive tool for large dust transport events.

Resilience of topological superconductivity under particle current

We investigate the robustness of topological superconductors under the perturbing influence of a finite charge current. To this aim, we introduce a modified Kitaev Hamiltonian parametrically dependent on the quasiparticle momentum induced by the current. Using different quantifiers of the topological phase, such as the Majorana polarization and the edge state quantum conditional mutual information, we prove the existence of a finite critical value of the quasiparticle momentum below which edge modes and topological superconductivity survive. We also discuss how a finite current breaks time reversal symmetry and changes the topological class in the Altland-Zirnbauer classification scheme compared to the case of isolated systems. Our findings provide a nontrivial example of the interplay between topology and the nonequilibrium physics of open quantum systems, a relation of crucial importance in the quest to a viable topological quantum electronics.

Noise‐tolerate and adaptive coefficient zeroing neural network for solving dynamic matrix square root

AbstractThe solving of dynamic matrix square root (DMSR) problems is frequently encountered in many scientific and engineering fields. Although the original zeroing neural network is powerful for solving the DMSR, it cannot vanish the influence of the noise perturbations, and its constant‐coefficient design scheme cannot accelerate the convergence speed. Therefore, a noise‐tolerate and adaptive coefficient zeroing neural network (NTACZNN) is raised to enhance the robust noise immunity performance and accelerate the convergence speed simultaneously. Then, the global convergence and robustness of the proposed NTACZNN are theoretically analysed under an ideal environment and noise‐perturbed circumstances. Furthermore, some illustrative simulation examples are designed and performed in order to substantiate the efficacy and advantage of the NTACZNN for the DMSR problem solution. Compared with some existing ZNNs, the proposed NTACZNN possesses advanced performance in terms of noise tolerance, solution accuracy, and convergence rate.

Robust poleward jet shifts in idealised baroclinic-wave life-cycle experiments with noisy initial conditions

Abstract. Idealised baroclinic-wave life-cycle experiments are a widely used tool to study fundamental characteristics of mid-latitude baroclinic instability. A typical life cycle evolves from an initialised baroclinically unstable jet through an exponential growth phase of a particular unstable wave mode, followed by wave breaking during the mature phase and wave–mean flow interaction driving a jet shift during the decay phase. Many authors distinguish between life cycles with predominantly anticyclonic (LC1) and cyclonic (LC2) wave breaking, and the transition between the two flavours is typically controlled via the strength of cyclonic meridional wind shear in the initial conditions. While baroclinic wave growth has traditionally been triggered via a specified initial perturbation with fixed zonal wave number, this study extends the concept of baroclinic-wave life cycles by analysing the influence of random initial perturbations without any preferred zonal dependency on the life-cycle evolution. We find that the growth phase shows a robust LC1–LC2 distinction as a function of initialised meridional shear, while a preference for LC1-like characteristics is observed during the decay phase for all life cycles with non-monochromatic initial perturbations. In particular, the persistent cut-off cyclones that typically form for LC2 initialisations are found to eventually become unstable, with the onset of instability coming sooner for larger noise perturbations. All non-monochromatic life cycles result in a poleward jet shift in their final state, regardless of the strength of the initial shear. Consistently, anticyclonic wave breaking tends to be predominant during the mature and decay phases, even for LC2 initialisations. Equatorward jet shifts associated with cyclonic wave breaking still exist, although purely as a transient interim state. We show that wave–wave interactions resulting from the initialised random wave spectrum play an important role during all phases of the life cycle.

Резонансный ПИ-регулятор для судовой электрогидравлической стабилизированной платформы

The problem of stabilizing the angular position of the platform installed on the deck of a water vessel is considered. The platform is used to accommodate navigational equipment and radar antennas of communication systems that require stabilization of the platform's angular position in space under conditions of wave perturbations of the aquatic environment to work efficiently. The task under discussion is to eliminate the influence of wave perturbations on the platform's angle of inclination relative to the horizon. A mathematical model of a stabilized platform with an electric hydraulic drive is considered and a technique for synthesizing a control system that provides effective suppression of the influence of wave perturbations on the angular position of the platform is developed. The novelty of the proposed approach to the synthesis of the control system of the stabilized platform position consists in applying the time-scale separation method for calculating the resonant proportional-integral controller of the electrohydraulic drive of the platform. The results of numerical simulation of the control system under discussion are presented.

Instantaneous Angular Speed Extraction Based on Nonuniform Local Polynomial Differentiator for the Stiffness Identification of the Robot Joint

In the identification of industrial robot joint system, in order to obtain the ideal frequency response of the system, additional excitation needs to be applied. The addition of excitation signals, such as chirp signals and pseudorandom binary signals, will make the instantaneous angular speed (IAS) obtained by the motor encoder present nonstationary characteristics. In order to solve this problem, this article proposes a method for system identification by IAS extraction under nonstationary conditions. Interferences, such as electrical perturbation, quantization error, and background noise, generally reduce the accuracy of extracted IAS. First, the influence of electrical perturbation on the accuracy of angle calculation is eliminated by utilizing the characteristics of the two-phase encoder signals. Second, considering the time-varying characteristics of the rotational speed in the identification process, a nonuniform local polynomial differentiator (NULPD) is proposed to optimize the estimation of IAS and reduce the influence of background noise and sampling error based on local polynomial differentiator (LPD). The IAS estimation under the condition of variable speed is simulated to verify the performance of NULPD. According to the transmission characteristics of the robot joint system, a two-mass dynamic model is established, and the transfer function between the torque and motor speed is obtained. The torque is calculated from the three-phase current signals, and the rotational speed is obtained by the encoder signal. The frequency sweep experiment is carried out on the single-degree-of-freedom articulated arm test bench, where the stiffness and inertia of the system are identified within a certain error range by the proposed method.

Modeling of the temperature field on the rake surface of the lathe cutter taking into account the evolution of cutting forces

This paper is devoted to modeling the temperature field on the rake surface of the hard alloy lathe cutter when turning the work piece from structural steel 30 for a given value of the operating time of the cutting system. The assessment of the thermal state is made taking into account the change in cutting forces during machining. To do this, a model of the evolution of the radial and axial components of the cutting force was built, taking into account its growth in time and the influence of irregular kinematic vibrational perturbations. The calculation of the average temperature values for each section of the rake surface was made on the basis of the scientific approach described earlier, according to which the heating of the contact occurs due to the viscous dissipation of the friction energy in the surface plastically deformed micro layers of the chip. The calculation of the temperature values along the rake surface was carried out by the finite element method on a solid-state model of a fragment of the cutting part of the tool, as a result of which temperature values for the control planes were obtained. The results of digital modeling demonstrate a good correspondence of the calculated temperature values to the experimental data obtained by the semi artificial thermocouple method. The error of modeling the temperature field without taking into account heat exchange with the environment was 7.7-8.6%.

Influence of resonant magnetic perturbation on sawtooth behavior in experimental advanced superconducting Tokamak

Sawtooth oscillation is one of the most important magneto-hydrodynamic (MHD) instabilities in Tokamak plasma, which can result in the periodic relaxation of the temperature and density of the core plasma when the safety factor on the magnetic axis (<i>q</i><sub>0</sub>) is lower than unity. Owing to the periodic relaxation of the plasma core parameters, sawtooth oscillations are beneficial to avoiding impurity accumulation in plasma core. However, the large sawtooth crash may trigger off other MHD instabilities, like tearing modes (TMs) or neoclassical tearing modes (NTMs), which is a matter of concern for the plasma stability. Therefore, it is essential to control sawtooth oscillations for ensuring safe operation in the future Tokamaks such as ITER. The resonant magnetic perturbation (RMP) is widely used to control edge-localized modes (ELMs) and divertor heat flux in Tokamak. The application of RMP has also been found to affect the sawtooth behaviors. This paper studies the influence of RMP coils at <i>n</i> = 2 on sawtooth behaviors in experimental advanced superconducting Tokamak (EAST), where <i>n</i> is the toroidal mode number of the applied RMP. It is found that the phase difference between upper RMP coil and lower RMP coil (<inline-formula><tex-math id="M3">\begin{document}$ \Delta {\phi }_{{\rm{U}}{\rm{L}}}\left(^\circ\right)={\phi }_{{\rm{U}}}\left(^\circ\right)-{\phi }_{{\rm{L}}}\left(^\circ\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M3.png"/></alternatives></inline-formula>) is a notable parameter of affecting sawtooth behavior. The experiments for scanning the phase difference <inline-formula><tex-math id="M4">\begin{document}$ \Delta {\phi }_{{\rm{U}}{\rm{L}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M4.png"/></alternatives></inline-formula> are carried out. When the phase difference <inline-formula><tex-math id="M5">\begin{document}$ \Delta {\phi }_{{\rm{U}}{\rm{L}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M5.png"/></alternatives></inline-formula> of RMP at <i>n</i> = 2 is changed, the sawtooth period and amplitude become subsequently different. The minimum sawtooth period and amplitude appear at <inline-formula><tex-math id="M6">\begin{document}$\Delta {\phi }_{{\rm{U}}{\rm{L}}}=270^\circ$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M6.png"/></alternatives></inline-formula>. At the same time, neutron yields measured by neutron diagnostic system have the same trend as sawtooth behavior during RMP phase difference scanning. The plasma response to RMP at <i>n</i> = 2 is analyzed by using the MARS-F code. The results show that the plasma responses much strongly at the <inline-formula><tex-math id="M7">\begin{document}$\Delta {\phi }_{{\rm{U}}{\rm{L}}}=270^\circ$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M7.png"/></alternatives></inline-formula>. The loss of fast ion, caused by RMP coils, is possibly stronger at the <inline-formula><tex-math id="M8">\begin{document}$\Delta {\phi }_{{\rm{U}}{\rm{L}}}=270^\circ$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M8.png"/></alternatives></inline-formula> than that at other phase difference <inline-formula><tex-math id="M9">\begin{document}$ \Delta {\phi }_{{\rm{U}}{\rm{L}}}. $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230347_M9.png"/></alternatives></inline-formula> The loss of fast ion can reduces its stabilization effect on sawtooth behavior, which results in the reduction of the sawtooth period and amplitude. Further research is needed to optimize the sawtooth control method with RMP to make it compatible with plasma performance.

Multi-Objective Optimization of 1T2R Parallel Mechanisms Without Fixed Orientation Center and Axis Under the Influence of Parameter Perturbation

To track moving targets and signals in space, multiple characteristics as large orientational workspace and excellent kinematic performance are required for the satellite antenna driving mechanism. Due to variable orientational center and axes, the 3-RSR mechanism is capable of 1T2R with continuous workspace and becomes a promising solution for the satellite antenna driving mechanism. Influenced by the topological structure characteristics as none fixed orientation center and axes, the performances of 3-RSR mechanism are significantly impacted by the parameter perturbation. According to the differential mapping between finite screw and instantaneous screw, the structure, kinematics, performance, and optimization are unified under the FIS theory. To be applied for the satellite antenna driving mechanism, this paper carries out the multi-objective optimization of 3-RSR mechanism under the influence of parameter perturbation based on the FIS theory. Firstly, the orientational workspace is obtained by finite screw and the instantaneous motion description of the mechanism is derived through calculation principle of FIS theory. Secondly, the orientational workspace and kinematics indices of the mechanism are proposed towards the actual requirements of the satellite antenna driving, and the relationship with the parameters is established. The discrete operation becomes extremely complex owing to parameter perturbation, and the RSMs (response surface model) of indices without considering and considering parameter perturbation are modeled. The multi-objectives optimization of 3-RSR mechanism influenced by parameter perturbation is carried out and its Pareto frontier is obtained. Finally, a point preferred strategy is proposed and the optimum value of the parameter from Pareto frontier is selected.

Resonances in asymptotically autonomous systems with a decaying chirped-frequency excitation

<p style='text-indent:20px;'>The influence of oscillatory perturbations on autonomous strongly nonlinear systems in the plane is investigated. It is assumed that the intensity of perturbations decays with time, and their frequency increases according to a power law. The long-term behaviour of perturbed trajectories is discussed. It is shown that, depending on the structure and the parameters of perturbations, there are at least two different asymptotic regimes: a phase locking and a phase drifting. In the case of phase locking, resonant solutions with an unlimitedly growing energy occur. The stability and asymptotics at infinity of such solutions are investigated. The proposed analysis is based on a combination of the averaging technique and the method of Lyapunov functions.</p>

Scaling behaviour under the influence of a homogeneous size-dependent perturbation

We study the finite-size scaling behaviour at the critical point, resulting from the addition of a homogeneous size-dependent perturbation, decaying as an inverse power of the system size. The scaling theory is first formulated in a general framework and then illustrated using three concrete problems for which exact results are obtained.

Research on disturbance rejection motion control method of USV for UUV recovery

AbstractThe recovery of unmanned underwater vehicle (UUV) by unmanned surface vehicle (USV) has the characteristics of autonomy, safety, and efficiency. Taking the recovery of UUV by USV as the engineering background, this paper studies the guidance and anti‐interference motion control of USV in the recovery process. Aiming at the problem of dynamic guidance when recovering UUV, the USV guidance strategy for UUV recovery is studied. Fuzzy guidance is introduced as the dynamic terminal guidance method, and a layered guidance strategy combining classical guidance and fuzzy guidance is proposed. On the basis of the theory of compact form dynamic linearization‐based model‐free adaptive control (CFDL‐MFAC), the motion control of USV in the process of recovering UUV under the influence of model perturbation, external interference, and other uncertainties is studied. Theoretical analysis and experimental results show that there is a contradiction in the matching of dynamic change speed between the USV heading control subsystem and CFDL‐MFAC. By introducing the difference item into the standard control criterion to weaken the integral effect in the heading control subsystem of USV, a difference‐type compact format model‐free adaptive control method (DCFDL‐MFAC) is proposed, and the stability of DCFDL‐MFAC method is proved theoretically. The effectiveness and practicability of the proposed method are verified by simulation tests and field tests of “Dolphin IB” small USV.

Circulation and stratification drivers during the summer season in the upwelling bay of Paracas (Peru): A modelling study

The circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll.Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products.The circulation in the bay under strong (>5.5 m s−1) and weak (<3 m s−1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay.

Electronic effects of amine-imine nickel and palladium catalysts on ethylene (co)polymerization

A series of bis-(aryl)-amine-imine nickel and palladium complexes with electron-donating (OMe), H, and -withdrawing (F and Br) groups at the para-aryl position were synthesized and characterized to probe the ligand electronic effects on homo- and copolymerization of ethylene. The influences of electronic perturbations on complex synthesis, polymerization property, and polymer microstructure were investigated systematically. The electronic effects of para-substituents were verified by Hammett constants and topographic steric maps of nickel and palladium complexes. Electron-rich ligands had stronger complexation ability to the nickel and palladium metal, thereby facilitating the synthesis of nickel and palladium complexes. Ethylene polymerizations at different temperatures showed that electron-deficient amine-imine nickel and palladium catalysts were more active than electron-rich analogues at low temperatures while the reverse trend was observed at high temperatures. The electronic effects of para-substituents affected polyethylene molecular weight, but had little influence on the branching density of highly branched polyethylenes. Copolymerization of ethylene and methyl acrylate (MA) using palladium catalysts demonstrated that the electron-donating group promoted copolymerization performance, and was favorable for direct insertion of MA to produce main-chain MA unit. Electronic effects of amine-imine nickel and palladium catalysts on ethylene polymerization were comprehensively summarized to electronic perturbations on the metal electrophilicity and the thermal tolerance of catalyst.