Vortex sound generation due to a flow impedance discontinuity on a flat surface

The sound generated by the unsteady motion of a vortex filament moving over a flat boundary with a sharp flow impedance discontinuity is studied theoretically. Theoretical results show that the vortex filament undergoes significant accelerating or decelerating motions and radiates sound at the instant when it moves across the plane of impedance discontinuity. The accelerations and decelerations of the vortex filament are shown to be the major mechanisms of sound generation. The sound so produced has a large low-frequency content such that the change in the flow impedance affects only the sound generation process but not the subsequent sound propagation to the far field.     

An Ultra-Wideband Janus Metastructure with Graphene for Detector Based on Anapole Mode in the Terahertz Region

In this paper, an ultra-wideband Janus metastructure (MS) utilizing anapole mode for detector in the terahertz (THz) range by graphene is proposed. Specifically, when Fermi level (E_f) is set to 0.9 eV, the MS demonstrates ultra-broadband absorption exceeding 0.9 from 0.754 to 5 THz in the −z-direction with a relative bandwidth of 147.6 %, in which perfect absorption of over 98% develops from 3.24 to 5 THz. In the case of the +z-direction, the absorptivity maintains around 0.6 within the 0.745 ∼ 5 THz range. As E_f equals 0 eV, the difference in absorption between the −z-direction and +z-direction exceeds 0.9 from 4.49 to 4.76 THz. The study also explores the MS for refractive index sensing near 3.71 THz by a unique difference detection, measuring two refractive index ranges: 1.2 ∼ 2.6 and 4.5 ∼ 4.7, with corresponding sensitivities of 0.0450 and 0.0304, respectively. Owing to its highly symmetrical structure, the MS is insensitive to the polarization state of the electromagnetic (EM) waves, performing remarkable angular stability as the incident angle varies from 0 to 60 degrees in the −z-direction. These splendid properties make the design a good candidate for biomedical sensing, EM cloaking, and full-space EM wave control.     

Generation of 15-nJ bunched noise-like pulses with 93-nm bandwidth in an erbium-doped fiber ring laser

We report on the generation of high power superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber ring laser without using the stretched-pulse technique. The maximum 3-dB spectral bandwidth of the noise-like pulses is about 93 nm with an energy of about 15 nJ. We further show numerically that the superbroad spectrum of the pulses is caused by the transform-limited feature of the pulses together with the Raman self-frequency shift effect. PACS 42.65.Dr; 42.55.Wd; 42.60.Fc; 42.81.Dp     

Membrane fluidity altering and enzyme inactivating in sarcoma 180 cells post the exposure to sonoactivated hematoporphyrin in vitro

Sonodynamic therapy (SDT) is a novel tumor therapy method. We investigated membrane fluidity, activity of the enzymes and membrane morphology in vitro post hematoporphyrin-SDT treatment. Furthermore, the potential mechanisms behind the changes in membrane fluidity and enzymic activity were discussed. Tumor cells were exposed to ultrasound at 1.75 MHz for up to 3 min in the presence and absence of hematoporphyrin. Fluorescence polarization, contents of Malonaldehyde, and levels of free fatty acid were assessed. Activity of enzymes was checked by the plumbic nitrate detection method. For the morphologic study, a scanning electron microscope was used to observe the cellular surface. Ultrasonically induced cell damage increased in the presence of HPD (from 15% to 24%). Compared with ultrasound treatment alone, the fluidity decreased from 5.037 to 3.908, malonaldehyde content and free fatty acid level increased from 0.743 nmol/mL to 0.979 nmol/mL and from 237.180 μmol/L to 730.769 μmol/L, respectively, post ultrasound combined with HPD treatment. Inactivity of adenylate cyclase and guanylate cyclase and significant deformation of the cellular surface were also observed post SDT treatment. Our results suggested that alterations in membrane modality and lipid composition played important roles in SDT-mediated inhibition of tumor growth, even inducing tumor cell death, which might be attributed to a sono-chemical activation mechanism.     

The time-dependent cellular response mechanism upon exposure to zinc oxide nanoparticles

Zinc oxide nanoparticle is one of the nanomaterials people engaged most in their life and its health effect has been taken into concern. In this work, A549 cell line was used as cell model, and the cytotoxicity of zinc oxide nanoparticles was revealed to be concentration-dependent. Through the measurement of cellular proteome, much more differentially expressed proteins were observed after the cells being treated for 9 h than 24 h. Also, most of these proteins expressed in the pattern which showed a significant decrease after exposure to zinc oxide nanoparticles and then an increase at 24 h. Intracellular reactive oxygen species and glutathione determination indicated that high level of oxidative stress was presented in cell after treatment with zinc oxide nanoparticles for 9 h. It can be observed from western blot analysis that the expression of NF-κB p65, PNPase, and HSP90 rose significantly after 9 h of exposure. Thus, a deduction was reached that toxicity of nanoparticles consists both of particle toxicity and ion toxicity, and a long-time treatment may conceal the toxicity induced by particles. The conclusion we made highlighted the importance of exposure time in the study of nanoparticle toxicity and would provide a new perspective for studying toxicity mechanism of nanoparticles.     

XANES/EPR Evidence of the Oxidation of Nickel(II) Quinolinylpropioamide and Its Application in Csp3−H Functionalization

An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved.     

Improving the gas barrier,mechanical and thermal properties of poly(vinyl alcohol) with molybdenum disulfide nanosheets

New multifunctional materials with both high structural and gas barrier performances are important for a range of applications. Herein we present a one‐step mechanochemical process to prepare molybdenum disulfide (MoS₂) nanosheets with hydroxy functional groups that can simultaneously improve mechanical strength, thermal conductivity, and gas permittivity of a polymer composite. By homogeneously incorporating these functionalized MoS₂ nanosheets at low loading of less than 1 vol %, a poly(vinyl alcohol) (PVA) polymer exhibits elongation at break of 154%, toughness of 82 MJ/m³, and in‐plane thermal conductivity of 2.31 W/m K. Furthermore, this composite exhibits significant gas barrier performance, reducing the permeability of helium by 95%. Under fire condition, the MoS₂ nanosheets form thermally stable char, thus enhancing the material's resistance to fire. Hydrogen bonding has been identified as the main interaction mechanism between the nanofillers and the polymer matrix. The present results suggest that the PVA composite reinforced with 2D layered nanomaterial offers great potentials in packaging and fire retardant applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 406–414     

Enhanced targeted energy transfer for adaptive vibration suppression of pipes conveying fluid

Nonlinear Dynamics - In this paper, a nonlinear energy sink and a negative stiffness element are integrated for achieving enhanced, passive, and adaptive vibration suppression for a pipe conveying...