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2012 1

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Diversity and distribution of proteorhodopsin-containing microorganisms in marine environments

Bo WEI

《环境科学与工程前沿（英文）》 2012年第6卷第1期页码 98-106 doi: 10.1007/s11783-010-0278-y

摘要： Proteorhodopsin (PR) is a recently discovered protein involved in the utilization of light energy. Several studies have shown that PR-containing microorganisms are widespread and compose a large proportion of the biomass in marine ecosystems. A better understanding of the ecological role of PR will help clarify the effect of the global flow of energy and the carbon cycle on marine communities. In this study, a bioinformatical database of PR codon sequences, the Global Distribution Database of Proteorhodopsin (GDDP), as a tool for analyzing the diversity and distribution of PR-containing microorganisms in marine environments throughout the world was designed. The community structure of PR microorganisms were also compared using PCR assays and UniFrac analyses of 12 samples collected from three water layers (0, 75, and 200 m) at four representative sites in the Pacific, Atlantic, and Indian Oceans. The results indicate that PR-containing microorganisms can be grouped into two distribution types: widespread and location-specific. Representative cases of the former include SAR11-PR and HOT2C01-PR. Interestingly, PR communities cluster by geographic locale but not by water depth.

关键词： proteorhodopsin (PR) microorganism community diversity marine environments

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Cusp points and assembly changing motions in the PRR-PR-PRR planar parallel manipulator

《机械工程前沿（英文）》 2023年第18卷第2期 doi: 10.1007/s11465-022-0743-x

摘要： Most parallel manipulators have multiple solutions to the direct kinematic problem. The ability to perform assembly changing motions has received the attention of a few researchers. Cusp points play an important role in the kinematic behavior. This study investigates the cusp points and assembly changing motions in a two degrees of freedom planar parallel manipulator. The direct kinematic problem of the manipulator yields a quartic polynomial equation. Each root in the equation determines the assembly configuration, and four solutions are obtained for a given set of actuated joint coordinates. By regarding the discriminant of the repeated roots of the quartic equation as an implicit function of two actuated joint coordinates, the direct kinematic singularity loci in the joint space are determined by the implicit function. Cusp points are then obtained by the intersection of a quadratic curve and a cubic curve. Two assembly changing motions by encircling different cusp points are highlighted, for each pair of solutions with the same sign of the determinants of the direct Jacobian matrices.

关键词： planar parallel manipulator assembly changing motions cusp points quartic polynomial discriminant of repeated roots