Two-step Integration Method Research Articles

Static and dynamic eigenvalues in unified stability studies

A framework for unified analysis of small-signal and large-signal power system stability based on static and dynamic eigenvalues is proposed in this paper. The presented implementation is based on Gear's method, which is a two-step integration method for numerical simulation with self-adaptive time-step. Furthermore, it can be easily configured for providing the state matrix as basis for calculating the system eigenvalues during simulation. Thus, the presented framework allows for eigenvalue-based analysis of small-signal dynamics and stability margin at any steady-state operating point during a time-domain simulation. Furthermore, Linear Time-Varying system theory is utilized for modal analysis during large-signal transients. For this purpose, dynamic eigenvalues and eigenvectors are calculated by solving a Riccati equation to generalize the modal analysis during transient conditions. The stability is evaluated by calculating the Lyapunov exponent of the mode-vector of the system. The results from numerical analysis of three case studies are presented to evaluate and illustrate the characteristics of the presented approach for unified small-signal and transient stability analysis.

Visualization of a Specific Genome Locus by the lacO/LacI-GFP System.

Observing the dynamics of a specific chromosome locus in living cells can provide important information as to the molecular mechanisms underlying events such as chromosome segregation, homologous chromosome pairing, chromosome arrangement, and gene expression. The lacO/LacI-GFP system provides a simple and useful method in which a chromosome locus is visualized by inserting lacO repeat arrays and then expressing an LacI-GFP fusion that specifically binds to the lacO sequence. This system has been adapted for use in Schizosaccharomyces pombe by expressing the LacI-GFP under a promoter of the dis1+ gene. Furthermore, a two-step integration method has been developed that ensures high-efficiency integration of lacO arrays to a desired target position.

Out-of-plane displacement field measurement by shearography

Abstract Existing shearography systems measuring out-of-plane displacements suffer from boundary-constraint or reference surface requirements. Therefore, we propose an accurate non-uniform out-of-plane displacement field measurement method based on a modified shearography system and two-step integration method. The proposed method combines high-resolution interferometry with the advantage of relaxing the environmental stability requirements. The modified shearography system adopts three beam splitters and two switches when compared with conventional optical configurations. The three beam splitters are used to construct a modified Michelson interferometer that shears the image along two orthogonal directions, and the shearing direction can be switched by the two hardware switches between the orthogonal directions. With phase shifting performed on the recorded images, the out-of-plane displacement gradients along the orthogonal directions are extracted sequentially. In general, without boundary restrictions on the object surface, it is difficult to directly extract out-of-plane displacement from a single displacement gradient field. Accordingly, the two-step integration method is proposed and applied to the orthogonal displacement gradients to extract the relative out-of-plane displacement field without any boundary conditions of the object surface provided. Experiments are performed on a clamped circular plate with uniform loading, and the results are compared with electronic speckle pattern interferometry (ESPI) results to validate the proposed method.

A two-step integration method for seamless gene deletion in baker’s yeast

In this study, we developed a seamless gene deletion method through a two-step integration protocol to construct an industrial baker’s yeast with NTH1 deletion. A fusion fragment consisted of the upstream sequence, and the downstream sequence of NTH1 was subcloned into an integrating plasmid containing a URA3 counter-selection marker for excision of unwanted DNA. The plasmid was integrated into the genomic NTH1 locus of recipient baker’s yeast, leading to tandem repeats of the upstream flank and the downstream flank. Pop-out of the URA3 marker occurs by integration recombination between either the downstream flank repeats or the upstream flank repeats. Integration recombination between the repeats results in NTH1 deletion without any heterologous DNA and reversion to a wild-type strain. The desired deletion occurred with a frequency of approximately 10−5. Polymerase chain reaction verification and sequence analysis confirmed the NTH1 disruption and the absence of integrated plasmid sequences in the genome of the selected strain. In addition, the mutant with NTH1 deletion exhibits a higher trehalose accumulation and consequently displays a higher viability of yeast cells after freezing. Thus, this method proposes a protocol to construct mutant yeast without leaving behind any heterologous DNA sequences and will facilitate the genetic engineering of any yeast.