A methodology for determining the true stress-strain curve of SA-508 low alloy steel from a tensile test with finite element analysis

The true stress-strain curve of a material should be determined for plastic property input to numerical analysis. This study proposes a simple methodology for determining the true stress-strain curve of SA-508 Grade 3 Class 1 low alloy steel using limited information from a general tensile test with finite element analysis. Measured engineering stresses and strains can be reasonably converted to true stresses and strains under uniform deformation before necking. True stress-strains are difficult to determine after necking because of nonuniform deformation without specialized measurement techniques. Five post-necking strain hardening models are considered, namely, linear, swift, Ludwick, Hollomon-linear (HL) and Hollomon-linear-constant (HLC) models. The equations for each model can be determined using the results of the tensile test, which include the true stress-strain value at the maximum load point and the corrected true stress-strain value at the fracture point plus the Considere instability criterion. The HL and HLC models suggested that the engineering stress-strains from the finite element analysis are consistent with the experimental results.     

Eleutheroside E,an active compound from Eleutherococcus senticosus,regulates adipogenesis in 3T3-L1 cells

In this study, we investigated the anti-adipogenic effects of Eleutherococcus senticosus and its active compounds in vitro to examine new functions. We first analyzed the active compounds in E. senticosus growing in Korea using HPLC and found that the concentration of eleutheroside B and E was higher in stems and roots than in other plant parts. There were no significant (p<0.05) differences in eleutheroside concentration between plant ages. Anti-adipogenic effects of E. senticosus on lipid accumulation in 3T3-L1 cells were examined. Extracts of stems and roots more effectively inhibited lipid accumulation in 3T3-L1 cells than extracts of other plant parts. Eleutheroside E was responsible for the pharmacological anti-adipogenic effects via regulation of the mTOR pathway. This is the first report of an anti-adipogenic effect of E. senticosus and the active compound eleutheroside E.     

Sample sizes required to detect interactions between two binary fixed-effects in a mixed-effects linear regression model

Mixed-effects linear regression models have become more widely used for analysis of repeatedly measured outcomes in clinical trials over the past decade. There are formulae and tables for estimating sample sizes required to detect the main effects of treatment and the treatment by time interactions for those models. A formula is proposed to estimate the sample size required to detect an interaction between two binary variables in a factorial design with repeated measures of a continuous outcome. The formula is based, in part, on the fact that the variance of an interaction is fourfold that of the main effect. A simulation study examines the statistical power associated with the resulting sample sizes in a mixed-effects linear regression model with a random intercept. The simulation varies the magnitude (Δ) of the standardized main effects and interactions, the intraclass correlation coefficient (ρ), and the number (k) of repeated measures within-subject. The results of the simulation study verify that the sample size required to detect a 2×2 interaction in a mixed-effects linear regression model is fourfold that to detect a main effect of the same magnitude.     

Monolithic carbon structures including suspended single nanowires and nanomeshes as a sensor platform

With the development of nanomaterial-based nanodevices, it became inevitable to develop cost-effective and simple nanofabrication technologies enabling the formation of nanomaterial assembly in a controllable manner. Herein, we present suspended monolithic carbon single nanowires and nanomeshes bridging two bulk carbon posts, fabricated in a designed manner using two successive UV exposure steps and a single pyrolysis step. The pyrolysis step is accompanied with a significant volume reduction, resulting in the shrinkage of micro-sized photoresist structures into nanoscale carbon structures. Even with the significant elongation of the suspended carbon nanowire induced by the volume reduction of the bulk carbon posts, the resultant tensional stress along the nanowire is not significant but grows along the wire thickness; this tensional stress gradient and the bent supports of the bridge-like carbon nanowire enhance structural robustness and alleviate the stiction problem that suspended nanostructures frequently experience. The feasibility of the suspended carbon nanostructures as a sensor platform was demonstrated by testing its electrochemical behavior, conductivity-temperature relationship, and hydrogen gas sensing capability.     

Construction application of Fibre/Mesh method for protecting concrete columns in fire

In this paper, a construction application of a technique to improve the fire resistance of high strength concrete is presented. Before the construction application, fire tests of three hours duration were carried out in accordance with ISO-834. Three types of mitigating methods, namely, a specimen with no protection (control), with fireproof panel protection and with the combination of polypropylene fibre reinforcement and metal mesh confinement (Fibre/Mesh), were applied to full sized columns for comparison purposes. The fire resistance performance of all columns was tested under loads. After the fire tests, the severity of spalling of specimens was assessed, and the best performing technique, Fibre/Mesh, for spalling protection was selected for an application in practice. The process of the construction application is described in detail, including pumping, pouring and compacting of the concrete. The concrete quality was examined and the behaviour of the concrete was observed. Consequently, it was verified that this new spalling resistance technique is feasible in practice.     

Power management system for a 2.5 W remote sensor powered by a sediment microbial fuel cell

One of the challenges in using wireless sensors that require high power to monitor the environment is finding a renewable power source that can produce enough power. Sediment microbial fuel cells (SMFCs) are considered an alternative renewable power source for remote monitoring, but current research on SMFCs has demonstrated that they can only produce several to tens of mW of continuous power. This limits the use of SMFCs as an alternative renewable remote power source to mW-level power. Such low power is only enough to operate a low-power sensors. However, there are many remote sensors that require higher power, on the order of watts. Current technology using a SMFC to power a remote sensor requiring watts-level intermittent power is limited because of limitations of power management technology. Our goal was to develop a power management system (PMS) that enables a SMFC to operate a remote sensor consuming 2.5 W of power. We designed a custom PMS to store microbial energy in capacitors and use the stored energy in short bursts. Our results demonstrate that SMFCs can be a viable alternative renewable power source for remote sensors requiring high power.     

An exploratory study on the gaps and pathways to the Korean fusion DEMO

With the vision of being an early demonstrator of fusion energy, the strategic plans for the Fusion DEMO program of Korea (K-DEMO program) has been developed. A staged development of the K-DEMO plant was considered in the strategic plans as to verify technical feasibility in the first stage and economic feasibility in the second stage. The top-tier design requirements and assumptions of the first stage K-DEMO plant are defined and postulated. With these requirements and assumptions, the desired and current status of nuclear fusion technologies are compared to identify the gaps to be filled to design, fabricate, construct, and operate it. The pathways from KSTAR, ITER to K-DEMO plant have also been studied to identify R&D activities for K-DEMO program that are to go in parallel with KSTAR and ITER are extracted from the pathways. Cross-cutting with the fusion R&D activities of the other countries and utilizing the commonalities with the existing systems are discussed with the provision of open-innovation strategy that is one of the key strategies of K-DEMO program. The priority of the R&D activities of K-DEMO program is qualitatively determined in consideration of the gaps, cross-cutting, and risks associated with the R&D investments.     

Influence of helical tube dimensions on open channel natural convection heat transfer

Natural convection heat transfer of a helical tube was investigated experimentally for varying tube diameter, length, height, pitch, radius, and number of turns, in order to determine an appropriate characteristic length to describe the phenomenon. Mass-transfer rates of a CuSO₄–H₂SO₄ electroplating system were measured by replacing the heat transfer system according to the analogy concept. When the pitch-to-diameter ratio was larger than 5 and the pitch-to-radius ratio was smaller than 2.3, the heat transfer rates were very close to those of a horizontal cylinder, and decreased with the diameter of the tube while remaining unaffected by the total length and height. The natural convection heat transfer of the Nth turn of a helical tube was measured for varying pitch-to-diameter ratio and number of turns, and the results were formulated as an empirical correlation.     

Hybrid DSO-GA-based sensorless optimal control strategy for wind turbine generators

The operation of a wind turbine generator involves natural uncertainty due to aerodynamic characteristics, resulting in a system that performs inefficiently. In general, the conventional controller now in wide use is not suitable for every operating point, because its tuning parameters and set-points do not meet the varying system characteristics. A study into an optimal control technique is conducted to reduce the negative effects of inherent uncertainty in system operation. In order to resolve the uncertainty problem, an optimal control method for an effective wind turbine generator is designed on the basis of a sensorless frame by utilizing a hybrid of the direct search optimization method (DSO) and the genetic algorithm (GA). This method is easy to implement and computation of functional derivatives is not necessary. The conventional GA is well known for its high performance in global optimization and its effectiveness in making ideal choices for control variables. The proposed DSO-GA hybrid differs from the conventional GA in terms of the sampling survey and the crossover operation. Moreover, the proposed multivariable optimal control strategy is a sensorless optimization technique that determines the pitch angle of the blades and the yaw angle of the nacelles to produce stable maximum power from a wind turbine system under steady-state operation. The proposed DSO-GA controller is implemented for a lab-scale wind turbine generator exposed to artificial wind, and the experimental results constitute a 3-D performance surface model of output voltage, which is used as an objective function for simulation. The optimization procedure with the objective function is carried out by means of the conventional and proposed methods, whose results reveal that the proposed DSO-GA optimizer yields far better performance in terms of generation number, convergence rate, and robustness. Both techniques are applied to a wind power generator through simulation and experiments. The performances are compared, and conclusions are drawn for each case.