分类： 地球科学 >> 空间物理学 提交时间： 2016-05-12
摘要： Based on a hybrid galactic cosmic-ray transport model, which incorporated MHD global heliospheric data into Parker's cosmic-ray transport equation, we studied the behavior of the transport of galactic cosmic rays and the corresponding gradients in their flux near the heliopause (HP). We found that, (1) by increasing the ratio of the parallel diffusion coefficient to the perpendicular diffusion coefficient in the interstellar magnetic field of the outer heliosheath, the simulated radial flux near the HP increases as well. As the ratio multiplying factor reached 1010, the radial flux experienced a sudden jump near the HP, similar to what Voyager 1 observed in 2012. (2) The effect of changing the diffusion coefficients' ratio on the radial flux variation depends on the energy of the cosmic rays, the lower the energy, the more pronounced the effect is. (3) The magnitude of the diffusion coefficients also affect the radial flux near the HP, the modulation beyond the HP varies by adjusting the magnitude multiplying factor.
分类： 天文学 >> 天文学 提交时间： 2024-02-28 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The scattered stray light of a coronagraph is a type of stray light that is generated by the objective lens as its surface defects are irradiated by sunlight. The defects mainly include dust and blemishes on the lens surface, microroughness of the lens surface, and impurity and inhomogeneity of the glass. Unlike the other types of relatively stable defects introduced when the objective lens is being manufactured, the scattered stray light caused by dusts on the lens surface is difficult to quantify accurately due to the disorder and randomness of the dust accumulation. The contribution of this type of stray light to the overall stray light level is difficult to determine through simulations and experiments. This can result in continuous deterioration of the stray light level of a coronagraph and thus affect the observation capabilities of the instrument. To solve this issue, through analyzing the forming mechanism of scattered stray light and ghost image generated by the inner-occulted coronagraph, we propose a novel method to monitor the scattered stray light from dusts by utilizing different stray light correlation coefficients. In this method, we first simulate and measure the level of stray light from the ghost image of the objective lens, and then determine the flux ratio of scattered light and ghost image on the conjugate plane. Although the flux ratio varies with the accumulation of dusts on the lens surface, it remains constant on the image plane. Therefore, the level of dust scattering light on the image plane can be obtained by using this ratio together with the level of ghost image stray light. The accuracy of this method has been validated in a laboratory by applying the objective lens with numerous surface cleanliness levels.
分类： 生物学 >> 生物工程 提交时间： 2024-03-05
Zhang, Ming
Tang, Chao
Wang, Zichun
Chen, Shanchuan
Xu, Mengying
Li, Kaiju
Sun, Ke
Zhao, Changjian
Wang, Yu
Dai, Lunzhi
Lu, Guangwen
Shi, Hubing
Chen, Lu
Geng, Jia
摘要： Single-molecule discrimination among amino acids is crucial to the realization of next-generation protein sequencing. Owing to the heterogeneous charge and subtle volume difference of underivatized amino acids, it remains a challenge for single-molecule techniques to recognize each of them. Here, we report the direct detection of twenty proteinogenic amino acids using a copper(II)-functionalized MspA nanopore. The binding sites for copper(II) ion are constructed by introducing histidine mutation (N91H) to M2MspA protein. With copper ion binding to histidine residues, amino acids can reversibly coordinate the copper-histidine complex, generating well-defined current signals. Using this strategy, all twenty amino acids can be detected. Assisted by a machine learning algorithm, we can identify 100% of signals with 70.2% accuracy or 60% of signals with 93.4% accuracy in the validation set. In successively addition experiment, each amino acid in a mixture of 10 amino acids can be identified precisely. Furthermore, we use carboxypeptidase A1 to partly release the C-terminal amino acids of peptides with different lengths (9, 10 and 22 residues). The hydrolysates of peptides can be identified and distinguished. These results demonstrate the feasibility of this system for amino acids detection and peptide identification, shedding new lights on the development of single-molecule protein sequencing.
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