A Non-Iterative Integration Scheme Enriching the Solution to the Coupled Maglev Vehicle–Bridge System

A non-iterative integration scheme is presented in this study to enrich the solutions to the coupled equations of the maglev vehicle–bridge system. The proposed integration scheme is composed of two integration methods aiming at providing the solutions to equation of motion and state-space equation. First, the equation of motion of the simply supported girder bridge is transformed by the modal superposition method. Then the state-space equation is used to describe the motions of both the vehicle and the suspension control system, with the associated matrices assembled using the fully computerized approach. By adopting this integration scheme, only pure vector calculations arise in the solution process, regardless of the existence of time-dependent displacement and velocity on the right-hand sides of the two coupled equations. The proposed integration method is of the second-order accuracy with and without damping. Being equipped with adequate numerical dissipation and dispersion, the method also possesses the characteristic of little computing errors, as can be achieved through the use of different pairs of parameters. Finally, numerical simulations have been conducted to assess the influence of different feedback gains, three types of bridges with different lengths, and guideway irregularity on the maglev vehicle–bridge system.

A CRISPR/Cas9-Mediated, Homology-Independent Tool Developed for Targeted Genome Integration in Yarrowia lipolytica

ABSTRACT Yarrowia lipolytica has been extensively used to produce essential chemicals and enzymes. As in most other eukaryotes, nonhomologous end joining (NHEJ) is the major repair pathway for DNA double-strand breaks in Y. lipolytica. Although numerous studies have attempted to achieve targeted genome integration through homologous recombination (HR), this process requires the construction of homologous arms, which is time-consuming. This study aimed to develop a homology-independent and CRISPR/Cas9-mediated targeted genome integration tool in Y. lipolytica. Through optimization of the cleavage efficiency of Cas9, targeted integration of a hyg fragment was achieved with 12.9% efficiency, which was further improved by manipulation of the fidelity of NHEJ repair, the cell cycle, and the integration sites. Thus, the targeted integration rate reached 55% through G1 phase synchronization. This tool was successfully applied for the rapid verification of intronic promoters and iterative integration of four genes in the pathway for canthaxanthin biosynthesis. This homology-independent integration tool does not require homologous templates and selection markers and achieves one-step targeted genome integration of the 8,417-bp DNA fragment, potentially replacing current HR-dependent genome-editing methods for Y. lipolytica. IMPORTANCE This study describes the development and optimization of a homology-independent targeted genome integration tool mediated by CRISPR/Cas9 in Yarrowia lipolytica. This tool does not require the construction of homologous templates and can be used to rapidly verify genetic elements and to iteratively integrate multiple-gene pathways in Y. lipolytica. This tool may serve as a potential supplement to current HR-dependent genome-editing methods for eukaryotes.

Research on the mechanical model of cord-reinforced air spring with winding formation

In this article, the parametric model for the stiffness characteristic and burst pressure of cord-reinforced air spring with winding formation is developed. Based on the non-geostrophic winding model and the assumption of cord cross-stability, the cord winding trajectory model of the capsule is established. Then, the anisotropic and nonlinear mechanics model of the capsule with complex cord winding trajectory variation characteristics is constructed by the classical thin-shell theory. The capsule state vector is solved by the extended homogeneous capacity precision integration method. Due to the complex coupling relationship between the capsule state vector and the internal air pressure, the stiffness characteristic is solved by the iterative integration method. The burst pressure of the air spring is solved by the Tsai–Hill strength theory. Eventually, the accuracy and reliability of the proposed method are verified by the experimental results. The effects of the material properties, winding parameters, and geometric structure parameters on stiffness characteristics and burst pressure are discussed. The results of this article provide an important theoretical basis for the performance design of cord-reinforced air springs with winding formation.

Strapdown Attitude Computation: Functional Iterative Integration versus Taylor Series Expansion

There are two basic approaches to strapdown attitude computation, namely, the traditional Taylor series expansion approach and the Picard iterative method. The latter was recently implemented in a recursive form basing on the Chebyshev polynomial approximation and resulted in the so-called functional iterative integration approach. Up to now a detailed comparison of these two approaches with arbitrary number of gyroscope samples has been lacking for the reason that the first one is based on the simplified rotation vector equation while the second one uses the exact form. In this paper, the mainstream algorithms are considerably extended by the Taylor series expansion approach using the exact differential equation and recursive calculation of high-order derivatives, and the functional iterative integration approach is re-implemented on the normal polynomial. This paper applies the two approaches to solve the strapdown attitude problem, using the attitude parameter of quaternion as a demonstration. Numerical results under the classical coning motion are reported to assess all derived attitude algorithms. It is revealed that in the low and middle relative conic frequency range all algorithms have the same order of accuracy, but in the range of high relative frequency the algorithm by the functional iterative integration approach performs the best in both accuracy and robustness if the Chebyshev polynomials and a larger number of gyroscope samples are to be used. The main conclusion applies to other attitude parameters as well.

Engineering the oleaginous yeast Yarrowia lipolytica for production of α-farnesene

Background Yarrowia lipolytica, a non-traditional oil yeast, has been widely used as a platform for lipid production. However, the production of other chemicals such as terpenoids in engineered Y. lipolytica is still low. α-Farnesene, a sesquiterpene, can be used in medicine, bioenergy and other fields, and has very high economic value. Here, we used α-farnesene as an example to explore the potential of Y. lipolytica for terpenoid production. Results We constructed libraries of strains overexpressing mevalonate pathway and α-farnesene synthase genes by non-homologous end-joining (NHEJ) mediated integration into the Y. lipolytica chromosome. First, a mevalonate overproduction strain was selected by overexpressing relevant genes and changing the cofactor specificity. Based on this strain, the downstream α-farnesene synthesis pathway was overexpressed by iterative integration. Culture conditions were also optimized. A strain that produced 25.55 g/L α-farnesene was obtained. This is the highest terpenoid titer reported in Y. lipolytica. Conclusions Yarrowia lipolytica is a potentially valuable species for terpenoid production, and NHEJ-mediated modular integration is effective for expression library construction and screening of high-producer strains.