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The low yield of microbial calcium carbonate precipitation due to the strong pH environment has limited the development of biotechnology-based concrete crack repair techniques. In this study, Bacillus megaterium was selected to determine the optimal nutrient formulation through orthogonal tests. The growth and reproduction characteristics and urease activity of this strain were analysed by controlling different pH values, and the calcium carbonate precipitation yield under different pH conditions was investigated, and the lower precipitation yield under strong alkaline conditions was improved by using alkaline environment domestication with the addition of urea to the nutrient solution. It has been shown that higher pH results in lower growth and multiplication of Bacillus megaterium and weaker urease activity, and a strong alkaline environment can significantly suppress its growth and multiplication and urease activity. At pH 7, the growth and multiplication of Bacillus megaterium were the fastest, the urease activity was the strongest, and the precipitation yield was greater. The addition of urea to the nutrient solution to domesticate Bacillus megaterium in an alkaline environment can significantly increase the growth rate and precipitation yield, which can effectively solve the problem of insufficient calcium carbonate precipitation under alkaline conditions. Comparing the effectiveness of microbially induced calcium carbonate precipitation (MICP) in repairing concrete after damage before and after microbial domestication shows that the domesticated Bacillus megaterium is more effective in reducing the permeability characteristics of concrete and improving its strength. [ABSTRACT FROM AUTHOR]

Road surface monitoring is a significant issue in providing smooth road infrastructure for vehicles, and the key to road condition monitoring is to detect road potholes that affect driving comfort and transportation safety. This paper presents a simple, efficient, and accurate way to evaluate road service performance based on the acquisition of road vibration data by vibration sensors installed in vehicles. Inspired by the discrete fast Fourier transform, the vibration acceleration is processed, and the RMS value of vibration acceleration at 1/2 octave is calculated, after which the road vibration level is calculated. The vibration level is optimized according to the human body's sensitivity to different frequencies of vibration, resulting in road service performance indicators that can reflect the human body's real feelings. According to the road service performance index values on the road grading, combined with GPS data on the electronic map color block labeling, the results obtained for the road condition warning, road maintenance, driver route selection have an important significance. [ABSTRACT FROM AUTHOR]

In soft soil areas, such as the Nanjing, it is very important to quantitatively analyze the dynamic behaviors of soft soils during the metro train operation. A nonlinear coupling model of wheel-track and a finite element calculation model of tunnel and soil were established based on the mechanical character of elastic supporting block ballastless track and the actual parameters of Nanjing soft soil. The time-variant vertical acceleration of the rail, the sleepers, and the surface of the tunnel can be calculated by the models, and the frequency dependence acceleration was verified by the fast Fourier transform algorithm. A modified vibration power level for human sensitivity was used to quantify the vibration energy of each part of the system, and the impact of the parameters in the model was evaluated. The results can be applied to the metro design and construction, which also can be the guidance during the tunnel construction. [ABSTRACT FROM AUTHOR]

High efficiency and low fuel consumption make the contrarotating open rotor (CROR) system a viable economic and environmentally friendly powerplant for future aircraft. While the potential benefits are well accepted, concerns still exist with respect to the vibrations and noise caused by the aerodynamic interactions of CROR systems. In this paper, emphasis is placed on the detailed analysis of the aerodynamic interactions between the front and aft propellers of a puller CROR configuration. For the first step, unsteady Reynolds-averaged Navier-Stokes (URANS) simulations coupled with dynamic patched grid technology are implemented on the isolated single-rotating propeller (SRP) configuration in various operating conditions in order to test the accuracy and feasibility of the numerical approach. The numerical results are verified by a wind tunnel test, showing good agreements with the experimental data. Subsequently, the URANS approach is applied to the CROR configuration. The numerical results obtained through the URANS approach help to improve the understanding of the complex flow field generated by the CROR configuration, and the comparison of SRP flow field and CROR flow field allows for a detailed analysis of the aerodynamic interactions of the front propeller blade wakes and tip vortices with the aft propeller. The main reason of the aerodynamic interactions is the mutual effects of the blade tip vortices, and the aft propeller reduces the strength of the blade tip vortices of the front propeller. Aerodynamic interactions will lead to the periodic oscillations of the aerodynamic forces, and the frequency of the oscillations is linked to the blade numbers. In addition, a CROR has a larger thrust and power coefficient than that of the SRP configuration in the same operating conditions. The URANS approach coupled with a dynamic patched grid method is tested to be an efficient and accurate tool in the analysis of propeller aerodynamic interactions. [ABSTRACT FROM AUTHOR]

A distributed energy resource (DER) system uses renewable generation and energy storage to provide power and ancillary services directly to users in the distribution system, and benefits the power grid by offering a solution to the energy crisis and mitigating the waste pollution to the environment. A key challenge in implementing a DER system is how to ensure the standardization of its communication network. The goal of this paper is to study and propose a common approach to standardize the communication network in the DER system using IEC 61850 and includes a design and implementation of the communication architecture. Two prototypical testbeds for the DER system have been developed in the SMERC laboratory and at KIER, with the aim to demonstrate a case study using the proposed approach. The testbeds contain various DERs such as photovoltaics, energy management systems, and electric vehicles. The procedure of integrating the IEC 61850 standard includes the system architecture configuration, data set design, test file write-up, and deployment of the gateway/client for communication. In the data set design, the specification of logical nodes, data object names, data attributes and common data classes are explained in detail. The research results and data collected from the current testbeds indicate a quality integration of the IEC 61850 standard with stable power flow and unified communication architecture in the DER system. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

EPS concrete was produced by mixing the expanded polystyrene spheres (EPS) and polymer emulsion and thickener to the matrix concrete, and this concrete had good vibration energy absorption characteristics. Based on the experimental data obtained on EPS volume ratio of 0%, 20%, 30%, and 40% by replacing matrix or coarse aggregate, the two design styles had nearly the same compressive strength. By applying frequency of 5 Hz, 50000 or 100000 times, 40 KN, 50 KN, and 60 KN cyclic loading, it is shown that the higher the inclusion size was, the lower the compressive strength of the EPS concrete would be; the larger the applying dynamic cyclic load was, the more obvious the compressive strength changing would be. Meanwhile, the strength of EPS concrete had no evident change after durability test. The results of this research had practical significance on using EPS concrete in some long-term cyclic dynamic load engineering. [ABSTRACT FROM AUTHOR]

This paper investigates the settlement behaviors of a metro tunnel during metro operation. A nonlinear vibration model of vehicle-track is established, and a series of vibration loadings for the frequency domain acting on segments are obtained based on a modal analysis method and applying the Fourier transformation algorithm. The displacements at any position in the soil are derived from the segment-soil interaction coupled model with the elastic continuum theory, and its accuracy is verified by comparing with the calculation result obtained by elastic-plastic finite element model. [ABSTRACT FROM AUTHOR]

User authentication in wireless sensor networks (WSNs) is a critical security issue due to their unattended and hostile deployment in the field. Since sensor nodes are equipped with limited computing power, storage, and communication modules, authenticating remote users in such resource-constrained environments is a paramount security concern. To overcome the weaknesses of Yeh et al.'s protocol, we proposed a new authentication protocol for wireless sensor networks using elliptic curves cryptography. The comparisons show that our protocol is more suitable for WSNs. [ABSTRACT FROM AUTHOR]