1,820 research outputs found
Functional analysis of the micro/nanostructures of dragonfly wing veins
This article studies the internal micro/nanostructures and reveals the relations between the structures and functions of dragonfly wing veins. Through SEM, we take the microscopic photos of the cross-sections of dragonfly wing veins. From these photos, we obtain the following results: (a) The micro/nanostructures vary along the axis of the vein, i.e., different cross-sections have different micro/nanostructures. (b) For a given cross-section, the micro/nanostructures are of multilevels and multiscales. (c) At large scale, the structures of the veins are of diversities and disorders. The larger is the size scale. The more complicated are the structures, and the higher are the diversities and disorders. At small scale, the structures of the veins are of unifications and orders. The smaller is the size scale, the simpler is the structures, and the higher are the unifications and orders. (d) At the micro scale, we may induce unified assembling mode for the vein’s structures, i.e., “nanofibers/nanolayers (or nanobunches)”. (e) Both the mechanical functions and biological functions of the micro/nanostructures of the veins are optimized synthetically
Computation of Wind Wave Flow Field with Moving Boundary Based on Image Processing
Based on image processing technology, a solution to the interference of moving boundary in wind wave flow field calculation is proposed. Invariant background is extracted from image sequence by means of the minimum method, and the differences between image sequence and invariant background image are used to remove the invariant background of image sequence. The image segmentation threshold is determined based on maximum interclass variance method, and the scatter interference is removed by image filtering and morphological technology, to obtain the target image. Then the flow field is calculated by PIV technology and the results of the flow field before and after the boundary treatment are compared. The experimental results show that the accuracy and speed of flow field calculation are greatly improved after removal of moving boundary disturbance, and the results of wind wave flow field calculation accord with the motion mechanism of hydraulic wind wave
Optimal scheduling for multiple description video streams in wireless multihop networks
International audience— In this work, we investigate the optimal system scheduling for competing multiple description (MD) video streams in a resource-limited wireless multihop network. By joint optimization of MD, rate control and multipath routing, optimal joint rate control and routing algorithm is proposed to solve this problem with constraints that arise from the MD streams among multiple users via multiple paths. We design this joint algorithm in a distributed manner that is amenable to on-line implementation for wireless networks
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Biosynthesis of Putrescine from L-arginine Using Engineered Escherichia coli Whole Cells
Putrescine, a biogenic amine, is a highly valued compound in medicine, industry, and agriculture. In this study, we report a whole-cell biocatalytic method in Escherichia coli for the production of putrescine, using L-arginine as the substrate. L-arginine decarboxylase and agmatine ureohydrolase were co-expressed to produce putrescine from L-arginine. Ten plasmids with different copy numbers and ordering of genes were constructed to balance the expression of the two enzymes, and the best strain was pACYCDuet-speB-speA. The optimal concentration of L-arginine was determined to be 20 mM for this strain. The optimum pH of the biotransformation was 9.5, and the optimum temperature was 45 °C; under these conditions, the yield of putrescine was 98%. This whole-cell biocatalytic method appeared to have great potential for the production of putrescine.</jats:p
Sulphur isotopes toward Sagittarius B2 extended envelope in the Galactic Center
The isotopic ratios are good tools for probing the stellar nucleosynthesis
and chemical evolution. We performed high-sensitivity mapping observations of
the J=7-6 rotational transitions of OCS, OC34S, O13CS, and OC33S toward the
Galactic Center giant molecular cloud, Sagittarius B2 (Sgr B2) with IRAM 30m
telescope. Positions with optically thin and uncontaminated lines are chosen to
determine the sulfur isotope ratios. A 32S/34S ratio of 17.1\pm0.9 was derived
with OCS and OC34S lines, while 34S/33S ratio of 6.8\pm1.9 was derived directly
from integrated intensity ratio of OC34S and OC33S. With independent and
accurate measurements of 32S/34S ratio, our results confirm the termination of
the decreasing trend of 32S/34S ratios toward the Galactic Center, suggesting a
drop in the production of massive stars at the Galactic centre.Comment: 20 pages, 7 figures, accepted by PAS
The SpeakIn System Description for CNSRC2022
This report describes our speaker verification systems for the tasks of the
CN-Celeb Speaker Recognition Challenge 2022 (CNSRC 2022). This challenge
includes two tasks, namely speaker verification(SV) and speaker retrieval(SR).
The SV task involves two tracks: fixed track and open track. In the fixed
track, we only used CN-Celeb.T as the training set. For the open track of the
SV task and SR task, we added our open-source audio data. The ResNet-based,
RepVGG-based, and TDNN-based architectures were developed for this challenge.
Global statistic pooling structure and MQMHA pooling structure were used to
aggregate the frame-level features across time to obtain utterance-level
representation. We adopted AM-Softmax and AAM-Softmax combined with the
Sub-Center method to classify the resulting embeddings. We also used the
Large-Margin Fine-Tuning strategy to further improve the model performance. In
the backend, Sub-Mean and AS-Norm were used. In the SV task fixed track, our
system was a fusion of five models, and two models were fused in the SV task
open track. And we used a single system in the SR task. Our approach leads to
superior performance and comes the 1st place in the open track of the SV task,
the 2nd place in the fixed track of the SV task, and the 3rd place in the SR
task.Comment: 4 page
Widespread Presence of Glycolaldehyde and Ethylene Glycol Around Sagittarius B2
We report the detection of widespread CHOHCHO and HOCHCHOH
emission in Galactic center giant molecular cloud Sagittarius B2 using the
Shanghai Tianma 65m Radio Telescope. Our observations show for the first time
that the spatial distribution of these two important prebiotic molecules
extends over 15 arc-minutes, corresponding to a linear size of approximately 36
pc. These two molecules are not just distributed in or near the hot cores. The
abundance of these two molecules seems to decrease from the cold outer region
to the central region associated with star-formation activity. Results present
here suggest that these two molecules are likely to form through a low
temperature process. Recent theoretical and experimental studies demonstrated
that prebiotic molecules can be efficiently formed in icy grain mantles through
several pathways. However, these complex ice features cannot be directly
observed, and most constraints on the ice compositions come from millimeter
observations of desorbed ice chemistry products. These results, combined with
laboratory studies, strongly support the existence of abundant prebiotic
molecules in ices.Comment: 20 pages, 7 figures, accepted by Ap
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