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We develop a model of the skin-friction coefficient based on scalar images in the compressible, spatially evolving boundary-layer transition. The images are extracted from a passive scalar field by a sliding window filter on the streamwise and wall-normal plane. The multi-scale and multi-directional geometric analysis is applied to characterize the averaged inclination angle of spatially evolving filtered component fields at different scales ranging from a boundary-layer thickness to several viscous length scales. In general, the averaged inclination angles increase along the streamwise direction, and the variation of the angles for large-scale structures is smaller than that for small-scale structures. Inspired by the coincidence of the increasing averaged inclination angle and the rise of the skin-friction coefficient, we propose a simple image-based model of the skin-friction coefficient. The model blends empirical formulae of the skin-friction coefficient in laminar and fully developed turbulent regions using the normalized averaged inclination angle of scalar structures at intermediate and small scales. The model prediction calculated from scalar images is validated by the results from the direct numerical simulation at two Mach numbers, 2.25 and 6, and the relative error can be less than 15 %.
Under conventional solidification conditions, immiscible alloy melt would undergo large-scale composition segregation after liquid–liquid phase separation, resulting in the loss of properties and application value. In the present study, the ternary immiscible Al70Bi10Sn20 alloy was chosen to study the effect of cooling rate on its resultant microstructure by casting the melt under different cooling conditions. The results indicated that the Al–Bi–Sn alloy with a slow cooling rate exhibits a strong spatial phase separation trend during solidification. However, as the cooling rate increases, the decreasing volume fraction of the segregated Bi–Sn-rich regions indicates the efficient suppression of spatial phase separation. The relatively dispersed distribution of Bi–Sn phase in the Al-rich matrix can be obtained by quenching the melt into water. The influence mechanism of cooling rate on the microstructure of the alloy is also discussed. The present study is beneficial to further tailoring the microstructure of immiscible alloys.
The present study was undertaken to investigate the antiparasitic activity of extracellular products of Streptomyces albus. Bioactivity-guided isolation of chloroform extracts affording a compound showing potent activity. The structure of the compound was elucidated as salinomycin (SAL) by EI-MS, 1H NMR and 13C NMR. In vitro test showed that SAL has potent anti-parasitic efficacy against theronts of Ichthyophthirius multifiliis with 10 min, 1, 2, 3 and 4 h (effective concentration) EC50 (95% confidence intervals) of 2.12 (2.22–2.02), 1.93 (1.98–1.88), 1.42 (1.47–1.37), 1.35 (1.41–1.31) and 1.11 (1.21–1.01) mg L−1. In vitro antiparasitic assays revealed that SAL could be 100% effective against I. multifiliis encysted tomonts at a concentration of 8.0 mg L−1. In vivo test demonstrated that the number of I. multifiliis trophonts on Erythroculter ilishaeformis treated with SAL was markedly lower than that of control group at 10 days after exposed to theronts (P < 0.05). In the control group, 80% mortality was observed owing to heavy I. multifiliis infection at 10 days. On the other hand, only 30.0% mortality was recorded in the group treated with 8.0 mg L−1 SAL. The median lethal dose (LD50) of SAL for E. ilishaeformis was 32.9 mg L−1.
Given the global water challenges, solar-driven steam generation has become a renewed topic recently as an energy-efficient way for clean water production. Here, a hybrid plasmonic structure consisting of a top layer of TiN nanoparticles (NPs) and a bottom layer of mesoporous anodized alumina membrane (AAM) was rationally designed and fabricated. The top TiN NPs with broadband light absorption acted as a plasmonic heating layer, which converted the absorbed light to heat efficiently for interfacial water heating. The AAM acted as the mechanical support layer, guaranteeing the heat isolation and continuous water replenishment. With optimized thickness of the TiN top layer, a solar steam generation efficiency of 87.7% was achieved in this study. This efficiency is comparable or even higher than prior studies. The current work proves the capability of the TiN NPs as an alternative photothermal material.
The ordering of polarization field of inhomogeneous ferroelectric systems were investigated. We found that these systems exhibit rather complex polarization ordering behaviors with the coexistence of polar and toroidal ordering, and particularly, a novel and tunable polar-toroidal phase transformation under external mechanical, electrical or thermal fields. Accompanying with this polar-toroidal phase transformation, there is a large change of polarization and strain. As a result, large eletromechanical and thermomechanical performance can be achieved in these systems. The polar/toroidal phase boundaries can be regarded a new kind of morphotropic phase boundary (MPB). The polar-toroidal phase transformation in nanoscale ferroelectric systems should provide us a novel strategy to develop energy conversion nanodevices.
The TiO2 hollow spheres (TiO2HS) were successfully prepared by a hydrothermal method and added to Vulcan XC-72 carbon black as the support materials for Pd nanoparticles. A facile approach to promote ethylene glycol (EG) electrooxidation in alkaline medium was carried out by the PdBi/TiO2HS-C catalyst. The results show that Pd and Bi nanoparticles are uniformly dispersed on the surface of carbon-doped TiO2 hollow spheres, the appropriate amount of Bi modification into Pd/TiO2HS-C catalyst can enhance remarkably the electrocatalytic activity for EG oxidation, in which the PdBi/TiO2HS-C (Pd:Bi = 1:0.1) catalyst exhibits excellent stability. The high electrochemical performance is attributed to the unique structure and high surface area of the TiO2HS, metal nanoparticles uniform distribution, the electronic effect between Pd and Bi as well as the bifunctional effect between metal nanoparticles and the support TiO2HS-C. The results obtained are significant for the development of new Pd-based TiO2HS-C electrocatalysts for alcohol fuel cells.
We investigate heterogeneous consumer preferences and willingness to pay (WTP) for various sweet cherry attributes using choice experiments. A mixed logit model and a latent-class logit model are used to estimate consumer WTP for the attributes and identify groups of consumers based on those preferences. We find that consumers of sweet cherries will pay the greatest premium for sweetness and the smallest premium for fruit size. Three groups of consumers are identified—flavor sensitive, price sensitive, and storage sensitive. The results are useful for suppliers of sweet cherries when adopting targeted marketing strategies.
Two transmission curved crystal spectrometers are designed to measure the hard x-ray emission in the laser fusion experiment of Compton radiography of implosion target on ShenGuang-III laser facility in China. Cylindrically curved
-quartz (10–11) crystals with curvature radii of 150 and 300 mm are used to cover spectral ranges of 10–56 and 17–100 keV, respectively. The distance between the crystal and the x-ray source can be changed over a broad distance from 200 to 1500 mm. The optical design, including the integral reflectivity of the curved crystal, the sensitivity, and the spectral resolution of the spectrometers, is discussed. We also provide mechanic design details and experimental results using a Mo anode x-ray source. High-quality spectra were obtained. We confirmed that the spectral resolution can be improved by increasing the working distance, which is the distance between the recording medium and the Rowland circle.
A dual-axis rotational Inertial Navigation System (INS) has received wide attention in recent years because of high performance and low cost. However, some errors of inertial sensors such as stochastic errors are not averaged out automatically during navigation. Therefore a Twice Position-fix Reset (TPR) method is provided to enhance accuracy of a dual-axis rotational INS by compensating stochastic errors. According to characteristics of an azimuth error introduced by stochastic errors of an inertial sensor in the dual-axis rotational INS, both an azimuth error and a radial-position error are much better corrected by the TPR method based on an optimised error propagation equation. As a result, accuracy of the dual-axis rotational INS is prominently enhanced by the TPR method, as is verified by simulations and field tests.
It is demonstrated by simulations and analysis that a wakefield driven by an ultrashort intense laser pulse in underdense plasma can emit tunable electromagnetic radiation along the laser propagation direction. The profile of such a kind of radiation is closely associated with the structure of the laser wakefield. In general, electromagnetic radiation in the terahertz range with its frequency a few times the electron plasma frequency can be generated in the moderate intensity regime. In the highly nonlinear case, a chain of radiation pulses is formed corresponding to the nonlinear structure of the wake. Study shows that the radiation is associated with the self-modulation process of the laser pulse in the wakefield and resulting transverse electron momenta from modulated asymmetric laser fields.
Celestial navigation is an important type of autonomous navigation technology which could be used as an alternative to Global Navigation Satellite Systems (GNSS) when a vessel is at sea. After several centuries of development, a variety of astronomical vessel position (AVP) determination methods have been invented, but the basic concepts of these methods are all based on angular observations with a device such as a sextant, which has disadvantages including low accuracy, manual operation, and a limited period of observation. This paper proposes a new method that utilises a fisheye camera to image the celestial bodies and horizon simultaneously. Then, we calculate the obliquity of the fisheye camera's principal optical axis according to the image coordinates of the horizon. Next, we calculate the altitude of the celestial bodies according to the image coordinates of the celestial bodies and the obliquity. Finally, the AVP is determined by the altitudes according to the robust estimation method. Experimental results indicate that this method not only could realize automation and miniaturization of the AVP determination system, but could also greatly improve the efficiency of celestial navigation.
An energy measurement system in a Large-aperture high power laser experiment platform
is introduced. The entire measurement system includes five calorimeters, which carry
out the energy measurement of the fundamental frequency before the frequency
conversion unit, remaining fundamental frequency, remain second-harmonics, third
harmonics, as well as the energy balance measurement after the frequency conversion
unit. Combinational indirect calibration and direct calibration are employed to
calibrate the sampling coefficients of the calorimeters. The analysis of the data
showed that, regarding the energy balance coefficients, combinational calibration
approach gives a higher precision, and leads to an energy balance with 1%; and
regarding the energy sampling coefficients for the various wavelengths after the
frequency conversion, the results from direct and combinational calibration are
consistent. The uncertainties for all energy sampling coefficients are within 3%,
which guarantees the reliability of the energy measurement for the laser
A facile and cost-effective fabrication approach of active strain sensor based on individual ZnO micro/nanowire was demonstrated. By connecting a ZnO micro/nanowire along polar growth direction with two Ag electrodes on flexible polystyrene (PS) substrate, the fabricated strain sensor was obtained as a typical M-S-M structure. The I-V characteristic of the device was highly sensitive to the strain caused by the obvious change of Schottky barrier height (SBH). Furthermore, both of the symmetric and asymmetric changes of the SBH at the source and drain were observed during device testing process. The respective contribution of piezoresistance effect and the piezoelectric effect to the change of SBHs were also systematically investigated.
The use of MgO nanoparticle (NP) loaded poly(methylsilsesquioxane) (PMSQ) as a low temperature processable composite dielectric has been investigated. The composite dielectrics have been synthesized using facile ultrasonic mixing of trimethoxymethylsilane (MTS), butanol (n-BuOH) and deionized water at 60 °C, with MgO loadings from 0.096 up to 0.39 wt% of the initial solution. Thin films of the composite materials produced have shown an increase in dielectric constant from 2.8 for raw PMSQ up to 3.4 for the 0.39 wt% loaded PMSQ + MgO NP composites at frequencies up to 2 MHz, comparable to 3.9 for SiO2. The composite dielectric materials have shown suitability as a dielectric material for a P3HT OFET, with the performance comparable to a standard SiO2 dielectric control sample.
A one-dimensional fluid model is built to study the effect of radio frequency (RF) on the characteristics of RF nitrogen discharge with induced argon plasma at high pressure. The model is solved by a finite difference method, and the numerical results are obtained. The numerical results show that by modulating driven frequency, the discharge can obtain higher plasma density. Moreover, the discharge is operated in a stable α mode in a range of 100 MHz of driven frequency.
The double tearing mode (DTM) instability with two qs = 1 rational surfaces is investigated by taking into account the collisionless effects, including electron inertia and electron viscosity in a cylindrical geometry. The calculations show that for q-profile with a small distance between two rational surfaces, Δrs, there exists a broad linear spectrum of collisionless DTMs. The collisionless effects not only can significantly increase the linear growth rate of DTMs but can also enlarge the width of spectrum of unstable modes. For the q-profile with fixed Δrs and fixed magnetic shears at two rational surfaces, the high-order harmonics with smaller wavelength, such as the m/n = 2/2, 3/3 and 4/4 modes, can be easily excited to have larger growth rates than the m/n = 1/1 mode by ‘lifting’ the safety factor value between two rational surfaces. The characteristics of eigenmode structures of the most unstable and secondly unstable DTMs with various mode numbers are analyzed in detail and the corresponding collisionless scalings are numerically obtained and verified theoretically based on the previous relevant analytical theories. In addition, the synergetic effects of plasma resistivity, electron inertia and electron viscosity on the linear growth rates of DTMs are analyzed.
We report a technique that can, in principle, selectively convert SiC into graphene at any location and in any size or shape, limited only by the ability of the available lithographic techniques. This technique relies on our discovery that, at ambient condition, a laser beam can convert SiC into graphene layers at the illuminated site, and the conversion can be realized in two ways. One can pattern the SiC film, which is already grown on a Si wafer, with desirable features and then illuminate the SiC film with the laser, or simply “write” the graphene features directly onto the unpatterned SiC film with the laser. Alternatively, one can pre-pattern the Si substrate to achieve selective growth of SiC, then perform the laser conversion. We have demonstrated the feasibility of both approaches. Fullerene (C60) was used to grow a thin SiC film on a Si (111) substrate using molecular beam epitaxy (MBE) at 700-800 oC. The results are verified by various structural, chemical and optical characterization techniques. This work yields the possibility of fabricating graphene based (electronic) nanostructures or superlattices, photonic crystals, and integrated electronic and optoelectronic devices on a large Si wafer.
Whale oocytes recovered from follicles can be matured in vitro. Whale sperm and mature oocytes can be used for in vitro fertilization (IVF), and IVF embryos have the ability to develop to morula stage. Whale sperm injected into bovine or mouse oocytes can activate the oocytes and form pronucleus. Interspecies somatic cell nuclear transfer embryos have been reconstructed with whale somatic cell nucleus and enucleated bovine or porcine oocytes, and interspecies cloned embryos can develop in vitro. This paper reviews recent progress in maturation, fertilization and development of whale oocytes.
A new series of side chain liquid crystalline-amorphous diblock copolymers has been successfully synthesized using chiral mesogens. Anionic polymerization techniques have been used to make these monodisperse diblock materials. Preliminary studies suggest that these microphase segregated diblock copolymers exhibit a smectic C* phase. This mesophase exists between and above the glass transition temperatures of the two polymer blocks. Synthesis and characterization of these novel materials are discussed.