The cleavage mechanism of severe acute respiratory syndrome (SARS) coronavirus main proteinase (M(pro) or 3CL(pro)) for the octapeptide AVLQSGFR is studied using molecular mechanics (MM) and quantum mechanics (QM). The catalytic dyad His-41 and Cys-145 in the active pocket between domain I and II seem to polarize the pi-electron density of the peptide bond between Gln and Ser in the octapeptide, leading to an increase of positive charge on C(CO) of Gln and negative charge on N(NH) of Ser. The possibility of enhancing the chemical bond between Gln and Ser based on the "distorted key" theory [Anal. Biochem. 233 (1996) 1] is examined. The scissile peptide bond between Gln and Ser is found to be solidified through "hybrid peptide bond" by changing the carbonyl group CO of Gln to CH(2) or CF(2). This leads to a break of the pi-bond system for the peptide bond, making the octapeptide (AVLQSGFR) a "distorted key" and a potential starting system for the design of anti SARS drugs.
This paper extends the recently developed cross modal strain energy (CMSE) method for damage localization and severity estimation, using limited modal data, with iterative process. For investigating the performance and verifying the effectiveness of the present CMSE method, the numerical study of this article chooses a damaged beam that was investigated in a published article. The numerical result indicates that the CMSE method is capable of detecting the damage locations and estimating their severities properly, even when only few spatially incomplete, noisy modes are utilized.
Offshore jacket platforms have been widely used in offshore oil and gas exploitation under hostile ocean environments. Finite element models of such structures need to have many degrees of freedom (DOFs) to represent the geometrical detail of complex structures, which leads to more computing power when performing the analysis and what’s more, the incompatibility in the number of degrees of freedom to the experimental models. Therefore, there is a need to simplify the analytical model by reducing the DOFs and in the process, making the essential eigen-properties agree with those of the experimental model is desired. In this paper, a scaled physical experimental model of an offshore jacket platform is simplified using the recently developed model refinement scheme. Mathematically, the procedure to implement the model refinement technique is an application of cross-model cross-mode (CMCM) method for model updating. The master degrees of freedom are chosen according to the placement of accelerometers in the experiment. Upon the completion of the refinement, the improved reduced jacket platform model matches the dynamic characteristics of the experimental model quite well.
Using GPS observations, this article studied the global TEC’s effect and its variation characters during the magnetic storm on August 5th, 2011. Results show that after sudden commencement and deep main phase of the magnetic storm, there are strong positive ionospheric TEC disturbances in the area along middle and low latitude with local time of 12:00 at noon. Besides, compared with TEC reference value, the maximum increase values are respectively 21.26 TECU and 25.29 TECU. TEC’s abnormal decline appeared in some area of high latitude at mid night on the northern semi-sphere. The analysis results reflect that the ionospheric disturbances are dependent on the local time. Moreover, observations on the BRMU GPS station show that the rate of TEC (ROT) rose and fell quickly, and its standard deviation ROTI index increased from less than 0.5 TECU/min to lager than 1.5 TECU/min, which meant that TEC temporal and spatial gradient had become larger and larger during the storm. The global ROTI map reflects the strong irregularity of the ionosphere density structure in the high-latitude area with higher time resolution in case of storm sudden commencement, and the maximum value rose up to 6 TECU/min. Then, the ionospheric irregularity appeared in wide area of the globe after noon.
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