A novel method of interference source direction-finding with an existing single antenna beam in communication satellites

Interference has recently become a critical factor in communication satellite performance, and the interference source location is one of the most important factors in resolving this issue. The article proposes an innovative method of interference source direction-finding suitable for communication satellites with an existing single antenna beam and single radio frequency (RF) channel, which utilizes the symmetry of the antenna pattern to search for interference sources. Compared to traditional position methods with time-frequency-synchronized multi-satellites or a directing antenna array in a single satellite, the method does not require any particular direction-finding payload in communication satellites and shares existing antennas and RF channels with communication systems in satellites. The ability to find the direction of the interference source is a software-defined function in the communication processor. The proposed method provides a novel way to solve the problems of interference source direction-finding with the least engineering complexity, and it has excellent coexistence with other existing systems in communication satellites. The computer simulation and out-field experiment results in this article show that the method has excellent performance with high direction-finding resolution within extensive coverage, offering significant value and bright prospects for resolving the growing interference issues in communication satellites

Functional Synchronization of Biological Rhythms in a Tritrophic System

In a tritrophic system formed by a plant, an herbivore and a natural enemy, each component has its own biological rhythm. However, the rhythm correlations among the three levels and the underlying mechanisms in any tritrophic system are largely unknown. Here, we report that the rhythms exhibited bidirectional correlations in a model tritrophic system involving a lima bean, a pea leafminer and a parasitoid. From the bottom-up perspective, the rhythm was initiated from herbivore feeding, which triggered the rhythms of volatile emissions; then the rhythmic pattern of parasitoid activities was affected, and these rhythms were synchronized by a light switch signal. Increased volatile concentration can enhance the intensity of parasitoid locomotion and oviposition only under light. From the top-down perspective, naive and oviposition-experienced parasitoids were able to utilize the different volatile rhythm information from the damaged plant to locate host leafminers respectively. Our results indicated that the three interacting organisms in this system can achieve rhythmic functional synchronization under a natural light-dark photoperiod, but not under constant light or darkness. These findings provide new insight into the rhythm synchronization of three key players that contribute to the utilization of light and chemical signals, and our results may be used as potential approaches for manipulating natural enemies

Dynamic bidding analysis in power market based on the supply function

AbstractThis paper presents a dynamic bidding model of the power market based on the Nash equilibrium and a supply function. The new model is composed of different dynamic systems and semismooth equations by means of the nonlinear complementarity method. Comparing with those existing bidding models, the remarkable characteristic of the new model is twofold: First, it adopts a dynamic bid so that the bidding limit point is the Nash equilibrium point of the market; Second, it considers the system requirement and the market property such as involving the transmission constraints in the network, and using a supply function which is suitable for the oligopolistic competitive power market. All of these imply that the new model is very close to the practical power market. The computation of the dynamic model is discussed by using the semismooth theory. A numerical simulation is presented to test the model behaviors in the uncogestion and the congestion cases, respectively. The numerical tests include the computing behavior of the dynamic model to reach Nash equilibrium points, the influence of the adjusted parameters and the system parameters to the Nash equilibrium, the local stability of the model, and the comparison of simulation effect between the proposed model and the Cournot model. The simulations show that the new bidding model is valid

Penalized sample average approximation methods for stochastic programs in economic and secure dispatch of a power system

In this paper, we develop a stochastic programming model for economic dispatch of a power system with operational reliability and risk control constraints. By defining a severity-index function, we propose to use conditional value-at-risk (CVaR) for measuring the reliability and risk control of the system. The economic dispatch is subsequently formulated as a stochastic program with CVaR constraint. To solve the stochastic optimization model, we propose a penalized sample average approximation (SAA) scheme which incorporates specific features of smoothing technique and level function method. Under some moderate conditions, we demonstrate that with probability approaching to 1 at an exponential rate with the increase of sample size, the optimal solution of the smoothing SAA problem converges to its true counterpart. Numerical tests have been carried out for a standard IEEE-30 DC power system

Finding A Stable Solution of A System of Nonlinear Equations ∗

This paper presents new methods for finding dynamically stable solutions of systems of nonlinear equations. The concepts of stability functions and the so-called stable solutions are defined. Based on those new concepts, two models of stable solutions and three stability functions are proposed. These stability functions are semismooth. Smoothing technology is applied to such stability functions. Smoothing Newton methods are proposed to solve the stable solution models. Convergence properties of these methods are studied. We report o