766 research outputs found
Kinematics of a Trinal-Branch Space Robotic Manipulator with Redundancy
AbstractThis paper presents a trinal branch space robotic manipulator with redundancy, due to hash application environments, such as in the station. One end- effector of the manipulator can be attached to the base, and other two be controlled to accomplish tasks. The manipulator permits operation of science payload, during periods when astronauts may not be present. In order to provide theoretic basis for kinematics optimization, dynamics optimization and fault-tolerant control, its inverse kinematics is analyzed by using screw theory, and its unified formulation is established. Base on closed form resolution of spherical wrist, a simplified inverse kinematics is proposed. Computer simulation results demonstrate the validity of the proposed inverse kinematics
Effect of Substrate Concentration on the Synthesis of Cefaclor by Penicillin Acylase with in Situ Product Removal
Enzymatic synthesis of 3-chloro-7-D-(2-phenylglycinamide)-3-cephem-4-carboxylic
acid (cefaclor) by penicillin acylase (PA) was carried out with in situ product removal (ISPR) under kinetic control. The yield of cefaclor highly depended on substrate concentrations and the ratio of nucleus to acyl donor. Substrate concentrations were optimized
as 50 mmol lâ1 of 7-aminodesacetoxymethyl-3-chlorocephalosporanic acid (7ACCA)
and 100 mmol lâ1 of phenylglycine methyl ester (PGME) at the conditions: temperature 20 °C, pH 6.3; and enzyme load was 8 IU mlâ1. It is effective to improve the transfer of acyl donor through controlling the substrate concentration with feeding acyl donor. The
conversion of nucleus and acyl donor was improved to 93 % and 62 %, respectively
Flavonoids with α-glucosidase inhibitory activities and their contents in the leaves of Morus atropurpurea
BACKGROUND: This study aims to isolate the α-glucosidase inhibitory compounds from mulberry leaves (Morus atropurpurea Roxb., Moraceae) and to develop an analytical method for quantification of the compounds. METHODS: Four flavonoids, rutin (1), isoquercetin (2), kaempferol-3-O-rutinoside (3) and astragalin (4), were isolated by column chromatography from mulberry leaf water extracts (MWE). The α-glucosidase inhibitory activities of MWE and the four isolated compounds were evaluated by a microplate-based in vitro assay. The content of the isolated flavonoids in M. atropurpurea leaves purchased from different local herbal stores or collected in different locations was determined by high performance liquid chromatography. RESULTS: The four flavonoids (1â4) showed α-glucosidase inhibitory activities, with rutin (1) and astragalin (4) showing high α-glucosidase inhibitory activities (IC(50) values of 13.19â±â1.10 and 15.82â±â1.11 ΌM, respectively). The total contents of the four flavonoids were different among eight samples examined, ranging from 4.34 mg/g to 0.53 mg/g. CONCLUSIONS: The four flavonoids in M. atropurpurea leaves could inhibit α-glucosidase activity
Silver spoon effects of hatching order in an asynchronous hatching bird
The silver spoon hypothesis proposes that individuals which develop under favourable conditions will gain fitness benefits throughout their lifetime. Hatching order may create a considerable size hierarchy within a brood and lead to earlier-hatched nestlings having a competitive advantage over their siblings, which has been illustrated in some studies. However, there have been few explorations into the effect on subsequent generations. Here, using a 15-year-long study, we investigated the long-term fitness consequence of hatching order in the endangered crested ibis, Nipponia nippon, a species with complete hatching asynchrony. In this study, we found strong support for silver spoon effects acting on hatching order. Compared to later-hatched nestlings, first-hatched nestlings begin reproduction at an earlier age, have higher adult survival rates, possess a longer breeding life span and achieve higher lifetime reproductive success. Interestingly, we found carry-over effects of hatching order into the next generation. Nestlings which hatched earlier and became breeders in turn also produced nestlings with larger tarsus and better body condition. Additionally, we found a positive correlation among life-history traits in crested ibis. Individuals which started reproduction at a younger age were shown to possess a longer breeding life span. And the annual brood size increased with an individualâs breeding life span. This suggests that the earlier-hatched nestlings are of better quality and the âsilver spoonâ effects of hatching order cover all life-history stages and next generation effects
An Improved Genetic Algorithm for the Large-Scale Rural Highway Network Layout
For the layout problem of rural highway network, which is often characterized by a cluster of geographically dispersed nodes, neither the Prim algorithm nor the Kruskal algorithm can be readily applied, because the calculating speed and accuracy are by no means satisfactory. Rather than these two polynomial algorithms and the traditional genetic algorithm, this paper proposes an improved genetic algorithm. It encodes the minimum spanning trees of large-scale rural highway network layout with Prufer array, a method which can reduce the length of chromosome; it decodes Prufer array by using an efficient algorithm with time complexity o(n) and adopting the single transposition method and orthoposition exchange method, substitutes for traditional crossover and mutation operations, which can effectively overcome the prematurity of genetic algorithm. Computer simulation tests and case study confirm that the improved genetic algorithm is better than the traditional one
Are We Building on the Rock? On the Importance of Data Preprocessing for Code Summarization
Code summarization, the task of generating useful comments given the code,
has long been of interest. Most of the existing code summarization models are
trained and validated on widely-used code comment benchmark datasets. However,
little is known about the quality of the benchmark datasets built from
real-world projects. Are the benchmark datasets as good as expected? To bridge
the gap, we conduct a systematic research to assess and improve the quality of
four benchmark datasets widely used for code summarization tasks. First, we
propose an automated code-comment cleaning tool that can accurately detect
noisy data caused by inappropriate data preprocessing operations from existing
benchmark datasets. Then, we apply the tool to further assess the data quality
of the four benchmark datasets, based on the detected noises. Finally, we
conduct comparative experiments to investigate the impact of noisy data on the
performance of code summarization models. The results show that these data
preprocessing noises widely exist in all four benchmark datasets, and removing
these noisy data leads to a significant improvement on the performance of code
summarization. We believe that the findings and insights will enable a better
understanding of data quality in code summarization tasks, and pave the way for
relevant research and practice
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