Hook Structures Research Articles

Microstructure and Mechanical Properties of Mg-Li/Al Dissimilar Joints via Dynamic Support Friction Stir Lap Welding.

In this study, two-mm-thick dual-phase LA103Z Mg-Li and 6061 Al alloys, known for their application in lightweight structural designs, were joined using dynamic support friction stir lap welding (DSFSLW). The microstructural evolution and mechanical properties of dissimilar joints were investigated at different welding speeds. The analysis revealed two distinct interfaces: the diffusion interface and the mixed interface. The diffusion interface, characterized by a pronounced diffusion zone, is formed under slower welding speeds. The diffusion zone height, the effective lap width, and the interface layer thickness decrease with increasing welding speed due to low plastic deformation capacity and weak interfacial reactions. Conversely, the mixed interface, associated with higher welding speeds, contained large Al fragments. The extremely high microhardness values (130.5 HV) can be ascribed to the formation of intermetallic compounds (IMCs) and strain-hardened Al fragments. Notably, the maximum shear strength achieved was 175 N/mm at a welding speed of 20 mm/min. The fracture behavior varied significantly with the interface type; the diffusion interface showed enhanced mechanical strength due to better intermetallic reactions and interlocking structures, while the mixed interface displayed more linear crack propagation due to weaker IMCs and the absence of hook structures. Fracture surface analysis indicates that fractures are more likely to propagate through the Al matrix and interface layers.

Nature‐Inspired Directional Microneedle Structures for Reversible Gripping on Skin and Fibrous Materials

Plants such as Galium aparine show directional gripping to various surfaces because of their microscale hook structures. A bio‐inspired artificial version of microhooks holds potential as a bidirectional, reversible, and reusable dry adhesive for soft, wet, or fibrous substrates such as skin or textiles. However, current methods for fabricating 3D structures are often costly, time‐consuming, or require precise alignment steps. Herein, a facile, cost‐effective, scalable, and unconventional microfabrication technique is proposed using tilted photolithography on a rotary stage and shear molding to fabricate a soft polydimethylsiloxane polymer mold containing the inverse replica of directional microneedle structures. To demonstrate the proof‐of‐concept, polyurethane is then added to the mold to obtain directional microneedles, referred to as microhooks. Friction force measurements using a nanotribometer show anisotropic performance (strong attachment in one direction and easy detachment in the opposite direction over multiple cycles) similar to the natural microhooks. Tribological characterization of the microhooks shows a gripping force 2.25 times greater than the sliding force. The fabricated microhook structures also provide an adhesion force of ≈0.62 N cm−2 to artificial skin. This biomimetic approach promises precise adhesion control and material versatility for attaching wearable devices and patches to the skin in biomedical applications.

Double side friction stir Z shape butt lap welding of dissimilar titanium aluminum alloys

Achieving excellent mechanical performance of medium-thick Ti/Al dissimilar joints is important in many industrial applications. However, due to the inherent heat generation mode associated with conventional friction stir welding (FSW), it is impossible to achieve sound medium-thick Ti/Al dissimilar joints. Although double side friction stir welding (DS-FSW) has been reported to solve the problems of conventional FSW. The inherent problems of forming hook structure and interface cracking in the center of the DS-FSW joints significantly weaken the joint performance. Therefore, an innovative double-side friction stir Z shape butt-lap welding (DS-FSZW) process was proposed to eliminate the inherent problems of conventional DS-FSW. The research objective of this work was to reveal the physical mechanisms of the novel DS-FSZW by the combination of numerical simulation and experimental characterization for optimizing the welding parameters. The influence of tool shoulder diameter on the heat generation, heat transfer, plastic material flow, microstructure evolution and mechanical properties of medium-thick dissimilar Ti/Al DS-FSZW joint has been systematically studied. The results indicate that the innovative DS-FSZW process lowers the axial force compared to the conventional DS-FSW, and the centerlines of the first and the second sides welds are staggered. Those are beneficial to inhibiting the cracking of the first-side weld at the interface. In addition, the DS-FSZW method eliminates the hook structures and cracks at the center of the conventional DS-FSW joint and also adds a lap joining interface, which significantly enhances the tensile strength of the joint from 150.7 MPa to 262.5 MPa, which is increased by 74%. Optimization of the shoulder diameter of DS-FSZW from 18 mm to 12 mm reduces the welding heat input and significantly thins the thickness of the IMCs layers at the Ti/Al interface. This helps to suppress the cracking at the Ti/Al lap interface and refine the grains. As a result, thus the tensile strength of the DS-FSZW joint increases from 262.5 MPa to 312.5 MPa, which is increased by 19%. The medium-thick Ti/Al dissimilar DS-FSZW joint at the tool shoulder diameter of 12 mm fracture at the SZ. It proves that the novel DS-FSZW is a suitable welding method for joining medium-thick dissimilar Ti to Al alloys.

Thermodynamic driving mechanisms for the formation of global precipitation extremes and ecohydrological effects

Global warming has altered the thermodynamic and dynamic environments of climate systems, affecting the biogeochemical processes between the geosphere and atmosphere, which has significant impacts on precipitation extremes and the terrestrial carbon budget of ecosystems. Existing studies have reported a hook structure for precipitation extreme-temperature relationships but have rarely examined the underlying physical mechanisms. Previous studies have also failed to quantify the impact of precipitation on ecosystem productivity, hindering the assessment of future extreme climatic hazards and potential ecosystem risks. To reveal the thermodynamic driving mechanisms for the formation of global precipitation extremes and ecohydrological effects, this study utilizes over ten multisource datasets (i.e., satellite, reanalysis, climate model, land surface model, machine learning reconstruction, and flux tower measurements). We first assess the response of water-heat-carbon flux to precipitation extremes and explain the underlying physical mechanisms behind the hook structures in terms of atmospheric thermodynamics and dynamics. Based on outputs from five global climate models (GCMs) under ISIMIP3b, we project future changes in the hook structures as well as their impacts on precipitation extremes. Finally, we discuss the impact of precipitation on the terrestrial carbon budget by using outputs from the CLM4.5 model. The results show that precipitation extremes are usually accompanied by strong exchanges of water and heat and demonstrate a nonlinear relationship between precipitation and ecosystem productivity. The intensity (duration) of extreme precipitation is intensifying (decreasing) over most areas of the globe, whereas three-dimensional precipitation events are becoming more concentrated. Atmospheric dynamics play a key role in shaping the hook structure. The structure is not stable; it shifts under climate change and is projected to result in a 10–10% intensification in precipitation by the end of this century. Moderate levels of precipitation contribute to carbon assimilation in ecosystems, and the response of the carbon budget to precipitation is relatively stable under climate change.

Morphological structure of the tongue of the European badger (Meles meles).

This study aimed to reveal the morphological aspects of the tongue and investigate the histologic and scanning electron microscopic (SEM) findings of the papillae on the tongue of the European badger. Two adult European badgers were used as material. The tongues of the European badgers were removed via the dissection method, and morphometric measurements were taken. The tongues were fixed in 10% buffered formalin solution for histological examination, and the SEM procedure was applied to the tongues. Three types of papillae were observed on the tongues: filiform, fungiform, vallate papillae. The different shapes (hook or conical structures) of filiform papillae were observed on the whole tongue. Fungiform papillae were found scattered in filiform papillae. Six vallate papillae were found on the dorsal face of the middle and root of the tongues. In the root of the tongue, the lingual tonsil was observed in the lentiform shape. The authors believe that this research will provide contributions to morphological knowledge about the tongue of the badger, which is a poorly known species.

Three Research-Based Quantitative Reasoning Modules for Introductory Organismal Biology Laboratories

We have designed three laboratory modules for an introductory organismal biology course with an emphasis on quantitative reasoning and data analysis skills. Module 1 tests for dimorphism in crayfish chelae using a paired statistical design. Module 2 tests for allometric growth of tapeworm hook structures using a regression model. Module 3 tests for differences in stomatal densities between two groups of plants using a two-sample statistical approach. For all three modules, we emphasize the use of confidence intervals to draw statistical conclusions about hypotheses. Knowledge about the basic biology of animals and plants is required, including arthropods, platyhelminths, and vascular plants. Background reading on dimorphism, allometry, and transpiration provides the necessary foundation to develop questions and hypotheses. Some familiarity with R is necessary for both students and instructors, although the activities can be modified for analysis with Excel or another statistical package. These modules can be taught independently or together as a unit within a course. As stated in the AAAS document, <em>Vision and Change: A Call to Action</em>, the ability to use quantitative reasoning is a core competency that must be developed by all biology students. These modules address the call for instruction in quantitative reasoning and provide a hands-on active introduction to key tools that will be required to build students&rsquo; statistical repertoire in more advanced courses. <em>Primary Image:</em>&nbsp;A highlight of the three modules used in our introductory organismal biology course, including the use of calipers to test for dimorphism in the size of crayfish chelae (upper right), a leaf impression (lower right) from a hydrangea plant (lower left) used to test hypotheses about stomata densities, and the image of an <em>Echinococcus </em>tapeworm (upper left) to test hypotheses about allometry.&nbsp;&nbsp;

Thermodynamic response of precipitation extremes to climate change and its impacts on floods over China

<p indent=0mm>As the planet warms, shifts in the thermodynamic and dynamic environments of the climate system exert substantial impacts on the energy budget and water cycle. Understanding the response of precipitation extremes to climate change is essential for mitigating weather-related hazards and facilitating adaptive water resources management. The moisture holding capacity of the atmosphere, governed by the Clausius-Clapeyron (C-C) relationship, increases with temperature at a rate of about 7%/°C. Thermodynamically, precipitation intensity is expected to increase exponentially and worsen flood conditions with atmospheric warming. However, both observational and satellite data have revealed a nonmonotonic (hook) scaling of precipitation and storm runoff, in which extremes strengthen with warming temperature up to a peak point (<italic>T</italic>_pp) and decline thereafter. Few studies have yet considered whether and why the hook structure might change in a future warming climate. Moreover, existing studies have largely failed to detect and attribute changes of extreme precipitation to atmospheric thermodynamics versus dynamics, limiting reliable projection of future hydrological hazards and climate simulations. Here, we build upon existing studies to understand how precipitation and storm runoff scaling might change over Chinese mainland. We use gridded observational data to examine the temperature scaling of precipitation and storm runoff extremes, extending the C-C relationship. Using the ERA5 reanalysis dataset, we diagnose the impacts of total column water vapor (TCWV), convective available potential energy (CAPE) and relative humidity on precipitation extremes. After partitioning the thermodynamic and dynamic contributions of precipitation extremes based on the energy budget and water vapor balance, we quantify the underlying physical mechanisms of hook structures. Future climate scenarios are projected by using a large ensemble from 21 global climate models (GCMs) within Coupled Model Inter-comparison Project Phase-6 (CMIP6). Future streamflow series of 151 basins are projected by forcing hydrological model with bias-corrected climate model outputs. We quantify changes in the hook structures and their <italic>T</italic>_pp, and investigate implications of these shifts for future storms and flooding. The results show that relative humidity usually decreases with warming near-surface temperatures over most areas of China, while the TCWV and CAPE exhibit positive scaling rates with temperatures. The ERA5 reanalysis data over China reveals that atmospheric dynamics are responsible for the intensification of precipitation extremes and even flooding under very warm temperatures. The daily bias correction method reduces the systematical biases of GCMs outputs adequately, and captures extreme precipitation and temperatures well. By using four different hydrological models, we find that the Xinanjiang model typically exhibits the best performance in simulating daily streamflow over Chinese mainland. Projections of future hydro-climatological scenarios indicate that the hook structures do not set a firm upper-bound constraint on the intensification of extremes; rather, both the hook structure and the <italic>T</italic>_pp shift toward warmer temperatures in a warming climate. Alongside the shifts in <italic>T</italic>_pp, future storm and flooding extremes are projected to intensify by 20%−30%. These findings highlight the urgency in enhancing societal resilience to climate change, and understanding how the intensification of weather-related hazards might affect existing infrastructure and ecosystems.

Does the Hook Structure Constrain Future Flood Intensification Under Anthropogenic Climate Warming?

AbstractAtmospheric moisture holding capacity increases with temperature by about 7% per °C according to the Clausius‐Clapeyron relationship. Thermodynamically then, precipitation intensity should exponentially intensify and thus worsen flood conditions as the climate warms. However, regional and global analyses often report a nonmonotonic (hook) scaling of precipitation and runoff, in which extremes strengthen with rising temperature up to a maximum or peak point (Tpp) and decline thereafter. The underlying cause of this hook structure is not yet well‐understood, and whether it may shift and/or regulate storm runoff extremes under anthropogenic climate warming remains unknown. Here, we examine temperature scaling of precipitation and storm runoff extremes under different climate conditions using observations and large ensemble hydroclimatic simulations over mainland China. In situ observations suggest a spatially homogeneous, negative response of relative humidity to warming climates over 34.6% of the land area, and the remaining hook‐dominated regions usually show a colder Tpp than that of precipitation or storm runoff extremes. The precipitation and streamflow series over mainland China's catchments throughout the 21st century are projected by a model cascade chain under a high‐end emission scenario (RCP 8.5), which involves 31 CMIP5 climate models, 11 CMIP6 climate members, a daily bias correction method, and four lumped conceptual hydrological models. The CMIP5 ensemble projects that the hook structures shift toward warmer temperature bins, resulting in 10%–30% increases in storm runoff extremes over mainland China, while the CMIP6 ensemble projects more severe flood conditions in future warming climates.

A Proline-Rich Element in the Type III Secretion Protein FlhB Contributes to Flagellar Biogenesis in the Beta- and Gamma-Proteobacteria.

Flagella are bacterial organelles of locomotion. Their biogenesis is highly coordinated in time and space and relies on a specialized flagellar type III secretion system (fT3SS) required for the assembly of the extracellular hook, rod, and filament parts of this complex motor device. The fT3SS protein FlhB switches secretion substrate specificity once the growing hook reaches its determined length. Here we present the crystal structure of the cytoplasmic domain of the transmembrane protein FlhB. The structure visualizes a so-far unseen proline-rich region (PRR) at the very C-terminus of the protein. Strains lacking the PRR show a decrease in flagellation as determined by hook- and filament staining, indicating a role of the PRR during assembly of the hook and filament structures. Phylogenetic analysis shows that the PRR is a primary feature of FlhB proteins of flagellated beta- and gamma-proteobacteria. Taken together, our study adds another layer of complexity and organismic diversity to the process of flagella biogenesis.

Flow mechanism between purge flow and mainstream in different turbine rim seal configurations

The rim seal is used to prevent mainstream ingestion to the gap between the vane of a turbine and its blade. In this article, the dolphin lip with a hook configuration and a large seal cavity with hook structures are designed based on the high-pressure turbine datum single shark lip rim seal configuration. The sealing effect and parameters of the flow field are measured by an experiment method and a numerical simulation is used to explain the mechanism. For three configurations, the effect of the leakage slot vortex on the efficiency of the seal and the influence of leakage vortex, generated by the interaction between purge flow and mainstream flow, are discussed in depth. The result shows that the reverse vortex formed by the dolphin lip rim seal with hook structure will increase the sealing efficiency. The seal configuration with a large cavity improves sealing efficiency to a greater extent than the datum structure. At different purge flow rates and with unequal seal structures, the purge flow produces three types of leakage vortices in the passage. Besides, the seal configuration with dolphin lip produces a Kelvin-Helmholtz instability at the interface of the purge and the mainstream flows at a low purge flow rate to induce new leakage vortex branches in the passage of the blade.

Increased Refractive Index Sensitivity by Circular Dichroism Sensing through Reduced Substrate Effect

An optical sensor based on the localized surface plasmon resonance (LSPR) of chiral Au nanohooks with increased refractive index (RI) sensitivity via circular dichroism (CD) measurements is presented. Programmed control of sample rotation combined with angled physical vapor deposition is applied to hole-mask colloidal lithography to provide in process modification of the hole-masks and generate arrays of chiral nanostructures with an adjustable optical response. Extinction spectra with unpolarized light as well as circular dichroism measurements are compared for left- and right-handed hook structures. Analysis of the LSPR peak shift of the substrate-attached nanostructures revealed the CD measurements to be twice as sensitive as the measurements with unpolarized light (304 and 146 nm RIU–1, respectively) and close to the maximum predicted for LSPR sensing at this spectral region (∼700 nm). Finite-difference time-domain simulations with different substrate materials show that the difference in RI sensitivi...

Grasping Claws of Bionic Climbing Robot for Rough Wall Surface: Modeling and Analysis

Aiming at the inspection of rough stone and concrete wall surfaces, a grasping module of cross-arranged claw is designed. It can attach onto rough wall surfaces by hooking or grasping walls. First, based on the interaction mechanism of hooks and rough wall surfaces, the hook structures in claw tips are developed. Then, the size of the hook tip is calculated and the failure mode is analyzed. The effectiveness and reliability of the mechanism are verified through simulation and finite element analysis. Afterwards, the prototype of the grasping module of claw is established to carry out grasping experiment on vibrating walls. Finally, the experimental results demonstrate that the proposed cross-arranged claw is able to stably grasp static wall surfaces and perform well in grasping vibrating walls, with certain anti-rollover capability. This research lays a foundation for future researches on wall climbing robots with vibrating rough wall surfaces.

Fluorescent Microscopy Techniques to Study Hook Length Control and Flagella Formation.

The bacterial flagellum is a sophisticated motility device made of about 30 different proteins and consists of three main structural parts: (1) a membrane-embedded basal body, (2) a flexible linking structure (the hook) that connects the basal body to, (3) the rigid filament that extends up to 10 μm from the cell surface. In Salmonella enterica serovar Typhimurium, the hook structure is controlled to a length of 55 nm by a molecular ruler protein, FliK. Only upon hook completion, FliK induces a switch in substrate specificity of the flagellar export apparatus, which allows secretion of filament-type substrates, such as flagellin. Up to 20,000 subunits of flagellin assemble one flagellar filament that extends several micrometers beyond the cell surface. The formation of hook and filament structures as hallmarks of the hook length control mechanism can be monitored by immunofluorescence microscopy as described in this chapter.

Chemical Sculpturing of Al Micro-Particles for Polymer Composites and Universal Polymer-Polymer Joints

Composite materials attract more and more attention due to their unique properties in many fields. For certain applications metal particle-polymer composites are very attractive, where e.g. lightweight heat-conductive composites are needed. For particle-polymer composites the typical problem is the deterioration of the mechanical properties of the polymer matrix due to poor adhesion at the polymer-metal particle interface. Our approach solves this problem by generating a mechanical interlocking surface structure on the metal particle surface via wet chemical etching which we call sculpturing. In this work commercially available granular Al micro-particles with a typical size distribution between 200 - 800 µm and a purity of 99.7 % is used. These Al particles are structured in an optimized aqueous HCl based electrolyte. The key idea is to balance the passivation and dissolution of the metal surface in such a way that the desired interlocking structures form. Similar to HNO3-HF based Si etchants, the employed electrolyte makes use of in-situ formed reaction products controlling the structuring homogeneity and reaction speed. Figure 1a) provides a top view on Al particles sculptured in such way with a magnification view in Fig. 1b). The sculptured surface structure consists of a multitude of rectangular structures with flat faces in a step-like arrangement or as free-standing hooks. These rectangular structures vary in size and are tilted towards each other depending on the crystal orientation. The EDX analysis confirms that the surface of these Al micro-particles after sculpturing is covered only by a native oxide layer. By adjusting the chemical fabrication process the Al micro-particles could be fully or partially sculptured. Correspondingly, the Al micro-particles showed a change in their optical properties depending on the etching duration. Fully-sculptured Al micro-particles are dark gray in color, partially structured ones are light-gray, and the untreated ones are silver colored. With these sculptured Al micro-particles polymer composites can be formed as shown in Fig. 1c. Here, a densely packed polythiourethane (PTU)-sculptured Al particle composite is formed in the shape of a dog bone. Tensile test results show that the addition of sculptured particles results in a strongly increased Young’s modulus and reaching at least the maximum tensile strength of the pure polymer, unlike in case of the addition of untreated Al micro-particles. In case of polydimethylsiloxane (PDMS) which is well-known for its poor adhesion to metals, polymers and ceramics, the effect on the increase of Young’s modulus is even far more pronounced as well as a tremendous increase in the maximum tensile strength. The fracture surfaces of all sculptured Al micro-particle-polymer composites showed always cohesive failure where even the particles themselves are torn apart, which is the best reachable adhesion strength. Another very important application for sculptured Al micro-particles could be adhesive-free joining of immiscible polymers like ethylene-vinyl acetate (EVA) and polyoximethylen (POM) or other low surface energy polymers. Here, the sculptured micro-particles are partially imprinted into the thermally-softened POM surface and then joined with the softened EVA. Owing to the hook and step structures of the sculptured particles a robust connection between the Al micro-particles and any polymer matrix is obtained. No matter how the sculptured particles are partially imprinted in the polymer surface, they stick to it and hinder delamination. This is impressively shown via tensile testing, where only cohesive failure within the EVA component is found, while the direct joint without particles and via untreated particles fail adhesively directly at the POM-EVA interface. Fig. 1: SEM top view on chemically sculptured a) Al micro-particles, b) in high magnification of the structured Al micro-particle surface and c) Al micro-particle filled PTU composite in the shape of dog bone. Figure 1

SLIPPING MAGNETIC RECONNECTIONS WITH MULTIPLE FLARE RIBBONS DURING AN X-CLASS SOLAR FLARE

ABSTRACT With the observations of the Solar Dynamics Observatory, we present the slipping magnetic reconnections with multiple flare ribbons (FRs) during an X1.2 eruptive flare on 2014 January 7. A center negative polarity was surrounded by several positive ones, and three FRs appeared. The three FRs showed apparent slipping motions, and hook structures formed at their ends. Due to the moving footpoints of the erupting structures, one tight semi-circular hook disappeared after the slippage along its inner and outer edges, and coronal dimmings formed within the hook. The east hook also faded as a result of the magnetic reconnection between the arcades of a remote filament and a hot loop that was impulsively heated by the under flare loops. Our results are accordant with the slipping magnetic reconnection regime in three-dimensional standard model for eruptive flares. We suggest that the complex structures of the flare are likely a consequence of the more complex flux distribution in the photosphere, and the eruption involves at least two magnetic reconnections.

Subsurface macro-inclusions and solidified hook character in aluminum-killed deep-drawing steel slabs

Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon (ULC) steel slabs and two low carbon (LC) aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-dispersive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200 μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density (ND) of subsurface inclusions larger than 200 μm decreased from 0.02 to 0 cm−2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200 μm were concentrated in the region near the slab center (3/8 width-5/8 width), where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.

Design, calibration and application of wireless sensors for structural global and local monitoring of civil infrastructures

Structural Health Monitoring (SHM) gradually becomes a technique for ensuring the health and safety of civil infrastructures and is also an important approach for the research of the damage accumulation and disaster evolving characteristics of civil infrastructures. It is attracting prodigious research interests and the active development interests of scientists and engineers because a great number of civil infrastructures are planned and built every year in mainland China. In a SHM system the sheer number of accompanying wires, fiber optic cables, and other physical transmission medium is usually prohibitive, particularly for such structures as offshore platforms and long-span structures. Fortunately, with recent advances in technologies in sensing, wireless communication, and micro electro mechanical systems (MEMS), wireless sensor technique has been developing rapidly and is being used gradually in the SHM of civil engineering structures. In this paper, some recent advances in the research, development, and implementation of wireless sensors for the SHM of civil infrastructures in mainland China, especially in Dalian University of Technology (DUT) and Harbin Institute of Technology (HIT), are introduced. Firstly, a kind of wireless digital acceleration sensors for structural global monitoring is designed and validated in an offshore structure model. Secondly, wireless inclination sensor systems based on Frequency-hopping techniques are developed and applied successfully to swing monitoring of large-scale hook structures. Thirdly, wireless acquisition systems integrating with different sensing materials, such as Polyvinylidene Fluoride(PVDF), strain gauge, piezoresistive stress/strain sensors fabricated by using the nickel powder-filled cement-based composite, are proposed for structural local monitoring, and validating the characteristics of the above materials. Finally, solutions to the key problem of finite energy for wireless sensors networks are discussed, with future works also being introduced, for example, the wireless sensor networks powered by corrosion signal for corrosion monitoring and rapid diagnosis for large structures.

Development of Wireless MEMS Inclination Sensor System for Swing Monitoring of Large-Scale Hook Structures

A modular wireless microelectromechanical system (MEMS) inclination sensor system (WMISS) is developed and tested for providing structural health monitoring of large-scale hook structures. The operating principle of a 3-D-MEMS-based dual-axis inclinometer is analyzed. A wireless MEMS sensor is integrated using sensing disposal, wireless communication, and power units. The WMISS is calibrated by using a laser displacement sensor in a pendular structure. The maximal error of the wireless MEMS inclination sensor is about 1%. The resolution is plusmn0.0025deg. With the new-type tuned mass damper control module, an experiment on a WMISS for the swing monitoring of a Lanjiang hook model is developed. Experimental results indicate that the developed WMISS is highly precise, convenient, stable, and low cost and has long range, and thus, a WMISS can accurately and conveniently monitor the swing of a Lanjiang hook model.

FlhB Regulates Ordered Export of Flagellar Components via Autocleavage Mechanism

The bacterial flagellum is a predominantly cell-external super-macromolecular construction whose structural components are exported by a flagellum-specific export apparatus. One of the export apparatus proteins, FlhB, regulates the substrate specificity of the entire apparatus; i.e. it has a role in the ordered export of the two main groups of flagellar structural proteins such that the cell-proximal components (rod-/hook-type proteins) are exported before the cell-distal components (filament-type proteins). The controlled switch between these two export states is believed to be mediated by conformational changes in the structure of the C-terminal cytoplasmic domain of FlhB (FlhB(C)), which is consistently and specifically cleaved into two subdomains (FlhB(CN) and FlhB(CC)) that remain tightly associated with each other. The cleavage event has been shown to be physiologically significant for the switch. In this study, the mechanism of FlhB cleavage has been more directly analyzed. We demonstrate that cleavage occurs in a heterologous host, Saccharomyces cerevisiae, deficient in vacuolar proteinases A and B. In addition, we find that cleavage of a slow-cleaving variant, FlhB(C)(P270A), is stimulated in vitro at alkaline pH. We also show by analytical gel-filtration chromatography and analytical ultracentrifugation experiments that both FlhB(C) and FlhB(C)(P270A) are monomeric in solution, and therefore self-proteolysis is unlikely. Finally, we provide evidence via peptide analysis and FlhB cleavage variants that the tertiary structure of FlhB plays a significant role in cleavage. Based on these results, we propose that FlhB cleavage is an autocatalytic process.

FlbT, the post-transcriptional regulator of flagellin synthesis in Caulobacter crescentus, interacts with the 5' untranslated region of flagellin mRNA.

Flagellar gene expression' in Caulobacter crescentus is regulated by a complex trans-acting hierarchy, in which the assembly of early structural proteins is required for the expression of later structural proteins. The flagellins that comprise the filament are regulated at both the transcriptional and the post-transcriptional levels. Post-transcriptional regulation is sensitive to the assembly of the flagellar basal body and hook structures. In mutant strains lacking these structures, flagellin genes are transcribed, but not translated. Mutations in the flagellar regulatory gene, flbT, restore flagellin translation in the absence of flagellar assembly. In this report, we investigate the mechanism of FlbT-mediated post-transcriptional regulation. We show that FlbT is associated with the 5' untranslated region (UTR) of fljK (25 kDa flagellin) mRNA and that this association requires a predicted loop structure in the transcript. Mutations within this loop abolished FlbT association and resulted in increased mRNA stability, indicating that FlbT promotes the degradation of flagellin mRNA by associating with the 5' UTR. We also assayed the effects on gene expression using mutant transcripts fused to lacZ. Interestingly, the mutant transcript that failed to associate with FlbT in vitro was still repressed in mutants defective in flagellum assembly, suggesting that other factors in addition to FlbT couple assembly to translation.