分类: 生物学 >> 动物学 提交时间: 2021-05-20 合作期刊: 《古脊椎动物学报》
摘要: 贝叶斯支端定年法是近些年开发的推断类群分异时间和演化速率的方法。它克服了传统分步计算的缺陷,但涉及到的统计学知识也更多。本文从贝叶斯统计计算的角度分层剖析了支端定年法的原理和计算过程,按照分异时间的先验分布、演化速率的先验分布、特征状态变化的模型和马氏链蒙特卡罗算法几个部分,叙述并讨论了定年计算中的主要模型和算法。旨在一定程度上为古生物学家分析实际数据提供参考。
分类: 生物学 >> 动物学 提交时间: 2019-06-11 合作期刊: 《古脊椎动物学报》
摘要: This paper provides an overview and a protocol of molecular clock dating using MrBayes. Two modern approaches, total-evidence dating and node dating, are demonstrated using a truncated dataset of Hymenoptera with molecular sequences and morphological characters. The similarity and difference of the two methods are compared and discussed. Besides, a non-clock analysis is performed on the same dataset to compare with the molecular clock dating analyses.
分类: 生物学 >> 动物学 提交时间: 2019-06-11 合作期刊: 《古脊椎动物学报》
摘要: This paper provides an overview and a protocol of molecular clock dating using MrBayes. Two modern approaches, total-evidence dating and node dating, are demonstrated using a truncated dataset of Hymenoptera with molecular sequences and morphological characters. The similarity and difference of the two methods are compared and discussed. Besides, a non-clock analysis is performed on the same dataset to compare with the molecular clock dating analyses.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: By studying the advantages and disadvantages of the conventional automatic linear door systems, it was found that flat permanent magnet linear synchronous motors (PMSLM) can satisfy high-speed long-stroke heavy-load door systems better than other techniques. In order to reach a long lifespan, the authors compared five possible topologies with flat PMLSM, and then designed a kind of magnetically suspended door system driven by a single-sided flat PMLSM and suspended by the normal force of the motor. The results demonstrate that the prototype door system satisfies the requirements.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: The free piston energy converter (FPEC) is a new type of power unit for hybrid electric vehicle. In a FPEC, an internal combustion engine driven permanent magnet linear generator (PMLG) may be utilized to produce electrical energy. This paper discusses the issues that are pertinent to the design of a linear permanent magnet generator for application in a FPEC. To achieve the required high power density and low moving mass, a tubular machine equipped with modular windings and axially magnetized is considered to be the most appropriate. Finite Element Analysis are adopted to analyse the PMLG. Magnetic field distribution, EMF, thrust force and No- load corl loss are obtained through the finite element method. An effective tool for design optimization is provided. It is shown that the machine design can be optimized with respect to three key dimensional ratios while satisfying other performance specifications.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Abstract. The paper presents multi-sensor image fusion and its relevant framework and technical characteristics. The image fusion is divided into three level fusions: pixel level, feature level and decision level. It mainly discusses the image fusion algorithm at all levels of fusion, and then makes the summary and comparison of these algorithms. Since the high-level algorithms are related to some relevant practical applications of the image fusion, it is in general difficult to be summarized. So this paper also presents some typical algorithms of the fea- ture and decision levels from the perspective of the applications, to provide the necessary summary of the high level image fusion algorithm. Further, the three levels of implementation schemes are described, followed by the comparison and summary for the image evaluation criteria of the fusion method. Some problems and future directions about the multi-sensor image fusion are finally given.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-05
摘要: Growing evidence indicates that B cells are not the only source of immunoglobulin (Ig). To investigate this discovery further, we used mu MT mice, which have a disruption of the first transmembrane exon of the mu heavy chain and do not express the membrane form of IgM. These mice lack mature B cells and thus serve as a good model to explore Ig expression by liver epithelial cells. We found that Ig heavy chains (mu, delta, gamma and alpha) and light chains (kappa and lambda) were expressed in sorted liver epithelial cells of mu MT mice. Surprisingly, each heavy chain class showed its respective variable region sequence characteristics in their variable region, instead of sharing the same VDJ usage, which suggests that class switching does not occur in liver epithelial cells. Moreover, the gamma and alpha chains, but not the mu and delta chains, showed mutations in the variable region, thus indicating that different classes of Ig have different activities. Our findings support the concept that non-B cells, liver epithelial cells here, can produce different classes of Ig.
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-05-09
摘要: This paper proposes a novel moving-coil voice coil motor(VCM) used for driving nano-positioning device. This VCM implements bilateral Halbach array permanent magnet as the stator and three separated coils with the slotted coil skeleton as the mover.. The VCM can achieve large stroke and nano-level positioning accuracy with the support of the compliant mechanism. Equivalent magnetic circuit method and the finite element analysis (FEA) are used in this paper to analyze the performance of the VCM. The analysis results show that the VCM can achieve a force-current ratio of 90 N/A and force ripple of ±0.19 N, which are superior than the previous designs in the literatures .
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: As there is no round optical grating and magnetic grating with large diameter that is over 0.5m in the market, a measuring system adopting dual magnetic sensors based on FPGA is proposed in this paper to measure the position/displacement and velocity of the rotating outer-rotor motor. Through using strip-type magnetic grating to stick around the outer rotor over half circumstance, the proposed system is able to produce continuous position pulse signals by switching the signals of dual magnetic sensors. The system core chip distinguishes, subdivides and filters the signals from two sensors, judging the operational state of the sensor and generating the dual magnetic sensor switching signals. It can switches the sensor signals in real time during motor operation and measures the position/displacement and velocity of motor in a precise manner. Moreover, the position/displacement, operating time and positive/negative rotation can be displayed through man-machine interactive unit. The experimental results show that arc-second control accuracy of the outer-rotor torque motor can be achieved by using the proposed system to measure the speed and position/ displacement of the outer-rotor torque motor as the feedback signal through the motion control system of motor.