Search Results

1 - 10 of 21 items

  • Author: Lei Wang x
Clear All Modify Search

Abstract

The kinematics of the heald frame of a rotary dobby with two different modulator types are analyzed and compared. Kinematic mathematical models of the modulator main shaft, cam unit, and heald frame driven by the rotary dobby with a cam-slider modulator and a cam-link modulator were constructed based on two different cam contours derived from measured points on the conjugate cams of the two modulators. The motion characteristics of the two modulators and a null modulator, the cam unit, and the motion transmission unit are analyzed. The purpose of the present study was to establish the kinematic models, investigate the motion characteristics, and analyze their differences. At the same time, a calculation method for each motion transmission process was established and numerical models were developed. The results demonstrated that the two different modulators produce almost the same heald frame motion characteristics. Despite that both modulator types can be adapted to the requirements of a loom, the cam-link modulator can produce a more stable and reliable motion.

Abstract

A sequence of N-doped carbon materials has been synthesized using poly(acrylonitrile)-ionic liquid copolymers as carbon precursors. The nitrogen content and configuration in carbon materials has been changed regularly within a certain range by adjusting the proportion of ionic liquids. We found that the capacity and rate performance increased dramatically after the introduction of ionic liquids, which was attributed to incorporation of higher amount pyridinic-N, pyrrolic-N into the carbon materials. Besides, with the increase of the graphitic-N, the initial Coulombic efficiency decreased from 58.5 % to 53.47 % and the RSEI raised from 66.34 Ω to 140.96 Ω, which was attributed to the higher cohesive energy of Li dimmer than adsorption energy of graphitic-N with Li, since more lithium clusters during the formation of SEI film were formed. The electrochemical tests also revealed the negative role of graphitic-N in the capacity. Therefore, this work provides a feasible method to design the nitrogen content and configuration of the N-doped carbon materials.

Abstract

For a subset S of edges in a connected graph G, S is a k-restricted edge cut if GS is disconnected and every component of GS has at least k vertices. The k-restricted edge connectivity of G, denoted by λk(G), is defined as the cardinality of a minimum k-restricted edge cut. Let ξk(G) = min{|[X, X̄]| : |X| = k, G[X] is connected}, where X̄ = V (G)\X. A graph G is super k-restricted edge connected if every minimum k-restricted edge cut of G isolates a component of order exactly k. Let k be a positive integer and let G be a graph of order ν ≥ 2k. In this paper, we show that if |N(u) ∩ N(v)| ≥ k +1 for all pairs u, v of nonadjacent vertices and ξk(G)ν2+k , then G is super k-restricted edge connected.

Abstract

We report on the development and characterization of ten microsatellite markers from repetitive DNA enriched libraries for Castanopsis fissa from lower subtropical China. The number of alleles ranged from three to thirteen. Observed and expected heterozygosities ranged from 0.265 to 0.818, and 0.270 to 0.873, respectively. These microsatellite markers will be used to study fine-scale spatial genetic structure of C. fissa in 20 ha Dinghushan plot in lower subtropical China.

Abstract

The issue of controlling a swarm of autonomous unmanned surface vehicles (USVs) in a practical maritime environment is studied in this paper. A hierarchical control framework associated with control algorithms for the USV swarm is proposed. In order to implement the distributed control of the autonomous swarm, the control framework is divided into three task layers. The first layer is the tele-operated task layer, which delivers the human operator’s command to the remote USV swarm. The second layer deals with autonomous tasks (i.e. swarm dispersion, or avoidance of obstacles and/or inner-USV collisions), which are defined by specific mathematical functions. The third layer is the control allocation layer, in which the control inputs are designed by applying the sliding mode control method. The motion controller is proved asymptotically stable by using the Lyapunov method. Numerical simulation of USV swarm motion is used to verify the effectiveness of the control framework.

Abstract

This article presents the kinematic modeling and analysis of cam profiles of two different types of modulator: a cam-link and a cam-slider modulators. Kinematic and dynamic models of the two different modulators were established based on the motion curves of the main shaft of the rotary dobby. Simulations were carried out in Simulink to analyze the vibration responses under different rotary speeds, and vibration responses of the two mechanisms were compared. The results show that the cam-link modulator vibrates smoothly at speeds of <700 rpm, and theoretically, the speed should not exceed 1,400 rpm. The cam-slider modulator vibrates smoothly at speeds of <500 rpm, and theoretically, the speed should not exceed 1,000 rpm. The cam-slider modulator is more suitable for use at low speeds, whereas the cam-link modulator is more appropriate for high speeds. When both the cam-slider and cam-link modulators operate at high speeds, vibration distortion occurs, leading to bifurcation and chaotic vibration. Further knowledge of the complex behaviors associated with detachment of the follower from the cam can support the design of more sophisticated controllers aimed at avoiding follower detachment.

Abstract

The paper proposes a solution to an inverse kinematics problem based on dual quaternions algebra. The method, relying on screw theory, requires less calculation effort compared with commonly used approaches. The obtained kinematic description is very concise, and the singularity problem is avoided. The dual quaternions formalism is applied to the problem decomposition and description. As an example, the kinematics problem of a multi-DOF serial manipulator is considered. Direct and inverse kinematics problems are solved using division into sub-problems. Each new sub-problem proposed is concerned with rotation about two subsequent axes by a given amount. The presented example verifies the correctness and feasibility of the proposed approach.

Abstract

This paper extends the use of network theory to the study of region network modeling between China and five central Asian countries (Kazakhstan, Kirghiz Tanzania, Tajikistan, Turkmenistan, Uzbekistan) using the DMSP/OLS nighttime light data. In this paper, first, regional scale index and region interaction index are designed and calculated. Then based on these indices, the 0–1 region incidence matrix is obtained and the region network is constructed. Furthermore, the regional economic activity is identified by using the region network. This study deepens the application of complex network in the field of regional cooperation.

Abstract

The lower subtropical monsoon evergreen broadleaved forest in South China (about 22° ~ 24° N) has a high conservation status, because of its uniqueness and high biodiversity. During the last few decades, most of these forests have been destroyed, and the remaining are being degraded by fragmentation. However, genetic information concerning the effects of fragmentation is currently lacking for plant species in these forests. In this study, therefore, eight microsatellites were used to study six Cryptocaya chinensis fragmented populations in Guangdong Province South China, and the results revealed a complex pattern of genetic variation within and among C. chinensis populations. Firstly, genetic variations demonstrate hitherto undetected clonal growth in C. chinensis. Secondly, current population structure of C. chinensis reflects an interaction between ancient homogeneous level of genetic variation and contemporary bottleneck via fragmentation. Small populations maintain substantial genetic variation of the initial populations through clonal growth, and do not show genetic depauperation compared to larger populations. Finally, two genetically distinct groups (West and Middle- East groups) are found in this area, connected by highly mixed contact zone.

Abstract

The electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations were calculated using the first-principles based on the density functional theory. The calculated results show that the forbidden band widths of Hgdoped anatase TiO2 widened along with the increase of O vacancy concentration, which is responsible for the blue shift in the absorption edges. It can be deduced from the present study that the Hg-doped TiO2 samples prepared in the experimental research contain a certain quantity of O vacancies.