Ion-driven Instabilities in the Inner Heliosphere. I. Statistical Trends

Instabilities described by linear theory characterize an important form of wave–particle interaction in the solar wind. We diagnose unstable behavior of solar wind plasma between 0.3 and 1 au via the Nyquist criterion, applying it to fits of ∼1.5M proton and α particle Velocity Distribution Functions (VDFs) observed by Helios I and II. The variation of the fraction of unstable intervals with radial distance from the Sun is linear, signaling a gradual decline in the activity of unstable modes. When calculated as functions of the solar wind velocity and Coulomb number, we obtain more extreme, exponential trends in the regions where collisions appear to have a notable influence on the VDF. Instability growth rates demonstrate similar behavior, and significantly decrease with Coulomb number. We find that for a nonnegligible fraction of observations, the proton beam or secondary component might not be detected, due to instrument resolution limitations, and demonstrate that the impact of this issue does not affect the main conclusions of this work.

Influence of the switching frequency of the switch and the amplitude of the reference voltage of a pulsed voltage regulator of the lowering type on its stability

On the basis of classical stability criteria, using the expressions of the transfer function, according to the block diagram, the stability of the impulse controller with feedback is estimated. The influence of the switching frequency of the switch and the amplitude of the reference voltage on the stability of a pulsed voltage regulator of a lowering type with deterministic parameters of the system is analyzed. In accordance with the Nyquist criterion for the transfer function of an open-loop system, both stability and phase stability margins for a closed-loop system can be estimated. When simulating the operation of the device, the phase stability margin was obtained, according to the Nyquist criterion, which is с = Н = 7. An increase in the sawtooth voltage is not a desirable phenomenon, which, although it increases the margin of stability, however, reduces stability. Moreover, the dependence of the ripple, affecting the stability of operation, on the amplitude of the sawtooth voltage is not a predictable value and takes on a random value.

Eigenvalue Decomposition Precoded Faster-Than-Nyquist Transmission of Index Modulated Symbols

Postprint accepted on 30 April 2021 for publication in IEEE International Symposium on Information Theory (ISIT), 2021. (c) 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.<div>In this paper, we propose a precoded faster-than-Nyquist (FTN) signaling technique for time-domain single-carrier index modulated (IM) symbol transmission. More precisely, eigenvalue decomposition precoding is adopted for the FTN transmission of data bits modulated by single-carrier time-domain IM. While the FTN scheme increases the spectral efficiency and data rate by packing more transmit symbols per block duration than those defined in the Nyquist criterion, time-domain IM works towards the same objective while maintaining symbol sparsity. We analytically derive the constrained capacity of the proposed system. Our simulation results show that the proposed scheme has better bit error ratio (BER) performance over the conventional FTN-IM scheme, particularly for the scenario of a higher packing ratio. In the proposed scheme, $2.5$-dB performance gain is observed at the BER of 10^-4, employing the packing ratio of $0.7$ and the roll-off factor of $0.5$ in a channel-uncoded scenario.<br></div>

Eigenvalue Decomposition Precoded Faster-Than-Nyquist Transmission of Index Modulated Symbols

Postprint accepted on 30 April 2021 for publication in IEEE International Symposium on Information Theory (ISIT), 2021. (c) 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.<div>In this paper, we propose a precoded faster-than-Nyquist (FTN) signaling technique for time-domain single-carrier index modulated (IM) symbol transmission. More precisely, eigenvalue decomposition precoding is adopted for the FTN transmission of data bits modulated by single-carrier time-domain IM. While the FTN scheme increases the spectral efficiency and data rate by packing more transmit symbols per block duration than those defined in the Nyquist criterion, time-domain IM works towards the same objective while maintaining symbol sparsity. We analytically derive the constrained capacity of the proposed system. Our simulation results show that the proposed scheme has better bit error ratio (BER) performance over the conventional FTN-IM scheme, particularly for the scenario of a higher packing ratio. In the proposed scheme, $2.5$-dB performance gain is observed at the BER of 10^-4, employing the packing ratio of $0.7$ and the roll-off factor of $0.5$ in a channel-uncoded scenario.<br></div>

Controller design by the motion separation method with applying stability criterions for non-linear objects with transport delays

Controllers and feedback are applied for performing many technical tasks, for example, maintaining the desired temperature stabilization in the thermostat and speed electric motor stabilization. Different methods such as the time-scale separation method, the frequency-response design method, and the Ziegler–Nichols method are applied to design controllers. The Ziegler–Nichols method does not provide the required transient process quality. The Smith predictor is sometimes applied to control objects with a transport delay. However, it may be difficult to apply the Smith predictor when a mathematical model is not fully known. There is a paper where the application of the motion separation method with a delay is considered. However, the calculation method proposed in that work requires solving a system of four nonlinear equations for a second-order object. Therefore, in this paper, we investigate the possibility of a simpler method for calculating the controller, namely, the possibility of using the Mikhailov criterion in the synthesis of a controller by the motion separation method for nonlinear objects with a delay. Also, the application of the Nyquist stability criterion with a simpler than the proposed earlier calculation procedure is considered in the paper. The values of the regulator coefficients obtained using the Nyquist criterion and the Mikhailov criterion are compared. The Mikhailov criterion and the Nyquist criterion are applied to estimate the stability of the fast motions subsystem. The derivation of formulas to calculate the parameters of the controller designed by the motion separation method for first-order non-linear objects with transport delays and second-order non-linear objects with transport delays with the use of the Mikhailov criterion is also considered in the paper. Transient processes are studied by numerical simulation. Transient processes plots are also given. The parameters of the controller that are needed to improve the performance of transient processes in the presence of a delay are found. The Peltier element, an aircraft strength test stand, a thermostat, and equipment for metal rolling are non-linear control objects with a transport delay. The Mikhailov hodographs for objects with a transport delay are presented.

P53-Mdm2 Loop Stability and Oscillatory Dynamics with Mdm2-Induced Delay Effect in P53

In this paper, we consider P53-Mdm2 negative feedback loop supposed to be the core circuit of genome. We study stability and the oscillatory dynamics of the loop. Many of the studies modeled this loop by delay-differential equations with P53-induced transcrip- tional delay in the production of Mdm2. We, however, highlight the importance of Mdm2- induced delay in the degradation of P53 protein. We consider two forms of P53 protein i.e., plain P53 and active P53 along with its principal antagonist protein Mdm2 to formulate a minimal model. Active P53 finds its inclusion in the loop in the presence of DNA damage represented by a Boolean variable ‘s’. The analysis of the model provides thresholds on delays using Nyquist criterion such that delays in the degradation of P53 lower than these thresholds guarantee stability of the loop in that all proteins plain P53, active P53 and Mdm2 approach to stable equilibrium state. The oscillatory dynamics in proteins, if any, would exist beyond these thresholds.

Automated System for Monitoring and Diagnostics Pilot's Emotional State in Flight

In this article, the system for monitoring of the emotional state changes of the air navigation system's human operator in the extreme situations, based on the using of the prior models of the operator activity which built on the posterior researches of actual material of the aviation accidents investigations, has been proposed. The stability of aviation man-machine system “human-operator – aircraft” during the deformations of the operator's emotional experience has been defined according to the Nyquist criterion. A computer program for diagnostics of the emotional state of the human operator has been developed. The system based on monitoring of the current emotional state of the air navigation system's human operator and diagnostics of the deformations of emotional experience with the determination of the operator's functional stability will allow preventing the development of potentially hazardous flight situations towards worsening in a proactive manner.