Health Monitoring of Metallic Structures with Electromechanical Impedance and Piezoelectric Sensors.

In order to monitor the health condition of structures in a more sensitive and accurate way, a novel and universal methodology called direct coupling mechanical impedance (DCMI) for characteristic signatures extraction is presented in this paper. This methodology is used to obtain DCMI signatures from measured raw signatures (RSs) with the surface-bonded piezoelectric sensors (PZT), which is developed from a pertinent electromechanical impedance (EMI) theoretical model for surface-bonded circular PZT. The proposed DCMI methodology has the advantages of simple calculation and magnifying the signatures when compared with the existing methods. Combining the extracted DCMI signatures with the root mean square deviation (RMSD) index is able to quantify the correlation between the health condition and the signatures variation more effectively. To verify the effectiveness of proposed DCMI methodology, experiments are conducted on aluminum plates and a part of fuselage in detail. The experimental results sufficiently demonstrate that the presented universal DCMI methodology possesses better sensitivity than the raw signatures when utilized for evaluating the health condition of metallic structures, including those made of metal-matrix nanomaterials

Monitoring of Fiber-Reinforced Composite Single-Lap Joint with Electromechanical Impedance of Piezoelectric Transducer.

The single-lap joint of fiber-reinforced composites is a common structure in the field of structure repair, which has excellent mechanical properties. To study and monitor its quasi-static response behavior under external load, two methodologies called effective structural mechanical impedance (ESMI) and reduced-ESMI (R-ESMI) are presented in this article. A two-dimensional electromechanical impedance (EMI) model for a surface-bonded square piezoelectric transducer (PZT) is adopted to extract more sensitive signatures from the measured raw signatures. There are two major advantages of the monitoring scheme based on ESMI and R-ESMI signatures: (1) excellent monitoring results with less signatures to process, (2) the ability to monitor the quasi-static behavior of a single-lap joint with previously ignored susceptance signatures. Combining the extracted ESMI signatures with the index of root-mean-square deviation, the quasi-static behavior of single-lap joints can be effectively quantified. To test the effectiveness of ESMI methodology, verifying experiments were conducted. The experimental results convincingly demonstrated that the presented ESMI and R-ESMI methodologies have good feasibility in monitoring the quasi-static behavior of a fiber-reinforced composite single-lap joint. The proposed method has potential application in the field of structural health monitoring (SHM)

Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Defect engineering of metal–organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of defects in MOFs—either point defects or extended ones—has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered ‘missing linker’ and ‘missing cluster’ defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose

A spatio-temporally constrained gene regulatory network directed by PBX1/2 acquires limb patterning specificity via HAND2.

A lingering question in developmental biology has centered on how transcription factors with widespread distribution in vertebrate embryos can perform tissue-specific functions. Here, using the murine hindlimb as a model, we investigate the elusive mechanisms whereby PBX TALE homeoproteins, viewed primarily as HOX cofactors, attain context-specific developmental roles despite ubiquitous presence in the embryo. We first demonstrate that mesenchymal-specific loss of PBX1/2 or the transcriptional regulator HAND2 generates similar limb phenotypes. By combining tissue-specific and temporally controlled mutagenesis with multi-omics approaches, we reconstruct a gene regulatory network (GRN) at organismal-level resolution that is collaboratively directed by PBX1/2 and HAND2 interactions in subsets of posterior hindlimb mesenchymal cells. Genome-wide profiling of PBX1 binding across multiple embryonic tissues further reveals that HAND2 interacts with subsets of PBX-bound regions to regulate limb-specific GRNs. Our research elucidates fundamental principles by which promiscuous transcription factors cooperate with cofactors that display domain-restricted localization to instruct tissue-specific developmental programs

Abnormal Placental Development and Early Embryonic Lethality in EpCAM-Null Mice

BACKGROUND: EpCAM (CD326) is encoded by the tacstd1 gene and expressed by a variety of normal and malignant epithelial cells and some leukocytes. Results of previous in vitro experiments suggested that EpCAM is an intercellular adhesion molecule. EpCAM has been extensively studied as a potential tumor marker and immunotherapy target, and more recent studies suggest that EpCAM expression may be characteristic of cancer stem cells. METHODOLOGY/PRINCIPAL FINDINGS: To gain insights into EpCAM function in vivo, we generated EpCAM -/- mice utilizing an embryonic stem cell line with a tacstd1 allele that had been disrupted. Gene trapping resulted in a protein comprised of the N-terminus of EpCAM encoded by 2 exons of the tacstd1 gene fused in frame to betageo. EpCAM +/- mice were viable and fertile and exhibited no obvious abnormalities. Examination of EpCAM +/- embryos revealed that betageo was expressed in several epithelial structures including developing ears (otocysts), eyes, branchial arches, gut, apical ectodermal ridges, lungs, pancreas, hair follicles and others. All EpCAM -/- mice died in utero by E12.5, and were small, developmentally delayed, and displayed prominent placental abnormalities. In developing placentas, EpCAM was expressed throughout the labyrinthine layer and by spongiotrophoblasts as well. Placentas of EpCAM -/- embryos were compact, with thin labyrinthine layers lacking prominent vascularity. Parietal trophoblast giant cells were also dramatically reduced in EpCAM -/- placentas. CONCLUSION: EpCAM was required for differentiation or survival of parietal trophoblast giant cells, normal development of the placental labyrinth and establishment of a competent maternal-fetal circulation. The findings in EpCAM-reporter mice suggest involvement of this molecule in development of vital organs including the gut, kidneys, pancreas, lungs, eyes, and limbs

Development of a Bioaerosol Experimental System for Virus Stability Measurement

Respiratory infections, such as SARS, MERS, and COVID-19, have highlighted the importance of studying the transmission mechanism in indoor environments. Virus stability affected by temperature, humidity or particle size has remained inadequately investigated. A bioaerosol experiment system is developed in this study for virus stability measurement. Virus-laden droplets are generated by a Collison nebulizer, and afterwards enter a mixing chamber, where is filled with conditioned air. After complete evaporation, droplet nuclei go through an impactor, and only those smaller than the cut-off size (1μm, 2.5μm or 10μm) can finally enter Goldberg Drum to suspend for a designed period for later sampling and stability measurement. Temperature (20℃-40℃) and relative humidity (30%-80%) can be well controlled throughout the experiment. According to the virus inactivation mechanism, the sampling process is divided into the initial stage involving droplet evaporation and the subsequent aerosol suspension stage. Decay coefficients obtained by this method can be used for evaluation of virus exposure risks in indoor environments and for the development of efficient engineering control strategies

Health Monitoring of Metallic Structures with Electromechanical Impedance and Piezoelectric Sensors

In order to monitor the health condition of structures in a more sensitive and accurate way, a novel and universal methodology called direct coupling mechanical impedance (DCMI) for characteristic signatures extraction is presented in this paper. This methodology is used to obtain DCMI signatures from measured raw signatures (RSs) with the surface-bonded piezoelectric sensors (PZT), which is developed from a pertinent electromechanical impedance (EMI) theoretical model for surface-bonded circular PZT. The proposed DCMI methodology has the advantages of simple calculation and magnifying the signatures when compared with the existing methods. Combining the extracted DCMI signatures with the root mean square deviation (RMSD) index is able to quantify the correlation between the health condition and the signatures variation more effectively. To verify the effectiveness of proposed DCMI methodology, experiments are conducted on aluminum plates and a part of fuselage in detail. The experimental results sufficiently demonstrate that the presented universal DCMI methodology possesses better sensitivity than the raw signatures when utilized for evaluating the health condition of metallic structures, including those made of metal-matrix nanomaterials

Controlling Charge Transport in Molecular Wires through Transannular <i>π–π</i> Interaction

This paper describes the influence of the transannular π–π interaction in controlling the carrier transport in molecular wires by employing the STM break junction technique. Five pentaphenylene-based molecular wires that contained [2.2]paracyclophane-1,9-dienes (PCD) as the building block were prepared as model compounds. Functional substituents with different electronic properties, ranging from strong acceptors to strong donors, were attached to the top parallel aromatic ring and used as a gate. It was found that the carrier transport features of these molecular wires, such as single-molecule conductance and a charge-tunneling barrier, can be systematically controlled through the transannular π–π interaction

Effect of Ultrafine Calcium Silicate on the Mechanical Properties of Oil Well Cement-Based Composite at Low Temperature

A low-temperature environment will reduce the hydration rate of oil well cement-based composites, resulting in the slow development of mechanical strength, which cannot meet the requirements of cementing operations. In order to improve the early strength of cement paste under low temperature, the influence of ultrafine calcium silicate powder on the rheological properties, water loss, thickening time and permeability of oil well cement-based composites was evaluated. The compressive strength, flexural strength and impact strength of cement paste with different contents of ultrafine calcium silicate were studied. The hydration process and microstructure of cement paste were analyzed by hydration heat measurement system, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results show that the ultrafine calcium silicate has a certain impact on the rheology and thickening time of cement slurry, and dispersants and retarders are required to adjust these properties when it is used. The ultrafine calcium silicate can improve the stability of cement slurry and reduce water loss and permeability. In addition, under the condition of curing at 20 °C for 24 h, the compressive strength, flexural strength and impact strength of cement paste with 8% ultrafine calcium silicate content increased by 243.0%, 278.5% and 66.3%, respectively, compared with the pure cement paste. The hydration of cement slurry is accelerated by ultrafine calcium silicate, the hydration temperature is enhanced and the heat release of hydration is increased. The ultrafine calcium silicate improves the formation degree of hydration products and makes the structure of cement paste more compact. The research results help to design a low-temperature and early-strength cement slurry system