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The primary objectives of this study are to investigate the interference of ground penetrating radar (GPR) signals with air-cavities behind concrete linings subjected to three experimental parameters (GPR antenna frequency, thickness of concrete lining, and thickness of air-cavities), and their effects on the evaluation of important engineering parameters (thickness of concrete, and length and thickness of air-cavities) for tunnel structure inspection using GPR. For these purposes, first, a concrete model specimen is fabricated in the laboratory, which simulates air-cavity defects with various thicknesses (0 mm, 30 mm, 100 mm, 200 mm, and 300 mm) behind concrete with four different thicknesses (100 mm, 200 mm, 300 mm, and 400 mm) in tunnel structures. Second, a series of GPR survey is performed on the fabricated concrete model specimen using three ground-coupled GPR antennas with nominal center frequencies of 400 MHz, 900 MHz, and 1600 MHz. Third, a practical signal interpretation method is proposed to evaluate air-cavities in concrete tunnel linings subjected to the three experimental parameters. It is demonstrated that the cross-correlation analysis is effective for identifying air-cavities behind concrete, and for characterizing the length of the air-cavities. In addition, the thicknesses of air-cavities are estimated by a new approach in this study, measuring the apparent time delay of partially overlapped electromagnetic wave reflections within air-cavities. The results in this study provide a fundamental basis to improve GPR signal interpretation techniques for the evaluation of air-cavities behind concrete tunnel linings.

The Imjin River is a representative transboundary river in the Korean Peninsula, originating from North Korea and flowing into South Korea. Upstream of Imjin River, on the North Korean side, is the Hwanggang Dam, with a 350 million m3 of storage capacity, which is in operation for power generation and water supply. The sharing of the operation information of Hwanggang Dam has been limited due to political and military tension. South Korea has constructed the Gunnam Flood Control Reservoir downstream of the Imjin River to prevent potential flood damage due to the urgent and unilateral release from the Hwanggang Dam. However, it is difficult to manage the flood of the Imjin River basin under the situation of limited shared real-time information on the Hwanggang Dam operation. In this study, a hydrological analysis system was established to estimate the inflow and release of the Hwanggang Dam by building a lumped hydrological model and an Auto ROM (Reservoir Operation Method)-based reservoir operation algorithm. To estimate the inflow of the Gunnam Flood Control Reservoir, the water level of the Hwanggang Dam was calculated using the Sentinel-2 multi-spectral images, and the hydrological analysis system was calibrated. The evaluation index of the water level of the ungauged Hwanggang Dam derived from January 2017 to August 2020 using the hydrological analysis system was shown to have a coefficient of determination of 0.76 and an RMSE of 3.97 m. In the case of the flood event in August 2020, the coefficient of determination of the flood inflow in the Gunnam Flood Control Zone was calculated to be 0.86.

In this paper, we present an energy-efficient resource directory update (ERDU) scheme for the constrained application protocol (CoAP) in Internet of Things (IoT), which is designed to prevent unnecessary energy consumption caused by dead nodes and the frequent transmission of update messages. The ERDU scheme improves the energy efficiency of centralized resource discovery procedures in the CoAP via two main mechanisms: (1) dead node detection and (2) update period adaptation. The former detects dead servers and removes their resource from resource directory (RD) entries to prevent the unnecessary retransmission of the client. The latter adjusts the update period of the server on the basis of its current energy level. Simulation results show that the energy efficiency of the ERDU scheme is better than that of the legacy RD update mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we present a stepwise adjustment of the constrained application protocol observing period (SACOP) for Internet of Things (IoT) applications using wireless sensor networks (WSNs), which dynamically adjust observing periods depending on the Rx queue status of the constrained application protocol (CoAP) client. The operation of SACOP consists of the following two consecutive phases: overflow alert and observing period adjustment. In the former phase, a client sends a buffer overflow alert when the queue of the client reaches the predefined queue threshold. In the latter phase, the servers change their own observing period level depending on whether or not they receive a buffer overflow alert message. Therefore, SACOP can significantly reduce the number of dropped messages caused by buffer overflow. A simulation showed that SACOP achieved a higher network performance than the legacy approach with regard to the number of dropped messages. [ABSTRACT FROM AUTHOR]

Uniformity of plasma etching has been conventionally examined only in terms of etch rate. A uniformity of etching profile surface is increasingly demanded to improve process quality. This is accomplished by applying a discrete wavelet transformation (DWT) profile images obtained with a scanning electron microscopy. Applicability of DWT-based profile uniformity was evaluated with a tungsten etch experiment, conducted in an SF6 helicon plasma. Its suitability was investigated as a function of process parameters and scale levels. Compared to a conventional metric, the wavelet-based one characterized more effectively the uniformity of profile variations. The proposed metric can be applied to any other plasma-processed surfaces. [ABSTRACT FROM AUTHOR]