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Thermal images are used to visualise the crack forming processes in mortar prisms under the flexural strength test with a UTM (Universal Testing Machine). The surface temperature of the prisms increases as the stress on them increases. When the prisms are reinforced by carbon fibres, the aggregated fibres along the crack paths becomes distinctive due to their higher temperature compared with their surrounding mortar areas of the prisms. This enables to visualise the crack forming process. In this process, there is a moment of abrupt increase in the temperature gradient of the aggregated fibres. This moment matches closely to that of the crack on-set obtained from the video images of crack forming process taken with a panchromatic camera, with less than 2.2 % difference. The moment is also matched with that of sharp dropping in the force from the UTM after the peak. This sudden temperature gradient increase can be used to determine the crack on-set times of the prisms with a high accuracy. [ABSTRACT FROM AUTHOR]

The thermal properties of electrically heated carbon-fiber-reinforced mortar prisms with 0.5%, 1.0%, 1.5% and 2.0% of their volumes are investigated. Each prism dimension is 40 mm × 40 mm × 160 mm. When the constant power of 30W is applied to two conductive-gel strips painted on the prisms' surfaces as the electrodes, for 5 min, the prisms show that: (1) their surface heating patterns have mostly the shape of two semi-circles centered at each of the electrodes; (2) their surface temperatures increase more for those with higher fiber percentages; (3) their surface's average temperature increments are the highest for the first 1 min of heating; (4) the lines representing the lowest and highest temperature zones and one of the normal lines to two electrodes record the highest temperature increment for the first 1 min of heating; (5) the temperature ratio of two points on the surface of each of four different percentage prisms has almost an unchanging value for all heating time periods especially when the two points are close to the volume defined by two electrodes; (6) the average temperature increments decrease with time. These facts are for all percentage prisms. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) cursor for autostereoscopic 3D displays was proposed. The cursor is based on voxel patterns. In the experiments, the cursor position is interactively controlled in 3D by a computer mouse with a scroll wheel. A computer program operates in the image plane of the 3D display directly without complicated geometric calculations. The results were verified in a 3D display with a parallax barrier and can be applied to other types of autostereoscopic displays. [ABSTRACT FROM AUTHOR]

The presence of monocular depth sense is identified with a light field imaging system which can project up to 8 different view images simultaneously to a viewer’s each eye. The depth of field of subjects’ eyes increases further as the number of simultaneously projected images to subjects’ each eye increases more, though the increasing rate is somewhat different for different subjects. The diopter values exceed more than those of real object as the number exceeds more than six for the binocular viewing while it is eight for monocular viewing. The increasing rate of the diopter values for the binocular viewing is more than that for monocular viewing. These results assure that a natural viewing condition can be incorporated in light field imaging systems. These results are derived from 7 subjects under age 35, having eye sight greater than 1.0. [ABSTRACT FROM AUTHOR]

The traces of carbon fibers along the cracked surfaces of mortar prisms, being 40 mm x 40 mm x 160 mm in size, are studied, assuming that the cracked surfaces in the prisms are the places with the lowest resistance to the stresses they are exposed to. This is to explain why the prisms with 1.0% carbon fibers in volume reveal higher flexural strength than those with 0.5%, 1.5% and 2.0% of fibers. Five distinctive traces of carbon fibers, such as uprootedness, avulsion, separation, overlay and dividedness are observed in the cracked surfaces. As the percentage increases by more than 1.0%, the number of the uprooted fibers reduces, while the numbers of the divided, avulsed and separated fibers increase. The percentage increase induces more fibers to be clustered together and overlap each other to make more divided, avulsed and separated fiber traces. At the same time, the fiber strands are mixed with the mortar to a greater extent. Consequently, the crack surfaces of the prisms with fiber percentages of 1.5% and 2.0% become mostly covered with fiber-laden mortar and cemented fiber clusters. Since the cemented fiber clusters work as air pockets of various volumes and act as the inhomogeneities together with the fiber-laden mortar, the cohesiveness of the mortar is greatly reduced. The deteriorating cohesiveness of the mortar and the increased inhomogeneity cause the reduction in the flexural strength of the prisms in comparison with those with 1.0% carbon fibers. [ABSTRACT FROM AUTHOR]

Storage racks are nonstructural components mainly designed to support the vertical load of goods. During strong external loads such as an earthquake, which acts in the lateral direction of the racks, stored goods become structurally vulnerable. To identify and reinforce the vulnerable parts of storage racks and improve their seismic performance, we developed a viscoelastic damper system with a capacity designed for storage racks. First, we performed an experiment to analyze the behavioral characteristics of a pallet rack — a representative storage rack used for large goods — under vibration. Based on the results of the experiment, we chose the members of storage racks that were vulnerable to vibration. For the proper seismic reinforcement of vulnerable members, we developed a viscoelastic damping system for storage racks by calculating the structural shear force on each floor of the rack and the capacity of the damper to distribute the shear force. First, three viscoelastic dampers of different capacities were fabricated using a viscoelastic material and subjected to cyclic loading tests to evaluate their mechanical performance. We determined the position on which the damper should be placed to improve the rack's seismic performance by considering the shear force on each floor of the storage rack and its operational characteristics. Finally, we conducted a shaking table test to verify the new viscoelastic damper system. The system improves the seismic performance of storage racks by controlling their elastic and permanent deformations. [ABSTRACT FROM AUTHOR]

Hyperspectral images in the spectral wavelength range of 500 nm to 650 nm are used to detect green mold pathogens, which are parasitic on the surface of lemons. The images reveal that the spectral range of 500 nm to 560 nm is appropriate for detecting the early stage of development of the pathogen in the lemon, because the spectral intensity is proportional to the infection degree. Within the range, it was found that the dominant spectral wavelengths of the fresh lemon and the green mold pathogen are 580 nm and 550 nm, respectively, with the 550 nm being the most sensitive in detecting the pathogen with spectral imaging. The spectral intensity ratio of the infected lemon to the fresh one in the spectral range of 500 nm to 560 nm increases with the increasing degree of the infection. Therefore, the ratio can be used to effectively estimate the degree of lemons infecting by the green mold pathogens. It also shows that the sudden decrease of the spectral intensity corresponding to the dominant spectral wavelength of the fresh lemon, together with the neighboring spectral wavelengths can be used to classify fresh and contaminated lemons. The spectral intensity ratio of discriminating the fresh lemon from the infected one is calculated as 1.15. [ABSTRACT FROM AUTHOR]

The 8-bit RGB image of a cracked concrete surface, obtained with a high-resolution camera based on a close-distance photographing and using an optical microscope, is used to estimate the geometrical parameters of the crack. The parameters such as the crack's width, depth, and morphology can be determined by the pixel intensity distribution of the image. For the estimation, the image is transformed into 16-bit gray scale to enhance the geometrical parameters of the crack and then a mathematical relationship relating the intensity distribution with the depth and width is derived based on the enhanced image. This relationship enables to estimate the width and depth with ±10% and ±15% accuracy, respectively, for the crack samples used for the experiments. It is expected that the accuracy can be further improved if the 8-bit RGB image is synthesized by the images of the cracks obtained with different illumination directions. [ABSTRACT FROM AUTHOR]

In South Korea, sewage pipeline exploration devices have been developed using high resolution digital camera of 2 mega-pixels or above. However, most of the devices are less than 300 kilo-pixels due to poverty of the business. Moreover, since 100 kilo-pixels devices are widely used, environment for image processing is very poor. In this study, we adapted very low resolution (240 × 320 = 76,800 pixels) images by which it is difficult to detect cracks. Considering that images of sewers in South Korea have very low resolution, this study selected low resolution images to be investigated. An automatic crack detection technique has been studied using digital image processing technology for low resolution images of sewage pipeline. Authors have developed a program to automatically detect cracks as per eight steps based on MATLAB's functions. In this study, the third step covers an algorithm developed to find optimal threshold value, and the sixth step deals with algorithm to determine cracks. When we select [1.11:1.29] of zero padding range, exact detection rate is 89.2% and error rate is 4.44%. As the result, in spite of very low-resolution images, the performance of crack detection turned out to be excellent. [ABSTRACT FROM AUTHOR]

There has recently been an increase in interest in structural health monitoring (SHM) using wireless sensor networks. For SHM, in particular, it is important to accurately and efficiently measure the dynamic acceleration response using wireless sensor networks in real-time. For the purpose, a CAFB (cochlea-inspired artificial filter bank) has been developed in a previous study, which is a dynamic data compression technology. Since the developed CAFB can select and compress only the interested range of frequency signals from an entire response of a structure, it efficiently provides a real-time dynamic response based on wireless networking. CAFB of the previous study is optimized to selectively acquire low-frequency signals of sub-10 Hz, which is required for SHM of long and large-scale structures. According to the CAFB's optimization using an El-Centro seismic waveform, six band-pass filters, 1.0 Hz interval, and 0.6 Hz bandwidth have been adapted. This article is to evaluate dynamic acceleration response performance of civil structures using the CAFB developed in the previous study. To achieve the purpose, the optimally-designed CAFB was embedded in an intelligent data acquisition (IDAQ) system. To evaluate the performance of the IDAQ system with the embedded CAFB, the real-time dynamic response was investigated for a model cable-stayed bridge, measured by a wire-measuring system and the CAFB-based IDAQ system simultaneously. The results show excellent agreement between the compressed dynamic response acquired by the CAFB-based IDAQ system and that acquired by the wire measuring system. In addition, the measurement from the CAFB-based IDAQ system revealed the modal information of the model bridge. The developed CAFB can determine and reconstruct the entire dynamic response from compression with modal information only; its efficient operation illustrates its potential to be utilized in real-time structural health monitoring. [ABSTRACT FROM AUTHOR]

Structural conditions assessment utilizes data analysis methods based on signals measured from subject structures. Among the various signal-based analysis methods available, a Statistical Pattern-recognition Technique (SPRT) based on Mahalanobis Distance (MD) theory is considered useful in assessing structural conditions; however, its evaluation of volatile signal data incurred by external loads such as seismic loads is usually limited. In this study, an experiment was conducted to attempt to overcome such limitations of MD theory. Furthermore, research was conducted on condition assessment methods based on SPRTs that can accurately assess structural conditions, even with highly volatile measured data. As a first step, the limitations of the standard MD theory were experimentally confirmed. Based on these limitations, a revised MD (RMD) theory was subsequently proposed. To verify the proposed SPRT, standardized cyclic loads and non-standardized seismic loads were used to conduct experiments on structural damage assessment. Based on these results, the RMD theory proposed in this study was confirmed to be a valid method for comprehending structural damage. [ABSTRACT FROM AUTHOR]

Wireless sensor networks based-structural health monitoring is being widely researched. To make a better structural health monitoring, real-time acquisition of structural responses is indispensable. However, the data, which is large in number especially when they are of moving structures, are difficult to be measured, and the adaptation of wireless sensor networks further limits structural health monitoring within the capacity of radio frequency. In this study, cochlea-inspired artificial filter bank was developed as a technological way to efficiently acquire dynamic responses at a wireless sensor networks based-structural health monitoring. The cochlea-inspired artificial filter bank developed in this article was enabled to acquire valid dynamic responses of compressed size around the frequency range of interest by simulating raw data to the full regarding to time and frequency of dynamic responses. In addition, the digitalized cochlea-inspired artificial filter bank was also found to fix the disadvantages of analogue filters by its easy and efficient development of logics, optimization, design of software, and real-time autonomous execution. Finally, the cochleainspired artificial filter bank makes it possible to compress and reduce the vast amount of real-time dynamic responses usually obtained by means of a uniform rate of sample, into a manageable size. It is thus expected to open up a new paradigm in the Wireless sensor networks based-structural health monitoring of civil structures by facilitating an efficient measurement and management of data base. [ABSTRACT FROM AUTHOR]

In this paper, a Cochlea-inspired Artificial Filter Bank (CAFB) was developed in order to efficiently acquire dynamic response of structure, and it was also evaluated via dynamic response experiments. To sort out signals containing significant modal information from all the dynamic responses of structure, it was made to adopt a Band-pass filter Optimizing Algorithm (BOA) and a Peak-Picking Algorithm (PPA). Optimally designed on the basis of Kobe earthquake signals, it was then embedded into the Wireless Variety Measurement System (WiVMS). In order to evaluate the performance of the developed CAFB, a vibration test was conducted using the Kobe earthquake signals, and structural responses of a two-span bridge were obtained and analyzed simultaneously by both a wired measurement system and a CAFB-based WiVMS. The test results showed that the compressed dynamic responses acquired by the CAFB-based WiVMS matched with those of the wired system, and they included significant modal information of the two-span bridge. Therefore this study showed that the developed CAFB could be used as a new, economic, and efficient measurement device for Wireless Sensor Networks (WSNs) based real time structural health monitoring because it could reconstruct the whole dynamic response using the compressed dynamic response with significant modal information [ABSTRACT FROM AUTHOR]

This paper aims to develop an SI (structural identification) technique using the KEOT and the DMUM to decide on optimal location of sensors and to update FE model, respectively, which ultimately contributes to a composition of more effective SHM. Owing to the characteristic structural flexing behavior of cable bridges (e.g., cable-stayed bridges and suspension bridges), which makes them vulnerable to any vibration, systematic and continuous structural health monitoring (SHM) is pivotal for them. Since it is necessary to select optimal measurement locations with the fewest possible measurements and also to accurately assess the structural state of a bridge for the development of an effective SHM, an SI technique is as much important to accurately determine the modal parameters of the current structure based on the data optimally obtained. In this study, the kinetic energy optimization technique (KEOT) was utilized to determine the optimal measurement locations, while the direct matrix updating method (DMUM) was utilized for FE model updating. As a result of experiment, the required number of measurement locations derived from KEOT based on the target mode was reduced by approximately 80% compared to the initial number of measurement locations. Moreover, compared to the eigenvalue of the modal experiment, an improved FE model with a margin of error of less than 1% was derived from DMUM. Thus, the SI technique for cable-stayed bridges proposed in this study, which utilizes both KEOT and DMUM, is proven effective in minimizing the number of sensors while accurately determining the structural dynamic characteristics. [ABSTRACT FROM AUTHOR]

While wireless sensor networks have been successfully deployed on a variety of civil infrastructure systems for structural monitoring, past studies have shown that there is room for improvement in terms of network robustness and overall resource consumption efficiency. The mechanisms employed by biological nervous systems (e.g. signal modulation, communication, and integration) can be used as inspiration for overcoming the performance bottlenecks seen in existing wireless sensor nodes and networks. The mammalian auditory system is of particular interest due to its unique signal decomposition techniques (performed by the cochlea) that enable real-time processing of complex sound signals. In this article, a novel wireless sensor architecture based on the operational principles of cochlea is described. The performance of the proposed sensor is validated on a single-degree-of-freedom structure that is excited by seismic ground motion signals, thus demonstrating its real-time monitoring capabilities while maintaining high data compression rates. [ABSTRACT FROM AUTHOR]

This error has now been corrected in the Supplementary Video S1 file that accompanies the original Article. Correction to: I Scientific Reports i https://doi.org/10.1038/s41598-020-70427-x, published online 02 September 2020 The Supplementary Video S1 published with this Article contained an error where the vector "Direction of move" deviated from its horizontal line. Author Correction: Static moiré patterns in moving grids. [Extracted from the article]

Author Correction: Static moiré patterns in moving grids This error has now been corrected in the Supplementary Video S1 file that accompanies the original Article. Correction to: I Scientific Reports i https://doi.org/10.1038/s41598-020-70427-x, published online 02 September 2020 The Supplementary Video S1 published with this Article contained an error where the vector "Direction of move" deviated from its horizontal line. [Extracted from the article]

This paper presents a new algorithm which is applicable in designing a smart damping system for vibration mitigation. The algorithm, which is extended into a unified system from Lyapunov stability theory, enables us to decrease the errors by its increased stability. The validity of this design method was proved in the experiment on a control model of three-storied building structure. Smart damper was used for MR (Magneto-Rheological fluid) damper in the experiment, and its control effectiveness was evaluated. In order to make a more accurate control model mathematically, we updated the model on the basis of the analysis of dynamic characteristics of structure and of the mathematical analysis of a lumped mass model, and then employed a state space model redefined by structural property matrix. Using this improved control model, control effect on structures that were under the influence of each different earthquake magnitude was analyzed with various performance indexes, and thus the algorithm presented here is proved to be valid. [ABSTRACT FROM AUTHOR]

In this paper, a smart monitoring system for infra-structure is developed with an integrated management system using ubiquitous computing techniques. This system is designed to enable to use TCP/IP network protocol, communicating the data measure by a wireless sensing unit based on Bluetooth technology. In order to verify this system, a randomly excited self-anchored suspension bridge is tested for real time monitoring by remote network user. Dynamic characteristics are identified to construct an integrity structure using the acquired data from the monitoring test. [ABSTRACT FROM AUTHOR]

We describe an optical phenomenon of unmovable moiré patterns in sliding (moving) grids and gratings. The phenomenon was observed visually in the planar straight movement of the black-and-white gratings with a period of several mm. This is a velocity-independent effect confirmed analytically and in a computer simulation based on the spatial averaging. We found the static directions of the moiré patterns in the regular grids, but our technique can be also applied to other objects. The orientation and period of the static moiré patterns are not obvious, especially in the presence of the distance effect. The phenomenon can be practically used in security applications. [ABSTRACT FROM AUTHOR]

A disaster preventive structural health monitoring (SHM) system needs to be equipped with the following abilities: First, it should be able to simultaneously measure diverse types of data (e.g., displacement, velocity, acceleration, strain, load, temperature, humidity, etc.) for accurate diagnosis. Second, it also requires standalone power supply to guarantee its immediate response in crisis (e.g., sudden interruption of normal AC power in disaster situations). Furthermore, it should be capable of prompt processing and realtime wireless communication of a huge amount of data. Therefore, this study is aimed at developing a wireless unified-maintenance system (WUMS) that would satisfy all the requirements for a disaster preventive SHM system of civil structures. The WUMS is designed to measure diverse types of structural responses in realtime based on wireless communication, allowing users to selectively use WiFi RF band and finally working in standalone mode by means of the field-programmable gate array (FPGA) technology. To verify its performance, the following tests were performed: (i) A test to see how far communication is possible in open field, (ii) a test on a shaker to see how accurate responses are, (iii) a modal test on a bridge to see how exactly characteristic real-time dynamic responses are of structures. The test results proved that the WUMS was able to secure stable communication far up to nearly 800 m away by acquiring wireless responses in realtime accurately, when compared to the displacement and acceleration responses which were acquired through wired communication. The analysis of dynamic characteristics also showed that the wireless acceleration responses in real-time represented satisfactorily the dynamic properties of structures. Therefore, the WUMS is proved valid as a SHM, and its outstanding performance is also proven. [ABSTRACT FROM AUTHOR]