Improving the rotordynamic stability of short labyrinth seals using positive preswirl

Introducing a negative preswirl at the upstream of annular gas seals has been considered as an effective way to improve the system stability. This paper demonstrates a stability enhancement approach for a short labyrinth seal using positive preswirls. The static and dynamic characteristics of the labyrinth seal with various blade numbers (5, 10, 15), inlet preswirl ratios (–0.3, –0.15, 0, 0.15, 0.3) were studied. Results show that the inlet preswirl ratio has a dramatic effect on the circumferential location of the high-pressure spot for each seal cavity, particularly for the first cavity. The inlet preswirl ratio has opposite effects on the system stability due to the difference of high-pressure spot locations between the first cavity and the others. An increasing positive inlet preswirl could improve the system stability for the labyrinth seal with fewer blades (e.g. 5 blades). Its characteristics is mainly dominated by the first seal cavity. For the labyrinth seal with 10 blades, the system characteristics shows slight dependency on the inlet preswirl ratio. For the labyrinth seal with more blades (e.g. 15 blades), the negative inlet preswirl still increases the system stability, which agrees with the conventional conclusion. The paper provides a deeper understanding on the stability improvement of the labyrinth seal

Three-Dimensional Simulation of the Shrinkage Behavior of Injection-Molded Poly Lactic Acid (PLA): Effects of Temperature, Shear Rate and Part Thickness

The effects of injection temperature, shear and part thickness on the linear shrinkage of injection-molded poly (lactic acid) (PLA) were intensively analyzed using the Autodesk Moldflow software. The obtained results showed that both melt temperature and shear rate had obvious effects on the linear shrinkage of PLA, i.e., the linear shrinkage of PLA increases significantly with the increase of melt temperature and shear rate. In addition, the shrinkage of high-crystallinity PLA was remarkably larger than that of low-crystallinity PLA, and thin-walled parts was larger than thick-walled ones in shrinkage

Orbit Decomposition Method for Rotordynamic Coefficients Identification of Annular Seals

The elliptical orbit whirl model is widely used to identify the frequency-dependent rotordynamic coefficients of annular seals. The existing solution technique of an elliptical orbit whirl model is the transient computational fluid dynamics (CFD) method. Its computational time is very long. For rapid computation, this paper proposes the orbit decomposition method. The elliptical whirl orbit is decomposed into the forward and backward circular whirl orbits. Under small perturbation circumstances, the fluid-induced forces of the elliptical orbit model can be obtained by the linear superposition of the fluid-induced forces arising from the two decomposed circular orbit models. Due to that the fluid-induced forces of circular orbit, the model can be calculated with the steady CFD method, and the transient computations can be replaced with steady ones when calculating the elliptical orbit whirl model. The computational time is significantly reduced. To validate the present method, its rotordynamic results are compared with those of the transient CFD method and experimental data. Comparisons show that the present method can accurately calculate the rotordynamic coefficients. Elliptical orbit parameter analysis reveals that the present method is valid when the whirl amplitude is less than 20% of seal clearance. The effect of ellipticity on rotordynamic coefficients can be ignored

HPO-RRT*: a sampling-based algorithm for UAV real-time path planning in a dynamic environment

Abstract The real-time path planning of unmanned aerial vehicles (UAVs) in dynamic environments with moving threats is a difficult problem. To solve this problem, this paper proposes a time-based rapidly exploring random tree (time-based RRT*) algorithm, called the hierarchical rapidly exploring random tree algorithm based on potential function lazy planning and low-cost optimization (HPO-RRT*). The HPO-RRT* algorithm can guarantee path homotopy optimality and high planning efficiency. This algorithm uses a hierarchical architecture comprising a UAV perception system, path planner, and path optimizer. After the UAV perception system predicts moving threats and updates world information, the path planner obtains the heuristic path. First, the path planner uses the bias sampling method based on the artificial potential field function proposed in this paper to guide sampling to improve the efficiency and quality of sampling. Then, the tree is efficiently extended by the improved time-based lazy collision checking RRT* algorithm to obtain the heuristic path. Finally, a low-cost path optimizer quickly optimizes the heuristic path directly to optimize the path while avoiding additional calculations. Simulation results show that the proposed algorithm outperforms the three existing advanced algorithms in terms of addressing the real-time path-planning problem of UAVs in a dynamic environment

Preparation of Polyethylene and Ethylene/Methacrylic Acid Copolymer Blend Films with Tunable Surface Properties through Manipulating Processing Parameters during Film Blowing

Polymer films based on polyethylene (PE) and ionomer ethylene/methacrylic acid (EMAA) copolymer blend were prepared by film blowing, whose surface properties were tuned by varying processing parameters, i.e., take up ratio (TUR). Blends of PE/EMAA copolymer were firstly prepared by the melt-mixing method, before being further blown to films. The wettability of the film was investigated by measuring the contact angle/water-film encounter time, and optical properties, i.e., the haze and transmittance. The wettability was found to be enhanced with the increase of TUR. So too was the haze, while the transmittance was found to be almost independent of TUR. The XPS and AFM results directly show the increasing polar functional groups (–COO−) on the surface and roughness with increasing TUR. Further analysis of the 2D SAXS and WAXS unveiled the origin of the invariant transmittance, which resulted from the minor change of the crystallinity and the monotonic increase of the haze, with TUR resulting from the evolution of crystal orientation. In addition to other post-modification methods, the current study provides an alternative route to prepare large-scale PE films as the template for the advanced potential applications, i.e., covering in the layer of roof, the privacy of protective windows, and multitudes of packaging

MicroRNA-191 blocking the translocation of GLUT4 is involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway

Environmental exposure to arsenic can cause a variety of health problems. Epidemiological and experimental studies have established a diabetogenic role for arsenic, but the mechanisms responsible for arsenic-induced impairment of insulin action are unclear. MicroRNAs (miRNAs) are involved in various metabolic disorders, particularly in the development of insulin resistance. The present study investigated whether arsenite, an active form of arsenic, induces hepatic insulin resistance and the mechanisms underlying it. After male C57BL/6J mice were exposed to arsenite (0 or 20 ppm) in drinking water for 12 months, intraperitoneal glucose tolerance tests (IPGTTs) and insulin tolerance tests (ITTs) revealed an arsenite-induced glucose metabolism disorder. Hepatic glycogen levels were lower in arsenite-exposed mice. Further, for livers of mice exposed to arsenite, miR-191 levels were higher, and protein levels of insulin receptor substrate 1 (IRS1), p-IRS1, and phospho-protein kinase B (p-AKT) were lower. Further, glucose transporter 4 (GLUT4) had lower levels on the plasma membrane. For insulin-treated L-02 cells, arsenite decreased glucose consumption and glycogen levels, increased miR-191 levels, and inhibited the IRS1/AKT pathway and the translocation of GLUT4 from the cytoplasm to the plasma membrane. For insulin-treated L-02 cells, the decreases of glucose consumption, glycogen levels, GLUT4 on the plasma membrane, and p-AKT levels induced by arsenite were reversed by SC79 (agonist of AKT) and an miR-191 inhibitor; these effects caused by miR-191 inhibitor were restored by IRS1 siRNA. In insulin-treated L-02 cells, miR-191, via IRS1, was involved in the arsenite-induced decreases of glucose consumption and glycogen levels and in inhibition of the translocation of GLUT4. Thus, miR-191 blocking the translocation of GLUT4 was involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway. Our study reveals a mechanism for arsenite-induced hepatic insulin resistance, which provides clues for discovering biomarkers for the development of type 2 diabetes and for prevention and treatment of arsenic poisoning

Melatonin Prevents NaAsO₂-Induced Developmental Cardiotoxicity in Zebrafish through Regulating Oxidative Stress and Apoptosis

Melatonin is an indoleamine hormone secreted by the pineal gland. It has antioxidation and anti-apoptosis effects and a clear protective effect against cardiovascular diseases. Our previous studies demonstrated that embryonic exposure to sodium arsenite (NaAsO2) can lead to an abnormal cardiac development. The aim of this study was to determine whether melatonin could protect against NaAsO2-induced generation of reactive oxygen species (ROS), oxidative stress, apoptosis, and abnormal cardiac development in a zebrafish (Danio rerio) model. We found that melatonin decreased NaAsO2-induced zebrafish embryonic heart malformations and abnormal heart rates at a melatonin concentration as low as 10−9 mol/L. The NaAsO2-induced oxidative stress was counteracted by melatonin supplementation. Melatonin blunted the NaAsO2-induced overproduction of ROS, the upregulation of oxidative stress-related genes (sod2, cat, gpx, nrf2, ho-1), and the production of antioxidant enzymes (Total SOD, SOD1, SOD2, CAT). Melatonin attenuated the NaAsO2-induced oxidative damage, DNA damage, and apoptosis, based on malonaldehyde and 8-OHdG levels and apoptosis-related gene expression (caspase-3, bax, bcl-2), respectively. Melatonin also maintained the control levels of heart development-related genes (nkx2.5, sox9b) affected by NaAsO2. In conclusion, melatonin protected against NaAsO2-induced heart malformations by inhibiting the oxidative stress and apoptosis in zebrafish

Compositional Engineering of Cu-Doped SnO Film for Complementary Metal Oxide Semiconductor Technology

Metal oxide semiconductor (MOS)-based complementary thin-film transistor (TFT) circuits have broad application prospects in large-scale flexible electronics. To simplify circuit design and increase integration density, basic complementary circuits require both p- and n-channel transistors based on an individual semiconductor. However, until now, no MOSs that can simultaneously show p- and n-type conduction behavior have been reported. Herein, we demonstrate for the first time that Cu-doped SnO (Cu:SnO) with HfO2 capping can be employed for high-performance p- and n-channel TFTs. The interstitial Cu+ can induce an n-doping effect while restraining electron–electron scatterings by removing conduction band minimum degeneracy. As a result, the Cu3 atom %:SnO TFTs exhibit a record high electron mobility of 43.8 cm2 V–1 s–1. Meanwhile, the p-channel devices show an ultrahigh hole mobility of 2.4 cm2 V–1 s–1. Flexible complementary logics are then established, including an inverter, NAND gates, and NOR gates. Impressively, the inverter exhibits an ultrahigh gain of 302.4 and excellent operational stability and bending reliability

Deformation Drives Alignment of Nanofibers in Framework for Inducing Anisotropic Cellulose Hydrogels with High Toughness

Deformation-driven alignment of macromolecules or nanofibers leading to anisotropy is a challenge in functional soft materials. Here, tough cellulose hydrogels that exhibited deformation-induced anisotropy are fabricated by reacting cellulose with a small amount of epichlorohydrin (EPI) in LiOH/urea solution and subsequent treating with dilute acid. The loosely cross-linked network that was obtained via chemical cross-linking of cellulose with EPI as a large framework maintained the elasticity of hydrogels, whereas nanofibers produced by the acid treatment formed physical cross-linked networks through hydrogen bonds which could efficiently dissipated mechanical energy. Meanwhile, the nanofibers could further aggregate to form submicrobundles and participate in the formation of frameworks during the acid treatment. Under deformation, the nanofibers and submicrobundles in the physical networks synchronize easily to align with the large framework, generating the rapidly responsive birefringence behaviors with highly stable colors. Thus, the cellulose hydrogels possessing sensitively mechano-responsive behavior could be utilized as a dynamic light switch and a soft sensor to accurately detect small external force, respectively. This work opens a novel pathway to construct tough and mechanoresponsive hydrogels via a green conversion of natural polysaccharide