Modal identification is critical for structural condition monitoring. Variational mode decomposition (VMD) has been widely applied to identify modal parameters and has achieved excellent performance. ...It is crucial for VMD to predefine the decomposition parameters, that is, the mode number and balance factor. However, in practical engineering, abnormal impulses and heavy noise render it difficult to preset the mode number and balance factor. Therefore, a novel method, termed orthogonal and recursive VMD (ORVMD), is proposed to overcome the difficulty of setting decomposition parameters in advance. ORVMD consists of two components: recursive VMD (RVMD) and a rough-to-precise decomposition scheme based on an orthogonal algorithm. RVMD is an iterative method of VMD that is used to circumvent the difficulty of predefining the mode number. A rough-to-precise decomposition scheme based on an orthogonal algorithm is proposed to address the difficulty of setting the balance factor. Furthermore, the proposed ORVMD in combination with the Hilbert transform (HT) is employed to estimate the modal parameters of the structures. The raw signals are pre-processed by using the random decrement technique (RDT) to obtain its random decrement signature (RDS) and then the proposed method is applied to the RDS to identify the modal parameters of a simulated system and a real arch bridge. The obtained results show that the proposed method outperforms other existing methods in separating multicomponent signals; thus, it is an efficient method for identifying the natural frequencies and damping ratios of structures.
Electrospinning is an efficient method of producing nanofibers out of polymers that shows a great potential for the filtration territory. Featuring water-soluble chitosan (WS-CS), a low-pollution ...process and a self-made needleless machine, PVA/WS-CS nanofibrous membranes were prepared and evaluated for nanofiber diameter, bacteriostatic property, filtration efficiency, pressure drop, and quality factor. Test results indicate that the minimal fiber diameter was 216.58 ± 58.15 nm. Regardless of the WS-CS concentration, all of the PVA/WS-CS nanofibrous membranes attained a high porosity and a high water vapor transmission rate (WVTR), with a pore size of 12.06-22.48 nm. Moreover, the membranes also exhibit bacteriostatic efficacy against
, an optimal quality factor of 0.0825 Pa
, and a filtration efficiency as high as 97.0%, that is 72.5% higher than that of common masks.
A novel platform for effective "turn-on" fluorescence sensing of lead ions (Pb(2+)) in aqueous solution was developed based on gold nanoparticle (AuNP)-functionalized graphene. The ...AuNP-functionalized graphene exhibited minimal background fluorescence because of the extraordinarily high quenching ability of AuNPs. Interestingly, the AuNP-functionalized graphene underwent fluorescence restoration as well as significant enhancement upon adding Pb(2+), which was attributed to the fact that Pb(2+) could accelerate the leaching rate of the AuNPs on graphene surfaces in the presence of both thiosulfate (S(2)O(3)(2-)) and 2-mercaptoethanol (2-ME). Consequently, this could be utilized as the basis for selective detection of Pb(2+). With the optimum conditions chosen, the relative fluorescence intensity showed good linearity versus logarithm concentration of Pb(2+) in the range of 50-1000 nM (R = 0.9982), and a detection limit of 10 nM. High selectivity over common coexistent metal ions was also demonstrated. The practical application had been carried out for determination of Pb(2+) in tap water and mineral water samples. The Pb(2+)-specific "turn-on" fluorescence sensor, based on Pb(2+) accelerated leaching of AuNPs on the surface of graphene, provided new opportunities for highly sensitive and selective Pb(2+) detection in aqueous media.
A numerical study is made on the dynamic through-soil interaction between underground station and nearby pile supported surface structure on viscous-elastic soil layer, under vertically incident S ...wave. This paper, as a companion of another paper written by the authors 1, focuses on the influence of presence of adjacent surface structure on seismic response of underground structure, while the reference 1 centers on the influence of presence of adjacent underground structure on seismic response of surface structure. To this end, a commercial software product for finite element analysis, ANSYS, has been further developed and enhanced for calculation in frequency domain, in which hysteretic damping can be considered for both the soil and the structures, so that structure-soil-structure interaction (SSSI) can be investigated by via a direct methodology. A discussion is made on the influence of arrangement of structures, distances between structures, shaking direction of seismic wave, shear wave velocity and damping of soil, scale and burial depth of underground structure, storey number, stiffness, style and pile length of surface structure on SSSI, in terms of horizontal relative displacement of underground structure. Maximum relative displacement responses are also presented for 12 seismic inputs. Arrangement and shaking direction are two of the most important factors. The system response can be either amplified or attenuated according to the distance between adjacent structures, related to dynamic properties of the overall system. Those underground structures, surrounded by buildings with the fundamental frequency approximate to that of free field, are heavily affected.
•We reviewed studies about interaction of surface structure and underground structure.•ANSYS has been further developed and enhanced for damping of hysteretic type.•We discussed the influence of sruface structure on the neighboring subway station.•We examined the influence parameter of the dynamic interaction.
The seismic behavior of a slope site has a critical impact on its stability and the seismic response of structures located on or near the slope. In this paper, a hybrid boundary method(HBM) is ...proposed for the site response analysis of slopes. Viscous and viscous-spring boundaries are applied in the HBM and equivalent loads are calculated separately on the bottom and the lateral boundary. A horizontally extended model is used to verify the HBM. The results show that the maximum error of the HBM is only 2.010%. On the ground surface of the slope site, amplification occurs at the crest side and de-amplification occurs at the toe side under various cases. The ratio of the maximum and minimum PGA on the ground surface could exceed 2. Therefore, great attention should be paid to the spatial variability of ground motion on slope sites. The HBM is also compared with four conventional approaches. The maximum errors of all the conventional approaches exceed 70%. These examples demonstrate that the HBM has much higher accuracy in practice than conventional approaches.
•A hybrid boundary method(HBM) is proposed for the site response analysis of slopes.•The effectiveness and accuracy of the proposed method has been verified.•The computational accuracy of the HBM and four conventional approaches are compared.
The dynamic through-soil interaction between underground station and nearby pile supported structure on viscous–elastic soil layer, under vertically incident S wave, is numerically studied. To this ...end, a commercial software for finite element analysis, ANSYS, has been further developed and enhanced for calculation in frequency domain, in which damping of hysteretic type can be considered for both the soil and the structures, so that structure–soil–structure interaction (SSSI) can be investigated making use of a direct methodology. The influence of arrangement of structures, shaking direction of seismic wave, distances between structures, shear wave velocity, damping of soil, burial depth and number of spans of underground structure on SSSI, in terms of horizontal acceleration magnification factor of ground structure, is addressed. For ground structure, different lengths of pile, stiffnesses, styles, and numbers of storeys and structures are considered. Maximum acceleration responses are also presented for 12 seismic inputs. Arrangement and shaking direction are two of the most important factors. The system response can be either amplified or attenuated according to the distance between adjacent buildings, which has been related to dynamic properties of the overall system. Those neighboring low-slung buildings around underground structure are heavily affected.
•We reviewed studies about interaction of ground structure and underground structure.•ANSYS has been further developed and enhanced for damping of hysteretic type.•We discussed the influence of subway station on the neighboring ground structure.•We examined the influence parameter of the dynamic interaction.
This paper first discusses the limitation that the intrinsic mode functions (IMFs) decomposed by the empirical mode decomposition (EMD) in Hilbert-Huang transform (HHT) are not orthogonal. As an ...improvement to the HHT method, three orthogonal techniques (the forward, backward and arbitrary sequence orthogonalization algorithms) based on the Gram-Schmidt method are then proposed to obtain the completely orthogonal IMFs. According to the orthogonal index and the energy index, the effectiveness of the proposed technique and algorithms is validated through a synthetic signal generated by the combination of three sinusoidal waves with different frequencies and the El Centro (1940, N-S) earthquake accelerogram. By taking the El Centro (1940, N-S) earthquake accelerogram as an example, the problem that whether the orthogonal IMFs satisfy the requirements of IMF is discussed, then the backward and the arbitrary sequence orthogonalization algorithms are recommended. Three historic earthquake accelerograms are analyzed by using the recommended orthogonalization algorithms combined with the Hilbert spectral analysis. The results show that the orthogonal Hilbert spectrum and the orthogonal Hilbert marginal spectrum can produce more faithful representation of earthquake accelerograms than the Hilbert spectrum and the Hilbert marginal spectrum, and they can be used to quantitatively characterize the energy distribution of earthquake accelerograms at different frequency regions.
•In-depth analyses for not exactly orthogonal nature of intrinsic mode functions.•New orthogonal technique and orthogonalization algorithms for obtaining completely orthogonal IMFs.•Validated effectiveness of the proposed technique and algorithms in practical applications.•More reliable representation of earthquake accelerograms produced by the proposed orthogonal Hilbert spectrum.
Cyclophilin 1 (TvCyP1), a cyclophilin type peptidyl-prolyl isomerase present in the human parasite Trichomonas vaginalis, interacts with Myb1 and assists in its nuclear translocation. Myb1 regulates ...the expression of ap65-1 gene that encodes for a disease causing cytoadherence enzyme. Here, we determined the crystal structures of TvCyP1 and its complex with the minimum TvCyP1-binding sequence of Myb1 (Myb1
), where TvCyP1 formed a homodimer, unlike other single domain cyclophilins. In the complex structure, one Myb1
peptide was bound to each TvCyP1 protomer, with G106-P107 and Y105 fitting well into the active site and auxiliary S2 pocket, respectively. NMR data further showed that TvCyP1 can catalyze the cis/trans isomerization of P107 in Myb1
. Interestingly, in the well-folded Myb1 protein (Myb1
), the minimum binding sequence adopted a different conformation from that of unstructured Myb1
peptide, that could make P107 binding to the active site of TvCyP1 difficult. However, NMR studies showed that similar to Myb1
peptide, Myb1
also interacted with the active site of TvCyP1 and the dynamics of the Myb1
residues near P107 was reduced upon interaction. Together, the structure of TvCyP1 and detailed structural insights on TvCyP1-Myb1 interaction provided here could pave the way for newer drugs to treat drug-resistant strains.
The seismic responses of a long-span cable-stayed bridge under uniform excitation and traveling wave excitation in the longitudinal direction are, respectively, computed. The numerical results show ...that the bridge’s peak seismic responses vary significantly as the apparent wave velocity decreases. Therefore, the traveling wave effect must be considered in the seismic design of long-span bridges. The bridge’s peak seismic responses do not vary monotonously with the apparent wave velocity due to the traveling wave resonance. A new traveling wave excitation method that can simplify the multisupport excitation process into a two-support excitation process is developed.
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