We study a four-dimensional system modified from a three-dimensional chaotic circuit by adding a memristor, which is a new fundamental electronic element with promising applications. Although the system has a line of infinitely many equilibria, our studies show that when the strength of the memristor increases, it can exhibit rich interesting dynamics, such as hyperchaos, long period-1 orbits, transient hyperchaos, as well as non-attractive behaviors frequently interrupting hyperchaos. To verify the existence of hyperchaos and reveal its mechanism, a horseshoe with two-directional expansion is studied rigorously in detail by the virtue of the topological horseshoe theory and the computer-assisted approach of a Poincaré map. At last, the system is implemented with an electronic circuit for experimental verification.

The plant Nervilia fordii (Hance) Schltr. is known for its antimicrobial and antitumor properties. It is a rare and vulnerable perennial herb of the Orchidaceae family. In this study, 984 isolates were isolated from various tissues of N. fordii. and were identified through the sequence analyses of the internal transcribed spacer region of the rRNA gene. Except for 12 unidentified fungi, all others were affiliated to at least 39 genera of 14 orders of Ascomycota (72.66%) and Basidiomycota (19.00%). Antimicrobial activity was determined by using the agar diffusion method. Subsequent assays revealed 20 strains of fungal endophytes exhibited antibacterial activity against at least one pathogenic bacterium or fungus. Moreover, the capability of promoting seed germination was evaluated on the basis of the interaction of Bletilla striata seeds with the isolates. Results revealed that the three isolates could promote B. striata seed germination. After 21 days, the germination rate under treatment with the best strain was 97.89%, which was higher than that under the control treatment (12.68%). Taken together, the present data suggested that various endophytic fungi of N. fordii could be exploited as sources of novel natural antimicrobial agents or used for the artificial breeding of rare orchids.

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