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Due to less light scattering and a better signal-to-noise ratio in deep imaging, two-photon fluorescence microscopy (TPFM) has been widely used in biomedical photonics since its advent. However, optical aberrations degrade the performance of TPFM in terms of the signal intensity and the imaging depth and therefore restrict its application. Here, we introduce adaptive optics based on the genetic algorithm to detect the distorted wavefront of the excitation laser beam and then perform aberration correction to optimize the performance of TPFM. By using a spatial light modulator as the wavefront controller, the correction phase is obtained through a signal feedback loop and a process of natural selection. The experimental results show that the signal intensity and imaging depth of TPFM are improved after aberration correction. Finally, the method was applied to two-photon fluorescence lifetime imaging, which helps to improve the signal-to-noise ratio and the accuracy of lifetime analysis. Furthermore, the method can also be implemented in other experiments, such as three-photon microscopy, light-sheet microscopy, and super-resolution microscopy.
There is no consensus on the existence of welfare gains from international monetary policy cooperation. This study adds to the debate by providing a new open macroeconomics model with incomplete exchange rate pass-through. We find that, from a global perspective, the welfare gains from international monetary policy cooperation arise with incomplete exchange rate pass-through. Furthermore, the country’s incentive for cooperation increases with its degree of exchange rate pass-through. Cooperation benefits small countries with high pass-through; however, it is disadvantageous to large countries with low pass-through. In addition, when there is in the absence of cooperation, fixed exchange rate regime is preferred for a country suffering from monetary uncertainty, particularly for small economies with high exchange rate pass-through.
We report the first experiments on divergent shock-driven Richtmyer–Meshkov instability (RMI) at well-controlled single-mode interfaces. These experiments are performed in a novel divergent shock tube designed by shock dynamics theory. Generally, the perturbation growth can be divided into three successive stages: linear growth, quick reduction in growth rate and instability freeze-out. It is observed that the growth rate at each stage is far lower than its counterpart in planar or convergent geometry due to geometric divergence. We also found that nonlinearity is much weaker than that in planar or convergent RMI, and has a negligible influence on the overall amplitude growth even at late stages when it has become strong. This weak nonlinear effect is because the growth of the third harmonic counteracts its feedback to the fundamental mode. As a consequence, the linear theory of Bell (report no. LA-1321) accounting for geometric divergence and Rayleigh–Taylor (RT) stabilization caused by flow deceleration can reasonably predict the present results from early to late stages. The instability freeze-out at late times is ascribed to the negative growth induced by geometric divergence and RT stabilization, and is also well reproduced by the linear theory.
The authors design six alumina hybrid structures consisting of stretching-dominated plates and different space-filling lattices comprised of hollow tubes and perform finite element simulations to study mechanical and failure behaviors of such hybrid structures. The authors investigate the effects of three geometrical parameters on the stiffness and failure of these hybrid structures and further compare their advantages and disadvantages. The authors find that the failure modes of these hybrid structures can be tuned by altering cell unit type and geometrical parameters. Among these hybrid structures, the ones with effective support from the lattice unit cells in the stretching direction exhibit better specific stiffness and strength. By varying the lattice and plate thickness, the authors find that the relations between stiffness/failure strength and density follow a power law. When intrinsic material failure occurs, the power law exponent is 1; when buckling failure arises, the power law exponent is 3. However, by varying tube thickness, their relations follow unusual power relations with the exponent changing from nearly 0 to nearly infinity. In addition, the hybrid structures also exhibit defect insensitivity. This study shows that such hybrid structures are able to greatly expand the design space of architectured cellular materials for engineering applications.
To reduce the operational complexity of the multipath estimating delay lock loop (MEDLL) and improve its anti-multipath performance for strobe correlators, a combination anti-multipath scheme, namely, the MEDLL on-strobe correlation technique, is proposed for global navigation satellite system (GNSS) signal processing. Short-delay multipath rays are separated from the strobe correlation function by the MEDLL mechanism; the dot product between the estimation residue and the standard correlation function or the BOC-PRN correlation function is then computed to eliminate the potential tracking ambiguity. Finally, this non-coherent combination result is sent to the loop filter to obtain anti-multipath code tracking. The proposed method is analysed via simulator data with a software receiver under different front-end bandwidth conditions. The results corroborate the better multipath mitigation capability and lower computational burden, although it is still difficult to eliminate all multipath interference, especially when the front-end bandwidth is insufficient.
Global Navigation Satellite System (GNSS) observations contain various errors, the separation and measurement of which is a popular research topic. Multipath effect on code measurements is investigated through the multipath combination, but carrier multipath error is small, and it is difficult to distinguish from other errors, such as hardware delay, carrier noise and satellite inherent biases. However, as the number of frequency points increases during the rapid development of GNSSs, it is possible to analyse the abovementioned errors in detail. Triple-frequency combination can be used to eliminate the first order ionospheric error, and a quad-frequency combination has one degree of freedom, which may be used to minimise carrier error effects. For this reason, an optimum method has been developed for multi-frequency GNSS code-multipath combination measurements, which has been verified by exploiting BeiDou System (BDS), three frequency data from an International GNSS Service (IGS) station and a city canyon as well as actual sampled quad-frequency data. By comparative analysis, we found that the fluctuations of an optimum triple-frequency combination are smaller than that of the non-optimum combination, which decreases the influence of inherent errors and biases on carrier phase. At the same time, second-order ionospheric error can be effectively eliminated as well. This provides a new code-multipath combination measurement optimisation methodology for future multi-frequency BDS and other GNSSs.
In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics (NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade (SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion (ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.
Photocatalytic reduction of carbon dioxide (CO2) into renewable hydrocarbon fuels using solar energy has gained much attention in the effort to conserve energy and enhance carbon cycling. This paper begins with a brief description of the basic concepts of the photocatalytic reduction of CO2, introduces some experimental challenges in the gas photoreaction system and provides a review of perovskite oxide semiconductor catalysts, including tantalates, niobates, titanates, zirconates and cerates, for use in the gas phase photoreduction of CO2. The prospects for the future research of CO2 photoreduction are also presented.
Beam positioning stability in a laser-driven inertial confinement fusion (ICF) facility is a vital problem that needs to be fixed. Each laser beam in the facility is transmitted in lots of optics for hundreds of meters, and then targeted in a micro-sized pellet to realize controllable fusion. Any turbulence in the environment in such long-distance propagation would affect the displacement of optics and further result in beam focusing and positioning errors. This study concluded that the errors on each of the optics contributed to the target, and it presents an efficient method of enhancing the beam stability by eliminating errors on error-sensitive optics. Optimizations of the optical system and mechanical supporting structures are also presented.
Li2M(WO4)2 (M = Co and Ni) were synthesized by a conventional solid-state reaction method and characterized by powder x-ray diffraction, Brunauer-Emmet-Teller (BET) measurement, ultraviolet-visible (UV-vis) diffuse reflectance spectra, Raman spectroscopy, and photocatalytic evaluation measurements. Photocatalytic water splitting results showed that Li2M(WO4)2 (M = Co and Ni) exhibited abilities for H2 evolution with Pt cocatalyst from an aqueous methanol solution and for O2 evolution from an aqueous AgNO3 solution under UV light irradiation. Theoretical calculation, absorbance analysis, and photocatalytic H2 evolution experiment revealed that the position of W 5d level shifted to the negative side with respect to the reduced potential of H+/H2. The photocatalytic H2 evolution over Li2M(WO4)2 is discussed from the view of crystal and electronic structure point.
The overall goal of our paper is to better understand water management reform in China's rural communities, especially focusing on the effect that improving incentives to water managers will have on the nation's water resources and the welfare of the rural population. To pursue this goal, the paper has three objectives. First, we track the evolution of water management reform and seek to identify the incentive mechanisms that encourage water managers to more efficiently use water. Second, we identify the impact on crop water use of the incentives provided to water managers during reform. Since we are also interested in the possible negative consequences of an incentive-led water management reform strategy, the paper also explores how changes in incentives also affect agricultural production, farmer income, and poverty. Based on a random sample of 51 villages, 189 farmers, and 378 plots in four large irrigation districts in Ningxia and Henan provinces, both provinces in China's Yellow River Basin, our results show that in our sample areas the two main forms of water management reform, Water User Associations and contracting, have begun to systematically replace traditional forms of collective management. Our analysis demonstrates, however, that it is not the nominal implementation of the reform that matters, but rather it is the creation of new management institutions that offer water managers monetary incentives that lead to water savings. Importantly, given China's concerns about national food production and poverty alleviation, the reductions in water, at least in our sample sites, do not lead to reductions in either production or income, and do not increase the incidence of poverty.
3-D displays, sensor skins, mechatronic structures, and e-textiles will rely on deformable and stretchable electronic circuits. It is likely that such circuits will be made of rigid semiconductor islands interconnected with one-time deformable or even elastic metallization. However, free-standing metal films fracture at tensile strains in the order of one percent, well short of the approximately ten-percent extension needed for deformable circuits. We have discovered that flat metal lines made on an elastomeric substrate can be stretched reversibly by ten percent without losing electrical conduction. While this phenomenon of “super-elastic” conductive films is as of yet unexplained, it appears to originate in the diversion of mechanical strain around cracks in the film and through the elastomer substrate. We fabricated 1mm thick poly-dimethylsiloxane (PDMS) membranes with up to 50-nm thick, 1-mm wide gold lines deposited by electron beam evaporation. Then we evaluated the structure of the gold films by optical and scanning electron microscopy, and measured the electro-mechanical characteristics in a strain tester, with contact electrodes applied to the film. We find that 50 nm thick lines retain their electrical conduction up to 30 percent strain. Also, when the tensile strain is cycled between 0 and 10 percent, the electrical resistance in the stressed and relaxed states are reproducible. We will describe substrate and conductor preparation, and their structural and electro-mechanical properties.
The electro-mechanical response of thin gold layers evaporated onto silicone substrates is reported. Gold layers are prepared either thin and flat or thin and wavy on the compliant substrate. The electrical resistance of gold/silicone stripes is measured and analyzed during tensile deformation. For a 100-nm thick gold layer evaporated on a 1-mm thick silicone membrane, we have observed electrical continuity up to ∼ 22 % strain. This maximum strain decreases when the gold layer thickness is raised.
We studied the postnatal body weight gain and development of 11 male and nine female giant panda Ailuropoda melanoleuca cubs born at Beijing Zoo from 1985 to 1998. Growth rates of the cubs appeared to be sexually dimorphic from the fourth month after birth; the male grew slightly faster than the female cubs. Growth rates between artificially fed and naturally fed cubs were significantly different from the fourth month after birth. The growth rate of the artificially fed cubs was slightly higher than that of the cubs fed by their mothers, indicating that the substitute milk satisfied the nutrient needs of the cubs. The body length of the cubs increased rapidly after birth; 8-month-old cubs were three times longer than newborn cubs. Chest circumferences of 8-month-old cubs also increased to twice that of newborn cubs. Tail length relative to body length was reduced from 14.9% at birth to about 8.6% in 8-month-old cubs. Cubs started to grow teeth when they were 3 months old. By the age of 1 year, the cubs had fully grown deciduous teeth. The teeth formula of one 1-year-old cub was 2·1·3·0/2·1·3·0=24. We recorded the changes in fur colour, development of the sense organs and limbs of the giant panda cubs. Finally, we compared the body weight and life-history parameters of giant pandas with those of bears and raccoons and discussed the management regime for the care of captive-born giant panda cubs.
There is a growing interest in the application of large area electronics on curved surfaces. One approach towards realizing this goal is to fabricate circuits on planar substrates of thin plastic or metal foil, which are subsequently deformed into arbitrary shapes. The problem that we consider here is the deformation of substrates into a spherical shape, where the strain is determined by geometry and cannot be reduced by simply using a thinner substrate. The goal is to achieve permanent, plastic deformation in the substrates, without exceeding fracture or buckling limits in the device materials.
Our experiments consist of the planar fabrication of amorphous silicon device structures onto stainless steel or Kapton® polyimide substrates, followed by permanent deformation into a spherical shape. We will present empirical experiments showing the dependence of the results on the island/line size of the device materials and the deformation temperature. We have successfully deformed Kapton® polyimide substrates with 100 [.proportional]m wide amorphous silicon islands into a one steradian spherical cap, which subtends 66 degrees, without degradation of the silicon. This work demonstrates the feasibility of building semiconductor devices on plastically deformed substrates despite a 5% average biaxial strain in the substrate after deformation.
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