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In order to solve joint-angle drift problem of dual redundant manipulators at acceleration-level, an acceleration-level tri-criteria optimization motion planning (ALTC-OMP) scheme is proposed, which combines the minimum acceleration norm, repetitive motion planning, and infinity-norm acceleration minimization solutions via weighting factor. This scheme can resolve the joint-angle drift problem of dual redundant manipulators which will arise in single criteria or bi-criteria scheme. In addition, the proposed scheme considers joint-velocity joint-acceleration physical limits. The proposed scheme can not only guarantee joint-velocity and joint-acceleration within their physical limits, but also ensure that final joint-velocity and joint-acceleration are near to zero. This scheme is realized by dual redundant manipulators which consist of left and right manipulators. In order to ensure the coordinated operation of manipulators, two motion planning problems are reformulated as two general quadratic program (QP) problems and further unified into one standard QP problem, which is solved by a simplified linear-variational-inequalities-based primal-dual neural network at the acceleration-level. Computer-simulation results based on dual PUMA560 redundant manipulators further demonstrate the effectiveness and feasibility of the proposed ALTC-OMP scheme to resolve joint-angle drift problem arising in the dual redundant manipulators.
A high energy electron density modulator from a high-intensity laser standing wave field is studied herein by investigating the ultrafast motion of electrons in the field. Electrons converge at the electric field antinodes, and the discrete electron density peaks modulated by the field located at the corresponding laser phases of kx = nπ, (n = 0, 1, 2, …), that is, the modulation period is 1/2 the wavelength of the individual laser. We also discussed the influence of the laser parameters such as laser intensity and waist size on the beam modulator. It is shown that a long interaction length (waist) or sufficiently high field intensity is essential for relativistic electron density modulation.
Energy chirp compensation of the electron bunch (e-bunch) in a laser wakefield accelerator, which is caused by the phase space rotation in the gradient wakefield, has been applied in many schemes for low energy spread e-bunch generation. We report the experimental observation of energy chirp compensation of the e-bunch in a nonlinear laser wakefield accelerator with a negligible beam loading effect. By adjusting the acceleration length using a wedge-roof block, the chirp compensation of the accelerated e-bunch was observed via an electron spectrometer. Apart from this, some significant parameters for the compensation process, such as the longitudinal dispersion and wakefield slope at the bunch position, were also estimated. A detailed comparison between experiment and simulation shows good agreement of the wakefield and bunch parameters. These results give a clear demonstration of the longitudinal characteristics of the wakefield in a plasma and the bunch dynamics, which are important for better control of a compact laser wakefield accelerator.
In this study, we investigate a new simple scheme using a planar undulator (PU) together with a properly dispersed electron beam (
beam) with a large energy spread (
) to enhance the free-electron laser (FEL) gain. For a dispersed
beam in a PU, the resonant condition is satisfied for the center electrons, while the frequency detuning increases for the off-center electrons, inhibiting the growth of the radiation. The PU can act as a filter for selecting the electrons near the beam center to achieve the radiation. Although only the center electrons contribute, the radiation can be enhanced significantly owing to the high-peak current of the beam. Theoretical analysis and simulation results indicate that this method can be used for the improvement of the radiation performance, which has great significance for short-wavelength FEL applications.
Many shorebird populations are in decline along the East Asian-Australasian Flyway. The rapid loss of coastal wetlands in the Yellow Sea, which provide critical stop-over sites during migration, is believed to be the cause of the alarming trends. The Yalu Jiang coastal wetland, a protected area in the north Yellow Sea, supports the largest known migratory staging populations of Bar-tailed Godwits Limosa lapponica (menzbieri and baueri subspecies) and Great Knots Calidris tenuirostris. Monitoring of the macrozoobenthos food for these shorebirds from 2011 to 2016 showed declines of over 99% in the densities of the bivalve Potamocorbula laevis, the major food here for both Bar-tailed Godwits and Great Knots. The loss of the bivalve might be caused by any combination of, but not limited to: (1) change in hydrological conditions and sediment composition due to nearby port construction, (2) run-off of agrochemicals from the extensive shoreline sea cucumber farms, and (3) parasitic infection. Surprisingly, the numbers of birds using the Yalu Jiang coastal wetland remained stable during the study period, except for the subspecies of Bar-tailed Godwit L. l. menzbieri, which exhibited a 91% decline in peak numbers. The lack of an overall decline in the number of bird days in Great Knots and in the peak numbers of L. l. baueri, also given the published simultaneous decreases in their annual survival, implies a lack of alternative habitats that birds could relocate to. This study highlights that food declines at staging sites could be an overlooked but important factor causing population declines of shorebirds along the Flyway. Maintaining the quality of protected staging sites is as important in shorebird conservation as is the safeguarding of staging sites from land claim. Meanwhile, it calls for immediate action to restore the food base for these beleaguered migrant shorebirds at Yalu Jiang coastal wetland.
The Yellow Sea region is of high global importance for waterbird populations, but recent systematic bird count data enabling identification of the most important sites are relatively sparse for some areas. Surveys of waterbirds at three sites on the coast of southern Jiangsu Province, China, in 2014 and 2015 produced peak counts of international importance for 24 species, including seven globally threatened and six Near Threatened species. The area is of particular global importance for the ‘Critically Endangered’ Spoon-billed Sandpiper Calidris pygmaea (peak count across all three study sites: 62 in spring  and 225 in autumn  and ‘Endangered’ Spotted Greenshank Tringa guttifer (peak count across all three study sites: 210 in spring  and 1,110 in autumn ). The southern Jiangsu coast is therefore currently the most important migratory stopover area in the world, in both spring and autumn, for both species. Several serious and acute threats to waterbirds were recorded at these study sites. Paramount is the threat of large-scale land claim which would completely destroy intertidal mudflats of critical importance to waterbirds. Degradation of intertidal mudflat habitats through the spread of invasive Spartina, and mortality of waterbirds by entrapment in nets or deliberate poisoning are also real and present serious threats here. Collisions with, and displacement by, wind turbines and other structures, and industrial chemical pollution may represent additional potential threats. We recommend the rapid establishment of effective protected areas for waterbirds in the study area, maintaining large areas of open intertidal mudflat, and the urgent removal of all serious threats currently faced by waterbirds here.
Two kinds of Ag/ZnO electrical contact materials were fabricated by powder metallurgy method. The electrical life testing was done to investigate the arc erosion behavior of the prepared contact materials. Their properties and morphologies were characterized and discussed in detail. Results showed that Ag/ZnO(c) with coprecipitated ZnO as the second phase had better mechanical and electrical properties compared with Ag/ZnO(a) with ZnO purchased from Aladdin Industrial, Inc. Besides, some typical morphologies, such as holes, Ag or ZnO enrichment zone, Ag skeletons and bubbling area, occurred on the surface of the contacts. Especially for Ag/ZnO(c), vertically aligned ZnO nanorod arrays were detected after the life testing without any other supporting equipment. The existence of a solid solution Zn1−xAgxO and different energy generated during arcing process were possible reasons resulting in this phenomenon. A solid–vapor–solid mechanism was put forward to analyze the phenomenon mentioned above. These evidences could also offer some valuable information desired for reducing the splashing of Ag droplet under arcing.
In this paper, a rigid–flexible planar parallel manipulator (PPM) actuated by three linear ultrasonic motors for high-accuracy positioning is proposed. Based on the extended Hamilton's principle, a rigid–flexible dynamic model of the proposed PPM is developed utilizing exact boundary conditions. To derive an appropriate low-order dynamic model for the design of the controller, the assumed modes method is employed to discretize elastic motion. Then to investigate the interaction between the rigid and elastic motions, a proportional derivative feedback controller combined with a feed-forward-computed torque controller is developed to achieve motion tracking while attenuating the residual vibration. Then the controller is extended to incorporate an input shaper for the further suppression of residual vibration of flexible linkages. Computer simulations are presented as well as experimental results to verify the proposed dynamic model and controller. The input shaping method is verified to be effective in attenuating residual vibration in a highly coupled rigid–flexible PPM. The procedure employed for dynamic modeling and control analysis provides a valuable contribution into the vibration suppression of such a PPM.
In order to resolve the redundancy of a wheeled mobile redundant manipulator comprising a two-wheel-drive mobile platform and a 6-degree-of-freedom manipulator, a physical-limits-constrained (PLC) minimum velocity norm (MVN) coordinating scheme (termed as PLC-MVN-C scheme) is proposed and investigated. Such a scheme can not only coordinate the mobile platform and the manipulator to fulfill the end-effector task and to achieve the desired optimal index (i.e., minimizing the norm of the rotational velocities of the wheels and the joint velocities of the manipulator) but also consider the physical limits of the robot (i.e., the joint-angle limits and joint-velocity limits of the manipulator as well as the rotational velocity limits of the wheels). The scheme is then reformulated as a quadratic program (QP) subject to equality and bound constraints, and is solved by a discrete QP solver, i.e., a numerical algorithm based on piecewise-linear projection equations (PLPE). Simulation results substantiate the efficacy and accuracy of such a PLC-MVN-C scheme and the corresponding discrete PLPE-based QP solver.
To address fundamental processes in the solar eruptive phenomena it is important to have imaging-spectroscopy over centimetric-decimetric wave range. The Chinese Spectral Radioheliograph (CSRH) in 0.4-15 GHz range with high time, space and frequency resolutions is being constructed to achieve this goal. The perspectives to open new observational windows on solar flares and CMEs will be achieved by mapping the radio emission from unstable electron populations during the basic processes of energy release. CSRH is located in a radio quiet region in Inner Mongolia of China. The array of CSRH-I in 0.4-2.0 GHz with 40 4.5m antennas has been established and starts test observations. The 60 2m antennas for array of CSRH-II in 2-15 GHz have been mounted and assembled. The progress and current status of CSRH are introduced.
Objective: Functional imaging studies of post-traumatic stress disorder (PTSD) have shown an increased activation of posterior cingulate gyrus (PCG) of the brain. The aim of this study was to explore white matter integrity of PCG in PTSD subjects.
Methods: White matter integrity, as determined from fractional anisotropy (FA) value using diffusion tensor imaging, was assessed for PCG in subjects with and without PTSD from a severe mine accident. All subjects were also measured by the PTSD Checklist Civilian Version (PCL-C), the State-Trait Anxiety Inventory (STAI), the logical memory subtest and the visual reproduction subtest of the Wechsler Memory Scale-Revised in China. Sixteen PTSD subjects (8 subjects in each group) in the longitudinal study and 13 PTSD subjects as well as 14 non-PTSD controls in the cross-sectional case–control study were respectively recruited.
Results: In the longitudinal study, subjects with PTSD showed increased FA values in left PCG during the follow-up scan. In the cross-sectional study, FA values in bilateral PCG in PTSD subjects were higher than controls. Within the PTSD group (n = 13), FA values in the left PCG correlated positively with logical memory and negatively with PCL-C intrusion and STAI-trait (STAI-t) subscores. FA values in right PCG correlated negatively with STAI-t and STAI-state subscores.
Conclusion: These findings suggest that alterations of white matter integrity in PCG link to mnemonic and affective processing in PTSD over the long-term follow-up period.
A new aphid species, Dracaphis angustata, has been found in China from the Middle Triassic. It is especially informative because its whole body is preserved except for the distal part of the antennae and part of the legs. Only wings of three other aphid species of Triassic age have previously been found: Triassoaphis cubitus, described by Evans (1956) from Australia and placed in its own family, Triassoaphididae Heie, 1999; Creaphis theodora, described by Shcherbakov and Wegierek (1991) from Central Asia and placed in its own family, Creaphididae; and Coccavus supercubitus, described by Shcherbakov (2007) from Kyrgyzstan and placed in Naibiidae together with Naibia from the Lower Tertiary. The new species described below must be placed in its own family Dracaphididae because it possesses a combination of characters unknown in any other aphid clade.
Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene has been suggested to be associated with major depressive disorder (MDD). There were a few reports of the relationship between the variant and late-onset depression (LOD) in Chinese Han population.
To investigate the relationship among BDNF Val66Met gene variants, BDNF plasma level and LOD.
Chinese Han patients with LOD (n = 99) and control subjects (n = 110) were assessed for BDNF Val66Met gene polymorphism. BDNF plasma level was tested only in LOD.
There were no significant differences in genotypes and allele frequencies between cases and controls (p = 0.744 and p = 0.845, respectively). Plasma BDNF level also did not show significant differences in three genotypes in LOD (p = 0.860).
The Val66Met polymorphism in BDNF gene may not confer susceptibility to LOD in Chinese Han population.
By Karamata regular variation theory, a perturbation method and construction of comparison functions, we show the exact asymptotic behaviour of solutions near the boundary to nonlinear elliptic problems Δu ± |Δu|q = b(x)g(u), u > 0 in Ω, u|∂Ω = ∞, where Ω is a bounded domain with smooth boundary in ℝN, q > 0, g ∈ C1[0, ∞) is increasing on [0, ∞), g(0) = 0, g′ is regularly varying at infinity with positive index ρ and b is non-negative in Ω and is singular on the boundary.
We show the existence and exact asymptotic behaviour of the unique solution u ∈ C2(Ω)∩C(Ω̄) near the boundary to the singular nonlinear Dirichlet problem −Δu = k(x)g(u) + λ|∇u|q, u > 0, x ∈ Ω, u|∂Ω = 0, where Ω is a bounded domain with smooth boundary in RN, λ ∈ R, q ∈ [0, 2], g(s) is non-increasing and positive in (0, ∞), lims→0+g(s) = +∞, k ∈ Cα(Ω) is non-negative non-trivial on Ω, which may be singular on the boundary.
The solar radio bursts and accompanying fine structures recorded by spectrometers at Huairou, Beijing during 1999-2003 are presented. The spectrometers are with high temporal (5-10 ms) and spectral (4-20 MHz) resolutions. We found 91 radio burst events that occurred within half hour of the onset of the CME events which cause solar energetic particle events. The associations of radio fine structures with CME events are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
Structure and ultraviolet emission characteristics of amorphous ZnO films grown on indium tin oxide coated glass substrates by electrophoretic deposition were investigated using Raman spectra and photoluminescence. The Raman spectrum shows a unique resonant multiphonon process within amorphous ZnO films. The photoluminescence spectrum of amorphous ZnO films shows a strong ultraviolet emission while the visible emission is nearly fully quenched. The transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectrum, and infrared spectrum are used to detect the structure of amorphous ZnO powder. The complex water plays an important role in the photoluminescence intensity emission.
A novel HIV-1 genome that stably utilizes tRNAHis
rather than tRNALys,3 to initiate reverse transcription
was used to study features for the interaction between
the tRNA and viral RNA genome. In addition to a primer
binding site (PBS) complementary to tRNAHis,
this virus contains a six-nucleotide sequence in U5 complementary
to the anticodon-loop of tRNAHis and three additional
substitutions: U174-to-G, G181-to-A,
and U200-to-C [HXB2(His-AC-GAC)].
Mutations in these three nucleotides resulted in viruses
with three different genotypes: one group maintained a
PBS complementary to tRNAHis with restored
or G174A181U200 configurations,
one group reverted to a PBS complementary to tRNALys,3,
and one group contained two or more PBSs complementary
to different tRNAs on the same viral genome. Characterization
of a previously identified virus with additional C152-to-A
and C160-to-U substitutions
revealed that this virus maintained a PBS complementary
to tRNAHis, whereas a mutant
reverted after culture to contain dual PBS complementary
to tRNALys,3 and tRNAHis, respectively.
Our results demonstrate that regions in U5 act in concert
with the PBS to promote use of the tRNA primer for initiation
of reverse transcription. These results are discussed with
respect to structural models for the U5-PBS interactions
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