Search

This paper investigates the event-triggered output feedback control problem for feedforward nonlinear systems with unknown measurement sensitivity. The nonlinear terms are assumed to be bounded by an unknown constant multiplied by fractional power of states and controller. We design an auxiliary system independent of the output signal to construct controller and propose a novel time-varying triggering mechanism. It is the first time to introduce the logarithmic function into the auxiliary system and state transformation to deal with event-triggered control problem. Under the designed event-triggered controller, the convergence of all states is obtained and the Zeno behavior is effectively avoided. Finally, two numerical examples are presented to demonstrate the effectiveness of the designed event-triggered controller.

In this paper, the output feedback stabilization problem is studied for a class of cascade nonlinear ODE-PDE systems. The nonlinear terms of ODE-subsystem are assumed to be bounded by a known constant multiplied by unmeasured states, and PDE-subsystem is a diffusion equation. Especially, the unstable diffusion equation is considered. Based on the low gain observer and a series of transformations, the output feedback stabilization problem is converted into designing proper gain parameters. Furthermore, the stability of the closed-loop system is analyzed by Lyapunov theorem. Finally, two numerical examples are given to demonstrate the effectiveness of the proposed control strategy.

Chalcogenide hollow-core anti-resonant fibers (HC-ARFs) are a promising propagation medium for high-power mid-infrared (3-5 µm) laser delivery, while their properties have not been well understood and their fabrications remain challenging. In this paper, we design a seven-hole chalcogenide HC-ARF with touching cladding capillaries, which was then fabricated from purified As40S60 glass by combining the “stack-and-draw” method with a dual gas path pressure control technique. In particular, we predict theoretically and confirm experimentally that such medium exhibits higher-order mode suppression properties and several low-loss transmission bands in the mid-infrared spectrum, with the measured fiber loss being as low as 1.29 dB/m at 4.79 µm. Our results pave the way for the fabrication and implication of various chalcogenide HC-ARFs in mid-infrared laser delivery systems.

The variation of load resistance and coupling coefficient are two key factors affecting the output characteristics of wireless power transfer system during the charging process. Both the variation of coupling coefficient caused by the position deviation of primary and secondary devices and the variation of load resistance during charging will result in the low output power and efficiency of the wireless charging system. In view of the above problems, this paper studied the constraint conditions of the compensation network of several wireless power transfer systems, and analyzed the output characteristics of the wireless power transfer system of each compensation network under the variation of load and coupling coefficient. The LCL-LCL type compensation network structure was selected for optimization design and according to the variation characteristics of output power and efficiency with load and coupling coefficient, the method of optimizing the compensation network parameters was proposed. The output power value of the design system was further optimized by adding a dc-dc converter circuit. Finally, the effectiveness of the proposed optimization design method was verified through the system simulation.

This paper constructs a fuzzy comprehensive evaluation system to evaluate the safety of medication in Chinese laying hens companies. Five first-grade indicators and 23 second-grade indicators are determined based on the Delphi method. The weight of every indicator is also distributed by the Delphi method. An evaluation of a case company is carried out. The evaluation results classified 0%, 0%, 35.09%, 47.22% and 17.7% of medication practices of this case company as unsafe, moderately unsafe, slightly safe, moderately safe, and safe, respectively. The evaluation results are consistent with the case company’s medication practices. Finally, this paper proposes several suggestions to improve the medication management practices of laying hens companies in China.

A novel “coupling agent” N-(4-amino-phenyl)-2-methyl-acrylamide (APMA) was synthesized to efficiently enhance interfacial interactions between the carbon fiber (CFs) and vinyl ester resin (VE). Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were employed to characterize functional groups and chemical compositions of a carbon fiber surface, which indicated that the vinyl groups of APMA were grafted successfully on the surface of the CFs. Four different treatments of CFs (pristine CFs, carboxylic-CFs, acrylamide-CFs and APMA-CFs) were used to prepare the CF-reinforced VE composites. The mechanical properties were analysed and a micro-droplet test was performed to investigate the enhancement effect of the coupling agent on the interfacial strength of the composites. Scanning electron microscopy (SEM) showed that APMA-CFs were uniformly distributed throughout the matrix, and no open ring holes were found at the cross-section of the composites; furthermore, after micro-droplet test, some matrix was still attached to the debonded CF surface. As a result, APMA functionalized CFs improved the flexural strength of the APMA-CF/VE composites by 19.4%, and significantly improved the interfacial shear strength between APMA-CFs and VE by 90.53%.

In this paper, we prepared and characterized nanocomposites of polyether ether ketone (PEEK) containing hexagonal boron nitride (h-BN) nanofiller from 1 to 5 wt%. Using various techniques, we studied the friction and wear properties, thermal conductivity, morphology, and mechanical and thermomechanical properties of the nanocomposites. Adding h-BN nanoparticles to the PEEK improved the properties of the resulting nanocomposites. At 5 wt% h-BN content, it exhibited optimum improvement of friction and wear properties, thermal conductivity, hardness, and storage modulus. Thus, we demonstrated that PEEK nanocomposites reinforced with h-BN have a great potential as multifunctional materials for future industrial applications.

Poly(ether ether ketone)/graphene/carbon fiber (PEEK/GE/CF) laminates with different weight percentages of GE were manufactured successfully through ball milling and hot-press processing. The effect of the GE on the morphology, thermal conductivity, friction performance, thermal and mechanical properties of composites was investigated. Scanning electron microscopy showed that the GE was uniformly distributed in matrix-rich regions. Thermal conductivity measurements demonstrated that addition of 0.7 wt% GE sharply improved the thermal conductivity of the laminates. Tribological tests revealed that the friction coefficient and wear rate rapidly decreased with the addition of GE. In the studied range, the friction reduction and wear resistance performance of PEEK/CF composites filled with 0.7 wt% GE is the most effective. Meanwhile, the obtained PEEK/GE/CF laminates also possessed excellent mechanical and thermal properties. Thus, graphene-reinforced PEEK/CF composites possessed better overall properties than conventional PEEK/CF composites.

Epigenetic programming is critical for normal development of mammalian embryos. Errors cause misexpression of genes and aberrant development (E. Li, C. Beard, and R. Jaenisch, Nature 366:362-365, 1993). Imprinted genes are important targets of epigenetic regulation, but little is known about how the epigenetic patterns are established in the parental germ lines and maintained in the embryo. Paternal allele-specific expression at the imprinted Rasgrf1 locus in mice is controlled by paternal allele-specific methylation at a differentially methylated domain (DMD). DMD methylation is in turn controlled by a direct repeat sequence immediately downstream of the DMD which is required for establishing Rasgrf1 methylation in the male germ line (B. J. Yoon et al., Nat. Genet. 30:92-96, 2002). To determine if these repeats have a role in methylation maintenance, we developed a conditional deletion of the repeat sequence in mice and showed that the repeats are also required during a narrow interval to maintain paternal methylation of Rasgrf1 in developing embryos. Removing the repeats upon fertilization caused a total loss of methylation by the morula stage, but by the epiblast stage, the repeats were completely dispensable for methylation maintenance. This developmental interval coincides with genome-wide demethylation and remethylation in mice which most imprinted genes resist. Our data show that the Rasgrf1 repeats serve at least two functions: first, to establish Rasgrf1 DNA methylation in the male germ line, and second, to resist global demethylation in the preimplantation embryo.

The yeast TREX complex physically couples elongating RNA polymerase II with RNA processing and nuclear RNA export factors to facilitate regulated gene expression. Hpr1p is an essential component of TREX, and loss of Hpr1p compromises transcriptional elongation, RNA export, and genome stability. Despite these defects, HPR1 is not essential for viability in yeast. A functional orthologue of Hpr1p has been identified in metazoan species and is variously known as Thoc1, Hpr1, or p84. However, the physiological functions of this protein have not been determined. Here, we describe the generation and phenotypic characterization of mice containing a null allele of the Thoc1 gene. Heterozygous null Thoc1 mice are born at the expected Mendelian frequency with no phenotype distinguishable from the wild type. In contrast, homozygous null mice are not recovered, indicating that Thoc1 is required for embryonic development. Embryonic development is arrested around the time of implantation, as blastocysts exhibit hatching and blastocyst outgrowth defects upon in vitro culture. Cells of the inner cell mass are particularly dependent on Thoc1, as these cells rapidly lose viability coincident with Thoc1 protein loss. While Hpr1p is not essential for the viability of unicellular yeasts, the orthologous Thoc1 protein is required for viability of the early mouse embryo.

Imprinted methylation of the paternal Rasgrf1 allele in mice occurs at a differentially methylated domain (DMD) 30 kbp 5' of the promoter. A repeated sequence 3' of the DMD regulates imprinted methylation, which is required for imprinted expression. Here we identify the mechanism by which methylation controls imprinting. The DMD is an enhancer blocker that binds CTCF in a methylation-sensitive manner. CTCF bound to the unmethylated maternal allele silences expression. CTCF binding to the paternal allele is prevented by repeat-mediated methylation, allowing expression. Optimal in vitro enhancer-blocking activity requires CTCF binding sites. The enhancer blocker can be bypassed in vivo and imprinting abolished by placing an extra enhancer proximal to the promoter. Together, the repeats and the DMD constitute a binary switch that regulates Rasgrf1 imprinting.

In mammals, imprinted genes have parent-of-origin–specific patterns of DNA methylation that cause allele-specific expression. At Rasgrf1 (encoding RAS protein-specific guanine nucleotide-releasing factor 1), a repeated DNA element is needed to establish methylation and expression of the active paternal allele1. At Igf2r (encoding insulin-like growth factor 2 receptor), a sequence called region 2 is needed for methylation of the active maternal allele2,3. Here we show that replacing the Rasgrf1 repeats on the paternal allele with region 2 allows both methylation and expression of the paternal copy of Rasgrf1, indicating that sequences that control methylation can function ectopically. Paternal transmission of the mutated allele also induced methylation and expression in trans of the normally unmethylated and silent wild-type maternal allele. Once activated, the wild-type maternal Rasgrf1 allele maintained its activated state in the next generation independently of the paternal allele. These results recapitulate in mice several features in common with paramutation described in plants4.

Rb1 is essential for normal embryonic development, as null mice die in midgestation with widespread unscheduled cell proliferation. Rb1 protein (pRb) mediates cell cycle control by binding E2F transcription factors and repressing expression from E2F-dependent promoters. An increasing amount of evidence suggests that pRb loss also compromises cellular differentiation. Since differentiation is often dependent on cell cycle exit, it is currently unclear whether the effects of pRb on differentiation are an indirect consequence of pRb/E2F-mediated cell cycle control or whether they reflect direct cell-type-specific pRb functions. We have mutated Rb1 in the mouse to express a protein (R654W) specifically deficient in binding E2F1, E2F2, and E2F3. R654W mutant embryos exhibit cell cycle defects the same as those of Rb1 null embryos, reinforcing the importance of the interactions of pRb with E2F1, E2F2, and E2F3 for cell cycle control. However, R654W embryos survive at least 2 days longer than Rb1 null embryos, and increased life span is associated with improved erythrocyte and fetal liver macrophage differentiation. In contrast, R654W pRb does not rescue differentiation defects associated with pRb-deficient retinae. These data indicate that Rb1 makes important cell-type-specific contributions to cellular differentiation that are genetically separable from its general ability to stably bind E2F1, E2F2, and E2F3 and regulate the cell cycle.