Pressure drop and optimization meta-models for arbitrary low-height pleated filter shapes and flowrates

Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations...     

Deep Q-network-based auto scaling for service in a multi-access edge computing environment

In 5G networks, it is necessary to provide services while meeting various service requirements, such as high data rates and low latency, in response to dynamic network conditions. Multi-access edge computing (MEC) is a promising concept to meet these requirements. The MEC environment enables service providers to deploy their low latency services that are composed of multiple components. However, operating a service manually and attempting to satisfy the quality of service (QoS) requirements is difficult because many factors need to be considered in an MEC scenario. In this paper, we propose an auto-scaling method using deep Q-networks (DQN), which is a reinforcement learning algorithm, to resize the number of instances assigned to service. In our evaluation, compared to other baseline methods, the proposed approach maintains the appropriate number of instances effectively in response to dynamic traffic change while satisfying QoS and minimizing the cost of operating the service in the MEC environment. The proposed method was implemented as a module running in OpenStack and published as open-source software.     

Rice PIN Auxin Efflux Carriers Modulate the Nitrogen Response in a Changing Nitrogen Growth Environment

Auxins play an essential role in regulating plant growth and adaptation to abiotic stresses, such as nutrient stress. Our current understanding of auxins is based almost entirely on the results of research on the eudicot Arabidopsis thaliana, however, the role of the rice PIN-FORMED (PIN) auxin efflux carriers in the regulation of the ammonium-dependent response remains elusive. Here, we analyzed the expression patterns in various organs/tissues and the ammonium-dependent response of rice PIN-family genes (OsPIN genes) via qRT–PCR, and attempted to elucidate the relationship between nitrogen (N) utilization and auxin transporters. To investigate auxin distribution under ammonium-dependent response after N deficiency in rice roots, we used DR5::VENUS reporter lines that retained a highly active synthetic auxin response. Subsequently, we confirmed that ammonium supplementation reduced the DR5::VENUS signal compared with that observed in the N-deficient condition. These results are consistent with the decreased expression patterns of almost all OsPIN genes in the presence of the ammonium-dependent response to N deficiency. Furthermore, the ospin1b mutant showed an insensitive phenotype in the ammonium-dependent response to N deficiency and disturbances in the regulation of several N-assimilation genes. These molecular and physiological findings suggest that auxin is involved in the ammonium assimilation process of rice, which is a model crop plant.     

Practical crack control during the construction of precast segmental box girder bridges

Cracks that occurred in the bottom slab of a precast segmental bridge were investigated through a construction sequence analysis, which revealed that the cracks were caused by excessive deformation during temporary post-tensioning while joining the segments. In addition, a parametric study was performed to evaluate the effects of the prestressing sequence, bottom slab thickness, and position of the prestressing anchors. The structural behavior of the girder sections was greatly affected by the thickness of the bottom slab and the position of prestressing anchors, but not by the prestressing sequence. Based on the results, a construction method that prevents the cracks is proposed.     

Transient analysis of hybrid rocket combustion by the zeldovich-novozhilov method

Hybrid rocket combustion has a manifestation of stable response to the perturbations compared to solid propellant combustion. Recently, it has revealed that the low frequency combustion instability about 10 Hz was occurred mainly due to thermal inertia of solid fuel. In this paper. the combustion response function was theoretically derived by use of ZN (Zeldovich-Novozhilov) method. The result with HTPB/LOX combination showed a quite good agreement in response function with previous works and could predict the low frequency oscillations with a peak around 10 Hz which was observed experimentally. Also, it was found that the amplification region in the frequency domain is independent of the regression rate exponentn but showed the dependence of activation energy. Moreover, the response function has shown that the hybrid combustion system was stable due to negative heat release of solid fuel for vaporization, even though the addition of energetic ingredients such as AP and Al could lead to increase heat release at the fuel surface.     

Molecular design of anti-biofouling materials from natural phenolic compounds

Many natural phenolic compounds found in plants are well known for their antibiotic and antioxidant activities. It has been hypothesized that these activities of natural phenols could be used for developing permanent anti-biofouling coatings. In this study, two phenolic components, anacardic acid and cardanol, were extracted from cashew nut shell liquid, and tested for their antibiotic and anti-biofouling activities against Pseudomonas fluorescens. Both compounds killed all the cells within 18 hours (anacardic acid) and 30 hours (cardanol) after the addition to the culture media at a concentration of 800 μg/ml. To form a stable permanent coating of these compounds, first they were polymerized by enzymatic polymerization, and the polymers were cross-linked on a glass slide. P. fluorescens were cultured on the coated and uncoated glasses for two weeks, and the images of the cells grown on the surfaces were taken by SEM. The coated surfaces clearly demonstrated anti-biofouling activities, showing not only fewer numbers of cells but also less exopolymer than the uncoated surfaces. Based on these results, a phenolic compound with a similar structure of anacardic acid was synthesized by using propylene diamine and fluorocarboxylic acid with cardanol. The synthesized phenolic compound was polymerized and cross-linked on a glass slide to test the anti-biofouling activity. The SEM images of the cells on the coated surface showed considerable decreases in the number of adhered cells and the amount of exopolymers even more than the anacardic acid and cardanol coatings. It is thought that the natural phenolic compounds with active functional groups can be used for anti-biofouling agents. This paper is dedicated to Prof. Chang Kyun Choi for celebrating his retirement from the School of chemical and biological engineering of Seoul National University.     

Onset of Soret convection in a nanoparticles-suspension heated from above

The onset of Soret-driven convection in a nanoparticles suspension heated from above is analyzed theoretically based on linear theory and relative instability concept. A new set of stability equations are derived and solved by using the dominant mode method. The dimensionless critical time τ _c to mark the onset of instability is presented here as a function of the Rayleigh number, the Lewis number and the separation ratio. Available experimental data indicate that for large Rayleigh number convective motion is detected starting from a certain time τ≈3 τ _c . This means that the growth period of initiated instabilities is needed for convective motion to be detected experimentally. It seems evident that during τ _c ≤ τ ≤ 3 τ _c convective motion is relatively very weak and the primary diffusive transfer is dominant. This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.     

Continuous viscosity measurement of non-Newtonian fluids over a range of shear rates using a mass-detecting capillary viscometer

A newly designed mass-detecting capillary viscometer uses a novel concept to continuously measure non-Newtonian fluids viscosity over a range of shear rates. A single measurement of liquid-mass variation with time replaces the flow rate and pressure drop measurements that are usually required by capillary tube viscometers. Using a load cell and a capillary, we measured change in the mass flow rate through a capillary tube with respect to the time,m(t), from which viscosity and shear rate were mathematically calculated. For aqueous polymer solutions, excellent agreement was found between the results from the mass-detecting capillary viscometer and those from a commercially available rotating viscometer. This new method overcomes the drawbacks of conventional capillary viscometers meassuring non-Newtonian fluid viscosity. First, the mass-detecting capillary viscometer can accurately and consistently measure non-Newtonian viscosity over a wide range of shear rate extending as low as 1 s⁻¹. Second, this design provides simplicity (i. e., ease of operation, no moving parts), and low cost.     

Blood viscosity measurements using a pressure-scanning capillary viscometer

A previously designed capillary viscometer with measuring differential pressure was modified to measure the viscosity of non-Newtonian fluids including unadulterated blood continuously over numerous shear rates in a single measurement. Because of unavoidable experimental noise and a limited number of data, the previous capillary viscometer experienced an inaccuracy and could not directly determine a viscosity without an iterative calculation. However, in the present measurement there are numerous data available near the point of interest so that the numeric-value of the derivative,d(lnQ)/dln τω), is no longer sensitive to the method of differentiation. In addition, relatively low and wide shear rate viscosity measurements were possible because of the present precision pressure-scanning method with respect to time. For aqueous polymer solutions, excellent agreement was found between the results from the pressure-scanning capillary viscometer and those from a commercially available rotating viscometer. In addition, the pressure-scanning capillary viscometer measured the viscosity of unadulterated whole blood without adding any anticoagulants.     

Advanced water treatment of high turbid source by hybrid module of ceramic microfiltration and activated carbon adsorption: Effect of organic/inorganic materials

We investigated the effect of organic or inorganic materials on membrane fouling in advanced drinking water treatment by hybrid module packed with granular activated carbon (GAC) outside a tubular ceramic microfiltration membrane. Instead of natural organic matters (NOM) and fine inorganic particles in the natural water source, synthetic water was prepared with humic acid and kaolin. Concentrations of kaolin or humic acid were changed to see effects of inorganic or organic matter. And periodic water-back-flushing using permeate water was performed during 10 sec per filtration of 10 min. As a result, both the resistance of membrane fouling (R _f ) and permeate flux (J) were influenced higher by concentration of humic acid rather than kaolin. It was proved that NOM like humic acid could be a more important factor on membrane fouling in drinking water treatment than fine inorganic particles. Treatment efficiencies of turbidity and UV₂₅₄ absorbance were very high above 97.4% and 92.0%, respectively. This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.