Properties and Durability of Cement Mortar Using Calcium Stearate and Natural Pozzolan for Concrete Surface Treatment.

Applying a concrete surface treatment method (epoxy or primer) can prevent water from penetrating concrete through surface pores. However, if the concrete surface is damaged, the subsequent reconstruction can be expensive and time-consuming. Concrete that is resistant to internal and external water has been extensively developed and used to supplement the surface treatment method. Herein, we prepared specimens by mixing cement mortar with fatty-acid-salt-based calcium stearate attached to two natural pozzolanic materials­diatomite and yellow clay. The physical tests measured (1) the air content, (2) flow test, (3) compressive strength, and (4) activity Factor. Durability experiments were performed on (1) the contact angle, (2) chloride ion diffusion coefficient, and (3) water absorption test. The results revealed that the compressive strength of concrete decreased as the calcium stearate content increased. Furthermore, it was confirmed that the contact angle of the test piece using the pozzolanic substance and calcium stearate was twice as high. It was confirmed that the sand test specimen had the highest water absorption rate, and the DT3% had the lowest. (Sand%: 11.8 > OPC: 6.5 > DT3%: 2.4), the chloride diffusion coefficient also showed similar results. (Sand%: 12.5 > OPC: 8.4 > DT1%: 8.8)Due to its unique insolubility, calcium stearate retards hydrate formation when mixed alone and negates compressive strength loss when combined with pozzolanic mixtures rich in SiO2 and Al2O3. Furthermore, the ideal method for producing water-resistant cement mortar is to evenly disperse calcium stearate in the porous powder of cement mortar.

Survey of Airborne Microorganisms in an Arcade-Type Traditional Market in Anseong, South Korea.

We aimed to analyze airborne microorganisms and assess air quality, temperature, and relative humidity at "J" Market, an arcade-type traditional market in Anseong (South Korea). Measurements were taken 16 times, twice per quarter (January, April, July, and October), at both the entrance and intersection of the market in 2020. The concentrations of airborne bacteria and fungi at the entrance and intersection were highest in October and lowest in April; however, they were below the recommended indoor levels (airborne bacteria: <800 CFU/m3, airborne fungi: <500 CFU/m3) in January (second measurement) and April (first and second measurements). The concentrations of microbes during the first measurement in January and both measurements in July and October exceeded the allowed limits. The concentration of microorganisms exceeded the acceptable levels at relative humidity ≥60%. At all time points, except during the eighth survey, when the microorganisms were too numerous to count, microbial concentrations were higher at the intersection than at the entrance. It was confirmed that the microorganisms detected in this experiment were 26 species of bacteria and 21 species of fungi. Three of the four species of bacteria and fungi detected in more than 50% of the 16 experimental results were pathogenic. Our findings suggest that air purification systems must be installed in the market to improve sanitary conditions.

Evaluation of the Corrosion Behavior of Reinforced Concrete with an Inhibitor by Electrochemical Impedance Spectroscopy.

In this study, the effect of NaCl and LiNO2 content on the deterioration of embedded rebars in concrete due to corrosion was examined by measuring the natural potential and impedance. Wet-dry cycles were performed to accelerate the corrosion of embedded rebars in reinforced concrete, following which the potential and impedance corresponding to the cycles were measured. For the reinforced concrete containing only NaCl, the passive film of the embedded rebar surfaces deteriorated after two weeks of accelerated corrosion, and its polarization resistance decreased. When 0.6 M LiNO2 per NaCl was added, the reinforced concrete deteriorated at the same rate as the normal embedded rebars, and the polarization resistance was higher than the initial values. When 1.2 M LiNO2 per NaCl was added, the passive film of the embedded rebars remained intact even after 10 weeks of accelerated corrosion, protecting the rebars from deterioration.

Variation in Service Life on RC Structure According to Concrete Binder Type.

When an additive is used to replace a certain amount of cement, a concrete pore structure becomes dense. Thus, it results in inhibiting the penetration of chlorine ions and suppressing corrosion of reinforcing bars. However, the pH level of the concrete decreases, and it deteriorates the performance of the passive film formed on the surface of the rebars embedded in the concrete. Therefore, in this study, the service lives of reinforced concrete containing different types of concrete binders were predicted and compared. The chloride ion diffusion coefficients of concretes with various binders were measured, and the critical chloride content of the rebar was assessed by the real-time monitoring on the corrosion initiation time of the rebar embedded in concrete. Moreover, Fick's 2nd law was applied to predict when the chloride content at the 40 mm depth of cover reached the critical chloride content based on the chloride ion diffusion coefficient. It was observed that the service life of S6 (OPC 40% + GGBFS 60%) was the highest, followed by TBC (OPC 40% + GGBFS 40% + FA 20%), S3 (OPC 70% + GGBFS 30%), and OPC (OPC 100%).

Effect of Curing Condition on Resistance to Chloride Ingress in Concrete Using Ground Granulated Blast Furnace Slag.

Changes in the salt attack resistance of concrete using ground granulated blast furnace slag (GGBFS) were examined based on different curing conditions. These conditions were divided into air and underwater curing. Three concrete mixes with GGBFS replacement ratios of 0% (control group), 30% and 60% were fabricated. Then, evaluation of concrete compressive strength, evaluation of chloride ion diffusion coefficient and electrochemical impedance spectroscopy (EIS) were performed. As the GGBFS replacement ratio increased, the concrete compressive strength of the air cured specimens decreased compared to the underwater cured specimens. With respect to the chloride ion diffusion coefficient measurements, the coefficient decreased as the GGBFS replacement ratio increased. However, the diffusion coefficient of the air cured specimen relative to the underwater cured ones increased up to two times. The EIS results showed that as the GGBFS replacement ratio increased, |Z| increased in every frequency range. However, the |Z| of the air cured specimen was lower than the underwater cured one. This showed the same tendency as the evaluation results of the chloride ion diffusion coefficient.

Output-Feedback Adaptive Neural Controller for Uncertain Pure-Feedback Nonlinear Systems Using a High-Order Sliding Mode Observer.

A novel adaptive neural output-feedback controller for SISO nonaffine pure-feedback nonlinear systems is proposed. The majority of the previously described adaptive neural controllers for pure-feedback nonlinear systems were based on the dynamic surface control (DSC) or backstepping schemes. This makes the control law as well as the stability analysis highly lengthy and complicated. Moreover, there has been very limited research till date on the output-feedback neural controller for this class of the systems. The proposed controller evades adopting adaptive backstepping or DSC scheme through reformulating the original system into the Brunovsky form, which considerably simplifies the control law. Combining a high-order sliding mode observer and single radial-basis function network with universal approximation property, it is shown that the controller guarantees closed-loop system stability in the Lyapunov sense.

Optical Tracking Data Validation and Orbit Estimation for Sparse Observations of Satellites by the OWL-Net.

An Optical Wide-field patroL-Network (OWL-Net) has been developed for maintaining Korean low Earth orbit (LEO) satellites' orbital ephemeris. The OWL-Net consists of five optical tracking stations. Brightness signals of reflected sunlight of the targets were detected by a charged coupled device (CCD). A chopper system was adopted for fast astrometric data sampling, maximum 50 Hz, within a short observation time. The astrometric accuracy of the optical observation data was validated with precise orbital ephemeris such as Consolidated Prediction File (CPF) data and precise orbit determination result with onboard Global Positioning System (GPS) data from the target satellite. In the optical observation simulation of the OWL-Net for 2017, an average observation span for a single arc of 11 LEO observation targets was about 5 min, while an average optical observation separation time was 5 h. We estimated the position and velocity with an atmospheric drag coefficient of LEO observation targets using a sequential-batch orbit estimation technique after multi-arc batch orbit estimation. Post-fit residuals for the multi-arc batch orbit estimation and sequential-batch orbit estimation were analyzed for the optical measurements and reference orbit (CPF and GPS data). The post-fit residuals with reference show few tens-of-meters errors for in-track direction for multi-arc batch and sequential-batch orbit estimation results.

Adaptive neural control for strict-feedback nonlinear systems without backstepping.

In this brief, a new adaptive neurocontrol algorithm for a single-input-single-output (SISO) strict-feedback nonlinear system is proposed. Most of the previous adaptive neural control algorithms for strict-feedback nonlinear systems were based on the backstepping scheme, which makes the control law and stability analysis very complicated. The main contribution of the proposed method is that it demonstrates that the state-feedback control of the strict-feedback system can be viewed as the output-feedback control problem of the system in the normal form. As a result, the proposed control algorithm is considerably simpler than the previous ones based on backstepping. Depending heavily on the universal approximation property of the neural network (NN), only one NN is employed to approximate the lumped uncertain system nonlinearity. The Lyapunov stability of the NN weights and filtered tracking error is guaranteed in the semiglobal sense.

Determination of analogs of sildenafil and vardenafil in foods by column liquid chromatography with a photodiode array detector, mass spectrometry, and nuclear magnetic resonance spectrometry.

Two analogs of sildenafil and vardenafil in food were detected by column liquid chromatography (LC) with a photodiode array detector. They were isolated by preparative LC; their structures were established by mass spectrometry and nuclear magnetic resonance spectrometry. One analog was found to be methisosildenafil (compound A), 5-(5-(3,5-dimethylpiperazin-1-ylsulfonyl)-2-ethoxy-phenyl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]-pyrimidin-7(6H)-one. It is a sildenafil analog with a dimethylpiperazine ring substituted for the methylpiperazine group. The second analog, hydroxyvardenafil (compound B) is reported for the first time in this study. Hydroxyvardenafil's International Union of Pure and Applied Chemistry name is 2-(2-ethoxy-5-(4-(2-hydroxyethyl)-piperazin-1-ylsulfonyl)phenyl)-5-methyl-7-propyl-imidazo[1,5-f][1,2,4]triazin-4(3H)-one. The novel vardenafil analog has a hydroxyl group added to the ethylpiperazine group.

Direct adaptive controller for nonaffine nonlinear systems using self-structuring neural networks.

A direct adaptive state-feedback controller is proposed for highly nonlinear systems. We consider uncertain or ill-defined nonaffine nonlinear systems and employ a neural network (NN) with flexible structure, i.e., an online variation of the number of neurons. The NN approximates and adaptively cancels an unknown plant nonlinearity. A control law and adaptive laws for the weights in the hidden layer and output layer of the NN are established so that the whole closed-loop system is stable in the sense of Lyapunov. Moreover, the tracking error is guaranteed to be uniformly asymptotically stable (UAS) rather than uniformly ultimately bounded (UUB) with the aid of an additional robustifying control term. The proposed control algorithm is relatively simple and requires no restrictive conditions on the design constants for the stability. The efficiency of the proposed scheme is shown through the simulation of a simple nonaffine nonlinear system.