Search

Abstract Particle damping (PD) has been successfully utilized in numerous aerospace and industrial applications. However, compared with the well-studied single-unit multi-particle dampers, multi-unit multi-particle dampers (MUPDs) have seldom been investigated because of the complex interactions among different damping units. This research presents two damping effect prediction methods that are based on the cyclic iterations of the damping effect of a single-unit particle damper. The first is a numerical method that uses the discrete element method, and the other is a semi-empirical method that adopts damping ratio versus normalized acceleration curves for PD. In both methods, interactions among dampers at different locations are considered. The damping effects of six different MUPDs applied to a wheel structure were experimentally investigated. Four of them, which were named multi-stage MUPDs, consisted of groups of dampers mounted at various radial location (The dampers were located at positions of different acceleration amplitudes.). The damping prediction results of the two proposed iteration methods, together with those of a simplified method that regards the MUPD as a single-unit particle damper with same equivalent particle mass ratio, were compared with experiments. Significant improvements in prediction accuracy for the two iteration methods were observed. [ABSTRACT FROM AUTHOR]

Particle damping (PD) has been well known for its simplicity and high efficiency in attenuating structure vibration. Recent studies on PD have focused mainly on new types of dampers and applications. Meanwhile, excitation applied to the primary structure is still limited to either horizontal or vertical direction, perpendicular or parallel to gravity. In this study, the characteristics of PD under horizontal–vertical excitations (HVE) are investigated numerically and experimentally. The particle damper, which is attached to the top free end of an L-shaped cantilever beam, is simultaneously excited in the horizontal and vertical directions in the context of free decay. An equivalent model capable of motion in both the horizontal and vertical directions is generated. Given an initial displacement disturbance, this model starts vibrating freely in the vertical plane. A code based on the 3D discrete element method is programmed, and the high coincidence between the numerical and experimental results shows that this equivalent model is capable of high-fidelity simulation for PD under HVE. Parametric studies have been implemented to characterize the basic nonlinear damping capacity of particle dampers under this new operating condition. The effects of seven dimensionless independent parameters on the specific damping capacity (SDC) are investigated, including dimensionless acceleration amplitude, particle mass ratio, dimensionless horizontal and vertical impact clearances, coefficients of friction and restitution, and amplitude ratio of the horizontal excitation to the vertical excitation. The results show that the basic damping properties of PD under HVE are similar to those of PD under only vertical excitation. However, PD under HVE signifies its own characteristics because of the existence of horizontal excitation: (1) The impact clearances in both the horizontal and vertical directions have significant effects on the SDC because of the significant increase in oblique impacts. (2) The shape and dimensions of a damper cavity should be designed according to the acceleration amplitude. If the amplitude is relatively low (such as Γ <3 in this study), the optimum shape of the damper cavity tends to be flat. By contrast, if the amplitude is high (such as Γ close to 10 ) , the optimum shape tends to be elongated. The damping differences between PD under HVE and vertical excitation are also investigated. For PD under HVE, the kinetic energy is mainly dissipated by friction rather than inelastic collision for PD under vertical excitation. In addition, by use of different amplitude ratios of the horizontal excitation to the vertical excitation, it is found that the total ratio of energy dissipation for the particle dampers under HVE generally becomes higher, and the optimum Γ region for high SDC is also expanded. [ABSTRACT FROM AUTHOR]

It has been demonstrated that the incorporation of Ni into metal oxide-based gas sensors often enhances the sensing performance by increasing the catalytic and heterojunction effects. However, it remains unclear how these two effects work either individually or synergistically in gas sensing. Herein, a series of Ni-doped In 2 O 3 nanotubes (NIO NTs) with different doping concentrations were synthesized through a traditional electrospinning technique. The as-prepared NIO NTs were uniform, with length of micron scale, an average diameter of approximately 70 nm, and a tube wall thickness of approximately 10 nm. Following their incorporation into gas sensors, the NIO NTs often showed improved sensing properties (including excellent response and selectivity) for ethanol vapor compared to the pristine In 2 O 3 NTs. Specifically, at 100 ppm ethanol and 220 °C, the response of NIO-7 NTs (7 mol% Ni) was approximately four-fold higher than that of pristine In 2 O 3 NTs (49.74 vs. 13.39). The gas sensing test results indicated that the improved sensing performance was due to the formation of a heterojunction between In 2 O 3 and NiO, as well as to the catalysis effects of Ni3+ ions. Additionally, simulation results indicated that the improved gas selectivity could be due to the Ni doping-induced change in surface adsorption energies of the tested gases. [ABSTRACT FROM AUTHOR]

The distribution characteristics of Na+, K+ and free proline were investigated in succulent xerophytes—Haloxylon ammodendron and Zygophyllum xanthoxylum; xerophytes—Artemisia sphaerocephala and Caragana korshinskii; and mesophytes—Agriophyllum squarrosum and Corispermum mongolicum in the Alxa Desert of China. The results showed that mesophytes and xerophytes were salt excluding species, and the concentrations of Na+ in these species were 1.5% to 3.8% of those in succulent xerophytes. Concentrations of K+ in Agriophyllum squarrosum and Corispermum mongolicum were 1.3–2.7 times those in Artemisia sphaerocephala and Caragana korshinskii. Concentrations of K+ in the stems of Agriophyllum squarrosum and Corispermum mongolicum were 1.8 and 2.2 times those in their roots, respectively. For mesophytes, accumulating large quantities of K+ in their stems may facilitate water movement along a soil–plant gradient. The xerophytes accumulated large quantities of K+ and free proline. Their proline concentrations in the whole plant were 6.0–16.0 times higher than those of mesophytes, and were 1.8–25.0 times higher than those of succulent xerophytes. In Artemisia sphaerocephala, the concentrations of proline increased by 3.1- and 10.5-fold from roots to stems, and from stems to leaves, respectively. A similar trend was observed in Caragana korshinskii. Therefore, accumulating K+ and free proline may play a role in drought adaptation in xerophytes. Succulent xerophytes Haloxylon ammodendron and Zygophyllum xanthoxylum were identified as salt diluting species that absorbed much Na+ by roots, and the Na+ was transported to the leaves and photosynthesizing branches. The succulent xerophytes accumulated larger quantities of Na+ than K+ for osmotic adjustment even at low soil salinities, resulting in the lowest values of selective absorption and selective transport capacities of the root systems. Our data suggest that Na+ accumulation rather than exclusion may be one of the most effective strategies for adaptation of succulent xerophytes to arid environments. [Copyright &y& Elsevier]

[Display omitted] Hydrogen can be regarded as an ideal type of secondary energy considering its potential for achieving renewable and sustainable development due to water being its sole combustion product and its possible production by solar energy-based water electrolysis. Monitoring the presence and concentration of hydrogen during production, transportation, and application requires a hydrogen gas sensor with high response, high selectivity, and fast response and recovery times. In an attempt to meet these requirements, NiO and PdO are used in the co-doping of In 2 O 3 nanotubes by subsequent electrospinning and impregnation under UV irradiation. The fabricated hydrogen gas sensor demonstrates an ultrahigh response of 487.52, a fast response time of 1 s and high selectivity at an operating temperature of 160 °C, which characteristics are superior to reported monometal-doped hydrogen sensors. The remarkable gas sensing performance could be attributed to the synergistic effect of the resistance modulation, the chemical sensitization of PdO, and the catalytic effect of NiO. This study demonstrates that co-doping of PdO and NiO on In 2 O 3 nanotubes is an effective way to improve hydrogen sensing characteristics more effectively than doping with PdO or NiO alone, and provides a potential application for the fast and accurate detection of hydrogen. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) is the result of the interaction between the airfoil vibration and vortex shedding, and it frequently achieves the peak vibration amplitude in the lock-in region. Therefore, distinguishing the effect of the two disturbances in the lock-in region is important for understanding VIV. In this study, the NACA 0012 airfoil was investigated at high angles of attack; thus, the vortex could form and shed regularly downstream. The VIV was analyzed numerically and verified using the test data in references. The process of the vortex shedding was observed to be similar under different incoming flows, vibration amplitudes, and frequency ratios. In the V-shape lock-in region, the phase between the airfoil vibration and vortex shedding changes with the frequency ratio. When the frequency ratio is 1, the phase and strength of the vortex shedding remain almost constant with the vibration amplitude. Based on the features of the vortex shedding, a method of separating the disturbances caused by the airfoil vibration and the vortex shedding is proposed to investigate the mechanism of VIV from the perspective of energy balance. As the phase between the airfoil vibration and vortex shedding changes in the lock-in region, the vortex shedding provides negative aerodynamic damping (AD) in some phases and positive AD in other phases. The stability of the airfoil depends on the two disturbances mentioned above. VIV occurs only when the disturbance of the vortex shedding performs positive work (negative AD) and the disturbance of the airfoil vibration performs negative work (positive AD). When the vibration amplitude is small, VIV is dominated by the disturbance of the vortex shedding. When the vibration amplitude is high, the VIV is dominated by the disturbance of the airfoil vibration. As the vibration amplitude increases, the two form a balance, and the airfoil exhibits limit cycle oscillations. Based on the assumption of linear superposition, the theoretical limit vibration amplitudes of the airfoil under the two conditions in this study were 3° and 13.4°, respectively. [ABSTRACT FROM AUTHOR]

Cryopreservation and transplantation of the ovarian tissue is an alternative method by which malignant tumor survivors can recover fertility. Previously, it was reported that follicle stimulating hormone (FSH) promoted the survival and functioning of the ovarian tissue after in vitro cultivation. In this study, the expression of the luteinizing hormone receptor (LHR) was observed on the granule cell membrane after luteinizing hormone (LH) (0.3 IU/mL) was supplied as an exogenous hormone into the cultivation medium during ovarian vitrification in the postnatal period (PND) (1, 7, 14, 21, 28, 42, and 56 days PND). The expression of vascular endothelial growth factor (VEGF) and Connexins (Cx), and the recovery of ovarian functions were then assessed in mice models. The results showed that LH increased the production of normal follicles, and upregulated the expression of VEGF, Cx37, and Cx43 in vitrified ovaries. LH administration also shortened the recovery time of the estrus cycle in mice models. Additionally, no difference was observed in the rate of pregnancy and size of the first litter between the experimental and control groups. In conclusion, LH could promote the survival and functioning of the ovaries by upregulating the expression of VEGF, Cx43, and Cx37 during ovarian cryopreservation and transplantation. • LH administration during ovarian cryopreservation and transplantation. • LH promotes the survival and functioning of transplanted ovaries in mice. • LH upregulates vascular endothelial growth factor (VEGF) and Connexins 43 and 37. • Comparing the effects of LH versus follicle stimulating hormone (FSH). • VEGF, and Connexins 43 and 37 upregulation was higher by LH than by FSH. [ABSTRACT FROM AUTHOR]

Fatty acid desaturases (FADs) are of great importance and play critical roles in regulating plant fatty acid (FA) compositions. But to date, no reports about characterization of the FAD genes have been reported in the model dicotyledonous grass species Medicago truncatula. In this study, using database searches, 20 full-length FAD genes were identified in M. truncatula . These FAD genes were unevenly distributed on six chromosomes except the chromosome 6 and 8. Phylogenetic analysis showed the FAD genes in M. truncatula were clustered into six subfamilies and had similar exon number and intron phase in the same subfamily. Moreover, expression analysis based on qRT-PCR indicated these FAD genes were extensively involved in cold and heat responses. This study would provide an important foundation for future cloning and functional studies of FAD genes in M. truncatula and other related legume species. [ABSTRACT FROM AUTHOR]

Drought and high salinity are two major abiotic factors that restrict alfalfa productivity. A dehydrin protein, CsLEA, from the desert grass Cleistogenes songorica was transformed into alfalfa ( Medicago sativa L.) via Agrobacterium -mediated transformation using the bar gene as a selectable marker, and the drought and salt stress tolerances of the transgenic plants were assessed. Thirty-nine of 119 transformants were positive, as screened by Basta, and further molecularly authenticated using PCR and RT-PCR. Phenotype observations revealed that the transgenic plants grew better than the wild-type (WT) plants after 15d of drought stress and 10d of salt stress: the leaves of WT alfalfa turned yellow, whereas the transgenic alfalfa leaves only wilted; after rewatering, the transgenic plants returned to a normal state, though the WT plants could not be restored. Evaluation of physiologic and biochemical indices during drought and salt stresses showed a relatively lower Na + content in the leaves of the transgenic plants, which would reduce toxic ion effects. In addition, the transgenic plants were able to maintain a higher relative water content (RWC), higher shoot biomass, fewer photosystem changes, decreased membrane injury, and a lower level of osmotic stress injury. These results demonstrate that overexpression of the CsLEA gene can enhance the drought and salt tolerance of transgenic alfalfa; in addition, carrying the bar gene in the genome may increase herbicide resistance. [ABSTRACT FROM AUTHOR]